modern sedimentary processes in the wilmington canyon area u s east coast abstract sedimentary processes active in the wilmington canyon area during the past century are documented from geochronologic sedimentologic and radiographic analysis of sediment cores collected using primarily d s r v alvin site selection for the alvin dives and for collection of box and kasten cores was achieved using sea marc and seabeam data allowing accurate sampling of numerous subenvironments from this extensively dissected area of the continental margin 210 pb sediment accumulation rates from intercanyon areas are highest on the upper slope 1 7 mm yr 140 mg cm 2 yr and decrease with water depth to about 0 4 mm yr 36 mg cm 2 yr on the upper rise within submarine canyons accumulation rates vary dramatically from a maximum of 6 mm yr 500 mg cm 2 yr to less than 0 3 mm yr 22 mg cm 2 yr higher accumulation rates in canyons occur as a result of additional supply of older sediment probably from bioerosion of the canyon walls this is supported by observations from d s r v alvin reduced 210 pb activities and indurated mud clasts observed in several canyon cores extremely low accumulation rates in wilmington and south wilmington canyons are probably the result of strong episodic boundary currents non steady state 210 pb profiles and sedimentologic data indicate small scale mass wasting in south heyes canyon and on the lower slope and rise just north of wilmington canyon

exchange of neodymium and its isotopes between seawater and small and large particles in the sargasso sea the concentrations and isotopic ratios of nd were measured in small 1 53 m and large 53 m in situ filtered particles sediment trap material sediment and aerosol samples collected during oligotrophic and productive conditions in the sargasso sea atmospheric input is the main source of exogeneous nd into the sargasso sea based on ndal ratios in trapped material we suggest that up to 50 of atmospheric nd could dissolve at the air sea interface the concentration and isotopic composition of nd vary with both depth and the particle size neodymium concentrations of small and large particles increase with depth from 2 9 12 g g and 5 8 11 8 g g respectively at 40 m the nd signature of large particles is significantly more negative nd 0 13 1 0 2 than that of the small ones nd 0 11 7 0 3 and the particles filtered deeper below 237 m the nd 0 values for small particles match the seawater whereas the nd 0 values of large particles remain less radiogenic these differences are related to the different behaviors of the particulate fractions small particles apparently exchange nd with seawater and then sink rapidly to depth as biologically formed aggregates large particles these aggregates isolate the small particles slowing the exchange with the water to produce different signatures between large particles and seawater since these exchange processes modify the particulate nd signature the shallow radiogenic nd 0 signature observed in the surface and subsurface waters in the nw atlantic is not due to external contributions and is likely of advective origin at depth below 800 m the magnitude of the aggregation disaggregation process varies significantly with season the fraction of small particles repackaged into large aggregates can vary from 0 8 to 80 100 in productive and oligotrophic conditions respectively this seasonal variation may correspond to sinking particles of different zooplanktonic origin vertical fluxes of nd into and out of the sargasso sea as well as exchange fluxes in the water column are examined about 50 of the particulate flux from the surface is remineralized at depth a net scavenging flux of 0 8 10 4 g m2 y is required this value corresponds to a scavenging nd residence time of 1900 y considerably longer than previous estimates of global oceanic residence time of nd on the order of 400 y

sh propagation in rocks with planar fractures i excess slowness summary a model for a fractured rock is a transversely isotropic solid containing randomly spaced plane parallel fractures with random compliance a fracture constitutive relation is the linear slip model in which the jump in motion across the fracture is proportional to the stress i study the propagation at normal and oblique angles of incidence of a shear wave with polarization parallel to the fractures obtaining the frequency dependent excess fracture normal slowness and attenuation i calculate these quantities using some new methods that are not restricted to weak anisotropy or to low frequency or to any particular fracture constitutive relation these are monte carlo mc averaged multiple imbedding ami path sum theory pst and a primary approximation pa finite frequency results from these dynamic theories are compared with results from quasi static theory for a variety of rocks all of which have the same quasi static anisotropy of 9 5 per cent i find that 1 quasi static theory works well at finite frequencies for high q fractures if the fractures are stiff and closely spaced but not if they are compliant and widely spaced 2 the primary approximation works well if the interfracture distance distribution is exponential but not if it is narrow periodic fractures or broad clumped fractures 3 reducing the q of the interfracture rock slightly increases the apparent anisotropy 4 reducing the q of the fracture filling material greatly reduces the apparent anisotropy and 5 increasing the variance of either the fracture spacing distribution or the fracture compliance distribution increases the attenuation a consequence of 4 is that estimates of fracturing derived from sh seismic data will be erroneously low if the fractures are low q elementary arguments suggest that overpressuring or lubrication increases the shear q of natural fractures thus making them more detectable with sh

lead 210 sediment geochronology in a changing coastal environment abstract sediment accumulation rate studies utilizing excess 210 pb and 137 cs were conducted as part of recent investigations of biogeochemical cycling at a single site in cape lookout bight a rapidly changing coastal basin on the outer banks of north carolina u s a cores three meters in length reveal a depositional history for the bight interior characterized by a gradual transition in texture from coarse grained to fine grained material over the period 1946 1979 this transition is controlled by progressive enclosure of the bight by an active northerly migrating recurved spit the textural gradation is periodically interrupted by layers of well sorted sand associated with major storm events lead 210 data indicate that the upper meter of the sediment has accumulated at a rate of 3 35 to 4 71 g cm 2 yr 1 or approximately 8 4 to 11 8 cm yr 1 at o 0 84 below 120 cm depth dilution of clay and silt by low activity sand necessitates correction of the 210 pb profile in order to establish a geochronology grain size 210 pb distribution measurements at three depths reveal that the specific activity dpm g 1 of clay is 3 2 times that of silt and 24 7 times that of sand corrections of bulk sediment excess 210 pb activities based on these measurements lead to dates for textural changes which are consistent with charted changes in basin morphology and major storm events sixteen 137 cs measurements between 33 241 cm depth reveal a peak activity at 105 115 cm and indicate a minimum sedimentation rate of approximately 2 7 g cm 2 yr 1

sedimentary processes on the atlantic continental slope of the united states abstract until recently the sedimentary processes on the united states atlantic continental slope were inferred mainly from descriptive studies based on the bathymetry and on widely spaced grab samples bottom photographs and seismic reflection profiles over the past 6 years however much additional information has been collected on the bottom morphology characteristics of shallow subbottom strata velocity of bottom currents and transport of suspended and bottom sediments a review of these new data provides a much clearer understanding of the kinds and relative importance of gravitational and hydrodynamic processes that affect the surface sediments on the rugged slope between georges bank and cape lookout n c these processes include 1 small scale mass wasting within submarine canyons and peripheral gullies 2 density flows within some submarine valleys 3 sand spillover near the shelf break 4 sediment creep on the upper slope and 5 hemipelagic sedimentation on the middle and lower slope the area between georges bank and hudson canyon is further distinguished by the relative abundance of large scale slump scars and deposits on the open slope the presence of ice rafted debris and the transport of sand within the heads of some submarine canyons between cape lookout and southern florida the slope divides into two physiographic units and the topography is smooth and featureless on the florida hatteras slope offshelf sand spillover and sediment winnowing related to gulf stream flow and possibly to storm driven currents are the major processes whereas hemipelagic sedimentation is dominant over the offshore slope along the seaward edge of the blake plateau north of the blake spur slumping generally is absent south of cape lookout although one large slump scarp related to uplift over salt diapirs has been identified east of cape romain future studies concerning sedimentary processes on the atlantic slope need to resolve 1 the ages and mechanisms of mass wasting 2 the accumulation rates and thicknesses of hemipelagic sediments and 3 the causes and variability of offshelf sand spillover sediment winnowing and canyon transport

plutonium 241am and 137cs ratios inventories and vertical profiles in washington and oregon continental shelf sediments abstract continental shelf sediments from nine locations off washington and oregon have 239 240 pu inventories which average 8 0 2 6 mci km 2 the columbia river and seawaters advecting over the shelf supply pu which is removed to underlying sediments principally through scavenging by inorganic paniculate matter mass balance calculations argue that less than 20 percent of the advected pu need be scavenged from the water column to balance river input and total shelf sediment inventories the percentage of the pu removed through scavenging is consistent with observed participate concentrations in shelf waters and published sediment water distribution coefficients no marked separation of pu from 137 cs is observed with depth in pacific shelf sediments as has been reported in atlantic coastal sediments this interocean distinctness can be explained by differences in particle mixing and downward diffusion of cs in sediments of varying porosities the transuranic inventories and pu cs ratios in the pacific sediments do not support the hypothesis of livingston and bowen that pu is remobilized within the sediment column by complexone formation with principally organic substances excess 210 pb 239 240 pu inventory ratios in eight representative cores from the washington shelf average 100 19 even though absolute values of both inventories vary by much larger factors this reasonably constant ratio for a given water depth permits estimation of total pu inventories and prediction of sites of unusual pu accumulation from data on the more easily measured natural radionuclide

transport and deposition of plutonium in the ocean evidence from gulf of mexico sediments abstract a study of sediments in the gulf of mexico shows dramatic gradients in pu content and isotope ratios from the continental shelf to the sigsbee abyssal plain in terms of predicted direct fallout inventory of pu one shelf core contains 745 of the predicted inventory while abyssal plain sediments contain only 15 20 of the predicted value absolute pu concentrations of shelf sediments are also conspicuously high up to 110 dpm kg compared to 13 5 dpm kg in mississippi river suspended sediment there is no evidence of pu remobilization in gulf of mexico shelf sediments based on comparison of pu profiles with mn al and fe al profiles horizontal transport of fallout nuclides from the open ocean to removal sites in ocean margin sediments is concluded to be the source of both the high concentrations and high inventories of pu reported here the shelf sediments show 240 pu 239 pu ratios close to 0 179 the average stratospheric fallout value but the ratios decrease progressively across the gulf to low values of 0 06 in abyssal plain sediments the source of low ratio pu in deep water sediments may be debris from low yield tests transported in the troposphere alternatively it may represent a fraction of the pu from global stratospheric fallout which has been separated in the water column from the remainder of the pu in the ocean in either case the low ratio material must have been removed rapidly to the sea floor where it composes a major fraction of the pu in abyssal plain sediments pu delivered by global atmospheric fallout from the stratosphere has apparently remained for the most part in the water or has been transported horizontally and removed into shallow water sediments

plutonium and210pb distributions in northeast atlantic sediments subsurface anomalies caused by non local mixing abstract the depth distributions of 210 pb and 239 240 pu measured in a suite of box cores collected from water depths of 4000 5000 m in the northeast atlantic ocean exhibit pronounced subsurface maxima caused by sediment reworking by benthic infauna small scale spatial heterogeneity in bioturbation rates is indicated by large differences in tracer profiles from duplicate cores separated only by a few centimeters 210 pb and 239 240 pu activity distributions from each subcore exhibit a high degree of correlation and most tracer profiles exhibit one or more subsurface maxima one dimensional biodiffusion analogue models do not adequately simulate the principal features of this data set however an inverse conveyer belt mixing model which simulates subsurface egestion or a functionally equivalent process of surficial material which is enriched both in organic debris and radioactive tracers can reproduce the subsurface tracer maxima single event and continuous subsurface egestion models have been formulated and solved for different feeding rates and background biodiffusive fields the single event model provides a better fit to the data and in particular ensures the observed high degree of correlation between the 210 pb and 239 240 pu activity profiles regardless of the different tracer input functions the most likely candidate responsible for subsurface tracer egestion is a large infaunal worm of the phylum sipunculida which dominates the biomass below a depth of 3 cm

the relative mobility of natural th pb and po and fallout pu am cs radionuclides in the coastal marine environment results from model ecosystems merl and narragansett bay the relative mobility of nuclides of pb th pu and cs which are widely used as geochemical tracers for sedimentation and bioturbation was investigated in artificial microcosm tanks merl and in narragansett bay their mobility was characterized by their removal rates from the water column their affinity toward particles and their degree of penetration into the surface sediments pb th and pu transport was controlled predominantly by the affinity of these elements to particles and the transport parameters of the particles themselves i e sediment resuspension and mixing rates because of its low distribution coefficient transport of cs was controlled by molecular diffusion through pore water in the winter while in summer cs transport was enhanced due to bioturbation the increase with depth of the cspu ratio in core profiles of merl and narragansett bay sediments is thus caused primarily by the higher mobility of cs

polar lows over the gulf of alaska in conditions of reverse shear abstract the formation of two polar lows over the gulf of alaska are studied using observations taken during the ocean storms field experiment synoptic scale and mesoscale analyses were constructed using noaa p 3 aircraft flight level and radar data and drop windsonde profiles in addition to conventional data sources the synoptic scale analyses show that polar low development occurred in a low level mesoscale baroclinic zone near the center of a mature occluded synoptic scale low pressure system the disturbances propagated along the zone in the reverse shear sense i e in the direction opposite to the thermal wind within the zone the mesoscale analysis reveals a boundary layer jet of 38 m s 1 on the cold side of the baroclinic zone accompanying the leading polar low indirect evidence suggests that a sawyer eliassen secondary circulation was present polar low development occurred in the region of a frontogenetical geostrophic deformation convective activity was not prominent during the growth p

rates of sediment reworking at the hebble site based on measurements of th 234 cs 137 and pb 210 abstract th 234 cs 137 and pb 210 measurements have been made on ten cores from the hebble site on the nova scotian continental rise th 234 mixing coefficients from hebble sediments show substantial lateral variability with values ranging from 1 to 33 cm 2 yr 1 these mixing coefficients are one to two orders of magnitude greater than values from typical continental rise and abyssal sediments because of high densities of benthic macrofauna th 234 data from hebble cores indicate that particles at the sediment water interface are mixed to depths of 1 5 cm on a 100 day time scale cs 137 and pb 210 data indicate that on time scales of 30 100 yrs surface sediments are reworked to depths ranging from 1 to 12 cm based on th 234 profiles from two hebble cores collected less than 200 m apart during consecutive years no temporal variability in mixing rate could be resolved in some hebble sediments there is good agreement between the th 234 mixing coefficient 100 day time scale and the pb 210 mixing coefficient 100 yr time scale in other hebble cores however th 234 data indicate that the pb 210 profile has not reached steady state if steady state solutions are used to model these non steady state profiles the calculated pb 210 mixing coefficient may underestimate the true mixing coefficient by as much as an order of magnitude

particle mixing rates in sediments of the eastern equatorial pacific evidence from 210pb 239 240pu and 137cs distributions at manop sites abstract particle mixing rates db calculated from excess 210pb gradients in sediments of the east equatorial pacific range from 0 04 to 0 5 cm2 y with variation of a factor of 3 4 at a single site diffusion of the 236ra daughter 222rn may affect 210pb distributions under conditions of slow mixing and low 210pb flux to the seafloor as shown by a siliceous ooze clay core which contained the fallout radionuclides 239 240pu and 137cs but no excess 210pb relative to 226ra there is no clear relationship between 210pbderived mixing rates and sediment type accumulation rate or organic carbon flux to the sediments comparison of 210pb mixing rates with those calculated from 239 240pu and 137cs distributions reveals better agreement for a pulse input of the fallout radionuclides db 0 03 0 4 cm2 y than for continuous input at a constant rate db 0 1 1 6 cm2 y although the pu and 137cs data are better fit by the latter model the agreement may be fortuitous because 239 240pu and 137cs appear significantly deeper than 210pb in at least one core tracer separation could be caused by particle size selective mixing by the benthic fauna or by chemical mobilization if the fallout radionuclides are scavenged from surface waters by large organic rich particles such as fecal pellets their release and migration may result from decomposition of the carrier in surface sediments either a relatively unreactive form of pu e g oxidized pu has been released by this process or a one dimensional model is inadequate to explain its observed penetration into the sediments activity ratios of 239 240 pu 137 cs in the sediments decrease with increasing north latitude and the trend reflects higher fluxes of 239 240pu near the weapons test site at christmas island 2 n the 239 240 pu 137 cs ratios and fluxes to the sediment assuming constant input at the siliceous ooze red clay site are consistent with published sediment trap data from a nearby site thus if fallout radionuclide fluxes to the sea floor were higher in the past both 239 240pu and 137cs have been released from sinking particles

the pore water chemistry of 239 240pu and 137cs in sediments of buzzards bay massachusetts abstract the collection of large volumes of pore water 1 2 liters per 2 cm horizon of sediment and low level radiochemical measurements of 239 240pu and 137cs have been combined to produce the first study of these fallout artificial radionuclides in marine pore waters profiles from box cores taken in june and september 1982 from buzzards bay mass are reported along with profiles of many diagenetic constituents i e so42 alkalinity fe mn doc and nutrients the 239 240pu pore water profile is characterized by a subsurface maximum of about 0 28 dpm 100 kg lying between 3 11 cm overlying seawater in contrast has an activity of 0 01 0 02 dpm 100 kg below about 11 cm the pore water 239 240pu distribution follows that of the solid phase which decreases rapidly with depth the pore water profiles of 137cs are characterized by a broad and deeply penetrating maximum where activities of about 35 40 dpm 100 kg extend from 3 to 20 cm overlying seawater in contrast has an activity of 17 24 dpm 100 kg the 137cs and 239 240pu pore water data show that there is preferential downward transport of 137cs and that 239 240pu does not have an active diagenetic chemistry and is not significantly mobile in these coastal sediments

plutonium and americium in anoxic marine sediments evidence against remobitization 239 240pu activities of 100 450dpm kg are found down to 15 18 cm in anoxic saanich inlet sediments with a subsurface maximum in undisturbed deposits integrated 239 240pu inventories which overlap delivery estimates are present both in two cores of anoxic sediments from saanich inlet and in one core of oxic sediments 65 km away in dabob bay washington 241am239 240pu ratios in saanich inlet sediments overlap ratios in unfractionated midnorthern latitude fallout in oxic sediments from the washington continental shelf and in anoxic sediments from two basins off southern california and mexico the 239 240pu137cs ratios in three intervals of saanich inlet sediments are also in agreement with ratios previously reported for oxic coastal marine sediments the pu inventories the ampu and pucs ratios and the saanich inlet dabob bay comparison all argue that pu is not rapidly remobilized in anoxic sediments the subsurface 239 240pu activity maximum is not in agreement with the historical record of peak pu fallout in 1963 1964 unless our 210pb derived sedimentation rates are incorrectly high however they are in good agreement with previous 210pb and varve chronologies in saanich inlet and also give reasonable dates for times when 239 240pu and snap 9a supplied 238pu first appear in the sediments we conclude they properly date the maximum in sedimentary 239 240pu activity at 1970 1973 and seek explanations for the 7 10yr time lag after peak fallout 239 240pu inventories in one core from the eastern basin of the cariaco trench and in two cores from golfo dulce an anoxic basin off the pacific coast of costa rica are also in reasonable agreement with fallout delivery to these latitudes when excess 210pb inventories and fluxes are used to verify recovery of at least a major fraction of the most recently deposited sediments

the geochemistry of fallout plutonium in the north atlantic ii ratios and their significance a systematic decrease in the 240pu239pu ratio in marine sediments is found with increasing water depth along a transect of cores between woods hole and bermuda the 240pu239pu atom ratios range from o 18 on the shelf to o 10 at 5000 m but do not change with depth in individual cores a model is presented which can account for the range of 240pu239pu ratios found in this and other similar studies noshkin and gatrousis 1974 scottet al 1983 we propose that there have been at least two distinct sources of fallout pu to this region the major source of pu is global stratospheric fallout characterized by a 240pu239pu ratio of 0 18 and a relatively long residence time in seawater the second source is characterized by a much lower 240pu239pu ratio and relative to global fallout it must have been much more efficiently removed from the water column to deep sea sediments we suggest that surface based low yield testing at the nevada test site is the only source of low ratio fallout pu which could account for the timing inventories and refractory characteristics of this second component of fallout pu inputs to the north atlantic

the geochemistry of plutonium in fresh and marine water environments abstract the chemical behaviour of plutonium in the hydrosphere is a subject of both great practical and intrinsic importance the production and eventual disposal of pu and other artificial radionuclides dictates that this be the case the main objective of this paper is to provide a synthesis and critical examination of currently published data and interpretations on the geochemistry of pu in natural waters and sediments where appropriate an attempt is made to reinterpret published data with the aim of establishing the relationships between geochemical and biological processes and the distribution concentration and speciation of pu particular attention is paid to the question of the potential for the chemical remobilization of pu from the solid to the aqueous phase approximately one third of the text deals with freshwaters mostly lakes while two thirds discusses the estuarine coastal and open ocean environments

determination of mixing parameters from tracer distributions in deep sea sediment cores abstract computer optimization and approximate analytical procedures are developed for the determination of the depth of bioturbation mixing d and the mixing coefficient d for instantaneous tracer inputs the methods have been applied to observations of microtektites volcanic ash and pumice in sixteen deep sea sediment cores the values for d are well determined generally with confidence intervals of a few centimeters or less and with an average value of d 11 cm for the sixteen cores the values for d are determined to first figure accuracy at best with values of around 10 cm 2 ka 1 or greater

the geochemistry of fallout plutonium in the north atlantic i a pore water study in shelf slope and deep sea sediments abstract the distribution of fallout plutonium between pore waters and sediments in the northwest atlantic is examined in order better to define the potential for pu migration from and within marine sediments along a transect of seven cores collected between woods hole and bermuda the solid phase 239 240pu 210pbex and 137cs results do not suggest that any of these tracers are preferentially mobile within the cores pore water pu activities appear to be controlled primarily by the distribution of pu in the solid phase with an operationally determined distribution coefficient kd in the range of 0 2 23 104 there is a trend in the kds along the transect with higher values in the 104 105 range on the shelf and slope to lower values 239 240 pu cm 2 year sediment mixing models are not significantly altered by the inclusion of pu diffusion terms since the pore water terms are so small relative to typical sediment mixing rates

plutonium in intertidal coastal and estuarine sediments in the northern irish sea abstract surface intertidal sediments from 35 sites in the irish sea have been analysed for their 238 pu and 239 240 pu activities together with an intensive study of plutonium in sediments of the esk estuary nw england the range of plutonium activities for the whole survey were 0 14 4118 and 1 3 16 026 bq kg 1 for 238 pu and 239 240 pu respectively the levels of pu activity derived from the sellafield nuclear fuel reprocessing effluents in sediments are controlled by lithological factors and the influence of transport and post depositional processes grain size distribution is particularly important the major part of plutonium activity being in the mud fraction of all sediments the data suggest that over the irish sea coastline dynamic mixing of sediment grains by reworking and resuspension and or by dispersion in tidal currents are important in determining plutonium distributions the exponential decrease in sediment plutonium activities away from the sellafield source is attributed to the progressive mixing with older contaminated and uncontaminated sediments

interpretation procedures for the determination of sediment parameters from time dependent flux inputs abstract a formulation for the effects of a time dependent input flux to a sedimentation system consisting of a diffusive layer underlain by a non diffusive medium has been developed the intent is to provide interpretation procedures for the determination of sedimentation rate diffusion coefficient and mixed layer thickness from observed tracer concentrations they have been applied for illustrative purposes to published137cs and239 240pu measurements

forward and reverse shear environments during polar low genesis over the northeast atlantic abstractthe synoptic and subsynoptic environments associated with polar low genesis are examined ambient pre polar low environments are classified as forward or reverse shear conditions based on the angle between the thermal and mean wind forward shear environments are associated with a synoptic scale ridge over scandinavia featuring a zonally oriented baroclinic zone extending throughout the troposphere with a wind speed maximum at the tropopause similar to typical midlatitude cyclogenesis concurrent wavelike development occurs both in the lower and upper troposphere along the baroclinic zone and the mean propagation direction is eastward parallel to isolines of sea surface temperature reverse shear environments exhibit a distinctly different structure and are characterized by a trough over scandinavia associated with a synoptic scale occluded cyclone the genesis area exhibits strong cold air advection on its right hand side and polar low development occurs on the warm side of an intense low le

particle mixing rates in deep sea sediments determined from excess 210pb and 32si profiles particle mixing rates have been determined for 5 south atlantic antarctic and 3 equatorial pacific deep sea cores using excess 210 pb and 32 si measurements radionuclide profiles from these siliceous calcareous and clay rich sediments have been evaluated using a steady state vertical advection diffusion model in antarctic siliceous sediments 210 pb mixing coefficients 0 04 0 16 cm 2 y are in reasonable agreement with the 32 si mixing coefficient 0 2 or 0 4 cm 2 y depending on 32 si half life in an equatorial pacific sediment core however the 210 pb mixing coefficient 0 22 cm 2 y is 3 7 times greater than the 32 si mixing coefficient 0 03 or 0 07 cm 2 y the difference in 210 pb and 32 si mixing rates in the pacific sediments results from 1 non steady state mixing and differences in characteristic time and depth scales of the two radionuclides 2 preferential mixing of fine grained clay particles containing most of the 210 pb activity relative to coarser particles large radiolaria containing the 32 si activity or 3 the supply of 222 rn from the bottom of manganese nodules which increases the measured excess 210 pb activity relative to 226 ra at depth and artificially increases the 210 pb mixing coefficient based on 32 si data and pore water silica profiles dissolution of biogenic silica in the sediment column appears to have a minor effect on the 32 si profile in the mixed layer deep sea particle mixing rates reported in this study and the literature do not correlate with sediment type sediment accumulation rate or surface productivity based on differences in mixing rate among three antarctic cores collected within 50 km of each other local variability in the intensity of deep sea mixing appears to be as important as regional differences in sediment properties

a numerical modeling study of mesoscale cyclogenesis to the east of the korean peninsula numerical simulations and the analysis of observational data are employed to understand the mesoscale cyclogenesis in a polar airstream that occurred over the sea to the east of the korean peninsula on 28 29 january 1995 the observational analysis shows that a mesoscale low develops over the southeastern east sea japan sea on 29 january 1995 satellite imagery also indicates that a meso b scale vortex forms on the lee side of the northern korean mountain complex kmc which is located in the northern korean peninsula and that a meso a scale cyclone develops over the southeastern east sea at a later time the mesoscale cyclone forms in the lower troposphere with strong baroclinicity and cyclonic circulation under the influence of an upper level synoptic scale cold vortex numerical simulation has captured major features of the observed cyclogenesis very well the cyclogenesis occurs in a progressive manner basically four distinctive stages of the cyclogenesis are identified 1 first a surface pressure trough forms on the lee side of the kmc under a northwesterly synoptic scale flow that is deflected anticyclonically over the kmc 2 second the lee trough deepens further into a strong convergence zone and a meso b scale vortex 3 next the meso b scale vortex develops into a meso a scale vortex as the vortex and the trough begin to move southeastward from the lee of the kmc 4 finally the surface trough deepens into a closed low and the meso a scale vortex becomes collocated with this deepening surface low to form a meso a scale cyclone over the southeastern east sea several sensitivity experiments are performed to isolate the effects of a topography warmer sea surface diurnal thermal forcing and latent heat release during stages 1 and 2 it is found that the kmc and low level baroclinicity are responsible for generating the strong lee trough and vortex during stage 3 the development of the meso a scale vortex is brought on by the tilting of horizontal vorticity and vertical stretching in a synopticscale cyclonic circulation in the final stage the condensational heating plays the key role for the development of the meso a scale cyclone under the influence of an upper level synoptic scale cold vortex the presence of the warm sea surface is found to be a necessary condition for the development of a polar air convergence zone and the mesoscale cyclone it is also found that the low level baroclinicity is essential for the present case of mesoscale cyclogenesis

the geochemistry of manganese carbonate in panama basin sediments abstract the mn distribution in panama basin area sediments and interstitial waters is discussed striking surficial mn enrichments produced by a well known diagenetic recycling process characterize the sediments of the region thermodynamic solubility calculations indicate that in at least one core interstitial waters approach saturation with respect to mnco3 a mixed carbonate phase of composition mn48 ca47 mg5 co3 was recovered from an ash band in the same core the association of this material with the coarse volcaniclastic debris is thought to result from facile manganous carbonate precipitation in sediment horizons of coarser mean grain size since sulphate reduction in the upper two metres of panama basin sediments is fairly minor little increase in alkalinity is observed and it is postulated that significant production of carbonate alkalinity is not a prerequisite for manganous carbonate generation in hemipelagic sediments a more important factor appears to be the availability of mn oxides for solution during early diagenesis stable c isotopic analyses indicate that little c of organic origin is used in the precipitation reaction in either panama basin or loch fyne scotland sediments

nonlinear parameter estimation for sediment cores abstract nonlinear parameter estimation techniques are applied to three distinctly different sediment cores for which concentrations of tracers with steady and time dependent flux inputs are available the mathematical model employed consists of a diffusive upper layer of finite depth underlain by a semi infinite nondiffusive medium confidence regions and intervals are reported for sedimentation rate diffusion coefficient and mixed layer depth based on ordinary least squares criteria for each tracer conflicting estimates are resolved using a weighted least squares procedure which combines observations of the individual tracers and exploits their strengths and weaknesses

airborne dual doppler observations of an intense frontal system approaching the pacific northwest coast airborne doppler radar data collected off the pacific northwest coast by a noaa wp 3d orion aircraft over an 8 h period on 8 december 1993 during the coastal observations and simulations with topography experiment reveal the mesoscale structure of an intense frontal system while it was well offshore and as it approached within 20 km of the oregon coastline during the offshore stage a portion of the narrow coldfrontal rainband was characterized by deep convective cores pseudo dual doppler analyses characterize the kinematic and precipitation structure of the deep convection pseudo dual doppler analyses describe the subsequent evolution of the narrow cold frontal rainband as it approached to within 20 km of the oregon coast deformation of the frontal zone appeared to cause the dissipation of one of three precipitation cores contained within the dual doppler area the precipitation cores and the strong convergence zone associated with the front conformed to some degree to the shape of the coastline near cape blanco oregon as the front neared the coast changes in the prefrontal flow that occurred as the front approached the coast were qualitatively consistent with theoretical and numerical studies of upstream orographic influence comparison of pseudo dual doppler derived velocity profiles with idealized numerical model calculations suggests that the nearshore evolution of the frontal rainband was significantly affected by an upstream influence of the coastal orography

structure and environment of polar mesocyclones over the northeastern part of the sea of japan abstractpolar mesocyclones pmcs are mesoscale cyclonic vortices that develop poleward of the main polar front the sea of japan is one region where pmcs frequently occur during winter in this paper the general characteristics of the structure and environment of pmcs that form over the northeastern part of the sea of japan and move southward are examined using composite analysis and numerical simulation the composite analyses show that the synoptic scale environment of the pmcs is characterized by a zonal temperature gradient at lower levels and a trough accompanied by cold air at upper levels these elements of the environmental field form a reverse shear the mesoscale structure of the pmcs exhibits characteristics of baroclinic development while it is also accompanied by condensational heating the numerical simulation in which the composite fields are used for the initial and boundary conditions successfully reproduces a realistic pmc in this numerical simulation the mesoscale structures are al

the importance of relict burrow structures and burrow irrigation in controlling sedimentary solute distributions abstract some areas of the seafloor particularly the deep sea are characterized by large numbers of apparently uninhabited or relict burrow structures formed by macrobenthic organisms because of low sedimentation rates or lack of physical disturbance these structures are stable for long periods of time and could potentially influence solute diffusion patterns in surface sediments a two dimensional diffusionreaction model which allows for diffusive rather than advective transport within stagnant water filled burrows demonstrates that in the absence of advective irrigation relict burrow structures are unlikely in most cases to significantly alter average solute distributions from those predicted by one dimensional vertical models this conclusion assumes changes in diffusive transport properties alone and does not account for any effects of relict structures on reaction rates or physical ventilation of deposits by bottom currents significant changes 5 in solute distributions are generally produced only when the ratio of the halfdistance between burrows to relict burrow radii is 10 and sedimentary diffusion coefficients are 60 that in free solution because solute distributions in stagnant burrow waters are nearly that in surrounding sediment sediment water solute fluxes are also essentially unaffected by relict burrows except at extremely high abundances or fairly large differential diffusion rates between sediment and free solution in contrast even at low abundance biologically irrigated or physically ventilated burrows produce major changes in solute transport and build up patterns

biological activity and associated sedimentary structures in hebble area deposits western north atlantic abstract biological and sedimentologic samples along with x radiographs of sediment slabs were taken from box cores in the hebble area 4700 m on the lower continental rise of nova scotia these data suggest that this bottom region is influenced by periods of strong near bottom currents which erode and physically transport sediments these high periods alternate with periods of weaker flow biogenic reworking of sediments by an active benthic infauna dominates particle transport during low flow conditions

multiple polar mesocyclones over the japan sea on 11 february 1997 abstract the characteristics and development mechanism of four meso scale polar mesocyclones m pcs which appeared as a vortex train over the japan sea from 0000 to 1700 utc on 11 february 1997 are studied by means of observational analyses and numerical simulations these four m pcs were first observed at 0000 utc along the southern edge of a meso scale cloud system that looked like an occluded extratropical cyclone in a japanese geostationary meteorological satellite 5 gms 5 infrared satellite image detailed evolutionary processes of these m pcs were described based on satellite and radar images the horizontal scales of these m pcs were on the order of 100 km and the spatial intervals between their centers were about 200 km their lifetimes were around 10 h the occlusion like features of the meso scale cloud system and the synoptic situation prior to the development of these m pcs are examined by using regional objective analysis ranal data of the japan meteorological agency jma in o

239 240pu and excess210pb inventories along the shelf and slope of the northeast u s a abstract sedimentary pu and excess 210 pb inventory data are examined from a large number of sites along the u s north atlantic shelf and slope from these data an estimate can be made of the magnitude and location of pu and 210 pb accumulation in this region a major feature of the data is a decrease in the pu and 210 pb inventories with water depth which appears to reflect a decrease in the net scavenging of these elements off shore when pu and 210 pb inventories are summed over water depths less than 4000 m in the north atlantic shelf and slope region the sediments can account for 24 8 of the expected pu and 83 15 of the expected 210 pb inputs at water depths greater than 4000 m in this region we find a greater deficiency in the measured inventories of both 210 pb and pu which cannot be accounted for in the shallower sediments this suggests that the northwest atlantic continental margin is not a major site of pu or 210 pb removal and storage when compared to atmospheric in situ and lateral inputs of these radionuclides