the pribilof islands temperature salinity and nitrate during summer 2004 abstract the pribilofs comprised of st paul and st george islands and two smaller islands are a highly productive area on the western edge of the eastern bering sea shelf proximity to both the slope and more shallow shelf waters and the confluence of multiple physical domains differentiates conditions in this region from those in other areas on this shelf this is a unique domain in the bering sea that we refer to as the pribilof domain hydrographic and biological data were collected during a 2004 summer research cruise in this region the study undertook testing the hypothesis that on shelf intrusion of slope waters supplies nutrients to this multi domain area thereby seasonally influencing new primary production and consequently the entire marine ecosystem the pribilof domain is characterized by enhanced mixing particularly the area between st paul and st george islands organized anti cyclonic flow around st paul island around st george island and around the island group strong tidal currents and is a location where nutrient rich water from the bottom layer of the middle shelf and deeper water from the slope are vertically mixed to sustain production throughout the summer

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

influences of sea ice on the eastern bering sea ncar cesm simulations and comparison with observations abstract we examine the influences of sea ice on the eastern bering sea ebs regional oceanography on seasonal and inter annual time scales using the national center for atmospheric research community earth system model ncar cesm simulations comparing the modeling results with satellite and in situ observations when possible while the modeled mean seasonal cycle of ice cover in the ebs middle shelf is generally within the uncertainty range of satellite observations in the northern domain north of 59 n the simulation reaches its annual maximum in april instead of in march as observed by satellite remote sensing modeled ice reduction in late spring in the region is also slower than observations despite this bias the simulation captures the observed seasonal transit of freshwater from the north to the south via ice advection en route the sea ice melts cooling and freshening the local water column on inter annual time scales modeling results suggest that extensive ice cover persisting into spring in the central ebs leads to cold anomalies in the bottom water especially on the middle and inner shelves of the southern domain the corresponding salinity anomalies are positive in the northern coastal domain and weak but negative in the southern middle shelf the associated 10 m ocean current anomalies are southward on the shelf and directed offshore in the slope region comparing years 1961 2005 versus years 2005 2050 the probability distribution function of ice cover on the ebs middle shelf shifts northward by 2 latitude

enhancement of coccolithophorid blooms in the bering sea by recent environmental changes 1 since 1997 ocean color satellite images have revealed large scale blooms of the coccolithophorid emiliania huxleyi in the eastern bering sea the blooms are often sustained over several months and have caused ecosystem changes in the arctic ocean as well as in the bering sea we examined continental shelf sediment profiles of alkenone a biomarker for e huxleyi covering the past 70 years the alkenone records suggest that large e huxleyi blooms are a novel feature in the bering sea as they have occurred only since the late 1970s recent changes in alkenone content were closely related to the 1976 77 climatic regime shift in the north pacific implying that warming and freshening of bering sea waters promoted e huxleyi blooms the production rate of diatoms total valves in sediment samples the dominant primary producers in the bering sea also increased during the past several decades however the ratio of alkenone content to total diatom valves in the sediments increased as e huxleyi production increased suggesting that the increase in the e huxleyi production rate frequently exceeded the increase in the diatom production rate overall our results indicate a possible subarctic region ecosystem shift driven by climate change

sea ice response to atmospheric and oceanic forcing in the bering sea abstract a coupled sea ice ocean model is developed to quantify the sea ice response to changes in atmospheric and oceanic forcing in the bering sea over the period 1970 2008 the model captures much of the observed spatiotemporal variability of sea ice and sea surface temperature sst and the basic features of the upper ocean circulation in the bering sea model results suggest that tides affect the spatial redistribution of ice mass by up to 0 1 m or 15 in the central eastern bering sea by modifying ice motion and deformation and ocean flows the considerable interannual variability in the pattern and strength of winter northeasterly winds leads to southwestward ice mass advection during january may ranging from 0 9 1012 m3 in 1996 to 1 8 1012 m3 in 1976 and averaging 1 4 1012 m3 which is almost twice the january may mean total ice volume in the bering sea the large scale southward ice mass advection is constrained by warm surface waters in the south that melt 1 5 1012 m3 of ice in mainly t

sea ice derived dissolved iron and its potential influence on the spring algal bloom in the bering sea 1 observational and modeling studies in the bering sea indicate that changes in the seasonal ice cover and time of ice retreat influence open water productivity in particular the timing of the spring bloom and its phytoplankton community composition are affected dissolved iron dfe data in the water column and ice cores collected during the 2007 bering ecosystem study best cruise indicate that the melting ice provided substantial dfe to the water column the additional dfe input from melting sea ice could be biologically important along the outer shelf and shelf break where in ice free areas insufficient dfe 20 m variability in sea ice dynamics are likely to result in a varying supply of dfe to the outer shelf and shelf break in early spring and to contribute to the observed changes in the timing and community composition of the spring phytoplankton bloom

snow and firn permeability at siple dome antarctica the nature of air snow exchange processes depends upon both the physical characteristics of the snow and forcing from the atmosphere an understanding of snow air transport processes and models of these processes are important for interpreting ice cores and for predicting remotely sensed snow surface characteristics accurate modeling requires knowledge of the physical characteristics of the snow and firn in this paper measurements of snow and firn permeability from the surface down to 12 m depth at siple dome antarctica are presented the permeability varies greatly as a function of layer and depth generally increasing to approximately 3 m and generally decreasing below that the maximum permeability 280 10 10 1 0 m2 occurs at approximately 3 m depth the lowest permeability in the top 12 m of snow and firn 10 10 10w m2 was measured in the surface wind pack the measurements show that layering and microstructure have large effects on permeability a mathematical expression for the overall variation of permeability with depth is presented it is shown that snow density is a poor indicator of permeability quantitative microscopy may be helpful in relating observed snow characteristics to permeability and useful in modeling firnification and chemical species transport

a pliocene to recent history of the bering sea at site u1340a iodp expedition 323 fossil diatoms are the principal component of bering sea sediments and reflect the paleoceanographic history of the region diatom accumulation rates and relative abundances at international ocean discovery program iodp site u1340a are presented overall the total diatom productivity record from 4 9 ma to the present day reveals a fourfold reduction at circa 4 2 ma from 45 107 down to 11 107 valves g wet sediment signifying a major shift in the upwelling and or nutrient regime coinciding with the end of the late miocene early pliocene bloom identified in the eastern equatorial pacific and california margin further abrupt shifts in the diatom assemblage occur at 1 2 78 2 55 ma 2 2 0 1 8 ma and 3 1 0 0 88 ma 1 at 2 78 2 55 ma the appearance of sea ice related species marks the regional cooling associated with the expansion of northern hemisphere ice sheets subsequent development of stratified nutrient depleted waters and increased influence of western basin water masses most likely due to the suppressed inflow of the alaskan stream 2 rapid cooling between 2 0 and 1 8 ma indicates increased sea ice duration and or frequency this coupled with low sea level stands caused prolonged closure of the aleutian passes coupled with further increased western basin water inflow 3 the shift to 100 ka glacial interglacial cycles at the middle pleistocene transition 1 0 0 88 ma marked an increase in upwelling related species indicating enhanced surface water mixing these records confirm that the development and changing dynamics of sea ice in the bering sea played a major role in sub arctic ocean circulation and is an integral component of global climate change

theory and numerical modeling of electrical self potential signatures of unsaturated flow in melting snow 1 we have developed a new theory and numerical model of electrical self potential sp signals associated with unsaturated flow in melting snow the model is applicable to continuous natural melt as well as transient flow phenomena such as meltwater pulses and is tested using laboratory column experiments sp signals fundamentally depend on the temporal evolution of snow porosity and meltwater flux electrical conductivity ec and ph we infer a reversal of the sign of the zeta potential a fundamental electrical property of grain surfaces in porous media consistent with well known elution sequences of ions that cause progressive increases and decreases in meltwater ph and ec respectively injection of fully melted snow samples containing the entire natural range of ions into melting snow columns caused additional temporary reversals of the sign of the zeta potential widely used empirical relationships between effective saturation meltwater fraction ec and ph as well as snow porosity grain size and permeability are found to be robust for modeling purposes thus nonintrusive sp measurements can serve as proxies for snow meltwater fluxes and the temporal evolution of fundamental snow textural hydraulic or water quality parameters adaptation of automated multisensor sp acquisition technology from other environmental applications thus promises to bridge the widely acknowledged gap in spatial scales between satellite remote sensing and point measurements of snow properties sp measurements and modeling may therefore contribute to solving a wide range of problems related to the assessment of water resource availability avalanche or flood risk or the amplification of climatic forcing of ice shelf ice sheet or glacier dynamics

late winter water column and sea ice conditions in the northern bering sea 1 seasonal sea ice concentration and thickness were evaluated on a weekly basis during two years with contrasting ice coverage 1998 1999 and 2000 2001 using data provided by the u s national ice center ice in the bering sea during 1998 1999 was extensive and thick but by contrast in 2000 2001 winter sea ice formed late with thin ice and ice melt proceeded earlier during spring the presence and timing of a winter polynya an area of relatively open water or thin ice surrounded by heavier ice located south of st lawrence island also varied between these two winters shipboard measurements south of st lawrence island during two late winter early spring cruises in 1999 and 2001 showed that some brine injected water was present resulting in localized areas of bottom water with salinities approaching or exceeding 33 psu the mean salinity of bottom water was significantly higher in 2001 32 6 psu than in 1999 32 3 psu these varying degrees of brine injection associated with large differences in ice conditions heavy in 1998 1999 light in 2000 2001 influenced bottom water salinity and density but there were indications that variation in water mass structure also can explain differences in salinity observed between the two winters the mean 18oh2o values of bottom seawater were significantly higher in 2001 0 78 0 16 sd than in 1999 0 98 0 20 sd consistent with a more saline nutrient rich water being present in 2001 consistent with these indications inorganic nutrients nitrate phosphate and silicate in bottom water were significantly higher in 2001 than in 1999 although it is seemingly paradoxical that salinities were higher in 2001 light ice than in 1999 heavy ice when brine injection might have been more prevalent the sampling period was approximately 1 month earlier in 2001 when ice formation may have been more active in addition 18oh2o values indicate a higher proportion of anadyr water with higher salinity and nutrients in 2001 despite these differences in both ice conditions and water mass nutrient chemistry water column chlorophyll was uniformly low in both years this indicates that changes in bering sea ice regimes during the late winter months such as may occur under various climate change scenarios will not necessarily lead to any higher productivity or an earlier onset of seasonal biological production despite relatively high inorganic nutrient concentrations in both years a well mixed water column was observed with low water column chlorophyll a chl a concentrations these observations suggest that there was little primary production during either cruise in spite of the relatively open water and high water column nutrient concentrations during 2001 strong southerly winds during winter likely impeded ice formation vertically mixed the water column and prevented early spring open water primary production

factors influencing physical structure and lower trophic levels of the eastern bering sea shelf in 2005 sea ice tides and winds abstract in spring and fall 2005 cross and along shelf transects were sampled to evaluate the influence of physical forcing including sea ice tides and winds on the lower trophic levels of the bering sea ecosystem the hydrography nutrients chlorophyll and zooplankton abundance and species composition were all affected by the presence or absence of sea ice on a north south transect along the 70 m isobath in may shelf waters between 59 n and 62 n were cold and relatively fresh and benthic invertebrate larvae and chaetognaths were a significant fraction of the zooplankton community while to the south the water was warmer saltier and the zooplankton community was dominated by copepods the position of the transition between ice affected and ice free portions of the shelf was consistent among temperature salinity nutrients and oxygen this transition in the hydrographic variables persisted through the summer but it shifted 150 km northward as the season progressed while a transition also occurred in zooplankton species composition it was farther north than the physical chemical transition and did not persist through the summer mooring data demonstrated that the change in the position of the transition in physical and chemical properties was due to northward or eastward advection of water onto and across the shelf from south to north along the 70 m isobath tidal energy decreased resulting in a less sharply stratified water column on the northern portion of the middle shelf as opposed to a well defined two layered system in the southern portion this more gradual stratification in the north permitted a greater response to mixing from winds which were homogeneous from north to south thus the physical and biological structure at any one location over the middle shelf is dynamic over the course of a year and results from a combination of in situ processes and climate mediated regional forcing which is dominated in most years by sea ice

oceanography of the eastern bering sea ice edge zone in spring1 the ice edge region of the southeast bering sea was studied in terms of the hydrographic regime phytoplankton biomass and primary productivity during the springs of 1975 through 1977 the results showed that a phytoplankton bloom occurs at the ice edge just as the spring ice decay period begins and that this accounts for a significant proportion of the annual carbon input over the shallow shelf the bloom is intensified in time and space by the influence of the ice edge on the physical structure of the water column specifically melting ice seems to increase the stability of the water column near and under the ice by lowering the salinity frontal structure in salinity and temperature are apparent at the ice edge and are attributed to the melting ice but also at times to wind driven ekman type upwelling these data are also related to recent short term ca months year climatic fluctuations that seem to control the seasonal position of the ice edge zone relative to the shelf break in cold years the ice edge comes southward to the shelf break and overlies the more nutrientrich alaska stream bering sea source water in warm years the ice edge zone does not reach this nutrient rich water this may be important to the biology of the ice edge ecosystem the edge zones of seasonal sea ice are biologically productive serving as focal points for the congregation of large numbers of marine birds and mammals and thus represent ecologically critical habitats in subpolar regions the presence of a cold and solid boundary influences the biological regime in several ways including effects on the physical and chemical regimes in the adjacent seawater at least three structural features of the water column often associated with high oceanic primary production can occur in such an area simultaneously water column stability frontal structures and under certain conditions ice edge upwelling we show here that there is enhanced primary production due to water column stability and frontal structure at the edge of the seasonal sea ice in spring our data also suggest that ice edge upwelling occurs we show further that the intense

spatial and year to year patterns in new and primary productivity in sea ice melt regions of the eastern bering sea abstract four years of data on for new nitrate regenerated ammonium and primary carbon productivity 2007 through 2010 confirm the elevated productivity associated with the marginal ice zone miz of the eastern bering sea ebs in spring the greatest levels of productivity were associated with ice melt regions along the western edge of the ice pack population seeding and the shallowing of the mixed layer depth near the ice edge were less important in the development of elevated miz productivity than was the amount of ice melt entering surface water suggesting that ice contributed substances stimulating phytoplankton growth based on ice melt as an index of bloom development primary productivity continued to increase after new productivity peaked at the miz environments with optimal growth conditions new productivity averaged 18 6 mmol n m 2 d 1 with a ratio of 0 61 and primary productivity averaged 492 mmol c m 2 d 1 although these features were consistently recorded in late april early may they varied with the dynamics of ice cover whose retreat was later in 2008 relative to 2007 and 2009 the intense but localized miz blooms appear to be under sampled in ocean color imagery under ice productivity was generally low ave no3 0 45 mmol n m 2 d 1 ave primary prod 4 16 mmol c m 2 d 1 although larger values were measured under the western edge of the ice pack and in the st lawrence polynya region the advection of ice and water may contribute to the large values under the western ice edge and the highly transparent new ice may play a role in the polynya new and primary productivity rates of under ice samples were significantly inhibited when exposed to ice free irradiance levels in situ productivity could be estimated to 35 from rates measured on deck by adjusting for the impact of ice on submarine light the carbon to nitrate uptake ratio was closely related to specific carbon production in the in situ incubations

coastal forms and quaternary processes along the arid pilbara coast of northwestern australia abstract the pilbara coast is set in the most arid part of coastal australia this coast and coastal plain composed of riverine plains deltas tidal flats coastal dunes and limestone barriers relic deltas and archipelago ria shores is predominantly a terrigenous and carbonate sediment complex the coastal landforms therein formed during the quaternary through influence of ancestral landforms and fluvial and shoreline accretion coastal erosion and cementation the pre holocene features controlled development of holocene coastal forms and a variety of holocene depositional styles climate also plays a significant part in the coastal processes and in the generation of sedimentary products through high evaporation rates coupled with the limited rainfall cyclonic storms wind wind waves and the limited sediment delivery to the coastal zone this results in a distinctive range of stratigraphic sequences and chemical products as a result this arid coast is characterised by a range of features such as construction of arid zone deltas delta destruction and sediment redistribution during times of sediment depletion cyclone induced erosion and sedimentation mangroves and their associated sedimentary deposits evolution of coastal groundwater hypersalinity formation of salt flats and precipitation and cementation to form beachrocks high tidal crusts and gypsum precipitates the pilbara coastal stratigraphy and geomorphology suggests aridity was intricately involved in the sedimentation geomorphic evolution and pedogenic and diagenetic alteration of this coastal zone throughout the whole of the holocene and pleistocene

formation and early diagenesis of varved evaporite sediments in a coastal hypersaline pool abstract this paper reports an occurrence of varved gypsum organic sediments from a recent shallow water hypersaline pool in ras mohamad southern sinai primary deposition and diagenetic features in this deposit were followed by studying the mineralogy the depositional textures the interstitial brine composition and the concentrations of ions coprecipitated with gypsum during the summer when evaporation is intense gypsum is deposited on the bottom of the pool during the winter evaporation is milder and the brine became undersaturated with respect to gypsum at these lower salinities a carpet of blue green algae floors the pool the sediments of the pool are composed of alternating layers of gypsum mush and algal mats the composition of the interstitial brine is essentially that of evaporated sea water but the concentrations of ca and so4 in the upper layers are anomalously high the calculated degrees of supersaturation with respect to gypsum are as high as about 2 the supersaturation was relieved in the lower layers by early diagenetic growth of gypsum some of the diagenetic gypsum has grown by displacement within the algal layers this growth eventually destroyed the fabric of the algal layer which was ultimately erased the diagenetic growth of gypsum is reflected also in the concentrations of cations coprecipitated with gypsum the coprecipitated ion concentrations decrease with depth and this is interpreted as due to the decrease in the average growth rate of the crystals

sea ice motion measurements from seasat sar images satellite imaging radar is expected to become the prime instrument for mapping the distribution and motion of sea ice on a periodic basis the observational independence from weather fog and clouds and the fact that it provides its own illumination are decisive advantages that imaging radar has in the remote sensing of sea ice the seasat spacecraft launched in 1978 included such an imaging radar and approximately one fourth of all seasat sar observations are of sea ice in the beaufort sea data from seven sequential orbits of the satellite were selected to study the capabilities and limitations of spaceborne radar application to sea ice mapping the results are encouraging 1 there is no difficulty in identifying homologue ice features on sequential radar images 2 the accuracy is entirely controlled by accuracy of the orbit data and the geometric calibration of the sensor 3 conventional radargrammetric methods serve well for satellite radar ice mapping 4 ground control points can be used to calibrate the ice location and motion measurements in the cases where orbit data and sensor calibration are lacking ice motion was found to be approximately 6 4 0 5 km per day however higher accuracies are feasible with better timing calibration of the sensor events and knowledge of the orbit the accuracy of pixel location was also determined over land areas it was found that with the use of one control point in 10 000 km2 the accuracy is about 150 m with higher density of control points 7 in 1000km2 the location accuracy improves to the image resolution i e 25 m this is applicable for both optical and digital data

observations of ice thickness and frazil ice in the st lawrence island polynya from satellite imagery upward looking sonar and salinity temperature moorings 1 for the 1999 winter this paper examines the behavior of the bering sea st lawrence island polynya using a combination of advanced very high resolution radiometer avhrr radarsat synthetic aperture radar sar meteorological data over winter moored upward looking sonars uls and seabird salinity temperature sensors we define a thermal ice thickness from the avhrr retrieval of ice surface temperature combined with meteorological observations and a heat flux model south of the island we compare the uls and thermal thicknesses for congelation and frazil ice when the satellites observe congelation ice over the ulss the uls and thermal ice thicknesses generally agree when sar observes langmuir plumes over the ulss which indicate frazil ice formation the ulss show scatterers at 5 20 m depths in the water column and the seawater temperatures are either within 0 01 c of freezing or are slightly supercooled this suggests that during frazil events crystals either nucleate at depth or are transported to depth by the langmuir circulation the combination of the sar imagery and uls observations also allow measurement of the pack ice advection velocity the polynya width and the downwind frazil accumulation thickness giving widths of 10 to 30 km and thicknesses of 0 1 0 2 m substitution of these observed values with the heat flux into the pease polynya model yields polynya widths that approximately agree with the observed

on some possible interactions between internal waves and sea ice in the marginal ice zone the ice edges of the world ocean are generally the site at times when winds are blowing off the ice of regularly spaced surface bands of ice floes these bands have size scales of the order of 1 10 km and their long axes are oriented approximately normal to the wind direction available oceanic temperature and salinity data from the bering and greenland sea ice edge regions suggest that these ice bands are commonly underlain by a two layered density structure which is maintained by net melting along the ice edges linear internal wave theory is applied to these data to compute first mode interfacial wave phase speeds a simple analytical model is developed that demonstrates the feasibility of generation of such interfacial internal waves by the stress discontinuity due to off ice winds blowing over either a stationary or a moving ice edge it is qualitatively shown that the computed internal wave phase speeds and wavelengths are under many conditions compatible with the speeds and spacings of the surface ice bands this compatibility suggests in turn that coupling between internal waves and ice bands may commonly occur some possible implications of the generation and presence of these internal waves upon other ice edge processes such as air sea heat and momentum transfer are qualitatively discussed

currents and transport on the eastern bering sea shelf an integration of over 20 years of data abstract more than 20 years of data from moorings satellite tracked drifters and hydrographic surveys are integrated to provide a comprehensive view of currents and transport on the eastern bering sea shelf the major sources of water onto the eastern bering sea shelf are north pacific water flowing through unimak pass and bering slope water flowing onto the shelf usually via the canyons that intersect the shelf break absolute geostrophic transport through unimak pass varies from an average of 0 25 106 m3 s 1 sv in the warm months to 0 43 sv in the cold months flow along the 50 m isobath is weak with a transport of 13 months and from amukta pass to bering strait via the bering slope current is 8 months consequently the source of most of the heat transported into the arctic through bering strait is a result of air sea interactions local to the northern bering sea analysis of the currents and water properties on the southern shelf indicates that 50 of the shelf water is exchanged with slope water during october january each year this exchange elevates the october mid shelf average nitrate level from 6 m to 14 16 m by the end of january

on the recent warming of the southeastern bering sea shelf abstract during the last decade the southeastern bering sea shelf has undergone a warming of 3 c that is closely associated with a marked decrease of sea ice over the area this shift in the physical environment of the shelf can be attributed to a combination of mechanisms including the presence over the eastern bering sea shelf of a relatively mild air mass during the winter especially from 2000 to 2005 a shorter ice season caused by a later fall transition and or an earlier spring transition increased flow through unimak pass during winter which introduces warm gulf of alaska water onto the southeastern shelf and the feedback mechanism whereby warmer ocean temperatures during the summer delay the southward advection of sea ice during winter while the relative importance of these four mechanisms is difficult to quantify it is evident that for sea ice to form cold arctic winds must cool the water column sea ice is then formed in the polynyas during periods of cold north winds and this ice is advected southward over the eastern shelf the other three mechanisms can modify ice formation and melt and hence its extent in combination these four mechanisms have served to temporally and spatially limit ice during the 5 year period 2001 2005 warming of the eastern bering sea shelf could have profound influences on the ecosystem of the bering sea from modification of the timing of the spring phytoplankton bloom to the northward advance of subarctic species and the northward retreat of arctic species

3 d water properties and geostrophic circulation on the eastern bering sea shelf abstract the national oceanic and atmospheric administration s noaa alaska fisheries science center bottom trawl survey samples demersal fish at over 350 sites on the eastern bering sea continental shelf each summer on a 37 37 km 2 grid rugged conductivity temperature depth sensors ctds were added to the net hauls to obtain gridded data sets of temperature and salinity measurements for 2008 2010 results reveal the three dimensional thermohaline structure of the shelf including the cold pool and areas of fresher water around st matthew island and in bristol bay horizontal gradients are often strongest roughly along the 50 m and 100 m isobaths that traditionally separate the inner and outer shelf from the middle shelf centered along the 70 m isobath the summer mixed layer depth is less than 30 m over much of the region it reaches the bottom along the alaska peninsula in water depths greater than 70 m showing that the boundary of the well mixed inner shelf is not always at the 50 m isobath the greatest upper to lower layer density difference is found across the shelf north of 59 n the salinity difference is the main contributor to this density difference over most of the region in 2008 and 2010 but the temperature difference dominates in 2009 due to decreased ice melt and reduced freshening near st matthew island the geostrophic velocity relative to the bottom shows northwestward flow seaward of the 100 m isobath and northwestward transports integrated across the shelf of 0 10 0 25 10 6 m 3 s in 2008 and 2010 there was clockwise circulation in a region of less saline water around st matthew island in 2009 that fresher lens did not exist and flow was more concentrated along the 100 m isobath bringing saltier water across the shelf

comparison of warm and cold years on the southeastern bering sea shelf and some implications for the ecosystem the southeastern middle shelf of the bering sea has exhibited extreme variability in sea ice extent temperature and the distribution and abundance of species at multiple trophic levels over the past four decades from 1972 2000 there was high interannual variability of areal extent of sea ice during spring march april in 2000 this shifted to a 5 year 2001 2005 period of low ice extent during spring which transitioned to a 4 year 2007 2010 period of extensive sea ice high low areal extent of sea ice in spring was associated with cold warm water column temperatures for the following 6 7 months the ocean currents also differed between warm and cold years during cold years the monthly mean currents over the shelf were largely westward while in warm years the direction of currents was more variable with northward flow during december february and relatively weak flow during the remainder of the year the types and abundance of zooplankton differed sharply between warm and cold years this was especially true during the prolonged warm period 2001 2005 and cold period 2007 2010 and was less evident during the years of high interannual variability during the warm period there was a lack of large copepods and euphausiids over the shelf however their populations rebounded during cold period small crustacean zooplankton taxa did not appear to vary between and warm and cold years for both walleye pollock and pacific cod year class strength recruitment was low during the prolonged warm period but improved during the following cold period year class strength did not appear to vary as a function of warm and cold years during the period of high year to year variability also recruitment of arrowtooth flounder a predator of pollock and cod did not appear influenced by the warm or cold years finally the distribution and relative abundance of fin whales appeared to differ in warm and cold years with fewer whales on the southeastern middle shelf during warm years

stratification on the eastern bering sea shelf revisited abstract the timing and magnitude of stratification can have profound influences on the marine ecosystem on the eastern bering sea shelf in the absence of strong wind mixing stratification can be initiated by the melting of seasonal sea ice or by springtime warming of the surface temperature and salinity both influence the stratification of the eastern bering sea shelf with their relative importance varying spatially and temporally in the northern middle shelf domain north of 60 n salinity stratification is often as important as temperature stratification on the southern middle shelf while the influence of temperature on stratification dominates during summer the influence of salinity stratification plays a role in the interannual variability mooring 2 m2 56 9 n 164 1 w has been deployed at 70 m depth in the southern middle shelf domain since 1995 data from this mooring show that stratification typically begins to set up in may and to break down in september october but these dates can vary by 30 d while no trend is found in the timing of the spring setup the fall stratification breakdown exhibited a trend toward later breakdown 2 d later per year from 1996 to 2009 results suggest that it may be difficult to forecast stratification on the eastern bering sea shelf from climate models as simple indices of wind mixing or heat fluxes are not correlated with stratification contrary to intuition the strength of summer stratification is not correlated with depth averaged temperature warm years such as 2000 and 2001 can have low stratification and cold years such as 2007 can have very high stratification this decoupling of stratification and temperature has implications for forecasting the ecosystem in the face of climate change as we cannot assume that projections of a warmer climate simply imply higher stratification in the future

spring and fall phytoplankton blooms in a productive subarctic ecosystem the eastern bering sea during 1995 2011 abstract the timing and magnitude of phytoplankton blooms in subarctic ecosystems often strongly influence the amount of energy that is transferred through subsequent trophic pathways in the eastern bering sea spring bloom timing has been linked to ice retreat timing and production of zooplankton and fish a large part of the eastern bering sea shelf 500 km wide is ice covered during winter and spring four oceanographic moorings have been deployed along the 70 m depth contour of the eastern bering sea shelf with the southern location occupied annually since 1995 the two northern locations since 2004 and the remaining location since 2001 chlorophyll a fluorescence data from the four moorings provide 37 realizations of a spring bloom and 33 realizations of a fall bloom we found that in the eastern bering sea if ice was present after mid march spring bloom timing was related to ice retreat timing p n 11 a fall bloom also commonly occurred usually in late september average day 274 se 4 2 n 33 and its timing was not significantly related to the timing of storms p 0 88 df 1 27 or fall water column overturn p 0 49 df 1 27 the magnitudes of the spring and fall blooms were correlated p 0 011 df 28 the interval between the spring and fall blooms varied between four to six months depending on year and location we present a hypothesis to explain how the large crustacean zooplankton taxa calanus spp likely respond to variation in the interval between blooms spring to fall and fall to spring

sedimentary records of bulk organic matter and lipid biomarkers in the bering sea a centennial perspective of sea ice variability and phytoplankton community abstract in this study organic geochemical analyses of two sediment cores bl16 and lv63 23 recovered from the western bering sea were carried out to examine the sea ice variability and its relationship to phytoplankton community evolution over the past century bulk stable organic carbon isotopic composition 13ctoc showed pronounced depletion on the northern shelf since the late 1970s indicating greater terrigenous organic matter om under warming during recent decades variation in sedimentary om in the southward core was closely associated with marine primary productivity and regional deposition processes arctic sea ice proxy ip25 throughout the two cores with different temporal profile patterns demonstrated sea ice presence with the spatio temporal variability across the study area over the past century the phytoplankton marker ip25 index pip25 a proxy for estimating semi quantitatively sea ice concentrations reflected a decreased sea ice cover with more distinct interannual fluctuations between 0 7 and 0 2 especially in core bl16 after the late 1970s coinciding with the recent warming scenario increased concentrations of phytoplankton biomarkers brassicasterol and dinosterol and their ratios as well as the pip25 record in core bl16 indicated a synchronous variability of reduced sea ice cover with the enhancement of phytoplankton productivity since the late 1970s these results suggested a coupled interaction of the sea ice condition and planktonic ecosystem in the north bering shelf our results also revealed recent since the 2000s spatial heterogeneity in sea ice coverage between the northern and southern parts of the bering sea

the abundance and distribution of euphausiids and zero age pollock on the inner shelf of the southeast bering sea near the inner front in 1997 1999 abstract acoustic data and net samples were collected during late spring and early fall 1997 1999 to assess zooplankton and micronekton abundance and distribution relative to the inner front at three sampling grids port moller cape newenham and nunivak island on the inner shelf of the southeast bering sea epibenthic scattering layers were observed during may june and august september in all three years acoustic data were scaled to euphausiid biomass using target strength models mean euphausiid biomass determined acoustically for each transect line was 0 7 21 g m 2 with most values below 5 g m 2 there was no consistent relationship between the distribution and biomass of euphausiids and the location of the inner front zero age pollock were observed on the inner shelf in august september during all years but were confined primarily to the stratified side of the inner front and to the frontal regime the acoustic data for pollock were scaled to biomass using laboratory measurements of gas bladder dimensions and target strength models acoustic determinations of mean transect biomass for euphausiids did not differ from literature values for the inner shelf of the southeast bering sea and pollock biomass on the inner shelf did not differ from that around the pribilof islands despite recent anomalies in climate and oceanographic conditions on the inner shelf and high mortality of shorttail shearwaters during 1997 we found no evidence of significant interannual differences in the biomass of euphausiids or zero age pollock on the inner shelf of the southeast bering sea

physically based modeling of atmosphere to snow to firn transfer of h2o2 at south pole quantitative interpretation of ice core chemical records requires a detailed understanding of the transfer processes that relate atmospheric concentrations to those in the snow firn and ice a unique 2 year set of year round surface snow samples at south pole and snow pits with associated accumulation histories were used to test a physically based model for atmosphere to firn transfer of h2o2 the model which extends our previous transfer modeling at south pole into the snowpack is based on the advection dispersion equation and spherical diffusion within representative snow grains required physical characteristics of the snowpack such as snow temperature and ventilation were estimated independently using established physical models the surface snow samples and related model simulations show that there is a repeatable annual cycle in h2o2 in the surface snow at south pole it peaks in early spring and surface snow concentration is primarily determined by atmospheric concentration and temperature with some dependence on grain size the snow pits and associated model simulations point out the importance of accumulation timing and annual accumulation rate in understanding the deposition and preservation of h2o2 and 18o at south pole long term snowpack simulations suggest that the firn continues to lose h2o2 to the atmosphere for at least 10 12 years 3 m after burial at current south pole temperatures and accumulation rates

recent bering sea warm and cold events in a 95 year context the meteorology and oceanography of the southeastern bering sea shelf was recently dominated by a multi year warm event 2000 2005 followed by a multi year cold event 2007 2010 we put these recent events into the context of the 95 year air temperature record from st paul island and with concurrent spatial meteorological fields for march 2000 2005 the mean air temperature anomaly at st paul was 2 1 1c above the long term mean and for march 2007 2010 the mean temperature anomaly at st paul was 4 7 1c below the long term mean the only multi year temperature deviations comparable to the first decade of the 2000s are a cold event from 1971 to 1976 followed by a warm event from 1978 to 1983 there was also a short warm event 1935 1937 the temperature transition between warm and cold events in the 1970s and 2000s took two years while there are theoretical arguments for some physical memory processes in the north pacific climate system we cannot rule out that the recent warm and cold events are of a random nature they are rare in the st paul temperature record they are dominated by north pacific wide sea level pressure events rather than local bering sea processes and they are consistent with a red noise model of climate variability the 1970s transition

sea ice and water column structure on the eastern bering sea shelf abstract seasonal sea ice is a defining characteristic of the eastern bering sea shelf and plays a critical role in determining the vertical structure of temperature and salinity over this shelf ice movement relative to local winds ice composition and the impact of both arrival and retreat of ice on the water column at four mooring sites over the middle shelf are examined ice forms primarily in coastal regions and is advected over the southern and outer shelves ice drift from satellite data for two representative years 2003 and 2007 was 2 of local ncep wind speed and oriented 44 to the right of the winds r 2 0 25 measurements from 30 ice cores collected in 2006 2009 gave an average salinity of 5 62 0 88 and an average nitrate concentration of 0 99 0 83 m time series data collected at the biophysical moorings in the bering sea 1995 2012 were used to explore the evolution of the water column under ice at the northern mooring m8 the water column had mixed and cooled to 1 c prior to the arrival of ice little melt occurred after ice arrival at the other three moorings the ocean temperature was 2 4 c when ice arrived resulting in extensive melt melting ice freshened and cooled the upper water column resulting in stratification which persisted for 10 25 days wind induced water column mixing occurred more slowly under the ice than in ice free waters an estimated 1 4 m of ice melted with the first arrival of ice at the three southern moorings where the latent heat of fusion accounted for approximately half the observed cooling during ice retreat there appeared to be little ice melt around the southern two moorings but an estimated 0 8 m at m5 and m8 the extent of ice melt sets up the water column for the following summer

the development of solar salt ponds along the pilbara coast western australia a coastline of global geoheritage significance used for industrial purposes the pilbara coast in nw australia stands unique as the most geologically geomorphologically diverse arid coast globally and as such it is a coastline of global significance ideally it should have been listed as a site of world heritage while there are a variety of coastal forms along the pilbara coast a ubiquitous feature of the region is the development of extensive salt flats landward of mangrove fringed coastlines and leeward of barrier limestone ridges and barrier dunes the aridity of the pilbara coast and the occurrence of extensive salt flats lend themselves to exploitation for development of solar salt production ponds but this has resulted in the destruction of unique coastal geomorphology salt flat habitats sand island ecology and the natural diagenesis of arid zone coastal geology this contribution explores the significance of solar salt pond development along a globally unique coastline and highlights that there needs to be a component of geoethics in government decision making that considers all the values of a site

late quaternary sea ice and sedimentary redox conditions in the eastern bering sea implications for ventilation of the mid depth north pacific and an atlantic pacific seesaw mechanism abstract on glacial interglacial and millennial timescales sea ice is an important player in the circulation and primary productivity of high latitude oceans affecting regional and global biogeochemical cycling in the modern north pacific brine rejection during sea ice freezing in the sea of okhotsk drives the formation of north pacific intermediate water npiw that ventilates the north pacific ocean at 300 m 1000 m water depth glacial intervals of the late quaternary however experienced a deepening of glacial npiw to at least 2000 m with the strongest ventilation observed during cold stadial conditions of the last deglaciation however the origin of the shifts in npiw ventilation is poorly understood numerical simulations suggest an atmospheric teleconnection between the north atlantic and the north pacific in response to a slowdown or shutdown of the atlantic meridional overturning circulation this leads to a build up of salinity in the north pacific surface ocean triggering deep ventilation alternatively increased sea ice formation in the north pacific and its marginal seas may have caused strengthened overturning in response to enhanced brine rejection here we use a multi proxy approach to explore sea ice dynamics sedimentary redox chemistry and benthic ecology at integrated ocean drilling program site u1343 in the eastern bering sea across the last 40 ka our results suggest that brine rejection from enhanced sea ice formation during early heinrich stadial 1 locally weakened the halocline aiding in the initiation of deep overturning additionally deglacial sea ice retreat likely contributed to increased primary productivity and expansion of mid depth hypoxia at site u1343 during interstadial conditions confirming a vital role of sea ice in the deglacial north pacific carbon cycle

origins of the subsurface ammonium maximum in the southeast bering sea abstract in the bering sea it has long been argued that ammonium rich bottom water from the middle shelf of bristol bay is tidally diffused seaward resulting in a mid depth ammonium tongue over the outer shelf weak horizontal mean flows in the region relative to an especially strong tidal component support this contention we examined the distribution of ammonium further north in the vicinity of the pribilof islands on the middle shelf bottom waters had concentrations of 4 7 mol kg 1 and over the outer shelf there was a mid depth ammonium tongue optimal multiparameter analysis of hydrographic data suggested that bottom waters from the middle shelf were prevalent across the outer shelf and could account for this ammonium tongue drifter tracks demonstrated that middle shelf water was incorporated into a westward flow along the shelf break south of st george island and mean flows derived from several decades of drifter tracks also show prominent cross shelf advection in the region this was consistent with a scalar argument suggesting that in the vicinity of the pribilof islands the seaward movement of middle shelf water and loss of nitrogen over the middle shelf was the result of advection rather than tidally driven lateral diffusion

ocean circulation and exchanges through the northern bering sea 1979 2001 model results abstract we have developed and run a model with sufficiently high resolution 9 km and 45 levels and a large enough spatial domain to allow for realistic representation of flow through the narrow and shallow straits in the northern bering sea this is potentially important for quantification of long term mean and time dependent ocean circulation and water mass and property exchanges between the pacific and arctic oceans over a 23 year interval 1979 2001 mean transport through bering strait is estimated to be 0 65 sv comparison of our model results with published observations indicates that ocean circulation is not only variable at seasonal to interdecadal scales but it is also responsive to short term atmospheric forcing one of such events occurred during the winter of 2000 2001 with reversed oceanic flow in some areas and much reduced sea ice cover analyses of eddy kinetic energy fields identify some high biological productivity regions of the chirikov basin coincident with persistent high energy up to 2700 cm 2 s 2 in the surface layer and up to 2600 cm 2 s 2 at mid depth throughout the annual cycle model output in the bering strait region is validated against several time series of moored observations of water mass properties comparison with shipboard observations of near bottom salinity from late winter through autumn indicates that the model reasonably represents the major water mass properties in the region the modeled vertical water column structure in the northern bering sea allows increased understanding of the mechanisms of water transformation and transport northward through bering strait into the chukchi and beaufort seas we conclude that the long term model results for the northern bering sea provide important insights into the ocean circulation and fluxes and they are a useful frame of reference for limited observations that are short term and or cover only a small geographic region

what processes contribute to the spring and fall bloom co variability on the eastern bering sea shelf abstract observations indicate that spring and fall phytoplankton blooms on the eastern bering sea ebs continental shelf tend to co vary on inter annual scales that is a year with a strong spring bloom also tends to have a strong fall bloom similar co variability of primary production is also seen in the multi year 1987 2007 integration of a coupled physical biological model moreover the modeled seasonal amplitudes of 10 meter chlorophyll a concentrations at the ebs middle shelf mooring locations computed using the canonical redfield ratio and a mean carbon to chlorophyll a ratio are generally consistent with the in situ mooring measurements the coupled physical biological model simulation is used to examine the relative contributions of wind mixing local nutrient recycling regeneration horizontal nutrient advection and water column stability to this co variability there is no significant correlation between the spring and fall surface wind mixing although wind mixing is an important mechanism for bringing nutrients in the lower water column to the surface layers it is not the mechanism tying the two seasons productivity together local regeneration recycling of the nutrients initially fueling spring production is an important mechanism for spring to fall nutrient accumulation in the bottom layers at the middle shelf horizontal advection does not appear to be the dominant factor for supplying nutrients to the middle shelf during the spring to fall period fall primary production in the model is strongly influenced by the lower water column stability stratification taken together these results highlight the importance of local recycling regeneration of nutrients assimilated by spring phytoplankton bloom in linking together the spring and fall primary productions on ebs middle shelf

distinctive spring phytoplankton bloom in the bering strait in 2018 a year of historically minimum sea ice extent abstract under climate change the bering chukchi continental shelves have experienced drastic sea ice loss breaking the minimum sea ice extent record in 2018 in this paper we report a distinctive spring phytoplankton bloom in the bering strait based on year round mooring observations during 2016 2018 a near bottom fluorescence sensor mounted on a mooring and satellite observations indicate that despite the early sea ice retreat in spring of 2018 mid april the spring phytoplankton bloom was not observed for more than 20 days after sea ice retreat in contrast in 2017 when sea ice retreat did not occur as early as it did in 2018 early may the bloom and sea ice retreat occurred in tighter synchrony mooring 2016 2018 and satellite observations 2003 2011 2013 2018 suggest that an open water bloom rather than an ice edge bloom occurred in the bering strait in the spring of 2018 early sea ice retreat apparently provided unfavorable conditions for an ice edge bloom due to weak sunlight and winter like weather mid winter sea ice loss was promoted by unusual southerly winds bringing in warm water from the south for the bering strait the end of april is a reference date for sea ice retreat that distinguishes between an open water bloom and an ice edge bloom which is approximately one month later than that in the southeastern bering sea

sea ice impacts on spring bloom dynamics and net primary production in the eastern bering sea 1 in the eastern bering sea changes in sea ice have been implicated in recent major upper trophic level shifts however the underlying relationships between sea ice and primary producers have not been well tested here we combine data from multiple satellite platforms reanalysis model results and biophysical moorings to explore the dynamics of spring and summer primary production in relation to sea ice conditions in the northern bering sea sea ice consistently retreated in late spring leading to ice edge phytoplankton blooms in cold 0 1 c waters however in the southeastern bering sea sea ice retreat was far more irregular although this did not significantly alter bloom timing late retreat led to blooms at the ice edge while early retreat led to blooms in open waters that were warmer 5 4 c and 70 more productive early sea ice retreat also led to higher productivity in summer likely due to weaker thermal stratification overall annual net primary production during warm years of early sea ice retreat was enhanced by 40 50 compared to years with late sea ice retreat in the southeastern bering sea these findings suggest the potential for future sea ice loss to enhance overall carrying capacity of the southeastern bering sea ecosystem consistently warm blooms in the future may also channel more energy flow toward the pelagic rather than benthic environment to date however neither sea ice extent nor the timing of its retreat have undergone long term changes in the eastern bering sea

variability of physical and chemical characteristics along the 70 m isobath of the southeastern bering sea abstract from observations of ice cover temperature salinity currents and nitrate it is evident that along shelf variability was significant over the middle shelf of the eastern bering sea but less distinct than that observed in the cross shelf domains along the 70 m isobath three zones were evident in the summer the southeastern cold pool centered at 57 n an intermediate zone consisting of warmer water with weaker stratification and the northern cold pool extending northward from 58 n small scale 20 km horizontal features that persisted for months were common nutrient concentrations were related to salinity and were replenished more uniformly over the southern shelf than north of the pribilof islands although mean currents were weak 1 cm s 1 short energetic advective events impacted the temperature and salinity structure

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

characteristics and variability of the inner front of the southeastern bering sea the inner front of the southeastern bering sea shows marked spatial variability in frontal characteristics created by regional differences in forcing mechanisms differences in forcing mechanisms sea ice advance retreat and storm strength and timing and early spring water properties result in strong interannual variability in biological chemical and physical features near the front we have developed a simple model based on surface heat flux and water column mixing to explain the existence of cold belts cont shelf res 19 14 1999 1833 associated with such fronts hydrography fluorescence and nutrient observations show that pumping of nutrients into the euphotic zone occurs and this can prolong primary production at the inner front the effectiveness of this process depends on two factors the existence of a reservoir of nutrients in the lower layer on the middle shelf and the occurrence of sufficient wind and tidal energy to mix the water column

linkages between sea ice coverage pelagic benthic coupling and the distribution of spectacled eiders observations in march 2008 2009 and 2010 northern bering sea icebreaker based sampling in the northern bering sea south of st lawrence island in march of 2008 2009 and 2010 has provided new data on overall ecosystem function early in the annual productive cycle while water column chlorophyll concentrations 5 m these data together with other physical biological and nutrient data are presented here in conjunction with observed sea ice dynamics and the distribution of an apex predator the spectacled eider somateria fischeri sea ice dynamics in addition to benthic food availability as determined by sedimentation processes play a role in the distribution of spectacled eiders which cannot always access the greatest biomass of their preferred bivalve prey overall the data and observations indicate that the northern bering sea is biologically active in late winter but with strong atmospheric and hydrographic controls these controls pre determine nutrient and chlorophyll distributions water column mixing as well as pelagic benthic coupling

variability in bering sea ice cover as affected by a regime shift in the north pacific in the period 1947 1996 in the late 1970s a regime shift or step occurred in the climate of the north pacific causing among many other effects a 5 reduction in the ice cover in the eastern bering sea as well as shifts in the position of the aleutian low analyses of the aleutian low from monthly mean northern hemisphere sea level pressure for winters december march for 1947 1996 are presented and compared with monthly mean ice cover from the bering sea for 1952 1996 the southern oscillation index and the western pacific oscillation before the regime shift below normal ice cover in the bering sea was typically associated with el nino conditions which caused the aleutian low to move eastward of normal carrying warm pacific air over the bering sea conversely above normal ice cover was associated with la nina conditions which caused the aleutian low to move westward of normal allowing higher pressure to move over the bering sea since the regime shift during el ninos the aleutian low has been moving even farther east causing winds to blow from the east and north off alaska and resulting in above normal ice in the bering sea before the regime shift the occurrence of el nino and la nina conditions was about even since the regime shift el nino conditions are about 3 times more prevalent in recent work e g mantua et al 1997 minobe 1997 there is evidence that this regime shift is the latest in a series of climate shifts going back to at least the late 1800s and may be due to a 50 to 70 year oscillation in a north pacific atmospheric ocean coupled system

biogeochemical cycling in the bering sea over the onset of major northern hemisphere glaciation the bering sea is one of the most biologically productive regions in the marine system and plays a key role in regulating the flow of waters to the arctic ocean and into the subarctic north pacific ocean cores from iodp expedition 323 to the bering sea provide the first opportunity to obtain reconstructions from the region that extend back to the pliocene previous research at bowers ridge south bering sea has revealed stable levels of siliceous productivity over the onset of major northern hemisphere glaciation nhg c 2 85 2 73 ma however diatom silica isotope records of oxygen 18odiatom and silicon 30sidiatom presented here demonstrate that this interval was associated with a progressive increase in the supply of silicic acid to the region superimposed on shift to a more dynamic environment characterized by colder temperatures and increased sea ice this concluded at 2 58 ma with a sharp increase in diatom productivity further increases in photic zone nutrient availability and a permanent shift to colder sea surface conditions these transitions are suggested to reflect a gradually more intense nutrient leakage from the subarctic northwest pacific ocean with increases in productivity further aided by increased sea ice and wind driven mixing in the bering sea in suggesting a linkage in biogeochemical cycling between the south bering sea and subarctic northwest pacific ocean mainly via the kamchatka strait this work highlights the need to consider the inter connectivity of these two systems when future reconstructions are carried out in the region

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

internal bores and breaking internal tides on the oregon continental slope abstractobservations of breaking internal tides on the oregon continental slope during a 40 day deployment of 5 moorings along 43 12 n are presented remotely generated internal tides shoal onto the slope steepen break and form turbulent bores that propagate upslope independently of the internal tide a high resolution snapshot of a single bore is captured from lowered acoustic doppler current profilers ladcp ctd profiles in a 25 h time series at 1200 m the bore is cold salty over 100 m tall and has a turbulent head where instantaneous dissipation rates are enhanced e 10 6 w kg 1 and sediment is resuspended at the two deepest slope moorings 1452 and 1780 m similar borelike phenomena are observed in near bottom high resolution temperature time series mean dissipation rates and diapycnal diffusivities increase by a factor of 2 when bores are present w kg 1 and m s 1 and observed internal tides are energetic enough to drive these enhanced dissipation rates globally the authors estimate

the relationship between sea ice break up water mass variation chlorophyll biomass and sedimentation in the northern bering sea the northern bering sea shelf is dominated by soft bottom infauna and ecologically significant epifauna that are matched by few other marine ecosystems in biomass the likely basis for this high benthic biomass is the intense spring bloom but few studies have followed the direct sedimentation of organic material during the bloom peak in may satellite imagery water column chlorophyll concentrations and surface sediment chlorophyll inventories were used to document the dynamics of sedimentation to the sea floor in both 2006 and 2007 as well as to compare to existing data from the spring bloom in 1994 an atmospherically derived radionuclide 7be that is deposited in surface sediments as ice cover retreats was used to supplement these observations as were studies of light penetration and nutrient depletion in the water column as the bloom progressed chlorophyll biomass as sea ice melted differed significantly among the three years studied 1994 2006 2007 the lowest chlorophyll biomass was observed in 2006 after strong northerly and easterly winds had distributed relatively low nutrient water from near the alaskan coast westward across the shelf prior to ice retreat by contrast in 1994 and 2007 northerly winds had less northeasterly vectors prior to sea ice retreat which reduced the westward extent of low nutrient waters across the shelf additional possible impacts on chlorophyll biomass include the timing of sea ice retreat in 1994 and 2007 which occurred several weeks earlier than in 2006 in waters with the highest nutrient content late winter brine formation and associated water column mixing may also have impacts on productivity that have not been previously recognized these observations suggest that interconnected complexities will prevent straightforward predictions of the influence of earlier ice retreat in the northern bering sea upon water column productivity and any resulting benthic ecosystem re structuring as seasonal sea ice retreats in the northern bering sea