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

geoacoustic inversion with ships as sources estimation of geoacoustic parameters using acoustic data from a surface ship was performed for a shallow water region in the gulf of mexico the data were recorded from hydrophones in a bottom mounted horizontal line array hla the techniques developed to produce the geoacoustic inversion are described and an efficient method for geoacoustic inversion with broadband beam cross spectral data is demonstrated the performance of cost functions that involve coherent or incoherent sums over frequency and one or multiple time segments is discussed successful inversions for the first sediment layer sound speed and thickness and some of the parameters for the deeper layers were obtained with the surface ship at nominal ranges of 20 30 or 50 water depths the data for these inversions were beam cross spectra from four subapertures of the hla spanning a little more than two water depths the subaperture beams included ten frequencies equally spaced in the 120 200 hz band the values of the geoacoustic parameters from the inversions are validated by comparisons with geophysical observations and with the parameter values from previous inversions by other invesigators and by comparing transmission loss tl measured in the experiment with modeled tl based on the inverted geoacoustic parameters

geomagnetic secular variation from holocene lake sediments of soro so denmark abstract a record of geomagnetic secular variation for the last 7500 years has been obtained from three cores of lake sediment from soro so in denmark the time scale has been derived from six radiocarbon age determinations on one of the cores variations in geomagnetic declination and inclination agree well with those found in a previous study using sediments from another danish lake skanderborg so some 120 km from soro so a correlation with the record from the u k has been made but with age differences of up to 1000 years which are attributed to the dating errors inherent in the radiocarbon method when applied to lake sediments in both the u k and danish sediments the virtual geomagnetic pole path since 7500 bp appears to have had periods of both clockwise and anticlockwise motion of 1000 year duration where the looping is open interspaced with shorter periods of 500 years in which the geomagnetic behaviour is more irregular it is suggested that this indicates a possible regularity in the pattern of field behaviour during the post glacial

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

nonlinear frequency dependence of the effective seabottom acoustic attenuation from low frequency field measurements in shallow water hamilton s seabed geo acoustic model which is widely accepted predicts that the attenuation of sound in marine sediments increases linearly with frequency over the full frequency range of interest in ocean acoustics a few hertz to megahertz however biot stoll s physics based seabed geo acoustic model predicts that the bottom attenuation should exhibit non linear frequency dependence particularly in sandy bottoms since the publication of previous papers zhou j acoust soc am 78 1003 1009 1985 kibblewhite ibid 86 716 738 1989 more low frequency field data collected from different coastal zones around the world have shown inconsistencies with the often used linear frequency dependence this paper attempts to support the non linear frequency dependence of sea bottom attenuation through a review of shallow water acoustic field measurements with a special emphasis on the 50 1000 hz frequency range the relevant measurements include bottom reflection loss sound transmission loss dispersion analysis vertical coherence of both propagation and reverberation normal mode spatial filtering and optimum frequency and transition range of sound propagation a non linear frequency dependence of equivalent bottom acoustic attenuation derived from these measurements will be introduced work supported by onr and nnsf of china

palaeomagnetism of post glacial lake sediments from skanderborg so jutland denmark abstract a palaeomagnetic record extending back to 8000 bp has been obtained from cores of sediment from lake skanderborg in denmark the time scale has been calibrated by 24 radiocarbon dates on three of the cores the main features in the declination and inclination records can be correlated with those in records from the united kingdom but with age differences of up to 1000 yr in general features younger than about 4500 bp appear to be older in the danish record than in the united kingdom record whereas features older than 4500 bp appear to be younger the motion of the geomagnetic vector since 6000 bp has included both clockwise and anticlockwise looping but most of the open looping is clockwise the magnetic properties of the sediment are consistent with the major carrier of the remanence both natural and induced being fine grained magnetite

tidal forcing on sea ice drift and deformation in the western weddell sea in early austral summer 2004 abstract sea ice drift and deformation in the western weddell sea in early austral summer of 2004 are characterised using in situ data from a meso scale array of 24 drifting ice buoys horizontal gps derived position measurements are available from drifting buoys deployed as part of the ice station polarstern ispol experiment for 26 days during late november and december 2004 at various temporal resolutions and spatial accuracies these data form the basis for sea ice velocity and deformation measurements across the meso scale ispol array and at two remote sites analysis of the sea ice velocities reveals coherence for sea ice drift at separations of less than 70 km and a correlation length scale of 60 km within the limits of the ispol array at larger separations zonal ice drift remains correlated while meridional ice drift becomes uncorrelated this together with the east west gradient in ice velocities indicates the influence of bathymetry via tidal forcing on local dynamic processes atmospheric forcing also contributes to the sea ice drift about 40 of variability in the sea ice velocity is explained by changes in wind velocity which is significantly less than other studies have found for the region during winter sea ice deformation has been derived for the overall array and four sub arrays there appeared to be no spatial scale dependency of ice deformation although considerable spatial variability was observed between sub arrays the net divergence of the ispol array was in excess of 30 with the largest contributions to divergence being from the southern section and along the eastern side of the overall ispol array temporal variability for all deformation parameters is dominated by high frequency sub daily processes namely tidal forcing and inertial response low frequency multiple days processes including atmospheric changes played a secondary role in forcing sea ice deformation during ispol

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

sequential inversion of modal data for sound attenuation in sediment at the new jersey shelf this paper presents a method for estimating bottom geoacoustic properties especially the sediment attenuation from information contained in normal modes of a broadband signal propagating modes are resolved using the time warping technique applied to signals from light bulb sound sources deployed at ranges of 5 and 7 km in the shallow water 06 experiment a sequential inversion approach is designed that uses specific features of the acoustic data that are highly sensitive to specific geoacoustic model parameters the first feature is the modal group speed which is inverted for seabed sound speed density and sediment thickness the second feature is the modal depth function for inverting receiver depths the third feature is related to the modal coefficient spectra and this is inverted for source depth and sediment attenuation in each subsequent stage estimates from the previous stage s are used as known values the sequential inversion is stable and generates estimates for the geoacoustic model parameters that agree very well with results from other experiments carried out in the same region notably the inversion obtains an estimated attenuation of 0 078 db in the band 120 180 hz for the de watered marine sediment characteristic of the continental shelf at the site

broadband sound propagation in shallow water and geoacoustic inversion part of an experiment to test a measurement package in a shallow water region in the gulf of mexico was designed to gather broadband acoustic data suitable for inversion to estimate seabed geoacoustic parameters continuous wave tow acoustic signals at multiple frequencies and broadband impulsive source signals were recorded on a horizontal line array in a high noise environment simulated annealing with a normal mode forward propagation model is utilized to invert for a geoacoustic representation of the seabed several inversions are made from different data samples of two light bulb implosions the measured sound speed profiles at the hla and at the positions of the light bulb deployments and for two different cost functions the different cost functions measured sound speed profiles and measured time series result in different inverted geoacoustic profiles from which transmission loss is generated for comparison with measurements on the basis of physical consistency and from the comparison of the transmission loss and time series a best estimate geoacoustic profile is selected and compared to those obtained from previously reported inversions uncertainties in the sound speed profile are shown to affect the uncertainties of the estimated seabed parameters

low frequency sound speed and attenuation in sandy seabottom from long range broadband acoustic measurements a joint china u s underwater acoustics experiment was conducted in the yellow sea with a very flat bottom and a strong and sharp thermocline broadband explosive sources were deployed both above and below the thermocline along two radial lines up to 57 2 km and a quarter circle with a radius of 34 km two inversion schemes are used to obtain the seabottom sound speed one is based on extracting normal mode depth functions from the cross spectral density matrix the other is based on the best match between the calculated and measured modal arrival times for different frequencies the inverted seabottom sound speed is used as a constraint condition to extract the seabottom sound attenuation by three methods the first method involves measuring the attenuation coefficients of normal modes in the second method the seabottom sound attenuation is estimated by minimizing the difference between the theoretical and measured modal amplitude ratios the third method is based on finding the best match between the

broadband localization by matched fields in range and bearing in shallow water data from a moving source received by three horizontally separated bottomed sensors in a shallow water environment are analyzed using a broadband matched field approach to source localization the water depth was approximately 150 m and the low bottom loss in the area results in low spatial coherence of the broadband field the modeled acoustic fields are constructed via a ray model localizations are made in the x y plane in a large search area the time evolution of the ambiguity surfaces produced from the data agree fairly well with simulated surfaces ambiguity surfaces are generated successively at intervals of about 1 6 s in small search areas with a fine spatial grid to test the possibility of tracking a source results of the source tracking are presented the analysis also considers the effects of the sea floor on localization in the context of spatial coherence

computer synthesis of geomagnetic palaeosecular variations computer models designed to synthesize palaeosecular variations of the geomagnetic field cast doubt on some widely accepted palaeomagnetic dogmas westward or eastward drift cannot be uniquely deduced from the sense of rotation of the geomagnetic vector the use of unit vectors in statistical analyses leads to systematic errors which render investigation of the global symmetry of the palaeofield more difficult than previously supposed at least some geomagnetic excursions may be regarded as large amplitude secular variations

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

sea ice drift and deformation in the coastal boundary zone small scale sea ice deformation was studied in the coastal boundary zone cbz sequences of coastal radar images from the northern baltic sea 13 february to 13 may 2011 were used and trajectories of identifiable objects calculated average drift velocities in cbz are small 0 01 m s and events of high drift speeds are short and local deformations follow power law scaling but with an exponent of greater magnitude than in the arctic we discovered a connection between air temperature and sea ice deformation on a short time scale during warm days the mean deformation rate was significantly higher in all length scales than during cold days this cannot be explained by changes in ice thickness or concentration which suggests that the ice pack strength responds to air temperature faster than previously assumed however we cannot quantify how much this response is enhanced by lower ice thickness compared to the arctic

maximum entropy inference of seabed attenuation parameters using ship radiated broadband noise the received acoustic field generated by a single passage of a research vessel on the new jersey continental shelf is employed to infer probability distributions for the parameter values representing the frequency dependence of the seabed attenuation and the source levels of the ship the statistical inference approach employed in the analysis is a maximum entropy methodology the average value of the error function needed to uniquely specify a conditional posterior probability distribution is estimated with data samples from time periods in which the ship receiver geometry is dominated by either the stern or bow aspect the existence of ambiguities between the source levels and the environmental parameter values motivates an attempt to partially decouple these parameter values the main result is the demonstration that parameter values for the attenuation and the frequency exponent the sediment sound speed and the source levels can be resolved through a model space reduction technique the results of this multi step statistical inference developed for ship radiated noise is then tested by processing towed source data over the same bandwidth and source track to estimate continuous wave source levels that were measured independently with a reference hydrophone on the tow body

seabed characterization on the new jersey middle and outer shelf correlatability and spatial variability of seafloor sediment properties abstract nearly 100 collocated grab samples and in situ 65 khz acoustic measurements were collected on the new jersey middle and outer shelf within an area that had previously been mapped with multibeam backscatter and bathymetry data and more recently with chirp seismic reflection profiling eighteen short cores were also collected and probed for resistivity based porosity measurements the combined data set provides a basis for empirically exploring the relationship among the remotely sensed data such as backscatter and reflection coefficients and directly measured seabed properties such as grain size distribution velocity attenuation and porosity we also investigate the spatial variability of these properties through semi variogram analysis to facilitate acoustic modeling of natural environmental variability grain size distributions on the new jersey shelf are commonly multi modal leading us to separately characterize coarse 4 mm fine

space time coupling in brittle deformation at geophysical scales strong intermittency as well as spatial heterogeneity characterize the brittle deformation of geophysical objects such as the earth s crust or the arctic sea ice cover they can be expressed through specific scaling laws that relate for a space time domain a the number of earthquakes or b the strain rate vs the size of the domain for the earth s crust or the arctic sea ice respectively however in both cases spatial respectively temporal scaling depends on the time respectively spatial scale considered i e the space and time scaling dependences are coupled here we show that this space time coupling of brittle deformation at geophysical scales can be summarized through a unique scaling law characterizing the discrete fracturing events earthquakes or displacement events along sea ice leads as suggested by an analysis of southern californian seismicity we argue that this space time coupling is likely to emerge from the complex correlation patterns related to chain triggering of earth or ice quakes

small scale sea ice deformation in the beaufort sea seasonal ice zone 1 during spring 2003 the deformation of a single lead in the beaufort sea was investigated using four global positioning system recording stations the lead was situated in first year ice in the transition zone between multiyear and seasonal ice packs we discuss the opening rate and shear of this lead in the context of weather system forcing of the beaufort sea sea ice it is found that in an opening mode the lead displays semidiurnal fluctuations in divergence it was also observed that the lead predominately ridged first year ice in closing the volume of ice ridged was the same order of magnitude as ice growth within the study region during the time period studied further work is required to fully understand the implications of the subdiurnal forcing of the ice pack on deformation in the shear zone at the edge of the perennial ice pack in the beaufort sea this study provides information about the temporal and spatial scales that must be resolved in these future investigations

geoacoustic inversion using low frequency broadband acoustic measurements from l shaped arrays in the shallow water 2006 experiment when using geoacoustic inversion methods one objective function may not result in a unique solution of the inversion problem because of the ambiguity among the unknown parameters this paper utilizes acoustic normal mode dispersion curves mode shapes and modal based longitudinal horizontal coherence to define a three objective optimization problem for geoacoustic parameter estimation this inversion scheme is applied to long range combustive sound source data obtained from l shaped arrays deployed on the new jersey continental shelf in the summer of 2006 based on the sub bottom layering structure from the compressed high intensity radiated pulse reflection survey at the experimental site a two layer sand ridge overlaying a half space basement range independent sediment model is utilized the ambiguities of the sound speed density and depth of the sand ridge layer are partially removed by minimizing these objective functions the inverted seabed sound speed over a frequency range of 15 170 hz is comparable to the ones from direct measurements and other inversion methods in the same general area the inverted seabed attenuation shows a nonlinear frequency dependence expressed as b 0 26f1 55 db m from 50 to 500 hz or b 0 32f1 65 db m from 50 to 250 hz where f is in khz

thin ice and storms sea ice deformation from buoy arrays deployed during n ice2015 arctic sea ice has displayed significant thinning as well as an increase in drift speed in recent years taken together this suggests an associated rise in sea ice deformation rate a winter and spring expedition to the sea ice covered region north of svalbard the norwegian young sea ice2015 expedition n ice2015 gave an opportunity to deploy extensive buoy arrays and to monitor the deformation of the first year and second year ice now common in the majority of the arctic basin during the 5 month long expedition the ice cover underwent several strong deformation events including a powerful storm in early february that damaged the ice cover irreversibly the values of total deformation measured during n ice2015 exceed previously measured values in the arctic basin at similar scales at 100 km scale n ice2015 values averaged above 0 1 d 1 compared to rates of 0 08 d 1 or less for previous buoy arrays the exponent of the power law between the deformation length scale and total deformation developed over the season from 0 37 to 0 54 with an abrupt increase immediately after the early february storm indicating a weakened ice cover with more free drift of the sea ice floes our results point to a general increase in deformation associated with the younger and thinner arctic sea ice and to a potentially destructive role of winter storms

spatial scaling of arctic sea ice deformation 1 arctic sea ice deformation arises from spatial gradients in the ice velocity field this deformation occurs across a wide range of spatial scales from meters to thousands of kilometers we analyze 7 years of sea ice deformation data from the radarsat geophysical processor system rgps covering the western arctic ocean we find that the mean deformation rate is related to the spatial scale over which it is measured according to a power law with exponent 0 2 over a scale range from 10 to 1000 km e g deformation rate doubles for a 30 fold reduction in scale both the exponent and the deformation rate have distinct annual cycles the exponent becomes more negative in summer as the ice pack weakens and internal stresses are not as readily transmitted over long distances the deformation rate reaches a minimum in late winter when the ice pack is strongest the deformation also exhibits considerable localization in which the largest deformation rates are confined to smaller and smaller areas as the scale of measurement decreases this supports a model for sea ice based on granular or fracture mechanics the scaling exponent in the power law relationship tends to be larger in magnitude where the concentration of multiyear ice is low consistent with a thinner and weaker ice pack with decreasing multiyear ice in the arctic and a thinning ice pack an increase in the deformation rate has already been documented from buoy data however the net effect of several deformation thickness feedbacks is still uncertain

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

estimating marine sediment attenuation at low frequency with a vertical line array this paper presents a method of determining the compressional wave attenuation in marine sediment from a short range measurement the data were collected on a vertical line array at a range of 230 m during the shallow water 2006 experiments the sediment attenuation is extracted from the signal strength ratio of the sea bottom reflection to a sub bottom reflection at different frequencies from 1 75 to 3 15 khz linear frequency dependence of the attenuation is found from the estimation the sediment attenuation estimate is lower than the values estimated from the inversions of acoustic field data previously done in the vicinity

subsynoptic scale spatial variability of sea ice deformation in the western weddell sea during early summer 1 ice station polarstern ispol deployed in the western weddell sea from november 2004 to january 2005 included a study of subsynoptic scale variability in sea ice velocity and deformation using an array of 24 buoys upon deployment the ispol buoy array measured 70 km in both zonal and meridional extent and consisted of subarrays that resolved sea ice deformation on scales from 10 to 70 km across the ispol array divergence varied and did not show a distinct coherent length scale spectral analysis of divergence and shear of subarrays revealed that deformation did not vary smoothly across the array this indicates variability of internal ice stress on the scale of 10 km ice conditions within the ispol array encompassed two distinct regimes separated by shear along the continental shelf break differences in spectral power of the tidal and inertial bands across the two regions do not mirror expected differences due to spatial variability of tide induced deformation on the shelf break instead they indicate that the pack ice s internal stress behaved anisotropically on the scale of the shear zone across the buoy array 70 km

scaling properties of arctic sea ice deformation in a high resolution viscous plastic sea ice model and in satellite observations sea ice models with the traditional viscous plastic vp rheology and very small horizontal grid spacing can resolve leads and deformation rates localized along linear kinematic features lkf in a 1 km pan arctic sea ice ocean simulation the small scale sea ice deformations are evaluated with a scaling analysis in relation to satellite observations of the envisat geophysical processor system egps in the central arctic a new coupled scaling analysis for data on eulerian grids is used to determine the spatial and temporal scaling and the coupling between temporal and spatial scales the spatial scaling of the modeled sea ice deformation implies multifractality it is also coupled to temporal scales and varies realistically by region and season the agreement of the spatial scaling with satellite observations challenges previous results with vp models at coarser resolution which did not reproduce the observed scaling the temporal scaling analysis shows that the vp model as configured in this 1 km simulation does not fully resolve the intermittency of sea ice deformation that is observed in satellite data

normal mode measurements and remote sensing of sea bottom sound velocity and attenuation in shallow water the dispersion analysis of explosive signals and measurements of individual mode attenuation in the yellow sea is reported by adjusting input parameters of a normal mode computer program and making the calculated results coincide with field data the compressional wave velocity and attenuation in the sediment for the frequency range of 80 800 hz is simultaneously deduced the sea bottom velocity attenuation and its frequency dependence probed from two sea areas with a different depth and sound velocity profile in the summer and the winter are very close resultant sea bottom attenuation approaches the results of earlier workers at the upper end of the frequency band and joins with the data obtained by others at the lower end and the absorption appears to have a nonlinear frequency dependence 0 37 f1 84 db m khz the errors due to the change of environmental parameters such as water depth water sound velocity profile sediment density and seafloor roughness are discussed

a preliminary palaeomagnetic study of the holocene and late wurmian sediments of lac du bouchet haute loire france summary lac du bouchet is a small maar type lake located at 45 n 4 e in central france the bottom sediments have been sampled down to a depth of 6 m with mackereth type corers a chronology has been established from pollen analytical and diatom zonations and by radiocarbon age determinations throughout the period covered which runs from 22 000 years ago through to the present time declination and inclination variations consist of oscillations of up to about 30 amplitude no abnormally large amplitude excursions in direction are recorded the main contribution of this study is the extension of the european secular variation sv records to the interval from 13000 bp years before present to 22000 bp the sediments deposited through this interval ancient dryas intc wurm originated from the erosion of the internal walls of the volcano spectrum analyses of the declination and inclination curves from 13000 to 22000 bp reveal peaks at periods of 3000 4000 1800 1150 and 700 yr cross spectrum analysis shows strong coherence of the two signals at the longest of these periods the phase relationship of all these peaks indicates clockwise rotation of the palaeomagnetic vector possibly suggesting westward drifting sources although the palaeomagnetic sv record through the holocene 0 10300 bp is compressed into 1 7m of highly organic sediments the principal features exhibited by the type curves established for uk can be identified and the resulting magnetic ages are consistent with the palynology the sense of rotation of the magnetic vector is biased equally in both senses the late glacial 10300 bp to 13000 bp is characterized by oscillating climatic conditions recent dryas allerod and bolling which resulted in poorly resolved and probably discontinuous palaeomagnetic sv records which show a strong bias to anti clockwise rotation all ages are given in radiocarbon years

thin and thinner sea ice mass balance measurements during sheba 1 as part of a large interdisciplinary study of the surface heat budget of the arctic ocean sheba we installed more than 135 ice thickness gauges to determine the sea ice mass balance while installing these gauges during the fall of 1997 we found that much of the multiyear ice cover was only 1 m thick considerably thinner than expected over the course of the yearlong field experiment we monitored the mass balance for a wide variety of ice types including first year ice ponded ice unponded ice multiyear ice hummocks new ridges and old ridges initial ice thicknesses for these sites ranged from 0 3 to 8 m and snow depths varied from a few centimeters to more than a meter however for all of their differences and variety these thickness gauges sites shared a common trait at every site there was a net thinning of the ice during the sheba year the thin ice found in october 1997 was even thinner in october 1998 the annual cycle of ice thickness was also similar at all sites there was a steady increase in thickness through the winter that gradually tapered off in the spring this was followed by a steep drop off in thickness during summer melt and another tapering in late summer and early fall as freeze up began maximum surface melting was in july while bottom ablation peaked in august combining results from the sites we found an average winter growth of 0 51 m and a summer melt of 1 26 m which consisted of 0 64 m of surface melt and 0 62 m of bottom melt there was a weak trend for thicker ice to have less winter growth and greater net loss for the year however ice growth was also impacted by the snow depth considerable variability was observed between sites in both accretion and ablation the total accretion during the 9 month growth season ranged from zero for thick ridged ice to more than a meter for young ice ponds tended to have a large amount of surface melting while ridges had considerable bottom ablation

inversion for geometric and geoacoustic parameters in shallow water experimental results experimental results on the estimation of both geometric and geoacoustic parameters in shallow water are presented genetic algorithms are used for estimation of the forward model parameters the estimated parameters are then used by a standard bartlett processor for source localization a stationary source at a range of 5 6 km and a moving source at ranges from 5 8 7 7 km were successfully localized in range and depth using a single frequency bartlett processor the results indicate that global estimation of the forward model parameters significantly improves source localization performance

late quaternary sedimentation off new jersey new results using 3 d seismic profiles and cores abstract regional seismic reflection surveys have delineated a wedge of late quaternary sediment extending 150 km south from the hudson apron along the edge of the continental shelf off new jersey the bottom of the sediment wedge is defined by a prominent reflector r assumed to represent an erosional surface carved during a low stand of sea level probably corresponding to the wisconsinan maximum glaciation a 3 d reflection survey of a 5 0 5 km area of the southern part of the wedge was carried out in october 1989 line spacing was 10 m and shot spacing 2 5 m navigation achieved position accuracies to the survey shows that the outer shelf sediment wedge has a complex internal structure unrelated to the present seafloor morphology the sedimentary sequence appears to have been formed by a series of depositional events related to glacial melting and interrupted by at least one erosional episode marked by a seismic surface that defines a system of meandering channels faunal studies of samples from cores indicate that the sediments were deposited at shallower depths than at present but there is no evidence for deposition in shallower water or closer proximity to land than the modern mid shelf it appears that the history of periglacial marine sedimentation which accompanied the post wisconsinan deglaciation is no less complex than its continental counterpart

geomagnetic secular variations in greece through the last 6000 years obtained from lake sediment studies summary geomagnetic declination and inclination secular variation curves have been constructed back to 6000 yr bp from palaeomagnetic measurements of sediments cored in lakes volvi trikhonis and begoritis greece they have been dated by palynological studies and by comparison with observatory and archaeomagnetic records radiocarbon ages are all affected by the old carbon factor cores from all three lakes contain a thin ash layer which we associate with the pompeii eruption of vesuvius in ad 79 averaged curves of secular variations of declination and inclination have been computed for the whole study the broader scale pattern of secular variations is basically similar to lake sediment records from the uk poland and switzerland though finer detail in the structure of some of the principal features is resolved

bayesian geoacoustic inversion in a dynamic shallow water environment this paper presents results for matched field bayesian geoacoustic inversion of multitonal continuous wave data collected on the new jersey continental shelf to account for effects of significant spatial and temporal variation of the water column sound speed the sound speed profile was represented by empirical orthogonal functions data error information for the inversion was estimated from multiple time windows of the data inversion results for the sediment sound speeds at three ranges are in excellent agreement with the ground truth

arctic marginal ice zone trending wider in summer and narrower in winter 1 declines in arctic sea ice extent and thickness suggest scientifically important changes in the spatial pattern of the marginal ice zone miz a dynamic and biologically active band of sea ice cover close to open ocean arctic miz widths were measured in satellite era sea ice concentrations over the years 1979 2011 using a recently published miz width analysis method over the record the warm season july september miz width increased by 13 km decade 1 amounting to a 39 widening this widening trend resulted from a marked poleward advancement of the miz poleward edge into regions where sea ice was increasingly younger and thinner at the beginning of annual melt while the miz s equatorward edge moved comparatively little the warm season miz widening contrasted in sign and strength with a cold season february april miz narrowing trend 4 km decade 1 amounting to a 15 narrowing

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

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

on the scaling laws derived from ice beacon trajectories in the southern beaufort sea during the international polar year circumpolar flaw lead study 2007 2008 1 sea ice motion is an important element in mass balance calculations ice thermodynamic modeling ice management plans for industry and ecosystems studies in the historical literature sea ice motion in the beaufort sea was characterized by a predominantly anticyclonic motion during winter months with episodic reversals to cyclonic activity during summer however recent studies have shown an increase in cyclonic activity throughout the annual cycle in this paper we examine circulation in the beaufort sea based on the trajectories of 22 ice beacons launched in the franklin bay area during the international polar year circumpolar flaw lead ipy cfl study during an over wintering experiment in 2007 2008 dispersion characteristics of ice motion show that absolute zonal dispersion follows a t2 scaling law characteristic of advection associated with beaufort gyre circulation whereas absolute meridional dispersion follows a scaling law of t5 4 characteristic of floaters and dispersion in 2 d turbulence temporal autocorrelations of ice velocity fluctuations highlight definitive timescales with values of 1 2 0 7 days in the zonal meridional direction near gaussian behavior is reflected in higher order moments for ice velocity fluctuation probability density functions pdfs non gaussian behavior for absolute displacement pdfs indicates spatial heterogeneity in the ice motion fields atmospheric forcing of sea ice is explored through analysis of daily north american regional reanalysis and in situ wind data where it is shown that ice in the cfl study region travels with an average speed of approximately 0 2 and an average angle of 51 5 to the right of the surface winds during the 2007 2008 winter the results from this analysis further demonstrate seasonality in ice drift to wind ratios and angles that corresponds to stress buoy data indicative of increases in internal ice stress and connectivity due to consolidation of the seasonal ice zone to the coast and perennial ice pack during winter in the beaufort sea region

large scale oceanography in fram strait during the 1984 marginal ice zone experiment the pattern of large scale circulation in fram strait during summer 1984 is inferred from hydrographic data and water mass analysis and direct current observations by use of surface and subsurface floats the west spitsbergen current carrying warm and salty atlantic water splits into several branches two flowing northward into the arctic ocean and two turning westward causing a recirculation across the main axis of fram strait the individual flow paths are topographically controlled suggesting a strong barotropic component of the circulation

magnetic characterization and mossbauer spectroscopy of magnetic concentrates from greek lake sediments abstract bulk magnetic properties of three greek lake sediments indicated that the main magnetic constituent was predominantly pseudo single domain magnetite this was confirmed by successfully extracting and directly identifying the magnetite the majority of the magnetite in the magnetic concentrates is present as grains of about 2 3 m in size the overall size ranging from with occasional grains up to 20 m the grains are roughly equidimensional and angular in form indicating that they are of primarily detrital origin although an authigenic origin for the very fine grains must be a possibility mossbauer spectra of the magnetic concentrates suggest that either the magnetite is slightly non stoichiometric to a similar degree in the three lakes or contains impurity ions haematite was also found in the concentrates but its abundance is only 10 15 that of magnetite and its is not detectable in any of the magnetic properties of the sediments

scaling properties of sea ice deformation from buoy dispersion analysis 1 a temporal and spatial scaling analysis of arctic sea ice deformation is performed over timescales from 3 h to 3 months and over spatial scales from 300 m to 300 km the deformation is derived from the dispersion of pairs of drifting buoys using the iabp international arctic buoy program buoy data sets this study characterizes the deformation of a very large solid plate the arctic sea ice cover stressed by heterogeneous forcing terms like winds and ocean currents it shows that the sea ice deformation rate depends on the scales of observation following specific space and time scaling laws these scaling properties share similarities with those observed for turbulent fluids especially for the ocean and the atmosphere however in our case the time scaling exponent depends on the spatial scale and the spatial exponent on the temporal scale which implies a time space coupling an analysis of the exponent values shows that arctic sea ice deformation is very heterogeneous and intermittent whatever the scales i e it cannot be considered as viscous like even at very large time and or spatial scales instead it suggests a deformation accommodated by a multiscale fracturing faulting processes

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

quantifying the uncertainty of geoacoustic parameter estimates for the new jersey shelf by inverting air gun data this paper describes geoacoustic inversion of low frequency air gun data acquired during an experiment on the new jersey shelf hybrid optimization and bayesian inversion techniques based on matched field processing were applied to multiple shots from three air gun data sets recorded by a vertical line array in a long range shallow water geometry for the bayesian inversions full data error covariance matrix was estimated from a set of consecutive shots that had high temporal coherence and small spatial variation in source position the effect of different data error information on the geoacoustic parameter uncertainty estimates was investigated by using the full data error covariance matrix a diagonalized version of the full error covariance and a diagonal matrix with identical variances the comparison demonstrated that inversion using the full data error information provided the most reliable parameter uncertainty estimates the inversions were highly sensitive to the near sea floor geoacoustic parameters including sediment attenuation of a simple single layer geoacoustic model the estimated parameter values of the model were consistent with depth averaged values over wavelength scales of a high resolution geoacoustic model developed from extensive ground truth information the interpretation of the frequency dependence of the estimated attenuation is also discussed

seabed acoustics of a sand ridge on the new jersey continental shelf acoustic measurements were made on a sand ridge on the new jersey continental shelf data collected on two l arrays separated by 20km from a single multi frequency tow suggest small horizontal environmental variability values for the sound speed structure of the seabed are extracted by first applying a geo acoustic inversion method to broadband and narrowband acoustic data from short range sources then a parabolic equation algorithm is used to properly include the bathymetry and sub bottom layering finally the frequency dependence of the seabed attenuation is inferred by optimizing the model fit to long range transmission loss data in the 50 3000hz band

lake sediment record of the geomagnetic secular variation in britain during holocene times summary a palaeomagnetic record of the geomagnetic secular variation during the last 10000 years has been obtained from 10 cores of sediment from loch lomond scotland lake windermere north england and llyn geirionydd north wales a time scale is provided by 30 radiocarbon age determinations and pollen analyses on several of the cores the main swings and much fine detail of both declination and inclination records repeat well between cores and between lakes and the overall record is much more detailed than previous european records the new record shows that neither declination nor inclination swings have been periodic over the past 10000 years but that the main swings have become progressively shorter in duration during that time each swing is characterized by fine detail which enables use of the record as a secondary method of dating other european sediments the motion of the geomagnetic vector has been predominantly clockwise throughout the time period spanned but confirms a period of anticlockwise motion from 1100 to 600 bp first discovered by british archaeomagnetic investigations the record agrees with british and czechoslovakian archaeomagnetic records but not with japanese archaeomagnetic or north american lake sediment records this suggests that the secular changes are controlled by local growing and decaying drifting sources rather than by wobbling of the main geomagnetic dipole

small scale sea ice deformation during n ice2015 from compact pack ice to marginal ice zone we studied small scale 50 m to 5 km sea ice deformation from ship radar images recorded during the n ice2015 campaign the campaign consisted of 4 consecutive drifting ice stations floes 1 to 4 north of svalbard with a total duration of nearly 5 months deformation was calculated using 5 different time intervals from 10 min to 24 h and the deformation rate was found to depend strongly on the time scale floes 1 to 3 had a mean deformation rate within the range of 0 06 to 0 07 h 1 with the interval of 10 min and 0 03 to 0 04 h 1 with the interval of 1 h floe 4 represented marginal ice zone miz with very high deformation rate 0 14 0 08 h 1 with the interval of 10 min 1 h deep in the ice pack high deformation rates occurred only with high wind and drift speed while in miz they were found also during calm conditions the deformation rates were found to follow power law scaling with respect to length and time scale even on this small scales and in small domain 15 km 15 km the length scale dependence of deformation rate depends on the time scale the power law scaling exponent of the whole study period decreases from 0 82 to 0 52 with the time interval increasing from 10 min to 24 h ship radar images reveal the importance of the deformation history of the ice pack since the deformation events were initialized along the lines of previous damages

statistical analysis of sound transmission results obtained on the new jersey continental shelf experiments have been conducted near the site of amcor borehole 6010 on the new jersey shelf to evaluate propagation predictability in sandy shallow water environments the influence of a nonlinear frequency dependence of the sediment volume attenuation in the uppermost sediment layer at this location is examined previously it was determined that a frequency power law exponent of 1 5 was required for the best modeling of experimental results over the band 50 1000hz the approach here references the attenuation to an accepted value at 1khz and makes extensive comparisons between measurements and calculations to determine a power law exponent of 1 85 0 15

sequential geoacoustic inversion at the continental shelfbreak environmental parameters can have large spatial and temporal variability in shelfbreak regions the capability of sequential bayesian filters in tracking this variation is investigated particle filtering pf is used to extract the environmental parameters and their uncertainties the method tracks the environment with fewer particles relative to conventional geoacoustic inversion methods using successive independent inversions as an example data from the shallow water 2006 experiment are processed the pf approach first is used to track the source and the environment with little spatial variation just northwest of the shelfbreak then the strongly range dependent shelfbreak region is analyzed and the pf results are compared to previous geoacoustic inversion studies from the region

analysis of geomagnetic secular variations 10 000 to 30 000 years bp lac du bouchet france abstract cores of the bottom sediments from lac du bouchet in the haute loire france 44 9 n 3 8 e have been taken using mackereth type pneumatic piston corers the sediments have been dated by palynological control back to 15 000 years bp years before present and by radiocarbon age determinations using both conventional and accelerator methods the depth time transform provisionally used here dates the sequence from 10 000 to 30 000 years bp the stacked records of demagnetised remanent magnetisation from eight cores have been examined fourier and maximum entropy method spectral analyses show good agreement inclination and declination spectra are different in that the dominant inclination periods tend to fall in the negative part of the complex spectrum while the dominant declination periods tend to fall in the positive part the vgp path traced out by the remanent magnetisation vector shows predominantly clockwise looping consistent with essentially westward drifting geomagnetic sources the detailed form of the vgp path is affected by the degree of smoothing but clockwise looping always predominates averaging 67 over the whole time interval investigated a band of frequencies between 0 9 and 0 3 cycles per thousand years is associated with the strongest bias towards clockwise rotation 80 to 90 while a band between 0 3 and 0 1 cycles per thousand years is associated with only 50 clockwise rotation individual core records show some negative inclinations at horizons where inclination minima occur suggesting that excursions should be regarded as extreme values of secular variation rather than aborted polarity reversals of the main field