sar imagery and surface truth comparisons of internal waves in georgia strait british columbia canada the surface roughness patterns caused by internal waves in georgia strait on the west coast of canada were used as an imagery target for the seasat synthetic aperture radar sar on july 30 1978 in these patterns there is strong modulation of short surface waves including the bragg wavelength for resonant microwave reflection in the sheltered waters of the strait the complicating effects of longer waves are greatly reduced the roughness patterns were also observed with an airborne sar by aerial photography and by shipborne surface roughness and subsurface current measurements the data show the response of the sar s to the anisotropic roughness patterns measured by the ship the sar signal intensity is shown to be moderately correlated with bragg wave or total roughness energy but not with the facet area aligned to give specular reflection

secondary circulation in a region of flow curvature relationship with tidal forcing and river discharge 1 on the basis of a 301 day acoustic doppler current profiler mooring in an estuarine tidal strait the strength and structure of secondary circulation in a region of flow curvature is related to variations in tidal forcing and river discharge during low flow conditions the structure of secondary flow is consistent with a centrifugally forced helical flow with bottom flow toward the inside of the bend and surface flow toward the outside of the bend the strength of secondary flow increases linearly with tidal range and is consistent with a vertical eddy viscosity that is linearly dependent on tidal current speed during times of high river discharge the strength of secondary flow is significantly reduced and its vertical structure undergoes a fundamental change over the spring neap cycle during spring tides the classic helical flow pattern is evident albeit weaker than during low flow conditions however during neap tides a more complex two cell structure is evident the change between these two states occurs with a spring neap transition in the subtidal flow indicating that it is also accompanied by changing stratification simple scaling analysis suggests that during weakly stratified conditions secondary circulation will influence stream wise dynamics and dispersion for channels with widths on order or less than 0 1 h cd where h is the water column depth and cd is a quadratic bottom drag coefficient in contrast during highly stratified conditions lateral excursions due to secondary flows are limited to approximately one tenth of the channel s width and are an ineffective lateral mixing agent

the distribution and speciation of iron along 6 e in the southern ocean abstract the distribution and speciation of iron was determined along a transect in the eastern atlantic sector 6 e of the southern ocean during a collaborative scandinavian south african antarctic cruise conducted in late austral summer december 1997 january 1998 elevated concentrations of dissolved iron 0 4 nm were found at 60 s in the vicinity of the spring ice edge sie in tandem with a phytoplankton bloom chiefly dominated by phaeocystis sp this bloom had developed rapidly after the loss of the seasonal sea ice cover the iron that fuelled this bloom was mostly likely derived from sea ice melt in the winter ice edge wie around 55 s dissolved iron concentrations were low 0 2 nm and corresponded to lower biological productivity biomass in the antarctic polar front at approximately 50 s a vertical profile of dissolved iron showed low concentrations 0 2 nm however a surface survey showed higher concentrations 1 3 nm and considerable patchiness in this dynamic frontal region the chemical speciation of iron was dominated by organic complexation throughout the study region organic iron complexing ligands l ranged from 0 9 to 3 0 nm fe equivalents with complex stability log k fe l 21 4 23 5 estimated concentrations of inorganic iron fe ranged from 0 03 to 0 79 pm with the highest values found in the phaeocystis bloom in the sie a vertical profile of iron complexing ligands in the wie showed a maximum consistent with a biological source for ligand production and near surface minimum possibly consistent with loss via photodecomposition this work further confirms the role iron that has in the southern ocean in limiting primary productivity

terrigenous sediment supply in the scotia sea southern ocean response to late quaternary ice dynamics in patagonia and on the antarctic peninsula geochemical and mineralogical compositions of modern and late quaternary marine sediments from the scotia sea trace sources and transport paths of terrigenous sediment we discuss downcore variations of compositional data of two sediment cores from the northern and southern scotia sea that correlate with fluctuations in magnetic susceptibility sediments were derived from very different sources at both localities as revealed by contrasting clay mineral assemblages however a common feature is the input of more basic and undifferentiated crustal material with the potential of high magnetic susceptibility during glacial periods indicated by variable quartz feldspar ratios and major trace and rare earth elements terrigenous sediments mainly originate from nearby terrestrial sources or are introduced through interbasinal sediment transfer from adjacent seas the observed temporal compositional variations have to be attributed to changes in the relative detrital contributions from the diverse source areas ice mass extensions in southern patagonia on the antarctic peninsula and adjacent islands likely control the supply of glaciogenic detritus to the open ocean during times of glacial expansion diluting the sediment input of interbasinal origin current transport is mainly responsible for sediment dispersal to the pelagic scotia sea and may amplify the glaciological source signals during glacial climate periods because of a stronger wind forcing of the antarctic circumpolar current

advanced remote sensing of internal waves by spaceborne along track insar a demonstration with terrasar x since the seasat mission in 1978 satellite based synthetic aperture radar sar images have been used to study oceanic internal waves internal waves become visible in sar images because their orbital currents modulate the surface roughness while this leads to an accurate spatial representation of internal wave patterns the complexity of the imaging mechanism makes it difficult to derive actual currents and internal wave amplitudes from sar signatures we demonstrate in this paper how a more robust parameter retrieval is possible with along track interferometric sar insar data that resolve amplitudes and temporal phase changes of the backscattered signal together the latter of which are directly related to the scatterers line of sight velocities our example data set which was acquired by terrasar x in dual receive antenna mode at dongsha south china sea exhibits strong signatures of internal waves in the interferogram amplitude and phase we use a simple internal soliton parameterization and a numerical radar imaging model to find a plausible combination of internal wave parameters which leads to good agreement between simulated and observed signatures testing the sensitivity of radar amplitude and phase signatures to various parameters we show that along track insar data should generally permit more accurate and less ambiguous internal wave parameter retrievals than conventional sar images

interaction of lateral baroclinic forcing and turbulence in an estuary 1 observations of density and velocity in a channel in northern san francisco bay show that the onset of vertical density stratification during flood tides is controlled by the balance between the cross channel baroclinic pressure gradient and vertical mixing due to turbulence profiles of velocity salinity temperature and suspended sediment concentration were measured in transects across suisun cutoff in northern san francisco bay on two days over the 12 5 hour tidal cycle during flood tides an axial density front developed between fresher water flowing from the shallows of grizzly bay into the northern side of suisun cutoff and saltier water flowing up the channel north of the front transverse currents were driven by the lateral salinity gradient with a top to bottom velocity difference greater than 30 cm s south of the front the secondary circulation was weak and along channel velocities were greater than to the north the gradient richardson number shows that stratification was stable north of the front while the water column was turbulently mixed south of the front time series measurements of velocity and salinity demonstrate that the front develops during each tidal cycle in estuaries longitudinal dynamics predict less stratification during flood than ebb tides these data show that stratification can develop during flood tides due to a lateral baroclinic pressure gradient in estuaries with complex bathymetry

iceberg trajectory modeling and meltwater injection in the southern ocean this is the first large scale modeling study of iceberg trajectories and melt rates in the southern ocean an iceberg model was seeded with climatological iceberg calving rates based on a calculation of the net surface accumulation from each snow catchment area on the antarctic continent in most areas modeled trajectories show good agreement with observed patterns of iceberg motion though discrepencies in the weddell sea have highlighted problems in the ocean general circulation model output used to force the iceberg model the coriolis force is found to be important in keeping bergs entrained in the coastal current around antarctica and topographic features are important in causing bergs to depart from the coastal regions the modeled geographic distribution of iceberg meltwater joining the ocean has been calculated and is found in many near coastal regions to be comparable in magnitude to the excess of precipitation over evaporation p e

the tidally averaged momentum balance in a partially and periodically stratified estuary abstract observations of turbulent stresses and mean velocities over an entire spring neap cycle are used to evaluate the dynamics of tidally averaged flows in a partially stratified estuarine channel in a depth averaged sense the net flow in this channel is up estuary due to interaction of tidal forcing with the geometry of the larger basin the depth variable tidally averaged flow has the form of an estuarine exchange flow downstream at the surface upstream at depth and varies in response to the neap spring transition the weakening of the tidally averaged exchange during the spring tides appears to be a result of decreased stratification on the tidal time scale rather than changes in bed stress the dynamics of the estuarine exchange flow are defined by a balance between the vertical divergence of the tidally averaged turbulent stress and the tidally averaged pressure gradient in the lower water column in the upper water column tidal stresses are important contributors particularly during the n

provenance and transport of terrigenous sediment in the south atlantic ocean and their relations to glacial and interglacial cycles nd and sr isotopic evidence sr and nd isotopic compositions of late quaternary surface sediment and sediment cores from the south atlantic and southeast pacific sectors of the southern ocean are used to constrain the provenance and transport mechanisms of their terrigenous component we report isotopic and mineralogical data for core samples from three localities the mid atlantic ridge at 41 s and the northern and southern scotia sea in addition data for surface sediment samples from the south atlantic and southeast pacific sectors of the southern ocean are presented the variations of sr and nd isotopic compositions of the bulk sediment samples in all cores were correlated with the magnetic susceptibility of the sediment and with the inferred glacial interglacial stages the isotopic data indicate that during glacial periods sediment was delivered from continental crust with a shorter residence time than that supplying material during interglacial periods at the core site near the mid atlantic ridge nd isotopic combined with mineralogical evidence indicates interglacial period deposition of a relatively high amount of kaolinite and silt with low nd values 4 5 probably derived from southern south america was indicated the glacial interglacial shift in sources may be due to either a decreasing influence of north atlantic deep water during glacial times or by a larger contribution of glaciogenic detritus from southern south america at the core site in the northern scotia sea sediment of interglacial periods is dominated by smectite with nd 4 we suggest that smectite was derived from the falkland shelf and silt was derived from the argentinian shelf during glacial periods the argentinian shelf was an important source for silt and chlorite with nd 4 the contribution from the falkland shelf seems to have remained similar during glacial and interglacial periods hydrographic transport by bottom currents and turbidites could account for the high glacial detrital flux an evaluation of the significance of an aeolian contribution to deep sea sediment suggests that it plays only a minor role in the southern scotia sea the antarctic peninsula is considered an important source for young material with nd 4 in particular during glacial periods during interglacial periods sediment supply from the antarctic peninsula was lower than during glacial times resulting in a relatively high contribution of old material nd 8 from east antarctica deep water currents and icebergs could account for the transport of the old component to the southern scotia sea the accumulation rates of material from the various source regions for glacial times are in agreement with an increase in the strength of the antarctic circumpolar current the production rate and the circulation pattern of bottom water in the weddell sea appear to have remained similar over most of the last 150 kyr

synthetic aperture radar observations of resonantly generated internal solitary waves at race point channel cape cod 1 synthetic aperture radar images revealed the two dimensional propagation characteristics of short period internal solitary waves in race point channel in massachusetts bay the images and in situ measurements of the flow in the channel are used to infer the likely generation mechanism of the waves the solitary waves are generated during the ebb phase of the tide within the channel on some occasions two trains of internal waves are generated presumably at the same location but at slightly different phases of the ebb tide the main characteristics of the two layer flow are described based on the criticality of the froude number it is suggested that these two individual packets of waves result from flow passage through resonance where the froude number is one one packet is generated as the flow passes through the transcritical regime during the acceleration phase of the ebb tidal current and another packet is generated during the deceleration phase both packets propagate upstream when the tide slacks but with slightly different propagation directions

longitudinal dispersion and lateral circulation in the intertidal zone 1 field observations indicate that a tidal salinity front that is regenerated each lower low water is a prominent feature of intertidal zone flow during wet winter months a strong longitudinal density gradient at the front influences flow dynamics through tidal straining and baroclinic forcing during each inundation period the salinity gradient disperses as it advects across the intertidal zone the average longitudinal dispersivity estimated from observations is about 10 m2 s 1 a three dimensional numerical model yields comparable estimates of tidally averaged dispersivity for an idealized bathymetry with a subtidal channel and intertidal shoals the instantaneous dispersivity through the tidal cycle depends on both vertical and lateral shear in along channel velocity dispersion due to vertical shear is greatest during stratified ebbs and inversely depends on tidal forcing dispersion due to lateral shear results from bathymetric variability between channel and shoal and increases with tidal amplitude similarly the along channel residual velocity is a combination of baroclinic and frictional processes frictional effects dominate the depth averaged residual such that net flow is upstream on the shoals and downstream in the channel however the frictional pattern is moderated by baroclinic forcing at the front although along channel dynamics dominate differential advection of the salinity front establishes lateral baroclinic circulation between channel and shoals lateral residual circulation is flood dominant with dense water moving out of channel near the bed and convergence from the shoals at the surface at times near the front the lateral salt flux can significantly affect the salinity budget in the channel

the effects of channels and shoals on exchange between the chesapeake bay and the adjacent ocean the role of bathymetric changes in determining the transport of water and salt in the lower chesapeake bay lcb was investigated using high resolution acoustic doppler current profiler adcp and conductivity temperature depth profiles a cross channel transect was repeated eight times during neap tides on october 6 7 1993 which illustrated the lateral structure of the longitudinal and transverse flow fields and the intratidal variations in the flow structure across the lcb amplitude and phase of the m2 tidal component as well as the mean flow velocity were calculated using least squares fitting at every point of a uniform grid obtained from the adcp data the results differ from the classical two layer pattern of estuarine circulation modified by coriolis effects but are consistent with recent hydrographic observations semidiurnal flow was highest over the navigational channels and lateral gradients were strongest in regions of sharp bathymetric changes the phase lag of the semidiurnal flow also showed lateral and vertical gradients that represented advances at the bottom with respect to the surface and over the shoals in relation to the channels the section of the water column measured indicated a mean outflow of 0 7 104 m3 s and a mean inflow of 1 3 104 m3 s the apparent gain of water by the estuary during the period of observation can be explained by meteorologically forced net barotropic inflow the depth averaged mean longitudinal flow consisted of inflow in the navigational channels and outflow over the shoals the mean transverse flow showed near surface convergence over the channels we propose a possible explanation for the observed flow and density structure as follows the barotropic and baroclinic forcing interact with the bathymetry to extend the inflow from the bottom to the surface thereby inducing a transverse circulation that yields near surface convergence over the channels

theory of radar imaging of internal waves radar images taken over ocean areas in particular those obtained by the synthetic aperture radar sar onboard the american seasat satellite in 19781 2 sometimes show features that seem to be surface manifestations of oceanic internal waves3 11 here i present a theory explaining the large radar signatures of internal waves in which the imaging is attributed to variations in the short scale surface roughness induced by current variations associated with internal waves

particle trapping in estuarine tidal flows particle trapping in estuarine turbidity maxima etm is caused primarily by convergent mean and or tidal fluxes of sediment the result is an approximately bell shaped along channel distribution of vertically integrated tidal cycle mean suspended sediment concentration observations from the columbia river estuary suggest that 1 strong two layer or internal along channel residual and overtide flows are generated by time varying stratification and 2 correlations between the near bed velocity and the suspended sediment fields at these frequencies are important in landward transport of sediment a new spatially and temporally integrated form of the sediment conservation equation has been derived to analyze this trapping process time changes in tidally averaged sediment concentration between two estuarine cross sections can be shown to be related to the divergence of the seaward river flow transport the divergence of velocity shear sediment stratification correlations for the mean flow and each tidal constituent and net erosion or deposition at the bed vertically integrated variables other than seaward river transport are absent from this integrated balance analysis of sediment fluxes using this balance supports the idea that internal residual and overtide circulations are primarily responsible for the landward sediment transport on the seaward side of etm found near the upstream limits of salinity intrusion the balance also shows that attempts to represent fluxes causing trapping of sediment in an etm as a product of a time mean vertically integrated along channel gradient and a diffusivity inevitably lead to the appearance of countergradient transport and thus a negative diffusivity on the seaward side of the etm this result occurs because the trapping process is inherently nonlinear and at least two dimensional and because a one dimensional representation is physically unrealistic

observation of very large and steep internal waves of elevation near the massachusetts coast 1 we report on near bottom waves of elevation with amplitude nearly half the 25 m water column very steep and propagating into a sheared turbulent wave guide the waves contained trapped cores transporting parcels of water shoreward these large waves depart strongly from weakly nonlinear and weakly nonhydrostatic conditions and challenge established paradigms they can also represent an important factor in the across shore transport of plankton and contaminants

coupling of sea level rise tidal amplification and inundation abstractwith the global sea level rising it is imperative to quantify how the dynamics of tidal estuaries and embayments will respond to increased depth and newly inundated perimeter regions with increased depth comes a decrease in frictional effects in the basin interior and altered tidal amplification inundation due to higher sea level also causes an increase in planform area tidal prism and frictional effects in the newly inundated areas to investigate the coupling between ocean forcing tidal dynamics and inundation the authors employ a high resolution hydrodynamic model of san francisco bay california comprising two basins with distinct tidal characteristics multiple shoreline scenarios are simulated ranging from a leveed scenario in which tidal flows are limited to present day shorelines to a simulation in which all topography is allowed to flood simulating increased mean sea level while preserving original shorelines produces additional tidal amplification however flooding of adj

three dimensional tidal flow in an elongated rotating basin the three dimensional tidal circulation in an elongated basin of arbitrary depth is described with a linear constant density model on the f plane rotation fundamentally alters the lateral flow introducing a lateral recirculation comparable in magnitude to the axial flow as long as friction is not too large this circulation is due to the imbalance between the cross channel sea level gradient which is in near geostrophic balance with the coriolis acceleration associated with the vertically averaged axial flow and the coriolis acceleration associated with the vertically sheared axial flow during flood condition for example the lateral coriolis acceleration near the surface exceeds the pressure gradient tending to accelerate the lateral flow while the converse is true near the bottom as a result with rotation fluid parcels tend to corkscrew into and out of the basin in a tidal period the axial flow is only weakly modified by rotation when friction is small the axial velocity is uniform in each section except in a narrow bottom boundary layer where it decreases to zero the boundary layer thickness increases with friction so that with moderate or large friction axial velocities are sheared from bottom to surface when friction is large the local and coriolis accelerations are both small and the dynamics are governed by a balance between friction and the pressure gradient

impact of the depth to width ratio of periodically stratified tidal channels on the estuarine circulation the dependency of the estuarine circulation on the depth to width ratio of a periodically weakly stratified tidal estuary is systematically investigated here for the first time currents salinity and other properties are simulated by means of the general estuarine transport model getm in cross sectional slice mode applying a symmetric gaussian shaped depth profile the width is varied over four orders of magnitude the individual along channel circulation contributions from tidal straining gravitation advection etc are calculated and the impact of the depth to width ratio on their intensity is presented and elucidated it is found that the estuarine circulation exhibits a distinct maximum in medium wide channels intermediate depth towidth ratio depending on various parameters which is caused by a maximum of the tidal straining contribution this maximum is related to a strong tidal asymmetry of eddy viscosity and shear created by secondary strain induced periodic stratification 2sips in medium channels transverse circulation generated by lateral density gradients due to laterally differential longitudinal advection induces stable stratification at the end of the flood phase which is further increased during ebb by longitudinal straining sips thus eddy viscosity is low and shear is strong in the entire ebb phase during flood sips decreases the stratification so that eddy viscosity is high and shear is weak the circulation resulting from this viscosity shear correlation the tidal straining circulation is oriented like the classical gravitational circulation with riverine outflow at the surface and oceanic inflow close to the bottom in medium channels it is about 5 times as strong as in wide quasi onedimensional channels in which 2sips is negligible

tracking large tabular icebergs using the seawinds ku band microwave scatterometer abstract knowledge of iceberg locations is important for safety reasons as well as for understanding many geophysical and biological processes originally designed to measure wind speed and direction over the ocean seawinds is a microwave scatterometer that operates at 13 4 ghz ku band on the quikscat satellite radar measurements from seawinds are collected and processed on a daily basis using resolution enhancement techniques to produce daily radar images because icebergs scatter microwave energy more than sea ice and sea water icebergs are detected as high backscatter targets surrounded by lower backscatter regions in daily seawinds images as a result iceberg positions are determined in real time and a time series of iceberg positions is maintained in an antarctic iceberg database by brigham young university s microwave earth remote sensing mers laboratory since seawinds operates independent of both solar illumination and cloud cover and has a large daily spatial coverage this paper demonstrates that seawinds is an excellent platform to detect and track large tabular icebergs these icebergs are generally larger than 5 km and are typically characterized as a rough ice plateau above the surrounding sea water or sea ice the number of icebergs tracked in the mers antarctic iceberg database is found to be generally greater than the number of icebergs tracked by the national ice center the movement patterns of all icebergs detected by seawinds are also analyzed and 90 of icebergs are found to travel a counter clockwise path around antarctica and accumulate in the weddell and scotia seas iceberg detection and tracking is demonstrated via multiple case studies that highlight icebergs c 19a and a 22a using the mers database and through real time operational support of the 2005 2008 and 2009 nsf antarctic cruises iceberg positions are validated by using collocated high resolution satellite imagery and by navigating the nsf ships to physically intercept several large tabular icebergs in the weddell and scotia seas

iceberg hosted nanoparticulate fe in the southern ocean mineralogy origin dissolution kinetics and source of bioavailable fe abstract sediments from icebergs and glaciers contain nanopartculate fe iii oxyhydroxides including ferrihydrite which form in aqueous oxic micro environments where fe ii bearing rock minerals oxidise and high degrees of supersaturation are promoted by freezing and thawing an ascorbic acid extraction dissolves only labile fe present in fresh loosely aggregated ferrihydrite that is directly or indirectly bioavailable glacial and iceberg sediments contain ferrihydrite aggregates that provide 0 04 to 0 17 fe soluble in ascorbic acid rather larger than the concentrations in a limited suite of atmospheric dusts the dissolution behaviour of labile fe from glacial and iceberg sediments by ascorbic acid is controlled by the access of reactant or removal of solute through micropores to or from active sites in the interior of ferrihydrite aggregates a first order kinetic model is presented to examine the rates at which bioavailable fe can be supplied by melting icebergs in the weddell sea the model utilizes rate constants from the literature for the processes which solubilise fe from nanoparticulate ferrihydrite dissolution photochemical reduction and grazing and the processes that remove fe nanoparticulates sinking scavenging and incorporation in faecal material and render them less reactive transformation aging model results demonstrate that icebergs can supply bioavailable fe to the weddell sea by the dissolution of nanoparticulate ferrihydrite despite loss removal of nanoparticles by sinking aging transformation scavenging and incorporation into faecal pellets at rates that are comparable to atmospheric dust dissolution enhanced by photochemical reduction and grazing provides the most rapid rates of bioavailable fe production

longitudinal versus lateral estuarine dynamics and their role in tidal stratification patterns in lower south san francisco bay author s hoang olivia abstract the dynamics of shoal channel estuaries require consideration of lateral gradients and transport which can create significant intratidal variability in stratification and circulation when the shoal channel system is strongly coupled by tidal exchange with mudflats marshes or other habitats the gradients driving intratidal stratification variations are expected to intensify to examine this dynamic hydrodynamic data was collected from january 27 2017 february 10 2017 in lower south san francisco bay a small subembayment fringed by extensive shallow vegetated habitats during this deployment salinity variations were captured through instrumentation of 6 stations arrayed longitudinally and laterally allowing for mechanisms of stratification creation and destruction to be calculated directly and compared with observed time variability of stratification at the central station we present observation based calculations of longitudinal straining longitudinal advection lateral straining and lateral advection the time dependence of stratification was observed directly and calculated by summing measured longitudinal and lateral mechanisms we found that the stratification dynamics switch between being longitudinally dominated during the middle of ebb and flood tides to being laterally dominated during the tidal transitions this variability is driven by the interplay between tidally variable lateral density gradients and turbulent mixing relatively constant along estuary density gradients are differentially advected during flood and ebb tides resulting in maximal lateral density gradients around tidal transitions simultaneous decrease in turbulent mixing at slack tides allows lateral density driven exchange to stratify the estuary channel at the slack after flood at the end of ebb barotropic forcing drives negatively buoyant shoal waters towards the channel plain language summary san francisco bay sits within a highly urbanized area the dense population creates large wastewater effluent resulting in high nutrient levels scientists wonder why there have not been annual phytoplankton blooms like observed in other estuaries with lower nutrient levels some have hypothesized it is due to high turbidity levels and tidal breakdown of stratification creating nonideal environments for phytoplankton growth however decadal trends show that the estuary is becoming less turbid and with changes in climate patterns there is potential for persistent stratification we observed development of stratification over the ebb tide and destratification in two distinct events as the tide reverses over the flood tide at the reversal of the tides water in the shoals exchange with the water in the channel creating a pulse of salty water to the channel at the ebb to flood transition and a pulse of fresh water at the flood to the ebb transition destratification occurs in the early flood tide due to a pulse of saline water received from the shoals then due to the advection of less stratified water being pulled to the center channel of the estuary finally stratification is destroyed completely due to longitudinal straining and turbulent mixing

input composition and potential impact of terrigenous material from free drifting icebergs in the weddell sea abstract the hypothesis that fe fertilization of the southern ocean could account for at least part of the glacial interglacial difference in atmospheric co2 has lead to a search for the fe source iron fertilization in the open ocean can occur naturally through increased dust input cross shelf export upwelling of fe replete deep water and release of terrigenous fe from icebergs however the relative importance of these mechanisms in terms of the flux and bioavailability of the fe is the source of much interest and debate an unambiguous tracer of terrigenous material excess 224ra was used to show that free drifting icebergs are a significant fe source to surface waters in the southern ocean activity of 224ra half life 3 7 days was measured in the weddell sea in surface waters surrounding three free drifting icebergs and in iceberg alley inventories of excess 224ra indicate a local terrigenous input 1 3 orders of magnitude greater than estimates of aeolian dust fluxes to the southern ocean burdens of fine terrigenous material associated with current rates of iceberg ejection are estimated to be on the order of 90 106 tons per year for antarctica yielding a total fe input of 3 106 tons per year chemical and mineralogical composition of the terrigenous material confirms that 0 04 0 4 exists as labile fe in ferrihydrite that is potentially bioavailable on the order of 4 40 104 tons of per year these results suggest that free drifting icebergs can contribute significantly to atmospheric co2 drawdown though fe fertilization in the southern ocean

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

internal waves in the gulf of california observations from a spaceborne radar pronounced signatures of internal waves were detected repeatedly in the gulf of california by the seasat synthetic aperture radar sar a series of nine images with exactly repeating ground coverage was used to study the temporal variability of the internal wave field in the area it was found that the number of observed wave groups was highly correlated with the strength of the local tides the maximum number occurred during spring tides and the minimum number occurred during neap tides indicating that the internal waves were tidally forced most of the wave activity was found to the north of 28 n where the tides were the strongest in the gulf the application of a simple nonlinear internal wave model to the observations indicated that the peak to peak amplitude of the observed waves was about 50 m with an uncertainty of a factor of 2 the estimated upper bound for the rate of the loss of tidal energy to internal waves was about 5 1015 erg s representing only 10 of the rate of the dissipation of the dominant m2 tide in the gulf

axial convergence in a well mixed estuary abstract transverse secondary circulations involving surface convergence observed in a well mixed estuary in north wales are made visible by the collection of surface material along an axial line which extends continuously for many kilometres through the estuary the circulation and axial convergence however are seen only during the flood phase of the tide and no similar behaviour has been observed during the ebb phase convergent circulations in the estuary are associated with small but steady transverse density gradients in the cross section produced by non uniform advection of the longitudinal gradient through the channel a diagnostic model using measured mean distributions of cross sectional density indicates surface transverse velocities 0 1 ms 1 similar to those observed in the estuary the model further predicts appreciable transverse divergent currents at a fractional depth of 0 75 a prediction which has been tested in the estuary using a vertical array of accurately resolving current direction indicators

accumulation of biogenic and lithogenic material in the pacific sector of the southern ocean during the past 40 000 years the 230th normalization technique was applied to surface sediments and down core records from the pacific sector of the southern ocean between 120 w and 170 w in order to reconstruct vertical rain rates corrected for lateral redistribution of sediment preserved rain rates of opal organic carbon and biogenic ba all indicate that biological productivity south of the antarctic polar front apf was much lower than today during the last glacial maximum lgm probably in response to increased ice cover however by analogy with modern opal fluxes south of the acc we show that year round ice cover is not a prerequisite for very low rates of opal accumulation available records from north of the apf indicate little to no change in opal export in contrast to records from the indian and atlantic sectors which show enhanced opal export north of the apf during the lgm glacial records from north of 66 s in the pacific all show lithogenic fluxes that were greater than today but significantly lower than lithogenic fluxes in the glacial atlantic and indian sectors together these new records from the pacific sector show that during the lgm the three basins of the southern ocean were significantly more differentiated than today the observed inter basin distribution of lithogenic fluxes and opal burial and the presumed geographical distribution of increased dust input to the southern ocean during the lgm are consistent with an atlantic indian pacific gradient in the degree of iron stimulated diatom productivity within the zone lying between the apf and the subantarctic front previous studies which focused primarily on the atlantic sector may have overestimated the glacial increase in the strength of the biological pump in the southern ocean

algal communities attached to free drifting antarctic icebergs abstract disintegration of the antarctic peninsula s eastern ice shelves has increased the population of icebergs traversing the weddell sea but until recently little was known about their ecological impact on the pelagic environment here we describe a class of algal communities that occur on the submerged flanks of large free drifting glacially derived tabular icebergs we used remotely operated vehicles to examine these icebergs directly for the first time to survey the algal communities and collect material for shipboard laboratory studies the communities principally diatoms were associated with a characteristic cupped configuration of the ice surface and they served as feeding sites for aggregations of antarctic krill production rate measurements indicate that these communities are providing a substantial contribution to regional primary production in summer as the number of icebergs grows the number of algae communities may also be increasing along with their cumulative contribution to organic carbon flux

entrainment in shallow rotating gravity currents a modeling study abstract the physics of shallow gravity currents passing through a rotating channel at subcritical froude number is investigated here with a series of idealized numerical experiments it is found that the combined effects of friction and rotation set up a complex transverse circulation that has some crucial implications for the entrainment process a key component of this secondary circulation is a geostrophically balanced transverse jet in the interface that laterally drains fluid from the interface this effect is shown to result in a strong cross channel asymmetry and a spatial separation of the entrainment process drained interfacial fluid is partly replaced by entrained ambient fluid on the deep side of the gravity current whereas the downward mixing of buoyant fluid occurs on the shallow side these results closely corresponding to recent measurements in a shallow channelized gravity current in the western baltic sea illustrate that the description of entrainment as a strictly vertical mixing p

analysis of nonlinear internal waves in the new york bight this paper presents the results on internal wave analysis of the current meter mooring data in the new york bight from the sar internal wave signature experiment sarsex selective sets of current and temperature measurements are analyzed for a parametric study of internal wave characteristics and shear effects on wave parameters are studied based on the limited data from moorings the solitary wave theory has been extended for the wave evolution on a continental shelf by including dissipation and shoaling effects a series of numerical simulations are performed to demonstrate the relative importance of dissipation and shoaling effects from an observed initial wave packet at the upstream mooring the numerical evolution simulation compares reasonably well with the measurements at the distant mooring for the leading two large solitons

terrigenous input and paleoproductivity in the southern ocean the geochemistry of several sites along the polar front zone of the southern ocean revealed significant changes in terrigenous input and productivity on glacial timescales our records indicate concentrations and fluxes of terrigenous elements i e fe al and ti are low during interglacials and increase tenfold to twentyfold during glacials phosphorus accumulation reactive p concentrations and p ti ratios exhibit similar trends as the terrigenous components suggesting increased export production during glacials in all cores elemental ratios remain relatively constant indicating terrigenous sources at each site have not likely varied over the past 250 kyr iron accumulation rates for these sites are 10 times higher during glacials than interglacials and exceed the estimated regional eolian fluxes by 50 times the source of this terrigenous material is thus likely to be hemipelagic rather than direct eolian input or ice rafting and we speculate fe upwelled from this source may have stimulated glacial productivity in the southern ocean

carbon export associated with free drifting icebergs in the southern ocean abstract enrichment of the pelagic ecosystem associated with the proliferation of free drifting icebergs prompts questions about increased productivity and the export flux of organic carbon to the deep ocean with continued climate warming lagrangian sediment traps lst were deployed autonomously beneath a large tabular free drifting iceberg c 18a in the nw weddell sea during march and april 2009 to collect sinking particles at a depth of 600 m three lst deployments associated with c 18a within a 30 km radius collected sinking diatom frustules dominated by corethron pennatum and fragilariopsis nana euphausiid fragments crustacean and fish fecal material detrital aggregates and mineral grains one lst deployment at a control site 74 km away in open water devoid of icebergs collected diatom frustules euphausiid molts crustacean fecal material and detrital aggregates phytoplankton abundance microbial abundance and biomass were significantly higher in the lst samples than in open water collections at 500 m depth the mean mass flux and organic carbon flux associated with iceberg c 18a were twice as high 124 mg m 2 d 1 and 5 6 mg corg m 2 d 1 respectively than at the control site a similar trend was observed in corg 234th activity being highest near c 18a and lowest at the control site extrapolation of the area of enrichment to 30 km radius around c 18a 2826 km2 produces an estimated mass flux of 350 tons d 1 and carbon flux of 15 8 tons corg d 1 five similar sized icebergs to c 18a were identified in satellite images in a surrounding 47 636 km2 area at the same time of sampling assuming a 30 km radius as the area of influence around each of these five icebergs 46 of the total area would be enhanced with an export flux at 600 m of 122 4 tons corg d 1 the large numbers of smaller icebergs identified visually in this area would only increase this area of influence icebergs serve as areas of local enrichment and with increased proliferation must be considered in the cycling of carbon in the southern ocean

the signature of river and wind borne materials exported from patagonia to the southern latitudes a view from rees and implications for paleoclimatic interpretations abstract riverine and wind borne materials transferred from patagonia to the sw atlantic exhibit a homogeneous rare earth element ree signature they match well with the ree composition of recent tephra from the hudson volcano and hence this implies a dominance of material supplied by this source and other similar andean volcanoes due to the trapping effect of proglacial and reservoir lakes the larger patagonian rivers deliver to the ocean a suspended load with a slightly modified andean signature that shows a ree composition depleted in heavy rees in this paper we redefine patagonia as a source of sediments which is in contrast with other sources located in southern south america quaternary sediments deposited in the northern and to a lesser extent in the southern scotia sea and most of the dust in ice cores of east antarctica have ree compositions very similar to the loess from buenos aires province and to patagonian eolian dust however we rule out buenos aires province as a holocene major source of sediments similarly to buenos aires loess a proximal facies it is likely that the ree compositions of most sediment cores of the scotia sea and antarctica reflect a distal transport of dust with an admixed composition from two main sources a major contribution from patagonia and a minor proportion from source areas containing sediments with a clear upper crustal signature e g western argentina or from bolivia s altiplano evidence indicates that only during the last glacial maximum patagonian materials were the predominant sediment source to the southern latitudes

shoaling of nonlinear internal waves in massachusetts bay 1 the shoaling of the nonlinear internal tide in massachusetts bay is studied with a fully nonlinear and nonhydrostatic model the results are compared with current and temperature observations obtained during the august 1998 massachusetts bay internal wave experiment and observations from a shorter experiment which took place in september 2001 the model shows how the approaching nonlinear undular bore interacts strongly with a shoaling bottom offshore of where kdv theory predicts polarity switching should occur it is shown that the shoaling process is dominated by nonlinearity and the model results are interpreted with the aid of a two layer nonlinear but hydrostatic model after interacting with the shoaling bottom the undular bore emerges on the shallow shelf inshore of the 30 m isobath as a nonlinear internal tide with a range of possible shapes all of which are found in the available observational record

a nonhydrostatic version of fvcom 2 mechanistic study of tidally generated nonlinear internal waves in massachusetts bay 1 the generation propagation and dissipation processes of large amplitude nonlinear internal waves in massachusetts bay during the stratified season were examined using the nonhydrostatic finite volume coastal ocean model fvcom nh the model reproduced well the characteristics of the high frequency internal waves observed in massachusetts bay in august 1998 the model experiments suggested that internal waves over stellwagen bank are generated by the interaction of tidal currents with steep bottom topography through a process of forming a large density front on the western slope of the bank by the release of an initial density perturbation near ebb flood transition nonlinear steepening of the density front into a deep density depression and disintegrating of the density depression into a wave train earth s rotation tends to transfer the cross bank tidal kinetic energy into the along bank direction and thus reduces the intensity of the density perturbation at ebb flood transition and density depression in the flood period the internal wave packet propagates as a leading edge feature of the internal tidal wave and the faster propagation speed of the high frequency internal waves in massachusetts bay is caused by earth s rotation the model experiments suggested that bottom friction can significantly influence the cross bank scale of the density perturbation and thus the density depression during wave generation and the dissipation during the wave s shoaling inclusion of vertical mixing using the mellor yamada level 2 5 turbulence closure model had only a marginal effect on wave evolution the model results support the internal wave theory proposed by lee and beardsley 1974 but are in disagreement with the lee wave mechanism proposed by maxworthy 1979

imaging and sampling beneath free drifting icebergs with a remotely operated vehicle abstract a commercially available small less than 100 kg remotely operated vehicle rov was modified to image and sample the marine ecosystem surrounding free drifting icebergs east of the antarctic peninsula during three field expeditions in 2005 2008 and 2009 modifications included fitting the vehicle with an accessory tool sled additional thrusters flotation and significant changes to internal wiring to support a wide array of sensors and samplers the rov was re configured aboard the r v nathaniel b palmer to perform either general exploration and biological sampling bio dives or water sampling chemistry dives in situ sensors and a suction sampler were used for bio dives while a suction pump and hose were fastened along the full length of the rov tether to enable continuous water sampling adjacent to each iceberg during chemistry dives details of the rov system are presented along with a discussion of the 18 dives that explored the sides and bottoms of six different icebergs during the 2009 field expedition

evidence against dust mediated control of glacial interglacial changes in atmospheric co2 the low concentration of atmospheric co2 inferred to have been present during glacial periods is thought to have been partly caused by an increased supply of iron bearing dust to the ocean surface1 this is supported by a recent model2 that attributes half of the co2 reduction during past glacial stages to iron stimulated uptake of co2 by phytoplankton in the southern ocean but atmospheric dust fluxes to the southern ocean even in glacial periods are thought to be relatively low and therefore it has been proposed that southern ocean productivity might be influenced by iron deposited elsewhere for example in the northern hemisphere3 4 which is then transported south via ocean circulation similar to the distal supply of iron to the equatorial pacific ocean5 6 7 here we examine the timing of dust fluxes to the north atlantic ocean in relation to climate records from the vostok ice core in antarctica around the time of the penultimate deglaciation about 130 kyr ago two main dust peaks occurred 155 kyr and 130 kyr ago but neither was associated with the co2 rise recorded in the vostok ice core this mismatch together with the low dust flux supplied to the southern ocean suggests that dust mediated iron fertilization of the southern ocean did not significantly influence atmospheric co2 at the termination of the penultimate glaciation

cooling dilution and mixing of ocean water by free drifting icebergs in the weddell sea abstract iceberg c 18a 35 7 0 184 km was studied repeatedly by five circumnavigational surveys in march april 2009 during the period of the surveys c 18a travelled 109 nautical miles in 23 days covering an area of 8 1 10 3 km 2 this iceberg was formed from iceberg c 18 76 7 km that originated from the ross ice shelf in may 2002 ship based measurements show that this iceberg produced fresh meltwater above the seasonal pycnocline that diluted and chilled the water it passed through from the surface to a depth of approximately 50 m summer mixed layer the surface meltwater effects were detectable as far away as 19 km and persisted for at least 10 days we also found evidence that this iceberg was disrupting the weddell deep water to depths up to 1500 m if we include these deep effects through the water column the estimate of ocean water altered by this single iceberg reaches 3 10 12 m 3 over 23 days chemical and biological effects were detected at the same space and time scales as the physical properties with decreasing partial pressure of carbon dioxide pco 2 close to the iceberg and lower particle and chlorophyll concentration ten days after the passage of c 18a chlorophyll a had increased by 15 these results are consistent with alternative hypotheses regarding the role of icebergs as mediators of a localized geophysical disturbance h 1 as well as promoters of chlorophyll a production h 2

free drifting icebergs as sources of iron to the weddell sea abstract in recent years glaciers on the antarctic peninsula have retreated resulting in loss of mass from ice shelves and increased supply of icebergs to the southern ocean free drifting icebergs may serve as an important source of fe to surrounding waters we measured concentrations of dissolved fe and fe content of suspended particulate material via flow injection chemiluminescence and icp ms respectively in the waters surrounding several icebergs during cruises to the scotia and weddell seas in june 2008 and march 2009 surface dissolved fe dfe concentrations varied from 0 58 to 2 92 nm and were elevated up to 60 at some stations 10 km from the icebergs indicating general fe enrichment in the lower salinity surface layer however surface dfe within 1 km of the iceberg was similar to that measured at depths below the draft of the iceberg a feature that may result from upwelling of circumpolar deep water caused by basal melting at the face of the iceberg iron concentrations in ice collected following calving events were highly variable 4 600 nm but were elevated above concentrations in seawater particulate fe normalized to particulate p in suspended particulate material was up to 20 fold higher within 0 6 km of two large tabular icebergs but no enrichment was observed at two smaller icebergs iron phosphorus ratios of suspended particulate material were also higher in deeper 40 m waters compared to shallow ca 15 m waters at the iceberg face iron release appeared to be episodic producing a spatially heterogeneous environment around icebergs this source term may increase in coming years as antarctic ice shelves degrade further potentially impacting the ecology and biogeochemistry of low fe waters of the southern ocean

near field zooplankton ice face biota and proximal hydrography of free drifting antarctic icebergs abstract a small rov was used to collect plankton make video surveys and take hydrographic measurements in close proximity to six free drifting antarctic icebergs the icebergs studied ranged in size from 32 km in length large icebergs have a greater scale of influence than do smaller ones and iceberg mediated differences in the hydrographic characteristics of their surrounding water depend on the scale sampled irrespective of size temperature generally decreased in close proximity to an iceberg while salinity increased chlorophyll a was often lower in the surface waters near the iceberg relative to the surface waters further away tabular icebergs typically had 3 distinct underwater features shelf side and bottom ablation pockets were a common feature of subsurface ice the ice itself is a dynamic and seemingly harsh environment with relatively few macrofauna living on it those that do inhabit the ice face are either highly specialized or highly mobile species composition of zooplankton within 40 m of an iceberg did not change relative to distance however biomass was generally greater within 5 m of an iceberg than it was 15 to 40 m distant

impacts on phytoplankton dynamics by free drifting icebergs in the nw weddell sea abstract glacier ice released to the oceans through iceberg formation has a complex effect on the surrounding ocean waters we hypothesized that phytoplankton communities would differ in abundance composition and production around or close to an iceberg this paper tests the influence of individual icebergs on scales of meters to kilometers observed through shipboard oceanographic sampling on march april 2009 surface waters integrated 0 100 m depth within the euphotic zone sampled close to the iceberg c 18a 10 m and the salps on smaller cells 3 10 m the iceberg s main influence in the austral fall is measured not so much by phytoplankton accumulation but by reactivation of the classic antarctic food chain facilitating diatom growth and sustaining high antarctic krill populations

turbulence dynamics at the shoal channel interface in a partially stratified estuary abstractturbulence observations at the shoal channel interface in south san francisco bay are described and analyzed in this work profiles of turbulent kinetic energy tke shear production and dissipation rate are estimated from adcp beam velocities over a nine day period during winter 2009 when the estuary was partially stratified the tke shear production profiles are consistent with a tidally driven bottom boundary layer except late in the ebb when shear production intensifies and the region of maximum production is located in the upper half of the water column a simple scaling for the depth averaged tke shear production based on bed friction performs well except during this late ebb period when it fails to predict the peak in shear production which suggests that a mechanism other than bottom drag drives turbulence dynamics during this period the profiles of tke dissipation rates also display a late ebb peak a lateral circulation develops at the shoal channel interface during this late ebb perio

detection of massachusetts bay internal waves by the synthetic aperture radar sar on seasat we have examined all eight seasat passes over massachusetts bay that yielded synthetic aperture radar sar imagery four of the passes showed banded surface features that suggested a group of internal waves propagating southwestward from stellwagen bank comparison of the positions of the sar features with predictions of internal wave locations derived from earlier in situ work at massachusetts bay confirms that the sar features are indeed rough and smooth bands of water caused by a propagating packet of internal waves the packet is caused by tidal currents interacting with the stratification over and the topography of stellwagen bank even the four passes that do not show internal waves are consistent with the above conclusions since the predicted packet positions occur outside the region covered by those four passes these comparisons are presented to show that the seasat sar is indeed capable of detecting internal waves in massachusetts bay even though these waves are considerably less intense than in some other reported areas of the world

convergence of lateral flow along a coastal plain estuary a set of velocity profiles obtained in the james river estuary with an acoustic doppler current profiler was used in combination with the results of an analytic tidal model to depict the appearance of surface lateral flow convergences v y during both flood and ebb stages of the tidal cycle the bathymetry of the estuary was characterized by a main channel and a secondary channel separated by relatively narrow shoals lateral surface flow convergences appeared over the edges of the channels and were produced by the phase lag of the flow in the channel relative to the shoals flood convergences developed in the late tidal stages and ebb convergences appeared soon after maximum currents most of these convergences caused fronts in the density field and flotsam lines that also appeared over the edges of the channel and that lasted 2 hours the transverse flows associated with the convergences were mostly in the same direction throughout the water column in fact the vertically averaged flow produced the same convergence patterns as those near the surface the analytic tidal model reproduced well the timing and location of the convergences as observed in the james river model results with different bathymetry emulated the results in other estuaries e g axial convergence in an estuary with a channel in the middle this work showed that the strength of lateral convergences along the estuary was proportional to the tidal amplitude and the channel steepness it also suggested that the convergences were produced mainly by the tidal flow interacting with the channel shoal bathymetry i e that they did not require the presence of density gradients however the analytic model underestimated the magnitude of the convergences and did not account for vertical circulations associated with fronts the formation of fronts resulted from the interaction of the tidal flow with the bathymetry and the density field

dissolved fe in the upper waters of the pacific sector of the southern ocean the concentration of dissolved fe was determined in upper ocean waters along 170 degreesw between 53 and 72 degreess during four cruises between october 1997 and march 1998 as part of the us jgofs southern ocean antarctic polar frontal zone cruises fe concentrations were extremely variable in both space and time as a result of advection of meso scale eddys through the region observed values ranged from a maximum of 0 34 nm at 64 degreess in november next to the retreating ice edge to 0 075 nm in march at 71 degreess in the northern ross sea gyre in general the highest average mixed layer fe concentrations and the largest seasonal changes were observed in the two frontal zones at similar to 60 degreess and similar to 64 degreess formation of deep mixed layers during winter and the entrainment of sub surface waters enriched in fe is the primary source of this element to surface waters in this region of the southern ocean additionally upwelling of circumpolar deep water in the circumpolar current along its northern boundary at the polar front and its southern boundary at the southern antarctic circumpolar current front is an important mechanism supplying fe to surface waters in these areas throughout the summer comparison of integrated fe concentrations and th derived poc export and n drawdown all suggest that the maximum changes in these properties are comparable to those that would be predicted by fe availability fe concentrations determined by shipboard flow injection analysis measures et al mar chem 50 1995 3 were significantly higher than those found in replicate samples determined by shored based flameless atomic absorption spectrophotometry after preconcentration by chelation solvent extraction johnson et al mar chem 57 1997 137 the concentration differences which appear to be restricted to the upper 200 300 m do not appear to arise from different sampling or handling processes but instead are believed to result from the different sensitivity of the methods to organic fractions of fe in seawater c 2001 elsevier science ltd all rights reserved

provenance and dispersal of glacial marine surface sediments in the weddell sea and adjoining areas antarctica ice rafting versus current transport abstract mineralogical and granulometric properties of glacial marine surface sediments of the weddell sea and adjoining areas were studied in order to decipher spatial variations of provenance and transport paths of terrigenous detritus from antarctic sources the silt fraction shows marked spatial differences in quartz contents in the sand fractions heavy mineral assemblages display low mineralogical maturity and are dominated by garnet green hornblende and various types of clinopyroxene cluster analysis yields distinct heavy mineral assemblages which can be attributed to specific source rocks of the antarctic hinterland the configuration of modern mineralogical provinces in the near shore regions reflects the geological variety of the adjacent hinterland in the distal parts of the study area sand sized heavy minerals are good tracers of ice rafting granulometric characteristics and the distribution of heavy mineral provinces reflect maxima of relative and absolute accumulation of ice rafted detritus in accordance with major iceberg drift tracks in the course of the weddell gyre fine grained and coarse grained sediment fractions may have different origins in the central weddell sea coarse ice rafted detritus basically derives from east antarctic sources while the fine fraction is discharged from weak permanent bottom currents and or episodic turbidity currents and shows affinities to southern weddell sea sources winnowing of quartz rich sediments through intense bottom water formation in the southern weddell sea provides muddy suspensions enriched in quartz the influence of quartz rich suspensions moving within the weddell gyre contour current can be traced as far as the continental slope in the northwestern weddell sea in general the focusing of mud by currents significantly exceeds the relative and absolute contribution of ice rafted detritus beyond the shelves of the study area

persistent iceberg groundings in the western weddell sea antarctica abstract we use the time average of a series of satellite synthetic aperture radar sar images from 2005 to 2007 to identify grounded icebergs in the western weddell sea satellite laser altimetry along repeated ground tracks confirms that regions of high mean backscatter are associated with stationary tabular icebergs the altimeter data also provide iceberg freeboard from which we infer maximum ice draft assuming the lightly grounded limit and a two layer density model consistent with a source at filchner ronne ice shelf the maximum iceberg draft agrees very well with the ocean depth at a point where the bathymetry is well constrained by ship soundings however for an extensive region near 71 s south of larsen c ice shelf the maximum grounding depth for several icebergs reveals the ocean to be locally more than 200 m shallower than in bathymetry products this previously uncharted bank is expected to have a profound effect on the northward flow of the western weddell gyre and the cross slope transport of offshore warm deep water towards the eastern antarctic peninsula ice shelves passive microwave data also show that sea ice concentration is reduced in the vicinity of this group of grounded icebergs indicating an iceberg influence on ocean atmosphere heat and freshwater exchanges

dissolved iron in the vicinity of the crozet islands southern ocean the annual phytoplankton bloom occurring north of the crozet plateau provides a rare opportunity to examine the hypothesis that natural iron fertilization can alleviate high nutrient low chlorophyll hnlc conditions normally associated with the southern ocean therefore during crozet natural iron bloom and export experiment crozex a large multidisciplinary study performed between november 2004 and january 2005 measurements of total dissolved iron dfe0 2 m were made on seawater from around the islands and atmospheric iron deposition estimated from rain and aerosol samples dfe concentrations were determined by flow injection analysis with n n dimethyl p phenylenediamine dihydrochloride dpd catalytic spectrophotometric detection dfe concentrations varied between 0 086 and 2 48 nm with low values in surface waters enrichment of dissolved iron 1 nm at close proximity to the islands suggests that the plateau and the associated sediments are a source of iron waters farther north also appear to be affected by this input of coastal and shelf origin although dissolved iron concentrations decrease as a function of distance to the north of the plateau with a gradient of 0 07 nm km 1 at the time of sampling using lateral and vertical diffusion coefficients derived from ra isotope profiles and also estimates of atmospheric inputs it was then possible to estimate a dfe concentration of 0 55 nm to the north of the islands prior to the bloom event which is sufficient to initiate the bloom the lateral island source being the largest component a similar situation is observed for other sub antarctic islands such as kerguelen south georgia that supply dissolved iron to their surrounding waters thus enhancing chlorophyll concentrations

observations of internal wave packets propagating along shelf in northern monterey bay internal waves of depression were observed propagating along shelf and into northern monterey bay california ca on the inner shelf these waves had amplitudes approximately equal to the thermocline depth 4 m and were unstable to shear and mix the thermocline isopycnal gradient spectra showed that the wave packets lead to an elevated mean dissipation rate of 2 63 10 5 m3 s 2 for up to 2 hours after wave passage the proximity to the surface created strong surface convergences that can actively transport buoyant material such as plankton back into the bay the wave packets were observed regularly over the upwelling season across multiple years suggesting they may have large effects on the documented spatial variation of phytoplankton and larvae on the inner shelf the timing of the waves suggests they are not formed by tides interacting with bathymetry but are generated by buoyant plume propagation

field studies of the flow structure in a straight reach of the conwy estuary abstract synchronous measurements of dye distributions from a single point source surface injection and of the turbulent mean flow structure in a straight reach of the conwy estuary have been obtained for several tidal cycles the resulting two dimensional temporal y z t variations of velocity and salinity together with the three dimensional x y z dye distributions have been used to provide both a qualitative and quantitative description of the vertical stability and transverse flows caused by the interaction of the longitudinal solute induced density gradient and fluid shear the results show that the flow structure is temporally dependent due to velocity and depth changes and is spatially dependent due to channel topography

intratidal dynamics of fronts and lateral circulation at the shoal channel interface in a partially stratified estuary abstractin partially stratified shoal channel estuaries variations in bathymetry at the shoal channel interface generate horizontal shears and density gradients and foam lines characteristic of convergence fronts are frequently observed this study is based on transect data collected every 30 min across the shoal channel interface in south san francisco bay to analyze the dynamics of the transverse circulation and convergence fronts at this interface throughout a tidal cycle during the ebb a lateral density gradient develops as a result of the competition between differential advection of the longitudinal salinity gradient lateral variations in vertical mixing and nonlinear advection terms which are strongest when convergence fronts develop early and late in the ebb the lateral circulation over the slope is characterized by a large intratidal variability reversing three times during the ebb this variability is driven by a balance dominated by inertia and lateral baroclinic pressure gradient duri

generation and propagation of nonlinear internal waves in massachusetts bay 1 during the summer nonlinear internal waves nliws are commonly observed propagating in massachusetts bay the topography of the area is unique in the sense that the generation area over stellwagen bank is only 25 km away from the shoaling area and thus it represents an excellent natural laboratory to study the life cycle of nliws to assist in the interpretation of the data collected during the 1998 massachusetts bay internal wave experiment mbiwe98 a fully nonlinear and nonhydrostatic model covering the generation shoaling region was developed to investigate the response of the system to the range of background and driving conditions observed simplified models were also used to elucidate the role of nonlinearity and dispersion in shaping the nliw field this paper concentrates on the generation process and the subsequent evolution inthe basin themodel was foundtoreproducewell the range of propagation characteristics observed arrival time propagation speed amplitude and provided a coherent framework to interpret the observations comparison with a fully nonlinear hydrostatic model shows that during the generation and initial evolution of the waves as they move away from stellwagen bank dispersive effects play a negligible role thus the problem can be well understood considering the geometry of the characteristics along which the riemann invariants of the hydrostatic problem propagate dispersion plays a role only during the evolution of the undular bore in the middle of stellwagen basin the consequences for modeling nliws within hydrostatic models are briefly discussed at the end

weddell sea iceberg drift five years of observations since 1999 52 icebergs have been tagged with gps buoys in the weddell seato enable monitoring of their position the chosen icebergs were of small tomedium size with a few icebergs larger than 10 km associatedwith the calving of icebergs a38 and a43 from the ronne ice shelf the majority of icebergs were tagged off neumayer station 8e 70s it was found that smaller bergs with edges shorter than 200 m had the shortestlife cycle 0 5 yr iceberg and thus freshwater export out of theweddell sea was found to be highly variable in one year the majority of buoysdeployed remained in the weddell sea constituting about 40 of the ncep p efreshwater input whereas in other years all of the tagged icebergs were exported the observed drifts of icebergs and sea ice showed a remarkably coherent motion the analysis of an iceberg sea ice buoy array in the western weddell seaand an iceberg array in the eastern weddell sea showed a coherent sea iceiceberg drift in sea ice concentrations above 86 dynamic kinematic parameter dkp during the course of coherent movement were low and deviations from the meancourse associated with the passage of low pressure system the length scale ofcoherent movement was estimated to be less than 250km about half the value found forthe arctic ocean

drivers of residual estuarine circulation in tidally energetic estuaries straight and irrotational channels with parabolic cross section the generation of residual circulation in a tidally energetic estuary with constant longitudinal salinity gradient and parabolic cross section is examined by means of a two dimensional cross sectional numerical model neglecting river runoff and stokes drift it is shown how the longitudinal and lateral residual circulation can be decomposed into contributions from various processes such as tidal straining circulation gravitational circulation advectively driven circulation and horizontal mixing circulation the sensitivity of the residual circulation and its components from various processes to changes in forcing is investigated by varying the simpson number nondimensional longitudinal buoyancy gradient and the unsteadiness parameter nondimensional tidal frequency as well as the bed roughness and the width of the estuary for relatively weak salinity gradient forcing the tidal straining circulation dominates the residual exchange circulation in support of classical estuarine circulation up estuary flow near the bed and down estuary flow near the surface the strength of the longitudinal estuarine circulation clearly increases with increased salinity gradient forcing however when the simpson number exceeds 0 15 the relative contributions of both gravitational circulation and advectively driven circulation to estuarine circulation increase substantially lateral residual circulation is relatively weak for small simpson numbers and becomes flood oriented divergent flow near the bed and convergent flow near the surface for larger simpson numbers because of increasing contributions from gravitational and advectively driven circulation increasing the unsteadiness number leads to decreased longitudinal and lateral residual circulation although changes in bed roughness result in relatively small changes in residual circulation results are sensitive to the width of the estuary mainly because of changes in residual exchange circulation driven by tidal straining

ice core evidence for the extent of past atmospheric co2 change due to iron fertilisation 1 an extended high resolution ice core record of dust deposition over the past 60 ka from dome c antarctica is presented the data are in conflict with the idea that changes in aeolian iron input into the southern ocean were the major cause for the 80 ppm glacial interglacial co2 increase during the deglaciation the co2 increase shows a linear relationship with the fall of the logarithm of the nss ca2 flux a proxy for dust deposition however the very large variations in the nss ca2 flux related to the glacial antarctic warm events a1 to a4 were accompanied by small co2 variations only our data based analysis suggests that decreased southern ocean dust deposition caused at most a 20 ppm increase in co2 at the last glacial interglacial transition rapid decreases in dust deposition to the northern pacific could have been responsible for a maximum of 8 ppm in addition

modeling the lateral circulation in straight stratified estuaries the dynamics of lateral circulation in an idealized straight estuary under varying stratification conditions is investigated using a three dimensional hydrostatic primitive equation model in order to determine the importance of lateral circulation to the momentum budget within the estuary for all model runs lateral circulation is about 4 times as strong during flood tides as during ebbs this flood ebb asymmetry is due to a feedback between the lateral circulation and the along channel tidal currents as well as to time varying stratification over a tidal cycle as the stratification is increased the lateral circulation is significantly reduced because of the adverse pressure gradient set up by isopycnals being tilted by the lateral flow itself when rotation is included a timedependent cross channel ekman circulation is driven and the tidally averaged bottom lateral circulation is enhanced toward the right bank when looking toward the ocean in the northern hemisphere this asymmetry in the tidally averaged bottom lateral circulation may lead to asymmetric sediment transport leading to asymmetric channel profiles in straight estuaries for the weakly stratified model run advection due to lateral currents is a dominant term in both the along channel and cross channel momentum equations over a tidal cycle and for the tidally averaged momentum equations in the tidally averaged along channel momentum equation lateral advection acts as a driving term for the estuarine exchange flow and can be larger than the along channel pressure gradient therefore it should not be ignored when estimating momentum budgets in estuaries

numerical analysis of stratification and destratification processes in a tidally energetic inlet with an ebb tidal delta stratification and destratification processes in a tidally energetic weakly stratified inlet in the wadden sea south eastern north sea are investigated in this modeling study observations of current velocity and vertical density structure show strain induced periodic stratification for the southern shoal of the tidal channel in contrast to this in the nearby central region of the channel increased stratification is already observed directly after full flood to investigate the processes leading to this different behavior a nested model system using getm is set up and successfully validated against field data the simulated density development along a cross section that includes both stations shows that cross channel stratification is strongly increasing during flood such that available potential energy is released in the deeper part of the channel during flood an analysis of the potential energy anomaly budget confirms that the early onset of vertical stratification during flood at the deeper station is mainly controlled by the stratifying cross channel straining of the density field in contrast to this in the shallow part of the channel the relatively weak cross channel straining is balanced by along channel straining and vertical mixing an idealized analytical model confirms the following hypothesis the laterally convergent flood current advecting laterally stratified water masses from the shallow and wide ebb tidal delta to the deep and narrow tidal channel has the tendency to substantially increase cross channel density gradients in the tidal channel this process leads to stratification during flood

the link between climate warming and break up of ice shelves in the antarctic peninsula a review of in situ and remote sensing data covering the ice shelves of the antarctic peninsula provides a series of characteristics closely associated with rapid shelf retreat deeply embayed ice fronts calving of myriad small elongate bergs in punctuated events increasing flow speed and the presence of melt ponds on the ice shelf surface in the vicinity of the break ups as climate has warmed in the antarctic peninsula region melt season duration and the extent of ponding have increased most break up events have occurred during longer melt seasons suggesting that meltwater itself not just warming is responsible regions that show melting without pond formation are relatively unchanged melt ponds thus appear to be a robust harbinger of ice shelf retreat we use these observations to guide a model of ice shelf flow and the effects of meltwater crevasses present in a region of surface ponding will likely fill to the brim with water we hypothesize building on weertman 1973 hughes 1983 and van der veen 1998 that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat a thermodynamic finite element model is used to evaluate ice flow and the strain field and simple extensions of this model are used to investigate crack propagation by meltwater the model results support the hypothesis