reconstruction of millennial changes in dust emission transport and regional sea ice coverage using the deep epica ice cores from the atlantic and indian ocean sector of antarctica continuous sea salt and mineral dust aerosol records have been studied on the two epica european project for ice coring in antarctica deep ice cores the joint use of these records from opposite sides of the east antarctic plateau allows for an estimate of changes in dust transport and emission intensity as well as for the identification of regional differences in the sea salt aerosol source the mineral dust flux records at both sites show a strong coherency over the last 150 kyr related to dust emission changes in the glacial patagonian dust source with three times higher dust fluxes in the atlantic compared to the indian ocean sector of the southern ocean so using a simple conceptual transport model this indicates that transport can explain only 40 of the atmospheric dust concentration changes in antarctica while factor 5 10 changes occurred accordingly the main cause for the strong glacial dust flux changes in antarctica must lie in environmental changes in patagonia dust emissions hence environmental conditions in patagonia were very similar during the last two glacials and interglacials respectively despite 2 4 c warmer temperatures recorded in antarctica during the penultimate interglacial than today 2 3 times higher sea salt fluxes found in both ice cores in the glacial compared to the holocene are difficult to reconcile with a largely unchanged transport intensity and the distant open ocean source the substantial glacial enhancements in sea salt aerosol fluxes can be readily explained assuming sea ice formation as the main sea salt aerosol source with a significantly larger expansion of summer sea ice in the weddell sea than in the indian ocean sector during the penultimate interglacial our sea salt records point to a 50 reduction of winter sea ice coverage compared to the holocene both in the indian and atlantic ocean sector of the so however from 20 to 80 ka before present sea salt fluxes show only very subdued millennial changes despite pronounced temperature fluctuations likely due to the large distance of the sea ice salt source to our drill sites

a reevaluation of crystal size distributions in chromite cumulates although studies have shown that igneous cumulates can form by in situ crystallization without requiring crystal settling it has not been demonstrated that crystal size distributions csds are consistent with such a process plots of crystal size fractions per unit volume vs crystal size for chromite grains from the stillwater complex show a log linear distribution with negative slope at larger sizes and a concave down distribution at smaller sizes the log linear portion of these trends is similar to previously reported trends for other silicate and oxide phases in crystallizing magmas however the lack of smaller grain sizes indicates that the original population was altered during a postnucleation crystalaging period that resulted in the loss of the smaller size fractions an interpretation consistent with textural and volume balance evidence the csd trends imply that cr was not concentrated by settling of chromite but was brought to the site of the growing chromite grains similarities between the stillwater data and csd trends for garnet in metapelites suggest that such trends are a characteristic feature of any geologic system undergoing crystal aging after an initial period of nucleation and crystal growth

an ice core indicator of antarctic sea ice production 1 the sea ice surface not open water is the dominant source of sea salt to aerosol and ice cores in coastal antarctica here we show that it may also form the dominant source for central antarctica we can then explain higher concentrations in the winter and last glacial maximum lgm as being due to increased sea ice production this suggests that ice core sea salt can indicate at least the timing of changes in antarctic sea ice production the pattern of sea salt in ice cores is consistent with marine evidence about sea ice changes in the holocene and lgm sea salt shows no change at the initial co2 increase out of the last glacial making it unlikely this was primarily due to changing sea ice cover the sea salt record should not be treated as an indicator of meridional transport

thickness distribution of antarctic sea ice 1 ship based observations are used to describe regional and seasonal changes in the thickness distribution and characteristics of sea ice and snow cover thickness around antarctica the data set comprises 23 373 observations collected over more than 2 decades of activity and has been compiled as part of the scientific committee on antarctic research scar antarctic sea ice processes and climate aspect program the results show the seasonal progression of the ice thickness distribution for six regions around the continent together with statistics on the mean thickness surface ridging snow cover and local variability for each region and season a simple ridge model is used to calculate the total ice thickness from the observations of level ice and surface topography to provide a best estimate of the total ice mass including the ridged component the long term mean and standard deviation of total sea ice thickness including ridges is reported as 0 87 0 91 m which is 40 greater than the mean level ice thickness of 0 62 m analysis of the structure function along north south and east west transects revealed lag distances over which sea ice thickness decorrelates to be of the order of 100 300 km which we use as a basis for presenting near continuous maps of sea ice and snow cover thickness plotted on a 2 5 5 0 grid

a role for newly forming sea ice in springtime polar tropospheric ozone loss observational evidence from halley station antarctica since march 2003 measurements of surface ozone have been made at the british antarctic survey clean air sector laboratory caslab at halley station in coastal antarctica detailed measurements of boundary layer meteorology as well as standard meteorological parameters are also measured at the caslab combining these data allows us to probe the transport pathway of air masses during ozone depletion events odes odes were observed at halley on several occasions during antarctic spring 2003 on some occasions extremely rapid loss of ozone was observed loss of 16 ppbv in 1 min on one occasion which was associated with regional scale transport for each such event during 2003 the air mass originated in the southern weddell sea an area of vigorous sea ice production on other occasions the development of the event and its recovery were strongly associated with the build up and decline of a stable boundary layer in these cases air masses had had recent contact with a nearby open water lead where sea ice production is known to occur the data presented here are entirely consistent with the idea that halogens responsible for ozone loss are derived during new sea ice formation from an associated surface such as brine slush or frost flowers

influence of sea ice on ocean water vapor isotopes and greenland ice core records a warming climate results in sea ice loss and impacts to the arctic water cycle the water isotope parameter deuterium excess a moisture source proxy can serve as a tracer to help understand hydrological changes due to sea ice loss however unlocking the sea ice change signal of isotopes from ice cores requires understanding how sea ice changes impact deuterium excess which is unknown here we present the first isotope data linking a gradient of sea ice extents to oceanic water vapor deuterium excess values initial loss of sea ice extent leads to lower deuterium excess moisture sources and then values progressively increase with further ice loss our new process based interpretation suggests that past rapid 1 3 years greenland ice core changes in deuterium excess during warming might not be the result of abrupt atmospheric circulation shifts but rather gradual loss of sea ice extent at northern latitude moisture sources

out of the woods driftwood insights into holocene pan arctic sea ice dynamics the collation of 913 driftwood samples from across the western arctic with spatiotemporal distribution and available provenance data enabled the production of a high resolution proxy based reconstruction of holocene arctic ocean surface current and sea ice dynamics regionally bounded driftwood based sea ice reconstructions studies suggest spatiotemporally complex past arctic sea ice extent and movement however a large scale compilation of holocene arctic driftwood has not previously been developed sparse driftwood in the early holocene 8 2 cal ka b p deglacial period was followed by increased driftwood deposition in the warmer mid holocene 8 2 4 2 cal ka b p characterized by an enhanced transpolar drift tpd 7 cal ka b p leading to sea ice loss through the fram strait driftwood incursion peaks show spatial e w progression from the eurasian archipelagos to greenland and the canadian arctic archipelago suggesting a progressive shift in the orientation of the tpd on centennial millennial time scales and intermediate phases in the arctic oscillation late holocene cooling 4 2 cal ka b p is indicated by increased influx of probably north american picea via a strengthened beaufort gyre bg which enhanced sea ice recirculation starting in the western arctic and progressing eastward in recent millennia 2 cal ka b p a more variable driftwood record alternates between bg and tpd dominance on centennial time scales to further constrain a spatiotemporal reconstruction of variations in holocene ocean current and sea ice dynamics a more definitive determination of driftwood provenance is recommended to build upon the current framework such as through radiogenic isotope tracing and adna analysis

a reinterpretation of sea salt records in greenland and antarctic ice cores it has recently been shown that much sea salt aerosol around the coast of antarctica is generated not from open water but from the surface of newly formed sea ice previous interpretations of ice core records have disregarded the sea ice surface as a source of sea salt the majority of sea salt aerosol at halley research station originates from frost flowers rather than open water and the seasonal cycle of sea salt in aerosol at halley appears to be controlled by ice production in the weddell sea as well as variations in wind speed frost flowers are also an important source of aerosol at siple dome suggesting that variations in sea salt concentrations in the core and other cores drilled in similar locations may be reflecting changes in sea ice production rather than changes in transportation patterns for greenland cores and those from low accumulation inland sites in antarctica it is not simple to calculate the proportion of sea salt originating from frost flowers rather than open water however modelling studies suggest that a sea ice surface source contributed much of the flux of sea salt to these sites in glacial periods suggesting that interpretations of ice core records from these locations should also be revisited

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

a year long record of size segregated aerosol composition at halley antarctica 1 size segregated aerosol samples were collected with a cascade impactor at 2 week intervals for a year at the research station halley situated near the coast in the weddell sea region of antarctica sea salt is a major component of aerosol throughout the year and we estimate that at least 60 of the total sea salt arriving at halley is from brine and frost flowers on the sea ice surface rather than open water chloride in sea salt particles is depleted relative to sodium in summer consistent with loss of hcl as sea salt particles react with gaseous acidic species but is enhanced in large particles in winter because of fractionation occurring during the production of new sea ice non sea salt sulphate peaks in the summer with the majority being in small particles indicative of a gas phase origin the distribution of methane sulphonic acid closely follows that of non sea salt sulphate in the winter non sea salt sulphate is frequently negative especially on stages collecting large particle sizes consistent with the source of sea salt during the winter being predominantly the sea ice surface rather than open water nitrate peaks in the spring and summer and shows some association with sea salt particles

potential and limitations of marine and ice core sea ice proxies an example from the indian ocean sector diatom assemblages in marine cores and sea salt deposition fluxes in ice cores have been used as sea ice proxies in the southern hemisphere here a marine and an ice core proxy record for the indian ocean covering the last two glacial cycles are compared in order to illustrate their potential and limitations the marine core was extracted in a location completely ice free under present day conditions and therefore was unable to record changes to the recent sea ice extent similarly no sea ice was recorded at that location during the previous interglacial period during the last glacial period however the site was seasonally covered by sea ice and the diatom assemblages allowed an estimation of average seasonal sea ice presence the ice core data originated from the east antarctic plateau the marine sodium present in the ice core was used as a proxy of the sea ice coverage and on average a larger sea ice surface led to an increased sea salt aerosol flux seen e g at the last glacial inception however the response of the sea salt flux to increasing sea ice extent diminished during peak glacial conditions when only minimal variability was recorded in the ice core record a first order approximation is used to take this non linear response of the ice core sea ice proxy into account based on the ice core proxy record sea ice extent was reduced considerably during the warm episodes of the previous two interglacial periods compared to modern sea ice extent in particular during the peak warmth of the last interglacial the ice core proxy also showed a very strong precessional variability pronounced spectral peak at 23 ka period over the past 240 ka the advantage of combining the two proxy records lies in the complementary nature of their response while the ice core proxy showed limited sensitivity during full glacial conditions the marine proxy recorded the seasonal sea ice coverage once the sea ice retreated south of the location of the marine core the ice core proxy responded to changes in sea ice extent a composite of marine and ice core records may thus provide a data basis for a more detailed reconstruction of sea ice around antarctica over the last few glacial interglacial cycles

the arctic sea ice biomarker ip25 a review of current understanding recommendations for future research and applications in palaeo sea ice reconstructions in recent years a novel proxy for the past occurrence of arctic sea ice has been proposed that is based on the variable marine sedimentary abundance of an organic geochemical lipid derived from sea ice diatoms in the spring this lipid termed ip25 ice proxy with 25 carbon atoms is a highly branched isoprenoid mono unsaturated alkene that appears to be sufficiently stable in sediments to permit meaningful palaeo sea ice reconstructions to be carried out over short to long term timescales since the first proposed use of ip25 as a proxy for palaeo sea ice by belt et al 2007 a number of laboratories have measured this biomarker in arctic sediments and it is anticipated that research activity in this area will increase further in the future the content of this review is divided into a number of sections firstly we describe the scientific basis for the ip25 proxy and its initial discovery in arctic sea ice sedimenting particles and sediments secondly we summarise the relatively few studies that have to date concentrated on examining the factors that influence the production and fate of ip25 and we identify some areas of future research that need to be addressed in order to improve our understanding of ip25 data obtained from sedimentary analyses what is clear at this stage however it that the presence of ip25 in arctic marine sediments appears to represent a proxy measure of past seasonal sea ice rather than permanent or multi year ice conditions thirdly we highlight the importance of rigorous analytical identification and quantification of ip25 especially if measurements of this biomarker are going to be used for quantitative sea ice reconstructions rather than qualitative analyses alone presence absence fourthly we review some recent attempts to make the interpretations of ip25 biomarker data more detailed and quantitative by combining sedimentary abundances with those of phytoplankton and other sea ice derived biomarkers thus the bases for the so called pip25 and dip25 indices are described together with an overview of potential limitations concluding that investigations into the use of these indices needs further research before their full potential can be realised in the final section we provide a summary of ip25 based palaeo sea ice reconstruction case studies performed to date these case studies cover different arctic regions and timescales spanning decades to tens of thousands of years

southern ocean sea ice extent productivity and iron flux over the past eight glacial cycles sea ice and dust flux increased greatly in the southern ocean during the last glacial period palaeorecords provide contradictory evidence about marine productivity in this region but beyond one glacial cycle data were sparse here we present continuous chemical proxy data spanning the last eight glacial cycles 740 000 years from the dome c antarctic ice core these data constrain winter sea ice extent in the indian ocean southern ocean biogenic productivity and patagonian climatic conditions we found that maximum sea ice extent is closely tied to antarctic temperature on multi millennial timescales but less so on shorter timescales biological dimethylsulphide emissions south of the polar front seem to have changed little with climate suggesting that sulphur compounds were not active in climate regulation we observe large glacial interglacial contrasts in iron deposition which we infer reflects strongly changing patagonian conditions during glacial terminations changes in patagonia apparently preceded sea ice reduction indicating that multiple mechanisms may be responsible for different phases of co2 increase during glacial terminations we observe no changes in internal climatic feedbacks that could have caused the change in amplitude of antarctic temperature variations observed 440 000 years ago

sea salt as an ice core proxy for past sea ice extent a process based model study sea ice is a reflection of and a feedback on the earth s climate we explore here using a global atmospheric chemistry transport model the use of sea salt in antarctic ice cores to obtain continuous long term regionally integrated records of past sea ice extent synchronous with ice core records of climate the model includes the production transport and deposition of sea salt aerosol from the open ocean and blowing snow on sea ice under current climate conditions we find that meteorology not sea ice extent is the dominant control on the atmospheric concentration of sea salt reaching coastal and continental antarctic sites on interannual timescales however through a series of idealized sensitivity experiments we demonstrate that sea salt has potential as a proxy for larger changes in sea ice extent e g glacial interglacial treating much of the sea ice under glacial conditions as a source of salty blowing snow we demonstrate that the increase in sea ice extent alone without changing the meteorology could drive for instance a 68 increase in atmospheric sea salt concentration at the site of the dome c ice core which exhibits an approximate twofold glacial increase in sea salt flux we also show how the sensitivity of this potential proxy decreases toward glacial sea ice extent the basis of an explanation previously proposed for the lag observed between changes in sea salt flux and d an ice core proxy for air temperature at glacial terminations the data thereby permit simultaneous changes in sea ice extent and climate

year round records of sea salt gaseous and particulate inorganic bromine in the atmospheric boundary layer at coastal dumont d urville and central concordia east antarctic sites multiple year round records of bulk and size segregated compositions of aerosol were obtained at the coastal dumont d urville ddu and inland concordia sites located in east antarctica they document the sea salt aerosol load and composition including for the first time in antarctica the bromide depletion of sea salt aerosol relative to sodium with respect to seawater in parallel measurements of bromide trapped in mist chambers and denuder tubes were done to investigate the concentrations of gaseous inorganic bromine species these data are compared to simulations done with an off line chemistry transport model coupled with a full tropospheric bromine chemistry scheme and a process based sea salt production module that includes both sea ice sourced and open ocean sourced aerosol emissions observed and simulated sea salt concentrations sometime differ by up to a factor of 2 to 3 particularly at ddu possibly due to local wind pattern in spite of these discrepancies both at coastal and inland antarctica the dominance of sea ice related processes with respect to open ocean emissions for the sea salt aerosol load in winter is confirmed for summer observations and simulations point out sea salt as the main source of gaseous inorganic bromine species investigations of bromide in snow pit samples do not support the importance of snowpack bromine emissions over the antarctic plateau to evaluate the overall importance of the bromine chemistry over east antarctica bro simulations were also discussed with respect data derived from gome 2 satellite observations over antarctica

glacial north atlantic sea surface conditions reconstructed by glamap 2000 the response of the tropical ocean to global climate change and the extent of sea ice in the glacial nordic seas belong to the great controversies in paleoclimatology our new reconstruction of peak glacial sea surface temperatures ssts in the atlantic is based on census counts of planktic foraminifera using the maximum similarity technique version 28 simmax 28 modern analog technique with 947 modern analog samples and 119 well dated sediment cores our study compares two slightly different scenarios of the last glacial maximum lgm the environmental processes of the ice age land oceans glaciers epilog and glacial atlantic ocean mapping glamap 2000 time slices the comparison shows that the maximum lgm cooling in the southern hemisphere slightly preceeded that in the north in both time slices sea ice was restricted to the north western margin of the nordic seas during glacial northern summer while the central and eastern parts were ice free during northern glacial winter sea ice advanced to the south of iceland and faeroe in the central northern north atlantic an anticyclonic gyre formed between 45degrees and 60degreesn with a cool water mass centered west of ireland where glacial cooling reached a maximum of 12degreesc in the subtropical ocean gyres the new reconstruction supports the glacial to interglacial stability of sst as shown by climap project members climap 1981 the zonal belt of minimum sst seasonality between 2degrees and 6degreesn suggests that the lgm caloric equator occupied the same latitude as today in contrast to the climap reconstruction the glacial cooling of the tropical east atlantic upwelling belt reached up to 6degrees 8degreesc during northern hemisphere summer differences between these simmax based and published u37 k and mg ca based equatorial sst records are ascribed to strong sst seasonalities and sst signals that were produced by different planktic species groups during different seasons

overview of glacial atlantic ocean mapping glamap 2000 glamap 2000 presents new reconstructions of the atlantic s sea surface temperatures sst at the last glacial maximum lgm defined at both 21 500 18 000 years b p last isotope maximum and 23 000 19 000 years b p maximum glacial sea level low stand and orbital minimum of solar insolation epilog working group see mix et al 2001 these reconstructions use 275 sediment cores between the north pole and 60 s with carefully defined chronostratigraphies four categories of core quality are distinguished more than 100 core sections provide a glacial record with subcentennial to multicentennial scale resolution sst estimates are based on a new set of almost 1000 reference samples of modern planktic foraminifera and on improved transfer function techniques to deduce sst from census counts of microfossils including radiolarians and diatoms new proxies also serve to deduce sea ice boundaries the glamap 2000 sst patterns differ significantly in crucial regions from the climap 1981 reconstruction and thus are important in providing updated boundary conditions to initiate and validate computational models for climate prediction

sources and transport pathways of marine aerosol species into west antarctica sixteen high resolution marine aerosol na so4 records from spatially distributed international trans antarctic scientific expedition itase ice cores spanning the last 200 years from the pine island thwaites and ross drainage systems and the south pole are used to examine sources sea spray and frost flowers and transport pathways of marine aerosols into west antarctica factors contributing to the amount of marine aerosols transported inland include sea ice extent the presence of open water features polynyas leads wind strength and direction and the strength and positioning of low pressure systems analysis of so4 na ratios indicates that frost flowers can contribute significantly 40 to the na budget of antarctic ice cores higher na concentrations in the ross drainage system may result from greater production of marine aerosols related to frost flowers in the ross sea region in association with greater sea ice extent and larger open water areas significant positive correlations of sea ice extent and the na time series exist in some regions of west antarctica higher wind speeds in winter and higher na concentrations when slp is

frost flowers implications for tropospheric chemistry and ice core interpretation 1 this paper discusses the chemical composition of frost flowers and their accompanying slush layers and the evidence for their role as a salt source in processes important to atmospheric chemistry and ice core interpretation analysis of antarctic frost flowers shows that they are highly saline and fractionated in sea salt ions with sulfate being depleted strongly relative to sodium because frost flowers give a bright return on satellite scatterometer images the times and places of their formation can be identified when winds blow towards an aerosol sampling station from areas identified by the scatterometer as covered with flowers the collected aerosol is also depleted in sulfate because the flowers have a large salinity bromide concentrations are elevated in frost flowers relative to seawater with their high surface area it is possible that bromine is released to the atmosphere from frost flowers with consequent implications for tropospheric ozone depletion the finding that quantities of fractionated sea salt are available at the sea ice interface in the winter months and may be transported inland as aerosol also has implications for the interpretation of ice core records analysis of one near coastal core shows that the majority of the sodium comes from a fractionated source rather than from open water hitherto strong sea salt signals in ice cores have been attributed to increased open water and more efficient transport inland perhaps due to stormier weather at least in coastal regions however these signals may be related instead to the increased formation of sea ice and frost flowers

the spatial structure of the 128 ka antarctic sea ice minimum we compare multi ice core data with 18o model output for the early last interglacial antarctic sea ice minimum the spatial pattern of 18o across antarctica is sensitive to the spatial pattern of sea ice retreat local sea ice retreat increases the proportion of winter precipitation depleting 18o at ice core sites however retreat also enriches 18o because of the reduced source to site distance for atmospheric vapor the joint overall effect is for 18o to increase as sea ice is reduced our data model comparison indicates a winter sea ice retreat of 67 59 and 43 relative to preindustrial in the atlantic indian and pacific sectors of the southern ocean a compilation of southern ocean sea ice proxy data provides weak support for this reconstruction however most published marine core sites are located too far north of the 128 000 years b p sea ice edge preventing independent corroboration for this sea ice reconstruction plain language summary the antarctic isotope and temperature maximum which occurred approximately 128 000 years before present b p during the warmer than present last interglacial period is associated with a major retreat of antarctic sea ice understanding the details of this major sea ice retreat is crucial in order to understand the sensitivity of the southern hemisphere sea ice system and to evaluate the performance of climate model simulations in response to future warming this work uses a multi ice and ocean core data model evaluation to assess the magnitude and spatial pattern of this sea ice retreat our results suggest that sea ice retreat was greatest in the atlantic and indian sectors of the southern ocean and less in the pacific sector these results may have had serious implications for the stability of marine terminating glaciers around the antarctic ice sheet and their contribution to the last interglacial sea level rise these results also support a hypothesized slowdown in northward ocean heat transport during the early last interglacial

modeling the water masses of the atlantic ocean at the last glacial maximum 1 we produced gridded monthly sea surface boundary conditions for the atlantic ocean at the last glacial maximum lgm based on the sea surface temperature reconstruction of the glamap project we used an ocean general circulation model ogcm subject to these sea surface boundary conditions and a corresponding wind stress field from an atmospheric general circulation model to study the differences in the distribution of the main water masses between the lgm and the present our global ogcm is characterized by high vertical resolution low vertical diffusion and isopycnal mixing and hence allows for a realistic representation of the hydrology and circulation of the modern atlantic ocean according to a series of lgm experiments with an increasing sea surface salinity anomaly in the weddell sea the ventilated thermocline was colder than today by 2 3 c in the north atlantic ocean and in the experiment with the largest anomaly 1 0 beyond the global anomaly by 4 5 c in the south atlantic ocean its depth was reduced by 50 m on average most notably in the tropics in the north atlantic ocean the outcrop locations of the thermocline isopycnal surfaces migrated southward by 5 10 and the ventilation increased in the south atlantic ocean the mixed layer and thermocline water masses were dominated by cold water originating from drake passage and the import of warm water from the indian ocean was reduced to about 4 sv or 40 of its modern value antarctic intermediate water was colder by 3 4 c and could be traced as far as 10 n the meridional overturning rates of north atlantic deep water nadw and antarctic bottom water aabw in the atlantic ocean were similar to those of the present day experiment 9 10 sv and 4 sv respectively however nadw cooled by 2 5 c and aabw by 1 c aabw was near the freezing point of seawater at the surface and the saltiest water mass in the atlantic ocean even saltier than nadw we show that the differences between the lgm and the present day experiments can be traced back to the changes in the subpolar and interhemispheric sea surface density gradients

century scale perspectives on observed and simulated southern ocean sea ice trends from proxy reconstructions since 1979 when continuous satellite observations began southern ocean sea ice cover has increased whilst global coupled climate models simulate a decrease over the same period it is uncertain whether the observed trends are anthropogenically forced or due to internal variability or whether the apparent discrepancy between models and observations can be explained by internal variability the shortness of the satellite record is one source of this uncertainty and a possible solution is to use proxy reconstructions which extend the analysis period but at the expense of higher observational uncertainty in this work we evaluate the utility for change detection of 20th century southern ocean sea ice proxies we find that there are reliable proxies for the east antarctic amundsen bellingshausen and weddell sectors in late winter and for the weddell sea in late autumn models and reconstructions agree that sea ice extent in the east antarctic amundsen and bellingshausen seas has decreased since the early 1970s consistent with an anthropogenic response however the decrease is small compared to internal variability and the change is not robustly detectable we also find that optimal fingerprinting filters out much of the uncertainty in proxy reconstructions the ross sea is a confounding factor with a significant increase in sea ice since 1979 that is not captured by climate models however existing proxy reconstructions of this region are not yet sufficiently reliable for formal change detection

a novel chemical fossil of palaeo sea ice ip25 a unique and novel organic compound has been detected in sea ice samples from three locations in the canadian arctic thousands of kilometers apart it is likely that this biomarker is produced by diatoms living in the sea ice and we provide evidence which suggests that the compound a c25 monounsaturated hydrocarbon ip25 may be a specific sensitive and stable proxy for sea ice in sediments over at least the holocene since it has not been reported before we confirmed its identity by synthesis and used the synthesized compound as a reference for quantifying ip25 in a range of sediments from an east west transect in the canadian arctic the recent sediments are either seasonally covered with ice or have permanent ice cover older sediments containing ip25 have been dated using radiocarbon methods to at least 9000 yr if the concept proves generally applicable monitoring ip25 in further sediment cores along with other accepted proxies should allow movements in the position of the ice edge throughout the holocene at least to be better determined which is essential for accurate calibration of climate prediction models a similar approach for antarctic samples of ice and sediments would also seem worthwhile

two billion year old isotopically heavy carbon evidence from the labrador trough canada forty eight samples of bulk carbonates were studied from the dunphy portage alder uve denault and abner formations and the undivided pistolet subgroup in the labrador trough quebec canada the carbonate units occur as a number of thick beds up to 300 m within 100 600 m thick formations they are interbedded with siliciclastic sediments and are composed of crystalline sparry micritic allochemical and stromatolitic dolostones the carbonate rocks are recrystallized and metamorphosed up to amphibolite grade they are chemically dolostones and include chemical or biochemical laminated and massive dolostones dolorudites dolarenites and dololitites which were deposited in shallow water dunphy denault and abner formations to relatively deep water uve formation marine environments reef facies are present in the denault and abner formations the dunphy portage alder and uve formations deposited between 2 17 and 2 14 ga yield isotopically heavy values of 13c pdb ranging from 5 3 to

ice sheet record of recent sea ice behavior and polynya variability in the amundsen sea west antarctica investigation of how regional sic is recorded in the ice sheet stratigraphy over the period 2002 2010 we find that the ice sheet chemistry is significantly correlated with sic variability within the as and pine island bay polynyas based on this result we evaluate the use of icecore chemistry as a proxy for interannual polynya variability in this region one of the largest and most persistent polynya areas in antarctica msa concentrations correlate strongly with summer sic within the polynya regions consistent with msa at this site being derived from marine biological productivity during the spring and summer cl concentrations correlate strongly with winter sic within the polynyas as well as some regions outside the polynyas consistent with cl at this site originating primarily from winter sea ice formation spatial correlations were generally insignificant outside of the polynya areas with some notable exceptions ice core glaciochemical records from this dynamic region thus may provide a proxy for reconstructing as and pine island bay polynya variability prior to the satellite era

precession modulation of the south pacific westerly wind belt over the past million years the southern westerly wind belt sww interacts with the antarctic circumpolar current and strongly impacts the southern ocean carbon budget and antarctic ice sheet dynamics across glacial interglacial cycles we investigated precipitation driven sediment input changes to the southeast pacific off the southern margin of the atacama desert over the past one million years revealing strong precession 19 23 ka cycles our simulations with 2 ocean atmosphere general circulation models suggest that observed cyclic rainfall changes are linked to meridional shifts in water vapor transport from the tropical pacific toward the southern atacama desert these changes reflect a precessional modulation of the split in the austral winter south pacific jet stream for precession maxima we infer significantly enhanced rainfall in the southern atacama desert due to a stronger south pacific split jet with enhanced subtropical subpolar jets and a weaker midlatitude jet conversely we derive dry conditions in northern chile related to reduced subtropical subpolar jets and an enhanced midlatitude jet for precession minima the presence of precessional cycles in the pacific sww and lack thereof in other basins indicate that orbital scale changes of the sww were not zonally homogeneous across the southern hemisphere in contrast to the hemispherewide shifts of the sww suggested for glacial terminations the strengthening of the jet is unique to the south pacific realm and might have affected winter controlled changes in the mixed layer depth the formation of intermediate water and the buildup of sea ice around antarctica with implications for the global overturning circulation and the oceanic storage of atmospheric co2

glacial interglacial changes in mineral dust and sea salt records in polar ice cores sources transport and deposition 1 sea salt and mineral dust records as represented by na and ca2 concentrations respectively in greenland and antarctic ice cores show pronounced glacial interglacial variations for the last glacial maximum lgm mineral dust sea salt concentrations in greenland show an increase of a factor of approximately 80 15 compared to the holocene and significant shifts by a factor of 15 5 during dansgaard oeschger events in antarctica the dust sea salt flux is enhanced by a factor of 15 3 during the lgm compared to the holocene and variations by approximately a factor of 8 1 2 exist in parallel to antarctic warm events primary glacial dust sources are the asian deserts for greenland and patagonia for antarctica ice core evidence and model results show that both changes in source strength as well as atmospheric transport and lifetime contributed to the observed changes in greenland ice cores in antarctica changes in ice core fluxes are in large parts related to source variations both for sea salt and dust where the formation of sea salt aerosol from sea ice may play a pivotal role summarizing our latest estimates on changes in sources transport and deposition these processes are roughly able to explain the glacial increase in sea salt in both polar regions while they fall short by at least a factor of 4 7 for mineral dust future improvements in model resolution and in the formulation of source and transport processes together with new ice core records e g on dust size distributions will eventually allow convergence of models and observations

a review of sea ice proxy information from polar ice cores sea ice plays an important role in earth s climate system the lack of direct indications of past sea ice coverage however means that there is limited knowledge of the sensitivity and rate at which sea ice dynamics are involved in amplifying climate changes as such there is a need to develop new proxy records for reconstructing past sea ice conditions here we review the advances that have been made in using chemical tracers preserved in ice cores to determine past changes in sea ice cover around antarctica ice core records of sea salt concentration show promise for revealing patterns of sea ice extent particularly over glacial interglacial time scales in the coldest climates however the sea salt signal appears to lose sensitivity and further work is required to determine how this proxy can be developed into a quantitative sea ice indicator methane sulphonic acid msa in near coastal ice cores has been used to reconstruct quantified changes and interannual variability in sea ice extent over shorter time scales spanning the last 160 years and has potential to be extended to produce records of antarctic sea ice changes throughout the holocene however the msa ice core proxy also requires careful site assessment and interpretation alongside other palaeoclimate indicators to ensure reconstructions are not biased by non sea ice factors and we summarise some recommended strategies for the further development of sea ice histories from ice core msa for both proxies the limited information about the production and transfer of chemical markers from the sea ice zone to the antarctic ice sheets remains an issue that requires further multidisciplinary study despite some exploratory and statistical work the application of either proxy as an indicator of sea ice change in the arctic also remains largely unknown as information about these new ice core proxies builds so too does the potential to develop a more comprehensive understanding of past changes in sea ice and its role in both long and short term climate changes

sea salt aerosol production and bromine release role of snow on sea ice 1 snow lying on sea ice could be a potentially important source of sea salt aerosol as small snow particles rich in salts can be easily lifted into the air though blowing snow events using a measured distribution of snow salinity on antarctic sea ice and a blowing snow sublimation parameterization we derive a method for estimating sea salt aerosol production and bromine release during blowing snow events compared with sea salt aerosol production rates from the open ocean we find that the aerosol production rate from snow can be more than an order of magnitude larger per unit area under typical weather conditions the large sea ice cover may thus enhance the supply of sea salt to the polar lower atmosphere this is consistent with observations of sea salt aerosol seasonality and with the ice core record this large emission of sea salt from snow also implies an additional tropospheric bromine source in these regions

twentieth century sea ice variability in the weddell sea and its effect on moisture transport evidence from a coastal east antarctic ice core record high resolution study of deuterium excess d excess sea salt sodium ss na and methane sulfonic acid msa in an ice core from coastal dronning maud land cdml east antarctica revealed the

frost flowers as a source of fractionated sea salt aerosol in the polar regions frost flowers collected from the surface of new sea ice near the brunt ice shelf antarctica show depletion in sulphate and sodium relative to other sea water ions this is consistent with loss of mirabilite na2so4 during formation of the brine from which the frost flowers grow aerosol generated from frost flowers would have higher sodium sulphate ratios than aerosol generated from sea water this would explain low values of non sea salt sulphate encountered in winter aerosol and winter layers in ice cores at coastal antarctic sites calculations confirm that the frost flower source should be significant compared to an open water source for coastal regions

frost flowers in the laboratory growth characteristics aerosol and the underlying sea ice 1 in the laboratory we have investigated the growth and composition of frost flowers their ionic composition has shown little difference from those of field measurements young frost flowers grown on sea ice are saline leading us to speculate that wicking occurs continually during their growth on sea ice the surface area of frost flowers is only a little larger than the area of ice underneath consistent with recent field measurements from the arctic time lapse photography has allowed us to observe the extreme mobility of freshly forming sea ice at the stage at which the mush has become rather solid and continuing while the flowers grow this mobility results in new brine being expelled to the surface which therefore remains wet during various stages of frost flower growth we observed their freshly formed dendritic parts rapidly diminishing in size after contacting the surface consistent with repeated wicking frost flowers proved to be very stable in the presence of wind such that no aerosol was observed when wind was blown across them in the laboratory chamber this is consistent with recent field observations of frost flowers coexisting with wind blown snow

year round record of size segregated aerosol composition in central antarctica concordia station implications for the degree of fractionation of sea salt particles the origin of sea salt aerosol that reaches the high antarctic plateau and is trapped in snow and ice cores remains still unclear in particular the respective role of emissions from the open ocean versus those from the sea ice surface is not yet quantified to progress on this question the composition of bulk and size segregated aerosol was studied in 2006 at the concordia station 75 s 123 e located on the high antarctic plateau a depletion of sulfate relative to sodium with respect to the seawater composition is observed on sea salt aerosol reaching concordia from april to september that suggests that in winter when the sea salt atmospheric load reaches a maximum emissions from the sea ice surface significantly contribute to the sea salt budget of inland antarctica citation jourdain b s preunkert o cerri h castebrunet r udisti and m legrand 2008 year round record of size segregated aerosol composition in central antarctica concordia station implications for the degree of fractionation of sea salt particles

a comprehensive mass flux scheme for cumulus parameterization in large scale models abstract observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large scale models but this approach through the introduction of a spectral cloud ensemble leads normally to rather complex schemes in this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions this is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection gate marshall islands tradewind cumuli atex bomex and extratropical organized convection sesame 79 and then in a nwp model the scheme considers a population of clouds where the cloud ensemble is described by a one dimensional bulk model as earlier applied by yanai et al in a diagnostic study of tropical convection cumulus scale downdrafts are included various types of convection are represented i e penetrative convection in c

changes in environment over the last 800 000 years from chemical analysis of the epica dome c ice core the epica ice core from dome c extends 3259 m in depth and encompasses 800 ka of datable and sequential ice numerous chemical species have been measured along the length of the cores here we concentrate on interpreting the main low resolution patterns of major ions we extend the published record for non sea salt calcium sea salt sodium and non sea salt sulfate flux to 800 ka the non sea salt calcium record confirms that terrestrial dust originating from south america closely mirrored antarctic climate both at orbital and millennial timescales a major cause of the main trends is most likely climate in southern south america which could be sensitive to subtle changes in atmospheric circulation sea salt sodium also follows temperature but with a threshold at low temperature we re examine the use of sodium as a sea ice proxy concluding that it is probably reflecting extent with high salt concentrations reflecting larger ice extents with this interpretation the sodium flux record indicates low ice extent operating as an amplifier in warm interglacials non sea salt sulfate flux is almost constant along the core confirming the lack of change in marine productivity for sulfur producing organisms in the areas of the southern ocean contributing to the flux at dome c for the first time we also present long records of reversible species such as nitrate and chloride and show that the pattern of post depositional losses described for shallower ice is maintained in older ice it appears possible to use these concentrations to constrain snow accumulation rates in interglacial ice at this site and the results suggest a possible correction to accumulation rates in one early interglacial taken together the chemistry records offer a number of constraints on the way the earth system combined to give the major climate fluctuations of the late quaternary period