wave induced advective transport below a rippled water sediment interface the exchange between the water column and the sediment bed and the transport inside the permeable sediment layer are important processes in the cycles of chemical elements in this paper we examine quantitatively the effects of modulations in the profile of the water sediment interface on this exchange and on the advective transport inside the sediment bed the flow field inside a sediment layer bounded between spatially periodic ripples on top and an impermeable bottom surface is modeled using darcy s law the forcing is due to progressive gravity waves in the water above the results of two different models for the pressure variation imposed on the upper boundary are compared the two pressure profiles are derived from potential flow theory and from a numerical solution to the navier stokes equations for the oscillatory flow over a rippled bed from an analytic solution to the two dimensional model the trajectories of pore water particles immediately below the ripple profile are found to be quite different from the simple elliptical pattern found below a flat bed the shapes of these trajectories can be quite complicated and vary considerably both along the length of the ripple and over the depth of the sediment layer close to its surface the total exchange across the water sediment interface averaged over one wave period is significantly higher across a rippled interface than across a flat bed this difference increases with increasing ripple slope and the strength of the wave motion and it decreases with increasing thickness of the sediment layer relative to the length of the gravity wave since rippled bed forms are commonly found in coastal waters the increase in the total exchange across a rippled water sediment boundary can enhance the exchange of solutes due to wave pumping immediately below the water sediment interface circulation cells with net advective transport over a wave period are found such net advection patterns can lead to spatial in the horizontal direction inhomogeneities of the vertical concentration or temperature profiles if the overlying water column and or the sediment bed act s as source or sink this gives a plausible physical mechanism to explain the spatial variations in vertical concentration profiles found in field measurements

dense water formation beneath a time dependent coastal polynya abstract recent modeling studies of dense water formation beneath an idealized steady coastal polynya have provided simple analytical expressions for the maximum density anomaly achievable as a function of the polynya geometry and the imposed surface buoyancy flux these studies have assumed that the buoyancy flux and polynya geometry are both constant and independent parameters to relax these assumptions dense water formation is examined beneath a coastal polynya whose size and surface buoyancy flux are computed from atmospheric temperature and wind velocity according to a polynya model developed by pease though highly idealized the pease model produces polynyas that open and close on reasonably realistic timescales and it thermodynamically couples the polynya size and buoyancy flux results reveal several interesting and potentially useful features of the ocean response to time dependent polynya forcing first under reasonable atmospheric conditions both the maximum density anomaly achievable and

horizontal acceleration corrections in airborne gravimetry the stabilized platforms used in marine and airborne gravimeters behave like damped long period pendulums when subjected to horizontal accelerations they tilt resulting in gravimeter reading errors the amount of tilt depends on the ratio of the period of the horizontal motion to that of the platform and is negligible if this ratio is less than about 0 1 lacoste 1967 this condition can be achieved in straight and level flight using an auto pilot provided the platform period is set to a sufficiently long period brozena and peters 1988 course changes are sometimes unavoidable however resulting in lost data bell et al 1991 brozena 1984 the aim of this paper is to show that such data loss is unnecessary since the tilt and hence the gravimeter error can be accurately modeled from the horizontal accelerations moreover the technique will improve data quality whenever long period horizontal accelerations occur measuring these accelerations is now straightforward with differential carrier p

impact of eastern arctic shelf waters on the nansen basin intermediate layers the eurasian shelves supply water to the nansen basin intermediate layers in two ways as buoyancy driven plumes of dense winter water and as permanent inflow of the barents sea branch of atlantic water while the plumes are local and seasonal phenomena the barents sea flow is part of the large scale circulation both interact with atlantic water which enters the arctic ocean through fram strait and moves as a subsurface boundary current eastward along the continental slope during the polarstern cruise ark ix 4 in summer 1993 the fram strait branch was observed as a narrow core within tens of kilometers of the barents sea shelf edge here several patches of cold low salinity water spread across the slope down to about 500 m depth their origin is assumed to be the northern barents sea they mix with the warm saline fram strait branch water fsbw so that the core properties of the latter become modified downstream in the eastern nansen basin the fram strait branch is displaced toward the inner basin by inflow of the barents sea branch of atlantic water bsbw this inflow appears as a broad 200 km wedge extending from 200 to 1300 m depth bsbw is colder and less saline than water of the fram strait branch and it is less dense and less stratified than the ambient water both branches appear to undergo vigorous mixing while spreading eastward so that any eastward continuation of the boundary flow transports about 50 bsbw and 50 fsbw above 600 m and about 80 bsbw and 20 fsbw below that level toward the canadian basin according to available observations the barents and kara seas are the only source areas for shelf waters ventilating the nansen basin below the halocline and these waters constitute a freshwater input rather than a salt input winter shelf water from the laptev sea cannot contribute to layers deeper than the upper halocline

airborne gravity reveals interior of antarctic volcano abstract understanding antarctic volcanoes is important as they provide a window on magmatic and tectonic processes of the antarctic plate and contain datable records of ice sheet changes we present the results from the first detailed airborne radar and gravity surveys across james ross island northern antarctic peninsula which is dominated by mt haddington an ice covered miocene recent alkaline stratovolcano the surveys provide new insights into the subsurface structure of the volcano and hence its development which are unavailable from the surface geology alone we show that mt haddington is associated with a significant negative bouguer gravity anomaly 26 mgal which suggests that there has not been significant pooling and solidification of a dense shallow level mafic magma chamber during the growth of the volcano over at least the past 6 m y which is consistent with independent geochemical evidence simple flexural isostatic models cannot explain the localised negative bouguer anomaly 3d modelling techniques show that the negative anomaly is best explained by a shallow low density intra crustal body with its top close to or at the surface although comparable gravity anomalies are commonly associated with large 20 km ash filled calderas as seen at yellowstone or toba there is no geological evidence on james ross island for a similar structure we therefore propose that the james ross island volcanic edifice subsided into the thick underlying pile of relatively soft jurassic and cretaceous sediments which were displaced by low density hyaloclastite breccia the type of deformation envisaged is similar to that associated with concepciou or iwaki volcanoes in south america although mt haddington is much larger

plate tectonic development of the south west indian ocean a revised reconstruction of east antarctica and africa a revised sequence of reconstructions for east antarctica relative to africa is generated from published seafloor spreading and fracture zone anomalies these date from the cretaceous tertiary boundary to the late jurassic and lead to a revised predrift reconstruction for east and west gondwanaland euler pole 1 67 s 35 99 e rotation angle 53 43 this reconstruction derived wholly from marine data places east antarctica adjacent to the lebombo mountains and south of and subparallel to the sabi acid volcanic suite supporting the postulate that these rocks represent mesozoic plate boundaries this refit implies that part of the coastal plain of mozambique is underlain by oceanic or very highly extended continental crust the reconstruction is supported by the alignment of 1 the cape fold belt with its antarctic equivalents and 2 the western limit of pan african reactivation of the mozambique mobile belt with the western limit of the sverdrupfjella metamorphic suite antarctica initially moved along a transform fault lying immediately east of and subparallel to the lebombo mountains the eastern face of the tugela cone the southeastern face of the falkland plateau in its reconstructed position and the eastern flank of the agulhas plateau in its reconstructed position at m10 time a triple junction formed near the tip of the falkland plateau implying that the oldest lineated magnetic anomalies in the eastern weddell sea associated with this triple junction cannot predate m10 at m2 time the mozambique ridge rifted from the astrid ridge in a ridge jump episode such an event may also explain the presence of magnetic anomalies in the southern mozambique basin gunnerus ridge conrad rise and del cano rise are all tectonically associated with the madagascar ridge

an arctic ocean cold core eddy detailed physical and chemical observations were obtained during september 1997 of a cold core eddy situated in the southern central canada basin of the arctic ocean the eddy was about 20 km in diameter had maximum current speeds exceeding 20 cm s 21 and extended from the base of the upper mixed layer near 40 m down to 400 m excess salt in the eddy core was consistent with addition of brine from 1mo f ice formation core tracer distributions indicated a lifetime exceeding 1 year and were consistent with an origin as near surface pacific water with some admixed terrestrial runoff the eddy was probably formed in association with a polynya along the alaskan chukchi sea coast through local water densification from surface ice formation followed by development of frontal instabilities formation and subsequent migration of such eddies which may have lifetimes of several years provide a mechanism for transporting water from the beaufort and chukchi sea coastal and shelf regions into the interior canada basin and for contributing to maintenance of the permanent halocline present light ice conditions throughout the arctic ocean favor the formation of such eddies and may contribute to enhanced ventilation of the halocline waters

uplift and tilting of the shackleton range in east antarctica driven by glacial erosion and normal faulting unravelling the long term evolution of the subglacial landscape of antarctica is vital for understanding past ice sheet dynamics and stability particularly in marine based sectors of the ice sheet here we model the evolution of the bedrock topography beneath the recovery catchment a sector of the east antarctic ice sheet characterized by fast flowing ice streams that occupy overdeepened subglacial troughs we use 3d flexural models to quantify the effect of erosional unloading and mechanical unloading associated with motion on border faults in driving isostatic bedrock uplift of the shackleton range and theron mountains which are flanked by the recovery slessor and bailey ice streams inverse spectral free air admittance and forward modeling of topography and gravity anomaly data allow us to constrain the effective elastic thickness of the lithosphere te in the shackleton range region to 20 km our models indicate that glacial erosion and the associated isostatic rebound has driven 40 50 of total peak uplift in the shackleton range and theron mountains a further 40 50 can be attributed to motion on normal fault systems of inferred jurassic and cretaceous age our results indicate that the flexural effects of glacial erosion play a key role in mountain uplift along the east antarctic margin augmenting previous findings in the transantarctic mountains the results suggest that at 34 ma the mountains were lower and the bounding valley floors were close to sea level which implies that the early ice sheet in this region may have been relatively stable

influence of porewater advection on denitrification in carbonate sands evidence from repacked sediment column experiments abstract porewater flow enhances mineralization rates in organic poor permeable sands here a series of sediment column experiments were undertaken to assess the potential effect of advective porewater transport on denitrification in permeable carbonate sands collected from heron island great barrier reef experimental conditions flow path length advection rate and temperature were manipulated to represent conditions similar to near shore tropical environments hgcl2 poisoned controls were used to assess whether reactions were microbially mediated overall significant correlations were found between oxygen consumption and n2 production the n o2 slope of 0 114 implied that about 75 of all the nitrogen mineralized was denitrified a 4 fold increase in sediment column length from 10 to 40 cm resulted in an overall increase in oxygen consumption 1 6 fold tco2 production 1 8 fold and denitrification 1 9 fold oxic respiration increased quickly until advection reached 80 l m 2 h 1 and then plateaued at higher advection rates interestingly denitrification peaked up to 336 mol n2 m 2 h 1 at intermediate advection rates 30 80 l m 2 h 1 we speculate that intermediate advection rates enhance the development of microniches i e steep oxygen gradients within porous carbonate sands perhaps providing optimum conditions for denitrification the denitrification peak fell within the broad range of advection rates often on scales of 1 100 l m 2 h 1 typically found on continental shelves implying that carbonate sands may play a major but as yet unquantified role in oceanic nitrogen budgets

upwelling in the alaskan beaufort sea atmospheric forcing and local versus non local response abstract the spin up and relaxation of an autumn upwelling event on the beaufort slope is investigated using a combination of oceanic and atmospheric data and numerical models the event occurred in november 2002 and was driven by an aleutian low storm the wind field was strongly influenced by the pack ice distribution resulting in enhanced winds over the open water of the chukchi sea flow distortion due to the brooks mountain range was also evident mooring observations east of barrow canyon show that the beaufort shelfbreak jet reversed to the west under strong easterly winds followed by upwelling of atlantic water onto the shelf after the winds subsided a deep eastward jet of atlantic water developed centered at 250 m depth an idealized numerical model reproduces these results and suggests that the oceanic response to the local winds is modulated by a propagating signal from the western edge of the storm the disparity in wave speeds between the sea surface height signal traveling at the fast barotropic shelf wave speed versus the interior density signal traveling at the slow baroclinic wave speed leads to the deep eastward jet the broad scale response to the storm over the chukchi sea is investigated using a regional numerical model the strong gradient in windspeed at the ice edge results in convergence of the offshore ekman transport leading to the establishment of an anti cyclonic gyre in the northern chukchi sea accordingly the chukchi shelfbreak jet accelerates to the east into the wind during the storm and no upwelling occurs west of barrow canyon hence the storm response is fundamentally different on the beaufort slope upwelling versus the chukchi slope no upwelling the regional numerical model results are supported by additional mooring data in the chukchi sea

a modeling study of coastal circulation and landfast ice in the nearshore beaufort and chukchi seas using ciom this study investigates sea ice and ocean circulation using a 3 d 3 8 km ciom coupled ice ocean model under daily atmospheric forcing for the period 1990 2008 the ciom was validated using both in situ observations and satellite measurements the ciom successfully reproduces some observed dynamical processes in the region including the bering inflow originated coastal current that splits into three branches alaska coastal water acw central channel branch and herald valley branch in addition the beaufort slope current bsc the beaufort gyre the east siberian current esc mesoscale eddies and seasonal landfast ice are well simulated the ciom also reproduces reasonable interannual variability in sea ice such as landfast ice and anomalous open water less sea ice during the positive dipole anomaly da years vice versa during the negative da years sensitivity experiments were conducted with regard to the impacts of the bering strait inflow heat transport onshore wind stress and sea ice advection on sea ice change in particular on the landfast ice it is found that coastal landfast ice is controlled by the following processes wind forcing bering strait inflow and sea ice dynamics

detecting rift basins in the evans ice stream region of west antarctica using airborne gravity data abstract a total of 11 500 line km of aerogravity data have been used to construct an free air gravity anomaly map for the antarctic region that may contain the microplate boundary between the haag nunataks block and southern antarctic peninsula along line free air gravity anomaly data resolved wavelengths of 9 km or greater with better than 5 mgal accuracy coincident radio echo soundings provided data to construct a digital terrain model the gravity effect of the terrain was calculated by gauss legendre quadrature glq and spectrally correlated with the free air gravity data terrain correlated free air anomalies related to possible isostatic imbalances of the crust were separated from terrain decorrelated anomalies that may reflect intra crustal density contrasts subtracting terrain correlated free air anomalies from the gravity effects of the terrain yielded compensated terrain gravity effects ctge that were used to model the moho by inversion the results indicate moderate but significant crustal thinning below the evans ice stream that is consistent with an extensional origin for the deep wide steep sided trough that contains the ice stream as well as the continued elevation of the footwall flank of the basin changes along the axis of the rift both in the gravity anomaly field and the distribution of moho topography can be explained by processes associated with continental lithospheric extension subsequently many of the features produced by extension have been modified by glacial erosion and the sub ice topography and gravity data reflect this

dynamic response of surface water groundwater exchange to currents tides and waves in a shallow estuary 1 in shallow fetch limited estuaries variations in current and wave energy promote heterogeneous surface water groundwater mixing benthic exchange which influences biogeochemical activity here we characterize heterogeneity in benthic exchange within the subtidal zone of the delaware inland bays by linking hydrodynamic circulation models with mathematical solutions for benthic exchange forced by current bedform interactions tides and waves benthic fluxes oscillate over tidal cycles as fluctuating water depths alter fluid interactions with the bed maximum current driven fluxes 1 10 cm d occur in channels with strong tidal currents maximum wave driven fluxes 1 10 cm d occur in downwind shoals during high energy storms simulated wave pumping rates increase by orders of magnitude demonstrating the importance of storms in solute transfer through the benthic layer under moderate wind conditions 5 m s integrated benthic exchange rates due to wave current and tidal pumping are each 1 10 m3 s on the order of fluid contributions from runoff and fresh groundwater discharge to the estuary benthic exchange is thus a significant and dynamic component of an estuary s fluid budget that may influence estuarine geochemistry and ecology

contributions of the siberian shelf polynyas to the arctic ocean intermediate and deep water the role of the open water regions or polynyas in the winter ice pack over the siberian continental shelves in the production of arctic ocean intermediate and deep water is examined through use of a combination of passive microwave satellite data coastal weather station data and oceanographic data the satellite data allow us to derive a time series of the open water areas of selected polynyas for the 1978 1982 winters the polynyas which occur north of svalbard around franz josef land along the west coast and north end of novaya zemlya and to the east of severnaya zemlya and the taymyr peninsula are the primary oceanographic contributors the open water time series for these polynyas are used in combination with coastal weather station data to estimate the heat loss from each polynya for the region north of svalbard which is historically known as whalers bay the study shows that the heat loss is sufficient to provide the observed cooling of the west spitsbergen current for the other polynyas the heat loss is used to compute the ice production rates and the oceanic salt flux we then use the historic oceanographic salinities with the salt fluxes to estimate the contribution of each polynya to the arctic ocean water masses if we assume that the salt contributes only to the arctic intermediate water our results show that the shelves are capable of producing about 20 60 of this water alternatively if the salt contributes only to the deep water of the eurasian basin then without consideration of the mixing of the bottom water with the greenland and norwegian sea water the contribution from the shelves yields a renewal time of about 100 years our results imply that there is insufficient water produced in the shelf polynyas to perform all of the roles that have been historically assigned to it

the nutrient salinity and stable oxygen isotope composition of bering and chukchi seas waters in and near the bering strait seawater nutrient salinity and oxygen 18 data collected from 1990 to 1993 in the bering and chukchi seas were used to identify potential sources of nutrients and water masses that result in formation of the arctic ocean upper halocline and its associated nutrient maximum water matching the delta sup 18 o values of the arctic ocean upper halocline and containing sufficient or a nearly sufficient nutrient and salinity concentration was collected in subsurface waters in the summer in portions of the bering sea particularly the gulf of anadyr however nutrient concentrations significantly declined in this north flowing water over the shallow continental shelf before it reached the bering strait as a consequence of biological utilization and dilution with nutrient poor and oxygen 18 depleted fresh water therefore it does not appear likely that the flow of unaltered water through the bering strait in the summer plays a critical role in the formation of the arctic ocean upper halocline the role of other mechanisms for contributing pacific derived waters to the arctic ocean nutrient maximum is considered copyright 1997 american geophysical union

flow of winter transformed pacific water into the western arctic abstract the dynamics of the flow of dense water through barrow canyon is investigated using data from a hydrographic survey in summer 2002 the focus is on the winter transformed bering water the highest volumetric mode of winter water in the chukchi sea which drains northward through the canyon in spring and summer the transport of this water mass during the time of the survey was 0 2 0 3 sv as the layer flowed from the head of the canyon to the mouth it sank decelerated and stretched strong cyclonic relative vorticity was generated on the seaward side of the jet which compensated for the stretching this adjustment was incomplete however in that it did not extend across the entire current possibly because of internal mixing due to shear instabilities the resulting vorticity structure of the flow at the canyon mouth was conducive for baroclinic instability and eddy formation multiple eddies of winter transformed bering water were observed along the chukchi beaufort shelfbreak those to the west of barrow canyon were in the process of being spawned by the eastward flowing shelfbreak current emanating from herald canyon while the single eddy observed to the east originated from the barrow canyon outflow it is argued that such an eddy formation is a major source of the ubiquitous cold core anti cyclones observed historically throughout the canada basin implications for the ventilation of the upper halocline of the western arctic are discussed

polynya dynamics a review of observations and modeling 1 polynyas are nonlinear shaped openings within the ice cover ranging in size from 10 to 105 km2 polynyas play an important climatic role first winter polynyas tend to warm the atmosphere thus affecting atmospheric mesoscale motions second ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation since 1990 there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas this article reviews polynya research carried out in the last 2 decades focusing on presenting a state of the art picture of the physical interactions between polynyas and the atmosphere sea ice ocean system observational and modeling studies the surface heat budget and water mass transformation within these features are addressed

an early cretaceous extinct spreading center in the northern natal valley abstract we have identified an extinct e w spreading center in the northern natal valley on the basis of magnetic anomalies which was active from chron m11 133 ma to 125 3 ma just before chron m2 124 ma in the early cretaceous seafloor spreading in the northern natal valley accounts for approximately 170 km of north south motion between the mozambique ridge and africa this extension resolves the predicted overlap of the continental central and southern mozambique ridge and antarctica in the chron m2 to m11 reconstructions from mesozoic finite rotation parameters for africa and antarctica in addition the magnetic data reveal that the mozambique ridge was an independent microplate from at least 133 to 125 ma the northern natal valley extinct spreading center connects to the spreading center separating the mozambique basin and the riiser larsen sea to the east it follows that the northern mozambique ridge was either formed after the emplacement of the surrounding oceanic crust or it is the product of a very robust spreading center to the west the extinct spreading center connects to the spreading center separating the southern natal valley and georgia basin via a transform fault prior to chron m11 there is still a problem with the overlap of mozambique ridge if it is assumed to be fixed with respect to either the african or antarctic plates some of the overlap can be accounted for by jurassic deformation of the mozambique ridge mozambique basin and dronning maud land it appears though that the mozambique ridge was an independent microplate from the breakup of gondwana 160 ma until it became part of the african plate 125 ma

offshore transport of dense shelf water in the presence of a submarine canyon the formation and offshore transport of dense water over a uniformly sloping shelf crosscut by a submarine canyon is examined using a three dimensional primitive equation numerical model a constant negative buoyancy flux is applied in a limited region adjacent to a straight coast to represent brine rejection from ice production in an idealized coastal polynya a sharp density front forms at the edge of the forcing region with surface and bottom intensified jets along the front the flow around the head of the submarine canyon triggers a frontal instability that initially grows only on one side of the canyon the unstable waves on the other side of the canyon are blocked by a localized barotropic flow that develops near the canyon head unstable waves also grow where the forcing region intersects the coast the frontal waves grow rapidly with o 1 day e folding timescales and form eddies with horizontal scales of o 15 km which extract the densest water from the forcing region and carry it offshore directly across isobaths in this way the eddies limit the maximum water density that appears in the model despite continued negative buoyancy forcing some dense water descends into the canyon forming a bottom trapped plume that transports the dense water offshore ahead of the eddies the plume moves relatively slowly i e small froude number with little turbulent entrainment so the advancement and structure of the plume nose can be described successfully as a simple gravity current with an advective diffusive heat balance eddies may slump into the canyon from the side altering both the density anomaly and speed of the canyon plume suggesting that canyon plumes are likely to be highly variable in both space and time

gravity anomalies flexure and crustal structure at the mozambique rifted margin abstract the free air gravity edge effect anomaly associated with passive continental margins is one of the most distinctive features of the marine gravity field early studies attributed the edge effect to the juxtaposition of thick continental with thin oceanic crust while thinning of the crust due to rifting at the time of continental break up is a major contributor it is now recognised that geological processes such as sedimentation and magmatic underplating also contribute the different amounts of sediment and underplate at rifted margins help in fact to explain the diversity of the edge effect although they obscure the mechanics styles and geometry of rifting in this paper combined 2 dimensional flexural backstripping and gravity modelling techniques are used to quantify the contribution of rifting sediment loading and magmatic underplating to the edge effect anomaly at the mozambique margin this margin formed as the result of a two stage break up the first of which resulted in the separation of africa and madagascar in the early jurassic by comparing the observed edge effect to calculations based on simple elastic plate models we have been able to constrain the elastic thickness te and hence flexural rigidity of the lithosphere that underlies the sediments which accumulated at the mozambique margin following break up the model that best explains the shape i e amplitude and wavelength of the edge effect high is one in which the earliest jurassic early cretaceous sediments were deposited on relatively weak lithosphere te 17 5 km while the later miocene recent sediments accumulated on relatively rigid lithosphere te 40 km these results suggest that sedimentation at the mozambique margin has involved lithosphere which responds to loads in a similar manner as would oceanic lithosphere therefore the thinned transitional crust that underlies much of the coastal plain of the mozambique margin is probably of oceanic rather than continental origin

generation of submesoscale vortices a new mechanism small scale intense vortices composed of water with anomalous values of quasi conservative tracers have been observed in many oceans they are particularly numerous in the beaufort gyre of the arctic ocean possible mechanisms responsible for the generation of these features are examined conservation of temperature salinity and nutrients requires that beaufort sea vortices be created from water that flows into the arctic ocean from the pacific ocean across the broad shallow chukchi sea much of this water passes through barrow canyon near point barrow alaska observations in the canyon show the generation of vortices of approximately the same size as those observed in the beaufort sea barrow canyon is therefore a likely site for the generation of beaufort sea vortices most observed beaufort sea vortices have a central potential vorticity near zero because of a relative vorticity close to their chukchi sea source water is typically stratified with little relative vorticity so that its potential vorticity is nonzero a key step in the generation of the vortices is therefore the reduction of the potential vorticity of chukchi sea water to nearly zero it is proposed that this occurs through the action of frictional torques occurring as the chukchi sea water flows through barrow canyon rather than througji the action of vertical mixing because this flow is driven by a downstream pressure gradient it is concentrated on the right hand wall of the canyon by the coriolis force the frictional torques thus preferentially reduce the potential vorticity of the fluid anticyclonic vortices are therefore preferentially generated it is suggested that a similar scenario may play a role in the generation of submesoscale vortices containing water from the mediterranean and labrador seas

first airborne gravity results over the thwaites glacier catchment west antarctica recent satellite observations of thwaites glacier in the amundsen sea embayment west antarctica have shown that the glacier is changing rapidly the causes of its dynamic behavior are uncertain but are of concern because this glacier has the most negative mass balance of all antarctic glaciers to better understand thwaites glacier s subglacial setting we conducted a multi instrumented aerogeophysical survey of its catchment and present here the first gravity results we employed a new gravimeter and it performed well despite extreme conditions and an unusual survey design the unleveled free air gravity anomalies have a 2 3 mgal rms error and a 9 km spatial resolution despite slightly higher than standard noise levels the free air anomalies correlate well with radar derived subglacial topography the new airborne gravity data assist in interpreting radar identified bedrock features and are an ideal basis for future studies of subglacial geology and its control on the dynamics of thwaites glacier

microstructure observations of turbulent heat fluxes in a warm core canada basin eddy abstractan intrahalocline eddy was observed on the chukchi slope in september of 2015 using both towed ctd and microstructure temperature and shear sections the core of the eddy was 6 c significa

initialization asymmetry and spindown of arctic eddies abstract initialization and development of cyclonic and anticyclonic eddies under the influence of a frictional surface as with arctic eddies under ice cover are examined both analytically and numerically using a three dimensional numerical model solutions of the linear rossby adjustment problem show that energy released from an initial density anomaly in the barotropic mode and the first few baroclinic modes destabilizes the numerical computation for small arctic eddies this result suggests the necessity of slow spinup to reduce energy release in these modes and sufficient vertical resolution to resolve higher baroclinic modes the numerical computation shows that in an initially stratified and motionless ocean a surface cyclone an anticyclone is produced by a localized salinity source sink in open waters the stable flow field consists of a vertically aligned pair of counterrotating eddies when dampened by surface friction an eddy pair produced by deep forcing has features dissimilar to the

effect of baroclinicity on double diffusive interleaving although ocean fronts are often baroclinic existing models of double diffusive interleaving have ignored such baroclinic effects as velocity shear and horizontal density gradients to determine the importance of these effects the authors have formulated a linear instability analysis applicable to baroclinic fronts two limiting cases are considered one for fronts with strong vertical and or horizontal shear the other for fronts with weak shear in both limits double diffusive interleaving can be enhanced or suppressed by baroclinicity interleaving motion is enhanced if isopycnals rise toward the fresh side of the front conversely interleaving is suppressed if isopycnals slope downward across the front a significant result is that the salinity gradient along isopycnals is not a good indicator of interleaving strength as an example the model is applied to a mediterranean salt lens the effect of baroclinicity is significant the predicted growth rates are increased by 35 90 the large scale velocity and hydrographic fields indicate that meddy sharon lies somewhere between the high and low shear limits nevertheless the model predictions agree reasonably well with the observed interleaving characteristics

physical and geochemical properties across the atlantic pacific water mass front in the southern canadian basin temperature salinity nutrients oxygen and halocarbon data collected in the arctic ocean reveal a frontal structure previously unrecognized in the hydrography of the canadian basin samples were collected on a 1300 km section extending from the beaufort sea in the canada basin to the east siberian sea in the makarov basin these data collected in 1993 aboard the ccgs henry larsen reveal a lateral boundary between water masses of atlantic and pacific origin the term water mass assembly is introduced to describe the basic arrangement or vertical stacking of water masses found in the arctic ocean recognizing that water mass components within each assembly may differ from basin to basin using historical data two primary water mass assemblies are defined each consisting of three layers an upper layer an atlantic layer and a deep layer these two assemblies are marked by important differences one assembly here defined as the western arctic wa assembly is characterized by an upper layer of relatively fresh high nutrient water of pacific origin below this by an atlantic layer with a core temperature generally below 0 5 c and finally by a deep layer of higher salinities and colder temperatures about 0 5 c than found in the overlying atlantic layer the second assembly here defined as eastern arctic ea assembly is characterized by the absence of pacific water in the upper layer below this by an atlantic layer core as warm as 2 to 3 c and by a colder about 0 9 c deep layer because the presence or absence of pacific origin water is a key characteristic distinguishing the two assemblies we will refer to the water mass boundary between the two assemblies as the atlantic pacific front earlier research indicated that water masses in the arctic ocean were separated by a front above the lomonosov ridge into the canadian and eurasian basins although all larsen 93 stations from the canada basin a1 d1 display classic wa assembly characteristics the makarov basin station e1 shows ea assembly characteristics in the upper and atlantic layers and a wa assembly deep layer this suggests a relocation in the position of the atlantic pacific boundary away from the lomonosov ridge further larsen 93 data show the transition region between the atlantic and deep layers is fresher in the makarov basin than corresponding water in either the canada or eurasian basins implying a source of cold low salinity water perhaps from the laptev and east siberian shelves the front separating these two assemblies lies above the mendeleyev ridge and is marked by large lateral gradients in all measured properties in particular the penetration of anthropogenic halocarbons is 2 to 3 times deeper in the makarov basin than in the canada basin implying enhanced rates of ventilation this suggests that direct exchange between the canadian and eurasian basins has occurred recently near the perimeter and that physical and chemical properties including contaminants may have been transported by boundary currents more quickly from one basin to the other

the form distribution and anisotropy of magnetic susceptibility of jurassic dykes in h u sverdrupfjella dronning maud land antarctica implications for dyke swarm emplacement abstract the mesozoic dyke swarms of western dronning maud land antarctica form a minor intrusive component of the karoo large igneous province five hundred and sixty one dykes were recorded intruding neoproterozoic gneisses and middle jurassic syenite plutons 40 ar 39 ar geochronology data reveal two temporally distinct components the 178 175 ma alkaline straumsvola dyke swarm that predominantly intrudes a nepheline syenite pluton and the 206 204 ma tholeiitic jutulrora dyke swarm found throughout the study area the straumsvola swarm exhibits highly variably dyke trends that display a restricted opening direction interpreted to be the result of high magma pressure equal to the maximum principal stress the jutulrora swarm displays a fan of dyke trends with dyke thickness and spacing increasing away from the inferred point of fan convergence anisotropy of magnetic susceptibility measurements reveal vertical magma transport within both dyke swarms in the straumsvola area with the southern outer exposures of the jutulrora swarm exhibiting lateral magma transport although associated with a long lived local igneous centre comparison of palaeostress estimates for the straumsvola dyke swarm and contemporaneous dykes in ahlmannryggen and vestfjella indicates the presence of a regional scale radial stress system in western dronning maud land between 178 175 ma supporting a mantle plume origin for the karoo large igneous province

mesoscale eddies of the arctic ocean subsurface baroclinic eddies in the arctic ocean have a diameter of 10 20 km and are confined in depth between 50 and 300m during the arctic ice dynamics joint experiment aidjex in the central beaufort sea between march 1975 and may 1976 extensive information on eddy characteristics statistics and behavior was collected from four manned drifting ice camps during this 14 month period 146 eddies were encountered of which 19 were found to be repeated crossings making a total of 127 separate eddies observed during this period on the basis of the 1975 1976 aidjex data set it is concluded that eddies are 1 prevalent in the amerasia basin of the arctic ocean and in particular the beaufort sea where they may occupy up to a quarter of the available surface area 2 located in the depth range of 50 300 m although a few deeper eddies are also present 3 the second largest producers 32 of kinetic energy found within the upper 200 m of the beaufort sea and 4 predominantly anticyclonic in rotational tendency these eddies apparently originate north of point barrow alaska as a result of instability in the eastward flowing alaskan coastal current and transfer seasonally varying water properties from the chukchi sea and alaskan shelf into the arctic ocean they appear to translate in response to barotropic forcing over short time scales and over longer time periods move with the mean geostrophic field the season of formation for an eddy may be identified by the anomalous thermal properties still residing in its core

evaluation of shelf basin interaction in the western arctic by use of short lived radium isotopes the importance of mesoscale processes shelf basin exchange in the western arctic was evaluated by use of water column analyses of 228 ra 226 ra ratios and the first measurements of the short lived 224 ra t1 2 3 64 d in the arctic during the 2002 shelf basin interaction sbi program excess 224 ra was detected over the shelf but was not found seaward of the shelf break similarly the 228 ra 226 ra ratio dropped rapidly from the shelf across the shelf break consequently the model age gradient elapsed time since shelf residence northward across the chukchi shelf increased from 1 5 years nearshore to approximately 14 years in surface waters sampled off shelf at the southern margin of the beaufort gyre this steep gradient is consistent with very slow exchange between the chukchi shelf and the beaufort gyre whereby bering strait inflow is constrained by the earth s rotation to follow local isobaths and does not easily move into deeper water the strong dynamic control inhibiting water that enters the system through bering strait from flowing north across isobaths also would lead to a long recirculation time of river water emptied into the beaufort gyre possible mechanisms that can generate cross shelf currents that break the topographic constraint to follow isobaths and thereby transport water and associated properties off the shelves include wind induced upwelling downwelling meandering jets and eddies evidence of such a process was found during the icex project in the beaufort sea in april 2003 when excess 224 ra was measured over 200 km from any shelf source this required an ne offshore flow of 40 cm s 1 assuming that the source water derives from the mouth of barrow canyon a weak northeastward flow was measured using an ladcp within the upper 300 m of the ocean but was of lower speed than required by the 224 raxs at the time of the icex occupation

a large eddy in the central arctic ocean 1 long term moored measurements of temperature salinity and velocity over the abyssal plain near the north pole show a rich array of eddy like structures over a wide range of depths here we demonstrate an anticyclone that extends from the surface to at least 1700 m is about 60 km across and has a likely origin along the eurasian continental margin

making ends meet in gondwana retracing the transforms of the indian ocean and reconnecting continental shear zones interpretation of the detailed patterns of ocean floor transforms revealed by satellite altimetry enables the creation of the indian ocean to be described quantitatively as four consecutive plate tectonic regimes separated at 200 136 89 and 43 ma each regime is reversed in turn by keeping transform termini coincident and colinear until conjugate points on the margins of pre existing plates regain their pre regime integrity progressive elimination of the indian ocean demonstrable as a smooth computer animation http www kartoweb itc nl gondwana leads to a refined re assembly of the continental fragments of central gondwana that is substantiated by new geological data a sequence of euler interval poles that describes the dispersal of the gondwana fragments time calibrated against available magnetic anomaly data is given the model requires a mid cretaceous position for india s southern tip about 1000 km south of madagascar prior to india s rapid northward migration

seawater circulation in sediments driven by interactions between seabed topography and fluid density 1 measurements of submarine groundwater discharge sgd in coastal areas often show that the saltwater discharge component is substantially greater than the freshwater discharge several mechanisms have been proposed to explain these high saltwater discharge values including saltwater circulation driven by wave and tidal pumping wave and tidal setup in intertidal areas currents over bedforms and density gradients resulting from mixing along the freshwater saltwater interface in this study a new mechanism for saltwater circulation and discharge is proposed and evaluated the process results from interaction between bedform topography and buoyancy forces even without flow or current over the bedform in this mechanism an inverted salinity and density profile in the presence of both a bedform on the seafloor and an upward flow of fresher groundwater from depth induces a downward flow of saline pore water under the troughs and upward flow under the adjacent crest of the bedform the magnitude and occurrence of the mechanism were tested using numerical methods the results indicate that this mechanism could drive seawater circulation under a limited range of conditions and contribute 20 30 of local sgd when and where the process is operative bedform shape hydraulic conductivity hydraulic head and salinity at depth in the porous media aquifer thickness effective porosity and hydrodynamic dispersion are among the factors that control the occurrence and magnitude of the circulation of seawater by this mechanism

geological evidence for a proterozoic to mesozoic link between southeastern africa and dronning maud land antarctica comparison of crustal provinces in southeastern africa and dronning maud land antarctica reveals considerable similarity in their evolution from the archaean until the mesozoic separation archaean granites and mid proterozoic supracrustal successions in these regions are so comparable that correlation is suggested a major mid to late proterozoic orogenic terrain in dronning maud land comprising the h u sverdrupfjella and heimefrontfjella subprovinces and termed the maudheim province is very similar in age lithology structural style and metamorphic history to the mozambique and natal orogenic provinces of kibaran age 1000 ma in southeastern africa deformed supracrustal sequences in all three provinces host syn tectonic granites intruded during upper amphibolite to granulite facies metamorphism isoclinal folding was accompanied by thrusting towards adjacent cratonic areas development of orogenic provinces of kibaran age in southeastern africa and antarctica reflects accretion of marginal basin volcanic arc sequences onto older continents the 500 ma pan african event was a widespread predominantly thermal overprinting of parts of the older orogenic provinces faulting and rifting of the supercontinent preceded break up and influenced the stratigraphy of phanerozoic sedimentary successions in se africa

convection beneath freezing leads new observations compared with numerical model results vertical distributions of temperature salinity and horizontal and vertical current speed were measured along the edges of a number of rapidly freezing leads in the southern central beaufort sea during march april 1992 these observations were restricted to cases having sufficiently small ice water relative speeds that brine driven convection was expected based on scaling arguments to dominate shear turbulence generated by the relative ice water motion the observed salinity and current features were consistent with an existing conceptual model for sublead convection consequent to brine rejection from ice formation and with the results of a numerical model which assumes two dimensionality in the cross lead direction and uses a brine input consistent with the field observations these models predict convection of brine enriched plumes beneath the lead downward to the pycnocline where they then spread outward away from the lead volume continuity is satisfied by horizontal inflow of water to the lead at the surface observed mean downward convection speeds varied from 0 2 to 0 7 cm s 1 and had maxima up to about 2 cm s 1 consistent with the numerical model salinities associated with the convecting parcels were about 0 001 practical salinity units psu above ambient which was an order of magnitude less than predicted by the model while plumes of water flowing away from the lead on the pycnocline had salinities as high as 0 004 psu above ambient these similarities and discrepancies are discussed within the context of a steady state model versus a nonsteady field situation and it is concluded that the steady convection cell concept is probably valid if viewed as a time averaged sequence of discrete convective plumes or thermals

renewal and circulation of intermediate waters in the canadian basin observed on the scicex 96 cruise during the summer of 1996 the nuclear submarine uss pogy occupied a line of stations extending through the middle of the canadian basin between about 88 n 44 w lomonosov ridge and about 78 n 144 w center of the canada basin ctd niskin bottle casts extending to 1600 m were carried out at eight stations providing the first high quality temperature salinity cfc tritium and 3he data obtained from this region although xctd data had previously been collected in this region these data along with data from stations at the basin boundary to the south and west reveal the presence of well ventilated intermediate water beneath the halocline in the center of the canada basin indicating renewal times of the order of 1 2 decades the least ventilated intermediate water was observed at the northern end of the canada basin along the southern flank of the alpha ridge intermediate water is derived from the atlantic ocean and enters the arctic ocean through fram strait and the barents sea it flows around the arctic basins in boundary currents and splits in the eastern amundsen basin with one branch crossing the lomonosov ridge and flowing along the east siberian continental slope and the other flowing along the eurasian flank of the lomonosov ridge from the 1996 scientific ice expedition scicex 96 observations we conclude that the branch that flows along the east siberian continental slope transports this water to the chukchi rise where it apparently enters the central canada basin with some flow continuing along the boundary to the southern canada basin the fram strait branch water mixes extensively with waters from the canadian basin during its transit along the east siberian continental slope being diluted by a factor of about 5 by the time it reaches the central canada basin the barents sea branch water does not undergo such extensive mixing and is diluted by a factor of only about 2 when it reaches the central canada basin

observations of small eddies in the beaufort sea the horizontal and vertical variations of velocity temperature density and turbulent kinetic energy dissipation in the central beaufort sea were measured with helicopter borne expendable current profilers and conductivity temperature depth units almost all velocity differences larger than 0 05 m s 1 could be consistently interpreted as being due to nearly circular eddies with a diameter of 10 20km a thickness of 50 500 m peak velocities of 0 07 0 3 m s 1 and little expression at the top of the ocean four such eddies were found two anticyclones were found and accurately sampled two cyclones were found but were only poorly sampled both were beneath and close to one of the anticyclones relative vorticity could be computed for two anticyclones and one cyclone within experimental error the two anticyclones and all historical beaufort sea anticyclones had a relative vorticity of and thus zero potential vorticity at the center the cyclone had a central relative vorticity of about 0 5 and thus a different value of potential vorticity than the surrounding fluid one anticyclonic eddy b was sampled seven times over a period of 23 days its measured velocity and density fields were in approximate gradient wind balance its central core contained values of temperature nitrate and silicate that were different from those outside the core at the same density it moved eastward at about 0 02 m s 1 through the surrounding fluid measurements of turbulent kinetic energy dissipation were almost always less than the noise level of the instrument about 10 9 w kg 1 corresponding to a mean dissipation much less than this and a minimum decay time due to turbulence much longer than 0 3 year the nondimensional strength rossby number and shape burger number of anticylcone b are very similar to those of other beaufort sea anticyclones and similar to those of small mid latitude eddies each of the eddies observed here was centered on a temperature maximum associated with one of the warm water masses that advect into the arctic ocean the two anticyclones were centered on temperature maxima originating in the pacific ocean whereas the two cyclones were centered on temperature maxima from the atlantic ocean this is consistent with the hypothesis that the eddies are formed as these water masses enter the arctic ocean

flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension we suggest that the uplift of rift flanks results from mechanical unloading of the lithosphere during extension and consequent isostatic rebound this mechanism is presented as an alternative to explanations for rift flank uplift involving thermal or dynamic processes and magmatic thickening of the crust our hypothesis is based on two critical concepts first the lithosphere retains finite mechanical strength or flexural rigidity during extension second isostatic rebound uplift of the lithosphere follows when the kinematics of extension produces a surface topographic depression that is deeper than the level to which the surface of the extended lithosphere would subside assuming local isostatic compensation we develop and analyze two kinematic models for instantaneous extension of the lithosphere to show that flexural rebound is a viable explanation for the uplift of rift flanks we first investigate the isostatic consequences of finite simple slip on an initially planar dipping normal fault cutting the entire lithosphere when the lithosphere retains flexural rigidity during extension the topography resulting from this model resembles a half graben and the footwall rift flank is flexurally uplifted this simple normal faulting model explains free air gravity anomalies and topography observed at rift flanks in oceanic lithosphere such as broken ridge in the eastern indian ocean the caroline ridges sorol trough in the western equatorial pacific and the coriolis trough behind the new hebrides island arc we then investigate a general kinematic model for lithospheric extension where simple slip on a surface of arbitrary shape is accompanied by pure shear extension in the upper and lower plates when the simple slip component is not zero or the distribution of pure shear in the upper and lower plates is not identical the surface of slip can be regarded as a detachment by simplification our general model accounts for pure shear extension of the lithosphere that is uniform with depth in this case detachments have no meaning in the geologic sense however the kinematics of depth independent pure shear may nevertheless be described in terms of a surface which we term a kinematic reference surface at some depth in the lithosphere we speculate that the depth of this surface may be rheologically controlled the magnitude of rift flank uplift by flexure depends critically on the depth of this reference surface in contrast if local isostasy is assumed when the lithosphere undergoes a given amount of depth independent pure shear the resulting topography will be the same regardless of how the kinematics of that extension are formulated the basin and rift flank topography and free air gravity anomaly over young continental rifts such as the rhine graben can be satisfied using our general extensional model with a small amount 5 km of extension along a listric shaped detachment soling into the crust mantle boundary because the flexural rebound mechanism explains the observed topography and gravity anomaly over both oceanic and continental extensional domains we suggest that rheological differences between the two lithospheric types may not be important in their overall response to extension

lead convection measured with an autonomous underwater vehicle the winter lead experiment leadex was conducted during 1992 in the beaufort sea there the autonomous conductivity temperature vehicle actv was operated under and around leads these are the first measurements of this kind measurements of temperature salinity and turbulence parameters were also made at lead edges with sensors fixed to rigid masts by combining information from the fixed measurements and the actv an inertial dissipation method is used to derive horizontal profiles of salt flux from actv salinity measurements comparisons also show that turbulent vertical velocity perturbations can be estimated from the vertical motion of the actv with these velocity estimates horizontal profiles of the turbulent fluxes of heat w t and salt w s are also computed directly data from a wide 1000 m wide lead with rapid ice motion indicate stronger turbulence under the lead than downstream but the character of the flow is that of a convective boundary layer modified by a change in surface buoyancy flux the convection is characterized by multiple intermittent plumes that scale in size with the mixed layer depth at a medium sized 100 m wide lead with slower ice motion the convective circulation set up by the lead is more apparent convective plumes are stronger and more prevalent at the lead edges particularly the downstream edge the comparison between the horizontal profiles from the actv and time series from fixed sensors suggests that lead convection is a combination of a near surface convective boundary layer and a deeper quasi stationary convection pattern

characterizing the eddy field in the arctic ocean halocline ice tethered profilers itp deployed in the arctic ocean between 2004 and 2013 have provided detailed temperature and salinity measurements of an assortment of halocline eddies a total of 127 mesoscale eddies have been detected 95 of which were anticyclones the majority of which had anomalously cold cores these cold core anticyclonic eddies were observed in the beaufort gyre region canadian water eddies and the vicinity of the transpolar drift stream eurasian water eddies an arctic wide calculation of the first baroclinic rossby deformation radius rd has been made using itp data coupled with climatology rd 13 km in the canadian water and 8 km in the eurasian water the observed eddies are found to have scales comparable to rd halocline eddies are in cyclogeostrophic balance and can be described by a rankine vortex with maximum azimuthal speeds between 0 05 and 0 4 m s the relationship between radius and thickness for the eddies is consistent with adjustment to the ambient stratification eddies may be divided into four groups each characterized by distinct core depths and core temperature and salinity properties suggesting multiple source regions and enabling speculation of varying formation mechanisms

on the circulation of atlantic water in the arctic ocean an idealized eddy resolving numerical model and an analytic three layer model are used to develop ideas aboutwhatcontrolsthecirculationofatlanticwaterinthearctic ocean thenumericalmodelisforcedwith a surface heat flux uniform winds and a source of low salinity water near the surface around the perimeter of an arctic basin despite this idealized configuration the model is able to reproduce many general aspects of the arctic ocean circulation and hydrography including exchange through fram strait circulation of atlantic water a halocline ice cover and transport surface heat flux and a beaufort gyre the analytic model depends on a nondimensional number and provides theoretical estimates of the halocline depth stratification freshwater content and baroclinic shear in the boundary current an empirical relationship between freshwater content and sea surface height allows for a prediction of the transport of atlantic water in the cyclonic boundary current parameters typical of the arctic ocean produce a cyclonic boundary current of atlantic water of o 1 2 2sv where 1sv 10 6 m 3 s 21 and a halocline depth of o 200m in reasonable agreement with observations the theory compares well with a series of numerical model calculations in which mixing and environmental parameters are varied thus lending credibility to the dynamics of the analytic model in these models lateral eddy fluxes from the boundary and vertical diffusion in the interior are important drivers of the halocline and the circulation of atlantic water in the arctic ocean

the contribution of alaskan siberian and canadian coastal polynyas to the cold halocline layer of the arctic ocean numerous arctic ocean circulation and geochemical studies suggest that ice growth in polynyas over the alaskan siberian and canadian continental shelves is a source of cold saline water which contributes to the maintenance of the arctic ocean halocline the purpose of this study is to estimate for the 1978 1987 winters the contributions of arctic coastal polynyas to the cold halocline layer of the arctic ocean the study uses a combination of satellite oceanographic and weather data to calculate the brine fluxes from the polynyas then an oceanic box model is used to calculate their contributions to the cold halocline layer of the arctic ocean this study complements and corrects a previous study of dense water production by coastal polynyas in the barents kara and laptev seas recurrent polynyas form on the canadian and alaskan coasts from banks island to the bering strait and on the siberian coast from the bering strait to the new siberian islands in the bering sea polynyas form in norton sound south and west of st lawrence island and in the gulf of anadyr two regions that account for almost 50 of the total dense water production are the siberian coastal polynyas in the adjacent regions of the gulf of anadyr and anadyr strait and the alaskan coastal polynyas which occur along the coast from cape lisburne to point barrow for all of the western arctic coastal regions examined the mean annual total brine flux is 0 5 0 2 sv combination of this flux with the contribution from the barents kara and laptev seas which is recalculated from data in the earlier study shows that over the entire arctic coastal polynyas generate about 0 7 1 2 sv of dense water this compares well with the theoretical estimates of 1 1 5 sv because an unknown fraction of the barents kara and laptev brine flux must go to the eurasian basin deep water the coastal polynyas alone cannot renew the halocline layer other potential brine generation mechanisms include overall freezing on the shelves and the response of the ice to infrequent violent storms for example during february 1982 an intense storm generated a large region of low ice concentration in the eastern chukchi sea over barrow canyon the refreezing of the region was followed by the flow of a dense plume down barrow canyon although the ocean dynamical response to this refreezing needs to be established the possible response of a barrow canyon flow to this refreezing event suggests that the overall refreezing in response to infrequent violent storms may be a potential source of the additional brine needed to maintain the arctic ocean halocline

modification of no po and no po during flow across the bering and chukchi shelves implications for use as arctic water mass tracers the no and po tracers 9 no3 o2 and 135 po4 o2 respectively and their derivative no po have found increasing use in arctic water mass analyses for identifying the specific basin or shelf areas from which surface waters originate based upon assumed differences in pacific and atlantic derived content and basin to basin differences within the arctic following shipboard sampling in june september 1993 and may june 1994 both north and south of bering strait we have found evidence that pacific derived waters flowing north to bering strait do not necessarily have any unique no po or no po identity that would permit unequivocal use as a water mass tracer in particular no po ratios in the bering sea continental shelf 150 m waters varied from 0 7 to 1 1 which encompasses ratios previously reported for arctic continental shelf and atlantic origin waters in the arctic ocean the highest no po ratios 1 in the bering sea were observed to the southwest of st lawrence island close to where high nutrient waters are first upwelled onto the shelf and seasonally early in the biological production cycle by contrast later in the summer north of bering strait at the depth of the arctic ocean nutrient maximum the highest concentrations of silica 60 m were associated with low no po ratios 0 7 apparent increases in the proportions of sea ice melt in these waters inferred from 18o and salinity regressions were associated with lower no po ratios this pattern the potential for sea air exchange and a significant relationship between decreases in nitrate phosphate ratios and both no po ratios and silica concentrations indicate that biological and physical processes north and south of bering strait affect the fidelity of these nutrient based tracers these results indicate the need for consideration of shelf based processes before no po ratios and other nutrient based tracers can be successfully applied as arctic circulation tracers

eddies in the canada basin arctic ocean observed from ice tethered profilers five ice tethered profilers itps deployed between 2004 and 2006 have provided detailed potential temperature and salinity s profiles from 21 anticyclonic eddy encounters in the central canada basin of the arctic ocean the 12 35 m thick eddies have center depths between 42 and 69 m in the arctic halocline and are shallower and less dense than the majority of eddies observed previously in the central canada basin they are characterized by anomalously cold and low stratification and have horizontal scales on the order of or less than the rossby radius of deformation about 10 km maximum azimuthal speeds estimated from dynamic heights assuming cyclogeostrophic balance are between 9 and 26 cm s 1 an order of magnitude larger than typical ambient flow speeds in the central basin eddy s and potential vorticity properties as well as horizontal and vertical scales are consistent with their formation by instability of a surface front at about 80 n that appears in historical ctd and expendable ctd xctd measurements this would suggest eddy lifetimes longer than 6 months while the baroclinic instability of boundary currents cannot be ruled out as a generation mechanism it is less likely since deeper eddies that would originate from the deeper reaching boundary flows are not observed in the survey region

the western arctic boundary current at 152 w structure variability and transport abstract from august 2002 to september 2004 a high resolution mooring array was maintained across the western arctic boundary current in the beaufort sea north of alaska the array consisted of profiling instrumentation providing a timeseries of vertical sections of the current here we present the first year velocity measurements with emphasis on the pacific water component of the current the mean flow is characterized as a bottom intensified jet of o 15 cm s 1 directed to the east trapped to the shelfbreak near 100 m depth its width scale is only 10 15 km seasonally the flow has distinct configurations during summer it becomes surface intensified as it advects buoyant alaskan coastal water in fall and winter the current often reverses flows westward under upwelling favorable winds between the storms as the eastward flow re establishes the current develops a deep extension to depths exceeding 700 m in spring the bottom trapped flow advects winter transformed pacific water emanating from the chukchi sea the year long mean volume transport of pacific water is 0 13 0 08 sv to the east which is less than 20 of the long term mean bering strait inflow this implies that most of the pacific water entering the arctic goes elsewhere contrary to expected dynamics and previous modeling results possible reasons for this are discussed the mean atlantic water transport to 800 m depth is 0 047 0 026 sv also smaller than anticipated

western arctic shelfbreak eddies formation and transport abstract the mean structure and time dependent behavior of the shelfbreak jet along the southern beaufort sea and its ability to transport properties into the basin interior via eddies are explored using high resolution mooring data and an idealized numerical model the analysis focuses on springtime when weakly stratified winter transformed pacific water is being advected out of the chukchi sea when winds are weak the observed jet is bottom trapped with a low potential vorticity core and has maximum mean velocities of o 25 cm s 1 and an eastward transport of 0 42 sv 1 sv 106 m3 s 1 despite the absence of winds the current is highly time dependent with relative vorticity and twisting vorticity often important components of the ertel potential vorticity an idealized primitive equation model forced by dense weakly stratified waters flowing off a shelf produces a mean middepth boundary current similar in structure to that observed at the mooring site the model boundary current is also highly v

vertical scales and dynamics of eddies in the arctic ocean s canada basin a decade of moored measurements from the arctic ocean s northwestern beaufort gyre collected as a component of the beaufort gyre exploration project are analyzed to examine the range of mesoscale eddies over the water column and the dynamical processes that set eddy vertical scales a total of 58 eddies were identified in the moored record all anticyclones with azimuthal velocities ranging from 10 to 43 cm s these are divided into three classes based on core depths shallow eddies core depths around 120 m are shown to be vertically confined by the strong stratification of the halocline typical thicknesses are around 100 m deep eddies core depths around 1200 m are much taller thicknesses around 1300 m owing to the weaker stratification at depth consistent with a previous study eddies centered around mid depths all have two cores vertically aligned and separated in depth characterized by velocity maxima and anomalous temperature and salinity properties one core is located at the base of the halocline around 200 m depth and the other at the depth of the atlantic water layer around 400 m depth these double core eddies have vertical scales between those of the shallow and deep eddies the strongly decreasing stratification in their depth range motivates a derivation for the quasi geostrophic adjustment of a nonuniformly stratified water column to a potential vorticity anomaly the result aids in interpreting the dynamics and origins of the double core eddies providing insight into transport across a major water mass front separating canadian and eurasian water

breathing of a coral cay tracing tidally driven seawater recirculation in permeable coral reef sediments 1 coral reefs are characterized by high gross productivity in spite of low nutrient concentrations this apparent paradox may be partially reconciled if seawater recirculation in permeable sediments over large meters and long hours to days scales is an important source of recycled nitrogen and phosphorus to coral reefs in this paper we use radon 222rn a natural tracer to quantify tidally driven pore water or groundwater exchange between 1 an offshore coral cay island and its fringing reef lagoon and 2 a reef lagoon and the surrounding ocean as seawater infiltrates heron island at high tide it acquires a radon signal that can be detected when pore waters emerge from carbonate sands at low tide a nonsteady state model indicated that vertical pore water upwelling rates or saline submarine groundwater discharge were 40 cm d within the reef lagoon and 100 cm d outside the lagoon at low tide within the lagoon tidal pumping and temperature driven convection were the main driving forces of pore water advection at low tide the reef lagoon level is about 1 m higher than the surrounding ocean as a result a steep hydraulic gradient develops at the reef edge driving unidirectional filtration through the reef framework groundwaters were highly enriched in nitrate average of 530 mol likely influenced by bird guano relative to lagoon waters 1 9 mol rough but conservative estimates indicated that groundwater derived nitrate fluxes 7 9 mmol m2 d can replace the entire lagoon nitrate inventory every 19 days we speculate that as offshore coral islands breath inhale seawater at high tide and exhale groundwater at low tide they release nutrients that lead to sustained productivity within coral reefs

development of an antarctic digital elevation model by integrating cartographic and remotely sensed data a geographic information system based approach we present a high resolution digital elevation model dem of the antarctic it was created in a geographic information system gis environment by integrating the best available topographic data from a variety of sources extensive gis based error detection and correction operations ensured that our dem is free of gross errors the carefully designed interpolation algorithms for different types of source data and incorporation of surface morphologic information preserved and enhanced the fine surface structures present in the source data the effective control of adverse edge effects and the use of the hermite blending weight function in data merging minimized the discontinuities between different types of data leading to a seamless and topographically consistent dem throughout the antarctic this new dem provides exceptional topographical details and represents a substantial improvement in horizontal resolution and vertical accuracy over the earlier continental scale renditions particularly in mountainous and coastal regions it has a horizontal resolution of 200 m over the rugged mountains 400 m in the coastal regions and approximately 5 km in the interior the vertical accuracy of the dem is estimated at about 100 130 m over the rugged mountainous area better than 2 m for the ice shelves better than 15 m for the interior ice sheet and about 35 m for the steeper ice sheet perimeter the antarctic dem can be obtained from the authors

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

a numerical study of dense water formation and transport on a shallow sloping continental shelf the circulation and transport of dense water generated by an idealized coastal polynya is studied using a three dimensional primitive equation model starting with a homogeneous quiescent ocean a constant negative buoyancy flux is imposed at the surface over a half elliptical region adjacent to the coastal boundary on a gently sloping continental shelf the flow response can be divided into the following three phases geostrophic adjustment instability and offshore eddy transport during geostrophic adjustment the fluid within the forcing region becomes denser and the flow at the edge of the forcing region accelerates in response to the strong density gradient there eventually the flow at the leading edge of the forcing region relative to kelvin wave propagation becomes unstable and a train of counterrotating eddies develops these eddies then form a complex three dimensional flow field and rapidly transport dense water offshore across isobaths the density within the forcing region reaches a maximum which remains fairly constant after the eddies begin to transport the dense fluid offshore the results are qualitatively insensitive to weakening of the negative buoyancy forcing and to changing the bottom slope eddy scales and velocities are consistent with observations in the arctic the results suggest that instability processes and eddy fluxes are important in transporting dense water off continental shelves and into marginal seas

major flux of terrigenous dissolved organic matter through the arctic ocean high latitude rivers supply the arctic ocean with a disproportionately large share of global riverine discharge and terrigenous dissolved organic matter dom we used the abundance of lignin a macromolecule unique to vascular plants and stable carbon isotope ratios 13c to trace the high molecular weight fraction of terrigenous dom in major water masses of the arctic ocean lignin oxidation products in ultrafiltered dom udom 1 000 da from arctic rivers were depleted in syringyl relative to vanillyl phenols s v 0 3 0 5 compared to udom in temperate and tropical rivers s v 0 5 1 2 indicating that gymnosperm vegetation is a major source of terrigenous udom to the arctic ocean high concentrations of lignin oxidation products 83 320 ng l 1 and a depletion of 13c 13c 23 0 to 21 9 in udom throughout the surface arctic ocean indicate that terrigenous udom accounts for a much greater fraction of the udom in the surface arctic 5 33 than in the pacific and atlantic oceans 0 7 2 4 in contrast udom in deep water from the arctic ocean as well as waters from throughout the greenland gyre had relatively low concentrations of lignin oxidation products 24 45 ng l 1 and was enriched in 13c 13c 21 0 to 20 8 terrigenous udom has a relatively short residence 1 6 yr in surface polar waters prior to export to the north atlantic ocean assuming that the bulk of arctic derived dom is compositionally similar to the udom fraction we estimate that 12 41 of terrigenous dom 2 9 10 3 tg c yr 1 discharged by rivers to the arctic ocean is exported to the north atlantic via surface waters of the east greenland current it appears very little terrigenous dom from the arctic is incorporated into north atlantic deep water and distributed globally via deep thermohaline circulation

eddy kinetic energy in the arctic ocean from a global simulation with a 1 km arctic simulating arctic ocean mesoscale eddies in ocean circulation models presents a great challenge because of their small size this study employs an unstructured mesh ocean sea ice model to conduct a decadal scale global simulation with a 1 km arctic it provides a basinwide overview of arctic eddy energetics increasing model resolution from 4 to 1 km increases arctic eddy kinetic energy eke and total kinetic energy tke by about 40 and 15 respectively eke is the highest along main currents over topography slopes where strong conversion from available potential energy to eke takes place it is high in halocline with a maximum typically centered in the depth range of 70 110 m and in the atlantic water layer of the eurasian basin as well the seasonal variability of eke along the continental slopes of southern canada and eastern eurasian basins is similar stronger in fall and weaker in spring

two configurations of the western arctic shelfbreak current in summer abstractdata from a closely spaced array of moorings situated across the beaufort sea shelfbreak at 152 w are used to study the western arctic shelfbreak current with emphasis on its configuration during the summer season two dynamically distinct states of the current are revealed in the absence of wind with each lasting approximately one month the first is a surface intensified shelfbreak jet transporting warm and buoyant alaskan coastal water in late summer this is the eastward continuation of the alaskan coastal current it is both baroclinically and barotropically unstable and hence capable of forming the surface intensified warm core eddies observed in the southern beaufort sea the second configuration present during early summer is a bottom intensified shelfbreak current advecting weakly stratified chukchi summer water it is baroclinically unstable and likely forms the middepth warm core eddies present in the interior basin the mesoscale instabilities extract energy from the mean flow such

canadian basin freshwater sources and changes results from the 2005 arctic ocean section 1 we present measurements of oxygen isotope ratios and nutrient concentrations along the 2005 arctic ocean section aboard the icebreaker oden the data are used to estimate freshwater contributions from meteoric water mainly river runoff sea ice meltwater and chukchi sea shelf water itself a combination of pacific and indigenous arctic water types nutrients ratios are combined to form quasi conservative water mass tracers phosphate star n star and the empirical arctic n p relationship and used along with salinity and 18o which are conservative in the ocean interior disagreements between two different freshwater analyses in the western arctic are largely resolved using a salinity dependent redfield ratio a new estimate of the pacific end member and an analysis of the bering strait inflow contribution to detraining shelf waters freshwater components from 2005 are placed into the context of the overlapping 1994 arctic ocean section aboard the louis st laurent and a time series of hydrographic tracer casts between 1987 and 1992 in the canada basin compared to 1987 1994 the 2005 transect exhibits increased meteoric water concentrations in the northern part of the canadian basin and a decrease in the southern part this pattern is related to changes in the distribution of wind stress curl during the several years prior to each sampling campaign in addition a previously observed correlation between sea ice formation and river runoff disappears over the central arctic in 2005 a change that we attribute to a northward shift of sea ice formation resampling approximately every 3 years should resolve the dynamics driving changes in freshwater and nutrient distributions

brine driven eddies under sea ice leads and their impact on the arctic ocean mixed layer abstract eddy generation induced by a line shaped salt flux under a sea ice lead and associated salt transport are investigated using a three dimensional numerical model the model is designed to represent a typical condition for the wintertime arctic ocean mixed layer where new ice formation within leads is known to be one of the primary sources of dense water the result shows that along lead baroclinic jets generate anticyclonic eddies at the base of the mixed layer and almost all the lead originated salt is contained inside these eddies these eddies survive for over a month after closing of the lead and transport the lead originated salt laterally consequently the lead origin salt settles only on the top of the halocline and is not used for increasing salinity of the mixed layer sensitivity experiments suggest that the horizontal scale of generated eddies depends only on the surface forcing and is proportional to the cube root of the total amount of salt input this scaling of eddy size is consi

geology and petrogenesis of the straumsvola nepheline syenite complex dronning maud land antarctica the 170 ma straumsvola nepheline syenite complex in western dronning maud land antarctica is located on the eastern edge of the penck jutul trough a major tectonic feature which may be a palaeozoic mesozoic rift system the 5 km diameter pluton consists entirely of nepheline syenite and can be divided into two volumetrically important units a relatively structureless outer zone which is overlain by a layered zone the latter exhibits continuous rhythmic alternations of layers containing different proportions of alkali feldspar to amphibole na rich pyroxene biotite nepheline throughout its 350 m thickness the mafic zone is a volumetrically minor unit which unconformably overlies the layered zone and consists almost entirely of mafic minerals and nepheline the layered zone shows no systematic stratigraphic variation in major or trace composition or mineral chemistry which is interpreted as being due to a combination of migration of intercumulus liquid and action of deuteric fluids the remarkably constant thickness of successive layers throughout the layered zone suggests that layering resulted from an internally self regulating processes the layering is defined by changing proportions of alkali feldspar to mafic minerals nepheline which is consistent with layering being caused by differences in nucleation rate during eutectic crystallization dykes associated with the complex show wide ranging compositions and include both over and undersaturated types low s l9 o values of the nepheline syenites mean 5 9 o n 9 suggest that the magma from which the nepheline syenites crystallized was mantle derived peralkaline microgranite dykes have higher s n o values mean 7 3 n 4 and it is suggested that they are either undersaturated liquids contaminated by siliceous crust or derived by partial melting of partly fenitized gneiss oxygen isotope ratios of the surrounding gneiss indicate that the intrusion of the nepheline syenite did not cause extensive circulation of meteoric or magmatic hydrothermal fluids

subglacial imprints of early gondwana break up as identified from high resolution aerogeophysical data over western dronning maud land east antarctica determining the location and geometry of possible subglacial rifts in western dronning maud land is a key element to address processes leading to early gondwana break up however previous geophysical investigations did not lead to unambiguous delineation of rift structures over this region we interpret high resolution airborne radar and aerogravity data to image subglacial rift structures subglacial topography free air and bouguer gravity maps coupled with 3d inverse gravity models image a rift rift rift triple junction at the intersection of the jutulstraumen ice stream and the pencksokket glacier these continental rifts were associated with alkaline and tholeiitic intrusions minor dyke swarms and flood basalts of jurassic age but not with huge volumes of karoo magmatism such as that which characterizes the southern africa conjugate margin the western dronning maud land triple junction may be linked to the karoo mantle plume and represents an early stage of magmatism and rifting during gondwana break up

enhanced diapycnal mixing due to near inertial internal waves propagating through an anticyclonic eddy in the ice free chukchi plateau abstractthe arctic ocean is known to be quiescent in terms of turbulent kinetic energy tke associated with internal waves to investigate the current state of tke in the seasonally ice free chukchi plateau arctic ocean this study performed a 3 week fixed point observation fpo using repeated microstructure hydrographic and current measurements in september 2014 during the fpo program the microstructure observation detected noticeable peaks of tke dissipation rate e during the transect of an anticyclonic eddy moving across the fpo station particularly e had a significant elevation in the lower halocline layer near the critical level reaching the order of 10 8 w kg 1 the adcp measured current displayed energetic near inertial internal waves niws propagating via the stratification at the top and bottom of the anticyclone according to spectral analyses of horizontal velocity the waves had almost downward energy propagation and its current amplitude reached 10 cm s 1 the wkb scaling inco

investigation of subsurface water flow along the continental margin of the eurasian basin using the transient tracers tritium 3he and cfcs during august september 1993 the r v polarstern expedition ark ix 4 was made to the eurasian continental margin of the arctic ocean sections of oceanographic stations leading from the outer shelf over the continental slopes toward the deep eurasian basin were occupied north of the barents and laptev seas the distributions of the transient tracers cfc 11 cfc 12 tritium and 3he were measured along these sections and are discussed in relation to water mass distribution and circulation along the continental margin of the eurasian basin the tracer data strongly corroborate the temperature and salinity data schauer et al 1997 clearly showing the inflow of atlantic water in two branches the fram strait branch and the barents sea branch high cfc and tritium concen trations extended down to 1300 m over the laptev continental slope indicating strong inflow of the barents sea branch between franz josef land and severnaya zemlya the apparent ages of water in the fram strait branch were estimated to be about 2 years north of the barents sea and 6 years at the eastern end of the nansen basin which corresponds to an apparent mean current speed of about 1 cm s 1 the age of the core of the barents sea branch was also estimated to be about 6 years over the laptev slope region and to increase by 0 5 years as it flowed through this region a lower limit for the inflow of newly formed barents sea branch water was estimated to be 0 5 sv and an overall transport for the sum of fram strait branch plus barents sea branch flow of 4 sv was estimated from this aging in the deep water there was clear evidence for the inflow of norwegian sea deep water through fram strait but there appeared to be no significant input of shelf derived water from the santa anna trough if there was any shelf derived input to eurasian basin bottom water it entered at a deeper depth than was sampled on the slope sections in the laptev sea or its flow is intermittent and was not occurring during the ark ix 4 expedition

circulation features in the central arctic ocean revealed by nuclear fuel reprocessing tracers from scientific ice expeditions 1995 and 1996 measurements of the tracer radionuclides 129 i and 137 cs were conducted on seawater samples collected during the scientific ice expedition cruises to the arctic ocean of the u s navy nuclear submarines uss cavalla and uss pogy in 1995 and 1996 respectively these radionuclides are derived mainly from discharges from the sellafield england united kingdom and la hague france nuclear fuel reprocessing plants and are subsequently transported with atlantic water into the arctic ocean through fram strait and the barents sea iodine 129 results from halocline waters water depths of 59 and 134 m collected virtually synoptically throughout the central arctic ocean during the uss cavalla cruise clearly show the front between atlantic origin water having high 129 i levels 100 10 7 atoms l 1 and pacific origin water labeled mainly by fallout 30 10 7 atoms l 1 measured in central regions of the canada basin indicate that the interior is more efficiently ventilated than previously thought possibly by separation from boundary currents flowing over the continental margin north of the chukchi plateau the 129 i and 137 cs data were interpreted using a transit time model that provided estimates of 6 7 years 0 5 years for the passage of halocline and atlantic water from the norwegian coastal current 60 n to the continental slope of the makarov basin and a lower limit of 8 years for transport to interior regions of the makarov and amundsen basins

saltwater freshwater mixing dynamics in a sandy beach aquifer over tidal spring neap and seasonal cycles the biogeochemical reactivity of sandy beach aquifers is closely linked to physical flow and solute transport processes thus a clearer understanding of the hydrodynamics in the intertidal zone is needed to accurately estimate chemical fluxes to the marine environment a field and numerical modeling study was conducted over a 1 year timeframe to investigate the combined effects of tidal stage spring neap variability in tidal amplitude and seasonal inland water table oscillations on intertidal salinity and flow dynamics within a tide dominated microtidal sandy beach aquifer measured and simulated salinities revealed an intertidal saline circulation cell with a structure and cross sectional mixing zone area that varied over tidal spring neap and seasonal time scales the size of the circulation cell and area of the mixing zone were shown for the first time to be most affected by seasonal water table oscillations followed by tidal amplitude and tidal stage the intertidal circulation cell expanded horizontally and vertically as the inland water table declined displacing the fresh discharge zone and lower interface seaward over monthly spring neap cycles the center of the circulation cell shifted from beneath the backshore and upper beachface to the base of the beach salinity variations in the intertidal zone over semidiurnal tidal cycles were minimal the dynamics of the circulation cell were similar in simulations with and without a berm the highly transient nature of intertidal salinity over multiple time scales may have important implications for the types and rates of chemical transformations that occur in groundwater prior to discharge to the ocean

inland extent of the weddell sea rift imaged by new aerogeophysical data the weddell sea rift was a major focus for jurassic extension and magmatism during the early stages of gondwana break up and underlies the weddell sea embayment which separates east antarctica from a collage of crustal blocks in west antarctica newly collected aerogeophysical data over the catchments of institute and moller ice streams reveal the inland extent of the weddell sea rift against the ellsworth whitmore block and a hitherto unknown major left lateral strike slip boundary between east and west antarctica aeromagnetic and gravity anomalies define the regional subglacial extent of proterozoic basement middle cambrian rift related volcanic rocks jurassic intrusions and sedimentary rocks of inferred post jurassic age 2d and 3d magnetic depth to source estimates were used to help constrain joint magnetic and gravity models for the region the models reveal that proterozoic crust similar to that exposed at haag nunataks extends southeast of the ellsworth mountains to the margin of the coastal basins thick granitic jurassic intrusions are modelled at the transition between the ellsworth whitmore block and the thinner crust of the weddell sea rift and within the pagano shear zone the crust beneath the inland extension of the weddell sea rift is modelled as being either 4 km thinner compared to the adjacent ellsworth whitmore block or as underlain by an up to 8 km thick mafic underplate

airborne gravity and precise positioning for geologic applications airborne gravimetry has become an important geophysical tool primarily because of advancements in methodology and instrumentation made in the past decade airborne gravity is especially useful when measured in conjunction with other geophysical data such as magnetics radar and laser altimetry the aerogeophysical survey over the west antarctic ice sheet described in this paper is one such interdisciplinary study this paper outlines in detail the instrumentation survey and data processing methodology employed to perform airborne gravimetry from the multi instrumented twin otter aircraft precise positioning from carrier phase global positioning sys tem gps observations are combined with measurements of acceleration made by the gravity me ter in the aircraft to obtain the free air gravity anomaly measurement at aircraft altitude gps data are processed using the kinematic and rapid static kars software program and aircraft vertical acceleration and corrections for gravity data reduction are calculated from the gps position solu tion accuracies for the free air anomaly are determined from crossover analysis after significant editing 2 98 mgal rms and from a repeat track 1 39 mgal rms the aerogeophysical survey covered a 300 000 km 2 region in west antarctica over the course of five field seasons the grav ity data from the west antarctic survey reveal the major geologic structures of the west antarctic rift system including the whitmore mountains the byrd subglacial basin the sinuous ridge the ross embayment and siple dome these measurements in conjunction with magnetics and ice penetrating radar provide the information required to reveal the tectonic fabric and history of this important region

eddy maintenance and attrition in a vertically sheared current under arctic ice abstract steady drift of an ice cover produces a vertically sheared current in the upper ocean of the arctic under the ice cover mesoscale shallow brine and freshening sources generate submerged anticyclones and cyclones respectively a submerged eddy extending deep into the water column experiences differential advections by the vertically sheared current interaction between subsurface eddies and the sheared current is examined using a three dimensional numerical model in a coordinate system moving with the ice the initial salinity field is in geostrophic balance with the sheared current and a pulse of brine or freshening forcing produces an anticyclone or a cyclone in a coordinate system moving with the ice eddies are in a vertically sheared backward ambient current to an observer looking into the direction of the backward ambient current eddies move with the current and deflect to the right left for counterclockwise clockwise rotating eddies in both hemispheres the lower half of the eddy

air and shipborne magnetic surveys of the antarctic into the 21st century the antarctic geomagnetics community remains very active in crustal anomaly mapping more than 1 5 million line km of new air and shipborne data have been acquired over the past decade by the international community in antarctica these new data together with surveys that previously were not in the public domain significantly upgrade the admap compilation aeromagnetic flights over east antarctica have been concentrated in the transantarctic mountains the prince charles mountains lambert glacier area and western dronning maud land dml coats land additionally surveys were conducted over lake vostok and the western part of marie byrd land by the us support office for aerogeophysical research projects and over the amundsen sea embayment during the austral summer of 2004 2005 by a collaborative us uk aerogeophysical campaign new aeromagnetic data over the gamburtsev subglacial mountains 120 000 line km acquired within the ipy antarctica s gamburtsev province project reveal fundamental geologic features beneath the east antarctic ice sheet critical to understanding precambrian continental growth processes roughly 100 000 line km of magnetic data obtained within the international collaboration for exploration of the cryosphere through aerogeophysical profiling promises to shed light on subglacial lithology and identify crustal boundaries for the central antarctic plate since the 1996 97 season the alfred wegener institute has collected 90 000 km of aeromagnetic data along a 1200 km long segment of the east antarctic coast over western dml recent cruises by australian german japanese russian british and american researchers have contributed to long standing studies of the antarctic continental margin along the continental margin of east antarctica west of maud rise to the george v coast of victoria land the russian polar marine geological research expedition and geoscience australia obtained 80 000 and 20 000 line km respectively of integrated seismic gravity and magnetic data additionally us expeditions collected 128 000 line km of shipborne magnetic data in the ross sea sector

spin down of baroclinic eddies under sea ice a linear model is used to examine the spin down of a baroclinic eddy under the sea ice for anti cyclonic eddies the ice stress besides directly spinning down the azimuthal flow within the mixed layer generates an ekman divergence that raises the pycnocline near the eddy axis for eddies of the size of the baroclinic radius of deformation based on the unperturbed mixed layer depth h and the density jump across the pycnocline the doming reaches a quasi stationary state on the frictional time scale t defined as h where is the resistence coefficient at the ice water interface which generally is of the order of days upward entrainment of the fluid across the pycnocline causes a flow convergence below the mixed layer that continues to spin down the deeper flow and flatten the dome the erosion of the dome however occurs over a much longer time scale of n 1t where and n are dimensionless parameters characterizing the entrainment rate and the deep stratification using realistic parameter values for the polar eddies this time scale is of the order of a year or longer the pycnocline dome observed over the antarctic warm cells is thus likely to survive into the following freezing season and provide a preconditioning for the deep convection in the weddell sea

geologic effects on groundwater salinity and discharge into an estuary summary submarine groundwater discharge sgd can be an important pathway for transport of nutrients and contaminants to estuaries a better understanding of the geologic and hydrologic controls on these fluxes is critical for their estimation and management we examined geologic features porewater salinity and sgd rates and patterns at an estuarine study site seismic data showed the existence of paleovalleys infilled with estuarine mud and peat that extend hundreds of meters offshore a low salinity groundwater plume beneath this low permeability fill was mapped with continuous resistivity profiling extensive direct sgd measurements with seepage meters n 551 showed fresh groundwater discharge patterns that correlated well with shallow porewater salinity and the hydrogeophysical framework small scale variability in fresh and saline discharge indicates influence of meter scale geologic heterogeneity while site scale discharge patterns are evidence of the influence of the paleovalley feature beneath the paleovalley fill fresh groundwater flows offshore and mixes with saltwater before discharging along paleovalley flanks on the adjacent drowned interfluve where low permeability fill is absent fresh groundwater discharge is focused at the shoreline shallow saltwater exchange was greatest across sandy sediments and where fresh sgd was low the geologic control of groundwater flowpaths and discharge salinity demonstrated in this work are likely to affect geochemical reactions and the chemical loads delivered by sgd to coastal surface waters because similar processes are likely to exist in other estuaries where drowned paleovalleys commonly cross modern shorelines the existence and implications of complex hydrogeology are important considerations for studies of groundwater fluxes and related management decisions

formation and evolution of the surface mixed layer and halocline of the arctic ocean fresh water from summer ice melt and the total freshwater content of the arctic ocean water column above the thermocline are estimated from vertical profiles of temperature and salinity observed on the i b oden 1991 cruise the seasonal ice melt ranges from 0 5 m to slightly above 1 m and is moderately uniform over the observation area regions of lower melting are seen over the morris jesup plateau the freshwater content is calculated relative to the salinity just above the thermocline north of the barents sea the freshwater content increases toward the interior of the arctic ocean showing that fresh water is advected from other regions into the observation area regions of different freshwater content are separated by fronts over the nansen gakkel ridge over the lomonosov ridge and in the western eurasian basin between waters derived from the eurasian and canadian basins denser water homogenized north of the barents sea is recognized by a temperature minimum layer the absence of the temperature minimum near the nansen gakkel ridge indicates that heat is transferred from the atlantic layer over a longer time than the shortest route would allow this observation can be explained if the layer circulates together with the atlantic layer i e toward the east and returns above the nansen gakkel ridge and along the amundsen basin north of the laptev sea this water formed north of the barents sea becomes covered by low salinity shelf water the increased freshwater content limits the winter convection so it no longer reaches the thermocline and an intermediate halocline is formed the halocline in the eurasian basin consists of water originating from winter convection in the arctic ocean north of the barents sea which then circulates around the basin such a formation mechanism also explains the observed distribution of low no water the strong density increase limits vertical exchange and the vertical diffusion coefficient in the halocline is small 1 10 6 m2 s 1 the increased temperature of the halocline shows that the heat lost upward by the atlantic layer mainly by double diffusive convection is trapped below the mixed layer

evidence of crustal thinning beneath the limpopo belt and lebombo monocline of southern africa based on regional gravity studies and implications for the reconstruction of gondwana abstract the 600 km long by 250 km wide limpopo belt forms a wedge shaped structure between the zimbabwe and kaapvaal cratons in southern africa the results of a gravity survey which included the part of the limpopo belt within zimbabwe are incorporated with other data and presented as a regional gravity map three gravity profiles crossing the limpopo belt and one within mozambique have been interpreted in terms of lateral changes in crustal structure these interpretations are controlled by density measurements and seismic refraction data across the northern and central parts of the belt the zimbabwe craton appears from gravity modelling to be characterised by a horizontal moho at 34 km depth the limpopo belt is parallel to the ene trending gravity contours and in the east has a southwest northeast line of gravity highs coincident with the nuanetsi sabi volcanic rocks this study has shown that the regional gravity high associated with these features is consistent with crustal thinning probably caused by the breakup of gondwana the crust thins in a south southeast direction to about 30 km in the central limpopo belt with a dip on the moho which varies from about 4 to 7 the short wavelength positive gravity anomalies occurring on the nuanetsi sabi regional gravity high are due to late karoo igneous intrusions and volcanics a north south similar line of gravity highs exists along the lebombo monocline on the mozambique south africa border beyond the lebombo monocline to the east the gravity anomaly suggests a thickness of 6 km or more of sediments that could represent a paleo deltaic environment prograding over the continental margin the lebombo nuanetsi sabi gravity anomaly that dominates the gravity response in the eastern part of the study area is likely to be a failed arm triple junction and could imply a much tighter fit of gondwana than has been previously suggested as such the geometry of such a margin may provide a major constraint on the geometric fit of east antarctica with africa

circulation dense water formation and outflow on the northeast chukchi shelf we investigated circulation and water mass modification processes in the chukchi sea using 1 temperature salinity and velocity data collected between september 1991 and september 1992 from moorings in bering strait and the northeast shelf and 2 meteorological data and ice concentrations derived from special sensor microwave imager ssm i imagery in october 1991 and from february to august 1992 the mean monthly circulation was steady and northward from november to january strong northeast winds diverted the low salinity bering inflow onto the western shelf and weakened and reversed flow over the northeast shelf the winds also opened extensive polynyas wherein cold hypersaline salinity 34 waters formed the fall winter circulation enhanced dense water formation by diverting low salinity waters away from and prolonging the residence time of water within the polynyas alongshore convergence of the coastal flow swept some of the cold hypersaline water offshore across isobaths but the coastal current carried most of it into the arctic ocean through barrow canyon the dense outflow mixed little during its descent through the upper canyon where bottom friction and rotation but not entrainment were important in the plume momentum balance if the outflow is not diluted by mixing in the lower canyon where theory suggests this will occur then the densest shelf waters can ventilate layers deeper than the halocline salt rejection estimates using ssm i data and surface heat budget calculations agree within a factor of 2 with independent estimates from the mooring hence remote sensing techniques can monitor winter salt rejection rates in the chukchi sea

generalized analytical model for benthic water flux forced by surface gravity waves 1 a generalized analytical model for benthic water flux forced by linear surface gravity waves over a series of layered hydrogeologic units is developed by adapting a previous solution for a hydrogeologic unit with an infinite thickness case i to a unit with a finite thickness case ii and to a dual unit system case iii the model compares favorably with laboratory observations the amplitude of wave forced benthic water flux is shown to be directly proportional to the amplitude of the wave the permeability of the hydrogeologic unit and the wave number and inversely proportional to the kinematic viscosity of water a dimensionless amplitude parameter is introduced and shown to reach a maximum where the product of water depth and the wave number is 1 2 submarine groundwater discharge sgd is a benthic water discharge flux to a marine water body the case i model estimates an 11 5 cm d sgd forced by a wave with a 1 s period and 5 cm amplitude in water that is 0 5 m deep as this wave propagates into a region with a 0 3 m thick hydrogeologic unit with a no flow bottom boundary the case ii model estimates a 9 7 cm d wave forced sgd as this wave propagates into a region with a 0 2 m thick hydrogeologic unit over an infinitely thick more permeable unit the case iii quasi confined model estimates a 15 7 cm d wave forced sgd the quasi confined model has benthic constituent flux implications in coral reef karst and clastic regions waves may undermine tracer and seepage meter estimates of sgd at some locations

the driving forces of porewater and groundwater flow in permeable coastal sediments a review abstract advective flows rapidly transport water solutes and particles into and out of permeable sand beds and significantly affects the biogeochemistry of coastal environments in this paper we reviewed the drivers of porewater and groundwater advection in permeable shelf sediments in an attempt to bridge gaps among different disciplines studying similar problems we identified the following driving forces 1 terrestrial hydraulic gradients 2 seasonal changes in the aquifer level on land moving the location of the subterranean estuary 3 wave setup and tidal pumping 4 water level differences across permeable barriers 5 flow and topography induced pressure gradients 6 wave pumping 7 ripple and other bed form migration 8 fluid shear 9 density driven convection 10 bioirrigation and bioturbation 11 gas bubble upwelling and 12 sediment compaction while these drivers occur over spatial scales ranging from mm to km and temporal scales ranging from seconds to years their ultimate biogeochemical implications are very similar i e they are often a source of new or recycled nutrients to seawater and transform organic carbon into inorganic carbon drivers 2 12 result in no net water input into the ocean taking all these mechanisms into account we conservatively estimate that a volume equivalent to that of the entire ocean is filtered by permeable sediments at time scales of about 3000 years quantifying the relative contribution of these drivers is essential to understand the contribution of sediments to the global cycles of matter

age characteristics of a shelf break eddy in the western arctic and implications for shelf basin exchange 1 radioisotope evaluation of a cold core anticyclonic eddy surveyed in september 2004 on the chukchi sea continental slope was used to determine its age since formation over the shelf environment because the eddy can be shown to have been generated near the shelf break initial conditions for several age dependent tracers could be relatively well constrained a combination of 228ra 226ra excess 224ra and 228th 228ra suggested an age on the order of months this age is consistent with the presence of elevated concentrations of nutrients organic carbon suspended particles and shelf derived neritic zooplankton within the eddy compared to ambient offshore water in the canada basin but comparable to values measured in the chukchi shelf and shelf break environment hence this feature at the edge of the deep basin was poised to deliver biogeochemically significant shelf material to the central arctic ocean