model experiments on large tabular iceberg evolution ablation and strain thinning antarctic tabular icebergs are important active components of the ice ocean system to investigate the relevance of inherent ice dynamics to iceberg evolution we developed a numerical model based on the fundamental equations of ice shelf flow and heat transfer forced by environmental parameters of the ice ocean atmosphere system model experiments with idealized icebergs of constant density show that the strain thinning rate for a typical iceberg with a thickness of 250 m and a temperature of 158c is about 1 m a 1 sensitivity studies for different scenarios of environmental conditions confirmed the reliability of our model a 5 year simulation of the evolution of iceberg a 38b yielded a mean decrease in thickness from 220 m to 106 3 m 95 of which was caused by basal melting 1 by surface melting and 4 by strain thinning we found iceberg spreading decelerating by about 75 and ice temperatures being strongly affected by progressive erosion of the relatively warm basal layers and warming in the uppermost part according to the model results basal melting is the primary cause of change of iceberg geometry during drift whereas strain thinning is only relevant in cold areas where basal melting is low

ice pumps and their rates an ice pump is a heat engine driven by the change of freezing point with pressure which will melt ice at depth in the ocean and deposit it at a shallower location it is self starting calculations of the maximum magnitude of this effect are made which show good agreement with field data available for sea and lake ice the discussion is applied to the general case of a moving pack ice sheet with a well mixed surface layer and to floating ice shelves the rate of melt from an 11 m deep pressure ridge keel due to ice pumping is estimated as 26 cm year and that from the front of the ross ice shelf at mcmurdo sound antarctica is estimated as 5 m year for the level of water movement noted in the authors field observations far from the ice front pumping between shelf areas of different thickness will still occur with tidal motion providing the necessary water exchange but its magnitude is now limited by the ability to remove the potentially stable layer of melt water out of the system it is important to realize that the pumping does not depend on the availability of sensible heat in the water column and its effects are additional to any melting caused by the advection of warmer water to the ice water interface

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

magnetostratigraphical dating of loess deposits in china the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene the new palaeomagnetic measurements reported here on a bore hole section near lochuan shaanxi province suggest a clearly defined magnetic polarity zonation which extends below the olduvai subchron a late pliocene age of 2 4 myr is assigned to the oldest loess sediments measured the intensity variations of natural remanent magnetization nrm and low field magnetic susceptibility are indicative of climatic changes during loess deposition

atmospheric and oceanic forcing of weddell sea ice motion the data from sea ice buoys which were deployed during the winter weddell sea project 1986 the winter weddell gyre studies 1989 and 1992 the ice station weddell in 1992 the antarctic zone flux experiment in 1994 and several ship cruises in austral summers are uniformly reanalyzed by the same objective methods geostrophic winds are derived after matching of the buoy pressure data with the surface pressure fields of the european centre for medium range weather forecasts the ratio between ice drift and geostrophic wind speeds is reduced when winds and currents oppose each other when the atmospheric surface layer is stably stratified and when the ice is under pressure near coasts over the continental shelves the spatial inhomogeneity of tidal and inertial motion effectively controls the variability of divergence for periods below 36 hours far from coasts speed ratios which presumably reflect internal stress variations in the ice cover are independent of drift divergence on the spatial scale of 100 km to study basin scale ice dynamics all ice drift data are related to the geostrophic winds based on the complex linear model thorndike and colony 1982 for daily averaged data the composite patterns of mean ice motion geostrophic winds and geostrophic surface currents document cyclonic basin wide circulations geostrophic ocean currents are generally small in the weddell sea significant features are the coastal current near the southeastern coasts and the bands of larger velocities of 6 cm s 1 following the northward and eastward orientation of the continental shelf breaks in the western and northwestern weddell sea in the southwestern weddell sea the mean ice drift speed is reduced to less than 0 5 of the geostrophic wind speed and increases rather continuously to 1 5 in the northern central and eastern weddell sea the linear model accounts for less than 50 of the total variance of drift speeds in the southwestern weddell sea and up to 80 in the northern and eastern weddell sea

thermophysical properties along curiosity s traverse in gale crater mars derived from the rems ground temperature sensor abstract the rems instrument onboard the mars science laboratory rover curiosity has measured ground temperature nearly continuously at hourly intervals for two mars years coverage of the entire diurnal cycle at 1 hz is available every few martian days we compare these measurements with predictions of surface atmosphere thermal models to derive the apparent thermal inertia and thermally derived albedo along the rover s traverse after accounting for the radiative effects of atmospheric water ice during fall and winter as is necessary to match the measured seasonal trend the rems measurements can distinguish between active sand other loose materials mudstone and sandstone based on their thermophysical properties however the apparent thermal inertias of bedrock dominated surfaces 350 550 j m 2 k 1 s are lower than expected we use rover imagery and the detailed shape of the diurnal ground temperature curve to explore whether lateral or vertical heterogeneity in the surface materials within the sensor footprint might explain the low inertias we find that the bedrock component of the surface can have a thermal inertia as high as 650 1700 j m 2 k 1 s for mudstone sites and 700 j m 2 k 1 s for sandstone sites in models runs that include lateral and vertical mixing although the results of our forward modeling approach may be non unique they demonstrate the potential to extract information about lateral and vertical variations in thermophysical properties from temporally resolved measurements of ground temperature

oxygen isotope record of paleorainwater in authigenic carbonates of chinese loess paleosol sequences and its paleoclimatic significance abstract oxygen isotopic compositions of rhizoconcretions and land snail shells were measured to reconstruct the 18o profiles of paleorainwater 18op for well dated loess paleosols in luochuan china to assess the paleoclimatic significance of 18op factors that control the spatial and temporal 18o variations of rainwater in east asian monsoon regions were investigated modern records indicate that the spatial 18o variations of modern rainwater 18om are closely related to near surface temperature t and the amount of precipitation p in order to separate the effects of t and p on the 18om a linear relationship between 18om t and the natural logarithm of p is established by multiple regressing analyses 18 o m 1 070 0 326 t 2 041 ln p the 18o of paleorainwater over the past 130 ka in luochuan area is calculated by the modern spatial 18o t p relationship using estimated t and p from other paleoclimate records the calculated 18o match well to those reconstructed from the authigenic carbonates which implies that the spatial and temporal 18o variations of rainwater in east asian monsoon regions have similar 18o t p relationships and the authigenic carbonates in chinese loess paleosol sequences can serve as valid records of 18op as an application of the 18o t p relationship p variation in the past 130 ka in luochuan was evaluated the reconstructed p is in good agreement with other studies using different approaches our results suggest higher precipitation in marine isotope stages 1 3 and 5 reflecting intense summer monsoon influences during these periods of time

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

a model study of ocean circulation beneath filchner ronne ice shelf antarctica implications for bottom water formation 1 an isopycnic coordinate ocean circulation model has been applied to the southern weddell sea including the cavity beneath filchner ronne ice shelf with the aim of investigating the buoyancy forced circulation on the continental shelf buoyancy forcing is associated with both the annual growth and decay of sea ice and the interaction between ice shelf and ocean in the model a generally anti cyclonic circulation develops beneath the ice shelf so that new shelf waters entering the cavity in the west emerge colder and fresher in the east the outflow contributes to a dense current that spills off the continental shelf and descends the slope oceanographic observations from the region are consistent with this picture and highlight the overflow as a major source of weddell sea bottom water

morphological characters and multi element isotopic signatures of carbonates from chinese loess paleosol sequences abstract morphological characters and multi element isotopic compositions of carbonates from the loess paleosol sequences in northwestern china are examined to explore the origin of the minerals samples are collected from various sections ranging from holocene to 0 9 ma within the sequences and fractions with grain sizes 45 and 45 m exhibit an almost perfect spherical shape while those 13 c and 18 o values between minerals and biologically originated samples indicates that the 206 pb 204 pb 207 pb 204 pb 208 pb 204 pb and 87 sr 86 sr these results suggest the utility of fine carbonate particles in the soil profile in reconstructing a potentially higher resolution 13 c and 18 o time series to elucidate the paleoclimatic fluctuation in the chinese loess plateau during pleistocene the discovery of the nano rod calcite in chinese loess together with previous findings of the similar mineral form in asian dust strongly suggests the possibility that these highly reactive caco 3 form may alter the aerosol properties during transport

data based estimation of anthropogenic carbon and acidification in the weddell sea on a decadal timescale 1 the amount of anthropogenic co2 cant that entered the weddell sea between 1992 and 2008 cant1992 2008 was assessed using the extended multiple linear regression emlr method in the warm deep water wdw and the weddell sea bottom water wsbw cant1992 2008 values were insignificant whereas values as high as 8 mol kg 1 were observed over the shelf cant1992 2008 concentrations in the surface layer varied with latitude between 2 and 11 mol kg 1 weak intrusion of anthropogenic co2 into weddell sea deep water wsdw was demonstrated cant1992 2008 yields 1 5 2 mol kg 1 that more cant1992 2008 was found in the wsdw than in the wsbw is surprising but can be explained by intense ventilation of the wsdw originating from east of the weddell gyre the invasion of cant1992 2008 provokes a shift in the equilibria of the carbonate system resulting in acidification and reduction of co32 concentration the mean decrease of ph in the upper 200 m layer was 0 016 the largest decrease of calcite and aragonite saturation states was observed at the surface this implies that surface waters might become undersaturated with respect to aragonite in the future while the underlying wdw is still saturated results of this analysis suggest that complete undersaturation of surface waters in the weddell sea will be reached after the 21st century

ocean circulation beneath filchner ronne ice shelf from three dimensional model results a high resolution three dimensional ocean circulation model is applied to the cavity beneath filchner ronne ice shelf fris the model predicts predominantly barotropic currents which form a series of cyclonic gyres in the deep basins and anticyclonic circulations around the islands the surface circulation can be such that the water moves in the direction of decreasing or increasing ice thicknesses in the former case leading to freezing while melting at the ice shelf base results in the latter case the pattern of melting and freezing is consistent with known distributions of marine ice and melting areas beneath fris an anticyclonic circulation around the korff and henry ice rises with melting west of korff ice rise and freezing on the eastern side and north of henry ice rise is the main source for an ice pumping mechanism that produces the observed large marine ice body in the central filchner ronne ice shelf the estimates for net melting for realistic conditions at the open ocean boundary are 40 50 km 3 yr 1 indicating that ice shelf ocean interaction is an important contribution to the mass balance of the ice shelf

a model of ice shelf ocean interaction with application to the filcher ronne and ross ice shelves a simple analytical model has been developed to study the formation of ice shelf water isw isw is assumed to flow as a buoyancy driven layer underneath the ice shelf a relation between potential temperature and salinity in the isw layer is calculated from the mass and energy balance this temperature salinity relation is shown to depend only on the temperature and the salinity of the source water mass and to be practically independent of entrainment and melt rates the model results are obtained without making any assumptions about entrainment and melt rates the model is in good agreement with observations under the ronne ice shelf and it indicates that isw in the filchner depression is formed from western shelf water wsw with salinity higher than 34 75 practical salinity units such high salinity water is only observed in the ronne depression in the western part of the continental shelf this implies a circulation of wsw under the filchner ronne ice shelf from the ronne depression into the filchner depression similarly the model shows that the isw observed under j9 at the ross ice shelf has been formed from low salinity shelf water lssw from the eastern parts of the ross sea continental shelf lssw must therefore circulate under the eastern parts of the ross ice shelf

ice shelf water overflow and bottom water formation in the southern weddell sea 1 cold shelf waters flowing out of the filchner depression in the southern weddell sea make a significant contribution to the production of weddell sea bottom water wsbw a precursor to antarctic bottom water aabw we use all available current meter records from the region to calculate the flux of cold water 1 9 c over the sill at the northern end of the filchner depression 1 6 0 5 sv and to determine its fate the estimated fluxes and mixing rates imply a rate of wsbw formation referenced to 0 8 c of 4 3 1 4 sv we identify three pathways for the cold shelf waters to enter the deep weddell sea circulation one path involves flow constrained to follow the shelf break the other two paths are down the continental slope resulting from the cold dense water being steered northward by prominent ridges that cross the continental slope near 36 w and 37 w mooring data indicate that the deep plumes can retain their core characteristics to depths greater than 2000 m probably aided by thermobaricity the plume water at this depth can flow at a speed approaching 1 m s 1 implying that the flow is occasionally supercritical we postulate that such supercriticality acts to limit mixing between the plume and its environment the transition from supercritical to slower more uniform flow is associated with very efficient mixing probably as a result of hydraulic jumps

on the near bottom variability in the northwestern weddell sea the thermohaline data from the first brazilian hydrographic cruise to the northwestern weddell sea ar xviii revealed significant near bottom changes in water column properties over seasonal and interannual time scales favorable ice conditions in 2000 allowed a dense station coverage of the area including the main pathways for weddell sea deep and bottom waters the new results are compared with the data from the 1998 german cruise ant xv 4 and other historical data a warming of the bottom layer was discovered that was more attributable to short term seasonal or interannual fluctuations in the formation of cold bottom water than to a long term trend there was both consistency and variation between and within seasons invariant bottom water characteristics were observed in different seasons summer winter and variable bottom water characteristics were observed in the same season summer at the same locations this reduces the possibility of a dominant seasonal effect instead we propose that the intermittent behavior of small cold water sources along the weddell sea s periphery causes the variability measured in the deep northwestern weddell sea the observed variability has consequences for the water mass export across the south scotia ridge as the absence of the fresher lighter weddell sea bottom water south of south orkney plateau during ar xviii might be linked to a reduced ventilation of the deep scotia sea the results of this study show the need for ongoing efforts for establishing a long term monitoring of this region with global importance

ice ocean processes over the continental shelf of the southern weddell sea antarctica a review 1 interactions between the southern ocean and the weddell sea ice shelves are important both to the antarctic ice sheet and to the production of globally significant water masses here we review the interaction between the filchner ronne ice shelf and the shelf sea in which it floats the continental shelf processes leading to the production of weddell sea deep and bottom waters from the original off shelf source waters are discussed and a new view is offered of the initial production of high salinity shelf water data from ship based measurements at the ice front from glaciological methods and from measurements made within the sub ice shelf cavity itself are used to describe the pattern of flows beneath the ice shelf we also consider the variability observed within the cavity from tidal to interannual time scales and finish with a discussion of future research priorities in the region

a primitive equation ocean circulation model using a general vertical coordinate transformation 1 description and testing of the model the ocean general circulation model of the geophysical fluid dynamics laboratory has been modified to accommodate a generalized vertical coordinate transformation the model with a slightly modified transformation z h is applied to three simple test cases a clear improvement of barotropic and baroclinic topographic rossby waves has been achieved compared with the z coordinate model a somewhat more typical time independent problem for the overflow of dense water masses over a zonal ridge exhibits the potential benefits as well as the flaws of the new model vertically integrated mass transport is very sensitive to changes in bottom slope in regions where planetary and topographic are of comparable magnitudes this translates into large errors in the z model due to the crude approximation to the actual topography the deep flow in the z model does not follow the bottom exactly horizontal overshoots of dense water lead to convective mixing on the southern side of the ridge this can be a serious problem for modeling more realistic overflow situations with the z model increased diapycnal diffusion has been identified as the most serious problem with the terrain following coordinate system for this specific application

numerical simulation of the filchner overflow the plume of ice shelf water isw flowing into the weddell sea over the filchner sill contributes to the formation of antarctic bottom water the filchner overflow is simulated using a hydrostatic primitive equation three dimensional ocean model with a 0 5 2 sv isw influx above the filchner sill the best fit to mooring temperature observations is found with influxes of 0 5 and 1 sv below a previous estimate of 1 6 0 5 sv based on sparse mooring velocities the plume first moves north over the continental shelf and then turns west along slope of the continental shelf break where it breaks up into subplumes and domes some of which then move downslope other subplumes run into the eastern submarine ridge and propagate along the ridge downslope in a chaotic manner the next western ridge is crossed by the plume through several paths despite a number of discrepancies with observational data the model reproduces many attributes of the flow in particular we argue that the temporal variability shown by the observations can largely be attributed to the unstable structure of the flow where the temperature fluctuations are determined by the motion of the domes past the moorings our sensitivity studies show that while thermobaricity plays a role its effect is small for the flows considered smoothing the ridges out demonstrate that their presence strongly affects the plume shape around the ridges an increase in the bottom drag or viscosity leads to slowing down and hence thickening and widening of the plume

chemical weathering of the loess deposits in the lower changjiang valley china and paleoclimatic implications abstract loess deposits xiashu loess are widely distributed in the lower changjiang valley east china and are considered to be of eolian origin with a similar provenance to the well documented loess of north central china the xiashu loess is characterized by strong dissolution of carbonate and considerable weathering of some silicate minerals especially plagioclase chemical mobility of ca sr na mg was observed in the xiashu loess sediments whilst most transition metals are relatively enriched chemical index of variation cia and element ratios of k na and k ca record several paleoclimate events in the lower changjiang valley during the mid late quaternary corresponding with isotopic records in deep sea sediments east china might be governed by stronger summer monsoons than north central china during interglacial periods of the mid late quaternary which may somewhat obscure the record of winter monsoons during glacial periods

glacier tongue calving reduced dense water formation and enhanced carbon uptake 1 dense shelf water formed in the mertz polynya supplies the lower limb of the global overturning circulation ventilating the abyssal indian and pacific oceans calving of the mertz glacier tongue mgt in february 2010 altered the regional distribution of ice and reduced the size and activity of the polynya the salinity and density of dense shelf water declined abruptly after calving consistent with a reduction of sea ice formation in the polynya breakout and melt of thick multiyear sea ice released by the movement of iceberg b9b and the mgt freshened near surface waters the input of meltwater likely enhanced the availability of light and iron supporting a diatom bloom that doubled carbon uptake relative to precalving conditions the enhanced biological carbon drawdown increased the carbonate saturation state outweighing dilution by meltwater input these observations highlight the sensitivity of dense water formation biological productivity and carbon export to changes in the antarctic icescape

on the structure and the transport of the eastern weddell gyre abstract the circulation pattern and volume transports in the eastern weddell gyre are estimated on the basis of hydrographic data collected by r v polarstern between 1989 and 1996 in the northeastern edge of the weddell gyre eastward flowing water masses from the antarctic circumpolar current and the weddell sea converge due to the strong effect of topographic constraints on ocean currents in the weakly stratified waters of high latitudes the wedge like structure of the southwest indian ridge can cause the convergence the increased shear leads to instabilities of the current at the eastern end of the ridge which produce an intense mesoscale eddy field between 15 and 30 e in the eddies water from the weddell cold regime and the antarctic circumpolar current waters mix and form the water masses of the weddell warm regime these waters are advected southward and flow towards the westward southern rim current which is driven by the antarctic eastwind band hence there is not a continous flow from the northern to the southern rim but a decay of the mean flow in the northeast and a reformation in the south volume transports across the greenwich meridian estimated on the basis of a combined ctd adcp data set result in an eastward flow of 61 sv in the northern rim current and a westward return flow of 66 sv in the southern part of the gyre the transport is about twice as high as previous estimates between kapp norvegia and the northern tip of the antarctic pensinsula indicating a significant gyre circulation north of 70 s

different paleoenvironments of late pleistocene age identified in verőce outcrop hungary preliminary results abstract complex geomorphological geological paleopedological and chronometrical investigations were started to reveal the development of the alluvial section and the loess paleosol sequence containing remnants of a late palaeolithic site near ver ce hungary different paleoenvironments were identified in the profiles of the abandoned brickyard influenced by different facies in the margin of fluvial alluvial palaeo danube and proluvial southeast pediment of borzsony mountain area and the environments affected by the climate fluctuation of late pleistocene loess paleosol sequence overlying the base of alluvial materials sediments possibly deposited by palaeo danube were identified in a basal section of the abandoned brickyard the alluvial facies was indicated by sand silt and clay layers in the sediment sequence some parts of the alluvial sediments were covered by loess in the glacial periods intercalated by four paleosol horizons formed during interglacial or interstadial periods the sedimentation of loess and the forming of paleosols were finished by pedimentation processes sheet wash redeposition indicated by the fine layered material at the top of each paleosol horizon another complex fluvial alluvial section was identified at a different part of the brickyard possibly developed synchronous with the loess paleosol sequence during the late pleistocene based on relative and chronometrical dating methods e g archaeological stratigraphy and correlation of the artifacts 14c and luminescence dating the development of the loess paleosol sequence started in marine isotope stage 6 mis6 and the youngest layer dated to mis2

stable isotope composition of the carbonate concretion in loess and climate change carbonate concretions are commonly found in the loess in china oxygen and carbon isotopic compositions of carbonate concretions collected from 14 different paleosols s1 s14 in the lishi formation of luochuan loess section china were analysed the isotopic compositions of concretion in loess are useful tools in paleoclimatic study usually the more developed the paleosol is the less negative the 18o values and the more negative the 13c values are the oxygen isotopic composition of these paleosols varies within a range of about 1 3 the carbon isotopic composition however shows larger variations from one paleosol to the other within a range of 5 3 an attempt was made to semi quantitatively estimate the paleosol formation temperature and precipitation based on the carbon and oxygen isotopic data obtained

the methane diurnal variation and microseepage flux at gale crater mars as constrained by the exomars trace gas orbiter and curiosity observations funding for this work was provided by the canadian space agency s mars science laboratory participating scientist program

iceberg drift and ocean circulation in the northwestern weddell sea antarctica abstract icebergs are distinctive features in the southern ocean and can influence the physicochemical properties of the ocean environment around them their trajectories are influenced by ocean currents sea ice bathymetry and wind action here twenty five icebergs were identified and tracked by applying image classification methods to a series of 142 advanced synthetic aperture radar asar images obtained during 2008 and 2009 tracking these icebergs made it possible to associate the patterns of iceberg drift with the main ocean currents and front systems in this region including the antarctic coastal current the antarctic slope front and the weddell front a case study investigated here revealed the recirculation of a weddell sea iceberg within the bransfield strait in the northern antarctic peninsula as well as its corresponding mass loss starting in the weddell sea and extending throughout the monitoring period the icebergs studied experienced an average disintegration percentage of 21 15 and an average drift speed of 0 22 0 11 km h 1 the icebergs that drifted at least 500 km had an average meltwater injection rate of 62 76 38 27 m3 s 1 in the ocean around the northern antarctic peninsula

future sea level rise due to projected ocean warming beneath the filchner ronne ice shelf a coupled model study a general ocean circulation model is coupled with a 3d thermodynamical ice sheet shelf model to simulate the response of the filchner ronne ice shelf fris antarctica and coastal parts of its catchment basin to a postulated inflow of warm deep water into the ice shelf cavity on a 1000 yr timescale prescribed ocean warming based on climate projections enters the ice shelf cavity in the up to 1500 m deep filchner trough and penetrates deep into the sub ice cavity increasing basal melt rates induce geometry changes of the cavity which in turn have an impact on the ocean circulation and therefore the modelled melt rates highest melt rates of about 20 m yr 1 follow the up to 180 km retreating grounding line basal mass loss reaches about 250 km3 yr 1 doubling the present day value the most vulnerable areas below the fris are the bailey ice stream and the area between the institute and moeller ice streams where the increased melting accounts for about 80 km of the modelled grounding line retreat on the backward sloping bedrock the potential additional contribution to the eustatic sea level rise due to the grounded ice loss simulated in an ensemble approach against a transient control experiment is about 0 05 mm yr 1 during the first 500 yr and about 0 17 mm yr 1 thereafter

calcium carbonate nodules in soils 13o 16o and 13c 12c ratios and 14c contents abstract 18 o values 13 c values and 14 c ages were determined in ten caco 3 nodule populations collected from soil and paleosols in the israeli coastal plain the selected soils were carbonate free when formed and the nodules in them represent either reprecipitation of carbonate illuviated from overlying horizons descending mode or precipitated from a raised brackish water table ascending mode the 14 c ages represent the times of migration illuviation or eustatic movement both climate related and the stable isotopic conditions reflect the environmental conditions at such times the 13 c values of most populations were found to have a wide range and cannot be used to reconstruct former climates this wide range is attributed to microvariations of pco 2 in the soil because the 18 o ranges in the same samples are usually comparable to analytical uncertainties and because the 18 o mean values follow an age correlated pattern they permit us to place the soils in one of three categories in two cases where nodules were soft both turned out to be young 1000 years and to have wide ranges in 18 o values the latter are apparently due to continual re equilibration with new soil solutions in three cases of the descending mode of nodule formation 12 000 14 000 year old hard nodules had very narrow 18 o whose means reflect the rainfall value at that time the period between 12 000 14 000 years b p is independently known to be one of higher precipitation evaporation ratio and of more intensive soil formation these ascending mode populations of hard nodules had narrow ranges in 18 o reflecting a mixture of sea water and rainfall and all turned out to be 3 000 4 000 years old at this period the sea reached its highest elevation resulting in raising the nearcoast water table

melting of ice shelves and the mass balance of antarctica we calculate the present ice budget for antarctica from measurements of accumulation minus iceberg calving run off and in situ melting beneath the floating ice shelves the resulting negative mass balance of 469 gt year 1 differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20 50 annual accumulation from an earlier review is adjusted to include the antarctic peninsula for a total of 2144 gt year 1 an iceberg production rate of 2016 gt year 1 is obtained from the volume of large icebergs calculated from satellite images since 1978 and from the results of an international iceberg census project ice shelf melting of 544 gt year 1 is derived from physical and geochemical observations of meltwater outflow glaciological field studies and modeling of the sub ice ocean circulation the highest melt rates occur near ice fronts and deep within sub ice cavities run off from the ice sheet surface and from beneath the grounded ice is taken to be 53 gt year 1 less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0 45 mm year 1 in the ipcc best estimate of the recent global sea level rise

how iceberg calving and grounding change the circulation and hydrography in the filchner ice shelf ocean system the formation of bottom water in the southern weddell sea is strongly influenced by the flow of ice shelf water isw out of the filchner ronne ice shelf cavity the breakout of three giant icebergs in 1986 and their grounding on the shallow berkner bank modified the circulation and water mass formation in the filchner trough and the adjacent sea areas hydrographic measurements along the filchner ice shelf front carried out with rv polarstern in 1995 show significant changes in the water mass characteristics and flow patterns in the filchner trough in comparison to measurements from the early 1980s changes in the trough will affect the flow over the sill to the deep weddell abyssal plain we combine a three dimensional ocean circulation model with conductivity temperature depth and stable isotope measurements to investigate the details of the circulation in front of and beneath the filchner ice shelf we assess the impact of stranded icebergs and a more southerly ice shelf front position caused by a 1986 iceberg calving event on the circulation and observed water mass properties results indicate variations of the flow pattern in the filchner trough and on berkner bank where high salinity shelf water the feedstock for isw is produced the calving and grounding impacts illustrate the sensitivity of the ice shelf ocean system to perturbations in local bathymetric settings

handbook of environmental isotope geochemistry vol 1 the terrestrial environment a p fritz and j ch fontes editors elsevier amsterdam 1980 xii 532 pp u s 90 25 dfl 185 00

the loess deposits of buca dei corvi section central italy revisited loess deposits have been described in the past for the upper section of buca dei corvi succession central italy in this paper the deposits were re analysed to clarify the depositional environment and to attempt a paleoclimate reconstruction two radiocarbon dates on pedogenic carbonate constrain the ages to the late glacial and are consistent with previous osl dating of the top of the succession the non marine mollusc assemblage shows typical character of cold and dry climatic conditions testified by strong oligotypical composition mineralogy and geochemistry of the sediments indicate the abundant presence of exotic quartz mineral which can be explained only by wind transport probably wind transport was also responsible of deposition of carbonate which then dissolved and re precipitated producing pedogenic concretions stable isotopes 13c 12c and 18o 16o ratios of the concretions are consistent with a climate drier than present conditions with an environment characterized by sparse vegetation

hydrography and circulation in the filchner depression weddell sea antarctica cold and dense ice shelf water isw emerging from the filchner ronne ice shelf cavity in the southwestern weddell sea flows northward through the filchner depression to eventually descend the continental slope and contribute to the formation of bottom water new ship born observations of hydrography and currents from filchner depression in january 2013 suggest that the northward flow of isw takes place in a middepth jet along the eastern flank of the depression thus questioning the traditional view with outflow along the western flank this interpretation of the data is supported by results from a regional numerical model which shows that isw flowing northward along the eastern coast of berkner island turns eastward and crosses the depression to its eastern side upon reaching the filchner ice front the ice front represents a sudden change in the thickness of the water column and thus a potential vorticity barrier transport estimates of northward isw flux based on observations ranges from 0 2 to 1 0 sv

climatic conditions recorded by terrestrial mollusc assemblages in the chinese loess plateau during marine oxygen isotope stages 12 10 abstract past analogs for our present interglacial have been sought for better understanding of our present and future climate marine isotope stage 11 mis 11 has long been considered to be a good candidate and has gained increasing attention in recent studies of marine and terrestrial records in the chinese loess paleosol sequences s4 soil interpreted as equivalent to mis 11 yields a very precise terrestrial paleoclimate record of environmental changes that prevailed during this period in this study two high resolution terrestrial mollusc records from the loess plateau have been analyzed to characterize climate variability during the periods of mis 12 10 the changes in environment and climate indicated by the variations in abundance of land mollusc species are thus documented our mollusc results show that the l5 loess equivalent of mis 12 developed under relatively cold and dry conditions climate during this period was not as severe as indicated in the marine isotopic records an episode of warmer and more humid condition occurred at the middle stage of the mis 12 reflecting a summer monsoon strengthened during the glacial interval a similar scenario has been observed in the middle part of mis 10 in addition our mollusc records provide insight into the climate conditions over the loess plateau during mis 11 a general warm humid climate dominated during the formation of s4 soil but at least four fluctuations occurred at xifeng region reflecting unstable climate conditions and regional climate differences within the loess plateau during this period our study shows that the early part of s4 spanning over 30 ka was very warm and humid while the late part was characterized by mild cool conditions comparison of mollusc species compositions of both mis 11 and holocene intervals reveals different climate conditions the early part of mis 11 was warmer and more humid than the holocene optimum period while the late part of mis 11 was similar or cooler our study indicates that the extent of warming during the holocene in the loess plateau might be significantly less than the conditions that prevailed during the mis 11 interglacial period

acetic acid leachable elements in pedogenic carbonate nodules and links to the east asian summer monsoon carbonate nodules at the base of paleosols within chinese loess are products of pedogenic neoformation and thus have great potential to document the summer monsoon history here we present mineralogical and elemental compositions of carbonate nodules from a north south loess transect of northern china for the last and penultimate interglacials x ray diffraction patterns show that the nodules are composed mainly of calcite together with some silicate minerals such as quartz plagioclase orthoclase illite and kaolinite elemental composition of the acetic acid leachable fraction is characterized by extremely high ca concentration and modest k and mg content followed by al si sr mn fe p na ba pb th and u based on the mineralogical data and relationship between carbonate and the leachable element content we suggest that k mg sr ba and u mainly come from clay minerals na from highly soluble salts trapped by calcite particles and al and si from amorphous phases of pedogenic origin for both the last and penultimate interglacials the na content decreases from north to south while the al si and u concentrations show a southward increasing pattern these characteristics all suggest a southward decrease in aridity across the chinese loess plateau for both interglacials consistent with the pattern of a southerly increase in pedogenic development for the two interglacial soils and with the pattern of the present north south rainfall gradient therefore na al and na si ratios in the acetic acid extract are efficient proxies for aridity and are ultimately controlled by the summer monsoon precipitation i e high ratios indicate weakened summer monsoon intensity in addition the significant content of highly soluble na salts in carbonate nodules highlights soil dewatering as an important mechanism for the formation of pedogenic carbonate at least in the case of the northern loess plateau

a full martian year of line of sight extinction within gale crater mars as acquired by the msl navcam through sol 900 we report on line of sight extinction in northern gale crater mars as seen by the mars science laboratory msl rover curiosity from sol 100 to sol 900 a little more than an entire martian year navcam images oriented due north which show the distant crater rim the near ground and the sky allow the extinction due to dust within the crater to be determined this line of sight extinction is compared to a complementary dataset of column extinctions derived from mastcam the line of sight extinction within the crater is less than the column extinction for the majority of the martian year this implies that the relatively low mixing ratio of dust within the crater as compared to the atmosphere above the crater rim persists through most of the year this suggests relatively little mixing between the atmosphere above the crater and the atmosphere inside the crater and suggests that northern gale crater is a net sink of dust in the current era the data does however show a yearly convergence of the line of sight extinction and the column averaged extinction around ls 270 290 this suggests that air above the crater mixes with air in the crater at this time as predicted by mesoscale models matching line of sight and column extinction values are also seen around ls 135 a season that has only been observed once in this dataset this is particularly interesting as the rover environmental monitoring station onboard curiosity reports increased convective boundary layer heights in the same season

a numerical model of the weddell sea large scale circulation and water mass distribution a circumpolar model for regional studies of the wind driven and thermohaline circulation of the southern ocean including the major sub ice shelf areas is described a first series of numerical experiments focusing on the weddell sea reveals a pronounced and persistent double cell structure of the weddell gyre with a maximum transport of 60 sv in agreement with observations experiments with artificial passive tracers point to the shallow shelf areas off the filchner ronne ice shelf as main locations for bottom water production the trajectories of lagrangian floats are used to determine the pathways and timescales of water mass spreading in the model in addition the effect of sub ice shelf forcing on the water mass characteristics is evaluated it is shown that water modified in the sub ice cavities contributes significantly to the deep and bottom water formation along the continental slope and affects the water mass characteristics throughout the weddell sea by increasing the stability of the near surface stratification and preventing deep convection

the effects of antarctic iceberg calving size distribution in a global climate model icebergs calved from the antarctic continent act as moving sources of freshwater while drifting in the southern ocean the lifespan of these icebergs strongly depends on their original size during calving in order to investigate the effects if any of the calving size of icebergs on the southern ocean we use a coupled general circulation model with an iceberg component iceberg calving length is varied from 62 m up to 2 3 km which is the typical range used in climate models results show that increasing the size of calving icebergs leads to an increase in the westward iceberg freshwater transport around antarctica in simulations using larger icebergs the reduced availability of meltwater in the amundsen and bellingshausen seas suppresses the sea ice growth in the region in contrast the increased iceberg freshwater transport leads to increased sea ice growth around much of the east antarctic coastline these results suggest that the absence of large tabular icebergs with horizontal extent of tens of kilometers in climate models may introduces systematic biases in sea ice formation ocean temperatures and salinities around antarctica

regional changes in icescape impact shelf circulation and basal melting ice shelf basal melt is the dominant contribution to mass loss from antarctic ice shelves however the sensitivity of basal melt to changes in icescape grounded icebergs ice shelves and sea ice and related ocean circulation is poorly understood here we simulate the impact of the major 2010 calving event of the mertz glacier tongue mgt east antarctica and related redistribution of sea ice and icebergs on the basal melt rate of the local ice shelves we find that the position of the grounded tabular iceberg b9b controls the water masses that reach the nearby ice shelf cavities after the calving of the mgt and the removal of b9b warmer water is present both within the mgt cavity and on the continental shelf driving a 57 increase of the deep mgt basal melting major changes in icescape influence the oceanic heat flux responsible for basal ice shelf melting

an isotopic study of paleosol carbonates from olduvai gorge the isotopic composition of paleosol carbonates from olduvai gorge can be used to give estimates of the paleoclimatic history of east africa during the plio pleistocene oxygen isotopes are indicative of major changes in the isotopic composition of meteoric water while carbon isotopes are indicative of major changes in the fraction of biomass using the hatch slack c4 photosynthetic pathway three major periods of climatic change in this terrestrial setting occurred at about 1 67 1 3 and 0 6 myr these involved major changes in flora as well as major changes in the isotopic composition of meteoric water overall the climate has become warmer and more arid over the past 2 2 myr

the meteorology of gale crater as determined from rover environmental monitoring station observations and numerical modeling part ii interpretation abstract numerical modeling results from the mars regional atmospheric modeling system are used to interpret the landed meteorological data from the rover environmental monitoring station onboard the mars science laboratory rover curiosity in order to characterize seasonal changes throughout the martian year simulations are conducted at ls 0 90 180 and 270 two additional simulations at ls 225 and 315 are explored to better understand the unique meteorological setting centered on ls 270 the synergistic combination of model and observations reveals a complex meteorological environment within the crater seasonal planetary circulations the thermal tide slope flows along the topographic dichotomy mesoscale waves slope flows along the crater slopes and mt sharp and turbulent motions all interact in nonlinear ways to produce the observed weather ls 270 is shown to be an anomalous season when air within and outside the crater is well mixed by strong flushing northerly flow and large amplitude breaking mountain waves at other seasons the air in the crater is more isolated from the surrounding environment the potential impact of the partially isolated crater air mass on the dust water noncondensable and methane cycles is also considered in contrast to previous studies the large amplitude diurnal pressure signal is attributed primarily to necessary hydrostatic adjustments associated with topography of different elevations with contributions of less than 25 to the diurnal amplitude from the crater circulation itself the crater circulation is shown to induce a suppressed boundary layer

evolution of ice shelf rifts implications for formation mechanics and morphological controls abstract ice shelf rifts are predecessors to iceberg calving events observations of their morphology over time and interaction with their surroundings are presented newly available landsat derived annual velocity data and laser altimetry from nasa s icesat icesat 2 and operation icebridge missions were used to characterize several ice shelf rift systems actively propagating ice shelf rifts exhibit uplift on both sides with an offset in height between the two rift walls suggesting an asymmetric buoyancy force resulting from the rifting process itself it is observed that the direction of the asymmetry is the same for rifts within a single ice shelf but not between ice shelves this finding suggests a rheological or basal properties influence on rift formation and buoyancy asymmetry it is shown that this asymmetry can be accounted for by modeling ice shelf rifts as subvertical faults with time and inactivity rift walls eventually relax and become rounded off measurements of widening suggest that rift infilling is active on many active rifts active rifts experience higher spreading rates than do dormant rifts lastly two candidate processes are identified for rift nucleation subvertical basal crevassing and localized melt it is found that more than any other ice shelf in this study rifting in pine island glacier is driven by ocean heat variations and is showing signs of increasing destabilization

a habitable fluvio lacustrine environment at yellowknife bay gale crater mars the curiosity rover discovered fine grained sedimentary rocks which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy this aqueous environment was characterized by neutral ph low salinity and variable redox states of both iron and sulfur species carbon hydrogen oxygen sulfur nitrogen and phosphorus were measured directly as key biogenic elements by inference phosphorus is assumed to have been available the environment probably had a minimum duration of hundreds to tens of thousands of years these results highlight the biological viability of fluvial lacustrine environments in the post noachian history of mars

circulation beneath the filchner ice shelf antarctica and its sensitivity to changes in the oceanic environment a case study we investigate the sensitivity of the ocean circulation in the filchner trough to changes in the large scale oceanic environment and its impact on the mass balance of the filchner ice shelf antarctica three experiments with a three dimen sional ocean model describe i the current situation ii a scenario with increased ocean temperatures and iii a scenario with reduced sea ice formation rates on the adjacent continental shelf in the final discussion brief results of a combined scenario with increased ocean temperatures and reduced sea ice formation are presented the changes from the current situation affect the circulation in the filchnert rough and melting and freezing processes beneath the ice shelf the latter affect the amount and propert ies ofice shelf water isw a component of antarctic bottom water net basal melt rates provide an overall measure for the changes while the control run yields 0 35 m a i net melting averaged over the filchner ice shelf area the warming scenario results in a more than twofold increase in ice shelf mass loss reduced production of high salinity shelf water due to smaller sea ice formation rates in the second scenario leads on the other hand to a decrease in basal mass loss because the deep cavity is less well ventilated than in the con trol run isw is cooled and the ice shelf is stabilized under this scenario which is arguably the more likely development in the southern weddell sea

thermohaline circulation and interaction between ice shelf cavities and the adjacent open ocean the circulation system in an ice shelf cavity is driven by buoyancy fluxes due to melting and freezing of ice and horizontal pressure gradients at the interface between the cavity and the open ocean hence the inflow and outflow pattern and the hydrography in the open ocean influence the general hydrographic condition in the cavity which at least provides the potential for melting and freezing processes applying a three dimensional ocean general circulation model to an idealized ice shelf cavity geometry coupled with an open ocean at a topographic ice shelf barrier we found an important parameter controlling the interaction between these two systems idealized studies for different ice shelf and sea bottom topographies and forcing mechanisms for the open ocean show that the ice shelf edge represents a natural barrier for barotropic interaction because of the sudden decrease in water column thickness since the water column thickness and the coriolis force determine the characteristics for geostrophic flow separated circulation systems arise for the open ocean and the ice shelf cavity only in areas where constant water column thickness and from the oceanographic point of view constant f h contours can be observed across the barrier an increased barotropic current can surmount the ice edge and ventilate the water mass beneath the ice shelf this is only the case at lateral sloping sidewalls or at deep depressions which can be found for example in the southern weddell sea in all other cases the circulation in the ice shelf cavity is closed and almost unaffected by the hydrography outside the barrier

monitoring the tabular icebergs c28a and c28b calved from the mertz ice tongue using radar remote sensing data abstract we analyzed the evolution processes of two tabular icebergs c28a and c28b originating from iceberg c28 using continuous multisource radar remote sensing data the monitoring began during the calving of iceberg c28 from the mertz ice tongue in february 2010 and ended in april 2012 the evolution of the iceberg area was determined from envisat asar images and the freeboard change was derived from cryosat 2 profiles two patterns of iceberg area decreases are observed during iceberg drifting in austral summer from october to next march iceberg area shows a gradual decrease and it is interpreted to represent edge wasting sidewall melting and wave erosion the gradual decrease of the area of c28a occurred at rates between 8 1 km2 month and 16 5 km2 month in austral winter from april to september iceberg area has several discrete decreases sudden drop while it remained constant for most of the time and it is interpreted to be large rift calving primarily caused by ocean swell and basal melting calving area of the two studied icebergs is observed to be greater in the winter the freeboard decreased at different rates at different locations on the same iceberg between 0 02 0 22 and 0 82 0 28 m month for c28a and c28b suggesting a laterally inhomogeneous melting of icebergs the average rate of change of the c28b freeboard during its 22 month grounding period was 0 03 0 01 m month which is considerably smaller than the 0 76 0 23 m month observed when it was freely drifting in the ocean the cold water regime surrounding the iceberg can help the iceberg maintain a stable state this study reveals the potential use of radar remote sensing when monitoring antarctic icebergs

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

water mass modification over the continental shelf north of ronne ice shelf antarctica 1 we use new data from the southern weddell sea continental shelf to describe water mass conversion processes in a formation region for cold and dense precursors of antarctic bottom water the cruises took place in early 1995 1998 and 1999 and the time series obtained from moored instruments were up to 30 months in length starting in 1995 we obtained new bathymetric data that greatly improve our definition of the ronne depression which is now shown to be limited to the southwestern continental shelf and so cannot act as a conduit to northward flow from ronne ice front large scale intrusions of modified warm deep water mwdw onto the continental shelf occur along much of the shelf break although there is only one location where the mwdw extends as far south as ronne ice front high salinity shelf water hssw produced during the winter months dominates the continental shelf in the west during summer ice shelf water isw exits the subice cavity on the eastern side of the ronne depression flows northwest along the ice front and reenters the cavity at the ice front s western limit during winter the isw is not observed in the ronne depression north of the ice front the flow of hssw into the subice cavity via the ronne depression is estimated to be 0 9 0 3 sv when combined with inflows along the remainder of ronne ice front reported elsewhere sufficient heat is transported beneath the ice shelf to power an average basal melt rate of 0 34 0 1 m yr 1

examining the interaction between multi year landfast sea ice and the mertz glacier tongue east antarctica another factor in ice sheet stability the mertz glacier tongue mgt east antarctica has a large area of multi year fast sea ice myfi attached to its eastern edge we use various satellite data sets to study the extent age and thickness of the myfi and how it interacts with the mgt we estimate its age to be at least 25 years and its thickness to be 10 55 m this is an order of magnitude thicker than the average regional sea ice thickness and too thick to be formed through sea ice growth alone we speculate that the most plausible process for its growth after initial formation is marine frazil ice accretion the satellite data provide two types of evidence for strong mechanical coupling between the two types of ice the myfi moves with the mgt and persistent rifts that originate in the mgt continue to propagate for large distances into the myfi the area of myfi decreased by 50 following the departure of two large tabular icebergs that acted as pinning points and protective barriers future myfi extent will be affected by subsequent icebergs from the ninnis glacier and the imminent calving of the mgt fast ice is vulnerable to changing atmospheric and oceanic conditions and its disappearance may have an influence on ice tongue ice shelf stability understanding the influence of thick myfi on floating ice tongues ice shelves may be significant to understanding the processes that control their evolution and how these respond to climate change and thus to predicting the future of the antarctic ice sheet

contribution of giant icebergs to the southern ocean freshwater flux 1 in the period 1979 2003 the mass of giant icebergs icebergs larger than 18 5 km in length calving from antarctica averaged 1089 300 gt yr 1 of ice under half the snow accumulation over the continent given by the intergovernmental panel on climate change 2246 86 gt yr 1 here we combine a database of iceberg tracks from the national ice center and a model of iceberg thermodynamics in order to estimate the amount and distribution of meltwater attributable to giant icebergs by comparing with published modeled meltwater distribution for smaller bergs we show that giant icebergs have a different melting pattern an estimated 35 of giant icebergs mass is exported north of 63 s versus 3 for smaller bergs although giant bergs spend more of the earlier part of their history nearer to the coast we combine both estimates to produce the first iceberg meltwater map that takes into account giant icebergs the average meltwater input is shown to exceed precipitation minus evaporation p e in certain areas and is a nonnegligible term in the balance of freshwater fluxes in the southern ocean the calving of giant icebergs is however episodic this might have implications for their impact on the freshwater budget of the ocean it is estimated that over the period 1987 2003 the meltwater flux in the weddell and ross seas has varied by at least 15 000 m3 s 1 over a month because of the potential sensitivity of the production of deep waters to abrupt changes in the freshwater budget variations in iceberg melt rates of this magnitude might be climatologically significant

seasonal ventilation of the cavity beneath filchner ronne ice shelf simulated with an isopycnic coordinate ocean model 1 the ocean cavity beneath filchner ronne ice shelf is observed to respond to the seasonal cycle of water mass production on the continental shelf of the southern weddell sea here we use a numerical model to investigate the propagation of newly formed shelf waters into the cavity we find that the model reproduces the most distinctive features of the observed seasonality and offers a plausible explanation for those features the most saline shelf waters are produced in the far west where the inflow to the cavity peaks twice each year the major peak occurs during the short period around midwinter when convection reaches full depth and the densest waters are generated once the surface density starts to decline dynamic adjustment of the restratified water column leads to a gradual fall in the salinity at depth and a secondary peak in the inflow that occurs in summer at the western coast beneath the ice shelf the arrival of the wintertime inflow at the instrumented sites is accompanied by a rapid warming while the slower decline in the inflow leads to a more gradual cooling water brought in by the secondary summer peak flows mainly to the eastern parts of the cavity here the seasonality is suppressed because the new inflows mix with older waters that recirculate within a topographic depression this pooling of waters in the east where the primary outflow of ice shelf water is generated dampens the impact of seasonality on the local production of weddell sea bottom water

variability and mixing of the filchner overflow plume on the continental slope weddell sea abstracta large fraction of antarctic bottom water is produced in the weddell sea through mixing between the cold and dense shelf water masses and the warm and saline off shelf water we present o

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

ice shelf basal melting in a global finite element sea ice ice shelf ocean model the finite element sea ice ocean model fesom has been augmented by an ice shelf component with a three equation system for diagnostic computation of boundary layer temperature and salinity ice shelf geometry and global ocean bathymetry have been derived from the rtopo 1 dataset a global domain with a triangular mesh and a hybrid vertical coordinate is used to evaluate sub ice shelf circulation and melt rates for present day climate the model is forced with ncep reanalysis data basal mass fluxes are mostly realistic with maximum melt rates in the deepest parts near the grounding lines and marine ice formation in the northern sectors of ross ice shelf and filchner ronne ice shelf total basal mass loss for the ten largest ice shelves reflects the importance of the amundsen sea ice shelves getz ice shelf is shown to be a major melt water contributor to the southern ocean despite their modest melt rates the cold water ice shelves in the weddell sea are still substantial sinks of continental ice in antarctica discrepancies between the model and observations can partly be attributed to deficiencies in the forcing data or to sometimes unavoidable smoothing of ice shelf and bottom topographies

persistent iceberg groundings in the western weddell sea antarctica abstract we use the time average of a series of satellite synthetic aperture radar sar images from 2005 to 2007 to identify grounded icebergs in the western weddell sea satellite laser altimetry along repeated ground tracks confirms that regions of high mean backscatter are associated with stationary tabular icebergs the altimeter data also provide iceberg freeboard from which we infer maximum ice draft assuming the lightly grounded limit and a two layer density model consistent with a source at filchner ronne ice shelf the maximum iceberg draft agrees very well with the ocean depth at a point where the bathymetry is well constrained by ship soundings however for an extensive region near 71 s south of larsen c ice shelf the maximum grounding depth for several icebergs reveals the ocean to be locally more than 200 m shallower than in bathymetry products this previously uncharted bank is expected to have a profound effect on the northward flow of the western weddell gyre and the cross slope transport of offshore warm deep water towards the eastern antarctic peninsula ice shelves passive microwave data also show that sea ice concentration is reduced in the vicinity of this group of grounded icebergs indicating an iceberg influence on ocean atmosphere heat and freshwater exchanges

wind driven upwelling around grounded tabular icebergs temperature and salinity data collected around grounded tabular icebergs in baffin bay in 2011 2012 and 2013 indicate wind induced upwelling at certain locations around the icebergs these data suggest that along one side of the iceberg wind forcing leads to ekman transport away from the iceberg which causes upwelling of the cool saline water from below the upwelling water mixes with the water above the thermocline causing the mixed layer to become cooler and more saline along the opposite side of the iceberg the surface ekman transport moves towards the iceberg which causes a sharpening of the thermocline as warm fresh water is trapped near the surface this results in higher mixed layer temperatures and lower mixed layer salinities on this side of the iceberg based on these in situ measurements we hypothesize that the asymmetries in water properties around the iceberg caused by the opposing effects of upwelling and sharpening of the thermocline lead to differential deterioration around the iceberg analysis of satellite imagery around iceberg pii b 1 reveals differential decay around the iceberg in agreement with this mechanism

borehole evidence for a thick layer of basal ice in the central ronne ice shelf the ronne ice shelf floating between berkner island and the antarctic peninsula is the biggest ice shelf in antarctica it drains an estimated 1 2 106km2 of the antarctic ice sheet much of it resting on bedrock below sea level consequently the balance and dynamics of this ice shelf is of importance to antarctic glaciology especially with regard to the integration of this part of the cryo sphere into the global processes that control the climate of the earth extensive radio echo sounding res by robin and others revealed reflections in the central part of the ronne ice shelf at the relatively shallow depth of 100 200 m below surface1 the interpretation of these echoes which varied in strength was ambiguous and the possibility of internal reflecting horizons was thoroughly discussed but after surface elevation measurements by radar altimeter from drifting balloons appeared to fit the presence of thin ice it was decided to base a thickness map of the ronne ice shelf on these res echoes1 4 we now present direct observational evidence from boreholes that the total ice thickness is much greater than mapped and that the shallow res reflections therefore do come from internal horizons

paleosol nodules as pleistocene paleoclimatic indicators luochuan p r china abstract loess deposits with their interbedded paleosols in central china record the world wide climatic changes of the past 2 5 ma the carbon and oxygen isotopic compositions of carbonate nodules in a loess profile at luochuan record paleoclimatic and paleoecologic conditions of paleosol formation interglacial periods during the past several 100 000 years it appears that the climatic and ecologic conditions during different periods of paleosol s 1 s 8 formation interglacial periods were very similar at luochuan and are marked by a presence of a mixed c 3 and c 4 type flora or mixed grass and wood and or shrublands

stable isotope record in mollusca and pedogenic carbonate from late pliocene soils of central italy abstract the late pliocene younger than 2 5 ma alluvial fan succession of toppetti quarry near todi umbria central italy includes many palaeosols pedogenic carbonate concretions and mollusc remains were separated from 73 palaeosols collected along 150 m of exposure and analysed for their oxygen and carbon stable isotope content 13c and 18o of the pedogenic carbonate and land snail shells suggest that no dramatic change in local climate took place values of the pedogenic carbonates are similar to other data reported for the mediterranean region 18o data suggest a mean annual temperature and or 18o similar to modern climatic conditions carbon isotope data from both land snails and pedogenic carbonate are consistent with a prevailing type c3 vegetation a mixture of forest and c3 grassland sustained by a mean annual precipitation between 300 and 1000 mm mainly in the cool periods of the year seems to be the most likely scenario the limited variation shown by the isotope composition of the biogenic and inorganically precipitated carbonate indicates that the environmental variations are referable mainly to change of humidity rather than temperature

cold stage formation of calcrete nodules in the chinese loess plateau evidence from u series dating and stable isotope analysis this pilot study shows that some calcrete nodules from the base of palaeosols in the chinese loess sequences can be dated by u series isochron methods the ages obtained suggest that the nodules did not form during interglacial climate stages rather they formed either during interglacial glacial transitions or glacial climate stages thus the nodules appear not to have formed contemporaneously with the soils beneath which they immediately lie but significantly post date them post pedogenic injection of carbonate into stratigraphically lower horizons is therefore identified this finding contradicts previous assumptions regarding the timing of nodule formation carbon and oxygen isotope analyses of the nodules identify isotopic compositions which independently suggest that climatic conditions cooler and possibly drier than at present prevailed at the time of nodule formation

evidence for basal marine ice in the filchner ronne ice shelf the filchner ronne ice shelf which drains most of the marine based portions of the west antarctic ice sheet is the largest ice shelf on earth by volume the origin and properties of the ice that constitutes this shelf are poorly understood because a strong reflecting interface within the ice and the diffuse nature of the ice ocean interface make seismic and radio echo sounding data difficult to interpret1 2 ice in the upper part of the shelf is of meteoric origin but it has been proposed2 5 that a basal layer of saline ice accumulates from below here we present the results of an analysis of the physical and chemical characteristics of an ice core drilled almost to the bottom of the ronne ice shelf we observe a change in ice properties at about 150 m depth which we ascribe to a change from meteoric ice to basal marine ice the basal ice is very different from sea ice formed at the ocean surface and we propose a formation mechanism in which ice platelets in the water column accrete to the bottom of the ice shelf

observational evidence of a suppressed planetary boundary layer in northern gale crater mars as seen by the navcam instrument onboard the mars science laboratory rover abstract the navigation cameras navcam of the mars science laboratory rover curiosity have been used to examine two aspects of the planetary boundary layer vertical dust distribution and dust devil frequency the vertical distribution of dust may be obtained by using observations of the distant crater rim to derive a line of sight optical depth within gale crater and comparing this optical depth to column optical depths obtained using mastcam observations of the solar disc the line of sight method consistently produces lower extinctions within the crater compared to the bulk atmosphere this suggests a relatively stable atmosphere in which dust may settle out leaving the air within the crater clearer than air above and explains the correlation in observed column opacity between the floor of gale crater and the higher elevation meridiani planum in the case of dust devils despite an extensive campaign only one optically thick vortex 1 5 0 5 10 3 was observed compared to 149 pressure events 0 5 pa observed in rems pressure data correcting for temporal coverage by rems and geographic coverage by navcam still suggests 104 vortices should have been viewable suggesting that most vortices are dustless additionally the most intense pressure excursions observed on other landing sites pressure drop 2 5 pa are lacking from the observations by the rems instrument taken together these observations are consistent with pre landing circulation modeling of the crater showing a suppressed shallow boundary layer they are further consistent with geological observations of dust that suggests the northern portion of the crater is a sink for dust in the current era

winds measured by the rover environmental monitoring station rems during the mars science laboratory msl rover s bagnold dunes campaign and comparison with numerical modeling using marswrf abstract a high density of rems wind measurements were collected in three science investigations during msl s bagnold dunes campaign which took place over 80 sols around southern winter solstice ls 90 and constituted the first in situ analysis of the environmental conditions morphology structure and composition of an active dune field on mars the wind characterization investigation was designed to fully characterize the near surface wind field just outside the dunes and confirmed the primarily upslope downslope flow expected from theory and modeling of the circulation on the slopes of aeolis mons in this season the basic pattern of winds is upslope from the northwest heading up aeolis mons during the daytime 09 00 17 00 or 18 00 and downslope from the southeast heading down aeolis mons at night 20 00 to some time before 08 00 between these times the wind rotates largely clockwise giving generally westerly winds mid morning and easterly winds in the early evening the timings of these direction changes are relatively consistent from sol to sol however the wind direction and speed at any given time shows considerable intersol variability this pattern and timing is similar to predictions from the marswrf numerical model run at a resolution of 490 m in this region although the model predicts the upslope winds to have a stronger component from the e than the w misses a wind speed peak at 09 00 and under predicts the strength of daytime wind speeds by 2 4 m s the namib dune lee investigation reveals blocking of northerly winds by the dune leaving primarily a westerly component to the daytime winds and also shows a broadening of the 1 hz wind speed distribution likely associated with lee turbulence the namib dune side investigation measured primarily daytime winds at the side of the same dune in support of aeolian change detection experiments designed to put limits on the saltation threshold and also appears to show the influence of the dune body on the local flow though less clearly than in the lee using a vertical grid with lower resolution near the surface reduces the relative strength of nighttime winds predicted by marswrf and produces a peak in wind speed at 09 00 improving the match to the observed diurnal variation of wind speed albeit with an offset in magnitude the annual wind field predicted using this grid also provides a far better match to observations of aeolian dune morphology and motion in the bagnold dunes however the lower overall wind speeds than observed and disagreement with the observed wind direction at 09 00 suggest that the problem has not been solved and that alternative boundary layer mixing schemes should be explored which may result in more mixing of momentum down to the near surface from higher layers these results demonstrate a strong need for in situ wind data to constrain the setup and assumptions used in numerical models so that they may be used with more confidence to predict the circulation at other times and locations on mars

palaeoclimatic records of the loess palaeosol sequences of the chinese loess plateau whether during past climate stages or into a progressively warming world changes in precipitation constitute a key component of climatic change quantitative proxies for palaeo precipitation are relatively rare the magnetic properties of the windblown loess units and interbedded palaeosols of the famous chinese loess plateau provide key palaeo precipitation data for this populous monsoon dominated region the loess palaeosol sediments record rainfall totals directly complementing the oxygen isotope records of chinese speleothems these isotopic records predominantly reflect moisture source and hence large scale atmospheric circulation changes the two major asian monsoon systems appear to display antiphase behaviour dominance of the indian summer monsoon system seems associated with minimum precession maximum northern hemisphere summer heating dominance of the east asian summer monsoons with maximum precession at 2 8 ma more intense development of the east asian winter monsoon initiated major increases in dust deposition rates and formation of relatively unweathered loess layers glacial stage loess units then interleaved with interglacial interstadial stage palaeosols throughout the quaternary period decoupling of the loess palaeosol rainfall records from the chinese cave records of moisture source shows that the indian and east asian monsoon winds were continuously driven by precessional forcing while summer monsoonal rainfall was greatly suppressed during cool glacial stages the timing of these east asian climatic transitions the subsequent intensification of northern hemisphere glaciations and the association between monsoon circulation changes and north atlantic temperatures indicates a possibly leading global role for these monsoonal changes via alterations in the poleward distribution of heat and moisture

on the seasonal signal of the filchner overflow weddell sea antarctica abstractthe cold ice shelf water isw that formed below the filchner ronne ice shelf in the southwestern weddell sea antarctica escapes the ice shelf cavity through the filchner depression and spills over its sill at a rate of 1 6 sverdrups sv 1 sv 106 m3 s 1 thus contributing significantly to the production of weddell sea bottom water here the authors examine all available observational data from the region including five year long time series of mooring data from the filchner sill to examine the seasonal variability of the outflow the temperature of the isw outflow is found to vary seasonally by 0 07 c with a maximum in april the accompanying signal in salinity causes a seasonal signal in density of 0 03 0 04 kg m 3 potentially changing the penetration depth of the isw plume by more than 500 m contrary to recent modeling the observations show no seasonal variability in outflow velocity the seasonality observed at the sill is at least partly due to the admixture of high salinity shelf

the fate of the southern weddell sea continental shelf in a warming climate abstractwarm water of open ocean origin on the continental shelf of the amundsen and bellingshausen seas causes the highest basal melt rates reported for antarctic ice shelves with severe consequences for the ice shelf ice sheet dynamics ice shelves fringing the broad continental shelf in the weddell and ross seas melt at rates orders of magnitude smaller however simulations using coupled ice ocean models forced with the atmospheric output of the hadcm3 sres a1b scenario run co2 concentration in the atmosphere reaches 700 ppmv by the year 2100 and stays at that level for an additional 100 years show that the circulation in the southern weddell sea changes during the twenty first century derivatives of circumpolar deep water are directed southward underneath the filchner ronne ice shelf warming the cavity and dramatically increasing basal melting to find out whether the open ocean will always continue to power the melting the authors extend their simulations applying twentieth century atmospheric

weddell sea iceberg drift five years of observations since 1999 52 icebergs have been tagged with gps buoys in the weddell seato enable monitoring of their position the chosen icebergs were of small tomedium size with a few icebergs larger than 10 km associatedwith the calving of icebergs a38 and a43 from the ronne ice shelf the majority of icebergs were tagged off neumayer station 8e 70s it was found that smaller bergs with edges shorter than 200 m had the shortestlife cycle 0 5 yr iceberg and thus freshwater export out of theweddell sea was found to be highly variable in one year the majority of buoysdeployed remained in the weddell sea constituting about 40 of the ncep p efreshwater input whereas in other years all of the tagged icebergs were exported the observed drifts of icebergs and sea ice showed a remarkably coherent motion the analysis of an iceberg sea ice buoy array in the western weddell seaand an iceberg array in the eastern weddell sea showed a coherent sea iceiceberg drift in sea ice concentrations above 86 dynamic kinematic parameter dkp during the course of coherent movement were low and deviations from the meancourse associated with the passage of low pressure system the length scale ofcoherent movement was estimated to be less than 250km about half the value found forthe arctic ocean

microcodium in chinese loess as a recorder for the oxygen isotopic composition of monsoonal rainwater abstract records of asia summer monsoon asm from the chinese loess and the speleothem display distinct features the very different proxies that were applied to the two archives may be responsible for this discrepancy a direct comparison between the speleothem and the loess records under the same proxy system of rainwater 18o may help to resolve this puzzle here we show that the calcified microcodium in the loess deposits may record the oxygen isotopic composition of the summer rainwater a microcodium based 18o record covering the past 140 kyrs was generated which shows similar magnitude of the overall variation to that of the speleothem records however much weaker precession variability was registered in the microcodium record during the last interglacial period instead the microcodium 18o record is more consistent with the widely used summer monsoon proxy of magnetic susceptibility in the loess deposits with clear glacial interglacial pattern this similarity may originate from the low sedimentation rate of the interglacial paleosol layer that preferentially record the peak asm signals on the precession band it is also possible that the orbital variability of asm between the north china and south china is inherently different with more ice volume related influence in the north a longer microcodium 18o record in sequences of higher sedimentation rate and a reliable record of summer rainfall may help to resolve these possibilities

the open boundary condition in the united kingdom fine resolution antarctic model abstract the united kingdom fine resolution antartic model fram project it a community program to study the southern ocean central to this is an eddy resolving three dimensional primitive equation ocean general circulation model the open boundary condition at the northern boundary is described here the boundary condition is based on that of stevens 1990

on the transport variability and origin of dense water masses crossing the south scotia ridge abstract the deep scotia sea is filled with ventilated weddell sea deep water this in turn is an essential contributor to the ventilation of the world ocean abyss depending on the formation process and or its location along the weddell sea periphery deep and bottom water masses follow different routes to cross the south scotia ridge a primitive equation hydrostatic terrain following coordinate ocean general circulation model brios 1 is used to investigate the water mass export from the weddell sea the model is circumpolar focusing on the weddell sea with particularly high resolution 20 km in the dovetail area eastward weddell sea deep water transport of 24 106 m3 s 1 is found in the northern limb of the weddell gyre across 44 w export rates of weddell sea deep water through gaps in the south scotia ridge are estimated to be 6 4 106 m3 s 1 with a semi annual cycle of 0 6 106 m3 s 1 which can be correlated to atmospheric cyclone activity and weddell gyre strength sensitivity studies considering extreme sea ice conditions in the weddell sea show higher lower exports in years of minimum maximum winter sea ice extent lagrangian particle trajectories illustrate the pathways of water masses from the inner weddell sea into the scotia sea through various gaps in the south scotia ridge they highlight the existing flow divergence on the northwestern continental shelf with one branch entering bransfield strait and the other continuing eastwards subsequently filling the deep weddell and scotia seas water masses flowing through the major gaps originate from the southwestern and southeastern weddell sea continental shelves however water masses formed east of the weddell sea e g prydz bay also seem to feed the deep scotia sea since a large portion of floats flowing northward through the gaps of the south scotia ridge have been in contact with the mixed layer processes outside the inner weddell sea

dating and characterization of polymorphic transformation of aragonite to calcite in pleistocene bivalves from rhodes greece by combined shell microstructure stable isotope and electron spin resonance study absolute dating of diagenesis is a challenging yet significant problem reconstructing the depositional and diagenetic history of a late pleistocene coralligene type red algal reef and overlying maerl red algal sand from the plimiri coastal cliff se island of rhodes greece is enabled using a combination of microstructure stable isotope analyses and electron spin resonance of large bivalve shells partially altered by diagenesis these shells consisting of both original shell aragonite and polymorphic transformed rims now consisting of neomorphic spar provide the opportunity to date the primary age when the shells were precipitated as well as the age of their polymorphic transformation the contamination of samples presented a significant problem for interpreting ages based on data from electron spin resonance esr alone however sample contamination was evaluated with quantitative xrd providing the opportunity to apply corrections which increased reliability of the ages the carbon and oxygen stable isotope values and the neomorphic spar microtexture suggested that the polymorphic transformation at plimiri took place in a meteoric environment with a high and increasing fluid rock ratio the electron spin resonance dates combined with the vertical sedimentary evolution allowed to assign the formation of the red algal reef to the marine isotope stages 6 to 5e transgressive event ca 135 to 120 ka and to identify meteoric diagenetic phases during possibly the marine isotope stage 5d and the upper marine isotope stage 5c to lower 3 the use of electron spin resonance dating of neomorphic spar and age correction for sample contamination is presented herein for the first time and the results suggest that it might provide a useful tool to date late pleistocene diagenesis

oxygen 18 and helium as tracers of ice shelf water and water ice interaction in the weddell sea oxygen 18 and helium isotope data from stations located in the filchner depression on the continental slope of the southern weddell sea and in the central weddell sea are presented and discussed the 18o and 4he signals imprinted on the water circulating under the filchner ronne ice shelf ice shelf water or isw due to melting of glacial ice at the base of the ice shelf are traced across the sill separating the filchner depression from the weddell sea low 18o values are correlated with high 4he concentrations in the isw found in the filchner depression minimum 18o values 0 8 maximum 4he concentrations about 4 7 10 8 cm3 stp g 1 the fraction of glacial meltwater contained in the isw found in the filchner depression is estimated to about 6 to 7 the 18o and helium isotope data from the overflowing shelf water component observed on the continental slope confirm the hypothesis that isw contributes significantly to the weddell sea bottom water wsbw on the basis of a inultiparameter water mass analysis it is discussed which fraction of the wsbw originates from isw and which other shelf waters potentially could contribute to wsbw

notes on southern ocean hydrography sea ice and bottom water formation abstract the southern ocean circulation and sea ice distribution is briefly described the formation of extremely cold bottom water in the weddell sea and its relation to the floating ronne filchner ice shelves is discussed it is shown that a concentrated swift eroding bottom current with anomalous low 18 o ratio transports the cold and dense ice shelf water from the shelf towards large depths comments are made on possible implications of this process for the large scale deep water circulation and for the interpretation of sediment cores

western ross sea continental slope gravity currents antarctic bottom water of the world ocean is derived from dense shelf water that is carried downslope by gravity currents at specific sites along the antarctic margins data gathered by the anslope and clima programs reveal the presence of energetic gravity currents that are formed over the western continental slope of the ross sea when high salinity shelf water exits the shelf through drygalski trough joides trough immediately to the east offers an additional escape route for less saline shelf water while the glomar challenger trough still farther east is a major pathway for export of the once supercooled low salinity ice shelf water that forms under the ross ice shelf the drygalski trough gravity currents increase in thickness from 100 to 400 m on proceeding downslope from 600 m the shelf break to 1200 m upper slope sea floor depth while turning sharply to the west in response to the coriolis force during their descent the mean current pathway trends 35 downslope from isobaths benthic layer current and thickness are correlated with the bottom water salinity which exerts the primary control over the benthic layer density a 1 year time series of bottom water current and hydrographic properties obtained on the slope near the 1000 m isobath indicates episodic pulses of shelf water export through drygalski trough these cold 34 75 pulses correlate with strong downslope bottom flow extreme examples occurred during austral summer fall 2003 comprising concentrated high salinity shelf water 1 9 c 34 79 and approaching 1 5 m s 1 at descent angles as large as 60 relative to the isobaths such events were most common during november may consistent with a northward shift in position of the dense shelf water during austral summer the coldest saltiest bottom water was measured from mid april to mid may 2003 the summer fall export of high salinity shelf water observed in 2004 was less than that seen in 2003 this difference if real may reflect the influence of the large iceberg c 19 over drygalski trough until its departure in mid may 2003 when there was a marked decrease in the coldest saltiest gravity current adjacent to drygalski trough northward transport of cold saline recently ventilated antarctic bottom water observed in march 2004 off cape adare was 1 7 sv including 0 4 sv of high salinity shelf water

sea ice transports in the weddell sea time series of sea ice draft in the weddell sea are evaluated together with hydrographic observations satellite passive microwave data and ice drift for estimation of the freshwater fluxes into and out of the weddell sea ice draft is measured with moored upward looking sonars since 1990 along two transects across the weddell gyre one transect extending from the tip of the antarctic peninsula to kapp norvegia was sampled between 1990 and 1994 and covers the flow into and out of the southern weddell sea the other transect sampled since 1996 and extending from the antarctic continent northward along the greenwich meridian covers the exchange of water masses between the eastern and the western weddell sea in order to relate results obtained during the different time periods empirical relationships are established between the length of the sea ice season derived from the satellite passive microwave data and defined as the number of days per year with the sea ice concentration exceeding 15 and 1 the annual mean ice draft and 2 the annual mean ice volume transport by using these empirical relationships estimates of annual mean ice drafts and ice volume transports are derived at all mooring sites for the period february 1979 through february 1999 wind and current force a westward ice transport in the coastal areas of the eastern weddell sea and a northward ice transport in the west during the 2 year period 1991 1992 the mean ice volume export from the weddell sea is 50 19 103 m3 s 1 this freshwater export is representative for a longer term 20 year mean and exceeds the average amount of freshwater gained by precipitation and ice shelf melt by about 19 103 m3 s 1 yielding an upper bound for the formation rate of newly ventilated bottom water in the weddell sea of 2 6 sv

methane seasonal cycle at gale crater on mars consistent with regolith adsorption and diffusion a strong repeatable seasonal cycle in the background methane mixing ratio has been observed at the gale crater landing site of the mars science laboratory rover with the tunable laser spectrometer of the sample analysis at mars instrument however as of yet no physical process has been proposed that can explain both the timing and amplitude of the observations here we show that a one dimensional numerical model considering adsorption onto and diffusion through the regolith can reproduce the variation including a phase lag if the regolith is impregnated with methane from a prior plume or supplied from below by microseepage combining the model results with geological constraints we estimate that the amount of microseepage at gale is at most 3 10 5 tonnes km 2 yr 1 gale s unique dynamical environment makes such seeps easier to detect in surface sampling measurements over most of the martian surface atmospheric mixing is stronger or atmospheric transport more effective and we expect the amplitude of the seasonal cycle to be smaller for the same strength of seep the seasonal cycle in the methane mixing ratio observed at gale crater on mars can be explained by adsorption onto and diffusion through the regolith suggests a one dimensional numerical model with geological constraints

multiproxy evidence of middle and late pleistocene environmental changes in the loess paleosol sequence of bůhzdař czech republic abstract loess paleosol sequences preserve information that can be used to reconstruct paleoenvironments a dense network of reliably analyzed sequences from different geographic locations is crucial to address ecological and climatic trends which occurred during the pleistocene this paper focuses on a loess paleosol sequence in b hzda situated 9 km nw of prague czech republic geochemical approaches total organic carbon xrf elemental analyses xrd mineralogy 13c and 18o stable isotopes are combined with grain size distributions and optically stimulated luminescence osl to assess the climatic conditions at the time of formation of the strata the oldest loess at this location was formed circa 200 ka ago mis 7 making it the oldest loess in central bohemia for now the b hzda loess paleosol sequence was highly affected by several erosion events eemian paleosols mis 5e being completely missing the partly relocated paleosols situated at the lower part of the b hzda sequence represent a period of increased humidity during late mis 7 and mis 6 despite the fact that the b hzda profile is not particularly thick 5 m significant changes in paleoclimate reconstructions have been detected