toxic alexandrium blooms in the western gulf of maine the plume advection hypothesis revisited the plume advection hypothesis links blooms of the toxic dinoflagellate alexandrium fundyensein the western gulf of maine gom to a buoyant plume derived from river outflows this hypothesis was examined with cruise and moored instrument observations in 1993 when levels of paralytic shellfish poisoning psp toxins were high and in 1994 when toxicity was low a coupled physical biological model simulated hydrography and a fundyense distributions initial a fundyense populations were restricted to low salinity nearshore waters near casco bay but also occurred in higher salinity waters along the plume boundary this suggests two sources of cells those from shallow water cyst populations and those transported to shore from offshore blooms in the eastern segment of the maine coastal current emcc observations confirm the role of the plume ina fundyense transport and growth downwelling favorable winds in 1993 transported the plume and its cells rapidly alongshore enhancing toxicity and propagating psp to the south in 1994 sustained upwelling moved the plume offshore resulting in low toxicity in intertidal shellfish a fundyense blooms were likely nutrient limited leading to low growth rates and moderate cell abundances these observations and mechanisms were reproduced by coupled physical biological model simulations the plume advection hypothesis provides a viable explanation for outbreaks of psp in the western gom but should be refined to include two sources for cells that populate the plume and two major pathways for transport one within the low salinity plume and another where a fundyense cells originating in the emcc are transported along the outer boundary of the plume front with the western segment of the maine coastal current

physical processes affecting circulation and hydrography in the sable gully of nova scotia abstract the sable gully is the largest submarine canyon along the shelf break off the east coast of north america the circulation and hydrography in the gully have significant temporal and spatial variability this paper presents a numerical study of the three dimensional circulation and hydrography in the gully using a multi nested ocean circulation model the model is forced by tides wind stress and surface heat freshwater fluxes model results are in fair agreement with the current and hydrographic observations made in the gully in 2006 and 2007 a process study is conducted to examine the main physical processes affecting the circulation and hydrography including tide topography interaction wind forcing and the shelf scale circulation over the eastern canadian shelf the model results demonstrate that the circulation and hydrography above the canyon rim are influenced significantly by wind particularly during storm events while the subsurface flow over the shelf slope is affected by the shelf scale circulation there is also significant tide topography interaction inside the gully

surface mass balance of small glaciers on james ross island north eastern antarctic peninsula during 2009 2015 two small glaciers on james ross island the north eastern antarctic peninsula experienced surface mass gain between 2009 and 2015 as revealed by field measurements a positive cumulative surface mass balance of 0 57 0 67 and 0 11 0 37 m w e was observed during the 2009 2015 period on whisky glacier and davies dome respectively the results indicate a change from surface mass loss that prevailed in the region during the first decade of the 21st century to predominantly positive surface mass balance after 2009 10 the spatial pattern of annual surface mass balance distribution implies snow redistribution by wind on both glaciers the mean equilibrium line altitudes for whisky glacier 311 16 m a s l and davies dome 393 18 m a s l are in accordance with the regional data indicating 200 300 m higher equilibrium line on james ross and vega islands compared with the south shetland islands the mean accumulation area ratio of 0 68 0 09 and 0 44 0 09 determined for whisky glacier and davies dome respectively is similar to the value reported for vega island and within the range of typical values for high latitude glaciers

explaining the weddell polynya a large ocean eddy shed at maud rise satellite observations have shown the occasional occurrence of a large opening in the sea ice cover of the weddell sea antarctica a phenomenon known as the weddell polynya the transient appearance position size and shape of the polynya is explained here by a mechanism by which modest variations in the large scale oceanic flow past the maud rise seamount cause a horizontal cyclonic eddy to be shed from its northeast flank the shed eddy transmits a divergent ekman stress into the sea ice leading to a crescent shaped opening in the pack atmospheric thermodynamical interaction further enhances the opening by inducing oceanic convection a sea ice ocean computer model simulation vividly demonstrates how this mechanism fully accounts for the characteristics that mark weddell polynya events

a tidal model for eastern juan de fuca strait and the southern strait of georgia a three dimensional barotropic finite element model is used to calculate the tidal flows in eastern juan de fuca strait and the southern strait of georgia the harmonics of eight constituents are computed and compared with those from previous finite difference models and those from historical tide gauge and current meter observations root mean square differences between observed and calculated sea level amplitudes are within 2 0 cm for all constituents and the phases are within 4 0 for all constituents except k2 horizontal currents from the model are found to reproduce the observed vertical variations in shear except in regions where stratification effects and internal tides exist in particular the model representation of currents at six stations in the canadian tide and current tables volume 5 is accurate the pattern of tidal residual currents has much more detail than previous coarser resolution models and numerous eddies are predicted computed energy flux fields reveal that over a 29 day period only 38 of the tidal power entering juan de fuca strait is transmitted into the southern strait of georgia and of the 39 entering haro strait 36 is dissipated within the strait itself

influence of stratification on residual tidal currents in the yellow sea the m 2 tide and residual current generation in the yellow sea are examined using the blumberg and mellor 1987 numerical coastal ocean circulation model with no stratification the model tide and tidal currents show good agreement with the observed tide and tidal currents coherent residual currents are predicted around the southwest of korea flowing northward as a strong jet with a maximum speed of 8cm s 1 and around yangtze bank flowing southeastward as a weak broad current with initial stratification tidal mixing occurs in the bottom boundary layer which leads to surface tidal fronts around yangtze bank and the southwest of korea and our model experiments reproduce successfully the basic water property structure in these regions the resulting stratified tidal rectification intensifies the residual currents at the front and at the top of the bottom boundary layer over the sloping bottom so that the vertical structure of the residual currents is modified the strong residual currents in the top of the bottom mixed layer around yangtze bank support the interpretation of kim et al 1991 for the southeastward movement of yellow sea bottom cold water in summer the residual currents in the surface layer reach 40 of the mean currents observed by beardsley et al 1992 using satellite tracked drifters deployed in the yellow sea in summer these results suggest that stratified tidal rectification is an important process in driving the summertime subtidal flow in the yellow sea

the adjoint method of data assimilation used operationally for shelf circulation a real time shelf circulation model with data assimilation has been successfully used possibly for the first time on the outer nova scotian shelf the adjoint method was used to infer the time histories of flows across the four open boundaries of a 60 km 60 km shallow water equation model of western bank the aim was to hindcast and nowcast currents over the bank so that a patch of water initially 15 km in diameter could be resampled over a 3 week period as part of a study of the early life history of atlantic cod observations available in near real time for assimilation were from 14 drifting buoys 2 telemetering moored current meters the ship s acoustic doppler current profiler and the local wind for the postcruise hindcasts presented here data from two bottom pressure gauges and two more current meters are also available the experiment was successful and the patch was sampled over a 19 day period that included two intense storms in this paper we 1 document the model and how the data are assimilated 2 present and discuss the observations 3 demonstrate that the interpolative skill of the model exceeds that of simpler schemes that use just the current velocity data and 4 provide examples of how particle tracking with the model enables asynoptically acquired data to be displayed as synoptic maps greatly facilitating both underway cruise planning and postcruise data analysis an interesting feature of the circulation on the bank was a nearly stationary eddy atop the bank crest larvae within the eddy were retained on the bank in a favorable environment until the onset of the storms the variable integrity of the eddy may contribute to fluctuations of year class success

wind effects on a front over the continental shelf slope a continuously stratified two dimensional vertical and seaward model is used to study the effects of alongshore wind on a front between lighter water over the continental shelf and heavier water in the offshore ocean the model produces three components of alongshore flows one component associated with the horizontal density front and two wind driven components one near the coast and one over the shelf break the cross shore circulation has two near surface features a seaward component resulting from the offshore density gradient and a shoreward seaward component resulting from the right hand left hand alongshore wind stress which has the coast to the right left facing downstream these two components contribute to the maintenance of the front with no wind low density water over the shelf tends to move toward the offshore ocean associated with the near surface seaward flow resulting in flatter isopycnal surfaces a moderate right hand alongshore wind suppresses the density driven surface flow and constrains the shelf water while a strong wind in the same direction pushes the front shoreward and makes isopycnal surfaces steeper resulting in increased exchange of the shelf water a left hand alongshore wind contributes to more rapid frontal relaxation and a seaward shift in its position these results are applied to the labrador shelf

the influence of eddy viscosity parameterization and turbulence energy closure scheme upon the coupling of tidal and wind induced currents a three dimensional model of the irish sea and the shelf and shelf edge region off the west coast of scotland is used to examine the interaction of wind induced surface currents and m 2 tidal currents which can lead to an increased near surface m 4 tidal current in the region calculations are performed using uniform southerly and westerly wind stresses with vertical eddy viscosity computed using either a simple flow dependent form of viscosity or one related to the flow and surface wind stress or derived using a two equation turbulence model resulting m 4 tidal distributions computed with the various viscosity formulations are compared with each other the spatial distribution the m 4 tidal current in the case of the flow dependent viscosity shows a significant enhancement of the surface m 4 tide due to non linear coupling between the surface shear and the tidally dependent viscosity in deep water this is the dominant mechanism giving rise to an enhancement in near surface m 4 current in shallow water however where other non linear processes are important in generating the m 4 tide namely changes in water depth and friction these are significant as well as the non linear surface shear effect in changing the m 4 tidal distribution however when an eddy viscosity formulation depending upon flow and surface wind stress is used the non linear coupling mechanism producing an enhanced m 4 tidal surface current is reduced and no increase in m 4 surface current occurs calculations with the two equation turbulence model do not produce an increase in the near surface m 4 tide as the near surface viscosity in this model is determined principally by the wind stress rather than the tidal current some conclusions concerned with developing a simple eddy viscosity model having similar characteristics to the turbulence energy model and experimental data sets for validation are considered at the end of the paper

subtidal response of scotian shelf circulation to local and remote forcing part i observations abstract data collected during the canadian atlantic storms program casp suggest that two primary current regimes exist on the scotian shelf during winter moorings inside the 100 m isobath feature currents that are parallel to the general bathymetry and have small eastward mean velocities the time varying part of the flow is nearly rectilinear alongshelf at typical maximum velocities of 0 2 0 3 m s 1 and oscillates on 2 5 day periods in response to meteorological forcing the current at locations beyond the 100 m isobath exhibits a persistent westward flow of about 0 3 m s 1 denoting the dominance of the nova scotian current although smaller magnitude along and cross shelf fluctuations occur at synoptic frequencies flow in both regions is largely uniform with depth at this time of year the velocity response to local and remote sources of forcing was examined using a frequency dependent multiple regression model flow is dominated by nonlocal forcing at 0 2 cpd alongshelf wind stress is t

analysis of a regional change in the sign of the sam temperature relationship in antarctica this study examines regional atmospheric circulation changes associated with a reversal in the sign of the relationship between the southern annular mode sam and near surface temperatures at halley station east antarctica during the 1980s we show that the key factor affecting the regional sam temperature relationship str is the relative magnitude of two climatological low pressure centres to the west and east of the area which determines the source region of air masses advected into the locality the principal difference affecting the str is shown to be a trend towards a significantly weaker climatological low higher pressure at 20 e during a positive phase of the sam specifically it is variations in the phase and magnitude of the wave number three patterns of atmospheric circulation the non annular component of the sam which are the principal factors governing the regional str a similar reversal is observed in the sign of the correlation between the sam and oxygen isotope values from an ice core located some 1 200 km east of halley this relationship is examined throughout the 20th century by comparing the isotope data to sam reconstructions and demonstrates marked decadal variability thus these data suggest that switches in the str are more likely to reflect natural variability in the long wave patterns over the southern ocean rather than the influence of an anthropogenic forcing this finding is important when considering the potential utility of antarctic isotope data as a proxy for the sam

reexamination of the near surface airflow over the antarctic continent and implications on atmospheric circulations at high southern latitudes abstract previous work has shown that winds in the lower atmosphere over the antarctic continent are among the most persistent on earth with directions coupled to the underlying ice topography in 1987 parish and bromwich used a diagnostic model to depict details of the antarctic near surface airflow a radially outward drainage pattern off the highest elevations of the ice sheets was displayed with wind speeds that generally increase from the high interior to the coast these winds are often referred to as katabatic with the implication that they are driven by radiational cooling of near surface air over the sloping ice terrain it has been shown that the antarctic orography constrains the low level wind regime through other forcing mechanisms as well dynamics of the lower atmosphere have been investigated increasingly by the use of numerical models since the observational network over the antarctic remains quite sparse real time numerical weather prediction for the u s antarctic program has been

spatial patterns of variability in antarctic surface temperature connections to the southern hemisphere annular mode and the southern oscillation 1 the 17 year 1982 1998 trend in surface temperature shows a general cooling over the antarctic continent warming of the sea ice zone with moderate changes over the oceans warming of the peripheral seas is associated with negative trends in the regional sea ice extent effects of the southern hemisphere annular mode sam and the extrapolar southern oscillation so on surface temperature are quantified through regression analysis positive polarities of the sam are associated with cold anomalies over most of antarctica with the most notable exception of the antarctic peninsula positive temperature anomalies and ice edge retreat in the pacific sector are associated with el nino episodes over the past two decades the drift towards high polarity in the sam and negative polarity in the so indices couple to produce a spatial pattern with warmer temperatures in the antarctic peninsula and peripheral seas and cooler temperatures over much of east antarctica

a 3 d prognostic numerical model study of the georges bank ecosystem part i physical model abstract the influence of tidal forcing and tidal and wind mixing on circulation and stratification over georges bank and adjacent regions in the gulf of maine has been examined using the 3 d semi implicit version of the blumberg and mellor 1987 primitive equation ocean circulation model the numerical domain covered the gulf of maine georges bank region with an open boundary starting at the new jersey coast and ending at the nova scotia coast with increased spatial resolution over georges bank numerical experiments were conducted using both smoothed and non smoothed high resolution 15 s bottom topography the model was forced by specifying the m 2 elevation and phase on the open boundary and several forms of the bottom roughness parameter z o were used the model provided a reasonable simulation of the m 2 tidal elevations and currents the model when run as an initial value problem with early summer stratification exhibited tidal mixing fronts around the 40 60 m isobath over georges bank and nantucket shoals and 100 m isobath on brown bank the formation of these tidal mixing fronts significantly enhanced the along isobath tidal rectified current over georges bank and the other two shoal regions a cool water band developed within the frontal zone along the eastern and southern flanks of georges bank and nantucket shoal and it became cooler owing to wind mixing and upwelling as a mean summer wind stress was added tidal mixing and turbulent dissipation varied in time asymmetrically over georges bank over georges bank tidal mixing was generally characterized as a local 1 d balance between turbulent shear production and dissipation the spatial structure of the tidal residual flow and local turbulent dissipation rate depended critically on the spatial resolution of the bottom topography and the spatial distribution of z 0 analysis of the 3 d momentum balance and the residual flow over the center of georges bank indicates that earlier results based on a 2 d cross bank model correctly captured the basic dynamics of stratified tidal rectification and tidal mixing in this idealized model setting

a predominant reversal in the relationship between the sam and east antarctic temperatures during the twenty first century abstractthe scientific literature portrays a temporally invariant spatial relationship between the phase of the southern annular mode sam and the sign of surface air temperature sat anomalies across antarctica however here the authors describe a predominant switch from a negative to positive sam temperature relationship str across east antarctica in austral summer autumn during the first decade of the twenty first century when the sam was generally weakly positive of the nine years that had a positive regional str from 1957 to 2010 seven occurred during the last decade this reversal appears to be a response to anomalous high pressure over east antarctica resulting from variability in the phase and amplitude of the local component of the zonal wavenumber 3 pressure pattern in years when a reversed positive regional str exists the anomalous circulation is such that there is greater energy flux into the region while enhanced katabatic drainage across the continental interior disrupts the sur

three dimensional modeling of tidal currents and mixing quantities over the newfoundland shelf major semidiurnal m2 s2 and n2 and diurnal k1 and o1 barotropic tides over the newfoundland shelf are computed using a three dimensional nonlinear primitive equation model with the vertical eddy viscosity calculated from a level 2 5 turbulence closure scheme computed elevation cotidal charts for the five constituents are generally consistent with previous knowledge for this region comparisons based on a statistical analysis of the differences between the computed elevations and currents and in situ observations indicate good agreement while m2 tidal currents up to 20 30 cm s are dominant there are locally intensified diurnal currents up to 5 10 cm s in some outer shelf locations the diurnal current intensification is attributed to first mode continental shelf waves an examination is carried out for the vertical structure of the computed m2 current and for the temporal and spatial variability of model turbulent kinetic energy mixing length scale vertical eddy viscosity and bottom friction velocity the examination indicates that large vertical eddy viscosity magnitudes and bottom friction velocities are associated with strong currents in shallow regions where strong vertical shears produce large turbulent kinetic energy solutions with both specified and evolving vertical stratification indicate that the stratification has a significant influence on the vertical profile of tidal mixing parameters and currents in shallow areas tidally induced turbulence is substantially reduced in the bottom boundary layer and completely suppressed above it tidal currents decrease in the log layer increase significantly in the rest of the bottom boundary layer and decrease in the upper and middle water column

surficial sediments of the outer banks scotian shelf canada the distribution thickness and mean grain size of surficial sediments on sable island bank middle bank and banquereau scotian shelf are used to re evaluate interpretations made by others on mechanisms controlling long term stability and net transport pathways of surface sand a holocene sand ridge complex the sable island catena extends 300 km across sable island bank and banquereau this sand ridge complex which is up to 50 m thick formed as a result of holocene sediment transport on the outer banks and controls the modern day distribution of bedforms and sediment size a clockwise circulation of sand centred around sable island which had been proposed as the mechanism maintaining the island does not take place sand is transported from southwest to northeast across sable island bank towards the sable island catena thereafter sand is dispersed eastward spillover of sand from the banks to the gully is not significant sand is trapped in depths less than 100 m the processes proposed to ha

low frequency circulation at the edge of the scotian shelf abstract records of current temperature and salinity from a two year mooring program at the shelf break off nova scotia are examined to determine the low frequency oceanic responses to the driving surface wind field and fluctuating offshore currents associated with the gulf stream the seasonal mean and subtidal variance at periods of 2 10 days of the cross shelf currents reflect the strong annual cycle in the wind field measured at sable island the mean vertical shear suggests a simple ekman response to winter increases in the longshore wind component but this model fails quantitatively because 1 the inferred surface layer 20 m transport is much too large and 2 the deep 150 m return flow shows no annual signal the excessive offshore near surface transport in winter must be reconciled with the relatively stationary position of the shelf slope water boundary ssb by invoking intense cross frontal mixing and or a seasonal mean alongshore pressure gradient the seasonal mean longshore currents

the circulation of eastern canadian seas abstract the eastern canadian seas including baffin bay the labrador sea and shelf the n e newfoundland shelf the scotian shelf and the gulf of st lawrence form an integrated hydro dynamical system the circulation is investigated using current meter data and a high resolution three dimensional coupled ice ocean circulation model cecom canadian east coast ocean model covering the entire area the model is forced with realistic atmosphere fluxes and the results are compared to the current meter data collected in four selected periods between 1987 and 2008 many features of the model current fields are similar to those from the previous regional circulation models for the shelves new findings from cecom include seasonal differences of the circulation around davis strait the detailed structure of the labrador current re circulation two cross shelf currents on the scotian shelf and strong currents in halibut channel which connects the waters of the western grand banks and scotian shelf the annual variation of the circulation is investigated both the model and data show the labrador current is strong in fall and weak in spring the outflow from the gulf of st lawrence through cabot strait and the currents on the inner scotian shelf are strong in winter and fall and weak in spring and are in phase with the labrador current the model currents are compared to observations using a qualitative method of visual comparison and a quantitative method based on statistical analysis the comparisons indicate that the main features of the current fields from the observations are successfully reproduced by the model the quantitative analysis indicates that the model currents are in reasonable agreement with the observations specifically a good agreement is found in the labrador shelf newfoundland shelf and flemish pass a fair agreement is found in davis strait the inner scotian shelf and sable bank however the agreement for cabot strait and the scotian shelf break is less satisfactory an analysis of the spatial variability of the current field suggests that the degree of agreement is closely related to the spatial variability of the current field the regions with low spatial variability generally have good agreements the volume and freshwater transports through several sections from the model are in good agreement with available estimates based on data

a comparison of the nonlinear frictional characteristics of two dimensional and three dimensional models of a shallow tidal embayment the nonlinear frictional behavior of two dimensional 2 d and three dimensional 3 d models are compared in this study of tides in the bight of abaco the shallow depths and the existence of an extensive set of tidal elevation data five astronomical and two overtide constituents at 25 stations from filloux and snyder 1979 offer an excellent opportunity to compare the effects of different frictional formulations in addition previous modeling efforts in the bight have consistently overpredicted the m6 and generally overdamped the o1 k1 and s2 tides the results indicate that although the 2 d and 3 d models may be calibrated to produce nearly identical responses for the dominant m2 tide there are systematic differences in the responses of the primary overrides these differences are explained using analytical expansions of the friction terms and are shown to be due to differences in the terms that are nonlinear in velocity and in water level the investigation concludes that the overgeneration of m6 and the overdamping of secondary astronomical tides will occur in 3 d models as well as 2 d models although several causes for these problems were considered improvement in these constituents could be achieved only by modifying the standard quadratic friction or flow dependent eddy viscosity relations to reduce the nonlinear frictional effect relative to the linear frictional effect the required modifications suggest the presence of a constant background velocity residual turbulence field or possibly the need for a more advanced frictional closure

a comparison between polynya area and associated ice production with mooring based measurements of temperature salinity and currents in the southwestern ross sea antarctica

processes influencing the internal tide its higher harmonics and tidally induced mixing on the malin hebrides shelf abstract a three dimensional prognostic hydrodynamic model with a turbulence energy submodel is used to examine the spatial distribution of the internal tide in the shelf edge region off the west coast of scotland in the initial series of calculations presented here the model is used in a cross shelf form the model contains all the non linear terms necessary to examine the generation of the higher harmonics of the tide and the generation of very short waves on the density interface near the shelf break initial calculations assuming a homogeneous sea region show a thick turbulent bottom boundary layer generated by bottom friction which reduces the tidal current in the near bed region although above this the flow is essential inviscid with no vertical variation calculations with a specified vertical stratification reduce the thickness of the bottom turbulent layer with an associated change in current profile in the case of specified stratification no internal tides are generated however when the density field is allowed to evolve a significant internal tide is generated with an associated internal shear giving rise to enhanced mixing in regions of largest shear results from the model show that higher harmonics of the internal tide and short internal waves are generated above the shelf break where horizontal mixing processes are important the magnitude of these short internal waves increases with increasing tidal forcing and also depends upon the size of the horizontal diffusion term regions of intense surface and bed turbulence associated with the internal tide are found in the shelf break area suggesting that turbulence energy measurements in this location may be a good test of turbulence closure models however the significant spatial variability associated with these regions shows that an intense measurement campaign is required to avoid significant undersampling

antarctic temperatures over the past two centuries from ice cores 1 we present a reconstruction of antarctic mean surface temperatures over the past two centuries based on water stable isotope records from high resolution precisely dated ice cores both instrumental and reconstructed temperatures indicate large interannual to decadal scale variability with the dominant pattern being anti phase anomalies between the main antarctic continent and the antarctic peninsula region comparative analysis of the instrumental southern hemisphere sh mean temperature record and the reconstruction suggests that at longer timescales temperatures over the antarctic continent vary in phase with the sh mean our reconstruction suggests that antarctic temperatures have increased by about 0 2 c since the late nineteenth century the variability and the long term trends are strongly modulated by the sh annular mode in the atmospheric circulation

a model study of the seasonal circulation in the gulf of maine the princeton ocean model is used to study the circulation in the gulf of maine and its seasonal transition in response to wind surface heat flux river discharge and the m2 tide the model has an orthogonal curvature linear grid in the horizontal with variable spacing from 3 km nearshore to 7 km offshore and 19 levels in the vertical it is initialized and forced at the open boundary with model results from the east coast forecast system the first experiment is forced by monthly climatological wind and heat flux from the comprehensive ocean atmosphere data set discharges from the saint john penobscot kennebec and merrimack rivers are added in the second experiment the semidiurnal lunar tide m2 is included as part of the open boundary forcing in the third experiment it is found that the surface heat flux plays an important role in regulating the annual cycle of the circulation in the gulf of maine the spinup of the cyclonic circulation between april and june is likely caused by the differential heating between the interior gulf and the exterior shelf slope region from june to december the cyclonic circulation continues to strengthen but gradually shrinks in size when winter cooling erodes the stratification the cyclonic circulation penetrates deeper into the water column the circulation quickly spins down from december to february as most of the energy is consumed by bottom friction while inclusion of river discharge changes details of the circulation pattern the annual evolution of the circulation is largely unaffected on the other hand inclusion of the tide results in not only the anticyclonic circulation on georges bank but also modifications to the seasonal circulation

morphology and composition of submarine barchan dunes on the scotian shelf canadian atlantic margin abstract submarine barchan dunes have been mapped on browns bank scotian shelf using multibeam sonar bathymetry and backscatter strength the morphology of subaerial barchans has been studied for almost a century but the advent of multibeam sonar technology now enables a quantitative investigation of their submarine counterparts the browns bank submarine barchans occur at a depth of 60 70 m and are crescentic in planform reaching almost 700 m in horn width and 5 m in height the barchans are convex to the se with steep lee faces to the nw indicating a dominant nw flowing current the barchans overlie a widespread gravel lag covered elsewhere with little or no sand obstacle marks emanate from the lee faces of the barchans and represent a lack of sand deposition and exposure of gravel lag on the sea floor the browns bank submarine barchan sediment texture is gravelly sand or sandy gravel and is primarily composed of subrounded to well rounded quartz grains the allometric relationship between submarine barchan slip face height and distance between horns is markedly different from that of subaerial barchans for the same dune height barchan horn width is about ten times greater in the marine environment the superimposition of megaripples on the stoss slopes of the submarine barchans suggests that the barchans are active and therefore represent an engineering risk to sea floor infrastructure current observations and models indicate that seasonal mean current strength is less than the critical velocity required for barchan migration however the barchans may be active under higher velocity storm induced currents repetitive multibeam sonar mapping is required to detect if barchan migration is occurring over longer time scales

wind induced interannual variability of sea level slope along shelf flow and surface salinity on the northwest atlantic shelf in this study we examine the importance of regional wind forcing in modulating advective processes and hydrographic properties along the northwest atlantic shelf with a focus on the nova scotian shelf nss gulf of maine gom region long term observational data of alongshore wind stress sea level slope and along shelf flow are analyzed to quantify the relationship between wind forcing and hydrodynamic responses on interannual time scales additionally a simplified momentum balance model is used to examine the underlying mechanisms our results show significant correlation among the observed interannual variability of sea level slope along shelf flow and alongshore wind stress in the nss gom region a mechanism is suggested to elucidate the role of wind in modulating the sea level slope and along shelf flow stronger southwesterly northeastward winds tend to weaken the prevailing southwestward flow over the shelf building sea level in the upstream newfoundland shelf region whereas weaker southwesterly winds allow stronger southwestward flow to develop raising sea level in the gom region the wind induced flow variability can influence the transport of low salinity water from the gulf of st lawrence to the gom explaining interannual variations in surface salinity distributions within the region hence our results offer a viable mechanism besides the freshening of remote upstream sources to explain interannual patterns of freshening in the gom

near surface recirculation over georges bank satellite tracked drifters with drogues centered near surface 5 m and below the seasonal thermocline 50 m were launched during late winter and spring of 1988 and 1989 in the northern great south channel in the western gulf of maine to investigate the regional circulation as part of the south channel ocean productivity experiment scopex many of the near surface drifters became entrained in the clockwise gyre over georges bank and eight drifters made a total of 16 complete circuits around the bank during the stratified season the average recirculation period of these eight drifters was 48 days and the average drifter speed around the bank was 12 cm s 1 there is no clear evidence from the drifter data that the strength of the clockwise gyre over the bank increased with time during the stratified season on average these drifters i followed a relatively narrow path around the bank except over the eastern end of the bank where three preferred paths were observed ii moved fastest over the northern and southern flanks of the bank iii did not enter a core area of 3500 km2 centered at 41 17 n 68 00 w approximately 30 km southwest of the topographic center of the bank and iv stopped circling the bank by the end of november due in part to strong wind events that appeared to drive drifters off the bank curiously none of the near surface drifters moved from the southern flank of georges bank onto the new england shelf as might be expected from continuity of flow along the outer shelf instead the drifters that circled the bank tended to move off the bank along its southern flank none of the drifters with drogues centered at 50 m appeared to recirculate around georges bank

autumn cooling of western east antarctica linked to the tropical pacific over the past 60 years the climate of east antarctica cooled while portions of west antarctica were among the most rapidly warming regions on the planet the east antarctic cooling is attributed to a positive trend in the southern annular mode sam and a strengthening of the westerlies while west antarctic warming is tied to zonally asymmetric circulation changes forced by the tropics this study finds recent post 1979 surface cooling of east antarctica during austral autumn to also be tied to tropical forcing namely an increase in la nina events the recent increase in la nina conditions forces a rossby wave into the southern hemisphere that increases anticyclonic circulation over the south atlantic the south atlantic anticyclone is associated with cold air advection weakened northerlies and increased sea ice concentrations across the western east antarctic coast which has increased the rate of cooling at novolazarevskaya and syowa stations after 1979 this enhanced cooling over western east antarctica is tied more broadly to a zonally asymmetric temperature trend pattern across east antarctica during autumn that is consistent with a tropically forced rossby wave rather than a sam pattern the positive sam pattern is associated with ubiquitous cooling across east antarctica which is not seen in temperature observations after 1979 we conclude that el nino southern oscillation related circulation anomalies particularly zonal asymmetries that locally enhance meridional wind are an important component of east antarctic climate variability during autumn and future changes in tropical pacific climate will likely have implications for east antarctica

the m2 tide and its residual on the outer banks of the gulf of maine abstract tidal computations are reported for the gulf of maine with emphasis on its seaward banks georges bank browns bank nantucket shoals and the nearshore region off cape sable the model is 3d and nonlinear with quadratic vertical viscosity stratification is ignored the objective is to establish a theoretical baseline for tidal and residual currents on detailed topography against which seasonal changes may be examined two triangular meshes are used the base case corresponds to earlier studies with roughly 6 km resolution on the banks a more refined and extended mesh provides resolution at 2 3 km in critical areas and has boundaries farther removed from the banks both meshes provide very good fits with observed m2 elevations comparison of computed and observed m2 current profiles at 76 sites reveals general agreement that improves with resolution for the refined mesh and the 48 sites with records exceeding 60 days average deviations for m2 ellipse parameters are 6 1 4 7 cm s 1 for the

polynya signature simulation method polynya area in comparison to amsr e 89 ghz sea ice concentrations in the ross sea and off the adelie coast antarctica for 2002 05 first results the polynya signature simulation method pssm is applied to special sensor microwave imager observations from different defense meteorological satellite program spacecraft for 2002 05 to analyze the polynya area in the ross sea ross ice shelf polynya risp and terra nova bay polynya tnbp and off the adelie coast mertz glacier polynya mgp antarctica on a sub daily scale the risp and the mgp exhibit similar average total polynya areas major area changes 10 000 km 2 tnpb 2000 km 2 occur over a range of 2 3 to 20 days in all regions sub daily area changes are largest for the mgp 5800 km 2 and smallest for the tnbp 800 km 2 underlining the persistence of the forcing of the latter artist sea ice asi algorithm concentration maps obtained using 89 ghz advanced microwave scanning radiometer amsr e data are compared to pssm maps yielding convincing agreement in the average similarly detailed winter polynya distribution average asi algorithm ice concentrations take values of 25 40 and 65 80 for the pssm open water and thin ice class respectively the discrepancy with expected values 0 and 100 can be explained by the different spatial resolution and frequency used by the methods a new land mask and a mask to flag icebergs are introduced comparison of pssm maps with thermal ice thickness based on avhrr infrared temperature and ecmwf era 40 data suggests an upper thickness limit for the pssm thin ice class of 20 25 cm

spatial and temporal structure of the barotropic response of the scotian shelf and gulf of maine to surface wind stress a model based study the barotropic current and pressure field responses of the scotian shelf and gulf of maine region to spatially uniform wind stress are examined using a three dimensional finite element numerical model the model is linear and harmonic with spatially varying eddy viscosity and bottom friction coefficients obtained from a nonlinear m2 tidal solution the solutions for low frequency 20 day period wind stress and upstream boundary forcing are generally consistent with previous depth averaged model results showing a substantially stronger response for along shelf compared to cross shelf stress and strong topographic shaping of the associated arrested topographic waves with their expanded domain and dimensionality the present solutions reveal important additional features of the responses such as the northeast channel being the primary conduit for cross shelf subsurface flow compensating the cross shelf ekman transport over the scotian shelf widespread areas of near bottom upwelling and downwelling along the coast and shelf break and leakage of the response across the shelf break model solutions for stress forcing with periods in the storm band 2 5 days show similar structures and elevation current gains to those in the low frequency solutions with the primary exception that the large northeast channel transport for along shelf stress excites a topographic wave over the continental slope south of georges bank the strength of bottom stress dependent on the magnitudes of both the bottom friction coefficient and near bottom viscosity in the model has a significant quantitative influence on the inner shelf response coastal elevation amplitudes and cross shelf decay scales in particular the implications of the model solutions for the interpretation of various observational features of the region s response to wind stress are discussed including coastal elevations offshore bottom pressures currents transports upwelling zones frequency dependences and seasonal and frictional influences

observations of the terra nova bay antarctica polynya by modis ice surface temperature imagery from 2005 to 2010 abstract ice surface temperature ist imagery from the thermal infrared bands of the satellite borne moderate resolution imaging spectroradiometer modis has been used to analyze the activity of the terra nova bay polynya from 2005 to 2010 in clear sky conditions the shape of the open water area of the polynya i e the portion of the ocean free of sea ice is revealed by the skin sea ice temperatures close to the water freezing point provided by the modis derived ist product the swaths of the modis sensors onboard terra and aqua satellites over the terra nova bay consist of about 5500 scenes per year useful to estimate the cloud cover too the open water area was extracted from clear sky scenes and from scenes affected by fog but providing continuity of the shape of the polynya using about 40 of the available swaths the polynya was detected for more than 80 of the sea ice period with a revisit time below 24 h and for more than 50 with a revisit time below 3 h the open water area was extracted using thresholds of ist based on the ist values detected within the open water area and within the band of sea ice surrounding the polynya obtained scene by scene an ice free area larger than 100 km 2 was observed near the nansen ice shelf for more than 70 of time larger than 500 km 2 for 50 of time the mean annual open water area around 900 km 2 was close to the lower limit of the reported range except during 2006 around 600 km 2 due to the limited activity in the second half of the cold season the largest extents between 6000 and 8500 km 2 occurred in different periods of the antarctic winter and exceeded maxima estimated in previous studies by thermal infrared data polynya openings developed from a few hours to several days in the latter case sustained by subsequent katabatic events visible in the ist sequence peaks of growing rate above 300 km 2 h were observed during intense katabatic events with gusts of 50 m s the fluctuations of the open water area resulted well correlated with wind records available from local automatic weather stations within the main katabatic routes and followed katabatic events at intervals between 0 and 6 h the analysis of the ist data set derived from the thermal infrared bands of modis provides new polynya observations of high horizontal resolution 1 km and frequent revisit time during the winter season complementing previously available observations with passive microwave imagery

georges bank residual circulation during weak and strong stratification periods prognostic numerical model results the seasonal extremes of the three dimensional residual circulation on georges bank are studied by numerically computing the circulation during weakly march april and strongly july august stratified periods the computations are performed using a prognostic i e including tidal time advection of the density field free surface nonlinear finite element model on realistic georges bank topography the dynamics considered result from the dominant m 2 tide baroclinic pressure gradients wind stress upstream boundary conditions and advanced turbulence closure comparison of these solutions with earlier diagnostic model results illustrates the importance of processes which could not be included in these earlier simulations such as density evolution and advanced turbulence closure in tidal time inclusion of nonlinear baroclinic effects improved treatment of other nonlinearities etc during the strongly stratified july august period the newly modeled processes intensify the residual circulation and result in recirculating transport on georges bank of 0 25 sv which is twice the diagnostic result the level of agreement between modeled and observed residual circulation improves very significantly for this period with the prognostic model predicting around bank currents as high as 46 cm s 1 in the frontal zone on the northeast peak analysis of the tidal time density and current structure in the frontal zone on the northeast peak indicates important tidal frequency dynamics and features which are supported by observational evidence during the weakly stratified march april period the dynamical impact of the newly modeled processes is small hence the prognostic and diagnostic models predict similar global structure with a recirculating transport on georges bank of 0 05 sv although there are local differences which result in the prognostic simulation agreeing more closely with the observed circulation

the wind induced circulation and the interaction of wind forced and tidally driven currents on the european shelf abstract a three dimensional hydrodynamic model of the continental shelf is used to examine the wind induced flow on the shelf produced by uniform northerly and westerly wind stresses the model has a functional approach in the vertical and a finite difference grid in the horizontal a flow dependent eddy viscosity is used to parameterize vertical mixing of momentum initial calculations of the wind driven flow in the absence of tides are used to examine the spatial variability of the currents in response to uniform northerly and westerly winds and the time taken to reach a steady state results of subsequent calculations including tidal turbulence show that the wind induced flow is modified by the non linear interaction between tidal and wind driven currents arising from the flow dependent eddy viscosity term and bottom friction effects the spatial variability of wind induced currents on the shelf is related to topographic features and used to explain some of the variability found in the flow fields on the shelf that have been deduced from measurements a comparison of tidal current ellipses at the fundamental frequency and higher harmonic derived from a harmonic analysis of tidal and wind driven flows shows that the surface current ellipses particularly those of the higher harmonic are modified by the presence of the wind driven flow the processes giving rise to this modification are the time variability of the eddy viscosity and the near surface shear produced by the wind stress

accumulation variability in the antarctic peninsula the role of large scale atmospheric oscillations and their interactions abstracta new ice core drilled in 2010 to bedrock from the bruce plateau bp on the antarctic peninsula ap provides a high temporal resolution record of environmental conditions in this region the extremely high annual accumulation rate at this site facilitates analysis of the relationships between annual net accumulation an on the bp and large scale atmospheric oscillations over the last 45 years an on the bp has been positively correlated with both the southern annular mode sam and southern oscillation index soi extending this analysis back to 1900 reveals that these relationships are not temporally stable and they exhibit major shifts in the late 1940s and the mid 1970s that are contemporaneous with phase changes in the pacific decadal oscillation pdo these varying multidecadal characteristics of the an oscillation relationships are not apparent when only data from the post 1970s era are employed analysis of the longer ice core record reveals that the influence of the sam on an depends

hydrographic and transport variability on the halifax section 1 archived data and geostrophic computations are used to examine variability in hydrographic properties and along shelf transport on the scotian shelf with focus on the halifax section and a decadal scale hydrographic anomaly during the late 1950s and early mid 1960s the long term annual cycle shows strong seasonal variations in baroclinic transport on the inner shelf and at the shelf edge and an associated steric change in adjusted sea level asl at halifax regional wind forcing and barotropic currents make smaller contributions to the annual cycle in asl in contrast regional wind forcing contributes about 40 of the asl variability for periods of 6 30 days hydrographic sections indicate that the 1950s 1960s anomaly arose from episodic extensions of labrador slope water along the shelf edge followed by on shelf intrusions primarily during the fall spring periods of 1958 1959 and 1963 1964 it ended with excursions of warm slope water into the region in 1967 1968 an analysis of monthly temperature anomalies indicates that slope temperatures can account for 50 of the variance of deep shelf temperatures 3 6 months later correlations between the hydrographic and baroclinic transport variations indicate increased southwestward flow associated with lower temperatures and salinities but no evidence was found for large local current events at the onset and termination times of the 1950s 1960s anomaly positive correlations between wind adjusted asl and steric anomalies point to the potential for sea level being helpful in monitoring baroclinic transport variability

quaternary geology and surficial sediment processes browns bank scotian shelf based on multibeam bathymetry abstract browns bank is located on the glaciated continental shelf off southern nova scotia geological mapping of browns bank is based on interpretation of multibeam bathymetric and backscatter data in conjunction with 220 line km of seismic reflection profiles and sidescan sonograms sea floor sediment samples and bottom photographs the fundian moraine part of the previously identified end moraine system on the continental shelf off nova scotia is a prominent west east flat topped multi lobate ridge identifiable in the multibeam bathymetric data and in geophysical records the fundian moraine was subjected to erosion in the surf zone during sea level rise in depths less than 100 m a series of north south roughly parallel till ridges continuous in the subsurface with the fundian moraine is interpreted as interlobate moraines suggesting formation by a tidewater glacier the browns bank moraine connected to the fundian moraine is evidence of a newly identified grounded ice position farther seaward than the latter bedforms including obstacle marks comet marks sand waves and megaripples are evidence of a vigorous anticyclonic current pattern on browns bank the combination of multibeam bathymetric imagery with high resolution geoscientific information represents a powerful technique for sea floor geological investigations

characterization of three dimensional lagrangian circulation associated with tidal rectification over a submarine bank abstract two approaches to the quantitative characterization of lagrangian circulation in three dimensional 3d time periodic current fields are used to describe major features of a model derived flow field for barotropic tidal rectification on georges bank the first approach is an extension of the 2d saddlepoint method used by ridderinkhof and loder to describe the vertically averaged lagrangian circulation associated with various forcings over outer gulf of maine banks application of the method to representative sigma terrain following surfaces and comparison with particle trajectories in the 3d current field indicate that the circulation saddlepoints and associated separation lines between recirculation and throughflow regions in the vertically averaged flow over georges bank are qualitatively representative of the entire water column but that there is significant vertical structure in the lagrangian circulation in particular the horizontal extent of the tidally rectified clockwise gyre on

circulation of tampa bay driven by buoyancy tides and winds as simulated using a finite volume coastal ocean model 1 the circulation of tampa bay is investigated using a high resolution three dimensional density dependent finite volume coastal ocean model fvcom that includes tampa bay the intracoastal waterway and the inner portion of the west florida continental shelf model performance over the three month interval september to november 2001 is assessed against available tide gauge and velocity profiler data before using the model to describe the circulation as driven by rivers tides and winds because of a mean wind velocity vector directed down the estuary axis we ran a parallel model experiment without winds to distinguish the estuarine circulation by gravitational convection from the mean wind effects with or without winds tampa bay exhibits a robust two layered estuarine circulation that concentrates on the deep channels the mean outflow at the surface tends to converge on the channels where the free surface elevation is locally minimum the mean inflow near the bottom also concentrates in the channels where the baroclinic pressure gradient force is largest geometry thus guides the mean circulation and salinity distributions at the tampa bay mouth mean outflows exist both in the deeper egmont channel and the shallower south pass whereas a mean inflow is limited to the egmont channel a residence time based on the egmont channel influx is estimated to be about 100 days consistent with previous studies we conclude that gravitational convection is a major contributor to the water property distributions of tampa bay and that the fvcom is suitable for estuary shelf interaction studies

the influence of atmospheric zonal wave three on antarctic sea ice variability 1 the study examines the relationship between atmospheric zonal wave three and antarctic sea ice variability using an index of zonal wave three and sea ice concentration the net sensible heat flux and the surface air temperature are used to explain the apparent atmosphere sea ice interaction the results show that zonal wave three forces an alternating pattern of equatorward colder and poleward warmer flow which influences the temperature difference between the atmosphere and the ocean the net sensible heat flux is positive ocean heat loss is greater and sea ice growth and expansion is greater in regions of colder air the reverse is true in regions of warmer air this influence of zonal wave three on sea ice concentration appears greatest in the southern fall and early winter it is most clearly seen in the ross and weddell seas outflows and off the amery iceshelf

three dimensional model simulations of tides and buoyancy currents along the west coast of vancouver island a three dimensional finite element model is used to calculate the barotropic tides and seasonal buoyancy flows off the western and northern coasts of vancouver island the model buoyancy currents and the harmonics of eight tidal constituents are compared with those from previous models and those from tide gauge and current meter observations the rms differences between observed and calculated sea level tidal amplitudes are within 2 3 cm for all constituents whereas the rms differences between observed and calculated phases are with the exception of q1 within 3 58 the model currents are more accurate than those from previous models of particular interest are the diurnal continental shelf waves it is shown that these waves are generated through the conservation of potental vorticity arising when the strong diurnal tidal currents in juan de fuca strait encounter the abrupt topography near the entrance to the strait these waves do not appear to propagate beyond brooks peninsula a large promontory cutting across the continental shelf a power budget analysis reveals that the reason for this is not the blocking effect of the peninsula but rather there is little energy left in the waves when they reach that point this energy loss is primarily through frictional dissipation in a series of trapped eddies along the shelf break the location of these eddies varies with the forcing frequency and appears to be related to the spacing of canyons it is also demonstrated that the strong diurnal currents observed over the shallow banks in queen charlotte sound to the north of brooks peninsula do not arise from the oscillatory diurnal flows in queen charlotte strait unlike the case for juan de fuca strait the region offshore of queen charlotte strait does not support diurnal coastally trapped waves seasonal changes in the wavelengths of the vancouver island shelf waves are shown to arise through an advective interaction doppler shift with the buoyancy driven vancouver island coastal current and the wind driven shelf break current

bellingshausen sea ice extent recorded in an antarctic peninsula ice core annual net accumulation an from the bruce plateau bp ice core retrieved from the antarctic peninsula exhibits a notable relationship with sea ice extent sie in the bellingshausen sea over the satellite era both bp an and bellingshausen sie are influenced by large scale climatic factors such as the amundsen sea low southern annular mode and southern oscillation in addition to the direct response of bp an to bellingshausen sie e g more open water as a moisture source these large scale climate phenomena also link the bp and the bellingshausen sea indirectly such that they exhibit similar responses e g northerly wind anomalies advect warm moist air to the antarctic peninsula and neighboring bellingshausen sea which reduces sie and increases an comparison with a time series of fast ice at south orkney islands reveals a relationship between bp an and sea ice in the northern weddell sea that is relatively consistent over the twentieth century except when it is modulated by atmospheric wave patterns described by the trans polar index the trend of increasing accumulation on the bruce plateau since 1970 agrees with other climate records and reconstructions in the region and suggests that the current rate of sea ice loss in the bellingshausen sea is unrivaled in the twentieth century

a model of tidal rectification by potential vorticity mixing part i homogeneous ocean abstract in previous studies of tidal generation of mean flow over varying topography the rectification mechanism has generally invoked bottom friction as a source of tidal flux of momentum and vorticity hence referred as friction mechanism the author proposes a different mechanism based on horizontal mixing of potential vorticity drawing analogy from tidal dispersion of passive tracers this mixing is parameterized through a diffusivity hence called diffusivity mechanism that is quadratic in the tidal amplitude in this part 1 the mean along isobath flow near a shelf break is determined for a homogeneous ocean and contrasted with that induced by friction mechanism in part 2 the effect of a front will be considered it is found that although the mean flow is pointing in the same direction as that induced by friction mechanism i e to the right when facing deep water in the northern hemisphere it varies more slowly with the tidal amplitude in the typical situation when the mean shear is

seasonal circulation on the western and central scotian shelf abstract a realistic representation of 3d seasonal circulation and hydrography on the western and central scotian shelf has been obtained from historical observations and a combination of diagnostic and prognostic numerical models with forcing by tides wind stress and baroclinic and barotropic pressure gradients the major current features the southwestward nova scotian and shelf edge currents and partial gyres around browns and sable island banks are found to persist year round but with significant seasonal changes comparison with current meter observations shows good agreement for the browns bank southwest nova scotia and inner shelf regions and poorer agreement in the sable island bank and shelf edge regions where current and density observations are sparser and tidal influences weaker there is significant spatial structure in the seasonal circulation and hydrography and in the underlying dynamical processes on the shelf scale there are substantial changes in stratification potential energy

annual sea level changes on the north american northeast coast influence of local winds and barotropic motions abstractunderstanding the relationship between coastal sea level and the variable ocean circulation is crucial for interpreting tide gauge records and projecting sea level rise in this study annual sea level records adjusted for the inverted barometer effect from tide gauges along the north american northeast coast over 1980 2010 are compared to a set of data assimilating ocean reanalysis products as well as a global barotropic model solution forced with wind stress and barometric pressure correspondence between models and data depends strongly on model and location at sites north of cape hatteras the barotropic model shows as much if not more skill than ocean reanalyses explaining about 50 of the variance in the adjusted annual tide gauge sea level records additional numerical experiments show that annual sea level changes along this coast from the barotropic model are driven by local wind stress over the continental shelf and slope this result is interpreted in the light of a simple dynamic

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

historical sam variability part i century length seasonal reconstructions seasonal reconstructions of the southern hemisphere annular mode sam index are derived to extend the record before the reanalysis period using station sea level pressure slp data as predictors two reconstructions using different predictands are obtained one jones and widmann jw based on the first principal component pc of extratropical slp and the other fogt on the index of marshall a regional based sam index visbeck is also considered these predictands agree well post 1979 correlations decline in all seasons except austral summer for the full series starting in 1958 predictand agreement is strongest in spring and summer hence agreement between the reconstructions is highest in these seasons the less zonally symmetric sam structure in winter and spring influences the strength of the sam signal over land areas hence the number of stations included in the reconstructions reconstructions from 1865 were therefore derived in summer and autumn and from 1905 in winter and spring this paper examines the skill of each reconstruction by comparison with observations and reanalysis data some of the individual peaks in the reconstructions such as the most recent in austral summer represent a full hemispheric sam pattern while others are caused by regional slp anomalies over the locations of the predictors the jw and fogt reconstructions are of similar quality in summer and autumn while in winter and spring the marshall index is better reconstructed by fogt than the pc index is by jw in spring and autumn the sam shows considerable variability prior to recent decades

modeling the circulation of western bank on the scotian shelf through sequential application of a variational algorithm and a nonlinear model 1 a new approach is presented for the modeling of the quasi stationary circulation through the sequential application of a variational algorithm and a nonlinear diagnostic model the model loop begins with data assimilation of temperature salinity surface elevation and velocity data in a simplified geostrophic model in which transport and continuity equations are treated as weak constraints the temperature salinity fields and balanced open boundary conditions points are then used as input to a nonlinear primitive equation model which employs a turbulent closure scheme the nonlinear model is then run to produce a diagnostic flow field a radiation open boundary condition is applied at the outflow points of the open boundaries these two steps are organized into an iteration cycle by using output from the nonlinear model as input to the variational model the proposed approach combines the advantages of variational data assimilation in simplified models with a complicated fully nonlinear primitive equation model we apply the approach to western bank on the scotian shelf comparisons with observed current from western bank in september and october 1998 show that the sequential application of the variational approach and the fully nonlinear model allow determination of the quasi stationary circulation whose agreement with the observations is 10 30 better than circulation determined from the variational or the nonlinear model alone our calculations of the cross shelf transport across western bank show that it varies from 0 20 sv to 0 35 sv over a 2 week period the combined models also allow us to determine the character of the circulation over the bank the role of wind forcing and the implications for resident biological populations index terms 4219 oceanography general continental shelf processes 4255 oceanography general numerical modeling 4223 oceanography general descriptive and regional oceanography 4263 oceanography general ocean prediction keywords numerical modeling scotian shelf variational algorithm shelf circulation

a high resolution assimilating tidal model for the northeast pacific ocean a high resolution nonlinear barotropic finite element tidal model is developed for removing tidal elevations from satellite altimeter observations in the northeast pacific ocean surface elevations and currents for the constitutents m2 s2 n2 k2 k1 o1 p1 and q1 are computed using boundary forcing from the oregon state university global tidal model tpxo 3 and the effects of the tidal potential earth tide and ocean self attraction and loading amplitudes and phases computed from the harmonic analyses of altimeter time series at crossover locations along the tracks of the topex poseidon satellite are assimilated into the model and the corrected harmonics are compared with pelagic and coastal tide and pressure gauge measurements and with the tpxo 3 and fes95 2 1 global models diurnal tidal currents along the british columbia and alaska continental shelves are shown to be strongly influenced by the presence of continental shelf waves the surface manifestation of these waves is clearly evident in k1 coamplitude plots k1 and m2 energy fluxes are calculated along these shelves and the potential generation of internal tides is discussed barotropic tidal dissipation is estimated in several key subregions and the m2 total for the gulf of alaska is found to be approximately half that of previous estimates

seasonal patterns in zooplankton community structure on the newfoundland and labrador shelf we report on the patterns in zooplankton community structure on the newfoundland and labrador shelf from seasonal collections along oceanographic sections during 2000 2007 we use a combination of constrained and unconstrained multivariate methods to assess latitudinal and cross shelf patterns in community structure both physical and biological features of the region are dominated by the cross shelf gradient in water mass characteristics although there is evidence of a latitudinal gradient that may be a reflection of the influence of freshwater outflow from the arctic all analyses reveal a strong and consistent pattern in species composition among water masses that extends across spring summer and autumn although there are some variations that occur among seasons that reflect differences in development state of certain taxa the strong association between community structure and water mass characteristics in the region may be the result of the newfoundland and labrador shelf being at the intersection of several major oceanographic domains bounded by strong labrador and gulf stream currents that allows the formation and persistence of well defined zooplankton communities our findings have implications for the region s potential as a monitoring location for long term changes in ocean state

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

the influence of wind stress and river runoff on a shelf sea front abstract runoff from land gives rise to the formation of a front jet system separating fresher coastal waters from more saline waters offshore over some continental shelves notably in the mid atlantic bight in winter three first order characteristics of such fronts are the anchor depth h where the front intersects the bottom the stretch l i e the distance between its surface and bottom intersections and the buoyancy contrast b across the front the three characteristics may be determined from the cross front property transfer rate the along front momentum balance and the turbulence energy dissipation rate key independent variables are the horizontal buoyancy transport bx the friction velocity u and direction of the wind and the coriolis parameters f simple approximate formulae connecting dependent to independent variables arewhere m and are constants of order 300 1 and 0 1 respectively the entrainment rate across the front is u2 f 1 cos which is small compared to ekman transpo

model simulations of the bay of fundy gyre 1 climatological results 1 the characteristics of a persistent gyre in the mouth of the bay of fundy are studied using model simulations a set of climatological runs are conducted to evaluate the relative importance of the different forcing mechanisms affecting the gyre the main mechanisms are tidal rectification and density driven circulation stronger circulation of the gyre occurs during the later part of the stratified season july august and september october the density driven flow around the gyre is set up by weak tidal mixing in the deep basin in the central bay of fundy and strong tidal mixing on the shallow flanks around grand manan island and western nova scotia spring river discharge has an important influence on near surface circulation but only a small effect when averaged over the entire water column retention of particles in the gyre is controlled by the residual tidal circulation increased frontal retention during stratified periods wind stress and interactions with the adjacent circulation of the gulf of maine residence times longer than 30 days are predicted for particles released in the proximity of the gyre

influence of stratification upon diurnal tidal currents in shelf edge regions abstract a three dimensional stratified tidal model of the hebrides shelf area off the west coast of scotland is used to examine the spatial distribution of the m2 o1 and k1 tides in the region the model has a finer horizontal finite difference grid than previous models of the region with a biharmonic form of horizontal diffusion and the total variation diminishing scheme for density advection by this means horizontal diffusion is kept to a minimum and internal tidal effects can be included preliminary calculations assuming a homogeneous sea region show that the model can accurately reproduce the m2 o1 and k1 tidal elevations in the region an enhancement of the o1 and k1 tidal elevations and currents at the shelf edge to the northwest of the hebrides is found in the model in agreement with theory and observations however the enhancement of the diurnal tides in particular tidal currents along the shelf edge is larger than that found in the observations with some regions of local enhancement

interaction between the tidal and seasonal variability of the gulf of maine and scotian shelf region abstractas part of a broader study of ocean downscaling the seasonal and tidal variability of the gulf of maine and scotian shelf and their dynamical interaction are investigated using a high resolution 1 36 circulation model the model s seasonal hydrography and circulation and its tidal elevations and currents are compared with an observed seasonal climatology local observations and results from previous studies numerical experiments with and without density stratification demonstrate the influence of stratification on the tides the model is then used to interpret the physical mechanisms responsible for the largest seasonal variations in the m2 surface current that occur over and to the north of georges bank the model generates a striation pattern of alternating highs and lows aligned with georges bank in the m2 surface summer maximum speed in the gulf of maine the striations are consistent with observations by a high frequency coastal radar system and can be explained in terms of a li

an overview of physical processes in the north water the presence of a polynya strongly affects biological processes by influencing underwater light levels water column stratification the upwelling of nutrients and the timing of production cycles an overview of the existing literature on the oceanography meteorology and sea ice conditions of the north water a large recurring polynya in northern baffin bay is presented the north water is influenced by a cold inflow of arctic ocean water from the north and in some areas a warmer inflow of atlantic water from the south earlier observations and modeling studies suggested that both wind and ocean advection of sea ice as well as heat input to the surface waters by either upwelling or mixing were responsible for the formation and maintenance of the polynya recent data indicate the north water to be primarily generated by the southward drift of ice by winds and currents as opposed to melting ice by sensible heat input over large areas localized sensible heat effects occur in fall winter and spring along the greenland side of the polynya

open windows to the polar oceans polynyas large holes in the polar sea ice caused by divergent sea ice drift may persist for weeks to years through mechanisms that are not well understood in his perspective lemke 1 highlights the report by holland 2 who has found an interesting new mechanism for the formation of the weddell polynya a hole the size of great britain that formed in the 1970s in three consecutive winters the mechanism which invokes eddies caused by a seamount helps explain the formation of the polynya but the question of why the polynya has not formed since the 1970s remains unanswered 1 http www sciencemag org cgi content full 292 5522 1670 2 http www sciencemag org cgi content short 292 5522 1697

vertical structure of bottom ekman tidal flows observations theory and modeling from the northern adriatic 1 from september 2002 to may 2003 fifteen bottom mounted acoustic doppler current profilers measured currents of the northern adriatic basin tidal fluctuations at all seven of the major adriatic frequencies were synthesized from a response tidal analysis of these measurements most observed tidal current ellipses were nearly reversing but near the bottom tidal current ellipses all shortened and broadened semidiurnal currents led upper water column currents and diurnal tidal current ellipse orientations rotated counterclockwise toward the bottom theoretical solutions for a tidally forced bottom ekman layer with vertical eddy viscosity of the form az z k were least squares fit to the observations average values were 3 10 4 m s and k 5 10 4 m2 s the value of k was important in matching tidal orientation and phase changes and a nonzero was important in matching tidal amplitude changes the navy coastal ocean model ncom and the quoddy model were also compared to the observations the average rms errors for the bottom ekman layer were 0 22 cm s for the best fit theory 0 35 cm s for ncom and 0 36 cm s for quoddy az structures from ncom and quoddy show that time variation in az is relatively unimportant for adriatic tides the bottom shear stresses from theory were larger in magnitude than those from the bottom drag formulations in ncom and quoddy

tidal dynamics in the gulf of maine and new england shelf an application of fvcom 1 the unstructured grid finite volume community ocean model fvcom was used to simulate the tides in the gulf of maine gom and new england shelf nes for homogeneous and summer stratified conditions fvcom captures the near resonant nature of the semidiurnal tide and energy flux in the gom and the complex dynamics governing the tide in the nes stratification has limited impact on tidal elevation but can significantly modify the tidal current profile internal tides are energetic in the stratified regions over steep bottom topography but their contribution to the total tidal energy flux is only significant over the northeast flank of georges bank the model suggests that the tidal flushing induced eddy east of monomoy island is the dynamic basis for the locally observed phase lead of the m2 tide the southward propagating tidal wave east of cape cod encounters the northeastward propagating tidal wave from the nes south of nantucket island forming a zone of minimum sea level along a southeast oriented line from nantucket island these two waves are characterized by linear dynamics in which bottom friction and advection are negligible in the momentum balance but their superposition leads to a strong nonlinear current interaction and large bottom stress in the zone of lowest sea elevation

review of recent developments in tidal hydrodynamic modeling i spectral models in this paper we present a brief overview with a comprehensive set of references to recently published papers for detail of a range of techniques used in tidal hydrodynamic modeling and recent progress in the field although the paper aims to introduce the topic to someone new to the area the main emphasis is on new developments in near coastal shallow sea tidal modeling and consequently we concentrate on three dimensional modeling which has progressed significantly in recent years the paper gives a brief account of methods used to discretize the hydrodynamic equations in the horizontal namely finite difference finite element and boundary fitted coordinates and through time the representation of tidal current structure in a three dimensional model using a spectral method in the vertical is also described in this method the subgrid scale vertical diffusion of momentum which has a major influence on tidal current profiles is parameterized using a flow dependent eddy viscosity recent work on

the steady state barotropic response of the gulf of maine and adjacent regions to surface wind stress abstract the response of the gulf of maine region to steady spatially uniform wind stress is examined using a linearized numerical model with the influence of the strong tidal currents in the region included in the bottom stress formulation the sensitivity of the model results to various idealizations is investigated including the assumption of linearity the bottom steam formulation cross shelf structure in the large scale alongshelf wind stress and the cross shelf boundary conditions the model solutions for the gulf are found to be sensitive to the backward boundary condition on the scotian shelf but not to the forward boundary condition in the middle atlantic bight for alongshelf stress the former is estimated using csanady s arrested topographic wave model and observed coastal sea level gains at halifax the model has a spinup time of about one day comparable to previous estimates for the region the alongshelf component of wind stress is generally much more effective than the cross s

barotropic tides in the south atlantic bight 1 the characteristics of the principal barotropic diurnal and semidiurnal tides are examined for the south atlantic bight sab of the eastern united states coast we combine recent observations from pressure gauges and adcps on fixed platforms and additional short term deployments off the georgia and south carolina coasts together with national ocean service coastal tidal elevation harmonics these data have shed light on the regional tidal propagation particularly off the georgia south carolina coast which is perforated by a dense estuary tidal inlet complex etic we have computed tidal solutions for the western north atlantic ocean on two model domains one includes a first order representation of the etic in the sab and the other does not include the etic we find that the etic is highly dissipative and affects the regional energy balance of the semidiurnal tides nearshore inner and midshelf model skill at semidiurnal frequencies is sensitive to the inclusion of the etic the numerical solution that includes the etic shows significantly improved skill compared to the solution that does not include the etic for the m2 constituent the largest tidal frequency in the sab overall amplitude and phase error is reduced from 0 25 m to 0 03 m and 13 8 to 2 8 for coastal observation stations similar improvement is shown for midshelf stations diurnal tides are relatively unaffected by the etic

tidal front entrainment and retention of fish larvae on the southern flank of georges bank abstract from a grid of stations across the southern flank of georges bank in may 1997 larval haddock and cod were observed to be concentrated across the tidal front in a band 10 20 km wide several cross bank ctd and acoustic doppler current profiler adcp sections indicated a narrow 35 m cross isobath residual flow 0 6 1 2 cm s

seasonal variation of the three dimensional mean circulation over the scotian shelf the seasonal mean circulation over the scotian shelf is studied numerically by computing mean and tidal current fields for winter spring and summer using a three dimensional nonlinear diagnostic model the mean current fields are forced by seasonal mean baroclinic pressure gradients tidal rectification uniform wind stresses and associated barotropic pressure gradients a historical hydrographic database is used to determine the climatological mean baroclinic forcing upstream open boundary conditions are estimated from the density fields to give no normal geostrophic bottom flow and are specified as either along boundary elevation gradients or depth integrated normal velocities the numerical solutions for nominal bimonthly periods january february april may and july august reveal the dominant southwestward nearshore and shelf break flows of relatively cool and fresh shelf water from the gulf of st lawrence and newfoundland shelf with speeds up to about 20 cm s the seasonal intensification of the southwestward flows is reproduced by the model with the transport increasing from 0 3 sv in summer to 0 9 sv in winter on the inner halifax section there are also pronounced topographic scale influences of submarine banks basins and cross shelf channels on the circulation such as anticyclonic gyres over banks and cyclonic gyres over basins baroclinicity is the dominant forcing throughout the domain but tidal rectification is comparable on the southwestern scotian shelf e g about 0 2 sv recirculating transport around browns bank for all the periods the mean wind stress generates offshore surface drift in winter the solutions are in approximate agreement with observed currents and transports over the scotian shelf although there are local discrepancies

new reconstruction of antarctic near surface temperatures multidecadal trends and reliability of global reanalyses a reconstruction of antarctic monthly mean near surface temperatures spanning 1958 2012 is presented itsprimarygoalistotakeadvantageofarecentlyrevisedkeytemperaturerecordfromwestantarctica byrd to shed further light on multidecadal temperature changes in this region the spatial interpolation relies on a kriging technique aided by spatiotemporal temperature covariances derived from three global reanalyses the european centre for medium range weather forecasts ecmwf interim re analysis erainterim modern era retrospective analysis for research and applications merra and climate forecast system reanalysis cfsr for 1958 2012 the reconstruction yields statistically significant annual warming in the antarctic peninsula and virtually all of west antarctica but no significant temperature change in east antarctica importantly the warming is of comparable magnitude both in central west antarctica and in most of the peninsula rather than concentrated either in one or the other region as previousreconstructions have suggested the transantarctic mountains act for the temperature trends as a clear dividing line between east and west antarctica reflecting the topographic constraint on warm air advection from the amundsen sea basin the reconstruction also serves to highlight spurious changes in the 1979 2009 time series of the three reanalyses that reduces the reliability of their trends illustrating a longstanding issue in high southern latitudes the study concludes with an examination of the influence of the southern annular mode sam on antarctic temperature trends the results herein suggest that the trend of the sam toward its positive phase in austral summer and fall since the 1950s has had a statistically significant cooling effect not only in east antarctica as already well documented and but also only in fall in west antarctica

the mean and seasonal circulation off southwest nova scotia abstract long term measurements off southwest nova scotia reveal the following features of the mean circulation a a westward longshore coastal current 4 10 cm s 1 b an anticyclonic gyre around brown bank 5 15 cm s 1 and c an upwelling circulation off cape sable 1 2 cm s 1 at bottom the gyre circulation appears permanent but the coastal current and upwelling exhibit annual variations of the same order as the means there is a distinct annual signal in the longshore transport at cape sable maximum westward in winter whereas the mean transport 0 14 106 m4 s 1 is consistent with both geostrophic estimates and budget requirements in the gulf of marine strong seasonal cycles are also found in the salinity and density fields at cape sable which appear to be controlled both by buoyancy input from the coastal current and local mixing effects a linear diagnostic model indicates that the primary dynamical balance for the circulation is between a longshore pressure gradient and longshore mean

comparison of observed and model computed low frequency circulation and hydrography on the new england shelf 1 the finite volume coastal ocean model fvcom is configured to study the interannual variability of circulation in the gulf of maine gom and georges bank the fvcom gom system incorporates realistic time dependent surface forcing derived from a high resolution mesoscale meteorological model mm5 and assimilation of observed quantities including sea surface temperature and salinity and temperature fields on the open boundary an evaluation of fvcom gom model skill on the new england shelf is made by comparison of computed fields and data collected during the coastal mixing and optics cmo program august 1996 june 1997 model mean currents for the full cmo period compare well in both magnitude and direction in fall and winter but overpredict the westward flow in spring the direction and ellipticity of the subtidal variability correspond but computed magnitudes are around 20 below observed partially due to underprediction of the variability by mm5 response of subtidal currents to wind forcing shows the model captures the directional dependence as well as seasonal variability of the lag hydrographic results show that fvcom gom resolves the spatial and temporal evolution of the temperature and salinity fields the model computed surface salinity field compares well except in may when there is no indication of the fresh surface layer from the connecticut river discharge noted in the observations analysis of model computed results indicates that the plume was unable to extend to the mooring location due to the presence of a westward mean model computed flow during that time that was stronger than observed overall fvcom gom captures well the dynamics of the mean and subtidal flow on the new england shelf

a detailed comparison of a range of three dimensional models of the m2 tide in the faeroe shetland channel and northern north sea abstract a three dimensional hydrodynamic model of the faeroe shetland channel and northern north sea is used to investigate the spatial variability of m2 tidal elevations and currents in the region this area is chosen because it covers a range of water depths also there is a significant database of tidal elevations namely 41 gauges and current meters namely 89 observations with which comparisons can be made with the exception of a couple of measurements made at the shelf edge which may be influenced by the internal tide namely a 180 phase shift across the thermocline due to a first mode internal tide the observations correspond to those of a barotropic tide two different approaches are used to represent the profile of tidal currents in the vertical in the first a spectral functional method is used while in the second a finite difference grid is applied a range of parameterizations of vertical eddy viscosity suitable for deep water regions are used from ones in which viscosity is relate

nonstationary impacts of the southern annular mode on southern hemisphere climate abstract the temporal stability of the southern annular mode sam impacts on southern hemisphere climate during austral spring is analyzed results show changes in the typical hemispheric circulation pattern associated with sam particularly over south america and australia between the 1960s 70s and 1980s 90s in the first decades the sam positive phase is associated with an anomalous anticyclonic circulation developed in the southwestern subtropical atlantic that enhances moisture advection and promotes precipitation increase over southeastern south america sesa on the other hand during the last decades the anticyclonic anomaly induced by the sam s positive phase covers most of southern south america and the adjacent atlantic producing weakened moisture convergence and decreased precipitation over sesa as well as positive temperature anomaly advection over southern south america some stations in the australia new zealand sector and africa exhibit significant correlations between the sam and prec

historical and recent evidence of scotian shelf water on southern georges bank abstract historical data from 1912 1987 indicate that low salinity less than 32 0 psu near surface water occurs occasionally on southern georges bank during may while none occurs during april composite monthly plots of historical near surface salinity and estimated advection rates show that the southwestern scotian shelf is the immediate upstream source of this low salinity water optimally interpolated satellite derived sst and hydrographic data reveal that very cold less than 2 0 c low salinity less than 32 0 psu scotian shelf water ssw initially located south of the 200 m isobath off southern georges bank in early march 1992 moved north onto southern georges bank during april 1992 ssw was not as extensive during the same period in 1993 as evidence by significantly higher temperatures and salinities these differences show large interannual variability in the transport and or properties of ssw flowing onto georges bank lower higher salinities measured during spring 1992 1993 on southern georges bank are consistent with higher lower st lawrence river discharge noted during spring 1991 1992 and the nine month lag between annual discharge maxima from rivers located upstream and minimum salinity at cape sable in february however comparisons between historical occurrences of low salinity less than 32 0 psu ssw on southern georges bank noted for may 1966 1971 and 1978 and cumulative st lawrence river discharge from the spring prior to each occurrence show no relationship this suggests that the occurrence of low salinity water on southern georges bank is not directly related to variations in upstream river discharge although an idealized model of wind forcing on a bank trapped density front shows that near surface flow is related to superposition of an ekman layer and the along bank gyral circulation evidence from late winter spring 1992 and 1993 on georges bank shows that except for on bank movement of the shelf slope front during late spring 1992 simple ekman theory does not explain on bank movement of the ssw plume during 1992 nor the immobile nature of the shelf slope front during late winter 1992 and late winter spring 1993 surface heat flux and satellite derived sst from georges bank and the scotian shelf together with a slab mixed layer model allows estimation of the advective heat flux and transport of ssw flowing onto georges bank from the scotian shelf during late winter spring 1992 mean advective heat flux onto georges bank during march may 1992 is 14 5 mw cm 2 with an estimated error of 3 5 mw cm 2 demonstrating that advection of cold ssw onto georges bank is required mean velocity and transport of ssw flowing onto georges bank during march may 1992 are 13 4 cm s 1 and 0 21 sv assuming a ssw depth width of 40 m 40 km demonstrating that flow of ssw onto georges bank was robust during the period at this time the dynamics that control the flow of ssw across northeast channel are unknown