statistical properties of the surface velocity field in the northern gulf of mexico sampled by glad drifters the grand lagrangian deployment glad used multiscale sampling and gps technology to observe time series of drifter positions with initial drifter separation of o 100 m to o 10 km and nominal 5 min sampling during the summer and fall of 2012 in the northern gulf of mexico histograms of the velocity field and its statistical parameters are non gaussian most are multimodal the dominant periods for the surface velocity field are 1 2 days due to inertial oscillations tides and the sea breeze 5 6 days due to wind forcing and submesoscale eddies 9 10 days and two weeks or longer periods due to wind forcing and mesoscale variability including the period of eddy rotation the temporal e folding scales of a fitted drifter velocity autocorrelation function are bimodal with time scales 0 25 0 50 days and 0 9 1 4 days and are the same order as the temporal e folding scales of observed winds from nearby moored national data buoy center stations the lagrangian integral time scales increase from coastal values of 8 h to offshore values of approximately 2 days with peak values of 3 4 days the velocity variance is large o 1 m2 s2 the surface velocity statistics are more anisotropic and increased dispersion is observed at flow bifurcations horizontal diffusivity estimates are o 103 m2 s in coastal regions with weaker flow to o 105 m2 s in flow bifurcations a strong jet and during the passage of hurricane isaac the gulf of mexico surface velocity statistics sampled by the glad drifters are a strong function of the feature sampled topography and wind forcing

holocene oceanographic changes in sw labrador sea off newfoundland benthic foraminiferal assemblages supported by selected geochemical data from three marine sediment cores collected in placentia bay se newfoundland are used to construct an 13 000 year long rec

ocean forcing of the greenland ice sheet calving fronts and patterns of retreat identified by automatic satellite monitoring of eastern outlet glaciers 1 we have developed an automatic method to identify changes in the position of calving glacier margins using daily modis imagery application of the method to 32 ocean terminating glaciers in east greenland produced 26 802 margin positions for a 10 year long period 2000 2009 we report these high resolution data and show that the glaciers exhibit seasonal cycles with magnitudes of advance and retreat proportional to glacier width despite similar seasonality there is a distinct difference between the interannual trends of calving front positions north and south of 69 n all glaciers above this latitude showed very limited or no change when seasonality was excluded while glaciers south of 69 n retreated significantly between 2001 and 2005 2 3 km on average approximately 26 of the retreat of southern glaciers was regained by readvance from 2005 to 2009 to explain the latitudinal boundary of glacier dynamics we review basic climatic factors including summer and winter atmospheric forcing sea ice conditions and ocean temperature we conclude that the southern retreats were strongly influenced by warm oceanic conditions associated with increased transport of subtropical waters to the irminger sea and to fjords and coastal regions south of 69 n northern glaciers remained stable despite significant increase in runoff in this region because fjords at latitudes higher than 69 n are less exposed to subtropical waters the southern retreats illustrate sensitive behavior of calving glaciers and we hypothesize that the calving fronts retreated because they were exposed to rapid ice front melting

quantifying upper ocean turbulence driven by surface waves 1 nearly all operational ocean models use air sea fluxes and the ocean shear and stratification to estimate upper ocean boundary layer mixing rates this approach implicitly parameterizes surface wave effects in terms of these inputs here we test this assumption using parallel experiments in a lake with small waves and in the open ocean with much bigger waves under the same wind stress and adjusting for buoyancy flux we find the mixed layer average turbulent vertical kinetic energy in the open ocean typically twice that in the lake the increase is consistent with models of langmuir turbulence in which the wave stokes drift and not wave breaking is the dominant mechanism by which waves energize turbulence in the mixed layer applying these same theories globally we find enhanced mixing and deeper mixed layers resulting from the inclusion of langmuir turbulence in the boundary layer parameterization especially in the southern ocean

upper ocean variability between iceland and newfoundland 1993 1998 we investigate the variability of upper ocean temperature and surface salinity between iceland and newfoundland along world ocean circulation experiment line ax2 in 1993 1998 north of 54 n as well as close to newfoundland deviations from the seasonal cycle indicate upper ocean warming from 1994 to 1998 with largest anomalous warming during late 1995 early 1996 and during the winter 1997 1998 north of 54 n surface salinity increases after mid 1996 the winter of 1995 1996 is the first winter of weak westerlies after more than 20 years of strong westerly conditions in the subarctic gyre and the ocean loses less heat during that winter than during a normal year the magnitude of upper ocean heat content change is at least twice as large as what results from the change in air sea fluxes which indicates a complementary contribution to heat content change by advection altimetric sea level data indicate also an increase of sea level of the order of 6 5 cm during that year out of which more than 4 cm is contributed by the steric change associated with the temperature increase a principal component analysis of the sea level data suggests that the increase sensed along line ax2 west of the reykjanes ridge is found in most of the subpolar gyre although to a lesser extent in most other areas

the anaerobic oxidation of methane and sulfate reduction in sediments from gulf of mexico cold seeps we determined the geochemical characteristics of sediments and measured rates of the anaerobic oxidation of methane aom and sulfate reduction sr in samples collected near thermogenic structure ii gas hydrate mounds and in areas lacking hydrates along the continental slope in the gulf of mexico we used radiotracer c 14 and s 35 techniques to determine rates of aom and sr over depth in sediment cores abundant mats of white and orange beggiatoa spp were common in areas of active seepage and these sediments were enriched in hydrogen sulfide and methane in cores collected from areas without beggiatoa or hydrate concentrations of redox metabolites showed little variation over depth and these sites were inferred to be areas of low seepage integrated aom rates were low in beggiatoa free cores 0 05 mmol m 2 day 1 and averaged 2 8 4 6 mmol m 2 day 1 in seep cores that contained beggiatoa or gas hydrate integrated sr rates were also low in beggiatoa free cores 1 mmol m 2 day 1 and averaged 54 94 mmol m 2 day 1 in cores with beggiatoa or hydrate rates of sr generally exceeded rates of aom and the two processes were loosely coupled suggesting that the majority of sr at gulf of mexico hydrocarbon seep sites is likely fueled by the oxidation of other organic matter possibly other hydrocarbons and oil rather than by aom

cold filamentary intensification and oceanic surface convergence lines 1 the reflectance images of the oceanic surface are full of surfactant lines created by surface velocity convergences with typical line spacings of 0 1 10 km i e in the submesoscale range here we propose a dynamical explanation by the process of filamentary intensification that shrinks the transverse scale of rectilinear surface temperature extrema at a super exponential rate by the action of horizontal deformation flows associated with mesoscale eddies this process is analogous to deformation induced frontogenesis with sharpening temperature gradients accelerated by its ageostrophic secondary circulation in the particular case of cold filaments the shrinking rate surface convergence and downwelling are especially strong because of the configuration of ageostrophic acceleration this behavior is demonstrated theoretically with idealized two dimensional solutions and illustrated in a realistic regional circulation simulation near peru

variability of the overflow water transport in the western subpolar north atlantic 1950 97 abstract one of the major topics in current field research is the question of whether or to what extent the north atlantic ocean is subject to changes in water mass transports and how they are related to atmospheric phenomena like the north atlantic oscillation nao bottle and ctd data from the 1950s to 1990s are presented to reconstruct spatially and temporally the baroclinic contribution to the deep water transports in the western subpolar north atlantic the focus is on the two densest components of north atlantic deep water the gibbs fracture zone water gfzw and the denmark strait overflow water dsow direct velocity measurements in the considered time period are sparse for this reason it was decided to calculate the geostrophic velocity relative to 1400 dbar this level is located in the weakly stratified labrador sea water the combined baroclinic volume transport of gfzw and dsow during the early 1990s was about 5 sv sv 106 m3 s 1 in the irminger sea and 7 8 sv in the labrador sea nea

numerical simulations of rotating bubble plumes in stratified environments the effects of system rotation on the turbulent dynamics of bubble plumes evolving in stratified environments are numerically investigated by considering variations in both the system rotation rate and the gas phase slip velocity the turbulent dispersion of a passive scalar injected at the source of a buoyant plume is strongly altered by the rotation of the system and the nature of the buoyancy at the source when the plume is driven by the density defect associated with the presence of slipping gas bubbles the location of the main lateral intrusion decreases with respect to the single phase case with identical inlet volume momentum and buoyancy fluxes enhanced downdrafts of carrier phase fluid result in increased turbulent mixing and short circuiting of detraining plume water that elevate near field effluent concentrations similarly rotation fundamentally alters dynamic balances within the plume leading to the encroachment of the trapping height on the source and an increase in turbulent dispersion in the near field system rotation even at modest rossby numbers produces a sustained robust anticyclonic precession of the plume core the effects of rotation and the presence of bubbles are cumulative the vertical encroachment of the primary intrusion and the overall dispersion of effluent are greatest at smallest rossby numbers and largest slip velocities the main characteristic feature in rotating single phase plumes namely the robust anticyclonic precession persists in bubble plumes analysis of the momentum budgets reveal that the mechanism responsible for the organized precession i e the establishment of an unstable vertical hydrostatic equilibrium related to radial cyclostrophic balance does not differ from the single phase case

transience and persistence of natural hydrocarbon seepage in mississippi canyon gulf of mexico analysis of the magnitude of oil discharged from natural hydrocarbon seeps can improve understanding of the carbon cycle and the gulf of mexico gom ecosystem with use of a large archive of remote sensing data in combination with geophysical and multibeam data we identified mapped and characterized natural hydrocarbon seeps in the macondo prospect region near the wreck site of the drill rig deepwater horizon dwh satellite image processing and the cluster analysis revealed locations of previously undetected seep zones including duplicate detections a total of 562 individual gas plumes were also observed in multibeam surveys in total sar imagery confirmed 52 oil producing seep zones in the study area in almost all cases gas plumes were associated with oil producing seep zones the cluster of seeps in the vicinity of lease block mc302 appeared to host the most persistent and prolific oil vents oil slicks and gas plumes observed over the dwh site were consistent with discharges of residual oil from the wreckage in contrast with highly persistent oil seeps observed in the green canyon and garden banks lease areas the seeps in the vicinity of macondo prospect were intermittent the difference in the number of seeps and the quantity of surface oil detected in green canyon was almost two orders of magnitude greater than in mississippi canyon

north atlantic climate response to lake agassiz drainage at coarse and ocean eddy permitting resolutions abstractthe north atlantic climate response to the catastrophic drainage of proglacial lake agassiz into the labrador sea is analyzed with coarse and ocean eddy permitting versions of a global coupled climate model the north atlantic climate response is qualitatively consistent in that a large scale cooling is simulated regardless of the model resolution or region of freshwater discharge however the magnitude and duration of the north atlantic climate response is found to be sensitive to model resolution and the location of freshwater forcing in particular the long term entrainment of freshwater along the boundary at higher resolution and its gradual partially eddy driven escape into the interior leads to low salinity anomalies persisting in the subpolar atlantic for decades longer as a result the maximum decline of the atlantic meridional overturning circulation amoc and the ocean meridional heat transport mht is amplified by about a factor of 2 at ocean eddy permitting resolution and the re

formation of rapidly sinking oil associated marine snow abstract significant amounts of oil accumulated at the sea surface and in a subsurface plume during the deepwater horizon dwh spill in the gulf of mexico gom in 2010 a substantial fraction of this oil was removed from the marine environment by mechanical recovery or burning or it reached shorelines whereas another fraction remained within the marine environment where it dispersed chemically or naturally emulsified or sedimented after the dwh accident the sedimentation of hydrocarbons to the seafloor via rapidly sinking oil associated marine snow has become a focus of attention and it has been hypothesized that marine snow formation significantly impacted the distribution of the oil from the dwh spill here roller table experiments are presented that investigated the conditions inducing the formation of oil associated marine snow focusing especially on the effects of oil type photochemical aging of oil and the presence of phytoplankton or dispersant large mucus rich marine snow termed microbial marine snow formed in treatments incubated with the oil that had accumulated at the sea surface this bacteria mediated formation of up to cm sized marine snow in the absence of particles 1 m represents a unique formation pathway different from that of the physical coagulation of particles microbial marine snow albeit smaller also formed in the presence of crude oil that had been aged for 3 weeks in sunlight but no particles formed in the presence of unaltered crude the dispersant corexit 9500a corexit oil ratio 1 100 impeded the formation of microbial marine snow requiring a re evaluation of the benefits and detriments of corexit 9500a as a mediating measure phytoplankton aggregates also incorporated fossil carbon providing an alternate pathway for the formation of oil associated marine snow the ubiquitous formation and rapid sedimentation of oil rich marine snow can explain the high accumulation rate of flocculent material at the seafloor and on corals observed after the dwh spill these results may raise awareness that oil spill response and assessment need to include sedimentation of hydrocarbons via marine snow as a significant distribution mechanism and may guide future modeling efforts and budget calculations

remote sensing evaluation of geophysical anomaly sites in the outer continental slope northern gulf of mexico abstract synthetic aperture radar sar images obtained from satellites are a reliable tool for localizing natural hydrocarbon seeps for this study we used the texture classifier neural network algorithm tcnna to interpret sar data from the radarsat satellite and a geostatistical clustering analysis to compare seeps detected in 579 sar images covering the northern gulf of mexico gom geostatistical analysis results indicate that in a typical active seep formation oil vents would be found within a seep formation 2 5 km in diameter repeated observations of slicks at a given seep formation indicate that advection of rising oil in the water column causes an offset from the vent depending on water depth at 500 m the radial offset is up to 1400 m at 2000 m it is up to 3270 m observations with submersibles showed that in 100 of the cases the calculated seep formations that are matched with active oil seeps correspond to anomalies interpreted from surface amplitude maps and migration pathways in the seismic data however episodically larger releases from persistent seeps occurred and also some other seep formations showed intermittent releases our analysis indicates that active oil seeps detected with sar represent a subset of the total array of geophysical features generated by hydrocarbon migration on the northern continental slope of the gulf of mexico

wind driven currents in the tropical pacific abstract an analysis is made of the ensemble mean ageostrophic near surface circulation measured by 1503 lagrangian drifters drogued to 15 m depth in the tropical pacific between 1987 and 1994 it was found that the physical model of the wind driven currents in a weakly stratified upper layer in which the richardson number remains near unity accounts for 40 of the vector variance of the observations in such a model the amplitude of the current is proportional to u n f 1 2 and the depth scale of the wind driven layer is proportional to u n f 1 2 when the ageostrophic currents at 15 m depth are binned by the scaled ekman depth a net rotation of 0 87 radians was observed through the layer depth these measurements suggest that the vertical austausch coefficient of the upper ocean is proportional to u2 n ekman proposed such a model based on two reports of wind driven currents in 1905 at widely separated latitudes

directly measured mid depth circulation in the northeastern north atlantic ocean the circulation of water masses in the northeastern north atlantic ocean has a strong influence on global climate owing to the northward transport of warm subtropical water to high latitudes but the ocean circulation at depths below the reach of satellite observations is difficult to measure and only recently have comprehensive direct observations of whole ocean basins been possible here we present quantitative maps of the absolute velocities at two levels in the northeastern north atlantic as obtained from acoustically tracked floats we find that most of the mean flow transported northward by the gulf stream system at the thermocline level about 600 m depth remains within the subpolar region and only relatively little enters the rockall trough or the nordic seas contrary to previous work our data indicate that warm saline water from the mediterranean sea reaches the high latitudes through a combination of narrow slope currents and mixing processes at both depths under investigation currents cross the mid atlantic ridge preferentially over deep gaps in the ridge demonstrating that sea floor topography can constrain even upper ocean circulation patterns

influence of the north atlantic sst on the atmospheric circulation using the monthly coads dataset and nmc ncar archives we show that significant anomalies of the atmospheric circulation are related to previous sst anomalies in the north atlantic a signal over the northwest labrador sea in late spring is associated with the dominant mode of sst variability during the preceeding winter it is more clearly seen in the mid troposhere than at sea level and appears to be related to the anomalous surface heat exchanges that slowly damp the sst anomalies in addition a nao like signal in early winter is associated with sst anomalies east of newfoundland and in the eastern subtropical north atlantic during the preceeding summer

decadal climate oscillations in the arctic a new feedback loop for atmosphere ice ocean interactions a combined complex empirical orthogonal function analysis of 40 years of annual sea ice concentration sic and winter sea level pressure slp data reveals the existence of an approximately 10 year climate cycle in the arctic and subarctic the cycle is characterized by a clockwise propagating signal in the sic anomalies and a standing oscillation in the slp anomalies the latter being linked to a fluctuation between the two phases of the north atlantic oscillation to describe the formation and evolution of the sic and slp anomalies associated with the cycle a simple feedback loop is proposed

interannual thermohaline changes in the northern north atlantic 1991 1996 abstract in the period 1991 1996 the woce hydrographic section a1e ar7e between greenland and ireland was repeated five times the observed thermohaline changes altered the baroclinic structure along the eastern margin of the subpolar gyre significantly between june 1995 and august 1996 an overall increase of the temperature and thickness and a decrease of the density of the subpolar mode water spmw layer were observed accompanied by an increase of its salinity east of the reykjanes ridge and a decrease of its salinity in the irminger sea the changes were most pronounced in the iceland basin where the subarctic front retreated westwards coinciding with a strong weakening of the westerlies as determined by the north atlantic oscillation they are related to a local reduction of the ekman upwelling and the ocean to atmosphere heat flux on the one hand and to the advection of anomalies from the subtropics on the other hand the eastward spreading of the different labrador sea water lsw vintages led to a corresponding cooling of the lsw in the irminger sea and in the iceland basin in the period 1991 1996 the renewal of the lsw in the rockall trough occurred more sporadically indicating that the north atlantic current nac impedes the southward spreading of lsw in the eastern atlantic the changes in 1996 seem to have also counteracted this spreading

rock fluidization during peak ring formation of large impact structures large meteorite impact structures on the terrestrial bodies of the solar system contain pronounced topographic rings which emerged from uplifted target crustal rocks within minutes of impact to flow rapidly over large distances these target rocks must have weakened drastically but they subsequently regained sufficient strength to build and sustain topographic rings the mechanisms of rock deformation that accomplish such extreme change in mechanical behaviour during cratering are largely unknown and have been debated for decades recent drilling of the approximately 200 km diameter chicxulub impact structure in mexico has produced a record of brittle and viscous deformation within its peak ring rocks here we show how catastrophic rock weakening upon impact is followed by an increase in rock strength that culminated in the formation of the peak ring during cratering the observations point to quasi continuous rock flow and hence acoustic fluidization as the dominant physical process controlling initial cratering followed by increasingly localized faulting

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

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

long term observations of north atlantic current transport at the gateway between western and eastern atlantic in the western north atlantic warm and saline water is brought by the north atlantic current nac from the subtropics into the subpolar gyre four inverted echo sounders with high precision pressure sensors pies were moored between 47 40 n and 52 30 n to study the main pathways of the nac from the western into the eastern basin the array configuration that forms three segments northern central and southern allows partitioning of the nac and some assessment of nac flow paths through the different mid atlantic ridge fracture zones we exploit the correlation between the nac transport measured between 2006 and 2010 and the geostrophic velocity from altimeter data to extend the time series of nac transports to the period from 1992 to 2013 the mean nac transport over the entire 21 years is 27 5 sv consisting of 60 warm water of subtropical origin and 40 subpolar water we did not find a significant trend in the total transport time series but individual segments had opposing trends leading to a more focused nac in the central subsection and decreasing transports in the southern and northern segments the spectral analysis exhibits several significant peaks the two most prominent are around 120 days identified as the time scale of meanders and eddies and at 4 9 years most likely related to the nao transport composites for the years of highest and lowest nao indices showed a significantly higher transport 2 9 sv during strong nao years mainly in the southern segment

simulated variability of the circulation in the north atlantic from 1953 to 2003 abstract the variability of the circulation in the north atlantic and its link with atmospheric variability are investigated in a realistic hindcast simulation from 1953 to 2003 the interannual to decadal variability of the subpolar gyre circulation and the meridional overturning circulation moc is mostly influenced by the north atlantic oscillation nao both circulations intensified from the early 1970s to the mid 1990s and then decreased the monthly variability of both circulations reflects the fast barotropic adjustment to nao related ekman pumping anomalies while the interannual to decadal variability is due to the baroclinic adjustment to ekman pumping buoyancy forcing and dense water formation consistent with previous studies an original characteristic of the oceanic response to nao is presented that relates to the spatial patterns of buoyancy and wind forcing over the north atlantic anomalous ekman pumping associated with a positive nao phase first induces a decrease of the southern sub

high resolution alkenone sea surface temperature variability on the north icelandic shelf implications for nordic seas palaeoclimatic development during the holocene the palaeoceanography of the northern icelandic shelf for the holocene period was reconstructed from alkenone indices measured in core jr51 gc35 this contains a continuous record of holocene sedimentation spanning 0 10 2 cal kyr bp with a resolution of 20 yr cm we have identified a general holocene cooling trend that has superimposed millennial scale oscillations of 28c their timing is in close agreement with the timing of glacier advances in northern iceland for the later half of the holocene the alkenone sea surface temperature sst record from jr51 gc35 correlates with proxy data for the strength of nadw formation recorded in cores south of iceland this is interpreted as evidence of a close connection existing between north icelandic sea surface temperatures and the north atlantic meridonal overturning circulation the timing of the millennial scale sst variability in our core off north iceland is found to be out of phase or anti phased with the sst variability of a record in the eastern nordic seas md952011 this suggests that the evolution of holocene climate in the nordic seas was more complex than previously proposed and it is likely to be caused by differential responses of the irminger and norwegian currents and modulated by changes in atmospheric circulation analogous to the north atlantic oscillation

on the nature of the frontal zone of the choctawhatchee bay plume in the gulf of mexico river plumes often feature turbulent processes in the frontal zone and interfacial region at base of the plume which ultimately impact spreading and mixing rates with the ambient coastal ocean the degree to which these processes govern overall plume mixing is yet to be quantified with microstructure observations a field campaign was conducted in a river plume in the northeast gulf of mexico in december 2013 in order to assess mixing processes that could potentially impact transport and dispersion of surface material near coastal regions current velocity density and turbulent kinetic energy values e were obtained using an acoustic doppler current profiler adcp a conductivity temperature depth ctd profiler a vertical microstructure profiler vmp and two acoustic doppler velocimeters advs the frontal region contained e values on the order of 10 5 m2 s 3 which were markedly larger than in the ambient water beneath o 10 9 m2 s 3 an energetic wake of moderate e values o 10 6 m2 s 3 was observed trailing the frontal edge the interfacial region of an interior section of the plume featured opposing horizontal velocities and a e value on the order of 10 6 m2 s 3 a simplified mixing budget was used under significant assumptions to compare contributions from wind tides and frontal regions of the plume the results from this order of magnitude analysis indicated that frontal processes 59 dominated in overall mixing this emphasizes the importance of adequate parameterization of river plume frontal processes in coastal predictive models

the west central florida inner shelf and coastal system a geologic conceptual overview and introduction to the special issue abstract this paper provides an overview for this special publication on the geologic framework of the inner shelf and coastal zone of west central florida this is a significant geologic setting in that it lies at the center of an ancient carbonate platform facing an enormous ramp that has exerted large scale control on coastal geomorphology the availability of sediments and the level of wave energy in order to understand the holocene geologic history of this depositional system a regional study defined by natural boundaries north end of a barrier island to the apex of a headland was undertaken by a group of government and university coastal geologists using a wide variety of laboratory and field techniques it is the purpose of this introductory paper to define the character of this coastal inner shelf system provide a historical geologic perspective and background of environmental information define the overall database present the collective objectives of this regional study and very briefly present the main aspects of each contribution specific conclusions are presented at the end of each paper composing this volume

unusual subpolar north atlantic phytoplankton bloom in 2010 volcanic fertilization or north atlantic oscillation in summer and autumn 2010 a highly anomalous phytoplankton bloom with chlorophyll concentration more than double that of previous years was observed in the irminger basin southwest of iceland two unusual events occurred during 2010 which had the potential to promote the unusual bloom first in spring 2010 the eyjafjallajokull volcano in iceland erupted depositing large quantities of tephra into the subpolar north atlantic second during the winter of 2009 2010 the north atlantic oscillation nao became extremely negative developing into the second strongest negative nao on record hydrographic conditions were highly anomalous in the region with an influx of freshwater spreading through the basin and unusual nutrient and mixed layer depth conditions here we use a combination of satellite modeled and in situ data to investigate whether the input of iron from the volcanic eruption or change in hydrographic conditions due to the extreme negative nao were responsible for the anomalous phytoplankton bloom we conclude that changes in physical forcing driven by the nao and not the volcanic eruption stimulated the unusual bloom

on the temporally varying northward penetration of mediterranean overflow water and eastward penetration of labrador sea water abstract historical hydrographic data in the eastern north atlantic are used to suggest a connection between the northward penetration of mediterranean overflow water mow and the location of the subpolar front the latter of which is shown to vary with the north atlantic oscillation nao during persistent high nao periods when the subpolar front moves eastward waters in the subpolar gyre essentially block the northward flowing mow preventing its entry into the subpolar gyre conversely during low nao periods the subpolar front moves westward allowing mow to penetrate past porcupine bank into the subpolar gyre the impacts of an intermittent penetration of mow into the subpolar gyre including the possible effect on water mass transformations remain to be investigated

information from low density expendable bathythermograph transects north atlantic mean temperature structure and quasi decadal variability the 1999 ocean observing system conference recommended that the low density ld expendable bathythermograph xbt network be discontinued contingent on the completion of studies showing that the global argo network and or satellite altimetry can provide equivalent information herein information content in north atlantic ld lines relative to quasi decadal variability in upper layer temperature structure is addressed as the first step in achieving this recommendation two ld lines are located in the subpolar gyre and support results from previous studies of shorter length that ocean advection and not only air sea fluxes plays an important role particularly in the eastern gyre in determining the characteristics of the water masses transported to the source regions of north atlantic deep water several sections cross the gulf stream and labrador current they provide evidence to support the hypothesis that changes in the intensity of labrador current properties cause meridional motions of the gulf stream decadal variability in the subtropical gyre of the north atlantic has been attributed to westward propagation of temperature anomalies by the mean currents and planetary waves modeling studies suggest that these signals are dominant in the thermocline at the northern latitudes order 30 of the subtropical gyre similar calculations from a line crossing the subtropical gyre at these same latitudes shows no indication of westward propagation quasi decadal signals in upper layer temperature are coincident across the entire gyre with some suggestion of eastward motion of temperature anomalies one line on the southern boundary of the subtropical gyre does include westward signal movement from the eastern boundary based on the information content of individual lines recommendations are made relative to the continuation of specific transects until it has been demonstrated that argo and satellite altimetry can provide equivalent results

significance of hydrocarbon seepage relative to petroleum generation and entrapment near surface indications of migrating hydrocarbons provide the petroleum systems analyst critical information about source organic matter type maturation organic maturity migration migration pathway delineation and in selected geologic settings specific prospect hydrocarbon charge all petroliferous basins exhibit some type of near surface signal but the hydrocarbon leakage to surface is not always detectable with conventional seep detection methods understanding the petroleum seepage system hence petroleum dynamics of a basin is key to understanding and using near surface geochemical methods for basin assessment and prospect evaluation the relationships between near surface hydrocarbon seepage and subsurface petroleum generation and entrapment are often complex the petroleum seepage system contain four key elements seepage activity qualitative expressions of relative leakage rates active vs passive and episodic vs continuous seepage type concentration of migrated thermogenic hydrocarbon relative to in situ material macro vs micro migration focus major direction of bulk flow leakage relative to the subsurface hydrocarbon generation and or entrapment and near surface seep disturbances near surface processes which can greatly alter or block seepage signals the rate and volume of hydrocarbon seepage to the surface greatly control near surface geological and biological responses and thus are the best method of sampling and analysis to detect hydrocarbon leakage effectively to properly predict subsurface petroleum properties interpretation of near surface geochemical data must recognize many potential problems including recent organic matter input transported hydrocarbons bacterial alteration mixing contamination and fractionation effects surface geochemical data should always be integrated with other geological data calibration datasets to determine the utility of near surface geochemical techniques within particular basinal settings are essential when evaluating prospects for hydrocarbon charge

the sensitivity of the atlantic meridional overturning circulation to freshwater forcing at eddy permitting resolutions the effect of increasing horizontal resolution is examined to assess the response of the atlantic meridional overturning circulation amoc to freshwater perturbations versions of a global climate model with horizontal resolutions ranging from 1 8 latitude 3 6 longitude to 0 2 0 4 are used to determine if the amoc response to freshwater forcing is robust to increasing resolution in the preindustrial equilibrium climate the representation of western boundary currents and meridional heat transport are improved with resolution freshwater forcings similar to the final drainage of proglacial lakes agassiz and ojibway are applied evenly over the labrador sea and exclusively along the western boundary the duration and maximum amplitude of model responses to freshwater forcing showed little sensitivity to increasing resolution an evaluation with tracers of the forcing impact on different regions of north atlantic deep water formation revealed the possibility that increases in labrador sea deep convection at higher resolution mitigate the effect of stronger boundary currents and enhanced mixing with increasing resolution there is less cooling in the subpolar west atlantic more cooling in the subpolar east atlantic and greater variability in the deep ocean response to the boundary forcing while differences exist the coarseresolution model response remains robust at finer horizontal resolutions

the north atlantic current based on trajectories of satellite tracked buoys and hydrographic sections both dietrich s and worthington s schemes of the north atlantic current are reconsidered ninety satellite tracked buoys have been analyzed in order to distinguish between these schemes neither could be confirmed the north atlantic current appears as a superposition of a broad west wind drift and a frontal jet in the western part of the north atlantic north of 40 n which becomes independent from the subtropical gyre neither a permanent branching suggested by dietrich nor a confinement of the subpolar gyre to the east of newfoundland per worthington can be found the north atlantic current extends over the entire north atlantic carrying more than 20 sverdrups sv toward the north this northward transport is mainly due to the northward flow around flemish cap and a sudden turn of the north atlantic current east of the mid atlantic ridge the buoy tracks have been used to determine speed and direction in the upper layers 100 m we combine these results with hydrographic data in order to obtain an estimate of the mass transport transport across the mid atlantic ridge is based on recent sections fahrbach et al 1985 while transport in the northeastern north atlantic has been derived from the erika dan sections at 53 5 n and 59 5 n according to these two sections the return flow occurs mainly below 1000 m after water mass conversion in the northern areas the results imply that about 7 sv of atlantic water are transformed into deep water in the area between 53 5 n and 60 n

late pliocene changes in the north atlantic current article i nfo during the late pliocene global climate changed drastically as the northern hemisphere glaciation nhg intensified it remains poorly understood how the north atlantic current nac changed in strength and position during this time interval such changes may alter the amount of northward heat transport and therefore have a large impact on climate in the circum north atlantic region and the growth of northern hemisphere ice sheets using the alkenone biomarker we reconstructed orbitally resolved sea surface temperature sst and productivity records at integrated ocean drilling project iodp expedition 306 site u1313 during the late pliocene and early pleistocene 3 68 2 45 million years ago ma before 3 1 ma ssts in the mid latitude north atlantic were up to 6 c higher than the present and surface water productivity was low indicating that an intense nac transported warm nutrient poor surface waters northwards starting at 3 1 ma surface water characteristics changed drastically as the nhg intensified during glacial periods at the end of the late pliocene and beginning of the pleistocene ssts decreased and surface water productivity in the mid latitude north atlantic increased reflecting a weakened influence of the nac at our site at the same time the increase in surface productivity suggests that the arctic front af reached down into the mid latitudes we propose that during the intensification of the nhg the nac had an almost pure west to east flow direction in glacials and did not penetrate into the higher latitudes the diminished northward heat transport would have led to a cooling of the higher latitudes which may have encouraged the growth of large continental ice sheets in the northern hemisphere

subannual and seasonal variability of atlantic origin waters in two adjacent west greenland fjords greenland fjords provide a pathway for the inflow of warm shelf waters to glacier termini and outflow of glacially modified waters to the coastal ocean characterizing the dominant modes of variability in fjord circulation and how they vary over subannual and seasonal time scales is critical for predicting ocean heat transport to the ice here we present a 2 year hydrographic record from a suite of moorings in davis strait and two neighboring west greenland fjords that exhibit contrasting fjord and glacier geometry kangerdlugssuaq sermerssua and rink isbrae hydrographic variability above the sill exhibits clear seasonality with a progressive cooling of near surface waters and shoaling of deep isotherms above the sill during winter to spring renewal of below sill waters coincides with the arrival of dense waters at the fjord mouth warm salty atlantic origin water cascades into fjord basins from winter to midsummer we then use seaglider observations at davis strait along with reanalysis of sea ice and wind stress in baffin bay to explore the role of the west greenland current and local air sea forcing in driving fjord renewal these results demonstrate the importance of both remote and local processes in driving renewal of near terminus waters highlighting the need for sustained observations and improved ocean models that resolve the complete slope trough fjord ice system

contribution of horizontal advection to the interannual variability of sea surface temperature in the north atlantic abstract the interannual variability of sea surface temperature sst in the north atlantic is investigated from october 1992 to october 1999 with special emphasis on analyzing the contribution of horizontal advection to this variability horizontal advection is estimated using anomalous geostrophic currents derived from the topex poseidon sea level data average currents estimated from drifter data scatterometer derived ekman drifts and monthly sst data these estimates have large uncertainties in particular related to the sea level product the average currents and the mixed layer depth that contribute significantly to the nonclosure of the surface temperature budget the large scales in winter temperature change over a year present similarities with the heat fluxes integrated over the same periods however the amplitudes do not match well furthermore in the western subtropical gyre south of the gulf stream and in the subpolar regions the time evolutions of both fields are different in both

variability of the oceanic mixed layer 1960 2004 abstract a new monthly uniformly gridded analysis of mixed layer properties based on the world ocean atlas 2005 global ocean dataset is used to examine interannual and longer changes in mixed layer properties during the 45 yr period 1960 2004 the analysis reveals substantial variability in the winter spring depth of the mixed layer in the subtropics and midlatitudes in the north pacific an empirical orthogonal function analysis shows a pattern of mixed layer depth variability peaking in the central subtropics this pattern occurs coincident with intensification of local surface winds and may be responsible for the sst changes associated with the pacific decadal oscillation years with deep winter spring mixed layers coincide with years in which winter spring sst is low in the north atlantic a pattern of winter spring mixed layer depth variability occurs that is not so obviously connected to local changes in winds or sst suggesting that other processes such as advection are more important interestingl

on the nature of decadal anomalies in north atlantic sea surface temperature north atlantic sea surface temperature data from the comprehensive ocean atmosphere data set were used to investigate the behavior of temperature anomalies on multiple year timescales during the period 1948 1992 monthly anomaly time series for each 2 square from the equator to 70 n were low pass filtered at 4 years and normalized by the local standard deviation attention is focused on the extreme events the upper and lower deciles of the anomaly time series a 45 year sequence of january maps shows the already familiar phenomena of generally cold conditions prior to 1951 a long warm interval from 1951 through 1967 and again a cold period from 1968 through 1977 the years 1978 through 1982 were largely devoid of persistent strong anomalies but moderate cold conditions returned during 1983 1986 warm conditions dominated the north atlantic from 1987 onward within these thermal epochs however a total of five cold anomaly features and nine warm anomaly features have been identified these features have individual lifetimes of 3 to 10 years a typical size is 20 of latitude or longitude but they range from barely detectable to spanning the width of the basin the latter especially in lower latitudes most of the anomalies move long distances along certain preferred paths these paths generally follow the routes of the subarctic and subtropical gyres anomalies originating off north america along the boundary between the gyres move northeastward toward the norwegian sea along the approximate route of the north atlantic current midlatitude anomalies originating at the eastern boundary tend to spread both northward and southward along the coast the speed of these movements 1 3 km d 1 is generally less than the expected speed of the near surface ocean circulation simple ideas about the effects of beta dynamics and air sea heat exchanges are briefly considered but do not provide a satisfactory explanation for the movements of the anomalies the long timescale of these extreme events and the continuity of their movements suggest a useful degree of predictability of sea surface temperature based on persistence and propagation of features

in pursuit of anomalies analyzing the poleward transport of atlantic water with surface drifters we examine the trajectories of 168 drifters as a proxy for atlantic water flowing through the nordic seas the drifters were released at or passed through the svinoy section off the west coast of norway for comparison we generate a set of synthetic trajectories using a stochastic model with a range of diffusivities with the both sets we determine the transit times of both drifters and particles from svinoy to arctic gateways the barents sea and spitsbergen the mean arrival times to these locations are roughly 200 and 500 days respectively this implies ample time for cooling of the surface waters which increases densities and permits subduction before reaching the arctic however a range of transit times is seen some parcels reach fram strait in only 4 months while others are still in the southern nordic seas after 2 years the results do not support the idea that temperature or salinity anomalies can exist as coherent packets the drifters passing svinoy when treated as a group quickly spread over large distances mixing with water in the norwegian and lofoten basins thus an anomaly entering the nordic seas would quickly be obliterated however the velocity of the clusters center of mass is consistent with anomaly propagation speeds inferred previously from hydrographic measurements suggesting the observed variability is advective in nature

tracing the intrusion of fossil carbon into coastal louisiana macrofauna using natural 14 c and 13 c abundances the deepwater horizon oil spill released a large volume of 13c and radiocarbon depleted organic matter to the northern gulf of mexico evidence of petroleum derived carbon entering the offshore planktonic foodweb as well as widespread oiling of coastal areas documented in previous studies suggests that hydrocarbons could have entered the near shore foodweb to test this hypothesis we measured radiocarbon 14c and stable carbon isotopes 13c in an assortment of fish tissue invertebrate tissue and shell samples collected within a year of the spill at seven sites from louisiana to florida usa across the northern gulf of mexico we observed a west east gradient with the most depleted radiocarbon values found in terrebonne bay louisana and increasingly enriched radiocarbon values in organisms collected at sites to the east depleted radiocarbon values as low as 10 in invertebrate soft tissue from terrebonne suggest assimilation of fossil carbon 2 8 1 2 consistent with the hypothesis that organic matter from petrochemical reservoirs released during the deepwater horizon spill entered the coastal food web to a limited extent further there was a significant correlation between radiocarbon and 13c values in invertebrate tissue consistent with this hypothesis both oyster tissue and hard head catfish tissue collected in impacted areas of coastal louisiana were significantly depleted in 14c and 13c relative to organisms collected in the unaffected apalachicola bay florida p 0 014 alternative explanations for these results include the influence of chronic hydrocarbon pollution along the western gulf coast or that the organisms ingest carbon derived from 14c depleted organic matter mobilized during the erosion of coastal marshes in southern louisiana

submesoscale cold filaments in the gulf stream abstracta set of realistic very high resolution simulations is made for the gulf stream region using the oceanic model regional oceanic modeling system roms to study the life cycle of the intense submesoscale cold filaments that form on the subtropical gyre interior wall of the gulf stream the surface buoyancy gradients and ageostrophic secondary circulations intensify in response to the mesoscale strain field as predicted by the theory of filamentogenesis it can be understood in terms of a dual frontogenetic process along the lines understood for a single front there is however a stronger secondary circulation due to the amplification at the center of a cold filament filament dynamics in the presence of a mixed layer are not adequately described by the classical thermal wind balance the effect of vertical mixing of momentum due to turbulence in the surface layer is of the same order of magnitude as the pressure gradient and coriolis force and contributes equally to a so called turbulent therm

decadal water mass variations along 20 w in the northeastern atlantic ocean abstract water mass variations in the northeastern atlantic ocean along 20 w are analyzed with pentadal resolution over the past 15 years using data from four repeat occupations of a meridional hydrographic section running south from iceland the section was sampled in 1988 1993 1998 and 2003 the results are interpreted in the context of changes in air sea forcing ocean circulation and water properties associated with the north atlantic oscillation nao the nao index oscillated around zero from 1984 to 1988 was strongly positive from 1989 to 1995 after which it shifted to lower positive and occasionally negative values from 1996 to 2003 previously published studies suggest that after the 1995 1996 shift of the nao the subpolar gyre largely retreated to the northwest in the northeastern atlantic ocean resulting in an increasingly southeastern character of local water masses with time water property changes extending from the subpolar mode water spmw just below the seasonal pycnocline through the density range shared by mediterranean outflow water and subarctic intermediate water saiw along 20 w are consistent with changes in wind driven ocean circulation and air sea heat flux associated with shifts in the nao especially after accounting for ocean memory after periods of lower nao index the spmw is warmer saltier and lighter at these same times large increases of apparent oxygen utilization aou and potential vorticity are found at the spmw base consistent with spmw ventilation to lighter densities during lower nao index periods deeper and denser in the water column the cold fresh and dense saiw signature within the permanent pycnocline that was most strongly present in 1993 near the culmination of a period of high nao index is much reduced in 1988 and 1998 in 2003 after a prolonged period of lower nao index increasing influence of warmer saltier subtropical waters is clear within the permanent pycnocline the deep penetration of the changes implies that they are caused primarily by circulation changes resulting from nao associated wind shifts but changes in air sea heat flux could also have played a role

farallon slab detachment and deformation of the magdalena shelf southern baja california 1 subduction of the farallon plate beneath northwestern mexico stalled by 12 ma when the pacific farallon spreading ridge approached the subduction zone coupling between remnant slab and the overriding north american plate played an important role in the capture of the baja california bc microplate by the pacific plate active source seismic reflection and wide angle seismic refraction profiles across southwestern bc 24 5 n are used to image the extent of remnant slab and study its impact on the overriding plate we infer that the hot buoyant slab detached 40 km landward of the fossil trench isostatic rebound following slab detachment uplifted the margin and exposed the magdalena shelf to wave base erosion subsequent cooling subsidence and transtensional opening along the shelf starting 8 ma starved the fossil trench of terrigenous sediment input slab detachment and the resultant rebound of the margin provide a mechanism for rapid uplift and exhumation of forearc subduction complexes

holocene climate variability reflected in diatom derived sea surface temperature records from the subpolar north atlantic a detailed investigation of two deep sea sediment cores from the gardar drift in the subpolar north atlantic cores md99 2251 and md99 2252 has been undertaken to determine the extent of holocene

rapid switches in subpolar north atlantic hydrography and climate during the last interglacial mis 5e plateauing just below early mis 5e values a planktonic d 18 o minimum during the cooling event indicates that marked freshening of the surface waters accompanied the cooling we suggest that switches in the subpolar gyre hydrography occurred during a warmer climate involving regional changes in freshwater fluxes balance and east greenland current influence in the study area the nature of these hydrographic transitions suggests that they are most likely related to large scale circulation dynamics potentially amplified by gis meltwater influences

temporal variability of in situ methane concentrations in gas hydrate bearing sediments near bullseye vent northern cascadia margin 1 to assess the temporal variability in the methane fluxes from marine sediments that overly gas hydrate bearing sediments and the factors that might control its rate in situ methane concentrations were measured near bullseye vent on the northern cascadia continental margin a long term sampling device collected overlying water and pore fluid samples from 25 cm above seafloor at the sediment water interface swi and 7 cmbsf centimeters below seafloor over a 9 month period august 2009 may 2010 these samples provide a record at 4 day resolution of in situ methane ethane propane sulfate and chloride concentrations as well as stable carbon isotope ratios of methane 13c ch4 and dissolved inorganic carbon 13c dic we show that pore fluids near the swi are saturated or supersaturated with respect to methane 80 mm and the methane flux from the seabed is variable over time we hypothesized that regional seismic activity controlled this variable ch4 flux in the northern cascadia continental margin setting however we found no direct correlation between earthquakes and ch4 flux we also posited alternative controls on ch4 flux variability such as storms regional oceanography and microbial activity again no direct correlation was seen this study takes first steps toward exploring which physical factors play a role in methane flux from hydrate bearing sediments

millennial scale variations of the holocene north atlantic mid depth gyre inferred from radiocarbon and neodymium isotopes in cold water corals abstract variations in north atlantic ocean mid depth circulation during the holocene are poorly understood it is believed that they had a significant influence on the properties of water entering the nordic sea by redistributing heat and freshwater potentially affecting deep water formation and climate to improve our knowledge of the ne atlantic mid depth circulation radiocarbon and neodymium isotope analyses have been then carried out on precisely dated u th l pertusa and m oculata coral fragments from two sediment cores taken at 750 m water depth on the sw rockall trough margin cold water coral cwc end values vary between 12 2 0 3 and 16 6 0 4 and result from variable contributions of unradiogenic mid depth subpolar gyre mid spg water 15 and more radiogenic eastern north atlantic water enaw 11 which is transported northward to the rockall trough by boundary currents along the european margin increased coral end reflects a westward contraction of the mid spg water and a higher proportion of enaw the mid holocene from 8 8 to 6 8 ka bp is marked by unradiogenic coral end from 16 6 0 4 to 14 6 0 5 indicating a greater eastward extension of the mid spg this is followed by a shift from 6 8 to 5 ka bp toward more radiogenic end values from 15 4 0 3 to 13 3 0 2 suggesting a westward contraction of the mid spg and a higher proportion of enaw the mid holocene long term change in end is characterized by millennial variations of up to 2 5 epsilon units well marked during the late holocene indicating that eastward extension of the mid spg coeval with warm periods in northern europe e g the medieval climatic anomaly and the roman warm period most of the cwc derived 14c values match the global ocean values indicating that the water masses bathing the corals were generally well ventilated the exceptions are a few short intervals of eastward extension of the mid spg which are characterized by lower 14c during the late holocene we propose that these minor 14c fluctuations in the rockall trough may be related to local changes in the mixed layer depth or to variability in the advection of water from the labrador sea where deep convection gives rise to thermocline waters that are relatively depleted in terms of 14c the eastward extension of the mid spg between 8 8 and 6 8 ka bp is associated with the holocene climatic optimum concurrent with a maximum strength of the iceland scotland overflow water isow which is indicative of an increase in the atlantic meridional overturning circulation amoc this period is followed by a transition in the north atlantic circulation which occurred around 6 8 ka bp and coincides with the onset of labrador sea water formation a decrease of the isow strength and a contraction of the mid spg leading to a greater intrusion of saline subtropical water into the subpolar atlantic

near surface circulation of the nordic seas as measured by lagrangian drifters in the period june 1991 to august 1993 107 argos tracked drifters drogued to 15 m depth were released in the nordic seas or greenland iceland and norwegian seas the drifter movements revealed the strong and spatially confined current systems along the surface salinity fronts of the iceland faroe frontal zone and of the norwegian coast and along the continental margins and their extensions to the barents sea and spitsbergen the norwegian atlantic current is composed of three distinct streams two continental margin and one coastal branches which join into one single swift mean current west of the lofoten and vesteralen islands where the strongest measured currents are in excess of 110 cm s 1 in addition to the general cyclonic gyre circulation in the nordic seas the drifters indicate smaller cyclonic circulation patterns in all the major subbasins i e the iceland plateau the norwegian the lofoten and the greenland basins no surface signature of the east icelandic current is disclosed by the drifters interpolated and low pass filtered position data were used to construct maps of 15 m depth ensemble mean velocity velocity variability and residence time vigorous eddy fields are dominant in the strong currents and in the lofoten basin eulerian correlations indicate that they tend to propagate to the west in contrast the iceland plateau appears quiescent both in the mean and eddy velocities single particle diffusivities are computed and are found to be in the range 1 7 107 cm2 s 1 the corresponding lagrangian timescale and space scale are 1 3 days and 10 40 km respectively these lagrangian drifter measurements compose the first basin scale accurate near surface velocity data set of the nordic seas

decadal variations in labrador sea ice cover and north atlantic sea surface temperatures 1 the spatial and temporal evolution of winter sea ice anomalies in the labrador sea and associated sea surface temperature sst variations in the north atlantic are documented for three periods of above normal ice cover 1972 1974 1983 1985 and 1990 1992 these events are notable for their winter to winter persistence despite the fact that the ice margin retreats to northern baffin bay each summer and for their spatial evolution progressing from the northern labrador sea to the southern tip of newfoundland over a 3 year period above normal sea ice is consistently accompanied by below normal ssts in the subpolar atlantic the latter persist 1 3 years after the decay of the ice anomalies and in some cases exhibit a tendency for eastward movement across the gyre spring summer freshwater anomalies at 100 m depth in the west greenland current are found to precede by 8 months the initial occurrence of above normal ice cover in the northern labrador sea the role of atmospheric forcing in the joint evolution of anomalous sea ice and sst is assessed by means of an ice ocean mixed layer model forced with observed air temperature and wind fields the model results indicate that thermodynamic atmospheric forcing accounts for much of the winter to winter persistence and spatial evolution of the ice and concurrent sst anomaly patterns however the subsequent persistence of sst anomalies in the subpolar region is not well simulated suggesting that oceanic processes omitted from the simple slab mixed layer formulation play a contributing role

submesoscale impacts on horizontal and vertical transport in the gulf of mexico 1 impacts of submesoscale processes on transport are investigated numerically in an energetic mesoscale flow with an ocean model run at two horizontal resolutions 1 and 5 km the focus is the northwestern gulf of mexico where the loop current eddies are surrounded by smaller vortices by increasing the horizontal resolution the number and strength of submesoscale eddies and vorticity filaments within the mixed layer increase dramatically and with them the vertical velocities inside the coherent eddies and at their peripheries increased vertical velocities for increasing resolution are associated to near inertial motions and they are not limited to the mixed layer but are found at all depths horizontal velocities on the contrary are similar lagrangian isobaric tracers are deployed close to the surface and at 100 m and three dimensional neutrally buoyant particles are released close to the surface at the base of the mixed layer and at 100 m the modeled horizontal dispersion curves for each deployment depth are independent of the kind of particles and of horizontal resolution close to the ocean surface however convergence zones generated by submesoscale ageostrophic motions and resolved at 1 km resolution influence the details of the tracer distributions vertical dispersion increases by several folds for increasing resolution at all depths explored with the largest differences found close to the surface therefore submesoscales processes play a fundamental role in driving vertical transport in eddy dominated flows both within and below the mixed layer for times comparable to the eulerian time scale

north atlantic surface circulation during the 1990 s observed with satellite tracked drifters a new compilation of lagrangian velocity observations describes the state of the north atlantic surface circulation during the 1990s gridded fields of velocity and eddy kinetic energy eke are constructed from trajectories of more than 1500 15 m drogued satellite tracked surface drifters in service between january 1990 and december 1999 this time period overlaps a coordinated field study of circulation and variability in the north atlantic completed between 1996 2000 as part of the world ocean circulation experiment we describe the construction of a self consistent drifter climatology present decadal mean quasi eulerian velocity and eke fields computed on a 1 grid and compare these results with contemporary satellite measurements detailed discussion of the inferred surface circulation is focused on three regions 1 the gulf stream and north atlantic current 2 the labrador sea and subpolar gyre and 3 the caribbean sea the swiftest drifter motions were found in the equatorial region and along the tropical subtropical and subpolar western boundaries the maximum instantaneous speed determined from a single quality controlled and filtered drifter observation was 273 cm s 1 in the gulf stream southeast of cape cod the highest eke value in the north atlantic 2790 cm2 s 2 was found in the gulf stream just downstream of the new england seamounts over most of the atlantic basin drifter derived eke values were found to be o 100 cm2 s 2 higher than corresponding values derived from satellite altimetry in the labrador sea a region of sharply elevated eke appears to be geographically related to the localized ejection of drifters and by extension mass and kinetic energy from the energetic west greenland current between 60 and 62 n when compared to drifter measurements made in the late 1970s our results suggest but do not statistically confirm an enhancement and slight northward shift of the zonal gulf stream extension such a shift is consistent in sign with expectations based on observed interdecadal variations in wind stress and subtropical gyre potential energy associated with the north atlantic oscillation

mixed layer instabilities and restratification abstract the restratification of the oceanic surface mixed layer that results from lateral gradients in the surface density field is studied the lateral gradients are shown to be unstable to ageostrophic baroclinic instabilities and slump from the horizontal to the vertical these instabilities which are referred to as mixed layer instabilities mlis differ from instabilities in the ocean interior because of the weak surface stratification spatial scales are o 1 10 km and growth time scales are on the order of a day linear stability analysis and fully nonlinear simulations are used to study mlis and their impact on mixed layer restratification the main result is that mlis are a leading order process in the ml heat budget acting to constantly restratify the surface ocean climate and regional ocean models do not resolve the scales associated with mlis and are likely to underestimate the rate of ml restratification and consequently suffer from a bias in sea surface temperatures and ml depths in a

structure transports and transformations of the water masses in the atlantic subpolar gyre we discuss the distributions and transports of the main water masses in the north atlantic subpolar gyre naspg for the mean of the period 2002 2010 ovide sections 2002 2010 every other year as well as the inter annual variability of the water mass structure from 1997 4x and meteor sections to 2010 the water mass structure of the naspg quantitatively assessed by means of an optimum multiparameter analysis with 14 water masses was combined with the velocity fields resulting from previous studies using inverse models to obtain the water mass volume transports we also evaluate the relative contribution to the atlantic meridional overturning circulation amoc of the main water masses characterizing the naspg identifying the water masses that contribute to the amoc variability the reduction of the magnitude of the upper limb of the amoc between 1997 and the 2000s is associated with the reduction in the northward transport of the central waters this reduction of the northward flow of the amoc is partially compensated by the reduction of the southward flow of the lower limb of the amoc associated with the decrease in the transports of polar intermediate water and subpolar mode water spmw in the irminger basin we also decompose the flow over the reykjanes ridge from the east north atlantic basin to the irminger basin 9 4 4 7 sv into the contributions of the central waters 2 1 1 8 sv labrador sea water lsw 2 4 2 0 sv subarctic intermediate water saiw 4 0 0 5 sv and iceland scotland overflow water isow 0 9 0 9 sv once lsw and isow cross over the reykjanes ridge favoured by the strong mixing around it they leave the irminger basin through the deep to bottom levels the results also give insights into the water mass transformations within the naspg such as the contribution of the central waters and saiw to the formation of the different varieties of spmw due to air sea interaction

a global perspective on langmuir turbulence in the ocean surface boundary layer the turbulent mixing in thin ocean surface boundary layers osbl which occupy the upper 100 m or so of the ocean control the exchange of heat and trace gases between the atmosphere and ocean here we show that current parameterizations of this turbulent mixing lead to systematic and substantial errors in the depth of the osbl in global climate models which then leads to biases in sea surface temperature one reason we argue is that current parameterizations are missing key surface wave processes that force langmuir turbulence that deepens the osbl more rapidly than steady wind forcing scaling arguments are presented to identify two dimensionless parameters that measure the importance of wave forcing against wind forcing and against buoyancy forcing a global perspective on the occurrence of wave forced turbulence is developed using re analysis data to compute these parameters globally the diagnostic study developed here suggests that turbulent energy available for mixing the osbl is under estimated without forcing by surface waves wave forcing and hence langmuir turbulence could be important over wide areas of the ocean and in all seasons in the southern ocean we conclude that surface wave forced langmuir turbulence is an important process in the osbl that requires parameterization citation belcher s e et al 2012 a global perspective on langmuir turbulence in the ocean surface boundary layer geophys res lett 39 l18605 doi 10 1029 2012gl052932

transient eastern mediterranean deep waters in response to the massive dense water output of the aegean sea in the 1990s abstract we present a detailed account of the changing hydrography and the large scale circulation of the deep waters of the eastern mediterranean emed that resulted from the unique high volume influx of dense waters from the aegean sea during the 1990s and of the changes within the aegean that initiated the event the so called eastern mediterranean transient emt the analysis uses repeated hydrographic and transient tracer surveys of the emed in 1987 1991 1995 1999 and 2001 2002 hydrographic time series in the southern aegean and southern adriatic seas and further scattered data aegean outflow averaged nearly 3 10 6 m 3 s 1 between mid 1992 and late 1994 and was largest during 1993 when south and west of crete aegean influenced deep waters extended upwards to 400 m depth emt related aegean outflow prior to 1992 confined to the region around crete and to 1800 m depth wise amounted to about 3 of the total outflow outflow after 1994 up to 2001 2002 derived from the increasing inventory of the tracer cfc 12 contributed 20 to the total of 2 8 10 14 m 3 densities in the southern aegean sea deep waters rose by 0 2 kg m 3 between 1987 and 1993 and decreased more slowly thereafter the aegean waters delivered via the principal exit pathway in kasos strait east of crete propagated westward along the cretan slope such that in 1995 the highest densities were observed in the hellenic trench west of crete aegean influenced waters also crossed the east mediterranean ridge south of crete and from there expanded eastward into the southeastern levantine sea transfer into the ionian mostly followed the hellenic trench largely up to the trench s northern end at about 37 n from there the waters spread further west while mixing with the resident waters additional transfer occurred through the herodotus trough in the south levantine waters after 1994 consistently showed temperature salinity t s inversions in roughly 1000 1700 m depth with amplitudes decreasing in time the t s distributions in the ionian sea were more diverse one cause being added aegean outflow of relatively lower density through the antikithira strait west of crete spreading of the aegean influenced waters was quite swift such that by early 1995 the entire emed was affected and strong mixing is indicated by near linear t s relationships observed in various places referenced to 2000 and 3000 dbar the highest aegean generated densities observed during the event equaled those generated by adriatic sea outflow in the northern ionian sea prior to the emt a precarious balance between the two dense water source areas is thus indicated a feedback is proposed which helped triggering the change from a dominating adriatic source to the aegean source but at the same time supported the previous long year dominance of the adriatic the emed deep waters will remain transient for decades to come

currents and mixing in the irminger sea and in the iceland basin on the basis of a hydrographic section from the faeroe islands toward greenland along 62m 0n and the deployment of about 20 satellite tracked buoys it is shown that the irminger current branches at the reykjanes ridge its total transport amounts to 17 18 sv the eastern branch of the irminger current 8 sv turns east and enters the norwegian sea both through the faeroe shetland channel 3 sv and by passing northeast of the faeroe islands maximum speeds of 70 cm s 1 are reached at the outer edge of the east and west greenland current very intensive mixing is observed between the four water masses that flow into the irminger basin stirring by eddies plays a dominant role for strong interleaving subsequent salt fingering and double diffusive layering conditions for these processes are optimal nearly everywhere in the irminger sea

changes in sediment redox conditions following the bp dwh blowout event abstract following the blowout of the macondo well a pulse in sedimentation resulted in changes in sedimentary redox conditions this is demonstrated by downcore and temporal changes in the concentration of redox sensitive metals mn re and cd sediment cores collected in the ne gulf of mexico gom reveal increased sedimentation after the deepwater horizon dwh blowout the formation of mucous rich marine snow in surface waters and subsequent rapid deposition to underlying sediments is the likely cause respiration of this material resulted in decreased pore water oxygen concentration and a shoaled redoxcline resulting in two distinct mn peaks in sediments following the event one typically in the top 10 mm with the other at 20 30 mm most cores near the wellhead reveal this non steady state behavior for up to two years after the event associated with the mn minimum between the two mn peaks a modest 15 30 enrichment of re consistent with reducing sediments typically exists a three year time series of three stations following the event reveal that sediment re increased 3 4 times compared to the pre impact baseline value for two years indicating sediments are increasingly more reducing for two years in the third year re concentration decreased suggesting a return towards pre impact conditions in select sites where the density of benthic foraminifera was determined an assemblage wide decrease occurred coincident with reducing conditions as determined by redox sensitive metals demonstrating the important consequences of changing redox conditions on benthic ecosystems determination of redox sensitive metals will continue to constrain the temporal evolution of reducing conditions which will serve to document the long term effects of the spill and the possible return to pre event conditions

microbial enzymatic activity and secondary production in sediments affected by the sedimentation pulse following the deepwater horizon oil spill abstract a large fraction of the spilled oil from the deepwater horizon dwh blowout in april 2010 reached the seafloor via sinking oil aggregates oil snow in a massive sedimentation that continued until late summer 2010 dirty blizzard we measured heterotrophic microbial metabolic rates as well as porewater and sedimentary geochemical parameters at sites proximate to and distant from the wellhead to investigate microbial responses to the dirty blizzard lipase activity and rates of bacterial protein production were highest and leucine aminopeptidase activity was lowest in 0 2 cm sediment layers at the sites proximate to the wellhead these results suggest that the presence of the oil snow stimulated benthic microbial enzymatic hydrolysis of oil derived organic matter that was depleted in peptide substrates at the time of our sampling the strong gradients in porewater doc nh 4 and hpo 4 3 concentrations in the upper 6 cm of the sediments near the wellhead likewise indicate elevated heterotrophic responses to recently sedimented organic matter in addition to enhanced microbial activities in the 0 2 cm sediment layers we found peaks of total organic carbon and elevated microbial metabolic rates down to 10 cm at the sites closest to the wellhead our results indicate distinct benthic metabolic responses of heterotrophic microbial communities even three months after the ending of the dirty blizzard compared to other deep sea environments however metabolic rates associated with the recently deposited particulate matter around the wellhead were only moderately enhanced oil contaminants at the seafloor may therefore have prolonged residence times enhancing the potential for longer term ecological consequences in deep sea environments

coral injuries observed at mesophotic reefs after the deepwater horizon oil discharge abstract pathologies in over 400 octocoral and antipatharian colonies were quantified in the aftermath of the dwh oil discharge observations were made in september 2011 at water depths of 65 75 m in the pinnacle reef trend area offshore from mississippi and alabama gulf of mexico using a digital macro camera deployed from an rov to examine the coral populations for injury at two principal sites alabama alps reef aar and roughtongue reef rtr taxa observed to exhibit injury included gorgonian octocorals hypnogorgia pendula bebryce spp thesea nivea and swiftia exserta the antipatharian antipathes atlantica and the sea whips stichopathes sp and ellisella barbadensis the most common type of injury was a biofilm with a clumped or flake like appearance covering sea fan branches extreme injuries were characterized by bare skeletons broken and missing branches comparing the 2011 results to previous photo surveys of the same study sites between 1997 and 1999 we found significantly more occurrences of injury in 2011 among taxa with growth forms 0 5 m we hypothesize that tropical storm bonnie facilitated and accelerated the mixing process of dispersant treated hydrocarbons into the water column resulting in harmful contact with coral colonies at mesophotic depths analysis of total polycyclic aromatic hydrocarbon tpah concentrations in sediments at aar and rtr found levels elevated above pre discharge values but orders of magnitude below toxicity thresholds established for fauna in estuarine sediments the tpah concentrations measured in octocoral and echinoderm tissue samples from aar and rtr were detectable mean values ranged from 51 to 345 ppb however bioeffect thresholds do not currently exist with which to evaluate the potential harm these levels may cause our findings indicate that coral injuries observed in 2011 may have resulted from an acute isolated event rather than ongoing natural processes

surface and deep ocean coupling in the subpolar north atlantic during the last 230 years the subpolar north atlantic ocean spna is of key importance for modulating the climate of nw europe because of heat loss to the atmosphere from the north atlantic current although hydrographic properties of the surface spna vary on interannual to multidecadal timescales hydrographic time series scarcely extend back beyond the 1950s we present a 230 year long record of spna surface conditions reconstructed from a very high accumulation rate core that also registers changes in deep flow speed in the iceland basin a lagged correlation is observed between the records of deep flow speed and stable oxygen isotopic composition of the surface spna d 18 o w with strongest correlation when the paleoflow speed record leads by 15 20 years this offset may to some extent reflect size selective biological mixing of the sediment nonetheless these records reveal a decadal scale coupling between surface and deep ocean variability over the past 230 years possibly driven by the north atlantic oscillation with implications for north atlantic circulation and climate

mesoscale to submesoscale transition in the california current system part i flow structure eddy flux and observational tests in computational simulations of an idealized subtropical eastern boundary upwelling current system similar to the california current a submesoscale transition occurs in the eddy variability as the horizontal grid scale is reduced to o 1 km this first paper in a series of three describes the transition in terms of the emergent flow structure and the associated time averaged eddy fluxes in addition to the mesoscale eddies that arise from a primary instability of the alongshore wind driven currents significant energy is transferred into submesoscale fronts and vortices in the upper ocean the submesoscale arises through surface frontogenesis growing off upwelled cold filaments that are pulled offshore and strained in between the mesoscale eddy centers in turn some submesoscale fronts become unstable and develop submesoscale meanders and fragment into roll up vortices associated with this phenomenon are a large vertical vorticity and rossby number a large vertical velocity relatively flat horizontal spectra contrary to the prevailing view of mesoscale dynamics a large vertical buoyancy flux acting to restratify the upper ocean a submesoscale energy conversion from potential to kinetic a significant spatial and temporal intermittency in the upper ocean and material exchanges between the surface boundary layer and pycnocline comparison with available observations indicates that submesoscale fronts and instabilities occur widely in the upper ocean with characteristics similar to the simulations

ocean processes underlying surface clustering ageostrophic ocean processes such as frontogenesis submesoscale mixed layer instabilities shelf break fronts and topographic interactions on the continental shelf produce surface divergent flows that affect buoyant material over time this study examines the ocean processes leading to clustering i e the increase of material density over time on the ocean surface the time series of divergence along a material trajectory the lagrangian divergence ld is the flow property driving clustering to understand the impacts of various ocean processes on ld numerical ocean model simulations at different resolutions are analyzed although the relevant processes differ patterns in clustering evolution from the deep ocean and the continental shelf bear similarities smaller scale ocean features are associated with stronger surface divergence and the surface material clustering is initially dominated by these features over time the effect of these small scale features becomes bounded as material traverses small scale regions of both positive and negative divergence lower frequency flow phenomena however continue the clustering as a result clustering evolves from initial small scale to larger scale patterns

multicentennial variability of the sea surface temperature gradient across the subpolar north atlantic over the last 2 8 kyr a 2800 year long august sea surface temperature asst record based on fossil diatom assemblages is generated from a marine sediment core from the northern subpolar north atlantic the record is compared with the asst record from the norwegian sea to explore the variability of the asst gradient between these areas during the late holocene the asst records demonstrate the opposite climate tendencies towards a persistent warming in the core site in the subpolar north atlantic and cooling in the norwegian sea at the multicentennial scale of asst variability of 600 900 years the records are nearly in anti phase with warmer colder periods in the subpolar north atlantic corresponding to the colder warmer periods in the norwegian sea at the shorter time scale of 200 450 years the records display a phase locked behaviour with a tendency for the positive asst anomalies in the norwegian sea to lead by 30 years the negative asst anomalies in the subpolar north atlantic this apparent asst seesaw might have an effect on two major anomalies of the european climate of the past millennium medieval warm period mwp and the little ice age lia during the mwp warming of the sea surface in the norwegian sea occurred in parallel with cooling in the northern subpolar north atlantic whereas the opposite pattern emerged during the lia the results suggest that the observed asst seesaw between the subpolar north atlantic and the norwegian sea could be a surface expression of the variability of the eastern and western branches of the atlantic meridional circulation amoc with a possible amplification through atmospheric feedback

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

climate related change of sea level in the extratropical north atlantic and north pacific in 1993 2003 1 climate related change of sea level is one of the most challenging concerns for the humankind here we present a comparative analysis of the interannual variability of sea level in the extratropical north atlantic and north pacific oceans based on the high accuracy topex poseidon jason 1 and ers 1 2 measurements from november 1992 to june 2003 we found indications of the interdecadal variability of the sea level in the north pacific possibly related to the pacific decadal oscillation and suggested that the observed decadal rise of sea level in the subpolar and eastern north atlantic may have been related to the interdecadal change while the north atlantic subtropical and subpolar gyres decelerated the opposite occurred in the north pacific the year to year variations of sea level showed coherence between the north atlantic oscillation el nino la nina and pacific decadal oscillation events and respective gyre scale changes

the north atlantic oscillation surface current velocities and sst changes in the subpolar north atlantic changes in surface circulation in the subpolar north atlantic are documented for the recent interannual switch in the north atlantic oscillation nao index from positive values in the early 1990s to negative values in 1995 96 data from lagrangian drifters which were deployed in the north atlantic from 1992 to 1998 were used to compute the mean and varying surface currents ncep winds were used to calculate the ekman component allowing isolation of the geostrophic currents the mean ekman velocities are considerably smaller than the mean total velocities that resemble historical analyses the northeastward flow of the north atlantic current is organized into three strong cores associated with topography along the eastern boundary in rockall trough in the iceland basin the subpolar front and on the western flank of the reykjanes ridge irminger current the last is isolated in this eulerian mean from the rest of the north atlantic current by a region of weak velocities on the east side of the reykjanes ridge the drifter results during the two different nao periods are compared with geostrophic flow changes calculated from the nasa pathfinder monthly gridded sea surface height ssh variability products and the advanced very high resolution radiometer avhrr sst data during the positive nao years the northeastward flow in the north atlantic current appeared stronger and the circulation in the cyclonic gyre in the irminger basin became more intense this was consistent with the geostrophic velocities calculated from altimetry data and surface temperature changes from avhrr sst data which show that during the positive nao years with stronger westerlies the subpolar front was sharper and located farther east sst gradients intensified in the north atlantic current irminger basin and east of the shetland islands during the positive nao phase associated with stronger currents sst differences between positive and negative nao years were consistent with changes in air sea heat flux and the eastward shift of the subpolar front sst advection as diagnosed from the drifters likely acted to reduce the sst differences

quantitative assessment of precipitation seasonality and summer surface wetness using ombrotrophic sediments from an arctic norwegian peatland article i nfo article history received 18 april 2008 available online xxxx seasonality of precipitation is an important yet elusive climate parameter in paleoclimatological reconstructions this parameter can be inferred qualitatively from pollen and other paleoecological methods but is difficult to assess quantitatively here we have assessed seasonality of precipitation and summer surface wetness using compound specific hydrogen and carbon isotope ratios of vascular plant leaf waxes and sphagnum biomarkers extracted from the sediments of an ombrotrophic peatland bostad bog nordland norway our reconstructed precipitation seasonality and surface wetness are consistent with regional vegetation reconstructions during the early holocene 11 5 7 5 ka fennoscandia experienced a cool moist climate the middle holocene 7 5 5 5 ka was warm and dry transitioning towards cooler and wetter conditions from the mid holocene to the present changes in seasonality of precipitation during the holocene show significant coherence with changes in sea surface temperature in the norwegian sea with higher sst corresponding to greater percentage of winter precipitation both high sst in the norwegian sea and increased moisture delivery to northern europe during winter are correlated with a strong gradient between the subpolar low and subtropical high over the north atlantic positive north atlantic oscillation

an inflated subpolar gyre blows life toward the northeastern atlantic abstract deep convection in the labrador and irminger seas inflates the cold and low saline subpolar gyre which is a rich nutrient and zooplankton source for the surrounding warmer waters of subtropical origin the zooplankton abundances on the south iceland shelf show characteristic sub decadal variability which closely reflect the oceanic abundances of the ecologically most important zooplankton species calanus finmarchicus much higher abundances of this species are observed during years when the winter mixed layer depths mld in the labrador irminger sea and over the reykjanes ridge are deep furthermore a tight relationship is identified between on shelf zooplankton abundances and lateral shifts of the biologically productive subarctic front southwest of iceland thus we suggest that northeastward expansion of the subpolar gyre results in biologically productive periods in the waters southwest of iceland both oceanic and on the shelf in addition to local atmospheric forcing we find that the mld and frontal position are also impacted by remote heat losses and convection in the labrador sea through northward advection of unstable mode waters the sub decadal oceanic and on shelf biological production peaks are possibly predictable by half a year local winter convection to subsequent summer production and the advective time lag from the labrador sea might induce an even longer predictability horizon up to 1 5 years

subsurface methane sources and migration pathways within a gas hydrate mound system gulf of mexico 1 geochemical profiles were coupled with seismic information to examine subsurface hydrocarbon source migration and fate at a gulf of mexico carbonate gas hydrate mound woolsey mound three seafloor features were investigated in detail 1 major faults resulting from a rising salt body 2 an acoustic backscatter anomaly and 3 a pockmark associated with a major fault we analyzed sulfate chloride dissolved inorganic carbon and hydrocarbon concentrations and carbon isotopes in pore water extracted from 20 m piston cores to characterize gas source and calculate methane flux dissolved biogenic methane dominated the off fault sites while the contribution of thermogenic methane increased near a major fault where thermogenic gas hydrates were recovered within the pockmark methane concentrations were low and isotopes indicated a biogenic source since pockmarks are typically formed from expulsive fluid flow this suggests that either the pockmark is the legacy of a conduit that has become plugged or that the expulsed fluid is confined within the fault walls at the acoustic anomaly nonsteady state sulfate profiles suggested temporal variability in methane flux estimates from 75 gravity cores collected across woolsey mound since 2002 were mapped to display the spatial variability in methane flux relative to the faults methane flux to the seafloor was generally low but increased several fold near the faults suggesting that the faults may provide conduits for hydrocarbons to bypass the microbial biofilter and cross the sediment water interface

enhanced particle fluxes and heterotrophic bacterial activities in gulf of mexico bottom waters following storm induced sediment resuspension abstract bottom nepheloid layers bnls in the deep sea transport and remobilize considerable amounts of particulate matter enhancing microbial cycling of organic matter in cold deep water environments we measured bacterial abundance bacterial protein production and activities of hydrolytic enzymes within and above a bnl that formed in the deep mississippi canyon northern gulf of mexico shortly after hurricane isaac had passed over the study area in late august 2012 the bnl was detected via beam attenuation in ctd casts over an area of at least 3 5 km 2 extending up to 200 m above the seafloor at a water depth of 1500 m a large fraction of the suspended matter in the bnl consisted of resuspended sediments as indicated by high levels of lithogenic material collected in near bottom sediment traps shortly before the start of our sampling campaign observations of suspended particle abundance and sizes throughout the water column using a combined camera ctd system marine snow camera msc revealed the presence of macroaggregates 1 mm in diameter within the bnl indicating resuspension of canyon sediments a distinct bacterial response to enhanced particle concentrations within the bnl was evident from the observation that the highest enzymatic activities peptidase glucosidase and protein production 3 h leucine incorporation were found within the most particle rich sections of the bnl to investigate the effects of enhanced particle concentrations on bacterial activities in deep bnls more directly we conducted laboratory experiments with roller bottles filled with bottom water and amended with experimentally resuspended sediments from the study area macroaggregates formed within 1 day from resuspended sediments by day 4 of the incubation bacterial cell numbers in treatments with resuspended sediments were more than twice as high as in those lacking sediment suspensions cell specific enzymatic activities were also generally higher in the sediment amended compared to the unamended treatments the broader range and higher activities of polysaccharide hydrolases in the presence of resuspended sediments compared to the unamended water reflected enzymatic capabilities typical for benthic bacteria our data suggest that the formation of bnls in the deep gulf of mexico can lead to transport of sedimentary organic matter into bottom waters stimulating bacterial food web interactions such storm induced resuspension may represent a possible mechanism for the redistribution of sedimented oil fallout from the deepwater horizon spill in 2010

assessing variability in the size and strength of the north atlantic subpolar gyre recent studies on the size and strength of the north atlantic subpolar gyre spg offer contrasting assessments of the gyre s temporal variability studies that use empirical orthogonal function eof analyses of satellite sea surface height ssh report a rapid decline in spg size and strength since 1992 20 per decade while concurrent in situ observations report either no trend or a slight decline here we investigate this discrepancy by analyzing the size and strength of the spg with satellite ssh from 1993 to 2015 with two separate methods indirectly via eof analysis and more directly through measurements of the gyre center and boundary we define the boundary of the gyre as the largest closed contour of ssh the center as the minimum ssh and the strength as the difference between the ssh at the boundary and the center we identify a linear decline over the study period in the spg strength 5 1 per decade but find no statistically significant trend in the spg area the trend in the gyre strength is weaker than the eof based trend and is most likely below the level of detection of the in situ measurements we conclude that the variability previously identified as a sharp decline in spg circulation can be more appropriately attributed to basin wide sea level rise during the satellite altimetry period in addition we find that the properties of the eastern spg do not co vary with the spg size suggesting that spg dynamics do not control the strength of the inter gyre throughput

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

interannual variability of the subpolar mode water properties over the reykjanes ridge during 1990 2006 combining hydrographic data from the ovide observatoire de la variabilite interannuelle a decennale observatory of the interannual to decadal variability section greenland portugal with argo and historical ctd data over the period 1990 2006 we estimate the variability of the core properties of a variety of subpolar mode water spmw observed on the eastern flank of the reykjanes ridge this spmw acquires its core properties in the winter mixed layer along the eastern side of the reykjanes ridge we find that the february sea surface temperature along the ridge is a proxy for its core temperature the sources of this mode water are water masses advected by the mean cyclonic circulation in the iceland basin a density compensated tendency for cooling and freshening of the spmw core properties is observed in the early 1990s it stops in 1996 and is followed by an increase in temperature and salinity 1 41 c and 0 11 psu and a decrease in density 0 12 kg m 3 until at least 2003 during the entire period the data do not show any significant modification in the depth of the mode water core while they suggest that the thickness of the layer shrank the variability of the local air sea freshwater and heat fluxes cannot explain the observed salinity and temperature variations they are most likely related to the modifications of the properties of the spmw sources due to the recently evidenced changes driven by the north atlantic oscillation in the relative contributions of subtropical waters and subpolar waters in the iceland basin

cold seep carbonates of the middle and lower continental slope northern gulf of mexico authigenic carbonates from cold seeps on the middle and lower continental slope of the northern gulf of mexico gom exhibit a wide range of mineralogical and stable isotopic compositions these carbonates consist of concretions and nodules in surface sediments hardgrounds of crusts and isolated slabs and mounded buildups of blocks and slabs of up to over 10 meters in relief above the surrounding seafloor mineralogically the carbonates are dominated by high mg calcite hmc and aragonite however low levels 5 wt of dolomite are present in most samples petrographically mg calcite peloidal matrix and acicular to botryoidal aragonitic void filling cements are the most frequent associations the carbon isotopic compositions of the carbonates range from 60 8 to 14 0 pdb indicating complex carbon sources that include 13c depleted biogenic and thermogenic methane biodegraded crude oil seawater co2 and 13c enriched residual co2 from methanogenesis a similarly large variability in 18o values 2 5 to 6 7 pdb demonstrates the geochemical complexity of the slope with some samples pointing toward an 18o enriched oxygen source that is possibly related to advection of 18o enriched formation water and or to the decomposition of gas hydrate a considerable range of mineralogical and isotopic variations in cold seep carbonate composition was noted even within individual study sites however common trends occur across multiple geographic areas this situation suggests that local controls on fluid and gas flux types of seep hydrocarbons the presence or absence of gas hydrate in the near surface sediment and chemosynthetic communities as well as the temporal evolution of the local hydrocarbon reservoir all may play a part in determining carbonate mineralogy and isotope geochemistry the carbon isotope data clearly indicate that between site variation is greater than within site variation seep carbonates formed on the middle and lower continental slope of the gom do not appear to be substantially different from those found on the upper slope 1000 m water depth the highly variable fluids and gases that leave their geochemical imprints on seep carbonate of the middle and lower continental slope are similar to their outer shelf and upper slope counterparts

the gulf of mexico ecosystem six years after the macondo oil well blowout abstract the gulf of mexico ecosystem is a hotspot for biological diversity and supports a number of industries from tourism to fishery production to oil and gas exploration that serve as the economic backbone of gulf coast states the gulf is a natural hydrocarbon basin rich with stores of oil and gas that lie in reservoirs deep beneath the seafloor the natural seepage of hydrocarbons across the gulf system is extensive and thus the system s biological components experience ephemeral if not frequent hydrocarbon exposure in contrast to natural seepage which is diffuse and variable over space and time the 2010 macondo oil well blowout represented an intense focused hydrocarbon infusion to the gulf s deepwaters the macondo blowout drove rapid shifts in microbial populations and activity revealed unexpected phenomena such as deepwater hydrocarbon plumes and marine oil snow sedimentation and impacted the gulf s pelagic and benthic ecosystems understanding the distribution and fate of macondo oil was limited to some degree by an insufficient ability to predict the physical movement of water in the gulf in other words the available physical oceanographic models lacked critical components in the past six years much has been learned about the physical oceanography of the gulf providing transformative knowledge that will improve the ability to predict the movement of water and the hydrocarbons they carry in future blowout scenarios similarly much has been learned about the processing and fate of macondo hydrocarbons here we provide an overview of the distribution fate and impacts of macondo hydrocarbons and offer suggestions for future research to push the field of oil spill response research forward

dispersion of a tracer in the deep gulf of mexico a 25 km streak of cf3sf5 was released on an isopycnal surface approximately 1100 m deep and 150 m above the bottom along the continental slope of the northern gulf of mexico to study stirring and mixing of a passive tracer the location and depth of the release were near those of the deep hydrocarbon plume resulting from the 2010 deepwater horizon oil well rupture the tracer was sampled between 5 and 12 days after release and again 4 and 12 months after release the tracer moved along the slope at first but gradually moved into the interior of the gulf diapycnal spreading of the patch during the first 4 months was much faster than it was between 4 and 12 months indicating that mixing was greatly enhanced over the slope the rate of lateral homogenization of the tracer was much greater than observed in similar experiments in the open ocean again possibly enhanced near the slope maximum concentrations found in the surveys had fallen by factors of 104 107 and 108 at 1 week 4 months and 12 months respectively compared with those estimated for the initial tracer streak a regional ocean model was used to simulate the tracer field and help interpret its dispersion and temporal evolution model data comparisons show that the model simulation was able to replicate statistics of the observed tracer distribution that would be important in assessing the impact of oil releases in the middepth gulf

the inference of north atlantic circulation patterns from climatological hydrographic data we present a review of spiral techniques which have recently been developed for the determination of absolute velocity profiles from hydrographic observations a specific technique is then designed and applied to the north atlantic part of levitus 1982 climatological hydrographic atlas with the aim of estimating reference velocities and diffusivities for heat salt and potential vorticity these quantities are determined on a 1 grid from the local gradients of temperature and salinity under the constraints of the thermal wind relations and the conservation of the respective tracers including diapycnic and isopycnic mixing terms the estimation procedure includes the statistical framework of inverse modeling in the weighting of the constraints by the data noise variances and the determination of the covariances of the model parameters the resulting circulation pattern bears strong resemblance to the classical view of the north atlantic circulation as put foreward by wust 1935 and defant 1941 the upper layers are dominated by the gulf stream north atlantic current system with a broad subtropical gyre recirculation in the lower layer a western boundary current is fed from norwegian sea overflow penetrating the gibbs fracture zone and partly circulating around the labrador sea as a consequence of the climatological averaging the currents appear in broad shape with much reduced velocities in particular in the upper layer the vertical structure reveals an almost horizontal level of no motion pattern much along the concepts of defant 1941 diffusion coefficients were determined for an upper layer depth of mixed layer to 800 m depth and a lower layer 800 m to 2000 m the spatial pattern of these coefficients correlates with maps of eddy activity showing higher values in the strong current regimes and low values within the subtropical and subpolar gyre average values in the lower layer of the quiet regions are 10 5 m s and 10 m s for the diapycnal and isopycnal diffusivity respectively and 10 1 m s for the vertical diffusivity of vorticity which yields 10 m s for the lateral diffusivity of potential vorticity toward the regions of strong currents and in the upper layer these values roughly increase by an order of magnitude