upwelling in the alaskan beaufort sea atmospheric forcing and local versus non local response abstract the spin up and relaxation of an autumn upwelling event on the beaufort slope is investigated using a combination of oceanic and atmospheric data and numerical models the event occurred in november 2002 and was driven by an aleutian low storm the wind field was strongly influenced by the pack ice distribution resulting in enhanced winds over the open water of the chukchi sea flow distortion due to the brooks mountain range was also evident mooring observations east of barrow canyon show that the beaufort shelfbreak jet reversed to the west under strong easterly winds followed by upwelling of atlantic water onto the shelf after the winds subsided a deep eastward jet of atlantic water developed centered at 250 m depth an idealized numerical model reproduces these results and suggests that the oceanic response to the local winds is modulated by a propagating signal from the western edge of the storm the disparity in wave speeds between the sea surface height signal traveling at the fast barotropic shelf wave speed versus the interior density signal traveling at the slow baroclinic wave speed leads to the deep eastward jet the broad scale response to the storm over the chukchi sea is investigated using a regional numerical model the strong gradient in windspeed at the ice edge results in convergence of the offshore ekman transport leading to the establishment of an anti cyclonic gyre in the northern chukchi sea accordingly the chukchi shelfbreak jet accelerates to the east into the wind during the storm and no upwelling occurs west of barrow canyon hence the storm response is fundamentally different on the beaufort slope upwelling versus the chukchi slope no upwelling the regional numerical model results are supported by additional mooring data in the chukchi sea

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

flow dynamics of a wide arctic canyon we extend and interpret acoustic doppler current profiler and conductivity temperature depth data collected in the summer of 1993 over barrow canyon in order to implement a high resolution 1 5 to 5 km model of the beaufort and chukchi seas this paper addresses physical processes relevant to the barrow canyon region using common dynamical analyses of both field data and numerical results the field data reveal the dominant physical processes that guide the design of our numerical experiments the observed velocity field shows an intense and variable down canyon flow with transports ranging from 0 5 to 1 4 sv a momentum analysis reveals that the cross canyon dynamic balance for the barotropic component is primarily geostrophic conversely the baroclinic cross canyon momentum balance is ageostrophic and secondary flow results from a local imbalance between the vertically varying coriolis acceleration and the cross canyon pressure gradient in addition to the moderate influence of stratification froude number of 0 4 and burger number of 0 06 the barotropic pressure gradient component across the canyon inferred from the large magnitude and little vertical variability of the residuals is dynamically important for both upcanyon and downcanyon flows that occur at different locations concurrently the along canyon dynamic balance is ageostrophic since the time derivative and the coriolis term are of the same order of magnitude temporal rossby number is approximately 1 an analysis of the longitudinal density and velocity fields from the model reveals that the main driving mechanism for generating the observed upcanyon flow is the nonlinear interaction of the variable barotropic flow with the steep topography stratification is maintained by the downcanyon advection of fresh and warm water from the bering and chukchi seas and the upcanyon advection of saltier and colder water from the arctic

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

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

circulation of the chukchi sea shelfbreak and slope from moored timeseries abstract data from a year long mooring array across the shelfbreak upper slope of the chukchi sea are used to describe and quantify the circulation and water masses of the region the timeseries revealed the year round existence of the eastward flowing shelfbreak jet and seaward of this the westward flowing chukchi slope current in the mean the slope current is estimated to transport 0 57 0 04 sv of pacific water while the bottom intensified shelfbreak jet transports 0 009 0 003 sv towards barrow canyon the slope current is surface intensified in summer and fall and in winter and spring it becomes middepth intensified moves shoreward and weakens two extreme states of the circulation were identified 1 an enhanced slope current and reversed westward flowing shelfbreak jet and 2 a strong eastward flowing shelfbreak jet and weak slope current the former state occurs when the wind stress curl on the chukchi shelf is positive and the latter state occurs when the curl is negative a simple theoretical model is used to determine the changes in sea surface height due to such wind stress curl forcing which is consistent with the observed changes in flow seaward of the shelf both in amplitude and phase via geostrophic set up shelfbreak upwelling occurred throughout the year but there was no correlation between the regional wind conditions and the upwelling furthermore there was no apparent relationship between upwelling and the extreme slope current shelfbreak jet events a comparison of water mass signals between the chukchi slope array and a mooring at the head of barrow canyon supports the notion that the slope current is fed by the outflow of pacific water from the canyon

seismic images of the deep structure of the san andreas fault system central coast ranges california three dimensional inversion of teleseimic p wave travel time residuals recorded at the u s geological survey central california array has resolved small scale approx tens of kilometers crustal and upper mantle heterogeneity down to depths of 90 km beneath the california coast ranges upper crustal lateral velocity variations of 8 correlate closely with surface geology lower than average velocities are associated with thick tertiary sedimentary fill and higher than average velocities with basement exposures lower crustal velocity heterogeneity of 4 appear to reflect crustal thickness variations a thinner crust is indicated southwest of the san andreas fault and northwest of san pablo bay a linear zone of low velocities 0 to 40 subparallel to the san andreas fault was resolved in the upper mantle the preferred interpretation is that the low velocities indicate a narrow upwarp of asthenosphere to unusually shallow depths approx 45 km beneath the coast ranges such an unusual upper mantle structure may have been produced by the northwestward migration along the california coast of a transiently unstable mendocino triple junction the inversion results also indicate the possibility of partial decoupling of the crust from the upper mantle

variations in the proportions of melted sea ice and runoff in surface waters of the chukchi sea a retrospective analysis 1990 2012 and analysis of the implications of melted sea ice in an under ice bloom abstract retrospective analysis of apparent freshwater isotopic end members through use of salinity 18 o mixing lines for 15 research cruises from 1990 to 2012 indicates that the freshwater contributed by melted seasonal sea ice does not directly reflect the large change in seasonal sea ice extent in the chukchi sea observed over the past several decades instead the freshwater that appears to be contributed by melting sea ice relative to runoff is highly dependent upon cruise track e g proximity to runoff and sampling capabilities in sea ice icebreakers sample waters with less melted sea ice although under certain circumstances including later seasonal sampling and recurrent cruise tracks between years increased melted sea ice in surface waters can be readily detected this suggests a more ephemeral influence of melted sea ice on ecosystem properties despite the significant decadal changes in sea ice extent as a recent case study the freshwater component present in waters within an under ice bloom in the chukchi sea reported by arrigo et al 2012 included a significant fraction 10 or more of freshwater primarily from melted sea ice these results suggest that this under ice bloom which extended more than 60 km under solid ice still might be reasonably interpreted as being part of a continuum with other ice melt associated blooms and not independent of sea ice retreat and dissolution

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

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

early summer water mass transformation in the eastern chukchi sea abstract pacific water entering the chukchi sea through bering strait can be modified by physical processes such as surface heating and cooling and internal mixing here we document the existence of a previously unobserved water mass in the eastern chukchi sea during the early summer using hydrographic and velocity data from the june july 2010 icescape survey the water mass in question is as salty as pacific winter water pww but is much warmer with temperatures typical of summer waters we label the water mass dense chukchi summer water dcsw which is dense enough to ventilate the upper halocline of the western arctic ocean normally ventilated by the much colder pww satellite sea surface temperature data long term mooring data from bering strait and the beaufort shelfbreak and atmospheric reanalysis fields are used to characterize the spatial and temporal variability of the dcsw and explore potential forcing scenarios that can lead to its formation in 2010 the dcsw did not enter the chukchi sea through bering strait hence it had to be formed locally on the shelf two distinct forcing mechanisms are considered 1 mixing of very warm alaskan coastal water with the cold pww when the two water masses come in contact in the energetic alaskan coastal current and 2 warming of pww when it experiences solar heating within the coastal polynya in the northeastern chukchi sea during the spring melt season finally we explore the conditions under which the springtime polynya has formed over the past three decades as it relates to the formation of dcsw

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

upwelling on the continental slope of the alaskan beaufort sea storms ice and oceanographic response 1 the characteristics of pacific born storms that cause upwelling along the beaufort sea continental slope the oceanographic response and the modulation of the response due to sea ice are investigated in fall 2002 a mooring array located near 152w measured 11 significant upwelling events that brought warm and salty atlantic water to shallow depths when comparing the storms that caused these events to other aleutian lows that did not induce upwelling interesting trends emerged upwelling occurred most frequently when storms were located in a region near the eastern end of the aleutian island arc and alaskan peninsula not only were these storms deep but they generally had northward tending trajectories while the steering flow aloft aided this northward progression the occurrence of lee cyclogenesis due to the orography of alaska seems to play a role as well in expanding the meridional influence of the storms in late fall and early winter both the intensity and frequency of the upwelling diminished significantly at the array site it is argued that the reduction in amplitude was due to the onset of heavy pack ice while the decreased frequency was due to two different upper level atmospheric blocking patterns inhibiting the far field influence of the storms

varieties of shallow temperature maximum waters in the western canadian basin of the arctic ocean the properties and spreading pathways of shallow temperature maximum waters stms in the western canadian basin are investigated using ctd and mooring data obtained in 1997 98 as part of the sheba surface heat budget of the arctic ocean drift experiment and available historical data three distinct varieties of stm are recognized on the basis of salinity range 1 surface mixed layer water smlw with s 32 psu these stms carry sufficient heat within the upper layers of the ocean to significantly affect the rates of ice cover and decay for example during the winter of 1997 98 anomalously warm stm 0 c originating from ecsw was observed to spread northwards along the northwind ridge and chukchi plateau where the maximum reduction of the ice covers was subsequently observed in late summer 1998 maslanik et al 1999 regional climate variability and ice cover in the western canadian basin are thus affected not only by anomalous atmospheric circulation patterns but also by the circulation of upper ocean water masses

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

winter mixed layer development in the central irminger sea the effect of strong intermittent wind events abstract the impact of the greenland tip jet on the wintertime mixed layer of the southwest irminger sea is investigated using in situ moored profiler data and a variety of atmospheric datasets the mixed layer was observed to reach 400 m in the spring of 2003 and 300 m in the spring of 2004 both of these winters were mild and characterized by a low north atlantic oscillation nao index a typical tip jet event is associated with a low pressure system that is advected by upper level steering currents into the region east of cape farewell and interacts with the high topography of southern greenland heat flux time series for the mooring site were constructed that include the enhancing influence of the tip jet events this was used to force a one dimensional mixed layer model which was able to reproduce the observed envelope of mixed layer deepening in both winters the deeper mixed layer of the first winter was largely due to a higher number of robust tip jet events which in turn was caused by the stee

identifying a dominant discharge for natural rivers in southern italy abstract natural rivers are subjected to continuous adjustments in response to any change in the environment these environmental changes may occur naturally as in the case of climatic variation or changes in vegetative cover or may be related to human activities including channelization damming bank protection and bridge construction identifying the value of that discharge dominant or effective discharge qd considered responsible for the main changes operated by a river has been a subject of great challenge to scientists and engineers during the last decades in fact this threshold value is largely adopted for stream management decisions for predicting the stable slope upstream of grade control structures and for designing moderate to large sized hydraulic structures in this paper a simple concept of dominant discharge corresponding to that value of qd that accounts for at least 50 of the total suspended sediment load transported by the river is introduced and discussed the work is based on a long term data set that includes measurements of monthly discharge and suspended sediment load in 27 stream gauge stations located in three different regions of southern italy the analysis showed that qd corresponds to values of the return time t ranging from 1 to 5 years confirming previous findings by other authors in similar analyses also as the values of qd were well correlated with the 1 5 year peak discharges of the same investigated rivers an empirical approach is suggested in order to estimate qd in rivers with no sediment load measurements

the encoding of wind forcing into the pacific arctic pressure head chukchi sea ice retreat and late summer barrow canyon water masses abstract barrow canyon which incises the northeast corner of the chukchi sea shelf is a major conduit through which pacific origin waters carrying nutrients biota freshwater and heat enter the arctic ocean as such barrow canyon was adopted as a long term monitoring site for the distributed biological observatory dbo in 2010 however annual hydrographic surveys across barrow canyon conducted during late august 2005 2015 along a location near what is the barrow canyon dbo survey line and in support of other research programs extend and complement the dbo hydrographic record these complementary hydrographic surveys show that volumes of pacific origin and melt water masses in barrow canyon are significantly correlated with daily sea ice areas in the eastern chukchi sea for most of the may august ice retreat season year to year differences in the timing and pattern of sea ice retreat across the chukchi sea are also shown to be well correlated with changes in seasonally averaged regional winds particularly as defined by the strength and longitudinal location of the beaufort sea high pressure cell these interdependent wind ice retreat water mass relationships are largely predicated on wind stress curl driven changes to sea level in the east siberian sea northwestern chukchi sea statistically significant correlations among wind forced sea surface heights ice areas and water mass volumes suggest that during the ice retreat season the east siberian sea western chukchi sea region serves as the arctic terminus for the pacific arctic pressure head

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

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

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

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

role of shelfbreak upwelling in the formation of a massive under ice bloom in the chukchi sea abstract in the summer of 2011 an oceanographic survey carried out by the impacts of climate on ecosystems and chemistry of the arctic pacific environment icescape program revealed the presence of a massive phytoplankton bloom under the ice near the shelfbreak in the central chukchi sea for most of the month preceding the measurements there were relatively strong easterly winds providing upwelling favorable conditions along the shelfbreak analysis of similar hydrographic data from summer 2002 in which there were no persistent easterly winds found no evidence of upwelling near the shelfbreak a two dimensional ocean circulation model is used to show that sufficiently strong winds can result not only in upwelling of high nutrient water from offshore onto the shelf but it can also transport the water out of the bottom boundary layer into the surface ekman layer at the shelf edge the extent of upwelling is determined by the degree of overlap between the surface ekman layer and the bottom boundary layer on the outer shelf once in the ekman layer this high nutrient water is further transported to the surface through mechanical mixing driven by the surface stress two model tracers a nutrient tracer and a chlorophyll tracer reveal distributions very similar to that observed in the data these results suggest that the biomass maximum near the shelfbreak during the massive bloom in summer 2011 resulted from an enhanced supply of nutrients upwelled from the halocline seaward of the shelf the decade long trend in summertime surface winds suggests that easterly winds in this region are increasing in strength and that such bloom events will become more common

the east greenland spill jet high resolution hydrographic and velocity measurements across the east greenland shelf break south of denmark strait have revealed an intense narrow current banked against the upper continental slope this is believed to be the result of dense water cascading over the shelf edge and entraining ambient water the current has been named the east greenland spill jet it resides beneath the east greenland irminger current and transports roughly 2 sverdrups of water equatorward strong vertical mixing occurs during the spilling although the entrainment farther downstream is minimal a vorticity analysis reveals that the increase in cyclonic relative vorticity within the jet is partly balanced by tilting vorticity resulting in a sharp front in potential vorticity reminiscent of the gulf stream the other components of the irminger sea boundary current system are described including a presentation of absolute transports

barrow canyon volume heat and freshwater fluxes revealed by long term mooring observations between 2000 and 2008 1 barrow canyon in the northeast chukchi sea is a major conduit for pacific water to enter the interior arctic basins assemblies of annual september 2000 to august 2008 temperature salinity and velocity data acquired from a mooring array in the mouth of barrow canyon and high resolution hydrographic and velocity transects along the mooring array in 2002 2010 and 2011 have enabled a direct computation of volume heat and freshwater fluxes annual mean volume transport through barrow canyon was 0 45 sv which consisted of 0 44 sv of pacific water and 0 01 sv of atlantic water annual mean pacific water transport through barrow canyon represents 55 of the long term mean pacific water inflow through the bering strait during summer more of the pacific inflow was advected to an eastern path as the alaskan coastal current that flows along the alaskan coast to barrow canyon the freshwater flux through barrow canyon was 904 km3 yr which is equivalent to 5 of the freshwater content of the canada basin the annual averaged heat flux displayed substantial interannual variability ranging from 0 93 to 3 02 tw which could melt 88 000 290 000 km2 of 1 m thick ice a relationship exists between the measured barrow canyon transport and local winds such that under southerly winds the northward flow of water through the canyon increases such wind conditions are induced by the weaker sea level pressure contrast between the arctic and north pacific caused by a decrease in the pressure over the arctic and an increase over the north pacific

evolution and dynamics of the flow through herald canyon in the western chukchi sea abstract the flow of summer and winter pacific water masses through herald canyon is investigated using data from a high resolution hydrographic velocity survey conducted in summer 2004 the survey was part of the russian american long term census of the arctic rusalca program and consisted of four cross canyon transects occupied over a 2 day period at the time of the survey dense winter water was entering the western side of the canyon from the chukchi sea flowing alongside a poleward jet of summer water on the canyon s eastern flank as the dense water progressed northward it switched sides of the canyon and underwent a sudden increase in layer thickness this coincided with vertical mixing near the interface of the winter and summer water producing a new water mass mode exiting the canyon all of these features are consistent with the notion of hydraulic activity occurring in the canyon a three layer hydraulic theory is applied to the flow which suggests that it is supercritical and that hydraulic control is likely a lock exchange formulation accurately predicts the northward transport of the winter water the origin of the winter water and the manner in which it drains into the canyon is investigated using satellite ice concentration data atmospheric re analysis fields historical in situ data and a simple circulation model finally the fate of the pacific water exiting the canyon and its connection to the chukchi shelfbreak current is discussed

a comparison between late summer 2012 and 2013 water masses macronutrients and phytoplankton standing crops in the northern bering and chukchi seas abstract survey data from the northern bering and chukchi sea continental shelves in august september 2012 and 2013 reveal inter annual differences in the spatial structure of water masses along with statistically significant differences in thermohaline properties chemical properties and phytoplankton communities we provide a set of water mass definitions applicable to the northern bering and chukchi continental shelves and we find that the near bottom bering chukchi summer water bcsw was more saline in 2012 and alaskan coastal water acw was warmer in 2013 both of these water masses carried higher nutrient concentrations in 2012 supporting a larger chlorophyll a biomass that was comprised primarily of small

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

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

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

optical properties and molecular diversity of dissolved organic matter in the bering strait and chukchi sea abstract changes in the molecular composition of dissolved organic matter dom and its light absorbing chromophoric component cdom are of particular interest in the arctic region because of climate change effects that lead to warmer sea surface temperatures and longer exposure to sunlight we used continuous uv vis uv vis spectroscopy excitation emission matrix fluorescence and ultrahigh resolution mass spectrometry during a transect from the aleutian islands in the bering sea to the chukchi sea ice edge through bering strait to determine the variability of dom and cdom these data were combined with discrete sampling for stable oxygen isotopes of seawater in order to evaluate the contributions of melted sea ice versus runoff to the dom and cdom components this study demonstrated that high geographical resolution of optical properties in conjunction with stable oxygen ratios and non targeted ultrahigh resolution mass spectrometry was able to distinguish between different dom sources in the arctic including identification of labile dom sources in bering strait associated with high algal blooms and sampling locations influenced by terrestrially derived dom such as the terrestrial dom signal originating from arctic rivers and dirty anchor sea ice results of this study also revealed the overall variability and chemodiversity of arctic dom present in the bering and chukchi seas

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

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

generation of submesoscale vortices a new mechanism small scale intense vortices composed of water with anomalous values of quasi conservative tracers have been observed in many oceans they are particularly numerous in the beaufort gyre of the arctic ocean possible mechanisms responsible for the generation of these features are examined conservation of temperature salinity and nutrients requires that beaufort sea vortices be created from water that flows into the arctic ocean from the pacific ocean across the broad shallow chukchi sea much of this water passes through barrow canyon near point barrow alaska observations in the canyon show the generation of vortices of approximately the same size as those observed in the beaufort sea barrow canyon is therefore a likely site for the generation of beaufort sea vortices most observed beaufort sea vortices have a central potential vorticity near zero because of a relative vorticity close to their chukchi sea source water is typically stratified with little relative vorticity so that its potential vorticity is nonzero a key step in the generation of the vortices is therefore the reduction of the potential vorticity of chukchi sea water to nearly zero it is proposed that this occurs through the action of frictional torques occurring as the chukchi sea water flows through barrow canyon rather than througji the action of vertical mixing because this flow is driven by a downstream pressure gradient it is concentrated on the right hand wall of the canyon by the coriolis force the frictional torques thus preferentially reduce the potential vorticity of the fluid anticyclonic vortices are therefore preferentially generated it is suggested that a similar scenario may play a role in the generation of submesoscale vortices containing water from the mediterranean and labrador seas