solubility of fe iii in seawater abstract recently kuma et al k kuma j nishioka k matsunaga controls on iron iii hydroxide solubility in seawater the influence of ph and natural organic chelators limnol oceanogr 41 1996 396 407 made some careful measurements of the solubility of fe iii in uv and non uv irradiated seawater as a function of ph 5 8 they showed that organic compounds can increase the solubility 32 65 at ph 8 1 apparently due to the formation of fe iii organic complexes in this paper i have examined how these results can be quantified using a speciation model for fe iii the results indicate that the effect of ph 2 9 on coastal and open ocean waters by kuma et al and the earlier filtration measurement of byrne and kester r h byrne d r kester solubility of hydrous ferric oxide and iron speciation in sea water mar chem 4 1976 255 274 can be adequately represented by considering the formation of feoh2 and fe oh 2 using the hydrolysis constants k 1 10 2 62 k 2 10 6 0 determined by millero et al f j millero w yao j aicher the speciation of fe ii and fe iii in natural waters mar chem 50 1995 21 39 the solubility measurements kuma et al 1996 on unaltered coastal and open ocean waters appear to require the consideration of the formation of fe oh 30 k 3 10 13 3 10 14 3 a more careful look at these measurements indicates that the curvature between ph 7 and 8 can be attributed to the formation of complexes of fe3 with organic ligands fel model speciation calculations ph 6 8 yield total ligand concentrations of l t 1 2 nm and 0 17 nm for unaltered coastal and open ocean waters respectively assuming k fel 1021 these estimates are in good agreement with the values found for ocean waters by voltammetric methods the model calculations for the solubility of fe iii 0 2 nm at ph 8 1 and 0 6 nm at ph 7 65 are in good agreement with measured open ocean surface 0 2 nm and deep waters 0 6 nm determined by various workers since these calculations are strongly dependent upon the total fe and organic ligand concentrations in the waters future studies should include solubility and voltammetric measurements on the same sample to clarify these relationships

a finite element model for tides and resonance along the north coast of british columbia a finite element barotropic tidal model is developed for the north coast of british columbia the model is run with eight tidal constituents and the results are compared with the flather 1987 finite difference model and with extensive tide gauge and current meter observations although the tidal potential earth tide and loading tide are included in the forcing their inclusion is shown to change the largest m2 amplitudes by only 2 5 and the largest k1 amplitudes by less than 1 root mean square differences between observed and calculated sea level amplitudes and phases are within 1 9 cm and 2 9 o for all but one constituent but the model currents do not in general compare as favourably the barotropic currents observed in hecate strait are reproduced well but elsewhere evidence is shown that model inaccuracies are due to baroclinic effects tidal residual currents calculated by the model suggest the existence of eddies off the tip of cape st james cape chacon and around goose island and learmonth banks the shallow water constituents in hecate strait are shown to have significant contributions from the constructive interference of signals propagating into dixon entrance and queen charlotte sound using the model the longest resonant period of the system is estimated to be 7 6 hours with an energy dissipation parameter q of 9 5

fluxes of particulate iron from the upper ocean around the crozet islands a naturally iron fertilized environment in the southern ocean despite a large macronutrient reservoir the southern ocean has low levels of chlorophyll primarily due to low iron availability exceptions to this situation are island systems where natural terrestrial iron inputs allow the development of large blooms particulate organic carbon poc and particulate labile and refractory iron analyses were performed on large 53 m particles collected at the base of the mixed layer within such a system the crozet islands and in adjacent high nutrient low chlorophyll hnlc waters biogenic iron was obtained by removal of estimated lithogenic fe from the total fe present we combine these data with 234th measurements to determine downward particulate fe fluxes fluxes of fe ranged from 4 to 301 nmol m 2 d 1 labile not detectable to 50 mol m 2 d 1 biogenic and from 3 to 145 mol m 2 d 1 total and on average were approximately four times larger below the highly productive naturally iron fertilized region than below the adjacent hnlc area downward labile iron fluxes are close to the sum of dissolved terrestrial atmospheric and upwelled iron calculated from the planquette et al 2007 model refractory iron fluxes are 2 orders of magnitude larger and these can only have come from particles advected from the plateau itself the biogenic fe is a substantial fraction 0 76 mean 23 of the total particulate fe to the north of the islands the origin of this fe pool must be dominantly biological conversion from the lithogenic fraction as other supply terms including aeolian deep mixing and lateral advection of dissolved fe are inadequate to account for the magnitude of this fe inclusion of the offshore biologically available fraction of the lithogenic iron flux is therefore required to calculate fully the yield of carbon exported per unit iron injected

cross shelf transport of terrestrial al enhanced by the transition of northeasterly to southwesterly monsoon wind over the east china sea aluminum al is one of the key parameters of geotraces in spring 2011 we examined the distribution of dissolved al in the east china sea ecs to assess the potential passage of coastal water across the shelf to the western pacific measurement of dissolved al in coastal shelf and shelf break waters indicated decreasing concentrations with distance from the coast however the northward increase of dissolved al in the upper 100 m along the shelf break transect corresponding to the northward flow of kuroshio water along the okinawa trough from the north of taiwan to the tokara strait indicates contributions of terrestrial material the presence of an al plume indicated cross shelf transport at the subsurface at a potential density of 23 3 24 0 kg m3 this plume originates from the near bottom layer along the coast off zhejiang and fujian provinces and first moves southeastward to the north of taiwan and then northeastward to shelf break with export at 29 n 127 e we calculated the cross shelf fluxes of water and dissolved al based on simulation results of the 3 d massachusetts institute of technology general circulation model mitgcm the calculated cross shelf fluxes of al at the subsurface layer indicate that the ecs is highly efficient in pumping al rich coastal waters northward to the japan sea east sea and or eastward into the western pacific we also identified an important role of the monsoon with a change from northeasterly wind to southwesterly wind in spring on the cross shelf transport of al by use of numerical tracer experiments

a revised global estimate of dissolved iron fluxes from marine sediments literature data on benthic dissolved iron dfe fluxes mol m 2 d 1 bottom water oxygen concentrations o2bw m and sedimentary carbon oxidation rates cox mmol m 2 d 1 from water depths ranging from 80 to 3700 m were assembled the data were analyzed with a diagenetic iron model to derive an empirical function for predicting benthic dfe fluxes inline image where 170 mol m 2 d 1 is the maximum flux for sediments at steady state located away from river mouths this simple function unifies previous observations that cox and o2bw are important controls on dfe fluxes upscaling predicts a global dfe flux from continental margin sediments of 109 55 gmol yr 1 of which 72 gmol yr 1 is contributed by the shelf 2000 m of 41 21 gmol yr 1 is unsupported by empirical data previous estimates of benthic dfe fluxes derived using global iron models are far lower approximately 10 30 gmol yr 1 this can be attributed to i inadequate treatment of the role of oxygen on benthic dfe fluxes and ii improper consideration of continental shelf processes due to coarse spatial resolution globally averaged dfe concentrations in surface waters simulated with the intermediate complexity university of victoria earth system climate model were a factor of 2 higher with the new function we conclude that i the dfe flux from marginal sediments has been underestimated in the marine iron cycle and ii iron scavenging in the water column is more intense than currently presumed

simulation of barotropic and baroclinic tides off northern british columbia abstract the tidal response of northern british columbia coastal waters is studied through simulations with a three dimensional prognostic primitive equation model the model is forced at the boundaries with the leading semidiurnal and diurnal constituents and experiments with stratified and homogeneous fluid are compared the barotropic response shows good agreement with previously published studies of tides in the region a comparison with tide gauge measurements indicates that average relative rms differences between observations and the model surface elevation field are less than 5 for the largest constituents an internal tide is generated in cases where the model is initialized with a vertical stratification diagnostic calculations of the baroclinic energy flux are used to identify regions of generation and propagation of internal tidal energy with a representative summer stratification the integrated offshore flux is about 0 5 gigawatts higher than previously estimated from theoretical model

organization of stratification turbulence and veering in bottom ekman layers 1 detailed observations of the ekman spiral in the stratified bottom boundary layer during a 3 month period in an upwelling season over the oregon shelf suggest a systematic organization counter clockwise veering in the bottom boundary layer is constrained to the weakly stratified layer below the pycnocline and its height is nearly identical to the turbulent boundary layer height veering reaches 13 4 degrees near the bottom and exhibits a very weak dependence on the speed and direction of the interior flow and the thickness of the veering layer a simple ekman balance model with turbulent viscosity consistent with the law of the wall parameterization modified to account for stratification at the top of the mixed layer is used to demonstrate the importance of stratification on the ekman veering the model agrees reasonably well with observations in the lower 60 70 of the bottom mixed layer above which it diverges from the data due to the unaccounted physics in the interior neglect of stratification in an otherwise identical model results in far worse agreement with the data yielding veering in the bottom ekman layer which is much smaller than measured but distributed over a much thicker layer

iron transport by mesoscale haida eddies in the gulf of alaska abstract a two year study of the iron distributions in anticyclonic mesoscale haida eddies of the eastern north pacific ocean has shown that such eddies are a major source of iron to the high nitrate low chlorophyll hnlc waters of the central gulf of alaska basin these eddies which are typically about 100 km in diameter form off the west coast of canada in winter and then track roughly westward into the open ocean therefore they carry large quantities of iron rich coastal waters into iron limited waters of the oligotrophic gyre when the eddies had first formed their dissolved iron concentrations were nearly two orders of magnitude higher than is typically observed at station papa 50 n 145 w 3 n m versus less than 0 05 n m and the total iron in the eddies surface waters 10 40 m was more than 13 n m higher than open ocean waters of the alaska gyre 14 n m versus 0 5 n m while the overall iron content of the eddies decreased rapidly during the first year after they formed the eddy we were able to track the longest still contained 1 5 2 times more iron than the surrounding waters 16 months after its formation therefore although iron concentrations in the surface mixed layers of the eddies drop to levels observed outside very rapidly within 4 months upward transport along isopycnals and upwelling due to eddy decay as well as vertical advective and diffusive transports typical of north pacific waters probably provide steady fluxes of iron into the euphotic zone from the still iron rich eddy core waters throughout the lifetime of the eddy

iron and macronutrients in california coastal upwelling regimes implications for diatom blooms the supply of iron relative to that of the macronutrients nitrate phosphate and silicic acid plays a critical role in allowing extensive diatom blooms to develop in coastal upwelling regimes the presence or absence of a broad continental shelf influences the supply of iron the iron input to central california upwelling waters varies spatially and can be characterized by two end member regimes one end member which includes monterey bay and extending north to pt reyes is an iron replete regime where upwelling occurs over a relatively broad continental shelf that results in waters with high concentrations of dissolved and particulate iron 10 nm entrained together with high concentrations of nitrate and silicic acid in these iron replete regions extensive blooms of large diatoms deplete macronutrient concentrations which results in correspondingly high chlorophyll a concentrations the other end member located to the south of monterey bay off the big sur coast is an iron deplete regime where upwelling is focused offshore of a narrow continental shelf upwelled waters in the big sur region are characterized by low dissolved and particulate iron concentrations 1 nm together with high concentrations of nitrate and silicic acid extremely low iron concentrations unused nitrate and silicic acid and a low abundance of large diatoms characterize surface waters in these iron deplete regions and thus represent coastal upwelling high nutrient low chlorophyll systems limited by the micronutrient iron

formation of the haida 1998 oceanic eddy 1 two large mesoscale anticyclonic eddies formed along the west coast of the queen charlotte islands of western canada in early 1998 altimetry measurements from topex poseidon and ers 2 satellites suggest that these eddies first appeared near cape st james at the southern tip of the islands the eddies merged in june to form haida 1998 the highest eddy ever observed in the region currents near cape st james in winter follow complicated patterns attributed to tidal rectification and pressure driven outflow from hecate strait the adjustment of these flows to the bathymetric features likely contributes to the formation of haida eddies eddies that first appear farther north along the west coast of the queen charlotte islands are set up by other processes such as baroclinic instability

dissolved iron speciation in two distinct river plumes and an estuary implications for riverine iron supply dissolved iron fe speciation in the columbia river plume the san francisco bay plume and the columbia river estuary was investigated using competitive ligand exchange adsorptive cathodic stripping voltammetry cle acsv with the added ligand salicylaldoxime a stronger l1 type fe binding ligand class was measured in all surface samples and in the columbia river estuary a weaker l2 type ligand class was present in the far field columbia river plume and the san francisco bay plume but was not observed in the low salinity s 1 4 22 5 waters of the near field columbia river plume or estuary concentrations of total dissolved fe were correlated with the concentrations of the stronger l1 type ligand in nonestuarine s 13 surface samples leachable particulate 0 4 m fe concentrations in the columbia river plume were measured to supplement existing data from the san francisco bay plume there is a large concentration of readily leachable particulate fe in the two plumes yet it is the concentration of ambient l1 type ligands that appears to dictate the concentration of dissolved fe in these waters and consequently the supply of dissolved fe to neighboring coastal waters the correlation between dissolved fe and l1 ligand concentrations in both plume waters as well as in california current and upwelled surface waters suggests that this relationship will persist in other coastal environments and should be considered when evaluating and modeling coastal fe cycling and supply

three dimensional model simulations of tides and buoyancy currents along the west coast of vancouver island a three dimensional finite element model is used to calculate the barotropic tides and seasonal buoyancy flows off the western and northern coasts of vancouver island the model buoyancy currents and the harmonics of eight tidal constituents are compared with those from previous models and those from tide gauge and current meter observations the rms differences between observed and calculated sea level tidal amplitudes are within 2 3 cm for all constituents whereas the rms differences between observed and calculated phases are with the exception of q1 within 3 58 the model currents are more accurate than those from previous models of particular interest are the diurnal continental shelf waves it is shown that these waves are generated through the conservation of potental vorticity arising when the strong diurnal tidal currents in juan de fuca strait encounter the abrupt topography near the entrance to the strait these waves do not appear to propagate beyond brooks peninsula a large promontory cutting across the continental shelf a power budget analysis reveals that the reason for this is not the blocking effect of the peninsula but rather there is little energy left in the waves when they reach that point this energy loss is primarily through frictional dissipation in a series of trapped eddies along the shelf break the location of these eddies varies with the forcing frequency and appears to be related to the spacing of canyons it is also demonstrated that the strong diurnal currents observed over the shallow banks in queen charlotte sound to the north of brooks peninsula do not arise from the oscillatory diurnal flows in queen charlotte strait unlike the case for juan de fuca strait the region offshore of queen charlotte strait does not support diurnal coastally trapped waves seasonal changes in the wavelengths of the vancouver island shelf waves are shown to arise through an advective interaction doppler shift with the buoyancy driven vancouver island coastal current and the wind driven shelf break current

a model of the distribution of crustal magnetization in central europe compatible with the field of magnetic anomalies deduced from magsat results summary magsat data have been used to design scalar magnetic anomaly maps in an area that covers about half of europe on both sides of the north south directed european geotraverse egt the two maps refer to different altitudes and are intended to place recent compilations of aeromagnetic surveys along the egt wonik et al 1992 into global perspective the presentation of the magnetic anomalies and their compatibility with the aeromagnetic data required i a suitable reference field for subtraction from the measured total field which was derived from the field model m102089 by cain and ii a proper function of time reduction to the epoch 1980 0 which has been obtained from the actual satellite data because of the considerable noise in the data only those anomalies have been chosen for mapping which show up in all magsat tracks independent of altitude and epoch of measurement the anomaly maps are based upon the less disturbed dawn track data but a few dusk tracks have also been used as tie lines the anomalies are interpreted in terms of a magnetization model which divides the earth s lithosphere in europe into blocks of extension 1 n s by 2 e w and attributes to each block the depth integrated magnetization of the magnetized layer i e the magnetization integrated over the vertical extension of the block each block is represented by a dipole parallel to the inducing core field and the calculated model field is adjusted to the anomaly maps by trial and error starting with an initial coarse distribution that seems plausible from the anomalies and from local geomagnetic surveys for a realistic model field in the egt area a rather large portion of the earth s magnetized lithosphere outside the area under investigation must be included in the calculation in order to check whether the features of the magnetization model are necessary for the interpretation of the field anomalies they are compared with the distribution of magnetization that is obtained by the application of linear inverse theory prominent features of the model of crustal magnetization are the contrast between high values over the east european platform and low values in the younger parts of europe maxima at the iron ore districts of kiruna and kursk a broad minimum centred at st petersburg and only small differences between the mediterranean sea and the adjacent continental areas there is a fairly good agreement of these anomaly maps with the corresponding maps presented by cain et al 1989a

distribution and variability of iron input to oregon coastal waters during the upwelling season generally higher in spring mean of 2 1 and 33 9 nmol l 1 respectively than in summer means of 1 4 and 15 4 nmol l 1 in spring and summer high iron concentrations in surface waters were associated with both cold and saline recently upwelled waters and with fresh relatively warm water influenced by the columbia river comparison of total dissolvable iron in 0 45 mm filtered and in unfiltered samples indicated a substantial contribution from particulate iron iron concentrations in summer were generally lower than in spring throughout the water column with the exception of the near bottom where concentrations were generally higher in summer than spring optical backscatter data from moored sensors were used to infer the vertical and cross shelf transport of iron bearing particles during the upwelling season over a steep shelf cross correlation analysis showed downslope movement of particles from the deep inner shelf to the deep midshelf there was also evidence for sinking of biogenic particles at the midshelf and inner shelf but we found no evidence of upslope transport of benthic particles sufficient iron is available in this system to meet the demands of the phytoplankton which are able to make full use of available nitrate citation chase z b hales t j cowles r schwartz and a van green 2005 distribution and variability of iron input to oregon coastal waters during the upwelling season j geophys res 110 c10s12 doi 10 1029 2004jc002590

modelling the generation of haida eddies abstract a numerical model forced with average annual cycles of climatological winds surface heat flux and temperature and salinity along the open boundaries is used to demonstrate that haida eddies are typically generated each winter off cape st james at the southern tip of the queen charlotte islands of western canada annual cycles of sea surface elevation measured at coastal tide gauges and topex poseidon crossover locations are reproduced with reasonable accuracy model sensitivity studies show that haida eddies are baroclinic in nature and are generated by the merging of several smaller eddies that have been formed to the west of cape st james the generation mechanism does not require the existence of instability processes and is associated with the mean advection of warmer and fresher water masses around the cape from hecate strait and from the southeast these advected water masses generate plumes of buoyant flow which intensify and sustain small patches of anticyclonic circulation immediately to the northwest of the cape when the flow is stronger several of these smaller eddies can merge to generate a larger eddy the haida eddy similar to observations a typical generation shedding cycle for larger haida eddies in the model is 3 4 months consistent with previous in situ water property measurements these experiments show that the eddies are generally comprised of mixed layer water from hecate strait queen charlotte sound and the continental shelves off northern vancouver island their vertical extent during the mature stage is roughly 1000 m

chromium speciation and existing natural attenuation conditions in lagoonal and pond sediments in the former chemical plant of porto romano albania near the outskirts of the albanian port of durres on the adriatic coast at a place called porto romano an old chemical complex has been producing chromate salts for a period of 20 years 1972 1993 as a result large quantities of chromite ore processing residue copr waste were released mainly as suspended particles and or dissolved species in effluents which settled in a decantation pond area 200 250 m in size east of the industrial plant unfortunately pollutants were spread out with time knowing that chromium mobility and toxicity in natural settings is species dependent the species characterization has been carried out in different sampling media pond sediments lagoonal sediments and water samples five pond profiles were sampled within the decantation area up to a depth of 1 m till the underlying quaternary lagoonal silty clays were reached total cr content is highly variable with values between 1 130 and 24 409 mg kg which is clearly higher than the defined local background values for lagoonal silty clays 198 mg kg of cr leaching of cr vi especially occurs in the pond sediments which are low in oc cec and clay content under acidic and neutral ph conditions e g up to 2 230 mg kg cr vi leached from a sample containing a total concentration of cr 12 200 mg kg moreover leaching of the cr iii occurs only under strictly acidic conditions maximum 1 144 mg kg leached from a sample containing a total cr concentration of 17 608 mg kg in this study also a number of natural attenuation conditions i e reaction with lagoonal clays rich in organic matter and iron as well as isomorphous substitution have been recognized

the continental margin is a key source of iron to the hnlc north pacific ocean here we show that labile particulate iron and manganese concentrations in the upper 500m of the western subarctic pacific an iron limited high nutrient low chlorophyll hnlc region have prominent subsurface maxima between 100 200 m reaching 3 nm and 600 pm respectively the subsurface concentration maxima in particulate fe are characterized by a more reduced oxidation state suggesting a source from primary volcagenic minerals such as from the kuril kamchatka margin the systematics of these profiles suggest a consistently strong lateral advection of labile mn and fe from redox mobilized labile sources at the continental shelf supplemented by a more variable source of fe from the upper continental slope this subsurface supply of iron from the continental margin is shallow enough to be accessible to the surface through winter upwelling and vertical mixing and is likely a key source of bioavailable fe to the hnlc north pacific

origin of modern heavy mineral deposits northern british columbia continental shelf abstract bottom sediments of the northern british columbia continental shelf contain on average 10 of heavy minerals by weight within the dominant sand fraction anomalous concentrations occur within selected sand samples from queen charlotte sound 25 and hecate strait 18 the heavy mineral suite here is dominated by amphibole and the titanium minerals ilmenite sphene and titaniferous magnetite dynamic modelling of the present oceanographic and sedimentary environment in queen charlotte sound suggests that the anomalous offshore concentrations of heavy minerals result from continuous differential sorting during extreme yearly storms the deposits are not considered to be relict

the anticyclonic baroclinic eddy off sitka alaska in the northeast pacific ocean abstract among the many mesoscale eddies found in the northeast pacific ocean is a well developed anticyclonic baroclinic eddy situated within a few hundred kilometers of sitka alaska 57 n 138 w it has definitely been observed during spring and summer 1958 summer 1960 and summer 1961 observations made at other times show some evidence of its occurrence also the trajectories of three norpax drifting buoys for april may 1977 also indicated the probable presence of an eddy there the eddy whose diameter ranges from 200 to 300 km and whose depth extends to 100 m and probably to as much as 2000 m recurs at the same location the center of the eddy is characterized by the following features the surface water is less saline and only somewhat warmer than at its periphery at depths within and below the halocline it is warmer less saline and contains more dissolved oxygen than at the periphery and a warm core is situated within the halocline the halocline is usually depressed by less than 100 m but

oceanic iron supply mechanisms which support the spring diatom bloom in the oyashio region western subarctic pacific 1 multiyear 2003 2008 time series observations along the a line provided information on the temporal variability of the dissolved iron diss fe concentration in the oyashio region of the western subarctic pacific and the data indicated that there was an annual cycle in the concentration of surface diss fe occurring every year diss fe was supplied into the surface water in this region every winter and supports the spring phytoplankton bloom after development of the thermocline the diss fe concentration was drawn down during the phytoplankton bloom period and was depleted in summer in some water masses then diss fe increased from autumn to winter with the increasing depth of the surface mixed layer the high diss fe concentrations in the surface layer in winter were controlled by mesoscale oceanic intrinsic processes such as vertical winter mixing and horizontal fe rich intermediate water transport difference in magnitude of the winter mixing processes among different water masses caused the heterogeneous distribution of diss fe concentration in the surface layer moreover the vertical section profiles along a cross oyashio transect showed the occurrence of fe rich intermediate water and upward transport of materials from the intermediate water to the surface layer via tidal and winter mixing processes are important mechanisms to explain the high winter surface diss fe concentrations additionally the substantially higher diss fe no3 ratio in the winter surface layer in this studied area other than the high nutrient low chlorophyll region indicates that the winter surface water in the oyashio and the oyashio kuroshio transition zone has a high potential to stimulate phytoplankton growth

british columbian continental shelf as a source of dissolved iron to the subarctic northeast pacific ocean 1 the distribution of dissolved 0 4 m iron fe across the continental shelf and slope of queen charlotte sound on the west coast of canada was examined to estimate the potential of these waters as a source of fe to the fe limited waters of the subarctic northeast pacific iron profiles obtained in shelf slope and offshore waters demonstrate decreasing concentrations of fe with distance from the continent within 50 m of the shelf sediments dissolved fe concentrations were 5 3 0 3 nm this signal was detected although attenuated by 80 along the isopycnal surface at offshore stations 40 50 km seaward of the shelf break strongly suggesting cross shelf transport of an fe rich plume originating in low dissolved oxygen 3 ml l 1 130 mol kg 1 waters in subsurface water over the continental shelf several physical mechanisms that may cause these fe enriched waters to advect offshore in this region i e tidal currents and ekman transport in the bottom boundary layer coastal downwelling relaxation from upwelling and the formation of anticyclonic westward propagating coastal eddies are discussed we suggest that strong tidal currents over broad continental shelves may play a key role in fe supply to ocean basins

a note on cross shelf exchange in the northern gulf of alaska the continental shelf of the gulf of alaska goa is a complex system characterized by large freshwater runoff and strong winds the goa supports one of the world s richest ecosystems including numerous species of fishes marine mammals and sea birds the mechanisms that provide nutrients to support this ecosystem are not well understood the rivers and streams that provide freshwater to the shelf are low in nitrate and the regional winds favor downwelling high concentrations of nitrate are available in the deep basin of the goa but these must be introduced to the shelf in order to support the high productivity we present evidence for cross shelf exchange due to three different mechanisms episodes of downwelling relaxation result in a flux of saline nutrient rich water onto the shelf at depth eddies formed in the northeastern goa propagate along the shelf break influencing cross shelf exchange by carrying shelf origin water from the formation region into the basin and by interacting with the shelf break circulation bathymetric steering in the many canyons that incise the goa shelf results in flow into the canyons where strong tidal mixing results in cross isobath movement of water properties