u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

late quaternary submarine bedforms and ice sheet flow in gerlache strait and on the adjacent continental shelf antarctic peninsula geophysical data from gerlache strait croker passage bismarck strait and the adjacent continental shelf reveal streamlined subglacial bedforms that were produced at the bed of the antarctic peninsula ice sheet apis during the last glaciation the spatial arrangement and orientation of these bedforms record the former drainage pattern and flow dynamics of an apis outlet up flow and feeding into a palaeo ice stream in the western bransfield basin evidence suggests that together they represent a single ice flow system that drained the apis during the last glaciation the ice sheet outlet flowed north northeastwards through gerlache strait and croker passage and converged with a second more easterly ice flow tributary on the middle shelf to form the main palaeo ice stream the dominance of drumlins with low elongation ratios suggests that ice sheet outlet draining through gerlache strait was comparatively slower than the main palaeo ice stream in the western bransfield basin although the low elongation ratios may also partly reflect the lack of sediment progressive elongation of drumlins further down flow indicates that the ice sheet accelerated through croker passage and the western tributary trough and fed into the main zone of streaming flow in the western bransfield basin topography would have exerted a strong control on the development of the palaeo ice stream system but subglacial geology may also have been significant given the transition from crystalline bedrock to sedimentary strata on the inner mid shelf in the broader context the apis was drained by a number of major fast flowing outlets through cross shelf troughs to the outer continental shelf during the last glaciation copyright 2004 john wiley sons ltd

radiocarbon constraints on ice sheet advance and retreat in the weddell sea antarctica we report here the results of a study aimed at providing radiometric age control on glacial events in the weddell sea during the late quaternary sediment cores from the eastern continental shelf where the east antarctic ice sheet was grounded have recovered glacial marine sediments resting on tills and the latter deposits predate the isotope stage 2 last glacial maximum sediment cores from the continental slope and rise sampled a prominent ice rafted debris layer and radiocarbon ages indicate that this ice rafting event took place prior to 26 000 yr b p thus the combined data indicate that significant deglaciation of the weddell sea continental shelf took place prior to the last glacial maximum our data also suggest that the ice masses that border the weddell sea are more extensive than they were during the previous glacial minimum

sedimentation associated with antarctic peninsula ice shelves implications for palaeoenvironmental reconstructions of glacimarine sediments abstract recent disintegration of a number of antarctic peninsula ice shelves has given us a unique opportunity to investigate sub ice shelf sediments we characterize three sediment facies associations of two antarctic peninsula ice shelves larsen a and larsen inlet subglacial facies consist mainly of basal till diamicton with high shear strengths deposited under a grounded ice sheet progressive upward decrease in shear strength reflects a gradual decrease in the confining vertical effective pressure of grounded ice during till deposition proximal ice shelf glacimarine facies diamicton gravel rich and sand rich facies gravelly mud dropstone mud and sandy muds were deposited by sub ice shelf rain out bottom current activity and sediment gravity flows following decoupling of grounded ice from the sea floor distal ice shelf glacimarine and or open marine facies comprise terrigenous and diatom bearing bioturbated muds and gravelly muds that contain limited ice rafted debris these accumulated after recession of the grounding line to the coast with coarse grained surface sediments possibly documenting most recent ice shelf break up antarctic peninsula ice shelf sediments are more heterogeneous than ice shelf facies deposited elsewhere in antarctica cold polar antarctic ice shelves can be differentiated from temperate and sub polar marine terminated glacial sedimentary systems by the dominance of coarse grained proximal ice shelf glacimarine facies and an absence of subaqueous outwash meltwater sediment facies

radiocarbon constraints on antarctic peninsula ice sheet retreat following the last glacial maximum lgm abstract we present marine sedimentologic and radiocarbon data for the timing of retreat of the largely marine based antarctic peninsula ice sheet since the last glacial maximum lgm our findings indicate minimum estimates of deglaciation between 18 000 and 9000 calibrated years before present cal yr bp roughly in phase with the northern hemisphere deglaciation and eustatic sea level rise our findings show this retreat occurred progressively from the outer middle and inner continental shelf regions as well as progressively from the north to the south retreat initiated on the outer shelf of the northern peninsula by 18 000 cal yr bp and continued southward by 14 000 cal yr bp on the outer shelf of marguerite bay several thousand years earlier than estimated by numeric models while individual cores yield estimates of glacial retreat that may vary up to 1100 years we note steps in the data occur at 14 000 and possibly 11 000 cal yr bp coincidental to rapidly rising eustatic sea level including the well documented melt water pulses mwp 1a and 1b these data support the hypothesis that rapidly rising sea level is associated with marine ice sheet destabilization although additional dates are necessary to substantiate this finding this study highlights problems with radiocarbon dating acid insoluble organic aio matter in proximal lateglacial sediments as well as the need for more accurate dating techniques

timing of meltwater pulse 1a and climate responses to meltwater injections the temporal relationship between meltwater pulse 1a mwp 1a and the climate history of the last deglaciation remains a subject of debate by combining the greenland ice core project d18o ice core record on the new greenland ice core chronology 2005 timescale with the u th dated barbados coral record we conclusively derive that mwp 1a did not coincide with the sharp bolling warming but instead with the abrupt cooling of the older dryas to evaluate whether there is a relationship between meltwater injections north atlantic deep water nadw formation and climate change we present a high resolution record of nadw flow intensity from eirik drift through the last deglaciation it indicates only a relatively minor 200 year weakening of nadw flow coincident with mwp 1a our compilation of records also indicates that during heinrich event 1 and the younger dryas there were no discernible sea level rises and yet these periods were characterized by intense nadw slowdowns shutdowns clearly deepwater formation and climate are not simply controlled by the magnitude or rate of meltwater addition instead our results emphasize that the location of meltwater pulses may be more important with nadw formation being particularly sensitive to surface freshening in the arctic nordic seas

ice stream retreat and ice shelf history in marguerite trough antarctic peninsula sedimentological and foraminiferal signatures the timing nature and causes of grounded ice sheet retreat following the last glacial maximum lgm in marguerite trough west antarctic peninsula and subsequent early holocene ice shelf decay are presented in this paper we use sedimentological foraminiferal geotechnical and accelerator mass spectrometer ams radiocarbon data from marine cores from the mid continental shelf together with previously published ams dates to establish a sedimentological and chronological model initial ice sheet retreat through the outer and mid shelf sectors of marguerite trough was under way by ca 14 ka b p was rapid and coincided with the sea level rise of meltwater pulse 1a an ice shelf formed during this retreat and fine grained laminated muds reflecting meltwater derived suspension settling and or tidal pumping were deposited during this time the ice sheet remained grounded on the inner shelf ice shelf breakup and retreat of the calving front from ca 13 2 to 12 5 ka b p was slow 100 m a 1 across the outer and mid shelf with calving bay conditions remaining for at least 3 5 ka we interpret this ice shelf decay to have been driven by an incursion of weddell sea transitional water onto the shelf in contrast grounding line and ice shelf retreat in the inner bay occurred from ca 9 3 ka b p and was driven by circumpolar warm deep water encroaching onto the continental shelf at this time the mid shelf was an open marine environment characterized by hemipelagic deposition these findings highlight the importance of oceanographic controls in the breakup of antarctic peninsula ice shelves during the holocene

the tectonic relationship of two early proterozoic dyke swarms to the kapuskasing structural zone a paleomagnetic and petrographic study a tea coloured cloudiness in groundmass feldspars characterizes dykes of two early proterozoic swarms 2 45 ga matachewan 2 04 ga kapuskasing that intrude amphibolite to granulite host rocks with

ice shelf history from petrographic and foraminiferal evidence northeast antarctic peninsula a detailed record of late pleistocene deglaciation followed by mid holocene ice shelf breakup and late holocene re growth is contained in continental shelf sediments in the northern larsen area northeast antarctic peninsula the zero age of core tops is confirmed by new and published 210pb profiles and 70 accelerator mass spectrometer ams 14c dates on bulk organic carbon define sedimentation rates of 7 6 92 cm ka the varied geology in the local ice drainage basins facilitates the use of ice rafted debris ird provenance in determining the presence or absence of ice shelves all inshore cores contain an interval of non local ird in the post glacial section demonstrating widespread ice shelf breakup in the mid holocene both breakup and re growth may have taken centuries and there are no widespread debris layers associated with breakup cores beyond and up to 30 km inside the historical ice shelf limit exhibit a varied ird provenance throughout the holocene suggesting the maximum ice shelf limit may date only from the little ice age benthic foraminiferal assemblages are related to water masses and position on the continental shelf and have been modified by taphonomic processes nevertheless we discern a deglaciation signal in prince gustav channel of a calcareous spike in predominantly agglutinated assemblages and this is repeated at the time of mid holocene ice shelf breakup the inferred mid holocene warm period occurred later in the northern larsen area than on the west coast of the antarctic peninsula

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

geological constraints on antarctic palaeo ice stream retreat submarine landforms preserved in bathymetric troughs on the antarctic continental shelf show that the style of ice stream retreat across the shelf following the last glacial maximum varied between different troughs three styles of retreat are inferred from the geological evidence rapid episodic and slow rapid retreat by ice stream floatation and calving is recorded by the preservation of a landform assemblage of unmodified streamlined subglacial bedforms including mega scale glacial lineations msgls that record streaming flow along these troughs these elongate bedforms are not overprinted by recessional glacial landforms formed transverse to ice flow such as moraines or grounding zone wedges and overlying deglacial sediments are thin a second type of landform assemblage consists of msgls overprinted or interrupted by transverse grounding zone wedges this assemblage implies episodic retreat between successive grounding zone positions the third type of landform assemblage is that of numerous closely spaced recessional moraines and intermittent grounding zone wedges that overlie and interrupt msgls this assemblage records the slow retreat of grounded ice across the shelf variation in the style of ice stream retreat between the different bathymetric troughs indicates that antarctic palaeo ice streams did not respond uniformly to external forcing at the end of the last glacial cycle rather their diachronous retreat reflects the dominance of local controls in the form of bathymetry and drainage basin size more broadly these data show that retreat of marine based ice sheets in areas of reverse bed slope is not necessarily catastrophic and they provide important constraints for numerical models that attempt to predict the dynamics of large polar ice sheets copyright 2008 john wiley sons ltd

submarine glacial landforms and rates of ice stream collapse the rate of deglacial ice sheet retreat across polar continental shelves and possible ice stream collapse and sea level rise has been much debated high resolution imagery of seafloor morphology is available for many polar shelves and fjords the rapidity of ice retreat is inferred from diagnostic assemblages of submarine landforms produced at ice stream sedimentary beds these landforms exposed by ice retreat across high latitude shelves demonstrate that deglaciation occurs in three main ways rapidly by flotation and breakup episodically by still stands and or grounding events punctuating rapid retreat or by slower retreat of grounded ice submarine landform assemblages imply through the presence of grounding zone wedges overprinting mega scale glacial lineations on many polar shelves that ice stream retreat is more often episodic than catastrophic these observations provide a robust test of the ability of numerical models to predict the varied response of ice sheet basins to environmental changes

glacial marine sedimentation and quaternary glacial history of marguerite bay antarctic peninsula abstract marguerite bay situated between the subpolar glacial regime of the northern antarctic peninsula and the polar glacial regime of west antarctica is ideally located to test various models of glacial and glacial marine sedimentation and specific scenarios of late wisconsin ice sheet expansion piston cores and single channel seismic reflection data were collected during the deep freeze 85 and 86 expeditions to determine the late quaternary history of the area seismic data in the bay show a rugged seafloor with numerous deep troughs and a very thin layer of sediment over crystalline basement or older sediments glacial erosion is important in modifying existing features although the ultimate repository of the eroded material is not known it is not found within the bay the piston cores are topped by diatomaceous muds which are underlain by terrigenous muds and muddy gravels that imply deposition beneath an ice shelf basal tills were penetrated at three sites reflecting deposition by a grounded marine ice sheet a reconstruction of the glacial history of marguerite bay since the last glacial maximum shows grounded ice filling the bay in late wisconsin time rising sea level caused an uncoupling of the ice sheet and slow retreat of an ice shelf throughout the holocene

oceanic and atmospheric forcing of early holocene ice shelf retreat george vi ice shelf antarctica peninsula we use lake sediment records from an epishelf lake on alexander island to provide a detailed picture of the holocene history of george vi ice shelf gvi is core analyses included micropaleontology diatoms foraminifera stable isotope 18o 13c geochemistry total organic carbon toc total nitrogen tn c n ratios and grain size analyses these data provide robust evidence for one period of past ice shelf absence during the early holocene the timing of this period has been constrained by 10 ams 14c dates performed on mono specific foraminifera samples these dates suggest that gvi is was absent between c 9600 cal yr bp and c 7730 cal yr bp this early holocene collapse immediately followed a period of maximum holocene warmth that is recorded in some antarctic ice cores and coincides with an influx of warmer ocean water onto the western antarctic peninsula ap shelf at c 9000 cal yr bp the absence of a currently extant ice shelf during this time interval suggests that early holocene ocean atmosphere variability in the ap was greater than that measured in recent decades

developing sediment geochronologies for high latitude continental shelf deposits a radiochemical approach during january and february of 1986 47 box cores and 55 piston cores were collected from the bransfield strait gerlache strait and marguerite bay antarctica apparent sediment accumulation rates established for 100 yr time scales with excess 210pb chronologies range from 0 08 to 0 34 cm yr in the bransfield strait 0 15 to 0 51 cm yr in gerlache strait and from 0 10 to 0 27 cm yr in marguerite bay for the antarctic peninsula continental shelf 137cs appears to have a limited usefulness in assessing the effects of deep sediment mixing by benthic fauna on seabed excess 210pb profiles because the observed activities for the regions examined are close to counter detection limits conventional 14c ages of surface sediments from the peninsula region range from 1370 to 2820 yr the spatial variations in the conventional 14c surface ages are thought to be influenced predominantly by inputs of older eroded sediment from lateral transport current winnowing mass wasting and or a variable carbon source on a 1000 yr time scale 14c measurements of five piston cores from the bransfield strait yielded sediment accumulation rates ranging from 0 06 to 0 49 cm yr these data support the assertion by nelson 1988 that the excess 210pb sediment accumulation rates range of 0 08 to 0 34 cm yr for this region represent true rates the two sediment accumulation rates of 0 01 and 0 08 cm yr for the gerlache strait are significantly lower than the observed apparent 210pb accumulation rates mean 0 27 0 12 cm yr for this region likewise two piston cores from marguerite bay yielded 14c sediment accumulation rates of 0 02 and 0 05 cm yr which also are considerably lower than the excess 210pb apparent accumulation rates mean 0 17 0 06 cm yr for this area the one dimensional advection diffusion equation of goldberg and koide geochim cosmochim acta vol 51 1962 was solved simulatneously with 210pb and 14c data for bc18 and bc113 to resolved the effects of sediment mixing and accumulation in bransfield strait and marguerite bay box core samples respectively this model indicates that 210pb and 14c sediment accumulation rates agree within a factor of 2 in the bransfield strait whereas in marguerite bay the apparent 210pb accumulation rates may be as much as an order of magnitude too high in the southern high latitude environments of the antarctic peninsula radiocarbon measurements in the seabed are a better approach than 210pb for establishing accurate rates of sediment accumulation the 14c chronologies when coupled with 210pb data provide more reliable assessments of biological deep mixing and sediment accumulation rates than do excess 210pb data coupled with measurements of bomb produced 137cs the sediment accumulation rates for both 100 yr and 1000 yr time scales tend to decrease southward from the bransfield strait to marguerite bay which is consistent with glacial marine sedimentation processes as modulated by climate for the western antarctic peninsula seabed measurements of 210pb 137cs and 14c also provides valuable insights on water circulation and upwelling atmospheric inputs and sediment depositional processes for the antarctic peninsula region

recent dramatic thinning of largest west antarctic ice stream triggered by oceans a growing body of observational data suggests that pine island glacier pig is changing on decadal or shorter timescales these changes may have far reaching consequences for the future of the west antarctic ice sheet wais and global sea levels because of pig s role as the ice sheet s primary drainage portal we test the hypothesis that these changes are triggered by the adjoining ocean specifically we employ an advanced numerical ice flow model to simulate the effects of perturbations at the grounding line on pig s dynamics the speed at which these changes are propagated upstream implies a tight coupling between ice sheet interior and surrounding ocean

effective utilization of seismic reflection technique with moderate cost in uranium exploration abstract in participation with numerous industrial partners the seismic laboratory of the university of saskatchewan has conducted a variety of active seismic reflection experiments both on the west and east sides of the athabasca basin results of the investigations at shea creek mcarthur river and keefe lake illustrate that the seismic investigations deliver effective highly relevant primary structural images of the subsurface with resolution that no other geophysical technique can match correlation of similar seismic signatures on several distant but inter related seismic sections allowed spatial extension of promising exploration target zones previously unrecognized within the three dimensional seismic volume comparable reflectivity patterns defined the complex areal distribution of mineralization related fault systems beyond these novel contributions extended analysis of seismic signal attributes amplitude and frequency optical televiewer and full wave sonic data offer detailed lithological characterization including alteration zones clay content as well as porosity and fracture density information although these structural and geologically relevant anomalies are primary indicators of mineralization presenting novel exploration advantages the seismic method is still not a standard component of the athabasca basin exploration approach due to the negative perception that it is very expensive comparing the costs of all geophysical techniques to the cost of a single logged drill hole illustrates that the results of a properly designed seismic data acquisition program not only leads to more effective planning of a drilling program but also would lead to a much quicker recognition of the major mineralized zone s and a reduction in the number of required exploration boreholes this integrated approach to exploration would then translate into a significant reduction of the total exploration expenditures unquestionably the drilling of boreholes provides the most explicit reliable information to a certain depth but only within a very small area directly connecting the borehole information to seismic results extends the local reliable data permitting reduction of the number of boreholes to create accurate two dimensional or three dimensional subsurface images and reduction of the expenditures of the total exploration program

distribution of glacial geomorphic features on the antarctic continental shelf and correlation with substrate implications for ice behavior surveys were conducted seaward of all the major drainage outlets of the antarctic ice sheet from the pennell coast north victoria land to marguerite bay antarctic peninsula the results show that the ice sheet extended onto the outer shelf glacial troughs occur offshore of all major glacial outlets where the substrate is crystalline bedrock ice flow tended to follow the structural grain of the bedrock deposited little sediment and eroded the underlying bedrock where ice flowed over relatively soft more easily eroded sedimentary strata the direction of ice flow was more directly offshore and depositional features characterize the sea floor in these areas the signature of the grounded ice consists of till deposits and large scale geomorphic features drumlins occur within the region of contact between crystalline and sedimentary substrates the different geological substrates are interpreted to have exerted a fundamental control on the behavior of past ice sheets the troughs in the areas of bedrock composed of sedimentary substrate are interpreted to have been occupied by relatively fast flowing ice ice streams and the troughs in the areas of crystalline substrate are interpreted to have been occupied by slower moving ice the area between these two zones was characterized by ice acceleration and is marked by drumlins

deglacial meltwater pulse 1b and younger dryas sea levels revisited with boreholes at tahiti reconstructing sea level changes during the last deglaciation provides a way of understanding the ice dynamics that can perturb large continental ice sheets the resolution of the few sea level records covering the critical time interval between 14 000 and 9 000 calendar years before the present is still insufficient to draw conclusions about sea level changes associated with the younger dryas cold event and the meltwater pulse 1b mwp 1b we used the uranium thorium method to date shallow living corals from three new cores drilled onshore in the tahiti barrier reef no significant discontinuity can be detected in the sea level rise during the mwp 1b period the new tahiti sea level record shows that the sea level rise slowed down during the younger dryas before accelerating again during the holocene

sedimentary record of disintegrating ice shelves in a warming climate antarctic peninsula 1 seafloor sediments from beneath the former larsen a and prince gustav ice shelves document the recent breakup of the shelves and provide evidence for interpretation of previous events at three of five sites sediment texture coarsens upward with up to 40 sand at the surface radiometric 210pb dating shows this to have occurred between 1985 and 1993 several years before breakup of the shelf and that rates of accumulation of sediment on the seafloor doubled to quadrupled during this period these events are related to the release of eolian sediment in periodic rapid draining of small lakes and crevasses on the ice shelf before breakup x ray radiographs of sediment cores also document the recent influx of coarse particles gravel related to ice rafting during ice shelf disintegration because sediment is released irregularly in time and space from well separated point sources on the ice shelf during at least several years before final disintegration only a portion of the seafloor is affected

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

a 13 200 year history of century to millennial scale paleoenvironmental change magnetically recorded in the palmer deep western antarctic peninsula abstract a 13 200 yr record of magnetic parameters from the palmer deep western antarctic peninsula records a sequence of five distinct shifts in glacimarine sedimentation coupled with century scale variations in paleoproductivity the five major shifts are manifested as abrupt order of magnitude changes in low field magnetic susceptibility accompanied by changes in magnetic particle size and mineralogy the late holocene 3 4 0 ka the early holocene 11 5 9 ka and the last glacial maximum prior to 13 2 ka are intervals of strong low field magnetic susceptibility and are characterized by multi domain md magnetite md magnetite is associated with zones of abundant gravel grains and is interpreted here as an indicator of material transported as ice rafted debris deglaciation 13 2 11 5 ka and the middle holocene 9 3 4 ka were times of enhanced productivity the middle holocene marks the onset of century scale productivity cycles seen in high field magnetic susceptibility which is responding to variations in biogenic silica deglaciation and the middle holocene interval contain pseudo single domain magnetite and titanomagnetite respectively these observations are surprising given the abundance of coarse md magnetite available in local source rocks the magnetic mineral assemblage in the deglaciation interval however can be explained by density sorting in meltwater plumes during the middle holocene the magnetic mineral assemblage suggests the reduction or cessation of locally derived terrigenous sediment and by inference the reduction or cessation of iceberg generation the early holocene middle holocene shift in terrigenous sedimentation may be responding in part to sea level which controls the position of the grounding line the palmer deep late holocene interval coincides with the neoglacial period a time of glacier re advances worldwide

sea level fingerprinting as a direct test for the source of global meltwater pulse ia the ice reservoir that served as the source for the meltwater pulse ia remains enigmatic and controversial we show that each of the melting scenarios that have been proposed for the event produces a distinct variation or fingerprint in the global distribution of meltwater we compare sea level fingerprints associated with various melting scenarios to existing sea level records from barbados and the sunda shelf and conclude that the southern laurentide ice sheet could not have been the sole source of the meltwater pulse whereas a substantial contribution from the antarctic ice sheet is consistent with these records

deep sea floor evidence of past ice streams off the antarctic peninsula the past existence of a giant ice stream off the northern end of the antarctic peninsula is suggested by a convex upward elongated sediment body now at a mean water depth of 1000 m because of its morphological characteristics i e a set of parallel to subparallel ridges and grooves to 100 km long with an overall width of 25 km we call this depositional body a bundle structure we hypothesize that bundle structures form by accumulation of basal deformation till under their parent ice streams from its location size and overall characteristics the bundle structure described here constitutes the best preserved largest deepest and relatively low latitude evidence of giant ice streams that flowed offshore antarctica during glacial maxima bundle structures reveal the very dynamic behavior of ice caps in the northern antarctic peninsula during the last glacial maximum with catchment areas draining rapidly under marine based critical subglacial conditions bundle structures represent a new megascale streamlined glacial landform

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change

pre bomb radiocarbon and the reservoir correction for calcareous marine species in the southern ocean four antarctic marine mollusc shells which were collected alive between 1917 and 1940 were analyzed by accelerator mass spectrometry to provide the first pre bomb radiocarbon measurements of biogenic carbonates from the southern ocean after correcting for the impact of fossil fuel combustion suess effect radiocarbon activities of the pre bomb shells averaged 149 8 10 4 in contrast the 14c values for post bomb molluscs echinoderms brachiopods and foraminifera averaged 96 1 25 2 these biogenic carbonate 14c values are nearly identical to pre bomb estimates 148 to 152 and post bomb measurements 98 4 22 0 of the surface waters in the southern ocean average radiocarbon ages of the biogenic carbonates before and after 1950 1303 84 years and 811 205 years respectively along with those from seals and penguins indicate that the antarctic marine radiocarbon reservoir has decreased in age by nearly 500 years during the second half of the 20th century marine species and seawater measurements firmly place the radiocarbon reservoir correction at 1300 100 years for calcareous marine fossils which are widespread abundant and well preserved organic materials for interpreting ice sheet climate and sea level impacts on the antarctic marine ecosystem during the holocene

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

geological and geomorphological insights into antarctic ice sheet evolution technical advances in the study of ice free parts of antarctica can provide quantitative records that are useful for constraining and refining models of ice sheet evolution and behaviour such records improve our understanding of system trajectory influence the questions we ask about system stability and help to define the ice sheet processes that are relevant on different time scales here we illustrate the contribution of cosmogenic isotope analysis of exposed bedrock surfaces and marine geophysical surveying to the understanding of antarctic ice sheet evolution on a range of time scales in the dry valleys of east antarctica 3 he dating of subglacial flood deposits that are now exposed on mountain summits provide evidence of an expanded and thicker mid miocene ice sheet the survival of surface boulders for approximately 14 myr the oldest yet measured demonstrates exceptionally low rates of subsequent erosion and points to the persistence and stability of the dry polar desert climate since that time increasingly there are constraints on west antarctic ice sheet fluctuations during quaternary glacial cycles in the sarnoff mountains of marie byrd land in west antarctica 10 be and 26 al cosmogenic isotope analysis of glacial erratics and bedrock reveal steady thinning of the ice sheet from 10 400 years ago to the present probably as a result of grounding line retreat in the antarctic peninsula offshore analysis reveals an extensive ice sheet at the last glacial maximum based on radiocarbon dating deglaciation began by 17 000 cal yr bp and was complete by 9500 cal yr bp deglaciation of the west and east sides of the antarctic peninsula ice sheet occurred at different times and rates but was largely complete by the early holocene at that time ice shelves were less extensive on the west side of the antarctic peninsula than they are today the message from the past is that individual glacier drainage basins in antarctica respond in different and distinctive ways to global climate change depending on the link between regional topography and climate setting

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

reconstruction of the west antarctic ice sheet in pine island bay during the last glacial maximum and its subsequent retreat history abstract marine geological and geophysical studies were conducted to determine the late quaternary glacial history of the west antarctic ice sheet in pine island bay antarctica the data set includes sea floor imagery in the form of multibeam swath bathymetry and deep tow side scan sonar surveys distribution of sedimentary deposits and basal surface conditions are revealed through intermediate resolution seismic data and chirp 3 5 khz sub bottom profiles sedimentary deposits were sampled with piston cores and calcareous material was dated using ams radiocarbon techniques results from the study indicate the ice sheet was grounded on the outer shelf during its maximum extent sometime in the past thick ice flowing slowly and resting on crystalline bedrock was influenced by significant amounts of subglacial meltwater on the inner shelf thinner but more rapidly flowing ice characterized the seaward extent of the ice sheet which was grounded on a sedimentary substrate deglaciation occurred in two phases beginning soon after the last glacial maximum the outer most extension of the ice sheet retreated gradually pausing on a bathymetric high on the middle shelf by 16 000 14c years ago between 16 000 and 12 000 14c years ago ice sheet retreat resumed and may have proceeded rapidly to reach a present day position by 10 000 14c years ago

melting and freezing beneath filchner ronne ice shelf antarctica 1 we use remote sensing data sets to evaluate the spatial distribution of melt beneath the filchner ronne ice shelf fris the net melt rate of 83 4 24 8 gtons yr is 2 5 5 times lower than previous glaciological estimates but is similar to existing oceanographic estimates the spatial distribution however differs significantly from standard conceptual and numerical models in which most melt occurs along the grounding lines our results suggest most grounding line melt is refrozen while the dominant ice shelf water isw source is melting near the ice shelf front probably associated with tidal action this suggests that changes in ice shelf extent can impact isw production rates in the weddell sea

holocene climate variability in antarctica based on 11 ice core isotopic records a comparison is made of the holocene records obtained from water isotope measurements along 11 ice cores from coastal and central sites in east antarctica vostok dome b plateau remote komsomolskaia dome c taylor dome dominion range d47 km105 and law dome and west antarctica byrd with temporal resolution from 20 to 50 yr the long term trends possibly reflect local ice sheet elevation fluctuations superimposed on common climatic fluctuations all the records confirm the widespread antarctic early holocene optimum between 11 500 and 9000 yr in the ross sea sector a secondary optimum is identified between 7000 and 5000 yr whereas all eastern antarctic sites show a late optimum between 6000 and 3000 yr superimposed on the long time trend all the records exhibit 9 aperiodic millennial scale oscillations climatic optima show a reduced pacing between warm events typically 800 yr whereas cooler periods are associated with less frequent warm events pacing 1200 yr

mechanisms of holocene palaeoenvironmental change in the antarctic peninsula region the antarctic peninsula is one of the three fastest warming regions on earth here we review holocene proxy records of marine and terrestrial palaeoclimate in the region and discuss possible forcing mechanisms underlying past change with a specific focus on past warm periods our aim is to critically evaluate the mechanisms by which palaeoclimate changes might have occurred in order to provide a longer term context for assessing the drivers of recent warming two warm events are well recorded in the holocene palaeoclimate record namely the early holocene warm period and the mid holocene hypsithermal mhh whereas there are fewer proxy data for the mediaeval warm period mwp and the recent rapid regional rrr warming we show that the early holocene warm period and mhh might be explained by relatively abrupt shifts in position of the southern westerlies superimposed on slower solar insolation changes a key finding of our synthesis is that the marine and terrestrial records in the ap appear to show markedly different behaviour during the mhh this might be partly explained by contrasts in the seasonal insolation forcing between these records circumpolar deep water cdw has been implicated in several of the prominent changes through the holocene but there are still differences in interpretation of the proxy record that make its influence difficult to assess further work is required to investigate contrasts between marine and terrestrial proxy records east west contrasts in palaeoclimate the history of cdw to retrieve a long onshore high resolution record of the holocene and determine the role of sea ice in driving or modulating palaeoclimate change along with further efforts to study the proxy record of the rrr and the mwp

laminated sediments in glacimarine environments diagnostic criteria for their interpretation abstract fine grained laminated deposits are often reported from contemporary and ancient glacimarine sedimentary sequences laminated glacimarine sediments form by a variety of processes including suspension settling from turbid overflow plumes turbidity current deposition and contour current activity subglacial deformation of pre existing sediments may also produce laminated deposits in the form of glacitectonite and deformation till the development of diagnostic criteria for genetic discrimination of laminated glacimarine sediments is important both for their correct interpretation in sedimentary sequences and also for the accurate reconstruction of former glacier extent and geometry as laminated sediments may form in subglacial ice proximal and ice distal environments this paper reviews the processes by which laminated glacimarine sediments form and their resulting sedimentology the aim is to provide a synthesis of diagnostic sedimentological criteria for laminated glacimarine deposits that will assist in the interpretation of such sediments in the geological record laminated sediments are genetically differentiated on the basis of sedimentary structures bedding contacts stratigraphic relationships and macrofaunal content bioturbation these attributes also facilitate discrimination between glacimarine and glacilacustrine rhythmites the paper concludes by discussing the glaciological significance of laminated glacimarine sediments in terms of glacier hydrology reconstructions of former ice dynamics and basal thermal regime