mean dynamic topography of the arctic ocean 1 icesat and envisat altimetry data provide measurements of the instantaneous sea surface height ssh across the arctic ocean using lead and open water elevation within the sea ice pack first these data were used to derive two independent mean sea surface mss models by stacking and averaging along track ssh profiles gathered between 2003 and 2009 the icesat and envisat mss data were combined to construct the high resolution icen mss second we estimate the 5 5 year mean dynamic topography mdt of the arctic ocean by differencing the icen mss with the new goco02s geoid model derived from grace and goce gravity using these satellite only data we map the major features of arctic ocean dynamical height that are consistent with in situ observations including the topographical highs and lows of the beaufort and greenland gyres respectively smaller scale mdt structures remain largely unresolved due to uncertainties in the geoid at short wavelengths

sea surface height determination in the arctic ocean from ers altimetry 1 accurate sea surface height measurements have been extracted from ers altimeter data in sea ice covered regions for the first time the data have been used to construct a mean sea surface of the arctic ocean between the latitudes of 60 degreesn and 81 5 degreesn based on 4 years of ers 2 data an rms value for the crossover differences of mean sea surface profiles of 4 2 cm was observed in the ice covered canada basin compared with 3 8 cm in the ice free greenland iceland norwegian seas comparisons are made with an existing global mean sea surface osumss95 highlighting significant differences between the two surfaces in permanently ice covered seas in addition we present the first altimeter derived sea surface height variability map of the arctic ocean comparisons with a high resolution coupled ocean sea ice general circulation model reveal a good qualitative agreement in the spatial distribution of variability quantitatively we found that the observed variability was on average a factor of 3 4 greater than model predictions

mount logan ice core record of tropical and solar influences on aleutian low variability 500 1998 a d continuous high resolution paleoclimate records from the north pacific region spanning the past 1500 years are rare and the behavior of the aleutian low alow pressure center the dominant climatological feature in the gulf of alaska remains poorly constrained here we present a continuous 1500 year long calibrated proxy record for the strength of the wintertime december march alow from the mount logan summit pr col 5200 m asl ice core soluble sodium time series we show that ice core sodium concentrations are statistically correlated with north pacific sea level pressure and zonal wind speed our alow proxy record reveals a weak alow from circa 900 1300 a d and 1575 1675 a d and a comparatively stronger alow from circa 500 900 a d 1300 1575 a d and 1675 a d to present the mount logan alow proxy record shows strong similarities with tropical paleoclimate proxy records sensitive to the el nino southern oscillation and is consistent with the hypothesis that the medieval climate anomaly was characterized by more persistent la nina like conditions while the little ice age was characterized by at least two intervals of more persistent el nino like conditions the mount logan alow proxy record is significantly p 0 05 correlated and coherent with solar irradiance proxy records over various time scales with stronger solar irradiance generally associated with a weaker alow and la nina like tropical conditions however a step like increase in alow strength during the dalton solar minimum circa 1820 is associated with enhanced walker circulation furthermore rising co2 forcing or internal variability may be masking the twentieth century rise in solar irradiance

lateral heterogeneity and azimuthal anisotropy in the north atlantic determined from ss s differential travel times to explore upper mantle heterogeneity beneath the north atlantic we have measured 70 ss s differential travel times using the waveform cross correlation method both the two way preliminary reference earth model prem and j b jeffreys bullen residuals exhibit a maximum variation of 17 s ranging from 10 to 7 and 9 to 8 s respectively the lack of correlation between ss s and s residuals along with the strong correlation between ss s and ss residuals suggests that ss s differential travel times eliminate source and receiver effects and sample the upper mantle anomalies near the ss bounce points without being strongly affected by lower mantle heterogeneities we find evidence for a strong local anomaly in the north atlantic residuals for bounce points immediately to the north of the azores gibraltar plate boundary average about 4 s faster than for the bounce points to the south of the boundary we infer that this velocity contrast exists in the lithosphere and continues below a depth of 200 km a series of linear multiple regression experiments demonstrate that variation in velocity with increasing age of the seafloor and azimuthal anisotropy are both significant contributors to the prem and j b residuals assuming that travel time delays are a linear function of the square root of the seafloor age we find the coefficient for age to be about 1 0 s m y this is smaller than but not significantly different from the corresponding slope for the s delays of intraplate earthquakes in the atlantic reported by j d duschenes and s c solomon 1977 and favors the presence of small amounts of water e g 0 1 in the upper mantle in modeling anisotropy we carry out an experiment using synthetic seismograms to examine the shear wave splitting phenomena in the anisotropic medium and investigate three possible forms for sh wave delay as a function of azimuth sinusoidal variations as a function of 2 4 and a combination of 4 predominant and 2 that mimics the delay expected in olivine crystals when the axis is aligned horizontally our regression models strongly prefer the predominance of a 4 to a 2 variation and the last type of anisotropy explains our data best from the preferred anisotropy model the olivine axis or the upper mantle shearing flow is inferred to be oriented n s the magnitude of the azimuthal variation suggests that anisotropy extends over a depth range of several hundred kilometers in the upper mantle

a seismic reflection and gloria study of compressional deformation in the gorringe bank region eastern north atlantic seismic reflection and gloria side scan sonar data obtained on rrs charles darwin cruise cd64 reveal new information on the styles of deformation in the gorringe bank region at the eastern end of the azores gibraltar plate boundary previous studies suggest that gorringe bank was formed by the overthrusting of a portion of the african plate upon the eurasian plate the new seismic data show however that the most intensely deformed region is located south of gorringe bank on the northern flanks of a nw se trending submarine ridge which includes the ampere and coral patch seamounts the deformation is expressed as long wavelength up to 60 km large amplitude up to 800 m folds in the sediments and underlying acoustic basement which in places are associated with one or more reverse faults and as a fabric of short wavelength folds up to 3 km with a ne trend in contrast the same sedimentary units when traced beneath the flanking plains are undeformed except for some faults with a small throw 30 m some of which offset the seafloor gloria data show that recent deformation is broadly distributed over the region structural trends rotate from 45 in the west to 70 in the east of the region nearly perpendicular to the nw verging plate motion vectors as determined from plate kinematic models flexure modelling suggests that a portion of gorringe bank has loaded 152 ma oceanic lithosphere and that a maximum of 50 km of shortening has occurred at gorringe bank since the mid miocene our observations support a model in which there is no single plate boundary in the region rather that the deformation is distributed over a 200 330 km wide zone

on the role of coastal troughs in the circulation of warm circumpolar deep water on antarctic shelves abstractoceanic exchanges across the continental shelves of antarctica play an important role in biological systems and the mass balance of ice sheets the focus of this study is on the mechanisms responsible for the circulation of warm circumpolar deep water cdw within troughs running perpendicular to the continental shelf this is examined using process oriented numerical experiments with an eddy resolving 1 km 3d ocean model that includes a static and thermodynamically active ice shelf three mechanisms that create a significant onshore flow within the trough are identified 1 a deep onshore flow driven by the melt of the ice shelf 2 interaction between the longshore mean flow and the trough and 3 interaction between a rossby wave along the shelf break and the trough in each case the onshore flow is sufficient to maintain the warm temperatures underneath the ice shelf and basal melt rates of o 1 m yr 1 the third mechanism in particular reproduces several features revealed by moorings from m

co2 induced ocean warming of the antarctic continental shelf in an eddying global climate model national oceanic and atmospheric administration noaa cpo project na13oar4310128 national science foundation opp 1513411 university of arizona faculty startup funding university of arizona department of geosciences national aeronautics and space administration nasa nnx14al40g princeton environmental institute pei grand challenge initiative southern ocean carbon and climate observations and modeling soccom project under the national science foundation plr 1425989

mean antarctic circumpolar current transport measured in drake passage the antarctic circumpolar current is an important component of the global climate system connecting the major ocean basins as it flows eastward around antarctica yet due to the paucity of data it remains unclear how much water is transported by the current between 2007 and 2011 flow through drake passage was continuously monitored with a line of moored instrumentation with unprecedented horizontal and temporal resolution annual mean near bottom currents are remarkably stable from year to year the mean depth independent or barotropic transport determined from the near bottom current meter records was 45 6 sv with an uncertainty of 8 9 sv summing the mean barotropic transport with the mean baroclinic transport relative to zero at the seafloor of 127 7 sv gives a total transport through drake passage of 173 3 sv this new measurement is 30 larger than the canonical value often used as the benchmark for global circulation and climate models

dependence of ice core relative trace element concentration on acidification to assess the role of methodological differences on measured trace element concentrations in ice cores we developed an experiment to test the effects of acidification strength and time on dust dissolution using snow samples collected in west antarctica and alaska we leached antarctic samples for 3 months at room temperature using nitric acid at concentrations of 0 1 1 0 and 10 0 v v at selected intervals 20 min 24 hours 5 days 14 days 28 days 56 days 91 days we analyzed 23 trace elements using inductively coupled plasma mass spectrometry concentrations of lithogenic elements scaled with acid strength and increased by 100 1380 in 3 months incongruent elemental dissolution caused significant variability in calculated crustal enrichment factors through time factor of 1 3 pb to 8 0 cs using snow samples collected in alaska and acidified at 1 v v for 383 days we found that the increase in lithogenic element concentration with time depends strongly on initial concentration and varies by element e g fe linear regression slope 1 66 r 0 98 our results demonstrate that relative trace element concentrations measured in ice cores depend on the acidification method used

sea surface height and dynamic topography of the ice covered oceans from cryosat 2 2011 2014 we examine 4 years 2011 2014 of sea surface heights ssh from cryosat 2 cs 2 over the ice covered arctic and southern oceans results are from a procedure that identifies and determines the heights of sea surface returns along 25 km segments of satellite ground tracks variability in the retrieved sshs is between 2 and 3 cm standard deviation in the arctic and is slightly higher 3 cm in the summer and the southern ocean average sea surface tilts along these 25 km segments are 0 01 3 8 cm 10 km in the arctic and slightly lower 0 01 2 0 cm 10 km in the southern ocean intra seasonal variability of cs 2 dynamic ocean topography dot in the ice covered arctic is nearly twice as high as that of the southern ocean in the arctic we find a correlation of 0 92 between 3 years of dot and dynamic heights dh from hydrographic stations further correlation of 4 years of area averaged cs 2 dot near the north pole with time variable ocean bottom pressure from a pressure gauge and from grace yields coefficients of 0 83 and 0 77 with corresponding differences of 3 cm rms these comparisons contrast the length scale of baroclinic and barotropic features and reveal the smaller amplitude barotropic signals in the arctic ocean broadly the mean dot from cs 2 for both poles compares well with those from the icesat campaigns and the dot2008a and dtu13mdt fields short length scale topographic variations due to oceanographic signals and geoid residuals are especially prominent in the arctic basin but less so in the southern ocean

eddy transport as a key component of the antarctic overturning circulation the exchange of water masses across the antarctic continental shelf break regulates the export of dense shelf waters to depth as well as the transport of warm mid depth waters towards ice shelves and glacial grounding lines the penetration of the warmer mid depth waters past the shelf break has been implicated in the pronounced loss of ice shelf mass over much of west antarctica in high resolution regional circulation models the antarctic shelf break hosts an energetic mesoscale eddy field but observations that capture this mesoscale variability have been limited here we show using hydrographic data collected from ocean gliders that eddy induced transport is a primary contributor to mass and property fluxes across the slope measurements along ten cross shelf hydrographic sections show a complex velocity structure and a stratification consistent with an onshore eddy mass flux we show that the eddy transport and the surface wind driven transport make comparable contributions to the total overturning circulation eddy induced transport is concentrated in the warm intermediate layers away from frictional boundaries we conclude that understanding mesoscale dynamics will be critical for constraining circumpolar heat fluxes and future rates of retreat of antarctic ice shelves

horizontal circulation and volume transports in the weddell gyre derived from argo float data argo floats provide both hydrographic and trajectory data affording the opportunity to investigate surface to mid depth ocean dynamics here argo float data are used to determine the absolute geostrophic velocity field of the upper 50 2000 m of the weddell gyre from which the overall circulation pattern is investigated the weddell gyre plays a pivotal role in the modification of climate by advecting heat towards the antarctic ice shelves and by modifying the water masses that feed into the lowest limb of the global ocean overturning circulation warm deep water the source water mass that delivers heat to the weddell gyre is conveniently located within the upper 2000 m domain covered by the floats we investigate its volume transport as it circulates the gyre full depth volume transports are estimated by applying a quadratic function to extrapolate the relative dynamic height field component to the full ocean depth using ctd profiles from ship based surveys to determine an extrapolation error major new insights are provided by this study there is an established double gyre structure to the circulation with a strong eastern cell and a weaker western cell regional variation of the baroclinic component of the flow field is revealed indicating a northeast to southwest reduction in the baroclinic flow along with a strong meridional gradient of baroclinic flow along the northern limb of the gyre especially east of 25 w the zonal mean gyre strength away from the shelf edge is 32 5 sv 1 sv 1 106 m3 s 1 of which 13 3 sv are associated with the advection of warm deep water there is a considerable amount of recirculation within the gyre interior where water does not traverse the full zonal extent of the gyre the recirculation is stronger in the eastern cell of the observed double gyre structure the interior circulation cells partly explain the large variations in previous gyre strength estimates we provide an extensive review of previous estimates in context of the new results obtained

compressional deformation north of the easter microplate a manned submersible and seafloor gravity investigation we have investigated an e w compressional ridge in 0 9 ma lithosphere of the nazca plate just north of the easter microplate on the east pacific rise using a combination of visual observation and seabed gravity measurements from four manned submersible dives three of the dives made a 26 km long traverse across the ridge during which 14 gravity measurements were made the observations confirm the presence of active thrust faulting on the 1 1 km high south face of the ridge however the gravity precludes the existence of a simple low angle thrust and is only compatible with significant crustal shortening and thickening if the block to the south of the thrust has a lower density than the overriding block visual and sonar observations of pervasive fine scale tectonism in this area lend some support to this idea alternatively there could be oblique thrusting on a high angle fault with relatively little crustal shortening in addition a small degree of crustal shortening may take place in the form of buckling of an elastic or plastic lithosphere though this cannot explain the strong asymmetry of the ridge which we believe must imply faulting

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

variability of the antarctic slope current system in the northwestern weddell sea the dense water outflow from the antarctic continental shelf is closely associated with the strength and position of the antarctic slope front this study explores the short term and spatial variability of the antarctic slope front system and the mechanisms that regulate cross slope exchange using highly temporally and spatially resolved measurements from three ocean gliders deployed in 2012 the 22 sections along the eastern antarctic peninsula and west of the south orkney islands are grouped regionally and composited by isobaths there is consistency in the front position around the powell basin varying mostly between the 500 and 800 m isobaths in most of the study area the flow is bottom intensified the along slope transport of the antarctic slope current upper 1000 m varies between 0 2 and 5 9 sv 1 sv 10 6 m 3 s 1 and does not exhibit a regional pattern the magnitude of the velocity field shows substantial variability up to twice its mean value higher eddy kinetic energy 0 003 m 2 s 2 is observed in sections with dense water possibly because of baroclinic instabilities in the bottom layer distributions of potential vorticity show an increase toward the shelf along isopycnals and also in the dense water layer glider sections located west of the south orkney islands indicate a northward direction of the flow associated with the weddell front which differs from previous estimates of the mean circulation this study provides some of the first observational confirmation of the high frequency variability associated with an active eddy field that has been suggested by recent numerical simulations in this region

ice core record of rising lead pollution in the north pacific atmosphere 1 a high resolution 8000 year long ice core record from the mt logan summit plateau 5300 m asl reveals the initiation of trans pacific lead pb pollution by ca 1730 and a 10 fold increase in pb concentration 1981 1998 mean 68 9 ng l above natural background 5 6 ng l attributed to rising anthropogenic pb emissions from asia the largest rise in north pacific pb pollution from 1970 1998 end of record is contemporaneous with a decrease in eurasian and north american pb pollution as documented in ice core records from greenland devon island and the european alps the distinct pb pollution history in the north pacific is interpreted to result from the later industrialization and less stringent abatement measures in asia compared to north america and eurasia the mt logan record shows evidence for both a rising pb emissions signal from asia and a trans pacific transport efficiency signal related to the strength of the aleutian low

chemical composition of fresh snow from glaciar marinelli tierra del fuego chile a fresh snow sampling campaign was conducted during the late austral summer of 2006 in the accumulation zone of glaciar marinelli located in the cordillera darwin tierra del fuego chile snow samples were analyzed for stable isotopes d 18 o major soluble ions na k ca 2 mg 2 cl no3 so4 2 ms and major and trace elements na mg al fe ca sr cd cs ba la ce pr dy ho er bi u as ti v cr mn the dominance of marine chemistry resembles that in studies from patagonian glaciers snow chemistry was dominantly loaded by marine species cl na and ssso4 2 while contributions of crustal species e g al and fe were very low empirical orthogonal function analysis suggests two possible dust sources one represented by al and fe and the other by la ce and pr enrichment factor calculations suggest the majority of elements are within average upper crustal ratios but major enrichments of bi and cd hundreds of times suggest possible anthropogenic sources linear correlation ofd 18 o and barometric pressure r 0 60 p 0 007 suggests a potential amount effect relationship between depletedd 18 o ratios and stronger storm conditions e g greater precipitation the snow chemistry records from glaciar marinelli are the first measured in tierra del fuego the southernmost glaciated region outside antarctica

extensional tectonics in the gorringe bank rocks eastern atlantic ocean evidence of an oceanic ultra slow mantellic accreting centre the gorringe bank corresponds to an upper mantle peridotite ridge enclosing a 500 m thick 50 km long laccolith like body of gabbro locally cut and poorly covered by tholeiitic rocks strain and kinematic analysis of orientated gabbros and peridotites sampled during the gorringe diving cruise 1996 provides new kinematic constraints on extensional high temperature deformation recorded at deep levels during stretching near an accreting centre axis of a mantle dominant oceanic lithosphere it is argued that the gorringe bank lithosphere formed at an oceanic ultra slow n010 020 trending accreting centre mostly by passive tectonic denudation of the mantle without any synchronous large magmatism this peculiar lithosphere may be representative of the iberia oceanic domain located between the continent and the j anomaly ridge which likely marks the beginning of true spreading at an oceanic spreading ridge

geoid anomalies over gorringe ridge north atlantic ocean abstract gorringe ridge is a strong uplifted block of oceanic crust and upper mantle lying at the eastern end of the azores gibraltar plate boundary the geoid over this structure derived from seasat altimeter data exhibits a 9 m height anomaly with a north south lateral extension smaller than 200 km an attempt is made to interpret this geoid together with the gravity anomalies and with the seismicity which has been compiled as a function of depth it is first shown that the flexure of the oceanic lithosphere due to the ridge loading does not provide a good fit of the geoid anomalies and probably should be discarded as it assumes a continuous unfractured elastic plate models involving local heterogeneities are then tested the comparison of the observed geoid anomalies with the anomalies due to the uncompensated relief indicates that the topographic high has no shallow compensation uncompensated models previously proposed to explain the gravity anomalies are tested using the geoid one model purdy and bonnin in bonnin 11 which involves an uplift of upper mantle material at depth generates too strong geoid anomalies and must be discarded another model which represents a nascent subduction zone le pichon et al 25 fits both the gravity and geoid anomalies but leads to difficulties in explaining the deep seismicity north of gorringe ridge a model in isostatic equilibrium is also able to fit both gravity and geoid anomalies this model involves a deep root of density 3 0 g cm 3 as has been previously proposed for many oceanic ridges and plateaus this model is compatible with the deep seismicity but the origin of this low density material at great depth is up to now an unresolved question more likely dynamical models taking into account the forces induced by the convection related to the slow plate convergence in this area will have to be considered

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

on the variability of antarctic circumpolar current fronts inferred from 1992 2011 altimetry abstractantarctic circumpolar current acc fronts defined as water mass boundaries have been known to respond to large scale atmospheric variabilities especially the southern hemisphere annular mode sam and el nino southern oscillation enso distinct patterns of localized variability in meridional front displacements during 1992 2011 are derived from the analysis of satellite sea surface height data major basin scale differences are found between the southeast pacific 150 90 w and the southeast indian 75 150 e sectors of the acc frontal positions in the southeast pacific show large year to year meridional fluctuations attributed mostly to enso and in part sam and no apparent seasonal cycles or long term trends in contrast summer winter frontal locations in the southeast indian extend farther to the south north of their long term mean distribution a southward drift of acc fronts is indicated over the indian sector during the past two decades this long term shift is not directly re

40ar 39ar ages for the alkaline volcanism and the basement of gorringe bank north atlantic ocean abstract gorringe bank is situated on the europe africa plate boundary at the eastern end of the azores gibraltar fracture zone it has two summits gettysburg bank to the southwest and ormonde bank to the northeast we applied the 40 ar 39 ar stepwise heating method to date six samples of the alkaline volcanic rocks two gabbros from the ormonde bank and a dolerite from the gettysburg bank the results that the alkaline volcanism lasted probably for less than 6 ma 66 60 ma although the nature of this volcanism precludes any subduction feature during its setting the alkaline volcanism of ormonde is probably linked to upper cretaceous eocene compressive tectonic events the basement rocks of gorringe bank reveal distrubed 40 ar 39 ar age spectra one plagioclase and one biotite from a gabbro give evidence for a thermic event whose age is tentatively estimated at about 75 ma and related to a variation in the direction of the relative movement between europe and africa the more probable age given by a plagioclase of another gabbro and by a dolerite 110 ma corresponds to tilting northeastward of the gorringe massif

dynamic topography of the ice covered arctic ocean from icesat 1 we construct the dynamic ocean topography dot of the arctic ocean for five icesat campaigns winter of 2004 2008 using sea surface height estimates in open leads results show that the mean winter dot over the arctic ocean varies by 1 m and features a distinct dome of 40 cm over the beaufort sea standard deviation of the mean field is 20 cm spatial coherence between the five winter dots is consistently high 0 9 whereas the coherence between the dots and the winter djfm sea level pressure fields over the arctic basin is variable this suggests persistence of the underlying hydrodynamic processes at interannual time scales compared to seasonal atmospheric forcing comparison of dynamic heights dh from hydrographic surveys and the dot in 2008 shows a remarkable correlation of 0 92 the geostrophic velocity fields computed from the dot and interpolated dh fields highlight the smaller scale oceanographic features in the satellite estimates

eddy overturning of the antarctic slope front controls glacial melting in the eastern weddell sea 1 the eastern weddell sea is characterized by narrow continental shelves and warm deep water wdw is located in close proximity to the ice shelves in this region the exchange of wdw across the antarctic slope front asf determines the rate of basal ice shelf melting here we present a unique data set consisting of 2351 vertical profiles of temperature and salinity collected by southern elephant seals mirounga leonina and a profile beneath the fimbul ice shelf fis obtained via drilling through 395 m of ice this data set reveals variations in salinity and temperature through winter and using a conceptual model of the coastal salt budget we quantify the main exchange processes our data show that modified wdw with temperatures below 1 5 c is advected onto the shelf and into the ice shelf cavities by an eddy overturning of the asf the onshore ekman flux of surface waters during summer is the main source of freshwater that leads to the formation of low salinity shelf waters in the region the modified wdw that reaches beneath the ice shelves is too cold for basal ice shelf melting to create such low salinity water a high resolution model of an idealized asf continental shelf ice shelf system supports the conclusions from the data analysis the inflow of wdw onto the continental shelf and into the ice shelf cavity occurs within a bottom boundary layer where the eddy advection in the model is particularly strong in close agreement with the observed vertical profile of temperature beneath the fis citation nost o a m biuw v tverberg c lydersen t hattermann q zhou l h smedsrud and k m kovacs 2011 eddy overturning of the antarctic slope front controls glacial melting in the eastern weddell sea j geophys res 116 c11014 doi 10 1029 2011jc006965

rapid sea level rise along the antarctic margins in response to increased glacial discharge melting of the antarctic ice sheet and ice shelves reduces the salinity of the coastal seas satellite and model data suggest that the freshwater discharge has also caused coastal antarctic sea level to rise by about 2 mm yr 1 more than the regional mean

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

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

on the fate of the antarctic slope front and the origin of the weddell front 1 data from the deep ocean ventilation through antarctic intermediate layers dovetail and antarctic large scale box analysis and the role of the scotia sea albatross projects are combined in the region of the antarctic peninsula and the south scotia ridge to determine the paths and transports associated with the antarctic coastal current the antarctic slope front and the weddell front the antarctic coastal current flows over the antarctic continental shelf and is not tied to a particular isobath it transports 1 sv westward to the bransfield strait its subsequent course is uncertain but we speculate that it may continue southwest along the western side of the antarctic peninsula close to the coast the antarctic slope front present almost all the way around antarctica tied to the continental slope has not previously been mapped after it reaches the tip of the antarctic peninsula we show that the frontal jet splits into two branches in the northwest powell basin where the isobaths diverge the shoreward portion of the water associated with the front lying above isobaths shallower than 1500 m is able to cross the south scotia ridge and head northwestward and retains many of the properties of the antarctic slope front it is associated with a transport of 7 sv the portion of the front constrained to lie above isobaths deeper than 1500 m becomes the weddell front this takes a path around the northern powell basin and south of the south orkney islands of the 13 sv that circulates around the southern flank of the south orkney plateau 8 sv of weddell sea deep water and warm deep water leaves the front to continue west the remaining shallow and intermediate water retroflects and returns south associated with the weddell front through the orkney passage approximately 5 7 sv is transported eastward associated with the weddell front tied closely to the southern flanks of the bruce and discovery banks above the 2000 2500 m isobaths and forming the southern boundary of the weddell scotia confluence

exchange of water between the ross gyre and acc assessed by lagrangian particle tracking to reach upwelling and downwelling zones deep within the southern ocean seasonal sea ice cover water masses must move across the antarctic circumpolar current and through current systems including the ross gyre weddell gyre and antarctic slope current in this study we focus our attention on the lagrangian exchange between the ross gyre and surrounding current systems we conducted numerical experiments using five day 3 d velocity fields from the southern ocean state estimate with a particle tracking package to identify pathways by which waters move from near the antarctic coastal margins or antarctic circumpolar current into the interior of the ross gyre and to identify the time scales of variability associated with these pathways waters from near the antarctic margins enter the ross gyre along the western and northern boundaries of gyre until the gyre separates from the pacific antarctic ridge near fracture zones at this juncture antarctic circumpolar current derived inflow dominates the across gyre transport up to the antarctic margin transport and exchange associated with different time average components of flow are calculated to determine the relative contributions of high and low frequency and time mean components

crustal architecture and tectonic evolution of the gulf of cadiz sw iberian margin at the convergence of the eurasian and african plates 1 the gulf of cadiz located at the southwestern iberian margin is characterized by widespread seismicity compressional and strike slip fault plane solutions and by a large elongated positive free air gravity anomaly the gulf of cadiz gravity high gcgh multichannel seismic profiles across and along gcgh together with bathymetric and gravity data allow us to study in detail the tectonic architecture and crustal structure of the gulf of cadiz the upper shelf and slope of the gulf of cadiz includes the main structural domains of the betic fold and thrust belt in the middle part of the gulf the paleozoic basement crops out on the shallow guadalquivir bank and is associated with the largest signature of the gcgh whereas toward the outer part of the gulf the basement deepens progressively a large nw se normal fault and conjugate ne sw faults define a prominent basement high associated with the gcgh modeling of the gcgh suggests localized crustal thinning of 10 km along the central part of the gulf of cadiz probably generated during the mesozoic rifting episode between the iberian and african plates concentric wedges of fold and thrust belts and large allochthonous masses were emplaced in the gulf of cadiz during the neogene compressional phase the final emplacement of these units becomes progressively young from the se pre early langhian toward the foreland in the nw late tortonian seafloor surface ruptures pockmarks and submarine landslides provide evidence of active faulting in the gulf of cadiz to accommodate the present day convergence between the african and eurasian plates previously extensional faults have probably been reactivated and inverted at depth as suggested by the intermediate depth seismicity

sensitivity of the ocean s deep overturning circulation to easterly antarctic winds we investigate the sensitivity of the deep meridional overturning circulation moc in the southern ocean to changes in the easterly wind stress over the antarctic continental slope the deep moc is driven by export of dense antarctic bottom water from the antarctic continental shelf and exerts a strong influence on climate by ventilating the deep ocean with oxygen and storing carbon dioxide the possibility that inter climatic modifications of the deep overturning may have been driven by changes in the atmospheric circulation has motivated the recent interest in evaluating the sensitivity of the southern ocean moc to modifications of the mid latitude westerlies using a high resolution eddy resolving model of a sector of the southern ocean we show that the deep cell of the moc is highly sensitive to the strength of the polar easterlies and relatively insensitive to the strength of the mid latitude westerlies our results highlight that determining the deep ocean ventilation in past and future climates demands an accurate evaluation of the concurrent surface wind stress throughout the southern ocean

coherent seasonal acceleration of the weddell sea boundary current system driven by upstream winds abstract the weddell sea is of global importance in the formation of dense bottom waters associated with sea ice formation and ocean ice sheet interaction occurring on the shelf areas in this context the weddell sea boundary current system bcs presents a major conduit for transporting relatively warm water to the weddell sea ice shelves and for exporting some modified form of wedell sea deep and bottom waters into the open ocean this study investigates the downstream evolution of the structure and the seasonality of the bcs along the weddell sea continental slope combining ocean data collected for the past two decades at three study locations the interannual mean geostrophic flow which follows planetary potential vorticity contours shifts from being surface intensified to bottom intensified along stream the shift occurs due to the densification of water masses and the decreasing surface stress that occurs westward towards the antarctic peninsula a coherent along slope seasonal acceleration of the barotropic flow exists with maximum speed in austral autumn and minimum speed in austral summer the barotropic flow significantly contributes to the seasonal variability in bottom velocity along the tip of the antarctic peninsula our analysis suggests that the winds on the eastern north eastern side of the gyre determines the seasonal acceleration of the barotropic flow in turn they might control the export of weddell sea bottom water on seasonal time scales the processes controlling the baroclinic seasonality of the flow need further investigation

recent increases in atmospheric concentrations of bi u cs s and ca from a 350 year mount everest ice core record 1 high resolution major and trace elements sr cs ba la ce pr nd sm eu tb dy ho er tm yb lu bi u tl al s ca ti v cr mn fe and co quantified in a mount everest ice core 6518 m above sea level spanning the period 1650 2002 ad provides the first asian record of trace element concentrations from the pre industrial era and the first continuous high resolution asian record from which natural baseline concentrations and subsequent changes due to anthropogenic activities can be examined modern concentrations of most elements remain within the pre industrial range however bi u and cs concentrations and their enrichment factors ef have increased since the 1950s and s and ca concentrations and their efs have increased since the late 1980s a comparison of the bi u cs s and ca data with other ice core records and production data indicates that the increase in atmospheric concentrations of trace elements is widespread but that enrichment varies regionally likely sources for the recent enrichment of these elements include mining metal smelting oil and coal combustion and end uses for bi and mining and refinement for u and cs the source of the synchronous enrichment of ca and s is less certain but may be related to land use and environmental change

trace element and physical response to melt percolation in summit greenland snow surface melt on a glacier can perturb the glaciochemical record beyond the natural variability while the centre of the greenland ice sheet is usually devoid of surface melt many higharctic and alpine ice cores document frequent summertime melt events current hypotheses interpreting melt affected ice core chemistry rely on preferential elution of certain major ions however the precise nature of chemistry alteration is unknown because it is difficult to distinguish natural variability from melt effects in a perennially melt affected site we use eight trace element snow chemistry records recovered from summit greenland to study spatial variability and melt effects on insoluble trace chemistry and physical stratigraphy due to artificially introduced meltwater differences between non melt and melt affected chemistry were significantly greater than the spatial variability in chemistry represented by nearest neighbour pairs melt perturbed trace elements particularly rare earth elements retained their seasonal stratigraphies suggesting that trace elements may serve as robust chemical indicators for annual layers even in melt affected study areas results suggest trace element transport via meltwater percolation will deposit eluted material down pit in refrozen areas below the nearest surface chemistry peak in our experiments snow chemistry analyses are more sensitive to melt perturbations than density changes or unprocessed near infrared digital imagery

gorringe ridge gravity and magnetic anomalies are compatible with thrusting at a crustal scale summary the main features of the deep structure of the gorringe ridge are analysed on the basis of gravity and magnetic measurements as well as seismic profiles drill holes rock dredges submersible observations and seismicity data the gravity and magnetic models of the gettysburg and ormonde seamounts which form the gorringe ridge suggest that the moho is approximately flat and the upper part of the ridge corresponds to a northwestwards vergent fold this structure is the result of a northwestward vergent thrust that deformed the oceanic crust with a minimum slip of approximately 20 km the activity of the thrust probably started 20 myr and produced the recent stages of seamount uplift the seamount is mainly composed of gabbros of the oceanic crust serpentinized rocks and alkaline basalts the large antiform located in the hangingwall of the thrust is probably deformed by minor faults this oceanic ridge is a consequence of the oblique convergence between the african plate and the overlapping eurasian plate

lithospheric structure of the gorringe bank insights into its origin and tectonic evolution 1 the gorringe bank is a 5000 m high seamount near the atlantic coast of iberia characterized by a 9 m high geoid anomaly and a 120 mgal bouguer anomaly relative to the surrounding abyssal plains it has been linked to a nw directed thrust carrying exhumed upper mantle rocks and transitional crust on top of flexed down eurasian oceanic crust along the tagus abyssal plain however estimations of crustal shortening have yielded dissimilar results and the deep structure of the ridge remains highly unknown we present a restored cross section and a new model of the lithospheric structure based on gravity geoid elevation and the presence of serpentinized peridotites at least 20 km of shortening took place along a flat ramp flat thrust fault and the density structure of the lithosphere is consistent with mantle serpentinization varying from 70 at the surface to 20 at 14 km depth and 0 at 40 km the topographic relief and gravity anomalies are explained by assuming a flexural isostatic model with an elastic thickness te of 30 km the evolution of the gorringe bank since the late jurassic is interpreted in relation to eurasia africa north america plate motion in four stages 1 transtension between newfoundland iberia and africa which generated small oceanic basins and mantle exhumation 2 opening of the north atlantic and seafloor spreading at the nw side of the exhumed gorringe which produced gabbro intrusions and serpentinization 3 a quiescent tectonic period dominated by subsidence and sediment accumulation and 4 a transpressional plate boundary between eurasia and africa with nw directed subcrustal thrusting and generation of the present gorringe relief

asian dustfall in the st elias mountains yukon canada in april 2001 a major atmospheric dustfall event occurred in the st elias mountains yukon territory canada field samples were collected and analyzed for particle size mineralogy chemical composition and sr nd and pb isotopes dusts found above 3000 m had their source in the gobi desert region of northern china and inner mongolia and were transported to the yukon following a series of major dust storms that took place in early april dusts found below 3000 m had local yukon or mixed source s the asian dusts had a modal volume diameter of 4 m typical of far traveled mineral aerosols however larger 10 m particles were also found at 5000 m suggesting a very rapid trans pacific transport in the mid troposphere we estimate that the april 2001 event deposited from 5500 to 6335 tons of dust over an area of 21 000 km2 in the southwestern yukon most of which probably fell within a week our findings are consistent with instrumental observations and model simulations of the april 2001 event while the dust cloud was reportedly mixed with volatile pollutants from asia we found no evidence of metal pollution associated with the dustfall in the yukon our findings contribute to clarify the dynamics and the geochemical impact of asian dust long range transport events and to better estimate eolian fluxes of dustborne elements e g fe to the ocean associated with such events they may also assist in identifying past asian dust events in ice cores drilled from the st elias mountains icefields to develop a long term record of their frequency magnitude and source s

postglacial evolution of a pacific coastal fjord in british columbia canada interactions of sea level change crustal response and environmental fluctuations results from mona core md02 2494this article is one of a series of papers published in this special issue on the theme polar climate stability network the sedimentary record in a 40 9 m giant calypso piston core md02 2494 raised from the inner basin within effingham inlet british columbia canada during the 2002 marges ouest nord americaines mona campaign spans from 14 360 14 c years bp 17 300 calibrated calendar cal years bp to about nine centuries before present the core ar chives changes in sedimentation and sea level immediately following deglaciation of the late wisconsin fraser glaciation which peaked about 15 000 14 c years bp the presence of the mazama ash in the core anchors a detailed chronology based on 49 radiocarbon dates and seven pleistocene paleomagnetic secular variation correlations diatom assemblages identify a marine freshwater marine transition in the basin which occurred 11 630 14 c years bp 13 500 cal years bp at this time a bedrock sill presently at 46 m depth was briefly exposed as sea level fell and then rose again during iso static crustal adjustments these data constrain a new sea level curve for the outer coast of vancouver island covering the past 12 000 14 c years bp 14 000 cal years bp providing new information on the nature of deglaciation along the west coast of canada and informing interpretations of regional paleoceanographic records and mantle viscosity models

petrology of the alkaline volcanism of gorringe bank southwest portugal abstract alkaline volcanic rocks of the gorringe bank overlie typical oceanic crust made up of spilitized dolerites differentiated gabbroic and ultramafic rocks two main series are distinguishable in alkaline volcanics one from nephelinite to phonolite the other from lamprophyre to trachyte each sequence is differentiated by fractional crystallization with separation of clinopyroxene in the first one and kaersutite and mica in the second an intermediate suite is rich in lamprophyric and trachytic ocelli and in cognate ijolitic inclusions hypotheses on the origins of the more mafic lavas and on the influence of fluids like h 2 o and co 2 are discussed these series have a similar petrology to that of the sines and monchique complexes which intrude the continental crust at the same time on the same structural trend the alkaline rocks of gorringe are among the most alkaline series of the atlantic islands close to those of fernando de noronha and trindade where similar rocks occur

unprecedented springtime retreat of antarctic sea ice in 2016 during austral spring 2016 antarctic sea ice extent sie decreased at a record rate of 75 103 km2 day 1 which was 46 faster than the mean rate and 18 faster than in any previous spring season during the satellite era the decrease of sea ice area was also exceptional and 28 greater than the mean anomalous negative retreat occurred in all sectors of the antarctic but was greatest in the weddell and ross seas record negative sie anomalies for the day of year were recorded from 3 november 2016 until 9 april 2017 rapid ice retreat in the weddell sea took place in strong northerly flow after an early maximum ice extent in late august rapid ice retreat occurred in november in the ross sea when surface pressure was at a record high level with the southern annular mode at its most negative for that month since 1968

petrology and mineralogy of dredged gabbro from gettysburg bank eastern atlantic gabbros have been dredged from gettysburg bank 110 km west of portugal on the azores gibraltar fracture zone primary minerals in olivine pyroxene and brown hornblende gabbros are partially replaced by metamorphic minerals igneous textures are inhomogeneously overprinted by a granular polyhedral deformation and a cataclastic deformation amphiboles show characteristics which indicate a transition from crystallisation in a magma chamber to formation of amphibole in solid gabbro under metasomatic conditions of the amphiboles analysed chlorine was present in the green amphiboles but below 0 05 in the brown suggesting the penetration of sea water after the formation of the brown amphibole but during the formation of the green

seasonal variability of sea surface height in the coastal waters and deep basins of the nordic seas sea surface height measured by the envisat radar altimeter over open ocean and from leads in sea ice are combined to generate a complete view of variability in the nordic seas geographically and seasonally the observed seasonal variability is decomposed using empirical orthogonal functions and is consistent with seasonal variations in steric and dynamic forcing wintertime increase in sea surface height on the east greenland shelf is hypothesised to be caused by wind forced downwelling which provides direct evidence for the regional play of coastal dynamics high levels of eddy kinetic energy around the sea ice edge in fram strait and off east greenland and svalbard are consistent with the interaction of the wind with the ice edge

the greenland ice sheet project 2 depth age scale methods and results the greenland ice sheet project 2 gisp2 depth age scale is presented based on a multiparameter continuous count approach to a depth of 2800 m using a systematic combination of parameters that have never been used to this extent before the ice at 2800 m is dated at 110 000 years b p with an estimated error ranging from 1 to 10 in the top 2500 m of the core and averaging 20 between 2500 and 2800 m parameters used to date the core include visual stratigraphy oxygen isotopic ratios of the ice electrical conductivity measurements laser light scattering from dust volcanic signals and major ion chemistry gisp2 ages for major climatic events agree with independent ages based on varve chronologies calibrated radiocarbon dates and other techniques within the combined uncertainties good agreement also is obtained with greenland ice core project ice core dates and with the specmap marine timescale after correlation through the 18 o of o 2 although the core is deformed below 2800 m and the continuity of the record is unclear we attempted to date this section of the core on the basis of the laser light scattering of dust in the ice

acceleration and overturning of the antarctic slope current by winds eddies and tides all exchanges between the open ocean and the antarctic continental shelf must cross the antarctic slope current asc previous studies indicate that these exchanges are strongly influenced by mesoscale and tidal variability yet the mechanisms responsible for setting the asc s transport and structure have received relatively little attention in this study the roles of winds eddies and tides in accelerating the asc are investigated using a global ocean sea ice simulation with very high resolution 1 48 grid spacing it is found that the circulation along the continental slope is accelerated both by surface stresses ultimately sourced from the easterly winds and by mesoscale eddy vorticity fluxes at the continental shelf break the asc exhibits a narrow 30 50 km swift 0 2 m s 1 jet consistent with in situ observations in this jet the surface stress is substantially reduced and may even vanish or be directed eastward because the ocean surface speed matches or exceeds that of the sea ice the shelfbreak jet is shown to be accelerated by tidal momentum advection consistent with the phenomenon of tidal rectification consequently the shoreward ekman transport vanishes and thus the mean overturning circulation that steepens the antarctic slope front asf is primarily due to tidal acceleration these findings imply that the circulation and mean overturning of the asc are not only determined by near antarctic winds but also depend crucially on sea ice cover regionally dependent mesoscale eddy activity over the continental slope and the amplitude of tidal flows across the continental shelf break

sensitivity of antarctic circumpolar current transport and eddy activity to wind patterns in the southern ocean abstractthe southern hemisphere westerly winds have intensified in recent decades associated with a positive trend in the southern annular mode sam however the response of the antarctic circumpolar current acc transport and eddy field to wind forcing remains a topic of debate this study uses global eddy permitting ocean circulation models driven with both idealized and realistic wind forcing to explore the response to interannual wind strengthening the response of the barotropic and baroclinic transports and eddy field of the acc is found to depend on the spatial pattern of the changes in wind forcing in isolation an enhancement of the westerlies over the acc belt leads to an increase of both barotropic and baroclinic transport within the acc envelope with lagged enhancement of the eddy kinetic energy eke in contrast an increase in wind forcing near antarctica drives a largely barotropic change in transport along closed f h contours free mode with little change in eddy activity under

a two century record of lead isotopes in high altitude alpine snow and ice a 140 m snow ice core drilled at mont blanc france has been analysed for pb isotopes pb and ba concentrations the 206pb 207pb ratio which was measured by thermal ionisation mass spectrometry decreased steadily from 1 18 about two centuries ago to 1 17 in 1960 then fell rapidly to 1 15 by 1968 evidence of the italian turin isotopic lead experiment iile was found in samples dated 1977 where the ratio dipped to 1 117 by the early 1990s it had returned to mid 1960s values large seasonal variations were found in pb and ba concentrations summer samples were associated with smooth changes in the 206pb 207pb ratio while larger fluctuations were encountered in winter which is consistent with a low altitude inversion near mont blanc in the winter and free transfer of pollutants from lower to higher altitudes at other times a plot of 208pb 207pb versus 206pb 207pb ratios reveals three isotopic groupings associated with the periods pre 1923 1923 1968 and 1969 1991 in the first group the isotopic composition is consistent with local mining smelting and coal burning while in the second motor vehicle exhaust emissions dominate in the third group motor vehicle emissions also dominate but the pb is even less radiogenic during this period the iile occurred and there was a reduction in the use of leaded gasoline in europe a comparison of the mont blanc and summit central greenland records shows they contain similar 206pb 207pb ratios between 1960 and 1968 although small differences in isotopic composition can be detected by also considering the 208pb 207pb ratio however after 1969 the two records diverge markedly with the greenland ratios being dominated by the highly radiogenic mississippi valley type pb from the usa and with the mont blanc ratios moving to lower values particularly about the time of the iile

atmospheric deposition of glacial iron in the gulf of alaska impacted by the position of the aleutian low our understanding of glacial flour dust storm delivery of iron to the gulf of alaska goa is limited here we interpret concurrent time series satellite meteorological and aerosol geochemical data from the goa to examine how interannual variability in regional weather patterns impacts offshore aerosol glacial fe deposition in 2011 when a northerly aleutian low al was persistent during fall dust emission was suppressed and highly intermittent due to prevalent wet conditions low winds and a deep early season snowpack conversely in 2012 frequent and prolonged fall dust storms and high offshore glacial fe transport were driven by dry conditions and strong offshore winds generated by persistent strong high pressure over the alaskan interior and bering sea and a southerly al twenty five fold interannual variability in regional offshore glacial aerosol fe deposition indicates that glacial dust s impact on goa nutrient budgets is highly dynamic and particularly sensitive to regional climate forcing

wintertime variability of the beaufort gyre in the arctic ocean derived from cryosat 2 siral observations we processed the sea surface height measured by the sar synthetic aperture radar interferometric radar altimeter siral on board cryosat 2 cs 2 and successfully estimated the monthly dynamic ocean topography dot of the arctic ocean the cs 2 monthly dot showed the interannual and monthly variability of the beaufort gyre bg during winter between 2010 2011 and 2014 2015 the northward flow at the western edge of the bg was primarily estimated over the chukchi borderland cbl however the bg extended across the cbl and the northward flow was estimated over the mendeleev ridge in the winter of 2012 2013 our analyses revealed a significantly variable bg in response to changes in the sea surface stress field our analysis indicated that 1 sea ice motion driven by wind fields acts as a driving force for the bg when sea ice motion was intensified during winter and 2 sea ice motion can also act as an inhibiting force for the bg when sea ice motion is weakened during winter in addition the relationship between the dot steric height and ocean bottom pressure implied that the dot during winter responded to varying wind stresses through baroclinic and barotropic adjustments according to a tracer experiment we inferred that in the winter of 2012 2013 the pacific origin water carried into the bg through the barrow canyon was transported to the northern shelf and shelf break of the chukchi sea rather than the cbl which is where the pacific origin water had been transported in the other years of the observation period

the impacts of el nino on the observed sea ice budget of west antarctica we assess the impact of el nino induced wind changes on seasonal west antarctic sea ice concentrations using reanalysis data and sea ice observations a novel ice budget analysis reveals that in autumn a previously identified east west dipole of sea ice concentration anomalies is formed by dynamic and thermodynamic processes in response to el nino generated circulation changes the dipole features decreased increased concentration in the ross sea amundsen and bellingshausen seas thermodynamic processes and feedback make a substantial contribution to ice anomalies in all seasons the eastward propagation of this anomaly is partly driven by mean sea ice drift rather than anomalous winds our results demonstrate that linkages between sea ice anomalies and atmospheric variability are highly nonlocal in space and time therefore we assert that caution should be applied when interpreting the results of studies that attribute sea ice changes without accounting for such temporally and spatially remote linkages

natural vs anthropogenic sources supply aeolian dust to the miaoergou glacier evidence from sr pb isotopes in the eastern tienshan ice core abstract the compositions of sr and pb isotopes in the soluble and insoluble dust in six samples from the miaoergou ice core in eastern tienshan china were measured the six samples were dated from top to bottom as follows 2000 ad 1991 ad 1983 ad 1977 ad 1962 ad and 1958 ad the 87sr 86sr ratios in the soluble fraction ranged from 0 709984 to 0 711031 the isotopic ratios of pb in the soluble and insoluble dust were between 17 962 18 182 and 18 198 18 409 for 206pb 207pb 15 540 15 606 and 15 560 15 581 for 208pb 207pb and 37 994 38 173 and 38 179 38 384 for 208pb 204pb respectively these isotopic results for insoluble dust allowed us to document the origins of the dust in the miaoergou glacier in eastern tienshan the major sources of the natural aeolian deposits were the taklamakan and gobi deserts natural and anthropogenic pb sources were assessed using a simple ternary model in which deserts lead ore and coal served as the primary sources of insoluble dust lead ore coal combustion and the use of leaded gasoline in the surrounding area may represent additional anthropogenic sources of soluble dust thus anthropogenic sources could be further investigated by using the dust free soluble fractions the pb concentration and pb isotopic compositions from the high asia ice cores provided distinct evidence of the positive influences of anthropogenic factors associated with industrial development and the prevailing atmospheric circulation patterns in these regions

variation of the stable isotopes of water with altitude in the saint elias mountains of canada the stable isotopes of water measured in melt samples taken from snow pits and cores at locations between 1750 and 5930 m altitude on mount logan 5951 m and between 2900 and 4900 m on mount steele 5079 m in the saint elias mountains yukon show a distinctive altitudinal distribution several 18o and d versus altitude profiles indicate the general persistence of a nearly iso step or staircase structure separating a lower region of altitude dependent isotopic fractionation between 1750 and 3350 m from another apparent fractionation sequence appearing above about 5300 m both of these sequences but especially the lower one indicate orderly processes on the one hand postdepositional changes to isotope ratios in snow at different altitudes may cause distortions to an otherwise nearly monotonic isotope fractionation sequence but the main anomaly appears to be far too large to be explained in this way on the other hand an explanation linked to processes occurring in the lower and midtroposphere is based on established meteorological principles as well as on upper air data this hypothesis is proposed as the primary one to explain the gross features of the observed isotope profiles it is compatible with the concept of secondary source moisture arriving via the upper troposphere and it does not exclude the effects of postdepositional stratigraphic and stable isotope ratio changes over interannual time scales any vertical modulation of the observed isotope altitude structure from for example changes in wind regime would give rise to an additional signal in any ice core time series these findings identify a potential difficulty in the interpretation of stable isotope records obtained from high mountain ice core sites it is possible that the results may have application to atmospheric circulation modeling where the effects of extreme topography are being studied

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

constraining recent lead pollution sources in the north pacific using ice core stable lead isotopes 1 trends and sources of lead pb aerosol pollution in the north pacific rim of north america from 1850 to 2001 are investigated using a high resolution subannual to annual ice core record recovered from eclipse icefield 3017 masl st elias mountains canada beginning in the early 1940s increasing pb concentration at eclipse icefield occurs coevally with anthropogenic pb deposition in central greenland suggesting that north american pb pollution may have been in part or wholly responsible in both regions isotopic ratios 208 pb 207 pb and 206 pb 207 pb from 1970 to 2001 confirm that a portion of the pb deposited at eclipse icefield is anthropogenic and that it represents a variable mixture of east asian chinese and japanese emissions transported eastward across the pacific ocean and a north american component resulting from transient meridional atmospheric flow based on comparison with source material pb isotope ratios chinese and north american coal combustion have likely been the primary sources of eclipse icefield pb over the 1970 2001 time period the eclipse icefield pb isotope composition also implies that the north pacific mid troposphere is not directly impacted by transpolar atmospheric flow from europe annually averaged pb concentrations in the eclipse icefield ice core record show no long term trend during 1970 2001 however increasing 208 pb 207 pb and decreasing 206 pb 207 pb ratios reflect the progressive east asian industrialization and increase in asian pollutant outflow the post 1970 decrease in north american pb emissions is likely necessary to explain the eclipse icefield pb concentration time series when compared with low lichen and high mt logan ice core elevation pb data the eclipse ice core record suggests a gradual increase in pollutant deposition and stronger trans pacific asian contribution with rising elevation in the mountains of the north pacific rim

combined satellite gravity field model goco01s derived from goce and grace 1 the satellite only gravity field model goco01s is a combination solution based on 61 days of goce gravity gradient data and 7 years of grace gps and k band range rate data resolved up to degree order 224 of a harmonic series expansion the combination was performed consistently by addition of full normal equations and stochastic modeling of goce and grace observations the model has been validated against external global gravity models and regional gps leveling observations while low to medium degrees are mainly determined by grace significant contributions by the new measurement type of goce gradients can already be observed at degree 100 beyond degree 150 goce becomes the dominant contributor correspondingly with goco01s a global gravity field model with high performance for the complete spectral range up to degree order 224 is now available this new gravity model will be beneficial for many applications in geophysics oceanography and geodesy

instability and mixing of zonal jets along an idealized continental shelf break abstractthe interaction between an antarctic circumpolar current like channel flow and a continental shelf break is considered using eddy permitting simulations of a quasigeostrophic and a primitive equation model the experimental setup is motivated by the continental shelf of the west antarctic peninsula numerical experiments are performed to study how the width and slope of an idealized continental shelf topography affect the characteristics of the flow the main focus is on the regime where the shelfbreak width is slightly greater than the eddy scale in this regime a strong baroclinic jet develops on the shelf break because of the locally stabilizing effect of the topographic slope the velocity of this jet is set at first order by the gradient of the background barotropic geostrophic contours which is dominated by the slope of the topography at statistical equilibrium an aperiodic cycle is observed initially over a long stable period an upper layer jet develops over the shelf break once the

age dependence of oceanic intraplate seismicity and implications for lithospheric evolution we have determined depths for 16 oceanic intraplate earthquakes using body wave modeling a data set composed of these and 11 other well constrained depths shows that the maximum depth of seismicity deepens with increasing lithospheric age and appears to be bounded by a 700 800 c isotherm the maximum depth to which intraplate earthquakes occur is approximately equal to the flexural elastic thickness but much less than the seismic thickness from surface wave dispersion the maximum faulting depth is consistent with the predictions of rapid weakening at high temperatures for dry olivine rheologies determined by experimental rock mechanics oceanic intraplate earthquakes can occur at greater depths and temperatures than has previously been reported for continental crustal events presumably because oceanic lithosphere is stronger at high temperatures both the number of earthquakes and the cumulative seismic moment decrease with lithospheric age the cause of this trend is unclear possibilities include nonrandom location of preexisting weak zones with respect to the age provinces fault strengthening with age or a decrease in the stress level a decrease in intraplate stress with age is opposite that expected from ridge push stresses which increase with age but may result either from thermoelastic stresses which are greatest in young lithosphere or near ridge stress concentrations due to local heterogeneities in the spreading process

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

man s footprint on the arctic environment as revealed by analysis of ice and snow abstract the date of the definitive start to the anthropocene is still under debate and although a lot of progress has been made currently available data is not precise enough to define the start of the human dominated geological epoch we know that during and after the industrial revolution humans started having a much greater impact on the earth s environment increases in population have led to increases in resource and fossil fuel use leaving a marked impact on our planet this impact in the northern hemisphere is effectively recorded in the snow and ice of the arctic human activity has changed various biogeochemical cycles to such an extent that the climate has started to change this has disturbed the biosphere pushing it to adapt in response to these changes through evolutionary pressure the arctic is a particularly vulnerable environment and mankind is having a profound impact on its fragile equilibrium higher concentrations of heavy metals organic compounds and radionuclides have been detected in ice cores as well as snow although climatic changes are evident on a global scale in the arctic these changes have been amplified advances in laboratory analysis methods have been applied to ice cores and surface snow samples to help us understand the mechanisms governing this fragile environment and to evaluate the impact and amplitude of human activity despite these advances the fluxes and distributions over time of anthropogenic organic compounds is largely unknown hopefully advances in analytical methods will mean that this is not the case in the future

rapid subsurface warming and circulation changes of antarctic coastal waters by poleward shifting winds the southern hemisphere westerly winds have been strengthening and shifting poleward since the 1950s this wind trend is projected to persist under continued anthropogenic forcing but the impact of the changing winds on antarctic coastal heat distribution remains poorly understood here we show that a poleward wind shift at the latitudes of the antarctic peninsula can produce an intense warming of subsurface coastal waters that exceeds 2 c at 200 700 m depth the model simulated warming results from a rapid advective heat flux induced by weakened near shore ekman pumping and is associated with weakened coastal currents this analysis shows that anthropogenically induced wind changes can dramatically increase the temperature of ocean water at ice sheet grounding lines and at the base of floating ice shelves around antarctica with potentially significant ramifications for global sea level rise

eddy mediated transport of warm circumpolar deep water across the antarctic shelf break the antarctic slope front asf modulates ventilation of the abyssal ocean via the export of dense antarctic bottom water aabw and constrains shoreward transport of warm circumpolar deep water cdw toward marine terminating glaciers along certain stretches of the continental shelf particularly where aabw is exported density surfaces connect the shelf waters to the middepth circumpolar deep water offshore offering a pathway for mesoscale eddies to transport cdw directly onto the continental shelf using an eddy resolving process model of the asf the authors show that mesoscale eddies can supply a dynamically significant transport of heat and mass across the continental shelf break the shoreward transport of surface waters is purely wind driven while the shoreward cdw transport is entirely due to mesoscale eddy transfer the cdw flux is sensitive to all aspects of the model s surface forcing and geometry suggesting that shoreward eddy heat transport may be localized to favorable sections of the continental slope

structure of the upper mantle in the northeastern atlantic close to the azores gibraltar ridge from surface wave and body wave observations abstract phase velocities of teleseismic rayleigh waves have been measured in the central north atlantic on both sides of the azores gibraltar ridge agr by means of a specially designed long period station network the dispersion data obtained were regionalized and then subjected to a hedgehog inversion which gives a set of upper mantle models compatible with the observational data within specified error bounds reasonable model solutions were selected by using regional body wave observations such as p n and s n wave velocities determined from earthquakes along the agr the s itn velocities measured indicate that the shear wave velocity in the mantle part of the lithosphere is much higher on the northern side of the agr strongly negative p wave residuals in this area indicate faster seismic propagation than implied by the jeffreys bullen travel time tables while propagation is much slower in the gulf of cadiz area furthermore the residuals show a clear difference for paths through oceanic and continental domains and suggest that the transition between these two domains extends much further into the ocean on the southern side of the agr than on the northern side the proposed model for the structure of the upper mantle in that region shows that there exists a pronounced velocity contrast across the agr thickening of the lithospheric plate with increasing plate age is indicated to the south of the ridge the greatest thickness is reached close to the continental margin within a zone about 500 km wide whose velocity close to the canary islands and madeira is significantly lower probably due to the well known volcanic activity there these observations together with the travel time residuals reveal that this zone seems to be of a transitional nature somewhere between a continental and oceanic structure

the deep structure of gorringe bank ne atlantic and its surrounding area summary the structure and origin of the disturbed oceanic area southwest of cape sao vicente south portugal is still a matter of debate what are the reasons for such a huge relief and for the high positive free air anomaly to go further in the understanding of this atypical region the deep structure has been investigated by means of 3 d gravity modelling taking into account other geophysical and geological information such as seismic reflection data the results clearly show that all topographic highs are associated with shallow moho and are consequently not isostatically balanced gorringe bank is shown to be strongly asymmetrical and to be associated with a major fracture within the lithosphere considering the geodynamical context of this area the mechanical equilibrium could be due to a distribution of vertical stresses an estimation of the required stresses is given showing no major evidence that this is impossible

a record high ocean bottom pressure in the south pacific observed by grace in late 2009 to early 2010 the gravity recovery and climate experiment grace satellite pair observed a record increase in ocean bottom pressure obp over a large mid latitude region of the south east pacific its magnitude is substantially larger than other oceanic events in the southern hemisphere found in the entire grace data records 2003 2010 on multi month time scales the obp data help to understand the nature of a similar signal in sea surface height ssh anomaly observed by altimetry the ssh increase is mainly due to mass convergence analysis of the barotropic vorticity equation using scatterometer data atmospheric reanalysis product and grace and altimeter an atmospheric reanalysis product observations suggests that the observed obp ssh signal was primarily caused by wind stress curl associated with a strong and persistent anticyclone in late 2009 in combination with effects of planetary vorticity gradient bottom topography and friction

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

ice core net snow accumulation and seasonal snow chemistry at a temperate glacier site mount waddington southwest british columbia canada a 141m ice core was recovered from combatant col 51 385 n 125 258 w 3000ma s l mount waddington coast mountains british columbia canada records of black carbon dust lead and water stable isotopes demonstrate that unambiguous seasonality is preserved throughout the core despite summer surface snowmelt and temperate ice high accumulation rates at the site 4 m ice eq a 1 limit modification of annual stratigraphy by percolation of surface meltwater the ice core record spans the period 1973 2010 an annually averaged time series of lead concentrations from the core correlates well with historical records of lead emission from north america and with ice core records of lead from the greenland ice sheet the depth age scale for the ice core provides sufficient constraint on the vertical strain to allow estimation of the age of the ice at bedrock total ice thickness at combatant col is 250 m an ice core to bedrock would likely contain ice in excess of 200 years in age accumulation at combatant col is significantly correlated with both regional precipitation and large scale geopotential height anomalies

ice layers as an indicator of summer warmth and atmospheric blocking in alaska samples were collected from a snow pit and shallow firn core near kahiltna pass 2970 m a s l denali national park alaska usa in may 2008 the record spans autumn 2003 to spring 2008 and reveals clusters of ice layers interpreted as summertime intervals of above freezing temperatures high correlation coefficients 0 75 1 00 between annual ice layer thickness and regional summertime station temperatures for 4 years n 4 indicate ice layer thickness is a good proxy for mean and extreme summertime temperatures across alaska at least over the short period of record a rex block aka high over low pattern a downstream trough over hudson bay canada and an upstream trough over eastern siberia occurred during the three melting events that lasted at least 2 weeks about half of all shorter melting events were associated with a cut off low traversing the gulf of alaska we hypothesize that a surface to bedrock core extracted from this location would provide a high quality record of summer temperature and atmospheric blocking variability for the last several hundred years

melt regimes stratigraphy flow dynamics and glaciochemistry of three glaciers in the alaska range we used ground penetrating radar gpr gps and glaciochemistry to evaluate melt regimes and ice depths important variables for mass balance and ice volume studies of upper yentna glacier upper kahiltna glacier and the mount hunter ice divide alaska we show the wet percolation and dry snow zones located below 2700ma s l at 2700 to 3900ma s l and above 3900ma s l respectively we successfully imaged glacier ice depths upwards of 480m using 40 100mhz gpr frequencies this depth is nearly double previous depth measurements reached using mid frequency gpr systems on temperate glaciers few holocene length climate records are available in alaska hence we also assess stratigraphy and flow dynamics at each study site as a potential ice core location ice layers in shallow firn cores and attenuated glaciochemical signals or lacking strata in gpr profiles collected on upper yentna glacier suggest that regions below 2800ma s l are inappropriate for paleoclimate studies because of chemical diffusion through melt flow complexities on kahiltna glacier preclude ice core climate studies minimal signs of melt or deformation and depth age model estimates suggesting 4815years of ice on the mount hunter ice divide 3912ma s l make it a suitable holocene age ice core location

transport and variability of the antarctic circumpolar current in drake passage the baroclinic transport of the antarctic circumpolar current acc above 3000 m through drake passage is 107 3 10 4 sv and has been steady between 1975 and 2000 for six hydrographic sections 1993 2000 along the world ocean circulation experiment woce line sr1b the baroclinic transport relative to the deepest common level is 136 7 7 8 sv the acc transport is carried in two jets the subantarctic front 53 10 sv and the polar front pf 57 5 5 7 sv southward of the acc the southern antarctic circumpolar current transports 9 3 2 4 sv we observe the pf at two latitudes separated by 90 km this bimodal distribution is related to changes in the circulation and properties of antarctic bottom water three realizations of the instantaneous velocity field were obtained with lowered adcps from these observations we obtain near bottom reference velocities for transport calculations net transport due to these reference velocities ranges from 28 to 43 sv consistent with previous estimates of variability the transport in density layers shows systematic variations due to seasonal heating in near surface layers volume transport weighted mean temperatures vary by 0 40 c from spring to summer a seasonal variation in heat flux of about 0 22 pw finally we review a series of papers from the international southern ocean studies program the average yearlong absolute transport is 134 sv and the standard deviation of the average is 11 2 sv the error of the average transport is 15 to 27 sv we emphasize that baroclinic variability is an important contribution to net variability in the acc

impact and implications of meltwater percolation on trace element records observed in a high alpine ice core past atmospheric pollution can be reconstructed from ice core trace element records retrieved from mountain glaciers however the current global temperature increase can result in post depositional melt processes significantly altering the originally stored information here we present a comprehensive study on the behaviour of 35 trace elements tes during meltwater percolation in a high alpine ice core segment from upper grenzgletscher switzerland some tes revealed significant concentration depletion whereas others were well preserved depending on their water solubility and location at the grain scale tes present in insoluble minerals typically enriched at grain boundaries were found to be mostly preserved because their insolubility in water results in immobility with meltwater percolation water soluble tes revealed a variable meltwater mobility whereas ultra tes tend to be preserved likely due to incorporation into the ice lattice abundant tes are prone to relocation from grain boundary regions we propose that at alpine sites ag al bi cu cs fe li mo pb rb sb th tl u v w zr and the rare earth elements may still be applicable as robust environmental proxies even if partial melting occurred whereas ba ca cd co mg mn na ni sr and zn are prone to significant depletion

vertical eddy fluxes in the southern ocean the overturning circulation of the southern ocean has been investigated using eddying coupled ocean sea ice models the circulation is diagnosed in both density latitude coordinates and in depth density coordinates depth density coordinates follow streamlines where the antarctic circumpolar current is equivalent barotropic capture the descent of antarctic bottom water follow density outcrops at the surface and can be interpreted energetically in density latitude coordinates wind driven northward transport of light water and southward transport of dense water are compensated by standing meanders and to a lesser degree by transient eddies consistent with previous results in depth density coordinates however wind driven upwelling of dense water and downwelling of light water are compensated more strongly by transient eddy fluxes than fluxes because of standing meanders model realizations are discussed where the wind pattern of the southern annular mode is amplified in density latitude coordinates meridional fluxes because of transient eddies can increase to counter changes in ekman transport and decrease in response to changes in the standing meanders in depth density coordinates vertical fluxes because of transient eddies directly counter changes in ekman pumping

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

direct observations of the antarctic slope current transport at 113 e the antarctic slope current asc defined here as the region of westward flow along the continental slope off antarctica forms the southern limb of the subpolar gyres it regulates the exchange of water across the shelf break and provides a path for interbasin westward transport despite its significance the asc remains largely unobserved around most of the antarctic continent here we present direct velocity observations from a 17 month current meter moored array deployed across the continental slope between the 1000 and the 4200 m isobaths in the southeastern indian ocean near 113 e the observed time mean flow consists of a surface intensified jet associated with the antarctic slope front asf and a broader bottom intensified westward flow that extends out to approximately the 4000 m isobath and is strongest along the upper slope the time mean transport of the asc is 29 2 sv fluctuations in the transport are large typically exceeding the mean by a factor of 2 they are mainly due to changes in the northward extent of the current over the lower slope however seasonal changes in the wind also drive variations in the transport of the asf and the flow in the upper slope both mean and variability are largely barotropic thus invisible to traditional geostrophic methods this article is protected by copyright all rights reserved

active in situ disaggregation of oceanic crust and mantle on gorringe bank analogy with ophiolitic massives the cyagor ii cruise may 1981 using submersible cyana sp 3000 on gorringe bank off south west portugal confirmed the scheme proposed at the end of cyagor i cruise1 2 that during the middle cretaceous 110 myr bp gorringe bank an old transform fault of triassic liassic age appears to have tilted to the north east leading to the exposure of a section of oceanic mantle and crust due to its location at the boundary between european and african plates gorringe bank suffered tectonic reactivation and uplifting during compressive and shearing type events that occurred at the cretaceous tertiary boundary and during the tertiary eocene miocene during the 12 dives of the cyagor ii cruise fig 1 phenomena linked to the disintegration of serpentinites and gabbros in the deep sea domain have been studied in situ with more detail than before3 such processes have been suggested from studies on samples dredged or cored in oceans or from observations in ophiolitic belts but direct observation had not enabled the magnitude of such phenomena to be measured the observations on gorringe bank suggest that the processes described here are active in many oceanic sites they help us to understand better the significance of many ophiolitic detritic beds more or less closely associated with pelagic sediments we now compare the observations made at sea especially on gorringe bank with similar observations in ophiolitic zones in mountain belts which suggests that the ophiolite complexes have formed in a similar way to the breccias seen on the ocean floor

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

isotopic evidence for the source of lead in the north pacific abyssal water national science foundation u s oce 0325031 oce 0325031 oce 0220978 oce 0321402 oce 0728930 and arc 0612538