tidal dissipation in the early eocene and implications for ocean mixing 1 the tidally driven vertical diffusivity in the abyssal ocean during the early eocene 55 ma is investigated using an established tidal model a weak tide is predicted in the eocene ocean except in the pacific consequently the integrated global tidal dissipation rate is a mere 1 44tw of which 40 dissipate in the pacific however due to a stronger abyssal vertical stratification the predicted eocene vertical diffusivities are consistently larger than at present the results support the hypothesis that altered tidal dissipation may play a role in explaining the maintenance of past climate regimes especially the anomalously warm temperatures in the southwest pacific in the eocene and the low dissipation rates may be important for lunar evolution history

stommel s box model of thermohaline circulation revisited the role of mechanical energy supporting mixing and the wind driven gyration the classical two box model of stommel is extended in two directions replacing the buoyancy constraint with an energy constraint and including the wind driven gyre stommel postulated a buoyancy constraint for the thermohaline circulation and his basic idea has evolved into the dominating theory of thermohaline circulation however recently it is argued that the thermohaline circulation is maintained by mechanical energy from wind stress and tides the major difference between these two types of models is the bifurcation structure the stommel like model has two thermal modes one stable and another one unstable and one stable haline mode whereas the energy constraint model has one stable thermal mode and two saline modes one stable and another one unstable adding the wind driven gyre changes the threshold value of thermohaline bifurcation greatly thus the inclusion of the wind driven gyre is a vital step in completely modeling the physical processes related to thermohaline circulation

huber inversion for logging while drilling resistivity measurements in high angle and horizontal wells logging while drilling lwd resistivity responses are inevitably contaminated by gaussian and non gaussian noise noise contamination can influence the stability and accuracy of the inversion of the data in addition the uncertainty of the bed boundary positions can complicate the inversion we propose a novel efficient nonlinear inversion algorithm called huber inversion to accurately estimate the layer by layer resistivity when lwd measurements are affected by both gaussian and non gaussian noise huber inversion combines the advantages of the l1 and l2 norm inversions which are more robust than the traditional least squares ls inversion algorithm we use a multiple initial bed boundary positions method to reduce the inversion uncertainty caused by uncertain bed boundary positions the initial bed boundary positions could be restricted into defined ranges based on the investigation depth of lwd instruments the geological environment and log data from adjacent wells the slipping inversion windo

temporal offsets between surface temperature ice rafting and bottom flow speed proxies in the glacial mis 3 northern north atlantic rapid climatic switches during marine isotope stage 3 29 59 ka bp are often attributed to ocean circulation changes caused by freshwater input into the north atlantic through the melting of large amounts of icebergs and sea ice however recent studies have questioned this direct coupling between factors influencing the ocean climate system by combining multiple proxies from two mid depth northern north atlantic sediment cores we assess temporal offsets and links between freshwater input and response of the near bottom flow as well as between near bottom flow and sea surface temperatures changes grain size mineralogical and magnetic proxies for ice rafting and near bottom flow speed interpreted as indicators of freshwater input and deep circulation strength consistently indicate a delay in the recovery of the deep circulation after freshwater perturbations sea surface temperature variability is inferred from foraminiferal assemblages and mg ca and 18o of neogloboquadrina pachyderma s the records show rapid switches towards higher temperatures following the ice rafting events interestingly near sea surface temperatures increased and decreased again during periods of accelerating bottom flow speed likely reflecting the sudden release of heat from deeper in the water column rather than circulation changes our data thus confirm the impact of freshwater forcing on the atlantic deep circulation but suggest that temperature variability at the surface was not directly linked to these circulation changes

oceanographic and climatic consequences of the tectonic evolution of the southern scotia sea basins antarctica abstract the scotia sea is a complex geological area located in the southern ocean which evolution is closely linked to the opening of the drake passage structural highs of continental nature derived from the former continental bridge between south america and the antarctic peninsula surround the abyssal plains of the scotia sea restricting small isolated sedimentary basins along its southern margin morpho structural and seismo stratigraphic analyses of multichannel seismic reflection profiles and additional geophysical data available in the region have been conducted decoding regional and global implications of the basins evolution the main aim of this work is to describe the stratigraphic evolution of the southern scotia sea basins from their opening in the back arc tectonic context of the scotia sea to the last oceanographic changes which have carried on global climatic implications the evolution of the south scotia sea occurred through two major tectonic stages registered in the sedimentary record of the region 1 the end of the subduction in the northwest part of the weddell sea during the early miocene which shortened the back arc subduction trench generating a major change in the regional tectonic field that determined the evolution of the southern basins towards two different types of passive margins magma poor and magma rich and 2 the full development of the southern scotia sea basins during the middle miocene that led to the opening of deep oceanic gateways along the south scotia ridge interplay among tectonics oceanography and climate is proposed to control the regional sedimentary stacking pattern with coeval changes globally identified

effect of tool eccentricity on some electrical well logging tools an algorithm is presented to compute efficiently the propagation of nonaxially symmetric waves induced by realistic eccentered sources with a mandrel in a multicylindrically layered geometry one of the applications of such a program is in electrical well logging where all exploration tools operate in a borehole drilled into the ground for geophysical subsurface sensing the borehole surrounded by an invasion zone can be modeled as a multicylindrically layered geometry the authors also present an algorithm to study the effect of eccentricity source and mandrel not in the center of the borehole in the presence of concentric invasion zones around the borehole the authors algorithm is used to study the eccentricity and invasion effects on an induction measurement and a dielectric logging measurement in the case of dielectric logging they find that the invasion zone can cause resonance effects and that these effects remain when the tool is eccentered

electromagnetic induction in a fully 3 d anisotropic earth the bulk electrical anisotropy of sedimentary formations is a macroscopic phenomenon which can result from the presence of porosity variations laminated shaly sands and water saturation accounting for its effect on induction log responses is an ongoing research problem for the well logging community since these types of sedimentary structures have long been correlated with productive hydrocarbon reservoirs such as the jurassic norphlet sandstone and permian rotliegendes sandstone presented here is a staggered grid finite difference method for simulating electromagnetic em induction in a fully 3 d anisotropic medium the electrical conductivity of the formation is represented as a full 3 3 tensor whose elements can vary arbitrarily with position throughout the formation to demonstrate the validity of this approach finite difference results are compared against analytic and quasi analytic solutions for tractable 1 d and 3 d model geometries as a final example we simulate 2c 40 induction tool responses in a crossbedded aeolian sandstone to illustrate the magnitude of the challenge faced by interpreters when electrical anisotropy is neglected

oceanic salt switch salinity and temperature the two determinants of the density of ocean waters play an important role in ocean circulation in today s ocean the saltiest deep waters derive from the northern north atlantic but as boyle 1 explains in his perspective the situation was very different during the last glaciation he highlights the report by adkins 2 et al who show that the saltiest waters then formed in the southern ocean the ocean circulation must thus differ substantially between glacial and interglacial periods 1 http www sciencemag org cgi content full 298 5599 1724 2 http www sciencemag org cgi content short 298 5599 1769

an indicator of the multiple equilibria regime of the atlantic meridional overturning circulation recent model results have suggested that there may be a scalar indicator s monitoring whether the atlantic meridional overturning circulation moc is in a multiple equilibrium regime the quantity s is based on the net freshwater transport by the moc into the atlantic basin it changes sign as soon as the steady atlantic moc enters the multiple equilibrium regime because of an increased freshwater input in the northern north atlantic this paper addresses the issue of why the sign of s is such a good indicator for the multiple equilibrium regime changes in the atlantic freshwater budget over a complete bifurcation diagram and in finite amplitude perturbation experiments are analyzed in a global ocean circulation model the authors show that the net anomalous freshwater transport into or out of the atlantic resulting from the interactions of the velocity perturbations and salinity background field is coupled to the background steady state state freshwater budget and hence to s the sign of s precisely shows whether this net anomalous freshwater transport is stabilizing or destabilizing the moc therefore it can indicate whether the moc is in a single or multiple equilibrium regime

atlantic meridional overturning circulation and the southern hemisphere supergyre 1 the ocean s role in climate manifests itself through its high heat capacity its own rich internal dynamics and its ability to transport vast quantities of heat and freshwater of particular interest is the global ocean circulation associated with the atlantic meridional overturning amoc because observations are sparse the detailed global structure of the amoc remains poorly understood particularly the pathways along which water returns to the atlantic to compensate the export of north atlantic deep water nadw here we provide the first quantitative 3 dimensional global view of the amoc using a lagrangian reconstruction which integrates hundred of thousands water particle trajectories in an ocean model the resulting pattern elucidates the role of the wind in structuring the pathways of the amoc in particular the lagrangian analysis reveals a strong link with the three subtropical gyres of the southern hemisphere sh which merge into a supergyre spanning the three ocean basins the coupling between the upper ocean wind driven circulation and the overturning in the model suggests that changes in the sh winds can alter the pathways of the amoc and therefore the water properties and the associated heat and freshwater transports

widespread late devonian marine anoxia in eastern north america a case study of the kettle point formation black shale southwestern ontario1 the kettle point formation of southwestern ontario consists of intervals of organic rich interlaminated black shale interbedded with organic poor greyish green mudstones and rare red beds separate

nonuniform response of the major surface currents in the nordic seas to insolation forcing implications for the holocene climate variability 1 high resolution sediment cores from the voring plateau the north iceland shelf and the east greenland shelf have been studied to investigate the stability of major surface currents in the nordic seas during the holocene results from diatom assemblages and reconstructed sea surface temperatures ssts indicate a division of the holocene into three periods the holocene climate optimum 9500 6500 calendar cal years bp the holocene transition period 6500 3000 cal years bp and the cool late holocene period 3000 0 cal years bp the overall climate development is in step with the decreasing insolation on the northern hemisphere but regional differences occur regarding both timing and magnitude of sst changes sites under the direct influence of the norwegian atlantic current and the irminger current indicate sst cooling of 4 5 c from early holocene to present compared to 2 c recorded under the east greenland current superimposed on the general holocene cooling trend there is a high frequency sst variability which is in the order of 1 1 5 c for the voring plateau and the east greenland shelf and 2 5 3 c on the north iceland shelf

ice ocean processes over the continental shelf of the southern weddell sea antarctica a review 1 interactions between the southern ocean and the weddell sea ice shelves are important both to the antarctic ice sheet and to the production of globally significant water masses here we review the interaction between the filchner ronne ice shelf and the shelf sea in which it floats the continental shelf processes leading to the production of weddell sea deep and bottom waters from the original off shelf source waters are discussed and a new view is offered of the initial production of high salinity shelf water data from ship based measurements at the ice front from glaciological methods and from measurements made within the sub ice shelf cavity itself are used to describe the pattern of flows beneath the ice shelf we also consider the variability observed within the cavity from tidal to interannual time scales and finish with a discussion of future research priorities in the region

thermohaline circulation hysteresis a model intercomparison we present results from an intercomparison of 11 different climate models of intermediate complexity in which the north atlantic ocean was subjected to slowly varying changes in freshwater input all models show a characteristic hysteresis response of the thermohaline circulation to the freshwater forcing which can be explained by stommel s salt advection feedback the width of the hysteresis curves varies between 0 2 and 0 5 sv in the models major differences are found in the location of present day climate on the hysteresis diagram in seven of the models present day climate for standard parameter choices is found in the bi stable regime in four models this climate is in the mono stable regime the proximity of the present day climate to the stommel bifurcation point beyond which north atlantic deep water formation cannot be sustained varies from less than 0 1 sv to over 0 5 sv

what is the thermohaline circulation the term thermohaline circulation is widely used in the context of past and future climate change in his perspective wunsch argues that there are many different and inconsistent definitions for this term he defines ocean circulation in terms of mass fluxes which are largely driven by surface forces such as wind and tides and argues that thermohaline circulation should only refer to the separate transport of heat and salinity in the ocean

comment on glacial interglacial circulation changes inferred from 231pa 230th sedimentary record in the north atlantic region by j m gherardi et al

a wind induced thermohaline circulation hysteresis and millennial variability regimes abstract the multiple equilibria of the thermohaline circulation thc used here in the sense of the meridional overturning circulation as function of the surface freshwater flux has been studied intensively following a stommel paper from 1961 it is shown here that multistability and hysteresis of the thc also exist when the wind stress amplitude is varied as a control parameter both the massachusetts institute of technology ocean general circulation model mitgcm and a simple three box model are used to study and explain different dynamical regimes of the thc and thc variability as a function of the wind stress amplitude starting with active winds and a thermally dominant thermohaline circulation state the wind stress amplitude is slowly reduced to zero over a time period of 40 000 yr 40 kyr and then increased again to its initial value over another 40 kyr it is found that during the decreasing wind stress phase the thc remains thermally dominant until very low wind stress amplitude at which

observations inferences and mechanisms of the atlantic meridional overturning circulation a review this is a review about the atlantic meridional overturning circulation amoc its mean structure temporal variability controlling mechanisms and role in the coupled climate system the amoc plays a central role in climate through its heat and freshwater transports northward ocean heat transport achieved by the amoc is responsible for the relative warmth of the northern hemisphere compared to the southern hemisphere and is thought to play a role in setting the mean position of the intertropical convergence zone north of the equator the amoc is a key means by which heat anomalies are sequestered into the ocean s interior and thus modulates the trajectory of climate change fluctuations in the amoc have been linked to low frequency variability of atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses on intra annual timescales variability in amoc is large and primarily reflects the response to local wind forcing meridional coherence of anomalies is limited to that of the wind field on interannual to decadal timescales amoc changes are primarily geostrophic and related to buoyancy anomalies on the western boundary a pacemaker region for decadal amoc changes is located in a western transition zone along the boundary between the subtropical and subpolar gyres decadal amoc anomalies are communicated meridionally from this region amoc observations as well as the expanded ocean observational network provided by the argo array and satellite altimetry are inspiring efforts to develop decadal predictability systems using coupled atmosphere ocean models initialized by ocean data

a perturbation method to model electromagnetic well logging tools in curved boreholes logging while drilling lwd or measuring while drilling tools are routinely used to guide well placement during exploration of hydrocarbons reservoirs these tools have become fundamental for directional and horizontal drilling operations in this paper we present a perturbation method to model electromagnetic fields produced by time harmonic sources in radially stratified and axially toroidal structures describing lwd tools inside curved boreholes i e boreholes with axial bending the proposed formulation is validated against brute force finite difference results in various representative scenarios numerical results indicate that the proposed perturbative approach can provide a reduction in the computational effort required to analyze this class of problems of several orders of magnitude versus brute force approaches

orbital changes and climate at the 41 000 period of orbital tilt summer insolation forces a lagged response in northern ice sheets this delayed ice signal is rapidly transferred to nearby northern oceans and landmasses by atmospheric dynamics these ice driven responses lead to late phased changes in atmospheric co2 that provide positive feedback to the ice sheets and also project late 41 k forcing across the tropics and the southern hemisphere responses in austral regions are also influenced by a fast response to summer insolation forcing at high southern latitudes at the 22 000 year precession period northern summer insolation again forces a lagged ice sheet response but with muted transfers to proximal regions and no subsequent effect on atmospheric co2 most 22 000 year greenhouse gas responses have the early phase of july insolation july forcing of monsoonal and boreal wetlands explains the early ch4 response the slightly later 22 k co2 response originates in the southern hemisphere the early 22 k ch4 and co2 responses add to insolation forcing of the ice sheets the dominant 100 000 year response of ice sheets is not externally forced nor does it result from internal resonance internal forcing appears to play at most a minor role the origin of this signal lies mainly in internal feedbacks co2 and ice albedo that drive the gradual build up of large ice sheets and then their rapid destruction ice melting during terminations is initiated by uniquely coincident forcing from insolation and greenhouse gases at the periods of tilt and precession

mechanisms for decadal scale variability in a simulated atlantic meridional overturning circulation variability in the atlantic meridional over turning circulation amoc has been analysed using a 600 year pre industrial control simulation with the bergen climate model the typical amoc variability has ampli tudes of 1 sverdrup 1 sv 10 6 m 3 s 1 and time scales of 40 70 years the model is reproducing the observed dense water formation regions and has very realistic ocean transports and water mass distributions the dense water produced in the labrador sea 1 3 and in the nordic seas including the water entrained into the dense overflows across the greenland scotland ridge gsr 2 3 are the sources of north atlantic deep water nadw forming the lower limb of the amoc s northern overturning the variability in the labrador sea and the nordic seas con vection is driven by decadal scale air sea fluxes in the convective region that can be related to opposite phases of the north atlantic oscillation the labrador sea convec tion is directly linked to the variability in amoc linkages between convection and water mass transformation in the nordic seas are more indirect the scandinavian pattern the third mode of atmospheric variability in the north atlantic is a driver of the ocean s poleward heat transport pht the overall constraint on northern water mass transformation increased pht is both associated with an increased water mass exchange across the gsr and a stronger amoc

vadose zone flow model parameterisation using cross borehole radar and resistivity imaging cross borehole geoelectrical imaging in particular electrical resistivity tomography ert and transmission radar tomography can provide high resolution images of hydrogeological structures and in some cases detailed assessment of dynamic processes in the subsurface environment through appropriate petrophysical relationships these tools offer data suitable for parameterising and constraining models of groundwater flow this is demonstrated using cross borehole radar and resistivity measurements collected during a controlled vadose zone tracer test performed at a field site in the uk sherwood sandstone both methods show clearly the vertical migration of the tracer over a 200 h monitoring period by comparing first and second spatial moments of changes in moisture content predicted from a numerical simulation of vadose zone flow with equivalent statistics from two and three dimensional ert and cross borehole radar profiles the effective hydraulic conductivity is estimated to be approximately 0 4 m d such a value is comparable to field estimates from borehole hydraulic tests carried out in the saturated zone at the field site and provides valuable information that may be utilised to parameterise pollutant transport models of the site

relating relative hydraulic and electrical conductivity in the unsaturated zone numerical modeling was used to generate pore scale structures with different structural properties they were partially saturated according to wetting and drainage regimes using morphological operations for a range of saturations the hydraulic and electrical conductivities of the resulting partially saturated grain packs were numerically computed to produce relative hydraulic conductivity versus saturation and relative electrical conductivity versus saturation curves the relative hydraulic conductivities were then compared to the relative electrical conductivities for the same saturations and it was found that relative hydraulic conductivity could be expressed as relative electrical conductivity to a power law exponent this exponent was not correlated to porosity specific surface area or tortuosity it did change according to whether the soil was wetting or draining however a value of 2 1 reproduced relative hydraulic conductivity from relative electrical conductivity with little added error the effects of surface conduction on the observed power law relationship due to either low fluid electrical conductivity or increased clay content were analyzed the relationship was found to hold for fluid conductivities typical of groundwater and for clay content of less than 5 if the clays were layered perpendicular to electrical flow the relationship breaks down for electrical flow parallel to clay layers which makes the choice of electrode arrangement important in cases where clay may be present this relationship can be used with secondary pressure or saturation data to characterize a soil s hydraulic conductivity curve

cylindrical fdtd analysis of lwd tools through anisotropic dipping layered earth media electrical logging while drilling lwd tools are commonly used in oil and gas exploration to estimate the conductivity resistivity of adjacent earth media in general earth media exhibit anisotropic conductivities this implies that when lwd tools are used for deviated and horizontal drilling the resulting borehole problem may include dipping layered media with dipping beds having full 3 times 3 conductivity tensors to model this problem we describe a 3 d cylindrical finite difference time domain fdtd algorithm extended to fully anisotropic conductive media and implemented with cylindrical perfectly matched layers to mimic open domain problems the 3 d fdtd algorithm is validated against analytical results in simple formations showing good agreement and used to simulate the response of lwd tools through anisotropic dipping beds for various values of anisotropic conductivities and dipping angles

separation of azimuthal effects for new generation resistivity logging tools part i symmetrization antisymmetrization of tensor resistivity measurements and data rotation technique enable separation of the formation response from the tool eccentricity effect in the borehole similar principles of data processing can be applied to tensor measurements acquired by both wireline and logging while drilling tools of the new generation i show how to directly determine the bed boundary positions and the formation anisotropy azimuth and how to perform visual interpretation of raw tool data in the presence of the tool eccentricity i study the tool behavior in conductive water based mud boreholes the situation that requires much more complicated numerical modeling than the case of resistive oil based mud boreholes i show when and how the tool eccentricity effect can be separated from the formation response the separation technique can accelerate and improve existing methods of formation interpretation

younger dryas sea level and meltwater pulse 1b recorded in barbados reef crest coral acropora palmata the younger dryas climate event occurred during the middle of the last deglacial cycle and is marked by an abrupt shift in the north atlantic polar front almost to its former glacial position trending east to west using high precision and high accuracy u th dated barbados reef crest coral acropora palmata we generate a detailed sea level record from 13 9 to 9000 years before present kyr b p and reconstruct the ice volume response to the younger dryas cooling from the mid allerod 13 9 kyr b p to the end of the younger dryas 11 65 kyr b p rates of sea level rise decreased smoothly from 20 mm yr 1 to 4 mm yr 1 culminating in a 400 year slow stand before accelerating into meltwater pulse 1b mwp 1b the mwp 1b event at barbados is better constrained as beginning by 11 45 kyr b p and ending at 11 1 kyr b p during which time sea level rose 14 2 m and rates of sea level rise reached 40 mm yr 1 we propose that mwp 1b is the direct albeit lagged response of the northern hemisphere ice sheets to the rapid warming marking the end of the younger dryas coinciding with rapid warming in the circum north atlantic region and the polar front shift from its zonal to meridional position 11 65 kyr b p as predicted by glaciological models the ice sheet response to rapid north atlantic warming was lagged by 400 years due to the thermal inertia of large ice sheets the regional circum north atlantic younger dryas climate event is elevated to a global response through sea level changes starting with the global slowdown in sea level rise during the younger dryas and culminating with mwp 1b no meltwater pulses are evident at the initiation of the younger dryas climate event as is often speculated

interdecadal variations of the thermohaline circulation in a coupled ocean atmosphere model abstract a fully coupled ocean atmosphere model is shown to have irregular oscillations of the thermohaline circulation in the north atlantic ocean with a time scale of approximately 50 years the irregular oscillation appears to be driven by density anomalies in the sinking region of the thermohaline circulation approximately 52 n to 72 n combined with much smaller density anomalies of opposite sign in the broad rising region the spatial pattern of see surface temperature anomalies associated with this irregular oscillation bears an encouraging resemblance to a pattern of observed interdecadal variability in the north atlantic the anomalies of sea surface temperature induce model surface air temperature anomalies over the northern north atlantic arctic and northwestern europe

the quaternary is here to stay the proposals to drop the name quaternary to extend the neogene period to the present day and to confirm the base of the pleistocene at 1 8 ma are reviewed it is concluded that there is no scientific case for dropping the name quaternary and that an overwhelming volume of evidence points to 2 6 ma as the most appropriate base for the quaternary pleistocene when extensive northern hemisphere mid latitude glaciation occurred under what were essentially similar physical boundary conditions of continents oceans seaways and mountain ranges that characterise and are unique to the quaternary it is desirable that all stratigraphical and geochronological evidence is tied rigorously into the global stratigraphic timescale copyright 2007 john wiley sons ltd

enhanced vertical propagation of storm induced near inertial energy in an eddying ocean channel model the interaction between inertial oscillations generated by a storm and a mesoscale eddy field is studied using a southern ocean channel model it is shown that the leakage of near inertial energy out of the surface layer is strongly enhanced by the presence of the eddies with the anticyclonic eddies acting as a conduit to the deep ocean given the ubiquity of the atmospheric storm tracks a source of near inertial energy for the ocean and regions of strong ocean mesoscale variability we argue that this effect could be important for understanding pathways by which near inertial energy enters the ocean and is ultimately available for mixing

an extensive anoxic event in the triassic of the south china block a pyrite framboid study from dajiang and its implications for the cause s of oxygen depletion water column oxygen deficiency has been considered as a potent driver of the extinction of marine benthos and is a main feature of marine environments in the aftermath of the end permian mass extinction the record of permian triassic anoxia is more complex than previously thought and is seen to vary between different palaeogeographic settings but a full understanding is hindered by a paucity of evidence during the permian triassic interval the south china block was located equatorially with palaeotethys to the north and western panthalassa to the south this specific configuration provides a unique opportunity to compare the extent and duration of oxygen deficiency in palaeotethys and panthalassa under broadly similar climatic conditions sedimentary facies and pyrite framboid size frequency distributions suggest that the oxygen poor conditions became widespread across the shallow marine carbonate platform of the south china block immediately above the permian triassic boundary and mass extinction level oxygen deficiency was most intense at the southern margin of the block where it met panthalassa proposed drivers of the expansion of oxygen minimum zones into platform settings include enhanced terrigenous input and or ocean stratification or alternatively the upwelling of nutrient rich deep ocean water the former mechanisms are theoretically more likely to have operated in the relatively restricted palaeotethys which was surrounded by ancient lands in contrast panthalassa would likely have experienced stronger oceanic circulation and therefore be more susceptible to the effects of upwelling although variations in the record of the south china block anoxic event might reflect local factors the greater intensity of oxygen deficiency and a concomitant larger negative shift in carbonate carbon isotopes on its panthalassan margin point to a key role for upwelling this mechanism was likely a major driver of the permian triassic global oceanic anoxic event which itself was at least partly responsible for the ongoing inhospitable conditions and delayed recovery following the end permian extinction

estimated decadal changes in the north atlantic meridional overturning circulation and heat flux 1993 2004 results from a global 1 model constrained by least squares to a multiplicity of datasets over the interval 1992 2004 are used to describe apparent changes in the north atlantic ocean meridional overturning circulation and associated heat fluxes at 26 n the least squares fit is both stable and adequately close to the data to make the analysis worthwhile changes over the 12 yr are spatially and temporally complex a weak statistically significant trend is found in net north atlantic volume flux above about 1200 m which drops slightly 0 19 0 05 sv yr 1 1s v 10 6 m 3 s 1 but with a corresponding strengthening of the outflow of north atlantic deep water and inflow of abyssal waters the slight associated trend in meridional heat flux is very small and not statistically significant the month to month variability implies that single section determinations of heat and volume flux are subject to serious aliasing errors

wally was right predictive ability of the north atlantic conveyor belt hypothesis for abrupt climate change linked abrupt changes of north atlantic deep water formation north atlantic sea ice extent and widespread climate occurred repeatedly during the last ice age cycle and beyond in response to changing freshwater fluxes and perhaps other causes this paradigm developed and championed especially by w s broecker has repeatedly proven to be successfully predictive as well as explanatory with high confidence much work remains to fully understand what happened and to assess possible implications for the future but the foundations for this work are remarkably solid

numerical modeling of eccentered lwd borehole sensors in dipping and fully anisotropic earth formations logging while drilling lwd borehole sensors are used to provide real time resistivity data of adjacent earth formations for hydrocarbon exploration this allows for a proactive adjustment of the dipping angle and azimuth direction of the drill and hence geosteering capabilities the analysis of borehole eccentricity effects on lwd sensor response in full 3 3 anisotropic earth formations is important for correct data interpretation in deviated or horizontal wells in this paper we present a cylindrical grid finite difference time domain model to tackle this problem the grid is aligned to the sensor axis to avoid staircasing error in the sensor geometry but in general misaligned to the eccentered borehole formation interface a locally conformal discretization is used to compute effective conductivity tensors of partially filled grid cells at those interfaces involving an isotropic medium borehole and a full 3 3 anisotropic medium in general dipped earth formation the numerical model is used to compute the response of eccentered lwd sensors in layered earth formations with anisotropic dipping beds

detecting atlantic moc changes in an ensemble of climate change simulations abstract signal to noise patterns for the meridional overturning circulation moc have been calculated for an ensemble of greenhouse scenario runs the greenhouse forced signal has been defined as the linear trend in ensemble mean moc after year 2000 it consists of an overall decrease and shoaling of the moc with maximum amplitudes of 10 sv sv 106 m3 s 1 per century in each member the internal variability is defined as the anomaly with respect to the ensemble mean signal the interannual variability of the moc is dominated by a monopole with a maximum amplitude of 2 sv at 40 n this variability appears to be driven by the north atlantic oscillation nao mainly through nao induced variations in the wind field the signal to noise ratio was estimated for various time spans all starting in 1950 or later different noise estimates were made both with and without intra annual variability relevant for episodic and continuous monitoring respectively and with and without an estimate of the observa

gravitational potential energy balance for the thermal circulation in a model ocean abstract the gravitational potential energy balance of the thermal circulation in a simple rectangular model basin is diagnosed from numerical experiments based on a mass conserving oceanic general circulation model the vertical mixing coefficient is assumed to be a given constant the model ocean is heated cooled from the upper surface or bottom and the equation of state is linear or nonlinear although the circulation patterns obtained from these cases look rather similar the energetics of the circulation may be very different for cases of differential heating from the bottom with a nonlinear equation of state the circulation is driven by mechanical energy generated by heating from the bottom on the other hand circulation for three other cases is driven by external mechanical energy which is implicitly provided by tidal dissipation and wind stress the major balance of gravitational energy in this model ocean is between the source of energy due to vertical mixing and the conversion from kinetic

oceanographic processes and morphosedimentary products along the iberian margins a new multidisciplinary approach abstract our understanding of bottom currents and associated oceanographic processes e g overflows barotropic tidal currents including intermittent processes e g vertical eddies deep sea storms horizontal vortices internal waves and tsunamis is rapidly evolving many deep water processes remain poorly understood due to limited direct observations but can generate significant depositional and erosional features on both short and long term time scales this paper represents a review work which describes for the first time these oceanographic processes and examines their potential role in the sedimentary features along the iberian continental margins this review explores the implications of the studied processes given their secondary role relative to other factors such as mass transport and turbiditic processes and highlights three major results a contourite depositional and erosional features are ubiquitous along the margins indicating that bottom currents and associated oceanographic processes control the physiography and sedimentation b the position of interfaces between major water masses and their vertical and spatial variation in time specifically appears to exert primary control in determining major morphologic changes along the slope gradient including the contourite terraces development and c contourites deposits exhibit greater variation than the established facies model suggests therefore a consistent facies model however faces substantial challenges in terms of the wide range of oceanographic processes that can influence in their development an integrated interpretation of these oceanographic processes requires an understanding of contourites seafloor features their spatial and temporal evolution and the near bottom flows that form them this approach will synthesize oceanographic data seafloor morphology sediments and seismic images to improve our knowledge of permanent and intermittent processes around iberia and evaluate their conceptual and regional role in the margin s sedimentary evolution given their complexes three dimensional and temporally variable nature integration of these processes into sedimentary oceanographic and climatological frameworks will require a multidisciplinary approach that includes geology physical oceanography paleoceanography and benthic biology

computation of triaxial induction logging tools in layered anisotropic dipping formations in order to interpret the logging data from triaxial induction tools inversion technology has been adopted to make the inversion process reasonably fast a fast forward method must be developed numerical methods such as the finite element method and finite difference method are flexible but slow for inversion purposes in this paper an analytic method is developed to simulate induction tools in deviated wells drilled in anisotropic formations this method can be applied to the triaxial induction tools with transmitting and receiving coils oriented in three mutually perpendicular directions the axis of the tool may intercept a formation with dip azimuthal and orientation angles formulations of the electromagnetic fields generated by these three transmitting coils are derived the derivation uses the coefficient propagator method with the assumption of negligible borehole effect and invasion zones this method overcomes the problem of numerical overflow without compromising the accuracy of the solution because the new induction tool has three transmitting and three receiving coils a total of nine logs are obtained at each logging depth compared with one or two logs in regular induction or logging while drilling tools

a monitoring design for the atlantic meridional overturning circulation 1 current hydrographic data can provide snapshots but no continuous timeseries of the meridional overturning circulation moc using output from two eddy permitting numerical ocean models we test the feasibility of a monitoring system for the moc in the north atlantic the results suggest that a relatively simple arrangement using moorings placed across a longitude depth section and the zonal wind stress is able to capture most of the moc strength and vertical structure as a function of time being closely related to the transport of energy to the north atlantic measuring the moc would open the prospect of having continuous information about a key element of northern hemisphere climate

electromagnetic logging technique based on borehole radar an electromagnetic logging technique based on borehole radar is introduced in this paper the tool consists of one transmitter and two receivers which can be used to cancel the effect of the antenna characteristics by taking the ratio of two receiver signals since receiver signals measured in the time domain can be converted into the frequency domain by fourier transformation the amplitude ratio and the phase difference between two receiver signals in a wide frequency band are obtainable the response of the tool to different formations is investigated and the algorithm that converts the amplitude and the phase information to the conductivity and the relative permittivity of the surrounding medium is given by a three dimensional finite difference time domain the effect of the borehole on measurement and the response of the tool to a formation interface are simulated and analyzed numerically the validity of this technique is confirmed by experiment this technique can be applied to detect physical properties including the conductivity and the relative permittivity of the surrounding medium and the locations of the fractures intersecting the borehole

freshwater teleconnections and ocean thermohaline circulation 1 asymmetry of the atlantic and pacific sea surface salinity sss is recognized as an important element of the global ocean thermohaline circulation however a threshold of such asymmetry that may trigger a true global deep ocean conveyor has not yet been examined a combined effect of the atlantic pacific and the southern ocean surface salinity asymmetries also has not yet been clearly shown we address these issues and conclude that atlantic pacific sss asymmetry is one of the most critical elements for maintaining the global ocean conveyor our experiments suggest albeit preliminary that high latitudinal freshwater impacts as a mechanism of altering global ocean thermohaline circulation may be less effective than inter basin freshwater communications

slowing of the atlantic meridional overturning circulation at 25 n the atlantic meridional overturning circulation carries warm upper waters into far northern latitudes and returns cold deep waters southward across the equator its heat transport makes a substantial contribution to the moderate climate of maritime and continental europe and any slowdown in the overturning circulation would have profound implications for climate change a transatlantic section along latitude 25 n has been used as a baseline for estimating the overturning circulation and associated heat transport here we analyse a new 25 n transatlantic section and compare it with four previous sections taken over the past five decades the comparison suggests that the atlantic meridional overturning circulation has slowed by about 30 per cent between 1957 and 2004 whereas the northward transport in the gulf stream across 25 n has remained nearly constant the slowing is evident both in a 50 per cent larger southward moving mid ocean recirculation of thermocline waters and also in a 50 per cent decrease in the southward transport of lower north atlantic deep water between 3 000 and 5 000 m in depth in 2004 more of the northward gulf stream flow was recirculating back southward in the thermocline within the subtropical gyre and less was returning southward at depth

analysis of eccentered dipole antenna for borehole radar a dipole antenna in a borehole may be placed away from the center of the borehole and this eccentricity produces additional complicated electromagnetic fields which may influence borehole radar signals in this paper we analyze an eccentric dipole antenna in a borehole for borehole radars our approach is an extended version of the pseudoanalytical formulation that was previously applied for analyzing an induction logging tool and a dielectric logging tool the proposed equations are suitable for modeling the finite dipole antenna utilizing a method of moments the eccentricity of the radar sonde has two consequences first it modifies the antenna characteristics such as its impedance and second it changes the electromagnetic field inside the borehole owing to the change of the structure of the cylindrical layers these two changes are evaluated by the proposed algorithm and two types of experiments the first one is a measurement of the input impedance of a monopole antenna which is in cylindrical layers on a ground plane in air the second one is about the transmission between two antennas one of which is eccentered in cylindrical layers this experiment was done in granite at a field test site and on a ground plane in air in the field experiments we controlled the position of the radar sonde in a borehole and made the antenna eccentered artificially we found that a 4 cm displacement resulted in changes of 4 db in amplitude and 4 ns in time delay comparing the experimental and calculated data obtained by the present method shows the validity of the proposed analytical formulation

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

decadal changes in meridional overturning circulation in the east sea sea of japan abstractmeridional overturning circulation moc is vital to distributing heat freshwater and dissolved matter in semi enclosed deep marginal seas such as the east sea es as our understanding

an efficient solution for the response of electrical well logging tools in a complex environment a symmetrical form of the solution for an electrical source in a multibed well logging environment is derived the method uses local reflection and transmission operators of a single bed boundary and a general recursive algorithm to derive generalized reflection and transmission operators using this method the computation time scales linearly as n where n is the number of beds in the environment a computer program was developed to implement the solution the program is robust and generates accurate results from 20 khz to 25 mhz

improved extraction of hydrologic information from geophysical data through coupled hydrogeophysical inversion 1 there is increasing interest in the use of multiple measurement types including indirect geophysical methods to constrain hydrologic interpretations to date most examples integrating geophysical measurements in hydrology have followed a three step uncoupled inverse approach this approach begins with independent geophysical inversion to infer the spatial and or temporal distribution of a geophysical property e g electrical conductivity the geophysical property is then converted to a hydrologic property e g water content through a petrophysical relation the inferred hydrologic property is then used either independently or together with direct hydrologic observations to constrain a hydrologic inversion we present an alternative approach coupled inversion which relies on direct coupling of hydrologic models and geophysical models during inversion we compare the abilities of coupled and uncoupled inversion using a synthetic example where surface based electrical conductivity surveys are used to monitor one dimensional infiltration and redistribution through this illustrative example we show that the coupled approach can provide significant reductions in uncertainty for hydrologic properties and associated predictions if the underlying model is a faithful representation of the hydrologic processes however if the hydrologic model exhibits structural errors the coupled inversion may not improve the hydrologic interpretation despite this limitation our results support the use of coupled hydrogeophysical inversion both for the direct benefits of reduced errors during inversion and because of the secondary benefits that accrue because of the extensive communication and sharing of data necessary to produce a coupled model which will likely lead to more thoughtful use of geophysical data in hydrologic studies

evaluation of eccentered electrode type resistivity logging in anisotropic geological formations with a matrix method a robust and succinct matrix based method is developed to simulate the response of eccentered resistivity logging tools in anisotropic geological formations this is done by first deriving the solution of the state vector describing the potential and the current component along the radial direction in a cylindrical system rescaled cylindrical eigenfunctions are employed to overcome the poor scaling inherent to the canonical cylindrical functions for very small or very large arguments a levin type method for approximating integrals with rapidly oscillatory functions is introduced to effectively perform the numerical integrals the influence of both the translational and rotational eccentricities of the logging tool within the borehole surrounded by an anisotropic formation is studied based on numerical results provided by the present matrix method we found that neither translational nor rotational eccentricity can be neglected especially in low resistive or anisotropic geological formations

the role of bottom pressure torques on the interior pathways of north atlantic deep water abstractfour versions of the same global climate model one with horizontal resolution of 1 8 3 6 and three with 0 2 0 4 are employed to evaluate the role of ocean bottom topography and viscosity on the spatial structure of the deep circulation this study is motivated by several recent observational studies that find that subsurface floats injected near the western boundary of the labrador sea most often do not continuously follow the deep western boundary current dwbc in contrast to the traditional view that the deep water formed in the north atlantic predominantly follows the dwbc it is found that with imposed large viscosity values the model reproduces the traditional view however as viscosity is reduced and the model bathymetry resolution increased much of the north atlantic deep water nadw separates from the western boundary and enters the low latitude atlantic via interior pathways distinct from the dwbc it is shown that bottom pressure torques play an important role in maintai

changes in moc and gyre induced atlantic ocean heat transport anthropogenic change of the atlantic meridional ocean heat transport aoht is diagnosed from a large ensemble of climate simulations over the period 1940 2080 as well as its relation to changes in the meridional overturning circulation moc and the gyre circulation in the atlantic internal variability in aoht is closely associated with moc variability the anthropogenic change in aoht however does not follow the forced decrease in the moc thermohaline changes in the intermediate and deep water masses that are formed in the subpolar gyre cause the vertical temperature gradient near the western boundary to increase as a result the heat transport by the baroclinic gyre component largely compensates the decreased heat transport by the moc

three dimensional finite volume analysis of directional resistivity logging sensors a finite volume fv technique is introduced to model directional resistivity logging sensors that employ tilted coil antennas in 3 d anisotropic earth formations the algorithm is based on a coupled scalar vector potential formulation on a 3 d cylindrical staggered grid the choice of discretization enforces the correct continuity equations across material boundaries avoids spurious modes and leads to a better conditioned system matrix in order to model situations where the sensor tool axis does not coincide with the borehole axis eccentered tools a locally conformal fv scheme is also implemented the proposed fv formulation is validated against pseudoanalytical solutions in cases where the latter is applicable showing very good agreement and utilized to investigate the effects of the drill collar borehole anisotropy and azimuthal rotations on the response of directional resistivity sensors

greenland antarctic phase relations and millennial time scale climate fluctuations in the greenland ice cores abstract the greenland grip gisp2 and antarctic byrd ice cores are examined in the frequency domain with the data synchronized using common methane variations using conventional time series analysis a simple picture emerges there is low frequency periods longer than about 10 kyr coherence between the two records consistent with a simple time delay antarctica leading by 1 2 kyr two geographical data points are however inadequate to infer causality from the south to north time lag at higher frequencies in the millennial band there is no measurable average relationship between the records and they appear to represent different processes with a regional character a serious question concerns the extent to which the greenland cores reflect tracer concentration change without corresponding abrupt climate change the large abrupt shifts in ice 18 o can be rationalized as owing to wind trajectory shifts perhaps of rather modest size many different physical phenomena probably do however contribute to the record as a function of time and time scale

reconstructing paleosalinity from δ18o coupled model simulations of the last glacial maximum last interglacial and late holocene reconstructions of salinity are used to diagnose changes in the hydrological cycle and ocean circulation a widely used method of determining past salinity uses oxygen isotope ow residuals after the extraction of the global ice volume and temperature components this method relies on a constant relationship between ow and salinity throughout time here we use the isotope enabled fully coupled general circulation model gcm hadcm3 to test the application of spatially and time independent relationships in the reconstruction of past ocean salinity simulations of the late holocene lh last glacial maximum lgm and last interglacial lig climates are performed and benchmarked against existing compilations of stable oxygen isotopes in carbonates oc which primarily reflect ow and temperature we find that hadcm3 produces an accurate representation of the surface ocean oc distribution for the lh and lgm our simulations show considerable variability in spatial and temporal ow salinity relationships spatial gradients are generally shallower but within 50 of the actual simulated lh to lgm and lh to lig temporal gradients and temporal gradients calculated from multi decadal variability are generally shallower than both spatial and actual simulated gradients the largest sources of uncertainty in salinity reconstructions are found to be caused by changes in regional freshwater budgets ocean circulation and sea ice regimes these can cause errors in salinity estimates exceeding 4 psu our results suggest that paleosalinity reconstructions in the south atlantic indian and tropical pacific oceans should be most robust since these regions exhibit relatively constant ow salinity relationships across spatial and temporal scales largest uncertainties will affect north atlantic and high latitude paleosalinity reconstructions finally the results show that it is difficult to generate reliable salinity estimates for regions of dynamic oceanography such as the north atlantic without additional constraints

what drives heat transport in the atlantic sensitivity to mechanical energy supply and buoyancy forcing in the southern ocean 1 climate model simulations are used to demonstrate that there is not a simple link between the mechanical energy supply and heat transport in the atlantic setting the flux of momentum into the ocean to zero between 35 60 s reduces the net mechanical energy input by more than a factor of two without much effect on the heat transport in the atlantic the strong westerly winds in the southern ocean are found to be more important for the circulation of bottom water and for localizing the upwelling of deep water around antarctica furthermore it is illustrated that the hydrological cycle plays a significant role in maintaining the global ocean circulation and the associated heat transport in the atlantic given sufficient mechanical energy to support the diapycnal mixing a reduction of the meridional moisture transport to the southern ocean by a factor of two reduces heat transport in the atlantic by about the same factor

abrupt climate change an alternative view hypotheses and inferences concerning the nature of abrupt climate change exemplified by the dansgaard oeschger d o events are reviewed there is little concrete evidence that these events are more than a regional greenland phenomenon the partial coherence of ice core y 18 o and ch4 is a possible exception claims however of d o presence in most remote locations cannot be distinguished from the hypothesis that many regions are just exhibiting temporal variability in climate proxies with approximately similar frequency content further suggestions that d o events in greenland are generated by shifts in the north atlantic ocean circulation seem highly implausible given the weak contribution of the high latitude ocean to the meridional flux of heat a more likely scenario is that changes in the ocean circulation are a consequence of wind shifts the disappearance of d o events in the holocene coincides with the disappearance also of the laurentide and fennoscandian ice sheets it is thus suggested that d o events are a consequence of interactions of the windfield with the continental ice sheets and that better understanding of the wind field in the glacial periods is the highest priority wind fields are capable of great volatility and very rapid global scale teleconnections and they are efficient generators of oceanic circulation changes and more speculatively of multiple states relative to great ice sheets connection of d o events to the possibility of modern abrupt climate change rests on a very weak chain of assumptions

an adjoint analysis of the meridional overturning circulation in an ocean model abstract using the adjoint of a fully three dimensional primitive equation ocean model in an idealized geometry spatial variations in the sensitivity to surface boundary forcing of the meridional overturning circulation s strength are studied steady state sensitivities to diapycnal mixing wind stress freshwater and heat forcing are examined three different commonly used boundary forcing scenarios are studied both with and without wind forcing almost identical circulation is achieved in each scenario but the sensitivity patterns show major quantitative and qualitative differences sensitivities to surface forcing and diapycnal mixing are substantially larger under mixed boundary conditions in which fluxes of freshwater and heat are supplemented by a temperature relaxation term or under flux boundary conditions in which climatological fluxes alone drive the circulation than under restoring boundary conditions the sensitivity pattern to diapycnal mixing which peaks in the tropics is similar

ocean gyre circulation changes associated with the north atlantic oscillation abstract observational evidence is presented for interannual to interdecadal variability in the intensity of the north atlantic gyre circulation related to the atmospheric north atlantic oscillation nao patterns a two point baroclinic pressure difference between the subtropical and subpolar gyre centers an oceanic analogue to the much used sea level pressure slp based atmospheric nao indices is constructed from time series of potential energy anomaly pea derived from hydrographic measurements in the labrador basin and at station s near bermuda representing the upper 2000 db eastward baroclinic mass transport between the two centers the transport index indicates a gulf stream and north atlantic current that gradually weakened during the low nao period of the 1960s and then intensified in the subsequent 25 years of persistently high nao to a record peak in the 1990s the peak to peak amplitude difference was 15 20 megatons per second mt s 1 with a 43 yr mean of about 60 mt s 1 a change of 25 33

a theory for the surface atlantic response to thermohaline variability abstract the response of the upper warm limb of the thermohaline circulation in the north atlantic to a rapid change in deep water formation at high latitudes is investigated using a reduced gravity ocean model changes in deep water formation rate initiate kelvin waves that propagate along the western boundary to the equator on a timescale of months the response in the north atlantic is therefore rapid the southern hemisphere response is much slower limited by a mechanism here termed the ldquo uatorial buffer since to leading order the flow is in geostrophic balance the pressure anomaly decreases in magnitude as the kelvin wave moves equatorward where the coriolis parameter is lower together with the lack of sustained pressure gradients along the eastern boundary this limits the size of the pressure field response in the southern hemisphere interior adjustment is by the westward propagation of rossby waves but only a small fraction of the change in thermohaline circulation strength is commun

theory of induction sonde in dipping beds the analysis necessary for the computation of the response of an induction sonde in dipping beds is developed the boundary value problem solved is for a bed of uniform thickness surrounded by two infinitely thick shoulder beds the source is a magnetic dipole oriented in an arbitrary direction and located in any of the three media the resulting electromagnetic fields in all three media are obtained from these fields induction logs are calculated for a focused induction sonde 6ff40 passing through a dipping bed under the assumptions of negligible borehole effect and no invasion the analysis is also used to obtain correction charts for dipping beds

the variability of the atlantic meridional overturning circulation the north atlantic oscillation and the el nino southern oscillation in the bergen climate model abstract the link between the interannual to interdecadal variability of the atlantic meridional overturning circulation amoc and the atmospheric forcing is investigated using 200 yr of a control simulation of the bergen climate model where the mean circulation cell is rather realistic as is also the location of deep convection in the northern north atlantic the amoc variability has a slightly red frequency spectrum and is primarily forced by the atmosphere the maximum value of the amoc is mostly sensitive to the deep convection in the irminger sea which it lags by about 5 yr the latter is mostly forced by a succession of atmospheric patterns that induce anomalous northerly winds over the area the impact of the north atlantic oscillation on deep convection in the labrador and greenland seas is represented realistically but its influence on the amoc is limited to the interannual time scale and is primarily associated with wind forcing the tropical pacific shows a strong variability in the model

the arctic atlantic thermohaline circulation abstractthe atlantic ocean s thermohaline circulation is an important modulator of global climate its northern branch extends through the nordic seas to the cold arctic a region that appears to be particularly influenced by climate change a thermohaline circulation is fundamentally concerned with two degrees of freedom this is in particular the case for the inflow of warm and saline atlantic water through the nordic seas toward the arctic that is balanced by two branches of outflow the authors present an analytical model rooted in observations that constrains the strength and structure of this arctic atlantic thermohaline circulation it is found maybe surprisingly that the strength of atlantic inflow is relatively insensitive to anomalous freshwater input it mainly reflects changes in northern heat loss freshwater anomalies are predominantly balanced by the inflow s partition into estuarine and overturning circulation with southward polar outflow in the surface and dense overflow at depth res

seasonal overturning of the labrador sea as observed by argo floats abstractargo floats are used to investigate labrador sea overturning and its variability on seasonal time scales this is the first application of argo floats to estimate overturning in a deep water formation region in the north atlantic unlike hydrographic measurements which are typically confined to the summer season floats offer the advantage of collecting data in all seasons seasonal composite potential density and absolute geostrophic velocity sections across the mouth of the labrador sea assembled from float profiles and trajectories at 1000 m are used to calculate the horizontal and overturning circulations the overturning exhibits a pronounced seasonal cycle in depth space the overturning doubles throughout the course of the year and in density space it triples the largest overturning 1 2 sv 1 sv 106 m3 s 1 in depth space and 3 9 sv in density space occurs in spring and corresponds to the outflow of recently formed labrador sea water the overturning decreases through summer and reac