impact of shelf basin freshwater transport on deep convection in the western labrador sea abstractfreshwater exiting the arctic ocean through the canadian arctic archipelago caa has been shown to affect meridional overturning circulation and thereby the global climate system however because of constraints of spatial resolution in most global ocean models neither the flow of low salinity water through the caa to the labrador sea nor the eddy activity that may transport freshwater from the shelf to areas of open ocean convection can be directly simulated to address these issues this study uses a high resolution ice ocean model of the pan arctic region with a realistic caa and forced with realistic atmospheric data this model resolves conditions in the arctic ocean upstream of the labrador sea and is coupled to a thermodynamic dynamic sea ice model that responds to the atmospheric forcing the major shelf basin exchange of liquid freshwater occurs south of hamilton bank whereas the largest ice flux occurs in the northwest of the basin freshwater flux anomalies entering the labrador sea

surprising return of deep convection to the subpolar north atlantic ocean in winter 2007 2008 in the process of open ocean convection in the subpolar north atlantic ocean surface water sinks to depth as a distinct water mass the characteristics of which affect the meridional overturning circulation and oceanic heat flux in addition carbon is sequestered from the atmosphere in the process in recent years this convection has been shallow or non existent which could be construed as a consequence of a warmer climate here we document the return of deep convection to the subpolar gyre in both the labrador and irminger seas in the winter of 2007 2008 we use profiling float data from the argo programme to document deep mixing analysis of a variety of in situ satellite and reanalysis data shows that contrary to expectations the transition to a convective state took place abruptly without going through a phase of preconditioning changes in hemispheric air temperature storm tracks the flux of fresh water to the labrador sea and the distribution of pack ice all contributed to an enhanced flux of heat from the sea to the air making the surface water sufficiently cold and dense to initiate deep convection given this complexity we conclude that it will be difficult to predict when deep mixing may occur again

quasi decadal salinity fluctuations in the labrador sea abstract the quasi decadal salinity fluctuations in the upper 300 m of the labrador sea are investigated by partitioning all available salinity station data since 1948 by region and bottom depth there are major freshwater anomalies in the early 1970s the great salinity anomaly mid 1980s and early 1990s these vary in amplitude throughout the region being least on the shelf and greatest over the slope region near the labrador current the labrador sea cannot be considered a simple conduit for freshwater anomalies originating in the east greenland current there is evidence that local processes modulate the anomaly the freshwater anomalies in the labrador current are approximately twice as large as those in the east greenland current the baffin island current flowing southward through the western davis strait is the only local source of freshwater with sufficient volume to account for this increase the propagation speed 2 3 cm s 1 of the anomaly along the labrador sea margin is much less than the

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

observations of irminger sea anticyclonic eddies mesoscale anticyclonic eddies in the irminger sea are observed using a mooring and a glider between 2002 and 2009 the mooring observed 53 anticyclones using a kinematic model objective estimates of eddy length scales and velocity structure are made for 16 eddies anticyclones had a mean core diameter of 12 km and their mean peak observed azimuthal speed was 0 1 m s 1 they had core salinities and potential temperatures of 34 91 34 98 and 4 488 5 34 degrees c respectively making them warm and salty features these properties represent a typical salinity anomaly of 0 03 and a temperature anomaly of 0 28 degrees c from noneddy values all eddies had small 1 rossby numbers in 2006 the glider observed two anticyclones having diameters of about 20 km and peak azimuthal speeds of about 0 3 m s 1 similar salinity anomalies were detected throughout the irminger sea by floats profiling in anticyclones two formation regions for the eddies are identified one to the west of the reykjanes ridge and the other off the east greenland irminger current near cape farewell close to the mooring observations indicate that eddies formed in the former region are larger than eddies observed at the mooring a clear increase in eddy salinity is observed between 2002 and 2009 the observed breakup of these eddies in winter implies that they are a source of salt for the central gyre the anticyclones are similar to those found in both the labrador sea and norwegian sea making them a ubiquitous feature of the subpolar north atlantic basins

the holocene labrador current changing linkages to atmospheric and oceanographic forcing factors the role of labrador current lc in providing freshwater to the north atlantic and hence modulating the atlantic meridional overturning circulation amoc has been debated with very few data this study provides the first data on the relative speed of the lc for the past 9 2 ka using mean size of the sortable silt of sediments as a proxy from a mid shelf basin in the western labrador sea lc speed progressively intensified from 9 2 5 ka during which two meltwater events had minor influence the lc was fastest between 5 ka and 3 1 ka and gradually weakened after 3 1 ka the mean size of the sortable silt data shows overall co variations with similar existing data from deep water areas of the greater north atlantic suggesting an overarching link that modulates changes in both the near surface and deep north atlantic a dynamical link between the lc and amoc vigor is hypothesized in which high meltwater discharge in the labrador sea oriented the subpolar gyre spg more north south meridional weakening the spg and thus decelerating the upper limb of the amoc conversely reduction in lc transport during the late holocene due to the greater export of sea ice oriented the spg more east west

buoyant eddies entering the labrador sea observed with gliders and altimetry abstract intense buoyant anticyclonic eddies spawned from the west greenland boundary current were observed with high resolution autonomous seaglider hydrography and satellite altimetry as they entered the labrador sea interior surveys of their internal structure establish the transport of both low salinity water in the upper ocean and warm saline irminger water at depth the observed eddies can contribute significantly to the rapid restratification of the labrador sea interior following wintertime deep convection these eddies have saline cores between 200 and 1000 m low salinity cores above 200 m and a velocity field that penetrates to at least 1000 m with 0 1000 m average speeds exceeding 40 cm s 1 their trajectory together with earlier estimates of the gyre circulation suggests why the observed region of deep convection is so small and does not occur where wintertime cooling by the atmosphere is most intense the cyclostrophic surface velocity field of the anticylones from satellite altimetry

the effect of arctic freshwater pathways on north atlantic convection and the atlantic meridional overturning circulation abstractthis study examines the relative roles of the arctic freshwater exported via different pathways on deep convection in the north atlantic and the atlantic meridional overturning circulation amoc deep water feeding the lower branch of the amoc is formed in several north atlantic marginal seas including the labrador sea irminger sea and the nordic seas where deep convection can potentially be inhibited by surface freshwater exported from the arctic the sensitivity of the amoc and north atlantic to two major freshwater pathways on either side of greenland is studied using numerical experiments freshwater export is rerouted in global coupled climate models by blocking and expanding the channels along the two routes the sensitivity experiments are performed in two sets of models cm2g and cm2m with different control simulation climatology for comparison freshwater via the route east of greenland is found to have a larger direct impact on labrador sea convection in response to the changes of

mechanisms behind the temporary shutdown of deep convection in the labrador sea lessons from the great salinity anomaly years 1968 71 abstractfrom 1969 to 1971 convection in the labrador sea shut down thus interrupting the formation of the intermediate dense water masses the shutdown has been attributed to the surface freshening induced by the great salinity anomaly gsa a freshwater anomaly in the subpolar north atlantic the abrupt resumption of convection in 1972 in contrast is attributed to the extreme atmospheric forcing of that winter here oceanic and atmospheric data collected in the labrador sea at ocean weather station bravo and a one dimensional mixed layer model are used to examine the causes of the shutdown and resumption of convection in detail these results highlight the tight coupling of the ocean and atmosphere in convection regions and the need to resolve both components to correctly represent convective processes in the ocean they are also relevant to present day conditions given the increased ice melt in the arctic ocean and from the greenland ice sheet the analysis herein shows that the shutdown was initiat

sea ice anomalies observed in the greenland and labrador seas during 1901 1984 and their relation to an interdecadal arctic climate cycle two independent ice data sets from the greenland and labrador seas have been analyzed for the purpose of characterizing interannual and decadal time scale sea ice extent anomalies during this century sea ice concentration data for the 1953 1984 period revealed the presence of a large positive anomaly in the greenland sea during the 1960s which coincided with the great salinity anomaly an upper ocean low salinity water mass that was observed to travel cyclonically around the northern north atlantic during 1968 1982 this ice anomaly as well as several smaller ones propagated into the labrador sea and then across to the labrador and east newfoundland coast over a period of 3 to 5 years a complex empirical orthogonal function analysis of the same data also confirmed this propagation phenomenon an inverse relation between sea ice and salinity anomalies in the greenland labrador sea region was also generally found an analysis of spring and summer ice limit data obtained from danish meteorological institute charts for the period 1901 1956 indicated the presence of heavy ice conditions i e positive ice anomalies in the greenland sea during 1902 1920 and in the late 1940s and generally negative ice anomalies during the 1920s and 1930s only limited evidence of the propagation of greenland sea ice anomalies into the labrador sea was observed however probably because the data were from the ice melt seasons on the other hand several large ice anomalies in the greenland sea occurred 2 3 years after large runoffs in the early 1930s and the late 1940s from northern canada into the western arctic ocean similarly a large runoff into the arctic during 1964 1966 preceded the large greenland sea ice anomaly of the 1960s these facts together with recent evidence of climatic jumps in the northern hemisphere tropospheric circulation suggest the existence of an interdecadal self sustained climate cycle in the arctic in the greenland sea this cycle is characterized by a state of large sea ice extent overlying an upper layer of cool relatively fresh water that does not convectively overturn which alternates every 10 15 years with a state of small sea ice extent and relatively warm saline surface water that frequently overturns

sources of eddy kinetic energy in the labrador sea experiments with a suite of north atlantic general circulation models are used to examine the sources of eddy kinetic energy eke in the labrador sea a high resolution model version 112 quantitatively reproduces the observed signature a particular feature of the eke in the labrador sea is its pronounced seasonal cycle with a maximum intensity in early winter as already found in earlier studies based on altimeter data in contrast to a previously advanced hypothesis the seasonally varying eddy field is not related to a forcing by high frequency wind variations but can be explained by a seasonally modulated instability of the west greenland current wgc the main source of eke in the labrador sea is an energy transfer due to reynolds interaction work barotropic instability in a confined region near cape desolation where the wgc adjusts to a change in the topographic slope geostrophic contours tend to converge upstream of cape desolation such that the topographically guided wgc narrows as well and becomes barotropically unstable the eddies spawned from the wgc instability area dominating the eke in the interior labrador sea are predominantly anticyclonic with warm and saline cores in the upper kilometer of the water column while the few cyclones originating as well from the instability area show a more depth independent structure companion experiments with a model exhibit the strength of the wgc influenced by either changes in the wind stress or heat flux forcing as a leading factor determining seasonal to interannual changes of eke in the labrador sea

a study of the interaction of the north atlantic oscillation with ocean circulation observed patterns of wind stress curl and air sea heat flux associated with the north atlantic oscillation nao are used to discuss the response of ocean gyres and thermohaline circulation to nao forcing and their possible feedback on the nao the observations motivate and are interpreted in the framework of a simple mathematical model that couples ekman layers ocean gyres and thermohaline circulation to the atmospheric jet stream meridional shifts in the zero wind stress curl line are invoked to drive anomalies in ocean gyres and north south dipoles in air sea flux drive anomalous thermohaline circulation both gyres and thermohaline circulation play a role in modulating sea surface temperature anomalies and hence through air sea interaction the overlying jet stream the model which can be expressed in the form of a delayed oscillator with ocean gyres and or thermohaline circulation providing the delay identifies key nondimensional parameters that control whether the ocean responds passively to nao forcing or actively couples it suggests that both thermohaline circulation and ocean gyres can play a role in coupled interactions on decadal timescales

origin and composition of seasonal labrador sea freshwater the depth of winter convection in the central labrador sea is strongly influenced by the prevailing stratification in late summer for this late summer stratification salinity is as important as temperature and in the upper water layers salinity even dominates to analyze the source of the spring and summer freshening in the central region seasonal freshwater cycles have been constructed for the interior labrador sea the west greenland current and the labrador current it is shown that none of the local freshwater sources is responsible for the spring summer freshening in the interior which appears to occur in two separate events in april to may and july to september comparing the timing and volume estimates of the seasonal freshwater cycles of the boundary currents with the central labrador sea helps in understanding the origin of the interior freshwater signals the first smaller pulse cannot be attributed clearly to either of the boundary currents the second one is about three times stronger and supplies 60 of the seasonal summer freshwater transport estimates and calculated mixing properties provide evidence that its source is the west greenland current the finding implies a connection also on interannual time scales between labrador sea surface salinity and freshwater sources in the west greenland current and farther upstream in the east greenland current the freshwater input from the west greenland current thus also is the likely pathway for the known modulation of labrador sea water mass formation by freshwater export from the arctic via the east greenland current which implies some predictability on longer time scales

phytoplankton biomass cycles in the north atlantic subpolar gyre a similar mechanism for two different blooms in the labrador sea an analysis of seasonal variations in climatological surface chlorophyll points to distinct biogeographical zones in the north atlantic subpolar gyre in particular the labrador sea appears well delineated into two regions on either side of the 60 n parallel with very different climatological phytoplankton biomass cycles indeed north of 60 n an early and short spring bloom occurs in late april while south of 60 n the bloom gradually develops 1 month later and significant biomass persists all summer long nevertheless at climatological scale the first order mechanism that controls the bloom is identical for both bioregions the light mixing regime can explain the bloom onset in both bioregions in the labrador sea the blooms seem to rely on a mean community compensation irradiance threshold value of 2 5 mol photon m 2 d 1 over the mixed layer

formation and propagation of great salinity anomalies north atlantic arctic ocean and sea ice variability for the period 1948 2001 is studied using a global ocean general circulation model coupled to a dynamic thermodynamic sea ice model forced by daily ncep ncar reanalysis data kalnay et al 1996 variability of arctic sea ice properties is analysed in particular the formation and propagation of sea ice thickness anomalies that are communicated via fram strait into the north atlantic these export events led to the great salinity anomalies gsa of the 1970s 1980s and 1990s in the labrador sea ls all gsas were found to be remotely excited in the arctic rather than by local atmospheric forcing over the ls sea ice and fresh water exports through the canadian archipelago caa are found to be only of minor importance except for the 1990s gsa part of the anomalies are tracked to the newfoundland basin where they enter the north atlantic current the experiments indicate only a minor impact of a single gsa event on the strength of the north atlantic thermohaline circulation thc

structure and variability of the west greenland current in summer derived from 6 repeat standard sections abstract six historical sections across the west greenland current are examined three sections have been regularly occupied since the late 1950s while the three southern ones have been taken since 1984 significant variability is observed for the freshwater core of the coastal current on the shelf with salinity varying by over 3 units between years there is also significant variability in the shape and offshore position of the main shelf break front leading to large variability in eulerian velocities significant presence of irminger water is seen during the 1960s and the 2000s being found right across the sections in recent years maximum mean transport relative to the 34 8 isohaline of 5 5 3 9 sv relative to 700 db for 1984 2005 is observed at the cape desolation section transports decrease to the north with the majority of the exchange with the interior of the labrador sea occurring between cape desolation and fylla bank inter decadal transport variability is observed at fylla bank while a decline in transports since peaks in the early 1990s is seen at cape farewell and cape desolation freshwater transport is largest at cape desolation with a mean summer transport of 60 2 20 5 msv freshwater transport increases slightly between cape farewell and cape desolation and we suggest it is related to local discharge by glaciers into juliannehaab bight as well as the melting of sea ice we also find that years of high greenland ice cap melt are consistently associated with years of high freshwater transport at cape desolation suggesting a portion of the freshwater transport of the west greenland current may be associated with melt from the greenland ice sheet finally significantly enhanced freshwater transports 33 msv at cape desolation compared to the long term mean are seen in 2008 probably a signature of the record arctic ocean ice melt and export in 2007

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

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

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

rates and mechanisms of water mass transformation in the labrador sea as inferred from tracer observations time series of hydrographic and transient tracer 3h and 3he observations from the central labrador sea collected between 1991 and 1996 are presented to document the complex changes in the tracer fields as a result of variations in convective activity during the 1990s between 1991 and 1993 as atmospheric forcing intensified convection penetrated to progressively increasing depths reaching 2300 m in the winter of 1993 over that period the potential temperature salinity s properties of labrador sea water stayed nearly constant as surface cooling and downward mixing of freshwater was balanced by excavating and upward mixing of the warmer and saltier northeast atlantic deep water it is shown that the net change in heat content of the water column 150 2500 m between 1991 and 1993 was negligible compared to the estimated mean heat loss over that period 110 w m 2 implying that the lateral convergence of heat into the central labrador sea nearly balances the atmospheric cooling on a surprisingly short timescale interestingly the 3h 3he age of labrador sea water increased during this period of intensifying convection starting in 1995 winters were milder and convection was restricted to the upper 800 m between 1994 and 1996 the evolution of 3h 3he age is similar to that of a stagnant water body in contrast the increase in and s over that period implies exchange of tracers with the boundaries via both an eddy induced overturning circulation and along isopycnal stirring by eddies with an exchange coefficient of o 500 m2 s 1 the authors construct a freshwater budget for the labrador sea and quantitatively demonstrate that sea ice meltwater is the dominant cause of the large annual cycle of salinity in the labrador sea both on the shelf and the interior it is shown that the transport of freshwater by eddies into the central labrador sea 140 cm between march and september can readily account for the observed seasonal freshening finally the authors discuss the role of the eddy induced overturning circulation with regard to transport and dispersal of the newly ventilated labrador sea water to the boundary current system and compare its strength 2 3 sv to the diagnosed buoyancy forced formation rate of labrador sea water

observations of the labrador sea eddy field this paper is an observational study of small scale coherent eddies in the labrador sea a region of dense water formation thought to be of considerable importance to the north atlantic overturning circulation numerical studies of deep convection emphasize coherent eddies as a mechanism for the lateral transport of heat yet their small size has hindered observational progress a large part of this paper is therefore devoted to developing new methods for identifying and describing coherent eddies in two observational platforms current meter moorings and satellite altimetry details of the current and water mass structure of individual eddy events as they are swept past by an advecting flow can then be extracted from the mooring data a transition is seen during mid 1997 with long lived boundary current eddies dominating the central labrador sea year round after this time and convectively formed eddies similar to those seen in deep convection modeling studies apparent prior to this time the topex poseidon altimeter covers the labrador sea with a loose net of observations through which coherent eddies can seem to appear and disappear by concentrating on locating and describing anomalous events in individual altimeter tracks a portrait of the spatial and temporal variability of the underlying eddy field can be constructed the altimeter results reveal an annual pulsation of energy and of coherent eddies originating during the late fall at a particular location in the boundary current pinpointing the time and place of the boundary current type eddy formation the interannual variability seen at the mooring is reproduced but the mooring site is found to be within a localized region of greatly enhanced eddy activity notably lacking in both the annual cycle and interannual variability is a clear relationship between the eddies or eddy energy and the intensity of wintertime cooling these eddy observations as well as hydrographic evidence suggest an active role for boundary current dynamics in shaping the energetics and water mass properties of the interior region

the mean surface circulation of the north atlantic subpolar gyre a comparison of estimates derived from new gravity and oceanographic measurements 1 a new mean sea surface topography msst is used to estimate the surface circulation of the subpolar gyre of the northwest atlantic the msst is produced using a new geoid model derived from a blend of gravity data from the gravity recovery and climate experiment grace satellite mission satellite altimeters and terrestrial measurements the msst is compared with a topography produced by an ocean model which is spectrally nudged to a new argo period temperature and salinity climatology the mean surface circulation associated with the geodetic msst is compared with estimates of the circulation from surface drifters moorings and other in situ measurements the geodetic msst and circulation estimate are found to be in good agreement with the other estimates both qualitatively and quantitatively the topography is found to be an improvement over an earlier geodetic estimate with better resolution of the coastal currents deficiencies are identified in the ocean model s estimate of flow over shelf regions

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

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

freshwater sources to the coastal ocean off northeastern north america evidence from h2 18o h2 16o oxygen isotope h218o h216o salinity data identify freshwater sources along the northeastern north american continental margin the oxygen isotope 18o salinity s properties of various water types are distinguished sea ice formation on the labrador shelf is shown to influence 18o s values it is estimated that 2 3 m of freshwater is extracted from the water column to form sea ice it is hypothesized that waters on the scotian shelf gulf of maine and the middle atlantic bight are composed of slope water diluted by an upstream low salinity source this upstream source is a mixture of brine enriched labrador shelf water and st lawrence river water the 18o value of the apparent freshwater component 18os 0 of waters on the scotian shelf and farther south is 20 which has been used to suggest a sole high latitude freshwater source we show instead that the st lawrence river contributes 35 of the freshwater on the scotian shelf in agreement with the physical oceanographic evidence the remaining freshwater is supplied by high latitude rivers dominated by arctic runoff finally the isotope evidence identifies baffin bay as an important pathway by which freshwater from the arctic ocean can reach the labrador sea

labrador sea boundary currents and the fate of the irminger sea water abstract the general circulation of the labrador sea is studied with a dataset of 53 surface drifters drogued at 15 m and several hydrographic sections done in may 1997 surface drifters indicate three distinct speed regimes fast boundary currents a slower crossover from greenland to labrador and a slow eddy dominated flow in the basin interior mean eulerian velocity maps show several recirculation cells located offshore of the main currents in addition to the cyclonic circulation of the labrador sea above the northern slope of the basin the surface drifters have two preferential paths one between the 1000 m and 2000 m isobaths and the other close to the 3000 m isobath the vertical shear estimated from ctd data supports the presence of two distinct currents around the basin one current more baroclinic flows between the 1000 m and 2000 m isobaths the other one more barotropic flows above the lower continental slope the irminger sea water carried by the boundary currents is altered as it tr

evolution of the freshwater coastal current at the southern tip of greenland abstractshipboard hydrographic and velocity measurements collected in summer 2014 are used to study the evolution of the freshwater coastal current in southern greenland as it encounters cape farew

the normalised optimised anisotropic wavelet coefficient noawc method an image processing tool for multi scale analysis of rock fabric the 2d anisotropic wavelet transform 2dawt is an image analysis tool which is able to decipher signals where information obtained from different scales are intermixed extended from the optimised anisotropic wavelet coefficient method oawc of ouillon et al 1995 we present a method which discriminates the objects and groups of objects depending on their area shape ratio orientation and position illustrated in a synthetic example we show that this method allows one to distinguish between different sub populations of objects within a single phase and quantify the anisotropies of shape orientation and spatial distribution at different scales objects clusters of objects alignments of objects or clusters applied to a natural rock sample sidobre granite montagne noire france the 2dawt has permitted us to detect and accurately characterise the different levels of mineral organisation and thus to contribute to the understanding of the physical processes such as crystallisation fluid migration deformation etc responsible for such organisations

labrador current variability over the last 2000 years the ice loaded labrador current lc is an important component of the western north atlantic circulation that influences the position and strength of the northern limb of the north atlantic current nac this flow of cold and fresh polar waters originating from the arctic has a marked impact on the north atlantic climate yet little is known about its variability beyond the instrumental period in this study we present the first sub decadal alkenone based 2000 year long sea surface temperature sst records from the western labrador sea a climatically crucial region at the boundary between the lc and the nac our results show a clear link between the lc strength and the northern annular mode nam with a stronger nam and a more vigorous lc during the medieval climate anomaly mca this suggests enhanced lc activity upon future global warming with implications for the atlantic meridional overturning circulation amoc

horizontal stratification during deep convection in the labrador sea abstractdeep convection the process by which surface waters are mixed down to 1000 m or deeper forms the primary downwelling of the meridional overturning circulation in the northern hemisphere high resolution hydrographic measurements from seagliders indicate that during deep convection though water is well mixed vertically there is substantial horizontal variation in density over short distances tens of kilometers this horizontal density variability present in winter january february contains sufficient buoyancy to restratify the convecting region to observed levels 2 5 months later as estimated from argo floating platforms these results highlight the importance of small scale heterogeneities in the ocean that are typically poorly represented in climate models potentially contributing to the difficulty climate models have in representing deep convection

holocene temperature and landscape history of southwest greenland inferred from isotope and geochemical lake sediment proxies abstract terrestrial temperature reconstructions from the ice free margins of greenland are critical for constraining the sensitivity of the greenland ice sheet to past climate change numerous investigations have clarified the glacial history of southwest greenland in recent decades however very few local quantitative temperature reconstructions exist as context for changes in the cryosphere we examine sedimentary records from two lakes south of nuuk greenland informally named lakes t1 and t2 and investigate millennial scale holocene climate change using a multi proxy approach changes in x ray fluorescence spectroscopy xrf 15n 13c and biogenic silica concentrations of bulk lake sediments mark the transition from a marine environment to isolated lakes as relative sea level fell in the early holocene 18o values of subfossil insects chironomids from lakes t1 and t2 decreased by 2 3 from c 8 8 ka bp minimum limiting age for the onset of lacustrine sediment deposition in lake t2 ka bp thousands of years before 1950 to 1 ka bp existing isotope independent temperature reconstructions from the west coast of greenland suggest that these changes in 18o values accompanied gradual cooling of 2 4 c concomitant with decreasing summer insolation there is widespread regional evidence that this cooling resulted in progressive regrowth of local glaciers and of the ice sheet the regional consensus on the magnitude of this temperature change indicates that the local modern modeled temperature precipitation 18o relationship cannot be used to quantify millennial scale temperature changes at these sites through the holocene this reinforces that studies utilizing 18o based proxies to infer temperature change should carefully assess local isotope temperature relationships over space and time

fram strait sea ice outflow 1 we summarize 24 years 1978 2002 of ice export estimates and examine over a 9 year record the associated variability in the time varying upward looking sonar uls thickness distributions of the fram strait a more thorough assessment of the pmw passive microwave ice motion with 5 years of synthetic aperture radar sar observations shows the uncertainties to be consistent with that found by kwok and rothrock 1999 giving greater confidence to the record of ice flux calculations interesting details of the cross strait motion profiles and ice cover characteristics revealed by high resolution sar imagery are discussed the average annual ice area flux over the period is 866 000 km2 yr between the 1980s and 1990s the decadal difference in the net exported ice area is 400 000 km2 approximately half the annual average except for the years with extreme negative nao correlation of winter ice area export with the nao index remains high r2 0 62 with thickness estimates from uls moorings we estimate the average annual ice volume flux 8 years to be 2218 km3 yr 0 07 sv over the 9 year uls ice thickness data set there is an overall decrease of 0 45 m in the mean ice thickness over the entire time series and a decrease of 0 23 m over the winter months december through march correspondingly the mode of the my ice thickness exhibits an overall decrease of 0 55 m and a winter decrease of 0 42 m these are significant trends whether these trends are indicative of the thickness trends of the arctic ocean is examined as the time varying behavior of the monthly uls thickness distributions can be related not only to the seasonal cycle in the basal growth and melt but also to the magnitude and pattern of ice motion in the arctic ocean and the proximity of the uls moorings to the ice edge

transient two dimensional simulation of real flood events in a mediterranean floodplain the application of a two dimensional 2d finite volume numerical model to real flood events in the ebro river is presented the hydraulic model used is based on the 2d transient shallow water equations on the irregular bed that are able to compute flow advance over a dry bed this study involves the reliable simulation of not only the flood wave advance but also the drying process in a series of events of different magnitude the importance of the correct characterization of the roughness coefficient and the topography is emphasized in the study the former is estimated from a previous classification of structurally homogeneous habitats and the latter is defined by merging the digital terrain model data with a hydraulic river bed elevation reconstruction algorithm the calibration of the full model resulting from the roughness bed river and flow simulation models is based on field measurements of the flooded area for two steady discharges the validation is performed by comparing the numerical results with the water levels measured during five flood events at certain times with the flooded area and time series of continuous point measurements of water depth during different situations throughout the year because the model provides correct predictions of the surface processes both for low and high flow discharges the simulation results are used to analyze the present floodplain hydrodynamics in the same way different topographic scenarios on the basis of changes in the hydraulic river floodplain connectivity are generated to analyze their potentially beneficial effect in the floodplain geomorphic dynamics doi 10 1061 asce hy 1943 7900 0000565 2012 american society of civil engineers ce database subject headings unsteady flow overland flow hydration dewatering flood plains shallow water mediterranean sea simulation author keywords unsteady surface flow wetting drying finite volume shallow water hydrodynamic floodplain hydraulic bed reconstruction