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

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

hydrothermal mounds and young ocean crust of the galapagos preliminary deep sea drilling results leg 70 a total of 32 holes at 5 sites near 1 n 86 w drilled on deep sea drilling project dsdp leg 70 november december 1979 provide unique data on the origin of the hydrothermal mounds on the south flank of the galapagos spreading center hydrothermal sediments primarily mn oxide and nontronite are restricted to the immediate vicinity of the mounds 100 m and are probably formed by the interaction of upward percolating hydrothermal solutions with sea water and pelagic sediments above locally permeable zones of ocean crust mounds as much as 25 m in height form in less than a few 10 5 yrs and geothermal and geochemical gradients indicate that they are actively forming today the lack of alteration of upper basement rocks directly below the mounds and throughout the galapagos region indicates that the source of the hydrothermal solutions is deeper in the crust

methane derived authigenic carbonates formed by subduction induced pore water expulsion along the oregon washington margin authigenic magnesian calcite dolomite and aragonite are precipitated in the uppermost terrigenous sediments of the washington oregon accretionary prism by subduction induced dewatering these distinctive carbonates are methane derived and occur at sites of concentrated pore water expulsion unique biologic communities that subsist at least indirectly on methane suess et al 1985 are also found at some of these sites the methane which is dominantly biogenic is carried to the uppermost sediments of the prism by fluids and is oxidized by sulfate reducers before being incorporated into a carbonate cement carbonate precipitation occurs below the oxic layer probably no deeper than several centimetres to a few metres below the seabed cementation may be induced by three factors 1 increased carbonate alkalinity resulting from microbial sulfate reduction 2 decreased co 2 solubility resulting from a pressure decrease when the pore water escapes the prism and or 3 the addition of ca 2 and mg 2 ions from sea water near the sediment water interface the convergent margin setting engenders precipitation of authigenic carbonates in several ways compressive stresses induce anomalously rapid compaction and dewatering rates and they may cause overpressuring in migrating pore water thereby delaying precipitation of carbonates until pressure is released near the sediment water interface structural deformation of the accretionary prism creates pathways such as fault zones secondary fracture porosity and dipping permeable layers often exposed by mass movement for efficient advection and expulsion of methane enriched pore water these characteristic conditions which lead to the precipitation of methane derived carbonates may be found at other convergent margins

a dynamical description of fall and winter mean current profiles over the northern california shelf abstract fall and winter mean current profiles from a midshelf water depth 90 m northern california site exhibit a similar vertical structure for several different years the alongshelf flow is poleward with a maximum velocity of 5 10 cm s 1 in the middle or upper water column there is an offshore flow of about 2 cm s 1 in the upper 20 30 m an onshore flow of about 2 cm s 1 in the interior depths 35 65 m and an offshore flow of about 1 cm s 1 within 20 m of the bottom profiles are similar for averages over timescales from weeks to months mean current profiles at other midshelf sites along northern california and two sites off peru also have a similar vertical structure the vertical shear in the mean alongshelf flow is geostrophic throughout the water column that is in thermal wind balance with the cross shelf density gradient for timescales of a week or longer the thermal wind balance extends to within 1 m of the bottom and reduces the mean near bottom alongshelf flow to 1 cm s 1 or less th

poleward coastal jets induced by westerlies in the bay of biscay 1 two hydrodynamic surveys based on acoustic doppler current profiler adcp and drift buoys measurements taken in summer 2008 and 2009 revealed poleward coastal jets of up to 32 cm s 1 that lasted up to 22 d along the aquitaine shelf in the southeastern area of the bay of biscay a strong increase in bottom temperature was associated with these currents up to 4 c in 5 d at 54 m depth these observations occurred after a few days of westerlies cross shore winds which were thought to have only a limited impact on longshore circulation here the mars3d hydrodynamic model was used with a schematic bathymetry of the southeastern area of the bay of biscay to reproduce and analyze these coastal jets simulations revealed that the triggering mechanism of the poleward currents is unequivocally due to downwelling circulation induced along the spanish coast this downwelling induces an external longshore pressure gradient which generates a high speed coastal trapped wave that propagates along the french coast with a phase velocity of about 3 to 4 m s 1 and an internal baroclinic kelvin wave with a phase velocity of about 1 m s 1 a sensitivity study of the role of stratification conditions wind strength and duration was then carried out to determine the periods that are the most sensitive to this wind induced circulation

thirty years of elevation change on antarctic peninsula ice shelves from multimission satellite radar altimetry 1 we use data acquired between 1978 and 2008 by four satellite radar altimeter missions seasat ers 1 ers 2 and envisat to determine multidecadal elevation change rates dhi dt for six major antarctic peninsula ap ice shelves in areas covered by the seasat orbit to 72 16 s regional averaged 30 year trends were negative surface lowering with rates between 0 03 and 0 16 m a 1 surface lowering preceded the start of near continuous radar altimeter operations that began with ers 1 in 1992 the average rate of lowering for the first 14 years of the period was typically smaller than the 30 year average the exception was the southern wilkins ice shelf which experienced negligible lowering between 2000 and 2008 when a series of large calving events began analyses of the continuous ers envisat time series to 81 5 for 1992 2008 reveal a period of strong negative dhi dt on most ice shelves between 1992 and 1995 based on prior studies of regional atmospheric and oceanic conditions we hypothesize that the observed elevation changes on larsen c ice shelf are driven primarily by firn compaction while the western ap ice shelves are responding to changes in both surface mass balance and basal melt rates our time series also show that large changes in dhi dt can occur on interannual time scales reinforcing the importance of long time series altimetry to separate long term trends associated with climate change from interannual to interdecadal natural variability

modelling circumpolar deep water intrusions on the amundsen sea continental shelf antarctica results are presented from an isopycnic coordinate model of ocean circulation in the amundsen sea focusing on the delivery of circumpolar deep water cdw to the inner continental shelf around pine island bay the warmest waters to reach this region are channeled through a submarine trough accessed via bathymetric irregularities along the shelf break temporal variability in the influx of cdw is related to regional wind forcing easterly winds over the shelf edge change to westerlies when the amundsen sea low migrates west and south in winter spring this drives seasonal on shelf flow while inter annual changes in the wind forcing lead to inflow variability on a decadal timescale a modelled period of warming following low cdw influx in the late 1980 s and early 1990 s coincides with a period of observed thinning and acceleration of pine island glacier

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

hydrothermal sulfide and oxide deposits on seamounts near 21 n east pacific rise hydrothermal deposits were sampled by submersible from the calderas and summit benches of two seamounts 20 and 30 km west of the east pacific rise at 21 n the deposits document a wide variety of off axis hydrothermal activity including samples from the interiors of seafloor sulfide deposits in contrast to most mid ocean ridge deposits sulfide deposits on green seamount are rich in si fe and cu are poor in zn and contain abundant quartz sulfide chimneys grew by quenching of hydrothermal fluids and deposition of walls of colloform pyrite marcasite zn sulfide and minor galena whereas coarse grained pyrite and chalcopyrite were deposited at higher temperatures 250 c in chimney interiors as chimney walls grew outward into sea water increased temperatures in the inner walls resulted in recrystallization to pyrite and deposition of pyrite and chalcopyrite in pore space cooling in the outer portions of chimneys caused deposition of opal at temperatures of about 80 170 c as chimneys coalesced and opal rich material was heated in the interiors of sulfide edifices opal was recrystallized to chalcedony and quartz faulting has exposed the interiors of sulfide deposits where further recrystallization and deposition of chalcopyrite and quartz occurred at temperatures of 230 320 c clogging of chimneys changes in flow paths and cooling of the deposits led to the deposition of late mixed layer illite smectite iron sulfides fe poor sphalerite opal and barite the sulfide deposits formed over a time span of at least 140 000 to 70 000 yr ago probably coincident with caldera and pit crater formation the ages of the sulfide deposits provide constraints on the last volcanic and tectonic activity and they also suggest that it took a maximum of 260 000 yr for the seamount to reach its present height red seamount is presently hydrothermally active and deposits consisting predominantly of amorphous fe oxyhydroxide are forming on small pillow cones in the caldera at temperatures of 10 15 c hydrothermal nontronite deposits capped by mn oxide crusts cover much of the southern summit bench of red seamount and formed at temperatures of around 30 c iron rich talc and sulfide grains in nontronite provide evidence of former high temperature activity and suggest that a sulfide deposit is present nearby

stable isotopes 14c dating and geochemical characteristics of carbonate nodules and sediment from an active vent field northern juan de fuca ridge northeast pacific abstract a record of early uplift events foreshadowing development of an active vent field in middle valley on northern juan de fuca ridge is preserved in a core taken on the margin of the field by a near surface mud fragment breccia dated 8 300 to 11 500 yr b p cementation of the breccia with low mn methanogenic calcite at 5 c formed a carbonate nodule layer by 6 800 yr b p recent hydrothermal overprinting at 6 m in the same core resulted in formation of carbonate nodules with late stage high mn calcite cements oxygen isotopic temperatures of 55 85 c and more positive 13 c values reworked vent detritus suggests that surface venting began by at least 2 900 yr b p localized lateral flow of hydrothermal fluid tens of cm below the seafloor is suggested by a barite rich zone in a permeable interval bounded sharply below by relatively impervious mud clast breccia carbonate and barite cementation near the seabed could eventually result in localized ponding or redirection of fluid flow in the shallow subsurface near the center of the active field a barite zone originating from reaction of hydrothermal ba with residual highly fractionated seawater sulfate barite 34 s 44 5 is found at 6 m below the seafloor

a numerical study of the adjustment of a narrow stratified current over a sloping bottom the adjustment of a narrow stratified cyclonic along isobath current over a uniformly sloping bottom and the coupling between the current and the bottom boundary layer that develops beneath are investigated using a primitive equation numerical model the current generates a bottom ekman layer immediately downstream of its origin with downslope transport everywhere beneath the current carrying lighter water under heavier water to produce a vertically well mixed bottom boundary layer at the top of the boundary layer ekman suction on the shallow side and pumping on the deep side lead to density advection in the vertical tilted interior isopycnals and thermal wind shear of the interior along isobath velocity flow above the bottom boundary layer is nearly perfectly geostrophic and along isopycnals buoyancy advection in the bottom boundary layer continues to cause growth of the boundary layer downstream with subsequent reduction in bottom stress until the flow reaches a steady downstream equilibrium beyond which only gradual changes occur as a result of viscosity and mixing the numerical results are compared with the idealized model of this adjustment process previously proposed by chapman and lentz the same basic dynamics dominate and some of the scales and parameter dependencies predicted by the idealized model apply to the numerical results for example the distance to the downstream equilibrium decreases with increasing buoyancy frequency and or bottom slope and the equilibrium structure is nearly independent of the bottom friction coefficient the equilibrium bottom boundary layer thickness and the interior along isobath velocity just above the boundary layer closely obey the idealized model scales that is the boundary layer thickness decreases with increasing buoyancy frequency and is independent of bottom slope and the overlying current decreases while its width increases as either the buoyancy frequency or bottom slope decreases however the interior vertical shear in the numerical model tends to decouple the overlying current from the bottom boundary layer so the structure of the bottom boundary layer in the downstream equilibrium is different from the idealized model and neither the current width nor the surface currents are as sensitive to parameter variations as the idealized model suggests finally the along isobath current is not geostrophic near the bottom of the bottom boundary layer as assumed in the idealized model so the bottom boundary layer is not fully arrested that is bottom stress never quite vanishes downstream suggesting that a completely frictionless downstream equilibrium is unlikely to be achieved

a note on the development of the bathymetry of the continental margin west of the antarctic peninsula from 65 to 71 s and 65 to 78 w multibeam data collected during the united states southern ocean global ocean ecosystems dynamics cruises in 2001 and 2002 aboard the r vib nathaniel b palmer were augmented with available multibeam and centerline bathymetry data from a variety of sources to compile a bathymetric data set for the continental shelf west of the antarctic peninsula this new bathymetry data set provides an improvement in the resolution of the bathymetry of the region the improved data set was used to construct a high resolution bathymetric map of the continental margin west of the antarctic peninsula from 65 to 71 s and from 65 to 78 w

antarctic bottom water production from the vincennes bay polynya east antarctica one year moorings at depths greater than 3000m on the continental slope off vincennes bay east antarctica reveal the cold 0 5 degrees c and fresh 34 64 signals of newly formed antarc

numerical study of winter water formation in the chukchi sea roles and impacts of coastal polynyas winter water formation is examined in the chukchi sea for the winters of 1992 2006 using a primitive equation ocean model forced by ncep wind and surface salinity flux derived from ssm i thin ice thickness estimates the model is also forced by an external inflow of 0 8 sv through the bering strait the model successfully reproduces the oceanic circulation on the chukchi shelf thus providing numerous insights into behaviors of salt enriched water produced on the shelf the experiments show that under northeasterly winds northward throughflow across barrow canyon is reduced this results in salinity buildup under freezing conditions and ultimately in greater enhancement of salinity of the waters carried into the arctic basin the flow and salinity enhancement of the flow through herald canyon is less extreme but more steady than through barrow canyon together with moored salinity in the bering strait the model results estimate the actual salinity to be 32 9 0 8 psu and 32 7 0 3 psu respectively for waters moving through the barrow and herald canyons both estimates are less than 33 1 psu that is typically observed for the cold halostad layer in the canada basin suggesting the importance of diapycnal mixing with saltier atlantic origin water

momentum balances on the north carolina inner shelf four months of moored current pressure temperature conductivity wave and wind observations on the north carolina shelf indicate three dynamically distinct regions the surf zone the inner shelf between the surf zone and the 13 m isobath and the midshelf in the surf zone the along shelf momentum balance is between the cross shelf gradient of the wave radiation stress and the bottom stress the linear drag coefficient in the surf zone is about 10 times larger than seaward of the surf zone on the inner shelf the along shelf momentum balance is also frictional the along shelf wind stress and pressure gradient are balanced by bottom stress in the cross shelf momentum balance the pressure gradient is the superposition of roughly equal contributions from the coriolis force geostrophy and wave setdown from shoaling unbroken surface gravity waves at midshelf the along shelf momentum balance is less frictional and hence flow accelerations are important the cross shelf momentum balance is predominantly geostrophic because the greater depth and smaller bottom slope at midshelf reduce the importance of wave setdown the cross shelf density gradient is in thermal wind balance with the vertical shear in the along shelf flow in depths as shallow as 10 m the dominant along shelf momentum balances provide a simple estimate of the depth averaged along shelf current in terms of the measured forcing i e wind stress wave radiation stress divergence and along shelf pressure gradient that reproduces accurately the observed cross shelf variation of the depth averaged along shelf current between the surf zone and midshelf

the presence of polynyas in the weddell sea during the last glacial period with implications for the reconstruction of sea ice limits and ice sheet history cores from a contourite drift on the continental slope in the nw weddell sea antarctica contain up to four sandy foraminifer rich layers wa1 4 with dispersed ice rafted debris ird interbedded with silty clayey sands and sandy muds accelerator mass spectrometry ams 14c dating on neogloboquadrina pachyderma from the foraminifer rich layers wa2 and wa3 yielded ages spanning the last glacial maximum lgm and marine isotope stage mis 2 20 319 28 543 cal yr bp and the middle part of mis 3 41 349 43 242 cal yr bp respectively we attribute the high abundances of planktonic and benthic foraminifera to deposition in a seasonally open marine environment given that the nw weddell sea shelf was covered by grounded ice at the lgm and probably during mis 2 and mis 3 and that diatom based reconstructions place the northern limit of winter and summer sea ice coverage to the north of the core sites during the last glacial period our results document the presence of a seasonal or perennial polynya in the nw weddell sea the polynya may have been formed by katabatic winds blowing off the antarctic peninsula ice sheet apis when it was grounded at the continental shelf break although polynya formation through upwelling of deep water cannot be ruled out in addition we argue that previously published data from the southern southeastern and southwestern weddell sea as well as the ross sea may indicate the widespread occurrence of polynyas along the antarctic continental margin during the last glacial period the widespread occurrence of polynyas could help explain how i aabw formation through brine rejection continued throughout the lgm and ii antarctic shelf benthos survived glacial periods the presence of polynyas through glacial periods also has implications for sea ice reconstructions from ice core records possibly biasing the signal towards a reduced sea ice cover finally we propose that the fringes of the apis which probably influence the presence or absence of polynyas in the nw weddell sea are sensitive to changes in antarctic temperature that may be related to a reduction in oceanic heat transport from the north atlantic

ice and ocean processes in the bellingshausen sea antarctica 1 in the vicinity of the antarctic peninsula observations show diminishing sea ice and a rapid warming of atmosphere and ocean these changes have led to the collapse of ice shelves and retreat acceleration and thinning of inland ice however ocean observations in the center of the nearby bellingshausen sea are spatially and temporally coarse in this study ocean and sea ice models forced by atmospheric reanalyses are used to investigate this data gap by simulating processes in the bellingshausen sea for the years 1979 2007 the model suggests flow features in the region and predicts the basal melting of local ice shelves modeled ocean conditions are found to be less variable than in the nearby amundsen sea which is situated closer to foci of annual and interannual atmospheric variability melt rates beneath george vi ice shelf are investigated in detail concluding that the ice shelf may have been melting out of balance and therefore thinning for decades the melt rate contains significant interannual variability that the model links to variation in sea ice conditions offshore of the southern end of the ice shelf this stands in contrast to the amundsen sea where models suggest that ice shelf melting is controlled by variable transport of circumpolar deep water onto the continental shelf

subinertial currents on the southern califoinia shelf abstract subinertial currents on the southern california shelf are investigated using observations from a current meter array deployed near san diego during the summer fall and winter of 1978 79 this region is characterized by weak winds order 1 2 m s 1 and thus other driving mechanisms for the subinertial currents may be important a simplified depth averaged longshore momentum equation consisting of a balance between current accelerations the adjusted sea level asl gradient and the wind and bottom stress is examined the asl gradient is estimated using sea level and atmospheric pressure observations separated by 350 km a linear parameterization of the bottom stress is used with a drag coefficient of 5 10 4 m s 1 during fall and winter the first order balance of terms in the longshore momentum equation over the inner shelf 15 m depth is between the wind and bottom stress over the outer shelf 60 m the primary balance is between the asl gradient and the bottom stress at midshelf 30 m bo

two modes of bottom water in the australian antarctic basin 1 recent data from the deep australian antarctic basin show that waters colder than about 0 4 c are fresher by as much as 0 02 than data collected prior to 1994 it is possible that the freshening represents a fundamental change in the sources of bottom water for the basin but it is more likely that the fresh mode recurs periodically and is underrepresented in the historical database the freshening may be caused by a change in fresh bottom water input from the antarctic coast between 120 e 160 e or by a reduction in the outflow of saline ross sea bottom water

estimation of thin sea ice thickness from noaa avhrr data in a polynya off the wilkes land coast east antarctica antarctic coastal polynyas are major areas of intense ocean atmosphere heat and moisture flux and associated high sea ice production and dense water formation their accurate detection including an estimate of thin ice thickness is therefore very important in this paper we apply a technique originally developed in the arctic to an estimation of sea ice thickness using us national oceanic and atmospheric administration noaa advanced very high resolution radiometer avhrr data and meteorological data in the vincennes bay polynya off wilkes land east antarctica the method is based upon the heat flux calculation using sea ice surface temperature estimates from the satellite thermal infrared data combined with global objective analysis european centre for medium range weather forecasts ecmwf data the validity of this method is assessed by comparing results with independent ice surface temperature and ice thickness data obtained during an australian led research cruise to the region in 2003 in thin ice polynya regions ice thicknesses estimated by the heat flux calculation using avhrr and ecmwf data show reasonable agreement with those estimated by a applying the heat flux calculation to in situ radiation thermometer and meteorological data and b in situ observations the standard deviation of the difference between the avhrr derived and in situ data is 0 02 m comparison of the avhrr ice thickness retrievals with coincident satellite passive microwave polarization ratio data confirms the potential of the latter as a means of deriving maps of thin sea ice thickness on the wider scale uninterrupted by darkness and cloud cover

temperate skeletal carbonate sediments on scott shelf northwestren vancouver island canada abstract scott shelf 2000 km 2 centred at scott islands northwestern vancouver island is mainly shallower than 150 m topographically diversified and floored by bedrock outcrops and terrigenous lithic gravels and sands left stranded following the post glacial rise in sea level 13 000 yrs b p it lies in a zone of vigorous wind wave currents and strong tidal flows but is largely starved of modern terrigenous sediment as a consequence it is slowly accumulating a thin discontinuous blanket of clean skeletal carbonate sands and gravels admixed to varying degrees with the underlying terrigenous deposits principal skeletal contributors are infaunal bivalves on coarse sandy and gravelly substrates barnacles on low amplitude gravelly ridges bryozoans on bedrock outcrops and boulders and benthic foraminifera on fine sands in deep 100 m waters south of the scott islands living carbonate benthos are scattered and generally sparse occupying specific ecologic niches and the shelf wide rate of carbonate production is low skeletons are fragmented transported and mixed during storms and are concentrated within bedrock hollows and crevices and shallow depressions between gravel ridges where infaunal bivalves are abundant the carbonates are dominated by aragonite but otherwise the skeletal hashes are predominantly calcitic many grains and especially aragonitic ones are corroded and weakened by epilithic and endolithic bioerosion and probably also by marine and dissolution the most corroded shells have ages of only about 1000 yrs so that their preservation potential is low the character of scott shelf skeletal carbonate deposits reflects their temperate latitude cold water heritage

estimation of the thin ice thickness and heat flux for the chukchi sea alaskan coast polynya from special sensor microwave imager data 1990 2001 1 one of the largest arctic polynyas occurs along the alaskan coast of the chukchi sea between cape lisburne and point barrow for this polynya a new thin ice thickness algorithm is described that uses the ratio of the vertically and horizontally polarized special sensor microwave imager ssm i 37 ghz channels to retrieve the distribution of thicknesses and heat fluxes at a 25 km resolution comparison with clear sky advanced very high resolution radiometer data shows that the ssm i thicknesses and heat fluxes are valid for ice thicknesses less than 10 20 cm and comparison with several synthetic aperture radar sar images shows that the 10 cm ice ssm i ice thickness contour approximately follows the sar polynya edge for the twelve winters of 1990 2001 the ice thicknesses and heat fluxes within the polynya are estimated from daily ssm i data then compared with field data and with estimates from other investigations the results show the following first our calculated heat losses are consistent with 2 years of over winter salinity and temperature field data second comparison with other numerical and satellite estimates of the ice production shows that although our ice production per unit area is smaller our polynya areas are larger so that our ice production estimates are of the same order because our salinity forcing occurs over a larger area than in the other models the oceanic response associated with our forcing will be modified index terms 4540 oceanography physical ice mechanics and air sea ice exchange processes 3360 meteorology and atmospheric dynamics remote sensing 4504 oceanography physical air sea interactions 0312 4572 oceanography physical upper ocean processes 4207 oceanography general arctic and antarctic oceanography keywords chukchi sea coastal polynya remote sensing

internal solitary waves in the warm pool of the western equatorial pacific abstract during the spring tides of late november 1992 early january and early february 1993 solitary internal wave packets were observed at 2 s 156 15 e in the western equatorial pacific apparently generated in the nuguria island group 3 s 153 e the waves propagate northeastward at 2 4 2 8 m s 1 appearing in fixed phase with the underlying semidiurnal baroclinic tide the initial solitary wave crests have downward displacements in excess of 60 m and peak velocities greater than 80 cm s 1 groups of 1 3 crests are observed with vertical structure resembling a first mode internal wave and horizontal variability consistent with third order comb kdv solitons many of the packets exhibit an overall organization reminiscent of undular bores this borelike behavior is confined primarily to the upper 70 m not sharing the mode one dependency of the crests the solitons displace the ambient equatorial currents including the equatorial undercurrent both vertically 80 m and laterally 1 2 km with l

water mass properties and circulation on the west antarctic peninsula continental shelf in austral fall and winter 2001 abstract hydrographic measurements made during the us southern ocean global ocean ecosystem dynamics cruises which took place from april to june and july to september 2001 provide a description of changes in water mass distributions and circulation patterns in the marguerite bay region of the west antarctic peninsula continental shelf that result from seasonal variability and offshore forcing by the southern boundary of the antarctic circumpolar current acc the primary seasonal change in water mass properties is the reduction in antarctic surface water and replacement by a thick winter water layer the primary effect of the acc is to pump warm 1 5 c salty 34 65 34 7 and nutrient rich circumpolar deep water cdw onto the continental shelf below 200 m at specific sites that correspond to bathymetric features such as marguerite trough the cdw intruded onto the continental shelf moved across shelf and entered marguerite bay this flow pattern was observed during both cruises suggesting that onshelf intrusions of cdw are a regular occurrence on this shelf the number of cdw intrusions observed suggests that 4 6 events can occur in a year regions where cdw intrusions occur are characterized by surface waters that are above freezing in winter diffusive heat fluxes based on estimated diffusivities are insufficient for the observed rate of temperature decay of cdw intrusions localized bathymetrically controlled vertical mixing is suggested as the primary heat transfer mechanism the hydrographic and acoustic doppler current profiler measurements show a southwesterly flowing coastal current along adelaide island that enters the north side of marguerite bay and exits around alexander island this current which may result from seasonal coastal buoyancy forcing was present in fall and winter but was better developed in fall this current may be part of a larger cyclonic gyre that overlies the northern part of the area surveyed during the two cruises

circulation and melting beneath george vi ice shelf antarctica introduction george vi ice shelf sandwiched between the western coast of palmer land and the eastern coast of alexander island is the largest and most studied of the west antarctic peninsula ice shelves it covers an area of approximately 25 000 km2 and is underlain by circumpolar deep water cdw with temperatures in excess of 1oc giving rise to rapid basal melting bishop and walton 1981 lennon et al 1982 the maximum ice thickness of about 500 m occurs about 70 km from the southern ice front where a ridge of thick ice extends across george vi sound near 70ow see figure 1 effectively dividing the upper water column into northern and southern regions the northern ice front which faces marguerite bay appears to be near the geographical limit of ice shelf viability and has undergone a gradual retreat in recent decades lucchitta and rosanova 1998 a timeframe over which much of the nearby wordie ice shelf disintegrated doake and vaughan 1991 there is extensive surface melting over the northern parts of the ice shelf and much of the ice column near the northern ice front appears to be temperate paren and cooper 1986 conditions in the south where the ice front faces into ronne entrance are colder and the ice front position appears to be steady the vast majority of the flow into the ice shelf comes from palmer land but basal melting is sufficient to remove most of this so that the ice is derived almost exclusively from local accumulation by the time it reaches the ice fronts potter et al 1984 there is some evidence at the margins of the ice shelf to suggest that it may have disappeared completely during the early holocene before reforming sugden and clapperton 1981 bentley et al 2005

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

bathymetric influences on antarctic ice shelf melt rates ocean bathymetry exerts a strong control on ice sheet ocean interactions within antarctic ice shelf cavities where it can limit the access of warm dense water at depth to the underside of floatin

on the total input of antarctic waters to the deep ocean a preliminary estimate from chlorofluorocarbon measurements 1 deep ocean inventories of dissolved chlorofluorocarbon 11 cfc 11 along representative sections off antarctica provide the first estimate of the overall strength of all dense water sources in the southern ocean their formation rates are reported for three density layers that span the main water masses involved in the lower limb of the thermohaline circulation thc the bottom layer is supplied via sinking of antarctic bottom water aabw produced at a few continental shelves the middle layer receives the offshore injection of ventilated modified circumpolar deep water mcdw produced along much of the lengthy antarctic slope front the top layer is ventilated by northward export of antarctic surface water into the upper circumpolar deep water of the antarctic circumpolar current average southern ocean inputs to the upper two layers of the deep ocean for the 1970 1990 period are derived on the basis of the cfc 11 distributions along meridional sections the mean cfc 11 saturations of all water mass ingredients and the inferred mixing leading to production of dense source waters about 5 4 1 7 sv 1 sv 10 6 m 3 s 1 of near freezing shelf water ventilate the bottom layer and 4 7 1 7 sv and 3 6 1 3 sv of cold antarctic surface water ventilate the middle and top layers therefore the total contribution of ventilated southern ocean waters to the lower limb of the global thc is about 14 sv this is close to the about 17 sv estimated for north atlantic near surface sources from cfc 11 inventories their entrainment of 7 4 2 4 sv of cfc poor subsurface lower circumpolar deep water during the formation and sinking of aabw and mcdw raises the total southern ocean input to the deep ocean to about 21 sv

modeling water mass formation in the mertz glacier polynya and adelie depression east antarctica 1 high rates of sea ice growth and brine rejection in the mertz glacier polynya drive the production of dense continental shelf waters in the adelie depression we consider the rate of outflow of waters having sufficient density to sink into the neighboring abyssal ocean and form adelie land bottom water albw along with weddell and ross sea bottom waters the albw is an important source of antarctic bottom water the relevant processes are modeled using a variant of the max planck institute ocean model mpiom under daily ncep ncar reanalysis forcing for the period 1991 2000 the orthogonal curvilinear horizontal grid allows for the construction of a global domain with high resolution in our region of interest the modeled mertz glacier polynya is realistic in location and extent exhibiting low ice thickness 0 4 m and low ice fraction 50 the net surface ocean to atmosphere heat flux exceeds 200 w m2 and is dominated by sensible heat exchange in wintertime may through september inclusive 7 5 m of sea ice forms over the adelie depression at a rate of 4 9 cm d 1 this results in annual average volumetric production of 99 km3 of sea ice the associated brine release drives dense shelf water formation the off shelf flow of dense water exhibits strong interannual variability in response to variability in both atmospheric forcing and ocean preconditioning averaged over the period 1991 2000 the off shelf flow of dense water is 0 15 sv for a period of strong outflow 1993 1997 this increases to 0 24 sv most of the outflow occurs during july through october at a rate of 0 40 0 63 sv over the period 1991 2000 1993 1997 the peak mean monthly outflow can exceed 1 sv

observations of the terra nova bay antarctica polynya by modis ice surface temperature imagery from 2005 to 2010 abstract ice surface temperature ist imagery from the thermal infrared bands of the satellite borne moderate resolution imaging spectroradiometer modis has been used to analyze the activity of the terra nova bay polynya from 2005 to 2010 in clear sky conditions the shape of the open water area of the polynya i e the portion of the ocean free of sea ice is revealed by the skin sea ice temperatures close to the water freezing point provided by the modis derived ist product the swaths of the modis sensors onboard terra and aqua satellites over the terra nova bay consist of about 5500 scenes per year useful to estimate the cloud cover too the open water area was extracted from clear sky scenes and from scenes affected by fog but providing continuity of the shape of the polynya using about 40 of the available swaths the polynya was detected for more than 80 of the sea ice period with a revisit time below 24 h and for more than 50 with a revisit time below 3 h the open water area was extracted using thresholds of ist based on the ist values detected within the open water area and within the band of sea ice surrounding the polynya obtained scene by scene an ice free area larger than 100 km 2 was observed near the nansen ice shelf for more than 70 of time larger than 500 km 2 for 50 of time the mean annual open water area around 900 km 2 was close to the lower limit of the reported range except during 2006 around 600 km 2 due to the limited activity in the second half of the cold season the largest extents between 6000 and 8500 km 2 occurred in different periods of the antarctic winter and exceeded maxima estimated in previous studies by thermal infrared data polynya openings developed from a few hours to several days in the latter case sustained by subsequent katabatic events visible in the ist sequence peaks of growing rate above 300 km 2 h were observed during intense katabatic events with gusts of 50 m s the fluctuations of the open water area resulted well correlated with wind records available from local automatic weather stations within the main katabatic routes and followed katabatic events at intervals between 0 and 6 h the analysis of the ist data set derived from the thermal infrared bands of modis provides new polynya observations of high horizontal resolution 1 km and frequent revisit time during the winter season complementing previously available observations with passive microwave imagery

the distribution and formative processes of latent heat polynyas in east antarctica a study of polynya characteristics in east antarctica was undertaken using ice concentrations derived from special sensor microwave imager data for the period july 1987 august 1994 the areas of polynyas were defined as having an ice concentration 75 the analysis revealed a total of 28 coastal polynyas within the study region the spatial and temporal variability in areal extent was quantified the timing of mean maximum areal extent varied from june to october the bathymetry and wind regime at each polynya site was examined to gauge the relative importance of these parameters in polynya formation and maintenance in 20 locations shallow banks and shoals form grounding zones for icebergs and anchoring sites for fast ice which form barriers to the predominantly westward drift of the pack ice elsewhere north south coastal protrusions or alignments form similar barriers the subsequent removal of newly formed sea ice from the lee of such barriers by katabatic and synoptic winds maintains areas of reduced ice concentration and open water very few coastal polynyas are attributed solely to katabatic outflow the combined influence of bathymetry topography and winds is responsible for the characteristics of the majority of polynyas many were considered to be marginal characterised by occasional periods when the ice concentration falls below 75 an analysis of annual winter totals of areas with ice concentrations 75 shows no trends in total polynya areal extent over the period 1987 94 known locations of emperor penguin aptenodytes forsteri rookeries were also found to be associated with the locations of coastal polynyas

deceleration of a finite width stratified current over a sloping bottom frictional spindown or buoyancy shutdown abstract the deceleration of an unforced two dimensional finite width current over a sloping bottom in a stratified fluid is studied to quantify the relative importance of frictional spindown and buoyancy shutdown when both act simultaneously frictional spindown decelerates the current through ekman suction and pumping at the current edges which transmit stresses into the interior fluid buoyancy shutdown is the process by which lateral advection of density in the bottom boundary layer generates thermal wind shears that reduce the bottom stress thereby halting deceleration a theoretical model of a downwelling current suggests that buoyancy shutdown always reduces the deceleration timescale from that for frictional spindown alone and produces a nonzero steady along isobath current overlying an arrested bottom mixed layer the model is most sensitive to the burger number s n f where n is the buoyancy frequency the bottom slope and f the coriolis parameter larger s produces a stronger steady cu

controls on circulation cross shelf exchange and dense water formation in an antarctic polynya circulation on the antarctic continental shelf influences cross shelf exchange antarctic bottom water formation and ocean heat flux to floating ice shelves the physical processes driving the shelf circulation and its seasonal and interannual variability remain poorly understood we use a unique time series of repeat hydrographic observations from the adelie land continental shelf and a box inverse model to explore the relationship between surface forcing shelf circulation cross shelf exchange and dense water formation a wind driven northwestward coastal current set up by onshore ekman transport dominates the summer circulation during winter strong buoyancy loss creates dense shelf water this dense water flows off the shelf with a compensating on shelf flow that is an order of magnitude larger in winter than in summer the results demonstrate the importance of winter buoyancy loss in driving the shelf circulation and cross shelf exchange as well as dense water mass formation

the fluctuating longshore pressure gradient on the pacific northwest shelf a dynamical analysis abstract the majority of papers on pacific northwest shelf dynamics have emphasized the relationship between longshore wind stress 3 and longshore velocity v however attempts to illustrate a balance of momentum in the longshore direction have not been encouraging 3 sol h where h is water depth has insufficient magnitude to balance the vertically averaged longshore acceleration vt at least during summer in this paper it is demonstrated that the missing momentum is provided by the longshore pressure gradient force py the pressure gradient was estimated using tide gauge and atmospheric pressure data at stations separated by roughly 400 km seasonal and long term means from hickey and pola and in some cases nonseasonal monthly anomalies from enfield and allen were added to the sum of the tide gauge and atmospheric pressure data to form time series of total subsurface pressure the pressure data were multiplied by an offshore deny factor to simulate coastal trapping the analysis was performed

thickness and production of sea ice in the okhotsk sea coastal polynyas from amsr e 1 from comparisons with thickness of sea ice from advanced very high resolution radiometer avhrr and ice profiling sonar data we have developed an advanced microwave scanning radiometer eos amsr e thin ice thickness algorithm for the sea of okhotsk this algorithm can estimate ice thickness of 0 2 m without snow using the polarization ratio of amsr e brightness temperature at a 36 5 ghz channel from a linear relationship with avhrr ice thickness when a snow cover exists on the thin ice surface as occurred a few times in each winter it is shown that the algorithm cannot detect the thin ice sea ice and dense shelf water dsw production in coastal polynya are estimated on the basis of heat flux calculation with the daily amsr e ice thickness for three winters december march of 2002 2003 to 2004 2005 the ice production is largest in the northwest shelf nws polynya which accounts for 45 of the sum of ice production in major coastal polynyas the ice production in major coastal polynyas would cover the maximum ice area of the okhotsk sea if the average ice thickness is assumed to be 1 m variability of the ice production is mainly modulated by air temperature in the nws polynya which is the main dsw production area the annual dsw formation rate is estimated to be 0 36 sv

antarctic palaeo ice streams we review the geomorphological sedimentological and chronological evidence for palaeo ice streams on the continental shelf of antarctica and use this information to investigate basal conditions and processes and to identify factors controlling grounding line retreat a comprehensive circum antarctic inventory of known palaeo ice streams their basal characteristics and minimum ages for their retreat following the last glacial maximum lgm is also provided antarctic palaeo ice streams are identified by a set of diagnostic landforms that nonetheless display considerable spatial variability due to the influence of substrate flow velocity and subglacial processes during the lgm palaeo ice streams extended via bathymetric troughs to the shelf edge of the antarctic peninsula and west antarctica and typically to the mid outer shelf of east antarctica the retreat history of the antarctic ice sheet since the lgm is characterised by considerable asynchroneity with individual ice streams exhibiting different retreat histories this variability allows antarctic palaeo ice streams to be classified into discrete retreat styles and the controls on grounding line retreat to be investigated such analysis highlights the important impact of internal factors on ice stream dynamics such as bed characteristics and slope and drainage basin size whilst grounding line retreat may be triggered and to some extent paced by external atmospheric and oceanic forcing the individual characteristics of each ice stream will modulate the precise timing and rate of retreat through time

lifetime and cyclicity of fluid venting at forearc mound structures determined by tephrostratigraphy and radiometric dating of authigenic carbonates at convergent margins fluids rise through the forearc in response to consolidation of the upper plate and dewatering of the subducting plate and produce various cold seep related features on the seafloor mud diapirs mud mounds at the central american forearc authigenic carbonates precipitated from rising fluids within such structures during active venting while typical mixed mud sediments were ejected onto the surrounding seafloor where they became intercalated with normal pelagic background sediments indicating that mud mounds evolved unsteadily through alternating active and inactive phases intercalated regional ash layers from plinian eruptions at the central american volcanic arc provide time marks that constrain the ages of mud ejection activity u th dating of drill core samples of authigenic carbonate caps of mud mounds yields ages agreeing well with those constrained by ash layers and showing that carbonate caps grow inward rather than outward during active venting both dating approaches show that offshore nicaragua and costa rica 1 active and inactive phases can occur simultaneously at neighboring mounds 2 mounds along the forearc have individual histories of activity but there are distinct time intervals when nearly all mounds have been active or inactive 3 lifetimes of mounds reach several hundred thousand years and 4 highly active periods last 10 50 k y with intervening periods of 10 k y of relative quiescence

volcanism and massive sulfide formation at a sedimented spreading center escanaba trough gorda ridge northeast pacific ocean seismic reflection profiles over the sediment filled escanaba trough at the southern gorda ridge reveal a series of volcanic centers that pierce the sediment the volcanic edifices are 3 to 6 km in diameter and are spaced at 15 to 20 km intervals along the axis of the trough the volcanic intrusions have uplifted the sediment as much as 100 m and in places fresh basaltic flows are exposed at the sea floor unoxidized pyrrhotite rich massive sulfide samples were obtained from the flanks of one of these volcanic centers the composition and form of the sulfide samples suggest significant interaction between hydrothermal fluids and sediment at depth and deposition of sulfide within the sediment pile

the inner shelf response to wind driven upwelling and downwelling abstract a two dimensional numerical model is used to study the response to upwelling and downwelling favorable winds on a shelf with a strong pycnocline during upwelling or downwelling the pycnocline intersects the surface or bottom forming a front that moves offshore the characteristics of the front and of the inner shelf inshore of the front are quite different for upwelling and downwelling for a constant wind stress the upwelling front moves offshore at roughly a constant rate while the offshore displacement of the downwelling front scales as t because the thickness of the bottom layer increases as the front moves offshore the geostrophic alongshelf transport in the front is larger during downwelling than upwelling for the same wind stress magnitude because the geostrophic shear is near the bottom in downwelling as opposed to near the surface in upwelling during upwelling weak stratification is maintained over the inner shelf by the onshore flux of denser near bottom water this weak stratif

a modeling study of shelf circulation off northern california in the region of the coastal ocean dynamics experiment response to relaxation of upwelling winds 1 a two part modeling study of the wind forced flow on the continental shelf off northern california in the region 37 40 n of the coastal ocean dynamics experiment code is pursued this paper involves a process oriented study with idealized wind stress forcing gan and allen 2002 involves forcing with observed winds and heat flux for april may 1982 and comparison of model results with code observations a characteristic but previously unexplained response observed during code following the weakening or relaxation of southward upwelling favorable winds is the time dependent development of northward currents over the inner shelf next to the coast the presence of northward winds is not necessary for this occurrence the objective in this paper is to investigate the dynamics of the shelf flow response to upwelling wind relaxation events under idealized conditions in the basic case experiment a spatially uniform upwelling favorable southward wind stress of 0 1 pa is applied to the ocean initially at rest the stress is held constant for 10 days and then decreased linearly to zero over 3 days in response to the southward wind stress southward alongshore currents develop on the shelf accompanied by upwelling of cold dense water near the coast considerable spatial variability in the shelf flow clearly related to the alongshore variations in coastline and bottom topography is found the alongshore currents tend to separate from the coast south of capes and the coldest surface water is found at those locations as the winds decrease northward currents similar to those observed develop on the inner shelf next to the coast at many alongshore locations examination of the alongshore momentum balances shows that the northward currents are forced by a northward pressure gradient force associated with negative alongshore pressure gradients these pressure gradients are set up by the interaction of the wind forced flow with the alongshore variations in shelf topography in general negative alongshore pressure gradients intensified off pt reyes and pt arena by the gradient wind balance are found south of capes the negative pressure gradients geostrophically balance onshore flow at depth and upwelling is strengthened in these locations north of capes positive pressure gradients that are primarily in balance with nonlinear advective effects are found after the winds cease the forced across shelf circulation weakens and the resulting unbalanced negative pressure gradients south of the capes accelerate the alongshore currents northward processes with similar dynamics are found embedded in the more complex coastal ocean response to observed time varying winds by gan and allen 2002

acceleration of a stratified current over a sloping bottom driven by an alongshelf pressure gradient abstract an idealized theoretical model is developed for the acceleration of a two dimensional stratified current over a uniformly sloping bottom driven by an imposed alongshelf pressure gradient and taking into account the effects of buoyancy advection in the bottom boundary layer both downwelling and upwelling pressure gradients are considered for a specified pressure gradient the model response depends primarily on the burger number s n f where n is the initial buoyancy frequency is the bottom slope and f is the coriolis parameter without stratification s 0 buoyancy advection is absent and the alongshelf flow accelerates until bottom stress balances the imposed pressure gradient the e folding time scale to reach this steady state is the friction time h r where h is the water depth and r is a linear bottom friction coefficient with stratification s 0 buoyancy advection in the bottom boundary layer produces vertical shear which prevents the bottom stress from becoming large

sea ice transport driving southern ocean salinity and its recent trends the southern ocean has freshened over the past few decades but the underlying mechanisms involved have remained unclear alex haumann and colleagues bring together multiple lines of evidence and despite large uncertainties in the underlying datasets they find that northward transport of sea ice formed around the antarctic coast can explain the bulk of the observed freshening

wind driven modification of the alaskan coastal current 1 across shelf transects over the eastern flank of barrow canyon were obtained in august 2005 with an autonomous underwater vehicle auv here the shelf topography creates a choke point in which a substantial portion of pacific inflow from the bering strait is concentrated within 30 km of the coast providing an ideal setup for monitoring the flow with the auv four transects extending 10 km offshore of barrow alaska inshore of the 80 m isobath were used in conjunction with a process oriented numerical model to diagnose the wind driven modification of the alaskan coastal current poleward transports of 0 12 sv were consistent among all sections although the transport weighted temperature was about 1 c colder in the transect obtained during peak winds an idealized numerical model reproduces the observed hydrographic structure and across shelf circulation reasonably well in that 1 winds were not sufficient to reverse the poleward flow 2 upwelling was most pronounced in the nearshore and 3 the onshore return flow occurred throughout the interior as opposed to the bottom boundary layer the across shelf circulation provides a possible mechanism for a meltwater intrusion observed on the offshore side of the auv transect made during peak winds also of interest is that the observed anticyclonic shear was much stronger u y f than previously measured in the region

southern ocean frontal structure and sea ice formation rates revealed by elephant seals polar regions are particularly sensitive to climate change with the potential for significant feedbacks between ocean circulation sea ice and the ocean carbon cycle however the difficulty in obtaining in situ data means that our ability to detect and interpret change is very limited especially in the southern ocean where the ocean beneath the sea ice remains almost entirely unobserved and the rate of sea ice formation is poorly known here we show that southern elephant seals mirounga leonina equipped with oceanographic sensors can measure ocean structure and water mass changes in regions and seasons rarely observed with traditional oceanographic platforms in particular seals provided a 30 fold increase in hydrographic profiles from the sea ice zone allowing the major fronts to be mapped south of 60 s and sea ice formation rates to be inferred from changes in upper ocean salinity sea ice production rates peaked in early winter april may during the rapid northward expansion of the pack ice and declined by a factor of 2 to 3 between may and august in agreement with a three dimensional coupled ocean sea ice model by measuring the high latitude ocean during winter elephant seals fill a blind spot in our sampling coverage enabling the establishment of a truly global ocean observing system

oceanic controls on the mass balance of wilkins ice shelf antarctica 0 8 m a 1 driven by a mean basal melt rate of wb 1 3 0 4 m a 1 interannual variability was large associated with changes in both surface mass accumulation and wb basal melt rate declined significantly around 2000 from 1 8 0 4 m a 1 for 1992 2000 to 0 75 0 55 m a 1 for 2001 2008 the latter value corresponding to approximately steady state ice shelf mass observations of ocean temperature t obtained during 2007 2009 by instrumented seals reveal a cold deep halo of winter water ww t 1 6 c surrounding wis the base of the ww in the halo is 170 m approximately the mean ice draft for wis we hypothesize that the transition in wb in 2000 was caused by a small perturbation 10 20 m in the relative depths of the ice base and the bottom of the ww layer in the halo we conclude that basal melting of thin ice shelves like wis is very sensitive to upper ocean and coastal processes that act on shorter time and space scales than those affecting basal melting of thicker west antarctic ice shelves such as george vi and pine island glacier

carbonate chemistry in the mertz polynya east antarctica biological and physical modification of dense water outflows and the export of anthropogenic co2 1 dense shelf water dsw is formed in east antarctica from enhanced sea ice production driven by air sea interaction in coastal polynyas cross shelf export and downslope mixing of this dsw produces antarctic bottom water contributing to the lower limb of the global overturning circulation we present biogeochemical observations from the mertz polynya region in summer 2007 2008 with additional observations from spring 2001 and winter 1996 the seasonal changes in mixed layer carbonate chemistry are driven by a combination of air sea co2 exchange biological activity and the formation and melt of sea ice the air sea fluxes in 2008 were 15 mmol c m 2 d 1 and net community production estimated from the summertime surface dissolved inorganic carbon dic deficit ranged from 0 9 to 1 2 mol c m 2 yr 1 we show that biological modification of carbonate chemistry over the shelf in summer preconditions the dsw outflows from the adelie depression this process appears to supply both organic material and water depleted in co2 and with enhanced carbonate saturation state relative to inflowing water to coral communities on the slope we combined model based transports of exported dsw with the natural and anthropogenic cant carbon concentrations and estimate that the annual outflows of dic and cant from the mertz polynya range from 320 to 560 tg c yr 1 and from 3 to 6 tg cant yr 1 respectively the formation and export of dense water from this region and by extension all similar polynyas around antarctica is an effective mechanism for the transfer of anthropogenic carbon into the deep ocean

sensitivity of circumpolar deep water transport and ice shelf basal melt along the west antarctic peninsula to changes in the winds circumpolardeepwater cdw can be found near the continental shelfbreak around most of antarctica advection of this relatively warm water up to 28c across the continental shelf to the base of floating ice shelves is thought to be a critical source of heat for basal melting in some locations a high resolution 4 km regional ocean sea ice ice shelf model of the west antarctic peninsula wap coastal ocean was used to examine the effects of changes in the winds on across shelf cdw transport and ice shelf basal melt increases and decreases in the strength of the wind fields were simulated by scaling the present day winds by a constant factor additional simulations considered effects of increased antarctic circumpolar current acc transport increased wind strength and acc transport increased the amount of cdw transported onto the wap continental shelf but did not necessarily increase cdw flux underneath the nearby ice shelves the basal melt underneath some of the deeper ice shelves actually decreased with increased wind strength increased mixing over the wap shelf due to stronger winds removed more heat from the deeper shelf waters than the additional heat gained from increased cdw volume transport the simulation results suggest that the effect on the wap ice shelves of the projected strengthening of the polar westerlies is not a simple matter of increased winds causing increased or decreased basal melt a simple budget calculation indicated that iron associated with increased vertical mixing of cdw could significantly affect biological productivity of this region

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

atlantic water variability on the se greenland continental shelf and its relationship to sst and bathymetry 1 interaction of warm atlantic origin water aw and colder polar origin water pw advecting southward in the east greenland current egc influences the heat content of water entering greenland s outlet glacial fjords here we use depth and temperature data derived from deep diving seals to map out water mass variability across the continental shelf and to augment existing bathymetric products we compare depths derived from the seal dives with the ibcao version 3 bathymetric database over the shelf and find differences up to 300 m near several large submarine canyons in the vertical temperature structure we find two dominant modes a cold mode with the typical aw pw layering observed in the egc and a warm mode where aw is present throughout the water column the prevalence of these modes varies seasonally and spatially across the continental shelf implying distinct aw pathways in addition we find that satellite sea surface temperatures sst correlate significantly with temperatures in the upper 50 m r 0 54 but this correlation decreases with depth r 0 22 at 200 m and becomes insignificant below 250 m thus care must be taken in using sst as a proxy for heat content as aw mainly resides in these deeper layers sample unit level copyright

genesis of the antarctic slope current in west antarctica the stability of the west antarctic ice sheet wais depends on ocean heat transport toward its base and remains a source of uncertainty in sea level rise prediction the antarctic slope current asc a major boundary current of the ocean s global circulation serves as a dynamic gateway for heat transport toward antarctica here we use observations collected from the bellingshausen sea to propose a mechanistic explanation for the initiation of the westward flowing asc waters modified throughout the bellingshausen sea by ocean sea ice and ocean ice shelf interactions are exported to the continental slope in a narrow topographically steered western boundary current this focused outflow produces a localized front at the shelf break that supports the emerging asc this mechanism emphasizes the importance of buoyancy forcing integrated over the continental shelf as opposed to local wind forcing in the generation mechanism and suggests the potential for remote control of melt rates of wais largest ice shelves

late weichselian environmental change in southern sweden and denmark a synthesis is presented of the envronmental and climatic variations that are inferred to have occurred in southern sweden up to latitude 59 n and denmark during the weichselian late glacial 14 9 ka bp the chronology and characteristics of the main phases of deglaciation sea level change periglacial activity soil development vegetation cover and climate change are summarised a curve representing the main changes in temperature including quantitative estimates based upon beetle data and using the mutual climatic range method is presented

mapping of sea ice production for antarctic coastal polynyas 1 active sea ice production in antarctic coastal polynyas causes dense water formation finally leading to antarctic bottom water aabw formation this study gives the first mapping of sea ice production in the antarctic ocean based on heat flux calculation with ice thickness data derived from satellite data the highest ice production occurs in the ross ice shelf polynya region the ice production there decreased by 30 from the 1990s to the 2000s which can be one candidate for causing the recent freshening of aabw the cape darnley polynya in east antarctica is found to be the second highest production area suggesting a possible aabw formation area according to our estimation around 10 of southern ocean sea ice is produced in the major antarctic coastal polynyas the mapping provides surface heat and salt flux conditions in the ice covered region which have not been well understood

seals map bathymetry of the antarctic continental shelf we demonstrate the first use of marine mammal dive depth data to improve maps of bathymetry in poorly sampled regions of the continental shelf a group of 57 instrumented elephant seals made on the order of 2 x 10 5 dives over and near the continental shelf on the western side of the antarctic peninsula during five seasons 2005 2009 maximum dive depth exceeded 2000 m for dives made near existing ship tracks with measured water depths h 700 m similar to 30 of dive depths were to the seabed consistent with expected benthic foraging behavior by identifying the deepest of multiple dives within small areas as a dive to the seabed we have developed a map of seal derived bathymetry our map fills in several regions for which trackline data are sparse significantly improving delineation of troughs crossing the continental shelf of the southern bellingshausen sea

wintertime ocean conditions over the southern weddell sea continental shelf antarctica 1 during the austral winter of 2007 a weddell seal tagged with a miniaturized conductivity temperature depth ctd instrument travelled over the central southern weddell sea continental shelf the instrument yielded 750 ctd profiles 250 of them to the sea floor the data show a full depth flow of water onto the shelf via a sill at the shelf break 74 s 44 w the warmth from the core of the flow was able to maintain the surface mixed layer above the freezing point resulting in a band of reduced ice production an estimate of the on shelf flux suggests that this flow accounts for most of the estimated 3 sv of water draining from the southern weddell sea continental shelf

the antarctic slope current in a changing climate the antarctic slope current asc is a coherent circulation feature that rings the antarctic continental shelf and regulates the flow of water towards the antarctic coastline the structure and variability of the asc influences key processes near the antarctic coastline that have global implications such as the melting of antarctic ice shelves and water mass formation that determines the strength of the global overturning circulation recent theoretical modeling and observational advances have revealed new dynamical properties of the asc making it timely to review earlier reviews of the asc focused largely on local classifications of water properties of the asc s primary front here we instead provide a classification of the current s frontal structure based on the dynamical mechanisms that govern both the along slope and cross slope circulation these two modes of circulation are strongly coupled similar to the antarctic circumpolar current highly variable motions such as dense overflows tides and eddies are shown to be critical components of cross slope and cross shelf exchange but understanding of how the distribution and intensity of these processes will evolve in a changing climate remains poor due to observational and modeling limitations results linking the asc to larger modes of climate variability such as el nino show that the asc is an integral part of global climate an improved dynamical understanding of the asc is still needed to accurately model and predict future antarctic sea ice extent the stability of the antarctic ice sheets and the southern ocean s contribution to the global carbon cycle

dynamics of the terra nova bay polynya the potential of multi sensor satellite observations research on processes leading to formation maintenance and disappearance of polynyas in the polar regions benefits significantly from the use of different types of remote sensing data the sentinels of the european space agency esa together with other satellite missions provide a variety of data from different parts of the electromagnetic spectrum at different spatial scales and with different temporal resolutions in a case study we demonstrate the advantage of merging data from different spaceborne instruments for analysing ice conditions and ice dynamics in and around the frequently occurring terra nova bay polynya tnbp in the ross sea in the antarctic starting with a list of polynya parameters that are typically retrieved from satellite images we assess the usefulness of different sensor types on regional scales several 100 km passive microwave radiometers provide a view on the mutual influence of the three ross sea polynyas on sea ice drift and deformation patterns optical sensors with meter scale resolution on the other hand allow very localized analyses of different polynya zones the combination of different ranges of the electromagnetic spectrum is essential for recognition and classification of ice types and structures radar images together with data from thermal infrared sensors operated at tens to hundreds of meters resolution improve the separation of the outlet zone of the polynya from the adjacent pack ice the direct comparison of radar and passive microwave images reveals the visibility of deformed ice zone in the latter a sequence of radar images was employed to retrieve ice drift around the tnb which allows analysing the temporal changes of the polynya area and the extension and structure of the outlet zone as well as ice movements and deformation that are influenced by the katabatic winds

a field and laboratory study of wave damping by grease ice in a field and laboratory study we discuss the formation growth and wave absorption properties of grease ice our field observations show that grease ice formation occurs under cold windy conditions in both leads and polynyas in leads grease ice forms in the open water then is herded to the down wind edge of the lead in polynyas a langmuir circulation herds the grease ice into long plumes parallel to the wind in the laboratory we grow grease ice in a wave tank and measure its wave absorption properties for single frequency two dimensional waves on a large scale we find that the thickness of the grease ice which increases away from the paddle is determined by a balance between the wave momentum flux and the free surface tilt on a small scale our photographs show that the crystals which make up the grease ice consist of discs measuring about 1 mm in diameter and 1 10 m thick which at low rates of shear sinter together into larger clumps yielding a viscosity increase to measure this non linear viscosity we study the decay of wave amplitude between two critical distances measured inwards from the leading edge the first occurs when the depth of grease ice exceeds k 1 where k is the wave number the second further distance is a line of transition from liquid to solid behavior which we call the dead zone between these two distances the wave amplitude decays with a linear slope which increases as a 0 k 2 where a0 is the wave amplitude in open water concurrent measurements of ice concentration show that it increases from values of 18 22 at the leading edge to a local maximum of 32 44 at the dead zone while the values at the dead zone increase non linearly with a0k finally comparison of the observed to that calculated from a yield stress viscosity model shows if the yield stress coefficient is proportional to the incident wave momentum flux the model predicts the observed

observations of supercooled water and frazil ice formation in an arctic coastal polynya from moorings and satellite imagery formation of supercooled water and frazil ice was studied in the chukchi sea coastal polynya off barrow alaska usa in winter 2009 10 using moored salinity temperature sensors and ice profiling sonar ips data along with satellite data oceanographic data from two moorings revealed episodic events of potential supercooling at 30 40m depth including the possibility of in situ supercooling while the polynya was open we identified frazil ice like signals in the ips data down to 5 15 m depth associated with large heat loss and windy turbulent conditions in an active polynya this likely represents the first ips observation of frazil ice in the marine environment on the day of the maximum signal of frazil ice spaceborne synthetic aperture radar shows streaks of high backscatter within the polynya indicating active frazil ice formation just downwind of the mooring sites in addition the longer term potential supercooling that persisted for 1 3 weeks occurred twice despite the absence of polynya activity at the mooring sites these events occurred during periods dominated by the northeastward current a series of coastal polynyas had formed southwest of the mooring sites prior to these events thus the water masses with potential supercooling were likely advected from these polynyas

massive sulfides in a sedimented rift valley northern juan de fuca ridge a number of mounds each several hundred meters across and up to sixty meters high have been observed with seamarc ii acoustic imagery and seabeam bathymetry in the sediment filled axial valley at the northern end of the juan de fuca ridge the mounds are located a few kilometers west of the eastern valley bounding normal fault scarp where the local sediment fill is approximately 300 m thick all of the mounds are believed to be of hydrothermal origin and one is associated with anomalously high heat flow in excess of 1 w m 2 a piston core collected from that mound comprises coarse clastic sulfide units interbedded with sulfidic muds hydrothermal minerals present in the 2 3 m section include pyrrhotite pyrite marcasite sphalerite chalcopyrite iss intermediate solid solution in the cufezns system chalcopyrrhotite galena talc barite and amorphous silica mineral fabrics of the clasts indicate that the material was precipitated at or near the sea floor by mixing of hot hydrothermal fluids with cold seawater low concentrations of zn cu cd and ag relative to those found in unsedimented ridge hydrothermal deposits and the presence of pyrrhotite as an early phase mineral indicates that the vent fluids have been modified by reaction with sediments beneath the mound rapid sedimentation in a rift valley is clearly conducive to the formation of large hydrothermal mineral deposits like those believed to be present within and beneath these mounds the relatively impermeable sediment cover insulates the crust inhibits groundwater recharge promotes long lived discharge at a restricted number of sites provides a substrate for the efficient subsurface precipitation of minerals and through continued sedimentation protects surficial deposits from the corrosive effects of seawater no reliable estimate of the bulk composition of the mounds can be made with existing data but their size is comparable to major hydrothermal mineral deposits found on land ancient settings in which many land deposits formed are in many ways similar to the one in which the features described here are currently forming

bottom friction and bed forms on the southern flank of georges bank kinetic energy typical bottom friction velocities are 1 1 1 2 cm s 1 in the time mean with standard deviations of 0 4 0 5 cm s 1 a representative drag coefficient is cd 3 0 0 1 10 3 at 1 2 m above the bottom our drag coefficient estimates at this and other elevations correspond to the apparent bottom roughness range z0 0 05 0 09 cm bottom photographs taken february june show that from february until april the sea floor was covered by sand ripples 1 2 cm in height these ripples were approximately aligned with the local isobath their flanks were perpendicular to the major axis of the tidal ellipse ripples exhibited stationary behavior that is they did not migrate with the flow intermittent modification of the ripple pattern happened during times of strong wavecurrent interaction but along isobath ripples formed again after each wave event observations of bed forms affected by surface waves coincided with periods of waveenhanced bottom stress predicted by the grant and madsen 1979 combined wavecurrent interaction model model results and bottom photographs indicate that sediments were kept in suspension only under extreme conditions here the february 1995 storm sand ripples gradually eroded during late march and april until the sea floor was almost flat coinciding with slow ripple erosion bioturbation levels increased our estimates of bottom stress do not exhibit seasonal changes so that seasonal variation of bottom shear stress cannot explain the transition from a rippled to a nearly flat bottom we conclude that biogenic modification of bottom sediment enhanced the critical shear stress for initiation of sediment movement thereby prohibiting ripple formation in spring and summer index terms 4219 oceanography general continental shelf processes 4211 oceanography general benthic boundary layers 4558 oceanography physical sediment transport 4560 oceanography physical surface waves and tides 1255 keywords bottom stress bottom roughness bottom drag coefficient wave current interaction sand waves georges bank citation werner s r r c beardsley and a j williams iii bottom friction and bed forms on the southern flank of georges bank j geophys res 108 c11 8004 doi 10 1029 2000jc000692 2003

antarctic circumpolar current frontal system in the south atlantic monitoring using merged argo and animal borne sensor data 1 we describe large scale features of the antarctic circumpolar current acc in the atlantic part of the southern ocean by merging argo data and data obtained by novel animal borne ctd sensors twenty one of these ctd satellite relay data loggers ctd srdls were attached to southern elephant seals mirounga leonina on south georgia the merged data yield unified gridded hydrogaphic fields with high temporal and spatial resolution enabling the determination of features absent in each of the data sets separately the structure and variability of the frontal field revealed by this data set were compared with those in daily quarter degree optimally interpolated sea surface temperature fields and fields of weekly gridded sea level anomaly in general the frontal positions derived using our data set are in agreement with previous work especially where the pathways are constrained by topography e g at the north scotia ridge and the south scotia ridge however with the improved temporal and spacial resolution provided by the ctd srdls we were able to observe some novel features all frontal positions are more variable than previously indicated across the scotia sea and west of the mid atlantic ridge on seasonal time scales the merged data set shows the temporal variability of the southern acc front saccf north of south georgia and in its position east of the island where the saccf lies further north than has been suggested in previous work in addition the subantarctic front crosses the mid atlantic ridge about 400 km further north when compared to previous work

a model study of circumpolar deep water on the west antarctic peninsula and ross sea continental shelves abstract transport of relatively warm nutrient rich circumpolar deep water cdw onto continental shelves around antarctica has important effects on physical and biological processes however the characteristics of the cdw along the shelf break as well as what happens to it once it has been advected onto the continental shelf differ spatially in the present study high resolution 4 5 km regional models of the ross sea and the west antarctic peninsula coastal ocean are used to compare differences in cdw transport the models compared very well with observations from both regions examining the fluxes not only of heat but also of a simulated dye representing cdw shows that in both cases cdw crosses the shelf break in specific locations primarily determined by the bathymetry but eventually floods much of the shelf the frequency of intrusions in marguerite trough was ca 2 3 per month similar to recent mooring observations a significant correlation between the along shelf break wind stress and the cross shelf break dye flux through marguerite trough was observed suggesting that intrusions are at least partially related to short duration wind events the primary difference between the cdw intrusions on the ross and west antarctic peninsula shelves is that there is more vigorous mixing of the cdw with the surface waters in the ross sea especially in the west where high salinity shelf water is created the models show that the cdw moving across the antarctic peninsula continental shelf towards the base of the ice shelves not only is warmer initially and travels a shorter distance than that advected towards the base of the ross ice shelf but it is also subjected to less vertical mixing with surface waters which conserves the heat available to be advected under the ice shelves this difference in vertical mixing also likely leads to differences in the supply of nutrients from the cdw into the upper water column and thus modulates the impacts on surface biogeochemical processes