characteristics of the modelled meteoric freshwater budget of the western antarctic peninsula abstract rapid climatic changes in the western antarctic peninsula wap have led to considerable changes in the meteoric freshwater input into the surrounding ocean with implications for ocean circulation the marine ecosystem and sea level rise in this study we use the high resolution regional atmospheric climate model racmo2 3 coupled to a firn model to assess the various contributions to the meteoric freshwater budget of the wap for 1979 2014 precipitation snowfall and rainfall meltwater runoff to the ocean and glacial discharge snowfall is the largest component in the atmospheric contribution to the freshwater budget and exhibits large spatial and temporal variability the highest snowfall rates are orographically forced and occur over the coastal regions of the wap 2000 mm water equivalent w e y 1 and extend well onto the ocean up to the continental shelf break a minimum 500 mm w e y 1 is reached over the open ocean rainfall is an order of magnitude smaller and strongly depends on latitude and season being large in summer when sea ice extent is at its minimum for antarctic standards wap surface meltwater production is relatively large 50 mm w e y 1 but a large fraction refreezes in the snowpack limiting runoff only at a few more northerly locations is the meltwater predicted to run off into the ocean in summer we find a strong relationship of the freshwater fluxes with the southern annular mode sam index when sam is positive and occurs simultaneously with a la nina event there are anomalously strong westerly winds and enhanced snowfall rates over the wap mountains marguerite bay and the bellingshausen sea when sam coincides with an el nino event winds are more northerly reducing snowfall and increasing rainfall over the ocean and enhancing orographic snowfall over the wap mountains assuming balance between snow accumulation mass gain and glacial discharge mass loss the largest glacial discharge is found for the regions around adelaide island 10 gt y 1 anvers island 8 gt y 1 and southern palmer land 12 gt y 1 while a minimum 2 gt y 1 is found in marguerite bay and the northern wap glacial discharge is in the same order of magnitude as the direct freshwater input into the ocean from snowfall but there are some local differences the spatial patterns in the meteoric freshwater budget have consequences for local productivity and carbon drawdown in the coastal ocean

surface mass balance of small glaciers on james ross island north eastern antarctic peninsula during 2009 2015 two small glaciers on james ross island the north eastern antarctic peninsula experienced surface mass gain between 2009 and 2015 as revealed by field measurements a positive cumulative surface mass balance of 0 57 0 67 and 0 11 0 37 m w e was observed during the 2009 2015 period on whisky glacier and davies dome respectively the results indicate a change from surface mass loss that prevailed in the region during the first decade of the 21st century to predominantly positive surface mass balance after 2009 10 the spatial pattern of annual surface mass balance distribution implies snow redistribution by wind on both glaciers the mean equilibrium line altitudes for whisky glacier 311 16 m a s l and davies dome 393 18 m a s l are in accordance with the regional data indicating 200 300 m higher equilibrium line on james ross and vega islands compared with the south shetland islands the mean accumulation area ratio of 0 68 0 09 and 0 44 0 09 determined for whisky glacier and davies dome respectively is similar to the value reported for vega island and within the range of typical values for high latitude glaciers

hydrography and energetics of a cold subpolar fjord andvord bay western antarctic peninsula abstract fjords along the western antarctic peninsula contain rich marine ecosystems and tidewater glaciers potentially sensitive to ocean change but much is unknown about the physical oceanography of these fjords this paper presents a comprehensive description of the physical environment of andvord bay a glacial fjord located in the gerlache strait on the northern end of the peninsula measurements were collected as part of the fjordeco program between november 2015 and march 2017 including during three research cruises and from a number of fixed installations sub surface moorings time lapse cameras and automatic weather stations andvord bay is located just north of a sill in the gerlache strait this sill inhibits the direct influence of warm upper circumpolar deep water from the shelf and deep waters in the fjord are therefore relatively cold as a result glaciers in andvord bay are not subject to the substantial ocean driven retreat observed farther south on the peninsula instead mass flux from the glaciers occurs mainly through calving the influence of meltwater in andvord bay is small compared to glacial fjords in the arctic and in the south shetland islands although summer freshening is evident in the fjord near surface layer likely as a result of glacial inputs the combination of surface freshening and the absence of strong mean wind forcing in the fjord results in salinity stratification extending well into the euphotic zone providing advantageous conditions for phytoplankton blooms andvord bay is generally dynamically quiet compared to the ambient ocean with the exception of during local katabatic wind events exchange with the gerlache strait is weak although the deep waters of the fjord are replenished on an annual scale through slow lateral exchange with the outside in addition deep convection may play a role in ventilating subsurface waters in winter

the link between climate warming and break up of ice shelves in the antarctic peninsula a review of in situ and remote sensing data covering the ice shelves of the antarctic peninsula provides a series of characteristics closely associated with rapid shelf retreat deeply embayed ice fronts calving of myriad small elongate bergs in punctuated events increasing flow speed and the presence of melt ponds on the ice shelf surface in the vicinity of the break ups as climate has warmed in the antarctic peninsula region melt season duration and the extent of ponding have increased most break up events have occurred during longer melt seasons suggesting that meltwater itself not just warming is responsible regions that show melting without pond formation are relatively unchanged melt ponds thus appear to be a robust harbinger of ice shelf retreat we use these observations to guide a model of ice shelf flow and the effects of meltwater crevasses present in a region of surface ponding will likely fill to the brim with water we hypothesize building on weertman 1973 hughes 1983 and van der veen 1998 that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat a thermodynamic finite element model is used to evaluate ice flow and the strain field and simple extensions of this model are used to investigate crack propagation by meltwater the model results support the hypothesis

polynya dynamics drive primary production in the larsen a and b embayments following ice shelf collapse 1 the climate driven collapses of the larsen a and b ice shelves have opened up new regions of the coastal antarctic to the influence of sea ice resulting in increases in seasonal primary production in this study passive microwave remote sensing of sea ice concentration and satellite imagery of ocean color are employed to quantify the magnitude of and variability in open water area and net primary productivity npp in the larsen embayments between 1997 and 2011 numerical model output provides context to analyze atmospheric forcing on the coastal ocean following ice shelf disintegration the embayments function as coastal sensible heat polynyas the larsen a and b are as productive as other antarctic shelf regions with seasonally averaged daily npp rates reaching 1232 and 1127 mg c m 2 d 1 and annual rates reaching 200 and 184 g c m 2 yr 1 respectively a persistent cross shelf gradient in npp is present with higher productivity rates offshore contrasting with patterns observed along the west antarctic peninsula embayment productivity is intimately tied to sea ice dynamics with large interannual variability in npp rates driven by open water area and the timing of embayment opening opening of the embayment is linked to periods of positive southern annular mode and stronger westerlies which lead to the vertical deflection of warm maritime air over the peninsula and down the leeward side causing increases in surface air temperature and wind velocity high productivity in these new polynyas is likely to have ramifications for organic matter export and marine ecosystem evolution

larsen ice shelf has progressively thinned the retreat and collapse of antarctic peninsula ice shelves in tandem with a regional atmospheric warming has fueled speculation as to how these events may be related satellite radar altimeter measurements show that between 1992 and 2001 the larsen ice shelf lowered by up to 0 27 0 11 meters per year the lowering is explained by increased summer meltwater and the loss of basal ice through melting enhanced ocean driven melting may provide a simple link between regional climate warming and the successive disintegration of sections of the larsen ice shelf

on land ice loss and glacial isostatic adjustment at the drake passage 2003 2009 1 land glacier extent and volume at the northern and southern margins of the drake passage have been in a state of dramatic demise since the early 1990s here time varying space gravity observations from the gravity recovery and climate experiment grace are combined with global positioning system gps bedrock uplift data to simultaneously solve for ice loss and for solid earth glacial isostatic adjustment gia to little ice age lia cryospheric loading the present day ice loss rates are determined to be 26 6 gt yr and 41 5 9 gt yr in the southern and northern patagonia ice fields npi spi and antarctic peninsula ap respectively these are consistent with estimates based upon thickness and flux changes bounds are recovered for elastic lithosphere thicknesses of 35 h 70 km and 20 h 45 km and for upper mantle viscosities of 4 8 1018 pa s and 3 10 1019 pa s using a half space approximation for npi spi and ap respectively using an iterative forward model strategy antarctic peninsula ice models with a prolonged lia extending to a d 1930 are favored in all 2 fits to the gps uplift data this result is largely decoupled from earth structure assumptions the gia corrections account for roughly 20 60 of the space determined secular gravity change collectively the on land ice losses correspond to volume increases of the oceans equivalent to 0 19 0 045 mm yr of sea level rise for the last 15 years

spatial patterns of variability in antarctic surface temperature connections to the southern hemisphere annular mode and the southern oscillation 1 the 17 year 1982 1998 trend in surface temperature shows a general cooling over the antarctic continent warming of the sea ice zone with moderate changes over the oceans warming of the peripheral seas is associated with negative trends in the regional sea ice extent effects of the southern hemisphere annular mode sam and the extrapolar southern oscillation so on surface temperature are quantified through regression analysis positive polarities of the sam are associated with cold anomalies over most of antarctica with the most notable exception of the antarctic peninsula positive temperature anomalies and ice edge retreat in the pacific sector are associated with el nino episodes over the past two decades the drift towards high polarity in the sam and negative polarity in the so indices couple to produce a spatial pattern with warmer temperatures in the antarctic peninsula and peripheral seas and cooler temperatures over much of east antarctica

a doubling in snow accumulation in the western antarctic peninsula since 1850 1 we present results from a new medium depth 136 metres ice core drilled in a high accumulation site 73 59 s 70 36 w on the south western antarctic peninsula during 2007 the gomez record reveals a doubling of accumulation since the 1850s from a decadal average of 0 49 mweq y 1 in 1855 1864 to 1 10 mweq y 1 in 1997 2006 with acceleration in recent decades comparison with published accumulation records indicates that this rapid increase is the largest observed across the region evaluation of the relationships between gomez accumulation and the primary modes of atmospheric circulation variability reveals a strong temporally stable and positive relationship with the southern annular mode sam furthermore the sam is demonstrated to be a primary factor in governing decadal variability of accumulation at the core site r 0 66 the association between gomez accumulation and enso is complex while sometimes statistically significant the relationship is not temporally stable thus at decadal scales we can utilise the gomez accumulation as a suitable proxy for sam variability but not for enso

the relative influence of enso and sam on antarctic peninsula climate recent warming of the antarctic peninsula during austral autumn winter and spring has been linked to sea surface temperature sst trends in the tropical pacific and tropical atlantic while warming of the northeast peninsula during summer has been linked to a strengthening of westerly winds traversing the peninsula associated with a positive trend in the southern annular mode sam here we demonstrate that circulation changes associated with the sam dominate interannual temperature variability across the entire antarctic peninsula during both summer and autumn while relationships with tropical pacific sst variability associated with the el nino southern oscillation enso are strongest and statistically significant primarily during winter and spring only we find the enso peninsula temperature relationship during autumn to be weak on interannual timescales and regional circulation anomalies associated with the sam more important for interannual temperature variability across the peninsula during autumn consistent with previous studies western peninsula temperatures during autumn winter and spring are closely tied to changes in the amundsen sea low asl and associated meridional wind anomalies the interannual variability of asl depth is most strongly correlated with the sam index during autumn while the enso relationship is strongest during winter and spring investigation of western and northeast peninsula temperatures separately reveals that interannual variability of northeast peninsula temperatures is primarily sensitive to zonal wind anomalies crossing the peninsula and resultant lee side adiabatic warming rather than to meridional wind anomalies which is closely tied to variability in the zonal portion of the sam pattern

late quaternary environmental changes in marguerite bay antarctic peninsula inferred from lake sediments and raised beaches the antarctic peninsula is one of the fastest warming regions on earth but its palaeoenvironmental history south of 63 latitude is relatively poorly documented relying principally on the marine geological record and short ice cores in this paper we present evidence of late quaternary environmental change from the marguerite bay region combining data from lake sediment records on horseshoe island and pourquoi pas island and raised beaches at horseshoe island pourquoi pas island and calmette bay lake sediments were radiocarbon dated and analysed using a combination of sedimentological geochemical and microfossil methods raised beaches were surveyed and analysed for changes in clast composition size and roundness results suggest a non erosive glacial regime could have existed on horseshoe island from 35 780 38 650 33 380 or 32 910 34 630 31 370 cal yr bp onwards there is radiocarbon and macrofossil evidence for possible local deglaciation events at 28 830 29 370 28 320 cal yr bp immediately post dating antarctic isotopic maximum 4 and 21 110 21 510 20 730 interpolated cal yr bp coinciding with or immediately post dating antarctic isotopic maximum 2 the holocene deglaciation of horseshoe island commenced from 10 610 11 000 10 300 cal yr bp at the same time as the early holocene temperature maximum recorded in antarctic ice cores this was followed by the onset of marine sedimentation in the narrows pourquoi pas island before 8850 8480 9260 cal yr bp relative sea level high stands of 40 79 m above present at pourquoi pas island and 40 55 m above present at calmette bay occurred sometime after 9000 cal yr bp and suggest that a thicker ice sheet including grounded ice streams was present in this region of the antarctic peninsula than that recorded at sites further north isolation of the narrows lake basin on pourquoi pas island shows relative sea level in this region had fallen rapidly to 19 41 m by 7270 7385 7155 cal yr bp chaetoceros resting spores suggest high productivity and stratified surface waters in the narrows after 8850 9260 8480 cal yr bp and beach clasts provide evidence of a period of increased wave energy at approximately 8000 yr bp lake sediment and beach data suggest an extended period of regional warming sometime between 6200 and 2030 cal yr bp followed by the onset of neoglacial conditions from 2630 and 2030 cal yr bp in narrows lake and col lake 1 respectively diatom and 13c vs c n and macrofossil evidence suggest a potential increase in the number of birds and seals visiting the narrows lake catchment sometime after 2100 2250 2000 cal yr bp with enhanced nutrient enrichment evident after 1150 1230 1080 cal yr bp and particularly from c 460 540 380 cal yr bp a very recent increase in gomphonema species and organic carbon in the top centimetre of the narrows lake sediment core after c 410 490 320 cal yr bp and increased sedimentation rates in the col lake 1 sediment core after c 400 490 310 cal yr bp may be a response to the regional late holocene warming of the antarctic peninsula

340 years of atmospheric circulation characteristics reconstructed from an eastern antarctic peninsula ice core 1 precipitation delivery mechanisms for dolleman island di located off the east coast of the antarctic peninsula are investigated using reanalysis and back trajectory data the southern annular mode sam and enso are both shown to influence precipitation delivery and event size precipitation delivery variability is compared against the interannual variation of chemical data from two di ice cores nitrate concentration in the cores is strongly linked with the ratio of easterly to westerly back trajectories arriving at di as described by a cross peninsula index cpi defined in this paper this cpi is used subsequently to reconstruct the atmospheric circulation characteristics for the 340 year ice core record the analysis highlights a period of increased easterlies during 1720 1780 and an increase in westerlies for 1950 1980 the latter concomitant with a positive sam trend and western peninsula warming the reconstruction also reveals periods when polynyas may have been present in the weddell sea

ocean forcing of glacier retreat in the western antarctic peninsula in recent decades hundreds of glaciers draining the antarctic peninsula 63 to 70 s have undergone systematic and progressive change these changes are widely attributed to rapid increases in regional surface air temperature but it is now clear that this cannot be the sole driver here we identify a strong correspondence between mid depth ocean temperatures and glacier front changes along the 1000 kilometer western coastline in the south glaciers that terminate in warm circumpolar deep water have undergone considerable retreat whereas those in the far northwest which terminate in cooler waters have not furthermore a mid ocean warming since the 1990s in the south is coincident with widespread acceleration of glacier retreat we conclude that changes in ocean induced melting are the primary cause of retreat for glaciers in this region

changes in ice dynamics elevation and mass discharge of dinsmoor bombardier edgeworth glacier system antarctic peninsula abstract the northern antarctic peninsula is one of the fastest changing regions on earth the disintegration of the larsen a ice shelf in 1995 caused tributary glaciers to adjust by speeding up surface lowering and overall increased ice mass discharge in this study we investigate the temporal variation of these changes at the dinsmoor bombardier edgeworth glacier system by analyzing dense time series from various spaceborne and airborne earth observation missions precollapse ice shelf conditions and subsequent adjustments through 2014 were covered our results show a response of the glacier system some months after the breakup reaching maximum surface velocities at the glacier front of up to 8 8 m d in 1999 and a subsequent decrease to 1 5 m d in 2014 using a dense time series of interferometrically derived tandem x digital elevation models and photogrammetric data an exponential function was fitted for the decrease in surface elevation elevation changes in areas below 1000 m a s l amounted to at least 130 15 m between 1995 and 2014 with change rates of 3 15 m a between 2003 and 2008 current change rates 2010 2014 are in the range of 1 7 m a mass imbalances were computed with different scenarios of boundary conditions the most plausible results amount to 40 7 3 9 gt the contribution to sea level rise was estimated to be 18 8 1 8 gt corresponding to a 0 052 0 005 mm sea level equivalent for the period 1995 2014 our analysis and scenario considerations revealed that major uncertainties still exist due to insufficiently accurate ice thickness information the second largest uncertainty in the computations was the glacier surface mass balance which is still poorly known our time series analysis facilitates an improved comparison with grace data and as input to modeling of glacio isostatic uplift in this region the study contributed to a better understanding of how glacier systems adjust to ice shelf disintegration

observed relationships between the el nino southern oscillation and the extratropical zonal mean circulation abstract there is increasing evidence indicating that the climate response to variations in the el nino southern oscillation enso includes not only thermally forced zonal wind anomalies in the subtropics but also eddy driven zonal wind anomalies that extend into the mid high latitudes of both hemispheres in this study new insights into the observed seasonally varying signature of enso in the extratropical zonal mean circulation are provided and the associated linkages with the dominant patterns of extratropical variability are examined the zonal mean extratropical atmospheric response to enso is characterized by two principal features an equivalent barotropic dipole in the southern hemisphere sh zonal mean zonal flow with centers of action located near 40 and 60 during austral summer and a weaker but analogous dipole in the northern hemisphere nh with centers of action located near 25 and 45 during early and late boreal winter both structures are accompanied by eddy momentum flux ano

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

freshening of antarctic bottom water in the indian ocean sector of southern ocean abstract recent observations reveal a rapid reduction in salinity and density of antarctic bottom water aabw in the indian ocean sector of southern ocean previous studies have shown fast freshening of aabw since 1995 but an increased rate of freshening from 2006 to 2010 was exhibited in the present study by both ecmwf oras4 reanalysis data as well as in situ data during the same period the degrees of change observed in the aabw were more predominant in the in situ data becoming warmer 0 05 c fresher 0 01 and lighter 0 01 kg m 3 between 2006 and 2010 the height of fresh water added per unit area for 500 m thickness 4000 4500 m was 2 2 cm per annum cm a 1 the aabw observed in the present study could have originated from weddell sea or cape darnley polynya the decadal changes indicate an enhanced sea ice formation due to increased positive phases of southern annular mode sam which may have led to the increase in fresh water input resulting in freshening of aabw

ice core evidence for significant 100 year regional warming on the antarctic peninsula we present a new 150 year high resolution stable isotope record delta o 18 from the gomez ice core drilled on the data sparse south western antarctic peninsula revealing a similar to 2 7 degrees c rise in surface temperatures since the 1950s the record is highly correlated with satellite derived temperature reconstructions and instrumental records from faraday station on the north west coast thus making it a robust proxy for local and regional temperatures since the 1850s we conclude that the exceptional 50 year warming previously only observed in the northern peninsula is not just a local phenomena but part of a statistically significant 100 year regional warming trend that began around 1900 a suite of coupled climate models are employed to demonstrate that the 50 and 100 year temperature trends are outside of the expected range of variability from pre industrial control runs indicating that the warming is likely the result of external climate forcing citation thomas e r p f dennis t j bracegirdle and c franzke 2009 ice core evidence for significant 100 year regional warming on the antarctic peninsula geophys res lett 36 l20704 doi 10 1029 2009gl040104

atmospheric patterns over the antarctic peninsula abstractusing clustering analysis for the sea level pressure field of the era interim reanalysis between 1979 and 2016 five synoptic pressure patterns have been obtained for the drake area and antarctic peninsula ap region 45 75 s 20 120 w and the resulting daily series has been made available to the scientific community the five patterns have been named according to their most important features as follows low over the weddell sea lws low over the amundsen and bellingshausen seas lab low over the drake passage ldp zonal flow over the drake passage zdp and ridge over the antarctic peninsula rap each atmospheric pattern is described after analyzing its development and evolution a frequency analysis shows that the five atmospheric patterns present a similar annual frequency but a large seasonal variability the transitions from one pattern to another tend to follow a cycle in which synoptic atmospheric waves are displaced eastward by a quarter wavelength four of the five atmosphe

late cenozoic fluvial lacustrine susceptibility increases in the linxia basin and their implications for tibetan plateau uplift the variations and mechanisms of fluvial lacustrine mass specific magnetic susceptibility in the northeastern ne tibetan plateau are complex in this study we compiled two miocene pliocene records the heilinding and maogou sections respectively from the linxia basin fluvial lacustrine sediments ne tibetan plateau to describe the increases and discuss their influential factors the in the heilinding section remained relatively stable at low values before ca 8 5 ma and has increased since ca 8 5 ma with strong fluctuations in the maogou section the increased at ca 6 0 ma with relatively weak fluctuations the mean values were higher in the heilinding section than the maogou section the rock magnetic results showed that hematite dominated both sites during the early periods 8 5 ma in the heilinding and 6 0 ma in the maogou respectively and was replaced by magnetite after that time based on the comparison of records in linxia basin with other magnetic and climate records from the surrounding regions the increase around 8 5 6 0 ma in the linxia basin was mainly driven by tectonics in the northeastern tibetan plateau

the relationship between the southern hemisphere annular mode and antarctic peninsula summer temperatures analysis of a high resolution model climatology abstract the large regional summer warming on the east coast of the northern antarctic peninsula ap which has taken place since the mid 1960s has previously been proposed to be caused by a trend in the southern hemisphere annular mode sam the authors utilize a high resolution regional atmospheric model climatology 14 km grid spacing to study the mechanisms that determine the response of the near surface temperature to an increase in the sam t sam month to month variations in near surface temperature and surface pressure are well represented by the model it is found that north of 68 s t sam is much larger on the eastern lee side than on the western windward side of the barrier this is because of the enhanced westerly flow of relatively warm air over the barrier which warms and dries further as it descends down the lee slope the downward motion on the eastern side of the barrier causes a decrease in surface mass balance and cloud cover south of 68 s vertical deflection across

strong surface melting preceded collapse of antarctic peninsula ice shelf 1 during the austral summer of 2001 02 melting at the surface of larsen ice shelf in the antarctic peninsula was three times greater than the average of five previous summers this exceptional melt event lasted for three months and was followed by the collapse of larsen b ice shelf during which 3 200 km2 of ice shelf surface was lost the strong melting was caused by a persistent atmospheric circulation anomaly which depleted sea ice concentrations in front of larsen ice shelf and transported warm air to the ice shelf throughout the 2001 02 summer this supports the theory that large meltwater fluxes accelerate the retreat of antarctic peninsula ice shelves

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

glacier acceleration and thinning after ice shelf collapse in the larsen b embayment antarctica 1 ice velocities derived from five landsat 7 images acquired between january 2000 and february 2003 show a two to six fold increase in centerline speed of four glaciers flowing into the now collapsed section of the larsen b ice shelf satellite laser altimetry from icesat indicates the surface of hektoria glacier lowered by up to 38 6 m in a six month period beginning one year after the break up in march 2002 smaller elevation losses are observed for crane and jorum glaciers over a later 5 month period two glaciers south of the collapse area flask and leppard show little change in speed or elevation seasonal variations in speed preceding the large post collapse velocity increases suggest that both summer melt percolation and changes in the stress field due to shelf removal play a major role in glacier dynamics

temporal and spatial variation of stable isotope ratios and accumulation rates in the hinterland of neumayer station east antarctica four firn cores were retrieved in 2007 at two ridges in the area of the ekstrom ice shelf dronning maud land coastal east antarctica in order to investigate the recent regional climate variability and the potential for future extraction of an intermediate depth core stable water isotope analysis tritium content and electrical conductivity were used to date the cores for the period 1981 2006 a strong and significant correlation between the stable isotope composition of firn cores in the hinterland and mean monthly air temperatures at neumayer station was r 0 54 0 71 no atmospheric warming or cooling trend is inferred from our stable isotope data for the period 1962 2006 the stable isotope record of the ice firn cores could expand well beyond the meteoro logical record of the region no significant temporal variation of accumulation rates was detected however decreasing accumulation rates were found from coast to hinterland as well as from east halvfarryggen to west sorasen the deuterium excess d exhibits similar differences higher d at sorasen lower d at halvfarryggen with a weak negative temporal trend on halvfarryggen 0 04 a 1 probably implying increasing oceanic input we conclude that halvfarryggen acts as a natural barrier for moisture carrying air masses circulating in the region from east to west

accumulation variability in the antarctic peninsula the role of large scale atmospheric oscillations and their interactions abstracta new ice core drilled in 2010 to bedrock from the bruce plateau bp on the antarctic peninsula ap provides a high temporal resolution record of environmental conditions in this region the extremely high annual accumulation rate at this site facilitates analysis of the relationships between annual net accumulation an on the bp and large scale atmospheric oscillations over the last 45 years an on the bp has been positively correlated with both the southern annular mode sam and southern oscillation index soi extending this analysis back to 1900 reveals that these relationships are not temporally stable and they exhibit major shifts in the late 1940s and the mid 1970s that are contemporaneous with phase changes in the pacific decadal oscillation pdo these varying multidecadal characteristics of the an oscillation relationships are not apparent when only data from the post 1970s era are employed analysis of the longer ice core record reveals that the influence of the sam on an depends

foehn winds link climate driven warming to ice shelf evolution in antarctica rapid warming of the antarctic peninsula over the past several decades has led to extensive surface melting on its eastern side and the disintegration of the prince gustav larsen a and larsen b ice shelves the warming trend has been attributed to strengthening of circumpolar westerlies resulting from a positive trend in the southern annular mode sam which is thought to promote more frequent warm dry downsloping foehn winds along the lee or eastern side of the peninsula we examined variability in foehn frequency and its relationship to temperature and patterns of synoptic scale circulation using a multidecadal meteorological record from the argentine station matienzo located between the larsen a and b embayments this record was further augmented with a network of six weather stations installed under the u s nsf larsen ice shelf system antarctica project significant warming was observed in all seasons at matienzo with the largest seasonal increase occurring in austral winter 3 71 c between 1962 1972 and 1999 2010 frequency and duration of foehn events were found to strongly influence regional temperature variability over hourly to seasonal time scales surface temperature and foehn winds were also sensitive to climate variability with both variables exhibiting strong positive correlations with the sam index concomitant positive trends in foehn frequency temperature and sam are present during austral summer with sustained foehn events consistently associated with surface melting across the ice sheet and ice shelves these observations support the notion that increased foehn frequency played a critical role in precipitating the collapse of the larsen b ice shelf

decadal freshening of the antarctic bottom water exported from the weddell sea recent decadal changes in southern hemisphere climate have driven strong responses from the cryosphere concurrently there has been a marked freshening of the shelf and bottom waters across a wide sector of the southern ocean hypothesised to be caused by accelerated glacial melt in response to a greater flux of warm waters from the antarctic circumpolar current onto the shelves of west antarctica however the circumpolar pattern of changes has been incomplete no decadal freshening in the deep layers of the atlantic sector had been observed in this study we document a significant freshening of the antarctic bottom water exported from the weddell sea which is the source for the abyssal layer of the atlantic overturning circulation and we trace its possible origin to atmospheric forced changes in the ice shelves and sea ice on the eastern flank of the antarctic peninsula that include an anthropogenic component these findings suggest that the expansive and relatively cool weddell gyre does not insulate the bottom water formation regions in the atlantic sector from the ongoing changes in climatic forcing over the antarctic region

foehn jets over the larsen c ice shelf antarctica previously unknown foehn jets have been identified to the east of the antarctic peninsula ap above the larsen c ice shelf these jets have major implications for the east coast of the ap a region of rapid climatic warming and where two large sections of ice shelf have collapsed in recent years during three foehn events across the ap leeside warming and drying is seen in new aircraft observations and simulated well by the met office unified model metum at 1 5 km grid spacing in case a weak southwesterly flow and an elevated upwind inversion characterise a highly nonlinear flow regime with upwind flow blocking in case c strong northwesterly winds characterise a relatively linear case with little upwind flow blocking case b resides somewhere between the two in flow regime linearity the foehn jets apparent in aircraft observations where available and metum simulations of all three cases are mesoscale features up to 60 km in width originating from the mouths of leeside inlets through back trajectory analysis they are identified as a type of gap flow in cases a and b the jets are distinct being strongly accelerated relative to the background flow and confined to low levels above the larsen c ice shelf they resemble the shallow foehn of the alps case c resembles a case of deep foehn with the jets less distinct the foehn jets are considerably cooler and moister relative to adjacent regions of calmer foehn air this is due to a dampened foehn effect in the jet regions in case a the jets have lower upwind source regions and in the more linear case c there is less diabatic warming and precipitation along jet trajectories due to the reduced orographic uplift across the mountain passes

analysis of the projected regional sea ice changes in the southern ocean during the twenty first century using the set of simulations performed with atmosphere ocean general circulation models aogcms for the fourth assessment report of the intergovernmental panel on climate change ipcc ar4 the projected regional distribution of sea ice for the twenty first century has been investigated averaged over all those model simulations the current climate is reasonably well reproduced however this averaging procedure hides the errors from individual models over the twentieth century the multimodel average simulates a larger sea ice concentration decrease around the antarctic peninsula compared to other regions which is in qualitative agreement with observations this is likely related to the positive trend in the southern annular mode sam index over the twentieth century in both observations and in the multimodel average despite the simulated positive future trend in sam such a regional feature around the antarctic peninsula is absent in the projected sea ice change for the end of the twenty first century the maximum decrease is indeed located over the central weddell sea and the amundsen bellingshausen seas in most models changes in the oceanic currents could play a role in the regional distribution of the sea ice especially in the ross sea where stronger southward currents could be responsible for a smaller sea ice decrease during the twenty first century finally changes in the mixed layer depth can be found in some models inducing locally strong changes in the sea ice concentration

trends in the deep southern ocean 1958 2010 implications for antarctic bottom water properties and volume export 1 regional formation of deep and bottom water masses around the antarctic continental shelf is one of the most important processes contributing to variability of the global meridional overturning circulation deep cell southern ocean hydrographic data collected during the years 1958 2010 indicate that dense shelf waters cooled and freshened during that period in the surrounding open ocean antarctic bottom water aabw warmed with no evidence of salinity change as a result of source water property changes aabw exported from the southern ocean to the deep world ocean became lighter over the period analyzed the average rate of density change within the areas that experienced statistically significant change was 0 0019 kg m 3 yr 1 for the last 20 years of the analysis a negative aabw volume anomaly relative to the half century average 1958 2010 was indicated possibly due to production of a lighter aabw variety or to changes in formation rates over the entire five decades the upper isopycnal of the aabw layer deepened at a rate of 8 1 m yr 1 changes in fundamental hydrographic properties such as these can have important implications for long term global ocean circulation and climate

the impact of a changing southern hemisphere annular mode on antarctic peninsula summer temperatures since the mid 1960s rapid regional summer warming has occurred on the east coast of the northern antarctic peninsula with near surface temperatures increasing by more than 2 degrees c this warming has contributed significantly to the collapse of the northern sections of the larsen ice shelf coincident with this warming the summer southern hemisphere annular mode sam has exhibited a marked trend suggested by modeling studies to be predominantly a response to anthropogenic forcing resulting in increased westerlies across the northern peninsula observations and reanalysis data are utilized to demonstrate that the changing sam has played a key role in driving this local summer warming it is proposed that the stronger summer westerly winds reduce the blocking effect of the antarctic peninsula and lead to a higher frequency of air masses being advected eastward over the orographic barrier of the northern antarctic peninsula when this occurs a combination of a climatological temperature gradient across the barrier and the formation of a fohn wind on the lee side typically results in a summer near surface temperature sensitivity to the sam that is 3 times greater on the eastern side of the peninsula than on the west sam variability is also shown to play a less important role in determining summer temperatures at stations west of the barrier in the northern peninsula similar to 62 degrees s both at the surface and throughout the troposphere this is in contrast to a station farther south similar to 65 degrees s where the sam exerts little influence

tropical connections to climatic change in the extratropical southern hemisphere the role of atlantic sst trends abstractthe austral spring relationships between sea surface temperature sst trends and the southern hemisphere sh extratropical atmospheric circulation are investigated using an atmospheric general circulation model agcm a suite of simulations are analyzed wherein the agcm is forced by underlying sst conditions in which recent trends are constrained to individual ocean basins pacific indian and atlantic allowing the impact of each region to be assessed in isolation when forced with observed global sst the model broadly replicates the spatial pattern of extratropical sh geopotential height trends seen in reanalyses however when forcing by each ocean basin separately similar structures arise only when atlantic sst trends are included it is further shown that teleconnections from the atlantic are associated with perturbations to the zonal walker circulation and the corresponding intensification of the local hadley cell the impact of which results in the development of atmospheric rossby w

labile organic carbon dynamics in continental shelf sediments after the recent collapse of the larsen ice shelves off the eastern antarctic peninsula a radiochemical approach abstract labile organic carbon loc dynamics i e of recently produced planktonic material and sediment dynamics were studied in the seabed using naturally occurring 14corg and 210pb measurements in the region where the larsen ice shelves a and b were floating almost two decades ago a non steady state diagenetic model was used to estimate sediment mixing coefficients as well as loc fluxes to the seabed and loc turnover times i e mean residence times in a suite of 14 sediment cores from the continental shelf including a glacial trough at four of the stations cores were collected during 2007 and 2011 cruises enabling a time series approach for understanding the evolution of sedimentary processes and loc dynamics in the deposits below a collapsed ice shelf sediment mixing coefficients based on non steady state 210pb profiles varied between 0 01 cm2 y 1 and 1 6 cm2 y 1 in these post ice shelf sediments these values were similar to those found in polar deep sea environments where sedimentary conditions are less dynamic than in shallower provinces loc whose abundance decreased uniformly with depth was detected to depths ranging from 2 to 16 cm with loc seabed inventories varying from 1 5 to 22 mg loc cm 2 excess 210pb and loc fluxes were relatively uniform across the study area suggesting that similar particle fluxes have taken place within the larsen system since the disintegration of the various ice shelves the loc mean residence time at the different stations varied from 3 y to 60 y the 14corg approach calculating loc content based on a two end member model with planktonic 14corg as the labile carbon end member most closely correlated with the lipid content of the sediment which has been considered one of the best descriptors of reactive organic matter readily available to benthic consumers we suggest that the irregular combination of sea ice coverage organic matter production and supply to the sea floor introduce scatter in the determination of sediment and loc dynamics such that short term temporal

2001 2009 elevation and mass losses in the larsen a and b embayments antarctic peninsula we investigate the elevation and mass balance response of tributary glaciers following the loss of the larsen a and b ice shelves antarctic peninsula in 1995 and 2002 respectively our study uses modis imagery to track ice extent and aster and spot5 digital elevation models dems plus atm and icesat laser altimetry to track elevation changes spanning the period 2001 09 the measured larsen b tributary glaciers hektoria green evans punchbowl jorum and crane lost up to 160 m in elevation during 2001 06 and thinning continued into 2009 elevation changes were small for the more southerly flask and leppard glaciers which are still constrained by a larsen b ice shelf remnant in the northern embayment continued thinning of 3 m a 1 on drygalski glacier 14 years after the larsen a ice shelf disintegrated suggests that mass losses for the exposed larsen b tributaries will continue for years into the future grounded ice volume losses exceed 13 km 3 for crane glacier and 30 km 3 for the hektoria green evans glaciers the combined mean loss rate for 2001 06 is at least 11 2 gt a 1 our values differ significantly from published mass budget based estimates for these embayments but are a reasonable fraction of grace derived rates for the region 40 gt a 1

reaction of a polar gravel spit system to atmospheric warming and glacier retreat as reflected by morphology and internal sediment geometries south shetland islands antarctica sedimentary architecture and morphogenetic evolution of a polar bay mouth gravel spit system are revealed based on topographic mapping sedimentological data radiocarbon dating and ground penetrating radar investigations data document variable rates of spit progradation in reaction to atmospheric warming synchronous to the termination of the last glacial re advance lgr 0 45 0 25 ka bp the southern hemisphere equivalent of the little ice age cooling period results show an interruption of spit progradation that coincides with the proposed onset of accelerated isostatic rebound in reaction to glacier retreat spit growth resumed in the late 19th century after the rate of isostatic rebound decreased and continues until today the direction of modern spit progradation however is rotated northwards compared with the growth axis of the early post lgr spit this is interpreted to reflect the shift and strengthening in the regional wind field during the last century a new concept for the interplay of polar gravel spit progradation and glacio isostatic adjustment is presented allowing for the prediction of future coastal evolution in comparable polar settings

accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf acceleration exceeds 27 km 3 per year and ice is thinning at rates of tens of meters per year we attribute this abrupt evolution of the glaciers to the removal of the buttressing ice shelf the magnitude of the glacier changes illustrates the importance of ice shelves on ice sheet mass balance and contribution to sea level change index terms 1827 hydrology glaciology 1863 1863 hydrology snow and ice 1827 3349 meteorology and atmospheric dynamics polar meteorology 6924 radio science interferometry 9310 information related to geographic region antarctica citation rignot e g casassa p gogineni w krabill a rivera and r thomas 2004 accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf geophys res lett 31 l18401 doi 10 1029 2004gl020697

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

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

characteristics of summer airflow over the antarctic peninsula in response to recent strengthening of westerly circumpolar winds abstract summer near surface temperatures over the northeast coast of the antarctic peninsula have increased by more than 2 c over the past 40 years a temperature increase 3 times greater than that on the northwest coast recent analysis has shown a strong correlation between this striking warming trend and significant change in the summer southern hemisphere annular mode sam which has resulted in greatly increased summer westerlies across the northern peninsula it has been proposed that the strengthening westerlies have resulted in increased vertical deflection of relatively warm maritime air over the northern peninsula contributing significantly to the observed warming and the recent collapse of northern sections of the larsen ice shelf in this study laboratory and numerical modeling of airflow incident to the peninsula are employed to further understand this mechanism it is shown that the effect of the strengthening westerlies has led to a distinct transition from a blocked regime to a flow

state of the antarctic and southern ocean climate system this paper reviews developments in our understanding of the state of the antarctic and southern ocean climate and its relation to the global climate system over the last few millennia climate over this and earlier periods has not been stable as evidenced by the occurrence of abrupt changes in atmospheric circulation and temperature recorded in antarctic ice core proxies for past climate two of the most prominent abrupt climate change events are characterized by intensification of the circumpolar westerlies also known as the southern annular mode between 6000 and 5000 years ago and since 1200 1000 years ago following the last of these is a period of major trans antarctic reorganization of atmospheric circulation and temperature between ad1700 and 1850 the two earlier antarctic abrupt climate change events appear linked to but predate by several centuries even more abrupt climate change in the north atlantic and the end of the more recent event is coincident with reorganization of atmospheric circulation in the north pacific improved understanding of such events and of the associations between abrupt climate change events recorded in both hemispheres is critical to predicting the impact and timing of future abrupt climate change events potentially forced by anthropogenic changes in greenhouse gases and aerosols special attention is given to the climate of the past 200 years which was recorded by a network of recently available shallow firn cores and to that of the past 50 years which was monitored by the continuous instrumental record significant regional climate changes have taken place in the antarctic during the past 50 years atmospheric temperatures have increased markedly over the antarctic peninsula linked to nearby ocean warming and intensification of the circumpolar westerlies glaciers are retreating on the peninsula in patagonia on the sub antarctic islands and in west antarctica adjacent to the peninsula the penetration of marine air masses has become more pronounced over parts of west antarctica above the surface the antarctic troposphere has warmed during winter while the stratosphere has cooled year round the upper kilometer of the circumpolar southern ocean has warmed antarctic bottom water across a wide sector off east antarctica has freshened and the densest bottom water in the weddell sea has warmed in contrast to these regional climate changes over most of antarctica near surface temperature and snowfall have not increased significantly during at least the past 50 years and proxy data suggest that the atmospheric circulation over the interior has remained in a similar state for at least the past 200 years furthermore the total sea ice cover around antarctica has exhibited no significant overall change since reliable satellite monitoring began in the late 1970s despite large but compensating regional changes the inhomogeneity of antarctic climate in space and time implies that recent antarctic climate changes are due on the one hand to a combination of strong multi decadal variability and anthropogenic effects and as demonstrated by the paleoclimate record on the other hand to multi decadal to millennial scale and longer natural variability forced through changes in orbital insolation greenhouse gases solar variability ice dynamics and aerosols model projections suggest that over the 21st century the antarctic interior will warm by 3 4 1oc and sea ice extent will decrease by 30 ice sheet models are not yet adequate enough to answer pressing questions about the effect of projected warming on mass balance and sea level considering the potentially major impacts of a warming climate on antarctica vigorous efforts are needed to better understand all aspects of the highly coupled antarctic climate system as well as its influence on the earth s climate and oceans

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

14c and 10be dated late holocene fluctuations of patagonian glaciers in torres del paine chile 51 s and connections to antarctic climate change abstract southern hemisphere holocene glacier chronologies are important for unraveling past climate change mid to high latitude teleconnections and regional to global climate forcing at present a significant number of glacier chronologies for patagonia are based on 14c dating which may afford only maximum or minimum limiting dates here we combine geomorphology and stratigraphy with radiocarbon 14c and beryllium 10 10be surface exposure age dating at three outlet glaciers zapata tyndall and pingo these glaciers drain the southernmost tip of the southern patagonian ice field at torres del paine national park chile 51 s after an expansion that we date at 3200 yr b p the torres del paine glaciers expanded to their last major late holocene maxima at 600 and 340 yr b p with the final dated readvance after 190 yr b p we use these data together with other patagonian glacier records to define the early mid and final glacial stages of the last millennium these cold events were separated by warm conditions that allowed the nothofagus forest to colonize deglaciated land the presence of near concurrent glacier fluctuations in patagonia and antarctic peninsula indicates widespread cooling punctuated the late holocene including the last millennium across much of the extratropical southern hemisphere we link this cooling to cold oceanographic atmospheric conditions forced by a northern shift or intensification of the southern westerly winds such scenario increased northward advection of cold antarctic circumpolar water along western patagonia and favored decreased upwelling of warm circumpolar deep water together with expanded sea ice around the antarctic peninsula

improving ice core interpretation using in situ and reanalysis data 1 back trajectory analysis provided by the british atmospheric data centre using meteorological parameters from the european centre for medium range weather forecasts ecmwf reanalysis era 40 1980 2001 and operational analysis 2002 2006 is used to investigate transport pathways and source regions of climate proxies preserved in a new ice core gomez from the southwestern antarctic peninsula the ecmwf data are compared with automatic weather station data and ice core annual accumulation records to demonstrate that the ecmwf data capture a large proportion of the annual and subseasonal precipitation variability at the site the back trajectories reveal that precipitation preserved in the ice core accumulation record and hence climate proxies contained therein originate from the low pressure systems from the bellingshausen sea transported via circumpolar westerly winds hence precipitation dependent ice core proxies such as isotopic composition will be influenced by both localized sea ice extent and large scale circulation changes such as the southern annular mode sea ice proxies from the ice core are expected to be dominated by sea ice extent in the bellingshausen sea but also influenced by sea ice in the weddell sea with a small proportion of air mass trajectories originating from this region during the summer comparison with other ice core sites reveals a stronger influence of easterly transport at more northerly locations thus explaining the observed differences in snow accumulation records between ice cores and the poor correlation with instrumental records at these sites

definition of antarctic oscillation index following walker s work about his thmous three oscillations published during the 1920 30s many papers were written about atmospheric oscillations a iburth atmospheric oscillation in the middle and high southern latitudes was lbund and nanted the grotarctic oscillation ao a refiers to a large scale alternation of atmospheric mass between the mid latitudes and high latitudes surthce pressure in order to understand the spatial structure of sea level pressure variation in detail empirical orthogonal fitnction analysis is applied an objective index of the antarctic oscillation index aoi is defined as the diffierence of zonal mean sea level pressure between 40os and 65os the aoi has the potential tbr clarifying climate regimes in the southern hemisphere similar to how the na and the npo has been used in the northern hemisphere were there other oscillation s besides nao npo and s especially in the southern hemisphere it had been supposed that there might be other atmospheric oscillation s in the high southern latitudes although as early as in the first quarter of this century walker 1928 had stated that just as in the north atlantic there is a pressure opposition between the azores and iceland there is an opposition between the high pressure belt across chile and the argentine on the one hand and the low pressure area of weddell sea and the bellingshausen sea on the other the scarcity of data in the southern hemisphere hindered the search tbr new oscillation s during the last two decades more comprehensive data over the southern hemisphere became available and more analyses were carried out see kidson 1975 rogers and van loon 1982 mo and l 7 ite 1985 2 4o 1986 connolley 1997 gong and wang 1998 a tburth atmospheric oscillation in the middle and high southern latitudes was tbund and nanted as the antarctic oscillation a wang 1992 gong and wang 1998 the term ao relrs to a large scale alternation of atmospheric mass between the mid latitude sur hce pressure

seasonal southern hemisphere multi variable reflection of the southern annular mode in atmosphere and ocean reanalyses variations of southern hemisphere sh climate variables are often linked to the southern annular mode sam variability we examined such linkage by seasons using state of the art atmosphere and ocean sea ice reanalyses the associated sam related anomaly sra fields of the climate variables denoting anomalies corresponding to the same variation in sam are overall consistent across the reanalyses among the atmospheric products 20crv2 differs from era interim and cfsr in the sea level pressure sras over the amundsen sea resulting in less warming over the antarctic peninsula among the ocean reanalyses orap5 and c glors exhibit the largest consistency the major difference between them and the lower resolution cfsr and soda reanalyses is deeper penetration of anomalous meridional currents compared to the other ocean reanalyses cfsr exhibits stronger and spatially more coherent surface current sras resulting in greater sras of sea ice motion and ice thickness along the ice edges the sras of sensible and total surface heat fluxes are reduced in cfsr due to ocean atmosphere coupling significant sea ice concentration sras are present on the west side of peninsulas along the east antarctica coast in spring and winter most notably in orap5 and c glors implying changes in new ice production and shelf water formation most atmosphere and ocean variables manifest an annular sra pattern in summer and a non annular pattern in the other seasons with a wavenumber 3 structure strongest in autumn and weakest in summer the wavenumber 3 structure should be related to the zonal wave three pattern of the sh circulation the relation of which to sam needs further exploration

characterizing the zonally asymmetric component of the sh circulation much research concerning the southern hemisphere sh zonally asymmetric circulation has focused on the pacific south american mode psa or the major zonal waves however these large scale decompositions may mask important local variability in this paper the month to month variability explained by the zonal waves 1 and 3 is examined and an alternative representation of the sh circulation is presented based on two quasi stationary anticyclones in the sub antarctic western hemisphere these anticyclones are related to the zonal waves but features of their variability are masked by the zonal wave decomposition in particular the anticyclones strengths are not positively covariant they are also compared with the leading principal components of the sh atmosphere we show that they capture variance independent of the southern annular mode additionally they explain a generally greater fraction of the variability than the psa and in a manner that also includes information regarding spatial variability these results have implications for analysis of the atmospheric forcing of western antarctic climate

a low level explanation for the recent large warming trend over the western antarctic peninsula involving blocked winds and changes in zonal circulation 1 we demonstrate a mechanism whereby the impact of stronger circumpolar westerly winds on the mountains of the antarctic peninsula contributes significantly to the enhanced warming trend observed over its western side in the last 50 years numerical and laboratory meteorological modelling demonstrate how when westerly winds impinge on this side warm air below the height 1 5 2 0 km of the peninsula is advected in a southerly direction the strength of the annual mean westerly winds has increased by about 15 20 since the 1960s while the modelling results indicate that contemporaneously the air advected to its western side originates from an increasingly northerly and warmer location this gives rise to increased northerlies and a greater transport of warm air into this region consequently there is a reduction in the sea ice extent further amplifying the local warming this low level orographic mechanism for the local climate trend is supported by observational evidence

the freshwater system west of the antarctic peninsula spatial and temporal changes climate change west of the antarctic peninsula is the most rapid of anywhere in the southern hemisphere with associated changes in the rates and distributions of freshwater inputs to the ocean here results from the firstcomprehensivesurveyofoxygenisotopesinseawaterinthisregionareusedtoquantifyspatialpatternsof meteoric water glacial discharge and precipitation separately from sea ice melt high levels of meteoric water are found close to the coast due to orographic effects on precipitation and strong glacial discharge concentrations decrease offshore driving significant southward geostrophic flows up to 30 cm s 21 these produce high meteoric water concentrations at the southern end of the sampling grid where collapse of the wilkins ice shelf may also have contributed sea ice melt concentrations are lower than meteoric water and patchier because of the mobile nature of the sea ice itself nonetheless net sea ice production in the northern part of the sampling grid is inferred combined with net sea ice melt in the south this indicates an overall southwardicemotion thesurveyiscontextualizedtemporallyusingadecade longseriesofisotopedatafrom a coastal antarctic peninsula site this shows a temporal decline in meteoric water in the upper ocean contrary to expectations based on increasing precipitation and accelerating deglaciation this is driven by the increasingoccurrenceofdeeperwintermixedlayersandhaspotentialimplications forconcentrations oftrace metals supplied to the euphotic zone by glacial discharge as the regional freshwater system evolves the continuing isotope monitoring described here will elucidate the ongoing impacts on climate and the ecosystem

foehn warming distributions in nonlinear and linear flow regimes a focus on the antarctic peninsula the structure of lee side warming during foehn events is investigated as a function of cross barrier flow regime linearity two contrasting cases of westerly flow over the antarctic peninsula ap are considered one highly nonlinear the other relatively linear westerly flow impinging on the ap provides one of the best natural laboratories in the world for the study of foehn owing to its maritime setting and the larsen c ice shelf lcis providing an expansive homogeneous and smooth surface on its east side numerical simulations with the met office unified model at 1 5 km grid size and aircraft observations are utilized in case a relatively weak southwesterly cross peninsula flow and an elevated upwind inversion dictate a highly nonlinear foehn event with mountain wave breaking observed the consequent strongly accelerated downslope flow leads to high amplitude warming and ice shelf melt in the immediate lee of the ap however this foehn warming diminishes rapidly downwind due to upward ascent of the foehn flow via a hydraulic jump in case c strong northwesterly winds dictate a relatively linear flow regime there is no hydraulic jump and strong foehn winds are able to flow at low levels across the entire ice shelf mechanically mixing the near surface flow preventing the development of a strong surface inversion and delivering large fluxes of sensible heat to the ice shelf consequently in case c ice melt rates are considerably greater over the lcis as a whole than in case a our results imply that although nonlinear foehn events cause intense warming in the immediate lee of mountains linear foehn events will commonly cause more extensive lee side warming and over an ice surface higher melt rates this has major implications for the ap where recent east coast warming has led to the collapse of two ice shelves immediately north of the lcis

clay mineralogy and unconventional hydrocarbon shale reservoirs in the usa ii implications of predominantly illitic clays on the physico chemical properties of shales abstract re interpretation of r3 mixed layer illite smectite i s as consisting only of thin

influence of the southern annular mode on the sea ice ocean system 1 the global sea ice ocean model orca2 lim driven by the ncep ncar national centers for environmental prediction national center for atmospheric research reanalysis daily 2 m air temperatures and 10 m winds and by monthly climatologies for precipitation cloud cover and relative humidity is used to investigate the impact of the southern annular mode sam on the antarctic sea ice ocean system our results suggest that the response of the circumpolar southern ocean consists of an annular and a nonannular component for the sea ice cover the non annular component seems to be the most important the annular component strongly affects the overall patterns of the upper ocean circulation when the sam is in its positive phase a northward surface ekman drift a downwelling at about 45 degreess and an upwelling in the vicinity of the antarctic continent are simulated the non annular component has a significant impact at the regional scale especially in the weddell ross amundsen and bellingshausen seas in those regions the pressure pattern associated with the sam induces meridional winds which advect warmer air in the weddell sea and around the antarctic peninsula and colder air in the amundsen and ross seas this implies a dipole response of sea ice to the sam with on average a decrease in ice area in the weddell sea and around the antarctic peninsula and an increase in the ross and amundsen seas during years with a high sam index the long term trend in the observed sea ice area does not appear to be related to the trend in the sam index

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

climate variability in the amundsen and bellingshausen seas satellite data reveal a 20 decline in sea ice extent in the amundsen and bellingshausen seas in the two decades following 1973 this change is negatively correlated with surface air temperatures on the west side of the antarctic peninsula which have increased 0 58c decade21 since the mid 1940s the recession was strongest during summer when monthly average minima in 1991 92 removed much of the incipient multiyear ice over the continental shelf this would have lowered the regional mean ice thickness impacting snow ice formation brine production and vertical heat flux the northern ice edge contracted by 18 of latitude in all seasons from 1973 79 to 1987 93 returning toward mean conditions in 1993 95 the decline included multiyear cycles of several years in length superimposed on high interannual variability a review of atmospheric forcing shows winds consistent with mean and extreme ice extents and suggests links to larger scale circulation changes in the south pacific historical ocean measurements are sparse in this sector but mixed layer depths and upper pycnoclines beneath the sea ice resemble those in the weddell sea weaker surface currents or changes in the upwelling of circumpolar deep water on the continental shelf could have contributed to the anomaly persistence

the spatial distribution and temporal variability of fohn winds over the larsen c ice shelf antarctica the eastern side of the antarctic peninsula ap mountain range and the adjacent ice shelves are frequently affected by fohn winds originating from upwind of the mountains six automatic weather stations aws and archived model output from 5km resolution antarctic mesoscale prediction system amps forecasts have been combined to identify the occurrence of fohn conditions and their spatial distribution over the larsen c ice shelf lcis from 2009 to 2012 algorithms for semi automatic detection of fohn conditions have been developed for both aws and amps data the frequency of fohn varies by location being most frequent at the foot of the ap and in the north of the ice shelf they are most common in spring when they can prevail for 50 of the time the results of this study have important implications for further research investigating the impact of fohn on surface melting and the surface energy budget of the ice shelf this is of particular interest due to the collapse of larsen a and b ice shelves in 1995 and 2002 respectively and the potential instability issues following a large calving event on larsen c in 2017

temperature change on the antarctic peninsula linked to the tropical pacific abstractsignificant summer warming over the eastern antarctic peninsula in the last 50 years has been attributed to a strengthening of the circumpolar westerlies widely believed to be anthropogenic in origin on the western side of the peninsula significant warming has occurred mainly in austral winter and has been attributed to the reduction of sea ice the authors show that austral fall is the only season in which spatially extensive warming has occurred on the antarctic peninsula this is accompanied by a significant reduction of sea ice cover off the west coast in winter and spring warming is mainly observed on the west side of the peninsula the most important large scale forcing of the significant widespread warming trend in fall is the extratropical rossby wave train associated with tropical pacific sea surface temperature anomalies winter and spring warming on the western peninsula reflects the persistence of sea ice anomalies arising from the tropically forced atmospheric circulation changes

on the temporal variability of intermediate and deep waters in the western basin of the bransfield strait abstract the western basin wb of the bransfield strait has a complex water mass structure derived from a variety of sources and is located next to the antarctic region most affected by climate change the wb is one of the three bransfield strait deep basins and the one most directly influenced by the waters from the bellingshausen sea and drake passage the objective of this paper is to study the variability of the inflow of water masses to the wb and to detect the possible impact of regional climate change we focus on the modified circumpolar deep water mcdw that enters the wb through the northwestern passages to achieve this goal this study uses historical hydrographic data collected between 1960 and 2014 warming 0 0161 0 0079 c yr 1 and lightening 0 0023 0 0010 kg m 3 yr 1 of the mcdw core n 27 85 28 27 kg m 3 are observed in the wb between 1960 and 2013 the waters within the 27 85 28 kg m 3 n range presented warming and salinization waters deeper than 500 m showed cooling and freshening between the 1960s and 1990s however warming and lightening are observed if 1981 2013 is considered these trends appear to be associated with the positive sam trend observed since the mid 20th century statistically significant negative correlations between s and of the mcdw core with enso were found between 1980 and 2014 during la nina phases the mcdw core extended along the southern slope of the south shetland islands while during el nino phases it was present in patches or was totally absent since the 2000s the mcdw core extends southward within the wb possibly associated to positive sam phases statistically significant negative correlations between and s of the wb deeper waters with enso and sam were found these waters were in general more saline and denser during negative enso and sam phases positive sam phases with la nina events suggest the increase decrease of mcdw weddell sea shelf waters contribution to the deep wb during the 2000s thus high interannual variability in the thermohaline properties within the wb seem to be linked to the effect of these modes of climate variability on the source water masses

new reconstruction of antarctic near surface temperatures multidecadal trends and reliability of global reanalyses a reconstruction of antarctic monthly mean near surface temperatures spanning 1958 2012 is presented itsprimarygoalistotakeadvantageofarecentlyrevisedkeytemperaturerecordfromwestantarctica byrd to shed further light on multidecadal temperature changes in this region the spatial interpolation relies on a kriging technique aided by spatiotemporal temperature covariances derived from three global reanalyses the european centre for medium range weather forecasts ecmwf interim re analysis erainterim modern era retrospective analysis for research and applications merra and climate forecast system reanalysis cfsr for 1958 2012 the reconstruction yields statistically significant annual warming in the antarctic peninsula and virtually all of west antarctica but no significant temperature change in east antarctica importantly the warming is of comparable magnitude both in central west antarctica and in most of the peninsula rather than concentrated either in one or the other region as previousreconstructions have suggested the transantarctic mountains act for the temperature trends as a clear dividing line between east and west antarctica reflecting the topographic constraint on warm air advection from the amundsen sea basin the reconstruction also serves to highlight spurious changes in the 1979 2009 time series of the three reanalyses that reduces the reliability of their trends illustrating a longstanding issue in high southern latitudes the study concludes with an examination of the influence of the southern annular mode sam on antarctic temperature trends the results herein suggest that the trend of the sam toward its positive phase in austral summer and fall since the 1950s has had a statistically significant cooling effect not only in east antarctica as already well documented and but also only in fall in west antarctica

holocene dynamics of the southern westerly winds over the indian ocean inferred from a peat dust deposition record abstract the southern westerly winds sww play a major role in climate variability in southern hemisphere mid and high latitudes regulating rainfall ocean circulation and the southern ocean carbon sink despite their importance little is known about millennial scale changes in the sww and how they have influenced the climate system in the past and interacted with the earth s surface elements such as dust nutrients and carbon here we present a dust record from a 6 6 kyr old peat core in amsterdam island ams situated at the northern edge of the sww 37 s in the southern indian ocean mineral dust flux was used to track atmospheric dust production long distance transport and subsequent deposition dust provenance was determined from rare earth element ree and nd isotopic signatures end in the peat core compared with a reference dataset of southern hemisphere dust sources using a multi proxy mixing model the end and ree ratios show a relatively uniform mixture of ca 40 local 15 southern african and 45 southern south american dust sources since 6 6 cal kyr bp however from 1910 ad onwards there is a doubling in the contribution from southern africa 32 two mineral dust flux minima occur at 6 2 4 9 cal kyr bp and 3 9 2 7 cal kyr bp interpreted as periods with equatorward shifted and or strengthened sww at the northern edge of the wind belt conversely periods of higher dust flux at 6 6 6 2 cal kyr bp 4 9 3 9 cal kyr bp and 1 4 cal kyr bp onwards are interpreted as poleward shifted and or weakened sww these interpretations are based on the findings that higher lower wind speeds lead to enhanced less removal of distal dust on the way to ams by wet deposition and turbulence published holocene sww records at the northern edge of the wind belt 33 41 s covering south america southern africa and australia show much variability over the last 6 6 kyr we suggest this reflects complex regional climate variability in the different sh longitudinal sectors indicating that sww are not zonally homogeneous at the northern edge of the wind belt the recent shift in dust provenance is not accompanied by enhanced total dust deposition at ams we therefore suggest that human impact e g land use changes and drier climate conditions in southern africa have led to enhanced dust mobilization

south pacific circulation changes and their connection to the tropics and regional antarctic warming in austral spring 1979 2012 after 1979 statistically significant warming in antarctica is only observed in austral spring september november son across west antarctica and the antarctic peninsula while previous work has linked this warming to reductions in sea ice cover we note that a substantial 30 60 portion of the warming is related to changes in the son atmospheric circulation in particular western antarctic peninsula warming is consistent with increasing pressure in the south atlantic while western west antarctica warming is tied to a deepening of the amundsen sea low near the eastern ross sea while both of these circulation changes are associated with increased warm northerly flow toward the antarctic continent they are connected with different aspects of tropical variability the increase in pressure in the south atlantic is associated with a trend toward more la nina like conditions in the tropical pacific and an associated rossby wave train in contrast the deepening of the amundsen sea low is more strongly tied to a shift in the pacific decadal oscillation pdo toward its negative phase since the 1990s compared to typical la nina events the recent negative pdo events display a different tropical forcing which drives a rossby wave train that propagates more meridionally across the south pacific culminating in the eastern ross sea rather than in the south atlantic the results suggest multiple independent forcing mechanisms governing the son pressure trends and associated antarctic peninsula and west antarctica warming after 1979 which partially cancel each other out in the amundsen sea and portions of eastern west antarctica

observed antarctic interannual climate variability and tropical linkages abstractthis study reviews the mechanisms associated with antarctic tropical climate linkages and presents new analyses of the seasonality and spatial patterns of tropical climate signals in the antarctic for the late 1950s to the present tropical climate signals are primarily communicated to the antarctic via the pacific south america psa pattern and the southern annular mode sam the impacts of these circulation patterns and their tropical linkages are evident in regressions of seasonally stratified antarctic station temperature data and annually resolved ice core records on global fields of sea surface temperature sea level pressure and precipitation temperature and ice core anomalies in the antarctic peninsula region and adjoining areas of west antarctica are significantly impacted by the psa interpreted as a rossby wave train driven by anomalous tropical deep convection during enso events this pattern is most evident in the austral spring consistent with recent studies suggesting that atm

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

nonstationary impacts of the southern annular mode on southern hemisphere climate abstract the temporal stability of the southern annular mode sam impacts on southern hemisphere climate during austral spring is analyzed results show changes in the typical hemispheric circulation pattern associated with sam particularly over south america and australia between the 1960s 70s and 1980s 90s in the first decades the sam positive phase is associated with an anomalous anticyclonic circulation developed in the southwestern subtropical atlantic that enhances moisture advection and promotes precipitation increase over southeastern south america sesa on the other hand during the last decades the anticyclonic anomaly induced by the sam s positive phase covers most of southern south america and the adjacent atlantic producing weakened moisture convergence and decreased precipitation over sesa as well as positive temperature anomaly advection over southern south america some stations in the australia new zealand sector and africa exhibit significant correlations between the sam and prec

dense waters of the weddell and scotia seas recent changes in properties and circulation the densest waters in the atlantic overturning circulation are sourced at the periphery of antarctica especially the weddell sea and flow northward via routes that involve crossing the complex bathymetry of the scotia arc recent observations of significant warming of these waters along much of the length of the atlantic have highlighted the need to identify and understand the time varying formation and export processes and the controls on their properties and flows here we review recent developments in understanding of the processes that control the changing flux of water through the main export route from the weddell sea into the scotia sea and the transformations of the waters within the scotia sea and environs we also present a synopsis of recent findings that relate to the climatic change of dense water properties within the weddell sea itself in the context of known atlantic scale changes among the most significant findings are the discovery that the warming of waters exported from the weddell sea has been accompanied by a significant freshening and that the episodic nature of the overflow into the scotia sea is markedly wind controlled and can lead to significantly enhanced abyssal stratification key areas for focusing future research effort are outlined

ice thickness areal and volumetric changes of davies dome and whisky glacier james ross island antarctic peninsula in 1979 2006 this study calculates area volume and elevation changes of two glaciers on james ross island antarctica during the period 1979 2006 davies dome is a small ice cap whisky glacier is a valley glacier ground penetrating radar surveys indicate ice thickness which was used for calculations of the bed topography and volume of both glaciers maximum measured ice thicknesses of davies dome and whisky glacier are 83 2 and 157 2 m respectively between 1979 and 2006 the area of the ice cap decreased from 6 23 0 05 km2 to 4 94 0 01 km2 20 7 while the area of the valley glacier reduced from 2 69 0 02 km 2 to 2 40 0 01 km2 10 6 over the same period the volume of the ice cap and valley glacier reduced from 0 23 0 03 km3 to 0 16 0 02 km3 30 4 and from 0 27 0 02 km3 to 0 24 0 01 km3 10 6 respectively the mean surface elevation decreased by 8 5 2 8 and 10 1 2 8 m the average areal 0 048 0 011 km2 a 1 and volumetric 0 003 0 001 km3 a 1 changes are higher than the majority of other estimates from antarctic peninsula glaciers