alongshelf variability of inner shelf circulation along the central oregon coast during summer the spatial and temporal variability of inner shelf circulation along the central oregon coast during the 2004 upwelling season is described using a 70 km long array of moorings along the 15 m isobath circulation at three stations located onshore of a submarine bank differed from that of a station north of the bank despite the relatively uniform wind forcing and inner shelf bathymetry present during upwelling favorable winds strong southward alongshelf flow occurred north of the bank no alongshelf flow occurred onshore of the northern part of the bank and increasing southward flow occurred onshore of the southern part of the bank during downwelling favorable winds strong northward flow occurred in the inner shelf onshore of the bank while weak flow occurred north of the bank these alongshelf differences in inner shelf circulation were due to the effects of the bank which isolated the inner shelf onshore of the bank from the regional upwelling circulation that was evident at the northernmost station as a result circulation onshore of the bank was drivenprimarily by local wind forcing whileflow north of the bank was only partiallydriven by local winds a secondary mode of variability attributed to the movement of the regional upwelling jet due to remote forcings contributed the bulk of the variability observed north of the bank with the time dependent wind forcing present acceleration was an important term in the depth averaged alongshelf momentum equation at all stations during upwelling bottom stress and acceleration opposed the wind stress north of the bank while bottom stress was weaker onshore of the bank where the across shelf momentum flux and the alongshelf pressure gradient balanced the residual of the acceleration and stresses during downwelling waters onshore of the bank surged northward at magnitudes much larger than that found north of the bank these spatial variations developed as the season progressed and the regional upwelling circulation intensified explaining known variations in growth and recruitment of nearshore invertebrate species

last abundant appearance datum of hemidiscus karstenii driven by climate change abstract the last abundant appearance datum of the endemic southern ocean diatom hemisdiscus karstenii jouse is dated at around 190 000 years before present which provides a robust and convenient biostratigraphic marker to late pleistocene paleoceanographic studies however no prior studies have sought to understand what processes may have driven h karstenii to extinction we here present the first morphometric investigation of h karstenii over marine isotope stage mis 10 to 6 355 000 years to 150 000 years the combination of these data to records of h karstenii absolute abundances fragilariopsis kerguelensis biometry and absolute abundances and southern high latitude air and ocean temperatures over the past 355 000 years suggests that h karstenii populations reduced their mean size and productivity in response to the rapid drop in temperatures across the mis 7 to mis 6 glacial inception this prolonged cooling event may have pushed h karstenii to its adaptive limit until it could not sustain physiological viability the repetitive occurrence of very cold events during the early mis 6 may have additionally prevented surviving populations of h karstenii from re establishing abundant communities leading to extinction late in mis 6

glacial valve size variation of the southern ocean diatom fragilariopsis kerguelensis preserved in the benguela upwelling system southeastern atlantic abstract the valve size variations of the southern ocean so diatom fragilariopsis kerguelensis from the sediments of antarctic polar front and subantarctic front were shown to be strongly correlated with iron availability at the glacial interglacial timescale however recent evidence from the subtropical region of the so has suggested sea surface temperature to be a key controlling factor by mediating silica uptake other than the iron availability we present here the first record of f kerguelensis size variation in core geob3606 1 collected in the benguela upwelling system bus se atlantic 25 28 s 13 05 e where f kerguelensis valves were preserved during the glacial period 68 30 ka as a consequence of silicic acid leakage from polar to mid latitudes our study presents the first record of diatom morphology variations of f kerguelensis from a mid latitude core location to test the previous hypotheses proposed for so our results demonstrate that f kerguelensis valves at geob3606 1 were almost half of the mean size of specimens compared to the so downcore records further f kerguelensis valves were smaller and more abundant during early marine isotope stage mis 3 and conversely larger and less abundant during mis4 and late mis3 however such patterns are not supported by the linear regression analyses suggesting that iron availability could have mediated the size changes of f kerguelensis rather than the species productivity during 68 30 ka these findings agree with the recently gained knowledge on the life cycle patterns of f kerguelensis related to reproduction strategies cell size range and formation of initial cells

mapping the u s west coast surface circulation a multiyear analysis of high frequency radar observations signals with phase speeds of o 10 and o 100 to 300 km day 1 and time scales of 2 to 3 weeks the signals with slow phase speed are only observed in southern california it is hypothesized that they are scattered and reflected by shoreline curvature and bathymetry change and do not penetrate north of point conception the seasonal transition of alongshore surfacecirculationforcedbyupwelling favorablewindsandtheirrelaxationiscapturedinfine detail submesoscaleeddies identifiedusingflowgeometry haverossbynumbersof0 1to3 diameters in the range of 10 to 60 km and persistence for 2 to 12 days the hfr surface currents resolve coastal surface ocean variability continuously across scales from

moored wind temperature and current observations made during coastal ocean dynamics experiments 1 and 2 over the northern california continental shelf and upper slope moored observations of winds currents and temperature made over the northern california shelf and upper slope during the 1981 and 1982 upwelling seasons as part of the coastal ocean dynamics experiment code are described in both field experiments code 1 and code 2 the onset of the upwelling season is triggered by the strengthening of the north pacific high off northern california and signalled by the presence of water colder than 9 c near the bottom over the shelf vertical temperature stratification over the shelf is reduced during active upwelling local winds and subtidal currents over the shelf are strongly polarized in the alongshelf direction and the mean wind stress is directed equatorward response of alongshelf currents to wind forcing is similar at all depths over the shelf the response of the cross shelf current is more complex in the surface layer offshelf flow is significantly and positively correlated with the upwelling favorable alongshelf wind stress beneath this layer a weak return flow exists the thickness of the upper mixed layer varies greatly reaching 60 m during upwelling events thus direct wind forcing affects a substantial fraction of the water over the shelf low frequency wind stress current and temperature fields are adequately described by a few energetic empirical orthogonal functions with simple spatial structure the most energetic mode typically accounts for 75 or more of the variance of wind stress and temperature over the middle and inner shelf the most energetic current mode accounts for 90 or more of the variance is dominated by he alongshelf component and veers to the left with depth the low frequency alongshelf flow fluctuations are quasi barotropic with some vertical shear but no reversal with depth vertical shear in alongshelf current and the cross shelf density gradient obey the thermal wind relation the simple structure of the subdiurnal currents allow estimation of the alongshelf volume transport between the 60 and 130 m isobaths through three cross shelf transects in code 2 volume transport over the shelf is often nearly two dimensional but occasional large differences indicate significant mass exchange between the shelf and the adjacent upper slope correlation of low frequency currents and alongshelf wind stress shows the response of alongshelf current to be maximum near the surface and near midshelf where a 15 cm 1 alongshelf flow lags a 1 dyn cm 2 alongshelf wind stress by the order of 10 hours currents over the upper slope are not significantly correlated with local wind alongshelf transport over the shelf is highly correlated with local wind stress explaining 80 of the variance in the low frequency transport during code 2 volume transport is best correlated with wind stress approximately 30 km to the south winds in the code area during spring and summer are characterized by strong and persistent upwelling favorable winds interrupted by shorter periods of weak winds regression analysis indicates that in the absence of wind a poleward barotropic current jet exists over the shelf with a maximum amplitude over the inner shelf in the code area an upwelling favorable wind counters this jet over the shelf so that the alongshore flow is everywhere equator ward during strong wind events since the maximum response to wind forcing is found at midshelf and near surface the mean current over the upwelling season is strongly sheared in both the vertical and cross shelf directions mean flow over the outer shelf is surface intensified and is directed offshelf and equatorward while the deeper flow at midshelf and through most of the water column over the inner shelf is directed poleward

failure to bloom intense upwelling results in negligible phytoplankton response and prolonged co2 outgassing over the oregon shelf during summer upwelled water with elevated co2 partial pressure pco2 and nutrients outcrops over the oregon or inner shelf as this water transits across the shelf high rates of primary production fueled by the upwelled nutrients results in net atmospheric co2 drawdown upwelled source waters typically have pco2 approaching 1000 atm that is then reduced to 200 atm for almost the entire month of july 2008 strong and persistent upwelling brought cold 8 c saline 33 5 high pco2 600 atm water to our midshelf buoy site and high pco2 water was broadly distributed over the shelf chlorophyll levels as a proxy for phytoplankton biomass were low 2 mg m 3 on the shelf during the period of most intense upwelling and satellite data showed no evidence of a downstream phytoplankton bloom a small chlorophyll increase to 4 mg m 3 was observed at our buoy site following a decrease in the strength of southward wind stress 10 days after upwelling initiated chlorophyll levels further increased to 10 mg m 3 only after a cease in upwelling these higher levels were coincident with the appearance of water masses having temperature and salinity properties distinct from recently upwelled water we suggest that rapid offshore transport and subsequent subduction before phytoplankton populations could respond is the most likely explanation for the persistent low chlorophyll and elevated surface water pco2 throughout the july upwelling event this mechanism likely dominates under conditions of strong and persistent upwelling favorable winds that coincide with close proximity of low density offshore waters which may have implications for the biogeochemical functioning of this system under future climate scenarios

time dependent wind driven flow over a shallow midshelf submarine bank 1 during summer 2001 high resolution hydrographic velocity and bio optical surveys were conducted over heceta bank off central oregon north of the bank upwelling over simple bottom topography exhibited a classic response with a midshelf baroclinic coastal jet and upwelled isopycnals the coastal upwelling jet follows the bank topography as it widens offshore before reaching the southern end of the bank where the shelf break turns almost 90 back toward the coast the ensuing adjustment involves the offshelf transport of coastal water and the material it contains the jet meanders anticyclonically in the lee of the bank before resuming its equatorward path seaward of the shelf break a pool of high chlorophyll 15 mg m 3 near surface water is found in the low velocity lee region created by the bank a low temperature high salinity bottom water pool supplied primarily from the south lies over the inshore region of the bank this bottom pool is up to 40 m thick and contains elevated levels of suspended material by creating an east west perturbation in the coastal upwelling front the flow topography interaction introduces an alongshore pressure gradient when southward upwelling favorable winds relax this alongshore pressure gradient can drive flow back to the north this leads to northward flow on the inshore side of the bank ultimately setting up the potential for recirculation around the entire bank complex on a timescale of about 10 days strong northward winds during summer lead to downwelling within 15 km of the coast accompanied by significant 0 2 m s 1 wind driven northward currents

a record of pleistocene diatom preservation from the amundsen sea west antarctica with possible implications on silica leakage article i nfo accumulation of fossil diatoms in marine sediments is variably affected by the production and dissolution of diatom frustules across space and time no quantitative proxy exists for estimating the amount of silica lost to dissolution in southern ocean sediment cores to address this gap cultured valves of fragilariopsis kerguelensis the dominant planktonic diatom in the pleistocene to recent southern ocean were dissolved progressively under controlled laboratory conditions expansion and eventual conjoining of the areolae of f kerguelensis advances through several phases which are presented herein as a measure of diatom dissolution in order to evaluate the validity of laboratory methods this proxy is applied to sediments from piston core ps58 254 from the amundsen sea dissolution induced degradation morphologies from laboratory experiments are seen to be identical to those preserved naturally in sediments thus suggesting the laboratory conditions accurately reflect the natural process of dissolution these resultsrepresentthe firstapplication of afullyquantitativeproxyfordiatomdissolution tosouthernocean sediments revealing that meaningful paleoceanographic data can be generated via taphonomic analysis of diatom valves intensity of diatom dissolution in core ps58 254 does not correspond to the relative abundance of any diatom species clay mineralogy or linear sedimentation rates however a correlation does exist between glacial cyclicity and diatom dissolution indicating that variation in average wall thickness and susceptibility to dissolution reflects primary conditions during formation of the silica wall transit through the water column and eventual deposition higher overall silica dissolution is observed during each glacial period and enhanced silica preservation during interglacials this result is consistent with the predictions of the silicic acid leakage hypothesis salh whereby reduced rates of si usage in the southern ocean lead to shifts in marine primary productivity in the tropics from coccolithophoriddominance duringinterglacialstodiatomdominanceduringglacials thiswouldfuela decrease in atmospheric pco2duringglacials silica acidleakage isdrivenbya decreaseinthe si nratioofdiatoms caused by increased iron input to glacial aged southern ocean waters this resulted in more lightly silicified diatom valves in the southern ocean which dissolved more quickly in the upper water column thereby maintaining the high silica content of glacial aged so waters and allowing for export of si to upwelling zones in the lower latitudes

coastal wind driven circulation in the vicinity of a bank part ii modeling flow over the heceta bank complex on the oregon coast abstract this study investigates wind driven circulation in the vicinity of the heceta bank complex along the oregon shelf numerical experiments forced with steady winds 0 1 pa are conducted upwelling and downwelling cases are compared the asymmetric bank bathymetry is the only configurational difference from the symmetric bank runs analyzed in part i whitney and allen upwelling favorable winds generate an upwelling front and southward baroclinic jet model results indicate the upwelling jet is centered on the 100 m isobath along the straight shelf the jet follows this isobath offshore around the northern part of the bank but separates from sharply turning isobaths in the southern half and flows over deeper waters the jet turns back toward the coast farther downstream inshore of the main jet currents reverse and flow back onto the bank these reversed currents turn southward again at the bank center and join a secondary southward coastal upwelling jet this secondary coastal jet converges wi

antarctic sea ice and palaeoproductivity variation over the last 156 000 years in the indian sector of southern ocean abstract antarctic sea ice plays a vital role in global climate via its impact on ocean circulation biological productivity and co2 partitioning between the ocean and the atmosphere however very little is known about its past history especially in the southwestern indian sector of the southern ocean so we here provide new quantitative records of winter sea ice concentration wsic and duration wsid sea surface temperatures sst and productivity in sediment core sk 200 33 55 s 45 e from the permanently open ocean zone over the last 156 000 years the new records combined with regional records indicate that the hydrological structures migrated northward by a few degrees of latitude during all glacial periods with the southern antarctic circumpolar current front reaching the core site the antarctic polar front located at 46 s and the winter sea ice wsi probably extending to 49 s in contrast hydrological fronts and wsi edge migrated poleward by a couple of degrees of latitude during the early holocene and last interglacial comparison to sst and wsi records from different sectors of the so suggests higher amplitude variations in wsi in the atlantic sector as compared to the indian and western pacific sectors over the last glacial interglacial cycle which we attribute to the presence of the weddell gyre transporting far to the north the sea ice produced in the weddell sea the new records also suggest a drop in productivity in the pooz during glacial periods probably related to greater wsi extent and reduced growing season

a nested grid model of the oregon coastal transition zone simulations and comparisons with observations during the 2001 upwelling season 1 the oregon coastal transition zone octz extends several hundred kilometers offshore where shelf flows interact with the northern california current a primitive equation numerical ocean model is used to study the upwelling circulation in this region from 1 may to 1 november 2001 this octz model obtains initial and boundary conditions from a larger scale model of the california current system and forcing from a regional atmospheric model product the model results are compared with extensive in situ and remotely sensed data and the model is found to provide a realistic representation of flows both over the shelf and in the broader octz simulation of coastal sea level and shelf currents over the complex topography of the central oregon coast is improved quantitatively relative to previous regional models a particularly significant qualitative improvement is realistic representation of coastal jet separation and eddy formation offshore of cape blanco three dimensional lagrangian analysis of water parcel displacement shows that the surface waters inshore of the separated jet are upwelled from near the bottom along the shelf as far north as 45 5 n a large eddy which incorporates some of this upwelled water and carries it farther westward forms offshore in the late summer ensemble simulations show a distinction between the strongly deterministic response to wind forcing over the shelf and the more unstable less predictable jet separation and offshore eddy formation processes in the region near cape blanco

ensemble based estimates of the predictability of wind driven coastal ocean flow over topography abstract the predictability of coastal ocean circulation over the central oregon shelf a region of strong wind driven currents and variable topography is studied using ensembles of 50 day primitive equation ocean model simulations with realistic topography simplified lateral boundary conditions and forcing from both idealized and observed wind time series representative of the summer upwelling season the main focus is on the balance relevant to practical predictability between deterministic response to known or well predicted forcing uncertainty in initial conditions and sensitivity to instabilities and topographic interactions large ensemble and single simulation variances are found downstream of topographic features associated with transitions between along isobath and cross isobath flow which are in turn related both to the time integrated amplitude of upwelling favorable wind forcing and to the formation of small scale eddies simulated predictability experiments are conducted and model fo

on the spatial structure of coastal circulation off newport oregon during spring and summer 2001 in a region of varying shelf width 1 a time series of hourly surface current maps in the shelf waters off newport oregon was made during april september 2001 using five seasonde hf current mappers during coastal advances in shelf transport coast the surface currents responded rapidly to the changing winds in repeated patterns that were strongly affected by bottom topography an equatorward current jet repeatedly formed in response to upwelling winds its strength but not its trajectory covarying with the meridional wind stress near cape foulweather 44 8 n where the shelf begins to widen the jet rotates weakens and trends offshore to the south first along then across the isobaths below cape foulweather inshore of the jet a lee region of generally weak currents was commonly observed the equatorward jet core was most commonly observed near the 80 m isobath between 45 0 n and 44 4 n but transited offshore between spring and summer over heceta bank at newport 44 6 n it was rarely observed less than 8 km from the coast a second inshore equatorward jet previously unknown was observed repeatedly south of waldport 44 4 n sustained downwelling wind episodes produced poleward currents though less responsively north of cape foulweather strongest poleward flow was generally trapped near the coast surface currents were correlated with the northward wind except regionally far from shore over heceta bank responding within half a day response to the wind varies spatially being intensified in the narrow shelf northern region the equatorward jet persists through periods of zero wind forcing coastal sea level covaries with the meridional wind and the primary mode of ocean current response

the spatial structure of tidal and mean circulation over the inner shelf south of martha s vineyard massachusetts abstractthe spatial structure of the tidal and background circulation over the inner shelf south of martha s vineyard massachusetts was investigated using observations from a high resolution high frequency coastal radar system paired with satellite ssts and in situ adcp velocities maximum tidal velocities for the dominant semidiurnal constituent increased from 5 to 35 cm s 1 over the 20 km wide domain with phase variations up to 60 a northeastward jet along the eastern edge and a recirculation region inshore dominated the annually averaged surface currents along with a separate along shelf jet offshore owing in part to this variable circulation the spatial structure of seasonal sst anomalies had implications for the local heat balance cooling owing to the advective heat flux divergence was large enough to offset more than half of the seasonal heat gain owing to surface heat flux tidal stresses were the largest terms in the mean along and across shelf momentum equations in the area of the reci

intensified diurnal tides along the oregon coast abstractintensified diurnal tides are found along portions of the oregon shelf u s west coast based on analyses of high frequency hf radar surface current data and outputs of a 1 km resolution ocean circulation model the k1 tidal currents with magnitudes near 0 07 m s 1 over a wider part of the shelf heceta bank complex 44 44 5 n previously predicted by erofeeva et al are confirmed here by newly available hf radar data intensified diurnal tides are also found along the narrow shelf south of heceta bank in the close vicinity of cape blanco 42 8 n diurnal tidal currents k1 and o1 constituents combined may reach 0 3 m s 1 appreciable differences in diurnal tide intensity are found depending on whether the model is forced with tides and winds tw or only tides also diurnal variability in wind forcing is found to affect diurnal surface velocities for the case forced by tides alone results strongly depend on whether the model ocean is stratified tides only stratified tos or not t

poleward propagating subinertial alongshore surface currents off the u s west coast 1 the network comprising 61 high frequency radar systems along the u s west coast uswc provides a unique high resolution and broad scale view of ocean surface circulation subinertial alongshore surface currents show poleward propagating signals with phase speeds of o 10 and o 100 300 km d 1 that are consistent with historical in situ observations off the uswc and that can be possibly interpreted as coastally trapped waves ctws the propagating signals in the slow mode are partly observed in southern california which may result from scattering and reflection of higher mode ctws due to curvature of shoreline and bathymetry near point conception california on the other hand considering the order of the phase speed in the slow mode the poleward propagating signals may be attributed to alongshore advection or pressure driven flows a statistical regression of coastal winds at national data buoy center buoys on the observed surface currents partitions locally and remotely wind forced components isolates footprints of the equatorward propagating storm events in winter off the uswc and shows the poleward propagating signals year round

morphometric variability in the diatom fragilariopsis kerguelensis implications for southern ocean paleoceanography abstract diatoms play a central role in the ecosystem of the southern ocean where they represent the main producers and carriers of organic carbon and dissolved silicon towards the deep ocean variability in space and time of the size of the most abundant species fragilariopsis kerguelensis may directly impact the way this ecosystem functions and also affect the nutrient balance of the global ocean as important water masses e g the antarctic intermediate water get their nutrient signature in this area we used a biometric approach and analyzed the size variability of f kerguelensis valves in sixty four surface sediment samples from the southern ocean in sediment trap samples from a mooring site pf3 at the antarctic polar front apf and along a nearby piston core ps1654 2 the average length and valve area of f kerguelensis displayed a distinct increase in the proximity of the apf and lower values to the north and south of it and also changed markedly over seasonal cycles as diatom blooms and nutrient availability waxe and wane the last glacial to interglacial transition also witnesses important changes in the general shape and valve size of f kerguelensis with specimens from glacial intervals being ca 30 larger than their interglacial counterparts 195 versus 150 m 2 valve area a sharp peak in average area and a very specific valve morphology correspond to the first signs of deglaciation and concurring sst sea surface temperature increase and sea ice retreat the latter together with melting icebergs may have contributed dissolved iron to surface waters the highest average sizes during glacial intervals are higher than what found anywhere in the southern ocean today the newly proposed proxy valve area and shape of f kerguelensis may thus prove useful for the reconstruction of the past position and nutrient characteristics of the apf and opal belt a region characterized by high production and export of biogenic silica in a particularly sensitive and dynamic area such as the southern ocean

large scale structure of the spring transition in the coastal ocean off western north america past measurements off the coast of central oregon and washington have shown that the rapid change from northward monthly mean winter winds to southward summer winds forces a spring transition of the coastal ocean sea levels and temperatures drop and mean surface currents shift from northward to southward current and water temperature data from 35 n to 48 n from 1981 and 1982 and sea level and wind stress data from 1971 1975 and 1980 1983 show the transition to have a large alongshore scale typically 500 to 2000 km the large scale wind stress appears to be the forcing mechanism at latitudes north of approximately 37 n south of 37 n sea level usually falls more gradually before the northern transition event both wind and sea level events generally progress from south to north over a 3 to 10 day period but this is not always true several aspects of the spring transition reflect coastal trapped wave dynamics previous studies at 45 n found persistent vertical shear of the southward summer current associated with a cross shelf density gradient during 1982 the shear and the density front develop over the shelf break immediately after the transition at 43 n and to the south but they are much less persistent than at 48 n the stronger winds between 38 n and 42 n and the narrower shelf result in an offshore displacement of the density front and vertical shear past the shelf break leaving the water over the shelf less stratified and more subject to barotropic reversals of the current than that farther north where the front stays closer to the coast

time dependent wind driven flow over a shallow midshelf submarine bank wind driven circulation and ecosystem response off the oregon coast results from the coastal ocean advances in shelf transport coast program during summer 2001 high resolution hydrographic velocity and bio optical surveys were conducted over heceta bank off central oregon north of the bank upwelling over simple bottom topography exhibited a classic response with a midshelf baroclinic coastal jet and upwelled isopycnals the coastal upwelling jet follows the bank topography as it widens offshore before reaching the southern end of the bank where the shelf break turns almost 90 back toward the coast the ensuing adjustment involves the offshelf transport of coastal water and the material it contains the jet meanders anticyclonically in the lee of the bank before resuming its equatorward path seaward of the shelf break a pool of high chlorophyll 15 mg m 3 near surface water is found in the low velocity lee region created by the bank a low temperature high salinity bottom water pool supplied primarily from the south lies over the inshore region of the bank this bottom pool is up to 40 m thick and contains elevated levels of suspended material by creating an east west perturbation in the coastal upwelling front the flow topography interaction introduces an alongshore pressure gradient when southward upwelling favorable winds relax this alongshore pressure gradient can drive flow back to the north this leads to northward flow on the inshore side of the bank ultimately setting up the potential for recirculation around the entire bank complex on a timescale of about 10 days strong northward winds during summer lead to downwelling within 15 km of the coast accompanied by significant 0 2 m s 1 wind driven northward currents

the relative importance of wind strength and along shelf bathymetric variations on the separation of a coastal upwelling jet abstract a high resolution numerical model with idealized topography is used to investigate the degree to which a coastal upwelling jet separates from the shelf as it flows around a submarine bank depending on the wind strength and the horizontal scale of the bank experiments were run using several wind forcing magnitudes and submarine banks with different geometries so as to explore a wide range of the flow strength as measured by the rossby number ro and the ratio of the squares of the internal rossby radius of deformation and curvature of the topography as denoted by the burger number bu the intensity of the jet separation is strongly dependent on both parameters with maximum separation with increasing ro and bu close to 1 when large amounts of upwelled water are exported toward deeper waters for small bu separation is minimal and independent of ro for high ro the degree of separation decreases at large bu since the bank acts only as a small perturbation to the flow term balances in the a

residual and tidal circulation revealed by vhf radar surface current measurements in the southern channel isles region english channel abstract two very high frequency radars vhfrs operating in the southern channel isles region english channel in february march 2003 provided a continuous 27 day long dataset of surface currents at 2 km resolution over an area extending approximately 20 km offshore the tidal range in the region of study is one of the highest in the world and the coastal circulation is completely dominated by tides the radar data resolve two modes which account for 97 of the variability of the surface current velocities with the major contribution of the first mode this mode accounts for oscillating tidal currents whereas the second mode represents motions emerging from the interaction of tidal currents with capes and islands eddy in the vicinity of the point of grouin and jet south of chausey a fortnightly modulation of the modal amplitudes causes the exceptional more than 600 variability of currents which is well captured by the vhfr observations the radar data revealed that tidal circulation in the region is flood dominated with a strong asymmetry of current velocity curve wind events and fortnightly variability affect the course of tidal cycle by modifying the magnitude and duration of ebb and flood in addition to expected features of coastal circulation tidally dominated flow eddies and high wind current coupling the residual currents revealed a strong cross shore structure in the mean and a significant variability which has the same order of magnitude

estimates of sea surface height and near surface alongshore coastal currents from combinations of altimeters and tide gauges 1 present methods used to retrieve altimeter data do not provide reliable estimates of sea surface height ssh in the nearshore region resulting in a measurement gap of 25 50 km next to the coast in the present work gridded ssh fields produced by archiving validation and interpretation of satellite oceanographic data aviso in the offshore region are combined with coastal tide gauge time series of ssh to improve estimation in that gap along the west coast of the united states in the northern california current system between 40 and 45n and 123 8 and 126w to assess the increase in skill provided by this procedure the geostrophic alongshore currents calculated from the new ssh fields in the gap region are compared to three in situ nearshore current measurements resulting in correlation coefficients of 0 73 0 83 and standard deviations of the differences of 11 6 12 6 cm s substantially improved from the aviso only results when the ekman current components are estimated and added to the geostrophic currents comparisons to the 10 m deep acoustic doppler current profiler velocities are only slightly improved the ekman components make a more significant contribution when compared to hf radar surface current measurements providing correlations of 0 94 and standard deviations of the differences of 6 4 9 5 cm s these results represent a dramatic improvement in the quality of the ssh fields and estimated alongshore currents when additional realistic ssh data from the coastal region are added here we use coastal tide gauges to provide the additional ssh data but also discuss more general approaches for altimeter ssh retrievals in coastal regions where tide gauge data are not available

climate evolution at the last deglaciation the role of the southern ocean abstract two sediment sequences recovered close to and south of the present polar front 50 53 s in the atlantic sector of the southern ocean were analysed in order to evaluate the environmental evolution of the southern ocean surface over the last deglaciation and the holocene our reconstruction is based on radiocarbon dated records of diatom based sea surface temperature and sea ice proxies and planktic foraminiferal stable isotopes the onset of the deglacial warming and gradual southward retreat of the winter sea ice field between 18 and 17 cal kyr bp occurrence of a thermal reversal centered at ca 13 cal kyr bp antarctic cold reversal or acr and early holocene occurrence of the climatic optimum well correlate with climatic reconstructions available from the indian southern ocean and from antarctic ice cores time correspondence of southern ocean warming and heinrich event 1 in the north atlantic is compatible with the transmission of the climate signal from the northern to the southern hemisphere through the bipolar seesaw our data support modeling results suggesting that the northern hemisphere bolling warming and turn on of the north atlantic deep water formation are triggered by gradual warming and sea ice retreat in the southern ocean meltwater shedding into the southern ocean associated with the acr may maintain northern hemisphere warming during the allerod the development of sea surface warming and sea ice retreat is compatible with a southern ocean control on the atmospheric co2 increase during the deglaciation during the early holocene 9 7 cal kyr bp our southern core records renewed surface ocean cooling and northward readvance of the winter sea ice field such early holocene cooling is common to cores from the high latitude atlantic sector and might be brought about by expansion of the weddell gyre circulation at that time

diatom distribution in southern ocean surface sediments atlantic sector implications for paleoenvironmental reconstructions abstract a study of 230 surface sediment samples collected in the atlantic sector of the southern ocean between the southernmost weddell sea and the subtropical zone documents the modern distribution of diatoms revealing patterns of paleoenvironmental significance estimations of diatom valves per gram dry sediment display numbers of 50 200 106 in the zone of high opal burial located between the mean position of the winter sea ice edge and the polar front and maximum values of greater than 200 106 in the near shore sedimentary basins off the antarctic peninsula lowest diatom concentrations and assemblages strongly affected by dissolution were encountered in the weddell basin despite alteration of the diatom assemblages prior to their incorporation into the sediment record the biogeographic distribution and the abundance pattern of most of the 35 studied diatom species shows a close relationship with the surface hydrography water temperature these relationships can be used to estimate past surface water temperatures based on statistical treatments of the assemblages or on simple relations of species occurrences in the geological record another close link occurs between the distribution of sea ice and sea ice related diatoms

influence of varying upper ocean stratification on coastal near inertial currents the influence of varying horizontal and vertical stratification in the upper layer o 10 m associated with riverine waters and seasonal atmospheric fluxes on coastal near inertial currents is investigated with remotely sensed and in situ observations of surface and subsurface currents and realistic numerical model outputs off the coast of oregon based on numerical simulations with and without the columbia river cr during summer the directly wind forced near inertial surface currents are enhanced by 30 60 when the near surface layer has a stratified condition due to riverine water inputs from the cr comparing model results without the cr for summer and winter conditions indicates that the directly wind forced near inertial surface current response to a unit wind forcing during summer are 20 70 stronger than those during winter depending on the cross shore location which is in contrast to the seasonal patterns of both mixed layer depth and amplitudes of near inertial currents the model simulations are used to examine aspects of coastal inhibition of near inertial currents manifested in their spatial coherence in the cross shore direction where the phase propagates upward over the continental shelf bounces at the coast and continues increasing upward offshore toward surface and then downward offshore at the surface with magnitudes and length scales in the near surface layer increasing offshore this pattern exhibits a particularly well organized structure during winter similarly the raypaths of clockwise near inertial internal waves are consistent with the phase propagation of coherence showing the influence of upper layer stratification and coastal inhibition

modeling upwelling circulation off the oregon coast 1 time dependent three dimensional upwelling circulation on the continental shelf off the oregon coast is studied using a primitive equation numerical model a limited area domain with a high resolution curvilinear grid is utilized the response of the coastal ocean to forcing by observed wind stress and heat flux during the summer 2001 time period of the coastal ocean advances in shelf transport coast field experiment is investigated model results are compared to coast current and hydrographic measurements the shelf velocity and density fields are generally characterized by the presence of a southward alongshore coastal jet with an upwelling density front on the shoreward side of the jet the large variability in shelf topography associated with heceta bank exerts a major influence on the shelf velocity and density fields over the bank the alongshore coastal jet is displaced offshore and colder upwelled water extends farther from the coast northward mean flow and upward motion are found inshore of the jet three dimensional flow structures in response to variable shelf bottom topography are presented and an analysis of time and space dependent alongshore momentum balances is applied to clarify the associated dynamics in general northward pressure gradients set up over the bank during southward upwelling winds accelerate currents on the inshore side of the jet northward when the winds relax analysis of term balances in the depth averaged equation for potential temperature shows that during upwelling across shore advection makes the major contribution to cooling over most of the region except inshore over heceta bank where alongshore advection also plays a significant role

near surface dynamics of a separated jet in the coastal transition zone off oregon 1 three dimensional circulation in the coastal transition zone ctz off oregon is studied using a 3 km resolution model based on the regional ocean modeling system the study period is spring and summer 2002 when extensive observations were available from the northeastern pacific component of the global ocean ecosystems dynamics project our main focus is on near surface transports particularly in an area off cape blanco where an energetic coastal current is separated in the ctz comparisons with available observations velocities from midshelf moorings surface velocities from high frequency radars satellite sea surface temperature maps along track sea surface height altimetry and seasoar hydrography show that the model reproduces qualitatively correctly the flow structure and variability in the study area the near surface flow behavior during 26 july to 21 august a late summer time period of strong time variable southward winds is examined during that period the coastal jet separates from the continental shelf around cape blanco 43 n the energetic separated jet continues to flow southward in a near coastal region between 42 2 n and 43 n it subsequently turns around 42 n to flow westward offshore past 127 w relatively vigorous up and downwelling is found concentrated in the region of the separated jet frontogenesis secondary circulation nonlinear effects of the relative vorticity on the ageostrophic ekman transport and submesoscale instabilities contribute to the vertical circulation within the jet vertical velocities are found to reach 50 m d 1 in the offshore part of the jet and 100 m d 1 in the near coastal part where the jet is aligned with the wind direction

on the accuracy of hf radar surface current measurements intercomparisons with ship based sensors high frequency hf radar systems can provide periodic two dimensional vector current estimates over an area approaching 1000 km as the use of these hf systems has gained wider acceptance a number of attempts have been made to estimate the accuracy of such systems however comparisons of hf radar current estimates with in situ sensors are difficult to interpret since hf systems measure currents averaged over an area of 1 km 2 and to a depth of only 50 cm while in situ sensors measure currents at a point and somewhat greater depths 1 to 10 m previous studies of the accuracy of hf radar technology have thus attributed the differences observed between hf radar and in situ sensors to an unknown combination of vertical shear horizontal inhomogeneity in situ instrument errors and hf radar system errors this study examines the accuracy of hf radar current measurements using data from the 1993 high resolution remote sensing experiment conducted off cape hatteras north carolina data from four shipborne in situ current meters are compared with data from an ocean surface current radar oscr a commercial current measuring radar we attempt to discern the predominant sources of error in these data by using multiple simultaneous measurements from different sensors and by examining the variation of observed current differences as a function of location the results suggest an upper bound on the accuracy of the oscr derived radial currents of 7 to 8 cm s the measurement of near surface currents in the coastal environ ment is an important problem

intensified upwelling over a widened shelf in the northeastern south china sea 1 observational and three dimensional modeling studies reveal that the intensified upwelling in the northeastern south china sea nscs is formed as a result of intensified upslope advection of dense deep waters that cross the middle shelf toward the inner shelf over a distinctly eastward widened shelf the strongest advection occurs over the converging isobaths near the head of the widened shelf as these dense deep waters advance shoreward they are advected downstream by the quickly developed upwelling current over the inner shelf and eventually outcropped at the lee of a coastal cape dynamically the shoreward cross isobath transport over the widened shelf is geostrophically enhanced by a quasi barotropic negative westward along isobath pressure gradient force as a result of the net rate of the momentum influx and by an intensified bottom frictional transport owing to the flow confluence near the head of the widened shelf a negative pressure gradient also exists at the lee of the coastal cape over the inner shelf and locally amplifies shoreward motion induced by the respective widened shelf and the coastal promontory the along isobath variations of cross isobath transport in the water column over the middle and inner shelves interactively characterize intensified upwelling in the nscs

a poleward jet and an equatorward undercurrent observed off oregon and northern california during the 1997 98 el nino abstract the timing and intensity of the effects of the 1997 98 el nino on sea surface temperature sst and coastal sea level along the us west coast are examined using in situ time series measurements and the effects on upper ocean currents on the continental shelf and slope off oregon and northern california are examined using repeated shipborne adcp transects a mid shelf mooring off newport oregon and an hf surface current radar an initial transient positive anomaly was observed in both adjusted sea level and sst during may june 1997 followed by anomalously high coastal sea levels generally strongest during september 1997 through february 1998 and abruptly returned to normal in late february 1998 and by positive temperatures anomalies over the mid shelf that persisted longer into april 1998 low frequency coastal sea level anomalies propagated poleward at 2 1 m s poleward flow over the shelf and slope was enhanced at most depths during the el nino compared with following years northward currents in the upper 12 m over the continental shelf off newport oregon averaged 13 7 cm s stronger during august 1997 through february 1998 than during the same period the following year enhanced poleward flow was present at all latitudes sampled during november 1997 and february 1998 particularly over the continental slope these transects also provided clear views of a fall winter equatorward undercurrent which was both strongest and had the most alongshore similarity of form during the enso finally subsurface intensified anticyclonic eddies originating in the poleward undercurrent appear to be a recurrent feature of the circulation off newport late in the upwelling season

growth rate and size effect on carbon isotopic fractionation in diatom bound organic matter in recent southern ocean sediments carbon isotopic fractionation during photosynthesis epep is used to reconstruct past co2 and phytoplankton growth rates typically by measuring the 13c of biomarkers produced by coccolithophorids however organic molecules bound within diatom frustules represent another phase for measurement of 13c and offer the opportunity to obtain epep for specific diatom sizes and geometries here from core top sediments covering a strong productivity gradient in the southern ocean we present determinations of 13c and epep from frustule bound organic matter from a fine opal fraction dominated by pennate diatoms and a coarse opal fraction dominated by larger centric diatoms the 13c of the pennate diatom fraction is typically 2 8 more positive than that of the centric fraction both fractions show a comparable range of 9 10 over the core top transect epep is lowest 6 3 in pennate fraction between the polar front pf and southern antarctic circumpolar current front saccf and increases both to the north and south with maximum values at greatest distance from the pf 18 in the pennate fraction these spatial changes in epep are too large to arise from the rather modest variation in dissolved co2 in surface waters across the core top transect we suggest instead that the maximum epep reflects higher diatom growth rates and in the case of pennate diatom f kerguelensis also an increase in the frustule width and volume to surface area ratio both processes may result from enhanced fe supply due to upwelling of circumpolar deep water between the pf and saccf farther south diatom growth is strongly fe limited and farther north it is fe and si co limited the optima of growth rates between the pf and saccf appears to be a general feature in all sectors of the southern ocean such growth rate induced changes in diatom epep allow us to resolve a 5 northward displacement of the pf during glacial times compared to interglacial times by estimating co2 aq in equilibrium with the holocene ice core atmospheric co2 concentrations we quantify this growth rate effect and document that it is strongly correlated with indicators of trace metal supply such as frustule zn content as well as indicators of diatom productivity such as opal and opal accumulation rates in sediments and sediment traps these relationships may be applied to constrain the effect of growth rate variations on epep and more accurately derive co2 variations from epep during periods prior to ice core co2 proxy records

plastic flow of omphacite in eclogites at temperatures below 500 c implications for interplate coupling in subduction zones in subduction zones oceanic crust of the downgoing plate presumably forms a continuous interlayer between the upper and the lower plate during subduction the basaltic material is transformed to eclogite thus the flow strength of eclogite must pose an upper bound to shear stresses across the plate boundary for the deeper levels of subduction zones up to now experimental flow laws for wet diopside have been applied to predict the strength of eclogites however based on experimental calibration the material would be essentially undeformable by dislocation creep at 650 c even at 700 c a strain rate of 10 14 s 1 would still imply a differential stress of ca 150 mpa omphacite microstructures in eclogites from the piemonte zone western alps reveal shape preferred orientation subgrains and sutured high angle grain boundaries due to migration recrystallization and a pronounced crystallographic preferred orientation these textures indicate that the omphacite was deformed by dislocation creep in contrast garnet forms rigid inclusions within the weaker pyroxene matrix fe mg exchange thermometry for garnet omphacite pairs indicates temperatures of 465 50 c valle di locana and 475 50 c vallone di saint marcel for a pressure of 1 5 gpa these results are not consistent with the predictions based on experimental flow laws for diopside our data suggest that the flow strength of sodic pyroxene is significantly lower than that of diopside this finding is consistent with the homologous temperature concept with the melting temperature of jadeite at 3 gpa being approximately 350 c lower than that of diopside in addition dynamic migration recrystallization of omphacite in the investigated samples can be linked to small chemical changes this indicates that mobile grain boundaries formed an effective pathway for the exchange of ions and that this exchange was fast compared to the rate of boundary migration thus the combined reduction of stored strain energy and chemical free energy provided the driving force for recrystallization the potential effects of these chemical changes on flow strength remain to be explored

flow topography interactions in the northern california current system observed from geostationary satellite data 1 data from geostationary operational environmental satellites are used to study the seasonal evolution of temperature fronts in the northern california current system ccs focusing on the interactions with topographic features fronts first appear close to the coast in response to upwelling winds moving offshore with the continuous input of energy to the system late in the upwelling season after july the upwelling front is persistently found over deeper waters south of heceta bank oregon than north of it suggesting that the equatorward jet separates from the shelf at heceta bank inshore of the upwelling front weak gradients are found on the bank the interaction of the equatorward flow with heceta bank and cape blanco oregon farther south substantially increases the mesoscale activity and oceanic frontal habitat downstream to the south in the ccs where fronts are persistently found greater than 100 km from the coast

a switch from si oh 4 to no 3 depletion in the glacial southern ocean 1 phytoplankton in the antarctic deplete silicic acid si oh 4 to a far greater extent than they do nitrate no3 this pattern can be reversed by the addition of iron which dramatically lowers diatom si oh 4 no3 uptake ratios higher iron supply during glacial times would thus drive the antarctic towards no3 depletion with excess si oh 4 remaining in surface waters new 30si and 15n records from antarctic sediments confirm diminished si oh 4 use and enhanced no3 depletion during the last three glaciations the present low si oh 4 water is transported northward to at least the subtropics we postulate that the glacial high si oh 4 water similarly may have been transported to the subtropics and beyond this input of si oh 4 may have caused diatoms to displace coccolithophores at low latitudes weakening the carbonate pump and increasing the depth of organic matter remineralization these effects may have lowered glacial atmospheric pco2 by as much as 60 ppm

a marine diatom record from the amundsen sea insights into oceanographic and climatic response to the mid pleistocene transition in the west antarctic sector of the southern ocean abstract the goal of this study is to assess the changes that have occurred during the mid pleistocene transition an important transitional period in cryosphere evolution by examining the siliceous microfossil record of sediments collected proximal to a major ice drainage outlet for the west antarctic ice sheet core ps58 254 was collected from a sediment drift on the upper continental rise in the amundsen sea directly offshore from pine island bay one of the three main discharge areas for the west antarctic ice sheet wais published data on physical properties geochemical composition grain size and clay mineral assemblages are complemented here by a high resolution record sample spacing 10 cm of the siliceous microfossil assemblages diatoms and silicoflagellates between 1200 ka and 621 ka the assemblage is relatively diverse with actinocyclus ingens thalassiothrix antarctica and fragilariopsis kerguelensis dominating the assemblages but diatom abundance is variable from low to barren additionally the occurrence of a ingens thalassiosira elliptipora and thalassiosira fasciculata is used to confirm and further refine the existing age model and extend it back to 1200 ka species composition during the last ca 621 ka is dominated by f kerguelensis which consistently comprises 80 90 of the assemblage a clear relationship between diatom abundance and glacial interglacial variability is apparent after 621 ka which resembles the glacial interglacial variability previously observed in other proxy data a significant change in both sediment composition and diatom assemblages is observed at 621 ka this change concurs with the last abundant occurrence of a ingens and the end of the mid pleistocene transition mpt i e the onset of modern eccentricity precession paced glacial cycles around 650 ka we suggest that during interglacial periods after 621 ka the amundsen sea low pressure system shifted seasonally southwestwards towards the shelf and thereby increased the advection of relatively warm circumpolar deep water cdw onto the amundsen sea shelf which is a major factor for present ice sheet melting in this part of west antarctica

coastal wind driven circulation in the vicinity of a bank part i modeling flow over idealized symmetric banks abstract this study examines how coastal banks influence wind driven circulation along stratified continental shelves numerical experiments are conducted for idealized symmetric banks the standard bank 200 km long and 50 km wide has dimensions similar to the heceta bank complex along the oregon shelf model runs are forced with 10 days of steady winds 0 1 pa upwelling and downwelling cases are compared the bank introduces significant alongshelf variability in the currents and density fields upwelling favorable winds create an upwelling front and a baroclinic jet flowing opposite coastal trapped wave propagation that bend around the standard bank approximately centered on the 90 m isobath the upwelling jet is strongest over the upstream bank half where it advects a tongue of dense water over the bank there is a current reversal shoreward of the main jet at the bank center upwelling is most intense over the upstream part of the bank while there is reduced upwelling and even downwelling over

sequence of events during the last deglaciation in southern ocean sediments and antarctic ice cores variation depends on the age model as 14 c determinations cannot be obtained for the time interval of 29 5 14 5 ka assuming a constant sedimentation rate for this interval our data suggest that sea ice and nutrient changes at about 19 ka b p lead the increase in atmospheric pco2 by approximately 2000 years our diatom based sea ice record is in phase with the sodium record of the vostok ice core which is related to sea ice cover and similarly leads the increase in atmospheric co2 if gas exchange played a major role in determining glacial to interglacial co2 variations then a delay mechanism of a few thousand years is needed to explain the observed sequence of events otherwise the main cause of atmospheric pco2 change must be sought elsewhere rather than in the southern ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4267 oceanography general paleoceanography 4845 oceanography biological and chemical nutrients and nutrient cycling 4870 oceanography biological and chemical stable isotopes 9325 information related to geographic region atlantic ocean keywords biogenic opal stable isotopes diatoms ird last glacial southern ocean

connectivity and larval dispersal along the oregon coast estimated by numerical simulations 1 connectivity and larval dispersal is explored off the oregon coast during the summer upwelling season of 2001 using numerical ocean circulation simulations the study region with strong wind driven currents and variable topography is modeled using the regional ocean modeling system roms forced by the coupled ocean atmosphere mesoscale prediction system a large number of passive particles as models of planktonic larvae are released daily for 120 days from 1 may to 28 august at depths of 1 7 15 20 50 and 75 m at every grid point shoreward of the 200 m isobath on average 32 km offshore the particles are transported by the three dimensional currents of the model simulation the competency time window for larval settlement is assumed to be in between days 15 and 35 after larvae are released larval settlement occurs at the shallowest location during the competency time window connectivity matrices reveal that some of the places of highest retention are similar to the proposed oregon marine reserve sites especially cape perpetua the heceta bank region has high probabilities as both a source and a destination for settled larvae larvae released in the heceta bank region often settle at higher latitudes than their release location there are strong correlations between the number of settled larvae shallower than the 50 m isobath and a 6 to 8 day running mean of the alongshore wind stress larvae are retained near the shore when the winds averaged over the previous 6 to 8 days are relaxed or downwelling favorable

variation in the position of the upwelling front on the oregon shelf 1 as part of an experiment to study wind driven coastal circulation 17 hydrographic surveys of the middle to inner shelf region off the coast of newport or 44 65 n from roughly the 90 m isobath to the 10 m isobath were performed during summer 1999 with a small towed undulating vehicle the cross shelf survey data were combined with data from several other surveys at the same latitude to study the relationship between upwelling intensity and wind stress field a measure of upwelling intensity based on the position of the permanent pycnocline is developed this measure is designed so as to be insensitive to density modifying surface processes such as heating cooling buoyancy plumes and wind mixing it is highly correlated with an upwelling index formed by taking an exponentially weighted running mean of the alongshore wind stress this analysis suggests that the front relaxes to a dynamic geostrophic equilibrium on a timescale of roughly 8 days consistent with a similar analysis of moored hydrographic observations this relationship allows the amount of time the pycnocline is outcropped to be estimated and could be used with historical wind records to better quantify interannual cycles in upwelling

shallow remineralization in the weddell gyre 1 the region influenced by the polar front in the southern ocean is characterized by relatively high productivity which is mirrored in strong depletions of 234th in the surface water a good tracer of export production and by high accumulation rates on the underlying seabed farther south the weddell sea is generally considered a low productivity region with very low export fluxes this finding is based on satellite observations sediment accumulation rates trap deployments and phytoplankton distribution if this would be true 234th should be close to equilibrium with its parent however in a series of high resolution transects of 234th 238u across the antarctic circumpolar current acc 234th was found to be depleted by 10 15 throughout the clear weddell gyre only to reach equilibrium in sea ice covered regions of the coastal zone vertical profiles showed that the depletion was limited to the upper mixed layer and was balanced by an enrichment of similar magnitude at 100 250m depth this implies that the export of particles below 250 m is negligible such shallow remineralization is in line with the discrepancies between biogenic silica production rates and sediment trap data observed in the weddell and ross seas these observations in the weddell sea are fully consistent with our inverse modeling results for both organic carbon and opal and they are not inconsistent with tco2 and oxygen sections that show a tco2 enriched oxygen reduced shallow subsurface layer this blue ocean characterized by upwelling of co2 enriched deep waters supports sufficient productivity to be a net sink for co2 to abyssal depths hoppema et al 1999 no record of this productivity and export is stored in the underlying sediment which has important palaeoceanographic consequences

extensive phytoplankton blooms in the atlantic sector of the glacial southern ocean 1 the sources and sinks of atmospheric carbon dioxide over glacial interglacial cycles are under debate variation in productivity of the antarctic circumpolar current acc could potentially play a significant role but current interpretations of sedimentary geochemical proxies suggest that glacial productivity was not higher than today we present areal and down core distribution patterns of previously overlooked diatom resting spores that indicate the occurrence of extensive phytoplankton blooms across the entire atlantic sector of the acc particularly in the seasonal ice zone siz linked to higher iron input during the last glacial sea ice acts as an effective transporter of iron and enhances its bioavailability the dominance of the deep living radiolarian cyladophora davisiana in glacial siz sediments indicates that organic carbon export to mesopelagic depths was at least tenfold higher than today

evaluation of directly wind coherent near inertial surface currents off oregon using a statistical parameterization and analytical and numerical models directly wind coherent near inertial surface currents off the oregon coast are investigated with a statistical parameterization of observations and outputs of a regional numerical ocean model and three one dimensional analytical models including the slab layer ekman and near surface averaged ekman models the transfer functions and response functions statistically estimated from observed wind stress at ndbc buoys and surface currents derived from shored based high frequency radars enable us to isolate the directly wind forced near inertial surface currents concurrent observations of the wind and currents are crucial to evaluate the directly wind forced currents thus the wind stress and surface current fields obtained from a regional ocean model which simulates variability of the wind and surface currents on scales comparable to those in observations are analyzed with the same statistical parameterization to derive the point by point transfer functions and response functions model and data comparisons show that the regional ocean model describes near inertial variability of surface currents qualitatively and quantitatively correctly the estimated response functions exhibit decay time scales in a range of 3 5 days and about 40 of the near inertial motions are explained by local wind stress among the one dimensional analytical models the near surface averaged ekman model explains the statistically derived wind current relationship better than other analytical models

quantifying the opal belt in the atlantic and southeast pacific sector of the southern ocean by means of 230th normalization 1 a set of 114 samples from the sediment surface of the atlantic eastern pacific and western indian sectors of the southern ocean has been analyzed for 230th and biogenic silica maps of opal content th normalized mass flux and th normalized biogenic opal flux into the sediment have been derived significant differences in sedimentation patterns between the regions can be detected the mean bulk vertical fluxes integrated into the sediment in the open southern ocean are found in a narrow range from 2 9 g m 2 yr 1 eastern weddell gyre to 15 8 g m 2 yr 1 indian sector setting upper and lower limits to the vertically received fraction of open ocean sediments the silica flux to sediments of the atlantic sector of the southern ocean is found to be 4 2 1 4 1011 mol yr 1 just one half of the last estimate this adjustment represents 6 of the output term in the global marine silica budget

coastal ocean response to summer upwelling favorable winds in a region of alongshore bottom topography variations off oregon 1 repeated mesoscale surveys of waters over the shelf and slope off oregon were conducted during spring and summer of 2001 to study the spatial structure of the velocity and hydrographic fields the ocean response to wind forcing is compared between a region of relatively simple topography with alongshore uniformity and a region of complex topography including a shallow submarine bank heceta bank in the simple topography region the upper water column is influenced by upwelling and fresh water from the columbia river during spring with the low salinity water located farther offshore during summer variability in the fields is mostly confined within 30 km from the coast over heceta bank the region of higher variability is broader spanning most of the shelf the coastal upwelling jet is located inshore of the pinnacle of the bank during spring moving offshore during summer the region inshore of the bank is characterized by low velocities and flow recirculation near surface fields show that the circulation evolves considerably between seasons in both regions the area influenced by upwelled water is much broader during summer dense waters found over midshelf off newport are upwelled to the north and advected south dense waters inshore of heceta bank are substantially influenced by water from the north during spring but their source is mostly from the south during summer south of the bank the separation of the jet significantly increases the cross isobath transport constituting an efficient mechanism for transport of material from the shelf into deeper waters

the reconstruction of late quaternary antarctic sea ice distribution the use of diatoms as a proxy for sea ice the study of annual diatom transfer from the southern ocean surface to the sea floor using time series sediment traps combined with the mapping of diatom assemblages from surface sediments results in the definition of a proxy for past variations of sea ice extent the application and robustness of the proposed proxy are demonstrated by the study of late pleistocene sediment cores recovered from different environmental regimes in the southern ocean relative amounts of the sea ice indicator diatoms fragilariopsis cylindrus and fragilariopsis curta of 3 in diatom assemblages preserved in sediments are representative of the presence of seasonal winter sea ice summer sea ice occurrence is signalled by a distinct drop in biogenic sedimentation rate as a result of strongly reduced biogenic export in the presence 3 of diatom assemblage of the deep temperature diatom fragilariopsis obliquecostata the spatial and temporal distribution pattern of the sea ice proxy indicates significant sea ice variations during marine isotope stages 1 and 5 in the present antarctic zone of the southern ocean during glacial maxima the antarctic winter sea ice was extended into the present polar front zone while the antarctic summer sea ice was most probably expanded into the area of the present winter sea ice edge during the short climatic optima at the onset of interglacial periods the winter sea ice extent was distinctly reduced

mesoscale surveys over the shelf and slope in the upwelling region near point arena california repeated mesoscale surveys of a 40 km wide 100 km long coastal region near point arena california were conducted during the upwelling season april august in 1981 and 1982 each survey included conventional conductivity temperature depth casts at standard locations over the continental shelf and slope between 38 n and 39 10 n and continuous operation of a doppler acoustic log to obtain velocity profiles in the 20 to 150 m depth range synoptic surveys covered the entire grid in 2 3 days winds were strongly favorable for upwelling during the three 1981 surveys and were weak or variable during the three 1982 surveys surface temperature and salinity fields reflect the influence of both the seasonal winds and day to day variations in the wind persistently low surface salinities offshore reflect the general southward advection of subarctic waters and sporadic low salinities over the inner shelf reflect north ward advection of local runoff through an intermittent narrow countercurrent along the coast circulation patterns during all but one of the surveys were very complex and included meandering equatorward flow cyclonic and anticyclonic eddies and inshore countercurrents the simple two dimensional equatorward baroclinic coastal jet usually associated with coastal upwelling was observed during only one of our surveys overall average fields are relatively simple they show broad equatorward surface flow a very weak inshore countercurrent and a definite poleward undercurrent at the shelf break average temperature salinity and density fields are generally congruent with the average flow pattern average isotherms and isohalines are not strictly parallel to the coastline south of the coastline bend at point arena they diverge gradually from the coast comparison of average sections calculated from 10 matched pairs of central and arena lines separated by 50 km shows there are systematic differences between them warmer fresher waters lie nearer shore and in shallower water off point arena than on the central line this suggests that the surface waters flowing past point arena have sufficient southward momentum to cross isobaths comparison of average velocity sections on these two lines shows some differences in structure since the variability is large these may not be significant comparison of the measured and geostrophic average shears suggests there is a significant ageostrophic component in the upper layers above 40 m it may be the signature of an average wind driven ekman spiral

observations on the circulation of the saronikos gulf a mediterranean embayment sea border of athens greece 1 the saronikos gulf three dimensional flow structure is mapped by objective analysis in 12 acoustic doppler current profiler surveys 4 seasonal surveys per period for the periods may 1998 may 1999 may 2000 may 2001 may 2003 may 2004 under various winds robust seasonal flows throughout the gulf are basically induced by thermohaline effects winter water subduction different responses to atmospheric heating of shallow and deeper areas of the gulf and density contrasts with inflowing aegean waters inner gulf observations show that the seasonal flows are modified by the wind while recurrent structures cyclonic and anticyclonic appear between the seasonal flows and the coast of attica in summer an anticyclonic and a cyclonic flow exists throughout the gulf above and below the pycnocline respectively with a jet observed to meander within the inner gulf in winter and early spring an anticyclonic flow prevails in the upper 100 m in late spring early summer cyclonic and anticyclonic flow occurs in the upper 0 40 m and deeper 60 100 m layers respectively the predominant northerly winds in summer and winter push the inner gulf eastward seasonal jet to the south and favor the formation of a recurrent cyclonic upwelling structure between this jet and attica northwesterly westerly and southerly winds favor the northward meandering of the seasonal jet in the inner gulf and no recurrent structures appear in the limited space between this jet and attica in the southeast area of the inner gulf the wind driven flow fluctuations at 30 m have time scales of 3 5 4 days observed meandering period is 13 days meandering characteristics are close to instability predictions time scales of flows due to recurrent structures are 8 days

a separating coastal upwelling jet at cape blanco oregon and its connection to the california current system the coastal upwelling region near cape blanco oregon 433n o the west coast of the united states was studied using a towed ctd on seasoar a shipboard acoustic doppler current pro ler adcp satellite sea surface temperature maps and surface drifters during august 1995 the equatorward upwelling jet was inshore of the shelfbreak north of cape blanco meandered gently o shore around the cape and then veered sharply o shore just to the south of the cape analysis of vertical sections of density velocity and spicinessa con rmed the separation of an upwelling jet and front the jet was followed from over the shelfbreak north of the cape to 100 km o shore downstream of the cape the separating jet originates from the coastal upwelling jet leaving the shelf but is augmented by an o shore branching of the poleward undercurrent by combining information from adcp streamfunction maps with analysis of hydrographic data including distributions of the tracer like quantity spicinessa a conceptual model of the three dimensional circulation near the cape emerges a mid shelf upwelling jet encounters a coastal promontory then turns o shore stretching and deepening as it crosses the continental margin the jet then turns back shoreward cyclonically where the deepened equatorward ow encounters the top of the poleward undercurrent owing along the continental slope this causes a portion of the undercurrent to turn o shore to join and strengthen the equatorward transport in the separated jet throughout the separation process the coastal upwelling front and jet are continuous robust features separation of a coastal upwelling jet is an important mechanism for cross shelf transport from the coast to the deep ocean cape blanco appears to be the northernmost point where an equatorward jet regularly separates from the coast to become an oceanic jet and thus serves as the northern boundary of the region where an intense meandering current characteristic of the california current system