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

the salinity temperature and δ18o of the glacial deep ocean we use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from ocean drilling program cores to reconstruct salinity and temperature of the deep ocean during the last glacial maximum lgm our data show that the temperatures of the deep pacific southern and atlantic oceans during the lgm were relatively homogeneous and within error of the freezing point of seawater at the ocean s surface our chloride data show that the glacial stratification was dominated by salinity variations in contrast with the modern ocean for which temperature plays a primary role during the lgm the southern ocean contained the saltiest water in the deep ocean this reversal of the modern salinity contrast between the north and south atlantic implies that the freshwater budget at the poles must have been quite different a strict conversion of mean salinity at the lgm to equivalent sea level change yields a value in excess of 140 meters however the storage of fresh water in ice shelves and or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level

pushing the boundaries glacial interglacial variability of intermediate and deep waters in the southwest pacific over the last 350 000 years glacial interglacial changes in southern ocean s air sea gas exchange have been considered as important mechanisms contributing to the glacial interglacial variability in atmospheric co2 hence understanding past variability in southern ocean intermediate to deep water chemistry and circulation is fundamental to constrain the role of these processes on modulating glacial interglacial changes in the global carbon cycle our study focused on the glacial interglacial variability in the vertical extent of southwest pacific antarctic intermediate water aaiw we compared carbon and oxygen isotope records from epibenthic foraminifera of sediment cores bathed in modern aaiw and upper circumpolar deep water ucdw 943 2066 m water depth to monitor changes in water mass circulation spanning the past 350 000 years we propose that pronounced freshwater input by melting sea ice into the glacial aaiw significantly hampered the downward expansion of southwest pacific aaiw consistent with climate model results for the last glacial maximum this process led to a pronounced upward displacement of the aaiw ucdw interface during colder climate conditions and therefore to an expansion of the glacial carbon pool

an oceanographic explanation for the apparent carbon isotope cadmium discordancy in the glacial antarctic the seeming discordance between the glacial to interglacial changes in the carbon isotope ratio and cadmium content of benthic foraminifera from the deep antarctic has cast a shadow on the reliability of these proxies as valid of paleocirculation indicators the problem is that while cadmium content shows little glacial to interglacial change lea and boyle 1990 boyle 1992 the carbon isotope change is larger than at any other place in the ocean curry et al 1988 innu et al 1990 charles and fairbanks 199o even after correction for the 0 35 glacial to interglacial change in the isotope ratio for mean ocean atmosphere carbon a difference of 0 5 to 0 6 remains on the basis of redfield ratios for today s ocean this is equivalent to a 25 increase in cadmium content which is not seen this puzzle has been with us for several years

temporal variability of ultraviolet cloud features in the venus stratosphere abstract statistics on the temporal variability of uv cloud features on venus during 66 days of nominal mission imaging by the pioneer venus orbiter cloud photopolarimeter reveal at least five types of systematic variability on large scales 1 a low latitude global scale wave of period 3 94 0 1 days corresponding to longitudinal motion of the dark equatorial band and propagating westward relative to the mean flow 2 a midlatitude wave of period 5 20 0 2 days corresponding to wavenumber 1 oscillations of the latitude of the bright polar bands and propagating eastward relative to the mean flow 3 2 to 3 week fluctuations in the slope of longitudinal cloud brightness power spectra at intermediate wavenumbers manifested by variations in the intensity of large bow shaped features 4 2 month variations in polar region brightness consistent with polar brightening episodes observed from earth and 5 a monotonic decrease in the disk integrated brightness of venus during the nominal mission which may be either a true time variation or a solar locked longitudinal dependence of brightness small scale features appear to correlate with large scale albedo patterns specifically cellular features exist primarily where large scale dark material is present while the orientation of streak features with respect to latitude circles oscillates with the same 4 day period as the large scale features at low latitudes the wide range of time scales present in the data suggests the complexity of venus stratospheric dynamics extended observations over many years may be becessary to define the general circulation

thermodynamic influences on the marine carbon isotope record air sea exchange represents an important controlling factor for the distribution of carbon isotopes in the modern ocean even below the surface mixed layer here we show that this thermodynamic influence varies between water masses with a magnitude which is large relative to the amplitude of typical deep sea sediment 13c records thus changes in air sea exchange processes must be regarded as a significant source of variability for any marine 13c signal

north atlantic ventilation of southern sourced deep water in the glacial ocean one potential mechanism for lowering atmospheric co2 during glacial times is an increase in the fraction of the global ocean ventilated by the north atlantic which produces deep water with a low concentration of unused nutrients and thus drives the ocean s biological pump to a high efficiency however the data indicate that during glacial times a water mass low in 13c 12c and 14c c occupied the deep atlantic apparently at the expense of north atlantic deep water nadw this water is commonly referred to as southern sourced because of its apparent entry into the atlantic basin from the south prompting the inference that it was ventilated at the southern ocean surface here we propose that this deep atlantic water mass actually included a large fraction of north atlantic ventilated water the chemical characteristics of which were altered by recirculation in the deep southern and indo pacific oceans in an ocean model sensitivity experiment that reduces antarctic bottom water formation and weakens its overturning circulation we find that a much greater fraction of nadw is transported into the southern ocean without contacting the surface and is entrained and mixed into the southern sourced deep water that spreads into the global abyssal ocean thus north atlantic ventilation takes over more of the ocean interior lowering atmospheric co2 and yet the abyssal atlantic is filled from the south with old water low in 13c 12c and 14c c consistent with glacial data

millennial scale evolution of the southern ocean chemical divide abstract the chemical properties of the mid depth and deep southern ocean are diagnostic of the mechanisms of abrupt changes in the global ocean throughout the late pleistocene because the regional water mass conversion and mixing help determine global ocean gradients here we define continuous time series of southern ocean vertical gradients by differencing the records from two high deposition rate deep sea sedimentary sequences that span the last several ice age cycles the inferred changes in vertical carbon and oxygen isotopic gradients were dominated by variability on the millennial scale and they followed closely the abrupt climate events of the high latitude northern hemisphere in particular the stadial events of at least the last 200 kyr were characterized by enhanced mid deep gradients in both 13 c dissolved inorganic carbon and 18 o temperature interstadial events conversely featured reduced vertical gradients in both properties the glacial terminations represented exceptions to this pattern of variability as the vertical carbon isotopic gradient flattened dramatically at times of peak warmth in the southern ocean surface waters and with little or no corresponding change 18 o gradient the available evidence suggests that properties of the upper layer of the southern ocean antarctic intermediate water were influenced by an atmospherically mediated teleconnection to high latitude northern hemisphere

association of sinking organic matter with various types of mineral ballast in the deep sea implications for the rain ratio 1 we compiled and standardized sediment trap data below 1000 m depth from 52 locations around the globe to infer the implications of the armstrong et al 2002 ballast model to the ratio of organic carbon to calcium carbonate in the deep sea the rain ratio we distinguished three forms of mineral ballast calcium carbonate opal and lithogenic material we concur with armstrong et al 2002 that organic carbon sinking fluxes correlate tightly with mineral fluxes based on the correlations seen in the trap data we conclude that most of the organic carbon rain in the deep sea is carried by calcium carbonate because it is denser than opal and more abundant than terrigenous material this analysis explains the constancy of the organic carbon to calcium carbonate rain ratio in the deep sea today and argues against large changes in the mean value of this ratio in the past however sediment trap data show variability in the ratio in areas of high relative calcium carbonate export mass caco3 mass ratio 0 4 unexplainable by the model leaving open the possibility of regional variations in the rain ratio in the past

the thermal springs of jordan the thermal springs alongside wadi araba dead sea and jordan valley jordan were investigated and sampled in a comprehensive field study of 2 weeks conventional physicochemical properties were measured in situ dissolved solids and isotopic composition were analyzed two main spring locations on the east side of the dead sea were mapped it became evident that the hottest springs are among the closest to prominent faults some springs are controlled by gas lift jordan s hot springs are described by means of a broad hydrochemical and physicochemical data set and several figures are presented based on their hydrochemistry the thermal springs are classified into four thermal provinces water genesis is discussed several geothermometers are applied to estimate reservoir temperatures observed discharge rate water temperature and isotopic composition are compared with data from the literature although discharge and water temperature are reported to be constant over the last decades groundwater overexploitation led to a shift of the isotopic composition what is documented for the first time in jordan thus the effect of groundwater mining on jordan s hot springs can be stated as a fact

high epibenthic foraminiferal δ13c in the recent deep arctic ocean implications for ventilation and brine release during stadials low planktic and benthic 18o and 13c values in sediments from the nordic seas of cold stadials of the last glaciation have been attributed to brines formed similar to modern ones in the arctic ocean to expand on the carbon isotopes of this hypothesis i investigated benthic 13c from the modern arctic ocean i show that mean 13c values of live epibenthic foraminifera from the deep arctic basins are higher than mean 13c values of upper slope epibenthic foraminifera this agrees with mean high 13c values of dissolved inorganic carbon dic in arctic bottom water abw which are higher than mean 13cdic values from shallower water masses of mainly atlantic origin however adjustments for oceanic 13c suess depletion raise subsurface and intermediate water 13cdic values over abw 13cdic ones accordingly during preindustrial holocene times the 13cdic of abw was as high or even higher than today but lower than the 13cdic of younger subsurface and intermediate water if brine enriched water significantly ventilated abw brines should have had high 13cdic values analogously high 13cdic brines may have been formed in the nordic seas during warm interstadials during cold stadials when most of the arctic ocean was perennially sea ice covered a cessation of high 13cdic brine rejection may have lowered 13cdic values of abw and ultimately the 13cdic in nordic seas intermediate and deep water so in contrast to the idea of enhanced brine formation during cold stadials the results of this investigation imply that a cessation of brine rejection would be more likely

no signature of abyssal carbon in intermediate waters off chile during deglaciation the rise in atmospheric carbon dioxide at the end of the last glacial maximum has been attributed to the release of carbon dioxide from the deep southern ocean however reconstructions of the radiocarbon signature of chilean margin intermediate waters during the glacial termination do not reflect the influence of such a release

densities and temperatures in the venus mesosphere and lower thermosphere retrieved from soir on board venus express retrieval technique the soir instrument flying on board venus express operates in the infrared spectral domain and uses the solar occultation technique to determine the vertical profiles of several key constituents of the venus atmosphere the retrieval algorithm is based on the optimal estimation method and solves the problem simultaneously on all spectra belonging to one occultation sequence vertical profiles of h2o co hcl and hf as well as some of their isotopologues are routinely obtained for altitudes ranging typically from 70 to 120 km depending on the species and the spectral region recorded in the case of co2 a vertical profile from 70 up to 150 km can be obtained by combining different spectral intervals rotational temperature is also retrieved directly from the co2 signature in the spectra the present paper describes the method used to derive the above mentioned atmospheric quantities and temperature profiles the method is applied on some retrieval cases illustrating the capabilities of the technique more examples of results will be presented and discussed in a following companion paper which will focus on the co2 vertical profiles of the whole data set

hydrochemistry and groundwater system of the zerka ma in zara thermal field jordan abstract a groundwater flow model through the different geological successions from the upper cretaceous through the lower cretaceous sandstone and older units is presented in this paper the model is supported by the hydrochemical evolution of water types from the recharge areas in the highlands to discharge sites of thermal water at the slopes overlooking the dead sea the thermal water discharged in the zerka ma in zara areas consists of three end members mixed in different ratios with a component of old many thousands of years thermal water undersaturated in carbonate minerals and containing hundreds of milligrams per liter of free co2 the release of co2 gas upon discharge renders the water oversaturated with respect to carbonate minerals which results in aragonite precipitation the elevated temperature of the water in the reservoir 73 82 c is attributed to the presence of a heat storing layer topping the aquifer

on the late pleistocene ocean geochemistry and circulation a box model of the atmosphere and ocean was developed to investigate how geochemical distributions extant during the late pleistocene may have come about the model simulates the regional distribution of calcium carbonate dissolution as well as the chemical oceanography and atmospheric co2 13c and radiocarbon if the downward biological flux of particulate carbon increases by a factor of 2 to 3 in the antarctic and if this increase is combined with a relative increase of the atlantic sector antarctic bottom water aabw versus north atlantic deep water nadw source ratio from 1 3 to about 2 1 then the model predicts several changes that seem to be recorded in the sedimentary record as follows 1 a global redistribution of nutrients and 12c from the intermediate to deep water takes place with the atlantic intermediate water phosphate decreasing 0 6 mole kg 1 and the 13c increasing 0 3 to 0 5 2 the dissolved oxygen level of the deep sea is reduced from an average of about 180 to 70 mole kg 1 but the intermediate water oxygen declines only a small amount 3 the decrease in intermediate water nutrient concentration results in lower average organic carbon and calcium carbonate production in the warm surface ocean 4 the atmospheric co2 decreases by 90 to 110 ppm 5 initially a global increase in calcium carbonate dissolution occurs which is followed by a relaxation toward better preservation than exists for the present ocean in the model in this paper the reduction of nadw by itself does not produce these effects rather the nutrient decrease that does occur is found mostly in north pacific intermediate water and the model atmospheric co2 decrease is only 10 to 30 ppm it is observed that 92 of the atmospheric co2 change takes place according to a 200 year time constant in the model this corresponds to the response time of the upper ocean and atmosphere to a change in the stationary state atmospheric pco2 thus according to this model the time lag between the nutrient based cause and the atmospheric co2 response is not expected to be particularly large

13c record of benthic foraminifera in the last interglacial ocean implications for the carbon cycle and the global deep water circulation the 13c 12c ratios of upper holocene benthic foraminiferal tests genera cibicides and uvigerina of deep sea cores from the various world ocean basins have been compared with those of the modern total carbon dioxide tco2 measured during the geosecs program the 13c difference between benthic foraminifera and tco2 is 0 07 0 04 for cibicides and 0 83 0 07 for uvigerina at the 95 confidence level 13c analyses of the benthic foraminifera that lived during the last interglaciation isotopic substage 5e about 120 000 yr ago show that the bulk of the tco2 in the world ocean had a 13c value 0 15 0 12 lower than the modern one at the 95 confidence level reflecting a depletion compared to the present value of the global organic carbon reservoir regional differences in 13c between the various oceanic basins are explained by a pattern of deep water circulation different from the modern one the antarctic bottom water production was higher than today during the last interglaciation but the eastward transport in the circumpolar deep water was lower

geomagnetic field intensity north atlantic deep water circulation and atmospheric δ14c during the last 50 kyr we present simulated records of past changes in the atmospheric 14c for the last 50 kyr due to changes in geomagnetic field intensity and in the strength of the north atlantic deep water nadw a new geomagnetic record was used largely based on the napis 75 record laj et al phil trans r soc london a 358 2000 1009 1025 which has been extended for the 0 20 kyr interval using archeomagnetic and volcanic data past changes of the nadw were derived from a mineral magnetic study of the cores used in the construction of napis 75 two box models of different complexity 4 and 17 boxes were used to simulate the carbon cycle calculated records of 14c are consistent with experimental determinations for the last 24 kyr for older ages the records calculated with variable oceanic circulation conditions reach values as high as 600 with an average of 500 between 20 and 40 kyr with maxima around 21 30 and 38 kyr gisp2 age model while low values are observed prior to 42 kyr although large inconsistencies in experimental data preclude precise comparison the average record simulated with the 17 box model is overall consistent with the icelandic sea record voelker et al radiocarbon 40 1998 517 534 42 2000 437 452 except for the extremely high peak observed in this record at 40 5 kyr on the other hand the results recently reported from a stalagmite recovered from a submerged cave in the bahamas beck et al science 292 2001 2453 2458 are inconsistent with all our model simulations in the 20 45 kyr interval the improved geomagnetic record combined with the new nadw profile allows us to give a modeled evaluation of the relative contribution of these factors to changes in atmospheric 14c the average simulation provides a first order modeled correction for conventional radiocarbon ages older than 25 kyr for which no calibration curve is available as yet

cooling and ventilating the abyssal ocean the abyssal ocean is filled with cold dense waters that sink along the antarctic continental slope and overflow sills that lie south of the nordic seas recent inte grations of chlorofluorocarbon 11 cfc measurements are similar in antarctic bottom water aabw and in lower north atlantic deep water nadw but antarctic inputs are 2 c colder than their northern counterparts this indicates comparable ventilation rates from both polar re gions and accounts for the southern ocean dominance over abyssal cooling the decadal cfc based estimates of recent ventilation are consistent with other hydrographic observa tions and with longer term radiocarbon data but not with hypotheses of a 20 th centuryslowdown in the rate of aabw formation significant variabilityis not precluded bythe available ocean measurements however and interannual to decadal changes are increasinglyevident at high latitudes

isotopic analyses and hydrochemistry of the thermal springs along the eastern side of the jordan dead sea wadi araba rift valley abstract the isotopic composition of the present precipitation as well as the groundwaters of jordan is found to lie between the eastern mediterranean and the meteoric water lines whereas the isotopic compositions of precipitation and groundwater from north and central jordan plot between both lines those of southern jordan cluster closer to the meteoric water line the deep sandstone aquifer complex in central jordan receives water from the overlying tertiary upper cretaceous units as well as from the sandstones of southern jordan both contributions mix in the eastern part of central jordan flow from there in a westerly direction and discharge on the slopes above the dead sea at the interface of fresh groundwater and dead sea water mixing between the latter two waters takes place under a normal geothermal gradient the water is then discharged as thermal water with an isotopic composition following the equation d 3 97 18 o 16 9

sunlight refraction in the mesosphere of venus during the transit on june 8th 2004 abstract many observers in the past gave detailed descriptions of the telescopic aspect of venus during its extremely rare transits across the solar disk in particular at the ingress and egress the portion of the planet s disk outside the solar photosphere has been repeatedly perceived as outlined by a thin bright arc aureole those historical visual observations allowed inferring the existence of venus atmosphere the bright arc being correctly ascribed to the refraction of light by the outer layers of a dense atmosphere on june 8th 2004 fast photometry based on electronic imaging devices allowed the first quantitative analysis of the phenomenon several observers used a variety of acquisition systems to image the event ranging from amateur sized to professional telescopes and cameras thus collecting for the first time a large amount of quantitative information on this atmospheric phenomenon in this paper after reviewing some elements brought by the historical records we give a detailed report of the ground based observations of the 2004 transit besides confirming the historical descriptions we perform the first photometric analysis of the aureole using various acquisition systems the spatially resolved data provide measurements of the aureole flux as a function of the planetocentric latitude along the limb a new differential refraction model of solar disk through the upper atmosphere allows us to relate the variable photometry to the latitudinal dependency of scale height with temperature in the south polar region as well as the latitudinal variation of the cloud top layer altitude we compare our measurements to recent analysis of the venus express virtis m vmc and spicav soir thermal field and aerosol distribution our results can be used a starting point for new more optimized experiments during the 2012 transit event

strong thermodynamic imprint on recent bottom water and epibenthic δ13c in the weddell sea revealed implications for glacial southern ocean ventilation abstract paleonutrient proxies are widely used to reconstruct the geometry of deep water masses during the last glacial maximum lgm epibenthic 13 c provides best spatial coverage and artifacts are well investigated discrepancies between reconstructed lgm circulation patterns derived from models or different benthic nutrient proxies can partly be resolved by varying air sea signatures of 13 c i e 13 c as however there are very few data available to calculate a 13 c as of modern bottom water dissolved inorganic carbon dic 13 c and to document how this signal is recorded in benthic foraminiferal 13 c here i show that today bottom water in the atlantic sector of the southern ocean is 13 c enriched with 13 c dic values between 0 4 and 1 0 and 13 c as values 0 4 and that this signal is recorded in live and dead epibenthic 13 c this is in contrast to a uniform modern antarctic circumpolar 13 c dic of rather 0 4 which hitherto is used as modern framework to compare to low lgm 13 c dic of southern sourced bottom water and glacial inter basin differences i conclude that a potential reduction of the strong recent thermodynamic imprint during bottom water generation in glacial times could explain depleted circum antarctic 13 c dic without associated co 2 enrichment and anoxia in antarctic bottom waters the present synoptic compilation of 13 c dic and live benthic foraminifera 13 c is in support of hypotheses that explain low lgm 13 c by a depletion of southern end member 13 c dic due to extensive sea ice formation with low 13 c as brine rejection and diminished air sea gas exchange

west antarctic ice sheet retreat driven by holocene warm water incursions glaciological and oceanographic observations coupled with numerical models show that warm circumpolar deep water cdw incursions onto the west antarctic continental shelf cause melting of the undersides of floating ice shelves because these ice shelves buttress glaciers feeding into them their ocean induced thinning is driving antarctic ice sheet retreat today here we present a multi proxy data based reconstruction of variability in cdw inflow to the amundsen sea sector the most vulnerable part of the west antarctic ice sheet during the holocene epoch from 11 7 thousand years ago to the present the chemical compositions of foraminifer shells and benthic foraminifer assemblages in marine sediments indicate that enhanced cdw upwelling controlled by the latitudinal position of the southern hemisphere westerly winds forced deglaciation of this sector from at least 10 400 years ago until 7 500 years ago when an ice shelf collapse may have caused rapid ice sheet thinning further upstream and since the 1940s these results increase confidence in the predictive capability of current ice sheet models

high altitude venus haze from pioneer venus limb scans abstract high vertical resolution scans of the venus limb made by the pioneer venus orbiter cloud photopolarimeter at 365 nm and 690 nm wavelengths are used to investigate the level of the haze top and haze particle properties and scale height haze particle vertical optical depth 0 01 occurs at altitude 80 to 85 km based on knowledge of instrument pointing the lowest haze tops were observed close to subsolar longitudes but the data set supports a longitude dependence no more than a temporal variation single scattering computations for a spherical shell atmosphere show good agreement with observed intensities for particles smaller than 0 3 m radius and refractive index less than 1 7 consistent with but not limited to concentrated sulfuric acid particle scale height in the 0 5 to 2 mbar pressure regions varies between 1 and 3 km over the season 12 of 92 days latitude 15 45 n and local time 0900 1800 ranges of the observations detached layers of haze are sometimes present an average particle scale height of 2 2 km at 84 km altitude yields an eddy diffusion coefficient of 1 3 10 5 cm 2 sec 1

changes in the mode of southern ocean circulation over the last glacial cycle revealed by foraminiferal stable isotopic variability benthic foraminiferal oxygen and carbon isotopic records from southern ocean sediment cores show that during the last glacial period the south atlantic sector of the deep southern ocean filled to roughly 2500 m with water uniformly low in 13c resulting in the appearance of a strong mid depth nutricline similar to those observed in glacial northern oceans concomitantly deep water isotopic gradients developed between the pacific and atlantic sectors of the southern ocean the 13c of benthic foraminifera in pacific sediments remained significantly higher than those in the atlantic during the glacial episode these two observations help to define the extent of what has become known as the southern ocean low 13c problem one explanation for this glacial distribution of 13c calls upon surface productivity overprints or changes in the microhabitat of benthic foraminifera to lower glacial age 13c values we show here however that glacial interglacial 13c shifts are similarly large everywhere in the deep south atlantic regardless of productivity regime or sedimentary environment furthermore the degree of isotopic decoupling between the atlantic and pacific basins is proportional to the magnitude of 13c change in the atlantic on all time scales thus we conclude that the profoundly altered distribution of 13c in the glacial southern ocean is most likely the result of deep ocean circulation changes while the characteristics of the southern ocean 13c records clearly point to reduced north atlantic deep water input during glacial periods the basinal differences suggest that the mode of southern ocean deep water formation must have been altered as well

the influence of air sea exchange on the isotopic composition of oceanic carbon observations and modeling although the carbon isotropic composition of ocean waters after they leave the surface ocean is determined by biological cycling air sea exchange affects the carbon isotopic composition of surface waters in two ways the equilibrium fractionation between oceanic and atmospheric carbon increases with decreasing temperature in southern ocean surface waters this isotopic equilibrium enriches delta sup 13 c relative to the delta sup 13 c expected from uptake and release of carbon by biological processes alone similarly surface waters in the subtropical gyres are depleted in delta sup 13 c due to extensive air sea exchange at warm temperatures countering the tendency toward isotopic equilibration with the atmosphere a relatively slow process are the effects of the equilibration of co sub 2 itself a much faster process in regions where there is a net transfer of isotopically light co sub 2 from the ocean to the atmosphere e g the equator surface waters become enriched in sup 13 c whereas in regions where isotopically light co sub 2 is entering the ocean e g the north atlantic surface waters become depleted in sup 13 c a compilation of high quality oceanic delta sup 13 c measurements along with experiments performed using a zonally averaged three basin dynamic ocean model are used to explore these processes 40 refs 14more figs 1 tab less

antarctic sea ice and the control of pleistocene climate instability a hypothesis is presented for the origin of pleistocene climate instability based on expansion of antarctic sea ice and associated changes in the oceans salinity structure the hypothesis assumes that thermohaline overturning is dominated by the reconfigured conveyor of toggweiler and samuels 1993b in which deepwater upwelling is restricted to high southern latitudes the reconfigured conveyor is shown to be potentially stabilized in an on mode by precipitation at high southern latitudes and potentially destabilized into on and off modes by the counteracting influence of antarctic sea ice the mechanism is clarified by the use of a hydraulic analogue we hypothesize that this mechanism accounts for dominant patterns of thermohaline overturning and climate instability between pleistocene warm and cold periods the hypothesis is shown to be consistent with a range of paleoceanographic evidence and to potentially account for details of observed rapid climate changes during glacial and interglacial periods including aspects of interhemispheric timing

microhabitat preferences of live benthic foraminifera and stable carbon isotopes off sw svalbard in the presence of widespread methane seepage abstract to constrain the use of and better calibrate benthic foraminiferal carbon isotope based proxies 13c we analyzed live rose bengal stained benthic foraminifera from fjords outer shelves and the upper continental slope of sw svalbard we further investigated whether the presence of widespread methane seepage altered benthic foraminiferal 13c the one to one relationship between the 13c of cibicidoides wuellerstorfi and cibicides lobatulus tests and the 13cdic of bottom water in nordic seas was reconfirmed we also confirmed an almost constant 13c of live specimens of infaunal species melonis zaandamae nonion labradoricum and globobulimina affinis independent of their subbottom sampling depth and pore water 13cdic at any given site this is in contrast to the wide range of intraspecific 13c values of both epifaunal as well as infaunal species observed between sites we did not find significant correlations between foraminiferal 13c minus site specific 13cdic 13cfor dic of the investigated species and the total organic carbon toc contents of surface sediments on the contrary a distinct relationship is observed between high marine organic carbon moc contents and low 13cfor dic values of n labradoricum and to a lesser extent g affinis these findings are important because on the one hand they confirm a systematic influence of the availability of labile moc on deep infaunal species 13c whereas on the other hand they document the independence of epifaunal and infaunal species 13c of toc contents in well ventilated bottom water and organic rich surface sediment generally species mean 13c reflects their average living depths ald5 such that epifaunal and shallow infaunal species depict highest and deep infaunal species lowest 13c values mean 13cfor dic values of neither epifaunal c lobatulus and c wuellerstorfi 0 05 0 06 nor of infaunal m zaandamae 2 40 0 07 n labradoricum 2 69 0 13 and g affinis 3 48 0 15 seem to be significantly influenced by strongly elevated methane concentrations in the water column widespread gas seepage at the sea floor and low pore water 13cdic the latter possibly partly due to methanotrophic oxidation the 13c values of deep infaunal n labradoricum and g affinis minus epifaunal 13c values 13cnlab cib and 13cgaff cib seem to decrease with increasing toc and moc contents however only the 13cnlab cib values correlate significantly with moc contents and thus marine primary productivity dissolved oxygen concentrations estimated on the basis of 13cgaff cib values of 230 mol kg are in accordance with reported well oxygenated bottom water conditions at all stations

enhanced δ13c and δ18o differences between the south atlantic and south pacific during the last glaciation the deep gateway hypothesis enhanced vertical gradients in benthic foraminiferal 13c and 18o in the atlantic and pacific during the last glaciation have revealed that ocean overturning circulation was characterized by shoaling of north atlantic sourced interior waters nonetheless our understanding of the specific mechanisms driving these glacial isotope patterns remains incomplete here we compare high resolution depth transects of cibicidoides spp 13c and 18o from the southwest pacific and the southwest atlantic to examine relative changes in northern and southern sourced deep waters during the last glacial maximum lgm and deglaciation during the lgm our transects show that water mass properties and boundaries in the south atlantic and pacific were different from one another the atlantic between 1 0 and 2 5 km was more than 1 enriched in 13c relative to the pacific and remained more enriched through the deglaciation during the lgm atlantic 18o was 0 5 more enriched than the pacific particularly below 2 5 km this compositional difference between the deep portions of the basins implies independent deep water sources during the glaciation we attribute these changes to a deep gateway effect whereby northern sourced waters shallower than the drake passage sill were unable to flow southward into the southern ocean because a net meridional geostrophic transport cannot be supported in the absence of a net east west circumpolar pressure gradient above the sill depth we surmise that through the lgm and early deglaciation shoaled northern sourced waters were unable to escape the atlantic and contribute to deep water formation in the southern ocean

scale heights and detached haze layers in the mesosphere of venus from spicav ir data abstract spicav ir one channel of spicav soir instrument suite onboard venus express performed solar occultation measurements of the atmosphere at terminators in 0 65 1 7 m spectral range we analyze the properties of the upper part of the venus aerosol layer upper haze 70 95 km altitude from 798 observations performed from may 2006 through november 2014 vertical profiles of slant optical depth extinction coefficient effective radius and number density of haze particles from 222 orbits were analyzed in a previous publication luginin et al 2016 their diurnal latitudinal and interannual variabilities were investigated the present paper is devoted to analysis of scale heights and properties of detached haze layers from 147 orbits at mid to high northern latitudes where the best spatial resolution was obtained scale heights retrieved from 43 orbits were equal to 4 5 5 km at the north pole 82 n 90 n decreasing to 2 4 km at 60 n 80 n latitudes as an explanation of such latitudinal variations we propose a mechanism based on vertical transport driven by winds that are directed upward at the north pole and downward at 60 n 80 n latitudes detached layers were detected in 93 occultations at 58 n 90 n the detached layers are presumably formed through condensation of water vapor on droplets of sulfuric acid water solution they were mostly seen at 80 88 km at the morning terminator and at 84 90 km at the evening one this difference in altitude of the detached layers can be explained by diurnal variations in thermal structure of venusian mesosphere the vertical optical depth of detached layers varies broadly around the mean dl 0 8 3 10 3 no difference between the morning and the evening terminators was observed the effective radius and number density of aerosol particles in the detached layers group around a very wide maximum at the morning terminator 0 65 0 25 m and 0 6 0 4 cm 3 and two maxima at the evening terminator 0 4 0 1 m and 0 85 0 15 m 0 3 0 2 cm 3 and 4 5 2 5 cm 3 this could be explained by differences in initial altitudes at which condensation of particles occurs

glacial interglacial changes in water mass structure and flow in the sw pacific ocean eight to ten point depth profiles from 1200 to 4800 m water depth of oxygen and carbon isotopic values derived from benthic foraminifera averaged over selected times in the past 160 ka are presented the data are from 10 sediment cores off eastern new zealand mainly north chatham rise this lies under the deep western boundary current in the southwest pacific and is the main point of entry for several water masses into the pacific ocean the benthic isotopic profiles are related to the structure of water masses at present and inferred for the past these have retained a constant structure of lower circumpolar deep water upper circumpolar deep water north pacific deep water antarctic intermediate water with no apparent changes in the depths of water mass boundaries between glacial and interglacial states sortable silt particle size data for four cores are also examined to show that the vigour of the inflow to the pacific while variable appears to have remained fairly constant on average among the lowest last glacial maximum values of benthic 13c in the world ocean 1 03 based on cibicidoides wullerstorfi occurs here at 2200 m comparable values occur in the atlantic sector of the southern ocean while those from the rest of the pacific are distinctly higher confirming that the southern ocean was the source for the unventilated nutrient enriched water seen here oxygen and carbon isotopic data are compatible with a glacial cold deep water mass of high salinity but lower nutrient content or better ventilated below 3500 m depth this contrasts with the south atlantic where unventilated nutrient enriched water extends all the way to the sea bed comparison with previous studies also suggests that the deeper reaches of the antarctic circumpolar current below 3500 m are not homogeneous all around the southern ocean with the kerguelen plateau and or the macquarie balleny ridges posing barriers to the eastward spread of the deepest low 13c water out of the south atlantic in glacials these barriers combined with inferred high density of bottom waters restricted inter basin exchange and allow three glacial domains dominated by bottom waters from weddell sea adelie coast and ross sea to be defined we suggest that the ross sea was the main source of the deep water entering the pacific below 3500 m

search for a glacial age 14c depleted ocean reservoir 1 measurements of the radiocarbon age difference between mixed benthic foraminifera and several coexisting planktic entities were made in hopes of finding evidence for the existence of an isolated glacial age abyssal ocean reservoir whose demise would explain the large drops in the 14 c to c ratio in atmosphere and surface ocean carbon which occurred during the period of deglaciation forty six new radiocarbon results were obtained at seven depths covering the full range of glacial time i e 27 to 15 14 c kyrs from an equatorial pacific sediment core at 4 4 km water depth even though age reversals for foraminifera but not for coccoliths at two of the eight depths and large age differences between g sacculifer and three submixed layer planktic species mar this data set there remains little likelihood that such a reservoir existed

deep water mass geometry in the glacial atlantic ocean a review of constraints from the paleonutrient proxy cd ca 1 paleonutrient proxies currently provide the strongest constraints on the past spatial distribution of deep water masses we review the state of knowledge derived from the trace metal proxy cd ca for the atlantic ocean during the last glacial maximum lgm we compile published benthic foraminiferal cd ca data supplemented with new data to reconstruct meridional cd sections through the holocene and lgm atlantic holocene cd ca reflects the modern water masses north atlantic deep water nadw antarctic bottom water aabw and antarctic intermediate water aaiw reasonably well except for anomalously high values in the intermediate to mid depth far north atlantic lgm cd ca clearly shows that nadw was replaced by the shallower glacial north atlantic intermediate water gnaiw with significant northward expansion of aabw the boundary level between gnaiw and aabw was very abrupt occurring between 2200 and 2500 m modern water depth combined cd ca and cibicidoides d 13 c data allow us to also calculate the air sea signature of d 13 c d 13 cas the lgm atlantic can be explained entirely by mixing between high d 13 cas gnaiwand low d 13 cas aabw negative d 13 cas values in glacial aabw were likely caused by poor ventilation during formation probably associated with extensive sea ice coverage overall our knowledge base would benefit from improved data coverage in the south atlantic and southern ocean and a better understanding of ancillary effects on the cd ca proxy itself

the release of 14 c depleted carbon from the deep ocean during the last deglaciation evidence from the arabian sea article i nfo during the last deglaciation the concentration of co2 in the atmosphere increased and the radiocarbon activity 14 c of the atmosphere declined in two steps corresponding in timing to heinrich stadial 1 and the younger dryas these changes have been attributed to the redistribution of 14 c depleted carbon from the deep ocean into the upper ocean and atmosphere recently reconstructions of 14 c in intermediate waters of the eastern tropical pacific have revealed pulses of very old water during the deglaciation consistent with the release of 14 c depleted carbon from the deep ocean at this time here we present reconstructions of intermediate water 14 c from the northern arabian sea near the coast of oman these reconstructions record significant aging of intermediate waters in the arabian sea during heinrich stadial 1 and to a lesser extent during the younger dryas the timing and magnitude of 14 c depletion in the arabian sea during heinrich stadial 1 is very similar to that previously observed in the eastern north pacific near baja california indicating that similar mechanisms were involved in controlling 14 c at these two sites the most parsimonious explanation of the 14 c records from the arabian sea and baja california remains the release of 14 c depleted carbon from the deep ocean by renewal of upwelling and mixing in the southern ocean these

changes in the carbon cycle during the last deglaciation as indicated by the comparison of 10be and 14c records the variations in atmospheric radiocarbon c 14 concentration during the last 50 000 years can be attributed to changes in the c 14 production rate due to changes in solar activity the geomagnetic field and or interstellar galactic cosmic ray flux and to changes in the global carbon cycle the relative contributions of these processes is the subject of current debate although the discrepancies between the various reconstructions of the past atmospheric radiocarbon concentration increase with age the relatively good agreement over the last 25 000 years allows a quantitative discussion of the causes of the observed c 14 variations for this period using be 10 measurements from greenland summit ice cores we show that in addition to solar and geomagnetically induced production rate changes significant changes in the carbon cycle have to be considered to explain the measured c 14 concentrations there is evidence that these changes are connected to 1 global deglaciation and 2 climate changes in the north atlantic region on centennial to millennial time scales related to changes in the ocean circulation differences between be 10 and geomagnetic field records however suggest that uncertainties of about 20 still exist in determinations of past changes in the c 14 production rate c 2004 elsevier b v all rights reserved less

the origin of thermal waters from the eastern flank of the dead sea rift valley western jordan thermal waters emerging along the eastern flank of the northernmost part of the dead sea rift valley close to the yarmuk river are dilute ca so4 hco3 and na cl water types with measured temperatures of 35 60 c and estimated teperatures according to silica solubility of 60 110 c they are fed only by present day recharged meteoric waters wadi hasa al himma and north shuna thermal baths and by meteoric waters contaminated with saline waters el ma in thermal bath although they have been known for a long time there is still dispute about their origins and the source of heat on the basis of new chemical and isotopic analyses the saline waters could represent residual pockets of groundwater in equilibrium with those filling the dead sea depression before the last retreat of lake lisan at 17 15 kyr bp or with the ancient seawaters of the sedom lagoon in the early pleistocene in both cases unaffected by significant evaporation processes but chemically and isotopically modified by water rock interaction

glacial to interglacial changes in surface nitrate utilization in the indian sector of the southern ocean as recorded by sediment δ15n we present a new approach for paleoceanographic reconstruction of surface nutrient utilization in the southern ocean it has been observed in the contemporary ocean that due to preferential uptake of 14no3 during photosynthesis the 15n of planktonic organic matter increases with increasing nitrate depletion in surface waters our results demonstrate that the 15n signal produced in surface waters is reflected in the underlying surface sediments core top 15n is inversely correlated with surface nitrate concentration along a transect across the subtropical convergence and the polar front in the southeast indian ocean these results are consistent with a four box model showing that the nitrogen isotopic composition of sinking organic matter depends on percent nitrate utilization in the euphotic zone by comparing the 15n of surface sediments with that measured in the glacial sections of several cores we infer changes in the intensity and latitudinal distribution of nitrate uptake in this region during the last glacial maximum these preliminary results argue against increased biological uptake of nutrients in southern polar waters as a major mechanism for glacial lowering of atmospheric co2 they also suggest that subantarctic waters in the se indian sector became more nutrient depleted as they migrated northward increased nitrate depletion might have also occurred slightly south of the glacial polar front we use a six box model to explore the possible impact of this observation on atmospheric co2

alternating influence of northern versus southern sourced water masses on the equatorial pacific subthermocline during the past 240 ka the eastern equatorial pacific eep is a key area to understand past oceanic processes that control atmospheric co2 concentrations many studies argue for higher nutrient concentrations by enhanced nutrient transfer via southern ocean intermediate water soiw to the low latitude pacific during glacials recent studies however argue against soiw as the primary nutrient source at least during early marine isotope stage 2 mis 2 as proxy data indicate that nutrients are better utilized in the southern ocean under glacial conditions new results from the subarctic pacific suggest that enhanced convection of nutrient rich glacial north pacific intermediate water gnpiw contributes to changes in nutrient concentrations in equatorial subthermocline water masses during mis 2 however the interplay between soiw versus gnpiw and its influence on the nutrient distribution in the eep spanning more than one glacial cycle are still not understood we present a carbon isotope 13c record of subthermocline waters derived from deep dwelling planktonic foraminifera globorotaloides hexagonus in the eep which is compared with published 13c records around the pacific results indicate enhanced influence of gnpiw during mis 6 and mis 2 compared to today with largest contributions of northern sourced intermediate waters during glacial maxima these observations suggest a mechanistic link between relative contributions of northern and southern intermediate waters and past eep nutrient concentrations a switch from increased gnpiw decreased soiw to diminished gnpiw enhanced soiw influence on equatorial subthermocline waters is recognized during glacial terminations and marks changes to modern like conditions in nutrient concentrations and biological productivity in the eep

near constancy of the pacific ocean surface to mid depth radiocarbon age difference over the last 20 kyr although 13c to 12c and cadmium to calcium ratios provide information regarding the distribution of deep water masses during late glacial time and during the period of deglaciation our knowledge of the rate at which these water masses were ventilated comes mainly from the difference in radiocarbon age between coexisting bottom and surface dwelling foraminifera paired benthic planktonic foraminiferal radiocarbon age differences covering last 20 kyr in a high deposition rate western equatorial pacific core md01 2386 from a water depth of 2 8 km show no significant climate related variations over this period this result is surprising for we would have expected a change in this age difference between the last glacial maximum lgm and the holocene and also during the mystery interval 17 5 14 5 kyr ago when the waters in a radiocarbon depleted abyssal reservoir were presumably being mixed back into the remainder of the ocean

pacific atlantic circumpolar deep water coupling during the last 500 ka investigating the interbasin deepwater exchange between the pacific and atlantic oceans over glacial interglacial climate cycles is important for understanding circum antarctic southern ocean circulation changes and their impact on the global meridional overturning circulation we use benthic foraminiferal 13c records from the southern east pacific rise to characterize the 13c composition of circumpolar deep water in the south pacific prior to its transit through the drake passage into the south atlantic a comparison with published south atlantic deepwater records from the northern cape basin suggests a continuous water mass exchange throughout the past 500 ka almost identical glacial interglacial 13c variations imply a common deepwater evolution in both basins suggesting persistent circumpolar deep water exchange and homogenization by contrast deeper abyssal waters occupying the more southern cape basin and the southernmost south atlantic have lower 13c values during most but not all stadial periods we conclude that these values represent the influence of a more southern water mass perhaps antarctic bottom water aabw during many interglacials and some glacial periods the gradient between circumpolar deep water and the deeper southern cape basin bottom water disappears suggesting either no presence of aabw or indistinguishable 13c values of both water masses

holocene oceanographic and glacial changes recorded in maxwell bay west antarctica abstract three holocene core sections from maxwell bay south shetland islands west antarctica are investigated using ms grain size toc foraminifera 18o and 13c 14c and 210pb in order to examine holocene oceanographic glacial and climatic changes in the region they come from 190 221 and 333 m water depths and the bay margin proximal locations complementing earlier studies from the deep central part the three records vary between locations and reflect combined marine and terrigenous influence from the open ocean and surrounding islands respectively the longest and best dated composite section comes from the inner part of the bay core jtc jpc 17 and extends back to 6 3 cal kyr bp close to the termination of the holocene climatic optimum a combination of dating problems and mixed foraminiferal assemblages prevented reliable interpretation of core jpc 15 from the outer part of the bay core jpc 16 collected from the inner bay near the inlet between king george and nelson islands revealed repeated highs in planktonic neogloboquadrina pachyderma occurrence during last 3000 yr these highs are interpreted as indicating periods of decreased meltwater flow into the bay and thus greater influence of open marine surface waters core jtc jpc 17 located closest to king george island and the collins ice cap records increased glacial conditions at 2000 cal yr bp this event is recorded by turbidite deposition at core site jpc 16 major components of the benthic foraminiferal assemblage indicate decreasing tolerance to near glacier or near shore conditions however local climate variability appears to have overall little impact on benthic foraminiferal biota thus it is unlikely that in similar settings recent warming would be strongly manifest as changes in benthic foraminiferal communities stable isotopic analysis is based on cassidulinoides parkerianus and globocassidulina biora subtle decrease in 18o at 3500 cal yr bp followed by episodic increases at 1000 cal yr bp and in the youngest part of the record appear to correlate with the period prior to the beginning of the neoglacial with medieval warm period and with post little ice age warming respectively the latest event is also marked by a significant increase in sediment accumulation rate in the second half of the 20th century

carbon dioxide effects of antarctic stratification north atlantic intermediate water formation and subantarctic nutrient drawdown during the last ice age diagnosis and synthesis in a geochemical box model in a box model synthesis of southern ocean and north atlantic mechanisms for lowering co2 during ice ages the co2 changes are parsed into their component geochemical causes including the soft tissue pump the carbonate pump and whole ocean alkalinity when the mechanisms are applied together their interactions greatly modify the net co2 change combining the antarctic mechanisms stratification nutrient drawdown and sea ice cover within bounds set by observations decreases co2 by no more than 36 ppm a drawdown that could be caused by any one of these mechanisms in isolation however these antarctic changes reverse the co2 effect of the observed ice age shoaling of north atlantic overturning in isolation the shoaling raises co2 by 16 ppm but alongside the antarctic changes it lowers co2 by an additional 13 ppm a 29 ppm synergy the total co2 decrease does not reach 80 ppm partly because antarctic stratification antarctic sea ice cover and the shoaling of north atlantic overturning all strengthen the sequestration of alkalinity in the deepest ocean which increases co2 both by itself and by decreasing whole ocean alkalinity increased nutrient consumption in the sub antarctic causes as much as an additional 35 ppm co2 decrease interacting minimally with the other changes with its inclusion the lowest ice age co2 levels are within reach these findings may bear on the two stepped co2 decrease of the last ice age

radiocarbon age anomaly at intermediate water depth in the pacific ocean during the last deglaciation 1 benthic and planktonic 14c ages are presented for the last glacial termination from marine sediment core vm21 30 from 617 m in the eastern equatorial pacific the benthic planktonic 14c age differences in the core increased to more than 6000 years between heinrich 1 time and the end of the younger dryas period several replicated 14c ages on different benthic and planktonic species from the same samples within the deglacial section of the core indicate a minimal amount of bioturbation scanning electron microscopy reveals no evidence of calcite alteration or contamination the oxygen isotope stratigraphy of planktonic and benthic foraminifera does not indicate anomalously old glacial age values and there is no evidence of a large negative stable carbon isotope excursion in benthic foraminifera that would indicate input of old carbon from dissociated methane it appears therefore that the benthic 14c excursion in this core is not an artifact of diagenesis bioturbation or a pulse of methane a benthic 14c stratigraphy reconstructed from the 14c ages from the deglacial section of vm21 30 appears to match that of baja margin core mv99 mc19 gc31 pc08 705 m but the magnitude of the low 14c excursion is much larger in the vm21 30 record this would seem to imply that the vm21 30 core was closer to the source of 14c depleted waters during the deglaciation but the source of this co2 remains elusive

impacts of climate change on the subduction of mode and intermediate water masses in the southern ocean abstract changes in the temperature salinity and subduction of subantarctic mode water samw and antarctic intermediate water aaiw between the 1950s and 2090s are diagnosed using the csiro mark version 3 5 mk3 5 climate system model caps under a co2 forcing that reaches 860 ppm by the year 2100 these southern ocean upper limb water masses ventilate the ocean interior and changes in their properties have been related to climate change in numerous studies over time the authors follow the low potential vorticity and salinity minimum layers describing samw and aaiw and find that the water column in the 2090s shifts to lighter densities by approximately 0 2 kg m 3 the model projects a reduction in the samw and aaiw annual mean subduction rates as a result of a combination of a shallower mixed layer increased potential vorticity at the base of the mixed layer and a net buoyancy gain there is little change in the projected total volume of samw transported into the ocean interior via the subduction

chloride hydrochemical and isotope methods of groundwater recharge estimation in eastern mediterranean areas a case study in jordan jordan is classified as an arid to semi arid country with a population according to 1999 estimates of 4 8 millions inhabitants and a growth rate of 3 4 efficient use of jordan s scarce water is becoming increasingly important as the urban population grows this study was carried out within the framework of the joint european research project groundwater recharge in the eastern mediterranean and describes a combined methodology for groundwater recharge estimation in jordan the chloride method as well as isotopic and hydrochemical approaches recharge estimations using the chloride method range from 14 mm year 1 mean annual precipitation of 500 mm for a shallow and stony soil to values of 3 7 mm year 1 for a thick desert soil mean annual precipitation of 100 mm and values of well below 1 mm year 1 for thick alluvial deposits mean annual rainfall of 250 mm isotopically most of the groundwater in the hammad basin east jordan falls below the global meteoric water line and far away from the mediterranean meteoric water line suggesting that the waters are ancient and were recharged in a climate different than mediterranean tritium levels in the groundwater of the hammad basin are less than the detection limit 1 3 tu however three samples in east hammad where the aquifer is unconfined present tritium values between 1 and 4 tu copyright 2007 john wiley sons ltd

deep south atlantic carbonate chemistry and increased interocean deep water exchange during last deglaciation abstract carbon release from the deep ocean at glacial terminations is a critical component of past climate change but the underlying mechanisms remain poorly understood we present a 28 000 year high resolution record of carbonate ion concentration a key parameter of the global carbon cycle at 5 km water depth in the south atlantic we observe similar carbonate ion concentrations between the last glacial maximum and the late holocene despite elevated concentrations in the glacial surface ocean this strongly supports the importance of respiratory carbon accumulation in a stratified deep ocean for atmospheric co 2 reduction during the last ice age after 9 mol kg decline during heinrich stadial 1 deep south atlantic carbonate ion concentration rose by 24 mol kg from the onset of bolling to pre boreal likely caused by strengthening north atlantic deep water formation bolling or increased ventilation in the southern ocean younger drays or both pre boreal the 15 mol kg decline in deep water carbonate ion since 10 ka is consistent with extraction of alkalinity from seawater by deep sea caco 3 compensation and coral reef growth on continental shelves during the holocene between 16 600 and 15 000 years ago deep south atlantic carbonate ion values converged with those at 3 4 km water depth in the western equatorial pacific as did carbon isotope and radiocarbon values these observations suggest a period of enhanced lateral exchange of carbon between the deep south atlantic and pacific oceans probably due to an increased transfer of momentum from southern westerlies to the southern ocean by spreading carbon rich deep pacific waters around antarctica for upwelling invigorated interocean deep water exchange would lead to more efficient co 2 degassing from the southern ocean and thus to an atmospheric co 2 rise during the early deglaciation

shortcomings of the isolated abyssal reservoir model for deglacial radiocarbon changes in the mid depth indo pacific ocean severely negative 14c anomalies from the mid depth pacific and the arabian sea have been taken as support for the hypothesized deglacial release of a previously isolated extremely 14c deplete deep ocean carbon reservoir we report box model simulations that cast doubt on both the existence of the hypothesized deep reservoir and its ability to explain the mid depth 14c anomalies first the degree of ice age isolation needed to substantially reduce the deep 14c of the deep reservoir causes anoxia and the trapping of alkalinity from caco3 dissolution the latter increasing atmospheric co2 second even with a completely 14c free deep reservoir achieving the mid depth 14c anomalies of observed duration requires ad hoc stifling of aspects of deep circulation to prevent rapid dissipation of the anomalous 14c free carbon to the rest of the ocean and the atmosphere we suggest that the mid depth anomalies do not record basin scale 14c changes but are instead local phenomena

marine radiocarbon evidence for the mechanism of deglacial atmospheric co2 rise we reconstructed the radiocarbon activity of intermediate waters in the eastern north pacific over the past 38 000 years radiocarbon activity paralleled that of the atmosphere except during deglaciation when intermediate water values fell by more than 300 per mil such a large decrease requires a deglacial injection of very old waters from a deep ocean carbon reservoir that was previously well isolated from the atmosphere the timing of intermediate water radiocarbon depletion closely matches that of atmospheric carbon dioxide rise and effectively traces the redistribution of carbon from the deep ocean to the atmosphere during deglaciation

oceanographic variability on the west antarctic peninsula during the holocene and the influence of upper circumpolar deep water recent intensification of wind driven upwelling of warm upper circumpolar deep water ucdw has been linked to accelerated melting of west antarctic ice shelves and glaciers to better assess the long term relationship between ucdw upwelling and the stability of the west antarctic ice sheet we present a multi proxy reconstruction of surface and bottom water conditions in marguerite bay west antarctic peninsula wap through the holocene a combination of sedimentological diatom and foraminiferal records are for the first time presented together to infer a decline in ucdw influence within marguerite bay through the early to mid holocene and the dominance of cyclic forcing in the late holocene extensive glacial melt limited sea ice and enhanced primary productivity between 9 7 and 7 0 ka bp is considered to be most consistent with persistent incursions of ucdw through marguerite trough from 7 0 ka bp sea ice seasons increased and productivity decreased suggesting that ucdw influence within marguerite bay waned coincident with the equatorward migration of the southern hemisphere westerly winds sww ucdw influence continued through the mid holocene and by 4 2 ka bp lengthy sea ice seasons persisted within marguerite bay intermittent melting and reforming of this sea ice within the late holocene may be indicative of episodic incursions of ucdw into marguerite bay during this period the cyclical changes in the oceanography within marguerite bay during the late holocene is consistent with enhanced sensitively to enso forcing as opposed to the sww forcing that appears to have dominated the early to mid holocene current measurements of the oceanography of the wap continental shelf suggest that the system has now returned to the early holocene like oceanographic configuration reported here which in both cases has been associated with rapid deglaciation

subarctic pacific evidence for a glacial deepening of the oceanic respired carbon pool abstract measurements of benthic foraminiferal cadmium calcium cd ca have indicated that the glacial interglacial change in deep north pacific phosphate po4 concentration was minimal which has been taken by some workers as a sign that the biological pump did not store more carbon in the deep glacial ocean here we present sedimentary redox sensitive trace metal records from ocean drilling program odp site 882 nw subarctic pacific water depth 3244 m to make inferences about changes in deep north pacific oxygenation and thus respired carbon storage over the past 150 000 yr these observations are complemented with biogenic barium and opal measurements as indicators for past organic carbon export to separate the influences of deep water oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment our results suggest that the deep subarctic pacific water mass was depleted in oxygen during glacial maxima though it was not anoxic we reconcile our results with the existing benthic foraminiferal cd ca by invoking a decrease in the fraction of the deep ocean nutrient inventory that was preformed rather than remineralized this change would have corresponded to an increase in the deep pacific storage of respired carbon which would have lowered atmospheric carbon dioxide co2 by sequestering co2 away from the atmosphere and by increasing ocean alkalinity through a transient dissolution event in the deep sea the magnitude of change in preformed nutrients suggested by the north pacific data would have accounted for a majority of the observed decrease in glacial atmospheric pco2

calibration of the carbon isotope composition δ13c of benthic foraminifera the carbon isotope composition 13c of seawater provides valuable insight on ocean circulation air sea exchange the biological pump and the global carbon cycle and is reflected by the 13c of foraminifera tests here more than 1700 13c observations of the benthic foraminifera genus cibicides from late holocene sediments 13ccibnat are compiled and compared with newly updated estimates of the natural preindustrial water column 13c of dissolved inorganic carbon 13cdicnat as part of the international ocean circulation and carbon cycling oc3 project using selection criteria based on the spatial distance between samples we find high correlation between 13ccibnat and 13cdicnat confirming earlier work regression analyses indicate significant carbonate ion 2 6 0 4 10 3 mol kg 1 co32 and pressure 4 9 1 7 10 5 m 1 depth effects which we use to propose a new global calibration for predicting 13cdicnat from 13ccibnat this calibration is shown to remove some systematic regional biases and decrease errors compared with the one to one relationship 13cdicnat 13ccibnat however these effects and the error reductions are relatively small which suggests that most conclusions from previous studies using a one to one relationship remain robust the remaining standard error of the regression is generally 0 25 with larger values found in the southeast atlantic and antarctic 0 4 and for species other than cibicides wuellerstorfi discussion of species effects and possible sources of the remaining errors may aid future attempts to improve the use of the benthic 13c record

the influence of air and sea exchange on the carbon isotope distribution in the sea we explore here the influence of the temperature dependence of isotope fractionation between atmospheric co2and ocean co2 on the distribution of carbon isotopes in the ocean this is accomplished by an analysis of departures from the expected redfield tie between po4 and 13c we find that for the surface ocean the temperature influence largely compensates for the biologic influence in the deep ocean the temperature influence imprinted at the sites of deepwater formation reduces somewhat the biologically induced difference between the carbon isotope ratios for deep waters produced in the northern atlantic and in the antarctic these same features are reproduced in the hamburg ocean model in order to assess the impact of changes in the ratio of ocean mixing rate to wind speed we have made a model run in which co2 exchange rates between air and sea were everywhere doubled as expected the influence of the thermodynamic effect on the oceanic carbon isotope distribution is magnified

relating estimates of caco3 production export and dissolution in the water column to measurements of caco3 rain into sediment traps and dissolution on the sea floor a revised global carbonate budget 1 the global caco3 budget is constrained by new estimates of standing stocks fluxes through the water column and dissolution in the water column and on the sea floor previous estimates of carbonate production and export are indistinguishable within a large range of values 0 4 1 8 gt pic yr 1 globally excess alkalinity ta and water mass tracers indicate dissolution of 1 0 gt pic yr 1 between 200 and 1500 m suggesting production and export must at least equal this amount most water column dissolution occurs at high latitudes and alkalinity fluxes from outer shelf and upper slope sediments 100 1500 m only support 5 10 of the ta inventory below 2000 m the sinking flux of pic 0 6 gt pic yr 1 is consistent with the rate of sea floor dissolution 0 4 gt pic yr 1 plus burial 0 1 gt pic yr 1 this rain rate constrains the export value to 1 6 gt pic yr 1 satellite based estimates of standing stocks of caco3 indicate a decrease equatorward which is opposite in trend to sediment trap fluxes this observation may be explained by an equatorward decrease in sinking particle dissolution systematic changes in pic residence time with latitude or satellite retrieval problems globally averaged euphotic zone standing stock 5 4 mmol m 2 and export estimates indicate pic residence times of 5 18 days

glacial deep water geometry south atlantic benthic foraminiferal cd ca and δ13c evidence a depth transect of cores from 1268 to 3909 m water depth in the western south atlantic are ideally situated to monitor the interocean exchange of deep water and variations in the relative strength of northern and southern sources of deep water production benthic foraminiferal cd ca and 13c data suggest that glacial north atlantic intermediate water gnaiw extended at least as far south as 28 s in the western south atlantic the core of nutrient depleted water was situated at 1500 m above and below water masses with higher nutrient concentrations when examined in conjunction with published paired cd ca and 13c from intermediate depth cores from other basins it appears that the extent of gnaiw influence on the intermediate waters of the world s oceans was less than suggested previously differentiating among possible pathways for the glacial deep ocean 3 km requires a better understanding of the controls on cd ca and 13c values of benthic foraminifera

late neogene history of deepwater ventilation in the southern ocean we compiled carbon isotope records from the north atlantic south atlantic and pacific oceans to estimate changes in vertical and interbasinal 13c gradients for the last 9 myr benthic 13c values of deep water in the south atlantic decreased in a series of steps at 7 2 75 and 1 55 ma away from the north atlantic and toward the pacific the benthic 13c of intermediate water in the south atlantic evolved differently from deep waters resulting in an increase in the intermediate to deep 13c gradient 13cid the 13cid increased in steps at 2 75 and 1 55 ma marking the development and intensification of a chemical divide in the atlantic ocean between well ventilated intermediate water and poorly ventilated deep water we suggest these changes in interbasinal and vertical gradients resulted from decreasing northern component water and reduced ventilation of southern component water scw the latter was caused by several interrelated processes in antarctic sources areas including increased sea ice cover enhanced surface water stratification decreased ekman induced upwelling and reduced vertical mixing across the thermocline because antarctic surface water processes and deepwater ventilation rates ultimately influence atmospheric co2 concentration these processes may have acted as a positive feedback that contributed to the major cooling steps in late neogene climate

the role of deep ocean circulation in setting glacial climates the glacial cycles of the pleistocene involve changes in the circulation of the deep ocean in important ways this review seeks to establish what were the robust patterns of deep sea water mass changes and how they might have influenced important parts of the last glacial cycle after a brief review of how tracers in the modern ocean can be used to understand the distribution of water masses i examine the data for biogeochemical circulation rate and conservative tracers during glacial climates some of the robust results from the literature of the last 30 years include a shoaled version of northern source deep water in the atlantic expanded southern source water in the abyss and deep ocean salt rather than heat stratification of the last glacial maximum lgm deep sea and several lines of evidence for slower overturning circulation in the southern deep cell we combine these observations into a new idea for how the ocean atmosphere system moves from interglacial to glacial periods across a single cycle by virtue of its influence on the melting of land based ice around antarctica cooling north atlantic deep water nadw leads to a cold and salty version of antarctic bottom water aabw this previously underappreciated feedback can lead to a more stratified deep ocean that operates as a more effective carbon trap than the modern helping to lower atmospheric co 2 and providing a mechanism for the deep ocean to synchronize the hemispheres in a positive feedback that drives the system to further cooling

vertical structure of the venus cloud top from the vera and virtis observations onboard venus express abstract we investigate the venus cloud top structure by joint analysis of the data from visual and thermal infrared imaging spectrometer virtis and the atmospheric temperature sounding by the radio science experiment vera onboard venus express the cloud top altitude and aerosol scale height are derived by fitting virtis spectra at 4 5 m with temperature profiles taken from the vera radio occultation our study shows gradual descent of the cloud top from 67 2 1 9 km in low latitudes to 62 8 4 1 km at the pole and decrease of the aerosol scale height from 3 8 1 6 km to 1 7 2 4 km these changes correlate with the mesospheric temperature field in the cold collar and high latitudes the cloud top position remarkably coincides with the sharp minima in temperature inversions suggesting importance of radiative cooling in their maintenance this behaviour is consistent with the earlier observations spectral trend of the cloud top altitude derived from a comparison with the earlier observations in 1 6 27 m wavelength range is qualitatively consistent with sulphuric acid composition of the upper cloud and suggests that particle size increases from equator to pole

cadmium and delta13c paleochemical ocean distributions during the stage 2 glacial maximum changes in heat and salt transport by ocean currents have been implicated in ice age climate cycles weyl 1 968 newell 1 974 broecker et al 1 990b in addition to the direct physical effects of the ocean on climate the ocean carbon system controls atmospheric co2 and the co2 fluctuations documented in ice core bubbles barnola et a1 1 987 neftel et a1 1 988 are thought to be a significant factor in climate oscillations hansen et al 1 984 dramatic changes in oceanic circulation patterns and carbon system chemistry have occurred during the late quaternary glacial interglacial global climate cycles boyle keigwin 1 982 curry lohmann 1 983 shackleton pisias 1 984 boyle keigwin 1 987 duplessy et al 1 988 curry et al 1 988 broecker et al i 990a these changes in the ocean system may be significant driving forces in the progression of ice age co2 cycles toggweiler sarmiento 1 985 ennever mcelroy 1 985 wenk siegenthaler 1 985 boyle 1 988a b broecker peng 1 990 the oceanic distributions of c513c cd and other carbon system linked properties are controlled by the interaction between biological uptake and decomposition with the general circulation of the ocean because records of past oceanic cd and c5 1 3c are preserved in shells of planktonic and benthic foraminifera

a 190 drop in atmosphere s δ14c during the mystery interval 17 5 to 14 5 kyr reconstructions of atmospheric 14c for the deglacial period reveal a 190 10 drop between 17 5 and 14 5 kyr before present during the mystery interval while it appears that the major contributor must be the mixing between an isolated low radiocarbon abyssal reservoir and the remainder of the ocean a combination of 14c measurements on coexisting benthic and planktic foraminifera shells and 13c 12c measurements on benthic foraminifera make it difficult to identify a sufficiently large volume for this reservoir an alternative scenario based on higher 14c production rates between about 38 and 18 kyr ago would escape the need for a large isolated reservoir prior to the mystery interval but instead would call for a better ventilated ocean afterwards the addition of 14c deficient sedimentary carbon appears not to be an important contributor while the unlikely explanation that the half life of 14c is 15 greater than the accepted value 5730 yr would eliminate the steady decrease in the 14c c over the last 40 kyr it would not explain the steep drop which occurred between 17 5 and 14 5 kyr

reduced ventilation and enhanced magnitude of the deep pacific carbon pool during the last glacial period it has been proposed that the ventilation of the deep pacific carbon pool was not significantly reduced during the last glacial period posing a problem for canonical theories of glacial interglacial co2 change however using radiocarbon dates of marine tephra deposited off new zealand we show that deep 2000 m 2000 m and shallow sub surface ocean atmosphere 14c age offsets i e reservoir or ventilation ages in the southwest pacific increased by 1089 and 337 yrs respectively reaching 2689 and 1037 yrs during the late glacial a comparison with other radiocarbon data from the southern high latitudes suggests that broadly similar changes were experienced right across the southern ocean if like today the southern ocean was the main source of water to the glacial ocean interior these observations would imply a significant change in the global radiocarbon inventory during the last glacial period possibly equivalent to an increase in the average radiocarbon age 2 km 2 km of 700 yrs 700 yrs simple mass balance arguments and numerical model sensitivity tests suggest that such a change in the ocean s mean radiocarbon age would have had a major impact on the marine carbon inventory and atmospheric co2 possibly accounting for nearly half of the glacial interglacial co2 change if confirmed these findings would underline the special role of high latitude shallow sub surface mixing and air sea gas exchange in regulating atmospheric co2 during the late pleistocene

the δ13c in benthic foraminiferal tests of fontbotia wuellerstorfi schwager relative to the δ13c of dissolved inorganic carbon in southern ocean deep water implications for glacial ocean circulation models on a transect between 20 and 70 s in the eastern atlantic ocean and weddell sea water samples from 19 hydrographic stations and bottom water from 55 surface sediment samples taken with a multiple corer were investigated for the stable carbon isotopic composition of the total dissolved inorganic carbon 13c co2 these measurements were compared to 13c values determined on live specimens of the benthic foraminifer fontbotia wuellerstorfi and closely related genera from the same stations in addition at 16 stations the stable carbon isotope composition of sedimentary organic carbon was measured general deepwater and bottom water mass circulation patterns as inferred from the 13c co2 are in close agreement with those known from other nonconservative tracers very low 13c values of upper circumpolar deep water 0 3 pee dee belemnite pdb in the polar front region and the eastern limb of the weddell gyre coincide with nutrient maxima however a significant decoupling of the dissolved phosphate signal from the 13c co2 signal is indicated in the abyssal weddell sea we attribute this to temperature dependent fractionation processes during gas exchange of surface waters with the atmosphere at sites of bottom water formation multiple corer water from the sediment water interface is slightly 13c depleted relative to deepwater and bottom water 13 co2 the surface sediment organic carbon 13c is 3 to 4 lower south of the polar front than north of it and the 13corg in freshly accumulated phytodetritus is 3 to 4 lower than surface sediment organic carbon 13c comparison of live f wuellerstorfi 13c and related genera with bottom water 13c co2 exhibits at most stations between the subtropical front 41 s and the southern boundary of the antarctic circumpolar current 55 s a significant lowering of foraminiferal 13c values compilation of a mean last glacial interglacial 13c amplitude 13c from six published southern ocean cores results in a shift of 0 99 0 13 pdb this shift is greater than that in all other regions however all of these cores are from positions close to recent oceanic fronts thus for these peripheral areas of the southern ocean we suggest about half of the glacial interglacial shift can be explained by varying frontal zone positions and widths accompanied by a change in mode and height of export production

testing the impact of seasonal phytodetritus deposition on δ13c of epibenthic foraminifer cibicidoides wuellerstorfi a 31 000 year high resolution record from the northwest african continental slope 1 studies of temporal changes of ocean circulation and deepwater ventilation often rely on 13c records of epibenthic foraminifer cibicidoides wuellerstorfi however primary productivity related overprints may distort the signal and simulate a chemical age of ambient water mass that is too old and simulates poorly ventilated ambient bottom waters to further constrain the use of c wuellerstorfi 13c records from high productivity areas we analyzed a 14cams dated gravity core from the upwelling regime off northwest africa at 12 n we compare this new record with 37 radiocarbon dated 13c records from the eastern atlantic ocean between 45 n and 25 s that are bathed by the same water mass only during heinrich events 1 and 2 when the investigated core site off northwest africa experienced year round sustained deposition of organic matter the 13c values at this site faithfully record deepwater ventilation states during times of predominantly seasonal deposition of fresh phytodetritus however 13c values were significantly lower than at the reference sites this underscores that reconstruction of paleocirculation and deep ocean ventilation using c wuellerstorfi 13c from regions that experienced seasonal phytodetritus deposition needs to be validated by additional proxies that are not affected by local productivity

decoupling of δ13cσco 2 and phosphate in recent weddell sea deep and bottom water implications for glacial southern ocean paleoceanography

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

global deep sea burial rate of calcium carbonate during the last glacial maximum global databases concentrations rates in holocene and last glacial of calcium carbonate and mass accumulation maximum sediments were used to estimate the deep sea sedimentary calcium carbonate burial rate during these two time intervals sparse calcite mass accumulation rate data were extrapolated across regions of varying calcium carbonate concentration using a gridded map of calcium carbonate concentrations and the assumption that accumulation of noncarbonate material is uncorrelated with calcite concentration within some geographical region mean noncarbonate accumulation rates were estimated within each of nine regions determined by the distribution and nature of the accumulation rate data for core top sediments data coverage 67 of the high calcite the regions of reasonable encompass 75 sediments globally and within these regions we estimate an accumulation rate of 55 9 3 6x1011 mol yr 1 the same regions cover 48 of glacial high caco3 sediments the smaller fraction is due to a shift of calcite deposition to the poorly sampled south pacific and total 44 1 6 0x1011 mol yr 1 projecting to 100 coverage south and total 44 1 6 0x1011 both estimates yields accumulation estimates of 8 3x1012 mol yr 1 today and 9 2x1012 mol yr 1 during glacial time this is little better than a guess given the incomplete data coverage but it suggests that glacial deep sea calcite burial rate was probably not considerably faster than today in spite of a presumed decreasein shallow water burial during glacial time

ventilation of the deep southern ocean and deglacial co2 rise past glacial interglacial increases in the concentration of atmospheric carbon dioxide co2 are thought to arise from the rapid release of co2 sequestered in the deep sea primarily via the southern ocean here we present radiocarbon evidence from the atlantic sector of the southern ocean that strongly supports this hypothesis we show that during the last glacial period deep water circulating around antarctica was more than two times older than today relative to the atmosphere during deglaciation the dissipation of this old and presumably co2 enriched deep water played an important role in the pulsed rise of atmospheric co2 through its variable influence on the upwelling branch of the antarctic overturning circulation

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

carbon isotope offsets between benthic foraminifer species of the genus cibicides cibicidoides in the glacial sub antarctic atlantic epibenthic foraminifer 13c measurements are valuable for reconstructing past bottom water dissolved inorganic carbon 13c 13cdic which are used to infer global ocean circulation patterns epibenthic 13c however may also reflect the influence of 13c depleted phytodetritus microhabitat changes and or variations in carbonate ion concentrations here we compare the 13c of two benthic foraminifer species cibicides kullenbergi and cibicides wuellerstorfi and their morphotypes in three sub antarctic atlantic sediment cores over several glacial interglacial transitions these species are commonly assumed to be epibenthic living above or directly below the sediment water interface while this might be consistent with the small 13c offset that we observe between these species during late pleistocene interglacial periods 13c 0 19 0 31 n 63 it is more difficult to reconcile with the significant 13c offset that is found between these species during glacial periods 13c 0 76 0 44 n 44 we test possible scenarios by analysing uvigerina spp 13c and benthic foraminifer abundances 1 c kullenbergi 13c is biased to light values either due to microhabitat shifts or phytodetritus effects and 2 c wuellerstorfi 13c is biased to heavy values relative to long term average conditions for instance by recording the sporadic occurrence of less depleted deep water 13cdic neither of these scenarios can be ruled out unequivocally however our findings emphasize that supposedly epibenthic foraminifer 13c in the sub antarctic atlantic may reflect several factors rather than being a sole function of bottom water 13cdic which directly bear on the interpretation of extremely light south atlantic 13c values at the last glacial maximum

glacial water mass structure and rapid δ18o and δ13c changes during the last glacial termination in the southwest pacific abstract changes in ocean circulation are thought to have contributed to lowering glacial atmospheric co 2 levels by enhancing deep ocean sequestration of carbon that was returned to the atmosphere during glacial terminations high resolution benthic foraminiferal 13 c and 18 o records from a depth transect of cores in the southwest pacific ocean presented here provide evidence that both wind and thermohaline driven circulation drove co 2 from the ocean during the last deglaciation shallow geochemical stratification in the glacial southern ocean was followed by a short pulse of rapid 13 c enrichment to intermediate water depths during heinrich stadial 1 indicative of better ventilated intermediate waters co occurring with documented wind driven upwelling in the southern ocean intermediate depth 13 c enrichment paused at the start of the antarctic cold reversal 14 7 ka implying a brief shallow restratification while deeper layers were progressively flushed of 13 c depleted and 18 o enriched waters likely caused by the increasing influence of deep waters sourced from the north atlantic the coincidence of atmospheric co 2 increases with these geochemical shifts in both shallow and deep cores suggests that shifts in both atmospheric and oceanic circulation contributed to the deglacial rise of co 2