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

a mechanism of ice band pattern formation caused by resonant interaction between sea ice and internal waves a theory abstractice bands are frequently observed over marginal ice zones in polar seas a typical ice band pattern has a regular spacing of about 10 km and extends over 100 km in the marginal ice zone further the long axis of an ice band lies to the left right with respect to the wind direction in the northern southern hemisphere here the study shows that the resonance between ice band pattern propagation and internal inertia gravity waves below the sea ice well explains the ice band pattern formation internal waves are generated by the difference between the stress on the open water and the stress on ice covered water this in turn reinforces the formation of an ice band pattern with a regular band spacing specifically the authors have found the following 1 a band spacing on the order of 10 km is selected by the resonance condition in which the ice band pattern propagation speed coincides with the phase speed of internal inertia gravity waves 2 the ice bands tend to develop favorably when the win

a density model of the andean subduction zone density changes in basement rock or the deeper crust tend to cause gravity anomalies that dominate the observed data now that oil companies have begun using airborne gravity in their exploration of remote regions of the andes interpreters are building detailed earth models which necessarily involve geologically constrained gravity regional fields to account for the overwhelming signal from deep crustal structure

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

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

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

an instability theory of ice air interaction for the formation of ice edge bands ice edge bands are well observed phenomena at the ice edge of the world ocean at times when winds are blowing off the ice differing from the wave radiation theory water wave theory wind wave theory and ice water coupling theory we propose an ice air feedback mechanism to generate the ice edge bands to eliminate ocean effects the water is set motionless thermally generated surface winds blowing from ice to water ice breeze with some deflection due to the earth s rotation force the drift of ice floes in the marginal ice zone miz by changing the surface temperature gradient the ice motion feeds back on the surface winds a coupled ice air model similar to the author s earlier paper is employed to discuss the instability properties of such a feedback mechanism the linearized governing equations are then solved as an eigenvalue problem with two model parameters mean ice thickness h i 0 5 m h i 2 5 m and a characteristic surface temperature difference over ice and water dt o 4oc dt o 20oc the model results show alternating ice divergence and convergence zones and demonstrate a great number of e folding acceleration modes excited by the coupled ice air system ice floes are transported from the divergence area to the convergence zone and are eventually rearranged into a band structure the e folding acceleration rate of ice motion depends on the width of two adjacent convergence zones i it increases with l l where l is the length of twice the miz width i e 200 km for 10 km l 200 km and then remains high for 2 km l 10 km the length scale 2 10 km of the high acceleration modes agrees well with the observed ice edge bandwidth 1 10 km the e folding acceleration rate increases with an increase in dt o and with a decrease in h i

on some possible interactions between internal waves and sea ice in the marginal ice zone the ice edges of the world ocean are generally the site at times when winds are blowing off the ice of regularly spaced surface bands of ice floes these bands have size scales of the order of 1 10 km and their long axes are oriented approximately normal to the wind direction available oceanic temperature and salinity data from the bering and greenland sea ice edge regions suggest that these ice bands are commonly underlain by a two layered density structure which is maintained by net melting along the ice edges linear internal wave theory is applied to these data to compute first mode interfacial wave phase speeds a simple analytical model is developed that demonstrates the feasibility of generation of such interfacial internal waves by the stress discontinuity due to off ice winds blowing over either a stationary or a moving ice edge it is qualitatively shown that the computed internal wave phase speeds and wavelengths are under many conditions compatible with the speeds and spacings of the surface ice bands this compatibility suggests in turn that coupling between internal waves and ice bands may commonly occur some possible implications of the generation and presence of these internal waves upon other ice edge processes such as air sea heat and momentum transfer are qualitatively discussed

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

air ice drag coefficients for first year sea ice derived from aircraft measurements turbulent flux measurements were made at four levels 42 90 195 and 340 m by the noaa p 3 aircraft over first year sea ice in the northern bering sea during february 1982 three profiles of momentum flux and mean wind were used to calculate an air ice drag coefficient cd of 3 0 6 10 3 referenced to a 10 m anemometer height the boundary layer was slightly unstable zi l 1 2 where zi was the inversion height of 660 m and l the monin obukhov length the mean wind speed at the 42 m height was 17 m s and the air temperature was 20 c from turbulent heat flux measurements the value of the bulk heat transfer coefficient ch was 0 73 1 6 10 3 giving a ch cd of 0 24 the bowen ratio was greater than 2 8 comparison of the present turbulent flux and variance profiles with those collected over the ocean shows agreement which increases confidence in the calculations the geostrophic drag coefficient u g where u is the friction velocity and g is the geostrophic wind was 0 047 the turning angle of the surface wind measured by an anemometer at a height of 3 m on the ice was 32 and the ratio of surface wind speed to the geostrophic wind speed was 0 76

dynamical evaluation of the surface circulation using remote sensing of drifting ice floes an analysis of ice drift from consecutive landsat multispectral scanner images of the same area taken at 24 h interval allowed the calculation of the surface circulation using a dynamical approach comparison between calculated and measured values shows that this method leads to a good approximation of the surface circulation in a region where ice floes are free drifting on the other hand the sole use of the floe drift over time to evaluate the currents leads to results that are far from the measured values tests made using various air and ice drag coefficients and wind speeds and directions for different drift distances show that the error associated with these parameters is small although the values obtained using the numerical data involved considerably more effort and expense the results were not significantly better than those found using photographic products a good approximation of the surface circulation can thus be made using a simple digitization of the floe positions on photographic products application of the methodology to a set of four image pairs led to the recognition of two modes of circulation in southeastern hudson bay in spring 1985 this method can thus become a useful tool for rapid evaluations of surface currents in ice covered areas that can hardly be sampled otherwise

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

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

seismic imaging of a convergent continental margin and plateau in the central andes andean continental research project 1996 ancorp 96 1 a 400 km long seismic reflection profile andean continental research project 1996 ancorp 96 and integrated geophysical experiments wide angle seismology passive seismology gravity and magnetotelluric depth sounding across the central andes 21 s observed subduction of the nazca plate under the south american continent an east dipping reflector nazca reflector is linked to the down going oceanic crust and shows increasing downdip intensity before gradual breakdown below 80 km we interpret parts of the nazca reflector as a fluid trap located at the front of recent hydration and shearing of the mantle the fluids being supplied by dehydration of the oceanic plate patches of bright quebrada blanca bright spot to more diffuse reflectivity underlie the plateau domain at 15 30 km depth this reflectivity is associated with a low velocity zone p to s wave conversions the upper limits of high conductivity and high vp vs ratios and to the occurrence of neogene volcanic rocks at surface we interpret this feature as evidence of widespread partial melting of the plateau crust causing decoupling of the upper and lower crust during neogene shortening and plateau growth the imaging properties of the continental moho beneath the andes indicate a broad transitional character of the crust mantle boundary owing to active processes like hydration of mantle rocks in the cooler parts of the plate margin system magmatic underplating and intraplating under and into the lowermost crust mechanical instability at moho etc hence all first order features appear to be related to fluid assisted processes in a subduction setting

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

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

an observational and numerical study of wind stress variations within marginal ice zones published studies of ocean mesoscale processes in marginal ice zones mizs using numerical coupled ice ocean models usually assume that the surface wind speed is constant over the model domain and that wind stress variations are simply proportional to surface roughness variations we show that this assumption is not realistic in most situations because the surface wind stress is also significantly affected by mesoscale pressure variations by changes in the surface wind vector and by changes in surface layer stability two numerical case studies utilizing detailed surface and atmospheric measurements examine the factors affecting small scale 5 km variations in wind stress within mizs these case studies and surveyed observational and modeling results demonstrate that wind stress fields are qualitatively different from the surface roughness fields a realistic wind stress scenario consists of a maximum just inside the ice edge and another maximum in the open ocean stress minima occur within the pack ice region away from the miz and over grease ice if present the effect of the rougher miz ice is counteracted when wind stresses over the open ocean are enhanced by large surface heat fluxes over the ocean by a strong low level inversion over the ice or by a sharp atmospheric front with surface winds paralleling the ice edge such situations are common in miz regions some simple methods for including first order atmospheric effects on wind stress variations which could be incorporated into current ice ocean mesoscale models of miz regions are suggested

a mechanism for the formation of ice edge bands we propose a mechanism for the formation of multiple bands at an ice edge that is subjected to an off ice wind the wind moves the outermost floes seaward faster than the interior ice dilating the marginal ice zone and opening up random polynyas in the largest of the polynyas the off ice wind generates a significant fetch limited wave spectrum which produces a wave radiation pressure on floes at the downwind end of the polynya increasing their velocity they are herded against their downwind neighbors creating a band of high ice concentration the band is stabilized by an internal compacting stress due to the exponential decay of the wind wave spectrum across the band and to a slower decay of swell incident from seaward the band s growth terminates when it encounters a second downwind polynya of sufficiently large size we show how an array of immature bands generated in this way matures by selective mergers into larger regularly spaced bands of approximately equal width

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

selective extinction and survival across the cretaceous tertiary boundary in the northern atlantic coastal plain the inner atlantic coastal plain in new jersey and the delmarva peninsula is underlain by an upper cretaceous lower tertiary sequence of marine and paralic sand clay and glauconitic beds campanian maastrichtian danian and thanetian deposits are especially fossiliferous and yield a succession of marine faunas that reveal a pattern of selective extinction and survival across the cretaceous tertiary k t boundary in this area cretaceous benthic invertebrate communities are dominated by oysters and other semi infaunal and infaunal molluscs with planktotrophic larval stages these are replaced in the danian by brachiopod dominated communities that are composed of epifaunal benthos with a variety of nonplanktotrophic reproductive strategies a similar pattern is observable in the nektonic cephalopod populations in this sequence the typical ammonites of the cretaceous became extinct at the k t boundary whereas the nautilids survived ammonites are thought to have had a planktotrophic larval stage whereas nautilids are known to lay large lecithotrophic eggs this pattern of differential survival is attributed to the planktonic population crash at the k t boundary which placed planktotrophically reproducing species at a disadvantage while favoring the varied groups that practiced alternative reproductive strategies

magmatism in the huarina belt bolivia and its geotectonic implications abstract the huarina belt is a tectono stratigraphic unit extending along the western side of the eastern cordillera and southern altiplano it includes the well known bolivian tin belt both geophysical and isotopic evidence suggest that the huarina belt is located between three cratonic blocks in a major lithospheric weakness zone that has probably been inherited from the proterozoic most of the phanerozoic backarc magmatism in the bolivian andes occurred along this belt local ordovician basalts and andesites and clasts of devonian granitoids occurring in late devonian early carboniferous sedimentary units are testimonies of a scarce palaeozoic igneous activity during the mesozoic rift related magmatism resulted in peraluminous to metaluminous high k calcalkaline triassic granitoids as well as discrete cretaceous centers of alkaline and carbonatitic rocks in the cenozoic huge high k generally peraluminous ignimbrite sheets along with numerous volcanic and intrusive centers were generated along the belt shoshonitic alkaline and ultrapotassic rocks have been locally described on the basis of both geochemical and geophysical evidence a general evolution model is proposed for the huarina belt during paleozoic and mesozoic times the predominant extensional regime of the continental crust led to lithospheric thinning basin generation and production of within plate magmas during the cenozoic prevailing compressional conditions led to a gradual thickening of the lithosphere inducing delamination of its denser and less viscous root the mantle generated magmas interplayed widely with crustal melts giving rise to the dominantly peraluminous magmas