eddy diffusivities estimated from observations in the labrador sea eddy diffusivities in the labrador sea ls are estimated from deep eddy resolving float trajectories moored current meter records and satellite altimetry a mean residence time of 248 days in the central ls is observed with several floats staying for more than 2 years by applying a simple random walk diffusion model the observed distribution of float residence times in the central ls could be explained by a mean eddy diffusivity of about 300 m2 s 1 estimates from float trajectories themselves and from moored current meter records yield significantly higher eddy diffusivities in the central ls of 950 1100 m2 s 1 this discrepancy can be explained by an inhomogeneity of the eddy diffusivity at middepth with high low values in the central ls region between central ls and deep labrador current which could be conjectured from the mean altimetric eddy kinetic energy eke distribution the different diffusivities explain both 1 a fast lateral homogenization of water masses in the central ls and 2 a weak exchange between central ls and boundary current the mean lagrangian length scale of 11 5 0 7 km as estimated from deep float trajectories is only slightly larger than the mean rossby radius of deformation 8 8 km largest eddy diffusivities within the central ls are associated with strong eddy drifts rather than with large swirl velocities and associated large eke between central ls and deep labrador current which could be conjectured from the mean altimetric eddy kinetic energy eke distribution the different diffusivities explain both 1 a fast lateral homogenization of water masses in the central ls and 2 a weak exchange between central ls and boundary current the mean lagrangian length scale of 11 5 0 7 km as estimated from deep float trajectories is only slightly larger than the mean rossby radius of deformation 8 8 km largest eddy diffusivities within the central ls are associated with strong eddy drifts rather than with large swirl velocities and associated large eke

radar imaging mechanism of marine sand waves at very low grazing angle illumination caused by unique hydrodynamic interactions 1 the investigations carried out between 2002 and 2004 during six field experiments within the operational radar and optical mapping in monitoring hydrodynamic morphodynamic and environmental parameters for coastal management oroma project aimed to improve the effectiveness of new remote sensing monitoring technologies such as shipborne imaging radars in coastal waters the coastal monitoring radar of the gkss research center geesthacht germany is based on a kelvin hughes rsr 1000 x band 9 42 ghz vertical vv polarized river radar and was mounted on board the research vessel ludwig prandtl during the experiments in the lister tief a tidal inlet of the german bight in the north sea the important progress realized in this investigation is the availability of calibrated x band radar data another central point of the study is to demonstrate the applicability of the quasi specular scattering theory in combination with the weak hydrodynamic interaction theory for the radar imaging mechanism of the seabed radar data have been taken at very low grazing angles 2 6 of flood and ebb tide oriented sand wave signatures at the sea surface during ebb tidal current phases current speeds perpendicular to the sand wave crest 0 6 m s 1 have been measured at wind speeds 4 5 m s 1 and water depths 25 m the difference between the maximum measured and simulated normalized radar cross section nrcs modulation of the ebb tide oriented sand wave is 27 for the flood tide oriented sand wave a difference of 21 has been calculated the difference between the minimum measured and simulated nrcs modulation of the ebb tide oriented sand wave is 10 and for the flood tide oriented sand wave a value of 43 has been derived phases of measured and simulated nrcs modulations correspond to asymmetric sand wave slopes the results of the simulated nrcs modulation show the qualitative trend but do not always quantitatively match the measured nrcs modulation profiles because the quasi specular scattering theory at very low grazing angle is a first order theory

aspects of the marine nitrogen cycle of the chukchi sea shelf and canada basin abstract as a highly productive seasonally ice covered sea with an expansive shallow continental shelf the chukchi sea fuels high rates of sedimentary denitrification this contributes to its fixed nitrogen n deficit relative to phosphorus p which is among the largest in the global ocean making the chukchi sea severely n limited during the phytoplankton growth season here we examine aspects of the n cycle on the chukchi sea shelf and the downstream canada basin using nutrients dissolved oxygen o 2 and the stable isotopes of nitrate no 3 in the northward flow path across the chukchi shelf bottom waters experienced strong o 2 drawdown from which we calculated a nitrification rate of 1 3 mmol m 2 d 1 this nitrification was likely primarily in sediments and directly fueled sedimentary denitrification historically measured at similar rates we observed significant accumulations of ammonium nh 4 in bottom waters of the chukchi shelf up to 5 m which were inversely correlated with 15 n no 3 indicating a sediment source of 15 n enriched nh 4 this is consistent with a process of coupled partial nitrification denitrification cpnd which imparts significant 15 n enrichment and 18 o depletion to pacific origin no 3 this cpnd mechanism is consistent with a significant decrease in 18 o no 3 relative to bering sea source waters indicating that at least 58 of no 3 populating the pacific halocline was regenerated during its transit across the north bering and chukchi shelves rather than arriving preformed from the bering sea slope this pacific origin no 3 propagates into the canada basin and towards the north atlantic being significantly 15 n enriched and 18 o depleted relative to the underlying atlantic waters

an annual study of inorganic and organic nitrogen and phosphorus and silicic acid in the southeastern beaufort sea 1 water column samples from the mackenzie shelf the beaufort sea and the amundsen gulf were obtained during 2003 2004 to investigate nutrient dynamics in an arctic ecosystem influenced by a large river and flaw lead polynya nutrient inventories in the upper water column showed a significant seasonal drawdown of nitrate no3 and silicic acid si oh 4 1 1 75 mol mol and subsequent accumulation of nitrite no2 and ammonium nh4 dissolved organic nitrogen and phosphorus concentrations don and dop were elevated in surface waters during the time of peak phytoplankton growth bloom and postbloom phases and covaried in a 17 1 molar ratio vertical profiles showed the typical middepth maxima in no3 po43 and si oh 4 at salinity 32 33 1 the concentration of dop 0 76 0 27 mol p l 1 was also 2 times higher in this layer compared to the surface average and inversely correlated with the water mass tracer n n no3 16 po43 2 9 0 87 suggesting that pacific derived waters were a source of the enrichment below the mixed layer don was generally constant with depth although averaged profiles like those of urea suggested the presence of subsurface maxima at 50 m and between 250 and 300 m regeneration ratios varied with depth and were approximately 9 0 mol o2 mol no3 and 122 5 mol o2 mol po43 in shallow pacific derived waters halocline layer and 17 4 and 193 5 in deep atlantic waters atlantic layer respectively deep waters of the amundsen gulf contained an excess of 1 7 mol no3 l 1 0 12 mol po43 l 1 and 6 2 mol si oh 4 l 1 and a deficit in o2 relative to waters of similar density in the beaufort sea in proportions consistent with the remineralization ratios derived from oxygen nutrient regressions enhanced export of particulate matter from the overlying polynya and subsequent remineralization at depth are hypothesized to create this nutrient enrichment

how does labrador sea water enter the deep western boundary current abstract labrador sea water lsw a dense water mass formed by convection in the subpolar north atlantic is an important constituent of the meridional overturning circulation understanding how the water mass enters the deep western boundary current dwbc one of the primary pathways by which it exits the subpolar gyre can shed light on the continuity between climate conditions in the formation region and their downstream signal using the trajectories of profiling autonomous lagrangian circulation explorer p alace floats operating between 1996 and 2002 three processes are evaluated for their role in the entry of labrador sea water in the dwbc 1 lsw is formed directly in the dwbc 2 eddies flux lsw laterally from the interior labrador sea to the dwbc and 3 a horizontally divergent mean flow advects lsw from the interior to the dwbc a comparison of the heat flux associated with each of these three mechanisms suggests that all three contribute to the transformation of the boundary current a

storm driven mixing and potential impact on the arctic ocean 1 observations of the ocean atmosphere and ice made by ice ocean environmental buoys indicate that mixing events reaching the depth of the halocline have occurred in various regions in the arctic ocean our analysis suggests that these mixing events were mechanically forced by intense storms moving across the buoy sites in this study we analyzed these mixing events in the context of storm developments that occurred in the beaufort sea and in the general area just north of fram strait two areas with quite different hydrographic structures the beaufort sea is strongly influenced by inflow of pacific water through bering strait while the area north of fram strait is directly affected by the inflow of warm and salty north atlantic water our analyses of the basin wide evolution of the surface pressure and geostrophic wind fields indicate that the characteristics of the storms could be very different the buoy observed mixing occurred only in the spring and winter seasons when the stratification was relatively weak this indicates the importance of stratification although the mixing itself was mechanically driven we also analyze the distribution of storms both the long term climatology and the patterns for each year in the past 2 decades the frequency of storms is also shown to be correlated but not strongly to arctic oscillation indices this study indicates that the formation of new ice that leads to brine rejection is unlikely the mechanism that results in the type of mixing that could overturn the halocline on the other hand synoptic scale storms can force mixing deep enough to the halocline and thermocline layer despite a very stable stratification associated with the arctic halocline the warm subsurface thermocline water is not always insulated from the mixed layer

boundary current eddies and their role in the restratification of the labrador sea an idealized model is used to study the restratification of the labrador sea after deep convection with emphasis on the role of boundary current eddies shed near the west coast of greenland the boundary current eddies carry warm buoyant irminger current water into the labrador sea interior for a realistic end of winter state it is shown that these irminger current eddies are efficient in restratifying the convected water mass in the interior of the labrador sea in addition it is demonstrated that irminger current eddies can balance a significant portion of the atmospheric heat loss and thus play an important role for the watermass transformation in the labrador sea

deep water bathymetric features imaged by spaceborne sar in the gulf stream region current 2 ms 1 and favorable ocean stratification sar image analysis shows the basic characteristics of these bathymetric features a coincident sea surface temperature image shows that the bathymetric feature is only visible by sar within the gs pathway the dominant wavelength of the wave like feature is about 2 3 km and their crests are perpendicular to the gs axis shipboard sounding measurements confirm the sar observation a theoretical consideration of the ocean current and corrugated bathymetry interaction in a 3 layer ocean is presented using representative ocean density profile data and the gs current data we analyze the requirements for the generation and upward propagation of the disturbance induced by the current bathymetry interaction citation li x x yang q zheng l j pietrafesa w g pichel z li and x li 2010 deep water bathymetric features imaged by spaceborne sar in the gulf stream region geophys res lett 37 l19603

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

on the connection between dense water formation overturning and poleward heat transport in a convective basin an isopycnal two layer idealized model for a convective basin is proposed consisting of a convecting interior region and a surrounding boundary current buoyancy and wind driven parameterized eddy fluxes govern the exchange between the two to balance the interior buoyancy loss the boundary current becomes denser as it flows around the basin geostrophy imposes that this densification be accompanied by sinking in the boundary current and hence by an overturning circulation the poleward heat transport associated with convection in the basin can thus be viewed as a result of both an overturning and a horizontal circulation when adapted to the labrador sea the model is able to reproduce the bulk features of the mean state the seasonal cycle and even the shutdown of convection from 1969 to 1972 according to the model only 40 of the poleward heat buoyancy transport of the labrador sea is associated with the overturning circulation an exact solution is presented for the linearized equations when changes in the boundary current are small numerical solutions are calculated for variations in the amount of convection and for changes in the remotely forced circulation around the basin these results highlight how the overturning circulation is not simply related to the amount of dense water formed a speeding up of the circulation around the basin due to wind forcing for example will decrease the intensity of the overturning circulation while the dense water formation remains unvaried in general it is shown that the fraction of poleward buoyancy or heat transport carried by the overturning circulation is not an intrinsic property of the basin but can vary as a result of a number of factors

impact of labrador sea convection on the north atlantic meridional overturning circulation abstract the overturning and horizontal circulations of the labrador sea are deduced from a composite vertical section across the basin the data come from the late spring early summer occupations of the world ocean circulation experiment woce ar7w line during the years 1990 97 this time period was chosen because it corresponded to intense wintertime convection the deepest and densest in the historical record suggesting that the north atlantic meridional overturning circulation moc would be maximally impacted the composite geostrophic velocity section was referenced using a mean lateral velocity profile from float data and then subsequently adjusted to balance mass the analysis was done in depth space to determine the net sinking that results from convection and in density space to determine the diapycnal mass flux i e the transformation of light water to labrador sea water the mean overturning cell is calculated to be 1 sv 1 sv 106 m3 s 1 as compared with a horizontal gyre of 18 sv the

color banding on georges bank as viewed by coastal zone color scanner observations of georges bank by coastal zone color scanner czcs show bandlike patterns that appear to be related to the large sand dunes and ridges which dominate the bottom topography there ship measurements of temperature and chlorophyll on georges bank in july 1979 also reflect the influence of the underwater dune fields the cause of the banding in the czcs data is unknown but is speculated to be the creation of alternating zones of divergence and convergence by tidal currents as the water flows over the underwater dune trough configuration the banding observed by czcs appears to be seasonal following the sequence of primary production in the gulf of maine and is believed to be important to biological processes as a site of new production and or as an effective transport mechanism any future models that attempt to interrelate tidal mixing and primary production must consider bottom topography and secondary flows

wave refraction in an ocean front side looking airborne radar near cape hatteras north carolina recorded images of ocean waves wind streaks and intermediate water bodies within the gulf stream front in the enclosed waters of pamlico sound the radar images showed good accuracy in defining directions and distinguished waves from wind streaks at overlapping frequencies in the spectrum in passing through the cyclonic shear in the gulf stream front waves from both sides turned to their left and so specified their directions of propagation differences between spectra obtained across the front are in accord with current refraction theory an inverse wave refraction calculation furnished current shear values from which horizontal profiles of water velocity were compiled the total calculated velocity change of 1 5 m s is similar to previous measurements a secondary front near shore contained a velocity difference of 0 25 m s velocity changes across the gulf stream front were correlated with temperature changes the radar there showed bands of high reflectivity at the edges of intermediate water bodies whose temperature differences implied very small velocity steps increased roughness at the intermediate water boundaries was attributed to current interaction with waves

distribution and circulation of labrador sea water abstract labrador sea water is the final product of the cyclonic circulation of subpolar mode water in the open northern north atlantic mccartney and talley 1982 the temperature and salinity of the convectively formed subpolar mode water decrease from 14 7 c 36 08 to 3 4 c 34 88 on account of the cumulative effects of excess precipitation and cooling the coldest mode water is labrador sea water which spreads at mid depths and is found throughout the north atlantic ocean north of 40 n and along its western boundary to 18 n a vertical minimum in potential vorticity is used as the primary tracer for labrador sea water labrador sea water is advected in three main directions out of the labrador sea 1 northeastward into the irminger sea 2 southeastward across the atlantic beneath the north atlantic current and 3 southward past newfoundland with the labrador current and thence westward into the slope water region crossing under the gulf stream off cape hatteras the labrador sea water core is

spatial and year to year patterns in new and primary productivity in sea ice melt regions of the eastern bering sea abstract four years of data on for new nitrate regenerated ammonium and primary carbon productivity 2007 through 2010 confirm the elevated productivity associated with the marginal ice zone miz of the eastern bering sea ebs in spring the greatest levels of productivity were associated with ice melt regions along the western edge of the ice pack population seeding and the shallowing of the mixed layer depth near the ice edge were less important in the development of elevated miz productivity than was the amount of ice melt entering surface water suggesting that ice contributed substances stimulating phytoplankton growth based on ice melt as an index of bloom development primary productivity continued to increase after new productivity peaked at the miz environments with optimal growth conditions new productivity averaged 18 6 mmol n m 2 d 1 with a ratio of 0 61 and primary productivity averaged 492 mmol c m 2 d 1 although these features were consistently recorded in late april early may they varied with the dynamics of ice cover whose retreat was later in 2008 relative to 2007 and 2009 the intense but localized miz blooms appear to be under sampled in ocean color imagery under ice productivity was generally low ave no3 0 45 mmol n m 2 d 1 ave primary prod 4 16 mmol c m 2 d 1 although larger values were measured under the western edge of the ice pack and in the st lawrence polynya region the advection of ice and water may contribute to the large values under the western ice edge and the highly transparent new ice may play a role in the polynya new and primary productivity rates of under ice samples were significantly inhibited when exposed to ice free irradiance levels in situ productivity could be estimated to 35 from rates measured on deck by adjusting for the impact of ice on submarine light the carbon to nitrate uptake ratio was closely related to specific carbon production in the in situ incubations

entrainment induced by near inertial drift of sea ice and its impact on under ice biogeochemical processes in marginal ice zones abstract mooring observation of hydrography hydrodynamics and suspended particles distribution under a drifting sea ice revealed the mixing and entrainment pattern in the upper mixed layer ml of the marginal ice zone the ice floe where the mooring system was installed drifted as near inertial motion with approximately 12 h cycle the mixing pattern induced by this near inertial drift can be divided into two distinct regimes first simple entrainment upward fluxes from the seasonal pycnocline to sea ice water boundary are induced by shear across ml and seasonal pycnocline during the period when ice floes drift toward pack ice the entrainment speed was in the range of 0 25 2 m h 1 which matches well with thickening and thinning of the ml during a near inertial period turbulent wakes on the boundary between sea ice and open water occurred behind the advancing edge of ice in the second regime when ice floes drift toward open ocean the turbulent wakes at the advancing edge of ice are combined with the entrainment caused by near inertial motion which results in a complex mixing pattern of both upward and downward fluxes in the ml the echo intensity observed by the acoustic doppler current profiler and beam attenuation from transmissometer revealed the elevated concentration of suspended particulate materials in the ml which can be direct evidence visualizing the mixing pattern results suggest that the mixing and entrainment found in our study sustain particulate matters in suspension within upper ml for a few months this may provide a potential mechanism to sustain abundant organic particulates in the ml and upper pycnocline for months after under ice bloom under strong wind events like storms the entrainment induced by near inertial motion may also get enhanced which causes elevated supply of nutrients from the deeper permanent pycnocline to the ml

deep convection in the irminger sea forced by the greenland tip jet open ocean deep convection one of the processes by which deep waters of the world s oceans are formed is restricted to a small number of locations for example the mediterranean and labrador seas recently the southwest irminger sea has been suggested as an additional location for open ocean deep convection the deep water formed in the irminger sea has the characteristic temperature and salinity of the water mass that fills the mid depth north atlantic ocean which had been believed to be formed entirely in the labrador basin here we show that the most likely cause of the convection in the irminger sea is a low level atmospheric jet known as the greenland tip jet which forms periodically in the lee of cape farewell greenland and is associated with elevated heat flux and strong wind stress curl using a history of tip jet events derived from meteorological land station data and a regional oceanic numerical model we demonstrate that deep convection can occur in this region when the north atlantic oscillation index is high which is consistent with observations this mechanism of convection in the irminger sea differs significantly from those known to operate in the labrador and mediterranean seas

impact of the large scale arctic circulation and the north water polynya on nutrient inventories in baffin bay 1 the distributions of nitrate phosphate and silicate in northern baffin bay were determined from 90 bottle casts taken between april 11 and july 21 1998 during late spring low salinity arctic water entered northern smith sound and mixed with baffin bay water bbw within the north water polynya the arctic water originated from the bering sea and contained high concentrations of phosphate and silicate referred to as silicate rich arctic water sraw the distribution of the two water masses was established using a new tracer siex which showed moderate penetration of sraw into smith sound during april and a very strong incursion in may and june consistent with the intensification of southward current velocities biological depletion of macronutrients in bbw began in april and continued until nitrate was exhausted from the upper mixed layer in early june beneath the polynya the deep waters 450 m showed a marked increase in nutrient concentration toward the bottom which was most pronounced in the south and much stronger for silicate than nitrate and phosphate the silicate enrichment was consistent with dissolution of diatom derived biogenic silica in deep waters the results indicate that the north water acts as a silicate trap in which the biota differentially transports surface silicate to depth thereby influencing local and downstream nutrient signatures

shallow water bottom topography from radar imagery radar imagery of shallow coastal waters usually 40 m deep contain unexplained features1 3 resembling the bottom topography since microwave radiation does not penetrate far in sea water these features must be the result of hydrodynamic processes coupled to the bottom topography that modulate the amplitude of the short bragg resonant sea surface waves the main contributors to the backscattered radar power4 5 because many different hydrodynamic processes operate in coastal waters and the precise mechanism which generates the radar images is not fully established a programme to explore the mechanism s was initiated at the us naval research laboratory here we give a brief description of the possible mechanisms and results from the pilot experiment conducted in july 1982 40 nautical miles south east of nantucket island

assessing the importance of terrestrial organic carbon in the chukchi and beaufort seas abstract the western arctic ocean is a unique part of the world s oceans and is an area undergoing significant climate changes the effects and possible climate feedbacks of these changes are not yet fully understood decreased sea ice cover could lead to increased productivity in the water column or a reduction in total productivity through the loss of sea ice algal contributions climate change could also alter the patterns of terrestrial inputs from rivers and coastal erosion in order to better understand the balance of organic material inputs in the western arctic ocean this report presents carbon and nitrogen elemental and isotopic compositions from 19 surface sediment samples and 7 cores from 4 shelf to basin transects as evidence of the sources of organic matter buried in the sediments of the chukchi and alaskan beaufort seas the c n ratios for surface sediments were between 5 3 and 11 5 mean 9 0 1 3 the mean toc was 1 2 0 3 and mean tn was 0 16 0 02 the highest toc contents were observed in the barrow canyon transect likely reflecting heightened overlying productivity the 13 c of this preserved material varied from 22 1 to 16 7 mean 19 4 1 3 a trend to depletion in 13 c and higher c n in eastern sites was observed among the surface samples 15 n varied from 4 1 to 7 6 mean 5 7 1 1 an evaluation of the inputs of organic matter to the western arctic sediment was accomplished using 13 c and 15 n values with the novel technique of a bayesian analysis multi source mixing model this model was used to estimate proportional contributions of sea ice algae water column phytoplankton and terrestrial organic matter we conclude that water column productivity is the source of between 50 and 70 of the organic carbon buried in this portion of the western arctic the remaining 25 35 of carbon is mainly supplied by sea ice algal productivity with at most 15 of sedimentary carbon derived from terrestrial inputs

determination of particulate organic carbon sources to the surface mixed layer of the canada basin arctic ocean stable isotope ratios of particulate organic carbon poc together with other tracers were analyzed in samples from the canada basin surface mixed layer in 2008 and 2009 sampling was conducted during the end of the 2008 melt season and at the beginning of the 2009 freezeup under a variety of surface conditions including open water newly formed seasonal ice and multiyear ice in both years poc exhibited a wide isotopic range 13c poc 24 5 to 31 1 with the most isotopically depleted material generally found in the central basin isotopically enriched material was found on the shelves consistent with higher biological production and strongly correlated with in situ carbon uptake rates in contrast offshore in the central basin there was no significant relationship between 13c poc distributions and either chlorophyll a or aqueous co2 concentrations suggesting that in situ biological production was not the dominant control analysis of freshwater sources suggested that the sea ice melt contribution of poc to surface waters in the central canada basin exerted a negligible influence on 13c poc distributions and instead isotopically depleted poc in the surface waters of the central canada basin were sourced externally through advective transport of riverine organic matter we show that alkalinity and meteoric water content can be used to distinguish poc inputs from north american and russian rivers and our analysis suggests that russian river inputs are the predominant source of 13c depleted organic matter to the mixed layer of the central canada basin

seasonal and interannual variations of irminger ring formation and boundary interior heat exchange in flame abstractthe contribution of warm core anticyclones shed by the irminger current off west greenland known as irminger rings to the restratification of the upper layers of the labrador sea is investigated in the 1 12 family of linked atlantic models experiment flame model the model output covering the 1990 2004 period shows strong similarities to observations of the irminger current as well as ring observations at a mooring located offshore of the eddy formation region in 2007 09 an analysis of fluxes in the model shows that while the majority of heat exchange with the interior indeed occurs at the site of the irminger current instability the contribution of the coherent irminger rings is modest 18 heat is provided to the convective region mainly through noncoherent anomalies and enhanced local mixing by the rings facilitating further exchange between the boundary and interior the time variability of the eddy kinetic energy and the boundary to interior heat flux in the model are strongly corr

contrasting inherent optical properties and particle characteristics between an under ice phytoplankton bloom and open water in the chukchi sea abstract variability in the inherent optical properties iops of seawater and characteristics of the particle assemblage were examined along a transect in the chukchi sea during july 2011 this transect encompassed samples from open waters of the marginal ice zone exhibiting low concentrations of chlorophyll a chl a 3 as well as an extensive phytoplankton bloom chl a 30 mg m 3 beneath consolidated pack ice measurements included the spectral coefficients for particulate beam attenuation backscattering and absorption bulk indicators of particle concentration and composition and the particle size distribution within the bloom microphytoplankton contributed 95 to the total chl a and relatively small amounts of nonalgal particles were present this assemblage exhibited low chl a specific phytoplankton absorption coefficients 0 006 m 2 mg 1 at 676 nm indicating a strong influence of pigment packaging and a weak spectral dependence of the particulate backscattering coefficient in contrast the phytoplankton community in nutrient depleted surface waters outside the sea ice had a strong contribution of picoplankton to chl a 54 and an increased abundance of nonalgal particles the chl a specific phytoplankton absorption coefficient approached maximum values at 676 nm 0 023 m 2 mg 1 and particle backscattering had much stronger spectral dependence additional samples from near the sea floor exhibited characteristics of either mineral dominated assemblages or a mixture of mineral and organic particles and also displayed optical differentiation from the surface samples the marked contrast in absorption attenuation and backscattering properties of these ecological regimes suggest that they can be discriminated from optical measurements available on a variety of in situ and remote sensing platforms

advection in polar and sub polar environments impacts on high latitude marine ecosystems we compare and contrast the ecological impacts of atmospheric and oceanic circulation patterns on polar and sub polar marine ecosystems circulation patterns differ strikingly between the north and south meridional circulation in the north provides connections between the sub arctic and arctic despite the presence of encircling continental landmasses whereas annular circulation patterns in the south tend to isolate antarctic surface waters from those in the north these differences influence fundamental aspects of the polar ecosystems from the amount thickness and duration of sea ice to the types of organisms and the ecology of zooplankton fish seabirds and marine mammals meridional flows in both the north pacific and the north atlantic oceans transport heat nutrients and plankton northward into the chukchi sea the barents sea and the seas off the west coast of greenland in the north atlantic the advected heat warms the waters of the southern barents sea and with advected nutrients and plankton supports immense biomasses of fish seabirds and marine mammals on the pacific side of the arctic cold waters flowing northward across the northern bering and chukchi seas during winter and spring limit the ability of boreal fish species to take advantage of high seasonal production there southward flow of cold arctic waters into sub arctic regions of the north atlantic occurs mainly through fram strait with less through the barents sea and the canadian archipelago in the pacific the transport of arctic waters and plankton southward through bering strait is minimal in the southern ocean the antarctic circumpolar current and its associated fronts are barriers to the southward dispersal of plankton and pelagic fishes from sub antarctic waters with the consequent evolution of antarctic zooplankton and fish species largely occurring in isolation from those to the north the antarctic circumpolar current also disperses biota throughout the southern ocean and as a result the biota tends to be similar within a given broad latitudinal band south of the southern boundary of the acc there is a large scale divergence that brings nutrient rich water to the surface this divergence along with more localized upwelling regions and deep vertical convection in winter generates elevated nutrient levels throughout the antarctic at the end of austral winter however such elevated nutrient levels do not support elevated phytoplankton productivity through the entire southern ocean as iron concentrations are rapidly removed to limiting levels by spring blooms in deep waters however coastal regions with the upward mixing of iron maintain greatly enhanced rates of production especially in coastal polynyas in these coastal areas elevated primary production supports large biomasses of zooplankton fish seabirds and mammals as climate warming affects these advective processes and their heat content there will likely be major changes in the distribution and abundance of polar biota in particular the biota dependent on sea ice

microwave probing of shallow water bottom topography in the nantucket shoals coordinated microwave and in situ measurements were performed during the 1982 naval research laboratory phelps bank experiment nantucket shoals the measurements including airborne x band apd 10 synthetic aperture radar imagery and airborne x and shipboard l band coherent radars together with extensive hydrographic oceanographic and meteorological information are reported the microwave measurements show large variations of backscatter power over 20 db at both l and x band for winds less than 7 m s generally regions of strong backscatter cluster near large bottom slopes suggesting their generation by the bottom topography however for winds greater than 7 m s 7 12 m s in this experiment the variations of microwave backscatter power decrease to 2 3 db for both frequency bands and become decorrelated from the bottom topography an explanation for this may be that wind drift near the surface layer tends to mask the ocean surface features relating to the bottom topography when its magnitude is comparable to the rotary tide and the residual circulation due to tidal stress a current gradient front seemingly not related to bottom topography also produced 20 db variations in the power backscattered to the l band radar

the impact of freshening on phytoplankton production in the pacific arctic ocean since the 1990s drastic melting of sea ice and continental ice in the arctic region triggered by global warming has caused substantial freshening of the arctic ocean while several studies attempted to quantify the magnitude of this freshening its consequences on primary producers remain poorly documented in this study we evaluate the impact of the freshwater content fwc of the upper arctic ocean on phytoplankton across the pacific sector from the bering strait 65 n to the north pole 86 n during summer 2008 we performed statistical analyses on the physical biogeochemical and biological data acquired during the chinare 2008 cruise to investigate the effect of sea ice melting on the arctic phytoplankton we found that the strong freshening observed in the canada basin had a negative impact on primary producers as a result of the deepening of the nitracline and the establishment of a subsurface chlorophyll maximum scm in contrast regions with lower freshening such as the chukchi shelf and the marginal ice zone miz over the chukchi borderland exhibited a shallower nitracline sustaining relatively high primary production and biomass our results imply that the predicted increase freshening in future years will likely cause the arctic deep basin to become more oligotrophic because of weaker surface nutrient renewal from the subsurface ocean despite higher light penetration

hydrography of the labrador sea during active convection the hydrographic structure of the labrador sea during wintertime convection is described the cruise part of the deep convection experiment took place in february march 1997 amidst an extended period of strong forcing in an otherwise moderate winter because the water column was preconditioned by previous strong winters the limited forcing was enough to cause convection to approximately 1500 m the change in heat storage along a transbasin section relative to an occupation done the previous october gives an average heat loss that is consistent with calibrated national centers for environmental prediction surface heat fluxes over that time period 200 wm 22 deep overturning was observed both seaward of the western continental slope which was expected as well as within the western boundary current itself something that had not been directly observed previously these two geographical regions separated by roughly the 3000 m isobath produce separate water mass products the offshore water mass is the familiar cold fresh dense classical labrador sea water lsw the boundary current water mass is a somewhat warmer saltier lighter vintage of classical lsw though in the far field it would be difficult to distinguish these products the offshore product was formed within the cyclonic recirculating gyre measured by lavender et al in a region that is limited to the north most likely by an eddy flux of buoyant water from the eastern boundary current the velocity measurements taken during the cruise provide a transport estimate of the boundary current throughput and offshore recirculation finally the overall trends in stratification of the observed mixed layers are described

wind driven shelf basin exchange on an arctic shelf the joint roles of ice cover extent and shelf break bathymetry 1 the efficiency of shelf basin exchange sbe in polar regions during summer is strongly moderated by the location of the ice edge relative to underlying topography numerical model calculations suggest that upwelling favorable winds generate very little sbe so long as the ice edge remains shoreward of the shelf break but an abrupt onset of shelf break upwelling takes place when the ice edge retreats beyond the shelf break a climatology 1968 2000 of ice conditions from the canadian shelf of the beaufort sea shows large interannual variability in ice edge extent and duration of ice free conditions in summer similarly available hydrographic data reflect a corresponding variability in water mass properties under scenarios of climate warming associated with greenhouse gas build up both the extent and duration of summer melt back are predicted to increase and this may have dramatic impacts on sbe and biological productivity

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

ekman and eddy exchange of freshwater and oxygen across the labrador shelf break abstracttransport of freshwater from the labrador shelf into the interior labrador sea has the potential to impact deep convection via its influence on the salinity of surface waters to examine this transport the authors deployed two underwater gliders on a mission to traverse the continental shelf break multiple times between 5 july and 22 august 2014 the period when arctic meltwater has historically peaked in transport down the labrador shelf the field campaign yielded a unique dataset of temperature salinity and oxygen across the shelf break to a depth of 1000 m at unprecedented spatial resolution two mechanisms of cross shelf transport were examined ekman transport and transport due to mesoscale eddies ekman transport is quantified using satellite wind stress and near surface hydrographic properties and eddy induced transport is scaled using a parameterized eddy diffusivity and thickness gradients of layers of uniform potential density as well as the tracer gradients along those isopycnals

is there a north south phase shift in the surface labrador current transport on the interannual to decadal scale 1 the transport of the labrador current has substantial interannual to decadal variability that may significantly impact the ocean climate and marine ecosystem off atlantic canada and northeast united states nevertheless the alongshore coherence of the labrador current on the interannual to decadal scales has been a long standing question here we have used satellite altimetry data to study interannual to decadal variability of the unit depth surface labrador current in the past two decades in the context of the subpolar gyre of the north atlantic the study for the first time reveals that the transport over the labrador and northeastern newfoundland slope is out of phase with that over the scotian slope the surface labrador current transport is positively and negatively correlated with the winter north atlantic oscillation nao index with the transport lagging by about 1 year in the north the labrador and northeastern newfoundland slope and in the south the scotian slope respectively in addition the surface labrador current transport declines over the labrador slope and northeastern newfoundland slope and increases over the scotian slope the north south phase shift suggests two distinct regimes which warrants further studies of underlying dynamic mechanisms and may have important implications for regional ecosystems and climate

on the behaviour of tidal current directions due to the presence of submarine sand waves abstract side scan sonar records reveal that the crestlines of megaripples in the troughs as well as on both sides of the slopes of sand waves form an angle with the crestline of the sand waves itself the existence of such an angle between the crestline of megaripples and sand waves indicates that changes of the tidal current direction across sand waves can be expected direct evidence that such tidal current direction changes occur above sand waves is derived from measurements of the air sea interaction drift buoy asib system at the sea surface and from side scan sonar records of the sea bed both systems were operated from on board research vessels during two c star field experiments in the hoek van holland study area off the dutch coast in april 1996 and in april 1997 measurements performed by electrical resistance wires on board the asib system indicate that variations of the short and moderate wave direction and the wave directional spread are associated with changes of the tidal current direction at the sea surface according to the results of the measurements derived from the asib system and the side scan sonar records it can be summarised that the variation of the direction of short and moderate period water waves as well as changes of the tidal current speed and direction across large sand waves must be considered for correct modelling of the wave current interaction mechanism

ocean surface patterns above sea floor bedforms as recorded by radar southern bight of north sea abstract airborne radar observations of the southern bight of the north sea have revealed sea surface patterns that reflect a constructional sea floor topography of tide built sand waves and sand ridges the patterns result from local horizontal differences in the amplitude of water surface waves with wavelengths less than 1 cm such modulations result from surface convergences and divergences as the water flows across structures on the ocean floor three sand ridges were observed which form a topological series defined by side slope asymmetry and sand wave pattern depth appears to be the controlling variable with shallow water leading to the steepest slopes most intense asymmetry and the most marked separation of sand waves into ebb and flood dominated domains

boundary circulation at the exit of the labrador sea the deep circulation and related transports of the southern labrador sea are determined from direct current observations from ship surveys and a moored current meter array the measurements covered a time span from summer 1997 to 1999 and show a well defined deep boundary current extending approximately out to the 3300 m depth contour and weak reverse currents farther offshore the flow has a strong barotropic component and significant baroclinic flow is only found in the shallow labrador current at the shelf break and associated with a deep core of denmark strait overflow water the total deep water transport below 27 74 kg m 3 was 26 5 sv sv 106 m3 s 1 comprising labrador sea water lsw gibbs fracture zone water gfzw and denmark strait overflow water dsow intraseasonal variability of the flow and transport was high ranging from 15 to 35 sv and the annual means differed by 17 a seasonal cycle is confined to the shallow labrador current in its deeper part where the mean flow is still strong no obvious seasonality could be detected the transport of the interior anticyclonic recirculation was estimated from lowered acoustic doppler current profiler stations and geostrophy yielding about 9 sv thus the net deep water outflow from the labrador sea was about 17 sv the baroclinic transport of gfzw and dsow referenced to the depth of the isopycnal 27 80 kg m 3 is only about one third of the total transport in these layers longer term variations of the total transports are not represented well by the baroclinic contribution

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

eddies of newly formed upper labrador sea water a new type of submesoscale eddy has been observed south of the labrador sea during late winter embedded in equatorward flow along the western boundary the eddy radius is 20 km with a weak dynamic signature swirl speed of 0 5 cm s the center of the eddy is characterized by weak stratification elevated concentrations of oxygen and anthropogenic tracers and low tracer ages all indicative of newly ventilated water strong lateral intrusions distort the shape of the feature the water mass contained in the eddy is not classical labrador sea water from the central labrador sea but is significantly fresher and hence lighter it is of the correct density to be the source of the high chlorofluorocarbon layer of the shallow deep western boundary current observed further south and hence is termed upper labrador sea water using a combination of hydrographic data sets along the western boundary to implement a simple lateral diffusion model it is shown that such eddies decay of the order of several months and are difficult to observe equatorward of the grand banks of newfoundland this is in contrast to deeper lenses of classical labrador sea water which persist further equatorward tracer derived ages of the upper labrador sea water eddy range from 3 to 5 years much older than the lifetime deduced from their lateral diffusion a simple convection model of tracer age shows that this age discrepancy is caused by gas exchange being unable to maintain equilibrium between the deep convecting mixed layer and the atmosphere during formation

the impact of resolution on the adjustment and decadal variability of the atlantic meridional overturning circulation in a coupled climate model variations in the atlantic meridional overturning circulation moc exert an important influence on climate particularly on decadal time scales simulation of the moc in coupled climate models is compromised to a degree that is unknown by their lack of fidelity in resolving some of the key processes involved there is an overarching need to increase the resolution and fidelity of climate models but also to assess how increases in resolution influence the simulation of key phenomena such as the moc in this study we investigate the impact of significantly increasing the ocean and atmosphere resolution of a coupled climate model on the simulation of moc variability by comparing high and low resolution versions of the same model in both versions decadal variability of the moc is closely linked to density anomalies that propagate from the labrador sea southward along the deep western boundary we demonstrate that the moc adjustment proceeds more rapidly in the higher resolution model due the increased speed of western boundary waves however the response of the atlantic sea surface temperatures to moc variations is relatively robust in pattern if not in magnitude across the two resolutions the moc also excites a coupled ocean atmosphere response in the tropical atlantic in both model versions in the higher resolution model but not the lower resolution model there is evidence of a significant response in the extratropical atmosphere over the north atlantic 6 years after a maximum in the moc in both models there is evidence of a weak negative feedback on deep density anomalies in the labrador sea and hence on the moc with a time scale of approximately ten years our results highlight the need for further work to understand the decadal variability of the moc and its simulation in climate models

physical and biological characteristics of the pelagic system across fram strait to kongsfjorden abstract the fram strait is very important with regard to heat and mass exchange in the arctic ocean and the large quantities of heat carried north by the west spitsbergen current wsc influence the climate in the arctic region as a whole a large volume of water and ice is transported through fram strait with net water transport of 1 7 3 2 sv southward in the east greenland current and a volume ice flux in the range of 0 06 0 11 sv the mean annual ice flux is about 866 000 km2 yr 1 the kongsfjorden krossfjorden fjord system on the coast of spitsbergen or at the eastern extreme of fram strait is mainly affected by the northbound transport of water in the wsc mixing processes on the shelf result in transformed atlantic water in the fjords and the advection of atlantic water also carries boreal fauna into the fjords the phytoplankton production is about 80 g c m 2 yr 1 in fram strait and has been estimated both below and above this for kongsfjorden the zooplankton fauna is diverse but dominated in terms of biomass by calanoid copepods particularly calanus glacialis and c finmarchicus other important copepods include c hyperboreus metridia longa and the smaller more numerous pseudocalanus p minutus and p acuspes microcalanus m pusillus and m pygmaeus and oithona similis the most important species of other taxa appear to be the amphipods themisto libellula and t abyssorum the euphausiids thysanoessa inermis and t longicaudata and the chaetognaths sagitta elegans and eukrohnia hamata a comparison between the open ocean of fram strait and the restricted fjord system of kongsfjorden krossfjorden can be made within limitations the same species tend to dominate but the fram strait zooplankton fauna differs by the presence of meso and bathypelagic copepods the seasonal and inter annual variation in zooplankton is described for kongsfjorden based on the record during july 1996 2002 the ice macrofauna is much less diverse consisting of a handful of amphipod species and the polar cod the ice associated biomass transport of ice amphipods was calculated based on the ice area transport at about 3 55 106 ton wet weight per year or about 4 2 105 t c yr 1 this represents a large energy input to the greenland sea but also a drain on the core population residing in the multi year pack ice myi in the arctic ocean a continuous habitat loss of myi due to climate warming will likely reduce dramatically the sympagic food source the pelagic and sympagic food web structures were revealed by stable isotopes the carbon sources of particulate organic matter pom being ice pom and pelagic pom revealed different isotopic signals in the organisms of the food web and also provided information about the sympagic pelagic and pelagic benthic couplings the marine food web and energy pathways were further determined by fatty acid trophic markers which to a large extent supported the stable isotope picture of the marine food web although some discrepancies were noted particularly with regard to predator prey relationships of ctenophores and pteropods

lagrangian observations of the deep western boundary current in the north atlantic ocean abstract in this study the authors analyze the trajectories of 18 rafos floats launched in the deep western boundary current dwbc between the grand banks and cape hatteras to investigate the kinematics and dynamics in the region where the dwbc crosses under the gulf stream near 36 n the crossover region floats deployed in the chlorofluorocarbon cfc maximum associated with upper labrador sea water depth 800 m illustrate the entrainment process of this water mass into the gulf stream the behavior of the floats and fluid parcels in the crossover region is strongly dependent on the meandering of the gulf stream when the stream is close to its mean position fluid parcels entrained from the upper dwbc travel along the northern edge of the stream when a meander trough is present downstream of the entrainment location dwbc fluid parcels cross the gulf stream and sometimes are expelled on the south side this represents a previously unrecognized mechanism for transporting upper labrador sea w

labrador sea water tracked by profiling floats from the boundary current into the open north atlantic fifteen profiling floats were injected into the deep boundary current off labrador they were ballasted to drift in the core depth of labrador sea water lsw at 1500 m depth and were deployed in two groups during march and july august 1997 initially for about three months the floats were drifting within the boundary current and the flow vectors were used to determine the mean horizontal structure of the deep labrador current which was found to be about 100 km wide with an average core speed of 18 cm s 1 north of flemish cap the boundary current encounters complicated topography around orphan knoll and there the lsw outflow splits up into different routes one obvious lsw path is eastward through the charlie gibbs fracture zone and another route is a narrow recirculation toward the central labrador sea a surprising result was that none of the floats were able to follow the boundary current southward to the grand banks area and exit into the subtropics trajectories and temperature profiles of the eastward drifting floats indicate the importance of the north atlantic current for dispersing the floats even at the level of lsw

on the linkage between labrador sea water volume and overturning circulation in the labrador sea a case study on proxies abstractalthough proxies have generally been used to study deep ocean convection and overturning circulation in the labrador sea their efficacy has not been explicitly evaluated because observations that directly measure those variables are scarce in this study the volume of newly formed labrador sea water lsw and the overturning circulation in the labrador sea are estimated using observational data and output from a high resolution ocean model and then compared to proxies used to represent those variables the comparisons reveal the limitations of proxies highlighting the desirability of robust estimates derived from direct monitoring in the region i e from argo and overturning in the subpolar north atlantic program osnap a linkage among lsw formation overturning circulation in the labrador sea and the export of lsw from the basin on interannual time scales is found in the model

sea surface manifestation of along tidal channel underwater ridges imaged by sar a group of submerged ocean bottom sand ridges in the bohai sea china are shown in radarsat 1 and envisat synthetic aperture radar sar images the sand ridges appear as fingerlike quasi linear features in the sar images examining the detailed local bathymetry chart we find that these features coincide with the satellite images the heights of the sand ridges are less than 10 m and the water depth is between 10 and 30 m the spacing of the sand ridges is about 10 km and the length of the sand ridges is about 20 km the same sand ridges are also visible on a moderate resolution imaging spectroradiometer modis true color image the semidiurnal and diurnal tidal currents in this area are almost parallel to the major axis of these sand ridges these observations cannot be explained using the existing 1 d sar imaging model which is not applicable to sand ridges parallel to the tidal current in this paper we consider the shallow water current bathymetry in a 2 d space an analytical ocean model was applied to demonstrate the temporal variations of the current divergence and convergence that are induced by the along sand ridge direction current and ridge interaction a radar simulation model is used to simulate the variation of normalized radar cross section nrcs induced by the ocean surface current the simulated nrcs variation is similar to that extracted from the calibrated sar image simulation results also show that the nrcs variation becomes negligible when the ocean current is set to about half of the maximum tidal current

isotopic fractionation of oxygen and nitrogen in coastal marine sediments abstract the bulk and isotopic exchanges of o2 n2 no3 and nh4 between sediments and the overlying water benthic flux were measured at three shallow locations in puget sound using a benthic tripod oxygen consumption by the sediments averaged 4 4 mmol m 2 d 1 while n2 gas fluxes averaged 1 1 mmol m 2 d 1 the nitrogen gas flux out of the sediments was always greater than the corresponding no3 flux into the sediments indicating a large nitrification contribution to the n2 flux isotopic changes in overlying water 18o of o2 were small with an average apparent sediment respiration fractionation factor e of 3 this fractionation factor is much smaller than that measured in either the open ocean or in the laboratory the low degree of fractionation is hypothesized to occur because of the interaction of diffusive layers around reactive microsites within these sediments there was no apparent isotopic fractionation of downward diffusing no3 e 0 while the ammonium that diffused out of the sediments averaged 4 5 o heavier than both source organic matter within the sediments and overlying water no3 the large discrepancy in isotopic composition between the source organic material and nh4 can be attributed to significant isotopic fractionation of ammonium during nitrification in the oxic zone finally the 15n of n2 did not change significantly over the course of the incubations in agreement with the nitrogen isotopic budget for these sediments

bloom dynamics in early opening waters of the arctic ocean we measured the isotopic composition and accumulation of particulate organic matter pom and the uptake of carbon c and nitrogen n in an early bloom of the most productive recurring polynya of the arctic ocean the estimated compensation irradiance at the onset of the bloom was similar to the average for the north atlantic ocean implying that shallow mixing was of critical importance for the bloom s early initiation planktonic pom had a much lower d 13 c than ice pom suggesting that ice algae contributed little to the pelagic biomass the overall isotopic fractionation of pelagic n during bloom development was consistent with in situ diatom growth under saturating irradiance and limiting no soon after the ice cleared rapid physiological changes induced an order of 2 3 magnitude increase in the c and no uptake capacity of diatoms leading to very high f ratios no uptake total 2 2 3 3 n uptake most of the no taken up appeared in the pom so that little net release of reduced n occurred during 2 3 the period of active growth given the tight coupling between photosynthesis and no uptake under n limitation 2 3 the magnitude of primary production in the arctic ocean is expected to respond to changes in n supply

role of resolved and parameterized eddies in the labrador sea balance of heat and buoyancy abstractdeep convection in the labrador sea is an important component of the global ocean ventilation the associated loss of heat to the atmosphere from the interior of the sea is thought to be mostly supplied by mesoscale eddies generated either remotely or as a result of convection itself processes that are not resolved by low resolution ocean climate models the authors first employ a high resolution ocean model forced with high resolution 33 km 3 h atmospheric fields to further elaborate on the role of mesoscale eddies in maintaining the balance of heat and buoyancy in the labrador sea in general agreement with previous studies it is found that eddies remove heat along the coast and supply it to the interior some of the eddies that are generated because of the barotropic instability off the west coast of greenland are recaptured by the boundary current in the region of deep convection the convergence of heat and buoyancy by eddies significantly increases with the deepening of the winter

variability of the deep western boundary current east of the grand banks the deep western boundary current east of the grand banks has been observed during 1999 2005 by moored current meter stations and shipboard current profiling sections these recent observations can be compared with those of a woce moored array deployed during 1993 95 at the same location overall the observations of deep water currents east of the grand banks reported here do not support suggestions of a basin wide slowdown of the atlantic meridional overturning circulation

observations of open ocean deep convection in the labrador sea from subsurface floats abstract the occurrence and extent of deep convection in the labrador sea in winters 1996 97 and 1997 98 is investigated from measurements of over 200 neutrally buoyant subsurface profiling autonomous lagrangian circulation explorer palace and sounding oceanographic lagrangian observer solo floats in addition to providing drift velocity data and vertical profiles of temperature and salinity 55 floats are equipped with vertical current meters vcms time series of vertical velocity derived from measured pressure and vertical flow past the float and temperature are obtained from the vcm floats mixed layer depths estimated from profile measurements indicate that convection reached depths greater than 1300 m in 1997 but no deeper than 1000 m in 1998 deep mixed layers were concentrated in the western basin although a number of deep mixed layers were observed southwest of cape farewell and also north of 60 n the highest variance in vertical velocity and the lowest mean temperatures were found in t

variability of the directly observed middepth subpolar north atlantic circulation satellite views of the ocean have suggested a decline of the subpolar north atlantic surface circulation during the 1990s and 2000s this was a period of unprecedented observational capacity in the basin thanks to the presence of many hundreds of profiling floats we use more than 40 000 subsurface displacements of these floats to characterize the circulation at 1000 m depth and its evolution from 1997 2013 we show a statistically significant slowdown in the labrador sea boundary currents of 0 8 cm s 1 per decade 95 confidence interval of 1 4 to 0 15 cm s 1 per decade a conservative estimate of the uncertainty otherwise the middepth circulation field was largely stable our analysis of the location where the north atlantic current crosses the mid atlantic ridge shows that profiling floats can reveal steering by bathymetric features but do not reveal of decadal variability in the position where the current crosses the ridge