variability of arctic sea ice topography and its impact on the atmospheric surface drag over the polar oceans near surface atmospheric transport of momentum is strongly influenced by sea ice surface topography the latter is analyzed on the basis of laser altimeter data obtained during airborne campaigns between 1995 and 2011 over more than 10 000 km of flight distance in different regions of the arctic ocean spectra of height and spacing between topographic features averaged over 10 km flight sections show that typical values are 0 45 m for the mean height and about 20 m for the mean spacing nevertheless the variability is high and the spatial variability is stronger than the temporal one the total topography spectrum is divided into a range with small obstacles between 0 2 m and 0 8 m height and large obstacles 0 8 m results show that large pressure ridges represent the dominant topographic feature only along the coast of greenland in the central arctic the concentration of large ridges decreased over the years accompanied by an increase of small obstacles concentration and this might be related to decreasing multiyear ice the application of a topography dependent parameterization of neutral atmospheric drag coefficients reflects the large variability in the sea ice topography and reveals characteristic differences between the regions based on the analysis of the two spectral ranges we find that the consideration of only large pressure ridges is not enough to characterize the roughness degree of an ice field and the values of drag coefficients are in most regions strongly influenced by small obstacles

meltwater circulation and permeability of arctic summer sea ice derived from hydrological field experiments abstractpermeability and meltwater flow have been studied in sea ice in the siberian and central arctic during the summers of 1995 and 1996 a bail test technique has been adapted to allow for measurements of in situ permeability found to range between 1011 and 108 m2 permeability varied by about a factor of 2 between 1995 above normal melt rates and 1996 below normal melt rates release of fluorescent tracers fluoresceine rhodamine furthermore allowed the derivation of flow velocities and assessment of the relevant driving forces hydraulic gradients in rough ice and wind stress in ponded ice were found to be particularly important driving meltwater over distances of several m day1 the mid to late summer ice was found permeable enough to completely divert meltwater from the surface into the ice interior it could be shown however that lower permeabilities of the upper ice layers as well as refreezing of meltwater are associated with significantly lower permeabilities in particular during the early melt season fostering development of surface melt ponds

long term ice variability in arctic marginal seas abstract examination of records of fast ice thickness 1936 2000 and ice extent 1900 2000 in the kara laptev east siberian and chukchi seas provide evidence that long term ice thickness and extent trends are small and generally not statistically significant while trends for shorter records are not indicative of the long term tendencies due to large amplitude low frequency variability the ice variability in these seas is dominated by a multidecadal low frequency oscillation lfo and to a lesser degree by higher frequency decadal fluctuations the lfo signal decays eastward from the kara sea where it is strongest in the chukchi sea ice variability is dominated by decadal fluctuations and there is no evidence of the lfo this spatial pattern is consistent with the air temperature north atlantic oscillation nao index correlation pattern with maximum correlation in the near atlantic region which decays toward the north pacific sensitivity analysis shows that dynamical forcing wind or surfac

survey of hydrothermally generated petroleums from the guaymas basin spreading center abstract the guaymas basin spreading center and hydrothermal system are generating an assortment of petroleum like bitumens by pyrolysis of organic matter in the overlying uncosolidated sediments samples collected by d s v alvin from hydrothermal fields in the southern trough exhibit large variations in the quantities and character of the solvent soluble organic materials various pyrolytic regimes combined with fluctuating thermal gradients and migration velocities may impart a compositional fractionation possibly by differential gaseous solubilization and hydrodynamic alteration of the multi component fluids the data suggest that differential condensation solidification biodegradation and water washing cause selective removal of components at the seabed many hydrothermal oils are unlike normal reservoir petroleums because they contain significant concentrations of polar material due to their rapid genesis and transport and probable solubilization or advection of polar immature components the biomarker distributions confirm high temperature pyrolysis at depth with variable entrainment of less thermally mature bitumens during transport data for shallow core samples from the northern trough indicate that those locations experienced variable influx predominantly volatiles of a low temperature pyrolysate

a key source area and constraints on entrainment for basin scale sediment transport by arctic sea ice combining field measurements remote sensing and numerical modelling a key site for ice entrainment and basinwide dispersal of sediments by sea ice has been identified near the new siberian islands the total ice bound sediment export of 18 5 x 10 6 t for an entrainment event documented in 1994 95 is of the same order of magnitude as annual sediment supply to the deep sea sector of the eurasian arctic and the greenland sea satellite imagery and ancillary data indicate that ice advection from this source may play an important role in sedimentation downstream in the transpolar drift

diagnosis of the record minimum in arctic sea ice area during 1990 and associated snow cover extremes the arctic sea ice cover exhibited its record minimum area during 1990 characterized by extensive ice free conditions during august along the siberian coast these reductions are consistent with warm windy conditions in may and continued warmth in june promoting early melt and reductions in ice concentration followed in august by strong coastal winds forcing a final breakup and retreat of the pack ice the unusually warm arctic conditions in 1990 are part of a larger scale temperature anomaly pattern linking the sea ice anomaly to accompanying record minima in eurasian snow cover

acoustically detected hydrocarbon plumes rising from 2 km depths in guaymas basin gulf of california plumes extending nearly 1000 m from the 1500 2000 m deep seafloor of guaymas basin were detected from below the 23 5 khz inverted echo sounder of the scripps deep two vehicle individual sound reflectors bubbles or drops rise at approximately 17 cm s in one plume the deep tow side scan records provide more information on the plumes structure at the altitude of the vehicle 75 m where some form multiple side scan targets one 20 m across near bottom 4 khz profiles show that plumes overlie young fault traces associated with extensional faulting at the basin s spreading centers of outcrops of tilted beds beside strike slip faults we infer from analysis of the deep tow observations field relationships and knowledge of the geology of this basin that the plumes are made of light hydrocarbons perhaps mainly methane that emanate from seabed seeps one of the acoustically detected plumes was at a spreading axis hydrothermal field which has many buoyant acoustically transparent thermal plumes some of which are rich in dissolved hydrocarbons

the effects of thermal maturity on distributions of dimethylnaphthalenes and trimethylnaphthalenes in some ancient sediments and petroleums abstract the distributions of di and trimethylnaphthalenes in two sedimentary sequences from western australia have been examined by capillary gas chromatography and combined gas chromatography mass spectrometry a general decrease was observed in the relative proportions of dimethylnaphthalenes and trimethylnaphthalenes with increasing thermal maturity similar trends were also observed for six crude oils which have very different ratios of ethylcholestane epimers indicating very different thermal histories these results suggest that changes in the relative abundances of certain methyl substituted naphthalenes may be useful indicators of thermal maturity of sedimentary organic matter and the use of a number of isomer ratios is illustrated

large scale ice thickness distribution of first year sea ice in spring and summer north of svalbard the large scale thickness distribution of sea ice was measured during several campaigns in the european arctic north of svalbard from 2007 using an airborne electromagnetic induction device in august 2010 and april may 2011 this was complemented by extensive on ice work including measurements of snow thickness and freeboard ice thicknesses show a clear difference between the seasons with thicker ice during spring than in summer in spring 2011 negative freeboard and flooding were observed as a result of the extensive snow cover we find that the characteristics of the first year sea ice allow combining observations from different years the ice thickness in the marginal ice zone increases with increasing latitude and increasing distance to the ice edge however in the inner ice pack from 100 km from the ice edge the thickness remains almost constant modal ice thickness in spring reaches 2 4 m whereas in summer it is 1 0 1 4 m our study provides new insight into ice thickness distributions of a typical ice cover consisting of mainly first and second year ice which may become the dominant ice type in the arctic in the future

sediment transport by sea ice in the chukchi and beaufort seas increasing importance due to changing ice conditions abstract sediment laden sea ice is widespread over the shallow wide siberian arctic shelves with off shelf export from the laptev and east siberian seas contributing substantially to the arctic ocean s sediment budget by contrast the north american shelves owing to their narrow width and greater water depths have not been deemed as important for basin wide sediment transport by sea ice observations over the chukchi and beaufort shelves in 2001 02 revealed the widespread occurrence of sediment laden ice over an area of more than 100 000 km2 between 68 and 74 n and 155 and 170 w ice stratigraphic studies indicate that sediment inclusions were associated with entrainment of frazil ice into deformed multiple layers of rafted nilas indicative of a flaw lead environment adjacent to the landfast ice of the chukchi and beaufort seas this is corroborated by buoy trajectories and satellite imagery indicating entrainment in a coastal polynya in the eastern chukchi sea in february of 2002 as well as formation of sediment laden ice along the beaufort sea coast as far eastward as the mackenzie shelf moored upward looking sonar on the mackenzie shelf provides further insight into the ice growth and deformation regime governing sediment entrainment analysis of radarsat synthetic aperture sar imagery in conjunction with bathymetric data help constrain the water depth of sediment resuspension and subsequent ice entrainment 20 m for the chukchi sea sediment loads averaged at 128 t km 2 with sediment occurring in layers of roughly 0 5 m thickness mostly in the lower ice layers the total amount of sediment transported by sea ice mostly out of the narrow zone between the landfast ice edge and waters too deep for resuspension and entrainment is at minimum 4 106 t in the sampling area and is estimated at 5 8 106 t over the entire chukchi and beaufort shelves in 2001 02 representing a significant term in the sediment budget of the western arctic ocean recent changes in the chukchi and beaufort sea ice regimes reduced summer minimum ice extent ice thinning reduction in multi year ice extent altered drift paths and mid winter landfast ice break out events have likely resulted in an increase of sediment laden ice in the area apart from contributing substantially to along and across shelf particulate flow an increase in the amount of dirty ice significantly impacts sub ice algal production and may enhance the dispersal of pollutants

two circulation regimes of the wind driven arctic ocean the major goal of this paper is to demonstrate the existence in the arctic ocean of two regimes of wind forced circulation we simulated the vertically averaged currents sea level heights and ice drift in the arctic ocean from 1946 to 1993 using a two dimensional wind forced barotropic model that includes frictional coupling between the ocean and ice the model has a spatial resolution of 55 5 km and is driven by winds river runoff and an imposed but realistic sea level slope between the pacific and the atlantic oceans there is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics the results indicate that wind driven motion in the central arctic alternates between anticyclonic and cyclonic circulation with each regime persisting for 5 7 years based upon our analysis of the modeled sea level and ice motion anticyclonic wind driven motion in the central arctic appeared during 1946 1952 1958 1963 1972 1979 and 1984 1988 and cyclonic motion appeared during 1953 1957 1964 1971 1980 1983 and 1989 1993 shifts from one regime to another are forced by changes in the location and intensity of the icelandic low and the siberian high the two regimes may help explain the significant basin scale changes in the arctic s temperature and salinity structure observed recently the great salinity anomaly and the variability of ice conditions in the arctic ocean

expulsion of petroleum hydrocarbons from shale source rocks there is compelling evidence that movement of petroleum from organic rich shales into sandstones and limestones occurs in the subsurface1 this expulsion of material must occur if crude oil accumulations are to form and it is termed primary migration2 earlier studies3 4 suggested that this movement occurs with chemical fractionation some components are more mobile than others one of the agents of expulsion at early maturity stages is compaction which is not only capable of forcing water but also organic components out of the pore network of a source rock2 5 6 because the fractionation effects associated with expulsion provide clues to the transport mechanisms involved we have made detailed quantitative comparisons of the hydrocarbons of shales of different thicknesses the centre and edges of thick shales and sandstones adjacent to shales from two cored interbedded shale and sandstone sequences from spitsbergen island svalbard norway these observations confirm considerable movement of hydrocarbons in the subsurface with lower molecular weight components being more mobile up to 90 the original amount of n pentadecane may be lost from very thin shales sandwiched between sandstone horizons and from shales close to a lithological boundary with sandstone

north pole ice thickness and association with ice motion history 1977 1992 ice drafts measured by u s navy submarine sonar near the north pole from 1977 to 1992 were used together with arctic ocean drifting buoy data from 1979 to 1992 to investigate north pole ice thickness changes during this 15 year period a primary objective was to determine dynamical forcing mechanisms and associated time scales relevant to ice thickness variation north pole ice thickness showed much interannual variability and no systematic decrease of ice thickness was observed changes in ice thickness were closely associated with long term directional deviation of ice motion from geostrophic wind forcing and with ice convergence and divergence at the north pole during the 1 2 weeks prior to submarine measurement the geographic origin of ice within the arctic ocean was not associated with its eventual thickness at the north pole

intercomparison of backscatter maps over arctic sea ice from nscat and the ers scatterometer c band and ku band arctic ocean sea ice backscatter maps at 40 incidence angle produced from the ers 2 active microwave instrument operating in scatterometer mode and advanced earth observing system nasa scatterometers respectively are presented and compared the noise level on these maps is estimated from the comparison of successive maps and is found comparable although larger at c band than at ku band in both cases the relative noise level increases as backscatter level decreases backscatter shows a greater dynamic range at ku band than at c band going from first year to multiyear ice moreover the ku band to c band backscatter ratio varies considerably as a function of sea ice type surface thawing in june leads to a brutal decrease in backscatter in both frequency bands as well as in the ku band to c band ratio the study of the time evolution of backscatter over five different regions of the arctic ocean demonstrates the influence of both advection and local evolution on this parameter

sediments in arctic sea ice implications for entrainment transport and release despite the arctic sea ice cover s recognized sensitivity to environmental change the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood sea ice sediment inclusions were studied in the central arctic ocean during the arctic 91 expedition and in the laptev sea east siberian arctic region expedition 1992 results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central arctic ocean this study documents the regional distribution and composition of particle laden ice investigates and evaluates processes by which sediment is incorporated into the ice cover and identifies transport paths and probable depositional centers for the released sediment in april 1992 sea ice in the laptev sea was relatively clean the sediment occasionally observed was distributed diffusely over the entire ice column forming turbid ice observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment in the central arctic ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes the surface sediment accumulation in central arctic multi year sea ice exceeds by far the amounts observed in first year ice from the laptev sea in april 1992 sea ice sediments are generally fine grained although coarse sediments and stones up to 5 cm in diameter are observed component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles the biogenous components namely shells of pelecypods and benthic foraminiferal tests point to a shallow benthic marine source area apparently sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing clay mineralogy of ice rafted sediments provides information on potential source areas a smectite maximum in sea ice sediment samples repeatedly occurred between 81 n and 83 n along the arctic 91 transect indicating a rather stable and narrow smectite rich ice drift stream of the transpolar drift the smectite concentrations are comparable to those found in both laptev sea shelf sediments and anchor ice sediments pointing to this sea as a potential source area for sea ice sediments in the central arctic ocean sea ice clay mineralogy is significantly different from deep sea clay mineral distribution patterns the contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms

snow contribution to first year and second year arctic sea ice mass balance north of svalbard the salinity and water oxygen isotope composition 18o of twenty nine first year fyi and second year syi arctic sea ice cores total length 32 0 m from the drifting ice pack north of svalbard were examined to quantify the contribution of snow to sea ice mass five cores total length 6 4 m were analyzed for their structural composition showing variable contribution of 10 30 by granular ice in these cores snow had been entrained in 6 to 28 of the total ice thickness we found evidence of snow contribution in about three quarter of the sea ice cores when surface granular layers had very low 18o values snow contributed 7 5 9 7 to sea ice mass balance on average including also cores with no snow using 18o mass balance calculations in syi cores snow fraction by mass 12 7 16 3 was much higher than in fyi cores 3 3 4 4 while the bulk salinity of fyi 4 9 was distinctively higher than for syi 2 7 we surmise that oxygen isotopes and salinity profiles can give information on the age of the ice and allows to distinguish between fyi and syi or older ice in the area north of svalbard this article is protected by copyright all rights reserved

ice thickness in the arctic ocean the statistical reliability of experimental data the statistical reliability of ice thickness distributions derived from submarine sonar data sets of finite length is examined focusing on the standard error eh l in the mean ice draft h derived from a record of length l km this is important in assessing the significance or otherwise of quoted temporal or spatial differences in mean ice draft estimates for eh 50 are derived from four different submarine surveys each of which involved repeated sampling of apparently homogeneous ice fields values ranged from 7 18 to 15 29 of the mean for climate related comparisons of data sets from different years in the same location a value of 12 75 is recommended derived from data gathered at the north pole this value is used to reassess the significance of published data on ice draft variability quoted variability at the north pole over the 1977 1990 period is found to be not statistically significant but a difference in area averaged ice draft over the eurasian basin between 1976 and 1987 remains highly significant using hitherto unreported 1987 data from the north pole area the statistical variability of other parameters of the ice cover is examined the frequency of lead occurrence the width of leads the fractional cover of smooth ice and the frequency of keel occurrence all show standard errors of 22 24 in their mean values while mean keel draft has a 4 error all over a 50 km track length finally unreported 1987 data for an area extending from the pole to 72 n along the prime meridian and the east greenland shelf break are examined in 1 bins using eh l to assess the significance of variations in the mean a statistically significant decline in mean ice draft is observed starting at 86 n and continuing to 72 n a linear regression gives a thinning rate of 0 22 m deg the decline within the arctic basin itself is tentatively ascribed to a mixture of under ice melt and mixing of ice types since data on young ice occurrence show that divergence did not occur north of fram strait

an estimate of the mean field of arctic sea ice motion the observational basis for our understanding of sea ice motion comes from the trajectories of particular ice floes these ice floes may have been marked by a manned research station or more recently by an automatic data buoy since 1893 almost 100 station years of drift data have been recorded using the principles of optimal linear estimation these data are used to obtain a quantitative estimate of the field of mean motion

sea ice thickness variability in the chukchi sea spring and summer 2002 2004 abstract measurements of sea ice thickness were obtained from drill holes an ice based electromagnetic induction instrument iem and a ship borne electromagnetic induction instrument sem during the early melt season in the southern chukchi sea in 2002 and 2004 and in late summer 2003 at the time of minimum ice extent in the northern chukchi sea an ice roughness criterion was applied to distinguish between level and rough or ridged ice ice thickness modes in the probability density functions pdfs derived from drill hole and iem measurements agreed well with modes at 1 5 1 6 and 1 8 1 9 m for all data from level ice the pdfs derived from sem measurements show that the primary modes are at 0 1 and 1 1 m in 2003 and 0 7 m in 2004 in 2002 and 2004 significant fractions between one third and one half of level ice were found to consist of rafted ice segments snow depth varied significantly between years with 2004 data showing more than half the snow cover on level ice to be at or below 0 05 m depth in late spring ice growth simulations and examination of ice drift and deformation history indicate that impacts of atmospheric and oceanic warming on level ice thickness in the region over the past few decades are masked to a large extent by variability in snow depth and the contribution of deformation processes in comparison with submarine sonar ice thickness data from previous decades a reduction in ice thickness by about 0 5 1 m is in part explained by the replacement of multi year with first year ice over the chukchi and beaufort shelves

hydrothermal petroleum in mineralized mounds at the seabed of guaymas basin petroleum has been dredged from an active hydrothermal mound area in the southern rift of guaymas basin gulf of california this organic matter is composed of gasoline range aliphatic and aromatic hydrocarbons and predominantly residual polar asphaltic material the aliphatic hydrocarbons of two bitumen samples have very different boiling range and composition both samples contain polynuclear aromatic hydrocarbons and olefins which indicate formation at pyrolytic temperatures the overall compositional data indicate an origin from biological detritus by thermal alteration and rapid quenching by hydrothermal removal followed by condensation at the seabed

organic geochemistry of deep sea drilling project sediments from the gulf of calofornia hydrothermal effects on unconsolidated diatom ooze abstract the effects of intrusive thermal stress have been studied on a number of pleistocene sediment samples obtained from leg 64 of the dsdp ipod program in the gulf of california samples were selected from sites 477 478 and 481 where the organic matter was subjected to thermal stress from sill intrusions for comparison purposes samples from sites 474 and 479 were selected as representative of unaltered material the gc and gc ms data show that lipids of the thermally unaltered samples were derived from microbial and terrestrial higher plant detritus samples from sill proximities were found to contain thermally derived distillates and those adjacent to sills contained essentially no lipids curie point pyrolysis combined with gc and gc ms was used to show that kerogens from the unaltered samples reflected their predominantly autochthonous microbial origin pyrograms of the altered kerogens were much less complex than the unaltered samples reflecting the thermal effects the kerogens adjacent to the sills produce little or no pyrolysis products since these intrusions into unconsolidated wet sediments resulted in in situ pyrolysis of the organic matter examination of the kerogens by esr showed that spin density and line width pass through a maximum during the course of alteration but esr g values show no correlation with maturity stable carbon isotope 13 c values of kerogens decrease by 1 1 5 near the sills at sites 477 and 481 and the atomic n c decreases slightly with proximity to a smaller sill at site 478 differences in maturation behavior between site 477 and 481 and site 478 are attributed to dissimilarities in thermal stress and to chemical and isotopic heterogeneity of guaymas basin protokerogen

comparison of sea ice thickness measurements under summer and winter conditions in the arctic using a small electromagnetic induction device drillhole determined sea ice thickness was compared with values derived remotely using a portable smalloffset loop loop steady state electromagnetic em induction device during expeditions to fram strait and the siberian arctic under typical winter and summer conditions simple empirical transformation equations are derived to convert measured apparent conductivity into ice thickness despite the extreme seasonal differences in sea ice properties as revealed by ice core analysis the transformation equations vary little for winter and summer thus the em induction technique operated on the ice surface in the horizontal dipole mode yields accurate results within 5 to 10 of the drillhole determined thickness over level ice in both seasons the robustness of the induction method with respect to seasonal extremes is attributed to the low salinity of brine or meltwater filling the extensive pore space in summer thus the average bulk ice conductivity for summer multiyear sea ice derived according to archie s law amounts to 23 ms m compared to 3 ms m for winter conditions these mean conductivities cause only minor differences in the em response as is shown by means of 1 d modeling however under summer conditions the range of ice conductivities is wider along with the widespread occurrence of surface melt ponds and freshwater lenses underneath the ice this causes greater scatter in the apparent conductivity ice thickness relation this can result in higher deviations between em derived and drillhole determined thicknesses in summer than in winter

thickness and surface properties of different sea ice regimes within the arctic trans polar drift data from summers 2001 2004 and 2007 1 large scale sea ice thickness and surface property data were obtained in three summers and in three different sea ice regimes in the arctic trans polar drift tpd by means of helicopter electromagnetic sounding distribution functions p of sea ice thickness and of the height spacing and density of sails were analyzed to characterize ice regimes of different ages and deformations results suggest that modal ice thickness is affected by the age of a sea ice regime and that the degree of deformation is represented by the shape of p mean thickness changes with both age and deformation standard error calculations showed that representative mean and modal thickness could be obtained with transect lengths of 15 km and 50 km respectively in less deformed ice regimes such as those around the north pole in heavier deformed ice regimes closer to greenland 100 km transects were necessary for mean thickness determination and a representative modal thickness could not be obtained at all mean sail height did not differ between ice regimes whereas sail density increased with the degree of deformation furthermore the fraction of level ice open melt ponds and open water along the transects were determined although overall ice thickness in the central tpd was 50 thinner in 2007 than in 2001 first year ice fyi was not significantly thinner in 2007 than fyi in 2001 with a decrease of only 0 3 m thinner fyi in 2007 only occurred close to the sea ice edge where open water covered more than 10 of the surface melt pond coverage retrieved from laser measurements was 15 in both the 2004 myi regime and the 2007 fyi regime

contour mapping of arctic basin ice draft and roughness parameters a data base of ice draft and roughness parameters has been constructed for selected portions of the arctic ocean based upon analysis of under ice draft distribution data acquired by inverted echo sounder systems on submarines from the voyages of 12 submarines which traversed the alaskan canadian and central arctic regions of the arctic ocean during the summer and winter seasons a series of mean ice draft and deep draft keel statistics was calculated for 50 km segments along each submarine track contour maps of the mean ice draft its standard deviation the mean keel draft and the spatial frequency of ice keels were constructed they show that the greatest ice drafts the roughest ice and the greatest number of deep draft keels are found off the north coasts of the canadian archipelago and greenland due to ice convergence on these land barriers

interannual variability of summer sea ice thickness in the siberian and central arctic under different atmospheric circulation regimes extensive drill hole and electromagnetic induction measurements of sea ice thickness in the siberian and central arctic seas in the summers of 1993 1995 and 1996 reveal significant interannual variability in the laptev sea minimum and maximum modal first year ice thicknesses amounted to 1 25 and 1 85 m in 1995 and 1996 respectively ice thickness correlates with ice extent which reached a record minimum in august 1995 and was well above average in 1996 these differences are explained by the strength and location of a summer cyclonic atmospheric circulation pattern affecting both ice advection and surface melt from drifting buoys deployed in 1995 and satellite radar backscatter data first and second year ice regimes are delineated differences in first year ice backscatter coefficients between 1993 1995 and 1996 are explained by differences in level ice surface roughness the lagrangian evolution of ice thickness between 1995 and 1996 is studied while the shape of the thickness distribution does not change significantly the mean modal ice thickness of the ice field increases from 1 80 m 1 25 m in 1995 to 2 86 m 2 25 m in 1996 the thickness distribution of second year ice in 1996 closely agrees with that of level multiyear ice downstream in the transpolar drift obtained in 1991 in 1996 mean level ice thickness increases at 0 23 and 0 16 m deg 1 with latitude in the kara and laptev sea sectors of the arctic ocean respectively

satellite altimetry the marine geoid and the oceanic general circulation for technical reasons the general circulation of the ocean has historically been treated as a steady laminar flow field the recent availability of extremely highaccuracy and high precision satellite altimetry has provided a graphic demonstration that the ocean is actually a rapidly time evolving turbulent flow field to render the observations quantitatively useful for oceanographic purposes has required order of magnitude improvements in a number of fields including orbit dynamics gravity field estimation and atmospheric variability with five years of very high quality data now available the nature of oceanic variability on all space and time scales is emerging including new findings about such diverse and important phenomena as mixing coefficients the frequency wavenumber spectrum and turbulent cascades because the surface elevation is both a cause and consequence of motions deep within the water column oceanographers soon will be able to provide general circulation numerical models tested against and then combined with the altimeter data these will be complete three dimensional timeevolving estimates of the ocean circulation permitting greatly improved estimates of oceanic heat carbon and other property fluxes

fluctuating arctic sea ice thickness changes estimated by an in situ learned and empirically forced neural network model abstract sea ice thickness sit is a key parameter of scientific interest because understanding the natural spatiotemporal variability of ice thickness is critical for improving global climate models in this paper changes in arctic sit during 1982 2003 are examined using a neural network nn algorithm trained with in situ submarine ice draft and surface drilling data for each month of the study period the nn individually estimated sit of each ice covered pixel 25 km resolution based on seven geophysical parameters four shortwave and longwave radiative fluxes surface air temperature ice drift velocity and ice divergence convergence that were cumulatively summed at each monthly position along the pixel s previous 3 yr drift track or less if the ice was 3 yr old average january sit increased during 1982 88 in most regions of the arctic 7 6 0 9 cm yr 1 decreased through 1996 arctic wide 6 1 1 2 cm yr 1 then modestly increased through 2003 mostly in the central arctic 2 1 0 6 c

reconstructing the origin and trajectory of drifting arctic sea ice recent studies have indicated that drifting arctic sea ice plays an important role in the redistribution of sediments and contaminants here we present a method to reconstruct the back ward trajectory of sea ice from its sampling location in the eurasian arctic to its possible site of ori gin on the shelf based on historical drift data from the international arctic buoy program this method is verified by showing that origins derived from the backward trajectories are generally con sistent with other indicators such as comparison of the predicted backward trajectories with known buoy drifts and matching the clay mineralogy of sediments sampled from the sea ice with that of the seafloor in the predicted shelf source regions the trajectories are then used to identify regions where sediment laden ice is exported to the transpolar drift stream from the new siberian islands and the central kara plateau calculation of forward trajectories shows that the kara sea is a major contributor of ice to the barents sea and the southern limb of the transpolar drift stream

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

loitering of the retreating sea ice edge in the arctic seas each year the arctic sea ice edge retreats from its winter maximum extent through the seasonal ice zone siz to its summer minimum extent on some days this retreat happens at a rapid pace while on other days parts of the pan arctic ice edge hardly move for periods of days up to 1 5 weeks we term this stationary behavior ice edge loitering and identify areas that are more prone to loitering than others generally about 20 25 of the siz area experiences loitering most often only one time at any one location during the retreat season but sometimes two or more times the main mechanism controlling loitering is an interaction between surface winds and warm sea surface temperatures in areas from which the ice has already retreated when retreat happens early enough to allow atmospheric warming of this open water winds that force ice floes into this water cause melting thus while individual ice floes are moving the ice edge as a whole appears to loiter the time scale of loitering is then naturally tied to the synoptic time scale of wind forcing perhaps surprisingly the area of loitering in the arctic seas has not changed over the past 25 years even as the siz area has grown this is because rapid ice retreat happens most commonly late in the summer when atmospheric warming of open water is weak we speculate that loitering may have profound effects on both physical and biological conditions at the ice edge during the retreat season

synoptic airborne thickness surveys reveal state of arctic sea ice cover 1 while summer arctic sea ice extent has decreased over the past three decades it is subject to large interannual and regional variations methodological challenges in measuring ice thickness continue to hamper our understanding of the response of the ice thickness distribution to recent change limiting the ability to forecast sea ice change over the next decade we present results from a 2400 km long pan arctic airborne electromagnetic em ice thickness survey in april 2009 the first ever large scale em thickness dataset obtained by fixed wing aircraft over key regions of old ice in the arctic ocean between svalbard and alaska the data provide detailed insight into ice thickness distributions characteristic for the different regions comparison with previous em surveys shows that modal thicknesses of old ice had changed little since 2007 and remained within the expected range of natural variability

seasonal variations of sea ice motion in the transpolar drift stream drifting buoy data for 1979 85 and meteorological fields for 1960 85 are used to assess sea ice motion in the transpolar drift stream although the long term mean ice drift in this stream is toward the fram strait three years 1979 81 with adequate drifting buoy data coverage show reversed ice motion over 30 day periods in summer this phenomenon is a response to seasonally changing wind forcing

dynamic thermodynamic sea ice model ridging and its application to climate study and navigation abstract a dynamic thermodynamic sea ice model with the ocean mixed layer forced by atmospheric data is used to investigate spatial and long term variability of the sea ice cover in the arctic basin the model satisfactorily reproduces the averaged main characteristics of the sea ice and its extent in the arctic basin as well as its decrease in the early 1990s employment of the average ridge shape for describing the ridging allows the authors to suggest that it occurs in winter and varies from year to year by a factor of 2 depending on an atmospheric circulation pattern production and horizontal movement of ridges are the focus in this paper as they show the importance of interannual variability of the arctic ice cover the observed thinning in the 1990s is a result of reduction in ridge formation on the pacific side during the cyclonic phase of the arctic oscillation the model yields a partial recovery of sea ice cover in the last few years of the twentieth century in addition to the sea ice cover

late summer sea ice thickness variability in the arctic transpolar drift 1991 2001 derived from ground based electromagnetic sounding 1 late summer thickness distributions of large ice floes in the transpolar drift between svalbard and the north pole in 1991 1996 1998 and 2001 are compared they have been derived from drilling and electromagnetic em sounding results show a strong interannual variability with significantly reduced thickness in 1998 and 2001 the mean thickness decreased by 22 5 from 3 11 m in 1991 to 2 41 m in 2001 and the modal thickness by 22 from 2 50 m in 1991 to 1 95 m in 2001 since modal thickness represents the thickness of level ice the observed thinning reflects changes in thermodynamic conditions together with additional data from the laptev sea obtained in 1993 1995 and 1996 results are in surprising agreement with recently published thickness anomalies retrieved from satellite radar altimetry for arctic regions south of 81 5 n this points to a strong sensitivity of radar altimetry data to level ice thickness

physical and morphological properties of sea ice in the chukchi and beaufort seas during the 2010 and 2011 nasa icescape missions abstract physical and morphological properties of sea ice in the chukchi and western beaufort seas were measured during the 2010 and 2011 june july icescape impacts of climate on the eco systems and chemistry of the arctic pacific environment missions aboard the uscgc healy observations of ice conditions including ice thicknesses types and concentrations of primary secondary and tertiary categories were reported at 2 h intervals while the ship was in transit using the antarctic sea ice processes and climate aspect protocol on ice surveys of ice thickness melt pond depth and ice properties including profiles of internal temperature salinity and isotopic composition were conducted at 21 total ice stations 12 in 2010 and 9 in 2011 comparison to historical ship based observations confirms a multi decadal transition from a multiyear to thinner first year dominated seasonal sea ice pack in the region with much earlier ice retreat than in past decades the ice encountered was predominantly 98 first year with un deformed ice thicknesses ranging from 0 73 to 1 2 m pond coverage was extensive averaging 29 in 2010 and 19 in 2011 resulting in considerable light absorption in the ice and transmission of light to the ocean enhanced melting near the ice edge is consistent with transport of pacific origin heat and or ice albedo feedbacks sediment entrainment was visible in 7 5 and 10 9 of the ice in 2010 and 2011 respectively overall the results indicate a regime shift in the characteristics of the ice cover has occurred in the region over recent decades with substantive implications for thermodynamic forcing light availability in the upper ocean and biological and biogeochemical processes in the ice and water column beneath the results presented have applications for the interpretation of optical and biological measurements in the chukchi sea and serve as record of ice conditions for assessing long term change

arctic sea ice thickness remained constant during the 1990s the ice cover of the arctic ocean is considered to be a sensitive indicator of global climate change recent research using submarine based observations suggests that the arctic ice cover was thinner in the 1990s compared to an earlier period 1958 1979 and that it continued to decrease in thickness in the 1990s here i analyze subsurface ice thickness draft of arctic sea ice from six submarine cruises from 1991 to 1997 this extensive data set shows that there was no trend towards a thinning ice cover during the 1990s data from the north pole shows a slight increase in mean ice thickness whereas the beaufort sea shows a small decrease none of which are significant transects between the two areas from 76 n to 90 n also show near constant ice thicknesses with a general spatial decrease from the pole towards the beaufort sea combining the present results with those of an earlier study i conclude that the mean ice thickness has remained on a near constant level around the north pole from 1986 to 1997

comparison of seasonal sea ice thickness change in the transpolar drift observed by local ice mass balance observations and floe scale em surveys local and transect ice thickness measurements were performed between may and november 2007 on an ice floe in the transpolar drift of the arctic ocean using an ice mass balance buoy and electromagnetic induction em sounding repeated em surveys along an originally 2160 m long profile including level and deformed ice showed that between june and september modal and mean thicknesses decreased by 0 6 and 0 86 m respectively the modal thickness decrease is in good agreement with the thinning of 0 6 m observed by the ice mass balance buoy at one location on unponded ice during the same period although the local observations do not capture the different melt rates on level and rough ice the paper discusses methodological and operational challenges in sustaining both measurements over periods of several months and concludes that more work needs to be done to better understand their representativeness

evolution of the passive and active microwave signatures of a large sea ice feature during its 2 year drift through the arctic ocean although estimation of the total ice concentration from special sensor microwave imagers ssm i has proven to be successful none of the various algorithms developed to discriminate new and older ice provide satisfying results while the strong contrast between the emissivity of sea ice and that of open water can be utilized to provide reliable estimators of the total ice concentration passive microwave characteristics of second year and multiyear ice may locally evolve in different ways even during the cold season scatterometers as the active microwave instrument in wind mode ami wind on board the european remote sensing satellites ers provide backscatter data which have a higher sensitivity to the surface topography of ice and a better stability in time at a resolution compatible with the ssm i measurements here we present the evolutions of the microwave properties of an ice feature appearing along the shores of novosibirskiye ostrova new siberian islands at the end of july 1992 as the ice ages during its 3 year drift toward the fram strait the track of this well defined ice surface is easily followed on the maps of the backscatter coefficient provided by the ami wind during the cold season in summer because of melting the ice undergoes critical changes which alter its microwave signatures and hamper automatic tracking moreover on approaching the fram strait the resolution of the scatterometer is not sufficient to capture the complex and rapid transformations of the ice cover to compensate for this buoy data obtained from the international arctic buoy program are used alone during summers or together with satellite data to build basin wide ice displacement fields these displacement fields successively applied to each pixel of the ice feature selected provide a series of lagrangian observations during the drift which ends in may 1995 the active and passive signatures evolve coherently except for the cold season 1992 1993 when unrealistic multiyear ice concentrations are deduced from the brightness temperatures which at that time are much less stable than the backscatter coefficient over the ice surface tracked identified as second year ice

the underside topography of sea ice over the continental shelf of the beaufort sea in the winter of 1990 a spatial section of draft across 348 km of sea ice was obtained by moored subsea sonars in the beaufort sea in the winter of 1990 the ice field was a mixture of first year and multiyear types with mean draft of the order of 3 m level ice of 0 to 4 m draft occupied approximately 50 of the section within this fraction draft values of 0 and 1 5 m were most common while at 2 to 3 m draft a noticeable contribution was made by rafted first year ice deformed ice was observed to a maximum draft of nearly 27 m keels within the section were identified using both the rayleigh criterion and a new criterion based on level ice both criteria defined exponentially distributed populations but with different e folding scales the observations revealed an ice cover whose statistical properties are consistent with other data from the periphery of the polar pack in the beaufort sea but which are much more severe than those of ice found in the seasonal ice zone only a few tens of kilometres to the south the cross sectional shape of individual keels was highly variable but on average the distribution of ice within a keel was an exponential function of draft the topography of both first year and old ice subsections of the data was fractal in character with a dimension of about 1 5 for both ice types the average mass of sea ice per unit area was estimated as 2540 2970 kg m 2 with 68 73 of this mass contributed by deformed ice the large uncertainties in these estimates arise because the porosity of keels and the burden of snow or melt water upon the ice are not known

thickness structure and properties of level summer multiyear ice in the eurasian sector of the arctic ocean in august and september 1991 thickness structure and properties of level multiyear ice were studied at 66 locations in the eurasian sector of the arctic ocean the mean ice thickness was 2 86 m with 0 31 m of freeboard including 0 08 m deteriorated ice of mean density 370 kg m 3 on the basis of the study of ice cores 61 of the ice cover consisted of undeformed columnar ice the remaining 39 consisted of a mixture of ice types including frazil 18 and deformed ice 9 through microstructural studies six main classes of pores could be identified the mean density of the ice cover increased from 720 kg m 3 at the top to 880 kg m 3 below 0 4 m depth sea ice salinities mean value 2 1 correlate with ice thickness on average salinity profiles exhibit a linear increase from values close to 0 at the top to 2 at 1 m depth with less steep salinity gradients below sampling from different depths within the ice cover indicates that the brine in summer sea ice is strongly stratified the influence of meltwater percolation is evident with salinities around 5 and ph values 15 and 8 at greater depths brine volumes ranging from 80 to 150 are controlled by the thermodynamic equilibrium between the solid and liquid phases gas volumes decrease from 200 at the top to 50 below 1 m depth pore microstructure is highly variable even on small scales salinity and other ice properties do not vary to a large degree between different regions the evolution of level multiyear sea ice is discussed with particular reference to hidden occurrence of deformed ice and the importance of ablation processes

variability of fast ice thickness in spitsbergen fjords detailed measurements of sea ice thickness and snow on sea ice were recorded at different locations in fjords along the western coast of spitsbergen the largest island in the svalbard archipelago in 2004 data corresponding to the ice situation before and after melt onset were collected for kongsfjorden and van mijenfjorden while hornsund was investigated once during early spring profiles of total thickness snow plus ice thickness were measured together with some snow thickness measure ments total thicknesses were measured with a portable electromagnetic instrument and at selected sites by drilling the three fjords show some differences in measured thicknesses connected to individual conditions however total thickness does not differ substantially between the three fjords before melt onset the modal total thickness for all three fjords before melt onset was 1 075 m and the corresponding modal snow thickness was 0 225 m bin width 0 05 m long term kongsfjorden ice thickness data since 1997 show that the maximum ice thickness varies significantly interannually as observed at other arctic sites the average maximum ice thickness for kongsfjorden was 0 71 m years 1997 98 2000 and 2002 05 and the respective average maximum snow thickness was 0 22 m in kongsfjorden 2004 was the year with highest maximum total thickness and snow thickness relative to the other years

sea ice thickness measurement using a small airborne electromagnetic sounding system the evaluation of a small electromagnetic induction sounding system for use in airborne measurement of sea ice thickness is discussed as are the results from arctic field testing also outlined are the system noise and drift problems encountered during arctic field evaluation problems which adversely affected the quality of the sounding data the sea ice sounding results indicate that for ice floes with moderate relief it should be possible to determine thickness to within 5 percent but that because of sounding footprint size and current model algorithm constraints steep sided pressure ridge keels cannot be well defined the findings also indicate that with further system improvement the day of routine sea ice thickness profiling from an airborne platform is close at hand

siliceous sediments of the guaymas basin the effect of high thermal gradients on diagenesis recent siliceous sediments of the guaymas basin a rapid spreading center in the gulf of california are intruded by basaltic sills which induced significant diagenetic and metamorphic changes in the sediments the transformation from opal a to opal ct opal ct to quartz and opal a directly to quartz in these sediments cored on dsdp leg 64 can be used to infer the temperature history and order of emplacement of intrusives at or near contacts with sills of 30 m or greater average thickness opal a inverts directly to authigenic quartz but there is less quartz than would be expected from the amount of opal a dissolution opal ct forms in sediments sandwiched between adjacent sills based on high rates of quartz nucleation and growth at high temperatures 150 c and on considerations of convective solution transfer opal ct is thought to form only where temperatures were lower or at positions between sills an environment which prevents rapid convective dissipation of silica in solution where temper

perylene occurrence alkylation and possible sources in deep ocean sediments abstract 81 deep ocean sediment samples obtained from the dsdp ipod program legs 63 66 and six gravity cores from dsdp ipod leg 64 guaymas basin gulf of california site survey cruise sio were analyzed for perylene s perylene was found to be most abundant in anoxic diatomaceous sediments containing moderate amounts of silts and or clays elevated perylene yields normalized to organic carbon contents coincided with enhanced preservation of autochthonous tetraterpenoid and tetrapyrrole pigments indicating a requirement of anoxia in the formation of perylene strongly euxinic conditions correlate with decreased perylene yields but not its total absence as found for strongly aerobic deposition and or redeposition perylene alkylation occurs in response to increasing in situ temperatures alt sub bottom depth this alkylation was found to begin with the generation of methyl c 1 perylene and to eventually yield a perylene alkyl perylene homologous series in decreasing abundance through the equivalent of c 3 trimethyl methyl ethyl propyl perylene the realm of most intense perylene alkylation for quaternary or pliocene miocene sediments corresponds with present in situ temperatures of 40 50 c or 30 35 c respectively thus the degree of perylene alkylation may represent an organic indicator for the thermal history of immature sediments geological phenomena such as reworking and igneous intrusions were found to complicate downhole perylene alkylation patterns a substituted c4h7o2 perylene was isolated from several anoxically deposited diatomaceous oozes and may represent one of the many possible perylene precursors the possible source compounds and biota for sedimentary perylene are discussed in light of the present study and review of past reports

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

tracer studies of pathways and rates of meltwater transport through arctic summer sea ice 1 at the surface heat budget of the arctic ocean sheba program s field site in the northern chukchi sea snow and ice meltwater flow was found to have a strong impact on the heat and mass balance of sea ice during the summer of 1998 pathways and rates of meltwater transport were derived from tracer studies h218o 7be and release of fluorescent dyes complemented by in situ sea ice permeability measurements it was shown that the balance between meltwater supply at the surface averaging between 3 5 and 10 5 mm d 1 and ice permeability between 10 9 m2 determines the retention and pooling of meltwater which in turn controls ice albedo we found that the seasonal evolution of first year and multiyear ice permeability and surface morphology determine four distinct stages of melt at the start of the ablation season stage 1 ponding is widespread and lateral melt flow dominates several tens of cubic meters of meltwater per day were found to drain hundreds to thousands of square meters of ice through flaws and permeable zones significant formation of underwater ice composed between 50 of meteoric water formed at these drainage sites complete removal of snow cover increase in ice permeability and reductions in hydraulic gradients driving fluid flow mark stage 2 concurrent with a reduction in pond coverage and albedo during stage 3 maximum permeabilities were measured with surface meltwater penetrating to 1 m depth in the ice and convective overturning and desalination found to dominate the lower layers of first year and thin multiyear ice enhanced fluid flow into flaws and permeable zones was observed to promote ice floe breakup and disintegration concurrent with increases in pond salinities and 7be advective heat flows of several tens of watts per square meter were derived promoting widening of ponds and increases in pond coverage stage 4 corresponds to freeze up roughly 40 of the total surface melt was retained by the ice cover within the ice matrix as well as in surface and under ice ponds with a total net retention of 15 based on this work areas of improvement for fully prognostic simulations of ice albedo are identified calling for parameterizations of sea ice permeability and the integration of ice topography and refined ablation schemes into atmosphere ice ocean models

sounding sea ice thickness using a portable electromagnetic induction instrument field trials using a man portable commercially available electromagnetic induction emi sounding instrument with a plug in data processing module for the remote measurement of sea ice thickness are discussed the processing module was made to allow for the direct determination of sea ice thickness and to show the result in a numerical display the processing module system was capable of estimating ice thickness within 10 percent of the the true ice value for ice from about 0 7 to 3 5 m thick the thickest of undeformed ice in our study area however since seawater under the arctic pack ice has relatively uniform conductivity 2 55 0 05 s m a simplified method can be used for estimating sea ice thickness using just an emi instrument this technique uses only the emi conductivity measurement is easy to put into use and does not rely on theoretically derived look up tables or phasor diagrams which may not be accurate for the conditions of the area

transpolar observations of the morphological properties of arctic sea ice save for an area between 8830 0 n and 8930 0 n where polynyas and thin ice were observed surveys of snow depth ice thickness and ice properties were conducted at ice stations thickness observations suggest a general latitudinal trend of increasing ice thickness moving northward with considerable variability from floe to floe and within a single floe average floe thicknesses varied from 1 0 to 2 8 m and the standard deviation of thickness on an individual floe was as large as 1 m ice crystallography showed a large amount of granular ice the average optical equivalent soot content was 4n g cg 1 for new snow 8 ng c g 1 for the surface granular layer of multiyear ice and 18 ng c g 1 for the interior of multiyear ice indicating a tendency of the particulates to concentrate at the surface with melting

reduced ice thickness in arctic transpolar drift favors rapid ice retreat 1 helicopter borne electromagnetic sea ice thickness measurements were performed over the transpolar drift in late summers of 2001 2004 and 2007 continuing ground based measurements since 1991 these show an ongoing reduction of modal and mean ice thicknesses in the region of the north pole of up to 53 and 44 respectively since 2001 a buoy derived ice age model showed that the thinning was mainly due to a regime shift from predominantly multi and second year ice in earlier years to first year ice in 2007 which had modal and mean summer thicknesses of 0 9 and 1 27 m measurements of second year ice which still persisted at the north pole in april 2007 indicate a reduction of late summer second year modal and mean ice thicknesses since 2001 of 20 and 25 to 1 65 and 1 81 m respectively the regime shift to younger and thinner ice could soon result in an ice free north pole during summer