interannual variability of summer biochemical enhancement in relation to mesoscale eddies at the shelf break in the vicinity of the pribilof islands bering sea abstract this study examined variability of the eddy field and primary production over the bering sea s eastern shelf break area during summer using a satellite multi sensor data set the eddy field and on shelf nutrient flux below 50 m water depth were also investigated using a numerical model the satellite altimeter data analysis and numerical experiments indicated that the eddy field was induced by perturbations of the bering slope current system and or instabilities in the bering sea basin via flow through the aleutian passes the distribution of high primary production roughly coincided with the high variability area of the eddy field numerical experiments showed a 70 increase in net on shelf flux and 54 increase in net on shelf transport by the generation propagation of eddies along the shelf break at pribilof canyon towed ctd fluorometer measurements during the summer of 2003 revealed a stable water column and high fluorescence 10 g l 1 in the area between the 200 and 1000 m isobaths at a time when there was a low level of on shelf flux regardless of the eddy field conversely the eddy induced on shelf flux and stable water column can enhance primary production from spring to summer at the shelf break moreover the eddy induced on shelf nutrient flux probably contributes to the primary productivity at the western shelf of the pribilof islands where the bering sea ecosystem is very dynamic this eddy related shelf break process can be applied to not only the bering sea shelf break but also all shelf break areas in which propagating eddies are found

sources sinks and storage of river sediment in the atlantic drainage of the united states the history of sediment and its movement in the atlantic drainage demonstrate some of the difficulties of modeling sediment on a river basin scale soil erosion was accelerated by a factor of at least 10 when european settlers cleared forests and planted crops although increasing soil conservation practice and decreasing crop farming have since reduced the rates of erosion large quantities of eroded material are still stored on hillslopes and in stream valleys where they continue to augment the sediment loads of the rivers the sediment from this episode of erosion that is largely past can be expected to emerge from storage for many decades and perhaps even several centuries to come the reservoirs that have been built on many of the major rivers trap significant portions of the moving sediment which in some places may be remobilized by large floods essentially all the river sediment that reaches the atlantic coastal zone is trapped in estuaries and coastal marshlands probably less than 5 is deposi

a major circulation anomaly in the western bering sea the alaskan stream ceased to flow northward into the western bering sea starting in summer 1990 this unexpected lack of inflow caused by a southward shift in the path of the alaskan stream persisted through at least fall 1991 if the anomalous flow continues substantial changes in the physical environment will occur possibly leading to impacts on the rich fisheries stocks in the region

circulation on the central bering sea shelf july 2008 to july 2010 1 we examine the july 2008 to july 2010 circulation over the central bering sea shelf using measurements at eight instrumented moorings hindcast winds and numerical model results at sub tidal time scales the vertically integrated equations of motion show that the cross shelf balance is primarily geostrophic the along shelf balance is also mainly geostrophic but local accelerations wind stress and bottom friction account for 10 40 of the momentum balance depending on season and water depth the shelf exhibits highly variable flow with small water column average vector mean speeds 5 cm s 1 mean peak speeds in summer 3 6 cm s 1 10 30 cm s 1 are smaller than in winter and fall 6 12 cm s 1 30 70 cm s 1 low frequency flows 1 4 cpd are horizontally coherent over distances exceeding 200 km vertical coherence varies seasonally degrading with the onset of summer stratification because effects of heating and freezing are enhanced in shallow waters warm summers increase the cross shelf density gradient and thus enhance northward transport cold winters with increased ice production and brine rejection increase the now reversed cross shelf density gradient and enhance southward transport although the baroclinic velocity is large enough to influence seasonal transports wind forced ekman dynamics are primarily responsible for flow variations the system changes from strong northward flow with coastal convergence to strong southward flow with coastal divergence for northerly and easterly winds respectively under northerly and northwesterly winds nutrient rich waters flow toward the central shelf from the north and northwest replacing dilute coastal waters that are carried south and west

the release and dispersal of pb and zn contaminated sediments within an arctic braided river system abstract this paper examines the release and dispersal of pb and zn contaminated mine tailings within the tunnelelv river ne greenland the tunnelelv is an arctic braided river system and results derived from this research provide interesting comparisons to conclusions gained from previous studies which have mainly concentrated on temperate river systems patterns of dispersion are shown to relate intimately to the macroscale morphology of the braided river valley and also to the vertical tendency of the channel network storage of fine contaminated sediments are shown to relate to the bar pool morphology of the channel attention is drawn to the performance and limitations of existing sediment dispersion models in relation to the complexity of the processes they are trying to model

evidence from diatom bound nitrogen isotopes for subarctic pacific stratification during the last ice age and a link to north pacific denitrification changes higher diatom bound d 15 n 70 wt lower opal content and 1200 ppm lower biogenic barium taken together and with constraints on sediment accumulation rate these results suggest a reduced supply of nitrate to the surface due to stronger stratification of the upper water column of the bering sea during glacial times with more complete nitrate consumption resulting from continued iron supply through atmospheric deposition this finding extends the body of evidence for a pervasive link between cold climates and polar ocean stratification in addition we hypothesize that more complete nutrient consumption in the glacial age subarctic pacific contributed to the previously observed ice age reduction in suboxia and denitrification in the eastern tropical north pacific by lowering the nutrient content of the intermediate depth water formed in the subpolar north pacific in the deglacial interval of the bering sea record two apparent peaks in export productivity are associated with maxima in diatom bound and bulk sediment d 15 n the high d 15 n in these intervals may have resulted from greater surface nutrient consumption during this period however the synchroneity of the deglacial peaks in the bering sea with similar bulk sediment d 15 n changes in the eastern pacific margin and the presence of sediment lamination within the bering sea during the deposition of the productivity peaks raise the possibility that both regional and local denitrification worked to raise the d 15 n of the nitrate feeding bering sea surface waters at these times

heavy metal storage in near channel sediments of the lahn river germany abstract heavy metal pollution in urban industrial and mined watersheds of europe is well documented but less is known about metal contamination in agrarian watersheds or those with no history of mining along a 75 km reach of the lahn river central germany near channel flood plain sediments

fluvial sediment budgets in the north carolina piedmont phillips j d 1991 fluvial sediment budgets in the north carolina piedmont geomorphology 4 231 241 sediment budgets for four large 1000 km 2 drainage basins in the piedmont physiographic province of north carolina were estimated from data compiled during erosion and sedimentation surveys budgets for the upper tar upper neuse haw and deep river basins showed broadly similar trends in allocation of eroded sediment among yield and storage sediment yield as a percentage of mean annual gross erosion within the basins averaged 10 this was less than the rate of alluvial storage which averaged 14 of annual gross erosion about 76 of the mean annual erosion was stored as colluvium on hillslopes there are relatively small differences in sediment delivery and storage ratios among the study basins this suggests that the relative order of magnitude of the allocation of eroded sediment for southern piedmont rivers is colluvial storage alluvial storage and yield of the sediment that does reach the streams more than half is stored as alluvium on an average annual basis aggrading channels and floodplains siltation of benthic habitats and sediment pollution problems are thus likely to persist unless dramatic reductions in upland erosion or in sediment delivery to streams are realized with respect to longer term basin evolution results point to the need for an improved understanding of the temporal scales of colluvial and alluvial sediment storage

dynamical analysis of a satellite observed anticyclonic eddy in the northern bering sea the characteristics and evolution of a satellite observed anticyclonic eddy in the northern bering sea during march and april 1999 are investigated using a three dimensional princeton ocean model pom the anticyclonic like current pattern and asymmetric feature of the eddy were clearly seen in the synthetic aperture radar sar sea surface temperature and ocean color images in april 1999 the results from model simulation reveal the three dimensional structure of the anticyclonic eddy its movement and dissipation energy analysis indicates that the barotropic instability bti is the main energy source for the growth of the anticyclonic eddy the momentum analysis further reveals that the larger magnitude of the barotropic pressure gradient in the meridional direction causes the asymmetry of the anticyclonic eddy in the zonal and meridional directions while the different magnitudes of the meridional baroclinic pressure gradient are responsible for the different intensity of currents between the northern and southern parts of the anticyclonic eddy

floodplain storage of sediment contaminated by mercury and copper from historic gold mining at gold hill north carolina usa abstract previous research on the environmental consequences of mining has shown that metal contaminants can have long lasting impacts on water quality and aquatic ecosystems because of the remobilization of sediment associated contaminants that have been stored in floodplains we examined the magnitude and distribution of mercury hg and copper cu contamination of floodplain deposits associated with nineteenth century gold au mining activities in the gold hill mining district north carolina a comparison of post mining metal concentrations in overbank deposits with sediment quality guidelines indicates that overall about 21 are contaminated above the probable effect concentration pec above which adverse effects are expected to occur more often than not for both cu and hg the highest contamination occurs upstream near the mine source where 51 of the samples exceed the pec for hg and 57 exceed the pec for cu of the three different methods used to estimate metal mass storage the most reliable estimate suggests that about 6 8 mg of hg and 619 mg of cu currently reside in floodplain deposits within this watershed although overbank sediment storage increases downstream and with valley width about 75 of the hg and cu mass are stored in the upstream portion of the watershed hg mass storage displays a strong negative relationship with cross sectional stream power but the relationship between cu mass storage and stream power is insignificant we used vertical changes in overbank metal concentrations and the mining history to estimate a mean sedimentation rate of 2 7 cm y 1 during the most intensive period of au mining at gold hill 1842 1856 that is three times the long term 1842 2007 rate of 0 9 cm y 1 long term average rates at gold hill are comparable to those reported elsewhere in the eastern piedmont the downstream increase in long term rates may indicate a spatial and temporal lag effect where the locus of deposition shifts downstream with time

tracing subarctic pacific water masses with benthic foraminiferal stable isotopes during the lgm and late pleistocene abstract as the largest ocean basin the pacific helps to set the global climate state since its circulation affects mean ocean properties air sea partitioning of carbon dioxide and the distribution of global oceanic poleward heat transport there is evidence that during the last glacial maximum lgm the subarctic pacific contained a better ventilated relatively fresh intermediate water mass above 2000 m that may have formed locally the source and spatial extent of this water mass is not known nor do we know how formation of this water mass varied during pleistocene glaciations with different orbital and ice sheet boundary conditions here we present a 0 5 my multi species benthic stable isotope record from site u1345 1008 m on the northern bering slope and a 1 0 my record from u1339 1868 m from the umnak plateau in the southeastern basin we find that the relatively well ventilated low 18o intermediate water reaches 1000 m in the bering sea during mis2 but that the hydrographic divide between this water mass and poorly ventilated deep water was shallower than 1000 m for earlier glaciations we also compare bering sea piston core and iodp expedition 323 uvigerina data from the holocene and lgm with the modern hydrography and to previously published profiles from the okhotsk sea and emperor seamounts we find that the carbon and oxygen stable isotope signatures of well ventilated water in the bering and okhotsk seas are distinct suggesting that there may have been intermediate water formation in both basins during the lgm

the bering slope current system revisited mean circulation and water properties within the aleutian basin of the bering sea are investigated using hydrographic and subsurface park pressure displacement data from a regional array of 14 profiling ctd floats after 10 days drifting at 1000 dbar each float measures temperature and salinity profiles as it rises to the surface and then transmits these data via satellites which also make several fixes of the float surface positions before it sinks again every fourth cycle the floats sink from 1000 dbar to a 2000 dbar target just prior to ascent to measure deeper profiles the 1000 dbar displacements estimated from the float surface position fixes reveal a coherent few centimeters per second northwestward flow along the northeastern boundary the deep signature of the bering slope current middepth water property distributions are consistent with cyclonic advection of warm water from the south around the basin eastward in the aleutian north slope current and then northwestward in the bering slope current geostrophic transport estimates relative to 1000 dbar also show cyclonic motion although with significant noise likely owing to the influence of mesoscale eddies the mean alongslope geostrophic transport of the bering slope current is determined between 0 and 1900 dbar relative to 1000 dbar and then combined with mean along slope velocities at 1000 dbar the result is an absolute geostrophic transport estimate with 95 confidence intervals for the along slope current offshore of the 1000 m isobath and between 0 and 1900 dbar of 5 8 61 7 3 106 m3 s 21

mesoscale oceanographic features associated with the central bering sea ice edge february march 1981 midwinter 1981 observations from the central bering sea shelf showed a hydrographic structure which was two layered in temperature salinity and density this structure was confined to a 100 km wide band which coincided approximately with the ice edge the colder lower salinity upper layer was continuous in its t s properties with homogeneous water to the north beneath the ice the warmer more saline lower layer was similarly continuous with water to the south near the shelf break a northwestward baroclinic flow of the surface relative to 75 dbar was associated with the layered structure the layered structure and associated flow appear to be regular winter features associated with the ice edge in this region input of low salinity water from melting of ice along the edge is adequate to maintain the layered structure and its associated baroclinic circulation against the effects of tidal and wind mixing the resulting observed oceanographic features were similar to those which have been found in association with midshelf and shelf break fronts in other regions and appear to define a dynamically controlled boundary between the cold low salinity water on the northern shelf and the warmer more saline water near the shelf break

flow and water property structures between the bering sea and fiji in the summer of 1993 an overview is given of the top to bottom flow thermohaline oxygen and nutrient structures between the bering sea and the fiji islands based on high resolution field measurements along 179 e the zonal flow is dominated by a banded mesoscale structure reflecting the highly sheared structure and instabilities of the major ocean currents crossing the date line the major midlatitude currents are 100 200 km wide have maximum speeds of 40 cm s 1 and extend to 2000 m when measured by the 5 cm s 1 isotach el nino conditions in 1993 caused a merger of the north equatorial countercurrent with the equatorial undercurrent leading to a 600 km wide band of equatorial eastward flow 40 60 cm s 1 in the upper 300 m beneath a 400 km wide and 1 2 km deep westward jet 10 30 cm s 1 is found between 1500 and 3500 m the equatorial flow is predominately to the southeast and between 3500 and 5000 m it is toward the northwest consonant with banded shear flow and flow topography interactions the physical and chemical property distributions along 179 e are complicated reflecting the effects of differential property advection mixing and water mass transformation well defined property fronts occur in shear zones between currents of different origin the thermohaline oxygen and nutrient tongues associated with north and south pacific intermediate and deep waters have considerable internal structure indicative of mesoscale processes and contorted flow paths the abyssal flow near the date line indicates northward movement of lower circumpolar water to the hess rise whence it turns westward and north west of the emperor seamounts properties east of this seamount chain are very uniform the deep and abyssal waters of the isolated aleutian basin differ substantially from those in the adjacent pacific by being warmer 0 1 c less saline 0 01 poorer in oxygen 50 mol kg 1 and much richer in silicate 80 mol kg 1 an isolated basin within the wake necker ridge also shows some unusual bottom water characteristics below sill depth

effects of mesoscale eddies on the flow of the alaskan stream 1 using a high resolution pan arctic ice ocean model forced with realistic atmospheric data we examine the mean transport and temporal and spatial variability within the alaskan stream model results are analyzed and compared with observations including satellite altimetry and ctd measurements the mean net transport of the alaskan stream is found to be between 34 and 44 sv intensifying downstream mesoscale eddies are found to periodically move along the path of the alaskan stream and alter the mean position of the typically westward flowing current however the strength of the current is not reduced as an anticyclonic eddy passes a point along the path instead there appears to be an offshore or southward shift in the current velocity core stationary measurement instruments may not be able to detect this shift in position over the slope if their southernmost location does not coincide with the current shift due to an eddy this may result in recording of a weakened or sometimes reversed flow finally we examine and demonstrate that modeled eddies within the alaskan stream have dominant effect on northward transport and variability through the eastern and central aleutian island passes

water column iron dynamics in the subarctic north pacific ocean and the bering sea 1 we measured water column iron concentrations from west to east along 47 n in the subarctic north pacific and in the bering sea in the north pacific dissolved fe d fe showed surface depletion mid depth maxima at 1000 1500 m west 1 3 1 6 nm east 0 9 1 1 nm and a gradual decrease with depth below 3500 4000 m depth west 1 1 1 4 nm east 0 6 0 7 nm d fe and total soluble fe t fe in deep water showed a decreasing trend eastward the higher iron concentrations in western deep waters probably result from higher inputs of dissolved fe through atmospheric deposition or lateral transport in contrast d fe throughout the bering sea showed a consistent depth regime characterized by a rapid increase with depth to mid depths a gradual increase with depth in intermediate water to a maximum of 1 6 1 7 nm at 1500 2250 m and a gradual decrease with depth to 1 3 1 4 nm at 3700 m higher iron concentrations and deeper d fe maxima in the bering sea are likely due to higher biological productivity and greater and deeper d fe input from the decomposition of sinking particulate organic matter in deep water we suggest that the higher concentrations and deeper input of d fe as well as po4 and humic type fluorescent dissolved organic matter in the bering sea probably results from the longer time for the accumulation of decomposition products resulting from iron supply from the organic rich downslope sediment along the steep continental slopes and slow replacement of the deep water in the bering sea basin

impacts of pre vs postcolonial land use on floodplain sedimentation in temperate north america abstract this paper evaluates the relative importance of anthropogeomorphic sedimentation on floodplains in the mid latitudes of north america before and after the arrival of euroamericans geohistorical and geoarchaeological theories have emerged that have conflicts concerning the relative effectiveness of pre and postcolonial anthropogeomorphic change in north america many geoarchaeologists paleoecologists historians and cultural geographers have concluded that intensive precolonial land use resulted in substantially humanized landscapes prior to the arrival of colonists this presents a geomorphic paradox to fluvial geomorphologists and river restorationists who interpret buried floodplain soils as evidence of landscape stability evidence for these theories is reviewed from a geomorphic perspective while making distinctions between ecological and geomorphic change and recognizing spatial and temporal variability in some locations mid millennial land use generated erosion and floodplain sedimentation subsequent indigenous population declines and reductions in land use intensity may have been followed by precolonial geomorphic stability and pedogenesis an abandoned landscape hypothesis that floodplain soils developed on precolonial anthropogenic alluvium and were subsequently buried should be considered where indigenous populations and land use activities were high variability is also noted in postcolonial floodplain sedimentation many stratigraphic studies show that rates of sedimentation increased greatly after colonization in response to land clearance for agriculture timbering and mining an inventory of studies that document postcolonial floodplain sediment shows strong spatial patterns most studies of postcolonial sedimentation cluster in the eastern usa from the mid atlantic southward and in the mississippi valley from wisconsin to mississippi but many occurrences of mining sediment are scattered throughout the west few of the studies reviewed in the west document anthropogenic floodplain sediment from agriculture or logging although more thorough regional inventories could change that vast areas of temperate north america do not have historical deposits that are well represented in the scientific literature so assumptions that legacy sediment on floodplains is ubiquitous are ill founded spatial and temporal variations in pre and postcolonial floodplain sedimentation are complex and more research is needed to fill in the knowledge gaps

the deglacial history of surface and intermediate water of the bering sea the lithology of deglacial sediments from the bering sea includes intervals of laminated or dysaerobic sediments these intervals are contemporaneous with the occurrence of laminated sediments from the california margin and gulf of california which suggests widespread low oxygen conditions at intermediate depths in the north pacific ocean the cause could be reduced intermediate water ventilation increased organic carbon flux or a combination of the two we infer abrupt decreases of planktonic foraminifer d 18 o at 14 400 and 11 650 yr bp which may be a combination of both freshening and warming on the shirshov ridge the abundance of sea ice diatoms of the genus nitzschia reach local maxima twice during the deglaciation the latter of which may be an expression of the younger dryas these findings expand the extent of the expression of deglacial millennial scale climate events to include the northernmost pacific r 2005 elsevier ltd all rights reserved

temperature inversions in the subarctic north pacific abstract hydrographic data from the world ocean database 2001 and argo profiling floats were analyzed to study temperature inversions in the subarctic north pacific ocean the frequency distribution of temperature inversions f t inv at a resolution of 1 latitude 3 longitude was calculated temperature inversions seldom occurred around 50 n in the eastern subarctic north pacific but were more common in the northern gulf of alaska and the southeastern subarctic north pacific 42 48 n 140 170 w large temperature inversions occurred throughout the year in the western and central subarctic north pacific north of 42 n and west of 180 except near the aleutian and kuril islands near those islands f t inv was characterized by pronounced seasonal variations forced by surface heating cooling and strong tidal mixing

a numerical study of the circulation of the bering sea basin and exchange with the north pacific ocean abstract a limited area primitive equation three layer hydrodynamic model with realistic coastlines and bathymetry and resolution is used to investigate the circulation of the bering sea basin and the adjacent north pacific ocean the westward flowing alaskan stream to the south of the aleutian island chain is specified as a boundary condition at inflow and outflow ports with a constant throughput of 15 sv sv 1 106 m3 s 1 atmospheric forcing is based an the hellerman and rosenstein monthly climatological wind field the model is spun up over 50 years and the statistics of the final decade are described the general features of the model circulation as discussed below are consistent with available hydrographic and buoy drift observations the model alaskan stream separates from the aleutian island chain near 175 beyond this point there is strong interannual variability associated with meandering and occasional eddy shedding along the northern arm of the western subarctic gyre there is a gen

toward reconciliation of late ordovician 440 ma glaciation with very high co2 levels although phanerozoic glaciations usually coincided with times of estimated low atmospheric co2 the late ordovician 440 ma glaciation is a significant exception co2 levels during that time may have been as much as 10 times greater than present in an earlier paper we suggested that the unique geographic configuration of gondwanaland may explain such a response as the edge of the supercontinent was essentially tangent to the south pole and the moderating effect of the nearby ocean may have suppressed the magnitude of summer warming on the landmass thereby allowing glacial inception one limitation to the earlier study was that it used a linear energy balance model ebm in this paper we further test the above hypothesis in a suite of experiments with a nonlinear ebm that allows for snow albedo feedback we also utilize updated estimates for co2 levels decreases in solar luminosity and variations in orbital forcing baseline experiments with no changes in luminosity or co2 resulted in an ice covered area of 6 3 106 km2 53 of the estimated area covered by the ordovician ice sheet additional experiments for different combinations of orbital forcing 7x 13x co2 and 3 5 5 0 luminosity yielded 0 35 of the estimated ice area in the late ordovician a crude estimate of possible topographic influences increased these numbers to7 47 of total estimated ice area additional factors related to ice sheet growth should increase these values somewhat these results provide additional support for the high co2 glaciation explanation with the caveat that even the partial success occurs only when parameters are at the extreme end of their permissible range the estimated duration of ordovician glaciation is also consistent with the migration of gondwanaland across the south pole with a centrally located pole yielding ice free conditions in the summer thus identical levels of external forcing yield either glaciated or ice free conditions with the solution dependent on location of the landmass although more work is required on this topic our experiments suggest that there may be a relatively parsimonious explanation for this perplexing paleoclimate paradox the results lend further support to the proposition that paleogeography significantly modifies the role of co2 in the long term evolution of climate

the contribution of alaskan siberian and canadian coastal polynyas to the cold halocline layer of the arctic ocean numerous arctic ocean circulation and geochemical studies suggest that ice growth in polynyas over the alaskan siberian and canadian continental shelves is a source of cold saline water which contributes to the maintenance of the arctic ocean halocline the purpose of this study is to estimate for the 1978 1987 winters the contributions of arctic coastal polynyas to the cold halocline layer of the arctic ocean the study uses a combination of satellite oceanographic and weather data to calculate the brine fluxes from the polynyas then an oceanic box model is used to calculate their contributions to the cold halocline layer of the arctic ocean this study complements and corrects a previous study of dense water production by coastal polynyas in the barents kara and laptev seas recurrent polynyas form on the canadian and alaskan coasts from banks island to the bering strait and on the siberian coast from the bering strait to the new siberian islands in the bering sea polynyas form in norton sound south and west of st lawrence island and in the gulf of anadyr two regions that account for almost 50 of the total dense water production are the siberian coastal polynyas in the adjacent regions of the gulf of anadyr and anadyr strait and the alaskan coastal polynyas which occur along the coast from cape lisburne to point barrow for all of the western arctic coastal regions examined the mean annual total brine flux is 0 5 0 2 sv combination of this flux with the contribution from the barents kara and laptev seas which is recalculated from data in the earlier study shows that over the entire arctic coastal polynyas generate about 0 7 1 2 sv of dense water this compares well with the theoretical estimates of 1 1 5 sv because an unknown fraction of the barents kara and laptev brine flux must go to the eurasian basin deep water the coastal polynyas alone cannot renew the halocline layer other potential brine generation mechanisms include overall freezing on the shelves and the response of the ice to infrequent violent storms for example during february 1982 an intense storm generated a large region of low ice concentration in the eastern chukchi sea over barrow canyon the refreezing of the region was followed by the flow of a dense plume down barrow canyon although the ocean dynamical response to this refreezing needs to be established the possible response of a barrow canyon flow to this refreezing event suggests that the overall refreezing in response to infrequent violent storms may be a potential source of the additional brine needed to maintain the arctic ocean halocline

altimeter observations of the bering slope current eddy field topex altimeter data is analyzed to describe the mesoscale eddy field associated with the bering slope current in the central bering sea the observed eddy field is well defined seasonally modulated and interannually variable the most energetic mesoscale eddy activity typically occurs during the spring and summer months and is characterized by a peak along isobath wavelength of 212 km and a representative wave period of 4 months spatial variability of annual period phase indicates that the axis of bering slope current exhibits seasonal offshore migration

use of mining contaminated sediment tracers to investigate the timing and rates of historical flood plain sedimentation abstract changes in land use practices following european settlement in the 1830s produced accelerated sedimentation on virtually all valley floors in the blue river watershed wisconsin the contamination of sediments by pb and zn mining allowed us to calculate cross valley rates of flood plain sedimentation for three time periods the pre mining period 1830 1900 the mining period 1900 1920 and the post mining period 1920 1997 most of the eight valley floors examined contained multiple presettlement surfaces significantly higher rates of sedimentation occurred on the lower flood plain surfaces while the terraces were high enough to prevent sedimentation from most floods higher rates of sedimentation on the lower surfaces eventually reduced valley floor relief and consequently lateral differences in sedimentation rates tributaries and larger valleys downstream exhibited differences in the timing and rates of historical flood plain sedimentation while rates of sedimentation were high during the pre mining period in tributary valleys the lower valleys were receiving little or no pre mining alluvium little pre mining alluvium was found in mid basin reaches suggesting that most of the pre mining sedimentation was limited to headwater locations during the mining period lateral channel migration and the development of meander belts increased the conveyance capacity of tributary and mid basin channels which decreased overbank flooding and produced lower rates of sedimentation during the post mining period the meander belt channels also had an effect on the lower portion of the watershed by increasing flood magnitudes and the transport of sediment downstream thereby shifting the locus of sedimentation from the tributaries to the larger lower valleys sedimentation rates in the largest most downstream site were an order of magnitude higher during the post mining period than any of the sites upstream

modern distribution of dinocysts from the north pacific ocean 37 64 n 144 e 148 w in relation to hydrographic conditions sea ice and productivity abstract palynological analyses were performed on 53 surface sediment samples from the north pacific ocean including the bering and okhotsk seas 37 64 n 144 e 148 w in order to document the relationships between the dinocyst distribution and sea surface conditions temperatures salinities primary productivity and sea ice cover samples are characterized by concentrations ranging from 18 to 143 816 cysts cm3 and the occurrence of 32 species a canonical correspondence analysis cca was carried out to determine the relationship between environmental variables and the distribution of dinocyst taxa the first and second axes represent respectively 47 and 17 8 of the canonical variance axis 1 is positively correlated with all parameters except to the sea ice and primary productivity in august which are on the negative side results indicate that the composition of dinocyst assemblages is mostly controlled by temperature and that all environmental variables are correlated together the cca distinguishes 3 groups of dinocysts the heterotrophic taxa the genera impagidinium and spiniferites as well as the cyst of pentapharsodinium dalei and operculodinium centrocarpum five assemblage zones can be distinguished 1 the okhotsk sea zone which is associated to temperate and eutrophic conditions seasonal upwellings and amur river discharges it is characterized by the dominance of o centrocarpum brigantedinium spp and islandinium minutum 2 the western subarctic gyre zone with subpolar and mesotrophic conditions due to the kamchatka current and alaska stream inflows assemblages are dominated by nematosphaeropsis labyrinthus pyxidinopsis reticulata and brigantedinium spp 3 the bering sea zone depicting a subpolar environment influenced by seasonal upwellings and inputs from the anadyr and yukon rivers it is characterized by the dominance of i minutum and brigantedinium spp 4 the alaska gyre zone with temperate conditions and nutrient enriched surface waters which is dominated by n labyrinthus and brigantedinium spp and 5 the kuroshio extension north pacific subarctic current zone characterized by a subtropical and oligotrophic environment which is dominated by o centrocarpum n labyrinthus and warm taxa of the genus impagidinium transfer functions were tested using the modern analog technique mat on the north pacific ocean 359 sites and the entire northern hemisphere databases 1419 sites results confirm that the updated northern hemisphere database is suitable for further paleoenvironmental reconstructions and the best results are obtained for temperatures with an accuracy of 1 7 c

thresholds and the spatial variability of flood power during extreme floods abstract analysis of the effects of extreme events on overall landscape form has shifted geomorphic attention away from a focus on the magnitude and frequency relationship of discharge to a focus on flood power this paper analyzes the variation in flood power both at a station and downstream in a basin of differing lithologies and discusses the geologic and geomorphic controls on flood power design floods ranging from the 2 year discharge tothe 500 year discharge are routed trough a drainage basin and channel boundary shear stress and unit stream power are calculated using hec 2 along 21 cross valley transects because of the strong lithologic control on valley width and channel slope an irregular downstream pattern of flood power emerges which reflects primarily the pattern in valley width narrow valleys correspond to a greater percent of channel conveyance during large magnitude floods and increasing rates of depth increases thus maximizing flood power in these zones the opposite occurs in anomalously wide valleys where flood power is minimized a downstream spatial pattern emerges reflecting both local and general controls for a given probability event flood power varies at least threefold within the basin with a maximum occuring in a specific downstream section holding flood power constant produces an extremely wide range in flow probabilities in order to establish a link between critical flood power magnitude and flow frequency minimum flood powers are developed from an analysis of previous work on catastrophic flooding for humid alluvial channels these minimum thresholds tentatively correspond to 100 n m2 or 300 w m2 for shear stress and unit stream power respectively discharges required to attain these critical flood powers vary from events roughly twice the 100 year flood to a maximum of roughly 18 times the discharge of the 100 year flood

observations of topographic planetary waves in the bering slope current using the geosat altimeter topographic planetary waves associated with the downstream leg of the bering slope current are observed in measurements of sea surface height anomalies acquired by the geosat altimeter during 1987 and 1988 the waves are most prominent from may to august 1987 during which time the estimated wave period and wavelength are about 72 days and 103 km respectively the direction of propagation is roughly north northeast

legacy sediment lead and zinc storage in channel and floodplain deposits of the big river old lead belt mining district missouri usa abstract the old lead belt of southeastern missouri was one of the leading producers of pb ore for more than a century 1869 1972 large quantities of contaminated mine waste have been and continue to be supplied to local streams this study assessed the magnitude and spatial distribution of mining contaminated legacy sediment stored in channel and floodplain deposits of the big river in the ozark highlands of southeastern missouri although metal concentrations decline downstream from the mine sources the channel and floodplain sediments are contaminated above background levels with pb and zn along its entire 171 km length below the mine sources mean concentrations in floodplain cores 2000 mg kg 1 for pb and 1000 mg kg 1 for zn extend 40 50 km downstream from the mining area in association with the supply of fine tailings particles that were easily dispersed downstream in the suspended load mean concentrations in channel bed and bar sediments ranging from 1400 to 1700 mg kg 1 for pb extend 30 km below the mines while zn concentrations of 1000 3000 mg kg 1 extend 20 km downstream coarse dolomite fragments in the 2 16 mm channel sediment fraction provide significant storage of pb and zn representing 13 20 of the bulk sediment storage mass in the channel and can contain concentrations of 4000 mg kg 1 for pb and 1000 mg kg 1 for zn these coarse tailings have been transported a maximum distance of only about 30 km from the source over a period of 120 years for an average of about 250 m y about 37 of the pb and 9 of the zn that was originally released to the watershed in tailings wastes is still stored in the big river a total of 157 million mg of contaminated sediment is stored along the big river with 92 of it located in floodplain deposits that are typically contaminated to depths of 1 5 3 5 m these contaminated sediments store a total of 188 549 mg of pb and 34 299 mg of zn of which 98 of the pb and 95 of the zn are stored in floodplain deposits most of the metal mass in channel deposits is stored near the mines with 72 of the pb and 78 of the zn occurring in the 25 km of channel proximal to the mine source although environmental assessments of streams contaminated by mines often focus on evaluating metal concentrations in the geochemically active fine sediment fractions about 60 of the pb stored in channels is associated with coarse dolomite tailings fragments deposited in channels within 25 km of the mines the magnitude and basinwide distribution of pb and zn storage in legacy floodplain sediments ensures that remobilization by bank erosion will be a continuing problem for water quality far into the future

aleutian basin of the bering sea thermohaline oxygen nutrient and current structure in july 1993 an overview is given of the surface to bottom thermohaline oxygen nutrient and baroclinic flow structures in the aleutian basin of the bering sea and the adjacent north pacific based on high resolution field measurements in july 1993 a basic four layer vertical structure is observed in the upper 1500 m the 30 m top layer is warm low in salinity and nutrients and high in oxygen beneath it a 100 to 150 m thick temperature minimum layer is found believed to be a remnant of winter convection this is followed by a 300 m thick warm layer in which the main halocline oxycline and nutricline are located below it lies a layer of minimum oxygens and maximum nitrates and phosphates centered at a depth of 900 m in the bering sea but rising to 400 m south of the aleutians this basic structure is disrupted in the vicinity of amchitka pass due to strong tidal mixing the deep and abyssal waters of the aleutian basin differ substantially from those at comparable depth in the adjacent pacific by being warmer 0 1 c less saline 0 01 less dense 0 01 kg m3 poorer in oxygen 50 mol kg and richer in silicates 80 mol kg nitrates 1 0 mol kg and phosphates 0 3 mol kg the highest silicate concentrations 240 mol kg occur at the foot of the bering shelf unusual hydrographic conditions exist in an isolated tidal mixing basin in amchitka pass where the bottom mixed layer is 600 m thick 0 7 c warmer 0 14 less saline and 21 mol kg less oxygenated than at comparable depths outside baroclinic currents indicate strong deep jetlike flows on both sides of the aleutian ridge weak shallow eddies in the middle of the aleutian basin and somehat enhanced flows near the bering shelf edge the alaska stream in july 1993 was 100 km wide had a double core with a top speed of 0 54 m s and had a westward volume transport of 38 sv with 14 sv below 1000 dbar the north aleutian current had a speed of 0 2 m s and an eastward transport of 10 sv with 4 sv below 1000 dbar off the bering slope both eastward and westward flows were observed with volume transports near 7 sv

deep currents in the central subarctic pacific ocean abstract sections of closely spaced ctd stations along longs 165 w 175 w and 175 e in combination with 14 month current records from the central longitude define two deep nearly zonal currants with speed increasing upward in the subarctic pacific one flows eastward above the aleutian rise and aleutian trench and appears to be a concentration of geostrophic flow forced by the bottom topography the other flows westward along the aleutian island arc and is the northern boundary current predicted by deep circulation theory both currents reach to the sea surface the boundary current being simply the deep part of the alaskan stream the current records were too few to permit better than rough estimates of volume transports but to the extent that they could be combined with thermal wind calculations they suggest at 175 w 1 a transport of 28 106 m3 s 1 for the alaskan stream of whch 5 106 m3 s 1 was found below 1500 m and 2 a transport of around 20 1o6 m3 s 1 for the eastward jet of wh

circulation in the bering sea basin observed by satellite tracked drifters 1986 1993 abstract from 1986 through april 1993 86 satellite tracked buoys were deployed in the north pacific and bering sea most of the buoys were drogued at 40 m a composite current pattern is derived using these data the two principal currents the alaskan stream and kamchatka current are clearly evident eddy kinetic mean kinetic energy ratios are low in the stream and along the western bering sea basin an eastward flowing current occurred along the north flank of the aleutian islands this flow was modified by inflow at the passes westward flow occurred north of 56 n its source was the bering slope current the kamchatka current originated near 175 e along the russian coast numerous eddies and meanders were observed in the kamchatka current eddies were also present on the eastern side of the basin

paleonutrient and productivity records from the subarctic north pacific for pleistocene glacial terminations i to v our study addresses fundamental questions of the mode and timing of orbital and millennial scale changes in the meridional overturning circulation moc of the subarctic north pacific particular concerns are the vertical mixing the present and past abundance of nutrients in surface waters despite strong stratification and the north pacific north atlantic seesaw of oscillations in sea surface temperature sst we do this by generating and interpreting multiple records for glacial terminations i v down two long piston cores one each from the western and eastern subarctic pacific chlorins and biogenic opal are proxies for surface water productivity delta 13 c of epibenthic foraminifera is a record of deepwater ventilation and the delta 13 c of n pachyderma sin is a tracer of nutrients in subsurface waters that extend up to the sea surface during times of vertical mixing the degree of mixing is traced by pairing sst and delta 18 o records of planktic surface and subsurface pycnocline dwellers tight age control is deduced from a suite of age calibrated 14 c plateau boundaries for termination i and benthic delta 18 o and geomagnetic events for the last 800 ka carbon 14 paleoreservoir ages record the ages of surface and deep waters to uncover short term changes in moc over termination i we have defined a standard sequence of short term productivity events for termination i also evident during terminations ii to v and subsequent interglacials over the last 450 ka the peak glacial regime of stable stratification and low productivity terminated together with the end of ice rafting and melting near 17 ka similar to 2000 years after the onset of termination i pulses of vertical mixing and incursion of warm surface waters from the subtropics followed convected young water masses finally penetrated down to 3600 m water depth at 17 0 to less than 14 5 ka significantly improving bottom water ventilation through the late deglacial and earliest interglacial mixing with upwelled nutrients from the pycnocline induced short term maxima in algal production of chlorins and biogenic opal near 17 15 and 15 12 ka respectively deglacial meltwater incursions in the aleutian current and silica input from north american rivers also promoted east pacific productivity after 15 5 ka productivity decreased during the late deglacial and early interglacial coeval with an exceptional peak in caco 3 preservation caused by both low organic flux and well ventilated deepwater subsequently low salinity and cool surface waters and in turn stratification were gradually restored a second opal dominated productivity maximum marked the ends of interglacials the deglacial pulses of vertical mixing around 17 11 ka imply an important contribution of the north pacific to the coeval release of oceanic co 2 into the atmosphere and support the east west seesaw model of climate change

diatoms as paleoenvironmental proxies for seasonal productivity sea ice and surface circulation in the bering sea during the late quaternary abstract diatom assemblages in suspended particulate matter spm surface sediments and piston core samples in the southern bering sea and the western subarctic pacific were examined the distribution of diatom assemblages in the southern bering sea shows not only differences in species composition between the spm and surface sediment samples but also preferential dissolution of different species in the upper water column or surface sediments furthermore we present the downcore profiles of selected diatom taxa for four piston cores to indicate changes in paleoceanographic conditions e g seasonal productivity sea ice and surface water circulation of the glacial and deglaciation periods during the late quaternary in particular we propose five models for the annual cycling of the water masses in the western subarctic pacific and the southern bering sea during the late quaternary significant regional differences in diatom accumulation rates and taxonomic composition between the southern bering sea and the western subarctic pacific reflect spatial shifts in water masses caused by the variable extent of sea ice cover and cold low salinity surface waters in these regions

recent observations of variability in the western bering sea current system data from two cruises in the western bering sea are presented and examined during spring 1990 conditions were typical and the kamchatka current had a transport of 11 sv on the other hand during fall 1990 this flow had weakened to 6 sv although a strong flow near the komandorski islands occurred various eddylike features were common during both cruises and were particularly developed in fall although some aspects of the flow patterns may be seasonal in nature the major weakening of transport probably represents an interannual change

millennial scale climate change and intermediate water circulation in the bering sea from 90 ka a high resolution record from iodp site u1340 1 millennial scale climate events in the north pacific are thought to be related to changes in the circulation of north pacific intermediate water which may have formed in the bering sea in the past to advance our understanding of the mechanisms that underlie millennial scale events bering sea sediment cores from the integrated ocean drilling program site u1340 were used to construct high resolution multiproxy climate records of the last 90 000 years sediment density records show millennial scale events resembling dansgaard oeschger events several of which are laminated interstadials were characterized by 3 5 c warming increased productivity driven by upwelling and reduced benthic oxygenation bering sea intermediate water also changed over longer timescales our records show the presence of intermediate water with lower salinity and higher oxygen content than modern beginning around 60 ka and persisting until the beginning of the deglaciation the bolling allerod was characterized by high productivity laminated sediments and strong denitrification signature our data support the idea that productivity derived changes in oxygenation at intermediate water source regions may have contributed to the intensification of the north pacific wide oxygen minima during the bolling allerod

circulation in the bering sea 1982 83 based on satellite tracked drifter observations abstract a satellite tracked drifting buoy deployed unintentionally in the bering sea in 1982 completed a circuit of that basin in about one year during its cyclonic passage around the bering sea it experienced many different flow regimes ranging from steady alongshelf motion at the shelf break to highly variable tidal flow on the shelf itself the buoy trajectory differs from previous descriptions of the deep bering sea circulation because it moved southwestward in the central bering sea rather than along the western boundary as other depictions have suggested many of the bering sea mesoscale eddies reported earlier were evident indicating that possibly these eddies are permanent features the forces which caused the buoy to move between the various flow regimes are unclear but the data suggest an annual period for the deep bering sea circulation

spatial patterns of historical overbank sedimentation and floodplain evolution blue river wisconsin abstract increased soil erosion and overbank flooding associated with land use changes following european settlement have buried pre settlement floodplain surfaces in many driftless area watersheds with as much as several meters of alluvium this paper examines the processes influencing spatial variations in the storage of post settlement vertical accretion alluvium and the impact on floodplain evolution in the blue river watershed wisconsin the cross sectional area of historical vertical accretion sediments stored on floodplains was measured at 41 cross valley transects in the 208 km2 watershed the storage of historical overbank sediments is influenced by valley width stream power and the development of meander belts post settlement alluvial storage increases with valley width and decreases with cross sectional stream power in a multivariate regression model valley width and cross sectional stream power explain 67 of the variance in the amount of post settlement alluvium the development of meander belts enlarged channels confined between alluvial terraces by accelerated lateral channel migration influences historical floodplain storage by decreasing the influence of valley width and modifying stream power characteristics for flows greater than bankfull meander belts are located in headwater and mid basin valley reaches where high stream power produces rapid lateral channel migration whereas low gradient channels in downstream valleys lack the power necessary to migrate laterally and develop meander belts meander belts influence the spatial pattern of historical sedimentation by 1 containing large magnitude floods and preventing overbank flow 2 increasing sediment transport capacities 3 initiating the erosion of previously deposited historical sediments 4 reducing the attenuation of flood peaks and 5 increasing the amount of sediment routed downstream to wide low gradient valley bottoms lacking meander belts continued high rates of lateral channel migration will eventually be damped as widening of the meander belt decreases flow depths and stream power

effects of a shelf polynya on flow and water properties in the northern bering sea we present long term 230 day measurements from three moorings in the vicinity of saint lawrence island on the northern bering sea shelf one mooring was deployed near the polynya which often exists south of the island these data confirm the existence of strong 0 15 m s 1 flow toward bering strait northwest of the island in anadyr strait and suggest that regional circulation results in a moderate 0 03 5 m s 1 mean flow eastward along the southern coast of saint lawrence island coherent variations in the regional circulation and variations in the geostrophic wind account for much of the low frequency current fluctuation south of saint lawrence island however there were 11 events when offshore northerly winds coincided with the temperature following the freezing point increasing salinity and reversal of the current this suggests that ice formation and the ensuing brine rejection affect flow in the vicinity of the polynya scaling of a simplified momentum equation indicates that the cross shelf density gradient was a possible mechanism for some of the reversals salinity data show a seasonal cycle as well as individual events of brine rejection during an average event time of 65 hours the salinity increased by 8 10 3 g kg 1 h 1 the heat flux can be estimated as 535 wm 2 these fluxes correspond to an ice production of 5 m during winter 1981 extrapolation of our results and comparison with the freshwater cycle suggest that brine rejection is an important component of the regional salt budget

zonal evolution of alaskan stream structure and transport quantified with argo data the alaskan stream as flows west southwestward along the south side of alaska and the aleutian island arc a western boundary current at the northern edge of the north pacific subpolar gyre the argo float array has improved sampling of the gulf of alaska allowing quantification of the as s zonal evolution from 140 w to 175 w geostrophic alongshore transport of the as in the upper 1000 dbar referenced to an assumed level of no motion at 1000 dbar shows little change from east to west however alongshore absolute geostrophic transports in the top 2000 dbar obtained by combining mean absolute 1000 dbar velocities from float displacements with the geostrophic velocity fields generally increase to the west we estimate full depth transports by fitting a barotropic and the first two baroclinic modes calculated from a climatology to the absolute geostrophic velocities in the upper 2000 dbar and applying the velocities from these fits from 2000 dbar to the seafloor flowing west from its formation region at 140 w 145 w the full depth as becomes stronger more barotropic and also narrower once it reaches 160 w with along shore transports increasing from 16 4 4 9 sv 1 sv 106 m3 s 1 at 140 w to 32 6 5 2 sv at 175 w mean concentrations of relatively warm salty oxygen poor and nutrient rich pacific equatorial water pew in the as decrease from 17 8 0 3 to 8 5 0 5 between 140 w and 175 w however the volume transport of pew by the as exhibits little change over the pew density range between these longitudes

abrupt changes of intermediate water properties on the northeastern slope of the bering sea during the last glacial and deglacial period 1 millennial scale variability in the behavior of north pacific intermediate water during the last glacial and deglacial period and its association with dansgaard oeschger d o cycles and heinrich events are examined based on benthic foraminiferal oxygen and carbon isotopes 18obf and 13cbf and caco3 using a sediment core recovered from the northeastern slope of the bering sea a suite of positive 18obf excursions at intermediate depths of the bering sea which seem at least in part associated with increases in the 18obf gradients between the bering and okhotsk seas suggest the bering sea as a proximate source of intermediate water during several severe stadial episodes in the last glacial and deglacial period absence of such 18obf gradients during periods of high surface productivity in the bering and okhotsk seas which we correlate to d o interstadials suggests a reduction in intermediate water production in the bering sea and subsequent introduction of nutrient rich deep waters from the north pacific into intermediate depths of the bering sea we argue that a reorganization of atmospheric circulation in the high latitude north pacific during severe cold episodes in the last glacial and deglacial period created favorable conditions for brine rejection in the northeastern bering sea the resulting salinity increase in the cold surface waters could have initiated intermediate and deep water formation that spread out to the north pacific

sea surface temperature across the subarctic north pacific and marginal seas through the past 20 000 years a paleoceanographic synthesis abstract deglacial sea surface conditions in the subarctic north pacific and marginal seas are the subject of increasing interest in paleoceanography however a cohesive picture of near surface oceanography from which to compare inter and intra regional variability through the last deglaciation is lacking we present a synthesis of sea surface temperature covering the open north pacific and its marginal seas spanning the past 20 ka using proxy records from foraminiferal calcite 18o and mg ca and coccolithophore alkenones uk 37 sea surface temperature proxies tend to be in agreement through the holocene though uk 37 records are often interpreted as warmer than adjacent 18o or mg ca records during the last glacial maximum and early deglaciation in the sea of okhotsk holocene discrepancies between 18o and uk 37 may be the result of changes in near surface stratification we find that sea surface warming occurred prior to the onset of the bolling allerod 14 7 ka and coincident with the onset of the holocene 11 7 ka in much of the north pacific and bering sea proxy records also show a cold reversal roughly synchronous with the younger dryas 12 9 11 7 ka after the onset of the holocene the influence of an intensified warm kuroshio current is evident at higher latitudes in the western pacific and an east west seesaw in sea surface temperature likely driven by changes in the strength of the north pacific gyre characterizes the open interglacial north pacific

surface nitrate utilization in the bering sea since 180 ka bp insight from sedimentary nitrogen isotopes we present high resolution records of sedimentary nitrogen 15nbulk and carbon isotope ratios 13cbulk from piston core so201 2 85kl located in the western bering sea the records reflect changes in surface nitrate utilization and terrestrial organic matter contribution in submillennial resolution that span the last 180 kyr the 15nbulk record is characterized by a minimum during the penultimate interglacial indicating low nitrate utilization 62 80 despite the relatively high export production inferred from opal concentrations along with a significant reduction in the terrestrial organic matter fraction mterr this suggests that the consumption of the nitrate pool at our site was incomplete and even more reduced than today 84 15nbulk increases from marine isotope stage mis 5 4 and culminates during the last glacial maximum which indicates that nitrate utilization in the bering sea was raised during cold intervals mis 5 4 5 2 4 and almost complete during mis 3 and 2 93 100 this is in agreement with previous hypotheses suggesting that stronger glacial stratification reduced the nutrient supply from the subeuphotic zone thereby increasing the iron to nutrient ratio and therefore the nitrate utilization in the mixed surface layer large variations in 15nbulk were also recorded from 180 to 130 ka bp mis 6 indicating a potential link to insolation and sea level forcing and its related feedbacks millennial scale oscillations were observed in 15nbulk and 13cbulk that might be related to greenland interstadials

the response of the bering sea gateway during the mid pleistocene transition abstract the mid pleistocene transition and the response of sea ice in the subarctic north pacific are examined using a diatom record from the north eastern bering sea slope iodp core u1344a high percentages of diatom sea ice species in the assemblage foster the development of groupings specific to differing ice conditions thalassiosira antarctica var borealis emerges as a key diatom species that delineates the development of thick multiannual sea ice and marks a series of advancements from 0 9 to1 2 ma after which it dominates the assemblage until 0 6 ma the decline of neodenticula seminae indicative of alaskan stream water inflow is in agreement with neighbouring core u1343e confirming the reduction of bering sea circulation after 0 9 ma we propose that during the mpt a stepped advancement of sea ice occurs in the bering sea as a response to increased moisture delivery to the high latitudes an extended period of diatom productivity between 0 75 and 0 65 ma marks major deglacial conditions towards the end of the mpt by 0 6 0 55 ma the work highlights the important role played by sea ice and supports the contention of a colder mpt in the subarctic pacific

phosphorus burial and diagenesis in the central bering sea bowers ridge iodp site u1341 perspectives on the marine p cycle abstract to reconstruct the cycling of reactive phosphorus p in the bering sea a p speciation record covering the last 4 ma was generated from sediments recovered during integrated ocean drilling program iodp expedition 323 at site u1341 bowers ridge a chemical extraction procedure distinguishing between different operationally defined p fractions provides new insight into reactive p input burial and diagenetic transformations reactive p mass accumulation rates mars are 20 110 mol cm2 ka which is comparable to other open ocean locations but orders of magnitude lower than most upwelling settings we find that authigenic carbonate fluorapatite cfa and opal bound p are the dominant p fractions at site u1341 an overall increasing contribution of cfa to total p with sediment depth is consistent with a gradual sink switching from more labile p fractions fish remains fe oxides organic matter to stable authigenic cfa however the positive correlation of cfa with al content implies that a significant portion of the supposedly reactive cfa is non reactive detrital contamination by eolian and or riverine cfa in contrast to cfa opal bound p has rarely been studied in marine sediments we find for the first time that opal bound p directly correlates with excess silica contents this p fraction was apparently available to biosiliceous phytoplankton at the time of sediment deposition and is a long term sink for reactive p in the ocean despite the likelihood for diagenetic re mobilisation of this p at depth indicated by increasing ratios of excess silica to opal bound p average reactive p mars at site u1341 increase by 25 if opal bound p is accounted for but decrease by 25 if 50 of the extracted cfa fraction based on the lowest cfa value at site u1341 is assumed to be detrital combining our results with literature data we present a qualitative perspective of terrestrial cfa and opal bound p deposition in the modern ocean riverine cfa input has mostly been reported from continental shelves and margins draining p rich lithologies while eolian cfa input is found across wide ocean regions underlying the northern hemispheric dust belt opal bound p burial is important in the southern ocean north pacific and likely in upwelling areas shifts in detrital cfa and opal bound p deposition across ocean basins likely occurred over time responding to changing weathering patterns sea level and biogenic opal deposition

seasonal and interannual variability of the bering slope current abstract time series of sea surface height anomalies derived from satellite altimeters and absolute dynamic topography are used to examine variability in the geostrophic surface currents in the eastern bering sea the data suggest that the primary source of water to the eastern boundary currents of the bering sea is flow from the north pacific through amukta pass an aleutian pass located at 172 w the aleutian north slope current ansc is strongest and most variable in the winter months upon turning the corner to feed the bering slope current bsc the ansc bifurcates resulting in a westward flow at 54 n in addition to the northwestward flowing bsc this westward countercurrent has not been previously observed in the winter the bsc flows strongly to the northwest and is located near the shelf break during the rest of the year the mean flow is broadly northwestward but weaker and farther from the shelf break a continuous northwestward flowing current is rarely observed in the altimetry data except during winter months as it is overwhelmed by mesoscale variability the strength of the bsc in winter is correlated with the multivariate enso index and the north pacific index on interannual timescales

spatial and temporal characteristics of the wind forcing of the bering sea abstract the surface wind stress over the bering sea is estimated for the period 1946 90 from sea level pressure analyses empirical relationships between the geostrophic wind and the surface wind and a bulk aerodynamic formula the focus is on the propagation and variability of the stress and the curl of the stress as a function of frequency the stress at high frequencies 0 1 cpd is dominated by northward and eastward propagating disturbances with mean wavelengths of 2500 and 10 000 km respectively at periods of 10 100 days the mean propagation is near zero there are however significant interannual variations in the zonal propagation wind driven ocean transports estimated by the sverdrup method for the deep bering basin account for 6 sv or roughly one half of the observed transport within the western boundary current along the kamchatka peninsula a low pass filtered retaining periods greater than 18 months time series of the sverdrup transport exhibits a standard deviation of 25 of th

chlorofluorocarbon evidence for recent ventilation of the deep bering sea the pattern of the global thermohaline circulation of today s oceans is controlled by deep water formation at the northern and southern limits of the atlantic the apparent lack of deep water formation in the north pacific on the other hand suggests that this ocean plays only a minor role in the global circulation but it is unclear whether this was also the case during periods of glaciation there is conflicting evidence in the sedimentary record for the existence of a deep water source in the north pacific during the last glacial maximum1 4 here we report the detection of anthropogenic chlorofluorocarbons in the bottom waters of the aleutian basin in the eastern bering sea which suggests that a small amount of bottom water has formed in this region during the past 40 years although the small volumes of water involved are unlikely to play a significant role in determining present day global circulation patterns the results lend credence to the possibility that this sea was an important source of deep water for the northwestern pacific ocean during the last glacial maximum

some controls on flow and salinity in bering strait 1 during 1993 1994 steric forcing of flow through bering strait represented a northward sea level drop of 0 7 m from the bering sea basin to the adjacent deep arctic ocean of which 2 3 was due to the salinity difference between the basins seasonal variability of steric forcing appears small 0 05 m in contrast to large seasonal wind effects interannual changes in steric forcing may exceed 20 however and warm inflow from the north atlantic accumulation of freshwater in the southwest canada basin and temperature and salinity changes in the upper bering sea have all contributed to recent changes the mean salinity balance in bering strait is primarily maintained by large runoff to the bering shelf dilute coastal inflow from the gulf of alaska and on shelf movement of saline and nutrient rich oceanic waters from the bering sea basin in bering strait therefore both the throughflow and its salinity are affected by remote events