twenty first century warming of a large antarctic ice shelf cavity by a redirected coastal current the redirection of warm water under the filchner ronne ice shelf during the second half of this century could cause the ice shelf base to melt at a rate 20 times higher than at present warm ocean currents are known to erode ice shelves from below but changes in currents can be forced by many different mechanisms leading to uncertain outcomes this study highlights the vulnerability to climate change of a small antarctic coastal region which has potentially severe consequences for the mass balance of a large antarctic ice shelf hellmer et al use climate modelling to show that the projected loss of sea ice in the weddell sea east of the antarctic peninsula leads to an increase in wind stress which in turn accelerates a warm ocean current far underneath the vast filchner ronne ice shelf the authors predict that the increased warmth could increase melt by a factor of 20 with possible consequences for ice stream dynamics in the east antarctic ice sheet the antarctic ice sheet loses mass at its fringes bordering the southern ocean at this boundary warm circumpolar water can override the continental slope front reaching the grounding line1 2 through submarine glacial troughs and causing high rates of melting at the deep ice shelf bases3 4 the interplay between ocean currents and continental bathymetry is therefore likely to influence future rates of ice mass loss here we show that a redirection of the coastal current into the filchner trough and underneath the filchner ronne ice shelf during the second half of the twenty first century would lead to increased movement of warm waters into the deep southern ice shelf cavity water temperatures in the cavity would increase by more than 2 degrees celsius and boost average basal melting from 0 2 metres or 82 billion tonnes per year to almost 4 metres or 1 600 billion tonnes per year our results which are based on the output of a coupled ice ocean model forced by a range of atmospheric outputs from the hadcm35 climate model suggest that the changes would be caused primarily by an increase in ocean surface stress in the southeastern weddell sea due to thinning of the formerly consolidated sea ice cover the projected ice loss at the base of the filchner ronne ice shelf represents 80 per cent of the present antarctic surface mass balance6 thus the quantification of basal mass loss under changing climate conditions is important for projections regarding the dynamics of antarctic ice streams and ice shelves and global sea level rise

a glimpse beneath antarctic sea ice platelet layer volume from multifrequency electromagnetic induction sounding in antarctica ice crystals emerge from ice shelf cavities and accumulate in unconsolidated layers beneath nearby sea ice such sub ice platelet layers form a unique habitat and serve as an indicator for the state of an ice shelf however the lack of a suitable methodology impedes an efficient quantification of this phenomenon on scales beyond point measurements in this study we inverted multifrequency electromagnetic em induction soundings obtained on fast ice with an underlying platelet layer along profiles of 100 km length in the eastern weddell sea em derived platelet layer thickness and conductivity are consistent with other field observations our results suggest that platelet layer volume is higher than previously thought in this region and that platelet layer ice volume fraction is proportional to its thickness we conclude that multifrequency em is a suitable tool to determine platelet layer volume with the potential to obtain crucial knowledge of associated processes in otherwise inaccessible ice shelf cavities

responses of basal melting of antarctic ice shelves to the climatic forcing of the last glacial maximum and co2 doubling abstractbasal melting of the antarctic ice shelves is an important factor in determining the stability of the antarctic ice sheet this study used the climatic outputs of an atmosphere ocean general circulation model to force a circumpolar ocean model that resolves ice shelf cavity circulation to investigate the response of antarctic ice shelf melting to different climatic conditions i e to a doubling of co2 and to the last glacial maximum conditions sensitivity experiments were also conducted to investigate the roles of both surface atmospheric change and changes of oceanic lateral boundary conditions it was found that the rate of change of basal melt due to climate warming is much greater by an order of magnitude than that due to cooling this is mainly because the intrusion of warm water onto the continental shelves linked to sea ice production and climate change is crucial in determining the basal melt rate of many ice shelves sensitivity experiments showed that changes of atmospheric heat

ice shelf melt response to changing winds and glacier dynamics in the amundsen sea sector antarctica it has been suggested that the coastal southern ocean subsurface may warm over the 21st century in response to strengthening and poleward shifting winds with potential adverse effects on west antarctic glaciers however using a 1 128 ocean regional model that includes ice shelf cavities we find a more complex response to changing winds in the amundsen sea simulated offshore subsurface waters get colder under strengthened and poleward shifted winds representative of the sam projected trend the buoyancy driven circulation induced by ice shelf melt transports this cold offshore anomaly onto the continental shelf leading to cooling and decreased melt below 450 m in the vicinity of ice shelf fronts ekman pumping contributes to raise the isotherms in response to changing winds this effect overwhelms the horizontal transport of colder offshore waters at intermediate depths between 200 and 450 m and therefore increases melt rates in the upper part of the ice shelf cavities which reinforces the buoyancydriven circulation and further contributes to raise the isotherms then prescribing an extreme grounding line retreat projected for 2100 the total melt rates simulated underneath thwaites and pine island are multiplied by 2 5 such increase is explained by a larger ocean ice interface exposed to cdw which is then amplified by a stronger melt induced circulation along the ice draft our main conclusions are that 1 outputs from ocean models that do not represent ice shelf cavities e g cmip5 models should not be directly used to predict the thermal forcing of future ice shelf cavities 2 coupled ocean ice sheet models with a velocity dependent melt formulation are needed for future projections of glaciers experiencing a significant grounding line retreat

climate response to increasing antarctic iceberg and ice shelf melt mass loss from the antarctic continent is increasing however climate models either assume a constant mass loss rate or return snowfall over land to the ocean to maintain equilibrium numerous studies have investigated sea ice and ocean sensitivity to this assumption and reached different conclusions possibly due to different representations of melt fluxes the coupled atmosphere land ocean sea ice model hadgem3 gc3 1 includes a realistic spatial distribution of coastal melt fluxes a new ice shelf cavity parameterization and explicit representation of icebergs this configuration makes it appropriate to revisit how increasing melt fluxes influence ocean and sea ice and to assess whether responses to melt from ice shelves and icebergs are distinguishable we present results from simulated scenarios of increasing meltwater fluxes and show that these drive sea ice increases and for increasing ice shelf melt a decline in antarctic bottom water formation in our experiments the mixed layer around the antarctic coast deepens in response to rising ice shelf meltwater and shallows in response to stratification driven by iceberg melt we find similar surface temperature and salinity responses to increasing meltwater fluxes from ice shelves and icebergs but midlayer waters warm to greater depths and farther north when ice shelf melt is present we show that as meltwater fluxes increase snowfall becomes more likely at lower latitudes and antarctic circumpolar current transport declines these insights are helpful for interpretation of climate simulations that assume constant mass loss rates and demonstrate the importance of representing increasing melt rates for both ice shelves and icebergs

modelling circumpolar deep water intrusions on the amundsen sea continental shelf antarctica results are presented from an isopycnic coordinate model of ocean circulation in the amundsen sea focusing on the delivery of circumpolar deep water cdw to the inner continental shelf around pine island bay the warmest waters to reach this region are channeled through a submarine trough accessed via bathymetric irregularities along the shelf break temporal variability in the influx of cdw is related to regional wind forcing easterly winds over the shelf edge change to westerlies when the amundsen sea low migrates west and south in winter spring this drives seasonal on shelf flow while inter annual changes in the wind forcing lead to inflow variability on a decadal timescale a modelled period of warming following low cdw influx in the late 1980 s and early 1990 s coincides with a period of observed thinning and acceleration of pine island glacier

atmospheric circulation impacts on winter maximum sea ice extent in the west antarctic peninsula region 1979 2001 increasing evidence exists that the strong warming of the west antarctic peninsula wap region since the 1950s is related to reduced sea ice that is likely to be due to changes in the atmospheric circulation over twenty years of sea ice extent ice motion and reanalysed near surface wind data are used to establish that winter ice extent in the west antarctic peninsula wap region is largely determined by the meridional north south atmospheric circulation a remarkably strong ice extent wind relationship is found in the wap no other antarctic or comparable sub arctic sea ice region shows this ice motion data confirm wind induced drift is crucial for extensive winter ice to occur reasons for winter ice extent and winds being more strongly correlated in the wap than in other parts of the antarctic are discussed along with implications for understanding the observed warming

acceleration of the contribution of the greenland and antarctic ice sheets to sea level rise 1 ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques over different time periods and at various levels of spatial detail considerable disparity remains between these estimates due to the inherent uncertainties of each method the lack of detailed comparison between independent estimates and the effect of temporal modulations in ice sheet surface mass balance here we present a consistent record of mass balance for the greenland and antarctic ice sheets over the past two decades validated by the comparison of two independent techniques over the last 8 years one differencing perimeter loss from net accumulation and one using a dense time series of time variable gravity we find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss in 2006 the greenland and antarctic ice sheets experienced a combined mass loss of 475 158 gt yr equivalent to 1 3 0 4 mm yr sea level rise notably the acceleration in ice sheet loss over the last 18 years was 21 9 1 gt yr2 for greenland and 14 5 2 gt yr2 for antarctica for a combined total of 36 3 2 gt yr2 this acceleration is 3 times larger than for mountain glaciers and ice caps 12 6 gt yr2 if this trend continues ice sheets will be the dominant contributor to sea level rise in the 21st century

the effect of increased fresh water from antarctic ice shelves on future trends in antarctic sea ice observations show that in contrast to the arctic the area of antarctic sea ice has increased since 1979 a potential driver of this significant increase relates to the mass loss of the antarctic ice sheet subsurface ocean warming causes basal ice shelf melt freshening the surface waters around antarctica which leads to increases in sea ice cover with climate warming ongoing future mass loss rates are projected to accelerate which has the potential to affect future antarctic sea ice trends here we investigate to what extent future sea ice trends are influenced by projected increases in antarctic freshwater flux due to subsurface melt using a state of the art global climate model ec earth in standardized climate model intercomparison project phase 5 cmip5 climate change simulations virtually all cmip5 models disregard ocean ice sheet interactions and project strongly retreating antarctic sea ice applying various freshwater flux scenarios we find that the additional fresh water significantly offsets the decline in sea ice area and is even able to reverse the trend in the strongest freshwater forcing scenario that can reasonably be expected especially in austral winter the model also simulates decreasing sea surface temperatures ssts with the sst trends exhibiting strong regional variations that largely correspond to regional sea ice trends

cmip5 temperature biases and 21st century warming around the antarctic coast projections of ice sheet mass balance require regional ocean warming projections derived from atmosphere ocean general circulation models aogcms however the coarse resolution of aogcms 1 may lead to systematic or aogcm specific biases and 2 makes it difficult to identify relevant water masses here we employ a large scale metric of antarctic shelf bottom water asbw to investigate circum antarctic temperature biases and warming projections in 19 different coupled model intercomparison project phase 5 cmip5 aogcms forced with two different representative concentration pathways rcps for high emissions rcp 8 5 the ensemble mean 21st century asbw warming is 0 66 0 74 and 0 58 c for the amundsen ross and weddell seas as rs and ws respectively rcp 2 6 ensemble mean projections are substantially lower 0 21 0 26 and 0 19 c all distributions of regional asbw warming are positively skewed for rcp 8 5 four aogcms project warming of greater than 1 8 c in the rs across the ensemble there is a strong rcp independent correlation between ws and rs warming as warming is more closely linked to warming in the southern ocean we discuss possible physical mechanisms underlying the spatial patterns of warming and highlight implications of these results on strategies for forcing ice sheet mass balance projections

remnants of a late triassic ocean island in the gufeng area northern tibet implications for the opening and early evolution of the bangong nujiang tethyan ocean abstract in this paper we present new major and trace element compositions of basaltic rocks in the gufeng ocean island gfoi area in the western segment of the bangong nujiang suture zone northern tibet our aim was to assess the genesis of these rocks and discuss the implications of this new dataset for the evolution of the bangong nujiang tethyan ocean an ocean island type double layer structure comprising a basaltic basement and an oceanic sedimentary cover sequence found within the gfoi provides direct evidence for the interpretation that the assemblage is a typical ocean island the basalts in the gfoi can be divided into three types named g1 g2 and g3 basalts and these basalts range in composition from morb to oib types which is typical of ocean islands the g1 basalts have morb type affinities possibly indicating the existence of morb oceanic crust under the gfoi the g2 basalts represent the early stage of formation of the gfoi and are produced by the interaction of rising oib type basaltic magma and the existing morb oceanic crust the g3 basalts are typical oib basalts and they are the products of the direct eruption of oib type basaltic magmas the g3 basalts have high la yb n 12 3 14 4 ce yb n 10 8 11 8 la sm n 2 39 2 76 and sm yb n 4 89 5 23 ratios indicating the presence of oceanic lithosphere below the gfoi with a thickness of 50 60 km geochemical analyses of the gfoi cherts show that they contain terrigenous material indicating the gfoi formed close to a continental margin norian conodont fossils within the gfoi limestones indicate the gfoi formed during the late triassic these data combined with geological evidence and a half space model of lithosphere cooling where the thickness of the oceanic lithosphere is determined from the age of the lithosphere indicate that the western segment of the bangong nujiang tethyan ocean opened initially in the late permian expanded rapidly during the early middle triassic and was a mature ocean during the late triassic

impact of antarctic ice shelf basal melting on sea ice and deep ocean properties 1 an approximation of antarctica s rocky and icy coastline normally forms the southern boundary in global climate models such a configuration neglects extensive ice shelf areas where ocean ice interaction initiates a net freshwater flux to the circumpolar continental shelf equal to 75 of the annual mean net precipitation in coastal seas the results of a numerical model for the southern ocean using two contrasting configurations with and without caverns beneath major antarctic ice shelves are compared they show that the freshwater flux due to deep basal melting significantly stabilizes the shelf water column in front of an ice shelf as well as downstream due to advection by the coastal current if the freshwater from the caverns is absent sea ice is thinner shelf waters are warmer and saltier and the southern ocean deep basins are flushed by denser waters

sipex 2012 extreme sea ice and atmospheric conditions off east antarctica abstract in 2012 antarctic sea ice coverage was marked by weak annual mean climate anomalies that consisted of opposing anomalies early and late in the year some setting new records which were interspersed by near average conditions for most of the austral autumn and winter here we investigate the ocean ice atmosphere system off east antarctica prior to and during the sea ice physics and ecosystems experiment sipex 2012 by exploring relationships between atmospheric and oceanic forcing together with the sea ice and snow characteristics during august and september 2012 just prior to sipex 2012 atmospheric circulation over the southern ocean was near average setting up the ocean ice atmosphere system for near average conditions however below average surface pressure and temperature as well as strengthened circumpolar winds prevailed during june and july 2012 this led to a new record 19 48 10 6 km 2 in maximum antarctic sea ice extent recorded in late september in contrast to the weak circum antarctic conditions the east antarctic sector including the sipex 2012 region experienced positive sea ice extent and concentration anomalies during most of 2012 coincident with negative atmospheric pressure and sea surface temperature anomalies heavily deformed sea ice appeared to be associated with intensified wind stress due to increased cyclonicity as well as an increased influx of sea ice from the east this increased westward ice flux is likely linked to the break up of nearly 80 of the mertz glacier tongue in 2010 which strongly modified the coastal configuration and hence the width of the westward coastal current combined with favourable atmospheric conditions the associated changed coastal configuration allowed more sea ice to remain within the coastal current at the expense of a reduced northward flow in the region around 141 145 e in addition a westward propagating positive anomaly of sea ice extent from the western ross sea during austral winter 2012 has been identified to have fed into the westward current of the sipex 2012 region a pair of large grounded icebergs appears to have modified the local stress state as well as the structure of the ice pack upstream and also towards the dalton glacier tongue together with the increased influx of sea ice into the regions this contributed to the difficulties in navigating the sipex 2012 region

recent changes in antarctic sea ice in contrast to the arctic total sea ice extent sie across the southern ocean has increased since the late 1970s with the annual mean increasing at a rate of 186103km2 per decade 1 5 per decade

tropically driven and externally forced patterns of antarctic sea ice change reconciling observed and modeled trends recent work suggests that natural variability has played a significant role in the increase of antarctic sea ice extent during 1979 2013 the ice extent has responded strongly to atmospheric circulation changes including a deepened amundsen sea low asl which in part has been driven by tropical variability nonetheless this increase has occurred in the context of externally forced climate change and it has been difficult to reconcile observed and modeled antarctic sea ice trends to understand observed model disparities this work defines the internally driven and radiatively forced patterns of antarctic sea ice change and exposes potential model biases using results from two sets of historical experiments of a coupled climate model compared with observations one ensemble is constrained only by external factors such as greenhouse gases and stratospheric ozone while the other explicitly accounts for the influence of tropical variability by specifying observed sst anomalies in the eastern tropical pacific the latter experiment reproduces the deepening of the asl which drives an increase in regional ice extent due to enhanced ice motion and sea surface cooling however the overall sea ice trend in every ensemble member of both experiments is characterized by ice loss and is dominated by the forced pattern as given by the ensemble mean of the first experiment this pervasive ice loss is associated with a strong warming of the ocean mixed layer suggesting that the ocean model does not locally store or export anomalous heat efficiently enough to maintain a surface environment conducive to sea ice expansion the pervasive upper ocean warming not seen in observations likely reflects ocean mean state biases

interpretation of recent antarctic sea ice variability 1 trends in the satellite derived antarctic sea ice concentrations 1979 2002 show pronounced increase decrease in the central pacific sector bellingshausen western weddell sector by 4 10 per decade confidence levels for these regional trends exceed 95 positive polarities of the antarctic oscillation aao lead to more less ice in the eastern ross amundsen sector bellingshausen northern weddell sector which are qualitatively opposite to the impacts of positive polarities of the el nino southern oscillation enso the mechanisms responsible for the covariability between the ice and the a aao and b enso are demonstrated over the last 24 years a positive aao trend and a slightly negative enso trend produce a spatial pattern of ice changes similar to the regional ice trends however the magnitude of the ice changes associated with the aao and enso is much smaller than the regional ice trends more local or less understood large scale processes should be investigated for the explanations

on the modified circumpolar deep water upwelling over the four ladies bank in prydz bay east antarctica analyses of hydrographic observation data sets revealed that modified circumpolar deep water mcdw tends to flood the western flank 73 78 degrees e 67 68 degrees s of the four ladies bank flb in prydz bay in this study we investigated the mechanism responsible for mcdw upwelling over the flb based on an eddy resolving coupled ocean sea ice ice shelf model in conjunction with the latest high accuracy bathymetry it was found that zonal step like declines in the seabed over the flb are crucial for the mcdw onshore upwelling through topographic dynamic effects on the alongshore antarctic slope current in the presence of meridional cross shelf sigma isopycnals warm mcdw at 500 m depth in the deep sea can make its approach to the shallower continental shelf 200 to 500 m depths characterized as a warm layer 1 8 degrees c bounded by the cross shelf sigma isopycnal surfaces of 27 5 and 27 7kg m 3 the simulated outflow of the prydz bay gyre is concentrated to the eastern flank of the prydz channel these results suggest that in addition to the depressions and troughs around the antarctic smaller topographic features such as step like declines in the seabed near the antarctic slope current are also favorable for onshore mcdw intrusion this study demonstrates that mcdw onshore transport around the antarctic continental shelf might be significantly underestimated by numerical models with coarse spatial representations of the topography plain language summary based the observational data sets warm circumpolar deep water was identified over the four ladies bank in prydz bay east antarctica the warm signals could be delivered into the ocean cavity beneath the downstream ice shelf and result in remarkable influences to the ice shelf basal melting in order to investigate the intrusion of warm circumpolar deep water we used a numerical model to simulate the oceanic circulations in prydz bay by assessing the simulated results we found that the topographic influences of the changes in seabed on the continental shelf break jet play a dominant role in the responsible mechanism for warm water intrusion our findings highlighted that the improvements in the spatial resolution of the numerical model and the accuracy of the topographical representations are very useful in the investigation of warm water intrusion around the antarctic continental shelf

decline in arctic sea ice thickness from submarine and icesat records 1958 2008 1 the decline of sea ice thickness in the arctic ocean from icesat 2003 2008 is placed in the context of estimates from 42 years of submarine records 1958 2000 described by rothrock et al 1999 2008 while the earlier 1999 work provides a longer historical record of the regional changes the latter offers a more refined analysis over a sizable portion of the arctic ocean supported by a much stronger and richer data set within the data release area dra of declassified submarine sonar measurements covering 38 of the arctic ocean the overall mean winter thickness of 3 64 m in 1980 can be compared to a 1 89 m mean during the last winter of the icesat record an astonishing decrease of 1 75 m in thickness between 1975 and 2000 the steepest rate of decrease is 0 08 m yr in 1990 compared to a slightly higher winter summer rate of 0 10 0 20 m yr in the five year icesat record 2003 2008 prior to 1997 ice extent in the dra was 90 during the summer minimum this can be contrasted to the gradual decrease in the early 2000s followed by an abrupt drop to 55 during the record setting minimum in 2007 this combined analysis shows a long term trend of sea ice thinning over submarine and icesat records that span five decades

mode of gypsum deposition in southeastern iranian soils as revealed by isotopic composition of crystallization water variations in d and 18o values of water of crystallization and meteoric water were used to elucidate the origin of mother brine and the gypsum mode of formation in selected southeastern iranian soils thirteen representative pedons were sampled at various geomorphic positions around the city of rafsanjan crystallization water in different parts of three gypsum pendants was also analyzed isotopically the slope of the d and 18o plot for crystallization water was found to be 2 8 showing that evaporation was the major process for gypsum accumulation in the studied area comparison of data for eight rainwater samples and the crystallization water shows that gypsum formation occurred in a climate that was probably lower in temperature than that of today the mean d and 18o values of gypsum crystallization water vary from 41 9 and 6 5 for rock pediment to 36 9 and 10 0 for mantled pediment and 28 8 and 13 8 for transitional surfaces and finally 8 8 and 19 2 for playa margins the existence of such a close relationship between the isotopic composition of gypsum crystallization water and geomorphic positions could be attributed to the deposition of gypsum in different landforms at various stages of evaporation and or progressive evaporation of moving surface and subsurface waters an increase in d and 18o values was also observed with increasing depth in almost all soil profiles studied different climates at the time of gypsum formation in different depths seem to be the possible reason with increasing depth from the pebble surface in gypsum pendants d and 18o values decrease which is also attributed to climatic changes during pendant development

the influence of atmospheric zonal wave three on antarctic sea ice variability 1 the study examines the relationship between atmospheric zonal wave three and antarctic sea ice variability using an index of zonal wave three and sea ice concentration the net sensible heat flux and the surface air temperature are used to explain the apparent atmosphere sea ice interaction the results show that zonal wave three forces an alternating pattern of equatorward colder and poleward warmer flow which influences the temperature difference between the atmosphere and the ocean the net sensible heat flux is positive ocean heat loss is greater and sea ice growth and expansion is greater in regions of colder air the reverse is true in regions of warmer air this influence of zonal wave three on sea ice concentration appears greatest in the southern fall and early winter it is most clearly seen in the ross and weddell seas outflows and off the amery iceshelf

trends and connections across the antarctic cryosphere satellite observations have transformed our understanding of the antarctic cryosphere the continent holds the vast majority of earth s fresh water and blankets swathes of the southern hemisphere in ice reductions in the thickness and extent of floating ice shelves have disturbed inland ice triggering retreat acceleration and drawdown of marine terminating glaciers the waxing and waning of antarctic sea ice is one of earth s greatest seasonal habitat changes and although the maximum extent of the sea ice has increased modestly since the 1970s inter annual variability is high and there is evidence of longer term decline in its extent this paper discusses how antarctic ice has changed over recent decades and how these changes have been recorded in satellite observations

anthropogenic influence on recent circulation driven antarctic sea ice changes observations reveal an increase of antarctic sea ice over the past three decades yet global climate models tend to simulate a sea ice decrease for that period here we combine observations with model experiments mpi esm to investigate causes for this discrepancy and for the observed sea ice increase based on observations and atmospheric reanalysis we show that on multidecadal time scales antarctic sea ice changes are linked to intensified meridional winds that are caused by a zonally asymmetric lowering of the high latitude surface pressure in our simulations this surface pressure lowering is a response to a combination of anthropogenic stratospheric ozone depletion and greenhouse gas increase combining these two lines of argument we infer a possible anthropogenic influence on the observed sea ice changes however similar to other models mpi esm simulates a surface pressure response that is rather zonally symmetric which explains why the simulated sea ice response differs from observations

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

new tools for the reconstruction of pleistocene antarctic sea ice abstract based on the quantitative analysis of diatom assemblages preserved in 274 surface sediment samples recovered in the pacific atlantic and western indian sectors of the southern ocean we have defined a new reference database for quantitative estimation of late middle pleistocene antarctic sea ice fields using the transfer function technique the detrended canonical analysis dca of the diatom data set points to a unimodal distribution of the diatom assemblages canonical correspondence analysis cca indicates that not only winter sea ice wsi but also summer sea surface temperature ssst represent the most prominent environmental variables that control the spatial species distribution to test the applicability of transfer functions for sea ice reconstruction in terms of concentration and occurrence probability we applied four different methods the imbrie and kipp method ikm the modern analog technique mat weighted averaging wa and weighted averaging partial least squares wapls using logarithm transformed diatom data and satellite derived 1981 2010 sea ice data as a reference the best performance for ikm results was obtained using a subset of 172 samples with 28 diatom taxa taxa groups quadratic regression and a three factor model ikm d172 28 3q resulting in root mean square errors of prediction rmsep of 7 27 and 11 4 for wsi and summer sea ice ssi concentration respectively mat estimates were calculated with different numbers of analogs 4 6 using a 274 sample 28 taxa reference data set mat d274 28 4an 6an resulting in rmsep ranging from 5 52 4an to 5 91 6an for wsi as well as 8 93 4an to 9 05 6an for ssi wa and wapls performed less well with the d274 data set compared to mat achieving wsi concentration rmsep of 9 91 with wa and 11 29 with wapls recommending the use of ikm and mat the application of ikm and mat to surface sediment data revealed strong relations to the satellite derived winter and summer sea ice field sea ice reconstructions performed on an atlantic and a pacific southern ocean sediment core both documenting sea ice variability over the past 150 000 yr mis 1 mis 6 resulted in similar glacial interglacial trends of ikm and mat based sea ice estimates on the average however ikm estimates display smaller wsi and slightly higher ssi concentration and probability at lower variability in comparison with mat this pattern is a result of different estimation techniques with integration of wsi and ssi signals in one single factor assemblage by applying ikm and selecting specific single samples thus keeping close to the original diatom database and included variability by mat in contrast to the estimation of wsi reconstructions of past ssi variability remain weaker combined with diatom based estimates the abundance and flux pattern of biogenic opal represents an additional indication for the wsi and ssi extent

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

seasonal evolution of an ice shelf influenced fast ice regime derived from an autonomous thermistor chain ice shelves strongly interact with coastal antarctic sea ice and the associated ecosystem by creating conditions favorable to the formation of a sub ice platelet layer the close investigation of this phenomenon and its seasonal evolution remains a challenge due to logistical constraints and a lack of suitable methodology in this study we characterize the seasonal cycle of antarctic fast ice adjacent to the ekstrom ice shelf in the eastern weddell sea we used a thermistor chain with the additional ability to record the temperature response induced by cyclic heating of resistors embedded in the chain vertical sea ice temperature and heating profiles obtained daily between november 2012 and february 2014 were analyzed to determine sea ice and snow evolution and to calculate the basal energy budget the residual heat flux translated into an ice volume fraction in the platelet layer of 0 18 0 09 which we reproduced by a independent model simulation and agrees with earlier results manual drillings revealed an average annual platelet layer thickness increase of at least 4 m and an annual maximum thickness of 10 m beneath second year sea ice the oceanic contribution dominated the total sea ice production during the study effectively accounting for up to 70 of second year sea ice growth in summer an oceanic heat flux of 21 w m 2 led to a partial thinning of the platelet layer our results further show that the active heating method in contrast to the acoustic sounding approach is well suited to derive the fast ice mass balance in regions influenced by ocean ice shelf interaction as it allows subdiurnal monitoring of the platelet layer thickness

antarctic grounding line mapping from differential satellite radar interferometry 1 the delineation of an ice sheet grounding line i e the transition boundary where ice detaches from the bed and becomes afloat in the ocean is critical to ice sheet mass budget calculations numerical modeling of ice sheet dynamics ice ocean interactions oceanic tides and subglacial environments here we present 15 years of comprehensive high resolution mapping of grounding lines in antarctica using differential satellite synthetic aperture radar interferometry dinsar data from the earth remote sensing satellites 1 2 ers 1 2 radarsat 1 and 2 and the advanced land observing system alos palsar for years 1994 to 2009 dinsar directly measures the vertical motion of floating ice shelves in response to tidal oceanic forcing with millimeter precision at a sample spacing better than 50 m simultaneously over areas several 100 km wide in contrast with earlier methods that detect abrupt changes in surface slope in satellite visible imagery or altimetry data on stagnant and slow moving areas we find that breaks in surface slope are reliable indicators of grounding lines but on most fast moving glaciers and ice streams our dinsar results reveal that prior mappings have positioning errors ranging from a few km to over 100 km a better agreement is found with icesat s data also based on measurements of vertical motion but with a detection noise one order of magnitude larger than with dinsar overall the dinsar mapping of antarctic grounding lines completely redefines the coastline of antarctica

linked trends in the south pacific sea ice edge and southern oscillation index previous work have shown that sea ice variability in the south pacific is associated with extratropical atmospheric anomalies linked to the southern oscillation so over a 32 year period 1982 2013 our study shows that the trend in southern oscillation index soi is also able to quantitatively explain the trends in sea ice edge drift and surface winds in this region on average two thirds of the winter ice edge trend in this sector linked to ice drift and surface winds could be explained by the positive soi trend thus subjecting the ice edge to strong decadal so variability if this relationship holds the negative soi trend prior to the recent satellite era suggests that ice edge trends opposite to that of the recent record over a similar time scale significant low frequency ice edge trends linked to the natural variability of so are superimposed upon any trends expected of anthropogenic forcing

accelerated west antarctic ice mass loss continues to outpace east antarctic gains a b s t r a c t article history while multiple data sources have confirmed that antarctica is losing ice at an accelerating rate different measurement techniques estimate the details of its geographically highly variable mass balance with different levels of accuracy spatio temporal resolution and coverage some scope remains for methodological improvements using a single data type in this study we report our progress in increasing the accuracy and spatial resolution of time variable gravimetry from the gravity recovery and climate experiment grace we determine the geographic pattern of ice mass change in antarctica between january 2003 and june 2014 accounting for glacio isostatic adjustment gia using the ij05 r2 model expressing the unknown signal in a sparse slepian basis constructed by optimization to prevent leakage out of the regions of interest we use robust signal processing and statistical estimation methods applying those to the latest time series of monthly grace solutions we map antarctica s mass loss in space and time as well as can be recovered from satellite gravity alone ignoring gia model uncertainty over the period 2003 2014 west antarctica has been losing ice mass at a rate of 121 8g t yr and has experienced large acceleration of ice mass losses along the amundsen sea coast of 18 5g t yr 2 doubling the mass loss rate in the past six years the antarctic peninsula shows slightly accelerating ice mass loss with larger accelerated losses in the southern half of the peninsula ice mass gains due to snowfall in dronning maud land have continued to add about half the amount of west antarctica s loss back onto the continent over the last decade we estimate the overall mass losses from antarctica since january 2003 at 92 10 gt yr

variability in the distribution of fast ice and the sub ice platelet layer near mcmurdo ice shelf variability in the volume of supercooled ice shelf water outflow in mcmurdo sound is reflected in the thickness and distribution of fast ice and the sub ice platelet layer beneath ground based electromagnetic induction and drill hole surveys of the distribution and thickness of ice shelf influenced fast ice and the sub ice platelet layer in mcmurdo sound were carried out in late spring of 2011 2013 2016 and 2017 in 2011 and 2017 thicker sub ice platelet layers of up to 7 5 and 6 m were observed respectively fast ice formation throughout the winters of 2011 and 2017 was influenced by a higher occurrence of strong southerly wind events and resultant activity of the ross sea polynya in contrast lower wind conditions in 2016 led to largely undisturbed sea ice growth and anomalously extensive fast ice coverage a thinner sub ice platelet layer of up to 4 m was observed in 2016 in 2011 and 2017 substantial and variable sub ice platelet layers were detected in a region of exchange of water masses between the ross sea and the mcmurdo ross ice shelf cavity which were not observed in 2013 and 2016 we hypothesize that a higher frequency of strong southerly wind events resultant polynya activity and high salinity shelf water production over winter accelerates circulation and increases melting in the proximal shallow mcmurdo ice shelf and the deeper ross ice shelf regions of the conjoined cavity the outflow of supercooled ice shelf water and sub ice platelet layer formation in mcmurdo sound are consequently promoted

antarctic ice sheet melting provides negative feedbacks on future climate warming we show by using a three dimensional climate model which includes a comprehensive representation of polar ice sheets that on centennial to millennial time scales antarctic ice sheet ais can melt and moderate warming in the southern hemisphere by up to 10 degrees c regionally in a 4 x co2 scenario this behaviour stems from the formation of a cold halocline in the southern ocean which limits sea ice cover retreat under global warming and increases surface albedo reducing local surface warming furthermore we show that ais melting by decreasing antarctic bottom water formation restrains the weakening of the atlantic meridional overturning circulation which is a new illustration of the effect of the bi polar oceanic seesaw consequently it appears that ais melting strongly interacts with climate and ocean circulation globally it is therefore necessary to account for this coupling in future climate and sea level rise scenarios

antarctic ice sheet loss driven by basal melting of ice shelves accurate prediction of global sea level rise requires that we understand the cause of recent widespread and intensifying glacier acceleration along antarctic ice sheet coastal margins atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves potentially limiting their ability to buttress the flow of grounded tributary glaciers indeed recent ice shelf collapse led to retreat and acceleration of several glaciers on the antarctic peninsula but the extent and magnitude of ice shelf thickness change the underlying causes of such change and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum antarctic pattern of ice shelf thinning through increased basal melt we deduce that this increased melt is the primary control of antarctic ice sheet loss through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow the highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of antarctic ice shelves through ocean upwelling in the amundsen and bellingshausen seas and atmospheric warming on the antarctic peninsula this implies that climate forcing through changing winds influences antarctic ice sheet mass balance and hence global sea level on annual to decadal timescales

preconditioning of antarctic maximum sea ice extent by upper ocean stratification on a seasonal timescale this study uses an observationally constrained and dynamically consistent ocean and sea ice state estimate the author presents a remarkable agreement between the location of the edge of antarctic maximum sea ice extent reached in september and the narrow transition band for the upper ocean 0 100 m depths stratification as early as april to june to the south of this edge the upper ocean has high stratification which forbids convective fluxes to cross through consequently the ocean heat loss to the atmosphere is an efficient way to cool the surface ocean to the freezing point during april to september to the north the upper ocean has low stratification such that the ocean heat loss to the atmosphere is not efficient to cool the upper ocean the upper ocean is instead cooled mainly through mixing with the colder inflow carried by northward ekman transport but cannot reach the freezing point due to the nature of mixing therefore upper ocean stratification dominated by salinity here provides an important constraint on the northward expansion of antarctic sea ice to its maximum

rapid subsurface warming and circulation changes of antarctic coastal waters by poleward shifting winds the southern hemisphere westerly winds have been strengthening and shifting poleward since the 1950s this wind trend is projected to persist under continued anthropogenic forcing but the impact of the changing winds on antarctic coastal heat distribution remains poorly understood here we show that a poleward wind shift at the latitudes of the antarctic peninsula can produce an intense warming of subsurface coastal waters that exceeds 2 c at 200 700 m depth the model simulated warming results from a rapid advective heat flux induced by weakened near shore ekman pumping and is associated with weakened coastal currents this analysis shows that anthropogenically induced wind changes can dramatically increase the temperature of ocean water at ice sheet grounding lines and at the base of floating ice shelves around antarctica with potentially significant ramifications for global sea level rise

pathways of basal meltwater from antarctic ice shelves a model study we investigate spreading pathways of basal meltwater released from all antarctic ice shelves using a circumpolar coupled ice shelf sea ice ocean model that reproduces major features of the southern ocean circulation including the antarctic circumpolar current acc several independent virtual tracers are used to identify detailed pathways of basal meltwaters the spreading pathways of the meltwater tracers depend on formation sites because the meltwaters are transported by local ambient ocean circulation meltwaters from ice shelves in the weddell and amundsen bellingshausen seas in surface subsurface layers are effectively advected to lower latitudes with the acc although a large portion of the basal meltwaters is present in surface and subsurface layers a part of the basal meltwaters penetrates into the bottom layer through active dense water formation along the antarctic coastal margins the signals at the seafloor extend along the topography showing a horizontal distribution similar to the observed spreading of antarctic bottom water meltwaters originating from ice shelves in the weddell and ross seas and in the indian sector significantly contribute to the bottom signals a series of numerical experiments in which thermodynamic interaction between the ice shelf and ocean is neglected regionally demonstrates that the basal meltwater of each ice shelf impacts sea ice and or ocean thermohaline circulation in the southern ocean

consistent past half century trends in the atmosphere the sea ice and the ocean at high southern latitudes simulations performed with the climate model loveclim aided with a simple data assimilation technique that forces a close matching of simulated and observed surface temperature variations are able to reasonably reproduce the observed changes in the lower atmosphere sea ice and ocean during the second half of the twentieth century although the simulated ice area slightly increases over the period 1980 2000 in agreement with observations it decreases by 0 5 106 km2 between early 1960s and early 1980s no direct and reliable sea ice observations are available to firmly confirm this simulated decrease but it is consistent with the data used to constrain model evolution as well as with additional independent data in both the atmosphere and the ocean the simulated reduction of the ice area between the early 1960s and early 1980s is similar to the one simulated over that period as a response to the increase in greenhouse gas concentrations in the atmosphere while the increase in ice area over the last decades of the twentieth century is likely due to changes in atmospheric circulation however the exact contribution of external forcing and internal variability in the recent changes cannot be precisely estimated from our results our simulations also reproduce the observed oceanic subsurface warming north of the continental shelf of the ross sea and the salinity decrease on the ross sea continental shelf parts of those changes are likely related to the response of the system to the external forcing modifications in the wind pattern influencing the ice production melting rates also play a role in the simulated surface salinity decrease

the influence of recent antarctic ice sheet retreat on simulated sea ice area trends 1 observations indicate that dynamic mass loss from the antarctic ice sheet has been accelerating over recent decades leading to a freshening of the southern ocean here we quantify the effect of several rates and spatial distributions of freshwater forcing on simulated sea ice area trends in contrast to a previous study our simulations show that the freshwater effect on sea ice trends over the historical period is small and fails to reproduce the observed regional pattern of trends when using observationally consistent rates of freshwater forcing the coupled model intercomparison project phase 5 cmip5 models do not represent this dynamic ice sheet mass loss and it has been suggested that this deficiency may significantly influence the simulated sea ice trends we show that when accounting for internal variability the average cmip5 sea ice area trend is statistically consistent with the observed trend and accounting for ice sheet derived freshwater forcing has little influence

stronger ocean circulation and increased melting under pine island glacier ice shelf the ice shelf buttressing antarctica s pine island glacier has been melting rapidly observations taken between 1994 and 2009 show that meltwater production has increased by about 50 since 1994 as a result of a stronger circulation below the ice shelf

indian summer monsoon variations and competing influences between hemispheres since 35 ka recorded in tengchongqinghai lake southwestern china abstract the southwestern yunnan province of china which is located at the southeastern margin of the tibetan plateau and close to bay of bengal is significantly influenced by the indian summer monsoon ism in this study we reconstruct proxies for the ism from 35 to 1 ka through detailed analysis of grain size distribution geochemical composition and environmental magnetism from a 7 96 m sediment core from tengchongqinghai lake yunnan province china globally recognized abrupt climatic events including heinrich events 0 3 h0 h3 and the bolling allerod b a warm period are identified in most of our proxies and the long term trend is consistent with other published records such as stalagmite oxygen isotopes 18o from sangxing cave northern hemisphere nh temperature which is influenced by nh solar insolation is commonly suggested to play a dominant role in controlling the ism a comparison of our record with the 18o variations of ice cores from greenland and antarctica a sea surface temperature sst record from the bay of bengal and summer solar insolation at 25 n latitude demonstrates that the general pattern of ism change does follow variations in summer insolation however the ism lags summer insolation by thousands of years while the ism fluctuations are highly correlated with nh temperature on shorter timescales centennial millennial the gradually weakened ism from 22 5 ka until the last glacial maximum lgm indicates a close relationship with the rise of southern hemisphere sh temperature and the relatively cold background of the sh our record expands on the findings of ism records from heqing paleolake basin in southwestern china and the arabian sea sediments suggesting that the nh and sh have a competitive influence on ism by controlling the cross equatorial pressure gradient this relationship means that when nh temperatures are relatively high it has a stronger influence on the ism than sh influences in contrast when the sh temperature is relatively low it has a dominant influence on ism in addition we speculate that the change of sh temperature not only influences the cross equatorial pressure gradient directly but also likely modulates the circulation system of ocean energy by influencing the atlantic meridional overturning circulation amoc

important role for ocean warming and increased ice shelf melt in antarctic sea ice expansion changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature in contrast to arctic sea ice sea ice surrounding antarctica has expanded1 with record extent2 in 2010 this ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling3 here we show that accelerated basal melting of antarctic ice shelves is likely to have contributed significantly to sea ice expansion specifically we present observations indicating that melt water from antarctica s ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves simulating these processes in a coupled climate model we find that cool and fresh surface water from ice shelf melt indeed leads to expanding sea ice in austral autumn and winter this powerful negative feedback counteracts southern hemispheric atmospheric warming although changes in atmospheric dynamics most likely govern regional sea ice trends4 our analyses indicate that the overall sea ice trend is dominated by increased ice shelf melt we suggest that cool sea surface temperatures around antarctica could offset projected snowfall increases in antarctica with implications for estimates of future sea level rise

stability of the west antarctic ice sheet in a warming world equivalent to 0 28 to 0 56 mm yr 1 sea level rise with the rate growing over at least the past two decades 1 4 these observations intensify concerns about the ice sheet s stability that were first raised more than four decades ago 5

turbulent plumes from a glacier terminus melting in a stratified ocean the melting of submerged faces of marine terminating glaciers is a key contributor to the glacial mass budget via direct thermodynamic ablation and the impact of ablation on calving this study considers the behavior of turbulent plumes of buoyant meltwater in a stratified ocean generated by melting of either near vertical calving faces or sloping ice shelves we build insight by applying a turbulent plume model to describe melting of a locally planar region of ice face in a linearly stratified ocean in a regime where subglacial discharge is insignificant the plumes rise until becoming neutrally buoyant before intruding into the ocean background for strong stratifications we obtain leading order scaling laws for the flow including the height reached by the plume before intrusion and the melt rate expressed in terms of the background ocean temperature and salinity stratifications these scaling laws provide a new perspective for parameterizing glacial melting in response to a piecewise linear discretization of the ocean stratification

sea ice ocean feedbacks in the antarctic shelf seas abstractobserved changes in antarctic sea ice are poorly understood in part due to the complexity of its interactions with the atmosphere and ocean a highly simplified coupled sea ice ocean mixe

platelet ice the southern ocean s hidden ice a review basal melt of ice shelves is not only an important part of antarctica s ice sheet mass budget but it is also the origin of one of the most peculiar types of sea ice found in the polar oceans platelet ice in many regions around coastal antarctica tiny ice crystals form and grow in supercooled plumes of ice shelf water releasing heat into the surrounding ocean they usually rise towards the surface eventually becoming trapped under an ice shelf as marine ice frequently masses of those crystals are advected out of the ice shelf cavity and accumulate below a solid sea ice cover to form a semiconsolidated layer when the overlying sea ice grows into this so called sub ice platelet layer the loose crystals are consolidated adding additional thickness to the sea ice these phenomena are generally referred to as platelet ice although confusion about the terminology is widespread in the literature the presence of platelet ice has a profound impact on sea ice properties and processes in several regions of antarctica with numerous implications for the local polar marine biosphere most notably sub ice platelet layers provide a stable sheltered nutrient and food rich habitat which usually results in a highly productive and uniquely adapted ecosystem it has also been hypothesised that platelet ice may be an indicator of the state of an ice shelf although comprehensive time series are limited to the ross sea this paper clears up the terminology by providing exact definitions of the relevant terms we review platelet ice formation observational methods as well as geographical and seasonal occurrence the physical properties and ecological implications are merged in a way understandable for physicists and biologists alike to lay the foundation for the interdisciplinary research that is necessary to tackle the current knowledge gaps

different magnitudes of projected subsurface ocean warming around greenland and antarctica accurate projections of global sea level rise require information of future ocean warming in the vicinity of the large ice sheets an analysis of 19 climate model projections suggests that subsurface ocean warming near both polar ice sheets will be substantial with the potential to lead to significant increases in ice mass loss

southern ocean warming delayed by circumpolar upwelling and equatorward transport unlike the arctic the southern ocean has shown little warming an analysis of observations and numerical simulations suggests that southern ocean warming patterns are shaped by meridional overturning more than surface heating