coupled ice ocean dynamics in the marginal ice zones upwelling downwelling and eddy generation this study is aimed at modeling mesoscale processes such as upwelling downwelling and ice edge eddies in the marginal ice zones a two dimensional coupled ice ocean model is used for the study the ice model is coupled to the reduced gravity ocean model through interfacial stresses the parameters of the ocean model were chosen so that the dynamics would be nonlinear the model was tested by studying the dynamics of upwelling winds parallel to the ice edge with the ice on the right produce upwelling because the air ice momentum flux is much greater than air ocean momentum flux thus the ekman transport is greater under the ice than in the open water the stability of the upwelling and downwelling jets is discussed the downwelling jet is found to be far more unstable than the upwelling jet because the upwelling jet is stabilized by the divergence a constant wind field exerted on a varying ice cover will generate vorticity leading to enhanced upwelling downwelling regions i e wind forced vortices steepening and strengthening of vortices are provided by the nonlinear terms when forcing is time varying the advection terms will also redistribute the vorticity the wind reversals will separate the vortices from the ice edge so that the upwelling enhancements are pushed to the open ocean and the downwelling enhancements are pushed underneath the ice

on the bering sea ice edge front an oceanographic field program was carried out along the bering sea ice edge in winter 1982 83 to investigate the temperature salinity front associated with and paralleling the winter ice edge currents were measured using taut wire moorings that were in place over winter and an intensive ctd survey was carried out of the frontal structure in midwinter february march the midwinter front separated cold 0 c more saline 32 5 outer shelf water the front had northwestward baroclinic currents paralleling the front ice edge with near surface speeds of 5 6 cm s and an associated transport of about 0 3 106 m3 s these baroclinic currents were superimposed on a regional barotropic along isobath flow resulting in north westward midwinter upper layer flows with monthly mean speeds exceeding 10 cm s an upper layer flow component was directed beneath the ice and provided heat adequate to melt the ice and limit advance of the edge the resulting low salinity meltwater was mixed vertically to maintain the front by wind acting across a highly mobile hydrodynamically rough ice cover subtidal fluctuations were not significantly affected by the front or the ice cover and local winds accounted for less than one quarter of the observed current variability the remainder being probably due to regional variations in the barotropic flow

intra annual oscillations at station aloha north of oahu hawaii inverted echo sounders have been used to make continuous measurements of dynamic height at a site chosen to be representative of the central pacific subtropical gyre these show that the dominant features in dynamic height are fluctuations having peak to peak amplitudes of up to 27 dyn cm and timescales of about 100 days empirical orthogonal function analyses of temperature and salinity profiles suggest that if the oscillations are due to vertical motion within the water column the motion is not that of first baroclinic mode but has much higher vertical wavenumber structure zonal wavenumbers associated with the oscillations indicate westward phase propagation and meridional wavenumbers are close to zero the dominant periods are too short for freely propagating rossby waves two explanations of these observations are that the waves could be doppler shifted by the mean flow or that the region could be an area of active forcing

fronts and shelf circulation models satellite imagery shows that fronts and frontal eddies are widespread on the northwest european continental shelf the implications for the numerical modelling of transports for example of pollutants are discussed a brief review of some models of shelf circulation is given it is argued that to include fronts in models of shelf circulation requires a better understanding of dynamics on the frontal scale a three dimensional numerical model of eddy formation in a coastal front is then presented that reproduces many of the observed features

boundary layer upper ocean and ice observations in the greenland sea marginal ice zone during the 1984 marginal ice zone experiment a coordinated ocean boundary layer and mixed layer experiment was carried out in concert with a complete heat and mass balance study in the summer marginal ice zone miz of the greenland sea the measurements were made at two drifting ice stations and included observations of ocean boundary layer turbulence profiles of water temperature salinity and velocity ice ablation ice concentration solar radiation and spectral albedos ocean conditions were found to be extremely variable the ice and water velocities were heavily influenced by tidal and inertial motions with amplitudes from 6 to 12 cm s 1 in the course of the drift a 30 km eddy was crossed wherein ice and water velocities exceeded 15 cm s 1 the northern extension of the east greenland polar front was encountered and a northward flow of atlantic water into the arctic basin was observed below the eastern edge of the front but the drift station never moved quite far enough west to be caught in the southward transport of arctic surface water heat from the ocean was a major factor in ice melt and when the ice was over atlantic water it was the dominant factor the events that had the greatest impact on the ice were two outbreaks during which off ice winds blew the ice across warm ice edge ocean fronts once south of these fronts and over surface water as warm as 1 c the ice bottom melted at rates up to 100 kg m 2 d 1 the rapid changes in stratification associated with the outbreaks had a dramatic impact on the drag and heat transfer coefficients the drag coefficient relative to the square of the relative water velocity at 30 m ranged from 0 002 to 0 02 and averaged 0 006 the heat transfer coefficient relative to the friction velocity u and the mixed layer temperature elevation above freezing ranged from 0 0025 to 0 009 and averaged 0 0038 in agreement with the idea that stratification inhibits turbulent exchange the heat transfer coefficient decreased when stratification increased in fact the observed melt rates can be simulated well if molecular heat and salt transfer through a thin near surface laminar boundary layer are accounted for as well as transfer through the turbulent outer boundary layer also in agreement with turbulent boundary layer theory the drag coefficient decreased when stratification increased slightly above neutral however for the large increases in surface stratification the drag coefficient increased this was due to the generation of internal gravity waves by ice bottom roughness because the surface exchange coefficients are so sensitive to surface stratification which is in turn highly variable in the miz accurate simulations of ice motion and ice melt will require realistic estimates of stratification and a good understanding of the relation between the ice ocean interactions and upper ocean conditions

long period transport changes in the eastern north atlantic and their simulation by propagating waves an analysis is presented of geostrophic volume transport across a zonal line along 28 degrees n in the eastern atlantic the data are from an array of five moorings with 200 km spacing carrying temperature sensors and one current meter each for 1 or 2 years transport changes in the main thermocline relative to a fixed depth level are obtained by the use of temperature salinity relationships the transport variability is simulated by two propagating waves with first order baroclinic mode structure solutions exist with annual and semi annual periods and zonal wavelengths of 100 200 km and 300 km respectively assuming quasi geostrophic dynamics and using results on the reynolds stress the dominating waves of annual and semi annual period are found to propagate to the southwest with 45 degrees 60 degrees and 25 degrees to the south off the westward direction respectively wave solutions with a 90 day period and a zonal wavelength of about 300 km are interpreted as an effect of barotropic waves arising due to horizontal temperature inhomogeneity the propagation is about 25 degrees off the westward direction in general good approximations are obtained with the propagating wave simulations in the western and central part of the array while large differences occur between observation and simulation close to the canary archipelago possible causes for these differences are discussed

geosat and advanced very high resolution radiometer observations of oceanic planetary waves adjacent to the hawaiian islands geosat observations of the central north pacific ocean show westward propagating mesoscale features with length scales 500 km time scales 105 155 days and observed zonal phase speeds commensurate with those of nearly nondispersive baroclinic rossby waves advanced very high resolution radiometer derived sea surface temperatures observed during april 1988 showed a cusp shaped pattern north of the hawaiian islands congruent with concurrent geosat derived sea level height anomalies it is believed that the cusp shaped pattern is the surface manifestation of a baroclinic rossby wave the observed wavelength of the cusp shaped pattern was 560 km it had an observed meridional extent horizontal amplitude of 200 300 km and an inferred zonal propagation speed of 0 052 m s 1 the westward propagating sea level height structure was observed to amplify as it approached 150 w reaching amplitudes of 0 06 0 08 m in the vicinity of the cusp shaped feature these waves are believed to be locally forced by the topography either as the result of eastward flow over the submerged island ridge or as a result of baroclinic instability during periods of westward flow

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

eddy near the molloy deep revisited a warm 60 km diameter cyclonic eddy was observed in late summer 1984 in the vicinity of the molloy deep at the eastern edge of the east greenland current depression of isotherms to at least 900 m indicates a deep reaching baroclinicity maximum baroclinic speeds of 0 1 to 0 17 m s are estimated as is a swirl transport of 1 sv

laboratory simulation of exchange through fram strait laboratory experiments and theory were conducted to observe the flow patterns and transport in both buoyancy driven and wind driven rotating fluids in lock exchange experiments water with one density flows into a second basin after a sliding gate is removed water of a second density flows back into the first basin the size and location of the currents for various values of density difference rotation rate and assorted sidewall geometries was recorded volume flux of the fluid was also measured and compared with a theory for lock exchange flow of a rotating fluid in a separate group of experiments with a passive upper layer easterly winds like those in the arctic ocean drive the upper level water into the arctic ocean and therefore oppose the buoyant exchange westerly winds would drive the water out of the arctic ocean this indicates that the exchange between the arctic ocean and the greenland norwegian sea is likely to be driven by buoyancy rather than by driven by wind crude estimates of the volumetric and fresh water exchange rate from the lock exchange formulas are compared with observed ocean fluxes and approximate agreement is found

oceanographic conditions in the marginal ice zone north of svalbard in early fall 1979 with an emphasis on mesoscale processes during september october 1979 the norwegian remote sensing experiment was carried out in the marginal ice zone north of svalbard convergence of the ice cover is correlated with along ice edge winds with the ice to the right while divergence occurs during office winds or calm conditions a wind driven ice edge jet is observed wind driven upwelling of the pycnocline of up to 7 m was present along the ice edge during a 10 to 15 m s easterly wind event the upwelling is due to ekman divergence at the ice edge caused by higher wind stress over ice than over open water the ice edge meanders with a scale of 20 40 km and sheds eddies with a scale of 5 to 15 km into the open water this scale is of the same order as the rossby radius of deformation eddies with the same scale are also seen in the conductivity temperature and depth observations conditions during the experiment were such that barotropic instabilities could have generated these eddies

a new class of microstructures which lead to transformation induced faulting in magnesium germanate 1 transformation induced faulting has been studied extensively in natural olivine ice and a variety of other olivine analog systems over the last 15 years and remains a likely candidate mechanism for initiating deep focus earthquakes the mechanism involves the formation of microscopic packets of fine grained denser materials from a metastable host which then behave as mode i features that coalesce to allow bulk mode ii shear failure we present evidence for a new class of transformation microstructures that also allows shear failure at high pressures but which does not require the formation of widely distributed mode i features prior to shear failure we have observed thin planar zones of transformation in coarse grained 150 m mg2geo4 olivine that form along crystallographic planes in deformed grains at temperatures cooler than those that allow significant development of anticracks the development of these zones is rapid and only occurs after 25 bulk strain increasing strain leads to progressive development of these zones in turn leading to bulk shear failure once a continuous pathway of fine grained spinel is formed that traverses the specimen transmission electron microscopy analysis shows that slip bands in olivine along 011 and 010 formed from dislocation pileups on these slip planes transform preferentially to a nanocrystalline aggregate of the denser spinel phase aided by the high strain energy of these bands this new partially strain driven mechanism compliments shear failure by anticracks as described in previous studies and adds new possibilities for the triggering of bulk shear failure by rapid mineralogical transformations

feedback between ice flow barotropic flow and baroclinic flow in the presence of bottom topography coupling between externally driven barotropic flow and locally driven baroclinic flow in the presence of an ice cover and topography is studied the topography is a necessary ingredient in this coupling this study shows that the observed mesoscale activity of the ice edge seen in satellite imagery does not necessarily reflect the mesoscale baroclinic activity in the ocean besides oceanic eddies the ice cover can trace the topographic changes via the coupling to the barotropic flow a two layer ocean model coupled to an ice model is constructed to simulate an ice ocean system with a varying bottom topography in the absence of wind forcing the ice cover reflects the externally driven barotropic ocean response especially topographically forced taylor columns by forming ice streamers or meanders some of these features propagate advected with the ocean currents as a whole downstream creating an image of eddy propagation even though there is no baroclinic structure underneath when downwelling favorable winds ice on the left from the wind direction are turned on in addition to this background barotropic flow the ekman flow in the ocean toward the open ocean will enhance the meandering of the ice edge due to the barotropic flow during upwelling favorable winds the ice edge stays rather compact including the case when a strong baroclinic cyclonic vortex is developing beneath an ice meander supported by the taylor column in the ocean

the ice cover in the greenland and norwegian seas the seasonal sea ice cover of the northern north atlantic is reviewed comprising the ice of the east greenland current the ice cover around svalbard and the ice of the barents sea as far east as franz josef land the review considers various types of ice cover 1 the fast ice along the coasts and in fjords including sikussak or very old fast ice of exceptional thickness 2 the transition zone between the fast ice and the main pack including the positions and causes of recurring winter polynyas and the nature of the shear zone in ne greenland 3 the constitution dynamics and seasonal extent of the drifting pack ice including interannual variations 4 the processes of air ice ocean interaction which occur in the marginal ice zone where the pack ice is influenced by an open ocean boundary

current regimes across the east greenland polar front at 78 40 north latitude during summer 1984 four weeks of concurrent temperature and current observations from three moorings across the east greenland polar front at approximately 78 40 n showed pronounced differences between the current regimes on either side of the front east of the front vertical shear was minimal mean flow was not statistically significant and fluctuations showed evidence of wind influence west of the front vertical shear and southward mean flow were significant however observed fluctuations were not strongly influenced by local winds the mean current and density structure of the front was similar to that of a two layer boundary current model with constant potential vorticity current fluctuations west of the front were in part related to mesoscale features generated farther north and subsequently advected downstream by the east greenland current or to eddylike features apparently generated through potential vorticity conservation local instabilities of the front most likely account for the remainder of the mesoscale variability seen in the records

an ice water vortex at the edge of the east greenland current during the y mer 80 cruise in august 1980 we observed an ice feature of 60 km diameter having the shape of a breaking wave it lay at the edge of the east greenland drift ice in fram strait with its center at 79 15 n 00 38 e and the wave was breaking upstream relative to the east greenland current two conductivity temperature and depth sections across the feature in n s and e w directions revealed warm up to 4 3 c water some 60 km inside the polar front in lenses centered at 40 m depth but with an effect to beyond 600 m the temperature anomalies were accompanied by salinity anomalies so that there was little net effect on the density profile the form of the sections together with the ice distribution observed by vertical photography from a helicopter and surface motion observed by tracking four radar transponders all suggest that the feature is a vortex produced by an instability in the polar front it has similar characteristics to vortices investigated experimentally and theoretically by griffiths and linden 1981a b 1982 and observationally by wadhams et al 1979

sea ice thickness distribution in the greenland sea and eurasian basin may 1987 upward sonar data from a 3400 km track in the greenland sea and the eurasian basin of the arctic ocean obtained by a british submarine in may 1987 have been statistically analyzed mean ice thicknesses in the greenland sea show significant melting with downstream distance at an average rate of 0 38 m per degree of latitude equivalent to about 2140 km3 yr 1 of freshwater input between 80 n and 75 n in the region north of fram strait between 82 n and 80 n there is remarkable consistency between mean ice drafts in 1987 and in three previous cruises 1976 1979 1985 while between greenland and the north pole there was a significant thinning in 1987 relative to 1976 in fram strait the mean ice draft shows evidence of thinning within the region of influence of a semipermanent eddy ice draft distributions show that the probability density function of deformed ice follows a negative exponential distribution and that the change of shape of the distribution with downstream distance in the greenland sea is due to preferential melting of thicker ice pressure ridge draft distributions also fit a negative exponential while their spacings fit a lognormal distribution lead width distribution follows a power law with an exponent of 1 45 for narrow leads and 2 50 for wider leads if leads are defined as having a 1 m maximum draft 1 67 and 2 76 for a 0 5 m maximum draft lead spacings follow a negative exponential distribution for moderate spacings 400 1500 m but with an excess of lead pairs at small and very large spacings

large scale oceanography in fram strait during the 1984 marginal ice zone experiment the pattern of large scale circulation in fram strait during summer 1984 is inferred from hydrographic data and water mass analysis and direct current observations by use of surface and subsurface floats the west spitsbergen current carrying warm and salty atlantic water splits into several branches two flowing northward into the arctic ocean and two turning westward causing a recirculation across the main axis of fram strait the individual flow paths are topographically controlled suggesting a strong barotropic component of the circulation

rossby wave analysis of subsurface temperature fluctuations along the honolulu san francisco great circle abstract seven years of xbt observations collected between honolulu and san francisco reveal subsurface temperature fluctuations with strong in phase vertical coherence and fair horizontal coherence over 1000 km distance their annual and semi annual harmonics exhibit randomness of phase suggesting that the fluctuations are modeled better as a stochastic process than as a deterministic signal cross spectral fitting of a stochastic first baroclinic mode rossby wave model to the fluctuations demonstrates the rossby waves could be producing 50 60 of the observed subsurface covariance at periods exceeding nine months phase is seen to propagate northwestward and energy westward and southwestward the corresponding sea surface velocities and sea level fluctuations are of the order 1 cm s 1 and 1 5 cm

horizontal reynolds stresses in the central equatorial pacific seven 13 month long current records from the north pacific experiment hawaii to tahiti shuttle experiment during 1979 1980 were analyzed to investigate eddy energetics of the upper ocean within 75 km of the equator profiling current meter data from the experiment were also used in an attempt to relate the eddy motions to the mean zonal flow the current fluctuations are highly anisotropic with zonal current dominating after removal of a linear trend plus annual and semiannual harmonics the residual high frequency current fluctuations are much more nearly isotropic the high frequency eddy kinetic energy decreases by a factor of 2 over the upper 250 m and at 100 m has a relative minimum on the equator the seasonal time scale eddy kinetic energy shows a much more dramatic decrease below the thermocline with the exception of tidal peaks the spectra of zonal current are red while meridional current spectra show a flattening at the lowest resolvable frequencies meridional current was non stationary with an energetic packet of 10 to 15 day period oscillations occurring in early 1980 the off diagonal component of the reynolds stress tensor u calculated from the high frequency residuals is everywhere positive decreasing from north to south and with depth the implied cross equatorial flux of zonal momentum is at odds with eddy viscosity parameterizations which relate u to the mean meridional shear of the zonal current the observed distribution of reynolds stresses might be explained by radiation of energy from an instability of the portion of the south equatorial current north of the equator in all cases the high frequency u time series are significantly skewed toward positive values and show no evidence of periodicity indicating that the process es responsible is are intermittent and broadband this is consistent with the instability mechanism

the 1982 1983 el nino signal off northern california the major el nino event of 1982 1983 affected the entire california current system the anomalous conditions along the west coast of north america were related to the equatorial anomalies and also to the anomalous atmospheric circulation in the northeast pacific where the aleutian low was east of its usual position and the associated 700 mbar height reached its lowest value on record in february march 1983 positive temperature and negative salinity anomalies in the upper ocean extending from the coast to at least 200 km offshore were reported from san diego to vancouver island in data acquired in domains centered approximately 180 km off northern california by the ocean prediction through observation modeling and analysis program anomalies in both temperature and salinity were most pronounced subsurface spatially and monthly averaged temperatures were about 3 c warmer than normal at 80 to 100 m in april and again in december 1983 at 100 to 120 m salinity was about 0 4 parts per thousand lower than normal in july 1983 and july 1984 several months later than the temperature anomaly maxima the temperature anomalies may be related to the poleward propagation of the equatorial el nino perturbation by coastally trapped waves with offshore propagation by planetary rossby waves possibly playing some role in the relaxation of the perturbed eastern boundary current circulation anomalous onshore advection associated with the perturbed atmospheric circulation deeper than normal mixed layers or depression of the thermocline and halocline by the passage of rossby waves could each account for coincident positive temperature and negative salinity anomalies

wave effects on ocean ice interaction in the marginal ice zone the effects of wave train on ice ocean interaction in the marginal ice zone are studied through numerical modeling a coupled two dimensional ice ocean model has been developed to include wave effects and wind stress for the predictions of ice edge dynamics the sea ice model is coupled to the reduced gravity ocean model through interfacial stresses the main dynamic balance in the ice momentum is between water ice stress wind stress and wave radiation stresses by considering the exchange of momentum between waves and ice pack through radiation stress for decaying waves a parametric study of the effects of wave stress and wind stress on ice edge dynamics has been performed the numerical results show significant effects from wave action the ice edge is sharper and ice edge meanders form in the marginal ice zone owing to forcing by wave action and refraction of swell system after a couple of days upwelling at the ice edge and eddy formation can be enhanced by the nonlinear effects of wave action wave action sharpens the ice edge and can produce ice meandering which enhances local ekman pumping and pycnocline anomalies the resulting ice concentration pycnocline changes and flow velocity field are shown to be consistent with previous observations