WorldWideScience

Sample records for surface ocean circulation

  1. Ocean Circulation

    OpenAIRE

    Thompson, Andrew F.; Rahmstorf, Stefan

    2009-01-01

    The ocean moderates the Earth's climate due to its vast capacity to store and transport heat; the influence of the large-scale ocean circulation on changes in climate is considered in this chapter. The ocean experiences both buoyancy forcing (through heating/cooling and evaporation/precipitation) and wind forcing. Almost all ocean forcing occurs at the surface, but these changes are communicated throughout the entire depth of the ocean through the meridional overturning circulation (MOC). In ...

  2. Circulation of the surface waters in the north Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Varadachari, V.V.R.; Sharma, G.S.

    The circulation pattern of the surface waters in the North Indian Ocean for different months of the year is discussed. In order to arrive at a reliable and detailed picture of the circulation pattern, streamlines are drawn using the isogon technique...

  3. Slow and Steady: Ocean Circulation. The Influence of Sea Surface Height on Ocean Currents

    Science.gov (United States)

    Haekkinen, Sirpa

    2000-01-01

    The study of ocean circulation is vital to understanding how our climate works. The movement of the ocean is closely linked to the progression of atmospheric motion. Winds close to sea level add momentum to ocean surface currents. At the same time, heat that is stored and transported by the ocean warms the atmosphere above and alters air pressure distribution. Therefore, any attempt to model climate variation accurately must include reliable calculations of ocean circulation. Unlike movement of the atmosphere, movement of the ocean's waters takes place mostly near the surface. The major patterns of surface circulation form gigantic circular cells known as gyres. They are categorized according to their general location-equatorial, subtropical, subpolar, and polar-and may run across an entire ocean. The smaller-scale cell of ocean circulation is known' as an eddy. Eddies are much more common than gyres and much more difficult to track in computer simulations of ocean currents.

  4. Arctic Ocean surface geostrophic circulation 2003–2014

    Directory of Open Access Journals (Sweden)

    T. W. K. Armitage

    2017-07-01

    Full Text Available Monitoring the surface circulation of the ice-covered Arctic Ocean is generally limited in space, time or both. We present a new 12-year record of geostrophic currents at monthly resolution in the ice-covered and ice-free Arctic Ocean derived from satellite radar altimetry and characterise their seasonal to decadal variability from 2003 to 2014, a period of rapid environmental change in the Arctic. Geostrophic currents around the Arctic basin increased in the late 2000s, with the largest increases observed in summer. Currents in the southeastern Beaufort Gyre accelerated in late 2007 with higher current speeds sustained until 2011, after which they decreased to speeds representative of the period 2003–2006. The strength of the northwestward current in the southwest Beaufort Gyre more than doubled between 2003 and 2014. This pattern of changing currents is linked to shifting of the gyre circulation to the northwest during the time period. The Beaufort Gyre circulation and Fram Strait current are strongest in winter, modulated by the seasonal strength of the atmospheric circulation. We find high eddy kinetic energy (EKE congruent with features of the seafloor bathymetry that are greater in winter than summer, and estimates of EKE and eddy diffusivity in the Beaufort Sea are consistent with those predicted from theoretical considerations. The variability of Arctic Ocean geostrophic circulation highlights the interplay between seasonally variable atmospheric forcing and ice conditions, on a backdrop of long-term changes to the Arctic sea ice–ocean system. Studies point to various mechanisms influencing the observed increase in Arctic Ocean surface stress, and hence geostrophic currents, in the 2000s – e.g. decreased ice concentration/thickness, changing atmospheric forcing, changing ice pack morphology; however, more work is needed to refine the representation of atmosphere–ice–ocean coupling in models before we can fully

  5. Surface Ocean Circulation and Dynamics in the Philippine Archipelago Region

    Science.gov (United States)

    Han, W.; Moore, A. M.; Levin, J.; Zhang, B.; Arango, H. G.; Curchitser, E.; di Lorenzo, E.; Gordon, A. L.; Lin, J.

    2008-12-01

    The dynamics of the seasonal surface circulation in the Philippine Archipelago (117E-128E, 0N-14N) are investigated using a high-resolution Regional Ocean Modeling System (ROMS) for the period of 2004 - March 2008. Three experiments are performed to estimate the relative importance of local, remote and tidal forcing. On annual mean, circulation in the Sulu Sea is dominated by the inflow from the South China Sea at the Mindoro and Balabac Straits, outflow into the Sulawesi Sea at the Sibutu Passage, and cyclonic circulation in the Sulu basin. A strong jet forms in the northeast Sulu Sea when currents from the Mindoro and Tablas Straits converge. Within the Archipelago, strong westward currents in the Bohol Sea carry the western Pacific (WP) Water from the Surigao Strait into the Sulu Sea via the Dipolog Strait. In the Sibuyan Sea, currents flow westward, which carry part of the WP water from the San Bernardino Strait into the Sulu Sea via the Tablas Strait. The surface circulations exhibit strong seasonal variations or reversals from winter to summer. The variations of volume transports above 40m at the Mindoro Strait, Balabac Strait and Sibutu Passage of the Sulu Sea and at the Verde Island Passage are dominated by remote forcing, although local forcing can be large sometimes. At the Tablas and Dipolog Straits, variations of transports result from both remote and local forcing. The cyclonic (anticyclonic) gyres during winter (summer) in the Sulu Sea and seasonally reversing currents in the Archipelago result mainly from local forcing. Nonlinear rectification of tides acts to reduce the mean transports at the Surigao, San Bernardino and Dipolog Straits, and it also affects the Sulu Sea circulation perhaps by tidal mixing and shifting the locations of jets and eddies.

  6. Near-surface circulation and kinetic energy in the tropical Indian Ocean derived from lagrangian drifters

    Digital Repository Service at National Institute of Oceanography (India)

    Shenoi, S.S.C.; Saji, P.K.; Almeida, A.M.

    Trajectories of 412 satellite-tracked drifting buoys deployed in the tropical Indian Ocean have been analyzed to document the surface circulation and kinetic energy field. Only drifters drogued at 15 m depth and having drag area ratio greater than...

  7. Ocean circulation studies

    Science.gov (United States)

    Koblinsky, C. J.

    1984-01-01

    Remotely sensed signatures of ocean surface characteristics from active and passive satellite-borne radiometers in conjunction with in situ data were utilized to examine the large scale, low frequency circulation of the world's oceans. Studies of the California Current, the Gulf of California, and the Kuroshio Extension Current in the western North Pacific were reviewed briefly. The importance of satellite oceanographic tools was emphasized.

  8. Ocean circulation using altimetry

    Science.gov (United States)

    Minster, Jean-Francois; Brossier, C.; Gennero, M. C.; Mazzega, P.; Remy, F.; Letraon, P. Y.; Blanc, F.

    1991-01-01

    Our group has been very actively involved in promoting satellite altimetry as a unique tool for observing ocean circulation and its variability. TOPEX/POSEIDON is particularly interesting as it is optimized for this purpose. It will probably be the first instrument really capable of observing the seasonal and interannual variability of subtropical and polar gyres and the first to eventually document the corresponding variability of their heat flux transport. The studies of these phenomena require data of the best quality, unbiased extraction of the signal, mixing of these satellite data with in situ measurements, and assimilation of the whole set into a dynamic description of ocean circulation. Our group intends to develop responses to all these requirements. We will concentrate mostly on the circulation of the South Atlantic and Indian Oceans: This will be done in close connection with other groups involved in the study of circulation of the tropical Atlantic Ocean, in the altimetry measurements (in particular, those of the tidal issue), and in the techniques of data assimilation in ocean circulation models.

  9. World Ocean Circulation Experiment

    Science.gov (United States)

    Clarke, R. Allyn

    1992-01-01

    The oceans are an equal partner with the atmosphere in the global climate system. The World Ocean Circulation Experiment is presently being implemented to improve ocean models that are useful for climate prediction both by encouraging more model development but more importantly by providing quality data sets that can be used to force or to validate such models. WOCE is the first oceanographic experiment that plans to generate and to use multiparameter global ocean data sets. In order for WOCE to succeed, oceanographers must establish and learn to use more effective methods of assembling, quality controlling, manipulating and distributing oceanographic data.

  10. Interaction between surface wind and ocean circulation in the Carolina Capes in a coupled low-order model

    Energy Technology Data Exchange (ETDEWEB)

    Xie, L.; Pietrafesa, L.J.; Raman, S.

    1997-03-18

    Interactions between surface winds and ocean currents over an east-coast continental shelf are studied using a simple mathematical model. The model physics include cross-shelf advection of sea surface temperature (SST) by Ekman drift, upwelling due to Ekman transport divergence, differential heating of the low-level atmosphere by a cross-shelf SST gradient, and the Coriolis effect. Additionally, the effects of diabatic cooling of surface waters due to air-sea heat exchange and of the vertical density stratification on the thickness of the upper ocean Ekman layer are considered. The model results are qualitatively consistent with observed wind-driven coastal ocean circulation and surface wind signatures induced by SST. This simple model also demonstrates that two-way air-sea interaction plays a significant role in the subtidal frequency variability of coastal ocean circulation and mesoscale variability of surface wind fields over coastal waters.

  11. Ocean General Circulation Models

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Jin-Ho; Ma, Po-Lun

    2012-09-30

    1. Definition of Subject The purpose of this text is to provide an introduction to aspects of oceanic general circulation models (OGCMs), an important component of Climate System or Earth System Model (ESM). The role of the ocean in ESMs is described in Chapter XX (EDITOR: PLEASE FIND THE COUPLED CLIMATE or EARTH SYSTEM MODELING CHAPTERS). The emerging need for understanding the Earth’s climate system and especially projecting its future evolution has encouraged scientists to explore the dynamical, physical, and biogeochemical processes in the ocean. Understanding the role of these processes in the climate system is an interesting and challenging scientific subject. For example, a research question how much extra heat or CO2 generated by anthropogenic activities can be stored in the deep ocean is not only scientifically interesting but also important in projecting future climate of the earth. Thus, OGCMs have been developed and applied to investigate the various oceanic processes and their role in the climate system.

  12. Spaceborne studies of ocean circulation

    Science.gov (United States)

    Patzert, W. C.

    1984-01-01

    The history and near-term future of ocean remote sensing to study ocean circulation are examined. Seasat provided the first-ever global data sets of sea surface topography (altimeter) and marine winds (scatterometer) and laid the foundation for the next generation of satellite missions planned for the late 1980s. The future missions are the next generation of altimeter and scatterometer to be flown aboard TOPEX (TOPography EXperiment) and NROSS (Navy Remote Sensing System), respectively. The data from these satellites will be coordinated with measurements made at sea to determine the driving forces of ocean circulation and to study the oceans' role in climate variability. The significance of such studies to such matters as climatic changes, fisheries, commerce, waste disposal, and national defense is noted.

  13. Ocean circulation and climate change

    Science.gov (United States)

    Hasselmann, Klaus

    1991-09-01

    Recent numerical simulations using global ocean circulation models are reviewed together with model experiments involving further important climate sub-systems with which the ocean interacts: the atmosphere, the air-sea interface and the global carbon cycle. A common feature of all ocean circulation experiments considered is the strong sensitivity of the circulation to relatively minor changes in surface forcing, particularly to the buoyancy fluxes in regions of deep water formation in high latitudes. This may explain some of the well-known deficiencies of past global ocean circulation simulations. The strong sensitivity may also have been the cause of rapid climate changes observed in paleoclimatic records and can lead further to significant natural climate variability on the time scales of a few hundred years through the stochastic forcing of the ocean by atmospheric weather variability. Gobal warming computations using two different coupled ocean-atmosphere models for the "business-as-usual" scenario of the Intergovernmental Panel on Climate Change yield a significantly stronger warming delay due to the heat uptake by the oceans in the Southern Ocean than estimated on the basis of box-diffusion models. Recent advances in surface wave modelling, illustrated by a comparison of wave height fields derived from the WAM model and the GEOSAT altimeter, hold promise for the development of an improved representation of ocean-atmosphere coupling based on an explicit description of the dynamical processes at the air-sea interface. Global carbon cycle simulations with a three dimensional carbon cycle model tuned to reproduce past variations of carbon cycle indices show a significant impact of variations in the ocean circulation on the CO2 concentration in the atmosphere and thereby on climate. The series of experiments suggest that for the study of climate in the time scale range from 101-103years, it would be highly desirable, and has indeed now become feasible, to couple

  14. Ocean circulation generated magnetic signals

    DEFF Research Database (Denmark)

    Manoj, C.; Kuvshinov, A.; Maus, S.

    2006-01-01

    of ocean tidal signatures in the CHAMP magnetic field data we estimate the ocean magnetic signals of steady flow using a global 3-D EM numerical solution. The required velocity data are from the ECCO ocean circulation experiment and alternatively from the OCCAM model for higher resolution. We assume......Conducting ocean water, as it flows through the Earth's magnetic field, generates secondary electric and magnetic fields. An assessment of the ocean-generated magnetic fields and their detectability may be of importance for geomagnetism and oceanography. Motivated by the clear identification...... an Earth's conductivity model with a surface thin shell of variable conductance with a realistic ID mantle underneath. Simulations using both models predict an amplitude range of +/-2 nT at Swarm altitude (430 km). However at sea level, the higher resolution simulation predicts a higher strength...

  15. Seasonal surface ocean circulation and dynamics in the Philippine Archipelago region during 2004-2008

    Science.gov (United States)

    Han, Weiqing; Moore, Andrew M.; Levin, Julia; Zhang, Bin; Arango, Hernan G.; Curchitser, Enrique; Di Lorenzo, Emanuele; Gordon, Arnold L.; Lin, Jialin

    2009-06-01

    The dynamics of the seasonal surface circulation in the Philippine Archipelago (117°E-128°E, 0°N-14°N) are investigated using a high-resolution configuration of the Regional Ocean Modeling System (ROMS) for the period of January 2004-March 2008. Three experiments were performed to estimate the relative importance of local, remote and tidal forcing. On the annual mean, the circulation in the Sulu Sea shows inflow from the South China Sea at the Mindoro and Balabac Straits, outflow into the Sulawesi Sea at the Sibutu Passage, and cyclonic circulation in the southern basin. A strong jet with a maximum speed exceeding 100 cm s -1 forms in the northeast Sulu Sea where currents from the Mindoro and Tablas Straits converge. Within the Archipelago, strong westward currents in the Bohol Sea carry the surface water of the western Pacific (WP) from the Surigao Strait into the Sulu Sea via the Dipolog Strait. In the Sibuyan Sea, currents flow westward, which carry the surface water from the WP near the San Bernardino Strait into the Sulu Sea via the Tablas Strait. These surface currents exhibit strong variations or reversals from winter to summer. The cyclonic (anticyclonic) circulation during winter (summer) in the Sulu Sea and seasonally reversing currents within the Archipelago region during the peak of the winter (summer) monsoon result mainly from local wind forcing, while remote forcing dominates the current variations at the Mindoro Strait, western Sulu Sea and Sibutu passage before the monsoons reach their peaks. The temporal variations (with the mean removed), also referred to as anomalies, of volume transports in the upper 40 m at eight major Straits are caused predominantly by remote forcing, although local forcing can be large during sometime of a year. For example, at the Mindoro Strait, the correlation between the time series of transport anomalies due to total forcing (local, remote and tides) and that due only to the remote forcing is 0.81 above 95

  16. Ocean circulation and biogeochemistry moderate interannual and decadal surface water pH changes in the Sargasso Sea

    Science.gov (United States)

    Nathalie F. Goodkin,; Bo-Shian Wang,; Chen-Feng You,; Konrad Hughen,; Prouty, Nancy G.; Bates, Nicholas; Scott Doney,

    2015-01-01

    The oceans absorb anthropogenic CO2 from the atmosphere, lowering surface ocean pH, a concern for calcifying marine organisms. The impact of ocean acidification is challenging to predict as each species appears to respond differently and because our knowledge of natural changes to ocean pH is limited in both time and space. Here we reconstruct 222 years of biennial seawater pH variability in the Sargasso Sea from a brain coral, Diploria labyrinthiformis. Using hydrographic data from the Bermuda Atlantic Time-series Study and the coral-derived pH record, we are able to differentiate pH changes due to surface temperature versus those from ocean circulation and biogeochemical changes. We find that ocean pH does not simply reflect atmospheric CO2 trends but rather that circulation/biogeochemical changes account for >90% of pH variability in the Sargasso Sea and more variability in the last century than would be predicted from anthropogenic uptake of CO2 alone.

  17. The ocean circulation inverse problem

    National Research Council Canada - National Science Library

    Wunsch, C

    1996-01-01

    .... This book addresses the problem of inferring the state of the ocean circulation, understanding it dynamically, and even forecasting it through a quantitative combination of theory and observation...

  18. Surface water and atmospheric underway carbon data obtained during the World Ocean Circulation Experiment Indian Ocean survey cruises (R/V Knorr, December 1998--January 1996)

    Energy Technology Data Exchange (ETDEWEB)

    Kozyr, A. [Univ. of Tennessee, Knoxville, TN (United States). Energy, Environment, and Resources Center; Allison, L. [Oak Ridge National Lab., TN (United States). Carbon Dioxide Information Analysis Center

    1997-11-01

    This data documentation presents the results of the surface water and atmospheric underway measurements of mole fraction of carbon dioxide (xCO{sub 2}), sea surface salinity, and sea surface temperature, obtained during the World Ocean Circulation Experiment (WOCE) Indian Ocean survey cruises (December 1994--January 1996). Discrete and underway carbon measurements were made by members of the CO{sub 2} survey team. The survey team is a part of the Joint Global Ocean Flux Study supported by the US Department of Energy to make carbon-related measurements on the WOCE global survey cruises. Approximately 200,000 surface seawater and 50,000 marine air xCO{sub 2} measurements were recorded.

  19. The effect of sudden ice sheet melt on ocean circulation and surface climate

    Science.gov (United States)

    Ivanovic, R. F.; Gregoire, L. J.; Wickert, A. D.; Valdes, P. J.; Burke, A.

    2017-12-01

    Collapse of ice sheets can cause significant sea-level rise and widespread climate change. Around 14.6 thousand years ago, global mean sea level rose by 15 m in less than 350 years during an event known as Meltwater Pulse 1a. Ice sheet modelling and sea-level fingerprinting has suggested that approximately half of this 50 mm yr-1 sea level rise may have come from a North American ice Saddle Collapse that drained into the Arctic and Atlantic Oceans. However, dating uncertainties make it difficult to determine the sequence of events and their drivers, leaving many fundamental questions. For example, was melting from the northern ice sheets responsible for the Older-Dryas or other global-scale cooling events, or did a contribution from Antarctica counteract the climatic effects? What was the role of the abrupt Bølling Warming? And how were all these signals linked to changes in Atlantic Ocean overturning circulation?To address these questions, we examined the effect of the North American ice Saddle Collapse using a high resolution network drainage model coupled to an atmosphere-ocean-vegetation General Circulation Model. Here, we present the quantitative routing estimates of the consequent meltwater discharge and its impact on climate. We also tested a suite of more idealised meltwater forcing scenarios to examine the global influence of Arctic versus Antarctic ice melt. The results show that 50% of the Saddle Collapse meltwater pulse was routed via the Mackenzie River into the Arctic Ocean, and 50% was discharged directly into the Atlantic/Gulf of Mexico. This meltwater flux, equivalent to a total of 7.3 m of sea-level rise, caused a strong (6 Sv) weakening of Atlantic Meridional Overturning Circulation (AMOC) and widespread Northern Hemisphere cooling of 1-5 °C. The greatest cooling is in the Arctic (5-10 °C in the winter), but there is also significant winter warming over eastern North America (1-3 °C). We propose that this robust submillennial mechanism was

  20. Circulation in the Arctic Ocean

    OpenAIRE

    Jones, E. Peter

    2001-01-01

    Much information on processes and circulation within the Arctic Ocean has emerged from measurements made on icebreaker expeditions during the past decade. This article offers a perspective based on these measurements, summarizing new ideas regarding how water masses are formed and how they circulate. Best understood at present is the circulation of the Atlantic Layer and mid-depth waters, to depths of about 1700 m, which move in cyclonic gyres in the four major basins of the Arctic Ocean. New...

  1. Diagnostic model of 3-D circulation in the Arabian Sea and western equatorial Indian Ocean: Results of monthly mean sea surface topography

    Digital Repository Service at National Institute of Oceanography (India)

    Bahulayan, N.; Shaji, C.

    A three-dimensional diagnostic model has been developed to compute the monthly mean circulation and sea surface topography in the Western Tropical Indian Ocean north of 20 degrees S and west of 80 degrees E. The diagnostic model equations...

  2. Ocean circulation generated magnetic signals

    DEFF Research Database (Denmark)

    Manoj, C.; Kuvshinov, A.; Maus, S.

    2006-01-01

    Conducting ocean water, as it flows through the Earth's magnetic field, generates secondary electric and magnetic fields. An assessment of the ocean-generated magnetic fields and their detectability may be of importance for geomagnetism and oceanography. Motivated by the clear identification...... of ocean tidal signatures in the CHAMP magnetic field data we estimate the ocean magnetic signals of steady flow using a global 3-D EM numerical solution. The required velocity data are from the ECCO ocean circulation experiment and alternatively from the OCCAM model for higher resolution. We assume...... of the magnetic field, as compared to the ECCO simulation. Besides the expected signatures of the global circulation patterns, we find significant seasonal variability of ocean magnetic signals in the Indian and Western Pacific Oceans. Compared to seasonal variation, interannual variations produce weaker signals....

  3. Reconstructing surface ocean circulation with129I time series records from corals.

    Science.gov (United States)

    Chang, Ching-Chih; Burr, George S; Jull, A J Timothy; Russell, Joellen L; Biddulph, Dana; White, Lara; Prouty, Nancy G; Chen, Yue-Gau; Shen, Chuan-Chou; Zhou, Weijian; Lam, Doan Dinh

    2016-12-01

    The long-lived radionuclide 129 I (half-life: 15.7 × 10 6  yr) is well-known as a useful environmental tracer. At present, the global 129 I in surface water is about 1-2 orders of magnitude higher than pre-1960 levels. Since the 1990s, anthropogenic 129 I produced from industrial nuclear fuels reprocessing plants has been the primary source of 129 I in marine surface waters of the Atlantic and around the globe. Here we present four coral 129 I time series records from: 1) Con Dao and 2) Xisha Islands, the South China Sea, 3) Rabaul, Papua New Guinea and 4) Guam. The Con Dao coral 129 I record features a sudden increase in 129 I in 1959. The Xisha coral shows similar peak values for 129 I as the Con Dao coral, punctuated by distinct low values, likely due to the upwelling in the central South China Sea. The Rabaul coral features much more gradual 129 I increases in the 1970s, similar to a published record from the Solomon Islands. The Guam coral 129 I record contains the largest measured values for any site, with two large peaks, in 1955 and 1959. Nuclear weapons testing was the primary 129 I source in the Western Pacific in the latter part of the 20th Century, notably from testing in the Marshall Islands. The Guam 1955 peak and Con Dao 1959 increases are likely from the 1954 Castle Bravo test, and the Operation Hardtack I test is the most likely source of the 1959 peak observed at Guam. Radiogenic iodine found in coral was carried primarily through surface ocean currents. The coral 129 I time series data provide a broad picture of the surface distribution and depth penetration of 129 I in the Pacific Ocean over the past 60 years. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

  4. Reconstructing surface ocean circulation with 129I time series records from corals

    Science.gov (United States)

    Chang, Ching-Chih; Burr, George S.; Jull, A. J. Timothy; Russell, Joellen L.; Biddulph, Dana; White, Lara; Prouty, Nancy G.; Chen, Yue-Gau; Chuan-Chou Shen,; Zhou, Weijian; Lam, Doan Dinh

    2016-01-01

    The long-lived radionuclide 129I (half-life: 15.7 × 106 yr) is well-known as a useful environmental tracer. At present, the global 129I in surface water is about 1–2 orders of magnitude higher than pre-1960 levels. Since the 1990s, anthropogenic 129I produced from industrial nuclear fuels reprocessing plants has been the primary source of 129I in marine surface waters of the Atlantic and around the globe. Here we present four coral 129I time series records from: 1) Con Dao and 2) Xisha Islands, the South China Sea, 3) Rabaul, Papua New Guinea and 4) Guam. The Con Dao coral 129I record features a sudden increase in 129I in 1959. The Xisha coral shows similar peak values for 129I as the Con Dao coral, punctuated by distinct low values, likely due to the upwelling in the central South China Sea. The Rabaul coral features much more gradual 129I increases in the 1970s, similar to a published record from the Solomon Islands. The Guam coral 129I record contains the largest measured values for any site, with two large peaks, in 1955 and 1959. Nuclear weapons testing was the primary 129I source in the Western Pacific in the latter part of the 20th Century, notably from testing in the Marshall Islands. The Guam 1955 peak and Con Dao 1959 increases are likely from the 1954 Castle Bravo test, and the Operation Hardtack I test is the most likely source of the 1959 peak observed at Guam. Radiogenic iodine found in coral was carried primarily through surface ocean currents. The coral 129I time series data provide a broad picture of the surface distribution and depth penetration of 129I in the Pacific Ocean over the past 60 years.

  5. Global ocean circulation by altimetry

    Science.gov (United States)

    Wunsch, Carl; Haidvogel, D.

    1991-01-01

    The overall objectives of this project are to determine the general circulation of the oceans and many of its climate and biochemical consequences through the optimum use of altimetry data from TOPEX/POSEIDON and related missions. Emphasis is on the global-scale circulation, as opposed to the regional scale, but some more local studies will be carried out. Because of funding limitations, the primary initial focus will be on the time-dependent global-scale circulation rather than the mean; eventually, the mean circulation must be dealt with as well.

  6. Late quaternary Southern Indian Ocean circulation

    International Nuclear Information System (INIS)

    Howard, W.R.

    1985-01-01

    The climate of the Southern Indian Ocean is controled by the distinctive mid-to-high latitude oceanographic circulation features of the region. The oceanographic features have distinctive biotic signatures, which can be recognized in surface sediment furnaces. Studies of the Southern Indian Ocean down core time series indicated that oceanographic changes similar in magnitude to LGM-Modern shifts have been a regular, consistent and cyclic feature of the late Quaternary history of the Southern Indian Ocean. Oxygen isotopes and estimated sea-surface temperature records were used for this

  7. The global ocean circulation on a retrograde rotating earth

    NARCIS (Netherlands)

    Kamphuis, V.; Huisman, S.E.; Dijkstra, H.A.

    2011-01-01

    To understand the three-dimensional ocean circulation patterns that have occurred in past continental geometries, it is crucial to study the role of the present-day continental geometry and surface (wind stress and buoyancy) forcing on the present-day global ocean circulation. This circulation,

  8. Internal variability of the thermohaline ocean circulation

    NARCIS (Netherlands)

    Raa, Lianke Alinda te

    2003-01-01

    Variations in the ocean circulation can strongly influence climate due to the large heat transport by the ocean currents. Variability of the thermohaline ocean circulation, the part of the ocean circulation driven by density gradients, occurs typically on (inter)decadal and longer time scales and is

  9. Satellite Altimetry, Ocean Circulation, and Data Assimilation

    Science.gov (United States)

    Fu, Lee-Lueng

    1999-01-01

    Ocean circulation is a critical factor in determining the Earth's climate. Satellite altimetry has been proven a powerful technique for measuring the height of the sea surface for the study of global ocean circulation dynamics. A major objective of my research is to investigate the utility of altimeter data for ocean circulation studies. The 6 years' data record of TOPEX/POSEIDON have been analyzed to study the spatial and temporal characteristics of large-scale ocean variability. A major result obtained in 1998 is the discovery of large-scale oscillations in sea level with a period of 25 days in the Argentine Basin of the South Atlantic Ocean (see diagram). They exhibit a dipole pattern with counterclockwise rotational propagation around the Zapiola Rise (centered at 45S and 317E), a small seamount in the abyssal plain of the basin. The peak-to-trough amplitude is about 10 cm over a distance of 500-1000 km. The amplitude of these oscillations has large seasonal-to-interannual variations. The period and rotational characteristics of these oscillations are remarkably similar to the observations made by two current meters deployed near the ocean bottom in the region. What TOPEX/POSEIDON has detected apparently are manifestations of the movement of the entire water column (barotropic motion). The resultant transport variation is estimated to be about 50 x 10(exp 6) cubic M/S, which is about 50% of the total water transport in the region. Preliminary calculations suggest that these oscillations are topographically trapped waves. A numerical model of the South Atlantic is used to investigate the nature of and causes for these waves. A very important property of sea surface height is that it is directly related to the surface geostrophic velocity, which is related to deep ocean circulation through the density field. Therefore altimetry observations are not only useful for determining the surface circulation but also for revealing information about the deep ocean. Another

  10. Seasonal cycle of surface circulation in the coastal North Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Shetye, S.R.; Shenoi, S.S.C.

    with similar patterns of longshore current and wind stress; (ii) circulation off the west coast of India is consistent with the dynamics of a wind-driven eastern boundary current only during the southwest monsoon. During the northeast monsoon it is possible...

  11. Internal variability of the thermohaline ocean circulation

    OpenAIRE

    Raa, Lianke Alinda te

    2003-01-01

    Variations in the ocean circulation can strongly influence climate due to the large heat transport by the ocean currents. Variability of the thermohaline ocean circulation, the part of the ocean circulation driven by density gradients, occurs typically on (inter)decadal and longer time scales and is an important issue in present-day climate research. Although there are many indications from observations and numerical modeling studies that internal variability of the thermohaline circulation m...

  12. Climate change and ocean deoxygenation within intensified surface-driven upwelling circulations.

    Science.gov (United States)

    Bakun, Andrew

    2017-09-13

    Ocean deoxygenation often takes place in proximity to zones of intense upwelling. Associated concerns about amplified ocean deoxygenation arise from an arguable likelihood that coastal upwelling systems in the world's oceans may further intensify as anthropogenic climate change proceeds. Comparative examples discussed include the uniquely intense seasonal Somali Current upwelling, the massive upwelling that occurs quasi-continuously off Namibia and the recently appearing and now annually recurring 'dead zone' off the US State of Oregon. The evident 'transience' in causal dynamics off Oregon is somewhat mirrored in an interannual-scale intermittence in eruptions of anaerobically formed noxious gases off Namibia. A mechanistic scheme draws the three examples towards a common context in which, in addition to the obvious but politically problematic remedy of actually reducing 'greenhouse' gas emissions, the potentially manageable abundance of strongly swimming, finely gill raker-meshed small pelagic fish emerges as a plausible regulating factor.This article is part of the themed issue 'Ocean ventilation and deoxygenation in a warming world'. © 2017 The Author(s).

  13. Climate change and ocean deoxygenation within intensified surface-driven upwelling circulations

    Science.gov (United States)

    Bakun, Andrew

    2017-08-01

    Ocean deoxygenation often takes place in proximity to zones of intense upwelling. Associated concerns about amplified ocean deoxygenation arise from an arguable likelihood that coastal upwelling systems in the world's oceans may further intensify as anthropogenic climate change proceeds. Comparative examples discussed include the uniquely intense seasonal Somali Current upwelling, the massive upwelling that occurs quasi-continuously off Namibia and the recently appearing and now annually recurring `dead zone' off the US State of Oregon. The evident `transience' in causal dynamics off Oregon is somewhat mirrored in an interannual-scale intermittence in eruptions of anaerobically formed noxious gases off Namibia. A mechanistic scheme draws the three examples towards a common context in which, in addition to the obvious but politically problematic remedy of actually reducing `greenhouse' gas emissions, the potentially manageable abundance of strongly swimming, finely gill raker-meshed small pelagic fish emerges as a plausible regulating factor. This article is part of the themed issue 'Ocean ventilation and deoxygenation in a warming world'.

  14. Estimating global air-sea fluxes from surface properties and from climatological flux data using an oceanic general circulation model

    Science.gov (United States)

    Tziperman, Eli; Bryan, Kirk

    1993-12-01

    A simple method is presented and demonstrated for estimating air-sea fluxes of heat and fresh water with the aid of a general circulation model (GCM), using both sea surface temperature and salinity data and climatological air-sea flux data. The approach is motivated by a least squares optimization problem in which the various data sets are combined to form an optimal solution for the air-sea fluxes. The method provides estimates of the surface properties and air-sea flux data that are as consistent as possible with the original data sets and with the model physics. The calculation of these estimates involves adding a simple equation for calculating the air-sea fluxes during the model run and then running the model to a steady state. The proposed method was applied to a coarse resolution global primitive equation model and annually averaged data sets. Both the spatial distribution of the global air-sea fluxes and the meridional fluxes carried by the ocean were estimated. The resulting air-sea fluxes seem smoother and significantly closer to the climatological flux estimates than do the air-sea fluxes obtained from the GCM by simply specifying the surface temperature and salinity. The better fit to the climatological fluxes was balanced by a larger deviation from the surface temperature and salinity. These surface fields were still close to the observations within the measurement error in most regions, except western boundary areas. The inconsistency of the model and data in western boundary areas is probably related to the inability of the coarse resolution GCM to appropriately simulate the large transports there. The meridional fluxes calculated by the proposed method differ very little from those obtained by simply specifying the surface temperature and salinity. We suggest therefore that these meridional fluxes are strongly influenced by the interior model dynamics; in particular, the too-weak model meridional circulation cell seems to be the reason for

  15. The Southern Ocean's role in ocean circulation and climate transients

    Science.gov (United States)

    Thompson, A. F.; Stewart, A.; Hines, S.; Adkins, J. F.

    2017-12-01

    The ventilation of deep and intermediate density classes at the surface of the Southern Ocean impacts water mass modification and the air-sea exchange of heat and trace gases, which in turn influences the global overturning circulation and Earth's climate. Zonal variability occurs along the Antarctic Circumpolar Current and the Antarctic margins related to flow-topography interactions, variations in surface boundary conditions, and exchange with northern basins. Information about these zonal variations, and their impact on mass and tracer transport, are suppressed when the overturning is depicted as a two-dimensional (depth-latitude) streamfunction. Here we present an idealized, multi-basin, time-dependent circulation model that applies residual circulation theory in the Southern Ocean and allows for zonal water mass transfer between different ocean basins. This model efficiently determines the temporal evolution of the ocean's stratification, ventilation and overturning strength in response to perturbations in the external forcing. With this model we explore the dynamics that lead to transitions in the circulation structure between multiple, isolated cells and a three-dimensional, "figure-of-eight," circulation in which traditional upper and lower cells are interleaved. The transient model is also used to support a mechanistic explanation of the hemispheric asymmetry and phase lag associated with Dansgaard-Oeschger (DO) events during the last glacial period. In particular, the 200 year lag in southern hemisphere temperatures, following a perturbation in North Atlantic deep water formation, depends critically on the migration of Southern Ocean isopycnal outcropping in response to low-latitude stratification changes. Our results provide a self-consistent dynamical framework to explain various ocean overturning transitions that have occurred over the Earth's last 100,000 years, and motivate an exploration of these mechanisms in more sophisticated climate models.

  16. Coastal ocean circulation during Hurricane Sandy

    Science.gov (United States)

    Miles, Travis; Seroka, Greg; Glenn, Scott

    2017-09-01

    Hurricane Sandy (2012) was the second costliest tropical cyclone to impact the United States and resulted in numerous lives lost due to its high winds and catastrophic storm surges. Despite its impacts little research has been performed on the circulation on the continental shelf as Sandy made landfall. In this study, integrated ocean observing assets and regional ocean modeling were used to investigate the coastal ocean response to Sandy's large wind field. Sandy's unique cross-shelf storm track, large size, and slow speed resulted in along-shelf wind stress over the coastal ocean for nearly 48 h before the eye made landfall in southern New Jersey. Over the first inertial period (˜18 h), this along-shelf wind stress drove onshore flow in the surface of the stratified continental shelf and initiated a two-layer downwelling circulation. During the remaining storm forcing period a bottom Ekman layer developed and the bottom Cold Pool was rapidly advected offshore ˜70 km. This offshore advection removed the bottom Cold Pool from the majority of the shallow continental shelf and limited ahead-of-eye-center sea surface temperature (SST) cooling, which has been observed in previous storms on the MAB such as Hurricane Irene (2011). This cross-shelf advective process has not been observed previously on continental shelves during tropical cyclones and highlights the need for combined ocean observing systems and regional modeling in order to further understand the range of coastal ocean responses to tropical cyclones.

  17. Reconstruction of Monsoon Driven South China Sea Surface Ocean Circulation using Coral Δ14C

    Science.gov (United States)

    Goodkin, N.; Bolton, A.; Karnauskas, K. B.; Hughen, K. A.; Griffin, S.; Druffel, E. R. M.

    2016-12-01

    The need to improve our understanding of annual and decadal climate behavior in the South China Sea is increasingly important, as this region includes the largest population density globally but encompasses few climate records. Here we present a record of annually resolved Δ14C from a coral collected off the coast of Nha Trang, Vietnam (12°12'49.90″N, 109°18'17.51″E), that reveals a significant correlation to regional winter sea level pressure (SLP) and sea surface temperature (SST), and extends back more than 400 years. Coral Δ14C during thermonuclear bomb testing indicates the presence of wet-season (summer) upwelling, demonstrated by low Δ14C values for both baseline and peak values relative to other records in the region (Bolton et al., 2016, Radiocarbon). However, annually resolved pre-bomb Δ14C correlates significantly to regional dry-season (winter) SLP and SST, indicating that annual variability is driven by changes to the East Asian Winter Monsoon (EAWM) and subsequent down-welling at this site. Spectral density is focused at 25, 11.8, 7, 4, and 3.2 years per cycle reflecting a range of influences on surface advection variability including the EAWM (D'Arrigo et al., 2005, GRL) and the El Nino Southern Oscillation (ENSO). Spectral power at all of these frequencies decreases following the Little Ice Age ( 1600-1850?) to today, indicating that wind driven surface advection was more variable when hemispheric temperatures were cooler. Decadal variance in the past 100 years is significantly correlated to variance records of the Arctic Oscillation (AO, Thompson and Wallace, 1989, GRL), suggesting that increasing variance in the EAWM may be tied to increasing variance of the AO during the Little Ice Age and vice versa.

  18. Tests of Parameterized Langmuir Circulation Mixing in the Oceans Surface Mixed Layer II

    Science.gov (United States)

    2017-08-11

    zero in deep mixed layers below the influence of the surface waves. When the SDC is zero, the GV and GS functions ((29) and (30)) will be zero, and...current and do not include the SDC. With the inclusion of the SDC in the Coriolis term in the momentum equations, the net transport of u is not zero, but...balances the net transport of the SDC us, so that the combined net downwind transport of the Eulerian current plus the SDC is zero. Hence, since the

  19. Effect of Vegetation on the Late Miocene Ocean Circulation

    Directory of Open Access Journals (Sweden)

    Gerrit Lohmann

    2015-11-01

    Full Text Available We examine the role of the vegetation cover and the associated hydrological cycle on the deep ocean circulation during the Late Miocene (~10 million years ago. In our simulations, an open Central American gateway and exchange with fresh Pacific waters leads to a weak and shallow thermohaline circulation in the North Atlantic Ocean which is consistent with most other modeling studies for this time period. Here, we estimate the effect of a changed vegetation cover on the ocean general circulation using atmospheric circulation model simulations for the late Miocene climate with 353 ppmv CO2 level. The Late Miocene land surface cover reduces the albedo, the net evaporation in the North Atlantic catchment is affected and the North Atlantic water becomes more saline leading to a more vigorous North Atlantic Deep Water circulation. These effects reveal potentially important feedbacks between the ocean circulation, the hydrological cycle and the land surface cover for Cenozoic climate evolution.

  20. Global warming and changes in ocean circulation

    Energy Technology Data Exchange (ETDEWEB)

    Duffy, P.B.; Caldeira, K.C.

    1998-02-01

    This final report provides an overview of the goals and accomplishments of this project. Modeling and observational work has raised the possibility that global warming may cause changes in the circulation of the ocean. If such changes would occur they could have important climatic consequences. The first technical goal of this project was to investigate some of these possible changes in ocean circulation in a quantitative way, using a state-of -the-art numerical model of the ocean. Another goal was to develop our ocean model, a detailed three-dimensional numerical model of the ocean circulation and ocean carbon cycles. A major non-technical goal was to establish LLNL as a center of excellence in modelling the ocean circulation and carbon cycle.

  1. The Application of Jason-1 Measurements to Estimate the Global Near Surface Ocean Circulation for Climate Research

    Science.gov (United States)

    Niiler, Peran P.

    2004-01-01

    The scientific objective of this research program was to utilize drifter, Jason-1 altimeter data and a variety of wind data for the determination of time mean and time variable wind driven surface currents of the global ocean. To accomplish this task has required the interpolation of 6-hourly winds on drifter tracks and the computation of the wind coherent motions of the drifters. These calculations showed that the Ekman current model proposed by Ralph and Niiler for the tropical Pacific was valid for all the oceans south of 40N latitude. Improvements to RN99 model were computed and poster presentations of the results were given in several ocean science venues, including the November 2004 GODAY meeting in St. Petersburg, FL.

  2. Early concepts and charts of ocean circulation

    Science.gov (United States)

    Peterson, R. G.; Stramma, L.; Kortum, G.

    Charts of ocean currents from the late nineteenth century show that already by then the patterns of surface circulation in regions away from polar latitudes were well understood. This fundamental knowledge accumulated gradually through centuries of sea travel and had reached a state of near correctness by the time dedicated research cruises, full-depth measurements and the practical application of the dynamical method were being instituted. Perhaps because of the foregoing, many of the pioneering works, critical to establishing what the upper-level circulation is like, the majority of the charts accompanying them, and several of the groundbreaking theoretical treatments on the physics of currents, are only poorly known to present-day oceanographers. In this paper we trace Western developments in knowledge and understanding of ocean circulation from the earliest times to the late-1800s transition into the modern era. We also discuss certain peripheral advances that proved critical to the subject. The earliest known ideas, dating from the Bronze Age and described by Homer, necessarily reflect severe limitations to geographical knowledge, as well as basic human predilections toward conjecture and exaggeration in the face of inadequate information. People considered the earth to be flat and circular, with the ocean flowing like a river around it. They also believed in horrific whirlpools, a concept that persisted into the Renaissance and which would later provide subject material for modern literature. From the Greek Classical Age, we find hydrologic theories of Earth's interior being laced with subterranean channels (Socrates) and all motion deriving from a divine force forever propelling the heavens toward the west, the primum mobile (Aristotle). These ideas, particularly the latter, dominated opinions about ocean circulation into the late Renaissance. By late Antiquity mariners had very likely acquired intimate knowledge of coastal currents in the Mediterranean, but

  3. Depth of origin of ocean-circulation-induced magnetic signals

    Science.gov (United States)

    Irrgang, Christopher; Saynisch-Wagner, Jan; Thomas, Maik

    2018-01-01

    As the world ocean moves through the ambient geomagnetic core field, electric currents are generated in the entire ocean basin. These oceanic electric currents induce weak magnetic signals that are principally observable outside of the ocean and allow inferences about large-scale oceanic transports of water, heat, and salinity. The ocean-induced magnetic field is an integral quantity and, to first order, it is proportional to depth-integrated and conductivity-weighted ocean currents. However, the specific contribution of oceanic transports at different depths to the motional induction process remains unclear and is examined in this study. We show that large-scale motional induction due to the general ocean circulation is dominantly generated by ocean currents in the upper 2000 m of the ocean basin. In particular, our findings allow relating regional patterns of the oceanic magnetic field to corresponding oceanic transports at different depths. Ocean currents below 3000 m, in contrast, only contribute a small fraction to the ocean-induced magnetic signal strength with values up to 0.2 nT at sea surface and less than 0.1 nT at the Swarm satellite altitude. Thereby, potential satellite observations of ocean-circulation-induced magnetic signals are found to be likely insensitive to deep ocean currents. Furthermore, it is shown that annual temporal variations of the ocean-induced magnetic field in the region of the Antarctic Circumpolar Current contain information about sub-surface ocean currents below 1000 m with intra-annual periods. Specifically, ocean currents with sub-monthly periods dominate the annual temporal variability of the ocean-induced magnetic field.

  4. Laboratory Models of Ocean Circulation

    National Research Council Canada - National Science Library

    Whitehead, John

    1997-01-01

    ...). The subsequent studies were then split into two separate experiments involving convection in the two types of configurations which are likely to produce the very coldest water in the oceans, one...

  5. The Application of Jason-Measurements to Estimate the Global Near Surface Ocean Circulation for Climate Research

    Science.gov (United States)

    Niiler, Pearn P.

    2004-01-01

    The scientific objective of this research program were to utilize drifter and satellite sea level data for the determination of time mean and time variable surface currents of the global ocean. To accomplish these tasks has required the processing of drifter data to include a wide variety of different configurations of drifters into a uniform format and to process the along track satellite altimeter data for computing the geostrophic current components normal to the track. These tasks were accomplished, which resulted in an increase of drifter data by about 40% and the development of new algorithms for obtaining satellite derived geostrophic velocity data that was consistent with the drifter observations of geostrophic time-variable currents. The methodologies and the research results using these methodologies were reported in the publications listed in this paper.

  6. Sustaining observations of the unsteady ocean circulation.

    Science.gov (United States)

    Frajka-Williams, E

    2014-09-28

    Sustained observations of ocean properties reveal a global warming trend and rising sea levels. These changes have been documented by traditional ship-based measurements of ocean properties, whereas more recent Argo profiling floats and satellite records permit estimates of ocean changes on a near real-time basis. Through these and newer methods of observing the oceans, scientists are moving from quantifying the 'state of the ocean' to monitoring its variability, and distinguishing the physical processes bringing signals of change. In this paper, I give a brief overview of the UK contributions to the physical oceanographic observations, and the role they have played in the wider global observing systems. While temperature and salinity are the primary measurements of physical oceanography, new transbasin mooring arrays also resolve changes in ocean circulation on daily timescales. Emerging technologies permit routine observations at higher-than-ever spatial resolutions. Following this, I then give a personal perspective on the future of sustained observations. New measurement techniques promise exciting discoveries concerning the role of smaller scales and boundary processes in setting the large-scale ocean circulation and the ocean's role in climate. The challenges now facing the scientific community include sustaining critical observations in the case of funding system changes or shifts in government priorities. These long records will enable a determination of the role and response of the ocean to climate change. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

  7. Oceanic nitrogen reservoir regulated by plankton diversity and ocean circulation.

    Science.gov (United States)

    Weber, Thomas; Deutsch, Curtis

    2012-09-20

    The average nitrogen-to-phosphorus ratio of marine phytoplankton (16N:1P) is closely matched to the nutrient content of mean ocean waters (14.3N:1P). This condition is thought to arise from biological control over the ocean's nitrogen budget, in which removal of bioavailable nitrogen by denitrifying bacteria ensures widespread selection for diazotrophic phytoplankton that replenish this essential nutrient when it limits the growth of other species. Here we show that in the context of a realistic ocean circulation model, and a uniform N:P ratio of plankton biomass, this feedback mechanism yields an oceanic nitrate deficit more than double its observed value. The critical missing phenomenon is diversity in the metabolic N:P requirement of phytoplankton, which has recently been shown to exhibit large-scale patterns associated with species composition. When we model these variations, such that diazotrophs compete with high N:P communities in subtropical regions, the ocean nitrogen inventory rises and may even exceed the average N:P ratio of plankton. The latter condition, previously considered impossible, is prevented in the modern ocean by shallow circulations that communicate stoichiometric signals from remote biomes dominated by diatoms with low N:P ratios. Large-scale patterns of plankton diversity and the circulation pathways connecting them are thus key factors determining the availability of fixed nitrogen in the ocean.

  8. Simulation Tool for GNSS Ocean Surface Reflections

    OpenAIRE

    Høeg, Per; von Benzon, Hans-Henrik; Durgonics, Tibor

    2015-01-01

    GNSS coherent and incoherent reflected signals have the potential of deriving large scale parameters of ocean surfaces, as barotropic variability, eddy currents and fronts, Rossby waves, coastal upwelling, mean ocean surfaceheights, and patterns of the general ocean circulation. In the reflection zone the measurements may deriveparameters as sea surface roughness, winds, waves, heights and tilts from the spectral measurements. Previous measurements from the top of mountains and airplanes have...

  9. Atlantic Meridional Overturning Circulation slowdown cooled the subtropical ocean.

    Science.gov (United States)

    Cunningham, Stuart A; Roberts, Christopher D; Frajka-Williams, Eleanor; Johns, William E; Hobbs, Will; Palmer, Matthew D; Rayner, Darren; Smeed, David A; McCarthy, Gerard

    2013-12-16

    [1] Observations show that the upper 2 km of the subtropical North Atlantic Ocean cooled throughout 2010 and remained cold until at least December 2011. We show that these cold anomalies are partly driven by anomalous air-sea exchange during the cold winters of 2009/2010 and 2010/2011 and, more surprisingly, by extreme interannual variability in the ocean's northward heat transport at 26.5°N. This cooling driven by the ocean's meridional heat transport affects deeper layers isolated from the atmosphere on annual timescales and water that is entrained into the winter mixed layer thus lowering winter sea surface temperatures. Here we connect, for the first time, variability in the northward heat transport carried by the Atlantic Meridional Overturning Circulation to widespread sustained cooling of the subtropical North Atlantic, challenging the prevailing view that the ocean plays a passive role in the coupled ocean-atmosphere system on monthly-to-seasonal timescales.

  10. Biogeochemical proxies in Scleractinian corals used to reconstruct ocean circulation

    International Nuclear Information System (INIS)

    Guilderson, T.P.; Kashgarian, M.; Schrag, D.P.

    2002-01-01

    We utilize monthly 14 C data derived from coral archives in conjunction with ocean circulation models to address two questions: 1) how does the shallow circulation of the tropical Pacific vary on seasonal to decadal time scales and 2) which dynamic processes determine the mean vertical structure of the equatorial Pacific thermocline. Our results directly impact the understanding of global climate events such as the El Nino-Southern Oscillation (ENSO). To study changes in ocean circulation and water mass distribution involved in the genesis and evolution of ENSO and decadal climate variability, it is necessary to have records of climate variables several decades in length. Continuous instrumental records are limited because technology for continuous monitoring of ocean currents has only recently been available, and ships of opportunity archives such as COADS contain large spatial and temporal biases. In addition, temperature and salinity in surface waters are not conservative and thus can not be independently relied upon to trace water masses, reducing the utility of historical observations. Radiocarbon ( 14 C) in sea water is a quasi-conservative water mass tracer and is incorporated into coral skeletal material, thus coral 14 C records can be used to reconstruct changes in shallow circulation that would be difficult to characterize using instrumental data. High resolution Δ 14 C time-series such as these, provide a powerful constraint on the rate of surface ocean mixing and hold great promise to augment onetime surveys such as GEOSECS and WOCE. These data not only provide fundamental information about the shallow circulation of the Pacific, but can be used as a benchmark for the next generation of high resolution ocean models used in prognosticating climate change. (author)

  11. A multi-level adaptation model of circulation for the western Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Shaji, C.; Bahulayan, N.; Dube, S.K.; Rao, A.D.

    on the observed circulation in the western tropical Indian Ocean. The model consists of equations of motion and continuity, sea surface topography, equations of state and temperature, and salinity diffusion equations. While the sea surface topography equation...

  12. Origin of surface and columnar Indian Ocean Experiment (INDOEX) aerosols using source- and region-tagged emissions transport in a general circulation model

    Science.gov (United States)

    Verma, S.; Venkataraman, C.; Boucher, O.

    2008-12-01

    We study the relative influence of aerosols emitted from different sectors and geographical regions on aerosol loading in south Asia. Sectors contributing aerosol emissions include biofuel and fossil fuel combustion, open biomass burning, and natural sources. Geographical regions include India (the Indo-Gangetic plain, central India, south India, and northwest India), southeast Asia, east Asia, Africa-west Asia, and the rest of the world. Simulations of the Indian Ocean Experiment (INDOEX), from January to March 1999, are made in the general circulation model of Laboratoire de Météorologie Dynamique (LMD-ZT GCM) with emissions tagged by sector and geographical region. Anthropogenic emissions dominate (54-88%) the predicted aerosol optical depth (AOD) over all the receptor regions. Among the anthropogenic sectors, fossil fuel combustion has the largest overall influence on aerosol loading, primarily sulfate, with emissions from India (50-80%) and rest of the world significantly influencing surface concentrations and AOD. Biofuel combustion has a significant influence on both the surface and columnar black carbon (BC) in particular over the Indian subcontinent and Bay of Bengal with emissions largely from the Indian region (60-80%). Open biomass burning emissions influence organic matter (OM) significantly, and arise largely from Africa-west Asia. The emissions from Africa-west Asia affect the carbonaceous aerosols AOD in all receptor regions, with their largest influence (AOD-BC: 60%; and AOD-OM: 70%) over the Arabian Sea. Among Indian regions, the Indo-Gangetic Plain is the largest contributor to anthropogenic surface mass concentrations and AOD over the Bay of Bengal and India. Dust aerosols are contributed mainly through the long-range transport from Africa-west Asia over the receptor regions. Overall, the model estimates significant intercontinental incursion of aerosol, for example, BC, OM, and dust from Africa-west Asia and sulfate from distant regions (rest

  13. Modeling the Middle Jurassic ocean circulation

    Directory of Open Access Journals (Sweden)

    Maura Brunetti

    2015-10-01

    Full Text Available We present coupled ocean–sea-ice simulations of the Middle Jurassic (∼165 Ma when Laurasia and Gondwana began drifting apart and gave rise to the formation of the Atlantic Ocean. Since the opening of the Proto-Caribbean is not well constrained by geological records, configurations with and without an open connection between the Proto-Caribbean and Panthalassa are examined. We use a sea-floor bathymetry obtained by a recently developed three-dimensional (3D elevation model which compiles geological, palaeogeographical and geophysical data. Our original approach consists in coupling this elevation model, which is based on detailed reconstructions of oceanic realms, with a dynamical ocean circulation model. We find that the Middle Jurassic bathymetry of the Central Atlantic and Proto-Caribbean seaway only allows for a weak current of the order of 2 Sv in the upper 1000 m even if the system is open to the west. The effect of closing the western boundary of the Proto-Caribbean is to increase the transport related to barotropic gyres in the southern hemisphere and to change water properties, such as salinity, in the Neo-Tethys. Weak upwelling rates are found in the nascent Atlantic Ocean in the presence of this superficial current and we discuss their compatibility with deep-sea sedimentological records in this region.

  14. South Atlantic circulation in a world ocean model

    Directory of Open Access Journals (Sweden)

    M. H. England

    1994-08-01

    Full Text Available The circulation in the South Atlantic Ocean has been simulated within a global ocean general circulation model. Preliminary analysis of the modelled ocean circulation in the region indicates a rather close agreement of the simulated upper ocean flows with conventional notions of the large-scale geostrophic currents in the region. The modelled South Atlantic Ocean witnesses the return flow and export of North Atlantic Deep Water (NADW at its northern boundary, the inflow of a rather barotropic Antarctic Circumpolar Current (ACC through the Drake Passage, and the inflow of warm saline Agulhas water around the Cape of Good Hope. The Agulhas leakage amounts to 8.7 Sv, within recent estimates of the mass transport shed westward at the Agulhas retroflection. Topographic steering of the ACC dominates the structure of flow in the circumpolar ocean. The Benguela Current is seen to be fed by a mixture of saline Indian Ocean water (originating from the Agulhas Current and fresher Subantarctic surface water (originating in the ACC. The Benguela Current is seen to modify its flow and fate with depth; near the surface it flows north-westwards bifurcating most of its transport northward into the North Atlantic Ocean (for ultimate replacement of North Atlantic surface waters lost to the NADW conveyor. Deeper in the water column, more of the Benguela Current is destined to return with the Brazil Current, though northward flows are still generated where the Benguela Current extension encounters the coast of South America. At intermediate levels, these northward currents trace the flow of Antarctic Intermediate Water (AAIW equatorward, though even more AAIW is seen to recirculate poleward in the subtropical gyre. In spite of the model's rather coarse resolution, some subtle features of the Brazil-Malvinas Confluence are simulated rather well, including the latitude at which the two currents meet. Conceptual diagrams of the recirculation and interocean exchange of

  15. South Atlantic circulation in a world ocean model

    Directory of Open Access Journals (Sweden)

    Matthew H. England

    Full Text Available The circulation in the South Atlantic Ocean has been simulated within a global ocean general circulation model. Preliminary analysis of the modelled ocean circulation in the region indicates a rather close agreement of the simulated upper ocean flows with conventional notions of the large-scale geostrophic currents in the region. The modelled South Atlantic Ocean witnesses the return flow and export of North Atlantic Deep Water (NADW at its northern boundary, the inflow of a rather barotropic Antarctic Circumpolar Current (ACC through the Drake Passage, and the inflow of warm saline Agulhas water around the Cape of Good Hope. The Agulhas leakage amounts to 8.7 Sv, within recent estimates of the mass transport shed westward at the Agulhas retroflection. Topographic steering of the ACC dominates the structure of flow in the circumpolar ocean. The Benguela Current is seen to be fed by a mixture of saline Indian Ocean water (originating from the Agulhas Current and fresher Subantarctic surface water (originating in the ACC. The Benguela Current is seen to modify its flow and fate with depth; near the surface it flows north-westwards bifurcating most of its transport northward into the North Atlantic Ocean (for ultimate replacement of North Atlantic surface waters lost to the NADW conveyor. Deeper in the water column, more of the Benguela Current is destined to return with the Brazil Current, though northward flows are still generated where the Benguela Current extension encounters the coast of South America. At intermediate levels, these northward currents trace the flow of Antarctic Intermediate Water (AAIW equatorward, though even more AAIW is seen to recirculate poleward in the subtropical gyre. In spite of the model's rather coarse resolution, some subtle features of the Brazil-Malvinas Confluence are simulated rather well, including the latitude at which the two currents meet. Conceptual diagrams of the recirculation and interocean

  16. Ocean circulation modeling by use of radar altimeter data

    Science.gov (United States)

    Olbers, Dirk; Alpers, W.; Hasselmann, K.; Maier-Reimer, E.; Kase, R.; Krauss, W.; Siedler, G.; Willebrand, J.; Zahel, W.

    1991-01-01

    The project will investigate the use of radar altimetry (RA) data in the determination of the ocean circulation models. RA data will be used to verify prognostic experiments of the steady state and seasonal cycle of large-scale circulation models and the statistical steady state of eddy-resolving models. The data will serve as initial and update conditions in data assimilation experiments and as constraints in inverse calculations. The aim of the project is a better understanding of ocean physics, the determination and mapping of ocean currents, and a contribution to the establishment of ocean circulation models for climate studies. The goal of the project is to use satellite radar altimetry data for improving our knowledge of ocean circulation both in a descriptive sense and through the physics that govern the circulation state. The basic tool is a series of ocean circulation models. Depending on the model, different techniques will be applied to incorporate the RA data.

  17. Glacial ocean circulation and stratification explained by reduced atmospheric temperature

    OpenAIRE

    Jansen, Malte F.

    2016-01-01

    To understand climatic swings between glacial and interglacial climates we need to explain the observed fluctuations in atmospheric carbon dioxide (CO2), which in turn are most likely driven by changes in the deep ocean circulation. This study presents a model for differences in the deep ocean circulation between glacial and interglacial climates consistent with both our physical understanding and various proxy observations. The results suggest that observed changes in ocean circulation and s...

  18. Impacts of pre-existing ocean cyclonic circulation on sea surface chlorophyll-a concentrations off northeastern Taiwan following episodic typhoon passages

    Science.gov (United States)

    Xu, Fanghua; Yao, Yuan; Oey, Leo; Lin, Yanluan

    2017-08-01

    Off northeastern Taiwan, enhancement of sea surface chlorophyll-a (Chl-a) concentration is frequently found after typhoon passages. From 1998 to 2013, 46 typhoon events are analyzed to examine the variations in Chl-a concentration from satellite ocean color data. On average, Chl-a concentration increased by 38% after a typhoon passage. Noticeably, four remarkable Chl-a increases after typhoons coincide with pre-existing oceanic cyclones in the study area. The Chl-a increase is significantly anticorrelated (p typhoons, we conduct a series of numerical experiments to simulate the oceanic response to Typhoon Kaemi (2006) with or without a pre-existing oceanic cyclone, and with or without strong typhoon winds. The results show that the experiment with a pre-existing oceanic cyclone produces the largest upwelling due to cyclone intensification, mainly induced by the positive wind stress curl dipole northeast of Taiwan.

  19. A Consortium for Ocean Circulation and Climate Estimation

    National Research Council Canada - National Science Library

    Stammer, Detlef

    2001-01-01

    We will improve the ocean general circulation models upon which assimilation is based, evaluate and improve assimilation techniques, and confront the practical problems of marshaling large data sets...

  20. Sensitivity experiments with an adaptation model of circulation of western tropical Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Bahulayan, N.; Shaji, C.; Rao, A.D.; Dube, S.K.

    circulation at 10 m depth is controlled by both wind stress and sea surface topography. Circulation at 50 m depth is mainly controlled by thermohaline forcing and sea surface topography. The current speed in the western tropical Indian Ocean is of the order...

  1. Isotopes as tracers of the oceanic circulation: Results from the World Ocean Circulation Experiment

    International Nuclear Information System (INIS)

    Schlosser, P.; Jenkins, W.J.; Key, R.; Lupton, J.

    2002-01-01

    During the past decades, natural and anthropogenic isotopes such as tritium ( 3 H), radiocarbon ( 14 C), 3 He, or the stable isotopes of water have been used in studies of the dynamics of natural systems. Early applications of tracers to studies of the ocean were directed at determination of circulation patterns and mean residence times of specific water masses, as well as estimates of mixing coefficients. These exploratory studies suggested that tracers can add significantly to our understanding of the oceanic circulation. In order to fully exploit this potential, the first global tracer study, the GEochemical Ocean SECtions Study (GEOSECS), was launched. From the GEOSECS results it was immediately apparent that very close coordination of tracer programs with physical oceanography studies is required for full utilization of tracer data. During the 1980s plans for the World OCean Experiment (WOCE) were developed. As part of its Hydrographic Program (WHP), especially during the one-time survey, a set of tracers were measured on a global scale with unprecedented spatial resolution (both lateral and vertical). The original plan included a larger number of tracers (CFCs, 3 H/ 3 He, 14 C, 39 Ar, stable isotopes of water, helium isotopes, 228 Ra, 90 Sr, 137 Cs, 85 Kr) than could actually be measured systematically (CFCs, 3 H/ 3 He, 14 C, H 2 18 O/H 2 16 O, helium isotopes). Nevertheless, the resulting data set, which presently is under evaluation, exceeds those obtained from pre-WOCE tracer studies by a wide margin. In this contribution, we describe the existing WOCE data set and demonstrate the type of results that can be expected from its interpretation on the basis of a few selected examples. These examples include: (1) the application of tritium and 3 He to studies of the ventilation of the upper waters in the Pacific Ocean, (2) the spreading of intermediate water in the Pacific and Indian oceans as derived from the distribution of 3 He, and (3) the evaluation of

  2. Internal variability of the wind-driven ocean circulation

    NARCIS (Netherlands)

    Katsman, C.A.

    2001-01-01

    The ocean circulation is known to vary on a multitude of time and spatial scales. Due to the large heat capacity of the oceans, variations in its circulation have a profound impact on climate. Therefore, understanding the origin of this variability and its sensitivity to physical parameters is an

  3. Changes in North Atlantic nitrogen fixation controlled by ocean circulation.

    Science.gov (United States)

    Straub, Marietta; Sigman, Daniel M; Ren, Haojia; Martínez-García, Alfredo; Meckler, A Nele; Hain, Mathis P; Haug, Gerald H

    2013-09-12

    In the ocean, the chemical forms of nitrogen that are readily available for biological use (known collectively as 'fixed' nitrogen) fuel the global phytoplankton productivity that exports carbon to the deep ocean. Accordingly, variation in the oceanic fixed nitrogen reservoir has been proposed as a cause of glacial-interglacial changes in atmospheric carbon dioxide concentration. Marine nitrogen fixation, which produces most of the ocean's fixed nitrogen, is thought to be affected by multiple factors, including ocean temperature and the availability of iron and phosphorus. Here we reconstruct changes in North Atlantic nitrogen fixation over the past 160,000 years from the shell-bound nitrogen isotope ratio ((15)N/(14)N) of planktonic foraminifera in Caribbean Sea sediments. The observed changes cannot be explained by reconstructed changes in temperature, the supply of (iron-bearing) dust or water column denitrification. We identify a strong, roughly 23,000-year cycle in nitrogen fixation and suggest that it is a response to orbitally driven changes in equatorial Atlantic upwelling, which imports 'excess' phosphorus (phosphorus in stoichiometric excess of fixed nitrogen) into the tropical North Atlantic surface. In addition, we find that nitrogen fixation was reduced during glacial stages 6 and 4, when North Atlantic Deep Water had shoaled to become glacial North Atlantic intermediate water, which isolated the Atlantic thermocline from excess phosphorus-rich mid-depth waters that today enter from the Southern Ocean. Although modern studies have yielded diverse views of the controls on nitrogen fixation, our palaeobiogeochemical data suggest that excess phosphorus is the master variable in the North Atlantic Ocean and indicate that the variations in its supply over the most recent glacial cycle were dominated by the response of regional ocean circulation to the orbital cycles.

  4. The stability of the thermohaline circulation in a coupled ocean-atmosphere general circulation model

    Energy Technology Data Exchange (ETDEWEB)

    Schiller, A. [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany); Mikolajewicz, U. [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany); Voss, R. [Deutsches Klimarechenzentrum (DKRZ), Hamburg (Germany)

    1996-02-01

    The stability of the Atlantic thermohaline circulation against meltwater input is investigated in a coupled ocean-atmosphere general circulation model. The meltwater input to the Labrador Sea is increased linearly for 250 years to a maximum input of 0.625 Sv and then reduced again to 0 (both instantaneously and slowly decreasing over 250 years). The resulting freshening forces a shutdown of the formation of North Atlantic deepwater and a subsequent reversal of the thermohaline circulation of the Atlantic, filling the deep Atlantic with Antarctic bottom water. The change in the overturning pattern causes a drastic reduction of the Atlantic northward heat transport, resulting in a strong cooling with maximum amplitude over the northern North Atlantic and a southward shift of the sea-ice margin in the Atlantic. Due to the increased meridional temperature gradient, the Atlantic intertropical convergence zone is displaced southward and the westerlies in the northern hemisphere gain strength. We identify four main feedbacks affecting the stability of the thermohaline circulation: the change in the overturning circulation of the Atlantic leads to longer residence times of the surface waters in high northern latitudes, which allows them to accumulate more precipitation and runoff from the continents, which results in an increased stability in the North Atlantic.

  5. The Atlantic Multidecadal Oscillation without a role for ocean circulation.

    Science.gov (United States)

    Clement, Amy; Bellomo, Katinka; Murphy, Lisa N; Cane, Mark A; Mauritsen, Thorsten; Rädel, Gaby; Stevens, Bjorn

    2015-10-16

    The Atlantic Multidecadal Oscillation (AMO) is a major mode of climate variability with important societal impacts. Most previous explanations identify the driver of the AMO as the ocean circulation, specifically the Atlantic Meridional Overturning Circulation (AMOC). Here we show that the main features of the observed AMO are reproduced in models where the ocean heat transport is prescribed and thus cannot be the driver. Allowing the ocean circulation to interact with the atmosphere does not significantly alter the characteristics of the AMO in the current generation of climate models. These results suggest that the AMO is the response to stochastic forcing from the mid-latitude atmospheric circulation, with thermal coupling playing a role in the tropics. In this view, the AMOC and other ocean circulation changes would be largely a response to, not a cause of, the AMO. Copyright © 2015, American Association for the Advancement of Science.

  6. NAO-ocean circulation interactions in a coupled general circulation model

    Energy Technology Data Exchange (ETDEWEB)

    Bellucci, A. [Centro Euro-Mediterraneo per i Cambiamenti Climatici, Bologna (Italy); Gualdi, S.; Navarra, A. [Centro Euro-Mediterraneo per i Cambiamenti Climatici, Bologna (Italy); Istituto Nazionale di Geofisica e Vulcanologia, Bologna (Italy); Scoccimarro, E. [Istituto Nazionale di Geofisica e Vulcanologia, Bologna (Italy)

    2008-12-15

    The interplay between the North Atlantic Oscillation (NAO) and the large scale ocean circulation is inspected in a twentieth century simulation conducted with a state-of-the-art coupled general circulation model. Significant lead-lag covariance between oceanic and tropospheric variables suggests that the system supports a damped oscillatory mode involving an active ocean-atmosphere coupling, with a typical NAO-like space structure and a 5 years timescale, qualitatively consistent with a mid-latitude delayed oscillator paradigm. The two essential processes governing the oscillation are (1) a negative feedback between ocean gyre circulation and the high latitude SST meridional gradient and (2) a positive feedback between SST and the NAO. The atmospheric NAO pattern appears to have a weaker projection on the ocean meridional overturning, compared to the gyre circulation, which leads to a secondary role for the thermohaline circulation in driving the meridional heat transport, and thus the oscillatory mode. (orig.)

  7. Ocean water cycle: its recent amplification and impact on ocean circulation

    Science.gov (United States)

    Vinogradova, Nadya

    2016-04-01

    Oceans are the largest reservoir of the world's water supply, accounting for 97% of the Earth's water and supplying more than 75% of the evaporated and precipitated water in the global water cycle. Therefore, in order to predict the future of the global hydrological cycle, it is essential to understand the changes in its largest component, which is the flux of freshwater over the oceans. Here we examine the change in the ocean water cycle and the ocean's response to such changes that were happening during the last two decades. The analysis is based on a data-constrained ocean state estimate that synthesizes all of the information available in the surface fluxes, winds, observations of sea level, temperature, salinity, geoid, etc., as well as in the physical constraints, dynamics, and conservation statements that are embedded in the equations of the MIT general circulation model. Closeness to observations and dynamical consistency of the solution ensures a physically realistic correspondence between the atmospheric forcing and oceanic fluxes, including the ocean's response to freshwater input. The results show a robust pattern of change in the ocean water cycle in the last twenty years. The pattern of changes indicates a general tendency of drying of the subtropics, and wetting in the tropics and mid-to-high latitudes, following the "rich get richer and the poor get poorer" paradigm in many ocean regions. Using a closed property budget analysis, we then investigate the changes in the oceanic state (salinity, temperature, sea level) during the same twenty-year period. The results are discussed in terms of the origin of surface signatures, and differentiated between those that are attributed to short-term natural variability and those that result from an intensified hydrological cycle due to warming climate.

  8. OW CCMP Ocean Surface Wind

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Cross-Calibrated Multi-Platform (CCMP) Ocean Surface Wind Vector Analyses (Atlas et al., 2011) provide a consistent, gap-free long-term time-series of monthly...

  9. OW ASCAT Ocean Surface Winds

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Advanced Scatterometer (ASCAT) sensor onboard the EUMETSAT MetOp polar-orbiting satellite provides ocean surface wind observations by means of radar...

  10. Application of Satellite Altimetry to Ocean Circulation Studies: 1987-1994

    Science.gov (United States)

    Fu, L. -L.; Cheney, R. E.

    1994-01-01

    Altimetric measurement of the height of the sea surface from space provides global observation of the world's oceans. The last eight years have witnessed a rapid growth in the use of altimetry data from the study of the ocean circulations, thanks to the multiyear data from the Geosat Mission.

  11. Impacts of the leading modes of tropical Indian Ocean sea surface temperature anomaly on sub-seasonal evolution of the circulation and rainfall over East Asia during boreal spring and summer

    Science.gov (United States)

    Liu, Senfeng; Duan, Anmin

    2017-02-01

    The two leading modes of the interannual variability of the tropical Indian Ocean (TIO) sea surface temperature (SST) anomaly are the Indian Ocean basin mode (IOBM) and the Indian Ocean dipole mode (IODM) from March to August. In this paper, the relationship between the TIO SST anomaly and the sub-seasonal evolution of the circulation and rainfall over East Asia during boreal spring and summer is investigated by using correlation analysis and composite analysis based on multi-source observation data from 1979 to 2013, together with numerical simulations from an atmospheric general circulation model. The results indicate that the impacts of the IOBM on the circulation and rainfall over East Asia vary remarkably from spring to summer. The anomalous anticyclone over the tropical Northwest Pacific induced by the warm IOBM is closely linked with the Pacific-Japan or East Asia-Pacific teleconnection pattern, which persists from March to August. In the upper troposphere over East Asia, the warm phase of the IOBM generates a significant anticyclonic response from March to May. In June and July, however, the circulation response is characterized by enhanced subtropical westerly flow. A distinct anomalous cyclone is found in August. Overall, the IOBM can exert significant influence on the western North Pacific subtropical high, the South Asian high, and the East Asian jet, which collectively modulate the precipitation anomaly over East Asia. In contrast, the effects of the IODM on the climate anomaly over East Asia are relatively weak in boreal spring and summer. Therefore, studying the impacts of the TIO SST anomaly on the climate anomaly in East Asia should take full account of the different sub-seasonal response during boreal spring and summer.

  12. Ocean Circulation and Mixing Relevant to the Global System

    National Research Council Canada - National Science Library

    Gordon, Arnold

    1999-01-01

    .... Arlindo's goal is to resolve the circulation and water mass stratification within the Indonesian Seas in order to formulate a thorough description of the source, spreading patterns, inter-ocean...

  13. Acoustic Studies of the Large Scale Ocean Circulation

    Science.gov (United States)

    Menemenlis, Dimitris

    1999-01-01

    Detailed knowledge of ocean circulation and its transport properties is prerequisite to an understanding of the earth's climate and of important biological and chemical cycles. Results from two recent experiments, THETIS-2 in the Western Mediterranean and ATOC in the North Pacific, illustrate the use of ocean acoustic tomography for studies of the large scale circulation. The attraction of acoustic tomography is its ability to sample and average the large-scale oceanic thermal structure, synoptically, along several sections, and at regular intervals. In both studies, the acoustic data are compared to, and then combined with, general circulation models, meteorological analyses, satellite altimetry, and direct measurements from ships. Both studies provide complete regional descriptions of the time-evolving, three-dimensional, large scale circulation, albeit with large uncertainties. The studies raise serious issues about existing ocean observing capability and provide guidelines for future efforts.

  14. Ocean topography mapping, improvement of the marine geoid, and global permanent ocean circulation studies from TOPEX/Poseidon altimeter data

    Science.gov (United States)

    Marsh, James G.; Lerch, F. J.; Koblinsky, C. J.; Nerem, R. S.; Klosko, S. M.; Williamson, R. G.

    1991-01-01

    The TOPEX/POSEIDON altimeter measurements will be the first global observations of the sea surface with accuracy sufficient to make quantitative determinations of the ocean's general circulation and its variations. These measurements are an important step to understanding global change in the ocean and its impact on the climate. Our investigation will focus on the examination of features in the sea surface elevation at the largest spatial and temporal scales. TOPEX/POSEIDON altimeter measurements will be used in conjunction with observations from past satellite-altimeter missions, such as NASA's GEOS-3 and Seasat, the U.S. Navy's Geosat and SALT, and the European Remote Sensing satellite in order to address the following issues: (1) Improve models of the marine geoid, especially at wavelengths needed to understand the basin-scale ocean dynamic topograpy. (2) Measure directly from the altimeter data the expression of the mean global ocean circulation in the sea surface at the largest scales through a simultaneous solution for gravity, orbital, and oceanographic parameters. (3) Examine the sea surface measurements for changes in global ocean mass or volume, interannual variations in the basin-scale ocean circulation, and annual changes in the heating and cooling of the upper ocean.

  15. Fritz Schott's Contributions to the Understanding of the Ocean Circulation

    Science.gov (United States)

    Visbeck, M.

    2009-04-01

    The ocean circulation and its central significance for global climate lay at the heart of Fritz's research. In the context of hard-won data from his more than 30 research cruises to key regions of the Atlantic and Indian oceans, he made fundamental contributions to our understanding of the wind-driven and thermohaline ocean circulation. His insights and explorations of circulation and dynamics of the tropical Indian and Atlantic Oceans have led the field and provided a large part of the basis for planning large, international experiments. Fritz's work is also distinguished by his making exceptional use of modeling results, increasingly as the models have improved. His research has provided a much clearer correspondence between the observed ocean-structure and dynamical theory-noting both theoretical successes and limitations. Besides his general interest in the physical oceanography of the World Oceans, most of his research was devoted to the dynamics of tropical oceans with its intense and highly variable current systems. Concerning the Indian Ocean, Fritz's investigated the response of the Somali Current system to the variable monsoon winds in the early 1980's, obtaining high-quality, hydrographic surveys and the first long term direct measurement of ocean currents from moored arrays. His analyses and interpretations provided a synthesis of the complex circulations there. In the tropical Atlantic Ocean Fritz research focused on the western boundary circulation with important contributions to the understanding of the North Brazil Current retroflection, and the variability of the shallow and deep western boundary currents. Trying to solve the fundamental question ‘what is the role of the tropical ocean for climate variability', Fritz initiated large multinational research programs under the umbrella of the World Climate Research Projects WOCE (World Ocean Circulation Experiment) and CLIVAR (Climate Variability and Predictability). Fritz was the initiator and

  16. Changes in ocean circulation in the South-east Atlantic Ocean during the Pliocene

    Science.gov (United States)

    Petrick, B. F.; McClymont, E.; Felder, S.; Leng, M. J.

    2013-12-01

    The Southeast Atlantic Ocean is an important ocean gateway because major oceanic systems interact with each other in a relatively small geographic area. These include the Benguela Current, Antarctic Circumpolar Current, and the input of warm and saline waters from the Indian Ocean via the Agulhas leakage. However, there remain questions about circulation change in this region during the Pliocene, including whether there was more or less Agulhas Leakage, which may have implications for the strength of the global thermohaline circulation. ODP Site 1087 (31°28'S, 15°19'E, 1374m water depth) is located outside the Benguela upwelling region and is affected by Agulhas leakage in the modern ocean. Sea-surface temperatures (SSTs) are thus sensitive to the influence of Agulhas Leakage at this site. Our approach is to apply several organic geochemistry proxies and foraminiferal analyses to reconstruct the Pliocene history of ODP 1087, including the UK37' index (SSTs), pigments (primary productivity) and planktonic foraminifera (water mass changes). SSTs during the Pliocene range from 17 to 22.5 °C (mean SSTs at 21 °C), and show variability on orbital and suborbital time scales. Our results indicate that the Benguela upwelling system had intensified and/or shifted south during the Pliocene. We find no evidence of Agulhas leakage, meaning that either Agulhas Leakage was severely reduced or displaced during the mid-Pliocene. Potential causes of the observed signals include changes to the local wind field and/or changes in the temperature of intermediate waters which upwell in the Benguela system. Pronounced cooling is observed during cold stages in the Pliocene, aligned with the M2 and KM2 events. These results may indicate that changes to the extent of the Antarctic ice sheet had impact on circulation in the south east Atlantic during the Pliocene via displacement of the Antarctic Circumpolar Currents.

  17. The global marine phosphorus cycle: sensitivity to oceanic circulation

    Directory of Open Access Journals (Sweden)

    C. P. Slomp

    2007-01-01

    Full Text Available A new mass balance model for the coupled marine cycles of phosphorus (P and carbon (C is used to examine the relationships between oceanic circulation, primary productivity, and sedimentary burial of reactive P and particulate organic C (POC, on geological time scales. The model explicitly represents the exchanges of water and particulate matter between the continental shelves and the open ocean, and it accounts for the redox-dependent burial of POC and the various forms of reactive P (iron(III-bound P, particulate organic P (POP, authigenic calcium phosphate, and fish debris. Steady state and transient simulations indicate that a slowing down of global ocean circulation decreases primary production in the open ocean, but increases that in the coastal ocean. The latter is due to increased transfer of soluble P from deep ocean water to the shelves, where it fuels primary production and causes increased reactive P burial. While authigenic calcium phosphate accounts for most reactive P burial ocean-wide, enhanced preservation of fish debris may become an important reactive P sink in deep-sea sediments during periods of ocean anoxia. Slower ocean circulation globally increases POC burial, because of enhanced POC preservation under anoxia in deep-sea depositional environments and higher primary productivity along the continental margins. In accordance with geological evidence, the model predicts increased accumulation of reactive P on the continental shelves during and following periods of ocean anoxia.

  18. A fully-implicit model of the global ocean circulation

    NARCIS (Netherlands)

    Weijer, Wilbert; Dijkstra, Henk A.; Öksüzoğlu, Hakan; Wubs, Fred W.; Niet, Arie C. de

    2003-01-01

    With the recent developments in the solution methods for large-dimensional nonlinear algebraic systems, fully-implicit ocean circulation models are now becoming feasible. In this paper, the formulation of such a three-dimensional global ocean model is presented. With this implicit model, the

  19. The DTU12MDT global mean dynamic topography and ocean circulation model

    DEFF Research Database (Denmark)

    Knudsen, Per; Andersen, Ole B.

    2013-01-01

    The Gravity and Ocean Circulation Experiment - GOCE satellite mission measure the Earth gravity field with unprecedented accuracy leading to substantial improvements in the modelling of the ocean circulation and transport. In this study of the performance of GOCE, a newer gravity model has been...... to results obtained using pre-GOCE gravity field models. The results of this study show that geostrophic surface currents associated with the mean circulation have been further improved and that currents having speeds down to 5 cm/s have been recovered....

  20. Ocean Salinity, Major Elements, and Thermohaline Circulation

    NARCIS (Netherlands)

    de Baar, H.J.W; van Heuven, S.M.A.C.; Middag, R.

    2017-01-01

    Ocean geochemistry is the discipline focusing mostly on the inorganic constituents of seawater in the world oceans. Interactions with biology and organic chemistry, and external sources and sinks, such as rivers, atmosphere, hydrothermal vents, and sediments, do play a role. Marine geochemistry

  1. The Hamburg oceanic carbon cycle circulation model. Cycle 1

    International Nuclear Information System (INIS)

    Maier-Reimer, E.; Heinze, C.

    1992-02-01

    The carbon cycle model calculates the prognostic fields of oceanic geochemical carbon cycle tracers making use of a 'frozen' velocity field provided by a run of the LSG oceanic circulation model (see the corresponding manual, LSG=Large Scale Geostrophic). The carbon cycle model includes a crude approximation of interactions between sediment and bottom layer water. A simple (meridionally diffusive) one layer atmosphere model allows to calculate the CO 2 airborne fraction resulting from the oceanic biogeochemical interactions. (orig.)

  2. Equatorial Indian Ocean subsurface current variability in an Ocean General Circulation Model

    Science.gov (United States)

    Gnanaseelan, C.; Deshpande, Aditi

    2018-03-01

    The variability of subsurface currents in the equatorial Indian Ocean is studied using high resolution Ocean General Circulation Model (OGCM) simulations during 1958-2009. February-March eastward equatorial subsurface current (ESC) shows weak variability whereas strong variability is observed in northern summer and fall ESC. An eastward subsurface current with maximum amplitude in the pycnocline is prominent right from summer to winter during strong Indian Ocean Dipole (IOD) years when air-sea coupling is significant. On the other hand during weak IOD years, both the air-sea coupling and the ESC are weak. This strongly suggests the role of ESC on the strength of IOD. The extension of the ESC to the summer months during the strong IOD years strengthens the oceanic response and supports intensification and maintenance of IODs through modulation of air sea coupling. Although the ESC is triggered by equatorial winds, the coupled air-sea interaction associated with IODs strengthens the ESC to persist for several seasons thereby establishing a positive feedback cycle with the surface. This suggests that the ESC plays a significant role in the coupled processes associated with the evolution and intensification of IOD events by cooling the eastern basin and strengthening thermocline-SST (sea surface temperature) interaction. As the impact of IOD events on Indian summer monsoon is significant only during strong IOD years, understanding and monitoring the evolution of ESC during these years is important for summer monsoon forecasting purposes. There is a westward phase propagation of anomalous subsurface currents which persists for a year during strong IOD years, whereas such persistence or phase propagation is not seen during weak IOD years, supporting the close association between ESC and strength of air sea coupling during strong IOD years. In this study we report the processes which strengthen the IOD events and the air sea coupling associated with IOD. It also unravels

  3. Glacial ocean circulation and stratification explained by reduced atmospheric temperature.

    Science.gov (United States)

    Jansen, Malte F

    2017-01-03

    Earth's climate has undergone dramatic shifts between glacial and interglacial time periods, with high-latitude temperature changes on the order of 5-10 °C. These climatic shifts have been associated with major rearrangements in the deep ocean circulation and stratification, which have likely played an important role in the observed atmospheric carbon dioxide swings by affecting the partitioning of carbon between the atmosphere and the ocean. The mechanisms by which the deep ocean circulation changed, however, are still unclear and represent a major challenge to our understanding of glacial climates. This study shows that various inferred changes in the deep ocean circulation and stratification between glacial and interglacial climates can be interpreted as a direct consequence of atmospheric temperature differences. Colder atmospheric temperatures lead to increased sea ice cover and formation rate around Antarctica. The associated enhanced brine rejection leads to a strongly increased deep ocean stratification, consistent with high abyssal salinities inferred for the last glacial maximum. The increased stratification goes together with a weakening and shoaling of the interhemispheric overturning circulation, again consistent with proxy evidence for the last glacial. The shallower interhemispheric overturning circulation makes room for slowly moving water of Antarctic origin, which explains the observed middepth radiocarbon age maximum and may play an important role in ocean carbon storage.

  4. Understanding variability of the Southern Ocean overturning circulation in CORE-II models

    Science.gov (United States)

    Downes, S. M.; Spence, P.; Hogg, A. M.

    2018-03-01

    The current generation of climate models exhibit a large spread in the steady-state and projected Southern Ocean upper and lower overturning circulation, with mechanisms for deep ocean variability remaining less well understood. Here, common Southern Ocean metrics in twelve models from the Coordinated Ocean-ice Reference Experiment Phase II (CORE-II) are assessed over a 60 year period. Specifically, stratification, surface buoyancy fluxes, and eddies are linked to the magnitude of the strengthening trend in the upper overturning circulation, and a decreasing trend in the lower overturning circulation across the CORE-II models. The models evolve similarly in the upper 1 km and the deep ocean, with an almost equivalent poleward intensification trend in the Southern Hemisphere westerly winds. However, the models differ substantially in their eddy parameterisation and surface buoyancy fluxes. In general, models with a larger heat-driven water mass transformation where deep waters upwell at the surface ( ∼ 55°S) transport warmer waters into intermediate depths, thus weakening the stratification in the upper 2 km. Models with a weak eddy induced overturning and a warm bias in the intermediate waters are more likely to exhibit larger increases in the upper overturning circulation, and more significant weakening of the lower overturning circulation. We find the opposite holds for a cool model bias in intermediate depths, combined with a more complex 3D eddy parameterisation that acts to reduce isopycnal slope. In summary, the Southern Ocean overturning circulation decadal trends in the coarse resolution CORE-II models are governed by biases in surface buoyancy fluxes and the ocean density field, and the configuration of the eddy parameterisation.

  5. Currents connecting communities: nearshore community similarity and ocean circulation.

    Science.gov (United States)

    Watson, J R; Hays, C G; Raimondi, P T; Mitarai, S; Dong, C; McWilliams, J C; Blanchette, C A; Caselle, J E; Siegel, D A

    2011-06-01

    Understanding the mechanisms that create spatial heterogeneity in species distributions is fundamental to ecology. For nearshore marine systems, most species have a pelagic larval stage where dispersal is strongly influenced by patterns of ocean circulation. Concomitantly, nearshore habitats and the local environment are also influenced by ocean circulation. Because of the shared dependence on the seascape, distinguishing the relative importance of the local environment from regional patterns of dispersal for community structure remains a challenge. Here, we quantify the "oceanographic distance" and "oceanographic asymmetry" between nearshore sites using ocean circulation modeling results. These novel metrics quantify spatial separation based on realistic patterns of ocean circulation, and we explore their explanatory power for intertidal and subtidal community similarity in the Southern California Bight. We find that these metrics show significant correspondence with patterns of community similarity and that their combined explanatory power exceeds that of the thermal structure of the domain. Our approach identifies the unique influence of ocean circulation on community structure and provides evidence for oceanographically mediated dispersal limitation in nearshore marine communities.

  6. Cloud-radiative effects on implied oceanic energy transport as simulated by atmospheric general circulation models

    Science.gov (United States)

    Gleckler, P. J.; Randall, D. A.; Boer, G.; Colman, R.; Dix, M.; Galin, V.; Helfand, M.; Kiehl, J.; Kitoh, A.; Lau, W.

    1995-01-01

    This paper summarizes the ocean surface net energy flux simulated by fifteen atmospheric general circulation models constrained by realistically-varying sea surface temperatures and sea ice as part of the Atmospheric Model Intercomparison Project. In general, the simulated energy fluxes are within the very large observational uncertainties. However, the annual mean oceanic meridional heat transport that would be required to balance the simulated surface fluxes is shown to be critically sensitive to the radiative effects of clouds, to the extent that even the sign of the Southern Hemisphere ocean heat transport can be affected by the errors in simulated cloud-radiation interactions. It is suggested that improved treatment of cloud radiative effects should help in the development of coupled atmosphere-ocean general circulation models.

  7. Marine geochemistry ocean circulation, carbon cycle and climate change

    CERN Document Server

    Roy-Barman, Matthieu

    2016-01-01

    Marine geochemistry uses chemical elements and their isotopes to study how the ocean works. It brings quantitative answers to questions such as: What is the deep ocean mixing rate? How much atmospheric CO2 is pumped by the ocean? How fast are pollutants removed from the ocean? How do ecosystems react to the anthropogenic pressure? The book provides a simple introduction to the concepts (environmental chemistry, isotopes), the methods (field approach, remote sensing, modeling) and the applications (ocean circulation, carbon cycle, climate change) of marine geochemistry with a particular emphasis on isotopic tracers. Marine geochemistry is not an isolated discipline: numerous openings on physical oceanography, marine biology, climatology, geology, pollutions and ecology are proposed and provide a global vision of the ocean. It includes new topics based on ongoing research programs such as GEOTRACES, Global Carbon Project, Tara Ocean. It provides a complete outline for a course in marine geochemistry. To favor a...

  8. Late Holocene slowdown of the Indian Ocean Walker circulation.

    Science.gov (United States)

    Mohtadi, Mahyar; Prange, Matthias; Schefuß, Enno; Jennerjahn, Tim C

    2017-10-18

    Changes in tropical zonal atmospheric (Walker) circulation induce shifts in rainfall patterns along with devastating floods and severe droughts that dramatically impact the lives of millions of people. Historical records and observations of the Walker circulation over the 20th century disagree on the sign of change and therefore, longer climate records are necessary to better project tropical circulation changes in response to global warming. Here we examine proxies for thermocline depth and rainfall in the eastern tropical Indian Ocean during the globally colder Last Glacial Maximum (19-23 thousand years ago) and for the past 3000 years. We show that increased thermocline depth and rainfall indicate a stronger-than-today Walker circulation during the Last Glacial Maximum, which is supported by an ensemble of climate simulations. Our findings underscore the sensitivity of tropical circulation to temperature change and provide evidence for a further weakening of the Walker circulation in response to greenhouse warming.

  9. Determination of the ocean circulation using Geosat altimetry

    Science.gov (United States)

    Nerem, R. S.; Tapley, B. D.; Shum, C. K.

    1990-01-01

    A spherical harmonic model of the sea surface topography complete to degree and order 10 and a model of the earth's geopotential field complete to degree and order 50 have been obtained in a simultaneous solution using Geosat altimeter data and tracking data from 14 different satellites. The sea surface topography model compares well with oceanographic models computed using hydrographic data and ship drift data. Currently, errors in the estimated gravity field model limit the determination of the spherical harmonic coefficients of the general ocean circulation to degrees 10 and lower, corresponding to a minimum wavelength of 4000 km. Error analysis indicates that the correlation between the geoid and the sea surface topography model is less than 0.2, indicating good separation of the geoid and the sea surface topography at wavelengths of 4000 km or longer. Estimates of the scale factor for the significant wave height (H1/3), which is used to compute the electromagnetic bias correction and the bias for the Geosat altimeter, are obtained. The estimate of the H1/3 correction is 3.6 + or - 1.5 percent, and the height bias estimate is zero.

  10. Indian Ocean circulation and productivity during the last glacial cycle

    Digital Repository Service at National Institute of Oceanography (India)

    Piotrowski, A.M.; Banakar, V.K.; Scrivner, A.E.; Elderfield, H.; Galy, A.; Dennis, A.

    Nd and δ 13 C records from the deep Cape Basin (Piotrowski et al., 2005; Piotrowski et al., 2008), suggesting that the δ 13 C of deep water in the deep South Atlantic changed independently of ocean circulation during glacial... isotopes can be interpreted as changes in deep-water δ 13 C composition independent of circulation, resulting from climate-dependant changes in either biological productivity, the pre-formed δ 13 C of a water mass by biological productivity, or air...

  11. Multiple states in the late Eocene ocean circulation

    Science.gov (United States)

    Baatsen, M. L. J.; von der Heydt, A. S.; Kliphuis, M.; Viebahn, J.; Dijkstra, H. A.

    2018-04-01

    The Eocene-Oligocene Transition (EOT) marks a major step within the Cenozoic climate in going from a greenhouse into an icehouse state, with the formation of a continental-scale Antarctic ice sheet. The roles of steadily decreasing CO2 concentrations versus changes in ocean circulation at the EOT are still debated and the threshold for Antarctic glaciation is obscured by uncertainties in global geometry. Here, a detailed study of the late Eocene ocean circulation is carried out using an ocean general circulation model under two slightly different geography reconstructions of the middle-to-late Eocene (38 Ma). Using the same atmospheric forcing, both geographies give a profoundly different equilibrium ocean circulation state. The underlying reason for this sensitivity is the presence of multiple equilibria characterised by either North or South Pacific deep water formation. A possible shift from a southern towards a northern overturning circulation would result in significant changes in the global heat distribution and consequently make the Southern Hemisphere climate more susceptible for significant cooling and ice sheet formation on Antarctica.

  12. The global marine phosphorus cycle : sensitivity to oceanic circulation

    NARCIS (Netherlands)

    Slomp, C.P.; Van Cappellen, P.

    2007-01-01

    A new mass balance model for the coupled marine cycles of phosphorus (P) and carbon (C) is used to examine the relationships between oceanic circulation, primary productivity, and sedimentary burial of reactive P and particulate organic C (POC), on geological time scales. The model explicitly

  13. The global marine phosphorus cycle: sensitivity to oceanic circulation

    NARCIS (Netherlands)

    Slomp, C.P.; Van Cappellen, P.

    2006-01-01

    A new mass balance model for the coupled marine cycles of phosphorus (P) and carbon (C) is used to examine the relationships between oceanic circulation, primary productivity, and sedimentary burial of reactive P and particulate organic C (POC), on geological time scales. The model explicitly

  14. Response of an ocean general circulation model to wind and ...

    Indian Academy of Sciences (India)

    The stretched-coordinate ocean general circulation model has been designed to study the observed variability due to wind and thermodynamic forcings. The model domain extends from 60°N to 60°S and cyclically continuous in the longitudinal direction. The horizontal resolution is 5° × 5° and 9 discrete vertical levels.

  15. Nd isotope constraints on ocean circulation, paleoclimate, and continental drainage during the Jurassic breakup of Pangea

    DEFF Research Database (Denmark)

    Dera, Guillaume; Prunier, Jonathan; Smith, Paul L.

    2015-01-01

    changes in continental drainage and surface oceanic circulation for the whole Jurassic period. For this purpose, we present 53 new neodymium isotope values (εNd(t)) measured on well-dated fossil fish teeth, ichthyosaur bones, phosphatized nodules, phosphatized ooids, and clastic sediments from Europe...

  16. The Sensitivity of Future Ocean Oxygen Concentrations to Changes in Ocean Circulation

    Science.gov (United States)

    Trossman, D. S.; Palter, J. B.

    2016-12-01

    One expected consequence of anthropogenically forced climate change is a general decrease in oceanic oxygen concentrations. The volume of hypoxic ocean waters is of particular interest, as fish and other organisms become physiologically stressed at low oxygen concentrations. Solubility decline, changes in the wind-driven circulation, and modification of the convective renewal of deep water have each been implicated as important physical controls on the oceanic oxygen concentrations in a warming world. Biological changes, such as those tied to export production and respiration may also play a critical role. The importance of large-scale ocean circulation changes in setting oxygen concentrations relative to other physical factors, such as changes in stratification and mixing, is unclear, with implications for the uncertainty in predicting future hypoxia. By comparing oxygen budgets in a suite of fully coupled climate change simulations to identical simulations in which the ocean circulation is held constant (Trossman et al., 2016), we address this challenge. Under a 1% to doubling of carbon dioxide scenario, our simulations predict a 25% decline in the Atlantic Meridional Overturning Circulation. However, this decline plays a relatively minor role in setting the spatial patterns of total ocean oxygen on a multi-decadal time scale. On the other hand, the ocean circulation perturbation due to climate change substantially slows the expansion of the tropical Pacific oxygen minimum zone (OMZ), due to a future weakening of the Walker circulation. A weaker Walker circulation reduces the upwelling of old, nutrient rich waters, suppressing export production and associated subsurface respiration. In the absence of this dynamic ocean response, the expansion of the Pacific OMZ would be much more dramatic.

  17. 14C-age tracers in global ocean circulation models

    Science.gov (United States)

    Koeve, W.; Wagner, H.; Kähler, P.; Oschlies, A.

    2014-10-01

    The natural abundance of 14C in total CO2 dissolved in seawater is a property applied to evaluate the water age structure and circulation in the ocean and in ocean models. In this study we use three different representations of the global ocean circulation augmented with a suite of idealised tracers to study the potential and limitations of using natural 14C to determine water age, the time elapsed since a body of water had contact with the atmosphere. We find that, globally, bulk 14C-age is dominated by two equally important components, one associated with aging, i.e. the time component of circulation and one associated with a "preformed 14C-age". This latter quantity exists because of the slow and incomplete atmosphere/ocean equilibration of 14C in particular in high latitudes where many water masses form. The relative contribution of the preformed component to bulk 14C-age varies regionally within a given model, but also between models. Regional variability, e.g. in the Atlantic Ocean is associated with the mixing of waters with very different end members of preformed 14C-age. In the Atlantic, variations in the preformed component over space and time mask the circulation component to an extent that its patterns are not detectable from bulk 14C-age alone. Between models the variability of age can also be considerable (factor of 2), related to the combinations of physical model parameters, which influence circulation dynamics, and gas exchange in the models. The preformed component was found to be very sensitive to gas exchange and moderately sensitive to ice cover. In our model evaluation exercise, the choice of the gas exchange constant from within the current range of uncertainty had such a strong influence on preformed and bulk 14C-age that if model evaluation would be based on bulk 14C-age it could easily impair the evaluation and tuning of a models circulation on global and regional scales. Based on the results of this study, we propose that considering

  18. Climatology of the HOPE-G global ocean general circulation model - Sea ice general circulation model

    Energy Technology Data Exchange (ETDEWEB)

    Legutke, S. [Deutsches Klimarechenzentrum (DKRZ), Hamburg (Germany); Maier-Reimer, E. [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany)

    1999-12-01

    The HOPE-G global ocean general circulation model (OGCM) climatology, obtained in a long-term forced integration is described. HOPE-G is a primitive-equation z-level ocean model which contains a dynamic-thermodynamic sea-ice model. It is formulated on a 2.8 grid with increased resolution in low latitudes in order to better resolve equatorial dynamics. The vertical resolution is 20 layers. The purpose of the integration was both to investigate the models ability to reproduce the observed general circulation of the world ocean and to obtain an initial state for coupled atmosphere - ocean - sea-ice climate simulations. The model was driven with daily mean data of a 15-year integration of the atmosphere general circulation model ECHAM4, the atmospheric component in later coupled runs. Thereby, a maximum of the flux variability that is expected to appear in coupled simulations is included already in the ocean spin-up experiment described here. The model was run for more than 2000 years until a quasi-steady state was achieved. It reproduces the major current systems and the main features of the so-called conveyor belt circulation. The observed distribution of water masses is reproduced reasonably well, although with a saline bias in the intermediate water masses and a warm bias in the deep and bottom water of the Atlantic and Indian Oceans. The model underestimates the meridional transport of heat in the Atlantic Ocean. The simulated heat transport in the other basins, though, is in good agreement with observations. (orig.)

  19. Perfluorinated acids as novel chemical tracers of global circulation of ocean waters.

    Science.gov (United States)

    Yamashita, Nobuyoshi; Taniyasu, Sachi; Petrick, Gert; Wei, Si; Gamo, Toshitaka; Lam, Paul K S; Kannan, Kurunthachalam

    2008-01-01

    Perfluorinated acids (PFAs) such as perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) are global environmental contaminants. The physicochemical properties of PFAs are unique in that they have high water solubilities despite the low reactivity of carbon-fluorine bond, which also imparts high stability in the environment. Because of the high water solubilities, the open-ocean water column is suggested to be the final sink for PFOS and PFOA. However, little is known on the distribution of PFAs in the oceans around the world. Here we describe the horizontal (spatial) and vertical distribution of PFAs in ocean waters worldwide. PFOS and PFOA concentrations in the North Atlantic Ocean ranged from 8.6 to 36pg l(-1) and from 52 to 338pg l(-1), respectively, whereas the corresponding concentrations in the Mid Atlantic Ocean were 13-73pg l(-1) and 67-439pg l(-1). These were completely different from the surface waters of the South Pacific Ocean and the Indian Ocean (overall range of PFAs in the marine water column were associated with the global ocean circulation theory. Vertical profiles of PFAs in water columns from the Labrador Sea reflected the influx of the North Atlantic Current in surface waters, the Labrador Current in subsurface waters, and the Denmark Strait Overflow Water in deep layers below 2000m. Striking differences in the vertical and spatial distribution of PFAs, depending on the oceans, suggest that these persistent acids can serve as useful chemical tracers to allow us to study oceanic transportation by major water currents. The results provide evidence that PFA concentrations and profiles in the oceans adhere to a pattern consistent with the global "Broecker's Conveyor Belt" theory of open ocean water circulation.

  20. The physical structure of the oceanic surface-layer

    Energy Technology Data Exchange (ETDEWEB)

    Fedorov, K.N.

    1981-01-01

    A study is presented of the structure of the near-surface layer of the ocean under various hydrometeorological conditions. Such a study allows the isolation of border measures for a four characteristic regime for the top ocean layer: 1) intensive wind-wave mixing; 2) Langmuir circulation; 3) intense solar heating during still and calm weather (with and without internal wave modulations); 4) a pressing-out of surface sediment. It is demonstrated that the spatial temperature change in the ocean surface, the thermal structure, and the heat attainment in the top layer have various characteristics during different regimes and this must be considered during the measuring of the ocean surface temperature with the contact method as well as during the comparison of contact and satallite data on the ocean surface temperature. The necessity for more research in this area is underscored.

  1. Sea surface salinity variability in the tropical Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Subrahmanyam, B.; Murty, V.S.N.; Heffner, D.M.

    . Thompson et al. (2006) reported the Indian Ocean circulation and SSS variability during IODZM events, using different OGCM (Ocean General Circulation Model) simulations and assimilated data sets of SODA (Simple Ocean Data Assimilation) and ECCO...

  2. Oceanic circulation models help to predict global biogeography of pelagic yellow-bellied sea snake.

    Science.gov (United States)

    Brischoux, François; Cotté, Cédric; Lillywhite, Harvey B; Bailleul, Frédéric; Lalire, Maxime; Gaspar, Philippe

    2016-08-01

    It is well recognized that most marine vertebrates, and especially tetrapods, precisely orient and actively move in apparently homogeneous oceanic environments. Here, we investigate the presumptive role of oceanic currents in biogeographic patterns observed in a secondarily marine tetrapod, the yellow-bellied sea snake (Hydrophis [Pelamis] platurus). State-of-the-art world ocean circulation models show how H. platurus, the only pelagic species of sea snake, can potentially exploit oceanic currents to disperse and maintain population mixing between localities that spread over two-thirds of the Earth's circumference. The very close association of these snakes with surface currents seems to provide a highly efficient dispersal mechanism that allowed this species to range extensively and relatively quickly well beyond the central Indo-Pacific area, the centre of origin, abundance and diversity of sea snakes. Our results further suggest that the pan-oceanic population of this species must be extraordinarily large. © 2016 The Author(s).

  3. The Hamburg large scale geostrophic ocean general circulation model. Cycle 1

    International Nuclear Information System (INIS)

    Maier-Reimer, E.; Mikolajewicz, U.

    1992-02-01

    The rationale for the Large Scale Geostrophic ocean circulation model (LSG-OGCM) is based on the observations that for a large scale ocean circulation model designed for climate studies, the relevant characteristic spatial scales are large compared with the internal Rossby radius throughout most of the ocean, while the characteristic time scales are large compared with the periods of gravity modes and barotropic Rossby wave modes. In the present version of the model, the fast modes have been filtered out by a conventional technique of integrating the full primitive equations, including all terms except the nonlinear advection of momentum, by an implicit time integration method. The free surface is also treated prognostically, without invoking a rigid lid approximation. The numerical scheme is unconditionally stable and has the additional advantage that it can be applied uniformly to the entire globe, including the equatorial and coastal current regions. (orig.)

  4. Oceanic dispersion of Fukushima-derived Cs-137 in the coastal, offshore, and open oceans simulated by multiple oceanic general circulation models

    Science.gov (United States)

    Kawamura, H.; Furuno, A.; Kobayashi, T.; In, T.; Nakayama, T.; Ishikawa, Y.; Miyazawa, Y.; Usui, N.

    2017-12-01

    To understand the concentration and amount of Fukushima-derived Cs-137 in the ocean, this study simulates the oceanic dispersion of Cs-137 by an oceanic dispersion model SEA-GEARN-FDM developed at Japan Atomic Energy Agency (JAEA) and multiple oceanic general circulation models. The Cs-137 deposition amounts at the sea surface were used as the source term in oceanic dispersion simulations, which were estimated by atmospheric dispersion simulations with a Worldwide version of System for Prediction of Environmental Emergency Dose Information version II (WSPEEDI-II) developed at JAEA. The direct release from the Fukushima Daiichi Nuclear Power Plant into the ocean based on in situ Cs-137 measurements was used as the other source term in oceanic dispersion simulations. The simulated air Cs-137 concentrations qualitatively replicated those measured around the North Pacific. The accumulated Cs-137 ground deposition amount in the eastern Japanese Islands was consistent with that estimated by aircraft measurements. The oceanic dispersion simulations relatively well reproduced the measured Cs-137 concentrations in the coastal and offshore oceans during the first few months after the Fukushima disaster, and in the open ocean during the first year post-disaster. It was suggested that Cs-137 dispersed along the coast in the north-south direction during the first few months post-disaster, and were subsequently dispersed offshore by the Kuroshio Current and Kuroshio Extension. Mesoscale eddies accompanied by the Kuroshio Current and Kuroshio Extension played an important role in dilution of Cs-137. The Cs-137 amounts were quantified in the coastal, offshore, and open oceans during the first year post-disaster. It was demonstrated that Cs-137 actively dispersed from the coastal and offshore oceans to the open ocean, and from the surface layer to the deeper layer in the North Pacific.

  5. OCEAN CIRCULATION. Observing the Atlantic Meridional Overturning Circulation yields a decade of inevitable surprises.

    Science.gov (United States)

    Srokosz, M A; Bryden, H L

    2015-06-19

    The importance of the Atlantic Meridional Overturning Circulation (AMOC) heat transport for climate is well acknowledged. Climate models predict that the AMOC will slow down under global warming, with substantial impacts, but measurements of ocean circulation have been inadequate to evaluate these predictions. Observations over the past decade have changed that situation, providing a detailed picture of variations in the AMOC. These observations reveal a surprising degree of AMOC variability in terms of the intraannual range, the amplitude and phase of the seasonal cycle, the interannual changes in strength affecting the ocean heat content, and the decline of the AMOC over the decade, both of the latter two exceeding the variations seen in climate models. Copyright © 2015, American Association for the Advancement of Science.

  6. The influence of orography on modern ocean circulation

    Science.gov (United States)

    Maffre, Pierre; Ladant, Jean-Baptiste; Donnadieu, Yannick; Sepulchre, Pierre; Goddéris, Yves

    2018-02-01

    The effects of orography on climate are investigated with a coupled ocean-atmosphere general circulation model (IPSL-CM5). Results are compared with previous investigations in order to dig out robust consequences of the lack of orography on the global scale. Emphasis is made on the thermohaline circulation whose sensitivity to orography has only been subject to a very limited number of studies using coupled models. The removal of the entire orography switches the Meridional Overturning Circulation from the Atlantic to the Pacific, following freshwater transfers from the latter to the former that reverse the salinity gradient between these oceans. This is in part due to the increased freshwater export from the Pacific to the Atlantic through North America in the absence of the Rocky Mountains and the consecutive decreased evaporation in the North Atlantic once the Atlantic MOC weakens, which cools the northern high-latitudes. In addition and unlike previous model studies, we find that tropical freshwater transfers are a major driver of this switch. More precisely, the collapse of the Asian summer monsoon, associated with westward freshwater transfer across Africa, is critical to the freshening of the Atlantic and the increased salt content in the Pacific. Specifically, precipitations are increasing over the Congo catchment area and induce a strong increase in runoff discharging into the tropical Atlantic. In addition, the removal of the Andes shifts the area of strong precipitation toward the Amazonian catchment area and results in a larger runoff discharging into the Tropical Atlantic.

  7. The influence of orography on modern ocean circulation

    Science.gov (United States)

    Maffre, Pierre; Ladant, Jean-Baptiste; Donnadieu, Yannick; Sepulchre, Pierre; Goddéris, Yves

    2017-04-01

    The effects of orography on climate are investigated with a coupled ocean-atmosphere general circulation model (IPSL-CM5). Results are compared with previous investigations in order to dig out robust consequences of the lack of orography on the global scale. Emphasis is made on the thermohaline circulation whose sensitivity to orography has only been subject to a very limited number of studies using coupled models. The removal of the entire orography switches the Meridional Overturning Circulation from the Atlantic to the Pacific, following freshwater transfers from the latter to the former that reverse the salinity gradient between these oceans. This is in part due to the increased freshwater export from the Pacific to the Atlantic through North America in the absence of the Rocky Mountains and the consecutive decreased evaporation in the North Atlantic once the Atlantic MOC weakens, which cools the northern high-latitudes. In addition and unlike previous model studies, we find that tropical freshwater transfers are a major driver of this switch. More precisely, the collapse of the Asian summer monsoon, associated with westward freshwater transfer across Africa, is critical to the freshening of the Atlantic and the increased salt content in the Pacific. Specifically, precipitations are increasing over the Congo catchment area and induce a strong increase in runoff discharging into the tropical Atlantic. In addition, the removal of the Andes shifts the area of strong precipitation toward the Amazonian catchment area and results in a larger runoff discharging into the Tropical Atlantic.

  8. Effect of ocean gateways on the global ocean circulation in the late Oligocene and early Miocene

    NARCIS (Netherlands)

    von der Heydt, A.S.|info:eu-repo/dai/nl/245567526; Dijkstra, H.A.|info:eu-repo/dai/nl/073504467

    2006-01-01

    We investigate the effect of changes in the tectonic boundary conditions on global ocean circulation patterns. Using a fully coupled climate model in an idealized setup, we compare situations corresponding to the late Oligocene, the early Miocene, and present day. The model results show the

  9. A Pacific Ocean general circulation model for satellite data assimilation

    Science.gov (United States)

    Chao, Y.; Halpern, D.; Mechoso, C. R.

    1991-01-01

    A tropical Pacific Ocean General Circulation Model (OGCM) to be used in satellite data assimilation studies is described. The transfer of the OGCM from a CYBER-205 at NOAA's Geophysical Fluid Dynamics Laboratory to a CRAY-2 at NASA's Ames Research Center is documented. Two 3-year model integrations from identical initial conditions but performed on those two computers are compared. The model simulations are very similar to each other, as expected, but the simulations performed with the higher-precision CRAY-2 is smoother than that with the lower-precision CYBER-205. The CYBER-205 and CRAY-2 use 32 and 64-bit mantissa arithmetic, respectively. The major features of the oceanic circulation in the tropical Pacific, namely the North Equatorial Current, the North Equatorial Countercurrent, the South Equatorial Current, and the Equatorial Undercurrent, are realistically produced and their seasonal cycles are described. The OGCM provides a powerful tool for study of tropical oceans and for the assimilation of satellite altimetry data.

  10. General circulation and tracers: studies in the Western Indian Ocean

    International Nuclear Information System (INIS)

    Jamous, Daniel

    1991-01-01

    The main question addressed in this thesis is how to best use the information obtained from hydro-biogeochemical tracer data, to study the oceanic general circulation in the Western Indian Ocean. First, a principal component analysis is performed on a historical data set. The tracers considered are temperature, salinity, density, oxygen, phosphate and silica. The method reduces the amount of data to be considered by a factor of 5. It reproduces correctly and efficiently the large-scale distributions of these oceanic properties. The analysed data are then used in a finite-difference nonlinear inverse model. The grid has a resolution of 4 deg. by 4 deg.. Dynamical as well as tracer conservation constraints are used. These constraints are well satisfied by the obtained solutions but the associated errors remain large. Additional constraints would be required in order to discuss the different solutions in more detail. Finally, a qualitative study is done on the deep distribution of helium-3. The data show several important features linked to hydrothermal input in the Gulf of Aden and on the Central Indian Ridge, and to the origin of water masses and deep circulation characteristics. However additional data are required in order to clarify the distribution of this tracer in other key areas. (author) [fr

  11. A global mean ocean circulation estimation using goce gravity models - the DTU12MDT mean dynamic topography model

    DEFF Research Database (Denmark)

    Knudsen, Per; Andersen, Ole Baltazar

    2012-01-01

    The Gravity and Ocean Circulation Experiment - GOCE satellite mission measure the Earth gravity field with unprecedented accuracy leading to substantial improvements in the modelling of the ocean circulation and transport. In this study of the performance of GOCE, a newer gravity model have been...... have been improved significantly compared to results obtained using pre-GOCE gravity field models. The results of this study show that geostrophic surface currents associated with the mean circulation have been further improved and that currents having speeds down to 5 cm/s have been recovered....

  12. Observation of the Global Ocean Circulation From the TOPEX/POSEIDON Mission

    Science.gov (United States)

    Fu, L. -L.

    1995-01-01

    Since 1992, the TOPEX/POSEIDON satellite has been making altimetric sea surface observations with a sea level accuracy of 4.4 cm. This data can be used for studying regional and seasonal differences in sea level and for evaluating oceanic circulation models and tidal models. Longer term changes can also be studied, such as El Nino and overall sea level rising (although the latter is still within the margin of error).

  13. Implementing Numerical Experiments Based on the Coupled Model of Atmospheric General Circulation and Thermohaline Ocean One

    Directory of Open Access Journals (Sweden)

    V. P. Parhomenko

    2015-01-01

    Full Text Available The paper presents a realized hydrodynamic three-dimensional global climatic model, which comprises the model blocks of atmospheric general circulation, thermohaline large-scale circulation of the ocean, and sea ice evolution. Before rather strongly aggregated heat-moisturebalance model of the atmosphere for temperature and humidity of a surface layer was used as a model of the atmosphere. The atmospheric general circulation model is significantly more complicated and allows us to describe processes in the atmosphere more adequately. Functioning of a coupled climatic model is considered in conditions of the seasonal cycle of solar radiation.The paper considers a procedure for coupled calculation of the ocean model and atmospheric general circulation model. Synchronization of a number of parameters in both models is necessary for their joint action. In this regard a procedure of two-dimensional interpolation of data defined on the grids of the ocean model and atmosphere model and back is developed. A feature of this task is discrepancy of grid nodes and continental configurations in models. Coupled model-based long-term calculations for more than 400 years have shown its stable work. Calculation results and comparison with observation data are under discussion.The paper shows distribution of mean global atmosphere temperature versus time in stable conditions to demonstrate that there is inter-annual variability of atmosphere temperature at the steady state of a climate system. It presents distribution of temperature difference of the ocean surface from the observations and from the model of the ocean thermohaline circulation for January. Noticeable deviations of temperature are observed near Antarctica. Apparently, it is because of inaccurate calculation of the sea ice distribution in model. The geographical distribution of the ocean surface temperature for January with coupled calculation shows, in general, a zonal uniform structure of isolines

  14. World Ocean Circulation Experiment (WOCE) Young Investigator Workshops

    Science.gov (United States)

    Austin, Meg

    2004-01-01

    The World Ocean Circulation Experiment (WOCE) Young Investigator Workshops goals and objectives are: a) to familiarize Young Investigators with WOCE models, datasets and estimation procedures; b) to offer intensive hands-on exposure to these models ard methods; c) to build collaborations among junior scientists and more senior WOCE investigators; and finally, d) to generate ideas and projects leading to fundable WOCE synthesis projects. To achieve these goals and objectives, the Workshop will offer a mixture of tutorial lectures on numerical models and estimation procedures, advanced seminars on current WOCE synthesis activities and related projects, and the opportunity to conduct small projects which put into practice the techniques advanced in the lectures.

  15. Interannual Variation of Surface Circulation in the Japan/East Sea due to External Forcings and Intrinsic Variability

    Science.gov (United States)

    Choi, Byoung-Ju; Cho, Seong Hun; Jung, Hee Seok; Lee, Sang-Ho; Byun, Do-Seong; Kwon, Kyungman

    2018-03-01

    The interannual variation of surface ocean currents can be as large as seasonal variation in the Japan/East Sea (JES). To identify the major factors that cause such interannual variability of surface ocean circulation in the JES, surface circulation was simulated from 1998 to 2009 using a three-dimensional model. Contributions of atmospheric forcing (ATM), open boundary data (OBC), and intrinsic variability (ITV) of the surface flow in the JES on the interannual variability of surface ocean circulation were separately examined using numerical simulations. Variability in surface circulation was quantified in terms of variance in sea surface height, 100-m depth water temperature, and surface currents. ITV was found to be the dominant factor that induced interannual variabilities of surface circulation, the main path of the East Korea Warm Current (EKWC), and surface kinetic energy on a time scale of 2-4 years. OBC and ATM were secondary factors contributing to the interannual variation of surface circulation. Interannual variation of ATM changed the separation latitude of EKWC and increased the variability of surface circulation in the Ulleung Basin. Interannual variation of OBC enhanced low-frequency changes in surface circulation and eddies in the Yamato Basin. It also modulated basin-wide uniform oscillations of sea level. This study suggests that precise estimation of initial conditions using data assimilation is essential for long-term prediction of surface circulation in the JES.

  16. Abrupt pre-Bølling-Allerød warming and circulation changes in the deep ocean.

    Science.gov (United States)

    Thiagarajan, Nivedita; Subhas, Adam V; Southon, John R; Eiler, John M; Adkins, Jess F

    2014-07-03

    Several large and rapid changes in atmospheric temperature and the partial pressure of carbon dioxide in the atmosphere--probably linked to changes in deep ocean circulation--occurred during the last deglaciation. The abrupt temperature rise in the Northern Hemisphere and the restart of the Atlantic meridional overturning circulation at the start of the Bølling-Allerød interstadial, 14,700 years ago, are among the most dramatic deglacial events, but their underlying physical causes are not known. Here we show that the release of heat from warm waters in the deep North Atlantic Ocean probably triggered the Bølling-Allerød warming and reinvigoration of the Atlantic meridional overturning circulation. Our results are based on coupled radiocarbon and uranium-series dates, along with clumped isotope temperature estimates, from water column profiles of fossil deep-sea corals in a limited area of the western North Atlantic. We find that during Heinrich stadial 1 (the cool period immediately before the Bølling-Allerød interstadial), the deep ocean was about three degrees Celsius warmer than shallower waters above. This reversal of the ocean's usual thermal stratification pre-dates the Bølling-Allerød warming and must have been associated with increased salinity at depth to preserve the static stability of the water column. The depleted radiocarbon content of the warm and salty water mass implies a long-term disconnect from rapid surface exchanges, and, although uncertainties remain, is most consistent with a Southern Ocean source. The Heinrich stadial 1 ocean profile is distinct from the modern water column, that for the Last Glacial Maximum and that for the Younger Dryas, suggesting that the patterns we observe are a unique feature of the deglacial climate system. Our observations indicate that the deep ocean influenced dramatic Northern Hemisphere warming by storing heat at depth that preconditioned the system for a subsequent abrupt overturning event during the

  17. A new geometrical approach to Eulerian transport: an application to the ocean circulation; final report

    Science.gov (United States)

    McWilliams, J. C.; Chao, Y.

    2003-01-01

    The main objective of this work is to investigate the transport processes in the large-scale ocean circulations using the new transport theory. We focus on the mid-latitude ocean circulation, especially the Gulf Stream, because it is recognized as a most energetic ocean current and plays a crucial role in maintaining the earth's climate system.

  18. The sensitivity of latent heat flux to the air humidity approximations used in ocean circulation models

    Science.gov (United States)

    Liu, W. Timothy; Niiler, Pearn P.

    1990-01-01

    In deriving the surface latent heat flux with the bulk formula for the thermal forcing of some ocean circulation models, two approximations are commonly made to bypass the use of atmospheric humidity in the formula. The first assumes a constant relative humidity, and the second supposes that the sea-air humidity difference varies linearly with the saturation humidity at sea surface temperature. Using climatological fields derived from the Marine Deck and long time series from ocean weather stations, the errors introduced by these two assumptions are examined. It is shown that the errors reach above 100 W/sq m over western boundary currents and 50 W/sq m over the tropical ocean. The two approximations also introduce erroneous seasonal and spatial variabilities with magnitudes over 50 percent of the observed variabilities.

  19. Glacial greenhouse-gas fluctuations controlled by ocean circulation changes.

    Science.gov (United States)

    Schmittner, Andreas; Galbraith, Eric D

    2008-11-20

    Earth's climate and the concentrations of the atmospheric greenhouse gases carbon dioxide (CO(2)) and nitrous oxide (N(2)O) varied strongly on millennial timescales during past glacial periods. Large and rapid warming events in Greenland and the North Atlantic were followed by more gradual cooling, and are highly correlated with fluctuations of N(2)O as recorded in ice cores. Antarctic temperature variations, on the other hand, were smaller and more gradual, showed warming during the Greenland cold phase and cooling while the North Atlantic was warm, and were highly correlated with fluctuations in CO(2). Abrupt changes in the Atlantic meridional overturning circulation (AMOC) have often been invoked to explain the physical characteristics of these Dansgaard-Oeschger climate oscillations, but the mechanisms for the greenhouse-gas variations and their linkage to the AMOC have remained unclear. Here we present simulations with a coupled model of glacial climate and biogeochemical cycles, forced only with changes in the AMOC. The model simultaneously reproduces characteristic features of the Dansgaard-Oeschger temperature, as well as CO(2) and N(2)O fluctuations. Despite significant changes in the land carbon inventory, CO(2) variations on millennial timescales are dominated by slow changes in the deep ocean inventory of biologically sequestered carbon and are correlated with Antarctic temperature and Southern Ocean stratification. In contrast, N(2)O co-varies more rapidly with Greenland temperatures owing to fast adjustments of the thermocline oxygen budget. These results suggest that ocean circulation changes were the primary mechanism that drove glacial CO(2) and N(2)O fluctuations on millennial timescales.

  20. 500 kyr of Indian Ocean Walker Circulation Variability Using Foraminiferal Mg/Ca and Stable Isotopes

    Science.gov (United States)

    Groeneveld, J.; Mohtadi, M.; Lückge, A.; Pätzold, J.

    2017-12-01

    The tropical Indian Ocean is a key location for paleoclimate research affected by different oceanographic and atmospheric processes. Annual climate variations are strongly controlled by the Indian and Asian Monsoon characterized by bi-annually reversing trade winds. Inter-annual climate variations in the Walker circulation are caused by the Indian Ocean Dipole and El Niño-Southern Oscillation resulting in either heavy flooding or severe droughts like for example the famine of 2011 in eastern Africa. Oceanographically the tropical western Indian Ocean receives water masses from the Indonesian Gateway area, sub-Antarctic waters that upwell south of the equator, and the outflow waters from the highly saline Red Sea. On the other hand, the tropical western Indian Ocean is a major source for providing water masses to the Agulhas Current system. Although the eastern Indian Ocean has been studied extensively, the tropical western Indian Ocean is still lacking in high quality climate-archives that have the potential to provide important information to understand how the ocean and atmospheric zonal circulation have changed in the past, and possibly will change in the future. Until now there were no long sediment cores available covering several glacial-interglacial cycles in the tropical western Indian Ocean. Core GeoB 12613-1, recovered during RV Meteor Cruise M75/2 east of the island of Pemba off Tanzania, provides an open-ocean core with well-preserved sediments covering the last five glacial-interglacial cycles ( 500 kyr). Mg/Ca and stable isotopes on both surface- and thermocline dwelling foraminifera have been performed to test how changes in sea water temperatures and relative sea water salinity were coupled on orbital time scales. The results are compared with similar records generated for the tropical eastern Indian Ocean in core SO139-74KL off Sumatra. Water column stratification on both sides of the Indian Ocean and the cross-basin gradients in sea water

  1. Interdecadal variability of the meridional overturning circulation as an ocean internal mode

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Xiuhua [Universitaet Hamburg, Meteorologisches Institut, Hamburg (Germany); Jungclaus, Johann [Max-Planck-Institut fuer Meteorologie, Hamburg (Germany)

    2008-11-15

    The meridional overturning circulation (MOC) in the coupled ECHAM5/MPIOM exhibits variability at periods of near 30 years and near 60 years. The 30-year variability, referred to as interdecadal variability (IDV), exist in an ocean model driven by climatological atmospheric forcing, suggesting that it is maintained by ocean dynamics; the 60-year variability, the multidecadal variability (MDV), is only observed in the fully coupled model and therefore is interpreted as an atmosphere-ocean coupled mode. The coexistence of the 30-year IDV and the 60-year MDV provides a possible explanation for the widespread time scales observed in climate variables. Further analyses of the climatologically forced ocean model shows that, the IDV is related to the interplay between the horizontal temperature-dominated density gradients and the ocean circulation: temperature anomalies move along the cyclonic subpolar gyre leading to fluctuations in horizontal density gradients and the subsequent weakening and strengthening of the MOC. This result is consistent with that from less complex models, indicating the robustness of the IDV. We further show that, along the North Atlantic Current path, the sea surface temperature anomalies are determined by the slow LSW advection at the intermediate depth. (orig.)

  2. Application of Satellite-Derived Ocean Surface Winds to the Detection of Weather Systems and the Prediction of Near-Ocean Surface Winds around Hawaii

    Directory of Open Access Journals (Sweden)

    Hsi-Chyi Yeh

    2010-01-01

    Full Text Available The Hawaiian Island chain is surrounded by the open ocean and is an ideal place to conduct the application of QuikSCAT satellite-derived ocean surface winds to the detection of weather systems. With the help of QuikSCAT winds, the associated circulation of the weather systems over the open ocean around Hawaii can be identified. In this study, the obvious cyclonic circulation associated with a Kona storm, the significant wind shift and wind confluence related to the surface cold front, and the anticyclonic circulation related to high-pressure systems for both a strong-wind event and a trade-wind condition are revealed over the open ocean through QuikSCAT winds. The propagation of a cold frontal boundary, defined by the wind shift and wind confluence, also can be clearly detected using the reanalyzed ocean-surface winds.

  3. On determining the large-scale ocean circulation from satellite altimetry

    Science.gov (United States)

    Tai, C.-K.

    1983-01-01

    It is contended that a spherical harmonic expansion of the difference between the altimeter-derived mean sea surface and the geoid estimate should reveal the large-scale circulation of the ocean surface layer when the low-degree terms are examined. Methods based on this principle are proposed and partially demonstrated over the Pacific Ocean with the aid of the mean sea surface derived from the Seasat altimeter and the Goddard Earth Model 9 earth gravity model. The preliminary results reveal a well-defined clockwise gyre in the North Pacific and a much less well defined counterclockwise gyre in the South Pacific. When the dynamic topography thus obtained is compared with Wyrtki's (1975) dynamic topography derived from hydrographic data, the agreement is found to be within the limit of geoid uncertainties and satellite orbital errors.

  4. The impact of the ocean observing system on estimates of the California current circulation spanning three decades

    Science.gov (United States)

    Moore, Andrew M.; Jacox, Michael G.; Crawford, William J.; Laughlin, Bruce; Edwards, Christopher A.; Fiechter, Jérôme

    2017-08-01

    Data assimilation is now used routinely in oceanography on both regional and global scales for computing ocean circulation estimates and for making ocean forecasts. Regional ocean observing systems are also expanding rapidly, and observations from a wide array of different platforms and sensor types are now available. Evaluation of the impact of the observing system on ocean circulation estimates (and forecasts) is therefore of considerable interest to the oceanographic community. In this paper, we quantify the impact of different observing platforms on estimates of the California Current System (CCS) spanning a three decade period (1980-2010). Specifically, we focus attention on several dynamically related aspects of the circulation (coastal upwelling, the transport of the California Current and the California Undercurrent, thermocline depth and eddy kinetic energy) which in many ways describe defining characteristics of the CCS. The circulation estimates were computed using a 4-dimensional variational (4D-Var) data assimilation system, and our analyses also focus on the impact of the different elements of the control vector (i.e. the initial conditions, surface forcing, and open boundary conditions) on the circulation. While the influence of each component of the control vector varies between different metrics of the circulation, the impact of each observing system across metrics is very robust. In addition, the mean amplitude of the circulation increments (i.e. the difference between the analysis and background) remains relatively stable throughout the three decade period despite the addition of new observing platforms whose impact is redistributed according to the relative uncertainty of observations from each platform. We also consider the impact of each observing platform on CCS circulation variability associated with low-frequency climate variability. The low-frequency nature of the dominant climate modes in this region allows us to track through time the

  5. Predictive Understanding of the Oceans' Wind-Driven Circulation on Interdecadal Time Scales

    Energy Technology Data Exchange (ETDEWEB)

    Ghil, Michael [Univ. of California, Los Angeles, CA (United States). Dept. of Atmospheric and Oceanic Sciences and IGPP; Temam, Roger [Indiana Univ., Bloomington, IN (United States). Dept. of Mathematics; Feliks, Y. [IIBR (France); Simonnet, E. [INLN (France); Tachim-Medjo, T. [Florida International Univ. (FIU), Miami, FL (United States)

    2008-09-30

    The goal of this project was to obtain a predictive understanding of a major component of the climate system's interdecadal variability: the oceans' wind-driven circulation. To do so, we developed and applied advanced computational and statistical methods to the problem of climate variability and climate change. The methodology was developed first for models of intermediate complexity, such as the quasi-geostrophic and the primitive equations, which describe the wind-driven, near-surface flow in mid-latitude ocean basins. Our computational work consisted in developing efficient multi-level methods to simulate this flow and study its dependence on physically relevant parameters. Our oceanographic and climate work consisted in applying these methods to study the bifurcations in the wind-driven circulation and their relevance to the flows observed at present and those that might occur in a warmer climate. Both aspects of the work are crucial for the efficient treatment of large-scale, eddy-resolving numerical simulations of the oceans and an increased understanding and better prediction of climate change. Considerable progress has been achieved in understanding ocean-atmosphere interaction in the mid-latitudes. An important by-product of this research is a novel approach to explaining the North Atlantic Oscillation.

  6. Variation of Marine Geoid Due to Ocean Circulation and Sea Level Change

    Science.gov (United States)

    Chu, P. C.

    2017-12-01

    Sea level (S) change and ocean circulation largely affect the gravity field and in turns the marine geoid (N). Difference between the two, D = S - N, is the dynamic ocean topography (DOT), whose gradient represents the large-scale surface geostrophic circulations. Thus, temporal variability of marine geoid (δN) is caused by the sea level change (δS) and the DOT variation (δD), δN = δS - δD. Here, δS is identified from temporally varying satellite altimeter measures; δD is calculated from the change of DOT. For large-scale processes with conservation of potential vorticity, the geostrophic flows take minimum energy state. Based on that, a new elliptic equation is derived in this study to determine D. Here, H is the water depth; and (X, Y) are forcing functions calculated from the in-situ density. The well-posed elliptic equation is integrated numerically on 1o grids for the world oceans with the boundary values taken from the mean DOT (1993-2006) field at the NASA/JPL website: https://grace.jpl.nasa.gov/data/get-data/dynamic-ocean-typography/, the forcing function F calculated from the three-dimensional temperature and salinity of the NOAA National Centers for Environmental Information (NCEI) World Ocean Atlas 2013 version 2, and sea-floor topography (H) from the NOAA ETOPO5. The numerical solution compares reasonably well (relative root mean square difference of 0.09) with the NASA/JPL satellite observation of the difference between the time-averaged sea surface height and the geoid. In-situ ocean measurements of temperature, salinity, and velocity have also rapidly advanced such that the global ocean is now continuously monitored by near 4,000 free-drifting profiling floats (called Argo) from the surface to 2000 m depth with all data being relayed and made publicly available within hours after collection (http://www.argo.ucsd.edu/). This provides a huge database of temperature and salinity and in turns the forcing function F for the governing elliptic

  7. Analysis of CHAMP scalar magnetic data to identify ocean circulation signals

    DEFF Research Database (Denmark)

    Manoj, C.; Maus, S.; Kuvshinov, Alexei

    Unlike tidal ocean signals, the magnetic signal of ocean circulation has not yet been identified in satellite magnetic data. In particular, the steady signal of mean ocean flow is indistinguishable from time invariant crustal signals. One option, therefore, is to predict the seasonal and annual...... variations in the ocean flow signal from ocean circulation models and compare them with the corresponding variations in satellite magnetic residuals. We used the 11 year ECCO-1 simulation data to derive the ocean transport. A 3D EM induction code in its low frequency limit, was used to simulate the magnetic...

  8. Orographic effects on tropical climate in a coupled ocean-atmosphere general circulation model

    Science.gov (United States)

    Okajima, Hideki

    Large-scale mountain modifies the atmospheric circulation directly through dynamic and thermodynamic process, and also indirectly through the interaction with the ocean. To investigate orographic impacts on tropical climate, a fully coupled general circulation model (CGCM) is developed by coupling a state-of-the-art atmospheric general circulation model and an ocean general circulation model. With realistic boundary conditions, the CGCM produces a reasonable climatology of sea surface temperature (SST), surface winds, and precipitation. When global mountains are removed, the model climatology displays substantial changes in both the mean-state and the seasonal cycle. The equatorial eastern Pacific SST acquires a semi-annual component as inter-tropical convergence zone (ITCZ) flips and flops across the equator following the seasonal migration of the sun. Without the Andes, wet air flows into the southeastern tropical Pacific from the humid Amazon, which weakens the meridional asymmetry during the Peruvian warm season (February-April). In addition, the northeasterly trade winds are enhanced north of the equator without the orographic blocking of Central American mountains and cools SST. Triggered by the SST cooling north and moistening south of the equator, the wind-evaporation-SST (WES) feedback further weakens the meridional asymmetry and prolongs the southern ITCZ. In the Atlantic Ocean, the equatorial cold tongue is substantially strengthened and develops a pronounced annual cycle in the absence of mountains. The easterly winds are overall enhanced over the equatorial Atlantic without orographic heating over the African highlands, developing a zonal asymmetry strengthened by the Bjerknes feedback. In the Indian Ocean, the thermocline shoals eastward and an equatorial cold tongue appears twice a year. During boreal summer, the Findlater jet is greatly weakened off Somalia and SST warms in the western Indian Ocean, forcing the equatorial easterly winds amplified

  9. Observing Global Ocean Circulation From Space: The First Year's Results From the TOPEX/POSEIDON Mission

    Science.gov (United States)

    Fu, L. -L.

    1993-01-01

    The joint U.S./France TOPEX/Poseidon satellite was launched on August 10, 1992, and became operational 42 days later. The major goal of the mission is to use a radar altimeter system for making precise measurements of the height of the sea surface for the study of the dynamics of large-scale ocean circulation, which is a key to understanding global climate change. Additionally, the data are used for studying ocean tides and marine geophysics. The radar altimeter also measures wave height and wind speed. The mission is being conducted to optimize the sea surface height measurements for a minimum of three years. The primary objective of the first six months of the mission was to calibrate and validate the mission's measurements. The verification results indicate that all the measurement objectives have been met...

  10. On the choice of orbits for an altimetric satellite to study ocean circulation and tides

    Science.gov (United States)

    Parke, Michael E.; Stewart, Robert H.; Farless, David L.; Cartwright, David E.

    1987-01-01

    The choice of an orbit for satellite altimetric studies of the ocean's circulation and tides requires an understanding of the orbital characteristics that influence the accuracy of the satellite's measurements of sea level and the temporal and spatial distribution of the measurements. The orbital characteristics that influence accurate calculations of the satellite's position as a function of time are examined, and the pattern of ground tracks laid down on the ocean's surface as a function of the satellite's altitude and inclination is studied. The results are used to examine the aliases in the measurements of surface geostrophic currents and tides. Finally, these considerations are used to specify possible orbits that may be useful for the upcoming Topex/Poseidon mission.

  11. The DTU12MDT global mean dynamic topography and ocean circulation model

    DEFF Research Database (Denmark)

    Knudsen, Per; Andersen, Ole B.

    2013-01-01

    The Gravity and Ocean Circulation Experiment - GOCE satellite mission measure the Earth gravity field with unprecedented accuracy leading to substantial improvements in the modelling of the ocean circulation and transport. In this study of the performance of GOCE, a newer gravity model has been...

  12. Hydrology of surface waters and thermohaline circulation during the last glacial period; Hydrologie des eaux de surface et circulation thermohaline au cours de la derniere periode glaciaire

    Energy Technology Data Exchange (ETDEWEB)

    Vidal, L.

    1996-03-27

    Sedimentological studies on oceanic cores from the north Atlantic have revealed, over the last glacial period, abrupt climatic changes with a periodicity of several thousand years which contrasts strongly with the glacial-interglacial periodicity (several tens of thousand years). These periods of abrupt climate changes correspond to massive icebergs discharges into the north Atlantic. The aim of this work was to study the evolution of the thermohaline circulation in relation to these episodic iceberg discharges which punctuated the last 60 ka. To reconstruct the oceanic circulation in the past, we have analysed oxygen and carbon stable isotopes on benthic foraminifera from north Atlantic deep-sea cores. First of all, the higher temporal resolution of sedimentary records has enabled us to establish a precise chrono-stratigraphy for the different cores. Then, we have shown the close linkage between surface water hydrology and deep circulation, giving evidence of the sensibility of thermohaline circulation to melt water input in the north Atlantic ocean. Indeed, changes in deep circulation are synchronous from those identified in surface waters and are recorded on a period which lasted {approx} 1500 years. Deep circulation reconstructions, before and during a typical iceberg discharge reveal several modes of circulation linked to different convection sites at the high latitudes of the Atlantic basin. Moreover, the study of the last glacial period gives the opportunity to differentiate circulation changes due to the external forcing (variations of the orbital parameters) and those linked to a more local forcing (icebergs discharges). 105 refs., 50 figs., 14 tabs., 4 appends.

  13. Towards improved estimation of the dynamic topography and ocean circulation in the high latitude and arctic ocean: The importance of GOCE

    DEFF Research Database (Denmark)

    Johannessen, J. A.; Raj, R. P.; Nilsen, J. E. Ø.

    2013-01-01

    The Arctic plays a fundamental role in the climate system and shows significant sensitivity to anthropogenic climate forcing and the ongoing climate change. Evidently changes in the Arctic and surrounding seas have far reaching influences on regional and global environment and climate variability...... dynamic topography for studies of the ocean circulation and transport estimates in the Nordic Seas and Arctic Ocean........ In this respect this study combines in-situ hydrographical data, surface drifter data and direct current meter measurements, with coupled sea ice - ocean models, radar altimeter data and the latest GOCE-based geoid in order to estimate and assess the quality, usefulness and validity of the new GOCE derived mean...

  14. Integrating Magnetic and Modelling Approaches to Reconstruct Ocean Circulation at the LGM

    Science.gov (United States)

    Watkins, S.; Maher, B.; Bigg, G.

    2008-12-01

    Formation of N. Atlantic Deep Water (NADW) is an important component of the ocean thermohaline circulation but debate exists over the ocean circulation state during glacial stages. Some geological and modelling studies suggest decreased NADW and increased formation of Southern Ocean deep water during the Last Glacial Maximum (LGM); others indicate similar, or higher, rates of NADW advection. Here, we use an innovative, integrated approach combining ocean and general circulation model results with ground- truthing measurements of sediment magnetic properties, in order to test two different potential LGM ocean states. We compare modelled iceberg trajectories produced by each of the stable modeled ocean states with magnetically-mapped patterns and sources of LGM ice-rafted debris (IRD). One LGM state is characterised by vigorous NADW formation; the other by dominant deep water production in the Southern Ocean. Cluster analysis of sediment magnetic properties was used to characterise N. Atlantic IRD patterns and sources, which match most closely iceberg trajectories arising from some combination of the 'southern-sinking' and 'intermediate' ocean circulation states. The magnetic data indicate two major IRD sources, Fennoscandia and Greenland/Iceland, and one minor source, the St Lawrence region. The model and magnetic data suggest that the LGM N. Atlantic circulation was dominated by a cyclonic central N. Atlantic gyre, separated from the N. Atlantic Current which was displaced south of ~ 42 oN. This approach can provide discriminatory evidence and validation of past ocean circulation states, on an ocean-wide and non-sample destructive basis.

  15. A Coupled Ocean General Circulation, Biogeochemical, and Radiative Model of the Global Oceans: Seasonal Distributions of Ocean Chlorophyll and Nutrients

    Science.gov (United States)

    Gregg, Watson W.; Busalacchi, Antonio (Technical Monitor)

    2000-01-01

    A coupled ocean general circulation, biogeochemical, and radiative model was constructed to evaluate and understand the nature of seasonal variability of chlorophyll and nutrients in the global oceans. Biogeochemical processes in the model are determined from the influences of circulation and turbulence dynamics, irradiance availability. and the interactions among three functional phytoplankton groups (diatoms. chlorophytes, and picoplankton) and three nutrients (nitrate, ammonium, and silicate). Basin scale (greater than 1000 km) model chlorophyll results are in overall agreement with CZCS pigments in many global regions. Seasonal variability observed in the CZCS is also represented in the model. Synoptic scale (100-1000 km) comparisons of imagery are generally in conformance although occasional departures are apparent. Model nitrate distributions agree with in situ data, including seasonal dynamics, except for the equatorial Atlantic. The overall agreement of the model with satellite and in situ data sources indicates that the model dynamics offer a reasonably realistic simulation of phytoplankton and nutrient dynamics on synoptic scales. This is especially true given that initial conditions are homogenous chlorophyll fields. The success of the model in producing a reasonable representation of chlorophyll and nutrient distributions and seasonal variability in the global oceans is attributed to the application of a generalized, processes-driven approach as opposed to regional parameterization and the existence of multiple phytoplankton groups with different physiological and physical properties. These factors enable the model to simultaneously represent many aspects of the great diversity of physical, biological, chemical, and radiative environments encountered in the global oceans.

  16. An update to the Surface Ocean CO

    NARCIS (Netherlands)

    Bakker, D.C.E.; de Baar, H.J.W.; van heuven, S.

    2014-01-01

    The Surface Ocean CO2 Atlas (SOCAT), an activity of the international marine carbon research community, provides access to synthesis and gridded fCO2 (fugacity of carbon dioxide) products for the surface oceans. Version 2 of SOCAT is an update of the previous release (version

  17. Upper-Ocean Heat Balance Processes and the Walker Circulation in CMIP5 Model Projections

    Science.gov (United States)

    Robertson, F. R.; Roberts, J. B.; Funk, C.; Lyon, B.; Ricciardulli, L.

    2012-01-01

    Considerable uncertainty remains as to the importance of mechanisms governing decadal and longer variability of the Walker Circulation, its connection to the tropical climate system, and prospects for tropical climate change in the face of anthropogenic forcing. Most contemporary climate models suggest that in response to elevated CO2 and a warmer but more stratified atmosphere, the required upward mass flux in tropical convection will diminish along with the Walker component of the tropical mean circulation as well. Alternatively, there is also evidence to suggest that the shoaling and increased vertical stratification of the thermocline in the eastern Pacific will enable a muted SST increase there-- preserving or even enhancing some of the dynamical forcing for the Walker cell flow. Over the past decade there have been observational indications of an acceleration in near-surface easterlies, a strengthened Pacific zonal SST gradient, and globally-teleconnected dislocations in precipitation. But is this evidence in support of an ocean dynamical thermostat process posited to accompany anthropogenic forcing, or just residual decadal fluctuations associated with variations in warm and cold ENSO events and other stochastic forcing? From a modeling perspective we try to make headway on this question by examining zonal variations in surface energy fluxes and dynamics governing tropical upper ocean heat content evolution in the WCRP CMIP5 model projections. There is some diversity among model simulations; for example, the CCSM4 indicates net ocean warming over the IndoPacific region while the CSIRO model concentrates separate warming responses over the central Pacific and Indian Ocean regions. The models, as with observations, demonstrate strong local coupling between variations in column water vapor, downward surface longwave radiation and SST; but the spatial patterns of changes in the sign of this relationship differ among models and, for models as a whole, with

  18. Seasonal Distributions of Global Ocean Chlorophyll and Nutrients: Analysis with a Coupled Ocean General Circulation Biogeochemical, and Radiative Model

    Science.gov (United States)

    Gregg, Watson W.

    1999-01-01

    A coupled general ocean circulation, biogeochemical, and radiative model was constructed to evaluate and understand the nature of seasonal variability of chlorophyll and nutrients in the global oceans. The model is driven by climatological meteorological conditions, cloud cover, and sea surface temperature. Biogeochemical processes in the model are determined from the influences of circulation and turbulence dynamics, irradiance availability, and the interactions among three functional phytoplankton groups (diatoms, chorophytes, and picoplankton) and three nutrient groups (nitrate, ammonium, and silicate). Phytoplankton groups are initialized as homogeneous fields horizontally and vertically, and allowed to distribute themselves according to the prevailing conditions. Basin-scale model chlorophyll results are in very good agreement with CZCS pigments in virtually every global region. Seasonal variability observed in the CZCS is also well represented in the model. Synoptic scale (100-1000 km) comparisons of imagery are also in good conformance, although occasional departures are apparent. Agreement of nitrate distributions with in situ data is even better, including seasonal dynamics, except for the equatorial Atlantic. The good agreement of the model with satellite and in situ data sources indicates that the model dynamics realistically simulate phytoplankton and nutrient dynamics on synoptic scales. This is especially true given that initial conditions are homogenous chlorophyll fields. The success of the model in producing a reasonable representation of chlorophyll and nutrient distributions and seasonal variability in the global oceans is attributed to the application of a generalized, processes-driven approach as opposed to regional parameterization, and the existence of multiple phytoplankton groups with different physiological and physical properties. These factors enable the model to simultaneously represent the great diversity of physical, biological

  19. Dynamics of large scale 3-dimensional circulation of the Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Swapna, P.

    . The state of art simulation model results were compared with results from Simple Ocean Data Assimilation Model (SODA) to validate the model. The ix circulation obtained from the simulation model are of agreement with the SODA results and also... Fig.4.3 Surface velocity fields for the month of January (cm/s) sigma co-ordinate model (upper panel) and SODA (lower panel) Fig.4.4 Velocity fields (cm/s) for the month of January at 50 m depth. sigma co-ordinate model (upper panel...

  20. Spiraling pathways of global deep waters to the surface of the Southern Ocean

    OpenAIRE

    Tamsitt, Veronica; Drake, Henri F.; Morrison, Adele K.; Talley, Lynne D.; Dufour, Carolina O.; Gray, Alison R.; Griffies, Stephen M.; Mazloff, Matthew R.; Sarmiento, Jorge L.; Wang, Jinbo; Weijer, Wilbert

    2017-01-01

    Upwelling of global deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. However, the exact pathways and role of topography in Southern Ocean upwelling remain largely unknown. Here we show detailed upwelling pathways in three dimensions, using hydrographic observations and particle trac...

  1. Mid-latitude wind forced ocean circulation studies

    Science.gov (United States)

    Harrison, D. E.

    1981-01-01

    A simple barotropic vorticity equation model was developed to study some of the various modeling factors that affect the characteristics of strong western boundary currents like the Gulf Stream and Kuroshio. Successful prediction of sea surface temperature, both in the climatological mean and over periods as short as 1 month requires that the heating tendency, due to horizontal advection of heat by these currents, be accurately modeled. Conventional, coarse resolution ocean models do not satisfactorily reproduce the dominant features of these currents. It is concluded that it is important to understand why they do not and what must be done to do so in the future.

  2. Impact of remote oceanic forcing on Gulf of Alaska sea levels and mesoscale circulation

    Science.gov (United States)

    Melsom, Arne; Metzger, E. Joseph; Hurlburt, Harley E.

    2003-11-01

    We examine the relative importance of regional wind forcing and teleconnections by an oceanic pathway for impact on interannual ocean circulation variability in the Gulf of Alaska. Any additional factors that contribute to this variability, such as freshwater forcing from river runoff, are disregarded. The study is based on results from numerical simulations, sea level data from tide gauge stations, and sea surface height anomalies from satellite altimeter data. At the heart of this investigation is a comparison of ocean simulations that include and exclude interannual oceanic teleconnections of an equatorial origin. Using lagged correlations, the model results imply that 70-90% of the interannual coastal sea level variance in the Gulf of Alaska can be related to interannual sea levels at La Libertad, Equador. These values are higher than the corresponding range from sea level data, which is 25-55%. When oceanic teleconnections from the equatorial Pacific are excluded in the model, the explained variance becomes about 20% or less. During poleward propagation the coastally trapped sea level signal in the model is less attenuated than the observed signal. In the Gulf of Alaska we find well-defined sea level peaks in the aftermath of El Niño events. The interannual intensity of eddies in the Gulf of Alaska also peaks after El Niño events; however, these maxima are less clear after weak and moderate El Niño events. The interannual variations in eddy activity intensity are predominantly governed by the regional atmospheric forcing.

  3. Multidecadal Weakening of Indian Summer Monsoon Circulation Induces an Increasing Northern Indian Ocean Sea Level

    Science.gov (United States)

    Swapna, P.; Jyoti, J.; Krishnan, R.; Sandeep, N.; Griffies, S. M.

    2017-10-01

    North Indian Ocean sea level has shown significant increase during last three to four decades. Analyses of long-term climate data sets and ocean model sensitivity experiments identify a mechanism for multidecadal sea level variability relative to global mean. Our results indicate that North Indian Ocean sea level rise is accompanied by a weakening summer monsoon circulation. Given that Indian Ocean meridional heat transport is primarily regulated by the annual cycle of monsoon winds, weakening of summer monsoon circulation has resulted in reduced upwelling off Arabia and Somalia and decreased southward heat transport, and corresponding increase of heat storage in the North Indian Ocean. These changes in turn lead to increased retention of heat and increased thermosteric sea level rise in the North Indian Ocean, especially in the Arabian Sea. These findings imply that rising North Indian Ocean sea level due to weakening of monsoon circulation demands adaptive strategies to enable a resilient South Asian population.

  4. Uncertainty quantification for large-scale ocean circulation predictions.

    Energy Technology Data Exchange (ETDEWEB)

    Safta, Cosmin; Debusschere, Bert J.; Najm, Habib N.; Sargsyan, Khachik

    2010-09-01

    Uncertainty quantificatio in climate models is challenged by the sparsity of the available climate data due to the high computational cost of the model runs. Another feature that prevents classical uncertainty analyses from being easily applicable is the bifurcative behavior in the climate data with respect to certain parameters. A typical example is the Meridional Overturning Circulation in the Atlantic Ocean. The maximum overturning stream function exhibits discontinuity across a curve in the space of two uncertain parameters, namely climate sensitivity and CO{sub 2} forcing. We develop a methodology that performs uncertainty quantificatio in the presence of limited data that have discontinuous character. Our approach is two-fold. First we detect the discontinuity location with a Bayesian inference, thus obtaining a probabilistic representation of the discontinuity curve location in presence of arbitrarily distributed input parameter values. Furthermore, we developed a spectral approach that relies on Polynomial Chaos (PC) expansions on each sides of the discontinuity curve leading to an averaged-PC representation of the forward model that allows efficient uncertainty quantification and propagation. The methodology is tested on synthetic examples of discontinuous data with adjustable sharpness and structure.

  5. The relationship between sea surface temperature anomalies and atmospheric circulation in general circulation model experiments

    International Nuclear Information System (INIS)

    Kharin, V.V.

    1994-01-01

    Several multi-year integrations of the Hamburg version of the ECMWF/T21 general circulation model driven by the sea surface temperature (SST) observed in the period 1970-1988 were examined to study the extratropical response of the atmospheric circulation to SST anomalies in the Northern Hemisphere in winter. In the first 19-years run SST anomalies were prescribed globally (GAGO run), and in two others SST variability was limited to extratropical regions (MOGA run) and to tropics (TOGA run), respectively. A canonical correlation analysis was applied to the monthly means to find the best correlated patterns of SST anomalies in the Atlantic and Pacific Oceans and the Northern Hemisphere atmospheric flow. Contrary to expectation, the extratropical response in the GAGO run is not equal to the linear combination of the responses in the MOGA and TOGA runs. In the GAGO integration with globally prescribed SST the best correlated atmospheric pattern is global and is characterized by dipole structures of the same polarity in the North Atlantic and the North Pacific sectors. In the MOGA and TOGA experiments the atmospheric response is more local with main centers in the North Atlantic and North Pacific, respectively. The atmospheric modes found by the CCA were compared with the normal modes of the barotropic vorticity equation linearized about the 500 mb winter climate of the control integration driven by the climatological SST. The normal modes with smallest eigenvalues are similar to the canonical patterns of 500 mb geopotential height. The corresponding eigenvectors of the adjoint operator, which represent an external forcing optimal for exciting normal modes, have a longitudinal structure with maxima in regions characterized by enhanced high frequency baroclinic activity over both oceans. It was suggested that variability of storm tracks could play an important role in variability of the barotropic normal modes. (orig.)

  6. The effect of gateways on ocean circulation patterns in the Cenozoic

    NARCIS (Netherlands)

    von der Heydt, A.S.|info:eu-repo/dai/nl/245567526; Dijkstra, H.A.|info:eu-repo/dai/nl/073504467

    2008-01-01

    Both geological data and climate model studies indicate that substantially different patterns of the global ocean circulation have existed throughout the Cenozoic. In a climate model study of the late Oligocene [von der Heydt, A., Dijkstra, H.A. (2006). Effect of ocean gateways on the global ocean

  7. Aluminium in an ocean general circulation model compared with the West Atlantic Geotraces cruises

    NARCIS (Netherlands)

    van Hulten, M. M. P.; Sterl, A.; Tagliabue, A.; Dutay, J. -C.; Gehlen, M.; de Baar, H. J. W.; Middag, R.

    2013-01-01

    A model of aluminium has been developed and implemented in an Ocean General Circulation Model (NEMO-PISCES). In the model, aluminium enters the ocean by means of dust deposition. The internal oceanic processes are described by advection, mixing and reversible scavenging. The model has been evaluated

  8. Monitoring the variability of sea level and surface circulation with satellite altimetry

    NARCIS (Netherlands)

    Volkov, Denis L. "Jr"

    2004-01-01

    Variability in the ocean plays an important role in determining global weather and climate conditions. The advent of satellite altimetry has significantly facilitated the study of the variability of sea level and surface circulation. Satellites provide high-quality regular and nearly global

  9. Millennial-scale interaction between ice sheets and ocean circulation during marine isotope stage 100

    Directory of Open Access Journals (Sweden)

    Masao eOhno

    2016-05-01

    Full Text Available Waxing/waning of the ice sheets and the associated change in thermohaline circulation have played an important role in global climate change since major continental ice sheets appeared in the northern hemisphere about 2.75 million years ago. In the earliest glacial stages, however, establishment of the linkage between ice sheet development and ocean circulation remain largely unclear. Here we show new high-resolution records of marine isotope stage 100 recovered from deep-sea sediments on the Gardar Drift, in the subpolar North Atlantic. Results of a wide range of analyses clearly reveal the influence of millennial-scale variability in iceberg discharge on ocean surface condition and bottom current variability in the subpolar North Atlantic during marine isotope stage 100. We identified eight events of ice-rafted debris, which occurred mostly with decreases in sea surface temperature and in current components indicating North Atlantic Deep Water. These decreases are interpreted by weakened deep water formation linked to iceberg discharge, similarly to observations from the last glacial period. Dolomite fraction of the ice-rafted events in early MIS 100 like the last glacial Heinrich events suggests massive collapse of the Laurentide ice sheet in North America. At the same time, our early glacial data suggest differences from the last glacial period: absence of 1470-year periodicity in the interactions between ice sheets and ocean, and northerly shift of the ice-rafted debris belt. Our high-resolution data largely improve the picture of ice-sheet/ocean interactions on millennial time scales in the early glacial period after major Northern Hemisphere glaciation.

  10. Global Observations and Understanding of the General Circulation of the Oceans

    Science.gov (United States)

    1984-01-01

    The workshop was organized to: (1) assess the ability to obtain ocean data on a global scale that could profoundly change our understanding of the circulation; (2) identify the primary and secondary elements needed to conduct a World Ocean Circulation Experiment (WOCE); (3) if the ability is achievable, to determine what the U.S. role in such an experiment should be; and (4) outline the steps necessary to assure that an appropriate program is conducted. The consensus of the workshop was that a World Ocean Circulation Experiment appears feasible, worthwhile, and timely. Participants did agree that such a program should have the overall goal of understanding the general circulation of the global ocean well enough to be able to predict ocean response and feedback to long-term changes in the atmosphere. The overall goal, specific objectives, and recommendations for next steps in planning such an experiment are included.

  11. Antarctic glaciation caused ocean circulation changes at the Eocene-Oligocene transition.

    Science.gov (United States)

    Goldner, A; Herold, N; Huber, M

    2014-07-31

    Two main hypotheses compete to explain global cooling and the abrupt growth of the Antarctic ice sheet across the Eocene-Oligocene transition about 34 million years ago: thermal isolation of Antarctica due to southern ocean gateway opening, and declining atmospheric CO2 (refs 5, 6). Increases in ocean thermal stratification and circulation in proxies across the Eocene-Oligocene transition have been interpreted as a unique signature of gateway opening, but at present both mechanisms remain possible. Here, using a coupled ocean-atmosphere model, we show that the rise of Antarctic glaciation, rather than altered palaeogeography, is best able to explain the observed oceanographic changes. We find that growth of the Antarctic ice sheet caused enhanced northward transport of Antarctic intermediate water and invigorated the formation of Antarctic bottom water, fundamentally reorganizing ocean circulation. Conversely, gateway openings had much less impact on ocean thermal stratification and circulation. Our results support available evidence that CO2 drawdown--not gateway opening--caused Antarctic ice sheet growth, and further show that these feedbacks in turn altered ocean circulation. The precise timing and rate of glaciation, and thus its impacts on ocean circulation, reflect the balance between potentially positive feedbacks (increases in sea ice extent and enhanced primary productivity) and negative feedbacks (stronger southward heat transport and localized high-latitude warming). The Antarctic ice sheet had a complex, dynamic role in ocean circulation and heat fluxes during its initiation, and these processes are likely to operate in the future.

  12. Southern Ocean origin for the resumption of Atlantic thermohaline circulation during deglaciation.

    Science.gov (United States)

    Knorr, Gregor; Lohmann, Gerrit

    2003-07-31

    During the two most recent deglaciations, the Southern Hemisphere warmed before Greenland. At the same time, the northern Atlantic Ocean was exposed to meltwater discharge, which is generally assumed to reduce the formation of North Atlantic Deep Water. Yet during deglaciation, the Atlantic thermohaline circulation became more vigorous, in the transition from a weak glacial to a strong interglacial mode. Here we use a three-dimensional ocean circulation model to investigate the impact of Southern Ocean warming and the associated sea-ice retreat on the Atlantic thermohaline circulation. We find that a gradual warming in the Southern Ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation, triggered by increased mass transport into the Atlantic Ocean via the warm (Indian Ocean) and cold (Pacific Ocean) water route. This effect prevails over the influence of meltwater discharge, which would oppose a strengthening of the thermohaline circulation. A Southern Ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of Southern and Northern hemispheric climate change at times of deglaciation, in agreement with the available proxy records.

  13. Improving NOAA's NWLON Through Enhanced Data Inputs from NASA's Ocean Surface Topography

    Science.gov (United States)

    Guest, DeNeice C.

    2010-01-01

    This report assesses the benefit of incorporating NASA's OSTM (Ocean Surface Topography Mission) altimeter data (C- and Ku-band) into NOAA's (National Oceanic and Atmospheric Administration) NWLON (National Water Level Observation Network) DSS (Decision Support System). This data will enhance the NWLON DSS by providing additional inforrnation because not all stations collect all meteorological parameters (sea-surface height, ocean tides, wave height, and wind speed over waves). OSTM will also provide data where NWLON stations are not present. OSTM will provide data on seasurface heights for determining sea-level rise and ocean circulation. Researchers and operational users currently use satellite altimeter data products with the GSFCOO NASA data model to obtain sea-surface height and ocean circulation inforrnation. Accurate and tirnely inforrnation concerning sea-level height, tide, and ocean currents is needed to irnprove coastal tidal predictions, tsunarni and storm surge warnings, and wetland restoration.

  14. Indian Ocean circulation changes over the Middle Pleistocene Transition.

    Science.gov (United States)

    Petrick, B.; Auer, G.; De Vleeschouwer, D.; Christensen, B. A.; Stolfi, C.; Reuning, L.; Martinez-Garcia, A.; Haug, G. H.; Bogus, K.

    2017-12-01

    The Mid-Pleistocene Transition (MPT; 1.4 - 0.4 Ma) represents a climatic shift towards climate cycles at a quasi-100-kyr frequency. Although, several high-resolution records covering the MPT from globally distributed archives exist, there is only sparse evidence on changes in heat exchange between the Pacific and Indian Oceans, which represents a crucial part of the global thermohaline circulation (THC). Deciphering the influence of this heat exchange via the Indonesian Throughflow (ITF) is an important step in understanding the causes of the MPT. The Leeuwin Current off Western Australia is directly influenced by the ITF and can therefore be used to reconstruct ITF variability during the MPT. Today, the Leeuwin Current is the only southward flowing eastern boundary current in the southern hemisphere. The onset of the current is unknown but is proposed to have occurred 1 Ma and was likely related to significant changes in ITF dynamics during the MPT We present the first continuous reconstruction of changes in the Leeuwin Current during the MPT using data from IODP Expedition 356 Site U1460. The site is located at 29°S in the path of the current. High sedimentation rates ( 30 cm/ka) at Site U1460 provide the opportunity for high-resolution reconstruction of the MPT. We reconstruct paleoenvironmental variability by combining XRF, organic geochemistry, ICP-MS and XRD data with shipboard data, to reconstruct Leeuwin Current and ITF variability. Initial analyses show clear indications that upwelling off Western Australia intensified during the MPT, indicated by increased primary productivity related to increased nutrient levels, from 900-600 ka. Our results also suggest that the west Australian current (WAC) strengthened during this time supplying cool eutrophic waters from the high southern latitutes to the site. This intensification of the WAC may have had major implications for the Indian Ocean current system, but also the THC at large. This seems to be coupled with

  15. Ocean circulation and sea-ice thinning induced by melting ice shelves in the Amundsen Sea

    Science.gov (United States)

    Jourdain, Nicolas C.; Mathiot, Pierre; Merino, Nacho; Durand, Gaël.; Le Sommer, Julien; Spence, Paul; Dutrieux, Pierre; Madec, Gurvan

    2017-03-01

    A 1/12° ocean model configuration of the Amundsen Sea sector is developed to better understand the circulation induced by ice-shelf melt and the impacts on the surrounding ocean and sea ice. Eighteen sensitivity experiments to drag and heat exchange coefficients at the ice shelf/ocean interface are performed. The total melt rate simulated in each cavity is function of the thermal Stanton number, and for a given thermal Stanton number, melt is slightly higher for lower values of the drag coefficient. Sub-ice-shelf melt induces a thermohaline circulation that pumps warm circumpolar deep water into the cavity. The related volume flux into a cavity is 100-500 times stronger than the melt volume flux itself. Ice-shelf melt also induces a coastal barotropic current that contributes 45 ± 12% of the total simulated coastal transport. Due to the presence of warm circumpolar deep waters, the melt-induced inflow typically brings 4-20 times more heat into the cavities than the latent heat required for melt. For currently observed melt rates, approximately 6-31% of the heat that enters a cavity with melting potential is actually used to melt ice shelves. For increasing sub-ice-shelf melt rates, the transport in the cavity becomes stronger, and more heat is pumped from the deep layers to the upper part of the cavity then advected toward the ocean surface in front of the ice shelf. Therefore, more ice-shelf melt induces less sea-ice volume near the ice sheet margins.Plain Language SummaryThe ice-shelf cavities of the Amundsen Sea, Antarctica, act as very powerful pumps that create strong inflows of warm water under the ice-shelves, as well as significant circulation changes in the entire region. Such warm inflows bring more heat than required to melt ice, so that a large part of that heat exits ice-shelf cavities without being used. Due to mixing between warm deep waters and melt freshwater, melt-induced flows are warm and buoyant when they leave cavities. Therefore, they reach

  16. Oceanic circulation models help to predict global biogeography of pelagic yellow-bellied sea snake

    OpenAIRE

    Brischoux, François; Cotté, Cédric; Lillywhite, Harvey B.; Bailleul, Frédéric; Lalire, Maxime; Gaspar, Philippe

    2016-01-01

    It is well recognized that most marine vertebrates, and especially tetrapods, precisely orient and actively move in apparently homogeneous oceanic environments. Here, we investigate the presumptive role of oceanic currents in biogeographic patterns observed in a secondarily marine tetrapod, the yellow-bellied sea snake (Hydrophis [Pelamis] platurus). State-of-the-art world ocean circulation models show how H. platurus, the only pelagic species of sea snake, can potentially exploit oceanic cur...

  17. Improvement in Geoid Models for Ocean Circulation Studies

    Science.gov (United States)

    Tapley, Byron D.; Chambers, Don P.; Poole, Steve; Ries, John c.

    2003-01-01

    At wavelengths of 500 km and longer, the GRACE GGM01 Model produces a significantly better marine geoid than any previous model. This conclusion follows from evaluating the geostrophic currents determined by combining the model with a mean sea surface from altimetry. The agreement with currents computed from a traditional hydrographic map is very close, which suggests that one of the primary missions of the TOPEX/POSEIDON mission, to determine the absolute dynamic ocean topography, may soon be met. This solution has been made available to the public at http://www.csr.utexs.edu/grace/gravity. The results reported in this paper have been presented at the 2003 EGS-AGU-EUG Joint Assembly. Two articles are currently being prepared for Geophysical Research Letters to summarize these results.

  18. An Evaluation of the Large-Scale Implementation of Ocean Thermal Energy Conversion (OTEC Using an Ocean General Circulation Model with Low-Complexity Atmospheric Feedback Effects

    Directory of Open Access Journals (Sweden)

    Yanli Jia

    2018-01-01

    Full Text Available Previous investigations of the large-scale deployment of Ocean Thermal Energy Conversions (OTEC systems are extended by allowing some atmospheric feedback in an ocean general circulation model. A modified ocean-atmosphere thermal boundary condition is used where relaxation corresponds to atmospheric longwave radiation to space, and an additional term expresses horizontal atmospheric transport. This produces lower steady-state OTEC power maxima (8 to 10.2 TW instead of 14.1 TW for global OTEC scenarios, and 7.2 to 9.3 TW instead of 11.9 TW for OTEC implementation within 100 km of coastlines. When power production peaks, power intensity remains practically unchanged, at 0.2 TW per Sverdrup of OTEC deep cold seawater, suggesting a similar degradation of the OTEC thermal resource. Large-scale environmental effects include surface cooling in low latitudes and warming elsewhere, with a net heat intake within the water column. These changes develop rapidly from the propagation of Kelvin and Rossby waves, and ocean current advection. Two deep circulation cells are generated in the Atlantic and Indo-Pacific basins. The Atlantic Meridional Overturning Circulation (AMOC is reinforced while an AMOC-like feature appears in the North Pacific, with deep convective winter events at high latitudes. Transport between the Indo-Pacific and the Southern Ocean is strengthened, with impacts on the Atlantic via the Antarctic Circumpolar Current (ACC.

  19. Anomalous circulation in the Pacific sector of the Arctic Ocean in July-December 2008

    Science.gov (United States)

    Francis, Oceana P.; Yaremchuk, Max; Panteleev, Gleb G.; Zhang, Jinlun; Kulakov, Mikhail

    2017-09-01

    Variability of the mean summer-fall ocean state in the Pacific Sector of the Arctic Ocean (PSAO) is studied using a dynamically constrained synthesis (4Dvar) of historical in situ observations collected during 1972 to 2008. Specifically, the oceanic response to the cyclonic (1989-1996) and anticyclonic (1972-1978, 1997-2006) phases of the Arctic Ocean Oscillation (AOO) is assessed for the purpose of quantitatively comparing the 2008 circulation pattern that followed the 2007 ice cover minimum. It is shown that the PSAO circulation during July-December of 2008 was characterized by a pronounced negative Sea Surface Height (SSH) anomaly along the Eurasian shelf break, which caused a significant decline of the transport in the Atlantic Water (AW) inflow region into the PSAO and increased the sea level difference between the Bering and Chukchi Seas. This anomaly could be one of the reasons for the observed amplification of the Bering Strait transport carrying fresh Pacific Waters into the PSAO. Largrangian analysis of the optimized solution suggests that the freshwater (FW) accumulation in the Beaufort Gyre has a negligible contribution from the East Siberian Sea and is likely caused by the enhanced FW export from the region north of the Canadian Archipelago/Greenland. The inverse modeling results are confirmed by validation against independent altimetry observations and in situ velocity data from NABOS moorings. It is also shown that presented results are in significantly better agreement with the data than the output of the PIOMAS model run utilized as a first guess solution for the 4dVar analysis.

  20. Idealised modelling of ocean circulation driven by conductive and hydrothermal fluxes at the seabed

    Science.gov (United States)

    Barnes, Jowan M.; Morales Maqueda, Miguel A.; Polton, Jeff A.; Megann, Alex P.

    2018-02-01

    Geothermal heating is increasingly recognised as an important factor affecting ocean circulation, with modelling studies suggesting that this heat source could lead to first-order changes in the formation rate of Antarctic Bottom Water, as well as a significant warming effect in the abyssal ocean. Where it has been represented in numerical models, however, the geothermal heat flux into the ocean is generally treated as an entirely conductive flux, despite an estimated one third of the global geothermal flux being introduced to the ocean via hydrothermal sources. A modelling study is presented which investigates the sensitivity of the geothermally forced circulation to the way heat is supplied to the abyssal ocean. An analytical two-dimensional model of the circulation is described, which demonstrates the effects of a volume flux through the ocean bed. A simulation using the NEMO numerical general circulation model in an idealised domain is then used to partition a heat flux between conductive and hydrothermal sources and explicitly test the sensitivity of the circulation to the formulation of the abyssal heat flux. Our simulations suggest that representing the hydrothermal flux as a mass exchange indeed changes the heat distribution in the abyssal ocean, increasing the advective heat transport from the abyss by up to 35% compared to conductive heat sources. Consequently, we suggest that the inclusion of hydrothermal fluxes can be an important addition to course-resolution ocean models.

  1. Surface changes in the North Atlantic meridional overturning circulation during the last millennium

    DEFF Research Database (Denmark)

    Wanamaker, Jr., Alan D.; Butler, Paul G.; Scourse, James D.

    2012-01-01

    the past 1,350 years, to reconstruct changes in surface ocean circulation and climate. The water mass tracer data presented here from the North Icelandic shelf, combined with previously published data from the Arctic and subtropical Atlantic, show that surface Atlantic meridional overturning circulation......Despite numerous investigations, the dynamical origins of the Medieval Climate Anomaly and the Little Ice Age remain uncertain. A major unresolved issue relating to internal climate dynamics is the mode and tempo of Atlantic meridional overturning circulation variability, and the significance...... of decadal-to-centennial scale changes in Atlantic meridional overturning circulation strength in regulating the climate of the last millennium. Here we use the time-constrained high-resolution local radiocarbon reservoir age offset derived from an absolutely dated annually resolved shell chronology spanning...

  2. Surface changes in the North Atlantic meridional overturning circulation during the last millennium

    Science.gov (United States)

    Wanamaker, Alan D.; Butler, Paul G.; Scourse, James D.; Heinemeier, Jan; Eiríksson, Jón; Knudsen, Karen Luise; Richardson, Christopher A.

    2012-01-01

    Despite numerous investigations, the dynamical origins of the Medieval Climate Anomaly and the Little Ice Age remain uncertain. A major unresolved issue relating to internal climate dynamics is the mode and tempo of Atlantic meridional overturning circulation variability, and the significance of decadal-to-centennial scale changes in Atlantic meridional overturning circulation strength in regulating the climate of the last millennium. Here we use the time-constrained high-resolution local radiocarbon reservoir age offset derived from an absolutely dated annually resolved shell chronology spanning the past 1,350 years, to reconstruct changes in surface ocean circulation and climate. The water mass tracer data presented here from the North Icelandic shelf, combined with previously published data from the Arctic and subtropical Atlantic, show that surface Atlantic meridional overturning circulation dynamics likely amplified the relatively warm conditions during the Medieval Climate Anomaly and the relatively cool conditions during the Little Ice Age within the North Atlantic sector. PMID:22692542

  3. Potential feedback mechanism between phytoplankton and upper ocean circulation with oceanic radiative transfer processes influenced by phytoplankton - Numerical ocean, general circulation models and an analytical solution

    Digital Repository Service at National Institute of Oceanography (India)

    Nakamoto, S.; Kano, M.; PrasannaKumar, S.; Oberhuber, J.M.; Muneyama, K.; Ueyoshi, K.; Subrahmanyam, B.; Nakata, K.; Lai, C.A.; Frouin, R.

    and Dickey (1987) demonstrate that the at- tenuation of visible energy and photosynthetically available radiation (PAR) (Morel, 1978) are primarily functions of chlorophyll pigments. iturriaga and Potential Feedback Mechanism 257 Siegel (1989) reported... isoPYcnal coordinate (BPYC) general circulation model (Oberhuber, 1993), Nakamoto et al. (2001) showed that surface chlorophyll pigments in the equatorial Pacific not only influence vertical penetration of solar ra- diation, but also modify...

  4. Northern South China Sea Surface Circulation and its Variability Derived by Combining Satellite Altimetry and Surface Drifter Data

    Directory of Open Access Journals (Sweden)

    N. Peter Benny

    2015-01-01

    Full Text Available The present study analyses the mean and seasonal mesoscale surface circulation of the Northern South China Sea (NSCS and determines the influence of El Niño/SouthernNiño/Southern Oscillation (ENSO. High resolution Eulerian velocity field is derived by combining the available satellite tracked surface drifter data with satellite altimetry during 1993 - 2012. The wind driven current is computed employing the weekly ocean surface mean wind fields derived from the scatterometers on board ERS 1/2, QuikSCAT and ASCAT. The derived mean velocity field exhibits strong boundary currents and broad zonal flow across NSCS. The anomalous field is quite strong in the southern part and the Seasonal circulation clearly depicts the monsoonal forcing. Eddy Kinetic Energy (EKE distribution and its spatial and temporal structures are determined employing Empirical Orthogonal Function (EOF analysis. The ENSO influence on NSCS surface circulation has been analyzed using monthly absolute geostrophic velocity fields during 1996 - 1999.

  5. Hydrology of surface waters and thermohaline circulation during the last glacial period

    International Nuclear Information System (INIS)

    Vidal, L.

    1996-01-01

    Sedimentological studies on oceanic cores from the north Atlantic have revealed, over the last glacial period, abrupt climatic changes with a periodicity of several thousand years which contrasts strongly with the glacial-interglacial periodicity (several tens of thousand years). These periods of abrupt climate changes correspond to massive icebergs discharges into the north Atlantic. The aim of this work was to study the evolution of the thermohaline circulation in relation to these episodic iceberg discharges which punctuated the last 60 ka. To reconstruct the oceanic circulation in the past, we have analysed oxygen and carbon stable isotopes on benthic foraminifera from north Atlantic deep-sea cores. First of all, the higher temporal resolution of sedimentary records has enabled us to establish a precise chrono-stratigraphy for the different cores. Then, we have shown the close linkage between surface water hydrology and deep circulation, giving evidence of the sensibility of thermohaline circulation to melt water input in the north Atlantic ocean. Indeed, changes in deep circulation are synchronous from those identified in surface waters and are recorded on a period which lasted ∼ 1500 years. Deep circulation reconstructions, before and during a typical iceberg discharge reveal several modes of circulation linked to different convection sites at the high latitudes of the Atlantic basin. Moreover, the study of the last glacial period gives the opportunity to differentiate circulation changes due to the external forcing (variations of the orbital parameters) and those linked to a more local forcing (icebergs discharges). 105 refs., 50 figs., 14 tabs., 4 appends

  6. A global mean dynamic topography and ocean circulation estimation using a preliminary GOCE gravity model

    DEFF Research Database (Denmark)

    Knudsen, Per; Bingham, R.; Andersen, Ole Baltazar

    2011-01-01

    The Gravity and steady-state Ocean Circulation Explorer (GOCE) satellite mission measures Earth’s gravity field with an unprecedented accuracy at short spatial scales. In doing so, it promises to significantly advance our ability to determine the ocean’s general circulation. In this study, an ini...

  7. An Improved Heat Budget Estimation Including Bottom Effects for General Ocean Circulation Models

    Science.gov (United States)

    Carder, Kendall; Warrior, Hari; Otis, Daniel; Chen, R. F.

    2001-01-01

    This paper studies the effects of the underwater light field on heat-budget calculations of general ocean circulation models for shallow waters. The presence of a bottom significantly alters the estimated heat budget in shallow waters, which affects the corresponding thermal stratification and hence modifies the circulation. Based on the data collected during the COBOP field experiment near the Bahamas, we have used a one-dimensional turbulence closure model to show the influence of the bottom reflection and absorption on the sea surface temperature field. The water depth has an almost one-to-one correlation with the temperature rise. Effects of varying the bottom albedo by replacing the sea grass bed with a coral sand bottom, also has an appreciable effect on the heat budget of the shallow regions. We believe that the differences in the heat budget for the shallow areas will have an influence on the local circulation processes and especially on the evaporative and long-wave heat losses for these areas. The ultimate effects on humidity and cloudiness of the region are expected to be significant as well.

  8. On multiple equilibria of the global ocean circulation and the preference for North Atlantic sinking

    NARCIS (Netherlands)

    Huisman, S.E.

    2010-01-01

    In the ocean circulation there is the peculiar feature that heat transport is northwards throughout the entire Atlantic ocean. This means that the Atlantic heat transport in the southern hemisphere is towards the equator. Also, the heat transport in the Atlantic is much larger that in the Pacific.

  9. Large-scale ocean circulation, dynamics, and air-sea exchanges : Argo observations of the mean and time- varying ocean

    OpenAIRE

    Giglio, Donata

    2014-01-01

    The large-scale ocean circulation, dynamics, and air-sea exchanges are investigated, based on observational datasets including Argo and satellite altimetry, and viewed in the framework of modern theoretical ideas. Initially, the wind-driven interannual variability of the subtropical North Pacific is described. Using the extensive Argo dataset, it is seen that the North Pacific gyre varies in the strength of its interior circulation and in its spatial orientation, on interannual timescales. Al...

  10. Consequences of future increased Arctic runoff on Arctic Ocean stratification, circulation, and sea ice cover

    OpenAIRE

    Nummelin, Aleksi; Ilicak, Mehmet; Li, Camille; Smedsrud, Lars Henrik

    2016-01-01

    The Arctic Ocean has important freshwater sources including river runoff, low evaporation, and exchange with the Pacific Ocean. In the future, we expect even larger freshwater input as the global hydrological cycle accelerates, increasing high-latitude precipitation, and river runoff. Previous modeling studies show some robust responses to high-latitude freshwater perturbations, including a strengthening of Arctic stratification and a weakening of the large-scale ocean circulation...

  11. Comment on "The Atlantic Multidecadal Oscillation without a role for ocean circulation".

    Science.gov (United States)

    Zhang, Rong; Sutton, Rowan; Danabasoglu, Gokhan; Delworth, Thomas L; Kim, Who M; Robson, Jon; Yeager, Stephen G

    2016-06-24

    Clement et al (Reports, 16 October 2015, p. 320) claim that the Atlantic Multidecadal Oscillation (AMO) is a thermodynamic response of the ocean mixed layer to stochastic atmospheric forcing and that ocean circulation changes have no role in causing the AMO. These claims are not justified. We show that ocean dynamics play a central role in the AMO. Copyright © 2016, American Association for the Advancement of Science.

  12. Deep circulation in the Indian and Pacific Oceans and its implication for the dumping of low-level radioactive waste

    International Nuclear Information System (INIS)

    Harries, J.R.

    1980-06-01

    The complexity of ocean transport processes has meant that the limits for the dumping of low-activity radioactive wastes have had to be based on very simplified models of the oceans. This report discusses the models used to determine dumping limits and contrasts them with the known ocean circulation patterns. The deep circulations of the Indian and Pacific Oceans are reviewed to provide a basis for estimating the possible destinations and likely transit times for dissolved material released at the ocean floor

  13. Widespread and synchronous change in deep-ocean circulation in the North and South Atlantic during the Late Cretaceous

    OpenAIRE

    Robinson, S. A.; Vance, D.

    2012-01-01

    Modern thermohaline circulation plays a role in latitudinal heat transport and in deep-ocean ventilation, yet ocean circulation may have functioned differently during past periods of extreme warmth, such as the Cretaceous. The Late Cretaceous (100–65 Ma) was an important period in the evolution of the North Atlantic Ocean, characterized by opening ocean gateways, long-term climatic cooling and the cessation of intermittent periods of anoxia (oceanic anoxic events, OAEs). However, how these ph...

  14. Asymmetric response of the Atlantic Meridional Ocean Circulation to freshwater anomalies in a strongly-eddying global ocean model

    NARCIS (Netherlands)

    Brunnabend, Sandra Esther|info:eu-repo/dai/nl/371740878; Dijkstra, Henk A.|info:eu-repo/dai/nl/073504467

    2017-01-01

    The Atlantic Meridional Overturning Circulation (AMOC) responds sensitively to density changes in regions of deepwater formation. In this paper, we investigate the nonlinear response of the AMOC to large amplitude freshwater changes around Greenland using a strongly-eddying global ocean model. Due

  15. Efficient computation of past global ocean circulation patterns using continuation in paleobathymetry

    Science.gov (United States)

    Mulder, T. E.; Baatsen, M. L. J.; Wubs, F. W.; Dijkstra, H. A.

    2017-07-01

    In the field of paleoceanographic modeling, the different positioning of Earth's continental configurations is often a major challenge for obtaining equilibrium ocean flow solutions. In this paper, we introduce numerical parameter continuation techniques to compute equilibrium solutions of ocean flows in the geological past, where we change the continental geometry and allow the flow to deform using a homotopy parameter. The methods are illustrated by computing equilibrium three-dimensional global ocean circulation patterns over the last 65 Ma under a highly idealized atmospheric forcing. These results already show interesting major transitions in ocean circulation patterns due to changes in ocean gateways, that may have been relevant for Cenozoic climate transitions. In addition, the techniques are shown to be computationally efficient compared to the established continuation spin-up approach.

  16. Impacts of Spatial Distribution of Parameterized Local and Remote Tidal Mixing on Large-scale Ocean Circulation and Climate.

    Science.gov (United States)

    Legg, S.; Melet, A.; Hallberg, R.

    2016-02-01

    Energy extracted from the barotropic tide as it flows over topography can ultimately be used for mixing, which in turn influences large-scale circulation and climate. While the physics of the energy conversion process is now well understood, the eventual location of the resultant mixing is still poorly known, and dependent on a variety of wave breaking processes. Here, we examine the impact of different horizontal and vertical distributions of the mixing by breaking internal tides on the large-scale ocean circulation and climate in a fully-coupled climate model, GFDL's ESM2G. Internal tides are assumed to dissipate either at the generation site, or in deep ocean basins, over continental slopes, or on continental shelves. The dissipation has a vertical profile which is specified to either: (a) decay exponentially with height above the bottom, or (b) scale with the buoyancy frequency, or (c) scale with the buoyancy frequency squared as suggested by observations of dissipation away from rough topography. The resultant large-scale ocean circulation is highly sensitive to the vertical distribution of dissipation, with bottom intensified mixing leading to enhanced deep overturning and sharper thermoclines, while profiles with greater dissipation near the surface have stronger subtropical cells, and more diffuse thermoclines. The climate appears less sensitive to these idealized horizontal distributions of mixing. An exception is mixing near regions of deep water formation, such as the continental slopes of the North Atlantic and the Antarctic, where substantial mixing in the descending branch of the overturning circulation leads to a dilution of dense water, and corresponding weakening of the overturning. Motivated by this demonstrated sensitivity of the large-scale ocean circulation, we are refining models of the spatial distribution of internal wave breaking, in collaboration with partners in the Internal Wave Driven Mixing climate process team.

  17. Seaglider surveys at Ocean Station Papa: Circulation and water mass properties in a meander of the North Pacific Current

    Science.gov (United States)

    Pelland, Noel A.; Eriksen, Charles C.; Cronin, Meghan F.

    2016-09-01

    A Seaglider autonomous underwater vehicle augmented the Ocean Station Papa (OSP; 50°N, 145°W) surface mooring, measuring spatial structure on scales relevant to the monthly evolution of the moored time series. During each of three missions from June 2008 to January 2010, a Seaglider made biweekly 50 km × 50 km surveys in a bowtie-shaped survey track. Horizontal temperature and salinity gradients measured by these surveys were an order of magnitude stronger than climatological values and sometimes of opposite sign. Geostrophically inferred circulation was corroborated by moored acoustic Doppler current profiler measurements and AVISO satellite altimetry estimates of surface currents, confirming that glider surveys accurately resolved monthly scale mesoscale spatial structure. In contrast to climatological North Pacific Current circulation, upper-ocean flow was modestly northward during the first half of the 18 month survey period, and weakly westward during its latter half, with Rossby number O>(0.01>). This change in circulation coincided with a shift from cool and fresh to warm, saline, oxygen-rich water in the upper-ocean halocline, and an increase in vertical fine structure there and in the lower pycnocline. The anomalous flow and abrupt water mass transition were due to the slow growth of an anticyclonic meander within the North Pacific Current with radius comparable to the scale of the survey pattern, originating to the southeast of OSP.

  18. Sunglitter Imagery Of The Ocean Surface Phenomena

    Science.gov (United States)

    Myasoedov, Alexander; Kudryavtsev, Vladimir; Chapron, Bertrand; Johannessen, Johnny

    2010-04-01

    An algorithm for retrieval of spatial variations of the mean square slope (MSS) of the sea surface from sunglint imagery is proposed. The retrieval algorithm is free on a prior suggestion on PDF model. The transfer function, relating the brightness contrast to the MSS contrasts, is found from observed sunglint brightness, where “real” PDF of the sea slopes has built-in. Developed approach was applied for analysis of the sunglint signature of the mesoscale ocean dynamics and internal waves. We found that the ocean currents (eddies, meanders, frontal lines) and internal waves are well visible on the sea surface as the MSS anomalies. Results of this study is further adopted by Kudryavtsev et al. (2010) for development of advanced approach for synergetic use of SAR and optical imagery in studies of meso-scale ocean dynamics.

  19. Possible Abrupt Changes in Ocean Circulation and Climate Due to the Changing Behavior of Ross Ice Streams, West Antarctica

    Science.gov (United States)

    Tulaczyk, S.; Hunke, E. C.; Joughin, I.; Bougamont, M. H.; Vogel, S. W.

    2001-12-01

    One of the most important recent results of glaciological research in West Antarctica is the discovery that ice discharge from Ross ice streams may have been decreasing for at least as long as ~150 years. This decrease may be driven by changes in the ice-stream basal thermal regime (Kamb 2001). The magnitude of the decrease amounted to ~1 cm less of global sea level rise in the last century than we would have otherwise experienced. Changes in discharge from Ross ice streams may also have important implications for near future stability of the Ross Ice Shelf (RIS), which is nourished by these ice streams. If ice-stream discharge will continue its recent decrease, RIS will thin and may start to retreat or break up. Additional impetus for retreat or break up of the RIS may come from future climatic warming that appears to have helped to destabilize some smaller ice shelves along the Antarctic Penninsula. Break up of RIS alone would expose ~0.5 mln km2 of new sea surface area and could have significant implications for exchange of energy and water between the ocean and the atmosphere-cryosphere system in the region. Moreover, brine exclusion during sea-ice formation could turn this newly exposed polar continental shelf into a key source of bottom ocean water. This strengthened Antarctic Bottom Water formation could outcompete the North Atlantic source of Bottom Water and switch the global ocean into a new mode of thermohaline circulation, with global climatic implications (Denton, 2000). At the present time, we begin to quantify the effects of removing West Antarctic ice shelves on global thermohaline circulation using a coupled, global sea-ice-ocean circulation model developed at LANL. Qualitatively, however, there is a strong potential for significant impact of the recent changes in flow rates of the West Antarctic ice streams on regional and global atmospheric and ocean circulation.

  20. Surface circulation and upwelling patterns around Sri Lanka

    Science.gov (United States)

    de Vos, A.; Pattiaratchi, C. B.; Wijeratne, E. M. S.

    2014-10-01

    Sri Lanka occupies a unique location within the equatorial belt in the northern Indian Ocean, with the Arabian Sea on its western side and the Bay of Bengal on its eastern side, and experiences bi-annually reversing monsoon winds. Aggregations of blue whale (Balaenoptera musculus) have been observed along the southern coast of Sri Lanka during the northeast (NE) monsoon, when satellite imagery indicates lower productivity in the surface waters. This study explored elements of the dynamics of the surface circulation and coastal upwelling in the waters around Sri Lanka using satellite imagery and numerical simulations using the Regional Ocean Modelling System (ROMS). The model was run for 3 years to examine the seasonal and shorter-term (~10 days) variability. The results reproduced correctly the reversing current system, between the Equator and Sri Lanka, in response to the changing wind field: the eastward flowing Southwest Monsoon Current (SMC) during the southwest (SW) monsoon transporting 11.5 Sv (mean over 2010-2012) and the westward flowing Northeast Monsoon Current (NMC) transporting 9.6 Sv during the NE monsoon, respectively. A recirculation feature located to the east of Sri Lanka during the SW monsoon, the Sri Lanka Dome, is shown to result from the interaction between the SMC and the island of Sri Lanka. Along the eastern and western coasts, during both monsoon periods, flow is southward converging along the southern coast. During the SW monsoon, the island deflects the eastward flowing SMC southward, whilst along the eastern coast, the southward flow results from the Sri Lanka Dome recirculation. The major upwelling region, during both monsoon periods, is located along the southern coast, resulting from southward flow converging along the southern coast and subsequent divergence associated with the offshore transport of water. Higher surface chlorophyll concentrations were observed during the SW monsoon. The location of the flow convergence and hence the

  1. Interannual variability of sea surface temperature and circulation in ...

    African Journals Online (AJOL)

    A regional ocean model was used to study interannual variations in the Tanzanian shelf region and offshore in the tropical western Indian Ocean for the period 1980–2007. The model was forced with surface winds and heat fluxes from the National Centers for Environmental Prediction (NCEP) reanalysis, and its initial and ...

  2. Natural variability in the surface ocean carbonate ion concentration

    Directory of Open Access Journals (Sweden)

    N. S. Lovenduski

    2015-11-01

    Full Text Available We investigate variability in the surface ocean carbonate ion concentration ([CO32−] on the basis of a~long control simulation with an Earth System Model. The simulation is run with a prescribed, pre-industrial atmospheric CO2 concentration for 1000 years, permitting investigation of natural [CO32−] variability on interannual to multi-decadal timescales. We find high interannual variability in surface [CO32−] in the tropical Pacific and at the boundaries between the subtropical and subpolar gyres in the Northern Hemisphere, and relatively low interannual variability in the centers of the subtropical gyres and in the Southern Ocean. Statistical analysis of modeled [CO32−] variance and autocorrelation suggests that significant anthropogenic trends in the saturation state of aragonite (Ωaragonite are already or nearly detectable at the sustained, open-ocean time series sites, whereas several decades of observations are required to detect anthropogenic trends in Ωaragonite in the tropical Pacific, North Pacific, and North Atlantic. The detection timescale for anthropogenic trends in pH is shorter than that for Ωaragonite, due to smaller noise-to-signal ratios and lower autocorrelation in pH. In the tropical Pacific, the leading mode of surface [CO32−] variability is primarily driven by variations in the vertical advection of dissolved inorganic carbon (DIC in association with El Niño–Southern Oscillation. In the North Pacific, surface [CO32−] variability is caused by circulation-driven variations in surface DIC and strongly correlated with the Pacific Decadal Oscillation, with peak spectral power at 20–30-year periods. North Atlantic [CO32−] variability is also driven by variations in surface DIC, and exhibits weak correlations with both the North Atlantic Oscillation and the Atlantic Multidecadal Oscillation. As the scientific community seeks to detect the anthropogenic influence on ocean carbonate chemistry, these results

  3. Natural variability in the surface ocean carbonate ion concentration

    Science.gov (United States)

    Lovenduski, N. S.; Long, M. C.; Lindsay, K.

    2015-11-01

    We investigate variability in the surface ocean carbonate ion concentration ([CO32-]) on the basis of a~long control simulation with an Earth System Model. The simulation is run with a prescribed, pre-industrial atmospheric CO2 concentration for 1000 years, permitting investigation of natural [CO32-] variability on interannual to multi-decadal timescales. We find high interannual variability in surface [CO32-] in the tropical Pacific and at the boundaries between the subtropical and subpolar gyres in the Northern Hemisphere, and relatively low interannual variability in the centers of the subtropical gyres and in the Southern Ocean. Statistical analysis of modeled [CO32-] variance and autocorrelation suggests that significant anthropogenic trends in the saturation state of aragonite (Ωaragonite) are already or nearly detectable at the sustained, open-ocean time series sites, whereas several decades of observations are required to detect anthropogenic trends in Ωaragonite in the tropical Pacific, North Pacific, and North Atlantic. The detection timescale for anthropogenic trends in pH is shorter than that for Ωaragonite, due to smaller noise-to-signal ratios and lower autocorrelation in pH. In the tropical Pacific, the leading mode of surface [CO32-] variability is primarily driven by variations in the vertical advection of dissolved inorganic carbon (DIC) in association with El Niño-Southern Oscillation. In the North Pacific, surface [CO32-] variability is caused by circulation-driven variations in surface DIC and strongly correlated with the Pacific Decadal Oscillation, with peak spectral power at 20-30-year periods. North Atlantic [CO32-] variability is also driven by variations in surface DIC, and exhibits weak correlations with both the North Atlantic Oscillation and the Atlantic Multidecadal Oscillation. As the scientific community seeks to detect the anthropogenic influence on ocean carbonate chemistry, these results will aid the interpretation of trends

  4. Monitoring the variability of sea level and surface circulation with satellite altimetry

    Science.gov (United States)

    Volkov, Denis L. "Jr"

    2004-10-01

    Variability in the ocean plays an important role in determining global weather and climate conditions. The advent of satellite altimetry has significantly facilitated the study of the variability of sea level and surface circulation. Satellites provide high-quality regular and nearly global measurements enabling us to study the oceanic variability on the spatial scales from the size of an eddy to global, and on the temporal scales from weeks to interannual and longer. This thesis demonstrates how satellite altimetry measurements can be used to study the mesoscale, seasonal and interannual variability of sea level and surface circulation. Oceanic variability at these time scales is mainly induced by the variations of heat and fresh water fluxes (buoyancy fluxes) at air-sea interface, the variations of heat and salt budget due to the advection of water masses with different properties, eddy generation mechanisms due to the instability of oceanic currents, Rossby waves, etc. It is shown how the sea level in the extratropical North Atlantic Ocean was changing during the investigated time interval from 1993 to 2003. The mesoscale, seasonal and inter-annual modes of the variability are revealed, and the magnitude and relative contribution of each mode to the total variance is assessed. The inter-annual change of the sea surface height in the northern North Atlantic, measured with altimetry, is coupled with in situ observations along the transatlantic section AR7E, repeated almost every year from 1990 to 2003 in the framework of the WOCE (World Ocean Circulation Experiment) and CLIVAR (CLImate VARiability) hydrographic programs. This allowed interpreting the observed inter-annual change of sea level in terms of changes in the sea water properties and the distribution of water masses. A comparative analysis of changes observed in the extratropical North Atlantic and in the extratropical North Pacific is performed. The magnitudes, spatial patterns, and also trends of the

  5. Southern Hemisphere anticyclonic circulation drives oceanic and climatic conditions in late Holocene southernmost Africa

    Science.gov (United States)

    Hahn, Annette; Schefuß, Enno; Andò, Sergio; Cawthra, Hayley C.; Frenzel, Peter; Kugel, Martin; Meschner, Stephanie; Mollenhauer, Gesine; Zabel, Matthias

    2017-06-01

    Due to the high sensitivity of southern Africa to climate change, a reliable understanding of its hydrological system is crucial. Recent studies of the regional climatic system have revealed a highly complex interplay of forcing factors on precipitation regimes. This includes the influence of the tropical easterlies, the strength of the southern hemispheric westerlies as well as sea surface temperatures along the coast of the subcontinent. However, very few marine records have been available in order to study the coupling of marine and atmospheric circulation systems. Here we present results from a marine sediment core, recovered in shallow waters off the Gouritz River mouth on the south coast of South Africa. Core GeoB18308-1 allows a closer view of the last ˜ 4 kyr. Climate sensitive organic proxies, like the distribution and isotopic composition of plant-wax lipids as well as indicators for sea surface temperatures and soil input, give information on oceanographic and hydrologic changes during the recorded time period. Moreover, the micropaleontology, mineralogical and elemental composition of the sediments reflect the variability of the terrigenous input to the core site. The combination of down-core sediment signatures and a catchment-wide provenance study indicate that the Little Ice Age ( ˜ 300-650 cal yr BP) was characterized by climatic conditions favorable to torrential flood events. The Medieval Climate Anomaly ( ˜ 950-650 cal yr BP) is expressed by lower sea surface temperatures in the Mossel Bay area and humid conditions in the Gouritz River catchment. These new results suggest that the coincidence of humid conditions and cooler sea surface temperatures along the south coast of South Africa resulted from a strengthened and more southerly anticyclonic circulation. Most probably, the transport of moisture from the Indian Ocean by strong subtropical easterlies was coupled with Agulhas Bank upwelling pulses, which were initiated by an increase in

  6. Toward Improved Estimation of the Dynamic Topography and Ocean Circulation in the High Latitude and Arctic Ocean: The Importance of GOCE

    DEFF Research Database (Denmark)

    Johannessen, J. A.; Raj, R. P.; Nilsen, J. E. Ø.

    2014-01-01

    quantify this. Moreover, changes in the temperature and salinity of surface waters in the Arctic Ocean and Nordic Seas may also influence the flow of dense water through the Denmark Strait, which are found to be a precursor for changes in the Atlantic meridional overturning circulation with a lead time......The Arctic plays a fundamental role in the climate system and shows significant sensitivity to anthropogenic climate forcing and the ongoing climate change. Accelerated changes in the Arctic are already observed, including elevated air and ocean temperatures, declines of the summer sea ice extent...... of around 10 years (Hawkins and Sutton in Geophys Res Lett 35:L11603, 2008). Evidently changes in the Arctic and surrounding seas have far reaching influences on regional and global environment and climate variability, thus emphasizing the need for advanced quantitative understanding of the ocean...

  7. A study on the ocean circulation and thermal diffusion near a nuclear power plant

    International Nuclear Information System (INIS)

    Shu, Kyung Suk; Han, Moon Hee; Kim, Eun Han; Hwang, Won Tae

    1994-08-01

    The thermal discharge used with cooling water at nuclear power plant is released to a neighbour sea and it is influenced on marine environment. The thermal discharge released from power plant is mainly transported and diffused by ocean circulation of neighbour sea. So the evaluation for characteristics of ocean circulation around neighbour sea is firstly performed. The purpose of this research is primarily analyzed the thermal diffusion in sea around Yongkwang nuclear power plant. For this viewpoint, fundamental oceanographic data sets are collected and analyzed in Yellow sea, west sea of Korea, sea around Yongkwang. The ocean circulation and the effects of temperature increase by thermal discharge are evaluated using these data. The characteristics of tide is interpreted by the analysis of observed tidal elevation and tidal currents. The characteristics of temperature and salinity is investigated by the long-term observation of Korea Fisheries Research and Development Agency and the short-term observation around Yongkwang. (Author)

  8. Multiple states in the late Eocene ocean circulation

    NARCIS (Netherlands)

    M.L.J. Baatsen; A.S. von der Heydt; M. Kliphuis; J.P. Viebahn (Jan); H.A. Dijkstra

    2018-01-01

    htmlabstractThe Eocene-Oligocene Transition (EOT) marks a major step within the Cenozoic climate in going from a greenhouse into an icehouse state, with the formation of a continental-scale Antarctic ice sheet. The roles of steadily decreasing CO2 concentrations versus changes in ocean

  9. The early Miocene onset of a ventilated circulation regime in the Arctic Ocean.

    Science.gov (United States)

    Jakobsson, Martin; Backman, Jan; Rudels, Bert; Nycander, Jonas; Frank, Martin; Mayer, Larry; Jokat, Wilfried; Sangiorgi, Francesca; O'Regan, Matthew; Brinkhuis, Henk; King, John; Moran, Kathryn

    2007-06-21

    Deep-water formation in the northern North Atlantic Ocean and the Arctic Ocean is a key driver of the global thermohaline circulation and hence also of global climate. Deciphering the history of the circulation regime in the Arctic Ocean has long been prevented by the lack of data from cores of Cenozoic sediments from the Arctic's deep-sea floor. Similarly, the timing of the opening of a connection between the northern North Atlantic and the Arctic Ocean, permitting deep-water exchange, has been poorly constrained. This situation changed when the first drill cores were recovered from the central Arctic Ocean. Here we use these cores to show that the transition from poorly oxygenated to fully oxygenated ('ventilated') conditions in the Arctic Ocean occurred during the later part of early Miocene times. We attribute this pronounced change in ventilation regime to the opening of the Fram Strait. A palaeo-geographic and palaeo-bathymetric reconstruction of the Arctic Ocean, together with a physical oceanographic analysis of the evolving strait and sill conditions in the Fram Strait, suggests that the Arctic Ocean went from an oxygen-poor 'lake stage', to a transitional 'estuarine sea' phase with variable ventilation, and finally to the fully ventilated 'ocean' phase 17.5 Myr ago. The timing of this palaeo-oceanographic change coincides with the onset of the middle Miocene climatic optimum, although it remains unclear if there is a causal relationship between these two events.

  10. What is Required to Model the Global Ocean Circulation?

    Science.gov (United States)

    2011-01-01

    energy estimates from surface drifter observations [Lumpkin and Pazos , 2007], satellite altimetry (150 m) [Ducet, et al., 2000], ARGO floats at 1,000...surface", IPRC Technical Note No. 4(2), Honolulu, HI. 16pp, 2007. Lumpkin, R. and M. Pazos , "Measuring surface currents with Surface Velocity Program

  11. "Going with the flow" or not: evidence of positive rheotaxis in oceanic juvenile loggerhead turtles (Caretta caretta) in the South Pacific Ocean Using Satellite Tags and Ocean Circulation Data.

    Science.gov (United States)

    Kobayashi, Donald R; Farman, Richard; Polovina, Jeffrey J; Parker, Denise M; Rice, Marc; Balazs, George H

    2014-01-01

    The movement of juvenile loggerhead turtles (n = 42) out-fitted with satellite tags and released in oceanic waters off New Caledonia was examined and compared with ocean circulation data. Merging of the daily turtle movement data with drifter buoy movements, OSCAR (Ocean Surface Current Analyses--Real time) circulation data, and three different vertical strata (0-5 m, 0-40 m, 0-100 m) of HYCOM (HYbrid Coordinate Ocean Model) circulation data indicated the turtles were swimming against the prevailing current in a statistically significant pattern. This was not an artifact of prevailing directions of current and swimming, nor was it an artifact of frictional slippage. Generalized additive modeling was used to decompose the pattern of swimming into spatial and temporal components. The findings are indicative of a positive rheotaxis whereby an organism is able to detect the current flow and orient itself to swim into the current flow direction or otherwise slow down its movement. Potential mechanisms for the means and adaptive significance of rheotaxis in oceanic juvenile loggerhead turtles are discussed.

  12. "Going with the flow" or not: evidence of positive rheotaxis in oceanic juvenile loggerhead turtles (Caretta caretta in the South Pacific Ocean Using Satellite Tags and Ocean Circulation Data.

    Directory of Open Access Journals (Sweden)

    Donald R Kobayashi

    Full Text Available The movement of juvenile loggerhead turtles (n = 42 out-fitted with satellite tags and released in oceanic waters off New Caledonia was examined and compared with ocean circulation data. Merging of the daily turtle movement data with drifter buoy movements, OSCAR (Ocean Surface Current Analyses--Real time circulation data, and three different vertical strata (0-5 m, 0-40 m, 0-100 m of HYCOM (HYbrid Coordinate Ocean Model circulation data indicated the turtles were swimming against the prevailing current in a statistically significant pattern. This was not an artifact of prevailing directions of current and swimming, nor was it an artifact of frictional slippage. Generalized additive modeling was used to decompose the pattern of swimming into spatial and temporal components. The findings are indicative of a positive rheotaxis whereby an organism is able to detect the current flow and orient itself to swim into the current flow direction or otherwise slow down its movement. Potential mechanisms for the means and adaptive significance of rheotaxis in oceanic juvenile loggerhead turtles are discussed.

  13. Assimilation of TOPEX/POSEIDON Altimeter Data into a Global Ocean Circulation Model: Are the Results Any Good?

    Science.gov (United States)

    Fukumori, I.; Fu, L. L.; Chao, Y.

    1998-01-01

    The feasibility of assimilating satellite altimetry data into a global ocean general ocean general circulation model is studied. Three years of TOPEX/POSEIDON data is analyzed using a global, three-dimensional, nonlinear primitive equation model.

  14. A Statistical Evaluation of Atmosphere-Ocean General Circulation Models: Complexity vs. Simplicity

    OpenAIRE

    Robert K. Kaufmann; David I. Stern

    2004-01-01

    The principal tools used to model future climate change are General Circulation Models which are deterministic high resolution bottom-up models of the global atmosphere-ocean system that require large amounts of supercomputer time to generate results. But are these models a cost-effective way of predicting future climate change at the global level? In this paper we use modern econometric techniques to evaluate the statistical adequacy of three general circulation models (GCMs) by testing thre...

  15. Transition from the Cretaceous ocean to Cenozoic circulation in the western South Atlantic - A twofold reconstruction

    Science.gov (United States)

    Uenzelmann-Neben, Gabriele; Weber, Tobias; Grützner, Jens; Thomas, Maik

    2017-10-01

    The Cretaceous oceanic circulation has been quite different from the modern with a different distribution of the continents on the globe. This has resulted in a much lower temperature gradient between poles and equator. We have studied seismic reflection data and used numerical simulations of atmosphere and ocean dynamics to identify important steps in modifications of the oceanic circulation in the South Atlantic from the Cretaceous to the Cenozoic and the major factors controlling them. Starting in the Albian we could not identify any traces of an overturning circulation for the South Atlantic although a weak proto-Antarctic Circumpolar Current (ACC) was simulated. No change in circulation was observed for the Paleocene/early Eocene South Atlantic, which indicated that this period has witnessed a circulation similar to the Albian and Cenomanian/Turonian circulation. The most drastic modifications were observed for the Eocene/Oligocene boundary and the Oligocene/early Miocene with the onset of an ACC and Atlantic meridional overturning circulation (AMOC) and hence southern sourced deep and bottom water masses in the western South Atlantic. A modern AMOC, which intensified in strength after closure of the Central American Seaway (CAS), and a strong ACC have resulted in current controlled sedimentary features and wide spread hiatusses in the South Atlantic since the middle Miocene. The opening of Drake Passage in early Oligocene times and the closure of the CAS at 6 Ma, i.e., tectonic processes, have been identified as the key triggers for the observed most severe changes in oceanic circulation in the South Atlantic.

  16. Theoretical research for natural circulation operational characteristic of ship nuclear machinery under ocean conditions

    Energy Technology Data Exchange (ETDEWEB)

    Yan Binghuo [Department of Nuclear Science and Engineering, Naval University of Engineering, Wuhan 430033 (China)], E-mail: yanbh1986@163.com; Yu Lei [Department of Nuclear Science and Engineering, Naval University of Engineering, Wuhan 430033 (China)], E-mail: yulei301@163.com

    2009-06-15

    Based on the two-phase drift flux model and the multi-pressure nodes matrix solving method, natural circulation thermal hydraulic analysis models for the Nuclear Machinery (NM) under ocean conditions are developed. The neutron physical activities and the responses of the reactivity control systems are described by the two-group, 3-dimensional space and time dependent neutron kinetics model. Reactivity feedback is calculated by coupling the neutron physics and thermal hydraulic codes, and is tested by comparison with experiments. Using the models developed, the natural circulation operating characteristics of NM in rolling and pitching motions and the transitions between forced circulation (FC) to natural circulation (NC) are analyzed. The results show that the influence of the rolling motion increases as the rolling amplitude is increased, and as the rolling period becomes shorter. The results also show that for this NM, with the same rolling period and rolling angle, the influence of pitching motion on natural circulation is greater than that of rolling motion. Furthermore, the oscillation period for pitching motion is the same as the pitching period, while the oscillation period for rolling is one half of the rolling period. In the ocean environment, excessive flow oscillation of the natural circulation may cause the control rods to respond so frequently that the NM would not be able to realize the transition from the FC to NC steadily. However, the influence of ocean environment on the transition from NC to FC is limited.

  17. Effects of Southern Hemisphere Wind Changes on the Meridional Overturning Circulation in Ocean Models.

    Science.gov (United States)

    Gent, Peter R

    2016-01-01

    Observations show that the Southern Hemisphere zonal wind stress maximum has increased significantly over the past 30 years. Eddy-resolving ocean models show that the resulting increase in the Southern Ocean mean flow meridional overturning circulation (MOC) is partially compensated by an increase in the eddy MOC. This effect can be reproduced in the non-eddy-resolving ocean component of a climate model, providing the eddy parameterization coefficient is variable and not a constant. If the coefficient is a constant, then the Southern Ocean mean MOC change is balanced by an unrealistically large change in the Atlantic Ocean MOC. Southern Ocean eddy compensation means that Southern Hemisphere winds cannot be the dominant mechanism driving midlatitude North Atlantic MOC variability.

  18. Scaling analysis for the ocean motions in single phase natural circulation

    International Nuclear Information System (INIS)

    Yan, B.H.; Wen, Q.L.

    2015-01-01

    Highlights: • The scaling criteria for ocean motions are obtained. • The optimization and selection of the scaling criteria is also analyzed. • The oscillating period in experiments is determined by the time scale. - Abstract: The effects of ocean motions should be analyzed properly in order to guarantee the safety margin of facilities in the engineering design of floating nuclear reactor system. The scaling analysis for the ocean motions in single phase natural circulation is performed. The scaling criteria for both single ocean motions and compound ocean motions are obtained. The selection and optimization of scaling criteria is also analyzed. The oscillating amplitude in experiments should be kept to be identical to that in actual ocean motions. The oscillating period is determined by the time scale. The length scale, oscillating period and experimental power should be taken into consideration synthetically to obtain a reasonable experimental period

  19. The Arctic Ocean as a dead end for floating plastics in the North Atlantic branch of the Thermohaline Circulation.

    Science.gov (United States)

    Cózar, Andrés; Martí, Elisa; Duarte, Carlos M; García-de-Lomas, Juan; van Sebille, Erik; Ballatore, Thomas J; Eguíluz, Victor M; González-Gordillo, J Ignacio; Pedrotti, Maria L; Echevarría, Fidel; Troublè, Romain; Irigoien, Xabier

    2017-04-01

    The subtropical ocean gyres are recognized as great marine accummulation zones of floating plastic debris; however, the possibility of plastic accumulation at polar latitudes has been overlooked because of the lack of nearby pollution sources. In the present study, the Arctic Ocean was extensively sampled for floating plastic debris from the Tara Oceans circumpolar expedition. Although plastic debris was scarce or absent in most of the Arctic waters, it reached high concentrations (hundreds of thousands of pieces per square kilometer) in the northernmost and easternmost areas of the Greenland and Barents seas. The fragmentation and typology of the plastic suggested an abundant presence of aged debris that originated from distant sources. This hypothesis was corroborated by the relatively high ratios of marine surface plastic to local pollution sources. Surface circulation models and field data showed that the poleward branch of the Thermohaline Circulation transfers floating debris from the North Atlantic to the Greenland and Barents seas, which would be a dead end for this plastic conveyor belt. Given the limited surface transport of the plastic that accumulated here and the mechanisms acting for the downward transport, the seafloor beneath this Arctic sector is hypothesized as an important sink of plastic debris.

  20. The Arctic Ocean as a dead end for floating plastics in the North Atlantic branch of the Thermohaline Circulation

    Science.gov (United States)

    Cózar, Andrés; Martí, Elisa; Duarte, Carlos M.; García-de-Lomas, Juan; van Sebille, Erik; Ballatore, Thomas J.; Eguíluz, Victor M.; González-Gordillo, J. Ignacio; Pedrotti, Maria L.; Echevarría, Fidel; Troublè, Romain; Irigoien, Xabier

    2017-01-01

    The subtropical ocean gyres are recognized as great marine accummulation zones of floating plastic debris; however, the possibility of plastic accumulation at polar latitudes has been overlooked because of the lack of nearby pollution sources. In the present study, the Arctic Ocean was extensively sampled for floating plastic debris from the Tara Oceans circumpolar expedition. Although plastic debris was scarce or absent in most of the Arctic waters, it reached high concentrations (hundreds of thousands of pieces per square kilometer) in the northernmost and easternmost areas of the Greenland and Barents seas. The fragmentation and typology of the plastic suggested an abundant presence of aged debris that originated from distant sources. This hypothesis was corroborated by the relatively high ratios of marine surface plastic to local pollution sources. Surface circulation models and field data showed that the poleward branch of the Thermohaline Circulation transfers floating debris from the North Atlantic to the Greenland and Barents seas, which would be a dead end for this plastic conveyor belt. Given the limited surface transport of the plastic that accumulated here and the mechanisms acting for the downward transport, the seafloor beneath this Arctic sector is hypothesized as an important sink of plastic debris. PMID:28439534

  1. The Arctic Ocean as a dead end for floating plastics in the North Atlantic branch of the Thermohaline Circulation

    KAUST Repository

    Cózar, Andrés

    2017-04-20

    The subtropical ocean gyres are recognized as great marine accummulation zones of floating plastic debris; however, the possibility of plastic accumulation at polar latitudes has been overlooked because of the lack of nearby pollution sources. In the present study, the Arctic Ocean was extensively sampled for floating plastic debris from the Tara Oceans circumpolar expedition. Although plastic debris was scarce or absent in most of the Arctic waters, it reached high concentrations (hundreds of thousands of pieces per square kilometer) in the northernmost and easternmost areas of the Greenland and Barents seas. The fragmentation and typology of the plastic suggested an abundant presence of aged debris that originated from distant sources. This hypothesis was corroborated by the relatively high ratios of marine surface plastic to local pollution sources. Surface circulation models and field data showed that the poleward branch of the Thermohaline Circulation transfers floating debris from the North Atlantic to the Greenland and Barents seas, which would be a dead end for this plastic conveyor belt. Given the limited surface transport of the plastic that accumulated here and the mechanisms acting for the downward transport, the seafloor beneath this Arctic sector is hypothesized as an important sink of plastic debris.

  2. Upper ocean circulation modulation by phytoplankton concentration in the Equatorial Pacific and the Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Nakamoto, S.; PrasannaKumar, S.; Oberhuber, J.M.; Sammarco, P.; Muneyama, K.; Sato, T.; AjoyKumar, A.; Frouin, R.

    Wind patterns in the equatorial Pacific and Indian oceans are the factors that regulate the chlorophyll pigment distributions in the equatorial region of these oceans. Trade winds and coastline of the Pacific basin supports wave-guide dynamics...

  3. Reconstructing Deep Ocean Circulation in the North Atlantic from Bermuda Rise, and Beyond

    Science.gov (United States)

    McManus, J. F.

    2016-12-01

    The large-scale subsurface circulation of the ocean is an important component of the Earth's climate system, and contributes to the global and regional transport of heat and mass. Assessing how this system has changed in the past is thus a priority for understanding natural climate variability. A long-coring campaign on Bermuda Rise has provided additional abundant high-quality sediments from this site of rapid accumulation in the deep western basin, situated beneath the subtropical gyre of the North Atlantic Ocean. These sediments allow the high-resolution reconstruction of deepwater chemistry and export from this key location throughout the last 150,000 years, covering the entire last glacial cycle in a continuous section of 35 meters in core KNR191-CDH19. The suite of proxy indicators analyzed includes uranium-series disequilibria, neodymium isotopes, and benthic stable isotopes. Combined with multiple previous studies of nearby cores on Bermuda Rise, the published and new proxy data from CDH19 confirm the variability of the deep circulation in the Atlantic Ocean in association with past climate changes. The multiple indicators, along with complementary data from other locations, display coherent evidence for contrasts between deep circulation during glacial and interglacial intervals, with persistent strong, deep ventilation only within the peak interglacial of marine isotope stage 5e (MIS 5e) and the Holocene. In contrast, repeated, dramatic variability in deep ocean circulation accompanied the millennial climate changes of the last glaciation and deglaciation. The largest magnitude circulation shifts occurred at the transitions into stadials associated with the Hudson strait iceberg discharges and between them and the ensuing northern interstadial warmings, significantly exceeding that of the overall glacial-interglacial difference, highlighting the potential oceanographic and climatic importance of short-term perturbations to the deep ocean circulation.

  4. North Atlantic ocean circulation during the Last Glacial Maximum: a combined modelling and magnetic sediment proxy study

    Science.gov (United States)

    Watkins, S. J.; Maher, B. A.; Bigg, G. R.

    2003-04-01

    An increasing number of ocean modelling and palaeo-data studies has provided evidence that the thermohaline circulation may have existed in the past in a different configuration to the present-day. Here, we use a twin approach, combining ocean model results and sediment proxy data, to investigate N. Atlantic circulation at the Last Glacial Maximum (LGM). Ocean model experiments at UEA (Norwich) indicate the existence of three possible stable ocean circulation states during the LGM. Two states have formation of intermediate/deep water in the North Atlantic (with different formation sites, rates and sinking depths), the third state has all deep water formation in the Southern Ocean. Forcing fields from these circulation states are used to provide input fields for an iceberg trajectory model, which is then used to investigate the effect of these different surface circulation patterns on iceberg drift. Magnetic measurements of deep-sea sediments have been used to identify ice-rafted detritus (IRD), allowing reconstruction of LGM iceberg trajectories. Magnetic measurements have the benefit of being relatively rapid and also non-destructive. The magnetic properties of > 130 deep-sea LGM sediment samples, from across the North Atlantic, have been measured, together with samples from potential source areas. Fuzzy c-means cluster analysis of selected, diagnostic magnetic parameters was used to characterise the sediment and identify the main controls on sedimentation. The clustering distinguishes lower-latitude, aeolian input west of Africa from other detrital sediment inputs to the north and west North Atlantic. The magnetic properties of sediments along the eastern coast of Greenland, and in the Labrador Sea and central Atlantic, indicate the presence of IRD rich in low-coercivity, coarse-grained magnetite. IRD in sediments east of the Gulf of St. Lawrence is characterised by the presence of both haematite and coarse-grained magnetite. Of the three modelled ocean states

  5. Acoustic remote sensing of ocean flows

    Digital Repository Service at National Institute of Oceanography (India)

    Joseph, A.; Desa, E.

    surface layer of the ocean surface and hence these techniques are unusable for measurement of subsurface circulation. The three methods of ocean circulation measurement using acoustic remote sensing techniques are the Lagrangian, Eulerian and single...

  6. Relaxation oscillations in an idealized ocean circulation model

    Science.gov (United States)

    Roberts, Andrew; Saha, Raj

    2017-04-01

    This work is motivated by a desire to understand transitions between stable equilibria observed in Stommel's 1961 thermohaline circulation model. We adapt the model, including a forcing parameter as a dynamic slow variable. The resulting model is a piecewise-smooth, three time-scale system. The model is analyzed using geometric singular perturbation theory to demonstrate the existence of attracting periodic orbits. The system is capable of producing classical relaxation oscillations as expected, but there is also a parameter regime in which the model exhibits small amplitude oscillations known as canard cycles. Forcing the model with obliquity variations from the last 100,000 years produces oscillations that are modulated in amplitude and frequency. The output shows similarities with important features of the climate proxy data of the same period.

  7. 3D movies for teaching seafloor bathymetry, plate tectonics, and ocean circulation in large undergraduate classes

    Science.gov (United States)

    Peterson, C. D.; Lisiecki, L. E.; Gebbie, G.; Hamann, B.; Kellogg, L. H.; Kreylos, O.; Kronenberger, M.; Spero, H. J.; Streletz, G. J.; Weber, C.

    2015-12-01

    Geologic problems and datasets are often 3D or 4D in nature, yet projected onto a 2D surface such as a piece of paper or a projection screen. Reducing the dimensionality of data forces the reader to "fill in" that collapsed dimension in their minds, creating a cognitive challenge for the reader, especially new learners. Scientists and students can visualize and manipulate 3D datasets using the virtual reality software developed for the immersive, real-time interactive 3D environment at the KeckCAVES at UC Davis. The 3DVisualizer software (Billen et al., 2008) can also operate on a desktop machine to produce interactive 3D maps of earthquake epicenter locations and 3D bathymetric maps of the seafloor. With 3D projections of seafloor bathymetry and ocean circulation proxy datasets in a virtual reality environment, we can create visualizations of carbon isotope (δ13C) records for academic research and to aid in demonstrating thermohaline circulation in the classroom. Additionally, 3D visualization of seafloor bathymetry allows students to see features of seafloor most people cannot observe first-hand. To enhance lessons on mid-ocean ridges and ocean basin genesis, we have created movies of seafloor bathymetry for a large-enrollment undergraduate-level class, Introduction to Oceanography. In the past four quarters, students have enjoyed watching 3D movies, and in the fall quarter (2015), we will assess how well 3D movies enhance learning. The class will be split into two groups, one who learns about the Mid-Atlantic Ridge from diagrams and lecture, and the other who learns with a supplemental 3D visualization. Both groups will be asked "what does the seafloor look like?" before and after the Mid-Atlantic Ridge lesson. Then the whole class will watch the 3D movie and respond to an additional question, "did the 3D visualization enhance your understanding of the Mid-Atlantic Ridge?" with the opportunity to further elaborate on the effectiveness of the visualization.

  8. Merged Land and Ocean Surface Temperature, Version 3.5

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The historical Merged Land-Ocean Surface Temperature Analysis (MLOST) is derived from two independent analyses, an Extended Reconstructed Sea Surface Temperature...

  9. The new version of the Institute of Numerical Mathematics Sigma Ocean Model (INMSOM) for simulation of Global Ocean circulation and its variability

    Science.gov (United States)

    Gusev, Anatoly; Fomin, Vladimir; Diansky, Nikolay; Korshenko, Evgeniya

    2017-04-01

    In this paper, we present the improved version of the ocean general circulation sigma-model developed in the Institute of Numerical Mathematics of the Russian Academy of Sciences (INM RAS). The previous version referred to as INMOM (Institute of Numerical Mathematics Ocean Model) is used as the oceanic component of the IPCC climate system model INMCM (Institute of Numerical Mathematics Climate Model (Volodin et al 2010,2013). Besides, INMOM as the only sigma-model was used for simulations according to CORE-II scenario (Danabasoglu et al. 2014,2016; Downes et al. 2015; Farneti et al. 2015). In general, INMOM results are comparable to ones of other OGCMs and were used for investigation of climatic variations in the North Atlantic (Gusev and Diansky 2014). However, detailed analysis of some CORE-II INMOM results revealed some disadvantages of the INMOM leading to considerable errors in reproducing some ocean characteristics. So, the mass transport in the Antarctic Circumpolar Current (ACC) was overestimated. As well, there were noticeable errors in reproducing thermohaline structure of the ocean. After analysing the previous results, the new version of the OGCM was developed. It was decided to entitle is INMSOM (Institute of Numerical Mathematics Sigma Ocean Model). The new title allows one to distingwish the new model, first, from its older version, and second, from another z-model developed in the INM RAS and referred to as INMIO (Institute of Numerical Mathematics and Institute of Oceanology ocean model) (Ushakov et al. 2016). There were numerous modifications in the model, some of them are as follows. 1) Formulation of the ocean circulation problem in terms of full free surface with taking into account water amount variation. 2) Using tensor form of lateral viscosity operator invariant to rotation. 3) Using isopycnal diffusion including Gent-McWilliams mixing. 4) Using atmospheric forcing computation according to NCAR methodology (Large and Yeager 2009). 5

  10. Atmosphere-surface interactions over polar oceans and heterogeneous surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Vihma, T.

    1995-12-31

    Processes of interaction between the atmospheric boundary layer and the planetary surface have been studied with special emphasis on polar ocean surfaces: the open ocean, leads, polynyas and sea ice. The local exchange of momentum, heat and moisture has been studied experimentally both in the Weddell Sea and in the Greenland Sea. Exchange processes over heterogeneous surfaces are addressed by modelling studies. Over a homogeneous surface, the local turbulent fluxes can be reasonably well estimated using an iterative flux-profile scheme based on the Monin-Obukhov similarity theory. In the Greenland Sea, the near-surface air temperature and the generally small turbulent fluxes over the open ocean were affected by the sea surface temperature fronts. Over the sea ice cover in the Weddell Sea, the turbulent sensible heat flux was generally downwards, and together with an upward oceanic heat flux through the ice it compensated the heat loss from the surface via long-wave radiation. The wind dominated on time scales of days, while the current became important on longer time scales. The drift dynamics showed apparent spatial differences between the eastern and western regions, as well as between the Antarctic Circumpolar Current and the rest of the Weddell Sea. Inertial motion was present in regions of low ice concentration. The surface heterogeneity, arising e.g. from roughness or temperature distribution, poses a problem for the parameterization of surface exchange processes in large-scale models. In the case of neutral flow over a heterogeneous terrain, an effective roughness length can be used to parameterize the roughness effects

  11. Impacts of Interannual Ocean Circulation Variability on Japanese Eel Larval Migration in the Western North Pacific Ocean.

    Science.gov (United States)

    Chang, Yu-Lin; Sheng, Jinyu; Ohashi, Kyoko; Béguer-Pon, Mélanie; Miyazawa, Yasumasa

    2015-01-01

    The Japanese eel larvae hatch near the West Mariana Ridge seamount chain and travel through the North Equatorial Current (NEC), the Kuroshio, and the Subtropical Countercurrent (STCC) region during their shoreward migration toward East Asia. The interannual variability of circulation over the subtropical and tropical regions of the western North Pacific Ocean is affected by the Philippines-Taiwan Oscillation (PTO). This study examines the effect of the PTO on the Japanese eel larval migration routes using a three-dimensional (3D) particle tracking method, including vertical and horizontal swimming behavior. The 3D circulation and hydrography used for particle tracking are from the ocean circulation reanalysis produced by the Japan Coastal Ocean Predictability Experiment 2 (JCOPE2). Our results demonstrate that bifurcation of the NEC and the strength and spatial variation of the Kuroshio affect the distribution and migration of eel larvae. During the positive phase of PTO, more virtual eels ("v-eels") can enter the Kuroshio to reach the south coast of Japan and more v-eels reach the South China Sea through the Luzon Strait; the stronger and more offshore swing of the Kuroshio in the East China Sea leads to fewer eels entering the East China Sea and the onshore movement of the Kuroshio to the south of Japan brings the eels closer to the Japanese coast. Significant differences in eel migration routes and distributions regulated by ocean circulation in different PTO phases can also affect the otolith increment. The estimated otolith increment suggests that eel age tends to be underestimated after six months of simulation due to the cooler lower layer temperature. Underestimation is more significant in the positive PTO years due to the wide distribution in higher latitudes than in the negative PTO years.

  12. Impacts of Interannual Ocean Circulation Variability on Japanese Eel Larval Migration in the Western North Pacific Ocean.

    Directory of Open Access Journals (Sweden)

    Yu-Lin Chang

    Full Text Available The Japanese eel larvae hatch near the West Mariana Ridge seamount chain and travel through the North Equatorial Current (NEC, the Kuroshio, and the Subtropical Countercurrent (STCC region during their shoreward migration toward East Asia. The interannual variability of circulation over the subtropical and tropical regions of the western North Pacific Ocean is affected by the Philippines-Taiwan Oscillation (PTO. This study examines the effect of the PTO on the Japanese eel larval migration routes using a three-dimensional (3D particle tracking method, including vertical and horizontal swimming behavior. The 3D circulation and hydrography used for particle tracking are from the ocean circulation reanalysis produced by the Japan Coastal Ocean Predictability Experiment 2 (JCOPE2. Our results demonstrate that bifurcation of the NEC and the strength and spatial variation of the Kuroshio affect the distribution and migration of eel larvae. During the positive phase of PTO, more virtual eels ("v-eels" can enter the Kuroshio to reach the south coast of Japan and more v-eels reach the South China Sea through the Luzon Strait; the stronger and more offshore swing of the Kuroshio in the East China Sea leads to fewer eels entering the East China Sea and the onshore movement of the Kuroshio to the south of Japan brings the eels closer to the Japanese coast. Significant differences in eel migration routes and distributions regulated by ocean circulation in different PTO phases can also affect the otolith increment. The estimated otolith increment suggests that eel age tends to be underestimated after six months of simulation due to the cooler lower layer temperature. Underestimation is more significant in the positive PTO years due to the wide distribution in higher latitudes than in the negative PTO years.

  13. Anomalous circulation in the eastern equatorial Indian Ocean during southwest monsoon of 1994

    Digital Repository Service at National Institute of Oceanography (India)

    Unnikrishnan, A.S.; Murty, V.S.N.; Babu, M.T.; Gopinathan, C.K.; Charyulu, R.J.K.

    and an eastward flow, constituting the southwest monsoon current (SWMC), in the vicinity of the equator characterise the upper ocean circulation. While low salinity waters (33.5 -34.75) in the upper layer are advected westward from 88 E via the westward flow...

  14. Coastal circulation in the North Indian Ocean: Coastal segment (14,S-W)

    Digital Repository Service at National Institute of Oceanography (India)

    Shetye, S.R.; Gouveia, A.D.

    The article provides an overview of the circulation of the coastal regime of the North Indian Ocean stretching from southern coast of Indonesia to the coast of East Africa. A special feature of this regime is that it experiences the Asian monsoons...

  15. Ocean circulation off the north-west coast of the United States is ...

    African Journals Online (AJOL)

    spamer

    Wind time- series were low-pass filtered, using a filter with a 40- h width at half amplitude to remove short-period. (e.g. diurnal) fluctuations. Satellite SST data were ... a Lagrangian pathway for passive particles to leave the coastal ocean, but to then return through the influence of seasonally and spatially varying circulation.

  16. Numerics-Characteristics-Asymptotics: A Case Study from Large Scale Ocean Circulation

    Science.gov (United States)

    Hodnett, P. F.; Courtney, C.

    2007-01-01

    This paper uses a partial differential equation which occurs in a reduced model of large scale circulation in an ocean basin as an educational vehicle through which to demonstrate the usefulness of a set of mathematical techniques in analysing the equation. A parameter occurring in the equation does in reality vary from very small through…

  17. Low-frequency oscillations of the Atlantic Ocean meridional overturning circulation in a coupled climate model

    Directory of Open Access Journals (Sweden)

    M. Schulz

    2007-01-01

    Full Text Available Using a 3-dimensional climate model of intermediate complexity we show that the overturning circulation of the Atlantic Ocean can vary at multicentennial-to-millennial timescales for modern boundary conditions. A continuous freshwater perturbation in the Labrador Sea pushes the overturning circulation of the Atlantic Ocean into a bi-stable regime, characterized by phases of active and inactive deep-water formation in the Labrador Sea. In contrast, deep-water formation in the Nordic Seas is active during all phases of the oscillations. The actual timing of the transitions between the two circulation states occurs randomly. The oscillations constitute a 3-dimensional phenomenon and have to be distinguished from low-frequency oscillations seen previously in 2-dimensional models of the ocean. A conceptual model provides further insight into the essential dynamics underlying the oscillations of the large-scale ocean circulation. The model experiments indicate that the coupled climate system can exhibit unforced climate variability at multicentennial-to-millennial timescales that may be of relevance for Holocene climate variations.

  18. A Fully Implicit Model of the Three-Dimensional Thermohaline Ocean Circulation

    NARCIS (Netherlands)

    Dijkstra, Henk A.; Oksuzoglu, Hakan; Wubs, Fred. W.; Botta, Eugen F.F.

    2001-01-01

    In this paper, a fully implicit numerical model of the three-dimensional thermohaline ocean circulation is presented. With this numerical model it is possible to follow branches of steady states in parameter space and monitor their linear stability. Also, transient flows can be computed allowing

  19. A bifurcation study of the three-dimensional thermohaline ocean circulation: the double-hemispheric case

    NARCIS (Netherlands)

    Weijer, W.; Dijkstra, H.A.

    2001-01-01

    Within a low-resolution primitive-equation model of the three-dimensional ocean circulation, a bifurcation analysis is performed of double-hemispheric basin flows. Main focus is on the connection between results for steady two-dimensional flows in a non-rotating basin and those for

  20. A bifurcation study of the three-dimensional thermohaline ocean circulation: The double hemispheric case

    NARCIS (Netherlands)

    Weijer, W.; Dijkstra, Henk A.

    2001-01-01

    Within a low-resolution primitive-equation model of the three-dimensional ocean circulation, a bifurcation analysis is performed of double-hemispheric basin flows. Main focus is on the connection between results for steady two-dimensional flows in a nonrotating basin and those for

  1. Oceanic circulation changes during early Pliocene marine ice-sheet instability in Wilkes Land, East Antarctica

    Science.gov (United States)

    Hansen, Melissa A.; Passchier, Sandra

    2017-06-01

    In the Southern Ocean, unconstrained Westerlies allow for intense mixing between deep waters and the atmosphere. How this system interacts with Antarctic ice sheets and the global ocean circulation is poorly understood due to a paucity of data. The poor abundance and preservation of foraminiferal carbonate in ice-proximal sediments is a major challenge in high-latitude paleoceanography. A new approach is to examine a sediment geochemical record of changing paleoproductivity and sediment redox environment that can be tied to changes in water mass properties. This study focuses on the paleoceanography of the George V Land margin between 4.7 and 4.3 Ma. This interval at the onset of the early Pliocene Climatic Optimum was characterized by the highest global sea surface temperatures and the lowest sea ice concentrations in East Antarctica in the past 5 million years. At IODP Site U1359, an abrupt increase in Mn/Al ratios 4.6 Ma indicates an episode of oxic bottom conditions resulting from enhanced wind-driven downwelling of Antarctic surface water. Above, extremely high concentrations of sedimentary barite (Ba excess >40,000 ppm) point to biogenic barite deposition, preservation, and concentration through enhanced upwelling of nutrient-rich Circumpolar Deep Water (CDW). Incursion of CDW onto the continental shelf affected ice discharge and resulted in a stable but reduced ice-sheet configuration over several glacial cycles. The geochemical results along with previous work on Site U1359 for the first time link paleoceanography and cryospheric change based on data from the same high-latitude site.

  2. Potential impact of ocean circulation on the declining Japanese eel catches.

    Science.gov (United States)

    Chang, Yu-Lin K; Miyazawa, Yasumasa; Miller, Michael J; Tsukamoto, Katsumi

    2018-04-03

    Recruitment of Japanese eels, Anguilla japonica, has declined in recent decades possibly due to both anthropogenic and ocean-atmosphere factors. The potential impact of ocean circulation on the decreasing Japanese eel catches in the western North Pacific was examined based on a three-dimensional particle-tracking method, in which virtual larvae (v-larvae) were programmed to swim horizontally and vertically, in addition to being transported by ocean currents after being released in their North Equatorial Current (NEC) spawning area. Transport patterns varied among years between 1993 and 2013, and dispersion of v-larvae towards East Asia decreased in the last two decades, especially for the western Taiwan and Japan regions. In recent years, instead of entering the Kuroshio and moving towards East Asia as in the 1990s', more v-larvae tended to enter the southern areas due to the weakening of the NEC and strengthening of subsurface southward flow near the spawning area. Changes in ocean circulation in the western Pacific appear to be caused by the weakening of subtropical and tropical wind stress curl in the past two decades. This suggests that decadal changes in ocean circulation have occurred that affect the larval migration success of the Japanese eel to their recruitment areas.

  3. Exploring the sensitivity of global ocean circulation to future ice loss from Antarctica

    Energy Technology Data Exchange (ETDEWEB)

    Condron, Alan

    2017-09-30

    The sensitivity of the global ocean circulation and climate to large increases in iceberg calving and meltwater discharges from the Antarctic Ice Sheet (AIS) are rarely studied and poorly understood. The requirement to investigate this topic is heightened by growing evidence that the West Antarctic Ice Sheet (WAIS) is vulnerable to rapid retreat and collapse on multidecadal-to-centennial timescales. Observations collected over the last 30 years indicate that the WAIS is now losing mass at an accelerated and that a collapse may have already begun in the Amundsen Sea sector. In addition, some recent future model simulations of the AIS show the potential for rapid ice sheet retreat in the next 50 – 300 years. Such a collapse would be associated with the discharge of enormous volumes of ice and meltwater to the Southern Ocean. This project funds PI Condron to begin assessing the sensitivity of the global ocean circulation to projected increases in meltwater discharge and iceberg calving from the AIS for the next 50 – 100 years. A series of climate model simulations will determine changes in ocean circulation and temperature at the ice sheet grounding line, the role of mesoscale ocean eddies in mixing and transporting freshwater away from the continent to deep water formation regions, and the likely impact on the northward transport of heat to Europe and North America.

  4. Going with the flow: the role of ocean circulation in global marine ecosystems under a changing climate.

    Science.gov (United States)

    van Gennip, Simon J; Popova, Ekaterina E; Yool, Andrew; Pecl, Gretta T; Hobday, Alistair J; Sorte, Cascade J B

    2017-07-01

    Ocean warming, acidification, deoxygenation and reduced productivity are widely considered to be the major stressors to ocean ecosystems induced by emissions of CO 2 . However, an overlooked stressor is the change in ocean circulation in response to climate change. Strong changes in the intensity and position of the western boundary currents have already been observed, and the consequences of such changes for ecosystems are beginning to emerge. In this study, we address climatically induced changes in ocean circulation on a global scale but relevant to propagule dispersal for species inhabiting global shelf ecosystems, using a high-resolution global ocean model run under the IPCC RCP 8.5 scenario. The ¼ degree model resolution allows improved regional realism of the ocean circulation beyond that of available CMIP5-class models. We use a Lagrangian approach forced by modelled ocean circulation to simulate the circulation pathways that disperse planktonic life stages. Based on trajectory backtracking, we identify present-day coastal retention, dominant flow and dispersal range for coastal regions at the global scale. Projecting into the future, we identify areas of the strongest projected circulation change and present regional examples with the most significant modifications in their dominant pathways. Climatically induced changes in ocean circulation should be considered as an additional stressor of marine ecosystems in a similar way to ocean warming or acidification. © 2017 John Wiley & Sons Ltd.

  5. A window on the deep ocean: The special value of ocean bottom pressure for monitoring the large-scale, deep-ocean circulation

    Science.gov (United States)

    Hughes, Chris W.; Williams, Joanne; Blaker, Adam; Coward, Andrew; Stepanov, Vladimir

    2018-02-01

    We show how, by focusing on bottom pressure measurements particularly on the global continental slope, it is possible to avoid the "fog" of mesoscale variability which dominates most observables in the deep ocean. This makes it possible to monitor those aspects of the ocean circulation which are most important for global scale ocean variability and climate. We therefore argue that such measurements should be considered an important future component of the Global Ocean Observing System, to complement the present open-ocean and coastal elements. Our conclusions are founded on both theoretical arguments, and diagnostics from a fine-resolution ocean model that has realistic amplitudes and spectra of mesoscale variability. These show that boundary pressure variations are coherent over along-slope distances of tens of thousands of kilometres, for several vertical modes. We illustrate the value of this in the model Atlantic, by determining the time for boundary and equatorial waves to complete a circuit of the northern basin (115 and 205 days for the first and second vertical modes), showing how the boundary features compare with basin-scale theoretical models, and demonstrating the ability to monitor the meridional overturning circulation using these boundary measurements. Finally, we discuss applicability to the real ocean and make recommendations on how to make such measurements without contamination from instrumental drift.

  6. Characterizing the surface circulation in Ebro Delta (NW Mediterranean) with HF radar and modeled current data

    Science.gov (United States)

    Lorente, P.; Piedracoba, S.; Sotillo, M. G.; Aznar, R.; Amo-Balandron, A.; Pascual, A.; Soto-Navarro, J.; Alvarez-Fanjul, E.

    2016-11-01

    Quality-controlled current observations from a High Frequency radar (HFR) network deployed in the Ebro River Delta (NW Mediterranean) were combined with outputs from IBI operational ocean forecasting system in order to comprehensively portray the ocean state and its variability during 2014. Accurate HFR data were used as benchmark for a rigorous validation of the Iberia-Biscay-Ireland (IBI) regional system, routinely operated in the frame of the Copernicus Marine Environment Monitoring Service (CMEMS). The analysis of skill metrics and monthly averaged current maps showed that IBI reasonably captured the prevailing dynamic features of the coastal circulation previously observed by the HFR, according to the moderate resemblance found in circulation patterns and the spatial distribution of eddy kinetic energy. The model skill assessment was completed with an exploration of dominant modes of spatiotemporal variability. The EOF analysis confirmed that the modeled surface current field evolved both in space and time according to three significantly dominant modes of variability which accounted for the 49.2% of the total variance, in close agreement with the results obtained for HFR (46.1%). The response of the subtidal surface current field to prevailing wind regime in the study area was examined in terms of induced circulation structures and immediacy of reaction by performing a conditional averaging approach and a time-lagged vector correlation analysis, respectively. This observations-model synergistic strategy has proved to be valid to operationally monitor the complex coastal circulation in Ebro Delta despite the observed model drawbacks in terms of reduced energy content in surface currents and some inaccuracies in the wind-driven low frequency response. This integrated methodology aids to improve the prognostic capabilities of IBI ocean forecasting system and also to facilitate high-stakes decision-making for coastal management in the Ebro River Delta marine

  7. Characterizing the surface circulation in the Ebro Delta using a HF radar data-model approach

    Science.gov (United States)

    Lorente Jimenez, Pablo; Piedracoba Varela, Silvia; Soto-Navarro, Javier; Garcia-Sotillo, Marcos; Alvarez Fanjul, Enrique

    2016-04-01

    One year-long (2014) quality-controlled current observations from a CODAR SeaSonde High Frequency (HF) radar network deployed in the Ebro Delta (northwestern Mediterranean) were combined with operational products provided by a regional ocean forecasting system named IBI (Iberia-Biscay-Ireland) in order to comprehensively portray the ocean state and its variability. First, accurate HF radar data were used as benchmark for the rigorous validation of IBI performance by means of the computation of skill metrics and quality indicators. The analysis of the monthly averaged current maps for 2014 showed that IBI properly captured the prevailing dynamic features of the coastal circulation observed by the HF radar, according to the resemblance of circulation patterns and the eddy kinetic energy spatial distribution. The model skill assessment was completed with an exploration of dominant modes of variability both in time and space. The EOF analysis confirmed that the modeled surface current field evolved in space and time according to three significantly dominant modes of variability which accounted for the 49.2% of the total variance, in close agreement with the results obtained for the HF radar (46.1%). The response of the subtidal surface current field to prevalent wind regimes in the study area was examined in terms of induced circulation structures by performing a conditional averaging approach. This data-model synergistic approach has proved to be valid to operationally monitor and describe the complex coastal circulation in Ebro Delta despite the observed model drawbacks in terms of reduced energy content in surface currents and some inaccuracies in the wind-driven low frequency response. This integrated methodology constitutes a powerful tool for improving operational ocean forecasting systems at European level within the frame of the Copernicus Marine Environment Monitoring Service (CMEMS). It also facilitates high-stakes decision-making for coastal management and

  8. Meridional overturning circulation: stability and ocean feedbacks in a box model

    NARCIS (Netherlands)

    Cimatoribus, A.A.; Drijfhout, S.S.; Dijkstra, H.A.|info:eu-repo/dai/nl/073504467

    2014-01-01

    A box model of the inter-hemispheric Atlantic meridional overturning circulation is developed, including a variable pycnocline depth for the tropical and subtropical regions. The circulation is forced by winds over a periodic channel in the south and by freshwater forcing at the surface. The model

  9. North Atlantic ocean circulation and abrupt climate change during the last glaciation.

    Science.gov (United States)

    Henry, L G; McManus, J F; Curry, W B; Roberts, N L; Piotrowski, A M; Keigwin, L D

    2016-07-29

    The most recent ice age was characterized by rapid and hemispherically asynchronous climate oscillations, whose origin remains unresolved. Variations in oceanic meridional heat transport may contribute to these repeated climate changes, which were most pronounced during marine isotope stage 3, the glacial interval 25 thousand to 60 thousand years ago. We examined climate and ocean circulation proxies throughout this interval at high resolution in a deep North Atlantic sediment core, combining the kinematic tracer protactinium/thorium (Pa/Th) with the deep water-mass tracer, epibenthic δ(13)C. These indicators suggest reduced Atlantic overturning circulation during every cool northern stadial, with the greatest reductions during episodic Hudson Strait iceberg discharges, while sharp northern warming followed reinvigorated overturning. These results provide direct evidence for the ocean's persistent, central role in abrupt glacial climate change. Copyright © 2016, American Association for the Advancement of Science.

  10. The effects of ocean circulation on ocean-ice interaction and potential feedbacks in an idealized shelf cavity

    Science.gov (United States)

    Bishop, S. P.; Thompson, A. F.; Schodlok, M.

    2016-02-01

    The West Antarctic ice sheet is melting at unprecedented rates, which will impact global sea level rise. The ocean may be playing the dominant role in this ice melt through the upwelling of warm and salty Circumpolar Deep Water (CDW) in regions such as Pine Island Glacier (PIG). There is evidence that the Antarctic Slope Front at the continental shelf constrains shoreward transport of CDW by mesoscale eddies. However, little is known about the ocean-ice interaction and potential feedbacks that take place once this water is advected into ice shelf cavities. In this talk we use MITgcm to simulate an idealized setup of the PIG ice shelf cavity, similar to the setup in De Rydt et al. 2014, to understand the effects of ocean circulation and potential feedbacks of ice-shelf melt on the ocean circulation. To do this we run the model in two different configurations with and without a wind-driven current at the northern edge of the ice shelf and annually updating the geometry of the ice shelf based on the parameterized ice-shelf melt. Eddy heat and potential vorticity fluxes are diagnosed and presented for each of the simulations and compared with control simulations where the ice-shelf cavity is not modified. Results show high ice shelf melt during the first year with maximum values in excess of 60 meters near the grounding line, but settle to tens of meters during the following years.

  11. Multi-mission mean sea surface and geoid models for ocean monitoring within the GOCINA project

    Science.gov (United States)

    Andersen, O. B.; Knudsen, P.; Anne, V. L.

    2004-05-01

    A major goal of the EU project GOCINA (Geoid and Ocean Circulation In the North Atlantic) is to develop tools for ocean monitoring using satellite altimetry combined with satellite gravimetry. Furthermore, the project will determine an accurate geoid in the region between Greenland and the UK and, hereby, create a platform for validation of future GOCE Level 2 data and higher order scientific products. The central quantity bridging the geoid and the ocean circulation is the mean dynamic topography, which is the difference between the mean sea surface and the geoid. The mean dynamic topography provides the absolute reference surface for the ocean circulation. The improved determination of the mean circulation will advance the understanding of the role of the ocean mass and heat transport in climate change. To calculate the best possible synthetic mean dynamic topographies a new mean sea surface (KMS03) has been derived from nine years of altimetric data (1993-2001). The regional geoid has furthermore being updated using GRACE and gravimetric data from a recent airborne survey. New synthetic mean dynamic topography models have been computed from the best available geoid models (EGM96, GRACE, GOCINA) and the present mean sea surface models (i.e. CLS01, GSFC00, KMS03). These models will be compared with state of the art hydrodynamic mean dynamic topography models in the North Atlantic GOCINA area. An extended comparison in the Artic Ocean will also be presented to demonstrate the impact of improved geoid and mean sea surface modeling. Particularly using the GRACE derived geoid models, and the KMS03 mean sea surface.

  12. Water Properties and Circulation in the Deep Southeast Pacific Ocean

    Science.gov (United States)

    Chen, T.; Johnson, G. C.

    2017-12-01

    We quantify the origins and distribution of deep water masses in the Bauer Basin of the southeast Pacific Ocean using Conductivity-Temperature-Depth (CTD) instrument data collected during nominally meridional oceanographic transects with high-quality, full-depth, closely spaced stations through the basin that were occupied in 1994, 2007, and 2016. We analyze spiciness on isopyncals to quantify the relative fractions of cold and fresh water entering the basin from the North Pacific (NP) to the northwest through fracture zones in the East Pacific Rise vs. warmer and saltier (spicier) water entering the basin from the Yupanqui Basin (YB) to the south through gaps in the Galapagos Rise. While water exceeding the maximum density observed in the Bauer Basin is found in both adjacent basins, our analysis reveals a wedge of primarily cold and fresh NP origin water (75-95%), thickest in the north and overlain by warmer and saltier water that is most prominent in the South. This wedge is invariant with time, with the exception of fine-structure interleaving of NP and YB water that varies among occupations. We apply rotating hydraulic control theory to the fracture zone using density-pressure profiles on either side of the deepest sill in the East Pacific Rise connecting the North Pacific to the Bauer Basin and the deepest gap in the Galapagos Rise connection the Yupanqui Basin to the Bauer Basin. The estimated deep inflows are under 1 Sv, smaller from the south than from the north, consistent with the observed water properties being mostly of North Pacific origin.

  13. (abstract) Ekman Pumping/Suction and Wind-Driven Ocean Circulation from ERS-1 Scatterometer Measurements Over the Arabian Sea During October 1994-October 1995

    Science.gov (United States)

    Halpern, D.; Freilich, M. H.; Weller, R. A.

    1996-01-01

    Spatial variations of the east-west and north-south components of surface wind stress are critical in studies of ocean circulation and biological-physical interactions because surface wind stress curl produces a vertical velocity in the upper ocean at the bottom of the Ekman Layer.The ERS-1 scatterometer provides reasonable coverage and direct measurements of vector of winds. Three schemes are evaluated relative to high-quality moored-bouy wind observations recorded in the central Arabian Sea, where high surface waves and high atmospheric water content during the southeast monsoon adversely affect the estimation of satellite-derived winds.

  14. Two regimes of the Arctic's circulation from ocean models with ice and contaminants.

    Science.gov (United States)

    Proshutinsky, A Y; Johnson, M

    2001-01-01

    A two-dimensional barotropic, coupled, ocean-ice model with a space resolution of 55.5 km and driven by atmospheric forces, river run-off, and sea-level slope between the Pacific and the Arctic Oceans, has been used to simulate the vertically averaged currents and ice drift in the Arctic Ocean. Results from 43 years of numerical simulations of water and ice motions demonstrate that two wind-driven circulation regimes are possible in the Arctic, a cyclonic and an anti-cyclonic circulation. These two regimes appear to alternate at 5-7 year intervals with the 10-15 year period. It is important to pollution studies to understand which circulation regime prevails at any time. It is anticipated that 1995 is a year with a cyclonic regime, and during this cyclonic phase and possibly during past cyclonic regimes as well, pollutants may reach the Alaskan shelf. The regime shifts demonstrated in this paper are fundamentally important to understanding the Arctic's general circulation and particularly important for estimating pollution transport.

  15. Impact of variable seawater conductivity on motional induction simulated with an ocean general circulation model

    Science.gov (United States)

    Irrgang, C.; Saynisch, J.; Thomas, M.

    2016-01-01

    Carrying high concentrations of dissolved salt, ocean water is a good electrical conductor. As seawater flows through the Earth's ambient geomagnetic field, electric fields are generated, which in turn induce secondary magnetic fields. In current models for ocean-induced magnetic fields, a realistic consideration of seawater conductivity is often neglected and the effect on the variability of the ocean-induced magnetic field unknown. To model magnetic fields that are induced by non-tidal global ocean currents, an electromagnetic induction model is implemented into the Ocean Model for Circulation and Tides (OMCT). This provides the opportunity to not only model ocean-induced magnetic signals but also to assess the impact of oceanographic phenomena on the induction process. In this paper, the sensitivity of the induction process due to spatial and temporal variations in seawater conductivity is investigated. It is shown that assuming an ocean-wide uniform conductivity is insufficient to accurately capture the temporal variability of the magnetic signal. Using instead a realistic global seawater conductivity distribution increases the temporal variability of the magnetic field up to 45 %. Especially vertical gradients in seawater conductivity prove to be a key factor for the variability of the ocean-induced magnetic field. However, temporal variations of seawater conductivity only marginally affect the magnetic signal.

  16. SWOT, The Surface Water and Ocean Topography Satellite Mission (Invited)

    Science.gov (United States)

    Alsdorf, D.; Andreadis, K.; Bates, P. D.; Biancamaria, S.; Clark, E.; Durand, M. T.; Fu, L.; Lee, H.; Lettenmaier, D. P.; Mognard, N. M.; Moller, D.; Morrow, R. A.; Rodriguez, E.; Shum, C.

    2009-12-01

    Surface fresh water is essential for life, yet we have surprisingly poor knowledge of its variability in space and time. Similarly, ocean circulation fundamentally drives global climate variability, yet the ocean current and eddy field that affects ocean circulation and heat transport at the sub-mesoscale resolution and particularly near coastal and estuary regions, is poorly known. About 50% of the vertical exchange of water properties (nutrients, dissovled CO2, heat, etc) in the upper ocean is taking place at the sub-mesoscale. Measurements from the Surface Water and Ocean Topography satellite mission (SWOT) will make strides in understanding these processes and improving global ocean models for studying climate change. SWOT is a swath-based interferometric-altimeter designed to acquire elevations of ocean and terrestrial water surfaces at unprecedented spatial and temporal resolutions. The mission will provide measurements of storage changes in lakes, reservoirs, and wetlands as well as estimates of discharge in rivers. These measurements are important for global water and energy budgets, constraining hydrodynamic models of floods, carbon evasion through wetlands, and water management, especially in developing nations. Perhaps most importantly, SWOT measurements will provide a fundamental understanding of the spatial and temporal variations in global surface waters, which for many countries are the primary source of water. An on-going effort, the “virtual mission” (VM) is designed to help constrain the required height and slope accuracies, the spatial sampling (both pixels and orbital coverage), and the trade-offs in various temporal revisits. Example results include the following: (1) Ensemble Kalman filtering of VM simulations recover water depth and discharge, reducing the discharge RMSE from 23.2% to 10.0% over an 84-day simulation period, relative to a simulation without assimilation. (2) Ensemble-based data assimilation of SWOT like measurements yields

  17. Zoogeography of intertidal communities in the West Indian Ocean as determined by ocean circulation systems: patterns from the Tetraclita barnacles.

    Science.gov (United States)

    Tsang, Ling Ming; Achituv, Yair; Chu, Ka Hou; Chan, Benny Kwok Kan

    2012-01-01

    The Indian Ocean is the least known ocean in the world with the biogeography of marine species in the West Indian Ocean (WIO) understudied. The hydrography of WIO is characterized by four distinct oceanographic systems and there were few glacial refugia formations in the WIO during the Pleistocene. We used the widely distributed intertidal barnacle Tetraclita to test the hypothesis that the distribution and connectivity of intertidal animals in the WIO are determined by the major oceanographic regime but less influenced by historical events such as Pleistocene glaciations. Tetraclita were studied from 32 locations in the WIO. The diversity and distribution of Tetraclita species in the Indian Ocean were examined based on morphological examination and sequence divergence of two mitochondrial genes (12S rDNA and COI) and one nuclear gene (histone 3, H3). Divergence in DNA sequences revealed the presence of seven evolutionarily significant units (ESUs) of Tetraclita in WIO, with most of them recognized as valid species. The distribution of these ESUs is closely tied to the major oceanographic circulation systems. T. rufotincta is distributed in the Monsoonal Gyre. T. ehsani is present in the Gulf of Oman and NW India. Tetraclita sp. nov. is associated with the Hydrochemical Front at 10°S latitude. T. reni is confined to southern Madagascan and Mauritian waters, influenced by the West Wind Drift. The endemic T. achituvi is restricted to the Red Sea. Tetraclita serrata consists of two ESUs (based on mtDNA analysis) along the east to west coast of South Africa. The two ESUs could not be distinguished from morphological analysis and nuclear H3 sequences. Our results support that intertidal species in the West Indian Ocean are associated with each of the major oceanographic circulation systems which determine gene flow. Geographical distribution is, however, less influenced by the geological history of the region.

  18. Late Archean Surface Ocean Oxygenation (Invited)

    Science.gov (United States)

    Kendall, B.; Reinhard, C.; Lyons, T. W.; Kaufman, A. J.; Anbar, A. D.

    2009-12-01

    Oxygenic photosynthesis must have evolved by 2.45-2.32 Ga, when atmospheric oxygen abundances first rose above 0.001% present atmospheric level (Great Oxidation Event; GOE). Biomarker evidence for a time lag between the evolution of cyanobacterial oxygenic photosynthesis and the GOE continues to be debated. Geochemical signatures from sedimentary rocks (redox-sensitive trace metal abundances, sedimentary Fe geochemistry, and S isotopes) represent an alternative tool for tracing the history of Earth surface oxygenation. Integrated high-resolution chemostratigraphic profiles through the 2.5 Ga Mt. McRae Shale (Pilbara Craton, Western Australia) suggest a ‘whiff’ of oxygen in the surface environment at least 50 M.y. prior to the GOE. However, the geochemical data from the Mt. McRae Shale does not uniquely constrain the presence or extent of Late Archean ocean oxygenation. Here, we present high-resolution chemostratigraphic profiles from 2.6-2.5 Ga black shales (upper Campbellrand Subgroup, Kaapvaal Craton, South Africa) that provide the earliest direct evidence for an oxygenated ocean water column. On the slope beneath the Campbellrand - Malmani carbonate platform (Nauga Formation), a mildly oxygenated water column (highly reactive iron to total iron ratios [FeHR/FeT] ≤ 0.4) was underlain by oxidizing sediments (low Re and Mo abundances) or mildly reducing sediments (high Re but low Mo abundances). After drowning of the carbonate platform (Klein Naute Formation), the local bottom waters became anoxic (FeHR/FeT > 0.4) and intermittently sulphidic (pyrite iron to highly reactive iron ratios [FePY/FeHR] > 0.8), conducive to enrichment of both Re and Mo in sediments, followed by anoxic and Fe2+-rich (ferruginous) conditions (high FeT, FePY/FeHR near 0). Widespread surface ocean oxygenation is suggested by Re enrichment in the broadly correlative Klein Naute Formation and Mt. McRae Shale, deposited ~1000 km apart in the Griqualand West and Hamersley basins

  19. Radiocarbon constraints on the glacial ocean circulation and its impact on atmospheric CO2.

    Science.gov (United States)

    Skinner, L C; Primeau, F; Freeman, E; de la Fuente, M; Goodwin, P A; Gottschalk, J; Huang, E; McCave, I N; Noble, T L; Scrivner, A E

    2017-07-13

    While the ocean's large-scale overturning circulation is thought to have been significantly different under the climatic conditions of the Last Glacial Maximum (LGM), the exact nature of the glacial circulation and its implications for global carbon cycling continue to be debated. Here we use a global array of ocean-atmosphere radiocarbon disequilibrium estimates to demonstrate a ∼689±53 14 C-yr increase in the average residence time of carbon in the deep ocean at the LGM. A predominantly southern-sourced abyssal overturning limb that was more isolated from its shallower northern counterparts is interpreted to have extended from the Southern Ocean, producing a widespread radiocarbon age maximum at mid-depths and depriving the deep ocean of a fast escape route for accumulating respired carbon. While the exact magnitude of the resulting carbon cycle impacts remains to be confirmed, the radiocarbon data suggest an increase in the efficiency of the biological carbon pump that could have accounted for as much as half of the glacial-interglacial CO 2 change.

  20. Comparison of three-dimensional ocean general circulation models on a benchmark problem

    International Nuclear Information System (INIS)

    Chartier, M.

    1990-12-01

    A french and an american Ocean General Circulation Models for deep-sea disposal of radioactive wastes are compared on a benchmark test problem. Both models are three-dimensional. They solve the hydrostatic primitive equations of the ocean with two different finite difference techniques. Results show that the dynamics simulated by both models are consistent. Several methods for the running of a model from a known state are tested in the French model: the diagnostic method, the prognostic method, the acceleration of convergence and the robust-diagnostic method

  1. A review of the Southern Oscillation - Oceanic-atmospheric circulation changes and related rainfall anomalies

    Science.gov (United States)

    Kousky, V. E.; Kagano, M. T.; Cavalcanti, I. F. A.

    1984-01-01

    The region of South America is emphasized in the present consideration of the Southern Oscillation (SO) oceanic and atmospheric circulation changes. The persistence of climate anomalies associated with El Nino-SO events is due to strong atmosphere-ocean coupling. Once initiated, the SO follows a certain sequence of events with clearly defined effects on tropical and subtropical rainfall. Excessive rainfall related to the SO in the central and eastern Pacific, Peru, Ecuador, and southern Brazil, are complemented by drought in Australia, Indonesia, India, West Africa, and northeast Brazil. El Nino-SO events are also associated with dramatic changes in the tropospheric flow pattern over a broad area of both hemispheres.

  2. The Influence of Indian Ocean Atmospheric Circulation on Warm Pool Hydroclimate During the Holocene Epoch

    Science.gov (United States)

    Tierney, J.E.; Oppo, D. W.; LeGrande, A. N.; Huang, Y.; Rosenthal, Y.; Linsley, B. K.

    2012-01-01

    Existing paleoclimate data suggest a complex evolution of hydroclimate within the Indo-Pacific Warm Pool (IPWP) during the Holocene epoch. Here we introduce a new leaf wax isotope record from Sulawesi, Indonesia and compare proxy water isotope data with ocean-atmosphere general circulation model (OAGCM) simulations to identify mechanisms influencing Holocene IPWP hydroclimate. Modeling simulations suggest that orbital forcing causes heterogenous changes in precipitation across the IPWP on a seasonal basis that may account for the differences in time-evolution of the proxy data at respective sites. Both the proxies and simulations suggest that precipitation variability during the September-November (SON) season is important for hydroclimate in Borneo. The preeminence of the SON season suggests that a seasonally lagged relationship between the Indian monsoon and Indian Ocean Walker circulation influences IPWP hydroclimatic variability during the Holocene.

  3. An implementation of a barotropic quasigeostrophic model of ocean circulation on the MPP

    Science.gov (United States)

    Grosch, C. E.; Fatoohi, R.

    1987-01-01

    The implementation on the Massively Parallel Processor (MPP) of a barotropic quasigeostrophic model of ocean circulation is discussed. The mathematical model, including scalings and boundary conditions is discussed. The numerical scheme, which uses compact differencing is also discussed. The implementation of this model on the MPP is then presented. Finally, some performance results are given and compared to results obtained using the VPS-32 and one processor of a CRAY-2.

  4. The Finite Element Sea Ice-Ocean Model (FESOM v.1.4: formulation of an ocean general circulation model

    Directory of Open Access Journals (Sweden)

    Q. Wang

    2014-04-01

    Full Text Available The Finite Element Sea Ice-Ocean Model (FESOM is the first global ocean general circulation model based on unstructured-mesh methods that has been developed for the purpose of climate research. The advantage of unstructured-mesh models is their flexible multi-resolution modelling functionality. In this study, an overview of the main features of FESOM will be given; based on sensitivity experiments a number of specific parameter choices will be explained; and directions of future developments will be outlined. It is argued that FESOM is sufficiently mature to explore the benefits of multi-resolution climate modelling and that its applications will provide information useful for the advancement of climate modelling on unstructured meshes.

  5. Antarctic climate, Southern Ocean circulation patterns, and deep water formation during the Eocene

    Science.gov (United States)

    Huck, Claire E.; van de Flierdt, Tina; Bohaty, Steven M.; Hammond, Samantha J.

    2017-07-01

    We assess early-to-middle Eocene seawater neodymium (Nd) isotope records from seven Southern Ocean deep-sea drill sites to evaluate the role of Southern Ocean circulation in long-term Cenozoic climate change. Our study sites are strategically located on either side of the Tasman Gateway and are positioned at a range of shallow (fish teeth at intermediate/deep Indian Ocean pelagic sites (Ocean Drilling Program (ODP) Sites 738 and 757 and Deep Sea Drilling Project (DSDP) Site 264), indicate a dominant Southern Ocean-sourced contribution to regional deep waters (ɛNd(t) = -9.3 ± 1.5). IODP Site U1356 off the coast of Adélie Land, a locus of modern-day Antarctic Bottom Water production, is identified as a site of persistent deep water formation from the early Eocene to the Oligocene. East of the Tasman Gateway an additional local source of intermediate/deep water formation is inferred at ODP Site 277 in the SW Pacific Ocean (ɛNd(t) = -8.7 ± 1.5). Antarctic-proximal shelf sites (ODP Site 1171 and Site U1356) reveal a pronounced erosional event between 49 and 48 Ma, manifested by 2 ɛNd unit negative excursions in seawater chemistry toward the composition of bulk sediments at these sites. This erosional event coincides with the termination of peak global warmth following the Early Eocene Climatic Optimum and is associated with documented cooling across the study region and increased export of Antarctic deep waters, highlighting the complexity and importance of Southern Ocean circulation in the greenhouse climate of the Eocene.

  6. Investigating the Potential Impact of the Surface Water and Ocean Topography (SWOT) Altimeter on Ocean Mesoscale Prediction

    Science.gov (United States)

    Carrier, M.; Ngodock, H.; Smith, S. R.; Souopgui, I.

    2016-02-01

    NASA's Surface Water and Ocean Topography (SWOT) satellite, scheduled for launch in 2020, will provide sea surface height anomaly (SSHA) observations with a wider swath width and higher spatial resolution than current satellite altimeters. It is expected that this will help to further constrain ocean models in terms of the mesoscale circulation. In this work, this expectation is investigated by way of twin data assimilation experiments using the Navy Coastal Ocean Model Four Dimensional Variational (NCOM-4DVAR) data assimilation system using a weak constraint formulation. Here, a nature run is created from which SWOT observations are sampled, as well as along-track SSHA observations from simulated Jason-2 tracks. The simulated SWOT data has appropriate spatial coverage, resolution, and noise characteristics based on an observation-simulator program provided by the SWOT science team. The experiment is run for a three-month period during which the analysis is updated every 24 hours and each analysis is used to initialize a 96 hour forecast. The forecasts in each experiment are compared to the available nature run to determine the impact of the assimilated data. It is demonstrated here that the SWOT observations help to constrain the model mesoscale in a more consistent manner than traditional altimeter observations. The findings of this study suggest that data from SWOT may have a substantial impact on improving the ocean model analysis and forecast of mesoscale features and surface ocean transport.

  7. Influence of glacial ice sheets on the Atlantic meridional overturning circulation through surface wind change

    Science.gov (United States)

    Sherriff-Tadano, Sam; Abe-Ouchi, Ayako; Yoshimori, Masakazu; Oka, Akira; Chan, Wing-Le

    2018-04-01

    Coupled modeling studies have recently shown that the existence of the glacial ice sheets intensifies the Atlantic meridional overturning circulation (AMOC). However, most models show a strong AMOC in their simulations of the Last Glacial Maximum (LGM), which is biased compared to reconstructions that indicate both a weaker and stronger AMOC during the LGM. Therefore, a detailed investigation of the mechanism behind this intensification of the AMOC is important for a better understanding of the glacial climate and the LGM AMOC. Here, various numerical simulations are conducted to focus on the effect of wind changes due to glacial ice sheets on the AMOC and the crucial region where the wind modifies the AMOC. First, from atmospheric general circulation model experiments, the effect of glacial ice sheets on the surface wind is evaluated. Second, from ocean general circulation model experiments, the influence of the wind stress change on the AMOC is evaluated by applying wind stress anomalies regionally or at different magnitudes as a boundary condition. These experiments demonstrate that glacial ice sheets intensify the AMOC through an increase in the wind stress at the North Atlantic mid-latitudes, which is induced by the North American ice sheet. This intensification of the AMOC is caused by the increased oceanic horizontal and vertical transport of salt, while the change in sea ice transport has an opposite, though minor, effect. Experiments further show that the Eurasian ice sheet intensifies the AMOC by directly affecting the deep-water formation in the Norwegian Sea.

  8. Response of Southern Ocean circulation to global warming may enhance basal ice shelf melting around Antarctica

    Energy Technology Data Exchange (ETDEWEB)

    Hattermann, Tore; Levermann, Anders [Potsdam University, Earth System Analysis, Potsdam Institute for Climate Impact Research, Potsdam (Germany)

    2010-10-15

    We investigate the large-scale oceanic features determining the future ice shelf-ocean interaction by analyzing global warming experiments in a coarse resolution climate model with a comprehensive ocean component. Heat and freshwater fluxes from basal ice shelf melting (ISM) are parameterized following Beckmann and Goosse [Ocean Model 5(2):157-170, 2003]. Melting sensitivities to the oceanic temperature outside of the ice shelf cavities are varied from linear to quadratic (Holland et al. in J Clim 21, 2008). In 1% per year CO{sub 2}-increase experiments the total freshwater flux from ISM triples to 0.09 Sv in the linear case and more than quadruples to 0.15 Sv in the quadratic case after 140 years at which 4 x 280 ppm = 1,120 ppm was reached. Due to the long response time of subsurface temperature anomalies, ISM thereafter increases drastically, if CO{sub 2} concentrations are kept constant at 1,120 ppm. Varying strength of the Antarctic circumpolar current (ACC) is crucial for ISM increase, because southward advection of heat dominates the warming along the Antarctic coast. On centennial timescales the ACC accelerates due to deep ocean warming north of the current, caused by mixing of heat along isopycnals in the Southern Ocean (SO) outcropping regions. In contrast to previous studies we find an initial weakening of the ACC during the first 150 years of warming. This purely baroclinic effect is due to a freshening in the SO which is consistent with present observations. Comparison with simulations with diagnosed ISM but without its influence on the ocean circulation reveal a number of ISM-related feedbacks, of which a negative ISM-feedback, due to the ISM-related local oceanic cooling, is the dominant one. (orig.)

  9. Ka-band Doppler Scatterometer for Measurements of Ocean Vector Winds and Surface Currents

    Data.gov (United States)

    National Aeronautics and Space Administration — Ocean surface currents impact heat transport, surface momentum and gas fluxes, ocean productivity and marine biological communities. Ocean currents also have social...

  10. Deglacial Tropical Atlantic subsurface warming links ocean circulation variability to the West African Monsoon.

    Science.gov (United States)

    Schmidt, Matthew W; Chang, Ping; Parker, Andrew O; Ji, Link; He, Feng

    2017-11-13

    Multiple lines of evidence show that cold stadials in the North Atlantic were accompanied by both reductions in Atlantic Meridional Overturning Circulation (AMOC) and collapses of the West African Monsoon (WAM). Although records of terrestrial change identify abrupt WAM variability across the deglaciation, few studies show how ocean temperatures evolved across the deglaciation. To identify the mechanism linking AMOC to the WAM, we generated a new record of subsurface temperature variability over the last 21 kyr based on Mg/Ca ratios in a sub-thermocline dwelling planktonic foraminifera in an Eastern Equatorial Atlantic (EEA) sediment core from the Niger Delta. Our subsurface temperature record shows abrupt subsurface warming during both the Younger Dryas (YD) and Heinrich Event 1. We also conducted a new transient coupled ocean-atmosphere model simulation across the YD that better resolves the western boundary current dynamics and find a strong negative correlation between AMOC strength and EEA subsurface temperatures caused by changes in ocean circulation and rainfall responses that are consistent with the observed WAM change. Our combined proxy and modeling results provide the first evidence that an oceanic teleconnection between AMOC strength and subsurface temperature in the EEA impacted the intensity of the WAM on millennial time scales.

  11. Simulation of the global ocean thermohaline circulation with an eddy-resolving INMIO model configuration

    Science.gov (United States)

    Ushakov, K. V.; Ibrayev, R. A.

    2017-11-01

    In this paper, the first results of a simulation of the mean World Ocean thermohaline characteristics obtained by the INMIO ocean general circulation model configured with 0.1 degree resolution in a 5-year long numerical experiment following the CORE-II protocol are presented. The horizontal and zonal mean distributions of the solution bias against the WOA09 data are analyzed. The seasonal cycle of heat content at a specified site of the North Atlantic is also discussed. The simulation results demonstrate a clear improvement in the quality of representation of the upper ocean compared to the results of experiments with 0.5 and 0.25 degree model configurations. Some remaining biases of the model solution and possible ways of their overcoming are highlighted.

  12. Quantifying the roles of ocean circulation and biogeochemistry in governing ocean carbon-13 and atmospheric carbon dioxide at the last glacial maximum

    Directory of Open Access Journals (Sweden)

    A. Tagliabue

    2009-11-01

    Full Text Available We use a state-of-the-art ocean general circulation and biogeochemistry model to examine the impact of changes in ocean circulation and biogeochemistry in governing the change in ocean carbon-13 and atmospheric CO2 at the last glacial maximum (LGM. We examine 5 different realisations of the ocean's overturning circulation produced by a fully coupled atmosphere-ocean model under LGM forcing and suggested changes in the atmospheric deposition of iron and phytoplankton physiology at the LGM. Measured changes in carbon-13 and carbon-14, as well as a qualitative reconstruction of the change in ocean carbon export are used to evaluate the results. Overall, we find that while a reduction in ocean ventilation at the LGM is necessary to reproduce carbon-13 and carbon-14 observations, this circulation results in a low net sink for atmospheric CO2. In contrast, while biogeochemical processes contribute little to carbon isotopes, we propose that most of the change in atmospheric CO2 was due to such factors. However, the lesser role for circulation means that when all plausible factors are accounted for, most of the necessary CO2 change remains to be explained. This presents a serious challenge to our understanding of the mechanisms behind changes in the global carbon cycle during the geologic past.

  13. Pathways of upwelling deep waters to the surface of the Southern Ocean

    Science.gov (United States)

    Tamsitt, Veronica; Drake, Henri; Morrison, Adele; Talley, Lynne; Dufour, Carolina; Gray, Alison; Griffies, Stephen; Mazloff, Matthew; Sarmiento, Jorge; Wang, Jinbo; Weijer, Wilbert

    2017-04-01

    Upwelling of Atlantic, Indian and Pacific deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of anthropogenic carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. Here we go beyond the two-dimensional view of Southern Ocean upwelling, to show detailed Southern Ocean upwelling pathways in three dimensions, using hydrographic observations and particle tracking in high-resolution ocean and climate models. The northern deep waters enter the Antarctic Circumpolar Current (ACC) via narrow southward currents along the boundaries of the three ocean basins, before spiraling southeastward and upward through the ACC. Upwelling is greatly enhanced at five major topographic features, associated with vigorous mesoscale eddy activity. Deep water reaches the upper ocean predominantly south of the southern ACC boundary, with a spatially nonuniform distribution, regionalizing warm water supply to Antarctic ice shelves and the delivery of nutrient and carbon-rich water to the sea surface. The timescale for half of the deep water to upwell from 30°S to the mixed layer is on the order of 60-90 years, which has important implications for the timescale for signals to propagate through the deep ocean. In addition, we quantify the diabatic transformation along particle trajectories, to identify where diabatic processes are important along the upwelling pathways.

  14. Changes in Ocean Circulation with an Ice-Free Arctic: Reconstructing Early Holocene Arctic Ocean Circulation Using Geochemical Signals from Individual Neogloboquadrina pachyderma (sinistral) Shells

    Science.gov (United States)

    Livsey, C.; Spero, H. J.; Kozdon, R.

    2016-12-01

    The impacts of sea ice decrease and consequent hydrologic changes in the Arctic Ocean will be experienced globally as ocean and atmospheric temperatures continue to rise, though it is not evident to what extent. Understanding the structure of the Arctic water column during the early/mid Holocene sea ice minimum ( 6-10 kya), a post-glacial analogue of a seasonally ice-free Arctic, will help us to predict what the changes we can expect as the Earth warms over the next century. Neogloboquadrina pachyderma (sinistral; Nps) is a species of planktonic foraminifera that dominates assemblages in the polar oceans. This species grows its chambers (ontogenetic calcite) in the surface waters and subsequently descends through the water column to below the mixed layer where it quickly adds a thick crust of calcite (Kohfeld et al., 1996). Therefore, geochemical signals from both the surface waters and sub-mixed layer depths are captured within single Nps shells. We were able to target ion mass spectrometry (SIMS), therefore capturing signals from both the ontogenetic and crust calcite in single Nps shells. This data was combined with laser ablation- inductively coupled mass spectrometry (LA-ICPMS) Mg/Ca profiles of trace metals through the two layers of calcite of the same shells, to determine the thermal structure of the water column. Combining δ18O, temperature, and salinity gradients from locations across the Arctic basin allow us to reconstruct the hydrography of the early Holocene Arctic sea ice minimum. These results will be compared with modern Arctic water column characteristics in order to develop a conceptual model of Arctic Ocean oceanographic change due to global warming. Kohfeld, K.E., Fairbanks, R.G., Smith, S.L., Walsh, I.D., 1996. Neogloboquadrina pachyderma(sinistral coiling) as paleoceanographic tracers in polar oceans: Evidence from northeast water polynya plankton tows, sediment traps, and surface sediments. Paleoceanography 11, 679-699.

  15. Ocean circulation in the southern Benguela region from the Pliocene to the Pleistocene: tracking Agulhas leakage into the SE Atlantic

    Science.gov (United States)

    Petrick, Benjamin; McClymont, Erin; Felder, Sojna; Leng, Melanie

    2013-04-01

    The transition from the warmth of the middle Pliocene to the large amplitude, 100 kyr glacial-interglacial cycles of the late Pleistocene provides a way to understand the forcings and impacts of regional and global climate change. Here, we investigate changes in ocean circulation over the period from 3.5 Ma to present using a marine sediment core, ODP Site 1087 (31o28'S, 15o19'E, 1374m water depth). ODP 1087 is located in the South-east Atlantic Ocean, outside the Benguela upwelling region. Its location allows investigation of the history of the heat and salt transfer to the Atlantic Ocean from the Indian Ocean ("Agulhas leakage"), which plays an important part in the global thermohaline circulation. It is not known how this transfer reacted to generally warmer global temperatures during the mid-Pliocene, nor to the transition to a globally cooler climate in the early Pleistocene. Our approach is to apply several organic geochemistry proxies and foraminiferal analyses to reconstruct the history of ODP 1087. These include the U37K' index to reconstruct sea surface temperatures, pigment analysis for understanding productivity changes, and foraminifera assemblage analysis to detect the presence of different water masses at the site. We have identified changes in SSTs and biological productivity that we argue to reflect shifts in the position of the Benguela upwelling cells, and a changing influence of Agulhas leakage. Our new data reveal a different organization in the Southeast Atlantic. It shows that during the Pliocene ODP 1087 was dominated by Benguela upwelling which had shifted south. We find no evidence for Agulhas leakage during the mid Pliocene, which could mean that Agulhas Leakage was severely reduced during the mid Pliocene. The implications of these results for understanding Plio-Pleistocene climate changes will be explored here.

  16. Insights From Magnesium Isotopic Compositions on the Oceanic Hydrothermal Circulation: Is Seamount Weathering the Solution?

    Science.gov (United States)

    Galy, A.; Carder, E.; Elderfield, H.

    2006-12-01

    It has been long recognised that the input of Mg in the ocean by river is removed by precipitation of Mg-rich bearing phases, either directly from the ocean such as dolomite or through hydrothermal circulation in the oceanic crust. The sampling of hydrothermal fluids demonstrated the efficiency of Mg consumption by the alteration of the oceanic crust, even at temperatures as low as 15°. For high-temperature fluids vented through black or white smokers in the vicinity of the ridge, the Mg concentration is up to 50 time lower than in seawater, and the close relationship between chlorine and Mg led to the idea that seawater was feeding the hydrothermal system and that Mg is quantitatively removed from it during high-T° alteration, the so called zero Mg hypothesis. Despite some hint for a non zero Mg hydrothermal end-member for a handful sites, the low concentration of Mg in oceanic hydrothermal fluids (around 1 mmol/l) has been mainly attributed to contamination by seawater during the sampling. Here we present Mg isotopic composition of 14 seawater samples from the Atlantic, Pacific and Indian Oceans and the Mediterranean and Red Seas and covering a range of depth of almost 5km and 26 hydrothermal fluids from 7 sites in the Atlantic and Pacific Oceans with temperature from 15° to 380°C. We find the magnesium isotope composition of seawater to be constant, with a δ^{26}Mg = -0.82±0.10 ‰ relative to the DSM3 standard. This value is consistent with a long residence time for Mg in seawater. In addition, out of the 26 hydrothermal fluids studied, more than 58% differ from seawater for their Mg isotopic composition by more than 2σ. This number rises up to 88% at 2σmean level and the shift is systematic with the fluids being either indistinguishable from seawater or enriched in light isotopes by up to 2.4‰ in δ^{26}Mg. This clearly demonstrates that fluids having low Mg concentrations are not solely bearing Mg added by contamination during sampling. The isotopic

  17. Linkages between ocean circulation, heat uptake and transient warming: a sensitivity study

    Science.gov (United States)

    Pfister, Patrik; Stocker, Thomas

    2016-04-01

    Transient global warming due to greenhouse gas radiative forcing is substantially reduced by ocean heat uptake (OHU). However, the fraction of equilibrium warming that is realized in transient climate model simulations differs strongly between models (Frölicher and Paynter 2015). It has been shown that this difference is not only related to the magnitude of OHU, but also to the radiative response the OHU causes, measured by the OHU efficacy (Winton et al., 2010). This efficacy is strongly influenced by the spatial pattern of the OHU and its changes (Rose et al. 2014, Winton et al. 2013), predominantly caused by changes in the Atlantic meridional overturning circulation (AMOC). Even in absence of external greenhouse gas forcing, an AMOC weakening causes a radiative imbalance at the top of the atmosphere (Peltier and Vettoretti, 2014), inducing in a net warming of the Earth System. We investigate linkages between those findings by performing both freshwater and greenhouse gas experiments in an Earth System Model of Intermediate Complexity. To assess the sensitivity of the results to ocean and atmospheric transport as well as climate sensitivity, we use an ensemble of model versions, systematically varying key parameters. We analyze circulation changes and radiative adjustments in conjunction with traditional warming metrics such as the transient climate response and the equilibrium climate sensitivity. This aims to improve the understanding of the influence of ocean circulation and OHU on transient climate change, and of the relevance of different metrics for describing this influence. References: Frölicher, T. L. and D.J. Paynter (2015), Extending the relationship between global warming and cumulative carbon emissions to multi-millennial timescales, Environ. Res. Lett., 10, 075022 Peltier, W. R., and G. Vettoretti (2014), Dansgaard-Oeschger oscillations predicted in a comprehensive model of glacial climate: A "kicked" salt oscillator in the Atlantic, Geophys. Res

  18. Dynamics and thermodynamics of the Indian Ocean warm pool in a high-resolution global general circulation model

    Digital Repository Service at National Institute of Oceanography (India)

    PrasannaKumar, S.; Ishida, A.; Yoneyama, K.; RameshKumar, M.R.; Kashino, Y.; Mitsudera, H.

    The time evolution of the Indian Ocean warm pool, studied using a global high-resolution general circulation model, shows strong seasonality. The warm pool has the largest spatial extent during April-May, and least in December. The spatio...

  19. Oceanic sill-overflow systems: Investigations and simulation with the Poseidon ocean general circulation model

    Science.gov (United States)

    Anderson, Whit G.

    Marginal seas transport dense water into the oceanic system by deep gravity currents through sill-overflow systems. This dense water is essential in establishing background characteristics and the density driven component of the meridional overturing of the ocean. This thesis investigates the controlling dynamics and several modeling issues related to oceanic deep gravity currents. The objectives and questions of this study center on the development of a climate scale model that adequately simulates sill-overflow deep gravity currents. These questions include the sensitivity of the model to resolution and various turbulence parameterizations when modeling these systems. A hybrid generalized vertical coordinate model is adapted to address these questions. This study uses theoretical model domains based on the Dynamics of Mixing and Entrainment group (DOME). Current, climate scale models typically have horizontal resolutions ranging from 1/2 to 1 degree resolution. The bulk of the vertical resolution in layered models is commonly placed in density or pressure space centered around the equatorial upper ocean, well away from the regions containing the deep gravity currents investigated in this study. Models solutions from this study show large dependence on both horizontal and vertical resolution. When horizontal resolution is decreased from 5 to 20 km, entrainment of ambient water into the gravity current decreases by approximately a factor of 3. The deep gravity currents in the lower (20 km) resolution experiments are deeper, denser and have larger along-slope velocities than the higher resolution experiments (5 km). This difference is explained by the homogenization of the gravity current in lower resolution simulations. The 5 km simulations show higher magnitudes and spatial variability of momentum. This homogenization results in underestimation of the applied bottom stress in the model. With a lower bottom stress, the current does not have sufficient shearing to

  20. Evaluation of OSCAR ocean surface current product in the tropical ...

    Indian Academy of Sciences (India)

    (Johnson et al. 2007). The OSCAR product is, however, a global product. Thus there is a pressing need to validate this product in the other basins of the world ocean, e.g., in the Indian Ocean. The present study is motivated by this need. In the present study, monthly climatology of OSCAR ocean surface currents in the TIO ...

  1. Late Holocene diatom-based sea-surface temperature reconstruction from the Conrad Rise, Southern Ocean

    Science.gov (United States)

    Orme, Lisa; Mietinnen, Arto; Crosta, Xavier; Mohan, Rahul

    2017-04-01

    The Southern Ocean plays an important role in the global climate system. The temperature and sea ice extent alter the latitudinal temperature gradient of the Southern Ocean, which can be transferred to the atmosphere resulting in changes in the southern westerly winds. The temperature, sea ice and wind variations are also factors influencing Antarctic Bottom Water formation, which is a control on the strength of the Atlantic Meridional Overturning Circulation. Therefore conditions in the Southern Ocean may influence the climate in the northern and southern hemispheres. The Southern Ocean and North Atlantic were connected during the Last Glacial during Dansgaard-Oeschger events, when variations in ocean circulation caused a bipolar seesaw of temperatures. For the Holocene there is less evidence for a bipolar seesaw, although recent research shows concurrent, opposite trends in ocean circulation in the North Atlantic and in the Southern Ocean. Further reconstructions are required from the Southern Ocean in particular to enable greater understanding of how the temperature and sea ice varied during the Holocene. The OCTEL project (Ocean-sea-ice-atmosphere teleconnections between the Southern Ocean and North Atlantic during the Holocene) aims to investigate the ocean, atmosphere and sea-ice teleconnections for the Holocene using new, high resolution records from both the Southern Ocean and North Atlantic. We here present initial results from diatom analysis conducted on a sediment core from the Southern Ocean, sampled from the Conrad Rise (54˚ 16.04'S, 39˚ 45.98'W). The preliminary results highlight a dominance of diatom species Fragilariopsis kerguelensis and Thalassiosira lentiginosa, with lower abundances of Thalassiothrix antarctica and Thalassiosira gracilis among others, which suggests an open ocean setting close to the polar front. The diatom data will be converted to quantitative reconstructions of summer sea surface temperature and sea ice presence using the

  2. Mid-Pliocene shifts in ocean overturning circulation and the onset of Quaternary-style climates

    Directory of Open Access Journals (Sweden)

    M. Sarnthein

    2009-06-01

    Full Text Available A major tipping point of Earth's history occurred during the mid-Pliocene: the onset of major Northern-Hemisphere Glaciation (NHG and of pronounced, Quaternary-style cycles of glacial-to-interglacial climates, that contrast with more uniform climates over most of the preceding Cenozoic and continue until today (Zachos et al., 2001. The severe deterioration of climate occurred in three steps between 3.2 Ma (warm MIS K3 and 2.7 Ma (glacial MIS G6/4 (Lisiecki and Raymo, 2005. Various models (sensu Driscoll and Haug, 1998 and paleoceanographic records (intercalibrated using orbital age control suggest clear linkages between the onset of NHG and the three steps in the final closure of the Central American Seaways (CAS, deduced from rising salinity differences between Caribbean and the East Pacific. Each closing event led to an enhanced North Atlantic meridional overturning circulation and this strengthened the poleward transport of salt and heat (warmings of +2–3°C (Bartoli et al., 2005. Also, the closing resulted in a slight rise in the poleward atmospheric moisture transport to northwestern Eurasia (Lunt et al., 2007, which probably led to an enhanced precipitation and fluvial run-off, lower sea surface salinity (SSS, and an increased sea-ice cover in the Arctic Ocean, hence promoting albedo and the build-up of continental ice sheets. Most important, new evidence shows that the closing of the CAS led to greater steric height of the North Pacific and thus doubled the low-saline Arctic Throughflow from the Bering Strait to the East Greenland Current (EGC. Accordingly, Labrador Sea IODP Site 1307 displays an abrupt but irreversible EGC cooling of 6°C and freshening by ~2 psu from 3.25/3.16–3.00 Ma, right after the first but still reversible attempt of closing the CAS.

  3. The influence of the ocean circulation state on ocean carbon storage and CO2 drawdown potential in an Earth system model

    Directory of Open Access Journals (Sweden)

    M. Ödalen

    2018-03-01

    Full Text Available During the four most recent glacial cycles, atmospheric CO2 during glacial maxima has been lowered by about 90–100 ppm with respect to interglacials. There is widespread consensus that most of this carbon was partitioned in the ocean. It is, however, still debated which processes were dominant in achieving this increased carbon storage. In this paper, we use an Earth system model of intermediate complexity to explore the sensitivity of ocean carbon storage to ocean circulation state. We carry out a set of simulations in which we run the model to pre-industrial equilibrium, but in which we achieve different states of ocean circulation by changing forcing parameters such as wind stress, ocean diffusivity and atmospheric heat diffusivity. As a consequence, the ensemble members also have different ocean carbon reservoirs, global ocean average temperatures, biological pump efficiencies and conditions for air–sea CO2 disequilibrium. We analyse changes in total ocean carbon storage and separate it into contributions by the solubility pump, the biological pump and the CO2 disequilibrium component. We also relate these contributions to differences in the strength of the ocean overturning circulation. Depending on which ocean forcing parameter is tuned, the origin of the change in carbon storage is different. When wind stress or ocean diapycnal diffusivity is changed, the response of the biological pump gives the most important effect on ocean carbon storage, whereas when atmospheric heat diffusivity or ocean isopycnal diffusivity is changed, the solubility pump and the disequilibrium component are also important and sometimes dominant. Despite this complexity, we obtain a negative linear relationship between total ocean carbon and the combined strength of the northern and southern overturning cells. This relationship is robust to different reservoirs dominating the response to different forcing mechanisms. Finally, we conduct a drawdown experiment

  4. The influence of the ocean circulation state on ocean carbon storage and CO2 drawdown potential in an Earth system model

    Science.gov (United States)

    Ödalen, Malin; Nycander, Jonas; Oliver, Kevin I. C.; Brodeau, Laurent; Ridgwell, Andy

    2018-03-01

    During the four most recent glacial cycles, atmospheric CO2 during glacial maxima has been lowered by about 90-100 ppm with respect to interglacials. There is widespread consensus that most of this carbon was partitioned in the ocean. It is, however, still debated which processes were dominant in achieving this increased carbon storage. In this paper, we use an Earth system model of intermediate complexity to explore the sensitivity of ocean carbon storage to ocean circulation state. We carry out a set of simulations in which we run the model to pre-industrial equilibrium, but in which we achieve different states of ocean circulation by changing forcing parameters such as wind stress, ocean diffusivity and atmospheric heat diffusivity. As a consequence, the ensemble members also have different ocean carbon reservoirs, global ocean average temperatures, biological pump efficiencies and conditions for air-sea CO2 disequilibrium. We analyse changes in total ocean carbon storage and separate it into contributions by the solubility pump, the biological pump and the CO2 disequilibrium component. We also relate these contributions to differences in the strength of the ocean overturning circulation. Depending on which ocean forcing parameter is tuned, the origin of the change in carbon storage is different. When wind stress or ocean diapycnal diffusivity is changed, the response of the biological pump gives the most important effect on ocean carbon storage, whereas when atmospheric heat diffusivity or ocean isopycnal diffusivity is changed, the solubility pump and the disequilibrium component are also important and sometimes dominant. Despite this complexity, we obtain a negative linear relationship between total ocean carbon and the combined strength of the northern and southern overturning cells. This relationship is robust to different reservoirs dominating the response to different forcing mechanisms. Finally, we conduct a drawdown experiment in which we investigate

  5. Ocean circulation model predicts high genetic structure observed in a long-lived pelagic developer.

    Science.gov (United States)

    Sunday, J M; Popovic, I; Palen, W J; Foreman, M G G; Hart, M W

    2014-10-01

    Understanding the movement of genes and individuals across marine seascapes is a long-standing challenge in marine ecology and can inform our understanding of local adaptation, the persistence and movement of populations, and the spatial scale of effective management. Patterns of gene flow in the ocean are often inferred based on population genetic analyses coupled with knowledge of species' dispersive life histories. However, genetic structure is the result of time-integrated processes and may not capture present-day connectivity between populations. Here, we use a high-resolution oceanographic circulation model to predict larval dispersal along the complex coastline of western Canada that includes the transition between two well-studied zoogeographic provinces. We simulate dispersal in a benthic sea star with a 6-10 week pelagic larval phase and test predictions of this model against previously observed genetic structure including a strong phylogeographic break within the zoogeographical transition zone. We also test predictions with new genetic sampling in a site within the phylogeographic break. We find that the coupled genetic and circulation model predicts the high degree of genetic structure observed in this species, despite its long pelagic duration. High genetic structure on this complex coastline can thus be explained through ocean circulation patterns, which tend to retain passive larvae within 20-50 km of their parents, suggesting a necessity for close-knit design of Marine Protected Area networks. © 2014 John Wiley & Sons Ltd.

  6. Changing currents: a strategy for understanding and predicting the changing ocean circulation.

    Science.gov (United States)

    Bryden, Harry L; Robinson, Carol; Griffiths, Gwyn

    2012-12-13

    Within the context of UK marine science, we project a strategy for ocean circulation research over the next 20 years. We recommend a focus on three types of research: (i) sustained observations of the varying and evolving ocean circulation, (ii) careful analysis and interpretation of the observed climate changes for comparison with climate model projections, and (iii) the design and execution of focused field experiments to understand ocean processes that are not resolved in coupled climate models so as to be able to embed these processes realistically in the models. Within UK-sustained observations, we emphasize smart, cost-effective design of the observational network to extract maximum information from limited field resources. We encourage the incorporation of new sensors and new energy sources within the operational environment of UK-sustained observational programmes to bridge the gap that normally separates laboratory prototype from operational instrument. For interpreting the climate-change records obtained through a variety of national and international sustained observational programmes, creative and dedicated UK scientists should lead efforts to extract the meaningful signals and patterns of climate change and to interpret them so as to project future changes. For the process studies, individual scientists will need to work together in team environments to combine observational and process modelling results into effective improvements in the coupled climate models that will lead to more accurate climate predictions.

  7. Exploiting coastal altimetry to improve the surface circulation scheme over the central Mediterranean Sea

    Science.gov (United States)

    Jebri, Fatma; Birol, Florence; Zakardjian, Bruno; Bouffard, Jérome; Sammari, Cherif

    2016-07-01

    This work is the first study exploiting along track altimetry data to observe and monitor coastal ocean features over the transition area between the western and eastern Mediterranean Basins. The relative performances of both the AVISO and the X-TRACK research regional altimetric data sets are compared using in situ observations. Both products are cross validated with tide gauge records. The altimeter-derived geostrophic velocities are also compared with observations from a moored Acoustic Doppler Current Profiler. Results indicate the good potential of satellite altimetry to retrieve dynamic features over the area. However, X-TRACK shows a more homogenous data coverage than AVISO, with longer time series in the 50 km coastal band. The seasonal evolution of the surface circulation is therefore analyzed by conjointly using X-TRACK data and remotely sensed sea surface temperature observations. This combined data set clearly depicts different current regimes and bifurcations, which allows us to propose a new seasonal circulation scheme for the central Mediterranean. The analysis shows variations of the path and temporal behavior of the main circulation features: the Atlantic Tunisian Current, the Atlantic Ionian Stream, the Atlantic Libyan Current, and the Sidra Gyre. The resulting bifurcating veins of these currents are also discussed, and a new current branch is observed for the first time.

  8. Retrieval and assimilation of velocities at the ocean surface

    OpenAIRE

    Isern-Fontanet, Jordi; Ballabrera-Poy, Joaquim; Turiel, Antonio; García-Ladona, Emilio

    2017-01-01

    Ocean currents play a key role in Earth’s climate, they are of major importance for navigation and human activities at sea, and impact almost all processes that take place in the ocean. Nevertheless, their observation and forecasting are still difficult. First, direct measurements of ocean currents are difficult to obtain synoptically at global scale. Consequently, it has been necessary to use Sea Surface Height and Sea Surface Temperature measurements and refer to dynamical frameworks to der...

  9. Orbital pacing and ocean circulation-induced collapses of the Mesoamerican monsoon over the past 22,000 y.

    Science.gov (United States)

    Lachniet, Matthew S; Asmerom, Yemane; Bernal, Juan Pablo; Polyak, Victor J; Vazquez-Selem, Lorenzo

    2013-06-04

    The dominant controls on global paleomonsoon strength include summer insolation driven by precession cycles, ocean circulation through its influence on atmospheric circulation, and sea-surface temperatures. However, few records from the summer North American Monsoon system are available to test for a synchronous response with other global monsoons to shared forcings. In particular, the monsoon response to widespread atmospheric reorganizations associated with disruptions of the Atlantic Meridional Overturning Circulation (AMOC) during the deglacial period remains unconstrained. Here, we present a high-resolution and radiometrically dated monsoon rainfall reconstruction over the past 22,000 y from speleothems of tropical southwestern Mexico. The data document an active Last Glacial Maximum (18-24 cal ka B.P.) monsoon with similar δ(18)O values to the modern, and that the monsoon collapsed during periods of weakened AMOC during Heinrich stadial 1 (ca. 17 ka) and the Younger Dryas (12.9-11.5 ka). The Holocene was marked by a trend to a weaker monsoon that was paced by orbital insolation. We conclude that the Mesoamerican monsoon responded in concert with other global monsoon regions, and that monsoon strength was driven by variations in the strength and latitudinal position of the Intertropical Convergence Zone, which was forced by AMOC variations in the North Atlantic Ocean. The surprising observation of an active Last Glacial Maximum monsoon is attributed to an active but shallow AMOC and proximity to the Intertropical Convergence Zone. The emergence of agriculture in southwestern Mexico was likely only possible after monsoon strengthening in the Early Holocene at ca. 11 ka.

  10. Regional eddy vorticity transport and the equilibrium vorticity budgets of a numerical model ocean circulation

    Science.gov (United States)

    Harrison, D. E.; Holland, W. R.

    1981-01-01

    A mean vorticity budget analysis is presented of Holland's (1978) numerical ocean general circulation experiment. The stable budgets are compared with classical circulation theory to emphasize the ways in which the mesoscale motions of the model alter (or leave unaltered) classical vorticity balances. The basinwide meridional transports of vorticity by the mean flow and by the mesoscale flow in the mean are evaluated to establish the role(s) of the mesoscale in the larger scale equilibrium vorticity transports. The vorticity equation for this model fluid system is presented and the budget analysis method is described. Vorticity budgets over the selected regions and on a larger scale are given, and a summary of budget results is provided along with remarks about the utility of this type of analysis.

  11. Modelling the Effect of Large Submarine Sandslides on the Ocean Circulation

    Science.gov (United States)

    Mozzato, A.; Munday, D. R.; Johnson, H. L.; Talling, P. J.

    2016-02-01

    Submarine landslide can be orders of magnitude larger than terrestrial landslide, moving up to thousands of kilometers of sediment. Submarine landslides have been suggested to be able to play an important role in extreme climate events although at present no study has been focused on this aspect. The Storegga Slide is the biggest Holocene Slide mapped off the Norwegian Margin, with an estimated volume of 3000 km3. The slide failure is coincident with the last major cold event, the 8.2k cold event. The work presented is focused on the investigation of the connection between the Storegga Slide and the 8.2k cold event. The main focus is the study of the dense mud cloud generated after the release of the landslide. Studies have suggested that the generated mud cloud have had a concentration as high as 4% and a height of 800m. The hypothesis tested is if this dense mud cloud can interfere with the meridional overturning circulation at to which extent. For this study a regional Arctic coupled ocean-sea-ice model was set up using the MITgcm general circulation model. The mud cloud was simulated using salinity perturbation as a proxy for the increased density of the water column. Results indicate a strong response from the ocean currents to the perturbation. The dense water mass formed by the perturbation moves northward slowly infilling the Arctic and affecting the whole water column up to the top. The results so far exclude a direct effect of the Storegga Slide on the MOC via a perturbation of the dense water formation in the North Atlantic. However, given the response of the circulation to the perturbation the results suggest that the Storegga Slide could have played a role in the 8.2k cold event. Work is still needed to precisely assess the magnitude of the impact of the perturbation on the circulation and the dynamics of this effect.

  12. On the role of the Agulhas system in ocean circulation and climate.

    Science.gov (United States)

    Beal, Lisa M; De Ruijter, Wilhelmus P M; Biastoch, Arne; Zahn, Rainer

    2011-04-28

    The Atlantic Ocean receives warm, saline water from the Indo-Pacific Ocean through Agulhas leakage around the southern tip of Africa. Recent findings suggest that Agulhas leakage is a crucial component of the climate system and that ongoing increases in leakage under anthropogenic warming could strengthen the Atlantic overturning circulation at a time when warming and accelerated meltwater input in the North Atlantic is predicted to weaken it. Yet in comparison with processes in the North Atlantic, the overall Agulhas system is largely overlooked as a potential climate trigger or feedback mechanism. Detailed modelling experiments--backed by palaeoceanographic and sustained modern observations--are required to establish firmly the role of the Agulhas system in a warming climate.

  13. Ocean regional circulation model sensitizes to resolution of the lateral boundary conditions

    Science.gov (United States)

    Pham, Van Sy; Hwang, Jin Hwan

    2017-04-01

    Dynamical downscaling with nested regional oceanographic models is an effective approach for forecasting operationally coastal weather and projecting long term climate on the ocean. Nesting procedures deliver the unwanted in dynamic downscaling due to the differences of numerical grid sizes and updating steps. Therefore, such unavoidable errors restrict the application of the Ocean Regional Circulation Model (ORCMs) in both short-term forecasts and long-term projections. The current work identifies the effects of errors induced by computational limitations during nesting procedures on the downscaled results of the ORCMs. The errors are quantitatively evaluated for each error source and its characteristics by the Big-Brother Experiments (BBE). The BBE separates identified errors from each other and quantitatively assess the amount of uncertainties employing the same model to simulate for both nesting and nested model. Here, we focus on discussing errors resulting from two main matters associated with nesting procedures. They should be the spatial grids' differences and the temporal updating steps. After the diverse cases from separately running of the BBE, a Taylor diagram was adopted to analyze the results and suggest an optimization intern of grid size and updating period and domain sizes. Key words: lateral boundary condition, error, ocean regional circulation model, Big-Brother Experiment. Acknowledgement: This research was supported by grants from the Korean Ministry of Oceans and Fisheries entitled "Development of integrated estuarine management system" and a National Research Foundation of Korea (NRF) Grant (No. 2015R1A5A 7037372) funded by MSIP of Korea. The authors thank the Integrated Research Institute of Construction and Environmental Engineering of Seoul National University for administrative support.

  14. Meridional overturning circulation conveys fast acidification to the deep Atlantic Ocean

    Science.gov (United States)

    Perez, Fiz F.; Fontela, Marcos; García-Ibáñez, Maribel I.; Mercier, Herlé; Velo, Anton; Lherminier, Pascale; Zunino, Patricia; de La Paz, Mercedes; Alonso-Pérez, Fernando; Guallart, Elisa F.; Padin, Xose A.

    2018-02-01

    Since the Industrial Revolution, the North Atlantic Ocean has been accumulating anthropogenic carbon dioxide (CO2) and experiencing ocean acidification, that is, an increase in the concentration of hydrogen ions (a reduction in pH) and a reduction in the concentration of carbonate ions. The latter causes the ‘aragonite saturation horizon’—below which waters are undersaturated with respect to a particular calcium carbonate, aragonite—to move to shallower depths (to shoal), exposing corals to corrosive waters. Here we use a database analysis to show that the present rate of supply of acidified waters to the deep Atlantic could cause the aragonite saturation horizon to shoal by 1,000-1,700 metres in the subpolar North Atlantic within the next three decades. We find that, during 1991-2016, a decrease in the concentration of carbonate ions in the Irminger Sea caused the aragonite saturation horizon to shoal by about 10-15 metres per year, and the volume of aragonite-saturated waters to reduce concomitantly. Our determination of the transport of the excess of carbonate over aragonite saturation (xc[CO32-])—an indicator of the availability of aragonite to organisms—by the Atlantic meridional overturning circulation shows that the present-day transport of carbonate ions towards the deep ocean is about 44 per cent lower than it was in preindustrial times. We infer that a doubling of atmospheric anthropogenic CO2 levels—which could occur within three decades according to a ‘business-as-usual scenario’ for climate change—could reduce the transport of xc[CO32-] by 64-79 per cent of that in preindustrial times, which could severely endanger cold-water coral habitats. The Atlantic meridional overturning circulation would also export this acidified deep water southwards, spreading corrosive waters to the world ocean.

  15. Carbon dioxide, climate and the deep ocean circulation: Carbon chemistry model

    International Nuclear Information System (INIS)

    Menawat, A.S.

    1992-01-01

    The objective of this study was to investigate the role of oceanic carbon chemistry in modulating the atmospheric levels of CO 2 . It is well known that the oceans are the primary sink of the excess carbon pumped into the atmosphere since the beginning of the industrial period. The suspended particulate and the dissolved organic matters in the deep ocean play important roles as carriers of carbon and other elements critical to the fate of CO 2 . In addition, the suspended particulate matter provides sites for oxidation-reduction reactions and microbial activities. The problem is of an intricate system with complex chemical, physical and biological processes. This report describes a methodology to describe the interconversions of different forms of the organic and inorganic nutrients, that may be incorporated in the ocean circulation models. Our approach includes the driving force behind the transfers in addition to balancing the elements. Such thermodynamic considerations of describing the imbalance in the chemical potentials is a new and unique feature of our approach

  16. Variability of surface circulation of the Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Murty, V.S.N.

    stream_size 7 stream_content_type text/plain stream_name Proc_Natl_Conf_Global_Temp_Rise_2007_138.pdf.txt stream_source_info Proc_Natl_Conf_Global_Temp_Rise_2007_138.pdf.txt Content-Encoding ISO-8859-1 Content-Type text...

  17. Ocean Surface Waves and Turbulence: Air-Sea Fluxes and Climate Variability

    Science.gov (United States)

    Melville, W. Kendall

    2009-11-01

    Apart from heating of the atmosphere, two of the most important consequences of current climate variability are changes in sea level, and acidification of the oceans. Over decadal time scales, changes in sea level are caused by changes in heat content and salinity of the ocean, and by changes in mass resulting from exchanges between the ocean, glaciers and other land-based reservoirs. The oceans have absorbed about one third of the anthropogenic CO2 due to fossil fuel burning. This reduces the green house effect in the atmosphere, but the CO2 reacts in the surface waters of the ocean to lower pH. Conservative projections of sea level rise over the next century are O(0.1 - 1) m, while ocean acidification is already having an impact on marine ecosystems. Both these processes depend on air-sea fluxes: heat flux for sea level rise, and gas flux for ocean acidification. These fluxes are among the most poorly constrained in current climate models, but both ultimately depend on fluid dynamics at the ocean surface and in the adjacent boundary layers. Traditional boundary layer models of the marine boundary layer and the marine atmospheric boundary layer were based on classical theories of boundary layers over rigid surfaces, but there is increasing evidence that these models must now include surface wave effects. In this talk the motivating climate data and modeling will be briefly reviewed, and then recent work on surface wave dynamics, air-sea fluxes and the adjacent boundary layers will be presented. The roles of surface wave breaking, Langmuir circulations, wave-turbulence interactions and gravity-capillary waves will be discussed.

  18. Simulation of anthropogenic CO2 uptake in the CCSM3.1 ocean circulation-biogeochemical model: comparison with data-based estimates

    Science.gov (United States)

    Wang, S.; Moore, J. K.; Primeau, F. W.; Khatiwala, S.

    2012-04-01

    The global ocean has taken up a large fraction of the CO2 released by human activities since the industrial revolution. Quantifying the oceanic anthropogenic carbon (Cant) inventory and its variability is important for predicting the future global carbon cycle. The detailed comparison of data-based and model-based estimates is essential for the validation and continued improvement of our prediction capabilities. So far, three global estimates of oceanic Cant inventory that are "data-based" and independent of global ocean circulation models have been produced: one based on the Δ C* method, and two that are based on constraining surface-to-interior transport of tracers, the TTD method and a maximum entropy inversion method (GF). The GF method, in particular, is capable of reconstructing the history of Cant inventory through the industrial era. In the present study we use forward model simulations of the Community Climate System Model (CCSM3.1) to estimate the Cant inventory and compare the results with the data-based estimates. We also use the simulations to test several assumptions of the GF method, including the assumption of constant climate and circulation, which is common to all the data-based estimates. Though the integrated estimates of global Cant inventories are consistent with each other, the regional estimates show discrepancies up to 50 %. The CCSM3 model underestimates the total Cant inventory, in part due to weak mixing and ventilation in the North Atlantic and Southern Ocean. Analyses of different simulation results suggest that key assumptions about ocean circulation and air-sea disequilibrium in the GF method are generally valid on the global scale, but may introduce errors in Cant estimates on regional scales. The GF method should also be used with caution when predicting future oceanic anthropogenic carbon uptake.

  19. Simulation of anthropogenic CO2 uptake in the CCSM3.1 ocean circulation-biogeochemical model: comparison with data-based estimates

    Directory of Open Access Journals (Sweden)

    S. Khatiwala

    2012-04-01

    Full Text Available The global ocean has taken up a large fraction of the CO2 released by human activities since the industrial revolution. Quantifying the oceanic anthropogenic carbon (Cant inventory and its variability is important for predicting the future global carbon cycle. The detailed comparison of data-based and model-based estimates is essential for the validation and continued improvement of our prediction capabilities. So far, three global estimates of oceanic Cant inventory that are "data-based" and independent of global ocean circulation models have been produced: one based on the Δ C* method, and two that are based on constraining surface-to-interior transport of tracers, the TTD method and a maximum entropy inversion method (GF. The GF method, in particular, is capable of reconstructing the history of Cant inventory through the industrial era. In the present study we use forward model simulations of the Community Climate System Model (CCSM3.1 to estimate the Cant inventory and compare the results with the data-based estimates. We also use the simulations to test several assumptions of the GF method, including the assumption of constant climate and circulation, which is common to all the data-based estimates. Though the integrated estimates of global Cant inventories are consistent with each other, the regional estimates show discrepancies up to 50 %. The CCSM3 model underestimates the total Cant inventory, in part due to weak mixing and ventilation in the North Atlantic and Southern Ocean. Analyses of different simulation results suggest that key assumptions about ocean circulation and air-sea disequilibrium in the GF method are generally valid on the global scale, but may introduce errors in Cant estimates on regional scales. The GF method should also be used with caution when predicting future oceanic anthropogenic carbon uptake.

  20. Overturn of the Oceasn Flow in the North Atlantic as a Trigger of Inertia Motion to Form a Meridional Ocean Circulation

    Science.gov (United States)

    Nakamura, Shigehisa

    2010-05-01

    This work is an introduction of a meridional ocean circulation. As for the zonal motions,there have been many contributions. Recent oceanographic works noticed an overturn of the ocean current in the North Atlantic. The author notices this overturn is a trigger to generate a meridional ocean circulation to have a track through the deep Atlantic, the deep circum-polar current, the deep branch flow to the Pacific between the Australian and the South America. The east part of the branch flow relates to the upwelling off Peru, and the west part relates to form a deep water in the Northwest Pacific. THe overturn of the North Atlantic suggests an outflow of the deep water and a storage of the old aged deep water in the Northwest Pacific. The storage water increase in the Northwest Pacific shoould be a trigger of the swelling up of the sea level mid Pacific to affect to the ocean front variations between the coastal waters and the ocean water. In order to keep a hydrodynamic balance on the earth, an increase of the deep water in the Pacific should flow through the Bering Sea and the Arctic Sea to get to the North Atlantic. It should be noted that a budget of the ocean water flow must be hold the condition of the water masses concservation on the earth surface. This inertia motion is maintained once induced after any natural effect or some man-made influences. At this stage, the author has to notice that there has been developed a meridional inertia path of the air particle as well as the ocean water parcel, nevertheless nobody has had pointed out this inertiamotion with a meridional path in the ocean. Air-sea interaction must be one of the main factors for driving the ocean water though the inertia motion in the global scale is more energetic. To the details, the scientists should pursue what geophysical dynamics must be developed in the future.

  1. Using Green's Functions to initialize and adjust a global, eddying ocean biogeochemistry general circulation model

    Science.gov (United States)

    Brix, H.; Menemenlis, D.; Hill, C.; Dutkiewicz, S.; Jahn, O.; Wang, D.; Bowman, K.; Zhang, H.

    2015-11-01

    The NASA Carbon Monitoring System (CMS) Flux Project aims to attribute changes in the atmospheric accumulation of carbon dioxide to spatially resolved fluxes by utilizing the full suite of NASA data, models, and assimilation capabilities. For the oceanic part of this project, we introduce ECCO2-Darwin, a new ocean biogeochemistry general circulation model based on combining the following pre-existing components: (i) a full-depth, eddying, global-ocean configuration of the Massachusetts Institute of Technology general circulation model (MITgcm), (ii) an adjoint-method-based estimate of ocean circulation from the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) project, (iii) the MIT ecosystem model "Darwin", and (iv) a marine carbon chemistry model. Air-sea gas exchange coefficients and initial conditions of dissolved inorganic carbon, alkalinity, and oxygen are adjusted using a Green's Functions approach in order to optimize modeled air-sea CO2 fluxes. Data constraints include observations of carbon dioxide partial pressure (pCO2) for 2009-2010, global air-sea CO2 flux estimates, and the seasonal cycle of the Takahashi et al. (2009) Atlas. The model sensitivity experiments (or Green's Functions) include simulations that start from different initial conditions as well as experiments that perturb air-sea gas exchange parameters and the ratio of particulate inorganic to organic carbon. The Green's Functions approach yields a linear combination of these sensitivity experiments that minimizes model-data differences. The resulting initial conditions and gas exchange coefficients are then used to integrate the ECCO2-Darwin model forward. Despite the small number (six) of control parameters, the adjusted simulation is significantly closer to the data constraints (37% cost function reduction, i.e., reduction in the model-data difference, relative to the baseline simulation) and to independent observations (e.g., alkalinity). The adjusted air-sea gas

  2. Circulation and water characteristics on isanosteric surfaces in the Northern Arabian Sea during February-April

    Digital Repository Service at National Institute of Oceanography (India)

    Das, V.K.; Gouveia, A.D.; Varma, K.K.

    Distribution of water characteristics and circulation were studied on 260, 160, 140, 120 and 80 cl/t surfaces using isanosteric analysis and geostrophic computation The circulation pattern consisted of several eddies and meanders The most prominent...

  3. Natural and anthropogenic radionuclide distributions in the Nansen Basin, Artic Ocean: Scavenging rates and circulation timescales

    Science.gov (United States)

    Kirk Cochran, J.; Hirschberg, David J.; Livingston, Hugh D.; Buesseler, Ken O.; Key, Robert M.

    Determination of the naturally occurring radionuclides 232Th, 230Th, 228 Th and 210Pb, and the anthropogenic radionuclides 241Am, 239,240Pu, 134Cs and 137Cs in water samples collected across the Nansen Basin from the Barents Sea slope to the Gakkel Ridge provides tracers with which to characterize both scavenging rates and circulation timescales in this portion of the Arctic Ocean. Large volume water samples (˜ 15001) were filtered in situ to separate particulate (> 0.5 μm) and dissolved Th isotopes and 241Am. Thorium-230 displays increases in both particulate and dissolved activities with depth, with dissolved 230Th greater and particulate 230Th lower in the deep central Nansen Basin than at the Barents Sea slope. Dissolved 228Th activities also are greater relative to 228Ra, in the central basin. Residence times for Th relative to removal from solution onto particles are ˜1 year in surface water, ˜10 years in deep water adjacent to the Barents Sea slope, and ˜20 years in the Eurasian Basin Deep Water. Lead-210 in the central basin deep water also has a residence time of ˜20 years with respect to its removal from the water column. This texture of scavenging is reflected in distributions of the particle-reactive anthropogenic radionuclide 241Am, which shows higher activities relative to Pu in the central Nansen Basin than at the Barents Sea slope. Distributions Of 137Cs show more rapid mixing at the basin margins (Barents Sea slope in the south, Gakkel Ridge in the north) than in the basin interior. Cesium-137 is mixed throughout the water column adjacent to the Barents Sea slope and is present in low but detectable activities in the Eurasian Basin Deep Water in the central basin. At the time of sampling (1987) the surface water at all stations had been labeled with 134Cs released in the 1986 accident at the Chernobyl nuclear power station. In the ˜1 year since the introduction of Chernobyl 134Cs to the Nansen Basin, it had been mixed to depths of ˜800 m at

  4. The Double ITCZ Syndrome in GCMs: A Coupled Problem among Convection, Atmospheric and Ocean Circulations

    Science.gov (United States)

    Zhang, G. J.; Song, X.

    2017-12-01

    The double ITCZ bias has been a long-standing problem in coupled atmosphere-ocean models. A previous study indicates that uncertainty in the projection of global warming due to doubling of CO2 is closely related to the double ITCZ biases in global climate models. Thus, reducing the double ITCZ biases is not only important to getting the current climate features right, but also important to narrowing the uncertainty in future climate projection. In this work, we will first review the possible factors contributing to the ITCZ problem. Then, we will focus on atmospheric convection, presenting recent progress in alleviating the double ITCZ problem and its sensitivity to details of convective parameterization, including trigger conditions for convection onset, convective memory, entrainment rate, updraft model and closure in the NCAR CESM1. These changes together can result in dramatic improvements in the simulation of ITCZ. Results based on both atmospheric only and coupled simulations with incremental changes of convection scheme will be shown to demonstrate the roles of convection parameterization and coupled interaction between convection, atmospheric circulation and ocean circulation in the simulation of ITCZ.

  5. Ocean Heat Uptake Slows 21st Century Surface Warming Driven by Extratropical Cloud Feedbacks

    Science.gov (United States)

    Frey, W.; Maroon, E.; Pendergrass, A. G.; Kay, J. E.

    2017-12-01

    Equilibrium climate sensitivity (ECS), the warming in response to instantaneously doubled CO2, has long been used to compare climate models. In many models, ECS is well correlated with warming produced by transient forcing experiments. Modifications to cloud phase at high latitudes in a state-of-the-art climate model, the Community Earth System Model (CESM), produce a large increase in ECS (1.5 K) via extratropical cloud feedbacks. However, only a small surface warming increase occurs in a realistic 21st century simulation including a full-depth dynamic ocean and the "business as usual" RCP8.5 emissions scenario. In fact, the increase in surface warming is only barely above the internal variability-generated range in the CESM Large Ensemble. The small change in 21st century warming is attributed to subpolar ocean heat uptake in both hemispheres. In the Southern Ocean, the mean-state circulation takes up heat while in the North Atlantic a slowdown in circulation acts as a feedback to slow surface warming. These results show the importance of subpolar ocean heat uptake in controlling the pace of warming and demonstrate that ECS cannot be used to reliably infer transient warming when it is driven by extratropical feedbacks.

  6. KARIN: The Ka-Band Radar Interferometer for the Proposed Surface Water and Ocean Topography (SWOT) Mission

    Science.gov (United States)

    Esteban-Fernandez, Daniel; Peral, Eva; McWatters, Dalia; Pollard, Brian; Rodriguez, Ernesto; Hughes, Richard

    2013-01-01

    Over the last two decades, several nadir profiling radar altimeters have provided our first global look at the ocean basin-scale circulation and the ocean mesoscale at wavelengths longer than 100 km. Due to sampling limitations, nadir altimetry is unable to resolve the small wavelength ocean mesoscale and sub-mesoscale that are responsible for the vertical mixing of ocean heat and gases and the dissipation of kinetic energy from large to small scales. The proposed Surface Water and Ocean Topography (SWOT) mission would be a partnership between NASA, CNES (Centre National d'Etudes Spaciales) and the Canadian Space Agency, and would have as one of its main goals the measurement of ocean topography with kilometer-scale spatial resolution and centimeter scale accuracy. In this paper, we provide an overview of all ocean error sources that would contribute to the SWOT mission.

  7. Enhanced Mean Dynamic Topography And Ocean Circulation Estimation Using Goce Preliminary Mode

    DEFF Research Database (Denmark)

    Knudsen, Per; Bingham, Rory; Andersen, Ole Baltazar

    2011-01-01

    have been combined with the recent DNSC08MSS mean sea surface model to construct a global GOCE satellite-only mean dynamic topography model. At a first glance, the GOCE MDT display the well known features related to the major ocean current systems. A closer look, however, reveals that the improved...

  8. Glacial Runoff From North America and its Possible Relationship to Changes in Ocean Circulation and Climate

    Science.gov (United States)

    Teller, J. T.; Lewis, C. M.

    2004-05-01

    Drainage basins during advances and retreats of the Laurentide Ice Sheet (LIS) were much different than today. Preglacial northward- and eastward-draining rivers were dammed by the advancing LIS, and rivers were diverted to other oceans; these new glacial routes evolved through time in response to ice margin fluctuations, isostasy, ice and land topography, and incision of drainage routes. A complex history of North American drainage developed following the Last Glacial Maximum. The main glacial routes for continental runoff were south through the Mississippi River to the Gulf of Mexico, east through the Great Lakes and then to the North Atlantic via the Hudson or St. Lawrence valleys, and northwest via the Athabasca-Mackenzie Valley to the Arctic Ocean. Postglacial drainage routes were establshed about 7.7 14C ka [8.45 cal ka], when Lake Agassiz breached the LIS in Hudson Bay basin and sent its remaining 163,000 km3 into the North Atlantic Ocean. Recent research on the eastern and northwestern outlets from Lake Agassiz, which played a major role in routing runoff from the continent, is prompting new thinking about the chronology of use of these outlets and their downstream river and ocean connections, especially during the Younger Dryas. Meltwater and precipitation runoff to the oceans was episodically supplemented by the release of stored water from ice-marginal lakes; during its latter stages (11-7.7 14C ka [13-8.45 cal ka]), Lake Agassiz provided by far the largest catastrophic additions. Because the flux of glacial runoff from North America has been linked to changes in thermohaline circulation (THC) and, in turn, to climate cooling, it is important to understand the chronology, routing, and magnitude of diversions and catastrophic outbursts from glacial basins. Outbursts may have triggered changes in THC and diversions may have sustained them.

  9. Juvenile recruitment in loggerhead sea turtles linked to decadal changes in ocean circulation.

    Science.gov (United States)

    Ascani, François; Van Houtan, Kyle S; Di Lorenzo, Emanuele; Polovina, Jeffrey J; Jones, T Todd

    2016-11-01

    Given the threats of climate change, understanding the relationship of climate with long-term population dynamics is critical for wildlife conservation. Previous studies have linked decadal climate oscillations to indices of juvenile recruitment in loggerhead sea turtles (Caretta caretta), but without a clear understanding of mechanisms. Here, we explore the underlying processes that may explain these relationships. Using the eddy-resolving Ocean General Circulation Model for the Earth Simulator, we generate hatch-year trajectories for loggerhead turtles emanating from Japan over six decades (1950-2010). We find that the proximity of the high-velocity Kuroshio Current to the primary nesting areas in southern Japan is remarkably stable and that hatchling dispersal to oceanic habitats itself does not vary on decadal timescales. However, we observe a shift in latitudes of trajectories, consistent with the Pacific Decadal Oscillation (PDO). In a negative PDO phase, the Kuroshio Extension Current (KEC) is strong and acts as a physical barrier to the northward transport of neonates. As a result, hatch-year trajectories remain mostly below 35°N in the warm, unproductive region south of the Transition Zone Chlorophyll Front (TZCF). During a positive PDO phase, however, the KEC weakens facilitating the neonates to swim north of the TZCF into cooler and more productive waters. As a result, annual cohorts from negative PDO years may face a lack of resources, whereas cohorts from positive PDO years may find sufficient resources during their pivotal first year. These model outputs indicate that the ocean circulation dynamics, combined with navigational swimming behavior, may be a key factor in the observed decadal variability of sea turtle populations. © 2016 John Wiley & Sons Ltd.

  10. Circulation constrains the evolution of larval development modes and life histories in the coastal ocean.

    Science.gov (United States)

    Pringle, James M; Byers, James E; Pappalardo, Paula; Wares, John P; Marshall, Dustin

    2014-04-01

    The evolutionary pressures that drive long larval planktonic durations in some coastal marine organisms, while allowing direct development in others, have been vigorously debated. We introduce into the argument the asymmetric dispersal of larvae by coastal currents and find that the strength of the currents helps determine which dispersal strategies are evolutionarily stable. In a spatially and temporally uniform coastal ocean of finite extent, direct development is always evolutionarily stable. For passively drifting larvae, long planktonic durations are stable when the ratio of mean to fluctuating currents is small and the rate at which larvae increase in size in the plankton is greater than the mortality rate (both in units of per time). However, larval behavior that reduces downstream larval dispersal for a given time in plankton will be selected for, consistent with widespread observations of behaviors that reduce dispersal of marine larvae. Larvae with long planktonic durations are shown to be favored not for the additional dispersal they allow, but for the additional fecundity that larval feeding in the plankton enables. We analyzed the spatial distribution of larval life histories in a large database of coastal marine benthic invertebrates and documented a link between ocean circulation and the frequency of planktotrophy in the coastal ocean. The spatial variation in the frequency of species with planktotrophic larvae is largely consistent with our theory; increases in mean currents lead to a decrease in the fraction of species with planktotrophic larvae over a broad range of temperatures.

  11. Finding the 'lost years' in green turtles: insights from ocean circulation models and genetic analysis.

    Science.gov (United States)

    Putman, Nathan F; Naro-Maciel, Eugenia

    2013-10-07

    Organismal movement is an essential component of ecological processes and connectivity among ecosystems. However, estimating connectivity and identifying corridors of movement are challenging in oceanic organisms such as young turtles that disperse into the open sea and remain largely unobserved during a period known as 'the lost years'. Using predictions of transport within an ocean circulation model and data from published genetic analysis, we present to our knowledge, the first basin-scale hypothesis of distribution and connectivity among major rookeries and foraging grounds (FGs) of green turtles (Chelonia mydas) during their 'lost years'. Simulations indicate that transatlantic dispersal is likely to be common and that recurrent connectivity between the southwestern Indian Ocean and the South Atlantic is possible. The predicted distribution of pelagic juvenile turtles suggests that many 'lost years hotspots' are presently unstudied and located outside protected areas. These models, therefore, provide new information on possible dispersal pathways that link nesting beaches with FGs. These pathways may be of exceptional conservation concern owing to their importance for sea turtles during a critical developmental period.

  12. Evaluation of OSCAR ocean surface current product in the tropical ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Earth System Science; Volume 122; Issue 1. Evaluation of OSCAR ocean surface current product in the tropical Indian Ocean using in situ data. Rajesh Sikhakolli Rashmi Sharma Sujit Basu B S Gohil Abhijit Sarkar K V S R Prasad. Volume 122 Issue 1 February 2013 pp 187-199 ...

  13. Indian Ocean surface winds from NCMRWF analysis as compared to ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    Indian Ocean surface winds from NCMRWF analysis as compared to QuikSCAT and moored buoy winds. B N Goswami1 and E N Rajagopal2. 1Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore 560 012, India. 2National Centre for Medium Range Weather Forecasting, Department of ...

  14. Northerly surface winds over the eastern North Pacific Ocean in spring and summer

    Science.gov (United States)

    Taylor, S.V.; Cayan, D.R.; Graham, N.E.; Georgakakos, K.P.

    2008-01-01

    Persistent spring and summer northerly surface winds are the defining climatological feature of the western coast of North America, especially south of the Oregon coast. Northerly surface winds are important for upwelling and a vast array of other biological, oceanic, and atmospheric processes. Intermittence in northerly coastal surface wind is characterized and wind events are quantitatively defined using coastal buoy data south of Cape Mendocino on the northern California coast. The defined wind events are then used as a basis for composites in order to explain the spatial evolution of various atmospheric and oceanic processes. Wind events involve large-scale changes in the three-dimensional atmospheric circulation including the eastern North Pacific subtropical anticyclone and southeast trade winds. Composites of QSCAT satellite scatterometer wind estimates from 1999 to 2005 based on a single coastal buoy indicate that wind events typically last 72-96 h and result in anomalies in surface wind and Ekman pumping that extend over 1000 kin from the west coast of North America. It may be useful to consider ocean circulation and dependent ecosystem dynamics and the distribution of temperature, moisture, and aerosols in the atmospheric boundary layer in the context of wind events defined herein. Copyright 2008 by the American Geophysical Union.

  15. SWOT: The Surface Water and Ocean Topography Mission. Wide- Swath Altimetric Elevation on Earth

    Science.gov (United States)

    Fu, Lee-Lueng (Editor); Alsdorf, Douglas (Editor); Morrow, Rosemary; Rodriguez, Ernesto; Mognard, Nelly

    2012-01-01

    The elevation of the surface of the ocean and freshwater bodies on land holds key information on many important processes of the Earth System. The elevation of the ocean surface, called ocean surface topography, has been measured by conventional nadirlooking radar altimeter for the past two decades. The data collected have been used for the study of large-scale circulation and sea level change. However, the spatial resolution of the observations has limited the study to scales larger than about 200 km, leaving the smaller scales containing substantial kinetic energy of ocean circulation that is responsible for the flux of heat, dissolved gas and nutrients between the upper and the deep ocean. This flux is important to the understanding of the ocean's role in regulatingfuture climate change.The elevation of the water bodies on land is a key parameter required for the computation of storage and discharge of freshwater in rivers, lakes, and wetlands. Globally, the spatial and temporal variability of water storage and discharge is poorly known due to the lack of well-sampled observations. In situ networks measuring river flows are declining worldwide due to economic and political reasons. Conventional altimeter observations suffers from the complexity of multiple peaks caused by the reflections from water, vegetation canopy and rough topography, resulting in much less valid data over land than over the ocean. Another major limitation is the large inter track distance preventing good coverage of rivers and other water bodies.This document provides descriptions of a new measurement technique using radar interferometry to obtain wide-swath measurement of water elevation at high resolution over both the ocean and land. Making this type of measurement, which addresses the shortcomings of conventional altimetry in both oceanographic and hydrologic applications, is the objective of a mission concept called Surface Water and Ocean Topography (SWOT), which was recommended by

  16. Oceanic Transport of Surface Meltwater from the Southern Greenland Ice Sheet

    Science.gov (United States)

    Luo, Hao; Castelao, Renato M.; Rennermalm, Asa K.; Tedesco, Marco; Bracco, Annalisa; Yager, Patricia L.; Mote, Thomas L.

    2016-01-01

    The Greenland ice sheet has undergone accelerating mass losses during recent decades. Freshwater runoff from ice melt can influence fjord circulation and dynamic1 and the delivery of bioavailable micronutrients to the ocean. It can also have climate implications, because stratification in the adjacent Labrador Sea may influence deep convection and the strength of the Atlantic meridional overturning circulation. Yet, the fate of the meltwater in the ocean remains unclear. Here, we use a high-resolution ocean model to show that only 1-15% of the surface meltwater runoff originating from southwest Greenland is transported westwards. In contrast, up to 50-60% of the meltwater runoff originating from southeast Greenland is transported westwards into the northern Labrador Sea, leading to significant salinity and stratification anomalies far from the coast. Doubling meltwater runoff, as predicted in future climate scenarios, results in a more-than-double increase in anomalies offshore that persists further into the winter. Interannual variability in offshore export of meltwater is tightly related to variability in wind forcing. The new insight that meltwaters originating from the west and east coasts have different fates indicates that future changes in mass loss rates and surface runoff will probably impact the ocean differently, depending on their Greenland origins.

  17. Oceanic transport of surface meltwater from the southern Greenland ice sheet

    Science.gov (United States)

    Luo, Hao; Castelao, Renato M.; Rennermalm, Asa K.; Tedesco, Marco; Bracco, Annalisa; Yager, Patricia L.; Mote, Thomas L.

    2016-07-01

    The Greenland ice sheet has undergone accelerating mass losses during recent decades. Freshwater runoff from ice melt can influence fjord circulation and dynamics and the delivery of bioavailable micronutrients to the ocean. It can also have climate implications, because stratification in the adjacent Labrador Sea may influence deep convection and the strength of the Atlantic meridional overturning circulation. Yet, the fate of the meltwater in the ocean remains unclear. Here, we use a high-resolution ocean model to show that only 1-15% of the surface meltwater runoff originating from southwest Greenland is transported westwards. In contrast, up to 50-60% of the meltwater runoff originating from southeast Greenland is transported westwards into the northern Labrador Sea, leading to significant salinity and stratification anomalies far from the coast. Doubling meltwater runoff, as predicted in future climate scenarios, results in a more-than-double increase in anomalies offshore that persists further into the winter. Interannual variability in offshore export of meltwater is tightly related to variability in wind forcing. The new insight that meltwaters originating from the west and east coasts have different fates indicates that future changes in mass loss rates and surface runoff will probably impact the ocean differently, depending on their Greenland origins.

  18. Surface temperature pattern of the Indian Ocean before summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Gopinathan, C.K.; Rao, D.P.

    The surface meteorological data collected during 1963 and 1964 indicate that the northward migration of the ITCZ is associated with a shift of the warm waters to the northern Indian Ocean. The warmer waters, found in the equatorial regions during...

  19. Spiraling pathways of global deep waters to the surface of the Southern Ocean.

    Science.gov (United States)

    Tamsitt, Veronica; Drake, Henri F; Morrison, Adele K; Talley, Lynne D; Dufour, Carolina O; Gray, Alison R; Griffies, Stephen M; Mazloff, Matthew R; Sarmiento, Jorge L; Wang, Jinbo; Weijer, Wilbert

    2017-08-02

    Upwelling of global deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. However, the exact pathways and role of topography in Southern Ocean upwelling remain largely unknown. Here we show detailed upwelling pathways in three dimensions, using hydrographic observations and particle tracking in high-resolution models. The analysis reveals that the northern-sourced deep waters enter the Antarctic Circumpolar Current via southward flow along the boundaries of the three ocean basins, before spiraling southeastward and upward through the Antarctic Circumpolar Current. Upwelling is greatly enhanced at five major topographic features, associated with vigorous mesoscale eddy activity. Deep water reaches the upper ocean predominantly south of the Antarctic Circumpolar Current, with a spatially nonuniform distribution. The timescale for half of the deep water to upwell from 30° S to the mixed layer is ~60-90 years.Deep waters of the Atlantic, Pacific and Indian Oceans upwell in the Southern Oceanbut the exact pathways are not fully characterized. Here the authors present a three dimensional view showing a spiralling southward path, with enhanced upwelling by eddy-transport at topographic hotspots.

  20. Fingerprints of changes in the terrestrial carbon cycle in response to large reorganizations in ocean circulation

    Directory of Open Access Journals (Sweden)

    A. Bozbiyik

    2011-03-01

    Full Text Available CO2 and carbon cycle changes in the land, ocean and atmosphere are investigated using the comprehensive carbon cycle-climate model NCAR CSM1.4-carbon. Ensemble simulations are forced with freshwater perturbations applied at the North Atlantic and Southern Ocean deep water formation sites under pre-industrial climate conditions. As a result, the Atlantic Meridional Overturning Circulation reduces in each experiment to varying degrees. The physical climate fields show changes qualitatively in agreement with results documented in the literature, but there is a clear distinction between northern and southern perturbations. Changes in the physical variables, in turn, affect the land and ocean biogeochemical cycles and cause a reduction, or an increase, in the atmospheric CO2 concentration by up to 20 ppmv, depending on the location of the perturbation. In the case of a North Atlantic perturbation, the land biosphere reacts with a strong reduction in carbon stocks in some tropical locations and in high northern latitudes. In contrast, land carbon stocks tend to increase in response to a southern perturbation. The ocean is generally a sink of carbon although large reorganizations occur throughout various basins. The response of the land biosphere is strongest in the tropical regions due to a shift of the Intertropical Convergence Zone. The carbon fingerprints of this shift, either to the south or to the north depending on where the freshwater is applied, can be found most clearly in South America. For this reason, a compilation of various paleoclimate proxy records of Younger Dryas precipitation changes are compared with our model results. The proxy records, in general, show good agreement with the model's response to a North Atlantic freshwater perturbation.

  1. Do the Brazilian sardine commercial landings respond to local ocean circulation?

    Science.gov (United States)

    Gouveia, Mainara B; Gherardi, Douglas F M; Lentini, Carlos A D; Dias, Daniela F; Campos, Paula C

    2017-01-01

    It has been reported that sea surface temperature (SST) anomalies, flow intensity and mesoscale ocean processes, all affect sardine production, both in eastern and western boundary current systems. Here we tested the hypothesis whether extreme high and low commercial landings of the Brazilian sardine fisheries in the South Brazil Bight (SBB) are sensitive to different oceanic conditions. An ocean model (ROMS) and an individual based model (Ichthyop) were used to assess the relationship between oceanic conditions during the spawning season and commercial landings of the Brazilian sardine one year later. Model output was compared with remote sensing and analysis data showing good consistency. Simulations indicate that mortality of eggs and larvae by low temperature prior to maximum and minimum landings are significantly higher than mortality caused by offshore advection. However, when periods of maximum and minimum sardine landings are compared with respect to these causes of mortality no significant differences were detected. Results indicate that mortality caused by prevailing oceanic conditions at early life stages alone can not be invoked to explain the observed extreme commercial landings of the Brazilian sardine. Likely influencing factors include starvation and predation interacting with the strategy of spawning "at the right place and at the right time".

  2. The relation between Arctic Ocean circulation and the Arctic Oscillation as revealed by satellite altimetry and gravimetry

    Science.gov (United States)

    Morison, J.; Kwok, R.; Peralta Ferriz, C.; Dickinson, S.; Morison, D.; Andersen, R.; Dewey, S.

    2017-12-01

    Arctic Ocean circulation is commonly characterized by the persistent anticyclonic Beaufort Gyre in the Canada Basin and the Transpolar Drift. While these are clearly important features, their role in changing Arctic Ocean circulation is at times distorted by sampling biases inherent in drifting buoy and standard shipboard measurements of western nations. Hydrographic measurements from SCICEX submarine cruises for science in the early 1990s revealed an increasingly cyclonic circulation along the Russian side of the Arctic Ocean related to the low sea level pressure pattern in the same region associated with a high Arctic Oscillation (AO) index. More recently satellite altimetry (ICESat and CryoSat2) and gravimetry (GRACE) have provided the basin-wide observational coverage needed to see shifts to increased cyclonic circulation in 2004 to 2008 and decreased cyclonic circulation in 2008 to 2015. These shifts are related to changes in the AO and are important for their effect on the trajectories of sea ice and freshwater through the Arctic Ocean.

  3. High Latitude North Atlantic Reservoir Age History: Implications for Age Models, Carbon Cycling, and the Timing of Ocean Circulation Changes

    Science.gov (United States)

    Stern, J.; Lisiecki, L. E.

    2012-12-01

    Unraveling the mechanisms responsible for past climate changes depends on the development of accurate and precise age models for paleoclimate records from widely distributed sites. The high latitude North Atlantic represents an area of particular interest because of its proximity to deepwater formation regions and the well-established importance of ocean circulation changes during millennial-scale and deglacial climate adjustments. However, high latitude North Atlantic time scales for marine cores are hampered by a lack of correlative features between surface ocean and Greenland ice core records between about 23-15 ka. Radiocarbon dating offers a route to circumvent these ambiguous surface proxy correlations. Our study is one of the first to constrain high latitude North Atlantic reservoir ages before 15 ka. We achieve regional-scale significance in our results by including constraints from many more sites than previous studies and a robust statistical treatment of the errors associated with our method. We developed an average high latitude North Atlantic reservoir age history for 0-40 ka by aligning benthic oxygen isotope records from 25 deep (>2000 m) North Atlantic sites and using these alignments to compare separate high (40-65°N; 12 sites) and low (0-40°N; 13 sites) latitude age models based on planktonic radiocarbon dates. This method assumes synchronous benthic oxygen isotopic change within the deep North Atlantic and constant low latitude reservoir ages of 400 yr. We find large average high latitude North Atlantic reservoir ages >1700 yr from 18.5-16.5 ka with similar-to-modern 400 yr reservoir ages for 40-24 ka and 12.5-0 ka. During the Last Glacial Maximum (approximately 23.5-19 ka), we find reservoir ages between 600-1000 yr. These results are significant for the development of accurate North Atlantic age models, provide an important constraint for understanding glacial and deglacial carbon cycling, and suggest that major ocean circulation changes

  4. Adaptation of an unstructured-mesh, finite-element ocean model to the simulation of ocean circulation beneath ice shelves

    Science.gov (United States)

    Kimura, Satoshi; Candy, Adam S.; Holland, Paul R.; Piggott, Matthew D.; Jenkins, Adrian

    2013-07-01

    Several different classes of ocean model are capable of representing floating glacial ice shelves. We describe the incorporation of ice shelves into Fluidity-ICOM, a nonhydrostatic finite-element ocean model with the capacity to utilize meshes that are unstructured and adaptive in three dimensions. This geometric flexibility offers several advantages over previous approaches. The model represents melting and freezing on all ice-shelf surfaces including vertical faces, treats the ice shelf topography as continuous rather than stepped, and does not require any smoothing of the ice topography or any of the additional parameterisations of the ocean mixed layer used in isopycnal or z-coordinate models. The model can also represent a water column that decreases to zero thickness at the 'grounding line', where the floating ice shelf is joined to its tributary ice streams. The model is applied to idealised ice-shelf geometries in order to demonstrate these capabilities. In these simple experiments, arbitrarily coarsening the mesh outside the ice-shelf cavity has little effect on the ice-shelf melt rate, while the mesh resolution within the cavity is found to be highly influential. Smoothing the vertical ice front results in faster flow along the smoothed ice front, allowing greater exchange with the ocean than in simulations with a realistic ice front. A vanishing water-column thickness at the grounding line has little effect in the simulations studied. We also investigate the response of ice shelf basal melting to variations in deep water temperature in the presence of salt stratification.

  5. Future changes in climate, ocean circulation, ecosystems, and biogeochemical cycling simulated for a business-as-usual CO2 emission scenario until year 4000 AD

    Science.gov (United States)

    Schmittner, Andreas; Oschlies, Andreas; Matthews, H. Damon; Galbraith, Eric D.

    2008-03-01

    A new model of global climate, ocean circulation, ecosystems, and biogeochemical cycling, including a fully coupled carbon cycle, is presented and evaluated. The model is consistent with multiple observational data sets from the past 50 years as well as with the observed warming of global surface air and sea temperatures during the last 150 years. It is applied to a simulation of the coming two millennia following a business-as-usual scenario of anthropogenic CO2 emissions (SRES A2 until year 2100 and subsequent linear decrease to zero until year 2300, corresponding to a total release of 5100 GtC). Atmospheric CO2 increases to a peak of more than 2000 ppmv near year 2300 (that is an airborne fraction of 72% of the emissions) followed by a gradual decline to ˜1700 ppmv at year 4000 (airborne fraction of 56%). Forty-four percent of the additional atmospheric CO2 at year 4000 is due to positive carbon cycle-climate feedbacks. Global surface air warms by ˜10°C, sea ice melts back to 10% of its current area, and the circulation of the abyssal ocean collapses. Subsurface oxygen concentrations decrease, tripling the volume of suboxic water and quadrupling the global water column denitrification. We estimate 60 ppb increase in atmospheric N2O concentrations owing to doubling of its oceanic production, leading to a weak positive feedback and contributing about 0.24°C warming at year 4000. Global ocean primary production almost doubles by year 4000. Planktonic biomass increases at high latitudes and in the subtropics whereas it decreases at midlatitudes and in the tropics. In our model, which does not account for possible direct impacts of acidification on ocean biology, production of calcium carbonate in the surface ocean doubles, further increasing surface ocean and atmospheric pCO2. This represents a new positive feedback mechanism and leads to a strengthening of the positive interaction between climate change and the carbon cycle on a multicentennial to millennial

  6. The timescales of global surface-ocean connectivity.

    Science.gov (United States)

    Jönsson, Bror F; Watson, James R

    2016-04-19

    Planktonic communities are shaped through a balance of local evolutionary adaptation and ecological succession driven in large part by migration. The timescales over which these processes operate are still largely unresolved. Here we use Lagrangian particle tracking and network theory to quantify the timescale over which surface currents connect different regions of the global ocean. We find that the fastest path between two patches--each randomly located anywhere in the surface ocean--is, on average, less than a decade. These results suggest that marine planktonic communities may keep pace with climate change--increasing temperatures, ocean acidification and changes in stratification over decadal timescales--through the advection of resilient types.

  7. Influence of Sea Ice on the Thermohaline Circulation in the Arctic-North Atlantic Ocean

    Science.gov (United States)

    Mauritzen, Cecilie; Haekkinen, Sirpa

    1997-01-01

    A fully prognostic coupled ocean-ice model is used to study the sensitivity of the overturning cell of the Arctic-North-Atlantic system to sea ice forcing. The strength of the thermohaline cell will be shown to depend on the amount of sea ice transported from the Arctic to the Greenland Sea and further to the subpolar gyre. The model produces a 2-3 Sv increase of the meridional circulation cell at 25N (at the simulation year 15) corresponding to a decrease of 800 cu km in the sea ice export from the Arctic. Previous modeling studies suggest that interannual and decadal variability in sea ice export of this magnitude is realistic, implying that sea ice induced variability in the overturning cell can reach 5-6 Sv from peak to peak.

  8. Current measurements from acoustic doppler current profilers (ADCP) in the southwest Atlantic Ocean from the World Ocean Circulation Experiment (WOCE) from 1991-01-03 to 1992-11-26 (NODC Accession 0087597)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Current meter data from the ADCP instruments of BE/335 and BW/333 from January 3, 1991 to November 26, 1992 collected as part of the World Ocean Circulation...

  9. Aspects on interactions between mid- to high latitude atmospheric circulation and some surface processes

    International Nuclear Information System (INIS)

    Byrkjedal, Oeyvind

    2006-01-01

    The Arctic is a hot topic in Climate Research. A large number of signs of a warming Arctic Climate have been identified the latest years. This is of major concern in light of the increasing atmospheric content of greenhouse gases. The climate research community projects future warming of the climate in the high latitudes as a response to increased amounts of anthropogenic release of greenhouse gases since the pre-industrial era. The overall objectives of this work has been to study the mid- and high latitude climate and climate variability, and to evaluate how well some climate processes that contribute to determine the Arctic climate and variability are represented and simulated in climate models. A new data set of storm tracks trajectories and statistics over the Northern Hemisphere for the period 1948-2002 has been developed. The variability of the cyclones extending to the Nordic Seas is studied in particular, and it is found that both the number of storms and their intensity exhibits a strong decadal and interannual variability. The ocean volume transports into and out of the Nordic Seas shows a relatively close relation to the wintertime cyclone intensity and cyclone count. To have confidence in future projections of climate, it is necessary to evaluate how the model behaves in a climate regime different from modern day. To do this two model simulations of the last glacial maximum (LGM) was performed. The reconstructions of sea surface temperatures in the Nordic Seas in LGM differ from perennial sea ice cover to having open ocean during the summer. The large scale atmospheric circulation patterns of the two different climate reconstructions are studied. It is found that the perennial sea ice cover produces a circulation pattern which may be too zonal to support the existence of the large north Eurasian ice sheets. In the case with seasonally open ocean the air masses carries larger amounts of heat and moisture towards the ice sheets and represents a larger

  10. Lidar equation for ocean surface and subsurface.

    Science.gov (United States)

    Josset, Damien; Zhai, Peng-Wang; Hu, Yongxiang; Pelon, Jacques; Lucker, Patricia L

    2010-09-27

    The lidar equation for ocean at optical wavelengths including subsurface signals is revisited using the recent work of the radiative transfer and ocean color community for passive measurements. The previous form of the specular and subsurface echo term are corrected from their heritage, which originated from passive remote sensing of whitecaps, and is improved for more accurate use in future lidar research. A corrected expression for specular and subsurface lidar return is presented. The previous formalism does not correctly address angular dependency of specular lidar return and overestimates the subsurface term by a factor ranging from 89% to 194% for a nadir pointing lidar. Suggestions for future improvements to the lidar equation are also presented.

  11. Impacts of changing ocean circulation on the distribution of marine microplastic litter.

    Science.gov (United States)

    Welden, Natalie Ac; Lusher, Amy L

    2017-05-01

    Marine plastic pollution is currently a major scientific focus, with attention paid to its distribution and impacts within ecosystems. With recent estimates indicating that the mass of plastic released to the marine environment may reach 250 million metric tons by 2025, the effects of plastic on our oceans are set to increase. Distribution of microplastics, those plastics measuring less than 5 mm, are of increasing concern because they represent an increasing proportion of marine litter and are known to interact with species in a range of marine habitats. The local abundance of microplastic is dependent on a complex interaction between the scale of local plastic sources and prevailing environmental conditions; as a result, microplastic distribution is highly heterogeneous. Circulation models have been used to predict plastic distribution; however, current models do not consider future variation in circulation patterns and weather systems caused by a changing climate. In this study, we discuss the potential impacts of global climate change on the abundance and distribution of marine plastic pollution. Integr Environ Assess Manag 2017;13:483-487. © 2017 SETAC. © 2017 SETAC.

  12. Interaction of Kuroshio Current with Global Oceanic and Atmospheric Circulations: Evidences of Grain Size from Okinawa Trough

    Science.gov (United States)

    Wang, J.; Li, A.; Xu, K.; Huang, J.

    2016-12-01

    Okinawa Trough is an ideal place for the study of paleoceanography and paleoenvironment changes. However, the provenances of the sediments and paleoenvironment evolution of the Okinawa Trough have still not been settled yet. Based on grain size, clay minerals and AMS 14C data of the Core OKI03, the provenances and paleoenvironemnt evolution in the middle Okinawa Trough during the last 8 ka were studied. The results indicate that terrigenous sediments deposited in the middle Okinawa Trough were mainly from Yangtze River and Taiwanese rivers since 8 ka. Kuroshio Current (KC), a Western Pacific Ocean boundary current, flows into Okinawa Trough by eastern Taiwan Island, and influences the sediments delivery and distribution within the trough, and also impact the regional and local marine environment in adjacent seas. Statistics study of high resolution grain size in the trough recognizes a millennial-scale oscillation (center around 1800 yr) and a centennial-scale oscillation (center around 512 yr) for KC evolution since last 8 ka. The millennial-scale oscillation is probably related to the North Atlantic Deep Water production with 1400-yr time lag, via the mixing upwelling and impacts on the sea surface temperature (SST) in equatorial Pacific. Meanwhile, the centennial-scale variation possibly corresponds to the solar irradiation with a 240-yr time uncertainty, through the SST change. KC possible influences the climate and North Atlantic Deep Water formation by transferring heat to the atmosphere in high latitude of Pacific Ocean, and also interacts with the thermohaline circulation by transferring heat to Indian Ocean through North Pacific Intermediate Water.

  13. Using a global ocean circulation model to conduct a preliminary risk assessment of oil spills in the Atlantic

    Science.gov (United States)

    Jacobs, Zoe; Popova, Katya; Hirschi, Joel; Coward, Andrew; Yool, Andrew; van Gennip, Simon; Anifowose, Babtunde; Harrington-Missin, Liam

    2017-04-01

    Although oil blowouts from deep-water drilling happen very rarely, they can cause catastrophic damage to the environment. Despite such potentially high impacts, relatively little research effort has gone into understanding subsurface oil plumes in the deep ocean. In this study, we demonstrate the significance of this problem and offer potential solutions using a novel approach based on a leading-edge, high-resolution global ocean circulation model. We present examples demonstrating: (a) the importance of ocean circulation in the propagation of oil spills; and (b) likely circulation footprints for oil spills at four key locations in the Atlantic Ocean that exist in different circulation regimes - the shelves of Brazil, the Gulf of Guinea, the Gulf of Mexico and the Faroe-Shetland Channel. In order to quantify the variability at each site on seasonal timescales, interannual timescales and at different depths, we utilize the Modified Hausdorff Distance (MHD), which is a shape-distance metric that measures the similarity between two shapes. The scale of the footprints across the four focus locations varies considerably and is determined by the main circulation features in their vicinity. For example, the hypothetical oil plume can be affected by variations in the speed and location of a particular current (e.g. Brazil Current at the Brazilian shelf site) or be influenced by different currents entirely depending on the release depth, month and year (e.g. Angola Current or Southern Equatorial Current at the Gulf of Guinea site). Overall, our results demonstrate the need to use state of the art global, or basin-scale, ocean circulation models when assessing the environmental impacts of proposed oil drilling activities.

  14. Serological evidence for the circulation of flaviviruses in seabird populations of the western Indian Ocean.

    Science.gov (United States)

    Jaeger, A; Lecollinet, S; Beck, C; Bastien, M; Le Corre, M; Dellagi, K; Pascalis, H; Boulinier, T; Lebarbenchon, C

    2016-02-01

    Birds play a central role in the epidemiology of several flaviviruses of concern for public and veterinary health. Seabirds represent the most abundant and widespread avifauna in the western Indian Ocean and may play an important role as host reservoirs and spreaders of arthropod-borne pathogens such as flaviviruses. We report the results of a serological investigation based on blood samples collected from nine seabird species from seven islands in the Indian Ocean. Using a commercial competitive enzyme-linked immunosorbent assay directed against the prototypic West Nile flavivirus, antibodies against flaviviruses were detected in the serum of 47 of the 855 seabirds tested. They were detected in bird samples from three islands and from four bird species. Seroneutralization tests on adults and chicks suggested that great frigatebirds (Fregata minor) from Europa were infected by West Nile virus during their non-breeding period, and that Usutu virus probably circulated within bird colonies on Tromelin and on Juan de Nova. Real-time polymerase chain reactions performed on bird blood samples did not yield positive results precluding the genetic characterization of flavivirus using RNA sequencing. Our findings stress the need to further investigate flavivirus infections in arthropod vectors present in seabird colonies.

  15. Adaptive subdomain modeling: A multi-analysis technique for ocean circulation models

    Science.gov (United States)

    Altuntas, Alper; Baugh, John

    2017-07-01

    Many coastal and ocean processes of interest operate over large temporal and geographical scales and require a substantial amount of computational resources, particularly when engineering design and failure scenarios are also considered. This study presents an adaptive multi-analysis technique that improves the efficiency of these computations when multiple alternatives are being simulated. The technique, called adaptive subdomain modeling, concurrently analyzes any number of child domains, with each instance corresponding to a unique design or failure scenario, in addition to a full-scale parent domain providing the boundary conditions for its children. To contain the altered hydrodynamics originating from the modifications, the spatial extent of each child domain is adaptively adjusted during runtime depending on the response of the model. The technique is incorporated in ADCIRC++, a re-implementation of the popular ADCIRC ocean circulation model with an updated software architecture designed to facilitate this adaptive behavior and to utilize concurrent executions of multiple domains. The results of our case studies confirm that the method substantially reduces computational effort while maintaining accuracy.

  16. Paleocene/Eocene boundary changes in atmospheric and oceanic circulation: A Southern Hemisphere record

    Science.gov (United States)

    Hovan, Steven A.; Rea, David K.

    1992-01-01

    Deep Sea Drilling Project (DSDP) Site 215 provides an expanded section across the Paleocene/Eocene boundary, the most complete mid-latitude sequence from a Southern Hemisphere location in the Indo-Pacific area. The events of this transition occurred during a span of about 1.2 m.y. Oxygen isotope values derived from benthic foraminiferal calcite decrease by about 1.0‰, a decrease most likely related to warming of deep ocean waters. Turnovers of benthic foraminifera accompany δ18O changes and culminate in the predominant extinction event at the end of the Paleocene Epoch. Carbon isotope ratios also shift dramatically toward lighter values near the end of the Paleocene, beginning about 0.45 m.y. after oxygen isotope values start to change. The intensity of Southern Hemisphere atmospheric circulation as recorded by grain sizes of eolian particles shows a large and rapid reduction beginning another 0.45 m.y. later. A significant reduction of zonal wind strength at the Paleocene/Eocene boundary, until now observed only at Northern Hemisphere locations, appears to have been a global phenomenon related to decreased latitudinal thermal gradients occasioned by more effective poleward heat transport via the deep ocean.

  17. A parallel domain decomposition algorithm for coastal ocean circulation models based on integer linear programming

    Science.gov (United States)

    Jordi, Antoni; Georgas, Nickitas; Blumberg, Alan

    2017-05-01

    This paper presents a new parallel domain decomposition algorithm based on integer linear programming (ILP), a mathematical optimization method. To minimize the computation time of coastal ocean circulation models, the ILP decomposition algorithm divides the global domain in local domains with balanced work load according to the number of processors and avoids computations over as many as land grid cells as possible. In addition, it maintains the use of logically rectangular local domains and achieves the exact same results as traditional domain decomposition algorithms (such as Cartesian decomposition). However, the ILP decomposition algorithm may not converge to an exact solution for relatively large domains. To overcome this problem, we developed two ILP decomposition formulations. The first one (complete formulation) has no additional restriction, although it is impractical for large global domains. The second one (feasible) imposes local domains with the same dimensions and looks for the feasibility of such decomposition, which allows much larger global domains. Parallel performance of both ILP formulations is compared to a base Cartesian decomposition by simulating two cases with the newly created parallel version of the Stevens Institute of Technology's Estuarine and Coastal Ocean Model (sECOM). Simulations with the ILP formulations run always faster than the ones with the base decomposition, and the complete formulation is better than the feasible one when it is applicable. In addition, parallel efficiency with the ILP decomposition may be greater than one.

  18. Successful insertion of barotropic and baroclinic tides into a global 1/12 degree ocean general circulation model

    Science.gov (United States)

    Arbic, B. K.; Metzger, E.; Wallcraft, A. J.

    2008-12-01

    In recent years, increasing computer power has allowed internal tide models to be run at high-resolution on a global scale (Arbic et al. 2004; Simmons et al. 2004; Hibiya et al. 2006; Simmons 2008). All of these models have been run as pure tide models (i.e., without wind and buoyancy forcing) with a horizontally uniform stratification (since the wind and buoyancy forcing required to support a nonuniform stratification is absent). We have recently completed a 5-year simulation in which the eight largest tidal constituents have been embedded into the HYCOM general circulation model, run globally at 1/12 degree resolution and with 32 vertical layers. The run includes realistic wind and buoyancy forcing. Hence a horizontally varying stratification as well as an energetic mesoscale eddy field are present in the model, and will interact with the internal tide field. We report here on some preliminary analyses of this simulation. The globally averaged rms elevation errors of the eight largest tidal constituents are comparable to those in previous forward tide models which include a tuned topographic internal wave drag. The amplitude and wavelength of the surface signature of internal tides compares well with that inferred from satellite altimetry data. The horizontally varying stratification leads to a very different surface signature of internal tides in polar regions, compared to results using a spatially uniform stratification. Ongoing and planned analyses of various aspects of the simulation--for instance eddy/tide interaction, the stationarity of internal tide beams, and the impact of tides on the general circulation, water masses, and the energy budget--will be briefly described. References Arbic, B.K., S.T. Garner, R.W. Hallberg, and H.L. Simmons, 2004: The accuracy of surface elevations in forward global barotropic and baroclinic tide models. Deep-Sea Research II 51, 3069-3101. Hibiya, T., M. Nagasawa, and Y. Niwa, 2006: Global mapping of diapycnal diffusivity in

  19. The warmer the ocean surface, the shallower the mixed layer. How much of this is true?

    Science.gov (United States)

    Somavilla, R; González-Pola, C; Fernández-Diaz, J

    2017-09-01

    Ocean surface warming is commonly associated with a more stratified, less productive, and less oxygenated ocean. Such an assertion is mainly based on consistent projections of increased near-surface stratification and shallower mixed layers under global warming scenarios. However, while the observed sea surface temperature (SST) is rising at midlatitudes, the concurrent ocean record shows that stratification is not unequivocally increasing nor is MLD shoaling. We find that while SST increases at three study areas at midlatitudes, stratification both increases and decreases, and MLD deepens with enhanced deepening of winter MLDs at rates over 10 m  decade-1. These results rely on the estimation of several MLD and stratification indexes of different complexity on hydrographic profiles from long-term hydrographic time-series, ocean reanalysis, and Argo floats. Combining this information with estimated MLDs from buoyancy fluxes and the enhanced deepening/attenuation of the winter MLD trends due to changes in the Ekman pumping, MLD variability involves a subtle interplay between circulation and atmospheric forcing at midlatitudes. Besides, it is highlighted that the density difference between the surface and 200 m, the most widely used stratification index, should not be expected to reliably inform about changes in the vertical extent of mixing.

  20. The warmer the ocean surface, the shallower the mixed layer. How much of this is true?

    Science.gov (United States)

    Somavilla, R.; González-Pola, C.; Fernández-Diaz, J.

    2017-09-01

    Ocean surface warming is commonly associated with a more stratified, less productive, and less oxygenated ocean. Such an assertion is mainly based on consistent projections of increased near-surface stratification and shallower mixed layers under global warming scenarios. However, while the observed sea surface temperature (SST) is rising at midlatitudes, the concurrent ocean record shows that stratification is not unequivocally increasing nor is MLD shoaling. We find that while SST increases at three study areas at midlatitudes, stratification both increases and decreases, and MLD deepens with enhanced deepening of winter MLDs at rates over 10 m decade-1. These results rely on the estimation of several MLD and stratification indexes of different complexity on hydrographic profiles from long-term hydrographic time-series, ocean reanalysis, and Argo floats. Combining this information with estimated MLDs from buoyancy fluxes and the enhanced deepening/attenuation of the winter MLD trends due to changes in the Ekman pumping, MLD variability involves a subtle interplay between circulation and atmospheric forcing at midlatitudes. Besides, it is highlighted that the density difference between the surface and 200 m, the most widely used stratification index, should not be expected to reliably inform about changes in the vertical extent of mixing.

  1. The Development of a Degree 360 Expansion of the Dynamic Ocean Topography of the POCM_4B Global Circulation Model

    Science.gov (United States)

    Rapp, Richard H.

    1998-01-01

    This paper documents the development of a degree 360 expansion of the dynamic ocean topography (DOT) of the POCM_4B ocean circulation model. The principles and software used that led to the final model are described. A key principle was the development of interpolated DOT values into land areas to avoid discontinuities at or near the land/ocean interface. The power spectrum of the POCM_4B is also presented with comparisons made between orthonormal (ON) and spherical harmonic magnitudes to degree 24. A merged file of ON and SH computed degree variances is proposed for applications where the DOT power spectrum from low to high (360) degrees is needed.

  2. "What Controls the Structure and Stability of the Ocean Meridional Overturning Circulation: Implications for Abrupt Climate Change?"

    Energy Technology Data Exchange (ETDEWEB)

    Fedorov, Alexey [Yale University

    2013-11-23

    The central goal of this research project is to understand the properties of the ocean meridional overturning circulation (MOC) – a topic critical for understanding climate variability and stability on a variety of timescales (from decadal to centennial and longer). Specifically, we have explored various factors that control the MOC stability and decadal variability in the Atlantic and the ocean thermal structure in general, including the possibility abrupt climate change. We have also continued efforts on improving the performance of coupled ocean-atmosphere GCMs.

  3. Reproduction of World Ocean Circulation by the CORE-II Scenario with the Models INMOM and INMIO

    Science.gov (United States)

    Volodin, E. M.; Gusev, A. V.; Diansky, N. A.; Ibrayev, R. A.; Ushakov, K. V.

    2018-01-01

    The results of simulations performed by the CORE-II scenario using the two Russian OGCMs, INMOM and INMIO, are presented. The models use different coordinate systems in the basic set of primitive equations and different numerical techniques. Both models are used as oceanic components of the INM RAS coupled models. Simulations have shown that reproducing ocean circulation using both models agrees with observations and simulations by other models. In general, the INMOM slightly underestimates the meridional heat transport in the ocean when compared to the INMIO model and climatic estimations. However, the INMIO yields a higher bias in temperature than the INMOM.

  4. Remote sensing of ocean surface currents: a review of what is being observed and what is being assimilated

    Science.gov (United States)

    Isern-Fontanet, Jordi; Ballabrera-Poy, Joaquim; Turiel, Antonio; García-Ladona, Emilio

    2017-10-01

    Ocean currents play a key role in Earth's climate - they impact almost any process taking place in the ocean and are of major importance for navigation and human activities at sea. Nevertheless, their observation and forecasting are still difficult. First, no observing system is able to provide direct measurements of global ocean currents on synoptic scales. Consequently, it has been necessary to use sea surface height and sea surface temperature measurements and refer to dynamical frameworks to derive the velocity field. Second, the assimilation of the velocity field into numerical models of ocean circulation is difficult mainly due to lack of data. Recent experiments that assimilate coastal-based radar data have shown that ocean currents will contribute to increasing the forecast skill of surface currents, but require application in multidata assimilation approaches to better identify the thermohaline structure of the ocean. In this paper we review the current knowledge in these fields and provide a global and systematic view of the technologies to retrieve ocean velocities in the upper ocean and the available approaches to assimilate this information into ocean models.

  5. Remote sensing of ocean surface currents: a review of what is being observed and what is being assimilated

    Directory of Open Access Journals (Sweden)

    J. Isern-Fontanet

    2017-10-01

    Full Text Available Ocean currents play a key role in Earth's climate – they impact almost any process taking place in the ocean and are of major importance for navigation and human activities at sea. Nevertheless, their observation and forecasting are still difficult. First, no observing system is able to provide direct measurements of global ocean currents on synoptic scales. Consequently, it has been necessary to use sea surface height and sea surface temperature measurements and refer to dynamical frameworks to derive the velocity field. Second, the assimilation of the velocity field into numerical models of ocean circulation is difficult mainly due to lack of data. Recent experiments that assimilate coastal-based radar data have shown that ocean currents will contribute to increasing the forecast skill of surface currents, but require application in multidata assimilation approaches to better identify the thermohaline structure of the ocean. In this paper we review the current knowledge in these fields and provide a global and systematic view of the technologies to retrieve ocean velocities in the upper ocean and the available approaches to assimilate this information into ocean models.

  6. A regional ocean circulation model for the mid-Cretaceous North Atlantic Basin: implications for black shale formation

    Directory of Open Access Journals (Sweden)

    R. P. M. Topper

    2011-03-01

    Full Text Available High concentrations of organic matter accumulated in marine sediments during Oceanic Anoxic Events (OAEs in the Cretaceous. Model studies examining these events invariably make use of global ocean circulation models. In this study, a regional model for the North Atlantic Basin during OAE2 at the Cenomanian-Turonian boundary has been developed. A first order check of the results has been performed by comparison with the results of a recent global Cenomanian CCSM3 run, from which boundary and initial conditions were obtained. The regional model is able to maintain tracer patterns and to produce velocity patterns similar to the global model. The sensitivity of the basin tracer and circulation patterns to changes in the geometry of the connections with the global ocean is examined with three experiments with different bathymetries near the sponges. Different geometries turn out to have little effect on tracer distribution, but do affect circulation and upwelling patterns. The regional model is also used to test the hypothesis that ocean circulation may have been behind the deposition of black shales during OAEs. Three scenarios are tested which are thought to represent pre-OAE, OAE and post-OAE situations. Model results confirm that Pacific intermediate inflow together with coastal upwelling could have enhanced primary production during OAE2. A low sea level in the pre-OAE scenario could have inhibited large scale black shale formation, as could have the opening of the Equatorial Atlantic Seaway in the post-OAE scenario.

  7. Interaction of additive noise and nonlinear dynamics in the double-gyre wind-driven ocean circulation

    NARCIS (Netherlands)

    Sapsis, T.; Dijkstra, H.A.

    2013-01-01

    In this paper the authors study the interactions of additive noise and nonlinear dynamics in a quasi-geostrophicmodel of the double-gyre wind-driven ocean circulation. The recently developed framework of dynamically orthogonal field theory is used to determine the statistics of the flows that arise

  8. Initiation of a Marinoan Snowball Earth in a state-of-the-art atmosphere-ocean general circulation model

    Directory of Open Access Journals (Sweden)

    A. Voigt

    2011-03-01

    Full Text Available We study the initiation of a Marinoan Snowball Earth (~635 million years before present with the state-of-the-art atmosphere-ocean general circulation model ECHAM5/MPI-OM. This is the most sophisticated model ever applied to Snowball initiation. A comparison with a pre-industrial control climate shows that the change of surface boundary conditions from present-day to Marinoan, including a shift of continents to low latitudes, induces a global-mean cooling of 4.6 K. Two thirds of this cooling can be attributed to increased planetary albedo, the remaining one third to a weaker greenhouse effect. The Marinoan Snowball Earth bifurcation point for pre-industrial atmospheric carbon dioxide is between 95.5 and 96% of the present-day total solar irradiance (TSI, whereas a previous study with the same model found that it was between 91 and 94% for present-day surface boundary conditions. A Snowball Earth for TSI set to its Marinoan value (94% of the present-day TSI is prevented by doubling carbon dioxide with respect to its pre-industrial level. A zero-dimensional energy balance model is used to predict the Snowball Earth bifurcation point from only the equilibrium global-mean ocean potential temperature for present-day TSI. We do not find stable states with sea-ice cover above 55%, and land conditions are such that glaciers could not grow with sea-ice cover of 55%. Therefore, none of our simulations qualifies as a "slushball" solution. While uncertainties in important processes and parameters such as clouds and sea-ice albedo suggest that the Snowball Earth bifurcation point differs between climate models, our results contradict previous findings that Snowball Earth initiation would require much stronger forcings.

  9. An ocean circulation model in σS- z- σB hybrid coordinate and its validation

    Science.gov (United States)

    Zhuang, Zhanpeng; Yuan, Yeli; Yang, Guangbing

    2018-02-01

    A 3D, two-time-level, σS- z- σB hybrid-coordinate Marine Science and Numerical Modeling numerical ocean circulation model (HyMOM) is developed in this paper. In HyMOM, the σ coordinate is employed in the surface and bottom regions, and the z coordinate is used in the intermediate layers. This method can overcome problems with vanishing surface cells and minimize the unwanted deviation in representing bottom topography. The connection between the σ and z layers vertically includes an expanded "ghost" method and the linear interpolation. The governing equations in the σS- z- σB hybrid coordinate based on the complete Reynolds-averaged Navier-Stokes equations are derived in detail. The two-level time staggered and Eulerian forward and backward schemes, which are of second-order of accuracy, are adopted for the temporal difference in internal and external mode, respectively. The computation of the baroclinic gradient force is tested in an analytic test problem; the errors for two methods in HyMOM, which are relatively large only in the bottom layers, are obviously smaller than those in the pure σ and z models in almost all of the vertical layers. A quasi-global climatologic numerical experiment is constructed to test the simulation performance of HyMOM. With the monthly mean Levitus climatology data as reference, the HyMOM can improve the simulating accuracy compared with its pure z or σ coordinate implementation.

  10. Indian Ocean surface winds from NCMRWF analysis as compared to ...

    Indian Academy of Sciences (India)

    The quality of the surface wind analysis at the National Centre for Medium Range Weather Forecasts (NCMRWF), New Delhi over the tropical Indian Ocean and its improvement in 2001 are examined by comparing it with in situ buoy measurements and satellite derived surface winds from NASA QuikSCAT satellite (QSCT) ...

  11. Auto-correlation analysis of ocean surface wind vectors

    Indian Academy of Sciences (India)

    The nature of the inherent temporal variability of surface winds is analyzed by comparison of winds obtained through different measurement methods. In this work, an auto-correlation analysis of a time series data of surface winds measured in situ by a deep water buoy in the Indian Ocean has been carried out. Hourly time ...

  12. Costa Rica Rift Revisited: Constraints on Shallow and Deep Hydrothermal Circulation in Oceanic Crust

    Science.gov (United States)

    Davis, E. E.; Becker, K.; He, J.

    2002-12-01

    New heat-flow observations made along two seismic reflection profiles on 6 Ma crust of the Costa Rica Rift flank show an inverse correlation between heat flow and sediment thickness similar to that observed on other sedimented ridges and young ridge flanks. Extrapolation of the seafloor heat-flow values to the top of the igneous crust - justified by comparing seafloor and borehole determinations where observations are colocated - show the surface of the igneous crust to be of uniform temperature despite large local sediment thickness variations. This is consistent with observations made at DSDP/ODP Holes 504B and 896A where basement temperatures are observed to be nearly identical, also despite contrasting sediment thicknesses. Efficient lateral heat exchange via vigorous crustal hydrothermal circulation is required to create the degree of uniformity inferred and observed. Permeability measurements at the two drill sites show that this vigorous circulation may be restricted to as little as the uppermost tens of m of the crust. Permeability determined deeper in Hole 504B is too low to permit thermally significant flow, although temperature logs suggest that thermally significant flow extends throughout the 2 km section penetrated at Site 504, presumably via pathways not intersected by the borehole. The laterally uniform temperatures in the uppermost igneous crust here and elsewhere are remarkable given the small apparent depth-extent of the circulation that so efficiently distributes heat. While certainly not as vigorous, the circulation at depth suggested by the temperature logs at Site 504 is also noteworthy; unfortunately the observation cannot be generalized because of the lack of other deep crustal holes that could permit direct observations, and the lack of a method for inferring deep hydrothermal structure.

  13. Ocean Surface Current Vectors from MODIS Terra/Aqua Sea Surface Temperature Image Pairs, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — Satellites that record imagery of the same sea surface area, at times separated by a few hours, can be used to estimate ocean surface velocity fields based on the...

  14. Satellite surface salinity maps to determine fresh water fluxes in the Arctic Ocean

    Science.gov (United States)

    Gabarro, Carolina; Estrella, Olmedo; Emelianov, Mikhail; Ballabrera, Joaquim; Turiel, Antonio

    2017-04-01

    Salinity and temperature gradients drive the thermohaline circulation of the oceans, and play a key role in the ocean-atmosphere coupling. The strong and direct interactions between the ocean and the cryosphere (primarily through sea ice and ice shelves) are also a key ingredient of the thermohaline circulation. Recent observational studies have documented changes in upper Arctic Ocean hydrography [1, 2]. The ESA's Soil Moisture and Ocean Salinity (SMOS) mission, launched in 2009, have the objective to measure soil moisture over the continents and sea surface salinity over the oceans [3]. However, SMOS is also making inroads in Cryospheric science, as the measurements of thin ice thickness and sea ice concentration. SMOS carries an innovative L-band (1.4 GHz, or 21-cm wavelength), passive interferometric radiometer (the so-called MIRAS) that measures the electromagnetic radiation emitted by the Earth's surface, at about 50 km spatial resolution wide swath (1200-km), and with a 3-day revisit time at the equator, but more frequently at the poles. Although the SMOS radiometer operating frequency offers almost the maximum sensitivity of the brightness temperature (TB) to sea surface salinity (SSS) variations, such sensitivity is rather low, even lower at cold waters [4]: 90% of ocean SSS values span a range of brightness temperatures of just 5K. This implies that the SMOS SSS retrieval requires a high performance of the MIRAS interferometric radiometer [5]. New algorithms, recently developed at the Barcelona Expert Center (BEC) to improve the quality of SMOS measurements [6], allow for the first time to derive cold-water SSS maps from SMOS data, and to observe the variability of the SSS in the higher north Atlantic and the Arctic Ocean. In this work, we will provide an assessment of the quality of these new SSS Arctic maps, and we will illustrate their potential to monitor the impact on ocean state of the discharges from the main rivers to the Arctic Ocean. Moreover

  15. The influence of Southern Ocean surface buoyancy forcing on glacial-interglacial changes in the global deep ocean stratification

    OpenAIRE

    Sun, S; Eisenman, I; Stewart, AL

    2016-01-01

    ©2016. American Geophysical Union. All Rights Reserved. Previous studies have suggested that the global ocean density stratification below ∼3000 m is approximately set by its direct connection to the Southern Ocean surface density, which in turn is constrained by the atmosphere. Here the role of Southern Ocean surface forcing in glacial-interglacial stratification changes is investigated using a comprehensive climate model and an idealized conceptual model. Southern Ocean surface forcing is f...

  16. Origin, dynamics and evolution of ocean garbage patches from observed surface drifters

    International Nuclear Information System (INIS)

    Van Sebille, Erik; England, Matthew H; Froyland, Gary

    2012-01-01

    Much of the debris in the near-surface ocean collects in so-called garbage patches where, due to convergence of the surface flow, the debris is trapped for decades to millennia. Until now, studies modelling the pathways of surface marine debris have not included release from coasts or factored in the possibilities that release concentrations vary with region or that pathways may include seasonal cycles. Here, we use observational data from the Global Drifter Program in a particle-trajectory tracer approach that includes the seasonal cycle to study the fate of marine debris in the open ocean from coastal regions around the world on interannual to centennial timescales. We find that six major garbage patches emerge, one in each of the five subtropical basins and one previously unreported patch in the Barents Sea. The evolution of each of the six patches is markedly different. With the exception of the North Pacific, all patches are much more dispersive than expected from linear ocean circulation theory, suggesting that on centennial timescales the different basins are much better connected than previously thought and that inter-ocean exchanges play a large role in the spreading of marine debris. This study suggests that, over multi-millennial timescales, a significant amount of the debris released outside of the North Atlantic will eventually end up in the North Pacific patch, the main attractor of global marine debris. (letter)

  17. Surface wind mixing in the Regional Ocean Modeling System (ROMS)

    Science.gov (United States)

    Robertson, Robin; Hartlipp, Paul

    2017-12-01

    Mixing at the ocean surface is key for atmosphere-ocean interactions and the distribution of heat, energy, and gases in the upper ocean. Winds are the primary force for surface mixing. To properly simulate upper ocean dynamics and the flux of these quantities within the upper ocean, models must reproduce mixing in the upper ocean. To evaluate the performance of the Regional Ocean Modeling System (ROMS) in replicating the surface mixing, the results of four different vertical mixing parameterizations were compared against observations, using the surface mixed layer depth, the temperature fields, and observed diffusivities for comparisons. The vertical mixing parameterizations investigated were Mellor- Yamada 2.5 level turbulent closure (MY), Large- McWilliams- Doney Kpp (LMD), Nakanishi- Niino (NN), and the generic length scale (GLS) schemes. This was done for one temperate site in deep water in the Eastern Pacific and three shallow water sites in the Baltic Sea. The model reproduced the surface mixed layer depth reasonably well for all sites; however, the temperature fields were reproduced well for the deep site, but not for the shallow Baltic Sea sites. In the Baltic Sea, the models overmixed the water column after a few days. Vertical temperature diffusivities were higher than those observed and did not show the temporal fluctuations present in the observations. The best performance was by NN and MY; however, MY became unstable in two of the shallow simulations with high winds. The performance of GLS nearly as good as NN and MY. LMD had the poorest performance as it generated temperature diffusivities that were too high and induced too much mixing. Further observational comparisons are needed to evaluate the effects of different stratification and wind conditions and the limitations on the vertical mixing parameterizations.

  18. Manganese in the west Atlantic Ocean in the context of the first global ocean circulation model of manganese

    NARCIS (Netherlands)

    van Hulten, Marco; Middag, Rob; Dutay, Jean-Claude; de Baar, Hein; Roy-Barman, Matthieu; Gehlen, Marion; Tagliabue, Alessandro; Sterl, Andreas

    2017-01-01

    Dissolved manganese (Mn) is a biologically essential element. Moreover, its oxidised form is involved in removing itself and several other trace elements from ocean waters. Here we report the longest thus far (17 500 km length) full-depth ocean section of dissolved Mn in the west Atlantic Ocean,

  19. About New Maps of Surface Currents of the World Ocean

    Science.gov (United States)

    Nikitin, O. P.; Kasyanov, S. Yu.

    2018-01-01

    Using the example of the surface currents map constructed for the Northern Atlantic on the basis of data of modern observations by means of drifting buoys, it is shown that the previously published maps of ocean surface currents, based on ship drift data, have become outdated and require an update. The influence of the bottom relief on the directions of surface layer currents is shown.

  20. The Proposed Surface Water and Ocean Topography (SWOT) Mission

    Science.gov (United States)

    Fu, Lee-Lueng; Alsdorf, Douglas; Rodriguez, Ernesto; Morrow, Rosemary; Mognard, Nelly; Vaze, Parag; Lafon, Thierry

    2012-01-01

    A new space mission concept called Surface Water and Ocean Topography (SWOT) is being developed jointly by a collaborative effort of the international oceanographic and hydrological communities for making high-resolution measurement of the water elevation of both the ocean and land surface water to answer the questions about the oceanic submesoscale processes and the storage and discharge of land surface water. The key instrument payload would be a Ka-band radar interferometer capable of making high-resolution wide-swath altimetry measurement. This paper describes the proposed science objectives and requirements as well as the measurement approach of SWOT, which is baselined to be launched in 2019. SWOT would demonstrate this new approach to advancing both oceanography and land hydrology and set a standard for future altimetry missions.

  1. The mean and variability of ocean circulation past northern New Zealand: Determining the representativeness of hydrographic climatologies

    Science.gov (United States)

    Roemmich, Dean; Sutton, Philip

    1998-06-01

    Eastward flow in the Tasman Sea, from the separated East Australia Current, reattaches to the shelf break near North Cape, New Zealand, and then continues alongshore to the southeast as the East Auckland Current. A series of three permanent warm core eddies occurs along the offshore side. The mean transport of the East Auckland Current is about 9 Sv, with an additional 10 Sv or more of circulation in the eddies. An extensive hydrographic data set, archived broad scale expendable bathythermograph (XBT) data, two repeating high-resolution XBT transects, neutrally buoyant float trajectories, and TOPEX altimetric data are used to estimate the temperature and absolute flow fields and to characterize variability. The aim is to examine the usefulness of time series information and absolute velocity measurements in the interpretation of hydrographic snapshots and climatologies, as well as to describe a region having intrinsic oceanographic interest and complexity. Issues of representativeness of the hydrographic data, of the magnitude and scales of the underlying variability, of the existence of permanent fine-scale features, and of the appropriateness of deep reference levels are addressed directly. The relatively well sampled hydrographic climatology is shown to contain the equivalent of as many as 10 independent realizations. Temperature errors, relative to the true mean, are typically a few tenths of a degree. Significant seasonal bias is identified in the surface layer, and interannual bias is seen in the position of an eddy near North Cape. The dynamic height field at 1000 dbar relative to 2000 dbar is similar to estimates based on float trajectories and the assumption of geostrophic dynamics. This study underlines the value of time series data in the interpretation of a hydrographic climatology, in quantifying the errors in the estimated mean field as well as determining the magnitude and nature of variability. It also highlights the fact that the mean circulation

  2. Simulation Tool for GNSS Ocean Surface Reflections

    DEFF Research Database (Denmark)

    Høeg, Per; von Benzon, Hans-Henrik; Durgonics, Tibor

    2015-01-01

    . This impedance concept gives an accurate lower boundary condition in the determination of the electromagnetic field, and makes itpossible to simulate reflections and the effects of transitions between different mediums. A semi-isotropic Philipsspectrum is used to represent the air-sea interaction.Simulated GPS...... on the solution of the parabolic equation. The parabolic equation in our simulator is solvedusing the split-step sine transformation. The Earth’s surface is modeled with the use of an impedance model. The value of the Earth impedance is given as a function of the range along the surface of the Earth...

  3. Global environmental cycling of gamma-HCH and DDT in the 1980s--a study using a coupled atmosphere and ocean general circulation model.

    Science.gov (United States)

    Guglielmo, Francesca; Lammel, Gerhard; Maier-Reimer, Ernst

    2009-09-01

    A coupled atmosphere-ocean general circulation model, ECHAM5-MPIOM, was used to study the multicompartmental cycling and long-range transport of persistent and semivolatile organics. Multiphase systems in air and ocean are covered by submodels for atmospheric aerosols, HAM, and marine biogeochemistry, HAMOCC5, respectively. The model, furthermore, encompasses 2D surface compartments, i.e. top soil, vegetation surfaces and sea-ice. The total environmental fate of gamma-hexachlorocyclohexane (gamma-HCH, lindane) and dichlorophenyltrichloroethane (DDT) in agriculture were studied. DDT is mostly present in the soils, the water-soluble gamma-HCH in soils and ocean. DDT has the longest residence time in almost all compartments. Quasi-steady state with regard to substance accumulation is reached within a few years in air and vegetation surfaces. In seawater the partitioning to suspended and sinking particles contributes to the vertical transport of substances. On the global scale deep water formation is, however, found to be more efficient. Up to 30% of DDT but only less than 0.2% of gamma-HCH in seawater are stored in particulate matter. On the time scale studied (1 decade) and on global scale substance transport in the environment is determined by the fast atmospheric circulation. The meridional transport mechanism, for both compounds, is significantly enhanced by multi-hopping. Net meridional transport in the ocean is effective only regionally, mostly by currents along the western boundaries of Africa and the Americas. The total environmental burdens of the substances experience a net northward migration from their source regions, which is more pronounced for DDT than for gamma-HCH. Due to the application distribution, however, after 10 years of simulation 21% of the global environmental burden of gamma-HCH and 12% of DDT have accumulated in the Arctic.

  4. Antarctic sea ice control on ocean circulation in present and glacial climates.

    Science.gov (United States)

    Ferrari, Raffaele; Jansen, Malte F; Adkins, Jess F; Burke, Andrea; Stewart, Andrew L; Thompson, Andrew F

    2014-06-17

    In the modern climate, the ocean below 2 km is mainly filled by waters sinking into the abyss around Antarctica and in the North Atlantic. Paleoproxies indicate that waters of North Atlantic origin were instead absent below 2 km at the Last Glacial Maximum, resulting in an expansion of the volume occupied by Antarctic origin waters. In this study we show that this rearrangement of deep water masses is dynamically linked to the expansion of summer sea ice around Antarctica. A simple theory further suggests that these deep waters only came to the surface under sea ice, which insulated them from atmospheric forcing, and were weakly mixed with overlying waters, thus being able to store carbon for long times. This unappreciated link between the expansion of sea ice and the appearance of a voluminous and insulated water mass may help quantify the ocean's role in regulating atmospheric carbon dioxide on glacial-interglacial timescales. Previous studies pointed to many independent changes in ocean physics to account for the observed swings in atmospheric carbon dioxide. Here it is shown that many of these changes are dynamically linked and therefore must co-occur.

  5. Drivers of Antarctic sea-ice expansion and Southern Ocean surface cooling over the past four decades

    Science.gov (United States)

    Purich, Ariaan; England, Matthew

    2017-04-01

    Despite global warming, total Antarctic sea-ice coverage has increased overall during the past four decades. In contrast, the majority of CMIP5 models simulate a decline. In addition, Southern Ocean surface waters have largely cooled, in stark contrast to almost all historical CMIP5 simulations. Subantarctic Surface Waters have cooled and freshened while waters to the north of the Antarctic Circumpolar Current have warmed and increased in salinity. It remains unclear as to what extent the cooling and Antarctic sea-ice expansion is due to natural variability versus anthropogenic forcing; due for example to changes in the Southern Annular Mode (SAM). It is also unclear what the respective role of surface buoyancy fluxes is compared to internal ocean circulation changes, and what the implications are for longer-term climate change in the region. In this presentation we will outline three distinct drivers of recent Southern Ocean surface trends that have each made a significant contribution to regional cooling: (1) wind-driven surface cooling and sea-ice expansion due to shifted westerly winds, (2) teleconnections of decadal variability from the tropical Pacific, and (3) surface cooling and ice expansion due to large-scale Southern Ocean freshening, most likely driven by SAM-related precipitation trends over the open ocean. We will also outline the main reasons why climate models for the most part miss these Southern Ocean cooling trends, despite capturing overall trends in the SAM.

  6. Compilation of ocean circulation and other data from ADCP current meters, CTD casts, tidal gauges, and other instruments from a World-Wide distribution by Oregon State University and other institutions as part of World Ocean Circulation Experiment (WOCE) and other projects from 24 November 1985 to 30 December 2000 (NODC Accession 0000649)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Compilation of ocean circulation and other data were collected from a World-Wide distribution by Oregon State University (OSU) and other institutions as part of...

  7. Ocean circulation and other data from SUBSURFACE FLOATS from the NE Atlantic (limit-40 W) and other locations as part of the World Ocean Circulation Experiment (WOCE) and other projects from 03 October 1984 to 03 June 1993 (NODC Accession 9500042)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Ocean circulation and other data from SUBSURFACE FLOATS from the NE Atlantic (limit-40 W) and other locations. Data were collected by Woods Hole Oceanographic...

  8. View-Dependent Tessellation and Simulation of Ocean Surfaces

    Directory of Open Access Journals (Sweden)

    Anna Puig-Centelles

    2014-01-01

    Full Text Available Modeling and rendering realistic ocean scenes have been thoroughly investigated for many years. Its appearance has been studied and it is possible to find very detailed simulations where a high degree of realism is achieved. Nevertheless, among the solutions to ocean rendering, real-time management of the huge heightmaps that are necessary for rendering an ocean scene is still not solved. We propose a new technique for simulating the ocean surface on GPU. This technique is capable of offering view-dependent approximations of the mesh while maintaining coherence among the extracted approximations. This feature is very important as most solutions previously presented must retessellate from the initial mesh. Our solution is able to use the latest extracted approximation when refining or coarsening the mesh.

  9. The modern and glacial overturning circulation in the Atlantic ocean in PMIP coupled model simulations

    Directory of Open Access Journals (Sweden)

    S. L. Weber

    2007-01-01

    Full Text Available This study analyses the response of the Atlantic meridional overturning circulation (AMOC to LGM forcings and boundary conditions in nine PMIP coupled model simulations, including both GCMs and Earth system Models of Intermediate Complexity. Model results differ widely. The AMOC slows down considerably (by 20–40% during the LGM as compared to the modern climate in four models, there is a slight reduction in one model and four models show a substantial increase in AMOC strength (by 10–40%. It is found that a major controlling factor for the AMOC response is the density contrast between Antarctic Bottom Water (AABW and North Atlantic Deep Water (NADW at their source regions. Changes in the density contrast are determined by the opposing effects of changes in temperature and salinity, with more saline AABW as compared to NADW consistently found in all models and less cooling of AABW in all models but one. In only two models is the AMOC response during the LGM directly related to the response in net evaporation over the Atlantic basin. Most models show large changes in the ocean freshwater transports into the basin, but this does not seem to affect the AMOC response. Finally, there is some dependence on the accuracy of the control state.

  10. Simulations of future climate with a coupled atmosphere-ocean general circulation model

    International Nuclear Information System (INIS)

    Stendel, M.; Schmith, T.; Hesselbjerg Christensen, J.

    2001-01-01

    A coupled atmosphere/ocean general circulation model to study the time-dependent climate response to changing concentrations of greenhouse gases, chlorofluorocarbons and aerosols according to the new IPCC SRES scenarios A2 and B2 has been used. The results of these experiments are compared to an unforced 300-year control experiment. The changes in the last three decades of the scenario simulations (2071-2100) are furthermore compared to the simulation of present-day climate (1961-1990). In accordance with previous experiments we find that greenhouse warming is reduced when aerosol effects are considered. Sulfur emissions, however, are lower than in the IS92a scenario. Consequently, the greenhouse warming effect, which leads to a bigger temperature increase than in the GSDIO experiment can outweigh the aerosol cooling effect. The result shows that there still are serious difficulties and uncertainties in this type of model simulation. Those are partially due to oversimplifications in the model, concerning the radiative properties of aerosols in particular, and therefore the indirect aerosol effect. Another inherent problem, however, is the uncertainty in the scenarios themselves. This is the case for short-lived substances with an inhomogeneous spatial and temporal distribution, such as aerosols. Therefore, on a decadal horizon, changes in the emissions of those substance can exert a significant effect on anthropogenic climate change. (LN)

  11. Total kinetic energy in four global eddying ocean circulation models and over 5000 current meter records

    KAUST Repository

    Scott, Robert B.

    2010-01-01

    We compare the total kinetic energy (TKE) in four global eddying ocean circulation simulations with a global dataset of over 5000, quality controlled, moored current meter records. At individual mooring sites, there was considerable scatter between models and observations that was greater than estimated statistical uncertainty. Averaging over all current meter records in various depth ranges, all four models had mean TKE within a factor of two of observations above 3500. m, and within a factor of three below 3500. m. With the exception of observations between 20 and 100. m, the models tended to straddle the observations. However, individual models had clear biases. The free running (no data assimilation) model biases were largest below 2000. m. Idealized simulations revealed that the parameterized bottom boundary layer tidal currents were not likely the source of the problem, but that reducing quadratic bottom drag coefficient may improve the fit with deep observations. Data assimilation clearly improved the model-observation comparison, especially below 2000. m, despite assimilated data existing mostly above this depth and only south of 47°N. Different diagnostics revealed different aspects of the comparison, though in general the models appeared to be in an eddying-regime with TKE that compared reasonably well with observations. © 2010 Elsevier Ltd.

  12. Measurements of Surface Ocean Carbon Dioxide Partial Pressure During WOCE; FINAL

    International Nuclear Information System (INIS)

    Weiss, R.F.

    1998-01-01

    All of the technical goals of the World Ocean Circulation Experiment (WOCE) field program which were supported under the Department of Energy research grant ''Measurements of Surface Ocean Carbon Dioxide Partial Pressure During WOCE'' (DE-FG03-90ER60981) have been met. This has included the measurement of the partial pressures of carbon dioxide (C0(sub 2)) and nitrous oxide (N(sub 2)O) in both the surface ocean and the atmosphere on 24 separate shipboard expedition legs of the WOCE Hydrographic Programme. These measurements were made in the Pacific, Indian and Atlantic Oceans over a six-and-a-half year period, and over a distance of nearly 200,000 kilometers of ship track. The total number of measurements, including ocean measurements, air measurements and standard gas measurements, is about 136,000 for each gas, or about 34,000 measurements of each gas in the ocean and in the air. This global survey effort is directed at obtaining a better understanding of the role of the oceans in th e global atmospheric budgets of two important natural and anthropogenic modulators of climate through the ''greenhouse effect'', CO(sub 2) and N(sub 2)O, and an important natural and anthropogenic modulator of the Earth's protective ozone layer through catalytic processes in the stratosphere, N(sub 2)O. For both of these compounds, the oceans play a major role in their global budgets. In the case of CO(sub 2), roughly half of the anthropogenic production through the combustion of fossil fuels has been absorbed by the world's oceans. In the case of N(sub 2)O, roughly a third of the natural flux to the atmosphere originates in the oceans. As the interpretation of the variability in the oceanic distributions of these compounds improves, measurements such as those supported by this research project are playing an increasingly important role in improving our understanding of natural and anthropogenic influences on climate and ozone

  13. State Estimates of the Northern Philippine Sea Circulation Including Ocean Acoustic Travel Times

    Science.gov (United States)

    Cornuelle, B. D.; Gopalakrishnan, G.; Mazloff, M. R.; Worcester, P. F.; Dzieciuch, M. A.

    2016-02-01

    The North Pacific Acoustic Laboratory (NPAL) Philippine Sea experiment deployed a variety of instruments in the northern Philippine Sea during April 2010 through April 2011, including 6 acoustic transceivers for reciprocal measurements of travel times between instruments. Five of the transceivers were moored in a pentagon approximately 660 km in diameter with the sixth transceiver mooring in the center. A seventh mooring approximately 130 km northwest of the center supported a Distributed Vertical Line Array (DVLA) which carried 149 acoustic receivers with thermistors covering the depths between 200 m and 5500 m. The goals of the experiment included studying the energetic westward-propagating eddies which travel through the region, their effect on underwater sound propagation, and the impact of acoustic measurements on estimates of the time-evolving ocean state. Observed travel-time time series were compared with travel times computed from ocean state estimates made using an eddy-active regional implementation of the MITgcm that were constrained by satellite sea surface height and sea surface temperature observations and by temperature and salinity profiles from Argo, CTDs, and XBTs but not by the acoustic data. The similarities cross-validate the state estimates, while the differences provide a simple estimate of the novel information present in the travel times. The ocean state estimates were then re-computed to fit the acoustic travel times as integrals of the sound speed, and therefore temperature and salinity, along the ray paths. Over the approximately 1 year experiment, the state estimate was able to match the travel times within their error bars and did not significantly increase the misfits with the other observations. Comparisons of the state estimates with and without the travel-time data showed significant changes to the temperature and salinity were made to fit the acoustic observations. The state estimates using the acoustic data compare favorably

  14. Circulation pathways and spreading rates of the Atlantic Water in the Arctic Ocean: Results from 25 years of tracer observations

    Science.gov (United States)

    Schlosser, Peter; Pasqualini, Angelica; Newton, Robert; Koffman, Tobias; Friedrich, Ronny; Smethie, William M.

    2017-04-01

    The Atlantic Ocean supplies heat to the Arctic Ocean along two pathways: one entering through Fram Strait (Fram Strait Branch) and one entering through the St. Anna Trough after seasonal modifications on the Barents Sea shelf (Barents Sea Branch). Although shielded from direct contact with the sea ice cover by the cold mixed layer and halocline, some of the heat reaches the sea ice via turbulent exchange and thus has impact on sea ice extent and thickness. This raises the question of the stability of the Atlantic Water circulation in the Arctic Ocean in a rapidly changing Arctic system and the consequences of potential changes in its position within the water column. The presently accepted circulation scheme of Atlantic Water in the Arctic Ocean was first depicted by Rudels et al. (1994) based on hydrographic data and dynamical considerations and has been extensively discussed in the literature and widely used in many studies. Although the general circulation patterns seem to be robust, so far not all of its branches have been verified by direct observations such as current meter measurements or geostrophic flow estimates. Additionally, there are few direct measurements of the spreading velocities of the individual components of the overall circulation scheme. We present tritium/3He data and discuss how they add to our understanding of the circulation patterns and spreading velocities. Specifically, we use 3H/3He and hydrographic data from 21 expeditions spanning 25 years of Arctic Ocean section work (1987-2013) to estimate spreading velocities and flow paths of both Atlantic Water branches on a pan-Arctic scale. Our tracer data corroborate and add a time dimension to previously estimated circulation schemes. The results confirm the presence of a well-organized boundary current that cyclonically flows along the continental slope and add insights on the other, typically topographically steered, circulation branches of Atlantic water, most notably those following the

  15. Early Pliocene onset of modern Nordic Seas circulation related to ocean gateway changes.

    Science.gov (United States)

    De Schepper, Stijn; Schreck, Michael; Beck, Kristina Marie; Matthiessen, Jens; Fahl, Kirsten; Mangerud, Gunn

    2015-10-28

    The globally warm climate of the early Pliocene gradually cooled from 4 million years ago, synchronous with decreasing atmospheric CO2 concentrations. In contrast, palaeoceanographic records indicate that the Nordic Seas cooled during the earliest Pliocene, before global cooling. However, a lack of knowledge regarding the precise timing of Nordic Seas cooling has limited our understanding of the governing mechanisms. Here, using marine palynology, we show that cooling in the Nordic Seas was coincident with the first trans-Arctic migration of cool-water Pacific mollusks around 4.5 million years ago, and followed by the development of a modern-like Nordic Seas surface circulation. Nordic Seas cooling precedes global cooling by 500,000 years; as such, we propose that reconfiguration of the Bering Strait and Central American Seaway triggered the development of a modern circulation in the Nordic Seas, which is essential for North Atlantic Deep Water formation and a precursor for more widespread Greenland glaciation in the late Pliocene.

  16. Early Pliocene onset of modern Nordic Seas circulation related to ocean gateway changes

    Science.gov (United States)

    de Schepper, Stijn; Schreck, Michael; Beck, Kristina Marie; Matthiessen, Jens; Fahl, Kirsten; Mangerud, Gunn

    2015-10-01

    The globally warm climate of the early Pliocene gradually cooled from 4 million years ago, synchronous with decreasing atmospheric CO2 concentrations. In contrast, palaeoceanographic records indicate that the Nordic Seas cooled during the earliest Pliocene, before global cooling. However, a lack of knowledge regarding the precise timing of Nordic Seas cooling has limited our understanding of the governing mechanisms. Here, using marine palynology, we show that cooling in the Nordic Seas was coincident with the first trans-Arctic migration of cool-water Pacific mollusks around 4.5 million years ago, and followed by the development of a modern-like Nordic Seas surface circulation. Nordic Seas cooling precedes global cooling by 500,000 years; as such, we propose that reconfiguration of the Bering Strait and Central American Seaway triggered the development of a modern circulation in the Nordic Seas, which is essential for North Atlantic Deep Water formation and a precursor for more widespread Greenland glaciation in the late Pliocene.

  17. Magnetic Signatures of Fine-scale Processes in the Ocean Surface Layer

    Science.gov (United States)

    Soloviev, A.; Dean, C.; Avera, W. E.

    2015-12-01

    Fine-scale processes in the upper ocean turbulent boundary layer may have a measurable electromagnetic signature. In order to study magnetic signatures of these fine-scale processes, we have applied a magnetohydrodynamic (MHD) model combining a 3D computational fluid dynamics model and electromagnetic block, based on ANSYS Fluent software. In addition, the hydrodynamic component of the MHD model is coupled with a radar imaging algorithm, which potentially provides a link to synthetic aperture radar (SAR) satellite imagery. Capabilities of this model have been demonstrated using a simulation and observation of an internal wave soliton in the Straits of Florida, observed with in situ instrumentation (ADCP mooring) and COSMO Sky Med (SAR) satellite image. We have applied this model to study magnetic signatures of surface waves, freshwater lenses, spatially coherent organized motions in the near-surface layer of the ocean (Langmuir circulation and ramp-like structures), and bio-turbulence induced by diel vertical migrations of zooplankton in some areas of the ocean. Investigation of electromagnetic signatures in upper ocean processes offers a valuable new prospect in air-sea interaction.

  18. Ocean Surface Wind Speed of Hurricane Helene Observed by SAR

    DEFF Research Database (Denmark)

    Xu, Qing; Cheng, Yongcun; Li, Xiaofeng

    2011-01-01

    The hurricanes can be detected by many remote sensors, but synthetic aperture radar (SAR) can yield high-resolution (sub-kilometer) and low-level wind information that cannot be seen below the cloud by other sensors. In this paper, an assessment of SAR capability of monitoring high......-resolution hurricane was conducted. A case study was carried out to retrieve ocean surface wind field from C-band RADARSAT-1 SAR image which captured the structure of hurricane Helene over the Atlantic Ocean on 20 September, 2006. With wind direction from the outputs of U.S. Navy Operational Global Atmospheric...... CIWRAP models have been tested to extract wind speed from SAR data. The SAR retrieved ocean surface winds were compared to the aircraft wind speed observations from stepped frequency microwave radiometer (SFMR). The results show the capability of hurricane wind monitoring by SAR....

  19. Ocean Surface Carbon Dioxide Fugacity Observed from Space

    Science.gov (United States)

    Liu, W. Timothy; Xie, Xiaosu

    2014-01-01

    We have developed and validated a statistical model to estimate the fugacity (or partial pressure) of carbon dioxide (CO2) at sea surface (pCO2sea) from space-based observations of sea surface temperature (SST), chlorophyll, and salinity. More than a quarter million in situ measurements coincident with satellite data were compiled to train and validate the model. We have produced and made accessible 9 years (2002-2010) of the pCO2sea at 0.5 degree resolutions daily over the global ocean. The results help to identify uncertainties in current JPL Carbon Monitoring System (CMS) model-based and bottom-up estimates over the ocean. The utility of the data to reveal multi-year and regional variability of the fugacity in relation to prevalent oceanic parameters is demonstrated.

  20. Current components, physical, ocean circulation, wind circulation, and other data from moored buoys, CTD casts, drifting buoys, and in situ wind recorders from AIRCRAFT and other platforms from the North Atlantic Ocean and other locations as part of the Seasonal Response of the Equatorial Atlantic Experiment/Français Océan et Climat dans l'Atlantique Equatorial (SEQUAL/FOCAL) project from 1980-01-25 to 1985-12-18 (NODC Accession 8700111)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Current components, physical, ocean circulation, wind circulation, and other data were collected from moored buoys, CTD casts, drifting buoys, and in situ wind...

  1. Role of Southern Ocean stratification in glacial atmospheric CO2 reduction evaluated by a three-dimensional ocean general circulation model

    Science.gov (United States)

    Kobayashi, Hidetaka; Abe-Ouchi, Ayako; Oka, Akira

    2015-09-01

    Atmospheric carbon dioxide (CO2) concentration during glacial periods is known to be considerably lower than during interglacial periods. However, previous studies using an ocean general circulation model (OGCM) fail to reproduce this. Paleoclimate proxy data of the Last Glacial Maximum indicate high salinity (>37.0 practical salinity unit) and long water mass residence time (>3000 years) in the Southern Ocean, suggesting that salinity stratification was enhanced and more carbon was stored there. Reproducibility of salinity and water mass age is considered insufficient in previous OGCMs, which might affect the reproducibility of atmospheric CO2 concentration. This study investigated the role of increased stratification of the Southern Ocean in the glacial CO2 variation using an OGCM. We found that deep water formation in East Antarctica is required to explain high salinity in South Atlantic. Saltier deep Southern Ocean resulted in increased atmospheric CO2 concentration against previous estimates. This is partly due to increased volume transport of Antarctic Bottom Water and associated decrease in the water mass age of the deep Pacific Ocean. On the other hand, weakening of vertical mixing contributed to increase of the vertical gradient of dissolved inorganic carbon and decrease of atmospheric CO2 concentration. However, we show that it is unable to explain all of the glacial CO2 variations by the contribution of the Southern Ocean. Our findings indicate that detailed understanding of the impact of enhanced stratification in the Southern Ocean on the Pacific Ocean might be crucial to understanding the mechanisms behind the glacial-interglacial ocean carbon cycle variations.

  2. Reduction in Surface Ocean Carbon Storage across the Middle Miocene

    Science.gov (United States)

    Babila, T. L.; Sosdian, S. M.; Foster, G. L.; Lear, C. H.

    2017-12-01

    During the Middle Miocene, Earth underwent a profound climate shift from the warmth of the Miocene Climatic Optimum (MCO; 14-17 Ma) to the stable icehouse of today during the Middle Miocene Climate transition (MMCT). Elevated atmospheric carbon dioxide concentrations (pCO2) revealed by boron isotope records (δ11B) link massive volcanic outputs of Columbia River Flood Basalts to the general warmth of MCO. Superimposed on the long-term cooling trend (MMCT) is a gradual pCO2 decline and numerous positive carbon isotope (δ13C) excursions that indicate dynamic variations in the global carbon cycle. Enhanced organic carbon burial via marine productivity, increased silicate weathering and volcanic emission cessation are each invoked to explain the drawdown of pCO2. To better constrain the oceanic role in carbon sequestration over the Middle Miocene detailed records of carbonate chemistry are needed. We present high resolution Boron/Calcium (B/Ca) and δ13C records in planktonic foraminifer T.trilobus spanning 12-17 Ma at ODP 761 (tropical eastern Indian Ocean) to document changes in surface ocean carbonate chemistry. An overall 30% increase in B/Ca ratios is expressed as two stepwise phases occurring at 14.7 and 13 Ma. Cyclic B/Ca variations are coherent with complimentary δ13C records suggesting a tight coupling between ocean carbonate chemistry parameters. Lower resolution B/Ca data at DSDP 588 (Pacific) and ODP 926 (Atlantic) corroborate the trends observed at ODP 761. We employ a paired approach that combines B/Ca (this study) to δ11B (Foster et al., 2012) and an ad hoc calibration to estimate changes in surface ocean dissolved inorganic carbon (DIC). We estimate a substantial decrease in surface ocean DIC spanning the Middle Miocene that culminates with modern day like values. This gradual decline in surface ocean DIC is coeval with existing deep-ocean records which together suggests a whole ocean reduction in carbon storage. We speculate that enhanced weathering

  3. A uniform, quality controlled Surface Ocean CO2 Atlas (SOCAT

    Directory of Open Access Journals (Sweden)

    B. Pfeil

    2013-04-01

    Full Text Available A well-documented, publicly available, global data set of surface ocean carbon dioxide (CO2 parameters has been called for by international groups for nearly two decades. The Surface Ocean CO2 Atlas (SOCAT project was initiated by the international marine carbon science community in 2007 with the aim of providing a comprehensive, publicly available, regularly updated, global data set of marine surface CO2, which had been subject to quality control (QC. Many additional CO2 data, not yet made public via the Carbon Dioxide Information Analysis Center (CDIAC, were retrieved from data originators, public websites and other data centres. All data were put in a uniform format following a strict protocol. Quality control was carried out according to clearly defined criteria. Regional specialists performed the quality control, using state-of-the-art web-based tools, specially developed for accomplishing this global team effort. SOCAT version 1.5 was made public in September 2011 and holds 6.3 million quality controlled surface CO2 data points from the global oceans and coastal seas, spanning four decades (1968–2007. Three types of data products are available: individual cruise files, a merged complete data set and gridded products. With the rapid expansion of marine CO2 data collection and the importance of quantifying net global oceanic CO2 uptake and its changes, sustained data synthesis and data access are priorities.

  4. Evaluation of OSCAR ocean surface current product in the tropical ...

    Indian Academy of Sciences (India)

    combined fashion, have contributed to the superior performance of the present algorithm for generat- ing ocean surface current. Validation and error analysis of the OSCAR pro- ..... EC (figure 4) through the appearance of strong semiannual periodicity. The SEC peaks in July, the peak being smoother in OSCAR climatology.

  5. Phase spectral composition of wind generated ocean surface waves

    Digital Repository Service at National Institute of Oceanography (India)

    Varkey, M.J.

    A study of the composition of the phase spectra of wind generated ocean surface waves is carried out using wave records collected employing a ship borne wave recorder. It is found that the raw phase spectral estimates could be fitted by the Uniform...

  6. Interpretation of nonlinearity in wind generated ocean surface waves

    Digital Repository Service at National Institute of Oceanography (India)

    Varkey, M.J.

    This study attempts to resolve a mix-up between a physical process and its mathematical interpretation in the context of wind waves on ocean surface. Wind generated wave systems, are conventionally interpreted as a result of interaction of a number...

  7. Auto-correlation analysis of ocean surface wind vectors

    Indian Academy of Sciences (India)

    M. Senthilkumar (Newgen Imaging) 1461 1996 Oct 15 13:05:22

    In this work, an auto-correlation analysis of a time series data of surface winds measured in situ by a deep water buoy in the Indian Ocean has been carried out. Hourly time series data available for 240 hours in the month of May, 1999 were subjected to an auto-correlation analysis. The analysis indicates an exponential fall ...

  8. The 1958-2009 Greenland ice sheet surface melt and the mid-tropospheric atmospheric circulation

    NARCIS (Netherlands)

    Fettweis, X.; Mabille, G.; Erpicum, M.; Nicolay, S.; van den Broeke, M.R.

    2010-01-01

    In order to assess the impact of the mid-tropospheric circulation over the Greenland ice sheet (GrIS) on surface melt, as simulated by the regional climate model MAR, an automatic Circulation type classification (CTC) based on 500 hPa geopotential height from reanalyses is developed. General

  9. NOAA Climate Data Record (CDR) of Ocean Near Surface Atmospheric Properties, Version 2

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The NOAA Ocean Surface Bundle (OSB) Climate Data Record (CDR) consist of three parts: sea surface temperature; near-surface wind speed, air temperature, and specific...

  10. Natural variability in the surface ocean carbonate ion concentration

    OpenAIRE

    N. S. Lovenduski; M. C. Long; K. Lindsay

    2015-01-01

    We investigate variability in the surface ocean carbonate ion concentration ([CO32−]) on the basis of a long control simulation with a fully-coupled Earth System Model. The simulation is run with a prescribed, pre-industrial atmospheric CO2 concentration for 1000 years, permitting investigation of natural [CO32−] variability on interannual to multi-decadal timescales. We find high interannual variability in surface [CO32−] in the tropical...

  11. Natural variability in the surface ocean carbonate ion concentration

    OpenAIRE

    Lovenduski, N. S.; Long, M. C.; Lindsay, K.

    2015-01-01

    We investigate variability in the surface ocean carbonate ion concentration ([CO32−]) on the basis of a~long control simulation with an Earth System Model. The simulation is run with a prescribed, pre-industrial atmospheric CO2 concentration for 1000 years, permitting investigation of natural [CO32−] variability on interannual to multi-decadal timescales. We find high interannual variability in surface [CO32−] in the tropical Pacific and ...

  12. Response of the North Atlantic dynamic sea level and circulation to Greenland meltwater and climate change in an eddy-permitting ocean model

    Science.gov (United States)

    Saenko, Oleg A.; Yang, Duo; Myers, Paul G.

    2017-10-01

    The response of the North Atlantic dynamic sea surface height (SSH) and ocean circulation to Greenland Ice Sheet (GrIS) meltwater fluxes is investigated using a high-resolution model. The model is forced with either present-day-like or projected warmer climate conditions. In general, the impact of meltwater on the North Atlantic SSH and ocean circulation depends on the surface climate. In the two major regions of deep water formation, the Labrador Sea and the Nordic Seas, the basin-mean SSH increases with the increase of the GrIS meltwater flux. This SSH increase correlates with the decline of the Atlantic meridional overturning circulation (AMOC). However, while in the Labrador Sea the warming forcing and GrIS meltwater input lead to sea level rise, in the Nordic Seas these two forcings have an opposite influence on the convective mixing and basin-mean SSH (relative to the global mean). The warming leads to less sea-ice cover in the Nordic Seas, which favours stronger surface heat loss and deep mixing, lowering the SSH and generally increasing the transport of the East Greenland Current. In the Labrador Sea, the increased SSH and weaker deep convection are reflected in the decreased transport of the Labrador Current (LC), which closes the subpolar gyre in the west. Among the two major components of the LC transport, the thermohaline and bottom transports, the former is less sensitive to the GrIS meltwater fluxes under the warmer climate. The SSH difference across the LC, which is a component of the bottom velocity, correlates with the long-term mean AMOC rate.

  13. Antarctic lakes suggest millennial reorganizations of Southern Hemisphere atmospheric and oceanic circulation.

    Science.gov (United States)

    Hall, Brenda L; Denton, George H; Fountain, Andrew G; Hendy, Chris H; Henderson, Gideon M

    2010-12-14

    The phasing of millennial-scale oscillations in Antarctica relative to those elsewhere in the world is important for discriminating among models for abrupt climate change, particularly those involving the Southern Ocean. However, records of millennial-scale variability from Antarctica dating to the last glacial maximum are rare and rely heavily on data from widely spaced ice cores, some of which show little variability through that time. Here, we present new data from closed-basin lakes in the Dry Valleys region of East Antarctica that show high-magnitude, high-frequency oscillations in surface level during the late Pleistocene synchronous with climate fluctuations elsewhere in the Southern Hemisphere. These data suggest a coherent Southern Hemisphere pattern of climate change on millennial time scales, at least in the Pacific sector, and indicate that any hypothesis concerning the origin of these events must account for synchronous changes in both high and temperate latitudes.

  14. Simulation of Lake Victoria Circulation Patterns Using the Regional Ocean Modeling System (ROMS).

    Science.gov (United States)

    Nyamweya, Chrispine; Desjardins, Christopher; Sigurdsson, Sven; Tomasson, Tumi; Taabu-Munyaho, Anthony; Sitoki, Lewis; Stefansson, Gunnar

    2016-01-01

    Lake Victoria provides important ecosystem services including transport, water for domestic and industrial uses and fisheries to about 33 million inhabitants in three East African countries. The lake plays an important role in modulating regional climate. Its thermodynamics and hydrodynamics are also influenced by prevailing climatic and weather conditions on diel, seasonal and annual scales. However, information on water temperature and circulation in the lake is limited in space and time. We use a Regional Oceanographic Model System (ROMS) to simulate these processes from 1st January 2000 to 31st December 2014. The model is based on real bathymetry, river runoff and atmospheric forcing data using the bulk flux algorithm. Simulations show that the water column exhibits annual cycles of thermo-stratification (September-May) and mixing (June-August). Surface water currents take different patterns ranging from a lake-wide northward flow to gyres that vary in size and number. An under flow exists that leads to the formation of upwelling and downwelling regions. Current velocities are highest at the center of the lake and on the western inshore waters indicating enhanced water circulation in those areas. However, there is little exchange of water between the major gulfs (especially Nyanza) and the open lake, a factor that could be responsible for the different water quality reported in those regions. Findings of the present study enhance understanding of the physical processes (temperature and currents) that have an effect on diel, seasonal, and annual variations in stratification, vertical mixing, inshore-offshore exchanges and fluxes of nutrients that ultimately influence the biotic distribution and trophic structure. For instance information on areas/timing of upwelling and vertical mixing obtained from this study will help predict locations/seasons of high primary production and ultimately fisheries productivity in Lake Victoria.

  15. Simulation of Lake Victoria Circulation Patterns Using the Regional Ocean Modeling System (ROMS.

    Directory of Open Access Journals (Sweden)

    Chrispine Nyamweya

    Full Text Available Lake Victoria provides important ecosystem services including transport, water for domestic and industrial uses and fisheries to about 33 million inhabitants in three East African countries. The lake plays an important role in modulating regional climate. Its thermodynamics and hydrodynamics are also influenced by prevailing climatic and weather conditions on diel, seasonal and annual scales. However, information on water temperature and circulation in the lake is limited in space and time. We use a Regional Oceanographic Model System (ROMS to simulate these processes from 1st January 2000 to 31st December 2014. The model is based on real bathymetry, river runoff and atmospheric forcing data using the bulk flux algorithm. Simulations show that the water column exhibits annual cycles of thermo-stratification (September-May and mixing (June-August. Surface water currents take different patterns ranging from a lake-wide northward flow to gyres that vary in size and number. An under flow exists that leads to the formation of upwelling and downwelling regions. Current velocities are highest at the center of the lake and on the western inshore waters indicating enhanced water circulation in those areas. However, there is little exchange of water between the major gulfs (especially Nyanza and the open lake, a factor that could be responsible for the different water quality reported in those regions. Findings of the present study enhance understanding of the physical processes (temperature and currents that have an effect on diel, seasonal, and annual variations in stratification, vertical mixing, inshore-offshore exchanges and fluxes of nutrients that ultimately influence the biotic distribution and trophic structure. For instance information on areas/timing of upwelling and vertical mixing obtained from this study will help predict locations/seasons of high primary production and ultimately fisheries productivity in Lake Victoria.

  16. Efficient computation of past global ocean circulation patterns using continuation in paleobathymetry

    NARCIS (Netherlands)

    Mulder, T. E.; Baatsen, M. L.J.; Wubs, F.W.; Dijkstra, H. A.

    2017-01-01

    In the field of paleoceanographic modeling, the different positioning of Earth's continental configurations is often a major challenge for obtaining equilibrium ocean flow solutions. In this paper, we introduce numerical parameter continuation techniques to compute equilibrium solutions of ocean

  17. Surface Ocean CO2 Atlas (SOCAT) gridded data products

    Energy Technology Data Exchange (ETDEWEB)

    Sabine, Christopher [NOAA Pacific Marine Environmental Laboratory; Hankin, S. [Pacific Northwest National Laboratory (PNNL); Koyuk, H [Joint Institute for the Study of the Atmosphere and Ocean, University of Washington; Bakker, D C E [School of Environmental Sciences, University of East Anglia, Norwich, UK; Pfeil, B [Geophysical Institute, University of Bergen; Uni Research AS, Bergen, Norway; Olsen, A [Bjerknes Centre for Climate Research, UNIFOB AS, Bergen, Norway; Metzl, N [Universite Pierre et Marie Curie, LOCEAN/IPSL, Paris, France; Kozyr, Alexander [ORNL; Fassbender, A [School of Oceanography, University of Washington, Seattle, WA; Manke, A [Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration; Malczyk, J [Jetz Laboratory, Department of Ecology and Evolutionary Biology, Yale University; Akl, J [CSIRO Wealth from Oceans Flagship, Hobart, Tasmania, Australia; Alin, S R [Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration; Bellerby, R G J [Geophysical Institute, University of Bergen, Bergen, Norway; Borges, A [University of Liege, Chemical Oceanography Unit, Institut de Physique, Liege, Belgium; Boutin, J [Universite Pierre et Marie Curie, LOCEAN/IPSL, Paris, France; Brown, P J [School of Environmental Sciences, University of East Anglia, Norwich, UK; Cai, W-J [Department of Marine Sciences, University of Georgia; Chavez, F P [Monterey Bay Aquarium Research Institute, Moss Landing, CA; Chen, A [Institute of Marine Geology and Chemistry, National Sun Yat-sen University, Kaohsiung, Taiwan; Cosa, C [Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration; Feely, R A [Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration; Gonzalez-Davila, M [Universidad de Las Palmas de Gran Canaria, Facultad de Ciencias del Mar, Las Palmas de Gran Canaria,; Goyet, C [Institut de Modélisation et d' Analyse en Géo-Environnement et Santé, Université de Perpignan; Hardman-Mountford, N [CSIRO, Marine and Atmospheric Research, Wembley, Western Australia, Australia; Heinze, C [Geophysical Institute, University of Bergen, Bergen, Norway; Hoppema, M [Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany; Hunt, C W [Ocean Process Analysis Lab, University of New Hampshire, Durham, New Hampshire; Hydes, D [National Oceanography Centre, Southampton, UK; Ishii, M [Japan Meteorological Agency, Meteorological Research Institute, Tsukuba, Japan; Johannessen, T [Geophysical Institute, University of Bergen, Bergen, Norway; Key, R M [Atmospheric and Oceanic Sciences, Princeton University, Princeton, New Jersey; Kortzinger, A [GEOMAR, Helmholtz Centre for Ocean Research, Kiel, Germany; Landschutzer, P [School of Environmental Sciences, University of East Anglia, Norwich, UK; Lauvset, S K [Geophysical Institute, University of Bergen, Bergen, Norway; Lefevre, N [Université Pierre et Marie Curie, LOCEAN/IPSL, Paris, France; Lenton, A [Centre for Australian Weather and Climate Research, Hobart, Tasmania, Australia; Lourantou, A [Université Pierre et Marie Curie, LOCEAN/IPSL, Paris, France; Merlivat, L [Université Pierre et Marie Curie, LOCEAN/IPSL, Paris, France; Midorikawa, T [Nagasaki Marine Observatory, Nagasaki, Japan; Mintrop, L [MARIANDA, Kiel, Germany; Miyazaki, C [Faculty of Environmental Earth Science, Hokkaido University, Hokkaido, Japan; Murata, A [Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan; Nakadate, A [Marine Division, Global Environment and Marine Department, Japan Meteorological Agency, Tokyo, Japan; Nakano, Y [Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan; Nakaoka, S [National Institute for Environmental Studies (NIES), Tsukuba, Japan; Nojiri, Y [National Institute for Environmental Studies, Tsukuba, Japan; et al.

    2013-01-01

    A well documented, publicly available, global data set for surface ocean carbon dioxide (CO2) parameters has been called for by international groups for nearly two decades. The Surface Ocean CO2 Atlas (SOCAT) project was initiated by the international marine carbon science community in 2007 with the aim of providing a comprehensive, publicly available, regularly updated, global data set of marine surface CO2, which had been subject to quality control (QC). SOCAT version 1.5 was made public in September 2011 and holds 6.3 million quality controlled surface CO2 data from the global oceans and coastal seas, spanning four decades (1968 2007). The SOCAT gridded data is the second data product to come from the SOCAT project. Recognizing that some groups may have trouble working with millions of measurements, the SOCAT gridded product was generated to provide a robust regularly spaced fCO2 product with minimal spatial and temporal interpolation which should be easier to work with for many applications. Gridded SOCAT is rich with information that has not been fully explored yet, but also contains biases and limitations that the user needs to recognize and address.

  18. An Overview of the Naval Research Laboratory Ocean Surface Flux (NFLUX) System

    Science.gov (United States)

    May, J. C.; Rowley, C. D.; Barron, C. N.

    2016-02-01

    The Naval Research Laboratory (NRL) ocean surface flux (NFLUX) system is an end-to-end data processing and assimilation system used to provide near-real time satellite-based surface heat flux fields over the global ocean. Swath-level air temperature (TA), specific humidity (QA), and wind speed (WS) estimates are produced using multiple polynomial regression algorithms with inputs from satellite sensor data records from the Special Sensor Microwave Imager/Sounder, the Advanced Microwave Sounding Unit-A, the Advanced Technology Microwave Sounder, and the Advanced Microwave Scanning Radiometer-2 sensors. Swath-level WS estimates are also retrieved from satellite environmental data records from WindSat, the MetOp scatterometers, and the Oceansat scatterometer. Swath-level solar and longwave radiative flux estimates are produced utilizing the Rapid Radiative Transfer Model for Global Circulation Models (RRTMG). Primary inputs to the RRTMG include temperature and moisture profiles and cloud liquid and ice water paths from the Microwave Integrated Retrieval System. All swath-level satellite estimates undergo an automated quality control process and are then assimilated with atmospheric model forecasts to produce 3-hourly gridded analysis fields. The turbulent heat flux fields, latent and sensible heat flux, are determined from the Coupled Ocean-Atmosphere Response Experiment (COARE) 3.0 bulk algorithms using inputs of TA, QA, WS, and a sea surface temperature model field. Quality-controlled in situ observations over a one-year time period from May 2013 through April 2014 form the reference for validating ocean surface state parameter and heat flux fields. The NFLUX fields are evaluated alongside the Navy's operational global atmospheric model, the Navy Global Environmental Model (NAVGEM). NFLUX is shown to have smaller biases and lower or similar root mean square errors compared to NAVGEM.

  19. Solutions Network Formulation Report: Improving NOAA's PORTS(R) Through Enhanced Data Inputs from NASA's Ocean Surface Topography Mission

    Science.gov (United States)

    Guest, DeNeice

    2007-01-01

    The Nation uses water-level data for a variety of practical purposes, including nautical charting, maritime navigation, hydrography, coastal engineering, and tsunami and storm surge warnings. Long-term applications include marine boundary determinations, tidal predictions, sea-level trend monitoring, oceanographic research, and climate research. Accurate and timely information concerning sea-level height, tide, and ocean current is needed to understand their impact on coastal management, disaster management, and public health. Satellite altimeter data products are currently used by hundreds of researchers and operational users to monitor ocean circulation and to improve scientists understanding of the role of the oceans in climate and weather. The NOAA (National Oceanic and Atmospheric Administration) National Ocean Service has been monitoring sea-level variations for many years. NOAA s PORTS (Physical Oceanographic Real-Time System) DST (decision support tool), managed by the Center for Operational Oceanographic Products and Services, supports safe and cost-efficient navigation by providing ship masters and pilots with accurate real-time information required to avoid groundings and collisions. This report assesses the capacity of NASA s satellite altimeter data to meet societal decision support needs through incorporation into NOAA s PORTS. NASA has a long heritage of collecting data for ocean research, including its current Terra and Aqua missions. Numerous other missions provide additional important information for coastal management issues, and data collection will continue in the coming decade with such missions as the OSTM (Ocean Surface Topography Mission). OSTM will provide data on sea-surface heights for determining ocean circulation, climate change, and sea-level rise. We suggest that NASA incorporate OSTM altimeter data (C- and Ku-band) into NOAA s PORTS DST in support of NASA s Coastal Management National Application with secondary support to the

  20. High-precision measurements of 14C as a circulation tracer in the Pacific, Indian, and Southern Oceans with Accelerator Mass Spectrometry (AMS)

    International Nuclear Information System (INIS)

    Reden, Karl F. von; Peden, John C.; Schneider, Robert J.; Bellino, Mary; Donoghue, Joanne; Elder, Kathryn L.; Gagnon, Alan R.; Long, Patricia; McNichol, Ann P.; Morin, Tracey; Stuart, Dana; Hayes, John M.; Key, Robert M.

    1999-01-01

    The National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS) has completed the carbon isotope analysis of a major fraction of the 13,500 sea water samples collected in the framework of the World Ocean Circulation Experiment (WOCE) from three of the major world oceans between 1991 and 1996. We will describe the AMS technique employed at NOSAMS and, using 3-D data visualization techniques we will demonstrate the present status of the data set and offer some preliminary conclusions about the distribution of natural and anthropogenic 14 C in the oceans. In particular, we will be able to compare some of the data with results from the Geochemical Ocean Sections Study (GEOSECS, 1972-1978) to obtain information about the time dependence of oceanic circulation processes, tracing the 14 C signal introduced into the oceans during the atmospheric nuclear bomb tests in the 1950's and 1960's

  1. Surface circulation in the Iroise Sea (western Brittany) derived from high resolution current mapping by HF radars

    Science.gov (United States)

    Sentchev, Alexei; Forget, Philippe; Barbin, Yves; Marié, Louis; Ardhuin, Fabrice

    2010-05-01

    The use of high frequency radar (HFR) systems for near-real-time coastal ocean monitoring necessities that short time scale motions of the radar-derived velocities are better understood. While the ocean radar systems are able to describe coastal flow patterns with unprecedented details, the data they produce are often too sparse or gappy for applications such as the identification of coherent structures and fronts or understanding transport and mixing processes. In this study, we address two challenges. First, we report results from the HF radar system (WERA) which is routinely operating since 2006 on the western Brittany coast to monitor surface circulation in the Iroise Sea, over an area extending up to 100 km offshore. To obtain more reliable records of vector current fields at high space and time resolution, the Multiple Signal Classification (MUSIC) direction finding algorithm is employed in conjunction with the variational interpolation (2dVar) of radar-derived velocities. This provides surface current maps at 1 km spacing and time resolution of 20 min. Removing the influence of the sea state on radar-derived current measurements is discussed and performed on some data sequences. Second, we examine in deep continuous 2d velocity records for a number of periods, exploring the different modes of variability of surface currents in the region. Given the extent, duration, and resolution of surface current velocity measurements, new quantitative insights from various time series and spatial analysis on higher frequency kinematics will be discussed. By better characterizing the full spectrum of flow regimes that contribute to the surface currents and their shears, a more complete picture of the circulation in the Iroise Sea can be obtained.

  2. Oceans circulation and electron cyclotron resonance sources: Measurement of the AR-39 isotopic ratio in Seawater

    International Nuclear Information System (INIS)

    Gaelens, M.; Loiselet, M.; Ryckewaert, G.; Pardo, R.C.; Scott, R.H.; Vondrasek, R.; Collon, Ph.; Kutchera, W.

    2004-01-01

    The radionuclide 39 Ar is produced in the atmosphere by cosmic rays and has an isotopic abundance of 8.1x10 -16 . Because its half life (T 1/2 =269 years) is well matched to the time periods involved in the oceanic currents around the Earth, the measurement of the 39 Ar isotopic ratio is an ideal tool to date ocean water from different depths. It would complement the information gained by the 14 C measurements (T 1/2 =5730 years). However, the measurement of the isotopic ratio 39 Ar/ 40 Ar is a technical challenge: 1 L of modern ocean water contains ∼6500 atoms of 39 Ar, and produces ∼17 decays per year. Although it has been possible to detect the 39 Ar decays in large volumes of sea water by using the low level counting technique, the possibility of measuring the number of 39 Ar atoms faster and in smaller samples using the accelerator mass spectrometry (AMS) technique would be a major breakthrough for this type of measurement. The development of a viable AMS method for 39 Ar has been underway for several years at Argonne National Laboratory, and is presently hampered by the presence of stable 39 K ions coming from the ion source. Although the intensity of this isobaric contaminant is low (∼pA extracted from the source), it has to be compared with the 39 Ar beam intensity (atoms per minutes). In order to separate these two beams (whose mass difference is only 1.6x10 -5 ), the intensity of the 39 K beam coming from the ion source has to be reduced by several orders of magnitude. This reduction has been investigated both at Argonne National Laboratory and at Louvain-la-Neuve. Two techniques have been tried out. In the first, a quartz liner is used to provide a clean surface, while in the second these impurities are buried in a SiO 2 layer formed in situ by running the source with a mixture of silane and oxygen. The 39 K background has been reduced by a factor of 100 with these treatments. These techniques and their results obtained both at Argonne and Louvain

  3. Microwave Remote Sensing Modeling of Ocean Surface Salinity and Winds Using an Empirical Sea Surface Spectrum

    Science.gov (United States)

    Yueh, Simon H.

    2004-01-01

    Active and passive microwave remote sensing techniques have been investigated for the remote sensing of ocean surface wind and salinity. We revised an ocean surface spectrum using the CMOD-5 geophysical model function (GMF) for the European Remote Sensing (ERS) C-band scatterometer and the Ku-band GMF for the NASA SeaWinds scatterometer. The predictions of microwave brightness temperatures from this model agree well with satellite, aircraft and tower-based microwave radiometer data. This suggests that the impact of surface roughness on microwave brightness temperatures and radar scattering coefficients of sea surfaces can be consistently characterized by a roughness spectrum, providing physical basis for using combined active and passive remote sensing techniques for ocean surface wind and salinity remote sensing.

  4. Decadal variability of the Tropical Atlantic Ocean Surface Temperature in shipboard measurements and in a Global Ocean-Atmosphere model

    Science.gov (United States)

    Mehta, Vikram M.; Delworth, Thomas

    1995-01-01

    Sea surface temperature (SST) variability was investigated in a 200-yr integration of a global model of the coupled oceanic and atmospheric general circulations developed at the Geophysical Fluid Dynamics Laboratory (GFDL). The second 100 yr of SST in the coupled model's tropical Atlantic region were analyzed with a variety of techniques. Analyses of SST time series, averaged over approximately the same subregions as the Global Ocean Surface Temperature Atlas (GOSTA) time series, showed that the GFDL SST anomalies also undergo pronounced quasi-oscillatory decadal and multidecadal variability but at somewhat shorter timescales than the GOSTA SST anomalies. Further analyses of the horizontal structures of the decadal timescale variability in the GFDL coupled model showed the existence of two types of variability in general agreement with results of the GOSTA SST time series analyses. One type, characterized by timescales between 8 and 11 yr, has high spatial coherence within each hemisphere but not between the two hemispheres of the tropical Atlantic. A second type, characterized by timescales between 12 and 20 yr, has high spatial coherence between the two hemispheres. The second type of variability is considerably weaker than the first. As in the GOSTA time series, the multidecadal variability in the GFDL SST time series has approximately opposite phases between the tropical North and South Atlantic Oceans. Empirical orthogonal function analyses of the tropical Atlantic SST anomalies revealed a north-south bipolar pattern as the dominant pattern of decadal variability. It is suggested that the bipolar pattern can be interpreted as decadal variability of the interhemispheric gradient of SST anomalies. The decadal and multidecadal timescale variability of the tropical Atlantic SST, both in the actual and in the GFDL model, stands out significantly above the background 'red noise' and is coherent within each of the time series, suggesting that specific sets of

  5. Late Quaternary surface circulation in the east equatorial South Atlantic: Evidence from Alkenone sea surface temperatures

    Science.gov (United States)

    Schneider, Ralph R.; Müller, Peter J.; Ruhland, GöTz

    1995-04-01

    Angola Basin and Walvis Ridge records of past sea surface temperatures (SST) derived from the alkenone Uk37 index are used to reconstruct the surface circulation in the east equatorial South Atlantic for the last 200,000 years. Comparison of SST estimates from surface sediments between 5° and 20°S with modern SST data suggests that the alkenone temperatures represent annual mean values of the surface mixed layer. Alkenone-derived temperatures for the warm climatic maxima of the Holocene and the penultimate interglacial are 1 to 4°C higher than latest Holocene values. All records show glacial to interglacial differences of about 3.5°C in annual mean SST, which is about 1.5°C greater than the difference estimated by CLIMAP (1981) for the eastern Angola Basin. At the Walvis Ridge, significant SST variance is observed at all of the Earth's orbital periodicities. SST records from the Angola Basin vary predominantly at 23- and 100-kyr periodicities. For the precessional cycle, SST changes at the Walvis Ridge correspond to variations of boreal summer insolation over Africa and lead ice volume changes, suggesting that the east equatorial South Atlantic is sensitive to African monsoon intensity via trade-wind zonality. Angola Basin SST records lag those from the Walvis Ridge and the equatorial Atlantic by about 3 kyr. The comparison of Angola Basin and Walvis Ridge SST records implies that the Angola-Benguela Front (ABF) (currently at about 14-16°S) has remained fairly stationary between 12° and 20°S (the limits of our cores) during the last two glacial-interglacial cycles. The temperature contrast associated with the ABF exhibits a periodic 23-kyr variability which is coherent with changes in boreal summer insolation over Africa. These observations suggest that surface waters north of the present ABF have not directly responded to monsoon-modulated changes in the trade-wind vector, that the central field of zonally directed trades in the southern hemisphere was not

  6. Surface Ocean CO2 Atlas (SOCAT gridded data products

    Directory of Open Access Journals (Sweden)

    C. L. Sabine

    2013-04-01

    Full Text Available As a response to public demand for a well-documented, quality controlled, publically available, global surface ocean carbon dioxide (CO2 data set, the international marine carbon science community developed the Surface Ocean CO2 Atlas (SOCAT. The first SOCAT product is a collection of 6.3 million quality controlled surface CO2 data from the global oceans and coastal seas, spanning four decades (1968–2007. The SOCAT gridded data presented here is the second data product to come from the SOCAT project. Recognizing that some groups may have trouble working with millions of measurements, the SOCAT gridded product was generated to provide a robust, regularly spaced CO2 fugacity (fCO2 product with minimal spatial and temporal interpolation, which should be easier to work with for many applications. Gridded SOCAT is rich with information that has not been fully explored yet (e.g., regional differences in the seasonal cycles, but also contains biases and limitations that the user needs to recognize and address (e.g., local influences on values in some coastal regions.

  7. Changes in Equatorial Atlantic Ocean Thermohaline Circulation Across the Mid-Pleistocene Transition

    Science.gov (United States)

    Yehudai, M.; Kim, J.; Seguí, M. J.; Goldstein, S. L.; Pena, L. D.; Haynes, L.; Hoenisch, B.; Farmer, J. R.; Ford, H. L.; Raymo, M. E.; Bickert, T.

    2016-12-01

    The Mid-Pleistocene Transition (MPT) marked a change in the duration of glacial-interglacial cycles from 41 to 100kyr between 1.3-0.7 Ma. A recent study (Pena and Goldstein, Science, 2014) from the Southern Atlantic Ocean found evidence for major disruptions in the global thermohaline circulation (THC) between MIS 25-21 ( 950-850ka), which may have triggered intensified glacial periods and the onset of the 100 kyr cycles. We report new Nd isotope data on Fe-Mn oxide encrusted foraminifera and fish debris from ODP Site 926 (3.719N, 42.908W, 3598m) between 1.2-0.4 Ma, in order to evaluate changes in the THC in the equatorial Atlantic, through comparison with North and South Atlantic sites. The ODP 926 ɛNd values fall in-between those in the North Atlantic (DSDP 607) and South Atlantic (ODP 1088 and 1090) throughout the studied interval, consistent with mixing between northern and southern end-members, and supporting the interpretation that the data represent the THC signal at this site. Pre-MPT data show smaller glacial-interglacial differences compared to the greater post-MPT glacial-interglacial variability. As Pena and Goldstein (2014) observed in the South Atlantic, during MIS 23 at 900 ka, ɛNd values do not shift significantly toward North Atlantic more negative values, consistent with a weak THC through this critical weak interglacial. Comparing ODP 926 and DSDP 607 data, ɛNd values converge during most interglacial peaks (excepting MIS 23) and diverge otherwise. This observation indicates that northern-sourced water masses dominate the site during peak interglacials, and confirms that the THC has been strongest during peak interglacials throughout the studied interval. Otherwise, diverging ɛNd values indicate a stronger southern-source signal and weaker northern-source signal at the ODP 926 site. This confirms that there was an active but variable THC system before, during, and after the MPT, with stronger deep water export from the North Atlantic during

  8. Deglacial and Holocene sea-ice variability north of Iceland and response to ocean circulation changes

    Science.gov (United States)

    Xiao, Xiaotong; Zhao, Meixun; Knudsen, Karen Luise; Sha, Longbin; Eiríksson, Jón; Gudmundsdóttir, Esther; Jiang, Hui; Guo, Zhigang

    2017-08-01

    Sea-ice conditions on the North Icelandic shelf constitute a key component for the study of the climatic gradients between the Arctic and the North Atlantic Oceans at the Polar Front between the cold East Icelandic Current delivering Polar surface water and the relatively warm Irminger Current derived from the North Atlantic Current. The variability of sea ice contributes to heat reduction (albedo) and gas exchange between the ocean and the atmosphere, and further affects the deep-water formation. However, lack of long-term and high-resolution sea-ice records in the region hinders the understanding of palaeoceanographic change mechanisms during the last glacial-interglacial cycle. Here, we present a sea-ice record back to 15 ka (cal. ka BP) based on the sea-ice biomarker IP25, phytoplankton biomarker brassicasterol and terrestrial biomarker long-chain n-alkanols in piston core MD99-2272 from the North Icelandic shelf. During the Bølling/Allerød (14.7-12.9 ka), the North Icelandic shelf was characterized by extensive spring sea-ice cover linked to reduced flow of warm Atlantic Water and dominant Polar water influence, as well as strong meltwater input in the area. This pattern showed an anti-phase relationship with the ice-free/less ice conditions in marginal areas of the eastern Nordic Seas, where the Atlantic Water inflow was strong, and contributed to an enhanced deep-water formation. Prolonged sea-ice cover with occasional occurrence of seasonal sea ice prevailed during the Younger Dryas (12.9-11.7 ka) interrupted by a brief interval of enhanced Irminger Current and deposition of the Vedde Ash, as opposed to abruptly increased sea-ice conditions in the eastern Nordic Seas. The seasonal sea ice decreased gradually from the Younger Dryas to the onset of the Holocene corresponding to increasing insolation. Ice-free conditions and sea surface warming were observed for the Early Holocene, followed by expansion of sea ice during the Mid-Holocene.

  9. Adaptation of a fully-unstructured-mesh, finite-element ocean model to the simulation of ocean circulation in the presence of ice shelf

    Science.gov (United States)

    Kimura, Satoshi; Candy, Adam; Holland, Paul; Piggott, Matthew; Jenkins, Adrian

    2013-04-01

    There have been many efforts to explicitly represent ice shelf cavities in ocean models. These ocean models employ isopycnic, terrain-following, or z coordinates. We will explore an alternate method by using the finite-element ocean model, Fluidity-ICOM, to represent an ice shelf. The Fluidity-ICOM model simulates non-hydrostatic dynamics on meshes that can be unstructured in all three dimensions. This geometric flexibility offers several advantages over previous approaches. The model represents melting or freezing on ice-ocean interfaces oriented in any direction, treats the ice shelf topography as continuous rather than stepped, and does not require any smoothing of the ice topography or any additional parameterisations of the ocean mixed layer used in isopycnal or z-coordinate models. We will demonstrate these capabilities by investigating the response of ice shelf basal melting to 1) variations in ocean temperature on an idealized ice shelf and 2) variation in sub-glacial discharge on an idealized Fjord. Melting near the grounding line of the ice shelf produces melt water that is lighter than the surrounding and therefore the meltwater ascends along the base. A band of melting area is concentrated at the Western region due to the Coriolis force in the Southern Hemisphere. As found in previous studies, the melt rate increases non-linearly as the temperature of the water forcing the cavity increases. However, the model is able to represent the dynamics of a meltwater plume that separates from the ice shelf when it reaches neutral buoyancy, unlike previous models with mixed-layer parameterisation. In the warmest case, the meltwater is lighter than the surrounding water, thereby warming the surface of the ocean. As the deep water temperature decreases, the meltwater is not light enough to penetrate to the surface, so it intrudes into the open ocean, cooling the deep water. In the case of the idealized Fjord, the discharged water ascends along the vertical ice base

  10. The influence of the circulation on surface temperature and precipitation patterns over Europe

    Directory of Open Access Journals (Sweden)

    P. D. Jones

    2009-06-01

    Full Text Available The atmospheric circulation clearly has an important influence on variations in surface temperature and precipitation. In this study we illustrate the spatial patterns of variation that occur for the principal circulation patterns across Europe in the standard four seasons. We use an existing classification scheme of surface pressure patterns, with the aim of considering whether the patterns of influence of specific weather types have changed over the course of the 20th century. We consider whether the long-term warming across Europe is associated with more favourable weather types or related to warming within some of the weather types. The results indicate that the latter is occurring, but not all circulation types show warming. The study also illustrates that certain circulation types can lead to marked differences in temperature and/or precipitation for relatively closely positioned sites when the sites are located in areas of high relief or near coasts.

  11. Duality of Ross Ice Shelf systems: crustal boundary, ice sheet processes and ocean circulation from ROSETTA-Ice surveys

    Science.gov (United States)

    Tinto, K. J.; Siddoway, C. S.; Padman, L.; Fricker, H. A.; Das, I.; Porter, D. F.; Springer, S. R.; Siegfried, M. R.; Caratori Tontini, F.; Bell, R. E.

    2017-12-01

    Bathymetry beneath Antarctic ice shelves controls sub-ice-shelf ocean circulation and has a major influence on the stability and dynamics of the ice sheets. Beneath the Ross Ice Shelf, the sea-floor bathymetry is a product of both tectonics and glacial processes, and is influenced by the processes it controls. New aerogeophysical surveys have revealed a fundamental crustal boundary bisecting the Ross Ice Shelf and imparting a duality to the Ross Ice Shelf systems, encompassing bathymetry, ocean circulation and ice flow history. The ROSETTA-Ice surveys were designed to increase the resolution of Ross Ice Shelf mapping from the 55 km RIGGS survey of the 1970s to a 10 km survey grid, flown over three years from New York Air National Guard LC130s. Radar, LiDAR, gravity and magnetic instruments provide a top to bottom profile of the ice shelf and the underlying seafloor, with 20 km resolution achieved in the first two survey seasons (2015 and 2016). ALAMO ocean-profiling floats deployed in the 2016 season are measuring the temperature and salinity of water entering and exiting the sub-ice water cavity. A significant east-west contrast in the character of the magnetic and gravity fields reveals that the lithospheric boundary between East and West Antarctica exists not at the base of the Transantarctic Mountains (TAM), as previously thought, but 300 km further east. The newly-identified boundary spatially coincides with the southward extension of the Central High, a rib of shallow basement identified in the Ross Sea. The East Antarctic side is characterized by lower amplitude magnetic anomalies and denser TAM-type lithosphere compared to the West Antarctic side. The crustal structure imparts a fundamental duality on the overlying ice and ocean, with deeper bathymetry and thinner ice on the East Antarctic side creating a larger sub-ice cavity for ocean circulation. The West Antarctic side has a shallower seabed, more restricted ocean access and a more complex history of

  12. Impact of land surface heterogeneity on urban heat island circulation and sea-land breeze circulation in Hong Kong

    Science.gov (United States)

    Wang, Y.; Di Sabatino, S.; Martilli, A.; Li, Y.; Wong, M. S.; Gutiérrez, E.; Chan, P. W.

    2017-04-01

    Hong Kong is one of the most high-rise and highly compact cities in the world. The urban land surface is highly heterogeneous, which creates low-level convergence zones in urban areas, particularly the Kowloon Peninsula. The low-level convergence zone is due to the combined effect of urban heat island circulation (UHIC) and sea-land breeze circulation (SLBC) under weak northeasterly synoptic flow. To study the impacts of anthropogenic fluxes and built-up areas on the local circulation, the Weather Research and Forecasting (WRF) mesoscale model is combined with the multilayer urban canopy building effect parameterization/building energy model (BEP/BEM) parameterization to produce a 3 day simulation of an air pollution episode in Hong Kong in September 2012. To better represent the city land surface features, building information is assimilated in the central part of the Kowloon Peninsula. The WRF-BEP-BEM model captures the 2 m temperature distribution and local wind rotation reasonably well but overestimates the 10 m wind speed with a mean bias error of 0.70 m/s. A dome-shaped feature with a high level of moisture is captured in the convergence zones due to intensified UHIC and inflowing SLBC. The anthropogenic heat increases the air temperature by around 0.3°C up to 250 m, which in turn modifies the SLBC. A new drag coefficient based on λP, plan area per unit ground area, is tested. Besides the basic physical characteristics captured by the WRF-BEP-BEM model, the stagnation of wind in the lower level convergence zone is better captured by this approach than by the traditional constant value coefficient.

  13. Ocean Circulation and Dynamics on the West Antarctic Peninsula Continental Shelf

    National Research Council Canada - National Science Library

    Varas, Carlos F

    2007-01-01

    Observations of current velocity, temperature, salinity and pressure from a 2-year moored array deployment and four hydrographic cruises conducted by the United States Southern Ocean GLOBEC program...

  14. Surface circulation and upwelling patterns around Sri Lanka and formation of the Sri Lanka Dome

    Science.gov (United States)

    Pattiaratchi, C. B.; Wijeratne, S.; De Vos, A.

    2014-12-01

    Sri Lanka, a relatively large island (length 440 km; width 225 km), occupies a unique location within the equatorial belt in the northern Indian Ocean with the Arabian Sea on its western side and the Bay of Bengal on its eastern side and experiences bi-annually reversing monsoon winds. This allows for the Island to interact with the seasonally reversing monsoon currents leading to the the island mass effect and enhanced primary production. We will present elements of the dynamics of the surface circulation and coastal upwelling in the waters around Sri Lanka using satellite imagery and numerical simulations using the Regional Ocean Modelling System (ROMS). The model was run for 4 years to examine the inter-annual, seasonal and shorter term (~10 days) variability. The results confirmed the presence of the reversing current system, between the equator and Sri Lanka, in response to the changing wind field: the eastward flowing Southwest Monsoon Current (SMC) during the Southwest (SW) monsoon transporting 11.5 Sv and the westward flowing Northeast Monsoon Current (NMC) transporting 9.5 Sv during the Northeast (NE) monsoon, respectively. A recirculation feature located to the east of Sri Lanka during the SW monsoon, the Sri Lanka Dome, is shown to result from the interaction between the SMC and the Island of Sri Lanka. Along the eastern and western coasts, during both monsoon periods, flow is southward converging along the south coast (see Figure). During the SW monsoon the Island deflects the eastward flowing SMC southward whilst along the east coast the southward flow results from the Sri Lanka Dome recirculation. The major upwelling region, during both monsoon periods, is located along the south coast resulting from southward flow converging along the south coast and subsequent divergence associated with the offshore transport of water(see Figure). Higher surface chlorophyll concentrations were observed during the SW monsoon. The location of the flow convergence and

  15. Rare earth element and neodymium isotope tracing of element input and past ocean circulation. Study from north and south pacific seawater and sediments

    International Nuclear Information System (INIS)

    Froellje, Henning

    2016-01-01

    Hawaiian Islands on coastal waters and the open ocean at Station ALOHA (chapter 2). These results indicate that contributions from volcanic islands (e.g., Hawaii) cannot be disregarded when investigating element budgets in the North Pacific. It is further shown that seasonal variability of Asian dust input most likely has significant influence on the Nd isotope signature of central North Pacific surface waters. New results from measurements of colloidal and truly dissolved REE concentrations indicate for the first time the absence of colloidal-bound REEs in open ocean waters at different depths. Further, a complete water column profile from Station ALOHA allows tracing of North Pacific water masses based on Nd isotopes. This study presents an adjustment of the Nd isotope signature and Nd concentration of North Pacific Deep Water (NPDW), which is considered the radiogenic endmember in the global overturning circulation, and therefore of particular importance for paleoceanographic studies. Moreover, REE patterns demonstrate that vertical processes overprint the REE concentrations in deep and bottom waters, precluding their use to trace water masses in the deep Pacific. Sedimentary Nd isotopes from the last 30,000 years demonstrate the variability in water mass structure in the South Pacific and the evolution of water mass mixing in Circumpolar Deep Water (CDW) during the last glacial-interglacial transition (chapter 3). Combined results from five sediment cores show an expansion of glacial bottom water and its isolation from CDW during the Last Glacial Maximum (LGM) based on differences in the Nd isotope signatures in cores below and above ∝4000 m. Admixture of bottom water into CDW during the early deglaciation is suggested based on the early deglacial decrease of Nd isotope signatures in CDW-bathed cores before the re-strengthening of North Atlantic Deep Water (NADW) advection. This is related to Southern Hemisphere climate and only later during the deglaciation did the

  16. Rare earth element and neodymium isotope tracing of element input and past ocean circulation. Study from north and south pacific seawater and sediments

    Energy Technology Data Exchange (ETDEWEB)

    Froellje, Henning

    2016-08-09

    Hawaiian Islands on coastal waters and the open ocean at Station ALOHA (chapter 2). These results indicate that contributions from volcanic islands (e.g., Hawaii) cannot be disregarded when investigating element budgets in the North Pacific. It is further shown that seasonal variability of Asian dust input most likely has significant influence on the Nd isotope signature of central North Pacific surface waters. New results from measurements of colloidal and truly dissolved REE concentrations indicate for the first time the absence of colloidal-bound REEs in open ocean waters at different depths. Further, a complete water column profile from Station ALOHA allows tracing of North Pacific water masses based on Nd isotopes. This study presents an adjustment of the Nd isotope signature and Nd concentration of North Pacific Deep Water (NPDW), which is considered the radiogenic endmember in the global overturning circulation, and therefore of particular importance for paleoceanographic studies. Moreover, REE patterns demonstrate that vertical processes overprint the REE concentrations in deep and bottom waters, precluding their use to trace water masses in the deep Pacific. Sedimentary Nd isotopes from the last 30,000 years demonstrate the variability in water mass structure in the South Pacific and the evolution of water mass mixing in Circumpolar Deep Water (CDW) during the last glacial-interglacial transition (chapter 3). Combined results from five sediment cores show an expansion of glacial bottom water and its isolation from CDW during the Last Glacial Maximum (LGM) based on differences in the Nd isotope signatures in cores below and above ∝4000 m. Admixture of bottom water into CDW during the early deglaciation is suggested based on the early deglacial decrease of Nd isotope signatures in CDW-bathed cores before the re-strengthening of North Atlantic Deep Water (NADW) advection. This is related to Southern Hemisphere climate and only later during the deglaciation did the

  17. Evaluation of Scaling Approaches for the Oceanic Dissipation Rate of Turbulent Kinetic Energy in the Surface Ocean

    Science.gov (United States)

    Esters, L. T.; Ward, B.; Sutherland, G.; Ten Doeschate, A.; Landwehr, S.; Bell, T. G.; Christensen, K. H.

    2016-02-01

    The air-sea exchange of heat, gas and momentum plays an important role for the Earth's weather and global climate. The exchange processes between ocean and atmosphere are influenced by the prevailing surface ocean dynamics. This surface ocean is a highly turbulent region where there is enhanced production of turbulent kinetic energy (TKE). The dissipation rate of TKE (ɛ) in the surface ocean is an important process for governing the depth of both the mixing and mixed layers, which are important length-scales for many aspects of ocean research. However, there exist very limited observations of ɛ under open ocean conditions and consequently our understanding of how to model the dissipation profile is very limited. The approaches to model profiles of ɛ that exist, differ by orders of magnitude depending on their underlying theoretical assumption and included physical processes. Therefore, scaling ɛ is not straight forward and requires open ocean measurements of ɛ to validate the respective scaling laws. This validated scaling of ɛ, is for example required to produce accurate mixed layer depths in global climate models. Errors in the depth of the ocean surface boundary layer can lead to biases in sea surface temperature. Here, we present open ocean measurements of ɛ from the Air-Sea Interaction Profiler (ASIP) collected during several cruises in different ocean basins. ASIP is an autonomous upwardly rising microstructure profiler allowing undisturbed profiling up to the ocean surface. These direct measurements of ɛ under various types of atmospheric and oceanic conditions along with measurements of atmospheric fluxes and wave conditions allow us to make a unique assessment of several scaling approaches based on wind, wave and buoyancy forcing. This will allow us to best assess the most appropriate ɛ-based parameterisation for air-sea exchange.

  18. On the role of the Agulhas system in ocean circulation and climate

    NARCIS (Netherlands)

    Beal, L.M.; de Ruijter, W.P.M.; Biastoch, A.; Zahn, R.; SCOR/WCRP/IAPSO Working Group 136; Zinke, J.; Ridderinkhof, H.

    2011-01-01

    The Atlantic Ocean receives warm, saline water from the Indo-Pacific Ocean through Agulhas leakage around the southern tip of Africa. Recent findings suggest that Agulhas leakage is a crucial component of the climate system and that ongoing increases in leakage under anthropogenic warming could

  19. An Analysis of Results of a High-Resolution World Ocean Circulation Model.

    Science.gov (United States)

    1988-03-01

    observed sections (as expected in the deep ocean, where a one year robust-diagnostic time constant easily overdrives much slower physical processes...Pacific Oceans by the ACC, as well as less dense AABW formed in the Ross Sea and perhaps also along the Amery Ice Shelf (Pickard and Emery, 1982). This

  20. Models for changes in atmospheric carbon dioxide, ocean geochemistry and circulation during the late Pleistocene

    Digital Repository Service at National Institute of Oceanography (India)

    Naqvi, S.W.A; SenGupta, R.

    in oceanic alkalinity (and hence a decrease in atmospheric CO@d2@@) due to CaCO@d3@@ compensation. A likely mechanism for this rearrangement could be an orbital-forced insolation related increase in biological production in the Southern Ocean. This, coupled...

  1. Rapid seawater circulation through animal burrows in mangrove forests - A significant source of saline groundwater to the tropical coastal ocean

    Science.gov (United States)

    Clark, J. F.; Stieglitz, T. C.; Hancock, G. J.

    2010-12-01

    A common approach for quantifying rates of submarine groundwater discharge (SGD) to the coastal ocean is to use geochemical tracers that are part of the U- and Th-decay chains such as Rn-222 and short lived radium isotopes. These radionuclides are naturally enriched in groundwater relative to seawater and have well understood chemistries within the marine environment. They occur in both fresh (continental) and saline (marine) groundwaters and thus the water source is often ambiguous. Stieglitz (2005, Marine Pollution Bulletin 51, 51-59) has shown that some coastal areas within the Great Barrier Reef (GBR) lagoon (Australia) are enriched in the SGD tracer, Rn-222; he attributed this to four possible processes including the tidal flushing of mangrove forest floors. Here, we present a detailed investigation into the tidal circulation of seawater through animal burrows using Rn-222 and isotopes of radium in the Coral Creek mangrove forest, Hinchinbrook Island, Queensland, Australia. The study was conducted at the end of the dry season in a creek with no freshwater inputs. Significant export of radionuclides and salt from the forest into the creek indicates continuous tidally driven circulation through the burrows. Results demonstrate that the forest sediment is efficiently flushed, with a water flux of about 30 L/m2/ day of forest floor, which is equivalent to flushing about 10% of the total burrow volume per tidal cycle. Annual average circulation flux through mangrove forest floors are of the same order as annual river discharge in the central GBR. However, unlike the river discharge, the tidal circulation should be relatively stable throughout the year. This work documents the importance of animal burrows in maintaining productive sediments in these systems, and illustrates the physical process that supports large exports of organic and inorganic matter from mangrove forests to the coastal zone. It also illustrates the importance of considering saline groundwater

  2. Regional climates in the GISS general circulation model: Surface air temperature

    Science.gov (United States)

    Hewitson, Bruce

    1994-01-01

    One of the more viable research techniques into global climate change for the purpose of understanding the consequent environmental impacts is based on the use of general circulation models (GCMs). However, GCMs are currently unable to reliably predict the regional climate change resulting from global warming, and it is at the regional scale that predictions are required for understanding human and environmental responses. Regional climates in the extratropics are in large part governed by the synoptic-scale circulation and the feasibility of using this interscale relationship is explored to provide a way of moving to grid cell and sub-grid cell scales in the model. The relationships between the daily circulation systems and surface air temperature for points across the continental United States are first developed in a quantitative form using a multivariate index based on principal components analysis (PCA) of the surface circulation. These relationships are then validated by predicting daily temperature using observed circulation and comparing the predicted values with the observed temperatures. The relationships predict surface temperature accurately over the major portion of the country in winter, and for half the country in summer. These relationships are then applied to the surface synoptic circulation of the Goddard Institute for Space Studies (GISS) GCM control run, and a set of surface grid cell temperatures are generated. These temperatures, based on the larger-scale validated circulation, may now be used with greater confidence at the regional scale. The generated temperatures are compared to those of the model and show that the model has regional errors of up to 10 C in individual grid cells.

  3. Does the sensitivity of Southern Ocean circulation depend upon bathymetric details?

    Science.gov (United States)

    Hogg, Andrew McC; Munday, David R

    2014-07-13

    The response of the major ocean currents to changes in wind stress forcing is investigated with a series of idealized, but eddy-permitting, model simulations. Previously, ostensibly similar models have shown considerable variation in the oceanic response to changing wind stress forcing. Here, it is shown that a major reason for these differences in model sensitivity is subtle modification of the idealized bathymetry. The key bathymetric parameter is the extent to which the strong eddy field generated in the circumpolar current can interact with the bottom water formation process. The addition of an embayment, which insulates bottom water formation from meridional eddy fluxes, acts to stabilize the deep ocean density and enhances the sensitivity of the circumpolar current. The degree of interaction between Southern Ocean eddies and Antarctic shelf processes may thereby control the sensitivity of the Southern Ocean to change. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

  4. Influence of various forcings on global climate in historical times using a coupled atmosphere-ocean general circulation model

    DEFF Research Database (Denmark)

    Stendel, Martin; Mogensen, Irene A.; Christensen, Jens H.

    2006-01-01

    The results of a simulation of the climate of the last five centuries with a state-of-the-art coupled atmosphere-ocean general circulation model are presented. The model has been driven with most relevant forcings, both natural (solar variability, volcanic aerosol) and anthropogenic (greenhouse...... gases, sulphate aerosol, land-use changes). In contrast to previous GCM studies, we have taken into account the latitudinal dependence of volcanic aerosol and the changing land cover for a period covering several centuries. We find a clear signature of large volcanic eruptions in the simulated...

  5. Surface ocean carbon dioxide during the Atlantic Meridional Transect (1995-2013); evidence of ocean acidification

    Science.gov (United States)

    Kitidis, Vassilis; Brown, Ian; Hardman-Mountford, Nicholas; Lefèvre, Nathalie

    2017-11-01

    Here we present more than 21,000 observations of carbon dioxide fugacity in air and seawater (fCO2) along the Atlantic Meridional Transect (AMT) programme for the period 1995-2013. Our dataset consists of 11 southbound and 2 northbound cruises in boreal autumn and spring respectively. Our paper is primarily focused on change in the surface-ocean carbonate system during southbound cruises. We used observed fCO2 and total alkalinity (TA), derived from salinity and temperature, to estimate dissolved inorganic carbon (DIC) and pH (total scale). Using this approach, estimated pH was consistent with spectrophotometric measurements carried out on 3 of our cruises. The AMT cruises transect a range of biogeographic provinces where surface Chlorophyll-α spans two orders of magnitude (mesotrophic high latitudes to oligotrophic subtropical gyres). We found that surface Chlorophyll-α was negatively correlated with fCO2, but that the deep chlorophyll maximum was not a controlling variable for fCO2. Our data show clear evidence of ocean acidification across 100° of latitude in the Atlantic Ocean. Over the period 1995-2013 we estimated annual rates of change in: (a) sea surface temperature of 0.01 ± 0.05 °C, (b) seawater fCO2 of 1.44 ± 0.84 μatm, (c) DIC of 0.87 ± 1.02 μmol per kg and (d) pH of -0.0013 ± 0.0009 units. Monte Carlo simulations propagating the respective analytical uncertainties showed that the latter were < 5% of the observed trends. Seawater fCO2 increased at the same rate as atmospheric CO2.

  6. Role of the Bering Strait on the hysteresis of the ocean conveyor belt circulation and glacial climate stability.

    Science.gov (United States)

    Hu, Aixue; Meehl, Gerald A; Han, Weiqing; Timmermann, Axel; Otto-Bliesner, Bette; Liu, Zhengyu; Washington, Warren M; Large, William; Abe-Ouchi, Ayako; Kimoto, Masahide; Lambeck, Kurt; Wu, Bingyi

    2012-04-24

    Abrupt climate transitions, known as Dansgaard-Oeschger and Heinrich events, occurred frequently during the last glacial period, specifically from 80-11 thousand years before present, but were nearly absent during interglacial periods and the early stages of glacial periods, when major ice-sheets were still forming. Here we show, with a fully coupled state-of-the-art climate model, that closing the Bering Strait and preventing its throughflow between the Pacific and Arctic Oceans during the glacial period can lead to the emergence of stronger hysteresis behavior of the ocean conveyor belt circulation to create conditions that are conducive to triggering abrupt climate transitions. Hence, it is argued that even for greenhouse warming, abrupt climate transitions similar to those in the last glacial time are unlikely to occur as the Bering Strait remains open.

  7. Interdecadal variations of the South Asian summer monsoon circulation variability and the associated sea surface temperatures on interannual scales

    Science.gov (United States)

    Gao, Ya; Wang, Huijun; Chen, Dong

    2017-07-01

    We investigate the interannual variability of the South Asian summer monsoon (SASM) circulation, which has experienced a significant interdecadal change since 2000. This change is primarily influenced by sea surface temperatures (SSTs) in the tropical Pacific and North Atlantic oceans. During the pre-2000 period examined in this study (1979-99), the SASM is negatively correlated with eastern Pacific SSTs (the canonical ENSO mode) and positively correlated with the negative phase of the North Atlantic SST tripole (NAT). During the post-2000 period (2000-14), the SASM is negatively correlated with central Pacific SSTs and positively correlated with the positive phase of the NAT pattern. The associated Pacific SSTs change from the eastern to central region, leading to the rising (subsiding) branch of the Walker circulation moving westwards to the Maritime Continent in the latter period, which can impact the interannual variability of the SASM through modulating the wind field in the troposphere. In addition to Pacific SSTs, the NAT SSTs can propagate energy from the North Atlantic to the South Asian High (SAH) region through the wave activity flux, and then further impact the SASM via the SAH. Because the SASM is intimately related with precipitation over the Asian region, we briefly discuss the features of the precipitation patterns associated with the SASM during the two periods. The westward shifting Walker circulation leads to the shrinking and weakened anomalous westerlies of the SASM in the lower level, inducing the Maritime Continent rainfall location to move westwards and more moisture to arrive in southern China from the Pacific Ocean in the latter period.

  8. Distribution of benthic foraminifers (>125 um) in the surface sediments of the Arctic Ocean

    Science.gov (United States)

    Osterman, Lisa E.; Poore, Richard Z.; Foley, Kevin M.

    1999-01-01

    Census data on benthic foraminifers (>125 ?m) in surface sediment samples from 49 box cores are used to define four depth-controlled biofacies, which will aid in the paleoceanographic reconstruction of the Arctic Ocean. The shelf biofacies contains a mix of shallow-water calcareous and agglutinated species from the continental shelves of the Beaufort and Chukchi Seas and reflects the variable sedimentologic and oceanic conditions of the Arctic shelves. The intermediate-depth calcareous biofacies, found between 500 and 1,100 meters water depth (mwd), contains abundant Cassidulina teretis , presumably indicating the influence of Atlantic-derived water at this depth. In water depths between 1,100 and 3,500 m, a deepwater calcareous biofacies contains abundant Oridorsalis umbonatus . Below 3,500 mwd, the deepwater mixed calcareous/agglutinated biofacies of the Canada, Makarov, and Eurasian Basins reflects a combination of low productivity, dissolution, and sediment transport. Two other benthic foraminiferal species show specific environmental preferences. Fontbotia wuellerstorfi has a depth distribution between 900 and 3,500 mwd, but maximum abundance occurs in the region of the Mendeleyev Ridge. The elevated abundance of F. wuellerstorfi may be related to increased food supply carried by a branch of Atlantic water that crosses the Lomonosov Ridge near the Russian Continental Shelf. Triloculina frigida is recognized to be a species preferring lower slope sediments commonly disturbed by turbidites and bottom currents. INTRODUCTION At present, our understanding of the Arctic Ocean lags behind our understanding of other oceans, and fundamental questions still exist about its role in and response to global climate change. The Arctic Ocean is particularly sensitive to climatic fluctuations because small changes in the amounts of sea-ice cover can alter global albedo and thermohaline circulation (Aagaard and Carmack, 1994). Numerous questions still exist regarding the nature

  9. A new technique for the estimation of sea surface salinity in the tropical Indian Ocean from OLR

    Digital Repository Service at National Institute of Oceanography (India)

    Murty, V.S.N.; Subrahmanyam, B.; Tilvi, V.; O'Brien, J.J.

    occupied during World Ocean Circulation Experiment (WOCE) and also other sections. The SSS differences bring out clearly the impact of the strong 1997-1998 El Nino on the rainfall in the southeastern Indian Ocean and the eastern equatorial region...

  10. Evolution of ocean-induced ice melt beneath Zachariæ Isstrøm, Northeast Greenland combining observations and an ocean general circulation model from 1978 to present

    Science.gov (United States)

    Cai, C.; Rignot, E. J.; Menemenlis, D.; Millan, R.; Bjørk, A. A.; Khan, S. A.; Charolais, A.

    2017-12-01

    Zachariæ Isstrøm, a major ice stream in northeast Greenland, lost a large fraction of its ice shelf during the last decade. We study the evolution of subaqueous melting of its floating section from 1978 to present. The ice shelf melt rate depends on thermal forcing from warm, salty, subsurface ocean waters of Atlantic origin (AW), the mixing of AW with fresh, buoyant subglacial discharge at the calving margin, and the shape of the sub-ice-shelf cavity. Subglacial discharge doubled as a result of enhanced ice sheet runoff caused by warmer air temperatures. Ocean thermal forcing has increased due to enhanced advection of AW. Using an Eulerian method, MEaSUREs ice velocity, Operation IceBridge (OIB) ice thickness, and RACMO2.3 surface balance data, we evaluate the ice shelf melt rate in 1978, 1999 and 2010. The melt rate doubled from 1999 to 2010. Using a Lagrangian method with World View imagery, we map the melt rate in detail from 2011 to 2016. We compare the results with 2D simulations from the Massachusetts Institute of Technology general circulation model (MITgcm), at a high spatial resolution (20-m horizontal and 40-m vertical grid spacing), using OIB ice thickness and sub-ice-shelf cavity for years 1978, 1996, 2010 and 2011, combined with in-situ ocean temperature/salinity data from Ocean Melting Greenland (OMG) 2017. We find that winter melt rates are 2 3 times smaller than summer rates and melt rates increase by one order magnitude during the transition from ice shelf termination to near-vertical calving wall termination. As the last remaining bits of floating ice shelf disappear, ice-ocean interaction will therefore play an increasing role in driving the glacier retreat into its marine-based basin. This work was performed under a contract with NASA Cryosphere Program at UC Irvine and Caltech's Jet Propulsion Laboratory.

  11. Sea surface temperature and salinity from the Global Ocean Surface Underway Data (GOSUD) from 1980-01-03 to present

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This collection contains the Global Ocean Surface Underway Data (GOSUD) from 1980-01-03 to present as submitted to NOAA/NCEI. The data includes information about sea...

  12. Response to Comment on "The Atlantic Multidecadal Oscillation without a role for ocean circulation".

    Science.gov (United States)

    Clement, Amy; Cane, Mark A; Murphy, Lisa N; Bellomo, Katinka; Mauritsen, Thorsten; Stevens, Bjorn

    2016-06-24

    Zhang et al interpret the mixed-layer energy budget in models as showing that "ocean dynamics play a central role in the AMO." Here, we show that their diagnostics cannot reveal the causes of the Atlantic Multidecadal Oscillation (AMO) and that their results can be explained with minimal ocean influence. Hence, we reaffirm our findings that the AMO in models can be understood primarily as the upper-ocean thermal response to stochastic atmospheric forcing. Copyright © 2016, American Association for the Advancement of Science.

  13. Adjustments of a global Finite-Element Sea Ice Ocean Model configuration to improve the general ocean circulation in the North Pacific and its marginal seas.

    Science.gov (United States)

    Scholz, Patrick; Lohmann, Gerrit

    2017-04-01

    The sub-Arctic oceans like the Sea of Okhotsk, the Bering Sea, the Labrador Sea or the Greenland- Irminger-Norwegian (GIN) Sea react particularly sensitive to global climate changes and have the potential to reversely regulate climate change by CO2 uptake in the other areas of the world. So far, the natural processes in the Arctic and Subarctic system, especially over the Pacific realm, remain poorly understood in terms of numerical modeling. As such, in this study we focus on the North Pacific and its adjacent marginal seas (e.g. the Sea of Okhotsk, the Bering Sea and the Sea of Japan), which have nowadays a significant role in the climate system of the Northwest Pacific by influencing the atmospheric and oceanic circulation as well as the hydrology of the Pacific water masses. The Sea of Okhotsk, in particular, is characterized by a highly dynamical sea-ice coverage, where, in autumn and winter, due to massive sea ice formation and brine rejection, the Sea of Okhotsk Intermediate Water (SOIW) is formed which contributes to the mid-depth (500-1000m) water layer of the North Pacific known as newly formed North Pacific Intermediate Water (NPIW). By employing a Finite-Element Sea-Ice Ocean Model (FESOM), in a global configuration, but with high resolution over the marginal seas of the Northwest Pacific Ocean ( 7 km), we tested different meshes and forcing improvements to correct the general ocean circulation in the North Pacific realm towards a more realistic pattern. By using different forcing data (e.g. CORE2, ERA-40/interim, CCMP-correction), adapting the mesh resolutions in the tropical and subtropical North Pacific and changing the bathymetry over important inflow straits (e.g. Amukta Passage, Kruzenstern Strait), we show that the better results are obtained (when compared with observational data) via a combination of CCMP corrected COREv2 forcing with increased resolution in the pathway of the Kuroshio Extension Current and Northern Equatorial Current.

  14. Preliminary assessment of the accuracy and precision of TOPEX/POSEIDON altimeter data with respect to the large-scale ocean circulation

    Science.gov (United States)

    Wunsch, Carl; Stammer, Detlef

    1994-01-01

    TOPEX/POSEIDON sea surface height measurements are examined for quantitative consistency with known elements of the oceanic general circulation and its variability. Project-provided corrections were accepted but are at tested as part of the overall results. The ocean was treated as static over each 10-day repeat cycle and maps constructed of the absolute sea surface topography from simple averages in 2 deg x 2 deg bins. A hybrid geoid model formed from a combination of the recent Joint Gravity Model-2 and the project-provided Ohio State University geoid was used to estimate the absolute topography in each 10-day period. Results are examined in terms of the annual average, seasonal average, seasonal variations, and variations near the repeat period. Conclusion are as follows: the orbit error is now difficult to observe, having been reduced to a level at or below the level of other error sources; the geoid dominates the error budget of the estimates of the absolute topography; the estimated seasonal cycle is consistent with prior estimates; shorter-period variability is dominated on the largest scales by an oscillation near 50 days in spherical harmonics Y(sup m)(sub 1)(theta, lambda) with an amplitude near 10 cm, close to the simplest alias of the M(sub 2) tide. This spectral peak and others visible in the periodograms support the hypothesis that the largest remaining time-dependent errors lie in the tidal models. Though discrepancies attribute to the geoid are within the formal uncertainties of the good estimates, removal of them is urgent for circulation studies. Current gross accuracy of the TOPEX/POSEIDON mission is in the range of 5-10 cm, distributed overbroad band of frequencies and wavenumbers. In finite bands, accuracies approach the 1-cm level, and expected improvements arising from extended mission duration should reduce these numbers by nearly an order of magnitude.

  15. Annual cycle of the upper-ocean circulation and properties in the ...

    African Journals Online (AJOL)

    East Madagascar Current (NEMC) throughout the year with volume transports peaking in June through July in the model forced by NCEP reanalysis. The variability of the volume transport, ocean currents, temperature and salinity to the north of ...

  16. Various approaches to the modelling of large scale 3-dimensional circulation in the Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Shaji, C.; Bahulayan, N.; Rao, A.D.; Dube, S.K.

    In this paper, the three different approaches to the modelling of large scale 3-dimensional flow in the ocean such as the diagnostic, semi-diagnostic (adaptation) and the prognostic are discussed in detail. Three-dimensional solutions are obtained...

  17. Plankton blooms, ocean circulation and the European slope current: Response to weather and climate in the Bay of Biscay and W English Channel (NE Atlantic)

    Science.gov (United States)

    Pingree, Robin D.; Garcia-Soto, Carlos

    2014-08-01

    The flow of upper-layer surface water and circulation for the Bay of Biscay, continental slope and in the wider region of the NE Atlantic is presented, as well as the seasonality of flow and internal tides. The marine plankton environments of Biscay Ocean, Biscay Eddies, Biscay Slope and Biscay Shelf are defined. The Shelf region (Armorican and Celtic) is further divided into Stratified Shelf, Frontal and Tidally Mixed. Seasonal distributions of chlorophyll a are given for all environment from in situ measurements and remote sensing data. Mixing and stabilisation of surface water in the euphotic layer for the start of the spring bloom using in situ profiling measurements is examined. Some regional responses for the slope current, dinoflagellate blooms and interannual variations in spring diatom numbers with respect to weather and climate in the Bay of Biscay and around the British Isles are suggested and discussed. An example of the Eastern European Ocean Margin continental slope response to winter weather (sea level atmospheric pressure forcing) resulting in warm winter water in the southern Bay of Biscay (Navidad, with eddy production) and off the Shetland continental slopes (the warm-water supply route to the Arctic) is given from the slope climate observation series.

  18. An assessment of Antarctic Circumpolar Current and Southern Ocean meridional overturning circulation during 1958-2007 in a suite of interannual CORE-II simulations

    Science.gov (United States)

    Farneti, Riccardo; Downes, Stephanie M.; Griffies, Stephen M.; Marsland, Simon J.; Behrens, Erik; Bentsen, Mats; Bi, Daohua; Biastoch, Arne; Böning, Claus; Bozec, Alexandra; Canuto, Vittorio M.; Chassignet, Eric; Danabasoglu, Gokhan; Danilov, Sergey; Diansky, Nikolay; Drange, Helge; Fogli, Pier Giuseppe; Gusev, Anatoly; Hallberg, Robert W.; Howard, Armando; Ilicak, Mehmet; Jung, Thomas; Kelley, Maxwell; Large, William G.; Leboissetier, Anthony; Long, Matthew; Lu, Jianhua; Masina, Simona; Mishra, Akhilesh; Navarra, Antonio; George Nurser, A. J.; Patara, Lavinia; Samuels, Bonita L.; Sidorenko, Dmitry; Tsujino, Hiroyuki; Uotila, Petteri; Wang, Qiang; Yeager, Steve G.

    2015-09-01

    In the framework of the second phase of the Coordinated Ocean-ice Reference Experiments (CORE-II), we present an analysis of the representation of the Antarctic Circumpolar Current (ACC) and Southern Ocean meridional overturning circulation (MOC) in a suite of seventeen global ocean-sea ice models. We focus on the mean, variability and trends of both the ACC and MOC over the 1958-2007 period, and discuss their relationship with the surface forcing. We aim to quantify the degree of eddy saturation and eddy compensation in the models participating in CORE-II, and compare our results with available observations, previous fine-resolution numerical studies and theoretical constraints. Most models show weak ACC transport sensitivity to changes in forcing during the past five decades, and they can be considered to be in an eddy saturated regime. Larger contrasts arise when considering MOC trends, with a majority of models exhibiting significant strengthening of the MOC during the late 20th and early 21st century. Only a few models show a relatively small sensitivity to forcing changes, responding with an intensified eddy-induced circulation that provides some degree of eddy compensation, while still showing considerable decadal trends. Both ACC and MOC interannual variabilities are largely controlled by the Southern Annular Mode (SAM). Based on these results, models are clustered into two groups. Models with constant or two-dimensional (horizontal) specification of the eddy-induced advection coefficient κ show larger ocean interior decadal trends, larger ACC transport decadal trends and no eddy compensation in the MOC. Eddy-permitting models or models with a three-dimensional time varying κ show smaller changes in isopycnal slopes and associated ACC trends, and partial eddy compensation. As previously argued, a constant in time or space κ is responsible for a poor representation of mesoscale eddy effects and cannot properly simulate the sensitivity of the ACC and MOC

  19. Simulating pathways of subsurface oil in the Faroe-Shetland Channel using an ocean general circulation model.

    Science.gov (United States)

    Main, C E; Yool, A; Holliday, N P; Popova, E E; Jones, D O B; Ruhl, H A

    2017-01-15

    Little is known about the fate of subsurface hydrocarbon plumes from deep-sea oil well blowouts and their effects on processes and communities. As deepwater drilling expands in the Faroe-Shetland Channel (FSC), oil well blowouts are a possibility, and the unusual ocean circulation of this region presents challenges to understanding possible subsurface oil pathways in the event of a spill. Here, an ocean general circulation model was used with a particle tracking algorithm to assess temporal variability of the oil-plume distribution from a deep-sea oil well blowout in the FSC. The drift of particles was first tracked for one year following release. Then, ambient model temperatures were used to simulate temperature-mediated biodegradation, truncating the trajectories of particles accordingly. Release depth of the modeled subsurface plumes affected both their direction of transport and distance travelled from their release location, and there was considerable interannual variability in transport. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

  20. Predicting East African spring droughts using Pacific and Indian Ocean sea surface temperature indices

    Science.gov (United States)

    Funk, C.; Hoell, A.; Shukla, S.; Bladé, I.; Liebmann, B.; Roberts, J. B.; Robertson, F. R.; Husak, G.

    2014-12-01

    In eastern East Africa (the southern Ethiopia, eastern Kenya and southern Somalia region), poor boreal spring (long wet season) rains in 1999, 2000, 2004, 2007, 2008, 2009, and 2011 contributed to severe food insecurity and high levels of malnutrition. Predicting rainfall deficits in this region on seasonal and decadal time frames can help decision makers implement disaster risk reduction measures while guiding climate-smart adaptation and agricultural development. Building on recent research that links more frequent East African droughts to a stronger Walker circulation, resulting from warming in the Indo-Pacific warm pool and an increased east-to-west sea surface temperature (SST) gradient in the western Pacific, we show that the two dominant modes of East African boreal spring rainfall variability are tied to SST fluctuations in the western central Pacific and central Indian Ocean, respectively. Variations in these two rainfall modes can thus be predicted using two SST indices - the western Pacific gradient (WPG) and central Indian Ocean index (CIO), with our statistical forecasts exhibiting reasonable cross-validated skill (rcv ≈ 0.6). In contrast, the current generation of coupled forecast models show no skill during the long rains. Our SST indices also appear to capture most of the major recent drought events such as 2000, 2009 and 2011. Predictions based on these simple indices can be used to support regional forecasting efforts and land surface data assimilations to help inform early warning and guide climate outlooks.

  1. A three-dimensional mixed finite-difference Galerkin function model for the oceanic circulation in the Yellow Sea and the East China Sea

    Science.gov (United States)

    Lee, Ho Jin; Jung, Kyung Tae; Foreman, M. G. G.; Chung, Jong Yul

    2000-06-01

    A three-dimensional mixed-type model which uses a finite-difference approximation in the horizontal plane and function expansions in the vertical direction is developed for the simulation of oceanic flows in the Yellow Sea (YS) and the East China Sea (ECS). The model assumes a hydrostatic balance and solves the three-dimensional, non-linear free-surface, primitive equations for homogeneous fluids. To represent the velocity structure of oceanic currents, a set of linear interpolation functions is used from the sea surface to a depth of 300 m, characterizing the thickness of the oceanic flow, and a similarity function of the exponential type underneath. The vertical eddy viscosity takes a flow-related form in which the strong mixing due to the M 2 tide is incorporated as the background eddy viscosity. A radiation condition developed by Flather (1976. Memories de la Societe Royale des Science de Liege 10, 141-164) is employed along the open boundaries. A series of numerical experiments have been carried out using linear and quadratic bottom friction formulae. The coefficient of linear bottom friction was given by Hunter's formula (1975. Estarine and Coastal Marine Science 3, 473-475), taking into account that the oceanic flows in shelf seas are of secondary importance. The quadratic bottom friction coefficient was taken as 0.0025, the same value used in previous numerical experiments of oceanic circulation in the study area (for example, Lee, 1996. Ph.D. Thesis, Kyushu University). Both results are quite similar over the outer shelf region (Okinawa Trough and the shelf break west of Kyushu) in which tidal effects on the bottom friction are relatively small, and are qualitatively in good agreement with recent observations by ARGOS buoy tracking ( Lie and Cho, 1997. The Journal of the Korean Society of Oceanography 32, 1-7; Lie et al., 1998. Journal of Geophysical Research 103, 2963-2976). A clear difference was, however, found in the distribution of sea surface

  2. Physical Retracking of Cryosat-2 Low Resolution Mode data for ocean surface height and gravity field estimation in open ocean

    Science.gov (United States)

    Jain, Maulik; Baltazar Andersen, Ole; Dall, Jorgen; Stenseng, Lars

    2014-05-01

    Cryosat-2 Low Resolution Mode (LRM) altimetric data is processed to determine precise ocean surface heights and gravity fields in open ocean. These ocean surface heights are corrected using various geophysical corrections available. The along track variation of the ocean surface height anomaly is used to determine the gravity field. The quality of this gravity field estimation is dependent on the precision in the ocean surface height anomaly. Thus a three/two parameter based physical model based on an error function is used, and the Cryosat-2 LRM waveforms are fit to this model. The fitting routines which employ the Levenberg Marquadt technique generate estimated values of retracked epochs which are used to compute the ocean surface heights. A two step processing system made up of sequential 3 parameter (amplitude, rise time, retracked epoch) and 2 parameter (amplitude, retracked epoch) fitting models are used to determine precise ocean surface heights. The quality of the processing system is judged by evaluating the standard deviation of the ocean surface height anomaly obtained after all corrections and the mean sea surface/geoid are removed. The lower the value of the standard deviation of the ocean surface height anomaly, the better the quality of processing is. Hence, different processing schemes are considered and evaluated in order to conclude towards the best retracking procedure which would eventually result in high accuracy gravity field estimations. Also, the quality on the precision is judged by analyzing the standard deviation in the gravity field anomaly. The gravity field anomaly is obtained by subtracting the retracked gravity field with the marine gravity field available. A lower value of the standard deviation in the gravity field anomaly indicates a more precise retracking algorithm. Using the two retracker performance evaluation strategies, namely the ocean surface height anomaly and the gravity field anomaly, it was concluded that the three

  3. Error estimates for CCMP ocean surface wind data sets

    Science.gov (United States)

    Atlas, R. M.; Hoffman, R. N.; Ardizzone, J.; Leidner, S.; Jusem, J.; Smith, D. K.; Gombos, D.

    2011-12-01

    The cross-calibrated, multi-platform (CCMP) ocean surface wind data sets are now available at the Physical Oceanography Distributed Active Archive Center from July 1987 through December 2010. These data support wide-ranging air-sea research and applications. The main Level 3.0 data set has global ocean coverage (within 78S-78N) with 25-kilometer resolution every 6 hours. An enhanced variational analysis method (VAM) quality controls and optimally combines multiple input data sources to create the Level 3.0 data set. Data included are all available RSS DISCOVER wind observations, in situ buoys and ships, and ECMWF analyses. The VAM is set up to use the ECMWF analyses to fill in areas of no data and to provide an initial estimate of wind direction. As described in an article in the Feb. 2011 BAMS, when compared to conventional analyses and reanalyses, the CCMP winds are significantly different in some synoptic cases, result in different storm statistics, and provide enhanced high-spatial resolution time averages of ocean surface wind. We plan enhancements to produce estimated uncertainties for the CCMP data. We will apply the method of Desroziers et al. for the diagnosis of error statistics in observation space to the VAM O-B, O-A, and B-A increments. To isolate particular error statistics we will stratify the results by which individual instruments were used to create the increments. Then we will use cross-validation studies to estimate other error statistics. For example, comparisons in regions of overlap for VAM analyses based on SSMI and QuikSCAT separately and together will enable estimating the VAM directional error when using SSMI alone. Level 3.0 error estimates will enable construction of error estimates for the time averaged data sets.

  4. Optimal nonlinear excitation of decadal variability of the North Atlantic thermohaline circulation

    NARCIS (Netherlands)

    Ziqing, Z.; Mu, M.; Dijkstra, H.A.

    2013-01-01

    Nonlinear development of salinity perturbations in the Atlantic thermohaline circulation (THC) is investigated with a three-dimensional ocean circulation model, using the conditional nonlinear optimal perturbation method. The results show two types of optimal initial perturbations of sea surface

  5. Sea level: measuring the bounding surfaces of the ocean.

    Science.gov (United States)

    Tamisiea, Mark E; Hughes, Chris W; Williams, Simon D P; Bingley, Richard M

    2014-09-28

    The practical need to understand sea level along the coasts, such as for safe navigation given the spatially variable tides, has resulted in tide gauge observations having the distinction of being some of the longest instrumental ocean records. Archives of these records, along with geological constraints, have allowed us to identify the century-scale rise in global sea level. Additional data sources, particularly satellite altimetry missions, have helped us to better identify the rates and causes of sea-level rise and the mechanisms leading to spatial variability in the observed rates. Analysis of all of the data reveals the need for long-term and stable observation systems to assess accurately the regional changes as well as to improve our ability to estimate future changes in sea level. While information from many scientific disciplines is needed to understand sea-level change, this review focuses on contributions from geodesy and the role of the ocean's bounding surfaces: the sea surface and the Earth's crust. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

  6. Sea level: measuring the bounding surfaces of the ocean

    Science.gov (United States)

    Tamisiea, Mark E.; Hughes, Chris W.; Williams, Simon D. P.; Bingley, Richard M.

    2014-01-01

    The practical need to understand sea level along the coasts, such as for safe navigation given the spatially variable tides, has resulted in tide gauge observations having the distinction of being some of the longest instrumental ocean records. Archives of these records, along with geological constraints, have allowed us to identify the century-scale rise in global sea level. Additional data sources, particularly satellite altimetry missions, have helped us to better identify the rates and causes of sea-level rise and the mechanisms leading to spatial variability in the observed rates. Analysis of all of the data reveals the need for long-term and stable observation systems to assess accurately the regional changes as well as to improve our ability to estimate future changes in sea level. While information from many scientific disciplines is needed to understand sea-level change, this review focuses on contributions from geodesy and the role of the ocean's bounding surfaces: the sea surface and the Earth's crust. PMID:25157196

  7. Surface Ocean CO2 Atlas Database Version 5 (SOCATv5) (NCEI Accession 0163180)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Surface Ocean CO2 Atlas (SOCAT, www.socat.info) is a synthesis activity by the international marine carbon research community and has more than 100 contributors...

  8. Ocean Surface Topography Mission (OSTM) /Jason-3: Auxiliary Files, 2015- (NODC Accession 0122597)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Jason-3 is the fourth mission in U.S.-European series of satellite missions that measure the height of the ocean surface. Scheduled to launch in 2015, the mission...

  9. Ocean Surface Topography Mission (OSTM) /Jason-3: Orbital Information, 2015- (NODC Accession 0122598)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Jason-3 is the fourth mission in U.S.-European series of satellite missions that measure the height of the ocean surface. Scheduled to launch in 2015, the mission...

  10. Ocean Surface Topography Mission (OSTM) /Jason-3: Ancillary Files, 2015- (NCEI Accession 0122596)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Jason-3 is the fourth mission in U.S.-European series of satellite missions that measure the height of the ocean surface. Scheduled to launch in 2015, the mission...

  11. Ocean Surface Topography Mission (OSTM) /Jason-3: Telemetry, 2015- (NODC Accession 0122599)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Jason-3 is the fourth mission in U.S.-European series of satellite missions that measure the height of the ocean surface. Scheduled to launch in 2015, the mission...

  12. Effect of the tropical Pacific and Indian Ocean warming since the late 1970s on wintertime Northern Hemispheric atmospheric circulation and East Asian climate interdecadal changes

    Science.gov (United States)

    Chu, Cuijiao; Yang, Xiu-Qun; Sun, Xuguang; Yang, Dejian; Jiang, Yiquan; Feng, Tao; Liang, Jin

    2018-04-01

    Observation reveals that the tropical Pacific-Indian Ocean (TPIO) has experienced a pronounced interdecadal warming since the end of the 1970s. Meanwhile, the wintertime midlatitude Northern Hemispheric atmospheric circulation and East Asian climate have also undergone substantial interdecadal changes. The effect of the TPIO warming on these interdecadal changes are identified by a suite of AMIP-type atmospheric general circulation model experiments in which the model is integrated from September 1948 to December 1999 with prescribed historical, observed realistic sea surface temperature (SST) in a specific region and climatological SST elsewhere. Results show that the TPIO warming reproduces quite well the observed Northern Hemispheric wintertime interdecadal changes, suggesting that these interdecadal changes primarily originate from the TPIO warming. However, each sub-region of TPIO has its own distinct contribution. Comparatively, the tropical central-eastern Pacific (TCEP) and tropical western Pacific (TWP) warming makes dominant contributions to the observed positive-phase PNA-like interdecadal anomaly over the North Pacific sector, while the tropical Indian Ocean (TIO) warming tends to cancel these contributions. Meanwhile, the TIO and TWP warming makes dominant contributions to the observed positive NAO-like interdecadal anomaly over the North Atlantic sector as well as the interdecadal anomalies over the Eurasian sector, although the TWP warming's contribution is relatively small. These remote responses are directly attributed to the TPIO warming-induced tropical convection, rainfall and diabatic heating increases, in which the TIO warming has the most significant effect. Moreover, the TPIO warming excites a Gill-type pattern anomaly over the tropical western Pacific, with a low-level anticyclonic circulation anomaly over the Philippine Sea. Of three sub-regions, the TIO warming dominates such a pattern, although the TWP warming tends to cancel this effect

  13. Molecular biogeochemical provinces in the Atlantic Surface Ocean

    Science.gov (United States)

    Koch, B. P.; Flerus, R.; Schmitt-Kopplin, P.; Lechtenfeld, O. J.; Bracher, A.; Cooper, W.; Frka, S.; Gašparović, B.; Gonsior, M.; Hertkorn, N.; Jaffe, R.; Jenkins, A.; Kuss, J.; Lara, R. J.; Lucio, M.; McCallister, S. L.; Neogi, S. B.; Pohl, C.; Roettgers, R.; Rohardt, G.; Schmitt, B. B.; Stuart, A.; Theis, A.; Ying, W.; Witt, M.; Xie, Z.; Yamashita, Y.; Zhang, L.; Zhu, Z. Y.; Kattner, G.

    2010-12-01

    One of the most important aspects to understand marine organic carbon fluxes is to resolve the molecular mechanisms which convert fresh, labile biomolecules into semi-labile and refractory dissolved and particulate organic compounds in the ocean. In this interdisciplinary project, which was performed on a cruise with RV Polarstern, we carried out a detailed molecular characterisation of dissolved organic matter (DOM) on a North-South transect in the Atlantic surface ocean in order to relate the data to different biological, climatic, oceanographic, and meteorological regimes as well as to terrestrial input from riverine and atmospheric sources. Our goal was to achieve a high resolution data set for the biogeochemical characterisation of the sources and reactivity of DOM. We applied ultrahigh resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS), nutrient, trace element, amino acid, and lipid analyses and other biogeochemical measurements for 220 samples from the upper water column (0-200m) and eight deep profiles. Various spectroscopic techniques were applied continuously in a constant sample water flow supplied by a fish system and the moon pool. Radiocarbon dating enabled assessing DOC residence time. Bacterial abundance and production provided a metabolic context for the DOM characterization work and pCO2 concentrations. Combining molecular organic techniques and inductively coupled plasma mass spectrometry (ICP-MS) established an important link between organic and inorganic biogeochemical studies. Multivariate statistics, primarily based on FT-ICR-MS data for 220 samples, allowed identifying geographical clusters which matched ecological provinces proposed previously by Longhurst (2007). Our study demonstrated that marine DOM carries molecular information reflecting the “history” of ocean water masses. This information can be used to define molecular biogeochemical provinces and to improve our understanding of element fluxes in

  14. Forcing mechanisms of the Bay of Bengal circulation

    Digital Repository Service at National Institute of Oceanography (India)

    Vinayachandran, P.N.; Shetye, S.R.; Sengupta, D.; Gadgil, S.

    A state-of-the-art ocean general circulation model, set up for the North Indian Ocean and driven by climatological wind stress simulates most of the observed features of the near-surface circulation of the Bay of Bengal. The prominent features...

  15. Dynamic Downscaling of the Impact of Climate Change on the Ocean Circulation in the Galápagos Archipelago

    Directory of Open Access Journals (Sweden)

    Yanyun Liu

    2013-01-01

    Full Text Available The regional impact of global climate change on the ocean circulation around the Galápagos Archipelago is studied using the Hybrid Coordinate Ocean Model (HYCOM configured for a four-level nested domain system. The modeling system is validated and calibrated using daily atmospheric forcing derived from the NCEP/NCAR reanalysis dataset from 1951 to 2007. The potential impact of future anthropogenic global warming (AGW in the Galápagos region is examined using the calibrated HYCOM with forcing derived from the IPCC-AR4 climate model. Results show that although the oceanic variability in the entire Galápagos region is significantly affected by global climate change, the degree of such effects is inhomogeneous across the region. The upwelling region to the west of the Isabella Island shows relatively slower warming trends compared to the eastern Galápagos region. Diagnostic analysis suggests that the variability in the western Galápagos upwelling region is affected mainly by equatorial undercurrent (EUC and Panama currents, while the central/east Galápagos is predominantly affected by both Peru and EUC currents. The inhomogeneous responses in different regions of the Galápagos Archipelago to future AGW can be explained by the incoherent changes of the various current systems in the Galápagos region as a result of global climate change.

  16. Closing the Seasonal Ocean Surface Temperature Balance in the Eastern Tropical Oceans from Remote Sensing and Model Reanalyses

    Science.gov (United States)

    Roberts, J. Brent; Clayson, C. A.

    2012-01-01

    Residual forcing necessary to close the MLTB on seasonal time scales are largest in regions of strongest surface heat flux forcing. Identifying the dominant source of error - surface heat flux error, mixed layer depth estimation, ocean dynamical forcing - remains a challenge in the eastern tropical oceans where ocean processes are very active. Improved sub-surface observations are necessary to better constrain errors. 1. Mixed layer depth evolution is critical to the seasonal evolution of mixed layer temperatures. It determines the inertia of the mixed layer, and scales the sensitivity of the MLTB to errors in surface heat flux and ocean dynamical forcing. This role produces timing impacts for errors in SST prediction. 2. Errors in the MLTB are larger than the historical 10Wm-2 target accuracy. In some regions, a larger accuracy can be tolerated if the goal is to resolve the seasonal SST cycle.

  17. The integration of remote sensing data into global weather prediction, wave forecasting, and ocean circulation computer based systems

    Science.gov (United States)

    Pierson, W. J., Jr.

    1970-01-01

    Data from infrared imaging systems and satellite infrared spectrometer (SIRS) for determining sea surface temperature and the atmospheric structure in cloudless areas over the oceans are discussed. Although some interpretations differ, it is clear that simultaneous measurements of radar sea return and passive microwave temperature will provide estimates of the wind speed, and perhaps wind direction, over the oceans, especially in cloudless areas, for a wide range of wind speeds. The problem of integrating the data that would be obtained by a spacecraft, especially one with a combination radar-radiometer, into global analysis procedures for meteorological, wave, and oceanographic predictions is described.

  18. Application of SMAP Data for Ocean Surface Remote Sensing

    Science.gov (United States)

    Fore, A.; Yueh, S. H.; Tang, W.; Stiles, B. W.; Hayashi, A.

    2017-12-01

    The Soil Moisture Active Passive (SMAP) mission was launched January 31st, 2015. It is designed to measure the soil moisture over land using a combined active / passive L-band system. Due to the Aquarius mission, L-band model functions for ocean winds and salinity are mature and are directly applicable to the SMAP mission. In contrast to Aquarius, the higher resolution and scanning geometry of SMAP allow for wide-swath ocean winds and salinities to be retrieved. In this talk we present the SMAP Sea Surface Salinity (SSS) and extreme winds dataset and its performance. First we discuss the heritage of SMAP SSS algorithms, showing that SMAP and Aquarius show excellent agreement in the ocean surface roughness correction. Then, we give an overview of some newly developed algorithms that are only relevant to the SMAP system; a new galaxy correction and land correction enabling SSS retrievals up to 40 km from coast. We discuss recent improvements to the SMAP data processing for version 4.0. Next we compare the performance of the SMAP SSS to in-situ salinity measurements obtained from ARGO floats, tropical moored buoys, and ship-based data. SMAP SSS has accuracy of 0.2 PSU on a monthly basis compared to ARGO gridded data in tropics and mid-latitudes. In tropical oceans, time series comparison of salinity measured at 1 m depth by moored buoys indicates SMAP can track large salinity changes within a month. Synergetic analysis of SMAP, SMOS, and Argo data allows us to identify and exclude erroneous buoy data from assessment of SMAP SSS. The resulting SMAP-buoy matchup analysis gives a mean standard deviation (STD) of 0.22 PSU and correlation of 0.73 on weekly scale; at monthly scale the mean STD decreased to 0.17 PSU and the correlation increased to 0.8. In addition to SSS, SMAP provides a view into tropical cyclones having much higher sensitivity than traditional scatterometers. We validate the high-winds using collocations with SFMR during tropical cyclones as well as

  19. The surface circulation in the eastern basin of the Mediterranean Sea

    Science.gov (United States)

    Hamad, N.; Millot, C.; Taupier-Letage, I.

    2003-04-01

    "Cilician Current" and the "Asia Minor Current", which clearly appear to be the continuity of the overall alongslope flow, meander and generate eddies of medium size. Then, this current can either flow into the Aegean, especially in winter, or soutwestwards, up to feeding Ierapetra. North of Crete, most eddies propagate eastwards. In the northern Ionian, the surface flow towards the Adriatic displays a marked seasonal variability, being especially intense in winter. In the Adriatic, it clearly surrounds the dense water formation zone in winter. The analysis of all monthly composites available since 1985 confirms that an alongslope and anticlockwise schema also applies to the late eighties - early nineties at least. In addition, all the features evidenced with in situ data during the various POEM campaigns can be seen with the infrared imagery. It is thus concluded that the POEM-schema results from a misinterpretation of the observed features. Although mainly descriptive, our detailed analysis of infrared images of the whole eastern basin of the Mediterranean Sea allows proposing an alternative realistic schema of the surface circulation there. ACKNOWLEDGEMENTS Najwa Hamad receives support for her PhD from the High Institute of Marine Research / University of Tishreen / Syria. Assef Abbas, Jean-Luc Fuda and Gilles Rougier are warmly acknowledged for their help. We used satellite infrared images from the German remote sensing centre (DLR/DFD, about 1 km, daily, weekly and monthly composites from March 1993-present: http://eoweb.dlr.de), from the SATMOS (agreement INSU/METEO-FRANCE, about 1 km, individual paths, October 2001-present), and from the PODAAC Pathfinder Archive (about 9km, daily, 8-day and monthly composites from about January 1985-present: http://podaac.jpl.nasa.gov/sst/). We also benefited from a catalogue of images kindly provided by Alex Lascaratos and from XBT data collected during MFSPP (http://www.santateresa.enea.it/www/ec/new/mfs2.htm). REFERENCES Le

  20. Coherency of European speleothem δ18O records linked to North Atlantic ocean circulation

    Science.gov (United States)

    Deininger, Michael; McDermott, Frank

    2016-04-01

    demonstrate that a common signal (expressed by the 1st PCs) is shared by the investigated speleothem δ18O records for each individual time window and that the 1st PCs agree in the overlapping periods. This allowed us to construct a common speleothem record (CSR) for the last 4.5 ka. The CSR shows a strong millennial cyclicity in the investigated period. We demonstrate that the large-scale changes in the European CSR, reflected by its millennial cyclicity, are in phase with the well-known Bond cycles during the last 4.5 ka that reflect changes of drift ice in the North Atlantic (Bond et al., 2001). Evidence for this link was also shown by Mangini et al. (2007) using a stalagmite from the Central Alps. Furthermore, the CSR shows a very good agreement with a recent, independently dated reconstruction for the strength of the sub-polar gyre (Thornalley et al., 2009) and we argue that these changes during the last 4.5 ka are likely caused by the variability of the atmospheric circulation affecting the interplay between the subpolar gyre and the subtropical gyre in the North Atlantic, as well as European speleothem δ18O records. BOND, G., KROMER, B., BEER, J., MUSCHELER, R., EVANS, M. N., SHOWERS, W., HOFFMANN, S., LOTTI-BOND, R., HAJDAS, I. & BONANI, G. 2001. Persistent solar influence on North Atlantic climate during the Holocene. Science, 294, 2130-6. MANGINI, A., VERDES, P., SPÖTL, C., SCHOLZ, D., VOLLWEILER, N. & KROMER, B. 2007. Persistent influence of the North Atlantic hydrography on central European winter temperature during the last 9000 years. Geophysical Research Letters, 34. THORNALLEY, D. J. R., ELDERFIELD, H. & MCCAVE, I. N. 2009. Holocene oscillations in temperature and salinity of the surface subpolar North Atlantic. Nature, 457, 711-714.

  1. Current meter components and other data from FIXED PLATFORMS as part of the World Ocean Circulation Experiment (WOCE) from 1992-02-26 to 1993-04-14 (NODC Accession 9700264)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Current meter components data were collected from FIXED PLATFORMS. Data were collected by Oregon State University (OSU) as part of the World Ocean Circulation...

  2. Impacts of Ocean Waves on the Atmospheric Surface Layer: Simulations and Observations

    National Research Council Canada - National Science Library

    Sullivan, Peter P; McWilliams, James C; Melville, W. K

    2008-01-01

    ... planetary boundary layers (PBL). Efforts were focused on the effects of surface gravity waves on the near-surface dynamics, surface fluxes, and coupling between the atmospheric and oceanic PBLs...

  3. Extracting quasi-steady Lagrangian transport patterns from the ocean circulation: An application to the Gulf of Mexico.

    Science.gov (United States)

    Duran, R; Beron-Vera, F J; Olascoaga, M J

    2018-03-26

    We construct a climatology of Lagrangian coherent structures (LCSs)-the concealed skeleton that shapes transport-with a twelve-year-long data-assimilative simulation of the sea-surface circulation in the Gulf of Mexico (GoM). Computed as time-mean Cauchy-Green strain tensorlines of the climatological velocity, the climatological LCSs (cLCSs) unveil recurrent Lagrangian circulation patterns. The cLCSs strongly constrain the ensemble-mean Lagrangian circulation of the instantaneous model velocity, showing that a climatological velocity can preserve meaningful transport information. The quasi-steady transport patterns revealed by the cLCSs agree well with aspects of the GoM circulation described in several previous observational and numerical studies. For example, the cLCSs identify regions of persistent isolation, and suggest that coastal regions previously identified as high-risk for pollution impact are regions of maximal attraction. We also show that cLCSs are remarkably accurate at identifying transport patterns observed during the Deepwater Horizon and Ixtoc oil spills, and during the Grand LAgrangian Deployment (GLAD) experiment. Thus it is shown that computing cLCSs is an efficient and meaningful way of synthesizing vast amounts of Lagrangian information. The cLCS method confirms previous GoM studies, and contributes to our understanding by revealing the persistent nature of the dynamics and kinematics treated therein.

  4. On the interaction between ocean surface waves and seamounts

    Science.gov (United States)

    Sosa, Jeison; Cavaleri, Luigi; Portilla-Yandún, Jesús

    2017-12-01

    Of the many topographic features, more specifically seamounts, that are ubiquitous in the ocean floor, we focus our attention on those with relatively shallow summits that can interact with wind-generated surface waves. Among these, especially relatively long waves crossing the oceans (swells) and stormy seas are able to affect the water column up to a considerable depth and therefore interact with these deep-sea features. We quantify this interaction through numerical experiments using a numerical wave model (SWAN), in which a simply shaped seamount is exposed to waves of different length. The results show a strong interaction that leads to significant changes in the wave field, creating wake zones and regions of large wave amplification. This is then exemplified in a practical case where we analyze the interaction of more realistic sea conditions with a very shallow rock in the Yellow Sea. Potentially important for navigation and erosion processes, mutatis mutandis, these results are also indicative of possible interactions with emerged islands and sand banks in shelf seas.

  5. Contributions of greenhouse gas forcing and the Southern Annular Mode to historical Southern Ocean surface temperature trends

    OpenAIRE

    Kostov, Yavor; Ferreira, David; Marshall, John; Armour, Kyle

    2018-01-01

    We examine the 1979-2014 Southern Ocean (SO) sea surface temperature (SST) trends simulated in an ensemble of coupled general circulation models and evaluate possible causes of the models’ inability to reproduce the observed 1979-2014 SO cooling. For each model we estimate the response of SO SST to step changes in greenhouse gas (GHG) forcing and in the seasonal indices of the Southern Annular Mode (SAM). Using these step-response functions, we skillfully reconstruct the models’ 1979-2014 SO ...

  6. Banaras in the Indian Ocean: Circulating, Connecting and Creolizing Island Stories

    Directory of Open Access Journals (Sweden)

    Srilata Ravi

    2012-06-01

    Full Text Available What links Bernardin de Saint Pierre’s 1788 novel about Isle de France, Paul et Virginie, with V.S. Naipaul’s 1972 piece, An overcrowded Barracoon? What is common to Joseph Conrad’s 1910 novella, A Smile of Fortune, and tourist brochures of La Grande Baie? What brings together the story of the ruins of Babylon and the Ghats of the Ganges? Actually, these seemingly disjointed narratives make up a vast library of inter-connecting Indian Ocean island stories. In this study I will use the image of ‘Banaras’ as the locus of an inter-textual reading exercise connecting the literary spaces of Mauritian writer and filmmaker Barlen Pyamootoo with other stories like those mentioned above. Pyamootoo’s literary universe reveals to us the dynamic, multilayered and polyphonic nature of Indian Ocean island cultures.

  7. Interhemispheric controls on deep ocean circulation and carbon chemistry during the last two glacial cycles

    Digital Repository Service at National Institute of Oceanography (India)

    Wilson, D.J.; Galy, A.; Piotrowski, A.M.; Banakar, V.K.

    Sample Preparation System attached to a VG SIRA or VG PRISM mass spectrometer. Each run of 30 samples was accompanied by 10 reference carbonates and 2 control samples. The results are reported with reference to the international standard Vienna Pee... of ~0.7‰ (Figure 5c), approximately twice as large as the deglacial whole-ocean change related to carbon budget reorganisation [Tagliabue et al., 2009], indicating additional controls such as from water mass sourcing or nutrient cycling. Both...

  8. Volcanic ash as fertiliser for the surface ocean

    Directory of Open Access Journals (Sweden)

    B. Langmann

    2010-04-01

    Full Text Available Iron is a key limiting micro-nutrient for marine primary productivity. It can be supplied to the ocean by atmospheric dust deposition. Volcanic ash deposition into the ocean represents another external and so far largely neglected source of iron. This study demonstrates strong evidence for natural fertilisation in the iron-limited oceanic area of the NE Pacific, induced by volcanic ash from the eruption of Kasatochi volcano in August 2008. Atmospheric and oceanic conditions were favourable to generate a massive phytoplankton bloom in the NE Pacific Ocean which for the first time strongly suggests a connection between oceanic iron-fertilisation and volcanic ash supply.

  9. An Estimate of the Global Ocean Transit Time Distribution Computed With an Eddy Rich General Circulation Model

    Science.gov (United States)

    Bryan, F. O.; Maltrud, M.; Peacock, S.; Lindsay, K.

    2008-12-01

    Transit time distributions (TTDs), or age spectra, provide a powerful conceptual framework for evaluating and interpreting the advective-diffusive transport properties of geophysical flows. Most calculations and practical applications of TTDs to date have considered only the case of steady circulations with parameterized turbulent mixing. We have computed the first decades of the global ocean TTD for the unsteady, but statistically stationary, flow using an ensemble of impulse boundary propagators in an eddy-rich general ciculation model. In this presentation we will provide an overview of the geographical and temporal structure of the computed TTD, consider the convergence properties of the TTD as a function of ensemble size, space-time coarsening, and lag time, and consider the utility of TTDs as a metric for testing eddy mixing parameterizations in coarse resolution models.

  10. A semi-diagnostic calculation of climatic circulation in the western Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Shaji, C.; Bahulayan, N.; Dube, S.K.; Rao, A.D.

    . The model involves the sea surface topography function used as the integral function, and is driven with the wind stress at surface and thermohaline forcing at different levels. A steady state solution is obtained within 40 days of model integration...

  11. The causes of alkalinity variations in the global surface ocean

    OpenAIRE

    Fry, Claudia Helen

    2016-01-01

    Human activities have caused the atmospheric concentration of carbon dioxide (CO2) to increase by 120 ppmv from pre-industrial times to 2014. The ocean takes up approximately a quarter of the anthropogenic CO2, causing ocean acidification (OA). Therefore it is necessary to study the ocean carbonate system, including alkalinity, to quantify the flux of CO2 into the ocean and understand OA. Since the 1970s, carbonate system measurements have been undertaken which can be analyzed to quantify the...

  12. Control of primary production in the Arctic by nutrients and light: insights from a high resolution ocean general circulation model

    Directory of Open Access Journals (Sweden)

    E. E. Popova

    2010-11-01

    Full Text Available Until recently, the Arctic Basin was generally considered to be a low productivity area and was afforded little attention in global- or even basin-scale ecosystem modelling studies. Due to anthropogenic climate change however, the sea ice cover of the Arctic Ocean is undergoing an unexpectedly fast retreat, exposing increasingly large areas of the basin to sunlight. As indicated by existing Arctic phenomena such as ice-edge blooms, this decline in sea-ice is liable to encourage pronounced growth of phytoplankton in summer and poses pressing questions concerning the future of Arctic ecosystems. It thus provides a strong impetus to modelling of this region.

    The Arctic Ocean is an area where plankton productivity is heavily influenced by physical factors. As these factors are strongly responding to climate change, we analyse here the results from simulations of the 1/4° resolution global ocean NEMO (Nucleus for European Modelling of the Ocean model coupled with the MEDUSA (Model for Ecosystem Dynamics, carbon Utilisation, Sequestration and Acidification biogeochemical model, with a particular focus on the Arctic basin. Simulated productivity is consistent with the limited observations for the Arctic, with significant production occurring both under the sea-ice and at the thermocline, locations that are difficult to sample in the field.

    Results also indicate that a substantial fraction of the variability in Arctic primary production can be explained by two key physical factors: (i the maximum penetration of winter mixing, which determines the amount of nutrients available for summer primary production, and (ii short-wave radiation at the ocean surface, which controls the magnitude of phytoplankton blooms. A strong empirical correlation was found in the model output between primary production and these two factors, highlighting the importance of physical processes in the Arctic Ocean.

  13. Ocean Circulation and Dynamics on the West Antarctic Peninsula Continental Shelf

    Science.gov (United States)

    2007-09-01

    d the shladig the stand( ardl error. 169 60 06S 720o\\ 68 OW 64 0W 60 OW 56 OW Longitude [m/yr]I 1 2 3 4 5 Figure 5-13: Modeled p)recipjitation ininus...for Climate and Ocean Research , both at WHOI. The atmospheric modelling presented in Chapter 5 was performed at the British Antarctic Survey with...Components ...... .................... 50 3.3.2 Diurnal Components ...... ....................... 52 3.3.3 Comparison with the AntPen04.01 Tidal Model

  14. The Impact of the Assimilation of Aquarius Sea Surface Salinity Data in the GEOS Ocean Data Assimilation System

    Science.gov (United States)

    Vernieres, Guillaume Rene Jean; Kovach, Robin M.; Keppenne, Christian L.; Akella, Santharam; Brucker, Ludovic; Dinnat, Emmanuel Phillippe

    2014-01-01

    Ocean salinity and temperature differences drive thermohaline circulations. These properties also play a key role in the ocean-atmosphere coupling. With the availability of L-band space-borne observations, it becomes possible to provide global scale sea surface salinity (SSS) distribution. This study analyzes globally the along-track (Level 2) Aquarius SSS retrievals obtained using both passive and active L-band observations. Aquarius alongtrack retrieved SSS are assimilated into the ocean data assimilation component of Version 5 of the Goddard Earth Observing System (GEOS-5) assimilation and forecast model. We present a methodology to correct the large biases and errors apparent in Version 2.0 of the Aquarius SSS retrieval algorithm and map the observed Aquarius SSS retrieval into the ocean models bulk salinity in the topmost layer. The impact of the assimilation of the corrected SSS on the salinity analysis is evaluated by comparisons with insitu salinity observations from Argo. The results show a significant reduction of the global biases and RMS of observations-minus-forecast differences at in-situ locations. The most striking results are found in the tropics and southern latitudes. Our results highlight the complementary role and problems that arise during the assimilation of salinity information from in-situ (Argo) and space-borne surface (SSS) observations

  15. Bidecadal North Atlantic ocean circulation variability controlled by timing of volcanic eruptions.

    Science.gov (United States)

    Swingedouw, Didier; Ortega, Pablo; Mignot, Juliette; Guilyardi, Eric; Masson-Delmotte, Valérie; Butler, Paul G; Khodri, Myriam; Séférian, Roland

    2015-03-30

    While bidecadal climate variability has been evidenced in several North Atlantic paleoclimate records, its drivers remain poorly understood. Here we show that the subset of CMIP5 historical climate simulations that produce such bidecadal variability exhibits a robust synchronization, with a maximum in Atlantic Meridional Overturning Circulation (AMOC) 15 years after the 1963 Agung eruption. The mechanisms at play involve salinity advection from the Arctic and explain the timing of Great Salinity Anomalies observed in the 1970s and the 1990s. Simulations, as well as Greenland and Iceland paleoclimate records, indicate that coherent bidecadal cycles were excited following five Agung-like volcanic eruptions of the last millennium. Climate simulations and a conceptual model reveal that destructive interference caused by the Pinatubo 1991 eruption may have damped the observed decreasing trend of the AMOC in the 2000s. Our results imply a long-lasting climatic impact and predictability following the next Agung-like eruption.

  16. Impact of Surface Waves on SWOT’s Projected Ocean Accuracy

    OpenAIRE

    Peral, Eva; Rodríguez, Ernesto; Esteban-Fernández, Daniel

    2015-01-01

    The Surface Water and Ocean Topography (SWOT) mission being considered by NASA has, as one of its main objectives, to measure ocean topography with centimeter scale accuracy over kilometer scale spatial resolution. This paper investigates the impact of ocean waves on SWOT’s projected performance. Several effects will be examined: volumetric decorrelation, aliasing of ocean waves, backscattering modulation, and the so-called surfboard sampling.

  17. Active Pacific meridional overturning circulation (PMOC) during the warm Pliocene

    OpenAIRE

    Burls, Natalie J.; Fedorov, Alexey V.; Sigman, Daniel M.; Jaccard, Samuel L.; Tiedemann, Ralf; Haug, Gerald H.

    2017-01-01

    An essential element of modern ocean circulation and climate is the Atlantic meridional overturning circulation (AMOC), which includes deep-water formation in the subarctic North Atlantic. However, a comparable overturning circulation is absent in the Pacific, theworld's largest ocean, where relatively fresh surface waters inhibitNorth Pacific deep convection. We present complementary measurement and modeling evidence that the warm, similar to 400-ppmv (parts per million by volume) CO2 world ...

  18. [Measurements of surface ocean carbon dioxide partial pressure during WOCE

    Energy Technology Data Exchange (ETDEWEB)

    1992-01-01

    This paper discusses the research progress of the second year of research under Measurement of Surface Ocean Carbon Dioxide Partial Pressure During WOCE'' and proposes to continue measurements of underway pCO[sub 2]. During most of the first year of this grant, our efforts to measure pCO[sub 2] on WOCE WHP legs were frustrated by ship problems. The R/V Knorr, which was originally scheduled to carry out the first work on WHP lines P19 and P16 in the southeastem Pacific during the 1990-91 austral summer, was delayed in the shipyard during her mid-life refit for more than a year. In the interim, the smaller R/V Thomas Washington, was pressed into service to carry out lower-latitude portions of WHP lines P16 and P17 during mid-1991 (TUNES Expedition). We installed and operated our underway chromatographic system on this expedition, even though space and manpower on this smaller vessel were limited and no one from our group would be aboard any of the 3 WHP expedition legs. The results for carbon dioxide and nitrous oxide are shown. A map of the cruise track is shown for each leg, marked with cumulative distance. Following each track is a figure showing the carbon dioxide and nitrous oxide results as a function of distance along this track. The results are plotted as dry-gas mole fractions (in ppm and ppb, respectively) in air and in gas equilibrated with surface seawater at a total pressure equal to the barometric pressure. The air data are plotted as a 10-point running mean, and appear as a roughly horizontal line. The seawater data are plotted as individual points, using a 5-point Gaussian smoother. Equal values Of xCO[sub 2] in air and surface seawater indicate air-sea equilibrium.

  19. The Ocean Surface Topography Sentinel-6/Jason-CS Mission

    Science.gov (United States)

    Giulicchi, L.; Cullen, R.; Donlon, C.; Vuilleumier@esa int, P.

    2016-12-01

    The Sentinel-6/Jason-CS mission consists of two identical satellites flying in sequence and designed to provide operational measurements of sea surface height significant wave high and wind speed to support operational oceanography and climate monitoring. The mission will be the latest in a series of ocean surface topography missions that will span nearly three decades. They follow the altimeters on- board TOPEX/Poseidon through to Jason-3 (launched in January 2016). Jason-CS will continue to fulfil objectives of the reference series whilst introducing a major enhancement in capability providing the operational and science oceanographic community with the state of the art in terms of spacecraft, measurement instrumentation design thus securing optimal operational and science data return. As a secondary objective the mission will also include Radio Occultation user services. Each satellite will be launched sequentially into the Jason orbit (up to 66 latitude) respectively in 2020 and 2025. The principle payload instrument is a high precision Ku/C band radar altimeter with retrieval of geophysical parameters (surface elevation, wind speed and SWH) from the altimeter data require supporting measurements: a DORIS receiver for Precise Orbit Determination; The Climate Quality Advanced Microwave Radiometer (AMR-C) for high stability path delay correction. Orbit tracking data are also provided by GPS & LRA. An additional GPS receiver will be dedicated to radio-occultation measurements. The programme is a part of the European Community Copernicus initiative, whose objective is to support Europe's goals regarding sustainable development and global governance of the environment by providing timely and quality data, information, services and knowledge. The Sentinel-6/Jason-CS in particular is a cooperative mission with contributions from NASA, NOAA, EUMETSAT, ESA, CNES and the European Union.

  20. Folic acid functionalized surface highlights 5-methylcytosine-genomic content within circulating tumor cells

    KAUST Repository

    Malara, Natalia

    2014-07-01

    Although the detection of methylated cell free DNA represents one of the most promising approaches for relapse risk assessment in cancer patients, the low concentration of cell-free circulating DNA constitutes the biggest obstacle in the development of DNA methylation-based biomarkers from blood. This paper describes a method for the measurement of genomic methylation content directly on circulating tumor cells (CTC), which could be used to deceive the aforementioned problem. Since CTC are disease related blood-based biomarkers, they result essential to monitor tumor\\'s stadiation, therapy, and early relapsing lesions. Within surface\\'s bio-functionalization and cell\\'s isolation procedure standardization, the presented approach reveals a singular ability to detect high 5-methylcytosine CTC-subset content in the whole CTC compound, by choosing folic acid (FA) as transducer molecule. Sensitivity and specificity, calculated for FA functionalized surface (FA-surface), result respectively on about 83% and 60%. FA-surface, allowing the detection and characterization of early metastatic dissemination, provides a unique advance in the comprehension of tumors progression and dissemination confirming the presence of CTC and its association with high risk of relapse. This functionalized surface identifying and quantifying high 5-methylcytosine CTC-subset content into the patient\\'s blood lead significant progress in cancer risk assessment, also providing a novel therapeutic strategy.© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Fractionation and current time trends of PCB congeners: evolvement of distributions 1950–2010 studied using a global atmosphere-ocean general circulation model

    Directory of Open Access Journals (Sweden)

    G. Lammel

    2012-08-01

    Full Text Available PCBs are ubiquitous environmental pollutants expected to decline in abiotic environmental media in response to decreasing primary emissions since the 1970s. A coupled atmosphere-ocean general circulation model with embedded dynamic sub-models for atmospheric aerosols and the marine biogeochemistry and air-surface exchange processes with soils, vegetation and the cryosphere is used to study the transport and fate of four PCB congeners covering a range of 3–7 chlorine atoms.

    The change of the geographic distribution of the PCB mixture reflects the sources and sinks' evolvement over time. Globally, secondary emissions (re-volatilisation from surfaces are on the long term increasingly gaining importance over primary emissions. Secondary emissions are most important for the congeners with 5–6 chlorine atoms. Correspondingly, the levels of these congeners are predicted to decrease slowest. Changes in congener mixture composition (fractionation are characterized both geographically and temporally. In high latitudes enrichment of the lighter, less persistent congeners and more delayed decreasing levels in response to decreasing emissions are found. The delivery of the contaminants to high latitudes is predicted to be more efficient than previously suggested. The results suggest furthermore that the effectiveness of emission control measures may significantly vary among substances. The trends of decline of organic contaminant levels in the abiotic environmental media do not only vary with latitude (slow in high latitudes, but do also show longitudinal gradients.

  2. Three Dimensional Dynamics of Freshwater Lenses in the Oceans Near Surface Layer

    Science.gov (United States)

    2016-09-14

    the potential impact of these fluxes on the barrier layer and Aquarius and Soil Moisture and Ocean Salinity (SMOS) satellite image formations. By...contributing to the salinity field detected in the Aquarius and Soil Moisture and Ocean Salinity (SMOS) sat- ellite footprints. The barrier layer (Lukas...operational algorithms for sea surface salinity satellites. Oceanic advection and mixing funda- mentally affect the sea surface salinity sig - nal

  3. Response of the North Atlantic surface and intermediate ocean structure to climate warming of MIS 11.

    Science.gov (United States)

    Kandiano, Evgenia S; van der Meer, Marcel T J; Schouten, Stefan; Fahl, Kirsten; Sinninghe Damsté, Jaap S; Bauch, Henning A

    2017-04-10

    Investigating past interglacial climates not only help to understand how the climate system operates in general, it also forms a vital basis for climate predictions. We reconstructed vertical stratification changes in temperature and salinity in the North Atlantic for a period some 400 ka ago (MIS11), an interglacial time analogue of a future climate. As inferred from a unique set of biogeochemical, geochemical, and faunal data, the internal upper ocean stratification across MIS 11 shows distinct depth-dependent dynamical changes related to vertical as well as lateral shifts in the upper Atlantic meridional circulation system. Importantly, transient cold events are recognized near the end of the long phase of postglacial warming at surface, subsurface, mid, and deeper water layers. These data demonstrate that MIS 11 coolings over the North Atlantic were initially triggered by freshwater input at the surface and expansion of cold polar waters into the Subpolar Gyre. The cooling signal was then transmitted downwards into mid-water depths. Since the cold events occurred after the main deglacial phase we suggest that their cause might be related to continuous melting of the Greenland ice sheet, a mechanism that might also be relevant for the present and upcoming climate.

  4. Surface Ocean CO2 Atlas (SOCAT) gridded data products

    Digital Repository Service at National Institute of Oceanography (India)

    Sabine, C.L.; Hankin, S.; Koyuk, H.; Bakker, D.C.E.; Pfeil, B.; Olsen, A; Metzl, N.; Kozyr, A; Fassbender, A; Manke, A; Malczyk, J.; Akl, J.; Alin, S.R.; Bellerby, R.G.J.; Borges, A; Boutin, J.; Brown, P.J.; Cai, W.-J.; Chavez, F.P.; Chen, A.; Cosca, C.; Feely, R.A.; Gonzalez-Davila, M.; Goyet, C.; Hardman-Mountford, N.; Heinze, C.; Hoppema, M.; Hunt, C.W.; Hydes, D.; Ishii, M.; Johannessen, T.; Key, R.M.; Kortzinger, A.; Landschutzer, P.; Lauvset, S.K.; Lefevre, N.; Lenton, A.; Lourantou, A.; Merlivat, L.; Midorikawa, T.; Mintrop, L.; Miyazaki, C.; Murata, A.; Nakadate, A.; Nakano, Y.; Nakaoka, S.; Nojiri, Y.; Omar, A.M.; Padin, X.A.; Park, G.-H.; Paterson, K.; Perez, F.F.; Pierrot, D.; Poisson, A.; Rios, A.F.; Salisbury, J.; Santana-Casiano, J.M.; Sarma, V.V.S.S.; et al.

    As a response to public demand for a well-documented, quality controlled, publically available, global surface ocean carbon dioxide (CO2) data set, the international marine carbon science community developed the Surface Ocean CO2...

  5. Polymer microfilters with nanostructured surfaces for the culture of circulating cancer cells

    Energy Technology Data Exchange (ETDEWEB)

    Makarova, Olga V. [Creatv MicroTech, Inc., 2242 West Harrison St., Chicago 60612, IL (United States); Adams, Daniel L., E-mail: dan@creatvmicrotech.com [Creatv MicroTech, Inc., 1 Deer Park Drive, Monmouth Junction, NJ 08852 (United States); Divan, Ralu; Rosenmann, Daniel [Center for Nanoscale Materials, Argonne National Laboratory, 9700 South Cass Ave., Argonne 60439, IL (United States); Zhu, Peixuan; Li, Shuhong; Amstutz, Platte; Tang, Cha-Mei [Creatv MicroTech, Inc., 11609 Lake Potomac Drive, Potomac 20854, MD (United States)

    2016-09-01

    There is a critical need to improve the accuracy of drug screening and testing through the development of in vitro culture systems that more effectively mimic the in vivo environment. Surface topographical features on the nanoscale level, in short nanotopography, effect the cell growth patterns, and hence affect cell function in culture. We report the preliminary results on the fabrication, and subsequent cellular growth, of nanoscale surface topography on polymer microfilters using cell lines as a precursor to circulating tumor cells (CTCs). To create various nanoscale features on the microfilter surface, we used reactive ion etching (RIE) with and without an etching mask. An anodized aluminum oxide (AAO) membrane fabricated directly on the polymer surface served as an etching mask. Polymer filters with a variety of modified surfaces were used to compare the effects on the culture of cancer cell lines in blank culture wells, with untreated microfilters or with RIE-treated microfilters. We then report the differences of cell shape, phenotype and growth patterns of bladder and glioblastoma cancer cell lines after isolation on the various types of material modifications. Our data suggest that RIE modified polymer filters can isolate model cell lines while retaining ell viability, and that the RIE filter modification allows T24 monolayering cells to proliferate as a structured cluster. - Highlights: • Surface topographical effects the growth patterns and cell function of cancer cells • Nanoscale surface topography on polymer filters for circulating tumor cell culture • Membrane fabricated directly on polymer surfaces utilized for polymer etching • Nanotopography alters cell shape, phenotype and growth patterns of cancer cells • Nanoscale surface topography dictates monolayering or 3D structured cell culture.

  6. Impact of Ocean Gateways on Ocean Circulation, Climate and Evolution: a multidisciplinary approach to the closing of the Isthmus of Panama.

    Science.gov (United States)

    Kinkel, H.; Crudeli, D.; Groeneveld, J.; Nürnberg, D.; Steph, S.; Tiedemann, R.

    2003-04-01

    We investigated evolutionary and geochemical trends in calcareous plankton organisms (coccolithophores and planktic foraminiferas) to address the changes in the paleoceanography and evolution associated with the closure of the Isthmus of Panama. The closing of this major ocean Gateway lead to substantial reorganizations of surface and deep ocean currents, and thus global climate change. Moreover it provides a unique opportunity to study the evolutionary development of planktic organisms, that are associated with these changes as well as their geographic separation in the Carribean and eastern Equatorial Pacific. The geochemical analysis of stable oxygen and carbon isotopes as well as Mg/Ca of planktic foraminiferas, provide a detailed view on the changing surface water properties of the investigated area. First results are already achieved on the evolution of the genus Gephyrocapsa and its origination from the genus Reticulofenestra. Morphometric studies have been carried out on both genera as well as on Pseudoemiliania ovata which evolves into Pseudoemiliania lacunosa during this interval. The ecological investigation of the total coccolithophore assemblages provide valuable insights to high frequency fluctuation in the trophic structure of coccolithophores which can be correlated to the paleoceanographic reconstructions based on the stable carbon and oxygen isotope and Mg/Ca records of planktic foraminiferas. The multidisciplinary approach enables us to decipher to what extend evolution is driven by intrinsic or extrinsic factors, and the high-resolution framework of this study provides valuable insights in the tempo of evolution and climate change.

  7. A model of the general ocean circulation determined from a joint solution for the Earth's gravity field

    Science.gov (United States)

    Nerem, R. S.; Tapley, B. D.; Shum, C. K.; Yuan, D. N.

    1989-01-01

    If the geoid and the satellite position are known accurately, satellite altimetry can be used to determine the geostrophic velocity of the surface ocean currents. The purpose of this investigation is to simultaneously estimate the sea surface topography, zeta, the model for the gravity field, and the satellite orbit. Satellite tracking data from fourteen satellites were used; along with Seasat and Geosat altimeter data as well as surface gravity data for the solution. The estimated model of zeta compares well at long wavelengths with the hydrographic model of zeta. Covariance studies show that the geoid is separable from zeta up to degree 9, at which point geoid error becomes comparable to the signal of zeta.

  8. Constraints on the Lost City Hydrothermal System from borehole thermal data; 3-D models of heat flow and hydrothermal circulation in an oceanic core complex.

    Science.gov (United States)

    Titarenko, S.; McCaig, A. M.

    2014-12-01

    A perennial problem in near-ridge hydrothermal circulation is that the only directly measurable data to test models is often vent fluid temperature. Surface heat flow measurements may be available but without the underlying thermal structure it is not known if they are transient and affected by local hydrothermal flow, or conductive. The Atlantis Massif oceanic core complex at 30 °N on the mid-Atlantic Ridge, offers a unique opportunity to better constrain hydrothermal circulation models. The temperature profile in gabbroic rocks of IODP Hole 1309D was measured in IODPExpedition 340T, and found to be near-conductive, but with a slight inflexion at ~750 mbsf indicating downward advection of fluid above that level. The lack of deep convection is especially remarkable given that the long-lived Lost City Hydrothermal Field (LCHF) is located only 5km to the south. We have modelled hydrothermal circulation in the Massif using Comsol Multiphysics, comparing 2-D and 3-D topographic models and using temperature-dependent conductivity to give the best estimate of heatflow into the Massif. We can constrain maximum permeability in gabbro below 750 mbsf to 5e-17 m2. The thermal gradient in the upper part of the borehole can be matched with a permeability of 3e-14 m2 in a 750 m thick layer parallel to the surface of the massif, with upflow occurring in areas of high topography and downflow at the location of the borehole. However in 3-D the precise flow pattern is quite model dependent, and the thermal structure can be matched either by downflow centred on the borehole at lower permeability or centred a few hundred metres from the borehole at higher permeability. The borehole gradient is compatible with the longevity (>120 kyr) and outflow temperature (40-90 °C) of the LCHF either with a deep more permeable (1e-14 m2 to 1e-15 m2) domain beneath the vent site in 2-D or a permeable fault slot 500 to 1000m wide and parallel to the transform fault in 3-D. In both cases topography

  9. Subantarctic Pacific hiatuses as clues to periods of enhanced oceanic circulation during the late Neogene

    Science.gov (United States)

    Waddell, L. M.; Hendy, I. L.; Moore, T. C.; Lyle, M. W.

    2009-12-01

    New stable isotope records from cores MV0502-4JC (50°20’S, 148°08’W, 4286m), ELT 25-11 (50°02’S, 127°31’W, 3969m), and ELT 20-11 (49°00’S, 144°50’W, 4517 m) obtained in close proximity to the Subantarctic Front in the southeast Pacific show a consistent pattern of hiatuses that could be related to late Neogene changes in the strength of the Antarctic Circumpolar Current (ACC). These subantarctic Pacific records show three hiatuses that we have dated to 1) the early Pliocene-early late Pliocene, 2) ~1.57-0.68 Ma, and 3) ~0.53-0.19 Ma. These hiatuses correspond well with the timing of the Pliocene Warm Period and the climatic transitions of the Mid-Pleistocene Revolution and the Mid-Brunhes, as well as with periods of reduced or non-deposition on the Maurice Ewing Bank, also located in the path of the ACC (Ciesielski, 1982). Interestingly, sediment cores recovered from regions outside of the ACC that experience significant bottom water flow (e.g. fracture zones and the western margins of continents), including the Vema Channel (Ledbetter et al., 1978), the South Australia Basin (Ledbetter, 1981), and the continental margin of Northwest Africa (Stein et al., 1986), also show intervals of reduced or non-deposition that correlate well with the timing of hiatuses in the subantarctic Pacific. This correlation could indicate that the Pliocene Warm Period and the climatic transitions of the Mid-Pleistocene Revolution and Mid-Brunhes were characterized not only by a more vigourous ACC but also by a stronger and more globally-distributed overturning circulation than the present day.

  10. Diagnosing the leading mode of interdecadal covariability between the Indian Ocean sea surface temperature and summer precipitation in southern China

    Science.gov (United States)

    Liu, Jingpeng; Ren, Hong-Li; Li, Weijing; Zuo, Jinqing

    2018-03-01

    Precipitation in southern China during boreal summer (June to August) shows a substantial interdecadal variability on the timescale longer than 8 years. In this study, based on the analysis of singular value decomposition, we diagnose the leading mode of interdecadal covariability between the observational precipitation in southern China and the sea surface temperature (SST) in the Indian Ocean. Results indicate that there exist a remarkable southern China zonal dipole (SCZD) pattern of interdecadal variability of summer precipitation and an interdecadal Indian Ocean basin mode (ID-IOBM) of SST. It is found that the SCZD is evidently covaried with the ID-IOBM, which may induce anomalous inter-hemispheric vertical circulation and atmospheric Kelvin waves. During the warm phase of the ID-IOBM, an enhanced lower-level convergence and upper-level divergence exist over the tropical Indian Ocean, which is a typical Gill-Matsuno-type response to the SST warming. Meanwhile, the accompanied upper-level outflow anomalies further converge over the Indo-China peninsula, resulting in a lower-level anticyclone that contributes to reduction of the eastward moisture transport from the Bay of Bengal to the west part of southern China. In addition, the Kelvin wave-like pattern, as a response of the warm ID-IOBM phase, further induces the lower-level anticyclonic anomaly over the South China Sea-Philippines. Such an anticyclonic circulation is favorable for more water vapor transport from the East China Sea into the east part of southern China. Therefore, the joint effects of the anomalous inter-hemispheric vertical circulation and the Kelvin wave-like pattern associated with the ID-IOBM may eventually play a key role in generating the SCZD pattern.

  11. Partial pressure (or fugacity) of carbon dioxide, salinity and SEA SURFACE TEMPERATURE collected from Surface underway observations using Carbon dioxide (CO2) gas analyzer, Shower head chamber equilibrator for autonomous carbon dioxide (CO2) measurement and other instruments from ODEN in the South Atlantic Ocean, South Pacific Ocean and Southern Oceans from 2006-12-14 to 2006-12-26 (NODC Accession 0108159)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — NCEI Accession 0108159 includes Surface underway data collected from ODEN in the South Atlantic Ocean, South Pacific Ocean and Southern Oceans (> 60 degrees...

  12. Auto-correlation analysis of ocean surface wind vectors

    Indian Academy of Sciences (India)

    M. Senthilkumar (Newgen Imaging) 1461 1996 Oct 15 13:05:22

    satellite and in situ measurements. A case study using the TRMM Microwave Imager (TMI) and. Indian Ocean buoy wind speed data resulted in an improvement of about 10%. 1. Introduction. The need for studying temporal variability of oceanic winds has been pointed out by many authors (for example, Ezraty R S 1989).

  13. Experimental investigation of moving surfaces for boundary layer and circulation control of airfoils and wings

    Science.gov (United States)

    Vets, Robert

    An experimental study was conducted to assess the application of a moving surface to affect boundary layers and circulation around airfoils for the purpose of altering and enhancing aerodynamic performance of finite wings at moderate Reynolds numbers. The moving surface was established by a wide, lightweight, nylon belt that enveloped a wing's symmetric airfoil profile articulated via a friction drive cylinder such that the direction of the upper surface was in the direction of the free stream. A water tunnel visualization study accompanied wind tunnel testing at the University of Washington, Kirsten Wind Tunnel of finite wings. An experimental study was conducted to assess the application of a moving surface to affect boundary layers and circulation around airfoils for the purpose of altering and enhancing aerodynamic performance of finite wings at moderate Reynolds numbers. The moving surface was established by a wide, lightweight, nylon belt that enveloped a wing's symmetric airfoil profile articulated via a friction drive cylinder such that the direction of the upper surface was in the direction of the free stream. A water tunnel visualization study accompanied wind tunnel testing at the University of Washington, Kirsten Wind Tunnel of finite wings. The defining non-dimensional parameter for the system is the ratio of the surface velocity to the free stream velocity, us/Uo. Results show a general increase in lift with increasing us/Uo. The endurance parameter served as an additional metric for the system's performance. Examining the results of the endurance parameter shows general increase in endurance and lift with the moving surface activated. Peak performance in terms of increased endurance along with increased lift occurs at or slightly above us/Uo = 1. Water tunnel visualization showed a marked difference in the downwash for velocity ratios greater than 1, supporting the measured data. Reynolds numbers for this investigation were 1.9E5 and 4.3E5, relevant

  14. On the Relative Influences of Different Ocean Basin Sea Surface Temperature Anomalies on Southern African Rainfall in 20th and 21st Century GCM Simulations

    Science.gov (United States)

    Lickley, M.; Solomon, S.

    2017-12-01

    Southern Africa rainfall (SAR) is generally projected to decrease during the 21st century as a result of climate change, though there is some disagreement regarding the location and magnitude of this reduction in General Circulation Models (GCMs). Here we examine the robustness of the rainfall response to sea surface temperature (SST) anomalies. Previous work argues that warmer SSTs in the Indian Ocean suppress SAR. Other studies argue that El Niños lead to suppressed SAR. We examine the SAR response to SST anomalies in the Indian Ocean, Atlantic Ocean and ENSO 3.4 region both in observations and in two large ensembles of GCMs run over the 20th and 21st century. We find that ENSO SSTs are most correlated with SAR, while correlations between SAR and the Indian Ocean are dominated by their respective responses to ENSO. This relationship appears to persist under a warming background state.

  15. Simulating transoceanic migrations of young loggerhead sea turtles: merging magnetic navigation behavior with an ocean circulation model.

    Science.gov (United States)

    Putman, Nathan F; Verley, Philippe; Shay, Thomas J; Lohmann, Kenneth J

    2012-06-01

    Young loggerhead sea turtles (Caretta caretta) from eastern Florida, USA, undertake a transoceanic migration in which they gradually circle the Sargasso Sea before returning to the North American coast. Loggerheads possess a 'magnetic map' in which regional magnetic fields elicit changes in swimming direction along the migratory pathway. In some geographic areas, however, ocean currents move more rapidly than young turtles can swim. Thus, the degree to which turtles can control their migratory movements has remained unclear. In this study, the movements of young turtles were simulated within a high-resolution ocean circulation model using several different behavioral scenarios, including one in which turtles drifted passively and others in which turtles swam briefly in accordance with experimentally derived data on magnetic navigation. Results revealed that small amounts of oriented swimming in response to regional magnetic fields profoundly affected migratory routes and endpoints. Turtles that engaged in directed swimming for as little as 1-3 h per day were 43-187% more likely than passive drifters to reach the Azores, a productive foraging area frequented by Florida loggerheads. They were also more likely to remain within warm-water currents favorable for growth and survival, avoid areas on the perimeter of the migratory route where predation risk and thermal conditions pose threats, and successfully return to the open-sea migratory route if carried into coastal areas. These findings imply that even weakly swimming marine animals may be able to exert strong effects on their migratory trajectories and open-sea distributions through simple navigation responses and minimal swimming.

  16. Multiple scales of hydrothermal circulation in the oceanic crust: Studies from the Juan de Fuca Ridge and flank

    Science.gov (United States)

    Stein, Joshua Stephenson

    Seafloor heat flow patterns influenced by hydrothermal circulation within the upper oceanic crust are used to constrain fluid flow, crustal permeability, and thermal budgets at Middle Valley, northern Juan de Fuca Ridge and along the eastern flank of the Juan de Fuca Ridge. We made 397 heat flow measurements in two areas of active venting in Middle Valley, a sedimented spreading center. Heat flow patterns suggest that the top of the hydrothermal reservoir at the Dead Dog vent area is located ˜30 m beneath the vent field and is separated from a shallow secondary circulation system by a thin, impermeable, diagenetic cap. This cap is a hydrologic barrier, separating the high-temperature, overpressured system at depth from a low-temperature, underpressured system near the seafloor. Circulation above the cap is influenced by hydrodynamic interactions with active vents. Vent fluid recharges at the unsedimented edges of Middle Valley and is driven toward the vent field by small driving forces documented by borehole observatories. These small driving forces, in combination with estimated fluid flux (150 l/min), imply that crustal permeability must be high (10 -12 to 10-10 m2). We estimate the total heat loss for a 260 km2 region of Middle Valley to be 274 MW. Conductive and advective heat loss are approximately equal, in contrast to bare-rock ridges that lose 90% or more of their heat advectively. Models of lateral heat and fluid flow across a 26 km transect of the eastern flank of the Juan de Fuca Ridge quantify relations between lateral specific discharge, flow layer thickness and formation permeability. Free flow simulations require non-hydrostatic initial conditions and permeabilities of 10-11 to 10-9 m2, but match heat flow observations with lateral specific discharges of 1.2 to 40 m/yr. These lateral flow rates are 10x to 1000x greater than predicted by apparent radiocarbon ages of the fluids. When apparent radiocarbon ages are corrected to account for diffusion

  17. Monitoring the regional ocean circulation around New Caledonia from a combination of repeated glider measurements and other in situ observing systems

    Science.gov (United States)

    Marin, Frédéric; Fuda, Jean-Luc; Durand, Fabien; Terre, Thierry; Panché, Jean-Yves; Mahiouz, Karim; Béguery, Laurent

    2013-04-01

    The South-West Pacific basin is a key region for the ocean circulation and the climate system of the tropical Pacific. First it is the region where a broad westward-flowing current - the South Equatorial Current - encounters a large number of islands and subdivides into multiple intense zonal jets. Second it is the region where thermocline waters of subtropical origin transit in their route towards the equator, giving to this area a potential role for the low-frequency modulation of El Niño - Southern Oscillation (ENSO). The main objective of the present poster is to describe a multi-observational program (AltiGlidEx) to monitor two major currents of the South-West Pacific ocean - the East Caledonian Current and the South Caledonian Jet - that flow respectively along the East coast of New Caledonia (167°E-168°E, 22°S-17°S) and South of New Caledonia (27°S-23°S). One expected achievement of the AltiGlidEx program is to provide a platform of multiple in situ observations, including repeated sections with SLOCUM and SPRAY gliders, a long-term subsurface current mooring and dedicated cruises, to ultimately assess the performance of the new AltiKa altimeter - that will be embarked on the SARAL satellite in 2013 - to observe swift boundary currents near the coast of New Caledonia in 2013-2014. This program takes full advantage of the potential of gliders to estimate (i) the geostrophic component of the velocity from the surface down to 1000 meters from hydrological measurements and (ii) the depth-averaged currents during each dive through the GPS-derived dead-reckoning of the vehicle (based on the comparison of the total horizontal distance during each dive that can be computed from the GPS positions of the diving/surfacing points with the one that would be expected in the absence of ocean currents from a flight model, once an adequate flight model is known for the glider). In this presentation, the preliminary results of the first 3 glider experiments (2010, 2011

  18. A computational analysis of sonic booms penetrating a realistic ocean surface.

    Science.gov (United States)

    Rochat, J L; Sparrow, V W

    2001-03-01

    The last decade has seen a revival of sonic boom research, a direct result of the projected market for a new breed of supersonic passenger aircraft, its design, and its operation. One area of the research involves sonic boom penetration into the ocean, one concern being the possible disturbance of marine mammals from the noise generated by proposed high-speed civil transport (HSCT) flyovers. Although theory is available to predict underwater sound levels due to a sonic boom hitting a homogeneous ocean with a flat surface, theory for a realistic ocean, one with a wavy surface and bubbles near the surface, is missing and will be presented in this paper. First, reviews are given of a computational method to calculate the underwater pressure field and the effects of a simple wavy ocean surface on the impinging sonic boom. Second, effects are described for the implementation of three additional conditions: a sonic boom/ocean "wavelength" comparison, complex ocean surfaces, and bubbles near the ocean surface. Overall, results from the model suggest that the realistic ocean features affect the penetrating proposed HSCT sonic booms by modifying the underwater sound-pressure levels only about 1 decibel or less.

  19. Evaluation of Oceanic Surface Observation for Reproducing the Upper Ocean Structure in ECHAM5/MPI-OM

    Science.gov (United States)

    Luo, Hao; Zheng, Fei; Zhu, Jiang

    2017-12-01

    Better constraints of initial conditions from data assimilation are necessary for climate simulations and predictions, and they are particularly important for the ocean due to its long climate memory; as such, ocean data assimilation (ODA) is regarded as an effective tool for seasonal to decadal predictions. In this work, an ODA system is established for a coupled climate model (ECHAM5/MPI-OM), which can assimilate all available oceanic observations using an ensemble optimal interpolation approach. To validate and isolate the performance of different surface observations in reproducing air-sea climate variations in the model, a set of observing system simulation experiments (OSSEs) was performed over 150 model years. Generally, assimilating sea surface temperature, sea surface salinity, and sea surface height (SSH) can reasonably reproduce the climate variability and vertical structure of the upper ocean, and assimilating SSH achieves the best results compared to the true states. For the El Niño-Southern Oscillation (ENSO), assimilating different surface observations captures true aspects of ENSO well, but assimilating SSH can further enhance the accuracy of ENSO-related feedback processes in the coupled model, leading to a more reasonable ENSO evolution and air-sea interaction over the tropical Pacific. For ocean heat content, there are still limitations in reproducing the long time-scale variability in the North Atlantic, even if SSH has been taken into consideration. These results demonstrate the effectiveness of assimilating surface observations in capturing the interannual signal and, to some extent, the decadal signal but still highlight the necessity of assimilating profile data to reproduce specific decadal variability.

  20. Design and Implementation of a Parallel Multivariate Ensemble Kalman Filter for the Poseidon Ocean General Circulation Model

    Science.gov (United States)

    Keppenne, Christian L.; Rienecker, Michele M.; Koblinsky, Chester (Technical Monitor)

    2001-01-01

    A multivariate ensemble Kalman filter (MvEnKF) implemented on a massively parallel computer architecture has been implemented for the Poseidon ocean circulation model and tested with a Pacific Basin model configuration. There are about two million prognostic state-vector variables. Parallelism for the data assimilation step is achieved by regionalization of the background-error covariances that are calculated from the phase-space distribution of the ensemble. Each processing element (PE) collects elements of a matrix measurement functional from nearby PEs. To avoid the introduction of spurious long-range covariances associated with finite ensemble sizes, the background-error covariances are given compact support by means of a Hadamard (element by element) product with a three-dimensional canonical correlation function. The methodology and the MvEnKF configuration are discussed. It is shown that the regionalization of the background covariances; has a negligible impact on the quality of the analyses. The parallel algorithm is very efficient for large numbers of observations but does not scale well beyond 100 PEs at the current model resolution. On a platform with distributed memory, memory rather than speed is the limiting factor.

  1. On estimating the basin-scale ocean circulation from satellite altimetry. Part 1: Straightforward spherical harmonic expansion

    Science.gov (United States)

    Tai, Chang-Kou

    1988-01-01

    Direct estimation of the absolute dynamic topography from satellite altimetry has been confined to the largest scales (basically the basin-scale) owing to the fact that the signal-to-noise ratio is more unfavorable everywhere else. But even for the largest scales, the results are contaminated by the orbit error and geoid uncertainties. Recently a more accurate Earth gravity model (GEM-T1) became available, providing the opportunity to examine the whole question of direct estimation under a more critical limelight. It is found that our knowledge of the Earth's gravity field has indeed improved a great deal. However, it is not yet possible to claim definitively that our knowledge of the ocean circulation has improved through direct estimation. Yet, the improvement in the gravity model has come to the point that it is no longer possible to attribute the discrepancy at the basin scales between altimetric and hydrographic results as mostly due to geoid uncertainties. A substantial part of the difference must be due to other factors; i.e., the orbit error, or the uncertainty of the hydrographically derived dynamic topography.

  2. Study of Groundwater Circulation Using Stable Isotopes : the Example of the Punaruu Watershed (Tropical Oceanic Island of Tahiti, French Polynesia)

    Science.gov (United States)

    Sichoix, L.; Hildenbrand, A.; Marlin, C.; Gillot, P. Y.; Pheulpin, L.; Barriot, J. P.

    2015-12-01

    The increasing demand for drinking and industrial water, especially in the most populated areas of the tropical oceanic Island of Tahiti in French Polynesia (South central Pacific), makes it necessary to conduct hydrological and hydrogeological studies on water resources and management. Our investigation area represents the second largest watershed of Tahiti called Punaruu. The largest industrial zone of Tahiti occupies the minor low valley of this catchment and is particularly impacted by dredging of the stream and rock removals since several decades whereas the major high part is naturally well preserved. This study aims to identify the main infiltration areas of the aquifers of this industrial zone as well as the areas at low elevations to be protected from potential pollutions. During the period between May 2013 and July 2015, we have collected rainwater samples from five rain gauges located at elevations ranging from 0 to 1420 m. We have also performed water sampling from the main rivers and three springs up to altitudes of 800 m as well as six pumping boreholes in the industrial zone. Chemical (major elements) and stable isotopic (δ18O and δ2H) analyses have been done from all these water samples and help us to constrain a conceptual model of groundwater circulation within such a complex discontinuous volcanic structure.

  3. A cold and fresh ocean surface in the Nordic Seas during MIS 11: Significance for the future ocean

    NARCIS (Netherlands)

    Kandiano, E.S.; Van der Meer, M.T.J.; Bauch, H.A.; Helmke, J.; Sinninghe Damsté, J.S.; Schouten, S.

    2016-01-01

    Paleoceanographical studies of Marine Isotope Stage (MIS) 11 have revealed higher-than-presentsea surface temperatures (SSTs) in the North Atlantic and in parts of the Arctic but lower-than-present SSTsin the Nordic Seas, the main throughflow area of warm water into the Arctic Ocean. We resolve

  4. A cold and fresh ocean surface in the Nordic Seas during MIS 11 : Significance for the future ocean

    NARCIS (Netherlands)

    Kandiano, Evgenia S.; van der Meer, M.T.J.; Bauch, H.A.; Helmke, Jan; Sinninghe Damsté, J.S.; Schouten, S.

    2016-01-01

    Paleoceanographical studies of Marine Isotope Stage (MIS) 11 have revealed higher-than-present sea surface temperatures (SSTs) in the North Atlantic and in parts of the Arctic but lower-than-present SSTs in the Nordic Seas, the main throughflow area of warm water into the Arctic Ocean. We resolve

  5. Marine isoprene production and consumption in the mixed layer of the surface ocean - a field study over two oceanic regions

    Science.gov (United Sta