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

temporal variability in currents and the benthic boundary layer at an abyssal station off central california abstract current meter records from seven sequential moorings were collected during 1993 1996 at an abyssal station off central california sta m 4100 m depth the entire 2 1 4 yr time series of the flow at 600 50 and 2 5 m above bottom above near the top of and within the benthic boundary layer were analyzed for mean flow statistics and subtidal and tidal variability the mean current vectors at each altitude were southward at profiles of light transmission and potential temperature collected intermittently during the 2 1 4 yr period showed that the benthic mixed layer at sta m extended on average 40 m above bottom range 15 80 mab evidence for local resuspension of recently deposited detritus came from time lapse photographs of the sea floor that showed a period of near bottom turbidity that corresponded to a period of high near bottom flow however rough estimates of friction velocity indicated that the bed stress usually was too low at sta m to cause local resuspension of sediments we hypothesize that the observed benthic mixed layers contained suspended particles advected from more energetic areas to the north of sta m

early diagenesis of plant pigments in hudson river sediments abstract plant pigment concentrations were measured using high performance liquid chromatography in hudson river sediments sedimentation rates and mixing characteristics were determined from depth profiles of the naturally occurring radionuclides 7be 210pb previous estimates of the mean lives 1 of plant pigments chlorophylls a and b fucoxanthin from laboratory experiments indicate a range of c 20 40 days however in the field we observed that these pigments decreased less rapidly with depth and penetrated deeper than 7be mean life 77 days in hudson sediments 95 of the time assuming similar mixing processes for particles carrying 7be and pigments this indicates that pigment decay rates in the field are slower than the 0 013 day 1 decay rate of 7be hence more than 2 fold slower than the derived laboratory rates we believe that high inputs of vascular plant detritus in the hudson may increase the complexation of humic substances with pigments resulting in slower decay rates while most pigments showed an exponential decrease with sediment depth lutein concentrations generally increased with depth this pattern of decay resistance is in agreement with laboratory experiments which show that lutein is the most decay resistant among dominant pigments these data along with other studies demonstrate that the carotenoids lacking the 5 6 epoxide group i e lutein are more decay resistant than pigments that contain it i e fucoxanthin

measuring the sea ice floe size distribution sea ice is broken into floes whose diameters range from meters to a hundred kilometers this fragmentation affects the resistance of the ice cover to deformation and the melting at floe sidewalls in summer floes are broken by waves and swell near the ice edge and throughout the pack by isostatic imbalances thermal cracking winds and currents in winter they are welded together by freezing floe size can be measured by several properties p for instance area or mean caliper diameter two definitions of floe size distribution seem useful f p the fraction of area covered by floes no smaller than p and n p the number of floes per unit area no smaller than p f p can be measured by sets other than areas such as the fraction of a line or of a point set covered by floes no smaller than p if n behaves like for small where is mean caliper diameter must be greater than 2 so that the small floes occupy finite area if 2 1 the perimeter of small floes is infinite several summertime distributions have been measured on a log log graph their slopes local values of range from 1 7 to 2 5 one distribution follows a power law the others have steeper slopes for larger floes and more gradual slopes for smaller floes another sampling strategy is to measure the lengths of line segments on floes the distribution of these chord lengths is equivalent to the distribution of floe diameters the variance of an estimate of the fraction g of area covered by floes in any size range is g 1 g k 1 where k is the equivalent number of independent samples k can be found from the autocovariance of the indicator function for the chosen size range for line sampling of a narrow range of floe diameters k is the ratio of the sample length to the floe diameter

analyzing lead information from sar images leads are relatively linear features in the sea ice cover which are composed of open water or new thin ice because of their composition leads impact the ocean air heat exchange automated analysis of leads from sea ice imagery may provide a means of gathering important information about the sea ice cover and its climatic influence this paper describes 1 a method for extracting and analyzing leads from ers 1 synthetic aperture radar sar images classified by ice type and 2 the results of using this method on images of the beaufort sea the methodology consists of identifying potential lead features in the image and measuring their characteristics both before and after using a thinning or skeletonization technique on the features the measurements obtained using this method include lead area average width number of leads in an area amount of branching and linearity of the lead these measurements were analyzed with respect to the time of year and the latitude of the images results indicate that the measurements produced by the methodology are consistent with lead measurement distributions that others have found the results of the study suggest that the methodology is appropriate to study lead characteristics on a large scale

pigment preservation and remineralization in oxic coastal marine sediments abstract complex mixtures of sedimentary chlorophyll degradation products were measured using high performance liquid chromatography hplc in 210 pb dated box and piston core sediments sediments were collected from dabob bay washington a coastal marine fjord conducive to studies yielding an understanding of the remineralization and diagenesis of organic carbon greater than 99 of the pheopigment flux out of the water column does not accumulate in the top 2 cm of sediment surface sediment pigment profiles indicate that pheophorbides are the dominant pheopigments observed with concentrations decreasing rapidly with depth concentrations of chlorophyll c derivatives also decrease rapidly but ratios of a c pheopigments remain within ranges reported for natural and cultured phytoplankton sharp pheopigment concentration decreases within the bioturbated surface sediments as defined by 210 pb activities were modeled using a one dimensional mixing model the in situ pheopigment decomposition rate corrected for bioturbation and sediment accumulation corresponds to an approximate half life of 40 days sedimentary humic acid fulvic acid and residual humin associated pheopigments in sediments which had been previously acetone extracted to remove the lipophilic pheopigment fraction were typed by chromic acid oxidation and release of pyrrole derived maleimides this humic associated pyrrole derived nitrogen while a small fraction of total sedimentary or humic nitrogen accounted for 16 75 of the total sedimentary pheopigment accumulation and may be significant in understanding the diagenetic fate and transformation of pheopigments to petroporphyrins

heat flow density measurements in the sediments of three lakes in northern sweden abstract heat flow density measurements in the sediments of three lakes 36 m 73 m and 99 m deep were carried out during a period of 3 5 years the gradient measurements were made from ice during the winter season with a bullard type probe with nine thermistors 0 5 m apart the thermal conductivity was measured in situ corrections were made for the disturbing temperature wave in the horizontally stratified sediments caused by seasonal variations in the bottom water temperature it is clearly shown that the differences in bottom water temperatures between different years can be fully corrected for only by very long time series the heat flow density values obtained are compared with measurements in boreholes and they seem to be correct to within 20 30

probable errors in width distributions of sea ice leads measured along a transect estimating the distribution of actual widths measured perpendicular to the local lead orientation knowing the apparent width distribution measured along the transect and vice versa the distribution of errors defined as the difference between the actual and apparent lead width can be estimated from the two width distributions and all moments of this distribution can be determined the problem isustrated with landsat imagery and the procedure is applied to a submarine sonar trarmect results are determined for a range of geometries and indicate the importance of orientation information ff data sampled along a transect are to be used for the description of lead geometries while the application here is to sea ice leads the methodology can be applied to measurements of any linear feature error for much of the archived sonar data an important polar sea ice is an important factor in the complex question concerns whether or not the data can be used for interaction of ocean and atmosphere reduction in the lead geometry statistics and if so what is the magnitude extent and thickness of sea ice due to global warming and of the maximum error in this paper a probabilistic the consequent increase in the number of cracks in the ice determination of this error is described providing a hereafter leads is expected to further increase global starting point for the application of stochastic geometry temperatures this positive feedback is a result of theorems in the analysis of lead geometries errors in reduced albedo and the increase in heat transfer from the ocean to the atmosphere model estimates indicate that an increase of 4 in the area covered by leads during winter could produce a hemisphere wide warming of 1 degree kelvin ledley 1988 understanding lead forma tion processes as well as the geographical and temporal distribution of lead networks is therefore important to studies of global climate measurements of ice thickness and lead coverage are commonly made along transects using upward looking submarine sonar the footprint of the sonar beam used by submarines to observe ice conditions is of sufficiently high resolution often 3 m or less as opposed to 25 m or more for satellite sensors to make it a potentially useful instrument for gathering lead statistics in fact sonar data have shown that the largest number of lead widths are in the 10 20 m range lead width statistics derived from submarine sonar data have been reported in the literature e g mclaren 1989 wadhams 1981 wadhams and horne 1950 but when lead orientation and width statistics derived for other lead and keel features are

observing the yield curve of compacted pack ice 1 a method for observing the yield curve of compacted pack ice is developed based on the characteristic analysis of the stress field within the pack ice the analysis shows that the slope of the yield curve is associated with the angle between intersecting linear kinematic features thus by measuring the intersection angles we can inversely estimate the yield curve applying this method to the observed angles generates a curved diamond yield curve which possesses almost all the advantages identified by the other methods however due to the limited data available more observations are favored to refine this yield curve

seasonal variations of sea ice motion in the canada basin and their implications ice velocities and sea level pressure data from arctic drifting buoys for 1979 85 are used to examine the seasonal variation of sea ice drift in the canada basin a recurring reversal of the mean anticyclonic gyre is demonstrated in late summer in response to changes in atmospheric forcing the identification of this reversal of ice motion is significant for numerical modeling of arctic atmosphere ocean ice interactions

coupling of near bottom pelagic and benthic processes at abyssal depths in the eastern north pacific ocean a time series site was established in the eastern north pacific ocean to study the coupling between near bottom pelagic and benthic processes at abyssal depths in an area with well documented seasonality in surface water productivity particulate total mass ptm particulate organic c poc particulate total n ptn and particulate calcium carbonate p caco fluxes were measured from sediment trap collections at 600 and 50 m above bottom from february 1990 to october 199 1 606 d the sea floor at 4 100 m was concurrently monitored with a time lapse camera over a 386 d period from july 1990 to july 199 1 during this study in situ measurements of sediment community oxygen consumption scoc were made and surface sediment samples collected seasonally with a free vehicle grab respirometer ptm poc ptn and p cac0 fluxes exhibited a strong seasonal signal with episodic peaks from spring through fall and lows in winter scoc increased sharply between winter and summer coinciding with spring peaks in particulate fluxes detrital aggregates appeared on the sea floor in pulses over a 6 month period from july to december 1990 coinciding with periods when particulate fluxes were elevated but delayed 1 5 months after the initial peaks in particulate flux mobile epibenthic megafauna monitored with time lapse photography consisted primarily of holothuroids and echinoids and were twice as active when detrital aggregates were observed on the sea floor as during the rest of the year our results show a temporal relationship between the flux of particulate matter entering the benthic boundary layer the arrival and residence of detritus on the sea floor and the activity of the sediment community and mobile epibenthic megafauna

modeling coulombic failure of sea ice with leads 1 sea ice failure under low confinement compression is modeled with a linear coulombic criterion that can describe either fractural failure or frictional granular yield along slip lines to study the effect of anisotropy we consider a simplified anisotropic sea ice model where the sea ice thickness depends on orientation accommodation of arbitrary deformation requires failure along at least two intersecting slip lines which are determined by finding two maxima of the yield criterion due to the anisotropy these slip lines generally differ from the standard coulombic slip lines that are symmetrically positioned around the compression direction and therefore different tractions along these slip lines give rise to a nonsymmetric stress tensor we assume that the skewsymmetric part of this tensor is counterbalanced by an additional elastic stress in the sea ice field that suppresses floe spin we consider the case of two leads initially formed in an isotropic ice cover under compression and address the question of whether these leads will remain active or new slip lines will form under a rotation of the principal compression direction decoupled and coupled models of leads are considered and it is shown that for this particular case they both predict lead reactivation in almost the same way the coupled model must however be used in determining the stress as the decoupled model does not resolve the stress asymmetry properly when failure occurs in one lead and at a new slip line

heat flow measurement in lacustrine or oceanic sediments without recording bottom temperature variations water bottom temperature variations btv introduce many uncertainties into heat flow density hfd values determined from the temperature depth t z plot from a one time probe insertion into the top few meters of sediments the btv have to be carefully monitored for a number of years up to the date of the probe measurements this makes the method time consuming and economically unattractive in this paper we present the theory for a promising new technique the method does not require monitoring of the btv but does require at least two t z profiles separated in time by only a few months a generalized inversion of the btv history using the separated t z data and any other a priori information that is available is then performed in the frequency domain to give the most probable bayesian estimates of various parameters and their error bounds numerical examples show that the inversion can resolve not only the hfd but also the mean sediment surface temperature and gives information on the longer term trend as well as details of the btv over the previous year these together with thermal properties structure are the factors that contribute most to the shape of the time dependent t z profiles used in a typical situation where a uniform half space with a background hfd 60 mw m 2 has been perturbed by complex btv with a maximum variation of 1 8 k using a misguessed hfd of 90 100 mw m 2 in the inversion of two t z profiles taken 3 months apart over a 2 to 5 m section results in a posteriori hfd of 58 11 m w m 2 although the technique gives an optimally determined mean hfd its principal value lies in the ability to place reliable error bounds on the mean

modelling the reorientation of sea ice faults as the wind changes direction a discrete element model of sea ice is used to study how a 900 change in wind direction alters the pattern of faults generated through mechanical failure of the ice the sea ice domain is 400 km in size and consists of polygonal floes obtained through a voronoi tessellation initially the floes are frozen together through viscous elastic joints that can break under sufficient compressive tensile and shear deformation a constant wind stress gradient is applied until the initially frozen ice pack is broken into roughly diamond shaped aggregates with crack angles determined by wing crack formation then partial refreezing of the cracks delineating the aggregates is modelled through reduction of their length by a particular fraction the ice pack deformation is neglected and the wind stress is rotated by 90 degrees new cracks form delineating aggregates with a different orientation our results show the new crack orientation depends on the refrozen fraction of the initial faults as this fraction increases the new cracks gradually rotate to the new wind direction reaching 90 degrees for fully refrozen faults such reorientation is determined by a competition between new cracks forming at a preferential angle determined by the wing crack theory and at old cracks oriented at a less favourable angle but having higher stresses due to shorter contacts across the joints

sedimentary pigments and nature of organic matter within the oxygen minimum zone omz of the eastern arabian sea indian margin abstract sedimentary pigments carbon and nitrogen content and their stable isotopes were studied in three short cores collected from the oxygen minimum zone omz of the eastern arabian sea eas nine pigments including chlorophyll a and their degradation products were quantified using high performance liquid chromatography hplc astaxanthin followed by canthaxanthin and zeaxanthin were the major carotenoids detected in these cores the total pigment concentration was high in the core collected from 500 m water depth 6 5 gg 1 followed by 800 m 1 7 gg 1 and 1100 m 1 1 gg 1 depths respectively the organic carbon did not have considerable control on sedimentary pigments preservation pigment degradation was comparatively high in the core collected from the 800 m site which depended not only the bottom dissolved oxygen levels but also on the faunal activity as reported earlier the bottom water dissolved oxygen and presence of fauna have good control on the organic carbon accumulation and preservation at indian margin omz sediments the c n ratios and 13 c values for all the cores conclude the marine origin of organic matter and 15 n profiles revealed signature of upwelling associated denitrification within the water column

modeling linear kinematic features in sea ice abstract sea ice deformation is localized in narrow zones of high strain rate that extend hundreds of kilometers for example across the arctic basin this paper demonstrates that these failure zones may be modeled with a viscous plastic sea ice model using an isotropic rheology if the ice is assumed to be heterogeneous at the grid scale and allowed to weaken in time intersecting failure zones propagate across the region the direction of failure propagation depends upon the stress applied to the ice wind stress and boundary conditions and the rheological model describing plastic failure of the ice the spacing between failure zones is controlled by the magnitude of the wind stress and the distribution describing spatial variability of ice strength sea ice motion and deformation oscillate at close to a 12 h period throughout the arctic and antarctic pack ice this oscillation is found at all spatial scales from hundreds of kilometers to the lead scale it is shown that with an inertial embedded mo

development of a new system for shallow sea heat flow measurement and its test application in the gulf of thailand abstract a new technique has been developed for the heat flow measurement in shallow seas the temperature in the sediment is measured at every 10 cm to the depth of 5 m by only one thermistor which moves up and down in the probe from the temperature data thus obtained the geothermal gradient is calculated in the least square sense by solving the thermal diffusion equation that is assuming an annual sinusoidal temperature variation at the sea bottom of which amplitude and initial phase are parameterized this system was used in the gulf of thailand and detailed temperature distributions were obtained in the future however to obtain more accurate heat flow values it is considered necessary to measure the temperature to at least the depth of 7 10 m

modeling ice dynamics of coastal seas a coupled sea ice barotropic ocean model with a 1 km resolution and a seaward domain of 200 km quantifies three coastal processes coupling of ice motion to wind driven coastal currents ice thickness redistribution under compaction at the coast and formation of coastal shear zones the model consists of an ice momentum balance mass concentration and two parameter ice thickness distribution and equations for horizontal water motion and continuity using vertical structure functions an appropriate constitutive law appears to be a hardening plastic based on qualitative observations from alaskan continental shelves for first year sea ice strength is taken to be proportional to the square of ice thickness a north wind example of 10 m s with the coastline to the west shows the depth dependence of rotational shear in the sea ice ocean boundary layer and sea surface tilt which contributes an alongshore slope current there is slight convergence of sea ice over the shelf a coastal shear zone of 4 km and an alongshore ice speed seaward of the shear zone of 6 of the wind speed caused by the combination of an under ice shear layer and an alongshore slope current for an onshore wind ice is near free drift at 3 of the wind seaward of a ridging front which propagates seaward a square dependence of ice strength on thickness is required for the rubble field to approach a limiting thickness consistent with observations the hardening plastic interpretation of the rubble field has the stress state at the yield limit in contrast with a rigid plastic of high constant strength that yields only at the coast we conclude that 1 ice thickness motion feedback is important on scales less than 10 km 2 the observational base to discriminate between mesoscale constitutive laws is not yet available and 3 the relation of ice velocity to wind stress is variable because the ocean slope current responds only to the alongshore component of the wind

a 5 year satellite climatology of winter sea ice leads in the western arctic the distribution of openings leads and polynyas in polar sea ice is not well known this study estimates the large scale distribution and variability of leads in the arctic of the western hemisphere in winter using a 5 year record of defense meteorological satellite program thermal and visible band imagery the occurrence density and orientation of leads are derived from gridded maps made at 10 day intervals their mean value and interannual seasonal and monthly variabilities are estimated lead densities are observed to be highest in early winter decreasing 20 from november through april the highest densities are observed in the central canada basin and the lowest are in the east siberian sea there is limited interannual variability in the positions of maximum and minimum densities preferred lead orientations are identified as generally north south in the beaufort sea sector and east west in the east siberian sea sector with transitional orientations in the intermediate area the mean distributions of lead density and orientation are observed to be associated with large scale mean fields of ice divergence and shear respectively

spatial and temporal characterization of sea ice deformation in late march 2007 an array of gps ice drifters was deployed in the beaufort sea as part of the sea ice experiment dynamic nature of the arctic sedna the drifters were deployed in an array designed to resolve four nested spatial scales of sea ice deformation from 10 to 140 km with the arrays maintaining appropriate shape for strain rate calculation until mid june in this paper we test whether sea ice deformation displays fractal properties in the vicinity of sedna we identify that deformation time series have different spectral properties depending on the spatial scale at the scales around 100 km deformation is a red noise process indicating the importance of the ice pack surface forcing in determining the deformation rate of sea ice at this scale at smaller scales the deformation becomes an increasingly whiter process it has pink noise properties which suggests an increasing role of dissipative processes at smaller scales at spatial scales of 10 100 km and sub daily scales there is no deformation coherence across scales coherence only becomes apparent at longer scales greater than 100 km the lack of coherence at small scales aids in understanding previous observations where correlation between 10km regions adjacent to each other varied widely with correlation coefficients between 0 3 and 1 this suggests it is not appropriate to think of sea ice as having a decorrelation length scale for deformation we find that lead scale observations of deformation are required when estimating ice growth in leads and ridging time series for the two sedna arrays we find coherence between 140 and 20 km scale deformation up to periods of 16 days this suggests sea ice deformation displays coherent deformation between 100 km scale and the scale of the beaufort sea of order 1000 km over synoptic time periods daily to weekly timescales organization of leads at synoptic and larger scales is an emergent feature of the deformation field that is caused by the smooth variation of surface forcing wind on the ice pack

a temperature probe survey on the louisiana shelf effects of bottom water temperature variations a survey of temperature gradients in the uppermost sediments of the louisiana continental shelf was done in 1983 by gulf oil corporation using a 5 m long temperature probe the survey covered 450 sq mi with an average grid spacing of less than 1 mi the purpose was to detect heat flow anomalies due to subsurface fluid flow however thermal perturbations due to seasonal variation of bottom water temperature mask the temperature gradients due to geological heat flow bottom water temperature variations similar to those recorded near the survey area in 1963 1965 explain most of the observed spatial and temporal changes in shallow temperature depth profiles the data set from this detailed survey has been donated to a publicly accessible scientific database to spur resear h into heat flow measurement on continental shelves

effect of shear rupture on aggregate scale formation in sea ice a discrete element model is used to study shear rupture of sea ice under convergent wind stresses the model includes compressive tensile and shear rupture of viscous elastic joints connecting floes that move under the action of the wind stresses the adopted shear rupture is governed by coulomb s criterion the ice pack is a 400 km long square domain consisting of 4 km size floes in the standard case with tensile strength 10 times smaller than the compressive strength under uniaxial compression the failure regime is mainly shear rupture with the most probable scenario corresponding to that with the minimum failure work the orientation of cracks delineating formed aggregates is bimodal with the peaks around the angles given by the wing crack theory determining diamond shaped blocks the ice block floe aggregate size decreases as the wind stress gradient increases since the elastic strain energy grows faster leading to a higher speed of crack propagation as the tensile strength grows shear rupture becomes harder to attain and compressive failure becomes equally important leading to elongation of blocks perpendicular to the compression direction and the blocks grow larger in the standard case as the wind stress confinement ratio increases the failure mode changes at a confinement ratio within 0 2 0 4 which corresponds to the analytical critical confinement ratio of 0 32 below this value the cracks are bimodal delineating diamond shape aggregates while above this value failure becomes isotropic and is determined by small scale stress anomalies due to irregularities in floe shape

heat flow and gravity responses over salt bodies a comparative model analysis two dimensional numerical modeling of sea floor heat flow and water bottom gravity responses to systematic variations in simple subsurface salt body geometries provides insight on the relative usefulness of these two data types for extracting salt geometry information for a given salt body geometry diffusion of heat through overlying sediments results in a dramatic decrease in the amplitude of heat flow anomalies as the depth to the top of the salt body increases for top of salt depths greater than about 1 km the heat flow response is insensitive to the length of salt feeder stocks and to the thickness of salt tongues sheets this shallow depth to top of salt sensitivity range in addition to a number of environmental factors that can adversely affect interpretation of heat flow anomalies in terms of heat refraction towards and through salt bodies severely limits the usefulness of sea floor heat flow data for constraining aspects of salt body geometry for gravity data the critical factor for addressing salt body geometry is the distribution of salt relative to the sediment salt density crossover depth above and below which salt is more and less dense respectively than the surrounding sediment except when the relevant geometry information being sought presence and or length of feeder stock thickness of salt tongue or sheet is near the density crossover depth the geometry related information content of the gravity field is greater than that of the heat flow field based on these model results measurement uncertainty considerations and data limitations we conclude that gravity data generally offer an order of magnitude greater resolution capability than sea floor heat flow data for addressing salt body geometry issues of exploration interest

early diagenetic alteration of chlorophyll a and bacteriochlorophyll a in a contemporaneous marl ecosystem florida bay abstract this report covers the analyses of tetrapyrrole pigments in sediments and numerous source biota from northern central florida bay sediment cores were all carbonate marls and bedrock pleistocene limestones was typically at 0 6 1 2 m bsf below sea floor extraction of the sediments was performed using tetrahydrofuran shown to be 3 7 times as effective as more common solvents surficial sediments were found to contain a pigment distribution indicating a diatomaceous cyanobacterial biofilm mat underlain with purple sulfur bacteria as the microphytobenthos downhole trends in pigment diagenesis revealed differences due to paleoenvironment that is when bacteriochlorophyll a bchla plus derivatives were elevated indicating strong syn depositional anoxia the pheophytins a ptinsa were the major chlorophyll a chla derivatives conversely when bchl a plus derivatives were low indicating oxic to dys oxic syn depositional conditions then pyropheophorbide a ppbida and 132 172 cyclopheophorbide a cyclo were strongly dominant the generation of cyclopheophorbide in carbonate marls with weakly anoxic to dysoxic syn depositional conditions may yield an oil source paleoenvironmental marker for bitumen containing compounds such as bicycloalkanoporphyrins bicaps downhole conversions were observed for the following diagenetic steps chla to pheophytin a ptina ptina to pyropheophytin a pptina ppbida to cyclo bchla to bacteriopheophytin a bptina and bptina to bacteriopyropheophytin a bpptina

on the effects of thermal properties structure and water bottom temperature variation on temperature gradients in lake sediments in heat flow determinations it is customary to treat the surface temperature variation as a finite sum of fourier components the medium is assumed to be homogeneous or horizontally stratified wit

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

compressive shear faults within arctic sea ice fracture on scales large and small 1 we examined fracture features within arctic sea ice as revealed by landsat 7 and radarsat imagery by an aerial survey and through observations in the laboratory of specimens loaded to brittle failure under biaxial compression regardless of scale which spans the range from kilometers to millimeters the features look alike they consist mainly of narrow lineaments that traverse the field of view plus wing like and comb like secondary cracks the lineaments occasionally intersect and generally exhibit either right lateral or left lateral relative movement like strike slip faults within earth s crust we term them brittle compressive shear faults they form through the linking of en echelon arrays of deformation induced secondary cracks from an application of wing crack and comb crack mechanics we estimated the maximum compressive stress near the onset of faulting and found that our estimates compare favorably with in situ measurements by earlier investigators of ice sheet failure stresses to account for the brittle behavior of the sea ice cover we applied a recent model of the ductile to brittle transition in which the key idea is the competition between stress buildup and stress relaxation at stress concentrators in identifying the nature of sea ice fracture features we advance the view that failure occurs on many scales through highly localized as opposed to uniformly distributed deformation via the operation of scale independent mechanisms

mathematical characteristics of sea ice dynamics models mathematical characteristics of plasticity models that describe large scale sea ice behavior are studied in an attempt to understand the models better and to compare the analytical results to observed ice behavior separate stress and velocity characteristics occur when a nonassociated flow rule is used the two sets coincide for associated flow rules the relative orientation of characteristic directions at a point can change depending on the stress state and the direction of plastic stretching two real velocity characteristic directions exist when the magnitude of shearing exceeds the magnitude of dilating one exists when they are equal and none exist when the shearing magnitude is less than the dilating magnitude the system is hyperbolic parabolic or elliptic respectively in these conditions quasi steady elastic plastic and viscous plastic models have identical characteristics so that we cannot use the characteristics to discriminate between these models attention has been focused on the velocity characteristics with the desire to relate these directions directly to leads and other features observed in satellite imagery the velocity characteristic curves cannot stretch so that floes lying along a characteristic line neither approach nor separate from each other therefore the amount of open water will not change between these floes which makes it unlikely that we will be able to observe fields of characteristic directions directly in satellite imagery we have however observed velocity discontinuities across large scale lead systems which are special characteristic curves this result offers a way to use remotely sensed imagery directly to estimate part of the deformation field

heat flow measurements in 17 perialpine lakes thirty eight heat flow measurements were carried out in 17 perialpine lakes to supplement the scanty information concerning the thermal conditions in the crust underlying central europe a probe of the corer type was built which allowed the measurement of 11 temperatures at equally spaced subbottom intervals to a maximum penetration of 10 5 m measurements of this type were made in lake constance greifensee lake zurich lake zug lake lucerne baldeggersee lake biel lake murten lake neuch tel lake geneva lac d9annecy lac de bourget lago maggiore lago di lugano lago di como lago d9iseo and lago di garda after retrieval of the probe a sediment core was collected for samples on which thermal conductivity was measured with the needle probe method after treating the material to remove exsolved gas pubbles continuous seismic reflection and reflection profiles in all of these lakes provided a set of parameters for gradient correction due to heat flow refraction additional corrections were applied on the basis of palynologically determined sedimentation rates and for the influence of the last period of glaciation final heat flow values obtained in this manner are given the lesser values are generally found in the more western lakes north of the alps the higher values are found in the more eastern lakes north and south of the alps the higher values are partially confirmed by earlier measurements in lakes but show considerable discrepancy with measurements from the central alps this could be explained by the underthrusting of a cold wedge under the aar and gotthard massif in the late miocene and early pliocene which then would lower the temperature gradient in the central alps

sub bottom temperature perturbations due to temperature variations at the boundary of inhomogeneous lake or oceanic sediments abstract for many years continental heat flow data were obtained from temperature gradients measured in boreholes and conductivity measurements made on representative cores because of the difficulty of obtaining deep holes in suitable regions increasing use is being made of measurements made in the top few meters of the sediments at the bottom of continental lakes for reliable heat flow results two conditions must be met first an accurate record of the temperature history at the top of the sediment should be available preferably over a time span of 4 or 5 years second if the thermal properties are not constant with depth then the depth dependence should be known errors that may arise if either or both of these conditions cannot be met can be serious using various surface thermal histories we compare results from models assuming constant diffusivity a diffusivity changing exponentially with depth and a layered medium all being structures based upon observed variations near the sediment water interface where conductivity may change by a factor of two over 2 or 3 m in some situations errors as large as several hundred percents may occur but in such cases it should be possible to deduce from the data that something has occurred to make the data unreliable more realistically there are occasions where a temperature depth plot which is linear within normally acceptable limits of accuracy and with a gradient that is within the range of expectations may be as much as 100 in error

small scale deformation of an arctic sea ice floe detected by gps and satellite imagery abstract small scale 100 200 m deformations of an arctic sea ice floe were detected from multiple gps equipped buoys that were deployed on the same ice floe over a nine month period three deformation events were recorded at each case the event was of limited duration each lasting less than a day the events were highly compressive in nature with the area occupied by the buoy array decreasing by over half of the original area the strain rate during the deformation of the order of 10 5 s 1 is about three orders of magnitude larger than previous estimates for brittle fracturing for cracks of about 100 m in length on the 2 day time scale the strain rate became too small and none of the deformation events could be detected this suggests that satellite data with longer time scales may significantly underestimate the amount of intermittent small scale brittle failure of total deformation taken as a whole our results show the influence that large scale wind stress can have on small scale deformation however it is important to note that the impact of large scale wind stress is also dependent on the properties of sea ice as well as on the spatial and temporal evolution of the underlying forces that influence the fracturing process

pyrophaeophorbide a as a tracer of suspended particulate organic matter from the ne pacific continental margin pyrophaeophorbide a a degradation product of chlorophyll a is predominantly formed by grazing processes in sediments as well as in the water column water column profiles of pyrophaeophorbide a suspended particulate organic carbon spoc concentrations at an abyssal site in the northeast ne pacific sta m 34 50 n 123 00 w 4100 m water depth show low concentrations 0 01 0 1 ng g spoc at surface and mesopelagic depths and increasing concentrations with closer proximity to the sea floor 0 05 0 6 ng g spoc however in june 1992 the deep maximum of pyrophaeophorbide a spoc in the water column of sta m extended higher into the water column as much as 1600 m above the bottom mab 2500 m water depth in other seasons they only extended up to 650 mab 3450 m water depth previous studies have demonstrated lateral transport of particulate matter from the continental shelf to the deep ocean off the coast of northern california recent work suggests that the benthic boundary layer bbl extends to 50 mab based on sediment trap and transmissometry measurements smith k l kaukmann r s baldwin r j 1994 coupling of near bottom pelagic and benthic processes at abyssal depths limnology and oceanography 39 1101 1118 and that lateral transport is significant only during summer which is consistent with our observations a partial vertical profile of pyrophaeophorbide a spoc from the north central nc pacific provides some evidence that the deep maximum may be absent due to the distance of this site from the continental margin thus the observed deep maximum of pyrophaeophorbide a spoc at sta m is likely due mainly to lateral transport from the continental slope rather than to local vertical resuspension in the bbl exclusively pyrophaeophorbide a concentrations in spoc at sta m were negatively correlated with 14c values of spoc spoc samples from druffel e r m bauer j e williams p m griffin s a and wolgast d 1996 seasonal variability of particulate organic radiocarbon in the northeast pacific ocean journal of geophysical research 101 20543 20552 further supporting our contention that pyrophaeophorbide apeaks in the deep water column are derived from older resuspended sediments that were laterally transported from continental margin sediments our molecular biomarker pyrophaeophorbide a data are reflective of a specific fraction of spoc that likely remains in the water column for long periods of time or is derived from resuspended sediments

two dimensional deformation patterns in sea ice the mechanical behaviour for the geome trical properties of two dimensional def ormation has been investi gated the mohr formulation of failure which is based on the concept of slip at the plane of weakness is used in this study it is shown that alteration of the shear stress t n at the plane of weakn ess requires self similarity of features in deformation patt erns a general relationship between the angle of internal friction and the breaking angle of deformation patterns is derived using imagery data this relat ionship is used to find the angle of internal friction from selected sea ice deforma tion patterns the value obtained for this angle is is 0 20 for deform ation on a scale from 100 m to 100 km

on the spacing and draft distributions for pressure ridge keels the negative exponential distribution is reconsidered as a description of pressure ridge spacings and drafts it is found to give an excellent fit for drafts but not for spacings the spacing distribution is found to be fitted much better by a three parameter lognormal distribution of which the third parameter the threshold is dependent on the beam width of the instrument used to collect the ice bottom profile

hierarchy and sea ice mechanics a case study from the beaufort sea hierarchy implies that the study of sea ice can be divided into analysis of subsets of processes based on scale and their interaction with adjacent scales we apply these concepts to regional sea ice dynamics the apparent self similar property of ice floes seen in aircraft or satellite images argues for an aggregate nature of sea ice that viscouslike regional behavior arises from discrete floe interactions however for some regions and some times characteristic behavior where lead patterns seen in basin wide advanced very high resolution radiometer images appear to be related to coastal orientation hundreds of kilometers away suggests that small regional scale processes o 10 km and discontinuities in the velocity or stress state along boundaries can affect the larger scale sea ice distribution and dynamics o 500 km thus sea ice displays both aggregate type behavior and discontinuous type behavior based on the history of forcing and shape of the enclosing basin the appropriate matching of atmospheric processes to sea ice processes in air ice interaction is through the sea ice deformation field rather than the response of ice velocity to the local wind this is because atmospheric forcing and sea ice deformation have matching energetic scales at several hundred kilometers and timescales of days an example of northerly winds during the april 1992 arctic leads experiment period suggests discontinuous type behavior upwind of the alaska coast followed by a general opening behavior with easterly winds there appear to be natural scale divisions between climate scale sea ice processes of o 100 300 km which resolve aggregate behavior regional scale o 10 50 km which is necessary to resolve observed shearing behavior and the floe scale o 1 km because the climate scale is two levels removed from the floe scale care must be exercised in using ice properties from the floe scale in climate scale models ice strength is an example of such a scale dependent parameter

warm water cells in the north water northern baffin bay during winter sea surface temperatures above the freezing point of seawater 1 8 c were observed in the north water during winter and early spring the result indicates a possibility of upwelling warm water presumably of atlantic origin brought from lower depths to the surface the warm water temperatures ranged from 1 7 to 0 1 c the highest occurrence frequency lay in the temperature interval from 1 0 to 0 8 c most warm water cells were found along the greenland coast in smith sound lady ann strait and barrow strait they occurred most frequently in smith sound west of cape alexander the highest temperatures of 0 1 c occurred however south of cape alexander the occurrence frequency and the total area of warm water patches decreased toward spring the predominantly northerly wind that is channeled in smith sound accounts for a mean ice drift of approximately 17 km d 1 this ice drift causes an ice divergence in smith sound and along the greenland coast the existence of warm water areas can be explained by the strong northerly wind resulting in a coriolis force that induces coastal upwelling the wind induced offshore transport of 3 5 105 m3 s 1 in the north water compensated by the upwelling of atlantic baffin bay water 0 c along the greenland coast will suffice to keep 10 of the north water ice free the combination of ice divergence and forced convection of warm water can be considered as a prime cause of the polynyas in the north water

inversion of temperature measurements in lake sediment summary the problem of determining heat flow density hfd from temperature data obtained in lake sediments is formulated using an iterated linear inverse theory with numerical results presented in the forms of probability density function and sensitivity coefficient the galerkin finite element method and a weighted finite difference scheme are used in the spatial and temporal domains respectively to allow for layered structure in the sediments and for transient disturbances arising from lake bottom temperature variation btv with time when a record of btv is lacking inversion of temperature data from a single probe penetration gives an unreliable estimate of hfd this difficulty is alleviated by using multiple probe measurements which if taken at intervals of several months prove adequate for a reliable estimation of the hfd and the most recent part of btv thermal properties of the sediments however must be accurately known a priori because a simultaneous estimation of hfd btv and the thermal properties remains unattainable in a practical case hfd is usually resolved to the same extent that thermal conductivity is known a priori

carotenoid diagenesis in recent marine sediments ii degradation of fucoxanthin to loliolide abstract the quantitative distributions of loliolide and the major phytoplankton carotenoids fucoxanthin diadinochrome diatoxanthin and carotene in two cores of anoxic marine sediment recovered from the peru continental shelf are reported our results demonstrate that the rapid degradation of carotenoids in sediments is not a result of their high degree of unsaturation as has been previously suggested instead carotenoids exhibit a wide range of degradation rates that are proportional to the ability of specific pigments to form unstable bicyclic furanoxides carotenoid furanoxides undergo subsequent fragmentation to loliolide isololiolide dihydroactinidiolide and other as yet undetermined low molecular weight products this degradation pathway accounts for the relative rates of removal for specific carotenoids fucoxanthin fucoxanthinol diadinoxanthin diatoxanthin carotene the distribution of carotenoids reported by wpatts and maxwell 1977 and c ardoso et al 1978 in ancient sediments the occurrence of novel carotenoid transformation products in surface sediments reported by r pidout et al 1984 and the distribution of loliolides in recent sediments recovered from the namibian shelf reported by k plok et al 1984a b we predict that loliolide and isololiolide will inherit a specific stereochemistry from their carotenoid precursors but that dihydroactinidiolide will be racemic for every mole of fucoxanthin degraded in peru sediments 0 7 1 1 mole of loliolide is produced summation of fucoxanthin and loliolide at each subsurface horizon yields an estimate of the total deposition of fucoxanthin at t 0 throughout the 0 20 cm depth of our samples this parameter is remarkably constant to 16 individual horizons exhibit excursions which may reflect changes in surface productivity extrapolation of our measurements to deeper sediments may therefore be of some value in deciphering questions on environmental conditions of deposition and paleoproductivity

thermal history of deep sea sediments as a record of recent changes in the deep circulation of the eastern mediterranean 1 during three cruises of the medriff project in 1993 and 1994 154 geothermal heat flow measurements and seven ctd profiles in the water column have been collected along a 300 km sw ne oriented transect traversing the mediterranean ridge accretionary complex the original goal of the measurements was to identify areas of anomalous heat flow that could be interpreted as possible sites for fluid outflow contrary to expectations the upper few meters of the temperature profiles in the sediments showed decreasing temperature from the seafloor down to 3 to 6 m depth indicating consistently transient temperature regimes the only exception positive heat flow was found in the sirte abyssal plain measurements collected in the same area at different times indicated that the thermal structure in the bottom water and sediments had changed significantly at weekly monthly and interannual timescales one dimensional forward modeling of the conductive heat propagation into the sediment explains the observed thermal anomalies assuming up to 0 5 k warming of the bottom waters that propagated south westward from the matapan trench to the crestal area of the mediterranean ridge analysis of nonsteady state thermal profiles in the upper sediment provided time information on the onset of bottom water warming by what is now called the eastern mediterranean transient emt the sediment warming started in the matapan trench between spring 1992 and spring 1993 and reached the mediterranean ridge crest in spring summer 1993 the average propagation velocity of the thermal perturbation along the profile is about 0 5 1 6 km d 1 0 6 1 8 cm s 1

regime shifts in mesoscale deformations of sea ice during the winter large temporary rigid areas in the arctic sea ice cover form and disintegrate in a few days during winter when these rigid areas are shore fast they eliminate moment flux from air to water via wind forcing on the ice temporary shore fast ice causes mixing of upper stratified waters below the ice in areas of strong tidal currents satellite data and observations by explorers in the arctic show that large rigid areas tend to break up during the summer we can conclude that formation and breakup of rigid areas are sensitive to temperature the present study illustrates techniques for satellite observation of the dynamics of the arctic sea ice cover during winter better understanding of the physical mechanisms involved will enhance codes for such satellite observations the study indicates anomalous critical dynamics and scale invariance in the formation and breakup of rigid areas these indications come from direct satellite observations and are supported by generic conceptual models for ice dynamics during winter critical phenomena often form fractal structures with no natural lengths

sources and transport of land derived particulate and dissolved organic matter in the gulf of mexico texas shelf slope the use of ligninphenols and loliolides as biomarkers the fate and transport of terrestrial organic matter across the continental margin in the gulf of mexico was studied in 1992 and 1993 using chemical biomarkers lignin phenols were utilized as biomarkers for terrestrial inputs and indicated that much of the terrestrial organic matter inputs were deposited on the shelf break and slope the lignin phenol concentrations normalized to carbon in poc hmw doc and sediments in slope waters were considerably higher than at other open ocean sites studied previously the dominant mechanism for transport of terrestrially derived poc and hmw doc across the shelf and slope was hypothesized to be advection of riverine and estuarine discharges through benthic nepheloid layers based on loliolide concentrations in the water column we believe that lateral transport of these materials at the shelf break through extensions of benthic nepheloid layers may have been an important mechanism for the injection of terrestrially derived organic matter into deep slope waters

a novel heat flux study of a geothermally active lake lake rotomahana new zealand abstract a new technique for measuring conductive heat flux in a lake was adapted from the marine environment to allow for multiple measurements to be made in areas where bottom sediment cover is sparse or even absent this thermal blanket technique pioneered in the deep ocean for use in volcanic mid ocean rift environments was recently used in the geothermally active lake rotomahana new zealand heat flow from the lake floor propagates into the 0 5 m diameter blanket and establishes a thermal gradient across the known blanket thickness and thereby provides an estimate of the conductive heat flux of the underlying terrain this approach allows conductive heat flux to be measured over a spatially dense set of stations in a relatively short period of time we used 10 blankets and deployed them for 1 day each to complete 110 stations over an 11 day program in the 6 3 km lake results show that lake rotomahana has a total conductive heat flux of about 47 mw averaging 6 w m2 over the geothermally active lake the western half of the lake has two main areas of high heat flux 1 a high heat flux area averaging 21 3 w m2 along the western shoreline which is likely the location of the pre existing geothermal system that fed the famous pink terraces mostly destroyed during the 1886 eruption 2 a region southwest of patiti island with a heat flux averaging 13 1 w m2 that appears to be related to the explosive rift that formed the lake in the 1886 tarawera eruption a small rise in bottom water temperature over the survey period of 0 01 c day suggests the total thermal output of the lake is 112 132 mw and when compared to the conductive heat output suggests that 18 42 of the total thermal energy is by conductive heat transfer