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

chirp 2 7 khz echo characters of the south korea plateau east sea styles of mass movement and sediment gravity flow abstract the south korea plateau is a complex of ridges seamount chains troughs and a basin detailed analysis of 12 019 line km chirp 2 7 khz subbottom profiles from the south korea plateau and the eastern continental slope of korea reveals a distinctive zonal distribution of echo types depending systematically on seafloor morphology pelagites hemipelagites type i 2 and basement highs type iii 1 prevail on the ridge summits seamount chains and the upper to middle part of the eastern continental slope of korea and are commonly bounded downslope by creeps type iii 3 and slides slumps type iv 1 that occur extensively over the entire slope areas of the ridges seamount chains and eastern continental slope the mass movement deposits change downslope to debrites and turbidites types ii iii 2 iv 2 and iv 3 in the troughs and onnuri basin suggesting successive downslope evolution from slide and slump to debris flow and turbidity current the voluminous creeps slides and slumps over the entire slope areas of the plateau and eastern continental slope deeper than 300 m in water depth were most likely generated by frequent seismic shakings

arctic sea ice extent and melt onset from nscat observations nscat ku band microwave observations of the arctic sea ice cover are described on their potential use for estimating ice extent and timing of spring melt a simple comparative analysis of the nscat arctic sea ice extent and high resolution radarsat imagery suggests that the ssm i 25 ice concentration contour appears to be a good indicator of the winter arctic ice edge for spring melt onset a comparative study of nscat sea ice observations and ncep ncar surface air temperature indicates that ku band backscatter of the snow cover over multiyear ice has a clear and steep change as the surface air temperature rises above freezing this signature of melt onset should provide useful large scale estimates of the dates of melt onset with spaceborne scatterometer data a more extensive validation of the potential of this dataset is suggested

regional strike slip in the eastern continental margin of korea and its tectonic implications for the evolution of ulleung basin east sea sea of japan air gun profiles delineate a large scale strike slip fault system along the eastern continental margin of korea this system comprises two right stepping curvilinear master faults hupo and yangsan faults that are closely associated with en echelon nominal faults and reverse faults and folds these structural features indicate two phases of regional deformation in the earlier phase late oligocene to early miocene the margin experienced extensional shear strain with dextral strike slip movements along the hupo and yangsan faults that guided a pull apart opening of the pohangyoungduk basin the later phase deformation late miocene to early pliocene was governed by shortening strain that induced a convergent strike slip reactivation of the hupo fault as well as widespread contractile faulting and folding the regional deformation in the eastern korean continental margin reflects three stages of tectonic evolution of the ulleung basin 1 pull apart opening stage from late oligocene to early miocene 2 rotational opening stage with a differential rotation of the japanese arc in middle miocene and 3 back arc closing stage from the end of middle miocene to present

blending sequential scanning multichannel microwave radiometer and buoy data into a sea ice model a method is presented for determining the concentrations of open water and of several ice types using multichannel satellite passive microwave data the method uses the kalman filter and provides the best fit to a time series of data a crucial element of the procedure is a physical model of how the concentrations of ice types change with time in response to freezing melting aging of one ice type to another and creation of open water by divergence of the ice cover a measurement model relates the state of the ice cover to the multivariate microwave data the procedure offers three distinct advantages over algorithms that interpret separately data from each instant in time it provides a framework for incorporating additional data into the diagnosis of ice concentrations it takes into account the known uncertainty in the microwave observations and the pure type signatures and it allows the resolution of ice types with ambiguous signatures two examples are presented which make use of scanning multichannel microwave radiometer data and surface temperature and ice velocity data from drifting buoys to estimate the concentrations of open water first year second year and older multiyear ice for a lagrangian region of ice two other examples include melt ponds in place of second year ice some of the parameters in the physical model melt rates and in the measurement model signature of second year ice or of frozen melt ponds are unknown reasonable but arbitrary values of the unknown parameters are used in the examples

origins and paleoceanographic significance of laminated muds from the ulleung basin east sea sea of japan abstract a detailed facies analysis of long piston core sediments from the ulleung basin reveals four mud facies laminated mud crudely laminated mud bioturbated mud and homogenous mud the laminated and homogeneous muds were most likely deposited from turbidity currents whereas the bioturbated and crudely laminated muds were formed by hemipelagic pelagic sedimentation under well oxygenated and poorly oxygenated bottom water conditions respectively a detailed analysis of vertical distribution of the mud facies together with a chronostratigraphic framework derived from correlative tephra layers with known eruption ages reveals paleoenvironmental changes during the late quaternary during the period between 49 and 23 ka eustatic lowering of sea level facilitated frequent slope failure resulting in repeated deposition of fine grained turbidites on the basin floor normal hemipelagic sediments were intensively bioturbated under well oxygenated bottom water conditions during the period between 23 and 13 to 11 ka deposition from turbidity currents continued but hemipelagic sediments were non bioturbated under poorly oxygenated bottom water conditions the bottom water deoxygenation is attributed to further lowering of sea level during the last glacial period and consequent intensified stratification in the water column by freshwater supply to the nearly isolated sea primary laminae preserved in the crudely laminated mud generally exhibit low compositional bimodality in backscattered electron images which suggests low surface primary productivity and presence of superficial micro bioturbation after rapid rise of sea level at 13 to 11 ka the slopes were stabilized and pelagic sedimentation has prevailed under well oxygenated bottom water conditions

cryosphere applications of nscat data though designed to measure vector winds over the ocean new imaging techniques facilitate the use of nasa scatterometer data nscat in cryosphere studies nscat provides data of unprecedented coverage resolution and quality which when coupled with the scatterometer image reconstruction with filtering sirf algorithm enables images of spl sigma sup o at resolutions approaching 8 km over stationary targets such images are useful in ice mapping and classification and multidecadal studies are possible by comparison with seasat scatterometer sass data the utility of nscat data in polar ice studies is illustrated through a review of two cryosphere applications of nscat data 1 sea ice mapping and tracking and 2 ice sheet change in greenland and antarctica the wide swath and frequent revisit coupled with incidence and azimuth angle diversity makes nscat data very effective in mapping the extent of sea ice in greenland snow and ice facies are clearly delineated on the basis of the seasonally dependent radar backscattering cross section due to sensitivity of radar backscatter to diagenetic changes occurring at and beneath the surface comparison of nscat and sass data enables study of change in greenland between 1978 and 1996

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

high resolution sea ice motions from amsr e imagery passive microwave remote sensing imagery has proven to be a useful source for sea ice motions because of its all sky capabilities however the low spatial resolution of the passive microwave sensors has not allowed the retrieval of small scale motion details such as lead and ridge formation the nasa earth observing system advanced microwave scanning radiometer amsr e has more than double the spatial resolution of previous passive microwave sensors allowing it to track the formation of moderate sized leads and yield much more detailed and more accurate ice motion estimates comparisons with buoys indicate that amsr e motions have errors 30 lower than ice motions derived from the previous passive microwave sensors while amsr e still cannot retrieve the same level of detail as synthetic aperture radars or visible infrared sensors amsr e s complete coverage can better capture the ephemeral motions of the sea ice cover on daily and potentially sub daily timescales

antarctic circumpolar deep water a quaternary paleoflow record from the northern scotia sea south atlantic ocean in the northern scotia sea the main pathway of circumpolar deep water cpdw flows north to pass through a deep gap in the north scotia ridge before turning east into the falkland trough a sediment drift has developed on the seabed since the early middle miocene coincident with the opening of drake passage and the inception of deep water flow seismic and acoustic surveys show that the drift covers an area of 10 500 km 2 and forms a broadly asymmetrical mound up to 800 m thick there is a zone of sediment thinning along the northwestern margin the result of accentuated cpdw flow around rough ocean floor topography small debris flows originating around the margins of the drift suggest localized instability and high sediment supply four cores 3 9 m long have been recovered from the crest and margins of the drift in water depths of 3900 4300 m biostratigraphy and chemostratigraphy reveal that the longest core extends down to oxygen isotope stage 10 approx 370 ka the sediments are predominantly fine grained contourites and diatom rich hemipelagites capped by sandy silty contourites rich in the planktonic foraminifer neogloboquadrina pachyderma grain size analysis of the fine fraction finer than 4 phi 63 mm combined with radiocarbon ams dating and magnetic susceptibility provide an indication of relative cpdw strength over the last 18 ka shortly after the last glacial maximum lgm at approximately 17 ka silt modes fluctuated from 5 5 phi to up to 6 25 phi this increased current winnowing is indicative of an unstable cpdw with stormier glacial benthic conditions producing sporadic high energy currents across the drift crest and flanks at approximately 12 280 ka an increase in sediment sorting is noted indicative of a strong flow of cpdw over the drift crest suggesting an unstable and fluctuating deep water flow during deglaciation and into the holocene at approximately 10 ka cpdw flow stabilized becoming less vigorous across the drift crest and flanks with silt modes from 6 phi to 5 5 phi accompanied by increased sorting of the sediments the gross average sedimentation rate from the crest of the drift is 11 2 cm ky compared to 2 3 cm ky on the southeastern flank the unsteadiness of cpdw during glacials compared to interglacial periods may be the result of stronger wind forcing and a northward shift in the polar front older cpdw flow records from the cores suggest variable and cyclic bottom current flow corresponding to glacial interglacial episodes modern cpdw flow across the crest of the drift averages 11 6 cm s super 1 but with intermittent benthic storm activity resuspending the fines

the arctic ocean ice balance a kalman smoother estimate the methodology of kalman filtering and smoothing is used to integrate a 7 year time series of buoy derived ice motion fields and satellite passive microwave observations the result is a record of the concentrations of open water first year ice and multiyear ice that we believe is better than the estimates based on the microwave data alone the kalman procedure interprets the evolution of the ice cover in terms of advection melt growth ridging and aging of first year into multiyear ice generally the regions along the coasts of alaska and siberia and the area just north of fram strait are sources of first year ice with the rest of the arctic ocean acting as a sink for first year ice via ridging and aging all the arctic ocean except for the beaufort and chukchi seas is a source of multiyear ice with the chukchi being the only internal multiyear ice sink export through fram strait is a major ice sink but we find only about two thirds the export and greater interannual variation than found in previous studies there is no discernible trend in the area of multiyear ice in the arctic ocean during the 7 years

global warming may have slowed down the deep conveyor belt of a marginal sea of the northwestern pacific japan sea weakening of the abyssal circulation conveyor belt in the japan sea during the 20th century is deduced from the decreasing trend of bottom dissolved oxygen o2 this trend indicates a shortened o2 supply caused by too inactive conveyor belt to compensate for biological o2 consumption at the bottom of the sea recent climatic changes during the winter season in the northern japan sea may play a significant role in prohibiting the formation of surface seawater dense enough to sink to the bottom it is predicted that the japan sea bottom water will become anoxic within a few hundred years as it was in the last glacial maximum

contour current accumulation off the vema channel mouth southern brazil basin pattern of a contourite fan abstract in the southern part of the brazil basin 3 5 khz echosounding reveals the existence of a cone shaped sedimentary accumulation 4480 m depth this sediment body is interpreted as deposited by the antarctic bottom water currents aabw at the downstream exit of deep valleys cutting through the rio grande rise it is located between two major channels that prolonged northeastward the valleys into the brazil basin the vema channel in the southeast and the sao paulo abyssal gap in the northwest as a consequence most of the aabw flow is channelized in two branches deposition of the current transported particles occurs below the shear zone which takes place between the two branches the quaternary sediments consist of silty clayey muddy contourites associated with manganiferous deposits the accumulation is built by lateral migration of secondary channels and by lateral construction of lobes between the two major channels which are both well stabilized on account of a morphotectonic control on their location the entire sediment body progrades upward and downstream toward the northeast on the basis of morphological seismic and lithological arguments we would like to propose the name of contourite fan for such a contour current controlled accumulation

the vema channel physiography structure and sediment current interactions abstract the east flank of the vema channel in the southwestern atlantic is an opportune location for interpreting the pleistocene holocene record of deep thermohaline circulation the channel and the adjacent sediment covered rio grande rise intersect each of the principal sub thermocline water masses of the western atlantic we analyzed a suite of 25 giant gravity cores in transects extending between 1400 and 4150 m depth this interval includes the upper and lower branches of circumpolar water north atlantic deep water and antarctic bottom water the late pleistocene holocene sediments along these transects are pelagic carbonates with excellent stratigraphic continuity shallower and deeper regions are relatively unsuitable due to poor core recovery or widespread erosional unconformities extensive hydrographic and direct current observations near the location of our prime coring transect at 30 s indicate a notable cross channel asymmetry in the abyssal hydrography and velocity structure which is reflected in the underlying lithofacies distribution the near bottom flow field shows marked temporal and spatial variability on a local scale even in the channel axis where one would anticipate relatively steady uniform flow much of this variability appears to reflect the effects of transient mesoscale eddies rather than regional variations in the integrated north ward transport of aabw in spite of temporal variations in the flow field the nadw aabw transition zone appears to have remained remarkably stable over time scales of 10 5 10 6 yrs on geological evidence discussed elsewhere in this volume jones 1984 jones and johnson 1984 this observation is somewhat surprising because in the modern oceans the density contrast between nadw and aabw is relatively small if the transition zone between the two water masses has indeed remained relatively stationary then the density determining water properties t and s may also have remained relatively constant with only the rates of production changing if this interpretation proves correct upon further studies it implies that pale oceanographic interpretations of deep thermohaline flow should in some instances utilize geological indices of non conservative water properties e g co 2 13 c for monitoring paleocirculation changes

origin and distribution of terrestrial organic matter in the nw mediterranean gulf of lions exploring the newly developed bit index the branched and isoprenoid tetraether bit index is based on the relative abundance of nonisoprenoidal glycerol dialkyl glycerol tetraethers gdgts derived from organisms living in terrestrial environments versus a structurally related isoprenoid gdgt crenarchaeol produced by marine crenarchaeota the bit index varies between 0 and 1 representing marine and terrestrial organic matter om end members respectively hopmans et al earth planet sci lett 224 107 116 2004 in this study the applicability of the bit index to trace terrestrial om is tested in combination with other organic parameters toc c n ratio 13corg total lipid and n alkane in the gulf of lions a river dominated continental margin of the western mediterranean we analyzed a variety of soils and riverbed sediments from the continent as well as surface sediments from the shelf and canyons the bit index in soils and riverbed sediments shows high values 0 9 while it varies between 0 02 and 0 83 in marine sediments decreasing seaward from the inner shelf to the slope for marine surface sediments high bit values are associated with lower 13corg values as well as higher toc contents and higher n alkane concentrations our results confirm that the bit index can be applied in coastal marine environments in order to characterize terrestrial om as proposed by hopmans et al 2004 therefore the bit index is a useful addition to the proxies presently available for studying the origin and distribution of om in continental margins and especially valuable in multiproxy studies

studies of the antarctic sea ice edge and ice extent from satellite and ship observations abstract passive microwave derived ice edge locations in the antarctic are assessed against in situ observations from ships between 1989 and 2000 during the growth season march october the ship data agrees with satellite data very well with r2 values of 0 99 and 0 97 for the bootstrap and team algorithms respectively during the melt season november february the agreement is not so good with the passive microwave ice edge typically 1 2 of latitude south of the observations this is due to the low concentration and saturated nature of the ice and the r2 values for this period are 0 92 and 0 80 for the bootstrap and team algorithms respectively sensitivity studies show that such an offset in the summer ice edge location can cause significant errors in trend studies of the extent of sea ice cover in the southern ocean the passive microwave ice concentration at the ice edge observed by ship varies greatly averaging 14 for the team algorithm and 19 for the bootstrap comparisons between passive microwave data and sar landsat and ols data during the ice growth season show that while small scale details in ice edge location are lost the passive microwave data generally provide good and consistent representation of the higher resolution imagery

enhanced short term sediment deposition within the nazare canyon north east atlantic abstract in january and may 1999 interface sediments were sampled within the nazare canyon a large submarine canyon that deeply indents the western iberian continental margin ne atlantic at around 39 35n excess 234th profiles were established with high resolution to calculate inventories and bioturbation coefficients a northern transect at 42 n is briefly presented as a reference for the western iberian margin synthesis of these parameters is used to examine short term deposition within the nazare canyon 234thxs was always detected with significant activities on surface in most of the samples along the reference transect and in the adjacent area surface 234th excesses are about 10 20 dpm g 1 in contrast 234thxs reaches very high levels up to 170 dpm g 1 in the canyon there is a large range of variability in inventories and bioturbation rates in relation with depth and location these results show a preferential deposition in the canyon and focus in the upper and middle part of the canyon on a monthly time scale the nazare canyon appears as a significant locus of sedimentation for the western iberian margin

turbidity current sediment waves on the submarine slopes of the western canary islands two sediment wave fields have been identified on the flanks of the western canary islands of la palma and el hierro using a high quality 2 d and 3 d dataset that includes geosea and tobi imagery 3 5 khz profiles and short sediment cores the la palma sediment wave field covers some 20 000 km2 of the continental slope and rise and consists of sediment waves with wave heights of up to 70 m and wavelengths of up to 2 4 km the wave crestlines have a complex morphology with common bifurcation and a clear sinuosity waves have migrated upslope through time cores recovered from the wave field contain volcaniclastic turbidites interbedded with pelagic hemipelagic layers the wave field is interpreted as having formed beneath unconfined turbidity currents a simple previously published two layer model is applied to the waves revealing that they formed beneath turbidity currents flowing at 10 100 cm s 1 with a flow thickness of 60 400 m and a sediment concentration of 26 427 mg l the el julan sediment wave field lies within a turbidity current channel on the southwest flank of el hierro the sediment waves display wave heights of about 6 m and wavelengths of up to 1 2 km the waves are migrating upslope and migration is most rapid in the centre of the channel where the flow velocity is highest this wave field has been formed by channelised turbidity currents originating on the flanks of el hierro

changes in the modeled ice thickness distribution near the surface heat budget of the arctic ocean sheba drifting ice camp 1 in the polar oceans the ice thickness distribution controls the exchange of heat between the ocean and the atmosphere and determines the strength of the ice the surface heat budget of the arctic ocean sheba experiment included a year long field program centered on a drifting ice station in the beaufort and chukchi seas in the arctic ocean from october 1997 through october 1998 here we use camp observations and develop methods to assimilate ice thickness and open water observations into a model in order to estimate the evolution of the thickness distribution in the vicinity of the camp a thermodynamic model is used to simulate the ice growth and melt and an ice redistribution model is used to simulate the opening and ridging processes data assimilation procedures are developed and then used to assimilate observations of the thickness distribution assimilated observations include those of the thin end of the distribution determined by aircraft surveys of the surface temperature and helicopter photographic surveys and aircraft microwave estimates of the open water fraction the deformation of the ice was determined primarily from buoy and radarsat geophysical processor system rgps measurements of the ice velocity because of the substantial convergence and ridging observed in the spring and summer the estimated mean ice thickness increases by 59 from 1 53 to 2 44 m over the year in spite of a net thermodynamic ice loss for most multiyear ice

surface based passive microwave studies of multiyear sea ice multifrequency passive microwave observations are reported from surface based field experiments carried out over multiyear sea ice in the eastern arctic basin the beaufort sea the canadian archipelago and the northern greenland sea dual polarized brightness temperatures at 6 7 10 18 7 37 and 90 ghz were obtained at selected multiyear ice sites covering a wide range of surface properties considerable variation was found in the observed spectra over short distances on individual floes under winter conditions where values of ev 37 ghz ev 18 ghz ev 37 ghz ev 18 ghz ranged from nearly zero to approximately 0 08 concurrent surface characterization observations consisting of temperature density salinity and grain size profiles in the snow and the upper meter of the ice were carried out frequently in conjunction with cold regions research and engineering laboratory personnel the present analysis shows that the magnitude of the spectral gradient of emissivity is directly related to the existence and thickness of a decomposed surface ice layer with very high porosity spectra for melt ponds with a frozen surface layer closely resembled those of lake ice and show a positive spectral gradient as soon as the ponds were completely frozen their spectra became nearly the same as those for first year ice fine grained winter snow produced a mild decrease in the emissivities at 90 ghz with increasing snow thickness from 0 to 0 2 m at which point the snow appears to be optically thick during the melt season the ice emissivities e depend most strongly on whether the surface layers are experiencing temporary freezing or not under melting conditions e depends on the liquid water content only over a very small range e g 0 5 by mass at 90 ghz if the liquid water in the surface layers is freezing which can occur at intervals throughout the melt season the spectral gradient is negative with a slope which depends on the thickness of the refrozen layer the variance among emissivity spectra for multiyear ice appears to be influenced primarily by the distribution of melt ponds and by the presence of significant amounts of scattering inhomogeneities greater than 1 mm in diameter in the snow and in the upper 20 30 cm of the ice we expect the signatures of multiyear ice to be regionally dependent perhaps yielding environmental information about the arctic ice pack

paleoenvironmental changes in the japan sea during the last 85 000 years five distinct changes in the paleoenvironment of the japan sea within the last 85 000 years are revealed from the sedimentary record of a piston core recovered from the oki ridge changes in both surface and deepwater conditions are registered by changes in lithology calcium carbonate content organic carbon content oxygen and carbon isotope ratios and microfossil assemblages including calcareous nannoplankton diatoms radiolaria and foraminifera between 85 and 27 ka the warm tsushima current did not flow into the japan sea and cold surface water conditions prevailed environments at the seafloor fluctuated between dysaerobic to weakly oxic conditions between 27 and 20 ka freshwater input to the japan sea probably from the huang ho river in china stratified the water column and the severe anoxic conditions eliminated most benthic fauna between 20 and 10 ka the cold oyashio current flowed into the japan sea through the tsugaru strait reestablishing deepwater ventilation shallow water benthic assemblages of the north pacific ocean subsequently colonized the japan sea and occupied the vacant niches of the deep basins between 10 and 8 ka the foraminifer compensation level fcl gradually rose to a depth shallower than 1000 m and bottom conditions changed from dysaerobic to oxic at 10 ka the warm tsushima current started to flow into the japan sea through the tsushima strait to establish the modern oceanographic regime which has existed since 8 ka the eustatic sea level during the last glacial maximum was above the sill depths 130 m of the tsushima and tsugaru straits assuming that tectonic movements at these straits were negligible for the last 20 ka

sea ice melting and floe geometry in a simple ice ocean model a coupled sea ice ocean numerical model has been developed that addresses the role of floe geometry during summertime melting the model contains a diagnostic equation for average floe diameter in addition to the usual prognostic equations for ice volume per unit area and ice concentration the partition between melting on the top bottom and lateral side surfaces of floes is examined using time dependent simulations with differing initial average floe diameters the different parameterizations for bottom and lateral melting in the literature are also compared and found to vary significantly the results show that lateral melting is important only for floes with diameters less than o 30 m given atmospheric thermal forcing typical of the central arctic in summer this means that the decrease in ice concentration over the summer is a strong function of floe diameter in keeping with simple geometrical arguments in all cases about 80 of the net thermal energy that enters the ocean through leads goes toward melting ice while the rest warms the ocean

the interplay between turbidity and contour current processes on the columbia channel fan drift southern brazil basin abstract the distribution of sedimentary processes and associated deposits on the columbia channel fan drift system southern brazil basin were investigated on the basis of 3 5 khz echosounding profiles and core lithology this system is composed of a sediment levee elongated downslope with a w e then sw ne trend bounded to the south by the columbia channel and to the north by the vitoria trindade seamounts turbidites are widespread on the shallowest part of the system 1 thick turbidite sequences composed of quartz rich sandy material originating from the upper continental margin are found in the axis of the channel the turbidity currents do not significantly overflow the northern levee where only sparse and thin silty muddy turbidites occur close to the axis of the channel 2 the major part of the levee shows quartz poor mica and foram rich turbidite material originating from the vitoria trindade seamounts the abundance of this material decreases southwards and eastwards the whole area is swept by the northward flowing antarctic bottom water contour current deposited muds are dominant on the southern flank of the columbia channel free of any turbidite supply as a consequence of the coriolis effect and on the deepest part of the northern levee remote from turbidite source areas however the contour currents interplay with the turbidity currents on the shallowest part of the levee contour current deposited muds are interbedded with silty sandy turbidite sequences and a part of the muddy material has probably been pirated from the finer tails of the turbidity flows the other part being transported from southernmost areas by the bottom currents the interplay of both processes is also responsible for the deposition of silty turbidite beds top truncated by contour currents and overlain by bioturbated muddy contourites

seasonal ice area and volume production of the arctic ocean november 1996 through april 1997 1 the radarsat geophysical processor system rgps produces estimates of sea ice motion deformation and thickness of the arctic ocean sea ice cover from time sequential synthetic aperture radar sar imagery acquired by radarsat based on these products we summarize the evolution of a region of the arctic ocean ice cover in terms of its area change ice volume production and multiyear ice coverage over a 6 month period between 7 november 1996 through 30 april 1997 this region encompasses a large part of the western arctic ocean the initial ice area covers 2 52 106 km2 at the end of april this region covers 2 59 106 km2 a net divergence of 3 over the period thin ice 0 20 cm typically covers 2 of this area the rgps estimates only the thickness distribution of sea ice volume produced by openings and closings of the ice cover since the initial observation thus only the ice volume of the seasonal ice cover can be determined between november 1996 and april 1997 1000 km3 0 4 m of sea ice is produced the amount stored in undeformed ice and ridged ice is dependent on the character of the redistribution function the rgps products also provide estimates of multiyear ice coverage from the time series of multiyear ice coverage we estimate that nearly 83 of the area is covered by multiyear ice for more detailed examination of the regional dependence of ice cover deformation volume production and my ice coverage the larger region is divided into five subregions where possible we provide an analysis of the errors in the above estimates in cases where quantification of the uncertainty is not feasible we list the potential error sources there are remaining sources of uncertainty in these calculations that remain unquantified but at this time there are no adequate in situ or remote sensing data for comprehensive evaluation of the above estimates

sea ice motion from satellite passive microwave imagery assessed with ers sar and buoy motions observing the motion of sea ice from space is analogous to observing wind stress over the wet oceans both provide surface forcing for modeling ocean dynamics ice motion also directly provides the advective component of the equations governing the mass balance of the sea ice cover thus its routine observation from space would be of great value to understanding ice and ocean behavior to demonstrate the feasibility of creating a global multidecadal ice motion record from satellite passive microwave imagery and to quantitatively assess the errors in the estimated ice motions we have tracked ice every 3 days in the arctic ocean and daily in the fram strait and baffin bay during the 8 winter months from october 1992 to may 1993 and daily in the weddell sea during the 8 winter months from march to october 1992 the method which has been well used previously involves finding the spatial offset that maximizes the cross correlation of the brightness temperature fields over 100 km patches in two images separated in time by from 1 to 3 days the resulting ice motions are compared with contemporaneous buoyand sar derived ice motions the uncertainties in the displacement vectors between 5 and 12 km are better than the spatial resolution of the data both 85 ghz data with 12 km spatial resolution and 37 ghz data with 25 km resolution are tracked these trials with the 37 ghz data are new and show quite surprisingly that the error is only about 1 km larger with these data than with the 12 km 85 ghz data errors are typically larger than average in areas of lower ice concentration in the most dynamic regions particularly near the ice edge in the barents and greenland seas and in zones of high shear these passive microwave ice motions show a large increase in spatial detail over motion fields optimally interpolated from buoy and wind observations especially where buoy data are virtually absent such as near coasts and in some passages between the arctic ocean and its peripheral seas the feasibility of obtaining ice motion from the 37 ghz data in addition to the 85 ghz data should allow an important record of ice motion to be established for the duration of the scanning multichannel microwave radiometer smmr special sensor microwave imager ssm i and future microwave sensors that is from 1978 into the next millenium

crustal deformation at the sumatran subduction zone revealed by coral rings analyses of coral rings grown in the interval 1970 1997 reveal a geographically distinct pattern of interseismic uplift off sumatra s western coast at distances less than 110 km from the sumatran trench coral reefs are submerging as fast as 5 mm y at 130 and 180 km distance from the trench they are emerging at similar rates we suggest that a locked or partially locked patch located above 30 km depth on the upper surface of the subducting oceanic plate generates this pattern

depletion of perennial sea ice in the east arctic ocean 1 the extent of perennial sea ice in the east arctic ocean 0 180 e decreased by nearly one half with an abrupt reduction of 0 95 106 km2 while the west arctic ocean 0 180 w had a slight gain of 0 23 106 km2 between 2004 and 2005 as observed by satellite scatterometer data during november december the net decrease in the total perennial ice extent is 0 72 106 km2 about the size of texas perennial ice in the east arctic ocean continued to be depleted with an areal reduction of 70 from october 2005 to april 2006 with the east arctic ocean dominated by seasonal sea ice a strong summer melt may open a vast ice free region with a possible record minimum ice extent largely confined to the west arctic ocean simultaneous scatterometer measurements of sea ice and winds will be crucial for sea ice monitoring and forecasts

slope stability change from late pleistocene to holocene in the ulleung basin east sea japan sea abstract a wide variety of mass movement deposits prevail along the entire margin of ulleung basin overlain by a hemipelagic mud unit 1 2 m thick the boundary between the lower turbidite sequence and the upper hemipelagic mud on the basin plain is distinct and approximately coincides with the well known basin wide ash layer ulleung ash of early holocene age in the absence of significant terrigenous sediment input the lithologic change from the turbidite to hemipelagic mud may reflect physical effects of glacio marine eustatic sea level change sea level lowering during the glacial period may have generated excess pore pressure within the sediments caused by reducing hydrostatic confining pressure and facilitated triggering of the deep water slope failure by earthquakes storm waves may also have affected the uppermost slope area to induce small scale slope instabilities during the lowered sea level stand these glacial factors destabilizing the slope appear to have enhanced large scale slope failures during the late pleistocene in contrast the topmost hemipelagic mud attests to a stable slope phase associated with raised sea level in the holocene consistent with the infinite slope stability analyses calculations of the sedimentation rates based on c 14 dates of several ash layers indicate that the pre holocene turbidites on the basin plain had accumulated at an average rate of 40 cm 1000 years with a minimum recurrence interval of 50 years during the late pleistocene mass flux estimations between the slumps and turbidites suggest a predominance of the nondisintegrative mode of slope failures in the ulleung basin in each event of slope failure most of the failed mass rested on the slope as slide slump blocks and only its meager portions were deposited on the basin plain as turbidite layers

arctic sea ice signatures for passive microwave algorithms passive microwave satellite data can be used to estimate the concentrations of three surface types open water first year ice and multiyear ice these estimates are made with an algorithm that requires knowing the microwave signatures of each of these three surface types for the scanning multichannel microwave radiometer the algorithm proposed by cavalieri et al 1984 known as the smmr team algorithm is widely used two unsatisfying properties of this algorithm are 1 its estimates of multiyear ice concentrations are much lower than its estimates of summer ice concentrations and are also significantly lower than independent estimates of arctic ocean multiyear ice and 2 it produces variations in estimated concentration that appear to be caused by spatial and temporal variations in the signatures we examine two alternative sets of signatures one set varies temporally but not spatially and is defined by the modes of major peaks in histograms of brightness temperature the other set is defined as the overall means of the temporally varying signatures we call these new constant signatures an estimate of the average bias of the winter multiyear ice is derived and a corresponding correction applied to the new constant signatures both sets of new signatures have essentially the same precision 0 05 fractional area for winter ice concentration 0 10 for summer ice concentration and 0 15 to 0 3 for winter multiyear ice concentration these error estimates are upper bounds to the true precision especially for multiyear ice for which some true concentration changes are included in the variability the precision estimates include all spatial and temporal signature variability and are compatible with estimates of sea ice emissivity variability given in the literature because the temporally varying signatures provide only a slightly better precision we prefer the new constant signatures both sets of new signatures result in about 0 6 to 0 7 winter multiyear ice for the arctic ocean substantially more than the 0 3 to 0 4 computed using the original team algorithm signatures and in the same range as several independent estimates of the multiyear ice 0 54 to 0 75

environmental and biological effects on the stable isotope composition of recent deep sea benthic foraminifera from the western mediterranean sea abstract the influence of microhabitat organic matter flux and metabolism on the stable oxygen and carbon isotope composition of live rose bengal stained and dead empty tests deep sea benthic foraminifera from the gulf of lions western mediterranean sea have been studied the total range of observed foraminiferal isotope values exceeds 1 0 for 18o and 2 2 for 13c demonstrating a wide range of coexisting disequilibria relative to 18o of equilibrium calcite 18oeq and 13c of bottom water dissolved inorganic carbon 13cdic the mean 18o values reveal strongest disequilibria for the studied epifaunal to shallow infaunal species cibicidoides pachydermus uvigerina mediterranea uvigerina peregrina while values approach equilibrium in deep infaunal species globobulimina affinis globobulimina pseudospinescens the mean 13c values decrease with increasing average living depths of the different species thus reflecting a dominant microhabitat pore water signal at the axis of the lacaze duthier canyon a minimum 13cdic pore water gradient of approximately 2 1 is assessed for the upper 6 cm of the surface sediment although live individuals of u mediterranea were found in different depth intervals their mean 13c values are consistent with calcification at an average living depth around 1 cm the deep infaunal occurrence of u mediterranea specimens suggests association with macrofaunal burrows creating a microenvironment with geochemical characteristics similar to the topmost centimeter this also explains the excellent agreement between stable isotope signals of live and dead individuals the ontogenetic enrichment in both 18o and 13c values of u mediterranea suggests a slow down of metabolic rates during test growth similar to that previously observed in planktic foraminifera enhanced organic carbon fluxes and higher proportion of resuspended terrestrial organic material at the canyon axis are reflected by 13c values of u mediterranea on average 0 58 lower than those from the open slope these results demonstrate the general applicability of the 13c signal of this species for the reconstruction of past organic matter fluxes in the mediterranean sea further studies on live specimens are needed for a more quantitative paleoceanographic approach

evolution of microwave sea ice signatures during early summer and midsummer in the marginal ice zone emissivities at frequencies from 5 to 94 ghz and backscatter at frequencies from 1 to 17 ghz were measured from sea ice in fram strait during the marginal ice zone experiment in june and july of 1983 and 1984 the ice observed was primarily multiyear the remainder first year ice was often deformed results from this active and passive microwave study include the description of the evolution of the sea ice during early summer and midsummer the absorption properties of summer snow the interrelationship between ice thickness and the state and thickness of snow and the modulation of the microwave signature especially at the highest frequencies by the freezing of the upper few centimeters of the ice

the formation and morphology of ice stalactites observed under deforming lead ice during the leadex main field experiment held in april 1992 in the alaskan beaufort sea a number of large ice stalactites were observed growing under young lead ice formation of the stalactites was associated with rafting of the thin highly saline ice the rafting caused the brine to drain rapidly from the ice at a temperature well below the freezing point of the surrounding water which in turn caused ice to form in a hollow cylinder around the brine plume within a 15 h period after the rafting event the stalactites which were located approximately 10 m apart in a line along the up wind edge of a 150 m wide lead had grown to a length of 2 m a detailed structural analysis of the upper part of one of these stalactites revealed that the interior channel down which the brine flowed was bounded by a zone of frazil ice that developed into a shell of columnar ice the growth of the columnar ice was directed radially outward and the c axes of these crystals were oriented perpendicular to their growth direction development of the stalactites illustrates the impact ice deformation can have on the process of brine rejection in freezing leads and potentially on the thermohaline structure of the upper ocean in ther immediate vicinity of the lead

characterization of gas hydrate reservoirs by integration of core and log data in the ulleung basin east sea abstract examinations of core and well log data from the second ulleung basin gas hydrate drilling expedition ubgh2 drill sites suggest that sites ubgh2 2 2 and ubgh2 6 have relatively good gas hydrate reservoir quality in terms of individual and total cumulative thicknesses of gas hydrate bearing sand hybs beds in both of the sites core sediments are generally dominated by hemipelagic muds which are intercalated with turbidite sands the turbidite sands are usually thin to medium bedded and mainly consist of well sorted coarse silt to fine sand anomalies in infrared core temperatures and porewater chlorinity data and pressure core measurements indicate that gas hydrate occurrence zones ghoz are present about 68 155 mbsf at site ubgh2 2 2 and 110 155 mbsf at site ubgh2 6 in both the ghoz gas hydrates are preferentially associated with many of the turbidite sands as pore filling type hydrates the hybs identified in the cores from site ubgh2 6 are medium to thick bedded particularly in the lower part of the ghoz and well coincident with significant high excursions in all of the resistivity density and velocity logs gas hydrate saturations in the hybs range from 12 to 79 with an average of 52 based on pore water chlorinity in contrast the hybs from site ubgh2 2 2 are usually thin bedded and show poor correlations with both of the resistivity and velocity logs owing to volume averaging effects of the logging tools on the thin hybs beds gas hydrate saturations in the hybs range from 15 to 65 with an average of 37 based on pore water chlorinity in both of the sites large fluctuations in biogenic opal contents have significant effects on the sediment physical properties resulting in limited usage of gamma ray and density logs in discriminating sand reservoirs

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

authigenic p formation and reactive p burial in sediments of the nazare canyon on the iberian margin ne atlantic profiles of different forms of sedimentary phosphorus were measured at four sites at the iberian margin ne atlantic which were chosen on the basis of differences in depositional environment a shelf site 113 m a mid slope station 1387 m and two stations at the head 396 m and base 3097 m of the nazarecanyon the sediment was sequentially extracted for fe bound p carbonate fluorapatite cfa biogenic p caco3 bound p and detrital ca p and non sequentially for total p and inorganic p where the difference between total and inorganic p was assumed to be organic p measurements of organic carbon and nitrogen citrate dithionite bicarbonate and citrate ascorbate bicarbonate extractable fe carbon oxidation rates fe reduction rates phosphate effluxes and sedimentation rates were used to quantify the cycling and burial of phosphorus at each site cfa formation was observed only in sediments of the nazarecanyon where enhanced rates of organic matter decomposition and fe reduction provided the necessary conditions the concentrations of reactive p were similar at all sites but the sediment accumulation rates differed greatly the high bulk accumulation rate at the base of the canyon results in a reactive p burial rate exceeding those estimated for continental margins including the iberian margin by an order of magnitude the estimated p burial efficiency is smallest at the slope station 3 24 reasonably high 63 86 at the shelf and head of the canyon stations and extremely high s 97 at the base of the canyon we propose that local depositories such as those at the base of canyons may be key sites for reactive p burial 2002 elsevier science b all rights reserved

sea ice identification using dual polarized ku band scatterometer data this paper describes a classification algorithm using dual polarized scatterometer measurements to identify the edge of the sea ice cover the distinct polarization scattering signatures of sea ice and open water are discussed and illustrated with the dual polarized radar measurements from the seasat a scatterometer sass the analysis of sass data suggests that the ratio of vertical and horizontal polarization backscatter denoted as the copol ratio is a useful discriminator of sea ice and open ocean a simple classification algorithm using the thresholds of the copol ratio and backscatter levels is proposed the feasibility of this algorithm is demonstrated using the sass data from the single sided dual polarization mode the results indicate that the dual polarized measurements from the nasa scatterometer nscat can be used to produce routine maps of sea ice edges

paleogene neogene depositional history of the middle u s atlantic continental rise mixed turbidite and contourite depositional systems abstract the construction of the middle u s atlantic continental rise from late paleogene to late pliocene time included downslope sediment gravity flows and alongslope contourite deposition some previous studies have suggested that contour following bottom currents were the dominant control on depositional patterns depositional relief from two large contourite drifts largely built in late miocene to late pliocene time continue to dominate present day lower rise morphology detailed seismic sequence mapping presented here suggests that significant turbidite fan systems also were active and are preserved in the stratigraphic section a single thick depositional sequence is mapped for oligocene to middle miocene sediments deposited when inferred fan systems off the norfolk washington canyons were reworked by bottom currents along the lower rise to form the proto hatteras outer ridge detailed mapping of three late miocene to late pliocene depositional sequences indicates that fan channel systems were active at the same time large contourite drifts were being constructed sediment delivered to the lower rise by these elongate turbidite systems undoubtedly was an important local source for construction of the hatteras outer ridge and through entrainment and resuspension was an important source for regional contourite deposition controlled by the deep western boundary undercurrent we suggest that submarine fans and current controlled sediment drifts may develop simultaneously as companion systems types of fan drift interaction include current only modification of fans transitional fan to drift and adjacent or overlapping submarine fan and sediment drift deposition

the under ice thickness distribution of the arctic basin as recorded in 1958 and 1970 the uss nautilus ssn 571 was the first vessel to cross the arctic basin via the north pole in early august 1958 during this expedition almost continuous acoustic under ice thickness profiles were recorded in august 1970 uss queenfish ssn 651 retraced nautilus route yielding the only duplicate transect of under ice topography across the arctic basin comparisons of the statistical analysis of the under ice draft measurements obtained through use of wide beam and narrow beam and narrow beam only acoustic profilers by nautilus and queenfish respectively along the coincidental route are presented geographic areas found to have distinct under ice characteristics and ice composition are identified the under ice statistics of both cruises are considered in relation to representative field observations and modeling results of other researchers principal findings are 1 nautilus recorded generally more severe ice conditions within the canada basin than did queenfish 12 years later overall mean drafts were 3 08 and 2 39 m respectively 2 the under ice topography becomes progressively more severe when proceeding from the canadian to the eurasian side of the arctic basin 3 the canada basin may contain the most moderate under ice topography and the greatest number of open water and refrozen polynyas and leads within the central arctic basin 4 the makarov and amundsen basins and the arctic mid ocean ridge may contain some of the most severe under ice topography within the arctic basin and 5 the present study indicates an overall arctic basin mean of 3 4 open water new ice less than 30 cm in summer

fossil contourites a critical review abstract despite three decades of study there is still great controversy over the recognition and interpretation of fossil contourites exposed in ancient series on land in order to best examine this problem we briefly review the evidence from modern systems including the many examples of cenozoic contourites that have been recovered from dsdp odp drilling on major drifts in the present day oceans the range of contourite facies described from both deep water 2000 m and mid water 300 2000 m drifts are mostly fine grained bioturbated and homogeneous often with a distinct bedding cyclicity and with some coarser grained sandy contourites developed under higher energy bottom currents there are also a number of current controlled sediment bodies that have formed in outer shelf upper slope settings 50 300 m under the influence of counter currents underflows and major surface currents these are not considered contourites sensu stricto but may be mistaken as such in ancient examples the most commonly described fossil contourites in the literature have been interpreted by the authors concerned as bottom current reworked turbidites however a critical review suggests that these are the facies most subject to misinterpretation and many of the sediments claimed as fossil contourites are almost certainly fine grained turbidites whereas others were more likely formed under outer shelf upper slope current systems there remain very few ancient examples that are more closely comparable to modern contourites these include the cretaceous talme yafe formation in israel the ordovician jiuxi drift in china and parts of the paleogene lefkara formation cyprus and the neogene misaki formation in japan we present a set of possible criteria for the recognition of fossil contourites and bottom current reworked turbidites

variability of fram strait ice flux and north atlantic oscillation we estimate the winter sea ice export through the fram strait using ice motion from satellite passive microwave data sea ice motion october may is obtained by tracking the displacement of common features in sequential 85 and 37 ghz brightness temperature fields the average winter area flux over the 18 year record 1978 1996 is 670 000 km2 7 of the area of the arctic ocean the winter area flux ranges from a minimum of 450 000 km2 in 1984 to a maximum of 906 000 km2 in 1995 the daily monthly and interannual variabilities of the ice area flux are high there is an upward trend in the ice area flux over the 18 year record the average winter volume flux over the winters of october 1990 through may 1995 is 1745 km3 ranging from a low of 1375 km3 in the 1990 flux to a high of 2791 km3 in 1994 the sea level pressure gradient across the fram strait explains more than 80 of the variance in the ice flux over the 18 year record we use the coefficients from the regression of the time series of area flux versus pressure gradient across the fram strait and ice thickness data to estimate the summer area and volume flux the average 12 month area flux and volume flux are 919 000 km2 and 2366 km3 we find a significant correlation r 0 86 between the area flux and positive phases of the north atlantic oscillation nao index over the months of december march correlation between our 5 years of volume flux estimates and the nao index gives r 0 56 during the high nao years a more intense icelandic low increases the gradient in the sea level pressure by almost 1 mbar across the fram strait thus increasing the atmospheric forcing on ice transport correlation is reduced during the negative nao years because of decreased dominance of this large scale atmospheric pattern on the sea level pressure gradient across the fram strait

evidence for thinning of the arctic ice cover north of greenland in may 1987 a british submarine carried out an ice profiling experiment in the arctic ocean in which the route closely approximated that of an earlier voyage in october 1976 over a zone extending more than 400 km to the north of greenland there is evidence of a significant decrease in mean ice thickness in 1987 relative to that found in 1976 this thinning amounts to a loss of volume of at least 15 over an area of 300 000 km2 the nature of the ice thickness distributions suggests that the thinning is primarily associated with the presence of a larger fraction of young and first year ice a consequence of wind driven divergence in the ice cover during the months preceding the 1987 observations such a large fluctuation in a region previously believed to possess consistently high ice thicknesses illustrates the importance of monitoring arctic ice thickness more systematically to determine whether such fluctuations fall within the limits of normal inter annual variability

backscatter characteristics of the winter ice cover in the beaufort sea the microwave backscatter statistics of the sea ice cover in the winter beaufort sea are characterized using c band synthetic aperture radar sar data collected by the european earth resources satellite 1 sea ice backscatter signatures were sampled from sar image data collected during the winter of 1991 1992 and winter of 1992 1993 the spatial and temporal variabilities of the backscatter signatures of different ice types are discussed the results show considerable seasonal stability of the backscatter signature of multiyear ice as well as of first year ice small amplitude regional variations of the multiyear ice backscatter can be observed consistent contrast between multiyear ice and first year ice is maintained throughout the season the highest radiometric variability is observed in sea ice in leads on the basis of these observations the backscatter from the principal ice types multiyear and first year are consistent with scatterometer observations and can be easily identified under winter conditions correlations of the regional variations of multiyear ice signatures to physical processes are suggested

assimilation of ice motion observations and comparisons with submarine ice thickness data 1 aided by submarine observations of ice thickness for model evaluation we investigate the effects of assimilating buoy motion data and satellite ssm i 85 ghz ice motion data on simulation of arctic sea ice the sea ice model is a thickness and enthalpy distribution model and is coupled to an ocean model ice motion data are assimilated by means of optimal interpolation assimilating motion data particularly from drifting buoys significantly improves the modeled ice motion reducing the error to 0 04 m s 1 from 0 07 m s 1 and increasing the correlation with observations to 0 90 from 0 66 without data assimilation the modeled ice moves too slowly with excessive stoppage assimilation leads to more robust ice motion with substantially reduced stoppage which in turn leads to strengthened ice outflow at fram strait and enhanced ice deformation everywhere enhanced deformation doubles the production of ridged ice to an arctic ocean average of 0 77 m yr 1 and raises the amount of ridged ice to half the total ice volume per unit area of 2 58 m assimilation also significantly alters the spatial distribution of ice mass and brings the modeled ice thickness into better agreement with the thickness observed in four recent submarine cruises reducing the error to 0 66 m from 0 76 m and increasing the correlation with observations to 0 65 from 0 45 buoy data are most effective in reducing model errors because of their small measurement error ssm i data because of their more complete spatial coverage are helpful in regions with few buoys particularly in coastal areas assimilating both ssm i and buoy data combines their individual advantages and brings about the best overall model performance in simulating both ice motion and ice thickness

late quaternary sedimentary processes and variations in bottom current activity in the ulleung interplain gap east sea korea abstract a detailed facies analysis of core sediments from the ulleung interplain gap uig reveals ten sedimentary facies which reflect a variety of sedimentary processes volcaniclastic high concentration sediment gravity flows low density turbidity currents pelagic settling under either well or poorly oxygenated bottom water conditions marine fallout of tephra hampered sedimentation by bottom currents top truncation of turbidites by bottom current reworking and mn carbonate precipitation under changing bottom water oxygenation states distribution of the facies in the cores integrated with echo characters of high resolution subbottom profiles delineates spatial and temporal changes in sedimentary processes influenced by variations in bottom current activity during the late quaternary the glacial 15 ka sediment units from the ulleung interplain channel uic an erosional axial channel system in the uig consist mainly of manganiferous and muddy contourites interbedded with coarse grained volcaniclastic turbidites or debrites and non bioturbated pelagites this indicates prevalent activity of bottom currents rarely interrupted by volcaniclastic high concentration sediment gravity flows and deep water stagnations which resulted in anoxic bottom water conditions on the other hand the glacial units of the southeastern margin of the uic where upslope migrating sediment waves developed are generally dominated by alternating fine grained turbidites and bioturbated or non bioturbated pelagites this suggests that frequent turbidity currents derived from upslope mass wasting were responsible for the generation of the sediment waves the post glacial

the early neogene continental rise off the eastern united states abstract single and multichannel seismic data were used to investigate depositional components comprising the late oligocene middle miocene constructional phase of the united states atlantic continental rise in the georges bank blake plateau region the seismic sequence studied was bounded by the eocene oligocene age horizon a u unconformity at the base and a newly defined late middle miocene age horizon g at the top late oligocene middle miocene accretion onlapping the paleocontinental slope and downlapping onto horizon a u basinward was derived primarily from erosion of the uplifted central appalachian mountains this accretion up to 3 2 km thick was characterized by seven depocenters the lower paleocontinental slope upper rise depocenters situated off southern new england and the delmarva peninsula were interpreted as deep sea fan complexes or a broadly overlapping series of sedimentary blankets a whereas the closely associated oceanographer and wilmington depocenters were inferred to be levee complexes immediately north of the developing blake bahama outer ridge two n ne oriented sediment ridges that were probably built by gulf stream flow during an early miocene sea level lowstand were observed on the lower continental rise the proto hatteras and mytilus outer ridges from 0 4 to 0 8 km thick were probably formed from the wilmington and oceanographer levee complexes in early middle miocene time through the interaction of the growing levee complex with the sw moving abyssal current late middle miocene 12 11 5 ma bottom current erosion created the horizon g unconformity and brought to an end this initial stage of continental rise construction nevertheless the basic morphological framework that controlled late neogene and quaternary continental rise evolution was now in place

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

trophic control of benthic foraminiferal abundance and microhabitat in the bathyal gulf of lions western mediterranean sea surface sediment was sampled at two bathyal sites in the southwestern gulf of lions in the western mediterranean sea in february and august 1997 to study the distribution and microhabitat of living rose bengal stained deep sea benthic foraminifera both standing stock and diversity of the faunas and the microhabitat of distinct species mirror the trophic situation and the depth of the oxidised layer at the different sites our results suggest that the faunas do not comprise highly opportunistic species and are adapted to rather stable environments in the axial channel of the lacaze duthiers canyon organic matter fluxes are enhanced due to advective transport of organic matter resulting in elevated oxygen consumption rates in the surface sediment and a rather thin oxidised layer the corresponding benthic foraminiferal fauna is characterised by rather high standing stock and diversity and a well developed deep infauna in addition to freshly deposited phytodetritus more degraded organic matter seems to be an important food source in contrast at the open slope organic matter fluxes and oxygen consumption rates in the surface sediment are lower and the oxidised layer is much thicker than inside the canyon the corresponding benthic foraminiferal fauna comprises mainly epifaunal and shallow infaunal species with much lower standing stocks and clear differences between february and august in august standing stocks are higher and the average living depths of most species shift towards the sediment surface these differences can be attributed to patchiness or represent a seasonal trophic signal

late quaternary sedimentation in the ulleung interplain gap east sea korea the ulleung interplain gap uig is a deep 2300 2700 m passage which has served as a conduit for deep water circulation between the ulleung and japan basins a detailed analysis of chirp 2 7 khz subbottom profiles ca 6270 linekm and nine sediment cores 8 6 11 4 m long together with age data of tephra layers and four ams 14 c from the uig and the adjacent areas reveals complex sedimentation caused by an interaction between bottom currents and mass flows during the lastand post glacial periods from high resolution subbottom data rock basement slide slump rock fall deposits mass flow chutes channels mass flow deposits bottom current deposits and a large scale bottom current channel system are recognized core sediments consist of various deposits of turbidites muddy contourites manganiferous contourites and pelagic hemipelagic sediments based on vertical distribution of sedimentary facies together with a chronostratigraphic framework core sediments can be divided into units i f15 ka the extensive mass flow deposits with slope failures on the entire slopes of topographic highs around the uig and the dominant turbidites in unit ii f15 ka suggest that a relatively large amount of sediment was delivered into the uig by frequent mass flows recurrence intervals of ca 250 500 years in the upper unit ii during the last glacial period erosion or hampered sedimentation by bottom currents is indicated by the truncated reflectors of channel walls and muddy manganiferous contourites in the ulleung interplain channel uic along the uig interbedded turbidites in the uic floor reflect that some large scale mass flows intermittently entered into the uic the uic has an asymmetric channel flank geometry the southeastern flank shows a gentle wide mound morphology of mass flow deposits derived from large scale slope failures on the slopes of the oki bank reflecting a dominance of downslope gravitational processes over alongslope bottom currents in contrast the northwestern flank is characterized by a narrow steep geometry of mass flow deposits where a relatively small amount of sediment derived from the slopes of the south korea plateau could not overcome bottom current activity the dominant muddy and manganiferous contourites with rare turbidites in unit i f15 ka reflect intensified bottom currents and infrequent slope failures recurrence intervals of ca 1700 5000 years during the post glacial period these

seismic patterns of a muddy contourite fan vema channel south brazilian basin and a sandy distal turbidite deep sea fan cap ferret system bay of biscay a comparison abstract the aim of this paper is to discriminate the depositional facies geometries and mechanisms of deposition of contouritic fans from those of turbidite distal fans with a view to provide better resolution of reservoir prediction two examples are analysed the vema contouritic drift in the south brazilian basin and the cap ferret turbiditic fan in the bay of biscaye the vema contourite fan is a neogene mud rich accumulation 200 400 m thick fed by antarctic bottom water bottom currents and located downstream of the rio grande rise it forms one single mound fan shaped body in between two major channels and where the main part of the deep circulation is funnelled into as a result of the morphological and hydrological background the comourite drift progrades mostly downstream the accumulation was built as several depositional units channel levee systems bounded by widespread discontinuities showing erosional patterns this resulted from episodes of strong and or unstable current activity producing the discontinuities alternating with periods of relatively weak and stable currents and major deposition the pliocene quaternary cap ferret distal deep sea fan is a thick 500 m sand rich turbiditic accumulation fed directly by an uplifting mountain range the accumulation is developed downstream of a main turbiditic feeder channel and the volume of sediment involved is much higher than for the vema contourite fan it shows a complex network of shallow channels and low relief levees which merge downstream into thin sandy sheet like deposits several depositional units are stacked vertically each unit is built by the lateral migration of a channel levee system the stacking pattern of the successive units is prograding towards the basin the presence of major discontinuities cutting throughout a whole accumulation and the fairly irregular geometry of the channel levee deposits absence of any obvious migrating trend appear to be the most distinctive features of a contourite fan on the other hand the lateral migration of the channel level geometries and the presence of erosional surfaces of limited extent and restricted to the channels are the main diagnostic features of a distal turbidite fan otherwise the seismo facies are fairly similar in both sedimentary bodies

discrimination of sediment provenance using rare earth elements in the ulleung basin east japan sea abstract in order to discriminate the origins of ulleung basin east japan sea sediments using rare earth elements rees sediments from 15 box cores and one piston core collected in the shelf slope and basin were analyzed for major elements al fe ca and mn and rees the major sedimentary components in this basin were presumed to be detrital materials from land even in the basin sediments based on al and organic contents carbon and opal post depositional recycling processes involving fe and mn were identified in the basin sediments thus the ce anomaly and the fractionation factors of light rees lrees and middle rees mrees relative to heavy rees hrees could not be used as provenance indicators in the deep basin sediments 2000 m of water depth based on a feasibility check using their covariation with fe and mn for the shelf slope and basin b sites near islands water depths of 1200 1800 m regions the eu anomaly lreen hreen and mreen hreen could be successfully used to discriminate possible provenances including nakdong river sediments nrs chinese river sediments crs ulleungdo volcanic rocks uvr and dokdo volcanic rocks dvr from the provenance indicators slope as well as the shelf sediments called the korea strait shelf mud kssm in the ulleung basin can be regarded as mixtures of nrs and crs with decreasing portions of nrs in the kssm with distance from the nakdong river basin b sediments were mixtures of uvr or dvr and crs these findings can be explained if sediments discharged from the nakdong river were transported and deposited kssm northward within the strong coastal front in normal periods and if sediment flumes from summer floods flowed out across the coastal front were carried with the tsushima warm current and then deposited in the slope area this study indicated that crs were very important detrital sediments and that ree compositions can be successfully used as a provenance indicator in even hemipelagic sediments close to land

detailed japan sea paleoceanography during the last 25 kyr constraints from ams dating and δ18o of planktonic foraminifera abstract we have reconstructed paleoceanographic changes in the japan sea for the period from the last glacial maximum lgm to the present using expanded paleoclimate proxy records from two cores together with previously published results from three others a suite of new accelerated mass spectrometer ams 14 c dates provides chronologies that differ from earlier age models and suggest correlation between conditions in the japan sea changes in the north pacific and global sea level and climate changes we present evidence that reduced salinity of the japan sea surface water during the late pleistocene was due primarily to the increased importance of the precipitation evaporation balance at a time when lowered sea level had reduced water exchange with the pacific to a few percent of the present value

a naive zero dimensional sea ice model a single observation of the microwave brightness temperature over sea ice cannot determine the composition of the ice surface in terms of the three constituents open water first year ice and multiyear ice the ambiguity can be removed by interpreting the time series of brightness temperatures at a fixed location in the context of a model of how the composition evolves in time a model is discussed which includes the effects of ice growth melting deformation and aging the aging process accounts for the change of first year ice into multiyear ice at the beginning of the cold season the model reproduces the annual cycle of brightness temperature a procedure based on kalman filtering is presented for estimating the fractional areas of the three surface types the procedure combines the model of ice evolution with the time series of brightness temperatures the estimation errors are in the range 2 12 these methods can be used with existing passive microwave data to construct a climatology of sea ice based on the three type classification it is also possible to use the observations to improve model parameters such as the rate of melting and the rate of creation of open water by mechanical processes

hydraulie control and flow separation in a multi layered fluid with applications to the vema channel abstract observations from a recent field experiment in the vema channel are briefly described these show a remarkable change in the configuration of isopycnal surfaces within the channel and the development of thick nearly homogeneous regions near the bottom which are capped by sharp vertical gradients contrary to previous speculation that these bottom boundary layer result from enhanced vertical mixing a dynamical mechanism is explored this involves the hydraulic adjustment of an inertial semi geostrophic flow to the channel geometry first an active two layer flow in a rectangular geometry is studied to show that internal flow separation can occur when the flow is accelerated sufficiently by a narrowing channel almost always this separation accompanies hydraulic control the slowest upstream moving kelvin wave is stopped and upstream and downstream states are not symmetric with respect to the channel width an active three layer flow with a variable bottom profile is then presented as a more

general patterns of circulation sediment fluxes and ecology of the palamos la fonera submarine canyon northwestern mediterranean abstract currents particle fluxes and ecology were studied in the palamos submarine canyon also known as the fonera canyon located in the northwestern mediterranean seven mooring arrays equipped with current meters and sediment traps were deployed along the main canyon axis on the canyon walls and on the adjacent slope additionally local and regional hydrographic cruises were carried out current data showed that mean near surface and mid depth currents were oriented along the mean flow direction ne sw although at 400 and 1200 m depth within the canyon current reversals were significant indicating a more closed circulation inside the canyon mean near bottom currents were constrained by the local bathymetry especially at the canyon head the most significant frequency at all levels was the inertial frequency a second frequency of about three days attributed to a topographic wave was observed at all depths suggesting that this wave was probably not trapped near the bottom the current field observed during the most complete survey revealed a meandering pattern with cyclonic vorticity just upstream from and within the canyon the associated vertical velocity ranged between 10 and 20 m day and was constrained to the upper 300 m this latter feature together with other computations suggests that during this survey the meander was not induced by the canyon but by some kind of instability of the mean flow in the canyon suspended sediment concentration downward particle fluxes chlorophyll and particulate c and n were significantly higher up canyon from about 1200 m depth than offshore defining along with the different hydrodynamics two canyon domains one from the canyon head to about 1200 m depth more affected by the canyon confinement and the other deeper than 1200 m depth more controlled by the mean flow and the shelf slope front the higher near bottom downward total mass fluxes were recorded in the canyon axis at 1200 m depth along with sharp turbidity increases and are related to sediment gravity flows during the deployment period the increase in downward particle fluxes occurred by mid november when a severe storm took place on the canyon walls at 1200 m depth suspended sediment concentrations downward particle fluxes chlorophyll and particulate c and n were higher on the southern wall than on the northern wall inversely to the current s energy this could be caused by an upward water supply on the southern canyon wall and or the mean flow interacting with the canyon bathymetry in the swimmers collected by the sediment traps the dominant species was an elasipod holothurian which has not been recorded in other canyons or elsewhere in the mediterranean indicating particular speciation

contourite drift types and their distribution in the north and south atlantic ocean basins abstract patterns of sediment accumulation under the control of deep bottom currents depend on interacting factors intensity of the regional deep circulation morphology of the sea floor coriolis effects abundance of terrigenous and biogenic supplies subsequent turbidity of deep nepheloid layers and depth of the ccd based on many examples of bottom current deposits from the atlantic and from other oceans we recognise three major types of contourite accumulation 1 giant elongate drifts 2 contourite sheets and 3 channel related drifts they generally occur in distinct topographic settings and show different geometries facies and rates of deposition in the north atlantic strong bottom circulation an open basin system and high sediment supply have led to the construction of large elongate contourite drifts which have striking relief 200 1000 m above the surrounding sea floor and are composed of muddy contourites rich in calcareous pelagic material in the south atlantic strong bottom currents are often trapped in gyre like circulation patterns around topographically closed basins or are accelerated through deep narrow connecting passages the resulting deposits are mainly extensive contourite sheets covered by fields of large sediment waves and channel related drifts including contourite fans constructed at the downstream exit of deep passages

physical and biological characteristics of the pelagic system across fram strait to kongsfjorden abstract the fram strait is very important with regard to heat and mass exchange in the arctic ocean and the large quantities of heat carried north by the west spitsbergen current wsc influence the climate in the arctic region as a whole a large volume of water and ice is transported through fram strait with net water transport of 1 7 3 2 sv southward in the east greenland current and a volume ice flux in the range of 0 06 0 11 sv the mean annual ice flux is about 866 000 km2 yr 1 the kongsfjorden krossfjorden fjord system on the coast of spitsbergen or at the eastern extreme of fram strait is mainly affected by the northbound transport of water in the wsc mixing processes on the shelf result in transformed atlantic water in the fjords and the advection of atlantic water also carries boreal fauna into the fjords the phytoplankton production is about 80 g c m 2 yr 1 in fram strait and has been estimated both below and above this for kongsfjorden the zooplankton fauna is diverse but dominated in terms of biomass by calanoid copepods particularly calanus glacialis and c finmarchicus other important copepods include c hyperboreus metridia longa and the smaller more numerous pseudocalanus p minutus and p acuspes microcalanus m pusillus and m pygmaeus and oithona similis the most important species of other taxa appear to be the amphipods themisto libellula and t abyssorum the euphausiids thysanoessa inermis and t longicaudata and the chaetognaths sagitta elegans and eukrohnia hamata a comparison between the open ocean of fram strait and the restricted fjord system of kongsfjorden krossfjorden can be made within limitations the same species tend to dominate but the fram strait zooplankton fauna differs by the presence of meso and bathypelagic copepods the seasonal and inter annual variation in zooplankton is described for kongsfjorden based on the record during july 1996 2002 the ice macrofauna is much less diverse consisting of a handful of amphipod species and the polar cod the ice associated biomass transport of ice amphipods was calculated based on the ice area transport at about 3 55 106 ton wet weight per year or about 4 2 105 t c yr 1 this represents a large energy input to the greenland sea but also a drain on the core population residing in the multi year pack ice myi in the arctic ocean a continuous habitat loss of myi due to climate warming will likely reduce dramatically the sympagic food source the pelagic and sympagic food web structures were revealed by stable isotopes the carbon sources of particulate organic matter pom being ice pom and pelagic pom revealed different isotopic signals in the organisms of the food web and also provided information about the sympagic pelagic and pelagic benthic couplings the marine food web and energy pathways were further determined by fatty acid trophic markers which to a large extent supported the stable isotope picture of the marine food web although some discrepancies were noted particularly with regard to predator prey relationships of ctenophores and pteropods

zoned facies of mass flow deposits in the ulleung tsushima basin east sea sea of japan abstract high resolution 3 5 khz reflection profiles in the ulleung tsushima basin made it possible to classify the uppermost ca 50 m thick sedimentary deposits into rock fall slide slump debris flow deposit debrite and turbidite in terms of their acoustic properties these deposits generally occur in a distinctive zonal facies slides and slumps on the slope debrites on the base of slope and turbidites on the basin floor the rock fall deposits occur along the bases of the korea plateau and ulleung and dok islands the zonal distribution of mass flow deposits suggests that they most likely are derived from a line source at the shelfbreak shelf sediments prograde toward the shelfbreak on the slope sediment masses move downslope mainly accompanied by progressive slumping upslope individual slides and slumps on the slope probably develop into debris flows on the base of slope and successively into turbidity currents on the basin floor mass flow processes on the ulleung basin slope played an important role in transporting a large volume of terrigenous sediments into the deep basin

lateral advection of organic matter in cascading dominated submarine canyons in the gulf of lions gol dense water overflowing off the shelf occurs seasonally and represents the main mechanism affecting the shelf slope exchange of particulate organic matter om most of the dense water export takes place in the south western gol and in particular through cap de creus cdc submarine canyon here benthic instruments were deployed to collect down canyon particulate fluxes whereas surface sediments were taken after the cascading event along the sediment dispersal system on the shelf in cdc canyon and in the nearby lacaze duthiers ld canyon the chemical composition of the suspended material and surface sediments were investigated using several proxies including organic and inorganic carbon total nitrogen biogenic silica 13c 14c and alkaline cuo oxidation products thermohaline anomalies and high current speed events were measured in cdc canyon since december 2004 until mid april 2005 indicating a marked off shelf export of dense water trough the canyon during the cascading mud and relatively coarse shelf and upper canyon sediments were the major component of the mass flux conversely advection of fine material via nepheloid layers dominated down slope fluxes during pre and post cascading the resulting change in grain size affected the flux of mineral bound terrigenous oc indicating that the down canyon transport of land derived om did not occur as bulk but rather its composition is driven by sediment sorting associated with different transport mechanisms both surface sediments and sediment trap samples indicated that cdc canyon is well connected to the gol terrigenous dispersal system conversely our results suggest an overall limited influence of land derived om in ld canyon in spite of the reduced fluvial nutrient supply a significant pulsed input of modern marine om was observed in april 2005 at the end of the cascading period both intense mixing and lack of strong water column stratification likely played a key role allowing for both diffusion of nutrients rich waters into the euphotic zone and efficient vertical sink of marine oc on its way toward the seafloor this fresh pool of oc interacted with the dense plume overflowing off the shelf becoming part of the material laterally advected to the slope

geometry and development of glacial continental margin depositional systems in the bellingshausen sea we present multi channel seismic mcs reflection profiles and bathymetry data acquired across a remote and poorly surveyed part of the antarctic continental margin in the bellingshausen and amundsen seas this new information has been combined with published data and used to interpret the style of sedimentation on the continental shelf slope and rise and to describe sedimentation processes which have been active in this region most seismic reflection profiles crossing the continental margin show prograded sequences beneath the outer shelf and upper slope and we infer that the stratal characteristics of these sequences indicate that grounded ice sheets reached the shelf edge during previous glacial times although there are general similarities in stratal geometry on these profiles in detail they reveal significant longitudinal variations in sediment input from the shelf to the upper slope on several profiles we found evidence of mass wasting of the continental slope in the form of slump and debris flow deposits at greater depth turbidity flows bottom currents and coriolis force have controlled the further transportation and deposition of sediment which has resulted in the development of mounds channels and sediment wave fields the distribution and variations in the size and geometry of the mounds reflect sediment input and the relative contribution of these other factors which control sedimentation on the continental rise

physical properties of summer sea ice in the fram strait the physical properties of sea ice in the fram strait region of the greenland sea were examined during june and july 1984 in conjunction with the marginal ice zone experiment field program most of the ice sampled within fram strait during this period was multiyear thicknesses and other properties indicated that none of the multiyear ice was older than 4 to 5 years snow cover on the multiyear ice averaged 29 cm while that on first year ice averaged only 8 cm deep this difference may be related to enhanced sublimation of the snow on the thinner first year ice the salinity profiles of first year ice clearly show the effects of ongoing brine drainage in that profiles from cores drilled later in the experiment are substantially less saline than earlier cores thin section examinations of crystal structure indicate that about 75 of the ice consisted of congelation ice with typically columnar type crystal structure the remaining 25 consisted of granular ice with only a few occurrences of snow ice the granular ice consisted primarily of frazil found in small amounts at the top of floes but mainly observed in multiyear ridges the horizontally oriented crystal c axes showed various degrees of alignment ranging from no alignment to strong alignments in which the alignment direction changed with depth implying a change in floe orientation with respect to the ocean current at the ice water interface during ice growth evidence of crystal retexturing was observed in the upper meter of nearly every multiyear core this retexturing consisting of grain boundary smoothing and nearly complete obliteration of the ice platelet brine layer substructure is attributed to summer warming

arctic sea ice type and concentration mapping using passive and active microwave sensors the mapping of ice type concentrations in the arctic is important for commercial operations and for climate related research algorithms based on moderate resolution passive microwave sensors for mapping first year ice and multiyear ice concentrations suffer from a number of known problems in this paper it has been shown that quikscat scatterometer data can add complimentary information to that available from passive microwave which can assist in separating different ice classes specifically we identify a class of ice that exhibits a passive microwave signature which is characteristic of first year ice but has a scatterometer signature which is typical of multiyear ice we track the evolution and distribution of this new ice class throughout the arctic during the winter season of 2003 2004 and compare the results against the u s national ice center nic ice charts it has been found that the new ice class is predominantly multiyear ice and is especially prevalent in the fram strait and the high arctic regions north of the islands franz josef land and severnaya zemlya a simple algorithm has been proposed that enables a passive microwave based partial ice concentration algorithm for example the nt algorithm based on special sensor microwave imager data to be adapted using quikscat scatterometer data so that the new ice class is corrected from the first year ice class to the multiyear ice category the algorithm performance is measured against the nic ice charts we provide a discussion regarding the possible physical causes of the effects that have been observed and described

the sedimentary regime beneath the deep western boundary current inflow to the southwest pacific ocean abstract a review of hydrographic sections single channel seismic profiles bottom photographs and nephelometer profiles collected by the u s n s eltanin plus new seismic and sedimentary data from the r v rapuhia provide an insight into the sedimentary regime beneath the pacific deep western boundary current dwbc where it enters the sw pacific off southernmost new zealand at macquarie ridge and campbell plateau there the dwbc is reinforced by the antarctic circumpolar current acc largely through the generation of deep reaching eddies formed by interaction of the acc with the pronounced bathymetry it is therefore a region of high eddy kinetic energy which induces widespread abyssal erosion it is also where the dwbc receives its first major injection of terrigenous se iment which is transferred from southern new zealand along the 450 km long solander channel from macquarie ridge the acc dwbc travels northeast onto the subantarctic slope of campbell plateau this high steep western boundary intensifies the flow causing erosion along the slope base east of the scour the 800 km long campbell drift has been deposited this drift extends to 51 s where the acc swings east to continue its circum antarctic journey while the dwbc continues northeast to bounty trough where the combination of abundant sediment supplied by bounty channel a subdued western boundary and a less energetic dwbc have allowed the bounty fan to form directly across the current path apart from localized winnowing near zones of high relief evidence for widespread dwbc in luence on the fan is inconclusive however current effects become more apparent north of bounty fan where the steep western boundary resumes in the form of chatham rise eroded fan sediments have contributed to a series of small drifts at 4400 5000 m depth whereas at 2400 3400 m depth on the flank of chatham rise the dwbc has molded a sinuous terrace like drift viewed regionally sedimentation beneath the boundary current south of chatham rise contrasts strongly with the regime to the north the southern current is energetic and terrigenous supply is intermittent being restricted to glacial lowstands consequently erosion is common and drifts are few and are themselves subject to erosion by comparison the current north of the rise is generally slower and has a more consistent terrigenous supply particularly near hikurangi channel which has been active irrespective of sea level thus widespread drift deposition is favored

a 36 kyr geochemical record from the sea of japan of organic matter flux variations and changes in intermediate water oxygen concentrations intervals of organic c and carbonate rich laminated sediments occur in the sea of japan with roughly the same frequency as temperature changes observed in greenland ice cores providing clear evidence of rapid oceanographic change during the past 36 kyr planktonic foraminiferal 18o data suggest that only the laminated sediments deposited during the last glacial maximum lgm and perhaps one other interval formed during a period of increased water column stratification sedimentary re and mo data are consistent with bottom waters that were sulfidic during the lgm and suboxic during other laminated intervals results of a numerical model of corg and re burial are consistent with a mechanism whereby an increased corg flux to the seafloor drove oxygen concentrations toward depletion during times of deposition of the suboxic laminated intervals such a process could have resulted from increased upwelling driven either by increased deep water formation due to colder and or more saline surface waters or by stronger northeasterly monsoonal winds

pliocene holocene contourite deposition under the antarctic circumpolar current western falkland trough south atlantic ocean the eastward flowing antarctic circumpolar current acc has influenced sedimentation on the slope and floor of the western falkland trough where the axis of the current is topographically constrained deep water flow below 3000 m has produced a symmetrical sediment drift on the trough floor with non depositional margins indicating higher current velocities at the base of slope to the southeast of the falkland islands there is a gap in the north scotia ridge north of which the floor of the trough is swept clean of sediment by the acc both echo character mapping and gloria side scan data indicate that currents follow the bathymetric contours along the slope redistributing sediment and locally eroding furrows from six cores on the drift and on the northern slope two styles of contourite deposition have been identified on the drift holocene biogenic sandy contourites overlie last glacial maximum muddy contourites and fine grained diatomaceous hemipelagites sedimentation rates here average 3 4 cm ka 1 the sandy contourites present in four of the cores from the sediment drift are sharply underlain by the finer grained diatomaceous hemipelagites the lack of a coarsening upward sequence commonly associated with an increase in current velocity may be indicative of high current activity eroding away the finer negative sequence pliocene and mid pleistocene glaucony rich sandy contourites containing radiolaria characterise the falkland plateau and the floor of the trough near the gap in the north scotia ridge we suggest that the glaucony is derived from a combination of authigenic formation and erosion of locally outcropping cretaceous and tertiary strata this is supported by dinoflagellate analysis sedimentation rates in these current swept areas average 1 cm ka 1

present day organic matter sedimentation on the nw mediterranean margin importance of off shelf export we present an overview of the organic matter distribution in surface sediments sampled on the gulf of lions margin from 600 to 2 300 m depth surface deposits are characterized by a fluff layer a few millimeters to a few centimeters thick in the underlying fine grained sediments the carbonate content is high 30 dw and the organic carbon content varies from 0 3 to 1 dw the highest organic carbon contents are along the axes and on the sides of the canyons 0 6 l and constitute midslope organic depocenters the organic carbon content at 1 000 m depth depends on the width of the adjacent shelf the lowest organic carbon value corresponds to the slightest declivity and consequently to a longer advective residence time in the settling sides of the axial channel of the canyons organic carbon concentrations decrease although sedimentation rate is constant from the upper to the lower part of the slope this results from an increasing residence time in the water column due to the advective transfer of organic material from epicontinental zone to upper and lower slope in the lower axes and open slopes increasing sedimentation rates due to sedimentary reworking and turbidity currents dilute organic carbon with mineral grains

error analysis and assimilation of remotely sensed ice motion within an arctic sea ice model new sea ice motion fields available from remotely sensed data are potentially useful for assessing and improving models of the polar ice pack here we investigate the error characteristics of the observed ice motions relative to drifting buoys and a dynamic thermodynamic ice model a data assimilation approach is then used to assess the potential of the motion data for reducing model biases as well as the potential of the model to serve as an interpolation tool to generate improved ice motion data sets special sensor microwave imager ssm i derived and model simulated ice motions for the years 1988 through 1993 are compared with ice displacement observations from drifting buoys variability and biases are summarized for seasonal and regional means ssm i motions are assimilated into the model using an optimal interpolation method that accounts for the modeled and ssm i motion error variances and the number and distribution of the ssm i motions modeled and ssm i derived motions are found to have comparable mean errors with some notable regional and seasonal differences assimilation substantially reduces the error standard deviation and improves the correlation of the simulated motions relative to the buoy observations but some biases remain in the model framework used here assimilation of the ssm i data substantially alters average ice thickness in some regions of the arctic and affects ice mass outflow through the fram strait but has a small effect on mean ice concentration the assimilation yields an increase in the spatial and temporal variability in ice deformation the observations are particularly suited for improving the simulation of specific synoptic events where substantial differences can occur between simulated and observed ice transport

assimilating satellite concentration data into an arctic sea ice mass balance model 1979 1985 using satellite ice concentration data observed buoy velocities and a thermodynamic ice growth model we compute the time histories of the thickness distributions of four ice types level and ridged first year ice and level and ridged multiyear ice these histories are computed for seven regions covering the arctic ocean with a 10 day time step for 1979 through 1985 a blend of observed buoy motions and wind driven free drift velocities drives the advective and ridging parts of the model while climatological growth and melt rates determine the ice thickness the model adjusts the thickness distributions so that the modeled concentrations of open water first year ice and multiyear ice match the concentrations derived by kalman filtering of satellite passive microwave observations the major adjustment is to reduce modeled ice concentrations in summer and particularly in the peripheral seas to account for unmodeled melt the model includes an ice salinity parameterization which along with changes in ice volume gives the salt or freshwater flux from the ice our results show that the arctic ice cover consists primarily of multiyear ice 60 by area and 82 by volume and that most of this ice is ridged the average ice thickness is 2 7 m with a seasonal variation of 30 and an interannual variation of 10 the study also shows that for each cell and the arctic as a whole the changes in ice volume caused by growth minus melt approximately balance the changes caused by import minus export the annual ice export through fram strait varies from 1100 to 3000 km3 primarily because of variations in ice velocity all regions except the chukchi sea have a net ice growth a net export and a net salt input to the ocean surface the annual mean salt flux to the ocean surface from net ice production is 7 3 kg m 2 downward fluxes along the transpolar drift stream are larger than elsewhere the largest downward flux of 33 kg m 2 yr 1 in the nansen basin can be attributed to the strong divergence near fram strait a companion paper steele et al this issue uses these fluxes and ice velocities to derive the arctic ocean freshwater balance

icesat observations of arctic sea ice a first look 1 analysis of near coincident icesat and radarsat imagery shows that the retrieved elevations from the laser altimeter are sensitive to new openings containing thin ice or open water in the sea ice cover as well as to surface relief of old and first year ice the precision of the elevation estimates measured over relatively flat sea ice is 2 cm using the thickness of thin ice in recent openings to estimate sea level references we obtain the sea ice freeboard along the altimeter tracks this step is necessitated by the large uncertainties in the sea surface topography compared to that required for accurate determination of freeboard unknown snow depth introduces the largest uncertainty in the conversion of freeboard to ice thickness surface roughness is also derived for the first time from the variability of successive elevation estimates along the altimeter track overall these icesat measurements provide an unprecedented view of the arctic ocean ice cover at length scales at and above the spatial dimension of the altimeter footprint of 70 m

area balance of the arctic ocean perennial ice zone october 1996 to april 1997 we use national aeronautics and space administration scatterometer nscat radarsat and ice motion data to examine the perennial ice zone piz of the arctic ocean between october 1996 and april 1997 the piz is identified by a simple backscatter based classification of the gridded nscat backscatter fields the area of the piz at the beginning of october occupies an area of 5 32 106 km2 76 of the arctic ocean by the first of may only 4 54 106 km2 of that area remains a decrease of 0 78 106 km2 over the 7 month period this area loss can be explained almost entirely by ice export over this period the total area flux of sea ice through fram strait estimated using satellite passive microwave ice motion is 0 80 106 km2 or 12 of the arctic ocean approximately 0 70 106 km2 or 88 of the exported area is from the piz nares strait outflow is small at 34 000 km2 and is estimated by summing the high backscatter areas exported into northern baffin bay after accounting for the outflow through the fram and nares straits an unexplained residual of 46 000 km2 remains we attribute this residual to errors in our estimation process the unaccounted for ice flux through the canadian archipelago and the net divergence and convergence of the piz over the period our interpretation of the radiometry seems to be sound on the basis of the area balance arguments provided here this study shows that 1 the piz converage of the arctic ocean can be derived from nscat backscatter fields and 2 the decrease in piz area over the winter is a good estimate of the piz net ice area exported through fram strait

sea level surface salinity of the japan sea and the younger dryas event in the northwestern pacific ocean abstract the japan sea was profoundly different during glacial times than today available 18 o evidence indicates that sea surface salinity was lower by several per mil this probably increased the stability of the water column and caused anoxic sedimentary conditions in the deep sea as shown by the absence of benthic microfossils and the presence of laminated sediment these changes are likely related to the effects of late quaternary sea level change on the shallow sills ca 130 m across which the japan sea exchanges with the open ocean the hwang he yellow river has previously been implicated as the source of fresh water to the japan sea during glaciation but the possible roles of the amur river and excess precipitation over evaporation must also be considered ambiguous radiocarbon chronologies for the latest quaternary of japan sea cores do not adequately constrain the timing of salinity lowering previous studies have suggested that lowest sea surface salinity was achieved 27 000 to 20 000 14 c yr b p however if global sea level fall restricted exchange with the open ocean circulation then lowest salinity in the japan sea may have occurred as recently as 15 000 to 20 000 yr ago when sea level was lowest if this alternative is correct then as sea level abruptly rose about 12 000 yr ago relatively fresh water must have been discharged to the open pacific this might have affected the dynamics of outflow local faunal and floral expression of the polar front and stable isotope ratios in foraminifera these environmental changes could be misinterpreted as evidence for the cooling of younger dryas age which has not been identified in nearby terrestrial records

marine sediment classification using the chirp sonar the chirp sonar is a calibrated wideband digital fm sonar that provides quantitative high resolution low noise subbottom data in addition it generates an acoustic pulse with special frequency domain weighting that provides nearly constant resolution with depth the chirp sonar was developed with the objective of remote acoustic classification of seafloor sediments in addition to producing high resolution images the calibrated digitally recorded data are processed to estimate surficial reflection coefficients as well as a complete sediment acoustic impulse profile in this paper surficial sediments in narragansett bay ri are used to provide ground truth for an acoustic model quantitative acoustic returns from the chirp sonar are used to estimate surficial acoustic impedance and to predict sediment properties a robust acoustic sediment classification model that uses core samples to account for the local depositional environment has been developed the model uses an estimate of acoustic impedance t

chirp subbottom profiler for quantitative sediment analysis a wide band frequency modulated subbottom profiling system the chirp sonar can remotely determine the acoustic attenuation of ocean sediments and produce artifact free sediment profiles in real time the chirp sonar is controlled by a minicomputer which performs analog to digital and digital to analog conversion correlation processing and attenuation estimation in real time the minicomputer generates an fm pulse that is phase and amplitude compensated to correct for the sonar system response such precise waveform control helps suppress correlation noise and source ringing the chirp sonar which has an effective bandwidth of 5 khz can generate chirp klauder wavelets with a tuning thickness rayleigh s criterion for resolution of approximately 0 1 ms after each return is correlated a computationally fast algorithm estimates the attenuation of subbottom reflections by waveform matching with a theoretically attenuated waveform this algorithm obtains an attenuation estimate by minimizing the m