relationships between dinoflagellate cyst assemblages in surface sediment and hydrographic conditions in the bering and chukchi seas palynological analyses were performed on 52 surface sediment samples from the eastern part of the bering sea and chukchi sea in order to document the regional distribution of dinoflagellate cyst assemblages and their relationship with sea surface conditions the assemblages present a relatively high species diversity 20 taxa are recovered routinely especially in the bering sea where they are dominated by operculodinium centrocarpum and the cyst of pentapharsodinium dalei accompanied mainly by spiniferites elongatus s l spiniferites ramosus impagidinium pallidum brigantedinium spp islandinium minutum selenopemphix quanta selenopemphix nephroides quinquecuspis concreta and the cyst of polykrikos kofoidii the percentages of the main taxa vary with latitude and principal component analysis shows that the distribution of assemblages is closely related to hydrographic conditions notably the seasonal duration of sea ice cover and the sea surface temperature in february the dinoflagellate cyst assemblages from the bering sea differ significantly from those of subarctic seas of the north atlantic with respect to their species composition and relationships with sea surface conditions in particular the occurrence of the cyst of polykrikos kofoidii and quinquecuspis concreta and the positive correlation between the percentages of operculodinium centrocarpum and the extent of sea ice constitute peculiar features in the bering sea assemblages copyright 2001 john wiley sons ltd journal of quaternary science

observed tides on the northeastern bering sea shelf bottom pressure observations november 1981 to august 1982 show that the diurnal tides dominate the outer reaches of the northeastern bering sea shelf the diurnal tides decrease inshore from the shelf break maximum k1 amplitude of 38 cm and appear to be evanescent sverdrup poincare waves on the outer shelf the k1 amplitude 2 3 cm in the bering strait is 6 of that at the shelf break the diurnal phase lags vary little 322 359 g for the k1 tide between the stations north and eastward from the shelf break the tides become smaller and more semidiurnal the semidiurnal amplitudes vary considerably between stations these observations show the effects of semidiurnal amphidromic systems predicted by numerical models the m2 amplitude 7 6 cm in the bering strait is about a third of that at the shelf break m2 amplitude of 23 cm the semidiurnal phase lags are earliest at the shelf break 87 g for m2 and appear to increase toward st lawrence island 336 g for m2 in shpanberg strait and the bering strait 202 g for m2 the tidal harmonic constants fluctuated seasonally possibly in response to the variations in ice cover the diurnal amplitudes generally increased during winter while the semidiurnal amplitudes decreased at the shelf break the k1 amplitude increased 2 5 cm or 7 but the o1 and semidiurnal m2 amplitudes 0 4 cm or 2 for m2 showed little variation in bering strait the variations in m2 amplitude up to 3 0 cm amounted to 37 of the mean amplitude the decrease may be due to attenuation of the m2 tide from the arctic ocean in addition to damping of the m2 tide on the northeastern bering sea shelf shorter term fluctuations were also observed in the tides the tidal fluctuations may contribute to those observed in the deep sea numerical models show a set of amphidromic systems including a semidiurnal system off cape navarin and rapid phase transitions in the vicinity of some of the stations these models are in relatively good agreement with the observations

regulation of south china sea throughflow by pressure difference sea surface height ssh data from the european centre for medium range weather forecasts ocean reanalysis system 4 ecmwf oras4 are used to determine the pressure difference in connection with variability of the south china sea throughflow scstf from 1958 to 2007 two branches of scstf the karimata sunda strait throughflow ksstf and the mindoro strait throughflow mstf are examined using the ensemble empirical mode decomposition method eemd time series of pressure difference and volume transport are decomposed into intrinsic mode functions and trend functions with the corresponding variability on different time scales pressure difference agrees with the ksstf volume transport on decadal time scale while for the mstf pressure difference varies similarly with volume transport on interannual time scale separating the dynamic height difference into the thermal and haline terms for the ksstf more than half of the dynamic height difference 32 cm is due to the thermal contributions while the remaining dynamic height difference 23 cm is due to the haline contributions for the mstf the dynamic height difference 29 cm is primarily due to the thermal contribution 26 cm

polynya dynamics a review of observations and modeling 1 polynyas are nonlinear shaped openings within the ice cover ranging in size from 10 to 105 km2 polynyas play an important climatic role first winter polynyas tend to warm the atmosphere thus affecting atmospheric mesoscale motions second ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation since 1990 there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas this article reviews polynya research carried out in the last 2 decades focusing on presenting a state of the art picture of the physical interactions between polynyas and the atmosphere sea ice ocean system observational and modeling studies the surface heat budget and water mass transformation within these features are addressed

wind driven ice drift in a shallow sea the free drift equations are solved for ice floes in a shallow sea of neutral stratification typical of many high latitude continental shelves solutions for ice drift and current velocity are obtained as a function of wind stress ice thickness and water depth the ocean is modeled by second order closure which allows continuous solutions from 5 m total depth to deep water results are presented with drag coefficients for the air ice ice water and water bottom interfaces specified from recent surveys from the bering sea shelf a region with broad areas of water depths between 20 and 50 m the solution shows little dependence on water depth for depths greater than 30 m this occurs because turbulent mixing is a decreasing function of water depth and offsets other influences of finite depth however for water depths less than 30 m ice velocities can change rapidly with wind speed and water depth and the presence of turbulence from tidal shear is very important for coupling wind driven ice drift to the bottom for the deep water limit the second order closure solution confirms analytic solutions that indicate an increase of 20 in the ratio of ice speed to wind speed as the wind speed increases from 10 to 25 m s

the summer hydrography and surface circulation of the east siberian shelf sea during the ice free summer season in 1995 the authors deployed and subsequently tracked 39 surface drifters to test the hypothesis that the discharge from the kolyma river forces a buoyancy driven coastal current from the east siberian sea toward bering strait the observed mean flow is statistically significant at the 95 level of confidence but its direction contradicts their initial hypothesis instead of a coastally trapped eastward flow the authors find a laterally sheared westward flow with maximum velocities offshore that correlate only weakly with the local winds at a daily wind dominated timescale the drifter data reveal spatially coherent flows of up to 0 5 m s21 the lagrangian autocorrelation scale is about 3 days and the lagrangian eddy length scale reaches 40 km this spatial scale exceeds the nearshore internal deformation radius by a factor of 3 however it more closely corresponds to the internal deformation radius associated with the offshore ice edge bulk estimates of the horizontal mixing coefficient resemble typical values of isotropic open ocean dispersion at midlatitudes hydrographic observations and oxygen isotope ratios of seawater indicate a low proportion of riverine freshwater relative to sea ice melt in most areas of the east siberian sea except close to the kolyma delta the observations require a reevaluation of the conceptual view of the summer surface circulation of the east siberian sea eastward buoyancy driven coastal currents do not always form on this shelf despite large river discharge instead ice melt waters of a retreating ice edge act as a line source of buoyancy that in 1995 forced a westward surface flow in the east siberian sea

coupling primary production and terrestrial runoff to ocean acidification and carbonate mineral suppression in the eastern bering sea water column ph and carbonate mineral saturation states were calculated from dissolved inorganic carbon dic and total alkalinity data collected over the eastern bering sea shelf in the spring and summer of 2008 the saturation states of the two most important carbonate minerals calcite calcite and aragonite aragonite were strongly coupled to terrestrial runoff from the yukon and kuskokwim rivers primary production in the surface waters and remineralization of organic matter at depth over the shelf in spring before ice melt occurred ph over the shelf was largely confined to a range of 7 9 8 1 and calcite and aragonite ranged from 1 5 to 3 0 and 0 8 to 2 0 respectively at the stations closest to river outflows aragonite was undersaturated in the water column from the surface to the bottom during the summer sea ice retreat high rates of primary production consumed dic in the mixed layer which increased ph and calcite and aragonite however calcite and aragonite decreased by 0 3 in the bottom waters over the middle and outer shelf over the northern shelf where export production is highest aragonite decreased by 0 35 and became highly undersaturated the observed suppression and undersaturation of calcite and aragonite in the eastern bering sea are correlated with anthropogenic carbon dioxide uptake into the ocean and will likely be exacerbated under business as usual emission scenarios therefore ocean acidification could threaten some benthic and pelagic calcifying organisms across the bering sea shelf in the coming decades

coupled wind forced controls of the bering chukchi shelf circulation and the bering strait throughflow ekman transport continental shelf waves and variations of the pacific arctic sea surface height gradient abstract we develop a conceptual model of the closely co dependent bering shelf bering strait and chukchi shelf circulation fields by evaluating the effects of wind stress over the north pacific and western arctic using atmospheric reanalyses current meter observations satellite based sea surface height ssh measurements hydrographic profiles and numerical model integrations this conceptual model suggests bering strait transport anomalies are primarily set by the longitudinal location of the aleutian low which drives oppositely signed anomalies at synoptic and annual time scales synoptic time scale variations in shelf currents result from local wind forcing and remotely generated continental shelf waves whereas annual variations are driven by basin scale adjustments to wind stress that alter the magnitude of the along strait meridional pressure gradient in particular we show that storms centered over the bering sea excite continental shelf waves on the eastern bering shelf that carry northward velocity anomalies northward through bering strait and along the chukchi coast the integrated effect of these storms tends to decrease the northward bering strait transport at annual to decadal time scales by imposing cyclonic wind stress curl over the aleutian basin and the western subarctic gyre ekman suction then increases the water column density through isopycnal uplift thereby decreasing the dynamic height sea surface height and along strait pressure gradient storms displaced eastward over the gulf of alaska generate an opposite set of bering shelf and aleutian basin responses while ekman pumping controls canada basin dynamic heights proshutinsky et al 2002 we do not find evidence for a strong relation between beaufort gyre sea surface height variations and the annually averaged bering strait throughflow over the western chukchi and east siberian seas easterly winds promote coastal divergence which also increases the along strait pressure head as well as generates shelf waves that impinge upon bering strait from the northwest

younger dryas cooling and sea ice feedbacks were prominent features of the pleistocene holocene transition in arctic alaska abstract declining sea ice extent is currently amplifying climate warming in the arctic instrumental records at high latitudes are too short term to provide sufficient historical context for these trends so paleoclimate archives are needed to better understand the functioning of the sea ice albedo feedback here we use the oxygen isotope values of wood cellulose in living and sub fossil willow shrubs 18owc salix spp that have been radiocarbon dated 14c to produce a multi millennial record of climatic change on alaska s north slope during the pleistocene holocene transition 13 500 7500 calibrated 14c years before present 13 5 7 5 ka we first analyzed the spatial and temporal patterns of 18owc in living willows growing at upland sites and found that over the last 30 years 18owc values in individual growth rings correlate with local summer temperature and inter annual variations in summer sea ice extent deglacial 18owc values from 145 samples of subfossil willows clearly record the allerod warm period 13 2 ka the younger dryas cold period 12 9 11 7 ka and the holocene thermal maximum 11 7 9 0 ka the magnitudes of isotopic changes over these rapid climate oscillations were 4 5 which is about 60 of the differences in 18owc between those willows growing during the last glacial period and today modeling of isotope precipitation relationships based on rayleigh distillation processes suggests that during the younger dryas these large shifts in 18owc values were caused by interactions between local temperature and changes in evaporative moisture sources the latter controlled by sea ice extent in the arctic ocean and bering sea based on these results and on the effects that sea ice have on climate today we infer that ocean derived feedbacks amplified temperature changes and enhanced precipitation in coastal regions of arctic alaska during warm times in the past today isotope values in willows on the north slope of alaska are similar to those growing during the warmest times of the pleistocene holocene transition which were times of widespread permafrost thaw and striking ecological changes

thermal regimes in the chukchi sea from 1941 to 2008 the summer june october temperature observations in the surface 0 m and subsurface 20 mbottom chukchi sea layers collected from 1941 to 2008 have been analyzed using the self consistent data recovery procedure based on correlation analysis and iterative empirical orthogonal function eof decomposition the analysis of the surface and subsurface eofs identified cold normal and warm thermal states with variability of 2 3 years and also 4 7 years we found that the chukchi sea water temperature has gradually increased since 1941 warming in the surface layer since 1941 has been minimal in the bering strait 0 012 1 cy r 1 total 0 8 1c and maximal in long strait 0 030 0 036 1 cy r 1 total 2 0 2 4 1c in the subsurface layer temperatures have increased about half as much minimal 0 0030 0 0075 1 cy r 1 total 0 2 0 5 1c in long strait and rather uniform 0 010 0 015 1 cy r 1 total 0 7 1 0 1c for the remaining chukchi sea analysis of the satellite sea surface height anomaly data shows that during the warm periods there is a stronger flow through the bering strait and intensification of the northwestward currents in the central chukchi sea extensive correlation analysis shows that the thermal state of the chukchi sea agrees well with the flow of pacific water through the bering strait and by an increase of the global atmospheric temperature in addition typical circulation during warm and cold periods was reconstructed using four dimensional variational 4dvar data assimilation into the ocean model and estimates of volume and heat fluxes in the chukchi sea during cold and warm periods were derived which are consistent with eof and correlation analyses

reconstruction and analysis of the chukchi sea circulation in 1990 1991 1 the chukchi sea cs circulation reconstructed for september 1990 to october 1991 from sea ice and ocean data is presented and analyzed the core of the observational data used in this study comprises the records from 12 moorings deployed in 1990 and 1991 in u s and russian waters and two hydrographic surveys conducted in the region in the fall of 1990 and 1991 the observations are processed by a two step data assimilation procedure involving the pan arctic ice ocean modeling and assimilation system employing a nudging algorithm for sea ice data assimilation and the semi implicit ocean model utilizing a conventional four dimensional variational 4d var assimilation technique the reconstructed cs circulation is studied to identify pathways and assess residence times of pacific water in the region quantify the balances of volume freshwater and heat content and determine the leading dynamical factors configuring the cs circulation it is found that in 1990 1991 high ao index and a cyclonic circulation regime pacific water transiting the cs toward the canada basin followed two major pathways namely via herald canyon herald branch of circulation 0 23 sv and between herald shoal and cape lisburne central branch of circulation and alaskan coastal current 0 32 sv the annual mean flow through long strait was negligible 0 01 sv typical residence time of pacific water in the region varied between 150 days for waters entering the cs in september and 270 days for waters entering in february march momentum balance analysis reveals that geostrophic balance between barotropic pressure gradient and coriolis force dominated for most of the year baroclinic effects were important for circulation only in the regions with large horizontal salinity gradients associated with the fresh alaskan and siberian coastal currents and the cape lisburne and great siberian polynyas in the polynyas the baroclinic effects were due to strong salinification and convection processes associated with sea ice formation

application of aerosondes to high resolution observations of sea surface temperature over barrow canyon 1 continuous observation of sea surface temperature sst were obtained for a period of 27 hours over barrow canyon on 20 21 september 2002 using a small robotic aircraft called the aerosonde these observations demonstrated significant spatial and temporal variations in the sst at scales that would be very difficult to measure using mooring and satellite observations over a region of 25 km2 sst values varied from 1 6 c a sharp sst front with a temperature gradient of 3 c was observed over the northwestern shelf of barrow canyon which moved northward during the observation period relatively cold water was transported from the southwest into the region current speeds were estimated using the time series of observations this analysis demonstrates new technology for oceanographic observations and supports previous evidence that the flow through barrow canyon has a strongly sheared flow into the arctic ocean

the north pacific a global scale estuary abstract the atmospheric net flow of water from the atlantic to the pacific ocean is supposed to maintain the salinity difference between the two oceans assuming the existence of a subsurface level of no horizontal pressure gradient in the ocean the mean sea level in the northern pacific must be higher than in the arctic ocean this mean sea level difference is supposed to drive the observed mean flow through the bering strait the estimated flow of freshwater through the bering strait is approximately equal to the estimated atmospheric net flow of water from the north atlantic to the north pacific this justifies the formulation of a simple estuary model for the north pacific in which the brackish water exits through the bering strait the salinity difference between the two oceans is shown to be controlled by the topography of the bering strait the estuary model gives residence times for water in the upper layer 1000 m thick of approximately 1000 years and in the lower layer of approximately 400

westward intensification of the mean circulation on the bering sea shelf abstract most of the water that eventually flows northward through bering strait originates about 500 km south seaward of the shelfbreak in the bering sea cumulative observational evidence supports the idea that most of this northward flow across the gently shoaling eastern bering sea continental shelf occurs as a western boundary current along the siberian coast a homogeneous rotating laboratory model and a barotropic numerical model each demonstrate this westward intensification of the mean flow the intensification results from the well known topographic effect the combination of rotation and the depth decrease in the direction of flow acts in a similar fashion to the meridional gradient of the coriolis parameter for reasonable values of bering strait transport and shelf bottom friction current speeds of 10 20 cm s 1 and a current width of 50 km are predicted

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

modeling ice dynamics of coastal seas a coupled sea ice barotropic ocean model with a 1 km resolution and a seaward domain of 200 km quantifies three coastal processes coupling of ice motion to wind driven coastal currents ice thickness redistribution under compaction at the coast and formation of coastal shear zones the model consists of an ice momentum balance mass concentration and two parameter ice thickness distribution and equations for horizontal water motion and continuity using vertical structure functions an appropriate constitutive law appears to be a hardening plastic based on qualitative observations from alaskan continental shelves for first year sea ice strength is taken to be proportional to the square of ice thickness a north wind example of 10 m s with the coastline to the west shows the depth dependence of rotational shear in the sea ice ocean boundary layer and sea surface tilt which contributes an alongshore slope current there is slight convergence of sea ice over the shelf a coastal shear zone of 4 km and an alongshore ice speed seaward of the shear zone of 6 of the wind speed caused by the combination of an under ice shear layer and an alongshore slope current for an onshore wind ice is near free drift at 3 of the wind seaward of a ridging front which propagates seaward a square dependence of ice strength on thickness is required for the rubble field to approach a limiting thickness consistent with observations the hardening plastic interpretation of the rubble field has the stress state at the yield limit in contrast with a rigid plastic of high constant strength that yields only at the coast we conclude that 1 ice thickness motion feedback is important on scales less than 10 km 2 the observational base to discriminate between mesoscale constitutive laws is not yet available and 3 the relation of ice velocity to wind stress is variable because the ocean slope current responds only to the alongshore component of the wind

response of thermohaline circulation to freshwater forcing under present day and lgm conditions responses of the thermohaline circulation thc to freshwater forcing hosing in the subpolar north atlantic ocean under present day and the last glacial maximum lgm conditions are investigated using the national center for atmospheric research community climate system model versions 2 and 3 three sets of simulations are analyzed with each set including a control run and a freshwater hosing run the first two sets are under present day conditions with an open and closed bering strait the third one is under lgm conditions which has a closed bering strait results show that the thc nearly collapses in all three hosing runs when the freshwater forcing is turned on the full recovery of the thc however is at least a century earlier in the open bering strait run than the closed bering strait and lgm runs this is because the excessive freshwater is diverged almost equally toward north and south from the subpolar north atlantic when the bering strait is open a significant portion of the freshwater flowing northward into the arctic exits into the north pacific via a reversed bering strait throughflow which accelerates the thc recovery when the bering strait is closed this arctic to pacific transport is absent and freshwater can only be removed through the southern end of the north atlantic together with the surface freshwater excess due to precipitation evaporation river runoff and melting ice in the closed bering strait experiments after the hosing the removal of the excessive freshwater takes longer and this slows the recovery of the thc although the background conditions are quite different between the present day closed bering strait run and the lgm run the thc responds to the freshwater forcing added in the north atlantic in a very similar manner

ocean circulation and fronts as related to ice melt back in the chukchi sea the work reported herein was supported in part by the arctic submarine laboratory naval ocean systems center san diego california under project order nos 000007 and 00164

on the wind driven variability of the flow through bering strait analysis of time series from 1981 to 1982 near bering strait shows the meridional wind component the current and the oceanic pressure gradient to be well correlated we argue that because of the constraining coastal geometry there are wind driven flow divergences which perturb the oceanic pressure field and account for most of the current variability for example northerly winds cause a pronounced set down of sea level southeast of bering strait and if the winds are strong enough they will reverse the mean slope downward to the north through the strait winds during 1976 1977 were also well correlated with the bering strait transport estimates of coachman and aagaard 1981 and we therefore use the calculated winds from 1946 to 1982 to examine the low frequency transport variability there is a marked seasonal cycle with summer transport about 50 greater than during winter the long term mean transport is calculated as less than 0 6 sv which is much lower than earlier estimates abnormally large transports apparently occurred during a number of years from 1948 to 1967 but during the past 15 years transports have tended to be considerably less corresponding to the stronger northerly winds during these years the interannual wind variability near bering strait together with the corresponding variability in the transport through the strait is in fact part of the large scale variability of the atmospheric circulation over the north pacific and its oceanic effects

air ice drag coefficients for first year sea ice derived from aircraft measurements turbulent flux measurements were made at four levels 42 90 195 and 340 m by the noaa p 3 aircraft over first year sea ice in the northern bering sea during february 1982 three profiles of momentum flux and mean wind were used to calculate an air ice drag coefficient cd of 3 0 6 10 3 referenced to a 10 m anemometer height the boundary layer was slightly unstable zi l 1 2 where zi was the inversion height of 660 m and l the monin obukhov length the mean wind speed at the 42 m height was 17 m s and the air temperature was 20 c from turbulent heat flux measurements the value of the bulk heat transfer coefficient ch was 0 73 1 6 10 3 giving a ch cd of 0 24 the bowen ratio was greater than 2 8 comparison of the present turbulent flux and variance profiles with those collected over the ocean shows agreement which increases confidence in the calculations the geostrophic drag coefficient u g where u is the friction velocity and g is the geostrophic wind was 0 047 the turning angle of the surface wind measured by an anemometer at a height of 3 m on the ice was 32 and the ratio of surface wind speed to the geostrophic wind speed was 0 76

summertime synoptic variability of frontal systems in the northern bering sea hydrographic observations in the northern bering sea during august and september 1987 indicate the presence of a front dividing relatively warm fresh bering shelf water from relatively cool saline anadyr water along the western and northern coasts of st lawrence island near anadyr strait a buoyant layer 20 m thick with surface salinities as low as 29 5 practical salinity units and a maximum temperature of 10 c was present adjacent to the island the surface outcrop of the front migrated 80 km north during the nine day time period of the hydrographic observations surface thermal patterns suggest that this front may extend the length of the northern coastline of st lawrence island during the summer the front veers north and passes through the bering strait where temperature differences as large as 6 c exist across the strait an examination of the water mass properties of the bering sea suggests that the buoyant water north of st lawrence island is bering shelf water which has been carried northward through anadyr strait the baroclinic transport assuming no flow at the bottom associated with the front is 0 07 sv which is roughly a third of the seasonal increase in transport through the bering strait in the summer

constraints on the nature of the subvolcanic reservoir at south sister volcano oregon from u series dating combined with sub crystal trace element analysis of plagioclase and zircon abstract we present sub crystal scale 238u 230th zircon ages and 238u 230th 226ra plagioclase ages of bulk mineral separates from the holocene 2 0 2 3 ka eruptions of the rock mesa rm and devil s hills dh rhyolites at south sister volcano oregon we link these age data with sub crystal trace element analyses of zircon and plagioclase to provide insight into the subvolcanic system at south sister as an example of a small volume continental arc volcano our results document the presence of coeval yet physically distinct regions within the magma reservoir and constrain the timescales over which these heterogeneities existed zircons from the rm and dh dominantly record ages from 20 to 80 ka with some grains recording ages 350 ka whereas plagioclase records 230th 226ra ages of 2 3 6 8 ka rm and 4 0 9 6 ka dh 3 and a 238u 230th age of 10 34 ka dh 3 we interpret zircons with ages 50 ka within a heterogeneous magmatic system and coexisted as physically distinct dominantly liquid bodies prior to eruption thus we favor a model where rhyolites are generated in independent batches by accumulation of evolved liquids in a heterogeneous largely crystalline reservoir similarities in crystal age and chemical data to that at other young silicic systems e g mount st helens okataina caldera complex suggest that this model may be more generally applicable to silicic magmas

a variational inverse method for the reconstruction of general circulation fields in the northern bering sea the knowledge of the dynamical structures associated with the general circulation in the northern bering sea and bering strait is improving as numerical models together with in situ observing systems become more and more sophisticated the ultimate objective being the design of a realistic model it is fundamental to confront the results stemming from numerical simulations with the extensive set of hydrographic data collected since the beginning of the century a variational inverse model has been developed for the study of continental seas with the aim of reconstructing on the basis of local measurements such as ctd profiles carried out at isolated hydrographic stations continuous fields of the state variables representative of the general circulation a numerical inverse methodology based on a variational principle and a finite element discretization has been designed to generate dynamically consistent patterns providing a practical tool for the visualization and the mathematical interpretation of observations horizontal distributions of temperature salinity nutrients chlorophyll and other chemical tracers as well as the horizontal transport of water are reconstructed by using synoptic data collected from the ishtar nsf research project among the three water masses that can be distinguished in the region the anadyr stream is obviously the main source of nutrients for the whole basin the trace of a permanent upwelling located close to the siberian coast can be detected on a series of general circulation patterns representative of various tracers the strong vertical motions resulting from this upwelling allow an intensive primary productivity and determine the particularly fertile conditions for the development of the ecosystem in the chukchi sea

phytoplankton blooms beneath the sea ice in the chukchi sea in the arctic ocean phytoplankton blooms on continental shelves are often limited by light availability and are therefore thought to be restricted to waters free of sea ice during july 2011 in the chukchi sea a large phytoplankton bloom was observed beneath fully consolidated pack ice and extended from the ice edge to 4100 km into the pack the bloom was composed primarily of diatoms with biomass reaching 1291 mg chlorophyll a m 2 and rates of carbon fixation as high as 3 7 g c m 2 d 1 although the sea ice where the bloom was observed was near 100 concentration and 0 8 1 2 m thick 30 40 of its surface was covered by melt ponds that transmitted 4 fold more light than adjacent areas of bare ice providing sufficient light for phytoplankton to bloom phytoplankton growth rates associated with the under ice bloom averaged 0 9 d 1

on the processes controlling shelf basin exchange and outer shelf dynamics in the bering sea abstract we use a 9 km pan arctic ice ocean model to better understand the circulation and exchanges in the bering sea particularly near the shelf break this region has historically been undersampled for physical chemical and biological properties very little is known about how water from the deep basin reaches the large shallow bering sea shelf to address this we examine here the relationship between the bering slope current and exchange across the shelf break and resulting mass and property fluxes onto the shelf this understanding is critical to gain insight into the effects that the bering sea has on the arctic ocean especially in regard to recent indications of a warming climate in this region the bering sea shelf break region is characterized by the northwestward flowing bering slope current previously it was thought that once this current neared the siberian coast a portion of it made a sharp turn northward and encircled the gulf of anadyr in an anticyclonic fashion our model results indicate a significantly different circulation scheme whereby water from the deep basin is periodically moved northward onto the shelf by mesoscale processes along the shelf break canyons along the shelf break appear to be more prone to eddy activity and therefore are associated with higher rates of on shelf transport the horizontal resolution configured in this model now allows for the representation of eddies with diameters greater than 36 km however we are unable to resolve the smaller eddies

mesoscale nowcasting of sea ice movement through the bering strait with a description of major driving forces abstract surface atmospheric pressure data from a triangular station network surrounding the bering strait are used to calculate hypothetical geostrophic wind velocities net daily strait sea ice movement is derived from visible and infrared noaa satellite imagery for november through may 1974 to 1984 these historical ice motion data and network wind velocity data are used to develop an empirical 12 h advance forecast nowcast sea ice movement model with all weather capabilities a necessary outgrowth of this study has been the identification and classification of three modes of ice movement and two modes of ice immobilization according to their major driving forces the first ice movement mode is from the chukchi to the bering sea requiring a minimum northeasterly geostrophic wind of 12 m s 1 the second and third modes represent ice movement from the bering to the chukchi sea mode 2 is driven by a preexisting north flowing ocean current that offsets weak winds from the northeast mode three is large

molecular and petrographic indicators of redox conditions and bacterial communities after the f f mass extinction kowala holy cross mountains poland abstract pyrite framboid diameter analysis and organic geochemistry of the triangularis crepida boundary section at kowala holy cross mountains poland imply suboxic to oxic and sporadically euxinic bottom waters during the lower famennian in addition morphological web like structures typical for microbial mats as well as the recognition of 2 methylhopanes and monomethyl alkane cyanobacteria biomarkers is evidenced of microbial activity after the global frasnian famennian f f extinction event the presence of cyanobacterial mats also suggests suboxic to oxic environments and at the same time photic bottom water conditions however isorenieratane and its derivatives were detected in almost all samples the presence of this well known biomarker of green sulfur bacteria implies that euxinic conditions were present in the upper part of the water column at least intermittently or that temporal euxinia occurred in the water column presence of euxinic conditions is confirmed by the occurrence of small sized pyrite framboids which were particularly dominant in the lower part of the section the shift towards low 13 c values in both micritic limestones and in sedimentary organic matter seen at the beginning of the period of diminished photic zone might reflect an influx of newly respired co 2 to surface waters caused by enhanced respiration at depth after the f f transition in the checiny zbrza basin

two configurations of the western arctic shelfbreak current in summer abstractdata from a closely spaced array of moorings situated across the beaufort sea shelfbreak at 152 w are used to study the western arctic shelfbreak current with emphasis on its configuration during the summer season two dynamically distinct states of the current are revealed in the absence of wind with each lasting approximately one month the first is a surface intensified shelfbreak jet transporting warm and buoyant alaskan coastal water in late summer this is the eastward continuation of the alaskan coastal current it is both baroclinically and barotropically unstable and hence capable of forming the surface intensified warm core eddies observed in the southern beaufort sea the second configuration present during early summer is a bottom intensified shelfbreak current advecting weakly stratified chukchi summer water it is baroclinically unstable and likely forms the middepth warm core eddies present in the interior basin the mesoscale instabilities extract energy from the mean flow such

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

geostrophic control of fluctuating barotropic flow through straits abstract a simple model in which the cross strait sea surface slope is geostrophically balanced and the along strait slope is balanced by acceleration and friction is shown to be supported by the results of buchwald and miles for fluctuating flow through a gap between two semi infinite oceans for a narrow gap compared with the rossby radius and the scale of the motion in the far field the transport through it is exactly the same as that predicted by the model provided that the gap is regarded as having an elective length as determined in this paper the importance of the models is that they demonstrate that at low frequency the flow may be geostrophically controlled and the transport limited to a value much less than that which would arise in a nonrotating system the neglect of nonlinear advective terms in the models is justified by a comparison or the bernoulli set down in the strait with the driving head and the mean water depth the formula for the flux through a strait may be applied in stu

recent variability in the pacific western subarctic boundary currents and sea of okhotsk abstract the objective of this research is to describe physical processes which are the cause of the recent variability of the pacific western subarctic waters rapid thermohaline changes have occurred within the oyashio and kamchatka current during the last decade this variability has included a warming of the kamchatka current warm intermediate layer but a cooling and freshening of the upper layer in the oyashio and sea of okhotsk the example presented here uses data obtained during the canada russia inpoc and woce projects as well as the new russian studies with high resolution station grid the possible physical mechanism that generated the upper layer freshening during the thermohaline transition is examined major components of the fresh water budget of the okhotsk sea are considered in order to describe the dramatic changes in salinity which have recently occurred in the pacific subarctic significant changes in precipitation and other fresh water inputs are demonstrated it is suggested that upper layer of the oyashio and kamchatka current became cooler and fresher because of the export of cold fresher waters from the bering and okhotsk seas these waters from the marginal seas have cooled the bottom of the halocline reducing evaporation and acting as a feedback that has kept the upper layer of the western subarctic boundary currents fresh it is also shown that the outflow of the cold sea of okhotsk water has changed its path during this recent thermohaline transition

the flow system in the japan sea caused by a sea level difference through shallow straits we investigate how the current system through the japan sea is driven and what determines the volume transport we suppose that a part of the difference in geopotential anomaly between the subtropical and subpolar gyre is converted into a barotropic sea level difference across the three shallow straits which connect the japan sea with the pacific and that this difference is the primary driving force of the current system then we examine the flow under the condition that there is a constant sea level difference between two oceans connected through a shallow strait we found that the strait acts as a source of arrested shelf waves or steady coastal flows for the timescale beyond the inertial period in the northern hemisphere steady flows are established along the shelves with the coast to the right left in the ocean of low high sea level we apply this notion to the current system through the japan sea the tsushima nearshore branch the tsugaru coastal mode and the soya current can all be interpreted as a coastally trapped flow whose source is the upstream strait further a series of northeastward flows along the south and east china seas shelves should be interpreted as coastally trapped flows whose source is the downstream tsushima strait numerical model experiments incorporating the realistic topography also simulate the observed flow fields the volume flux through each strait being limited geostrophically relations between the sea level difference and volume transport can be represented by simple formulas

northward flow in the bering and chukchi seas the ocean circulation on the bering and chukchi sea shelves is investigated using a barotropic numerical model in the presence of the winter seasonal wind stress from the northeast observed northward transport through bering strait of 0 6 sv for the 8 month winter season 1981 1982 can be driven by a sea level difference of 0 4 m between the pacific and arctic oceans this sea level difference between basins is in agreement with hydrographic estimates in the absence of wind stress a 0 4 m sea level difference drives a northward transport through bering strait of 1 1 sv maximum transport through bering strait is geostrophically limited not frictionally or inertially limited major qualitative circulation features of the region are evident in the simulations westward intensification of the northward transport across the bering sea shelf is confirmed with the major transport occurring in the relatively deep gulf of anadyr in the absence of wind anadyr strait contributes 72 of the northward transport through bering strait with northeasterly winds there is a net clockwise circulation around saint lawrence island within the 20 m isobath norton and kotzebue sounds are little influenced by the general circulation northward transport in the chukchi sea bifurcates in the vicinity of point hope the predominant branch is directed toward the northwest in a broad canyon feature south of herald shoal and the balance becomes the alaskan coastal current between cape lisburne and point barrow

sea ice drift near bering strait during 1982 six argos ice stations were deployed in the northeastern bering sea in january and february 1982 four moved north through bering strait and made between one and five passes through the strait before they sank or were crushed by the ice and two remained in western norton sound and shpanberg strait net winds in the region were directed toward the southwest and were relatively uniform geographically net currents were northward and both mean velocity and mean speed were greater at bering strait than at shpanberg strait norton sound contributed ice northward through bering strait in the mean during winter and spring there was also a net divergence of ice near cap lisburne a theory for open shelf shallow water ice drift is developed that adds terms for bottom drag and stress feedback from the water column a stress analysis for a station that remained in western norton sound and shpanberg strait showed that bottom drag did not contribute significantly but that stress feedback from the accelerated shallow water current can be of the same order as the coriolis force however the analysis contained a residual possibly associated with internal ice stress coastal setup or unknown measurement error which was of roughly the same order as the wind and current stress

direct evidence for northward flow on the northwestern bering sea shelf during the summer of 1994 a satellite tracked drifter transited from the southeastern bering sea slope through bering strait by a route westward along the slope and then northward through anadyr canyon and strait the trajectory emphasizes the importance of a western location of northward flow on the bering sea shelf the transit time was 2 months from cape navarin to bering strait with northward drift velocities of 5 40 cm s

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

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

atmospheric boundary layer structure and drag coefficients over sea ice this paper estimates the air sea drag coefficient for first year ice from recent aircraft measurements and reconciles the range of observed drag coefficients 103cd 1 2 3 7 referenced to 10 m for all sea ice types based on ice roughness and seasonal meteorology for the purpose of sea ice modeling it is necessary to define an effective drag coefficient which relates regional stress to regional wind because sea ice is heterogeneous on scales less than 20 km regional stress is influenced by the distribution of surface roughness the buoyancy flux from quasi periodic leads and external atmospheric conditions principally the inversion height 103cd is 1 3 1 5 for smooth ice but is much greater for nonflat surfaces for wind speeds greater than 5 m s and air temperatures below freezing the effective 103cd is 2 5 3 0 for nearly continuous pack ice such as first year ice in seasonal ice zones and central arctic basin the range of values of 103cd is 3 0 3 7 for unstable boundary layers typical of off ice winds in the marginal ice zone miz or even greater if the ice has been broken by a recent storm cd values at the lower end of these ranges are associated with low inversion heights these coefficients are confirmed by 103cd of 2 9 2 5 and 3 1 for first year sea ice calculated from gust probe data collected by the noaa p 3 aircraft interior to the inner miz in the bering sea during the marginal ice zone experiment mizex west in february 1983 and 103cd of 2 6 for the arctic calculated from arctic ice dynamics joint experiment aidjex aircraft data for february 1976 the effective drag coefficient with the presence of even a small concentration of sea ice is greater than the oceanic value as shown by a 103cd of 2 2 calculated from noaa p 3 gust probe data over a 40 km track of 0 4 ice concentration in the outer miz of the greenland sea in june 1984 during mizex 84 the relation of surface wind and stress to the geostrophic wind for shallow inversion heights typical of high latitudes is reviewed with a turbulent closure atmospheric boundary layer model the winter arctic is typified by low inversions 100 m low geostrophic drag coefficients and large geostrophic surface wind turning angles with low functional dependence on surface roughness seasonal ice zones are typified by a more modest influence of the inversion on boundary layer characteristics

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

transit time of river water in the bering and chukchi seas estimated from δ 18 o and radium isotopes abstract seawater samples for the measurements of 226ra 228ra and stable oxygen isotope 18o were collected from the bering and chukchi seas in the summer of 2014 the fractions of meteoric water fmw and sea ice melted water fsim were estimated based on the mass balance of salinity and 18o with a three end member mixing model our results showed that the average fmw increased northward from the bering basin to the canada basin while the fsim distributed homogeneously the lowest fmw and 228ra 226ra a r values were found in the upper bering basin with little terrestrial input the highest fmw but low 228ra 226ra a r appeared in the northern chukchi sea and the canada basin ascribing to the current driven accumulation of freshwater and its long residence time more abundant sea ice melted water was found on the pack ice edge indicating the trap of earlier melted waters by the ice pack based upon the linear relationships between 228ra 226ra a r and fmw in the bering shelf and the chukchi shelf the transit time for the pacific inflow was constrained the transit time of river water from the bering shelf to the chukchi shelf was estimated as 0 2 4 4 years with an average of 1 6 1 5 years while that from the chukchi shelf to the canada basin was 10 2 13 2 years with an average of 11 8 1 1 years the spatial variation of the transit time was mainly affected by the current intensity our study highlights the importance of in depth evaluation for the subarctic arctic exchange