generation and propagation of near inertial waves in a baroclinic current on the tasmanian shelf abstractnear inertial waves niws are often an energetic component of the internal wave field on windy continental shelves the effect of baroclinic geostrophic currents which introduce both rela

study of the impact of ice formation in leads upon the sea ice pack mass balance using a new frazil and grease ice parameterization abstractleads are cracks in sea ice that often form because of deformation during winter months leads expose the ocean to the cold atmosphere resulting in supercooling and the formation of frazil ice crystals within the mixed layer here the authors investigate the role of frazil ice formation in leads on the mass balance of the sea ice pack through the incorporation of a new module into the los alamos sea ice model cice the frazil ice module considers an initial cooling of leads followed by a steady state formation of uniformly distributed single size frazil ice crystals that precipitate to the ocean surface as grease ice the grease ice is pushed against one of the lead edges by wind and water drag that the authors represent through a variable collection thickness for new sea ice simulations of the sea ice cover in the arctic and antarctic are performed and compared to a model that treats leads the same as the open ocean the processes of ice formation in the new module slow down the refreezing o

texture analysis of radiometric signatures of new sea ice forming in arctic leads analysis of 33 6 ghz high resolution passive microwave images suggests that new sea ice accumulating in open leads is characterized by a unique textural signature which can be used to discriminate new ice forming in this environment from adjacent surfaces of similar radiometric temperature data analyzed were acquired in march 1988 in conjunction with the joint us navy nasa special sensor microwave imager smm i sea ice validation experiment using the navy ka band radiometric mapping system krms an airborne passive microwave imager ten training areas were selected from the data set three of which consisted entirely of first year ice four entirely of multilayer ice and three of new ice in open leads in the process of freezing a simple gradient operator was used to characterize the radiometric texture in each training region in terms of the degree to which radiometric gradients are oriented

evolution of near inertial waves during an upwelling event on the new jersey inner shelf abstract a 1996 field program provided a nearly three dimensional view of the temporal evolution of near inertial motion toward the end of an upwelling event on new jersey s inner shelf the appearance of near inertial motion is marked by a rapid rise in kinetic energy at the surface that is of the same magnitude and temporal structure of the work done by the wind indicating that the inertial motions are forced by local winds the incipient near inertial motion is surface intensified and spatially coherent it has a horizontal wavelength of 300 km and a mean kinetic energy of 0 04 m2 s 2 both of which decrease to less than 100 km and 0 01 m2 s 2 within two inertial periods an energy budget suggests that the rapid decline in surface kinetic energy is primarily due to vertical propagation into the thermocline near inertial motion in the thermocline is heterogeneous suggesting interaction between near inertial motion and subinertial shears the heterogeneous nature of near inertial waves poses a practica

poincare wave induced mixing in a large lake a 10 000 km2 hypoxic dead zone forms during most years in the central basin of lake erie to investigate the processes driving the hypoxia we conducted a 2 yr field campaign where the mixing in the lake interior during the stratification period was examined using current meters and temperature loggers data as well as 600 temperature microstructure profiles from which turbulent mixing was computed near inertial poincare waves drive shear instability generating 1 m amplitude and 10 m wavelength high frequency internal waves with 1 mdensity overturns that lead to an increase in turbulent dissipation by one order of magnitude the instabilities are associated with enhanced vertical shear at the crests and troughs of the poincare waves and may be correlated with the local gradient richardson number poincare wave induced mixing should be an important factor when the burger number 0 25 the strong diapycnal mixing induced by the poincare wave activity will also significantly modify the energy flux paths for example we estimate that in lake erie 0 85 of the wind energy is transferred to the lake interior below the surface layer of this 40 is dissipated in the interior metalimnion and 60 is dissipated at the bottom boundary in smaller lakes 0 42 of wind energy is transferred to the deeper water with 90 dissipated in the boundary and 10 in the interior metalimnion 2012 by the association for the sciences of limnology and oceanography inc

the laptev sea flaw polynya russian arctic effects on the mesoscale hydrography a detailed analysis of hydrographic data from a period of 20 years 1980 99 has shown that the persistent presence of a flaw polynya influences mesoscale hydrography of the laptev sea russian arctic based on these data the interannual variability of surface water salinity within the polynya has been estimated as the salinity increase in the water layer is mainly caused by the formation of new ice within the polynya the average ice production rate of the polynya was calculated the results indicate all ice production of 3 4 in per season further aim of this study was to calculate the probability that the convective mixing in the polynya penetrates to the sea floor it is demonstrated that the probability is maximal in the flaw polynya area but does not exceed 20 in the eastern and 70 in the western part of the polynya as a result of strong vertical density stratification from river runoff especially in the eastern laptev sea additional studies of water circulation in the marginal zone of the flaw polynya were carried out during field observations in april may 1999 on the basis of conductivity temperature depth and current measurements we deduce that high current velocities 62 cm s 1 recorded in surface waters near the fast ice edge are caused by a convectively driven circulation system under the polynya our measurements indicate that these high velocity currents are part of a cellular circulation which results from the rejection of brine during intensive ice formation in the polynya the observed azimuthal alignment of the crystalline structure of sea ice is also most probably the consequence of this quasi stationary cellular circulation

estimating internal waves and diapycnal mixing from conventional mooring data in a lake a methodology is described to analyze and interpret the temporal variation of temperature and current measured in lakes or on the continental shelf by generally available standard and robusi equipment a single thermistor chain and current meters it is assumed that variations are mainly produced by internal wave modes propagating in the mean flow and mean stratification the analysis provides estimates of the propagation characteristics energy density and directional flux of the internal waves as well as the temporal and vertical distribution of richardson number ri on scales that may be smaller than those separating the measuring instruments the method is tested with measurements made in lake geneva and provides realistic quantitative estimates of the rate of dissipation of turbulent kinetic energy per unit mass e and of the vertical diffusivity k which are useful in establishing the processes leading to diapycnal mixing

upper ocean temperature structure inertial currents and richardson numbers observed during strong meteorological forcing abstract upper ocean currents and temperature in the northeastern pacific were measured during a 14 day period in november 1980 as part of strex velocities in the upper ocean are dominated by near inertial frequency oscillations thew oscillations are modified by wind stress variations associated with the passage of a strong cold front the change in the inertial currents both in the mixed layer and below is qualitatively consistent with linear internal wave dynamics if turbulent stresses during the storm are assumed to extend 10 20 m below the mixed layer the ratio of mean squared buoyancy frequency n2 and mean squared shear s2 computed over a 10 m interval defines an average richardson number r0 n2 s2 r0 is approximately 2 5 except in regions of high inertial shear in particular values as low as 0 7 are obtained in a 20 m thick region immediately below the base of the mixed layer the data are consistent with a model of the oecanic shear field consisting of a background shear corresponding to a va

on the dimensionality of multiparameter microwave image data from thin sea ice in the labrador sea thin ice is typically defined as comprising the world meteorological organization s young and new ice categories referring to sea ice that is less than 0 3 m thick this ice type is an extremely important factor in both the thermodynamic and dynamic properties of both polar and marginal ice covers in the limex 89 experiment spatially and temporally registered multipolarization data from 5 3 and 9 25 ghz sars and from 37 and 90 ghz imaging radiometers were acquired over a region containing a wide range of new ice growth stages in the labrador ice pack the temperatures at the data acquisition time were 10 and correspond to ice growth conditions in this paper the dimensionality of the multifrequency multipolarization active and passive data set is examined to determine the complementarity of the sensor parameters and sensor types for thin ice measurements principal component analysis is used to provide estimates of the information content of individual measurement channels and their combinations various measurement subspaces are examined criteria for channel redundance are proposed and tested and the classification potential of the multidimensional measurement set is tested for thin ice growth stages that are known to present classification difficulties for microwave sensors given six nominally independent sar measurement channels the information space dimension of this subspace is shown to be greater than five the four radiometer channels are shown to have information space dimension two and are redundant in frequency the combined ten element sar radiometer measurement space was shown to have information space dimension eight under the criteria used when the scattering polarization ratios are included

arctic ocean mixed layer eddy generation under leads in sea ice 1 convection in the arctic ocean mixed layer occurs under openings in sea ice where new sea ice is formed the process of brine rejection during ice formation creates negatively buoyant fluid at the surface of ice leads when the fluid convects downward the ocean mixed layer below the lead is stirred vertically and through planetary rotational effects along lead flows at the lead edges are induced these vertical and lateral motions have been previously studied using two dimensional numerical ocean models and observed in field programs such as leadex in this paper the generation of arctic ocean eddies through dynamic instabilities is investigated using a three dimensional nonhydrostatic ocean model results suggest that salt enriched vortices can develop at the base of the mixed layer as a consequence of brine rejection but the vortex formation requires a time period of several days a time long enough that the progenitor lead would likely have closed the scale of the eddies is found to depend on the magnitude of the buoyancy forcing the width of the lead and the duration of the buoyancy forcing the number of vortices produced depends on lead width and duration of buoyancy forcing but is less sensitive to the magnitude of the buoyancy forcing vortex sizes scaled appropriately and vortex numbers are compared with those found in recent laboratory studies of convectively driven flows from line segment sources

internal swell generation the spatial distribution of energy flux from the wind to mixed layer near inertial motions the energy flux from the wind to inertial mixed layer motions is computed for all oceans from 50 8 st o 508n for the years 1996 99 the wind stress t is computed from 6 h 2 58 resolution ncep ncar global reanalysis surface winds the inertial mixed layer response ui and the energy flux p5 t ui are computed using a slab model the validity of the reanalysis winds and the slab model is demonstrated by direct comparison with wind and adcp velocity records from ndbc buoys at latitudes 508 the inertial response is too fast to be resolved by the reanalysis wind 6 h output interval midlatitude storms produce the greatest fluxes resulting in broad maxima near 40 8 latitude during each hemisphere s winter concentrated in the western portion of each basin northern hemisphere fluxes exceed those in the southern hemisphere by about 50 the global mean energy flux from 1996 to 1999 and 508 st o 508n is 0 98 6 0 08 3 1023 wm 22 for a total power of 0 29 tw 1 tw 5 1012 w this total is the same order of magnitude as recent estimates of the global power input to baroclinic m2 tidal motions suggesting that windgenerated near inertial waves may play an important role in the global energy balance

winds waves and turbulence on a shallow continental shelf during passage of a tropical storm abstractmeasurements of collocated fields of atmospheric forcing surface waves and mean and turbulent velocities associated with passage of tropical storm ts barry over the u s navy tower r2 o

shear and baroclinic energy flux on the summer new england shelf observations are presented of internal wave properties and energy fluxes through a site near the 70 m isobath on the new england shelf in late summer data collected from a shipboard adcp and microstructure profiler over a three week period and projected onto dynamic vertical modes reveals large variations in the magnitude and vertical structure of internal waves baroclinic energy and shear were primarily associated with low mode near inertial and semidiurnal waves and at times high frequency solibores the energies in each mode varied by factors from 2 to 10 over several days and were not significantly correlated with one another the associated shear variance was concentrated in the thermocline however the strength and vertical range of shear varied significantly throughout the research period and depended sensitively on both the magnitude and evolving vertical mode content of the wave field shear during the quasi two layer solibores was strong enough to temporarily lower the 4 m richardson number below the threshold for shear instability energy flux through the site came primarily from the mode 1 internal tide in both linear and nonlinear solibore forms the average energy flux from the first five baroclinic modes was 130 w m 21 a comparison of energy fluxes from each mode and locally measured average dissipation rates suggests that near inertial and high mode waves were generated near the experimental site

probing the interior of arctic leads investigations using high frequency sound in preparation for the arctic leads experiment leadex two side scan doppler sonars were deployed from the edge of beaufort sea leads in april 1991 the instruments originally developed for ocean surface wave research were used to investigate ice and water motions in the near lead environment as well as to collect preliminary acoustic data required in the design of a more capable leadside sonar the sonars could determine lead geometry with great accuracy identifying regions of open water and young ice opening and closing speeds of the lead ice cover could be measured to 0 01 cm s 1 using pulse to pulse coherent techniques the flow velocity of the water just beneath the ice of order 1 10 cm s 1 was estimated using pulse to pulse incoherent processing perhaps surprisingly the strongest acoustic returns from the lead surface came from regions of open water not ice cover frazil ice was a likely source of this scattering although temperature microstructure might also play a role on the basis of the 1991 measurements a 28 beam sector scan doppler sonar was developed for use in the leadex main field experiment march april 1992 with the fan of beams oriented in a vertical plane the sonar formed an image of the velocity field over a 45 sector to ranges of 250 m depths of 200 m the instrument was deployed at leadex lead 3 on april 8 9 at this point a significant ice cover had developed limiting local convective forcing the dominant motions observed beneath the lead were near inertial internal waves significant variability in acoustic scattering was observed at the base of the mixed layer and in the upper thermocline this presumably resulted from strong temperature and salinity fluctuations observed at these depths the near inertial modulation of the ice water relative velocity affects the transit time of water parcels under a lead probability density functions of parcel transit time have extremely high kurtosis for mean transit times less than an inertial day resultant distributions of near surface properties such as salt uptake or primary production will thus be extremely patchy

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

strong inertial currents and marginal internal wave stability in the central north sea solar insolation stabilizes the water column and suppresses vertical exchange observations from the central north sea clearly show that increased heating in summer is accompanied by enhanced de stabilizing vertical current differences shear surprisingly to such extent that the equilibrium state is marginally stable under calm weather conditions the shear is predominantly generated by near inertial motions while the internal wave spectrum primarily results from nonlinear interaction between the dominating tidal and near inertial motions in terms of the associated enhanced vertical mixing across the largest vertical temperature gradients shelf seas are not different from the abyssal ocean despite the proximity to energy sources near boundaries in the former by the lack of sufficiently strong wind and tidal mixing this internal mixing is considered to be responsible for the diapycnal transport of nutrients leading to the observed increase in near surface values and triggering the late summer phytoplankton bloom

surface mixed layer deepening through wind shear alignment in a seasonally stratified shallow sea inertial oscillations are a ubiquitous feature of the surface ocean here we combine new observations with a numerical model to investigate the role of inertial oscillations in driving deepening of the surface mixed layer in a seasonally stratified sea observations of temperature and current structure from a mooring in the western irish sea reveal episodes of strong currents 0 3 m s 1 lasting several days resulting in enhanced shear across the thermocline while the episodes of strong currents are coincident with windy periods the variance in the shear is not directly related to the wind stress the shear varies on a subinertial time scale with the formation of shear maxima lasting several hours occurring at the local inertial period of 14 85 h these shear maxima coincide with the orientation of the surface current being at an angle of approximately 90 to the right of the wind direction observations of the water column structure during windy periods reveal deepening of the surface mixed layer in a series of steps which coincide with a period of enhanced shear during the periods of enhanced shear gradient richardson number estimates indicate ri 1 4 at the base of the surface mixed layer implying the deepening as a result of shear instability a one dimensional vertical exchange model successfully reproduces the magnitude and phase of the shear spikes as well as the step like deepening the observations and model results therefore identify the role of wind shear alignment as a key entrainment mechanism driving surface mixed layer deepening in a shallow seasonally stratified sea

an investigation of the link between lead induced thermohaline convection and arctic eddies a recent laboratory study indicates that a turbulent buoyant line plume discharging into a rotating stratified fluid provides a natural mechanism for generating a series of anticyclonic geostrophic vortices bush and woods 1999 here we examine the implications of these experimental results in the context of the thermohaline convection which develops when saline water is released as leads freeze over in the polar oceans using the experimental results in conjunction with a simple numerical model of plume dynamics in a non uniformly stratified environment we develop a model which characterizes the geometry of the eddies which would develop owing to lead induced convection the model predicts that in the absence of strong currents lead induced thermohaline convection may generate anticyclonic geostrophic vortices of characteristic radius 2 10 km at the base of the mixed layer however this mechanism cannot account for the arctic eddies observed at substantial depths beneath the mixed layer cyclonic or strongly ageostrophic eddies

shallow brine driven free convection in polar oceans nonhydrostatic numerical process studies a three dimensional nonhydrostatic convection model which accounts for small scale ice ocean interactions is used to study convection in shallow sea coastal ice formation regions which contribute significantly to water mass formation in both the arctic and antarctic ocean for certain conditions the results presented in this paper are also transferable to shallow open ocean convection the model is applied to an initial well mixed ocean at rest with a temperature close to the freezing point the ocean initially free of ice is exposed to cold and dry polar air we consider situations in which the mean wind stress is negligible but wind fluctuations result in small sensible and latent heat fluxes corresponding to a wind speed of 2 m s 1 cellular convection patterns develop in the ocean finally occupying a mean aspect ratio of 2 convection is driven by salt release during frazil ice formation due to supercooling newly forming sea ice is collected along convergent downwelling regions at the surface thus showing also cellular structures because the area of insulating sea ice remains small new ice can be formed continuously and the surface buoyancy forcing remains large this collection of ice in small fractions of the sea surface results in a latent heat polynya type which is very effective in terms of dense water mass formation a comparison of the three dimensional model and a two dimensional slice model shows that key results can be reproduced with the slice model in summary the results of the process studies indicate that cellular features in the sea ice cover which may be detectable by remote sensing techniques are closely related to active brine driven convection

internal wave mixing in the baltic sea near inertial waves in the absence of tides 1 the dynamics of near inertial motions and their relation to mixing is investigated here with an extensive data set including turbulence and high resolution velocity observations from two cruises conducted in 2008 summer and 2010 winter in the bornholm basin of the baltic sea in the absence of tides it is found that the basin scale energetics are governed by inertial oscillations and low mode near inertial wave motions that are generated near the lateral slopes of the basin these motions are shown to be associated with persistent narrow shear bands strongly correlated with bands of enhanced dissipation rates that are the major source of mixing inside the permanent halocline of the basin in spite of different stratification near inertial wave structure and atmospheric forcing during summer and winter conditions respectively the observed dissipation rates were found to scale with local shear and stratification in a nearly identical way this scaling was different from the gregg henyey type models used for the open ocean but largely consistent with the mackinnon gregg scaling developed for the continental shelf

modeling winds and open water buoy drift along the eastern beaufort sea coast including the effects of the brooks range the united states coast guard deployed a cluster of satellite transmitting surface drifting buoys in the beaufort sea north of prudhoe bay alaska on august 17 1983 the surface currents in this coastal area are predominantly wind driven an unusual stand of westerly winds led to eastward drift with the surviving buoys moving into mackenzie bay canada by mid september the buoy motion suggested that they were driven by the geostrophic wind modified by the orographic umbrella of the brooks range this mesoscale effect can create changes in wind direction and regions of super and subgeostrophic speeds it influenced an arcuate zone at least 50 km seaward of the coast from camden bay alaska to mackenzie bay a simple model was developed to predict the wind modifications and resultant wind driven buoy drift the model s initial wind velocity input is a calculated geostrophic wind derived from triangular shaped mesoscale atmospheric pressure network data these networks were chosen because their boundaries alternately contained the trajectories of the eastward moving buoys the model then used this network velocity to generate an orographically modified wind field at buoy locations in offshore areas north of the brooks range the actual buoy drift during the open water season covered approximately 650 km in 60 days with the final model predicted buoy drift position in error by less than 50 km the brooks range influence did not appear to affect the october buoy drift which was north of richards island canada above 70 n and east of 135 n

bubble momentum plume as a possible mechanism for an early breakdown of the seasonal stratification in the northern north sea the presence of a seasonal thermocline likely plays a key role in restraining methane released from a seabed source in the deeper water column thereby inhibiting exchange to the atmosphere the bubble plume itself however generates an upward motion of fluid e g upwelling and may thereby be partially responsible for an early breakdown of the seasonal thermocline measurements at site 22 4b located at 57 550n 1 380e in the uk central north sea 200 km east of the scottish mainland where gas is still being released since a blow out in 1990 have been used to identify the generation of the seasonal thermocline and thus the depth of the upper mixed layer and its breakdown in autumn data derived from two landers containing an acoustic doppler current profiler and a conductivity temperature depth recorder were used to determine the mixed layer depth and the breakdown of the thermocline mixing of upper layer fluid into the lower layer has been inferred from large amplitude variations in the nearbottom temperature the adcps estimate velocity profiles in four beam directions using doppler shifted frequency from acoustic pings sent out and received by four different transducers in a specific configuration besides that the intensity of the backscattered sound per transducer is also recorded bubbles from the nearby plume contaminate the signal during part of the tidal cycle but in bubble free periods the mixed layer depth can be estimated using the acoustic backscatter signal as local maxima results show that the thermocline broke down between mid october and early november several weeks earlier than the breakdown of the thermocline in nearby comparable areas likely caused by bubble induced downwelling at the site the early breakdown of the thermocline was accompanied by multiple occurrence of a strong jet like structure associated with the seasonal tidal mixing front

turbulent mixing induced by nonlinear internal waves in mono lake california describing the spatial and temporal occurrence of turbulent mixing and the mechanisms of turbulence production are fundamental problems in physical limnology and oceanography here we present results from mono lake california that illustrate pronounced steepening of the pycnocline upon cessation of strong wind forcing and the enhanced turbulence resulting from this nonlinearity three events occurred with wind speed of 10 m s21 upwind the upper pycnocline upwelled but on relaxation of the wind it downwelled 6 10 m and compressed the similarity of wave amplitude during compression to mixed layer depth and lake numbers 4 were indicative of significant nonlinearity energy in the internal wave field increased by two orders of magnitude but 50 of the energy was lost within 24 h the largest energy losses occurred at low frequencies rather than via an energy flux from low to moderate and high frequencies eddy diffusivities computed over 6 d intervals using the heat budget method averaged 1026 m2 s21 in the energized pycnocline but were five to 10 times higher during the initial upwelling and downwelling periods microstructure casts taken 1 2 d after the first event revealed that the percentage of the pycnocline that was turbulent varied with bottom slope being 80 turbulent where bottom slopes were up to 10 6 0 where bottom slopes were 3 and less than 7 where bottom slopes were 0 1 the threshold for turbulent transport was exceeded only 10 of the time and only where bottom slopes were highest

observations of nonlinear internal waves on the outer new england continental shelf during the summer shelfbreak primer study observations are presented of nonlinear internal waves on the outer new england continental shelf during the summer shelfbreak primer study conducted between july 26 and august 5 1996 current and temperature measurements were made with an upward looking acoustic doppler current profiler adcp located on the 147 m isobath near the shelfbreak and three vertical thermistor moorings located upshelf data from the adcp and two nearby thermistor chains show energetic internal tides propagating at roughly 0 9 m s 21 to the north northwest nearly perpendicular to the local topography with 10 15 cm s 21 horizontal currents and 15 30 m vertical displacements these waves evolve rapidly within a 5 8 km range into an undular internal tidal bore cross isobath barotropic tidal currents responsible for generating the internal tides are in the 5 12 cm s 21 range the bore formation is highly variable there is evidence of a correlation between internal tide steepening and a shelfbreak front jet orientation that is oppositely directed to the internal tide propagation there is no correlation between steepening and the jet s vertical shear statistics of the undular bores show rms travel time fluctuations from 0 8 to 1 7 hours and average tidal bore durations from 12 to 9 hours the average undular bore speed is 0 9 m s 21 with an rms fluctuation of 0 4 m s 21 the number of high frequency waves in the bore varies from 0 to 8 near the shelfbreak and increases to 30 waves 26 7 km upshelf the observed distribution function of temporal spacing between high frequency internal waves is spread between 4 and 20 min

a fine resolution numerical model of the iceland farœ front with open boundary conditions an eddy resolving limited area primitive equation model of the iceland far frontal region is developed the spatial and temporal evolution of the front is examined on time scales of up to 2 months experiments are performed changing the open boundary conditions at the lateral boundaries using passive and active open boundary conditions the experiment with the passive open boundary conditions reproduces many observed features of the iceland far frontal region discrepancies between these results and observations in the area are noted in particular the western end of the front drifts too far north the model is then forced at the lateral boundaries using two contrasting barotropic velocity fields improvements in the results are noted comparison of the results illustrate to what extent and how far field currents can affect the dynamics of this frontal region the east icelandic current is found to have the following important effect on the front maintaining its vertical structure and confining the western end of the front to more southerly latitudes

mixing in seasonally stratified shelf seas a shifting paradigm although continental shelf seas make up a relatively small fraction ca 7 of the world ocean s surface they are thought to contribute significantly 20 50 of the total to the open ocean carbon dioxide storage through processes collectively known as the shelf sea pump the global significance of these processes is determined by the vertical mixing which drives the net co 2 drawdown which can occur only in stratified water in this paper we focus on identifying the processes that are responsible for mixing across the thermocline in seasonally stratified shelf seas we present evidence that shear instability and internal wave breaking are largely responsible for thermocline mixing a clear development from the first order paradigm for the water column structure in continental shelf seas the levels of dissipation observed are quantitatively consistent with the observed dissipation rates of the internal tide and near inertial oscillations it is perhaps because these processes make such a small contribution to the total energy dissipated in shelf seas that they are not well represented in current state of the art numerical models of continental shelf seas the results thus present a clear challenge to oceanographic models

variability of frontal structure in the southern norwegian sea abstract a hydrographic survey ctd was conducted in the vicinity of the iceland faeroe island oceanic front iff north of the faeroe islands during october 1980 it consisted of ctd transects on three horizontal scales ranging from kilometers to hundreds of kilometers intense interleaving of different water masses is found in the iff in the presence of horizontal current shear significant alongfront variability on scales of about 50 km is present consistent with earlier findings estimates of cross front heat flux of 5 16 104 w m 2 and salt flux of 1 58 g m 2 s 1 are greater than those found for the antarctic polar front but are of the same order as eddy heat flux across the iff found by willebrand and meincke evidence suggests that intrusive interleaving in the iff on 50 m vertical scales is driven by double diffusive convection

solidification of leads theory experiment and field observations thin sea ice plays a central role in the surface heat and mass balance of the arctic ocean in order to develop understanding of these balances we describe and analyze highly resolved temperature data taken through the air sea ice interface during the transition from an ice free to an ice covered arctic ocean surface the data were taken to observe the thermodynamic evolution of a lead a process that has previously only been accessible to measurement techniques confined to the lead edge our detailed analysis of the field data is guided by recent theoretical and experimental advances in understanding the phase dynamics of directionally solidified alloys because of the dearth of direct observations we also present time series of the relevant heat fluxes inferred from our data and demonstrate the controlling influence that the internal phase evolution has on these quantities we have previously examined the stability of the brine trapped in a growing sea ice matrix both theoretically and experimentally and now find that haline convection driven from within the growing layer is consistent with this previous work and with the nature of direct turbulence measurements the importance of this process is that although ice growth is continuous the local brine flux commences abruptly only after some time in contrast to what had previously been supposed hence the ice growth process itself is a source of intermittency in oceanic boundary layer turbulence furthermore we find that in this particular situation the sea ice growth is not simply a square root function of time in contrast to the model typically used in numerical simulations by far the most practical methods of studying lead convection are numerical simulations and laboratory models and a strong conclusion of this study is the importance of the proper treatment of the boundary conditions describing the buoyancy flux

the formation and morphology of ice stalactites observed under deforming lead ice during the leadex main field experiment held in april 1992 in the alaskan beaufort sea a number of large ice stalactites were observed growing under young lead ice formation of the stalactites was associated with rafting of the thin highly saline ice the rafting caused the brine to drain rapidly from the ice at a temperature well below the freezing point of the surrounding water which in turn caused ice to form in a hollow cylinder around the brine plume within a 15 h period after the rafting event the stalactites which were located approximately 10 m apart in a line along the up wind edge of a 150 m wide lead had grown to a length of 2 m a detailed structural analysis of the upper part of one of these stalactites revealed that the interior channel down which the brine flowed was bounded by a zone of frazil ice that developed into a shell of columnar ice the growth of the columnar ice was directed radially outward and the c axes of these crystals were oriented perpendicular to their growth direction development of the stalactites illustrates the impact ice deformation can have on the process of brine rejection in freezing leads and potentially on the thermohaline structure of the upper ocean in ther immediate vicinity of the lead

convection beneath freezing leads new observations compared with numerical model results vertical distributions of temperature salinity and horizontal and vertical current speed were measured along the edges of a number of rapidly freezing leads in the southern central beaufort sea during march april 1992 these observations were restricted to cases having sufficiently small ice water relative speeds that brine driven convection was expected based on scaling arguments to dominate shear turbulence generated by the relative ice water motion the observed salinity and current features were consistent with an existing conceptual model for sublead convection consequent to brine rejection from ice formation and with the results of a numerical model which assumes two dimensionality in the cross lead direction and uses a brine input consistent with the field observations these models predict convection of brine enriched plumes beneath the lead downward to the pycnocline where they then spread outward away from the lead volume continuity is satisfied by horizontal inflow of water to the lead at the surface observed mean downward convection speeds varied from 0 2 to 0 7 cm s 1 and had maxima up to about 2 cm s 1 consistent with the numerical model salinities associated with the convecting parcels were about 0 001 practical salinity units psu above ambient which was an order of magnitude less than predicted by the model while plumes of water flowing away from the lead on the pycnocline had salinities as high as 0 004 psu above ambient these similarities and discrepancies are discussed within the context of a steady state model versus a nonsteady field situation and it is concluded that the steady convection cell concept is probably valid if viewed as a time averaged sequence of discrete convective plumes or thermals

near inertial oscillations over the texas louisiana shelf wind induced near inertial oscillations over the texas louisiana shelf in spring and summer 1992 are described using the current and wind observations taken during the first year of the texas louisiana shelf circulation and transport processes study latex a rotary spectral analysis shows clockwise rotating energy peaks at near inertial frequencies for records from all current meter moorings after the suppression of principal tidal signals the vertical structure of near inertial oscillations is characterized by a first baroclinic mode with a near 180 phase difference between the upper mixed layer and the lower stratified layer the oscillations are intermittent with a modulation timescale of about 5 10 days they are surface intensified and have maximum values near the shelf break decaying gradually toward the coast but rapidly offshore near inertial oscillations appear to accompany a sudden change of the wind stress during frontal passages diagnostic analysis suggests that the large near inertial oscillations over the latex shelf are mainly generated by high frequency near inertial variation of the wind stress accompanying the passage of atmospheric fronts when the downward transfer of the near inertial energy to the deep stratified layer is small a simple mixed layer model forced by the observed wind stress provides a reasonable prediction of the near inertial currents in the mixed layer

the gin sea a synthesis of its physical oceanography and literature review 1972 1985 abstract a synthesis and review of the physical oceanography of the gin sea greenland iceland and norwegian seas is presented an accompanying bibliography is included from 1972 through 1985 some 1986 works are also noted emphasis is placed on describing the gin sea as a major semi enclosed basin that plays a role unique among the world s oceans by providing a strong two way advective exchange between the ice covered polar sea and the north atlantic ocean and at the same time acting as the primary site for northern hemisphere bottom water formation the water masses for the gin sea are defined in a manner as consistent as possible with the literature the large scale oceanographic and meteorological factors influencing the water mass formation and circulation are described a sample calculation of the various horizontal and vertical thermohaline driven exchanges is given

upper ocean inertial currents forced by a strong storm part i data and comparisons with linear theory abstract a strong isolated october storm generated 0 35 0 7 m s 1 inertia frequency currents in the 40 m deep mixed layer of a 300 km 300 km region of the northeast pacific ocean the authors describe the evolution of these currents and the background flow in which they evolve for nearly a month following the storm instruments included ctd profilers 36 surface drifters an array of 7 moorings and air deployed velocity profilers the authors then test whether the theory of linear internal waves propagating in a homogeneous ocean can explain the observed evolution of the inertial frequency currents the subinertial frequency flow is weak with typical currents of 5 cm s 1 and steady over the period of interest the storm generates inertial frequency currents in and somewhat below the mixed layer with a horizontal scale much larger than the rossby radius of deformation reflecting the large scale and rapid translation speed of the storm this scale is too large for significant linear propagation of the

optics particles stratification and storms on the new england continental shelf in situ beam attenuation and chlorophyll fluorescence were correlated with concentration and bulk composition of particles in shelf waters during summer and spring under different physical forcing conditions to determine if optical parameters could be used as an additional tracer in examining the process of mixing in shelf waters time series measurements were made for two 18 day periods during high stratification late summer 1996 t 3 0 kg m 3 surface to bottom and low but rapidly developing stratification spring 1997 t 0 05 to 0 5 kg m 3 in 70 m of water in a midshelf environment south of martha s vineyard massachusetts when defined by hydrography and optical profiles four layers were identified during the summer the surface mixed layer the particle chlorophyll maximum the midwater particle minimum and the bottom nepheloid layer fast moving solitons perturbed the water column briefly but no storms perturbed the system until large surface swells from hurricane edouard intensified and thickened the nepheloid layer bulk composition and optics of particles in and above the nepheloid layer were distinctly different after the passage of hurricane edouard the hurricane passage demonstrated that intense atmospheric forcing greatly influences both hydrographic and optical properties in the entire water column even when highly stratified t 3 0 kg m 3 decreasing to 0 8 kg m 3 post hurricane and causes massive resuspension due initially to wave shear stress that was later dominated by current shear restratification progressed rapidly after the hurricane passed during spring the water column started as a weakly stratified two layer system hydrographically and optically but evolved into three layers as stratification developed strong spring storms affected both surface and bottom layers but with decreasing impact as the water column stratified

bottom stress estimates from vertical dissipation rate profiles on the continental shelf abstract measurements of the near bottom distribution of the turbulent dissipation rate on the continental shelf west of vancouver island are used to calculate bottom stress a free failing vertical profiler with microstructure shear probes was used to measure the dissipation rate from near the surface to within 0 15 m of the bottom the shear probes measure velocity gradients at scales within the viscous subrange of the turbulence and therefore directly measure the rate at which kinetic energy is dissipated by viscosity friction velocities are computed from the formula uast z where the dissipation rate is measured in the constant stress layer the technique is more reliable than estimates of the dissipation rate obtained by fitting spectral slopes to velocity spectra at scales in the inertial subrange near bottom current measurements indicate that the bottom stress values obtained from the turbulent measurements are well correlated with the current magnitude an estimate of the drag coeff

near inertial waves on the new england shelf the role of evolving stratification turbulent dissipation and bottom drag abstract energetic variable near inertial internal waves were observed on the springtime new england shelf as part of the coastal mixing and optics cmo project surface warming and freshwater advection tripled the average stratification during a 3 week observational period in april may 1997 the wave field was dominated by near inertial internal waves generated by passing storms wave evolution was controlled by a balance among wind stress bottom drag and turbulent dissipation as the stratification evolved the vertical structure of these near inertial waves switched from mode 1 to mode 2 with associated changes in the magnitude and location of wave shear the growth of mode 2 waves was attributable to a combination of changing wind stress forcing and a nonlinear coupling between the first and second vertical modes through quadratic bottom stress to explore both forcing mechanisms an open ocean mixed layer model is adapted to the continental shelf in this model surface wind stress and bottom stre

observations of seasonal subduction at the iceland faroe front the polar front in the north atlantic is bound to the ridge between iceland and the faroe islands where about one half of the northward transport of warm atlantic water into the nordic seas occurs as well as about one sixth of the equatorward dense overflow we find a low salinity water mass at the surface of the iceland faroe front iff which in wintertime subducts along outcropping isopycnals and is found in much modified form on the atlantic side of the iceland faroe ridge ifr crest the features found on the atlantic side of the crest at depth have temperature and salinity characteristics which are clearly traceable to the surface outcrop of the iff the presence of coherent low salinity layers on the atlantic side of the ifr crest has not been previously reported warm waters above the ifr primarily feed the faroe current and injection of a low salinity water mass may play an early role in the water mass transformation taking place in the nordic seas the seasonality of the intrusive features suggests a link between winter convection mixed layer instability and deep frontal subduction these low salinity anomalies as well as a low oxygen water mass from the iceland basin can be used as tracers of the intermediate circulation over the ifr

generation of bulk shear spikes in shallow stratified tidal seas abstract recent finescale observations of shear and stratification in temperate shelf sea thermoclines show that they are of marginal stability suggesting that episodes of enhanced shear could potentially lead to shear instability and diapcynal mixing the bulk shear between the upper and lower boundary layers in seasonally stratified shelf seas shows remarkable variability on tidal inertial and synoptic time scales that has yet to be explained in this paper observations from the seasonally stratified northern north sea are presented for a time when the water column has a distinct two layer structure bulk shear estimates based on adcp measurements show a bulk shear vector that rotates in a clockwise direction at the local inertial period with episodes of bulk shear spikes that have an approximately twice daily period and occur in bursts that last for several days to explain this observation a simple two layer model based on layer averaging of the one dimensional momentum equation is developed

near inertial waves in lake erie near inertial poincare waves with a period t p similar to 17 h are the dominant wind induced internal wave motions in central lake erie and consequently have a substantial influence on lake circulation mixing and biogeochemistry however due to the complex three basin bathymetry in lake erie the vertical and horizontal modal structure of these waves remain poorly understood in this study we analyze field data to show wind events energize frequent vertical mode one poincare waves the horizontal modal structure was also investigated in a sensitivity analysis using a calibrated three dimensional hydrodynamic transport model forced with observed and idealized spatially uniform wind events strong horizontal mode one poincare wave cells form in both the central and eastern basins when wind events have a duration of 0 25 t p to 0 5 t p are impulsive and periodic at t p or have anticyclonic rotation with a duration of t p momentum transfer from longer wind events 0 5 tp will oppose the coriolis force rotated currents and damp poincare wave generation in agreement with theory the most efficient wind events are observed and computationally modeled to have a duration of 0 25 t p causing an excitation peak at similar to 0 4 t p and converting similar to 0 8 of the wind energy input to poincare waves the efficiency of wind work in generating poincare wave kinetic energy is given by 1 cos 2 pi f t t 1 where f is the inertial frequency and t is the wind duration therefore the efficiency peaks during each nt p period where n is a non negative integer and decreases significantly for longer wind events

modulation of near inertial oscillations by low frequency current variations on the inner scotian shelf abstractnear inertial oscillations nios on the inner scotian shelf are studied using observations a simple slab model and two operational shelf circulation models high frequency radar and adcp

sensitivity of simulated cfc 11 distributions in a global ocean model to the treatment of salt rejected during sea ice formation we show that simulated oceanic absorption of an atmospheric gas is very sensitive to the representation of a process that occurs beneath sea ice as sea ice forms salt is rejected locally increasing surface sea water density this dense water can sink to the pycnocline at the base of the mixed layer previous studies have not considered the impact of this subgrid scale process on transient tracers in the ocean to assess the potential importance of this process to the oceanic absorption of atmospheric gases we performed two idealized simulations a control simulation in which salt rejected during sea ice formation is placed in the model s 25 m thick surface layer and a test simulation in which salt rejected during sea ice formation is distributed uniformly through the upper 160 m beneath the forming sea ice our treatment of rejected salt is highly idealized and is intended to demonstrate the need for a physically based parameterization of subgrid scale convection for use in ocean general circulation models that takes into account the subgrid scale heterogeneity of surface buoyancy forcing distributing rejected salt more deeply during periods of ice formation helps to maintain vertical density gradients inhibiting grid scale convection especially in the southern ocean this greatly diminishes simulated ocean uptake of cfc 11 and generally improves simulated cfc 11 and salinity fields the modeled global ocean inventory of cfc 11 for year 1990 is about 30 lower and modeled column inventories in the southern ocean are up to 90 lower in our test simulation relative to our control simulation we infer that a more detailed treatment of subgrid scale processes occurring beneath sea ice may diminish simulated oceanic absorption of anthropogenic co2 especially in the southern ocean

initial model results for arctic mixed layer circulation under a refreezing lead at the temperatures in the arctic ocean mixed layer during lead induced surface water cooling convection is primarily salinity controlled owing to continuous brine expulsion from newly forming ice a nonlinear time dependent convective model has been developed that simulates existing field data obtained on the circulation characteristics under and near a refreezing lead the model uses typical arctic ocean ambient conditions as initial input and allows for imposition of varying geostrophic currents the zero geostrophic current free convective case model output for typical lead surface salt input resulted in maximum horizontal current velocities of 0 05 m s 1 eddy viscosities on the order of 0 01 m2 s 1 average salt fluxes beneath the lead of 3 3 10 5 kg m 2 s 1 and a subsequent increase in the depth of the mixed layer the circulation cells are symmetric with respect to the lead axis imposition of a cross lead constant geostrophic current shows a resultant circulation cell asymmetry associated with increased salt advection in a forced convective regime

a study of the iceland faeroe frontal variability using the multiscale energy and vorticity analysis the multiscale nonlinear interactive iceland faeroe frontal iff variability during 14 22 august 1993 is investigated for complex dynamics with the localized multiscale energy and vorticity analysis ms eva in terms of multiscale window transform the cold meandering intrusion observed in the iff experiment is represented on a mesoscale window the resulting mesoscale energetics for the deep layer show an isolated center of transfer of potential energy from the large scale window into the mesoscale window in the study domain this large to mesoscale potential energy transfer or bc for short is a baroclinic instability indicator by the ms eva based stability theory signatures on other energetics maps and the reconstructed mesoscale structures all support this baroclinic instability on the bc map the transfer hotspot originally resides near the western boundary it travels along the front into the interior domain in a form of convective instability and then on 19 august changes into another instability that is absolute in character correspondingly disturbances switch from a spatial growing pattern into a time growing mode culminating on 21 august the day just before the intrusion matures the whole process lasts for about five days limited within a small horizontal region and beneath a depth of approximately 150 m by interaction analysis the energy locally gained from this process goes to the submesoscale window as well but most of it remains in the mesoscale window serving to fuel the growth of the meandering intrusion

the oceanography of winter leads leads in pack ice have long been considered important to the thermodynamics of the polar regions a winter lead affects the ocean around it because it is a density source as the surface freezes salt is rejected and forms more dense water which sinks under the lead this sets up a circulation with freshwater flowing in from the sides near the surface and dense water flowing away from the lead at the base of the mixed layer if the mixed layer is fully turbulent this pattern may not occur rather the salt rejected at the surface may simply mix into the surface boundary layer in either event the instability produced at the surface of leads is the primary source of unstable buoyancy flux and as such exerts a strong influence on the mixed layer here as many as possible of the disparate and almost anecdotal observations of lead oceanography are assembled and combined with theoretical arguments to predict the form and scale of oceanographic disturbances caused by winter leads the experimental data suggest the velocity disturbances associated with lead convection are about 1 5 cm s 1 these appear as jets near the surface and the base of the mixed layer when ice velocities across the lead are less than about 5 cm s 1 the salinity disturbances are about 0 01 to 0 05 psu scaling arguments suggest that the geostrophic currents set up by the lead density disturbances are also of the order of 1 5 cm s 1 the disturbances are most obvious when freezing is rapid and ice velocity is low because the salinity and velocity disturbances in the upper ocean are not smeared out by turbulence in this vein lead convection may be characterized at one extreme as free convection in which the density disturbance forces the circulation at the other extreme lead convection may be characterized as forced convection in which the density disturbance is mixed rapidly by boundary layer turbulence the lead number lo which is the ratio of the pressure term to the turbulence term in the momentum equation and the turbulent lead number lot which is the ratio of buoyant production to shear production in the turbulent kinetic energy equation define the boundary between the free and forced regimes for lo and lot less than one both the large scale circulation and the turbulence are forced by surface stress for lo and lot greater than one both the large scale circulation and the turbulence are forced by the buoyancy flux the magnitudes of velocity and salinity disturbances from a model developed elsewhere suitable to free convection agree with what few observations we have the results of a forced convection model developed here suggest salinity disturbances of the order of 0 01 0 02 practical salinity units with the maximum occurring at the surface of the lead and decreasing substantially below 5 10 m this unstable gradient is a unique characteristic of lead convection though the salinity disturbances may be small when ice velocities are large the buoyancy flux in leads has a major effect on the boundary layer turbulence

on the behavior of internal waves in the wakes of storms abstract the rossby adjustment process in the wake of a storm is studied with a view to finding within the context of linear theory how wave dispersion in both the vertical and meridional directions spreads energy which is initially confined entirely to the mixed layer comparisons are made between three cases 1 a periodic storm on the f plane where dispersion is purely vertical 2 a bounded storm on the f plane and 3 a bounded storm centered 2700 km from the equator on an equatorial beta plane particular attention is paid to the initial rate of loss of energy from the mixed layer and some simple formulas which work very well in the cases studied are derived these show that the rate of loss goes up when the mixed layer depth is increased and also that the rate scales as the square of the wavenumber values of the rates are sufficient to provide a major source of energy for internal waves below the mixed layer the often observed tendency for phase lines to propagate upward is found in all case

intermittent intense turbulent mixing under ice in the laptev sea continental shelf vertical mixing in the bottom boundary layer and pycnocline of the laptev sea is evaluated from a rapidly sampled 12 h time series of microstructure temperature conductivity and shear observations collected under 100 sea ice during october 2008 the bottom boundary turbulent kinetic energy dissipation was observed to be enhanced 10 4 w m 3 beyond background levels 10 6 w m 3 extending up to 10 m above the seabed when simulated tidal currents were directed on slope upward heat fluxes into the halocline class waters along the laptev sea seabed peaked at 4 8 w m 2 averaging out to 2 w m 2 over the 12 h sampling period in the laptev sea pycnocline an isolated 2 h episode of intense dissipation 10 3 w m 3 and vertical diffusivities was observed that was not due to a localized wind event observations from an acoustic doppler current meter moored in the central laptev sea near the m2 critical latitude are consistent with a previous model in which mixing episodes are driven by an enhancement of the pycnocline shear resulting from the alignment of the rotating pycnocline shear vector with the under ice stress vector upward cross pycnocline heat fluxes from the arctic halocline peaked at 54 w m 2 resulting in a 12 h average of 12 w m 2 these results highlight the intermittent nature of arctic shelf sea mixing processes and how these processes can impact the transformation of arctic ocean water masses the observations also clearly demonstrate that absence or presence of sea ice profoundly affects the availability of near inertial kinetic energy to drive vertical mixing on the arctic shelves

an investigation of internal mixing in a seasonally stratified shelf sea the shelf sea seasonal thermocline is a critical interface within the marine environment separating the euphotic zone from nutrient rich deep water fluxes across the thermocline therefore represent a key biogeochemical pathway in this paper we quantify the rate of mixing across the seasonal thermocline for a location in the celtic sea and investigate the processes responsible for driving thermocline fluxes profiles of the rate of dissipation of turbulent kinetic energy e show enhanced dissipation within the thermocline region similar to 6 x 10 5 w m 3 the diffusivity implied by these measurements is similar to 0 5 cm 2 s 1 similar to previous shelf sea studies and is sufficient to explain the observed warming of the deep water suggesting that vertical mixing is the dominant control on water column structure two potential sources of mixing energy are identified the internal tide and near inertial waves the mechanism of energy transfer from the candidate mixing mechanisms to turbulence is not clear thermocline dissipation rates were found to have no richardson number dependence but scaled positively with n 2 and s 2 in agreement with a previous turbulence parameterization application of this model to our data does a good job of capturing the mean characteristics of the observed heating flux across the thermocline although none of the short term fluctuations in mixing were reproduced

seascape level variation in turbulence and wave generated hydrodynamic signals experienced by plankton abstract plankton exhibit diverse and dramatic responses to fluid motions and these behaviors are likely critical for survival and fitness fluid motions can be generated by organisms or by physical processes including turbulence and surface gravity waves physical processes vary geographically in their intensity and generate hydrodynamic signals experienced by plankton as fluid forces on their sensory receptors in this synthesis we review how turbulence and waves vary in space the scales and statistics of their motions and the forces exerted on plankton we then quantify the hydrodynamic signals produced by turbulence and waves in four seascape types surf zones inlets and estuaries the continental shelf and the open ocean using published dissipation rates wind and wave data from buoys and observations from two coastal sites in massachusetts usa we relate these geographic patterns in signals to the observed behaviors of example species and to the forces sensed by typical plankters with different receptor types turbulence generated shears are largest in the surf zone inlets and estuaries while wave generated accelerations are larger offshore as a result each seascape exhibits some range of combined shears and accelerations that is distinct these signals generate forces on plankton that vary among habitats and with plankton size and swimming speed spatial patterns in fluid forces create a potential mechanism for dispersing larvae to distinguish habitats by their hydrodynamic signatures however turbulence can be strong in all seascapes and may cause widespread interference in signaling among predators and prey plankton with a single receptor type could identify nearshore habitats while those with multiple receptor types potentially could distinguish inshore vs offshore seascapes or decode signals produced by physical processes and by other organisms

a review of oceanographic and meteorological controls on the north sea circulation and hydrodynamics with a view to the fate of north sea methane from well site 22 4b and other seabed sources abstract the north sea hydrodynamics are key to the redistribution of methane released at the 22 4b site located at 57 55 n 1 38 e in the uk central north sea 200 km east of the scottish mainland this review summarizes the current state of knowledge on the north sea circulation stratification and variability therein and briefly discusses the potential consequences for the distribution and fate of methane released from site 22 4b or other seabed sources astronomical tidal waves follow a counter clockwise path and tide topography interaction generates a residual circulation in the same direction wind stress forcing can enhance reduce or even reverse this circulation variations in the strength of the fair isle current fic are important the fic enters the north sea between the orkneys and shetland follows approximately the 100 m isobath passes along site 22 4b and ends up in the norwegian trench the north atlantic oscillation nao also causes variability a positive negative nao index is associated with stronger weaker than normal westerly winds nao situations strengthen the circulation in the north sea whereas it weakens during nao conditions and is directed northeastward high positive correlations exist between the sst at site 22 4b and the nao index climate change can have a long term effect on the hydrodynamics of the north sea seasonal stratification has potentially the most important imprint on methane derived from the well 22 4b site summertime heating stratifies the northern part of the north sea in autumn loss of heat to the atmosphere causes the stratification to breakdown until tides and storms mix the entire water column during the period of stratification the bulk of dissolved methane released from site 22 4b gets trapped below the thermocline the loss of methane to the atmosphere thus becomes a function of the relative time scales of transport and horizontal and vertical mixing processes versus the time scale of microbial degradation oxidation in the water column

observations of the internal tide and associated mixing across the malin shelf 1 an energetic internal tide was observed at two contrasting shelf continental sites to the west of scotland the first site was 5 km shoreward of the continental shelf break and the second was 45 km directly to the east of the first site each site was instrumented with a seabed mounted acoustic doppler current profiler and thermistor chain for a 2 week period in july 1996 when thermal stratification was well developed in addition to the measurements of the evolution of the water column structure and flow field two series of measurements of the rate of dissipation of turbulent kinetic energy were made at each of the sites the barotropic tide was found to contain an unusually strong diurnal component thought to be due to a coastally trapped wave as a result there is a significant diurnal component to the baroclinic energy spectra significant peaks are also present in the baroclinic energy spectra at interaction frequencies between the main semidiurnal m2 and diurnal k1 tidal constituents at both sites observations of profiles of the rate of dissipation of turbulent kinetic energy show a significant proportion of the measured rate of dissipation took place within the thermocline close to the shelf edge detailed observations of a hydraulic jump and nonlinear internal waves are analyzed to show significantly stronger mixing at this site characterized by diffusion coefficients of 1 6 and 6 1 10 4 m2 s 1 than at the site farther onshore where the diffusion coefficient is estimated to be 0 7 10 4 m2 s 1

brine driven eddies under sea ice leads and their impact on the arctic ocean mixed layer abstract eddy generation induced by a line shaped salt flux under a sea ice lead and associated salt transport are investigated using a three dimensional numerical model the model is designed to represent a typical condition for the wintertime arctic ocean mixed layer where new ice formation within leads is known to be one of the primary sources of dense water the result shows that along lead baroclinic jets generate anticyclonic eddies at the base of the mixed layer and almost all the lead originated salt is contained inside these eddies these eddies survive for over a month after closing of the lead and transport the lead originated salt laterally consequently the lead origin salt settles only on the top of the halocline and is not used for increasing salinity of the mixed layer sensitivity experiments suggest that the horizontal scale of generated eddies depends only on the surface forcing and is proportional to the cube root of the total amount of salt input this scaling of eddy size is consi

observations of shear and vertical stability from a neutrally buoyant float measurements of 1 to 5 m shear and strain from a neutrally buoyant float are used to examine the statistics and causes of shear instability in a 9 day record unstable conditions defined as vz n 2 where vz vz are due to higher than average shear rather than lower than average buoyancy frequency and there are no instances of unstable buoyancy frequency or overturns on the 0 5 m spacing of the thermistors shear is dominated by upward propagating near inertial motions unstable events were more frequent when a near inertial wave packet occupied the water parcel tracked by the float groups of unstable events occur roughly every 5 7 hours at scales 2 5 m and much less often at larger scales events typically last 10 min one buoyancy period or longer these time scales appear to be controlled by vertical advection of 1 m fine structure past the float sensors so do not represent the intrinsic time scales of instability turbulent and mixing quantities are estimated from these fine scale measurements giving a dissipation rate of e 2 3 16 10 10 w kg and an eddy diffusivity of k 3 10 6 m2 s in agreement with direct microstructure estimates therefore the float adequately resolves those quantities needed to estimate turbulent dissipation and could be used to monitor turbulent mixing in the ocean

internal tide observations from the australian north west shelf in summer 1995 abstract observations are presented of the internal tide over the continental shelf and slope from a cross section on the australian north west shelf data collected from moored instruments and repeated profile measurements during the summer months of 1995 show an energetic large amplitude shoreward propagating semidiurnal internal tide multiple generation sites are suggested coinciding with near critical bottom slopes in water less than approximately 200 m deep the vertical structure of the internal tide is predominantly a first vertical mode whereas in deeper water over the slope the vertical structure is more complicated with currents and vertical displacements intensified in the lower part of the water column the internal tide is largely confined to a region approximately 100 km wide from water depths between 70 and 1000 m strong generation and dissipation of the internal tide energy is observed over this region and there is evidence that the dissipated energy impacts on the vertical mixing

oceanographic conditions east of iceland circulation and hydrography on the shelf east of iceland and on the western portion of the iceland faeroe ridge is described by a series of surveys using temperature salinity profilers moored current meters and satellite tracked drifters the dominant surface current of the region is the northeastward flow of north atlantic water at the shelf break southeast of iceland as it leaves the shelf to join the iceland faeroe front on the bottom beneath it flowing in the opposite direction is a strong steady current composed of water from the nordic seas that has overflowed the ridge and followed along bathymetric contours north of the front three comparatively weak currents are identified formed by splitting of the north icelandic irminger current after it has rounded the northeast corner of iceland one branch the east icelandic current is confined to the shelf and produces a mean southward flow until it turns eastward to join the iceland faeroe front another leaves the shelf to form the shallow southeastward flowing icelandic current the third follows deeper contours of the continental slope and renews waters on the northern flank of the iceland faeroe ridge

influence of environmental conditions on acoustical properties of sea ice sonar echo amplitude data have been collected at carrier frequencies of 188 and 120 khz from the underside of different sea ice types histograms of normal incidence echo amplitudes were formed from over 90 samples of each ice type experiments were conducted on saline ice grown in an outdoor pond under relatively controlled conditions at the usa cold regions research and engineering laboratory crrel and on the sea ice cover in the fram strait analysis shows marked variations about a factor of 5 in the magnitude of the coherent reflection coefficients as congelation ice at the bottom of an ice sheet evolves from a growing dendritic interface to an ablating thermally altered interface larger differences about a factor of 10 are observed between growing congelation ice and slush ice used to simulate frazil these results indicate that important variations in acoustic regime exist in areas where different ice types are intermingled

shallow ocean response to tropical cyclones observed on the continental shelf of the northwestern south china sea based on observed temperature and velocity in 2005 in northwestern south china sea the shallow ocean responses to three tropical cyclones were examined the oceanic response to washi was similar to common observations with 2 degrees c cooling of the ocean surface and slight warming of the thermocline resulted from vertical entrainment moreover the wavefield was dominated by first mode near inertial oscillations which were red shifted and trapped by negative background vorticity leading to an e folding timescale of 12 days the repeated reflections by the surface and bottom boundaries were thought to yield the successive emergence of higher modes the oceanic responses to vicente appeared to be insignificant with cooling of the ocean surface by only 0 5 degrees c and near inertial currents no larger than 0 10 m s as a result of a deepened surface mixed layer however the oceanic responses to typhoon damrey were drastic with cooling of 4 5 degrees c near the surface and successive barotropic like near inertial oscillations during the forced stage the upper ocean heat content decreased conspicuously by 11 65 and the stratification was thoroughly destroyed by vertical mixing in the relaxation stage the water particle had vertical displacement of 20 30 m generated by inertial pumping the current response to damrey was weaker than washi due to the deepened mixed layer and the destroyed stratification our results suggested that the shallow water oceanic responses to tropical cyclones varied significantly with the intensity of tropical cyclones and was affected by local stratification and background vorticity

enhanced turbulence due to the superposition of internal gravity waves and a coastal upwelling jet to vertical aspect ratios of 10 2 to 10 3 median value 300 these patches are clearly defined by regions of low richardson number and occur where and when the linear superposition of the three dominant shear constituents near inertial m2 and thermal wind interferes constructively this is most pronounced at the base of the coastal jet where the thermal wind shear is largest while the effect of the turbulence stress divergence on the jet is small compared to geostrophy 1 it is significant in the second order force balance governing secondary circulation the timescale associated with the decay of the thermal wind shear via turbulence stress is o 10 days we confirm that the vertical salt flux due to mixing is comparable to the net ekman transport of salt onto the shelf within the bottom boundary layer because numerical models of coastal circulation lack turbulence in midwater column any vertical transport of scalars including salt and heat must be achieved inshore of the 40 m isobath this is inconsistent with the observations presented in this study in which significant vertical turbulent salt transport is found to exist across the entire shelf

turbulent mixing induced by upgoing near inertial waves in the seasonal thermocline of the norwegian sea acoustic doppler current profiler and towed thermistor chain measurements made in the seasonal thermocline in the norwegian sea are examined for evidence that near inertial shear leads to small scale turbulent mixing as inferred from meter scale temperature fluctuations for the 1 day of data examined here spatial variability in shear is dominated by near inertial waves having upward energy propagation 30 m vertical wavelength and 5 to 10 km horizontal extent 20 km wavelength repeated samples of one of these waves had high froude number and enhanced small scale variability dominated by 20 m long waveforms which we conjecture are kelvin helmholtz instabilities arising from the near inertial shear

seasonal variations in the upper arctic ocean as observed at t 3 hydrographic data from t 3 are analyzed to illustrate the behavior of the arctic mixed layer the mixed layer depth fluctuates 11 m annually and mixed layer salinity fluctuates 0 32 the fluctuations in total salt content are consistent with theoretical work by maykut and are in phase with mixed layer depth indicating changes in the mixed layer are controlled by salt flux deepening of the mixed layer brings 0 3 kcal cm 2 yr 1 of heat to the surface from the ocean below

effects of a shelf polynya on flow and water properties in the northern bering sea we present long term 230 day measurements from three moorings in the vicinity of saint lawrence island on the northern bering sea shelf one mooring was deployed near the polynya which often exists south of the island these data confirm the existence of strong 0 15 m s 1 flow toward bering strait northwest of the island in anadyr strait and suggest that regional circulation results in a moderate 0 03 5 m s 1 mean flow eastward along the southern coast of saint lawrence island coherent variations in the regional circulation and variations in the geostrophic wind account for much of the low frequency current fluctuation south of saint lawrence island however there were 11 events when offshore northerly winds coincided with the temperature following the freezing point increasing salinity and reversal of the current this suggests that ice formation and the ensuing brine rejection affect flow in the vicinity of the polynya scaling of a simplified momentum equation indicates that the cross shelf density gradient was a possible mechanism for some of the reversals salinity data show a seasonal cycle as well as individual events of brine rejection during an average event time of 65 hours the salinity increased by 8 10 3 g kg 1 h 1 the heat flux can be estimated as 535 wm 2 these fluxes correspond to an ice production of 5 m during winter 1981 extrapolation of our results and comparison with the freshwater cycle suggest that brine rejection is an important component of the regional salt budget

a year of internal poincare waves in southern lake michigan 1 a unique set of full year deep water observations from the middle of lake michigan s southern basin are analyzed to quantify the seasonal variability of the dominant near inertial internal poincare wave at this mid lake location the poincare wave is seen to describe more than 80 of the observed surface current variability for much of the year with characteristic near inertial frequency and clockwise rotating velocities the dominance of the near inertial seiche on the flow decreases with depth the wave persists during the stratified period roughly may through late december and is supported by as few as 1 2 degrees of thermal stratification over 150 m only after complete water column mixing does the wave go dormant for january through april the strongest poincare wave activity is seen to correspond to the period of strongest summer thermal stratification august in spite of the relatively weak winds at this time a simple inertial slab model optimized with linear friction is shown to capture the seasonal variability of the near inertial energy at this location reasonably well the vertical structure of the wave shows good agreement with that calculated with a standard normal modes formulation which is in turn used to characterize the potential shear and mixing caused by the wave late spring and summer events of elevated poincare wave activity are shown to generate sufficiently strong shear with persistent periods of sub 1 richardson numbers within the thermocline suggesting that the near inertial seiche is likely generating thermocline instabilities in the lake s interior

oceanic thermohaline intrusions observations intrusions are commonly observed in the upper deep and coastal oceans and are closely linked to lateral fluxes of heat salt and momentum this is a review of observations of intrusions and the results of comparisons of properties such as scale slopes microstructure activity and fluxes with theoretical models a summary of estimates of lateral heat fluxes indicates a wide range of lateral diffusivities we conclude by noting that our present knowledge is insufficient to predict the structure length scales and lateral fluxes of thermohaline intrusions with confidence and list a number of unresolved questions suggestions are made for compilation of existing data into a database for exploratory analysis and testing of theoretical hypotheses an outline is given of a potential collaborative field experiment using ctd fluorescent dye and microstructure observations

lead convection measured with an autonomous underwater vehicle the winter lead experiment leadex was conducted during 1992 in the beaufort sea there the autonomous conductivity temperature vehicle actv was operated under and around leads these are the first measurements of this kind measurements of temperature salinity and turbulence parameters were also made at lead edges with sensors fixed to rigid masts by combining information from the fixed measurements and the actv an inertial dissipation method is used to derive horizontal profiles of salt flux from actv salinity measurements comparisons also show that turbulent vertical velocity perturbations can be estimated from the vertical motion of the actv with these velocity estimates horizontal profiles of the turbulent fluxes of heat w t and salt w s are also computed directly data from a wide 1000 m wide lead with rapid ice motion indicate stronger turbulence under the lead than downstream but the character of the flow is that of a convective boundary layer modified by a change in surface buoyancy flux the convection is characterized by multiple intermittent plumes that scale in size with the mixed layer depth at a medium sized 100 m wide lead with slower ice motion the convective circulation set up by the lead is more apparent convective plumes are stronger and more prevalent at the lead edges particularly the downstream edge the comparison between the horizontal profiles from the actv and time series from fixed sensors suggests that lead convection is a combination of a near surface convective boundary layer and a deeper quasi stationary convection pattern

turbulence beneath sea ice and leads a coupled sea ice large eddy simulation study the importance of leads sea ice motion and frazil ice on the wintertime ocean boundary layer was examined by using a large eddy simulation turbulence model coupled to a thermodynamic slab ice model coupling was achieved through exchange coefficients that accounted for the differing diffusion rates of heat and salinity frazil ice concentrations were modeled by using an ice crystal parameterization with constant crystal size and shape stationary ice without leads produced cellular structures similar to atmospheric convection without winds ice motion caused this pattern to break down into a series of streaks aligned with the flow eddy fluxes were strongly affected by ice motion with relatively larger entrainment fluxes at the mixed layer base under moving ice whereas stationary ice produced larger fluxes near the top of the boundary layer opening of leads caused significant changes in the turbulent structure of the boundary layer leads in stationary ice produced concentrated plumes of higher salinity water beneath the lead ice motion caused the lead convection to follow preexisting convective rolls enhancing the roll circulation salinity and vertical velocity under the lead comparison of model time series data with observations from the arctic leads experiment showed general agreement for both pack ice and lead conditions simulated heat flux carried by frazil ice had a prominent role in the upper boundary layer suggesting that frazil ice is important in the heat budget of ice covered oceans

observations of the transition layer abstract the transition layer is the poorly understood interface between the stratified weakly turbulent interior and the strongly turbulent surface mixed layer the transition layer displays elevated thermohaline variance compared to the interior and maxima in current shear vertical stratification and potential vorticity a database of 91 916 km or 25 426 vertical profiles of temperature and salinity from seasoar a towed vehicle is used to define the transition layer thickness acoustic doppler current measurements are also used when available statistics of the transition layer thickness are compared for 232 straight seasoar sections which range in length from 65 to 1129 km with typical horizontal resolution of 4 km and vertical resolution of 8 m transition layer thicknesses are calculated in three groups from 1 vertical displacements of the mixed layer base and of interior isopycnals into the mixed layer 2 the depths below the mixed layer depth of peaks in shear stratification and potenti