arctic ocean circulation patterns revealed by grace abstractmeasurements of ocean bottom pressure obp anomalies from the satellite mission gravity recovery and climate experiment grace complemented by information from two ocean models are used to investigate the variations and distribution of the arctic ocean mass from 2002 through 2011 the forcing and dynamics associated with the observed obp changes are explored major findings are the identification of three primary temporal spatial modes of obp variability at monthly to interannual time scales with the following characteristics mode 1 50 of the variance is a wintertime basin coherent arctic mass change forced by southerly winds through fram strait and to a lesser extent through bering strait these winds generate northward geostrophic current anomalies that increase the mass in the arctic ocean mode 2 20 reveals a mass change along the siberian shelves driven by surface ekman transport and associated with the arctic oscillation mode 3 10 reveals a mass dipole with mass decreasing

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

nonseasonal fluctuations of the arctic ocean mass observed by the grace satellites 1 time variable gravity observations from the grace satellites reveal strong nonseasonal fluctuations of bottom pressure in the arctic ocean on the time scales from 2 to 6 months and a record high bottom pressure anomaly in february of 2011 here we examine the nature and driving forces behind those fluctuations we find that the nonseasonal variability of the arctic ocean mass is strongly coupled to wind forcing the zonal wind pattern is correlated with a dipole pattern of arctic ocean mass changes westerly wind intensification over the north atlantic at about 60 n as well as over the russian arctic continental shelf break cause the ocean mass to decrease in the nordic seas and in the central arctic and to increase over the russian arctic shelf basin wide arctic ocean mass fluctuations are correlated with northward wind anomalies over the northeastern north atlantic and nordic seas and over the bering sea we show that positive negative arctic ocean mass anomalies are associated with anticyclonic cyclonic anomalies of the large scale ocean circulation pattern based on ocean model simulations we conclude that the observed nonseasonal arctic ocean mass variability is mostly explained by the net horizontal wind driven transports and the contribution of fresh water fluxes is negligible we demonstrate that transport anomalies across both the atlantic and pacific gateways were equally important for generating large arctic ocean mass anomalies in 2011

eastern boundary contribution to the residual and meridional overturning circulations a model of the thermocline linearized around a specified stratification and the barotropic linear winddriven stommel solution is constructed the forcings are both mechanical the surface wind stress and thermodynamical the surface buoyancy boundarycondition the effects of diapycnal diffusivity and of eddy fluxesofbuoyancy parameterizedintermsofthelarge scalebuoyancygradient areincluded theeddyfluxes of buoyancy are especially important near the boundaries where they mediate the transport in and out of the narrow ageostrophic down upwelling layers the dynamics of these narrow layers can be replaced by effective boundary conditions on the geostrophically balanced flow the effective boundary conditions state that the residual flow normal to the effective coast vanishes the separate eulerian and eddy induced components may be nonzero this formulation conserves the total mass and the total buoyancy while permitting an exchangebetweentheeulerianandeddytransportofbuoyancy withinthedown upwellinglayers inturn this exchange allows buoyancy gradients along all solid boundaries including the eastern one a special focus is on the buoyancy along the eastern and western walls since east west buoyancy difference determines the meridional overturning circulation the inclusion of advection of buoyancy by the barotropic flow allows a meaningful distinction between the meridional and the residual overturning circulations while retaining the simplicity of a linear model the residual flow in both meridional and zonal directions reveals how the subsurface buoyancy distribution is established and in particular how the meridional buoyancy gradient is reversed at depth in turn the horizontal buoyancy gradient maintains stacked counterrotating cells in the meridional and residual overturning circulations quantitative scaling arguments are given for each of these cells which show how the buoyancy forcing the wind stress and the diapycnal and eddy diffusivities as well as the other imposed parameters affect the strength of the overturn

grace measurements of mass variability in the earth system monthly gravity field estimates made by the twin gravity recovery and climate experiment grace satellites have a geoid height accuracy of 2 to 3 millimeters at a spatial resolution as small as 400 kilometers the annual cycle in the geoid variations up to 10 millimeters in some regions peaked predominantly in the spring and fall seasons geoid variations observed over south america that can be largely attributed to surface water and groundwater changes show a clear separation between the large amazon watershed and the smaller watersheds to the north such observations will help hydrologists to connect processes at traditional length scales tens of kilometers or less to those at regional and global scales

stable reconstruction of arctic sea level for the 1950 2010 period reconstruction of historical arctic sea level is generally difficult due to the limited coverage and quality of both tide gauge and altimetry data in the area here a strategy to achieve a stable and plausible reconstruction of arctic sea level from 1950 to today is presented this work is based on the combination of tide gauge records and a new 20 year reprocessed satellite altimetry derived sea level pattern hence the study is limited to the area covered by satellite altimetry 68 n and 82 n it is found that time step cumulative reconstruction as suggested by church and white 2011 may yield widely variable results and is difficult to stabilize due to the many gaps in both tide gauge and satellite data a more robust sea level reconstruction approach is to use datum adjustment of the tide gauges in combination with satellite altimetry as described by ray and douglas 2011 in this approach a datum fit of each tide gauges is used and the method takes into account the entirety of each tide gauge record this makes the arctic sea level reconstruction much less prone to drifting from our reconstruction we found that the arctic mean sea level trend is around 1 5 mm 0 3 mm yr for the period 1950 2010 between 68 n and 82 n this value is in good agreement with the global mean trend of 1 8 0 3 mm yr over the same period as found by church and white 2004

contributions to atmospheric methane by natural seepages on the uk continental shelf natural gas seepages occur on the united kingdom s continental shelf and although published reports suggest that they are very rare the petroleum industry has identified but not publicly reported many more there is also very little data on the flux of gas from seabed seepages and even less on the contribution of seepages to atmospheric concentrations of gases such as methane potential gas source rocks include quaternary peats as well as petroliferous source rocks such as the carboniferous coal measures and the upper jurassic kimmeridge clays there are also other organic rich sediments which are potential source rocks together these cover a considerable part of the u k continental shelf analogue seismic reflection pinger profiles acquired during the british geological survey s regional mapping programme have been reviewed to identify water column targets including fish and plumes of gas bubbles the ability to distinguish targets is critical to an assessment of the distribution of gas seepages both theoretical predictions of target identity and the habits of shoaling fish have been investigated in order to identify a method of distinction data from seabed seepages and measurements of seepage rates have been used to establish likely ranges of gas flux rates and the sizes of gas bubbles the likelihood that a rising bubble will survive and escape into the atmosphere is determined primarily by bubble size and water depth methane the principal constituent of seepage gas is relatively unreactive and sparingly soluble the studies have enabled a new estimate of the distribution of gas seepages on the u k continental shelf and of the contribution to atmospheric methane levels the results suggest that natural gas seepages are significantly more important as a source of methane than had hitherto been established it is estimated that between 120 000 and 3 5 mtonnes of methane per year come from a continental shelf area of about 600 000 km2 this represents between 2 and 40 of the total united kingdom methane emission it is suggested that similar contributions arise from other continental shelf areas worldwide and that geological sources of atmospheric methane are more significant than is generally acknowledged

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

relation between sea level and bottom pressure and the vertical dependence of oceanic variability 1 the relation between large scale sea level and bottom pressure variability is studied using long 50 yr simulations of a general circulation model under realistic forcing admittance and coherence analyses are used to characterize the bottom pressure and sea level relationship as a function of period horizontal spatial scale and location at the model grid scale 1 bottom pressure is found to be essentially equivalent to sea level at periods 60 and in shallow depths 200 m elsewhere bottom pressure and sea level fields can differ significantly results indicate an increase of the importance of baroclinic signals with decreasing latitude and spatial scale with significant baroclinic signals at intra seasonal and longer periods present in many subtropical and mid latitude regions variability is clearly baroclinic at inter annual periods regardless of location and spatial scale results have broad implications for the interpretation and processing of both satellite altimetry and gravity data and for their assimilation into numerical models

a basin coherent mode of sub monthly variability in arctic ocean bottom pressure 1 a sub monthly mode of non tidal variability of ocean bottom pressure obp is observed in a 5 year record of deep sea bottom pressure at the north pole obp records from other regions in the arctic show that the north pole non tidal mass fluctuation is part of a non propagating basin coherent variation that is well represented by the ice ocean model piomas with a basin averaged winter only rms of 3 3 cm wavelet analysis of the modeled obp shows that the basin averaged mass variations are non stationary and only significant during the winter the basin averaged obp is strongly related to the meridional wind component over the nordic seas the ocean response is consistent with episodic wind forcing driving a northward geostrophic slope current the mass transport anomaly associated with the mode is significant relative to the annual net mean flow

nonseasonal mass fluctuations in the midlatitude north atlantic ocean measurements from the gravity recovery and climate experiment reveal spatially coherent nonseasonal fluctuations in bottom pressure pb in the midlatitude north atlantic ocean the spatial structure of the pb anomalies is centered on the north atlantic current along the intergyre region separating subtropical and subpolar ocean basins and their temporal behavior is tied to indices of climate variability namely the north atlantic oscillation and the arctic oscillation correspondence to variations in wind stress curl suggests an interpretation of the midlatitude north atlantic pb variability in terms of a barotropic sverdrup balance anomalous mass in the midlatitude north atlantic ocean covaries with mass anomalies in abutting marginal seas including the mediterranean sea and the arctic ocean as well as the north sea and hudson bay results have implications for diagnosing ocean meridional heat transports due to depth independent gyre circulation changes

controls on structural styles basin development and petroleum prospectivity in the midland valley of scotland integration of well calibrated seismic data from the firth of forth with field and subsurface data from neighbouring onshore areas provides important new insights into the structural evolution and petroleum habitat in the midland valley of scotland the results demonstrate that the nne ssw striking midlothian leven syncline and its flanking burntisland and d arcy cousland anticlines developed as major growth folds during the late palaeozoic under a predominantly dextral strike slip regime these syn sedimentary folds controlled depositional thicknesses facies and dispersal patterns in early to late carboniferous visean westphalian times structural geometries suggest that the folds experienced tightening during late carboniferous variscan deformation events before being transected by e w striking dykes and extensional faulting during the late carboniferous westphalian d and early permian although direct evidence for the basin s post permian burial history is no longer present it can be inferred that the area had at least 1 km of cover prior to paleogene uplift the new understanding of the eastern midland valley s structural and subsidence history provides the means by which the occurrence of petroleum in the basin can be explained burial of lower carboniferous mississippian oil shale source rocks beneath the midlothian leven syncline now appears to have been the primary driver in the maturation and up dip migration of waxy crude oil into age equivalent clastic reservoirs located in the adjacent anticlines rather than oil generation by direct contact between the source rocks and igneous intrusions initial oil charging is thought to have taken place during the late carboniferous was renewed during mesozoic reburial and appears to continue locally today despite the detrimental effect of significant early cenozoic uplift it is now evident that the basin s limited exploration success has been almost entirely governed by the presence of unbreached palaeostructures lying directly up dip from an oil kitchen developed in the core of the midlothian leven syncline during late carboniferous and mesozoic recent burial

do the north atlantic winds drive the nonseasonal variability of the arctic ocean sea level the gravity recovery and climate experiment grace satellites have observed coherent and nearly uniform nonseasonal fluctuations of bottom pressure throughout the arctic ocean and the nordic seas strong correlation between the nonseasonal grace and satellite altimetry data is found in the nordic and barents seas which suggests a possibility of using the longer altimetry records in these areas as a proxy for the nonseasonal sea level variability over the entire arctic this study identifies the dominant pattern of the nonseasonal atmospheric pressure variability that drives strong zonal wind anomalies over the northeastern north atlantic associated with the nonseasonal sea level anomalies in the nordic seas our results show that wind driven northward ekman transport anomalies in the northeastern north atlantic may induce coherent changes of sea level across the entire arctic ocean

ventilation potential vorticity homogenization and the structure of the ocean circulation abstract a model for the vertical structure of the oceanic circulation is presented that combines elements of the theory of the ventilated thermocline given by luyten pedlosky and stommel with the theory of rhines and young for the wind driven circulation of an unventilated ocean our model consists of a ventilated thermocline region above an unventilated zone in which motion is limited to pools of constant potential vorticity the model is nonlinear and hence the presence of ventilation affects the dynamics of the unventilated motion and vice versa the planetary geostrophic equations are used and so the quasi geostrophic assumption of rhines and young is relaxed allowing large isopycnal excursions it is shown that the presence of ventilation generally shrinks and weakens the size and vigor of the subsurface pools of homogenized potential vorticity at the same time within those domains the strength of circulation in the ventilated zone is somewhat diminished as the subsurface layers carry a porti

adjustment of the ventilated thermocline the time dependence of the ventilated thermocline is examined via analytical and numerical means the original henderschott model is modified such that the outcrops all occur on the same geopotential surface rather than at staggered geopotential surfaces this model has the advantage that the ocean interior can be ventilated directly by the sverdrup flow rather than by western boundary processes the propagation of disturbances governed by linearized forms of the three layer or four layer modified henderschott model nonlinear solutions of the full modified henderschott model and numerical solutions of the planetary geostrophic equations are considered low frequency disturbances are predicted by the linear models to move on characteristics jointly set by advection and wave dynamics it is shown that perturbations due to wind stress anomalies project strongly onto the first mode and propagate westward similarly to the classical first baroclinic rossby mode they do not experience much interaction with the mean flow the so called non doppler effect on the other hand perturbations generated by buoyancy anomalies have strong projections onto the second or third modes and propagate along pathways very close to the mean circulation their speed is somewhat slower than the current speed however these properties appear in the linearized and simplified nonlinear models and their occurrence in planetary geostrophic results argues the relevance of the henderschott model also these properties are consistent with results from other studies

recent trends in arctic ocean mass distribution revealed by grace 1 measurements of ocean bottom pressure by the gravity recovery and climate experiment grace and new in situ bottom pressure measurements confirm the accuracy and utility of grace measurements in the arctic ocean they reveal a declining trend in bottom pressure that corresponds to mass changes due to decreasing upper ocean salinities near the north pole and in the makarov basin the spatial distribution and magnitude of these trends suggest the arctic ocean is reverting from the cyclonic state characterizing the 1990s to the anticyclonic state that was prevalent prior to the 1990s

quality assessment of a satellite altimetry data product in the nordic barents and kara seas 1 satellite altimetry provides high quality sea surface height data that have been successfully used to study the variability of sea level and surface geostrophic circulation at different spatial and temporal scales however the high latitude regions have traditionally been avoided due to the persistent sea ice cover most of the validation studies have focused on the areas below the polar circles in this paper we examine the quality and performance of a gridded satellite altimetry product in the nordic barents and kara seas the altimetric sea level in coastal areas is validated using available tide gauge records we show that at most locations in the nordic seas the altimetry and tide gauge measurements are in a good agreement in terms of the root mean square differences and the amplitudes and phases of the seasonal cycle the agreement deteriorates in the shallow areas of the barents and kara seas subject to the seasonal presence of sea ice and where the altimetry data are contaminated by the residual aliasing of unresolved high frequency signals the comparison of linear trends at the locations of tide gauges reveals discrepancies that need to be taken into account when interpreting long term changes of sea level in the region away from the coast the altimetry data are compared to drifter trajectories corrected for ekman currents the drifter trajectories are found consistent with the mesoscale variability of the altimetric sea level this study provides the first comprehensive validation of a gridded satellite altimetry data product in the high latitude seas

three dimensional isoneutral potential vorticity structure in the indian ocean the three dimensional isoneutral potential vorticity structure of the indian ocean is examined using world ocean circulation experiment and national oceanic and atmospheric administration conductivity temperature depth data and historical bottle data the distribution of the potential vorticity is set by the indian ocean s source waters and their circulation inside the basin the lower thermocline has a high potential vorticity signal extending westward from northwest of australia and a low signal from the subantarctic mode water in the south the antarctic intermediate water inflow creates patches of high potential vorticity at intermediate depths in the southern indian ocean below which the field becomes dominated by planetary vorticity indicating a weaker meridional circulation and weaker potential vorticity sources wind driven gyre depths have lower potential vorticity gradients primarily due to same source waters homogenization and western shadow zones are not observed the effect dominates the effect of the somali current and the red sea water on the potential vorticity distribution isopleths tilt strongly away from latitude lines in the deep and abyssal waters as the circumpolar deep water fills the basins in deep western boundary currents indicating a strong meridional circulation north of the antarctic circumpolar current the lower gradient intermediate layer surrounded vertically by layers with higher meridional potential vorticity gradients in the subtropical indian ocean suggests that rossby waves will travel 1 3 times faster than standard theory predicts to the south several pools of homogenized potential vorticity appear in the upper 2000 m of the southern ocean where gyres previously have been identified south of australia the abyssal potential vorticity structure is set by a combination of the antarctic circumpolar current and the bathymetry

buoyancy and wind driven circulation in an extended model of potential vorticity homogenization an analytical model is proposed on the middepth water circulation between the surface wind driven circulation and the deep buoyancy driven circulation the model consists of three and a half layers with the second and third layers being the middepth layers the model includes thermohaline processes by allowing diapycnal flows at interfaces between layers in addition to the potential vorticity homogenization proposed by rhines and young the velocities of diapycnal flow are calculated from the density stratification which can be given solely by a wind driven model as a good approximation the divergence of diapycnal velocity causes a circulation in addition to the wind driven circulation although in pure wind driven theories motion was absent outside the region of homogenized potential vorticity the present model gives significant currents there in particular a prominent eastward flow appears in the third layer along the southern rim of the homogeneous potential vorticity region in the second layer the flow pattern in the present model is consistent with that estimated diagnostically from the climatological density distribution in the north pacific the diagnosed flow field is further supported by the oxygen distribution there

proxy representation of arctic ocean bottom pressure variability bridging gaps in grace observations using time varying ocean bottom pressure obp from the gravity recovery and climate experiment grace a 9 year in situ obp record at the north pole and wind reanalysis products we perform a linear regression analysis to identify primary predictor time series that enable us to create a proxy representation of the arctic time varying obp that explains the largest fraction of the observed arctic obp variability after cross validation two predictors north pole obp record and wind obp coupling from maximum covariance analysis explain 50 of the total variance of the arctic obp this work provides a means for bridging existing short gaps in grace measurements and potentially longer future gaps that may result if grace and its follow on mission do not overlap the technique may be applicable to bridge gaps in grace measurements in other oceanic regions

a near uniform fluctuation of ocean bottom pressure and sea level across the deep ocean basins of the arctic ocean and the nordic seas across the arctic ocean and the nordic seas a basin wide mode of ocean bottom pressure and sea level fluctuation is identified using satellite and in situ observations in conjunction with a global ocean circulation model and its adjoint the variation extends across the interconnected deep ocean basins of these semi enclosed arctic seas collectively called the arctic mediterranean with spatially near uniform amplitude and phase the basin wide fluctuation is barotropic and dominates the region s large scale variability from sub monthly to interannual timescales the fluctuation results from bifurcating coastally trapped waves generated by winds along the continental slopes of the arctic mediterranean and its neighboring seas including the north atlantic ocean the winds drive ekman transport across the large bathymetric gradients forcing mass divergence between the shallow coastal area and the deep ocean basins and creating ocean bottom pressure anomalies of opposite signs in the two regions the anomalies rapidly propagate away as barotropic coastally trapped waves with the coast and continental slope as respective boundaries the waves subsequently bifurcate at the shallow straits connecting the arctic mediterranean with the rest of the globe the straits transmit the shallow anomalies but not the deep variations thereby inhibiting the anomalies mutual cancelation by geographically separating the two anomalies that enter the deep arctic basins equilibrate uniformly across the domain characterized by a homogeneous depth integrated planetary potential vorticity distribution the potential vorticity s steep gradient that borders the basins shields the region from neighboring shallow variations giving rise to the observed spatially confined fluctuation compensating anomalies outside the arctic adjust similarly across the rest of the globe but are comparatively negligible in amplitude because of the global ocean s larger area relative to that of the deep arctic mediterranean the study from a technical perspective illustrates the utility of a model s adjoint in identifying causal mechanisms underlying a complex system