Microbial iron mats at the Mid-Atlantic Ridge and evidence that Zetaproteobacteria may be restricted to iron-oxidizing marine systems.

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Jarrod J Scott

Full Text Available Chemolithoautotrophic iron-oxidizing bacteria play an essential role in the global iron cycle. Thus far, the majority of marine iron-oxidizing bacteria have been identified as Zetaproteobacteria, a novel class within the phylum Proteobacteria. Marine iron-oxidizing microbial communities have been found associated with volcanically active seamounts, crustal spreading centers, and coastal waters. However, little is known about the presence and diversity of iron-oxidizing communities at hydrothermal systems along the slow crustal spreading center of the Mid-Atlantic Ridge. From October to November 2012, samples were collected from rust-colored mats at three well-known hydrothermal vent systems on the Mid-Atlantic Ridge (Rainbow, Trans-Atlantic Geotraverse, and Snake Pit using the ROV Jason II. The goal of these efforts was to determine if iron-oxidizing Zetaproteobacteria were present at sites proximal to black smoker vent fields. Small, diffuse flow venting areas with high iron(II concentrations and rust-colored microbial mats were observed at all three sites proximal to black smoker chimneys. A novel, syringe-based precision sampler was used to collect discrete microbial iron mat samples at the three sites. The presence of Zetaproteobacteria was confirmed using a combination of 16S rRNA pyrosequencing and single-cell sorting, while light micros-copy revealed a variety of iron-oxyhydroxide structures, indicating that active iron-oxidizing communities exist along the Mid-Atlantic Ridge. Sequencing analysis suggests that these iron mats contain cosmopolitan representatives of Zetaproteobacteria, but also exhibit diversity that may be uncommon at other iron-rich marine sites studied to date. A meta-analysis of publically available data encompassing a variety of aquatic habitats indicates that Zetaproteobacteria are rare if an iron source is not readily available. This work adds to the growing understanding of Zetaproteobacteria ecology and suggests

Mapping the mantle transition zone beneath the central Mid-Atlantic Ridge using Ps receiver functions.

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Agius, M. R.; Rychert, C.; Harmon, N.; Kendall, J. M.

2017-12-01

Determining the mechanisms taking place beneath ridges is important in order to understand how tectonic plates form and interact. Of particular interest is establishing the depth at which these processes originate. Anomalies such as higher temperature within the mantle transition zone may be inferred seismically if present. However, most ridges are found in remote locations beneath the oceans restricting seismologists to use far away land-based seismometers, which in turn limits the imaging resolution. In 2016, 39 broadband ocean-bottom seismometers were deployed across the Mid-Atlantic Ridge, along the Romanche and Chain fracture zones as part of the PI-LAB research project (Passive Imaging of the Lithosphere and Asthenosphere Boundary). The one-year long seismic data is now retrieved and analysed to image the mantle transition zone beneath the ridge. We determine P-to-s (Ps) receiver functions to illuminate the 410- and 660-km depth mantle discontinuities using the extended multitaper deconvolution. The data from ocean-bottom seismometers have tilt and compliance noise corrections and is filtered between 0.05-0.2 Hz to enhance the signal. 51 teleseismic earthquakes generated hundreds of good quality waveforms, which are then migrated to depth in 3-D. The topography at the d410 deepens towards the west of the Romanche and Chain fracture zone by 15 km, whereas the topography of d660 shallows beneath the ridge between the two zones. Transition zone thickness thins from 5 to 20 km. Thermal anomalies determined from temperature relationships with transition zone thickness and depth variations of the d410 and d660 suggests hotter temperatures of about 200 K. Overall, the result suggests mid-ocean ridges may have associated thermal signatures as deep as the transition zone.

Seismicity And Accretion Process Along The North Mid-Atlantic Ridge From The SIRENA Autonomous Hydrophone Data

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Perrot, J.; Goslin, J.; Dziak, R. P.; Haxel, J. H.; Maia, M. A.; Tisseau, C.; Royer, J.

2009-12-01

The seismicity of the North Atlantic Ocean was recorded by the SIRENA array of 6 autonomous underwater hydrophones (AUH) moored within the SOFAR channel on the flanks of the Mid-Atlantic Ridge (MAR). The instruments were deployed north of the Azores Plateau between 40° and 50°N from June 2002 to September 2003. The low attenuation properties of the SOFAR channel for earthquake T-wave propagation result in a detection threshold reduction to a magnitude completeness level (Mc) of ~2.8, to be compared to a Mc~4.7 for MAR events recorded by land-based seismic networks. A spatio-temporal analysis was performed over the 1696 events localized inside the SIRENA array. For hydrophone-derived catalogs, the acoustic magnitude, or Source Level (SL), is used as a measure of earthquake size. The ''source level completeness'', above which the data set is complete, is SLc=208 dB. The SIRENA catalog was searched for swarms using the cluster software of the SEISAN distribution. A minimum SL of 210 dB was chosen to detect a possible mainshock, and all subsequent events within 40 days following the possible mainshock, located within a radius of 15 km from the mainshock were considered as events of the swarm. 15 km correspond to the maximum fault length in a slow-ridge context. 11 swarms with more than 15 events were detected along the MAR between 40°et 50°N during the SIRENA deployment. The maximum number of earthquakes in a swarm is 40 events. The SL vs. time distribution within each swarm allowed a first discrimination between the swarms occurring in a tectonic context and those which can be attributed to volcanic processes, the latter showing a more constant SL vs. time distribution. Moreover, the swarms occurring in a tectonic context show a "mainshock-afterschock" distribution of the cumulative number of events vs. time, fitting a Modified Omori Law. The location of tectonic and volcanic swarms correlates well with regions where a positive and negative Mantle Bouguer

Local Prediction Models on Mid-Atlantic Ridge MORB by Principal Component Regression

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Ling, X.; Snow, J. E.; Chin, W.

2017-12-01

The isotopic compositions of the daughter isotopes of long-lived radioactive systems (Sr, Nd, Hf and Pb ) can be used to map the scale and history of mantle heterogeneities beneath mid-ocean ridges. Our goal is to relate the multidimensional structure in the existing isotopic dataset with an underlying physical reality of mantle sources. The numerical technique of Principal Component Analysis is useful to reduce the linear dependence of the data to a minimum set of orthogonal eigenvectors encapsulating the information contained (cf Agranier et al 2005). The dataset used for this study covers almost all the MORBs along mid-Atlantic Ridge (MAR), from 54oS to 77oN and 8.8oW to -46.7oW, including replicating the dataset of Agranier et al., 2005 published plus 53 basalt samples dredged and analyzed since then (data from PetDB). The principal components PC1 and PC2 account for 61.56% and 29.21%, respectively, of the total isotope ratios variability. The samples with similar compositions to HIMU and EM and DM are identified to better understand the PCs. PC1 and PC2 are accountable for HIMU and EM whereas PC2 has limited control over the DM source. PC3 is more strongly controlled by the depleted mantle source than PC2. What this means is that all three principal components have a high degree of significance relevant to the established mantle sources. We also tested the relationship between mantle heterogeneity and sample locality. K-means clustering algorithm is a type of unsupervised learning to find groups in the data based on feature similarity. The PC factor scores of each sample are clustered into three groups. Cluster one and three are alternating on the north and south MAR. Cluster two exhibits on 45.18oN to 0.79oN and -27.9oW to -30.40oW alternating with cluster one. The ridge has been preliminarily divided into 16 sections considering both the clusters and ridge segments. The principal component regression models the section based on 6 isotope ratios and PCs. The

Local Seismicity of the Rainbow Massif on the Mid-Atlantic Ridge

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Horning, G.; Sohn, R. A.; Canales, J. P.; Dunn, R. A.

2018-02-01

The Rainbow massif, an oceanic core complex located in a nontransform discontinuity on the Mid-Atlantic Ridge (36°N), is notable for hosting high-temperature hydrothermal discharge through ultramafic rocks. Here we report results from a 9 month microearthquake survey conducted with a network of 13 ocean bottom seismometers deployed on and around the Rainbow massif as part of the MARINER experiment in 2013-2014. High rates ( 300 per day) of low-magnitude (average ML 0.5) microearthquakes were detected beneath the massif. The hypocenters do not cluster along deeply penetrating fault surfaces and do not exhibit mainshock/aftershock sequences, supporting the hypothesis that the faulting associated with the exhumation of the massif is currently inactive. Instead, the hypocenters demarcate a diffuse zone of continuous, low-magnitude deformation at relatively shallow (serpentinized ultramafic host rock, and although the seismic network we deployed was not capable of constraining the focal mechanism of most events, our analysis suggests that serpentinization may play an important role in microearthquake generation at the Rainbow massif.

Noble gases in basalt glasses from a Mid-Atlantic Ridge topographic high at 14deg N - geodynamic consequences

International Nuclear Information System (INIS)

Staudacher, T.; Sarda, P.; Richardson, S.H.; Allegre, C.J.; Sagna, I.; Dmitriev, L.V.

1989-01-01

We present a complete noble gas study of mid-oceanic ridge basalt glasses (MORB) from a small ridge segment, centered on an along-strike topographic elevation of the Mid-Atlantic Ridge at about 14deg N. We have found the highest 40 Ar/ 36 Ar ratio ever observed for a MORB glass, i.e. 28,150±330 for sample 2ΠD40, correlated with high 129 Xe/ 130 Xe ratios and the highest noble gas concentrations in a so-called popping-rock, labeled 2ΠD43. The latter sample displays a 4 He/ 40 Ar * ratio of 2.0-2.7, which is close to the production ratio in the mantle due to the radioactive decay of U, Th and K. Hence, this sample probably best represents the elemental noble gas ratios in the mantle, from which we have computed the 4 He concentration in the mantle source of MORB to be 1.5x10 -5 cm 3 STP g -1 . High 4 He/ 3 He ratios in two of the samples from the summit of the topographic high indicate the presence of a U, Th-rich component in the mantle source, possibly old subducted oceanic crust and/or sediments, which could originate in the so-called mesosphere boundary layer. (orig.)

Trace element and isotopic effects arising from magma migration beneath mid-ocean ridges

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Kenyon, P.M.

1990-01-01

The trace element concentrations and isotopic ratios in the magma erupted on mid-ocean ridges may differ from those in the source material due to physical effects such as porous flow dispersion, exchange of trace elements between the fluid and solid phases during magma migration, and convective mixing in magma chambers. These differences are in addition to those produced by better known processes such as fractional crystallization and partial melting. The effects of the three former processes are described. It is predicted that magma typically reaches the sub-ridge magma chambers with a spatial heterogeneity only slightly reduced from that of the source material, but with a subdued variation in time. Convective mixing then further reduces the spatial heterogeneity. Application of the results for convective mixing to a recent Fourier analysis of 87 Sr/ 86 Sr variations along the Mid-Atlantic Ridge suggests that the falloff in amplitude of variation observed with decreasing wavelength in the Mid-Atlantic Ridge data cannot be explained by convective mixing in magma chambers. Instead, it is postulated that this falloff is due to the mechanics of the production and/or the solid-state convective mixing of chemical and isotopic heterogeneities in the solid mantle. (orig.)

Depth-varying seismogenesis on an oceanic detachment fault at 13°20‧N on the Mid-Atlantic Ridge

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Craig, Timothy J.; Parnell-Turner, Ross

2017-12-01

Extension at slow- and intermediate-spreading mid-ocean ridges is commonly accommodated through slip on long-lived faults called oceanic detachments. These curved, convex-upward faults consist of a steeply-dipping section thought to be rooted in the lower crust or upper mantle which rotates to progressively shallower dip-angles at shallower depths. The commonly-observed result is a domed, sub-horizontal oceanic core complex at the seabed. Although it is accepted that detachment faults can accumulate kilometre-scale offsets over millions of years, the mechanism of slip, and their capacity to sustain the shear stresses necessary to produce large earthquakes, remains subject to debate. Here we present a comprehensive seismological study of an active oceanic detachment fault system on the Mid-Atlantic Ridge near 13°20‧N, combining the results from a local ocean-bottom seismograph deployment with waveform inversion of a series of larger teleseismically-observed earthquakes. The unique coincidence of these two datasets provides a comprehensive definition of rupture on the fault, from the uppermost mantle to the seabed. Our results demonstrate that although slip on the deep, steeply-dipping portion of detachment faults is accommodated by failure in numerous microearthquakes, the shallow, gently-dipping section of the fault within the upper few kilometres is relatively strong, and is capable of producing large-magnitude earthquakes. This result brings into question the current paradigm that the shallow sections of oceanic detachment faults are dominated by low-friction mineralogies and therefore slip aseismically, but is consistent with observations from continental detachment faults. Slip on the shallow portion of active detachment faults at relatively low angles may therefore account for many more large-magnitude earthquakes at mid-ocean ridges than previously thought, and suggests that the lithospheric strength at slow-spreading mid-ocean ridges may be concentrated

The ecosystem of the Mid-Atlantic Ridge at the sub-polar front and Charlie-Gibbs Fracture Zone; ECO-MAR project strategy and description of the sampling programme 2007-2010

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Priede, Imants G.; Billett, David S. M.; Brierley, Andrew S.; Hoelzel, A. Rus; Inall, Mark; Miller, Peter I.; Cousins, Nicola J.; Shields, Mark A.; Fujii, Toyonobu

2013-12-01

The ECOMAR project investigated photosynthetically-supported life on the North Mid-Atlantic Ridge (MAR) between the Azores and Iceland focussing on the Charlie-Gibbs Fracture Zone area in the vicinity of the sub-polar front where the North Atlantic Current crosses the MAR. Repeat visits were made to four stations at 2500 m depth on the flanks of the MAR in the years 2007-2010; a pair of northern stations at 54°N in cold water north of the sub-polar front and southern stations at 49°N in warmer water influenced by eddies from the North Atlantic Current. At each station an instrumented mooring was deployed with current meters and sediment traps (100 and 1000 m above the sea floor) to sample downward flux of particulate matter. The patterns of water flow, fronts, primary production and export flux in the region were studied by a combination of remote sensing and in situ measurements. Sonar, tow nets and profilers sampled pelagic fauna over the MAR. Swath bathymetry surveys across the ridge revealed sediment-covered flat terraces parallel to the axis of the MAR with intervening steep rocky slopes. Otter trawls, megacores, baited traps and a suite of tools carried by the R.O.V. Isis including push cores, grabs and a suction device collected benthic fauna. Video and photo surveys were also conducted using the SHRIMP towed vehicle and the R.O.V. Isis. Additional surveying and sampling by landers and R.O.V. focussed on the summit of a seamount (48°44‧N, 28°10‧W) on the western crest of the MAR between the two southern stations.

Comparison between the shrimp species richness (Caridea and Dendrobranchiata, Decapoda, Crustacea of the south and north mid Atlantic ridge

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Irene Azevedo Cardoso

2014-03-01

Full Text Available The Mid Atlantic Ridge (MAR is a seamount chain extending for 60.000 km, divided into south and north regions by the Equatorial Fracture which cuts across it. This latter has a maximum depth of 7,760 m and an average width of 19 km. In this study we include data from the two cruises of the international project MAR-ECO, undertaken, respectively, one on the north and the other on the south MAR. Our main objective is to compare the species richness and species composition of pelagic and benthic decapod shrimps of these two areas to observe the patterns of their latitudinal distribution along the MAR. Using rarefaction methods, we obtained interesting results: the pelagic samples curve of the northern MAR is almost an asymptote, so we concluded that we are close to the true number of pelagic shrimp species for this region. The pelagic samples curve of the southern MAR had the greatest slope, so our conclusion is that we are still far from the true number of species for this region. A comparison of species richness at 12 samples (the smallest number of samples shared by both the surveys revealed that the pelagic species richness was greater than the demersal, and that the northern MAR contained a larger number of species than the southern.

Anisotropy of the upper mantle beneath the equatorial part of the Mid-Atlantic Ridge

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Kendall, J. M.; Rychert, C.; Harmon, N.; Tharimena, S.; Agius, M. R.

2017-12-01

It has been long-known that the mantle beneath ocean spreading centres is anisotropic, holding the signature of the formation of new oceanic lithosphere and its coupling with the underlying convecting asthenosphere. Numerical studies have suggested that there should be significant differences between the anisotropy at slow versus fast spreading centres, but there is little observational evidence to calibrate these simulations, especially at slow spreading centres. Near the ridge axis, the anisotropic effects of melt versus the lattice preferred orientation of minerals is not well understood. Finally, the mantle flow near ridge-transform interactions is also poorly understood. Here we present observations of SKS splitting in a region of the Mid-Atlantic Ridge near the equator and offset by the Romanche and Chain Fracture Zones. An array of 37 ocean-bottom seismometers were deployed for a year in depths of up to nearly 6000m, with the aim of studying the nature of the lithosphere-asthenosphere boundary as it forms (the PiLAB - Passive Imaging of the lithosphere-asthenosphere boundary - experiment). Stations were deployed on crust that varies from newly formed to 80 My old. We analyse 40 teleseismic events of magnitude greater than 5.8 and with epicentral distances between 88 and 130 degrees. The ocean-bottom is a noisy environment and a range of filters are used to isolate the SKS, SKKS, and related signals. Furthermore, stacking splitting error envelopes is used to improve confidence in the splitting parameters. Many of the splitting measurements show an orientation parallel to the direction of plate spreading, as expected, but variability in the orientation of the anisotropy increases towards the ridge axis. The magnitude of the anisotropy is also quite variable and suggests larger delay times near the ridge axis. Off-axis anisotropy is interpreted in terms of deformation of peridotite due to mantle flow. Near the ridge axis, the effect of ridge-parallel melt

Methane- and Hydrogen-Influenced Microbial Communities in Hydrothermal Plumes above the Atlantis Massif, Mid Atlantic Ridge

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Stewart, C. L.; Schrenk, M.

2017-12-01

Ultramafic-hosted hydrothermal systems associated with slow-spreading mid ocean ridges emit copious amounts of hydrogen and methane into the deep-sea, generated through a process known as serpentinization. Hydrothermal plumes carrying the reduced products of water-rock interaction dissipate and mix with deep seawater, and potentially harbor microbial communities adapted to these conditions. Methane and hydrogen enriched hydrothermal plumes were sampled from 3 sites near the Atlantis Massif (30°N, Mid Atlantic Ridge) during IODP Expedition 357 and used to initiate cultivation experiments targeting methanotrophic and hydrogenotrophic microorganisms. One set of experiments incubated the cultures at in situ hydrostatic pressures and gas concentrations resulting in the enrichment of gammaproteobacterial assemblages, including Marinobacter spp. That may be involved in hydrocarbon degradation. A second set of experiments pursued the anaerobic enrichment of microbial communities on solid media, resulting in the enrichment of alphaproteobacteria related to Ruegeria. The most prodigious growth in both case occurred in methane-enriched media, which may play a role as both an energy and carbon source. Ongoing work is evaluating the physiological characteristics of these isolates, including their metabolic outputs under different physical-chemical conditions. In addition to providing novel isolates from hydrothermal habitats near the Lost City Hydrothermal Field, these experiments will provide insight into the ecology of microbial communities from serpentinization influenced hydrothermal systems that may aid in future exploration of these sites.

Seismicity And Accretion Processes Along The Mid-Atlantic Ridge south of the Azores using data from the MARCHE Autonomous Hydrophone Array

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Perrot, Julie; Cevatoglu, Melis; Cannat, Mathilde; Escartin, Javier; Maia, Marcia; Tisseau, Chantal; Dziak, Robert; Goslin, Jean

2013-04-01

The seismicity of the South Atlantic Ocean has been recorded by the MARCHE network of 4 autonomous underwater hydrophones (AUH) moored within the SOFAR channel on the flanks of the Mid-Atlantic Ridge (MAR). The instruments were deployed south of the Azores Plateau between 32° and 39°N from July 2005 to August 2008. The low attenuation properties of the SOFAR channel for earthquake T-wave propagation result in a detection threshold reduction from a magnitude completeness level (Mc) of ~4.3 for MAR events recorded by the land-based seismic networks to Mc=2.1 using this hydrophone array. A spatio-temporal analysis has been performed among the 5600 events recorded inside the MARCHE array. Most events are distributed along the ridge between lat. 39°N on the Azores Platform and the Rainbow (36°N) segment. In the hydrophone catalogue, acoustic magnitude (Source Level, SL) is used as a measure of earthquake size. The source level above which the data set is complete is SLc=205 dB. We look for seismic swarms using the cluster software of the SEISAN package. The criterion used are a minimum SL of 210 to detect a possible mainshock, and a radius of 30 km and a time window of 40 days after this mainshock (Cevatoglu, 2010, Goslin et al., 2012). 7 swarms with more than 15 events are identified using this approach between 32°et 39°N of latitude. The maximum number of earthquake in a swarm is 57 events. This result differs from the study of Simao et al. (2010) as we processed a further year of data and selected sequences with fewer events. Looking at the distribution of the SL as a function of time after the mainshock, we discuss the possible mechanism of these earthquakes : tectonic events with a "mainshock-aftershock" distribution fitting a modified Omori law or volcanic events showing more constant SL values. We also present the geophysical setting of these 7 swarms, using gravity, bathymetry, and available local geological data. This study illustrates the potential of

Mid-ocean ridges produced thicker crust in the Jurassic than in Recent times

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Van Avendonk, H. J.; Harding, J.; Davis, J. K.; Lawver, L. A.

2016-12-01

We present a compilation of published marine seismic refraction data to show that oceanic crust was 1.7 km thicker on average in the mid-Jurassic (170 Ma) than along the present-day mid-ocean ridge system. Plate reconstructions in a fixed hotspot framework show that the thickness of oceanic crust does not correlate with proximity to mantle hotspots, so it is likely that mid-plate volcanism is not the cause of this global trend. We propose that more melt was extracted from the upper mantle beneath mid-ocean ridges in the Jurassic than in recent times. Numerical studies show that temperature increase of 1 degree C in the mantle can lead to approximately 50-70 m thicker crust, so the upper mantle may have cooled 15-20 degrees C/100 Myr since 170 Ma. This average temperature decrease is larger than the secular cooling rate of the Earth's mantle, which is roughly 10 degrees C/100 Myr since the Archean. Apparently, the present-day configuration and dynamics of continental and oceanic plates removes heat more efficiently from the Earth's mantle than in its earlier history. The increase of ocean crustal thickness with plate age is also stronger in the Indian and Atlantic oceans than in the Pacific Ocean basin. This confirms that thermal insulation by the supercontinent Pangaea raised the temperature of the underlying asthenospheric mantle, which in turn led to more magmatic output at the Jurassic mid-ocean ridges of the Indian and Atlantic oceans.

Long-term seismicity of the Reykjanes Ridge (North Atlantic) recorded by a regional hydrophone array

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Goslin, Jean; Lourenço, Nuno; Dziak, Robert P.; Bohnenstiehl, DelWayne R.; Haxel, Joe; Luis, Joaquim

2005-08-01

The seismicity of the northern Mid-Atlantic Ridge was recorded by two hydrophone networks moored in the sound fixing and ranging (SOFAR) channel, on the flanks of the Mid-Atlantic Ridge, north and south of the Azores. During its period of operation (05/2002-09/2003), the northern `SIRENA' network, deployed between latitudes 40° 20'N and 50° 30'N, recorded acoustic signals generated by 809 earthquakes on the hotspot-influenced Reykjanes Ridge. This activity was distributed between five spatio-temporal event clusters, each initiated by a moderate-to-large magnitude (4.0-5.6 M) earthquake. The rate of earthquake occurrence within the initial portion of the largest sequence (which began on 2002 October 6) is described adequately by a modified Omori law aftershock model. Although this is consistent with triggering by tectonic processes, none of the Reykjanes Ridge sequences are dominated by a single large-magnitude earthquake, and they appear to be of relatively short duration (0.35-4.5 d) when compared to previously described mid-ocean ridge aftershock sequences. The occurrence of several near-equal magnitude events distributed throughout each sequence is inconsistent with the simple relaxation of mainshock-induced stresses and may reflect the involvement of magmatic or fluid processes along this deep (>2000 m) section of the Reykjanes Ridge.

Joint inversion of shear wave travel time residuals and geoid and depth anomalies for long-wavelength variations in upper mantle temperature and composition along the Mid-Atlantic Ridge

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Sheehan, Anne F.; Solomon, Sean C.

1991-01-01

Measurements were carried out for SS-S differential travel time residuals for nearly 500 paths crossing the northern Mid-Atlantic Ridge, assuming that the residuals are dominated by contributions from the upper mantle near the surface bounce point of the reflected phase SS. Results indicate that the SS-S travel time residuals decrease linearly with square root of age, to an age of 80-100 Ma, in general agreement with the plate cooling model. A joint inversion was formulated of travel time residuals and geoid and bathymetric anomalies for lateral variation in the upper mantle temperature and composition. The preferred inversion solutions were found to have variations in upper mantle temperature along the Mid-Atlantic Ridge of about 100 K. It was calculated that, for a constant bulk composition, such a temperature variation would produce about a 7-km variation in crustal thickness, larger than is generally observed.

Popping Rocks Revealed: Investigations from 14°N on the Mid-Atlantic Ridge

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Wanless, V. D.; Jones, M.; Kurz, M. D.; Soule, S. A.; Fornari, D. J.; Bendana, S.; Mittelstaedt, E. L.

2017-12-01

The popping rock, recovered in dredge 2πD43 in 1985, is commonly considered to be one of the most representative samples of undegassed upper mantle, based on high volatile and noble gas abundances. While this basalt is used to reconstruct mantle volatile contents and CO2 fluxes from mid-ocean ridges (MOR), the origin of the popping rock has remained ambiguous due to a lack of geologic context. Here, we present results from the first combined geochemical, geophysical, and geologic investigation of popping rocks from 14N on the Mid-Atlantic Ridge. By combining lava compositions with high-resolution bathymetric maps, we show that the popping rocks are confined to a single geographic area, at the transition between magmatic and tectonic segments. Fifteen popping rocks were collected in situ using the Alvin submersible in 2016. X-ray microtomography indicates that these lavas have variable vesicle abundances; including the highest vesicularities (>19%) recorded for any MOR basalt. Dissolved CO2 contents (163-175 ppm) are similar to proximal non-popping rocks and are in equilibrium at their eruption depths (>3600 m); however, total CO2 contents (based on vesicularity, dissolved CO2, and vesicle gas contents) are higher than non-popping rocks, ranging from 2800-14150 ppm. The popping rocks have average 3He/4He ratios of 8.17 ± 0.1 Ra and 4He concentrations of 1.84e-5 to 7.67e-5 cc/g STP. Compared to non-popping lavas, the popping rocks have a narrow range of major and trace element concentrations, suggesting little to no crystallization occurred during ascent or eruption. REE patterns and trace element ratios are indistinguishable in the popping rocks (La/Sm = 2.89 ± 0.05), indicating similar mantle sources and extents of melting. Based on lava compositions and spatial distribution, we suggest that the popping rocks at 14N were produced under similar magmatic conditions and erupted over short timescales, perhaps during a series of closely timed eruptions.

Changes in Bottom Water Physical Properties Above the Mid-Atlantic Ridge Flank in the Brazil Basin

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Zhao, Jian; Thurnherr, Andreas M.

2018-01-01

Warming of abyssal waters in recent decades has been widely documented around the global ocean. Here repeat hydrographic data collected in 1997 and 2014 near a deep fracture zone canyon in the eastern Brazil Basin are used to quantify the long-term change. Significant changes are found in the Antarctic Bottom Water (AABW) within the canyon. The AABW in 2014 was warmer (0.08 ± 0.06°C), saltier (0.01 ± 0.005), and less dense (0.005 ± 0.004 kg m-3) than in 1997. In contrast, the change in the North Atlantic Deep Water has complicated spatial structure and is almost indistinguishable from zero at 95% confidence. The resulting divergence in vertical displacement of the isopycnals modifies the local density stratification. At its peak, the local squared buoyancy frequency (N2) near the canyon is reduced by about 20% from 1997 to 2014. Similar reduction is found in the basinwide averaged profiles over the Mid-Atlantic Ridge flank along 25°W in years 1989, 2005, and 2014. The observed changes in density stratification have important implications for internal tide generation and dissipation.

Seismic Velocity Variation and Evolution of the Upper Oceanic Crust across the Mid-Atlantic Ridge at 1.3°S

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Jian, H.; Singh, S. C.

2017-12-01

The oceanic crust that covers >70% of the solid earth is formed at mid-ocean ridges, but get modified as it ages. Understanding the evolution of oceanic crust requires investigations of crustal structures that extend from zero-age on the ridge axis to old crust. In this study, we analyze a part of a 2000-km-long seismic transect that crosses the Mid-Atlantic Ridge segment at 1.3°S, south of the Chain transform fault. The seismic data were acquired using a 12-km-long multi-sensor streamer and dense air-gun shots. Using a combination of downward continuation and seismic tomography methods, we have derived a high-resolution upper crustal velocity structure down to 2-2.5 km depth below the seafloor, from the ridge axis to 3.5 Ma on both sides of the ridge axis. The results demonstrate that velocities increase at all depths in the upper crust as the crust ages, suggesting that hydrothermal precipitations seal the upper crustal pore spaces. This effect is most significant in layer 2A, causing a velocity increase of 0.5-1 km/s after 1-1.5 Ma, beyond which the velocity increase is very small. Furthermore, the results exhibit a significant decrease in both the frequency and amplitude of the low-velocity anomalies associated with faults beyond 1-1.5 Ma, when faults become inactive, suggesting a linkage between the sealing of fault space and the extinction of hydrothermal activity. Besides, the off-axis velocities are systematically higher on the eastern side of the ridge axis compared to on the western side, suggesting that a higher hydrothermal activity should exist on the outside-corner ridge flank than on the inside-corner flank. While the tomography results shown here cover 0-3.5 Ma crust, the ongoing research will further extend the study area to older crust and also incorporating pre-stack migration and full waveform inversion methods to improve the seismic structure.

Panmixia in a fragmented and unstable environment: the hydrothermal shrimp Rimicaris exoculata disperses extensively along the Mid-Atlantic Ridge.

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Sara Teixeira

Full Text Available Dispersal plays a fundamental role in the evolution and persistence of species, and especially for species inhabiting extreme, ephemeral and highly fragmented habitats as hydrothermal vents. The Mid-Atlantic Ridge endemic shrimp species Rimicaris exoculata was studied using microsatellite markers to infer connectivity along the 7100-Km range encompassing the sampled sites. Astonishingly, no genetic differentiation was found between individuals from the different geographic origins, supporting a scenario of widespread large-scale dispersal despite the habitat distance and fragmentation. We hypothesize that delayed metamorphosis associated to temperature differences or even active directed migration dependent on physical and/or chemical stimuli could explain these results and warrant further studies on adaptation and dispersal mechanisms.

Controls of Plume Dispersal at the Slow Spreading Mid-Atlantic Ridge

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Walter, M.; Mertens, C.; Koehler, J.; Sueltenfuss, J.; Rhein, M.; Keir, R. S.; Schmale, O.; Schneider v. Deimling, J.; German, C. R.; Yoerger, D. R.; Baker, E. T.

2011-12-01

The slow-spreading Mid-Atlantic Ridges hosts a multitude of different types of hydrothermal systems. Here, we compare the fluxes and the plume dispersal at three high temperature sites located in very diverse settings at comparable depths (~3000m): The recently discovered sites Turtle Pits, and Nibelungen on the southern MAR, and the Logatchev field in the North Atlantic. Plume mapping for these sites on cruises between 2004 and 2009 consisted of CTD Towyo-, Yoyo,- and station work, including velocity profiling, as well as water sampling for analysis of trace gases (CH4, H2, 3He/4He) and metals; temperature measurements and fluid sampling at the vent sites were carried out with an ROV. The aim of this work is to gain a better understanding of how the setting of a vent site affects the dispersal of the particle plume, and what means can be used to infer possible locations of vent sites based on the hydrographic properties and plume observations, using high resolution bathymetric mapping and hydrographic information. The ultramafic-hosted Nibelungen site (8°18'S) consists of a single active smoking crater, along with several extinct smokers, which is located off-axis south of a non-transform offset. The setting is characterized by rugged topography, favorable for the generation of internal tides, internal wave breaking, and vertical mixing. Elevated mixing with turbulent diffusivities Kρ up to 0.1 m2 s-1, 3 to 4 orders of magnitude higher than open ocean values, was observed close to the vent site. The mixing as well as the flow field exhibited a strong tidal cycle; the plume dispersal is thus dominated by the fast and intermittent vertical exchange and characterized by small scale spatial and temporal variability. The Turtle Pits vent fields (4°48'S) are located on a sill in a north-south orientated rift valley. The site consists of three (known) high temperature fields: Turtle Pits, Comfortless Cove, and Red Lion. The particle plume is confined to the rift

Spatiotemporal distribution of the seismicity along the Mid-Atlantic Ridge north of the Azores from hydroacoustic data: Insights into seismogenic processes in a ridge-hot spot context

Science.gov (United States)

Goslin, J.; Perrot, J.; Royer, J.-Y.; Martin, C.; LourençO, N.; Luis, J.; Dziak, R. P.; Matsumoto, H.; Haxel, J.; Fowler, M. J.; Fox, C. G.; Lau, A. T.-K.; Bazin, S.

2012-02-01

The seismicity of the North Atlantic was monitored from May 2002 to September 2003 by the `SIRENA array' of autonomous hydrophones. The hydroacoustic signals provide a unique data set documenting numerous low-magnitude earthquakes along the section of the Mid-Atlantic Ridge (MAR) located in a ridge-hot spot interaction context. During the experiment, 1696 events were detected along the MAR axis between 40°N and 51°N, with a magnitude of completeness level ofmb≈ 2.4. Inside the array, location errors are in the order of 2 km, and errors in the origin time are less than 1 s. From this catalog, 15 clusters were detected. The distribution of source level (SL) versus time within each cluster is used to discriminate clusters occurring in a tectonic context from those attributed to non-tectonic (i.e. volcanic or hydrothermal) processes. The location of tectonic and non-tectonic sequences correlates well with regions with positive and negative Mantle Bouguer Anomalies (MBAs), indicating the presence of thinner/colder and thicker/warmer crust respectively. At the scale of the entire array, both the complete and declustered catalogs derived from the hydroacoustic signals show an increase of the seismicity rate from the Azores up to 43°30'N suggesting a diminishing influence of the Azores hot spot on the ridge-axis temperature, and well correlated with a similar increase in the along-axis MBAs. The comparison of the MAR seismicity with the Residual MBA (RMBA) at different scales leads us to think that the low-magnitude seismicity rates are directly related to along-axis variations in lithosphere rheology and temperatures.

Turbulence and finestructure in a deep ocean channel with sill overflow on the mid-Atlantic ridge

Science.gov (United States)

Tippenhauer, Sandra; Dengler, Marcus; Fischer, Tim; Kanzow, Torsten

2015-05-01

Diapycnal mixing in the deep ocean is known to be much stronger in the vicinity of rough topography of mid-ocean ridges than above abyssal plains. In this study a horizontally profiling microstructure probe attached to an autonomous underwater vehicle (AUV) is used to infer the spatial distribution of the dissipation rate of turbulent kinetic energy (ε) in the central valley of the Mid-Atlantic Ridge. To the authors' knowledge, this is the first successful realization of a horizontal, deep-ocean microstructure survey. More than 22 h of horizontal, near-bottom microstructure data from the Lucky Strike segment (37°N) are presented. The study focuses on a channel with unidirectional sill overflow. Density was found to decrease along the channel following the mean northward flow of 3 to 8 cm/s. The magnitude of the rate of turbulent kinetic energy dissipation was distributed asymmetrically relative to the position of the sill. Elevated dissipation rates were present in a segment 1-4 km downstream (north) of the sill with peak values of 1 ×10-7 W/kg. Large flow speeds and elevated density finestructure were observed within this segment. Lowered hydrographic measurements indicated unstable stratification in the same region. The data indicate that hydraulic control was established at least temporarily. Inside the channel at wavelengths between 1 m and 250 m the slopes of AUV-inferred horizontal temperature gradient spectra were found to be consistent with turbulence in the inertial-convective subrange. Integrated temperature gradient variance in this wavelength interval was consistent with an ε2/3 dependence. The results illustrate that deep-reaching AUVs are a useful tool to study deep ocean turbulence over complex terrain where free-falling and lowered turbulence measurements are inefficient and time-consuming.

Free-living nematode species (Nematoda) dwelling in hydrothermal sites of the North Mid-Atlantic Ridge

Science.gov (United States)

Tchesunov, Alexei V.

2015-12-01

Morphological descriptions of seven free-living nematode species from hydrothermal sites of the Mid-Atlantic Ridge are presented. Four of them are new for science: Paracanthonchus olgae sp. n. (Chromadorida, Cyatholaimidae), Prochromadora helenae sp. n. (Chromadorida, Chromadoridae), Prochaetosoma ventriverruca sp. n. (Desmodorida, Draconematidae) and Leptolaimus hydrothermalis sp. n. (Plectida, Leptolaimidae). Two species have been previously recorded in hydrothermal habitats, and one species is recorded for the first time in such an environment. Oncholaimus scanicus (Enoplida, Oncholaimidae) was formerly known from only the type locality in non-hydrothermal shallow milieu of the Norway Sea. O. scanicus is a very abundant species in Menez Gwen, Lucky Strike and Lost City hydrothermal sites, and population of the last locality differs from other two in some morphometric characteristics. Desmodora marci (Desmodorida, Desmodoridae) was previously known from other remote deep-sea hydrothermal localities in south-western and north-eastern Pacific. Halomonhystera vandoverae (Monhysterida, Monhysteridae) was described and repeatedly found in mass in Snake Pit hydrothermal site. The whole hydrothermal nematode assemblages are featured by low diversity in comparison with either shelf or deep-sea non-hydrothermal communities. The nematode species list of the Atlantic hydrothermal vents consists of representatives of common shallow-water genera; the new species are also related to some shelf species. On the average, the hydrothermal species differ from those of slope and abyssal plains of comparable depths by larger sizes, diversity of buccal structures, presence of food content in the gut and ripe eggs in uteri.

Phytoplankton Assemblage Patterns in the Southern Mid-Atlantic Bight

Science.gov (United States)

Makinen, Carla; Moisan, Tiffany A. (Editor)

2012-01-01

As part of the Wallops Coastal Oceans Observing Laboratory (Wa-COOL) Project, we sampled a time-series transect in the southern Mid-Atlantic Bight (MAB) biweekly. Our 2-year time-series data included physical parameters, nutrient concentrations, and chlorophyll a concentrations. A detailed phytoplankton assemblage structure was examined in the second year. During the 2-year study, chlorophyll a concentration (and ocean color satellite imagery) indicated that phytoplankton blooms occurred in January/February during mixing conditions and in early autumn under stratified conditions. The chlorophyll a concentrations ranged from 0.25 microgram 1(exp -1) to 15.49 microgram 1(exp -1) during the 2-year period. We were able to discriminate approximately 116 different species under phase contrast microscopy. Dominant phytoplankton included Skeletonema costatum, Rhizosolenia spp., and Pseudo-nitzschia pungens. In an attempt to determine phytoplankton species competition/succession within the assemblage, we calculated a Shannon Weaver diversity index for our diatom microscopy data. Diatom diversity was greatest during the winter and minimal during the spring. Diatom diversity was also greater at nearshore stations than at offshore stations. Individual genera appeared patchy, with surface and subsurface patches appearing abruptly and persisting for only 1-2 months at a time. The distribution of individual species differed significantly from bulk variables of the assemblage (chlorophyll a ) and total phytoplankton assemblage (cells), which indicates that phytoplankton species may be limited in growth in ways that differ from those of the total assemblage. Our study demonstrated a highly diverse phytoplankton assemblage throughout the year, with opportunistic species dominating during spring and fall in response to seasonal changes in temperature and nutrients in the southern MAB.

Long-Term Seismicity of Northern (15° N-60° N) Mid-Atlantic Ridge (MAR) Recorded by two Regional Hydrophone Arrays: a Widespread Along-Ridge Influence of the Azores and Iceland Hotspots

Science.gov (United States)

Goslin, J.; Bazin, S.; Dziak, R. P.; Fox, C.; Fowler, M.; Haxel, J.; Lourenco, N.; Luis, J.; Martin, C.; Matsumoto, H.; Perrot, J.; Royer, J.

2004-12-01

The seismicity of the North Atlantic was recorded by two networks of hydrophones moored in the SOFAR channel, north and south of the Azores Plateau. The interpretation of the hydro-acoustic signals recorded during the first six-month common period of operation of the two networks (June 2002 to Nov. 2002) provides a unique data set on the spatial and time distributions of the numerous low-magnitude earthquakes which occurred along the Mid-Atlantic Ridge. Close to 2000 events were localized during this six-month period between latitudes 15° N and 63° N, 501 of which are localized within the SIRENA network (40° N-51° N) and 692 within the wider South Azores network (17° N-33° N). Using hydrophones to locate seafloor earthquakes by interpreting T-wave signals lowers the detection threshold of Mid-Atlantic Ridge events to 3.0 mb from the 4.7 mb of global seismic networks. This represents an average thirty-fold increase in the number of events: 62 events were detected by global seismological networks within the same area during the same period. An along-ridge spatial distribution of the seismicity is obtained by computing the cumulated numbers of events in 1° -wide latitudinal bins. When plotted vs. latitude, this first-order distribution shows remarkable long-wavelength patterns: the seismicity rate is low when approaching the Azores and Iceland (reaching values as low as 10 events/d° ), while it peaks to 70 events/d° in the vicinity of the Gibbs FZ. Moreover, the latitudinal distribution of the seismicity hints at an asymmetric influence of the Azores hotpot on the MAR. Finally, the spatial distribution of the seismicity anti-correlates well at long wavelengths with the zero-age depths along the MAR and correlates with the zero-age Mantle Bouguer (MBA) anomaly values and the Vs velocity anomalies at 100 km in the upper mantle. It is thus proposed that the seismicity level would be partly tied to the rheology and thickness of the brittle layer and be thus

Hydrothermal sediments as a potential record of seawater Nd isotope compositions: The Rainbow vent site (36°14'N, Mid-Atlantic Ridge)

Science.gov (United States)

Chavagnac, ValéRie; Palmer, Martin R.; Milton, J. Andrew; Green, Darryl R. H.; German, Christopher R.

2006-09-01

Geochemical compositions and Sr and Nd isotopes were measured in two cores collected ˜2 and 5 km from the Rainbow hydrothermal vent site on the Mid-Atlantic Ridge. Overall, the cores record enrichments in Fe and other metals from hydrothermal fallout, but sequential dissolution of the sediments allows discrimination between a leach phase (easily leachable) and a residue phase (refractory). The oxy-anion and transition metal distribution combined with rare earth element (REE) patterns suggest that (1) the leach fraction is a mixture of biogenic carbonate and hydrothermal Fe-Mn oxy-hydroxide with no significant contribution from detrital material and (2) >99.5% of the REE content of the leach fraction is of seawater origin. In addition, the leach fraction has an average 87Sr/86Sr ratio indistinguishable from modern seawater at 0.70916. Although we lack the ɛNd value of present-day deep water at the Rainbow vent site, we believe that the REE budget of the leach fraction is predominantly of seawater origin. We suggest therefore that the leach fraction provides a record of local seawater ɛNd values. Nd isotope data from these cores span the period of 4-14 ka (14C ages) and yield ɛNd values for North East Atlantic Deep Water (NEADW) that are higher (-9.3 to -11.1) than those observed in the nearby Madeira Abyssal Plain from the same depth (-12.4 ± 0.9). This observation suggests that either the Iceland-Scotland Overflow Water (ISOW) and Lower Deep Water contributions to the formation of NEADW are higher along the Mid-Atlantic Ridge than in the surrounding basins or that the relative proportion of ISOW was higher during this period than is observed today. This study indicates that hydrothermal sediments have the potential to provide a higher-resolution record of deep water ɛNd values, and hence deepwater circulation patterns in the oceans, than is possible from other types of sediments.

Geochemical features of sulfides from the Deyin-1 hydrothermal field at the southern Mid-Atlantic Ridge near 15°S

Science.gov (United States)

Wang, Shujie; Li, Huaiming; Zhai, Shikui; Yu, Zenghui; Cai, Zongwei

2017-12-01

In this study, geochemical compositions of elements in sulfide samples collected from the Deyin-1 hydrothermal field near the 15°S southern Mid-Atlantic Ridge (SMAR) were analyzed by the X-ray fluorescence spectrometry (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) to examine the enrichment regulations of ore-forming elements and hydrothermal mineralization. These sulfide precipitates can be classified macroscopically into three types: Fe-rich sulfide, Fe-Cu-rich sulfide and Fe-Zn-rich sulfide, and are characterized by the enrichment of base metal elements along with a sequence of Fe>Zn>Cu. Compared with sulfides from other hydrothermal fields on MAR, Zn concentrations of sulfides in the research area are significantly high, while Cu concentrations are relatively low. For all major, trace or rare-earth elements (REE), their concentrations and related characteristic parameters exhibit significant variations (up to one or two orders of magnitude), which indicates the sulfides from different hydrothermal vents or even a same station were formed at different stages of hydrothermal mineralization, and suggests the variations of chemical compositions of the hydrothermal fluid with respect to time. The hydrothermal temperatures of sulfides precipitation decreased gradually from station TVG10 (st.TVG10) to st.TVG12, and to st.TVG11, indicating that the precipitation of hydrothermal sulfides is subjected to conditions changed from high temperature to low temperature, and that the hydrothermal activity of study area was at the late stage of a general trend of evolution from strong to weak. The abnormally low concentrations of REE in sulfides and their similar chondrite-normalized REE patterns show that REEs in all sulfides were derived from a same source, but underwent different processes of migration or enrichment, or sulfides were formed at different stages of hydrothermal mineralization. The sulfides collected from the active hydrothermal vent were

Modelling of hydrothermal fluid circulation in a heterogeneous medium: Application to the Rainbow Vent site (Mid-Atlantic-Ridge, 36°14N)

Science.gov (United States)

Perez, F.; Mügler, C.; Jean-Baptiste, P.; Charlou, J. L.

2012-04-01

Hydrothermal activity at the axis of mid-ocean ridges is a key driver for energy and matter transfer from the interior of the Earth to the ocean floor. At mid-ocean ridges, seawater penetrates through the permeable young crust, warms at depth and exchanges chemicals with the surrounding rocks. This hot fluid focuses and flows upwards, then is expelled from the crust at hydrothermal vent sites in the form of black or white smokers completed by diffusive emissions. We developed a new numerical tool in the Cast3M software framework to model such hydrothermal circulations. Thermodynamic properties of one-phase pure water were calculated from the IAPWS formulation. This new numerical tool was validated on several test cases of convection in closed-top and open-top boxes. Simulations of hydrothermal circulation in a homogeneous-permeability porous medium also gave results in good agreement with already published simulations. We used this new numerical tool to construct a geometric and physical model configuration of the Rainbow Vent site at 36°14'N on the Mid-Atlantic Ridge. In this presentation, several configurations will be discussed, showing that high temperatures and high mass fluxes measured at the Rainbow site cannot be modelled with hydrothermal circulation in a homogeneous-permeability porous medium. We will show that these high values require the presence of a fault or a preferential pathway right below the venting site. We will propose and discuss a 2-D one-path model that allows us to simulate both high temperatures and high mass fluxes. This modelling of the hydrothermal circulation at the Rainbow site constitutes a first but necessary step to understand the origin of high concentrations of hydrogen issued from this ultramafic-hosted vent field.

Delta-proteobacterial SAR324 group in hydrothermal plumes on the South Mid-Atlantic Ridge

KAUST Repository

Cao, Huiluo

2016-03-08

In the dark ocean, the SAR324 group of Delta-proteobacteria has been associated with a chemolithotrophic lifestyle. However, their electron transport chain for energy generation and information system has not yet been well characterized. In the present study, four SAR324 draft genomes were extracted from metagenomes sampled from hydrothermal plumes in the South Mid-Atlantic Ridge. We describe novel electron transport chain components in the SAR324 group, particularly the alternative complex III, which is involved in energy generation. Moreover, we propose that the C-type cytochrome, for example the C553, may play a novel role in electron transfer, adding to our knowledge regarding the energy generation process in the SAR324 cluster. The central carbon metabolism in the described SAR324 genomes exhibits several new features other than methanotrophy e.g. aromatic compound degradation. This suggests that methane oxidation may not be the main central carbon metabolism component in SAR324 cluster bacteria. The reductive acetyl-CoA pathway may potentially be essential in carbon fixation due to the absence of components from the Calvin-Benson cycle. Our study provides insight into the role of recombination events in shaping the genome of the SAR324 group based on a larger number of repeat regions observed, which has been overlooked thus far.

Serpentinization of abyssal peridotites from the MARK area, Mid-Atlantic Ridge: Sulfur geochemistry and reaction modeling

Science.gov (United States)

Alt, J.C.; Shanks, Wayne C.

2003-01-01

The opaque mineralogy and the contents and isotope compositions of sulfur in serpentinized peridotites from the MARK (Mid-Atlantic Ridge, Kane Fracture Zone) area were examined to understand the conditions of serpentinization and evaluate this process as a sink for seawater sulfur. The serpentinites contain a sulfur-rich secondary mineral assemblage and have high sulfur contents (up to 1 wt.%) and elevated ??34Ssulfide (3.7 to 12.7???). Geochemical reaction modeling indicates that seawater-peridotite interaction at 300 to 400??C alone cannot account for both the high sulfur contents and high ??34Ssulfide. These require a multistage reaction with leaching of sulfide from subjacent gabbro during higher temperature (???400??C) reactions with seawater and subsequent deposition of sulfide during serpentinization of peridotite at ???300??C. Serpentinization produces highly reducing conditions and significant amounts of H2 and results in the partial reduction of seawater carbonate to methane. The latter is documented by formation of carbonate veins enriched in 13C (up to 4.5???) at temperatures above 250??C. Although different processes produce variable sulfur isotope effects in other oceanic serpentinites, sulfur is consistently added to abyssal peridotites during serpentinization. Data for serpentinites drilled and dredged from oceanic crust and from ophiolites indicate that oceanic peridotites are a sink for up to 0.4 to 6.0 ?? 1012 g seawater S yr-1. This is comparable to sulfur exchange that occurs in hydrothermal systems in mafic oceanic crust at midocean ridges and on ridge flanks and amounts to 2 to 30% of the riverine sulfate source and sedimentary sulfide sink in the oceans. The high concentrations and modified isotope compositions of sulfur in serpentinites could be important for mantle metasomatism during subduction of crust generated at slow spreading rates. ?? 2003 Elsevier Science Ltd.

Does presence of a mid-ocean ridge enhance biomass and biodiversity?

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Imants G Priede

Full Text Available In contrast to generally sparse biological communities in open-ocean settings, seamounts and ridges are perceived as areas of elevated productivity and biodiversity capable of supporting commercial fisheries. We investigated the origin of this apparent biological enhancement over a segment of the North Mid-Atlantic Ridge (MAR using sonar, corers, trawls, traps, and a remotely operated vehicle to survey habitat, biomass, and biodiversity. Satellite remote sensing provided information on flow patterns, thermal fronts, and primary production, while sediment traps measured export flux during 2007-2010. The MAR, 3,704,404 km(2 in area, accounts for 44.7% lower bathyal habitat (800-3500 m depth in the North Atlantic and is dominated by fine soft sediment substrate (95% of area on a series of flat terraces with intervening slopes either side of the ridge axis contributing to habitat heterogeneity. The MAR fauna comprises mainly species known from continental margins with no evidence of greater biodiversity. Primary production and export flux over the MAR were not enhanced compared with a nearby reference station over the Porcupine Abyssal Plain. Biomasses of benthic macrofauna and megafauna were similar to global averages at the same depths totalling an estimated 258.9 kt C over the entire lower bathyal north MAR. A hypothetical flat plain at 3500 m depth in place of the MAR would contain 85.6 kt C, implying an increase of 173.3 kt C attributable to the presence of the Ridge. This is approximately equal to 167 kt C of estimated pelagic biomass displaced by the volume of the MAR. There is no enhancement of biological productivity over the MAR; oceanic bathypelagic species are replaced by benthic fauna otherwise unable to survive in the mid ocean. We propose that globally sea floor elevation has no effect on deep sea biomass; pelagic plus benthic biomass is constant within a given surface productivity regime.

Rapid cooling rates at an active mid-ocean ridge from zircon thermochronology

Science.gov (United States)

Schmitt, Axel K.; Perfit, Michael R.; Rubin, Kenneth H.; Stockli, Daniel F.; Smith, Matthew C.; Cotsonika, Laurie A.; Zellmer, Georg F.; Ridley, W. Ian

2011-01-01

Oceanic spreading ridges are Earth's most productive crust generating environment, but mechanisms and rates of crustal accretion and heat loss are debated. Existing observations on cooling rates are ambiguous regarding the prevalence of conductive vs. convective cooling of lower oceanic crust. Here, we report the discovery and dating of zircon in mid-ocean ridge dacite lavas that constrain magmatic differentiation and cooling rates at an active spreading center. Dacitic lavas erupted on the southern Cleft segment of the Juan de Fuca ridge, an intermediate-rate spreading center, near the intersection with the Blanco transform fault. Their U–Th zircon crystallization ages (29.3-4.6+4.8 ka; 1δ standard error s.e.) overlap with the (U–Th)/He zircon eruption age (32.7 ± 1.6 ka) within uncertainty. Based on similar 238U-230Th disequilibria between southern Cleft dacite glass separates and young mid-ocean ridge basalt (MORB) erupted nearby, differentiation must have occurred rapidly, within ~ 10–20 ka at most. Ti-in-zircon thermometry indicates crystallization at 850–900 °C and pressures > 70–150 MPa are calculated from H2O solubility models. These time-temperature constraints translate into a magma cooling rate of ~ 2 × 10-2 °C/a. This rate is at least one order-of-magnitude faster than those calculated for zircon-bearing plutonic rocks from slow spreading ridges. Such short intervals for differentiation and cooling can only be resolved through uranium-series (238U–230Th) decay in young lavas, and are best explained by dissipating heat convectively at high crustal permeability.

Similar mid-depth Atlantic water mass provenance during the Last Glacial Maximum and Heinrich Stadial 1

Science.gov (United States)

Howe, Jacob N. W.; Huang, Kuo-Fang; Oppo, Delia W.; Chiessi, Cristiano M.; Mulitza, Stefan; Blusztajn, Jurek; Piotrowski, Alexander M.

2018-05-01

The delivery of freshwater to the North Atlantic during Heinrich Stadial 1 (HS1) is thought to have fundamentally altered the operation of Atlantic meridional overturning circulation (AMOC). Although benthic foraminiferal carbon isotope records from the mid-depth Atlantic show a pronounced excursion to lower values during HS1, whether these shifts correspond to changes in water mass proportions, advection, or shifts in the carbon cycle remains unclear. Here we present new deglacial records of authigenic neodymium isotopes - a water mass tracer that is independent of the carbon cycle - from two cores in the mid-depth South Atlantic. We find no change in neodymium isotopic composition, and thus water mass proportions, between the Last Glacial Maximum (LGM) and HS1, despite large decreases in carbon isotope values at the onset of HS1 in the same cores. We suggest that the excursions of carbon isotopes to lower values were likely caused by the accumulation of respired organic matter due to slow overturning circulation, rather than to increased southern-sourced water, as typically assumed. The finding that there was little change in water mass provenance in the mid-depth South Atlantic between the LGM and HS1, despite decreased overturning, suggests that the rate of production of mid-depth southern-sourced water mass decreased in concert with decreased production of northern-sourced intermediate water at the onset of HS1. Consequently, we propose that even drastic changes in the strength of AMOC need not cause a significant change in South Atlantic mid-depth water mass proportions.

Heat flow, morphology, pore fluids and hydrothermal circulation in a typical Mid-Atlantic Ridge flank near Oceanographer Fracture Zone

Science.gov (United States)

Le Gal, V.; Lucazeau, F.; Cannat, M.; Poort, J.; Monnin, C.; Battani, A.; Fontaine, F.; Goutorbe, B.; Rolandone, F.; Poitou, C.; Blanc-Valleron, M.-M.; Piedade, A.; Hipólito, A.

2018-01-01

Hydrothermal circulation affects heat and mass transfers in the oceanic lithosphere, not only at the ridge axis but also on their flanks, where the magnitude of this process has been related to sediment blanket and seamounts density. This was documented in several areas of the Pacific Ocean by heat flow measurements and pore water analysis. However, as the morphology of Atlantic and Indian ridge flanks is generally rougher than in the Pacific, these regions of slow and ultra-slow accretion may be affected by hydrothermal processes of different regimes. We carried out a survey of two regions on the eastern and western flanks of the Mid-Atlantic Ridge between Oceanographer and Hayes fracture zones. Two hundred and eight new heat flow measurements were obtained along six seismic profiles, on 5 to 14 Ma old seafloor. Thirty sediment cores (from which porewaters have been extracted) have been collected with a Kullenberg corer equipped with thermistors thus allowing simultaneous heat flow measurement. Most heat flow values are lower than those predicted by purely conductive cooling models, with some local variations and exceptions: heat flow values on the eastern flank of the study area are more variable than on the western flank, where they tend to increase westward as the sedimentary cover in the basins becomes thicker and more continuous. Heat flow is also higher, on average, on the northern sides of both the western and eastern field regions and includes values close to conductive predictions near the Oceanographer Fracture Zone. All the sediment porewaters have a chemical composition similar to that of bottom seawater (no anomaly linked to fluid circulation has been detected). Heat flow values and pore fluid compositions are consistent with fluid circulation in volcanic rocks below the sediment. The short distances between seamounts and short fluid pathways explain that fluids flowing in the basaltic aquifer below the sediment have remained cool and unaltered

Carbon isotopes and concentrations in mid-oceanic ridge basalts

International Nuclear Information System (INIS)

Pineau, F.; Javoy, M.

1983-01-01

In order to estimate carbon fluxes at mid-ocean ridges and carbon isotopic compositions in the convective mantle, we have studied carbon concentrations and isotopic compositions in tholeiitic glasses from the FAMOUS zone (Mid-Atlantic Ridge at 36 0 N) and East Pacific Rise from 21 0 N (RITA zone) to 20 0 S. These samples correspond essentially to the whole spectrum of spreading rates (2-16 cm/yr). The contain: -CO 2 vesicles in various quantities (3-220 ppm C) with delta 13 C between -4 and -9per mille relative to PDB, in the range of carbonatites and diamonds. - Carbonate carbon (3-100 ppm C) with delta 13 C between -2.6 and -20.0per mille relative to PDB. - Dissolved carbon at a concentration of 170+-10 ppm under 250 bar pressure with delta 13 C from -9 to -21per mille relative to PDB. This dissolved carbon, not contained in large CO 2 vesicles, corresponds to a variety of chemical forms among which part of the above carbonates, microscopic CO 2 bubbles and graphite. The lightest portions of this dissolved carbon are extracted at low temperatures (400-600 0 C) whereas the CO 2 from the vesicles is extracted near fusion temperature. These features can be explained by outgassing processes in two steps from the source region of the magma: (1) equilibrium outgassing before the second percolation threshold, where micron size bubbles are continuously reequilibrated with the magma; (2) distillation after the second percolation threshold when larger bubbles travel faster than magma concentrations to the surface. The second step may begin at different depths apparently related to the spreading rate, shallower for fast-spreading ridges than for slow-spreading ridges. (orig./WL)

Ca/Al of plagioclase-hosted melt inclusions as an indicator for post-entrapment processes at mid-ocean ridges?

Energy Technology Data Exchange (ETDEWEB)

Zhang, H.T.; Yang, Y.M.; Yan, Q.S.; Shi, Z.F.; Zhu, Z.W.; Su, W.C.; Qin, C.J.; Ye, J.

2016-07-01

The composition of melt inclusions in basalts erupted at mid-ocean ridges may be modified by post-entrapment processes, so the present composition of melt inclusions may not represent their original composition at the time of entrapment. By combining the melt inclusion composition in samples from the South Mid-Atlantic Ridge at 19°S analyzed in this study, and from the Petrological Database, we found that post-entrapment crystallization processes resulted in higher Ca/Al, Mg#[100×atomic Mg2+/(Mg2++Fe2+)], MgO and FeO contents, and lower CaO and Al2O3 contents of plagioclase-hosted melt inclusions relative to those hosted in olivine. In addition, melt inclusions hosted in plagioclase with anorthite content larger than 80mol.% had been modified more readily than others. By discussing the relationships between Ca/Al and fractional crystallization, post-entrapment crystallization, and the original melt composition, we propose that Ca/Al can be regarded as an indicator of the effect of post-entrapment processes on melt inclusion composition. Specifically, i) when Ca/Al<0.78, melt inclusion compositions corrected for fractional crystallization to Mg#=72 can represent the primary magma at mid-ocean ridges; ii) when 0.781.0, the compositions of melt inclusions do not reflect the original melt composition nor preserve information about the mantle source. According to these criteria, plagioclase-hosted melt inclusions with Ca/Al>1.0 in basalts from the South Mid-Atlantic Ridge at19°S cannot represent the composition of the melt at the moment of their entrapment. (Author)

Mid-ocean ridge serpentinite in the Puerto Rico Trench: Accretion, alteration, and subduction of Cretaceous seafloor in the Atlantic Ocean

Science.gov (United States)

Klein, F.; Marschall, H.; Bowring, S. A.; Horning, G.

2016-12-01

Serpentinite is believed to be one of the main carriers of water and fluid mobile elements into subduction zones, but direct evidence for serpentinite subduction has been elusive. The Antilles island arc is one of only two subduction zones worldwide that recycles slow-spreading oceanic lithosphere where descending serpentinite is both exposed by faulting and directly accessible on the seafloor. Here we examined serpentinized peridotites dredged from the North Wall of the Puerto Rico Trench (NWPRT) to assess their formation and alteration history and discuss geological ramifications resulting from their emplacement and subduction. Lithospheric accretion and serpentinization occurred, as indicated by U-Pb geochronology of hydrothermally altered zircon, at the Cretaceous Mid-Atlantic Ridge (CMAR). In addition to lizardite-rich serpentinites with pseudomorphic textures after olivine and pyroxene typical for static serpentinization at slow spreading mid-ocean ridges, recovered samples include non-pseudomorphic antigorite-rich serpentinites that are otherwise typically associated with peridotite at convergent plate boundaries. Antigorite-serpentinites have considerably lower Fe(III)/Fetot and lower magnetic susceptibilities than lizardite-serpentinites with comparable Fetot contents. Rare earth element (REE) contents of lizardite-serpentinites decrease linearly with increasing Fe(III)/Fetot of whole rock samples, suggesting that oxidation during seafloor weathering of serpentinite releases REEs to seawater. Serpentinized peridotites recorded multifaceted igneous and high- to low-temperature hydrothermal processes that involved extensive chemical, physical, and mineralogical modifications of their peridotite precursors with strong implications for our understanding of the accretion, alteration, and subduction of slow-spreading oceanic lithosphere.

Sublatitudinal Isotope Heterogeneity of The Atlantic and Adjacent Continents: A Relation To The Litospheric Plates and Superplums

Science.gov (United States)

Mironov, Yu. V.; Ryakhovsky, V. M.; Pustovoy, A. A.; Lapidus, I. V.

Four Sr-Nd-Pb isotope sublatitudinal provinces are chosen in the Atlantic and on ad- jacent continents. They include mid-ocean ridges, oceanic rises and islands, as well as Late Mesozoic - Cenozoic continental rifts and traps. A modified Zindler-Hart "man- tle tetrahedron" (1986) have been used for rock systematics. Its major classification element alongside with known end-members (DM, HIMU, EM1, EM2) is any in- tratetrahedron component F ("focal") (Mironov et al., 2000; Rundquist et al., 2000; Ryakhovsky, 2000). It represents average characteristic of all known intratetrahedron components (FOZO, C, PREMA etc.), updated by methods of multidimensional statis- tics. Northern province includes Mid-Atlantic Ridge from a southern part of Reykjanes ridge up to 24S, numerous islands and rises, located at the same latitudes, Cameroon Line, African and European rifts, Aden and Red sea spreading centres, and also Co- mores in Indian ocean. The main composition dispersion of volcanics from withinplate oceanic and continental structures is determined by mixture of F and HIMU (rarely with admixture EM2). MORB within this area are characterized by stable admixture HIMU. Similar composition have the rocks in Bouvet-Antarctic province, within the limits of which the rises Spiss and Shona, the most southern part of Mid-Atlantic ridge, island Bouvet, an adjacent part of Southwest-Indian Ridge, and also traps and rifts on northern coast of Antarctic Continent are located. The Southern province lies in outlines of known Southern hemisphere DUPAL-anomaly (Hart, 1984). The with- inplate oceanic rocks (Gough, Tristan-da-Kunha, Walvis ridge, Rio Grande Plateau, Discovery) correspond to a mixture F + EM1 (sometimes F + EM1 + EM2) and are similar with traps of Southern America and Africa. Further to east this province is traced on islands and mid-ocean ridges in Indian ocean. MORB of Southern Atlantic and Indian ocean are enriched EM1. The Arctic province includes spreading ridges of

Ca/Al of plagioclase-hosted melt inclusions as an indicator for post-entrapment processes at mid-ocean ridges?

International Nuclear Information System (INIS)

Zhang, H.T.; Yang, Y.M.; Yan, Q.S.; Shi, Z.F.; Zhu, Z.W.; Su, W.C.; Qin, C.J.; Ye, J.

2016-01-01

The composition of melt inclusions in basalts erupted at mid-ocean ridges may be modified by post-entrapment processes, so the present composition of melt inclusions may not represent their original composition at the time of entrapment. By combining the melt inclusion composition in samples from the South Mid-Atlantic Ridge at 19°S analyzed in this study, and from the Petrological Database, we found that post-entrapment crystallization processes resulted in higher Ca/Al, Mg#[100×atomic Mg2+/(Mg2++Fe2+)], MgO and FeO contents, and lower CaO and Al2O3 contents of plagioclase-hosted melt inclusions relative to those hosted in olivine. In addition, melt inclusions hosted in plagioclase with anorthite content larger than 80mol.% had been modified more readily than others. By discussing the relationships between Ca/Al and fractional crystallization, post-entrapment crystallization, and the original melt composition, we propose that Ca/Al can be regarded as an indicator of the effect of post-entrapment processes on melt inclusion composition. Specifically, i) when Ca/Al 1.0, the compositions of melt inclusions do not reflect the original melt composition nor preserve information about the mantle source. According to these criteria, plagioclase-hosted melt inclusions with Ca/Al>1.0 in basalts from the South Mid-Atlantic Ridge at19°S cannot represent the composition of the melt at the moment of their entrapment. (Author)

Metabasalts from the Mid-Atlantic Ridge: new insights into hydrothermal systems in slow-spreading crust

Science.gov (United States)

Gillis, Kathryn M.; Thompson, Geoffrey

1993-12-01

An extensive suite of hydrothermally altered rocks were recovered by Alvin and dredging along the MARK [Mid-Atlantic Ridge, south of the Kane Fracture Zone (23 24°N)] where detachment faulting has provided a window into the crustal component of hydrothermal systems. Rocks of basaltic composition are altered to two assemblages with these characteristics: (i) type I: albitic plagioclase (An02 10)+mixed-layer smectite/chlorite or chlorite±actinolite±quartz±sphene, 20% of the clinopyroxene is altered, and Cu and Zn are leached. The geochemical signature of these alteration types reflects the relative proportion and composition of secondary minerals, and the degree of alteration of primary phases, and does not show simple predictive relationships. Element mobilities indicate that both alteration types formed at low water/rock ratios. The MARK assemblages are typical of the greenschist and transition to the amphibolite facies, and represent two distinct, albeit overlapping, temperature regimes: type I-180 to 300°C and type II-250 to 450°C. By analogy with DSDP/ODP Hole 504B and many ophiolites, the MARK metabasalts were altered within the downwelling limb of a hydrothermal cell and type I and II samples formed in the upper and lower portions of the sheeted like complex, respectively. Episodic magmatic and hydrothermal events at slow-spreading ridges suggest that these observed mineral assemblages represent the cumulative effects of more than one hydrothermal event. Groundmass and vein assemblages in the MARK metabasalts indicate either that alteration conditions did not change during successive hydrothermal events or that these assemblages record only the highest temperature event. Lack of retrograde reactions or overprinting of lower temperature assemblages (e.g., zeolites) suggests that there is a continuum in alteration conditions while crustal segments remain in the ridge axis environment. The type II samples may be representative of the reaction zone where

Biodiversity patterns, environmental drivers and indicator species on a High-temperature Hydrothermal edifice, mid-Atlantic ridge

KAUST Repository

Sarrazin, Jozée

2015-04-25

Knowledge on quantitative faunal distribution patterns of hydrothermal communities in slow-spreading vent fields is particularly scarce, despite the importance of these ridges in the global mid-ocean system. This study assessed the composition, abundance and diversity of 12 benthic faunal assemblages from various locations on the Eiffel Tower edifice (Lucky Strike vent field, Mid-Atlantic Ridge) and investigated the role of key environmental conditions (temperature, total dissolved iron (TdFe), sulfide (TdS), copper (TdCu) and pH) on the distribution of macro- and meiofaunal species at small spatial scales (< 1 m). There were differences in macro- and meiofaunal community structure between the different sampling locations, separating the hydrothermal community of the Eiffel Tower edifice into three types of microhabitats: (1) cold microhabitats characterized by low temperatures (<6 °C), high TdCu (up to 2.4±1.37 µmol l−1), high pH (up to 7.34±0.13) but low TdS concentrations (<6.98±5.01 µmol l−1); (2) warm microhabitats characterized by warmer temperatures (>6 °C), low pH (<6.5) and high TdS/TdFe concentrations (>12.8 µmol l−1/>1.1 µmol l−1 respectively); and (3) a third microhabitat characterized by intermediate abiotic conditions. Environmental conditions showed more variation in the warm microhabitats than in the cold microhabitats. In terms of fauna, the warm microhabitats had lower macro- and meiofaunal densities, and lower richness and Shannon diversity than the cold microhabitats. Six macrofaunal species (Branchipolynoe seepensis, Amathys lutzi, Bathymodiolus azoricus, Lepetodrilus fucensis, Protolira valvatoides and Chorocaris chacei) and three meiofaunal taxa (Paracanthonchus, Cephalochaetosoma and Microlaimus) were identified as being significant indicator species/taxa of particular microhabitats. Our results also highlight very specific niche separation for copepod juveniles among the different hydrothermal microhabitats. Some sampling

Initial chronology of a recently discovered hydrothermal field at 14°45‧N, Mid-Atlantic Ridge

Science.gov (United States)

Lalou, Claude; Reyss, Jean Louis; Brichet, Evelyne; Krasnov, Sergey; Stepanova, Tamara; Cherkashev, Georgiy; Markov, Vladimir

1996-11-01

Two expeditions of the 'Sevmorgeologija' association (1991-1994) led to the discovery of two new hydrothermal sites on the Mid Atlantic Ridge (MAR), south of the 15°20‧ North Fracture Zone, one around 14°45‧N and the other around 14°42‧N. The northern one, between 14°45‧ and 14°45.3‧N has been studied in detail. About 12 mounds have been mapped and 3 of them have been sampled using a large hydraulic grab sampler. The largest one is about 200 m long and 200 m wide. When progressively moving up on the slope of an uplifted block of the rift valley floor, the sulphide samples have revealed ages ranging from about 10 ka to 60 ka. The ages were obtained using the 230Th/234U dating method used for chronological studies of diverse hydrothermal fields. The general picture of this lateral location of the samples of different ages provides evidence of a shift in the focus of hydrothermal activity with time. Moreover, there were rejuvenation stages of hydrothermal activity, including black and white smokers.

Abundance, distribution and diversity of gelatinous predators along the northern Mid-Atlantic Ridge: A comparison of different sampling methodologies.

Directory of Open Access Journals (Sweden)

Aino Hosia

Full Text Available The diversity and distribution of gelatinous zooplankton were investigated along the northern Mid-Atlantic Ridge (MAR from June to August 2004.Here, we present results from macrozooplankton trawl sampling, as well as comparisons made between five different methodologies that were employed during the MAR-ECO survey. In total, 16 species of hydromedusae, 31 species of siphonophores and four species of scyphozoans were identified to species level from macrozooplankton trawl samples. Additional taxa were identified to higher taxonomic levels and a single ctenophore genus was observed. Samples were collected at 17 stations along the MAR between the Azores and Iceland. A divergence in the species assemblages was observed at the southern limit of the Subpolar Frontal Zone. The catch composition of gelatinous zooplankton is compared between different sampling methodologies including: a macrozooplankton trawl; a Multinet; a ringnet attached to bottom trawl; and optical platforms (Underwater Video Profiler (UVP & Remotely Operated Vehicle (ROV. Different sampling methodologies are shown to exhibit selectivity towards different groups of gelatinous zooplankton. Only ~21% of taxa caught during the survey were caught by both the macrozooplankton trawl and the Multinet when deployed at the same station. The estimates of gelatinous zooplankton abundance calculated using these two gear types also varied widely (1.4 ± 0.9 individuals 1000 m-3 estimated by the macrozooplankton trawl vs. 468.3 ± 315.4 individuals 1000 m-3 estimated by the Multinet (mean ± s.d. when used at the same stations (n = 6. While it appears that traditional net sampling can generate useful data on pelagic cnidarians, comparisons with results from the optical platforms suggest that ctenophore diversity and abundance are consistently underestimated, particularly when net sampling is conducted in combination with formalin fixation. The results emphasise the importance of considering

Abundance, distribution and diversity of gelatinous predators along the northern Mid-Atlantic Ridge: A comparison of different sampling methodologies

Science.gov (United States)

Falkenhaug, Tone; Baxter, Emily J.

2017-01-01

The diversity and distribution of gelatinous zooplankton were investigated along the northern Mid-Atlantic Ridge (MAR) from June to August 2004.Here, we present results from macrozooplankton trawl sampling, as well as comparisons made between five different methodologies that were employed during the MAR-ECO survey. In total, 16 species of hydromedusae, 31 species of siphonophores and four species of scyphozoans were identified to species level from macrozooplankton trawl samples. Additional taxa were identified to higher taxonomic levels and a single ctenophore genus was observed. Samples were collected at 17 stations along the MAR between the Azores and Iceland. A divergence in the species assemblages was observed at the southern limit of the Subpolar Frontal Zone. The catch composition of gelatinous zooplankton is compared between different sampling methodologies including: a macrozooplankton trawl; a Multinet; a ringnet attached to bottom trawl; and optical platforms (Underwater Video Profiler (UVP) & Remotely Operated Vehicle (ROV)). Different sampling methodologies are shown to exhibit selectivity towards different groups of gelatinous zooplankton. Only ~21% of taxa caught during the survey were caught by both the macrozooplankton trawl and the Multinet when deployed at the same station. The estimates of gelatinous zooplankton abundance calculated using these two gear types also varied widely (1.4 ± 0.9 individuals 1000 m-3 estimated by the macrozooplankton trawl vs. 468.3 ± 315.4 individuals 1000 m-3 estimated by the Multinet (mean ± s.d.) when used at the same stations (n = 6). While it appears that traditional net sampling can generate useful data on pelagic cnidarians, comparisons with results from the optical platforms suggest that ctenophore diversity and abundance are consistently underestimated, particularly when net sampling is conducted in combination with formalin fixation. The results emphasise the importance of considering sampling methodology

Abundance, distribution and diversity of gelatinous predators along the northern Mid-Atlantic Ridge: A comparison of different sampling methodologies.

Science.gov (United States)

Hosia, Aino; Falkenhaug, Tone; Baxter, Emily J; Pagès, Francesc

2017-01-01

The diversity and distribution of gelatinous zooplankton were investigated along the northern Mid-Atlantic Ridge (MAR) from June to August 2004.Here, we present results from macrozooplankton trawl sampling, as well as comparisons made between five different methodologies that were employed during the MAR-ECO survey. In total, 16 species of hydromedusae, 31 species of siphonophores and four species of scyphozoans were identified to species level from macrozooplankton trawl samples. Additional taxa were identified to higher taxonomic levels and a single ctenophore genus was observed. Samples were collected at 17 stations along the MAR between the Azores and Iceland. A divergence in the species assemblages was observed at the southern limit of the Subpolar Frontal Zone. The catch composition of gelatinous zooplankton is compared between different sampling methodologies including: a macrozooplankton trawl; a Multinet; a ringnet attached to bottom trawl; and optical platforms (Underwater Video Profiler (UVP) & Remotely Operated Vehicle (ROV)). Different sampling methodologies are shown to exhibit selectivity towards different groups of gelatinous zooplankton. Only ~21% of taxa caught during the survey were caught by both the macrozooplankton trawl and the Multinet when deployed at the same station. The estimates of gelatinous zooplankton abundance calculated using these two gear types also varied widely (1.4 ± 0.9 individuals 1000 m-3 estimated by the macrozooplankton trawl vs. 468.3 ± 315.4 individuals 1000 m-3 estimated by the Multinet (mean ± s.d.) when used at the same stations (n = 6). While it appears that traditional net sampling can generate useful data on pelagic cnidarians, comparisons with results from the optical platforms suggest that ctenophore diversity and abundance are consistently underestimated, particularly when net sampling is conducted in combination with formalin fixation. The results emphasise the importance of considering sampling methodology

Insights on the evolution of mid-ocean basins: the Atlantis Basin of southern Azores

Science.gov (United States)

Alves, T.; Bouriak, S.; Volkonskaya, A.; Monteiro, J.; Ivanov, M.

2003-04-01

Single-channel seismic reflection and sidescan (OKEAN) data acquired in an unstudied region of the North Atlantic give important insights on the evolution of mid-ocean basins. Located on the eastern flank of the Mid-Atlantic Ridge, south of the Azores Islands, the study area contains more than 1,000 ms two-way travel-time of sediments with a similar seismic stratigraphy to that of ODP sites 950-952 in the Madeira Abyssal Plain. Processed thickness values correspond to a maximum thickness of about 1450 m and an average thickness of more than 500 m based on velocity data from ODP sites 950-952. The structure of the surveyed area and its location in relation to the Madeira Abyssal Plain and Mid-Atlantic Ridge indicate the existence, south of Azores, of two distinct sedimentary basins separated by major structural lineaments (Azores-Gibraltar and Atlantis Fracture Zones) and by seamount chains (Cruiser-Great Meteor Chain, Plato-Atlantis Chain). The basement of the sedimentary basins is irregular, showing multiple dome-shaped volcanic structures identical to those in the Norwegian-Greenland Sea and Madeira Abyssal Plain. However, half-graben/graben basement blocks predominate east of 30ºW underneath a moderately deformed overburden. The complex structure observed most likely reflects changes in the direction and velocity of ocean spreading plus variations in the regional thermal gradients induced by local hot spots. In parallel, some of the sub-surface structures identified next to basin-bounding Fracture Zones may have resulted from transtensional and transpressional tectonism.

Millennial-scale variations in dustiness recorded in Mid-Atlantic sediments from 0 to 70 ka

Science.gov (United States)

Middleton, Jennifer L.; Mukhopadhyay, Sujoy; Langmuir, Charles H.; McManus, Jerry F.; Huybers, Peter J.

2018-01-01

Sedimentary records of dust deposition in the subtropical Atlantic provide important constraints on millennial- and orbital-scale variability in atmospheric circulation and North African aridity. Constant flux proxies, such as extraterrestrial helium-3, yield dust flux records that are independent of the biases caused by lateral sediment transport and limited resolution that may be associated with age-model-derived mass accumulation rates. However, Atlantic dust records constrained using constant flux proxies are sparsely distributed and generally limited to the past 20 ka. Here we extend the Atlantic record of North African dust deposition to 70 ka using extraterrestrial helium-3 and measurements of titanium, thorium, and terrigenous helium-4 in two sediment cores collected at 26°N and 29°N on the Mid-Atlantic Ridge and compare results to model estimates for dust deposition in the subtropical North Atlantic. Dust proxy fluxes between 26°N and 29°N are well correlated, despite variability in lateral sediment transport, and underscore the utility of extraterrestrial helium-3 for constraining millennial-scale variability in dust deposition. Similarities between Mid-Atlantic dust flux trends and those observed along the Northwest African margin corroborate previous interpretations of dust flux variability over the past 20 ka and suggest that long distance transport and depositional processes do not overly obscure the signal of North African dust emissions. The 70 ka Mid-Atlantic record reveals a slight increase in North African dustiness from Marine Isotope Stage 4 through the Last Glacial Maximum and a dramatic decrease in dustiness associated with the African Humid Period. On the millennial-scale, the new records exhibit brief dust maxima coincident with North Atlantic cold periods such as the Younger Dryas, and multiple Heinrich Stadials. The correlation between Mid-Atlantic dust fluxes and previous constraints on North African aridity is high. However

Exploring tectonomagmatic controls on mid-ocean ridge faulting and morphology with 3-D numerical models

Science.gov (United States)

Howell, S. M.; Ito, G.; Behn, M. D.; Olive, J. A. L.; Kaus, B.; Popov, A.; Mittelstaedt, E. L.; Morrow, T. A.

2016-12-01

Previous two-dimensional (2-D) modeling studies of abyssal-hill scale fault generation and evolution at mid-ocean ridges have predicted that M, the ratio of magmatic to total extension, strongly influences the total slip, spacing, and rotation of large faults, as well as the morphology of the ridge axis. Scaling relations derived from these 2-D models broadly explain the globally observed decrease in abyssal hill spacing with increasing ridge spreading rate, as well as the formation of large-offset faults close to the ends of slow-spreading ridge segments. However, these scaling relations do not explain some higher resolution observations of segment-scale variability in fault spacing along the Chile Ridge and the Mid-Atlantic Ridge, where fault spacing shows no obvious correlation with M. This discrepancy between observations and 2-D model predictions illuminates the need for three-dimensional (3-D) numerical models that incorporate the effects of along-axis variations in lithospheric structure and magmatic accretion. To this end, we use the geodynamic modeling software LaMEM to simulate 3-D tectono-magmatic interactions in a visco-elasto-plastic lithosphere under extension. We model a single ridge segment subjected to an along-axis gradient in the rate of magma injection, which is simulated by imposing a mass source in a plane of model finite volumes beneath the ridge axis. Outputs of interest include characteristic fault offset, spacing, and along-axis gradients in seafloor morphology. We also examine the effects of along-axis variations in lithospheric thickness and off-axis thickening rate. The main objectives of this study are to quantify the relative importance of the amount of magmatic extension and the local lithospheric structure at a given along-axis location, versus the importance of along-axis communication of lithospheric stresses on the 3-D fault evolution and morphology of intermediate-spreading-rate ridges.

Drift pumice in the Indian and South Atlantic oceans

International Nuclear Information System (INIS)

Frick, C.; Kent, L.E.

1984-01-01

Sixty-three samples of drift pumice, collected at the coasts of South Africa, East Africa, Madagascar, Mauritius, the Cocos Islands, Australia, Indonesia, Brazil, Marion Island and Bouvet Island, were investigated petrographically and geochemically with a view to establishing the possible source areas. Geochemically five distinct groups could be distinguished and some could be liked to specific eruptions in the Indian, Atlantic and Pacific oceans. Group A pumice originated from a submarine eruption off Zavodovski Island in the South Sandwich Island Group in 1962. The pumice in Group B occurs mainly on the beaches bordering the Atlantic Ocean, and was found on the west coast of South Africa, on the sea floor south-west of South Africa, and in Brazil. The source of this group is unknown, but all the evidence indicates that it must have been from the Mid-Atlantic Ridge in the South Atlantic Ocean. The Group C pumice was found in the southern Indian Ocean, probably from the Mid-Indian Ridge. The fourth group originated from a submarine eruption along the Tonga Trench in the Pacific Ocean. Group E, which is by far the most homogeneous, includes samples from Australia, the Indian Ocean islands, East and South Africa and samples of the undisputed Krakatoan origin. Specimens from the Krakatoan eruption are still the most abundant type of drift pumice that can be found

Hydrothermal circulation, serpentinization, and degassing at a rift valley-fracture zone intersection: Mid-Atlantic Ridge near 15[degree]N, 45[degree]W

Energy Technology Data Exchange (ETDEWEB)

Rona, P.A.; Nelson, T.A. (National Oceanic and Atmospheric Administration, Miami, FL (United States)); Bougault, H.; Charlou, J.L.; Needham, H.D. (Inst. Francais de Recherche pour I' Exploitation de la Mer, Centre de Brest (France)); Appriou, P. (Univ. of Western Brittany, Brest (France)); Trefry, J.H. (Florida Inst. of Technology, Melbourne (United States)); Eberhart, G.L.; Barone, A. (Lamont-Doherty Geological Observatory, Palisades, NY (United States))

1992-09-01

A hydrothermal system characterized by high ratios of methane to both manganese and suspended particulate matter was detected in seawater sampled at the eastern intersection of the rift valley of the Mid-Atlantic Ridge with the Fifteen-Twenty Fracture Zone. This finding contrasts with low ratios in black smoker-type hydrothermal systems that occur within spreading segments. Near-bottom water sampling coordinated with SeaBeam bathymetry and camera-temperature tows detected the highest concentrations of methane at fault zones in rocks with the appearance of altered ultramafic units in a large dome that forms part of the inside corner high at the intersection. The distinct chemical signatures of the two types of hydrothermal systems are inferred to be controlled by different circulation pathways related to reaction of seawater primarily with ultramafic rocks at intersections of spreading segments with fracture zones but with mafic rocks within spreading segments.

Petrological systematics of mid-ocean ridge basalts: Constraints on melt generation beneath ocean ridges

Science.gov (United States)

Langmuir, Charles H.; Klein, Emily M.; Plank, Terry

Mid-ocean ridge basalts (MORB) are a consequence of pressure-release melting beneath ocean ridges, and contain much information concerning melt formation, melt migration and heterogeneity within the upper mantle. MORB major element chemical systematics can be divided into global and local aspects, once they have been corrected for low pressure fractionation and interlaboratory biases. Regional average compositions for ridges unaffected by hot spots ("normal" ridges) can be used to define the global correlations among normalized Na2O, FeO, TiO2 and SiO2 contents, CaO/Al2O3 ratios, axial depth and crustal thickness. Back-arc basins show similar correlations, but are offset to lower FeO and TiO2 contents. Some hot spots, such as the Azores and Galapagos, disrupt the systematics of nearby ridges and have the opposite relationships between FeO, Na2O and depth over distances of 1000 km. Local variations in basalt chemistry from slow- and fast-spreading ridges are distinct from one another. On slow-spreading ridges, correlations among the elements cross the global vector of variability at a high angle. On the fast-spreading East Pacific Rise (EPR), correlations among the elements are distinct from both global and slow-spreading compositional vectors, and involve two components of variation. Spreading rate does not control the global correlations, but influences the standard deviations of axial depth, crustal thickness, and MgO contents of basalts. Global correlations are not found in very incompatible trace elements, even for samples far from hot spots. Moderately compatible trace elements for normal ridges, however, correlate with the major elements. Trace element systematics are significantly different for the EPR and the mid-Atlantic Ridge (MAR). Normal portions of the MAR are very depleted in REE, with little variability; hot spots cause large long wavelength variations in REE abundances. Normal EPR basalts are significantly more enriched than MAR basalts from normal

Distribution and feeding ecology of dolphins along the Mid-Atlantic Ridge between Iceland and the Azores

Science.gov (United States)

Doksæter, L.; Olsen, E.; Nøttestad, L.; Fernö, A.

2008-01-01

During Leg 1 of the MAR-ECO expedition on the R.V. G.O. Sars in June 2004 four main species of dolphins were observed along the Mid-Atlantic Ridge from Iceland to the Azores: pilot whale ( Globicephala melas) ( n=326), short-beaked common dolphin ( Delphinus delphis) ( n=273), white-sided dolphin ( Lagenorhynchus acutus) ( n=103), and striped dolphin ( Stenella coeruleoalba) ( n=86). Pilot whales and white-sided dolphins were found in cold (5-16 °C) and less-saline (34.6-35.8‰) water masses in the northern part of the study area, whereas common and striped dolphins inhabited warmer (12-22 °C) and more-saline (34.8-36.7‰) waters in the south. Dolphins tended to aggregate in areas of steep slopes, but actual bottom depth appeared to be less important. Based on spatial correlations between dolphin occurrence and candidate prey organisms recorded acoustically and by midwater trawling, mesopelagic fishes and squids were assumed to be important prey items, with Benthosema glaciale probably being the most important prey for pilot whales and white-sided dolphins, while Lampanyctus macdonaldi, Stomias boa ferox and Chauliodus sloani were probably of particular importance for common dolphins. Cephalopods, especially Gonatus sp. and Teuthowenia megalops were the most likely prey species of pilot whales and striped dolphins, respectively. The difference in physical habitat north and south of the Sub-polar Frontal Zone seemed to have important effects on prey distribution, in turn influencing dolphin distribution.

Vertical structure, biomass and topographic association of deep-pelagic fishes in relation to a mid-ocean ridge system

Science.gov (United States)

Sutton, T. T.; Porteiro, F. M.; Heino, M.; Byrkjedal, I.; Langhelle, G.; Anderson, C. I. H.; Horne, J.; Søiland, H.; Falkenhaug, T.; Godø, O. R.; Bergstad, O. A.

2008-01-01

The assemblage structure and vertical distribution of deep-pelagic fishes relative to a mid-ocean ridge system are described from an acoustic and discrete-depth trawling survey conducted as part of the international Census of Marine Life field project MAR-ECO . The 36-station, zig-zag survey along the northern Mid-Atlantic Ridge (MAR; Iceland to the Azores) covered the full depth range (0 to >3000 m), from the surface to near the bottom, using a combination of gear types to gain a more comprehensive understanding of the pelagic fauna. Abundance per volume of deep-pelagic fishes was highest in the epipelagic zone and within the benthic boundary layer (BBL; 0-200 m above the seafloor). Minimum fish abundance occurred at depths below 2300 m but above the BBL. Biomass per volume of deep-pelagic fishes over the MAR reached a maximum within the BBL, revealing a previously unknown topographic association of a bathypelagic fish assemblage with a mid-ocean ridge system. With the exception of the BBL, biomass per volume reached a water column maximum in the bathypelagic zone between 1500 and 2300 m. This stands in stark contrast to the general "open-ocean" paradigm that biomass decreases exponentially from the surface downwards. As much of the summit of the MAR extends into this depth layer, a likely explanation for this mid-water maximum is ridge association. Multivariate statistical analyses suggest that the dominant component of deep-pelagic fish biomass over the northern MAR was a wide-ranging bathypelagic assemblage that was remarkably consistent along the length of the ridge from Iceland to the Azores. Integrating these results with those of previous studies in oceanic ecosystems, there appears to be adequate evidence to conclude that special hydrodynamic and biotic features of mid-ocean ridge systems cause changes in the ecological structure of deep-pelagic fish assemblages relative to those at the same depths over abyssal plains. Lacking terrigenous input of

Massive Sulphide Exploration at the Mid-Atlantic Ridge 26oN: an interdisciplinary geophysical study

Science.gov (United States)

Gehrmann, R. A. S.; Hölz, S.; Jegen, M. D.; Graber, S.; Szitkar, F.; Petersen, S.; Yeo, I. A.; North, L. J.; Gil, A.; Vardy, M. E.; Haroon, A.; Schroeder, H.; Bialas, J.; Tan, Y. Y.; Attias, E.; Sommer, M.; Minshull, T. A.; Murton, B. J.

2017-12-01

During the summer 2016 two cruises (M127 and JC138) conducted an interdisciplinary survey as part of the EU FP7 project `Blue Mining' in the Trans-Atlantic Geotraverse (TAG) hydrothermal field, at the Mid-Atlantic Ridge (26° N), to study the geophysical and geochemical signature of extinct seafloor massive sulphide (eSMS) deposits. The survey comprised AUV-based high-resolution bathymetric mapping, magnetic and self-potential data acquisition, reflection and refraction seismic imaging and three types of controlled source electromagnetic (CSEM) experiments (Geomar, UoS). Additionally seafloor coring, drilling and video imaging (NOC, University of Lisbon, BGS) were realized. Laboratory measurements of physical and chemical properties were taken on and post-cruise from rock samples and sediment cores. Here, we present results from the geophysical data analysis with emphasis on the electromagnetic studies in respect to eSMS detection. Six multi-kilometre-long profiles were acquired with the towed CSEM experiment (UoS) and preliminary results indicate the sensitivity to the conductive eSMS deposits and the resistive background to a depth of about 200 m. The system is also sensitive to the rough topography and interpretation of eSMS deposits requires validation from other methods such as measurements with the MARTEMIS system, a seafloor source-receiver coil (Geomar), which were conducted in two collocated work areas for high-resolution imaging with a depth penetration of up to 50 m. Each geophysical method is sensitive to different SMS characteristics, for example, bathymetric and seismic data are sensitive to the shape and structure of the whole deposit, magnetic data are susceptive to the hydrothermal alteration of magnetic minerals, and self-potential and electromagnetic data respond to the electrically conductive sulphide bodies. Each method has different resolution, penetration depths and challenges with the rough-topographic terrain and navigation. Only

Absolute migration of Pacific basin mid-ocean ridges since 85 Ma ...

African Journals Online (AJOL)

Mid-ocean ridges are major physiographic features that dominate the world seafloor. Their absolute motion and tectonics are recorded in magnetic lineations they created. The absolute migration of mid-ocean ridges in the Pacific basin since 85 Ma and their tectonic implications was investigated in this work and the results ...

Different TDM/CH4 hydrothermal plume signatures: TAG site at 26N and serpentinized ultrabasic diapir at 15 degrees 05'N on the Mid-Atlantic ridge

Energy Technology Data Exchange (ETDEWEB)

Charlou, J.L.; Bougault, H. (IFREMER Centre de Brest, Plouzane (France)); Appriou, P. (Univ. de Bretagne Occidentale, Brest (France)); Nelsen, T.; Rona, P. (NOAA-AOML-OCD, Miami, FL (United States))

1991-11-01

As a part of the 1988 NOAA VENTS Program, CH{sub 4} and Mn tracers were used to identify and compare hydrothermal plumes found above the TAG Field (26{degrees}N) and in the rift valley at 15{degrees}N close to the eastern intersection of the ridge axis with the 15{degrees}20'N Fracture Zone at the Mid-Atlantic Ridge (MAR). Active hydrothermal venting was confirmed at TAG, based on elevated concentrations of total dissolved Mn (TDM up to 30 nmol/kg), high CH{sub 4} concentrations (up to 200 nL/L), and elevated nephelometry signals. Plumes of a different composition were identified at 15{degree}N with high CH{sub 4} concentrations (up to 400 nL/L), low total dissolved Mn concentrations (TDM < 1 nmol/kg) and no significant nephelometry signal. The different properties of these tracers and the different tracer ratios can be used to deduce vent fluid characteristics and compare one hydrothermal area to another. TDM/CH{sub 4} and Nephel/CH{sub 4} ratios at TEG are of the same order of magnitude as those observed at other spreading axis hydrothermal fields. At 15{degrees}N, the low TDM/CH{sub 4} ratio provides evidence of fluid circulation into ultrabasic rocks and offers a potentially useful and single method of exploring for hydrothermal activity associated with serpentinization. Mantle degassing through hydrothermal activity associated with serpentinization is an important process with respect to chemical and thermal exchanges between the upper mantle and the ocean. Different ratios of hydrothermal tracers (i.e., TDM/CH{sub 4}) provide a useful framework for identifying subseafloor processes along mid-oceanic ridges.

Meso- and bathy-pelagic fish parasites at the Mid-Atlantic Ridge (MAR): Low host specificity and restricted parasite diversity

Science.gov (United States)

Klimpel, Sven; Busch, Markus Wilhelm; Sutton, Tracey; Palm, Harry Wilhelm

2010-04-01

Seven meso- and bathy-pelagic fish species from the Mid-Atlantic Ridge (MAR) were firstly studied for fish parasites and feeding ecology. With a total of seven parasite species, the 247 meso- and bathy-pelagic deep-sea fish specimens belonging to the families Melamphaidae (3 spp.), Myctophidae (3 spp.) and Stomiidae (1 sp.) revealed low parasite diversity. The genetically identified nematodes Anisakis simplex (s.s.) and Anisakis pegreffii from the body cavity, liver and muscles of Myctophum punctatum were the most abundant parasites, reaching a prevalence of 91.4% and mean intensity of 3.1 (1-14). Anisakis sp. (unidentified) infected Chauliodus sloani and Poromitra crassiceps. Bothriocephalidean and tetraphyllidean cestode larvae infected Benthosema glaciale, the latter also occurring in C. sloani and Scopelogadus beanii, at low prevalences. Adult parasites at low infection rates included the digenean Lethadena sp. (2.9%), and the two copepod species Sarcotretes scopeli (5.7%) and Tautochondria dolichoura (5.3-11.4%). The myctophid Lampanyctus macdonaldi and the melamphaid Scopelogadus mizolepis mizolepis were free of parasites. Analyses of the stomach contents revealed crustaceans, especially copepods and euphausiids for the myctophids and also amphipods for the melamphaids as predominant prey items. While all stomachs showing distinct content comprising often unidentified 'tissue' (possibly gelatinous zooplankton), only C. sloani preyed upon fish. Though this feeding habit would enable transfer of a variety of crustacean-transmitted parasites into the fish, the parasite fauna in the meso- and bathy-pelagic fish was species poor. All observed parasites showed low host specificity, demonstrating no distinct pattern of host-parasite co-evolution. The MAR is no barrier for the parasite distribution in the North Atlantic meso- and bathy-pelagial.

Review of the Diversity, Ecology, and Conservation of Elasmobranchs in the Azores Region, Mid-North Atlantic

OpenAIRE

Diya Das; Diya Das; Pedro Afonso; Pedro Afonso

2017-01-01

A vulnerable species group, such as, the elasmobranchs, in a data-deficient context presents a complicated management problem. Evidence suggests that the Azores islands, a remote archipelago on the Mid-Atlantic Ridge, serve essential functions in the life-history of species across taxa. The diversity of marine resources within its EEZ are exploited by local to international fleets, and the full extent of fishing pressure can often be underestimated. Although sharks and rays appear to be of mi...

St Paul fracture zone intratransform ridge basalts (Equatorial Atlantic): Insight within the mantle source diversity

Science.gov (United States)

Hemond, C.; Brunelli, D.; Maia, M.; Prigent, S.; Sichel, S. E.

2017-12-01

The St Paul Transform System offsets by 630 km the Equatorial Mid Atlantic Ridge at 1° N. It consists of four Major faults separating three intra transform ridge axes. Volcanic glassy samples were collected inside two intratransform ridge (ITR) segments during the COLMEIA cruise (Maia et al ; 2016) and samples from the third ITR available from a previous cruise ST PAUL (Hékinian et al. 2000). Major, trace elements and Hf, Pb, Sr and Nd isotopes were determined on selected hand picked glass chips. Few glassy samples recovered and analysed from abyssal hill samples open a time window of about 4.5 million years in the chemistry of the northern ITR. Results show that all samples are basaltic in composition but trace elements display contrasting images for the three ITR. The northern ITR samples are all light REE and highly incompatible enriched and are E-MORB; the central ITR samples display rather flat REE pattern with a level on enrichment of the HREE higher than the other two ITR and are T-MORB. Southern ITR samples are more heterogeneous N-MORB to T-MORB with a lower level of HREE. Isotopes reveal that the ITRs sample distinct mantle sources. In various isotope plans, the northern ITR samples plot together with published results from the MAR directly north of the St Paul F.Z. Therefore they exhibit some flavor of the Sierra Leone hotspot interacting with the MAR at 1.7°N. Central and southern ITR samples have very distinct composition from the northern ITR but resemble each other. However, for identical 206Pb/204Pb ratios, central ITR has slightly but significantly higher 207Pb/204Pb and 208Pb/204Pb, also higher 143Nd/144Nd for a given 87Sr/86Sr. Southern ITR is in chemical continuity of the MAR southward. So that central ITR samples display a rather specific composition. Off axis samples corresponding to the activity of the northern ITR up to 4.6 m.y. show that the hotspot contribution was even bigger on the spreading axis than today and might be fading with

Biogeographical distribution of Rimicaris exoculata resident gut epibiont communities along the Mid-Atlantic Ridge hydrothermal vent sites.

Science.gov (United States)

Durand, Lucile; Roumagnac, Marie; Cueff-Gauchard, Valérie; Jan, Cyrielle; Guri, Mathieu; Tessier, Claire; Haond, Marine; Crassous, Philippe; Zbinden, Magali; Arnaud-Haond, Sophie; Cambon-Bonavita, Marie-Anne

2015-10-01

Rimicaris exoculata is a deep-sea hydrothermal vent shrimp whose enlarged gill chamber houses a complex trophic epibiotic community. Its gut harbours an autochthonous and distinct microbial community. This species dominates hydrothermal ecosystem megafauna along the Mid-Atlantic Ridge, regardless of contrasting geochemical conditions prevailing in them. Here, the resident gut epibiont community at four contrasted hydrothermal vent sites (Rainbow, TAG, Logatchev and Ashadze) was analysed and compiled with previous data to evaluate the possible influence of site location, using 16S rRNA surveys and microscopic observations (transmission electron microscopy, scanning electron microscopy and fluorescence in situ hybridization analyses). Filamentous epibionts inserted between the epithelial cell microvilli were observed on all examined samples. Results confirmed resident gut community affiliation to Deferribacteres, Mollicutes, Epsilonproteobacteria and to a lesser extent Gammaproteobacteria lineages. Still a single Deferribacteres phylotype was retrieved at all sites. Four Mollicutes-related operational taxonomic units were distinguished, one being only identified on Rainbow specimens. The topology of ribotype median-joining networks illustrated a community diversification possibly following demographic expansions, suggesting a more ancient evolutionary history and/or a larger effective population size at Rainbow. Finally, the gill chamber community distribution was also analysed through ribotype networks based on sequences from R. exoculata collected at the Rainbow, Snake Pit, TAG, Logatchev and Ashadze sites. Results allow the refining of hypotheses on the epibiont role and transmission pathways. © FEMS 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Dynamical instability produces transform faults at mid-ocean ridges.

Science.gov (United States)

Gerya, Taras

2010-08-27

Transform faults at mid-ocean ridges--one of the most striking, yet enigmatic features of terrestrial plate tectonics--are considered to be the inherited product of preexisting fault structures. Ridge offsets along these faults therefore should remain constant with time. Here, numerical models suggest that transform faults are actively developing and result from dynamical instability of constructive plate boundaries, irrespective of previous structure. Boundary instability from asymmetric plate growth can spontaneously start in alternate directions along successive ridge sections; the resultant curved ridges become transform faults within a few million years. Fracture-related rheological weakening stabilizes ridge-parallel detachment faults. Offsets along the transform faults change continuously with time by asymmetric plate growth and discontinuously by ridge jumps.

76 FR 68719 - Mid-Atlantic Fishery Management Council; Public Meeting

Science.gov (United States)

2011-11-07

... Mid-Atlantic Fishery Management Council's (Council) Scientific and Statistical Committee (SSC) will... Fishery Management Council; Public Meeting AGENCY: National Marine Fisheries Service (NMFS), National....org . Council address: Mid-Atlantic Fishery Management Council, 800 North State Street, Suite 201...

77 FR 51968 - Mid-Atlantic Fishery Management Council; Public Meeting

Science.gov (United States)

2012-08-28

... Mid-Atlantic Fishery Management Council's (Council) Scientific and Statistical Committee (SSC) will... Fishery Management Council; Public Meeting AGENCY: National Marine Fisheries Service (NMFS), National....mafmc.org . Council address: Mid-Atlantic Fishery Management Council, 800 North State Street, Suite 201...

75 FR 2488 - Mid-Atlantic Fishery Management Council; Public Meeting

Science.gov (United States)

2010-01-15

... Mid-Atlantic Fishery Management Council's (MAFMC) Scientific and Statistical Committee (SSC) will hold... Fishery Management Council; Public Meeting AGENCY: National Marine Fisheries Service (NMFS), National... 21240; telephone: (410) 859-3300. Council address: Mid-Atlantic Fishery Management Council, 300 S. New...

75 FR 55743 - Mid-Atlantic Fishery Management Council; Public Meeting

Science.gov (United States)

2010-09-14

... Mid-Atlantic Fishery Management Council's (MAFMC) Scientific and Statistical Committee (SSC) will hold... Fishery Management Council; Public Meeting AGENCY: National Marine Fisheries Service (NMFS), National... address: Mid-Atlantic Fishery Management Council, 800 N. State Street, Suite 201, Dover, DE 19901...

76 FR 9553 - Mid-Atlantic Fishery Management Council; Public Meeting

Science.gov (United States)

2011-02-18

... DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration RIN 0648-XA226 Mid-Atlantic... Oceanic and Atmospheric Administration (NOAA), Commerce. ACTION: Notice of public meeting. SUMMARY: The Social and Economic Sub-Committee of the Mid-Atlantic Fishery Management Council's (Council) Scientific...

76 FR 16620 - Mid-Atlantic Fishery Management Council (MAFMC); Meeting

Science.gov (United States)

2011-03-24

... DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration RIN 0648-XA316 Mid-Atlantic... Oceanic and Atmospheric Administration (NOAA), Commerce. ACTION: Notice of public meeting. SUMMARY: The Social and Economic Sub-Committee of the Mid-Atlantic Fishery Management Council's (Council) Scientific...

76 FR 3878 - Mid-Atlantic Fishery Management Council; Public Meeting

Science.gov (United States)

2011-01-21

... Mid-Atlantic Fishery Management Council's (MAFMC) Scientific and Statistical Committee (SSC) will hold... Fishery Management Council; Public Meeting AGENCY: National Marine Fisheries Service (NMFS), National.... ADDRESSES: The webinar will be held at Mid-Atlantic Fishery Management Council, 800 N. State Street, Suite...

75 FR 56994 - Mid-Atlantic Fishery Management Council; Public Meeting

Science.gov (United States)

2010-09-17

... Mid-Atlantic Fishery Management Council's (MAFMC) Scientific and Statistical Committee (SSC) will hold... Fishery Management Council; Public Meeting AGENCY: National Marine Fisheries Service (NMFS), National.... ADDRESSES: The webinar will be held at Mid-Atlantic Fishery Management Council, 800 N. State Street, Suite...

77 FR 23662 - Mid-Atlantic Fishery Management Council; Public Meeting

Science.gov (United States)

2012-04-20

... DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration RIN 0648-XB170 Mid-Atlantic... Oceanic and Atmospheric Administration (NOAA), Commerce. ACTION: Notice of a public meeting. SUMMARY: The Social and Economic Sub-Committee of the Mid-Atlantic Fishery Management Council's (Council) Scientific...

Mid-Atlantic elasmobranchs: Suitable metal scouts?

International Nuclear Information System (INIS)

Torres, Paulo; Tristão da Cunha, Regina; Rodrigues, Armindo dos Santos

2017-01-01

Heavy metals are a hazard to marine fauna and human health. In this study we assess stable isotopes and metal content in Prionace glauca and Isurus oxyrinchus and analyse these results within and among other species and across regions and geographical areas. Also, we evaluate their suitability, together with Raja clavata and Galeorhinus galeus, as Mid-Atlantic bioindicators. Prionace glauca and I. oxyrinchus shared the same trophic level in a pelagic food web and did not present significant differences between genders or metals, except for As. Arsenic and Hg accumulated while Cd and Pb were not detected. One I. oxyrinchus presented Hg values above regulatory limits. A high Hg exposure was associated with I. oxyrinchus since its maximum weekly intake was exceeded. Elasmobranchs can be used as metal sentinels, each presenting different key features which defines a good marine bioindicator, allowing long-term monitoring at different temporal and spatial scales. - Highlights: • We analysed P. glauca and I. oxyrinchus muscle from Mid-Atlantic. • We determined stable isotopes, trophic ecology and heavy metal content. • Results reflect bioaccumulation for As and Hg. • Oxyrinchus already presented Hg values above regulatory limits. • Mid-Atlantic elasmobranchs appear to be effective metal bioindicators.

Modes and implications of mantle and lower-crust denudation at slow-spreading mid-ocean ridges

Science.gov (United States)

Schroeder, Timothy John

Slow-spreading mid-ocean ridges (Cann, 1993, Cannat, 1993). Extension at mid-ocean ridges is most commonly manifested by slip on high angle (˜60°) normal faults that dip into, and define the rift valley walls (Smith and Cann, 1993). Less commonly, extension occurs by long periods of slip along low-angle normal faults that penetrate to structurally deep levels of oceanic lithosphere and denude gabbro and/or pendotite to the seafloor in domal massifs termed "oceanic core complexes" (Dick et al., 1981; Dick et al., 1991; Tucholke et al., 1998; Mutter and Karson, 1992; Cann et al., 1997; MacLeod et al., 2002). This dissertation addresses processes and implications of tectonic extension at two oceanic core complexes. Atlantis Massif (30°N, Mid-Atlantic Ridge) is formed dominantly of serpentinized peridotite with lesser gabbro, and Atlantis Bank (57°E, Southwest Indian Ridge) is dominated by gabbro. Localization of brittle strain at Atlantis Massif occurred by reaction-softening processes associated with metasomatic alteration of peridotite and serpentmite to amphibole-, chlorite- and talc-bearing assemblages. Ductile strain at Atlantis Massif and Atlantis Bank is localized into intervals of highly-fractionated, oxide-rich gabbro. Two-oxide geothermometry of gabbro indicates that it was not penetratively deformed below ˜500°C. Denuded peridotite at Atlantis Massif is host to hydrothermal circulation driven in part by exothermic serpentinization reactions. Serpentinization decreases the seismic velocity of peridotite and leads to acquisition of a magnetic signature. Venting of highly-alkaline, methane- and hydrogen-rich serpentinization-derived fluids leads to lithification of seafloor carbonate ooze by precipitation of carbonate cement in a zone of mixing with "normal" seawater. This process may be the primary depositional mechanism of ophicalcite deposits and likely occurs wherever peridotite is exposed near the Earth's surface and is fractured to permit water

The influence of climate modes on streamflow in the Mid-Atlantic region of the United States

Directory of Open Access Journals (Sweden)

Justin A. Schulte

2016-03-01

Full Text Available Study region: The Mid-Atlantic region of the United States. Study focus: An understanding of past streamflow variability is necessary for developing future management practices that will help mitigate the impacts of extreme events such as drought or floods on agriculture and other human activities. To better understand mechanisms driving streamflow variability at all timescales, annual to multi-decadal streamflow variability of three major rivers in the Mid-Atlantic region of the United States (the Susquehanna, Delaware, and Hudson Rivers was studied in the context of climate modes using correlation and wavelet analyses. New hydrological insights for the region: Results from the correlation analysis detected statistically significant relationships between climate indices and streamflow that were similar for the three rivers. The results from the wavelet analysis showed that 18- and 26-year periodicities were embedded in the streamflow time series. Decadal variability of streamflow was coherent with the El-Niño Southern Oscillation (SO and the Pacific Decadal Oscillation (PDO. The time series for the PDO and SO indices and precipitation were found to be synchronized to the decadal variability of a global circulation pattern consisting of a Rossby wave train emanating from the North Pacific. The SO explained 37–54% of the 1960s drought, 33–49% of the 1970s pluvial, and 19–50% of the 2000s pluvial in the three river basins. Keywords: Streamflow, Climate, Climate variability, Wavelet analysis, El-Niño-Southern Oscillation, Mid-Atlantic region

North Atlantic octocorals: Distribution, Ecology and Phylogenetics

OpenAIRE

Morris, Kirsty Janet

2011-01-01

Most studies of deep-sea benthic fauna have concentrated on soft sediments with little sampling in rocky areas and even less on non-vent mid-ocean ridges and within submarine canyons, mainly as a result of difficulty accessing them. To assess the distribution and abundance of cold-water corals along an Axial Volcanic Ridges along the Mid-Atlantic ridge at 45oN 27oW, and within the Whittard Canyon along the Irish Margin video footage from the ROV Isis taken during a three scientific cruises wa...

Radiogenic isotopes in enriched mid-ocean ridge basalts from Explorer Ridge, northeast Pacific Ocean

Science.gov (United States)

Cousens, Brian; Weis, Dominique; Constantin, Marc; Scott, Steve

2017-09-01

Extreme gradients in topography related to variations in magma supply are observed on the Southern Explorer Ridge (SER), part of the northern Juan de Fuca ridge system. We report radiogenic isotope (Pb, Sr, Nd, Hf) and geochemical data for twenty-four basalt whole-rock and glass samples collected from the length of the SER and from Explorer Deep, a rift to the north of the SER. Lavas from the SER form a north-south geochemical gradient, dominated by E-MORB at the northern axial high, and range from T-MORB to N-MORB towards the southern deepest part of the ridge. Linear relationships between incompatible element ratios and isotopic ratios in MORB along the ridge are consistent with mixing of magmas beneath the ridge to generate the geographic gradient from E- to N-MORB. The E-MORB have high Sr and Pb, and low Nd and Hf isotopic ratios, typical of enriched mantle that includes a FOZO or HIMU isotopic component. The West Valley and Endeavour segments of the northern Juan de Fuca ridge also include this isotopic component, but the proportion of the FOZO or HIMU component is more extreme in the SER basalts. The FOZO or HIMU component may be garnet-bearing peridotite, or a garnet pyroxenite embedded in peridotite. Recycled garnet pyroxenite better explains the very shallow SER axial high, high Nb/La and La/Sm, and the ;enriched; isotopic compositions.

Mechanical Mixing and Metamorphism of Mafic and Ultramafic Lithologies during Mylonisis at the ST. Paul Transform System, Mid-Atlantic Ridge

Science.gov (United States)

Adrião, Á.; Maia, M.; Hemond, C.; Kaczmarek, M. A.; Briais, A.; Vincent, C.; Brunelli, D.

2017-12-01

The St. Paul Transform System offsets by 630 km the Equatorial Mid Atlantic Ridge at 1° N. It consists of four major faults separating three intra transform ridge axes. This region shows a transition from a transpressive, hot spot affected, regional-scale shear zone to the North to a region dominated by a particular oceanic core complex spreading to the South (Vincent et al., this congress). Samples collected in the region during the COLMEIA cruise (Maia et al., 2016) were studied for textures and whole-rock major and trace element contents. All samples experienced pervasive deformation at ductile to brittle conditions overprinted by late low-T alteration. Mylonitic and ultramylonitic rocks can be grouped in three main types: peridotitic, gabbroic and talc-chlorite schist. Peridotitic ultramylonites preserve few opx, cpx and sp porphyroclasts; they have homogeneous nano-micro grain size groundmass, banded foliation and late amphibole and sulfide crystallization. Locally S-C fabric overprints the mylonitic texture. Micro cracks, filled with serpentine, chlorite and oxides are common, as well fluid inclusions trails in olivine and plagioclase crystals of peridotite and gabbros respectively. Major and trace element content of the peridotitic mylonites plot in the depleted field of the abyssal peridotites; however, they present marked LREE enrichment and Eu positive anomaly. Gabbroic and talc-chlorite mylonites display REE-enriched patterns (up to 100x CI) and variable Eu anomalies. Major elements show a remarkable linear trend in the talc-chlorite group suggesting mixing of pure talc and chlorite end-members. These compositional characteristics suggest variable assimilation of MORB and E-MORB during mylonisis or early melt-rock interaction and hydrothermal evolution at variable metamorphic conditions. Vincent et al., 2017. Particular Oceanic Core Complex evolution …; this congress Maia et al., 2016. Extreme mantle uplift and exhumation ... Nat. Geo. doi:10

78 FR 23223 - Mid-Atlantic Fishery Management Council (MAFMC); Public Meeting

Science.gov (United States)

2013-04-18

.... SUMMARY: The Scientific and Statistical Committee (SSC) of the Mid- Atlantic Fishery Management Council... Fishery Management Council (MAFMC); Public Meeting AGENCY: National Marine Fisheries Service (NMFS...: (410) 522-7377. Council address: Mid-Atlantic Fishery Management Council, 800 N. State Street, Suite...

78 FR 13867 - Mid-Atlantic Fishery Management Council (MAFMC); Public Meeting

Science.gov (United States)

2013-03-01

...: The Mid-Atlantic Fishery Management Council's Scientific and Statistical Committee (SSC) will hold a... Fishery Management Council (MAFMC); Public Meeting AGENCY: National Marine Fisheries Service (NMFS... address: Mid-Atlantic Fishery Management Council, 800 North State Street, Suite 201, Dover, DE 19901...

78 FR 21915 - Mid-Atlantic Fishery Management Council (MAFMC); Public Meeting

Science.gov (United States)

2013-04-12

.... SUMMARY: The Scientific and Statistical Committee (SSC) of the Mid- Atlantic Fishery Management Council... Fishery Management Council (MAFMC); Public Meeting AGENCY: National Marine Fisheries Service (NMFS...://www.mafmc.org . Council address: Mid-Atlantic Fishery Management Council, 800 North State Street...

78 FR 53731 - Mid-Atlantic Fishery Management Council (MAFMC); Public Meeting

Science.gov (United States)

2013-08-30

...: The Scientific and Statistical Committee (SSC) of the Mid- Atlantic Fishery Management Council... Fishery Management Council (MAFMC); Public Meeting AGENCY: National Marine Fisheries Service (NMFS..., MD 21231, telephone: (410) 522-7380. Council address: Mid-Atlantic Fishery Management Council, 800 N...

77 FR 55192 - Mid-Atlantic Fishery Management Council (MAFMC); Public Meeting

Science.gov (United States)

2012-09-07

.... SUMMARY: The Scientific and Statistical Committee (SSC) of the Mid- Atlantic Fishery Management Council... Fishery Management Council (MAFMC); Public Meeting AGENCY: National Marine Fisheries Service (NMFS.... Council address: Mid-Atlantic Fishery Management Council, 800 N. State Street, Suite 201, Dover, DE 19901...

Grain-Size Dynamics Beneath Mid-Ocean Ridges: Implications for Permeability and Melt Extraction

Science.gov (United States)

Turner, A. J.; Katz, R. F.; Behn, M. D.

2014-12-01

The permeability structure of the sub-ridge mantle plays an important role in how melt is focused and extracted at mid-ocean ridges. Permeability is controlled by porosity and the grain size of the solid mantle matrix, which is in turn controlled by the deformation conditions. To date, models of grain size evolution and mantle deformation have not been coupled to determine the influence of spatial variations in grain-size on the permeability structure at mid-ocean ridges. Rather, current models typically assume a constant grain size for the whole domain [1]. Here, we use 2-D numerical models to evaluate the influence of grain-size variability on the permeability structure beneath a mid-ocean ridge and use these results to speculate on the consequences for melt focusing and extraction. We construct a two-dimensional, single phase model for the steady-state grain size beneath a mid-ocean ridge. The model employs a composite rheology of diffusion creep, dislocation creep, dislocation accommodated grain boundary sliding, and a brittle stress limiter. Grain size is calculated using the "wattmeter" model of Austin and Evans [2]. We investigate the sensitivity of the model to global variations in grain growth exponent, potential temperature, spreading-rate, and grain boundary sliding parameters [3,4]. Our model predicts that permeability varies by two orders of magnitude due to the spatial variability of grain size within the expected melt region of a mid-ocean ridge. The predicted permeability structure suggests grain size may promote focusing of melt towards the ridge axis. Furthermore, the calculated grain size structure should focus melt from a greater depth than models that exclude grain-size variability. Future work will involve evaluating this hypothesis by implementing grain-size dynamics within a two-phase mid-ocean ridge model. The developments of such a model will be discussed. References: [1] R. F. Katz, Journal of Petrology, volume 49, issue 12, page 2099

New Noble Gas Studies on Popping Rocks from the Mid-Atlantic Ridge near 14°N

Science.gov (United States)

Kurz, M. D.; Curtice, J.; Jones, M.; Péron, S.; Wanless, V. D.; Mittelstaedt, E. L.; Soule, S. A.; Klein, F.; Fornari, D. J.

2017-12-01

New Popping Rocks were recovered in situ on the Mid-Atlantic Ridge (MAR) near 13.77° N, using HOV Alvin on cruise AT33-03 in 2016 on RV Atlantis. We report new helium, neon, argon, and CO2 step-crushing measurements on a subset of the glass samples, with a focus on a new procedure to collect seafloor samples with minimal exposure to air. Glassy seafloor basalts were collected in sealed containers using the Alvin mechanical arm and transported to the surface without atmospheric exposure. On the ship, the seawater was drained, the volcanic glass was transferred to stainless steel ultra-high-vacuum containers (in an oxygen-free glove box), which were then evacuated using a turbo-molecular pump and sealed for transport under vacuum. All processing was carried out under a nitrogen atmosphere. A control sample was collected from each pillow outcrop and processed normally in air. The preliminary step-crushing measurements show that the anaerobically collected samples have systematically higher 20Ne/22Ne, 21Ne/22Ne and 40Ar/36Ar than the control samples. Helium abundances and isotopes are consistent between anaerobically collected samples and control samples. These results suggest that minimizing atmospheric exposure during sample processing can significantly reduce air contamination for heavy noble gases, providing a new option for seafloor sampling. Higher vesicle abundances appear to yield a greater difference in neon and argon isotopes between the anaerobic and control samples, suggesting that atmospheric contamination is related to vesicle abundance, possibly through micro-fractures. The new data show variability in the maximum mantle neon and argon isotopic compositions, and abundance ratios, suggesting that the samples experienced variable outgassing prior to eruption, and may represent different phases of a single eruption, or multiple eruptions.

78 FR 48419 - Mid-Atlantic Fishery Management Council (MAFMC); Public Meeting

Science.gov (United States)

2013-08-08

...: The Mid-Atlantic Fishery Management Council's (Council) Bluefish Advisory Panel (AP) will meet to develop a Fishery Performance Report for the Bluefish fishery in preparation for the Council and the... Council address below. Webinar link: http://mafmc.adobeconnect.com/bluefish/ Council address: Mid-Atlantic...

2014 Mid-Atlantic Telehealth Resource Center Annual Summit

Directory of Open Access Journals (Sweden)

Katharine Hsu Wibberly

2013-12-01

Full Text Available The Mid-Atlantic Resource Center (MATRC; http://www.matrc.org/ advances the adoption and utilization of telehealth within the MATRC region and works collaboratively with the other federally funded Telehealth Resource Centers to accomplish the same nationally. MATRC offers technical assistance and other resources within the following mid-Atlantic states: Delaware, District of Columbia, Kentucky, Maryland, North Carolina, Pennsylvania, Virginia and West Virginia.   The 2014 MATRC Summit “Adding Value through Sustainable Telehealth” will be held March 30-April 1, 2014, at the Fredericksburg Expo & Conference Center, Fredericksburg, VA. The Summit will explore how telehealth adds value to patients, practitioners, hospitals, health systems, and other facilities. Participants will experience a highly interactive program built around the case history of “Mr. Doe” as he progresses through the primary care, inpatient hospitalization, and post-discharge environments. The Summit will conclude with a session on financial and business models for providing sustainable telehealth services.   For further information and registration, visit: http://matrc.org/component/content/article/2-uncategorised/80-mid-atlantic-telehealth-resource-summit-2014    

The Production of Methane, Hydrogen, and Organic Compounds in Ultramafic-Hosted Hydrothermal Vents of the Mid-Atlantic Ridge

Science.gov (United States)

Charlou, J.L.; Holm, N.G.; Mousis, O.

2015-01-01

Abstract Both hydrogen and methane are consistently discharged in large quantities in hydrothermal fluids issued from ultramafic-hosted hydrothermal fields discovered along the Mid-Atlantic Ridge. Considering the vast number of these fields discovered or inferred, hydrothermal fluxes represent a significant input of H2 and CH4 to the ocean. Although there are lines of evidence of their abiogenic formation from stable C and H isotope results, laboratory experiments, and thermodynamic data, neither their origin nor the reaction pathways generating these gases have been fully constrained yet. Organic compounds detected in the fluids may also be derived from abiotic reactions. Although thermodynamics are favorable and extensive experimental work has been done on Fischer-Tropsch-type reactions, for instance, nothing is clear yet about their origin and formation mechanism from actual data. Since chemolithotrophic microbial communities commonly colonize hydrothermal vents, biogenic and thermogenic processes are likely to contribute to the production of H2, CH4, and other organic compounds. There seems to be a consensus toward a mixed origin (both sources and processes) that is consistent with the ambiguous nature of the isotopic data. But the question that remains is, to what proportions? More systematic experiments as well as integrated geochemical approaches are needed to disentangle hydrothermal geochemistry. This understanding is of prime importance considering the implications of hydrothermal H2, CH4, and organic compounds for the ocean global budget, global cycles, and the origin of life. Key Words: Hydrogen—Methane—Organics—MAR—Abiotic synthesis—Serpentinization—Ultramafic-hosted hydrothermal vents. Astrobiology 15, 381–399. PMID:25984920

Heavy metal bioaccumulation in the organisms at hydrothermal fields of the Mid-Atlantic Ridge and East-Pacific Rise

International Nuclear Information System (INIS)

Demina, L.L.; Galkin, S.V.

2008-01-01

The influence of geochemical environment as well as biological parameters on the heavy metal bioaccumulation in the hydrothermal fauna at certain fields of the Mid-Atlantic ridge (MAR) and East Pacific Rise (EPR) are studied. The highest concentration of Fe, Zn, Cu, Mn, Ni, Cr, Co, Pb, Cd, Ag, Se, Sb, As, and Hg were detected in the tubes of the most thermophilic organism Alvinella caudata inhabited sulfide chimneys at 9 0 50 ' N EPR, i.e. at place where the influence of hydrothermal fluids was the maximal. Elevated heavy metals levels were typical for organs associated with the endo symbiotic bacteria activity, such as gills of specialized mussels Bathymodiolus, clams Archivestica gigas (Calyptogena magnifica), trophosome of vestimentifera Riftia, maxillipeds of shrimps Rimicaris exoculata. Inter-site (Broken Spur vs. Rainbow) comparison of the partitioning of metals within soft tissues has revealed that metal concentrations in the fauna habitats is an important albeit not the single factor that controls the metal content in the interior organs of the taxa. The external parts of mussels, such as shells, demonstrate patterns of bioaccumulation reflecting the metal concentrations in the micro-habitats. In spite of the minimal metal content was found in the mussel shells, they serve as a great reservoirs for heavy metal deposition and storage at the hydrothermal regions. For some elements a trend of heavy metal transferring through the food chains was revealed. There were no clear dependence between age of mussels and metal content (except Hg) in the soft tissues

Origin of major element chemical trends in DSDP Leg 37 basalts, Mid-Atlantic Ridge

Science.gov (United States)

Byerly, G.R.; Wright, T.L.

1978-01-01

In this paper we summarize the major element chemical variation for basalts from the Deep Sea Drilling Project Leg 37 and relate it to stratigraphic position in each of five drilling sites. Least-squares techniques are successfully used to quantify the nature and extent of alteration in these basalts, and to correct the major element analysis back to a magmatic, or alteration-free, composition on the assumption that alteration takes place in two ways: (1) secondary minerals are introduced into veins and vesicles, and (2) CO2 and H2O react with components in the rock to form a simple alteration assemblage. A chemical stratigraphy is defined for these basalts by grouping lavas whose chemistries are related by low-pressure phenocryst-liquid differentiation as identified by least-squares calculation. Major chemical-stratigraphic units are as much as 200 m thick; correlations of these units can be made between the holes at site 332 (about 100 m apart), but not between the other sites. Compositions of parental magmas are calculated by extrapolating low-pressure variations to a constant value of 9% MgO. The differences in these extrapolated compositions reflect high-pressure processes, and suggest that clinopyroxene may be an important phase in either intermediate-level fractionation of basaltic liquids, or as a residual phase during the partial melting which produces these basaltic liquids. Several of the basaltic liquids calculated as parental to the Leg 37 basalts have CaO contents greater than 14% and indicate that the oceanic mantle is richer in CaO and Al2O3 than values used in pyrolite models for the upper mantle. A model for magma generation and eruption beneath the Mid-Atlantic Ridge embodies the following characteristics: 1. (1) Separate magma batches are generated in the mantle. 2. (2) Each of these may be erupted directly or stored at shallow depth where significant fractionation takes place. Common fractionation processes are inferred to be gravitative

Research Drilling on the Mid-Atlantic Ridge: IDDP Wells of Opportunity at Reykjanes, Iceland

Science.gov (United States)

Fridleifsson, G. O.; Franzson, H.; Thorhallsson, S.; Elders, W. A.

2005-12-01

There are some 10 new geothermal wells at Reykjanes, in SW-Iceland, being considered by the Iceland Deep Drilling Project (IDDP) as potential candidate wells of opportunity to explore for deep (4-5 km) supercritical fluids. The drill field is located where the Mid-Atlantic Ridge emerges from the Atlantic ocean at the tip of the Reykjanes Peninsula. The site is an ideal locality for a combined study on the evolution of a rifted oceanic crust and an active black smoker-type geothermal system. However, the oceanic pillow basaltic crust at Reykjanes is some 2-3 times thicker than normal ocean floor crust, which undoubtedly relates to it being part of the Icelandic Large Igneous Province. The deepest of the geothermal wells at Reykjanes is Drillhole RN-17, that was completed to 3082 m depth in February 2005. It is currently the prime candidate for deepening by the IDDP. The plan is to deepen it to 4 km in 2006, and to 5 km depth in 2007, with funding coming from Icelandic energy companies (Hitaveita Sudurnesja, Landsvirkjun and Orkuveita Reykjavikur), the Government of Iceland, the International Scientific Continental Drilling Program (ICDP) and the US National Science Foundation (NSF). The well RN-17 was drilled as a conventional production well with a 12 ¼ inch drillbit to 3082 m depth, and left barefoot, with a 13 3/8 inch production casing cemented down to 900 m. It will be flow tested this autumn. If the RN-17 well is selected by the IDDP for deepening, a 9 5/8 inch in casing will be cemented to 3081 m and drilling will be continued with an 8 ½ inch tricone bit to 4 km in the autumn of 2006. The ICDP and NSF will fund spot coring for scientific studies in this depth interval and a second flow test would be performed in winter 2007. The following autumn, a 7 inch casing would be cemented to 4 km depth and then a 5 inch retrievable liner would be inserted to support a hybrid coring system to continuously core down to 5 km depth, retrieving HQ sized core. A third

Increased ventilation of Antarctic deep water during the warm mid-Pliocene.

Science.gov (United States)

Zhang, Zhongshi; Nisancioglu, Kerim H; Ninnemann, Ulysses S

2013-01-01

The mid-Pliocene warm period is a recent warm geological period that shares similarities with predictions of future climate. It is generally held the mid-Pliocene Atlantic Meridional Overturning Circulation must have been stronger, to explain a weak Atlantic meridional δ(13)C gradient and large northern high-latitude warming. However, climate models do not simulate such stronger Atlantic Meridional Overturning Circulation, when forced with mid-Pliocene boundary conditions. Proxy reconstructions allow for an alternative scenario that the weak δ(13)C gradient can be explained by increased ventilation and reduced stratification in the Southern Ocean. Here this alternative scenario is supported by simulations with the Norwegian Earth System Model (NorESM-L), which simulate an intensified and slightly poleward shifted wind field off Antarctica, giving enhanced ventilation and reduced stratification in the Southern Ocean. Our findings challenge the prevailing theory and show how increased Southern Ocean ventilation can reconcile existing model-data discrepancies about Atlantic Meridional Overturning Circulation while explaining fundamental ocean features.

Magma plumbing system and seismicity of an active mid-ocean ridge volcano.

Science.gov (United States)

Schmid, Florian; Schlindwein, Vera; Koulakov, Ivan; Plötz, Aline; Scholz, John-Robert

2017-02-20

At mid-ocean ridges volcanism generally decreases with spreading rate but surprisingly massive volcanic centres occur at the slowest spreading ridges. These volcanoes can host unexpectedly strong earthquakes and vigorous, explosive submarine eruptions. Our understanding of the geodynamic processes forming these volcanic centres is still incomplete due to a lack of geophysical data and the difficulty to capture their rare phases of magmatic activity. We present a local earthquake tomographic image of the magma plumbing system beneath the Segment 8 volcano at the ultraslow-spreading Southwest Indian Ridge. The tomography shows a confined domain of partial melt under the volcano. We infer that from there melt is horizontally transported to a neighbouring ridge segment at 35 km distance where microearthquake swarms and intrusion tremor occur that suggest ongoing magmatic activity. Teleseismic earthquakes around the Segment 8 volcano, prior to our study, indicate that the current magmatic spreading episode may already have lasted over a decade and hence its temporal extent greatly exceeds the frequent short-lived spreading episodes at faster opening mid-ocean ridges.

Intense CH{sub 4} plumes generated by serpentinization of ultramafic rocks at the intersection of the 15{degree}20[minutes]N fracture zone and the Mid-Atlantic Ridge

Energy Technology Data Exchange (ETDEWEB)

Charlou, J.L.; Fouquet, Y.; Bougault, H.; Donval, J.P.; Etoubleau, J. [IFREMER Centre de Brest, Plouzane (France). Dept. Geosciences Marines; Jean-Baptiste, P.; Dapoigny, A. [CEA Saclay, Gif-sur-Yvette (France); Appriou, P. [Univ. de Bretagne Occidentale, Brest (France); Rona, P.A. [Rutgers-the State Univ. of New Jersey, New Brunswick, NJ (United States)

1998-07-01

As part of the FARA French-US Program designed to study the Mid-Atlantic Ridge (MAR) between 15{degree}N and the Azores, twenty-three dives with the submersible Nautile were conducted during the French-US Faranaut 15N cruise on the eastern and western parts of the Fracture Zone/Ridge axis intersection. South of the eastern ridge-transform fault intersection, nine Nautile dives were made within the rift valley and along the western rift valley wall. CH{sub 4} concentrations in the bottom waters reach 53.2 nmol/kg along faulted zones on top and on the east flank of the ultramafic inner corner high where serpentinized rocks outcrop. No {sup 3}He anomaly is associated with methane, ruling out any primary mantle component. High CH{sub 4} anomalies (up to 22 nmol/kg) are also present in the bottom waters of the rift valley northern segment on both the western and eastern valley walls and on the inner high adjacent to the eastern wall where ultramafic rocks outcrop. Seven vertical hydrocasts carried out in the axial valley (4500 M deep) show an intense CH{sub 4} anomaly, with a maximum (35.8 nmol/kg) at 3200 m depth. CH{sub 4} concentrations of 9.9--14.9 nmol/kg are also present on the western wall along the 3200 m isobath. CH{sub 4} output from ultramafic outcrops on the western and eastern intersections of the Fracture Zone with the MAR is believed to reflect ongoing serpentinization.

Patagonian and southern South Atlantic view of Holocene climate

Science.gov (United States)

Kaplan, M. R.; Schaefer, J. M.; Strelin, J. A.; Denton, G. H.; Anderson, R. F.; Vandergoes, M. J.; Finkel, R. C.; Schwartz, R.; Travis, S. G.; Garcia, J. L.; Martini, M. A.; Nielsen, S. H. H.

2016-06-01

We present a comprehensive 10Be chronology for Holocene moraines in the Lago Argentino basin, on the east side of the South Patagonian Icefield. We focus on three different areas, where prior studies show ample glacier moraine records exist because they were formed by outlet glaciers sensitive to climate change. The 10Be dated records are from the Lago Pearson, Herminita Península-Brazo Upsala, and Lago Frías areas, which span a distance of almost 100 km adjacent to the modern Icefield. New 10Be ages show that expanded glaciers and moraine building events occurred at least at 6120 ± 390 (n = 13), 4450 ± 220 (n = 7), 1450 or 1410 ± 110 (n = 18), 360 ± 30 (n = 5), and 240 ± 20 (n = 8) years ago. Furthermore, other less well-dated glacier expansions of the Upsala Glacier occurred between 1400 and ∼1000 and ∼2300 and ∼2000 years ago. The most extensive glaciers occurred over the interval from ∼6100 to ∼4500 years ago, and their margins over the last ∼600 years were well within and lower than those in the middle Holocene. The 10Be ages agree with 14C-limiting data for the glacier histories in this area. We then link southern South American, adjacent South Atlantic, and other Southern Hemisphere records to elucidate broader regional patterns of climate and their possible causes. In the early Holocene, a far southward position of the westerly winds fostered warmth, small Patagonian glaciers, and reduced sea ice coverage over the South Atlantic. Although we infer a pronounced southward displacement of the westerlies during the early Holocene, these conditions did not occur throughout the southern mid-high latitudes, an important exception being over the southwest Pacific sector. Subsequently, a northward locus and/or expansion of the winds over the Patagonia-South Atlantic sector promoted the largest glaciers between ∼6100 and ∼4500 years ago and greatest sea ice coverage. Over the last few millennia, the South Patagonian Icefield has experienced

75 FR 8673 - Mid-Atlantic Fishery Management Council; Public Meeting

Science.gov (United States)

2010-02-25

... Fishery Management Council; Public Meeting AGENCY: National Marine Fisheries Service (NMFS), National... Mid-Atlantic Fishery Management Council (Council) will conduct an educational workshop on catch shares in cooperation with the Fisheries Leadership and Sustainability Forum (FLSF), the Atlantic States...

The Kane fracture zone in the Central Atlantic Ocean

NARCIS (Netherlands)

Purdy, G.M.; Rabinowitz, P.D.; Velterop, J.J.A.

1979-01-01

The Kane fracture zone has been traced as a distinct topographic trough from the Mid-Atlantic Ridge near 24°N to the 80-m.y. B.P. isochron (magnetic anomaly 34) on either side of the ridge axis for a total of approximately 2800 km. Major changes in trend of the fracture zone occur at approximately

Variability of Fe isotope compositions of hydrothermal sulfides and oxidation products at mid-ocean ridges

Science.gov (United States)

Li, Xiaohu; Wang, Jianqiang; Chu, Fengyou; Wang, Hao; Li, Zhenggang; Yu, Xing; Bi, Dongwei; He, Yongsheng

2018-04-01

Significant Fe isotopic fractionation occurs during the precipitation and oxidative weathering of modern seafloor hydrothermal sulfides, which has an important impact on the cycling of Fe isotopes in the ocean. This study reports the Fe-isotope compositions of whole-rock sulfides and single-mineral pyrite collected from hydrothermal fields at the South Mid-Atlantic Ridge (SMAR) and the East Pacific Rise (EPR) and discusses the impacts of precipitation and late-stage oxidative weathering of sulfide minerals on Fe isotopic fractionation. The results show large variation in the Fe-isotope compositions of the sulfides from the different hydrothermal fields on the mid-oceanic ridges, indicating that relatively significant isotope fractionation occurs during the sulfide precipitation and oxidative weathering processes. The Fe-isotope compositions of the sulfides from the study area at the SMAR vary across a relatively small range, with an average value of 0.01‰. This Fe-isotope composition is similar to the Fe-isotope composition of mid-oceanic ridge basalt, which suggests that Fe was mainly leached from basalt. In contrast, the Fe-isotope composition of the sulfides from the study area at the EPR are significantly enriched in light Fe isotopes (average value - 1.63‰), mainly due to the kinetic fractionation during the rapid precipitation process of hydrothermal sulfide. In addition, the pyrite from different hydrothermal fields is enriched in light Fe isotopes, which is consistent with the phenomenon in which light Fe isotopes are preferentially enriched during the precipitation of pyrite. The red oxides have the heaviest Fe-isotope compositions (up to 0.80‰), indicating that heavy Fe isotopes are preferentially enriched in the oxidation product during the late-stage oxidation process. The data obtained from this study and previous studies show a significant difference between the Fe-isotope compositions of the sulfides from the SMAR and EPR. The relatively heavy

230Th-238U radioactive disequilibria in tholeiites from the FAMOUS zone (Mid-Atlantic Ridge, 36050'N): Th and Sr isotopic geochemistry

International Nuclear Information System (INIS)

Condomines, M.; Morand, P.; Allegre, C.J.

1981-01-01

We analyzed, U, Th and 230 Th/ 232 Th activity ratios for a few tholeiites from the Mid-Atlantic Ridge FAMOUS zone at 36 0 50'N. The results show a fairly wider scatter for both Th/U and ( 230 Th/ 232 Th) ratios. Seawater contamination appears to be responsible for this scatter and, for the uranium, produces an increase in content yielding a ( 234 U/ 238 U) ratio greater than 1 and, for the Th, an increase of the ( 230 Th/ 232 Th) ratio which is a very sensitive indicator for contamination. Also, the latter often is selective: U, Th and Sr are not affected in the same manner. When discarding all data for contaminated samples, the FAMOUS zone appears to be very homogeneous with a Th/U ratio value of 3.05 and a ( 230 Th/ 232 Th) ratio value of 1.24. Comparison with other active volcanic areas reveals a negative correlation between ( 230 Th/ 232 Th) and 87 Sr/ 86 Sr ratios for present lavas which is indicative of a consistency in Th-U and Rb-Sr fractionation in the source regions of these magmas. The Th isotopic geochemistry can thus provide useful information for the study of present volcanism, information as valuable as that from Sr, Pb or Nd isotopes. (orig.)

Arsenic speciation in shrimp and mussel from the Mid-Atlantic hydrothermal vents

DEFF Research Database (Denmark)

Larsen, Erik Huusfeldt; Quetel, C. R.; Munoz, R.

1997-01-01

Specimens of shrimp (Rimicaris exoculata) and mussel (Bathymodiolus puteoserpentis) were collected 3500 m below the ocean surface at the hydrothermal vents of the mid-Atlantic Ridge (TAG and Snake Pit sites, respectively). Arsenic, a potentially toxic element, is among the substances emitted...... by the hydrothermal vents. The hydrothermal vent shrimp, which are known to be a primary consumer of the primary producing chemolithoautotrophic bacteria, contained arsenic at 13 mu g g(-1) almost exclusively as arsenobetaine (AsB). Arsenic was present in the soft:issues of the mussel at 40 mu g g(-1) and the major...... of arsenic species found in the shrimp and mussel species in the deep-sea is similar to that found in their counterparts from the ocean surface. It is concluded that the autotrophic bacteria of the hydrothermal vent ecosystem and the symbiotic bacteria harboured in the mussel species are responsible...

Geoelectric Hazard Maps for the Mid-Atlantic United States: 100 Year Extreme Values and the 1989 Magnetic Storm

Science.gov (United States)

Love, Jeffrey J.; Lucas, Greg M.; Kelbert, Anna; Bedrosian, Paul A.

2018-01-01

Maps of extreme value geoelectric field amplitude are constructed for the Mid-Atlantic United States, a region with high population density and critically important power grid infrastructure. Geoelectric field time series for the years 1983-2014 are estimated by convolving Earth surface impedances obtained from 61 magnetotelluric survey sites across the Mid-Atlantic with historical 1 min (2 min Nyquist) measurements of geomagnetic variation obtained from a nearby observatory. Statistical models are fitted to the maximum geoelectric amplitudes occurring during magnetic storms, and extrapolations made to estimate threshold amplitudes only exceeded, on average, once per century. For the Mid-Atlantic region, 100 year geoelectric exceedance amplitudes have a range of almost 3 orders of magnitude (from 0.04 V/km at a site in southern Pennsylvania to 24.29 V/km at a site in central Virginia), and they have significant geographic granularity, all of which is due to site-to-site differences in magnetotelluric impedance. Maps of these 100 year exceedance amplitudes resemble those of the estimated geoelectric amplitudes attained during the March 1989 magnetic storm, and, in that sense, the March 1989 storm resembles what might be loosely called a "100 year" event. The geoelectric hazard maps reported here stand in stark contrast with the 100 year geoelectric benchmarks developed for the North American Electric Reliability Corporation.

Wind effects on coastal zone color scanner chlorophyll patterns in the U.S. Mid-Atlantic Bight during spring 1979

Science.gov (United States)

Eslinger, David L.; Iverson, Richard L.

1986-01-01

Coastal zone color scanner (CZCS) chlorophyll concentration increases in the Mid-Atlantic Bight were associated with high wind speeds in continental shelf waters during March and May 1979. Maximum spring CZCS chlorophyll concentrations occurred during April when the water column was not thermally stratified and were spatially and temporally associated with reductions in wind speed both in onshelf and in offshelf regions. Increased chlorophyll concentrations in offshelf waters were associated with high wind speeds during May when a deep chlorophyll maximum was present. Chlorophyll patchiness was observed on length scales typical of those controlled by biological processes during the April low-wind period but not during March or May when wind speeds were greater. The spring CZCS chlorophyll maximum in the southern portion of the Mid-Atlantic Bight occurred in response to a reduction in mixed layer depth caused by decreased wind speeds and not by increased water column stratification.

Deformation associated with the denudation of mantle-derived rocks at the Mid-Atlantic Ridge 13°-15°N: The role of magmatic injections and hydrothermal alteration

Science.gov (United States)

Picazo, Suzanne; Cannat, Mathilde; Delacour, AdéLie; EscartíN, Javier; RouméJon, StéPhane; Silantyev, Sergei

2012-09-01

Outcrops of deeply derived ultramafic rocks and gabbros are widespread along slow spreading ridges where they are exposed in the footwall of detachment faults. We report on the microstructural and petrological characteristics of a large number of samples from ultramafic exposures in the walls of the Mid-Atlantic Ridge (MAR) axial valley at three distinct locations at lat. 13°N and 14°45'N. One of these locations corresponds to the footwall beneath a corrugated paleo-fault surface. Bearing in mind that dredging and ROV sampling may not preserve the most fragile lithologies (fault gouges), this study allows us to document a sequence of deformation, and the magmatic and hydrothermal history recorded in the footwall within a few hundred meters of the axial detachment fault. At the three sampled locations, we find that tremolitic amphiboles have localized deformation in the ultramafic rocks prior to the onset of serpentinization. We interpret these tremolites as hydrothermal alteration products after evolved gabbroic rocks intruded into the peridotites. We also document two types of brittle deformation in the ultramafic rocks, which we infer could produce the sustained low magnitude seismicity recorded at ridge axis detachment faults. The first type of brittle deformation affects fresh peridotite and is associated with the injection of the evolved gabbroic melts, and the second type affects serpentinized peridotites and is associated with the injection of Si-rich hydrothermal fluids that promote talc crystallization, leading to strain localization in thin talc shear zones. We also observed chlorite + serpentine shear zones but did not identify samples with serpentine-only shear zones. Although the proportion of magmatic injections in the ultramafic rocks is variable, these characteristics are found at each investigated location and are therefore proposed as fundamental components of the deformation in the footwall of the detachment faults associated with denudation of

Mid-Atlantic Consumer Purchasing Behavior and Knowledge of Locally Grown and Seasonal Produce

Science.gov (United States)

Chamberlain, Amy J.; Kelley, Kathleen M.; Hyde, Jeffrey

2013-01-01

Mid-Atlantic urban consumers were surveyed on their fruit and vegetable purchasing behaviors and their knowledge of produce grown in the region. Consumers were generally unaware of what produce is grown in the mid-Atlantic and during what months they are harvested. Additionally, differences pertaining to number of produce items purchased were…

Comparative visual ecophysiology of mid-Atlantic temperate reef fishes

Directory of Open Access Journals (Sweden)

Andrij Z. Horodysky

2013-11-01

The absolute light sensitivities, temporal properties, and spectral sensitivities of the visual systems of three mid-Atlantic temperate reef fishes (Atlantic spadefish [Ephippidae: Chaetodipterus faber], tautog [Labridae: Tautoga onitis], and black sea bass [Serranidae: Centropristis striata] were studied via electroretinography (ERG. Pelagic Atlantic spadefish exhibited higher temporal resolution but a narrower dynamic range than the two more demersal foragers. The higher luminous sensitivities of tautog and black sea bass were similar to other benthic and demersal coastal mid-Atlantic fishes. Flicker fusion frequency experiments revealed significant interspecific differences at maximum intensities that correlated with lifestyle and habitat. Spectral responses of the three species spanned 400–610 nm, with high likelihood of cone dichromacy providing the basis for color and contrast discrimination. Significant day-night differences in spectral responses were evident in spadefish and black sea bass but not tautog, a labrid with characteristic structure-associated nocturnal torpor. Atlantic spadefish responded to a wider range of wavelengths than did deeper-dwelling tautog or black sea bass. Collectively, these results suggest that temperate reef-associated fishes are well-adapted to their gradient of brighter to dimmer photoclimates, representative of their unique ecologies and life histories. Continuing anthropogenic degradation of water quality in coastal environments, at a pace faster than the evolution of visual systems, may however impede visual foraging and reproductive signaling in temperate reef fishes.

Interactions Between Mantle Plumes and Mid-Ocean Ridges: Constraints from Geophysics, Geochemistry, and Geodynamical Modeling

National Research Council Canada - National Science Library

Georgen, Jennifer

2001-01-01

This thesis studies interactions between mid-ocean ridges and mantle plumes. Chapter 1 investigates the effects of the Marion and Bouvet hotspots on the ultra-slow spreading, highly-segmented Southwest Indian Ridge (SWIR...

Heat export from the tropics drives mid to late Holocene palaeoceanographic changes offshore southern Australia

Science.gov (United States)

Perner, Kerstin; Moros, Matthias; De Deckker, Patrick; Blanz, Thomas; Wacker, Lukas; Telford, Richard; Siegel, Herbert; Schneider, Ralph; Jansen, Eystein

2018-01-01

The Leeuwin Current (LC), an eastern boundary current, transports tropical waters from the Indo-Pacific Warm Pool (IPWP) towards southern latitudes and modulates oceanic conditions offshore southern Australia. New, high-resolution planktic foraminifer assemblage data and alkenone-derived sea surface temperatures (SST) provide an in-depth view on LC variability and mechanisms driving the current's properties during the mid to late Holocene (last c. 7.4 ka BP). Our marine reconstructions highlight a longer-term mid to late Holocene reduction of tropical heat export from the IPWP area into the LC. Mid Holocene (c. 7.4 to 3.5 ka BP) occurrence of high SSTs (>19.5 °C), tropical planktic foraminifera and a well-stratified water column document an enhanced heat export from the tropics. From c. 3.5 ka BP onwards, a weaker LC and a notably reduced tropical heat export cause oceanic cooling offshore southern Australia. The observed mid to late Holocene trends likely result from large-scale changes in the IPWP's heat storage linked to the El Niño-Southern Oscillation (ENSO) phenomenon. We propose that a strong and warm LC occurs in response to a La Niña-like state of ENSO during the mid Holocene. The late Holocene LC cooling, however, results from a shift towards an El Niño-like state and a more variable ENSO system that causes cooling of the IPWP. Superimposed on these longer-term trends we find evidence of distinct late Holocene millennial-scale phases of enhanced El Niño/La Niña development, which appear synchronous with northern hemispheric climatic variability. Phases of dominant El Niño-like states occur parallel to North Atlantic cold phases: the '2800 years BP cooling event', the 'Dark Ages' and the 'Little Ice Age', whereas the 'Roman Warm Period' and the 'Medieval Climate Anomaly' parallel periods of a predominant La Niña-like state. Our findings provide further evidence of coherent interhemispheric climatic and oceanic conditions during the mid to late

Chemical characteristics of hydrothermal fluids from the TAG Mound of the Mid-Atlantic Ridge in August 1994: Implications for spatial and temporal variability of hydrothermal activity

Science.gov (United States)

Gamo, Toshitaka; Chiba, Hitoshi; Masuda, Harue; Edmonds, Henrietta N.; Fujioka, Kantaro; Kodama, Yukio; Nanba, Hiromi; Sano, Yuji

The TAG hydrothermal mound on the Mid-Atlantic Ridge (26°08‧N, 44°50‧W) was revisited in August 1994 with the submersible Shinkai 6500 in order to characterize time-series fluid chemistry prior to the ODP drilling. Fluid samples were taken from both black smokers and white smokers. Si, pH, alkalinity, H2S, major cations (Na+, K+, Ca2+, Mg2+), major anions (Cl-, SO42-), and minor elements (Li, Sr, B, Fe, Mn, Cu, Zn, Br) as well as Sr isotope ratios were measured. We report the first Br/Cl ratios for the TAG hydrothermal fluids, showing no fractionation between Br and Cl during the fluid-rock interaction. This study shows small changes in composition of the black smoker fluids from the 1990 data (Edmond et al., 1995). Changes of pH, alkalinity, Fe, K, and 87Sr/86Sr values are suggestive of subsurface FeS precipitation and a decrease of water/rock ratio at a deeper reaction zone. Differences in chemical characteristics between the black and white smoker fluids were similarly observed as in 1990.

Analysis of the Spatial and Temporal Distribution of the Seismicity of the Mid-Atlantic Ridge Using the SIRENA and the South Azores Autonomous Hydrophone Arrays

Science.gov (United States)

Simão, N.; Goslin, J.; Perrot, J.; Haxel, J.; Dziak, R.

2006-12-01

Acoustic data recorded by two Autonomous Hydrophone Arrays (AHA) were jointly processed in Brest (IUEM) and Newport (PMEL-VENTS) to monitor the seismicity of the Mid-Atlantic Ridge (MAR) over a ten month period, at a wide range of spatial scales. Over the deployment period, nearly 6000 T-phase generating earthquakes were localized using a semi-automatic algorithm. Our analysis of the temporal and spatial distribution of these events combined with their acoustic energy source levels provides important insights for the generation mechanisms and characteristic behavior of MAR seismicity. It shows for the AHA catalog a variation of the cumulative number of events with time almost linear. Taking in account the area inside the arrays, the section of the ridge north of the Azores is more seismically active than the southern part of it and the seismic activity occurs in large localized clusters. Our (AHA) catalog of acoustic events was used to compare locations, focal mechanisms and magnitude observations with correlated data from land-based stations of the NEIC global seismic network to establish completeness levels from both within and outside of the hydrophone array. The (AHA) catalog has a Source Level of Completeness (SLc) of 204dB, and a b-value of 0.0605. The NEIC catalog for this region during this period has a Magnitude of Completeness (Mc) of 4.6 and a b-value of 1.01. Regressing the AHA values onto the NEIC derived Mc/b-value relationship suggests a Mc of 3.2 for the AHA catalog. By restricting the events to the region inside the AHA, the NEIC catalog has an Mc of 4.7 with a b-value of 1.09, while the AHA catalog has a SLc of 205dB with a b-value of 0.0753. Comparing the b-values of the NEIC catalog with the AHA catalog, we obtain an improved Mc of 3.0 for the AHA inside the array. A time- and space-dependent Single-Link-Cluster algorithm was applied to the events localized inside the AHA. This allowed us to gather cluster sequences of earthquakes for higher

Mobility and immobility of mid-ocean ridges and their implications to ...

African Journals Online (AJOL)

absolute migration) have been correlated with major observable features, such as, spreading asymmetry and asymmetry in the abundance of seamounts. The mobility of mid-ocean ridges is also thought to be an important factor that influences ...

78 FR 54644 - 2013 Fall Joint Meeting of the Ozone Transport Commission and the Mid-Atlantic Northeast...

Science.gov (United States)

2013-09-05

... Transport Commission and the Mid-Atlantic Northeast Visibility Union AGENCY: Environmental Protection Agency...-Atlantic Northeast Visibility Union (MANE-VU). The meeting agenda will include topics regarding reducing...-level ozone formation, transport, and control within the OTR. The Mid-Atlantic/Northeast Visibility...

Crustal accretion along the global mid-ocean ridge system based on basaltic glass and olivine-hosted melt inclusion compositions

Science.gov (United States)

Wanless, V. D.; Behn, M. D.

2015-12-01

The depth and distribution of crystallization at mid-ocean ridges controls the overall architecture of the oceanic crust, influences hydrothermal circulation, and determines geothermal gradients in the crust and uppermost mantle. Despite this, there is no overall consensus on how crystallization is distributed within the crust/upper mantle or how this varies with spreading rate. Here, we examine crustal accretion at mid-ocean ridges by combining crystallization pressures calculated from major element barometers on mid-ocean ridge basalt (MORB) glasses with vapor-saturation pressures from melt inclusions to produce a detailed map of crystallization depths and distributions along the global ridge system. We calculate pressures of crystallization from >11,500 MORB glasses from the global ridge system using two established major element barometers (1,2). Additionally, we use vapor-saturation pressures from >400 olivine-hosted melt inclusions from five ridges with variable spreading rates to constrain pressures and distributions of crystallization along the global ridge system. We show that (i) crystallization depths from MORB glasses increase and become less focused with decreasing spreading rate, (ii) maximum glass pressures are greater than the maximum melt inclusion pressure, which indicates that the melt inclusions do not record the deepest crystallization at mid-ocean ridges, and (iii) crystallization occurs in the lower crust/upper mantle at all ridges, indicating accretion is distributed throughout the crust at all spreading rates, including those with a steady-state magma lens. Finally, we suggest that the remarkably similar maximum vapor-saturation pressures (~ 3000 bars) in melt inclusion from all spreading rates reflects the CO2 content of the depleted upper mantle feeding the global mid-ocean ridge system. (1) Michael, P. & W. Cornell (1998), Journal of Geophysical Research, 103(B8), 18325-18356; (2) Herzberg, C. (2004), Journal of Petrology, 45(12), 2389.

Mid-Atlantic Wind - Overcoming the Challenges

Energy Technology Data Exchange (ETDEWEB)

Daniel F. Ancona III; Kathryn E. George; Richard P. Bowers; Dr. Lynn Sparling; Bruce Buckheit; Daniel LoBue

2012-05-31

This study, supported by the US Department of Energy, Wind Powering America Program, Maryland Department of Natural Resources and Chesapeake Bay Foundation, analyzed barriers to wind energy development in the Mid-Atlantic region along with options for overcoming or mitigating them. The Mid-Atlantic States including Delaware, Maryland, North Carolina and Virginia, have excellent wind energy potential and growing demand for electricity, but only two utility-scale projects have been installed to date. Reasons for this apathetic development of wind resources were analyzed and quantified for four markets. Specific applications are: 1) Appalachian mountain ridgeline sites, 2) on coastal plains and peninsulas, 3) at shallow water sites in Delaware and Chesapeake Bays, Albemarle and Pamlico Sounds, and 4) at deeper water sites off the Atlantic coast. Each market has distinctly different opportunities and barriers. The primary barriers to wind development described in this report can be grouped into four categories; state policy and regulatory issues, wind resource technical uncertainty, economic viability, and public interest in environmental issues. The properties of these typologies are not mutually independent and do interact. The report concluded that there are no insurmountable barriers to land-based wind energy projects and they could be economically viable today. Likewise potential sites in sheltered shallow waters in regional bay and sounds have been largely overlooked but could be viable currently. Offshore ocean-based applications face higher costs and technical and wind resource uncertainties. The ongoing research and development program, revision of state incentive policies, additional wind measurement efforts, transmission system expansion, environmental baseline studies and outreach to private developers and stakeholders are needed to reduce barriers to wind energy development.

Mid-Atlantic Wind - Overcoming the Challenges

Energy Technology Data Exchange (ETDEWEB)

Daniel F. Ancona III; Kathryn E. George; Lynn Sparling; Bruce C. Buckheit; Daniel LoBue; and Richard P. Bowers

2012-06-29

This study, supported by the US Department of Energy, Wind Powering America Program, Maryland Department of Natural Resources and Chesapeake Bay Foundation, analyzed barriers to wind energy development in the Mid-Atlantic region along with options for overcoming or mitigating them. The Mid-Atlantic States including Delaware, Maryland, North Carolina and Virginia, have excellent wind energy potential and growing demand for electricity, but only two utility-scale projects have been installed to date. Reasons for this apathetic development of wind resources were analyzed and quantified for four markets. Specific applications are: 1) Appalachian mountain ridgeline sites, 2) on coastal plains and peninsulas, 3) at shallow water sites in Delaware and Chesapeake Bays, Albemarle and Pamlico Sounds, and 4) at deeper water sites off the Atlantic coast. Each market has distinctly different opportunities and barriers. The primary barriers to wind development described in this report can be grouped into four categories; state policy and regulatory issues, wind resource technical uncertainty, economic viability, and public interest in environmental issues. The properties of these typologies are not mutually independent and do interact. The report concluded that there are no insurmountable barriers to land-based wind energy projects and they could be economically viable today. Likewise potential sites in sheltered shallow waters in regional bay and sounds have been largely overlooked but could be viable currently. Offshore ocean-based applications face higher costs and technical and wind resource uncertainties. The ongoing research and development program, revision of state incentive policies, additional wind measurement efforts, transmission system expansion, environmental baseline studies and outreach to private developers and stakeholders are needed to reduce barriers to wind energy development.

East Greenland Ridge in the North Atlantic Ocean

DEFF Research Database (Denmark)

Andreasen, Arne Døssing; Dahl-Jensen, T.; Thybo, Hans

2008-01-01

The combined Greenland-Senja Fracture Zones (GSFZ) represent a first-order plate tectonic feature in the North Atlantic Ocean. The GSFZ defines an abrupt change in the character of magnetic anomalies with well-defined seafloor spreading anomalies in the Greenland and Norwegian basins to the south...... but ambiguous and weak magnetic anomalies in the Boreas Basin to the north. Substantial uncertainty exists concerning the plate tectonic evolution of the latter area, including the role of the East Greenland Ridge, which is situated along the Greenland Fracture Zone. In 2002, a combined ocean-bottom seismometer...

The Effects of Ridge Axis Width on Mantle Melting at Mid-Ocean Ridges

Science.gov (United States)

Montesi, L.; Magni, V.; Gaina, C.

2017-12-01

Mantle upwelling in response to plate divergence produces melt at mid-ocean ridges. Melt starts when the solidus is crossed and stops when conductive cooling overcomes heat advection associated with the upwelling. Most mid-ocean ridge models assume that divergence takes place only in a narrow zone that defines the ridge axis, resulting in a single upwelling. However, more complex patterns of divergence are occasionally observed. The rift axis can be 20 km wide at ultraslow spreading center. Overlapping spreading center contain two parallel axes. Rifting in backarc basins is sometimes organized as a series of parallel spreading centers. Distributing plate divergence over several rifts reduces the intensity of upwelling and limits melting. Can this have a significant effect on the expected crustal thickness and on the mode of melt delivery at the seafloor? We address this question by modeling mantle flow and melting underneath two spreading centers separated by a rigid block. We adopt a non-linear rheology that includes dislocation creep, diffusion creep and yielding and include hydrothermal cooling by enhancing thermal conductivity where yielding takes place. The crustal thickness decreases if the rifts are separated by 30 km or more but only if the half spreading rate is between 1 and 2 cm/yr. At melting depth, a single upwelling remains the norm until the separation of the rifts exceeds a critical value ranging from 15 km in the fastest ridges to more than 50 km at ultraslow spreading centers. The stability of the central upwelling is due to hydrothermal cooling, which prevents hot mantle from reaching the surface at each spreading center. When hydrothermal cooling is suppressed, or the spreading centers are sufficiently separated, the rigid block becomes extremely cold and separates two distinct, highly asymmetric upwellings that may focus melt beyond the spreading center. In that case, melt delivery might drive further and further the divergence centers, whereas

Does the bipolar seesaw extend to the terrestrial southern mid-latitudes?

Science.gov (United States)

Newnham, Rewi M.; Vandergoes, Marcus J.; Sikes, Elisabeth; Carter, Lionel; Wilmshurst, Janet M.; Lowe, David J.; McGlone, Matt S.; Sandiford, Anna

2012-03-01

High precision comparison of Greenland and Antarctic ice cores, suggesting a pervasive antiphased temperature relationship between the polar hemispheres during the last glaciation, lends strong support to the bipolar seesaw model (EPICA, 2006). The extent to which reorganisation of ocean-heat transport during abrupt climate change events affected the southern mid-latitudes remains unclear, however, owing to a paucity of well-dated records with robust climate proxies, variability between some records, and varying interpretations of their significance. Here we present temperature reconstructions for three key pollen records recognised by the NZ-INTIMATE (NZ-I) group which, along with the preliminary NZ-I climate event stratigraphy (Alloway et al., 2007) and published marine records, are compared with polar ice core records for the interval 30-10 cal. ka. We focus on key events within the context of Dansgard Oeschger cycles 4-1 and The Antarctic Cold Reversal/Younger Dryas intervals. The New Zealand records are broadly consistent with an extended bipolar seesaw whereby the oceanic southern mid-latitudes are warmed at times of MOC weakening or cessation in the North Atlantic, and vice versa. Variability between records indicate that other factors must be involved, however, and nor do these records refute alternative models that predict an antiphased inter-hemispheric pattern. Nevertheless an extended bipolar model may explain an early onset of LGM conditions in New Zealand and elsewhere in the Southern Hemisphere at a time when interstadials GI3 and GI4 kept Greenland warm. Similar inter-hemispheric dynamics have been invoked to explain an earlier termination of the LGM in Antarctica than in Greenland (Wolff et al., 2009) which is also evident in the New Zealand records. A prominent mid-LGM interstadial complex observed in several New Zealand records, connected by tephrochronology may represent another antiphased event although stronger chronological control is needed

The Role of Mid-Atlantic Ocean Data Portal in Supporting Ocean Planning

Directory of Open Access Journals (Sweden)

Richard G. Lathrop

2017-08-01

Full Text Available The Mid-Atlantic Regional Council on the Ocean (MARCO was established in 2009 to enhance the vitality of the region's ocean ecosystem and economy. One of MARCO's first action items was the development of the Mid-Atlantic Ocean Data Portal to serve as an on-line platform to engage stakeholders across the region with the objective of improving their understanding of how ocean resources and places are being used, managed, and conserved. A key component is the Marine Planner, an interactive map-based visualization and decision support tool. These types of on-line tools are becoming increasingly popular means of putting essential data and state-of-the-art visualization technology into the hands of the agencies, industry, community leaders, and stakeholders engaged in ocean planning. However, to be effective, the underlying geospatial data has to be seen as objective, comprehensive, up-to-date and regionally consistent. To meet this challenge, the portal utilizes a distributed network of web map services from credible and authoritative sources. Website analytics and feedback received during the review and comment period of the 2016 release of the Mid-Atlantic Ocean Action Plan confirm that the Data Portal is viewed as integral to this ocean planning process by the MidAtlantic Regional Planning Body and key stakeholders. While not all stakeholders may agree with specific planning decisions, there is broad based agreement on the need for better data and making access to that data widely available.

76 FR 56742 - Mid-Atlantic Fishery Management Council; Workshop

Science.gov (United States)

2011-09-14

... DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration RIN 0648-XA700 Mid-Atlantic... and Atmospheric Administration (NOAA), Commerce. ACTION: Notice of a workshop. SUMMARY: The Eight..., economic and social perspectives. DATES: The workshop will be held Tuesday, October 4 through Thursday...

Mapping Shear-wave Velocity Structures of the "African Anomaly" Along a Northwest to Southeast Arc From New Zealand to the Mid-Atlantic Ridge

Science.gov (United States)

Frodsham, A. E.; Wen, L.

2006-12-01

A previous study [Wang and Wen, 2006] investigated the geometry and shear velocity structure of the "African Anomaly" along a great circle arc from the East Pacific Rise to the Japan Sea, and concluded the anomaly extends 1300 km above the core-mantle boundary, that the sides of the anomaly slope towards the apex and has velocity deviations of -5% in the base and -2% to -3% in the mid-lower mantle. Wang and Wen [2004] also reported on the very low velocity province that forms the base of the "African Anomaly" and its lateral extent, but the northern edge of the anomaly was poorly constrained because of the nature of the seismic data. In this presentation we focus on the nature of the anomaly in a cross-section of the mantle along a great arc, from New Zealand, to the Mid-Atlantic Ridge off the coast of Newfoundland, centered over the anomaly. In particular, we focus on the northern edge of the "African Anomaly" where a paucity of large, deep focus earthquakes makes seismic arrivals from the northwest difficult to analyze. We map the lateral extent, thickness, and shear velocity structures of the "African Anomaly" on the basis of forward travel time and waveform modeling of direct S, ScS, and SKS waves. Seismic data used in this study were collected from PASSCAL arrays: KAAPVAAL seismic array (operating years 1997-1999), Tanzania seismic array (1994- 1995), Ethiopia/Kenya seismic array (2000-2002), and the Global Seismographic Network (1994-2002). We minimize uncertainty from earthquake mislocation by relocation of the earthquakes using a global tomographic shear wave velocity model and also correct for heterogeneities outside the anomaly. We explore various methods of data processing, such as frequency filtration, low fold stacking, and cross correlation, to best interpret the arrival times of the various seismic phases and constrain the nature of the "African Anomaly" along a northwest to southeast cross-section.

Forests and People in the Mid-Atlantic Region

Science.gov (United States)

Stephanie Fulton; Evan Mercer; M. Patricia Bradley

2012-01-01

Human populations in the Mid-Atlantic region over the last 250 years have increased nearly 100-fold, from an estimated few hundred thousand people to over 30 million people (Mercer and Murthy 2000). Increased population growth usually results in the conversion of forestland to nonforest uses, particularly agriculture, pastureland, and urban development. Not only is the...

Metal interactions between the polychaete Branchipolynoe seepensis and the mussel Bathymodiolus azoricus from Mid-Atlantic-Ridge hydrothermal vent fields.

Science.gov (United States)

Bebianno, Maria João; Cardoso, Cátia; Gomes, Tânia; Blasco, Julian; Santos, Ricardo Serrão; Colaço, Ana

2018-04-01

The vent blood-red commensal polynoid polychaete Branchipolynoe seepensis is commonly found in the pallial cavity of the vent mussel Bathymodiolus azoricus, the dominant bivalve species along the Mid-Atlantic-Ridge (MAR) and is known to be kleptoparasitic. Mussels were collected from three hydrothermal vent fields in the MAR: Menez Gwen (850 m depth, MG2, MG3 and MG4), Lucky Strike (1700 m depth, Montségur-MS and Eiffel Tower-ET) and Rainbow (2300 m depth). Polychaetes were absent in all Menez Gwen vent mussels, while the highest percentage was detected in mussels from Lucky Strike, where more than 70% of the mussels had at least one polychaete in their mantle cavity, followed by Rainbow with 33% of mussels with polychaetes. Total metal concentrations (Ag, Cd, Co, Cu, Fe, Mn, Ni and Zn) were determined in polychaetes whole body and in the mussel tissues (gills, digestive gland and mantle). To understand the possible metal interactions between symbiont and host, the activity of antioxidant defence (catalase (CAT), metallothioneins (MTs)), biotransformation enzymes (glutathione-s-transferases (GST)) activities and lipid peroxidation (LPO) were determined in polychaete whole soft tissues and in mussel tissues (gills, digestive gland and mantle). Metal concentrations in polychaetes and mussels tissues indicated that the accumulation patterns were species specific and also influenced by, and possibly dependent upon, the inter- and intra-variation of vent physico-chemistry between hydrothermal fields. Despite not detecting any strong correlations between metal and enzymes activities in polychaetes and mussels, when in presence of polychaetes, mussels presented less metal concentrations in the gills and digestive gland and lower activity of enzymatic biomarkers. This leads to infer that the polychaete plays a role on the detoxification process, and the interaction between the polychaete mussel association is probably an adaptation to metals concentrations at the

Arsenic speciation in food chains from mid-Atlantic hydrothermal vents

Science.gov (United States)

Taylor, Vivien F.; Jackson, Brian P.; Siegfried, Matthew R.; Navratilova, Jana; Francesconi, Kevin A.; Kirshtein, Julie; Voytek, Mary

2012-01-01

Arsenic concentration and speciation were determined in benthic fauna collected from the Mid-Atlantic Ridge hydrothermal vents. The shrimp species, Rimicaris exoculata, the vent chimney-dwelling mussel, Bathymodiolus azoricus, Branchipolynoe seepensis, a commensal worm of B. azoricus and the gastropod Peltospira smaragdina showed variations in As concentration and in stable isotope (δ13C and δ15N) signature between species, suggesting different sources of As uptake. Arsenic speciation showed arsenobetaine to be the dominant species in R. exoculata, whereas in B. azoricus and B. seepensis arsenosugars were most abundant, although arsenobetaine, dimethylarsinate and inorganic arsenic were also observed, along with several unidentified species. Scrape samples from outside the vent chimneys covered with microbial mat, which is a presumed food source for many vent organisms, contained high levels of total As, but organic species were not detectable. The formation of arsenosugars in pelagic environments is typically attributed to marine algae, and the pathway to arsenobetaine is still unknown. The occurrence of arsenosugars and arsenobetaine in these deep sea organisms, where primary production is chemolithoautotrophic and stable isotope analyses indicate food sources are of vent origin, suggests that organic arsenicals can occur in a foodweb without algae or other photosynthetic life.

Arsenic speciation in food chains from mid-Atlantic hydrothermal vents.

Science.gov (United States)

Taylor, Vivien F; Jackson, Brian P; Siegfried, Matthew; Navratilova, Jana; Francesconi, Kevin A; Kirshtein, Julie; Voytek, Mary

2012-05-04

Arsenic concentration and speciation were determined in benthic fauna collected from the Mid-Atlantic Ridge hydrothermal vents. The shrimp species, Rimicaris exoculata , the vent chimney-dwelling mussel, Bathymodiolus azoricus , Branchipolynoe seepensis , a commensal worm of B. azoricus , and the gastropod Peltospira smaragdina showed variations in As concentration and in stable isotope (δ 13 C and δ 15 N) signature between species, suggesting different sources of As uptake. Arsenic speciation showed arsenobetaine to be the dominant species in R. exoculata , whereas in B. azoricus and B. seepensis arsenosugars were most abundant, although arsenobetaine, dimethylarsinate, and inorganic arsenic were also observed, along with several unidentified species. Scrape samples from outside the vent chimneys, covered with microbial mat, which is a presumed food source for many vent organisms, contained high levels of total As, but organic species were not detectable. The formation of arsenosugars in pelagic environments is typically attributed to marine algae, and the pathway to arsenobetaine is still unknown. The occurrence of arsenosugars and arsenobetaine in these deep sea organisms, where primary production is chemolithoautotrophic and stable isotope analyses indicate food sources are of vent origin, suggests that organic arsenicals can occur in a food web without algae or other photosynthetic life.

Dacite petrogenesis on mid-ocean ridges: Evidence for oceanic crustal melting and assimilation

Science.gov (United States)

Wanless, V.D.; Perfit, M.R.; Ridley, W.I.; Klein, E.

2010-01-01

Whereas the majority of eruptions at oceanic spreading centers produce lavas with relatively homogeneous mid-ocean ridge basalt (MORB) compositions, the formation of tholeiitic andesites and dacites at mid-ocean ridges (MORs) is a petrological enigma. Eruptions of MOR high-silica lavas are typically associated with ridge discontinuities and have produced regionally significant volumes of lava. Andesites and dacites have been observed and sampled at several locations along the global MOR system; these include propagating ridge tips at ridge-transform intersections on the Juan de Fuca Ridge and eastern Gal??pagos spreading center, and at the 9??N overlapping spreading center on the East Pacific Rise. Despite the formation of these lavas at various ridges, MOR dacites show remarkably similar major element trends and incompatible trace element enrichments, suggesting that similar processes are controlling their chemistry. Although most geochemical variability in MOR basalts is consistent with low-pressure fractional crystallization of various mantle-derived parental melts, our geochemical data for MOR dacitic glasses suggest that contamination from a seawater-altered component is important in their petrogenesis. MOR dacites are characterized by elevated U, Th, Zr, and Hf, low Nb and Ta concentrations relative to rare earth elements (REE), and Al2O3, K2O, and Cl concentrations that are higher than expected from low-pressure fractional crystallization alone. Petrological modeling of MOR dacites suggests that partial melting and assimilation are both integral to their petrogenesis. Extensive fractional crystallization of a MORB parent combined with partial melting and assimilation of amphibole-bearing altered crust produces a magma with a geochemical signature similar to a MOR dacite. This supports the hypothesis that crustal assimilation is an important process in the formation of highly evolved MOR lavas and may be significant in the generation of evolved MORB in

77 FR 65380 - 2012 Fall Joint Meeting of the Ozone Transport Commission and the Mid-Atlantic Northeast...

Science.gov (United States)

2012-10-26

... ENVIRONMENTAL PROTECTION AGENCY [FRL-9745-9] 2012 Fall Joint Meeting of the Ozone Transport Commission and the Mid-Atlantic Northeast Visibility Union AGENCY: Environmental Protection Agency (EPA... Fall Meeting of the Ozone Transport Commission (OTC) and the Mid-Atlantic Northeast Visibility Union...

State of mid-atlantic region forests in 2000

Science.gov (United States)

Kenneth W. Stolte; Barbara L. Conkling; Stephanie Fulton; M. Patricia Bradley

2012-01-01

Wet and warm climate, mountainous topography, and deep rich soils produced one of the most magnificent and diverse temperate forests in the world. In 1650 the Mid-Atlantic forests covered 95 percent of the region, but were greatly reduced in 1900 by extensive tree harvesting, and conversion to farms and pastures. Settlement of forests also led to severe wildfires, soil...

First data on benthic and fish communities from the Mid-Atlantic Ridge, 16°40‧- 17°14‧N

Science.gov (United States)

Molodtsova, Tina N.; Galkin, Sergey V.; Kobyliansky, Stanislav G.; Simakova, Ulyana V.; Vedenin, Andrey A.; Dobretsova, Irina G.; Gebruk, Andrey V.

2017-03-01

The first ecological survey in the tropical part of the northern Mid-Atlantic Ridge (MAR) was conducted between 17°14‧N and 16°40‧N in February-March 2015 during the 37th cruise of the RV Professor Logachev. Significant effort of the survey was aimed at studies of benthic non-vent soft sediment fauna at depths from 2270 m to 3900 m. Samples of this fauna at seven stations revealed 780 specimens and at least 136 species. The most common species was the hermit crab Parapagurus cf. nudus. Also common were the ophiuroids Ophiotypa simplex and Ophiomusium cf. lymani. Most benthic organisms were the depth range from 0 to 3850 m included 1128 specimens represented by 48 species from 16 families. The highest number of species was in the families Myctophidae (18), Gonostomatidae (9) and Sternoptychidae (5). In the course of the cruise, two new fields of massive sulphide deposits were discovered on the south-western slope of the seamount on the eastern flank of the rift valley, one at 17°08.7‧N and second at 17°07.45‧N. During video profiling in this area indications of modern hydrothermal activity were recorded. Extensive fields of shells of Bathymodiolus puteoserpentis and Thyasira sp. were discovered and samples of bivalves were taken using the TV-grab and geological square corer. Surprisingly high concentration of drowned pelagic algae Sargassum sp. (Phaeophyceae, Fucales) in different state of degradation was observed at TV transects at the seafloor both on soft and hard substrates. Thalli of Sargassum fluitans appeared in trawl catches. Massive aggregations of Sargassum also were abundant at the sea surface in the area from December 2014 to April 2015.

Ferromanganese oxides from Mid-Indian ridge, seamounts and abyssal plains from the Indian Ocean

Digital Repository Service at National Institute of Oceanography (India)

Rao, P.S.; Pattan, J.N.

.47%) in the seamount crusts. The ferromanganese oxides from the Mid-Indian Ridge, seamount crusts and abyssal nodules appear to be of hydrothermal, hydrogenous and early-diagenetic in origin respectively...

Did the Chicxulub meteorite impact trigger eruptions at mid-ocean ridges globally?

Science.gov (United States)

Byrnes, J. S.; Karlstrom, L.

2017-12-01

Are there causal links between the eruption of large igneous provinces, meteorite impacts, and mass extinctions? Recent dating suggests that state shifts in Deccan Traps eruptions, including erupted volumes, feeder dike orientations, and magma chemistry, occurred shortly after the Chicxulub impact. A proposed explanation for this observation is an increase in upper mantle permeability following the Chicxulub impact that accelerated the pace of Deccan volcanism [Richards et al., 2015]. If such triggering occurred, at global distances not associated with the impact antipode, it is reasonable to hypothesize that other reservoirs of stored melt may have been perturbed as well. We present evidence that mid-ocean ridge activity increased globally following the impact. Anomalously concentrated free-air gravity and sea-floor topographic roughness suggest volumes of excess oceanic ridge magmatism in the range of 2 x 105 to 106 km3 within 1 Myrs of the Chicxulub impact. This signal is only clearly observed for half-spreading rates above 35 mm/yr, possibly because crust formed at slower spreading rates is too complex to preserve the signal. Because similar anomalies are observed separately in the Indian and Pacific Oceans, and because the timing of the signal does not clearly align with changes in spreading rates, we do not favor plume activity as an explanation. Widespread mobilization of existing mantle melt by post-impact seismic radiation, and subsequent emplacement of melt as crustal intrusions and eruptions, can explain the volume and distribution of anomalous crust without invoking impact-induced melt production. Although the mechanism for increasing permeability is not clear at either Deccan or mid-ocean ridges, these results support the hypothesis that the causes and consequences of the Deccan Traps, Chicxulub impact, and K-Pg mass extinction should not be considered in isolation. We conclude by discussing several enigmatic observations from K-Pg time that heightened

75 FR 20567 - Mid-Atlantic Fishery Management Council; Public Meeting

Science.gov (United States)

2010-04-20

... Mid-Atlantic Fishery Management Council's (MAFMC) Scientific and Statistical Committee (SSC) will hold... Fishery Management Council; Public Meeting AGENCY: National Marine Fisheries Service (NMFS), National... Fishery Management Council, 800 N. State Street, Suite 201, Dover, DE 19901; telephone: (302) 674-2331...

78 FR 52505 - Mid-Atlantic Fishery Management Council; Public Meeting

Science.gov (United States)

2013-08-23

... Mid-Atlantic Fishery Management Council's (MAFMC) Bluefish Monitoring Committee and Summer Flounder...: The Bluefish Monitoring Committee and Summer Flounder, Scup, and Black Sea Bass Monitoring Committee... associated management measures for the bluefish, summer flounder, scup, and black sea bass fisheries. Multi...

U-Pb, Sm-Nd and Rb-Sr systematics of mid-ocean ridge basalt glasses

Energy Technology Data Exchange (ETDEWEB)

Cohen, R S; Evensen, N M; Hamilton, P J; O' Nions, R K [Columbia Univ., Palisades, NY (USA). Lamont-Doherty Geological Observatory

1980-01-10

The measurement of Pb, Nd and Sr isotopes in basalt glasses from mid-ocean ridges reveals correlations in isotope parameters which have important implications for the differentiation history of the mantle.

Pathways of fish invasions in the Mid-Atlantic region of the United States

Science.gov (United States)

Lapointe, Nicolas W. R.; Fuller, Pam; Neilson, Matthew; Murphy, Brian R.; Angermeier, Paul

2016-01-01

Non-native fish introductions are a major threat to biodiversity and fisheries, and occur through numerous pathways that vary regionally in importance. A key strategy for managing invasions is to focus prevention efforts on pathways posing the greatest risk of future introductions. We identified high-risk pathways for fish establishment in the Mid-Atlantic region of the United States based on estimates of probability of establishment and records of previous introductions, which were considered in the context of emerging socioeconomic trends. We used estimates of propagule pressure, species’ environmental tolerance, and size of species pool to assess the risk of establishment by pathway. Pathways varied considerably in historic importance and species composition, with the majority of species introduced intentionally via stocking (primarily for sport, forage, or biocontrol) or bait release. Bait release, private stocking, illegal introductions intended to establish reproducing populations (e.g., of sport fish), aquaculture, and the sale of live organisms all create risks for future invasions in the Mid-Atlantic region. Of these pathways, bait release probably poses the greatest risk of introductions for the Mid-Atlantic region because propagule pressure is moderate, most released species are tolerant of local environmental conditions, and the pool of species available for transplantation is large. Our findings differ considerably from studies in other regions (e.g., bait release is a dominant pathway in the Mid-Atlantic region, whereas illegal introduction of sport fish is dominant in the western US and aquarium releases are dominant in Florida), demonstrating the need for regional-scale assessments of, and management strategies for, introduction pathways.

Uranium accumulation in modern and ancient Fe-oxide sediments: Examples from the Ashadze-2 hydrothermal sulfide field (Mid-Atlantic Ridge) and Yubileynoe massive sulfide deposit (South Urals, Russia)

Science.gov (United States)

Ayupova, N. R.; Melekestseva, I. Yu.; Maslennikov, V. V.; Tseluyko, A. S.; Blinov, I. A.; Beltenev, V. E.

2018-05-01

Fe-oxyhydroxide sediments (gossans) from the Ashadze-2 hydrothermal sulfide field (Mid-Atlantic Ridge) and hematite-carbonate-quartz rocks (gossanites) from the Yubileynoe Cu-Zn VHMS deposit (South Urals) are characterized by anomalously high U contents (up to 352 ppm and 73 ppm, respectively). In gossans from the Ashadze-2 hydrothermal sulfide field, rare isometric anhedral uraninite grains (up to 2 μm) with outer P- and Ca-rich rims, and numerous smaller (<1 μm) grains, occur in Fe-oxyhydroxides and sepiolite, associated with pyrite, isocubanite, chalcopyrite, galena, atacamite and halite. In gossanites from the Yubileynoe deposit, numerous uraninite particles (<3 μm) are associated with apatite, V-rich Mg-chlorite, micro-nodules of pyrite, Se-bearing galena, hessite and acanthite in a hematite-carbonate-quartz matrix. Small (1-3 μm) round grains of uraninite, which locally coalesce to large grains up to 10 μm in size, are associated with authigenic chalcopyrite. The similar diagenetic processes of U accumulation in modern and ancient Fe-oxyhydroxide sediments were the result of U fixation from seawater during the oxidation of sulfide minerals. Uraninite in gossanites was mainly deposited from diagenetic pore fluids, which circulated in the sulfide-hyaloclast-carbonate sediments.

Properties and pathways of Mediterranean water eddies in the Atlantic

Science.gov (United States)

Bashmachnikov, I.; Neves, F.; Calheiros, T.; Carton, X.

2015-09-01

within 1-2 years, although may take over 3 years. Collisions with the Mid-Atlantic Ridge and seamounts sensibly decrease meddy lifetimes. Meddy decay also speeds up when meddies meet the Azores Current or the North Atlantic Current. A rapid drop in the number of meddies south of the Azores Current proves that it represents a dynamic barrier for weak meddies.

Microbe-mediated transformations of marine dissolved organic matter during 2,100 years of natural incubation in the cold, oxic crust of the Mid-Atlantic Ridge.

Science.gov (United States)

Shah Walter, S. R.; Jaekel, U.; Huber, J. A.; Dittmar, T.; Girguis, P. R.

2015-12-01

On the western flank of the Mid-Atlantic Ridge, oxic seawater from the deep ocean is downwelled into the basaltic crust, supplying the crustal aquifer with an initial inoculum of organic matter and electron acceptors. Studies have shown that fluids circulating within the crust are minimally altered from original seawater, making this subsurface environment a unique natural experiment in which the fate of marine organic matter and the limitations of microbial adaptability in the context of reduced carbon supply can be examined. To make the subsurface crustal aquifer accessible, two CORK (Circulation Obviation Retrofit Kit) observatories have been installed at North Pond, a sediment-filled depression beneath the oligotrophic Sargasso Sea. Radiocarbon analysis of dissolved inorganic (DIC) and organic carbon (DOC) in samples recovered from these observatories show uncoupled aging between DOC and DIC with Δ14C values of DOC as low as -933‰ despite isolation from the open ocean for, at most, 2,100 years. This extreme value is part of a general trend of decreasing DOC δ13C and Δ14C values with increasing incubation time within the aquifer. Combined with reduced concentrations of DOC, our results argue for selective microbial oxidation of the youngest, most 13C-enriched components of downwelled DOC, possibly identifying these as characteristics of the more bioavailable fractions of deep-ocean dissolved organic matter. They also suggest that microbial oxidation during low-temperature hydrothermal circulation could be an important sink for aged marine dissolved organic matter.

Serpentinization of mantle-derived peridotites at mid-ocean ridges: Mesh texture development in the context of tectonic exhumation

Science.gov (United States)

Rouméjon, Stéphane; Cannat, Mathilde

2014-06-01

At slow spreading ridges, axial detachment faults exhume mantle-derived peridotites and hydrothermal alteration causes serpentinization in a domain extending more than 1 km next to the fault. At the microscopic scale, serpentinization progresses from a microfracture network toward the center of olivine relicts and forms a mesh texture. We present a petrographic study (SEM, EBSD, and Raman) of the serpentine mesh texture in a set of 278 abyssal serpentinized peridotites from the Mid-Atlantic and Southwest Indian Ridges. We show that serpentinization initiated along two intersecting sets of microfractures that have consistent orientations at the sample scale, and in at least one studied location, at the 100 m scale. We propose that these microfractures formed in fresh peridotites due to combined thermal and tectonic stresses and subsequently served as channels for serpentinizing fluids. Additional reaction-induced cracks developed for serpentinization extents <20%. The resulting microfracture network has a typical spacing of ˜60 µm but most serpentinization occurs next to a subset of these microfractures that define mesh cells 100-400 µm in size. Apparent mesh rim thickness is on average 33 ± 19 µm corresponding to serpentinization extents of 70-80%. Published laboratory experiments suggest that mesh rims formation could be completed in a few years (i.e., quasi instantaneous at the plate tectonic timescale). The depth and extent of the serpentinization domain in the detachment fault's footwall are probably variable in time and space and as a result we expect that the serpentine mesh texture at slow spreading ridges forms at variable rates with a spatially heterogeneous distribution.

Structural Iron (II) of Basaltic Glass as an Energy Source for Zetaproteobacteria in an Abyssal Plain Environment, Off the Mid Atlantic Ridge.

Science.gov (United States)

Henri, Pauline A; Rommevaux-Jestin, Céline; Lesongeur, Françoise; Mumford, Adam; Emerson, David; Godfroy, Anne; Ménez, Bénédicte

2015-01-01

To explore the capability of basaltic glass to support the growth of chemosynthetic microorganisms, complementary in situ and in vitro colonization experiments were performed. Microbial colonizers containing synthetic tholeitic basaltic glasses, either enriched in reduced or oxidized iron, were deployed off-axis from the Mid Atlantic Ridge on surface sediments of the abyssal plain (35°N; 29°W). In situ microbial colonization was assessed by sequencing of the 16S rRNA gene and basaltic glass alteration was characterized using Scanning Electron Microscopy, micro-X-ray Absorption Near Edge Structure at the Fe-K-edge and Raman microspectroscopy. The colonized surface of the reduced basaltic glass was covered by a rind of alteration made of iron-oxides trapped in a palagonite-like structure with thicknesses up to 150 μm. The relative abundance of the associated microbial community was dominated (39% of all reads) by a single operational taxonomic unit (OTU) that shared 92% identity with the iron-oxidizer Mariprofundus ferrooxydans PV-1. Conversely, the oxidized basaltic glass showed the absence of iron-oxides enriched surface deposits and correspondingly there was a lack of known iron-oxidizing bacteria in the inventoried diversity. In vitro, a similar reduced basaltic glass was incubated in artificial seawater with a pure culture of the iron-oxidizing M. ferrooxydans DIS-1 for 2 weeks, without any additional nutrients or minerals. Confocal Laser Scanning Microscopy revealed that the glass surface was covered by twisted stalks characteristic of this iron-oxidizing Zetaproteobacteria. This result supported findings of the in situ experiments indicating that the Fe(II) present in the basalt was the energy source for the growth of representatives of Zetaproteobacteria in both the abyssal plain and the in vitro experiment. In accordance, the surface alteration rind observed on the reduced basaltic glass incubated in situ could at least partly result from their activity.

Tissue and size-related changes in the fatty acid and stable isotope signatures of the deep sea grenadier fish Coryphaenoides armatus from the Charlie-Gibbs Fracture Zone region of the Mid-Atlantic Ridge

Science.gov (United States)

Mayor, Daniel J.; Sharples, Caroline J.; Webster, Lynda; Walsham, Pamela; Lacaze, Jean-Pierre; Cousins, Nicola J.

2013-12-01

Coryphaenoides armatus is a cosmopolitan deep-sea fish that plays a major role in the ecology of abyssal ecosystems. We investigated the trophic ecology and physiology of this species by determining the δ13C, δ15N and fatty acid signatures of muscle, liver and ovary tissues of individuals collected from ∼2700 m to the north and south of the Charlie-Gibbs Fracture Zone (CGFZ) of the Mid-Atlantic Ridge, NE Atlantic. Fatty acid and δ13C data both suggested that C. armatus shows an ontogenetic dietary shift, with the relative contributions of benthic and pelagic prey decreasing and increasing respectively as the animals grow. They also indicated that dietary overlap between animals living to the north and south of the CGFZ increases as they grow, suggesting that larger animals forage over greater distances and are not hindered by the presence of the CGFZ. Comparison of tissue-specific fatty acid signatures with previously published data suggests compositional homeostasis of the fatty acids 20:5(n-3) and 22:6(n-3) in the muscle, and 18:1(n-9) in the liver tissues. We ascribe this primarily to strict physiological requirements for these compounds, rather than simply to their abundance in the diet. We pose several speculative mechanisms to explain the observed trends in tissue-specific δ13C and δ15N values, illustrating some of the numerous processes that can influence the isotopic signatures of bulk tissues.

Copepod colonization of organic and inorganic substrata at a deep-sea hydrothermal vent site on the Mid-Atlantic Ridge

Science.gov (United States)

Plum, Christoph; Pradillon, Florence; Fujiwara, Yoshihiro; Sarrazin, Jozée

2017-03-01

The few existing studies on deep-sea hydrothermal vent copepods indicate low connectivity with surrounding environments and reveal high endemism among vents. However, the finding of non-endemic copepod species in association with engineer species at different reduced ecosystems poses questions about the dispersal of copepods and the colonization of hydrothermal vents as well as their ecological connectivity. The objective of this study is to understand copepod colonization patterns at a hydrothermal vent site in response to environmental factors such as temperature and fluid flow as well as the presence of different types of substrata. To address this objective, an in situ experiment was deployed using both organic (woods, pig bones) and inorganic (slates) substrata along a gradient of hydrothermal activity at the Lucky Strike vent field (Eiffel Tower, Mid-Atlantic Ridge). The substrata were deployed in 2011 during the MoMARSAT cruise and were recovered after two years in 2013. Overall, copepod density showed significant differences between substrata types, but was similar among different hydrothermal activity regimes. Highest densities were observed on woods at sites with moderate or low fluid input, whereas bones were the most densely colonized substrata at the 2 sites with higher hydrothermal influence. Although differences in copepod diversity were not significant, the observed trends revealed overall increasing diversity with decreasing temperature and fluid input. Slates showed highest diversity compared to the organic substrata. Temperature and fluid input had a significant influence on copepod community composition, resulting in higher similarity among stations with relatively high and low fluid inputs, respectively. While vent-specialists such as dirivultids and the tegastid Smacigastes micheli dominated substrata at high vent activity, the experiment demonstrated increasing abundance and dominance of non-vent taxa with decreasing temperature and fluid

WATER TEMPERATURE and SALINITY - SURFACE WATER, and other parameters collected from R.V. Celtic Explorer in Mid Atlantic Ridge from 2016-05-12 to 2016-05-21 (NCEI Accession 0157069)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — This dataset contains in situ sea surface measurements from R.V. Celtic Explorer in Mid Altlantic Ridge. The survey was conducted between May 12th and May 21, 2016...

DECISION TOOL FOR RIPARIAN ECOSYSTEM MANAGMENT IN THE MID-ATLANTIC HIGHLANDS

Science.gov (United States)

In the Canaan Valley Highlands of the Mid-Atlantic, riparian zone restoration has been identified as a critical watershed management practice not only for the ecosystem services provided but also for the potential socioeconomic growth from environmental investment and job creatio...

A holistic model for the role of the axial melt lens at fast-spreading mid-ocean ridges

Science.gov (United States)

MacLeod, C. J.; Loocke, M. P.; Lissenberg, J. C. J.

2016-12-01

Axial melt lenses (AML) are melt or crystal mush1 bodies located at the dyke-gabbro transition beneath intermediate- and fast-spreading mid-ocean ridges (MORs)2,3. Although it is generally thought that AMLs play a major role in the storage and differentiation of mid-ocean ridge basalts (MORB)1, the melt compositions within the AML and its role in the accretion of the lower crust are heavily debated4-6. Here we present the first comprehensive study of the AML horizon at a fast-spreading MOR (Hess Deep, equatorial Pacific Ocean). We show that plagioclase and pyroxene within the AML are much too evolved to be in equilibrium with MORB, with mean An (54.85) and Mg# (65.01) consistent with derivation from basaltic andesite to andesite melts (Mg# 43-26). We propose that, in between decadal eruptions, the AML is predominantly crystal mush and is fed by small volumes of evolved interstitial melts. Short-lived, focused injection of primitive melt leads to mixing of primitive melts with the extant highly fractionated melt, and triggers eruptions. This model reconciles the paradoxical compositional mismatch between the volcanic and plutonic records with the geophysical characteristics of the AML, the short residence times of Pacific MORB phenocrysts, and the incompatible trace element over-enrichments in MORB. 1Marjanović, M. et al., 2015. Distribution of melt along the East Pacific Rise from 9°30' to 10°N from an amplitude variation with angle of incidence (AVA) technique. Geophys. J. Int. 203. 2Detrick, R. S. et al., 1987. Multi-channel seismic imaging of a crustal magma chamber along the EPR. Nature 326. 3Sinton, J. M. & Detrick, R. S., 1992. Mid-ocean ridge magma chambers. J. Geophys. Res. 97. 4Coogan, L. A., Thompson, G. & MacLeod, C. J., 2002. A textural and geochemical investigation of high level gabbros from the Oman ophiolite: implications for the role of the axial magma chamber at fast-spreading ridges. Lithos 63. 5Pan, Y. & Batiza, R., 2002. Mid-ocean ridge magma

Investigation of extractable organic compounds in deep-sea hydrothermal vent fluids along the Mid-Atlantic Ridge

Science.gov (United States)

McCollom, Thomas M.; Seewald, Jeffrey S.; German, Christopher R.

2015-05-01

The possibility that deep-sea hydrothermal vents may contain organic compounds produced by abiotic synthesis or by microbial communities living deep beneath the surface has led to numerous studies of the organic composition of vent fluids. Most of these studies have focused on methane and other light hydrocarbons, while the possible occurrence of more complex organic compounds in the fluids has remained largely unstudied. To address this issue, the presence of higher molecular weight organic compounds in deep-sea hydrothermal fluids was assessed at three sites along the Mid-Atlantic Ridge that span a range of temperatures (51 to >360 °C), fluid compositions, and host-rock lithologies (mafic to ultramafic). Samples were obtained at several sites within the Lucky Strike, Rainbow, and Lost City hydrothermal fields. Three methods were employed to extract organic compounds for analysis, including liquid:liquid extraction, cold trapping on the walls of a coil of titanium tubing, and pumping fluids through cartridges filled with solid phase extraction (SPE) sorbents. The only samples to consistently yield high amounts of extractable organic compounds were the warm (51-91 °C), highly alkaline fluids from Lost City, which contained elevated concentrations of C8, C10, and C12n-alkanoic acids and, in some cases, trithiolane, hexadecanol, squalene, and cholesterol. Collectively, the C8-C12 acids can account for about 15% of the total dissolved organic carbon in the Lost City fluids. The even-carbon-number predominance of the alkanoic acids indicates a biological origin, but it is unclear whether these compounds are derived from microbial activity occurring within the hydrothermal chimney proximal to the site of fluid discharge or are transported from deeper within the system. Hydrothermal fluids from the Lucky Strike and Rainbow fields were characterized by an overall scarcity of extractable dissolved organic compounds. Trace amounts of aromatic hydrocarbons including

77 FR 77036 - Mid-Atlantic Fishery Management Council (MAFMC); Public Meeting

Science.gov (United States)

2012-12-31

...: The Scientific and Statistical Committee (SSC) of the Mid- Atlantic Fishery Management Council... Fishery Management Council (MAFMC); Public Meeting AGENCY: National Marine Fisheries Service (NMFS... Management Council, 800 N. State Street, Suite 201, Dover, DE 19901; telephone: (302) 674-2331. FOR FURTHER...

77 FR 2961 - Mid-Atlantic Fishery Management Council (MAFMC); Public Meeting

Science.gov (United States)

2012-01-20

... DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration RIN 0648-XA943 Mid-Atlantic...), National Oceanic and Atmospheric Administration (NOAA), Commerce. ACTION: Notice of a public meeting... with the Council's Social and Economic Sub-committee of the Scientific and Statistical Committee (SSC...

78 FR 44539 - Mid-Atlantic Fishery Management Council (MAFMC); Public Meetings

Science.gov (United States)

2013-07-24

... DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration RIN 0648-XC777 Mid-Atlantic Fishery Management Council (MAFMC); Public Meetings AGENCY: National Marine Fisheries Service (NMFS... Amendment, Amendment 5 to Dolphin/Wahoo, Amendment 19 and 20 to the Joint Coastal Migratory Pelagics (CMP...

The Othris Ophiolite, Greece: A snapshot of subduction initiation at a mid-ocean ridge

NARCIS (Netherlands)

Barth, M.G.; Mason, P.R.D.; Davies, G.R.; Drury, M.R.

2008-01-01

The mantle section of the Tethyan-type Othris Ophiolite, Greece, records tectono-magmatic processes characteristic of both mid-ocean ridges and supra-subduction zones. The Othris Ophiolite is a remnant of the Jurassic Neotethys Ocean, which existed between Eurasia and Gondwanaland. Othris

76 FR 42684 - Mid-Atlantic Fishery Management Council (MAFMC); Public Meeting

Science.gov (United States)

2011-07-19

.... SUMMARY: The Mid-Atlantic Fishery Management Council Staff will hold a meeting of the Visioning Project Advisory Panel to discuss communications strategies and data gathering tools for the Visioning Project... project's results to develop future management actions. Although non-emergency issues not contained in...

Glacial modulation of mid-ocean ridge magmatism and anomalous Pacific Antarctic Ridge volcanism during Termination II

Science.gov (United States)

Asimow, P. D.; Lewis, M.; Lund, D. C.; Seeley, E.; McCart, S.; Mudahy, A.

2017-12-01

Glacially-driven sea level rise and fall may modulate submarine volcanism by superposing pressure changes on the tectonic decompression that causes melt production in the mantle below mid-ocean ridges. A number of recent studies have considered whether this effect is recorded in the periodicity of ridge flank bathymetry (Tolstoy, 2015; Crowley et al., 2015) but interpretation of the bathymetric data remains controversial (Goff, 2016; Olive et al., 2016). We have pursued an independent approach using hydrothermal metals in well-dated near-ridge sediment cores. Along the full length of the East Pacific Rise, in areas of the ocean with widely variable biologic productivity, there are large and consistent rises in Fe, Mn, and As concentrations during the last two glacial terminations. We interpret these cores as records of excess hydrothermal flux due to delayed delivery to the axis of excess melt generated by the preceding falls in sea level. Here we discuss the potentially related discovery, in a core near the Pacific Antarctic Ridge (PAR), of a 10 cm thick layer of basaltic ash shards up to 250 mm in size, coincident with the penultimate deglaciation (Termination II). Although the site was 8 km off-axis at the time, the glasses have major element, volatile, and trace element composition consistent with more evolved members of the axial MORB suite from the nearby ridge axis. Their morphologies are typical of pyroclastic deposits created by explosive submarine volcanism (Clague et al., 2009). We propose that a period of low magmatic flux following a sea-level rise caused cooling of crustal magmatic systems, more advanced fractionation in the axial magma chamber, and increases in viscosity and volatile concentration. We hypothesize subsequent arrival of high magmatic flux during Termination II then reactivated the system and triggered an unusually vigorous series of explosive eruptions along this segment of the PAR. Ash layers recording large eruptions such as this one

Karst of the Mid-Atlantic region in Maryland, West Virginia, and Virginia

Science.gov (United States)

Doctor, Daniel H.; Weary, David J.; Brezinski, David K.; Orndorff, Randall C.; Spangler, Lawrence E.; Brezinski, David K.; Halka, Jeffrey; Ortt, Richard A.

2015-01-01

The Mid-Atlantic region hosts some of the most mature karst landscapes in North America, developed in highly deformed rocks within the Piedmont and Valley and Ridge physiographic provinces. This guide describes a three-day excursion to examine karst development in various carbonate rocks by following Interstate 70 west from Baltimore across the eastern Piedmont, across the Frederick Valley, and into the Great Valley proper. The localities were chosen in order to examine the structural and lithological controls on karst feature development in marble, limestone, and dolostone rocks with an eye toward the implications for ancient landscape evolution, as well as for modern subsidence hazards. A number of caves will be visited, including two commercial caverns that reveal strikingly different histories of speleogenesis. Links between karst landscape development, hydrologic dynamics, and water resource sustainability will also be emphasized through visits to locally important springs. Recent work on quantitative dye tracing, spring water geochemistry, and groundwater modeling reveal the interaction between shallow and deep circulation of groundwater that has given rise to the modern karst landscape. Geologic and karst feature mapping conducted with the benefit of lidar data help reveal the strong bedrock structural controls on karst feature development, and illustrate the utility of geologic maps for assessment of sinkhole susceptibility.

Energy situation in the Mid-Atlantic region

Energy Technology Data Exchange (ETDEWEB)

Munson, J S; Brainard, J P

1977-08-01

This report presents a review of the energy situation in the Mid-Atlantic Region. It describes the patterns of energy production, supply and demand by state and compares these to national and regional averages. It presents a picture of existing energy and environmental interactions and a view of potential energy and environmental conflicts. A review of the major issues by energy sector is included as is a description of the existing energy actors and major energy programs for Ohio, West Virginia, Virginia, Pennsylvania, New Jersey, New York, Delaware, Maryland, Puerto Rico, Virgin Islands, and Washington, DC.

National Assessment of Shoreline Change; historical shoreline change along the New England and Mid-Atlantic coasts

Science.gov (United States)

Hapke, Cheryl J.; Himmelstoss, Emily A.; Kratzmann, Meredith G.; List, Jeffrey H.; Thieler, E. Robert

2011-01-01

Beach erosion is a chronic problem along many open-ocean shores of the United States. As coastal populations continue to grow and community infrastructures are threatened by erosion, there is increased demand for accurate information regarding past and present trends and rates of shoreline movement. There is also a need for a comprehensive analysis of shoreline movement that is consistent from one coastal region to another. To meet these national needs, the U.S. Geological Survey (USGS) is conducting an analysis of historical shoreline changes along open-ocean sandy shores of the conterminous United States and parts of Hawaii, Alaska, and the Great Lakes. One purpose of this work is to develop standard, repeatable methods for mapping and analyzing shoreline movement so that periodic, systematic, internally consistent updates regarding coastal erosion and land loss can be made nationally. In the case of this study, the shoreline is the interpreted boundary between the ocean water surface and the sandy beach. This report on the New England and Mid-Atlantic coasts is the fifth in a series of reports on historical shoreline change. Previous investigations include analyses and descriptive reports of the Gulf of Mexico, the Southeast Atlantic, and, for California, the sandy shoreline and the coastal cliffs. The rates of change presented in this report represent conditions up to the date of the most recent shoreline data and therefore are not intended for predicting future shoreline positions or rates of change. Because of the geomorphology of the New England and Mid-Atlantic (rocky coastlines, large embayments and beaches) as well as data gaps in some areas, this report presents beach erosion rates for 78 percent of the 1,360 kilometers of the New England and Mid-Atlantic coasts. The New England and Mid-Atlantic shores were subdivided into a total of 10 analysis regions for the purpose of reporting regional trends in shoreline change rates. The average rate of long

Climate change and fire management in the mid-Atlantic region

Science.gov (United States)

Kenneth L. Clark; Nicholas Skowronski; Heidi Renninger; Robert. Scheller

2014-01-01

In this review, we summarize the potential impacts of climate change on wildfire activity in the mid-Atlantic region, and then consider how the beneficial uses of prescribed fire could conflict with mitigation needs for climate change, focusing on patters of carbon (C) sequestration by forests in the region. We use a synthesis of field studies, eddy flux tower...

77 FR 44216 - Mid-Atlantic Fishery Management Council (MAFMC); Public Meetings

Science.gov (United States)

2012-07-27

... MAFMC Strategic Planning--Objective, Process, and Possible Outcomes and an introduction to the new.... SUMMARY: The Mid-Atlantic Fishery Management Council (Council) and its Strategic Planning Working Group... INFORMATION: Monday, August 13, 2012 9 a.m. until 5 p.m.--The Visioning and Strategic Planning Working Group...

U-series disequilibrium constraints on magma generation at the Jan Mayen hotspot

Science.gov (United States)

Rivers, E. R.; Chernow, R.; Elkins, L. J.; Sims, K. W.; Blichert-Toft, J.; Devey, C. W.

2013-12-01

The incompatible element-enriched magma source beneath the Jan Mayen Island hotspot influences melt generation on the adjacent northern Mid-Atlantic Ridge system and likely derives from either a small, local mantle plume, ancient Icelandic plume material emplaced in the mantle source, and/or sub-continental lithospheric mantle remnants emplaced locally by rifting of Greenland. The slow spreading Northern Kolbeinsey and Southern Mohns Ridges are immediately adjacent to Jan Mayen Island. Both have relatively shallow ridge axes, particularly the extremely shallow Eggvin Bank region of the Northern Kolbeinsey Ridge, which host anomalously large central volcanic edifices. We are currently collecting U-series disequilibrium and long-lived radiogenic isotope data for fresh, glassy mid-ocean ridge basalts from the Northern Kolbeinsey and Southern Mohns Ridge segments to better constrain source composition, depth of melting in the garnet peridotite stability field, solid mantle upwelling rates, and the nature of melt extraction beneath those segments. In particular, we are measuring isotopic data for geographically well-located samples collected from hummocky pillow basalt flows within the axial valley of the Northern Kolbeinsey Ridge segment as well as from the large volcanoes on both ridge segments, to further determine the role of the Jan Mayen hotspot in crustal construction on the Mid-Atlantic Ridge. Recently collected data show particularly high strontium isotope ratios consistent with trace element patterns that suggest a distinct local plume located beneath the Jan Mayen hotspot. A plume model for Jan Mayen is supported by new bathymetric imaging of adjacent ridge segments that reveals excess volcanism beneath the large axial volcanoes and a radial distribution of enrichment surrounding Jan Mayen Island. We predict that age-constrained U-series disequilibrium measurements will support active mantle upwelling focused beneath both Jan Mayen Island and the large axial

Extreme incompatibility of helium during mantle melting: Evidence from undegassed mid-ocean ridge basalts

Science.gov (United States)

Graham, David W.; Michael, Peter J.; Shea, Thomas

2016-11-01

We report total helium concentrations (vesicles + glass) for a suite of thirteen ultradepleted mid-ocean ridge basalts (UD-MORBs) that were previously studied for volatile contents (CO2, H2O) plus major and trace elements. The selected basalts are undersaturated in CO2 + H2O at their depths of eruption and represent rare cases of undegassed MORBs. Sample localities from the Atlantic (2), Indian (1) and Pacific (7) Oceans collectively show excellent linear correlations (r2 = 0.75- 0.92) between the concentrations of helium and the highly incompatible elements C, K, Rb, Ba, Nb, Th and U. Three basalts from Gakkel Ridge in the Arctic were also studied but show anomalous behavior marked by excess lithophile trace element abundances. In the Atlantic-Pacific-Indian suite, incompatible element concentrations vary by factors of 3-4.3, while helium concentration varies by a factor of 13. The strong correlations between the concentrations of helium and incompatible elements are explained by helium behavior as the most incompatible element during mantle melting. Partial melting of an ultradepleted mantle source, formed as a residue of earlier melt extraction, accounts for the observed concentrations. The earlier melting event involved removal of a small degree melt (∼1%) at low but non-zero porosity (0.01-0.5%), leading to a small amount of melt retention that strongly leveraged the incompatible element budget of the ultradepleted mantle source. Equilibrium melting models that produce the range of trace element and helium concentrations from this source require a bulk solid/melt distribution coefficient for helium that is lower than that for other incompatible elements by about a factor of ten. Alternatively, the bulk solid/melt distribution coefficient for helium could be similar to or even larger than that for other incompatible elements, but the much larger diffusivity of helium in peridotite leads to its more effective incompatibility and efficient extraction from a

Active spreading processes at ultraslow mid-ocean ridges: The 1999-2001 seismo-volcanic episode at 85°E Gakkel ridge, Arctic Ocean

Science.gov (United States)

Schlindwein, Vera; Riedel, Carsten; Korger, Edith; Läderach, Christine

2010-05-01

The rate of magma and crustal production at mid-ocean ridges is thought to decrease with decreasing spreading rate. At ultraslow spreading rates below 10-20 mm/y full rate, heat loss by conduction greatly reduces melt production with less melt produced at increasingly greater depths. Gakkel Ridge, the actively spreading mid-ocean ridge in the Arctic Ocean, opens at rates of 14 mm/y in the west decreasing to less than 6 mm/y at its eastern termination and demonstrates that magma production is not only a function of spreading rate. Whereas amagmatic spreading takes place at rates of about 12-10 mm/y, focussed melt production occurs at even lower spreading rates in long-lived discrete volcanic centres. One such centre is the 85°E volcanic complex at eastern Gakkel ridge where in 1999 a teleseismically recorded earthquake swarm consisting of more than 250 earthquakes over 9 months signalled the onset of an active spreading episode. The earthquake swarm is believed to be associated with volcanic activity although no concurrent lava effusion was found. We analysed the teleseismic earthquake swarm together with visual observation and microseismic data recorded at this site in 2001 and 2007 and noted the following characteristics which may be indicative for volcanic spreading events at the still poorly explored ultraslow spreading ridges: - unusual duration: The 1999 earthquake swarm lasted over 9 months rather than a few weeks as observed on faster spreading ridges. In addition, in 2001 seismoacoustic sounds which we interpret as gas discharge in Strombolian eruptions and a giant event plume maintained over more than one year indicate waxing and waning volcanic activity since 1999. - unusual strength: The earthquake swarm was detected at teleseismic distances of more than 1000 km and included 11 events with a magnitude >5. No other confirmed mid-ocean ridge eruption released a comparable seismic moment. Rather than focussing in a narrow area or showing pronounced

State of mid-atlantic region forests in 2000-Summary Report

Science.gov (United States)

Kenneth W. Stolte

2012-01-01

Wet and warm climate, mountainous topography, and deep rich soils produced one of the most magnificent and diverse temperate forests in the world. In 1650 the Mid-Atlantic forests covered 95 percent of the region, but were greatly reduced in 1900 by extensive tree harvesting, and conversion to farms and pastures. Settlement of forests also led to severe wildfires, soil...

AN APPLIED ONTOLOGY TO THE MID-ATLANTIC CABLE: HISTORICAL TO MODERN INFORMATICS CONSIDERATION FROM A MATH PERSPECTIVE KAIEM L. FRINK ELIZABETH CITY STATE UNIVERSITY(ECSU)KAIEM_FRINK@HOTMAIL.COM, DR. DEWAYNE B. BRANCH ECSU, DR. ROB RASKIN JET PROPULSIONS LABORATORY GLENDA THOMAS ECSU,KENNETH JONES ECSU

Science.gov (United States)

Frink, K.; Branch, B. D.; Raskin, R.

2009-12-01

As early as the 1600's scientists in various fields world to address a global human need of human communication on a global basis by implementing the trans-Atlantic cable. The Mid 4Trans-Atlantic cable is one of the earliest forms of global commutation. Here may be the first evidence of informatics needs where science, data, and engineering were collaborated across disciplines to advance a world standard of living. This work investigates what applied ontology may have been consisting with the thought pattern of such expertise who conducted informatics arguably without computers, ontology’s, and a cyber infrastructure. In modern context, an applied ontology may best represent the body of intentional learning, research and collaboration among scientists to achieve a human goal. Perhaps if such intentional non-partisan work can achieve a solution such as Trans-Atlantic Cable, climate change may benefit from intentional collaborative ontology’s and systems of multi user knowledgebase or expert informatics systems. 1Bruce C. Heezen 1924 -1977 American Geologist famous for mapping the Mid Atlantic Mountain Ridge in the 1950’s. Heezen died in 1977 on a submarine cruise to study the Mid-Atlantic ridge near Ice land aboard the NR-1 submarine. 7Marie Tharp academic background is Bachelors Degree in English, Master Degree in Geology University of Michigan, and Mathematics Degree at the University of Tulsa. Tharp worked at Lamont- Doherty Earth Observatory at Columbia University. History of the Digital Divide during the 1600’s touches on the availability of information. 3Issue of Mathematics during the 1600’s would be lack of communications and assessment. The scientific communities cannot address climate change most largely due to language barriers amongst humans. Weight per meter for the cable and the ships weight capacity in the 1600’sWeight/per meter 2w/m=X1 taking into account that maximum depths or Atlantic Ocean was unknown at that time and still is.

Estuarine Living Marine Resources: Mid-Atlantic Regional Distribution and Abundance (NCEI Accession 0162403)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — This is the Mid-Atlantic regional component of NOAA’s Estuarine Living Marine Resources (ELMR) Project, a national database of ecologically and economically...

77 FR 16811 - Mid-Atlantic Fishery Management Council (MAFMC); Public Meetings

Science.gov (United States)

2012-03-22

... meet. 5 p.m. until 6 p.m.--There will be a public listening session. Wednesday, April 11, 2012 9 a.m... Coral and discussion of Mid-Atlantic Council action will follow. The public listening session will focus..., finalize goals and objectives, purpose and need, discuss transition strategies to move EBFM, and...

Using bathymetry and reflective seismic profiles to tests a suspected link between melt flux and cumulative fault heave at mid-ocean ridges

Science.gov (United States)

Haughton, G.; Murton, B. J.; Le Bas, T.; Henstock, T.

2017-12-01

The interplay between magma supply and spreading rate is believed to play a major role in determining large scale seafloor morphology. Here we use bathymetry to test this relationship in areas with similar spreading rates and differing magma supplies. By using open source bathymetry data we have developed a repeatable, automated method for categorising seafloor cumulative fault heave and then attempt to identify the controlling variables. We measure the total apparent fault heave along axis and off-axis at 29°N and 60°N on the Mid-Atlantic Ridge then compare this to proxies for deformation and magma supply. Two approaches are adopted for identifying faults: one using bathymetry and the other spreading-parallel seismic reflection data. The first re-examines the orthogonally spreading Broken Spur segment (26°N) spreading at 23 mm yr-1 (full rate). The other examines the Reykjanes Ridge (60°N) spreading obliquely at 21 mm yr-1 (full rate), which may be influenced by the Icelandic hotspot. Each have contrasting residual depth and structure, with the former being typical of slow spreading ridges, with marked axial valleys, whereas the latter is more typical of fast spreading ridge morphology, with smooth axial rise. We find that high total heave (indicating high tectonic spreading) on the Broken Spur segment does not correlate with high mantle Bouguer anomalies (indicating thin crust and low melt flux). From this we hypothesise that total heave on the large scale at the Broken Spur segment is not controlled by crustal thickness or melt supply. At the Raykjanes Ridge, V-shaped ridges have thicker crust (measured seismically) which converge south of Iceland. These are thought to reflect transient (every 4-6 Myrs) pulses of hot mantle radiating away from the Iceland plume. We find ridge-symmetrical variation in fault heave but with a lower frequency (6-8 Myrs) and longer wavelength (3-7 Myrs) than the V-shaped ridges. Our analysis shows that plume pulses do not

75 FR 48666 - Calpine Mid-Atlantic Marketing, LLC; Supplemental Notice That Initial Market-Based Rate Filing...

Science.gov (United States)

2010-08-11

...-Atlantic Marketing, LLC; Supplemental Notice That Initial Market-Based Rate Filing Includes Request for... proceeding, of Calpine Mid-Atlantic Marketing, LLC's application for market-based rate authority, with an... of protests and interventions in lieu of paper, using the FERC Online links at http://www.ferc.gov...

Hydrothermal activity at slow-spreading ridges: variability and importance of magmatic controls

Science.gov (United States)

Escartin, Javier

2016-04-01

Hydrothermal activity along mid-ocean ridge axes is ubiquitous, associated with mass, chemical, and heat exchanges between the deep lithosphere and the overlying envelopes, and sustaining chemiosynthetic ecosystems at the seafloor. Compared with hydrothermal fields at fast-spreading ridges, those at slow spreading ones show a large variability as their location and nature is controlled or influenced by several parameters that are inter-related: a) tectonic setting, ranging from 'volcanic systems' (along the rift valley floor, volcanic ridges, seamounts), to 'tectonic' ones (rift-bounding faults, oceanic detachment faults); b) the nature of the host rock, owing to compositional heterogeneity of slow-spreading lithosphere (basalt, gabbro, peridotite); c) the type of heat source (magmatic bodies at depth, hot lithosphere, serpentinization reactions); d) and the associated temperature of outflow fluids (high- vs.- low temperature venting and their relative proportion). A systematic review of the distribution and characteristics of hydrothermal fields along the slow-spreading Mid-Atlantic Ridge suggests that long-lived hydrothermal activity is concentrated either at oceanic detachment faults, or along volcanic segments with evidence of robust magma supply to the axis. A detailed study of the magmatically robust Lucky Strike segment suggests that all present and past hydrothermal activity is found at the center of the segment. The association of these fields to central volcanos, and the absence of indicators of hydrothermal activity along the remaining of the ridge segment, suggests that long-lived hydrothermal activity in these volcanic systems is maintained by the enhanced melt supply and the associated magma chamber(s) required to build these volcanic edifices. In this setting, hydrothermal outflow zones at the seafloor are systematically controlled by faults, indicating that hydrothermal fluids in the shallow crust exploit permeable fault zones to circulate. While

Platinum-group elements, S, Se and Cu in highly depleted abyssal peridotites from the Mid-Atlantic Ocean Ridge (ODP Hole 1274A): Influence of hydrothermal and magmatic processes

Science.gov (United States)

Marchesi, Claudio; Garrido, Carlos J.; Harvey, Jason; González-Jiménez, José María; Hidas, Károly; Lorand, Jean-Pierre; Gervilla, Fernando

2013-11-01

Highly depleted harzburgites and dunites were recovered from ODP Hole 1274A, near the intersection between the Mid-Atlantic Ocean Ridge and the 15°20'N Fracture Zone. In addition to high degrees of partial melting, these peridotites underwent multiple episodes of melt-rock reaction and intense serpentinization and seawater alteration close to the seafloor. Low concentrations of Se, Cu and platinum-group elements (PGE) in harzburgites drilled at around 35-85 m below seafloor are consistent with the consumption of mantle sulfides after high degrees (>15-20 %) of partial melting and redistribution of chalcophile and siderophile elements into PGE-rich residual microphases. Higher concentrations of Cu, Se, Ru, Rh and Pd in harzburgites from the uppermost and lowest cores testify to late reaction with a sulfide melt. Dunites were formed by percolation of silica- and sulfur-undersaturated melts into low-Se harzburgites. Platinum-group and chalcophile elements were not mobilized during dunite formation and mostly preserve the signature of precursor harzburgites, except for higher Ru and lower Pt contents caused by precipitation and removal of platinum-group minerals. During serpentinization at low temperature (desulfurization to S-poor sulfides (mainly heazlewoodite) and awaruite. Contrary to Se and Cu, sulfur does not record the magmatic evolution of peridotites but was mostly added in hydrothermal sulfides and sulfate from seawater. Platinum-group elements were unaffected by post-magmatic low-temperature processes, except Pt and Pd that may have been slightly remobilized during oxidative seawater alteration.

Characterisation of dissolved organic compounds in hydrothermal fluids by stir bar sorptive extraction - gas chomatography - mass spectrometry. Case study: the Rainbow field (36°N, Mid-Atlantic Ridge

Directory of Open Access Journals (Sweden)

Konn Cecile

2012-11-01

Full Text Available Abstract The analysis of the dissolved organic fraction of hydrothermal fluids has been considered a real challenge due to sampling difficulties, complexity of the matrix, numerous interferences and the assumed ppb concentration levels. The present study shows, in a qualitative approach, that Stir Bar Sorptive Extraction (SBSE followed by Thermal Desorption – Gas Chromatography – Mass Spectrometry (TD-GC-MS is suitable for extraction of small sample volumes and detection of a wide range of volatile and semivolatile organic compounds dissolved in hydrothermal fluids. In a case study, the technique was successfully applied to fluids from the Rainbow ultramafic-hosted hydrothermal field located at 36°14’N on the Mid-Atlantic Ridge (MAR. We show that n-alkanes, mono- and poly- aromatic hydrocarbons as well as fatty acids can be easily identified and their retention times determined. Our results demonstrate the excellent repeatability of the method as well as the possibility of storing stir bars for at least three years without significant changes in the composition of the recovered organic matter. A preliminary comparative investigation of the organic composition of the Rainbow fluids showed the great potential of the method to be used for assessing intrafield variations and carrying out time series studies. All together our results demonstrate that SBSE-TD-GC-MS analyses of hydrothermal fluids will make important contributions to the understanding of geochemical processes, geomicrobiological interactions and formation of mineral deposits.

Seismofocal zones and mid-ocean ridges - look outside of the plate paradigm

Science.gov (United States)

Anokhin, Vladimir; Kholmianskii, Mikhail

2014-05-01

Seismofocal zones and mid-ocean ridges - look outside of the plate paradigm Vladimir M. Anokhin, Mikhail A. Kholmianskii Configuration of the seismofocal zones (SFZ), visible in a real position of the focuses of earthquakes, has a significant step component (jagged) expressed by the presence of several sub-horizontal "seismoplanes", which concentrates focuses of earthquakes (depths 10, 35 km and other). Orientation of seismolines inside of SFZ tends to 4 main directions: 0-5 dgr, 120-145 dgr, 40-55 dgr, 85-90 dgr. These facts suggest significantly block, a terraced structure of the body of Benioff zone. The borders of blocks have orientation according directions regmatic net of the Earth. In accordance with this, SFZ can be presented as the most active segments of the border of the crossing: «continent-ocean», having the following properties: - block (terraced) structure; - in some sites - dive under the continental crust (in present time); - prevailing compression (in present time), perhaps, as the period of the oscillatory cycle; Infinite "subduction" in SFZ is unlikely. One of the areas where there is proof of concept of far "spreading" is the southernmost tip of the mid-oceanic Gakkel ridge in the Laptev sea (Arctic ocean). Here active "spreading" ridge normal approaches to the boundary of the continental crust - the shelf of the Laptev sea. On the shelf there are a number of subparallel NW grabens. NE fault zone Charlie, controlling the continental slope is established stepped fault without shift component. This means that the amount of extending of the offshore grabens does not significantly differ from the scale of spreading in the Gakkel ridge. However, the total spreads grabens (50-100 km) 6-10 times less than the width of the oceanic crust (600 km) in the surrounding area. Conclusion: the oceanic crust in the Laptev sea was formed mainly not due to "spreading". It is very likely that here was sinking and the processing of continental crust in the ocean

The Usumacinta-Grijalva beach-ridge plain in southern Mexico : A high-resolution archive of river discharge and precipitation

NARCIS (Netherlands)

Nooren, C.A.M.; Hoek, W.Z.; Winkels, T.G.; Huizinga, A.; van der Plicht, J.; Van Dam, R.; Van Heteren, S.; van Bergen, M.J.; Prins, M.A.; Reimann, T.; Wallinga, J.; Cohen, K.M.; Minderhoud, P.S.J.; Middelkoop, H.

2017-01-01

The beach-ridge sequence of the Usumacinta-Grijalva delta borders a 300 km long section of the southern Gulf of Mexico coast. With around 500 beach ridges formed in the last 6500 years, the sequence is unsurpassed in the world in terms of numbers of individual ridges preserved, continuity of the

Mechanisms of northeastern Brazil rainfall anomalies due to Southern Tropical Atlantic variability

Science.gov (United States)

Neelin, J.; Su, H.

2004-05-01

Observational studies have shown that the rainfall anomalies in eastern equatorial South America, including Nordeste Brazil, have a positive correlation with tropical southern Atlantic sea surface temperature (SST) anomalies. Such relationships are reproduced in model simulations with the quasi-equilibrium tropical circulation model (QTCM), which includes a simple land model. A suite of model ensemble experiments is analysed using observed SST over the tropical oceans, the tropical Atlantic and the tropical southern Atlantic (30S-0), respectively (with climatological SST in the remainder of the oceans). Warm tropical south Atlantic SST anomalies yield positive precipitation anomalies over the Nordeste and the southern edge of the Atlantic marine intertropical convergence zone (ITCZ). Mechanisms associated with moisture variations are responsible for the land precipitation changes. Increases in moisture over the Atlantic cause positive anomalies in moisture advection, spreading increased moisture downwind. Where the basic state is far from the convective stability threshold, moisture changes have little effect, but the margins of the climatological convection zone are affected. The increased moisture supply due to advection is enhanced by increases in low-level convergence required by moist static energy balances. The moisture convergence term is several times larger, but experiments altering the moisture advection confirm that the feedback is initiated by wind acting on moisture gradient. This mechanism has several features in common with the recently published "upped-ante" mechanism for El Nino impacts on this region. In that case, the moisture gradient is initiated by warm free tropospheric temperature anomalies increasing the typical value of low-level moisture required to sustain convection in the convection zones. Both mechanisms suggest the usefulness of coordinating ocean and land in situ observations of boundary layer moisture.

Geomagnetic Paleointensity Variations as a Cheap, High-Resolution Geochronometer for Recent Mid-Ocean Ridge Processes

Science.gov (United States)

DYMENT, J.; HEMOND, C.

2001-12-01

The sequence of geomagnetic field reversals is widely used to date events younger than 160 Ma, with a resolution of a million years. In oceanic domains, Vine and Matthews (1963) magnetic anomalies have been successfully used for more than 35 years. The major limitation of this chronometer is its low temporal resolution, especially for the recent times: the youngest polarity reversal, between Brunhes normal and Matuyama reversed periods, is dated ~800 ka. Studies of pelagic sedimentary cores have shown the existence of consistent variations of the geomagnetic field intensity within this period. If accurately dated, these variations may refine the magnetic geochronometer to a much higher resolution of 10-100 ka. Recent studies have demonstrated that the "tiny wiggles" of lower amplitude and shorter wavelength superimposed to the Vine and Matthews anomalies are of geomagnetic origin and correspond to the paleointensity variations identified on sediment cores. Using a large set of magnetic data acquired in 1996 on the Mid-Atlantic Ridge at 21° N (surface and submersible magnetic anomalies, natural remanent magnetization and absolute paleointensities measured on samples), we have shown that the oceanic crust confidently records the geomagnetic intensity variations. It was unfortunately impossible to date the samples, made of basalt too depleted in K2O and in trace elements required by the various methods of radiochronology. In 2000 we have collected a similar data set at the Central Indian Ridge axis at 19° S (surface, deep-tow, and submersible magnetic anomalies, natural remanent magnetization and absolute paleointensities measured on samples). This area offers the advantages of 1) a faster spreading rate, and therefore a higher temporal resolution of the geomagnetic signal, and 2) the presence of moderately enriched basalt as a consequence of the interaction of the ridge with the nearby Reunion hotspot, making possible radiochronologic dating. Our first evaluation

Palaeomagnetic constraints on the evolution of the Atlantis Massif oceanic core complex (Mid-Atlantic Ridge, 30°N)

Science.gov (United States)

Morris, A.; Pressling, N.; Gee, J. S.

2012-04-01

Oceanic core complexes expose lower crustal and upper mantle rocks on the seafloor by tectonic unroofing in the footwalls of large-slip detachment faults. They represent a fundamental component of the seafloor spreading system at slow and ultraslow axes. One of the most extensively studied oceanic core complexes is Atlantis Massif, located at 30°N at the intersection of the Atlantis Transform Fault and the Mid Atlantic Ridge (MAR). The central dome of the massif exposes the corrugated detachment fault surface and was drilled during IODP Expedition 304/305 (Hole U1309D). This sampled a 1.4 km faulted and complexly layered footwall section dominated by gabbroic lithologies with minor ultramafic rocks. Palaeomagnetic analyses demonstrate that the gabbroic sequences at Atlantis Massif carry highly stable remanent magnetizations that provide valuable information on the evolution of the section. Thermal demagnetization experiments recover high unblocking temperature components of reversed polarity (R1) throughout the gabbroic sequences. Correlation of structures observed on oriented borehole (FMS) images and those recorded on unoriented core pieces allows reorientation of R1 remanences. The mean remanence direction in true geographic coordinates constrains the tectonic rotation experienced by the Atlantis Massif footwall, indicating a 46°±6° counterclockwise around a MAR-parallel horizontal axis trending 011°±6°. The detachment fault therefore initiated at a steep dip of >50° and then rotated flexurally to its present day low angle geometry (consistent with a 'rolling-hinge' model for detachment evolution). In a number of intervals, the gabbros exhibit a complex remanence structure with the presence of additional intermediate temperature normal (N1) and lower temperature reversed (R2) polarity components, suggesting an extended period of remanence acquisition during different polarity intervals. Sharp break-points between different polarity components suggest

Magnetic anomalies across the southern Central Indian Ridge: evidence for a new transform fault

Digital Repository Service at National Institute of Oceanography (India)

Chaubey, A.K.; Krishna, K.S.; SubbaRaju, L.V.; Rao, D.G.

, Vol. 37. No. 4. pp. MT-~a56, 1990. 0198-.0149/90 $3.(gl + 0.00 Pnnled in Great Britain. (~ 1990 Pergartma Ptes6 pie Magnetic anomalies across the southern Central Indian Ridge: evidence for a new transform fault A. K. CHAUBEY,* K. S. KRISHNA,* L. V... to the ridge are identified as sea-floor spreading lineations 2.2A,3.3A and 4. A half spreading rate of 2.2 cm y- t is estimated for the last I0 Ma. The ridge jump between the anomalies 2-2A (approx. 2.5 Ma) and a new left lateral transform fault offsetting...

Copepod distribution and production in a Mid-Atlantic Ridge archipelago

Directory of Open Access Journals (Sweden)

PEDRO A.M.C. MELO

2014-12-01

Full Text Available The Saint Peter and Saint Paul Archipelago (SPSPA are located close to the Equator in the Atlantic Ocean. The aim of this study was to assess the spatial variations in the copepod community abundance, and the biomass and production patterns of the three most abundant calanoid species in the SPSPA. Plankton samples were collected with a 300 µm mesh size net along four transects (north, east, south and west of the SPSPA, with four stations plotted in each transect. All transects exhibited a tendency toward a decrease in copepod density with increasing distance from the SPSPA, statistically proved in the North. Density varied from 3.33 to 182.18 ind.m−3, and differences were also found between the first perimeter (first circular distance band and the others. The total biomass varied from 15.25 to 524.50 10−3 mg C m−3 and production from 1.19 to 22.04 10−3 mg C m−3d−1. The biomass and production of Undinula vulgaris (Dana, 1849, Acrocalanus longicornis Giesbrecht, 1888 and Calocalanus pavo (Dana, 1849 showed differences between some transects. A trend of declining biodiversity and production with increasing distance from archipelago was observed, suggesting that even small features like the SPSPA can affect the copepod community in tropical oligotrophic oceanic areas.

Hydrothermal and Chemosynthetic Ecosystems in the Southern Ocean: Current Knowledge on their Biology Paper 217790

Science.gov (United States)

Linse, K.; Rogers, A. D.; Bohrmann, G.; Copley, J.; Tyler, P. A.

2017-12-01

The existence of hydrothermal and other chemosynthetic ecosystems is not surprising in the Antarctic, with its active volcanoes, mid-ocean ridges and back-arc basins, and abundance of marine mammals. In the last two decades a variety of active chemosynthetic ecosystems have been discovered in the Southern Ocean, including low- and high-temperature hydrothermal vents, methane seeps, and whalefalls. Here a summary of the data from the known chemosynthetic communites will be presented, comparing the faunas of vent sites in the Bransfield Strait with those of the East Scotia Ridge (ESR) and the South Sandwich Arc, assessing the fauna at the South Georgia methane seep sites, and discussing the fauna on Antarctic whale falls. As the faunal assemblages of the ESR vents are the most studied in detail to date, this talk therefore focusses on the diversity and composition of the ESR macrofaunal assemblages, their foodweb structure and microdistributions in relation to fluid chemistry and microbiology, and their phylogenetic and biogeographic relationships. The Southern Ocean drives the global ocean conveyor belt, and is suggested to be the centre of origin for global deep-sea fauna, as well as a region of high deep-sea species diversity. In the context of chemosynthetic environments, it may provide a gateway connecting the global vent and seep systems. The mostly endemic species of Southern Ocean vent macrofauna show links to either one or more oceans (Atlantic, Indian, and Pacific), with some evidence for circum-Antarctic connection. The ESR species Gigantopelta chessoia, Kiwa tyleri and Vulcanolepas scotiaensis have their closest known relatives at the Longqi Vent Field on the Southwest Indian Ridge (SWIR), and one species of polynoid polychaete is known from ESR and SWIR vents. Meanwhile, Lepetdrilus sp. and a vesiocomyid clam are linked with species in the Atlantic vent fields. The stichasterid Paulasterias tyleri, the polychaete Rarricirrus jennae and the anthozoan

AMPLITUDES OF DISJUNCTIVE DISLOCATIONS IN THE KNIPOVICH RIDGE FLANKS (NORTHERN ATLANTIC AS AN INDICATOR OF MODERN REGIONAL GEODYNAMICS

Directory of Open Access Journals (Sweden)

S. Yu. Sokolov

2017-01-01

Full Text Available This article presents the first map showing the vertical amplitudes of modern disjunctive dislocations inNorthern Atlantic, based on the estimated phase shifts of reflected waves recorded by high-frequency seismic acoustic surveys. The amplitude distribution pattern is mosaic with alternating areas of compression and extension in the flanks of the Knipovich rift system. The modern structure of the Knipovich Ridge, including two strike-slip faults, represents a local rift in the pull-apart setting. The asymmetry of stresses and the presence of compression in the ridge flanks is evidenced by the distribution of the focal mechanisms of strong earthquakes related to reverse faults. In the southeastern Knipovich Ridge, tectonic activity is marked by the asymmetric pattern of the epicenters of small earthquakes.

The Imaging and Evolution of Seismic Layer 2A Thickness from a 0-70 Ma Oceanic Crustal Transect in the South Atlantic

Science.gov (United States)

Estep, J. D.; Reece, R.; Kardell, D. A.; Christeson, G. L.; Carlson, R. L.

2017-12-01

Seismic layer 2A, the uppermost igneous portion of oceanic crust, is commonly used to refer to the seismic velocities of upper crust that are bounded below by a steep vertical velocity gradient. Layer 2A velocities are known to increase with crustal age, from 2.5 km/s in crust 15 Ma. Thickness of layer 2A has been shown to increase by a factor of 2 within 1 Ma at fast spreading ridges and then remain relatively constant, while layer 2A maintains a fairly consistent thickness, irrespective of age, at slow-intermediate spreading ridges. Layer 2A thickness and velocity evolution studies to date have been largely focused on young oceanic crust very proximal to a spreading center with little investigation of changes (or lack thereof) that occur at crustal ages >10 Ma. We utilize a multichannel seismic dataset collected at 30° S in the western South Atlantic that continuously images 0 - 70 Ma oceanic crust along a single flowline generated at the slow-intermediate spreading Mid-Atlantic Ridge. We follow the methods of previous studies by processing the data to image the layer 2A event, which is then used for calculating thickness. 1D travel time forward modeling at regularly spaced age intervals across the transect provides for the conversion of time to depth thickness, and for determining the evolution of velocities with age. Our results show layer 2A in 20 Ma crust is roughly double the thickness of that in crust 0-5 Ma (830 vs. 440 m), but thickness does not appear to change beyond 20 Ma. The layer 2A event is readily observable in crust 0-50 Ma, is nearly completely absent in crust 50-65 Ma, and then reappears with anomalously high amplitude and lateral continuity in crust 65-70 Ma. Our results suggest that layer 2A thickens with age at the slow-intermediate spreading southern Mid-Atlantic Ridge, and that layer 2A either continues to evolve at the older crustal ages, well beyond the expected 10-15 Ma "mature age", or that external factors have altered the crust at

Energy landscapes shape microbial communities in hydrothermal systems on the Arctic Mid-Ocean Ridge

OpenAIRE

Dahle, H?kon; ?kland, Ingeborg; Thorseth, Ingunn H; Pederesen, Rolf B; Steen, Ida H

2015-01-01

Methods developed in geochemical modelling combined with recent advances in molecular microbial ecology provide new opportunities to explore how microbial communities are shaped by their chemical surroundings. Here, we present a framework for analyses of how chemical energy availability shape chemotrophic microbial communities in hydrothermal systems through an investigation of two geochemically different basalt-hosted hydrothermal systems on the Arctic Mid-Ocean Ridge: the Soria Moria Vent f...

Preface for Discussion on Mid-Ocean Ridges: dynamics of processes associated with creation of new ocean crust

Science.gov (United States)

Cann, J. R.; Elderfield, H.; Laughton, A.

Preface for Discussion on Mid-Ocean Ridges: dynamics of processes associated with creation of new ocean crust. A Discussion held at the Royal Society on 6th and 7th March 1996. Organized and edited by J. R. Cann, H. Elderfield and A. Laughton.

Potassium-argon radiometric dates of the mid-atlantic ocean floor

International Nuclear Information System (INIS)

Agyei, E.K.

1989-01-01

The basalt and six trachyte rock samples from the King's Trough in the mid-Atlantic ocean floor have been dated by the conventional potassium-argon method. The basalts give two different ages, 155+/-6 Ma (late Jurassic) and 53+/-6 Ma (lower Eocene), while the trachytes give a range of ages from 31.6+/-0.6 Ma to 35.2=0.2 Ma and an average of 33.0+/=0.4 Ma (lower oligocene). The Lower Eocene age of the in-situ basalt matches the age of the original volcanic activity of the region while the lower Oligocene age is associated with the subsequent faulting event. The late Jurassic age of the erratic basalt is interesting because of the scarcity of extrusive igneous rocks of that age along the margins of the North Atlantic and, therefore,needs to be investigated further. (author). 4 refs. 2 tabs

Ca isotope fractionation and Sr/Ca partitioning associated with anhydrite formation at mid-ocean ridge hydrothermal systems: An experimental approach

Science.gov (United States)

Syverson, D. D.; Scheuermann, P.; Pester, N. J.; Higgins, J. A.; Seyfried, W. E., Jr.

2016-12-01

throughout Earth's history. 1 Tivey, M. K. Generation of Seafloor Hydrothermal Deposits. Oceanography 20, 50-66 (2007).2 Amini, M. et al. Calcium isotope (δ44/40Ca) fractionation along hydrothermal pathways, Logatchev field (Mid-Atlantic Ridge, 14°45'N). Geochimica et Cosmochimica Acta 72, 4107-4122 (2008).

Recent massive sulfide deposits of the Semenov ore district, Mid-Atlantic Ridge, 13°31' N: Associated rocks of the oceanic core complex and their hydrothermal alteration

Science.gov (United States)

Pertsev, A. N.; Bortnikov, N. S.; Vlasov, E. A.; Beltenev, V. E.; Dobretsova, I. G.; Ageeva, O. A.

2012-09-01

The oceanic core complexes and large-offset detachment faults characteristic of the slow-spreading Mid-Atlantic Ridge are crucial for the structural control of large hydrothermal systems, including those forming sub-seafloor polymetallic sulfide mineralization. The structural-geological, petrographic, and mineralogical data are considered for the oceanic core complex enclosing the Semenov-1, -2, -3, -4, and -5 inactive hydrothermal sulfide fields recently discovered on the Mid-Oceanic Ridge at 13°31' N. The oceanic core complex is composed of serpentinized and talc-replaced peridotites and sporadic gabbroic rocks, however, all hydrothermal fields reveal compositional indications of basaltic substrate. The volcanic structures superposed on the oceanic core complex are marked by outcrops of pillow lavas with fresh quenched glass. Dolerites regarded as volcanic conduits seem to represent separate dike swarms. The superposed volcanic structures develop largely along the near-latitudinal high-angle tectonic zone controlling the Semenov-1, -2, -5, and -3 hydrothermal sulfide fields. The manifestations of hydrothermal metasomatic alteration are diverse. The widespread talcose rocks with pyrrhotite-pyrite mineralization after serpentinite, as well as finding of talc-chlorite metabasalt are interpreted as products of hydrothermal activity in the permeable zone of detachment fault. Chloritization and brecciation of basalts with superposed quartz or opal, barite, and pyrite or chalcopyrite mineralization directly related to the sub-seafloor sulfide deposition. The native copper mineralization in almost unaltered basalts at the Semenov-4 field is suggested to precipitate from ore-forming fluids before they reach the level of sub-seafloor sulfide deposition. Amphibolites with plagiogranite veinlets are interpreted as tectonic fragments of the highest-temperature portions of hydrothermal systems, where partial melting of basic rocks in the presence of aqueous fluid with

European temperature responses to blocking and ridge regional patterns

Science.gov (United States)

Sousa, Pedro M.; Trigo, Ricardo M.; Barriopedro, David; Soares, Pedro M. M.; Santos, João A.

2018-01-01

Blocking occurrence and its impacts on European temperature have been studied in the last decade. However, most previous studies on blocking impacts have focused on winter only, disregarding its fingerprint in summer and differences with other synoptic patterns that also trigger temperature extremes. In this work, we provide a clear distinction between high-latitude blocking and sub-tropical ridges occurring in three sectors of the Euro-Atlantic region, describing their climatology and consequent impacts on European temperature during both winter and summer. Winter blocks (ridges) are generally associated to colder (warmer) than average conditions over large regions of Europe, in some areas with anomalies larger than 5 °C, particularly for the patterns occurring in the Atlantic and Central European sectors. During summer, there is a more regional response characterized by above average temperature for both blocking and ridge patterns, especially those occurring in continental areas, although negative temperature anomalies persist in southernmost areas during blocking. An objective analysis of the different forcing mechanisms associated to each considered weather regime has been performed, quantifying the importance of the following processes in causing the temperature anomalies: horizontal advection, vertical advection and diabatic heating. While during winter advection processes tend to be more relevant to explain temperature responses, in summer radiative heating under enhanced insolation plays a crucial role for both blocking and ridges. Finally, the changes in the distributions of seasonal temperature and in the frequencies of extreme temperature indices were also examined for specific areas of Europe. Winter blocking and ridge patterns are key drivers in the occurrence of regional cold and warm extreme temperatures, respectively. In summer, they are associated with substantial changes in the frequency of extremely warm days, but with different signatures in

Fast reconnaissance of carbonate dissolution based on the size distribution of calcareous ooze on Walvis Ridge, SE Atlantic Ocean.

NARCIS (Netherlands)

Stuut, J.-B. W.; Prins, M.A.; Jansen, J.H.F.

2002-01-01

We present a new index of carbonate fragmentation based on the size distribution of bulk sediments in core MD962094 from Walvis Ridge (SE Atlantic Ocean). The carbonate fragmentation index is constructed by taking a ratio of the two coarsest fractions in the grain size distributions of the bulk

Bimodal volcanism in northeast Puerto Rico and the Virgin Islands (Greater Antilles Island Arc): Genetic links with Cretaceous subduction of the mid-Atlantic ridge Caribbean spur

Science.gov (United States)

Jolly, Wayne T.; Lidiak, Edward G.; Dickin, Alan P.

2008-07-01

Bimodal extrusive volcanic rocks in the northeast Greater Antilles Arc consist of two interlayered suites, including (1) a predominantly basaltic suite, dominated by island arc basalts with small proportions of andesite, and (2) a silicic suite, similar in composition to small volume intrusive veins of oceanic plagiogranite commonly recognized in oceanic crustal sequences. The basaltic suite is geochemically characterized by variable enrichment in the more incompatible elements and negative chondrite-normalized HFSE anomalies. Trace element melting and mixing models indicate the magnitude of the subducted sediment component in Antilles arc basalts is highly variable and decreases dramatically from east to west along the arc. In the Virgin Islands, the sediment component ranges between 4% during the Cenomanian-Campanian interval. The silicic suite, consisting predominantly of rhyolites, is characterized by depleted Al 2O 3 (average Virgin Islands on the east, rhyolites comprise up to 80% of Lower Albian strata (112 to 105 Ma), and about 20% in post-Albian strata (105 to 100 Ma). Farther west, in Puerto Rico, more limited proportions (Atlantic Ridge, which was located approximately midway between North and South America until Campanian times. Within this hypothetical setting the centrally positioned Virgin Islands terrain remained approximately fixed above the subducting ridge as the Antilles arc platform swept northeastward into the slot between the Americas. Accordingly, heat flow in the Virgin Islands was elevated throughout the Cretaceous, giving rise to widespread crustal melting, whereas the subducted sediment flux was limited. Conversely, toward the west in central Puerto Rico, which was consistently more remote from the subducting ridge, heat flow was relatively low and produced limited crustal melting, while the sediment flux was comparatively elevated.

Migrating Toward Fully 4-D Geodynamical Models of Asthenospheric Circulation and Melt Production at Mid-Ocean Ridges

Science.gov (United States)

van Dam, L.; Kincaid, C. R.; Pockalny, R. A.; Sylvia, R. T.; Hall, P. S.

2017-12-01

Lateral migration of mid-ocean ridge spreading centers is a well-documented phenomenon leading to asymmetric melt production and the surficial expressions thereof. This form of plate motion has been difficult to incorporate into both numerical and analogue geodynamical models, and consequently, current estimates of time-dependent flow, material transport, and melting in the mantle beneath ridges are lacking. To address this, we have designed and built an innovative research apparatus that allows for precise and repeatable simulations of mid-ocean ridge spreading and migration. Three pairs of counter-rotating belts with adjustable lateral orientations are scaled to simulate spreading at, and flow beneath, three 600km wide ridge segments with up to 300km transform offsets. This apparatus is attached to a drive system that allows us to test a full range of axis-parallel to axis-normal migration directions, and is suspended above a reservoir of viscous glucose syrup, a scaled analogue for the upper mantle, and neutrally buoyant tracers. We image plate-driven flow in the syrup with high-resolution digital cameras and use particle image velocimetry methods to obtain information about transport pathlines and flow-induced anisotropy. Suites of experiments are run with and without ridge migration to determine the overall significance of migration on spatial and temporal characteristics of shallow mantle flow. Our experiments cover an expansive parameter space by including various spreading rates, migration speeds and directions, degrees of spreading asymmetry, transform-offset lengths, and upper mantle viscosity conditions. Preliminary results highlight the importance of modeling migratory plate forces. Mantle material exhibits a significant degree of lateral transport, particularly between ridge segments and towards the melt triangle. Magma supply to the melting region is highly complex; parcels of material do not necessarily move along fixed streamlines, rather, they can

The NAO Influence on the Early to Mid-Holocene North Atlantic Coastal Upwelling

Science.gov (United States)

Hernandez, A.; Cachão, M.; Sousa, P.; Trigo, R. M.; Freitas, M. C.

2017-12-01

Coastal upwelling regions yield some of the oceanic most productive ecosystems, being crucial for the worldwide social and economic development. Most upwelling systems, emerging cold nutrient-rich deep waters, are located in the eastern boundaries of the Atlantic and Pacific basins, and are driven by meridional wind fields parallel to the coastal shore. These winds are associated with the subsiding branch of the large-scale Anticyclonic high pressure systems that dominate the subtropical ocean basins, and therefore can be displaced or intensified within the context of past and future climate changes. However, the role of the current global warming influencing the coastal upwelling is, as yet, unclear. Therefore it is essential to derive a long-term perspective, beyond the era of instrumental measurements, to detect similar warm periods in the past that have triggered changes in the upwelling patterns. In this work, the upwelling dynamics in the Iberian North Atlantic margin during the early and mid-Holocene is reconstructed, using calcareous nannofossils from a decadally resolved estuarine sediment core located in southwestern Portugal. Results suggest that the coastal dynamics reflects changes in winds direction likely related to shifts in the NAO-like conditions. Furthermore, the reconstructed centennial-scale variations in the upwelling are synchronous with changes in solar irradiance, a major external forcing factor of the climate system that is known to exert influence in atmospheric circulation patterns. In addition, these proxy-based data interpretations are in agreement with wind field and solar irradiance simulation modelling for the mid-Holocene. Therefore, the conclusion that the solar activity via the NAO modulation controlled the North Atlantic upwelling of western Iberia during the early and mid-Holocene at decadal to centennial timescales can be derived. The financial support for attending this meeting was possible through FCT project UID/GEO/50019

Preliminary Analysis of the Knipovich Ridge Segmentation - Influence of Focused Magmatism and Ridge Obliquity on an Ultraslow Spreading System

Science.gov (United States)

Okino, K.; Curewitz, D.; Asada, M.; Tamaki, K.

2002-12-01

Bathymetry, gravity and deep-tow sonar image data are used to define the segmentation of a 400 km long portion of the ultraslow-spreading Knipovich Ridge in the Norwegian-Greenland Sea, Northeast Atlantic Ocean. Discrete volcanic centers marked by large volcanic constructions and accompanying short wavelength mantle Bouguer anomaly (MBA) lows generally resemble those of the Gakkel Ridge and the easternmost Southwest Indian Ridge (SWIR). These magmatically robust segment centers are regularly spaced about 85-100 km apart along the ridge, and are characterized by accumulated hummocky terrain, high relief, off-axis seamount chains and significant MBA lows. We suggest that these eruptive centers correspond to areas of enhanced magma flux, and that their spacing reflects the geometry of underlying mantle upwelling cells. The large-scale thermal structure of the mantle primarily controls discrete and focused magmatism, and the relatively wide spacing of these segments may reflect cool mantle beneath the ridge. Segment centers along the southern Knipovich Ridge are characterized by lower relief and smaller MBA anomalies than along the northern section of the ridge. This suggests that ridge obliquity is a secondary control on ridge construction on the Knipovich Ridge, as the obliquity changes from 35° to 49° from north to south, respectively, while spreading rate and axial depth remain approximately constant. The increased obliquity may contribute to decreased effective spreading rates, lower upwelling magma velocity and melt formation, and limited horizontal dike propagation near the surface. We also identify small, magmatically weaker segments with low relief, little or no MBA anomaly, and no off axis expression. We suggest that these segments are either fed by lateral melt migration from adjacent magmatically stronger segments or represent smaller, discrete mantle upwelling centers with short-lived melt supply.

Preliminary analysis of the Knipovich Ridge segmentation: influence of focused magmatism and ridge obliquity on an ultraslow spreading system

Science.gov (United States)

Okino, Kyoko; Curewitz, Daniel; Asada, Miho; Tamaki, Kensaku; Vogt, Peter; Crane, Kathleen

2002-09-01

Bathymetry, gravity and deep-tow sonar image data are used to define the segmentation of a 400 km long portion of the ultraslow-spreading Knipovich Ridge in the Norwegian-Greenland Sea, Northeast Atlantic Ocean. Discrete volcanic centers marked by large volcanic constructions and accompanying short wavelength mantle Bouguer anomaly (MBA) lows generally resemble those of the Gakkel Ridge and the easternmost Southwest Indian Ridge. These magmatically robust segment centers are regularly spaced about 85-100 km apart along the ridge, and are characterized by accumulated hummocky terrain, high relief, off-axis seamount chains and significant MBA lows. We suggest that these eruptive centers correspond to areas of enhanced magma flux, and that their spacing reflects the geometry of underlying mantle upwelling cells. The large-scale thermal structure of the mantle primarily controls discrete and focused magmatism, and the relatively wide spacing of these segments may reflect cool mantle beneath the ridge. Segment centers along the southern Knipovich Ridge are characterized by lower relief and smaller MBA anomalies than along the northern section of the ridge. This suggests that ridge obliquity is a secondary control on ridge construction on the Knipovich Ridge, as the obliquity changes from 35° to 49° from north to south, respectively, while spreading rate and axial depth remain approximately constant. The increased obliquity may contribute to decreased effective spreading rates, lower upwelling magma velocity and melt formation, and limited horizontal dike propagation near the surface. We also identify small, magmatically weaker segments with low relief, little or no MBA anomaly, and no off-axis expression. We suggest that these segments are either fed by lateral melt migration from adjacent magmatically stronger segments or represent smaller, discrete mantle upwelling centers with short-lived melt supply.

Review of the Diversity, Ecology, and Conservation of Elasmobranchs in the Azores Region, Mid-North Atlantic

Directory of Open Access Journals (Sweden)

Diya Das

2017-11-01

Full Text Available A vulnerable species group, such as, the elasmobranchs, in a data-deficient context presents a complicated management problem. Evidence suggests that the Azores islands, a remote archipelago on the Mid-Atlantic Ridge, serve essential functions in the life-history of species across taxa. The diversity of marine resources within its EEZ are exploited by local to international fleets, and the full extent of fishing pressure can often be underestimated. Although sharks and rays appear to be of minor importance in the fishery, the possibilities of illegal, unreported, and unregulated fishing raises concerns about these threatened species. However, this group has failed to attract management attention, visible in the lack of regional studies focused on biodiversity, ecology, or threats of elasmobranchs. Our work attempts to review and update the information on elasmobranchs of the Azores and identify potential threats, mainly by the local fisheries. We aim to highlight knowledge gaps that require further research and conservation actions. We (1 update the annotated checklist of elasmobranch species, (2 compare species distribution across a biogeographically similar section of the North Atlantic, and (3 analyze the interaction of elasmobranch species with local fisheries. We confirm 61 chondrichthyan species for the Azores (39 sharks, 17 rays, and 5 chimaeras, adding 19 species to the previous annotated checklist of 1997. The Azores elasmobranch species assemblage most resembles Madeira, the neighboring Macaronesian archipelago. Biogeographic affinities between the chosen regions of the North Atlantic are reflected in the taxonomic structure of families. Although underestimated in the local fisheries, elasmobranchs constitute a regular but highly variable portion of total landings. Misreporting and misidentification is perhaps the greatest concern in the local fisheries records, further aggravated by few existing catch regulations for elasmobranchs

Waveform modeling of the seismic response of a mid-ocean ridge axial melt sill

Science.gov (United States)

Xu, Min; Stephen, R. A.; Canales, J. Pablo

2017-12-01

Seismic reflections from axial magma lens (AML) are commonly observed along many mid-ocean ridges, and are thought to arise from the negative impedance contrast between a solid, high-speed lid and the underlying low-speed, molten or partially molten (mush) sill. The polarity of the AML reflection ( P AML P) at vertical incidence and the amplitude vs offset (AVO) behavior of the AML reflections (e.g., P AML P and S-converted P AML S waves) are often used as a diagnostic tool for the nature of the low-speed sill. Time-domain finite difference calculations for two-dimensional laterally homogeneous models show some scenarios make the interpretation of melt content from partial-offset stacks of P- and S-waves difficult. Laterally heterogeneous model calculations indicate diffractions from the edges of the finite-width AML reducing the amplitude of the AML reflections. Rough seafloor and/or a rough AML surface can also greatly reduce the amplitude of peg-leg multiples because of scattering and destructive interference. Mid-crustal seismic reflection events are observed in the three-dimensional multi-channel seismic dataset acquired over the RIDGE-2000 Integrated Study Site at East Pacific Rise (EPR, cruise MGL0812). Modeling indicates that the mid-crustal seismic reflection reflections are unlikely to arise from peg-leg multiples of the AML reflections, P-to- S converted phases, or scattering due to rough topography, but could probably arise from deeper multiple magma sills. Our results support the identification of Marjanović et al. (Nat Geosci 7(11):825-829, 2014) that a multi-level complex of melt lenses is present beneath the axis of the EPR.

The Subduction of an Exhumed and Serpentinized Magma-Poor Basement Beneath the Northern Lesser Antilles Reveals the Early Tectonic Fabric at Slow-Spreading Mid-Oceanic Ridges

Science.gov (United States)

Marcaillou, B.; Klingelhoefer, F.; Laurencin, M.; Biari, Y.; Graindorge, D.; Jean-Frederic, L.; Laigle, M.; Lallemand, S.

2017-12-01

Multichannel and wide-angle seismic data as well as heat-flow measurements (ANTITHESIS cruise, 2016) reveal a 200x200km patch of magma-poor oceanic basement in the trench and beneath the outer fore-arc offshore of Antigua to Saint Martin in the Northern Lesser Antilles. These data highlight an oceanic basement with the following features: 1/ Absence of any reflection at typical Moho depth and layer2/layer3 limit depths. 2/ High Velocity Vp at the top (>5.5 km/s), low velocity gradient with depth (serpentinized at the slow-spreading mid-Atlantic Ridge 80 Myr ago, is currently subducting beneath the Northern Lesser Antilles. During the exhumation, early extension triggers penetrative shear zones sub-parallel to the ridge and to the transform fault. Eventually, this early extension generates sliding along the so-called detachment fault, while the other proto-detachment abort. Approaching the trench, the plate bending reactivates these weak zones in normal faults and fluid pathways promoting deep serpentinisation and localizing tectonic deformation at the plate interface. These subducting fluid-rich mechanically weak mantle rocks rise questions about their relation to the faster slab deepening, the lower seismic activity and the pervasive tectonic partitioning in this margin segment.

Sensitivity of seafloor bathymetry to climate-driven fluctuations in mid-ocean ridge magma supply.

Science.gov (United States)

Olive, J-A; Behn, M D; Ito, G; Buck, W R; Escartín, J; Howell, S

2015-10-16

Recent studies have proposed that the bathymetric fabric of the seafloor formed at mid-ocean ridges records rapid (23,000 to 100,000 years) fluctuations in ridge magma supply caused by sealevel changes that modulate melt production in the underlying mantle. Using quantitative models of faulting and magma emplacement, we demonstrate that, in fact, seafloor-shaping processes act as a low-pass filter on variations in magma supply, strongly damping fluctuations shorter than about 100,000 years. We show that the systematic decrease in dominant seafloor wavelengths with increasing spreading rate is best explained by a model of fault growth and abandonment under a steady magma input. This provides a robust framework for deciphering the footprint of mantle melting in the fabric of abyssal hills, the most common topographic feature on Earth. Copyright © 2015, American Association for the Advancement of Science.

Persistence of Allegheny woodrats Neotoma magister across the mid-Atlantic Appalachian Highlands landscape, USA

Science.gov (United States)

W. Mark Ford; Steven B. Castleberry; Michael T. Mengak; Jane L. Rodrigue; Daniel J. Feller; Kevin R. Russell

2006-01-01

We examined a suite of macro-habitat and landscape variables around active and inactive Allegheny woodrat Neotoma magister colony sites in the Appalachian Mountains of the mid-Atlantic Highlands of Maryland, Virginia, and West Virginia using an information-theoretic modeling approach. Logistic regression analyses suggested that Allegheny woodrat presence was related...

The Mid-Atlantic Twin Registry, revisited.

Science.gov (United States)

Lilley, Emily C H; Silberg, Judy L

2013-02-01

The Mid-Atlantic Twin Registry (MATR) is a population-based registry of more than 56,000 twins primarily born or living in Virginia, North Carolina, and South Carolina. The MATR employs several methods of ascertaining twins, and devotes considerable resources to tracking and maintaining communication with MATR participants. Researchers may utilize the MATR for administration of research services including study recruitment, collection of DNA, archival data set creation, as well as data collection through mailed, phone, or online surveys. In addition, the MATR houses the MATR Repository, with over 1,200 blood samples available for researchers interested in DNA genotyping. For over 35 years MATR twins have participated in research studies with investigators from diverse scientific disciplines and various institutions. These studies, which have resulted in numerous publications, have covered a range of topics, including the human microbiome, developmental psychopathology, depression, anxiety, substance use, epigenetics of aging, children of twins, pre-term birth, social attitudes, seizures, eating disorders, as well as sleep homeostasis. Researchers interested in utilizing twins are encouraged to contact the MATR to discuss potential research opportunities.

Seafloor Tectonic Fault Fabric and the Evolution of the Walvis Ridge-Rio Grande Rise Hot Spot Twins in the South Atlantic

Science.gov (United States)

Sager, W. W.; Engfer, D.; Thoram, S.; Koppers, A. A. P.; Class, C.

2015-12-01

Walvis Ridge (WR) and Rio Grande Rise (RGR) are Cretaceous-Cenozoic large igneous provinces (LIPs) formed by the Tristan-Gough hot spot interacting with the Mid-Atlantic Ridge (MAR). Although hot spot-ridge interaction has long been considered a primary factor controlling WR-RGR morphology, details are fuzzy owing to sparse geophysical data. We examined tectonic fabric revealed in satellite altimetry-derived gravity data to infer details about RGR-WR evolution. Plate tectonic reconstructions indicate that the main RGR plateau and large N-S plateau in the eastern WR erupted at the same point at ~90 Ma. Over the next ~8 Myr, these conjunct LIPs formed a "V" shape with a basin in between. Curved fracture zones within the basin imply the two LIPs formed around a microplate. The prominent rift in the middle of RGR formed nearly perpendicular to the RGR-WR intersection, suggesting an extensional microplate boundary. Hot spot eruptions continued at the MAR, emplacing the eastern WR and two main RGR plateaus until ~60 Ma. During this period, the N-S trending Eastern Rio Grande Rise (ERGR) was erupted along the MAR. Both the ERGR and WR formed bathymetric lineaments parallel to seafloor fault fabric and were likely connected. This resulted in WR seamounts with a "tadpole" shape, the head being small to medium seamounts on the WR track and the tails being low, spreading-fabric-parallel ridges extending up to ~150 km northward. Similar, small seamounts are found in the contemporaneous ERGR. Another critical observation is that the WR-RGR formed at a large crustal discontinuity (~700 km at anomaly C33, ~84 Ma) at one or more fracture zone offsets. By late Cenozoic time (anomaly C5, ~10 Ma), the offset was reduced by half while several new fracture zones formed at the junction between RGR and WR. This implies a connection between ridge reorganization and RGR-WR volcanism that may have resulted from the fracture zones becoming oblique to the spreading direction as Euler poles

Consistency of cruise data of the CARINA database in the Atlantic sector of the Southern Ocean

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M. Hoppema

2009-12-01

Full Text Available Initially a North Atlantic project, the CARINA carbon synthesis was extended to include the Southern Ocean. Carbon and relevant hydrographic and geochemical ancillary data from cruises all across the Arctic Mediterranean Seas, Atlantic and Southern Ocean were released to the public and merged into a new database as part of the CARINA synthesis effort. Of a total of 188 cruises, 37 cruises are part of the Southern Ocean, including 11 from the Atlantic sector. The variables from all Southern Ocean cruises, including dissolved inorganic carbon (TCO₂, total alkalinity, oxygen, nitrate, phosphate and silicate, were examined for cruise-to-cruise consistency in one collective effort. Seawater pH and chlorofluorocarbons (CFCs are also part of the database, but the pH quality control (QC is described in another Earth System Science Data publication, while the complexity of the Southern Ocean physics and biogeochemistry prevented a proper QC analysis of the CFCs. The area-specific procedures of quality control, including crossover analysis between stations and inversion analysis of all crossover data (i.e. secondary QC, are briefly described here for the Atlantic sector of the Southern Ocean. Data from an existing, quality controlled database (GLODAP were used as a reference for our computations – however, the reference data were included into the analysis without applying the recommended GLODAP adjustments so the corrections could be independently verified. The outcome of this effort is an internally consistent, high-quality carbon data set for all cruises, including the reference cruises. The suggested corrections by the inversion analysis were allowed to vary within a fixed envelope, thus accounting for natural variability. The percentage of cruises adjusted ranged from 31% (for nitrate to 54% (for phosphate depending on the variable.

Mid-depth South Atlantic Ocean circulation and chemical stratification during MIS-10 to 12: implications for atmospheric CO2

Directory of Open Access Journals (Sweden)

M. A. Maslin

2008-12-01

Full Text Available A detailed record of benthic foraminifera carbon isotopes from the intermediate-depth South East Atlantic margin shows little glacial-interglacial variability between MIS-12 to MIS-10, suggesting that Northern Atlantic deepwaters consistently penetrated to at least 30° S. Millennial-scale increases in either the mass or flux of northern-sourced deepwaters over the core site occurred alongside reductions in Lower North Atlantic Deep Water recorded in North Atlantic sediment cores and show that the lower and intermediate limb of the Atlantic deepwater convective cell oscillated in anti-phase during previous glacial periods. In addition, a 500 yr resolution record of the Cape Basin intermediate-deep δ13C gradient shows that a reduction in deep Southern Ocean ventilation at the end of MIS-11 was consistent with a modelled CO2 drawdown of ~21–30 ppm. Further increases in the Southern Ocean chemical divide during the transition into MIS-10 were completed before minimum CO2 levels were reached, suggesting that other mechanisms such as alkalinity changes were responsible for the remaining ~45 ppm drawdown.

Chemical provinces and dynamic melting of the NE Atlantic mantle

Science.gov (United States)

Tronnes, R. G.

2009-12-01

melting zone by the Iceland plume. However, a regional isotopic variation pattern indicates that this material originated from the nearby continents and became partially delaminated and embedded in the upper mantle during the recent continental rifting and separation of Greenland the Jan Mayen Ridge and of Greenland and Spitsbergen. The influence of SCLM is most clearly recognized north of central Iceland, in the Northern Rift Zone, along the Kolbeinsey, Mohns, Knipovich and Gakkel Ridges, and especially at Jan Mayen and along the westernmost Gakkel Ridge close to the Yermak Plateau (Goldstein et al. 2008, Nature). The SCLM-signal is weaker for Snæfellsnes, the Mid-Icelandic Belt and the Western and Eastern Rift Zones, and weakest for Vestmannaeyjar, the Southern Volcanic Flank Zone, the Reykjanes Peninsula and the Reykjanes Ridge. The regional geochemical patterns have interesting implications for the probable interaction between lateral plume flow, ridge-focussed asthenospheric flow and delaminated patches of SCLM.

Mid Ocean Ridge Processes at Very Low Melt Supply : Submersible Exploration of Smooth Ultramafic Seafloor at the Southwest Indian Ridge, 64 degree E

Science.gov (United States)

Cannat, M.; Agrinier, P.; Bickert, M.; Brunelli, D.; Hamelin, C.; Lecoeuvre, A.; Lie Onstad, S.; Maia, M.; Prampolini, M.; Rouméjon, S.; Vitale Brovarone, A.; Besançon, S.; Assaoui, E. M.

2017-12-01

Mid-ocean ridges are the Earth's most extensive and active volcanic chains. They are also, particularly at slow spreading rates, rift zones, where plate divergence is in part accommodated by faults. Large offset normal faults, also called detachments, are characteristic of slow-spreading ridges, where they account for the widespread emplacement of mantle-derived rocks at the seafloor. In most cases, these detachments occur together with ridge magmatism, with melt injection and faulting interacting to shape the newly formed oceanic lithosphere. Here, we seek to better understand these interactions and their effects on oceanic accretion by studying the end-member case of a ridge where magmatism is locally almost absent. The portion of the Southwest Indian ridge we are studying has an overal low melt supply, focused to discrete axial volcanoes, leaving almost zero melt to intervening sections of the axial valley. One of these nearly amagmatic section of the ridge, located at 64°E, has been the focus of several past cruises (sampling, mapping and seismic experiments). Here we report on the most recent cruise to the area (RV Pourquoi Pas? with ROV Victor; dec-jan 2017), during which we performed high resolution mapping, submersible exploration and sampling of the ultramafic seafloor and of sparse volcanic formations. Our findings are consistent with the flip-flop detachment hypothesis proposed for this area by Sauter et al. (Nature Geosciences, 2013; ultramafic seafloor forming in the footwall of successive detachment faults, each cutting into the footwall of the previous fault, with an opposite polarity). Our observations also document the extent and geometry of deformation in the footwall of a young axial detachment, the role of mass-wasting for the evolution of this detachment, and provide spectacular evidence for serpentinization-related hydrothermal circulation and for spatial links between faults and volcanic eruptions.

Interaction between Tropical Atlantic Variability and El Niño-Southern Oscillation.

Science.gov (United States)

Saravanan, R.; Chang, Ping

2000-07-01

The interaction between tropical Atlantic variability and El Niño-Southern Oscillation (ENSO) is investigated using three ensembles of atmospheric general circulation model integrations. The integrations are forced by specifying observed sea surface temperature (SST) variability over a forcing domain. The forcing domain is the global ocean for the first ensemble, limited to the tropical ocean for the second ensemble, and further limited to the tropical Atlantic region for the third ensemble. The ensemble integrations show that extratropical SST anomalies have little impact on tropical variability, but the effect of ENSO is pervasive in the Tropics. Consistent with previous studies, the most significant influence of ENSO is found during the boreal spring season and is associated with an anomalous Walker circulation. Two important aspects of ENSO's influence on tropical Atlantic variability are noted. First, the ENSO signal contributes significantly to the `dipole' correlation structure between tropical Atlantic SST and rainfall in the Nordeste Brazil region. In the absence of the ENSO signal, the correlations are dominated by SST variability in the southern tropical Atlantic, resulting in less of a dipole structure. Second, the remote influence of ENSO also contributes to positive correlations between SST anomalies and downward surface heat flux in the tropical Atlantic during the boreal spring season. However, even when ENSO forcing is absent, the model integrations provide evidence for a positive surface heat flux feedback in the deep Tropics, which is analyzed in a companion study by Chang et al. The analysis of model simulations shows that interannual atmospheric variability in the tropical Pacific-Atlantic system is dominated by the interaction between two distinct sources of tropical heating: (i) an equatorial heat source in the eastern Pacific associated with ENSO and (ii) an off-equatorial heat source associated with SST anomalies near the Caribbean

Beach- ridge internal architecture and use for Holocene sea-level reconstruction: A case study from the Miquelon-Langlade Isthmus (NW Atlantic)

Science.gov (United States)

Hein, C. J.; Billy, J.; Robin, N.; FitzGerald, D.; Certain, R.

2017-12-01

The internal architecture of beach-ridge systems can provide insight into processes ongoing during its period of formation, such as changing relative sea-level (RSL). The paraglacial beach-ridge plain at Miquelon-Langlade (south of Newfoundland - NW Atlantic) is an example of a well-preserved regressive barrier. Initiation of this plain correlates with a decrease in the rate of RSL rise (from +4.4 mm/yr to 1.3 mm/yr) at around 3000 years ago. The combination of stratigraphic (ground-penetrating radar and sediment cores), topographic (RTK-GPS) and chronologic (optically stimulated luminescence, OSL) data provide a detailed understanding of the constructional history of the plain. The internal architecture of individual beach ridges are characterized by sigmoidal configurations with seaward-dipping (2.3-4.7°) beds. Field mapping data reveal the processes associated with development of individual ridges in relation to sea level elevation. First, wave-built facies (sand-and-gravel) are deposited as beach berms, likely by fair-weather waves, with their elevations controlled by sea level and the swash height of constructive waves. This is followed by the accretion of aeolian sand deposits (foredunes) on the previous relict ridge, and then colonization by pioneer grasses. The well-defined contact between coarse-grained, wave-built facies and overlying aeolian deposits is used to demonstrate the dominant influence of RSL change in the development of the barrier system and, with chronology provided by OSL dating, produce a RSL curve for the 2500-year period of its formation. A net increase of 2.4 m in the surface elevation of wave-built facies is observed across the plain, corresponding to an overall increase in mean sea level through time. Three distinct periods can be distinguished: (1) an increase from 2.4 to 1 m below modern MSL between 2400 and 1500 years (rate: +1.3 mm/yr); (2) relatively stable or slowly rising RSL (<+0.2 mm/yr) from 1400 to 700 years; and (3) a

Biodiversity of polycyclic aromatic hydrocarbon-degrading bacteria from deep sea sediments of the Middle Atlantic Ridge

OpenAIRE

Cui, Zhisong; Lai, Qiliang; Dong, Chunming; Shao, Zongze

2008-01-01

The bacteria involved in the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in deep sea subsurface environments are largely unknown. In order to reveal their biodiversity, sediments from 2.2 m under the bottom surface at a water depth of 3542 m were sampled on the Middle Atlantic Ridge with a gravity column sampler. The sediments were promptly enriched with either crude oil or a mixture of PAHs (naphthalene, phenanthrene and pyrene) as the sole carbon source, and further enriched w...

Importance of Foliar Nitrogen Concentration to Predict Forest Productivity in the Mid-Atlantic Region

Science.gov (United States)

Yude Pan; John Hom; Jennifer Jenkins; Richard Birdsey

2004-01-01

To assess what difference it might make to include spatially defined estimates of foliar nitrogen in the regional application of a forest ecosystem model (PnET-II), we composed model predictions of wood production from extensive ground-based forest inventory analysis data across the Mid-Atlantic region. Spatial variation in foliar N concentration was assigned based on...

Observed and Modeled Pathways of the Iceland Scotland Overflow Water in the eastern North Atlantic

Science.gov (United States)

Zou, Sijia; Lozier, Susan; Zenk, Walter; Bower, Amy; Johns, William

2017-04-01

The Iceland Scotland Overflow Water (ISOW), one of the major components of the lower limb of the Atlantic Meridional Overturning Circulation (AMOC), is formed in the Nordic Seas and enters the eastern North Atlantic subpolar gyre via the Iceland-Scotland sill. After entraining the ambient waters, the relatively homogeneous ISOW spreads southward into the North Atlantic. An understanding of the distribution and variability of the spreading pathways of the ISOW is fundamental to our understanding of AMOC structure and variability. Three major ISOW pathways have been identified in the eastern North Atlantic by previous studies: 1) across the Reykjanes Ridge via deep gaps, 2) through the Charlie Gibbs Fracture Zone, and 3) southward along the eastern flank of the Mid Atlantic Ridge (MAR). However, most of these studies were conducted using an Eulerian frame with limited observations, especially for the third pathway along the eastern flank of the MAR. In this work, we give a comprehensive description of ISOW pathways in the Eulerian and Lagrangian frames, quantify the relative importance of each pathway and examine the temporal variability of these pathways. Our study distinguishes itself from past studies by using both Eulerian (current meter data) and Lagrangian (eddy-resolving RAFOS float data) observations in combination with modeling output (1/12° FLAME) to describe ISOW spreading pathways and their variability.

Response of the everglades ridge and slough landscape to climate variability and 20th-century water management

Science.gov (United States)

Bernhardt, C.E.; Willard, D.A.

2009-01-01

The ridge and slough landscape of the Florida Everglades consists of a mosaic of linear sawgrass ridges separated by deeper-water sloughs with tree islands interspersed throughout the landscape. We used pollen assemblages from transects of sediment cores spanning sawgrass ridges, sloughs, and ridge-slough transition zones to determine the timing of ridge and slough formation and to evaluate the response of components of the ridge and slough landscape to climate variability and 20th-century water management. These pollen data indicate that sawgrass ridges and sloughs have been vegetationally distinct from one another since initiation of the Everglades wetland in mid-Holocene time. Although the position and community composition of sloughs have remained relatively stable throughout their history, modern sawgrass ridges formed on sites that originally were occupied by marshes. Ridge formation and maturation were initiated during intervals of drier climate (the Medieval Warm Period and the Little Ice Age) when the mean position of the Intertropical Convergence Zone shifted southward. During these drier intervals, marsh taxa were more common in sloughs, but they quickly receded when precipitation increased. Comparison with regional climate records suggests that slough vegetation is strongly influenced by North Atlantic Oscillation variability, even under 20th-century water management practices. ?? 2009 by the Ecological Society of America.

Decadal-scale thermohaline variability in the Atlantic sector of the Southern Ocean

CSIR Research Space (South Africa)

Hutchinson, K

2016-05-01

Full Text Available . This AGEM has improved accuracy compared to traditional climatologies and other proxy methods. The AGEM for the Atlantic Southern Ocean offers an ideal technique to investigate the thermohaline variability over the past two decades in a key region for water...

The discovery of new deep-sea hydrothermal vent communities in the southern ocean and implications for biogeography.

Directory of Open Access Journals (Sweden)

Alex D Rogers

2012-01-01

Full Text Available Since the first discovery of deep-sea hydrothermal vents along the Galápagos Rift in 1977, numerous vent sites and endemic faunal assemblages have been found along mid-ocean ridges and back-arc basins at low to mid latitudes. These discoveries have suggested the existence of separate biogeographic provinces in the Atlantic and the North West Pacific, the existence of a province including the South West Pacific and Indian Ocean, and a separation of the North East Pacific, North East Pacific Rise, and South East Pacific Rise. The Southern Ocean is known to be a region of high deep-sea species diversity and centre of origin for the global deep-sea fauna. It has also been proposed as a gateway connecting hydrothermal vents in different oceans but is little explored because of extreme conditions. Since 2009 we have explored two segments of the East Scotia Ridge (ESR in the Southern Ocean using a remotely operated vehicle. In each segment we located deep-sea hydrothermal vents hosting high-temperature black smokers up to 382.8°C and diffuse venting. The chemosynthetic ecosystems hosted by these vents are dominated by a new yeti crab (Kiwa n. sp., stalked barnacles, limpets, peltospiroid gastropods, anemones, and a predatory sea star. Taxa abundant in vent ecosystems in other oceans, including polychaete worms (Siboglinidae, bathymodiolid mussels, and alvinocaridid shrimps, are absent from the ESR vents. These groups, except the Siboglinidae, possess planktotrophic larvae, rare in Antarctic marine invertebrates, suggesting that the environmental conditions of the Southern Ocean may act as a dispersal filter for vent taxa. Evidence from the distinctive fauna, the unique community structure, and multivariate analyses suggest that the Antarctic vent ecosystems represent a new vent biogeographic province. However, multivariate analyses of species present at the ESR and at other deep-sea hydrothermal vents globally indicate that vent biogeography is more

A Southern Ocean trigger for Northwest Pacific ventilation during the Holocene?

Science.gov (United States)

Rella, S. F.; Uchida, M.

2014-02-01

Holocene ocean circulation is poorly understood due to sparsity of dateable marine archives with submillennial-scale resolution. Here we present a record of mid-depth water radiocarbon contents in the Northwest (NW) Pacific Ocean over the last 12.000 years, which shows remarkable millennial-scale variations relative to changes in atmospheric radiocarbon inventory. Apparent decoupling of these variations from regional ventilation and mixing processes leads us to the suggestion that the mid-depth NW Pacific may have responded to changes in Southern Ocean overturning forced by latitudinal displacements of the southern westerly winds. By inference, a tendency of in-phase related North Atlantic and Southern Ocean overturning would argue against the development of a steady bipolar seesaw regime during the Holocene.

Biogeography and potential exchanges among the atlantic Equatorial belt cold-seep faunas.

Directory of Open Access Journals (Sweden)

Karine Olu

2010-08-01

Full Text Available Like hydrothermal vents along oceanic ridges, cold seeps are patchy and isolated ecosystems along continental margins, extending from bathyal to abyssal depths. The Atlantic Equatorial Belt (AEB, from the Gulf of Mexico to the Gulf of Guinea, was one focus of the Census of Marine Life ChEss (Chemosynthetic Ecosystems program to study biogeography of seep and vent fauna. We present a review and analysis of collections from five seep regions along the AEB: the Gulf of Mexico where extensive faunal sampling has been conducted from 400 to 3300 m, the Barbados accretionary prism, the Blake ridge diapir, and in the Eastern Atlantic from the Congo and Gabon margins and the recently explored Nigeria margin. Of the 72 taxa identified at the species level, a total of 9 species or species complexes are identified as amphi-Atlantic. Similarity analyses based on both Bray Curtis and Hellinger distances among 9 faunal collections, and principal component analysis based on presence/absence of megafauna species at these sites, suggest that within the AEB seep megafauna community structure is influenced primarily by depth rather than by geographic distance. Depth segregation is observed between 1000 and 2000 m, with the middle slope sites either grouped with those deeper than 2000 m or with the shallower sites. The highest level of community similarity was found between the seeps of the Florida escarpment and Congo margin. In the western Atlantic, the highest degree of similarity is observed between the shallowest sites of the Barbados prism and of the Louisiana slope. The high number of amphi-atlantic cold-seep species that do not cluster according to biogeographic regions, and the importance of depth in structuring AEB cold-seep communities are the major conclusions of this study. The hydrothermal vent sites along the Mid Atlantic Ridge (MAR did not appear as "stepping stones" for dispersal of the AEB seep fauna, however, the south MAR and off axis regions

Timber harvesting patterns for major states in the central, northern, and mid-Atlantic hardwood regions

Science.gov (United States)

William G. Luppold; Matthew S. Bumgardner

2018-01-01

Timber harvesting is a major disturbance agent influencing the composition and structure of eastern hardwood forests. To better understand timber harvesting practices, we examined roundwood harvesting patterns in 13 eastern states in the Central, Mid-Atlantic, and Northern regions that contained high proportional volumes of hardwood in their forest inventories. Nearly...

Microbial ecology of deep-water mid-Atlantic canyons

Science.gov (United States)

Kellogg, Christina A.

2011-01-01

The research described in this fact sheet will be conducted from 2012 to 2014 as part of the U.S. Geological Survey's DISCOVRE (DIversity, Systematics, and COnnectivity of Vulnerable Reef Ecosystems) Program. This integrated, multidisciplinary effort will be investigating a variety of topics related to unique and fragile deep-sea ecosystems from the microscopic level to the ecosystem level. One goal is to improve understanding, at the microbiological scale, of the benthic communities (including corals) that reside in and around mid-Atlantic canyon habitats and their associated environments. Specific objectives include identifying and characterizing the microbial associates of deep-sea corals, characterizing the microbial biofilms on hard substrates to better determine their role in engineering the ecosystem, and adding a microbial dimension to benthic community structure and function assessments by characterizing micro-eukaryotes, bacteria, and archaea in deep-sea sediments.

Geology and Geochemistry of Magmatic Rocks from the Southern Part of the Kyushu-Palau Ridge in the Philippine Sea

Science.gov (United States)

Lelikov, E. P.; Sedin, V. T.; Pugachev, A. A.

2018-03-01

The paper reports the results of a geochemical study of volcanogenic rocks from the southern part of the Kyushu-Palau Ridge. Volcanic structures, such as plateaulike rises, mountain massifs, and single volcanoes, are the major relief-forming elements of the southern part of the Kyushu-Palau Ridge. They are divided into three types according to the features of the relief and geological structure: shield, cone-shaped, and dome-shaped volcanoes. The ridge was formed on oceanic crust in the Late Mesozoic and underwent several stages of evolution with different significance and application of forces (tension and compression). Change in the geodynamic conditions during the geological evolution of the ridge mostly determined the composition of volcanic rocks of deep-mantle nature. Most of the ridge was formed by the Early Paleogene under geodynamic conditions close to the formation of oceanic islands (shield volcanoes) under tension. The island arc formed on the oceanic basement in the compression mode in the Late Eocene-Early Oligocene. Dome-shaped volcanic edifices composed of alkaline volcanic rocks were formed in the Late Oligocene-Early Miocene under tension. Based on the new geochemical data, detailed characteristics of volcanic rocks making up the shield, cone-shape, and dome-shape stratovolcanoes resulting in the features of these volcanic edifices are given for the first time. Continuous volcanism (with an age from the Cretaceous to the Late Miocene and composition from oceanic tholeiite to calc-alkaline volcanites of the island arc type) resulting in growth of the Earth's crust beneath the Kyushu-Palau Ridge was the major factor in the formation this ridge.

Evolution of spreading rate and H2 production by serpentinization at mid-ocean ridges from 200 Ma to Present

Science.gov (United States)

Andreani, M.; García del Real, P.; Daniel, I.; Wright, N.; Coltice, N.

2017-12-01

Mid-oceanic ridge (MOR) spreading rate spatially varies today from 20 to 200 mm/yr and geological records attest of important temporal variations, at least during the past 200 My. The spreading rate has a direct impact on the mechanisms accomodating extension (magmatic vs tectonic), hence on the nature of the rocks forming the oceanic lithosphere. The latter is composed of variable amount of magmatic and mantle rocks, that dominate at fast and (ultra-) slow spreading ridges, respectively. Serpentinization of mantle rocks contributes to global fluxes and notably to those of hydrogen and carbon by providing a pathways for dihydrogen (H2) production, carbone storage by mineralization, and carbon reduction to CH4 and possibly complex organic compounds. Quantification of the global chemical impact of serpentinization through geological time requires a coupling of geochemical parameters with plate-tectonic reconstructions. Here we quantify serpentinization extent and concurrent H2 production at MOR from the Jurassic (200 Ma) to present day (0 Ma). We coupled mean values of relevant petro-chemical parameters such as the proportion of mantle rocks, initial iron in olivine, iron redox state in serpentinites, % of serpentinization to high-resolution models of plate motion within the GPlates infrastructure to estimate the lengths in 1 Myr intervals for the global MOR plate boundary (spreading and transform components), and spreading ridges as a function of their rate. The model sensitivity to selected parameters has been tested. The results show that fragmentation of Pangea resulted in elevated H2 rates (>1012 to 1013 mol/yr) starting at 160 Ma compared to Late Mesozoic (<160 Ma) rates (<1011-1012 mol/yr). From 160 Ma to present, the coupled opening of the Atlantic and Indian oceans as well as the variation in spreading rates maintained H2 generation in the 1012 mol/yr level, but with significant excursions mainly related to the length of ultra-slow spreading segments. For

Appendix E of the Final Report of the Mid-Atlantic Marine Wildlife Surveys, Modeling, and Data

Energy Technology Data Exchange (ETDEWEB)

None

2013-07-01

The Wind Program hosted a two-day workshop on July 24-25, 2012 with scientists and regulators engaged in marine ecological survey, modeling, and database efforts pertaining to the waters of the Mid-Atlantic region. This is the fifth appendix to the report, the bibliography of references.

Assessing Phytoplankton Nutritional Status and Potential Impact of Wet Deposition in Seasonally Oligotrophic Waters of the Mid-Atlantic Bight

Science.gov (United States)

Sedwick, P. N.; Bernhardt, P. W.; Mulholland, M. R.; Najjar, R. G.; Blumen, L. M.; Sohst, B. M.; Sookhdeo, C.; Widner, B.

2018-04-01

To assess phytoplankton nutritional status in seasonally oligotrophic waters of the southern Mid-Atlantic Bight, and the potential for rain to stimulate primary production in this region during summer, shipboard bioassay experiments were performed using natural seawater and phytoplankton collected north and south of the Gulf Stream. Bioassay treatments comprised iron, nitrate, iron + nitrate, iron + nitrate + phosphate, and rainwater. Phytoplankton growth was inferred from changes in chlorophyll a, inorganic nitrogen, and carbon-13 uptake, relative to unamended control treatments. Results indicated the greatest growth stimulation by iron + nitrate + phosphate, intermediate growth stimulation by rainwater, modest growth stimulation by nitrate and iron + nitrate, and no growth stimulation by iron. Based on these data and analysis of seawater and atmospheric samples, nitrogen was the proximate limiting nutrient, with a secondary limitation imposed by phosphorus. Our results imply that summer rain events increase new production in these waters by contributing nitrogen and phosphorus, with the availability of the latter setting the upper limit on rain-stimulated new production.

Appendix C of the Final Report of the Mid-Atlantic Marine Wildlife Surveys, Modeling, and Data

Energy Technology Data Exchange (ETDEWEB)

None

2013-07-01

The Wind Program hosted a two-day workshop on July 24-25, 2012 with scientists and regulators engaged in marine ecological survey, modeling, and database efforts pertaining to the waters of the Mid-Atlantic region. This is the third appendix to the report, the compendium of pre-workshop answers.

76 FR 66273 - Snapper-Grouper Fishery Off the Southern Atlantic States and Coral and Coral Reefs Fishery in the...

Science.gov (United States)

2011-10-26

...-Grouper Fishery Off the Southern Atlantic States and Coral and Coral Reefs Fishery in the South Atlantic... the South Atlantic Region and the FMP for Coral, Coral Reefs, and Live/Hard Bottom Habitats of the... Aquariums to collect, with certain conditions, various species of reef fish and live rock in Federal waters...

Potential effects of climate change on freshwater ecosystems of the New England/Mid-Atlantic Region

Science.gov (United States)

Marianne V. Moore; Michael L. Pace; John R. Mather; [and others; [Editor’s note: Patricia A. Flebbe is the SRS co-author for this publication.

1997-01-01

Numerous freshwater ecosystems, dense concentrations of humans along the eastern seaboard, extensive forests, and a history of intensive land use distinguish the New England/Mid-Atlantic Region. Human population densities are forecast to increase in portions of the region at the same time that climate is expected to be changing. Consequently, the effects of humans and...

Modeling complex effects of multiple environmental stresses on carbon dynamics of Mid-Atlantic temperate forests

Science.gov (United States)

Yude Pan; Richard Birdsey; John Hom; Kevin McCullough

2007-01-01

We used our GIS variant of the PnET-CN model to investigate changes of forest carbon stocks and fluxes in Mid-Atlantic temperate forests over the last century (1900-2000). Forests in this region are affected by multiple environmental changes including climate, atmospheric CO2 concentration, N deposition and tropospheric ozone, and extensive land disturbances. Our...

CARINA TCO2 data in the Atlantic Ocean

Directory of Open Access Journals (Sweden)

R. Wanninkhof

2010-07-01

Full Text Available Water column data of carbon and carbon-relevant hydrographic and hydrochemical parameters from 188 cruises in the Arctic Mediterranean Seas, Atlantic and Southern Ocean have been retrieved and merged in a new data base: the CARINA (CARbon IN the Atlantic Project. These data have gone through rigorous quality control (QC procedures so as to improve the quality and consistency of the data as much as possible. Secondary quality control, which involved objective study of data in order to quantify systematic differences in the reported values, was performed for the pertinent parameters in the CARINA data base. Systematic biases in the data have been tentatively corrected in the data products. The products are three merged data files with measured, adjusted and interpolated data of all cruises for each of the three CARINA regions (Arctic Mediterranean Seas, Atlantic and Southern Ocean. Ninety-eight cruises were conducted in the "Atlantic" defined as the region south of the Greenland-Iceland-Scotland Ridge and north of about 30° S. Here we report the details of the secondary QC which was done on the total dissolved inorganic carbon (TCO2 data and the adjustments that were applied to yield the final data product in the Atlantic. Procedures of quality control – including crossover analysis between stations and inversion analysis of all crossover data – are briefly described. Adjustments were applied to TCO2 measurements for 17 of the cruises in the Atlantic Ocean region. With these adjustments, the CARINA data base is consistent both internally as well as with GLODAP data, an oceanographic data set based on the WOCE Hydrographic Program in the 1990s, and is now suitable for accurate assessments of, for example, regional oceanic carbon inventories, uptake rates and model validation.

Behavioural study of two hydrothermal crustacean decapods: Mirocaris fortunata and Segonzacia mesatlantica, from the Lucky Strike vent field (Mid-Atlantic Ridge)

Science.gov (United States)

Matabos, M.; Cuvelier, D.; Brouard, J.; Shillito, B.; Ravaux, J.; Zbinden, M.; Barthelemy, D.; Sarradin, P. M.; Sarrazin, J.

2015-11-01

Identifying the factors driving community dynamics in hydrothermal vent communities, and in particular biological interactions, is challenged by our ability to make direct observations and the difficulty to conduct experiments in those remote ecosystems. As a result, we have very limited knowledge on species' behaviour and interactions in these communities and how they in turn influence community dynamics. Interactions such as competition or predation significantly affect community structure in vent communities, and video time-series have successfully been used to gain insights in biological interactions and species behaviour, including responses to short-term changes in temperature or feeding strategies. In this study, we combined in situ and ex situ approaches to characterise the behaviour and interactions among two key species encountered along the Mid-Atlantic Ridge (MAR): the shrimp Mirocaris fortunata and the crab Segonzacia mesatlantica. In situ, species small-scale distribution, interactions and behaviour were studied using the TEMPO observatory module deployed on the seafloor at the base of the active Eiffel Tower edifice in the Lucky Strike vent field as part of the EMSO-Açores MoMAR observatory. TEMPO sampled 2 min of video four times a day from July 2011 to April 2012. One week of observations per month was used for 'long-term' variations, and a full video data set was analysed for January 2012. In addition, observations of crab and shrimp individuals maintained for the first time under controlled conditions in atmospheric pressure (classic tank) and pressurised (AbyssBox) aquaria allowed better characterisation and description of the different types of behaviour and interactions observed in nature. While the identified in situ spatial distribution pattern was stable over the nine months, both species displayed a significant preference for mussel bed and anhydrite substrata, and preferentially occupied the area located directly in the fluid flow axis

Commercial fishing gear modifications to reduce interactions between Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) and the southern flounder (Paralichthys lethostigma) fishery in North Carolina (USA).

Science.gov (United States)

Levesque, Juan C; Hager, Christian; Diaddorio, Eric; Dickey, R Jason

2016-01-01

Bycatch of protected species in commercial fishing operations is a primary concern to fishery managers because it threatens the conservation, protection, and recovery of fragile species, such as the Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus). One potential solution to reduce the risk associated with commercial fishing operations is to design commercial fishing gear that is more selective in terms of interactions between Atlantic sturgeon and commercial fisheries. Given this conservation and management need, the overarching goal was to reduce Atlantic sturgeon fishery interactions and maintain southern flounder (Paralichthys lethostigma) catch in North Carolina. The specific objectives of this study were to design and evaluate the effectiveness of a modified gillnet. Overall, the results proved that lowering the profile and amount of webbing had a beneficial impact at reducing Atlantic sturgeon incidental encounters and bycatch. The modified gillnet reduced bycatch and Atlantic sturgeon encounters by 39.6% and 60.9%, respectively. Our design entangled 51.6% fewer southern flounder, which corresponded to a 48.9% reduction in total weight; the modified gear entangled slightly larger southern flounder than the control gear. Our findings showed the number of Atlantic sturgeon encounters was positively associated with mean water depth, with more Atlantic sturgeon encountered in deeper (5.1-6.3 m) than shallower waters; 75% were encountered at depths between 4.6 and 6.1 m. Most southern flounder (n = 518, 39.7%) were taken at a water depth between 3.76 and 5.0 m. This observation suggests that southern flounder prefer slightly shallower waters than Atlantic sturgeon.

[Predominant strains of polycyclic aromatic hydrocarbon-degrading consortia from deep sea of the Middle Atlantic Ridge].

Science.gov (United States)

Cui, Zhisong; Shao, Zongze

2009-07-01

In order to identify the predominant strains of polycyclic aromatic hydrocarbon (PAH)-degrading consortia harboring in sea water and surface sediment collected from deep sea of the Middle Atlantic Ridge. We employed enrichment method and spread-plate method to isolate cultivable bacteria and PAHs degraders from deep sea samples. Phylogenetic analysis was conducted by 16S rRNA gene sequencing of the bacteria. Then we analyzed the dominant bacteria in the PAHs-degrading consortia by denaturing gradient gel electrophoresis (DGGE) combined with DNA sequencing. Altogether 16 cultivable bacteria were obtained, including one PAHs degrader Novosphingobium sp. 4D. Phylogenetic analysis showed that strains closely related to Alcanivorax dieselolei NO1A (5/16) and Tistrella mobilis TISTR 1108T (5/16) constituted two biggest groups among the cultivable bacteria. DGGE analysis showed that strain 4L (also 4M and 4N, Alcanivorax dieselolei NO1A, 99.21%), 4D (Novosphingobium pentaromativorans US6-1(T), 97.07%) and 4B (also 4E, 4H and 4K, Tistrella mobilis TISTR 1108T, > 99%) dominated the consortium MC2D. While in consortium MC3CO, the predominant strains were strain 5C (also 5H, Alcanivorax dieselolei NO1A, > 99%), uncultivable strain represented by band 5-8 (Novosphingobium aromaticivorans DSM 12444T, 99.41%), 5J (Tistrella mobilis TISTR 1108T, 99.52%) and 5F (also 5G, Thalassospira lucentensis DSM 14000T, degrading consortia in sea water and surface sediment of Middle Atlantic Ridge deep sea, with Novosphingobium spp. as their main PAHs degraders.

Distributions and habitat associations of deep-water corals in Norfolk and Baltimore Canyons, Mid-Atlantic Bight, USA

NARCIS (Netherlands)

Brooke, S.D.; Watts, M.W.; Heil, A.D.; Rhode, M.; Mienis, F.; Duineveld, G.C.A.; Davies, A.J.; Ross, S.W.

2017-01-01

A multi-disciplinary study of two major submarine canyons, Baltimore Canyon and Norfolk Canyon, off the US mid-Atlantic coast focused on the ecology and biology of canyon habitats, particularly those supporting deep-sea corals. Historical data on deep-sea corals from these canyons were sparse with

A serpentinite-hosted ecosystem in the Southern Mariana Forearc.

Science.gov (United States)

Ohara, Yasuhiko; Reagan, Mark K; Fujikura, Katsunori; Watanabe, Hiromi; Michibayashi, Katsuyoshi; Ishii, Teruaki; Stern, Robert J; Pujana, Ignacio; Martinez, Fernando; Girard, Guillaume; Ribeiro, Julia; Brounce, Maryjo; Komori, Naoaki; Kino, Masashi

2012-02-21

Several varieties of seafloor hydrothermal vents with widely varying fluid compositions and temperatures and vent communities occur in different tectonic settings. The discovery of the Lost City hydrothermal field in the Mid-Atlantic Ridge has stimulated interest in the role of serpentinization of peridotite in generating H(2)- and CH(4)-rich fluids and associated carbonate chimneys, as well as in the biological communities supported in highly reduced, alkaline environments. Abundant vesicomyid clam communities associated with a serpentinite-hosted hydrothermal vent system in the southern Mariana forearc were discovered during a DSV Shinkai 6500 dive in September 2010. We named this system the "Shinkai Seep Field (SSF)." The SSF appears to be a serpentinite-hosted ecosystem within a forearc (convergent margin) setting that is supported by fault-controlled fluid pathways connected to the decollement of the subducting slab. The discovery of the SSF supports the prediction that serpentinite-hosted vents may be widespread on the ocean floor. The discovery further indicates that these serpentinite-hosted low-temperature fluid vents can sustain high-biomass communities and has implications for the chemical budget of the oceans and the distribution of abyssal chemosynthetic life.

Gravimetric structure for the abyssal mantle massif of Saint Peter and Saint Paul peridotite ridge, Equatorial Atlantic Ocean, and its relation to active uplift

Directory of Open Access Journals (Sweden)

KENJI F. MOTOKI

2014-06-01

Full Text Available This paper presents gravimetric and morphologic analyses based on the satellite-derived data set of EGM2008 and TOPEX for the area of the oceanic mantle massif of the Saint Peter and Saint Paul peridotite ridge, Equatorial Atlantic Ocean. The free-air anomaly indicates that the present plate boundary is not situated along the longitudinal graben which cuts peridotite ridge, but about 20 km to the north of it. The high Bouguer anomaly of the peridotite ridge suggests that it is constituted mainly by unserpentinised ultramafic rocks. The absence of isostatic compensation and low-degree serpentinisation of the ultramafic rocks indicate that the peridotite ridge is sustained mainly by active tectonic uplift. The unparallel relation between the transform fault and the relative plate motion generates near north-south compression and the consequent tectonic uplift. In this sense, the peridotite massif is a pressure ridge due to the strike-slip displacement of the Saint Paul Transform Fault.

A watershed-based method for environmental vulnerability assessment with a case study of the Mid-Atlantic region

Energy Technology Data Exchange (ETDEWEB)

Tran, Liem T., E-mail: ltran1@utk.edu [Department of Geography, University of Tennessee, Knoxville, TN (United States); O& #x27; Neill, Robert V. [OTIE and Associates, Oak Ridge, TN (United States); Smith, Elizabeth R. [U.S. Environmental Protection Agency, Office of Research and Development, National Exposure Research Laboratory, Research Triangle Park, NC (United States)

2012-04-15

The paper presents a method for environmental vulnerability assessment with a case study of the Mid-Atlantic region. The method is based on the concept of 'self-/peer-appraisal' of a watershed in term of vulnerability. The self-/peer-appraisal process is facilitated by two separate linear optimization programs. The analysis provided insights on the environmental conditions, in general, and the relative vulnerability pattern, in particular, of the Mid-Atlantic region. The suggested method offers a simple but effective and objective way to perform a regional environmental vulnerability assessment. Consequently the method can be used in various steps in environmental assessment and planning. - Highlights: Black-Right-Pointing-Pointer We present a method for regional environmental vulnerability assessment. Black-Right-Pointing-Pointer It is based on the self-/peer-appraisal concept in term of vulnerability. Black-Right-Pointing-Pointer The analysis is facilitated by two separate linear optimization programs. Black-Right-Pointing-Pointer The method provides insights on the regional relative vulnerability pattern.

Cold-climate slope deposits and landscape modifications of the Mid-Atlantic Coastal Plain, Eastern USA

Science.gov (United States)

Newell, Wayne L.; Dejong, B.D.

2011-01-01

The effects of Pleistocene cold-climate geomorphology are distributed across the weathered and eroded Mid-Atlantic Coastal Plain uplands from the Wisconsinan terminal moraine south to Tidewater Virginia. Cold-climate deposits and landscape modifications are superimposed on antecedent landscapes of old, weathered Neogene upland gravels and Pleistocene marine terraces that had been built during warm periods and sea-level highstands. In New Jersey, sequences of surficial deposits define a long history of repeating climate change events. To the south across the Delmarva Peninsula and southern Maryland, most antecedent topography has been obscured by Late Pleistocene surficial deposits. These are spatially variable and are collectively described as a cold-climate alloformation. The cold-climate alloformation includes time-transgressive details of climate deterioration from at least marine isotope stage (MIS) 4 through the end of MIS 2. Some deposits and landforms within the alloformation may be as young as the Younger Dryas. Southwards along the trend of the Potomac River, these deposits and their climatic affinities become diffused. In Virginia, a continuum of erosion and surficial deposits appears to be the product of ‘normal’ temperate, climate-forced processes. The cold-climate alloformation and more temperate deposits in Virginia are being partly covered by Holocene alluvium and bay mud.

Tectonics of ridge-transform intersections at the Kane fracture zone

Science.gov (United States)

Karson, J. A.; Dick, H. J. B.

1983-03-01

The Kane Transform offsets spreading-center segments of the Mid-Atlantic Ridge by about 150 km at 24° N latitude. In terms of its first-order morphological, geological, and geophysical characteristics it appears to be typical of long-offset (>100 km), slow-slipping (2 cm yr-1) ridge-ridge transform faults. High-resolution geological observations were made from deep-towed ANGUS photographs and the manned submersible ALVIN at the ridge-transform intersections and indicate similar relationships in these two regions. These data indicate that over a distance of about 20 km as the spreading axes approach the fracture zone, the two flanks of each ridge axis behave in very different ways. Along the flanks that intersect the active transform zone the rift valley floor deepens and the surface expression of volcanism becomes increasingly narrow and eventually absent at the intersection where only a sediment-covered ‘nodal basin’ exists. The adjacent median valley walls have structural trends that are oblique to both the ridge and the transform and have as much as 4 km of relief. These are tectonically active regions that have only a thin (young volcanics passes laterally into median valley walls with a simple block-faulted character where only volcanic rocks have been found. Along strike toward the fracture zone, the youngest volcanics form linear constructional volcanic ridges that transect the entire width of the fracture zone valley. These volcanics are continuous with the older-looking, slightly faulted volcanic terrain that floors the non-transform fracture zone valleys. These observations document the asymmetric nature of seafloor spreading near ridge-transform intersections. An important implication is that the crust and lithosphere across different portions of the fracture zone will have different geological characteristics. Across the active transform zone two lithosphere plate edges formed at ridge-transform corners are faulted against one another. In the non

Assessing the Impacts of Forests on Human Welfare: Prelimnary Results from the Mid-Atlantic Integrated Assessement

Science.gov (United States)

D. Evan Mercer; P.B. Aruna

2000-01-01

Abstract. This paper presents results from the first phase of the socio-economic assessment of forest ecosystems in the Mid-Atlantic Integrated Assessment (MAIA). First, we present results of the analysis of changes in the distribution of human population and forest land use in the region. Then, trends in wood products employment and income between...

Physical trajectory profile data from glider ru23 deployed by Rutgers, the State University of New Jersey in the Mid-Atlantic Bight from 2014-08-14 to 2014-09-06 (NCEI Accession 0137967)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — U.S. IOOS Mid-Atlantic Regional Consortium of Ocean Observing Systems (MARACOOS) glider deployment to survey the physical and biological properties of Mid-Atlantic...

Physical trajectory profile data from glider ru23 deployed by Rutgers, the State University of New Jersey in the Mid-Atlantic Bight from 2013-03-05 to 2013-03-23 (NCEI Accession 0137964)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — U.S. IOOS Mid-Atlantic Regional Consortium of Ocean Observing Systems (MARACOOS) glider deployment to survey the physical and biological properties of Mid-Atlantic...

Physical trajectory profile data from glider ru23 deployed by Rutgers, the State University of New Jersey in the Mid-Atlantic Bight from 2014-09-16 to 2014-09-29 (NCEI Accession 0137968)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — U.S. IOOS Mid-Atlantic Regional Consortium of Ocean Observing Systems (MARACOOS) glider deployment to survey the physical and biological properties of Mid-Atlantic...

Physical trajectory profile data from glider ru23 deployed by Rutgers, the State University of New Jersey in the Mid-Atlantic Bight from 2015-10-08 to 2015-10-27 (NCEI Accession 0153545)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — U.S. IOOS Mid-Atlantic Regional Consortium of Ocean Observing Systems (MARACOOS) glider deployment to survey the physical and biological properties of Mid-Atlantic...

Physical trajectory profile data from glider ru23 deployed by Rutgers, the State University of New Jersey in the Mid-Atlantic Bight from 2013-10-17 to 2013-11-06 (NCEI Accession 0137966)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — U.S. IOOS Mid-Atlantic Regional Consortium of Ocean Observing Systems (MARACOOS) glider deployment to survey the physical and biological properties of Mid-Atlantic...

Topography of upper mantle seismic discontinuities beneath the North Atlantic: the Azores, Canary and Cape Verde plumes

Science.gov (United States)

Saki, Morvarid; Thomas, Christine; Nippress, Stuart E. J.; Lessing, Stephan

2015-04-01

We are mapping the topography of upper mantle seismic discontinuities beneath the North Atlantic and surrounding regions by using precursor arrivals to PP and SS seismic waves that reflect off the seismic discontinuities. Many source-receiver combinations have been used in order to collect a large dataset of reflection points beneath our investigating area. We analyzed over 1700 seismograms from MW>5.8 events using array seismic methods to enhance the signal to noise ratio. The measured time lag between PP (SS) arrivals and their corresponding precursors on robust stacks are used to measure the depth of the transition zone boundaries. The reflectors' depths show a correlation between the location of hotspots and a significantly depressed 410 km discontinuity indicating a temperature increase of 200-300 K compared to the surrounding mantle. For the 660 km discontinuity three distinct behaviours are visible: i) normal depths beneath Greenland and at a distance of a few hundred kilometres away from the hotspots and ii) shallower 660 km discontinuity compared with the global average value near hotspots closer to the Mid-Atlantic Ridge and iii) very few observations of a 660 km discontinuity at the hotspot locations. We interpret our observations as a large upwelling beneath the southern parts of our study region, possibly due to the South Atlantic convection cell. The thermal anomaly may be blocked by endothermic phase transformation and likely does not extend through the top of the transition zone as whole except for those branches which appear as the Azores, Canaries and Cape Verde hotspots at the surface.

The link between eddy-driven jet variability and weather regimes in the North Atlantic-European sector

Science.gov (United States)

Madonna, E.; Li, C.; Grams, C. M.; Woollings, T.

2017-12-01

Understanding the variability of the North Atlantic eddy-driven jet is key to unravelling the dynamics, predictability and climate change response of extratropical weather in the region. This study aims to 1) reconcile two perspectives on wintertime variability in the North Atlantic-European sector and 2) clarify their link to atmospheric blocking. Two common views of wintertime variability in the North Atlantic are the zonal-mean framework comprising three preferred locations of the eddy-driven jet (southern, central, northern), and the weather regime framework comprising four classical North Atlantic-European regimes (Atlantic ridge AR, zonal ZO, European/Scandinavian blocking BL, Greenland anticyclone GA). We use a k-means clustering algorithm to characterize the two-dimensional variability of the eddy-driven jet stream, defined by the lower tropospheric zonal wind in the ERA-Interim reanalysis. The first three clusters capture the central jet and northern jet, along with a new mixed jet configuration; a fourth cluster is needed to recover the southern jet. The mixed cluster represents a split or strongly tilted jet, neither of which is well described in the zonal-mean framework, and has a persistence of about one week, similar to the other clusters. Connections between the preferred jet locations and weather regimes are corroborated - southern to GA, central to ZO, and northern to AR. In addition, the new mixed cluster is found to be linked to European/Scandinavian blocking, whose relation to the eddy-driven jet was previously unclear. The results highlight the necessity of bridging from weather to climate scales for a deeper understanding of atmospheric circulation variability.

Distribution of the species of Lucifer Thompson, 1829 in the subtropical South Atlantic between parallels 20º and 30ºs

Directory of Open Access Journals (Sweden)

André Marafon-Almeida

Full Text Available Abstract The distribution of the species of Lucifer Thompson, 1829 (Decapoda: Luciferidae in the South Atlantic Subtropical Gyre was assessed by the Brazil Transatlantic Commission in November and December 2009. The samples were collected at 83 stations on two profiles between Brazil and Africa (20 º and 30 ºS. Oblique hauls were performed with a WP-2 net up to 150 meters deep. A distinct sexual relationship was noted between the two species found and L. faxoni presented a significantly higher number of females relative to males 1:0.5 (X2 = 21.77, p = 0.0001. The L. typus sex ratio had significantly more males than females 1.86:1 (X2=50.84, p = 0.0001. The distribution of L. typus occurred in both the western and the eastern portions of the Mid-Oceanic Ridge. This distribution was significantly related to salinity (R2 = 0:13; F = 3.79, p = 0.009, which was higher in the western portion of the study area. In addition, the recordings of the two species were extended to the Atlantic Subtropical Gyre. Overall, Luciferidae shrimp were more common and abundant at the stations west of the Mid-Oceanic Ridge and L. typus was the most frequent and abundant species.

75 FR 20591 - AES Sparrows Point LNG, LLC and Mid-Atlantic Express, LLC; Notice of Final General Conformity...

Science.gov (United States)

2010-04-20

...] AES Sparrows Point LNG, LLC and Mid-Atlantic Express, LLC; Notice of Final General Conformity... revised draft Final General Conformity Determination (GCD) for Pennsylvania to assess the potential air... the above-referenced dockets. In accordance with the General Conformity Regulations under the Code of...

A 300 kyr record of aridity and wind strength in southwestern Africa: evidence from grain-size distributions of sediments on Walvis Ridge, SE Atlantic.

NARCIS (Netherlands)

Stuut, J.-B. W.; Prins, M.A.; Schneider, R.S.; Weltje, G.J.; Jansen, J.H.F.; Postma, G.

2002-01-01

The terrigenous fraction of sediments recovered from Walvis Ridge, SE Atlantic Ocean, reveals a history of southwestern African climate of the last 300 kyr. End-member modelling of a data set of grain-size distributions (n = 428) results in three end members. The two coarsest end members are

Expedition 357 Preliminary Report: Atlantis Massif Serpentinization and Life

OpenAIRE

Früh-Green, GL; Orcutt, BN; Green, S; Cotterill, C; McCaig, AM; Expedition 357 Scientists,

2016-01-01

International Ocean Discovery Program (IODP) Expedition 357 successfully cored an east–west transect across the southern wall of Atlantis Massif on the western flank of the Mid-Atlantic Ridge to study the links between serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic sequences that have been uplifted to the seafloor along a major detachment fault zone. The primary goals of this expedition were to (1) examine the role of serpent...

A continuous time delay-difference type model (CTDDM) applied to stock assessment of the southern Atlantic albacore Thunnus alalunga

Institute of Scientific and Technical Information of China (English)

LIAO Baochao; LIU Qun; ZHANG Kui; Abdul BASET; Aamir Mahmood MEMON; Khadim Hussain MEMON; HAN Yanan

2016-01-01

A continuous time delay-difference model (CTDDM) has been established that considers continuous time delays of biological processes.The southern Atlantic albacore (Thunnus alalunga) stock is the one of the commercially important tuna population in the marine world.The age structured production model (ASPM) and the surplus production model (SPM) have already been used to assess the albacore stock.However,the ASPM requires detailed biological information and the SPM lacks the biological realism.In this study,we focus on applying a CTDDM to the southern Atlantic albacore (T.alalunga) species,which provides an alternative method to assess this fishery.It is the first time that CTDDM has been provided for assessing the Atlantic albacore (T.alalunga) fishery.CTDDM obtained the 80％ confidence interval of MSY (maximum sustainable yield) of(21510 t,23118 t).The catch in 2011 (24100 t) is higher than the MSY values and the relative fishing mortality ratio (F2011/FMSY) is higher than 1.0.The results of CTDDM were analyzed to verify the proposed methodology and provide reference information for the sustainable management of the southern Atlantic albacore stock.The CTDDM treats the recruitment,the growth,and the mortality rates as all varying continuously over time and fills gaps between ASPM and SPM in this stock assessment.

Using Resource Economics to Anticipate Forest Land Use Change in the U.S. Mid-Atlantic Region

Science.gov (United States)

Peter J. Parks; Ian W. Hardie; Cheryl A. Tedder; David N. Wear

2000-01-01

Demands for forest, farm, and developed land are evolving in the U.S. mid-Atlantic region. The demand for land in developed uses, as well as demands for various forest and farm products are changing in response to population growth, demographic shifts, and market forces. As demand factors change so do relative land values. Land area in future forest, farm, and...

Scientists and Stakeholders in the Chesapeake Bay: How the Mid-Atlantic RISA Strengthens Climate Resilience Through Participatory Decision-Making Processes

Science.gov (United States)

Knopman, D.; Berg, N.

2017-12-01

The NOAA Mid-Atlantic Regional Integrated Sciences and Assessments (MARISA) program was formed in September 2016 to increase climate resilience in the Mid-Atlantic, with an initial focus on the Chesapeake Bay Watershed. In this talk, we will discuss how the program's unique structure and approach are designed to advance resilience to a changing climate through improved data, place-based decision support, and public engagement. Emphasis will be placed on MARISA's approach to integrating stakeholder perspectives from the onset of decision scoping, through the creation of actionable data sets, and concluding with the co-development of adaptation strategies between the scientific community, decision-makers, and stakeholders. Specific examples of this process involving climate-sensitive decisions and investments regarding water resources, land management, and urban corridors will be discussed.

Masirah – the other Oman ophiolite: A better analogue for mid-ocean ridge processes?

Directory of Open Access Journals (Sweden)

Hugh Rollinson

2017-11-01

Full Text Available Oman has two ophiolites – the better known late Cretaceous northern Oman (or Semail ophiolite and the lesser known and smaller, Jurassic Masirah ophiolite located on the eastern coast of the country adjacent to the Indian Ocean. A number of geological, geochronological and geochemical lines of evidence strongly suggest that the northern Oman ophiolite did not form at a mid-ocean ridge but rather in a supra-subduction zone setting by fast spreading during subduction initiation. In contrast the Masirah ophiolite is structurally part of a series of ophiolite nappes which are rooted in the Indian Ocean floor. There are significant geochemical differences between the Masirah and northern Oman ophiolites and none of the supra-subduction features typical of the northern Oman ophiolite are found at Masirah. Geochemically Masirah is MORB, although in detail it contains both enriched and depleted MORB reflecting a complex source for the lavas and dykes. The enrichment of this source predates the formation of the ophiolite. The condensed crustal section on Masirah (ca. 2 km contains a very thin gabbro sequence and is thought to reflect its genesis from a cool mantle source associated with the early stages of sea-floor spreading during the early separation of eastern and western Gondwana. These data suggest that the Masirah ophiolite is a suitable analogue for an ophiolite created at a mid-ocean ridge, whereas the northern Oman ophiolite is not. The stratigraphic history of the Masirah ophiolite shows that it remained a part of the oceanic crust for ca. 80 Ma. The chemical variability and enrichment of the Masirah lavas is similar to that found elsewhere in Indian Ocean basalts and may simply reflect a similar provenance rather than a feature fundamental to the formation of the ophiolite.

Circumventing shallow air contamination in Mid Ocean Ridge Basalts

Science.gov (United States)

Mukhopadhyay, Sujoy; Parai, Rita; Tucker, Jonathan; Middleton, Jennifer; Langmuir, Charles

2016-04-01

Noble gases in mantle-derived basalts provide a rich portrait of mantle degassing and surface-interior volatile exchange. However, the ubiquity of shallow-level air contamination frequently obscures the mantle noble gas signal. In a majority of samples, shallow air contamination dominates the noble gas budget. As a result, reconstructing the variability in heavy noble gas mantle source compositions and inferring the history of deep recycling of atmospheric noble gases is difficult. For example, in the gas-rich popping rock 2ΠD43, 129Xe/130Xe ratios reach 7.7±0.23 in individual step-crushes, but the bulk composition of the sample is close to air (129Xe/130Xe of 6.7). Here, we present results from experiments designed to elucidate the source of shallow air contamination in MORBs. Step-crushes were carried out to measure He, Ne, Ar and Xe isotopic compositions on two aliquots of a depleted popping glass that was dredged from between the Kane and Atlantis Fracture Zones of the Mid-Atlantic Ridge in May 2012. One aliquot was sealed in ultrapure N2 after dredge retrieval, while the other aliquot was left exposed to air for 3.5 years. The bulk 20Ne/22Ne and 129Xe/130Xe ratios measured in the aliquot bottled in ultrapure N2 are 12.3 and 7.6, respectively, and are nearly identical to the estimated mantle source values. On the other hand, step crushes in the aliquot left exposed to air for several years show Ne isotopic compositions that are shifted towards air, with a bulk 20Ne/22Ne of 11.5; the bulk 129Xe/130Xe, however, was close to 7.6. These results indicate that lighter noble gases exchange more efficiently between the bubbles trapped in basalt glass and air, suggesting a diffusive or kinetic mechanism for the incorporation of the shallow air contamination. Importantly, in Ne-Ar or Ar-Xe space, step-crushes from the bottled aliquot display a trend that can be easily fit with a simple two-component hyperbolic mixing between mantle and atmosphere noble gases. Step

US Geological Survey BLM/OCS Baltimore Canyon (Mid-Atlantic) Sediment Analyses (Samples collected 1 July 1975 to 30 June 1976)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — This data set contains analytical data from samples acquired from the Baltimore Canyon (Mid-Atlantic) area of the Outer Continental Shelf, U.S. East Coast, by the...

Atlantic Ocean CARINA data: overview and salinity adjustments

Directory of Open Access Journals (Sweden)

T. Tanhua

2010-02-01

Full Text Available Water column data of carbon and carbon-relevant hydrographic and hydrochemical parameters from 188 previously non-publicly available cruise data sets in the Arctic Mediterranean Seas, Atlantic and Southern Ocean have been retrieved and merged into a new database: CARINA (CARbon dioxide IN the Atlantic Ocean. The data have gone through rigorous quality control procedures to assure the highest possible quality and consistency. The data for the pertinent parameters in the CARINA database were objectively examined in order to quantify systematic differences in the reported values, i.e. secondary quality control. Systematic biases found in the data have been corrected in the three data products: merged data files with measured, calculated and interpolated data for each of the three CARINA regions, i.e. the Arctic Mediterranean Seas, the Atlantic and the Southern Ocean. These products have been corrected to be internally consistent. Ninety-eight of the cruises in the CARINA database were conducted in the Atlantic Ocean, defined here as the region south of the Greenland-Iceland-Scotland Ridge and north of about 30° S. Here we present an overview of the Atlantic Ocean synthesis of the CARINA data and the adjustments that were applied to the data product. We also report the details of the secondary QC (Quality Control for salinity for this data set. Procedures of quality control – including crossover analysis between stations and inversion analysis of all crossover data – are briefly described. Adjustments to salinity measurements were applied to the data from 10 cruises in the Atlantic Ocean region. Based on our analysis we estimate the internal consistency of the CARINA-ATL salinity data to be 4.1 ppm. With these adjustments the CARINA data products are consistent both internally as well as with GLODAP data, an oceanographic data set based on the World Hydrographic Program in the 1990s, and is now suitable for accurate assessments of, for example

Surface elevation dynamics in vegetated Spartina marshes versus unvegetated tidal ponds along the mid-Atlantic coast, USA, with implications to waterbirds

Science.gov (United States)

Erwin, R. Michael; Cahoon, Donald R.; Prosser, Diann J.; Sanders, Geoffrey; Hensel, Philippe

2006-01-01

Mid Atlantic coastal salt marshes contain a matrix of vegetation diversified by tidal pools, pannes, and creeks, providing habitats of varying importance to many species of breeding, migrating, and wintering waterbirds. We hypothesized that changes in marsh elevation were not sufficient to keep pace with those of sea level in both vegetated and unvegetated Spartina alterniflora sites at a number of mid lagoon marsh areas along the Atlantic coast. We also predicted that northern areas would suffer less of a deficit than would southern sites. Beginning in August 1998, we installed surface elevation tables at study sites on Cape Cod, Massachusetts, southern New Jersey, and two locations along Virginia's eastern shore. We compared these elevation changes over the 4-4.5 yr record with the long-term (> 50 yr) tidal records for each locale. We also collected data on waterbird use of these sites during all seasons of the year, based on ground surveys and replicated surveys from observation platforms. Three patterns of marsh elevation change were found. At Nauset Marsh, Cape Cod, the Spartina marsh surface tracked the pond surface, both keeping pace with regional sea-level rise rates. In New Jersey, the ponds are becoming deeper while marsh surface elevation remains unchanged from the initial reading. This may result in a submergence of the marsh in the future, assuming sea-level rise continues at current rates. Ponds at both Virginia sites are filling in, while marsh surface elevation rates do not seem to be keeping pace with local sea-level rise. An additional finding at all sites was that subsidence in the vegetated marsh surfaces was less than in unvegetated areas, reflecting the importance of the root mat in stabilizing sediments. The implications to migratory waterbirds are significant. Submergence of much of the lagoonal marsh area in Virginia and New Jersey over the next century could have major negative (i.e., flooding) effects on nesting populations of marsh

Ridge interaction features of the Line Islands

Science.gov (United States)

Konter, J. G.; Koppers, A. A. P.; Storm, L. P.

2016-12-01

The sections of Pacific absolute plate motion history that precede the Hawaii-Emperor and Louisville chains are based on three chains: the Line Islands-Mid-Pacific Mountains, the Hess Rise-Shatsky Rise, and the Marshall Islands-Wake Islands (Rurutu hotspot). Although it has been clear that the Line Islands do not define a simple age progression (e.g. Schlanger et al., 1984), the apparent similarity to the Emperor Seamount geographic trend has been used to extend the overall Hawaii-Emperor track further into the past. However, we show here that plate tectonic reconstructions suggest that the Mid-Pacific Mountains (MPMs) and Line Islands (LIs) were erupted near a mid-ocean ridge, and thus these structures do not reflect absolute plate motion. Moverover, the morphology and geochemistry of the volcanoes show similarities with Pukapuka Ridge (e.g. Davis et al., 2002) and the Rano Rahi seamounts, presumed to have a shallow origin. Modern 40Ar/39Ar ages show that the LIs erupted at various times along the entire volcanic chain. The oldest structures formed within 10 Ma of plate formation. Given the short distance to the ridge system, large aseismic volcanic ridges, such as Necker Ridge and Horizon Guyot may simply reflect a connection between MPMs and the ridge, similar to the Pukapuka Ridge. The Line Islands to the south (including Karin Ridge) define short subchains of elongated seamounts that are widespread, resembling the Rano Rahi seamount field. During this time, the plate moved nearly parallel to the ridge system. The change from few large ridges to many subchains may reflect a change in absolute plate motion, similar to the Rano Rahi field. Here, significant MPMs volcanism is no longer connected to the ridge along plate motion. Similar to Pukapuka vs. Rano Rahi, the difference in direction between plate motion and the closest ridge determines whether larger ridges or smaller seamount subchains are formed. The difference between the largest structures (MPMs and LIs

Final Report of the Mid-Atlantic Marine Wildlife Surveys, Modeling, and Data

Energy Technology Data Exchange (ETDEWEB)

Saracino-Brown, Jocelyn [Energy Efficiency and Renewable Energy (EERE), Washington, DC (United States); Smith, Courtney [Energy Efficiency and Renewable Energy (EERE), Washington, DC (United States); Gilman, Patrick [Energy Efficiency and Renewable Energy (EERE), Washington, DC (United States)

2013-07-01

The Wind Program hosted a two-day workshop on July 24-25, 2012 with scientists and regulators engaged in marine ecological survey, modeling, and database efforts pertaining to the waters of the Mid-Atlantic region. The workshop was planned by Federal agency, academic, and private partners to promote collaboration between ongoing offshore ecological survey efforts, and to promote the collaborative development of complementary predictive models and compatible databases. The meeting primarily focused on efforts to establish and predict marine mammal, seabird, and sea turtle abundance, density, and distributions extending from the shoreline to the edge of the Exclusive Economic Zone between Nantucket Sound, Massachusetts and Cape Hatteras, North Carolina.

Plasmodium simium/Plasmodium vivax infections in southern brown howler monkeys from the Atlantic Forest

Directory of Open Access Journals (Sweden)

Daniela Camargos Costa

2014-08-01

Full Text Available Blood infection by the simian parasite, Plasmodium simium, was identified in captive (n = 45, 4.4% and in wild Alouatta clamitans monkeys (n = 20, 35% from the Atlantic Forest of southern Brazil. A single malaria infection was symptomatic and the monkey presented clinical and haematological alterations. A high frequency of Plasmodium vivax-specific antibodies was detected among these monkeys, with 87% of the monkeys testing positive against P. vivax antigens. These findings highlight the possibility of malaria as a zoonosis in the remaining Atlantic Forest and its impact on the epidemiology of the disease.

Potential for shoreline changes due to sea-level rise along the U.S. mid-Atlantic region

Science.gov (United States)

Gutierrez, Benjamin T.; Williams, S. Jeffress; Thieler, E. Robert

2007-01-01

Sea-level rise over the next century is expected to contribute significantly to physical changes along open-ocean shorelines. Predicting the form and magnitude of coastal changes is important for understanding the impacts to humans and the environment. Presently, the ability to predict coastal changes is limited by the scientific understanding of the many variables and processes involved in coastal change, and the lack of consensus regarding the validity of existing conceptual, analytical, or numerical models. In order to assess potential future coastal changes in the mid-Atlantic U.S. for the U.S. Climate Change Science Program (CCSP), a workshop was convened by the U.S. Geological Survey. Assessments of future coastal change were made by a committee of coastal scientists with extensive professional experience in the mid-Atlantic region. Thirteen scientists convened for a two-day meeting to exchange information and develop a consensus opinion on potential future coastal changes for the mid-Atlantic coast in response to sea-level rise. Using criteria defined in past work, the mid-Atlantic coast was divided into four geomorphic compartments: spits, headlands, wave-dominated barriers, and mixed-energy barriers. A range of potential coastal responses was identified for each compartment based on four sea-level rise scenarios. The four scenarios were based on the assumptions that: a) the long-term sea-level rise rate observed over the 20th century would persist over the 21st century, b) the 20th century rate would increase by 2 mm/yr, c) the 20th century rate would increase by 7 mm/yr, or d) sea-level would rise by 2 m over the next few hundred years. Potential responses to these sea-level rise scenarios depend on the landforms that occur within a region and include increased likelihood for erosion and shoreline retreat for all coastal types, increased likelihood for erosion, overwash and inlet breaching for barrier islands, as well as the possibility of a threshold

Expanded U.S. mid-Atlantic Margin Deep-Water Allostratigraphy; Bottom-Current Controls on Margin Evolution

Science.gov (United States)

Gibson, J. C.; Miller, N. C.; Hutchinson, D. R.; Ten Brink, U. S.; Mountain, G. S.; Chaytor, J. D.; Shillington, D. J.

2017-12-01

There is a long history of seismic stratigraphic interpretation/analysis of the sedimentary sequence along the U.S. mid-Atlantic Margin (MAM). Here we expand the allostratigraphic (unconformity-bound) framework from the outer continental shelf to the Hatteras Abyssal Plain by correlating recently acquired 2D multi-channel seismic reflection data with existing drill sites and legacy 2D seismic data collected over the past 42 yrs. The new 2D post-stack Kirchhoff time migrated seismic data were acquired using R/V Marcus G. Langseth in 2014-2015 during USGS ECS surveys MGL1407 & MGL1506 and NSF-funded ENAM-CSE survey MGL1408. We map six seismic horizons along 1.5x104 km of 2D data and tie each to stratigraphic unconformities sampled at DSDP site 603 (lower rise). From shallow to deep they are: (1) M2, latest Miocene; (2) X, middle Miocene; (3) Au, late Oligocene; (4) A*, Late Cretaceous; (5) Km, early Late Cretaceous; and (6) Beta, middle Early Cretaceous. The horizons were converted to depth (mbsl) using high-resolution interval velocity models generated for each 2D survey line and isopachs were produced using the depth-converted stratigraphic framework for each allostratigraphic unit. The time-to-depth function was confirmed to be within 5% of drilling results at DSDP Sites 603 and nearby 105. Additionally, we tie horizon Au to upper-slope ODP Sites 902 & 1073, and trace it to the outer shelf. Interpretation of the framework and resulting isopachs show total sediment thickness uniformly decreasing seaward from the shelf edge, and overall thickening to the south. Regional depositional trends display a combination of both down slope and along slope processes (e.g. mass wasting, submarine fan formation, contourite and sediment drift deposits). The unit bound by horizons Au & Beta confirms pervasive excavation from the mid-slope to the continental rise and across the central and southern MAM (from New Jersey to North Carolina). How the excavated sediments were

Bathymetric controls on Pliocene North Atlantic and Arctic sea surface temperature and deepwater production

Science.gov (United States)

Robinson, M.M.; Valdes, P.J.; Haywood, A.M.; Dowsett, H.J.; Hill, D.J.; Jones, S.M.

2011-01-01

The mid-Pliocene warm period (MPWP; ~. 3.3 to 3.0. Ma) is the most recent interval in Earth's history in which global temperatures reached and remained at levels similar to those projected for the near future. The distribution of global warmth, however, was different than today in that the high latitudes warmed more than the tropics. Multiple temperature proxies indicate significant sea surface warming in the North Atlantic and Arctic Oceans during the MPWP, but predictions from a fully coupled ocean-atmosphere model (HadCM3) have so far been unable to fully predict the large scale of sea surface warming in the high latitudes. If climate proxies accurately represent Pliocene conditions, and if no weakness exists in the physics of the model, then model boundary conditions may be in error. Here we alter a single boundary condition (bathymetry) to examine if Pliocene high latitude warming was aided by an increase in poleward heat transport due to changes in the subsidence of North Atlantic Ocean ridges. We find an increase in both Arctic sea surface temperature and deepwater production in model experiments that incorporate a deepened Greenland-Scotland Ridge. These results offer both a mechanism for the warming in the North Atlantic and Arctic Oceans indicated by numerous proxies and an explanation for the apparent disparity between proxy data and model simulations of Pliocene northern North Atlantic and Arctic Ocean conditions. Determining the causes of Pliocene warmth remains critical to fully understanding comparisons of the Pliocene warm period to possible future climate change scenarios. ?? 2011.

Comparison of the rift and post-rift architecture of conjugated salt and salt-free basins offshore Brazil and Angola/Namibia, South Atlantic

Science.gov (United States)

Strozyk, Frank; Back, Stefan; Kukla, Peter A.

2017-10-01

This study presents a regional comparison between selected 2D seismic transects from large, conjugated salt and salt-free basins offshore southern Brazil (Campos Basin, Santos Basin, Pelotas Basin) and southwest Africa (Kwanza Basin, northern and southern Namibe Basin, Walvis Basin). Tectonic-stratigraphic interpretation of the main rift and post-rift units, free-air gravity data and flexural isostatic backstripping were used for a comprehensive basin-to-basin documentation of key mechanisms controlling the present-day differences in conjugated and neighbouring South Atlantic basins. A significant variation in the tectonic-sedimentary architecture along-strike at each margin and between the conjugated basins across the South Atlantic reflects major differences in (1) the structural configuration of each margin segment at transitional phase between rifting and breakup, as emphasized in the highly asymmetric settings of the large Santos salt basin and the conjugated, salt-free southern Namibe Basin, (2) the post-breakup subsidence and uplift history of the respective margin segment, which caused major differences for example between the Campos and Espirito Santo basins and the conjugated northern Namibe and Kwanza basins, (3) variations in the quantity and distribution of post-breakup margin sediments, which led to major differences in the subsidence history and the related present-day basin architecture, for example in the initially rather symmetric, siliciclastic Pelotas and Walvis basins, and (4) the deposition of Aptian evaporites in the large rift and sag basin provinces north of the Rio Grande Rise and Walvis Ridge, highly contrasting the siliciclastic basins along the margin segments south of the ridges. The resulting present-day architecture of the basins can be generally classified as (i) moderately symmetric, salt-free, and magma-rich in the northern part of the southern segment, (i) highly asymmetric, salt-bearing and magma-poor vs. salt-free and magma

Geomorphology, active tectonics, and landscape evolution in the Mid-Atlantic region: Chapter

Science.gov (United States)

Pazzaglia, Frank J.; Carter, Mark W.; Berti, Claudio; Counts, Ronald C.; Hancock, Gregory S.; Harbor, David; Harrison, Richard W.; Heller, Matthew J.; Mahan, Shannon; Malenda, Helen; McKeon, Ryan; Nelson, Michelle S.; Prince, Phillip; Rittenour, Tammy M.; Spotilla, James; Whittecar, G. Richard

2015-01-01

In 2014, the geomorphology community marked the 125th birthday of one of its most influential papers, “The Rivers and Valleys of Pennsylvania” by William Morris Davis. Inspired by Davis’s work, the Appalachian landscape rapidly became fertile ground for the development and testing of several grand landscape evolution paradigms, culminating with John Hack’s dynamic equilibrium in 1960. As part of the 2015 GSA Annual Meeting, the Geomorphology, Active Tectonics, and Landscape Evolution field trip offers an excellent venue for exploring Appalachian geomorphology through the lens of the Appalachian landscape, leveraging exciting research by a new generation of process-oriented geomorphologists and geologic field mapping. Important geomorphologic scholarship has recently used the Appalachian landscape as the testing ground for ideas on long- and short-term erosion, dynamic topography, glacial-isostatic adjustments, active tectonics in an intraplate setting, river incision, periglacial processes, and soil-saprolite formation. This field trip explores a geologic and geomorphic transect of the mid-Atlantic margin, starting in the Blue Ridge of Virginia and proceeding to the east across the Piedmont to the Coastal Plain. The emphasis here will not only be on the geomorphology, but also the underlying geology that establishes the template and foundation upon which surface processes have etched out the familiar Appalachian landscape. The first day focuses on new and published work that highlights Cenozoic sedimentary deposits, soils, paleosols, and geomorphic markers (terraces and knickpoints) that are being used to reconstruct a late Cenozoic history of erosion, deposition, climate change, and active tectonics. The second day is similarly devoted to new and published work documenting the fluvial geomorphic response to active tectonics in the Central Virginia seismic zone (CVSZ), site of the 2011 M 5.8 Mineral earthquake and the integrated record of Appalachian

Loki's Castle: Discovery and geology of a black smoker vent field at the Arctic Mid-Ocean Ridge

Science.gov (United States)

Pedersen, R.; Thorseth, I. H.; Lilley, M. D.; Barriga, F. J.; Früh-Green, G.; Nakamura, K.

2010-12-01

Previous attempts to locate hydrothermal vent fields and unravel the nature of venting at the ultraslow spreading and magma starved parts of the Arctic Mid Ocean Ridge (AMOR) have been unsuccessful. A black smoker vent field was eventually discovered at the Mohns-Knipovich bend at 73.5°N in 2008, and the field was revisited in 2009 and 2010. The Loki’s Castle vent field is located on the crest of an axial volcanic ridge that is bordered by a tectonic terrain dominated by core complexes to the NW, and a ridge flank that is buried by sediments from the Bear Island Fan to the SE. Fluid compositions are anomalous to other basalt-hosted fields and indicate interactions with sediments at depths. The vent field is associated with an unusually large hydrothermal deposit, which documents that extensive venting occurs at ultraslow spreading ridges despite the strongly reduced magmatic heat budget. ROV surveys have shown that venting occurs in two areas separated by around 100 m. Micro-bathymetry acquired by a Hugin AUV documents that two 20-30 tall mounds that coalesce at the base have developed around the vent sites. The micro-bathymetry also shows that the venting is located above two normal faults that define the NW margin of a rift that runs along the crest of the volcano. The black smoker fluids reach 317 °C, with an end-member SiO2 content of 16 mmol/kg. End-member chlorinity is around 85% of seawater suggesting that the fluids have phase-separated at depth. The fluid compositions indicate that the rock-water reactions occur around 2 km below the seafloor. The crustal thickness is estimated to be 4 +/- 0.5 km in the area. Whereas the depth of the reaction zone is comparable with faster spreading ridges, the fraction of crust cooled convectively by hydrothermal circulation is two times that of vent fields at ridges with normal crustal thickness.

Marine Geophysical Characterization of the Chain Fracture Zone in the Equatorial Atlantic

Science.gov (United States)

Harmon, N.; Rychert, C.; Agius, M. R.; Tharimena, S.; Kendall, J. M.

2017-12-01

The Chain Fracture zone is part of a larger system of fracture zones along the Mid Atlantic Ridge that is thought to be one of the original zones of weakness during the break up of Pangea. It is over 300 km long and produces earthquakes as large as Mw 6.9 on segments of the active fault zone. Here we present the results of two marine geophysical mapping campaigns over the active part of the Chain Fracture zone as part of the PI-LAB (Passive Imaging of the Lithosphere-Asthenosphere Boundary) experiment. We collected swath bathymetry, backscatter imagery, gravity and total field magnetic anomaly. We mapped the fault scarps within the transform fault system using the 50 m resolution swath and backscatter imagery. In addition, a 30-40 mGal residual Mantle Bouguer Anomaly determined from gravity analysis suggests the crust is by up to 1.4-2.0 km beneath the Chain relative to the adjacent ridge segments. However, in the eastern 75 km of the active transform we find evidence for thicker crust. The active fault system cuts through the region of thicker crust and there is a cluster of MW > 6 earthquakes in this region. There is a cluster of similar sized earthquakes on the western end where thinner crust is inferred. This suggests that variations in melt production and crustal thickness at the mid ocean ridge systems may have only a minor effect on the seismicity and longevity of the transform fault system.

A new species of Nidalia Gray, 1835 from Mid-Atlantic seamounts (Octocorallia, Alcyonacea, Nidaliidae)

Science.gov (United States)

López-González, Pablo J.; Gili, Josep-Maria

2008-12-01

A new soft coral species of the genus Nidalia, from seamounts to the south of the Azores Archipelago is described. The main features of Nidalia aurantia n. sp. are as following: colony torch-like, a capitulum light orange in colour, not laterally flattened, dome-shaped and not distinctly projecting beyond the stalk, an introvert with sparse sclerites transversally placed, and an anthocodial crown with 13 17 sclerite rows. The new species is compared with its closest congeners. This is the first time that a species of Nidalia has been located in the Mid-Atlantic Ocean.

Benthic megafaunal community structure of cobalt-rich manganese crusts on Necker Ridge

Science.gov (United States)

Morgan, Nicole B.; Cairns, Stephen; Reiswig, Henry; Baco, Amy R.

2015-10-01

In the North Pacific Ocean, the seamounts of the Hawaiian Archipelago and the Mid-Pacific Mountains are connected by Necker Ridge, a 600 km-long feature spanning a depth range of 1400-4000 m. The Necker Ridge is a part of a large area of the central and western Pacific under consideration for cobalt-rich manganese crust mining. We describe the fauna and community structure of the previously unsampled Necker Ridge based on explorations with the submersible Pisces IV. On five pinnacles and a portion of the Ridge ranging from 1400 to 2000 m deep, 27 transects were recorded using HD video, and voucher specimens were collected to aid in species identification. The video was analyzed to identify and count the megafauna found on each transect and to characterize the substrate. Diversity increased from south to north along the feature. There was a significant difference in community structure between southern and northern pinnacles, with southern pinnacles dominated by crinoids of the Family Charitometridae and northern pinnacles dominated by octocorals, especially the Families Isididae and Chrysogorgiidae. DistLM demonstrated a correlation between community structure on the pinnacles and at least six environmental variables, including latitude, sediment cover, and oxygen concentration, but not including depth. The discontinuous and patchy nature of these distinct megafaunal communities highlights growing evidence that cobalt-rich seamounts are highly heterogeneous habitats, and that managing seamounts may require more complex regulations than treating them as a single ecological unit. These results suggest that extensive community analysis should occur at a given site to determine management priority areas, prior to consideration of that site for exploitation of natural resources.

Demographic Structure and Evolutionary History of Drosophila ornatifrons (Diptera, Drosophilidae) from Atlantic Forest of Southern Brazil.

Science.gov (United States)

Gustani, Emanuele C; Oliveira, Ana Paula F; Santos, Mateus H; Machado, Luciana P B; Mateus, Rogério P

2015-04-01

Drosoph1la ornatifrons of the guarani group (Diptera: Drosophilidae) is found mainly in humid areas of the Atlantic Forest biome, especially in the southern region of Brazil. Historical and contemporary fragmentation events influenced species diversity and distribution in this biome, although the role of paleoclimatic and paleogeographic events remain to be verified. The objective of the present study was to evaluate the demographic structure of D. ornatifrons from collection sites that are remnants of Atlantic Forest in southern Brazil, in order to contribute to the understanding of the processes that affected the patterns of genetic variability in this species. To achieve this goal, we sequenced 51 individuals from nine localities and 64 individuals from six localities for the mitochondrial genes Cytochrome Oxidase I and II, respectively. Our results indicate that D. ornatifrons may have experienced a demographic expansion event from the southernmost locations of its distribution, most likely from those located next to the coast and in fragments of Atlantic Forest inserted in the Pampa biome (South 2 group), towards the interior (South 1 group). This expansion probably started after the last glacial maximum, between 20,000 and 18,000 years ago, and was intensified near the Pleistocene-Holocene transition, around 12,000 years ago, when temperature started to rise. In this work we discuss how the haplotypes found barriers to gene flow and dispersal, influenced by the biogeographic pattern of Atlantic Forest.

Boulder Deposits on the Southern Spanish Atlantic Coast: Possible Evidence for the 1755 AD Lisbon Tsunami?

Directory of Open Access Journals (Sweden)

Dieter Kelletat

2005-01-01

Full Text Available Field evidence of visible tsunami impacts in Europe is scarce. This research focused on an analysis of large littoral debris and accompanying geomorphic features and their rela- tionship to a tsunami event at Cabo de Trafalgar, located on the southern Spanish Atlantic coast. Relative dating of weathering features as well as minor bioconstructive forms in the littoral zone suggest the Lisbon tsunami of 1755 AD as the event responsible for the large deposits described. This tsunami had run up heights of more than 19 m and was generated at the Gorringe Bank, located 500 km west off the Cape. Tsunami deposits at Cabo de Tra- falgar are the first boulder deposits identified on the southern Spanish Atlantic coast and are located approximately 250 km southeast of the Algarve coast (Portugal, where other geo- morphic evidence for the Lisbon tsunami has been reported.

Volcanogenic-hydrothermal iron-rich materials from the southern part of the Central Indian Ocean Basin

Digital Repository Service at National Institute of Oceanography (India)

Iyer, S; Gupta, S; Charan, S; Mills, O.P.

. This may further be corroborated by the E–W elongation of some of the N–S-oriented seamounts, caused by the addition of magmatic materials and are thus indicative of more than one episode of volcanism. There are additional evidences which indicate volcanic...-brown material from the Japan Basin. Mar. Geol. 129, 331–336. Aumento, F., Mitchell, W.S., 1975. Magnetic spherules from the Mid-Atlantic Ridge. Geology 3, 407–410. Barrett, T.J., Friedrichsen, H., 1982. Elemental and isotopic composition of some metalliferous...

Strong signatures of high-latitude blocks and subtropical ridges in winter PM10 over Europe

Science.gov (United States)

Ordonez, C.; Garrido-Perez, J. M.; Garcia-Herrera, R.

2017-12-01

Atmospheric blocking is associated with persistent, slow-moving high pressure systems that interrupt the eastward progress of extratropical storm systems at middle and high latitudes. Subtropical ridges are low latitude structures manifested as bands of positive geopotential height anomalies extending from sub-tropical latitudes towards extra-tropical regions. We have quantified the impact of blocks and ridges on daily PM10 (particulate matter ≤ 10 µm) observations obtained from the European Environment Agency's air quality database (AirBase) for the winter period of 2000-2010. For this purpose, the response of the PM10 concentrations to the location of blocks and ridges with centres in two main longitudinal sectors (Atlantic, ATL, 30˚-0˚ W; European, EUR, 0˚-30˚ E) is examined. EUR blocking is associated with a collapse of the boundary layer as well as reduced wind speeds and precipitation occurrence, yielding large positive anomalies which average 12 µg m-3 over the whole continent. Conversely, the enhanced zonal flow around 50˚-60˚ N and the increased occurrence of precipitation over northern-central Europe on days with ATL ridges favour the ventilation of the boundary layer and the impact of washout processes, reducing PM10 concentrations on average by around 8 µg m-3. The presence of EUR blocks is also concurrent with an increased probability of exceeding the European air quality target (50 µg m-3 for 24-h averaged PM10) and the local 90th percentiles for this pollutant at many sites, while the opposite effect is found for ridges. In addition, the effect of synoptic persistence on the PM10 concentrations is particularly strong for EUR blocks. Finally, we have found that the effect of both synoptic patterns can partly control the interannual variability of winter mean PM10 at many sites of north-western and central Europe, with coefficients of determination (R2) exceeding 0.80 for southern Germany. These results indicate that the response of the

कार्ल्सवर्ग पर्वतश्रेणी के तलछट की विशेषता

Digital Repository Service at National Institute of Oceanography (India)

Valsangkar, A.B.

The sediment coverage in the Carlsberg Ridge is similar in appearance to those in the Mid-Atlantic Ridge. The Carlsberg Ridge sediments show that their sources are continental, biogenic and diagenetic. The sedimentation rate determined by Th232...

Long-term Bat Monitoring on Islands, Offshore Structures, and Coastal Sites in the Gulf of Maine, mid-Atlantic, and Great Lakes—Final Report

Energy Technology Data Exchange (ETDEWEB)

Peterson, Trevor [Stantec Consulting Services Inc., Topsham, ME (United States); Pelletier, Steve [Stantec Consulting Services Inc., Topsham, ME (United States); Giovanni, Matt [Stantec Consulting Services Inc., Topsham, ME (United States)

2016-01-15

This report summarizes results of a long-term regional acoustic survey of bat activity at remote islands, offshore structures, and coastal sites in the Gulf of Maine, Great Lakes, and mid-Atlantic coast.

Initiation of long-term coupled microbiological, geochemical, and hydrological experimentation within the seafloor at North Pond, western flank of the Mid-Atlantic Ridge

Science.gov (United States)

Edwards, K.J.; Backert, N.; Bach, W.; Becker, K.; Klaus, A.; Griffin, Dale W.; Anderson, L.; Haddad, A.G.; Harigane, Y.; Campion, P.L.; Hirayama, H.; Mills, H.J.; Hulme, S.M.; Nakamura, K.; Jorgensen, S.L.; Orcutt, B.; Insua, T.L.; Park, Y.-S.; Rennie, V.; Salas, E.C.; Rouxel, O.; Wang, F.; Russel, J.A.; Wheat, C.G.; Sakata, K.; Brown, M.; Magnusson, J.L.; Ettlinger, Z.

2012-01-01

Integrated Ocean Drilling Program (IODP) Expedition 336 successfully initiated subseafloor observatory science at a young mid-ocean-ridge flank setting. All of the drilled sites are located in the North Pond region of the Atlantic Ocean (22??45'N, 46??05'W) in 4414-4483 m water depth. This area is known from previous ocean drilling and site survey investigations as a site of particularly vigorous circulation of seawater in permeable 8 Ma basaltic basement underlying a logged in Holes U1382A and U1383C. Upper oceanic crust in Hole U1382A, which is only 50 m west of Deep Sea Drilling Project (DSDP) Hole 395A, recovered 32 m of core between 110 and 210 meters below seafloor (mbsf). Core recovery in basement was 32%, yielding a number of volcanic flow units with distinct geochemical and petrographic characteristics. A unit of sedimentary breccia containing clasts of basalt, gabbroic rocks, and mantle peridotite was found intercalated between two volcanic flow units and was interpreted as a rock slide deposit. From Hole U1383C we recovered 50.3 m of core between 69.5 and 331.5 mbsf (19%). The basalts are aphyric to highly plagioclase-olivine-phyric tholeiites that fall on a liquid line of descent controlled by olivine fractionation. They are fresh to moderately altered, with clay minerals (saponite, nontronite, and celadonite), Fe oxyhydroxide, carbonate, and zeolite as secondary phases replacing glass and olivine to variable extents. In addition to traditional downhole logs, we also used a new logging tool for detecting in situ microbial life in ocean floor boreholes-the Deep Exploration Biosphere Investigative tool (DEBI-t). Sediment thickness was ???90 m at Sites U1382 and U1384 and varied between 38 and 53 m at Site U1383. The sediments are predominantly nannofossil ooze with layers of coarse foraminiferal sand and occasional pebble-size clasts of basalt, serpentinite, gabbroic rocks, and bivalve debris. The bottommost meters of sections cored with the advanced

Investigations of a novel fauna from hydrothermal vents along the Arctic Mid-Ocean Ridge (AMOR) (Invited)

Science.gov (United States)

Rapp, H.; Schander, C.; Halanych, K. M.; Levin, L. A.; Sweetman, A.; Tverberg, J.; Hoem, S.; Steen, I.; Thorseth, I. H.; Pedersen, R.

2010-12-01

The Arctic deep ocean hosts a variety of habitats ranging from fairly uniform sedimentary abyssal plains to highly variable hard bottoms on mid ocean ridges, including biodiversity hotspots like seamounts and hydrothermal vents. Deep-sea hydrothermal vents are usually associated with a highly specialized fauna, and since their discovery in 1977 more than 400 species of animals have been described. This fauna includes various animal groups of which the most conspicuous and well known are annelids, mollusks and crustaceans. The newly discovered deep sea hydrothermal vents on the Mohns-Knipovich ridge north of Iceland harbour unique biodiversity. The Jan Mayen field consists of two main areas with high-temperature white smoker venting and wide areas with low-temperature seepage, located at 5-700 m, while the deeper Loki Castle vent field at 2400 m depth consists of a large area with high temperature black smokers surrounded by a sedimentary area with more diffuse low-temperature venting and barite chimneys. The Jan Mayen sites show low abundance of specialized hydrothermal vent fauna. Single groups have a few specialized representatives but groups otherwise common in hydrothermal vent areas are absent. Slightly more than 200 macrofaunal species have been identified from this vent area, comprising mainly an assortment of bathyal species known from the surrounding area. Analysis of stable isotope data also indicates that the majority of the species present are feeding on phytodetritus and/or phytoplankton. However, the deeper Loki Castle vent field contains a much more diverse vent endemic fauna with high abundances of specialized polychaetes, gastropods and amphipods. These specializations also include symbioses with a range of chemosynthetic microorganisms. Our data show that the fauna composition is a result of high degree of local specialization with some similarities to the fauna of cold seeps along the Norwegian margin and wood-falls in the abyssal Norwegian Sea

The onset of modern-like Atlantic meridional overturning circulation at the Eocene-Oligocene transition: Evidence, causes, and possible implications for global cooling

Science.gov (United States)

Abelson, Meir; Erez, Jonathan

2017-06-01

A compilation of benthic δ18O from the whole Atlantic and the Southern Ocean (Atlantic sector) shows two major jumps in the interbasinal gradient of δ18O (Δδ18O) during the Eocene and the Oligocene: one at ˜40 Ma and the second concomitant with the isotopic event of the Eocene-Oligocene transition (EOT), ˜33.7 Ma ago. From previously published circulation models and proxies, we show that the first Δδ18O jump reflects the thermal isolation of Antarctica associated with the proto-Antarctic circumpolar current (ACC). The second marks the onset of interhemispheric northern-sourced circulation cell, similar to the modern Atlantic meridional overturning circulation (AMOC). The onset of AMOC-like circulation slightly preceded (100-300 kyr) the EOT, as we show by the high-resolution profiles of δ18O and δ13C previously published from DSDP/ODP sites in the Southern Ocean and South Atlantic. These events coincide with the onset of antiestuarine circulation between the Nordic seas and the North Atlantic which started around the EOT and may be connected to the deepening of the Greenland-Scotland Ridge. We suggest that while the shallow proto-ACC supplied the energy for deep ocean convection in the Southern Hemisphere, the onset of the interhemispheric northern circulation cell was due to the significant EOT intensification of deepwater formation in the North Atlantic driven by the Nordic antiestuarine circulation. This onset of the interhemispheric northern-sourced circulation cell could have prompted the EOT global cooling.Plain Language SummaryThe Eocene-Oligocene transition is the major abrupt climatic event during the Cenozoic, which marks the major step to the icehouse world. We show that this transition is a shift to a world with Atlantic meridional overturning circulation (AMOC) and slightly preceded this transition. Thus, possibly was a major factor in this climatic shift.

Recent coastal evolution in a carbonate sandy environments and relation to beach ridge formation: the case of Anegada, British Virgin Islands

Science.gov (United States)

Cescon, Anna Lisa; Cooper, J. Andrew G.; Jackson, Derek W. T.

2014-05-01

In a changing climate context coastal areas will be affected by more frequent extreme events. Understanding the relationship between extreme events and coastal geomorphic response is critical to future adaptation plans. Beach ridge landforms commonly identified as hurricane deposits along tropical coasts in Australia and in the Caribbean Sea. However their formative processes in such environments are still not well understood. In particular, the role of different extreme wave events (storm waves, tsunami waves and extreme swell), in generating beach ridges is critical to their use as palaeotempestology archives. Anegada Island is a carbonate platform situated in the British Virgin Island between the Atlantic Ocean and the Caribbean Sea. Pleistocene in age, Anegada is surrounded by the Horseshoe fringing coral reef. Two Holocene sandy beach ridge plains are present on the western part of the island. The north beach ridge plain is Atlantic facing and has at least 30 ridges; the south beach ridge plain is Caribbean Sea facing and contains 10 ridges. Historical aerial photos enabled the shoreline evolution from 1953 to 2012 to be studied. Three different coastal domains are associate with the beach ridge plains: strong east-west longshore transport affects the north coastline, the south-west coastline from West End to Pomato Point represents an export corridor for these sediments and finally, along the southern coastline, from Pomato Point to Settling Point the area presents a depositional zone with little to no change in the last 70 years. The link between the extreme wave events that have affected Anegada Island in the last 70 years and beach ridge creation is discussed. Hurricane Donna crossed over Anegada Island in 1960: its geomorphological signature is tracked in the shoreline change analysis and its implication in beach ridge formation is discussed. Anegada Island has also been impacted by tsunami waves (Atwater et al., 2012) and a comparative discussion of the

Atmospheric circulation changes and neoglacial conditions in the Southern Hemisphere mid-latitudes: insights from PMIP2 simulations at 6 kyr

Science.gov (United States)

Rojas, Maisa; Moreno, Patricio I.

2011-07-01

Glacial geologic studies in the Southern Hemisphere (SH) mid-latitudes (40-54°S) indicate renewed glacial activity in southern South America (Patagonia) and New Zealand's (NZ) South Island starting at ˜7 kyr, the so-called neoglaciation. Available data indicate that neoglacial advances in these regions occurred during a rising trend in atmospheric CO2 and CH4 concentrations, lower-than-present but increasing summer insolation and seasonality contrasts. In this paper we examine the climatological context in which neoglaciations occurred through analysis of the complete Paleoclimate Modelling Inter-comparison Project (PMIP2) database of simulations at 6 kyr for the SH. We observe that the amplitude of the annual insolation cycle in the SH did not change significantly at 6 kyr compared to the pre-industrial values, the largest difference occurring in autumn (MAM, negative anomalies) and spring (SON, positive anomalies). The simulated changes in temperatures over the SH respond to the insolation changes, with a 1-2 month delay over the oceans. This results in a reduced amplitude of the annual cycle of temperature and precipitation over most continental regions, except over Patagonia and NZ, that show a slight increase. In contrast, large-scale circulation features, such as the low and upper level winds and the subtropical anticyclones show an amplified annual cycle, as a direct response to the increased/decreased insolation during the transitional seasons SON/MAM. In the annual mean, there is a small but consistent equatorward shift of the latitude of maximum wind speed of 1-3° over the entire SH, which results in a small increase of wind speed over the South Pacific and Atlantic Oceans north of ˜50°S and a widespread decline south of 50°S. PMIP2 simulations for 6 kyr, indicate that in the annual mean, the SH mid-latitudes were colder, wetter and with stronger winds north of about 50°S. These conditions are consistent with the observed neoglacial advances in the

Atmospheric circulation changes and neoglacial conditions in the Southern Hemisphere mid-latitudes: insights from PMIP2 simulations at 6 kyr

Energy Technology Data Exchange (ETDEWEB)

Rojas, Maisa [University of Chile, Department of Geophysics, Santiago (Chile); Moreno, Patricio I. [University of Chile, Department of Ecology, Santiago (Chile)

2011-07-15

Glacial geologic studies in the Southern Hemisphere (SH) mid-latitudes (40-54 S) indicate renewed glacial activity in southern South America (Patagonia) and New Zealand's (NZ) South Island starting at {proportional_to}7 kyr, the so-called neoglaciation. Available data indicate that neoglacial advances in these regions occurred during a rising trend in atmospheric CO{sub 2} and CH{sub 4} concentrations, lower-than-present but increasing summer insolation and seasonality contrasts. In this paper we examine the climatological context in which neoglaciations occurred through analysis of the complete Paleoclimate Modelling Inter-comparison Project (PMIP2) database of simulations at 6 kyr for the SH. We observe that the amplitude of the annual insolation cycle in the SH did not change significantly at 6 kyr compared to the pre-industrial values, the largest difference occurring in autumn (MAM, negative anomalies) and spring (SON, positive anomalies). The simulated changes in temperatures over the SH respond to the insolation changes, with a 1-2 month delay over the oceans. This results in a reduced amplitude of the annual cycle of temperature and precipitation over most continental regions, except over Patagonia and NZ, that show a slight increase. In contrast, large-scale circulation features, such as the low and upper level winds and the subtropical anticyclones show an amplified annual cycle, as a direct response to the increased/decreased insolation during the transitional seasons SON/MAM. In the annual mean, there is a small but consistent equatorward shift of the latitude of maximum wind speed of 1-3 over the entire SH, which results in a small increase of wind speed over the South Pacific and Atlantic Oceans north of {proportional_to}50 S and a widespread decline south of 50 S. PMIP2 simulations for 6 kyr, indicate that in the annual mean, the SH mid-latitudes were colder, wetter and with stronger winds north of about 50 S. These conditions are consistent

Generation of Mid-Ocean Ridge Geometries by Strain Induced Damage

Science.gov (United States)

Hieronymus, C. F.

2001-12-01

Motivated by the success of wax models in which spreading segments, transform faults, and overlapping spreading centers form in a thin plate of solid wax under tension overlying a reservoir of molten wax, the dynamics of an elastic plate with damage is investigated. The effects of the underlying medium are neglected. A thin elastic plate with localized weaknesses in the elastic moduli is exposed to a deviatoric stress field. Stresses and strains are concentrated near the boundaries and inside the weak zones. Weakening of the material is assumed to occur where stress and strain are high, i.e. in regions of high elastic energy. The weak zones typically develop into linear bands of reduced elastic strength resembling fractures and shear zones. Different dependencies of the elastic moduli on damage result in different geometries of weak zones. An initially circular weakness has two locations of normal stress concentration; reduction of bulk and shear modulus there results in formation of an opening mode fracture with low resistance to any type of deformation. Two such fractures offset from each other and propagating toward each other interact by overlapping and curving toward each other. This overlapping geometry, which is observed along the East Pacific Rise, is stable; the fractures do not cut each other off. Introduction of a second type of damage causes the overlapping region between the two fractures to fail, and the more commonly observed transform offset develops. With another type of damage-strain dependency, oblique spreading occurs along lines 45o from the applied stress. Such patterns form frequently in certain types of wax, but are not observed along mid-ocean ridges. The model results suggest that it is the rheology of the solid plate, not the dynamics of the underlying mantle that control the morphology of the spreading ridge. Standard damage theory uses only a single damage parameter. The fact that the failure modes described above are limited to systems

Mid-Atlantic Technology Applications Center. Quarters 1-4

Science.gov (United States)

1997-01-01

Mid-atlantic Technology Application Center (MTAC) pursued a number of initiatives designed to enhance the strategic position of the Langley Research Center (LaRC) and NASA in industry. Among these was a closer association with the ISA, International Society for Measurement and Control. During 1997, MTAC placed articles regarding NASA-developed technologies in each In Tech magazine. The monthly magazine is sent to 46,000 sensors and instrumentation professionals. In addition, MTAC coordinated NASXs participation in the ISA Tech 97 Conference, securing $112,000 of free exhibit space, 1500 NASA sensors posters at no cost to NASA, and thousands of dollars of free publicity. MTAC was awarded a contract by ISA to operate its Technical Resource Center (TRC). The goal of this project is to determine what user needs are in order to identify opportunities for collaboration between NASA centers and companies. In addition, the TRC work will lay the groundwork for the Technology Development Consortium (TDC) proposed by MTAC. The purpose of the TDC is to: match current industry needs with NASA technologies available now, and to identify future needs of NASA and industry which may lead to dual use projects. The goal of these activities is twofold: to infuse NASA technologies into the sensors and instrumentation industry and to secure industry funds to support NASA technology development projects. The instrumentation and sensors industry is valued at $30 billion worldwide, with $12 billion in sales in the United States. The growth rate averages 13.5%, so that by the year 2000, the industry will produce products worth $49 billion. More than 80% of instruments, sensors and control systems are currently manufactured in the United States. NASA and the industry do not have a history of collaborative projects; MTAC's initiatives in this area are designed to foster working relationships between the two parties that will help maintain U.S. leadership in this field. Mid-atlantic Technology

Reevaluating the age of the Walden Creek Group and the kinematic evolution of the western Blue Ridge, southern Appalachians

Science.gov (United States)

Thigpen, J. Ryan; Hatcher, Robert D.; Kah, Linda C.; Repetski, John E.

2016-01-01

An integrated synthesis of existing datasets (detailed geologic mapping, geochronologic, paleontologic, geophysical) with new paleontologic and geochemical investigations of rocks previously interpreted as part of the Neoproterozoic Walden Creek Group in southeastern Tennessee suggest a necessary reevaluation of the kinematics and structural architecture of the Blue Ridge Foothills. The western Blue Ridge of Tennessee, North Carolina, and Georgia is composed of numerous northwest-directed early and late Paleozoic thrust sheets, which record pronounced variation in stratigraphic/structural architecture and timing of metamorphism. The detailed spatial, temporal, and kinematic relationships of these rocks have remained controversial. Two fault blocks that are structurally isolated between the Great Smoky and Miller Cove-Greenbrier thrust sheets, here designated the Maggies Mill and Citico thrust sheets, contain Late Ordovician-Devonian conodonts and stable isotope chemostratigraphic signatures consistent with a mid-Paleozoic age. Geochemical and paleontological analyses of Walden Creek Group rocks northwest and southeast of these two thrust sheets, however, are more consistent with a Late Neoproterozoic (550–545 Ma) depositional age. Consequently, the structural juxtaposition of mid-Paleozoic rocks within a demonstrably Neoproterozoic-Cambrian succession between the Great Smoky and Miller Cove-Greenbrier thrust sheets suggests that a simple foreland-propagating thrust sequence model is not applicable in the Blue Ridge Foothills. We propose that these younger rocks were deposited landward of the Ocoee Supergroup, and were subsequently plucked from the Great Smoky fault footwall as a horse, and breached through the Great Smoky thrust sheet during Alleghanian emplacement of that structure.

Inter-Rifting and Inter-Seismic Strain Accumulation in a Propagating Ridge System: A Geodetic Study from South Iceland

Science.gov (United States)

Travis, M. E.; La Femina, P. C.; Geirsson, H.

2012-12-01

The Mid-Atlantic Ridge, a slow spreading (~19 mm/yr) mid-ocean ridge boundary between the North American and Eurasian plates, is exposed subaerially in Iceland as the result of ridge-hotspot interaction. Plate spreading in Iceland is accommodated along neovolcanic zones comprised of central volcanoes and their fissure swarms. In south Iceland plate motion is partitioned between the Western Volcanic Zone (WVZ) and Eastern Volcanic Zone (EVZ). The EVZ is propagating to the southwest, while the WVZ is dying out from the northeast. Plate motion across both systems has been accommodated by repeated rifting events and fissure eruptions. In this study we investigate whether the WVZ is active and accumulating strain, and how strain is partitioned between the WVZ and EVZ. We also test how strain is accumulating along fissure swarms within the EVZ (i.e. is strain accumulation localized to one fissure swarm, or are multiple systems active?). We use GPS data and elastic block models run using the program DEFNODE to investigate these issues. GPS data are processed using the GIPSY-OASIS II software, and have been truncated to the 2000.5-2011 time period to avoid co-seismic displacement from the two June 2000 South Iceland Seismic Zone earthquakes. We also truncate the time series for sites within 20 km of Eyjafjallajökull to the beginning of 2010 to eliminate deformation associated with the March 2010 eruption of that volcano. We correct for co-seismic displacement from the two May 2008 SISZ earthquakes, inflation at Hekla volcano and the horizontal component of glacial isostatic rebound (GIA). Our best-fit model for inter-rifting and inter-seismic elastic strain accumulation suggests 80-90% of spreading is accommodated in the EVZ with the other 10-20% accommodated by the WVZ. The best-fit location of the EVZ is between Veidivotn and Lakigigar in an area of no Holocene volcanic activity. We suggest the WVZ is only active at Hengill and its associated fissure swarm. Geologic and

The morphostructure of the atlantic ocean floor its development in the meso-cenozoic

CERN Document Server

Litvin, V M

1984-01-01

The study of the topography and structure of the ocean floor is one of the most important stages in ascertaining the geological structure and history of development of the Earth's oceanic crust. This, in its turn, provides a means for purposeful, scientifically-substantiated prospecting, exploration and development of the mineral resources of the ocean. The Atlantic Ocean has been geologically and geophysically studied to a great extent and many years of investigating its floor have revealed the laws governing the structure of the major forms of its submarine relief (e. g. , the continental shelf, the continental slope, the transition zones, the ocean bed, and the Mid-Oceanic Ridge). The basic features of the Earth's oceanic crust structure, anomalous geophysical fields, and the thickness and structure of its sedimentary cover have also been studied. Based on the investigations of the Atlantic Ocean floor and its surrounding continents, the presently prevalent concept of new global tectonics has appeared. A g...

Common Core State Standards and Teacher Effectiveness. Q&A with Ross Wiener, Ph.D. REL Mid-Atlantic Teacher Effectiveness Webinar Series

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Regional Educational Laboratory Mid-Atlantic, 2013

2013-01-01

In this REL Mid-Atlantic webinar, Dr. Ross Wiener, Vice President and Executive Director of the Education and Society Program, Aspen Institute, discussed strategies for integrating the Common Core State Standards (CCSS) into teacher effectiveness systems, including ways in which the CCSS can support professional growth and inform teacher…

Grenville age of basement rocks in Cape May NJ well: New evidence for Laurentian crust in U.S. Atlantic Coastal Plain basement Chesapeake terrane

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Sheridan, R.E.; Maguire, T.J.; Feigenson, M.D.; Patino, L.C.; Volkert, R.A.

1999-01-01

The Chesapeake terrane of the U.S. mid-Atlantic Coastal Plain basement is bounded on the northwest by the Salisbury positive gravity and magnetic anomaly and extends to the southeast as far as the Atlantic coast. It underlies the Coastal Plain of Virginia, Maryland, Delaware and southern New Jersey. Rubidium/Strontium dating of the Chesapeake terrane basement yields an age of 1.025 ?? 0.036 Ga. This age is typical of Grenville province rocks of the Middle to Late Proterozoic Laurentian continent. The basement lithologies are similar to some exposed Grenville-age rocks of the Appalachians. The TiO2 and Zr/P2O5 composition of the metagabbro from the Chesapeake terrane basement is overlapped by those of the Proterozoic mafic dikes in the New Jersey Highlands. These new findings support the interpretation that Laurentian basement extends southeast as far as the continental shelf in the U.S. mid-Atlantic region. The subcrop of Laurentian crust under the mid-Atlantic Coastal Plain implies unroofing by erosion of the younger Carolina (Avalon) supracrustal terrane. Dextral-transpression fault duplexes may have caused excessive uplift in the Salisbury Embayment area during the Alleghanian orogeny. This extra uplift in the Salisbury area may have caused the subsequent greater subsidence of the Coastal Plain basement in the embayment.

Otolith shape analysis as a tool for stock identification of the southern blue whiting, Micromesistius australis

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Javier Leguá

2013-07-01

Full Text Available The southern blue whiting, Micromesistius australis (Norman, 1937, is an important demersal resource associated with the slope and continental shelf of southern Chile, Argentina and the Malvinas/Falkland Islands. Recent studies have reported schools of adult fish from Atlantic waters migrating along the southern Chilean coast in mid-winter, moving northwards to spawn in August (47°-51°S, and then returning to Atlantic waters, presumably to feed. The migratory pattern suggests the presence of one or more stock units associated with the South American coast. In the present study, "otolith morphometry" is used to determine the stock structure of M. australis based on applications of basic size descriptors (SDs (area, perimeter and otolith size, shape indices (SIs (circularity, squareness, shape factor, roundness, ellipticity, and normalised elliptical Fourier descriptors (NEFDs. Samples were collected during the winter and spring of 2010, during the reproductive period, in the economic zone of southern Chile (36°-57°S, in the Pacific Ocean and around the Falkland Islands economic zone (50°-52°S in the Atlantic Ocean. Analyses were conducted to include the effects of size, sex and age. A stepwise canonical discriminant analysis showed that fish were successfully discriminated with SDs, SIs and NEFDs. In this analysis, 86.4% and 70.1% of the fish were correctly classified as belonging to the Atlantic and Pacific stocks, respectively. A multivariate analysis of variance showed that the mean values of the NEFDs, SDs, and SIs did not vary significantly between sexes within areas (P > 0.05, but varied significantly between the Pacific and Atlantic oceans (P < 0.05. These results highlighted that otolith shape analysis can be a useful tool to evaluate the potential level of mixing in feeding areas where both stocks, the Pacific and Atlantic units, are expected to co-occur.

Tectono-Magmatic Evolution of the South Atlantic Continental Margins with Respect to Opening of the Ocean

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Melankholina, E. N.; Sushchevskaya, N. M.

2018-03-01

The history of the opening of the South Atlantic in Early Cretaceous time is considered. It is shown that the determining role for continental breakup preparation has been played by tectono-magmatic events within the limits of the distal margins that developed above the plume head. The formation of the Rio Grande Rise-Walvis Ridge volcanic system along the trace of the hot spot is considered. The magmatism in the South Atlantic margins, its sources, and changes in composition during the evolution are described. On the basis of petrogeochemical data, the peculiarities of rocks with a continental signature are shown. Based on Pb-Sr-Nd isotopic studies, it is found that the manifestations of magmatism in the proximal margins had features of enriched components related to the EM I and EM II sources, sometimes with certain participation of the HIMU source. Within the limits of the Walvis Ridge, as magmatism expanded to the newly formed oceanic crust, the participation of depleted asthenospheric mantle became larger in the composition of magmas. The role played by the Tristan plume in magma generation is discussed: it is the most considered as the heat source that determined the melting of the ancient enriched lithosphere. The specifics of the tectono-magmatic evolution of the South Atlantic is pointed out: the origination during spreading of a number of hot spots above the periphery of the African superplume. The diachronous character of the opening of the ocean is considered in the context of northward progradation of the breakup line and its connection with the northern branch of the Atlantic Ocean in the Mid-Cretaceous.

Trans-pacific glacial response to the Antarctic Cold Reversal in the southern mid-latitudes

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Sagredo, Esteban A.; Kaplan, Michael R.; Araya, Paola S.; Lowell, Thomas V.; Aravena, Juan C.; Moreno, Patricio I.; Kelly, Meredith A.; Schaefer, Joerg M.

2018-05-01

Elucidating the timing and regional extent of abrupt climate events during the last glacial-interglacial transition (∼18-11.5 ka) is critical for identifying spatial patterns and mechanisms responsible for large-magnitude climate events. The record of climate change in the Southern Hemisphere during this time period, however, remains scarce and unevenly distributed. We present new geomorphic, chronological, and equilibrium line altitude (ELA) data from a climatically sensitive mountain glacier at Monte San Lorenzo (47°S), Central Patagonia. Twenty-four new cosmogenic 10Be exposure ages from moraines provide a comprehensive glacial record in the mid-latitudes of South America, which constrain the timing, spatial extent and magnitude of glacial fluctuations during the Antarctic Cold Reversal (ACR, ∼14.5-12.9 ka). Río Tranquilo glacier advanced and reached a maximum extent at 13.9 ± 0.7 ka. Three additional inboard moraines afford statistically similar ages, indicating repeated glacier expansions or marginal fluctuations over the ACR. Our record represents the northernmost robust evidence of glacial fluctuations during the ACR in southern South America, documenting not only the timing of the ACR maximum, but also the sequence of glacier changes within this climate event. Based on ELA reconstructions, we estimate a cooling of >1.6-1.8 °C at the peak of the ACR. The Río Tranquilo record along with existing glacial reconstructions from New Zealand (43°S) and paleovegetation records from northwestern (41°S) and central-west (45°S) Patagonia, suggest an uniform trans-Pacific glacier-climate response to an ACR trigger across the southern mid-latitudes. We posit that the equatorial migration of the southern westerly winds provides an adequate mechanism to propagate a common ACR signal across the Southern Hemisphere.

Multi-millennial record of erosion and fires in the southern Blue Ridge Mountains, USA In: Greenberg, CH and BS Collins (eds.)

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David S. Leigh

2016-01-01

Bottomland sediments from the southern Blue Ridge Mountains provide a coarse-resolution, multi-millennial stratigraphic record of past regional forest disturbance (soil erosion). This record is represented by 12 separate vertical accretion stratigraphic profi les that have been dated by radiocarbon, luminescence, cesium-137, and correlation methods...

Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean

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Lechtenfeld, Oliver J.; Kattner, Gerhard; Flerus, Ruth; McCallister, S. Leigh; Schmitt-Kopplin, Philippe; Koch, Boris P.

2014-02-01

More than 90% of the global ocean dissolved organic carbon (DOC) is refractory, has an average age of 4000-6000 years and a lifespan from months to millennia. The fraction of dissolved organic matter (DOM) that is resistant to degradation is a long-term buffer in the global carbon cycle but its chemical composition, structure, and biochemical formation and degradation mechanisms are still unresolved. We have compiled the most comprehensive molecular dataset of 197 Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses from solid-phase extracted marine DOM covering two major oceans, the Atlantic sector of the Southern Ocean and the East Atlantic Ocean (ranging from 50° N to 70° S). Molecular trends and radiocarbon dating of 34 DOM samples (comprising Δ14C values from -229‰ to -495‰) were combined to model an integrated degradation rate for bulk DOC resulting in a predicted age of >24 ka for the most persistent DOM fraction. First order kinetic degradation rates for 1557 mass peaks indicate that numerous DOM molecules cycle on timescales much longer than the turnover of the bulk DOC pool (estimated residence times of up to ~100 ka) and the range of validity of radiocarbon dating. Changes in elemental composition were determined by assigning molecular formulae to the detected mass peaks. The combination of residence times with molecular information enabled modelling of the average elemental composition of the slowest degrading fraction of the DOM pool. In our dataset, a group of 361 molecular formulae represented the most stable composition in the oceanic environment (“island of stability”). These most persistent compounds encompass only a narrow range of the molecular elemental ratios H/C (average of 1.17 ± 0.13), and O/C (average of 0.52 ± 0.10) and molecular masses (360 ± 28 and 497 ± 51 Da). In the Weddell Sea DOC concentrations in the surface waters were low (46.3 ± 3.3 μM) while the organic radiocarbon was significantly

Microbial Community Structure of Deep-sea Hydrothermal Vents on the Ultraslow Spreading Southwest Indian Ridge

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Jian Ding

2017-06-01

Full Text Available Southwest Indian Ridge (SWIR is a typical oceanic ultraslow spreading ridge with intensive hydrothermal activities. The microbial communities in hydrothermal fields including primary producers to support the entire ecosystem by utilizing geochemical energy generated from rock-seawater interactions. Here we have examined the microbial community structures on four hydrothermal vents from SWIR, representing distinct characteristics in terms of temperature, pH and metal compositions, by using Illumina sequencing of the 16S small subunit ribosomal RNA (rRNA genes, to correlate bacterial and archaeal populations with the nature of the vents influenced by ultraslow spreading features. Epsilon-, Gamma-, Alpha-, and Deltaproteobacteria and members of the phylum Bacteroidetes and Planctomycetes, as well as Thaumarchaeota, Woesearchaeota, and Euryarchaeota were dominant in all the samples. Both bacterial and archaeal community structures showed distinguished patterns compared to those in the fast-spreading East Pacific Ridge or the slow-spreading Mid-Atlantic Ridge as previously reported. Furthermore, within SWIR, the microbial communities are highly correlated with the local temperatures. For example, the sulfur-oxidizing bacteria were dominant within bacteria from low-temperature vents, but were not represented as the dominating group recovered from high temperature (over 300°C venting chimneys in SWIR. Meanwhile, Thaumarchaeota, the ammonium oxidizing archaea, only showed high relative abundance of amplicons in the vents with high-temperature in SWIR. These findings provide insights on the microbial community in ultraslow spreading hydrothermal fields, and therefore assist us in the understanding of geochemical cycling therein.

Simulation of the 1979 spring bloom in the Mid-Atlantic Bight - A coupled physical/biological/optical model

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Gregg, Watson W.; Walsh, John J.

1992-01-01

A coupled physical/biological/optical model is developed for studies of phytoplankton variability in the spring 1979 Mid-Atlantic Bight, as observed by CZCS imagery. The model incorporates advection, mixing, sinking, growth as a function of light, temperature, nutrient availability, and death as a function of ingestion. It produced chlorophyll concentrations within the first attenuated depth within 1 standard deviation of CZCS imagery on large scale. The primary production estimates obtained using this model were within reasonable agreement with those measured in situ.

Implications for anomalous mantle pressure and dynamic topography from lithospheric stress patterns in the North Atlantic Realm

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Schiffer, Christian; Nielsen, Søren Bom

2016-08-01

With convergent plate boundaries at some distance, the sources of the lithospheric stress field of the North Atlantic Realm are mainly mantle tractions at the base of the lithosphere, lithospheric density structure and topography. Given this, we estimate horizontal deviatoric stresses using a well-established thin sheet model in a global finite element representation. We adjust the lithospheric thickness and the sub-lithospheric pressure iteratively, comparing modelled in plane stress with the observations of the World Stress Map. We find that an anomalous mantle pressure associated with the Iceland and Azores melt anomalies, as well as topography are able to explain the general pattern of the principle horizontal stress directions. The Iceland melt anomaly overprints the classic ridge push perpendicular to the Mid Atlantic ridge and affects the conjugate passive margins in East Greenland more than in western Scandinavia. The dynamic support of topography shows a distinct maximum of c. 1000 m in Iceland and amounts <150 m along the coast of south-western Norway and 250-350 m along the coast of East Greenland. Considering that large areas of the North Atlantic Realm have been estimated to be sub-aerial during the time of break-up, two components of dynamic topography seem to have affected the area: a short-lived, which affected a wider area along the rift system and quickly dissipated after break-up, and a more durable in the close vicinity of Iceland. This is consistent with the appearance of a buoyancy anomaly at the base of the North Atlantic lithosphere at or slightly before continental breakup, relatively fast dissipation of the fringes of this, and continued melt generation below Iceland.

Appendix D of the Final Report of the Mid-Atlantic Marine Wildlife Surveys, Modeling, and Data. Workshop to Establish Coordination and Communication

Energy Technology Data Exchange (ETDEWEB)

None

2013-07-01

The Wind Program hosted a two-day workshop on July 24-25, 2012 with scientists and regulators engaged in marine ecological survey, modeling, and database efforts pertaining to the waters of the Mid-Atlantic region. This is the fourth appendix to the report, the presentations from the workshop.

First data on the age of rocks from the central part of the Vitoria-Trindade Ridge (Brazil Basin, South Atlantic)

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Skolotnev, S. G.; Bylinskaya, M. E.; Golovina, L. A.; Ipat'eva, I. S.

2011-03-01

Micropaleontological and isotope-geochronological investigations of calcareous sedimentary rocks and volcanites dredged out from the central portion of the submarine Vitoria-Trindade Ridge during the 24th cruise of R/V Akademik Vavilov have been conducted. It has been established based on micropaleontological analysis, which included determination of the species composition of foraminifera and nannoplankton, that the sequence of sedimentary rocks having a pelagic nature formed on the slopes of the volcanic seamounts in the central portion of the Vitoria-Trindade Ridge from the Early to Mid-Miocene to the Holocene; a good correlation between the degree of lithification of these rocks and their age is observed. It has also been established that the carbonate platforms on the abraded tops of the Davis Seamount and the Dogaressa Bank, which are located in the east-central portion of the Vitoria-Trindade Ridge, started forming in the Early Miocene (19-24 Ma). It has been determined using local U-Pb dating of zircon grains with a SHRIMP-II high resolution secondary ion mass spectrometer that the volcanites forming the upper portion of the volcanic rock sequence of the Jaseur Seamount (29.8 ± 6.6 Ma) located in the west-central portion of the Vitoria-Trindade Ridge date to the Oligocene. The investigations conducted have confirmed the opinion that the Vitoria-Trindade Ridge formed in general because of the activity of the hot spot located under the volcanic Trindade and Martin Vaz Islands. However, separate extended lenticular segments of this ridge existed for a long time as single structures, within which the age of the seamounts was not linearly dependent on the distance from the location of the hot spot. Lenses of hot mantle matter that form at the sublithospheric level as a result of impulses of plume activity and move along with the lithospheric plate play a defining role in the development of individual segments forming the Vitoria-Trindade Ridge.

Zooplankton biomass (displacement volume) data collected in Indian Ocean, Southern Pacific and Southern Atlantic Ocean during Discovery Investigations project from 1931-01-02 to 1951-10-18 by Discovery II, data were acquired from the NMFS-COPEPOD database (NODC Accession 0071064)

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National Oceanic and Atmospheric Administration, Department of Commerce — Zooplankton biomass (displacement volume) data collected in Indian Ocean, Southern Pacific and Southern Atlantic Ocean during Discovery Investigations project from...

Abundant Hydrothermal Venting in the Southern Ocean Near 62°S/159°E on the Australian-Antarctic Ridge

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Baker, E. T.; Hahm, D.; Rhee, T. S.; Park, S. H.; Lupton, J. E.; Walker, S. L.; Choi, H.

2014-12-01

Circum-Antarctic Ridges (CARs) comprise almost one-third of the global Mid-Ocean Ridge, yet remain terra incognita for hydrothermal activity and chemosynthetic ecosystems. The InterRidge Vents Database lists only 3 confirmed (visualized) and 35 inferred (plume evidence) active sites along the ~21,000 km of CARs. Here, we report on a multi-year effort to locate and characterize hydrothermal activity on two 1st-order segments of the Australian-Antarctic Ridge that are perhaps more isolated from other known vent fields than any other vent site on the Mid-Ocean Ridge. KR1 is a 300-km-long segment near 62°S/159°E, and KR2 a 90-km-long segment near 60°S/152.5°E. We used profiles collected by Miniature Autonomous Plume Recorders (MAPRs) on rock corers in March and December of 2011 to survey each segment, and an intensive CTD survey in Jan/Feb 2013 to pinpoint sites and sample plumes on KR1. Optical and oxidation-reduction potential (ORP, aka Eh) anomalies indicate multiple active sites on both segments. Seven profiles on KR2 found 3 sites, each separated by ~25 km. Forty profiles on KR1 identified 13 sites, some within a few km of each other. The densest site concentration on KR1 occurred along a relatively inflated, 90-km-long section near the segment center. CTD tows covered 20 km of the eastern, most inflated portion of this area, finding two 6-km-long zones centered near 158.6°E and 158.8°E with multiple plume anomalies. Three ORP anomalies within 50 m of the seafloor indicate precise venting locations. We call this area the Mujin "Misty Harbor" vent field. Vent frequency sharply decreases away from Mujin. 3He/heat ratios determined from 20 plume samples in the Mujin field were mostly <0.015 fM/J, indicative of chronic venting, but 3 samples, 0.021-0.034 fM/J, are ratios typical of a recent eruption. The spatial density of hydrothermal activity along KR1 and KR2 is similar to other intermediate-rate spreading ridges. We calculate the plume incidence (ph) along

Dropout Prevention Programs in Nine Mid-Atlantic Region School Districts: Additions to a Dropout Prevention Database. Issues & Answers. REL 2011-No. 103

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Burzichelli, Claudia; Mackey, Philip E.; Bausmith, Jennifer

2011-01-01

The current study replicates work of Regional Educational Laboratory (REL) Northeast and Islands. It describes dropout prevention programs in nine Mid-Atlantic Region (Delaware, the District of Columbia, Maryland, New Jersey, and Pennsylvania) school districts serving communities with populations of 24,742-107,250 (as of July 2008). All nine…

Directly measured currents and estimated transport pathways of Atlantic Water between 59.5°N and the Iceland–Faroes–Scotland Ridge

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Katelin H. Childers

2015-11-01

Full Text Available Using vessel-mounted acoustic Doppler current profiler data from four different routes between Scotland, Iceland and Greenland, we map out the mean flow of water in the top 400 m of the northeastern North Atlantic. The poleward transport east of the Reykjanes Ridge (RR decreases from ~8.5 to 10 Sv (1 Sverdrup=106 m3 s−1 at 59.5°N to 61°N to 6 Sv crossing the Iceland–Faroes–Scotland Ridge. The two longest ~1200 km transport integrals have 1.4–0.94 Sv uncertainty, respectively. The overall decrease in transport can in large measure be accounted for by a ~1.5 Sv flow across the RR into the Irminger Sea north of 59.5°N and by a ~0.5 Sv overflow of dense water along the Iceland–Faroes Ridge. A remaining 0.5 Sv flux divergence is at the edge of detectability, but if real could be accounted for through wintertime convection to >400 m and densification of upper ocean water. The topography of the Iceland Basin and the banks west of Scotland play a fundamental role in controlling flow pathways towards and past Iceland, the Faroes and Scotland. Most water flows north unimpeded through the Iceland Basin, some in the centre of the basin along the Maury Channel, and some along Hatton Bank, turning east along the northern slopes of George Bligh Bank, Lousy Bank and Bill Bailey's Bank, whereupon the flow splits with ~3 Sv turning northwest towards the Iceland–Faroes Ridge and the remainder continuing east towards and north of the Wyville-Thomson Ridge (WTR to the Scotland slope thereby increasing the Slope Current transport from ~1.5 Sv south of the WTR to 3.5 Sv in the Faroes–Shetland Channel.

Rift systems in the southern North Atlantic: why did some fail and others not?

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Nirrengarten, M.; Manatschal, G.; Tugend, J.; Kusznir, N. J.; Sauter, D.

2017-12-01

Orphan, Rockall, Porcupine, Parentis and Pyrenean Basins are failed rift systems surrounding the southern North Atlantic Ocean. The failure or succeessing of a rift system is intimately linked to the question of what controls lithospheric breakup and what keeps oceanic spreading alive. Extension rates and the thermal structure are usually the main parameters invoked. However, between the rifts that succeeded and those that failed, the relative control and relative importance of these parameters is not clear. Cessation of driving forces, strain hardening or competition between concurrent rifts are hypotheses often used to explain rift failure. In this work, we aim to analyze the influence of far field forces on the abandon of rift systems in the southern North Atlantic domain using plate kinematic modeling. A new reconstruction approach that integrates the spatio-temporal evolution of rifted basins has been developed. The plate modeling is based on the definition, mapping and restoration of rift domains using 3D gravity inversions methods that provide crustal thickness maps. The kinematic description of each rift system enables us to discuss the local rift evolution relative to the far field kinematic framework. The resulting model shows a strong segmentation of the different rift systems during extreme crustal thinning that are crosscut by V-shape propagators linked to the exhumation of mantle and emplacement of first oceanic crust. The northward propagating lithospheric breakup of the southern North Atlantic may be partly triggered and channeled by extreme lithospheric thinning. However, at Aptian-Albian time, the northward propagating lithospheric breakup diverts and is partitioned along a transtensional system resulting in the abandon of the Orphan and Rockall basins. The change in the propagation direction may be related to a local strain weakening along existing/inherited transfer zones and/or, alternatively, to a more global plate reorganization. The

Anthropocene streams and base-level controls from historic dams in the unglaciated mid-Atlantic region, USA

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Merritts, Dorothy; Walter, Robert; Rahnis, Michael; Hartranft, Jeff; Cox, Scott; Gellis, Allen; Potter, Noel; Hilgartner, William; Langland, Michael; Manion, Lauren; Lippincott, Caitlin; Siddiqui, Sauleh; Rehman, Zain; Scheid, Chris; Kratz, Laura; Shilling, Andrea; Jenschke, Matthew; Datin, Katherine; Cranmer, Elizabeth; Reed, Austin; Matuszewski, Derek; Voli, Mark; Ohlson, Erik; Neugebauer, Ali; Ahamed, Aakash; Neal, Conor; Winter, Allison; Becker, Steven

2011-01-01

Recently, widespread valley-bottom damming for water power was identified as a primary control on valley sedimentation in the mid-Atlantic US during the late seventeenth to early twentieth century. The timing of damming coincided with that of accelerated upland erosion during post-European settlement land-use change. In this paper, we examine the impact of local drops in base level on incision into historic reservoir sediment as thousands of ageing dams breach. Analysis of lidar and field data indicates that historic milldam building led to local base-level rises of 2-5 m (typical milldam height) and reduced valley slopes by half. Subsequent base-level fall with dam breaching led to an approximate doubling in slope, a significant base-level forcing. Case studies in forested, rural as well as agricultural and urban areas demonstrate that a breached dam can lead to stream incision, bank erosion and increased loads of suspended sediment, even with no change in land use. After dam breaching, key predictors of stream bank erosion include number of years since dam breach, proximity to a dam and dam height. One implication of this work is that conceptual models linking channel condition and sediment yield exclusively with modern upland land use are incomplete for valleys impacted by milldams. With no equivalent in the Holocene or late Pleistocene sedimentary record, modern incised stream-channel forms in the mid-Atlantic region represent a transient response to both base-level forcing and major changes in land use beginning centuries ago. Similar channel forms might also exist in other locales where historic milling was prevalent.

Tropospheric mid-latitude geopotential wave characteristics associated with strong wind events in the North Atlantic/European region

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Wild, Simon; Simmonds, Ian; Leckebusch, Gregor C.

2015-04-01

The variability of strong synoptic scale wind events in the mid-latitudes have long been linked to baroclinic wave activity in the mid troposphere. Previous studies have also shown that greater amplitudes of planetary waves in the mid troposphere are likely to increase the occurrence of regional extremes in temperature and precipitation. In this study we examine whether characteristics of planetary and synoptic mid-latitude waves show systematic anomalies in the North Atlantic/ European region which can be related to the occurrence of a strong surface wind event. We will mainly focus on two questions: 1) Do amplitudes for waves with different wave lengths show a systematic anomaly when a strong wind event occurs? 2) Can phases of the individual wave components be detected that favour strong wind events? In order to decompose the mid-tropospheric flow into longitudinal waves we employ the fast Fourier transform to the meridional mean of the geopotential height in 500hPa between 35° and 60°N for i) the entire latitude belt and ii) for a North Atlantic/European sector (36°W to 36°E). Our definition of strong wind events is based on the Storm Severity Index (SSI) alongside a wind tracking algorithm identifying areas of exceedances of the local 98th percentile of the 10m wind speed. First results using ERA-Interim Reanalysis from 1979 - 2014 for the extended winter season (ONDJFM) for the 50 most intense strong wind systems with respect to the SSI reveal a greater amplitude for all investigated wave numbers. Especially waves with wave lengths below 2000km show an increase of about 25% of the daily standard deviation on average. The distribution of wave phases for the different wave numbers with respect to the location of a strong wind event shows a less homogenous picture. There is however a high proportion of events that can be associated with phases around 3π/4 and 5π/4 of waves with lengths of around 6000km, equivalent to wave number 5 on a planetary scale

Decadal Declines of Mercury in Adult Bluefish (1972-2011) from the Mid-Atlantic Coast of the U.S.A.

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Cross, Ford A; Evans, David W; Barber, Richard T

2015-08-04

Concentrations of total mercury were measured in muscle of adult bluefish (Pomatomus saltatrix) collected in 2011 off North Carolina and compared with similar measurements made in 1972. Concentrations of mercury decreased by 43% in the fish between the two time periods, with an average rate of decline of about 10% per decade. This reduction is similar to estimated reductions of mercury observed in atmospheric deposition, riverine input, seawater, freshwater lakes, and freshwater fish across northern North America. Eight other studies between 1973 and 2007 confirm the decrease in mercury levels in bluefish captured in the Mid-Atlantic Bight. These findings imply that (1) reductions in the release of mercury across northern North America were reflected rather quickly (decades) in the decline of mercury in adult bluefish; (2) marine predatory fish may have been contaminated by anthropogenic sources of mercury for over 100 years; and (3) if bluefish are surrogates for other predators in the Mid-Atlantic Bight, then a reduction in the intake of mercury by the fish-consuming public has occurred. Finally, with global emissions of mercury continuing to increase, especially from Asia, it is important that long-term monitoring programs be conducted for mercury in marine fish of economic importance.

Extreme Morphologic and Venting Changes in Methane Seeps at Southern Hydrate Ridge, Cascadia Margin

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Bigham, K.; Kelley, D. S.; Solomon, E. A.; Delaney, J. R.

2017-12-01

Two highly active methane hydrate seeps have been visited over a 7-year period as part of the construction and operation of NSF's Ocean Observatory Initiative's Regional Cable Array at Southern Hydrate Ridge. The site is located 90 km west of Newport, Oregon, at a water depth of 800 m. The seeps, Einstein's Grotto (OOI instrument deployment site) and Smokey Tavern (alternate site to the north), have been visited yearly from 2010 to 2017 with ROVs. Additionally, a digital still camera deployed from 2014 to 2017 at Einstein's Grotto, has been documenting the profound morphologic and biological changes at this site. A cabled pressure sensor, Acoustic Doppler Current Profiler, hydrophone, seismometer array, and uncabled fluid samplers have also been operational at the site for the duration of the camera's deployment. During this time, Einstein's Grotto has evolved from a gentle mound with little venting, to a vigorously bubbling pit bounded by a near vertical wall. Early on bubble emissions blew significant amounts of sediment into the water column and thick Beggiatoa mats coverd the mound. Most recently the face of the pit has collapsed, although bubble plumes are still emitted from the site. The Smokey Tavern site has undergone more extreme changes. Similar to Einstein's Grotto it was first characterized by gentle hummocks with dispersed bacterial mats. In subsequent years, it developed an extremely rugged, elongated collapsed area with vertical walls and jets of methane bubbles rising from small pits near the base of the collapse zone. Meter-across nearly sediment-free blocks of methane hydrate were exposed on the surface and in the walls of the collapse zone. In 2016, this area was unrecognizable with a much more subdued topography, and weak venting of bubbles. Exposed methane hydrate was not visible. From these observations new evolutionary models for methane seeps are being developed for Southern Hydrate Ridge.

Cover Crop-Based, Organic Rotational No-Till Corn and Soybean Production Systems in the Mid-Atlantic United States

Directory of Open Access Journals (Sweden)

John M. Wallace

2017-04-01

Full Text Available Cover crop-based, organic rotational no-till (CCORNT corn and soybean production is becoming a viable strategy for reducing tillage in organic annual grain systems in the mid-Atlantic, United States. This strategy relies on mechanical termination of cover crops with a roller-crimper and no-till planting corn and soybean into cover crop mulches. Here, we report on recent research that focuses on integrated approaches for crop, nutrient and pest management in CCORNT systems that consider system and regional constraints for adoption in the mid-Atlantic. Our research suggests that no-till planting soybean into roller-crimped cereal rye can produce consistent yields. However, constraints to fertility management have produced less consistent no-till corn yields. Our research shows that grass-legume mixtures can improve N-release synchrony with corn demand and also improve weed suppression. Integration of high-residue inter-row cultivation improves weed control consistency and may reduce reliance on optimizing cover crop biomass accumulation for weed suppression. System-specific strategies are needed to address volunteer cover crops in later rotational phases, which result from incomplete cover crop termination with the roller crimper. The paucity of adequate machinery for optimizing establishment of cash crops into thick residue mulch remains a major constraint on CCORNT adoption. Similarly, breeding efforts are needed to improve cover crop germplasm and develop regionally-adapted varieties.

High-resolution model-projected changes in mid-tropospheric closed-lows and extreme rainfall events over southern Africa

CSIR Research Space (South Africa)

Engelbrecht, CJ

2012-01-01

Full Text Available Mid-tropospheric closed-lows (cold-core cut-off lows and warm-core tropical lows) are important rain producing weather systems for the southern Africa region. Over South Africa, most wide-spread flood events are caused by these systems...

Spatial variation of dung beetle assemblages associated with forest structure in remnants of southern Brazilian Atlantic Forest

Directory of Open Access Journals (Sweden)

Pedro Giovâni da Silva

2016-01-01

Full Text Available The Brazilian Atlantic Forest is one of the world's biodiversity hotspots, and is currently highly fragmented and disturbed due to human activities. Variation in environmental conditions in the Atlantic Forest can influence the distribution of species, which may show associations with some environmental features. Dung beetles (Coleoptera: Scarabaeinae are insects that act in nutrient cycling via organic matter decomposition and have been used for monitoring environmental changes. The aim of this study is to identify associations between the spatial distribution of dung beetle species and Atlantic Forest structure. The spatial distribution of some dung beetle species was associated with structural forest features. The number of species among the sampling sites ranged widely, and few species were found in all remnant areas. Principal coordinates analysis indicated that species composition, abundance and biomass showed a spatially structured distribution, and these results were corroborated by permutational multivariate analysis of variance. The indicator value index and redundancy analysis showed an association of several dung beetle species with some explanatory environmental variables related to Atlantic Forest structure. This work demonstrated the existence of a spatially structured distribution of dung beetles, with significant associations between several species and forest structure in Atlantic Forest remnants from Southern Brazil. Keywords: Beta diversity, Species composition, Species diversity, Spatial distribution, Tropical forest

A mid-Pleistocene rainforest corridor enabled synchronous invasions of the Atlantic Forest by Amazonian anole lizards.

Science.gov (United States)

Prates, Ivan; Rivera, Danielle; Rodrigues, Miguel T; Carnaval, Ana C

2016-10-01

Shifts in the geographic distribution of habitats over time can promote dispersal and vicariance, thereby influencing large-scale biogeographic patterns and ecological processes. An example is that of transient corridors of suitable habitat across disjunct but ecologically similar regions, which have been associated with climate change over time. Such connections likely played a role in the assembly of tropical communities, especially within the highly diverse Amazonian and Atlantic rainforests of South America. Although these forests are presently separated by open and dry ecosystems, paleoclimatic and phylogenetic evidence suggest that they have been transiently connected in the past. However, little is known about the timing, magnitude and the distribution of former forest connections. We employ sequence data at multiple loci from three codistributed arboreal lizards (Anolis punctatus, Anolis ortonii and Polychrus marmoratus) to infer the phylogenetic relationships among Amazonian and Atlantic Forest populations and to test alternative historical demographic scenarios of colonization and vicariance using coalescent simulations and approximate Bayesian computation (ABC). Data from the better-sampled Anolis species support colonization of the Atlantic Forest from eastern Amazonia. Hierarchical ABC indicates that the three species colonized the Atlantic Forest synchronously during the mid-Pleistocene. We find support of population bottlenecks associated with founder events in the two Anolis, but not in P. marmoratus, consistently with their distinct ecological tolerances. Our findings support that climatic fluctuations provided key opportunities for dispersal and forest colonization in eastern South America through the cessation of environmental barriers. Evidence of species-specific histories strengthens assertions that biological attributes play a role in responses to shared environmental change. © 2016 John Wiley & Sons Ltd.

The Once and Future North Atlantic: How the Mid-Pliocene Warm Period Can Increase Stakeholder Preparedness in a Warming World

Science.gov (United States)

Jacobs, P.; de Mutsert, K.

2013-12-01

Paleoclimatic reconstructions, particularly from periods that may serve as an analog to the present and future greenhouse-driven warming, are increasingly being used to validate climate models as well as to provide constraints on broad impacts such as global temperature and sea level change. However, paleoclimatic data remains under-utilized in decision-making processes by stakeholders, who typically rely on scenarios produced by computer models or naive extrapolation of present trends. We hope to increase the information available to stakeholders by incorporating paleoclimatic data from the mid-Pliocene Warm Period (mPWP, ~3ma) into a fisheries model of the North Atlantic. North Atlantic fisheries are economically important and are expected to be sensitive to climatic change. State of the art climate models remain unable to realistically simulate the North Atlantic, both over the observational record as well as during times in the geologic past such as the mPWP. Given that the mPWP shares many of the same boundary conditions as those likely to be seen in the near future, we seek to answer the question 'What if the climate of the future looks more like the climate of the past?' relative to what state of the art computer models currently project. To that end we have created a suite of future North Atlantic Ocean scenarios using output from the CMIP3 and CMIP5 modeling experiments, as well as the PRISM group's Mid-Pliocene ocean reconstruction. We use these scenarios to drive an ecosystem-based fisheries model using the Ecopath with Ecosim (EwE) software to identify differences between the scenarios as the North Atlantic Ocean changes through time. Additionally, we examine the spatial component of these differences by using the Ecospace module of EwE. Whereas the Ecosim realizations are intended to capture the dynamic response to changing oceanographic parameters (SST, SSS, DO) over time, the Ecospace experiments are intended to explore the impact of different

New and additional records of Salmoneus Holthuis, 1955 (Decapoda, Caridea, Alpheidae from Brazil, with a key to the southern Atlantic species

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Arthur Anker

2013-01-01

Full Text Available Two species of the alpheid shrimp genus Salmoneus Holthuis, 1955, are reported from shallow waters of São Sebastião (SP, southeastern Brazil. Salmoneus depressus Anker, 2011 is recorded for the first time in Brazil and the southwestern Atlantic; this species was previously known only from the Caribbean region. Salmoneus ortmanni (Rankin, 1898 is recorded for the first time in southern Brazil (23°S, being previously known in Brazilian waters from a single confirmed record from Atol das Rocas (03°S, with older records referring to Salmoneus carvachoi Anker, 2007. A hitherto unknown morphological variation in S. depressus is discussed and illustrated. Both species are shown in colour to facilitate their identification in the field. A key to the southern Atlantic species of Salmoneus is also provided.

Dropout Prevention Programs in Nine Mid-Atlantic Region School Districts: Additions to a Dropout Prevention Database. Summary. Issues & Answers. REL 2011-No. 103

Science.gov (United States)

Burzichelli, Claudia; Mackey, Philip E.; Bausmith, Jennifer

2011-01-01

The current study replicates work of Regional Educational Laboratory (REL) Northeast and Islands. It describes dropout prevention programs in nine Mid-Atlantic Region (Delaware, the District of Columbia, Maryland, New Jersey, and Pennsylvania) school districts serving communities with populations of 24,742-107,250 (as of July 2008). All nine…

The orchid-bee faunas (Hymenoptera: Apidae of two Atlantic Forest remnants in southern Bahia, eastern Brazil

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A Nemésio

Full Text Available The orchid-bee faunas of the ‘Parque Nacional do Pau Brasil’ (8,500 ha and ‘RPPN Estação Veracel’ (6,000 ha, two Atlantic Forest remnants in the southern state of Bahia, northeastern Brazil, were surveyed. Seventeen chemical compounds were used as scent baits to attract orchid-bee males. Seven hundred and twelve males belonging to 20 species were actively collected with insect nets during 80 hours in February and April, 2009. Euglossa marianae Nemésio, 2011, the most sensitive orchid-bee species of the Atlantic Forest, was recorded at both preserves, though in low abundance. ‘RPPN Estação Veracel’ is the smallest forest patch where Euglossa marianae has ever been recorded.

Morphotectonic and petrological variations along the southern Central Indian Ridge

Digital Repository Service at National Institute of Oceanography (India)

Mukhopadhyay, R.; Iyer, S.D.; Ray, Dwijesh; Karisiddaiah, S.M.; Drolia, R.K.

above the DM and Enriched Mantle (EM2) end member and resemble a linear mixing with Indian Ocean pelagic sediments (Fig. 4a, b). By contrast, the isotope data of IOTJ-MORB occupy a distinct field in the radiogenic Pb-Pb and Sr-Pb binary plots... EM, Karsten JL, 1995 Ocean-ridge basalts with convergent-margin geochemical affinities from the Chile Ridge. Nature 374:52-57 Klein EM, Langmuir CH, 1987 Global correlations of ocean ridge basalt chemistry with axial depth and crustal chemistry...

Emergency Contraceptive Pills: A 10-Year Follow-up Survey of Use and Experiences at College Health Centers in the Mid-Atlantic United States

Science.gov (United States)

Miller, Laura McKeller; Sawyer, Robin G.

2006-01-01

The authors conducted a 10-year follow-up study using a telephone survey to investigate the availability of emergency contraceptive pills (ECPs) at college health centers in the mid-Atlantic region of the United States. They also examined related issues, such as distribution procedure, existence of a written protocol, personnel involved,…

Distributions of dissolved trace metals (Cd, Cu, Mn, Pb, Ag in the southeastern Atlantic and the Southern Ocean

Directory of Open Access Journals (Sweden)

M. Boye

2012-08-01

Full Text Available Comprehensive synoptic datasets (surface water down to 4000 m of dissolved cadmium (Cd, copper (Cu, manganese (Mn, lead (Pb and silver (Ag are presented along a section between 34° S and 57° S in the southeastern Atlantic Ocean and the Southern Ocean to the south off South Africa. The vertical distributions of Cu and Ag display nutrient-like profiles similar to silicic acid, and of Cd similar to phosphate. The distribution of Mn shows a subsurface maximum in the oxygen minimum zone, whereas Pb concentrations are rather invariable with depth. Dry deposition of aerosols is thought to be an important source of Pb to surface waters close to South Africa, and dry deposition and snowfall may have been significant sources of Cu and Mn at the higher latitudes. Furthermore, the advection of water masses enriched in trace metals following contact with continental margins appeared to be an important source of trace elements to the surface, intermediate and deep waters in the southeastern Atlantic Ocean and the Antarctic Circumpolar Current. Hydrothermal inputs may have formed a source of trace metals to the deep waters over the Bouvet Triple Junction ridge crest, as suggested by relatively enhanced dissolved Mn concentrations. The biological utilization of Cu and Ag was proportional to that of silicic acid across the section, suggesting that diatoms formed an important control over the removal of Cu and Ag from surface waters. However, uptake by dino- and nano-flagellates may have influenced the distribution of Cu and Ag in the surface waters of the subtropical Atlantic domain. Cadmium correlated strongly with phosphate (P, yielding lower Cd / P ratios in the subtropical surface waters where phosphate concentrations were below 0.95 μM. The greater depletion of Cd relative to P observed in the Weddell Gyre compared to the Antarctic Circumpolar Current could be due to increase Cd uptake induced by iron-limiting conditions in these high

Geophysical studies of aseismic ridges in northern Indian Ocean-crustal structure and isostatic models

Digital Repository Service at National Institute of Oceanography (India)

Sreejith, K.M.

. The important conclusions derived from this study are as follows. 1. The Comorin Ridge extends for about 500 km in NNW-SSE direction in north central Indian Ocean, close to the southern tip of India and western continental margin of Sri Lanka. The ridge... topography has variable reliefs along its strike and uneven gradients on both sides of the ridge flanks. The southern part of the ridge (between 1.5°N and 3°N) has an elevation of up to 0.5 km from the adjacent seafloor of about 4 km deep; in the central...

What English Language Arts, Math, and Science Instructional Materials Have Districts in the Mid-Atlantic Region States Adopted? Issues & Answers. REL 2010-No. 096

Science.gov (United States)

Burzichelli, Claudia; Morrill, William; Bausmith, Jennifer; Mackey, Philip E.; Magarelli, Christopher

2010-01-01

Despite increasing accountability requirements and a national call for transparency in public policy, Mid-Atlantic Region state education agencies indicate that they have little information about what instructional materials districts adopt. This report describes first-year results of an ongoing project to generate and share information on core…

First insights into genus level diversity and biogeography of deep sea benthopelagic calanoid copepods in the South Atlantic and Southern Ocean

Science.gov (United States)

Renz, Jasmin; Markhaseva, Elena L.

2015-11-01

Calanoid copepods constitute the most numerous organisms not only in the pelagic realm, but also in the benthic boundary layer, which gives them an important role in the turnover of organic matter in the benthopelagic habitat. During seven expeditions to the South Atlantic and Southern Ocean, the diversity and biogeography of deep-sea benthopelagic calanoid copepods were studied. The communities of calanoids living in the vicinity of the seabed were characterized by high diversity comparable to many pelagic habitats, but low abundance of individuals. Members of the taxon Clausocalanoidea dominated the communities, and within this taxon most individuals belonged to detritivore calanoids characterized by sensory setae on the second maxillae or aetideid copepods. 73% of all genera classified as obligate or predominantly benthopelagic copepods detected during these expeditions were new to science and a vast number of genera and species have been described since then. Comparing the communities of calanoid genera between different regions, the assemblages in the Southern Ocean differed significantly from the Southeast and Southwest Atlantic. A latitudinal diversity gradient could be observed, with highest numbers of genera in the Southwest Atlantic and low numbers at stations in the Southern Ocean. Reviewing the literature, endemism for benthopelagic calanoids appeared to be low on a latitudinal range caused by connectivity in benthopelagic habitats through spreading water masses. However, considering the habitats structuring the water column vertically, a high number of genera are endemic in the benthopelagial and specialized to living within the vicinity of the seabed.

Sociocultural dimensions of supply and demand for natural aggregate; examples from the Mid-Atlantic region, United States

Science.gov (United States)

Robinson, Gilpin R.; Brown, William M.

2002-01-01

The United States uses large quantities of natural aggregate to build and maintain a continuously expanding infrastructure. In recent years, per capita demand for aggregate in the United States has grown to about 9.7 metric tons (10.7 tons) per person per year. Over the next 25 years, the aggregate industry expects to mine quantities equivalent to all aggregate mined in the United States over the past 100 years. The issues surrounding supply and demand for aggregate in the mid-Atlantic states of Maryland, Pennsylvania, Virginia, and West Virginia illustrate competing requirements for industrial minerals and many simultaneous social and environmental objectives.

Conceptual ecological model for management of breeding shrubland birds in the Mid-Atlantic Region

Science.gov (United States)

Peterjohn, Bruce G.

2006-01-01

While grassland birds have become the focus of increased conservation activities, the status of birds occupying shrubland habitats has received relatively little attention (Hunter et al. 2001). Yet, in eastern North America, shrubland birds exhibited consistent population declines during the past 40 years, based on data from the North American Breeding Bird Survey (Pardieck and Sauer 2001). These population declines primarily reflect large-scale changes in land use patterns during the previous century (Lorimer 2001). Large areas of marginal farmland were abandoned and underwent secondary succession during the first half of the twentieth century, producing abundant successional habitats favored by shrubland birds. As these habitats matured, combined with strict fire-suppression policies (Hunter et al. 2001), shrublands succeeded into mature forests, and shrubland bird communities were replaced by woodland birds (Irland 1982; Askins 1993). For example, while nearly 29% of New England forests were classified as sapling stage in 1950, only 8% remained at that stage in the 1980s (Askins 1993). The trend towards forest maturation and loss of shrubland habitats continues, yet concerted conservation activities have not been directed to benefit declining shrubland bird populations. The National Park Service (NPS) could contribute to shrubland bird conservation in the Mid- Atlantic Region. The NPS maintains a number of historic sites and former battlefields managed for their cultural significance but also support wildlife populations. Many of these “cultural parks” maintain open landscapes, recreating land use patterns existing at the times of the historical events. While these open landscapes are frequently managed grasslands, some parks also support successional habitats that could be managed to benefit shrubland birds. In 2005, the NPS initiated a project exploring the potential of “cultural parks” to support significant breeding grassland and shrubland bird

The Mozambique Ridge: a document of massive multistage magmatism

Science.gov (United States)

Fischer, Maximilian D.; Uenzelmann-Neben, Gabriele; Jacques, Guillaume; Werner, Reinhard

2017-01-01

The Mozambique Ridge, a prominent basement high in the southwestern Indian Ocean, consists of four major geomorphological segments associated with numerous phases of volcanic activity in the Lower Cretaceous. The nature and origin of the Mozambique Ridge have been intensely debated with one hypothesis suggesting a Large Igneous Province origin. High-resolution seismic reflection data reveal a large number of extrusion centres with a random distribution throughout the southern Mozambique Ridge and the nearby Transkei Rise. Intrabasement reflections emerge from the extrusion centres and are interpreted to represent massive lava flow sequences. Such lava flow sequences are characteristic of eruptions leading to the formation of continental and oceanic flood basalt provinces, hence supporting a Large Igneous Province origin of the Mozambique Ridge. We observe evidence for widespread post-sedimentary magmatic activity that we correlate with a southward propagation of the East African Rift System. Based on our volumetric analysis of the southern Mozambique Ridge we infer a rapid sequential emplacement between ˜131 and ˜125 Ma, which is similar to the short formation periods of other Large Igneous Provinces like the Agulhas Plateau.

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.

Tornado Strikes Southern Maryland

Science.gov (United States)

2002-01-01

Evening light catches the tops of towering thunderheads over the Mid-Atlantic states on April 28, 2002. The powerful storms spawned several tornados, one of which was classified as an F4 tornado. The powerful tornado touched down in the southern Maryland town of La Plata, destroying most of the historic downtown. The twister-one of the strongest ever to hit the state-beat a 24-mile swath running west to east through the state and claimed at least three lives. The image above was taken by the Geostationary Operational Environmental Satellite (GOES) at 7:15 PM Eastern Daylight Savings Time. A large version of the animation shows more detail. (5.9 MB Quicktime) Image courtesy National Oceanic and Atmospheric Administration (NOAA) and the GOES Project Science Office. Animation by Robert Simmon, NASA GSFC.

Volcanic eruption of the mid-ocean ridge along the East Pacific Rise crest at 9°45-52'N: direct submersible observations of seafloor phenomena associated with an eruption event in April, 1991

Science.gov (United States)

Haymon, R.M.; Fornari, D.J.; Von Damm, Karen L.; Lilley, M.D.; Perfit, M.R.; Edmond, J.M.; Shanks, Wayne C.; Lutz, R.A.; Grebmeier, J.M.; Carbotte, S.; Wright, D.; McLaughlin, E.; Smith, M.; Beedle, N.; Olson, E.

1993-01-01

In April, 1991, we witnessed from the submersible Alvin a suite of previously undocumented seafloor phenomena accompanying an in-progress eruption of the mid-ocean ridge on the East Pacific Rise crest at 9°45′N–52′N. The volume of the eruption could not be precisely determined, although comparison of pre- and post-eruption SeaBeam bathymetry indicate that any changes in ridge crest morphology resulting from the eruption were < 10 m high.

What English Language Arts, Math, and Science Instructional Materials Have Districts in the Mid-Atlantic Region States Adopted? Summary. Issues & Answers. REL 2010-No. 096

Science.gov (United States)

Burzichelli, Claudia; Morrill, William; Bausmith, Jennifer; Mackey, Philip E.; Magarelli, Christopher

2010-01-01

Despite increasing accountability requirements and a national call for transparency in public policy, Mid-Atlantic Region state education agencies indicate that they have little information about what instructional materials districts adopt. This report describes first-year results of an ongoing project to generate and share information on core…

Geophysical Investigation of Upper Mantle Anomalies of the Australian-Antarctic Ridge

Science.gov (United States)

Park, S. H.; Choi, H.; Kim, S. S.; Lin, J.

2017-12-01

Australian-Antarctic Ridge (AAR) is situated between the Pacific-Antarctic Ridge (PAR) and Southeast Indian Ridge (SEIR), extending eastward from the Australian-Antarctic Discordance (AAD). Much of the AAR has been remained uncharted until 2011 because of its remoteness and harsh weather conditions. Since 2011, four multidisciplinary expeditions initiated by the Korea Polar Research Institute (KOPRI) have surveyed the little-explored eastern ends of the AAR and investigated the tectonics, geochemistry, and hydrothermal activity of this intermediate spreading system. Recent isotope studies using the new basalt samples from the AAR have led to the new hypothesis of the Southern Ocean mantle domain (SOM), which may have originated from the super-plume activity associated with the Gondwana break-up. In this study, we characterize the geophysics of the Southern Ocean mantle using the newly acquired shipboard bathymetry and available geophysical datasets. First, we computed residual mantle Bouguer gravity anomalies (RMBA), gravity-derived crustal thickness, and residual topography along the AAR in order to obtain a geological proxy for regional variations in magma supply. The results of these analyses revealed that the southern flank of the AAR is associated with shallower seafloor, more negative RMBA, thicker crust, and/or less dense mantle in comparison to the conjugate northern flank. Furthermore, this north-south asymmetry becomes more prominent toward the central ridge segments of the AAR. Interestingly, the along-axis depths of the entire AAR are significantly shallower than the neighboring ridge systems and the global ridges of intermediate spreading rates. Such shallow depths are also correlated with regional negative geoid anomalies. Furthermore, recent mantle tomography models consistently showed that the upper mantle (< 250 km) below the AAR has low S-wave velocities, suggesting that it may be hotter than the nearby ridges. Such regional-scale anomalies of the

Crustal processes of the Mid-Ocean Ridge

Science.gov (United States)

Ballard, Richard D.; Craig, H.; Edmond, J.; Einaudi, M.; Holcomb, R.; Holland, H.D.; Hopson, C.A.; Luyendyk, B.P.; Macdonald, K.; Morton, J.; Orcutt, J.; Sleep, N.

1981-01-01

Independent geological and geophysical investigations of the Mid-Ocean Ridge system have begun to focus on the nature of the magma chamber system underlying its central axis. Thermal models predict the existence of a steady-state chamber beneath a thin crustal lid ranging in thickness from 2 to 13 kilometers. The only aspect of the system that these models fail to account for is the extremely slow spreading rates. Seismological studies reveal the existence of a low-velocity zone beneath segments of the East Pacific Rise, which is thought to correspond to a chamber system having a half-width of approximately 5 to 10 kilometers. These estimates compare favorably with those derived separately through petrological investigations of deep-sea drilling results, various sampling programs, and field and laboratory studies of ophiolites. The chamber is thought to be wing-shaped and to remain continuously open; it is thought to be fed from the center while simultaneously solidifying at the sides as spreading carries the two halves apart. Progressive fractionation occurs by crystal settling coupled with repeated replenishment and magma mixing in an open steady-state system. Near-bottom studies reveal that the zone of extrusion above the chamber is narrow, but its eruptive history is cyclic in nature, in conflict with the predictions of a steady-state model. On-bottom gravity data at 21 ??N on the East Pacific Rise reveal a negative gravity anomaly that may be related to the uppermost part of the chamber. The anomaly is only 2 kilometers wide and 1 kilometer below the sea floor. This feature may be associated with a short-term upper magma reservoir. The cyclic volcanic activity is directly related to the active phase of hydrothermal circulation responsible for the observed negative thermal anomaly. The volume of water associated with this circulation is equal to the entire ocean volume passing through the accretion zone approximately every 8 million years. This is about 0

Crustal processes of the mid-ocean ridge.

Science.gov (United States)

1981-07-03

Independent geological and geophysical investigations of the Mid-Ocean Ridge system have begun to focus on the nature of the magma chamber system underlying its central axis. Thermal models predict the existence of a steady-state chamber beneath a thin crustal lid ranging in thickness from 2 to 13 kilometers. The only aspect of the system that these models fail to account for is the extremely slow spreading rates. Seismological studies reveal the existence of a low-velocity zone beneath segments of the East Pacific Rise, which is thought to correspond to a chamber system having a half-width of approximately 5 to 10 kilometers. These estimates compare favorably with those derived separately through petrological investigations of deep-sea drilling results, various sampling programs, and field and laboratory studies of ophiolites. The chamber is thought to be wing-shaped and to remain continuously open; it is thought to be fed from the center while simultaneously solidifying at the sides as spreading carries the two halves apart. Progressive fractionation occurs by crystal settling coupled with repeated replenishment and magma mixing in an open steady-state system. Near-bottom studies reveal that the zone of extrusion above the chamber is narrow, but its eruptive history is cyclic in nature, in conflict with the predictions of a steady-state model. On-bottom gravity data at 21 degrees N on the East Pacific Rise reveal a negative gravity anomaly that may be related to the uppermost part of the chamber. The anomaly is only 2 kilometers wide and 1 kilometer below the sea floor. This feature may be associated with a short-term upper magma reservoir. The cyclic volcanic activity is directly related to the active phase of hydrothermal circulation responsible for the observed negative thermal anomaly. The volume of water associated with this circulation is equal to the entire ocean volume passing through the accretion zone approximately every 8 million years. This is about 0

Variations in deep-sea hydrothermal vent communities on the Mid-Atlantic Ridge near the Azores plateau

Science.gov (United States)

Desbruyères, D.; Biscoito, M.; Caprais, J.-C.; Colaço, A.; Comtet, T.; Crassous, P.; Fouquet, Y.; Khripounoff, A.; Le Bris, N.; Olu, K.; Riso, R.; Sarradin, P.-M.; Segonzac, M.; Vangriesheim, A.

2001-05-01

Near the Azores Triple Junction as the Azores Plateau is approached, the ridge axis becomes shallower; its depth decreases from ca. 2400 m in the R AINBOW vent field (36°13'N) to ca. 850 m in the M ENEZ G WEN vent field (37°35'N). In this area, extensive mussel beds of the mytilid Bathymodiolus azoricus dominate the hydrothermal vent fauna, along with populations of three shrimps ( Rimicaris exoculata, Mirocaris fortunata and Chorocaris chacei). The main physical and chemical characteristics of the vent habitat were studied by discrete sampling, in situ analysis and sediment trap moorings. The vent fauna is distributed along a variable band where the vent fluids and seawater mix, with R. exoculata living in the most concentrated areas and Bathymodiolus azoricus in the most diluted zones. Various non-endemic species live at the border of the vent field. The variations observed in structure and composition of the communities along the depth gradient are most likely due to changes in vent fluid toxicity (metallic and sulphide content) and suspended mineral particles, which render the fluids harsher for species living there. The main faunal differences observed between L UCKY S TRIKE and M ENEZ G WEN hydrothermal fields are due to an impoverishment in the hydrothermal endemic species and to the penetration of bathyal species. The comparison of the three studied vent fields suggests the existence of a succession of several biogeographic islands rather than a single province.

An Investigation of the Relationship between the Components of School Climate and Leadership Behaviors on Student Achievement: Urban School Districts in the Mid-Atlantic Region

Science.gov (United States)

Collins, Karmen J.

2015-01-01

The purpose of this research study was to investigate the relationship between the components of school climate and leadership behaviors on student achievement in an urban school district in the mid-atlantic region. School climate and leadership behaviors for the participating school districts was determined by the School Climate Survey (Corner…

Observed and modeled pathways of the Iceland Scotland Overflow Water in the eastern North Atlantic

Science.gov (United States)

Zou, Sijia; Lozier, Susan; Zenk, Walter; Bower, Amy; Johns, William

2017-12-01

The spreading of Iceland Scotland Overflow Water (ISOW) in the eastern North Atlantic has largely been studied in an Eulerian frame using numerical models or with observations limited to a few locations. No study to date has provided a comprehensive description of the ISOW spreading pathways from both Eulerian and Lagrangian perspectives. In this paper, we use a combination of previously unreported current meter data, hydrographic data, RAFOS float data, and a high resolution (1/12°) numerical ocean model to study the spreading pathways of ISOW from both of these perspectives. We identify three ISOW transport cores in the central Iceland Basin (∼59°N), with the major core along the eastern boundary of the Reykjanes Ridge (RR) and the other two in the basin interior. Based on trajectories of observed and/or numerical floats seeded along 59°N, we also describe the ISOW spreading pathways and quantify their relative importance. Within 10 years, 7-11% of ISOW from 59°N escapes into the Irminger Sea via gaps in the RR north of the Charlie Gibbs Fracture Zone (CGFZ); the water that moves through these gaps principally originates from the shallower ISOW layer along the RR eastern boundary. 10-13% travels further southward until the CGFZ, where it crosses westward into the western subpolar gyre. 18-21% of ISOW spreads southward along the eastern flank of the Mid-Atlantic Ridge into the Western European Basin (WEB). Most of the remaining water stays in the Iceland Basin over the 10-year period. A model-based investigation provides a first look at the temporal variability of these ISOW pathways. We find that the fraction of southward water exported into the WEB is anti-correlated with the export through the CGFZ, a result assumed to reflect these pathways' interactions with the North Atlantic Current in magnitude and/or position shift.

The Mysterious Southern Torque

Science.gov (United States)

McDowell, M. S.

2004-05-01

Something weird happened to twist the southern hemisphere out of alignment with the northern, as evidenced by the positions of the mountain ranges of North and South America, the Atlantic MAR, and the closure of West Africa to North America - all smooth were the torque reversed. What happened, and when, and why? We identify a number of global "cracks" of almost exactly the same length and direction, with some, even more peculiarly, turning the same angle, and proceeding an equal distance in the new direction. The Emperor-Hawaiian chain, the Louisville chain and the west coast of North America, as examples, are essentially parallel. Their northerly legs follow the angle of the axis of orbital ellipse. But then they all make equal 45 degree easterly bends, to 17.5 NW, and continue on, still parallel, for very similar distances. It is the same at the north coast of South America, and the mid-section of the MAR from 46W to 12W. It is the distance from the Cameroons to Kenya, from the south end of the Red Sea to the SE Indian Ridge at the Nema Fracture zone, from west to east of the Nazca plate.What is all this? Coincidence? Seeing things? Researchers have attributed plate motion or hot spot motion or both or absolutely none, to all of the above. Geophysicists have dated the surfaces from Archean to Pleistocene by all possible scientific means, certainly no possible correlation can be made. Yet we postulate the physical reality can be demonstrated. It is so global a phenomenon that it is well beyond what a hot spot or a plate could do. Even a really tremendous impact would have trouble making such precise geometric arrangements. So what is it - perhaps the angle of rotation, or the inertia of northern hemisphere mass above the geoid? And if so, then, what changed it? It would seem that some huge imbalance occurred. Suppose the whole bottom blew out of the southern hemisphere, and the center of mass drastically altered. Suppose some unknown universal force changed our

Unexpected HIMU-type late-stage volcanism on the Walvis Ridge

Science.gov (United States)

Homrighausen, S.; Hoernle, K.; Geldmacher, J.; Wartho, J.-A.; Hauff, F.; Portnyagin, M.; Werner, R.; van den Bogaard, P.; Garbe-Schönberg, D.

2018-06-01

Volcanic activity at many oceanic volcanoes, ridges and plateaus often reawakens after hiatuses of up to several million years. Compared to the earlier magmatic phases, this late-stage (rejuvenated/post-erosional) volcanism is commonly characterized by a distinct geochemical composition. Late-stage volcanism raises two hitherto unanswered questions: Why does volcanism restart after an extended hiatus and what is the origin of this volcanism? Here we present the first 40Ar/39Ar age and comprehensive trace element and Sr-Nd-Pb-Hf isotopic data from seamounts located on and adjacent to the Walvis Ridge in the South Atlantic ocean basin. The Walvis Ridge is the oldest submarine part of the Tristan-Gough hotspot track and is famous as the original type locality for the enriched mantle one (EM I) end member. Consistent with the bathymetric data, the age data indicates that most of these seamounts are 20-40 Myr younger than the underlying or nearby Walvis Ridge basement. The trace element and isotope data reveal a distinct compositional range from the EM I-type basement. The composition of the seamounts extend from the St. Helena HIMU (high time-integrated 238U/204Pb mantle with radiogenic Pb isotope ratios) end member to an enriched (E) Mid-Ocean-Ridge Basalt (MORB) type composition, reflecting a two-component mixing trend on all isotope diagrams. The EMORB end member could have been generated through mixing of Walvis Ridge EM I with normal (N) MORB source mantle, reflecting interaction of Tristan-Gough (EM I-type) plume melts with the upper mantle. The long volcanic quiescence and the HIMU-like geochemical signature of the seamounts are unusual for classical hotspot related late-stage volcanism, indicating that these seamounts are not related to the Tristan-Gough hotspot volcanism. Two volcanic arrays in southwestern Africa (Gibeon-Dicker Willem and Western Cape province) display similar ages to the late-stage Walvis seamounts and also have HIMU-like compositions

A Review of ENSO Influence on the North Atlantic. A Non-Stationary Signal

Directory of Open Access Journals (Sweden)

Belén Rodríguez-Fonseca

2016-06-01

Full Text Available The atmospheric seasonal cycle of the North Atlantic region is dominated by meridional movements of the circulation systems: from the tropics, where the West African Monsoon and extreme tropical weather events take place, to the extratropics, where the circulation is dominated by seasonal changes in the jetstream and extratropical cyclones. Climate variability over the North Atlantic is controlled by various mechanisms. Atmospheric internal variability plays a crucial role in the mid-latitudes. However, El Niño-Southern Oscillation (ENSO is still the main source of predictability in this region situated far away from the Pacific. Although the ENSO influence over tropical and extra-tropical areas is related to different physical mechanisms, in both regions this teleconnection seems to be non-stationary in time and modulated by multidecadal changes of the mean flow. Nowadays, long observational records (greater than 100 years and modeling projects (e.g., CMIP permit detecting non-stationarities in the influence of ENSO over the Atlantic basin, and further analyzing its potential mechanisms. The present article reviews the ENSO influence over the Atlantic region, paying special attention to the stability of this teleconnection over time and the possible modulators. Evidence is given that the ENSO–Atlantic teleconnection is weak over the North Atlantic. In this regard, the multidecadal ocean variability seems to modulate the presence of teleconnections, which can lead to important impacts of ENSO and to open windows of opportunity for seasonal predictability.

Magma production rate along the Ninetyeast Ridge and its relationship to Indian plate motion and Kerguelen hot spot activity

Digital Repository Service at National Institute of Oceanography (India)

Sreejith, K.M.; Krishna, K.S.

production rate along the Walvis Ridge in the Atlantic Ocean. The present study suggests that variations in the Indian plate motion and frequent ridge jumps have a major role in controlling the magma production, particularly on long-period cycles (~16 Myr...

Chaparral in southern and central coastal California in the mid-1990s: area, ownership, condition, and change.

Science.gov (United States)

Jeremy S. Fried; Charles L. Bolsinger; Debby Beardsley

2004-01-01

This report summarizes an inventory of chaparral-dominated lands in southern California conducted during the mid-1990s and provides a review of contemporary literature on the ecological dynamics of chaparral vegetation with emphases on stand development, species composition, and the role of fire. Detailed tables provide estimates of chaparral area by owner, type, size...

Water content within the oceanic upper mantle of the Southwest Indian Ridge: a FTIR analysis of orthopyroxenes of abyssal peridotites

Science.gov (United States)

Li, W.; Li, H.; Tao, C.; Jin, Z.

2013-12-01

Water can be present in the oceanic upper mantle as structural OH in nominally anhydrous minerals. Such water has marked effects on manlte melting and rheology properties. However, the water content of MORB source is mainly inferred from MORB glass data that the water budget of oceanic upper mantle is poorly constrained. Here we present water analysis of peridotites from different sites on the Southwest Indian Ridge. The mineral assemblages of these peridotites are olivine, orthopyroxene, clinopyroxene and spinel. As the peridotites have been serpentinized to different degrees, only water contents in orthopyroxnene can be better determined by FTIR spectrometry. The IR absorption bands of all measured orthopyroxenes can be devided into four different groups: (1)3562-3596 cm-1, (2)3515-3520 cm-1, (3)3415-3420 cm-1, (4)3200-3210 cm-1. The positions of these absorption bands are in good agreement with perivious reports. Hydrogen profile measurements performed on larger opx grains in each suite of samples show no obvious variations between core and rims regions, indicating that diffusion of H in orthopyroxene is insignificant. Preliminary measured water contents of orthopyroxene differ by up to one order of magnitude. Opx water contents (80-220 ppm) of most samples are within the range of those found in mantle xenoliths of contentinal settings [1]. Opx water contents of one sample (VM-21V-S9-D5-2: 38-64 ppm) are similar to those from Gakkel Ridge abyssal peridotites (25-60 ppm) [2] but higher than those from Mid-Atlantic Ridge ODP-Leg 209(~15 ppm) [3]. Two other samples show high water concentrations (VM-19ΙΙΙ-S3-TVG2-4: 260-275 ppm, Wb-18-b: 190-265 ppm) which compare well with those from Mid-Atlantic Ridge ODP-Leg 153(160-270 ppm) [4]. Most opx water contents decrease with increasing depletion degree (spl Cr#) consistent with an incompatible behavior of water during partial melting. Recalculated bulk water contents (27-117 ppm) of these peridotites overlap

Amphibians of Serra Bonita, southern Bahia: a new hotpoint within Brazil's Atlantic Forest hotspot.

Science.gov (United States)

Dias, Iuri Ribeiro; Medeiros, Tadeu Teixeira; Vila Nova, Marcos Ferreira; Solé, Mirco

2014-01-01

We studied the amphibian community of the Private Reserve of Natural Heritage (RPPN) Serra Bonita, an area of 20 km(2) with steep altitudinal gradients (200-950 m a.s.l.) located in the municipalities of Camacan and Pau-Brasil, southern Bahia State, Brazil. Data were obtained at 38 sampling sites (including ponds and transects within the forest and in streams), through active and visual and acoustic searches, pitfall traps, and opportunistic encounters. We recorded 80 amphibian species distributed in 15 families: Aromobatidae (1), Brachycephalidae (3), Bufonidae (4), Centrolenidae (2), Ceratophryidae (1), Craugastoridae (7), Eleutherodactylidae (2), Hemiphractidae (2), Hylidae (42), Hylodidae (1), Leptodactylidae (7), Microhylidae (3), Siphonopidae (1), Odontophrynidae (3) and Pipidae (1). Species richness was positively correlated with monthly rainfall. Near 36% of the species were found in strictly forest environments, 15% are endemic to Bahia State and 77.2% are endemic to the Atlantic Forest biome. The large species diversity of this small area, the high degree of endemism and the taxonomic and biogeographic significance turn the Serra Bonita mountain into a hotpoint for amphibians within Brazil's Atlantic Forest hotspot.

Organic storage of CO/sub 2/ on the continental slope off the mid-Atlantic bight, the southeastern Bering Sea, and the Peru coast

Energy Technology Data Exchange (ETDEWEB)

Walsh, J.J.; Premuzic, E.T.; Gaffney, J.S.; Rowe, G.T.; Harbottle, G.; Stoenner, R.W.; Balsam, W.L.; Betzer, P.R.; Macko, S.A.

1985-01-01

A comparison is made of organic content, sedimentation rates derived from /sup 14/C and /sup 210/Pb analyses, /sup 13/C and /sup 15/N isotope ratios, amorphous silica, particle size, and calcium carbonate within sediments from slopes off the mid-Atlantic bight, the southeastern Bering Sea, and the Peru coast. These sediments are mainly marine, diatom-rich, and about one-third of the organic carbon is recent, reflecting a possible transient of shelf export in response to man's increased activities since the industrial revolution. Using a combination of sedimentation and mixing rates of carbon, the C:N ratio of sediments within the upper 50 cm, and the amount of nitrogen thought to be released from the coastal zone, independent estimates suggest a carbon loading to world slopes of approx. 0.3 to 0.5 x 10/sup 9/ tons C y/sup -1/. The Bering slope exhibits no anthropogenic transients, however, while increased carbon loading may have occurred off Peru in response to overfishing and off the mid-Atlantic bight in response to eutrophication. The generality of their results depends on which of the three systems is most representative of world slopes.

Uniformity and diversity in the composition of mineralizing fluids from hydrothermal vents on the southern Juan de Fuca Ridge.

Science.gov (United States)

Philpotts, J.A.; Aruscavage, P. J.; Von Damm, Karen L.

1987-01-01

Abundances of Li, Na, K, Rb, Ca, Sr, Ba, Mn, Fe, Zn, and Si have been determined in fluid samples from 7 vents located in three areas on the southern Juan de Fuca Ridge. The hydrothermal component estimated from the Mg contents of the samples ranges from 7% to 76%. Concentrations of Fe and Si, among other elements, in acid-stabilized solutions appear to be generally representative of the parental hydrothermal fluids, but some Zn determinations and most Ba values appear to be too low.-from Authors

Effects of Watershed Land Use and Geomorphology on Stream Low Flows During Severe Drought Conditions in the Southern Blue Ridge Mountains, Georgia and North Carolina, United States

Science.gov (United States)

Land use and physiographic variability influence stream low flows, yet their interactions and relative influence remain unresolved. Our objective was to assess the influence of land use and watershed geomorphic characteristics on low-flow variability in the southern Blue Ridge Mo...

Impact of the invasive brown marmorated stink bug, Halyomorpha halys (Stal) in Mid-Atlantic tree fruit orchards in the United States: case studies of commercial management

Science.gov (United States)

Four commercial orchards in the mid-Atlantic region of the United States were surveyed weekly in 2010 and 2011 for the presence of brown marmorated stink bug and the injury caused to both apple and peaches. Among tested sampling techniques, baited pyramid traps yielded the most brown marmorated sti...

Further Interpretation of the Relationship between Faunal Community and Seafloor Geology at Southern Hydrate Ridge, Cascadia Margin: Exploring Machine Learning

Science.gov (United States)

Bigham, K.; Kelley, D. S.; Marburg, A.; Delaney, J. R.

2017-12-01

In 2011, high-resolution, georeferenced photomoasiacs were taken of Einstein's Grotto, an active methane hydrate seep within the field at Southern Hydrate Ridge located 90 km west of Newport, Oregon at a water depth of 800 m. Methods used to analyze the relationships between the seep site, seafloor geology, and the spatial distribution and abundances of microbial and macrofaunal communities at Einstein's Grotto were expanded to three other sites over the 200 by 300 m active seep field. These seeps were documented in the same survey in 2011 conducted by the remotely operated vehicle ROPOS on board the R/V Thompson. Over 10,000 high definition images allowed for the further quantification and characterization of the diversity and structure of the faunal community at this seep field. The new results support the study's initial findings of high variability in the distribution and abundance of seep organisms across the field, with correlation to seafloor geology. The manual classification of organisms was also used to train a series of convolutional neural networks in Nvidia DIGITS and Google Tensorflow environments for automated identification. The developed networks proved highly accurate at background/non-background segmentation ( 96%) and slightly less reliable for fauna identification ( 89%). This study provides a baseline for the faunal community at the Southern Hydrate Ridge methane seeps and a more efficient computer assisted method for processing follow on studies.

NEFSC 2006 Atlantic Herring Acoustic/Midwater Trawl Survey (DE0615, EK500)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

NEFSC 2008 Atlantic Herring Acoustic/Midwater Trawl Survey (DE0809, EK500)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

NEFSC 2003 Atlantic Herring Acoustic/Midwater Trawl Survey (DE0308, EK500)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

NEFSC 2004 Atlantic Herring Acoustic/Midwater Trawl Survey (DE0413, EK500)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

NEFSC 1999 Atlantic Herring Acoustic/Midwater Trawl Survey (DE9909, EK500)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

NEFSC 1998 Atlantic Herring Acoustic/Midwater Trawl Survey (DE9810, EK500)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

NEFSC 2011 Atlantic Herring Acoustic/Midwater Trawl Survey (DE1108, EK60)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

NEFSC 2002 Atlantic Herring Acoustic/Midwater Trawl Survey (DE0208, EK500)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

NEFSC 2010 Atlantic Herring Acoustic/Midwater Trawl Survey (DE1010, EK60)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

NEFSC 2000 Atlantic Herring Acoustic/Midwater Trawl Survey (DE0008, EK500)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

NEFSC 2001 Atlantic Herring Acoustic/Midwater Trawl Survey (DE0109, EK500)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

NEFSC 2005 Atlantic Herring Acoustic/Midwater Trawl Survey (DE0512, EK500)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

NEFSC 2007 Atlantic Herring Acoustic/Midwater Trawl Survey (DE0710, EK500)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

NEFSC 2012 Atlantic Herring Acoustic/Midwater Trawl Survey (PC1206, EK60)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

NEFSC 1998 Atlantic Herring Acoustic/Midwater Trawl Survey (DE9809, EK500)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

NEFSC 2009 Atlantic Herring Acoustic/Midwater Trawl Survey (DE0910, EK500)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NEFSC Atlantic herring acoustic survey is a fisheries independent survey that provides scientific data for Atlantic herring assessments in the U.S. mid-Atlantic...

Grain size dependent magnetic discrimination of Iceland and South Greenland terrestrial sediments in the northern North Atlantic sediment record

Science.gov (United States)

Hatfield, Robert G.; Stoner, Joseph S.; Reilly, Brendan T.; Tepley, Frank J.; Wheeler, Benjamin H.; Housen, Bernard A.

2017-09-01

We use isothermal and temperature dependent in-field and magnetic remanence methods together with electron microscopy to characterize different sieved size fractions from terrestrial sediments collected in Iceland and southern Greenland. The magnetic fraction of Greenland silts (3-63 μm) and sands (>63 μm) is primarily composed of near-stoichiometric magnetite that may be oxidized in the finer clay (samples, in contrast to coarser PSD and multi-domain (MD) discrete magnetites from southern Greenland. We demonstrate the potential of using magnetic properties of the silt fraction for source unmixing by creating known endmember mixtures and by using naturally mixed marine sediments from the Eirik Ridge south of Greenland. We develop a novel approach to ferrimagnetic source unmixing by using low temperature magnetic susceptibility curves that are sensitive to the different crystallinity and cation substitution characteristics of the different source regions. Covariation of these properties with hysteresis parameters suggests sediment source changes have driven the magnetic mineral variations observed in Eirik Ridge sediments since the last glacial maximum. These observations assist the development of a routine method and interpretative framework to quantitatively determine provenance in a geologically realistic and meaningful way and assess how different processes combine to drive magnetic variation in the North Atlantic sediment record.

Geology along the Blue Ridge Parkway in Virginia

Science.gov (United States)

Carter, Mark W.; Southworth, C. Scott; Tollo, Richard P.; Merschat, Arthur J.; Wagner, Sara; Lazor, Ava; Aleinikoff, John N.

2017-01-01

Detailed geologic mapping and new SHRIMP (sensitive high-resolution ion microprobe) U-Pb zircon, Ar/Ar, Lu-Hf, 14C, luminescence (optically stimulated), thermochronology (fission-track), and palynology reveal the complex Mesoproterozoic to Quaternary geology along the ~350 km length of the Blue Ridge Parkway in Virginia. Traversing the boundary of the central and southern Appalachians, rocks along the parkway showcase the transition from the para-autochthonous Blue Ridge anticlinorium of northern and central Virginia to the allochthonous eastern Blue Ridge in southern Virginia. From mile post (MP) 0 near Waynesboro, Virginia, to ~MP 124 at Roanoke, the parkway crosses the unconformable to faulted boundary between Mesoproterozoic basement in the core of the Blue Ridge anticlinorium and Neoproterozoic to Cambrian metasedimentary and metavolcanic cover rocks on the western limb of the structure. Mesoproterozoic basement rocks comprise two groups based on SHRIMP U-Pb zircon geochronology: Group I rocks (1.2-1.14 Ga) are strongly foliated orthogneisses, and Group II rocks (1.08-1.00 Ga) are granitoids that mostly lack obvious Mesoproterozoic deformational features.Neoproterozoic to Cambrian cover rocks on the west limb of the anticlinorium include the Swift Run and Catoctin Formations, and constituent formations of the Chilhowee Group. These rocks unconformably overlie basement, or abut basement along steep reverse faults. Rocks of the Chilhowee Group are juxtaposed against Cambrian rocks of the Valley and Ridge province along southeast- and northwest-dipping, high-angle reverse faults. South of the James River (MP 64), Chilhowee Group and basement rocks occupy the hanging wall of the nearly flat-lying Blue Ridge thrust fault and associated splays.South of the Red Valley high-strain zone (MP 144.5), the parkway crosses into the wholly allochthonous eastern Blue Ridge, comprising metasedimentary and meta-igneous rocks assigned to the Wills Ridge, Ashe, and Alligator

Pb-Sr-Nd isotopic data of Indian Ocean ridges: New evidence of large-scale mapping of mantle heterogeneities

International Nuclear Information System (INIS)

Hamelin, B.; Dupre, B.; Allegre, C.J.

1986-01-01

A Pb-Sr-Nd isotope study of South West and East Indian Ridges confirms that the Indian Ocean belongs to a specific regional isotopic domain, as previously suggested by the results from islands of this ocean. The isotopic domain defined by the Indian MORB is indeed different from that of the North Atlantic and East Pacific Oceans. This demonstrates that the convective circulation of the upper mantle does not allow a rapid homogenization from one region to the other. The isotopic data of the Indian ridges can be interpreted by a contamination model, in which the depleted upper mantle (identical to that under the North Atlantic) is contaminated by two different types of contaminant, one corresponding to the source of the ''central Indian Ocean'' islands (Amsterdam, St. Paul, Marion, Prince Edward, Reunion, Rodriguez, Mauritius), and the other to a source similar to that of Walvis or Ninety East aseismic ridges. These two contaminants would have contributed to the ridge volcanism in different proportion over time. (orig.)

The glacial record of New Zealand's Southern Alps

Science.gov (United States)

Schaefer, J. M.; Denton, G.; Lowell, T.; Anderson, B.; Rinterknecht, V.; Schlosser, P.; Ivy-Ochs, S.; Kubik, P.; Schluechter, C.; Chinn, T.; Barrell, D.; Lifton, N.; Jull, T.

2004-12-01

We present detailed mapping and surface exposure dating using in-situ Be-10 and C-14 of the moraine set of Lake Pukaki, New Zealand's Southern Alps, spanning from the penultimate glaciation, over several Last Glacial Maximum (LGM) moraines, the late glacial event to Holocene glacial advances. New Zealand, a mountain ridge in the middle of the Southern Ocean, has one of the best preserved moraine records world-wide, offering the opportunity to reconstruct amplitude and timing of climate changes from Southern mid-latitudes, an area where paleoclimate data is scarce. The extensive mapping effort by G. Denton and colleagues (http://wyvern.gns.cri.nz/website/csigg/) provides a unique background for sample selection for Surface Exposure Dating. Our extensive data set (>40 samples analyzed so far) indicate that (i) the LGM in New Zealand terminated clearly prior to the Boelling/Alleroed warming, (ii) the late glacial advance is within uncertainties consistent with the timing of the Younger Dryas cold reversal; (iii) there occurred an early Holocene glacial event of the same amplitude than the Little Ice Age. This latter event is the first Holocene glacial event from the Southern Hemisphere dated by in-situ Be-10 and C-14.

Zoogeography of fish parasites of the pearlside (Maurolicus muelleri), with genetic evidence of Anisakis simplex (s.s.) from the Mid-Atlantic Ridge

Czech Academy of Sciences Publication Activity Database

Klimpel, S.; Kellermanns, E.; Palm, H. W.; Moravec, František

2007-01-01

Roč. 152, č. 3 (2007), s. 725-732 ISSN 0025-3162 Grant - others:German Research Council(DE) DFG KL 2087/1, PA 664/4-1; German Academic Exchange Service(DE) DAAD Klimpel D/05/51605 Institutional research plan: CEZ:AV0Z60220518 Keywords : Anisakis * Maurolicus * Atlantic Ocean Subject RIV: EG - Zoology Impact factor: 2.215, year: 2007

Bathymetry and oceanic flow structure at two deep passages crossing the Lomonosov Ridge

Science.gov (United States)

Björk, Göran; Jakobsson, Martin; Assmann, Karen; Andersson, Leif G.; Nilsson, Johan; Stranne, Christian; Mayer, Larry

2018-01-01

The Lomonosov Ridge represents a major topographical feature in the Arctic Ocean which has a large effect on the water circulation and the distribution of water properties. This study presents detailed bathymetric survey data along with hydrographic data at two deep passages across the ridge: a southern passage (80-81° N), where the ridge crest meets the Siberian continental slope, and a northern passage around 84.5° N. The southern channel is characterized by smooth and flat bathymetry around 1600-1700 m with a sill depth slightly shallower than 1700 m. A hydrographic section across the channel reveals an eastward flow with Amundsen Basin properties in the southern part and a westward flow of Makarov Basin properties in the northern part. The northern passage includes an approximately 72 km long and 33 km wide trough which forms an intra-basin in the Lomonosov Ridge morphology (the Oden Trough). The eastern side of the Oden Trough is enclosed by a narrow and steep ridge rising 500-600 m above a generally 1600 m deep trough bottom. The deepest passage (the sill) is 1470 m deep and located on this ridge. Hydrographic data show irregular temperature and salinity profiles indicating that water exchange occurs as midwater intrusions bringing water properties from each side of the ridge in well-defined but irregular layers. There is also morphological evidence that some rather energetic flows may occur in the vicinity of the sill. A well expressed deepening near the sill may be the result of seabed erosion by bottom currents.

Transpressive mantle uplift at large offset oceanic transform faults

Science.gov (United States)

Maia, M.; Briais, A.; Brunelli, D.; Ligi, M.; Sichel, S. E.; Campos, T.

2017-12-01

Large-offset transform faults deform due to changes in plate motions and local processes. At the St. Paul transform, in the Equatorial Atlantic, a large body of ultramafic rocks composed of variably serpentinized and mylonitized peridotites is presently being tectonically uplifted. We recently discovered that the origin of the regional mantle uplift is linked to long-standing compressive stresses along the transform fault (1). A positive flower structure, mainly made of mylonitized mantle rocks, can be recognized on the 200 km large push-up ridge. Compressive earthquakes mechanisms reveal seismically active thrust faults on the southern flank of the ridge . The regional transpressive stress field affects a large portion of the ridge segment south of the transform, as revealed by the presence of faults and dykes striking obliquely to the direction of the central ridge axis. A smaller thrust, affecting recent sediments, was mapped south of this segment, suggesting a regional active compressive stress field. The transpressive stress field is interpreted to derive from the propagation of the Mid-Atlantic Ridge (MAR) segment into the transform domain as a response to the enhanced melt supply at the ridge axis. The propagation forced the migration and segmentation of the transform fault southward and the formation of restraining step-overs. The process started after a counterclockwise change in plate motion at 11 Ma initially resulting in extensive stress of the transform domain. A flexural transverse ridge formed in response. Shortly after plate reorganization, the MAR segment started to propagate southwards due to the interaction of the ridge and the Sierra Leone thermal anomaly. 1- Maia et al., 2016. Extreme mantle uplift and exhumation along a transpressive transform fault Nat. Geo. doi:10.1038/ngeo2759

Production, pathways and budgets of melts in mid-ocean ridges: An enthalpy based thermo-mechanical model

Science.gov (United States)

Mandal, Nibir; Sarkar, Shamik; Baruah, Amiya; Dutta, Urmi

2018-04-01

Using an enthalpy based thermo-mechanical model we provide a theoretical evaluation of melt production beneath mid-ocean ridges (MORs), and demonstrate how the melts subsequently develop their pathways to sustain the major ridge processes. Our model employs a Darcy idealization of the two-phase (solid-melt) system, accounting enthalpy (ΔH) as a function of temperature dependent liquid fraction (ϕ). Random thermal perturbations imposed in this model set in local convection that drive melts to flow through porosity controlled pathways with a typical mushroom-like 3D structure. We present across- and along-MOR axis model profiles to show the mode of occurrence of melt-rich zones within mushy regions, connected to deeper sources by single or multiple feeders. The upwelling of melts experiences two synchronous processes: 1) solidification-accretion, and 2) eruption, retaining a large melt fraction in the framework of mantle dynamics. Using a bifurcation analysis we determine the threshold condition for melt eruption, and estimate the potential volumes of eruptible melts (∼3.7 × 106 m3/yr) and sub-crustal solidified masses (∼1-8.8 × 106 m3/yr) on an axis length of 500 km. The solidification process far dominates over the eruption process in the initial phase, but declines rapidly on a time scale (t) of 1 Myr. Consequently, the eruption rate takes over the solidification rate, but attains nearly a steady value as t > 1.5 Myr. We finally present a melt budget, where a maximum of ∼5% of the total upwelling melt volume is available for eruption, whereas ∼19% for deeper level solidification; the rest continue to participate in the sub-crustal processes.

Geoelectric hazard maps for the Mid-Atlantic United States: 100 year extreme values and the 1989 magnetic storm

Science.gov (United States)

Love, Jeffrey J.; Lucas, Greg M.; Kelbert, Anna; Bedrosian, Paul A.

2018-01-01

Maps of extreme value geoelectric field amplitude are constructed for the Mid‐Atlantic United States, a region with high population density and critically important power grid infrastructure. Geoelectric field time series for the years 1983–2014 are estimated by convolving Earth surface impedances obtained from 61 magnetotelluric survey sites across the Mid‐Atlantic with historical 1 min (2 min Nyquist) measurements of geomagnetic variation obtained from a nearby observatory. Statistical models are fitted to the maximum geoelectric amplitudes occurring during magnetic storms, and extrapolations made to estimate threshold amplitudes only exceeded, on average, once per century. For the Mid‐Atlantic region, 100 year geoelectric exceedance amplitudes have a range of almost 3 orders of magnitude (from 0.04 V/km at a site in southern Pennsylvania to 24.29 V/km at a site in central Virginia), and they have significant geographic granularity, all of which is due to site‐to‐site differences in magnetotelluric impedance. Maps of these 100 year exceedance amplitudes resemble those of the estimated geoelectric amplitudes attained during the March 1989 magnetic storm, and, in that sense, the March 1989 storm resembles what might be loosely called a “100 year” event. The geoelectric hazard maps reported here stand in stark contrast with the 100 year geoelectric benchmarks developed for the North American Electric Reliability Corporation.

Biodiversity of polycyclic aromatic hydrocarbon-degrading bacteria from deep sea sediments of the Middle Atlantic Ridge.

Science.gov (United States)

Cui, Zhisong; Lai, Qiliang; Dong, Chunming; Shao, Zongze

2008-08-01

The bacteria involved in the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in deep sea subsurface environments are largely unknown. In order to reveal their biodiversity, sediments from 2.2 m under the bottom surface at a water depth of 3542 m were sampled on the Middle Atlantic Ridge with a gravity column sampler. The sediments were promptly enriched with either crude oil or a mixture of PAHs (naphthalene, phenanthrene and pyrene) as the sole carbon source, and further enriched with the PAH mixture mentioned above in the lab. The resulting consortia were named C2CO and C2PPN respectively. Their bacterial composition was analysed with plate cultivation, PCR-DGGE and 16S rDNA library analysis. On plates, isolates belonging to Pseudoalteromonas, Halomonas, Marinobacter, Thalassospira and Tistrella dominated the culturable populations. With PCR-DGGE, five major bands closely related to Cycloclasticus, Alteromonas, Thalassospira, Alcanivorax and Rhodospirillaceae were detected in consortium C2CO, while only one major band of Cycloclasticus was detected in consortium C2PPN. In addition, the dynamics of community structure in response to aromatic substrate alterations were examined. As a result, three ribotypes of Cycloclasticus were detected by 16S rDNA library analysis, one which played a key role in phenanthrene degradation; two Alteromonas bacteria dominated the naphthalene reselected consortium. Although bacteria of the two genera grew as the main members of the communities, none of them were isolated, probably owing to their poor cultivability. These results confirm that bacteria of Cycloclasticus are important obligate PAH degraders in marine environments, and coexist with other degrading bacteria that inhabit the deep subsurface sediment of the Atlantic. This supports the view that PAH accumulation and bioattenuation occur in remote areas consistently and continuously.

The impact of gyre dynamics on the mid-depth salinity signature of the eastern North Atlantic

Science.gov (United States)

Burkholder, K. C.; Lozier, M. S.

2009-04-01

The Mediterranean Overflow Water (MOW) is widely recognized for its role in establishing the mid-depth salinity signature of the subtropical North Atlantic. However, recent work has revealed an intermittent impact of MOW on the salinity signature of the eastern subpolar basin. This impact results from a temporally variable penetration of the northward flowing branch of the MOW past Porcupine Bank into the eastern subpolar basin. It has been shown that the salinity signature of the eastern subpolar basin, in particular the Rockall Trough, varies with the state of the North Atlantic Oscillation (NAO): during persistent periods of strong winds (high NAO index), when the subpolar front moves eastward, waters in the subpolar gyre block the northward flowing MOW, preventing its entry into the subpolar gyre. Conversely, during persistent periods of weak winds (low NAO index), the front moves westward, allowing MOW to penetrate north of Porcupine Bank and into the subpolar gyre. Here, we investigate the manner in which the spatial and temporal variability in the northward penetration of the MOW and the position of the eastern limb of the subpolar front affect the mid-depth property fields not only in the subpolar gyre, but in the subtropical gyre as well. Using approximately 55 years of historical hydrographic data and output from the 1/12° FLAME model, we analyze the temporal variability of salinity along the eastern boundary and compare this variability to the position of the subpolar front in both the observational record and the FLAME model. We conclude that when the zonal position of the subpolar front moves relatively far offshore and the MOW is able to penetrate to the north, high salinity anomalies are observed at high latitudes and low salinity anomalies are observed at low latitudes. Conversely, when the frontal position shifts to the east, the MOW (and thus, the high salinity signature) is blocked, resulting in a drop in salinity anomalies at high latitudes

Quality assurance project plan for the Chestnut Ridge Fly Ash Pond Stabilization Project at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee

International Nuclear Information System (INIS)

1996-07-01

The Chestnut Ridge Fly Ash Pond Stabilization (CRFAPS) Project will stabilize a 19-m-high (62-ft-high) earthen embankment across Upper McCoy Branch situated along the southern slope of Chestnut Ridge. This task will be accomplished by raising the crest of the embankment, reinforcing the face of the embankment, removing trees from the face and top of the embankment, and repairing the emergency spillway. The primary responsibilities of the team members are: Lockheed Martin Energy Systems, Inc., (Energy Systems) will be responsible for project integration, technical support, Title 3 field support, environmental oversight, and quality assurance (QA) oversight of the project; Foster Wheeler Environmental Corporation (FWENC) will be responsible for design and home office Title 3 support; MK-Ferguson of Oak Ridge Company (MK-F) will be responsible for health and safety, construction, and procurement of construction materials. Each of the team members has a QA program approved by the US Department of Energy (DOE) Oak Ridge Operations. This project-specific QA project plan (QAPP), which is applicable to all project activities, identifies and integrates the specific QA requirements from the participant's QA programs that are necessary for this project

Continental breakup of the Central Atlantic and the initiation of the southern Central Atlantic Magmatic Province: revisiting the role of a mantle plume

Science.gov (United States)

Rohrman, M.

2017-12-01

Central Atlantic breakup is strongly associated with magmatism of the Central Atlantic Magmatic Province (CAMP), although the exact mechanism, as well as the temporal and spatial relations, have so far been poorly constrained. Here, I propose a mantle plume origin for the 200 Ma southern Central Atlantic Province (CAMP), based on an original plume conduit location off southeastern Florida, linking Early Jurassic rift systems: One rift arm is defined by the Takutu rift in present-day Guyana and Brazil, extending all the way past the Demerara Rise. This rift is linking up with a second arm from the Bahamas basin to the Blake Plateau basin. Finally, there is the third, failed rift between the Demerara Rise and the Guinea Plateau. This rift system post-dates earlier Triassic rift systems along the US eastcoast and in the subsurface of Arkansas, Texas, the Gulf of Mexico and northern South America. Chronostratigraphic analysis of outcrop, wells and seismic data near the proposed conduit, suggest initial Rhaetian uplift, followed by dike/sill intrusions feeding flood basalts and the initiation of igneous centers at the triple point. The latter resulted in various subsequent uplift and subsidence events, as a result of volcanic construction and erosion. The load of the volcanic edifice generated a point of weakness, allowing favorable plate stresses to generate rift systems, propagating away from the rift junction and eventually break up Pangea. The breakup is marked by the magmatic breakup (un)conformity on seismic data, separating hotspot/plume sourced Seaward Dipping reflectors (SDRs) within the continental rift system, from early ocean spreading sourced SDRs. As ocean spreading continued, the volcanic construction evolved into a hotspot track, now recognized as the Bahamas island trail. Time progression of this hotspot track resembles the present-day Iceland hotspot track, as suggested by plate reconstructions (Figure 1). Based on melting depth estimates from Sm

Virginia Atlantic Coast Recreational Use

Data.gov (United States)

Virginia Department of Environmental Quality — As a member of the Mid-Atlantic Regional Council on the Ocean (MARCO), Virginia, through its Coastal Zone Management (CZM) Program, collected information on how the...

VA Atlantic Coast Recreational Use

Data.gov (United States)

Virginia Department of Environmental Quality — As a member of the Mid-Atlantic Regional Council on the Ocean (MARCO), Virginia, through its Coastal Zone Management (CZM) Program, collected information on how the...

Evidence for spawning aggregations of the endangered Atlantic goliath grouper Epinephelus itajara in southern Brazil.

Science.gov (United States)

Bueno, L S; Bertoncini, A A; Koenig, C C; Coleman, F C; Freitas, M O; Leite, J R; De Souza, T F; Hostim-Silva, M

2016-07-01

In this study, seasonal numerical abundance of the critically endangered Atlantic goliath grouper Epinephelus itajara was estimated by conducting scuba dive surveys and calculating sightings-per-unit-effort (SPUE) at three sites in southern Brazil. Seasonal differences in size and reproductive condition of captured or confiscated specimens were compared. The SPUE differed significantly with season, increasing in late spring and peaking during the austral summer months. A significant effect was observed in the number of fish relative to the lunar cycle. All females sampled during the summer were spawning capable, while all those sampled during other seasons were either regressing or regenerating. What these data strongly infer is that the E. itajara spawning aggregation sites have been located in the southern state of Paraná and the northern state of Santa Catarina and summer is the most likely spawning season. Size frequency distributions, abundance and reproductive state were estimated and correlated with environmental variables. © 2016 The Fisheries Society of the British Isles.

Restoration practicesin Brazil's Atlantic rainforest.

Science.gov (United States)

Jorge Correa de Lima Palidon; Maisa dos Santos Guapyassu

2005-01-01

The atlantic Rain Forst (Mata Atlantica) extends along the southern coast of Brazil and inland into Argentina and Paraguay. Originally covering 15% of the land area of Brazil, it was a region of an estimated 1.3 million km2 (MMA 2000). Today, remnants of the Atlantic Forest represents about 8% of the original area, or some 94,000 km2...

Southern Appalachian Regional Seismic Network

Energy Technology Data Exchange (ETDEWEB)

Chiu, S.C.C.; Johnston, A.C.; Chiu, J.M. [Memphis State Univ., TN (United States). Center for Earthquake Research and Information

1994-08-01

The seismic activity in the southern Appalachian area was monitored by the Southern Appalachian Regional Seismic Network (SARSN) since late 1979 by the Center for Earthquake Research and Information (CERI) at Memphis State University. This network provides good spatial coverage for earthquake locations especially in east Tennessee. The level of activity concentrates more heavily in the Valley and Ridge province of eastern Tennessee, as opposed to the Blue Ridge or Inner Piedmont. The large majority of these events lie between New York - Alabama lineament and the Clingman/Ocoee lineament, magnetic anomalies produced by deep-seated basement structures. Therefore SARSN, even with its wide station spacing, has been able to define the essential first-order seismological characteristics of the Southern Appalachian seismic zone. The focal depths of the southeastern U.S. earthquakes concentrate between 8 and 16 km, occurring principally beneath the Appalachian overthrust. In cross-sectional views, the average seismicity is shallower to the east beneath the Blue Ridge and Piedmont provinces and deeper to the west beneath the Valley and Ridge and the North American craton. Results of recent focal mechanism studies by using the CERI digital earthquake catalog between October, 1986 and December, 1991, indicate that the basement of the Valley and Ridge province is under a horizontal, NE-SW compressive stress. Right-lateral strike-slip faulting on nearly north-south fault planes is preferred because it agrees with the trend of the regional magnetic anomaly pattern.

Southern Appalachian Regional Seismic Network

International Nuclear Information System (INIS)

Chiu, S.C.C.; Johnston, A.C.; Chiu, J.M.

1994-08-01

The seismic activity in the southern Appalachian area was monitored by the Southern Appalachian Regional Seismic Network (SARSN) since late 1979 by the Center for Earthquake Research and Information (CERI) at Memphis State University. This network provides good spatial coverage for earthquake locations especially in east Tennessee. The level of activity concentrates more heavily in the Valley and Ridge province of eastern Tennessee, as opposed to the Blue Ridge or Inner Piedmont. The large majority of these events lie between New York - Alabama lineament and the Clingman/Ocoee lineament, magnetic anomalies produced by deep-seated basement structures. Therefore SARSN, even with its wide station spacing, has been able to define the essential first-order seismological characteristics of the Southern Appalachian seismic zone. The focal depths of the southeastern U.S. earthquakes concentrate between 8 and 16 km, occurring principally beneath the Appalachian overthrust. In cross-sectional views, the average seismicity is shallower to the east beneath the Blue Ridge and Piedmont provinces and deeper to the west beneath the Valley and Ridge and the North American craton. Results of recent focal mechanism studies by using the CERI digital earthquake catalog between October, 1986 and December, 1991, indicate that the basement of the Valley and Ridge province is under a horizontal, NE-SW compressive stress. Right-lateral strike-slip faulting on nearly north-south fault planes is preferred because it agrees with the trend of the regional magnetic anomaly pattern

Energy landscapes shape microbial communities in hydrothermal systems on the Arctic Mid-Ocean Ridge.

Science.gov (United States)

Dahle, Håkon; Økland, Ingeborg; Thorseth, Ingunn H; Pederesen, Rolf B; Steen, Ida H

2015-07-01

Methods developed in geochemical modelling combined with recent advances in molecular microbial ecology provide new opportunities to explore how microbial communities are shaped by their chemical surroundings. Here, we present a framework for analyses of how chemical energy availability shape chemotrophic microbial communities in hydrothermal systems through an investigation of two geochemically different basalt-hosted hydrothermal systems on the Arctic Mid-Ocean Ridge: the Soria Moria Vent field (SMVF) and the Loki's Castle Vent Field (LCVF). Chemical energy landscapes were evaluated through modelling of the Gibbs energy from selected redox reactions under different mixing ratios between seawater and hydrothermal fluids. Our models indicate that the sediment-influenced LCVF has a much higher potential for both anaerobic and aerobic methane oxidation, as well as aerobic ammonium and hydrogen oxidation, than the SMVF. The modelled energy landscapes were used to develop microbial community composition models, which were compared with community compositions in environmental samples inside or on the exterior of hydrothermal chimneys, as assessed by pyrosequencing of partial 16S rRNA genes. We show that modelled microbial communities based solely on thermodynamic considerations can have a high predictive power and provide a framework for analyses of the link between energy availability and microbial community composition.

Use of tritium and helium-3 for oceanographic processes study. An example: the Northeastern Atlantic Ocean

International Nuclear Information System (INIS)

Andrie, C.; Merlivat, L.

1987-01-01

These results are relative to the TOPOGULF cruise during summer 1983. The sampled area is located near the Azores Islands on the both sides of the mid atlantic ridge. The tritium content of the surface waters reveals a strong front along the Azores current. At depth, the spatial distribution of tritium is studied along isopycnals. In the thermocline, it is essentially the anticyclonic gyre which is responsible for the northeast - southwest gradient in tritium concentration. Some informations about the age of the water masses are given by the use of both tritium and Helium-3. By this way are identified some areas where ventilation processes are active. At middepth, a strong contrast exists between the young waters originating from the Labrador Sea and the more stagnant waters in the South East of the sampled area

Mixing, Hydrography, and Flow in the eastern Channel of the Lucky Strike Segment

OpenAIRE

Tippenhauer, Sandra

2015-01-01

Diapycnal mixing in the deep ocean is known to be much stronger in the vicinity of rough topography of mid-ocean ridges than over abyssal plains. In this thesis a microstructure probe attached to an autonomous underwater vehicle (AUV) was used to infer the spatial distribution of the dissipation rate of turbulent kinetic energy in the central valley of the Mid-Atlantic Ridge. This represents the first successful realization of a horizontal, AUV-based, deep-ocean microstructure survey. The stu...

Orbital forcing of the late Pleistocene boreal summer monsoon: Links to North Atlantic cold events and El Nino; Southern Oscillation. Geologica Ultraiectina (313)

NARCIS (Netherlands)

Ziegler, M.

2009-01-01

This thesis revolves about the timing of precession-related variations in the boreal summer monsoon and the impact of North Atlantic cold events and the El Nino Southern Oscillation on this timing. Transient climate modelling experiments indicate that the intensity of the Northern Hemisphere summer

Physical trajectory profile data from glider blue deployed by University of Massachusetts; University of Massachusetts - Dartmouth in the Mid-Atlantic Bight from 2016-08-18 to 2016-08-22 (NCEI Accession 0156657)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — U.S. IOOS Mid-Atlantic Regional Association Coastal Ocean Observing System (MARACOOS) glider deployment. This is the second of a series of yearly seasonal...

Current glaciation of the Chikhachev ridge (South-Eastern Altai and its dynamics after maximum of the Little Ice Age

Directory of Open Access Journals (Sweden)

D. A. Ganyushkin

2016-01-01

Full Text Available Glaciation of the Chikhachev ridge (South-Eastern Altai remains poorly known: field observations were not performed since the mid-twentieth century, available schemes and estimates of the glaciation and its scale made on the basis of remote sensing cover only a part of the glaciers, reconstructions of the Little Ice Age (LIA glaciations are absent. This research was based on interpretation of the satellite images: Landsat-4 (1989, Landsat-7 (2001, and Spot-5 (2011, as well as with the use of data of the field season of 2015. Characteristics of glaciations of the Chikhachev ridge as the whole and of its individual centers (Talduair massif, Mongun-Taiga-Minor massif, and southern part of the Chikhachev ridge were determined for the first time. Recent glaciation is represented by 7 glaciers with their total area of 1.12 km2 in the Talduair massif, by 5 glaciers with total area of 0.75 km2 in the Mongun-Taiga-Minor massif, and by 85 glaciers with total area of 29 km2 in the southern part of the Chikhachev ridge. Since the LIA maximum, areas of glaciers decreased by 61% in the Talduair massif, by 74% in the Mongun-Taiga-Minor massif, by 56% in the southern part of the Chikhachev ridge with simultaneous lifting of the firn line by 50 m, 65 m, and 70 m, respectively.The largest rates of the glacier contractions were determined for the period 1989–2011. Different mechanisms of the glacier retreats were shown by the example of the glacier complexes Burgastyn-Gol (one-sided retreat and disintegration and the Grigorjev glacier (gradual retreat of the tongue. Retreat of the Grigorjev glacier has been reconstructed for the period from the LIA maximum until 2015. Average rate of the retreat increased from 1,6 m/year in 1957–1989 up to 11,3 m/year in 2011–2015. The present-day scales of the glaciers and rates of their retreating do not significantly differ from estimations made by other researchers for the nearest centers of glaciation of the

78 FR 17358 - Mid-Atlantic Fishery Management Council (MAFMC); Public Meetings

Science.gov (United States)

2013-03-21

... Organizational Reports, the New England and South Atlantic Liaison Reports, the Executive Director's Report, the... December 2012 and February 2013 minutes, receive Organizational Reports, the New England and South Atlantic... recommendation on the workshop results to include control dates, roll-over provisions, GRAs, port meetings, etc...

Dynamic Management of NOx and SO2 Emissions in the Texas and Mid-Atlantic Electric Power Systems and Implications for Air Quality.

Science.gov (United States)

McDonald-Buller, Elena; Kimura, Yosuke; Craig, Michael; McGaughey, Gary; Allen, David; Webster, Mort

2016-02-02

Cap and trade programs have historically been designed to achieve annual or seasonal reductions in emissions of nitrogen oxides and sulfur dioxide from power plants. Emissions reductions may not be temporally coincident with meteorological conditions conducive to the formation of peak ozone and fine particulate matter concentrations. Integrated power system and air quality modeling methods were developed to evaluate time-differentiated emissions price signals on high ozone days in the Mid-Atlantic portion of the Pennsylvania-New Jersey-Maryland (PJM) Interconnection and Electric Reliability Council of Texas (ERCOT) grids. Sufficient flexibility exists in the two grids with marked differences in demand and fuel generation mix to accommodate time-differentiated emissions pricing alone or in combination with a season-wide program. System-wide emissions reductions and production costs from time-differentiated pricing are shown to be competitive with those of a season-wide program on high ozone days and would be more cost-effective if the primary policy goal was to target emissions reductions on these days. Time-differentiated pricing layered as a complement to the Cross-State Air Pollution Rule had particularly pronounced benefits for the Mid-Atlantic PJM system that relies heavily on coal-fired generation. Time-differentiated pricing aimed at reducing ozone concentrations had particulate matter reduction co-benefits, but if particulate matter reductions are the primary objective, other approaches to time-differentiated pricing may lead to greater benefits.

The Sternoptychidae (Pisces, Stomiatoidei) of the Amsterdam Mid North Atlantic Plankton Expedition 1980, with a note on specimens intermediate between Argyropelecus aculeatus Valenciennes, 1849 and A. olfersi (Cuvier, 1829)

NARCIS (Netherlands)

Pafort-Van Iersel, Trudie

1981-01-01

The Sternoptychidae caught during a spring expedition in the Mid North Atlantic in 1980 are studied. Distribution patterns and data on abundance are recorded. It is proposed that Argyropelecus aculeatus and A. olfersi are two formae belonging to one species, the existing phenotypical differences

North Atlantic atmospheric and ocean inter-annual variability over the past fifty years - Dominant patterns and decadal shifts

Science.gov (United States)

Hauser, Tristan; Demirov, Entcho; Zhu, Jieshun; Yashayaev, Igor

2015-03-01

The atmosphere and ocean of the North Atlantic have undergone significant changes in the past century. To understand these changes, their mechanisms, and their regional implications requires a quantitative understanding of processes in the coupled ocean and atmosphere system. Central to this understanding is the role played by the dominant patterns of ocean and atmospheric variability which define coherent variations in physical characteristics over large areas. Cluster analysis is used in this article to identify the patterns of the North Atlantic atmospheric variability in the subseasonal and interannual spectral intervals. Four dominant subseasonal weather regimes are defined using Bayesian Gaussian mixture models. All correlation patterns of the Sea Level Pressure (SLP) anomalies with the membership probability time series for the weather regimes show similarities with the dipole structure typical for the North Atlantic Oscillation (NAO). The SLP patterns of two of the regimes represent the opposite phases NAO+ and NAO-. The two other weather regimes, the Atlantic Ridge (AR) and Scandinavian-Greenland dipole (SG), have dipole spatial structures with the northern and southern centers of action shifted with respect to the NAO pattern. These two patterns define blocking structures over Scandinavia and near the southern tip of Greenland, respectively. The storm tracks typical for the four regimes resemble the well known paths for positive/negative phases of NAO for the NAO+/NAO- weather regimes, and paths influenced by blocking off the south Greenland tip for AR and over Scandinavia for SG. The correlation patterns of momentum and heat fluxes to the ocean for the four regimes have tripole structures with positive (warm) downward heat flux anomalies over the Subpolar North Atlantic (SPNA) for the NAO- and the AR and negative heat flux anomalies over the SPNA for the NAO+. The downward heat flux anomalies associated with the SG are negative over the Labrador Sea and

Reconstruction of the North Atlantic end-member of the Atlantic Meridional Overturning Circulation over glacial-interglacial cycles

Science.gov (United States)

Kim, J.; Seguí, M. J.; Knudson, K. P.; Yehudai, M.; Goldstein, S. L.; Pena, L. D.; Basak, C.; Ferretti, P.

2017-12-01

North Atlantic Deep Water (NADW) represents the major water mass that drives the Atlantic Meridional Ocean Circulation (AMOC), which undergoes substantial reorganization with changing climate. In order to understand its impact on ocean circulation and climate through time, it is necessary to constrain its composition. We report Nd isotope ratios of Fe-Mn oxide encrusted foraminifera and fish debris from DSDP Site 607 (41.00N 32.96W, 3427m), in the present-day core of NADW, and ODP 1063 (33.68N 57.62W, 4585m), on the deep abyssal plain at the interface between NADW and Antarctic Bottom Water. We provide a new North Atlantic paleocirculation record covering 2 Ma. At Site 607 interglacial ɛNd-values are consistently similar to present-day NADW (ɛNd -13.5), with median ɛNd-values of -14.3 in the Early Pleistocene and -13.8 in the Late Pleistocene. Glacial ɛNd-values are higher by 1 ɛNd-unit in the Early Pleistocene, and 1.5-2 ɛNd-units in the Late Pleistocene. Site 1063 shows much greater variability, with ɛNd ranging from -10 to -26. We interpret the North Atlantic AMOC source as represented by the Site 607 interglacial ɛNd-values, which has remained nearly stable throughout the entire period. The higher glacial ɛNd-values reflect incursions of some southern-sourced waters to Site 607, which is supported by coeval shifts to lower benthic foraminiferal d13C. In contrast, the Site 1063 ɛNd-values do not appear to reflect the AMOC end-member, and likely reflects local effects from a bottom source. A period of greatly disrupted ocean circulation marks 950-850 Ma, which may have been triggered by enhanced ice growth in the Northern Hemisphere that began around 1.2 Ma, as suggested by possible input events of Nd from the surrounding cratons into the North Atlantic observed in Site 607. Interglacial AMOC only recovers to the previously observed vigor over 200 ka following the disruption, whereas further intensified SSW incursion into the deep North Atlantic come to

Temperature and other data collected using visual observations and other instruments in the Mid-Atlantic Bight and other Seas from GYRE from 01 August 1985 to 26 May 1990 (NODC Accession 9300074)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Temperature and other data were collected using visual observations, bottle casts, and other instruments from GYRE and other platforms in the Mid-Atlantic Bight and...

Physical trajectory profile data from glider blue deployed by University of Massachusetts; University of Massachusetts - Dartmouth in the Mid-Atlantic Bight from 2016-05-18 to 2016-06-06 (NCEI Accession 0153544)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — U.S. IOOS Mid-Atlantic Regional Association Coastal Ocean Observing System (MARACOOS) glider deployment. This is the first of a series of yearly seasonal deployments...

Influences of sediment redistribution on sea-level changes along the U.S. Atlantic margin since the mid-Pliocene

Science.gov (United States)

Li, Q.; Ferrier, K.; Austermann, J.; Mitrovica, J. X.

2017-12-01

The Orangeburg Scarp is a paleo-shoreline formed along the southeastern U.S. Atlantic coast during the mid-Pliocene warm period (MPWP; 3.3 - 2.9 Ma). The MPWP is a time of interest because it is often cited as an analog for modern climate and thus an important target for understanding sea-level responses to climate change. The present Orangeburg Scarp exhibits 40-meter variations in elevation along its length, implying that it has been warped since its formation, which complicates efforts to infer global ice volume at the MPWP. Previous studies have shown that the effects of glacial isostatic adjustment (GIA) and dynamic topography (DT) on sea level can explain a significant fraction of the observed variability in elevation along the Orangeburg Scarp. Here we build on these studies by using a gravitationally self-consistent ice age sea-level model to compute the effects of sediment loading and unloading on paleo-shoreline elevation since the mid-Pliocene. To constrain the sediment loading history in this region, we present a new compilation of erosion and deposition rates along the U.S. Atlantic margin, from which we generate a range of sediment redistribution scenarios since the MPWP. We simultaneously drive the sea-level model with these sediment redistribution histories and existing ice and dynamic topography histories. Our results show that sediment loading and unloading is capable of warping the elevation of this paleo-shoreline by 20 meters since its formation, similar in magnitude to the contributions from GIA and DT over the same time period. These results demonstrate that sediment redistribution can induce significant perturbations in sea-level markers from the MPWP, and thus accounting for its influence will improve reconstructions of sea level and global ice volume during the MPWP and perhaps other periods of relative ice age warmth.

Are the North Atlantic oscillation and the southern oscillation related in any time-scale?

Energy Technology Data Exchange (ETDEWEB)

Garcia, R.; Ribera, P.; Hernandez, E. [Universidad Complutense de Madrid (Spain). Facultad de Ciencias Fisicas; Gimenoo, L. [Fac. Ciencias, Univ. Vigo, Ourense (Spain)

2000-02-01

The north Atlantic oscillation (NAO) and the southern oscillation (SO) are compared from the standpoint of a possible common temporal scale of oscillation. To do this a cross-spectrum of the temporal series of NAO and SO indices was determined, finding a significant common oscillation of 6-8 years. To assure this finding, both series were decomposed in their main oscillations using singular spectrum analysis (SSA). Resulting reconstructed series of 6-8 years' oscillation were then cross-correlated without and with pre-whitened, the latter being significant. The main conclusion is a possible relationship between a common oscillation of 6-8 years that represents about 20% of the SO variance and about 25% of the NAO variance. (orig.)

Mid-late Holocene changes in the El Niño Southern Oscillation and Hadley Cell intensity; their effect on sea-surface conditions in the mid-latitude southeast Pacific Ocean (41°S)

OpenAIRE

Verleye, T.

2010-01-01

The study focuses on the observed effects of changes in the El Niño Southern Oscillation (ENSO) and Hadley Cell intensity on sea-surface water conditions in the SE Pacific (41°S; Site ODP1233) during the last 8.000 years. Recent studies suggest that periods characterised by a negative Southern Oscillation Index (SOI; El Niño) cause positive precipitation anomalies during austral winter (and annually) in Mid-South Chile, while austral summer periods are rather drier. This because El Niño weake...

Chemical Evidence for Vertical Transport from Magma Chambers to the Surface During Mid-Ocean Ridge Volcanic Eruptions

Science.gov (United States)

Sinton, J. M.; Rubin, K. H.

2009-12-01

Many mid-ocean ridge eruptions show significant internal chemical heterogeneity; in general, the amount of chemical heterogeneity within eruptions scales with erupted volume. These variations reflect magmatic processes occurring in magma reservoirs prior to or possibly during eruption. For example, systematic variations in Mg# with along-axis distance in the early 90’s Aldo-Kihi (S. EPR near 17.5°S), 1996 N. Gorda, 1993 Co-Axial (Juan de Fuca Ridge), and 1991-2 and 2005-6 9°50’N EPR eruptions is unlikely to be related to fractionation during emplacement, and rather reflects variations in sub-axial magma reservoirs prior to eruption. Such variations are inconsistent with well-mixed sub-axial reservoirs and, in some cases, require relatively long-lived, systematic variations in reservoir temperatures along axis. Chemical heterogeneity within the Aldo-Kihi eruption preserves spatial variations in mantle-derived isotopic and trace element ratios with implications for the temporal and spatial scales of magma injections to the crust and along-axis mixing within shallow reservoirs. These spatial variations are difficult to reconcile with significant (> ~1 km) along-axis magma transport, as are striking correlations of chemical compositions with surface geological discontinuities or seismically imaged sub-axial magma chamber reflectors in the S. Hump (S. EPR), 9°50’N EPR, N. Gorda and 1975-1984 Krafla (N. Iceland) eruptive units. Rather, spatial correlations between surface lava compositions and sub-axial magma chamber properties or long-lived axial morphology suggest that most of the erupted magma was transported nearly vertically from the underlying reservoirs to the surface during these eruptions. In the case of the Krafla eruption, coincident deformation suggests a component of lateral melt migration at depth, despite chemical evidence for vertical transport of erupted lava from more than one chemical reservoir. In addition, along-ridge movement of earthquake

Genetic stock identification of Atlantic salmon (Salmo salar populations in the southern part of the European range

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McGinnity Philip

2010-04-01

boundaries, allowing reporting regions to be defined. The implications of these results on the accuracy of MSA are evaluated and indicate that the success of MSA is not uniform across the range studied; our findings indicate large differences in the relative accuracy of stock composition estimates and MSA apportioning across the geographical range of the study, with a much higher degree of accuracy achieved when assigning and apportioning to populations in the south of the area studied. This result probably reflects the more genetically distinct nature of populations in the database from Spain, northwest France and southern England. Genetic stock identification has been undertaken and validation of the baseline microsatellite dataset with rod-and-line and estuary net fisheries of known origin has produced realistic estimates of stock composition at a regional scale. Conclusions This southern European database and supporting phylogeographic and mixed-stock analyses of net samples provide a unique tool for Atlantic salmon research and management, in both their natal rivers and the marine environment. However, the success of MSA is not uniform across the area studied, with large differences in the relative accuracy of stock composition estimates and MSA apportioning, with a much higher degree of accuracy achieved when assigning and apportioning to populations in the south of the region. More broadly, this study provides a basis for long-term salmon management across the region and confirms the value of this genetic approach for fisheries management of anadromous species.

Deep-water chemosynthetic ecosystem research during the census of marine life decade and beyond: a proposed deep-ocean road map.

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Christopher R German

Full Text Available The ChEss project of the Census of Marine Life (2002-2010 helped foster internationally-coordinated studies worldwide focusing on exploration for, and characterization of new deep-sea chemosynthetic ecosystem sites. This work has advanced our understanding of the nature and factors controlling the biogeography and biodiversity of these ecosystems in four geographic locations: the Atlantic Equatorial Belt (AEB, the New Zealand region, the Arctic and Antarctic and the SE Pacific off Chile. In the AEB, major discoveries include hydrothermal seeps on the Costa Rica margin, deepest vents found on the Mid-Cayman Rise and the hottest vents found on the Southern Mid-Atlantic Ridge. It was also shown that the major fracture zones on the MAR do not create barriers for the dispersal but may act as trans-Atlantic conduits for larvae. In New Zealand, investigations of a newly found large cold-seep area suggest that this region may be a new biogeographic province. In the Arctic, the newly discovered sites on the Mohns Ridge (71 °N showed extensive mats of sulfur-oxidisng bacteria, but only one gastropod potentially bears chemosynthetic symbionts, while cold seeps on the Haakon Mossby Mud Volcano (72 °N are dominated by siboglinid worms. In the Antarctic region, the first hydrothermal vents south of the Polar Front were located and biological results indicate that they may represent a new biogeographic province. The recent exploration of the South Pacific region has provided evidence for a sediment hosted hydrothermal source near a methane-rich cold-seep area. Based on our 8 years of investigations of deep-water chemosynthetic ecosystems worldwide, we suggest highest priorities for future research: (i continued exploration of the deep-ocean ridge-crest; (ii increased focus on anthropogenic impacts; (iii concerted effort to coordinate a major investigation of the deep South Pacific Ocean - the largest contiguous habitat for life within Earth's biosphere, but

Deep-water chemosynthetic ecosystem research during the census of marine life decade and beyond: a proposed deep-ocean road map.

Science.gov (United States)

German, Christopher R; Ramirez-Llodra, Eva; Baker, Maria C; Tyler, Paul A

2011-01-01

The ChEss project of the Census of Marine Life (2002-2010) helped foster internationally-coordinated studies worldwide focusing on exploration for, and characterization of new deep-sea chemosynthetic ecosystem sites. This work has advanced our understanding of the nature and factors controlling the biogeography and biodiversity of these ecosystems in four geographic locations: the Atlantic Equatorial Belt (AEB), the New Zealand region, the Arctic and Antarctic and the SE Pacific off Chile. In the AEB, major discoveries include hydrothermal seeps on the Costa Rica margin, deepest vents found on the Mid-Cayman Rise and the hottest vents found on the Southern Mid-Atlantic Ridge. It was also shown that the major fracture zones on the MAR do not create barriers for the dispersal but may act as trans-Atlantic conduits for larvae. In New Zealand, investigations of a newly found large cold-seep area suggest that this region may be a new biogeographic province. In the Arctic, the newly discovered sites on the Mohns Ridge (71 °N) showed extensive mats of sulfur-oxidisng bacteria, but only one gastropod potentially bears chemosynthetic symbionts, while cold seeps on the Haakon Mossby Mud Volcano (72 °N) are dominated by siboglinid worms. In the Antarctic region, the first hydrothermal vents south of the Polar Front were located and biological results indicate that they may represent a new biogeographic province. The recent exploration of the South Pacific region has provided evidence for a sediment hosted hydrothermal source near a methane-rich cold-seep area. Based on our 8 years of investigations of deep-water chemosynthetic ecosystems worldwide, we suggest highest priorities for future research: (i) continued exploration of the deep-ocean ridge-crest; (ii) increased focus on anthropogenic impacts; (iii) concerted effort to coordinate a major investigation of the deep South Pacific Ocean - the largest contiguous habitat for life within Earth's biosphere, but also the

Geochemical implications of gabbro from the slow-spreading Northern Central Indian Ocean Ridge, Indian Ocean

Digital Repository Service at National Institute of Oceanography (India)

Ray, Dwijesh; Misra, S.; Banerjee, R.; Weis, D.

., 1989) and the dynamics of crystallization of plutonic rocks (Bloomer et al., 1989; Meyer et al., 1989). The recovery of gabbroic rocks is mostly restricted to major transform faults or fracture zones transecting mid-ocean ridges, e.g., Mid... gabbro of Indian Ocean Ridge System (Fig 1) is ODP leg 118 from SWIR (Dick et al., 2002; Coogan et al, 2001). Gabbro from Leg 179 (ODP Hole 735B from Atlantis II fracture zone, Dick et al., 2000) and Leg 179 (Hole 1105A) near Leg 118 have also been...

Evaluating leaf litter beetle data sampled by Winkler extraction from Atlantic forest sites in southern Brazil

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Philipp Werner Hopp

2011-06-01

Full Text Available Evaluating leaf litter beetle data sampled by Winkler extraction from Atlantic forest sites in southern Brazil. To evaluate the reliability of data obtained by Winkler extraction in Atlantic forest sites in southern Brazil, we studied litter beetle assemblages in secondary forests (5 to 55 years after abandonment and old-growth forests at two seasonally different points in time. For all regeneration stages, species density and abundance were lower in April compared to August; but, assemblage composition of the corresponding forest stages was similar in both months. We suggest that sampling of small litter inhabiting beetles at different points in time using the Winkler technique reveals identical ecological patterns, which are more likely to be influenced by sample incompleteness than by differences in their assemblage composition. A strong relationship between litter quantity and beetle occurrences indicates the importance of this variable for the temporal species density pattern. Additionally, the sampled beetle material was compared with beetle data obtained with pitfall traps in one old-growth forest. Over 60% of the focal species captured with pitfall traps were also sampled by Winkler extraction in different forest stages. Few beetles with a body size too large to be sampled by Winkler extraction were only sampled with pitfall traps. This indicates that the local litter beetle fauna is dominated by small species. Hence, being aware of the exclusion of large beetles and beetle species occurring during the wet season, the Winkler method reveals a reliable picture of the local leaf litter beetle community.

The Influence of the North Atlantic Oscillation on Tropospheric Distributions of Ozone and Carbon Monoxide.

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Knowland, K. E.; Doherty, R. M.; Hodges, K.

2015-12-01

The influence of the North Atlantic Oscillation (NAO) on the tropospheric distributions of ozone (O3) and carbon monoxide (CO) has been quantified. The Monitoring Atmospheric Composition and Climate (MACC) Reanalysis, a combined meteorology and composition dataset for the period 2003-2012 (Innes et al., 2013), is used to investigate the composition of the troposphere and lower stratosphere in relation to the location of the storm track as well as other meteorological parameters over the North Atlantic associated with the different NAO phases. Cyclone tracks in the MACC Reanalysis compare well to the cyclone tracks in the widely-used ERA-Interim Reanalysis for the same 10-year period (cyclone tracking performed using the tracking algorithm of Hodges (1995, 1999)), as both are based on the European Centre for Medium-Range Weather Forecasts' (ECMWF) Integrated Forecast System (IFS). A seasonal analysis is performed whereby the MACC reanalysis meteorological fields, O3 and CO mixing ratios are weighted by the monthly NAO index values. The location of the main storm track, which tilts towards high latitudes (toward the Arctic) during positive NAO phases to a more zonal location in the mid-latitudes (toward Europe) during negative NAO phases, impacts the location of both horizontal and vertical transport across the North Atlantic and into the Arctic. During positive NAO seasons, the persistence of cyclones over the North Atlantic coupled with a stronger Azores High promotes strong horizontal transport across the North Atlantic throughout the troposphere. In all seasons, significantly more intense cyclones occur at higher latitudes (north of ~50°C) during the positive phase of the NAO and in the southern mid-latitudes during the negative NAO phase. This impacts the location of stratospheric intrusions within the descending dry airstream behind the associated cold front of the extratropical cyclone and the venting of low-level pollution up into the free troposphere within

Sea-level records from the U.S. mid-Atlantic constrain Laurentide Ice Sheet extent during Marine Isotope Stage 3.

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Pico, T; Creveling, J R; Mitrovica, J X

2017-05-30

The U.S. mid-Atlantic sea-level record is sensitive to the history of the Laurentide Ice Sheet as the coastline lies along the ice sheet's peripheral bulge. However, paleo sea-level markers on the present-day shoreline of Virginia and North Carolina dated to Marine Isotope Stage (MIS) 3, from 50 to 35 ka, are surprisingly high for this glacial interval, and remain unexplained by previous models of ice age adjustment or other local (for example, tectonic) effects. Here, we reconcile this sea-level record using a revised model of glacial isostatic adjustment characterized by a peak global mean sea level during MIS 3 of approximately -40 m, and far less ice volume within the eastern sector of the Laurentide Ice Sheet than traditional reconstructions for this interval. We conclude that the Laurentide Ice Sheet experienced a phase of very rapid growth in the 15 kyr leading into the Last Glacial Maximum, thus highlighting the potential of mid-field sea-level records to constrain areal extent of ice cover during glacial intervals with sparse geological observables.

Influence of internal tides on Antarctic Bottom Water propagation through abyssal channels

Science.gov (United States)

Morozov, Eugene

2010-05-01

Antarctic Bottom Water (AABW) propagates in the Atlantic Ocean from the Weddell Sea to the north through narrow passages in submarine ridges. Submarine ridges are regions of strong internal tide generation in the ocean that causes mixing and eventually AABW loses its distinguishing properties such as low temperature and salinity. The Vema Fracture Zone (11 N) and Romanche Fracture Zone (equator) in the Mid-Atlantic Ridge (MAR) are pathways for AABW to the Northeast Atlantic. The deep basin of the Northeast Atlantic (Canary Basin and Gambia Abyssal Plain) are filled with the bottom water propagating through the Vema FZ rather than through the equatorial fracture zones because strong internal tides and mixing over the slopes of the MAR near the equator cause warming of AABW and decrease of its density. Further propagation of AABW through the Kane Gap is low. Recent field measurements in the fracture zones confirm this concept based on modeling results. Results of recent cruises are presented.

Watershed Scale Impacts of Stormwater Green Infrastructure on Hydrology and Nutrient Fluxes in the Mid-Atlantic Region.

Science.gov (United States)

Jaffe, P. R.; Pennino, M. J.; McDonald, R.

2015-12-01

Stormwater green infrastructure (SGI), including rain gardens, detention ponds, bioswales, and green roofs, is being implemented in cities across the globe to help reduce flooding, decrease combined sewer overflows, and lessen pollutant transport to streams and rivers. Despite the increasing use of urban SGI, there is much uncertainty regarding the cumulative effects of multiple SGI projects on hydrology and water quality at the watershed scale. To assess the cumulative effects of SGI, major cities across the mid-Atlantic were selected based on availability of SGI, water quality, and stream flow data. The impact of SGI was evaluated by comparing similar watersheds, with and without SGI or by assessing how long-term changes in SGI impact hydrologic and water quality metrics over time. Most mid-Atlantic cities have a goal of achieving 10-75% SGI by 2030. Of these cites, Washington D.C. currently has the highest density of SGI (15.5%), while Philadelphia, PA and New York, NY have the lowest (0.14% and 0.28%, respectively). When comparing watersheds of similar size and percent impervious surface cover, watersheds with lower amounts of SGI, on average, show up to 40% greater annual total nitrogen and 75% greater total phosphorus loads and show flashier hydrology (as indicated by 35% greater average peak discharge, 26% more peak discharge events per year, and 21% higher peak-to-volume ratio) compared to watersheds with higher amounts of SGI. However, for cities with combined sewer systems (e.g. Washington, D.C. and Philadelphia, PA), there was no relationship between the level of combined sewer overflows (CSOs) and the amount of SGI, indicating the level of SGI may not yet be sufficient to reduce CSOs as intended. When comparing individual watersheds over time, increases in SGI show no significant effect on the long-term trends in nutrient loads or hydrologic variables, potentially being obscured by the larger effect of interannual variability.

An Atlantic influence on Amazon rainfall

Energy Technology Data Exchange (ETDEWEB)

Yoon, Jin-Ho [University of Maryland, Department of Atmospheric and Oceanic Science, College Park, MD (United States); Zeng, Ning [University of Maryland, Earth System Science Interdisciplinary Center, College Park, MD (United States); University of Maryland, Department of Atmospheric and Oceanic Science, College Park, MD (United States)

2010-02-15

Rainfall variability over the Amazon basin has often been linked to variations in Pacific sea surface temperature (SST), and in particular, to the El Nino/Southern Oscillation (ENSO). However, only a fraction of Amazon rainfall variability can be explained by ENSO. Building upon the recent work of Zeng (Environ Res Lett 3:014002, 2008), here we provide further evidence for an influence on Amazon rainfall from the tropical Atlantic Ocean. The strength of the North Atlantic influence is found to be comparable to the better-known Pacific ENSO connection. The tropical South Atlantic Ocean also shows some influence during the wet-to-dry season transition period. The Atlantic influence is through changes in the north-south divergent circulation and the movement of the ITCZ following warm SST. Therefore, it is strongest in the southern part of the Amazon basin during the Amazon's dry season (July-October). In contrast, the ENSO related teleconnection is through anomalous east-west Walker circulation with largely concentrated in the eastern (lower) Amazon. This ENSO connection is seasonally locked to boreal winter. A complication due to the influence of ENSO on Atlantic SST causes an apparent North Atlantic SST lag of Amazon rainfall. Removing ENSO from North Atlantic SST via linear regression resolves this causality problem in that the residual Atlantic variability correlates well and is in phase with the Amazon rainfall. A strong Atlantic influence during boreal summer and autumn is particularly significant in terms of the impact on the hydro-ecosystem which is most vulnerable during the dry season, as highlighted by the severe 2005 Amazon drought. Such findings have implications for both seasonal-interannual climate prediction and understanding the longer-term changes of the Amazon rainforest. (orig.)

Aerosol-radiation-cloud interactions in the South-East Atlantic: first results from the ORACLES-2016 deployment and plans for future activities

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Redemann, J.; Wood, R.; Zuidema, P.; Haywood, J. M.; Piketh, S.; Formenti, P.; Abel, S.

2016-12-01

Southern Africa produces almost a third of the Earth's biomass burning (BB) aerosol particles. Particles lofted into the mid-troposphere are transported westward over the South-East (SE) Atlantic, home to one of the three permanent subtropical stratocumulus (Sc) cloud decks in the world. The SE Atlantic stratocumulus deck interacts with the dense layers of BB aerosols that initially overlay the cloud deck, but later subside and may mix into the clouds. These interactions include adjustments to aerosol-induced solar heating and microphysical effects, and their global representation in climate models remains one of the largest uncertainties in estimates of future climate. Hence, new observations over the SE Atlantic have significant implications for regional and global climate change predictions. Our understanding of aerosol-cloud interactions in the SE Atlantic is severely limited. Most notably, we are missing knowledge on the absorptive and cloud nucleating properties of aerosols, including their vertical distribution relative to clouds, on the locations and degree of aerosol mixing into clouds, on the processes that govern cloud property adjustments, and on the importance of aerosol effects on clouds relative to co-varying synoptic scale meteorology. We describe first results from various synergistic, international research activities aimed at studying aerosol-cloud interactions in the region: NASA's airborne ORACLES (ObseRvations of Aerosols Above Clouds and Their IntEractionS) deployment in August/September of 2016, the DoE's LASIC (Layered Atlantic Smoke Interactions with Clouds) deployment of the ARM Mobile Facility to Ascension Island (June 2016 - October 2017), the ground-based components of CNRS' AEROCLO-sA (Aerosols Clouds and Fog over the west coast of southern Africa), and ongoing regional-scale integrative, process-oriented science efforts as part of SEALS-sA (Sea Earth Atmosphere Linkages Study in southern Africa). We expect to describe experimental

Species richness and structure of an anuran community in an Atlantic Forest site in southern Brazil

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Adriele Karlokoski Cunha

2010-06-01

Full Text Available The species richness and spatial distribution of an anuran community were studied over 12 months in an Atlantic Forest area in São José dos Pinhais Municipality, Paraná State, southern Brazil. During field surveys, we registered 32 species from ten families: Brachycephalidae (2, Bufonidae (2, Centrolenidae (1, Cycloramphidae (1, Hemiphractidae (1, Hylidae (18, Hylodidae (1, Leiuperidae (2, Leptodactylidae (3, and Microhylidae (1. Sixteen species were registered in open areas, while seventeen species were found on forest borders and twenty species in forest areas. In relation to the microhabitat utilization, species were registered according to stratum of vocalization: 1 on the ground (eight; 2 in the water (two; 3 in the lower stratum (eleven; 4 in the intermediate stratum (five; 5 in the upper stratum (four. Five species were abundant (15.6%, while twelve were common (37.5%, and fifteen were considered rare (46.9%. The biological aspects of the majority of the species described in this work as related to forest areas are not well known. This fact reinforces the importance of Atlantic Forest conservation.

Disking and mid- and understory removal following an above-average acorn crop in three mature oak forests in southern Indiana

Science.gov (United States)

Ronald A. Rathfon; Nathanael I. Lichti; Robert K. Swihart

2008-01-01

We disked using small-scale equipment in the understory of three mature upland oak (Quercus) forests in southern Indiana immediately following acorn dispersal in an aboveaverage seed crop year as a means of improving oak seedling establishment. Three different mid- and understory removal treatments were also applied to create favorable light...

Atlantic update, July 1986--June 1990: Outer Continental Shelf oil and gas activities

Energy Technology Data Exchange (ETDEWEB)

Karpas, R.M.; Gould, G.J.

1990-10-01

This report describes outer continental shelf oil and gas activities in the Atlantic Region. This edition of the Atlantic Update includes an overview of the Mid-Atlantic Planning Area and a summary of the Manteo Prospect off-shore North Carolina. 6 figs., 8 tabs.

Effects of watershed land use and geomorphology on stream low flows during severe drought conditions in the southern Blue Ridge Mountains, Georgia and North Carolina, United States

Science.gov (United States)

Katie Price; C. Jackson; Albert Parker; Trond Reitan; John Dowd; Mike Cyterski

2011-01-01

Land use and physiographic variability influence stream low flows, yet their interactions and relative influence remain unresolved. Our objective was to assess the influence of land use and watershed geomorphic characteristics on low-flow variability in the southern Blue Ridge Mountains of North Carolina and Georgia. Ten minute interval discharge data for 35 streams (...

Circulation in the region of the Reykjanes Ridge in June-July 2015

Science.gov (United States)

Tillys, Petit; Herle, Mercier; Virginie, Thierry

2017-04-01

The Reykjanes Ridge is a major topographic feature of the North-Atlantic Ocean lying south of Iceland that strongly influences the pathways of the upper and lower limbs of the meridional overturning cell. The circulation in the vicinity of the Reykjanes Ridge is anticyclonic and characterized by a southwestward flow (the East Reykjanes Ridge Current, ERRC) along the eastern flank and a northeastward flow (the Irminger Current, IC) along the western flank. Even if it is admitted that the ERRC feeds the IC through a cross-ridge flow, details and magnitude of this circulation remain unclear. In this study, the circulation in the region of the Reykjanes Ridge was investigated based on ADCP and CTDO2 measurements carried out from the R/V Thalassa during the RREX cruise, which provided a snapshot of the water mass distribution and circulation during summer 2015. One hydrographic section followed the top of the Reykjanes Ridge between Iceland and 50˚ N and three other sections were carried out perpendicularly to the ridge at 62˚ N, 58.5˚ N and 56˚ N. Geostrophic transports were estimated by combining ADCP and hydrographic data. Those observations were used to provide an estimate of the circulation around the Ridge and to discuss the meridional evolutions of the ERRC and IC transports along the Ridge and their connection to the cross-Ridge flows. The section along the top of the Reykjanes Ridge allowed us to describe the cross ridge exchanges. A westward flow crossed the Ridge between Iceland and 53˚ N. Its top to bottom integrated transport was estimated at 17.7 Sv. Two main passages were identified for the westward crossing. A first passage is located near 57˚ N (Bight Fracture Zone, BFZ) in agreement with previous studies. More surprisingly, a second passage is located near 59˚ N. The top-to-bottom transports of those two main flows were estimated at 6.5 and 8 Sv respectively. The IC and ERRC top-to-bottom integrated transports were maximum at 58.5˚ N and

Genotypic Diversity of Phytophthora cinnamomi and P. plurivora in Maryland's Nurseries and Mid-Atlantic Forests.

Science.gov (United States)

Beaulieu, Justine; Ford, Blaine; Balci, Yilmaz

2017-06-01

Genetic diversity of two Phytophthora spp.-P. cinnamomi (102 isolates), commonly encountered in Maryland nurseries and forests in the Mid-Atlantic United States, and P. plurivora (186 isolates), a species common in nurseries-was characterized using amplified fragment length polymorphism. Expected heterozygosity and other indices suggested a lower level of diversity among P. cinnamomi than P. plurivora isolates. Hierarchical clustering showed P. cinnamomi isolates separated into four clusters, and two of the largest clusters were closely related, containing 80% of the isolates. In contrast, P. plurivora isolates separated into six clusters, one of which included approximately 40% of the isolates. P. plurivora isolates recovered from the environment (e.g., soil and water) were genotypically more diverse than those found causing lesions. For both species, isolate origin (forest versus nursery or among nurseries) was a significant factor of heterozygosity. Clonal groups existed within P. cinnamomi and P. plurivora and included isolates from both forest and nurseries, suggesting that a pathway from nurseries to forests or vice versa exists.

A new species of Pristimantis from southern Ecuador (Anura, Craugastoridae)

Science.gov (United States)

Székely, Paul; Cogălniceanu, Dan; Székely, Diana; Páez, Nadia; Ron, Santiago R.

2016-01-01

Abstract A new species of Pristimantis is described from Reserva Buenaventura, southern Ecuador, at elevations between 878 and 1082 m. A molecular phylogeny based on nuclear and mitochondrial genes shows that the new species is closely related to Pristimantis phoxocephalus, Pristimantis riveti, and Pristimantis versicolor. The new species differs from them and other morphologically similar congeners in having a low W-shaped dermal ridge in the scapular region, a large conical tubercle on the upper eyelid and on the heel, a thin mid dorsal fold, and a longitudinal lateral fold starting behind the tympanic fold and extending along the anterior two thirds of the flank. The new species inhabits cloud forests in the Pacific slopes of the Andes. PMID:27551223

Amphibians of Serra Bonita, southern Bahia: a new hotpoint within Brazil’s Atlantic Forest hotspot

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Iuri Dias

2014-10-01

Full Text Available We studied the amphibian community of the Private Reserve of Natural Heritage (RPPN Serra Bonita, an area of 20 km2 with steep altitudinal gradients (200–950 m a.s.l. located in the municipalities of Camacan and Pau-Brasil, southern Bahia State, Brazil. Data were obtained at 38 sampling sites (including ponds and transects within the forest and in streams, through active and visual and acoustic searches, pitfall traps, and opportunistic encounters. We recorded 80 amphibian species distributed in 15 families: Aromobatidae (1, Brachycephalidae (3, Bufonidae (4, Centrolenidae (2, Ceratophryidae (1, Craugastoridae (7, Eleutherodactylidae (2, Hemiphractidae (2, Hylidae (42, Hylodidae (1, Leptodactylidae (7, Microhylidae (3, Siphonopidae (1, Odontophrynidae (3 and Pipidae (1. Species richness was positively correlated with monthly rainfall. Near 36% of the species were found in strictly forest environments, 15% are endemic to Bahia State and 77.2% are endemic to the Atlantic Forest biome. The large species diversity of this small area, the high degree of endemism and the taxonomic and biogeographic significance turn the Serra Bonita mountain into a hotpoint for amphibians within Brazil’s Atlantic Forest hotspot.

Amphibians of Serra Bonita, southern Bahia: a new hotpoint within Brazil’s Atlantic Forest hotspot

Science.gov (United States)

Dias, Iuri Ribeiro; Medeiros, Tadeu Teixeira; Vila Nova, Marcos Ferreira; Solé, Mirco

2014-01-01

Abstract We studied the amphibian community of the Private Reserve of Natural Heritage (RPPN) Serra Bonita, an area of 20 km2 with steep altitudinal gradients (200–950 m a.s.l.) located in the municipalities of Camacan and Pau-Brasil, southern Bahia State, Brazil. Data were obtained at 38 sampling sites (including ponds and transects within the forest and in streams), through active and visual and acoustic searches, pitfall traps, and opportunistic encounters. We recorded 80 amphibian species distributed in 15 families: Aromobatidae (1), Brachycephalidae (3), Bufonidae (4), Centrolenidae (2), Ceratophryidae (1), Craugastoridae (7), Eleutherodactylidae (2), Hemiphractidae (2), Hylidae (42), Hylodidae (1), Leptodactylidae (7), Microhylidae (3), Siphonopidae (1), Odontophrynidae (3) and Pipidae (1). Species richness was positively correlated with monthly rainfall. Near 36% of the species were found in strictly forest environments, 15% are endemic to Bahia State and 77.2% are endemic to the Atlantic Forest biome. The large species diversity of this small area, the high degree of endemism and the taxonomic and biogeographic significance turn the Serra Bonita mountain into a hotpoint for amphibians within Brazil’s Atlantic Forest hotspot. PMID:25408616

High occurrence of Calodium hepaticum (syn. Capillaria hepatica spurious infection in a village in the Atlantic Forest of southern Brazil

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Débora do Rocio Klisiowicz

2014-06-01

Full Text Available Calodium hepaticum (syn. Capillaria hepatica is a nematode of the Capillariidae family that infects rodents and other mammals. In Brazil, human spurious infections of C. hepaticum have been detected in indigenous or rural communities from the Amazon Basin, but not in the southern states of the country. Here, we report the highest occurrence (13.5% of 37 residents of C. hepaticum human spurious infection detected in Brazil and the first record in a southern region, Guaraqueçaba. The finding is explained by the area being located in the Atlantic Forest of the state of Paraná, surrounded by preserved forests and because the inhabitants consume the meat of wild mammals.

High-resolution bathymetry as a primary exploration tool for seafloor massive sulfide deposits - lessons learned from exploration on the Mid-Atlantic and Juan de Fuca Ridges, and northern Lau Basin

Science.gov (United States)

Jamieson, J. W.; Clague, D. A.; Petersen, S.; Yeo, I. A.; Escartin, J.; Kwasnitschka, T.

2016-12-01

High-resolution, autonomous underwater vehicle (AUV)-derived multibeam bathymetry is increasingly being used as an exploration tool for delineating the size and extent of hydrothermal vent fields and associated seafloor massive sulfide deposits. However, because of the limited amount of seafloor that can be surveyed during a single dive, and the challenges associated with distinguishing hydrothermal chimneys and mounds from other volcanic and tectonic features using solely bathymetric data, AUV mapping surveys have largely been employed as a secondary exploration tool once hydrothermal sites have been discovered using other exploration methods such as plume, self-potential and TV surveys, or ROV and submersible dives. Visual ground-truthing is often required to attain an acceptable level of confidence in the hydrothermal origin of features identified in AUV-derived bathymetry. Here, we present examples of high-resolution bathymetric surveys of vent fields from a variety of tectonic environments, including slow- and intermediate-rate mid-ocean ridges, oceanic core complexes and back arc basins. Results illustrate the diversity of sulfide deposit morphologies, and the challenges associated with identifying hydrothermal features in different tectonic environments. We present a developing set of criteria that can be used to distinguish hydrothermal deposits in bathymetric data, and how AUV surveys can be used either on their own or in conjunction with other exploration techniques as a primary exploration tool.

Decadal variability and metastability in the Southern Hemisphere

Science.gov (United States)

O'Kane, Terence; Risbey, James; Franzke, Christian; Horenko, Illia; Monselesan, Didier

2014-05-01

An examination of systematic changes in the metastability of the southern hemisphere 500hPa circulation is performed using both cluster analysis techniques and split flow blocking indices. The cluster methodology is a purely data-driven approach for parametrisation whereby a multi-scale approximation to non-stationary dynamical processes is achieved through optimal sequences of locally stationary fast Vector Auto-Regressive Factor (VARX) processes and some slow (or persistent) hidden process switching between them. Comparison is made with blocking indices commonly used in weather forecasting and climate analysis to identify dynamically relevant metastable regimes in the 500hPa circulation in both reanalysis and AMIP model data sets. Our analysis characterises the metastable regime in both reanalysis and model data sets prior to 1978 as positive and negative phases of a hemispheric mid-latitude blocking state with the Southern Annular Mode (SAM) associated with a transition state. Post 1978, SAM emerges as a true metastable state replacing the negative phase of the hemispheric blocking pattern. The hidden state frequency of occurrences exhibits strong trends. The blocking pattern dominates in the early 1980s then gradually decreases. There is a corresponding increase in the SAM frequency of occurrence. This trend is largely evident in the reanalysis summer and spring but was not evident in the AMIP data set. Non-stationary cluster analysis was then further used to identify the Southern Oceans response to the systematic changes in the mid-latitude atmospheric circulation and identify dynamical regimes associated with subsurface thermocline anomalies which were found to teleconnect the Pacific and Atlantic regions of the Antarctic Circumpolar Current (ACC).

Evidence for small-scale convection in the Pacific and Atlantic upper mantle from joint analysis of surface wave phase velocity and seafloor bathymetry

Science.gov (United States)

Ma, Z.; Dalton, C. A.

2017-12-01

It has been long observed that the rate of seafloor subsidence in the Pacific Ocean is lower than predicted by half-space cooling at ages older than 70 Myr. The magnitude, geographical distribution, onset time, and physical origin of the flattening are fundamental to our understanding of the evolution of oceanic lithosphere, and give important constraints on the Earth's heat budget and ocean volume throughout its history. However, none of these quantities is well established even after a long history of debates. Here, we present evidence from bathymetry and seismic tomography for the wide-scale operation of small-scale convection in the Pacific and Atlantic upper mantle. We track the temporal evolution of surface wave phase velocity and seafloor topography along age trajectories, which connect each piece of seafloor with the ridge segment that created it. The half-space cooling model (HSCM) and plate cooling model are used to predict the age dependence of phase velocity and bathymetry and to identify, for each age trajectory, the age at which the HSCM fails to explain the observations. The phase velocity and bathymetry are analyzed independently and yet yield identical results for more than 80% of points. We observe a wide range of ages at which the HSCM fails in the Atlantic and a much narrower range in the Pacific. We find that the age at which the HSCM fails is anti-correlated with the present-day depth of the ridge axis, with younger failure ages corresponding to deeper ridge axes and therefore colder mantle beneath the ridge.Such dependence is best explained by the small-scale convection model in which the effective viscosity of the lithosphere is regulated by the dehydration process that happens at the mid-ocean ridges. Decompression melting at a ridge removes water from the mantle and generates a depleted, dehydrated, and viscous layer. Since high mantle potential temperatures cause decompression melting to begin at greater depths, the thickness of the

Pb sbnd Sr sbnd Nd isotopic data of Indian Ocean ridges: new evidence of large-scale mapping of mantle heterogeneities

Science.gov (United States)

Hamelin, Bruno; Dupré, Bernard; Allègre, Claude J.

1986-01-01

A Pb sbnd Sr sbnd Nd isotope study of South West and East Indian Ridges confirms that the Indian Ocean belongs to a specific regional isotopic domain, as previously suggested by the results from islands of this ocean. The isotopic domain defined by the Indian MORB is indeed different from that of the North Atlantic and East Pacific Oceans. This demonstrates that the convective circulation of the upper mantle does not allow a rapid homogenization from one region to the other. The isotopic data of the Indian ridges can be interpreted by a contamination model, in which the depleted upper mantle (identical to that under the North Atlantic) is contaminated by two different types of contaminant, one corresponding to the source of the "central Indian Ocean" islands (Amsterdam, St. Paul, Marion, Prince Edward, Réunion, Rodriguez, Mauritius), and the other to a source similar to that of Walvis or Ninety East aseismic ridges. These two contaminants would have contributed to the ridge volcanism in different proportions over time.

Multibeam collection for CE16007: Multibeam data collected aboard Celtic Explorer from 2016-04-08 to 2016-04-22, Galway, Ireland to St. John's, Canada

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Coverage includes a swath of multibeam data with focus on a previously unidentified seabed feature in the Mid-Atlantic Ridge. The survey was conducted between 08/04...

Temporal and Directional Patterns of Nymphal Halyomorpha halys (Hemiptera: Pentatomidae) Movement on the Trunk of Selected Wild and Fruit Tree Hosts in the Mid-Atlantic Region.

Science.gov (United States)

Acebes-Doria, Angelita L; Leskey, Tracy C; Bergh, J Christopher

2017-04-01

Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) is an invasive and polyphagous herbivore that has been problematic in Mid-Atlantic fruit orchards, many of which are adjacent to woodlands containing its wild hosts. Our tree census in woodlands bordering 15 Mid-Atlantic apple orchards revealed 47 species of deciduous trees and shrubs, 76.6% of which were recorded hosts of H. halys. Tree of heaven was most common and abundant overall. Halyomorpha halys nymphs have a substantial walking dispersal capacity, and their fitness is enhanced by feeding on multiple hosts. Directional and temporal patterns of nymphal H. halys movement on selected wild hosts and apple and peach trees at the orchard-woodland interface were monitored in 2014 and 2015 using passive traps to capture nymphs walking up and down tree trunks. Weekly captures from mid-May to late September or mid-October were compared among hosts across both seasons. Despite higher total nymphal captures in 2014 than 2015, the seasonal trends for both years were similar and indicated bivoltine H. halys populations. In both years, more nymphs were intercepted while walking up than down and captures of upward- and downward-walking nymphs varied significantly among the hosts. All instars were captured, but captures of second instars predominated. Captures reflected seasonal changes in instar distribution and consisted predominantly of younger and older nymphs, early and later in the season, respectively. Results are discussed in relation to host and seasonal effects on the movement of nymphs at the orchard-woodland interface, and the implications for H. halys management. © The Authors 2017. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Physical trajectory profile data from glider ru23 deployed by Rutgers, the State University of New Jersey in the Mid-Atlantic Bight from 2012-10-25 to 2012-11-05 (NCEI Accession 0145723)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Slocum glider ru23 was deployed prior to the movement of Hurrican Sandy into the Mid-Atlantic Bight and was deployed to sample the sub-surface waters during the...

Breeding biology and conservation of hawk-eagles (Spizaetus spp. (Aves, Accipitridae in southern Atlantic Forest, Brazil

Directory of Open Access Journals (Sweden)

Felipe Zilio

2017-10-01

Full Text Available ABSTRACT Neotropical hawk-eagles (Spizaetus spp. are large forest raptors, having low population densities and high sensitivity to human disturbance. The three species of Brazil’s Atlantic forest (S. ornatus, S. melanoleucus, S. tyrannus are threatened and little is known of many aspects of their biology, such habitat requirements, nesting behavior, and food habitats. Here I present data about the breeding biology, diet and behavior of the Ornate Hawk-Eagle (S. ornatus; OHE and the Black-and-white Hawk-Eagle (S. melanoleucus; BWHW, and estimations of distribution - extent of occurrence (EOO - and population sizes for the three hawk-eagles of the southern Atlantic Forest. I compiled data from nine years of field studies done in Rio Grande do Sul and Santa Catarina combined with data from the literature (n = 191 records. I calculated the total amount of forest available for each species by GIS analyses and estimated population sizes based on species density data from the literature. The EOO was 123,551 km² for BWHE, 92,512 km² for OHE, and 67,824 km² for Black Hawk-Eagle (S. tyrannus; BHE. All species experienced more than 30% shrinkage in their historical distribution (before the year 2000. Forest remnants comprise 32% of BHE’s EOO and around 20% for other hawk-eagle species. Population sizes estimated for the southern region were 869 pairs for BHE (1,684 individuals, 1,532 pairs for BWHE (2,849 individuals, and 2,020 pairs for OHE (1,192 individuals. Population size estimates based only on forest patches larger than 10 km² were 542 pairs for BHE (RS = 48 pairs; SC = 494 pairs, 818 pairs for BWHE (RS = 67 pairs; SC = 751 pairs, and 1,178 pairs for OHE (RS = 67 pairs; SC = 1,111 pairs. I recorded displays and copulation of BWHE in July; the nest was built in an inaccessible, emergent tree in the hillside of a valley. Two nests of OHE were found in emergent trees (20 m and 30 m height measured 138 x 115 x 45 cm and 132 x 100 x 100 cm; one

Diatom and silicoflagellate biostratigraphy for the late Eocene: ODP 1090 (sub-Antarctic Atlantic)

Science.gov (United States)

Barron, John A.; Bukry, David B.; Gersonde, Rainer

2014-01-01

Abundant and well-preserved diatoms and silicofl agellate assemblages are documented through a complete late Eocene sequence, ODP Hole 1090B, recovered from the southern Agulhas Ridge in the sub-Antarctic South Atlantic. A sequence of Cestodiscus (diatom) species occurrence events involving C. pulchellus var. novazealandica, C. fennerae, C. antarcticus, C. convexus, C. trochus, and C. robustus is tied with paleomagnetic stratigraphy and provides the basis of proposing a new diatom zonation for the latest middle Eocene to early Oligocene (~37.6–33.4 Ma) of the sub-Antarctic South Atlantic. Comparison with previously published diatom occurrence charts suggested this zonation should be applicable throughout the low latitude regions of the world’s oceans. Silicofl agellates belong to the Dictyocha hexacantha and the overlying Corbisema apiculata Zones. The late Eocene succession of silicofl agellate species is dominated by Naviculopsis (20–60%). Naviculopsis constricta and N. foliacea dominate the D. hexacantha Zone, followed by the N. constricta, then N. biapiculata in the C. apiculata Zone. Cold-water Distephanus is most abundant in the latest Eocene along with N. biapiculata. The tops of zonal guide fossils Dictyocha hexacantha and Hannaites quadria (both 36.6 Ma) and Dictyocha spinosa (37.1 Ma) are tied with paleomagnetic stratigraphy.

Petroleum data for the pre-mid-Devonian basal clastics play, southern Mackenzie Valley

Energy Technology Data Exchange (ETDEWEB)

Lemieux, Y. [Natural Resources Canada, Yellowknife, NT (Canada). Geological Survey of Canada; Gal, L.P. [Northwest Territories Geoscience Office, Yellowknife, NT (Canada)

2008-07-01

This document presented petroleum data from the Mackenzie Corridor exploration area in the Northwest Territories. Both quantitative and qualitative geoscience data was compiled as part of a project under the Secure Canadian Energy Supply program of the Geological Survey of Canada. Three separate reservoir facies have been identified within the study area for their attributes relevant to petroleum exploration. This document defined and described the pre-mid-Devonian basal clastics play in the southern Great Slave Plains region where potential Lower Paleozoic source rocks include organic-rich beds of the Mirage Point and Chinchaga Formations, and regionally widespread, Middle to lower Upper Devonian shale. The play is analogous to the oil producing Middle Devonian clastic plays onlapping the Peace River Arch in northwestern Alberta. The seals, migration and trap styles for the reservoirs were discussed. Exploration risks include a thin and discontinuous reservoir with poor porosity; isolation from potential source beds; inadequate reservoir seals; and timing of hydrocarbon migration with respect to trap development. The petroleum play information was based on very few well penetrations. As such, the pre-mid-Devonian basal clastics play is considered to be a conceptual play that has not yet been adequately explored. 40 refs., 3 tabs., 12 figs.

Discovery and Distribution of Black Smokers on the Western Galapagos Spreading Center: Implications for Spatial and Temporal Controls on High Temperature Venting at Ridge/Hotspot Intersections

Science.gov (United States)

Haymon, R. M.; Anderson, P. G.; Baker, E. T.; Resing, J. A.; White, S. M.; MacDonald, K. C.

2006-12-01

flows of visually-similar ages (estimated to be tens-to-hundreds of years old). Possibly a volcanic pulse may have activated the hotspot- affected western GSC, and powered contemporaneous hydrothermal vents that now are waning. It may be that hotspots produce episodes of near-synchronous, extensive ridge volcanism and hydrothermal activity, followed by periods of quiescence. This idea is consistent with: the episodic eruption histories of Hawaii and Iceland; variably anomalous hydrothermal plume incidence (low on RR, SEIR, GSC; high on Mid-Atlantic Ridge near Azores hotspot); models of episodic melt extraction from mantle plumes; and evidence for magma propagation along hotspot-influenced ridges. Our hypothesis potentially can be tested by studies of gene flow between animal communities located on either side of the Galapagos hotspot, and by dating of GSC hydrothermal chimneys and the lava flows on which they are constructed.

Pressures of Partial Crystallization of Magmas Along Transforms: Implications for Crustal Accretion

Science.gov (United States)

Scott, J. L.; Zerda, C.; Brown, D.; Ciaramitaro, S. C.; Barton, M.

2016-12-01

Plate spreading at mid-ocean ridges is responsible for the creation of most of the crust on earth. The ridge system is very complex and many questions remain unresolved. Among these is the nature of magma plumbing systems beneath transform faults. Pervious workers have suggested that increased conductive cooling along transforms promotes higher pressures of partial crystallization, and that this explains the higher partial pressures of crystallization inferred for magmas erupted along slow spreading ridges compared to magmas erupted along faster spreading ridges. To test this hypothesis, we undertook a detailed analysis of pressures of partial crystallization for magmas erupted at 3 transforms along the fast to intermediate spreading East Pacific Rise(Blanco, Clipperton, and Siqueiros) and 3 transforms along the slow spreading Mid Atlantic Ridge(Famous Transform B, Kane, and 15°20'N). Pressures of partial crystallization were calculated from the compositions of glasses (quenched liquids) lying along the P (and T) dependent olivine, plagioclase, and augite cotectic using the method described by Kelley and Barton (2008). Published analyses of mid-ocean ridge basalt glasses sampled from these transforms and surrounding ridge segments were used as input data. Samples with anomalous chemical compositions and samples that yielded pressures associated with unrealistically large uncertainties were filtered out of the database. The pressures of partial crystallization for the remaining 916 samples ranged from 0 to 520 MPa with the great majority ( 95%) of sample returning pressures of less than 300 MPa. Pressures of 300 MPa) are associated with a small number of samples from the Pacific segments. Except for the Blanco, pressures of partial crystallization do not increase as transforms are approached. These observations contrast with those of previous workers, who reported anomalously high pressures (up to 1000 MPa) for a large number of samples erupted near both Atlantic

Sea surface temperatures from the southern Benguela region from the Pliocene and Pleistocene: tracking Agulhas Current input into the SE Atlantic

Science.gov (United States)

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

2011-12-01

The Pliocene and-Pleistocene epochs provide a way to understand the effect of past climate changes on key ocean currents. Here, we show results from ODP Site1087 (31.28'S, 15.19'E, 1374m water depth) to investigate changes in ocean circulation over the period of the mid-Pliocene warm period 3.0-3.5 Ma and compare these to the time of the 100 kyr Pleistocene glacial cycles. ODP 1087 is located in the South-eastern Atlantic Ocean, outside of the Benguela upwelling region; reconstructing the temperature history of the site will therefore provide an important data set from a part of the ocean that has few orbital-scale and continuous Pliocene temperature reconstructions. ODP 1087 can be used to investigate the history of the heat and salt transfer to the Atlantic Ocean from the Indian Ocean via the Agulhas Retroflection, which plays an important part in the global thermohaline circulation (Lutjeharms, 2007). Climate models and reconstructions for the most recent glacial-interglacial cycles have shown that changes to the strength of the heat transfer may cause major climatic changes and may play a role in transitions from glacial to interglacial events (Knorr & Lohmann, 2003). It is unknown how this transfer reacted to generally warmer global temperatures during the mid-Pliocene. Because the mid-Pliocene is seen as a model for future climate change it might provide a model for ocean circulations in a warmer world. Our approach is to apply several organic geochemistry proxies and foraminiferal analyses to reconstruct the history of ODP 1087. The UK37' index records differences in the unsaturated bonds in the C37 alkenones to reconstruct sea surface temperatures (Brassell et al., 1986). We present SSTs generated for the mid-Pliocene Warm period with a resolution of 4000 years. We compare this data to the time of the 100 kyr glacial cycles during the late Pleistocene. Even though ODP 1087 is located outside the Benguela upwelling system, it has lower Pliocene temperatures

Monitoring stink bugs (Hemiptera: Pentatomidae) in mid-Atlantic apple and peach orchards.

Science.gov (United States)

Leskey, T C; Hogmire, H W

2005-02-01

Pyramid traps coated with "industrial safety yellow" exterior latex gloss enamel paint and baited with Euschistus spp. aggregation pheromone, methyl (2E,4Z)-decadienoate captured more stink bugs than all other baited and unbaited trap types in both apple and peach orchards in 2002 and 2003. Commercial sources of dispensers of methyl (2E,4Z)-decadienoate deployed in association with pyramid traps had a significant impact on trap captures. Captures in pyramid traps were four-fold greater when baited with lures from IPM Technologies, Inc. (Portland, OR) than with lures from Suterra (Bend, OR). Variation in yellow pyramid trap color ("industrial safety yellow" and "standard coroplast yellow") and material (plywood, plastic, and masonite) did not affect trap captures. Brown stink bug was the predominant species captured (58%), followed by dusky stink bug, Euschistus tristigmus (Say) (20%); green stink bug, Acrosternum hilare (Say) (14%); and other stink bugs (Brochymena spp. and unidentified nymphs) (8%). Captures in baited pyramid traps were significantly correlated with tree beating samples in both managed and unmanaged apple orchards and with sweep netting samples in the unmanaged apple orchard. However, problems associated with trapping mechanisms of pyramid trap jar tops and jar traps likely resulted in reduced captures in baited traps. Improved trapping mechanisms must be established to develop an effective monitoring tool for stink bugs in mid-Atlantic orchards.

Iron-Oxidizing Bacteria Found at Slow-Spreading Ridge: a Case Study of Capelinhos Hydrothermal Vent (Lucky Strike, MAR 37°N)

Science.gov (United States)

Henri, P. A.; Rommevaux, C.; Lesongeur, F.; Emerson, D.; Leleu, T.; Chavagnac, V.

2015-12-01

Iron-oxidizing bacteria becomes increasingly described in different geological settings from volcanically active seamounts, coastal waters, to diffuse hydrothermal vents near seafloor spreading centers [Emerson et al., 2010]. They have been mostly identified and described in Pacific Ocean, and have been only recently found in hydrothermal systems associated to slow spreading center of the Mid-Atlantic Ridge (MAR) [Scott et al., 2015]. During the MoMARSAT'13 cruise at Lucky Strike hydrothermal field (MAR), a new hydrothermal site was discovered at about 1.5 km eastward from the lava lake and from the main hydrothermal vents. This active venting site, named Capelinhos, is therefore the most distant from the volcano, features many chimneys, both focused and diffuses. The hydrothermal end-member fluids from Capelinhos are different from those of the other sites of Lucky Strike, showing the highest content of iron (Fe/Mn≈3.96) and the lowest chlorinity (270 mmol/l) [Leleu et al., 2015]. Most of the chimneys exhibit rust-color surfaces and bacterial mats near diffuse flows. During the MoMARSAT'15 cruise, an active chimney, a small inactive one, and rust-color bacterial mat near diffuse flow were sampled at Capelinhos. Observations by SEM of the hydrothermal samples revealed the presence of iron oxides in an assemblage of tubular "sheaths", assembled "stalks", helical "stalks" and amorphous aggregates. These features are similar to those described from the Loihi iron-mats deposits and argue for the occurrence of iron-oxidizing bacteria. Cultures under micro-aerobic and neutral pH conditions allowed us to isolate strains from the small inactive chimney. Pyrosequencing of the 16S rRNA gene of the isolates and environmental samples will soon be performed, which should confirm the presence of iron-oxidizing bacteria and reveal the organization of bacterial communities in this original and newly discovered hydrothermal site of the slow spreading Mid-Atlantic Ridge. Emerson

Oak Ridge Reservation Site Management Plan for the Environmental Restoration Program

Energy Technology Data Exchange (ETDEWEB)

1994-06-01

This site management plan for the Oak Ridge Reservation (ORR) describes the overall approach for addressing environmental contamination problems at the ORR Superfund site located in eastern Tennessee. The ORR consists of three major US Department of Energy (DOE) installations constructed in the early to mid 1940s as research, development, and process facilities in support of the Manhattan Project. In addition to the three installations -- Oak Ridge National Laboratory (ORNL), the Oak Ridge Y-12 Plant, and the Oak Ridge K-25 Site (formerly the Oak Ridge Gaseous Diffusion Plant) -- the ORR Superfund Site also includes areas outside the installations, land used by the Oak Ridge Associated Universities and waterways that have been contaminated by releases from the DOE installations. To date, {approximately} 400 areas (Appendix A) requiring evaluation have been identified. Cleanup of the ORR is expected to take two to three decades and cost several billion dollars. This site management plan provides a blueprint to guide this complex effort to ensure that the investigation and cleanup activities are carried out in an efficient and cost-effective manner.

Oak Ridge Reservation Site Management Plan for the Environmental Restoration Program

International Nuclear Information System (INIS)

1994-06-01

This site management plan for the Oak Ridge Reservation (ORR) describes the overall approach for addressing environmental contamination problems at the ORR Superfund site located in eastern Tennessee. The ORR consists of three major US Department of Energy (DOE) installations constructed in the early to mid 1940s as research, development, and process facilities in support of the Manhattan Project. In addition to the three installations -- Oak Ridge National Laboratory (ORNL), the Oak Ridge Y-12 Plant, and the Oak Ridge K-25 Site (formerly the Oak Ridge Gaseous Diffusion Plant) -- the ORR Superfund Site also includes areas outside the installations, land used by the Oak Ridge Associated Universities and waterways that have been contaminated by releases from the DOE installations. To date, ∼ 400 areas (Appendix A) requiring evaluation have been identified. Cleanup of the ORR is expected to take two to three decades and cost several billion dollars. This site management plan provides a blueprint to guide this complex effort to ensure that the investigation and cleanup activities are carried out in an efficient and cost-effective manner

The East Atlantic - West Russia Teleconnection in the North Atlantic: Climate Impact and Relation to Rossby Wave Propagation

Science.gov (United States)

Lim, Young-Kwon

2014-01-01

Large-scale winter teleconnection of the East Atlantic - West Russia (EA-WR) over the Atlantic and surrounding regions is examined in order to quantify its impacts on temperature and precipitation and identify the physical mechanisms responsible for its existence. A rotated empirical orthogonal function (REOF) analysis of the upper-tropospheric monthly height field captures successfully the EA-WR pattern and its interannual variation, with the North Atlantic Oscillation as the first mode. EA-WRs climate impact extends from eastern North America to Eurasia. The positive (negative) EA-WR produces positive (negative) temperature anomalies over the eastern US, western Europe and Russia east of Caspian Sea, with negative (positive) anomalies over eastern Canada, eastern Europe including Ural Mountains and the Middle East. These anomalies are largely explained by lower-tropospheric temperature advections. Positive (negative) precipitation anomalies are found over the mid-latitude Atlantic and central Russia around 60E, where lower-level cyclonic (anticyclonic) circulation anomaly is dominant. The eastern Canada and the western Europe are characterized by negative (positive) precipitation anomalies.The EA-WR is found to be closely associated with Rossby wave propagation. Wave activity fluxes show that it is strongly tied to large-scale stationary waves. Furthermore, a stationary wave model (SWM) forced with vorticity transients in the mid-latitude Atlantic (approximately 40N) or diabatic heat source over the subtropical Atlantic near the Caribbean Sea produces well-organized EA-WR-like wave patterns, respectively. Sensitivity tests with the SWM indicate improvement in the simulation of the EA-WR when the mean state is modified to have a positive NAO component that enhances upper-level westerlies between 40-60N.

El Niño Variability in the Coastal Desert of Southern Peru during the Mid-Holocene

Science.gov (United States)

Fontugne, Michel; Usselmann, Pierre; Lavallée, Danièle; Julien, Michèle; Hatté, Christine

1999-09-01

Fourteen organic-rich sedimentary layers in the deposits at Quebrada de los Burros, in coastal southern Peru (Tacna department), lie between two debris-flow units, interpreted to result from El Niño events, at 8980 cal yr B.P. and after 3380 cal yr B.P., respectively. The accumulation of the fine-grained and low-energy sediments of this deposit during the mid-Holocene is incompatible with the occurrence of El Niño events in this region, as these would produce catastrophic flood deposits. The occurrence of organic-rich sediments and evidence of an enhancement of upwelling strength at this time imply the existence of a permanent water supply resulting from an increased condensation of fog at mid-altitudes. These results suggest a lower intensity and, perhaps, a lower frequency of occurrence of the El Niño phenomenon during the mid-Holocene. It is precisely during this period that the most important human settlements are found at this site, probably indicating the presence of reliable supply of fresh water. The chronologies for wetlands in the central south altiplano are out of phase with those indicating increased soil moisture episodes on the coast, implying a long-term difference in climate between these two regions.

Southern high latitude squat lobsters II: description of Uroptychus macquariae sp. nov. from Macquarie Ridge.

Science.gov (United States)

Schnabel, Kareen E; Burghardt, Ingo; Ahyong, Shane T

2017-11-23

Squat lobsters have only recently been recorded from the Macquarie Ridge, which extends south between New Zealand and Antarctica. Among these, Uroptychus insignis (Henderson, 1885) was recorded for the first time outside the western Indian Ocean, exhibiting only subtle morphological differences. Reexamination of the Macquarie Ridge and Indian Ocean specimens attributed to U. insignis using morphological and molecular data revealed the Macquarie Ridge form to represent a separate species. Subtle but consistent morphological differences are evident and partial CO1 sequence data indicates that the specimens collected on Macquarie Ridge differ from those collected in the Indian Ocean by more than 7%. The Macquarie Ridge species is described herein as Uroptychus macquariae n.sp. Subtle morphological differences between the new species and U. insignis are discussed.

Near-inertial motions over a mid-Ocean Ridge; Effects of topography and hydrothermal plumes

Science.gov (United States)

Thomson, Richard E.; Roth, Sharon E.; Dymond, Jack

1990-05-01

We investigate the spatial structure of near-inertial motions in the vicinity of the Endeavour segment of Juan de Fuca Ridge (approximately 48°N, 129°W) in the northeast Pacific Ocean. On the basis of time series current and water property data collected from September 1984 to September 1987, near-inertial motions are ubiquitous features of the 2200-m water column, with root-mean-square (rms) current speeds comparable to those of the dominant M2 tidal currents. Within the lower 1000 m of the water column where most of the observations were obtained, near-inertial oscillations have rms current speeds of O(1 cm/s) and vertical isotherm displacements of O(10 m). The fluctuations are confined to the frequency band 0.966-1.079 f(f is the local Coriolis parameter) and have characteristic event durations of 1 week. Although the spectra of subsurface motions are dominated by the "blue-shifted" superinertial band, significant spectral peaks are found also in the subinertial and inertial frequency bands. Marked alteration of the near-inertial current amplitudes occurs over two well-defined depth zones within the study region. Within the 200-m zone immediately above the 2100-m ridge crest, current amplitudes are amplified by a factor of 1.2-1.7 because of bottom reflection and/or scattering of the downward propagating energy. Evidence that the amplification may be linked to bottom reflection rather than to scattering is provided by flattening and cross-slope rotation of the near-inertial current ellipses with increased proximity to the top of the ridge. Reflection would occur at grazing angles of less than 1° and would be associated with surface-generated waves originating at distances of over 100 km from the observational site. In contrast to the enhanced amplitudes immediately above the top of the ridge, near-inertial currents within the 1600- to 1800-m depth range undergo pronounced attenuation and frequency alteration. Amplitude attenuation is especially pronounced for

Impact of hydrothermalism on the ocean iron cycle.

Science.gov (United States)

Tagliabue, Alessandro; Resing, Joseph

2016-11-28

As the iron supplied from hydrothermalism is ultimately ventilated in the iron-limited Southern Ocean, it plays an important role in the ocean biological carbon pump. We deploy a set of focused sensitivity experiments with a state of the art global model of the ocean to examine the processes that regulate the lifetime of hydrothermal iron and the role of different ridge systems in governing the hydrothermal impact on the Southern Ocean biological carbon pump. Using GEOTRACES section data, we find that stabilization of hydrothermal iron is important in some, but not all regions. The impact on the Southern Ocean biological carbon pump is dominated by poorly explored southern ridge systems, highlighting the need for future exploration in this region. We find inter-basin differences in the isopycnal layer onto which hydrothermal Fe is supplied between the Atlantic and Pacific basins, which when combined with the inter-basin contrasts in oxidation kinetics suggests a muted influence of Atlantic ridges on the Southern Ocean biological carbon pump. Ultimately, we present a range of processes, operating at distinct scales, that must be better constrained to improve our understanding of how hydrothermalism affects the ocean cycling of iron and carbon.This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'. © 2016 The Author(s).

Feeding ecology of Rivulus luelingi (Aplocheiloidei: Rivulidae in a Coastal Atlantic Rainforest stream, southern Brazil

Directory of Open Access Journals (Sweden)

Vinícius Abilhoa

Full Text Available Feeding habits of the killifish Rivulus luelingi collected in a black water stream of the Coastal Atlantic Rainforest in southern Brazil were investigated. Eight samplings were made between April 2003 and January 2004. The diet, assessed through a similarity matrix with the estimated contribution values of food items, included microcrustaceans, aquatic immature insects (larvae and pupae, aquatic adult insects, terrestrial insects, insect fragments, spiders, and plant fragments. Differences in the diet according to temporal variations (months were registered, but changes related with size classes evaluated and high/low precipitation period were not observed. The species presented an insectivorous feeding habit, and its diet in the studied stream was composed of autochthonous (mainly aquatic immature insects and allochthonous (mainly insect fragments material.

Bacterial diversity and biogeography in deep-sea sediments of the South Atlantic Ocean

DEFF Research Database (Denmark)

Schauer, Regina; Bienhold, Christina; Ramette, Alban

2010-01-01

in 1051 sequences. Phylotypes affiliated with Gammaproteobacteria, Deltaproteobacteria and Acidobacteria were present in all three basins. The distribution of these shared phylotypes seemed to be influenced neither by the Walvis Ridge nor by different deep water masses, suggesting a high dispersal......Microbial biogeographic patterns in the deep sea depend on the ability of microorganisms to disperse. One possible limitation to microbial dispersal may be the Walvis Ridge that separates the Antarctic Lower Circumpolar Deep Water from the North Atlantic Deep Water. We examined bacterial...... communities in three basins of the eastern South Atlantic Ocean to determine diversity and biogeography of bacterial communities in deep-sea surface sediments. The analysis of 16S ribosomal RNA (rRNA) gene clone libraries in each basin revealed a high diversity, representing 521 phylotypes with 98% identity...

Short term effects of particle exposure on hospital admissions in the Mid-Atlantic states: a population estimate.

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Itai Kloog

Full Text Available Many studies report significant associations between PM(2.5 (particulate matter <2.5 micrometers and hospital admissions. These studies mostly rely on a limited number of monitors which introduces exposure error, and excludes rural and suburban populations from locations where monitors are not available, reducing generalizability and potentially creating selection bias.Using prediction models developed by our group, daily PM(2.5 exposure was estimated across the Mid-Atlantic (Washington D.C., and the states of Delaware, Maryland, New Jersey, Pennsylvania, Virginia, New York and West Virginia. We then investigated the short-term effects of PM(2.5exposures on emergency hospital admissions of the elderly in the Mid-Atlantic region.We performed case-crossover analysis for each admission type, matching on day of the week, month and year and defined the hazard period as lag01 (a moving average of day of admission exposure and previous day exposure.We observed associations between short-term exposure to PM(2.5 and hospitalization for all outcomes examined. For example, for every 10-µg/m(3 increase in short-term PM(2.5 there was a 2.2% increase in respiratory diseases admissions (95% CI = 1.9 to 2.6, and a 0.78% increase in cardiovascular disease (CVD admission rate (95% CI = 0.5 to 1.0. We found differences in risk for CVD admissions between people living in rural and urban areas. For every10-µg/m(3 increase in PM(2.5 exposure in the 'rural' group there was a 1.0% increase (95% CI = 0.6 to 1.5, while for the 'urban' group the increase was 0.7% (95% CI = 0.4 to 1.0.Our findings showed that PM(2.5 exposure was associated with hospital admissions for all respiratory, cardio vascular disease, stroke, ischemic heart disease and chronic obstructive pulmonary disease admissions. In addition, we demonstrate that our AOD (Aerosol Optical Depth based exposure models can be successfully applied to epidemiological studies investigating the health

77 FR 33443 - Mid-Atlantic Fishery Management Council (MAFMC); Meeting

Science.gov (United States)

2012-06-06

...-Atlantic Fishery Management Council's (Council) Summer Flounder, Scup, Black Sea Bass, and Bluefish... Summer Flounder, Scup, Black Sea Bass, and Bluefish. Although non-emergency issues not contained in this...

Gondwana subduction-modified mantle domain prevents magmatic seafloor generation in the Central Indian Ridge

Science.gov (United States)

Morishita, T.; Nakamura, K.; Senda, R.; Suzuki, K.; Kumagai, H.; Sato, H.; Sato, T.; Shibuya, T.; Minoguchi, K.; Okino, K.

2013-12-01

The creation of oceanic crust at mid-ocean ridges is essential to understanding the genesis of oceanic plate and the evolution of the Earth. Detailed bathymetric measurements coupled with dense sample recovery at mid-ocean ridge revealed a wide range of variations in the ridge and seafloor morphologies, which cannot be simply explained by a spreading rate, but also by ridge geometry, mantle compositions and thermal structure (Dick et al., 2003 Nature; Cannat et al. 2006 Geology). It is now widely accepted that very limited magmatic activity with tectonic stretching generates oceanic core complex and/or smooth seafloor surface in the slow to ultraslow-spreading ridges, where serpentinized peridotite and gabbros are expected to be exposed associated with detachment faults (Cann et al., 1997 Nature; Cannat et al., 2006), although magmatism might be an essential role for the formation of oceanic core complexes (Buck et al., 2005 Nature; Tucholke et al 2008 JGR). A rising question is why magmatic activity is sometimes prevented during the oceanic plate formation. Ancient melting domain, that are too refractory to melt even in adiabatically upwelling to the shallow upper mantle, might cause the amagmatic spreading ridges (Harvey et al., 2006 EPSL, Liu et al.,2008 Nature). Its origin and effect on seafloor generations are, however, not well understood yet. We report an oceanic hill as an example of an ancient subduction-modified mantle domain, probably formed at continental margin of the Gondwanaland~Pangea supercontinent, existing beneath the Central Indian Ridge. This domain is the most likely to have prevented magmatic seafloor generation, resulting in creation of very deep oceanic valley and serpentine diaper (now the studied oceanic hill) at the present Central Indian ridge.

Heat Source for Active Venting at the Lost City Hydrothermal Field

Science.gov (United States)

Smith, J. E.; Germanovich, L. N.; Lowell, R. P.

2014-12-01

Located at the inside corner high of the Mid-Atlantic Ridge (MAR), 30°N and the Atlantis Transform Fault (ATF), the Atlantis Massif has been uplifted over the past ~2 my. The Southern Ridge of this massif hosts the Lost City Hydrothermal Field (LCHF), an off-axis hydrothermal vent field with carbonate chimney ages surpassing 120,000 yrs. The fluids discharging at LCHF carry geochemical signals that show a direct interaction with serpentinites. However, mineralogical evidence suggests that peridotite hydration began early in the formation of oceanic core complexes and previous modeling results indicate that serpentinization is unlikely to generate the heat necessary to maintain current levels of discharge at LCHF. This work develops a model for the LCHF venting based on the evidence of tectonic strain, detachment faulting, serpentinization, and convective fluid flow. We constrain fluid flow at the LCHF by vent geochemistry, vent temperature, seismically inferred faulting, and expected geothermal gradient ≈100°C/km. Present understanding of tectonic processes at the intersection of MAR and ATF suggests that unroofing of the footwall and crustal flexing of the massif induced normal faults, which run parallel to the MAR, throughout the Southern Ridge. In the absence of the evidence of magmatism, we test the feasibility of the geothermal gradient to cause fluid circulation in the high-permeability, sub-vertical fault zone. Fluid circulation in the fault zone is complemented by the bulk porous flow driven through the Southern Ridge by the lateral temperature gradient between the cold water on the steep face along the ATF side and the hot interior of the massif. In this scenario, the high pH hydrothermal fluids pass through the serpentinized zone before discharging as both high-temperature focused flow (40°-91°C) and low-temperature (≈15°C) diffuse flow at the LCHF.

Supra-subduction and mid-ocean ridge peridotites from the Piranshahr area, NW Iran

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Hajialioghli, Robab; Moazzen, Mohssen

2014-11-01

The Piranshahr metaperidotites in the northwestern end of the Zagros orogen were emplaced following the closure of the Neotethys ocean. The ophiolitic rocks were emplaced onto the passive margin of the northern edge of the Arabian plate as a result of northeastward subduction and subsequent accretion of the continental fragments. The metaperidotites have compositions ranging from low-clinopyroxene lherzolite to harzburgite and dunite. They are mantle residues with distinct geochemical signatures of both mid-ocean ridge and supra subduction zone (SSZ) affinities. The abyssal peridotites are characterized by high Al2O3 and Cr2O3 contents and low Mg-number in pyroxenes. The Cr-number in the coexisting spinel is also low. The SSZ mantle peridotites are characterized by low Al2O3 contents in pyroxenes as well as low Al2O3 and high Cr-number in spinel. Mineral chemical data indicate that the MOR- and SSZ-type peridotites are the residues from ∼15-20% and ∼30-35% of mantle melting, respectively. Considering petrography, mineralogy and textural evidence, the petrological history of the Piranshahr metaperidotites can be interpreted in three stages: mantle stable stage, serpentinization and metamorphism. The temperature conditions in the mantle are estimated using the Ca-in-orthopyroxene thermometer as 1210 ± 26 °C. The rocks have experienced serpentinization. Based on the textural observations, olivine and pyroxene transformed into lizardite and/or chrysotile with pseudomorphic textures at temperatures below 300 °C during the initial stage of serpentinization. Subsequent orogenic metamorphism affected the rocks at temperatures lower than 600 °C under lower-amphibolite facies metamorphism.

Earthquake swarms and the semidiurnal solid earth tide

Energy Technology Data Exchange (ETDEWEB)

Klein, F W

1976-01-01

Several correlations between peak earthquake activity during swarms and the phase and stress orientation of the calculated solid earth tide are described. The events correlating with the tide are clusters of swarm earthquakes. Swarm clusters from many sequences recorded over several years are used. Significant tidal correlations (which have less than a 5% chance of being observed if earthquakes were random) are found in the Reykjanes Peninsula in Iceland, the central Mid-Atlantic Ridge, the Imperial Valley and northern Gulf of California, and larger (m/sub b/ greater than or equal to 5.0) aftershocks of the 1965 Rat Islands earthquake. In addition, sets of larger single earthquakes on Atlantic and north-east Pacific fracture zones are significantly correlated with the calculated solid tide. No tidal correlation, however, could be found for the Matsushiro Japan swarm of 1965 to 1967. The earthquake-tide correlations other than those of the Reykjanes Peninsula and Mid-Atlantic Ridge can be interpreted as triggering caused by enhancement of the tectonic stress by tidal stress, i.e. the alignment of fault and tidal principal stresses. All tidal correlations except in the Aleutians are associated with oceanic rifts or their landward extensions. If lithospheric plates are decoupled at active rifts, then tidal stresses channeled along the lithospheric stress guide may be concentrated at ridge-type plate boundaries. Tidal triggering of earthquakes at rifts may reflect this possible amplification of tidal strains in the weakened lithosphere at ridges. 25 figures, 2 tables.

Interdecadal change of the controlling mechanisms for East Asian early summer rainfall variation around the mid-1990s

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Yim, So-Young; Wang, Bin; Kwon, MinHo

2014-03-01

East Asian (EA) summer monsoon shows considerable differences in the mean state and principal modes of interannual variation between early summer (May-June, MJ) and late summer (July-August, JA). The present study focuses on the early summer (MJ) precipitation variability. We find that the interannual variation of the MJ precipitation and the processes controlling the variation have been changed abruptly around the mid-1990s. The rainfall anomaly represented by the leading empirical orthogonal function has changed from a dipole-like pattern in pre-95 epoch (1979-1994) to a tripole-like pattern in post-95 epoch (1995-2010); the prevailing period of the corresponding principal component has also changed from 3-5 to 2-3 years. These changes are concurrent with the changes of the corresponding El Nino-Southern Oscillation (ENSO) evolutions. During the pre-95 epoch, the MJ EA rainfall anomaly is coupled to a slow decay of canonical ENSO events signified by an eastern Pacific warming, which induces a dipole rainfall feature over EA. On the other hand, during the post-95 epoch the anomalous MJ EA rainfall is significantly linked to a rapid decay of a central Pacific warming and a distinct tripolar sea surface temperature (SST) in North Atlantic. The central Pacific warming-induced Philippine Sea anticyclone induces an increased rainfall in southern China and decreased rainfall in central eastern China. The North Atlantic Oscillation-related tripolar North Atlantic SST anomaly induces a wave train that is responsible for the increase northern EA rainfall. Those two impacts form the tripole-like rainfall pattern over EA. Understanding such changes is important for improving seasonal to decadal predictions and long-term climate change in EA.

Rainfall declines over Queensland from 1951-2007 and links to the Subtropical Ridge and the SAM

International Nuclear Information System (INIS)

Cottrill, D A; Ribbe, J

2010-01-01

Much of southern and eastern Australia including Queensland have experienced rainfall declines over recent decades affecting agricultural production and accelerating water infrastructure development. Rainfall declines from southern Australia have now been directly related to changes in the Southern Annular Mode (SAM) and the subtropical ridge. In southern and coastal Queensland, the rainfall declines have occurred mostly in the austral summer and autumn. Observations from this region reveal the rainfall decline is correlated to an increase in the mean sea level pressure (MSLP) at many stations. The largest increases in MSLP are over southeast Queensland and coastal regions, where some of the largest rainfall declines occur. This study indicates the subtropical ridge as one of the main factors in the rainfall decline over this region. SAM is also likely to be important, although its seasonal influence, apart from winter, is harder to determine.

Potential contribution of surface-dwelling Sargassum algae to deep-sea ecosystems in the southern North Atlantic

Science.gov (United States)

Baker, Philip; Minzlaff, Ulrike; Schoenle, Alexandra; Schwabe, Enrico; Hohlfeld, Manon; Jeuck, Alexandra; Brenke, Nils; Prausse, Dennis; Rothenbeck, Marcel; Brix, Saskia; Frutos, Inmaculada; Jörger, Katharina M.; Neusser, Timea P.; Koppelmann, Rolf; Devey, Colin; Brandt, Angelika; Arndt, Hartmut

2018-02-01

Deep-sea ecosystems, limited by their inability to use primary production as a source of carbon, rely on other sources to maintain life. Sedimentation of organic carbon into the deep sea has been previously studied, however, the high biomass of sedimented Sargassum algae discovered during the VEMA Transit expedition in 2014/2015 to the southern North Atlantic, and its potential as a regular carbon input, has been an underestimated phenomenon. To determine the potential for this carbon flux, a literature survey of previous studies that estimated the abundance of surface water Sargassum was conducted. We compared these estimates with quantitative analyses of sedimented Sargassum appearing on photos taken with an autonomous underwater vehicle (AUV) directly above the abyssal sediment during the expedition. Organismal communities associated to Sargassum fluitans from surface waters were investigated and Sargassum samples collected from surface waters and the deep sea were biochemically analyzed (fatty acids, stable isotopes, C:N ratios) to determine degradation potential and the trophic significance within deep-sea communities. The estimated Sargassum biomass (fresh weight) in the deep sea (0.07-3.75 g/m2) was several times higher than that estimated from surface waters in the North Atlantic (0.024-0.84 g/m2). Biochemical analysis showed degradation of Sargassum occurring during sedimentation or in the deep sea, however, fatty acid and stable isotope analysis did not indicate direct trophic interactions between the algae and benthic organisms. Thus, it is assumed that components of the deep-sea microbial food web form an important link between the macroalgae and larger benthic organisms. Evaluation of the epifauna showed a diverse nano- micro-, meio, and macrofauna on surface Sargassum and maybe transported across the Atlantic, but we had no evidence for a vertical exchange of fauna components. The large-scale sedimentation of Sargassum forms an important trophic link

Regional characteristics of land use in northeast and southern Blue Ridge province: Associations with acid-rain effects on surface-water chemistry

International Nuclear Information System (INIS)

Liegel, L.; Cassell, D.; Stevens, D.; Shaffer, P.; Church, R.

1991-01-01

The Direct/Delayed Response Project (DDRP) is one of several being conducted by the United States Environmental Protection Agency to assess risk to surface waters from acidic deposition in the eastern United States. In one phase of DDRP, land use, wetland, and forest cover data were collected for statistical samples of 145 northeast lakes and 35 southern Blue Ridge Province stream watersheds. Land use and other data were then extrapolated from individual to target watershed populations in both study regions. Project statistical design allows summarization of results for various subsets of the target population. The article discusses results and implications of the land-use and land-cover characterization for both regions

Geophysical survey work plan for White Wing Scrap Yard (Waste Area Grouping 11) at Oak Ridge National Laboratory, Oak Ridge, Tennessee

International Nuclear Information System (INIS)

1994-02-01

The White Wing Scrap Yard, located on the U.S. Department of Energy's Oak Ridge Reservation, served as an aboveground storage and disposal area for contaminated debris and scrap from the Oak Ridge K-25 Site, the Oak Ridge Y-12 Plant, and the Oak Ridge National laboratory. The site is believed to have been active from the early 1950s until the mid-1960s. A variety of materials were disposed of at the site, including contaminated steel tanks and vehicles. As an interim corrective action, a surface debris removal effort was initiated in November 1993 to reduce the potential threat to human health and the environment from the radionuclide-contaminated debris. Following this removal effort, a geophysical survey will be conducted across the site to locate and determine the lateral extent of buried nonindigenous materials. This survey will provide the data necessary to prepare a map showing areas of conductivity and magnetic intensity that vary from measured background values. These anomalies represent potential buried materials and therefore can be targeted for further evaluation. This work plan outlines the activities necessary to conduct the geophysical survey

Mid-Ocean Ridge Melt Supply and Glacial Cycles: A 3D EPR Study of Crustal Thickness, Layer 2A, and Bathymetry

Science.gov (United States)

Boulahanis, B.; Aghaei, O.; Carbotte, S. M.; Huybers, P. J.; Langmuir, C. H.; Nedimovic, M. R.; Carton, H. D.; Canales, J. P.

2017-12-01

Recent studies suggest that eustatic sea level fluctuations induced by glacial cycles in the Pleistocene may influence mantle-melting and volcanic eruptions at mid-ocean ridges (MOR), with models predicting variation in oceanic crustal thickness linked to sea level change. Previous analyses of seafloor bathymetry as a proxy for crustal thickness show significant spectral energy at frequencies linked to Milankovitch cycles of 1/23, 1/41, and 1/100 ky-1, however the effects of faulting in seafloor relief and its spectral characteristics are difficult to separate from climatic signals. Here we investigate the hypothesis of climate driven periodicity in MOR magmatism through spectral analysis, time series comparisons, and statistical characterization of bathymetry data, seismic layer 2A thickness (as a proxy for extrusive volcanism), and seafloor-to-Moho thickness (as a proxy for total magma production). We utilize information from a three-dimensional multichannel seismic study of the East Pacific Rise and its flanks from 9°36`N to 9°57`N. We compare these datasets to the paleoclimate "LR04" benthic δ18O stack. The seismic dataset covers 770 km2 and provides resolution of Moho for 92% of the imaged region. This is the only existing high-resolution 3-D image across oceanic crust, making it ideal for assessing the possibility that glacial cycles modulate magma supply at fast spreading MORs. The layer 2A grid extends 9 km (170 ky) from the ridge axis, while Moho imaging extends to a maximum of 16 km (310 ky). Initial results from the East Pacific Rise show a relationship between sea level and both crustal thickness and sea floor depth, consistent with the hypothesis that magma supply to MORs may be modulated by glacial cycles. Analysis of crustal thickness and bathymetry data reveals spectral peaks at Milankovitch frequencies of 1/100 ky-1 and 1/41 ky-1 where datasets extend sufficiently far from the ridge. The layer 2A grid does not extend sufficiently far from the

Observation of carbonaceous aerosols and carbon monoxide in Mid-Atlantic region: Seasonal and inter-annual variations

Science.gov (United States)

Chen, L. A.; Doddridge, B. G.; Doddridge, B. G.; Dickerson, R. R.; Dickerson, R. R.

2001-05-01

As part of Maryland Aerosol Research and Characterization (MARCH-Atlantic) study, a long-term monitoring of ambient elemental and organic carbon (EC and OC) aerosols has been made at Fort Meade, MD (39.16° N 76.51° W; elevation 46 m MSL), a suburban site within the Baltimore-Washington (B-W) corridor, since July 1999. 24-hr average EC and OC are measured every day during the season-representative months (July 1999, October 1999, January 2000, April 2000 and July 2000). Carbon monoxide (CO) was also measured nearly continuously over the period. Strong correlation between EC and CO (r = 0.7 ~ 0.9) in every month suggests common or proximate sources, likely traffic emissions. The EC versus CO slope, however, varies in different seasons and is found to increase nonlinearly with the ambient temperature. EC source strength may peak in summer. OC shows strong correlation with EC (r ~ 0.95) only in winter, suggesting that OC is also of the same primary sources during wintertime. The Interagency Monitoring of Protected Visual Environments (IMPROVE) network has been measuring EC and OC around the United States since 1988. The FME data during July 1999 are also compared with simultaneous measurements at nearby IMPROVE sites, showing B-W corridor could be a major contributor to the carbonaceous aerosols in the Mid-Atlantic region. A decreasing trend of EC level is found in three IMPROVE sites in this region. This actually agrees with the decreasing trend of CO observed previously at Big Meadow, Shenandoah National Park if CO and EC are both influenced by traffic emissions.

Remedial Investigation Report on Chestnut Ridge Operable Unit 2 (Filled Coal Ash Pond/Upper McCoy Branch) at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee. Volume 1. Main Text

International Nuclear Information System (INIS)

1994-08-01

This document is a report on the remedial investigation (RI) of Chestnut Ridge Operable Unit (OU) 2 at the Oak Ridge Y-12 Plant. Chestnut Ridge OU 2 consists of Upper McCoy Branch (UMB), the Filled Coal Ash Pond (FCAP), and the area surrounding the Sluice Channel formerly associated with coal ash disposal in the FCAP. Chestnut Ridge OU 2 is located within the U.S. Department of Energy's (DOE's) Oak Ridge Reservation in Anderson County, Tennessee, approximately 24 miles west of Knoxville. The pond is an 8.5-acre area on the southern slope of Chestnut Ridge, 0.5 mile south of the main Y-12 Plant and geographically separated from the Y-12 Plant by Chestnut Ridge. The elevation of the FCAP is ∼ 950 ft above mean sea level (msl), and it is relatively flat and largely vegetated. Two small ponds are usually present at the northeast and northwest comers of the FCAP. The Sluice Channel Area extends ∼1000 ft from the northern margin of the FCAP to the crest of Chestnut Ridge, which has an elevation of ∼1100 ft above msl. The Sluice Channel Area is largely vegetated also. McCoy Branch runs from the top of Chestnut Ridge across the FCAP into Rogers Quarry and out of the quarry where it runs a short distance into Milton Hill Lake at McCoy Embayment, termed UMB. The portion south of Rogers Quarry, within Chestnut Ridge OU 4, is termed Lower McCoy Branch. The DOE Oak Ridge Y-12 Plant disposed of coal ash from its steam plant operations as a slurry that was discharged into an ash retention impoundment; this impoundment is the FCAP. The FCAP was built in 1955 to serve as a settling basin after coal ash slurried over Chestnut Ridge from the Y-12 Plant. The FCAP was constructed by building an earthen dam across the northern tributary of McCoy Branch. The dam was designed to hold 20 years of Y-12 steam plant ash. By July 1967, ash had filled up the impoundment storage behind the dam to within 4 ft of the top

Remedial Investigation Report on Chestnut Ridge Operable Unit 2 (Filled Coal Ash Pond/Upper McCoy Branch) at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee. Volume 1. Main Text