on the hemispheric origins of meltwater pulse 1a abstract during the glacial interglacial transition that began subsequent to the last glacial maximum approximately 21 000 calendar years ago globally averaged eustatic sea level rose by approximately 120 m as climate warmed to its current holocene state this rise of relative sea level rsl did not occur smoothly however but was characterized by the occurrence of one or more episodes of extremely rapid increase the most extreme of these events has come to be referred to as meltwater pulse 1a and was initially identified in the coral based record of rsl history from the island of barbados in the caribbean sea although it has usually been assumed that this episode of rapid rsl rise was derivative of a partial collapse of the northern hemisphere ice sheets it has recently been suggested that this pulse could have originated in a dramatic melt back of the antarctic ice sheet in this paper the arguments presented in favour of the southern hemisphere source are revisited in order to assess the plausibility of this alternative scenario based upon the analyses presented it is concluded that the evidence previously provided in support of the southern hemisphere scenario is in fact unable to rule out an entirely northern hemisphere source for the meltwater pulse 1a since explicit evidence does exist that both the laurentide and fennoscandian ice sheets contributed to this event and that antarctic ice sheet melting occurred significantly later the southern hemisphere appears not to have been a prime mover of northern hemisphere events

ice sheet sources of sea level rise and freshwater discharge during the last deglaciation we review and synthesize the geologic record that constrains the sources of sea level rise and freshwater discharge to the global oceans associated with retreat of ice sheets during the last deglaciation the last glacial maximum 26 19 ka was terminated by a rapid 5 10 m sea level rise at 19 0 19 5 ka sourced largely from northern hemisphere ice sheet retreat in response to high northern latitude insolation forcing sea level rise of 8 20 m from 19 to 14 5 ka can be attributed to continued retreat of the laurentide and eurasian ice sheets with an additional freshwater forcing of uncertain amount delivered by heinrich event 1 the source of the abrupt acceleration in sea level rise at 14 6 ka meltwater pulse 1a 14 15 m includes contributions of 6 5 10 m from northern hemisphere ice sheets of which 2 7 m represents an excess contribution above that derived from ongoing ice sheet retreat widespread retreat of antarctic ice sheets began at 14 0 15 0 ka which together with geophysical modeling of far field sea level records suggests an antarctic contribution to this meltwater pulse as well the cause of the subsequent younger dryas cold event can be attributed to eastward freshwater runoff from the lake agassiz basin to the st lawrence estuary that agrees with existing lake agassiz outlet radiocarbon dates much of the early holocene sea level rise can be explained by laurentide and scandinavian ice sheet retreat with collapse of laurentide ice over hudson bay and drainage of lake agassiz basin runoff at 8 4 8 2 ka to the labrador sea causing the 8 2 ka event

lgm ice sheet extent in the weddell sea evidence for diachronous behavior of antarctic ice sheets abstract inaccessibility due to harsh weather conditions and perennial sea ice has resulted in the weddell sea being one of the more under studied regions of antarctica re examination of existing cores and unpublished multibeam bathymetric data provide new insight into the lgm configuration of the ice sheet in the region sediment cores from the eastern continental shelf where the east antarctic ice sheet eais drains display a retreat stratigraphy with distal glacimarine sediments overlying proximal glacimarine sediments and till the distinction between distal and proximal glacimarine sediments is based on degrees of marine influence based on grain size distributions and foraminiferal abundance and diversity glacimarine sediments yielded ams radiocarbon ages that span the past 30 476 cal yr bp indicating that retreat of the eais from the continental shelf occurred prior to the lgm multibeam swath bathymetry data show mega scale glacial lineations in two troughs on the southern continental shelf which indicates the existence of two ice streams draining the west antarctic ice sheet wais more subtle lineations within filchner trough imply more sluggish flow across bedrock and older strata within this trough although there are no radiocarbon ages to absolutely constrain the timing of this grounding event on the southern continental shelf we interpret the lineations as lgm age based on their pristine nature this interpretation is consistent with results from other sectors of the west antarctic continental shelf where compelling evidence for significant wais advance during the lgm exists in the weddell sea this apparent diachronous behavior of the eais and wais is consistent with results from onshore studies

evolution of the antarctic ice sheet throughout the last deglaciation a study with a new coupled climate north and south hemisphere ice sheet model the aim of this paper is to assess through the understanding of deglaciation processes the contribution of the antarctic ice sheet to sea level rise during the last deglaciation to achieve this goal we use an earth system model in which the interactions between the atmosphere the ocean the vegetation and the northern and antarctic ice sheets are represented this new tool allows the simulation of the evolution of the antarctic ice volume which starts to decrease at around 15 ka at the end of deglaciation the melting of the antarctic ice sheet contributes to an ice equivalent sea level rise of 9 5 m in the standard experiment and 17 5 m in a more realistic sensitivity experiment accounting for a different bathymetry in the weddell sea which succeeds in producing both major ice shelves ross and ronne filchner in both experiments the melting of all ice sheets contributes to 121 5 m and 129 5 m respectively which is very consistent with data the new coupled model provides a timing and amplitude of the antarctic deglaciation different from those previously obtained by prescribing the temperature record from the vostok antarctic ice core 78 27 s 106 52 e as a uniform temperature forcing sensitivity experiments have also been performed to analyse the impact of the parameters at the origin of the deglaciation process insolation changes atmospheric co2 variation basal melting and sea level rise all those parameters have an influence on the timing of the deglaciation the prescribed global sea level rise is shown to be a major forcing factor for the evolution of the antarctic ice volume during the last deglaciation we quantify the direct effect of the sea level rise due to the northern hemisphere ice sheet melting on the grounding line retreat which in turn favours enhancement of grounded ice flow by lowering the buttressing effect of ice shelves

glacial interglacial ice stream stability in the weddell sea embayment antarctica the resilience of the antarctic ice sheet and its effect on global sea level depends on the dynamics of ice streams antarctic ice streams are known to be responsive to changes at the ocean interface and as expected most have thinned in response to ocean warming and sea level rise since the last glacial maximum lgm here we provide direct and unexpected evidence that points toward the glacial interglacial stability of the slessor and recovery glaciers ice streams of the east antarctic ice sheet eais which merge with the west antarctic ice sheet wais to form the filchner ice shelf in the weddell sea embayment cosmogenic nuclide measurements in the shackleton range suggest that the slessor and recovery ice streams were not significantly thicker than today during the lgm we hypothesise that the glaciers did not thicken because the grounding line was not able to migrate seaward beyond the deep thiel crary trough beneath the filchner ice shelf immediately offshore this discovery reveals how a topographic threshold can affect the dynamics of ice streams it also reduces uncertainties on the thickness extent and volume of the antarctic ice sheet in a large but unknown sector of the antarctic ice sheet it constrains the potential sea level rise from antarctica it helps explain observed anomalies in glacio isostatic adjustment above all it suggests that the behaviour of the atlantic facing weddell sea sector of the wais contrasts with that of the pacific facing ross and amundsen sea sectors

antarctic mass rates from grace 1 we estimate mass trends over antarctica using gravity variations observed by the gravity recovery and climate experiment grace satellite mission during its first 3 5 years april 2002 november 2005 an image of surface mass trends is constructed from 1 1 pixels over the entire continent and shows two prominent features a region of mass loss along the coast of west antarctica and one of accumulation in east antarctica after adjusting for bias due to smoothing and to grace s limited spatial resolution and removing post glacial rebound pgr effects the rate in west antarctica is 77 14 km3 year similar to a recent estimate of ice mass loss from satellite altimetry and remote sensing data the prominent east antarctic feature in the enderby land region has a rate of 80 16 km3 year published snow ice mass rates from remote sensing measurements indicate approximate ice mass balance in this region suggesting that this feature is either from unquantified snow accumulation in this region or more likely due to unmodeled pgr

an indicator of the multiple equilibria regime of the atlantic meridional overturning circulation recent model results have suggested that there may be a scalar indicator s monitoring whether the atlantic meridional overturning circulation moc is in a multiple equilibrium regime the quantity s is based on the net freshwater transport by the moc into the atlantic basin it changes sign as soon as the steady atlantic moc enters the multiple equilibrium regime because of an increased freshwater input in the northern north atlantic this paper addresses the issue of why the sign of s is such a good indicator for the multiple equilibrium regime changes in the atlantic freshwater budget over a complete bifurcation diagram and in finite amplitude perturbation experiments are analyzed in a global ocean circulation model the authors show that the net anomalous freshwater transport into or out of the atlantic resulting from the interactions of the velocity perturbations and salinity background field is coupled to the background steady state state freshwater budget and hence to s the sign of s precisely shows whether this net anomalous freshwater transport is stabilizing or destabilizing the moc therefore it can indicate whether the moc is in a single or multiple equilibrium regime

a community based geological reconstruction of antarctic ice sheet deglaciation since the last glacial maximum a robust understanding of antarctic ice sheet deglacial history since the last glacial maximum is important in order to constrain ice sheet and glacial isostatic adjustment models and to explore the forcing mechanisms responsible for ice sheet retreat such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and sub antarctic islands here we report a new synthesis of those datasets based on an accompanying series of reviews of the geological data organised by sector we present a series of timeslice maps for 20 ka 15 ka 10 ka and 5 ka including grounding line position and ice sheet thickness changes along with a clear assessment of levels of confidence the reconstruction shows that the antarctic ice sheet did not everywhere reach the continental shelf edge at its maximum that initial retreat was asynchronous and that the spatial pattern of deglaciation was highly variable particularly on the inner shelf the deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small antarctic contribution to meltwater pulse 1a we discuss key areas of uncertainty both around the continent and by time interval and we highlight potential priorities for future work the synthesis is intended to be a resource for the modelling and glacial geological community

past and future grounding line retreat of the west antarctic ice sheet the history of deglaciation of the west antarctic ice sheet wais gives clues about its future southward grounding line migration was dated past three locations in the ross sea embayment results indicate that most recession occurred during the middle to late holocene in the absence of substantial sea level or climate forcing current grounding line retreat may reflect ongoing ice recession that has been under way since the early holocene if so the wais could continue to retreat even in the absence of further external forcing

late quaternary grounded ice extent in the filchner trough weddell sea antarctica new marine geophysical evidence the last glacial maximum lgm ca 23 19 ka bp extent of grounded ice in the filchner trough a major cross shelf trough extending seaward from the filchner ice shelf in the southern weddell sea has been much debated here we present data from the first extensive multibeam swath bathymetry and sub bottom acoustic profiling surveys in the filchner trough that include several parallel survey lines with overlapping swaths we interpret these new data combined with published observations and radiocarbon dates from sediment cores as indicating that the grounding line in the filchner trough during the lgm advanced beyond the middle shelf probably to within 40 km of the shelf break and possibly reached the shelf break three different hypotheses are discussed that could reconcile this interpretation with interpretations based on ice coring and surface exposure age data that lgm ice surface elevations in areas draining into the filchner and ronne ice shelves were no more than a few hundred metres higher than today 1 ice plain conditions extended along most of the filchner trough 2 the ice shelf advanced and thickened so that it touched down on the continental shelf for a short period 3 lgm ice drainage pathways in the interior of the weddell sea embayment were different from those observed today

selective glacial erosion and weathering zones in the coastal mountains of marie byrd land antarctica in the coastal mountains of marie byrd land antarctica there is a juxtaposition of ice moulded landforms at lower altitudes and upstanding summits with weathered surfaces bearing tors this paper uses geomorphological mapping and exposure dating to test two hypotheses commonly used to explain such a landscape contrast either the pattern reflects contrasts in glacial erosion related to the basal thermal regime beneath a former ice sheet or it represents a periglacial trimline marking the upper limit of ice cover during the last glacial maximum lgm cosmogenic nuclide measurements on erratics show that the mountains were covered by ice on several occasions most recently during the lgm similar measurements on bedrock show that fragile landforms on weathered surfaces survived many glaciations nuclide concentrations in bedrock indicate both that subglacial erosion is insignificant and that ice free periods of periglacial weathering are longer at higher elevations we conclude that the pattern of landscape modification reflects both topographically controlled contrasts in the basal thermal regime of overriding ice and the longer exposure to periglacial conditions at higher elevations in addition the combination of nuclide data and the wider pattern of striations shows that the lgm ice cover was thinner than predicted by ice sheet models assuming equilibrium conditions that ice sheet thinning has occurred from 10 400 years ago to the present and that regional flow by overriding ice has been replaced by radial ice flow from local glaciers centred on individual mountain massifs

ice dammed lateral lake and epishelf lake insights into holocene dynamics of marguerite trough ice stream and george vi ice shelf alexander island antarctic peninsula abstract we present new data regarding the past dynamics of marguerite trough ice stream george vi ice shelf and valley glaciers from ablation point massif on alexander island antarctic peninsula this ice free oasis preserves a geological record of ice stream lateral moraines ice dammed lakes ice shelf moraines and valley glacier moraines which we dated using cosmogenic nuclide ages we provide one of the first detailed sediment landform assemblage descriptions of epishelf lake shorelines marguerite trough ice stream imprinted lateral moraines against eastern alexander island at 120 m at ablation point massif during deglaciation lateral lakes formed in the ablation and moutonnee valleys dammed against the ice stream in george vi sound exposure ages from boulders on these shorelines yielded ages of 13 9 to 9 7 ka following recession of the ice stream george vi ice shelf formed in george vi sound an epishelf lake formed at 15 20 m asl in ablation and moutonnee valleys dated from 9 4 to 4 6 ka suggesting that the lake was stable and persistent for some 5000 years lake level lowering occurred after this with the lake level at 12 m at 3 1 0 4 ka and at 5 m asl today a readvance of the valley glaciers on alexander island at 4 4 0 7 ka is recorded by valley glacier moraines overlying epishelf lake sediments we speculate that the glacier readvance which occurred during a period of warmth may have been caused by a dynamic response of the glaciers to a lowering in surface elevation of george vi ice shelf

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

millennial scale variability in antarctic ice sheet discharge during the last deglaciation two well dated high resolution records of iceberg rafted debris are presented that document variability in antarctic ice sheet discharge during the last deglaciation global sea levels have risen by more than 100 metres since the last glacial maximum around 20 000 years ago with several meltwater pulses of several metres or more in the most dramatic of these meltwater pulse 1a sea level rose by about 16 metres at 14 600 years ago this magnitude of sea level rise strongly suggests major antarctica contributions but to date there has been no firm physical evidence now michael weber and colleagues present a record of iceberg rafted debris from the scotia sea and show clear signals of pulsed iceberg release from antarctica as early as 19 000 years ago the largest iceberg release occurred during meltwater pulse 1a providing the long sought confirmation of antarctic contributions to this major jump in sea level rise our understanding of the deglacial evolution of the antarctic ice sheet ais following the last glacial maximum 26 000 19 000 years ago 1 is based largely on a few well dated but temporally and geographically restricted terrestrial and shallow marine sequences2 3 4 this sparseness limits our understanding of the dominant feedbacks between the ais southern hemisphere climate and global sea level marine records of iceberg rafted debris ibrd provide a nearly continuous signal of ice sheet dynamics and variability ibrd records from the north atlantic ocean have been widely used to reconstruct variability in northern hemisphere ice sheets5 but comparable records from the southern ocean of the ais are lacking because of the low resolution and large dating uncertainties in existing sediment cores here we present two well dated high resolution ibrd records that capture a spatially integrated signal of ais variability during the last deglaciation we document eight events of increased iceberg flux from various parts of the ais between 20 000 and 9 000 years ago in marked contrast to previous scenarios which identified the main ais retreat as occurring after meltwater pulse 1a3 6 7 8 and continuing into the late holocene epoch the highest ibrd flux occurred 14 600 years ago providing the first direct evidence for an antarctic contribution to meltwater pulse 1a climate model simulations with ais freshwater forcing identify a positive feedback between poleward transport of circumpolar deep water subsurface warming and ais melt suggesting that small perturbations to the ice sheet can be substantially enhanced providing a possible mechanism for rapid sea level rise

west antarctic ice sheet elevations in the ohio range geologic constraints and ice sheet modeling prior to the last highstand abstract knowledge of the timing and extent of past west antarctic ice sheet wais elevation changes provides insight to the wais response to sea level and climate forcing as well as constraints for ice sheet models trimlines and erratics indicate that maximum ice elevation at the ohio range located near the wais divide was 125 m above the present ice surface and was reached at 10 ka however 3 he and 10 be exposure ages of most granitic erratics and supra glacial boulders in adjacent blue ice areas are older than the last highstand and provide constraints on earlier interior wais elevation changes although diffusive loss of 3 he occurs in quartz an excellent correlation between 3 he and 10 be concentrations in samples up to 400 ka is observed in the ohio range demonstrating the utility of 3 he measurements in antarctic quartz the correlation is used to calculate equivalent 10 be exposure ages from the larger 3 he data set the exposure ages occur in distinct clusters 10 20 ka 70 80 ka 130 140 ka and 180 190 ka that we relate to pulses in the emergence of englacial debris in localized blue ice ablation areas a combined ice sheet ice shelf model predicts that wais elevations near the ohio range have varied only 125 m over the last 200 kyr with highstands at 10 ka and 130 ka in good agreement with observations of trimlines and peaks in the exposure age distribution at the ohio range in the model interior wais elevations are controlled by the interaction of accumulation rates and ice dynamics related to ice sheet ocean interactions at the grounding line wais highstands occur early in interglacial periods during intervals of warmer temperatures and high accumulation rates prior to the arrival of a wave of thinning we hypothesize that the correspondence of rising regional wais elevation with debris pulses relates to increased ice debris flux and ablation in the local blue ice areas resulting from the warmer temperatures the occurrence of clasts with exposure ages up to 200 ka on the wais surface indicates elevation changes near the ohio range were limited in extent during stage 5e the geologic observations combined with model results place constraints on wais geometry during stage 5e and limit the wais contribution to the higher sea levels observed during the last interglacial to 3 m

low post glacial rebound rates in the weddell sea due to late holocene ice sheet readvance many ice sheet reconstructions assume monotonic holocene retreat for the west antarctic ice sheet but an increasing number of glaciological observations infer that some portions of the ice sheet may be readvancing following retreat behind the present day margin a readvance in the weddell sea region can reconcile two outstanding problems i the present day widespread occurrence of seemingly stable ice streams grounded on beds that deepen inland and ii the inability of models of glacial isostatic adjustment to match present day uplift rates by combining a suite of ice loading histories that include a readvance with a model of glacial isostatic adjustment we report substantial improvements to predictions of present day uplift rates including reconciling one problematic observation of land sinking we suggest retreat behind present grounding lines occurred when the bed was lower and isostatic recovery has since led to shallowing ice sheet re grounding and readvance the paradoxical existence of grounding lines in apparently unstable configurations on reverse bed slopes may be resolved by invoking the process of unstable advance in accordance with our load modelling

upper ocean singular vectors of the north atlantic climate with implications for linear predictability and variability the limits of predictability of the meridional overturning circulation moc and upper ocean temperatures due to errors in ocean initial conditions and model parametrizations are investigated in an idealized configuration of an ocean general circulation model gcm singular vectors optimal perturbations are calculated using the gcm its tangent linear and adjoint models to determine an upper bound on the predictability of north atlantic climate the maximum growth time scales of moc and upper ocean temperature anomalies excited by the singular vectors are 18 5 and 13 years respectively and in part explained by the westward propagation of upper ocean anomalies against the mean flow as a result of the linear interference of non orthogonal eigenmodes of the non normal dynamics the ocean dynamics are found to actively participate in the significant growth of the anomalies an initial density perturbation of merely 0 02 kg m 3 is found to lead to a 1 7 sv moc anomaly after 18 5 years in addition northern hemisphere upper ocean temperature perturbations can be amplified by a factor of 2 after 13 years the growth of upper ocean temperature and moc anomalies is slower and weaker when excited by the upper ocean singular vectors than when the deep ocean is perturbed this leads to the conclusion that predictability experiments perturbing only the atmospheric initial state may overestimate the predictability time interestingly optimal moc and upper ocean temperature excitations are only weakly correlated thus limiting the utility of sst observations to infer moc variability the excitation of anomalies in this model might have a crucial impact on the variability and predictability of atlantic climate the limit of predictability of the moc is found to be different from that of the upper ocean heat content emphasizing that errors in ocean initial conditions will affect various measures differently and such uncertainties should be carefully considered in decadal prediction experiments copyright c

cosmogenic nuclides 10be and 26al imply limited antarctic ice sheet thickening and low erosion in the shackleton range for 1 m y concentrations of the cosmogenic nuclides 1 0 be and 2 6 al on bedrock surfaces in the shackleton range antarctica indicate minimum exposure ages between 3 0 03 and 1 16 0 10 ma the isotope data indicate that the maximum long term erosion rate is 0 10 0 35 m m y and the ratios suggest no prolonged periods of burial by cold based ice the findings are important because of the location of the massif close to the junction of the east antarctic ice sheet and the landward extent of the filchner ice shelf these results point to three conclusions first the massif has not been overridden by the east antarctic ice sheet during the late quaternary rather moraines 200 340 m above outlet glaciers are likely to represent the maximum thickening of the filchner ronne ice shelf during the quaternary second the high radionuclide concentrations on bedrock surfaces one of which is striated suggest that some glacial landforms were created in at least pliocene or more likely miocene time third the exceptionally low erosion rates imply that the modern cold arid climate has persisted for millions of years these findings provide evidence of old stable landscapes over a wider area of antarctica than the mc murdo dry valleys

controls on subaerial erosion rates in antarctica erosion rates offer insight on landscape development and the relative importance of chemical and physical processes of weathering minimal chemical weathering makes antarctica an ideal location in which to compare the physical weathering of carbonate rocks to other lithologies here we report the first cosmogenic nuclide derived erosion rates for carbonate rocks in antarctica carbonate samples collected in the southernmost ellsworth mountains reflect a 36cl erosion rate of 0 22 0 02 mm ka this erosion rate is consistent with other reported antarctic erosion rates but is lower than 36cl erosion rates derived from other arid regions in the world these results are integrated with a continent wide reanalysis of 28 erosion rate studies 200 measurements which comprise numerous rock types and other cosmogenic nuclides by combining cosmogenic nuclide derived erosion rates across studies the larger trends provide insight into factors e g lithology glacial history and availability of abrasive material affecting subaerial erosion rates in antarctica statistical analysis of the compiled data set shows differences based on lithology with sandstone having the largest range of erosion rates the compiled data also reveals higher erosion rates in areas with a large potential sediment supply like the dry valleys samples collected from boulders yield lower erosion rates than those collected from bedrock likely due to a combination of physical processes that affect boulders and bedrock differently and glacial history which can affect the apparent cosmogenic nuclide derived erosion rate

optimal excitation of amoc decadal variability links to the subpolar ocean this study describes the excitation of variability of the atlantic meridional overturning circulation amoc by optimal perturbations in surface temperature and salinity our approach is based on a generalized stability analysis within a realistic ocean general circulation model which extends the conventional linear stability analysis to transient growth unlike methods based on singular value decomposition our analysis invokes an optimization procedure using lagrangian multipliers which is a more general approach allowing us to impose relevant constraints on the perturbations and use linear measures of the amoc meridional volume and heat transports we find that the structure of the optimal perturbations is characterized by anomalies in surface temperature or salinity centered in the subpolar regions of the north atlantic off the east coasts of greenland and canada south of the denmark strait the maximum impact of such perturbations on the amoc is reached after 7 9 yr this is a robust result independent of the perturbations type the optimization measures the model surface boundary conditions or other constraints the transient growth involves the following mechanism after the initial positive surface density perturbation reaches the deep ocean it generates a cyclonic geostrophic flow that extracts a zonally varying temperature anomaly from the mean temperature field in the upper ocean in turn the anomalous zonal temperature gradient induces by thermal wind balance a northward flow in the upper ocean and a southward flow in the deep ocean thus strengthening the amoc subsequently the transient growth gives way to a decaying oscillation corresponding to a damped oceanic eigenmode with a period of about 24 yr this mode is controlled by westward propagating large scale thermal rossby waves modifying the density field in the north atlantic and hence the amoc simple estimates show that realistic changes in salinity or temperature in the upper ocean such as those due to the great salinity anomaly can induce amoc variations of several sverdups via this mechanism or 10 20 of the mean overturning an idealized model is formulated to investigate the transient growth and highlight the role of mean convection in communicating surface density anomalies to the deep ocean 2014 published by elsevier ltd

tritium corrected 14c and atmospheric noble gas corrected 4he applied to deduce ages of mixed groundwaters examples from the baden region switzerland abstract mixing of recent water post 1953 and old water up to a limit of 25 000 years can be identified by tritium and 14 c values the age of an old endmember may be deduced applying a tritium correction to the measured 14 c value 4 he may be used as a second semi quantitative age indicator of old groundwaters overlapping the 14 c range and extending beyond it tritium may be used to deduce the radiogenic 4 he concentration in the old endmember in addition the atmospheric noble gases may be used to check he retention and to correct for losses the corrected 14 c and 4 he values may be used to check concordance between computed ages in mixed and unmixed groundwaters concordant ages indicate that the basic dating premises were not violated whereas discordant ages indicate that secondary processes were active the suggested approach is demonstrated for a number of springs and wells studied in the regions of baden and yverdon switzerland

major ice sheet change in the weddell sea sector of west antarctica over the last 5 000 years until recently little was known about the weddell sea sector of the west antarctic ice sheet in the last 10 years a variety of expeditions and numerical modelling experiments have improved knowledge of its glaciology glacial geology and tectonic setting two of the sector s largest ice streams rest on a steep reverse sloping bed yet despite being vulnerable to change satellite observations show contemporary stability there is clear evidence for major ice sheet reconfiguration in the last few thousand years however knowing precisely how the ice sheet has changed in the past and when would allow us to better understand whether it is now at risk two competing hypotheses have been established for this glacial history in one the ice sheet retreated and thinned progressively from its last glacial maximum position retreat stopped at or very near the present position in the late holocene alternatively in the late holocene the ice sheet retreated significantly upstream of the present grounding line and then advanced to the present location due to glacial isostatic adjustment and ice shelf and ice rise buttressing both hypotheses point to data and theory in their support yet neither has been unequivocally tested or falsified here we review geophysical evidence to determine how each hypothesis has been formed where there are inconsistencies in the respective glacial histories how they may be tested or reconciled and what new evidence is required to reach a common model for the late holocene ice sheet history of the weddell sea sector of west antarctica

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

the last glaciation of bear peninsula central amundsen sea embayment of antarctica constraints on timing and duration revealed by in situ cosmogenic 14c and 10be dating abstract ice streams in the pine island thwaites region of west antarctica currently dominate contributions to sea level rise from the antarctic ice sheet predictions of future ice mass loss from this area rely on physical models that are validated with geological constraints on past extent thickness and timing of ice cover however terrestrial records of ice sheet history from the region remain sparse resulting in significant model uncertainties we report glacial geological evidence for the duration and timing of the last glaciation of hunt bluff in the central amundsen sea embayment a multi nuclide approach was used measuring cosmogenic 10be and in situ 14c in bedrock surfaces and a perched erratic cobble bedrock 10be ages 118 144 ka reflect multiple periods of exposure and ice cover not continuous exposure since the last interglacial as had previously been hypothesized in situ 14c dating suggests that the last glaciation of hunt bluff did not start until 21 1 5 8 ka probably during the last glacial maximum and finished by 9 6 0 9 ka at the same time as ice sheet retreat from the continental shelf was complete thickening of ice at hunt bluff most likely post dated the maximum extent of grounded ice on the outer continental shelf flow re organisation provides a possible explanation for this with the date for onset of ice cover at hunt bluff providing a minimum age for the timing of convergence of the dotson and getz tributaries to form a single palaeo ice stream this is the first time that timing of onset of ice cover has been constrained in the amundsen sea embayment

ice flow reorganization in west antarctica 2 5 kyr ago dated using radar derived englacial flow velocities we date a recent ice flow reorganization of an ice divide in the weddell sea sector west antarctica using a novel combination of inverse methods and ice penetrating radars we invert for two dimensional ice flow within an ice divide from data collected with a phase sensitive ice penetrating radar while accounting for the effect of firn on radar propagation and ice flow by comparing isochronal layers simulated using radar derived flow velocities with internal layers observed with an impulse radar we show that the divide s internal structure is not in a steady state but underwent a disturbance potentially implying a regional ice flow reorganization 2 5 1 8 2 9 kyr b p our data are consistent with slow ice flow in this location before the reorganization and the ice divide subsequently remaining stationary these findings increase our knowledge of the glacial history of a region that lacks dated constraints on late holocene ice sheet retreat and provides a key target for models that reconstruct and predict ice sheet behavior

lower satellite gravimetry estimates of antarctic sea level contribution a new model of glacial isostatic adjustment used in conjunction with grace satellite data suggests that ice loss from antarctica is contributing 0 19 millimetres per year to global mean sea level which is substantially less than previous grace based estimates estimates for recent mass loss from antarctica vary widely making it difficult to calculate any subsequent contributions to sea level rise one prominent approach uses the grace gravity recovery and climate experiment satellites to detect changes in gravity but the final estimates are dependent on the modelled response of the continent to changes in ice loading over time and to changes in lithospheric elastic rebound matt king and colleagues apply a new model of this glacial isostatic adjustment to the grace data and estimate antarctic mass loss between 2002 and 2010 to be about 69 gigatonnes per year much lower than previous estimates and equivalent to an annual sea level rise of about 0 2 millimetres recent estimates of antarctica s present day rate of ice mass contribution to changes in sea level range from 31 gigatonnes a year gt yr 1 ref 1 to 246 gt yr 1 ref 2 a range that cannot be reconciled within formal errors3 time varying rates of mass loss2 4 5 6 contribute to this but substantial technique specific systematic errors also exist3 in particular estimates of secular ice mass change derived from gravity recovery and climate experiment grace satellite data are dominated by significant uncertainty in the accuracy of models of mass change due to glacial isostatic adjustment7 8 gia here we adopt a new model of gia developed from geological constraints which produces gia rates systematically lower than those of previous models and an improved fit to independent uplift data9 after applying the model to 99 months from august 2002 to december 2010 of grace data we estimate a continent wide ice mass change of 69 18 gt yr 1 0 19 0 05 mm yr 1 sea level equivalent this is about a third to a half of the most recently published grace estimates2 5 which cover a similar time period but are based on older gia models plausible gia model uncertainties and errors relating to removing longitudinal grace artefacts destriping confine our estimate to the range 126 gt yr 1 to 29 gt yr 1 0 08 0 35 mm yr 1 sea level equivalent we resolve 26 independent drainage basins and find that antarctic mass loss and its acceleration is concentrated in basins along the amundsen sea coast outside this region we find that west antarctica is nearly in balance and that east antarctica is gaining substantial mass

stochastic models of the meridional overturning circulation time scales and patterns of variability the global meridional overturning circulation moc varies over a wide range of space and time scales in response to fluctuating weather perturbations that may be modelled as stochastic forcing th

modelling antarctic sea level data to explore the possibility of a dominant antarctic contribution to meltwater pulse ia abstract we compare numerical predictions of glaciation induced sea level change to data from 8 locations around the antarctic coast in order to test if the available data preclude the possibility of a dominant antarctic contribution to meltwater pulse ia mwp ia results based on a subset of 7 spherically symmetric earth viscosity models and 6 different antarctic deglaciation histories indicate that the sea level data do not rule out a large antarctic source for this event our preliminary analysis indicates that the weddell sea is the most likely source region for a large 9 m antarctic contribution to mwp ia the ross sea is also plausible as a significant contributor 5 m from a sea level perspective but glacio geological field observations are not compatible with such a large and rapid melt from this region our results suggest that the lambert glacier component of the east antarctic ice sheet experienced significant retreat at the time of mwp ia but only contributed 0 15 m eustatic sea level change all of the ice models considered under predicted the isostatic component of the sea level response in the antarctic peninsula and the soya coast region of the east antarctic ice sheet indicating that the maximum ice thickness in these regions is underestimated it is therefore plausible that ice melt from these areas the antarctic peninsula in particular could have made a significant contribution to mwp ia

interdecadal variations in north atlantic sea surface temperature and associated atmospheric conditions abstract evidence is presented for a distinct pattern of ocean atmosphere relationship associated with interdecadal variability in the north atlantic region using a century of surface marine observations it is shown that middle and high latitude sea surface temperature sst display a long term fluctuation with negative anomalies before 1920 and during the 1970s and 1980s positive sst conditions prevailed from about 1930 to 1960 the pattern of interdecadal sst variability is constructed by subtracting the average field during 15 cold years from that during a similar interval of warm years the early century warming and the more recent cooling display a similar spatial pattern in both cases the pattern is basin scale and largely of one polarity with maxima in the vicinity of iceland in the labrador sea and northeast of bermuda the corresponding differences in surface atmospheric conditions are determined by averaging and subtracting in the same manner fields of sea level pressure slp and surf

controls on last glacial maximum ice extent in the weddell sea embayment antarctica the weddell sea sector of the antarctic ice sheet is hypothesized to have made a significant contribution to sea level rise since the last glacial maximum using a numerical flowline model we investigate the controls on grounding line motion across the eastern weddell sea and compare our results with field data relating to past ice extent specifically we investigate the influence of changes in ice temperature accumulation sea level ice shelf basal melt and ice shelf buttressing on the dynamics of the foundation ice stream we find that ice shelf basal melt plays an important role in controlling grounding line advance while a reduction in ice shelf buttressing is found to be necessary for grounding line retreat there are two stable positions for the grounding line under glacial conditions at the northern margin of berkner island and at the continental shelf break global mean sea level contributions associated with these two scenarios are 50 mm and 130 mm respectively comparing model results with field evidence from the pensacola mountains and the shackleton range we find it unlikely that ice was grounded at the continental shelf break for a prolonged period during the last glacial cycle however we cannot rule out a brief advance to this position or a scenario in which the grounding line retreated behind present during deglaciation and has since re advanced better constraints on past ice sheet and ice shelf geometry ocean temperature and ocean circulation are needed to reconstruct more robustly past behavior of the foundation ice stream

baroclinic instability an oceanic wavemaker for interdecadal variability numerical simulations of coarse resolution idealized ocean basins under constant surface heat flux are analyzed to show that the interdecadal oscillations that emerge naturally in such configurations are driven by baroclinic instability of the mean state and damped by horizontal diffusion when the surface heat fluxes are diagnosed from a spinup in which surface temperatures are strongly restored to apparent atmospheric temperatures the most unstable regions diagnosed by large downgradient eddy heat fluxes are located in the basin northwest corner where the surface heat losses are largest the long wave limit of the baroclinic instability of idealized mean flows in a three layer model with vertical shears as observed in the gcms demonstrates that growth rates of order one cycle per year can be produced locally large enough to amplify thermal anomalies in the face of lateral diffusion the proposed instability mechanism that favors surface intensified perturbations also explains the lack of oscillations if the restoring to a surface climatology is too strong to assess whether this instability process of oceanic origin is robust enough to cause interdecadal variability of coupled ocean atmosphere models a four box ocean atmosphere model is constructed given the large heat capacity of the ocean as compared to the atmosphere the dynamical system that governs the model evolution is reduced to only two degrees of freedom the oceanic overturning thermohaline circulation and the interior north south temperature gradient the authors show that when the baroclinic instability growth rate exceeds the overall dissipation caused by turbulent eddy diffusion in the atmosphere and ocean and infrared back radiation the dynamical system undergoes a hopf bifurcation and interdecadal oscillations emerge through a limit cycle

flow at ice divide triple junctions 2 three dimensional views of isochrone architecture from ice penetrating radar surveys 1 ground based surveys of ice divide triple junctions in two antarctic ice rises the fletcher promontory and berkner island have been carried out using low frequency ice penetrating radars these surveys have focused on understanding the internal layer architecture at and around the triple junctions with a particular emphasis on understanding how the raymond effect operates a variety of features have been observed including raymond cupolas under the junctions bump stacks of varying amplitude with distance from the divide double bumps crooked stacks implying divide motion and the presence of ridges containing weak and strong bump stacks it was generally not possible to elucidate the three dimensional structure by correlation of pick crossovers so instead a least squares cross correlation technique was used which computes nominal age surfaces using radial basis function interpolation double bumps are absent from the central cupola of fletcher promontory permitting us to infer that the ice here has thinned by around 500 m in the past 5000 years estimates of the age scale suggest that there will be recoverable eemian ice a technique for inferring the velocity profile at divides using layer traces and assumed velocities in the flanks is presented

relative sea level history from the lambert glacier region east antarctica and its relation to deglaciation and holocene glacier readvance we present a relative sea level rsl history constrained by ams radiocarbon dated marine freshwater transitions in isolation basins from a site adjacent to the lambert glacier east antarctica the rsl data suggest an initial ice retreat between c 15 370 and 12 660 cal yr b p within this period meltwater pulse ia mwp ia between c 14 600 14 200 and 14 100 13 700 cal yr b p occurred an exceptionally large ice melting event inferred from far field sea level records the rsl curve shows a pronounced highstand of approximately 8 m between c 7570 7270 and 7250 6950 cal yr b p that is consistent with the timing of the rsl highstand in the nearby vestfold hills this is followed by a fall in rsl to the present in contrast to previous findings the isolation of the lakes in the larsemann hills postdates the isolation of lakes with similar sill heights in the vestfold hills an increase in rsl fall during the late holocene may record a decline in the rate of isostatic uplift in the larsemann hills between c 7250 6950 and 2847 2509 cal yr b p that occurred in response to a documented mid holocene glacier readvance followed by a late holocene retreat

controls on interior west antarctic ice sheet elevations inferences from geologic constraints and ice sheet modeling abstract knowledge of the west antarctic ice sheet wais response to past sea level and climate forcing is necessary to predict its response to warmer temperatures in the future the timing and extent of past interior wais elevation changes provides insight to wais behavior and constraints for ice sheet models constraints prior to the last glacial maximum lgm however are rare surface exposure ages of glacial erratics near the wais divide at mt waesche in marie byrd land and at the ohio range in the transantarctic mountains range from 10 ka to 500 ka without a dependence on elevation the probability distribution functions pdf of the exposure ages at both locations are remarkably similar during the last glaciation maximum interior ice elevations as recorded by moraines and erratics were reached between 10 ka and 12 ka however most exposure ages are older than the lgm and cluster around 40 ka and 80 ka the peak in the exposure age distributions at 40 ka includes ages of alpine moraine boulders at mercer ridge in the ohio range comparison of the pdf of exposures ages from the ohio range and mt waesche with the temperature record from the fuji dome ice core indicates that the youngest peak in the exposure age distributions corresponds to the abrupt warming during the last glacial termination a prominent peak in the ohio range pdf corresponds to the penultimate termination stage 5e during the intervening glacial period there is not a consistent relationship between the peaks in the pdf at each location and temperature a combined ice sheet ice shelf model with forcing scaled to marine 18 o predicts that interior wais elevations near the ice divide have varied 300 m over the last glacial cycle peaks in the pdf correspond to model highstands over the last 200 ka in the simulated elevation history maximum ice elevations at ohio range 100 m and mt waesche 60 m occur at 10 ka in agreement with observations from these sites during collapse of the marine portion of the wais ice elevations at ohio range and mt waesche are drawn down at least 200 m below the present ice elevation the good correspondence between the model results and observations at both the ohio range and mt waesche supports the conclusion that interior wais highstands do not occur during glacial maximums rather the highstands are controlled primarily by increased accumulation during temperature maximums that occur early in the interglacials interior down draw events follow highstands resulting from the arrival of a wave of thinning triggered by retreat of the wais grounding line coupled with decreasing accumulation rates

late pleistocene and holocene melting history of the antarctic ice sheet derived from sea level variations abstract spatial and temporal variations of the late pleistocene and holocene sea levels provide important constraints on the melting history of the major ice sheets in this study we have examined the sea level variations at eight sites along the coast of antarctica to investigate the melting history of antarctic ice sheet complexes comparisons of sea level variations between observations and predictions due to glacio hydro isostatic adjustment suggest that the ice thicknesses removed from the last glacial maximum lgm around the weddell sea are significantly thicker than those around the ross embayment sea level observations also indicate that climap derived models predict too much relative sea level change and that consequently ice mass change along the coast has to be scaled down improvement of the late pleistocene antarctic ice model is required to evaluate more accurate predictions of present day geophysical observables associated with this history thus these more accurate predictions can then be subtracted from observables and the residual field can be analyzed to constrain ongoing mass changes from the ice sheet we therefore predicted present day geophysical observables such as the rate of change of solid surface gravity and crustal movement these geophysical observables based on the ice models constructed from observed sea level variations are significantly different from those based on previous models on the other hand detailed sea level observations around syowa indicate the existence of a sea level highstand of about 10 m around 40 kyr bp to investigate these sea level observations we have performed preliminary numerical calculations comparisons between these observations and predictions indicate the synchronous melting of the northern and southern ice sheets suggesting a strong link between the melting histories of both polar ice sheets

periglacial features in patriot hills ellsworth mountains antarctica abstract this work describes periglacial features identified at patriot hills at the southernmost part of ellsworth mountains antarctica during the 2008 2009 brazilian antarctic expedition and discusses their morphogenetic environment identified periglacial features were classified into a rock glacier like landform b slightly creeping debris mantled slopes c steep debris mantled slopes and d rock falls results obtained from sediment sample analysis suggest activity and passive movement of a rock glacier like landform albeit minimal wind seems to play an important role in patriot hills local geomorphology periglacial features such as slightly creeping debris mantled slope appear to have preferred slope orientation they are commonly found onto slopes where the katabatic wind flows down slopewash and groundwater movement processes may be limited or non existent since most snow disappears through sublimation

preservation of arctic landscapes overridden by cold based ice sheets for nearly 40 years a massive well preserved glaciomarine delta more than 54 000 years old and ancillary landforms have formed the cornerstone of models positing limited ice sheet extent in arctic canada during the late wisconsinan we present exposure ages for large boulders on the delta surface which coupled with preservation of relict landforms demonstrate that the region was covered by minimally erosive cold based ice during the late wisconsinan our data suggest that surficial features commonly used to define the pattern of late wisconsinan ice movement cannot be used on their own to constrain late wisconsinan ice sheet margins in arctic regions

the antarctic ice sheet during the last glacial maximum and its subsequent retreat history a review abstract an emerging body of evidence from studies of the last glacial interglacial cycle suggests that the east and west antarctic ice sheets have not advanced and retreated in concert the west antarctic ice sheet advanced to the outer shelf in most regions during the last glacial maximum lgm the retreat from the shelf commenced shortly after the lgm and continued into the late holocene the west antarctic ice sheet in ross and amundsen seas slid across a deforming bed at least during the final phases of extended glaciation this implies that at this time the ice sheet had a low profile differences in the number and locations of grounding zone wedges and smaller grounding zone features from trough to trough imply that individual west antarctic ice sheet ice streams retreated episodically details concerning the expansion retreat and behavior of the east antarctic ice sheet eais are more sparse the picture emerging is that the eais did not expand to the continental shelf edge during the lgm rather it achieved a maximum extent of a mid shelf position in some locations while in other areas the ice terminus was situated near its present location the timing of retreat along sectors within the eais appears diachronous and in places occurred prior to the lgm the antarctic peninsula shelf contained considerably more ice during the lgm than previously proposed the results presented in this paper support more recent published ice sheet models that call for greater contributions of melting ice from west antarctica including the antarctic peninsula to the post glacial rise in sea level

late quaternary evolution of reedy glacier antarctica abstract fresh deposits above the margins of reedy glacier show that maximum ice levels during the last glaciation were several hundred meters above present near the glacier mouth and converged to less than 60 m above the present day surface at the head of the glacier exposure ages of samples from five sites along its margin show that reedy glacier and its tributaries thickened asynchronously between 17 and 7 kyr bp at the quartz hills located midway along the glacier maximum ice levels were reached during the period 17 14 kyr bp farther up glacier the ice surface reached its maximum elevation more recently 14 7 10 2 kyr bp at the caloplaca hills 9 1 7 7 kyr bp at mims spur and around 7 kyr bp at hatcher bluffs we attribute this time transgressive behavior to two different processes at the glacier mouth growth of grounded ice and subsequent deglaciation in the ross sea embayment caused a wave of thickening and then thinning to propagate up glacier during the lateglacial and holocene increased snow accumulation on the east antarctic ice sheet caused transient thickening at the head of the glacier an important result of this work is that moraines deposited along reedy glacier during the last ice age cannot be correlated to reconstruct a single glacial maximum longitudinal profile the profile steepened during deglaciation of the ross sea thinning at the quartz hills after 13 kyr bp while thickening upstream near its confluence with mercer ice stream rapid thinning beginning prior to 7 8 kyr bp reduced the level of reedy glacier to close to its present level thinning over the past 1000 years has lowered the glacier by less than 20 m

deglacial meltwater discharge north atlantic deep circulation and abrupt climate change high resolution paleogeochemical data from the north atlantic ocean indicate that in the interval 15 000 to 10 000 14c years before present b p north atlantic deep water nadw production was decreased or eliminated four times at about 14 500 and probably older 13 500 12 000 and 10 500 years b p each of these changes occurred at the same time as abrupt events of meltwater discharge to the surface ocean inferred from oxygen isotope studies of planktonic foraminifera and from glacial geological studies on land in addition each of these times may be associated with brief episodes of cooler climate in the north atlantic region the best example of which is the younger dryas cooling of 10 500 years ago these results support models linking meltwater discharge decreased nadw production and decreased north atlantic heat flux

antarctic palaeo ice streams we review the geomorphological sedimentological and chronological evidence for palaeo ice streams on the continental shelf of antarctica and use this information to investigate basal conditions and processes and to identify factors controlling grounding line retreat a comprehensive circum antarctic inventory of known palaeo ice streams their basal characteristics and minimum ages for their retreat following the last glacial maximum lgm is also provided antarctic palaeo ice streams are identified by a set of diagnostic landforms that nonetheless display considerable spatial variability due to the influence of substrate flow velocity and subglacial processes during the lgm palaeo ice streams extended via bathymetric troughs to the shelf edge of the antarctic peninsula and west antarctica and typically to the mid outer shelf of east antarctica the retreat history of the antarctic ice sheet since the lgm is characterised by considerable asynchroneity with individual ice streams exhibiting different retreat histories this variability allows antarctic palaeo ice streams to be classified into discrete retreat styles and the controls on grounding line retreat to be investigated such analysis highlights the important impact of internal factors on ice stream dynamics such as bed characteristics and slope and drainage basin size whilst grounding line retreat may be triggered and to some extent paced by external atmospheric and oceanic forcing the individual characteristics of each ice stream will modulate the precise timing and rate of retreat through time

holocene deglaciation of marie byrd land west antarctica surface exposure ages of glacial deposits in the ford ranges of western marie byrd land indicate continuous thinning of the west antarctic ice sheet by more than 700 meters near the coast throughout the past 10 000 years deglaciation lagged the disappearance of ice sheets in the northern hemisphere by thousands of years and may still be under way these results provide further evidence that parts of the west antarctic ice sheet are on a long term trajectory of decline west antarctic melting contributed water to the oceans in the late holocene and may continue to do so in the future

decoding the dipstick thickness of siple dome west antarctica at the last glacial maximum ice thickness in west antarctica at the last glacial maximum lgm is poorly known yet is key information for understanding ice streams and interpreting ice cores although trim lines moraine limits and exposure age dating provide geologic constraints on ice thickness near the transantarctic mountains and in marie byrd land lack of exposed bedrock hampers traditional geologic methods in a central 2 3 10 6 km 2 region here we infer ice sheet thickness changes in the central ross sea embayment by using a tran sient ice flow model to find combinations of accumulation rate and ice sheet thickness histories that match the depth age relationship and the measured layer thickness pattern in the siple dome ice core after we reject unreasonable accumulation rate histories the remaining history pairs indicate thinning of 200 400 m since the lgm our estimate is lower than previous reconstructions that were constrained by geologic evidence from the transantarctic mountains and by marine data from the ross sea floor which indicate that a grounded ice sheet extended to the continental shelf margin during the last glacial period low surface elevations in the central ross sea embayment during the lgm do not preclude thicker ice along its boundaries however if this grounded ice sheet came over 1000 km from interior west antarctica as is usually assumed then it had very low surface slope requiring a very slippery bed alternatively the grounded ross sea ice might have flowed from the transantarctic mountains and western marie byrd land

the ross sea s contribution to eustatic sea level during meltwater pulse 1a abstract radiocarbon dates obtained from ross sea sediments combined with constraints on maximum ice extent based on sedimentological data and ice sheet modeling results indicate that the ross embayment antarctica is unlikely to have been a substantial contributor to meltwater pulse mwp 1a at 12 5 14c ka the ice sheet in the ross embayment during the last glacial maximum is estimated to have contained ice volume equivalent to 3 6 m eustatic sea level rise and does not show evidence of rapid retreat grounded ice advance occurred during initial late pleistocene eustatic rise and ice sheet retreat began coeval with or subsequent to mwp 1a chronological and sedimentological data from the ross embayment indicate that deglaciation in this region has occurred throughout the holocene and the maximum possible contribution of eustatic rise from the ross embayment is

reconstructing the antarctic ice sheet at the last glacial maximum abstract a reconstruction of the antarctic ice sheet at the last glacial maximum lgm constrained by geologic data shows expansion across continental shelves accompanied by little inland change this added peripheral ice volume contributed 14 m to the lowering of eustatic sea level at the lgm of the total expansion one third took place in east antarctica and two thirds in west antarctica

reconstruction of changes in the weddell sea sector of the antarctic ice sheet since the last glacial maximum the weddell sea sector is one of the main formation sites for antarctic bottom water and an outlet for about one fifth of antarctica s continental ice volume over the last few decades studies on glacial geological records in this sector have provided conflicting reconstructions of changes in ice sheet extent and ice sheet thickness since the last glacial maximum lgm at ca 23 19 calibrated kiloyears before present cal ka bp terrestrial geomorphological records and exposure ages obtained from rocks in the hinterland of the weddell sea ice sheet thickness constraints from ice cores and some radiocarbon dates on offshore sediments were interpreted to indicate no significant ice thickening and locally restricted grounding line advance at the lgm other marine geological and geophysical studies concluded that subglacial bedforms mapped on the weddell sea continental shelf subglacial deposits and sediments over compacted by overriding ice recovered in cores and the few available radiocarbon ages from marine sediments are consistent with major ice sheet advance at the lgm reflecting the geological interpretations different ice sheet models have reconstructed conflicting lgm ice sheet configurations for the weddell sea sector consequently the estimated contributions of ice sheet build up in the weddell sea sector to the lgm sea level low stand of 130 m vary considerably in this paper we summarise and review the geological records of past ice sheet margins and past ice sheet elevations in the weddell sea sector we compile marine and terrestrial chronological data constraining former ice sheet size thereby highlighting different levels of certainty and present two alternative scenarios of the lgm ice sheet configuration including time slice reconstructions for post lgm grounding line retreat moreover we discuss consistencies and possible reasons for inconsistencies between the various reconstructions and propose objectives for future research the aim of our study is to provide two alternative interpretations of glacial geological datasets on antarctic ice sheet history for the weddell sea sector which can be utilised to test and improve numerical ice sheet models

ice stream subglacial access for ice sheet history and fast ice flow the beamish project on rutford ice stream west antarctica and initial results on basal conditions

uplift rates from a new high density gps network in palmer land indicate significant late holocene ice loss in the southwestern weddell sea the measurement of ongoing ice mass loss and associated melt water contribution to sea level change from regions such as west antarctica is dependent on a combination of remote sensing methods a key method the measurement of changes in earth s gravity via the grace satellite mission requires a potentially large correction to account for the isostatic response of the solid earth to ice load changes since the last glacial maximum in this study we combine glacial isostatic adjustment modelling with a new gps dataset of solid earth deformation for the southern antarctic peninsula to test the current understanding of ice history in this region a sufficiently complete history of past ice load change is required for glacial isostatic adjustment models to accurately predict the spatial variation of ongoing solid earth deformation once the independently constrained effects of present day ice mass loss have been accounted for comparisons between the gps data and glacial isostatic adjustment model predictions reveal a substantial misfit the misfit is localized on the southwestern weddell sea where current ice models under predict uplift rates by approximately 2 mm yr 1 this under prediction suggests that either the retreat of the ice sheet grounding line in this region occurred significantly later in the holocene than currently assumed or that the region previously hosted more ice than currently assumed this finding demonstrates the need for further fieldwork to obtain direct constraints on the timing of holocene grounding line retreat in the southwestern weddell sea and that grace estimates of ice sheet mass balance will be unreliable in this region until this is resolved

decadal predictability of the atlantic ocean in a coupled gcm forecast skill and optimal perturbations using linear inverse modeling abstract the decadal predictability of three dimensional atlantic ocean anomalies is examined in a coupled global climate model the third climate configuration of the met office unified model hadcm3 using a linear inverse modeling lim approach it is found that the evolution of temperature and salinity in the atlantic and the strength of the meridional overturning circulation moc can be effectively described by a linear dynamical system forced by white noise the forecasts produced using this linear model are more skillful than other reference forecasts for several decades furthermore significant nonnormal amplification is found under several different norms the regions from which this growth occurs are found to be fairly shallow and located in the far north atlantic initially anomalies in the nordic seas impact the moc and the anomalies then grow to fill the entire atlantic basin especially at depth over one to three decades it is found that the structure of the optimal initial conditio

evidence for late pleistocene thinning of siple dome west antarctica 1 we use a two dimensional full stress thermomechanical flow band model to investigate late pleistocene and holocene histories of ice thickness and ice flow at siple dome in west antarctica measurements obtained from an ice core and borehole near the ice divide and measurements of radar detected internal stratigraphy are used as targets for modeling models that account for the climate history accumulation rate and temperature alone yield a poor match to observations histories of ice dynamics ice thickness ice divide location and ice flow enhancement also need to be included our favored model includes 350 m of thinning at siple dome between 15 000 and 14 000 years ago onset of divide flow 3000 years ago ongoing divide migration starting 2500 years ago and evolution of ice fabric over the past 30 000 years the timing of thinning is earlier than that inferred from geologic evidence from the margins but is coincident with a 20 m rise in global sea level about 14 500 years ago meltwater pulse 1a this opens the possibility that thinning was a result of increased activity of the ice streams in the late pleistocene forced by meltwater pulse 1a the contribution to meltwater pulse 1a as a result of this thinning was likely small

modeling the surface mass balance response of the laurentide ice sheet to bolling warming and its contribution to meltwater pulse 1a meltwater pulse mwp 1a occurred 14 5 14 ka and is the largest abrupt rise in sea level 10 20 m of sea level rise of the last deglaciation the timing of mwp 1a is coincident with or shortly follows the abrupt warming of the north atlantic region into the bolling warm period which could have triggered a large laurentide ice sheet lis contribution to mwp 1a given that outside of the arctic lis iceberg discharge probably did not increase during the bolling much of the lis mwp 1a contribution likely occurred through surface ablation here we test the response of lis surface mass balance to bolling warming by forcing a lis energy mass balance model with climate from an atmosphere ocean general circulation model our modeling approach neglects changes in lis mass from dynamics and iceberg calving allowing us to isolate the surface mass balance response model results suggest that lis surface ablation can explain much of the sea level rise just prior to mwp 1a lis surface mass balance becomes more negative in response to the bolling warming contributing an additional 2 9 1 0 m of sea level rise in 500 yr in addition to the background contribution of 4 0 0 8 m the modeled lis mwp 1a contribution is less than previous assumptions but agrees with geochemical runoff and lis area volume estimates the fraction of mwp 1a attributable to other ice sheets particularly antarctica depends on the total sea level rise that occurred during this mwp

volume of antarctic ice at the last glacial maximum and its impact on global sea level change abstract the volume of antarctic ice at the last glacial maximum is a key factor for calculating the past contribution of melting ice sheets to late pleistocene global sea level change at present there are large uncertainties in our knowledge of the extent and thickness of the formerly expanded antarctic ice sheets and in the timing of their release as meltwater into the world s oceans this paper reviews the four main approaches to determining former antarctic ice volume namely glacial geology glacio isostatic studies glaciological modelling and ice core analysis and attempts to reconcile these to give a best estimate for ice volume in the ross sea there was a major expansion of grounded ice at the last glacial maximum accounting for 2 3 3 2 m of global sea level at some time in the weddell sea a large grounded ice sheet corresponding to c 2 7 m of global sea level extended to the shelf break however this ice expansion has not yet been confidently dated and may not relate to the last glacial maximum around east antarctica there was thickening and advance offshore of ice in coastal regions ice core evidence suggests that the interior of east antarctica was either close to its present elevation or thinner during the last glacial so the effect of east antarctica on sea level depends on the net balance between marginal thickening and interior thinning suggested east antarctic contributions vary from a 3 5 5 m lowering to a 0 64 m rise in global sea level the antarctic peninsula ice sheet thickened and extended offshore at the last glacial maximum with a sea level equivalent contribution of c 1 7 m thus the antarctic ice sheets accounted for between 6 1 and 13 1 m of global sea level fall at the last glacial maximum this is substantially less than has been suggested by most previous studies but the maximum figure matches well with one modelling estimate the timing of antarctic deglaciation is not well known in the ross sea terrestrial evidence suggests deglaciation may have begun at c 13 000 yr bp 1 but that grounded ice persisted until c 6 500 yr bp marine evidence suggests the western ross sea was deglaciated by c 11 500 yr bp deglaciation of the weddell sea is poorly constrained grounded ice in the northern antarctic peninsula had retreated by c 13 000 yr bp and further south deglaciation occurred sometime prior to c 6 000 yr bp many parts of coastal east antarctica apparently escaped glaciation at the lgm but in those areas that were ice covered deglaciation was underway by 10 000 yr bp with existing data the timing of deglaciation shows no firm relation to northern hemisphere driven sea level rise this is probably due partly to lack of antarctic dating evidence but also to the combined influence of several forcing mechanisms acting during deglaciation

rapid deglaciation of marguerite bay western antarctic peninsula in the early holocene glacial geological evidence of rapid ice stream retreat is important for the potential insight it can bring to understanding of contemporary rapid ice sheet change here we report new chronological constraints on the deglacial history of the marguerite trough ice stream which formerly drained part of the western margin of the antarctic peninsula this ice stream has been previously identified on geomorphological grounds as an example of an outlet that underwent rapid retreat following the last glacial maximum but the precise timing of this retreat has not been conclusively determined we obtained cosmogenic surface exposure dates on erratic boulders that record the thinning history of ice flowing into the ice stream these dates show that the ice stream underwent 270 m of thinning very rapidly at 9 6 ka bp the timing of ice stream thinning agrees closely with previously published data on ice shelf retreat the age of the first post glacial beaches and minimum constraining ages for the onset of lacustrine sedimentation and post glacial sedimentation in inner shelf fjords we compare the timing of retreat to the similarly sized anvers trough ice stream further north and find that retreat in marguerite bay was more rapid and earlier than in the anvers trough we argue that the intrusion of circumpolar deep water is the most likely forcing mechanism for retreat in marguerite bay a key finding of this study is that rapid retreat occurred in deep water with reverse continent dipping slope but also in relatively shallow water with a positive slope this may have implications for understanding of oceanographically forced ice sheet change in other parts of west antarctica

sea level changes at the lgm from ice dynamic reconstructions of the greenland and antarctic ice sheets during the glacial cycles abstract new experiments were performed with three dimensional thermomechanical models of the greenland and antarctic ice sheets to simulate their behaviour during the glacial cycles to reconstruct their thickness and extent at the last glacial maximum lgm and to estimate their glacio eustatic contribution to the global sea level stand the calculations used improved ice dynamic and isostatic treatments updated datasets on higher grid resolutions and refined climatic treatments based on newly calibrated transfer functions between ice core records and climatic perturbations results are discussed from a reference run with standard parameters that is compared with available glacial geological observations and from a series of sensitivity experiments focusing on isostatic adjustment thermomechanical coupling climatic forcing mass balance changes and basal melting rates and viscosity changes of antarctic ice shelves for the antarctic ice sheet we find that volume changes are closely linked with grounding line changes of the west antarctic ice sheet at the lgm the grounding line extended close to the continental shelf break almost everywhere ice over central east antarctica was generally thinner than today and varied mainly in accordance with accumulation fluctuations for the greenland ice sheet melting is important only during interglacial periods and the most sensitive period concerns the size of the ice sheet during the eemian at the lgm the greenland ice sheet extended beyond the present coastline to cover at least the inner continental shelf and thinned by up to several hundred meters in central areas for a plausible range of parameters the experiments indicate that at the time of maximum sea level depression 21 kyr bp the antarctic ice sheet contributed 14 18 m to the sea level lowering and the greenland ice sheet 2 3 m significantly less than the older climap reconstructions whereas both ice sheets were at 21 kyr bp close to their maximum extent the experiments also indicate that their maximum volumes were reached only by 16 5 kyr bp greenland and 10 kyr bp antarctica equal to an additional sea level lowering of respectively 0 4 and 3 7 m holocene retreat was essentially complete by 5 kyr bp in greenland but is found to still continue today in west antarctica before reversing to growth during the next millenium the models were found to reproduce gross features of the ice sheet s history since the lgm in reasonably good agreement with available glacial geological data although observational control on ice thickness changes remains very limited

airborne radar evidence for tributary flow switching in institute ice stream west antarctica implications for ice sheet configuration and dynamics despite the importance of ice streaming to the evaluation of west antarctic ice sheet wais stability we know little about mid to long term dynamic changes within the institute ice stream iis catchment here we use airborne radio echo sounding to investigate the subglacial topography internal stratigraphy and holocene flow regime of the upper iis catchment near the ellsworth mountains internal layer buckling within three discrete topographically confined tributaries through ellsworth independence and horseshoe valley troughs provides evidence for former enhanced ice sheet flow we suggest that enhanced ice flow through independence and ellsworth troughs during the mid to late holocene was the source of ice streaming over the region now occupied by the slow flowing bungenstock ice rise although buckled layers also exist within the slow flowing ice of horseshoe valley trough a thicker sequence of surface conformable layers in the upper ice column suggests slowdown more than 4000 years ago so we do not attribute enhanced flow switch off here to the late holocene ice flow reorganization intensely buckled englacial layers within horseshoe valley and independence troughs cannot be accounted for under present day flow speeds the dynamic nature of ice flow in iis and its tributaries suggests that recent ice stream switching and mass changes in the siple coast and amundsen sea sectors are not unique to these sectors and that they may have been regular during the holocene and may characterize the decline of the wais

great salinity anomalies in the north atlantic abstract we revisited the great salinity anomaly of the 1970s gsa 70s dickson et al 1988 and documented the newly identified great salinity anomaly of the 1980s hence termed gsa 80s both propagated around the north atlantic in a similar fashion the advective mechanism initially proposed to explain the observed sequence of low salinity low temperature events during the gsa 70s apparently holds also for the gsa 80s the latter was successively observed in the west greenland current 1982 the labrador current 1983 the flemish pass 1984 near the charlie gibbs fracture zone 1984 1985 in the rockall channel 1985 south of iceland 1985 1988 in the north sea 1986 1987 norwegian sea 1987 1988 barents sea 1988 1989 and iceland sea 1989 1990 the advection speed of the gsa 80s seems to be greater than the one of the gsa 70s the 1980s anomaly reached the barents sea 6 to 7 years after peaking in the west greenland current while the 1970s anomaly traveled the same route in 8 to 10 years these anomalies however seem to be of different origin the gsa 70s was apparently boosted remotely by a freshwater sea ice pulse from the arctic via fram strait consequently the gsa 70s was accompanied by a large sea ice extent anomaly in the greenland and iceland seas which propagated into the labrador sea in contrast the gsa 80s was likely formed locally in the labrador sea baffin bay mainly because of the extremely severe winters of the early 1980s but supplemented with a possible contribution of the arctic freshwater outflow via the canadian archipelago facilitated by strong northerly winds which would have enhanced stability and ice formation this anomaly was also associated with a positive sea ice extent anomaly in the labrador sea baffin bay which however had no upstream precursor in the greenland sea thus the gsas are not necessarily caused solely by an increased export of freshwater and sea ice from the arctic via fram strait these results are corroborated by the early 1990s data when a new fresh cold anomaly was formed in the labrador sea and accompanied by a large positive sea ice extent anomaly the harsh winters of the early 1990s were however confined to the labrador sea baffin bay area while the atmospheric and oceanic conditions in the greenland iceland and irminger seas were normal the labrador sea baffin bay area appears therefore to play a key role in formation of gsas as well as in propagation of the gsas formed upstream a likely contribution of the enhanced canadian archipelago freshwater outflow to the gsa formation also seems to be significant two major modes of the gsa origin are thus identified remote generated by an enhanced arctic ocean freshwater export via either fram strait or the canadian archipelago and local resulting from severe winters in the labrador sea baffin bay both modes should be taken into account to model decadal variability of the coupled ocean ice atmosphere system in the north atlantic arctic basin

do blue ice moraines in the heritage range show the west antarctic ice sheet survived the last interglacial abstract we present a hypothesis that best explains cosmogenic isotope data on blue ice moraines in the heritage range west antarctica the age of the moraines implies that they and the related ice sheet surface with which they are associated have persisted on the flanks of nunataks throughout at least the last interglacial glacial cycle the implication is that although the west antarctic ice sheet wais may have fluctuated in thickness during glacial cycles the central dome has remained intact for at least 200 kyr and possibly even for 400 kyr such a finding if substantiated would contribute to our understanding of the sensitivity of the wais to climate change further it would be a powerful geomorphic constraint on models of the past behaviour of the ice sheet during glacial cycles and thus those predicting the future of the ice sheet in a warming world

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

refining the eustatic sea level curve since the last glacial maximum using far and intermediate field sites the eustatic component of relative sea level change provides a measure of the amount of ice transferred between the continents and oceans during glacial cycles this has been quantified for the period since the last glacial maximum by correcting observed sea level change for the glacio hydro isostatic contributions using realistic ice distribution and earth models during the last glacial maximum lgm the eustatic sea level was 125 5 m lower than the present day equivalent to a land based ice volume of 4 6 4 9 107 km3 evidence for a non uniform rise in eustatic sea level from the lgm to the end of the deglaciation is examined the initial rate of rise from ca 21 to 17 ka was relatively slow with an average rate of ca 6 m ka 1 followed by an average rate of ca 10 m ka 1 for the next 10 ka significant departures from these average rates may have occurred at the time of the younger dryas and possibly also around 14 ka most of the decay of the large ice sheets was completed by 7 ka but 3 5 m of water has been added to the oceans since that time

late pleistocene and early holocene change in the weddell sea a new climate record from the patriot hills ellsworth mountains west antarctica the transition from the late pleistocene to the holocene 30 000 5000 years ago was a period of considerable climate variability which has been associated with changes in deep water formation and the intensity of the meridional overturning circulation although numerous records exist across the north atlantic region few antarctic ice core records have been obtained from the south here we exploit the potential of upwelling ancient ice so called blue ice areas bias from the patriot hills in the ellsworth mountains to derive the first deuterium isotope record d from continental antarctica south of the weddell sea gas analysis and glaciological considerations provide a first relative chronology inferred temperature trends from the patriot hills bia and snow pit suggest changing climate influences during the transition between the last glacial period and holocene under modern conditions the interplay between the antarctic high pressure system and the southern annular mode appears to play a significant role in controlling katabatic wind flow over the site while the bia record suggests that greater sea ice extent during the last glacial period was a major control our results demonstrate the considerable potential of the patriot hills site for reconstructing past climate change in the south atlantic region

optimal initial excitations of decadal modification of the atlantic meridional overturning circulation under the prescribed heat and freshwater flux boundary conditions within a three dimensional ocean circulation model the nonlinear optimal initial perturbations noip of sea surface salinity sss and sea surface temperature sst to excite variability in the atlantic meridional overturning circulation amoc were obtained under prescribed heat and freshwater flux boundary conditions using the conditional nonlinear optimal perturbation cnop method after 10 years the optimal sss and sst perturbations lead to reductions of the amoc by 3 6 and 2 5 sv 1 sv 10 6 m 3 s 1 respectively followed by multidecadal oscillations with a period of about 50 years during the first 30 years nonlinear processes have an important influence on the amoc strength convection strengthens the amoc during years 0 2 zonal density advection promotes the slowdown of the amoc during years 7 20 and meridional density advection inhibits the slowdown of meridional velocities in the upper ocean during years 5 18 the linear optimal initial perturbation loip was also computed using the first singular vector fsv method for sss perturbations with an amplitude of 0 5 psu the loip will cause an underestimation of the amplitude of the multidecadal amoc variability by about 1 sv compared to that induced by the noip this underestimation will become more significant as the amplitudes of sss perturbations increase

deglacial history of the west antarctic ice sheet in the weddell sea embayment constraints on past ice volume change the retreat history of the west antarctic ice sheet wais since the last glacial maximum is important for understanding the process of rapid deglaciation constraining models that seek to predict the future trajectory of the ice sheet and for estimating rates of sea level change here we report new glacial geologic data from the southwestern weddell sea embayment that demonstrate that this part of the wais was thinner than previously suggested and that there was progressive thinning of the ice sheet by 230 480 m since ca 15 ka we use geomorphological data and a numerical ice sheet model to reconstruct the ice sheet in the weddell sea at the last glacial maximum the volume of this ice would have added between 1 4 and 2 0 m to postglacial sea level rise and would not have been sufficient to contribute significantly to meltwater pulse 1a a rapid rise in sea level 14 200 yr ago

miocene to pleistocene glacial history of west antarctica inferred from nunatak geomorphology and cosmogenic nuclide measurements on bedrock surfaces we report geomorphic observations and cosmogenic nuclide measurements on bedrock surfaces from three isolated nunatak groups in west antarctica the pirrit hills and nash hills located in the weddell sea sector and the whitmore mountains located on the ross weddell divide the objectives of this paper are to i establish a chronology for landscape development at these sites and ii quantify the long term history of ice thickness variations in west antarctica these nunataks display relic alpine landscapes on which weathered bedrock surfaces are superimposed in the pirrit hills an erosional trimline is etched into alpine ridges and separates smooth crested ridges below from serrated ridges above below the trimline geomorphic evidence indicates repeated frozen based ice cover while above the trimline evidence for ice cover is entirely absent there is also no geomorphic evidence for thicker than present ice at the whitmore mountains cosmogenic nuclide concentrations in the oldest bedrock surfaces from the whitmore mountains and from above the pirrit hills trimline indicate uninterrupted exposure for 12 myr at extraordinarily low erosion rates this places a lower limit on the timing of the formation of alpine landscapes in west antarctica and we hypothesize that this occurred during the relatively warm climates prior to the mid miocene cooling the absence of evidence for thicker ice at the whitmore mountains is consistent with the hypothesis that the divide was typically thinner than present during pleistocene glacial periods due to reduced accumulation bedrock surfaces below the trimline have much lower nuclide concentrations and are most easily explained by a scenario of repeated frozen based ice cover and occasional subglacial plucking which is consistent with geomorphic observations bedrock surfaces near the modern ice level appear to have been covered more than half of the time while higher elevation surfaces indicate progressively less cover the trimline and associated geomorphic features are very similar to a prominent trimline in the ellsworth mountains and we conclude that these are in fact part of the same feature the ellsworth trimline is hypothesized to have formed during the mid miocene cooling and the transition from alpine to continental glaciation and our results are consistent with this hypothesis

interhemispheric ice sheet synchronicity during the last glacial maximum the timing of the last maximum extent of the antarctic ice sheets relative to those in the northern hemisphere remains poorly understood we develop a chronology for the weddell sea sector of the east antarctic ice sheet that combined with ages from other antarctic ice sheet sectors indicates that the advance to and retreat from their maximum extent was within dating uncertainties synchronous with most sectors of northern hemisphere ice sheets surface climate forcing of antarctic mass balance would probably cause an opposite response whereby a warming climate would increase accumulation but not surface melting our new data support teleconnections involving sea level forcing from northern hemisphere ice sheets and changes in north atlantic deep water formation and attendant heat flux to antarctic grounding lines to synchronize the hemispheric ice sheets

exposure ages from mountain dipsticks in mac robertson land east antarctica indicate little change in ice sheet thickness since the last glacial maximum past changes in east antarctic ice sheet eais volume are poorly known and diffi cult to measure yet are critical for predicting the response of the ice sheet to modern climate change in particular it is important to identify the sources of sea level rise since the last glacial maximum lgm and ascertain the present day stability of the world s largest ice sheet we present altitudinal transects of 10 be and 26 al exposure ages across the framnes mountains in mac robertson land that allow the magnitude and timing of eais retreat to be quantifi ed our data show that the coastal eais thinned by at most 350 m in this region during the past 13 k y this reduction in ice sheet volume occurred over a 5 k y period and the present icesheet profi le was attained ca 7 ka in contrast to the west antarctic ice sheet which continues to retreat today combined with regional offshore and terrestrial geologic evidence our data suggest that the reduction in eais volume since the lgm was smaller than that indicated by contemporary ice sheet models and added little meltwater to the global oceans stability of the ice margin since the middle holocene provides support for the hypothesis that eais volume changes are controlled by growth and decay of northern hemisphere ice sheets and associated global sea level changes

ice flow structure and ice dynamic changes in the weddell sea sector of west antarctica from radar imaged internal layering recent studies have aroused concerns over the potential for ice draining the weddell sea sector of west antarctica to figure more prominently in sea level contributions should buttressing from the filchner ronne ice shelf diminish to improve understanding of how ice stream dynamics there evolved through the holocene we interrogate radio echo sounding res data from across the catchments of institute and moller ice streams iis and mis focusing especially on the use of internal layering to investigate ice flow change as an important component of this work we investigate the influence that the orientation of the res acquisition track with respect to ice flow exerts on internal layering and find that this influence is minimal unless a res flight track parallels ice flow we also investigate potential changes to internal layering characteristics with depth to search for important temporal transitions in ice flow regime our findings suggest that ice in northern iis draining the ellsworth subglacial highlands has retained its present ice flow configuration throughout the holocene this contrasts with less topographically constrained ice in southern iis and much of mis whose internal layering evinces spatial changes to the configuration of ice flow over the past 10 000 years our findings confirm siegert et al s 2013 inference that fast flow was diverted from bungenstock ice rise during the late holocene and suggest that this may have represented just one component of wider regional changes to ice flow occurring across the iis and mis catchments as the west antarctic ice sheet has thinned since the last glacial maximum

deglacial history of the west antarctic ice sheet in the weddell sea embayment constraints on past ice volume change comment boundaries along valley or mountain slopes separating fresh largely unweathered glacial deposits or bedrock below from more highly weathered deposits or bedrock above weathering zones have long been used to constrain vertical ice limits in scandinavia dahl 1966 1 and the canadian arctic

cosmogenic radionuclides from fiord landscapes support differential erosion by overriding ice sheets the interpretation of differentially weathered mountainous areas along the fringes of pleistocene ice sheets is fundamental for determining ice sheet behavior and thickness during the last glaciation two existing interpretations are either that highly weathered uplands remained as nunataks while freshly eroded troughs held outlet glaciers during the last glaciation or that uplands and lowlands were equally covered by ice but that it was differentially erosive as a function of its spatially variable basal thermal regime cosmogenic radionuclide measurements from 33 bedrock samples and 27 upland erratics from differentially weathered fi ord landscapes on northeastern baffi n island shed light on laurentide ice sheet lis dynamics and thickness tors on weathered upland surfaces have minimum 10 be ages between ca 50 and ca 170 ka n 12 whereas the majority of erratics perched in the uplands range from ca 10 to ca 13 ka n 14 indicating that the whole landscape was glaciated during the last glacial maximum lgm glacially sculpted bedrock n 7 near sea level refl ects the age of deglaciation and increasing amounts of isotopic inheritance in highelevation sculpted bedrock n 3 higher elevation intermediately weathered bedrock n 11 and highest elevation intensely weathered bedrock refl ect the weakening of erosive power as the ice sheet transitioned from fi ords to interfi ord plateaus cold based glaciation of uplands was contemporaneous with warm based glaciation in fi ords suggesting the presence of ice streams 26 al and 10 be concentrations measured in 10 bedrock samples indicate that tors have experienced a complex history of alternating periods of exposure burial and limited glacial erosion the paired isotope data reveal a minimum duration of burial of 80 500 k y presumably by cold based ice and indicate that the tors have an age of at least 150 580 ka these data together with other reconstructions of ice streams in the eastern canadian arctic suggest that ice streams were a large infl uence on northeastern lis dynamics throughout the late quaternary thus the northeastern lis was sensitively tied with north atlantic thermohaline circulation and abrupt climate change

late quaternary glacial history constrains glacio isostatic rebound in enderby land east antarctica measurements of the loss or gain of ice mass from large ice sheets are presently achieved through satellite based techniques such as grace gravity recovery and climate experiment the accuracy of these satellite based measurements to changes in modern ice sheet mass depends on our knowledge of present day glacio isostatic crustal uplift rates caused by past ice sheet changes to improve models of glacio isostatic rebound in east antarctica we investigated ice histories along rayner glacier enderby land and a little explored sector of the ice sheet where grace data had suggested significant mass gain during the last decade observations from a recent glacial geomorphic reconnaissance coupled with cosmogenic nuclide dating indicate that in the lower part of the rayner glacier enderby land ice heights lowered by at least 300 m and the calving margin retreated by at least 10 km in the early holocene 6 to 9 ka b p the magnitude and timing of deglaciation are consistent with ice histories used to model the postglacial rebound corrections for present day grace mass trends these observations strengthen the body of evidence that suggests ice mass gain in enderby land is presently partly offsetting mass loss in other parts of antarctica

north atlantic interdecadal variability oceanic response to the north atlantic oscillation 1865 1997 abstract in contrast to the atmosphere knowledge about interdecadal variability of the north atlantic circulation is relatively restricted it is the objective of this study to contribute to understanding how the north atlantic circulation responds to a forcing by the north atlantic oscillation nao on interdecadal timescales for this purpose the authors analyze observed atmospheric and sea surface temperature sst data along with the response of an ocean general circulation model to a realistic monthly surface flux forcing that is solely associated with the nao for the period 1865 1997 in agreement with previous studies it is shown that the relationship between the local forcing by the nao and observed sst anomalies on interdecadal timescales points toward the importance of oceanic dynamics in generating sst anomalies a comparison between observed and modeled sst anomalies reveals that the model results can be used to assess interdecadal variability of the north atlantic circulation the observed

temporal variability of the atlantic meridional overturning circulation at 26 5 n the vigor of atlantic meridional overturning circulation moc is thought to be vulnerable to global warming but its short term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain we combine continuous measurements of the moc beginning in 2004 using the purposefully designed transatlantic rapid climate change array of moored instruments deployed along 26 5 n with time series of gulf stream transport and surface layer ekman transport to quantify its intra annual variability the year long average overturning is 18 7 5 6 sverdrups sv range 4 0 to 34 9 sv where 1 sv a flow of ocean water of 106 cubic meters per second interannual changes in the overturning can be monitored with a resolution of 1 5 sv

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

seawater density variations in the north atlantic and the atlantic meridional overturning circulation seawater property changes in the north atlantic ocean affect the atlantic meridional overturning circulation amoc which transports warm water northward from the upper ocean and contributes to the temperate climate of europe as well as influences climate globally previous observational studies have focused on salinity and freshwater variability in the sinking region of the north atlantic since it is believed that a freshening north atlantic basin can slow down or halt the flow of the amoc here we use available data to show the importance of how density patterns over the upper ocean of the north atlantic affect the strength of the amoc for the long term trend the upper ocean of the subpolar north atlantic is becoming cooler and fresher whereas the subtropical north atlantic is becoming warmer and saltier on a multidecadal timescale the upper ocean of the north atlantic has generally been warmer and saltier since 1995 the heat and salt content in the subpolar north atlantic lags that in the subtropical north atlantic by about 8 9 years suggesting a lower latitude origin for the temperature and salinity anomalies because of the opposite effects of temperature and salinity on density for both long term trend and multidecadal timescales these variations do not result in a density reduction in the subpolar north atlantic for slowing down the amoc indeed the variations in the meridional density gradient between the subpolar and subtropical north atlantic ocean suggest that the amoc has become stronger over the past five decades these observed results are supported by and consistent with some oceanic reanalysis products

geomorphological evidence and cosmogenic 10be 26al exposure ages for the last glacial maximum and deglaciation of the antarctic peninsula ice sheet this paper presents the first systematic attempt to map the last glacial maximum lgm configuration of the southern and central parts of the antarctic peninsula ice sheet and to determine the timing of onshore ice sheet retreat geomorphologic evidence shows that the lgm ice sheet expanded to form two ice domes in palmer land and merged with an expanded and thicker west antarctic ice sheet in the weddell sea ice from the antarctic peninsula merged with alexander island ice in george vi sound cosmogenic 10 be and 26 al data from 29 erratics on nunataks yield model ages between 7 2 ka and older than 1 ma the data set contains a high proportion of erratics with evidence of nuclide inheritance once these ages have been excluded the cosmogenic ages suggest that thinning of the west side of the antarctic peninsula ice sheet to near present configuration was almost complete by the early holocene these data combined with previously published 14 c data exclude the possibility that the west side of the antarctic peninsula ice sheet has been thinning throughout the holocene as has been demonstrated for some other sectors of the west antarctic ice sheet on the east side of the antarctic peninsula ice sheet thinning was under way prior to the early holocene but our data do not constrain the ice sheet behavior more recently than 7 2 ka

history of the grounded ice sheet in the ross sea sector of antarctica during the last glacial maximum and the last termination knowledge of variations in the extent and thickness of the antarctic ice sheet is key for understanding the behaviour of southern hemisphere glaciers during the last ice age and for addressing issues involving global sea level ocean circulation and climate change insight into past ice sheet behaviour also will aid predictions of future ice sheet stability here we review ter restrial evidence for changes in ice geometry that occurred in the ross sea sector of antarctica at the last glacial maximum lgm and during subsequent deglaciation during the lgm a thick grounded ice sheet extended close to the continental shelf edge in the ross embayment this ice reached surface elevations of more than 1000 m along the coast of the central and southern trans antarctic mountains and marie byrd land the local lgm occurred by 18 ka on the coast but as late as 7 10 ka inland the first significant thinning took place at roughly 13 ka with most ice loss happening in the holocene this history makes it unlikely that the ross sea sector was a major contributor to meltwater pulse 1a mwp 1a resolution of a possible antarctic origin for mwp 1a awaits detailed reconstructions from all sectors of the ice sheet the antarctic ice sheet contains the world s larg est reservoir of fresh water and is a major control on southern hemisphere climate a history of changes in ice sheet extent and thickness is vital for answering questions involving the initiation of southern hemisphere glaciation and deglaciation