sea ice motion in response to geostrophic winds it is an old rule of thumb that sea ice moves with a speed of about 2 of the surface wind and about 45 to the right of the wind a similar relationship between the ice velocity and the geostrophic wind is examined here it is found that only about half of the long term several month average ice motion is directly related to the geostrophic wind the other half being due to the mean ocean circulation on shorter time scales and in all seasons more than 70 of the variance of the ice velocity in the central arctic ocean is explained by the geostrophic wind within about 400 km of the coasts the geostrophic wind is less successful in explaining the ice motion the spatial variations in ice velocity are also partly explained by the geostrophic wind about half of the variance in the large scale ice vorticity and shear are accounted for on the other hand none of the large scale ice divergence can be explained by the wind the long term average ocean current is estimated by subtracting the share of the ice motion caused by the wind from the total ice motion

mesoscale oceanographic processes beneath the ice of fram strait a major component of the fram strait marginal ice zone experiment was the investigation of air sea ice interactions processes and circulation patterns found behind the local ice edge and on scales greater than 10 kilometers mesoscale and large scale neutrally buoyant floats ice tethered cyclesondes and helicopter based measurements were used to obtain uniquely integrated and consistent views of the mesoscale ocean features beneath the ice cover of fram strait within the vicinity of the yermak plateau three distinct regions of mesoscale motion were observed that coincided with the shallow topography of the plateau the northward flowing atlantic water over the western flank of the plateau and the strong current shear zone of the east greenland polar front a subice meander of the front was also observed which was probably occluded subsequently

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

seasonal cycle of mesoscale instability of the west spitsbergen current abstractthe west spitsbergen current wsc is a topographically steered boundary current that transports warm atlantic water northward in fram strait the 16 yr 1997 2012 current and temperature salinity measurements from moorings in the wsc at 78 50 n reveal the dynamics of mesoscale variability in the wsc and the central fram strait a strong seasonality of the fluctuations and the proposed driving mechanisms is described in winter water is advected in the wsc that has been subjected to strong atmospheric cooling in the nordic seas and as a result the stratification in the top 250 m is weak the current is also stronger than in summer and has a greater vertical shear this results in an e folding growth period for baroclinic instabilities of about half a day in winter indicating that the current has the ability to rapidly grow unstable and form eddies in summer the wsc is significantly less unstable with an e folding growth period of 2 days observations of the eddy kinetic energy eke show a p

wind drag coefficient over first year sea ice in the bering sea profiles of relative wind speed and temperature were collected from four levels over rough sea ice in the marginal ice zone of the bering sea and used to compute surface wind drag coefficients based upon 138 profiles for near constant ice conditions northeast winds of 3 15 m s 1 and near neutral stability the mean near neutral 10 m drag coefficient was 0 00309 0 00049 this is among the largest drag coefficients measured for neutral atmospheric conditions over sea ice sixty five percent of the variance of this estimate is explained by orientation of the ice floe to the wind an additional 5 of the variance is explained by wind speed dependence provided that diabatic atmospheric stability over the bering sea ice pack is well correlated with low wind speed the significant ice advecting wind stress on the ice is determined from the neutral value of the drag coefficient a function of ice roughness length alone the ice forecaster thus may use remote measurements or estimates of wind speed and surface roughness to assess the wind component of ice advection

high frequency internal wave observations in the marginal ice zone three thermistor chains extending from 15 to 65 m were deployed from ice floes in the marginal ice zone north of svalbard in a triangle with sides of 500 800 m for a period of 7 days vertical displacement spectra indicate that the internal wave energy level is lower than the garrett and munk spectrum by a factor of 2 3 but higher than other observations in the arctic a group of internal waves a wave train with frequency of 2 3 cph was observed to propagate at 0 05 m s through the triangle in a west southwesterly direction during a 4 to 6 hour period a case study of this wave train where the horizontal phase differences between the three thermistor chains were analyzed showed wavelengths of 100 200 m and phase velocities of 0 10 0 15 m s observation of the density field and the velocity field indicated that stratification dominated over vertical shear consequently the dispersion relation was calculated by solving numerically the vertical mode equation for internal waves in a shearless ocean the estimated wavelengths and phase velocities agree with the dispersion relation for first mode internal waves the generating mechanisms may be tidal oscillations associated with a seamount located east of the triangle or ice keels moving in relation to the water creating lee waves in the pycnocline

modeling deep convection in the greenland sea the development of deep convective events in the high latitude ocean is studied using a three dimensional coupled ice ocean model oceanic mixing is described according to the level 2 5 turbulence closure scheme in which convection occurs in a continuous way i e convective adjustment is not invoked the model is forced by strong winds and surface cooling strong upwelling at the multiyear ice edge and consequent entrainment of warm atlantic waters into the mixed layer is produced by winds parallel to the ice edge concomitant cooling drives deep convection and produces chimneylike structures inclusion of a barotropic mean flow over topography to the model provides important preconditioning and selects the location of deep convection the most efficient preconditioning occurs at locations where the flow ascends a slope in a stratified environment similar to the greenland sea with a 12 m s 1 wind the model simulations show that localized deep convection takes place after about 10 days to depths of 1000 m

modeling wind driven circulation and landfast ice edge processes during polynya events in northern baffin bay abstract a high resolution sea ice ocean numerical model of the north water polynya has been developed to study the wind driven circulation during polynya events an idealized three layer stratified ocean is used to initialize the model to characterize the baroclinic response to realistic wind and ice conditions the model general circulation pattern is mainly forced by an along channel sea level gradient between the arctic ocean and baffin bay which determines the magnitude of the southward baffin current and by an across channel sea level gradient in baffin bay which drives the northward west greenland current wgc these two currents are found to be anticorrelated to each other in the smith sound area during strong northerly wind events occurring quite frequently in the winter spring period in the polynya nutrient rich baffin bay waters transported by the wgc are forced toward the greenland shelf coinciding with upwelling events along the greenland coast whenever an ice bridge is present i e

a coupled ice ocean model of ice breakup and banding in the marginal ice zone a coupled ice ocean numerical model for the marginal ice zone is considered the model consists of a nonlinear sea ice model and a two layer reduced gravity ocean model the dependence of the upwelling response on wind stress direction is discussed the results confirm earlier analytical work it is shown that there exist directions for which there is no upwelling while other directions give maximum upwelling in terms of the volume of uplifted water the ice and ocean is coupled directly through the stress at the ice ocean interface an interesting consequence of the coupling is found in cases when the ice edge is almost stationary in these cases the ice tends to break up a few tenths of kilometers inside of the ice edge

supradetachment basin evolution during continental extension the aegean province of western anatolia turkey we present a detailed structural and stratigraphic record of a neogene quaternary supradetachment sedimentary succession in the aegean extensional province of western anatolia and we compare its tectonic features and evolution to those of other well documented supradetachment basins around the world the sedimentary fill of the alasehir basin records the uplift and exhumation of a core complex in the footwall of a detachment fault within the central menderes massif accumulation of footwall derived clastic sediments in this basin started ca 20 ma shortly after the initiation of the approximately e w trending alasehir detachment and its shear zone and continued until ca 2 ma major sedimentary facies types include fluvial and alluvial fan deposits debris flow and mass flow deposits and locally developed lacustrine rocks these sedimentary units were accumulated largely in distal depocenters within the extending basin as the low angle 15 28 detachment faulting created little accommodation space near the basin margins while producing high back shed topography in the uplifted menderes core complex the drainage system was dominated mainly by extension parallel transverse streams during the main phases of basin evolution extension parallel scissor hinge faulting produced differential uplift and subsidence in the adjacent fault blocks changed the direction of sediment transport and drainage patterns over short distances and resulted in the local uplift of the older basin strata these processes led to the development of subbasins with lateral variations in basement topography strata thickness and sedimentary facies distribution and generated a segmented basin architecture high angle synthetic and antithetic faults that formed extensively after 3 ma caused back tilting of the sedimentary strata formation of half grabens with their own axial drainage systems and development of angular unconformities with the onset of this crustal scale block faulting the detachment fault ceased to operate and the quaternary gediz graben started to develop at the northern end of the alasehir supradetachment basin our comparative evaluation of select basins shows a maximum sediment thickness of 3 km average extension rates of 6 to 8 9 mm yr 1 and accumulation rates of 0 1 0 2 mm yr 1 uncorrected for compaction in supradetachment basins in general the rates and amounts of extension the geometry of detachment faulting the rates of footwall uplift and the kinematics and interplay of different fault systems are the most important factors controlling three dimensional structural architecture and evolution of supradetachment basins

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

a case study of atmospheric boundary layer mean structure for flow parallel to the ice edge aircraft observations from cearex this paper describes a case study of the mean structure of the atmospheric boundary layer abl in the marginal ice zone of the barents sea for flow nearly parallel to the ice edge data were collected by the noaa p 3 orion research aircraft on march 24 1989 the geostrophic wind above the boundary layer was oriented approximately 15 off ice with a speed of 12 m s 1 and the atmosphere above the abl showed little cross ice edge variability a lidar on the aircraft revealed over the water the downward slope of a stratocumulus deck toward the ice edge the associated inversion continued to slope downward over the ice creating large thermal wind effects within the boundary layer the inversion slope combined with horizontal boundary layer temperature gradients produced a factor of 2 decrease in surface geostrophic wind from water to ice below the inversion the data revealed an abl that remained well mixed for 100 km into the ice a gust probe system on the aircraft provided a mapping of low level fluxes from a 200 km leg perpendicular to the ice edge

a coupled ice ocean model of a wind driven coastal flow ice movement driven by winds along the coast is studied using a two dimensional vertical seaward ice ocean coupled model right hand alongshore winds are given when internal ice stresses are important to determine the ice movement these winds induce right hand coastal currents and ice movement a shoreward ekman flow beneath the ice is a major mechanism to constrain the ice over the shelf balancing the internal ice pressure gradient when the wind ceases the ice decreases its alongshore velocity and the ice covered band becomes wider the alongshore ice velocity is sensitive to ice shear strength which determines the shear stress at the coast i e weak strong shear strength allows a large small ice velocity at the coast resulting in intense weak ekman flow and downwelling which induces a fast slow coastal current the alongshore velocity is also sensitive to the relatively small cross shore component of the wind i e the seaward shoreward component reduces induces the shear stress and allows large small ice velocity the results are applied to the ice over the labrador shelf

nature of the southwestern boundary of the central mojave tertiary province rodman mountains california tertiary volcanic and sedimentary rocks in the central mojave desert are largely confined to the barstow bristol trough an elongate tectonic depression filled with lower miocene strata the southwestern boundary of the trough is sharply defined and separates thick 2 km tertiary sequences from an area to the southwest that is virtually devoid of tertiary rocks segments of this boundary have been interpreted as a buttress unconformity as a right slip sidewall fault that formed the lateral boundary of an early miocene extensional terrane and as a dip slip fault caused by flexure of the north american plate above the subducted mendocino fracture zone the silver bell fault in the rodman mountains central mojave desert is the best exposed segment of the boundary and relations exposed along it can be used to test these hypotheses the tertiary sequence north of the silver bell fault is at least 2 3 km thick and comprises at least 1 9 km of mafic lava flows overlain by and intercalated with coarse clastic rocks derived from the south side of the fault stratigraphic relations require faulting during volcanism and indicate that the minimum throw across the fault is at least equal to the thickness of the exposed tertiary section tuff layers intercalated in the lower part of the clastic deposits are 23 24 m y old indicating that faulting and volcanism were contemporaneous with extension and plutonism in the nearby central mojave metamorphic core complex structural and stratigraphic data indicate that the silver bell fault is primarily a dip slip fault the tertiary section is folded into a west trending upright to overturned syncline located near the southern edge of exposed tertiary rocks the syncline records late cenozoic north south shortening along the northwest striking calico fault which in this area accommodated about 10 km of right slip and perhaps 1 km of reverse slip southwestward dipping strata in the areally extensive north limb of the syncline resemble tilted strata in nearby highly extended areas and have been interpreted to reflect crustal extension however bedding dip does not decrease upward in the tertiary section paleocurrent directions trend obliquely updip and northeast dipping normal faults are rare stratal tilting postdated the accumulation of the exposed section which therefore was not deposited during rotational normal faulting the new data contradict interpretation of the silver bell fault as a major right slip fault bounding the central mojave extensional terrane although they permit small magnitude extension across the fault the amount of early miocene crustal extension in this area therefore is apparently small in spite of stratal tilting and the lateral limit of large magnitude crustal extension in the central mojave block is farther northwest the data are consistent with the fault having formed by failure during plate flexure above the subducted mendocino fracture zone

c band sar observations of marginal ice zone rheology in the labrador sea synthetic aperture radar sar imagery collected during the limex 87 field program in the labrador sea is used to qualitatively interpret the deformation modes in play throughout the experiment the ice cover exhibited two distinct rheologies separated by a clear line of shear a nonlinear viscous outer regime and a quasi brittle inner regime a single constitutive relation capable of effectively modeling both is unlikely within a plastic rate independent formulation rate dependent effects are discussed in relation to favoring brittle fraction in an otherwise ductile material

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

origin of contrasting devonian supradetachment basin types in the scandinavian caledonides supradetachment basins that formed during the devonian extensional collapse of the scandinavian caledonides have been explained as hanging wall basins formed along the listric breakaway zone of a major detachment fault system this model involves significant rotation of bedding as the detachment flattens to an approximately horizontal orientation and explains the large stratigraphic thicknesses of east dipping layers overlying in tectonic contact the top to the west nordfjord sogn detachment zone nsdz however it fails to explain one of the basins the hasteinen basin where east dipping devonian strata rest unconformably on a metamorphic substrate that forms part of the upper plate of the detachment system based on detailed field mapping we present a model where the hasteinen forms as a ramp basin that develops on the upper plate above a major west facing ramp in the nsdz we test both of these models by forward modeling using 2dmove two dimensional kinematic modeling software the results show how two different types of supradetachment basins can coexist in a subhorizontal detachment zone in an area that underwent many tens of kilometers of lateral crustal extension

the role of plastic ice interaction in marginal ice zone dynamics under appropriate conditions the nonlinear nature of plastic ice interaction together with a nonlinear coupling between ice thickness characteristics and ice rheology can substantially modify the character of marginal ice zone dynamics this paper examines the steady state ramifications of these nonlinearities by using a one dimensional simplification of hibler s 1979 two level viscous plastic sea ice model a series of idealized small scale simulations 4 km resolution are carried out with the model formulated in a moving lagrangian grid in order to remove diffusion effects analytic solutions for the equilibrium plastic adjustment case are also constructed the results show that if the ice thickness distribution is allowed to equilibrate in response to a constant wind field the thickness strength coupling will yield a sharp ice edge with the compactness dropping rapidly to zero near the ice margin despite this compactness falloff the steady adjusted ice velocity is nearly constant across the marginal ice zone however the adjustment to a steady state constant velocity can be preceded by a period of shearing which will abate as the ice strengthens by ridging with an increase in forcing near the edge the ice velocity scales with the wind velocity but with a speed less than free drift in the absence of water drag and wind stress the model exhibits a very slow outward creep but yields no ice edge jet effects the ramifications of plastic interaction on upwelling and downwelling are also examined with the same drag coefficients over ice and ocean and for a north south ice edge the model yields in the northern hemisphere upwelling for northward winds downwelling for southward winds and no effect for off ice winds

ocean ice interaction in the marginal ice zone using synthetic aperture radar imagery ocean ice interaction processes in the marginal ice zone miz by wind waves and mesoscale features such as up downwelling and eddies are studied using earth remote sensing satellite ers 1 synthetic aperture radar sar images and an ocean ice interaction model a sequence of seven sar images of the miz in the chukchi sea with 3 or 6 days interval are investigated for ice edge advance retreat simultaneous current measurements from the northeast chukchi sea as well as the barrow wind record are used to interpret the miz dynamics sar spectra of waves in ice and ocean waves in the bering and chukchi sea are compared for the study of wave propagation and dominant sar imaging mechanism by using the sar observed ice edge configuration and wind and wave field in the chukchi sea as inputs a numerical simulation has been performed with the ocean ice interaction model after 3 days of wind and wave forcing the resulting ice edge configuration eddy formation and flow velocity field are shown to be consistent with sar observations

mesoscale eddies in the fram strait marginal ice zone during the 1983 and 1984 marginal ice zone experiments during the summer marginal ice zone experiment in fram strait in 1983 and 1984 fourteen mesoscale eddies in both deep and shallow water were studied between 78 o and 81on sampling combined satellite and aircraft remote sensing observations conductivity temperature depth observations drift of surface and subsurface floats and current meter measurements typical scales of these eddies were 20 40 km rotation was mainly cyclonic with a maximum speed in several cases subsurface of up to 40 cm s observations further suggest that the eddy lifetime was at least 20 to 30 days five generation sources are suggested for these eddies several of the eddies were topographically trapped while others primarily formed by combined baroclinic and barotropic instability moved as much as 10 15 km d with the mean current the vorticity balance in the nontrapped eddies is dominated by the stretching of isopycnals accompanied by a change in the radial shear in the most completely observed eddy south of 79on the available potential energy exceeded the kinetic energy by a factor of 2 quantitative estimates suggest that the abundance of these eddies enhances the ice edge melt up to 1 2 km d

formation of ice bands by winds 1 a mechanism for the formation of ice bands is proposed as a coupled response of ice edge and lee waves to wind under the hydrostatic approximation a high resolution ice ocean coupled model is used in an x z domain with grid sizes x z 250 m 1 m under an along ice edge wind such that the ekman transport is away from the ice edge the nearly discontinuous surface stress between the ice covered and open seas generates lee waves a thin layer of high potential vorticity fluid under the ice is produced by the ekman forcing enabling the ice edge to rapidly slip over less stratified water this is favorable for supercritical conditions when lee waves are generated ice bands are formed by the corresponding convergences and divergences the flow becomes subcritical farther behind the ice edge but secondary lee waves and ice bands form because of the secondary stress discontinuity behind the lead ice band an analytical solution is derived to show that ice bands have longer widths than the lee wavelengths because the ice ocean stress creates the smoothing effect vertical motions associated with the lee waves have speed of the order of 10 m day extend to the bottom 300 m and contribute to deep vertical mixing and the subsequent melting of the ice these small scale features are not modeled well with horizontal grids coarser than approximately 2 5 km

oceanography of the eastern bering sea ice edge zone in spring1 the ice edge region of the southeast bering sea was studied in terms of the hydrographic regime phytoplankton biomass and primary productivity during the springs of 1975 through 1977 the results showed that a phytoplankton bloom occurs at the ice edge just as the spring ice decay period begins and that this accounts for a significant proportion of the annual carbon input over the shallow shelf the bloom is intensified in time and space by the influence of the ice edge on the physical structure of the water column specifically melting ice seems to increase the stability of the water column near and under the ice by lowering the salinity frontal structure in salinity and temperature are apparent at the ice edge and are attributed to the melting ice but also at times to wind driven ekman type upwelling these data are also related to recent short term ca months year climatic fluctuations that seem to control the seasonal position of the ice edge zone relative to the shelf break in cold years the ice edge comes southward to the shelf break and overlies the more nutrientrich alaska stream bering sea source water in warm years the ice edge zone does not reach this nutrient rich water this may be important to the biology of the ice edge ecosystem the edge zones of seasonal sea ice are biologically productive serving as focal points for the congregation of large numbers of marine birds and mammals and thus represent ecologically critical habitats in subpolar regions the presence of a cold and solid boundary influences the biological regime in several ways including effects on the physical and chemical regimes in the adjacent seawater at least three structural features of the water column often associated with high oceanic primary production can occur in such an area simultaneously water column stability frontal structures and under certain conditions ice edge upwelling we show here that there is enhanced primary production due to water column stability and frontal structure at the edge of the seasonal sea ice in spring our data also suggest that ice edge upwelling occurs we show further that the intense

greenland sea odden sea ice feature intra annual and interannual variability the odden is a large sea ice feature that forms in the east greenland sea that may protrude eastward to 5 e from the main sea ice pack at about 8 w between 73 and 77 n it generally forms at the beginning of the winter season and can cover 300 000 km2 throughout the winter the outer edge of the odden may advance and retreat by several hundred kilometers on timescales of a few days to weeks satellite passive microwave observations from 1978 through 1995 provide a continuous record of the spatial and temporal variations of this extremely dynamic phenomenon aircraft synthetic aperture radar satellite passive microwave and ship observations in the odden show that the odden consists of new ice types rather than older ice types advected eastward from the main pack the 17 year record shows both strong interannual and intra annual variations in odden extent and temporal behavior for example in 1983 the odden was weak in 1984 the odden did not occur and in 1985 the odden returned late in the season an analysis of the ice area and extent time series derived from the satellite passive microwave observations along with meteorological data from the international arctic buoy program iabp determined the meteorological forcing associated with odden growth maintenance and decay the key meteorological parameters that are related to the rapid ice formation and decay associated with the odden are in order of importance air temperature wind speed and wind direction oceanographic parameters must play an important role in controlling odden formation but it is not yet possible to quantify this role because of a lack of long term oceanographic observations

wind induced stratified ocean response in the ice edge region an analytical approach the response of a continuously stratified ocean to a moving ice edge is considered in terms of an analytical model it is assumed that the principal cause for the generation of such phenomena as upwelling near the edge is due to divergence in the across edge ekman transports the semi infinite ice cover is considered to act only as a modifier of an applied wind stress thus the ice edge is simulated by a discontinuity in the ocean surface stress distribution the results show that a stationary state relative to the moving edge develops the amplitude of the response is finite and it includes a system of standing waves relative to the edge these results parallel the generation of lee waves in a rotating wave regime how prominent the waves will be depends on the ratio u0 cn where u0 is the edge velocity and cn an eigenvalue corresponding to a vertical mode of the solution as the stationary solution builds up an along edge jet is established it is pointed out that this jet could cause divergence in the surface layer which could explain the generation of ice bands if the ice edge consists of broken ice

ice edge eddies in the fram strait marginal ice zone five prominent ice edge eddies in fram strait on the scale of 30 to 40 kilometers were observed over deep water within 77 n to 79 n and 5 w to 3 e the use of remote sensing a satellite tracked buoy and in situ oceanographic measurements showed the presence of eddies with orbital speeds of 30 to 40 centimeters per second and lifetimes of at least 20 days ice ablation measurements made within one of these ice ocean eddies indicated that melting which proceeded at rates of 20 to 40 centimeters per day is an important process in determining the ice edge position these studies give new insight on the formation propagation and dissipation of ice edge eddies

granular flow in the marginal ice zone the region of sea ice near the edge of the sea ice pack is known as the marginal ice zone miz and its dynamics are complicated by ocean wave interaction with the ice cover strong gradients in the atmosphere and ocean and variations in sea ice rheology this paper focuses on the role of sea ice rheology in determining the dynamics of the miz here sea ice is treated as a granular material with a composite rheology describing collisional ice floe interaction and plastic interaction the collisional component of sea ice rheology depends upon the granular temperature a measure of the kinetic energy of flow fluctuations a simplified model of the miz is introduced consisting of the along and across momentum balance of the sea ice and the balance equation of fluctuation kinetic energy the steady solution of these equations is found to leading order using elementary methods this reveals a concentrated region of rapid ice flow parallel to the ice edge which is in accordance with field observations and previously called the ice jet previous explanations of the ice jet relied upon the existence of ocean currents beneath the ice cover we show that an ice jet results as a natural consequence of the granular nature of sea ice

waves in frazil and pancake ice and their detection in seasat synthetic aperture radar imagery a theoretical model of waves propagating into an ice cover composed of frazil and pancake ice is developed and compared with measurements of wavelength and direction derived from synthetic aperture radar sar imagery obtained from seasat in october 1978 the theoretical model is based on the concept that ice of these types which consists of small crystals or cakes has only a mass loading effect on the water surface we derive the dispersion relation for phase and group velocities finding that there is an upper frequency limit for propagation into the ice from the reflection coefficient at the ice edge we derive the wave radiation pressure exerted on the ice showing that it will cause a slick of frazil ice backed by thicker floes to become more dense or thick with increasing penetration the implications for radar scattering enabling detection on sar are that the bragg resonant wavelength corresponds to waves above the frequency limit for propagation so that a frazil slick appears dark on an sar image when the frazil ice becomes transformed into pancake ice through slick compression or other means the raised edges of the pancakes cause the ice to appear bright despite the fact that there are no waves present at the bragg wavelength these results are applied to a seasat sar image obtained from the chukchi sea the appearance of the ice in the image corresponds to what we expect for frazil ice gradually transforming itself into pancake ice backed by thicker floes we derive directional wave number spectra outside and inside the ice cover by digital fourier analysis of image subscenes and we find that the change of wavelength and angle of refraction of the dominant wave entering the ice field are both characteristic of the dispersion relation derived theoretically mean ice thicknesses extracted from the theory correspond to thicknesses expected for such slicks the technique offers a possible means of extracting the thickness of fields of frazil and pancake ice from sar imagery this may be of considerable utility when ers 1 sar is used to study the advancing winter ice edge in the antarctic which consists of vast areas of these ice types

drift of pancake ice floes in the winter antarctic marginal ice zone during polar cyclones high temporal resolution in situ measurements of pancake ice drift are presented from a pair of buoys deployed on floes in the antarctic marginal ice zone during the winter sea ice expansion over 9 days in which the region was impacted by four polar cyclones concomitant measurements of wave in ice activity from the buoys are used to infer that the ice remained unconsolidated and pancake ice conditions were maintained over at least the first 7 days analysis of the data shows i the fastest reported ice drift speeds in the southern ocean ii high correlation of drift velocities with the surface wind velocities indicating absence of internal ice stresses 100 km from the ice edge where remotely sensed ice concentration is 100 and iii presence of a strong inertial signature with a 13 hr period a lagrangian free drift model is developed including a term for geostrophic currents that reproduce the 13 hr period signature in the ice motion the calibrated model provides accurate predictions of the ice drift for up to 2 days and the calibrated parameters provide estimates of wind and ocean drag for pancake floes under storm conditions

beaufort chukchi seas summer and fall ice margin data from seasat conditions with similarities to the labrador sea the margin of the sea ice pack of the beaufort and chukchi seas is examined using the microwave data from seasat taken during the summer to early fall july 4 through october 8 1978 and the observations are compared to the analogous observations taken in limex 87 the sensors used are synthetic aperture radar sar the seasat a scatterometer system and the scanning multichannel microwave radiometer

regional middle paleozoic metamorphism in the southwestern gyeonggi massif south korea its implications for tectonics in northeast asia abstract the hongseong area in the southwestern gyeonggi massif in south korea is considered to represent the eastward extension of the qinling dabie sulu collision belt in china we have carried out zircon u pb shrimp dating and p t estimations of the gneisses and amphibolites in the eastern wolhyeonri complex within the hongseong area in order to constrain their metamorphic and tectonic evolutions the protoliths of the migmatitic biotite gneisses formed during the neoproterozoic and underwent granulite facies metamorphism 750 880 c 12 15 kbar at 442 413 ma these rocks subsequently experienced amphibolite facies retrograde metamorphism at 585 660 c and 7 5 10 3 kbar mylonitic biotite gneiss hornblende gneiss and folded amphibolite in the study area yield metamorphic ages that range from 429 to 420 ma the protoliths of some garnet amphibolites that formed at 470 456 ma are arc magmatic rocks they experienced metamorphism at the boundary between amphibolite and eclogite facies ca 625 700 c and 13 15 5 kbar before 418 ma and underwent retrograde amphibolite facies metamorphism ca 625 700 c and 8 9 kbar at 418 405 ma these data suggest that a regional intermediate p t metamorphic event occurred during the middle paleozoic in contrast paleoproterozoic augen gneiss blocks enclosed in the deokjeongri gneiss complex preserve evidence of high pressure hp metamorphism 840 960 c 17 21 8 kbar at 234 230 ma which are similar to the previously reported results from eclogite blocks in this area the occurrence of middle paleozoic regional metamorphism before the permo triassic hp metamorphism in the hongseong area may be correlated with the middle paleozoic metamorphism in the qinling belt in china such regional metamorphic events were caused by the collision of microcontinents with the north or south china cratons prior to the collision between the north and south china cratons in the permo triassic

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

a note on chimney formation in ice edge regions wind driven ice ocean interaction in the marginal ice zone has been shown to contribute to enhanced entrainment when the winds are favorable for upwelling at the ice edge if a strong surface heat loss is present formation of a deep convective region is possible resulting from an ever decreasing buoyancy and a rapid deepening of the mixed layer i e a chimney this chimney does not extend to the bottom but loss of buoyancy would indicate eventual overturning to the bottom in the studied two layer ocean model where initially a fresh and cold freezing mixed layer lies above a stagnant warm and saline lower layer a catalyst for the convection is the ice and especially the existence of the ice edge which has both a dynamic and thermodynamic interaction with the ocean in the coupled ice ocean model the entrainment between the mixed layer and the lower layer consists of both the wind mixing component involving the frictional velocity at the ocean surface a kraus turner parameterization and the convectively induced entrainment no dissipation of convective turbulence the latter is necessary in producing the chimney the results are an extension to the earlier model results hakkinen 1987 which did not include the convective component of entrainment

ice banding as a response of the coupled ice ocean system to temporally varying winds in this study we model formation of ice bands in the marginal ice zones a one dimensional coupled ice ocean model is used in which the ice model is coupled to a reduced gravity ocean model through interfacial stresses the internal ice stresses are important only at high ice concentrations 90 100 otherwise the main balance for the ice motion is between the air ice stress and the ice water stress i e free drift the drag coefficients were chosen so that the air ice momentum flux is 3 times greater than the air ocean momentum flux thus the ekman transport is larger under the ice than in the open water so that winds parallel to the ice edge with the ice on the right produce upwelling the upwelling simulation was extended to include temporally varying forcing which was chosen to vary sinusoidally with a 4 day period this forcing resembles successive cyclone passings perpendicular to the ice edge when the oceanic upper layer was thin which means that the dynamics are strongly nonlinear the ice bands were formed the up downwelling signals do not disappear in wind reversals because of nonlinear advection this leads to convergences and divergences in oceanic and ice velocities that manifest themselves as ice banding at least one wind reversal is needed to produce one ice band

possible sources driving the potential vorticity structure and long wave instability of coastal upwelling and downwelling currents it is well known that upwelling and downwelling currents are unstable to perturbations less is however known about the physical mechanism responsible for the observed and modeled instabilities it is shown that the origin of the long wave barotropic baroclinic instability observed on upwelling currents has to be sought among diabatic or thermobaric mechanisms in particular the role of mixing associated with kelvin helmholtz instability and of wind forcing is investigated low richardson numbers occur when the pycnocline outcrops at the sea surface the criterion for instability ri 1 4 can be reached in a narrow region close to the upwelling front permitting kelvin helmholtz instability and mixing this can precondition the current for long wave instability by transforming the current s potential vorticity a constant wind can likewise modify the potential vorticity the resulting potential vorticity anomaly is always negative for both upwelling and downwelling currents and this anomaly interacts with the outcropped front destabilizing it examples are provided via numerical calculations using an idealized front a wind stress is an effective means of inducing the negative pv necessary for instability with wind kelvin helmholz instability when present merely modifies the instability characteristics in addition upwelling fronts are always less stable than comparable downwelling fronts

bowl shaped basin related to low angle detachment during continental extension the case of the controversial neogene siena basin central italy northern apennines abstract this paper deals with the tectonic evolution of a bowl shaped neogene basin siena basin located in the inner northern apennines and developed during an articulated tectonic evolution this basin was controversially interpreted by different authors as graben half graben or thrust top basin structural and stratigraphic data from the basin substratum and filling sediments integrated with the interpretation of reflection seismic profiles and borehole logs highlight that the siena basin consists of a tectonic depression with a complex internal architecture such a basin developed on a multilayered substratum deeply affected by extensional tectonics since the middle miocene extensional detachments produced a widespread thinning of the basin substratum and superimposed on contractional structures developed during the northern apennines collisional events extensional detachments accommodated within weak horizons and gave rise to the lateral segmentation of most competent stratigraphic horizons sediments filling the siena basin mainly deposited on the ligurian units the topmost tectonic units forming the tectonic pile in the gap between two laterally segmented geological bodies made up of the triassic siliciclastic succession of the verrucano group such a lateral segmentation produced a synformal structural depression not delimited by faults filled by late serravallian late messinian marine to continental sediments which deposited during the extensional faulting from the latest early pliocene to the middle pliocene the architecture of the basin was modified by an high angle normal fault system which affected the eastern side of the basin and produced new accommodation space for marine sediments in sum the siena basin consists of a sin tectonic basin developed on the hanging wall of staircase extensional detachments later affected by high angle normal to oblique faults the latter faults defined a half graben during the latest evolution of the basin the tectonic evolution of the siena basin made it possible to point out some differences with respect to the types of bowl shaped basins related to extensional detachments and named as supradetachment basins

ice drift in the weddell sea in 1990 1991 as tracked by a satellite buoy ice drift in the weddell sea has been studied by using a satellite buoy deployed on an ice floe the buoy survived for a 20 month period indicating a drift trajectory of 10 000 km and yielding 13 months of marine meteorological data the drift of the ice floe was studied with respect to the winds measured by the buoy in the central weddell sea the mean drift speed of the ice floe was 0 15 m s which was about 3 of the wind speed more specifically the drift ratio was 3 4 in the marginal ice zone and 2 4 in the inner pack ice field on average the drift was directed 36 left of the wind direction but the turning angle was larger during the austral summer and smaller during the winter on time scales of days the drift was primarily wind dependent except for cases during winter periods of high ice concentration and internal ice resistance for time scales of several months purely wind based simulations of the drift resulted in a discrepancy between the observed and simulated trajectories but the inclusion of a slow 0 02 m s residual current made the simulations significantly better the geostrophic wind based on european centre for medium range weather forecasts pressure analyses was estimated for a 1 month period and the ice floe was found to drift almost parallel to the geostrophic wind with a speed of 2 of the geostrophic wind speed inertial type motion superimposed on the wind induced drift was found to be a characteristic feature in the marginal ice zone during the austral summer but it could not be found from the drift in winter when kinetic energy was transferred to larger scales of motion and dissipated into the ice field

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

seasonal variability of sea surface height in the coastal waters and deep basins of the nordic seas sea surface height measured by the envisat radar altimeter over open ocean and from leads in sea ice are combined to generate a complete view of variability in the nordic seas geographically and seasonally the observed seasonal variability is decomposed using empirical orthogonal functions and is consistent with seasonal variations in steric and dynamic forcing wintertime increase in sea surface height on the east greenland shelf is hypothesised to be caused by wind forced downwelling which provides direct evidence for the regional play of coastal dynamics high levels of eddy kinetic energy around the sea ice edge in fram strait and off east greenland and svalbard are consistent with the interaction of the wind with the ice edge

hydrography of the west spitsbergen current svalbard branch autumn 2001 1 the atlantic inflow is the primary source of water and heat to the arctic ocean a large portion enters through fram strait where it splits into the yermak and svalbard branches in october to november 2001 the uscgc healy occupied five oceanographic transects across the svalbard branch west and north of spitsbergen temperature and salinity sections show the warm salty atlantic water cooling and freshening as it flows along the continental slope for 553 km the temperature in the upper 500 m of the water column decreased by 0 25 c 100 km implying a heat flux across the sea surface of up to 520 w m2 if one assumes a nominal current of speed of 0 1 m s a temperature salinity t s analysis shows that the shape of the t s curves can be explained in terms of the ratio of the atmospheric to ice melt heat flux the observations imply that ice melt accounts for progressively more surface cooling as the flow moves toward the arctic ocean an autonomous underwater vehicle completed a vertical section in the region of maximum water mass gradient and revealed layer interleaving in fine detail data from this cruise extend a long time series of atlantic layer source temperature beginning in 1910 saloranta and haugan 2001 the extended observations show that after the temperature of the atlantic layer inflow reached a peak in 1992 it cooled to a minimum in 1998 and rose again through 2001

sensitivity studies with a coupled ice ocean model of the marginal ice zone an analytical coupled ice ocean model is considered which is forced by a specified wind stress acting on the open ocean as well as the ice the analysis supports the conjecture that the upwelling dynamics at ice edges can be understood by means of a simple analytical model in similarity with coastal problems it is shown that the ice edge upwelling is determined by the net mass flux at the boundaries of the considered region the model is used to study the sensitivity of the upwelling dynamics in the marginal ice zone to variation in the controlling parameters these parameters consist of combinations of the drag coefficients used in the parameterization of the stresses on the three interfaces atmosphere ice atmosphere ocean and ice ocean the response is shown to be sensitive to variations in these parameters in that one set of parameters may give upwelling while a slightly different set of parameters may give downwelling

winter oceanographic conditions in the fram strait yermak plateau region temperature salinity and currents were measured in the yermak plateau and northern fram strait region during march april 1989 an isothermal upper layer was near the freezing point everywhere except seaward of the ice edge near western svalbard temperatures in the underlying atlantic water layer decreased in general toward the northwest from maximum values in the west spitsbergen current west of svalbard mesoscale features were superimposed on this trend and the most apparent of these was a middepth 200 300 m warm filament overlying the northwestern flank of the plateau currents in the warm filament were northward at 2 4 cm s for a 10 day period in april providing a possible advective explanation for presence of the filament the mechanism for these currents may involve topographic control over a western extension of the north flowing west spitsbergen current or alternately rectification of diurnal currents which are enhanced by the bottom topography of the plateau our data favor the tidal rectification mechanism a warm core anticyclonic eddy associated with the filament contained atlantic water which was virtually unmodified from that occurring more than 200 km farther south characteristics of this eddy were consistent with an origin in the west spitsbergen current in the upper layer a generally cyclonic baroclinic circulation was present about the plateau measured upper layer current speeds were greatest 8 cm s in the southward flowing east greenland current where they exceeded the baroclinic currents by approximately 1 cm s which may represent a southward barotropic component farther to the northeast both measured and baroclinic upper layer currents were weak and variable

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

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

development of three genetically related basins associated with detachment style faulting predicted characteristics and an example from the central mojave desert california three types of sedimentary basins may develop in large magnitude detachment type extensional systems possible early miocene examples of these basin types have been identified in association with northeast directed extension on the central mojave metamorphic core complex southern california from west to east the basins are 1 the tropico basin a flexural basin formed on the unextended footwall behind and bounded by the detachment breakaway zone 2 the pickhandle basin a supradetachment half graben bounded to the southwest by the detachment breakaway and to the northeast by the hanging wall and 3 the clews basin an intra hanging wall basin that formed on the upper plate of the detachment system different basin types may be recognized by the nature and geometry of their strata the footwall flexural basin should be shallow and areally extensive with basin fill dominated by fine grained low energy deposits the supradetachment basin typically will be elongate normal to the extension direction and characterized by a thick sequence of volcanic and coarse grained deposits that reflect its fault controlled margins intra hanging wall basins may be of half or full graben geometry and will vary in dimension depending on the spacing of the transfer elements recognition of these basin types is potentially useful in delineating features of the extensional system that are important to its reconstruction including the detachment breakaway zone and the boundaries of the extensional system parallel and normal to the extension direction

on the ice and heat balance in fram strait the sea ice margin northwest of spitsbergen is schematically represented by a stationary wedge maintained by opposing ice and warm atlantic water advection ice melt and cooling of the surface water generate a mixed layer with properties approximating those found elsewhere in the arctic basin the heat energy required to melt the advancing ice is roughly comparable to the rate of heat loss of the west spitsbergen current and suggests that direct heat exchange with the atmosphere is less important only a small fraction of the nearly fresh water from ice melt exits through eastern fram strait and most of it appears to return to the arctic basin whether or not it contributes to the formation and maintenance of the arctic mixed layer depends on the largely unknown circulation pattern north of fram strait an example of the large interannual variation of the mean wind stress field is shown to illustrate the likelihood of an equally large variance of the ice and surface water circulation

low angle faulting in strike slip dominated settings seismic evidence from the maritimes basin canada abstract the maritimes basin is an upper paleozoic sedimentary basin centered in the gulf of st lawrence canada early phases of basin formation included the development of partly connected sub basins bounded by high angle faults in an overall strike slip setting interpretation of reprocessed seismic reflection data indicates that a low angle detachment contributed to the formation of a highly asymmetric sub basin this detachment was rotated toward a lower angle and succeeded by high angle faults that sole into the detachment or cut it this model bears similarities to other highly extended terranes and appears to be applicable to strike slip and or transtensional settings

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

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

response of sea ice drift to wind forcing on the northeastern newfoundland shelf observations of sea ice drift obtained with satellite tracked ice beacons in march april of 1988 and 1989 have been used to examine the response of sea ice drift to wind forcing over the northern newfoundland continental shelf the short term 5 20 days response of sea ice drift ranges from 2 6 to 5 4 of the local wind over much of the inner continental shelf which is comparable to that in the bering sea and the antarctic but larger than that in arctic sea ice drifts to the right of the local wind at angles ranging from 10 to 63 the response to wind forcing is largest near the ice edge both over the middle portions of the shelf and along the southern margins of the seasonal ice zone and during strong and steady wind of several days duration the large wind driven response of ice drift observed in this study in comparison with the arctic may result from 1 reduced levels of internal ice stress associated with the generally thin ice cover and lower areal concentration of sea ice 2 large atmospheric drag coefficients associated with the small ice floes in areas of comparatively higher ice concentration and 3 smooth ice bottom caused by melting in nearshore areas the ice to wind coupling is reduced owing to larger internal ice stresses experienced locally due to ice pileup

effects of sub ice mesoscale features within the marginal ice zone of fram strait four distinct sub ice mesoscale features were observed during the 1983 marginal ice zone experiment in fram strait the first one was an anticyclonic eddy located over the yermak plateau and strongly correlated with bottom topography however it appears not to have been topographically generated the remaining features were observed along the ice edge of the east greenland current two were closely related in that one was a filament of atlantic water that was apparently entrained by a warm core cyclonic eddy located northwest of the molloy deep the last one could not be shown conclusively as a westward extension of a branch of atlantic water or an isolated cyclonic eddy simplified estimates show that on average each of the three features had enough available heat energy residing within the first 30 m of their cores to melt over 600 km2 of 2 m thick ice other estimates of potential melting and retreat rates of the marginal ice zone are calculated on the basis of various utilization depths from which available heat energy can be drawn further consideration is also given to the possibility that these types of features may also act as destructive preconditioners of sea ice since it is unlikely that complete melting would occur because of their relative movements eddies and intrusions significantly increase the amount of available temperature salinity t s space within which mixing can be accomplished these admixtures produced by direct interaction of atlantic water or atlantic intermediate water and the polar waters of the east greenland current further provide a very effective mechanism which transports salt to deeper levels through salt fingering and double diffusion calculations of heat mass and salt fluxes for the observed features show that the heat transported by the ice edge eddies was significant in comparison with a depth comparable flux of the east greenland current while mass and salt fluxes were roughly 7 times less

drag measurements for first year sea ice over a shallow sea for a free drift case a method is developed for simultaneously determining air ca and water cw drag coefficients by solving the vertically integrated stress balance equation for sea ice the method allows the algebraic determination of ca and cw from measurements of relative wind and relative current at single reference levels from estimates of the densities of all three fluids and ice thickness and from estimates of the accelerations caused by the nonsurface stress terms derived from position measurements the method treats the ice as a natural drag plate and therefore includes contributions from both skin and form drag one shortcoming of the technique is that if the relative wind and current are colinear then only the ratio of ca and cw can be determined another is that the accelerations caused by other forces need to be independently determined an experiment was conducted on a single floe in the eastern bering sea over the continental shelf during march 1981 the site was about 80 km from the ice edge and was occupied for approximately 3 days following the passage of a storm which had broken the pack into 10 20 m diameter floes both profile and slab inversion estimates of drag were made from the current meter and anemometer measurements at the site ca at 3 m was 4 55 10 3 by the profile method compared to 3 63 4 39 10 3 for slab depending on assumptions cw at 1 1 m by profile was 24 2 10 3 compared to 18 3 22 0 10 3 for slab the two methods gave results which were not statistically separable and which were among the highest drags observed for sea ice the instantaneous stress balance on the floe included contributions from material acceleration coriolis force the two surface stresses and sea surface tilt relative to mean current and tide

sar retrieved wind in polar regions comparison with in situ data and atmospheric model output european remote sensing ers satellites synthetic aperture radar sar wind retrievals using cmod ifr2 are for the first time retrieved in the marginal ice zone miz and in arctic coastal areas and compared with in situ observations from reseach vessels rvs and output from a high resolution atmospheric model the root mean squares rms of the comparisons were 1 6 m s sup 1 and 2 m s sup 1 respectively the spatial variation of the sar wind fields established a decrease in wind speed close to the ice edge for the late summer situations where the wind was along the ice edge with the ice to the left this decrease is believed to be due to changes in atmospheric stability possibly through development of an internal boundary layer caused by the cold ice cover and melt water lower wind speed near the ice edge is confirmed by the atmospheric model and the in situ observations furthermore good results are obtained from sar wind retrieval in leads when compared with model output during a cold air outbreak routine measurements in the miz are useful for estimating the wind stress and therefore sar may play an important role in this region finally the identification of a jet out from hinlopen strait in the svalbard region and low wind wakes along the coast in the sar retrieved wind field is confirmed by in situ observations as the rv moves through the region the jet is also confirmed by the atmospheric model which is able to reproduce the situation

the movement and decay of ice edge bands in the winter bering sea during periods of off ice winds the winter bering sea ice edge consists of ice bands that measure 1 10 km in length 0 1 1 km in width and are oriented at approximately right angles to the wind the bands are composed of small floes 10 20 m in diameter and 1 5 m in thickness in march 1981 working from the noaa ship surveyor we mounted two radar transponders 4 km apart on ice floes within such a band and then tracked them for 46 h over an 80 km distance as the band moved into warmer water and melted comparison of the band position with that of a satellite tracked argos station deployed in the ice interior shows that the band moved 30 faster than the interior ice analysis of our observations strongly suggest that the cause of the speed increase is the wind wave radiation stress on the upwind side of the band we also observed that wind waves contribute to band ablation by the following mechanism at the upwind edge these waves break up the floes into small pieces because these pieces are no longer good wave reflectors or absorbers they drift in the upwind direction away from the band to melt so that the band width as well as the individual floe thicknesses decrease with time in summary because the bands provide an efficient way for the export and ablation of sea ice the bands play a major role in the maintenance of the ice edge position

a coupled dynamic thermodynamic model of an ice ocean system in the marginal ice zone wind driven ice ocean processes in the marginal ice zone are studied when thermodynamics is included into a coupled ice ocean model the ocean is considered to be a two layer ocean where a fresh and cold freezing mixed layer is lying above the stagnant warm and saline lower layer the essential part of the thermodynamics is the entrainment between the mixed layer and the lower layer which is parameterized using the frictional velocity at the ocean surface a kraus turner type parameterization it is shown that upwelling at the ice edge which is generated by the difference in the air ice and air water surface stresses will give rise to a strong entrainment by bringing the pycnocline nearer to the surface furthermore the entrainment is negligible outside the areas affected by the ice edge upwelling when cooling at the top is included the heat and salt exchange are further enhanced in the upwelling areas because the entrainment depends inversely on the density difference between the layers new ice formation occurs in the area which is not affected by ice edge upwelling that is no entrainment of the warm lower layer fluid so the mixed layer temperature stays at the freezing point the ice growth will give rise to a large salt flux to the upper layer but the subsequent salinity change is not as large as that due to the entrainment of the lower layer fluid the mixed layer in the areas affected by the ice edge upwelling is only slightly less saline than the lower layer it is suggested that these high salinity mixed layer regions with a scale of a few rossby radii of deformation 10 km will overturn due to cooling possibly as a plume and may this contribute to the formation of deep water

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

cenozoic evolution of the mojave block of southern california the recorded cenozoic history of the mojave desert region of southern california began in the latest oligocene when intense volcanism and tectonism interrupted a long early tertiary silence volcanism commenced across the region in an east west band ca 24 22 ma northwest of barstow volcanism was accompanied by intense crustal extension and development of a metamorphic core complex outside of this relatively restricted area extension was minor or absent after extension ceased ca 18 ma volcanism shifted to small volume eruptions of basalt post extensional deformation has largely been by strike slip faulting along northwest striking dextral faults and west striking sinistral faults and total dextral slip across the mojave desert region since the early miocene is 45 60 km strike slip deformation has been overprinted locally by intense north south contraction that is the dominant style of deformation in the western mojave block paleomagnetic data indicate that parts of the mojave block were rotated clockwise although the magnitude and timing of this rotation are poorly determined the best evidence for large 45 rotation comes from the area east of barstow where large clockwise declination anomalies and mesozoic and cenozoic dikes with anomalous strikes may reflect early miocene clockwise deflection along the mojave river fault volcanism and tectonism in the mojave block resulted from interactions among the north american pacific and various oceanic plates patterns of volcanism and tectonism do not correlate with growth of slab windows beneath the continent but do correlate with the position of the subducted mendocino fracture zone plate circuit reconstructions suggest that the driving force for extension was divergence between the pacific and north american plates along the transform margin that separated the two this hypothesis accounts for the direction magnitude and rate of extension in the mojave block

upwelling at the ice edge a mechanism for deep water formation this study sets forward a hypothesis which anticipates deep water formation due to ice edge upwelling the upwelling can raise thermocline waters the lower arctic intermediate water to the surface or near it where the water is exposed to cooling evaporation mixing and oxygenation thus upwelling can act as a preconditioning mechanism for deep convection the conjecture would also explain the salinity range of the greenland sea deep water if the upper and lower arctic intermediate water masses are mixed so that the latter has at least an 80 contribution also the convection events induced by ice edge upwelling during winter season we anticipate could give rise to a new deep water annual production rate consistent with observations

a coupled ice ocean model of upwelling in the marginal ice zone a dynamical coupled ice ocean numerical model for the marginal ice zone miz is suggested and used to study upwelling dynamics in the miz the nonlinear sea ice model has a variable ice concentration and includes internal ice stress the model is forced by stresses on the air ocean and air ice surfaces the main coupling between the ice and the ocean is in the form of an interfacial stress on the ice ocean interface the ocean model is a linear reduced gravity model the wind stress exerted by the atmosphere on the ocean is proportional to the fraction of open water while the interfacial stress ice ocean is proportional to the concentration of ice a new mechanism for ice edge upwelling is suggested based on a geostrophic equilibrium solution for the sea ice medium the upwelling reported in previous models invoking a stationary ice cover is shown to be replaced by a weak downwelling due to the ice motion most of the upwelling dynamics can be understood by analysis of the divergence of the across ice edge upper ocean transport on the basis of numerical model an analytical model is suggested that reproduces most of the upwelling dynamics of the more complex numerical model

a numerical study of mesoscale ocean eddy interaction with a marginal ice zone observations made during the marginal ice zone experiment mizex program indicated the presence of mesoscale eddies in a marginal ice edge ocean front in the east greenland current the eddies range in scale from 5 to 80 km physical mechanisms including barotropic and baroclinic instability may be responsible for their presence although the evolution of isolated eddies at low latitudes has been the focus of many studies the effect of ice cover on eddy evolution and vice versa has had less attention here an examination of the interaction of isolated mesoscale ocean eddies with a marginal ice zone is presented results are obtained with a two layer nonlinear primitive equation ocean model and a coupled free drift ice model in the absence of winds the ice equilibrates rapidly to the ocean eddy velocity resulting in radial ice motion the ocean sea surface slope is found to provide an important force in the ice momentum balance in no wind simulations with along ice edge 10 m s winds the ice responds largely to the wind and to a lesser extent to the ocean eddy under ice the ocean eddy can be rapidly eroded by wind driven ice motion cyclones anticyclones are rapidly destroyed by along ice edge winds with ice on the left right

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

the west spitsbergen current disposition and water mass transformation recent work suggests that the west spitsbergen current which provides the principal contribution to the arctic ocean of salt and sensible heat as well as of a variety of anthropogenic tracers is a rather complex circulation feature north of 79 n where the isobaths diverge markedly the current contains two separate warm cores that follow different isobaths the western core carried by the offshore branch of the current follows the western flank of the yermak plateau and north of 80 n at least part of this flow detaches from the plateau probably to contribute to the recirculation in fram strait in contrast the inshore branch follows the shelf break into the arctic ocean it is this inshore branch that provides the primary focus in this paper during the transit of the inshore waters past northwestern spitsbergen the core properties change primarily through vertical heat flux which during ice free conditions in winter is estimated to be of the order of 200 w m 2 from the core layer alone together with some freshening within the arctic ocean this process is responsible for fully transforming the original atlantic water into arctic intermediate water within about 600 km of fram strait

the response of the sea ice edge to atmospheric and oceanic jet formation abstractthe sea ice edge presents a region of many feedback processes between the atmosphere ocean and sea ice maslowski et al here the authors focus on the impact of on ice atmospheric and oceanic flows at the sea ice edge mesoscale jet formation due to the coriolis effect is well understood over sharp changes in surface roughness such as coastlines hunt et al this sharp change in surface roughness is experienced by the atmosphere and ocean encountering a compacted sea ice edge this paper presents a study of a dynamic sea ice edge responding to prescribed atmospheric and oceanic jet formation an idealized analytical model of sea ice drift is developed and compared to a sea ice climate model the los alamos sea ice model cice run on an idealized domain the response of the cice model to jet formation is tested at various resolutions it is found that the formation of atmospheric jets at the sea ice edge increases the wind speed parallel to the sea ice edge and results in the formation of a

barotropic instability in the west spitsbergen current 1 barotropic instability in the shoreward branch of the west spitsbergen current is investigated on the basis of data from an array of current meter moorings along 78 83 n across the upper continental slope and shelf break west of svalbard the slowly varying background current profile is modeled as an along slope asymmetric jet anchored to the shelf break numerical linear stability analyses are performed on the idealized current profile and topography revealing the characteristic period wavelength and growth rate of unstable vorticity waves detailed analysis of the ambient current profile in 2007 2008 shows that unstable conditions are present during 40 of the 10 month measurement record depending on the localization width and amplitude of the current jet the resulting vorticity waves are localized at the shelf break and are able to exchange water masses across the oceanic arctic front typical wavelengths and periods are 20 40 km and 40 70 h respectively wavelet coherence and complex demodulation analyses of the current meter data confirm that transient signals of similar periodicity as predicted by the stability analysis exist in the data record prominently during the winter and spring months estimates of the heat loss contribution from isopycnal diffusion reach 1 4 tw during the time intervals when unstable vorticity waves are active at the shelf break implying that the dynamics of the west spitsbergen current play a significant role in the cooling process of the atlantic water on the way to the arctic ocean this cooling corresponds to an along shelf cooling rate of 0 08 c per 100 km

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

the interaction of an ocean eddy with an ice edge ocean jet in a marginal ice zone remotely sensed images in the east greenland current marginal ice zone region indicate a variety of mesoscale motions these range from isolated monopoles and dipoles to multiple eddy fields recent observations indicate that many of the eddies may be advected into the region from the west spitsbergen current region they then interact with the east greenland current marginal ice zone and its associated along ice edge jet in this paper we illustrate how the ice floe fields can evolve during the interaction of an ocean eddy with an along ice edge ocean jet the effects of eddy sense of rotation flow strength and bottom topography are considered in barotropic and baroclinic two layer numerical experiments initially barotropic experiments involve the combined effects of flat bottom eddy jet interactions and eddy topography interactions over a flat bottom anticyclones interact with the cyclonically sheared side of the jet and move seaward exporting ice away from the ice edge in a dipolar distribution cyclones move toward the jet and are advected downstream a second dipole formation mechanism is associated with eddy topography interaction and is a consequence of the shallow pycnocline depth of the region rapid topographic rossby wave radiation in the lower layer spreads energy along slope and upslope downslope for cyclones anticyclones the upper ocean response to this process is a dipole which propagates parallel to the ice edge with shallow water to the left topographic eastward jet induced and topography induced eddy propagation tendencies combine to enhance cyclone jet interaction and limit anticyclone jet interactions the dipole formation associated with eddy topography interaction is weakened by the presence of the jet but not eliminated eddy induced distortions in the ice edge are suppressed by the stabilizing effect of topography on the jet sensitivity of the initially barotropic results to variation in the rossby number and degree of topographic slope illustrates that eddies are more efficient in producing ice edge distortions for stronger flows and weaker topographic slopes for initially baroclinic simulations over topography results are comparable to flat bottom cases strong upper layer eddy jet interactions can occur independent of topographic effects which are constrained to the lower layer

antarctic sea ice microwave signatures and their correlation with in situ ice observations the general characteristics and microwave radiative properties of sea ice in the weddell sea region during the onset of spring are studied by using the nimbus 7 scanning multichannel microwave radiometer smmr and other satellite sensors in conjunction with in situ observations from the mikhail somov the position of the ice edge the gradient of ice concentration and the width of the marginal ice zone are inferred from the microwave data and are found to be consistent with ship observations especially at 18 ghz the sensitivities of the various smmr frequencies to surface and other effects are investigated by using multi spectral cluster analysis the results show considerable variability in emissivity especially at 37 ghz likely associated with varying degrees of surface wetness ice concentrations are derived by using two methods one that assumes fixed emissivities for consolidated ice and an iterative procedure that accounts for the variable emissivities observed by using the procedure that allows the emissivities to be variable gives ice concentrations that are more consistent with qualitative field observations

middle eocene sedimentary and volcanic infilling of an evolving supradetachment basin white lake basin south central british columbia the middle eocene white lake and skaha formations in the white lake basin british columbia record the sedimentary and volcanic infilling of a supradetachment basin that developed during the latter stages of shuswap metamorphic core complex exhumation the 1 1 km thick white lake formation is characterized by volcanogenic sediment gravity flow fluvial and sheetflood facies interbedded with volcanic deposits facies relations suggest white lake strata accumulated on coalesced west sloping alluvial fans that drained an active volcanic center the overlying 0 3 km thick skaha formation records increased tectonism and mass wasting pervasively shattered skaha avalanche slide and sheetflood deposits accumulated on alluvial fans shed from hanging wall and footwall sources exposed along the okanagan valley fault clast compositions of the white lake and skaha formations record alluvial and tectonic stripping that locally eliminated hanging wall blocks mylonite clasts in upper skaha beds imply significant okanagan valley fault footwall uplift during the middle eocene and syntectonic erosion of the shuswap metamorphic core complex the syntectonic sedimentary record preserved within the white lake basin elucidates the relations and timing between core complex exhumation and extensional tectonism in this region the white lake and skaha formations are the apparent age equivalent of the klondike mountain formation of northern washington usa white lake basin strata however are more complexly interstratified post depositionally disrupted and contain a more complete record of core complex unroofing variations in the spatial distributions and textural and compositional character of middle eocene strata in this area underscore the need to exercise care when developing regional scale sedimentary tectonic volcanic models