utilizing the aspect sea ice thickness data set to evaluate a global coupled sea ice ocean model 1 simulated sea ice thickness in the orca2 lim coupled sea ice ocean model is compared with thicknesses from the antarctic sea ice processes and climate aspect database we find a qualitative agreement of the large scale patterns of ice thickness distribution regional averages for the various sectors of the southern ocean yield a very good correspondence between observations and model data exceptions are the eastern bellingshausen and northwestern weddell seas a poor representation of the antarctic peninsula in the atmospheric forcing data and the related overestimation of westerly winds in this region lead to a spurious accumulation of sea ice on the western side of the peninsula and to an underestimation of sea ice coverage on the eastern side since the spatial scale of observations is not comparable to the size of a model grid cell there is little agreement between individual observations and the corresponding model ice thicknesses a model analysis of the seasonal and interannual variability indicates that the aspect data underestimate the climatological ice thickness in the central and southern weddell sea and the eastern ross sea by up to 1 m because of a winter bias in the observations an overestimation of similar magnitude is expected in the bellingshausen sea ice thickness data in most of the indo pacific sector appear to be representative for the long term climatology a model estimate of the bias is used to compute a revised distribution of climatological sea ice thickness

heat flux through sea ice in the western weddell sea convective and conductive transfer processes the heat flux through the snow and sea ice cover and at the ice ocean interface were calculated at five sites in the western weddell sea during autumn and early winter 1992 the ocean heat flux averaged 7 2 w m2 from late february to early june and average ice air heat flux in the second year floes depended on the depth of the snow cover and ranged from 9 to 17 0 8 w m2 in late february three of the five sites had an ice surface which was depressed below sea level resulting at two of the sites in a partially flooded snow cover and a slush layer at the snow ice interface as this slush layer froze to form snow ice the dense brine which was rejected flowed out through brine drainage channels and was replaced by lower salinity nutrient rich seawater from the ocean upper layer we estimate that about half of the second year ice in the region was covered with this slush layer early in the winter as the slush layer froze over a 2 to 3 week period the convection within the ice transported salt from the ice to the upper ocean and increased total heat flux through the overlying ice and snow cover on an area wide basis approximately 10 cm of snow ice growth occurred within second year pack ice primarily during a 2 to 3 week period in february and march this ice growth near the surface of the ice provides a salt flux to the upper ocean equivalent to 5 cm of ice growth despite the thick about 1 m ice cover in addition to the ice growth in the small area less than 5 open water regions

the sea ice thickness distribution in the northwestern weddell sea we present new data on distribution of snow and sea ice thicknesses in the northwestern weddell sea the data were obtained through direct measurements along 19 profiles each approximately 100 m long on 17 different floes located between 54 46 w and 59 64 s the overall probability density functions pdfs for ice thicknesses reflect the complex mixture of first second and multi year ice to be expected in the outflowing branch of the weddell gyre further differentiation of the data reveals four distinct thickness classes which reflect differences in the formation and subsequent histories of the ice encountered these classes i iv represent strongly deformed first year ice less deformed first and second year ice and deformed second or multi year ice respectively each of the classes is characterized by a specific set of quantities related to ice texture and surface snow characteristics and by distinct pdfs for snow and ice thicknesses in addition geometric surface and bottom roughness characteristics differ significantly for each of the floe classes

thickness distribution of antarctic sea ice 1 ship based observations are used to describe regional and seasonal changes in the thickness distribution and characteristics of sea ice and snow cover thickness around antarctica the data set comprises 23 373 observations collected over more than 2 decades of activity and has been compiled as part of the scientific committee on antarctic research scar antarctic sea ice processes and climate aspect program the results show the seasonal progression of the ice thickness distribution for six regions around the continent together with statistics on the mean thickness surface ridging snow cover and local variability for each region and season a simple ridge model is used to calculate the total ice thickness from the observations of level ice and surface topography to provide a best estimate of the total ice mass including the ridged component the long term mean and standard deviation of total sea ice thickness including ridges is reported as 0 87 0 91 m which is 40 greater than the mean level ice thickness of 0 62 m analysis of the structure function along north south and east west transects revealed lag distances over which sea ice thickness decorrelates to be of the order of 100 300 km which we use as a basis for presenting near continuous maps of sea ice and snow cover thickness plotted on a 2 5 5 0 grid

the indian monsoon and its variability for over 300 years the monsoon has been viewed as a gigantic land sea breeze it is shown in this paper that satellite and conventional observations support an alternative hypothesis which considers the monsoon as a manifestation of seasonal migration of the intertropical convergence zone itcz with the focus on the indian monsoon the mean seasonal pattern is described and why it is difficult to simulate it is discussed some facets of the intraseasonal variation such as active weak cycles break monsoon and a special feature of intraseasonal variation over the region namely poleward propagations of the itcz at intervals of 2 6 weeks are considered vertical moist stability is shown to be a key parameter in the variation of monthly convection over ocean and land as well as poleward propagations special features of the bay of bengal and the monsoon brought out by observations during a national observational experiment in 1999 are briefly described

origin of felsic volcanism in the izu arc intra arc rift an intra arc rift iar is developed behind the volcanic front in the izu arc japan bimodal volcanism represented by basalt and rhyolite lavas and hydrothermal activity is active in the iar the constituent minerals in the rhyolite lavas are mainly plagioclase and quartz whereas mafic minerals are rare and are mainly orthopyroxene without any hydrous minerals such as amphibole and biotite both the phenocryst and groundmass minerals have felsic affinities with a narrow compositional range the petrological and bulk chemical characteristics are similar to those of melts from some partial melting experiments that also yield dry rhyolite melts the hydrous mineral free narrow mineral compositions and low al2o3 affinities of the iar rhyolites are produced from basaltic middle crust under anhydrous low temperature melting conditions the iar basalt lavas display prominent across arc variation with depleted elemental compositions in the volcanic front side and enriched compositions in the rear arc side the across arc variation reflects gradual change in the slab derived components as demonstrated by decreasing ba zr and th zr values to the rear arc side rhyolite lavas exhibit different across arc variations in either the fluid mobile elements or the immobile elements such as nb zr la yb and chondrite normalized rare earth element patterns reflecting that the felsic magmas had different source the preexisting arc crust formed during an earlier stage of arc evolution most probably during the oligocene prior to spreading of the shikoku back arc basin the lack of systematic across arc variation in the iar rhyolites and their dry shallow crustal melting origin combines to suggest re melting of preexisting oligocene middle crust by heat from the young basaltic magmatism

a one dimensional percolation model of flooding and snow ice formation on antarctic sea ice a one dimensional thermodynamic sea ice growth model is developed with emphasis on seawater flooding and snow ice formation on antarctic sea ice to examine the possibility that flooding is the result of brine percolation through a porous ice matrix and the consequences of this percolation on the salinity structure and mass balance of the ice flooding is modeled in a semiheuristic fashion by examining two possible regimes for seawater and brine infiltration through the porous ice into the snowpack a standard model assumes that the upward flow of brine is horizontally homogeneous and brine flow is modeled using a darcian scheme a simple model assumes that the infiltrating brine does not interact with the internal ice brine network but instead percolates upward through cracks or is restricted in spatial extent results of simulations are shown for the climatology in the ross sea and compared to field data from one autumn and one winter cruise aboard the r v nathaniel b palmer in 1995 sensitivity studies are performed to show the effects of variations in climate forcing the dependence of brine percolation and snow ice formation on key thermophysical parameters is investigated results indicate that the mass balance depends very strongly on the brine flow regime in the standard model ice salinities and brine volumes are greatly affected by brine percolation creating a strong feedback between flooding and future snow ice production snow ice formation for the simple model was much more predictable and depended primarily on snow load comparison of results with field data indicate that if brine percolation is the major mechanism for flooding and snow ice formation then there must be either substantial convective redistribution of salt to maintain ice porosity or the flow must be spatially inhomogeneous

seasonal changes of sea ice characteristics off east antarctica data on antarctic sea ice characteristics and their spatial and temporal variability are presented from cruises between 1986 and 1993 for the region spanning 60 150 e between october and may in spring the sea ice zone is a variable mixture of different thicknesses of ice plus open water and in some regions only 30 40 of the area is covered with ice 0 3 m thick the thin ice and open water areas are important for air sea heat exchange crystallographic analyses of ice cores supported by salinity and stable isotope measurements show that approximately 50 of the ice mass is composed of small frazil crystals these are formed by rapid ice growth in leads and polynyas and indicate the presence of open water throughout the growth season the area averaged thickness of undeformed ice west of 120 e is typically less than 0 3 m and tends to increase with distance south of the ice edge ice growth by congelation freezing rarely exceeds 0 4 m with increases in ice thickness beyond this mostly attributable to rafting and ridging while most of the total area is thin ice or open water in the central pack much of the total ice mass is contained in ridges taking account of the extent of ridging the total area averaged ice thickness is estimated to be about 1m for the region 60 90 e and 2 m for the region 120 150 e by december new ice formation has ceased in all areas of the pack and only floes 0 3 m remain in most regions these melt completely over the summer and the new season s ice formation starts in late february by march the thin ice has reached a thickness of 0 15 0 30 m with nilas formation being an important mechanism for ice growth within the ice edge

seasonal variations in the properties and structural composition of sea ice and snow cover in the bellingshausen and amundsen seas antarctica sixty three ice cores were collected in the bellingshausen and amundsen seas in august and september 1993 during a cruise of the r v nathaniel b palmer the structure and stable isotopic composition 18 o 16 o of the cores were investigated in order to understand the growth conditions and to identify the key growth processes particularly the contribution of snow to sea ice formation the structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the bellingshausen sea in march 1992 are reassessed frazil ice and congelation ice contribute 44 and 26 respectively to the composition of both the winter and summer ice core sets evidence that the relatively calm conditions that favour congelation ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil ice growth and pancake ice formation both frazil and congelation ice layers have an av erage thickness of 0 12 m in winter evidence that congelation ice and pancake ice thicken primarily by dynamic processes the thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover snow ice layers have a mean thickness of 0 20 and 0 28 m in the winter and summer cores respectively and the contribution of snow ice to the winter 24 and summer 16 core sets exceeds most quantities that have been reported previously in other antarctic pack ice zones the thickness and quantity of snow ice may be due to a combination of high snow accumulation rates and snow loads environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow ice interface and bottom melting losses being compensated by snow ice formation layers of superimposed ice at the top of each of the summer cores make up 4 6 of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice the accumulation of superimposed ice is evidence that melting in the snow cover on antarctic sea ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass

18o concentrations in sea ice of the weddell sea antarctica we present data on ice texture salinity and delta o 18 obtained from identical sections of ice cores during the winter weddell sea project 1986 on rv polarstern from july through august 1986 in the longitude range between 5 degrees w and 7 degrees e we find no uniquely definable relationship between delta o 18 values and ice texture in a particular section however most of the snow ice as well as some sections of frazil ice ar found to have negative delta o 18 concentrations this is due to varying degrees of admixtures of meteoric ice snow and sea water during formation of snow ice in contrast to common assumptions our results seem to indicate that a snow cover contributes positively to sea ice growth rather than slowing down the overall growth rate based on a simple model we have estimated the contributions of meteoric ice mean of 3 3 and the combined meteoric ice sea water fraction a minimum of 7 6 to the total ice thickness for the majority of the sampled floes although this is only a moderate contribution to the overall mass balance in the absence of congelation growth it nevertheless enhances ice growth in general this hypothesis is dependently supported by our snow and ice thickness data wadhams and others 1987 which demonstrate that the depression of the snow ice interface below the water line i e a negative freeboard and the formation of snow ice is a common occurrence in the weddell sea therefore we hypothesize that the major part of the observed apparent increase in ice thickness between our inbound and outbound tracks of wwsp 86 may not be derived from regular thermodynamically driven congelation growth but rather from the snow ice component in floes of the weddell sea

changes in the thickness distribution of arctic sea ice between 1958 1970 and 1993 1997 1 submarine sonar data collected in the central arctic basin during middle and late summer were used to examine differences in the sea ice thickness distribution function g h between the periods 1958 1970 and 1993 1997 cruises during the former period were made in july and august whereas the 1993 1997 cruises were made in september and october seasonal correction was applied to adjust for the differences in thickness while ice drafts were from only seven submarine cruises and somewhat spatially limited results indicate that the fractional area covered by open water and first year ice increased from 0 19 to 0 30 during the time interval this was balanced by an 11 reduction of level multiyear and ridged ice substantial losses occurred in ice thicker than 2 m with an increase in the amount of 1 2 m ice the volume of ice less than 4 m thick remained nearly the same and the total volume decreased about 32 losses in the volume of thicker ice increased with increasing thickness part of the change in g h is likely caused by increased ice area export through fram strait in the late 1980s and early 1990s because decadal variations in the north atlantic oscillation and arctic oscillation indices correlate with ice export anomalies export induced changes in g h probably tend to be cyclical in nature however a substantial shift in the peak of g h suggests that changes in thermal forcing were also a major factor in the observed thinning

east antarctic sea ice albedo thickness distribution and snow cover characteristics of springtime sea ice off east antarctica were investigated during a cruise of the australian national antarctic research expedition in october through december 1988 the fractional coverage of the ocean surface the ice thickness and the snow cover thickness for each of several ice types were estimated hourly for the region near the ship these observations were carried out continuously during the 4 weeks the ship was in the ice thin and young ice types were prevalent throughout the region and the observations show a systematic increase in the total area weighted pack ice thickness including open water area from only 0 2 m within 50 km of the ice edge to 0 45 m close to the coast ice thickness averaged over the ice covered region only is also relatively thin ranging from 0 35 m near the ice edge to 0 65 m in the interior these values are probably typical of average winter thickness for the area the average snow cover thickness on the ice increased from 0 05 m near the ice edge to 0 15 m in the interior average ice concentration increased from less than 6 10 near the ice edge to 8 10 in the interior the ship observed concentrations were in good agreement with concentrations derived from passive microwave satellite imagery except in some regions of high concentration in these regions the satellite derived concentrations were consistently lower than those estimated from the ship possibly because of the inability of the satellite sensors to discriminate the appreciable percentage of very thin ice observed within the total area spectral albedo was measured for nilas young grey ice grey white ice snow covered ice and open water at wavelengths from 420 to 1000 nm allwave albedo was computed by using the spectral measurements together with estimates of near infrared albedo and modeled spectral solar flux area averaged albedos for the east antarctic sea ice zone in spring were derived from representative allwave albedos together with the hourly observations of ice types these area averaged surface albedos increased from about 0 35 at the ice edge to about 0 5 at 350 km from the edge remaining at 0 5 to the coast of antarctica the low average albedo is in part due to the large fraction of open water within the pack but extensive fractions of almost snow free thin ice also play an important role

evaluation of amsr e snow depth product over east antarctic sea ice using in situ measurements and aerial photography 1 the antarctic remote ice sensing experiment arise was conducted in the east antarctic sea ice zone during september october 2003 a key objective of this program was the acquisition of in situ measurements suitable for evaluating the eos aqua advanced microwave scanning radiometer amsr e snow depth product a strategy is presented for comparing snow thickness measurements over spatial scales ranging from point measurements to satellite pixels in situ measurements of snow thickness were taken across eight lagrangian grid cells defined and tracked using an array of drifting buoys these data are coupled with ice type analyses from digital aerial photographs to calculate area averaged snow thicknesses that are compared with the amsr e derived snow thickness product the results show considerable underestimates of the amsr e snow depths for rough sea ice by a factor of 2 3 we investigate the impact of underlying sea ice roughness on snow depth retrievals and conclude that in situ measurements of snow thickness underrepresent snow depth over rough ice which is then not adequately accounted for in the development of the algorithm coefficients

the ice thickness distribution across the atlantic sector of the antarctic ocean in midwinter during the first leg of the winter weddell sea project antarktis v 2 cruise of f s polarstern the entire width of the antarctic sea ice zone was traversed in the vicinity of 0 longitude in the period july 18 to september 10 1986 ice thicknesses were measured by direct drilling and by helicopter profiling using an exstar 100 mhz impulse radar system in addition aerial photography of the ice cover was done from 100 to 2000 m altitude using a 70 mm aerial camera mounted in the helicopter the results of the point measurements drilling are reported in this paper together with an indication of how the radar and photography data will be used to extend them so as to yield area averaged ice thickness distributions it was found that the main ice type across the entire width of the ice cover was consolidated pancake ice occurring in vast floes this formed out of a 250 km wide band at the advancing ice edge which comprised a concentrated field of individual pancakes in a matrix of frazil ice preferred thicknesses of undeformed floes were 40 60 cm of ice covered with 5 15 cm of snow the individual pancakes attained almost all of this thickness before consolidation subsequent congelation growth was slow estimated at 0 4 cm d 1 the floes contained much small scale roughness on the upper and lower surfaces due to rafting of pancakes at the time of consolidation but pressure ridging was modest except in the far south a few very thick 8 11 m multiyear floes were observed embedded in the pack at latitudes beyond 66 s

evidence for rapid thinning of sea ice in the western arctic ocean at the end of the 1980s examination of springtime ice drafts obtained from submarine profiles in a narrow band of the western arctic ocean from offshore alaska to 89 n indicates that the mean ice draft decreased 1 5 m between the mid 1980s and early 1990s no similar trend was evident in ice drafts near the north pole the 1980s drafts were composed largely of ice exceeding 3 5 m while the early 1990s drafts contained more ice in thinner categories the differences in drafts between the two periods appear to be related largely to ice dynamics effects associated with the presence and strength of the beaufort gyre which weakened considerably in the early 1990s

the pattern and variability of antarctic sea ice drift in the indian ocean and western pacific sectors sea ice drift physically redistributes pack ice and changes ice extent concentration and through deformation the ice thickness distribution in this paper data are presented from 39 satellite tracked buoys deployed during various seasons from 1985 to 1996 in the sea ice of the southern ocean off east antarctica between 20 and 160 e longitude the dominant features of the ice motion in the region are a westward drift parallel to the bathymetry near the antarctic continent a cyclonic circulation cell in prydz bay and eastward drift of the ice to the north of the zonal shear zone the oceanic circulation along the coast is generally barotropic and the ice drift is well correlated with bottom topography northward outflows the locations of which are determined by both bottom topography and the seasonally varying position of the zonal shear zone allow the discharge of sea ice from the westward drift in the south into the northerly belt of eastward flow but with considerable variability in the net northward ice transport the ice translation monitored by the buoys is used to derive the spatial pattern of the ice velocity field the daily average ice drift speed in the westward flow is 0 23 m s 1 19 8 km d 1 with considerable spatial and temporal variability and in the eastward flow the average is 0 17 m s 1 15 1 km d 1 seasonal and interannual ice drift variabilities are analyzed the results are compared with satellite data of sea ice extent and concentration over the same time as well as with hydrographic observation of the position of the antarctic divergence

the thickness distribution of sea ice and snow cover during late winter in the bellingshausen and amundsen seas antarctica data collected from a voyage of rv nathaniel b palmer to the bellingshausen and amundsen seas during august september 1993 are used to investigate the thickness distribution of sea ice and snow cover and the processes that influence the development of the first year pack ice the data are a combination of in situ and ship based measurements and show that the process of floe thickening is highly dependent on ice deformation in particular rafting and ridging play important roles at different stages of floe development rafting is the major mechanism in the early stages of development and core structure data show the mean thickness of individual layers of crystals to be only 0 12 m most ice 0 6 m having some surface deformation blocks within ridge sails are typically in the range 0 3 0 6 m thick and ship based observations estimate approximately 25 of the pack exhibits surface ridging when corrected for biases in the observational methods the data show that the dominant ice and snow thickness categories are 0 7 m and 0 2 0 5 m respectively and account for 40 and 36 of the surface area of the pack ice approximately 8 of the pack is open water an estimate of the effects of ridging on the distribution of ice mass within the pack suggests that between 50 and 75 of the total mass is contained within the 25 of the pack that exhibits surface ridging

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

further evidence of ice thinning in the arctic ocean a sea ice thickness profile obtained in september 1996 from the eurasian basin of the arctic ocean between fram strait and the north pole was compared with a profile obtained in the same region in september october 1976 a decline in mean ice draft of 43 was observed over the 20 year interval in agreement with changes observed in other parts of the arctic ocean by rothrock et al 1999

numerical simulation of the weddell sea pack ice to investigate the role of ice dynamics on the seasonal cycle of antarctic sea ice a series of 2 year simulations of the weddell sea pack ice are carried out the simulations employ the dynamic thermodynamic model developed by hibler 1979 and use a 1 day time step on an 18 15 grid with a resolution of 222 km daily atmospheric data from 1979 are used to drive the simulations with atmospheric temperature fields modified to reflect buoy observations the simulations yield a seasonal cycle of ice with maximum and minimum extents close to that observed except for portions of the western weddell the advance of the ice is found to be primarily thermodynamic in nature while the rapid decay depends critically on the presence of both leads and lateral ice advection the average fraction of open water is substantial even in winter and varies from a minimum of 10 in september to a maximum of 35 in march these values are in general agreement with estimates from satellite microwave data in early summer the ice motion causes a residual tongue of ice to extend eastward from the antarctic peninsula in agreement with observations mean ice thicknesses are consistent with observations and vary from about 3 m in the perennial ice in the western weddell to 1 m in first year ice in the eastern weddell possible feedback between the ice extent and atmosphere are investigated by simulations with the surface air temperatures constrained to below freezing values in the presence of ice these coupled simulations yield a more realistic rapid decay in summer with dynamics included but an unrealistically small decay without dynamics simulated ice drift results yield mean drift rates of about 5 km day in good agreement with buoy drift observations but with slightly inadequate northward transport in the western weddell near the ice edge the drift rates are relatively insensitive to the ice strength near the coast however lower strengths are found to yield a decrease in northward drift rates

laser profiling of the ice surface topography during the winter weddell gyre study 1992 a laser profiler mounted on a helicopter was used to measure the surface topography of sea ice in the weddell sea the measurements were carried out during the cruise antarktis x 4 of r v polarstern as part of the winter weddell gyre study 1992 wwgs 92 the total length of the measured surface profiles amounts to 793 km the observed mean ridge heights and mean ridge spacings are fairly well correlated therefore the ridging intensity r1 which is the ratio of ridge height and spacing was used as a quantitative classifier in order to arrange the laser data into different groups at a cutoff height of 0 8 m the average ridge height and spacing are 1 16 m and 160 m at the lowermost range of ridging intensities r1 0 04 respectively the best fits to the observed ridge height distributions are achieved by negative exponentials at lower ridging intensities as a function of ridge height at the regime of highest ridging intensity as a function of the ridge height squared the distributions of ridge spacing are well described by a lognormal distribution function a simple model is used to estimate the average thickness hd and the areal fraction of ridged ice from the laser data the values of hd range from 3 1m with an areal coverage of 5 at the lowermost range of r1 to 3 7 m with an areal coverage of 31 at the uppermost range if the ridged ice is distributed as a uniform layer over a unit area the corresponding effective thickness values are 0 14 m and 1 16 m respectively mean ridge heights and spacings are determined for different cutoff heights in order to enable comparisons to other measurements the effect of ridges on the surface stress over the ice is estimated using the drag partition theory which is applicable to the regime of lowest ridging intensity the contribution of ice ridge form drag to the total wind drag for an average ridging intensity of 0 007 and a cutoff height of 0 8 m is about 35 to 40 at neutral stability if it is assumed that the aerodynamic roughness length z0 of the intervening ice surface varies between 3 3 10 4 m and 5 5 10 4 m the drag coefficient cdn ranges from 2 08 10 3 to 2 24 10 3 at a reference height of 10 m