meridional overturning transports at 30 s in the indian and pacific oceans in 2002 2003 and 2009 abstract the meridional circulation and transports at 30 s in the pacific and indian oceans for the years 2002 2003 and 2009 are compared using go ship hydrographic section data with an inverse box model and several choices of constraints southward heat transport across the combined indian pacific sections reflecting net heating north of these sections doubled from 0 7 0 2 pw in 2002 2003 to 1 4 0 1 pw in 2009 negative sign is southward with the increase concentrated in the indian ocean 0 6 pw compared with 0 2 pw in the pacific and was insensitive to model choices for the indonesian throughflow diagnosed net evaporation also more than doubled in the indian ocean from 0 21 0 27 sv in 2002 2003 to 0 51 0 58 in 2009 with a smaller but significant increase in net evaporation in the pacific from 0 06 0 08 sv to 0 16 0 32 sv these increased heat and freshwater exports coincided with indian ocean warming a shift in the indian s shallow gyre overturning transport to lower densities and an increase in southward agulhas current transport from 75 sv in 2002 to 92 sv in 2009 the indian s deep overturn weakened from about 11 sv in 2002 to 7 sv in 2009 in contrast the pacific ocean overturning circulation was nearly unchanged from 2003 to 2009 independent of model within the uncertainties the east australian current transport decreased only slightly from 52 sv to 46 sv the southward pacific deep water transport was at a higher density than the southward indian deep water transport in both years and all models similar to prior results estimated diapycnal diffusivity and velocity are strongly enhanced near the ocean bottom and are higher farther up in the water column in the indian than in the pacific likely extending the reach of indian ocean overturning up to shallower depths than in the pacific the horizontal distribution of transports in the pacific at all depths changed notably from 2003 to 2009 despite the stability of its meridional overturning structure the 2009 horizontal structure resembles a bowed gyre the hydrographic section data show that this disturbance extends to the abyss and disrupts the deep western boundary current structure in the southwest pacific basin satellite altimetry suggests association with slow westward rossby wave propagation generated in the eastern pacific with no apparent effect on the net overturning circulation the indian ocean s upper ocean horizontal structure was stable between the two years even though its shallow gyre overturning transports changed significantly on the other hand northward abyssal transports concentrated in the central indian ocean crozet basin in 2002 shifted westward to the mozambique and madagascar basins in 2009 although the crozet basin s deep western boundary current existed in both years

changes in antarctic bottom water properties in the western south atlantic in the late 1980s data collected in 1988 1989 as part of the south atlantic ventilation experiment have been combined with the historical database to study the circulation and water mass variability of the abyssal water in the argentine basin a map of potential temperature at 4000 m used as an indication of geostrophic shear defines a south and western intensified crescent shaped abyssal recirculation within this recirculation and its northward extension to the brazil basin antarctic bottom water aabw properties have undergone two modifications during the 1980s 1 the water mass cooled 0 05 c and freshened 0 008 in salinity ratio on surfaces of constant density 2 the densest layer of aabw was altered to less dense water through mixing or advection out of the study area this water mass change does not appear to have affected the flow pattern data collected in 1983 and 1988 to the north in the brazil basin show penetration of the freshwater mass in the deep western boundary current to between 18 s and 10 s indicating very rapid propagation of the anomaly from the argentine basin into the brazil basin as a deep western boundary current it is suggested that open ocean convective events within the weddell sea contributed to the change in aabw documented here

heat content change in the pacific ocean between the 1990s and 2000s we studied the change in heat content in the pacific ocean using data from repeat hydrographic surveys the most recent trans pacific surveys along 47 n and 179 e conducted in 2007 reveal that circumpolar deep water has warmed along 179 e as suggested by previous studies and also that the deep water was warmer along 47 n even since 1999 simple estimates show that the heat content increased in the layer deeper than 4000 m over almost the entire pacific ocean the increase in heat content below 3000 m was about 5 of the ocean wide increase heat content changes in the deep layer are not uniform and a vertical profile of heat content change has a minimum at a depth around 3000 m the non uniform distribution of heat content change in the mid to bottom layer demonstrates the existence of overturn circulation and may indicate that this circulation is changing

variability in southern hemisphere ocean circulation from the 1980s to the 2000s abstractinterannual to decadal variability of ocean circulation in the southern hemisphere was examined using data from the 1980s to the 2000s in a box inverse model to estimate transport across hydrographic sections and three ocean general circulation models ogcms the westerly wind stress over the ogcm southern ocean showed a steady increase of 5 8 decade 1 the meridional overturning circulation was quantified by the transport across 30 s the ogcms suggested a slight strengthening from 0 2 1 0 to 0 8 1 3 sv decade 1 1 sv 106 m3 s 1 of the upper meridional cell deacon cell and two ogcms showed a weakening 0 8 0 6 and 1 0 0 3 sv decade 1 of the lower meridional antarctic bottom water aabw cell partly explained by contraction of the aabw volume the box inverse estimates did not contradict these two findings for antarctic circumpolar current transport quantified by zonal transport across four key sections the box inverse model estimated a decrease of 5 21 sv decomposition

warming of global abyssal and deep southern ocean waters between the 1990s and 2000s contributions to global heat and sea level rise budgets abyssalglobalanddeepsouthern oceantemperature trendsarequantifiedbetweenthe1990sand2000sto assesstheroleofrecentwarmingoftheseregionsin globalheatandsealevelbudgets theauthors1 compute warming rates with uncertainties along 28 full depth high quality hydrographic sections that have been occupied two or more times between 1980 and 2010 2 divide the global ocean into 32 basins defined by the topography and climatological ocean bottom temperatures and then 3 estimate temperature trends in the 24 sampled basins the three southernmost basins show a strong statistically significant abyssal warming trend with that warming signal weakening to the north in the central pacific western atlantic and eastern indian oceans eastern atlantic and western indian ocean basins show statistically insignificant abyssal cooling trends excepting the arctic ocean and nordic seas the rate of abyssal below 4000 m global ocean heat content change in the 1990s and 2000s is equivalent to a heat flux of 0 027 60 009 w m 22 applied over the entire surface of the earth deep 1000 4000 m warming south of the subantarctic front of the antarctic circumpolar current adds 0 068 60 062 w m 22 the abyssal warming produces a 0 053 60 017 mm yr 21 increase in global average sea level and the deep warming south of the subantarctic front adds another 0 093 60 081 mm yr 21 thus warmingin theseregions ventilatedprimarilyby antarcticbottomwater accounts for a statistically significant fraction of the present global energy and sea level budgets

seismic and geologic characteristics of drowning events on carbonate platforms carbonate platform drowning events are recorded in upper jurassic lower cretaceous carbonates of the baltimore canyon area offshore united states east coast and lower miocene carbonates of the pearl river mouth basin offshore people s republic of china cursory examination of seismic data from both areas would indicate that the platforms fit the classic definition of a drowning unconformity however detailed lithologic and paleontologic data indicate that the depositional erosional hiatuses vary widely in each area from 0 25 m y in the baltimore canyon area to a condensed section with no hiatus in the pearl river mouth basin the sedimentary sequence produced during drowning the drowning sequence in both areas is gradational with underlying shallow platform carbo ates and in some places overlying deeper marine limestones and shales the generalized facies models proposed for drowning events suggest that they may appear as instantaneous or gradual changes in geologic and seismic data however high resolution seismic data across the baltimore canyon and pearl river mouth basins show that some drowning sequences may be masked on conventionally processed seismic sections because of this resolution problem a distinction should be made between seismically and geologically defined unconformity surfaces the geologic characteristics of drowning events on carbonate platforms include a gradational lower and sometimes upper contact chemical sedimentation glauconite phosphate open marine shelf sediments and a variable hiatus at the upper boundary late growth shelf margin reefs also can be a diagnostic feature of drowned platforms seismic characteristics include horizontal to sub horizontal basinal marine onlap basin parallel reflector continuity above the carbonate sequence boundary and downlap of later highstand units evidence from platforms adjacent to continental margins baltimore canyon indicates that drowning occurs in a step wise fashion advancing more or less symmetrically across the platform from shelf to nearshore environments data from isolated open ocean atolls pearl river mouth basin indicate that they respond differently to drowning showing an asymmetric decrease in shallow platform environments as drowning occurs proper recognition by a geoscientist of the seismic and geologic characteristics of drowning events can lead to better reservoir and seal estimates and the correct reconstruction of the depositional tectonic and eustatic histories of an area

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

evolution of the deep atlantic water masses since the last glacial maximum based on a transient run of ncar ccsm3 during the last deglaciation from approximately 21 to 11 thousand years ago the high latitudes of the atlantic ocean underwent major changes besides the continuous warming the polar and subpolar ocean surface received a large amount of meltwater from the retracting ice sheets these changes in temperature and salinity affected deep waters such as the antarctic bottom water aabw and the north atlantic deep water nadw which are formed in the southern ocean and in the northern north atlantic respectively in this study we present the evolution of the physical properties and distribution of the aabw and the nadw since the last glacial maximum using the results of a transient simulation with ncar ccsm3 in this particular model scenario with a schematic freshwater forcing we find that modern nadw with its characteristic salinity maximum at depth was absent in the beginning of the deglaciation while its intermediate version glacial north atlantic intermediate water gnaiw was being formed gnaiw was a cold and relatively fresh water mass that dominated intermediate depths between 60 and 20 n at this time most of the deep and abyssal atlantic basin was dominated by aabw within the onset of the bolling allerod period at nearly 15 thousand years ago ka gnaiw expanded southwards when the simulated meridional overturning circulation overshoots the transition between gnaiw and nadw ocurred after that when aabw was fresh enough to allow nadw to sink deeper in the water column when the nadw appears 11 ka aabw retracts and is constrained to lie near the bottom

bottom temperatures in drake passage abstractlong time series of bottom temperatures in the southern ocean are rare the cdrake array with over 40 current and pressure recording inverted echo sounders moored across drake passage to monitor the antarctic circumpolar current acc variability and transport measured temperature at 1 and 50 m above the seafloor at depths 3500 m and at the southern continental margin the 4 yr dataset provided an opportunity to examine the temporal and spatial scales of bottom temperature variability high variability was observed ranges were 0 5 0 9 c in the northern passage and 0 3 0 6 c in the southern passage standard deviations in the two regions were 0 1 0 15 c and 0 05 c respectively meandering of the acc with its deep reaching thermocline accounted for up to 50 of the observed bottom temperature variance northern passage temperatures spaced less than 40 km apart were correlated with each other while those in the southern portion separated by 60 70 km were not a gap in the west scotia

decadal response of global circulation to southern ocean zonal wind stress perturbation abstract a substantial component of north atlantic deep water formation may be driven by westerly wind stress over the southern ocean variability of this wind stress on decadal time scales may lead to circulation variability far from the forcing region the hybrid coordinate ocean model hycom a numerical ocean model is used to investigate the spatial patterns and the time scales associated with such wind variability the evolution of circulation and density anomalies is observed by comparing one 80 yr simulation forced in part by relatively strong southern hemisphere westerlies with a simulation driven by climatological wind the volume transport anomaly takes about 10 yr to reach near full strength in the entire southern hemisphere however in the northern hemisphere it grows for the duration of the run the southern hemisphere indo pacific volume transport anomaly is about twice the strength of that found in the atlantic in the thermocline water exits the southern westerlies belt in a broad f

recent bottom water warming in the pacific ocean decadal changes of abyssal temperature in the pacific ocean are analyzed using high quality full depth hydrographic sections each occupied at least twice between 1984 and 2006 the deep warming found over this time period agrees with previous analyses the analysis presented here suggests it may have occurred after 1991 at least in the north pacific mean temperature changes for the three zonal and three meridional hydrographic sections analyzed here exhibit abyssal warming often significantly different from zero at 95 confidence limits for this time period warming rates are generally larger to the south and smaller to the north this pattern is consistent with changes being attenuated with distance from the source of bottom water for the pacific ocean which enters the main deep basins of this ocean southeast of new zealand rough estimates of the change in ocean heat content suggest that the abyssal warming may amount to a significant fraction of upper world ocean heat gain over the past few decades

decadal warming of the coldest antarctic bottom water flow through the vema channel a decadal warming trend of antarctic bottom water flowing through the vema channel is reanalyzed our data base consists of 94 high precision full depth stations from 19 visits to the vema sill plus twelve stopovers at two additional key locations originally a long term temperature increase in the near bottom jet was noted from 1992 onward after a period of rather constant abyssal temperatures since 1972 from today s perspective the apparent stagnant temperature level until 1991 can be interpreted as a period of feeble rising in comparison with a perspicuous warming trend of 2 8 mk yr 1 in the following 15 years however the clearly manifested temperature rise is superimposed with fluctuations for the first time the available time series appears long enough to indicate an associated slight freshening of the bottom water an attempt is made to trace the observed variability back to its source region in the weddell sea

freshening of the ross sea during the late 20th century ocean measurements in the ross sea over the past four decades one of the longest records near antarctica reveal marked decreases in shelf water salinity and the surface salinity within the ross gyre these changes have been accompanied by atmospheric warming on ross island ocean warming at depths of 300 meters north of the continental shelf a more negative southern oscillation index and thinning of southeast pacific ice shelves the freshening appears to have resulted from a combination of factors including increased precipitation reduced sea ice production and increased melting of the west antarctic ice sheet

40ar39ar ages and tectonic setting of ophiolite from the neyriz area southeast zagros range iran abstract an ophiolite considered to be an allochthonous fragment of tethyan oceanic crust and mantle crops out near neyriz in the zagros range iran 40 ar 39 ar ages ranging from 76 8 23 8 ma to 105 23 3 ma were measured on hornblende from five samples of plagiogranite and diabase from the ophiolite the most precise ages are 85 9 3 8 ma for a diabase and 83 6 8 4 ma for a plagiogranite the weighted mean age of hornblende from the five samples is 87 5 7 2 ma which indicates that the igneous part of the neyriz ophiolite formed during the early part of the late cretaceous pargasite from amphibolite below peridotite of the neyriz ophiolite has a 40 ar 39 ar age of 94 9 7 6 ma the pargasite age agrees within analytical uncertainty with the ages measured on diabase and plagiogranite comparable ages have been measured on igneous rocks from the samail ophiolite of oman and on amphibolite below peridotite of the samail ophiolite

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

variability of antarctic bottom water at 24 5 n in the atlantic a recent hydrographic section at 24 5 n in the atlantic and 6 months of observations from a moored array show that antarctic bottom water aabw the densest and deepest water mass in the world oceans has been warming while johnson et al 2008 showed that northward aabw transport at 24 5 n has been declining from 1981 to 2004 suggesting that the lower cell of the overturning circulation could halt in the near future estimates from the latest hydrographic section in 2010 indicate a partial recovery of northward aabw transport from 6 months of temperature and salinity observations at a deep moored array at 24 26 n we find that short term variability between april and november 2009 is of the same magnitude as the changes observed from hydrographic sections between 1981 and 2004 these observations highlight the possibility that transport changes estimated from hydrographic sections may be aliased by short term variability the observed aabw transport variability affects present estimates of the upper meridional overturning circulation by 0 4 sv 1 sv 106 m3 s 1

warming and weakening of the abyssal flow through samoan passage abstractthe abyssal flow of water through the samoan passage accounts for the majority of the bottom water renewal in the north pacific thereby making it an important element of the meridional overturning circulation here the authors report recent measurements of the flow of dense waters of antarctic and north atlantic origin through the samoan passage a 15 month long moored time series of velocity and temperature of the abyssal flow was recorded between 2012 and 2013 this allows for an update of the only prior volume transport time series from the samoan passage from woce moored measurements between 1992 and 1994 while highly variable on multiple time scales the overall pattern of the abyssal flow through the samoan passage was remarkably steady the time mean northward volume transport of about 5 4 sv 1 sv 106 m3 s 1 in 2012 13 was reduced compared to 6 0 sv measured between 1992 and 1994 this volume transport reduction is significant within 68 confidence limits 0 4 sv but not at 95 conf

changes in global ocean bottom properties and volume transports in cmip5 models under climate change scenarios abstractchanges in bottom temperature salinity and density in the global ocean by 2100 for cmip5 climate models are investigated for the climate change scenarios rcp4 5 and rcp8 5 the mean of 24 models shows a decrease in density in all deep basins except the north atlantic which becomes denser the individual model responses to climate change forcing are more complex regarding temperature the 24 models predict a warming of the bottom layer of the global ocean in salinity there is less agreement regarding the sign of the change especially in the southern ocean the magnitude and equatorward extent of these changes also vary strongly among models the changes in properties can be linked with changes in the mean transport of key water masses the atlantic meridional overturning circulation weakens in most models and is directly linked to changes in bottom density in the north atlantic these changes are the result of the intrusion of modified antarctic bottom water made possible by the decrease i

are the near antarctic easterly winds weakening in response to enhancement of the southern annular mode abstractprevious studies have highlighted the sensitivity of the southern ocean circulation to the strengthening poleward shifting westerlies associated with the increasingly positive southern an

tracer applications of noble gas radionuclides in the geosciences noble gas radionuclides including 81kr t1 2 229 000 years 85kr t1 2 10 8 years and 39ar t1 2 269 years possess nearly ideal chemical and physical properties for studies of earth and environmental processes recent advances in atom trap trace analysis atta a laser based atom counting method have enabled routine measurements of the radiokrypton isotopes as well as the demonstration of the ability to measure 39ar in environmental samples here we provide an overview of the atta technique and a survey of recent progress made in several laboratories worldwide we review the application of noble gas radionuclides in the geosciences and discuss how atta can help advance these fields specifically determination of groundwater residence times using 81kr 85kr and 39ar dating old glacial ice using 81kr and an 39ar survey of the main water masses of the oceans to study circulation pathways and estimate mean residence times other scientific questions involving a deeper circulation of fluids in the earth s crust and mantle are also within the scope of future applications we conclude that the geoscience community would greatly benefit from an atta facility dedicated to this field with instrumentation for routine measurements as well as for research on further development of atta methods

the little ice age and 20th century deep pacific cooling proxy records show that before the onset of modern anthropogenic warming globally coherent cooling occurred from the medieval warm period to the little ice age the long memory of the ocean suggests that these historical surface anomalies are associated with ongoing deep ocean temperature adjustments combining an ocean model with modern and paleoceanographic data leads to a prediction that the deep pacific is still adjusting to the cooling going into the little ice age whereas temperature trends in the surface ocean and deep atlantic reflect modern warming this prediction is corroborated by temperature changes identified between the hms challenger expedition of the 1870s and modern hydrography the implied heat loss in the deep ocean since 1750 ce offsets one fourth of the global heat gain in the upper ocean

global thermosteric sea level change contributed by the deep ocean below 2000 m estimated by argo and ctd data abstract due to an insufficient amount of observational data little is known about the temperature variation in the global abyssal ocean and its contribution to sea level change in this study we estimated the monthly seawater temperature below 2000 m from 2005 2015 by combining array for real time geostrophic oceanography argo and conductivity temperature depth ctd data for this purpose we divided the global ocean into 38 regions according to the ctd temperature profile properties for each region we used ctd data to construct a mathematical model to describe the relation of temperatures between 1000 2000 m and those below 2000 m we then used this mathematical model and the argo data to reconstruct the temperature profile below 2000 m and evaluate its thermostatic contribution to sea level change we discovered that the deep ocean below 2000 m contributed 0 12 0 03 mm yr to the mean global thermosteric sea level rise from 2005 2015 our result was confirmed by geodetic observations i e the rate of thermosteric sea level rise calculated using altimeter gravity recovery and climate experiment grace and argo data was approximately 0 15 0 41 mm yr the contribution of each ocean layer generally decreased with depth and there was an obvious fluctuation between approximately 4000 5000 m interpreted as being caused by geothermal heating of the ocean floor

recent western south atlantic bottom water warming 1 potential temperature differences are computed from hydrographic sections transiting the western basins of the south atlantic ocean from 60 s to the equator in 2005 2003 and 1989 1995 while warming is observed throughout much of the water column the most statistically significant warming is about 0 04 c in the bottom 1500 dbar of the brazil basin with similar but less statistically significant warming signals in the abyssal argentine basin and scotia sea these abyssal waters of antarctic origin spread northward in the south atlantic the observed abyssal argentine basin warming is of a similar magnitude to that previously reported between 1980 and 1989 the brazil basin abyssal warming is similar in size to and consistent in timing with previously reported changes in abyssal southern inflow and northern outflow the temperature changes reported here if they were to hold throughout the abyssal world ocean would contribute substantially to global ocean heat budgets

antarctic bottom water warming and freshening contributions to sea level rise ocean freshwater budgets and global heat gain abstractfreshening and warming of antarctic bottom water aabw between the 1980s and 2000s are quantified assessing the relative contributions of water mass changes and isotherm heave the analysis uses highly accurate full depth ship based conductivity temperature depth measurements taken along repeated oceanographic sections around the southern ocean fresher varieties of aabw are present within the south pacific and south indian oceans in the 2000s compared to the 1990s with the strongest freshening in the newest waters adjacent to the antarctic continental slope and rise indicating a recent shift in the salinity of aabw produced in this region bottom waters in the weddell sea exhibit significantly less water mass freshening than those in the other two southern basins however a decrease in the volume of the coldest deepest waters is observed throughout the entire southern ocean this isotherm heave causes a salinification and warming on isobaths from the bottom up to the shallow potential tem

the deep ocean buoyancy budget and its temporal variability abstractdespite slow rates of ocean mixing observational and modeling studies suggest that buoyancy is redistributed to all depths of the ocean on surprisingly short interannual to decadal time scales the mechanisms responsible for this redistribution remain poorly understood this work uses an earth system model to evaluate the global steady state ocean buoyancy and related steric sea level budget its interannual variability and its transient response to a doubling of co2 over 70 years with a focus on the deep ocean at steady state the simple view of vertical advective diffusive balance for the deep ocean holds at low to midlatitudes at higher latitudes the balance depends on a myriad of additional terms namely mesoscale and submesoscale advection convection and overflows from marginal seas and terms related to the nonlinear equation of state these high latitude processes rapidly communicate anomalies in surface buoyancy forcing to the deep ocean locally the deep high latitude changes th

large multidecadal salinity trends near the pacific antarctic continental margin abstract ocean temperature and salinity measurements on and near the antarctic continental shelf in the southwest pacific sector are evaluated for evidence of temporal change shelf water in the southwest ross sea has declined in salinity by 0 03 decade 1 from 1958 to 2008 while its temperatures have increased in proportion to the influence of salinity on the sea surface freezing point modified deep water intrusions that reach the central ross ice shelf have freshened at a similar rate and cooled by 0 5 c since the late 1970s salinity has decreased by 0 08 decade 1 in the westward coastal and slope front currents consistent with increased melting of continental ice upstream in the amundsen sea overturning of those near surface waters during winter sea ice formation and mixing across the slope front is sufficient to account for the 5 decade shelf water salinity change a strong correlation between the freshening and change in the southern annular mode index suggests a link with the large scale atmosp

impact of self attraction and loading effects induced by shelf mass loading on projected regional sea level rise we investigate the effect of self attraction and loading sal induced by the projected accumulation of sea water on shallow continental shelf areas using output from a climate model we compute 21st century changes in regional steric sea surface height and find that steric changes are largest over the deep ocean and relatively small on the shallow continental shelves the resulting redistribution of sea water towards the shelf areas leads to mass accumulation on the shelves and therefore to increased gravitational attraction as well as increased loading on the sea floor we find that depending on the scenario and region sal effects may result in an additional sea level rise of 1 3 cm on the world s continental shelf areas by the end of the 21st century these estimates are at most 15 of the combined changes in sea surface height induced by redistribution of water masses and steric expansion

unabated bottom water warming and freshening in the south pacific ocean author posting american geophysical union 2019 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 124 3 2019 1778 1794 doi 10 1029 2018jc014775

global and full depth ocean temperature trends during the early twenty first century from argo and repeat hydrography the early 21st century s warming trend of the full depth global ocean is calculated by combining the analysis of argo top 2000m and repeat hydrography into a blended full depth observing system the surface to bottom temperature change over the last decade of sustained observation is equivalent to a heat uptake of 0 72 0 09 w m 2 applied over the surface of the earth 90 of it being found above 2000m depth we decompose the temperature trend point wise into changes in isopycnal depth heave and temperature changes along an isopycnal spiciness to describe the mechanisms controlling the variability the heave component dominates the global heat content increase with the largest trends found in the southern hemisphere s extratropics 0 2000m highlighting a volumetric increase of subtropical mode waters significant heave related warming is also found in the deep north atlantic and southern ocean 2000m 4000m reflecting a potential decrease in deep water mass renewal rates the spiciness component shows its strongest contribution at intermediate levels 700m 2000m with striking localised warming signals in regions of intense vertical mixing north atlantic and southern oceans finally the agreement between the independent argo and repeat hydrography temperature changes at 2000m provides an overall good confidence in the blended heat content evaluation on global and ocean scales but also highlights basin scale discrepancies between the two independent estimates those mismatches are largest in those basins with the largest heave signature southern ocean and reflect both the temporal and spatial sparseness of the hydrography sampling

circumpolar structure and distribution of the antarctic circumpolar current fronts 2 variability and relationship to sea surface height 1 in part 1 of this study we showed that the antarctic circumpolar current acc consisted of multiple fronts each of which was consistently associated with a particular contour of sea surface height ssh or approximate streamline in part 2 we have used maps of ssh to examine the variability of the acc fronts between 1992 and 2007 the ssh label associated with each frontal branch is nearly constant around the circumpolar belt the front labels are also nearly constant in time the bands of enhanced ssh gradient i e fronts occur along the same streamlines throughout the 15 year period of observations both short and long period changes of the ssh frontal labels of the acc are small based on a tight relationship between dynamic height and cumulative baroclinic transport of the acc the baroclinic transport variability of the individual branches of the acc is also expected to be small the major change in the total acc baroclinic transport occurs in the drake passage the streamline associated with the northern branch of the saf saf n does not pass through drake passage and the waters carried by this branch are not observed there instead the transport of the saf n turns north in the pacific to supply the export of water to the indian ocean north and south of australia strong eddy activity in the southeast pacific acts to dissipate the hydrographic signature of the saf n there in the atlantic the saf n reappears as the same streamline is again associated with enhanced ssh gradients to the east of the brazil malvinas confluence zone while the large changes in ssh have occurred in the southern ocean between 1992 and 2007 there are strong regional differences because the acc fronts are robustly associated with particular ssh contours the changes in ssh reflect shifts in the position of the acc fronts in the circumpolar average each of the acc fronts has shifted to the south by about 60 km the changes in ssh in the southern ocean are largely due to changes in ocean circulation rather than warming and freshening by atmospheric fluxes much larger changes in ssh are observed in some locations of the southern ocean particularly where the fronts interact with large scale topography the northern branch of the pf pf n near the kerguelen plateau is an extreme example where the pf n followed a path around the northern end of kerguelen plateau between 1992 and 1997 passed through the fawn trough after 2003 and oscillated between the two paths between 1997 and 2003

observed ocean bottom temperature variability at four sites in the northwestern argentine basin evidence of decadal deep abyssal warming amidst hourly to interannual variability during 2009 2019

benefits of cmip5 multimodel ensemble in reconstructing historical ocean subsurface temperature variations abstracta complete map of the ocean subsurface temperature is essential for monitoring aspects of climate change such as the ocean heat content ohc and sea level changes and for understanding the dynamics of the ocean climate variation however global observations have not been available in the past so a mapping strategy is required to fill the data gaps in this study an advanced mapping method is proposed to reconstruct the historical ocean subsurface 0 700 m temperature field from 1940 to 2014 by using ensemble optimal interpolation with a dynamic ensemble enoi de approach and a multimodel ensemble of phase 5 of the coupled model intercomparison project cmip5 historical and representative concentration pathway 4 5 simulations the reconstructed field is a combination of two parts a first guess provided by the ensemble mean of cmip5 models and an adjustment by minimizing the analysis error with the assistance of error covariance determined by the cmip5 models the uncertainty of the field ca

warming and freshening in the abyssal southeastern indian ocean abstract warming and freshening of abyssal waters in the eastern indian ocean between 1994 95 and 2007 are quantified using data from two closely sampled high quality occupations of a hydrographic section extending from antarctica northward to the equator these changes are limited to abyssal waters in the princess elizabeth trough and the australian antarctic basin with little abyssal change evident north of the southeast indian ridge as in previous studies significant cooling and freshening is observed in the bottom potential temperature salinity relations in these two southern basins in addition analysis on pressure surfaces shows abyssal warming of about 0 05 c and freshening of about 0 01 practical salinity scale 1978 pss 78 in the princess elizabeth trough and warming of 0 1 c with freshening of about 0 005 in the abyssal australian antarctic basin these 12 yr differences are statistically significant from zero at 95 confidence intervals over the bottom few to several hundred decibars of t

turbulent mixing in a deep fracture zone on the mid atlantic ridge abstractmidocean ridge fracture zones channel bottom waters in the eastern brazil basin in regions of intensified deep mixing the mechanisms responsible for the deep turbulent mixing inside the numerous midocean fracture zones whether affected by the local or the nonlocal canyon topography are still subject to debate to discriminate those mechanisms and to discern the canyon mean flow two moorings sampled a deep canyon over and away from a sill contraction a 2 layer exchange flow accelerated at the sill transports 0 04 0 10 sv 1 sv 106 m3 s 1 up canyon in the deep layer at the sill the dissipation rate of turbulent kinetic energy e increases as measured from microstructure profilers and as inferred from a parameterization of vertical kinetic energy cross sill density and microstructure transects reveal an overflow potentially hydraulically controlled and modulated by fortnightly tides during spring to neap tides e varies from o 10 9 to o 10 10 w kg 1 below 3500 m around the 2 layer inte

rapid freshening of antarctic bottom water formed in the indian and pacific oceans 1 repeat hydrographic sections occupied in 1995 and 2005 reveal a rapid decline in the salinity and density of antarctic bottom water throughout the australian antarctic basin the basin wide shift of the deep potential temperature salinity s relationship reflects freshening of both the indian and pacific sources of antarctic bottom water the s curves diverge for waters cooler than 0 1 c corresponding to a layer up to 1000 m thick over the antarctic continental slope and rise changes over the last decade are in the same direction but more rapid than those observed between the late 1960s and the 1990s when combined with recent observations of similar freshening of north atlantic deep water these results demonstrate that dense water formed in both hemispheres is freshening in response to changes in the high latitude freshwater balance and rapidly transmitting the signature of changes in surface climate into the deep ocean

low sea level rise projections from mountain glaciers and icecaps under global warming the mean sea level has been projected to rise in the 21st century as a result of global warming such projections of sea level change depend on estimated future greenhouse emissions and on differing models but model average results from a mid range scenario a1b suggests a 0 387 m rise by 2100 refs 1 2 the largest contributions to sea level rise are estimated to come from thermal expansion 0 288 m and the melting of mountain glaciers and icecaps 0 106 m with smaller inputs from greenland 0 024 m and antarctica 0 074 m here we apply a melt model and a geometric volume model to our lower estimate of ice volume and assess the contribution of glaciers to sea level rise excluding those in greenland and antarctica we provide the first separate assessment of melt contributions from mountain glaciers and icecaps as well as an improved treatment of volume shrinkage we find that icecaps melt more slowly than mountain glaciers whose area declines rapidly in the 21st century making glaciers a limiting source for ice melt using two climate models we project sea level rise due to melting of mountain glaciers and icecaps to be 0 046 and 0 051 m by 2100 about half that of previous projections

reduced antarctic meridional overturning circulation reaches the north atlantic ocean 1 we analyze abyssal temperature data in the western north atlantic ocean from the 1980s 2000s showing that reductions in antarctic bottom water aabw signatures have reached even that basin trans basin oceanographic sections occupied along 52 w from 1983 2003 and 66 w from 1985 2003 quantify abyssal warming resulting from deepening of the strong thermal boundary between aabw and north atlantic deep water nadw hence a local aabw volume reduction repeat section data taken from 1981 2004 along 24 n also show a reduced zonal gradient in abyssal temperatures consistent with decreased northward transport of aabw the reduction in the antarctic limb of the moc within the north atlantic highlights the global reach of climate variability originating around antarctica

the imprint of southern ocean overturning on seasonal water mass variability in drake passage seasonal changes in water mass properties are discussed in thermohaline coordinates from a seasonal climatology and repeat hydrographic sections the sr1b ctd transects along drake passage are used as a case study the amount of water within temperature and salinity classes and changes therein are used to estimate dia thermal and dia haline transformations these transformations are considered in combination with climatologies of surface buoyancy flux to determine the relative contributions of surface buoyancy fluxes and subsurface mixing to changes in the distribution of water in thermohaline coordinates the framework developed provides unique insights into the thermohaline circulation of the water masses that are present within drake passage including the erosion of antarctic winter water aaww during the summer months and the interaction between the circumpolar deep waters cdw and antarctic intermediate water aaiw the results presented are consistent with summertime wind driven inflation of the cdw layer and deflation of the aaiw layer and with new aaiw produced in the winter as a mixture of cdw remnant aaww and surface waters this analysis therefore highlights the role of surface buoyancy fluxes in the southern ocean overturning

decadal freshening of the antarctic bottom water exported from the weddell sea recent decadal changes in southern hemisphere climate have driven strong responses from the cryosphere concurrently there has been a marked freshening of the shelf and bottom waters across a wide sector of the southern ocean hypothesised to be caused by accelerated glacial melt in response to a greater flux of warm waters from the antarctic circumpolar current onto the shelves of west antarctica however the circumpolar pattern of changes has been incomplete no decadal freshening in the deep layers of the atlantic sector had been observed in this study we document a significant freshening of the antarctic bottom water exported from the weddell sea which is the source for the abyssal layer of the atlantic overturning circulation and we trace its possible origin to atmospheric forced changes in the ice shelves and sea ice on the eastern flank of the antarctic peninsula that include an anthropogenic component these findings suggest that the expansive and relatively cool weddell gyre does not insulate the bottom water formation regions in the atlantic sector from the ongoing changes in climatic forcing over the antarctic region

global contraction of antarctic bottom water between the 1980s and 2000s abstracta statistically significant reduction in antarctic bottom water aabw volume is quantified between the 1980s and 2000s within the southern ocean and along the bottom most southern branches of the meridional overturning circulation moc aabw has warmed globally during that time contributing roughly 10 of the recent total ocean heat uptake this warming implies a global scale contraction of aabw rates of change in aabw related circulation are estimated in most of the world s deep ocean basins by finding average rates of volume loss or gain below cold deep potential temperature surfaces using all available repeated hydrographic sections the southern ocean is losing water below 0 c at a rate of 8 2 2 6 106 m3 s 1 this bottom water contraction causes a descent of potential isotherms throughout much of the water column until a near surface recovery apparently through a southward surge of circumpolar deep water from the north to the north smaller losses of bottom waters are see

trends in the deep southern ocean 1958 2010 implications for antarctic bottom water properties and volume export 1 regional formation of deep and bottom water masses around the antarctic continental shelf is one of the most important processes contributing to variability of the global meridional overturning circulation deep cell southern ocean hydrographic data collected during the years 1958 2010 indicate that dense shelf waters cooled and freshened during that period in the surrounding open ocean antarctic bottom water aabw warmed with no evidence of salinity change as a result of source water property changes aabw exported from the southern ocean to the deep world ocean became lighter over the period analyzed the average rate of density change within the areas that experienced statistically significant change was 0 0019 kg m 3 yr 1 for the last 20 years of the analysis a negative aabw volume anomaly relative to the half century average 1958 2010 was indicated possibly due to production of a lighter aabw variety or to changes in formation rates over the entire five decades the upper isopycnal of the aabw layer deepened at a rate of 8 1 m yr 1 changes in fundamental hydrographic properties such as these can have important implications for long term global ocean circulation and climate

dense bottom layers in the scotia sea southern ocean creation lifespan and destruction the lower limb of the atlantic overturning circulation is renewed by dense waters from the southern ocean a substantial portion of which flow through the scotia sea we report dense bottom layers here with gradients in temperature and salinity comparable to those seen near the surface of the southern ocean these are overlain by layers with much weaker stratification and are caused by episodic overflows of dense waters across the south scotia ridge and topographic trapping within deep trenches one such layer was found to be at least 3 4 years older than the water immediately above the estimated vertical diffusivity to which this layer was subject is substantially less than the strong basin average deep mixing reported previously we conjecture that a vertical mixing in the scotia sea is strongly spatially inhomogeneous and b the flushing of these layers like their formation is related to overflow events and hence also strongly episodic

unsupervised clustering of southern ocean argo float temperature profiles the southern ocean has complex spatial variability characterized by sharp fronts steeply tilted isopycnals and deep seasonal mixed layers methods of defining southern ocean spatial structures traditionally rely on somewhat ad hoc combinations of physical chemical and dynamic properties as a step towards an alternative approach for describing spatial variability in temperature here we apply an unsupervised classification technique that is gaussian mixture modelling or gmm to southern ocean argo float temperature profiles gmm without using any latitude or longitude information automatically identifies several spatially coherent circumpolar classes influenced by the antarctic circumpolar current in addition gmm identifies classes that bear the imprint of mode intermediate water formation and export large scale gyre circulation and the agulhas current among others because gmm is robust standardized and automated it can potentially be used to identify structures such as fronts in both observational and model datasets possibly making it a useful complement to existing classification techniques

deep ocean warming assessed from altimeters gravity recovery and climate experiment in situ measurements and a non boussinesq ocean general circulation model 1 observational surveys have shown significant oceanic bottom water warming but they are too spatially and temporally sporadic to quantify the deep ocean contribution to the present day sea level rise slr in this study altimetry sea surface height ssh gravity recovery and climate experiment grace ocean mass and in situ upper ocean 0 700 m steric height have been assessed for their seasonal variability and trend maps it is shown that neither the global mean nor the regional trends of altimetry slr can be explained by the upper ocean steric height plus the grace ocean mass a non boussinesq ocean general circulation model ogcm allowing the sea level to rise as a direct response to the heat added into the ocean is then used to diagnose the deep ocean steric height constrained by sea surface temperature data and the top of atmosphere toa radiation measurements the model reproduces the observed upper ocean heat content well combining the modeled deep ocean steric height with observational upper ocean data gives the full depth steric height adding a grace estimated mass trend the data model combination explains not only the altimetry global mean slr but also its regional trends fairly well the deep ocean warming is mostly prevalent in the atlantic and indian oceans and along the antarctic circumpolar current suggesting a strong relation to the oceanic circulation and dynamics its comparison with available bottom water measurements shows reasonably good agreement indicating that deep ocean warming below 700 m might have contributed 1 1 mm yr to the global mean slr or one third of the altimeter observed rate of 3 11 0 6 mm yr over 1993 2008

increased ocean heat convergence into the high latitudes with co2 doubling enhances polar amplified warming we isolate the role of the ocean in polar climate change by directly evaluating how changes in ocean dynamics with quasi equilibrium co2 doubling impact high latitude climate with co2 doubling the ocean heat flux convergence ohfc shifts poleward in winter in both hemispheres imposing this pattern of perturbed ohfc in a global climate model results in a poleward shift in ocean to atmosphere turbulent heat fluxes both sensible and latent and sea ice retreat the high latitudes warm while the midlatitudes cool thereby amplifying polar warming furthermore midlatitude cooling is propagated to the polar midtroposphere on isentropic surfaces augmenting the positive lapse rate feedback at high latitudes these results highlight the key role played by the partitioning of meridional energy transport changes between the atmosphere and ocean in high latitude climate change

importance of the eastern indian ocean for the abyssal pacific 1 the role of the eastern indian ocean in controlling the abyssal circulation in the pacific is examined using a 1 1 world ocean model thanks to the improvement of bottom topography and the incorporation of a bottom boundary layer model the bottom water formation off the adelie coast is produced this bottom water is not only the source of the abyssal water in the eastern indian but also has a great influence on the whole abyssal pacific the lower part of circumpolar deep water cdw which enters the abyssal pacific passing through south of new zealand changes its property through mixing with this bottom water flowing underneath cdw in the australian antarctic basin and the south australia basin the tracer experiments show that the water ventilated off the adelie coast occupies about 20 of the abyssal pacific whereas north atlantic deep water nadw occupies about 50 the weddell sea bottom water about 20 and the ross sea bottom water about 10 the flux of the ventilated water estimated by the tracer experiments is 17 1 sv for nadw 6 3 sv from the weddell sea 6 2 sv from off the adelie coast and 3 5 sv from ross sea in this model the total flux of 33 1 sv is not far from the estimate from observations though it may overestimate by 1 4 sv this does not directly indicate that the real world ocean should have the large amount of the bottom water sources in the pacific indian sector however the model offers a picture of the water properties consistent with the observation

wind controlled export of antarctic bottom water from the weddell sea recent studies suggest that the variability in antarctic bottom water aabw properties in the scotia sea on time scales up to decadal may be linked to changes in the baroclinicity of the weddell gyre with vertical variations in the density structure at the gyre s northern edge acting to control the export of aabw over the south scotia ridge and toward the mid latitude south atlantic we test this hypothesis by analysing the aabw properties in fifteen occupations of the sr1b hydrographic section 1993 2009 in eastern drake passage alongside possible forcings as derived from atmospheric reanalysis data we show that variability in the wind stress over the weddell gyre leads changes in aabw properties in the sr1b section by approximately five months the sign of the lagged correlation is consistent with the notion of the aabw export from the weddell sea being controlled by the gyre s baroclinic adjustment to wind forcing on time scales of several months variability in the regional winds is found to be closely linked to the southern annular mode sam these results suggest that there may be a causal relationship between the sam s positive tendency observed in recent decades and the subsequent warming of aabw detected across much of the atlantic ocean citation jullion l s c jones a c naveira garabato and m p meredith 2010 wind controlled export of antarctic bottom water from the weddell sea geophys res lett 37 l09609 doi 10 1029 2010gl042822

quantifying antarctic bottom water and north atlantic deep water volumes 1 a near global census of antarctic bottom water aabw and north atlantic deep water nadw is essayed through a nonnegative least squares analysis of conservative and quasi conservative seawater properties aabw thickness generally decreases from south to north modulated by ocean bathymetry likewise nadw thickness generally decreases from north to south in the atlantic ocean nadw dominates below the thermocline of the atlantic ocean at least as far south as the subtropical gyre of the south atlantic with a lesser but still significant influence around the entire antarctic circumpolar current in the indian ocean and in the pacific ocean however in the pacific and indian oceans aabw dominates below the thermocline in addition measurable quantities of aabw reach into the abyssal north atlantic on both sides of the mid atlantic ridge the census results suggest that aabw occupies roughly twice the volume of nadw in the three main oceans and that aabw is in contact with roughly twice the area of the deep main ocean floor compared with nadw however these results are somewhat sensitive to choices of water masses their values of seawater properties and the weightings of the seawater properties used in the analysis

decadal spinup of the south pacific subtropical gyre abstract an increase in the circulation of the south pacific ocean subtropical gyre extending from the sea surface to middepth is observed over 12 years datasets used to quantify the decadal gyre spinup include satellite altimetric height the world ocean circulation experiment woce hydrographic and float survey of the south pacific a repeated hydrographic transect along 170 w and profiling float data from the global argo array the signal in sea surface height is a 12 cm increase between 1993 and 2004 on large spatial scale centered at about 40 s 170 w the subsurface datasets show that this signal is predominantly due to density variations in the water column that is to deepening of isopycnal surfaces extending to depths of at least 1800 m the maximum increase in dynamic height is collocated with the deep center of the subtropical gyre and the signal represents an increase in the total counterclockwise geostrophic circulation of the gyre by at least 20 at 1000 m a comparison of woce and

potential for bias in 21st century semiempirical sea level projections we examine the limitations of a semiempirical model characterized by a sea level projection of 73 cm with rcp4 5 scenario by 2100 calibrating the model with data to 1990 and then simulating the period 1993 2009 produces sea level in close agreement with acceleration in sea level rise observed by satellite altimetry nonradiative forcing contributors such as long term adjustment of greenland and antarctica ice sheets since last glacial maximum abyssal ocean warming and terrestrial water storage may bias model calibration which if corrected for tend to reduce median sea level projections at 2100 by 2 10 cm though this is within the confidence interval we apply the semiempirical approach to simulate individual contributions from thermal expansion and small glacier melting steric sea level projections agree within 3 cm of output from process based climate models in contrast semiempirical simulation of melting from glaciers is 26 cm which is twice large as estimates from some process based models however all process models lack simulation of calving which likely accounts for 50 of small glacier mass loss worldwide furthermore we suggest that changes in surface mass balance and dynamics of greenland ice sheet made contributions to the sea level rise in the early 20th century and therefore are included within the semiempirical model calibration period and hence are included in semiempirical sea level projections by 2100 antarctic response is probably absent from semiempirical models which will lead to a underestimate in sea level rise if as is probable antarctica loses mass by 2100

multidecadal warming of antarctic waters decadal trends in the properties of seawater adjacent to antarctica are poorly known and the mechanisms responsible for such changes are uncertain antarctic ice sheet mass loss is largely driven by ice shelf basal melt which is influenced by ocean ice interactions and has been correlated with antarctic continental shelf bottom water asbw temperature we document the spatial distribution of long term large scale trends in temperature salinity and core depth over the antarctic continental shelf and slope warming at the seabed in the bellingshausen and amundsen seas is linked to increased heat content and to a shoaling of the mid depth temperature maximum over the continental slope allowing warmer saltier water greater access to the shelf in recent years regions of asbw warming are those exhibiting increased ice shelf melt

evolution of the deep and bottom waters of the scotia sea southern ocean during 1995 2005 the southern ocean hosts the formation of the densest layers of the oceanic overturning circulation and provides a climatically sensitive element of deep ocean ventilation an oceanographic section across the eastern scotia sea occupied in 1995 1999 and 2005 reveals significant variability in the deep and bottom waters of southern ocean origin warming 0 1 c of the warm midlayer waters in the scotia sea between 1995 and 1999 reversed through to 2005 reflecting changes seen earlier upstream in the weddell sea the volume of deep waters with potential temperature less than 0 c decreased during 1995 2005 though such a reduction was only clear between 1995 and 1999 at the southern end of the section the abyssal waters of the eastern scotia sea changed circulation between 1995 and 1999 with the dominant point of their entry to the basin shifting from the south to the northeast by 2005 the former route had regained dominance these changes are best explained by interannual variations in the deep waters exiting the weddell sea superimposed on a longer term decadal warming trend the interannual variations are related to changes in the strength of the weddell gyre reflecting large scale atmospheric variability that may include the el nino southern oscillation phenomenon the scotia sea is the most direct pathway for dense waters of the overturning circulation emanating from the weddell sea to fill much of the world ocean abyss the regional changes reported here have the potential to affect the climatically significant ventilation of the global ocean abyss

meridional displacement of the antarctic circumpolar current observed long term warming trends in the southern ocean have been interpreted as a sign of increased poleward eddy heat transport or of a poleward displacement of the entire antarctic circumpolar current acc frontal system the two decade long record from satellite altimetry is an important source of information for evaluating the mechanisms governing these trends while several recent studies have used sea surface height contours to index acc frontal displacements here altimeter data are instead used to track the latitude of mean acc transport altimetric height contours indicate a poleward trend regardless of whether they are associated with acc fronts the zonally averaged transport latitude index shows no long term trend implying that acc meridional shifts determined from sea surface height might be associated with large scale changes in sea surface height more than with localized shifts in frontal positions the transport latitude index is weakly sensitive to the southern annular mode but is uncorrelated with el nino southern oscillation

physiographic influences on dense shelf water cascading down the antarctic continental slope abstract predicting the source areas for antarctic bottom water aabw requires knowledge of how cold dense water masses form and move from the antarctic shelves to the continental slope here we use a review of nearly 50 years of direct hydrographic observations to infer the main broad scale influences on the distribution of dense shelf water dsw overflows that cascade down the continental slope around antarctica the dynamics and distribution of large ice shelves coastal polynyas and the physiography of the antarctic continental shelves are each considered the catalogue we present increases the number of dsw observations to 27 adds 20 additional stations where this process is likely to have occurred and identifies 41 areas where dsw appears to be absent our pan antarctic multi decadal review enhances the understanding of the formation and export of dsw and highlights the variability and complexity of ice ocean systems on high latitude continental margins the study also provides a context for understanding recent episodes of antarctic ice shelf instability and how the relationship between dsw and aabw may evolve with climatic and oceanographic changes

global assessment of semidiurnal internal tide aliasing in argo profiles abstractthough unresolved by argo floats internal waves still impart an aliased signal onto their profile measurements recent studies have yielded nearly global characterization of several consti

detection of sea level fingerprints derived from grace gravity data mass changes of ice sheets glaciers ice caps land water hydrology atmosphere and ocean cause a non uniform sea level rise due to the gravitational and self attraction and loading effects called sea level fingerprints slf slf have been previously derived from a combination of modeled and observed mass fluxes from the continents into the ocean here we derive improved slf from time series of time variable gravity data from the grace mission for april 2002 october 2014 we evaluate the grace derived slf using ocean bottom pressure obp data from stations in the tropics where obp errors are the lowest we detect the annual phase of the slf in the obp signal and separate it unambiguously from the barystatic sea level bsl at two stations at the basin scale the slf explain a larger fraction of the variance in steric corrected altimetry than the bsl which has implications for evaluating mass transport between ocean basins

weddell polynya transport mechanisms in the abyssal ocean abstractweddell polynya transport mechanisms in the deep and abyssal oceans are examined in the noaa geophysical fluid dynamics laboratory s gfdl coupled climate model cm2g during an 1820 yr long integration of the model polynyas are forced every 29 years in the weddell sea via an increase in the diapycnal diffusivity composites of the events are used to examine the mechanisms responsible for transporting polynya signals away from the weddell sea polynya signal transport is governed by two dynamical mechanisms that act on different time scales and spread at different rates large scale waves such as kelvin and planetary and topographic rossby waves propagate the polynya signal rapidly on interannual to decadal time scales while advection transports the signal more slowly on decadal to centennial time scales despite their different spreading rates these mechanisms can act contemporaneously and it is often their combined effect that governs the property changes in the global deep and abyssal o

internal tide oceanic tomography a concept of internal tide oceanic tomography itot is proposed to monitor ocean warming on a global scale itot is similar to acoustic tomography but that work waves are internal tides itot detects ocean temperature changes by precisely measuring travel time changes of long range propagating internal tides the underlying principle is that upper ocean warming strengthens ocean stratification and thus increases the propagation speed of internal tides this concept is inspired by recent advances in observing internal tides by satellite altimetry in particular a plane wave fit method can separately resolve multiple internal tidal waves and thus accurately determines the phase of each wave two examples are presented to demonstrate the feasibility and usefulness of itot in the eastern tropical pacific the yearly time series of travel time changes of the m2 internal tide is closely correlated with the el nino southern oscillation index in the north atlantic significant interannual variations and bidecadal trends are observed and consistent with the changes in ocean heat content measured by argo floats itot offers a long term cost effective environmentally friendly technique for monitoring global ocean warming future work is needed to quantify the accuracy of this technique

oceanography replenishing the abyss antarctic bottom water is formed along the fringes of antarctica and fills much of the abyssal oceans data from moored instruments and tagged marine mammals confirm an unexpected site of bottom water formation at cape darnley west of the amery ice shelf

dense waters of the weddell and scotia seas recent changes in properties and circulation the densest waters in the atlantic overturning circulation are sourced at the periphery of antarctica especially the weddell sea and flow northward via routes that involve crossing the complex bathymetry of the scotia arc recent observations of significant warming of these waters along much of the length of the atlantic have highlighted the need to identify and understand the time varying formation and export processes and the controls on their properties and flows here we review recent developments in understanding of the processes that control the changing flux of water through the main export route from the weddell sea into the scotia sea and the transformations of the waters within the scotia sea and environs we also present a synopsis of recent findings that relate to the climatic change of dense water properties within the weddell sea itself in the context of known atlantic scale changes among the most significant findings are the discovery that the warming of waters exported from the weddell sea has been accompanied by a significant freshening and that the episodic nature of the overflow into the scotia sea is markedly wind controlled and can lead to significantly enhanced abyssal stratification key areas for focusing future research effort are outlined

synchronous intensification and warming of antarctic bottom water outflow from the weddell gyre 1 antarctic bottom water aabw the densest water in the global overturning circulation has warmed in recent decades most notably in the atlantic time series recorded within the boundary currents immediately upstream and downstream of the most significant outflow of aabw from the weddell sea indicate that raised outflow temperatures are synchronous with stronger boundary current flows these changes occur rapidly in response to changes in wind forcing suggesting that barotropic dynamics and the response of the bottom ekman layer are significant the observed synchronicity indicates that the previously detected weakening of the export of the colder forms of aabw from the weddell sea need not be associated with a reduction in the total flux of aabw exported via this route these points need careful consideration when attributing the observed aabw warming in the atlantic and when determining its contribution to global heat budgets and sea level rise citation meredith m p a l gordon a c naveira garabato e p abrahamsen b a huber l jullion and h j venables 2011 synchronous intensification and warming of antarctic bottom water outflow from the weddell gyre geophys res lett 38 l03603 doi 10 1029 2010gl046265