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DescriptionHigh resolution records of catchment response after the Younger Dryas event and to Holocene climate, vegetation and land-use change are rare and/or incomplete for Scotland. Lacustrine sedimentary deposits provide a record of landscape response through analysis of sediment properties and mineral analyses, and a chronology can be developed by interating OSL, radiocarbon and lead dating methods. These data allow accumulation rate changes to be determined since the Younger Dryas (the last ~11,000 ye [continued...]
Would North American Paleoindians have Noticed Younger Dryas Age Climate Changes?
2010-01-01
Paleoindian groups occupied North America throughout the Younger Dryas Chronozone. It is often assumed that cooling temperatures during this interval, and the impact these would have had on biotic communities, posed significant adaptive challenges to those groups. That assessment of the nature, severity and abruptness of Younger Dryas changes is largely based on ice core records from the Greenland ice sheet where changes were indeed dramatic. This paper reviews climatic and environmental records from this time period in continental North America. We conclude that, on the Great Plains and in the Rocky Mountains, conditions were in reality less extreme. It therefore follows that conditions during the Younger Dryas interval may not have measurably added to the challenge routinely faced by Pal...
An independent evaluation of the Younger Dryas extraterrestrial impact hypothesis
2009-10-27
Full Text Available.Based on elevated concentrations of a set of “impact markers” at the onset of the Younger Dryas stadial from sedimentary contexts across North America, Firestone, Kennett, West, and others have argued that 12.9 ka the Earth experienced an impact by an extraterrestrial body, an event that had devastating ecological consequences for humans, plants, and animals in the New World [Firestone RB, et al. (2007) Proc. Natl. Acad. Sci. USA 104:16016–16021]. Herein, we report the results of an independent analysis of magnetic minerals and microspherules from seven sites of similar age, including two examined by Firestone et al. We were unable to reproduce any results of the Firestone et al. study and find no support for Younger Dryas extraterrestrial impact.
A possible Younger Dryas record in southeastern Alaska
1990-12-07
A stratigraphic record of climatic cooling equal in timing and severity to the Younger Dryas event of the North Atlantic region has been obtained form lacustrine sediments in the Glacier Bay area of southeastern Alaska. Fossil pollen show that a late Wisconsin pine parkland was replaced about 10,800 years ago by shrub- and herb-dominated tundra, which lasted until about 9,800 years ago. This vegetational change is matched by geochemical evidence for loss of organic matter from catchment soils and increased mineral erosion. If this event represents the Younger Dryas, then an explanation for a hemisphere-wide propagation of a North Atlantic climatic perturbation must be sought.
Impact of the Younger Dryas cooling event upon lowland vegetation of Maritime Canada
The aim of this research is to determine the response of the vegetation in coastal Maritime Canada to the Younger Dryas cooling event ({approx} 10800-10000 {sup 14}C yr BP) that interrupted the warming trend following the last glaciation. Detailed paleoecological studies were carried out on the organic, pollen, and plant macrofossil content of sediment cores recovered from six small lakes in New Brunswick and Nova Scotia. Results show that there was regional variation in the vegetation response to the cooling. Records from Splan Pond, Mayflower Lake, and Little Lake show a change from boreal forest or woodland to shrub-tundra as a result of the cooling, while Lac a Magie shows floristic changes of shrub-tundra, and Chase Pond and Main-a-Dieu Pond show replacement of shrub-tundra by herb-tundra in response to the Younger Dryas. The climate warming signifying the end of the Younger Dryas caused succession from shrub-tundra to boreal forest, or from herb-tundra to shrub-tundra. Macrofossil evidence of arctic/alpine species such as Dryas integrifolia, Salix herbacea, and Cassiope hypnoides attests to the severity of the Younger Dryas cooling. Vegetation changes in response to the climate cooling and warming, marketing the onset and termination of the Younger Dryas respectively, were very rapid, taking only 50-100 yr. However, the response of some taxa, such as dwarf birch, appears to have lagged the onset of the climate change by several decades, although the duration of the lag varies between sites. 53 refs., 15 figs., 2 tabs.
Impact of the Younger Dryas cooling event upon lowland vegetation of Maritime Canada
1995-05-01
The aim of this research is to determine the response of the vegetation in coastal Maritime Canada to the Younger Dryas cooling event ({approx} 10800-10000 {sup 14}C yr BP) that interrupted the warming trend following the last glaciation. Detailed paleoecological studies were carried out on the organic, pollen, and plant macrofossil content of sediment cores recovered from six small lakes in New Brunswick and Nova Scotia. Results show that there was regional variation in the vegetation response to the cooling. Records from Splan Pond, Mayflower Lake, and Little Lake show a change from boreal forest or woodland to shrub-tundra as a result of the cooling, while Lac a Magie shows floristic changes of shrub-tundra, and Chase Pond and Main-a-Dieu Pond show replacement of shrub-tundra by herb-tundra in response to the Younger Dryas. The climate warming signifying the end of the Younger Dryas caused succession from shrub-tundra to boreal forest, or from herb-tundra to shrub-tundra. Macrofossil evidence of arctic/alpine species such as Dryas integrifolia, Salix herbacea, and Cassiope hypnoides attests to the severity of the Younger Dryas cooling. Vegetation changes in response to the climate cooling and warming, marketing the onset and termination of the Younger Dryas respectively, were very rapid, taking only 50-100 yr. However, the response of some taxa, such as dwarf birch, appears to have lagged the onset of the climate change by several decades, although the duration of the lag varies between sites. 53 refs., 15 figs., 2 tabs.
Study adds new clue to how last ice age ended
2010-09-08
A new study in Nature finds that in addition to Antarctica, New Zealand was warming at the end of the last ice age, indicating that the deep freeze up north, called the Younger Dryas for the white flower that grows near ...
Pubs.GISS: Publications by Dorothy M. Peteet
... during the last millennium in the lower Hudson Valley, New York, USA. .... 1994: Extent and timing of the Last Glacial Maximum in southwestern Alaska. ... the last deglaciation: Implications to the cause of the Younger Dryas event. ...
2007-09-30
ObjectivesThis proposal is focused on improving the temporal resolution of the available AMS 14C chronology through the last deglacial interval (including Younger Dryas) from a series of highly expanded NE Atlantic sediment records. These include existing core material which is housed at St Andrews e.g. IMAGES giant piston cores MD95-2007 and MD95-2006. In addition, Austin is co-PI on a NERC-supported (NER/T/S/2001/01189) research cruise aboard the RV Marion Dufresne which will provide additional new mate [continued...]DescriptionRecords of changing atmospheric radiocarbon concentration (?14C, reported as per mil deviations from pre-industrial values after correction for decay and fractionation) from the last deglaciation suggest that an anomaly during the Younger Dryas cold phase is the largest of the last 15,000 years. However, the cause of the Younger Dryas ?14C changes are debated, and are either attributed to changes in the production rate of 14C due to changes in solar activity or the Earth's magnetic field and/or [continued...]
DescriptionAfter the retreat of the last (Devensian) ice sheet in the UK approximately 18,00 years ago, climate warming was not linear in its trend, rather it experienced a number of step-wise cold and warm climatic events (termed stadial and interstadials) each lasting approximately 1,500 years, before the full warm interglacial of the present Holocene was achieved. In western Scotland the last cold stadial (termed the Younger Dryas) resulted in a re-advance of glaciers within, and beyond the fjords, prom [continued...]
2004-12-18
DescriptionChironomids will be used to estimate Younger Dryas (YD) summer temperatures at one site in eastern Scotland and one in western Scotland to investigate climatic gradients across Scotland. We will estimate winter precipitation during the YD using the relationship between glacier equilibrium line altitude and summer temperature. We will investigate whether glacier retreat during the YD resulted from reduction in snowfall or climate warming. We will compare midge-inferred July temperatures with the [continued...]
2010-01-01
On the basis of location levels of push marginal formations and maximal distribution heights of charted lateral moraine, the surface form of the Late Valdai ice sheet in the region of Khibini and Lovozerskii massifs during cool stadial phases of the Middle and Younger Dryas was reconstructed. It has been established that the glacier surface came to 700 m and 500 m, respectively, and its inclination varied from 30 to 70 m per 10 km, which is well below that in marginal fields of ice sheets of Western Greenland and East Antarctica. The maximal ice thickness in the Middle Dryas came to about 600 m, and in the Younger Dryas, it was about 400 m. The inclination of the glacier surface increased during the cool stadial phase. On the whole, it coincides well with the drift directions of detrital s...
Shock-synthesized hexagonal diamonds in Younger Dryas boundary sediments
2009-08-04
The long-standing controversy regarding the late Pleistocene megafaunal extinctions in North America has been invigorated by a hypothesis implicating a cosmic impact at the Ållerød-Younger...Full Text Available
2010-01-01
Significant changes in the global atmospheric and oceanic circulation system occurred during the Younger Dryas cold period. Several researchers have demonstrated a weakening of intensity of the Indian Ocean Summer Monsoon during that period. However, the exact characteristics of the East Asian Summer Monsoon still remain vague. Here we present a late-glacial precipitation proxy record of the East Asian Summer Monsoon, based on the peat cellulose d^1^3C found in Hani, Northeast China. Both the peat cellulose record and a pollen record from Lake Sihailongwan sediment indicate an abrupt increase in precipitation in the region during the Younger Dryas period. These results support the occurrence of wet conditions in the north and of dry conditions in the south of the Chinese Mainland during th...
2010-01-01
Werner, K., Tarasov, P. E., Andreev, A. A., Muller, S., Kienast, F., Zech, M., Zech, W. &Diekmann, B. 2009: A 12.5-kyr history of vegetation dynamics and mire development with evidence of Younger Dryas larch presence in the Verkhoyansk Mountains, East Siberia, Russia. Boreas, 10.1111/j.1502-3885.2009.00116.x. ISSN 0300-9483. A 415 cm thick permafrost peat section from the Verkhoyansk Mountains was radiocarbon-dated and studied using palaeobotanical and sedimentological approaches. Accumulation of organic-rich sediment commenced in a former oxbow lake, detached from a Dyanushka River meander during the Younger Dryas stadial, at 12.5 kyr BP. Pollen data indicate that larch trees, shrub alder and dwarf birch were abundant in the vegetation at that time. Local presence of larch during the Youn...
The Younger Dryas and the Sea of Ancient Ice
2008-01-01
We propose that prior to the Younger Dryas period, the Arctic Ocean supported extremely thick multi-year fast ice overlain by superimposed ice and firn. We re-introduce the historical term paleocrystic ice to describe this. The ice was independent of continental (glacier) ice and formed a massive floating body trapped within the almost closed Arctic Basin, when sea-level was lower during the last glacial maximum. As sea-level rose and the Barents Sea Shelf became deglaciated, the volume of warm Atlantic water entering the Arctic Ocean increased, as did the corresponding egress, driving the paleocrystic ice towards Fram Strait. New evidence shows that Bering Strait was resubmerged around the same time, providing further dynamical forcing of the ice as the Transpolar Drift became established...
Reconstruction of the White Sea Basin during the late Younger Dryas
2010-01-01
Pasanen, A., Lunkka, J. P. &Putkinen, N. 2009: Reconstruction of the White Sea Basin during the late Younger Dryas. Boreas, 10.1111/j.1502-3885.2009.00128.x. ISSN 0300-9483 The Weichselian Scandinavian Ice Sheet (SIS) in the White Sea Basin retreated from its maximum position to the Kalevala end moraine between 17 000 and 11 500 years ago. Even though the deglaciation history is relatively well known, the palaeoenvironments in front of the ice sheet are still poorly understood and partly controversial. In the present paper, we use geomorphological, sedimentological and ground-penetrating radar survey methods to study glaciofluvial plains and shorelines at the Kalevala end moraine. These data are used to define the shoreline gradient for the area and to numerically reconstruct the palaeotop...
2010-01-01
A technique for identifying non-visible basaltic tephra-rich horizons of Younger Dryas (YD)/Greenland Stadial (GS) 1 age in northeast Atlantic sediments using rapid, non-destructive magnetic measurements is presented. Three high-resolution marine sediment cores have been studied in an E-W transect across the Hebridean margin: St Kilda Basin (MD95-2007), Barra Fan (MD95-2006) and Rockall Trough (MD04-2822). Magnetic susceptibilities and remanent magnetisations were measured at contiguous 1 cm resolution on bulk sediments. In all three cores, an interval with higher proportions of hard magnetic minerals coincides with a clearly defined peak in basaltic tephra shard (
Glacial geomorphology in Utsjoki, Finnish Lapland proposes Younger Dryas fault-instability
2009-01-01
Northern Fennoscandia has experienced high-magnitude postglacial fault (PGF) events, yet the role of seismic tremors in subglacial deformations and meltwater discharge has remained obscure. We studied glacial geomorphology in Utsjoki, Finnish Lapland, an area characterized by the Utsjoki drumlin field fanning out north and northeast to the Younger Dryas End Moraines (YDEMs) in northern Norway. Paleolandslides were common on fells (i.e. mountains shaped by Pleistocene glaciations) and were formed in nunatak position evidencing fault-instability in app. 11,900calibrated (cal) BP. An anastomosing network of eskers was found throughout Utsjoki, and was probably generated through short-lived sliding bed stages during the discharge of subglacial lake(s). The formation of networks is different fr...
Evidence for a variable and wet Younger Dryas in southern Alaska
2010-01-01
Pollen, macro- and micro-fossils, and sedimentologic indicators in sediment cores from Discovery Pond (DP) in south-central Alaska indicate that the coldest interval of the last deglacation was coincident with the onset of the Younger Dryas (YD), around 12.8calka. The multi-proxy record from DP together with a compilation of recently published YD records from southern Alaska and the adjacent northern Pacific Ocean shows that, during the course of the YD, temperatures increased, then reached a maximum sometime around 11calka. At DP, a pronounced increase in the abundance of Isoetes and Pediastrum, including species associated with oligotrophic lakes and known to respond to increased precipitation, combined with a reduction in wetland aquatics and an increase in the minerogenic component of ...
Absence of geochemical evidence for an impact event at the Bølling–Allerød/Younger Dryas transition
2009-12-22
Full Text Available.High concentrations of iridium have been reported in terrestrial sediments dated at 12.9 ka and are interpreted to support an extraterrestrial impact event as the cause of the observed extinction in the Rancholabrean fauna, changes in the Paleoindian cultures, and the onset of the Younger Dryas cooling [Firestone RB, et al. (2007) Proc Natl Acad Sci USA 104:16016–16021]. Here, we report platinum group element (PGE: Os, Ir, Ru, Rh, Pt, Pd), gold (Au) concentrations, and
Evidence for a landslide origin of New Zealand's Waiho Loop Moraine
2008-01-01
The Waiho Loop Moraine has been interpreted as evidence for Younger Dryas cooling in southern New Zealand, but recent dating and climatological studies have questioned this idea. A detailed analysis of the sedimentology of the moraine suggests it was formed after a large landslide onto the Franz Josef glacier triggered a glacial surge, independent of climate forcing. Publisher: Nature Pub. Group Coverage: 2008-08-01T00:00:00Z
1994-05-01
A suite of sediment core samples was recovered from two lakes, Crowfoot and Bow lakes, that are adjacent to the Crowfoot moraine type locality, to identify and radiocarbon date sediments related to the Crowfoot advance. The Crowfoot moraine system, widely recognized throughout northwestern North America, represents a glacial advance that is post-Wisconsin and pre-Mazama tephra in age. An interval of inorganic sediments bracketed by accelerator mass spectrometry radiocarbon ages of ca. 11,330 and 10,100 [sup 14]C yr B.P. is associated with the Crowfoot moraine. The Crowfoot advance is therefore approximately synchronous with the European Younger Dryas cold event (ca. 11,000-10,000 [sup 14]C yr B.P.). Furthermore, the termination of the Crowfoot advance also appears to have been abrupt. These findings illustrate that the climatic change responsible for the European Younger Dryas event extended beyond the northern Atlantic basin and western Europe. Equilibrium-line altitude (ELA) depressions associated with the Crowfoot advance are similar to those determined for the Little Ice Age advance, whereas Younger Dryas ELA depressions in Europe significantly exceed Little Ice Age ELA depressions. 26 refs., 3 figs., 1 tab.
2008-01-01
Until now, availability of wood from the Younger Dryas abrupt cooling event (YDE) in N. America ca. 12.9 to 11.6 ka has been insufficient to develop high-resolution chronologies for refining our understanding of YDE conditions. Here we present a multi-proxy tree-ring chronology (ring widths, events? evidenced by microanatomy and macro features, stable isotopes) from a buried black spruce forest in the Great Lakes area (Liverpool East site), spanning 116yr at ca. 12,000cal yr BP. During this largely cold and wet period, the proxies convey a coherent and precise forest history including frost events, tilting, drowning and burial in estuarine sands as the Laurentide Ice Sheet deteriorated. In the middle of the period, a short mild interval appears to have launched the final and large...
Cometary airbursts and atmospheric chemistry: Tunguska and a candidate Younger Dryas event
2009-07-07
We estimate atmospheric chemistry changes from ionization at the 1908 Tunguska airburst event, finding agreement with nitrate enhancement in GIS2PH and GISP2 ice cores and noting an unexplained accompanying ammonium spike. We then consider the candidate Younger Dryas comet impact. The estimated NOx production and O3 depletion are large, beyond accurate extrapolation. A modest nitrate deposition signal exists in ice core data. The predicted very large impulsive deposition might be visible in higher resolution data. Ammonium has been attributed to biomass burning, and found coincident with nitrate spikes at YD onset in both the GRIP and GISP2 ice cores. A similar result is well-resolved in Tunguska ice core data, but the Tunguska forest fire was far too small to account for this. Direct input of ammonia from a comet into the atmosphere is consistent with the spike for the candidate YD object, but also inadequate for Tunguska. An analog of the Haber process with hydrogen contributed by the cometary or surface water, atmospheric nitrogen, high temperatures, pressures, and the possible presence of catalytic iron from a comet could in principle divert a variable fraction of the reaction products to ammonia, accounting for ice core data in both events.
2010-01-01
Mangerud, J., Gulliksen, S. &Larsen, E. 2009: 14C-dated fluctuations of the western flank of the Scandinavian Ice Sheet 45-25 kyr BP compared with Bolling-Younger Dryas fluctuations and Dansgaard-Oeschger events in Greenland. Boreas, 10.1111/j.1502-3885.2009.00127.x. ISSN 0300-9483. We present 32 accelerator mass spectrometry (AMS) 14C dates obtained on well-preserved bones from caves in western Norway. The resulting ages of 34-28 14C kyr BP demonstrate that the coast was ice-free during the so-called Alesund Interstadial. New AMS 14C dates on shells aged 41-38 14C kyr BP are evidence of an earlier (Austnes) ice-free period. The Alesund Interstadial correlates with Greenland interstadials 8-7 and the Austnes Interstadial with Greenland interstadials 12-11. Between and after the two interst...
1996-10-01
By measuring the concentration of a cosmogenic isotope (e.g. {sup 10}Be, {sup 26}Al, {sup 36}Cl), the length of time since formation or uncovering of a rock surface can be determined rather precisely. The useful time range of these isotopes is dependent upon the production rates, the half-lives as well as on sample analysis limitations. The interplay of the various factors is shown by two examples; the dating of very old surfaces in Antarctica and the dating of a Younger Dryas moraine in the Swiss Alps. (author) 1 fig., 3 refs.
Quick corruption of conveyor circulation? A geochemical approach.
2006-09-30
DescriptionPreliminary data suggest that the proposed shutdown in thermohaline circulation associated with the abrupt climate shifts, which pepper the last glacial period and transition to the relatively stable interglacial, hinges on inadequate evidence. I propose to resolve the mode of deep ocean circulation during these suborbital climate events, focusing on the sharp deglacial warmings at about 14.65 and 11.6 ka, and the Younger Dryas cooling at 13.3 ka, using coupled d13C-Cd/CaZn/Ca measurements of h [continued...]
Younger Dryas “black mats” and the Rancholabrean termination in North America
2008-05-06
Full Text Available.Of the 97 geoarchaeological sites of this study that bridge the Pleistocene-Holocene transition (last deglaciation), approximately two thirds have a black organic-rich layer or “black mat” in the form of mollic paleosols, aquolls, diatomites, or algal mats with radiocarbon ages suggesting they are stratigraphic manifestations of the Younger Dryas cooling episode 10,900 B.P. to 9,800 B.P. (radiocarbon years). This layer or mat covers the Clovis-age landscape or surface on which the last remnants of the terminal Pleistocene megafauna are recorded. Stratigraphically and chronologically the extinction appears to have been catastrophic, seemingly too sudden and extensive for either human predation or climate change to have been the primary cause. This sudden Rancholabrean termination at 10,900 ± 50 B.P. appears to have coincided with the sudden climatic switch from Allerød warming to Younger Dryas cooling. Recent evidence for extraterrestrial impact, although not yet compelling, needs further testing because a remarkable major perturbation occurred at 10,900 B.P. that needs to be explained.
The timing and magnitude of mountain glaciation in the tropical Andes
2008-01-01
The Andes of Ecuador, Peru and Bolivia host the majority of the worlds tropical glaciers. In the tropical Andes, glaciers accumulate during the wet season (austral summer) and ablate year-round. Precipitation is delivered mainly by easterlies, and decreases both N-S and E-W. Chronological control for the timing of glacial advances in the tropical Andes varies. In Ecuador, six to seven advances have been identified; dating is based on radiocarbon ages. Timing of the local Last Glacial Maximum (LGM) and the existence of Younger Dryas advances remain controversial. In Peru, local variability in glaciation patterns is apparent. Surface exposure dating in the Cordillera Blanca and Junin Plain suggests that the local LGM may have been early (30 ka), although uncertainties in age calculations rem...
The origin of glaciations; L`origine des glaciations
1996-01-01
This paper describes the methods used by paleo-climatologists to reconstruct the climatic changes that have occurred during the last hundred thousands of years. The last real cold period, the younger Dryas lasted about 11000 years ago. Older changes in the global climate are recorded in the lake and ocean sediments of the northern hemisphere and in the ice layers of the Greenland and Antarctica ice-caps. Cadmium concentrations and isotope ratios of carbon 13, carbon 14 and oxygen 18 in the marine sediments (foraminifera) are used to determine the temperature changes in the deep and surface sea waters and to reconstruct the changes in the oceanic circulation. Other paleo-climatic informations are inferred from the analysis of methane, carbon dioxide and oxygen 18 preserved in the ice bubbles. (J.S.). 5 refs., 5 figs., 6 photos.
2010-01-01
A new timescale has recently been established for human mitochondrial DNA (mtDNA) lineages, making mtDNA at present the most informative genetic marker system for studying European prehistory. Here, we review the new chronology and compare mtDNA with Y-chromosome patterns, in order to summarize what we have learnt from archaeogenetics concerning five episodes over the past 50,000 years which significantly contributed to the settlement history of Europe: the pioneer colonisation of the Upper Palaeolithic, the Late Glacial re-colonisation of the continent from southern refugia after the Last Glacial Maximum, the postglacial re-colonization of deserted areas after the Younger Dryas cold snap, the arrival of Near Easterners with an incipient Neolithic package, and the small-scale migrations al...
2010-01-01
The present study represents the first attempt of reconstructing fire history through soil charcoal dating. The investigated area is located in the Guandera Biological Reserve (western Cordillera Real, northern Ecuador). Six AMS radiocarbon dating, performed at the base of five soil profiles allowed a fire phase to be identified during the Pleistocene-Holocene transition. A strong correspondence was highlighted between the age of the Guandera fires and the El Abra stadial, which is considered the Younger Dryas equivalent in South America. This local evidence of fires contributes to define the geographic area in which the El Abra stadial was recorded and suggests a wider use of the soil charcoal analysis
Sedimentary evidence of deglacial megafloods in the northern Gulf of Mexico (Pigmy Basin)
2009-01-01
Cored sediments from the Pigmy Basin, northern Gulf of Mexico, were analyzed in order to better constrain late deglacial and early Holocene paleoenvironmental and sedimentary changes in response to North American climate evolution. Mineralogical and geochemical proxies indicate the succession of two sedimentary regimes: dominantly detrital during the deglaciation (15-12.9cal ka BP) whereas biogenic contribution relatively increased later on during the Younger Dryas and early Holocene (12.9 and 10cal ka BP). Geochemical data reveal that the deglacial record mainly reflects variations of terrigenous supply via the Mississippi River rather than modifications of redox conditions in the basin. Specific variations of almost all the parameters measured in this paper are synchronous with the main ...
Postglacial rebound promotes glacial re-advances - a case study from the European Alps
2010-01-01
Terra Nova, 22, 297-302, 2010 Abstract Although deglaciation after the Last Glacial Maximum (LGM) caused a considerable isostatic rebound of orogens worldwide, the effect of this uplift on glacier mass balance has never been quantified. Here, we propose that postglacial rebound promotes the re-advance of glaciers by enlarging their accumulation areas, and test our hypothesis for the European Alps. Using a three-dimensional numerical model with a rheologically layered lithosphere and a reconstructed LGM ice distribution, we show that deglaciation caused up to 128 m of rebound between 21 and 13 ka. The rebound-induced increase in the total glacier accumulation area is 50% at the onset of the Younger Dryas. This shows that postglacial rebound results in a positive glacier mass balance, which ...
2009-01-01
A complex study including palynological and diatom analysis, palaeontological investigation of molluscan fauna, carbonates analyses and radiocarbon dating was performed in the northern part of the Curonian Spit (Western Lithuania). Environmental changes were reconstructed during the Late Glacial and Holocene. Cold and dry climate, unstable soils, open habitats of tundra vegetation spread in the surroundings of the northern part of the Curonian Spit during the Younger Dryas. Birch was dominant. The relatively deep Baltic Ice Lake with a freshwater planktonic diatom complex existed. During the Preboreal and the beginning of Boreal forest (birch and pine) was not dense, and wetland development occurred in coastal areas. Forest spread rapidly in response to significant warming during Boreal ti...
Ostracods and stable isotopes of a late glacial and Holocene lake record from the NE Tibetan Plateau
2010-01-01
Ostracod assemblage changes and stable isotopes of ostracod shells were used to reconstruct the salinity history of Lake Donggi Cona on the northeastern Tibetan Plateau in response to the late glacial and Holocene climate history. Brackish and relatively unstable conditions were inferred for the earlier part of the late glacial between 18.9 and 13.4calkaBP and for the early to mid Holocene (11.9-6.8calkaBP). A saline lake existed in the intervening period probably representing colder and drier conditions during the Greenland Stadial 1 (=Younger Dryas in North Atlantic region). Freshwater conditions similar to the present stage of Lake Donggi Cona were established for the first time at 6.8calkaBP. This inference and the implied increase in moisture availability in the latter half of the Hol...
Late Quaternary record of pteropod preservation from the Andaman Sea
2010-01-01
In order to understand the glacial to interglacial fluctuations in pteropod preservation and productivity during the late Quaternary (~54ka BP to present), we investigated pteropod, organic carbon (Corg) and Globigerina bulloides abundance in a deep sea core from the western Andaman Sea. Pteropod abundance and preservation is similar to the ''Indo-Pacific carbonate preservation type'', showing better preservation during glacial and poor preservation during interglacial periods. The core site appears to have remained below the aragonite compensation depth (ACD) throughout the Holocene, indicated by the total absence of pteropods. Maximum abundance and good preservation of pteropods was observed during stadials such as Younger Dryas (YD), Heinrich Events (HEs) and Last Glacial Maxima (LGM) i...
2009-01-01
This study used organic matter in oligotrophic Lake Constance (southern Germany) to reconstruct lake environment and to disentangle the multiple factors, such as climate change and human impacts, which influence sedimentation in large lakes. A sediment core from Upper Lake Constance, which represents 16,000years of Late Glacial and Holocene lake history, was analysed for organic biomarkers, hydrogen index and elements calcium, strontium, and magnesium. Magnetic susceptibility was measured to establish a high-resolution stratigraphic framework for the core and to obtain further information about changes with respect to relative allochthonous versus autochthonous sedimentation. Dinosterola biomarker for dinoflagellatesand calcium have low concentrations in Younger Dryas sediments and...
Influence of seasonality on glacier mass balance, and implications for palaeoclimate reconstructions
2010-01-01
Climates inferred from former glacier geometries in some areas exhibit discrepancies with regional palaeoclimates predicted by General Circulation Models (GCMs) and modelling of palaeoecological data, possibly as a consequence of their differing treatments of climatic seasonality. Since glacier-based climate reconstructions potentially offer an important tool in the calibration of GCMs, which themselves need validation if used to predict future climate scenarios, we attempt to resolve mismatches between these techniques by (1) investigating the influence of seasonality on glacier mass balance, and (2) refining the methodology used for the derivation of glacier-based palaeoclimates. Focussing on the Younger Dryas stadial glaciation of Scotland, northeast Atlantic, we show that sea-ice ampli...
Evidence for early postglacial warming in Mount Field National Park, Tasmania
2010-01-01
Situated between the Western Pacific Warm Pool to the north and Antarctica to the south, Tasmania is an ideal location to study both postglacial and Holocene paleoclimates. Few well-dated, quantitative temperature reconstructions exist for the region so that important questions about the occurrence and magnitude of events, such as the Antarctic Cold Reversal and Younger Dryas, in Tasmania remain unanswered. Here, we provide chironomid-based reconstructions of temperature of the warmest quarter (TWARM) for two small subalpine lakes, Eagle and Platypus Tarns, Mount Field National Park. Shortly after deglaciation, TWARM reached modern values by approximately 15 000cal a BP and remained high until 13 000cal a BP after which temperatures began to cool steadily, reaching a minimum by 11 100-10 0...
2009-01-01
Uranium-series dating of pedogenic carbonate crusts from fluvial gravels is tested using Optically Stimulated Luminescence (OSL) ages as references. OSL dating yielded ages of 30-15ka and 13-11ka, which correlate with the cold periods of the Last Glacial Maximum and the Younger Dryas. These ages are internally coherent and consistent with the geological background and are thus regarded as reliable. Most of the U/Th results scatter widely in the 230Th/232Th vs. 234U/232Th isochron diagram, making regression unrealistic. Semiquantitative age estimates from the data were found to be mostly older than the OSL ages and the geological context. It is suggested that a heterogeneous initial 230Th input, not relatable to a detrital component, is responsible for the observed discrepancies. This input...
2010-01-01
Two sediment cores recovered from Dahu Swamp, which is located in eastern Nanling Mountains in south China, were selected for investigation of palaeoclimatic changes. Multi-proxy records of the two cores including lithological variation, organic carbon isotope ratio, dry bulk density, organic matter content, magnetic susceptibility, humification degree, median grain size and geochemical proxies reveal that during the last deglaciation three drier phases correspond to the Oldest, Older and Younger Dryas cooling events, and the intercalated two wetter phases synchronise with the Bolling and Allerod warming events. The Holocene Optimum, which was resulted from a strengthening of the East Asian (EA) summer monsoon, occurred in the early and mid Holocene (ca. 10-6 cal. ka BP). In the mid and la...
2009-01-01
Modeling the bulk sediment XRD patterns allows insight into the environmental and depositional histories of two neighboring rift lake basins within the Baikal watershed. Parallel 14C-dated LGM-Holocene records in Lakes Baikal and Hovsgol are used to discuss the mineralogical signatures of regional climate change. In both basins, it is possible to distinguish `glacial' and `interglacial' mineral associations. Clay minerals comprise in excess of 50% of layered silicates in bulk sediment. The abundance of smectite (expandable) layers in mixed-layer illite-smectites and the total illite abundance are the main paleoclimatic indices in the clay mineral assemblage. Both indices exhibit coherent responses to the Bolling-Allerod and the Younger Dryas. The smectite layer index is not equivalent to t...
2009-01-01
We analysed the composition of phyllosilicate minerals in sediments deposited by the Rhne and Oberaar glaciers (Swiss Alps), in order to identify processes and rates of biogeochemical weathering in relation to glacial erosion. The investigated sediments are part of chronosequences consisting of (A) suspended, ?fresh? sediment in melt water; (B) terminal moraines from the Little Ice Age (LIA; approximately 15601850); and (C) tills of the Younger Dryas interval (YD; approximately 11'500y BP). Secondary weathering products associated with the suspended sediment have not been observed; we therefore exclude intermittent subglacial storage and weathering of this material and assume that the suspended sediment is directly derived from mechanically abraded bedrock. This implies that bioge...
2010-01-01
The north-western Black Sea shelf is the widest continental shelf of the Black Sea, where the Danube delta/prodelta system includes important records on the Black Sea water level fluctuations. This study integrates newly acquired high-resolution single channel seismic reflection profiles and Calypso piston cores recovered along a transect extending from the Danube delta deep into its deep sea fan. The correlated results provide information on the Late Quaternary architecture of the Danube Black Sea shelf and on the role of global glacio-eustatic fluctuations on the building of the Danube delta/prodelta. The sedimentary sequences in the Black Sea are strongly affected by water level changes. For the whole duration of Late Glacial-Holocene period, the level of the Black Sea was controlled by...
1992-01-01
Reconstructed Younger Dryas (11000-10000 y BP) valley- and cirque glaciers west of the Jostedalsbre ice cap suggest an equilibrium-line altitude (ELA) depression of (450{+-}200 y BP) deglaciation was characterized by vertical wastage, indicating that the LA was above the summit plateaus. During the Erdalen event (9100{+-}200 y BP) marginal moraines were formed up to 1 km beyond the Little Ice Age (LIA) moraines which lie in front of the present valley outlet glaciers of the Jostedalsbre ice cap. The average ELA lowering during this event is calculated to 325 m below the modern level. Lithostratigraphic and paleobotanical studies show that the Hypsithermal (ca. 8000-6000 y BP) ELA was about 450 m higher than at present. As a result, Jostedalsbreen probably disappeared entirely during that period. The glacier reformed about 5300 y BP. The ELA intersected the modern mean equilibrium line altitude five times from ca. 2600 y BP to the present. The outlet valley glaciers reached their maximum Neoglacial extent during the LIA in the mid-18th century, when the ELA was depressed 100-150 m below the present level. 25 refs., 9 figs.
Paleoclimatic inference from glacial fluctuations on Svalbard during the last 20,000 years
1992-01-01
The climate history of western Spitsbergen, Svalbard is deduced from variations of glaciers during the last 20000 years. A major depression of the regional equilibrium line altitude (ELA) occurred during the Late Weichselian glacial maximum (18000-13000 y ago) when low summer temperatures may have caused year-round snow accumulation on the ground. This rapid expansion of the glaciers also indicates nearby moisture sources, suggesting partly open conditions in the Norwegian Sea during the summers. A rapid glacial retreat around 13000-12500 y BP was caused by a sudden warming. During the Younger Dryas the ELA along the extreme western coast of Spitsbergen was not significantly lower than at present. In contrast to Fennoscandia, the British Isles and the Alps, there is no evidence for readvance of local glaciers during Younger Dryas on western Spitsbergen. This difference is attributed to a much dryer climate on Spitsbergen and probably only slight changes in sea surface temperatures. In addition, summer melting in this high arctic area is more sensitive to orbitally increased insolation. Around 10000 y BP another rapid warming occurred and during early and mid Holocene the summer temperatures were significantly higher than at present. A temperature decline during the late Holocene caused regrowth of the glaciers which reached their maximum Holocene position during the last century. 72 refs., 6 figs.
Modelling the concentration of atmospheric CO[sub 2] during the Younger Dryas climate event
1999-05-01
The Younger Dryas (YD, dated between 12.7-11.6 ky BP in the GRIP ice core, Central Greenland) is a distinct cold period in the North Atlantic region during the last deglaciation. A popular, but controversial hypothesis to explain the cooling is a reduction of the Atlantic thermohaline circulation (THC) and associated northward heat flux as triggered by glacial meltwater. Recently, a CH[sub 4]-based synchronization of GRIP [delta][sup 18]O and Byrd CO[sub 2] records (West Antarctica) indicated that the concentration of atmospheric CO[sub 2] (CO[sup atm][sub 2]) rose steadily during the YD, suggesting a minor influence of the THC on CO[sup atm][sub 2] at that time. Here we show that the CO[sup atm][sub 2] change in a zonally averaged, circulation-biogeochemistry ocean model when THC is collapsed by freshwater flux anomaly is consistent with the Byrd record. Cooling in the North Atlantic has a small effect on CO[sup atm][sub 2] in this model, because it is spatially limited and compensated by far-field changes such as a warming in the Southern Ocean. The modelled Southern Ocean warming is in agreement with the antiphase evolution of isotopic temperature records from GRIP (Northern Hemisphere) and from Byrd and Vostok (East Antarctica) during the YD. [delta][sup 13]C depletion and PO[sub 4] enrichment are predicted at depth in the North Atlantic, but not in the Southern Ocean. This could explain a part of the controversy about the intensity of the THC during the YD. Potential weaknesses in our interpretation of the Byrd CO[sub 2] record in terms of THC changes are discussed. (orig.) With 5 figs., 1 tab., 91 refs.
Land-ice teleconnections of cold climatic periods during the last Glacial/Interglacial transition
2000-02-01
Independent calendar year chronologies are a basic requirement for the establishment of high resolution land-ice teleconnections. The annually laminated Meerfelder Maar record provides both an independent chronology, established by varve counting, and high resolution lithological proxy data for the period of the last Glacial/Interglacial transition. These data reveal a series of four periods of climatic deterioration coinciding with negative isotopic deviations in the GRIP record signal, thus demonstrating the synchronicity of environment changes in Western Germany and temperature shifts in Greenland. The terrestrial data supports a further subdivision of the event stratigraphy based on the GRIP core, by introducing the cold event GI-1c2 between 13 500 and 13 400 calendar years BP. Multiproxy analyses reveal that the environmental response at Meerfelder Maar was not linear throughout the Lateglacial but was modified by local processes. A change in the response of the lake environment to climate deterioration was observed during substage GI-1b (Gerzensee oscillation), the only event with gradual rather than abrupt transitions. The two-fold character of the Younger Dryas as seen in the GRIP record is more pronounced in the Meerfelder Maar record. This lithological signal occurred with a delay of 60 years to the GRIP signal, and has been linked to a shift in the catchment. It is proposed that the trigger for this shift was a trend towards a more humid second half of the Younger Dryas. (orig.)
Despite more than a century of study, scant attention has been paid to the glacial record in the northern end of the Sierra Nevada, and to the smaller moraines deposited after the retreat of the Tioga (last glacial maximum) glaciers. Equilibrium-line altitude (ELA) estimates of the ice fields indicate that the Tioga ELA gradients there are consistent with similar estimates for the southern half of the range, and with an intensification of the modern temperature/precipitation pattern in the region. The Recess Peak advance has traditionally been considered to be mid-Neoglacial age, about 2--3,000 yr B.P., on the basis of relative weathering estimates. Sediment cores of lakes dammed behind moraines correlative with Recess Peak in four widely spaced sites yields a series of high-resolution AMS radiocarbon dates which demonstrate that Recess Peak glaciers retreated before {approximately} 13,100 cal yr B.P.. This minimum limiting age indicates that the advance predates the North Atlantic Younger Dryas cooling. It also implies that there have been no advances larger than the Matthes in the roughly 12,000 year interval between it and the Recess Peak advance. This finding casts doubt on several recent studies that claim Younger Dryas glacier advances in western North America. The 13,100 cal yr B.P. date is also a minimum age for deglaciation of the sample sites used to calibrate the in situ production rates of cosmogenic {sup 10}Be and {sup 26}Al. The discrepancy between this age and the 11,000 cal yr B.P. exposure age assumed in the original calibration introduces a large (> 19%) potential error in late-Pleistocene exposure ages calculated using these production rates.
1995-12-31
Despite more than a century of study, scant attention has been paid to the glacial record in the northern end of the Sierra Nevada, and to the smaller moraines deposited after the retreat of the Tioga (last glacial maximum) glaciers. Equilibrium-line altitude (ELA) estimates of the ice fields indicate that the Tioga ELA gradients there are consistent with similar estimates for the southern half of the range, and with an intensification of the modern temperature/precipitation pattern in the region. The Recess Peak advance has traditionally been considered to be mid-Neoglacial age, about 2--3,000 yr B.P., on the basis of relative weathering estimates. Sediment cores of lakes dammed behind moraines correlative with Recess Peak in four widely spaced sites yields a series of high-resolution AMS radiocarbon dates which demonstrate that Recess Peak glaciers retreated before {approximately} 13,100 cal yr B.P.. This minimum limiting age indicates that the advance predates the North Atlantic Younger Dryas cooling. It also implies that there have been no advances larger than the Matthes in the roughly 12,000 year interval between it and the Recess Peak advance. This finding casts doubt on several recent studies that claim Younger Dryas glacier advances in western North America. The 13,100 cal yr B.P. date is also a minimum age for deglaciation of the sample sites used to calibrate the in situ production rates of cosmogenic {sup 10}Be and {sup 26}Al. The discrepancy between this age and the 11,000 cal yr B.P. exposure age assumed in the original calibration introduces a large (> 19%) potential error in late-Pleistocene exposure ages calculated using these production rates.
2007-10-09
Full Text Available.A carbon-rich black layer, dating to ≈12.9 ka, has been previously identified at ≈50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at ≅12.9 ka, which we hypothesize caused abrupt environmental changes that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period. Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal, (iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at ≈12.9 ka. This layer also extends throughout at least 15 Carolina Bays, which are unique, elliptical depressions, oriented to the northwest across the Atlantic Coastal Plain. We propose that one or more large, low-density ET objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggering YD cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America.
A carbon-rich black layer, dating to ≈12.9 ka, has been previously identified at ≈50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at ≅12.9 ka, which we hypothesize caused abrupt environmental changes that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period. Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal, (iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at ≈12.9 ka. This layer also extends throughout at least 15 Carolina Bays, which are unique, elliptical depressions, oriented to the northwest across the Atlantic Coastal Plain. We propose that one or more large, low-density ET objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggering YD cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America.
A carbon-rich black layer, dating to ~;;12.9 ka, has been previously identified at ~;;50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at ~;;12.9 ka, which we hypothesize caused abrupt environmentalchanges that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period. Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal, (iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at ~;;12.9 ka. This layer also extends throughout at least 15 Carolina Bays, which are unique, elliptical depressions, oriented to the northwest across the Atlantic Coastal Plain. We propose that one or more large, low-density ET objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggering YD cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America.
2007-03-13
A carbon-rich black layer, dating to ~;;12.9 ka, has been previously identified at ~;;50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at ~;;12.9 ka, which we hypothesize caused abrupt environmentalchanges that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period. Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal, (iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at ~;;12.9 ka. This layer also extends throughout at least 15 Carolina Bays, which are unique, elliptical depressions, oriented to the northwest across the Atlantic Coastal Plain. We propose that one or more large, low-density ET objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggering YD cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America.
A new 14C calibration data set for the last deglaciation based on marine varves
1999-02-22
Varved sediments of the tropical Cariaco basin provide a new {sup 14}C calibration data set for the period of deglaciation (10,000 to 14,500 years before present: 10-14.5 cal ka BP). Independent evaluations of the Cariasco Basin calendar and {sup 14}C chronologies were based on the agreement of varve ages with the GISP2 ice core layer chronology for similar high-resolution paleoclimate records, in addition to {sup 14}C age agreement with terrestrial {sup 14}C dates, even during large climatic changes. These assessments indicate that the Cariaco Basin {sup 14}C reservoir age remained stable throughout the Younger Dryas and late Alleroed climatic events and that the varve and {sup 14}C chronologies provide an accurate alternative to existing calibrations based on coral U/Th dates. The Cariaco Basin calibration generally agrees with coral-derived calibrations but is more continuous and resolves century-scale details of {sup 14}C change not seen in the coral records. {sup 14}C plateaus can be identified at 9.6, 11.4, and 11.7 {sup 14}C ka BP, in addition to a large, sloping plateau during the Younger Dryas ({approximately}10 to 11 {sup 14}C ka BP). Accounting for features such as these is crucial to determining the relative timing and rates of change during abrupt global climate changes of the last deglaciation.
The paleoclimate record of long-term climate variability
1993-06-01
Climate variability occurs on time scales ranging from decades or shorter to millions of years. An important step in determining the effects of trace-gas-induced warming on climate variability and ecosystems is characterizing past natural variability and change. Throughout the Quaternary long-term climate variability has been dominated by Milankovitch forcing of glacial/interglacial cycles. Superimposed on this millennia-scale orbitally forced variability have been more rapid climate events (e.g. Younger Dryas, Little Ice Age, Medieval Warm Period, Sahelian droughts). Although highly relevant to understanding possible responses of ecosystems to future climate change, most decade to century scale climate variability remains poorly understood. Insights into mechanisms and responses can be obtained from tree rings, ice cores, corals, marine, lake and fluvial sediments, pollen, and macrofossils. These paleoclimate records reveal that the range of natural climate variability is much larger than indicated by the instrumental record of the past 150 years. Global networks of well-dated, high-resolution paleocrunate records for key intervals of the past are currently being assembled. These networks should provide the baseline of natural variability required to understand climate-ecosystem dynamics and to identify anthropogenic-induced change.
Steady-state and transient modeling of tracer and nutrient distributions in the global ocean
1993-03-08
The balance of stable and decaying tracers was incorporated into a latitude-depth ocean circulation model which resolves the major ocean basin and is coupled to an atmospheric energy balance model. The modern distribution of radiocarbon and the analysis of artificial color tracers enabled the census of the deep water masses. We show that good agreement with the observation can be achieved if the surface forcing is modified. The same process could also account for long-term, large-scale changes of the global thermohaline circulation. Uptake rates of carbon are investigated using an inorganic carbon cycle model and performing 2 [times] CO[sub 2]-experiments. We prescribe the industrial evolution of pCO[sub 2] in the atmosphere from 1792 to 1988 and calculate the total flux of carbon into the world ocean. Results are in good agreement with two recent 3-dimensional model simulation. First results using an organic carbon cycle in this model are presented. Changes in the hydrological cycle can stabilize the thermohaline circulation in the Atlantic and enable simulation of climate events resembling the Younger Dryas. By adding the balance of radiocarbon the evolution of its atmospheric concentration is studied during rapid changes of deep ocean ventilation. A resumption of ventilation creates a rapid decrease of atmospheric radiocarbon which is able to mask the natural decay.
Sources of organic carbon in the Portuguese continental shelf sediments during the Holocene period
2008-01-01
Organic C (OC) and total N (TN) concentrations, and stable isotope ratios (delta13C) in muddy deposit sediments of the Northern and Southern Portuguese continental shelf were used to identify sources of fine-sized organic matter (mum) during the Holocene period. Sedimentary columns off the Guadiana (core CRIDA 05), Tagus (core MD 992332) and Douro (core KSGX 57) estuaries are characterised by elemental and isotopic values that reflect distinct sources of organic matter (OC/TN and delta13C ranging, respectively, from 8.5 to 21 and from -22.4 per mille to -27 per mille ). Intense supplies to the Guadiana continental shelf of fine terrigenous particles during the Younger-Dryas Event are closely linked with higher OC/TN values and lower delta13C ratios. During the postglacial ...
Radiocarbon dating as a tool for a correlation between climatic records
1997-12-31
Although from the recent results of dating laminated lake sediments one can see that changes in atmospheric radiocarbon content complicate the time scale of the Late Glacial period, these variations can also be used as time markers. The global character of changes in atmospheric {sup 14}C content such as dramatic rises in atmospheric radiocarbon content at the beginning of the Younger Dryas or radiocarbon plateaux (decreases in {sup 14}C content) at 10 kyr BP gives an opportunity for a close correlation between paleo records around the globe. Such procedure however, requires high resolution radiocarbon dating of correlated records. There is a number of records from European lakes, some of them laminated, which have been dated with very high resolution and can be used for correlation with records from other than the North Atlantic region. Results of a high resolution radiocarbon dating of macrofossils selected from sediment of Phalarope Pond (Kodiak Island, Alaska) and foraminifera and shell selected from Solberga site in Sweden, provide a direct link between these two records of climate changes of the last deglaciation.
2010-01-01
Based on 33 U/Th dates and 1020 oxygen isotopic data from stalagmite Y1 from Yamen Cave, Guizhou Province, China, a record of the Asian Summer Monsoon (ASM) was established. The record covers the last deglaciation and the early Holocene (from 16.2 to 7.3 ka BP) with an average oxygen isotope resolution of 9 years. The main millennial-scale deglacial events first identified in Greenland (Greenland Interstadial Events: GIS 1e through GIS 1a) and later in China are clearly present in the Y1 record. By analogy to earlier work, we refer to these as Chinese Interstadials (CIS): CIS A.1e to CIS A.1a. The onset of these events in Y1 18O records are nominally dated at: 1475050, 1410060, 1387080, 1337080, and 1299080 a BP. The end of CIS A.1a or the beginning of the Younger Dryas (YD) e...
Post-glacial climate change and its effect on a shallow dimictic lake in Nova Scotia, Canada
2010-01-01
A high-resolution, multi-proxy lake sediment record was used to establish the timing of Holocene environmental change in Canoran Lake, southwest Nova Scotia, Canada. Proxies include %C, ?15N, ?13C, HI, magnetic susceptibility, and pollen. Canoran Lake is a small, shallow (11m) lake with two ephemeral inlets and an outlet. The site was deglaciated at ca. 15,300cal (calibrated) year BP and elevated %C values indicate the establishment of a productive aquatic environment that is consistent with Allerd warming. The Allerd was interrupted by rapid air temperature cooling during the Younger Dryas (ca. 12,90011,600calyear BP). The Early Hypsithermal (ca. 11,6008,500calyear BP) was relatively warm and wet. A slight increase in clastic input occurred between 9,100 and 8,500c...
2010-01-01
Geochemical and rock-magnetic investigations were carried out on a sediment core collected from the SE Arabian Sea at 1420 m depth in oxygenated waters below the present-day oxygen minimum zone. The top 250 cm of the core sediments represent the last 35 kaBP. The 18O values of Globigerinoides ruber are heaviest during the Last Glacial Maximum (LGM) and appear unaffected by low-saline waters transported from the Bay of Bengal by the strong northeast monsoon and West Indian coastal current. The signatures of Blling-Allerd and Younger Dryas events are distinct in the records of magnetic susceptibility, organic carbon (OC) and 18O. Glacial sediments show higher OC, CaCO3, Ba, Mo, U and Cd, while the early-to-late Holocene sediments show increasing concentrations of OC, CaCO3, Ba, Cu,...
2009-01-01
We present a pollen record from a fen at the eastern shore of Brazo Sur south of Lago Argentino, Argentina (core BRS 1/06, 503454S, 725452W, 198m a.s.l.). The coring site is located in the transition zone from humid grass steppe to Andean Nothofagus forest. With the exception of a mid-Holocene sand layer, the record covers the interval between 13,350 and 1,700cal b.p., indicating that there could have been no recurrence of Late-glacial conditions in Brazo Sur, as has been suggested in the literature as having been contemporary with the Younger Dryas interval in the northern hemisphere. The Late-glacial and early Holocene periods at Brazo Sur are characterized by fluctuations between humid grass-dominated steppe associations and drier ones dominated by Asteraceae and Eri...
2005-01-01
Paleohydrology studies at Mathews Pond and Whitehead Lake in northern Maine revealed synchronous changes in lake levels from about 12,00014C yrs BP to the present. We analyzed gross sediment structure, organic and carbonate content, mineral grain size, and macrofossils of six cores from each of the two lakes, and obtained 72 radiocarbon dates. Interpretation of this paleo-environmental data suggests that the late-glacial and Younger Dryas climate was dry, and lake levels were low. Early Holocene lake levels were considerably higher but declined for an interval from about 8000 to 720014C yrs BP. Sediment of both lakes contains evidence of a dry period at 740014C yrs BP (8200cal yr). Lake levels of both sites declined abruptly about 480014C yrs BP and remained low until 300014C y...
Late glacial stage and holocene tropical ice core records from Huascaran, Peru
Two ice cores from the col of Huascaran in the north-central Andes of Peru contain a paleoclimatic history extending well into the Wisconsinan (Wuerm) Glacial Stage and include evidence of the Younger Dryas cool phase. Glacial stage conditions at high elevations in the tropics appear to have been as much as 8{degree} to 12{degree}C cooler than today, the atmosphere contained about 200 times as much dust, and the Amazon Basin forest cover may have been much less extensive. Differences in both the oxygen isotope ratio {delta}{sup 18}O (8 per mil) and the deuterium excess (4.5 per mil) from the Late Glacial Stage to the Holocene are comparable with polar ice core records. These data imply that the tropical Atlantic was possibly 5{degree} to 6{degree}C cooler during the Late Glacial Stage, that the climate was warmest from 8400 to 5200 years before present, and that it cooled gradually, culminating with the Little Ice Age (200 to 500 years before present). A strong warming has dominated the last two centuries.
Late glacial stage and holocene tropical ice core records from Huascaran, Peru
1995-07-07
Two ice cores from the col of Huascaran in the north-central Andes of Peru contain a paleoclimatic history extending well into the Wisconsinan (Wuerm) Glacial Stage and include evidence of the Younger Dryas cool phase. Glacial stage conditions at high elevations in the tropics appear to have been as much as 8{degree} to 12{degree}C cooler than today, the atmosphere contained about 200 times as much dust, and the Amazon Basin forest cover may have been much less extensive. Differences in both the oxygen isotope ratio {delta}{sup 18}O (8 per mil) and the deuterium excess (4.5 per mil) from the Late Glacial Stage to the Holocene are comparable with polar ice core records. These data imply that the tropical Atlantic was possibly 5{degree} to 6{degree}C cooler during the Late Glacial Stage, that the climate was warmest from 8400 to 5200 years before present, and that it cooled gradually, culminating with the Little Ice Age (200 to 500 years before present). A strong warming has dominated the last two centuries.
Late Pleistocene-Holocene environments in Valle Carbajal, Tierra del Fuego, Argentina
2007-01-01
ResumenEn base al analisis palinologico, sedimentologico y geomorfologico de dos sitios ubicados en las cercanias del Canal Beagle, se discute el ambiente depositacional durante el Pleistoceno Tardio - Holoceno en uno de los valles de montana de los Andes Fueguinos. Los resultados obtenidos para este valle de montana refuerzan y refinan el patron climatico del Pleistoceno Tardio - Holoceno registrado previamente a lo largo del Canal Beagle. Digno de atencion es la evidencia de un periodo frio asociado con el evento estadial Younger Dryas, sugerido por un minimo en el porcentaje de polen de Nothofagus mientras que las comunidades de gramineas, matorrales y arbustos bajos se extendian por las pendientes bajas y medias (Unidad 2, 10,310 14C a AP). Alrededor de los 9500 a AP, la tendencia haci...
2010-01-01
The vegetation history of the Faroe Islands has been investigated in numerous studies all broadly showing that the early-Holocene vegetation of the islands largely consisted of fellfield with gravely and rocky soils formed under a continental climate which shifted to an oceanic climate around 10,000calyrBP when grasses, sedges and finally shrubs began to dominant the islands. Here we present data from three lake sediment cores and show a much more detailed history from geochemical and isotope data. These data show that the Faroe Islands were deglaciated by the end of Younger Dryas (11,700 - 10,300 cal yr BP), at this time relatively high sedimentation rates with high d13C imply poor soil development. d13C, Ti and data reveal a much more stable and warm mid-Holocene until 7410calyrBP charac...
Interpretation of our present terrestrial climatic record
1987-09-01
Detailed studies of profiles of delta/sup 18/O in oceanic and glacial cores and of pollen deposits in bogs indicate that the terrestrial climatic system, consisting of the atmosphere, hydrosphere, lithosphere and biosphere, is capable of oscillations with amplitudes, such as that of the Melisey II stadial of northern France, approaching or equaling that of the glacial-interglacial cycle but on time scales too short for the usually envisioned transfer of mass between the oceans and continental glaciers. Abrupt oscillations or shifts to new equilibrium are well documented in the Boelling-Aleroed warming and Younger Dryas readvance, the 0.4/sup 0/C rise in NH continental air temperature circa 1920 and the year-to-year oscillations in NH continental air temperatures from 1976 to 1984. Such abrupt oscillations defy explanation in terms of external forcing functions and suggest rather internal rearrangements within the climate system as the driving mechanism. Suggestions are made as to mechanisms for possible internal rearrangements which might lead to different hemispheric or global mean surface temperatures.
Holocene vegetation and climate change on the Haanja heights, South-East Estonia
1997-01-01
The development of forests on the Haanja Heights has been controlled by external factors, including climate, soils, hydrology, and human impact. The sediment sequence from Lake Kirikumaee, which covers about 12 000 years, records the vegetation history throughout the Late Glacial and Holocene. In the Alleroed, woodland tundra with sparse birch and willow was established. Grass-shrub tundra in the Younger Dryas was replaced by birch forest in the Pre-Boreal. During the Holocene two major shifts in vegetation dynamics occurred: the first about 8500 BP with a sharp decline in Betula-Pinus forest and development of broad-leaved forest, and the second about 3500 BP, with a decline in broad-leaved forest and regeneration of Pinus-Betula forest with a high share of Picea. The climate modelling, based on pollen record and lake-level changes, suggest cold, severe climate with low ...
2010-01-01
Earlier studies indicated that the general pattern of the Holocene climate in the northeastern United States changed from cool and dry (11.6-8.2ka; 1ka=1000 cal yr BP) to warm and wet (8.2-5.4ka) to warm and dry (5.4-3ka) to cool and wet (after 3ka). A new 35-year resolution stable isotope record of endogenic calcite from a sediment core for Lake Grinnell in northern New Jersey provided a chance to examine the Holocene climate variations of the region in a finer detail. After the Younger Dryas cold climate reversal, the d18O fluctuated around a constant value of -7.4permil until 5.8ka, thereafter shifted to a steadily decreasing trend to the most recent value of -8.2permil. Responding to this shift, the widely observed hemlock decline in the northeastern USA occurred about 350-500 (+-143.5...
Evidence for a Global Warming at the Termination I Boundary and Its Possible Cosmic Dust Cause
2005-03-18
A comparison of northern and southern hemispheric paleotemperature profiles suggests that the Bolling-Allerod Interstadial, Younger Dryas stadial, and subsequent Preboreal warming which occurred at the end of the last ice age were characterized by temperatures that changed synchronously in various parts of the world, implying that these climatic oscillations were produced by significant changes in the Earth's energy balance. These globally coordinated oscillations are not easily explained by ocean current mechanisms such as bistable flipping of ocean deep-water production or regional temperature changes involving the NW/SE migration of the North Atlantic polar front. They also are not accounted for by Earth orbital changes in seasonality or by increases in atmospheric CO-2 or CH-4. On the other hand, evidence of an elevated cosmic ray flux and of a major interstellar dust incursion around 15,800 years B.P. suggest that a cosmic ray wind driven incursion of interstellar dust and gas may have played a key role through its activation of the Sun and alteration of light transmission through the interplanetary medium.
2010-01-01
Kirkbride, M.P. &Bell, C.M. 2009: Edge-roundness of boulders of Torridonian Sandstone (northwest Scotland): applications for relative dating and implications for warm and cold climate weathering rates. Boreas, 10.1111/j. 1502-3885.2009.00131.x. ISSN 0300-9483. The relative ages of late Quaternary morainic and rock avalanche deposits on Late Precambrian Torridonian Sandstone are determined from the characteristic edge-roundness of constituent boulders. Because weathering of sandstone is manifest as edge-rounding by granular disintegration, a relative chronology can be derived by measuring the effective radii of curvature of a sample of boulder edges. Thirteen samples totalling 597 individual boulder edges fall into two statistically distinct groups. Moraines of inferred Younger Dryas age (1...
2010-01-01
High-resolution planktonic foraminifer Mg/Ca sea surface temperature (SST) and d^1^8O records of IMAGES core MD052896 from the southern South China Sea (SCS) provide a history of East Asian winter monsoon variability over the past 23kyr. Specifically, we find that the latitudinal SST gradient of the north-south SCS shows promise as a useful proxy of East Asian winter monsoon changes. The DSST record of core MD052896 from the southern SCS and ODP site 1145 from the northern SCS documents several positive anomalies indicating East Asia winter monsoon maxima during cold periods of the past 23kyr, including the H1 and Younger Dryas events. The DSST record also indicates that after ~8.5ka the East Asian winter monsoon strengthened relative to the deglaciation, reaching levels of the last glacia...
2009-01-01
We constrain a three-dimensional thermomechanical model of Greenland ice sheet (GrIS) evolution from the Last Glacial Maximum (LGM, 21ka BP) to the present-day using, primarily, observations of relative sea level (RSL) as well as field data on past ice extent. Our new model (Huy2) fits a majority of the observations and is characterised by a number of key features: (i) the ice sheet had an excess volume (relative to present) of 4.1m ice-equivalent sea level at the LGM, which increased to reach a maximum value of 4.6m at 16.5ka BP; (ii) retreat from the continental shelf was not continuous around the entire margin, as there was a Younger Dryas readvance in some areas. The final episode of marine retreat was rapid and relatively late (c. 12ka BP), leaving the ice sheet land based by 10ka BP;...
A peat core based estimate of Late-glacial and Holocene methane emissions from northern peatlands
2006-01-01
We estimate the intensity of Late-glacial and Holocene methane emissions from peatlands based on their paleo net primary production (PNPP). The PNPP is derived from the carbon accumulation rates of the studied bog profile (Etang de la Grure, Switzerland), which are corrected for the degree of peat degradation. The obtained PNPP curve is taken as a proxy for methane emissions. It shows relatively high values (90g C m2 yr1) early in the Bolling/Allerod and drops to low values (40g C m2 yr1) during the Younger Dryas cold period. With the onset of the Holocene the PNPP increases strongly up to 150g C m2 yr1 around ca. 10,000Cal. yr bp. This is followed by a decline to minimum values (30 to 40g C m2 yr1) between 6500 and 4000Cal. yr bp. Thereafter, the PNPP...
2010-01-01
Elemental (C, N, Pb) and isotopic (d13C, d15N) measurements of cored sediment from a small bog in northern New Mexico reveal changes in climate during the Late Pleistocene and Holocene. Abrupt increases in Pb concentration and d13C values ca. 14 420 cal. YBP indicate significant runoff to the shallow lake that existed at that time. Weathering and transport of local volcanic rocks resulted in the delivery of Pb-bearing minerals to the basin, while a 13C-enriched terrestrial vegetation source increased the d13C values of the sedimentary material. Wet conditions developed over a 300 a period and lasted for a few hundred years. The Younger Dryas period (ca. 12 700-11 500 cal. YBP) caused a reduction in terrestrial productivity reflected in decreasing C/N values, d15N values consistently greate...
Ice marginal fluctuations during the Weichselian glaciation in Fennoscandia, a literature review
2006-12-15
This report presents an overview regarding ice marginal fluctuations during the last glacial, the Weichselian. It is focusing on marginal positions in Sweden with surroundings. The results are used to calibrate a computer simulation of the Weichselian ice sheet. The report also contains some information regarding basal conditions beneath the Swedish part of the Weichselian ice sheet. This information will be used to validate the results of the simulation of the Weichselian ice sheet. The Weichselian glaciation started 115 ka BP (thousands of years before present) and ended at the transition to the Holocene 11.5 ka BP. Terrestrial and marine records show that ice volumes fluctuated drastically during the Weichselian. The marine isotope record shows the global variations in climate and ice volume during the last ice age and has been divided into Marine Isotope Stages (MIS), which are well dated (MIS5d to MIS 2). Dating of terrestrial records is, however, problematic due to stratigraphical gaps and deposits, which are difficult to date. In many areas the timing of local and regional ice marginal fluctuations, prior to the Last Glacial Maximum (LGM), is therefore poorly understood. Age attribution of terrestrial deposits is often interpreted from bio- and litostratigraphical information, which has been correlated to other records, e.g. marine stratigraphies. The marine record from Early Weichselian (MIS 5d-5a) shows that two relatively warm periods, interstadials (MIS 5c and 5a), prevailed 105-9 ka BP and 85-74 ka BP. After MIS 5a global ice volume increased and remained large throughout Middle Weichselian (74-24 ka BP). During the LGM (c 21 ka BP), before the onset of the deglaciation, the ice volume was at its largest. Stratigraphical data indicate at least two periods with ice-free conditions in northern Fennoscandia, which have been correlated with the two early Weichselian interstadials Broerup and Odderade (MIS 5c and 5a). Few absolute dates have, however, been obtained from deposits formed during these interstadials. It has been suggested that two ice advances occurred during the Early Weichselian and covered a large part of northern Fennoscandia. There are, however, different opinions regarding the southernmost extension of these ice sheets. It has also been suggested that large parts of northern Fennoscandia were free of ice from the onset of MIS 5c until the end of 5a. Several researchers suggest that most of Fennoscandia was covered by an ice sheet from Middle Weichselian until the latest deglaciation. Data from Norway suggests, however, that the youngest of the ice-free interstadials, correlated with MIS 5a, actually occurred during the late part of Middle Weichselian. There are indications of several ice marginal fluctuations along the Norwegian coast during Middle Weichselian. Furthermore, several new data suggest ice-free conditions in large parts of Finland during Middle Weichselian. The timing of the ice oscillations during Early and Middle Weichselian is therefore still an open question, which hopefully will be resolved by better dates of the terrestrial material. The ice advanced south to its maximum extent during the beginning of the Late Weichselian 24-12 ka BP. The ice reached its maximum position at different times in different regions. After the LGM the ice started to retreat across northern Germany and Poland. The timing of the deglaciation is well dated and the ages have recently been converted into calibrated years. Several re advances took place during the deglaciation of the Danish and Norwegian coast. There are several ice marginal zones in south-west Sweden, which indicate stillstands or re advances of the ice front. These zones have been correlated to other ice marginal zones in Fennoscandia. The deglaciation was interrupted during the Younger Dryas stadial (12.5-11.5 ka BP) and there were ice re advances and standstills in the middle part of Sweden and southern Finland, whereas coastal areas in the west were characterised by large re advances. The ice marginal deposits formed during Younger Dryas can be followed around the entire Fennoscandia. After the Younger Dryas the ice retreated more or less continuously. Deep weathered bedrock of Pre-Quaternary age occurs in parts of Smaaland and in the inner parts of northern Sweden. These deposits indicate low erosion during the Quaternary glacials in these regions. In the inner part of Norrbotten there are morphological features, Veiki moraines, which according to several authors were formed during the first Weichselian ice advance (MIS 5d). In Smaaland there are till covered eskers, which may have been formed prior to the latest glacial advance. Areas with deep weathered bedrock and those with Quaternary deposits older than the last glaciation coincide to a large extent. These areas are indicators of cold based ice and of low glacial erosion.
Age-related differences in white matter microstructure: Region-specific patterns of diffusivity
2010-01-01
We collected MRI diffusion tensor imaging data from 80 younger (20-32 years) and 63 older (60-71 years) healthy adults. Tract-based spatial statistics (TBSS) analysis revealed that white matter integrity, as indicated by decreased fractional anisotropy (FA), was disrupted in numerous structures in older compared to younger adults. These regions displayed five distinct region-specific patterns of age-related differences in other diffusivity properties: (1) increases in both radial and mean diffusivity; (2) increases in radial diffusivity; (3) no differences in parameters other than FA; (4) a decrease in axial and an increase in radial diffusivity; and (5) a decrease in axial and mean diffusivity. These patterns suggest different biological underpinnings of age-related decline in FA, such as...
2006-01-01
The relative timing of late Quaternary glacial advances in mid-latitude (40-55° S) mountain belts of the Southern Hemisphere (SH) has become a critical focus in the debate on global climate teleconnections. On the basis of glacial data from New Zealand (NZ) and southern South America it has been argued that interhemispheric synchrony or asynchrony of Quaternary glacial events is due to Northern Hemisphere (NH) forcing of SH climate through either the ocean or atmosphere systems. Here we present a glacial snow-mass balance model that demonstrates that large scale glaciation in the temperate and hyperhumid Southern Alps of New Zealand can be generated with moderate cooling. This is because the rapid conversion of precipitation from rainfall to snowfall drives massive ice accumulation at small thermal changes (1-4°C). Our model is consistent with recent paleo-environmental reconstructions showing that glacial advances in New Zealand during the Last Glacial Maximum (LGM) and the Last Glacial Interglacial Transition (LGIT) occurred under very moderate cooling. We suggest that such moderate cooling could be generated by changes in synoptic climatology, specifically through enhanced regional flow of moist westerly air masses. Our results imply that NH climate forcing may not have been the exclusive driver of Quaternary glaciations in New Zealand and that synoptic style climate variations are a better explanation for at least some late Quaternary glacial events, in particular during the LGIT (e.g. Younger Dryas and/or Antarctic Cold Reversal). Publisher: European Geosciences Union Coverage: 2006-01-01T00:00:00Z
1993-03-08
The balance of stable and decaying tracers was incorporated into a latitude-depth ocean circulation model which resolves the major ocean basin and is coupled to an atmospheric energy balance model. The modern distribution of radiocarbon and the analysis of artificial color tracers enabled the census of the deep water masses. We show that good agreement with the observation can be achieved if the surface forcing is modified. The same process could also account for long-term, large-scale changes of the global thermohaline circulation. Uptake rates of carbon are investigated using an inorganic carbon cycle model and performing 2 {times} CO{sub 2}-experiments. We prescribe the industrial evolution of pCO{sub 2} in the atmosphere from 1792 to 1988 and calculate the total flux of carbon into the world ocean. Results are in good agreement with two recent 3-dimensional model simulation. First results using an organic carbon cycle in this model are presented. Changes in the hydrological cycle can stabilize the thermohaline circulation in the Atlantic and enable simulation of climate events resembling the Younger Dryas. By adding the balance of radiocarbon the evolution of its atmospheric concentration is studied during rapid changes of deep ocean ventilation. A resumption of ventilation creates a rapid decrease of atmospheric radiocarbon which is able to mask the natural decay.
Paleoindian demography and the extraterrestrial impact hypothesis
2008-08-19
Full Text Available.Recently it has been suggested that one or more large extraterrestrial (ET) objects struck northern North America 12,900 ± 100 calendar years before present (calBP) [Firestone RB, et al. (2007) Proc Natl Acad Sci USA 104: 16016–16021]. This impact is claimed to have triggered the Younger Dryas major cooling event and resulted in the extinction of the North American megafauna. The impact is also claimed to have caused major cultural changes and population decline among the Paleoindians. Here, we report a study in which ≈1,500 radiocarbon dates from archaeological sites in Canada and the United States were used to test the hypothesis that the ET resulted in population decline among the Paleoindians. Following recent studies [e.g., Gamble C, Davies W, Pettitt P, Hazelwood L, Richards M (2005) Camb Archaeol J 15:193–223), the summed probability distribution of the calibrated dates was used to identify probable changes in human population size between 15,000 and 9,000 calBP. Subsequently, potential biases were evaluated by modeling and spatial analysis of the dated occupations. The results of the analyses were not consistent with the predictions of extraterrestrial impact hypothesis. No evidence of a population decline among the Paleoindians at 12,900 ± 100 calBP was found. Thus, minimally, the study suggests the extraterrestrial impact hypothesis should be amended.
This study reveals for the first time biostratigraphical evidence of nunataks emerging from the Late Weichselian ice-sheet in central Scandinavia. Almost 1 m of minerogenic basal layers from Lake Flfattjnn, 1110 m a.s.l., at Tynset, Norway, was deposited in the Lateglacial, possibly as early as 16,000 cal. yr BP. The sediments contain well-preserved remains of plants, diatoms and chironomids and indicate: (1) a mosaic pioneer vegetation of dwarf-shrub tundra, snow bed vegetation and xerophytes on wind-blown ridges, (2) an ice-free lake during summers with clear water at low pH due to little inwash, (3) a continental climate with summers slightly warmer than today (ca 10 C), and most probably with very cold winters, according to indications of permafrost, and (4) a hiatus/reduced sedimentation during at least the first half of the Younger Dryas when the lake was sealed by a more-or-less permanent ice-cover. The existence of Lateglacial nunataks indicates a thin and multi-domed Lateglacial ice-sheet in Scandinavia. Early migration of arctic-alpine plants to nunataks could explain their centric distribution in S Norway. Furthermore, vegetation establishment on the Flfatet Lateglacial nunatak indicates that S Norway could have been vegetated by successions along the retreating ice from alpine nunataks and from coastal and southern areas. The upland and lowland vegetation met at the final deglaciation.
Late-glacial atmospheric CO{sub 2} reconstructions from western Norway using fossil leaves
1995-12-31
Analyses of air bubbles trapped in Antarctic ice-cores have shown that atmospheric CO{sub 2} concentrations are 180-200 ppmv during glacial periods, and ca. 280 ppmv during interglacials, including the Holocene. The change from glacial to Holocene concentrations occurred steadily over ca. 5000 years, slightly lagging the temperature increase inferred from {delta}{sup 18}. Antarctic ice cores lack fine time resolution over the late-glacial/early Holocene period 12-9000 {sup 14}C yr BP, that includes the Younger Dryas cold oscillation. The stomatal density on leaves is inversely proportional to the concentration of atmospheric CO{sub 2}. A late glacial sequence at Kraakenes, western Norway, contains well-preserved Salix herbacea (dwarf willow) leaves, dated from 11700-9600 {sup 14}C yr BP. If the stomatal density is measured on the fossil leaves, a calibration derived from the relationship of stomatal density of modern material of the same species to known CO{sub 2} concentrations can be used to reconstruct CO{sub 2} concentrations of the past. Because of the decadal time-resolution available at Kraakenes through the late-glacial and early Holocene, a detailed record of CO{sub 2} concentrations can be reconstructed over this period, that will complement the ice core record. (author)
Palynological (species assemblage, pollen accumulation rate), geochemical (carbon to nitrogen ratios, organic carbon and biogenic silica content), and sedimentological (particle size, magnetic susceptibility) data combined with improved chronology and greater sampling resolution from a new core from Elikchan 4 Lake provide a stronger basis for defining paleoenvironmental changes than was previously possible. Persistence of herb-dominated tundra, slow expansion of Betula and Alnus shrubs, and low percentages of organic carbon and biogenic silica suggest that the Late-Glacial transition (ca. 16,000-11,000 cal. yr BP) was a period of gradual rather than abrupt vegetation and climatic change. Consistency of all Late-Glacial data indicates no Younger Dryas climatic oscillation. A dramatic peak in pollen accumulation rates (ca. 11,000-9800 cal. yr BP) suggests a possible summer temperature optimum, but finer grain-sizes, low magnetic susceptibility, and greater organic carbon and biogenic silica, while showing significant warming at ca. 11,000 cal. yr BP, offer no evidence of a Holocene thermal maximum. When compared to trends in other paleo-records, the new Elikchan data underscore the apparent spatial complexity of climatic responses in Northeast Siberia to global forcings between ca. 16,000-9000 cal. yr BP.
2008-05-20
Palynological (species assemblage, pollen accumulation rate), geochemical (carbon to nitrogen ratios, organic carbon and biogenic silica content), and sedimentological (particle size, magnetic susceptibility) data combined with improved chronology and greater sampling resolution from a new core from Elikchan 4 Lake provide a stronger basis for defining paleoenvironmental changes than was previously possible. Persistence of herb-dominated tundra, slow expansion of Betula and Alnus shrubs, and low percentages of organic carbon and biogenic silica suggest that the Late-Glacial transition (ca. 16,000-11,000 cal. yr BP) was a period of gradual rather than abrupt vegetation and climatic change. Consistency of all Late-Glacial data indicates no Younger Dryas climatic oscillation. A dramatic peak in pollen accumulation rates (ca. 11,000-9800 cal. yr BP) suggests a possible summer temperature optimum, but finer grain-sizes, low magnetic susceptibility, and greater organic carbon and biogenic silica, while showing significant warming at ca. 11,000 cal. yr BP, offer no evidence of a Holocene thermal maximum. When compared to trends in other paleo-records, the new Elikchan data underscore the apparent spatial complexity of climatic responses in Northeast Siberia to global forcings between ca. 16,000-9000 cal. yr BP.
1992-01-01
Much less is known about the paleoclimate and paleoceanography of the North Pacific than the North Atlantic despite the North Pacific's important role in the global ocean-climate system. Kodiak Island lies in the northwestern Gulf of Alaska astride the eastern end of the Aleutian Low. On southwestern Kodiak Island, coastal bluffs section a series of moraines, kettle ponds, and bogs formed between 15 and 9 ka BP. Distinctive tephras from volcanoes on the Alaska Peninsula provide time-lines within the stratigraphy. Deformation events recorded in sediment stacks from basins within glaciotectonic landforms allows precise dating of glacial events. An ice cap occupied the Kodiak archipelago during the last glaciation. Three glacial advances of the southwestern margin of this ice cap occurred after 15 ka BP. At 13.4 ka, piedmont ice lobes formed large push moraines extending into Shelikof Strait during the Low Cape Advance. The less-extensive Tundra Advance culminated between 12 and 11.7 ka BP followed by glacier retreat then readvance to form the prominent Olga Moraine system between 11 and 10 ka BP. The timing of the Tundra and Olga Advances correlates closely with that of the Older and Younger Dryas cold episodes in northwestern Europe suggesting that these climatic oscillations were synchronous throughout the northern hemisphere.
1992-01-01
Ice core analysis provides the most direct evidence of changes in some major greenhouse gases (CO[sub 2], CH[sub 4] and N[sub 2]O) over the climatic cycle covering approximately the last 150,000 years. A remarkable overall correlation is observed between the CO[sub 2] or CH[sub 4] record and the climatic changes in the high latitudes of the Southern Hemisphere, with lowest greenhouse gas concentrations found under full glacial conditions. In terms of phase relationship, CO[sub 2] and CH[sub 4] are roughly in phase with the climatic signal during the deglaciation periods; when entering the glaciation, CH[sub 4] appears to decrease in phase with the Antarctic cooling but CO[sub 2] lags strikingly behind. The CH[sub 4] record exhibits a marked signal which is most likely associated with the abrupt cooling of the Younger Dryas. Existing differences between CO[sub 2] and CH[sub 4] records in comparison with climate reflect differences in sources which are mainly oceanic in the case of CO[sub 2] and continental in the case of CH[sub 4]. For N[sub 2]O only few data are available suggesting that the N[sub 2] concentrations may also have been lower during the Last Glacial Maximum than during the Holocene. Greenhouse gases are likely to have played an important climatic role in amplifying, together with continental ice, the initial orbital forcing of the glacial-interglacial climatic changes.
Climatic change about 11,000 years ago in the Near East
1995-12-31
Pollen records show that Near Eastern vegetation since about 11,000 years ago has been marked by trees of olive and pistachio, which are adapted to the distinctive mediterranean climate of winter rains and summer drought. The same applied during earlier interglacial intervals. This climate is also believed to favor the spread of annual plants depend for survival on storage of nutrients in seeds rather than roots and tend to spread on bare soils with little vegetation cover. Disturbed ground was presumably common near Natufian settlements and provided habitats suitable for the spread of wild cereal grains. Prior to about 11,000 years ago steppe vegetation prevailed throughout the Near East, with woodland confined to middle elevations of mountains in Greece and the Levant. The summer climate then was cool and cloudy, and reduced evaporation permitted the expansion of lakes on the Anatolian Plateau. The climate then was still under the influence of prevailing westerly winds, which had bleen displaced southward by the North American and Eurasian ice sheets in summer as well as winter. As the ice sheets accelerated their retreat the westerlies withdrew and the subtropical high-pressure belt expanded to the north in the summer. At the same time summer insolation in the continental interior reached a maximum, according to Milankovitch curves for Earth/Sun orbital changes. This reconstruction is supported by paleoclimatic model simulations, which indicate that before about 11,000 years ago summers had more storms, more cloudiness, and cooler temperatures. The occurrence of a Younger Dryas climatic reversal 11,000 - 10,000 years ago in the Near East is not well documented in pollen diagrams, but the chronology is complicated by the existence of {open_quotes}radiocarbon pleateaus{close_quotes} centering on 10,000 and 9500 radiocarbon years ago.
2000-07-01
The international scientific community has come to the conclusion that human activities are a non negligible factor influencing the global climate. The leading Swiss climate researchers are supporting this statement. What is the impact of climate change in Switzerland ? After six years of scientific research, the results of the National Research Programme 'Climate Change and Natural Hazards' (NRP 31) are available now. They contribute to a better understanding of the complex nature of the global climate and its specific alpine aspects. This book provides the newest estimations about the impact of temperature and precipitation changes on the environment, the economy and infrastructures. It also describes the possibilities of political and social actions regarding these changes. In the introductory chapter the essential processes necessary to understand the climate system are explained, such as the role of ocean, mechanism of the greenhouse effect, ENSO, NAO, younger Dryas climate, Dansgaard/Oeschger and Heinrich events, to mention just a few. This chapter provides a good foundation for the later chapters which are dedicated to the history of observed climate changes in Switzerland, regionally specific future climate simulations with a high resolution model, impacts of climate changes on earth's surface processes, such as river discharges, glaciers, permafrost, land slides, forestry, agriculture and human activities. With its concrete proposal of a methodology to investigate the impacts of climate changes on human activities, the present volume will offer valuable information for decision makers, concerned citizens as well as teachers and students in climate and environmental sciences. The volume is supplemented by the conclusions of the accompanying group of experts and by a list of all reports published within the NRP 31.
An empirical model of glacio-isostatic movements and shore-level displacement in Fennoscandia
2001-08-01
Shore-level displacement in Fennoscandia is mainly due to two co-operative vertical movements, glacio-isostatic uplift and global eustatic sea level rise. The course of the glacio-isostatic uplift has been made discernible according to an investigation of the lake-tilting phenomenon. This information made it possible to start an iteration process that has given mathematical expression for factors involved both within the isostatic movements and the eustatic rise. There are two components involved in glacio-isostatic uplift. The main uplift, still in progress, acts slowly and is thus called the slow component. Arctan functions have proved to be suitable tools for describing the slow component. There are two main factors involved in the function used for calculation; A{sub s} (m), the download factor and B{sub s} (y{sup -1} ), which is an inertia factor. A strong linear correlation between the inertia factor Bs and lithosphere thickness has been found in the model. There was also a fast component involved in the crustal changes at the end of Late Weichselian and early Holocene. This component gave rise to fast subsidence followed by fast uplift during the final part of the deglaciation. Crustal subsidence is assumed to be due to reloading of the crust in the central parts of Fennoscandia during the Younger Dryas stadial. Normal distribution functions are used for calculating this component. Glacio-isostatic uplift and thus a regressive shore-level displacement was extremely rapid around 10,300 years BP. This fast regression was contemporaneous and occurred in a similar way at the West Coasts of Norway and Sweden as well as in the Baltic. The 'drainage' of the Baltic Ice Lake has been interpreted in the model as due to this fast regression. The slow component is most probably due to viscous flow in the asthenosphere and the fast component is assumed to be due to its elasticity.
Agulhas ring injection into the South Atlantic during glacials and interglacials
Recent proxies suggest that, at the end of the last glacial, there was a significant increase in the injection of Agulhas rings into the South Atlantic (SA). This brought about a dramatic increase in the salt-influx (from the Indian Ocean) into the SA helping re-start the then-collapsed meridional overturning cell (MOC), leading to the termination of the Younger Dryas (YD). Here, we propose a mechanism through which large variations in ring production take place. Using nonlinear analytical solutions for eddy shedding, we show that there are restricted possibilities for ring detachment when the coast is oriented in the north-south direction. We define a critical coastline angle below which there is rings shedding and above which there is almost no shedding. In the case of the Agulhas region, the particular shape of the African continent implies that rings can be produced only when the retroflection occurs beyond a specific latitude where the angle is critical. During glaciation, the wind stress curl (WSC) vanished at a latitude lower than that of the critical angle, which prohibited the retroflection from producing rings. When the latitude at which the WSC vanishes migrated poleward towards its present day position, the corresponding coastline angle decreased below the critical angle and allowed for a vigorous production of rings. Simple process-oriented numerical simulations (using the Bleck and Boudra model) are in satisfactory agreement with our results and enable us to affirm that, during the glacials, the behavior of the Agulhas Current (AC) was similar to that of the modern East Australian Current (EAC), for which the coastline slant is supercritical.
Agulhas ring injection into the South Atlantic during glacials and interglacials
Recent proxies analysis suggest that, at the end of the last glacial, there was a significant increase in the injection of Agulhas rings into the South Atlantic (SA). This brought about a dramatic increase in the salt-influx (from the Indian Ocean) into the SA helping re-start the then-collapsed meridional overturning cell (MOC), leading to the termination of the Younger Dryas (YD). Here, we propose a mechanism through which large variations in ring production take place. Using nonlinear analytical solutions for eddy shedding we show that there are restricted possibilities for ring detachment when the coast is oriented in the north-south direction. We define a critical coastline angle below which there is rings shedding and above which there is almost no shedding. In the case of the Agulhas region, the particular shape of the African continent implies that rings can be produced only when the retroflection occurs beyond a specific latitude where the angle is critical. During glaciation, the wind stress curl (WSC) vanished at a latitude lower than that of the critical angle, which prohibited the retroflection from producing rings. When the latitude at which the WSC vanishes migrated poleward towards its present day position, the corresponding coastline angle decreased below the critical angle and allowed for a vigorous production of rings. Simple process-oriented numerical simulations (using the Bleck and Boudra model) are in very good agreement with our results and enable us to affirm that, during the glacials, the behavior of the Agulhas Current (AC) was similar to that of the modern East Australian Current (EAC), for which the coastline slant is supercritical.
Life state response to environmental crisis: the case of the Love Canal, Niagara Falls, New York
1986-01-01
This thesis explored the differences between two life stages - young and old - in perceiving and responding to man-made environmental disaster, as well as the support resources utilized to cope with disaster - personal, familial/friendship, and organizational. Because of the characteristics of man-made environmental disaster, and because of the different conditions of life and constructions of reality of older and younger families, it was expected that definitions of the situation would vary by life stage and locus of control - authoritative and personal. The research took place in the Love Canal neighborhood of Niagara Falls, New York. Fifty-eight families were interviewed in the fall of 1978, and thirty-nine of these families were reinterviewed in the spring of 1979. Interviews were tape recorded, transcribed, and coded. The data were presented in contingency tables and interview excerpts. The interview schedules elicited information of perception of impact, responses to impact, and the utilization of support resources. In an authoritative locus of control situation, the major findings were that both older and younger families perceived impact, that older families were slightly less disrupted, that younger families relied on organizational and familial/friendship support resources, and that older families relied on familial/friendship support resources.
Porous red cell ultrastructure and loss of membrane asymmetry in a novel case of hemolytic anemia
2008-01-01
Abstract Transmission electron microscopic study revealed large pores on the erythrocyte ghost membranes, disrupted cytoskeleton and microcytosis of circulating erythrocytes in a novel case of hemolytic anemia. Greater loss of phosphatidylserine (PS) asymmetry was observed in younger erythrocytes compared with the aged ones in contrast to the normal red cells. Levels of sialylated glycoconjugates, such as glycophorin, measured by the binding of wheat germ agglutinin, showed greater loss upon aging. Such drastic loss of PS asymmetry leads to faster eryptosis, mediated by shedding of glycophorin-containing microvesicles leaving highly PS-exposed erythrocytes accessible to the phagocytes.
10Be and 36Cl Surface Exposure age of the Puerto Banderas Moraine, Lago Argentino, Argentina, 50S
The Antarctic Cold Reversal (ACR) and Younger Dryas (YD) are prominent late deglacial cool periods expressed in polar ice and high latitude marine sediments between 14.8-12.7 and 12.7-11.5 ka, respectively. Debate centers on the extent to which YD cooling affected the earth`s surface, particularly in the mid- to high latitudes of the Southern Hemisphere. Resolving the timing of late glacial cooling is critical to determining the degree of inter-hemispheric synchroneity as the climate system evolved after the global Last Glaciation Maximum (LGM) 16 ka. The Puerto Banderas moraine was deposited at 50S in the rain shadow east of the Andes and between LGM moraines 60 km to the east and the present south Patagonian Ice Cap 40 km to the west. It is a sharp-crested ridge 30 km long and 10-15 m high, topped by numerous erratic boulders >1 m high ideally suited for surface exposure dating. Radiocarbon dating provides only broad age limits. A weighted mean of three 14C ages on peat younger than the moraine of 11.70.3 cal. ka (2 ?), along with glacier behavior elsewhere in the Andes, led John Mercer to propose that the Puerto Banderas moraine is late glacial, ca. 15 ka. Recent mapping and two additional 14C ages suggest that the moraine may have been deposited in stages between 15.4 and 11.9 ka. New cosmogenic surface exposure ages from the most prominent part of this moraine, however, indicate a considerably younger age. The weighted mean of 10Be ages from quartz in 8 boulders is 11.30.7 ka. Moreover, the weighted mean of 36Cl ages from 8 other boulders is 10.90.9 ka. The weighted mean age of all 16 boulders is 11.10.5 ka. Uncertainties include analytical and production rate contributions. Our previous work in the region suggests that production rates may be 10% higher than expected owing to reduced air pressure during the late glacial and the early Holocene. Thus, the age of 11.10.5 ka is a maximum for the Puerto Banderas moraine and although it is possible that it formed after the YD, it is highly unlikely that it was deposited during the ACR. Lago Cardiel, a closed lake basin 175 km to the NE, was highest at 11.7 ka. Marine sediments cored west of the Andes at 41S show warm sea surface temperatures and low salinity at 11.0 ka, consistent with increased precipitation and glacial erosion. These paleoclimate proxies imply that the Puerto Banderas records southern Patagonian Ice Cap expansion due to increased precipitation, likely tied to focusing of the moisture-laden southern Westerly storm track at 50S between 12 and 11 ka.
Tunguska-1908 and similar events in light of the New Explosive Cosmogony of minor bodies
2009-03-20
The well-known Tunguska-1908 phenomenon (TP) problems (the fast transfer of the kinetic energy of the meteoroid W~10-50 Mt TNT to air, with its heating to T>10^4 K at an altitude of 5-10 km, the final turn of the smoothly sloping, ~0-20^o to horizon, trajectory of the body through ~10^o to the West, the pattern and area of the tree-fall and trees' scorching by heat radiation, etc.) allow a simple solution within the New Explosive Cosmogony (NEC) of minor bodies, as opposed to other approaches. The NEC considers the short-period (SP) comet nuclei, to which the Tunguska body belonged, to be fragments produced in explosions of massive icy envelopes of Ganymede-type bodies saturated by products of bulk electrolysis of ices to the form of a 2H2+O2 solid solution. The nearly tangent entry into the Earth's atmosphere with V~20 km/s of such a nucleus, ~200-500 m in size and ~(5-50)x10^12 g in mass, also saturated by 2H2+O2, initiated detonation of its part of ~10^12 g at an altitude of 5-10 km. This resulted in deflection of this fraction trajectory by 5^o-10^o, and fast expansion with ~2 km/s of its detonation products brought about their fast slowing down by the air, heating of the latter to T>10^4 K and a phenomenon of high-altitude explosion. On crossing the Earth's atmosphere, the main part of the unexploded nucleus escaped into space, and this body moving presently in an SP orbit should eventually be identified in time. Its impac t with W~250-3000 Mt TNT on the Earth's surface (which could occur in 1908) would have produced a crater up to ~3.5-8 km in size, with an ejection of dust that would have brought about a climatic catastrophe. The processes involved in the TP are resembling those accompanying falling P/Shoemaker-Levy 9 onto Jupiter and, possibly, the impact-caused Younger Dryas cooling ~13 ka ago.
2006-05-15
The paleo-evolution of the Black Sea level during the Lateglacial-Holocene transition is still unclear, which motivates us to provide new estimates for that period based on the analysis of water budget. Hydrological conditions in the Black Sea catchment area are reconstructed here using water balance equation, available data, and constraints based on simple theory relating the runoff ratio with climatic characteristics. In order to estimate the impact of the aridity of climate we consider two alternative scenarios: (1) climate change under constant in time gradient in precipitation and evaporation over land and sea, and (2) climate change accounting for changes in the horizontal distribution of precipitation and evaporation. Hydrological data are compiled from available present-day data and paleo-observations. A number of sensitivity experiments is carried out revealing that the hydrological conditions in the Black Sea watershed should have evolved towards a very arid climate (similar to the present-day climate in the Caspian Sea area) in order to initiate a drop of sea level of {proportional_to}100 m below the sill depth of the Bosporus Straits, as speculated in some recent research. Estimates of sea level changes reveal a qualitative agreement with the coast-line evolution inferred from paleo-observations. The Younger Dryas draw down of the Black Sea starts at about 13.3 to 13 kyr BP, with a maximum low-stand of 104 m at 11.5 kyr BP. In an arid climate scenario the sea level reaches the outlet at about 8.8 to 7.4 kyr BP. Approximately at that time, Mediterranean sea level was about 10 m higher, making flooding events of the Black Sea possible. However, the nature and exact timing of the Holocene reconnection depends also on other (not well known) factors; one of them is the Bosporus sill depth, motivating further research in this field. Estimates of the water transport through the Bosporus Straits are also provided for the time of Lateglacial-Holocene transition. (orig.)
THE STAR CLUSTER POPULATION OF THE COLLISIONAL RING GALAXY NGC 922
2010-01-01
We present a detailed study of the star cluster population detected in the galaxy NGC 922, one of the closest collisional ring galaxies known to date, using Hubble Space Telescope/Wide Field Planetary Camera 2 UBVI photometry, population synthesis models, and N-body/smoothed particle hydrodynamics simulations. We find that 69% of the clusters are younger than 7 Myr, and that most of them are located in the ring or along the bar, consistent with the strong Halpha emission. The cluster luminosity function slope of 2.1-2.3 for NGC 922 is in agreement with those of young clusters in nearby galaxies. Models of the cluster age distribution match the observations best when cluster disruption is considered. We also find clusters with ages (
1995-01-01
At the Nevada Test Site, one potentially disruptive scenario being evaluated for the Greater Confinement Disposal (GCD) Facility Performance Assessment is deep post-closure erosion that would expose buried radioactive waste to the accessible environment. The GCD Facility located at the Area 5 Radioactive Waste Management Site (RWMS) lies at the juncture of three alluvial fan systems. Geomorphic surface mapping in northern Frenchman Flat indicates that reaches of these fans where the RWMS is now located have been constructional since at least the middle Quaternary. Mapping indicates a regular sequence of prograding fans with entrenchment of the older fan surfaces near the mountain fronts and construction of progressively younger inset fans farther from the mountain fronts. At the facility, the oldest fan surfaces are of late Pleistocene and Holocene age. More recent ...
2009-01-01
Most of the studies on the large igneous provinces (LIPs) focus on Phanerozoic times, and in particular, those related to the disruption of Pangea (e.g. CAMP, Karoo, ParanaEtendeka) while Precambrian LIPs (e.g. Ventersdorpf, Fortescue) remain less studied. Although the investigation of Precambrian LIPs is difficult because they are relatively poorly preserved, assessment of their geochemical characteristics in parallel with younger overlapping LIP is fundamental for monitoring the evolution of the mantle composition through time. Recent 40Ar/39Ar dating of the Okavango giant dyke swarm (and related sills) in southern Africa showed that ~90% of the dykes were emplaced at 1791Ma and belong to the Karoo large igneous province whereas ~10% of dykes yielded Proterozoic ages (~11.1Ga...
CONCENTRATED DISADVANTAGE, TRADITIONAL MALE ROLE MODELS, AND AFRICAN-AMERICAN JUVENILE VIOLENCE
2008-01-01
In a stagnating urban economy, Elijah Anderson's (1999) Code of the Street depicts a disadvantaged environment where residents face high levels of joblessness, poverty, racial residential isolation, and family disruption. Anderson argues that the loss of job opportunities for African-American men deprived younger generations of traditional male role models. That is, in a disadvantaged urban setting with a lack of male role models participating in legitimate labor market activity, many young people may turn to violence. Drawing on insights from Anderson's ethnographic work, we assess the generality of Anderson's claims more broadly and explore the potential connection between his work and the macrolevel research on urban violence. Specifically, we explore the influence of male role models (...
2008-01-01
Honeybee colonies are highly integrated functional units characterized by a pronounced division of labor. Division of labor among workers is mainly age-based, with younger individuals focusing on in-hive tasks and older workers performing the more hazardous foraging activities. Thus, experimental disruption of the age composition of the worker hive population is expected to have profound consequences for colony function. Adaptive demography theory predicts that the natural hive age composition represents a colony-level adaptation and thus results in optimal hive performance. Alternatively, the hive age composition may be an epiphenomenon, resulting from individual life history optimization. We addressed these predictions by comparing individual worker longevity and brood production in hive...
2010-01-01
Conventional wisdom suggests that older adults are more likely than young adults to speak their mind. Age-related executive function (EF) decline is believed to underlie this tendency by weakening older adults' capacity to inhibit responses. While age-related EF decline disrupts social and cognitive functioning in many domains, such degeneration may also carry the unforeseen benefit of improving communication in uncomfortable social contexts. We examined the performance of relatively low and high EF older adults and young adults on the socially distressing task of providing critical advice to a troubled obese teenager. Relative to higher EF older adults and younger adults, lower EF older adults were more open, provided more advice, and were seen as more empathic. Moreover, doctors speciali...
On the Evolution of Moving Groups$$bAn Application to the Pleiades Moving Group
The disruption of stellar systems, such as open clusters or stellar complexes, stands out as one of the most reasonable physical processes accounting for the young moving groups observed in the solar neighbourhood. In the present study we analyse some of the mechanisms that are important in the kinematic evolution of a group of unbound stars, such as the focusing phenomenon and its ability to recover the observed moving group's velocity dispersions, and the efficiency of disc heating and galactic differential rotation in disrupting unbound stellar systems. Our main tools used to perform this analysis are both the epicycle theory and the integration of the equations of motion using a realistic gravitational potential of the Galaxy. The study of the trajectories followed by stars in each of the Pleiades moving group substructures found by Asiain et al. (1999) allows us to determine their stellar spatial and velocity distribution evolution. The kinematic properties of these substructures are compared to those of a simulated stellar complex which has evolved under the influence of the galactic gravitational potential and the disc heating. We conclude that a constant diffusion coefficient compatible with the observational heating law is able to explain the velocity and spatial dispersions of the Pleiades moving group substructures that are younger than $\\sim 1.5 \\cdot 10^8$ yr.
1988-02-01
The most prominent and well-preserved remnants of the convergent margins are present in southern Alaska and California. The southern Alaska convergent margin appears to have developed in response to northward-directed subduction of the Kula plate and the California margin in response to eastward-directed subduction of the Farallon plate. The chief elements of the southern Alaska convergent margin, on the basis of paleomagnetic data, appear to have subsequently migrated northward and rotated in the post-Cretaceous. The chief elements of the California margin have been disrupted by Neogene strike-slip displacements on the San Andreas fault system and accretion of younger terranes to the west. In both southern Alaska and California, the forearc-basin deposits are well preserved and produce major amounts of gas. The principal reservoirs in Alaska are Tertiary nonmarine deposits and in California are Late Cretaceous and Tertiary deep marine and deltaic deposits. The accretionary wedge in southern Alaska forms a remarkably well-preserved assemblage of trench and trench-slope deposits that extend for about 2000 km along the Gulf of Alaska, flanked oceanward by younger accreted terranes. The accretionary wedge in California consists of a great variety of older and younger terranes, including some fragments of ocean crust that originated in southern latitudes. Comparative structural and stratigraphic analyses of the two Late Cretaceous margins reveals the complexity of tectonic, depositional, and stratigraphic patterns associated with subduction of very large oceanic plates at the margins of very large continental plates.
2008-02-15
We present the results obtained from an objective search for stellar clusters, both in the currently active nuclear starburst region, and in the post-starburst disk of M82. Images obtained with the HST/ACS in F435W(B), F555W(V), and F814W(I) filters were used in the search for the clusters. We detected 653 clusters of which 393 are located outside the central 450 pc in the post-starburst disk of M82. The luminosity function of the detected clusters show an apparent turnover at B=22 mag (M_B=-5.8), which we interpret from Monte Carlo simulations as due to incompleteness in the detection of faint clusters, rather than an intrinsic log-normal distribution. We derived a photometric mass of every detected cluster from models of simple stellar populations assuming a mean age of either an 8 (nuclear clusters) or 100 (disk clusters) million years old. The mass functions of the disk (older) and the nuclear (younger) clusters follow power-laws, the former being marginally flatter (alpha=1.5+/-0.1) than the latter (alpha=1.8+/-0.1). The distribution of sizes (Full Width at Half Maximum) of clusters brighter than the apparent turn-over magnitude (mass>2E+4 Mo) can be described by a log-normal function. This function peaks at 10 pc for clusters more massive than 1E+5 Mo, whereas for lower masses, the peak is marginally shifted to larger values for the younger, and smaller values for the older clusters. The observed trend towards flattening of the mass function with age, together with an over-abundance of older compact clusters, imply that cluster disruption in M82 is both dependent on the mass and size of the clusters.
1986-08-01
Older-over-younger low-angle faults occur within a north-south-trending belt that includes the Pancake, Fish Creek, Diamond, and Carlin/Pinon Ranges in east-central Nevada. Collectively, these ranges form the western boundary of Nevada's only oil-producing basins, Railroad Valley and Pine Valley. These structures lie parallel to, but are east of and distinct from, the Roberts Mountain thrust. The faults involve eastern assemblage Paleozoic rocks in both upper and lower plates. The Chainman Shale is commonly the surface of decollement. A Late Cretaceous and possibly younger age is assigned to the faults, based on evidence that the Late Cretaceous Newark Canyon Formation is locally overridden by Paleozoic rocks in the Diamond and Pancake Ranges. The areal extent of this thrust belt was assessed using systematic lithostratigraphy from measured sections. This method was found useful and necessary owing to the disruptive influence of younger basin-and-range block faults on the earlier structures. Lithostratigraphic parameters used include formation thicknesses, color logs, grain-size logs, chert horizons, and quartz sandstone zones within Ordovician to Devonian rocks. It is reasoned that the boundaries of displaced blocks will show relatively sharp gradients of change in a number of lithostratigraphic parameters within the Paleozoic section.
2007-01-01
It is widely recognised that the acquisition of high-resolution palaeoclimate records from southern mid-latitude sites is essential for establishing a coherent picture of inter-hemispheric climate change and for better understanding of the role of Antarctic climate dynamics in the global climate system. New Zealand is considered to be a sensitive monitor of climate change because it is one of a few sizeable landmasses in the Southern Hemisphere westerly circulation zone, a critical transition zone between subtropical and Antarctic influences. New Zealand has mountainous axial ranges that amplify the climate signals and, consequently, the environmental gradients are highly sensitive to subtle changes in atmospheric and oceanic conditions. Since 1995, INTIMATE has, through a series of international workshops, sought ways to improve procedures for establishing the precise ages of climate events, and to correlate them with high precision, for the last 30 000 calendar years. The NZ-INTIMATE project commenced in late 2003, and has involved virtually the entire New Zealand palaeoclimate community. Its aim is to develop an event stratigraphy for the New Zealand region over the past 30 000 years, and to reconcile these events against the established climatostratigraphy of the last glacial cycle which has largely been developed from Northern Hemisphere records (e.g. Last Glacial Maximum (LGM), Termination I, Younger Dryas). An initial outcome of NZ-INTIMATE has been the identification of a series of well-dated, high-resolution onshore and offshore proxy records from a variety of latitudes and elevations on a common calendar timescale from 30 000 cal. yr BP to the present day. High-resolution records for the last glacial coldest period (LGCP) (including the LGM sensu stricto) and last glacial-interglacial transition (LGIT) from Auckland maars, Kaipo and Otamangakau wetlands on eastern and central North Island, marine core MD97-2121 east of southern North Island, speleothems on northwest South Island, Okarito wetland on southwestern South Island, are presented. Discontinuous (fragmentary) records comprising compilations of glacial sequences, fluvial sequences, loess accumulation, and aeolian quartz accumulation in an andesitic terrain are described. Comparisons with ice-core records from Antarctica (EPICA Dome C) and Greenland (GISP2) are discussed. A major advantage immediately evident from these records apart from the speleothem record, is that they are linked precisely by one or more tephra layers. Based on these New Zealand terrestrial and marine records, a reasonably coherent, regionally applicable, sequence of climatically linked stratigraphic events over the past 30 000 cal. yr is emerging. Three major climate events are recognised: (1) LGCP beginning at ca. 28 000 cal. yr BP, ending at Termination I, ca. 18 000 cal. yr BP, and including a warmer and more variable phase between ca. 27 000 and 21 000 cal. yr BP, (2) LGIT between ca. 18 000 and 11 600 cal. yr BP, including a Lateglacial warm period from ca. 14 800 to 13 500 cal. yr BP and a Lateglacial climate reversal between ca. 13 500 and 11 600 cal. yr BP, and (3) Holocene interglacial conditions, with two phases of greatest warmth between ca. 11 600 and 10 800 cal. yr BP and from ca. 6 800 to 6 500 cal. yr BP. Some key boundaries coincide with volcanic tephras. Copyright © 2007 John Wiley & Sons, Ltd. Publisher: John Wiley & Sons Ltd Coverage: 2007-01-01T00:00:00Z
2005-11-15
In connection with previous aerial photo interpretation, a number of prominent escarpments, hypothetically indicative of late- or postglacial faulting, were noted in the mainland part of the investigation area. Most of these scarps were field-checked in 2004 and found to be more or less intensely glacially abraded, i.e. formed prior to the last deglaciation. On the island of Oeland a very distinct, straight lineament was likewise noticed in connection with aerial photo interpretation. In the field the lineament was identified as a step in the ground surface or as a very distinct vegetational boundary, the latter due to a difference in thickness of the soil cover on either side of the lineament. The step in the ground surface clearly derives from a bedrock scarp but it was not possible to determine its nature or age in the absence of stratigraphical information. No systematic search for unstable boulders, tentatively refuting the occurrence of major earthquakes in the vicinity, was carried out, but a few specimens were encountered during minor excursions in different parts of the investigation area. However, without estimating how much earthquake-induced ground motion these boulders could withstand before they would topple over, it is difficult to judge their significance as palaeo-earthquake indicators. Stratigraphical investigations in machine-dug trenches were carried out at three localities along the Faarbo esker, all situated west of the candidate area at Simpevarp. A total of some 170 m of trenches were excavated and investigated. Deposits of loosely packed sand and coarse silt were encountered in almost all the trenches and in some of them a clayey bed covered the sandy-silty deposits. When shaken by strong earthquakes in a water saturated state, such deposits are highly likely to liquefy but no significant features related to liquefaction were noted in any of the trenches. However, as the excavation sites are situated some 30-100 m above the present sea level, they must have been raised above the ancient sea fairly soon after the deposition of sediments. Consequently, the deposits were completely waterlogged and susceptible to liquefaction only during a limited period of time. The most remarkable observation made during the stratigraphical investigations was the occurrence of slide deposits at Faarbosjoen, near Simpevarp. It was not possible to date the sliding in any of the trenches but, as the slide deposits were covered with beach sand, sliding must have occurred some time between deglaciation and the upheaval above the sea, some 11,000 years ago. It is an open question whether the sliding occurred spontaneously due solely to loading, or whether the phenomenon was triggered by an external event. Hypothetically this may have been moderately strong earthquakes in the vicinity or more distant earthquakes of greater magnitude. The frequent occurrence of periglacial features in those parts of the investigation area located above the sea during the Younger Dryas period some 12,000 years ago suggests that frost processes must be seriously considered as an alternative to seismically induced liquefaction when deformed sediments are encountered.
Evidence for a Massive Extraterrestrial Airburst over North America 12.9 ka Ago
A carbon-rich black layer commonly referred to as a black mat, with a basal age of approximately 12.9 ka, has been identified at over 50 sites across North America1. The age of the base of the black mat coincides with the abrupt onset of Younger Dryas cooling and megafaunal extinctions in North America. In situ bones of extinct mammals, including mammoths, mastodons, ground sloths, horses, camels, many smaller mammals and birds, and Clovis tool assemblages occur below the black mat but not within or above it. In this paper, we provide evidence for an ejecta layer at the base of the black mat from an extraterrestrial impact event 12.9 ka ago. We have investigated nine terminal Clovis-age sites in North America and a comparable site in Lommel, Belgium that are all marked by a thin, discrete layer containing varying peak abundances of (1) magnetic grains/microspherules containing iridium concentrations up to 117 ppb, (2) charcoal, (3) soot, (4) vesicular carbon spherules, (5) glass-like carbon, and (6) fullerenes enriched in 3He. This layer also extends throughout the rims of at least fifteen Carolina Bays, unique, elliptical, oriented lakes and wetlands scattered across the Atlantic Coastal Plain whose major axes point towards the Great Lakes and Canada. Microspherules, highly enriched in titanium, were found only in or near the YD boundary (YDB) layer with greatest deposition rates (35 per cm2) occurring near the Great Lakes. Magnetic grains also peak in the YDB with maximum deposition near the Great Lakes (30 mg/cm2). Magnetic grains near the Great Lakes are enriched in magnetite (4 mg/cm2) and silicates (23 mg/cm2) but contain less ilmenite/rutile (1 mg/cm2) than distant sites where ilmentite/rutile deposition ranges up to 18 mg/cm2. Analysis of the ilmenite/rutile-rich magnetic grains and microspherules indicates that they contain considerable water, up to 28 at.% hydrogen, and have TIO2/FeO, TIO2/Zr, Al2O3/FeO+MgO, CaO/Al2O3, REE/chondrite, K/Th, FeO/MnO ratios and SIO2, Na2O, K2O, Cr2O3, Ni, Co, Ir, Th, U, and other trace element abundances that are inconsistent with all terrestrial and extraterrestrial sources except for Lunar Procellarum KREEP terrain (PKT). We propose that the YDB layer is the ejecta layer from an airburst over the Laurentide Ice Sheet that deposited local, low-speed terrestrial material near the airburst site and KREEP-like, high-speed projectile material farther away, leaving little or no permanent crater. The associated blast wave and thermal pulse would have contributed to the megafaunal extinctions and destabilized the Laurentide Ice Sheet, loading the atmosphere with dust, soot, NOx, and water vapor and triggered the YD cooling. 1 Haynes, C. V., Jr. in Murray Springs: a Clovis site with multiple activity areas in the San Pedro Valley, Arizona. C. V. Haynes, Jr. and Bruce B. Huckell, eds. Tucson: Univ. of Arizona Press, in press, 2007.
Tidal breakup of binary stars at the Galactic Center. II. Hydrodynamic simulations
2010-09-01
In Paper I, we followed the evolution of binary stars as they orbited near the supermassive black hole (SMBH) at the Galactic center, noting the cases in which the two stars would come close enough together to collide. In this paper we replace the point-mass stars by fluid realizations, and use a smoothed-particle hydrodynamics (SPH) code to follow the close interactions. We model the binary components as main-sequence stars with initial masses of 1, 3 and 6 Solar masses, and with chemical composition profiles taken from stellar evolution codes. Outcomes of the close interactions include mergers, collisions that leave both stars intact, and ejection of one star at high velocity accompanied by capture of the other star into a tight orbit around the SMBH. For the first time, we follow the evolution of the collision products for many ($\\gtrsim 100$) orbits around the SMBH. Stars that are initially too small to be tidally disrupted by the SMBH can be puffed up by close encounters or collisions, with the result that tidal stripping occurs in subsequent periapse passages. In these cases, mass loss occurs episodically, sometimes for hundreds of orbits before the star is completely disrupted. Repeated tidal flares, of either increasing or decreasing intensity, are a predicted consequence. In collisions involving a low-mass and a high-mass star, the merger product acquires a high core hydrogen abundance from the smaller star, effectivel y resetting the nuclear evolution "clock" to a younger age. Elements like Li, Be and B that can exist only in the outermost envelope of a star are severely depleted due to envelope ejection during collisions and due to tidal forces from the SMBH. In the absence of collisions, tidal spin-up of stars is only important in a narrow range of periapse distances, $r_t/2\\lesssim r_per \\lesssim r_t$ with $r_t$ the tidal disruption radius.
The Star Cluster Population of the Collisional Ring Galaxy NGC 922
2010-02-02
We present a detailed study of the star cluster population detected in the galaxy NGC922, one of the closest collisional ring galaxies known to date, using HST/WFPC2 UBVI photometry, population synthesis models, and N-body/SPH simulations.We find that 69% of the clusters are younger than 7Myr, and that most of them are located in the ring or along the bar, consistent with the strong Halpha emission. The cluster luminosity function slope of 2.1-2.3 for NGC922 is in agreement with those of young clusters in nearby galaxies. Models of the cluster age distribution match the observations best when cluster disruption is considered. We also find clusters with ages (>50Myr) and masses (>10^5 Msun) that are excellent progenitors for faint fuzzy clusters. The images also show a tidal plume pointing toward the companion. Its stellar age from our analysis is consistent with pre-existing stars that were stripped off during the passage of the companion. Finally, a comparison of the star-forming complexes observed in NGC922 with those of a distant ring galaxy from the GOODS field indicates very similar masses and sizes, suggesting similar origins.
1988-01-01
Large portions of the Late Cretaceous continental margin of western North America were dominated by a convergent tectonic framework characterized by the development of trenches, accretionary wedges, forearc basins, magmatic arcs, and back arc basins. The most prominent and well-preserved remnants of the convergent margins are present in southern Alaska and California. The southern Alaska convergent margin appears to have developed in response to northward-directed subduction of the Kula plate and the California margin in response to eastward-directed subduction of the Farallon plate. The chief elements of the southern Alaska convergent margin, on the basis of paleomagnetic data, appear to have subsequently migrated northward and rotated in the post-Cretaceous. The chief elements of the California margin have been disrupted by Neogene strike-slip displacements on the San Andreas fault system and accretion of younger terranes to the west. In both southern Alaska and California, the forearc-basin deposits are well preserved and produce major amounts of gas. The principle reservoirs in Alaska are Tertiary nonmarine deposits and in California are Late Cretaceous and Tertiary deep marine and deltaic deposits.
Effects of repetition and configural changes on the development of face recognition processes.
We investigated the effect of repetition on recognition of upright, inverted and contrast-reversed target faces in children from 8 to 15 years when engaged in a learning phase/test phase paradigm with target and distractor faces. Early (P1, N170) and late ERP components were analysed Children across age groups performed equally well, and were better at recognizing upright faces. However, teenagers and adults were equally accurate for all three face types. The neurophysiological responses to upright, inverted and negative faces matured until adulthood and showed different effects at different ages. P1 and N170 components were affected by face type at all ages, suggesting early configural disruption on encoding processes regardless of age. Frontal ERPs reflected the difficulty of processing these stimuli. Distinct repetition effects were seen at frontal, temporal frontal and parietal sites, suggesting differential involvement of these brain regions underlying working memory and recognition processes. Thus, a learning phase was sufficient (a) for 8-year-olds to perform as accurately as 15-year-olds and (b) to eliminate face type effects in teenagers and adults, but not in younger children.
2007-01-15
In 1998, the Aznalcollar mine tailings dyke in southwestern Spain broke, flooding the Agrio-Guadiamar river system with acid tailings up to the borders of one of the largest breeding colonies of white storks in the western Palearctic, Dehesa de Abajo. Over the following years, a high proportion of nestlings developed leg defects not seen before the spill, prompting this study. Nestlings with deformed legs had significantly lower plasma phosphorous (P) and higher Ca:P ratios than non-deformed cohorts in the first two years, but in the third year, when more, younger birds were studied, plasma P ranged from much higher to much lower in the affected colony compared with reference birds. Coefficients of variation for phosphorous were 19% and 60%, in reference and contaminated colonies, respectively. Storks from the contaminated colony were unable to control P levels and Ca:P ratios within the narrow limits necessary for normal bone development. - Since a large mine tailings spill near a stork colony in southwestern Spain, nestlings had leg deformities and could not control serum phosphorous levels and Ca:P ratios.
2007-01-01
In 1998, the Aznalcollar mine tailings dyke in southwestern Spain broke, flooding the Agrio-Guadiamar river system with acid tailings up to the borders of one of the largest breeding colonies of white storks in the western Palearctic, Dehesa de Abajo. Over the following years, a high proportion of nestlings developed leg defects not seen before the spill, prompting this study. Nestlings with deformed legs had significantly lower plasma phosphorous (P) and higher Ca:P ratios than non-deformed cohorts in the first two years, but in the third year, when more, younger birds were studied, plasma P ranged from much higher to much lower in the affected colony compared with reference birds. Coefficients of variation for phosphorous were 19% and 60%, in reference and contaminated colonies, respectively. Storks from the contaminated colony were unable to control P levels and Ca:P ...
An updated catalog of M31 globular-like clusters: UBVRI photometry, ages, and masses
2010-09-21
We present an updated UBVRI photometric catalog containing 970 objects in the field of M31, selected from the Revised Bologna Catalog (RBC v.4.0), including 965, 967, 965, 953, and 827 sources in the individual UBVRI bands, respectively, of which 205, 123, 14, 126, and 109 objects do not have previously published photometry. Photometry is performed using archival images from the Local Group Galaxies Survey, which covers 2.2 deg^2 along the major axis of M31. We focus on 445 confirmed `globular-like' clusters and candidates, comprising typical globular and young massive clusters. The ages and masses of these objects are derived by comparison of their observed spectral-energy distributions with simple stellar population synthesis. Approximately half of the clusters are younger than 2 Gyr, suggesting that there has been significant recent active star formation in M31, which is consistent with previous results. We note that clusters in the halo (r_ projected>30kpc) are composed of two different components, older clusters with ages >10 Gyr and younger clusters with ages around 1 Gyr. The spatial distributions show that the young clusters ( 2 Gyr) are spatially correlated with the bulge and halo. We also estimate the masses of the 445 confirmed clusters and candidates in M31 and find that our estimates agree well with previously published values. We find that none of the young disk clusters can survive the inevitable encounters with giant molecular clouds in the galaxy's disk and that they will eventually disrupt on timescales of a few Gyr. Specifically, young disk clusters with a mass of 10^4 M_\\odot are expected to dissolve within 3.0 Gyr and will, thus, not evolve to become globular clusters.
Aspirin recommendations changed for many younger diabetic patients
2010-06-01
Experts are now recommending that low-dose aspirin therapy to prevent heart attacks be used somewhat more conservatively -- that men younger than 50 and women younger than 60, who have diabetes but no other major risk ...
2007-08-02
We present new Hubble Space Telescope photometry of the massive globular cluster M54 (NGC 6715) and the superposed core of the tidally disrupted Sagittarius (Sgr) dSph galaxy as part of the ACS Survey of Galactic Globular Clusters. Our deep (F606W~26.5), high-precision photometry yields an unprecedentedly detailed color-magnitude diagram showing the extended blue horizontal branch and multiple main sequences of the M54+Sgr system. The distance and reddening to M54 are revised usingboth isochrone and main-sequence fitting to (m-M)_0=17.27 and E(B-V)=0.15. Preliminary assessment finds the M54+Sgr field to be dominated by the old metal-poor populations of Sgr and the globular cluster. Multiple turnoffs indicate the presence of at least two intermediate-aged star formation epochs with 4 and 6 Gyr ages and [Fe/H]=-0.4 to -0.6. We also clearly show, for the first time, a prominent, 2.3 Gyr old Sgr population of near-solar abundance. A trace population of even younger (0.1-0.8 Gyr old), more metal-rich ([Fe/H]\\sim0.6) stars is also indicated. The Sgr age-metallicity relation is consistent with a closed-box model and multiple (4-5) star formation bursts over the entire life of the satellite, including the time since Sgr began disrupting.
Status of volcanic hazard studies for the Nevada Nuclear Waste Storage Investigations
Volcanism studies of the Nevada Test Site (NTS) region are concerned with hazards of future volcanism with respect to underground disposal of high-level radioactive waste. The hazards of silicic volcanism are judged to be negligible; hazards of basaltic volcanism are judged through research approaches combining hazard appraisal and risk assessment. The NTS region is cut obliquely by a N-NE trending belt of volcanism. This belt developed about 8 Myr ago following cessation of silicic volcanism and contemporaneous with migration of basaltic activity toward the southwest margin of the Great Basin. Two types of fields are present in the belt: (1) large-volume, long-lived basalt and local rhyolite fields with numerous eruptive centers and (2) small-volume fields formed by scattered basaltic scoria cones. Late Cenozoic basalts of the NTS region belong to the second field type. Monogenetic basalt centers of this region were formed mostly by Strombolian eruptions; Surtseyean activity has been recognized at three centers. Geochemically, the basalts of the NTS region are classified as straddle A-type basalts of the alkalic suite. Petrological studies indicate a volumetric dominance of evolved hawaiite magmas. Trace- and rare-earth-element abundances of younger basalt (<4 Myr) of the NTS region and southern Death Valley area, California, indicate an enrichment in incompatible elements, with the exception of rubidium. The conditional probability of recurring basaltic volcanism and disruption of a repository by that event is bounded by the range of 10{sup -8} to 10{sup -10} as calculated for a 1-yr period. Potential disruptive and dispersal effects of magmatic penetration of a repository are controlled primarily by the geometry of basalt feeder systems, the mechanism of waste incorporation in magma, and Strombolian eruption processes.
Status of volcanic hazard studies for the Nevada Nuclear Waste Storage Investigations
Volcanism studies of the Nevada Test Site (NTS) region are concerned with hazards of future volcanism with respect to underground disposal of high-level radioactive waste. The hazards of silicic volcanism are judged to be negligible; hazards of basaltic volcanism are judged through research approaches combining hazard appraisal and risk assessment. The NTS region is cut obliquely by a N-NE trending belt of volcanism. This belt developed about 8 Myr ago following cessation of silicic volcanism and contemporaneous with migration of basaltic activity toward the southwest margin of the Great Basin. Two types of fields are present in the belt: (1) large-volume, long-lived basalt and local rhyolite fields with numerous eruptive centers and (2) small-volume fields formed by scattered basaltic scoria cones. Late Cenozoic basalts of the NTS region belong to the second field type. Monogenetic basalt centers of this region were formed mostly by Strombolian eruptions; Surtseyean activity has been recognized at three centers. Geochemically, the basalts of the NTS region are classified as straddle A-type basalts of the alkalic suite. Petrological studies indicate a volumetric dominance of evolved hawaiite magmas. Trace- and rare-earth-element abundances of younger basalt (<4 Myr) of the NTS region and southern Death Valley area, California, indicate an enrichment in incompatible elements, with the exception of rubidium. The conditional probability of recurring basaltic volcanism and disruption of a repository by that event is bounded by the range of 10{sup -8} to 10{sup -10} as calculated for a 1-yr period. Potential disruptive and dispersal effects of magmatic penetration of a repository are controlled primarily by the geometry of basalt feeder systems, the mechanism of waste incorporation in magma, and Strombolian eruption processes.
Status of volcanic hazard studies for the Nevada Nuclear Waste Storage Investigations
1983-03-01
Volcanism studies of the Nevada Test Site (NTS) region are concerned with hazards of future volcanism with respect to underground disposal of high-level radioactive waste. The hazards of silicic volcanism are judged to be negligible; hazards of basaltic volcanism are judged through research approaches combining hazard appraisal and risk assessment. The NTS region is cut obliquely by a N-NE trending belt of volcanism. This belt developed about 8 Myr ago following cessation of silicic volcanism and contemporaneous with migration of basaltic activity toward the southwest margin of the Great Basin. Two types of fields are present in the belt: (1) large-volume, long-lived basalt and local rhyolite fields with numerous eruptive centers and (2) small-volume fields formed by scattered basaltic scoria cones. Late Cenozoic basalts of the NTS region belong to the second field type. Monogenetic basalt centers of this region were formed mostly by Strombolian eruptions; Surtseyean activity has been recognized at three centers. Geochemically, the basalts of the NTS region are classified as straddle A-type basalts of the alkalic suite. Petrological studies indicate a volumetric dominance of evolved hawaiite magmas. Trace- and rare-earth-element abundances of younger basalt (<4 Myr) of the NTS region and southern Death Valley area, California, indicate an enrichment in incompatible elements, with the exception of rubidium. The conditional probability of recurring basaltic volcanism and disruption of a repository by that event is bounded by the range of 10{sup -8} to 10{sup -10} as calculated for a 1-yr period. Potential disruptive and dispersal effects of magmatic penetration of a repository are controlled primarily by the geometry of basalt feeder systems, the mechanism of waste incorporation in magma, and Strombolian eruption processes.
Full Text Available.BackgroundAlthough the burden experienced by families of people with schizophrenia has long been recognized as one of the most important consequences of the disorder, there are no reports from the Arab world. Following the example of the five - nation European (EPSILON) study, we explored the following research question: How does the relationship between domains of caregiving (as in the Involvement Evaluation Questionnaire - IEQ-EU) and caregiver psychic distress on the one hand, and caregiver's/patient's socio-demographics, clinical features and indices of quality of care, on the other hand, compare with the pattern in the literature?MethodConsecutive family caregivers of outpatients with schizophrenia were interviewed with the IEQ-EU. Patients were interviewed with measures of needs for care, service satisfaction, quality of life (QOL) and psychopathology.ResultsThere were 121 caregivers (66.1% men, aged 39.8). The IEQ domain scores (total: 46.9; tension: 13.4; supervision: 7.9; worrying: 12.9; and urging: 16.4) were in the middle of the range for the EU data. In regression analyses, higher burden subscale scores were variously associated with caregiver lower level of education, patient's female gender and younger age, as well as patient's lower subjective QOL and needs for hospital care, and not involving the patient in outdoor activities. Disruptive behavior was the greatest determinant of global rating of burden.ConclusionOur results indicate that, despite differences in service set-up and culture, the IEQ-EU can be used in Kuwait as it has been used in the western world, to describe the pattern of scores on the dimensions of caregiving. Differences with the international data reflect peculiarities of culture and type of service. Despite generous national social welfare provisions, experience of burden was the norm and was significantly associated with patient's disruptive behavior. The results underscore the need for provision of community - based programs and continued intervention with the families in order to improve the quality of care.
2006-09-12
[Abridged] We present first results from a large-area (~80degx20deg), sparsely sampled two-filter (B,R) imaging survey towards the Canis Major stellar over-density, claimed to be a disrupting Milky Way satellite galaxy. Utilizing stellar colour-magnitude diagrams reaching to B ~ 22 mag, we provide a first delineation of its surface density distribution using main sequence stars. Its projected shape is highly elongated, nearly parallel to the Galactic plane, with an axis ratio of >~ 5:1, substantially more so than what Martin et al. originally found. We also provide a first map of a prominent over-density of blue, presumably younger main sequence stars, which appears to have a maximum near [l,b = 240,-7 deg]. The young population is markedly more localized. We estimate an upper limit on the line-of-sight (l.o.s.) depth of the old population based on the main sequence width, obtaining sigma_los < 1.8 +/- 0.3 kpc, at an adopted D_helio = 7.5 +/- 1 kpc. For the young stellar population, we find sigma_los < 1.5 kpc. There are different explanations for the CMa over-density: (a) a partially disrupting dwarf galaxy on a low-latitude orbit, (b) a projection of the warped outer Galactic disk, and (c) a projection of an out-of-plane spiral arm. While the data provide no firm arguments against the less well-defined third scenario, they have clear implications for each of the others: (a) We infer from the strong elongation in longitude, and simulations in the literature, that the over-density is unlikely to be a gravitationally bound system at the present epoch, but may well be just a recently disrupted satellite remnant. (b) Based on modeling, the line-of-sight depth of the over-density in old stars is clearly inconsistent with published locally axi-symmetric descriptions of the warped Galactic disk.
2008-01-01
Growth rates, δ18O and δ13C of five stalagmites from the west coasts of North and South Islands, New Zealand, provide records of millennial-scale climate variability over the last ~75 kyr. Thirty-five uranium-series ages were used to provide the chronology. δ18O of stalagmite calcite was influenced by changes in moisture source region, temperature and both δ18O and δ13C primarily display a negative relationship with rainfall. To assist interpretation of climatic signals δ18O profiles were adjusted for the ice-volume effect. Changes in these proxies reflect changes in the strength of the circumpolar westerly circulation and the frequency of southwesterly flow across New Zealand. MIS 4 was a period of wet and cool climate lasting from 67.7 to 61.3 kyr B.P., expressed in the stalagmites by an interval of strongly negative isotope ratios and increased growth rate. This contrasts with less negative δ18O and δ13C, and slow growth, interpreted as dry and cold climate, during much of MIS 2. This difference between MIS 2 and MIS 4 provides an explanation for why glacial moraines in the Southern Alps of MIS 4 age lie beyond those deposited during the last glacial maximum (MIS 2). Heinrich events, with the exception of H0 (the Younger Dryas), are interpreted from high-resolution South Island stalagmite HW05-3, from Hollywood Cave, West Coast, as times of wetter and cooler climate. Minima in δ18O and δ13C (wet periods) occurred at 67.7-61.0, 56-55, 50.5-47.5, 40-39, 30.5-29, 25.5-24.3 and 16.1-15. kyr B.P. matching Heinrich events H6-H1 (including H5a) respectively. This demonstrates a robust teleconnection between events in the North Atlantic and New Zealand climate. Minima in δ18O also occurred at similar times in less well-dated North Island stalagmite RK05-3 from Ruakuri Cave, Waitomo. Speleothems from low-latitudes have revealed that Heinrich events forced southerly displacement of the Intertropical Convergence Zone. This caused steepening of the temperature gradient across mid-southern latitudes, increased westerly circulation and resulted in wet conditions on the west coast of both islands. Immediately following H1 in the HW05-3 stable isotope profiles is another excursion to more negative isotopic values, suggesting wet and cold climate, lasting from 14.6 to 13.0 kyr B.P. Such a climate on the West Coast at this time has been previously suggested from glacier advance (e.g. Waiho Loop moraine) and decreased abundance of tall trees on the landscape. This event occurred too early to be a response to H0, but is synchronous with a return to cool climate in Antarctica. Thus West Coast climate appears to have been sensitive to changes in Antarctica as well as the North Atlantic. Isotopic minima (wet and cool climate) in South Island stalagmite GT05-5, which formed during the Holocene, first occurred 4.6 kyr B.P. This began a series of four oscillations in isotope ratios, the last terminating when the stalagmite was collected (2006). Onset of these oscillations is associated with initiation of ice advance in the Southern Alps, and beginning of the Neoglacial. The last oscillation displays enriched isotope ratios lasting from 1.2 to 0.8 kyr B.P. succeeded by depleted ratios lasting until 0.15 kyr B.P., mirroring the Medieval Climate Optimum and Little Ice Age, respectively, of European palaeoclimate records. Publisher: The University of Waikato Language: en Rights: http://www.waikato.ac.nz/library/research_commons/rc_about.shtml#copyright
Attitudes toward Younger and Older Adults: The German Aging Semantic Differential
The present study used the German Aging Semantic Differential (ASD) to assess attitudes toward younger and older adults in a heterogeneous sample of n = 151 younger and n = 143 older adults. The questionnaire was administered in two versions, one referring to the evaluation of younger adults, the other to the evaluation of older adults. Multiple-group confirmatory factor analysis replicated the four-factor solution reported in the literature. Younger compared to older adults were rated as higher in terms of instrumentality (i.e., more active, adaptive to change) and
2010-05-06
The ACS and NICMOS have been used to obtain new HST images of NGC 4038/4039 ("The Antennae"). These new observations allow us to better differentiate compact star clusters from individual stars, based on both size and color. We use this ability to extend the cluster luminosity function by approximately two magnitudes over our previous WFPC2 results, and find that it continues as a single power law, dN/dL propto L^alpha with alpha=-2.13+/-0.07, down to the observational limit of Mv~-7. Similarly, the mass function is a single power law dN/dM propto M^beta with beta=-2.10+/-0.20 for clusters with ages t<3x10^8 yr, corresponding to lower mass limits that range from 10^4 to 10^5 Msun, depending on the age range of the subsample. Hence the power law indices for the luminosity and mass functions are essentially the same. The luminosity function for intermediate-age clusters (i.e., ~100-300 Myr old objects found in the loops, tails, and outer areas) shows no bend or turnover down to Mv~-6, consistent with relaxation-driven cluster disruption models which predict the turnover should not be observed until Mv~-4. An analysis of individual ~0.5-kpc sized areas over diverse environments shows good agreement between values of alpha and beta, similar to the results for the total population of clusters in the system. Several of the areas studied show evidence for age gradients, with somewhat older clusters appearing to have triggered the form ation of younger clusters. The area around Knot B is a particularly interesting example, with an ~10-50 Myr old cluster of estimated mass ~10^6 Msun having apparently triggered the formation of several younger, more massive (up to 5x10^6 Msun) clusters along a dust lane.
Volcanism Studies: Final Report for the Yucca Mountain Project
This report synthesizes the results of volcanism studies conducted by scientists at the Los Alamos National Laboratory and collaborating institutions on behalf of the Department of Energy's Yucca Mountain Project. An assessment of the risk of future volcanic activity is one of many site characterization studies that must be completed to evaluate the Yucca Mountain site for potential long-term storage of high-level radioactive waste. The presence of several basaltic volcanic centers in the Yucca Mountain region of Pliocene and Quaternary age indicates that there is a finite risk of a future volcanic event occurring during the 10,000-year isolation period of a potential repository. Chapter 1 introduces the volcanism issue for the Yucca Mountain site and provides the reader with an overview of the organization, content, and significant conclusions of this report. The risk of future basaltic volcanism is the primary topic of concern including both events that intersect a potential repository and events that occur near or within the waste isolation system of a repository. Future volcanic events cannot be predicted with certainty but instead are estimated using formal methods of probabilistic volcanic hazard assessment (PVHA). Chapter 2 describes the volcanic history of the Yucca Mountain region (YMR) and emphasizes the Pliocene and Quaternary volcanic record, the interval of primary concern for volcanic risk assessment. The distribution, eruptive history, and geochronology of Plio-Quaternary basalt centers are described by individual center emphasizing the younger postcaldera basalt (<5 Ma). The Lathrop Wells volcanic center is described in detail because it is the youngest basalt center in the YMR. The age of the Lathrop Wells center is now confidently determined to be about 75 thousand years old. Chapter 3 describes the tectonic setting of the YMR and presents and assesses the significance of multiple alternative tectonic models. The Crater Flat volcanic zone is defined and described as one of many alternative models of the structural controls of the distribution of Plio-Quaternary basalt centers in the YMR. Geophysical data are described for the YMR and are used as an aid to understand the distribution of basaltic volcanic centers. Chapter 4 discusses the petrologic and geochemical features of basaltic volcanism in the YMR, the southern Great Basin and the Basin and Range province. Geochemical and isotopic data are presented for post-Miocene basalts of the Yucca Mountain region. Alternative petrogenetic models are assessed for the formation of the Lathrop Wells volcanic center. Based on geochemical data, basaltic ash in fault trenches near Yucca Mountain is shown to have originated from the Lathrop Wells center. Chapter 5 synthesizes eruptive and subsurface effects of basaltic volcanism on a potential repository and summarizes current concepts of the segregation, ascent, and eruption of basalt magma. Chapter 6 synthesizes current knowledge of the probability of disruption of a potential repository at Yucca Mountain. In 1996, an Expert Elicitation panel was convened by DOE that independently conducted PVHA for the Yucca Mountain site. Chapter 6 does not attempt to revise this PVHA; instead, it further examines the sensitivity of variables in PVHA. The approaches and results of PVHA by the expert judgment panel are evaluated and incorporated throughout this chapter. The disruption ratio (E2) is completely re-evaluated using simulation modeling that describes volcanic events based on the geometry of basaltic feeder dikes. New estimates of probability bounds are developed. These comparisons show that it is physically implausible for the probability of magmatic disruption of the Yucca Mountain site to be > than about 7 x 10{sup {minus}8} events yr{sup {minus}1} . Simple probability estimates are used to assess possible implications of not drilling aeromagnetic anomalies in the Amargosa Valley. The sensitivity of the disruption probability to the location of northeast boundaries of volcanic zones near the Yucca Mountain sit
Volcanism Studies: Final Report for the Yucca Mountain Project
1998-12-01
This report synthesizes the results of volcanism studies conducted by scientists at the Los Alamos National Laboratory and collaborating institutions on behalf of the Department of Energy's Yucca Mountain Project. An assessment of the risk of future volcanic activity is one of many site characterization studies that must be completed to evaluate the Yucca Mountain site for potential long-term storage of high-level radioactive waste. The presence of several basaltic volcanic centers in the Yucca Mountain region of Pliocene and Quaternary age indicates that there is a finite risk of a future volcanic event occurring during the 10,000-year isolation period of a potential repository. Chapter 1 introduces the volcanism issue for the Yucca Mountain site and provides the reader with an overview of the organization, content, and significant conclusions of this report. The risk of future basaltic volcanism is the primary topic of concern including both events that intersect a potential repository and events that occur near or within the waste isolation system of a repository. Future volcanic events cannot be predicted with certainty but instead are estimated using formal methods of probabilistic volcanic hazard assessment (PVHA). Chapter 2 describes the volcanic history of the Yucca Mountain region (YMR) and emphasizes the Pliocene and Quaternary volcanic record, the interval of primary concern for volcanic risk assessment. The distribution, eruptive history, and geochronology of Plio-Quaternary basalt centers are described by individual center emphasizing the younger postcaldera basalt (<5 Ma). The Lathrop Wells volcanic center is described in detail because it is the youngest basalt center in the YMR. The age of the Lathrop Wells center is now confidently determined to be about 75 thousand years old. Chapter 3 describes the tectonic setting of the YMR and presents and assesses the significance of multiple alternative tectonic models. The Crater Flat volcanic zone is defined and described as one of many alternative models of the structural controls of the distribution of Plio-Quaternary basalt centers in the YMR. Geophysical data are described for the YMR and are used as an aid to understand the distribution of basaltic volcanic centers. Chapter 4 discusses the petrologic and geochemical features of basaltic volcanism in the YMR, the southern Great Basin and the Basin and Range province. Geochemical and isotopic data are presented for post-Miocene basalts of the Yucca Mountain region. Alternative petrogenetic models are assessed for the formation of the Lathrop Wells volcanic center. Based on geochemical data, basaltic ash in fault trenches near Yucca Mountain is shown to have originated from the Lathrop Wells center. Chapter 5 synthesizes eruptive and subsurface effects of basaltic volcanism on a potential repository and summarizes current concepts of the segregation, ascent, and eruption of basalt magma. Chapter 6 synthesizes current knowledge of the probability of disruption of a potential repository at Yucca Mountain. In 1996, an Expert Elicitation panel was convened by DOE that independently conducted PVHA for the Yucca Mountain site. Chapter 6 does not attempt to revise this PVHA; instead, it further examines the sensitivity of variables in PVHA. The approaches and results of PVHA by the expert judgment panel are evaluated and incorporated throughout this chapter. The disruption ratio (E2) is completely re-evaluated using simulation modeling that describes volcanic events based on the geometry of basaltic feeder dikes. New estimates of probability bounds are developed. These comparisons show that it is physically implausible for the probability of magmatic disruption of the Yucca Mountain site to be > than about 7 x 10{sup {minus}8} events yr{sup {minus}1} . Simple probability estimates are used to assess possible implications of not drilling aeromagnetic anomalies in the Amargosa Valley. The sensitivity of the disruption probability to the location of northeast boundaries of volcanic zones near the Yucca Mountain sit
SYSTHESIS OF VOLCANISM STUDIES FOR THE YUCCA MOUNTAIN SITE CHARACTERIZATION PROJECT
This report synthesizes the results of volcanism studies conducted by scientists at the Los Alamos National Laboratory and collaborating institutions on behalf of the Department of Energy's Yucca Mountain Project. Chapter 1 introduces the volcanism issue for the Yucca Mountain site and provides the reader with an overview of the organization, content, and significant conclusions of this report. The hazard of future basaltic volcanism is the primary topic of concern including both events that intersect a potential repository and events that occur near or within the waste isolation system of a repository. Future volcanic events cannot be predicted with certainty but instead are estimated using formal methods of probabilistic volcanic hazard assessment (PVHA). Chapter 2 describes the volcanic history of the Yucca Mountain region (YMR) and emphasizes the Pliocene and Quaternary volcanic record, the interval of primary concern for volcanic risk assessment. The distribution, eruptive history, and geochronology of Plio-Quaternary basalt centers are described by individual center emphasizing the younger postcaldera basalt (<5 Ma). The Lathrop Wells volcanic center is described in detail because it is the youngest basalt center in the YMR. The age of the Lathrop Wells center is now confidently determined to be about 75 thousand years old. Chapter 3 describes the tectonic setting of the YMR and presents and assesses the significance of multiple alternative tectonic models. The distribution of Pliocene and Quaternary basaltic volcanic centers is evaluated with respect to tectonic models for detachment, caldera, regional and local rifting, and the Walker Lane structural zone. Geophysical data are described for the YMR and are used as an aid to understand the distribution of past basaltic volcanic centers and possible future magmatic processes. Chapter 4 discusses the petrologic and geochemical features of basaltic volcanism in the YMR, the southern Great Basin and the Basin and Range province. Geochemical and isotopic data are presented for post-Miocene basalts of the Yucca Mountain region. Alternative petrogenetic models are assessed for the formation of the Lathrop Wells volcanic center. Based on geochemical data, basaltic ash in fault trenches near Yucca Mountain is shown to have originated from the Lathrop Wells center. Chapter 5 synthesizes eruptive and subsurface effects of basaltic volcanism on a potential repository and summarizes current concepts of the segregation, ascent, and eruption of basalt magma. Chapter 6 synthesizes current knowledge of the probability of disruption of a potential repository at Yucca Mountain. In 1996, an Expert Elicitation panel was convened by DOE that independently conducted PVHA for the Yucca Mountain site. Chapter 6 does not attempt to revise this PVHA; instead, it further examines the sensitivity of variables in PVHA. The approaches and results of PVHA by the expert judgment panel are evaluated and incorporated throughout this chapter. The disruption ratio (E2) is completely re-evaluated using simulation modeling that describes volcanic events based on the geometry of basaltic feeder dikes. New estimates of probability bounds are developed. These comparisons show that it is physically implausible for the probability of magmatic disruption of the Yucca Mountain site to be greater than 10{sup -7} events per year. Bounding probability estimates are used to assess possible implications of not drilling aeromagnetic anomalies in the Arnargosa Valley and Crater Flat. The results of simulation modeling are used to assess the sensitivity of the disruption probability for the location of northeast boundaries of volcanic zones near the Yucca Mountain site. A new section on modeling of radiological releases associated with surface and subsurface magmatic activity has been added to chapter 6. The modeling results are consistent with past total system performance assessments that show future volcanic and magmatic events are not significant components of repository performance and volcanism is not a priority issue for performance assessment studies.
SYSTHESIS OF VOLCANISM STUDIES FOR THE YUCCA MOUNTAIN SITE CHARACTERIZATION PROJECT
1997-09-23
This report synthesizes the results of volcanism studies conducted by scientists at the Los Alamos National Laboratory and collaborating institutions on behalf of the Department of Energy's Yucca Mountain Project. Chapter 1 introduces the volcanism issue for the Yucca Mountain site and provides the reader with an overview of the organization, content, and significant conclusions of this report. The hazard of future basaltic volcanism is the primary topic of concern including both events that intersect a potential repository and events that occur near or within the waste isolation system of a repository. Future volcanic events cannot be predicted with certainty but instead are estimated using formal methods of probabilistic volcanic hazard assessment (PVHA). Chapter 2 describes the volcanic history of the Yucca Mountain region (YMR) and emphasizes the Pliocene and Quaternary volcanic record, the interval of primary concern for volcanic risk assessment. The distribution, eruptive history, and geochronology of Plio-Quaternary basalt centers are described by individual center emphasizing the younger postcaldera basalt (<5 Ma). The Lathrop Wells volcanic center is described in detail because it is the youngest basalt center in the YMR. The age of the Lathrop Wells center is now confidently determined to be about 75 thousand years old. Chapter 3 describes the tectonic setting of the YMR and presents and assesses the significance of multiple alternative tectonic models. The distribution of Pliocene and Quaternary basaltic volcanic centers is evaluated with respect to tectonic models for detachment, caldera, regional and local rifting, and the Walker Lane structural zone. Geophysical data are described for the YMR and are used as an aid to understand the distribution of past basaltic volcanic centers and possible future magmatic processes. Chapter 4 discusses the petrologic and geochemical features of basaltic volcanism in the YMR, the southern Great Basin and the Basin and Range province. Geochemical and isotopic data are presented for post-Miocene basalts of the Yucca Mountain region. Alternative petrogenetic models are assessed for the formation of the Lathrop Wells volcanic center. Based on geochemical data, basaltic ash in fault trenches near Yucca Mountain is shown to have originated from the Lathrop Wells center. Chapter 5 synthesizes eruptive and subsurface effects of basaltic volcanism on a potential repository and summarizes current concepts of the segregation, ascent, and eruption of basalt magma. Chapter 6 synthesizes current knowledge of the probability of disruption of a potential repository at Yucca Mountain. In 1996, an Expert Elicitation panel was convened by DOE that independently conducted PVHA for the Yucca Mountain site. Chapter 6 does not attempt to revise this PVHA; instead, it further examines the sensitivity of variables in PVHA. The approaches and results of PVHA by the expert judgment panel are evaluated and incorporated throughout this chapter. The disruption ratio (E2) is completely re-evaluated using simulation modeling that describes volcanic events based on the geometry of basaltic feeder dikes. New estimates of probability bounds are developed. These comparisons show that it is physically implausible for the probability of magmatic disruption of the Yucca Mountain site to be greater than 10{sup -7} events per year. Bounding probability estimates are used to assess possible implications of not drilling aeromagnetic anomalies in the Arnargosa Valley and Crater Flat. The results of simulation modeling are used to assess the sensitivity of the disruption probability for the location of northeast boundaries of volcanic zones near the Yucca Mountain site. A new section on modeling of radiological releases associated with surface and subsurface magmatic activity has been added to chapter 6. The modeling results are consistent with past total system performance assessments that show future volcanic and magmatic events are not significant components of repository performance and volcanism is not a priority issue for performance assessment studies.
Family:the strength of support
2008-01-01
O-026 - Family : The Strength Of Suport Elisabeth Coyne, RN, RM, BN, MN Hons, PhD Candiate - Griffith University, Australia The family often forms the main source of support for younger women during breast cancer treatment, which tends to occur in the outpatient setting with little sustained contact with health professionals. While this support is increasingly acknowledged; currently there is little understanding of the family's role and strengths (communication, leadership, coping styles), or how they may be used to enhance treatment outcomes. Breast cancer is the most common cancer diagnosis for women world wide (World Health Organisation WHO, 2006), with approximately one in eight women in Australia diagnosed each year under the age of 75 years (Australian Institute of Health and Welfare AIHW, 2007). The incidence for women under fifty years of age accounts for 25% of all breast cancer cases in Australia (AIHW, 2007) however there is not a corresponding rate of focused research on this cohort to increase the understanding of the needs of this age group. One of the important considerations for this age group is their life phase, which is often premenopausal and with family responsibilities (AIHW, 2007; Dunn & Steginga, 2000). Hence diagnosis and treatment of breast cancer in younger women may cause significant life and family role disruptions that subsequently have repercussions through the whole-of-family for an extended period (Bloom, Stewart, Johnston, Banks, & Fobair, 2001). Research to date, indicates that although health professionals provide support and education for individual women, this has little long-term acknowledgement of the strengths and influence from the family on the long term family function and adaptation (Mellon & Northouse, 2001). The family is a dynamic group of individuals who bring different strengths to the family adaptation. This paper presents the literature and early findings exploring the strengths of the family. It aims to increase our understanding of the complex nature of the family and their functional and supportive roles during therapy for breast cancer; the strengths of the family, thus enhancing the long term adaptation of younger women with breast cancer. AIHW (2007) Australian Institute of Health and Welfare. Retrieved 2007 from http://www.aihw.gov.au/ Bloom, JR Stewart, SL, Johnston, M, Banks, P, & Fobair, P (2001) Sources of support and the physical and mental well-being of young women with breast cancer. Social Science & Medicine, 53(11), 1513 - 1524. Dunn, J, & Steginga, SK (2000) Young women's experience of breast cancer: Defining young and identifying concerns. Psycho-Oncology, 9, 137-146. Mellon, S & Northouse, L (2001). Family survivorship and quality of life following a cancer diagnosis. Research in Nursing & Health, 24(6), 446-459. WHO (2006) World Health Organisation. Retrieved 2006 from http://www.who.int/en/ Publisher: http://www.isncc.org/conference/; International Society of Nurses in Cancer Care; http://www.isncc.org/conference/15th_ICCN_Abstract_Presentations.aspx; http://www.isncc.org/ Contributor: Patsy Yates; Sanchia Aranda Relation: 15th International Conference on Cancer Nursing; Family: the strength of support; 2008-08-17; 2008-08-21; Singapore; N Language: en_AU Rights: Y
Older Chinese consumers perceive themselves younger than actual age
2010-05-18
University of Missouri researcher Rui Yao studied how older Chinese consumers perceived their age. Yao found that a majority of older Chinese consumers perceive themselves to be younger than their actual age. Twenty ...
Estimated radiation risks associated with abdominal CT scans are greater in younger ...
2010-05-03
In younger patients, the estimated radiation risks associated with abdominal and pelvic computed tomography scans are twice those of older patients, according to a study to be presented at the ARRS 2010 Annual Meeting ...
Breast cancer screening program should give higher importance to younger women
2010-04-01
Screening younger women for breast cancer is fairer and makes sound economic sense, according to new research by the University of East Anglia. Public release date: 1-Apr-2010 | E-mail | Share Contact: UEA Press ...
2010-03-25
It is generally assumed that a large fraction of stars are initially born in clusters. However, a large fraction of these disrupt on short timescales and the stars end up belonging to the field. Understanding this process is of paramount importance if we wish to constrain the star formation histories of external galaxies using star clusters. We attempt to understand the relation between field stars and star clusters by simultaneously studying both in a number of nearby galaxies. As a pilot study, we present results for the late-type spiral NGC 4395 using HST/ACS and HST/WFPC2 images. Different detection criteria were used to distinguish point sources (star candidates) and extended objects (star cluster candidates). Using a synthetic CMD method, we estimated the star formation history. Using simple stellar population model fitting, we calculated the mass and age of the cluster candidates. The field star formation rate appears to have been roughly constant, or to have possibly increased by up to about a factor of two, for ages younger than $\\sim$300 Myr within the fields covered by our data. Our data do not allow us to constrain the star formation histories at older ages. We identify a small number of clusters in both fields. Neither massive ($>10^5$ M$_\\odot$) clusters nor clusters with ages $\\geq1$ Gyr were found in the galaxy and we found few clusters older than 100 Myr. Based on our direct comparison of field stars and cluste rs in NGC 4395, we estimate the ratio of star formation rate in clusters that survive for $10^7$ to $10^8$ years to the total star formation to be $\\Gamma\\sim0.03$. We suggest that this relatively low $\\Gamma$ value is caused by the low star formation rate of NGC 4395.
2008-08-22
We use 16 micron, Spitzer-IRS, blue peakup photometry of 50 early-type galaxies in the Coma cluster to define the mid-infrared colour-magnitude relation. We compare with recent simple stellar population models that include the mid-infrared emission from the extended, dusty envelopes of evolved stars. The K-[16] colour in these models is very sensitive to the relative population of dusty AGB stars. We find that the passively evolving early-type galaxies define a sequence of approximately constant age ~10Gyr with varying metallicity. Several galaxies that lie on the optical/near-infrared colour-magnitude relation do not lie on the mid-infrared relation. This illustrates the sensitivity of the K-[16] colour to age. The fact that a colour-magnitude relation is seen in the mid-infrared underlines the extremely passive nature of the majority (68%) of early-type galaxies in the Coma cluster. The corollary of this is that 32% of the early-type galaxies in our sample are NOT `passive', insofar as they are either significantly younger than 10 Gyr or they have had some rejuvenation episode within the last few Gyr. We also conclude that external effects, such as disruption of the dusty AGB star envelopes by the interstellar medium, does not effect the 16 micron emission. This mid-infrared emission is relatively short-lived and occurs well within the radius at which such effects become important. Given the robustness of mid-infrared emittin g envelopes to environmental effects, the observation that galaxies with excess 16 micron emission lie preferentially at small radii within the cluster, indicates that the cluster environment influences the star formation history.
The Metallicity of Diffuse Intrahalo Light
2008-05-21
We make predictions for the metallicity of diffuse stellar components in systems ranging from small spiral galaxies to rich galaxy clusters. We extend the formalism of Purcell et al. (2007), in which diffuse stellar mass is produced via galaxy disruption, and we convolve this result with the observed mass-metallicity relation for galaxies in order to analyze the chemical abundance of intrahalo light (IHL) in host halos with virial mass 10^10.5 M_sun < M_host < 10^15 M_sun. We predict a steep rise of roughly two dex in IHL metallicity from the scales of small to large spiral galaxies. In terms of the total dynamical mass M_host of the host systems under consideration, we predict diffuse light metallicities ranging from Z_IHL < -2.5 for M_host ~ 10^11 M_sun, to Z_IHL ~ -0.7 for M_host ~ 10^12 M_sun. In larger systems, we predict a gradual flattening of this trend with Z_IHL ~ -0.2 for M_host ~ 10^13 M_sun, increasing to Z_IHL ~ 0.2 for M_host ~ 10^15 M_sun. This plateau is coincident with a narrowing of the intrahalo metallicity distribution as host mass increases. The observable distinction in surface brightness between old, metal-poor IHL stars and more metal-rich, dynamically-younger tidal streams is of crucial importance when estimating the chemical abundance of an intrahalo population with multiple origins.
THE STAR CLUSTER POPULATION OF THE COLLISIONAL RING GALAXY NGC 922
We present a detailed study of the star cluster population detected in the galaxy NGC 922, one of the closest collisional ring galaxies known to date, using Hubble Space Telescope/Wide Field Planetary Camera 2 UBVI photometry, population synthesis models, and N-body/smoothed particle hydrodynamics simulations. We find that 69% of the clusters are younger than 7 Myr, and that most of them are located in the ring or along the bar, consistent with the strong H{alpha} emission. The cluster luminosity function slope of 2.1-2.3 for NGC 922 is in agreement with those of young clusters in nearby galaxies. Models of the cluster age distribution match the observations best when cluster disruption is considered. We also find clusters with ages (>50 Myr) and masses (>10{sup 5} M {sub sun}) that are excellent progenitors for faint fuzzy clusters. The images also show a tidal plume pointing toward the companion. Its stellar age from our analysis is consistent with pre-existing stars that were stripped off during the passage of the companion. Finally, a comparison of the star-forming complexes observed in NGC 922 with those of a distant ring galaxy from the GOODS field indicates very similar masses and sizes, suggesting similar origins.
2002-12-12
We present a detailed analysis of the dynamical properties of a simulated disk galaxy assembled hierarchically in the Lambda CDM cosmogony. At z=0, two distinct dynamical components are identified on the basis of the orbital parameters of stars in the galaxy: a slowly rotating, centrally concentrated spheroid and a disk-like component largely supported by rotation. These components are also recognized in the surface brightness profile of the galaxy, which can be very well approximated by the superposition of an R^{1/4} spheroid and an exponential disk. However, neither does the dynamically-identified spheroid follow de Vaucouleurs' law nor is the disk purely exponential, a resultwhich calls for caution when estimating the importance of the disk from traditional photometric decomposition techniques. The disk may be further decomposed into a thin, dynamically cold component with stars on nearly circularorbits and a hotter, thicker component with orbital parameters transitional between the thin disk and the spheroid. The spheroid is old, and has essentiallyno stars younger than the time elapsed since the last major accretion event ~8 Gyr ago. The majority of thin disk stars, form after the merging activity is over, although a significant fraction ~15% of thin-disk stars are old enough to predate the last major merger event. This unexpected population of old disk stars consists mainly of the tidal debris of satellites whose orbital plane was coincident with the disk and whose orbits were circularized by dynamical friction prior to full disruption. Our results highlight the role of satellite accretion events in shaping the disk and the spheroidal component and reveal some of the clues to the assembly process of a galaxy preserved in the detailed dynamics of old stellar populations.
Environmental stresses generally decrease photosynthetic rates and growth of plants, and alter biomass partitioning. Nutrient deficiency and drought cause root:shoot ratios to increase, whereas the air pollutant ozone (O[sub 3]) causes an opposite shift in carbon allocation. Plants in nature usually grow under suboptimal conditions; therefore plants were raised with O[sub 3] combined with other stresses to analyze the mechanisms whereby multiple stresses influence gas exchange and growth. Physiological and growth responses to stress were determined for radish (raphanus sativus), soybean (Glycine max) willow (Salix nigra), alder (Alnus serrulata) and aspen (Populus tremuloides) in laboratory and field trials. In willow, high-nutrient status plants had more visible injury, but a smaller decline in leaf area with O[sub 3] than did low-nutrient plants. Ultrastructure of host plant cells in alder root nodules was disrupted by O[sub 3], suggesting that this air pollutant can affect the ability of plants to acquire nutrients via symbiosis. Biomass and root:shoot ratios decreased with O[sub 3] in radish and soy-bean. Shifts in stable carbon isotope ratios were caused by O[sub 3], and this technique was used to integrate the effects of O[sub 3] on gas exchange over time. In aspen, O[sub 3] enhanced photosynthesis and foliar areas in young leaves of well-watered aspen, partially compensating for declines in older leaves. This effect was more pronounced in plants raised at a high nitrogen level than in N-deficient plants. Carboxylation efficiency decreased in older, but increased in younger leaves with O[sub 3]. Prior exposure to drought reduced effects of O[sub 3] on photosynthesis and leaf area.
1991-01-01
Environmental stresses generally decrease photosynthetic rates and growth of plants, and alter biomass partitioning. Nutrient deficiency and drought cause root:shoot ratios to increase, whereas the air pollutant ozone (O[sub 3]) causes an opposite shift in carbon allocation. Plants in nature usually grow under suboptimal conditions; therefore plants were raised with O[sub 3] combined with other stresses to analyze the mechanisms whereby multiple stresses influence gas exchange and growth. Physiological and growth responses to stress were determined for radish (raphanus sativus), soybean (Glycine max) willow (Salix nigra), alder (Alnus serrulata) and aspen (Populus tremuloides) in laboratory and field trials. In willow, high-nutrient status plants had more visible injury, but a smaller decline in leaf area with O[sub 3] than did low-nutrient plants. Ultrastructure of host plant cells in alder root nodules was disrupted by O[sub 3], suggesting that this air pollutant can affect the ability of plants to acquire nutrients via symbiosis. Biomass and root:shoot ratios decreased with O[sub 3] in radish and soy-bean. Shifts in stable carbon isotope ratios were caused by O[sub 3], and this technique was used to integrate the effects of O[sub 3] on gas exchange over time. In aspen, O[sub 3] enhanced photosynthesis and foliar areas in young leaves of well-watered aspen, partially compensating for declines in older leaves. This effect was more pronounced in plants raised at a high nitrogen level than in N-deficient plants. Carboxylation efficiency decreased in older, but increased in younger leaves with O[sub 3]. Prior exposure to drought reduced effects of O[sub 3] on photosynthesis and leaf area.
Epigenetic histone modifications of human transposable elements: genome defense versus exaptation
Full Text Available.BackgroundTransposition is disruptive in nature and, thus, it is imperative for host genomes to evolve mechanisms that suppress the activity of transposable elements (TEs). At the same time, transposition also provides diverse sequences that can be exapted by host genomes as functional elements. These notions form the basis of two competing hypotheses pertaining to the role of epigenetic modifications of TEs in eukaryotic genomes: the genome defense hypothesis and the exaptation hypothesis. To date, all available evidence points to the genome defense hypothesis as the best explanation for the biological role of TE epigenetic modifications.ResultsWe evaluated several predictions generated by the genome defense hypothesis versus the exaptation hypothesis using recently characterized epigenetic histone modification data for the human genome. To this end, we mapped chromatin immunoprecipitation sequence tags from 38 histone modifications, characterized in CD4+ T cells, to the human genome and calculated their enrichment and depletion in all families of human TEs. We found that several of these families are significantly enriched or depleted for various histone modifications, both active and repressive. The enrichment of human TE families with active histone modifications is consistent with the exaptation hypothesis and stands in contrast to previous analyses that have found mammalian TEs to be exclusively repressively modified. Comparisons between TE families revealed that older families carry more histone modifications than younger ones, another observation consistent with the exaptation hypothesis. However, data from within family analyses on the relative ages of epigenetically modified elements are consistent with both the genome defense and exaptation hypotheses. Finally, TEs located proximal to genes carry more histone modifications than the ones that are distal to genes, as may be expected if epigenetically modified TEs help to regulate the expression of nearby host genes.ConclusionsWith a few exceptions, most of our findings support the exaptation hypothesis for the role of TE epigenetic modifications when vetted against the genome defense hypothesis. The recruitment of epigenetic modifications may represent an additional mechanism by which TEs can contribute to the regulatory functions of their host genomes.
Disruption in the development of dopamine-containing neurons has been postulated to underlie several CNS disorders. However, there have been no quantitative studies on the normal development of primate dopamine neurons. Thus, the fetal maturation of primate midbrain dopamine neurons was examined to establish changes that occur in the A9/A10 groups during the second and third trimesters. Eleven fetal African green monkey midbrains were immunostained for tyrosine hydroxylase (TH-ir) as a marker for dopamine neurons and quantified using stereological techniques (nucleator method). The number and size of defined dopamine neurons and the volume occupied by A9/A10 neurons increased in near linear fashion throughout the term. The estimated number of defined dopamine neurons in each hemisphere rose from approximately 50,000 at embryonic day (E) 70 to 225,000 at birth (E165), similar to the adult population. The size and the area occupied by them at birth were, however, well below the estimated adult levels. Additionally, the younger fetal midbrains had far less diversity in dopamine cell volumes compared with older fetuses and adult brains. Until midway through gestation (E81), clusters of apparently immature midbrain TH-ir cells were observed, but could not be counted. Even though the majority of cells destined to become dopamine neurons are generated in the first trimester, phenotypical maturation of A9 and A10 cell bodies continues steadily throughout gestation and extends well into the postnatal period. These data have relevance to transplantation studies that employ fetal dopaminergic grafts, and to disorders hypothesized to result from damage to developing midbrain dopamine neurons.
Chronic administration of anabolic steroids disrupts pubertal onset and estrous cyclicity in rats.
Use of anabolic-androgenic steroids (AASs) is becoming increasingly popular among adolescent girls, yet the effects of AASs on female physiology and development are not well understood. The present study compared the effects of chronic exposure to three individual AASs, stanozolol (0.05-5 mg/kg), 17alpha-methyltestosterone (0.5-5 mg/kg), and methandrostenolone (0.5-5 mg/kg) on the onset of puberty and estrous cyclicity in the rat. Female rats received daily injections of AASs for 30 days (Postnatal Day [PN] 21-51). Rats receiving the highest dose of each of the AASs (5 mg/kg) displayed vaginal opening at a younger age than rats receiving the oil vehicle. The day of first vaginal estrus was delayed in rats receiving stanozolol (5 mg/kg) or 17alpha-methyltestosterone (0.5-5 mg/kg) but not in rats receiving methandrostenolone. At the highest dose (5 mg/kg), each of the AASs reduced the incidence of regular estrous cyclicity during the treatment period. Concurrent administration (on PN21-51) of the androgen receptor antagonist, flutamide (10 mg/kg, twice daily), reversed the effects of 17alpha-methyltestosterone (5 mg/kg) on vaginal opening. Flutamide administration also eliminated the effects of stanozolol (5 mg/kg) and 17alpha-methyltestosterone (5 mg/kg) on the day of first vaginal estrus. In contrast, rats receiving flutamide and methandrostenolone (5 mg/kg) exhibited first vaginal estrus earlier than controls. The present results indicate that chronic exposure to AASs during development has deleterious effects on the female neuroendocrine axis and that these effects appear be mediated via multiple mechanisms.
2010-08-01
Full Text Available.BackgroundGrief is a normal phenomenon but showing great variation depending on cultural and personal features. Bonanno and Kaltman have nonetheless proposed five aspects of normal grief. The aim of this study was to investigate if women with miscarriage experience normal grief.Material and methodsContent analyses of 25 transcribed conversations with women 4 weeks after their early miscarriages were classified depending on the meaning-bearing units according to Bonanno and Kaltman's categories. In the factor analyses, these categories were compared with the Perinatal Grief Scale and women's age, number of children and number of miscarriages, and gestational weeks.ResultsWomen with miscarriage fulfill the criteria for having normal grief according to Bonanno and Kaltman. All of the 25 women had meaning-bearing units that were classified as cognitive disorganization, dysphoria, and health deficits, whereas disrupted social and occupational functioning and positive aspects of bereavement were represented in 22 of 25 women. From the factor analysis, there are no differences in the expression of the intensity of the grief, irrespective of whether or not the women were primiparous, younger, or had suffered a first miscarriage.ConclusionWomen's experience of grief after miscarriage is similar to general grief after death. After her loss, the woman must have the possibility of expressing and working through her grief before she can finish her pregnancy emotionally. The care-giver must facilitate this process and accept that the intensity of the grief is not dependent on the woman's age, or her number of earlier miscarriages.
Anatomy of a disruption in MTX (Microwave Tokamak Experiment)
1990-10-15
Disruptions are observed in the Microwave Tokamak Experiment, MTX (nee Alcator C), over a wide range of plasma parameters. Indeed, disruptions often occur far from the boundaries of the operating space as defined by Hugill and l{sub i}-q plots. Despite this, the general behavior during the disruptive process is generally similar whatever the operating parameters. This report will describe one disruption in detail in order to provide a detailed anatomy of the event.
Against all odds: Australian women's experiences of recovery from breast cancer
2010-01-01
Aim. The aim of this study was to generate insight into younger women's experiences of recovery from breast cancer-related breast surgery and to contribute to the knowledge base for clinicians practising in this field. Background. Despite the abundance of literature concerning the impact of breast cancer and breast loss on older women over 50 years of age, fewer studies have been conducted specifically with women younger than 50 years focusing on the recovery from breast cancer and related breast surgery. The effects of breast cancer on younger women differ to those of older women; younger women may have difficulty coming to terms with loss of fertility, perceived loss of femininity, sexuality and may experience body image disfigurement. Younger women may face these issues as a result of t...
Previously, we demonstrated that atrazine suppressed the ovulatory surge of luteininzing hormone and disrupted estrous cycles in the female rat. We also reported that this disruption of ovulation is likely the result of atrazine's effect on hypothalamic gonadotropin hormone rele...
The objective of this basic research is to characterize the potential of common hydrocarbon contaminants in ecosystems to act as endocrine disrupters. Although the endocrine disrupting effects of contaminants such as dioxin and PCBs have been well characterized in both animals an...
1982-07-01
Calculations of disruption time and energy dissipation have been obtained by simulating the plasma as an electrical conducting loop that varies in resistivity, current density, major radius. The calculations provide results which are in good agreement with experimental observations. It is believed that this approach allows engineering designs for disruptions to be completed in large tokamaks such as INTOR or FED.
Disrupting Rituals of Debate in the Indian Parliament
2010-01-01
Disruptions to debate in India's national parliament by members have generated concern among critics, who have associated disruptions with a larger narrative of the decline of India's political institutions. The violation of debate through disruption is perceived by parliament as a threat to its prestige, legitimacy, and therefore its institutional reproduction. This article discusses institutional responses, which have, however, avoided formally disciplining members and have instead followed a more accommodative, informal approach to managing disruptions. It employs a framework which posits debate as a parliamentary ritual imbued with symbolic significance for both participants (including MPs) and audiences (including citizens, voters, media) and argues that disruption can be viewed as a ...
The Advanced Camera for Surveys and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) have been used to obtain new Hubble Space Telescope images of NGC 4038/4039 ("The Antennae"). These new observations allow us to better differentiate compact star clusters from individual stars, based on both size and color. We use this ability to extend the cluster luminosity function (LF) by approximately 2 mag over our previous WFPC2 results, and find that it continues as a single power law, dN/dL vprop L ? with ? = ?2.13 0.07, down to the observational limit of MV ? ?7. Similarly, the mass function (MF) is a single power law dN/dM vprop M ? with ? = ?2.10 0.20 for clusters with ages <3 108 yr, corresponding to lower mass limits that range from 104 to 105 M sun, depending on the age range of the subsample. Hence, the power-law indices for the luminosity and MFs are essentially the same. The LF for intermediate-age clusters (i.e., ~100-300 Myr old objects found in the loops, tails, and outer areas) shows no bend or turnover down to MV ? ?6, consistent with relaxation-driven cluster disruption models which predict the turnover should not be observed until MV ? ?4. An analysis of individual ~0.5 kpc sized areas over diverse environments shows good agreement between values of ? and ?, similar to the results for the total population of clusters in the system. There is tentative evidence that the values of both ? and ? are flatter for the youngest clusters in some areas, but it is possible that this is caused by observational biases. Several of the areas studied show evidence for age gradients, with somewhat older clusters appearing to have triggered the formation of younger clusters. The area around Knot B is a particularly interesting example, with a ~10-50 Myr old cluster of estimated mass ~106 M sun having apparently triggered the formation of several younger, more massive (up to 5 106 M sun) clusters along a dust lane. A comparison with new NICMOS observations reveals that only 16% 6% of the IR-bright clusters in the Antennae are still heavily obscured, with values of AV >3 mag. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555. Also based on data obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA), and the Canadian Astronomy Data Centre (CADC/NRC/CSA).
2010-01-01
The first fossil mite of the family Pyemotidae (Acari: Heterostigmata) is recorded. Pyemotes primus sp. nov. is described from the Late Eocene of the Rovno amber from a syninclusion with the bark beetles Taphramites rovnoensis Petrov et Perkovsky, 2008. In the presence of well developed longitudinal striation on hysterosomal tergites, the new species is similar to species from scolyti group, which is characterized by parasitoidism on immature stages of bark beetles and phoresy on adult stages. P. primus differs from the closely related species P. dryas (Vitzthum, 1923), P. parviscolyti Cross et Moser, 1971, P. johnmoseri Khaustov, 2004, and P. mandelshtami Khaustov, 1998 in the subequal setae h 1 and h 2.
2010-01-01
Environmental changes in the surface and bottom water layers of the Ingydjupet Basin and the history of the Atlantic Water inflow to the southwestern Barents Sea during the last 16 ka are reconstructed based on planktic and benthic foraminiferal assemblages. The multiproxy study of sediment cores PSh-5159R and PSh-5159N, including AMS 14C dating, provides a time resolution of about 200 years for the deglaciation, 100 years for the Holocene, and 2550 years for the last 400 years. Stable polar conditions with the sea ice at the surface were typical for the Early Deglaciation period. Unstable bottom settings and the onset of ice rafting marked the Oldest Dryas. The cold Atlantic Water inflow increased notably during the Blling-Allerd interstadial nearby the site location and then dec...
2000-08-01
The morainic deposits of the middle Durance from the last glaciation (Wurm in the alpine chronology) have for the first lime delivered two samples of fossilized wood (La Peyrerie gully, above Sisteron). The {sup 14}C BP datings, around 18000 BP, allow us to attribute to the upper Pleniglacial (oceanic isotopic stage 2) the Plan Roman glacial maximum ('Last Glacial Maximum' or LGM) as well as the Poet-Rourebeau retreat stages. Therefore the Durance valley deglaciation has been very fast since it finished at the beginning of the old Dryas. In conclusion, a correlation of these events with the isotopic records of Greenland ice is proposed. (authors)
2000-01-01
The morainic deposits of the middle Durance from the last glaciation (Wurm in the alpine chronology) have for the first lime delivered two samples of fossilized wood (La Peyrerie gully, above Sisteron). The 14C BP datings, around 18000 BP, allow us to attribute to the upper Pleniglacial (oceanic isotopic stage 2) the Plan Roman glacial maximum ('Last Glacial Maximum' or LGM) as well as the Poet-Rourebeau retreat stages. Therefore the Durance valley deglaciation has been very fast since it finished at the beginning of the old Dryas. In conclusion, a correlation of these events with the isotopic records of Greenland ice is proposed. (authors)
Loess ecosystems of northern Alaska: Regional gradient and toposequence at Prudhoe Bay
1991-01-01
Loess-dominated ecosystems cover approx 14% (11,000 km2) of the Arctic Coastal Plain and much of the northern portion of the Arctic Foothills. Knowledge of this poorly known ecosystem is important for sound land-use planning of the expanding developments in the region and for understanding the paleoecological dynamics of eolian systems that once dominated much of northern Alaska. A conceptual alkaline-tundra toposequence includes eight common vegetation types and associated soils and vegetation downwind of the Sagavanirktok River. Properties of loess tundra important for land-use planning include: (1) its high ice content, which contributes to its susceptibility to thermokarst. (2) high salinities, which hamper revegetation efforts. And (3) presence of certain plant species such as Dryas intergrifolia, which are particularly sensitive ...
A multi-proxy Late-glacial palaeoenvironmental record from Lake Bled, Slovenia
2009-01-01
This study investigates the palaeoecological record (18O, 13C, pollen, plant macrofossils, chironomids and cladocera) at Lake Bled (Slovenia) sedimentary core to better understand the response of terrestrial and aquatic ecosystems to Late-glacial climatic fluctuations. The multi-proxy record suggests that in the Oldest Dryas, the landscape around Lake Bled was rather open, presumably because of the cold and dry climate, with a trend towards wetter conditions, as suggested by an increase in tree pollen as well as chironomid and cladocera faunas typical for well-oxygenated water. Climatic warming at the beginning of the Late-glacial Interstadial at ca. 14,800calyr BP is suggested by an increase in the 18O value, the appearance of Betula and Larix pollen and macrofossils, and a warm...
Fathead minnows (Pimephales promelas) are one of the most widely-used small fish models for regulatory ecotoxicology testing and research related to endocrine disrupting chemicals (EDCs). In this study, we isolated and sequenced cDNAs for fathead minnow follicle-stimulating hormone-like and luteinizing hormone-like (FSH and LH) and glycoprotein (GP) subunits. Quantitative real-time PCR assays for measuring gonadotropin (GtH) subunit transcripts were developed and used to examine baseline transcript levels over a range of age classes and reproductive states encompassed in EDC testing. In females, FSH and LH transcripts were greater in 4-5 month old than in younger fish and were significantly correlated with one another across all age classes examined. In males, FSH transcripts were greatest in 2-3 month old fish and were inversely correlated with various measures of testis development including, gonadal-somatic index (GSI), and histological stage. Overall, the pattern of GtH expression over age classes associated with gonad development was similar to that reported for other asynchronous-spawning fish. Despite significant changes in female GSI, gonad stage, and plasma vitellogenin within 24 h of spawning, GtH transcript levels in fish that had spawned within the preceding 24 h were not significantly different from those in fish that were 2-3 days post-spawn and expected to spawn within the next 24 h based on spawning history. Results of this study provide insights related to the role of GtHs in fathead minnow reproductive development and function. Additionally they provide useful baseline data needed to design and interpret effective experiments for studying direct and indirect effects of EDCs on GtH subunit mRNA expression, which will facilitate a greater understanding of integrated system-wide responses of the fathead minnow brain-pituitary-gonadal axis to stressors including EDCs.
2007-03-01
Fathead minnows (Pimephales promelas) are one of the most widely-used small fish models for regulatory ecotoxicology testing and research related to endocrine disrupting chemicals (EDCs). In this study, we isolated and sequenced cDNAs for fathead minnow follicle-stimulating hormone-like and luteinizing hormone-like (FSH and LH) and glycoprotein (GP) subunits. Quantitative real-time PCR assays for measuring gonadotropin (GtH) subunit transcripts were developed and used to examine baseline transcript levels over a range of age classes and reproductive states encompassed in EDC testing. In females, FSH and LH transcripts were greater in 4-5 month old than in younger fish and were significantly correlated with one another across all age classes examined. In males, FSH transcripts were greatest in 2-3 month old fish and were inversely correlated with various measures of testis development including, gonadal-somatic index (GSI), and histological stage. Overall, the pattern of GtH expression over age classes associated with gonad development was similar to that reported for other asynchronous-spawning fish. Despite significant changes in female GSI, gonad stage, and plasma vitellogenin within 24 h of spawning, GtH transcript levels in fish that had spawned within the preceding 24 h were not significantly different from those in fish that were 2-3 days post-spawn and expected to spawn within the next 24 h based on spawning history. Results of this study provide insights related to the role of GtHs in fathead minnow reproductive development and function. Additionally they provide useful baseline data needed to design and interpret effective experiments for studying direct and indirect effects of EDCs on GtH subunit mRNA expression, which will facilitate a greater understanding of integrated system-wide responses of the fathead minnow brain-pituitary-gonadal axis to stressors including EDCs.
2009-01-01
Over the past two decades there has been increasing interest in the distinction between reactive (RA) and proactive aggression (PA; Card & Little, 2006; Polman, Orobio de Castro, Koops, van Boxtel & Merk, 2007). RA describes aggression that is defensive, impulsive and affect-laden, while PA comprises instrumental, calculated and typically unemotional aggressive behaviours (Vitaro, Brendgen & Tremblay, 2002). There is growing consensus that developmental models of RA and PA may help clarify risk pathways associated with the three disruptive behaviour disorders (DBD), attention-deficit hyperactivity disorder, oppositional defiant disorder and conduct disorder (Kempes, Matthys, de Vries & van Engeland, 2005; Raine et al., 2006; Waschbusch, Willoughby & Pelham, 1998). However, some confusion remains regarding etiological influences responsible for the differential shaping of aggression subtypes (Baker, Raine, Liu & Jacobson, 2008).Contributing the first elucidation of developmental relations between aggression subtypes and DBDs, caregiver ratings were ascertained from a large community sample of families of twins (aged 6-18 years) using the Australian Twin Behaviour Rating Scales (ATBRS, n=2082), and at 9-month follow-up via an online electronic version of the ATBRS (n=511). These data were partitioned according to two age cohorts (6-10 years, and 10-18 years) and subsequently submitted to a series of univariate and multivariate cross-sectional and longitudinal analyses.Consistent with previous research (e.g., Baker et al., 2008), cross-sectional models indicated strong influence of genes on both RA and PA—with genes showing greater effects on PA compared to RA, particularly in the older cohort. Multivariate longitudinal analyses revealed a substantial differential role for genes in the continuity of aggression subtypes over time for both RA and PA in the younger cohort, and for PA in the older cohort. At odds with etiological models that posit differential psychosocial factors underpinning RA and PA (Crick & Dodge, 1996; Dodge, 1991), no evidence was found for shared environmental effects on persistence in RA over time. Conversely, shared environmental effects explained a significant portion of covariance in childhood PA across time points. However, contrary to predictions derived from psychosocial explanations (e.g., Dodge, 1991), these shared environmental influences were mediated through a general risk for (undifferentiated) overt physical aggression.Data provide preliminary, albeit modest, evidence for a recent sequential model of RA and PA (i.e., Vitaro & Brendgen, 2005) which implicates RA as an early developmental precursor to PA. This model reformulates the role of social learning mechanisms invoked by seminal psychosocial formulations (i.e., Dodge, 1991). Specifically, the sequential hypothesis postulates that early RA which is reinforced in childhood, may increasingly come to be used operantly (i.e., instrumentally). In this way, RA is effectively converted to PA-type aggression. As predicted by this model, current data revealed the longitudinal relationship from RA to PA was predominantly explained by shared environmental influences (over and above a general risk for overt aggression) in the younger cohort. By contrast, the pathway from RA to PA in the older cohort was explained mainly by the influence of genes. These data provide some support for the suggestion that putative social learning mechanisms impact on the sequential pathway in childhood but not adolescence.The expected high levels of phenotypic overlap between aggression subtypes and DBDs were consistently explained by genes and nonshared environmental influences with the former accounting for the majority of covariance in most bivariate models. Age cohort differences in multivariate models of aggression subtypes and DBDs were in line with the smorgasbord hypothesis suggesting the effects of genes generally increase, while the effects of shared environment generally decrease, as a function of age. This pattern was most consistent and pervasive in RA-related models. Notable exceptions to this pattern occurred in bivariate models involving PA on the one hand, and hyperactivity or CD on the other—with these models showing greater influence of shared environment in the older versus younger age cohort. Additionally, the current research indicates a trend towards greater segregation of genetic effects across aggression subtypes and DBDs as a function of age, while conversely, shared environmental effects were more likely to simultaneously affect multiple syndromes in the older versus younger cohort.In regards to clinically specified risk pathways, relevant longitudinal analyses suggested that impulsivity confers only limited risk for future RA, while partial support was obtained for recent suggestions that both hyperactivity and PA are important cofactors in risk pathways associated with ODD and CD. Overall, the data that include DBDs broadly support RA and hyperactivity as key early markers of long-term risk.The online component of the study also included two neuropsychological tasks adapted for the internet and completed by 310 twin siblings. Representing an attempt to integrate multiple explanatory frameworks, this latter study evaluated differerential putative neuro-biogenic mechanisms underpinning RA and PA. Results from this study were inconclusive and issues pertaining to the delivery of neuropsychological tasks online are considered. In contrast to results from the adapted neuropsychological tasks, the online electronic ATBRS yielded higher data integrity and higher scale reliabilities than its original paper-and-pencil counterpart.All results are discussed and implications for future research and clinical practice relating to childhood and adolescent aggression are considered. Finally, limitations of the current research project are examined. Publisher: Curtin University of Technology, School of Psychology. Language: en Rights: unrestricted
Overview of core disruptive accidents
An overview of the analysis of core-disruptive accidents is given. These analyses are for the purpose of understanding and predicting fast reactor behavior in severe low probability accident conditions, to establish the consequences of such conditions and to provide a basis for evaluating consequence limiting design features. The methods are used to analyze core-disruptive accidents from initiating event to complete core disruption, the effects of the accident on reactor structures and the resulting radiological consequences are described.
Overview of core disruptive accidents
1977-01-01
An overview of the analysis of core-disruptive accidents is given. These analyses are for the purpose of understanding and predicting fast reactor behavior in severe low probability accident conditions, to establish the consequences of such conditions and to provide a basis for evaluating consequence limiting design features. The methods are used to analyze core-disruptive accidents from initiating event to complete core disruption, the effects of the accident on reactor structures and the resulting radiological consequences are described.
Heterodyne ECE diagnostic in the mode detection and disruption avoidance at TEXTOR
2003-07-01
Disruptions cause major concerns for the operation of tokamaks. During disruption large forces act on the tokamak vessel and its interior parts. The huge amount of plasma energy deposited on the first wall components within one millisecond causes serious damage. Therefore disruptions should be avoided. One way to avoid disruptions is the operation of a tokamak in a regime which is easy to handle from the control point of view. However, the operation in the advanced scenarios or improved confinement modes is very complicated and even small deviation in one of the control parameters can cause a disruption. In this cases a method should be available to detect the disruption in advance and mitigate or even better avoid the energy quench by appropriate means. At TEXTOR we developed a method to detect the disruption precursor. The module is integrated in the plasma control system. The detection method was tested at TEXTOR for (i) combination with tangential neutral beam injection to increase the toroidal rotation profile and to tear apart the m = 2 disruption precursor by a steep rotation gradient across the island (ii) gas puff experiments with He used to mitigate the disruption effects specially to suppress the generation of the runaway electrons. The paper demonstrates the possibility to detect disruptions precursors and to avoid disruptions using two ECE-channels out of the standard electron temperature diagnostic. The system demonstrated its reliability during the last month of TEXTOR operation. The injection of co- as well as counter neutral beam to avoid the disruption was successful tested and a detailed analysis of the mode development is presented. The measured rotation profiles show the development of a step in the toroidal velocity in the vicinity of the q = 2 surface which prevents the plasma from a disruption. Furthermore detailed analysis of the frequency development of the m = 2 mode could explain the observed sudden increase in the mode frequency observed in the discharges with low power co-injection prior to the disruption. The module is quite flexible and it is planned to use also with other mode-diagnostics. Furthermore other mechanisms to avoid or mitigate a disruption are foreseen. With the restart of TEXTOR the use of ECRH for a local heating of the island is planned too. (authors)
The response of two arctic tundra plant communities to human trampling disturbance.
A 4-year study was conducted to evaluate the consequences of human trampling on dryas and tussock tundra plant communities. Treatments of 25, 75, 200 and 500 trampling passes were applied in 0.75 m2 vegetation plots at a time of approximately peak seasonal biomass. Immediately after and 1 and 4 years after trampling, plots were evaluated on the basis of plant species cover, percent bare ground, vegetation height, and soil penetration resistance. One year after trampling, soils were collected for nitrogen analysis in highly disturbed and control plots. Immediately after trampling, 500 trampling passes resulted in approximately 50% cover loss in the dryas tundra and 70% cover loss in tussock tundra, but both communities showed a substantial capacity for regrowth. Plots where low and moderate levels of trampling were applied returned to pre-disturbance conditions by 4 years after trampling, but impact was still evident in plots subjected to high levels of disturbance. These results suggest that these tundra communities can tolerate moderate levels of hiking and camping provided that use is maintained below disturbance thresholds and that visitors employ appropriate minimum-impact techniques. By utilizing this information in a visitor education program combined with impact monitoring and management, it is possible to allow dispersed camping and still maintain these vegetation communities with a minimum of observable impact.
Selection of supply portfolio under disruption risks
2011-01-01
This paper deals with the optimal selection of supply portfolio in a make-to-order environment in the presence of supply chain disruption risks. Given a set of customer orders for products, the decision maker needs to decide from which supplier to purchase custom parts required for each customer order to minimize total cost and mitigate the impact of disruption risks. The selection of suppliers and allocation of orders is based on price and quality of purchased parts and reliability of delivery. The two types of disruption scenarios are considered: scenarios with independent local disruptions of each supplier and scenarios with local and global disruptions that may result in all suppliers disruption simultaneously. The problem is formulated as a single- or bi-objective mixed integer progra...
Disruptions in surgical flow and their relationship to surgical errors: An exploratory investigation
2007-01-01
BackgroundDisruptions in surgical flow have the potential to increase the occurrence of surgical errors; however, little is known about the frequency and nature of surgical flow disruptions and their effect on the etiology of errors, which makes the development of evidence-based interventions extremely difficult. The goal of this project was to study surgical errors and their relationship to surgical flow disruptions in cardiovascular surgery prospectively to understand better the effect of these disruptions on surgical errors and ultimately patient safety.MethodsA trained observer recorded surgical errors and flow disruptions during 31 cardiac surgery operations over a 3-week period and categorized them by a classification system of human factors. Flow disruptions were then reviewed and a...
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