did antarctic sea ice expansion cause glacial co2 decline 1 recently stephens and keeling 2000 have put forward an appealing theory for explaining the decrease in glacial atmospheric co2 they argue that a compact sea ice cover extending southward of 55 s trapped large amounts of co2 beneath the sea surface thus accounting for the lower atmospheric concentrations an atmosphere ocean box model in which sea ice area is prescribed allows them to simulate 80 of the co2 drawdown however glacial co2 levels can be attained in their model only when the fraction of ice covered area southward of the antarctic polar front rises to 99 100 we present simulations with a coupled sea ice upper ocean model indicating that ice area fractions so large might have not prevailed even under rather extreme glacial conditions the combination of our glacial ice coverage estimates with the ice area co2 relation derived by stephens and keeling suggests that co2 sequestration under sea ice could account for at most 15 50 of the total glacial co2 decline

the granular sea ice model in spherical coordinates and its application to a global climate model abstract the granular sea ice model gran from tremblay and mysak is converted from cartesian to spherical coordinates in this conversion the metric terms in the divergence of the deviatoric stress and in the strain rates are included as an application the gran is coupled to the global earth system climate model from the university of victoria the sea ice model is validated against standard datasets the sea ice volume and area exported through fram strait agree well with values obtained from in situ and satellite derived estimates the sea ice velocity in the interior arctic agrees well with buoy drift data the thermodynamic behavior of the sea ice model over a seasonal cycle at one location in the beaufort sea is validated against the surface heat budget of the arctic ocean sheba datasets the thermodynamic growth rate in the model is almost twice as large as the observed growth rate and the melt rate is 25 lower than observed the larger growth rate is due to thinner ice at the beginning of

ice deformation near sheba 1 the deformation rate of sea ice is a key parameter for determining the evolution of the ice thickness distribution it determines the rate of new ice formation through opening and the rate of ridging through closing and shear an extensive suite of ground based and satellite based measurements of ice motion is used to construct a daily time series of the ice velocity and deformation in the vicinity of the surface heat budget of the arctic ocean sheba ice camp that is suitable for forcing a model of the ice thickness distribution the velocity is interpolated to a square grid that remains centered on the camp has a spacing of 25 km is 400 km on a side and is determined for a 371 day period from 2 october 1997 to 7 october 1998 velocity measurements from buoys advanced very high resolution radiometer avhrr special sensor microwave imager ssmi and radarsat geophysical processing system rgps are merged using optimal interpolation and a kalman filter approach the deformation rate is taken directly from the rgps measurements when available the daily total deformation rate measured on a scale of 100 km near the camp averaged 2 21 d 1 and the standard deviation was 1 78 d 1 the divergence was positive in the early winter and negative through most of the spring and summer there were two major opening closing events one in january and one at the end of july the net divergence over the year was very near zero the vorticity indicated a net rotation of 87 over the year with the winter showing strong anticyclonic turning and the summer showing strong cyclonic turning

a random discontinuous model of sea ice motion the rate at which the sea ice pack spreads apart exposing the warm ocean to the cold atmosphere controls the air sea heat exchange in the arctic and the production of ice mass the rate of spreading or opening can be estimated from observations of ice motion using a model of the ice pack which accounts for the random manner in which the ice is broken into rigid pieces in a region intersected by many cracks some cracks will typically be opening while others are closing in this case the total of the openings will exceed the average divergence of the region a few measurements of the ice motion cannot resolve the openings at each crack so that any estimate of opening will be accompanied by estimation errors the random model adopted here imagines the leads to be distributed according to the poisson distribution and the relative displacements at any crack to be gaussian under these assumptions it is determined how the total opening is related to the average deformation and how this relationship depends on the size of the region and on the number of points used to determine the average deformation

210 pb and 14 c as indicators of callianassid bioturbation in coral reef sediment abstract callianassid shrimps are the dominant endofauna of reef top sediments on john brewer reef a small platform reef in the central section of australia s great barrier reef province sediment reworking by these shrimps was investigated using the 210pb radioisotope in conjunction with 14c radiometry and textural data 210pb analyses of cores from two reef top sites revealed a classical tripartite subdivision characteristic of depositional settings in which sediment reworking dominates over sediment accumulation 1 a vertical surface mixed layer sml extending to a depth of 50 cm beneath the sediment surface and representing a zone of intensive callianassid reworking 2 an intermediate region of radioa tive attenuation in which excess 210pb activity decreases logarithmically to a depth of slightly more than one meter beneath the sediment surface and interpreted as representing a region utilized less frequently by callianassa for coarse grain storage and predator avoidance 3 a basal region beyond callianassid influence of consistently low background levels of 210pb activity sediment turnover rates in excess of 120 cm2 yr 1 in the sml and up to 32 cm2 yr 1 in the region of radioactive attenuation were high compared to those typical of siliciclastic continental shelf and deep sea deposits emphasizing the intensity of callianassid reworking in shallow coral reef environments 210pb geochronology is unsuitable for determining sediment accumulation rates in such settings because the disruptive impact of callianassa gives rise to unacceptably high figures the depth of callianassid influence established by 210pb radiometry corresponds to points of inflection indicating the bases of vertical surficial sections in 14c subsurface age profiles for the two john brewer reef sites inflection points in other 14c profiles may similarly indicate sediment reworking depths at locations across the reef where 210pb data were not obtained

contrasts in sea ice deformation and production in the arctic seasonal and perennial ice zones 1 four years 1997 2000 of radarsat geophysical processor system rgps data are used to contrast the sea ice deformation and production regionally and in the seasonal siz and perennial piz ice zones ice production is of seasonal ice in openings during the winter three day estimates of these quantities are provided within lagrangian elements initially 10 km on a side a distinct seasonal cycle is seen in both zones with these estimates highest in the late fall and with seasonal minimums in the midwinter regional divergence over the winter could be up to 30 spatially the highest deformation is seen in the siz north of coastal alaska both ice deformation and production are higher in the siz deformation related ice production in the siz 0 5 m is 1 5 2 3 times that of the piz 0 3 m this is connected to ice strength and thickness atmospheric forcing and boundary layer structure contribute to only the seasonal and interannual variability seasonal ice growth in ice fractures accounts for 25 40 of the total ice production of the arctic ocean uncertainties in these estimates are discussed by itself this deformation ice production relationship could be considered a negative feedback when thickness is perturbed however the overall effect on ice production in the face of increasing seasonal and thinner weaker ice coverage could be modified by local destabilization of the water column promoting overturning of warmer water due to increased brine rejection and the upwelling of the pynocline associated with increased occurrence of large shear motion in sea ice divergence is shown to be negligibly correlated to cyclonic motion in summer and winter in both ice zones

sea ice type maps from alaska synthetic aperture radar facility imagery an assessment synthetic aperture radar sar imagery received at the alaska sar facility is routinely and automatically classified on the geophysical processor system gps to create ice type maps we evaluated the wintertime performance of the gps classification algorithm by comparing ice type percentages from supervised classification with percentages from the algorithm the rms difference for multiyear ice is about 6 while the inconsistency in supervised classification is about 3 the algorithm separates first year from multiyear ice well although it sometimes fails to correctly classify new ice and open water owing to the wide distribution of backscatter for these classes our results imply a high degree of accuracy and consistency in the growing archive of multiyear and first year ice distribution maps these results have implications for heat and mass balance studies which are furthered by the ability to accurately characterize ice type distributions over a large part of the arctic

simulating the ice thickness distribution in a coupled climate model climate simulations in a global coupled model are investigated using a dynamic thermodynamic sea ice and snow model with sophisticated thermodynamics and a subgrid scale parameterization for multiple ice thicknesses in addition to the sea ice component the model includes a full primitive equation ocean and a simple energy moisture balance atmosphere we introduce a formulation of the ice thickness distribution that is lagrangian in thickness space the method is designed to use fewer thickness categories because it adjusts to place resolution where it is needed most and it is free of diffusive effects that tend to smooth eulerian distributions experiments demonstrate that the model does reasonably well in simulating the mean arctic climate we find the climate of the arctic and northern north atlantic is sensitive to resolving the ice thickness distribution when comparing the model results to a simulation with a two level sea ice model the ice thickness distribution causes ice export through fram strait to be more variable and more strongly linked to meridional overturning in the north atlantic ocean the lagrangian formulation of the ice thickness distribution allows for the inclusion of a vertical temperature profile with relative ease compared to an eulerian method we find ice growth rates and ocean surface salinity differ in our model with a well resolved vertical temperature profile in the ice and snow and an explicit brine pocket parameterization compared to a simulation with semtner zero layer thermodynamics although these differences are important for the climate of the arctic the effects of an ice thickness distribution are more dramatic and extend into the northern north atlantic sensitivity experiments indicate that five ice thickness categories with 50 cm vertical temperature resolution capture the effects of the ice thickness distribution on the heat and freshwater exchange across the surface in the presence of sea ice in these simulations

open water production in arctic sea ice satellite measurements and model parameterizations sequential synthetic aperture radar sar images from the ers 1 spacecraft were routinely used as input to the geophysical processor system at the alaska sar facility from 1992 through 1994 to produce sea ice displacement vectors on a 5 km grid we have combined some 5000 of these products consisting of nearly 700 000 displacement vectors into a set of 914 strips or mosaics of ice motion that span mostly 3 day intervals for each strip we compute the opening and closing of leads based on the change in area of the 5 km grid cells we also compute the area averaged deformation or strain invariants of the motion the small scale several kilometer lead activity can be parameterized fairly well in terms of the large scale several hundred kilometer strain invariants sea ice models implicitly contain such a parameterization through their constitutive equations the well known model of hibler 1979 that uses a viscous plastic rheology and an elliptical yield curve is in good agreement with our data the variance in the data about this theoretical relationship is less than that suggested by a random model of sea ice motion the data also indicate that shearing deformation contributes to the opening and closing of leads models with two categories or levels of ice thickness generally do not take shearing deformation into account in the evolution of the ice concentration nor do they redistribute ice as a result of ridging we show how to add these features to two level models however we argue that three level models consisting of open water thin ice and thick ice are much better suited to the proper treatment of open water production and we present such a model

ridging and strength in modeling the thickness distribution of arctic sea ice a theory describing evolution of the ice thickness distribution the probability density of ice thickness was proposed by thomdike et al 1975 and has been used in several sea ice models the advantage of this theory over the widely used two level formulation is that it treats ridging explicitly as a redistribution of ice thickness and ice strength as a function of energy losses incurred by ridge formation however the parameterization of these processes remains rather speculative and largely untested and so our purpose here is to explore these parameterizations using a numerical model based on this theory the model uses a 160 km resolution grid of the arctic and 7 years of observed atmospheric forcing data 1979 1985 monthly oceanic heat flux and current fields are obtained from a 40 km resolution coupled ice ocean model run separately with the same forcing by requiring the computed monthly mean ice drift to have the same magnitude as observed buoy drift we estimate the primary strength parameter the ratio of total to potential energy change during ridging this ratio depends on the value of other parameters however the standard case has a ratio of 17 which is within the range estimated by hopkins 1994 in simulations of individual ridging events the effects of ridge redistribution and shear ridging parameters are illustrated by a series of sensitivity studies and comparisons between observed and modeled ice thickness distributions and ridge statistics in addition these comparisons highlight the following shortcomings of the thickness distribution theory as it is presently implemented first the process of first year to multiyear ridge consolidation is ignored and second the observed preferential melt of thick ridged ice is not reproduced

ice atmosphere interactions during sea ice advance and retreat in the western antarctic peninsula region 1 the seasonal evolution of sea ice extent concentration and drift in the western antarctic peninsula wap region along with regional atmospheric synoptic variability are described for a winter period 1992 when sea ice advance and retreat were both anomalously early daily time series of winds opening and closing of the sea ice cover and volume fluxes in and out of the wap region indicate that synoptic variability in meridional winds determines whether the ice edge advances or retreats on daily to weekly timescales the importance of this finding is that the dynamics as opposed to the thermodynamics initiate and thereby dominate in the production of ice edge anomalies further the abrupt mid winter shift from persistently positive to negative ice edge anomalies indicates that there was a distinct change in the regional atmospheric circulation the ice atmosphere interactions in the winter of 1992 are then compared to those in the winter of 1990 when sea ice advance and retreat were both late instead of early but again the mid winter shift was abrupt the comparison highlights possible circumpolar and tropical polar atmospheric linkages in the south pacific that involve changes in the amplitude phase of the semi annual oscillation sao which in turn appear

identification of sea ice types in spaceborne synthetic aperture radar data an approach for identification of sea ice types in spaceborne synthetic aperture radar sar image data is presented the unsupervised classification approach involves cluster analysis for segmentation of the image data followed by cluster labeling based on previously defined look up tables containing the expected backscatter signatures of different ice types measured by land based scatterometer the particular look up table used for labeling a segmented image is selected based on the seasonal and meteorological conditions at the time of data acquisition the extensive scatterometer observations and experience accumulated in field campaigns during the last 10 years were used to construct these look up tables these tables are expected to evolve as sea ice observations from the european ers 1 sar become available this paper presents the classification approach its expected performance the dependence of this performance on radar system performance and expected ice scattering characteristics results using both aircraft and simulated ers 1 sar data are presented the results are compared to limited field ice property measurements and coincident passive microwave imagery an algorithm based on this experimental approach has been implemented in the geophysical processor system at the alaska sar facility for classification of sea ice data in ers 1 c band sar data the importance of an integrated postlaunch program for validation and improvement of this approach is discussed

the relation between ice deformation oceanic heat flux and the ice thickness distribution in the arctic ocean a one dimensional ocean model coupled with an ice model where the ice cover is partitioned into a number of thickness categories is used to investigate how the ice thickness distribution in the arctic ocean depends on the two deformation processes export net divergence and ridging the model standard case generates vertical profiles of temperature salinity and an ice thickness distribution similar to the observations the standard case oceanic heat flux agrees well with recently deduced heat fluxes from arctic ice dynamics joint experiment aidjex data the oceanic heat flux is about 18 w m 2 during summer and about 1 w m 2 during winter it is found that the mean ice thickness decreases with increasing ice export in close agreement with other investigations however the dependence of the mean ice thickness on ridging activity is found to be very weak the change of the mean ice thickness is only 12 cm when increasing the ridging activity in the model from 0 to 0 4 yr 1 where the larger value represents an estimate of the actual ridging activity in the arctic ocean in a sensitivity study different types of ridging and albedo parameterizations are tested and this weak dependence is found to be very robust other properties of the model ice cover are sensitive to ridging though the equilibrium thickness of undeformed ice decreases with both export and ridging activity the annual maximum open water fraction and the amplitude of the seasonal thickness variation increases with export and ridging

determination of the age distribution of sea ice from lagrangian observations of ice motion a procedure for monitoring the local age distribution of the arctic sea ice cover is presented the age distribution specifies the area covered by ice in different age classes in our approach a regular array of grid points is defined initially on the first image of a long time series and an ice tracker finds the positions of those points in all subsequent images of the series these lagrangian points mark the corners of a set of cells that move and deform with the ice cover the area of each cell changes with each new image or time step a positive change indicates that ice in a new age class was formed in the cell a negative change is assumed to have ridged the youngest ice in the cell reducing its area the ice in each cell ages as it progresses through the time series the area of multiyear ice in each cell is computed using an ice classification algorithm any area that is not accounted for by the young ice or multiyear ice is assigned to a category of older first year ice we thus have a fine age resolution in the young end of the age distribution and coarse resolution for older ice the age distribution of the young ice can be converted to a thickness distribution using a simple empirical relation between accumulated freezing degree days and ice thickness or using a more complicated thermodynamic model we describe a general scheme for implementing this procedure for the arctic ocean from fall freeze up until the onset of melt in the spring the concept is illustrated with a time series of five ers 1 sar images spanning a period of 12 days such a scheme could be implemented with radarsat sar imagery to provide basin wide ice age and thickness information

modeling the high frequency component of arctic sea ice drift and deformation abstract buoy observations of sea ice drift show that sea ice motion and deformation contain substantial high frequency variability at subdaily timescales however numerical simulations of the sea ice dynamics normally do not include processes on such short timescales instead by applying traditional water drag formulations for the ocean sea ice boundary layer the inertial frequencies tend to be omitted in the spectra of modeled sea ice motion and deformation due to fictitious ocean damping here a dynamic thermodynamic sea ice model is presented that includes inertial embedding of the sea ice into the oceanic boundary layer to reproduce sea ice motion and deformation not only at daily and lower frequencies but also at subdaily frequencies up to 2 cycles per day and higher comparison with buoy data shows that the embedded model much more successfully simulates the observed sea ice motion in regard to the high frequency component the results demonstrate that both inertial embedding of the sea ice oc

annual cycles of sea ice motion and deformation derived from buoy measurements in the western arctic ocean over two ice seasons data collected by two buoy arrays that operated during the ice seasons of 2014 2015 and 2016 2017 were used to characterize annual cycles of ice motion and deformation in the western arctic ocean an anomalously strong and weak beaufort gyre in 2014 2015 and 2016 2017 induced generally anticyclonic and cyclonic sea ice drift during 2014 2015 and 2016 2017 respectively cyclonic ice motion resulted in higher contributions of ice divergence to total ice deformation in 2016 2017 than in 2014 2015 in 2014 the autumn ice concentration and multiyear ice coverage were higher than in 2016 consequently the response of ice motion to wind forcing was weak and less ice deformation was observed in autumn 2014 during the autumn winter transition the ice wind speed ratio ice deformation rate and its spatial and temporal scaling exponents and localization of ice deformation decreased markedly in both 2014 2015 and 2016 2017 as a result of freeze up and consolidation of ice floes such dynamic behavior was maintained through to spring with the further thickening of ice cover ice deformation increased due to weakened ice strength as summer approached the amplitude of the annual cycle of ice deformation rate in the western arctic ocean in 2014 2015 and especially in 2016 2017 was larger than that observed during the surface heat budget of the arctic ocean sheba program in 1997 1998 we attribute this phenomenon to ice loss during the recent summers especially of thick multiyear ice

large scale drift of arctic sea ice retrieved from passive microwave satellite data a method of determining the large scale sea ice drift using 85 5 ghz special sensor microwave imager data are presented a cross correlation method is applied to sequential images of gridded data covering the entire arctic individual correlation results are validated with ice velocities derived from buoy data the satellite derived mean drift values and the variabilities of the ice drift correspond closely with the buoy data similarly time series of buoy data and associated satellite data are in good agreement even over large time periods an example of a satellite retrieved 3 day mean drift field demonstrates the potential of the method for providing large scale ice circulation patterns mean drift fields of the winter periods 1987 1988 and 1992 1993 indicate a considerable interannual variability of the sea ice drift pattern in the arctic ocean the arctic region is divided into seven larger areas and the area flux between these regions has been derived the kara sea and the laptev sea show the largest area ice export with 0 02 and 0 015 km 2 s 1 respectively the central arctic export through fram strait amounts to 0 12 sv during the winter of 1992 1993 with a maximum of 0 15 sv in january

effect of sea ice rheology in numerical investigations of climate 1 plastic sea ice rheologies that employ teardrop and parabolic lens yield curves and allow varying biaxial tensile stresses have been developed these rheologies together with the previously developed ellipse and mohr coulomb ellipse rheologies are implemented in a thickness and enthalpy distribution sea ice model to examine the rheological effect in numerical investigations of arctic climate the teardrop lens and ellipse rheologies obey a normal flow rule and result in a two peak shear stress distribution the first peak is at the zero shear stress the second is near 16 000 n m 1 for the ellipse and two lens rheologies and near 30 000 n m 1 for the two teardrop rheologies the location of the second peak depends on the fatness of the yield curve and the amount of biaxial tensile stress allowed in contrast the mohr coulomb ellipse rheology based on coulombic friction failure does not tend to create the second peak the incorporation of biaxial tensile stress tends to increase ice thickness in most of the arctic a fatter yield curve tends to increase the frequency of large shear stresses an increased frequency of large shear stresses in conjunction with the inclusion of biaxial tensile stress tends to reduce ice speed and ice export to enhance ice ridging in the arctic interior and to reduce ice ridging in the coastal areas which has a significant impact on arctic spatial ice mass distribution and the total ice budget the teardrop rheologies reduce spatial bias of modeled ice draft against submarine observations more than others by changing ice motion deformation and thickness the choice of plastic rheology also considerably affects the simulated surface energy exchanges particularly in the arctic marginal seas

contributions of growth and deformation to monthly variability in sea ice thickness north of the coasts of greenland and the canadian arctic archipelago regional variability in monthly cryosat 2 sea ice thickness is partitioned into contributions from dynamics and thermodynamics using ice deformation calculated from large scale ice drift for five winters december to april 2011 2015 over a region of persistent convergence north of the coasts of greenland and the canadian arctic archipelago deformation explains 34 of the overall variance up to 69 in 2014 2015 in monthly thickness changes approximately 42 56 or 0 6 m of the seasonal changes in mean regional ice thickness can be attributed to divergence and shear the estimated area averaged growth of 0 12 0 03 m month compares favorably with measurements from ice mass balance buoys examination of the time variable thickness distributions shows areas covered by ice 3 m increased albeit at fairly coarse resolution this coupled analysis of thickness changes and deformation offered a first look at the character of the regional thickness redistribution process

the force balance of sea ice in a numerical model of the arctic ocean the balance of forces in the sea ice model of hibler 1979 is examined the model predicts that internal stress gradients are an important force in much of the arctic ocean except in summer when they are significant only off the northern coasts of greenland and the canadian archipelago a partition of the internal stress gradient between the pressure gradient and the viscous terms reveals that both are significant although they operate on very different timescales the acceleration term is generally negligible while the sum of coriolis plus sea surface tilt is small thus the seasonal average force balance in fall winter and spring is mostly between three terms of roughly equal magnitudes air drag water drag and internal stress gradients this is also true for the monthly average force balance however we find that there is a transition around the weekly timescale and that on a daily basis the force balance at a particular location and time is often between only two terms either between air drag and water drag or between air drag and internal stress gradients the model is in agreement with the observations of thorndike and colony 1982 in that the correlation between geostrophic wind forcing and the model s ice velocity field is high this result is discussed in the context of the force balance we show that the presence of significant internal stress gradients does not preclude high wind ice correlation a breakdown of the internal stress gradient into component parts reveals that the shear viscous force is far from negligible which casts strong doubt on the theoretical validity of the cavitating fluid approximation in which this component is neglected finally the role of ice pressure is examined by varying the parameter p we find a strong sensitivity in terms of the force balance as well as ice thickness and velocity

sea ice kinematics and surface properties from radarsat synthetic aperture radar during the sheba drift 1 satellite data are important for providing the large scale context of the surface heat budget of the arctic ocean sheba station and for characterizing the spatial variability of the sea ice in its vicinity the canadian radarsat satellite collected 195 synthetic aperture radar sar images of the sheba site over the course of the 1 year drift the radarsat geophysical processor system rgps used these images to compute the spatial pattern of ice motion within 100 km of the sheba station by tracking features in sequential images from the ice motion data the divergence and shear of the pack ice are estimated the divergence is large from november to january followed by a gradual convergence from february through july the character of the ice motion changes at the end of july from piecewise rigid motion to free drift the ice motion reverts to its winterlike character in late september thus the kinematic summer runs from late july to late september the radar backscatter also goes through seasonal transitions capturing the abrupt onset of melt 29 may and freeze up 15 august the concentration of multiyear ice is about 94 in the fall and its backscatter signature remains stable through spring multiyear and first year ice cannot be distinguished during the summer melt season when the mean backscatter is negatively correlated with the surface air temperature the thermodynamic summer runs from late may to mid august index terms 4207 oceanography general arctic and antarctic oceanography 4275 oceanography general remote sensing and electromagnetic processes 0689 4540 oceanography physical ice mechanics and air sea ice exchange processes keywords sea ice synthetic aperture radar sar sheba

opening and closing of sea ice leads digital measurements from synthetic aperture radar the coming opportunity to extract quantitative sea ice data from routine synthetic aperture radar imagery requires the development of automated image processing techniques an algorithm is described for measuring the opening and the closing of leads by comparing two sequential synthetic aperture radar sar digital images the pair of images is classified into leads and ice correcting for variation in brightness with range displacements are determined automatically on a regular 2 km grid on a 100 km square scene by cross correlation an algorithm groups together cells which cover a lead event the lead area change is estimated for each cell group by counting lead pixels before and after deformation all positive changes are summed to obtain the amount of opening and all negative changes give closing errors are estimated by comparison with area changes determined from manually digitized lead boundaries and are about 0 2 of the area of the scene for comparison the measured opening and closing are in the range of 1 to 3 of the scene area in ice models the openings and closings of leads are parameterized in terms of the large scale deformation sar allows us to study these parametric relations by giving us access both to direct observations of opening and closing and to detailed kinematic data from which to estimate the mean deformation in this image pair for which the deformation is nearly pure shear we find relatively small amounts of opening and closing consistent with previous observations and with parameterizations in most models the large values of opening and closing predicted by the poisson gauss kinematic model are not in evidence

paraglacial slope instability in scottish fjords examples from little loch broom nw scotland lateglacial holocene fjord sediments in little loch broom preserve evidence of extensive slope instability the major area of reworking is in the outer loch and mid loch sill region where ice contact ice proximal deposits of the lateglacial assynt glacigenic formation have been disrupted by sliding and mass flow processes linked to the little loch broom slide complex and the adjacent badcaul slide mass failure was instigated about14 13 ka bp and is probably the response of the landscape to deglaciation immediately following the removal of ice support during glacial retreat an initial phase of translational sliding was followed by rotational sliding as revealed by the superimposition of scalloped shaped slumps on a larger scale rectilinear pattern of failure paraglacial landscape readjustment may have also been enhanced by episodic seismic activity linked to glacio isostatic unloading in the inner fjord evidence of holocene mass failure includes the ardessie debris lobe and a discrete intact slide block preserved within the postglacial basinal deposits the former is a localised accumulation linked to a fluvial catchment on the adjacent an teallach massif these mass transport deposits may represent an ongoing response to paraglacial processes albeit much reduced relative to the major slides in terms of sediment supply to the fjord

influence of the southern annular mode on the sea ice ocean system 1 the global sea ice ocean model orca2 lim driven by the ncep ncar national centers for environmental prediction national center for atmospheric research reanalysis daily 2 m air temperatures and 10 m winds and by monthly climatologies for precipitation cloud cover and relative humidity is used to investigate the impact of the southern annular mode sam on the antarctic sea ice ocean system our results suggest that the response of the circumpolar southern ocean consists of an annular and a nonannular component for the sea ice cover the non annular component seems to be the most important the annular component strongly affects the overall patterns of the upper ocean circulation when the sam is in its positive phase a northward surface ekman drift a downwelling at about 45 degreess and an upwelling in the vicinity of the antarctic continent are simulated the non annular component has a significant impact at the regional scale especially in the weddell ross amundsen and bellingshausen seas in those regions the pressure pattern associated with the sam induces meridional winds which advect warmer air in the weddell sea and around the antarctic peninsula and colder air in the amundsen and ross seas this implies a dipole response of sea ice to the sam with on average a decrease in ice area in the weddell sea and around the antarctic peninsula and an increase in the ross and amundsen seas during years with a high sam index the long term trend in the observed sea ice area does not appear to be related to the trend in the sam index

meso and microscale sea ice motion in the east siberian sea as determined from ers 1 sar data synthetic aperture radar sar derived ice motion vectors and sar interferometry were used to study the sea ice conditions in the region between the coast and 75 n 560 km in the east siberian sea in the vicinity of the kolyma river ers 1 sar data were acquired between 24 december 1993 and 30 march 1994 during the 3 day repeat ice phase of the satellite the time series of the ice motion vector fields revealed rapid 3 day changes in the direction and displacement of the pack ice longer term 1 month trends also emerged which were related to changes in large scale atmospheric circulation on the basis of this time series three sea ice zones were identified the near shore stationary ice zone a transitional ice zone and the pack ice zone three 3 day interval and one 9 day interval interferometric sets amplitude correlation and phase diagrams were generated for the end of december the begining of february and mid march they revealed that the stationary ice zone adjacent to the coast is in constant motion primarily by lateral displacement bending tilting and rotation induced by atmospheric oceanic forcing the interferogram patterns change through time as the sea ice becomes thicker and a network of cracks becomes established in the ice cover it was found that the major features in the interferograms were spatially correlated with sea ice deformation features cracks and ridges and major discontinuities in ice thickness

arctic sea ice as a granular plastic an important consideration in understanding sea ice mechanics is the integration of observed sea ice behavior on a floe neighborhood scale 1 10 km into ice dynamics on a regional scale o 50 km we investigate sea ice kinematics from october 1993 through april 1994 using relative motions from 13 drifting buoys with global positioning system navigation in a 20 km array centered on the sea ice mechanics initiative ice camp and we compare these motions to synthetic aperture radar sar derived ice velocities over a 100 by 500 km region in the beaufort sea there is excellent correspondence between the deformation of the buoy array and that from the sar inferred ice dynamics from analysis of the two major northerly wind convergence events of the winter are consistent with a granular hardening plastic conceptual model for beaufort sea ice under continued northerly winds the ice from the alaskan shore to the camp failed in shear and convergence in a progressive manner away from the coast the continuum scale o 10 km is an order of magnitude larger than the grain i e floe size o 1 km the ice motion often forms aggregates of 20 200 km separated by narrow 10 km shear zones similar to granular materials at moderate forcing i e wind stress multiplied by fetch the ice appears to fail along slip lines that occur at an acute angle to each other and to the direction of the wind forcing characteristic of a plastic material at critical state with longer fetch the ice appears to fail in compression perpendicular to the wind direction sea ice appeared to harden on a regional scale after the first event during the second northerly wind event there was a sea ice breakout toward the west apparently due to a lack of lateral confining stress our observations suggest that the ice floes advect through relatively stationary stress fields created by the wind forcing and coastal boundaries for example while the sar and advanced very high resolution radiometer images indicated the presence of the shear feature at the same geographic location for nearly a week buoys would show shearing only for several days as they transited across the region of shear there is a high correspondence between the major internal ice deformation events and persistent weather patterns on a 3 to 5 day temporal scale this implies that sar data collection and analysis for regional sea ice dynamics should be consistent with the wind forcing and have a sampling of less than 3 days

on modeling the anisotropic failure and flow of flawed sea ice the failure and flow of sea ice on scales small and large is characterized by the propagation of oriented leads and cracks in this paper a theory for the dynamical treatment of anisotropic oriented flaws in sea ice is developed and used to examine the interaction of these oriented flaws under idealized stress forcing the essential idea of the theory is to take one or more oriented weak leads imbedded in thick ice a constitutive law for both the thin and thick ice is taken to be similar to laboratory observations which are consistent with mohr coulomb like failure application of normal continuum mechanics boundary conditions leads to anisotropic flow and failure characteristics of this anisotropic composite under both near and far field forcing the local failure characteristics show that there is a preferred orientation for failure with the intersection between leads increasing as confinement increases for spatially separated interacting flaws the theory predicts a preference for the weakening of flaws in a narrow range of angles of 10 20 relative to the principal far field stress imbedding isolated flaws leads to simulated damage directions consistent with local failure characteristics in the case where the ice is considered to have available flaws in all directions fracture propagation is found to proceed by picking out oriented flaws alternating in direction along large scale damage strikes with individual flaw alignments of 20 relative to far field principal stresses the mechanisms responsible for these results and how this anisotropic sea ice rheology might be implemented in current dynamic thermodynamic sea ice models are discussed