the palsar polarimetric mode for sea oil slick observation a study on sea oil slick observation by means of l band polarimetric synthetic aperture radar sar data is accomplished it is based on different sea surface scattering mechanism expected with and without surface slicks polarimetric measurements are processed by means of a simple and very effective filtering technique which is electromagnetically based on the mueller scattering matrix moreover some polarimetric features evaluated on both slick free and slick covered sea surfaces are analyzed for confirming the filter output experiments are accomplished on the polarimetric sar data acquired by the phased array type l band synthetic aperture radar palsar sensor mounted on board of the advanced land observing satellite alos and are relevant to oil slick due to a tank accident and look alikes results demonstrate for the first time that l band polarimetric sar measurements are useful for oil slick observation purposes and witness the capability of the alos palsar data for such application

intrusion of warm bering chukchi waters onto the shelf in the western beaufort sea 1 wind driven changes in the path of warm bering chukchi waters carried by the alaska coastal current acc through barrow canyon during late summer are described from high resolution hydrography acoustic doppler current profiler measured currents and satellite measured sea surface temperature imagery acquired from mid august to mid september 2005 2007 near barrow alaska numerical simulations are used to provide a multidecadal context for these observational data four generalized wind regimes and associated circulation states are identified when winds are from the east or east southeast the acc jet tends to be relatively strong and flows adjacent to the shelf break along the southern flank of barrow canyon these easterly winds drive inner shelf currents northwestward along the alaskan beaufort coast where they oppose significant eastward intrusions of warm water from barrow canyon onto the shelf because these easterly winds promote sea level set down over the beaufort shelf and upwelling along the beaufort slope the acc jet necessarily becomes weaker broader and displaced seaward from the beaufort shelf break upon exiting barrow canyon winds from the northeast promote separation of the acc from the southern flank of barrow canyon and establish an up canyon current along the southern flank that is fed in part by waters from the western beaufort shelf when winds are weak or from the southwest warm bering chukchi waters from barrow canyon intrude onto the western beaufort shelf

a barotropic inverse tidal model for the arctic ocean 1 we describe high resolution 5 km grid linear dynamics and inverse models of arctic ocean barotropic tides obtained with the osu tidal inversion software otis package the 8 constituent dynamics based model uses the latest ibcao bathymetry and open boundary forcing from the recent tpxo 6 2 global barotropic tidal solution this model performs significantly better than the present benchmark arctic tidal model 14 km grid by z kowalik and a proshutinsky as judged by comparisons with 300 coastal tide gauges the greatest improvements are found in the canadian arctic archipelago nares strait and the baffin bay and labrador sea and can be explained by the higher resolution of the new model in these topographically complex regions the new arctic inverse model assimilates coastal and benthic tide gauges and topex poseidon and ers altimetry for further improvements of the 4 dominant constituents m2 s2 k1 and o1

flow of winter transformed pacific water into the western arctic abstract the dynamics of the flow of dense water through barrow canyon is investigated using data from a hydrographic survey in summer 2002 the focus is on the winter transformed bering water the highest volumetric mode of winter water in the chukchi sea which drains northward through the canyon in spring and summer the transport of this water mass during the time of the survey was 0 2 0 3 sv as the layer flowed from the head of the canyon to the mouth it sank decelerated and stretched strong cyclonic relative vorticity was generated on the seaward side of the jet which compensated for the stretching this adjustment was incomplete however in that it did not extend across the entire current possibly because of internal mixing due to shear instabilities the resulting vorticity structure of the flow at the canyon mouth was conducive for baroclinic instability and eddy formation multiple eddies of winter transformed bering water were observed along the chukchi beaufort shelfbreak those to the west of barrow canyon were in the process of being spawned by the eastward flowing shelfbreak current emanating from herald canyon while the single eddy observed to the east originated from the barrow canyon outflow it is argued that such an eddy formation is a major source of the ubiquitous cold core anti cyclones observed historically throughout the canada basin implications for the ventilation of the upper halocline of the western arctic are discussed

suspended sediment response to semidiurnal and fortnightly tidal variations in a mesotidal estuary columbia river u s a abstract a turbidity maximum is the dominant feature of the suspended sediment concentration field in the columbia river estuary u s a in this estuary the turbidity maximum is an unsteady feature which changes on semidiurnal fortnightly and seasonal time scales in response to the semidiurnal tides the turbidity maximum is advected landward and seaward and may have an excursion of approximately 20 km in response to the fortnightly tidal variations the turbidity maximum degenerates or decreases in concentration during neap tides and regenerates or increases in concentration during spring tides finally in response to seasonal freshwater discharge variations suspended sediment concentrations in the turbidity maximum increase and its general location is pushed seaward during high discharge conditions and conversely concentrations decrease and its general location is farther landward during low discharge conditions the magnitude of suspended sediment concentration variations for these three time scales is similar therefore any consideration of estuarine dynamics and the suspended sediment concentration field in the columbia river estuary should include the semidiurnal and fortnightly time scales as well as the seasonal ones because the columbia is a mesotidal estuary and fortnightly tidal variations are not extremely large it is expected that these time scales and associated processes may be important in many other estuarine systems

seasonal variation of upwelling in the alaskan beaufort sea impact of sea ice cover 1 data from a mooring array deployed from august 2002 to september 2004 are used to characterize differences in upwelling near the shelf break in the alaskan beaufort sea due to varying sea ice conditions the record is divided into three ice seasons open water partial ice and full ice the basic response is the same in each of the seasons roughly 8 h after the onset of easterly winds the shelf break jet reverses followed approximately 10 h later by upwelling of saltier water which is cold near the shelf break pacific winter water and warm at depth atlantic water the secondary circulation at the outer shelf is to first order consistent with a two dimensional ekman balance of offshore flow in the upper layer and onshore flow at depth there are however important seasonal differences in the upwelling overall the response is strongest in the partial ice season and weakest in the full ice season it is believed that these differences are dictated by the degree to which wind stress is transmitted through the pack ice as the strength of the wind forcing was comparable over the three seasons an eof based upwelling index is constructed using information about the primary flow secondary flow and hydrography the ability to predict upwelling using the wind record alone is explored which demonstrates that 90 of easterly wind events exceeding 9 5 m s 1 drive significant upwelling during certain periods the ice cover on the shelf became landfast which altered the upwelling and circulation patterns near the shelf break

hydrographic conditions during the 2002 sbi process experiments abstract a review of the hydrographic data from the 2002 western arctic shelf basin interactions sbi process cruises permits the following conclusions 1 temperature salinity relationships were similar to canonical descriptions but at five stations in the outer shelf slope region warm high salinity atlantic layer water appeared to have risen displaced the lower halocline and mixed with shelf upper halocline water 2 primary production in the sbi study region was strongly influenced by the advection of dissolved inorganic nitrogen din entering via bering strait this import of din ammonium nitrate nitrite is modified by local processes but without the bering strait inflow biological productivity in the sbi region would be much lower 3 in comparison to the inflowing atlantic waters din urea phosphate and din urea silicate ratios in the pacific waters that dominated the upper 150 m of the water column were low they were also low relative to redfield uptake ratios for phytoplankton 4 microbial processes continue to destroy din in significant quantities as the pacific waters transit the sbi region 5 nitrate and ammonium were the principal contributors to din nitrite concentrations were always

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

hydroclimatological and geomorphic controls on the timing and spatial variability of floods in new england usa abstract numerous methods exist to express a region s flood regime but because of the various controls on flooding no salient method emerges we have used directional also known as orientation statistics to express some of the hydroclimatological and geomorphic controls on flooding in new england and mapped these statistics for 36 gages to reveal the regional groupings of similarly responding basins directional statistics express the temporal variance of flood timings and characterize the seasonality of floods and thus begin to demonstrate some of the climatic controls on flood timing and their spatial effects contour maps of the vector mean timing of floods indicate the strong control of coastal influences on the hydrologic regime and multiple regression analyses indicate that both the surrogate variables for climate latitude and distance to the coast strongly explain the timing of the vector mean although both the geomorphic variables basin size and altitude are also significant explanatory variables an autumnal flood season exists along coastal locations but disappears moving both inland and northward through the region for many of these coastal locations especially in the south the autumn mode reflects the occurrence of hurricane induced floods which for many basins represent the largest flood in the annual series the strength of the seasonality as expressed by the mean resultant magnitude is controlled primarily by basin size with distance to the coast and altitude also important finally these results suggest that directional statistics are an appropriate method for depicting regional hydrologic regimes and in describing some of the hydroclimatological controls on flood occurrence

oil spill detection in radarsat and envisat sar images we present algorithms for automatic detection of oil spills in synthetic aperture radar sar images the algorithms consist of three main parts namely 1 detection of dark spots 2 feature extraction from the dark spot candidates and 3 classification of dark spots as oil spills or look alikes the algorithms have been trained on a large number of radarsat and envisat advanced synthetic aperture radar asar images the performance of the algorithm is compared to manual and semiautomatic approaches in a benchmark study using 59 radarsat and envisat images the algorithms can be considered to be a good alternative to manual inspection when large ocean areas are to be inspected

holocene and modern sediment storage in the subtropical macrotidal fitzroy river estuary southeast queensland australia the fitzroy river estuary is a macrotidal tide dominated estuary located in the dry tropics of central queensland and represents the major source of terrestrial sediment to the southern great barrier reef gbr lagoon the estuary currently receives most of its sediment during large episodic floods that are typically associated with cyclones mean annual sediment budgets for such systems are difficult to estimate due to the sporadic nature of flood discharge events which are highly seasonal and vary greatly in magnitude between years we have estimated the quantity and long term rate of accumulation of catchment derived sediment in the estuarine floodplain using the holocene stratigraphic sequence determined from a series of sediment cores dated with radiocarbon and optically stimulated luminescence osl methods approximately 13 760 million tonnes mt of fluvial sediment has accumulated in the fitzroy estuary during the past 8000 years which equates to an average of 1720 kt yr 1 sediment has accumulated in the fitzroy estuary during the past 8000 years which equates to an average of 1720 kt yr 1 over the past 100 years sediment accumulation has been focused around mangrove and tidal creek environments which cover an area of 13 0 km 2 cores from the tidal creeks dated using cs c 137 pb 210 and osl provide sedimentation rates of approximately 15 mm yr 1 for the past 45 120 years or sediment mass accumulation of 1700 kt yr 1 which includes a component that is reworked into the estuary by tidal currents combined with the small amount of sediment that accumulates on the floodplain during floods similar to 1 mm yr 1 640 kt yr 1 we estimate that approximately 2350 kt yr 1 of sediment is trapped in the modem lower floodplain and estuary this estimate of sediment storage suggests that greater than 50 of the modem mean annual sediment discharge of the fitzroy river 4162 kt yr 1 may be retained in the lower floodplain and estuary these results provide useful insights into the spatial pattern of sedimentation long term rates of accumulation and estimates of sediment trapping in a tropical macrotidal sedimentary system crown copyright c 2007 published by elsevier b v all rights reserved

mapping sea surface oil slicks using radarsat 2 quad polarization sar image 1 polarimetric sar decomposition parameters average alpha angle and entropy h are estimated for oil slick contaminated sea surfaces and slick free conditions using a radarsat 2 quad polarization sar image the values of h and within oil slick areas are significantly higher than those of the ambient sea surface indicating the dominance of bragg scattering for the slick free ocean and non bragg scattering for the oil slick area in land classification the conformity coefficient is often used to discriminate surface scattering with double bounce or volume scattering based on this rationale we also develop a method using as a logical scalar descriptor to map oil slicks under low to moderate wind conditions the proposed method is assessed using a radarsat 2 quad polarization sar image of oil slicks in the gulf of mexico analysis shows that when is positive the sea surface is slick free whereas is negative for oil slick areas this method provides a simple and effective mapping technique for oil slick detection

pathways timing and evolution of pacific winter water through barrow canyon abstract observations from a ship based campaign in july august 2009 combined with idealized numerical simulations are used to investigate the seasonal delivery of pacific winter water to barrow canyon and the subsequent adjustment of the flow down the canyon as the current advects dense water it transitions from a nearly barotropic structure near the canyon head to a strongly baroclinic flow with a subsurface maximum near the canyon mouth both the data and model indicate that the transit times along the three chukchi shelf pathways feeding barrow canyon a coastal pathway a southern hanna shoal pathway and a northern hanna shoal pathway modulate the mode of winter water that occupies the canyon at a given time in particular remnant pacific winter water carried along the rapid coastal pathway can precede the arrival of newly ventilated pacific winter water carried along the two interior pathways the observations and model indicate that the transition between water types draining from the canyon can occur rapidly over time scales of days to weeks we also demonstrate that mixing along the path of the current is unlikely to result in the observed down canyon transition from newly ventilated pacific winter water to remnant winter water further supporting the dominant role of advection while the focus here is on the transition of winter water modes the implication that seasonality within barrow canyon is tied to seasonality of the bering strait inflow together with the relative transit times along advective pathways should hold for other water types as well

sar imaging of ocean surface oil seep trajectories induced by near inertial oscillation abstract in the gulf of mexico repeated satellite synthetic aperture radar sar observations show circular trajectories of oil slicks with a radius of several km some circles overlay onto each other while in other cases the circles are modified by the ambient current to form a train of spirals we show that these sar observed features originate from oil seeps of the ocean bottom and the circles are induced by near inertial oscillation nio from the sar images we have estimated the ambient current velocity from a train of spiral like circles and verified the nio by calculating its oscillation period in this study we also analyze time series of wind and velocity profiles obtained from a moored buoy and acoustic doppler current profilers mounted on oil platforms in the area covered by the sar images the ocean current analysis confirms that during the sar imaging times there were nios buoy measurements also show that moderate wind of 7 ms 1 existed 24 h prior to a sar observation and it diminished to 2 ms 1 in 6 h and remained very low for the next 18 h a condition ideal for producing nios

geochemistry and deposition of 7be in river estuarine and coastal waters the atmospheric flux of cosmogenic 7be 53 3 day half life and the mode of 7be deposition in river estuarine and coastal environments have been examined the atmospheric flux of 7be commonly supports inventories ranging from 1 0 to 2 0 pci cm2 1 pci 0 037 bq beryllium 7 concentrations in water phase samples collected across salinity gradients in several estuaries along the eastern coastline of the united states range from 0 03 to 0 53 pci l and primarily reflect variations in 7be supply and sorption kinetics the major process controlling the concentration of 7be on estuarine suspended particles appears to be the length of time that these particles remain in the water column field particle to water distribution coefficients for 7be have a median value of about 4 104 but range over an order of magnitude reflecting short term variations in 7be input particle dynamics and particulate iron content rather than equilibrium sorption desorption responses to changes in water salinity or particle type residence times of 7be in the water column range from a few days in estuarine areas of rapid fine particle deposition to several weeks in high energy environments where pronounced sediment resuspension reintroduces deposited 7be back into the water column inventories of 7be in sediments range from nondetectable to 3 3 pci cm2 with the highest inventories in areas where fine particles are accumulating rapidly such sites are also major repositories for other particle reactive substances a 7be budget for the james estuary indicates that less than 5 of the expected 7be input is in the water column and that the short term estuarine trapping efficiency for atmospherically derived 7be is somewhere between 50 and 100

salt wedge dynamics lead to enhanced sediment trapping within side embayments in high energy estuaries off river coves and embayments provide accommodation space for sediment accumulation particularly for sandy estuaries where high energy in the main channel prevents significant long term storage of fine grained material seasonal sediment inputs to hamburg cove in the connecticut river estuary usa were monitored to understand the timing and mechanisms for sediment storage there unlike in freshwater tidal coves sediment was primarily trapped here during periods of low discharge when the salinity intrusion extended upriver to the cove entrance during periods of low discharge and high sediment accumulation deposited sediment displayed geochemical signatures consistent with a marine source numerical simulations reveal that low discharge conditions provide several important characteristics that maximize sediment trapping first these conditions allow the estuarine turbidity maximum etm to be located in the vicinity of the cove entrance which increases sediment concentrations during flood tide second the saltier water in the main channel can enter the cove as a density current enhancing near bed velocities and resuspending sediment providing an efficient delivery mechanism finally higher salinity water accumulates in the deep basin of the cove creating a stratified region that becomes decoupled from ebb currents promoting retention of sediment in the cove this process of estuarine enhanced sediment accumulation in off river coves will likely extend upriver during future sea level rise

winter currents and hydrographic conditions on the northern central bering sea shelf current observations obtained from the northern bering shelf region in winter 1984 1985 indicate that midwinter circulation patterns differed from those during the rest of the year annual mean circulation in this region is dominated by vigorous northward currents from 10 cm s in shpanberg strait to more than 50 cm s in bering strait these northward currents are accompanied by a weak northwestward coastal flow south of st lawrence island in february april 1985 however flow was weakly 0 5 cm s southward through shpanberg strait and southeastward south of st lawrence island while remaining northward through anadyr and bering straits comparison with current data obtained from previous years suggests that midwinter reversal of flow in shpanberg strait is a recurrent winter feature it generally occurs at about the same time that the winter ice cover undergoes its major advance and it is associated with strong northerly winds northward flow through anadyr strait persists conversely through the winter and is the northward extension of a western intensified northward flow over the bering shelf its source is bering sea water farther south rather than water from the northern central shelf the resultant trapping of shelf water on the northern central shelf coupled with intensive regional ice formation during the same period as the flow reversal led in 1985 to significant about 1 5 brine enrichment this salinity increase agrees qualitatively with historical data which suggest that the northern central bering shelf is the site both of sluggish winter circulation and of elevated salinities due to brine enrichment from ice formation

effect of wind direction and incidence angle on polarimetric sar observations of slicked and unslicked sea surfaces abstract the objective of this paper is to investigate the dependency of oil spill observations in polarimetric sar data on imaging geometry i e on incidence angle and look direction relative to the wind the study is based on quad polarization data acquired by the uninhabited aerial vehicle synthetic aperture radar over experimental oil slicks under relatively high winds of 10 12 m s over an 8 hour period the data is collected over a wide range of incidence angles and alternates between looking upwind uw and downwind dw the unique time series enables a detailed study of the behavior of multipolarization parameters over clean sea and oil slicks under varying imaging geometry to be carried out for the first time for clean sea backscatter our findings are in agreement with previous studies showing decreasing backscatter as the incidence angle increases and from uw to dw with the highest sensitivity in the hh channel we also find similar variations in oil covered areas the results suggest that the oil slick backscatter is slightly more sensitive to the relative wind direction than the clean sea and higher oil sea damping ratios are found in dw than in uw cases particularly in the hh channel all multipolarization features investigated have some degree of dependency on imaging geometry the lowest sensitivities are found in the magnitude of the copolarization correlation coefficient the standard deviation of the copolarized phase difference the polarization difference the mean scattering angle and the entropy several features clearly change behavior when the signal approaches the sensor noise floor and we find that the measurements and derived parameters may be affected at even higher signal to noise ratio snr levels than previously proposed i e closer to 7 9 db above the sensor noise floor overall the polarization difference is clearly identified as the most interesting parameter for oil spill observation producing high oil sea contrast in addition to low sensitivity to imaging geometry the results show that both the relative wind direction and the incidence angle in combination with the snr should be taken into account when developing operational methods based on multipolarization sar data

salinity intrusion in estuaries abstract one dimensional time averaged solutions are examined for salinity intrusion in estuaries with a breadth variation bl x n and a depth variation h x m where x is the distance from the head of the estuary these solutions emphasize the importance of the rate of change of cross sectional area in determining salinity distribution assuming a constant longitudinal dispersion coefficient dx d the salinity distribution is shown to be highly dependent on the dimensionless parameter v u1 x1 d with u1 the velocity of the fresh water flow at position x1 where the estuary is effectively at oceanic salinity this parameter v is equivalent to the flushing number f introduced by arons and stommel 1951 for the case of an estuary of rectangular cross section for eight estuaries comparisons are made between calculated and observed salinity distributions where for each estuary the value of d in the calculated distribution was chosen to produce the best agreement with the observed distribution

circulation and water mass transformation in a model of the chukchi sea 1 the circulation and water mass transformation in a regional ocean ice model of the chukchi sea are discussed the model has horizontal resolution of o 4 km is forced by fluxes derived from daily ncep reanalysis fields and has seasonally varying transport temperature and salinity imposed at bering strait many of the observed characteristics of the mean circulation and seasonal cycle in the chukchi sea are reproduced the discussion focuses on the branching of the inflow transport into pathways following herald canyon central channel and the alaskan coast the pattern of ice melt and the water mass transformation and formation of winter water and hypersaline water the ice melt pattern and timing is strongly influenced by advection through bering strait high frequency forcing results in a larger region of ice melt particularly over the shoals and in the northern chukchi sea compared to monthly mean forcing in the model the seasonal cycle of salinity in the southern and central chukchi sea is dominated by advection through bering strait while local atmospheric forcing and brine rejection are more important north of herald and hanna shoals and in barrow canyon however since the residence time in the chukchi sea is generally less than 1 year interannual variability in the bering strait salinity will be reflected in the salinity across the chukchi sea and at barrow canyon

bathymetric controls on sediment transport in the hudson river estuary lateral asymmetry and frontal trapping 1 analyses of field observations and numerical model results have identified that sediment transport in the hudson river estuary is laterally segregated between channel and shoals features frontal trapping at multiple locations along the estuary and varies significantly over the spring neap tidal cycle lateral gradients in depth and therefore baroclinic pressure gradient and stratification control the lateral distribution of sediment transport within the saline estuary sediment fluxes are strongly landward in the channel and seaward on the shoals at multiple locations bottom salinity fronts form at bathymetric transitions in width or depth sediment convergences near the fronts create local maxima in suspended sediment concentration and deposition providing a general mechanism for creation of secondary estuarine turbidity maxima at bathymetric transitions the lateral bathymetry also affects the spring neap cycle of sediment suspension and deposition in regions with broad shallow shoals the shoals are erosional and the channel is depositional during neap tides with the opposite pattern during spring tides narrower deeper shoals are depositional during neaps and erosional during springs in each case the lateral transfer is from regions of higher to lower bed stress and depends on the elevation of the pycnocline relative to the bed collectively the results indicate that lateral and along channel gradients in bathymetry and thus stratification bed stress and sediment flux lead to an unsteady heterogeneous distribution of sediment transport and trapping along the estuary rather than trapping solely at a turbidity maximum at the limit of the salinity intrusion

circulation on the north central chukchi sea shelf abstract mooring and shipboard data collected between 1992 and 1995 delineate the circulation over the north central chukchi shelf previous studies indicated that pacific waters crossed the chukchi shelf through herald valley in the west and barrow canyon in the east we find a third branch through the central channel onto the outer shelf the central channel transport varies seasonally in phase with bering strait transport and is 0 2 sv on average although some of this might include water entrained from the outflow through herald valley a portion of the central channel outflow moves eastward and converges with the alaskan coastal current at the head of barrow canyon the remainder appears to continue northeastward over the central outer shelf toward the shelfbreak joined by outflow from herald valley the mean flow opposes the prevailing winds and is primarily forced by the sea level slope between the pacific and arctic oceans current variations are mainly wind forced but baroclinic forcing associated with upstream dense water formation in coastal polynyas might occasionally be important winter water mass modification depends crucially on the fall and winter winds which control seasonal ice development an extensive fall ice cover delays cooling limits new ice formation and results in little salinization in such years bering shelf waters cross the chukchi shelf with little modification in contrast extensive open water in fall leads to early and rapid cooling and if accompanied by vigorous ice production within coastal polynyas results in the production of high salinity 33 shelf waters such interannual variability likely affects slope processes and the transport of pacific waters into the arctic ocean interior

oil slick observation at low incidence angles in ku band on the 20 april 2010 the oil platform deep water horizon in the gulf of mexico suffered an explosion during the final phases of drilling an exploratory well as a result an oil film covered the sea surface area of several thousand square kilometers in the present paper the data of the ku band precipitation radar which operates at low incidence angles were used to explore the oil spill event the two scale model of the scattering surface was used to describe radar backscatter from the sea surface the algorithm for retrieval of normalized radar cross section at nadir and the total slope variance of large scale waves compared to the wavelength of electromagnetic wave 22 mm was developed for the precipitation radar swath it is shown that measurements at low incidence angles can be used for oil spill detection this is the first time that the dependence of mean square slope of large scale waves on wind speed has been obtained for oil slicks from ku band data and compared to mean square slope obtained by cox and munk from optical data

polarimetric analysis of compact polarimetry sar architectures for sea oil slick observation in this paper a theoretical and experimental analysis of polarimetric synthetic aperture radar sar architectures is undertaken for sea oil slick observation purposes reference is made to the conventional full polarimetric fp sar that is here contrasted with new generation polarimetric sar architectures known as compact polarimetric cp sar two cp modes are considered i e the hybrid polarity and 4 modes whose measurements are emulated from actual l and c band fp sar data polarimetric sea surface scattering is predicted according to an extended version of the bragg scattering model x bragg in order to point out the differences exhibited between fp and cp sar architectures and among cp sar modes theoretical predictions are then contrasted with experiments undertaken on actual polarimetric sar data collected over well known oil slicks and weak damping surfactants results confirm model prediction showing that differences mainly apply when polarimetric features are estimated over slick free sea surface using different sar architectures with the 4 mode behaving closer to fp sar although cp sar architectures measure only a subset of the fp information content they represent an interesting operational alternative for both detecting oil slicks and discriminating them from weak damping surfactants

circulation of winter water on the chukchi shelf in early summer abstract using a variety of data sources we investigate the properties and pathways of pacific origin winter water as it spreads across the eastern chukchi shelf in early summer the focus is on the time period june july 2011 during which an extensive shipboard hydrographic velocity survey was undertaken as part of the impacts of climate on ecosystem and chemistry of the arctic pacific environment icescape program a revised circulation scheme is constructed revealing that the transport pathways on the chukchi shelf are more complex than previously thought notably the well known branch progressing northward from the central channel bifurcates as it reaches hanna shoal flowing around both sides of the shoal and dividing into smaller filaments that continue towards barrow canyon mass is conserved in the circulation scheme with approximately 1 sverdrup flowing poleward across the chukchi shelf within these pathways then exiting barrow canyon the salinity of the winter water varied on the shelf in 2011 with saltier water found in the upstream portion of what is defined as the central pathway using sea ice concentration data and atmospheric reanalysis fields we argue that salinization of the winter water in the central pathway occurred via brine rejection as the parcels progressed north and passed through the cape lisburne polynya this demonstrates that winter water pervading the interior shelf can be transformed by convective overturning north of bering strait presumably stirring up nutrients from the sediments and thereby influencing primary productivity in the region of hanna shoal

turbulent kinetic energy dissipation in barrow canyon pacificwaterflowsacross theshallowchukchisea beforereachingthe arctic ocean where it isa sourceof heat freshwater nutrients and carbon a substantial portion of pacific water is routed through barrow canyon located in the northeast corner of the chukchi barrow canyon is a region of complex geometry and forcing where a variety of water masses have been observed to coexist these factors contribute to a dynamic physical environment with the potential for significant water mass transformation the measurements of turbulent kinetic energy dissipation presented here indicate diapycnal mixing is important in the upper canyon elevated dissipation rates were observed near the pycnocline effectively mixing winter and summer water masses as well as within the bottom boundary layer the slopes of shear stratification layers combined with analysis of rotary spectra suggest that near inertial wave activity may be important in modulating dissipation near the bottom because the canyon is known to be a hotspot of productivity with an active benthic community mixing may be an important factor in maintenance of the biological environment

the western arctic boundary current at 152 w structure variability and transport abstract from august 2002 to september 2004 a high resolution mooring array was maintained across the western arctic boundary current in the beaufort sea north of alaska the array consisted of profiling instrumentation providing a timeseries of vertical sections of the current here we present the first year velocity measurements with emphasis on the pacific water component of the current the mean flow is characterized as a bottom intensified jet of o 15 cm s 1 directed to the east trapped to the shelfbreak near 100 m depth its width scale is only 10 15 km seasonally the flow has distinct configurations during summer it becomes surface intensified as it advects buoyant alaskan coastal water in fall and winter the current often reverses flows westward under upwelling favorable winds between the storms as the eastward flow re establishes the current develops a deep extension to depths exceeding 700 m in spring the bottom trapped flow advects winter transformed pacific water emanating from the chukchi sea the year long mean volume transport of pacific water is 0 13 0 08 sv to the east which is less than 20 of the long term mean bering strait inflow this implies that most of the pacific water entering the arctic goes elsewhere contrary to expected dynamics and previous modeling results possible reasons for this are discussed the mean atlantic water transport to 800 m depth is 0 047 0 026 sv also smaller than anticipated

the chukchi slope current abstract using a collection of 46 shipboard hydrographic velocity transects occupied across the shelfbreak and slope of the chukchi sea between 2002 and 2014 we have quantified the existence of a current transporting pacific origin water westward over the upper continental slope it has been named the chukchi slope current which is believed to emanate from barrow canyon the current is surface intensified order 50 km wide and advects both summer and winter waters it is not trapped to a particular isobath but instead is reminiscent of a free jet there is no significant variation in pacific water transport with distance from barrow canyon a potential vorticity analysis suggests that the flow is baroclinically unstable consistent with the notion that it meanders the current is present during all synoptic wind conditions but increases in strength from summer to fall presumably due to the seasonal enhancement of the easterly winds in the region its transport increased over the 12 year period of data coverage also likely in response to wind forcing in the mean the slope current transports 0 50 0 07 sv of pacific water this estimate allows us to construct a balanced mass budget of the chukchi shelf inflows and outflows our study also confirms the existence of an eastward flowing chukchi shelfbreak jet transporting 0 10 0 03 sv of pacific water towards barrow canyon

seasonal to mesoscale variability of water masses and atmospheric conditions in barrow canyon chukchi sea abstract twenty four repeat hydrographic transects occupied across barrow canyon from 2010 to 2013 are used to study the seasonal evolution of water masses in the canyon from july october as well as the occurrence of upwelling the mean sections revealed that the alaskan coastal water is mainly confined to the eastern flank of the canyon corresponding to a region of sloped isopycnals indicative of the surface intensified alaskan coastal current which advects the water the pacific origin winter water is found at depth banked against the western flank of the canyon its isopycnal structure is consistent with a bottom intensified flow of this dense water mass out of the canyon for the months that were sampled the alaskan coastal water is most prevalent in august and september while the coldest winter water is observed in the month of august it is argued that this newly ventilated winter water is delivered to the canyon via pathways on the central chukchi shelf as opposed to the coastal pathway roughly a third of the hydrographic sections were preceded by significant up canyon winds and hence were deemed to be under the influence of upwelling during these periods anomalously salty water is found throughout the eastern flank of the canyon and on occasion atlantic water fills the deepest part of the section using atmospheric reanalysis data it is shown that upwelling occurs when the beaufort high is strengthened and the aleutian low is deepened two modes of storm tracks were identified northward progressing storms mode 1 and eastward progressing storms mode 2 both of which can drive upwelling mode 1 is prevalent in july august while mode 2 is more common in september october these seasonal patterns appear to be dictated by regional variations in blocking highs

detection of natural oil slicks in the nw gulf of mexico using modis imagery i we demonstrate the unique capability of the modis instruments in detecting oil slicks in an open ocean environment on 13 may 2006 in the nw gulf of mexico where water depth ranges from 50 to 2500 m one 250 m resolution modis image showed at least 164 surface slicks under sun glint glint reflectance l g ranged between 0 0001 and 0 06 sr 1 after discounting other possible causes we believe these are the result of natural seeps our analysis showed total coverage of 1900 km 2 with individual slicks varying in surface area 1 1 7 14 8 km 2 and length 19 2 12 4 km concurrent sar imagery showed similar area estimates to within 30 this estimate based on a single image is higher than earlier estimates from a database of multi date sar images for the same region inspection of 200 images for the month of may between 2000 and 2008 revealed similar slicks on at least 50 images on 2 june 2005 slicks were detected under sun glint with both negative contrast l g 0 05 sr 1 these slicks could not be detected in glint free modis images collected on the same day because of the near daily revisit and wide sun glint coverage e g 800 km e w between march and october at 25 n systematic and global application of the modis 250 m imagery can help locate natural seeps and improve estimates of seepage rates in the world s ocean

wind driven modification of the alaskan coastal current 1 across shelf transects over the eastern flank of barrow canyon were obtained in august 2005 with an autonomous underwater vehicle auv here the shelf topography creates a choke point in which a substantial portion of pacific inflow from the bering strait is concentrated within 30 km of the coast providing an ideal setup for monitoring the flow with the auv four transects extending 10 km offshore of barrow alaska inshore of the 80 m isobath were used in conjunction with a process oriented numerical model to diagnose the wind driven modification of the alaskan coastal current poleward transports of 0 12 sv were consistent among all sections although the transport weighted temperature was about 1 c colder in the transect obtained during peak winds an idealized numerical model reproduces the observed hydrographic structure and across shelf circulation reasonably well in that 1 winds were not sufficient to reverse the poleward flow 2 upwelling was most pronounced in the nearshore and 3 the onshore return flow occurred throughout the interior as opposed to the bottom boundary layer the across shelf circulation provides a possible mechanism for a meltwater intrusion observed on the offshore side of the auv transect made during peak winds also of interest is that the observed anticyclonic shear was much stronger u y f than previously measured in the region

pathways of pacific water across the chukchi sea a numerical model study 1 pathways of pacific water flowing from the north pacific ocean through bering strait and across the chukchi sea are investigated using a two dimensional barotropic model in the no wind case the flow is driven only by a prescribed steady northward flow of 0 8 sv through bering strait the resulting steady state circulation consists of a broad northeasterly flow basically following the topography with a few areas of intensified currents about half of the inflow travels northwest through hope valley while the other half turns somewhat toward the northeast along the alaskan coast the flow through hope valley is intensified as it passes through herald canyon but much of this flow escapes the canyon to move eastward joining the flow in the broad valley between herald and hanna shoals another area of slightly intensified currents there is a confluence of nearly all of the flow along the alaskan coast west of pt barrow to create a very strong and narrow coastal jet that follows the shelf topography eastward onto the beaufort shelf thus in this no wind case nearly all of the pacific water entering the chukchi sea eventually ends up flowing eastward along the narrow beaufort shelf with no discernable flow across the shelf edge toward the interior canada basin travel times for water parcels to move from bering strait to pt barrow vary tremendously according to the path taken e g less than 6 months along the alaskan coast but about 30 months along the westernmost path through herald canyon this flow field is relatively insensitive to idealized wind forcing when the winds are from the south west or north in which cases the shelf transports tend to be intensified however strong northeasterly to easterly winds are able to completely reverse the flows along the beaufort shelf and the alaskan coast and force most of the throughflow in a more northerly direction across the chukchi sea shelf edge potentially supplying the surface waters of the interior canada basin with pacific water the entire shelf circulation reacts promptly to changing wind conditions with a response time of 2 3 days the intense coastal jet between icy cape and pt barrow implies that dense water formed here from winter coastal polynyas may be quickly swept away along the coast in contrast there is a relatively quiet nearshore region to the west between cape lisburne and icy cape where dense water may accumulate much longer and continue to become denser before it is carried across the shelf

spatial patterns of primary production on the shelf slope and basin of the western arctic in 2002 in the spring and summer of 2002 primary production in the chukchi sea was measured using 14 c uptake experiments our cruise track encompassed the shelf and continental slope area of the chukchi and beaufort seas progressing into deep water over the canada basin the study area experienced upwards of 90 ice cover during the spring with ice retreating into the basin during the summer production in the spring was light limited due to ice cover with average euphotic zone production rates of o0 3 g c m 2 d 1 values of 8 g c m 2 d 1 were observed in association with surface bloom conditions during the initial ice breakup considerable nutrient reduction in the surface waters took place between the spring and summer cruise and although not observed this was attributed to a spring bloom decreased ice cover and increased clarity of surface waters in the summer allowed greater light penetration the highest rates of production during the second cruise were found at 25 30 m coincident with the top of the nutricline daily euphotic zone productivity in the summer averaged 0 78 g c m 2 d 1 on the shelf and 0 32 g c m 2 d 1 on the edge of the canada basin these data provide an estimated annual production of 90 g c m 2 yr 1 in the study area

circulation of summer pacific halocline water in the arctic ocean 1 we present an analysis of arctic ocean hydrographic and sea ice observations from the 1990s with a focus on the circulation of water that originates in the north pacific ocean previous studies have shown the presence of two varieties of relatively warm summer halocline water in the vicinity of the chukchi sea i e the relatively fresh alaskan coastal water acw and the relatively saltier summer bering sea water sbsw here we extend these studies by tracing the circulation of these waters downstream into the arctic ocean we find that acw is generally most evident in the southern beaufort gyre while sbsw is strongest in the northern portion of the beaufort gyre and along the transpolar drift stream we find that this separation is most extreme during the early mid 1990s when the arctic oscillation was at historically high index values this leads us to speculate that the outflow to the north atlantic ocean through the canadian archipelago and fram strait may be similarly separated as arctic oscillation index values fell during the later 1990s acw and sbsw began to overlap in their regions of influence these changes are evident in the area north of ellesmere island where the influence of sbsw is highly correlated with a 3 year lag with the arctic oscillation index we also note the presence of winter bering sea water wbsw which underlies the summer varieties all together this brings the number of distinct pacific water types in our arctic ocean inventory to three acw sbsw and wbsw

the use of 7be to identify event and seasonal sedimentation near the po river delta adriatic sea in october 2000 a major flood event of the po river occurred the resulting seabed deposit was initially sampled in december 2000 and most sites were reoccupied on subsequent cruises over a 3 yr period using the maximum penetration depth of the short lived radioisotope 7be half life 53 3 d the flood deposit was found to be up to 15 cm thick individual depocenters of thick strata were located immediately adjacent to the distributaries at the river mouth in relatively shallow water 30 m these flood deposit thicknesses are minimum estimates because the depth of 234th half life 24 1 d exceeds that of 7be in physically stratified flood sediment indicating that the first sediment deposited during the flood event likely originated from the river channel 30 55 of the estimated sediment load delivered to the shelf during the flood event can be accounted for using 7be penetration depths seasonal deposition also can be quantified using 7be after removing the effects of biological mixing seasonal deposition rates are a maximum of 6 cm yr 1 near the pila distributary decreasing to 2 cm yr 1 in the southern portions of the dispersal system

classification of ocean surface slicks in simulated hybrid polarimetric sar data in this paper we consider hybrid polarimetric synthetic aperture radar sar data of ocean surface slicks and hypothesize that we can design a system that is able to discriminate between mineral oil plant oil and clean sea we focus particularly on challenges related to data set shift between the training and test data in sar images of ocean surfaces data set shift is typically caused by the variation of wind level and incident angles that directly impact the backscatter intensities we evaluate several classifiers domain adaptation strategies and multilooking strategies hybrid polarimetric sar data are simulated from the radarsat 2 quad pol images the proposed methodology was trained using five different radarsat 2 quad pol images that cover slicks of known types and tested on 10 different radarsat 2 quad pol images covering various ocean surface slicks the results show that we were able to a large degree to classify the type of various surface slicks the average classification accuracy obtained from cross validation on the training data was 91 the results also show that we were able to correctly classify surface slick in new test images even if the wind surface and acquisition conditions were different from the training images we conclude that hybrid polarity is an attractive mode for future enhanced sar based oil spill monitoring however to fully exploit the imaging mode single look complex images are necessary

rain footprints on c band synthetic aperture radar images of the ocean revisited abstract it is well known that rain leaves footprints on the sea surface that sometimes become visible on synthetic aperture radar sar images rain cells can easily be detected on sar images at all radar frequencies when they are associated with a downdraft pattern but rain cells are not always associated with downdraft and rain can also occur in other forms as stratified rain rain bands and squall lines it turns out that radar signatures of rain at c band are much more complex than at l or x band radar and that it is particularly difficult to identify unambiguously rain events on c band sar images acquired over the ocean this is because c band lies in the transition region where raindrops impinging onto the sea surface can increase usually or decrease the backscattered radar power and where volume scattering and attenuation by rain drops in the atmosphere are not always negligible at very high rain rates in order to get an insight into the physical mechanisms causing the c band radar signatures of rain we first revisit results obtained from historic laboratory and field experiments and multi frequency multi polarization sar data acquired during the sir c x sar spaceshuttle mission in 1994 then we analyze several c band sar images acquired by the european satellites envisat and sentinel 1a and the canadian satellite radarsat 2 and compare them whenever possible with quasi coincident and collocated weather radar images the observational data show that at low to medium rain rates the main physical mechanism causing c band radar signatures of rain is bragg scattering at ring waves generated by the rain drops impinging onto the sea surface which increase the radar backscatter however areas of increased radar backscatter are often accompanied by adjacent areas of decreased radar backscatter which is due to attenuation of the bragg waves by turbulence also generated by the impinging rain drops furthermore we present a full polarimetric radarsat 2 sar image of a rain cell together with a polarimetric decomposition analysis which shows that the c band radar signature of a rain cell is caused by surface scattering the observation show that radar signatures of rain cells often contain segments where the co polarized as well the cross polarized radar backscatter are strongly enhanced which indicates non bragg scattering contributions to the scattering process furthermore the polarimetric decomposition analysis shows that the c band radar signature of a rain cell is dominated by surface scattering possible mechanisms like scattering at splash products are discussed whether the normalized radar cross section nrcs due to rain is increased or decreased depends on rain rate wind speed incidence angle and history of the rain event at low to moderate wind speeds 10 m s 1 and low to high rain rates but

synoptic flow and density observations near an arctic shelf break analyses of data from three shipborne surveys describe the quasi synoptic density and velocity fields near barrow canyon alaska the canyon parallels the northwestern coast of alaska and contains three different water masses these are 1 warm and fresh alaskan coastal waters that originate from the bering strait 2 cold and moderately salty waters that originate from the chukchi shelf and 3 warm and salty waters that originate from the atlantic layer of the arctic ocean a halocline separates the chukchi shelf and atlantic layer waters the halocline slopes upward into the canyon where it is then twisted to slope across the wide canyon an intensification of the beaufort gyre near the shelf break just seaward of barrow canyon raises the halocline more than 100 m toward the surface locally upwelling favorable winds raise the arctic halocline which thus is ventilated within barrow canyon adjacent to the coast in the absence of winds the halocline slopes acrosscanyon in the thermal wind sense due to a northward flowing coastal current velocity measurements from a towed acoustic doppler current profiler reveal a northward flowing jet that transports about 0 3 sv sv 106 kg m23 of bering sea summer water into the arctic ocean at speeds that exceed 0 7 m s21 total northward transports through the canyon exceed 1 0 sv the warm waters of this coastal current supply more than 100 w m22 of heat to the atmosphere the jet separates both from the bottom and from the coast hence a laterally and vertically sheared jet forms which breaks into three branches at about 71 88n latitude

characterization of marine surface slicks by radarsat 2 multipolarization features in this paper we study surface slick characterization in polarimetric c band synthetic aperture radar sar data the objective is to identify the most powerful multipolarization sar descriptors for mineral oil spill versus biogenic slick discrimination a systematic comparison of eight well known multipolarization features is provided the analysis is performed on data that we collected during a large scale oil spill exercise at the frigg field situated northwest of stavanger in june 2011 controlled oil spills and simulated look alikes were simultaneously captured within fine quad polarization radarsat 2 acquisitions during this experiment multipolarization features derived from only the copolarized complex scattering coefficients are explored we find that the two most powerful multipolarization features extracted from this data set are the geometric intensity measuring the combined intensity based on the determinant of the coherency matrix and the real part of the copolarization cross product which is related to the scattering behavior of the target we show that these two features can distinguish between the simulated biogenic slicks and mineral oil types such as balder and oseberg blend and that the discriminative power seems to be persistent with time

compact polarimetric synthetic aperture radar for marine oil platform and slick detection compact polarimetric cp synthetic aperture radar sar can provide ocean surface observations with large coverage swath and abundant polarimetric scattering information these distinctive characteristics make cp sar a potential tool for operational monitoring oil slicks and oil platforms overcoming the shortcomings of small spatial coverage by the traditional quad polarization quad pol sar in this paper we use the radarsat 2 c band quad pol sar data to generate cp covariance matrix elements and subsequently construct pseudoquad pol backscatter coefficients using two cp reconstruction algorithms to evaluate cp sar s applications in detection of oil slicks and oil platforms the reconstructed co and cross polarization data show good agreement with original radar observations acquired at different incidence angles and wind speeds furthermore we develop an unsupervised classification method using the relative phase a logical scalar threshold that separates odd and multiple scattering events as an indicator to discriminate oil slicks and platforms from clean ocean waters the relative phase is positive for clean ocean surfaces where odd scattering is dominant but negative for oil platforms and oil slick covered areas associated with multiple scattering the detections of oil spills and oil platforms are validated against known oil platform geographic positions and optical aircraft surveys of the oil slicks the proposed method provides a promising technique to detect oil slicks and oil platforms from cp imaging mode sar data i e as may be acquired by the risat 1 alos 2 and the future radarsat constellation mission

characteristics and dynamics of wind driven upwelling in the alaskan beaufort sea based on six years of mooring data abstract six years of mooring data from the alaskan beaufort sea slope together with meteorological observations and reanalysis fields are used to quantify the occurrence of wind driven upwelling and the associated atmospheric forcing the canonical upwelling event composited from 115 individual events reveals that when the easterly wind is strongest the entire shelfbreak jet is reversed to the west at the end of the event a bottom intensified eastward flowing rebound jet spins up that is stronger than the normal shelfbreak jet the cross isobath flow has a three layer structure with onshore flow in the surface layer offshore flow in the middle of the water column and onshore flow near the bottom this is because the reversed shelfbreak jet is oriented slightly onshore which overwhelms the cross isobath surface ekman transport the vertically integrated along isobath momentum balance supports this interpretation and indicates that the rebound jet is driven by the zonal gradient in sea surface height during over two thirds of the events atlantic water aw is upwelled to the shelfbreak while for the remaining events only pacific water pw is upwelled the primary driving factor behind this is the seasonal variation in the pw aw interface depth offshore of the shelfbreak which is controlled by the local wind stress curl during summer when pw type events dominate ekman pumping associated with negative wind stress curl deepens the interface depth limiting access to the atlantic layer over the remainder of the year when aw events dominate ekman suction associated with positive wind stress curl raises the interface these variations are due to the influence of the two regional atmospheric centers of action the aleutian low and the beaufort high

circulation dense water formation and outflow on the northeast chukchi shelf we investigated circulation and water mass modification processes in the chukchi sea using 1 temperature salinity and velocity data collected between september 1991 and september 1992 from moorings in bering strait and the northeast shelf and 2 meteorological data and ice concentrations derived from special sensor microwave imager ssm i imagery in october 1991 and from february to august 1992 the mean monthly circulation was steady and northward from november to january strong northeast winds diverted the low salinity bering inflow onto the western shelf and weakened and reversed flow over the northeast shelf the winds also opened extensive polynyas wherein cold hypersaline salinity 34 waters formed the fall winter circulation enhanced dense water formation by diverting low salinity waters away from and prolonging the residence time of water within the polynyas alongshore convergence of the coastal flow swept some of the cold hypersaline water offshore across isobaths but the coastal current carried most of it into the arctic ocean through barrow canyon the dense outflow mixed little during its descent through the upper canyon where bottom friction and rotation but not entrainment were important in the plume momentum balance if the outflow is not diluted by mixing in the lower canyon where theory suggests this will occur then the densest shelf waters can ventilate layers deeper than the halocline salt rejection estimates using ssm i data and surface heat budget calculations agree within a factor of 2 with independent estimates from the mooring hence remote sensing techniques can monitor winter salt rejection rates in the chukchi sea

measurement of ocean surface slopes and wave spectra using polarimetric sar image data abstract methods have been investigated which use fully polarimetric synthetic aperture radar sar image data to measure ocean slopes and wave spectra independent techniques have been developed to measure wave slopes in the sar azimuth and range directions the azimuth slope technique in particular is a more direct measurement than conventional intensity based backscatter cross section measurements in the azimuth direction wave induced perturbations of the polarimetric orientation angle are used to sense the wave slopes in the range direction a new technique involving the alpha parameter from the cloude pottier h a entropy anisotropy and averaged alpha polarimetric scattering decomposition theorem is used to measure slopes both measurement types are sensitive to ocean wave slopes and are directional taken together they form a means of using polarimetric sar polsar image data to make complete measurements of either ocean wave slopes or directional wave spectra these measurements must still contend with fundamental nonlinearities in the sar image processing i e azimuth direction velocity bunching that are due to wave velocity and acceleration effects nasa jpl airsar l and p band data from california coastal waters were used in the studies wave parameters measured using the new methods are compared with those developed using both conventional sar intensity based methods and with in situ noaa national data center buoy measurement products

estuarine controls on fine grained sediment storage in the lower mississippi and atchafalaya rivers observations of the lower mississippi river channel in 1999 2003 with side scan and subbottom seismic profilers multibeam bathymetry core radiotracers 7be 137cs 210pb and 234th and water column profiles of fluid and suspended sediment properties are utilized to constrain the timing location and intensity of the seasonal storage of fine grained sediments in the estuarine channel reach below venice louisiana unlike earlier studies that suggested little or no estuarine sedimentation was taking place in the river the present study demonstrates that the river channel above the head of passes seasonally stores as much as 10 of the annual suspended sediment discharge during periods of falling to low mississippi water discharge associated with salt stratification in the channel thalweg mud deposits are up to 3 2 m thick with 7be derived sediment deposition rates of up to 8 9 mm day water column profiling and 234th 7be ratios suggest that 1 particles are transported and settled mainly as flocs and 2 riverine flocs are settling through the strong salt wedge halocline and are protected from re erosion by the salt stratification with onset of the spring freshet and the corresponding seaward retreat of the saltwater wedge the entire volume of fine grained material stored in the lower river except in low freshet years is remobilized and transported to the gulf of mexico in the turbid freshwater plume this tidal hysteresis strongly influences the timing of sediment supply to the ocean high turbidities in the shelf plume during rising water discharge spikes of 1 to 2 week duration are the product of local channel floor remobilization as well as increased supply from the drainage basin pulsed resupply of sediments and the pore water products of early diagenesis potentially have major implications for issues such as continental margin carbon budgets and coastal eutrophication companion surveys conducted in the lowermost 12 km reach of the atchafalaya distributary of the mississippi show no evidence of saltwater wedge intrusion at low discharge or seasonal fine grained sediment storage likely due to the shallow 7 m river mouth sill that impedes the upstream movement of gulf water

summertime circulation in the eastern chukchi sea abstract the transport of pacific origin water across the eastern chukchi sea during summer is studied using shipboard hydrographic and acoustic doppler current profiler data from multiple surveys the study identifies two major transport pathways in this region the well known alaskan coastal current acc flows poleward along the alaska coast while a more recently discovered and slower current flows northward through the central channel between herald and hanna shoals the two currents separate past point hope and appear to merge again in barrow canyon via previously unresolved pathways flowing west to east across the chukchi sea the collective flow that transports pacific water from bering strait to barrow canyon is termed the bering to barrow current system bbcs the coastal branch of the bbcs which encompasses the acc is a weakly baroclinic flow with a maximum speed in excess of 80 cm s inside barrow canyon the central channel branch of the bbcs is considerably weaker with a maximum flow speed under 20 cm s a portion of the pacific water that flows towards herald canyon to the west may also contribute to the bbcs the amount but the amount is within the margin of error of our data the difference in the advective time scales of the various branches allows water masses of different seasonal characteristics to be transported simultaneously by the bbcs summer water masses occupy most of the southern and central chukchi sea while winter water masses occupy hanna shoal and shelfbreak regions in the northern chukchi sea during summer the total bbcs volume transport in summer is measured at four different locations in the eastern chukchi sea and found to be generally consistent the overall mean transport is 0 86 sv compared to the summer bering strait transport of 1 08 sv this study suggests that the bbcs is the main transport pathway delivering pacific water masses into the western arctic basin