circulation and transport of water along the western weddell sea margin ocean current temperature and salinity data obtained from the western weddell sea during the austral winter 1992 u s russian drifting ice station experiment ice station weddell 1 isw 1 are used to describe water circulation and transport surface to bottom baroclinic currents were computed by applying the geostrophic approximation to derived density data these were corrected using current measurements obtained from drifting current meter arrays and the resulting total currents were vertically integrated to obtain volume transports transport was found to be northward in the region which encompassed the western boundary current of the cyclonic weddell sea gyre this northward transport increased from south to north by more than a factor of 2 from about 12 106m3 s 1 in the southwestern weddell to about 28 106m3s 1 farther north the increase in northward transport was compensated for by westward flow from the interior of the gyre into the western boundary region about 5 6 106m3s 1 of the northward transport was contained in a 300 500 m thick bottom layer of cold water this layer whose transport increased by about 1 106 m3 s 1 from south to north was identifiable by its water mass characteristics as weddell sea bottom water originating on the southwestern and western shelf regions its north flowing volume was consistent with past estimates of a 1 5 2 106 m3 s 1 production rate coupled with a 300 400 transport increase due to entrainment during downslope flow from the shelves to the deep basin the maximum northernmost northward transport less the bottom water transport is consistent with previous estimates for wind driven transport in the weddell gyre provided that bottom friction and the sea ice influence on wind forcing are taken into consideration

circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

isotope data from ice station weddell implications for deep water formation in the weddell sea helium isotope data 3he 4he ratios and 4he concentrations and h218o h216o ratios obtained from stations occupied during the drift of ice station weddell february to june 1992 are used together with hydrographic data to study formation of deep and bottom water in the western weddell sea the data indicate deep and bottom water formation along the entire track of the ice station 71 4 to 65 8 s 53 w ice shelf water isw seems to contribute significantly to the formation of weddell sea deep water wsdw and weddell sea bottom water wsbw in the southern part of the drift track toward the north the fraction of isw contained in wsdw wsbw decreases this trend is overlaid by high isw fractions in the deep and bottom waters found in the vicinity of the larsen ice shelf the fraction of western shelf water wsw in wsbw shows the opposite trend increasing from south to north the combined fraction of isw and wsw in waters with potential temperatures below 0 c is about 20 corresponding to a roughly 200 m thick layer overall wsw seems to contribute approximately 2 to 3 times more water than isw to the water column below the 0 c isotherm using the estimated flow of isw over the sill north of the filchner depression of 1 sv foldvik et al 1985a together with the ratio of wsw plus winter water ww to isw we calculate a value of about 5 sv for the formation rate of wsbw with a potential temperature of 0 7 c about one third of this flux represents near surface waters wsw ww which have recently been equilibrated with the atmosphere whereas pure isw contributes about 10

contribution of small glaciers to global sea level observed long term changes in glacier volume and hydrometeorological mass balance models yield data on the transfer of water from glaciers excluding those in greenland and antarctica to the oceans the average observed volume change for the period 1900 to 1961 is scaled to a global average by use of the seasonal amplitude of the mass balance these data are used to calibrate the models to estimate the changing contribution of glaciers to sea level for the period 1884 to 1975 although the error band is large these glaciers appear to account for a third to half of observed rise in sea level approximately that fraction not explained by thermal expansion of the ocean

chlorofluorocarbon derived formation rates of the deep and bottom waters of the weddell sea the spreading and mixing of deep and bottom waters from the weddell sea originating with potential temperature 0 c are investigated through analysis of new and historical cfc measurements we investigate the component that enters the southern indian ocean with a simple one dimensional advection diffusion model of the deep boundary current this model does not require a condition of mixing solely with tracer free water to be imposed as boundary conditions we derive time histories for the cfc concentrations of newly formed weddell sea deep and bottom waters a range of best fit velocities is obtained by determining which model velocities produce model tracer concentrations closest to measured concentrations from this we derive a formation rate of 3 2 1 5 sv for the waters originating with temperatures lower than 0 c that subsequently enter the southern indian ocean this compares to an upper limit for these waters of 5 7 sv derived from the cfc 11 cfc 12 ratio whilst the former value is dependent on the highly idealized concepts of the model used the latter is a more robust upper limit using the cfc 11 cfc 12 ratio measured at vema channel during the world ocean circulation experiment cruise a23 an upper limit of 0 9 sv is derived for the formation rate of waters colder than 0 c that enter the south atlantic overall an upper limit of 6 6 sv is derived for the rate of formation of the deep and bottom waters of the weddell sea a better representation is obtained by combining the upper limit to the south atlantic component with the model derived southern indian ocean estimate we thus estimate the formation rate of the deep and bottom waters in the weddell sea to be 3 7 1 6 sv whilst the range obtained is large and the assumptions implicit in the calculations are potentially significant we believe this more realistically represents the true formation rate than estimates derived using an imposed condition of tracer free mixing the range can be narrowed in future as more data become available

warming of deep and abyssal water masses along the greenwich meridian on decadal time scales the weddell gyre as a heat buffer abstract the southern ocean renders a significant contribution to the global overturning system through the formation of deep and bottom waters the weddell sea is one of the most prominent regions in this respect data obtained between 1984 and 2008 from eight repeat hydrographic sections moored instruments and profiling floats in the weddell gyre on the greenwich meridian almost all of them collected with rv polarstern were used to identify variations in the weddell system fluctuations in the water mass properties were detected in the warm deep water with a temperature maximum in the 1990s and a minimum in 2005 but also significant variations occurred in the weddell sea deep and bottom waters whereas the warm deep water is dominated by decadal variations the average temperature and salinity of the whole water column is subject to a positive trend over 24 years the variations of the water mass properties are induced by variations of the inflow of circumpolar deep water at the boundary due to asymmetric wind forcing at the northern and the southern limb of the gyre variable in and outflows occur at the open boundaries internal processes redistribute heat and salt in the gyre resulting in a long term increase of the temperature and salinity in the whole water column the transfer of heat to deeper layers assigns to the weddell gyre the role of a buffer with potential impact on the global climate

turbulent mixing under drifting pack ice in the weddell sea by providing cold dense water that sinks and mixes to fill the abyssal world ocean high latitude air sea ice interaction is the main conduit through which the deep ocean communicates with the rest of the climate system a key element in modeling and predicting oceanic impact on climate is understanding the processes that control the near surface exchange of heat salt and momentum in 1992 the united states russian ice station weddell 1 traversed the western weddell sea during the onset of winter providing a platform for direct measurement of turbulent heat flux and reynolds stress in the upper ocean data from a storm early in the drift indicated i well formed ekman spirals in both velocity and turbulent stress ii high correlation between mixed layer heat flux and temperature gradients iii that eddy viscosity and eddy thermal diffusivity were similar about 0 02 square meters per second and iv that the significant turbulent length scale 2 to 3 meters through most of the boundary layer was proportional to the wavelength at the peak in the weighted vertical velocity spectrum the measurements were consistent with a simple model in which the bulk eddy viscosity in the neutrally buoyant mixed layer is proportional to kinematic boundary stress divided by the coriolis parameter

river floodplain aggradation history and cultural activities geoarchaeological investigation at the yuezhuang site lower yellow river china abstract archaeobotanical research at the yuezhuang and xihe sites of the houli culture in the lower yellow river has found abundant carbonised plant remains including rice millet weed seeds and many other plants 7800 7000 cal bp although studies of the diverse economic practices of the houli people have begun issues such as ecological diversity and relationships between site formation processes with environmental changes are still poorly understood applying soil micromorphology and related methods such as particle size distribution and loss on ignition at yuezhuang this paper presents results of the geoarchaeological investigation and the implications for the reconstruction of site formation processes in relation to river alluvial history a long alluvial sequence is reconstructed consisting of frequent alternations of short periods surface stabilities and succeeding alluviations human occupations corresponded to those short term surface stabilities and are evidenced by the presence of anthropogenic inclusions in thin sections including burned bone fragments and pottery sherds the significances of this study to an ecological approach focusing on environmental changes and cultural adaption are discussed

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

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

distribution of oxygen isotopes in the water masses of drake passage and the south atlantic measurements of the ratio of stable isotopes of oxygen 18o and 16o from samples collected on world ocean circulation experiment sections sr1b eastern drake passage and a11 punta arenas to cape town are used together with hydrographic data to deduce information about the formation and variability of south atlantic and southern ocean water masses the drake passage surface waters south of the polar front pf are isotopically light 18o around 0 4 owing to the influence of meteoric waters the salinity and 18o of the a11 surface waters yield an apparent freshwater end member which is much isotopically lighter than the local precipitation thus advection of these waters from farther south dominates over local effects in determining the surface water properties the drake passage section shows unusual proximity of the two main fronts of the antarctic circumpolar current the pf and subantarctic front saf and we observe cold fresh and isotopically light water derived from the temperature minimum winter water at the saf this water is of the correct density to freshen the intermediate water north of the saf and thus play a role in the formation of the comparatively fresh antarctic intermediate water aaiw of the south atlantic this confirms the role of antarctic water in forming the south atlantic variety of aaiw across the a11 section the oxygen isotope and salinity data at the aaiw core show very similar traces with waters in the malvinas current loop showing lowest values of both at the eastern boundary of the south atlantic the input of red sea water from east of south africa is observed via the presence of anomalously isotopically heavy aaiw we deduce potentially significant temporal variability in the isotopic composition of weddell sea deep water wsdw by comparing the drake passage data to earlier data covering the outflow of the weddell sea the a11 data show wsdw consistent with such variability indicating that its effects could persist in the waters as they flow north into the western south atlantic we speculate that such variability could be due to small changes in the amount of glacial ice melt in wsdw

local and regional trends in plio pleistocene δ18o records from benthic foraminifera we present new orbital resolution pliocene pleistocene benthic stable oxygen isotope 18ob records from ocean drilling program sites 1264 and 1267 from walvis ridge in the southeast atlantic we compare long term 250 kyr interbasin 18ob gradients between pacific and north atlantic regional stacks as well as intra and interbasin gradients from the perspective of walvis ridge the 18ob values from sites 1264 and 1267 are almost always higher than deep north atlantic and pacific sites with large gradients 0 5 emerging abruptly at 2 4 ma and persisting until 1 3 ma from this we infer the presence of a new water mass which resulted from the influence of dense 18o enriched nordic sea overflow waters via the abyssal east atlantic meanwhile long term average 18ob values in the north atlantic appear to have remained within 0 0 25 lower than in the pacific however the magnitude of this difference is sensitive to the inclusion of records from the equatorial west atlantic these results together with constraints based on temperature salinity and density suggest an influence of the seawater 18o 18osw versus salinity relationship of source waters on 18ob values within the atlantic in particular the abrupt emergence at 2 4 ma of higher 18ob values at sites 1264 and 1267 relative to north atlantic records appears to require a low latitude surface water 18osw signal this implies a connection between northward heat transport and deep water export into the abyssal east atlantic hence our results have implications for the interpretation of 18ob records and highlight the potential for 18ob to constrain deep atlantic water mass sources and pathways during the plio pleistocene

repeated cfc sections at the greenwich meridian in the weddell sea 1 repeated observations of the tracer chlorofluorocarbon 11 cfc 11 for a section along the greenwich meridian from antarctica 70 s to about 50 s are presented for the period 1984 1998 the cfc sections display a highly persistent pattern a middepth cfc minimum in the central weddell sea is bounded laterally by elevated levels of dissolved cfcs at the southern margin of the weddell basin and by a column of elevated cfc concentrations around 55 s near to the northern margin part of the latter column covers waters of the antarctic circumpolar current which indicates that a moderate portion of these waters was ventilated in the weddell sea deep cfc maxima adjoining the southern and northern margins of the weddell basin indicate advective cores of recently ventilated waters the southern core supports previous notions of deep water import into the weddell sea from the east for all deep and bottom waters the portions ventilated on the cfc timescale 50 years are small effective initial cfc saturations for these portions are estimated to be between 60 and 70 using in part new data from off the filchner ronne ice shelf for various cfc features along the section mostly advective cores ventilated fractions and mean ages of these fractions were obtained with error limits the procedure was to fit an age distribution of a prescribed form to cfc 11 time series for these features constructed from the various realizations of the cfc section the ages are between 3 and 19 years and the ventilated fractions range between 6 and 23 indicating a rather limited ventilation of the interior weddell sea subsurface layer waters on the cfc timescale it is shown that the concurrent cfc 12 data provide little additional information the work demonstrates a high information content of repeated tracer observations and encourages similar approaches also in other ocean regions

the freshwater budget and under ice spreading of mackenzie river water in the canadian beaufort sea based on salinity and 18o 16o measurements in water and ice observations of salinity and oxygen isotope composition 18o were made for the beaufort shelf mackenzie estuary waters in september 1990 just prior to ice formation and for both the water column and ice in april may 1991 at the end of winter these measurements are used to determine the apportioning of fresh water in the estuary between its two main sources runoff and sea ice melt changes in disposition of water between seasons and amounts frozen into the growing ice sheet are also derived two domains are considered in order to construct a freshwater budget for the mackenzie shelf the nearshore within which landfast ice grows in winter and the outer shelf most of the winter inflow from the mackenzie river appears to remain impounded as liquid under the ice within the landfast zone at the end of winter and about 15 of it is incorporated into the landfast ice oxygen isotopes 18o in ice cores collected from across the shelf record the progress beneath the ice of new mackenzie inflow as it invades the nearshore throughout winter rates of spreading are about 0 2 cm s 1 away from the coast and 1 3 cm s 1 along the coast as this inflow spreads across the shelf it progressively shuts off convection driven by brine production at locations within the landfast ice salinity and 18o in the offshore water column suggest that about 3 m of sea ice was formed in the outer shelf domain since both brine and newly formed sea ice can be advected off the shelf a complete budget for brine or sea ice production cannot be established without first measuring the advection of one of these two components

internal tides and baroclinicity in the southern weddell sea 1 model description near the continental shelf break in the southern weddell sea warm deep water and western shelf water meet mixing mechanisms such as internal tides have the potential to mix these water masses and form antarctic bottom water a modified version of the princeton ocean model was utilized to investigate the internal tidal fields generated by the interaction of the m 2 barotropic tide with topography for transects across the continental shelf and slope in the southern weddell sea internal tides were generated over the upper continental slope as predicted by linear internal wave theory although the essentially two dimensional domain resulted in differences between the model elevations and the observations exceeding the observational uncertainties the cross slope velocities agreed well with differences less than the uncertainties for 78 of the existing observations

sensitivity experiments with a model of the ice age cycle the response to milankovitch forcing abstract we address the question of the extent to which a simple one dimensional time dependent climate model is able to explain the fluctuations of continental ice volume which have occurred during the last quarter of the pleistocene epoch the model includes explicit ice physics based on the glen flow law and explicit glacial isostatic adjustment based on a realistic viscoelastic field theory when the model is forced by the milankovitch variations of insulation it delivers ice volume fluctuations which are very similar to those implied by the specmap 18o record in particular the model appears capable of explaining the observed correlation between eccentricity and ice volume variations the dominance of the 105 year period in the power spectrum of the ice volume time series and the thickness and latitudinal extents of the continental ice sheets which existed at wurm wisconsin maximum 18 000 years ago

an optimized estimate of glacial melt from the ross ice shelf using noble gases stable isotopes and cfc transient tracers 1 isotopes of helium and neon and the h218o h216o ratio of water are proven proxies for melt from glacial ice beneath floating ice shelves and at ice shelf fronts their high concentrations in glacial meltwater compared to other environmental sources make them ideal tracers for studies of the pathways of glacial meltwater from its origins into the ocean interior we combine noble gas and stable isotopes with temperature salinity and dissolved oxygen measurements from three cruises along the ross ice shelf during the austral summers of 1993 1994 and 1999 2000 and to the ross sea in 2000 2001 and use optimal multiparameter analysis to compute the water mass concentration including glacial meltwater the distribution of meltwater at the front of the ross ice shelf extended east from 180 w with the highest concentrations found near 165 w in both 1994 and 2000 the mean meltwater concentration at the ice shelf front was 2 0 0 33 in 1994 2 2 0 36 in 2000 and 0 25 0 1 in the western ross sea in 2001 water mass concentrations are used to correct for bias in the cfc age introduced by mixing with cfc free waters an effect revealed by comparing cfc age with transit time distribution curves the water residence time within the ice shelf cavity using cfcs and the mean meltwater concentration implies a basal melt rate of 33 50 km3 a 1

on the sources of weddell gyre antarctic bottom water in march april 1995 as part of the world ocean circulation experiment section a23 we completed 49 hydrographic stations across the weddell gyre and southern antarctic circumpolar current from the antarctic continental shelf 72 5 s 16 5 w to south georgia 55 s 34 5 w chlorofluorocarbon cfc 11 cfc 12 and cfc 113 data collected at these stations reveal that distinct sources renew the antarctic bottom water defined as waters with potential temperatures less than 0 c of the weddell gyre weddell sea bottom water defined as waters with potential temperatures less than 0 7 c formed in the western weddell sea has cfc concentrations about 5 to 6 times higher in the eastward flowing northern weddell gyre than in the westward flowing southern limb our cfc measurements suggest that distinct sources of weddell sea bottom water exist in the western weddell sea in agreement with previous descriptions based on potential temperature and salinity signals in the northern weddell gyre high cfc concentrations in weddell sea deep water potential temperatures between 0 c and 0 7 c confirm the long recognized sources for this water mass in the western and southwestern weddell sea in the southern weddell gyre at about 20 w and along the antarctic continental slope weddell sea deep water with potential temperatures around 0 45 c shows a deep cfc maximum about 1000 m above the seafloor cfc concentrations in this deep southern core are about 80 of those of new weddell sea deep water in the northern weddell gyre near 30 w the a23 cfc and hydrographic data are not consistent with the hypothesis that weddell sea deep waters are derived from a single source in the western weddell sea instead these tracers suggest that an important portion of the weddell sea deep water in the southern weddell gyre originates outside the western weddell sea probably near the amery basin and environs around 75 e these features of the circulation and renewal of the deep weddell gyre should be carefully considered in simulations dealing with fluxes pathways and formation rates of antarctic bottom water

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

flow of bottom water in the northwestern weddell sea the weddell sea is known to feed recently formed deep and bottom water into the antarctic circumpolar water belt from whence it spreads into the basins of the world ocean the rates are still a matter of debate to quantify the flow of bottom water in the northwestern weddell sea data obtained during five cruises with r v polarstern between october 1989 and may 1998 were used during the cruises in the weddell sea five hydrographic surveys were carried out to measure water mass properties and moored instruments were deployed over a time period of 8 5 years to obtain quasi continuous time series the average flow in the bottom water plume in the northwestern weddell sea deduced from the combined conductivity temperature depth and moored observations is 1 3 0 4 sv intensive fluctuations of a wide range of timescales including annual and interannual variations are superimposed the variations are partly induced by fluctuations in the formation rates and partly by current velocity fluctuations related to the large scale circulation taking into account entrainment of modified warm deep water and weddell sea deep water during the descent of the plume along the slope between 0 5 sv and 1 3 sv of surface ventilated water is supplied to the deep sea this is significantly less than the widely accepted ventilation rates of the deep sea if there are no other significant sources of newly ventilated water in the weddell sea either the dominant role of weddell sea bottom water in the southern ocean or the global ventilation rates have to be reconsidered

the impact of melting ice on ocean waters abstract ice melts when it is in contact with ocean waters that have temperatures above the in situ freezing point the product is a mixture of meltwater and seawater having properties intermediate between those of the two components density is one of the properties that is affected and this has important implications for how the melt induced changes are eventually manifested although the direct impact of melting is to cool and dilute the ocean subsequent convection can carry the products of melting to parts of the water column where they are comparatively warm and salty these principles are illustrated with a set of observations from the continental shelf of the amundsen sea measurements made near a floating glacier are used to calculate the concentration of meltwater in the water column concentrations approaching 2 are associated with comparatively high temperatures low dissolved oxygen concentrations and negligible stable isotope anomalies the impact of drifting icebergs on the southern ocea

excess helium and neon in the southeast pacific tracers for glacial meltwater 1 we analyze helium he and neon ne isotope data sets from the southeast pacific sector of the southern ocean collected in 1992 and 1994 and describe a new method to estimate glacial meltwater fluxes independent of previous approaches the waters sampled during these cruises reveal large atmospheric he and ne excess concentrations in the upper 500 m that are derived predominantly from the dissolution of air contained in glacial ice during melting underneath and at the front of floating ice shelves at elevated hydrostatic pressure on the stations sampled the meltwater fractions are largest near the northern and southern ice shelf fronts of george vi ice shelf 1 5 2 5 consistent with prior inferences from 18o the inventories of 4he and ne with local glacial meltwater origin south of 70 s between 210 e and 295 e are 2 5 0 7 1011 cm3stp 4he and 7 9 2 7 1011 cm3stp ne respectively the associated meltwater volumes are 430 120 gt for 4he and 400 140 gt for ne for an estimated seawater residence time of 2 years on the continental shelf the amounts of glacial meltwater translate into bulk melting rates of 215 170 gt yr 1 for 4he and 200 170 gt yr 1 for ne the values derived from 4he are expected to be larger than those obtained from ne because of the terrigenic he component which accounts for 10 15 of the he excess in this region our regional melting rate of 200 215 gt yr 1 is comparable to a prior estimate but subject to uncertainties resulting from the station distribution the air sea gas exchange and the estimate of the net transport through the study region

quaternary sea level changes relative changes of the land sea interface have occurred throughout geologic time although these changes can be caused by several factors alternating global events such as glaciation deglaciation are the most effective in the quaternary period other causes e g volumetric changes in the mid oceanic ridge system have been proposed to explain sea level changes from the upper cretaceous to the mid miocene pitman 1978 however the evidence available suggests that no uniform response can be expected worldwide as a result of global glacio eustatic events this is due to tectonics glacial isostasy hydroisostasy and geoidal configuration of the ocean surface among other variables all these factors have been operative at various timescaies and have been subject to local and regional variations this explains why sea level curves for the holocene fail to provide a uniform global trend instead several local curves have been derived from many areas the variability of postglacial sea levels has been explained by different models considering glacial isostasy clark et al 1978 the redistribution of ice and water loads from antarctic deglaciation peltier 1988 and future sea level rise due to the melting of the greenland and antarctic ice sheets has been predicted by clark and primus 1987 as will be discussed more fully later a global warming is expected to take place due to the increasing accumulation of co2 and other

basal melt and freezing rates from first noble gas samples beneath an ice shelf a climatically induced acceleration in ocean driven melting of antarctic ice shelves would have consequences for both the discharge of continental ice into the ocean and thus global sea level and for the formation of antarctic bottom water and the oceanic meridional overturning circulation using a novel gas tight in situ water sampler noble gas samples have been collected from six locations beneath the filchner ice shelf the first such samples from beneath an antarctic ice shelf helium and neon are uniquely suited as tracers of glacial meltwater in the ocean basal meltwater fractions range from 3 6 near the ice shelf base to 0 5 near the sea floor with distinct regional differences we estimate an average basal melt rate for the filchner ronne ice shelf of 177 95 gt year independently confirming previous results we calculate that up to 2 7 of the meltwater has been refrozen and we identify a local source of crustal helium

palaeochannels on the north china plain palaeoriver geomorphology abstract variations in the geomorphology of the north china plain are related to differences between river deposits the river deposits from different periods form the various geomorphological features different combinations of palaeochannels form different geomorphological regions different kinds of palaeochannels form different kinds of micro geomorphology during the early glaciation of the late pleistocene the river deposits formed piedmont plains and floodplains by the early holocene the rivers had cut the piedmonts into dissected valleys and deposited alluvial fans at the front edge of the piedmonts to form alluvial plains below by the middle holocene lake sediments covered the alluvial plains and filled in the dissected valleys of the piedmont plains by the late holocene rivers dissected the piedmonts again to form dissected valleys and deposited alluvial fans in the lower reaches to form alluvial plains and deltas at the river mouths

palaeochannels on the north china plain stage division and palaeoenvironments abstract the late pleistocene and holocene palaeochannels in the north china plain were divided into six stages on the basis of seven indicators basal erosion surface and channel lag deposits macropalaeontology organic matter content ground water quality heavy minerals grain size and sedimentary structures they were called the stages i vi palaeochannels from oldest to youngest on the basis of the percentage area and thickness of fluvial sand bodies of the total area and thickness of sediments of the same period there were three palaeochannel development stages or periods of fluvial activity and two palaeoswamp development stages or periods of fluvial inactivity on the north china plain during the late pleistocene and the holocene

helium a new tracer in antarctic oceanography the abyssal characteristics of the world oceans are strongly influenced by the northward propagation of antarctic bottom water aabw an important source of aabw is weddell sea bottom water wsbw which is formed in part on the continental slope of the southern weddell sea1 3 the formation of wsbw on the continental slope is related to the floating ice shelves of the southern weddell sea filchner ronne ice shelves western shelf water wsw is modified under the ice shelves by cooling and admixture of melt water to form ice shelf water isw and a substantial part of the isw flows over the sill that separates the filchner depression from the weddell sea and participates in the formation of wsbw4 5 the data reported here demonstrate that the water ice interaction leads to a strong 4he supersaturation of the isw due to dissolution of air entrapped in the ice shelf melt water the 4he supersaturation of the isw can be used as a tracer of this water mass and also influences the 4he balance of the wsbw

evidence of deep and bottom water formation in the western weddell sea abstract during ice station polarstern ispol r v polarstern cruise ant xxii 2 november 2004 january 2005 hydrographic and tracer observations were obtained in the western weddell sea while drifting closely in front of the larsen ice shelf these observations indicate recently formed weddell sea bottom water which contains significant contributions of glacial melt water in its upper part and high salinity shelf water in its lower layer the formation of this bottom water cannot be related to the known sources in the south the filchner ronne ice shelf we show that this bottom water is formed in the western weddell sea most likely in interaction with the larsen c ice shelf by applying an optimum multiparameter analysis omp using temperature salinity and noble gas observations helium isotopes and neon we obtained mean glacial melt water fractions of about 0 1 in the bottom water on sections across the weddell gyre farther north melt water fractions are still on the order of 0 04 using chlorofluorocarbons cfcs as age tracers we deduced a mean transit time between the western source and the bottom water found on the slope toward the north 9 3 years this transit time is larger and the inferred transport rate is small in comparison to previous findings but accounting for a loss of the initially formed bottom water volume due to mixing and renewal of weddell sea deep water a formation rate of 1 1 0 5 sv in the western weddell sea is plausible this implies a basal melt rate of 35 19 gt year or 0 35 0 19 m year at the larsen ice shelf this bottom water is shallow enough that it could leave the weddell basin through the gaps in the south scotia ridge to supply antarctic bottom water these findings emphasize the role of the western weddell sea in deep and bottom water formation particularly in view of changing environmental conditions due to climate variability which might induce enhanced melting or even decay of ice shelves

the distribution of 14c and 39ar in the weddell sea carbon 14 and 39ar data from the weddell sea are presented and discussed values of 14c and 39ar are low in the winter mixed layer 14c 90 to 125 39ar 85 modern these low values are consistent with the surface layer dynamics which is dominated by entrainment of relatively old water of circumpolar origin and reduced gas exchange during sea ice cover the 14c and 39ar values of the deep and bottom waters range from 160 to 150 and 38 to 57 modern respectively the 14c values of weddell sea bottom water wsbw found in the central weddell sea along a 0 longitude section are only slightly higher than those of the overlying weddell sea deep water wsdw showing that the influence of bomb 14c on these waters is small part of the wsbw with higher 14c values observed in the northwestern weddell sea seems to escape through the south sandwich trench and part seems to mix from a boundary current into the central weddell sea the observed 14c distribution is consistent with the hypothesis that ice shelf water isw is a source of wsbw a simple conceptual model of the surface layer dynamics is used to estimate the prebomb 14c values of surface water and winter water to be about 140 and 130 respectively using mixing ratios between wsdw and shelf water derived from temperature salinity and 3he data the prebomb 14c values of wsbw are estimated to be 157 potential temperature of wsbw 0 7 c the 39ar concentration of wsbw with a potential temperature of 0 7 c is determined to be 57 modern bomb radiocarbon water column inventories are estimated and discussed

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

interannual variability of bottom temperatures in drake passage a continuous 4 year record of in situ bottom temperature measurements at 3690 m within drake passage 59 43 7s 55 29 5w from november 1992 to november 1996 is presented the record shows fluctuations of order 0 02 c over monthly periods throughout the 4 years but the annual mean temperature is the subject under discussion in this work between june 1994 and may 1995 the water sampled was of the order of 0 1 c cooler than the water sampled on either side of this time period this temporal temperature anomaly has only become apparent because of the availability of a continuous data set hydrographic data sampled from the same location as part of the world ocean circulation experiment sr1 repeat section provide potential temperature and salinity values that enable the bottom temperature record to be linked to variability in weddell sea deep water wsdw oxygen isotope measurements demonstrate that the year long period of cooler wsdw measured in drake passage is a signature of ice shelf water in the formation process of deep and bottom waters within the weddell sea

compiling the map of shallow buried palaeochannels on the north china plain abstract the 4 methods used in compiling the shallow buried palaeochannel maps are as follows geohydrologic electrical resistivity areo electro magnetism and drilling methods on the north china plain the drilling method was used mainly accompanied by the geohydrologic and the electrical resistivity methods before compiling the map detailed studies of typical palaeochannels were undertaken of palaeochannel sediments their ages and relation to the storage of shallow groundwater quantity and quality this provides the theoretical foundation for compiling the map of a large area and for dividing the palaeochannels then data from drilling samples were collected and each drilling hole divided into zones 1 and 2 and marked on the base map the boundaries of zones 1 and 2 were drawn on the base map from the map of the shallow buried palaeochannels we can conclude that the shallow buried palaeochannel zones and shallow groundwater zones are identical with the sand bodies of stage i iii and iv palaeochannels

export of weddell sea deep and bottom water an extensive set of conductivity temperature depth ctd lowered acoustic doppler current profiler ladcp data obtained within the northwestern weddell sea in august 1997 characterizes the dense water outflow from the weddell sea and overflow into the scotia sea along the outer rim of the weddell gyre there is a stream of relatively low salinity high oxygen weddell sea deep water defined as water between 0 and 0 7 c constituting a more ventilated form of this water mass than that found farther within the gyre its enhanced ventilation is due to injection of relatively low salinity shelf water found near the northern extreme of antarctic peninsula s weddell sea shelf shelf water too buoyant to descend to the deep sea floor the more ventilated form of weddell sea deep water flows northward along the eastern side of the south orkney plateau passing into the scotia sea rather than continuing along an eastward path in the northern weddell sea weddell sea bottom water also exhibits two forms a low salinity better oxygenated component confined to the outer rim of the weddell gyre and a more saline less oxygenated component observed farther into the gyre the more saline weddell sea bottom water is derived from the southwestern weddell sea where high salinity shelf water is abundant the less saline weddell sea bottom water like the more ventilated weddell sea deep water is derived from lower salinity shelf water at a point farther north along the antarctic peninsula transports of weddell sea deep and bottom water masses crossing 44 w estimated from one ladcp survey are 25 106 and 5 106 m3 s 1 respectively the low salinity better ventilated forms of weddell sea deep and bottom water flowing along the outer rim of the weddell gyre have the position and depth range that would lead to overflow of the topographic confines of the weddell basin whereas the more saline forms may be forced to recirculate within the weddell gyre

the changing mangrove shorelines in kuala kurau peninsular malaysia abstract a considerable extent of the shoreline along the west coast of peninsular malaysia is vegetated by mangrove forests typically one observes frequent change of position of the mangrove outer shore limit the kuala kurau coastline in northwest perak which provides a good example is selected for this study the geological evidence indicates that marine sediments prevail throughout the kuala kurau coastal plain greenish gray clay predominates with varying amounts of silt and sand underlying the basically flat topography the present shoreline has prograded from its initial position within a time span of about 5000 years similarly from 1914 to 1969 a prograding shoreline trend is indicated however from 1969 to 1986 there was widespread erosion although both accreting and retreating situations were indicated erosion in the mangrove fringes in the later years is related to sediment budget freshwater supply over exploitation and utilisation of mangrove forest and the effects indirect of the fishing industry

paleochannel controlled earth fissures in daming north china plain and their implication for underground paleogeomorphology abstract earth fissures are a geologic phenomenon that mainly affects the medium with shallow surface soil and mainly developed in the quaternary sediment cover in the yellow river qinghe river zhanghe river shallow buried paleochannel band hqz qh2 ii band on the north china plain 93 earth fissures are developed among them 29 fissures are evolved in the daming zone in the upper reaches of the paleochannel band thus the zone belongs to a densely grouped fissure area this study through a series of field trenching and surveying revealed that these earth fissures have unique plane distribution rules and profile structure features of short length several meters to several hundred meters shallow depth smaller than 10 m and good correspondence to daming paleochannels these basic characteristics reveal that unlike other tectonic earth fissures daming earth fissures are a new and unknown type of fissures i e paleochannel controlled earth fissures theoretical analysis of their features showed that they were formed due to the actions of gravity primary joint factors and groundwater pumping activities and controlled by ancient river factors including paleochannels sediments and groundwater among them the process of mode i can be summed up as self gravity action tensile cracks surface water scouring earth fissures the process of mode ii is primary join surface water infiltration piping cave in earth fissures the process of mode iii is groundwater extraction aquifer compression inhomogeneous ground subsidence earth fissures these formation mechanisms of paleochannel induced earth fissures can be used to predict the fine distribution of shallow buried paleochannels and the overall migration process of the rivers thus this kind of earth fissures is of great significance for understanding the underground paleogeomorphology buried paleochannel of the north china plain and other alluvial plains of the world

the transport of the weddell gyre across the prime meridian abstract current meter observations from instruments moored from 1996 to 2001 are used to determine the structure and the volume transport of the weddell gyre on the greenwich meridian the record length mean volume transport is 45 sv to the east within the northern and 56 sv to the west within the southern limb of the weddell gyre thus 11 sv must leave the gyre circulation west of the greenwich meridian and enter it east of it the deficit occurs with 8 sv mainly in the circumpolar deep water cdw warm deep water wdw layer surface waters and weddell sea deep water wsdw contribute 2 and 3 sv respectively in contrast to this 3 sv more of weddell sea bottom water wsbw flow in the northern limb to the east than in the southern limb to the west which suggests a wsbw formation rate of about 3 sv in the western weddell sea in the southern boundary of the antarctic circumpolar current acc a volume transport of 35 16 sv was found using geostrophic calculations adjusted with two measurements of the absolute velocity the large heat content of the northern limb points to an extensive heat exchange between the weddell sea and the world ocean west of the prime meridian hence the heat transport as well as the volume transport suggest that the water masses of the weddell gyre are not exclusively replaced in its eastern part but that there is a significant exchange of water masses to the west of the prime meridian

the distribution of tritium and cfcs in the weddell sea during the mid 1980s abstract transient tracer data tritium cfc11 and cfc12 from the southern central and northwestern weddell sea collected during polarstern cruises ant iii 3 ant v 2 3 4 and during andenes cruise nare 85 are presented and discussed in the context of hydrographic observations a kinematic time dependent multi box model is used to estimate mean residence times and formation rates of several water masses observed in the weddell sea ice shelf water is marked by higher tritium and lower cfc concentrations compared to surface waters the tracer signature of ice shelf water can only be explained by assuming that its source water mass western shelf water has characteristics different from those of surface waters using the transient nature of tritium and the cfcs the mean residence time of western shelf water on the shelf is estimated to be approximately 5 years ice shelf water is renewed on a time scale of about 14 years from western shelf water by interaction of this water mass with glacial ice underneath the filchner ronne ice shelf the ice shelf water signature can be traced across the sill of the filchner depression and down the continental slope of the southern weddell sea on the continental slope new weddell sea bottom water is formed by entrainment of weddell deep water and weddell sea deep water into the ice shelf water plume in the northwestern weddell sea new weddell sea bottom water is observed in two narrow deep boundary currents flowing along the base of the continental slope classically defined weddell sea bottom water 0 7 c and weddell sea deep water 0 7 c 0 c are ventilated from the deeper of these boundary currents by lateral spreading and mixing model based estimates yield a total formation rate of 3 5sv for new weddell sea bottom water 1 0 c and a formation rate of at least 11sv for antarctic bottom water 0 5 c

northern source for deglacial and holocene deepwater composition changes in the eastern north atlantic basin over the last decades extensive research has been carried out on changes in the atlantic meridional overturning circulation and its role during the last deglacial period at present only a few high resolution data sets from the deep eastern north atlantic exist for this period it therefore remains uncertain whether deepwater changes in the eastern north atlantic basin were governed by alternating contributions of northern and southern deepwater or whether the eastern north atlantic basin reflects changes in the initial composition and source of north atlantic deepwater furthermore it is still debated whether such changes are triggered by northern or southern hemisphere climatic changes in this centennial to decadal scale resolution study we investigate deepwater composition changes in the eastern north atlantic basin over the last 15 ka br we used sediment cores geofar kf16 and md08 3180 37 984 degrees n 31 118 degrees w wd 3050 m 37 999 degrees n 31 134 degrees w wd 3064 m obtained from a small basin at the eastern flank of the mid atlantic ridge south of the azores islands under modern conditions the coring site is situated at the boundary between southern lower deep water and northern eastern north atlantic deep water consisting of iceland scotland overflow water and labrador sea water distinct differences between the three water masses in terms of ventilation state temperature and salinity signatures are ideal for tracking changes in the deglacial north atlantic deepwater distribution using paired benthic foraminiferal stable isotopes delta c 13 delta o 18 and mg ca bottom water temperature reconstructions the results show a close coupling of low bottom water temperature 1 5 degrees c and delta c 13 0 0 5 parts per thousand values during cold heinrich event 1 the younger dryas and the preboreal that were coeval with a major delta o 18 depletion of deepwater the strong similarities between subtropical eastern north atlantic deep water and subpolar north atlantic surface and deepwater changes indicate that deglacial changes in eastern north atlantic deep water distribution were triggered in the north atlantic consequently this would imply that changes in the north atlantic also contributed to deglacial changes in antarctic bottom water composition during the early holocene stepwise increasing delta c 13 values suggest increasing eastern north atlantic deep water production and or increasing eastern north atlantic deep water ventilation with minor but distinct interruptions at 10 8 10 6 9 1 8 4 8 1 and 7 2 ka bp which were most probably also triggered in the subpolar north atlantic c 2015 elsevier b v all rights reserved

formation and spreading of antarctic deep and bottom waters inferred from a chlorofluorocarbon cfc simulation 1 the formation of deep and bottom waters along antarctica s perimeter is determined by ocean interaction with the atmosphere sea ice ice shelves and bottom topography it initiates a chain of processes that contribute to the ventilation of the global abyss to identify the formation sites and investigate the combined effects of the local forcing mechanisms on water mass transformation and spreading in the southern ocean chlorofluorocarbon cfc simulations with the regional ocean circulation model brios 1 were performed the model uses terrain following vertical coordinates to better represent both near bottom and mixed layer processes and includes an explicit formulation of the ice shelf ocean interaction in agreement with observations the results show the main deep and bottom water formations sites to be located in the ross sea prydz bay and southwestern weddell sea the ross sea ventilates the south east pacific and australian antarctic basins both ross sea and prydz bay ventilate via the antarctic coastal current the weddell enderby basin the latter signal is overprinted by sources in the weddell sea which ventilate the south scotia sea and also the weddell enderby basin despite the general agreement between observed and simulated quantities like bottom layer cfc distribution and inventories along the greenwich meridian the model tends to underestimate the ventilation of the abyssal ocean like other models with coarse resolution

variability in the freshwater balance of northern marguerite bay antarctic peninsula results from δ18o abstract we investigate the seasonal variability in freshwater inputs to the marguerite bay region western antarctic peninsula using a time series of oxygen isotopes in seawater from samples collected in the upper mixed layer of the ocean during 2002 and 2003 we find that meteoric water mostly in the form of glacial ice melt is the dominant freshwater source accounting for up to 5 of the near surface ocean during the austral summer sea ice melt accounts for a much smaller percentage even during the summer maximum around 1 the seasonality in meteoric water input to the ocean around 2 of the near surface ocean is not dissimilar to that of sea ice melt around 2 in 2002 and 1 in 2003 contradicting the assumption that sea ice processes dominate the seasonal evolution of the physical ocean environment close to the antarctic continent three full depth profiles of oxygen isotopes collected in successive decembers 2001 2003 indicate that around 4 m of meteoric water is present in the water column at this time of year and around 1 m of sea ice formed from this same water column the predominance of glacial melt is significant since it is known to be an important factor in the operation of the ecosystem for example by providing a source of nutrients and modifying the physical environment to control the spatial extent and magnitude of phytoplankton blooms the western antarctic peninsula is undergoing a very rapid change in climate with increasing ocean and air temperatures retreating glaciers and increases in precipitation associated with changes in atmospheric circulation as climate change continues we expect meteoric water inputs to the adjacent ocean to rise further sea ice in this sector of the antarctic has shown a climatic decrease and we expect a reduction in oceanic sea ice melt fractions if this change continues continued monitoring of the oceanic freshwater budget at the western peninsula is needed to track these changes as they occur and to better understand their ecological consequences

the international dovetail program abstract the deep ocean ventilation through antarctic intermediate layers dovetail program is an international field and modeling study of the dense deep and bottom waters of the northwestern weddell sea a primary program goal has been to estimate the volume transport and pathways of these waters long considered to be a major source of antarctic bottom water as they escape from the weddell sea over and through the south scotia ridge into the scotia sea corollary goals are to assess modification of the stratification during passage through the narrow steep sided and irregular channels that transect the ridge the program has evolved since its start in 1997 as a primarily process oriented project into a multiyear observational study of the northwestern weddell sea southern scotia sea including the weddell scotia confluence region an additional program goal therefore has become the estimation of interannual variability in the physical system this volume contains a collection of papers that present recent field and model derived results from the dovetail program

subducted slabs and the geoid constraints on mantle rheology and flow geoid anomalies are primarily the result of the density contrasts driving mantle convection and plate motion the total geoid anomaly resulting from a given density contrast in a convecting earth is affected by the mass anomalies associated with the flow induced deformation of the upper surface and internal compositional boundaries as well as by the density contrast itself these boundary deformations and hence the total gravity field depend on the radial distribution of effective viscosity if the internal density contrasts can be estimated as is the case for subducted slabs useful constraints can be placed on the depth and on the variation of viscosity with depth of the convecting system the degree 4 9 components of the observed long wavelength geoid are highly correlated with those predicted by a density model for seismically active subducted slabs the positive sign of the correlation requires that the effective viscosity increases with depth by a factor of 30 or more the amplitude of the correlation cannot be explained by the density contrasts associated with just the seismically active parts of subducted slabs however the amplitude can be explained if the density contrasts associated with subduction extend into the lower mantle or if old lithosphere is piled up at the base of the upper mantle beneath subduction zones to a thickness in excess of 350 km over horizontal distances of thousands of kilometers mantlewide convection in a mantle that has a viscosity increasing with depth provides a simple explanation of the long wavelength geoid anomalies over subduction zones

deep and bottom water of the weddell sea s western rim oceanographic observations from the ice station weddell 1 show that the western rim of the weddell gyre contributes to weddell sea bottom water a thin 300 meters highly oxygenated benthic layer is composed of a low salinity type of bottom water overlying a high salinity component this complex layering disappears near 66 s because of vertical mixing and further inflow from the continental margin the bottom water flowing out of the western rim is a blend of the two types additionally the data show that a narrow band of warmer weddell deep water hugged the continental margin as it flowed into the western rim providing the continental margin with the salt required for bottom water production

lithospheric thickness antarctic deglaciation history and ocean basin discretization effects in a global model of postglacial sea level change a summary of some sources of nonuniqueness the global model of postglacial relative sea level variations that has been developed over the past decade is employed to investigate the constraints that it may be invoked to place on the timing of the deglaciation of west antarctica the analyses presented here confirm the suggestion of p wu and w r peltier 1983 geophysical journal of the royal astronomical society74 377 450 that the model of this event employed inj a clark and c s lingle 1979quaternary research11 279 298 may be simply modified to rectify the misfits between theory and observation that are otherwise obtained at southern hemisphere sites a large number of southern hemisphere relative sea level data are shown to require that the retreat of antarctic ice substantially lagged the retreat of northern hemisphere ice if the deglaciation of antarctica was abrupt the time of onset of antarctic deglaciation is thereby shown to coincide with the time of most rapid northern hemisphere deglaciation sensitivity tests are performed which demonstrate that this result is relatively insensitive to the discretization employed to represent the ocean basins the only exception to this general rule obtains at some coastal sites at which a trade off is revealed between the delay of west antarctic melting and the thickness of the lithosphere required to reconcile the observed local variations of relative sea level at such sites which are all in the far field of the ice sheets some attention must be paid to the accuracy of the local finite element representation of the oceans and to the details of the antarctic deglaciation history

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

wintertime ocean conditions over the southern weddell sea continental shelf antarctica 1 during the austral winter of 2007 a weddell seal tagged with a miniaturized conductivity temperature depth ctd instrument travelled over the central southern weddell sea continental shelf the instrument yielded 750 ctd profiles 250 of them to the sea floor the data show a full depth flow of water onto the shelf via a sill at the shelf break 74 s 44 w the warmth from the core of the flow was able to maintain the surface mixed layer above the freezing point resulting in a band of reduced ice production an estimate of the on shelf flux suggests that this flow accounts for most of the estimated 3 sv of water draining from the southern weddell sea continental shelf

multidecadal freshening and lightening in the deep waters of the bransfield strait antarctica the deep waters of the bransfield strait receive considerable amounts of water from the weddell sea continental shelf the restricted connections to the surrounding ocean and relatively easier access makes the bransfield strait an important proxy region for monitoring changes in the dense weddell sea shelf water masses which are an important precursor of antarctic bottom water aabw long term hydrographic data from the period 1960s 2010s showed freshening and lightening of the deep water masses of the bransfield strait which was likely caused by large freshwater inputs originating from the western shelf of the weddell sea the rates of freshening and lightening were 0 0010 0 0005 yr 1 and 0 0016 0 0014 kg m 3 yr 1 for the central basin respectively and 0 0010 0 0006 yr 1 and 0 0029 0 0013 kg m 3 yr 1 for the eastern basin respectively the deep waters showed a high degree of interannual thermohaline variability which appeared to be caused by changes in the proportions of source water mass mixing between the years statistically significant negative correlations between salinity neutral density fields and the southern annular mode sam were observed 0 56 and 0 62 for the central basin respectively and 0 58 and 0 68 for the eastern basin respectively between 1980 and 2014 during sam positive phases communication between the weddell sea and the bransfield strait is reduced which leads to less saline and lighter water masses in the bransfield strait however the opposite trends are observed during sam negative phases

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

thermohaline stratification below the southern ocean sea ice the end of winter stratification within the cold cyclonic trough of the weddell gyre near 60 s between 5 e and the greenwich meridian is resolved with the mikhail somov data set the temperature maximum of the weddell deep water wdw is for the most part less than 0 5 c but warmer cells of wdw are found these warm wdw cells have temperature salinity and oxygen properties similar to the wdw characteristic of the weddell gyre inflow which is situated to the southeast of the mikhail somov study region the warm wdw cells are accompanied by domes in the pycnocline of 40 m amplitude over the surrounding pycnocline while deeper isopycnals are depressed anticyclonic shear below the 27 83 isopycnal within the warm wdw cells is compensated by the cyclonic shear associated with the pycnocline dome the pycnocline domes are exposed to about 50 greater entrainment by the turbulently active winter mixed layer relative to the regional entrainment rate this entrainment can significantly erode the warm cells in a single winter season introducing excess heat and salt into the mixed layer while the heat is lost to the atmosphere the excess salt is not necessarily compensated by increased fresh water introduction it is hypothesized that the warm wdw cells within the weddell gyre trough are derived from instability within the frontal zone which extends from maud rise to the northeast separating the weddell warm regime from the cold regime greater than normal injection of warm wdw cells into the weddell gyre trough would increase the surface salinity which would tend to destabilize the pycnocline increasing the probability of deep convection and polynya events

southern ocean winter mixed layer austral winter 1986 observations from the polarstern along the greenwich meridian from the ice edge to the antarctic margin show the mixed layer beneath the winter sea ice cover to be significantly depressed in oxygen saturation incorporation of weddell deep water wdw into the winter mixed layer responsible for this undersaturation also introduces heat and salinity into the surface layer which strongly influences the mixed layer sea air exchanges and sea ice formation processes the total wdw transfer into the mixed layer averages 45 myr 1 implying a residence time for the surface water of 2 5 years the associated winter heat flux is 41 w m 2 which limits ice thickness to about 0 55 m agreeing quite well with observations the air temperatures during the cruise are just sufficient to remove the wdw heat input in the presence of observed ice thickness and concentration this suggests that the sea ice cover and wdw heat input into the mixed layer are in approximate balance by midwinter the annual heat flux from wdw to the surface layer and hence into the atmosphere is estimated as 16 w m 2 extrapolation of the greenwich meridian wdw entrainment value to the full circumpolar 60 70 s belt yields total up welling of 24 106 m3 s 1 similar extrapolation of the heat flux value gives a circumpolar total of 2 8 1014 w as a consequence of circulation topography interaction the maud rise water column stands out as an anomaly relative to the surrounding region with a significantly more saline and dense mixed layer below the mixed layer the water column over the crest of the rise is identical to that over the flanks if the latter water column is upwelled by 400 m this uplifting is believed to be a response of the upstream flow encountering the rise increased upstream flow would be expected to increase maud rise upwelling and the dependent salinity density of the mixed layer slight increases in the mixed layer density could trigger a convective mode and generation of a polynya it is hypothesized that spin up of the weddell gyre s barotropic circulation induced by an increase of the regional wind stress curl would enhance the probability of polynya development over maud rise

the stratification and water masses at drake passage the waters at drake passage are known to be separated horizontally into four distinct zones of relatively small geostrophic shear by three fronts in which the shear and eastward flow are large the two northern fronts subantarctic front and polar front that bound the polar frontal zone comprise most of the transport of the antarctic circumpolar current vertical sections of closely spaced 50 km oceanographic stations made across drake passage in the summers of 1975 and 1976 produced quality measurements of temperature salinity oxygen silicate nitrate and phosphate based on these data a traditional description of characteristic distributions is presented good sampling resolution in the vertical allows maxima in hydrostatic stability to be traced laterally approximately along isopycnals between individual stations eleven strata of maximum stability are identified most vertically separate distinct water masses the most pronounced stability stratum is associated with the seasonal pycnocline north of the polar front it separates the subantarctic surface waters from subantarctic mode water to the south of the polar front the seasonal pycnocline is found slightly above the temperature minimum characteristic of the antarctic surface waters in austral summer this stability stratum extends northward near the base of the subantarctic mode water another stability stratum extending across the entire passage forms the upper boundary for the circumpolar deep water south of the polar front this stratum is at the base of the antarctic surface water to the north it is the lower boundary of the antarctic intermediate water although subantarctic mode water and antarctic intermediate water are separated by a stability stratum north of the polar front there is no such separation between antarctic intermediate water and the temperature minimum of the antarctic surface water south of the front this suggests that subantarctic mode water and antarctic intermediate water are distinct and that the latter derives from the surface waters south of the polar front at greater depths a horizontally discontinuous stratum is found between the upper and lower circumpolar deep water two horizontally continuous stability strata are found near the base of the circumpolar deep water marking the transition to a high silicate variety of denser deep water from the southeast pacific basin the densest water mass found is weddell sea deep water which flows through a gap in the south scotia ridge and along the southern scotia sea to fill the trough in the southern drake passage it is overlain by a laterally continuous stratum of relative maximum stability

noble gases in ocean waters and sediments noble gases are widely used in studies of the basic properties and dynamics of natural systems including the ocean this chapter describes some of the more extensive applications of noble gases mainly helium isotopes to studies of oceanographic problems they include the modern oceanic circulation paleo oceanography hydrothermal and cold brine systems in the deep ocean and ocean atmosphere gas exchange originally oceanic noble gas studies were focused on geochemical problems such as the question of the existence of excess helium in seawater derived from radioactive decay of the elements of the uranium and thorium series in ocean sediments suess and wanke 1965 bieri et al 1966 after the discovery of mantle primordial helium during the 1960s clarke et al 1969 craig and weiss 1971 craig et al 1975 and 3he derived from decay of tritium in the near surface waters of the ocean jenkins and clarke 1976 large programs were developed to exploit helium isotopes frequently in combination with tritium for studies of water mass formation circulation and variability e g jenkins 1987 schlosser et al 1991 more recent studies started to explore the use of helium isotopes to paleoceanographic objectives these studies build upon the discovery of extraterrestrial helium in deep sea sediments in the early 1960s merrihue 1964 this signal is now being systematically examined for its potential as a tool for investigations of sediment accumulation rates on very long time scales millions of years and their correlation with changes in paleoceanography e g farley 1995 farley and patterson 1995 marcantonio et al 1995 1996 2001 soon after the discovery of mantle helium in seawater noble gases were applied to studies of hydrothermal systems originally these studies were focused on the source of the fluids emanating from hydrothermal vents as well as

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

last glacial benthic foraminiferal δ18o anomalies in the polar north atlantic a modern analogue evaluation modern processes are evaluated to understand the possible mechanisms behind last glacial benthic foraminiferal 18o anomalies that occurred concurrent with meltwater events in the polar north atlantic such anomalies in the nordic seas were recently interpreted to be caused by brine formation despite intensive sea ice production on circumarctic shelves modern data show that brines ejected from sea ice formation containing low 18o water do not significantly contribute to deep waters in the arctic ocean today assuming that this process was nevertheless responsible for 18o anomalies in nordic seas deep water during the last glaciation a broad shallow shelf area adjacent to the nordic seas such as the barents sea had to be seasonally free of sea ice in order to serve as an area for brine formation another process which may explain 18o depleted water at depth is found in the weddell sea today where a low 18o signal in deep waters originates from ice shelf interactions if temperature were considered the main mechanism for the low benthic 18o values an increase of 4 c must have occurred in the deep water an analogous situation with a reversed water temperature pattern due to a subsurface inflow of warm atlantic water is found today in the eastern arctic ocean and deep water warming is observed in the greenland gyre in the absence of deep convection because paleoproxy data also indicate an atlantic water inflow into the nordic seas during such benthic 18o anomalies temperature as a principal mechanism of changing 18o cannot be excluded

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

eddy driven exchange between the open ocean and a sub ice shelf cavity the exchange between the open ocean and sub ice shelf cavities is important to both water mass transformations and ice shelf melting here we use a high resolution 500 m numerical model to investigate to which degree eddies produced by frontal instability at the edge of a polynya are capable of transporting dense high salinity shelf water hssw underneath an ice shelf the applied surface buoyancy flux and ice shelf geometry is based on ronne ice shelf in the southern weddell sea an area of intense wintertime sea ice production where a flow of hssw into the cavity has been observed results show that eddies are able to enter the cavity at the southwestern corner of the polynya where an anticyclonic rim current intersects the ice shelf front the size and time scale of simulated eddies are in agreement with observations close to the ronne ice front the properties and strength of the inflow are sensitive to the prescribed total ice production flushing the ice shelf cavity at a rate of 0 2 0 4 106 m3 s 1 depending on polynya size and magnitude of surface buoyancy flux eddy driven hssw transport into the cavity is reduced by about 50 if the model grid resolution is decreased to 2 5 km and eddies are not properly resolved

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

the five stable noble gases are sensitive unambiguous tracers of glacial meltwater the five inert noble gases he ne ar kr and xe exhibit a unique dissolved gas saturation pattern resulting from the formation and addition of glacial meltwater to seawater he and ne become oversaturated and ar kr and xe become undersaturated to varying percentages for example addition of 10 glacial meltwater to seawater results in a saturation anomaly of he 12 8 ne 8 9 ar 0 5 kr 2 2 and xe 3 3 this pattern in noble gas saturation reflects a unique meltwater signature that is distinct from the other major physical processes that modify the gas concentration and saturation namely seasonal changes in temperature at the ocean surface and bubble mediated gas exchange we use optimum multiparameter analysis to illustrate how all five noble gases can help distinguish glacial meltwater from wind driven bubble injection making them a potentially valuable suite of tracers for glacial melt and its concentration in the deep waters of the world ocean

baroclinic instability of density current along a sloping bottom and the associated transport process numerical experiments with a three dimensional nonhydrostatic ocean model have been carried out to investigate the dynamic processes of downslope density current and associated transport of dense water focusing on the effects of bottom slope for the range of slope inclination s from 0 to 0 04 bottom slope has two effects on baroclinic instability of the flow one is the stabilizing effect due to the topographic effect and to offshoreward increase in water depth the other is the destabilizing effect due to steepened inclination of isopycnal surface which increases available potential energy since the destabilizing effect over the upper slope overcomes the stabilizing one in the early stage unstable waves develop more rapidly with increasing s nonlinear energy conversion due to reynolds stresses also affects the flow stability and then the growth rate of instability increases linearly with s in this stage after the unstable waves have finite amplitudes in the mature stage the stabilizing effect of bottom slope becomes dominant especially over the lower slope thus vigorous unstable eddies are confined to the upper slope region in steep slope cases while they cover the whole slope region in gentle slope cases and this difference in the eddy field causes a drastic change in downslope transport of dense water in gentle slope cases efficiency of the transport becomes higher with increasing s since the destabilizing effect overcomes the stabilizing one as a whole on the contrary the efficiency becomes lower with increasing s in steep slope cases since the stabilizing effect surpasses the destabilizing one as a result the most effective transport is realized in the case with s 0 005 although the transport due to eddies in steep slope cases becomes weak over the lower slope it is still larger than that due to the bottom ekman current since the eddy transport occurs in the bottom layer with a thickness of 100 200 m which is 4 8 times the ekman layer thickness