foraminiferal assemblages from bottom sediments at marian cove south shetland islands west antarctica abstract foraminiferal samples were taken from bottom sediments at marian cove west antarctica in order to determine the depth zonation and foraminiferal species composition benthic foraminiferal communities are mainly composed of calcareous agglutinated and mixed associations the fisher diversity of the total assemblage groups is close to 6 0 the dominance diversity patterns are characterized by low dominance and high diversity three zones are recognized at marian cove with depth boundaries at 22 and 65 5 m areas shallower than 22 m are nearly devoid of any toraminifera calcareous forms and or calcareous forms mixed with agglutinated forms are relatively abundant between 22 and 65 5 m while agglutinated forms dominate below 65 5 m

high resolution holocene climate record from maxwell bay south shetland islands antarctica the highest resolution holocene sediment core from the antarctic peninsula to date was collected during the first shaldril cruise nbp0502 drilling yielded a 108 2 m long core 87 recovery site nbp0502 1b from maxwell bay south shetland islands this high resolution sediment record comes from a region that is currently experiencing dramatic climate change and associated glacial retreat such records can help to constrain the nature of past climate change and causal mechanisms and to provide a context for evaluating current climate change and its impacts the base of the drill site sampled till and or proximal glacimarine sediments resting directly on bedrock glacimarine suspension deposits composed of dark greenish gray silty mud with variable diatom abundance and scattered very fine sand laminations make up the majority of the sedimentary section detailed sedimentological and geochemical analyses including magnetic susceptibility total organic carbon toc content carbon and nitrogen isotopic composition pebble content and biogenic silica content allow subdivision of the glacimarine section into nine units and seismic facies analyses resulted in the identification of six distinct seismic units we used 29 radiocarbon ages to construct an age model and calculate sedimentation rates that vary by two orders of magnitude from 0 7 mm a to 30 mm a radiocarbon ages from glacimarine sediments just above the till date back to between 14 1 and 14 8 ka thus ice was grounded in the fjord during the last glacial maximum and eroded older sediments from the fjord following initial retreat of grounded ice from maxwell bay the fjord was covered by a permanent floating ice canopy probably an ice tongue the highest sedimentation rate corresponds to an interval that contains abundant sand laminations and gravelly mud intervals and likely represents a melt out phase or period of rapid glacial retreat from 10 1 ka to 8 2 ka there is no evidence for an early holocene climatic reversal as recorded farther south at the palmer deep drill site minimum sea ice cover and warm water conditions occurred between 8 2 and 5 9 ka from 5 9 to 2 6 ka there was a gradual cooling and more extensive sea ice cover in the bay after 2 6 ka the climate varied slightly causing only subtle variation in glacier grounding lines there is no compelling evidence for a little ice age readvance in maxwell bay the current warming and associated glacial response in the northern antarctic peninsula appears to be unprecedented in its synchroneity and widespread impact

composition and distribution of sediments and benthic foraminifera in a submerged caldera after 30 years of volcanic quiescence abstract deception island 62 59 s 60 34 w is an active volcano with a submerged caldera port foster located northwest of the antarctic peninsula surveys following the most recent eruption of the volcano in 1970 showed that direct deposition of coarse pyroclastics into port foster decimated the benthic communities the objective of this study is to examine how the submarine sediment distributions and the composition distribution and abundance of benthic foraminiferal communities in port foster have changed after 30 years of volcanic quiescence grab core and settling particulate matter were collected on a series of five cruises during 1999 2000 to monitor seasonal changes in the ecosystem of port foster the caldera floor is covered with a layer at least 15 cm thick of yellowish brown volacaniclastic sandy mud composed primarily of basaltic andesitic lithic fragments and volcanic glass with mean and median grain diameters of 26 10 and 32 12 m respectively we suggest that these sandy muds were deposited since the last volcanic eruption in 1970 yielding a minimum sediment accumulation rate of at least 5 mm year settling particulate matter during the fall winter and spring of 1999 and 2000 were finer grained than the seafloor samples with mean and median grain diameters of 11 2 and 13 3 m respectively except for a slight coarsening of the mean grain diameter in the late spring we observed no temporal changes in either the granulometry or the mineralogy of the settling particulate matter the concentration of biogenous sediment in port foster is relatively low due to dilution by a high volume of lithogenic material being deposited in the bay the abundance from foraminifera numbers and diversity of benthic foraminifera within port foster is spatially variable and patchy although previous studies of the benthic foraminiferal community following the 1967 1970 eruptions showed an increase in abundance foraminifera number of port foster s benthic foraminifera community from 1972 to 1976 our data show that these increases did not continue beyond the mid 1970s the most notable similarities between the mid 1970s and 2000 assemblages are the predominance of miliammina arenacea and trochammina malovensis in port foster since the 1970s there has been an increase in importance of globocassidulina the most abundant genera a decrease in the relative abundance of stainforthia fusiformis and nonionella bradii and the introduction of reophax dentaliniformis and cassidulinoides parkerianus which were not abundant in either port foster or on the outer slopes surrounding the flanks deception island during the 1970s the later arrival of r dentaliniformis to port foster suggests that it is not a pioneer colonizer following disturbance in all environments

anomalous atmospheric circulation over the weddell sea antarctica during the austral summer of 2001 02 resulting in extreme sea ice conditions during the austral summer of 2001 02 exceptionally heavy sea ice conditions were experienced over the eastern weddell sea satellite microwave imagery showed that large negative positive ice anomalies were present from october 2001 to january 2002 over the north western weddell sea off the coast of dronning maud land these were a result of anomalously high low atmospheric pressure over the south atlantic southern weddell sea and bellingshausen sea which gave strong north to north westerly cyclonic flow over the northern and eastern weddell sea this resulted in convergence of sea ice into the southern weddell sea and inhibited ice advection along the coast of dronning maud land the atmospheric anomalies around the weddell sea were part of an antarctic wide amplification of the mean wavenumber 3 pattern resulting in more intrusions of mid latitude air into the interior of the continent giving rise to near record warm temperatures at several locations

oceanographic controls on benthic foraminifers from the bellingshausen margin of the antarctic peninsula abstract surface sediment samples collected from the bellingshausen sea continental margin of the antarctic peninsula were analyzed for benthic foraminifers a total fauna including live and dead specimen counts was used to statistically identify discrete benthic foraminifer assemblages two major assemblages were defined the bulimina aculeata and fursenkoina spp assemblages the distribution of the bulimina aculeata and fursenkoina spp assemblages are closely associated with the distribution of the two dominant bottom water masses on the continental margin the circumpolar warm deep water and weddell sea transitional water respectively their distributions cannot be related to organic carbon content or sediment texture of the surface sediments the faunal composition of the bellingshausen sea margin assemblages and their water mass associations are similar to faunal water mass relationships observed in the weddell sea and south atlantic ocean where bulimina aculeata is associated with circumpolar deep water and nonionella iridea n bradii and trifarina earlandi are associated with eastern shelf and modified weddell sea water

foraminiferal assemblages and caco3 dissolution since the last deglaciation in the maxwell bay king george island antarctica abstract three sediment cores a10 01 02 and 08 from the maxwell bay king george island antarctica were quantitatively analyzed for foraminiferal fauna planktonic foraminifera of three cores are rare due to the special antarctica environment benthic foraminifera is mainly composed of globocassidulina biora globocassidulina crassa rossensis cassidulinoides parkerianus and miliammina arenacea g biora and g crassa rossensis show high percentages in the shallower core a10 08 while m arenacea displays obviously high percentage in deeper core a10 02 the lower parts of the cores have a lower abundance of foraminifera while the upper parts have a relatively higher abundance the down core variations of benthic foraminifera reflect the contrast of surface water environment between the last deglaciation and post glacial during the last deglaciation lower parts of the cores the lower abundant foraminifera was consistent with the lower toc which reflected that the extensive sea ice prevented the production of primary organisms and therefore lower flux of organic particles was delivered to the sea floor abundant foraminifera together with higher toc in the upper parts of the cores suggested a higher primary productivity after the glaciation the shallowest water depth core a10 08 45 m displayed a better carbonate preservation than the other two cores a10 01 and 02 from the depths of 85 and 105 m respectively the disparity in carbonate dissolution reflected the remarkable shallow lysocline and carbonate compensation depth ccd in the antarctic area and also reflected significant variations in water properties even within such a difference only about 60 m in water depth down core variations of benthic foraminifera dissolution index bdi and caco 3 content indicated the existence of stronger carbonate dissolution in the upper parts than those in the lower parts of the cores the down core variations of carbonate dissolution suggested changes of water properties linked to the shallow ccd in this area it was supposed that the less influence of the saline shelf water during the last deglaciation enhanced the carbonate preservation with the sea level increasing and retreat of the coastal ice after the glacial erosive water masses and the higher co 2 accumulated by the increased flux of organic material led to severe dissolution of caco 3 and foraminiferal shells in the sediment

recent ice loss from the fleming and other glaciers wordie bay west antarctic peninsula satellite radar interferometry data from 1995 to 2004 and airborne ice thickness data from 2002 reveal that the glaciers flowing into former wordie ice shelf west antarctic peninsula discharge 6 8 0 3 km3 yr of ice which is 84 30 percent larger than a snow accumulation of 3 7 0 8 km3 yr over a 6 300 km2 drainage basin airborne and icesat laser altimetry elevation data reveal glacier thinning at rates up to 2 m yr fifty km from its ice front fleming glacier flows 50 percent faster than it did in 1974 prior to the main collapse of wordie ice shelf we conclude that the glaciers accelerated following ice shelf removal and have been thinning and losing mass to the ocean over the last decade this and other observations suggest that the mass loss from the northern part of the peninsula is not negligible at present copyright 2005 by the american geophysical union

glacial retreat patterns and processes determined from integrated sedimentology and geomorphology records abstract although hundreds of cores have been collected on the antarctic continental shelf over the past five decades definitive interpretations of depositional environments associated with marine based ice advance and retreat are hindered by similarities in sediment facies and a lack of geomorphic context the recent use of an advanced multibeam bathymetry system allows for more detailed ice sheet reconstructions from glacial landforms that were previously not resolved with older generation systems here we present results from a recent cruise to the ross sea antarctica that focuses on integrating sediment facies analyses into a geomorphic framework to confidently determine depositional environments and sedimentological processes since the last glacial maximum grain size analysis geotechnical properties and micropaleontology from targeted sediment cores are used to develop improved criteria for making the distinction between subglacial diamictons and ice proximal diamictons which can be applied to geomorphically blind sediment cores our consideration of geomorphic context while interpreting sediment facies has also allowed us to determine that most debris melted out of the base of paleo ice shelves in the ross sea only 1 2 km seaward of the grounded ice margin additionally we find that agglutinated foraminifera specimens are characteristic of sluggish marine currents and a resulting accumulation of siliceous detritus rich in organic matter however calcareous specimens dominate in higher energy current settings and in ice proximal environments with lesser amounts of siliceous detritus and associated organic material overall sedimentary successions record contrasting behaviors of the west antarctic and east antarctic ice sheets that extended onto the continental shelf during the last glacial maximum not only is this coupled geomorphic and sedimentologic approach useful for understanding glacimarine processes and ice sheet retreat patterns but it is essential for selecting appropriate facies transitions for chronological constraints of past ice sheet behavior

productivity cycles of 200 300 years in the antarctic peninsula region understanding linkages among the sun atmosphere oceans sea ice and biota compared to the rest of the world9s oceans high resolution late holocene paleoclimatic data from the southern ocean are still rare we present a multiproxy record from a sediment core retrieved from a deep basin on the western side of the antarctic peninsula that reveals a dramatic perspective on paleoclimatic changes over the past 3700 yr analyses completed include measurement of magnetic susceptibility and granulometry bed thickness particle size percent organic carbon bulk density and microscopic evaluation of diatom and benthic foraminiferal assemblages and abundances downcore variability of these parameters demonstrates the significance of both short term cycles which recur approximately every 200 yr and longer term events 2500 yr cycles that are most likely related to global climatic fluctuations in the upper 600 cm of the core lower values of magnetic susceptibility ms are correlated with lower bulk density the presence of thinly laminated units specific diatom assemblages and generally higher total organic carbon content below 600 cm magnetic susceptibility is uniformly low though variability in other parameters continues the magnetic susceptibility signal is controlled primarily by dilution of ferromagnetic phases with biosiliceous material this signal may be enhanced further by dissolution of magnetite in the magnetic susceptibility lows high total organic carbon the role of variable primary productivity and its relationship to paleoclimate is assessed through the diatom data in particular magnetic susceptibility lows are characterized by higher than normal abundances of chaetoceros resting spores corethron criophilum and or rhizosolenia spp also are found as is a higher ratio of the most common species of fragilariopsis versus species of thalassiosira these assemblages are indicative of periods of high primary productivity driven by the presence of a meltwater stabilized water column the 200 yr cyclicity noted in other paleoclimatic records around the world suggests a global forcing mechanism possibly solar variability in addition to the cyclic changes in productivity overall elevated productivity is noted below 600 cm or prior to ca 2500 yr b p this increased productivity may represent the tail end of a holocene climatic optimum which is widely recognized in other parts of the world but as yet is poorly documented in antarctica

benthic foraminiferal distributions in chilean fjords 47 s to 54 s abstract surface sediment samples collected from the fjord region of southern chile 47 to 54 south were analyzed for benthic foraminifera a total of 175 species were identified including agglutinated and calcareous benthic taxa hierarchical cluster analysis of the foraminiferal data resulted in the recognition of three distinct biofacies inner fjord intermediate fjord and channel and oceanic biofacies geographically controlled by relative position between the pacific ocean and fjord heads similarity percentage simper analysis identified key taxa in the definition of the biofacies that include globocassidulina rossensis cassidulina laevigata and bulimina notovata principal components analysis resulted in two principal components representing sediment size and bottom water temperature and salinity regional distributions are strongly controlled by the oceanographic conditions influenced from the pacific in the west and the glacial freshwater input from the east localized distributions of foraminifera are controlled by conditions influenced by the physiography of the individual fjords and channels the distribution of chilean fjord foraminifera and their environmental associations are consistent with results from other temperate to high latitude fjord foraminiferal studies

bathymetric distribution of fossil foraminifera within marine sediment cores from the eastern part of lutzow holm bay east antarctica and its paleoceanographic implications abstract faunal analysis of fossil foraminifera from marine gravity and piston cores collected by the japanese antarctic research expeditions 1981 and 1992 is used to estimate the impact of the latest quaternary paleoceanography on coastal environments of the eastern part of lutzow holm bay east antarctica accelerator mass spectrometry ams carbon 14 ages produced from sedimentary organic carbon were less than 16 ka non corrected detailed correlation among submarine cores and holocene elevated marine deposits exposed on the eastern shore of the embayment is difficult due to the indefinite reservoir correction value for marine organic matter and to upward increasing abnormal ages for some cores a local carbonate dissolution level can be delineated around the present depth of 300 400 m or shallower in the eastern part of lutzow holm bay during the holocene based on distributional trends of arenaceous calcareous benthic and planktonic foraminifera recognized within a depth less than 600 m downcore recovery of calcareous foraminifera containing bulimina aculeata from two cores obtained in a drowned glacial trough deeper than 600 m situated far beyond the dissolution depth of caco3 indicates the incursion of warm high nutrient and caco3 saturated circumpolar deep water cdw from the offshore area along the trough toward the southeastern coast of lutzow holm bay during the holocene the intrusion of cdw impacted on the marine environments of the southeastern coast thereby contributing to peripheral retreat of the ice sheet as well as increasing calcareous benthic foraminiferal productivity along the southeastern coast of lutzow holm bay

late holocene palaeoclimatic records from lake sediments on james ross island antarctica sediment profiles from several lakes ponds in the northern ice free area of james ross island antarctica were the subject of a multi disciplinary palaeoenvironmental investigation the results obtained from lithological geomagnetic geochemical and diatom analyses and the frequency of branchinecta eggs were evaluated with multivariate statistics and provide a fairly detailed picture of climate change during the last 5000 years new radiocarbon dates are combined with previously published 14c dates so as to date the palaeoenvironmental and palaeohydrological changes identified by the stratigraphic studies in combination with the findings of glacial geological studies our data suggest that the brandy bay glacier began to recede rapidly just before 5000 yr b p due to calving and moisture starvation caused by cold and arid conditions in one of the ponds studied gypsum began to precipitate as a consequence of these conditions when the influence of glacial meltwater ceased this hypothesis was tested by hydrochemical modeling at approximately 4200 yr b p the climate became more humid and warmer and the pond supported a fairly diverse biota which included a variety of diatom species and for example branchinecta gaini a crustacean that feeds on benthic cyanobacterial mats the brandy bay glacier probably advanced during this humid period but the advance was interrupted by subsequent arid conditions which started at 3000 yr b p during this arid phase glaciers became completely absent from the study area as a result formerly large lakes fed by glacial meltwater transformed into small enclosed brackish water bodies that contained b gaini the arid and fairly cold conditions lasted for 1500 2000 years until approximately 1200 yr b p when the aquatic systems expanded and their salinity was lowered as a result of increased snow accumulation and glacial expansion the increased deposition of minerogenic matter caused by glacial erosion and meltwater inflow probably caused the disappearance of branchinecta on james ross island we regard this most recent phase as a period of increased humidity and warmth compared to the previous period although the conditions appear to be less warm and humid than those which prevailed during the climatic optimum between 4200 and 3000 yr b p in spite of certain correlation problems we tentatively correlate our results to other studies of holocene environments in antarctica and from that it can be suggested that the climatic optimum was of circumpolar significance therefore the climatic oscillations recorded in sediments on james ross island may reflect oscillations in the anticyclonic stormtracks and the strength of the high pressure cell over the inland ice sheet

holocene foraminiferal assemblages from firth of tay antarctic peninsula paleoclimate implications abstract the 77 m sediment core from firth of tay provides complete record of glacial retreat and holocene climate change on the weddell sea side of the antarctic peninsula that began 9400 yr bp benthic foraminiferal data indicate significant environmental changes as recorded at 600 m water depth at the drill site three foraminiferal assemblages fas globocassidulina spp fursenkoina fusiformis fa miliammina arenacea fa and paratrochammina bartrami portatrochammina antarctica fa reflect increasingly glacier distal conditions they started with most glacier proximal conditions that lasted until 8800 yr bp which is indicated by cribroelphidium cf webbi and continued with elevated input of coarse glacial sediment until 7750 yr bp the mid holocene climatic optimum between 7750 and 6000 yr bp appears to be the time of highest primary production which led to higher corrosiveness of bottom waters and biased species composition of the m arenacea fa it was terminated by minor cooling the neoglacial that took place after 3500 yr bp is marked by an increase in p bartrami and p antarctica the major constituents of the p bartrami p antarctica fa this fa became periodically dominant after 900 yr bp indicating increasingly glacier distal conditions due to cooling coinciding with increasing aridity rising altitude of the glacial equilibrium line and less glacial influence on marine biota episodic high abundances of a fourth foraminiferal assemblage globocassidulina biora fa that occurs practically throughout the core is difficult to interpret explicitly although there are some concerns if g biora fa represents in situ fauna it appears to be an opportunistic fauna that dominated during periods of more glacial sediment input and sediment remobilization leading to better carbonate preservation

recent benthic foraminifera from the eastern south atlantic ocean dependence on food supply and water masses abstract sixty surface sediment samples from the eastern south atlantic ocean including the walvis ridge the angola and cape basins and the southwest african continental margin were analysed for their benthic foraminiferal content to unravel faunal distribution patterns and ecological preferences live stained with rose bengal and dead faunas were counted separately and then each grouped by q mode principal component analysis into seven principal faunal end members then multiple regression technique was used to correlate recent assemblages with available environmental variables and to finally differentiate between four principal groups of environmental agents acting upon the generation of benthic foraminiferal assemblages 1 seasonality of food supply and organic carbon flux rates together with oxygen content in the pore and bottom waters 2 lateral advection of deep water masses 3 bottom water carbonate corrosiveness and 4 energetic state at the benthic boundary layer and grain size composition of the substrate food supply and corresponding dissolved oxygen contents in the pore and bottom waters turned out to be the most important factors which control the distribution pattern of the recent benthic foraminifera at the continental margin in the zone of coastal upwelling and its mixing area benthic foraminiferal assemblages are dominated by stenobathic high productivity faunas characterized by elevated standing stocks low diversities and a large number of endobenthic living species at the continental shelf and upper continental slope the live assemblages are characterized by rectuvigerina cylindrica uvigerina peregrina s 1 uvigerina auberiana and rhizammina spp while the dead assemblages are characterized by cassidulina laevigata bolivina dilatata bulimina costata and b mexicana at the lower continental slope strong influence of high organic matter fluxes on the species composition is restricted to the area off the cunene river mouth where the live assemblage is dominated by uvigerina peregrina s 1 the corresponding dead assemblage by melonis barleeanum and m zaandamae in the adjacent areas of the lower continental slope the biocoenosis is characterized by reophax bilocularis and epistominella exigua which becomes dominant in the corresponding dead assemblage at the walvis ridge and in the abyssal angola and cape basins where organic matter fluxes are low and highly seasonal benthic foraminiferal assemblages reflect both the oligotrophic situation and the deep and bottom water mass configuration the top and flanks of the walvis ridge are inhabited by the rhizammina psammosphaera and r bilocularis live assemblages the corresponding dead assemblages are dominated by g subglobosa on the ridge top and e exigua on the flanks within the highly diverse e exigua dead assemblage several associated epibenthic species coincide with the core of nadw between about 1600 and 3700 m water depth these species include osangularia culter cibicidoides kullenbergi melonis pompilioides bolivinita pseudothalmanni and bulimina alazanensis the assemblages of the abyssal cape and angola basins are characterized by nuttallides umbonifer and a high proportion of agglutinated species these species are adapted to very low organic matter fluxes and a carbonate corrosive environment

retracted advance of the outlet glaciers during regional warming as inferred from late holocene massive diamicton in the king george island fjords the south shetland islands west antarctica marine sediment cores were obtained from in front of the tidewater glaciers in the marian and potter coves in the south shetland islands in the austral summer of 2001 2002 sedimentological paleontological and geochemical data from these cores document an advance of ice tongue for the deposition of clast supported massive diamicton interpreted as having been produced by ice rafting in front of glacier margin and or releasing of clasts from basal debris zones in the sub ice tongue setting a 14 c chronology for a core indicates that glacial advance took place c 1450 1700 14 c yr b p coincident with warm humid phase in the study area during this period the glacier margin was likely to have advanced and released diamicton clasts as inferred from a reduction in the total organic carbon content and an increase in sand and clasts within the diamicton facies the glacial advance probably caused enhanced ice edge blooms near the core sites resulting in increased abundance of sea ice related diatoms i e fragilariopsis curta and fragilariopsis cylindrus in the diamicton the warm and humid conditions between 1450 and 1700 14 c yr b p might have allowed the intrusion of warm antarctic circumpolar water within the fjords bringing about increased abundance of warm water form i e fragilariopsis kerguelensis on the other hand this warming condition probably prohibited the intrusion of weddell ice shelf water from the fjord as evidenced by lack of cold water form thalassiosira antarctica in the diamicton clearly the response of the outlet glacier system along the periphery of the south shetland islands ice sheet during the late holocene warm humid period 1450 1700 14 c yr b p was expansion thus the process of clast supported massive diamicton formation is likely to be applicable to a number of areas of the modem and late quaternary antarctic peninsula

distribution and ecology of benthic foraminifera in mcmurdo sound antarctica abstract foraminifera from modern sediments in mcmurdo sound have been studied to provide a basis for interpreting fossil assemblages there the sound is 50 km across more than 900 m deep and ice covered for at least nine months of the year the salinity and temperature of the bottom water are nearly constant 33 96 34 99 and 1 95 c 1 4 c sea floor sediment is mainly fine sand and mud with a little ice rafted gravel nearly 40 000 specimens of foraminifers 2334 living and 36 875 dead were identified from 28 samples collected by gravity corer and grab from sites varying in depth between 79 and 856 m three present day assemblages can be recognised 1 1 shallow open water assemblage swa from 110 to 560 m found in shallower areas of the open sound dominated by calcareous species 2 2 deep open water assemblage dwa from 620 to 856 m found in deeper areas of central mcmurdo sound dominated by agglutinated species and 3 3 harbour assemblages ha from 79 to 796 m in the enclosed basins and harbours of the area dominated by agglutinates species the composition of the assemblages is controlled chiefly by the calcium carbonate compensaion depth ccd calcareous species are abundant and varied 84 calcareous species in the swa above 620 m but are almost absent from the dwa the dominance of agglutinated foraminifera in the ha indicates a shallower ccd about 230 m in restricted coastal settings comparison of mcmurdo sound assemblages to those from other areas of the antarctic the arctic and the deep ocean indicates that there are grpss similarities in the over all faunas but actual species in commin range from 6 to 41 of the mcmurdo sound total assemblage 124 species death assemblages have a similar species diversity to corresponding life assemblages from 620 the ccd to 420 m where death assembalges are representative of them except for open water assemblages from 620 the ccd to 420 m where death assemblages are depleted in calcareous taxa the diversity of the agglutinated component of each assemblage remains nearly constant in all habitats and at all water depths

airborne and spaceborne dem and laser altimetry derived surface elevation and volume changes of the bering glacier system alaska usa and yukon canada 1972 2006 using airborne and spaceborne high resolution digital elevation models and laser altimetry we present estimates of interannual and multi decadal surface elevation changes on the bering glacier system alaska usa and yukon canada from 1972 to 2006 we find 1 the rate of lowering during 1972 95 was 0 9 0 1 m a 1 2 this rate accelerated to 3 0 0 7 m a 1 during 1995 2000 and 3 during 2000 03 the lowering rate was 1 5 0 4 m a 1 from 1972 to 2003 70 of the area of the system experienced a volume loss of 191 17 km 3 which was an area average surface elevation lowering of 1 7 0 2 m a 1 from november 2004 to november 2006 surface elevations across bering glacier from mcintosh peak on the south to waxell ridge on the north rose as much as 53 m up glacier on bagley ice valley about 10 km east of juniper island nunatak surface elevations lowered as much as 28 m from october 2003 to october 2006 nasa terra modis observations from may to september 2006 indicated muddy outburst floods from the bering terminus into vitus lake this suggests basal englacial hydrologic storage changes were a contributing factor in the surface elevation changes in the fall of 2006

retreating glacier fronts on the antarctic peninsula over the past half century the continued retreat of ice shelves on the antarctic peninsula has been widely attributed to recent atmospheric warming but there is little published work describing changes in glacier margin positions we present trends in 244 marine glacier fronts on the peninsula and associated islands over the past 61 years of these glaciers 87 have retreated and a clear boundary between mean advance and retreat has migrated progressively southward the pattern is broadly compatible with retreat driven by atmospheric warming but the rapidity of the migration suggests that this may not be the sole driver of glacier retreat in this region

foraminiferal assemblages from ice proximal paleo settings in the whales deep basin eastern ross sea antarctica abstract reconstructions of ross sea paleoenvironments based on foraminifera are hindered by the dearth of actualistic data especially from below the ross ice shelf to fill this gap we used a recently developed well resolved deglaciation record from the whales deep basin of the eastern ross sea to understand the ecological affinities of different foraminiferal assemblages during open water conditions similar to the present two benthic foraminiferal communities are strongly dominated by agglutinated species however in the underlying sediments that represent sub ice shelf and grounding zone proximal settings on the outer continental shelf we identified five different assemblages of calcareous foraminifera by antarctic margin standards these calcareous assemblages are periodically truly abundant along with assemblages dominated by benthic calcareous species that are well known from many antarctic settings i e globocassidulina biora trifarina earlandi and astrononion echolsi two important assemblages are dominated by a heretofore undescribed pustulose morphotype of g biora and poorly known spinose morphotype of t earlandi based on our correlations to the deglacial record these two assemblages live near the grounding line or in environments with especially intense bottom water currents as grounded and floating ice retreated south to the middle continental shelf these later sub ice shelf and grounding zone proximal settings were largely devoid of calcareous foraminifera and instead were inhabited by agglutinated taxa this improved understanding of foraminiferal assemblage distributions from a variety of environments within the eastern ross sea may contribute to better use of foraminiferal data to investigate the evolution of environmental changes in grounding line proximal environments

benthic foraminiferal record of holocene deep water evolution in the palmer deep western antarctic peninsula benthic foraminiferal data from ocean drilling program site 1098 indicate significant changes in deep water conditions of the palmer deep western antarctic peninsula margin throughout the holocene 13 ka to present the earliest holocene represents a period of transition from the last glacial maximum lgm cold bottom waters similar to saline shelf water ssw dominated the middle holocene the late holocene in the palmer deep has been characterized by alternating dominance of circumpolar deep water cdw and saline shelf water these changes have global oceanographic and climatic implications we suggest that the middle holocene bottom water record in the absence of circumpolar deep water on the western antarctic peninsula shelf indicates high saline shelf water production and or weakened circumpolar deep water production during the middle holocene climatic optimum the late holocene benthic foraminiferal record indicates rapidly fluctuating sea ice conditions and may indicate a teleconnection between the south pacific and southern ocean thus having implications related to the southern oscillation index

holocene glacial history and sea level changes on james ross island antarctic peninsula a reconstruction of deglaciation and associated sea level changes on northern james ross island antarctic peninsula based on lithostratigraphical and geomorphological studies shows that the initial deglaciation of presently ice free areas occurred slightly before 7400 14 c yr bp sea level in connection with the deglaciation was around 30 m a s l a glacier readvance in brandy bay of at least 7 km with the initial 3 km over land reached a position off the present coast at ca 4600 yr bp the culmination of the advance was of short duration and by 4300 yr bp the coastal lowlands again were ice free a distinct marine level at 16 18 m a s l was contemporaneous with or slightly post dates the brandy bay advance thus indicating the relative sea level around 4600 4500 yr bp our results from james ross island confirm that over large areas in this part of antarctica the last deglaciation occurred late 1997 by john wiley sons ltd

marine record of holocene climate ocean and cryosphere interactions herbert sound james ross island antarctica abstract the sediment record offshore james ross island northeast antarctic peninsula presents an unparalleled opportunity to directly compare marine and terrestrial climate records spanning the holocene in maritime antarctica an 11 m drill core was collected between herbert sound and croft bay as part of the shaldril nbp 0502 initiative and produced the southernmost sediment record from the eastern side of the ap thirty eight radiocarbon ages are used to construct an age model of centennial scale resolution multi proxy records including magnetic susceptibility pebble content particle size total organic carbon and diatom assemblages were interrogated in the context of nearby holocene age ice core lake and drift records from james ross island differences in the timing and expression of holocene events reflect marine controls on tidewater glaciers such as water mass configurations and sea ice glacial behavior mimics ice core paleotemperatures during the holocene with the exception of distinct ocean warming events herbert sound was fully occupied by grounded ice during the last glacial maximum and experienced rapid lift off followed by a floating ice phase the canopy of floating ice receded by 10 2 4 cal kyr bp presumably in response to early holocene warming herbert sound and croft bay fully deglaciated by 7 2 cal kyr bp when the mid holocene hypsithermal commenced and the sound became open and productive an extreme peak in productivity 6 1 cal kyr bp indicates an oceanic warming event that is not reflected in atmospheric temperature or lacustrine sediment records increase in sea ice cover and ice rafting mark the onset of the neoglacial 2 5 cal kyr bp when pronounced atmospheric cooling is documented in the james ross island ice core our comparison facilitates more holistic understanding of atmosphere ocean cryosphere interactions that may aid predictions of glacial response to future warming and sea level scenarios

precipitation sublimation and snow drift in the antarctic peninsula region from a regional atmospheric model 1 a regional atmospheric model with a horizontal grid spacing x of 14 km is used to study the surface mass balance components precipitation sublimation and snow drift in the region of the antarctic peninsula ap an integration is performed for the 7 year period 1987 1993 using a realistic forcing at the lateral model boundaries and at the sea surface output from this integration indicates that the precipitation reaches its maximum value on the northwestern slope of the ap where the upward motion in the atmosphere is largest uplift occurs upstream of the barrier affecting the precipitation distribution over sea the effect of the barrier on the precipitation distribution over the bellingshausen sea might have important implications for the ocean circulation in this region the mean precipitation over the grounded ice of the ap 1 20 m water eq yr 1 is 6 times larger than the mean value over all the grounded ice of antarctica our estimates for the surface sublimation and wind transport of snow over the grounding line toward the sea are 9 and 6 1 of the precipitation respectively in situ data of the wind distribution at three coastal sites located on the northern eastern and western sides of the ap are used to evaluate the modeled wind field which is important for the snow drift calculations for two of the three sites considered the prevailing wind direction and bimodal wind distribution are correctly represented by the model the calculated distribution of accumulation and ablation due to snow drift shows a complex pattern the wind removes snow from the spine of the ap where the near surface flow field diverges whereas deposition occurs mainly on the eastern slopes where the near surface flow field converges an intercomparison between two 7 year integrations at different horizontal resolution x 14 km and x 55 km shows that the precipitation on the northwestern slope is very sensitive to the model resolution in the x 14 km integration precipitation on the northwestern slope is higher than in x 55 km because of higher vertical velocities resulting in a 35 increase in average precipitation over the grounded ice of the ap

cenozoic tectonic evolution of liaodong dome northeast liaodong bay bohai offshore china constraints from seismic stratigraphy vitrinite reflectance and apatite fission track data abstract the liaodong dome is a region of localized uplift and deformation within the liaodong bay bohai offshore china 3 d seismic dataset vitrinite reflectance and apatite fission track data provide an exceptional opportunity to document the evolution of the liaodong dome which developed coeval with the tan lu strike slip fault zone with a rift system the 3 d seismic data demonstrates that the dome formed before the deposition stage of esm sequence 40 ma and it uplifted again during or after the depositional stage of ed sequence 32 24 ma apatite fission track and vitrinite reflectance data indicate that the dome experienced two stages of cooling episodes paleocene to early middle eocene 65 40 ma and late oligocene to late miocene 30 11 5 ma usually indicating uplifting both the seismic stratigraphy and thermal history analysis show that 1 the liaodong dome is part of the jiaoliao terrane 2 regional continental rifting climaxed during 65 40 ma as it did the rift shoulder uplift of the dome 3 the reactivation of the tan lu fault caused a second uplift processes of the liaodong dome during 30 11 5 ma 4 the liaodong dome uplifted independently and separated from the jiaoliao terrane our results also suggest that it is important to take uplifting evolution into consideration to target a potential petroleum reservoir

glacier surge after ice shelf collapse the possibility that the west antarctic ice sheet will collapse as a consequence of ice shelf disintegration has been debated for many years this matter is of concern because such an event would imply a sudden increase in sea level evidence is presented here showing drastic dynamic perturbations on former tributary glaciers that fed sections of the larsen ice shelf on the antarctic peninsula before its collapse in 1995 satellite images and airborne surveys allowed unambiguous identification of active surging phases of boydell sjogren edgeworth bombardier and drygalski glaciers this discovery calls for a reconsideration of former hypotheses about the stabilizing role of ice shelves

holocene climate and glacial history of the northeastern antarctic peninsula the marine sedimentary record from a long shaldril core abstract a high resolution record of holocene deglacial and climate history was obtained from a 77 m sediment core from the firth of tay antarctic peninsula as part of the shaldril initiative this study provides a detailed sedimentological record of holocene paleoclimate and glacial advance and retreat from the eastern side of the peninsula a robust chronostratigraphy was derived from thirty three radiocarbon dates on carbonate material this chronostratigraphic framework was used to establish the timing of glacial and climate events derived from multiple proxies including magnetic susceptibility electric resistivity porosity ice rafted debris content organic carbon content nitrogen content biogenic silica content and diatom and foraminiferal assemblages the core bottomed out in a stiff diamicton interpreted as till gravelly and sandy mud above the till is interpreted as proximal glaciomarine sediment that represents decoupling of the glacier from the seafloor circa 9400 cal yr bp and its subsequent landward retreat this was approximately 5000 yr later than in the bransfield basin and south shetland islands on the western side of the peninsula the firth of tay core site remained in a proximal glaciomarine setting until 8300 cal yr bp at which time significant glacial retreat took place deposition of diatomaceous glaciomarine sediments after 8300 cal yr bp indicates that an ice shelf has not existed in the area since this time the onset of seasonally open marine conditions between 7800 and 6000 cal yr bp followed the deglacial period and is interpreted as the mid holocene climatic optimum open marine conditions lasted until present with a minor cooling having occurred between 6000 and 4500 cal yr bp and a period of minor glacial retreat and or decreased sea ice coverage between 4500 and 3500 cal yr bp finally climatic cooling and variable sea ice cover occurred from 3500 cal yr bp to near present and it is interpreted as being part of the neoglacial the onset of the neoglacial appears to have occurred earlier in the firth of tay than on the western side of the antarctic peninsula the medieval warm period and little ice age were not pronounced in the firth of tay the breadth and synchroneity of the rapid regional warming and glacial retreat observed in the antarctic peninsula during the last century appear to be unprecedented during the holocene epoch

microfossil distributions in modern amundsen sea sediments abstract acquisition of 20 piston cores from the amundsen sea continental shelf provides material for the first determinations of modern and paleo distributions of microfossils including planktonic and benthic foraminifera diatoms and radiolaria in this region microfossil analyses of filtered sea water and sea ice samples allow comparisons of the biocoenosis with the thanatocoenosis in the sediments in all three biotic provinces are distinguished 1 the outer shelf region north of thurston island is characterized by high abundances of planktonic and calcareous benthic foraminifera low diatom abundances in sediments here despite high abundances in the sea ice may reflect prevention of deposition by ocean currents 2 the southernmost province in pine island bay is marked by very low abundances of all microfossil groups possibly because the floating terminus of pine island glacier has retreated from this area only during the last 100 years in that case the polynya that exists today in this region during some austral summers is so recent a feature that little or no biogenic sediment has had an opportunity to accumulate beneath it 3 the eastern margin province situated between the pine island bay and outer margin provinces along the eastern coast of the amundsen sea is characterized by high abundances of diatoms and arenaceous benthic foraminifera which probably record the presence of the amundsen sea polynya in this area during the last 1000 to 2500 years dominance of the benthic fauna in this area by arenaceous foraminifera is a function of the great depth from which most cores in this area were retrieved 500 924 m below the ccd

benthic foraminiferal assemblages from the eastern weddell sea between 68 and 73 s distribution ecology and fossilization potential surface sediment samples taken with a vented box corer from the eastern weddell sea on four profiles perpendicular to the continental margin have been investigated for their benthic foraminiferal content the live fauna was differentiated from empty tests comprising the foraminiferal death assemblage based on the dead assemblages potential fossil assemblages were calculated to facilitate the analogy with late neogene core material five distinct live assemblages inhabit the continental margin today six dead assemblages and five potential fossil assemblages respectively correspond to these biocoenoses a predominantly calcareous live fauna dominated by trifarina angulosa is correlated with strong bottom currents and sandy sediments at the shelf break and on the uppermost continental slope below this on the upper slope down to 2000 m water depth the predominantly calcareous bulimina aculeata assemblage coincides with the core of warm 0 c weddell deep water and with fine and more organic rich sediments these calcareous live assemblages completely change composition during early diagenesis because of calcite dissolution within the uppermost sediment which depends largely on the grain size distribution of the sediment and the fluxes of organic matter therefore a still calcareous t angulosa dominated fossil assemblage indicates the sandy substrates on the shelf break and the upper slope whereas the deeper slope with hemipelagic calm sedimentation and with high fluxes of organic matter is indicated by martinottiella nodulosa the characteristic arenaceous fossil remnant of the former predominantly calcareous live b aculeata fauna on a continental terrace between 2500 and 3500 m water depth cribrostomoides subglobosus dominates the live fauna but because of rapid disintegration of the empty tests of this agglutinated species a predominantly calcareous fauna characterized by oridorsalis umbonatus and epistominella exigua comprises the dead assemblage and the potential fossil assemblage respectively on the lower continental slope between the carbonate lysocline 3500 m and the carbonate compensation depth 4000 m tests of nuttallides umbonifer are the characteristic dead and potential fossil remnants of a former predominantly arenaceous live fauna which is associated with the lower part of the antarctic bottom water aabw this corroborates earlier investigations suggesting a relationship between the carbonate corrosiveness of water masses and the distribution of n umbonifer this is important for inferring paleo routes and estimates of paleo production rates of aabw during the neogene

environmental connotations of benthic foraminiferal assemblages from coastal west antarctica abstract this paper examines the variability in foraminiferal assemblages in surface samples from coastal settings along the northwestern antarctic peninsula as well as in the pine island bay area material comes from water depths ranging between 20 and 1257 m latitudes between 62 and 73 s and bottom water temperatures from 1 5 to 1 2 c the microfossil analysis within this broad geographical and environmental context provides a basis for paleo environmental studies environmental affinities of the assemblages were interpreted based on a wide array of ecological conditions including ctd data as well as on faunal indices and ecological affinities of the key taxa six foraminiferal assemblages are dominated by calcareous taxa among other factors they correspond to variable food supply terrigenous sedimentation and water mass properties another two assemblages are dominated by arenaceous foraminifera and reflect conditions corrosive to carbonate our findings indicate that preserved fossil assemblages in cores from these locations may not be accurate representations of living assemblages

chronology of the palmer deep site antarctic peninsula a holocene palaeoenvironmental reference for the circum antarctic palmer deep sediment cores are used to produce the first high resolution continuous late pleistocene to holocene time series from the antarctic marine system the sedimentary record is dated using accelerator mass spectrometer radiocarbon methods on acid insoluble organic matter and foraminiferal calcite fifty four radiocarbon analyses are utilized in the dating which provides a calibrated timescale back to 13 ka bp reliability of resultant ages on organic matter is assured because duplicates produce a standard deviation from the surface age of less than laboratory error i e 50 years in addition surface organic matter ages at the site are in excellent agreement with living calcite ages at the accepted reservoir age of 1260 years for the antarctic peninsula spectral analyses of the magnetic susceptibility record against the age model reveal unusually strong periodicity in the 400 200 and 50 70 year frequency bands similar to other high resolution records from the holocene but so far unique f

antarctic holocene climate change a benthic foraminiferal stable isotope record from palmer deep the first moderate to high resolution holocene marine stable isotope record from the nearshore antarctic continental shelf ocean drilling program odp hole 1098b suggests sensitivity of the western antarctic peninsula hydrography to westerly wind strength and el nino southern oscillation enso like climate variability despite proximity to corrosive antarctic water masses sufficient caco3 in palmer deep sediments exists to provide a high quality stable isotopic record especially in the late holocene coherence of benthic foraminifer delta 18 o delta 13 c sedimentologic and caco3 fluctuations suggests that rapid 20 years palmer deep bottom water temperature fluctuations of 1d 1 5dc are associated with competitive interactions between two dominant oceanographic climatic states an abrupt shift from a warmer stable upper circumpolar deep water ucdw state to a cooler variable shelf water state occurred at s3 6 ka palmer deep bottom waters oscillated between ucdw and shelf water dominated states between s3 6 and 0 05 ka cool shelf water intervals correlate with neoglacial events the most recent and largest being the little ice age lia s0 7 0 2 ka similarities between palmer deep and global holocene records and the rapidity of inferred bottom water fluctuations suggest that western antarctic peninsula shelf hydrography has not been controlled by thermohaline reorganizations but by variable strength and or position of the southern hemisphere westerly wind field we suggest that these atmospheric perturbations may have originated in the low latitude tropical pacific

seismic reflection imaging of a major strike slip fault zone in a rift system paleogene structure and evolution of the tan lu fault system liaodong bay bohai offshore china the tan lu fault system in the liaodong bay bohai offshore china affords an exceptional opportunity to document the structural features of a major strike slip fault using two and three dimensional seismic reflection data as well as evolution of a strike slip fault developed coeval with a rift system the fault zone displays a relatively straight throughgoing trace longitudinally bisecting the rift valley it consists of positive and negative flower structures and en echelon folds in the south bay and three parallel flower structure systems northward the middle fault bifurcates northward into two semiparallel vertical fault strands to the north the west strand bends clockwise and merges with the east strand the stepping pattern and orientation of en echelon structures indicate right lateral sense and about n10 35e azimuth of slip the fault apparently accrued about 30 40 km 20 25 mi of post early eocene slip based on the current distribution of deformation zones and depocenters tan lu fault segments with clockwise and counterclockwise orientation relative to the regional slip direction are characterized by divergent and convergent structures i e restraining and releasing bends respectively waning of rifting eliminated the cause of a major restraining bend putting an end to development of associated convergent structures in the south bay area near the central north bay deformation occurred along major normal faults related to the basin rifting although a prominent feature reflecting regional strain partitioning the tan lu fault apparently was not a major factor in the paleogene opening of the liaodong bay basin and the larger north china rift basin

living stained and dead foraminifera from the newly ice free larsen ice shelf weddell sea antarctica ecology and taphonomy within the past 7 years the northern larsen ice shelf has broken up so it is now possible to sample the sea floor that formerly lay beneath it box cores have yielded surface sediment samples 0 1 cm that give information on living and dead foraminiferal assemblages the living assemblages are of moderate diversity and four have 50 calcareous tests while five have 50 agglutinated tests this is an area of high primary production and the standing crops of the benthic foraminiferal assemblages are high all the dead assemblages are much enriched in agglutinated tests often 90 they give a time averaged record of the past 7 ice free years and several decades of ice cover the loss of permanent ice cover there is still seasonal ice cover may have caused some response from the fauna but it is likely that it was mainly changes in relative absolute abundance of the existing fauna the differences between the live and dead assemblages in the surface 1 cm are attributed mainly to taphonomic effects dissolution of calcareous tests and loss of fragile agglutinated tests subsurface samples down to 5 cm show that dissolution of calcareous tests is widespread and there may be some loss of fragile agglutinated forms such as reophax subdentaliniformis for these reasons in this area it may be best to make palaeoecological interpretations on the agglutinated component of the fossil assemblages

mg ca temperature calibration of polar benthic foraminifera species for reconstruction of bottom water temperatures on the antarctic shelf benthic foraminifera mg ca is a well established bottom water temperature bwt proxy used in paleoclimate studies the relationship between mg ca and bwt for numerous species has been determined using core top and culturing studies however the scarcity of calcareous microfossils in antarctic shelf sediments and poorly defined calibrations at low temperatures has limited the use of the foraminiferal mg ca paleothermometer in ice proximal antarctic sediments here we present paired ocean temperature and modern benthic foraminifera mg ca data for three species trifarina angulosa bulimina aculeata and globocassidulina subglobosa but with a particular focus on trifarina angulosa the core top data from several antarctic sectors span a bwt range of 1 7 to 1 2 c and constrain the relationship between mg ca and cold temperatures we compare our results to published lower latitude core top data for species in the same or related genera and in the case of trifarina angulosa produce a regional calibration the resulting regional equation for trifarina angulosa is temperature c mg ca 1 14 0 035 0 069 0 033 addition of our trifarina angulosa data to the previously published uvigerina spp dataset provides and alternative global calibration although some data points appear to be offset from this relationship and are discussed mg temperature relationships for bulimina aculeata and globocassidulina subglobosa are also combined with previously published data to produce calibration equations of temperature c mg ca 1 04 0 07 0 099 0 01 and temperature c mg ca 0 99 0 03 0 087 0 01 respectively these refined calibrations highlight the potential utility of benthic foraminifera mg ca paleothermometry for reconstructing past bwt in antarctic margin settings although further work is required before they are routinely used