southern ocean frontal system changes precede antarctic ice sheet growth during the middle miocene abstract the middle miocene climate approximately 14 ma ago was characterized by the glaciation of antarctica deep ocean cooling and variations in the global carbon cycle although the southern ocean underwent significant oceanographic changes there is limited information on their spatial extent and timing however such knowledge is crucial for understanding the role of the southern ocean and the antarctic circumpolar current acc for antarctic glaciation and the coupling between the ocean and continental climate we have reconstructed surface temperatures and seawater oxygen isotopes at ocean drilling program odp site 1092 in the polar frontal zone of the atlantic sector of the southern ocean from foraminiferal oxygen isotopes 18 o and magnesium to calcium ratios mg ca sea surface cooling by 4 c and freshening indicated by the 1 reduction of seawater 18 o 18 o sw at 14 2 ma precede the major step in antarctic ice sheet growth at 13 8 13 9 ma this pattern qualitatively mirrors previous findings from the pacific sector and we interpret the surface hydrographic changes to reflect the circum antarctic northward shift of the southern ocean fronts and specifically at site 1092 the passage of the subantarctic front the magnitude of change in reconstructed 18 o sw requires a 18 o sw salinity gradient significantly higher than the modern value 0 52 and it possibly exceeded 1 1 this implies the polar frontal zone was influenced by freshwater derived from antarctica which in turn confirms higher than modern continental precipitation the latter has previously been suggested to have contributed to antarctic glaciation

hydrographic biases in global coupled climate models and their relation to the meridional overturning circulation comparison of the volumetric s distribution of models participating in the climate model intercomparison project 3 cmip3 indicates that these models differ widely in their ability to represent the thermohaline properties of water masses relationships between features of the quasi equilibrium hydrographic mean state of these models and aspects of their overturning circulations are investigated this is achieved quantitatively with the help of seven diagnostic hydrographic stations these few stations were specifically selected to provide a minimalist schematic of the global water mass system relationships between hydrographic conditions in the north atlantic measured with a subset of these stations suggest that hydrographic properties in the subpolar north atlantic are set by the circulation field of each model pointing towards deficiencies in the models ability to resolve the gulf stream north atlantic current system as a major limitation since diapycnal mixing and viscosity parameterizations differ across cmip3 models and exert a strong control on the overturning it is likely that these architectural differences ultimately explain the main across model differences in overturning circulation temperature and salinity in the north atlantic the analysis of properties across the quasi equilibrium states of the cmip3 models agrees with previously reported relationships between meridional steric height gradients or horizontal density contrasts at depth and the strength of the deep water cell robust relationships are also found in the southern ocean linking measures of vertical stratification with the strength of the abyssal circulations across the cmip3 models consistent correlations between aspects of the quasi equilibrium hydrography in the southern ocean and the sensitivity of the abyssal cell to increasing radiative forcing by 2100 were found using these relations in conjunction with modern hydrographic observations to interpolate the fate of the abyssal cell suggests that the southern abyssal cell may decrease by roughly 20 by the end of the century similar systematic relationships between the quasi equilibrium hydrographic states of the models and the sensitivity of their atlantic deep water cell could not be found

antarctic intermediate water circulation and variability in a coupled climate model the variability of antarctic intermediate water aaiw in a long term natural integration of a coupled climate model is examined the mean state of the climate model includes a realistic representation of aaiw which appears centered on the su 5 27 2 kg m23 density surface hereinafter s 27 2 both in observations and the model an assessment of ventilation rates on the s 27 2 surface suggests that this particular climate model forms aaiw in a mostly circumpolar fashion with a significant contribution from antarctic surface water this motivates the assessment of oceanic variability along this core aaiw isopycnal surface complex empirical orthogonal function analyses decompose the variability into three dominant modes showing circumpolar patterns of zonal wavenumber 1 2 and 3 on the s 27 2 density surface the modes contain eastward propagating signals at interannual to centennial time scales mechanisms forcing this variability are investigated using heat and salt budget analyses at the wintertime outcrop of the s 27 2 surface such an approach ignores the mechanism of aaiw variability sourced by subantarctic mode water variations which has been examined previously and is for the most part beyond the present study variability in meltwater rates and atmospheric heat and freshwater fluxes are found to dominate the intermediate water variability at the outcrop region in contrast northward ekman transport of heat and salt plays a significant but localized role in aaiw temperature salinity variability there is also an important contribution from the antarctic circumpolar current to the variability at the outcrop region via zonal transport of heat and salt while the magnitude of aaiw natural variability can be large near the outcrop of the salinity minimum layer recent observations of cooling and freshening at depth are suggested to be beyond that of the unperturbed system

importance of wind driven sea ice motion for the formation of antarctic intermediate water in a global climate model an ocean atmosphere sea ice model is used to show the importance of wind driven sea ice motion in the formation of antarctic intermediate water aaiw the model is able to reasonably simulate a tongue of low salinity aaiw even when the direct momentum transfer from wind to the ocean is neglected provided that the wind stress is applied to sea ice in contrast when the wind stress exclusively drives the ocean the model fails to capture the properties of aaiw the growth and subsequent offshore transport of sea ice acts as a freshwater conduit from near shore regions where aabw is formed to subpolar regions where aaiw is formed sea ice dynamics are also shown to be important in the simulation of a local salinity minimum at intermediate depths in the southern indian ocean and a local salinity maximum in the western weddell sea

oxygen minimum zone expansion in the eastern tropical north pacific during deglaciation concentrations lamination preservation and d 15 n values from cores located between 540 750 m water depth in the gulf of tehuantepec southern mexico these results differ from similar proxies found even 5 n of the site where there is evidence for omz changes related to rapid climate change in the northern hemisphere instead omz expansion in the gulf was contemporaneous with changes in sea ice extent and zonal wind shifts around antarctica pointing to subantarctic mode water and antarctic intermediate water as likely sources of oxygen depleted water these observations reinforce the importance of the southern ocean as a primary modulator of northern hemisphere ocean climate as far as 15 n in the etnp citation hendy i l and t f pedersen 2006 oxygen minimum zone expansion in the eastern tropical north pacific during deglaciation geophys res lett 33 l20602 doi 10 1029 2006gl025975

subduction of pacific antarctic intermediate water in an eddy resolving model the subduction process of pacific antarctic intermediate water paaiw in the pacific is investigated using output from an eddy resolving ocean model focus is on contribution of eddies to the subduction process to separate the subduction rate into contributions by eddies and mean flows the temporal residual mean trm velocity is used in the mean subduction rate lateral induction caused by the strong eastward flow of the antarctic circumpolar current acc is dominant the largest rate is located in the drake passage the estimated eddy induced subduction rate is comparable with the mean subduction rate and it tends to cancel the vertical mean component in many regions in the west of the drake passage however the eddy induced subduction is larger than the vertical mean component and this eddy induced subduction was not detected in previous studies using the thickness diffusion parameterization and an eddy permitting model results of idealized sensitivity studies to model resolution suggest that the subduction rate would be larger using a model with higher vertical resolution therefore the vertical resolution should be paid more attention in model studies investigating eddy induced subduction and not just the horizontal resolution

the antarctic dipole and its predictability this study investigates the nature of interan nualvariability ofantarcticseaiceanditsrelationshipwith the tropical climate we nd that the dominant interan nual variance structure in the sea ice edge and surface air temperature elds is organized as a quasi stationary wave which we call the antarctic dipole adp it is charac terized by an out of phase relationship between the ice and temperature anomalies in the central eastern pacic and atlantic sectors of the antarctic the dipole consists of a strong standing mode and a weaker propagating motion within each basin s ice eld it has the same wavelength as the antarctic circumpolar wave acw and dominates the acw variance the dipole is clearly associated with tropical enso events it can be predicted with moderate skill using linear regression involving surface temperature two to four months ahead the prediction performs better in extreme warm cold years and best in la ni na years

climate and antarctic intermediate water coupling during the late holocene little is known about the scale of natural variability of the southern hemisphere upper ocean on decadal to centennial time scales despite its potential importance for influencing regions as distant as the tropical pacific el nino southern oscillation enso or even the north atlantic overturning circulation here we present the first subdecadally sampled reconstruction of variability in the southeast pacific upper intermediate ocean from ca a d 0 1300 using foraminiferal oxygen and carbon isotope records our results reveal large variability in surface ocean physical properties on both decadal and centennial time scales in the southeast pacific as much as 3 c or more in as little as 50 yr on centennial time scales changes in antarctic intermediate water physical properties benthic foraminiferal 18 o covary with those in the surface and are associated with shifts in tropical temperatures thermocline nutrient dynamics and enso suggesting that they are part of a common pacific wide phenomenon our results reveal that natural variability in upper ocean properties is greater than previously appreciated and coherent with changes in the tropical thermocline supporting both theories and models postulating the importance of extratropical tropical teleconnections and the oceanic tunnel in interdecadal to centennial climate variability

multi and quasi decadal variations of sea surface temperature in the north atlantic abstract the multi and quasi decadal variabilities of the sea surface temperature sst anomaly over the north atlantic are investigated by means of two dimensional propagating ceof forty six years of the coads sst dataset from 1947 to 1992 are used after removing the monthly climatology and four year low pass filtering the sst anomaly is submitted to ceof the total variance of the three largest modes accounts for 87 0 of the total variance mode 1 is a very slow oscillation with an approximate 42 yr period and has basinwide spatial evolution with alternate warm and cold anomalies appearing off newfoundland and migrating northward until they disappear south of greenland the center of action of the anomalies both occur in the vicinity of the labrador sea newfoundland and south of greenland where deep water formation takes place mode 2 3 is a quasi decadal fluctuation with an approximate 14 yr period mode 2 3 contains quasi decadal timescales with alternating warm and cold anomalies propagati

the role of oscillating southern hemisphere westerly winds global ocean circulation abstractin the framework of a sea ice ocean general circulation model coupled to an energy balance atmospheric model an intensity oscillation of southern hemisphere sh westerly winds affects the

climatic warming of atlantic intermediate waters abstract interdecadal temperature variability of the atlantic ocean is investigated by differencing hydrographic sections taken from the 1920s through the 1990s a comprehensive reanalysis of north atlantic sections and the inclusion of south atlantic sections show that warming seen previously in the north atlantic extends to the south atlantic the largest statistically significant changes occur on pressure surfaces between 1000 and 2000 decibars db over this pressure range and for latitudes between 32 s and 36 n temperatures have warmed by 0 5 c century 1 at 48 n a cooling of 3 c century 1 occurred between the 1950s and 1980s these isobaric temperature trends are decomposed into ones along surfaces of constant neutral density and ones due to the vertical movement of neutral surfaces the two components are associated with different processes in the southern north atlantic 8 36 n the subthermocline warming between the 1950s and 1980s appears to be due primarily to downward displacements of n

variability of subantarctic mode water and antarctic intermediate water in the drake passage during the late twentieth and early twenty first centuries a time series of the physical and biogeochemical properties of subantarctic mode water samw and antarctic intermediate water aaiw in the drake passage between 1969 and 2005 is constructed using 24 transects of measurements across the passage both water masses have experienced substantial variability on interannual to interdecadal time scales samw is formed by winter overturning on the equatorward flank of the antarctic circumpolar current acc in and to the west of the drake passage its interannual variability is primarily driven by variations in wintertime air sea turbulent heat fluxes and net evaporation modulated by the el nino southern oscillation enso despite their spatial proximity the aaiw in the drake passage has a very different source than that of the samw because it is ventilated by the northward subduction of winter water originating in the bellingshausen sea changes in aaiw are mainly forced by variability in winter water properties resulting from fluctuations in wintertime air sea turbulent heat fluxes and spring sea ice melting both of which are linked to predominantly enso driven variations in the intensity of meridional winds to the west of the antarctic peninsula a prominent exception to the prevalent modes of samw and aaiw formation occurred in 1998 when strong wind forcing associated with constructive interference between enso and the southern annular mode sam triggered a transitory shift to an ekman dominated mode of samw ventilation and a 1 2 yr shutdown of aaiw production the interdecadal evolutions of samw and aaiw in the drake passage are distinct and driven by different processes samw warmed by 0 3 c and salinified by 0 04 during the 1970s and experienced the reverse trends between 1990 and 2005 when the coldest and freshest samw on record was observed in contrast aaiw underwent a net freshening by 0 05 between the 1970s and the twenty first century although the reversing changes in samw were chiefly forced by a 30 yr oscillation in regional air sea turbulent heat fluxes and precipitation associated with the interdecadal pacific oscillation with a sam driven intensification of the ekman supply of antarctic surface waters from the south contributing significantly too the freshening of aaiw was linked to the extreme climate change that occurred to the west of the antarctic peninsula in recent decades there a freshening of the winter water ventilating aaiw was brought about by increased precipitation and a retreat of the winter sea ice edge which were seemingly forced by an interdecadal trend in the sam and regional positive feedbacks in the air sea ice coupled climate system all in all these findings highlight the role of the major modes of southern hemisphere climate variability in driving the evolution of samw and aaiw in the drake passage region and the wider south atlantic and suggest that these modes may have contributed significantly to the hemispheric scale changes undergone by those waters in recent decades

a region of enhanced northward antarctic intermediate water transport in a coupled climate model abstract a global coupled model is used to examine pathways of freshwater transport in the southern ocean on the background of a strong zonal freshwater transport along the pathway of the antarctic circumpolar current acc there are meridional freshwater flows distributed nonuniformly around the globe including in the upper ocean the analysis does not support a simple two dimensional scheme of antarctic intermediate water aaiw formation according to which the fresh aaiw forms uniformly around the circumpolar ocean rather a more complex three dimensional picture of the freshwater transport in the southern ocean is revealed with enhanced aaiw formation in the southeast pacific ocean both north and south of the drake passage latitudes freshened by intense precipitation and surface waters from around antarctica the acc transports freshwater from the northwest to the southeast toward drake passage there a fraction of this freshwater is transported southward across 60 s with the subsurface acc an

formation and pathways of intermediate water in the parallel ocean circulation model s southern ocean 1 the formation mechanisms and pathways of intermediate water in the southern ocean are analyzed from output of a high resolution ocean general circulation model deep winter mixed layer formation in the southern ocean is diagnosed from the model results and is found to be mostly consistent with observations diapycnal water mass transformations by air sea fluxes and internal mixing are quantified and split into mean and eddy components the diapycnal formation of the water masses that constitute the antarctic intermediate water layer in the southeast pacific is found to occur mainly in the western pacific ocean in this model in winter convection up to 900 m is found to set the potential vorticity characteristics of this layer eddy fluxes of heat and buoyancy play an important role in the formation of the intermediate waters by transferring water from the southern parts of the subtropical gyres into the antarctic circumpolar current acc and vice versa the effects of eddy fluxes are found to vary significantly along the path of the acc they are strongly concentrated in the regions near the agulhas return current in the indian ocean and the brazil malvinas confluence in the atlantic

mixing and remineralization in waters detrained from the surface into subantarctic mode water and antarctic intermediate water in the southeastern pacific a hydrographic data set collected in the region and season of subantarctic mode water and antarctic intermediate water samw and aaiw formation in the southeastern pacific allows us to estimate the preformed properties of surface water detrained into these water masses from deep mixed layers north of the subantarctic front and antarctic surface water south of the front using 10 measured seawater properties we estimate the fractions of samw aaiw that originate as surface source waters as well as fractions that mix into these water masses from subtropical thermocline water above and upper circumpolar deep water below the subducted samw aaiw ages associated with the detrained surface water and remineralization and dissolution rates and ratios the mixing patterns imply that cabbeling can account for 0 005 0 03 kg m 3 of additional density in aaiw and 0 0 02 kg m 3 in samw we estimate a shallow depth 300 700 m above the aragonite saturation horizon calcium carbonate dissolution rate of 0 4 0 2 mol caco3 kg 1 yr 1 a phosphate remineralization rate of 0 031 0 009 mol p kg 1 yr 1 and remineralization ratios of p n o2 corg of 1 15 5 0 6 143 10 104 22 for samw aaiw our shallow depth calcium carbonate dissolution rate is comparable to previous estimates for our region our o2 p ratio is smaller than many global averages our model suggests neglecting diapycnal mixing of preformed phosphate has likely biased previous estimates of o2 p and corg p high but that the corg p ratio bias may have been counteracted by a second bias in previous studies from neglecting anthropogenic carbon gradients

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

control of mode and intermediate water mass properties in drake passage by the amundsen sea low the evolutionof the physical properties of subantarctic mode water samw and antarctic intermediate water aaiw in the drake passage region is examined on time scales down to intraseasonal within the 1969 2009 period both samw and aaiw experience substantial interannual to interdecadal variability significantly linked to the action of the amundsen sea low asl in their formation areas observations suggest that the interdecadal freshening tendency evident in samw over the past three decades has recently abated while aaiw has warmed significantly since the early 2000s the two water masses have also experienced a substantial lightening since the start of the record examination of the mechanisms underpinning water mass property variability shows that samw characteristics are controlled predominantly by a combination of air sea turbulent heat fluxes cross frontal ekman transport of antarctic surface waters and the evaporation precipitation balance in the subantarctic zone of the southeast pacific and drake passage while aaiw properties reflect air sea turbulent heat fluxes and sea ice formation in the bellingshausen sea the recent interdecadal evolution of the asl is consistent with both the dominance of the processes described here and the response of samw and aaiw on that time scale

carbon chemostratigraphy of the cambrian ordovician transition in a midlatitude mixed platform montagne noire france the cambrian drumian carbon isotope excursion dice and the steptoean positive carbon isotope excursion spice have been so far reported in subtropical platforms the dice event is a large negative excursion in 13ccarb record that nearly coincides with the beginning of the drumian cambrian series 3 whereas the spice event is a large positive shift in 13ccarb identified close to the base of the paibian furongian series the chemostratigraphic excursions have been recognized in carbonate dominated platforms and their application to mid and high latitude siliciclastic dominated platforms has been problematic this paper offers for the first time a high resolution stratigraphic analysis of this time span in a temperate water platform montagne noire france that recorded episodes of carbonate productivity in nearshore environments two sections were analyzed in detail a complete cambrian series 3 tremadocian succession devoid of carbonate interbeds and paleogeographically located in the distal part of the platform pardailhan nappe and a furongian tremadocian succession which has limestone interbeds and represents the proximal part of the platform minervois nappe the lower part of the la gardie formation in the pardailhan nappe displays background 13corg values of 22 punctuated by a large negative middle languedocian regional substage shift peaking at 24 5 this negative excursion is similar to the dice event reported close to the base of the drumian although the latter is exclusively based on 13ccarb values stable isotopes of 13ccarb and 13corg from both sections also indicate a common chemostratigraphic shift at the onset of the furongian in nearshore deposits of the minervois nappe the 13ccarb background values for the interbedded limestone strata of the val d homs formation gradually increase from 3 to 1 and are punctuated by a sharp increase in 13ccarb values to 3 0 by contrast in basinal shales of the la gardie formation in the pardailhan nappe the 13corg background values decrease from 22 to 27 1 this trend is directly controlled by total organic carbon toc contents and is interpreted to have been initiated by changes in the degree of biodegradation of organic matter sulfate reduction and methanogenesis before or soon after burial despite this overprinting and the very low degree of metamorphism reached by the shales the 13corg background trend is also punctuated by a sharp positive shift in 13corg values to 4 0 similar to the spice event in addition the asymmetric shape of the spice excursion in the montagne noire shows evidence for the herb event a late furongian negative carbon isotope excursion not yet accepted as a worldwide chemostratigraphic anomaly the recognition of both chemostratigraphic shifts in mixed and clayey strata opens new possibilities of chemostratigraphic correlation in mid and high latitude platforms where carbonate factories did not widely develop and strata only contain endemic fauna this implication has a major consequence because the global stratotype section and point gssp of the drumian and paibian stages occurs near the base of both excursions

representing the global scale water masses in ocean general circulation models abstract a hierarchy of coarse resolution world ocean experiments were integrated with a view to determining the most appropriate representation of the global scale water masses in ocean general circulation models the largest scale response of the simulated ocean to the prescribed forcing in each model run is described the world ocean model eventually has a realistic approximation of continental outlines and bottom bathymetry the model forcing at the sea surface is derived from climatological fields of temperature salinity and wind stress the first experiment begins with a quite unrealistic and idealized world ocean subsequent experiments then employ more realistic surface boundary conditions model geometry and internal physical processes in all 16 changes to the model configuration are investigated a fundamental dynamical constraint in the drake passage gap appears to limit the outflow rate of bottom water in the antarctic region this constraint acts to decouple the extreme antarctic waters

circumpolar deep water circulation and variability in a coupled climate model abstract the natural variability of circumpolar deep water cdw is analyzed using a long term integration of a coupled climate model the variability is decomposed using a standard eof analysis into three separate modes accounting for 68 and 82 of the total variance in the upper and lower cdw layers respectively the first mode exhibits an interbasin scale variability on multicentennial time scales originating in the north atlantic and flowing southward into the southern ocean via north atlantic deep water nadw salinity dipole anomalies appear to propagate around the atlantic meridional overturning circulation on these time scales with the strengthening and weakening of nadw formation the anomaly propagates northward from the midlatitude subsurface of the south atlantic and sinks in the north atlantic before flowing southward along the cdw isopycnal layers this suggests an interhemispheric connection in the generation of the first cdw variability mode the second mode shows a localized s varia

coupled ocean atmosphere ice response to variations in the southern annular mode abstract the coupled ocean atmosphere ice response to variations in the southern annular mode sam is examined in the national center for atmospheric research ncar community coupled climate model version 2 the model shows considerable skill in capturing the predominantly zonally symmetric sam while regional deviations between model and observation sam winds go a long way in explaining the generally small differences between simulated and observed sam responses in the ocean and sea ice systems vacillations in the position and strength of the circumpolar winds and the ensuing variations in advection of heat and moisture result in a dynamic and thermodynamic forcing of the ocean and sea ice both meridional and zonal components of ocean circulation are modified through ekman transport which in turn leads to anomalous surface convergences and divergences that strongly affect the meridional overturning circulation and potentially the pathways of intermediate water ventilation a heat budget analysis de

investigation of the dynamic sea ice component of a coupled atmosphere sea ice general circulation model this paper discusses the development of a coupled atmospheric ice model with a comprehensive ice dynamics cavitating fluid rheology and an open water parameterization the results center on the ice thickness and concentration distribution in the arctic basin where the inclusion of ice rheology has maximum impact the influence of the wind stresses calculated by an atmospheric model with stability dependent surface drag coefficients is discussed along with the role of the ocean currents and ocean ice drag coefficient under winter wind stress conditions the model had a tendency to buildup ice on the siberian coast the introduction of a partial slip condition at land ice boundaries in the model designed to prevent this buildup is discussed and the best choice for the amplitude of the slip at the land boundaries in this model is found to be 0 4 the ice model results are compared with the available observational data sets on ice thickness concentration and ice velocity fields to test the validity of the model simulations

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

an antarctic circumpolar wave in surface pressure wind temperature and sea ice extent the southern ocean is the only oceanic domain encircling the globe it contains the strong eastward flow of the antarctic circumpolar current and is the unifying link for exchanges of water masses at all depths between the world s major ocean basins1 as these exchanges are an important control on mean global climate the southern ocean is expected to play an important role in transmitting climate anomalies around the globe interannual variability has been often observed at high southern latitudes and observations of sea ice extent suggest that such features propagate eastwards around the southern ocean2 3 here we use data from a variety of observational techniques to identify significant interannual variations in the atmospheric pressure at sea level wind stress sea surface temperature and sea ice extent over the southern ocean these anomalies propagate eastward with the circumpolar flow with a period of 4 5 years and taking 8 10 years to encircle the pole this system of coupled anomalies which we call the antarctic circumpolar wave is likely to play an important role in climate regulation and dynamics both within and beyond the southern ocean

deep water properties and surface buoyancy flux as simulated by a z coordinate model including eddy induced advection abstract a parameterization for the adiabatic transport effect of eddies is introduced into a world ocean model based on the bryan cox code the model topography is only lightly smoothed and retains realistic sill depths and representation of continental shelves commensurate with the model s 1 6 latitude by 2 8 longitude resolution the parameterization allows the model to be run without horizontal diffusivity though only under certain conditions as discussed a first control run features a typical horizontal diffusivity and no eddy induced transport a second run features the eddy induced transport scheme and zero horizontal diffusivity substantial changes occur between the runs in subsurface temperature salinity and density throughout the model ocean the most profound changes occur in the deep ocean and feature a marked increase in density in the second run associated with a substantial decline in temperature especially in the atlantic and an increase in salinity especially in the southern

southwest pacific ocean water mass changes between 1968 69 and 1990 91 abstract water mass changes are estimated in the southwest pacific ocean by comparing a meridional hydrographic section along 170 w between 60 s and the equator occupied in 1968 69 during the southern cross cruise and again in 1990 during a noaa climate and global change cruise another comparison is made using a hydrographic section along 35 s between the date line and 169 w occupied in 1969 during usns eltanin cruise 40 and again in 1991 during a mapkiwi cruise the most robust change consists of cooling and freshening on isopycnals with peak differences exceeding 1 0 c 0 25 pss at the base of the subtropical thermocline the cooling and freshening starts above the stratification minimum of the subantarctic mode water and persists to below the salinity minimum of the antarctic intermediate water amplitudes are largest at 48 s near where these water masses subduct and decay toward 20 s near the axis of the subtropical gyre this change is likely the result of surface warming and or freshening

cadmium isotope variations in the southern ocean abstract cadmium concentrations and isotope compositions were determined for 47 seawater samples from the high nutrient low chlorophyll hnlc zone of the atlantic sector of the southern ocean the samples include 13 surface waters from a transect of the weddell gyre and 3 depth profiles from the weddell sea and drake passage the southern ocean mixed layer samples from this study and abouchami et al 2011 define a clear but broad hnlc trend in a plot of e cd 114 110 versus cd which is primarily a consequence of isotopic fractionation associated with biological uptake e cd 114 110 is the deviation of the 114cd 110cd ratio of a sample from nist srm 3108 cd in parts per 10 000 the trend is especially apparent in comparison to the large range of values shown by a global set of seawater cd data for shallow depths the southern ocean samples are also distinguished by their relatively high cd concentrations typically 0 2 to 0 6 nmol kg and moderately fractionated e cd 114 110 generally between 4 and 8 that reflect the limited biological productivity of this region detailed assessment reveals fine structure within the hnlc trend which may record differences in the biological fractionation factor different scenarios of closed and open system isotope fractionation and or distinct source water compositions southern ocean seawater from depths 1000 m has an average e cd 114 110 of 2 5 0 2 2se n 16 and together with previous results this establishes a relatively constant e cd 114 110 value of 3 0 0 3 2se n 27 for global deep waters significant isotopic variability was observed at intermediate depths in the southern ocean seawater from 200 m to 400 m in weddell sea has high cd concentrations and e cd 114 110 as low as 1 presumably due to remineralization of cd from biomass that records incomplete nutrient utilization antarctic intermediate water which was sampled at 150 to 750 m depth in the drake passage features a distinct cd isotope signature of e cd 114 110 4 which reflects biological isotope fractionation at the surface and subsequent mixing into the ocean interior taken together our results demonstrate that coupled cd isotope and concentration data provide valuable insights into the distribution and biological cycling of cd in the water column the highly systematic nature of cd isotope signatures may furthermore prove to be of utility for future research in marine geochemistry and paleoceanography

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

on the sub decadal variability of south atlantic antarctic intermediate water variability of antarctic intermediate water salinity in the south atlantic is investigated on interannual and intradecadal timescales novel observations of slow westward propagating salinity anomalies in argo data are presented the features have no corresponding signal in temperature and are anomalous in density analysis of 40 years of model output supports the existence of these westward propagating salinity anomalies and indicates that they are typical occurrences in time the features are intensified in a latitude band around 30 s associated with the propagation of agulhas rings however the features are much larger than agulhas rings and occur on decadal timescales in the model they propagate westward with speeds of 2 3 cm s in observations and 1 7 cm s in model data they are more consistent with planetary waves than with the advection of large scale salinity anomalies the observation of these features has implications for the interpretation of salinity anomalies such as the linking of hydrological cycle changes to salinity changes

the mechanism for antarctic intermediate water renewal in a world ocean model abstract realistic representation of the low salinity tongue of antarctic intermediate water aaiw has been achieved in a coarse resolution ocean general circulation model the authors find that this water mass is not generated by direct subduction of surface water near the polar front instead the renewal process is concentrated in the southeast pacific ocean off southern chile the outflow of the east australian current progressively cools by heat loss to the atmosphere and freshens by assimilation of polar water carried north by the surface ekman drift during its slow movement across the south pacific toward the aaiw formation zone further deep warm advection near chile enables more convective overturn resulting in very deep mixed layers from which aaiw is fed into the south pacific and also into the malvinas current along with this isolated region of aaiw renewal the model relies on alongisopycnal mixing of fresh surface water from the polar front to capture a realistic circumpolar tongue

comments on southern mid to high latitude variability a zonal wavenumber 3 pattern and the antarctic circumpolar wave in the csiro coupled model abstract variability in the southern atmospheric circulation at mid to high latitudes with a dominant quasi stationary wavenumber 3 pattern has been reported in many observational studies the variability is barotropic in nature with signals in the middle troposphere as well as at the atmosphere ocean interface moreover there are preferred fixed centers for the strongest anomalies these features are well reproduced by the commonwealth scientific and industrial research organisation coupled model on various timescales on the interannual timescale an index of the modeled wavenumber 3 pattern shows little correlation with the modeled southern oscillation index suggesting that the variability associated with wavenumber 3 anomalies is separate to modeled enso like events however the variation of the pattern index is strikingly similar to and highly correlated with the modeled oceanic variability the associated oceanic anomalies move eastward and are similar to those of the observed antarctic circum

18o16o and 13c12c in lower paleozoic articulate brachiopods implications for the isotopic composition of seawater three hundred and eleven articulate brachiopods with extensive geographic coverage spanning the cambrian to silurian stratigraphic interval were analyzed for oxygen and carbon isotopic composition cambrian samples have 18o 7 ordovician samples 2 4 and silurian samples 1 9 confirming the previously established trend towards lighter isotopic compositions with increasing age throughout the lower paleozoic forty nine best preserved ordovician and silurian samples were identified based on scanning electron microscopy and trace element analysis they were found to bracket the isotopic compositions of over 85 of specimens from these stratigraphic intervals supporting widespread preservation of the isotopic signal some latest ordovician and lower ludlovian samples associated with shale sequences are apparently enriched in 18o these are interpreted as an environmental phenomenon perhaps related to water temperature and glaciation a number of silurian samples of varying genera and stratigraphic levels are highly enriched in 13c up to 6 some are shale related but some are associated with carbonate bearing basins these are also thought to represent near original compositions but a single environmental cause is unknown the present data show that luminescence is not a decisive criterion for evaluating the degree of brachiopod preservation whole shell values were isotopically similar to their nonluminescent portions for both oxygen and carbon