on the relationship between southern ocean overturning and acc transport the eddy field in the southern ocean offsets the impact of strengthening winds on the meridional overturning circulation and antarctic circumpolar current acc transport there is widespread belief that the sensitivities of the overturning and acc transport are dynamically linked with limitation of the acc transport response implying limitation of the overturning response here an idealized numerical model is employed to investigate the response of the large scale circulation in the southern ocean to wind stress perturbations at eddy permitting to eddy resolving scales significant differences are observed between the sensitivities and the resolution dependence of the overturning and acc transport indicating that they are controlled by distinct dynamical mechanisms the modeled overturning is significantly more sensitive to change than the acc transport with the possible implication that the southern ocean overturning may increase in response to future wind stress changes without measurable changes in the acc transport it is hypothesized that the dynamical distinction between the zonal and meridional transport sensitivities is derived from the depth dependence of the extent of cancellation between the ekman and eddy induced transports

an analytical model of the response of the meridional overturning circulation to changes in wind and buoyancy forcing abstractan analytical model of the full depth ocean stratification and meridional overturning circulation for an idealized atlantic basin with a circumpolar channel is presented the model explicitly describes the ocean response to both southern ocean winds and the global pattern and strength of prescribed surface buoyancy fluxes the construction of three layers defined by the two isopycnals of overturning extrema allows the description of circulation and stratification in both the upper and abyssal ocean the system is fully solved in the adiabatic limit to yield scales for the surface layer thickness buoyancies of each layer and overturning magnitudes the analytical model also allows scaling of the antarctic circumpolar current acc transport the veracity of the three layer framework and derived scales is confirmed by applying the analytical model to an idealized geometry eddy permitting ocean general circulation model consistent with previous results the abyssal overturning is found to scale

residual mean solutions for the antarctic circumpolar current and its associated overturning circulation abstract residual mean theory is applied to the streamwise averaged antarctic circumpolar current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated residual meridional overturning circulation

contribution of topographically generated submesoscale turbulence to southern ocean overturning the ocean s global overturning circulation regulates the transport and storage of heat carbon and nutrients upwelling across the southern ocean s antarctic circumpolar current and into the mixed layer coupled to water mass modification by surface buoyancy forcing has been highlighted as a key process in the closure of the overturning circulation here using twelve high resolution hydrographic sections in southern drake passage collected with autonomous ocean gliders we show that circumpolar deep water originating from the north atlantic known as lower circumpolar deep water intersects sloping topography in narrow and strong boundary currents observations of strong lateral buoyancy gradients enhanced bottom turbulence thick bottom mixed layers and modified water masses are consistent with growing evidence that topographically generated submesoscale flows over continental slopes enhance near bottom mixing and that cross density upwelling occurs preferentially over sloping topography interactions between narrow frontal currents and topography occur elsewhere along the path of the antarctic circumpolar current which leads us to propose that such interactions contribute significantly to the closure of the overturning in the southern ocean

the missing silica sink revisiting the marine sedimentary si cycle using cosmogenic 32si burial of biogenic silica bsitotal in high sedimentation rate continental margins remains highly uncertain cosmogenic 32si t1 2 140 years can be used to trace the fates of bsitotal postdeposition including as opal bsiopal and diagenetically altered opal bsialtered the latter dominantly authigenic clay bsiclay to determine the magnitude and form of bsitotal storage in coastal sediments conventional operational leaches targeting bsiopal and bsialtered including bsiclay were modified for large scale samples necessary for measurement of 32si the 32si activity was used to estimate total biogenic silica burial bsitotal bsiopal bsialtered in several depositional settings gulf of papua gulf of mexico long island sound and in the previously studied amazon guianas deltaic system in subtropical and temperate regions 32si was detected in both traditional biogenic silica leaches bsiopal and residual authigenic clays traditional bsiopal and modified operational leaches designed to target the most reactive authigenic silicates bsialtered consistently underestimate authigenic clay formation bsiclay and thus the magnitude of bsitotal burial in temperate coastal zones and subtropical deltas by 2 4 fold in tropical deltas 32si activities in the residual fraction after removal of bsiopal demonstrate rapid and almost complete alteration of initial bsiopal to new forms most likely bsiclay globally 4 5 4 9 tmol yr si may be trapped in marine nearshore deposits as rapidly formed clay bsiclay 100 of the missing silica sink in the marine silica budget

abyssal circulation driven by near boundary mixing water mass transformations and interior stratification the emerging view of the abyssal circulation is that it is associated with bottom enhanced mixing which results in downwelling in the stratified ocean interior and upwelling in a bottom boundary layer along the insulating and sloping seafloor in the limit of slowly varying vertical stratification and topography however boundary layer theory predicts that these upslope and downslope flows largely compensate such that net water mass transformations along the slope are vanishingly small using a planetary geostrophic circulation model that resolves both the boundary layer dynamics and the large scale overturning in an idealized basin with bottom enhanced mixing along a midocean ridge we show that vertical variations in stratification become sufficiently large at equilibrium to reduce the degree of compensation along the midocean ridge flanks the resulting large net transformations are similar to estimates for the abyssal ocean and span the vertical extent of the ridge these results suggest that boundary flows generated by mixing play a crucial role in setting the global ocean stratification and overturning circulation requiring a revision of abyssal ocean theories

biogenic silica dissolution in sediments of the southern ocean i solubility abstract a stirred flow through reactor technique was used to determine silica solubilities in sediments collected with a multicorer in the indian sector of the southern ocean antares i cruise the results show that the apparent silica solubility in the cores may decrease increase or remain constant with depth the silica solubility profiles are best explained by the early diagenetic interactions between biogenic silica and soluble aluminum derived from detrital material by combining the solubility data with measured dissolved silica profiles it is shown that the variable asymptotic pore water silica levels in the cores cannot be explained solely by differences in silica solubility in sediments that experience a significant detrital input the simultaneous reprecipitation of dissolved aluminum and dissolved silica prevents water silicic acid from reaching saturation with the dissolving biogenic silica the principal oceanographic control on pore water silica build up in the cores studied is the ratio of the deposition fluxes of biogenic silica and detrital material solubility differences inherited from the biomineralization process in the surface waters do not appear to have a significant effect on the observed pore water silica levels

acc meanders energy transfer and mixed barotropic baroclinic instability along stream variations in the dynamics of the antarctic circumpolar current acc impact heat and tracer transport regulate interbasin exchange and influence closure of the overturning circulation topography is primarily responsible for generating deviations from zonal mean properties mainly through standing meanders associated with regions of high eddy kinetic energy here an idealized channel model is used to explore the spatial distribution of energy exchange and its relationship to eddy geometry as characterized by both eddy momentum and eddy buoyancy fluxes variations in energy exchange properties occur not only between standing meander and quasi zonal jet regions but throughout the meander itself both barotropic and baroclinic stability properties as well as the magnitude of energy exchange terms undergo abrupt changes along the path of the acc these transitions are captured by diagnosing eddy fluxes of energy and by adopting the eddy geometry framework the latter typically applied to barotropic stability properties is applied here in the depth along stream plane to include information about both barotropic and baroclinic stability properties of the flow these simulations reveal that eddy momentum fluxes and thus barotropic instability play a leading role in the energy budget within a standing meander this result suggests that baroclinic instability alone cannot capture the dynamics of acc standing meanders a challenge for models where eddy fluxes are parameterized

global ocean meridional overturning abstract a decade mean global ocean circulation is estimated using inverse techniques incorporating air sea fluxes of heat and freshwater recent hydrographic sections and direct current measurements this information is used to determine mass heat freshwater and other chemical transports and to constrain boundary currents and dense overflows the 18 boxes defined by these sections are divided into 45 isopycnal neutral density layers diapycnal transfers within the boxes are allowed representing advective fluxes and mixing processes air sea fluxes at the surface produce transfers between outcropping layers the model obtains a global overturning circulation consistent with the various observations revealing two global scale meridional circulation cells an upper cell with sinking in the arctic and subarctic regions and upwelling in the southern ocean and a lower cell with sinking around the antarctic continent and abyssal upwelling mainly below the crests of the major bathymetric ridges

on the importance of surface forcing in conceptual models of the deep ocean in the major ocean basins diapycnal mixing upwells dense antarctic bottom water which returns southward and closes the deepest cell of the meridional overturning circulation moc this cell ventilates the deep ocean and regulates the partitioning of co2 between the atmosphere and the ocean the oceanographic community s conceptual understanding of the deep stratification and moc has evolved from classic abyssal recipes arguments to a more recent appreciation of along isopycnal upwelling in the southern ocean consistent with a weakly mixed ocean interior both the deep stratification and the deep moc are shown here to be sensitive to the form of the surface buoyancy forcing in a two dimensional model that includes a circumpolar channel and northern basin for a fixed surface buoyancy condition the deep stratification is essentially prescribed whereas for a fixed surface buoyancy flux the deep stratification varies by orders of magnitude over the range of diapycnal diffusivity observed in the ocean these cases also produce different scalings for the deep moc with in both weak and strong regimes in addition these scalings are shown to be sensitive not only to the type of surface boundary condition but also to the latitudinal structure of the surface fluxes this latter point is crucial as buoyancy budgets and dynamical features of the circulation are poorly constrained along the antarctic margins this study emphasizes the need for caution in the interpretation of simple conceptual models that while useful may not include all mechanisms that contribute to the moc s strength and structure

eddy saturation of equilibrated circumpolar currents abstractthis study uses a sector configuration of an ocean general circulation model to examine the sensitivity of circumpolar transport and meridional overturning to changes in southern ocean wind stress and global diapycnal mixing at eddy permitting and finer resolution the sensitivity of circumpolar transport to forcing magnitude is drastically reduced at sufficiently high resolution there is little or no sensitivity of circumpolar transport to wind stress even in the limit of no wind in contrast the meridional overturning circulation continues to vary with southern ocean wind stress but with reduced sensitivity in the limit of high wind stress both the circumpolar transport and meridional overturning continue to vary with diapycnal diffusivity at all model resolutions the circumpolar transport becomes less sensitive to changes in diapycnal diffusivity at higher resolution although sensitivity always remains in contrast the overturning circulation is more sensitive to change in diapycnal

southern ocean overturning compensation in an eddy resolving climate simulation the southern ocean s antarctic circumpolar current acc and meridional overturning circulation moc response to increasing zonal wind stress is for the first time analyzed in a high resolution 0 1 ocean and 0 25 atmosphere fully coupled global climate simulation using the community earth system model results from a 20 yr wind perturbation experiment where the southern hemisphere zonal wind stress is increased by 50 south of 30 s show only marginal changes in the mean acc transport through drake passage an increase of 6 136 144 sverdrups sv 1 sv 10 6 m 3 s 1 in the perturbation experiment compared with the control however the upper and lower circulation cells of the moc do change the lower cell is more affected than the upper cell with a maximum increase of 64 versus 39 respectively changes in the moc are directly linked to changes in water mass transformation from shifting surface isopycnals and sea ice melt giving rise to changes in surface buoyancy forcing the increase in transport of the lower cell leads to upwelling of warm and salty circumpolar deep water and subsequent melting of sea ice surrounding antarctica the moc is commonly supposed to be the sum of two opposing components a wind and transient eddy overturning cell here the transient eddy overturning is virtually unchanged and consistent with a large scale cancellation of localized regions of both enhancement and suppression of eddy kinetic energy along the mean path of the acc however decomposing the time mean overturning into a time and zonal mean component and a standing eddy component reveals partial compensation between wind driven and standing eddy components of the circulation

transformation of silicon in a sandy beach ecosystem insights from stable silicon isotopes from fresh and saline groundwaters abstract dissolved silicon isotope compositions 30si have been analysed for the first time in groundwaters of beach sediments which represent a subterranean estuary with fresh groundwater discharge from a freshwater reservoir and mixing with recirculated seawater the fresh groundwater reservoir has high and variable dissolved silica concentrations between 136 and 736 m but homogeneous 30si of 1 0 0 15 by contrast the seawater is strongly depleted in dissolved silica with concentrations of 3 m and consequently characterised by high 30si of 3 0 the beach groundwaters are variably enriched in dissolved silica compared to seawater 23 192 m and concentrations increase with depth at all sampling sites the corresponding 30si values are highly variable 0 3 to 2 2 and decrease with depth at each site all groundwater 30si values are lower than seawater and most values are lower than dissolved 30si of freshwater discharge indicating a significant amount of lithogenic silica dissolution in beach sediments in contrast to open north sea sediments diatom dissolution or formation of authigenic silica in beach sediments is very low ca 5 mol si g 1 silica discharge from the beach to the coastal ocean is estimated as approximately 210 mol si yr 1 per meter shoreline considering the extent of coastline this is at least for the study area a significant amount of the total si budget and amounts to ca 1 of river and 3 5 of backbarrier tidal flat area si input

what sets the strength of the middepth stratification and overturning circulation in eddying ocean models abstract the processes maintaining stratification in the oceanic middepth between approximately 1000 and 3000 m are explored using an eddy resolving general circulation model composed of a two hemisphere semienclosed basin with a zonal reentrant channel in the southernmost eighth of the domain the middepth region lies below the wind driven main thermocline but above the diffusively driven abyssal ocean here it is argued that middepth stratification is determined primarily in the model s antarctic circumpolar current competition between mean and eddy overturning in the channel leads to steeper isotherms and thus deeper stratification throughout the basin than would exist without the channel isotherms that outcrop only in the channel are nearly horizontal in the semienclosed portion of the domain whereas isotherms that also outcrop in the northern hemisphere deviate from horizontal and are accompanied by geostrophically balanced meridional transport a northern source of deep water water with temp

the dependence of southern ocean meridional overturning on wind stress an eddy resolving numerical model of a zonal flow meant to resemble the antarctic circumpolar current is described andanalyzedusing the framework of j marshallandt radko in additionto windand buoyancy forcing at the surface the model contains a sponge layer at the northern boundary that permits a residual meridional overturning circulation moc to exist at depth the strength of the residual moc is diagnosed for different strengths of surface wind stress it is found that the eddy circulation largely compensates for the changes in ekman circulation the extent of the compensation and thus the sensitivity of the moc to the winds depend on the surface boundary condition a fixed heat flux surface boundary severely limits the ability of the moc to change an interactive heat flux leads to greater sensitivity to explain the moc sensitivity to the wind strength under the interactive heat flux transformed eulerian mean theory is applied in which the eddy diffusivity plays a central role in determining the eddy response a scaling theory for the eddy diffusivity based on the mechanical energy balance is developed and tested the average magnitude of the diffusivity is found to be proportional to the square root of the wind stress the moc sensitivity to the winds based on this scaling is compared with the true sensitivity diagnosed from the experiments

the continental si cycle and its impact on the ocean si isotope budget abstract the silicon isotope composition of biogenic silica 30sibsi in the ocean is a function of the 30si of the available dissolved si dsi h2sio4 the degree of utilisation of the available dsi and for some organisms the concentration of dsi this makes 30sibsi in sediment archives a promising proxy for past dsi concentrations and utilisation at steady state mean 30sibsi must equal a weighted average of the inputs the majority of which are of continental origin variation in the functioning of the continental si cycle on timescales similar to the residence time of dsi in the ocean 10 ka may therefore contribute to downcore variability in 30sibsi on millennial or longer timescales the direction and magnitude of change in published 30sibsi records over the last few glacial cycles is consistent among ocean basins and between groups of silicifiers they document glacial values that are typically 0 5 to 1 0 lower than interglacial values and together hint at coherent and predictable glacial interglacial variability in whole ocean 30si driven by a change in mean 30si of the inputs in this contribution we review the modern inputs of dsi to the ocean and the controls on their isotopic composition and assess the evidence for their variability on millennial plus timescales today 9 55 1012 mol yr 1 dsi enters the ocean of which roughly 64 and 25 are direct riverine inputs of dsi and dsi from dissolution of aeolian and riverborne sediment respectively the remainder derives from alteration or weathering of the ocean crust each input has a characteristic 30si with our current best estimate for a weighted mean being 0 74 although much work remains to be done to characterise the individual fluxes many aspects of the continental si cycle may have differed during glacial periods that together can cumulatively substantially lower the mean 30si of dsi entering the ocean these changes relate to i a cooler drier glacial climate ii lowered sea level and the exposure of continental shelves iii the presence of large continental ice sheets and iv altered vegetation zonation using a simple box model with a monte carlo approach to parameterisation we find that a transition from a hypothesised glacial continental si cycle to the modern si cycle can drive an increase in whole ocean 30si of comparable rate and magnitude to that recorded in 30sibsi this implies that we may need to revisit our understanding of aspects of the si cycle in the glacial ocean although we focus on the transition from the last glacial our synthesis suggests that the continental si cycle should be seen as a potential contributory factor to any variability observed in ocean 30sibsi on millennial or longer timescales

jets and topography jet transitions and the impact on transport in the antarctic circumpolar current the southern ocean s antarctic circumpolar current acc naturally lends itself to interpretations using a zonally averaged framework yet navigation around steep and complicated bathymetric obstacles suggests that local dynamics may be far removed from those described by zonally symmetric models in this study both observational and numerical results indicate that zonal asymmetries in the form of topography impact global flow structure and transport properties the conclusions are based on a suite of more than 1 5 million virtual drifter trajectories advected using a satellite altimetry derived surface velocity field spanning 17 years the focus is on sites of cross front transport as defined by movement across selected sea surface height contours that correspond to jets along most of the acc cross front exchange is localized in the lee of bathymetric features with more than 75 of crossing events occurring in regions corresponding to only 20 of the acc s zonal extent these observations motivate a series of numerical experiments using a two layer quasigeostrophic model with simple zonally asymmetric topography which often produces transitions in the front structure along the channel significantly regimes occur where the equilibrated number of coherent jets is a function of longitude and transport barriers are not periodic jet reorganization is carried out by eddy flux divergences acting to both accelerate and decelerate the mean flow of the jets eddy kinetic energy is amplified downstream of topography due to increased baroclinicity related to topographic steering the combination of high eddy kinetic energy and recirculation features enhances particle exchange these results stress the complications in developing consistent circumpolar definitions of the acc fronts

antarctic sea ice control on the depth of north atlantic deep water abstractchanges in deep ocean circulation and stratification have been argued to contribute to climatic shifts between glacial and interglacial climates by affecting the atmospheric carbon dioxide

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

antarctic sea ice control on ocean circulation in present and glacial climates in the modern climate the ocean below 2 km is mainly filled by waters sinking into the abyss around antarctica and in the north atlantic paleoproxies indicate that waters of north atlantic origin were instead absent below 2 km at the last glacial maximum resulting in an expansion of the volume occupied by antarctic origin waters in this study we show that this rearrangement of deep water masses is dynamically linked to the expansion of summer sea ice around antarctica a simple theory further suggests that these deep waters only came to the surface under sea ice which insulated them from atmospheric forcing and were weakly mixed with overlying waters thus being able to store carbon for long times this unappreciated link between the expansion of sea ice and the appearance of a voluminous and insulated water mass may help quantify the ocean s role in regulating atmospheric carbon dioxide on glacial interglacial timescales previous studies pointed to many independent changes in ocean physics to account for the observed swings in atmospheric carbon dioxide here it is shown that many of these changes are dynamically linked and therefore must co occur

geomorphology of the oceans abstract we present the first digital seafloor geomorphic features map gsfm of the global ocean the gsfm includes 131 192 separate polygons in 29 geomorphic feature categories used here to assess differences between passive and active continental margins as well as between 8 major ocean regions the arctic indian north atlantic north pacific south atlantic south pacific and the southern oceans and the mediterranean and black seas the gsfm provides quantitative assessments of differences between passive and active margins continental shelf width of passive margins 88 km is nearly three times that of active margins 31 km the average width of active slopes 36 km is less than the average width of passive margin slopes 46 km active margin slopes contain an area of 3 4 million km2 where the gradient exceeds 5 compared with 1 3 million km2 on passive margin slopes the continental rise covers 27 million km2 adjacent to passive margins and less than 2 3 million km2 adjacent to active margins examples of specific applications of the gsfm are presented to show that 1 larger rift valley segments are generally associated with slow spreading rates and smaller rift valley segments are associated with fast spreading 2 polar submarine canyons are twice the average size of non polar canyons and abyssal polar regions exhibit lower seafloor roughness than non polar regions expressed as spatially extensive fan rise and abyssal plain sediment deposits all of which are attributed here to the effects of continental glaciations and 3 recognition of seamounts as a separate category of feature from ridges results in a lower estimate of seamount number compared with estimates of previous workers

the accumulation and cycling of biogenic silica in the southern ocean revisiting the marine silica budget abstract in many of the recent marine silica budgets e g science 268 1995 375 a majority of the world s biogenic silica accumulation is attributed to the siliceous ooze deposits in the antarctic deep sea based on 230 th normalized sediment accumulation rates as well as comparative studies of silica preservation seabed accumulation compared to surface biogenic production the rate of biogenic silica accumulation in antarctic siliceous ooze deposits has been over estimated by as much as 35 the current estimate for silica accumulation in these high latitude deposits is 3 1 10 12 mol yr 1 as compared to previous values of 4 1 4 8 10 12 mol yr 1 to maintain balance between silicate supply and biogenic silica removal in the oceans an additional repository is needed evidence from continental shelf and upper slope sediments suggests that biogenic silica accumulation in continental margin deposits may account for a much larger fraction of the marine silica burial than previously thought compensating for the diminished accumulation in the antarctic deep sea if biogenic silica accumulation in continental margin sediments replaces nearly a third of the silica accumulation in the antarctic deep sea the marine cycles of organic matter and biogenic silica are coupled to a greater extent than reported in previous budgets

control of lower limb overturning circulation in the southern ocean by diapycnal mixing and mesoscale eddy transfer a simple model is developed of the lower limb of the meridional overturning circulation in the southern ocean based on residual mean theory it is hypothesized that the strength of the lower limb overturning is strongly controlled by the magnitude of abyssal diapycnal mixing and that of mesoscale eddy transfer k in particular it is argued that k the scaling and associated theory find support in a suite of sensitivity experiments with an idealized ocean general circulation model this study shows that intense diapycnal mixing is required to close the buoyancy budget of the lower limb overturning circulation in contrast to the upper limb where air sea buoyancy fluxes can provide the required diabatic forcing

a toy model for the response of the residual overturning circulation to surface warming abstracta simple model for the deep ocean overturning circulation is presented and applied to study the ocean s response to a sudden surface warming the model combines one dimensional predictive r

the diabatic deacon cell abstract southern ocean air sea fluxes from the coads dataset are examined for compatibility between buoyancy gain and northward ekman transport an analysis in density classes points to an upwelling of upper circumpolar deep water and subsequent buoyancy gain from air sea exchange as water flows northward in the ekman layer the upper circumpolar deep water layer is too shallow to admit southward geostrophic flow along topography and an eddy mass flux mechanism for southward transport in this layer to replenish the upwelling is advanced based on observed large scale potential vorticity gradients estimates of the strength and vertical structure of the meridional flow are given using repeated hydrographic sections and a new climatology

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

control of bering strait transport by the meridional overturning circulation author s cessi paola abstract abstractit is well established that the mean transport through bering strait is balanced by a sea level difference between the north pacific and the arctic ocean but no mechanism has been proposed to explain this sea level difference it is argued that the sea level difference across bering strait which geostrophically balances the northward throughflow is associated with the sea level difference between the north pacific and the north atlantic arctic in turn the latter difference is caused by deeper middepth isopycnals in the indo pacific than in the atlantic especially in the northern high latitudes because there is deep water formation in the atlantic but not in the pacific because the depth of the middepth isopycnals is associated with the dynamics of the upper branch of the meridional overturning circulation moc a model is formulated that quantitatively relates the sea level difference between the north pacific and the arctic north atlantic with the wind stress in the antarctic circumpolar region since this forcing powers the moc and with the outcropping isopycnals shared between the northern hemisphere and the antarctic circumpolar region since this controls the location of deep water formation this implies that if the sinking associated with the moc were to occur in the north pacific rather than the north atlantic then the bering strait flow would reverse these predictions formalized in a theoretical box model are confirmed by a series of numerical experiments in a simplified geometry of the world ocean forced by steady surface wind stress temperature and freshwater flux

overturning circulation pathways in a two basin ocean model abstracta toy model for the deep ocean overturning circulation in multiple basins is presented and applied to study the role of buoyancy forcing and basin geometry in the ocean s global overturning

the glacial mid depth radiocarbon bulge and its implications for the overturning circulation published reconstructions of radiocarbon in the atlantic sector of the southern ocean indicate that there is a mid depth maximum in radiocarbon age during the last glacial maximum lgm this is in contrast to the modern ocean where intense mixing between water masses results in a relatively homogenous radiocarbon profile ferrari et al 2014 suggested that the extended antarctic sea ice cover during the lgm necessitated a shallower boundary between the upper and lower branches of the meridional overturning circulation this shoaled boundary lay above major topographic features associated with strong diapycnal mixing isolating dense southern sourced water in the lower branch of the overturning circulation this isolation would have allowed radiocarbon to decay and thus provides a possible explanation for the mid depth radiocarbon age bulge we test this hypothesis using an idealized 2 d residual mean dynamical model of the global overturning circulation concentration distributions of a decaying tracer that is advected by the simulated overturning are compared to published radiocarbon data we find that a 600 km 5 of latitude increase in sea ice extent shoals the boundary between the upper and lower branches of the overturning circulation at 45 s by 600 m and shoals the depth of north atlantic deep water convection at 50 n by 2500 m this change in circulation configuration alone decreases the radiocarbon content in the mid depth south atlantic at 45 s by 40 even without an increase in surface radiocarbon age in the source region of deep waters during the lgm

a decay function model for the integrity loss of rock when subjected to recurrent cycles of freezing thawing and heating cooling rocks are used in engineering works as monument or building stone and as architectural covering stone as a result they can be subjected to recurrent cycles of freezing and thawing and will be subjected to heating and cooling they loose some of their integrity under these cyclic temperature variations and the more frequent and severe these cycles the higher the integrity loss however the rates of progressive disintegration is not the same for different rock types or even within rock types this paper presents a mathematical model describing the integrity loss process when a rock is subjected to such recurrent cycles the model postulates a first order process and provides meaningful parameters for the integrity characteristic of rocks the validity of the model has been established by an experimental laboratory study carried out on 10 different rock types

role of mesoscale eddies in cross frontal transport of heat and biogeochemical tracers in the southern ocean abstractthis study examines the role of processes transporting tracers across the polar front pf in the depth interval between the surface and major topographic sills which this study refers to as the pf core a preindustrial control simulation of an eddying climate model coupled to a biogeochemical model gfdl climate model version 2 6 cm2 6 simplified version of the biogeochemistry with light iron nutrients and gas minibling 0 1 ocean model is used to investigate the transport of heat carbon oxygen and phosphate across the pf core with a particular focus on the role of mesoscale eddies the authors find that the total transport across the pf core results from a ubiquitous ekman transport that drives the upwelled tracers to the north and a localized opposing eddy transport that induces tracer leakages to the south at major topographic obstacles in the ekman layer the southward eddy transport only partially compensates the northward ekman transport while below the ekman layer the sout

interbasin transport of the meridional overturning circulation abstractthe meridional overturning circulation moc is studied in an idealized domain with two basins connected by a circumpolar channel in the southernmost region flow is forced at the surface by longitude independent wind stress freshwater flux and fast temperature relaxation to prescribed profiles the only longitudinal asymmetry is that one basin is twice as wide as the other two states a preferred one with sinking in the narrow basin and an asymmetrically forced one with sinking in the wide basin are compared in both cases sinking is compensated by upwelling everywhere else including the passive basin despite the greater area of the wide basin the residual overturning transport is the same regardless of the location of sinking the two basins exchange flow at their southern edge by a geostrophic transport balanced by the difference in the depth of isopycnals at the eastern boundaries of each basin gnanadesikan s model for the upper branch of the moc is extended to include two basins conn

an idealized model of weddell gyre export variability recent observations suggest that the export of antarctic bottom water aabw from the weddell sea has a seasonal cycle in its temperature and salinity that is correlated with annual wind stress variations this variability has been attributed to annual vertical excursions of the isopycnals in the weddell gyre modifying the water properties at the depth of the orkney passage recent studies attribute these variations to locally wind driven barotropic dynamics in the northern weddell sea boundary current this paper explores an alternative mechanism in which the isopycnals respond directly to surface ekman pumping which is coupled to rapidly responding mesoscale eddy buoyancy fluxes near the gyre boundary a conceptual model of the interface that separates weddell sea deep water from circumpolar deep water is described in which the bounding isopycnal responds to a seasonal oscillation in the surface wind stress different parameterizations of the mesoscale eddy diffusivity are tested the model accurately predicts the observed phases of the temperature and salinity variability in relationship to the surface wind stress the model despite its heavy idealization also accounts for more than 50 of the observed oscillation amplitude which depends on the strength of the seasonal wind variability and the parameterized eddy diffusivity these results highlight theimportanceofmesoscaleeddiesinmodulatingtheexportofaabwinnarrowboundarylayersaroundthe antarctic margins

a model of the upper branch of the meridional overturning of the southern ocean a zonal average model of the upper branch of the meridional overturning circulation of the southern ocean is constructed and used to discuss the processes wind buoyancy eddy forcing and boundary conditions that control its strength and sense of circulation the geometry of the thermocline wedge set by the mapping between the vertical spacing of buoyancy surfaces the stratification on the equatorial flank of the antarctic circumpolar current and their outcrop at the sea surface is seen to play a central role by setting the interior large scale potential vorticity distribution it is shown that the action of eddies mixing this potential vorticity field induces a residual flow in the meridional plane much as is observed with upwelling of fluid around antarctica northward surface flow and subduction to form intermediate water

the three dimensional overturning circulation of the southern ocean during the woce era a box inverse model of the southern ocean during the world ocean circulation experiment is constructed to investigate the three dimensional structure of the regional overturning circulation in that era the model has many features in common with various preceding inverse studies but also contains several novel elements that make it well suited for addressing many of the significant uncertainties that surround the circulation at present the net overturning circulation of the southern ocean is found to consist of two well defined cells of similar strength the upper cell consists of a northward transport of 18 8 5 5 sv of surface mode and intermediate waters lighter than the 27 5 kg m 3 isoneutral and an equivalent southward flow in the approximate 27 5 27 9 kg m 3 neutral density range encompassing the bulk of the upper circumpolar deep water the lower cell involves the northward export of 18 6 0 9 sv of antarctic bottom water and lower circumpolar deep water denser than 28 08 kg m 3 and an opposing transport in the lighter classes of that water mass substantial structural differences between the overturning circulations of the atlantic indian and pacific basins are indicated by the model s solution overall the diagnosed southern ocean circulation shares many qualitative and some quantitative features with previous inverse estimates particularly as regards the large scale depth integrated lateral circulation and associated energy fluxes in the subtropics and in the antarctic circumpolar current and the strength of the upper overturning cell however it also suggests several significant adjustments to current views of the regional circulation most notable amongst these are the subpolar circulation of the southern ocean is more vigorous and zonally interconnected than generally thought the associated lower overturning cell is more intense than indicated by most preceding estimates contrary to common perception sub surface mixing processes play a role of comparable importance to air sea ice exchanges of buoyancy in underpinning the dianeutral closure of the southern ocean overturning even at shallow mode and intermediate water levels and the connection between north atlantic deep water formation and southern ocean upwelling is fundamentally three dimensional such that deep waters from the north atlantic must upwell dianeutrally before being returned to the permanent pycnocline of the northern oceans

isopycnal averaging and the residual mean circulation abstract the zonally averaged circulation in the atmosphere or ocean can be misleading if the averaging is performed at constant height in the ocean there is apparently anomalously large diapycnal motion forming the so called deacon cell the atmospheric equivalents are the ferrel cells there are two zonal averaging techniques commonly used to avoid these spurious cells one involves averaging at constant density and this technique has been used in both fluids the other technique which has so far been applied only in the atmosphere involves taking into account perturbation correlation terms to form the residual mean circulation using a taylor series expansion we show that these apparently dissimilar techniques are formally equivalent at leading order in perturbation amplitude the equivalence is demonstrated using output from the fram southern ocean numerical model

the role of thermal stress fatigue in the breakdown of rock in cold regions abstract many geomorphological studies have ignored the role of thermal stress fatigue engineers have long maintained that thermal stress is an effective process physicists and the ceramics industry have provided a theoretical foundation to explain the nature and mode of operation of thermal breakdown recent geomorphological studies have shown the importance of thermal stress in cold regions by means of high frequency rock temperature data which can identify rates of temperature change in excess of 2 c min 1 the occurrence of weathered material in cold but dry regions can be explained by thermal stress shock differential radiation receipts on slopes of varying orientation and gradient can exert a very strong effect

census of seafloor sediments in the world s ocean knowing the patterns of distribution of sediments in the global ocean is critical for understanding biogeochemical cycles and how deep sea deposits respond to environmental change at the sea surface we present the first digital map of seafloor lithologies based on descriptions of nearly 14 500 samples from original cruise reports interpolated using a support vector machine algorithm we show that sediment distribution is more complex with significant deviations from earlier hand drawn maps and that major lithologies occur in drastically different proportions globally by coupling our digital map to oceanographic data sets we find that the global occurrence of biogenic oozes is strongly linked to specific ranges in seasurface parameters in particular by using recent computations of diatom distributions from pigment calibrated chlorophyll a satellite data we show that contrary to a widely held view diatom oozes are not a reliable proxy for surface productivity their global accumulation is instead strongly dependent on low surface temperature 0 9 5 7 c and salinity 33 8 34 0 pss practical salinity scale 1978 and high concentrations of nutrients under these conditions diatom oozes will accumulate on the seafloor regardless of surface productivity as long as there is limited competition from biogenous and detrital components and diatom frustules are not significantly dissolved prior to preservation quantifying the link between the seafloor and the sea surface through the use of large digital data sets will ultimately lead to more robust reconstructions and predictions of climate change and its impact on the ocean environment

connecting antarctic cross slope exchange with southern ocean overturning previous idealized investigations of southern ocean overturning have omitted its connection with the antarctic continental shelves leaving the influence of shelf processes on antarctic bottom water aabw export unconsidered in particular the contribution of mesoscale eddies to setting the stratification and overturning circulation in the antarctic circumpolar current acc is well established yet their role in cross shelf exchange of water masses remains unclear this study proposes a residual mean theory that elucidates the connection between antarctic cross shelf exchange and overturning in the acc and the contribution of mesoscale eddies to the export of aabw the authors motivate and verify this theory using an eddy resolving process model of a sector of the southern ocean the strength and pattern of the simulated overturning circulation strongly resemble those of the real ocean and are closely captured by the residualmean theory over the continental slope baroclinic instability is suppressed and so transport by mesoscale eddies is reduced this suppression of the eddy fluxes also gives rise to the steep v shaped isopycnals that characterize the antarctic slope front in aabw forming regions of the continental shelf furthermore to produce water on the continental shelf that is dense enough to sink to the deep ocean the deep overturning cell must be at least comparable in strength to wind driven mean overturning on the continental slope this results in a strong sensitivity of the deep overturning strength to changes in the polar easterly winds

siliceous deep sea sponge monorhaphis chuni a potential paleoclimate archive in ancient animals abstract the deep sea sponge monorhaphis chuni forms giant basal spicules which can reach lengths of 3 m they represent the largest biogenic silica structures on earth that is formed from an individual metazoan the spicules offer a unique opportunity to record environmental change of past oceanic and climatic conditions a giant spicule collected in the east china sea in a depth of 1110 m was investigated the oxygen isotopic composition and mg ca ratios determined along center to surface segments are used as geochemical proxies for the assessment of seawater paleotemperatures calculations are based on the assumption that the calculated temperature near the surface of the spicule is identical with the average ambient temperature of 4 c a seawater temperature of 1 9 c is inferred for the beginning of the lifespan of the monorhaphis specimen the temperature increases smoothly to 2 3 c to be followed by sharply increased and variable temperatures up to 6 10 c in the outer part of the spicule the inferred seawater temperature is about 4 c the lifespan of the spicule can be estimated to 11 000 3000 years using the long term trend of the inferred temperatures fitted to the seawater temperature age relationships since the last glacial maximum specimens of monorhaphis therefore represents one the oldest living animals on earth the remarkable temperature spikes of the ambient seawater occurring 9500 3100 years b p are explained by discharges of hydrothermal fluids in the neighborhood of the spicule the irregular lamellar organization of the spicule and the elevated mn concentrations during the high temperature growth are consistent with a hydrothermal fluid input

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

a theory of the interhemispheric meridional overturning circulation and associated stratification abstracta quantitative theoretical model of the meridional overturning circulation and associated deep stratification in an interhemispheric single basin ocean with a circumpolar channel is presented the theory includes the effects of wind eddies and diapycnal mixing and predicts the deep stratification and overturning streamfunction in terms of the surface forcing and other parameters of the problem it relies on a matching among three regions the circumpolar channel at high southern latitudes a region of isopycnal outcrop at high northern latitudes and the ocean basin between the theory describes both the middepth and abyssal cells of a circulation representing north atlantic deep water and antarctic bottom water it suggests that although the strength of the middepth overturning cell is primarily set by the wind stress in the circumpolar channel middepth stratification results from a balance between the wind driven upwelling in the channel and deep water formation at high northern latitudes d

sponge skeletons as an important sink of silicon in the global oceans silicon si is a pivotal element in the biogeochemical and ecological functioning of the ocean the marine si cycle is thought to be in internal equilibrium but the recent discovery of si entries through groundwater and glacial melting have increased the known si inputs relative to the outputs in the global oceans known outputs are due to the burying of diatom skeletons or their conversion into authigenic clay by reverse weathering here we show that non phototrophic organisms such as sponges and radiolarians also facilitate significant si burial through their siliceous skeletons microscopic examination and digestion of sediments revealed that most burial occurs through sponge skeletons which being unusually resistant to dissolution had passed unnoticed in the biogeochemical inventories of sediments the preservation of sponge spicules in sediments was 45 2 27 4 but only 6 8 10 1 for radiolarian testa and 8 for diatom frustules sponges lead to a global burial flux of 1 71 1 61 tmolsi yr 1 and only 0 09 0 05 tmolsi yr 1 occurs through radiolarians collectively these two non phototrophically produced silicas increase the si output of the ocean to 12 8 tmolsi yr 1 which accounts for a previously ignored sink that is necessary to adequately assess the global balance of the marine si cycle inclusion of sponge spicules and radiolarians increases the global ocean biological sink of silicon by 28 with 95 of that increase attributed to sponges according to examination of sediments from 17 marine cores

strong export of antarctic bottom water east of the kerguelen plateau deep western boundary currents east of the antarctic peninsula and the kerguelen plateau are important pathways for transporting deep antarctic water masses to the global ocean an array of moored current meters used to quantify the water transport in this system reveals a flow that is stronger than any measured in a deep western boundary current at similar depths so far the primary paths for the transport of antarctic bottom water from the southern ocean into the global ocean are the deep western boundary currents east of the antarctic peninsula and the kerguelen plateau1 previous ship based observations documented distinct water properties and velocities associated with a deep western boundary current in the kerguelen region2 3 4 5 6 7 but the mean flow is as yet unconstrained here we report measurements from a coherent array of eight current meter moorings that reveal a narrow and intense equatorward flow extending throughout the water column just east of the kerguelen plateau velocities averaged over two years exceed 20 cm s 1 at depths of about 3 500 m the strongest mean deep western boundary current flow yet observed at similar depths we estimate the mean equatorward transport of water colder than 0 c at 12 3 1 2 106 m3 s 1 partially compensated by poleward flow we also estimate the net equatorward flow of water colder than 0 2 c at about 8 106 m3 s 1 substantially higher than the 1 9 106 m3 s 1 reported from the boundary current that carries dense water from the weddell sea into the atlantic ocean north of the falkland plateau8 we conclude that the kerguelen deep western boundary current is a significant pathway of the global ocean s deep overturning circulation

semi adiabatic model of the deep stratification and meridional overturning abstractan analytical model of the atlantic deep stratification and meridional overturning circulation is presented that illustrates the dynamic coupling between the southern ocean and the midlatitude gyres the model expressed here in terms of the two and a half layer framework predicts the stratification and meridional transport as a function of the mechanical and thermodynamic forcing at the sea surface the approach is based on the classical elements of large scale circulation theory ideal thermocline inertial western boundary currents and eddy controlled antarctic circumpolar current acc models which are combined to produce a consistent three dimensional view of the global overturning the analytical tractability is achieved by assuming and subsequently verifying that the pattern of circulation in the model is largely controlled by adiabatic processes the time mean and eddy induced isopycnal advection of buoyancy the mean stratification of the lower thermocline is determined by the surface fo

sensitivity of the southern ocean overturning circulation to surface buoyancy forcing 1 the sensitivity of the southern ocean overturning to altered surface buoyancy forcing is investigated in a series of eddy permitting idealised simulations the modelled response indicates that heat and freshwater fluxes in the southern hemisphere mid latitudes may play a significant role in setting the strength of the overturning circulation enhanced buoyancy fluxes act to increase the meridional overturning up to a limit approaching the wind driven ekman transport the sensitivity of the overturning to surface buoyancy forcing is strongly dependent on the relative locations of the wind stress profile buoyancy forcing and upwelling region the numerical simulations provide support for the hypothesis that changes in upwelling during deglaciations may have been driven by changes in heat and freshwater fluxes instead of or in addition to changes in wind stress

equilibration of the antarctic circumpolar current by standing meanders the insensitivity of the antarctic circumpolar current acc s prominent isopycnal slope to changes in wind stress is thought to stem from the action of mesoscale eddies that counterbalance the wind driven ekman overturning a framework verified in zonally symmetric circumpolar flows substantial zonal variations in eddy characteristics suggest that local dynamics may modify this balance along the path of the acc analysis of an eddy resolving ocean gcm shows that the acc can be broken into broad regions of weak eddy activity where surface winds steepen isopycnals and a small number of standing meanders across which the isopycnals relax meanders are coincident with sites of i strong eddy induced modification of the mean flow and its vertical structure as measured by the divergence of the eliassen palm flux and ii enhancement of deep eddy kinetic energy by up to two orders of magnitude over surrounding regions within meanders the vorticity budget shows a balance between the advection of relative vorticity and horizontal divergence providing a mechanism for the generation of strong vertical velocities and rapid changes in stratification temporal fluctuations in these diagnostics are correlated with variability in both the eliassen palm flux and bottom speed implying a link to dissipative processes at the ocean floor at larger scales bottom pressure torque is spatially correlated with the barotropic advection of planetary vorticity which links to variations in meander structure from these results it is proposed that the flexing of standing meanders provides an alternative mechanism for reducing the sensitivity of the acc s baroclinicity to changes in forcing separate from an acc wide change in transient eddy characteristics

lagrangian pathways of upwelling in the southern ocean the spatial and temporal variability of upwelling into the mixed layer in the southern ocean is studied using a 1 10 ocean general circulation model virtual drifters are released in a regularly spaced pattern across the southern ocean at depths of 250 500 and 1000 m during both summer and winter months the drifters are advected along isopycnals for a period of four years unless they outcrop into the mixed layer where lateral advection and a parameterization of vertical mixing is applied the focus of this study is on the discrete exchange between the model mixed layer and the interior localization of interior mixed layer exchange occurs downstream of major topographic features across the indian and pacific basins creating hotspots of outcropping minimal outcropping occurs in the atlantic basin while 59 of drifters outcrop in the pacific sector and in drake passage the region from 140 w to 40 w a disproportionately large amount even when considering the relative basin sizes due to spatial and temporal variations in mixed layer depth the lagrangian trajectories provide a statistical measure of mixed layer residence times for each exchange into the mixed layer the residence time has a rayleigh distribution with a mean of 30 days the cumulative residence time of the drifters is 261 194 days over a period of four years these results suggest that certain oceanic gas concentrations such as co 2 and 14 c will likely not reach equilibrium with the atmosphere before being re subducted

abyssal atlantic circulation during the last glacial maximum constraining the ratio between transport and vertical mixing transport to vertical diffusivity in the deep atlantic our calculations suggest that the ratio was at least twice as large at the lgm we speculate that the primary cause was reduced mixing between northern and southern component waters associated with movement of this water mass boundary away from the zone of intense mixing near the seafloor the shallower water mass boundary yields an order of magnitude increase in the volume of southern component water suggesting its residence time may have increased substantially our analysis supports the idea that an expanded volume of antarctic bottom water and limited vertical mixing enhanced the abyssal ocean s ability to trap carbon during glacial times

the force balance of the southern ocean meridional overturning circulation the southern ocean so limb of the meridional overturning circulation moc is characterized by three vertically stacked cells each with a transport of about 10 sv sv 10 6 m 3 s 1 the buoyancy transport in the so is dominated by the upper and middle moc cells with the middle cell accounting for most of the buoyancy transport across the antarctic circumpolar current a southern ocean state estimate for the years 2005 and 2006 with 1 6 resolution is used to determine the forces balancing this moc diagnosing the zonal momentum budget in density space allows an exact determination of the adiabatic and diapycnal components balancing the thickness weighted residual meridional transport it is found that to lowest order the transport consists of an eddy component a directly wind driven component and a component in balance with mean pressure gradients nonvanishing time mean pressure gradients arise because isopycnal layers intersect topography or the surface in a circumpolar integral leading to a largely geostrophic moc even in the latitude band of drake passage it is the geostrophic water mass transport in the surface layer where isopycnals outcrop that accomplishes the poleward buoyancy transport

a multibasin residual mean model for the global overturning circulation the ocean s overturning circulation is inherently three dimensional yet modern quantitative estimates of the overturning typically represent the subsurface circulation as a two dimensional two cell streamfunction that varies with latitude and depth only this approach suppresses information about zonal mass and tracer transport in this article the authors extend earlier zonally averaged overturning theory to explore the dynamics of a figure eight circulation that cycles through multiple basins a three dimensional residual mean model of the overturning circulation is derived and then simplified to a multibasin isopycnal box model to explore how stratification and diabatic water mass transformations in each basin depend on the basin widths and on deep and bottom water formation in both hemispheres the idealization to multiple two dimensional basins permits zonal mass transport along isopycnals in a southern ocean like channel while retaining the dynamical framework of residual mean theory the model qualitatively reproduces the deeper isopycnal surfaces in the pacific basin relative to the atlantic this supports a transfer of antarctic bottom water from the atlantic sector to the pacific sector via the southern ocean which subsequently upwells in the northern pacific basin a solution for the full isopycnal structure in the southern ocean reproduces observed stratification differences between atlantic and pacific basins and provides a scaling for the diffusive boundary layer in which the zonal mass transport occurs these results are consistent with observational indications that north atlantic deep water is preferentially transformed into antarctic bottom water which undermines the importance of an adiabatic upper overturning cell in the modern ocean

localized subduction of anthropogenic carbon dioxide in the southern hemisphere oceans the southern ocean makes a substantial contribution to the oceanic carbon sink observationally based estimates of carbon subduction suggest that carbon sequestration depends on physical properties such as mixed layer depth ocean currents wind and eddies that are potentially sensitive to climate variability and change

the antarctic circumpolar current in three dimensions a simple theory is developed for the large scale three dimensional structure of the antarctic circumpolar current and the upper cell of its overturning circulation the model is based on a perturbation expansion about the zonal average residual mean model developed previously by marshall and radko the problem is solved using the method of characteristics for idealized patterns of wind and buoyancy forcing constructed from observations the equilibrium solutions found represent a balance between the eulerian meridional overturning eddy induced circulation and downstream advection by the mean flow depth and stratification of the model thermocline increase in the atlantic indian oceans sector where the mean wind stress is large residual circulation in the model is characterized by intensification of the overturning circulation in the atlantic indian sector and reduction in strength in the pacific ocean region predicted three dimensional patterns of stratification and residual circulation in the interior of the acc are compared with observations

surface constraints on the depth of the atlantic meridional overturning circulation southern ocean versus north atlantic abstractpaleoclimate proxy evidence suggests that the atlantic meridional overturning circulation amoc was about 1000 m shallower at the last glacial maximum lgm compared to the present yet it

antarctic bottom water production by intense sea ice formation in the cape darnley polynya antarctic bottom water fills much of the global abyssal ocean and is known to form in three main sites in the southern ocean data from instrumented elephant seals and moorings suggest an additional source of bottom water formation in the cape darnley polynya that is driven by sea ice production

a theory of deep stratification and overturning circulation in the ocean abstract a simple theoretical model of the deep stratification and meridional overturning circulation in an idealized single basin ocean with a circumpolar channel is presented the theory includes the effects of wind eddies and diapycnal mixing predicts the deep stratification in terms of the surface forcing and other problem parameters makes no assumption of zero residual circulation and consistently accounts for the interaction between the circumpolar channel and the rest of the ocean the theory shows that dynamics of the overturning circulation can be characterized by two limiting regimes corresponding to weak and strong diapycnal mixing the transition between the two regimes is described by a nondimensional number characterizing the strength of the diffusion driven compared to the wind driven overturning circulation in the limit of weak diapycnal mixing deep stratification throughout the ocean is produced by the effects of wind and eddies in a circumpolar channel and maintained even in the