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

interpentadal variability of temperature and salinity at intermediate depths of the north atlantic ocean 1970 1974 versus 1955 1959 we have composited historical hydrographic observations for the world ocean for two pentads 1955 1959 and 1970 1974 and have objectively analyzed these data for the purpose of studying the temporal variability of temperature and salinity in the north atlantic ocean the subtropical gyre 500 1300 m of the north atlantic was colder and fresher during 1970 1974 compared to 1955 1959 the relatively large changes in temperature and salinity on constant depth surfaces in the subtropical gyre were due to upward displacements of isopycnal surfaces at intermediate depths the eastern portion of the subarctic gyre was also colder and fresher during the 1970 1974 pentad in contrast the western portion of the subarctic gyre exhibited higher temperatures and salinities during 1970 1974 compared to 1955 1959 characteristic differences in temperature and salinity for both gyres were 0 5 c and 0 025 respectively analysis of changes in potential vorticity indicates that in the subtropical gyre potential vorticity increased in all density layers above the 26 5 surface suggesting that convection in this region may have been shallower in 1970 1974 compared to 1955 1959 below the 26 5 surface potential vorticity decreased through the 27 3 surface indicating that deeper than normal convection may have formed the water masses in these layers at 250 m depth relatively large changes in temperature and salinity occurred along the line of maximum climatological mixed layer depth that extends northeast to southwest across the north atlantic ocean

climate fluctuations of the weddell sea and its surroundings in a transient climate change scenario the response of the weddell sea and antarctic peninsula to anthropogenic forcing simulated by a global climate model is analyzed the model despite its low resolution is able to capture several aspects of the observed regional pattern of climate change a strong warming and depletion of the sea ice cover in the western weddell sea contrasts with a slight cooling and a sea ice extension in the eastern weddell sea this simulated long term climate change is modulated by interdecadal variability but also affected by some abrupt regional changes in the oceanic mixed layer depth between 1960 and 2030 a reorganization of the deep convection activity in the weddell sea sustains the opposition between the eastern and western weddell sea the deep convection collapses in the western weddell sea in the 2030s the sea ice retreat trend is then followed by an increase of the sea ice cover in the western weddell sea in the eastern weddell sea another abrupt collapse of the deep convection activity occurs around 2080 this event is followed by a rapid cooling and sea ice extension during the next 20 years most of the surface changes are associated with large scale atmospheric circulation changes that project on the dominant mode of natural variability but also with oceanic convection and circulation changes

a model of sea level rise caused by ocean thermal expansion abstract warming of the atmosphere as a result of an increased concentration of greenhouse gases is expected to lead to a significant rise is global sea level we present estimates of the component of this sea level rise caused by thermal expansion of the ocean these estimates are based on the idea that the upper layers of the main gyres of the ocean are ventilated by the subduction of water at higher latitudes and its subsequent equatorward and downward flow into the main thermocline along surfaces of constant density in this mechanism heat enters the ocean by an advection process rather than by vertical diffusion as in previous estimates of the component of sea level rise that is caused by thermal expansion after the heat initially enters the subtropical gyres by subduction it is then redistributed to preserve gradients of the depth integrated pressure field by an adjustment involving low vertical mode baroclinic waves estimates of historical sea level rise based on this simple ventilation sch

iceberg trajectory modeling and meltwater injection in the southern ocean this is the first large scale modeling study of iceberg trajectories and melt rates in the southern ocean an iceberg model was seeded with climatological iceberg calving rates based on a calculation of the net surface accumulation from each snow catchment area on the antarctic continent in most areas modeled trajectories show good agreement with observed patterns of iceberg motion though discrepencies in the weddell sea have highlighted problems in the ocean general circulation model output used to force the iceberg model the coriolis force is found to be important in keeping bergs entrained in the coastal current around antarctica and topographic features are important in causing bergs to depart from the coastal regions the modeled geographic distribution of iceberg meltwater joining the ocean has been calculated and is found in many near coastal regions to be comparable in magnitude to the excess of precipitation over evaporation p e

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

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

deep ocean changes near the western boundary of the south pacific ocean repeated occupations of two hydrographic sections in the southwest pacific basin from the 1990s to 2000s track property changes of antarctic bottom water aabw the largest property changes warming freshening increase in total carbon and decrease in oxygen are found near the basin s deep western boundary between 508 and 208s the magnitude of the property changes decreases with increasing distance from the western boundary at the deep western boundary analysis of the relative importance of aabw g n 28 1kgm 23 freshening heating orisopycnalheavesuggeststhatthedeepoceanstratificationchangeisthe result of both warming and freshening processes the consistent deep ocean changes near the western boundary of the southwest pacific basin dispel the notion that the deep ocean is quiescent high latitude climate variability is being directly transmitted into the deep southwest pacific basin and the global deep ocean through dynamic deep western boundary currents

recent recovery of antarctic bottom water formation in the ross sea driven by climate anomalies antarctic bottom water aabw supplies the lower limb of the global overturning circulation ventilates the abyssal ocean and sequesters heat and carbon on multidecadal to millennial timescales aabw originates on the antarctic continental shelf where strong winter cooling and brine released during sea ice formation produce dense shelf water which sinks to the deep ocean the salinity density and volume of aabw have decreased over the last 50 years with the most marked changes observed in the ross sea these changes have been attributed to increased melting of the antarctic ice sheet here we use in situ observations to document a recovery in the salinity density and thickness that is depth range of aabw formed in the ross sea with properties in 2018 2019 similar to those observed in the 1990s the recovery was caused by increased sea ice formation on the continental shelf increased sea ice formation was triggered by anomalous wind forcing associated with the unusual combination of positive southern annular mode and extreme el nino conditions between 2015 and 2018 our study highlights the sensitivity of aabw formation to remote forcing and shows that climate anomalies can drive episodic increases in local sea ice formation that counter the tendency for increased ice sheet melt to reduce aabw formation interacting atmospheric circulation patterns are responsible for a recent reversal of a decades long decline in deepwater formation on the antarctic shelf according to an analysis of in situ and remote sensing data from the ross sea

freshening drives contraction of antarctic bottom water in the australian antarctic basin antarctic bottom water aabw in the australian antarctic basin has become fresher and lighter since the late 1960s with largest changes observed near the sources of aabw the volume of aabw with neutral density n 28 30 kg m 3 decreased by 50 between 1969 1971 and 2008 2012 thinning at a rate of 100 m per decade contraction of dense aabw was balanced primarily by expansion of water lighter than n 28 15 kg m 3 prior to 1995 and by inflation of less dense classes of aabw after 1995 oxygen concentrations remained unchanged in the densest aabw and increased on neutral surfaces for aabw with n 28 31 kg m 3 between 1995 and 2011 2012 consistent with continued ventilation over this time period the observed changes in potential temperature salinity density volume and oxygen of aabw can be accounted for by freshening of the source waters but cannot be explained by changes in formation rate alone key points freshening drives contraction of antarctic bottom water aabw aabw has contracted by about 50 and thinned more than 100 m per decade since 1970 small increase in oxygen on isopycnals suggests continued ventilation of aabw 2014 american geophysical union all rights reserved

multiple episodes of mineralization revealed by re os molybdenite geochronology in the lala fe cu deposit sw china the lala fe cu deposit is one of the largest iron oxide copper gold iocg deposits in the kangdian copper belt southwest china the paragenetic sequence of the lala deposit includes six hydrothermal stages pre ore pervasive na alteration i magnetite stage with k feldspar and apatite ii polymetallic disseminated massive magnetite sulfide stage iii banded magnetite sulfide stage iv sulfide vein stage v and late quartz carbonate vein stage vi fifteen molybdenite separates from stages iii to vi were analyzed for re os dating our new re os data together with previous studies identify four distinct hydrothermal events at the lala deposit molybdenite from the stage iii disseminated to massive chalcopyrite magnetite ores yielded a weighted average re os age of 1306 8 ma mswd 1 1 n 6 which represents the timing of main ore formation molybdenite from the stage iv banded magnetite chalcopyrite ores yielded a weighted average re os age of 1086 8 ma mswd 2 2 n 7 i e a second ore forming event molybdenite from the stage v sulfide veins yielded a weighted average re os age of 988 8 ma mswd 1 3 n 7 which represents the timing of a third hydrothermal event molybdenite from the quartz carbonate veins stage vi yielded a weighted average re os age at 835 4 ma mswd 0 66 n 10 and documented the timing of a late hydrothermal event our results indicate that the lala deposit formed during multiple protracted mineralization events over several hundred million years the first three mesoproterozoic mineralization events are coeval with intra continental rifting breakup of the supercontinent nuna and share a temporal link to other iocg style deposits within the kangdian copper belt and the last neoproterozoic hydrothermal event is coeval with the sibao orogeny which culminated with the amalgamation of the yangtze block with the cathaysia block at 860 815 ma

cooling and freshening of the subpolar north atlantic ocean since the 1960s little is known of the interdecadal variability in the thermohaline circulation of the world s oceans yet such knowledge is essential as a background to studies of the effects of natural and anthropogenic climate change the subpolar north atlantic is an area of extensive water mass modification by heat loss to the atmosphere lying as it does at the northern limit of the global thermohaline conveyor belt 12 changes in this region may ultimately have global consequences here we report that in august 1991 the waters between greenland and the united kingdom were on average 0 08 c and 0 15 c colder than in 1962 and 1981 respectively and slightly less saline than in 1962 the cause appears to be renewed formation of intermediate water in the labrador sea from cooler and fresher source waters and the spreading of this water mass from the west variations in the source characteristics of labrador sea water can be traced across the north atlantic with a circulation time of 18 19 years between the labrador sea and rockall trough more recently formed labrador sea water with even lower temperature and salinity should cool and freshen the north atlantic still further as it circulates around the ocean in the coming decade

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

freshening of subsurface waters in the northwest pacific subtropical gyre observations and dynamics subsurface salinity anomalies propagating between mid and low latitudes along isopycnal surfaces have been shown to play an important role in modulating ocean and climate variability in this study a sustained freshening and southwestward propagation of subsurface salinity anomalies in the northwest pacific subtropical gyre and its dynamical mechanism are investigated using observations numerical outputs and a predictive model analyses of the observations show a pronounced subsurface freshening with salinity decreasing about 0 25 psu near the 24 5 sigma surface in the northwest pacific subtropical gyre during 2003 11 this freshening is found to be related to the surface forcing of salinity anomalies in the outcrop zone 25 degrees 35 degrees n 130 degrees 160 degrees e a predictive model based on the assumption of salinity conservation along the outcrop isopycnals is derived and used to examine this surface forcing mechanism the resemblance between the spatial structures of the subsurface salinity derived from the predictive model and from observations and numerical outputs suggests that subsurface salinity anomalies are ventilated over the outcrop zone a salinity anomaly with an amplitude of about 0 25 psu generated by the surface forcing is subducted in the outcrop zone and then propagates southwestward accompanied by potential vorticity anomalies to the east of luzon strait similar to 15 degrees n in roughly one year when the anomalies reach 15 degrees n they turn and move gradually eastward toward the central pacific associated with an eastward countercurrent on the southern subtropical gyre

impact of antarctic ice shelf basal melting on sea ice and deep ocean properties 1 an approximation of antarctica s rocky and icy coastline normally forms the southern boundary in global climate models such a configuration neglects extensive ice shelf areas where ocean ice interaction initiates a net freshwater flux to the circumpolar continental shelf equal to 75 of the annual mean net precipitation in coastal seas the results of a numerical model for the southern ocean using two contrasting configurations with and without caverns beneath major antarctic ice shelves are compared they show that the freshwater flux due to deep basal melting significantly stabilizes the shelf water column in front of an ice shelf as well as downstream due to advection by the coastal current if the freshwater from the caverns is absent sea ice is thinner shelf waters are warmer and saltier and the southern ocean deep basins are flushed by denser waters

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

linear trends of temperature at intermediate and deep layers of the north atlantic and the north pacific oceans 1957 1981 abstract using all available hydrographic station data on ocean temperature observations from world data center b obninsk russia investigation of temperature changes in the north atlantic and north pacific oceans within the depth range of 300 to 3000 m has been carried out for the period 1957 1981 results of statistical data analysis show that in the upper layer to about 500 m depths of both oceans on average seawater temperature declined deeper than 500 600 m in the north pacific ocean no significant temperature changes have been revealed for this 25 year time interval on average for the north atlantic ocean a statistically significant temperature rise about 0 1 c 25 yr 1 is observed in the 800 to 2500 m layer

interdecadal water mass changes in the southern ocean between 30 e and 160 e interdecadal water mass changes in the indian western pacific sectors of the southern ocean were investigated using the japanese antarctic research expeditions and historical hydrographic observations from the 1950s to 1990s freshening and cooling occurred on the neutral density surfaces of 27 0 kgm3 equatorward of sub antarctic front results for the area south of the polar front show warm and saline anomalies and oxygen decreases on the surfaces around 27 9 kgm3 which correspond to the upper circumpolar deep water these latter anomalies are most simply explained by the mixing of these shallow waters with warmer and fresher surface waters steric sea level has also increased with an average change of 1mmyr1 from the 1970s to 1990s the changes are larger north of the sub antarctic front implying a strengthening of the antarctic circumpolar current it appears that the observed changes are consistent with the results from coupled climate model results for a similar period

hydrography of the eastern south pacific ocean results from the sonne 102 cruise may june 1995 abstract full depth conductivity temperature depth hydrographic measurements were taken in may june 1995 along 28 15 35 15 and 43 15 s from the chilean coast to 86 88 w from the r v sonne sections of potential temperature salinity neutral density and oxygen are presented to illustrate the water column structure in this sparsely sampled region a more comprehensive database on all available hydrographic data from the region was compiled these data and available meteorological data are used to help in the interpretation of the sonne results a number of important features found in the sections are discussed including a shallow salinity minimum apparently ventilated from south of 37 s salt fingering as a possible mechanism to transport high salinity subtropical water into the shallow salinity minimum equatorial subsurface water subantarctic mode water and antarctic intermediate water geostrophic calculations of alongshore flow show the poleward peru chile undercurrent at each of the three sections with a poleward descending core and peak velocities of 10 cm s 1 as in earlier works a deep pacific outflow is found near the chilean coast part of a clockwise deep circulation in the chile basin

observing the advection of sea ice in the weddell sea using buoy and satellite passive microwave data this study examines the progress and behavior of an area of sea ice as it drifts from the southwestern weddell sea by using data from four buoys tracked by nimbus 6 and concurrent ice concentrations retrieved from nimbus 7 scanning multichannel microwave radiometer data it covers the entire growth season of 1980 the overall drift characteristics and their relationship to ice edge displacement are examined within the framework of four zones three phases are identified in the large scale behavior of the weddell sea ice cover namely a rapid equatorward and eastward advance a quasi equilibrium phase and a period of rapid recession a broad division is made between the sectors to the east and west of 35 40 w in terms of the nature of ice edge advance transient departures from the mean northward advection are linked to the passage of cyclones certain such events may be significant in terms of the formation and maintenance of the region of highly consolidated perennial ice observed in the western weddell sea mean daily drift rates up to 0 9 m s 1 from within the central western weddell pack are high in 1980 particularly early in the growth season and when compared with rates to the west of 50 w outbreaks of cold continental air alternate with incursions of relatively warm air from the north warm conditions are recorded as far as 1200 km in from the ice edge in winter closed loops in the buoy trajectories which are clockwise to the south of 63 s reverse to become anticlockwise to the north mid ocean islands impede the eastward progress of the ice a coherence is noted in the response of the buoys to the passage of storms even though the buoys separated by a distance of over 100 km

weddell sea ice drift kinematics and wind forcing ice drift in the weddell sea was studied on the basis of positional and meteorological data from argos buoys drifting in 1990 1992 and surface pressure analyses from the european centre for medium range weather forecasts ecmwf the drift kinematics showed differences between the eastern and western parts of the weddell sea close to the antarctic peninsula the ice drifted as an almost nonrotating uniform field at a low speed having reduced small scale motions with little meandering compared to regions further to the east inertial motion was detected from the ice drift in areas east of 35 w and in the region of the antarctic circumpolar current on timescales of days wind was the primary forcing factor for the drift a linear model between the wind and ice drift explained 40 80 of the drift velocity variance the degree of explanation was higher in the central weddell sea around 40 w and lower closer to the antarctic peninsula the geostrophic wind was found to provide almost as good a basis for the general drift estimation as the surface wind observed by the buoys although strong cyclones were not well detected by the ecmwf analyses the data suggest a dependency upon atmospheric stability such that stable stratification reduces the wind forcing on the drift for 60 80 of the time the direction of the drift deviated less than 45 from the geostrophic wind and for 45 70 of the time less than 45 from the ocean current ice transport through a transect crossing the weddell sea from the antarctic peninsula tip to kapp norwegia was estimated on the basis of the geostrophic winds the drift s observed response to the wind and literature based information on ice concentration and thickness the estimated annual mean net export in 1992 1994 varied from 8000 to 22 000 m3 s most of the net export took place in winter and spring export prevailing west of 35 w and import east of it

melting of ice shelves and the mass balance of antarctica we calculate the present ice budget for antarctica from measurements of accumulation minus iceberg calving run off and in situ melting beneath the floating ice shelves the resulting negative mass balance of 469 gt year 1 differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20 50 annual accumulation from an earlier review is adjusted to include the antarctic peninsula for a total of 2144 gt year 1 an iceberg production rate of 2016 gt year 1 is obtained from the volume of large icebergs calculated from satellite images since 1978 and from the results of an international iceberg census project ice shelf melting of 544 gt year 1 is derived from physical and geochemical observations of meltwater outflow glaciological field studies and modeling of the sub ice ocean circulation the highest melt rates occur near ice fronts and deep within sub ice cavities run off from the ice sheet surface and from beneath the grounded ice is taken to be 53 gt year 1 less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0 45 mm year 1 in the ipcc best estimate of the recent global sea level rise

how iceberg calving and grounding change the circulation and hydrography in the filchner ice shelf ocean system the formation of bottom water in the southern weddell sea is strongly influenced by the flow of ice shelf water isw out of the filchner ronne ice shelf cavity the breakout of three giant icebergs in 1986 and their grounding on the shallow berkner bank modified the circulation and water mass formation in the filchner trough and the adjacent sea areas hydrographic measurements along the filchner ice shelf front carried out with rv polarstern in 1995 show significant changes in the water mass characteristics and flow patterns in the filchner trough in comparison to measurements from the early 1980s changes in the trough will affect the flow over the sill to the deep weddell abyssal plain we combine a three dimensional ocean circulation model with conductivity temperature depth and stable isotope measurements to investigate the details of the circulation in front of and beneath the filchner ice shelf we assess the impact of stranded icebergs and a more southerly ice shelf front position caused by a 1986 iceberg calving event on the circulation and observed water mass properties results indicate variations of the flow pattern in the filchner trough and on berkner bank where high salinity shelf water the feedstock for isw is produced the calving and grounding impacts illustrate the sensitivity of the ice shelf ocean system to perturbations in local bathymetric settings

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

basal melting of a 38b a physical model constrained by satellite observations abstract we observed the large tabular iceberg a 38b in the time period from the calving event at the ronne ice shelf in 1998 until its grounding near south georgia in 2004 by means of various space borne sensors the initial ice thickness was determined by radar altimetry the iceberg shape from radar imaging and optical instruments the freeboard change at different stages of the drift was derived from icesat laser altimeter profiles the analysis of the satellite data confirms that the decay of a 38b is governed mainly by basal erosion we then used a numerical model for simulating iceberg melting and fitted the melt rate by varying the turbulent exchange parameters for temperature t and salt s to match the results obtained by icesat data our results show that the iceberg passed through three melting regimes characterized by iceberg drift velocity 1 in the weddell sea melting conditions are similar to the situation under an ice shelf with strong tidal currents which corresponds to a t of 1 0 10 4 m s 1 2 in the scotia sea where the iceberg drifts unhindered with the ocean current and is surrounded by its own melt water t is 0 4 10 4 m s 1 3 at the grounding position friction velocity is again high due to tidal currents and t is 1 8 10 4 m s 1 s is set to 0 00505 t in all cases the analysis shows that icesat glas data together with satellite imagery can provide better estimates of turbulent exchange parameters which is a step forward in improving the knowledge of fresh water input from melting icebergs into the southern ocean

multidecadal warming and shoaling of antarctic intermediate water antarctic intermediate water aaiw is a dominant southern hemisphere water mass that spreads from its formation regions just north of the antarctic circumpolar current acc to at least 20 s in all oceans this study uses an isopycnal climatology constructed from argo conductivity temperature depth ctd profile data to define the current state of the aaiw salinity minimum its core and thence compute anomalies of aaiw core pressure potential temperature salinity and potential density since the mid 1970s from ship based ctd profiles the results are used to calculate maps of temporal property trends at the aaiw core where statistically significant strong circumpolar shoaling 30 50 dbar decade 1 warming 0 05 0 15 c decade 1 and density reductions up to 0 03 kg m 3 decade 1 are found these trends are strongest just north of the acc in the southeast pacific and atlantic oceans and decrease equatorward salinity trends are generally small with their sign varying regionally bottle data are used to extend the aaiw core potential temperature anomaly analysis back to 1925 in the atlantic and to 1960 elsewhere the modern warm aaiw core conditions appear largely unprecedented in the historical record biennially and zonally binned median aaiw core potential temperatures within each ocean basin are with the notable exception of the subtropical south atlantic in the 1950s 70s 0 2 1 c colder than modern values zonally averaged sea surface temperature anomalies around the aaiw formation latitudes in each ocean and sectoral southern annular mode indices are used to put the aaiw core property trends and variations into context

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

variability of the lower circumpolar deep water in drake passage 1926 2004 lower circumpolar deep water lcdw is an important component of the global overturning circulation as it upwells south of the antarctic circumpolar current acc renewing the ocean interior the lcdw also aids the transport of water properties between the major ocean basins the property variability of the lcdw salinity maximum layer was examined using 37 meridional sections across drake passage between 1926 2004 within the limits of experimental error and high frequency variability the core properties of this layer have remained constant between 1926 2004 a comparison of modern sections and the 1932 discovery ii cruise indicates that this observation may be true for lcdw throughout the southern ocean the significance of this result in terms of the observations of decadal changes in the southern ocean intermediate and mode waters is that these changes are most likely due to contemporary atmospheric forcing and not due to variations in the source water properties

a numerical model of the weddell sea large scale circulation and water mass distribution a circumpolar model for regional studies of the wind driven and thermohaline circulation of the southern ocean including the major sub ice shelf areas is described a first series of numerical experiments focusing on the weddell sea reveals a pronounced and persistent double cell structure of the weddell gyre with a maximum transport of 60 sv in agreement with observations experiments with artificial passive tracers point to the shallow shelf areas off the filchner ronne ice shelf as main locations for bottom water production the trajectories of lagrangian floats are used to determine the pathways and timescales of water mass spreading in the model in addition the effect of sub ice shelf forcing on the water mass characteristics is evaluated it is shown that water modified in the sub ice cavities contributes significantly to the deep and bottom water formation along the continental slope and affects the water mass characteristics throughout the weddell sea by increasing the stability of the near surface stratification and preventing deep convection

how is the ocean filled 1 the ocean surface rapidly exchanges heat freshwater and gases with the atmosphere but once water sinks into the ocean interior the inherited properties of seawater are closely conserved previous water mass decompositions have described the oceanic interior as being filled by just a few different property combinations or water masses here we apply a new inversion technique to climatological tracer distributions to find the pathways by which the ocean is filled from over 10 000 surface regions based on the discretization of the ocean surface at 2 by 2 resolution the volume of water originating from each surface location is quantified in a global framework and can be summarized by the estimate that 15 of the surface area fills 85 of the ocean interior volume ranked from largest to smallest the volume contributions scaled by surface area follow a power law distribution with an exponent of 1 09 0 03 that appears indicative of the advective diffusive filling characteristics of the ocean circulation as demonstrated using a simple model this work quantifies the connection between the surface and interior ocean allowing insight into ocean composition atmosphere ocean interaction and the transient response of the ocean to a changing climate

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

warming and circulation change in the eastern south pacific ocean deep ocean temperature salinity and dissolved oxygen observations in the eastern south pacific ocean collected during the late austral fall in 1995 are compared with observations made there 28 years earlier during the same season and similar el nino southern oscillation phase warming observed above 800 m at 43 s reflects the production of warmer subantarctic mode water in recent decades warming observed above 1600 m at 28 s is due to downward isotherm displacement and southward movement of water masses by 100 200 km as revealed by joint analysis of temperature and oxygen data such changes would be expected for a weaker subtropical gyre in the south pacific an observed oxygen decrease between about 1800 m and 2900 m at 28 s may indicate enhanced southward boundary current flow at mid depths off chile

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

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

modeling giant iceberg drift under the influence of sea ice in the weddell sea antarctica the drift trajectory of giant iceberg c 7 traversing the weddell sea antarctica for 2 years was successfully simulated application of the classical driving forces like wind and ocean currents resulted in a significant discrepancy between modeled and observed iceberg velocities in the western weddell sea the most realistic drift pattern in space and time was achieved by adding a sea ice force which represents the ability of a dense sea ice cover 90 to lock in icebergs and collect the momentum of the wind over an area much larger than the area of the iceberg proper this process was parameterized using a sea ice strength p which depends on sea ice concentration and thickness both having highest values in winter and in the western weddell sea which is covered with multi year sea ice as a consequence of the sensitivity to sea ice the timing of the iceberg drift becomes important revealing the region off brunt ice shelf eastern weddell sea as a location where bergs either continue westward with the coastal current or follow a southern branch onto the shallow continental shelf

persistent iceberg groundings in the western weddell sea antarctica abstract we use the time average of a series of satellite synthetic aperture radar sar images from 2005 to 2007 to identify grounded icebergs in the western weddell sea satellite laser altimetry along repeated ground tracks confirms that regions of high mean backscatter are associated with stationary tabular icebergs the altimeter data also provide iceberg freeboard from which we infer maximum ice draft assuming the lightly grounded limit and a two layer density model consistent with a source at filchner ronne ice shelf the maximum iceberg draft agrees very well with the ocean depth at a point where the bathymetry is well constrained by ship soundings however for an extensive region near 71 s south of larsen c ice shelf the maximum grounding depth for several icebergs reveals the ocean to be locally more than 200 m shallower than in bathymetry products this previously uncharted bank is expected to have a profound effect on the northward flow of the western weddell gyre and the cross slope transport of offshore warm deep water towards the eastern antarctic peninsula ice shelves passive microwave data also show that sea ice concentration is reduced in the vicinity of this group of grounded icebergs indicating an iceberg influence on ocean atmosphere heat and freshwater exchanges

subantarctic mode water variability influenced by mesoscale eddies south of tasmania 1 subantarctic mode water samw is formed by deep mixing on the equatorward side of the antarctic circumpolar current the subduction and export of samw from the southern ocean play an important role in global heat freshwater carbon and nutrient budgets however the formation process and variability of samw remain poorly understood largely because of a lack of observations to determine the temporal variability of samw in the australian sector of the southern ocean we used a 15 year time series of repeat expendable bathythermograph sections from 1993 to 2007 seven repeat conductivity temperature depth sections from 1991 to 2001 and sea surface height maps the mean temperature of the samw lies between 8 5 c and 9 5 c mean of 8 8 c standard deviation of 0 3 c and there is no evidence of a trend over the 18 year record however the temperature salinity and pycnostad strength of the samw can change abruptly from section to section in addition the samw pool on a single section often consists of two or more modes with distinct temperature salinity and vertical homogeneity characteristics but similar density we show that the multiple types of mode water can be explained by the advection of anomalous water from eddies and meanders of the fronts bounding the subantarctic zone and by recirculation of samw of different ages our results suggest that infrequently repeated sections can potentially produce misleading results because of aliasing of high interannual variability

dissolved oxygen change and freshening of antarctic bottom water along 62 s in the australian antarctic basin between 1995 1996 and 2012 2013 abstract significant warming and freshening signals observed in the world s deep oceans are generally stronger southward in the australian antarctic basin along 62 s near the southern edge of the western pacific and indian oceans we compared water properties of antarctic bottom water observed in 1995 1996 and 2012 2013 the basin collects newly ventilated dense water from the western pacific sector of the antarctic coast and the ross sea compared on pressure surfaces freshening of more than 0 003 g kg in absolute salinity 0 003 in practical salinity scale 1978 or pss 78 was found below 3000 dbar the freshening was stronger 0 02 g kg or 0 02 in pss 78 eastward and towards the bottom suggesting that it originated from the regions of new bottom water production we also detected warming 0 2 c on pressure surfaces below the surface layer freshening of similar magnitudes were observed on density surfaces neutral densities 1028 1 kg m 3 adiabatic southward migration of water masses observed by satellite altimetry can explain the warming but not the freshening a notable increase in dissolved oxygen on density surfaces was found near the bottom the increase appears due to density decrease of near bottom water which can be explained by a change in the mixing ratio of bottom water from near the adelie depression adelie land bottom water albw higher oxygen with that from the more distant ross sea ross sea bottom water rsbw lower oxygen an increased contribution of albw and a decreased contribution of rsbw this change might be associated with a decrease in the rsbw supply following an earlier ice calving event in the polynya region oxygen rich 242 mol kg and dense 1028 35 kg m 3 bottom water observed in 1995 1996 in troughs near 130 e disappeared in 2012 2013 which also might reflect changes in bottom water production along the coast possibly in mertz and dibble polynyas

weddell sea iceberg drift five years of observations since 1999 52 icebergs have been tagged with gps buoys in the weddell seato enable monitoring of their position the chosen icebergs were of small tomedium size with a few icebergs larger than 10 km associatedwith the calving of icebergs a38 and a43 from the ronne ice shelf the majority of icebergs were tagged off neumayer station 8e 70s it was found that smaller bergs with edges shorter than 200 m had the shortestlife cycle 0 5 yr iceberg and thus freshwater export out of theweddell sea was found to be highly variable in one year the majority of buoysdeployed remained in the weddell sea constituting about 40 of the ncep p efreshwater input whereas in other years all of the tagged icebergs were exported the observed drifts of icebergs and sea ice showed a remarkably coherent motion the analysis of an iceberg sea ice buoy array in the western weddell seaand an iceberg array in the eastern weddell sea showed a coherent sea iceiceberg drift in sea ice concentrations above 86 dynamic kinematic parameter dkp during the course of coherent movement were low and deviations from the meancourse associated with the passage of low pressure system the length scale ofcoherent movement was estimated to be less than 250km about half the value found forthe arctic ocean

late winter generation of spiciness on subducted isopycnals the origins of density compensating anomalies of temperature and salinity spice are investigated using a model forced with the most realistic surface products available over the 40 years 1958 97 in this hindcast the largest interannual spiciness anomalies are found in the pacific ocean near the isopycnal s 0 5 25 5 where deviations as great as 1 28c and 0 6 psu are generated equatorward of winter outcropping in the eastern subtropics in both hemispheres these source regions are characterized by very unstable salinity gradients and low mean density stratification in winter two related signatures of winter mixing in the southeast pacific sep are density that is well mixed deeper than either temperature or salinity and subsurface density ratios that approach 1 all ocean basins in the model are shown to have regions with these characteristics and signatures however the resultant spiciness signals are focused on different isopycnals ranging from s 0 5 25 0 in the northeast pacific to s 0 5 26 5 in the south indian ocean a detailed examination of the sep finds that large positive anomalies are generated by diapycnal mixing across subducted isopycnals e g s 0 5 25 5 whereas negative anomalies are the result of a steady isopycnal advection moderated by vertical advection and heave there is considerable interannual variability in the strength of anomalies and in the density on which they occur historical observations are consistent with the model results but are insufficient to verify all aspects of the hindcast including the processes of anomaly generation in the sep it was not possible to relate isopycnal anomaly genesis to local surface forcing of any kind a complex scenario involving basinwide circulation of both the ocean and atmosphere especially of surface water through the subtropical evaporation zones is put forward to explain the decadal time scale evident in sep salinity anomalies on s 0 5 25 5 pacific anomalies generated on s 0 5 25 5 can be traced along mean geostrophic streamlines to the western boundary where decadal salinity variations at 78s are about 2 times as large order 60 1 psu as at 128n although there may be more variance on shallower isopycnals in the north at least portions of the s 0 5 25 5 signals appear to continue along the boundary to a convergence at the equator suggesting that the most robust sources of pacific spiciness variance coincide with equatorial exchange pathways

a 170 year sr ca and ba ca coral record from the western pacific warm pool 2 a window into variability of the new ireland coastal undercurrent 1 a porites coral from new ireland 2 5 s 150 5 e at the heart of the pacific warm pool records variations of ba ca back to the early 1820s the new ireland coastal undercurrent which flows along the north coast and transports high nutrient thermocline waters is thought to be the main source of the ba enrichment observed in the coral during el nino between the 1850s and the 1960s frequent large ba peaks indicate that nutrients were available during both phases of el nino southern oscillation enso during la nina ba could be advected along the south equatorial current also during this period clusters of ba ca peaks at nearly decadal timescale generally coincide with the return time of a strong el nino in accord with the high decadal variance of nino3 sea surface temperatures ba enrichment in this coral primarily reflects the stratification in the thermocline that controls vertical mixing the coral records long term changes in those properties affecting nutrients in surface waters with reduced ba after the 1960s and even less between 1823 and 1850 these reductions are tentatively attributed to the high rate of warming at the end of the dalton minimum and since the mid 20th century an ensuing weakening of the trade winds may have produced a more stratified equatorial thermocline hindering the transport of ba and nutrients from the undercurrent to the shallow coastal waters north of new ireland

observations of decadal time scale salinity changes in the subtropical thermocline of the north pacific ocean abstract data from argo floats indicate that significant salinity changes have occurred in the north pacific thermocline relative to data collected in the previous two decades including observations obtained as part of the woce hydrographic program such a salinity decrease on both isopyncals and isobars implies a freshening scenario in the near surface source region of this water mass the frequently repeated meridional section p16 supports this inference the subsurface salinity freshening likely began in the early 1990s strengthened through 1997 and continued into the 2000s the surface salinity freshening had commenced by 1984 and continued through the first decade of the 21st century the spatial distribution of salinity change on the density surface 25 5 is examined through comparisons of argo and most of the north pacific woce sections 1985 1994 and between argo and the hydrobase climatology largely composed of data from the late 1970s through the mid 1980s both comparisons show a large scale basin wide decrease in subsurface salinity through the argo time period used in this analysis 2003 2006 the salinity difference is maximum in the northeast area and spreads southward and westward approximately following geostrophic streamlines

sea ice transports in the weddell sea time series of sea ice draft in the weddell sea are evaluated together with hydrographic observations satellite passive microwave data and ice drift for estimation of the freshwater fluxes into and out of the weddell sea ice draft is measured with moored upward looking sonars since 1990 along two transects across the weddell gyre one transect extending from the tip of the antarctic peninsula to kapp norvegia was sampled between 1990 and 1994 and covers the flow into and out of the southern weddell sea the other transect sampled since 1996 and extending from the antarctic continent northward along the greenwich meridian covers the exchange of water masses between the eastern and the western weddell sea in order to relate results obtained during the different time periods empirical relationships are established between the length of the sea ice season derived from the satellite passive microwave data and defined as the number of days per year with the sea ice concentration exceeding 15 and 1 the annual mean ice draft and 2 the annual mean ice volume transport by using these empirical relationships estimates of annual mean ice drafts and ice volume transports are derived at all mooring sites for the period february 1979 through february 1999 wind and current force a westward ice transport in the coastal areas of the eastern weddell sea and a northward ice transport in the west during the 2 year period 1991 1992 the mean ice volume export from the weddell sea is 50 19 103 m3 s 1 this freshwater export is representative for a longer term 20 year mean and exceeds the average amount of freshwater gained by precipitation and ice shelf melt by about 19 103 m3 s 1 yielding an upper bound for the formation rate of newly ventilated bottom water in the weddell sea of 2 6 sv