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Lofoten and Vesterålen region in Northern Norway contains the main spawning areas for the Northeast Arctic (NEA) cod. A large embayment, partially sheltered from the continental slope and open ocean by the Lofoten-Vesterålen archipelago, called Vestfjorden contains approximately 60 % of the NEA cod spawning in this region. The dynamical ocean processes that control transport paths and transport times of cod eggs and larvae out of this embayment are of major importance, not only for the fish stock, but in general for the marine ecosystem in the region. This study investigates the net impact of nonlinear tidal dynamics on transport and dispersion of particles, resembling cod eggs and larvae, out of Vestfjorden. The coastal ocean circulation in and around Vestfjorden is simulated with a variable mesh model, both with and without tides. The two different flow fields are used to advect passive particles seeded near Henningsværstraumen, a key spawning location within the embayment. A comparison of the two transport calculations reveals that nonlinear tidal dynamics clearly impact the particle drift in the region. When including tides in the model simulation, transport through the various straits that cut through the Lofoten-Vesterålen archipelago becomes more important, causing the total particle drift out of Vestfjorden to increase by about 10%. One strait in particular, Moskstraumen, contributes with a significant transport (∼ 30%) in the model simulation with tides included, but other straits contribute as well. For comparison, in the simulation where tides are excluded, almost 90% of the particles are transported out of the embayment around the southern tip of the archipelago and only 6% through Moskstraumen. A key implication of the tidal transport through the straits is that the journey for a large fraction of the cod eggs/larvae from Vestfjorden to the shelf is considerably shortened.

Understanding the distribution of chlorophyll on the continental shelves adjacent to western boundary currents is important, both from an ecosystem perspective, as well as for their role as a net sink of atmospheric CO2. However, in‐situ observations of chlorophyll in these dynamic regions are rare. Here, using more than a decade of underwater glider observations from 29 deployments in the East Australian Current (EAC) system, we examine the effect of the mesoscale western boundary current (WBC) circulation on chlorophyll distribution across the shelf. The extensive hydrographic dataset reveals that the mode of boundary current separation has a strong persistent spatial influence on both the stratification and chlorophyll distribution on the shelf between 31.5° and 34°S, a productive area adjacent to the EAC separation zone. We identify that subsurface chlorophyll maxima are common, and their depth and strength is dictated by the offshore mesoscale circulation associated with the WBC separation. The vertical chlorophyll distribution is modulated by the combination of the seasonal cycle and the sporadic influence of mesoscale eddies associated with WBC jet separation. Of the three dominant WBC separation scenarios, eddy dipoles result in shelf waters that are on average more stratified, have higher chlorophyll values, and a deeper chlorophyll maximum compared to other circulation modes. These results suggest that it is necessary to consider the influence of WBC dynamics on chlorophyll concentrations for accurate estimates of atmospheric CO2 uptake. Plain Language Summary: In the past, our understanding of chlorophyll distributions in East Australian Current came mainly from satellite data. However, satellites cannot see far below the surface of the ocean. We use data from a decade of underwater glider missions to look at subsurface chlorophyll and find that the East Australian Current and its eddies strongly influence shelf chlorophyll at depth, even giving it a different seasonal cycle to the surface. We think that this is important for how this region takes up carbon dioxide from the atmosphere. Key Points: Mesoscale circulation has a strong influence on shelf stratification and chlorophyll distribution with implications for oceanic CO2 uptakeEAC separation modulates the upwelling processes which drive a stronger chlorophyll response during summer at depthA re‐occurring EAC eddy dipole results in an enhanced subsurface chlorophyll maximum and increased cross‐shelf exchange [ABSTRACT FROM AUTHOR]

The dynamical balance on the Amazon shelf and its implication on the properties of the Amazon River plume is not fully understood and poorly represented in global‐ and basin‐scale ocean models. In this study, the sensitivity of the Amazon shelf dynamics to tidal forcing is explored with a set of high‐resolution numerical simulations (1/36°) with and without the tide. A comparison of the simulations with sea surface salinity in situ measurements at 5°N (a location where the plume seasonally detaches from the coast and retroflects toward the east) revealed that the explicit resolution of the tide significantly improves the representation of the offshore spread of the river plume. This study further highlights the finding that tidal currents affect the properties of the whole Amazon plume. This sensitivity is explained by a near total collapse of the northwestward alongshore mean flow located near the river mouth, once the tidal forcing is included. This weakening of the ambient flow reduces (i) the dilution ratio between the ambient salty shelf waters and the riverine freshwaters and (ii) the constraint on the cross‐shore extension of the low‐salinity bulge. With tides, the plume is fresher near the river mouth (by up to 5 units), more extended in the cross‐shore direction, and more easily exported offshore by the North Brazil Current at the shelf break. Key Points: The sensitivity of the Amazon shelf dynamics to tidal forcing is explored with a set of high‐resolution numerical simulationsExplicit resolution of the tides significantly improves the representation of the offshore spread of the river plumeWith tides, the plume is more easily exported offshore by the North Brazil Current at the shelf break [ABSTRACT FROM AUTHOR]

A linear coastal-trapped-wave (CTW) model is used to examine the effects of large-scale winds, with time scale ranging from a few days to a few weeks, on the West India Coastal Current (WICC), particularly on the shelf off the central west coast of India. We show that unlike the seasonal cycle of WICC, which is primarily forced by the winds along the east coast of India, the high-frequency WICC is mostly driven by the west-coast winds. Nevertheless, the influence of winds as far as Sri Lanka and east coast of India cannot be neglected. Simple numerical experiments with the CTW model show that the strong current observed at Goa (15° N) compared to Bhatkal (13° N) and Jaigarh (17° N) is due to two factors: (1) the superposition of local and remote CTWs and (2) the widening of shelf width north of Goa, which decreases the amplitude of the currents poleward of Goa. If the local winds are weak, the amplitude of current decreases poleward due to friction, and the current at the south leads the north. We also note that the observed phase difference between sea level and alongshore current at Goa could be attributed to the propagation of remotely forced higher-order modes of CTWs. [ABSTRACT FROM AUTHOR]

The coastal area north of Yucatan has experienced a cooling SST trend from 1982 to 2015 during the upwelling season (May–September) that contrasts with the warming observed at the adjacent ocean area. Different drivers were analyzed to identify the possible causes of that unusual coastal cooling. Changes in coastal upwelling and in sea-atmosphere heat fluxes are not consistent with the observed coastal cooling. The eastward shift of the Yucatan Current observed over the last decades is hypothesized as the most probable cause of coastal cooling. This shift enhances the vertical transport of cold deeper water to the continental shelf from where it is pumped to the surface by upwelling favorable westerly winds. [ABSTRACT FROM AUTHOR]

Continental shelves are recognized to play a key role in the biogeochemical cycle of carbon, linking terrestrial and marine carbon reservoirs. In this study we investigate the physical and biogeochemical processes that control the source, transport and fate of organic carbon (OC) in the continental shelf off Barcelona city, in the NW Mediterranean Sea. Surface sediment samples were collected from depths of 10–40 m during late summer and autumn 2012. Grain size and biogeochemical parameters such as OC, its stable isotope δ 13 C, total nitrogen (TN) and OC/TN ratios were analysed in size-fractionated sediments. The influence of environmental factors over the study area was determined using hydrological and oceanographic time series, together with video images of the Barcelona coast line and nearshore region. We have found a wide range of OC contents, from 0.13 to 8.68%, depending on water depth and sediment particle size. The highest OC concentration was always found in the clay fraction (<4 μm), followed by the sand fraction (>63 μm) that contained terrestrial plant debris. Wave activity, discharge of the Besòs River and the “Espigó de Ginebra” outfall were the main mechanisms controlling the sorting of sediments by their grain size and thus the distribution of OC in the inner shelf off Barcelona. In addition, we observed that the organic matter in clay particles was progressively degraded seawards, probably because these particles remain suspended in the water column much more time compared to those that are heavier and, therefore, they are exposed for longer time periods to oxygenated conditions. Both OC/TN ratios and δ 13 C values found suggest that the organic matter preserved was predominantly land supplied. [ABSTRACT FROM AUTHOR]

For the first time a taxonomic and ecological study of species belonging to Helicostomella was performed over a mesoscale spatial distribution by examining ca. 3000 loricae collected in Argentine shelf waters during the austral autumn. Microscopic and statistical analysis revealed that the general shape and the oral diameter remained practically constant in the whole area surveyed, despite a continuous length fluctuation of ca. 300 µm, which includes the entire range present in eight previously reported species. Consequently, we consider that the genus may be represented only by H. subulata, whose strong fluctuations in length (mostly attributed to an increase in the collar length), density and biomass seem to respond to temperature, food availability and front-related processes. In Buenos Aires coastal waters associated with a quasi permanent estuarine front (40-40.5°S), mixed conditions would favour moderate abundances of long loricae, whereas in northern (42.5-45.5°S) and southern (46-54.5°S) Patagonian waters, high (103 ind. L-1) and low (< 5 ind. L-1) densities of short loricae seem to be a consequence of stratification and encystment, respectively. The non-occurrence of the species at 41-42°S, together with a three-fold reduction in length-related parameters between specimens from Buenos Aires and Patagonian waters, suggests a disjunct distribution.

The analysis of an eddy census for the East Australian Current (EAC) region yielded a total of 497 individual short-lived (7–28 days) cyclonic and anticyclonic eddies for the period 1993 to 2015. This was an average of about 23 eddies per year. 41% of the tracked individual cyclonic and anticyclonic eddies were detected off southeast Queensland between about 25 °S and 29 °S. This is the region where the flow of the EAC intensifies forming a swift western boundary current that impinges near Fraser Island on the continental shelf. This zone was also identified as having a maximum in detected short-lived cyclonic eddies. A total of 94 (43%) individual cyclonic eddies or about 4–5 per year were tracked in this region. The census found that these potentially displaced entrained water by about 115 km with an average displacement speed of about 4 km per day. Cyclonic eddies were likely to contribute to establishing an on-shelf longshore northerly flow forming the western branch of the Fraser Island Gyre and possibly presented an important cross-shelf transport process in the life cycle of temperate fish species of the EAC domain. In-situ observations near western boundary currents previously documented the entrainment, off-shelf transport and export of near shore water, nutrients, sediments, fish larvae and the renewal of inner shelf water due to short-lived eddies. This study found that these cyclonic eddies potentially play an important off-shelf transport process off the central east Australian coast. [ABSTRACT FROM AUTHOR]

Mesoscale and submesoscale eddies and fronts in the upper ocean are often closely coupled with biogeochemical processes. Improved instrumentation provides high–resolution data in both the horizontal and vertical capturing this large range of scales (1–100 km), but novel analysis methods are still needed to take full advantage of this advancement. A new method using wavelet analysis is therefore proposed to identify the horizontal scales at which biophysical interactions occur, defined by concurrent fluctuations in temperature and phytoplankton patchiness. The method is applied to temperature and chlorophyll–a fluorescence data measured in the North Sea’s German Bight during early spring using a towed undulating vehicle. The wavelet analysis identified the scale and location of individual features characterized by horizontal gradients of temperature and chlorophyll–a fluorescence. Applied to multiple transects, the method can also retrieve the statistics of relevant biophysical scales in a particular region. The combined analysis of seven transects suggests that physical and biogeochemical tracers tend to align at scales of 3–15 km in the German Bight, highlighting the likely relevance of submesoscale processes in this region. In general, the proposed wavelet analysis method is shown to be a robust tool for the analysis of biophysical interactions across a range of scales. [ABSTRACT FROM AUTHOR]

At the Gulf of Cadiz (GoC), poleward currents leaning along the coast alternate with coastal upwelling jets of opposite direction. Here the patterns of these coastal countercurrents (CCCs) are derived from ADCP data collected during 7 deployments at a single location on the inner shelf. The multiyear (2008–2014) time-series, constituting ~ 18 months of hourly records, are further analysed together with wind data from several sources representing local and basin-scale conditions. During one deployment, temperature sensors were also installed near the mooring site to examine the vertical thermal stratification associated with periods of poleward flow. These observations indicate that the coastal circulation is mainly alongshore and barotropic. However, a baroclinic flow is often observed shortly at the time of flow inversion to poleward. CCCs develop all year-round and exclusively control the occurrence of warm coastal water during the upwelling season. On average, one poleward flow lasting 3 days was observed every week, corresponding to CCCs during ~ 40% of the time without seasonal variability. Thus, the studied region is distinct from typical upwelling systems where equatorward coastal upwelling jets largely predominate. CCCs often start to develop near the bed and are frequently associated with 2-layer cross-shore flows characteristic of downwelling conditions (offshore near the bed). In general, the action of alongshore wind stress alone does not justify the development of CCCs. The coastal circulation is best correlated and shows the highest coherence with south-eastward wind in the basin that proceeds from the rotation of southward wind at the West coast of Portugal, hence suggesting a dominant control of large-scale wind conditions. In agreement, wavelet analyses indicate that CCCs are best correlated with alongshore wind occurring in a band period characteristic of the upwelling system (8–32 days). Furthermore, in the absence of wind coastal currents tend to be poleward during summer. This set of observations supports that CCCs develop in response to the unbalance of an alongshore pressure gradient during the relaxation of (system-scale) upwelling-favourable winds, oriented south-eastward in the basin. The relaxation periods defined based on this wind direction show a good correspondence with the periods of poleward flow. [ABSTRACT FROM AUTHOR]

The Lena plume dynamics in the Lena Delta region of the Laptev Sea are explored in simulations performed with the Finite Volume Coastal Ocean Model (FVCOM) on a mesh with the horizontal resolution 0.4-5 km. The impact of wind and tides on the Lena plume propagation is analysed based on simulations for the summer season of 2008 and also on idealised experiments. All main Lena River freshwater channels (Trofimovskaya, Bykovskaya, Tumatskaya and Olenekskaya) produce buoyant outflows in the summer season. The surface plume buoyancy signature proves to be highly variable in time, especially in case of upwelling favourable wind events. Winds stronger than 6 m s can already turn the dynamics of flows from all main freshwater channels to the wind-driven state. During the summer season, the bulk of freshwater from the Lena River stays in the eastern Laptev Sea because of location of the main Lena River freshwater channels, their large Kelvin numbers and light summer winds. Westward and northward plume excursions are wind-driven, and the model skill in simulating them depends on the available wind forcing. The main mechanism of tidal influence in the freshwater plume zone is through tidally induced mixing, except for the northern vicinity of the delta, where residual circulation may contribute to the plume eastward transport significantly. [ABSTRACT FROM AUTHOR]

Abstract: The performance of the ensemble adjustment Kalman filter (EAKF) to estimating volume transports at open boundaries was investigated for a coastal ocean model of the Palma Bay, Mallorca Island, Mediterranean Sea. The circulation in the Palma Bay is mainly driven by the remotely wind-generated island trapped waves (ITWs) propagating around Mallorca and by a local wind response. Thus, for a model of the bay proper only, the large-scale ITWs must be incorporated into the open ocean boundary conditions. To take into account the effect of ITWs, an EAKF was used to assimilate the moored Acoustic Doppler Current Profiler (ADCP) velocity time series collected in the inner part of the Bay through a simultaneous state and parameter estimation. In this approach, flows at open boundaries were included in the model state as time-dependent parameters and were updated in each assimilation step. The simulation was validated with moored ADCP data as well as with independent towed ADCP spatial velocity survey data. The new results are markedly improved over the model experiments without data assimilation or with state estimation only. In particular, simulation using the estimated values at open boundaries significantly outperforms simulation with ‘a priori’ prescribed values at boundaries. The error reduction is about 45% when ITWs dominate the circulation. Our results present a promising approach in dealing with the open boundary conditions in a coastal ocean model. [Copyright &y& Elsevier]

Abstract: Population dynamics in open systems are complicated by the interactions of local demography and local environmental forcing with processes occurring at larger scales. A local system such as an estuary or bay may contain a zooplankton population that effectively becomes independent of regional dynamics or the local dynamics may be closely coupled to a broader scale pattern. As an alternative, the details of migration and advection may mean that dynamics in a local system are coupled to other specific areas rather than tracking the overall dynamics at a larger scale. We used a reconstructed time series (1973–1987) for copepod taxa to examine the extent to which zooplankton dynamics in Galway Bay reflect processes in broader areas of the NE Atlantic. Continuous Plankton Recorder (CPR) counts were used to establish time series for nine offshore ecoregions, with the regions themselves defined using underlying patterns of chlorophyll variability. The open nature of Galway Bay was reflected in strong associations between bay zooplankton counts and offshore CPR data in a majority of cases (7/10). For each zooplankton taxon, there were large differences among regions in the degree of association with Galway Bay time series. Akaike weights indicated that one ecoregion tended to be the dominant link for each taxon. This indicates that the zooplankton of the Bay reflect more than the local modification of a regional signal and that different zooplankton in the bay may have separate source regions. The data from Galway Bay also fall within a ‘sampling shadow’ of the CPR. Later years of the time series showed evidence for changes in phenology, with spring zooplankton peaks generally occurring earlier in the year for smaller species. [Copyright &y& Elsevier]

In November 2009, an autonomous underwater glider (AUG) was deployed for a period of 12 days on the Wisconsin Shelf of Lake Superior. During this period, the AUG made repeated cross-shelf transects from 3 km to 13 km offshore, making 26 cross-shelf transects in all, during which time temperature was measured. Each of these transects displayed a mid-shelf temperature maximum roughly 8 km offshore, with cooler waters both inshore and offshore of this. This is hypothesized to be due to a balance of persistent cooling at the surface and vertical mixing of cooler sub-thermocline waters offshore. [ABSTRACT FROM PUBLISHER]

Interest in the coastal dynamics of river plumes has mainly focused on large rivers, but plumes from the more numerous smaller rivers have important local consequences and may, in aggregate, be significant contributors to coastal circulation. We studied the dynamics of the plume from the Saco River in Saco Bay, Gulf of Maine, over a 3-year period. The transport and salinity in the region are governed by river discharge, tides, winds, and interaction with the Western Maine Coastal Current. The dynamics of the flow field vary with location within the plume and discharge. The far-field dynamics of the Saco River plume are dominated by inertial processes (hence qualifying it as a small-scale river plume), during times of low discharge, with low salinity water present both up and downstream of the river mouth, but are dominated by rotational processes during times of high discharge (thus qualifying it as a large-scale river plume), with buoyant water primarily advected downshelf. Near-field dynamics are governed by weak, subcritical flow during low discharge but strongly inertial, supercritical flow during high discharge. Offshore movement of the plume is not governed by Ekman dynamics but is instead a result of discharge, wind-induced vertical mixing, and the geography of the coastline and adjacent islands. [ABSTRACT FROM AUTHOR]

In this study the capability of numerical models to transport anomalously dense bottom waters from the areas of their generation on the shelf to deepwater areas is considered. These numerical models have a number of mechanisms that are favorable for this transport, but unrelated directly with the real physics of that motion. A more accurate account of the resupply of oceanic deep waters requires either a very fine resolution for the numerical model or an efficient parametrization. Two such parametrizations are proposed in this study. The first is based on amplified lateral diffusion exchange if slope instability exists. The second is related to an additional procedure allowing dense waters to leak under waters of lesser density along a shelf slope with their displacement to higher layers. The first parametrization is shown to be less efficient because it leads to a significant interaction between anomaly waters and ambient waters and to a quick loss of their original features. The second procedure is more preferable because it leads to a significant resupply of dense deep waters at the expense of dense waters generated at a distance significantly far from the shelf break. With the help of the given parametrization, during a numerical experiment these waters can be transported considerable distances away from their place of generation to the shelf boundary and deepwater areas of the ocean with a slight change in their original density characteristics. [ABSTRACT FROM AUTHOR]

In this study the specific features of deepwater generation in an area of wind polynia and the capability of numerical models to transport bottom-density anomalies from shelf to deepwater areas are considered. The results of regional modeling indicate that the displacement method presented in the first part of this study leads to a considerable supply of dense deep waters at the expense of waters generated in shelf areas of the Barents and Kara seas. With the help of the given parametrization, these waters are shown to be able to numerically transport at significant distances from where they are generated to a shelf edge and deepwater oceanic areas with slightly changed initial density characteristics. This technique was tested within a large-scale combined ocean-ice model for the Arctic Ocean and the North Atlantic. With the displacement method, the numerical model was shown to have a less clearly expressed trend of decreasing the total amount of deep waters. However, this method does not eliminate the problem of adequately reproducing bottom waters in a large-scale numerical model. Based on a trend analysis of the numerical results, we found that a longer period of atmospheric influence with a prevalent cyclonic circulation leads to a decreased amount of deep waters in the Arctic Ocean, while a prevalent anticyclonic-type circulation leads to its recovery. [ABSTRACT FROM AUTHOR]

Abstract: The structure and dynamics of errors in a 3D coastal model of the Catalan sea is characterized through stochastic modelling. Wind forcing and large scale circulation are identified as the main sources of model errors. Ensemble simulations perturbing the wind field and the model initial and open boundary conditions are performed. The dispersion of model trajectories in the ensemble allows us to characterize the errors structure and dynamics. Model errors induced by errors in the wind forcing are linear but non-stationary, while those induced by errors in the description of the large scale circulation are non-linear but stationary. The ensemble results are also used to characterize the error covariance spatial patterns through the use of multivariate EOFs. The capability of this EOF decomposition to control the model evolution is investigated using a reduced order optimal interpolation (ROOI) data assimilation scheme. [Copyright &y& Elsevier]

The hydrodynamics, salinity circulation, and transport of suspended fine sediment from major rivers on the northern Gulf of Mexico (GOM) were simulated with the numerical model H3D. Tides, river inflow, wind, and heat exchanges were used to drive the three-dimensional baroclinic model. Tide propagation in the northern Gulf and seasonality in the sediment plume advection from the Mississippi and Atchafalaya rivers into the GOM were well represented in the model. The similarity between the model's results and the sediment plume as seen in MODIS satellite images and the salinity structure as observed in previous studies is demonstrated. This qualitatively valid model is used for initial guidance in design of new Mississippi River (MR) diversions by studying the effects of five conceptual MR diversions on the fate of its suspended fine material. The diversions were positioned halfway between Port Sulphur and Venice, southeast Louisiana. The scenario transporting 70% of the MR to the west and 30% to the east of the delta presents the best configuration in terms of retention of sediment within the continental shelf. This configuration redirects the main sediment and freshwater flow from the river to the nearshore and the upper continental shelf with the least losses to deeper GOM waters. Given the local dominant westward wind regime, increased discharges diverted to the east will increase the amount of sediment that travels west around the MR birdfoot delta and over the Mississippi Canyon, with a higher chance of being lost to deeper waters. [ABSTRACT FROM AUTHOR]

Abstract: Abundance and composition of marine benthic communities have been relatively well studied in the SE Brazilian coast, but little is known on patterns controlling the distribution of their planktonic larval stages. A survey of larval abundance in the continental margin, using a Multi-Plankton Sampler, was conducted in a cross-shelf transect off Cabo Frio (23°S and 42°W) during a costal upwelling event. Hydrographic conditions were monitored through discrete CDT casts. Chlorophyll-a in the top 100 m of the water column was determined and changes in surface chlorophyll-a was estimated using SeaWiFS images. Based on the larval abundances and the meso-scale hydrodynamics scenario, our results suggest two different processes affecting larval distributions. High larval densities were found nearshore due to the upwelling event associated with high chlorophyll a and strong along shore current. On the continental slope, high larval abundance was associated with a clockwise rotating meander, which may have entrapped larvae from a region located further north (Cabo de São Tomé, 22°S and 41°W). In mid-shelf areas, our data suggests that vertical migration may likely occur as a response to avoid offshore transport by upwelling plumes and/or cyclonic meanders. The hydrodynamic scenario observed in the study area has two distinct yet extremely important consequences: larval retention on food-rich upwelling areas and the broadening of the tropical domain to southernmost subtropical areas. [Copyright &y& Elsevier]

Abstract: Surface and sub-surface currents along the ocean boundary of Western Australia were simulated using Regional Ocean Modelling System (ROMS) to examine the circulation within the Perth Canyon. Two major current systems influenced the circulation within the canyon: (1) The Leeuwin current interacted weakly with the canyon as the majority of the canyon was below the depth of the Leeuwin current and (2) Leeuwin undercurrent interacted strongly with the canyon, forming eddies within the canyon at depths of 400–800m. The results indicated that within the canyon, the current patterns changed continuously although there were some repeated patterns. Recurrent eddies produced regions where upwelling or downwelling dominated during the model runs. Deep upwelling was stronger within the canyon than elsewhere on the shelf, but vertical transport in the upper ocean was strong everywhere when wind forcing was applied. Upwelling alone appeared to be insufficient to transport nutrients to the euphotic zone because the canyon rims were deep. Increased upwelling, combined with entrapment within eddies and strong upwelling-favourable winds, which could assist mixing, may account for the high productivity attributed to the canyon. The Leeuwin current is otherwise a strong barrier to the upwelling of nutrients. [Copyright &y& Elsevier]

Abstract: The Faroe Shelf surrounds the Faroe Islands (62°N, 7°W) and strong tidal currents and wave action induce intensive mixing that produce a very homogeneous water mass on the shelf. The boundary of this water is the Faroe Shelf Front. Previous studies have shown large variations in all trophical levels in this system, which have been linked to cross-frontal exchanges between the waters on-shelf and off-shelf. Here, we combine data from different sources to describe and explain the front. The front is mainly generated by heat loss from the ocean to the air and it has a consistent seasonal variation from being almost non-existing in autumn to its most pronounced character in March. It fits fairly well to the theory of Soulsby in which the front is located where the bottom mixed layer, under the influence of rotating tidal currents, exactly occupies the whole water column. Export of water in the bottom Ekman layer and the associated inflow higher up in the water column imports sufficient heat onto the shelf to maintain a quasi-stationary state in early spring. Additional exchange is produced by cascading of on-shelf water down a canyon on the western side of the Faroe Shelf, but the available data do not allow a quantitative estimate of the importance of this process as an exchange mechanism. [Copyright &y& Elsevier]

Abstract: The Ushant tidal front is the dominant feature of the summer season hydrological structure of the Iroise Sea. It separates tidally mixed coastal waters from thermally stratified open Celtic Sea waters. This article reports on observations made in September 2007 during two short cruises that took place aboard R/V “Côtes de la Manche”, and gives a general account of the physical structure of the front along one cross-frontal transect. The data set comprises data from a 4 month ADCP mooring, short CTD/fluorescence/nutrients transects, Lagrangian drifter trajectories, and HF radar surface current measurements. One finding is that the surface and bottom fronts, being affected by different dynamical influences, are not necessarily coincident in the vertical. This entails that the opposite density gradients located above and below the thermocline depth do not necessarily compensate, and can each be associated with a significant surface geostrophic expression. A second finding is that mixing effects bear a very strong influence on the thermal structure of the warm-water intrusions associated with frontal cyclonic eddies of the kind described by Pingree [1978. Cyclonic eddies and cross-frontal mixing. Journal of the Marine Biological Association of the United Kingdom 58 (4), 955–963]. [Copyright &y& Elsevier]

Abstract: Faroe Shelf Water (FSW) is the water mass that occupies the shallow parts of the Faroe Shelf, surrounding the Faroe Islands (62°N, 7°W). Intensive tidal mixing induces a high degree of homogeneity and the circulation system allows a partial isolation from surrounding waters. This water mass, therefore, supports a unique ecosystem of great importance for commercial fish stocks and studies have shown a clear dependence of the ecosystem on the physical processes that maintain this system and control the exchange between the FSW and the off-shelf waters. In order to identify and quantify these processes, a large observational dataset has been analysed and related to alternative theories. From this analysis, the extent and properties of the FSW have been quantified and the degree of stratification explained in terms of the Simpson–Hunter theory. The residual clockwise circulation system, which is responsible for the partial isolation from off-shelf waters, is shown to be mainly generated by tidal rectification. The typical exchange rate of water between the FSW and the off-shelf regimes has been determined by the use of simple models based on the heat and the salt budgets but the actual exchange rate is found to vary considerably in time and space. These results support earlier suggestions that this exchange is the main limiting factor for the phytoplankton spring bloom on the Faroe Shelf and that variations in exchange rate are responsible for the large inter-annual variation in spring bloom timing and intensity. The observations indicate that the on-shelf/off-shelf exchange intensity is not symmetrically distributed around the shelf, but rather concentrated around the narrow southern tip of the Faroe Shelf, where off-shelf waters during intensive exchange events may be imported all the way to the shore. [Copyright &y& Elsevier]

Abstract: An unstructured-mesh parallel hydrodynamic model of the whole Great Barrier Reef is presented. This model simultaneously simulates most scales of motion. It allows interactions between small- and large-scale processes. The depth-averaged equations of motion are discretized in space by means of a mixed finite element formulation while the time-marching procedure is based on a third order explicit Adams–Bashforth scheme. The mesh is made up of triangles. Their size and shape can be modified easily so as to resolve a wide range of scales of motion, from those of the regional flows to those of the eddies or tidal jets that develop in the vicinity of reefs and islands. The forcings are the surface wind stress, the tides and the inflow from the Coral Sea (East Australian Current, Coral Sea Coastal Current), the latter two forcings being applied along the open boundaries of the computational domain. The numerical results compare favourably with observations of both longshore currents and the local perturbations due to narrow reef passages. Comparisons are also performed with the simulations of a three-dimensional model applied to a small domain centered on Rattray Island, showing that both models produce similar horizontal flow fields. For a structured-mesh model to yield results of the same accuracy, there is no doubt that the computational cost would be much higher. [Copyright &y& Elsevier]

Abstract: The key features of the western Galician shelf hydrography and dynamics are analyzed on a solid statistical and experimental basis. The results allowed us to gather together information dispersed in previous oceanographic works of the region. Empirical orthogonal functions analysis and a canonical correlation analysis were applied to a high-resolution dataset collected from 47 surveys done on a weekly frequency from May 2001 to May 2002. The main results of these analyses are summarized bellow. Salinity, temperature and the meridional component of the residual current are correlated with the relevant local forcings (the meridional coastal wind component and the continental run-off) and with a remote forcing (the meridional temperature gradient at latitude 37°N). About 80% of the salinity and temperature total variability over the shelf, and 37% of the residual meridional current total variability are explained by two EOFs for each variable. Up to 22% of the temperature total variability and 14% of the residual meridional current total variability is devoted to the set up of cross-shore gradients of the thermohaline properties caused by the wind-induced Ekman transport. Up to 11% and 10%, respectively, is related to the variability of the meridional temperature gradient at the Western Iberian Winter Front. About 30% of the temperature total variability can be explained by the development and erosion of the seasonal thermocline and by the seasonal variability of the thermohaline properties of the central waters. This thermocline presented unexpected low salinity values due to the trapping during spring and summer of the high continental inputs from the River Miño recorded in 2001. The low salinity plumes can be traced on the Galician shelf during almost all the annual cycle; they tend to be extended throughout the entire water column under downwelling conditions and concentrate in the surface layer when upwelling favourable winds blow. Our evidences point to the meridional temperature gradient acting as an important controlling factor of the central waters thermohaline properties and in the development and decay of the Iberian Poleward Current. [Copyright &y& Elsevier]

Abstract: The purpose of this study is to quantify the cross-shelf transport of water masses and organic carbon at the Gulf of Tehuantepec and relate this to the physical processes in the area. A medium-complexity, nitrogen-based ecosystem model is developed in order to simulate the ecosystem in the northeast tropical Pacific. The ecosystem model is run “offline” using a hindcast from a realistic physical ocean model as input. The physical model is forced with daily heat and momentum fluxes and therefore captures the intense, but short-lived, wind events at the Gulf of Tehuantepec. Assimilation of altimeter data facilitates a realistic representation of eddies and meso-scale variability. The ecosystem model includes two nutrients (nitrate and ammonium), two size classes of phytoplankton, two size classes of zooplankton, and detritus. The model is validated using SeaWiFS ocean color data and ship-based observations. Cross-shelf fluxes of water, nutrients, and plankton are calculated from the model and related to physical processes. The results show that at the Gulf of Tehuantepec there is substantial offshore export of organic material, particularly during wind events that generate an eddy (on the order of 10GgC/day). During these events, there is an even larger onshore carbon flux to the south of the gulf. The model-estimated transport of carbon away from the coast at the Gulf of Tehuantepec is 0.32TgC/year, and the onshore transport to the south of the gulf is 2.23TgC/year. The volume flux in the upper 150m is comparable in magnitude, but of opposite sign, at the gulf and to the south of the gulf. The reasons why the carbon flux is seven times larger to the south of the gulf are (1) because of the high organic carbon content of the water advected onshore and (2) because the onshore flux persists throughout the year. At the gulf, the majority of nutrients upwelled by the wind events are upwelled offshore rather than on the shelf; hence the water that is transported offshore is not as rich in organic carbon. In addition, while the transport at the gulf is small or onshore during summer, it remains onshore to the south of the gulf. The total offshore flux of carbon at the Gulf of Tehuantepec could be underestimated since the model underestimates the amount of organic material close to the coast. [Copyright &y& Elsevier]

Abstract: The Gulf of Aigues-Mortes (NW Mediterranean Sea) is a midshelf zone whose scale is an intermediate between the nearshore scale (0–10m depth) and the coastal scale (including the whole continental shelf). Its hydrodynamics is investigated for the first time. ADCP, CTD and thermosalinograph data were collected during three short cruises (HYGAM; March 6–7, 20–21, April 5–6, 2005). They were scheduled approximately every 15 days to sample the gulf circulation under different weather conditions. Moreover, the cruise data were used to validate the Symphonie model, a 3D primitive equations circulation model. The circulation features displayed by in situ data were well reproduced by Symphonie. A downscaling modelling approach was implemented, the largest scale being obtained by the replay of the MFSTEP regional model of the North-Western Mediterranean Sea. The analysis, closely coupling in situ measurements and model results, provides information that would not have been obtained using data separately. The great variability of the oceanic circulation at this scale is well evidenced. Winds are the main forces, not only locally but also at a larger scale. North winds generate coherent structures interacting with the general Mediterranean circulation. The explanation of the induced currents is then not straightforward, some of them being, for example, northward. South and southeast winds reinforce the sloping surface, the latter allowing the geostrophic equilibrium with longshore currents. This study, focused on the end of winter 2004–2005, also enhances the heat fluxes from offshore to nearshore, as well as the initiation of shelf dense waters. The knowledge of the midshelf oceanic circulation is then applied to run a numerical experiment which describes both the dispersion of a fictive contaminant from a point S (at the centre of the GAM), and evaluates the risk of contamination of the beaches along the GAM shores. [Copyright &y& Elsevier]

Abstract: A three-dimensional finite-element model is used to investigate the tidal flow around Rattray Island, Great Barrier Reef, Australia. Field measurements and visual observations show both stable eddies developing at rising and falling tide in the wake of the island. The water turbidity suggests intense upwelling able to carry bed sediments upwards. Based on previous numerical studies, it remains unclear at this point whether the most intense upwelling occurs near the centre of the eddies or off the island''s tips, closer to the island. All these studies resorted to a very simple turbulence closure, with a zero-equation model whereby the coefficient of vertical viscosity is computed via an algebraic expression. In this work, we aim at studying the influence of the turbulence closure on model results, with emphasis on the prediction of vertical motions. The Mellor and Yamada level 2.5 closure scheme is used and an increase in the intensity of vertical transport is observed. This increase is partly explained by the fact that the Mellor and Yamada model takes into account the hysteresis effect in the time variation of turbulence variables. The influence of the advection of turbulence variables is estimated to be negligible. By a better representation of transient coastal phenomena, the Mellor and Yamada level 2.5 turbulence closure improves the model to a significant degree. [Copyright &y& Elsevier]

Abstract: The surface and subsurface circulation off south-west Australia was simulated using the Regional Ocean Modelling System (ROMS), a primitive equation ocean model with terrain-following s-coordinates. The major currents in this region—the Leeuwin Current and Leeuwin Undercurrent—were reproduced by specifying only temperature and salinity distributions from climatology. The application of wind stress subsequent to the model reaching a quasi-steady state, resulted in the generation of the seasonal Capes Current, a northward-flowing current on the continental shelf associated with coastal upwelling. The simulated currents compared well with the observed current patterns including the location and maximum current speeds. Shelf topography variations and bottom shear, which generated vorticity, influenced eddy formation. Eddies separated from the Leeuwin Current and the Leeuwin Undercurrent, migrated westward, and exited the model domain through merging, dissipating or through an open boundary. In the model simulations, the Undercurrent produced mostly cyclonic eddies due to strong negative vorticity where the current flowed against the continental slope. The Leeuwin Current produced anticyclonic warm-core eddies initiated from the formation of meanders, which were strongest at the surface. The eddy field was dominated by anticyclonic eddies at the surface and cyclonic eddies at 500m. The interaction between the Leeuwin Current and Leeuwin Undercurrent led to the formation of eddy pairs. [Copyright &y& Elsevier]

Abstract: Acoustic doppler current profiler (ADCP), CTD and thermosalinograph data from the Gulf Of Lion Time Series (GOLTS) cruise of December 2003, and corresponding AVHRR images, show the unusual presence of the Rhone river dilution zone far east from the Rhone river mouth. It is the first time this event is studied with simultaneous hydrological and current data. This dilution zone extends as far as 5.27°E in longitude (45km from the Rhone river mouth). At longitude 5.13°E (37km from the Rhone river mouth), the dilution zone is 40m deep and spreads over 0.075° latitude (8km). It is due to an eastward current present there throughout the ADCP-detected range (12–120m). The analysis of moored ADCP time series reveals that such eastward currents occur there about 18% of the time and that diluted waters from the Rhone reach the Station d’Observation Fixe (SOFI) site between 3.9% and 8.4% of the time. This December 2003 event is the consequence of the combined effects of a storm with east winds and the presence of freshwater along the coast. [Copyright &y& Elsevier]

Abstract: This work constitutes an attempt to assess the relative importance of natural versus anthropogenic forcing for sediment resuspension on the shelf of the Thermaikos Gulf (NW Aegean) through a 2-year experiment in the framework of the E.U. project INTERPOL. Four periods of different hydrographic characteristics were identified, including two periods of stronger vertical homogenisation and two of stratified conditions. The former periods were characterized by stronger near-bed currents, while relatively weak internal wave motions dominated the periods of stratification. The near-bed currents showed strong coherence with the wind during the period of full homogenisation, whereas during stratification periods the wind provided indirect forcing evident mostly in the internal-wave bands. The site was too deep for the surface waves to cause any sediment resuspension. In conclusion, the observed near-bed currents at the site of interest did not appear to produce significant local resuspension of sediment; notably, the current-turbidity correlation suggested a shoreward transport of suspended material. The large-scale turbidity variability was rather related to the onset of the trawling period in mid-October 2001 and the increased riverine discharge in late summer/autumn 2002. [Copyright &y& Elsevier]

Abstract: The hydrography, circulation and distribution of particulate matter in Thermaikos Gulf (NW Aegean Sea) are described, for September 2001 and October 2001 and February 2002. The observations were obtained to assess the impact of anthropogenic and natural resuspension processes on the coastal ecosystem. The first two periods represent highly stratified conditions and mild weather conditions; in September trawling is prohibited, whilst the October cruise took place following the commencement of the activity. The sampling in February was undertaken to record the contribution of natural resuspension to the system, in a stormy period. The water circulation was mainly baroclinic during autumn and barotropic in winter; this was due to vertical homogenisation of the water column, during the latter period. The distribution of the bottom nepheloid layer (BNL) was very different in the winter than in the autumn. Microstructure measurements were undertaken, which allowed the vertical eddy diffusivity to be estimated, together with the near-bed shear stresses. Computation of the diffusive flux of particulate matter (PM), from the BNL into the intermediate water column in response to turbulent motions, reveals that the PM flux was much higher in October than in September; this is despite the fact that the friction velocities were similar. This observation could explain partly the observed higher PM concentrations (PMC) in the intermediate layer, in October. Likewise suggest that the higher PMC in October could be attributed to trawling. The limited shear stress and friction velocity values obtained during the September and October cruises were always low; these were possibly capable of resuspending only recently deposited, “fluffy” material. Thus, the observed nepheloid layers are likely to be maintained by advection from the shallow water regions and trawled areas. [Copyright &y& Elsevier]

Abstract: Mooring and shipboard data collected between 1992 and 1995 delineate the circulation over the north central Chukchi shelf. Previous studies indicated that Pacific waters crossed the Chukchi shelf through Herald Valley (in the west) and Barrow Canyon (in the east). We find a third branch (through the Central Channel) onto the outer shelf. The Central Channel transport varies seasonally in phase with Bering Strait transport, and is ∼0.2Sv on average, although some of this might include water entrained from the outflow through Herald Valley. A portion of the Central Channel outflow moves eastward and converges with the Alaskan Coastal Current at the head of Barrow Canyon. The remainder appears to continue northeastward over the central outer shelf toward the shelfbreak, joined by outflow from Herald Valley. The mean flow opposes the prevailing winds and is primarily forced by the sea-level slope between the Pacific and Arctic oceans. Current variations are mainly wind forced, but baroclinic forcing, associated with upstream dense-water formation in coastal polynyas might occasionally be important. Winter water-mass modification depends crucially on the fall and winter winds, which control seasonal ice development. An extensive fall ice cover delays cooling, limits new ice formation, and results in little salinization. In such years, Bering shelf waters cross the Chukchi shelf with little modification. In contrast, extensive open water in fall leads to early and rapid cooling, and if accompanied by vigorous ice production within coastal polynyas, results in the production of high-salinity (>33) shelf waters. Such interannual variability likely affects slope processes and the transport of Pacific waters into the Arctic Ocean interior. [Copyright &y& Elsevier]

Abstract: Year-long time-series of temperature, salinity and velocity from 12 locations throughout the Chukchi Sea from September 1990 to October 1991 document physical transformations and significant seasonal changes in the throughflow from the Pacific to the Arctic Ocean for one year. In most of the Chukchi, the flow field responds rapidly to the local wind, with high spatial coherence over the basin scale—effectively the ocean takes on the lengthscales of the wind forcing. Although weekly transport variability is very large (ca. to ), the mean flow is northwards, opposed by the mean wind (which is southward), but presumably forced by a sea-level slope between the Pacific and the Arctic, which these data suggest may have significant variability on long (order a year) timescales. The high flow variability yields a significant range of residence times for waters in the Chukchi (i.e. one to six months for half the transit) with the larger values applicable in winter. Temperature and salinity (TS) records show a strong annual cycle of freezing, salinization, freshening and warming, with sizable interannual variability. The largest seasonal variability is seen in the east, where warm, fresh waters escape from the buoyant, coastally trapped Alaskan Coastal Current into the interior Chukchi. In the west, the seasonally present Siberian Coastal Current provides a source of cold, fresh waters and a flow field less linked to the local wind. Cold, dense polynya waters are observed near Cape Lisburne and occasional upwelling events bring lower Arctic Ocean halocline waters to the head of Barrow Canyon. For about half the year, at least at depth, the entire Chukchi is condensed into a small region of TS-space at the freezing temperature, suggesting ventilation occurs to near-bottom, driven by cooling and brine rejection in autumn/winter and by storm-mixing all year. In 1990–1991, the ca. 0.8Sv annual mean inflow through Bering Strait exits the Chukchi in four outflows—via Long Strait, Herald Valley, the Central Channel, and Barrow Canyon—each outflow being comparable (order 0.1–0.3Sv) and showing significant changes in volume and water properties (and hence equilibrium depth in the Arctic Ocean) throughout the year. The clearest seasonal cycle in properties and flow is in Herald Valley, where the outflow is only weakly related to the local wind. In this one year, the outflows ventilate above and below (but not in) the Arctic halocline mode of 33.1psu. A volumetric comparison with Bering Strait indicates significant cooling during transit through the Chukchi, but remarkably little change in salinity, at least in the denser waters. This suggests that, with the exception of (in this year small) polynya events, the salinity cycle in the Chukchi can be considered as being set by the input through Bering Strait and thus, since density is dominated by salinity at these temperatures, Bering Strait salinities are a reasonable predictor of ventilation of the Arctic Ocean. [Copyright &y& Elsevier]

Abstract: The narrow continental shelf off Troms has a complex topography with deep trenches separating shallow banks. The front between Atlantic Water (AW) and Norwegian Coastal Water (NCW) is found near the shelf break and the currents in the area are topographically steered by the shelf slope. We have investigated the combined effects of topography, seasonal stratification, wind and tides on circulation and shelf–ocean interaction using field measurements and numerical simulations of hydrography and currents. Comparisons between simulation results and field measurements show that the model behaves realistically in terms of the distribution of NCW and general circulation. Effects of wind, tides and topography on the currents are shown to be strongly dependent on the stratification, which shows large seasonal variations in the area. Topographical effects on surface circulation are weakened when stratification increases. During stratified conditions winds have a strong impact on surface circulation and shelf–ocean exchange, and the wind direction is crucial for drift paths and residence times for particles (e.g. plankton) in the shelf area. When stratification is weak, tidal effects combined with topographic steering dominate the circulation. [Copyright &y& Elsevier]

Abstract: Temporal variations of the current field on the shelf of the South East Atlantic off Walvis Bay were studied during austral summer and fall by moored current profiler and temperature-salinity recorder located on the shelf 20nm off Walvis Bay, Namibia. Spatial and temporal variations of the wind field in the South East Atlantic were investigated by 3-day averaged wind fields measured by the QuikSCAT satellite. The local wind was provided by a time series of hourly wind vectors measured on a moored buoy off Swakopmund. The significant tidal motion on the shelf off Walvis Bay is composed of the anticlockwise rotating barotropic semidiurnal constituents M2 and S2. The tidal currents are described to a first order by a barotropic deep ocean Kelvin wave. The land-sea breeze forces anticlockwise rotating diurnal variations of the current in the surface mixed layer and an opposite directed current below the thermocline, which compensates the mass flux normal to the coast in the surface layer. Most of the energy of the current fluctuations were concentrated around the local inertial period of . These fluctuations consisted of at least four significant anti-clockwise rotating vertical modes with amplitudes ranging between 10 and 20cm/s. On a large scale the amplitudes of inertial motions correlate with the wind fluctuations but locally the motions consist of a superposition of locally wind forced inertial oscillations and inertial waves generated at larger distances as well near the surface as close to the bottom. The vertical structure of the inertial motion suggests that it could be a possible candidate for mixing in the bottom boundary layer by differential advection. Coastal trapped waves of horizontal mode number less that four were observed at periods of about 7 days. The mean cross shelf circulation consisted of a two cell structure. The upper cell was made of the Ekman offshore current and a compensating onshore current at intermediate depth below the thermocline. The lower cell consisted of an offshore current in the bottom layer below 80m depth and was closed by the onshore current in the intermediate depth range. The cross shelf circulation controlled the fraction of ESACW on the shelf water mass. The long shelf circulation consisted in the surface mixed layer of an equatorward coastal jet driven by the local meridional wind stress and an almost barotropic poleward counter current appearing partly as free Kelvin wave emanating from the Angola-Benguela front and as coastal counter current forced by the local negative curl of the wind stress. The longshore current controlled the fraction of the SACW on the shelf water mass, which increased continuously between austral summer and fall. [Copyright &y& Elsevier]

Abstract: The differences between two oceanographic patterns observed in the Galician (NW Spain) shelf/slope are described and analysed using wind, CTD and current meter data obtained during two cruises INCOCEANO-I and INCOCEANO-II, conducted in April–May 1997 and September 1998, respectively. Geopotential anomaly fields as well as potential temperature vs. salinity (θ–S) diagrams are derived from CTD casts. The upper layer (0–80 m) shows strong seasonal variability. Despite both cruises beginning under similar weather conditions, the resulting oceanographic pattern is different: while in April–May 1997, a downwelling event was observed; in September 1998, the situation is predominantly upwelling. We suggest that the different oceanographic response was related to the hydrographic conditions prevailing in the region during the weeks previous to the samplings, which correspond to the beginning (INCOCEANO-I) and end (INCOCEANO-II) of the upwelling period. Current meter data revealed the importance of inertial currents, which surpass that of tidal currents in shallower moorings (mean inertial velocity=15 cm s−1 at 20-m depth). [Copyright &y& Elsevier]

Abstract: In many numerical ocean models, the hydrostatic approximation is made. This approximation causes a considerable saving in computing time. However, for phenomena involving large vertical speeds, for many small scale phenomena, and in areas with weak stratification, the approximation becomes questionable. In this report, a -coordinate hydrostatic C-grid model is extended to include non-hydrostatic dynamics. The test cases involve gravitational adjustment of a downslope flow. The first test case has a simplified slope profile and no ambient stratification in the deep basin. The second test case has ambient stratification and more realistic topography. The differences between hydrostatic and non-hydrostatic simulations are described and discussed. It is shown that the shapes of the head and the body of density driven plumes are better preserved in the non-hydrostatic experiments. The wave propagation away from the plume head is considerably reduced when including non-hydrostatic effects. [Copyright &y& Elsevier]

This paper describes thermohaline properties in the north and middle Adriatic Sea in 1999 based on temperature and salinity data collected along the Po-Rovinj, Jabuka Pit and Palagruǽa Sill profiles. The preconditioning, generation and spread of North Adriatic Dense Water (NAdDW), as well as their relationship to surface fluxes and river discharge are analyzed in detail. A strong Bora wind event in November 1998 resulted in heat loss exceeding 800W/m2, homogenizing and cooling the whole water column by 2.4°C, while another similar Bora episode in January/February with a cooling rate of 1.4°C ended with NAdDW generation. River discharge was low during the preconditioning and generation phases. Following its generation, the NAdDW flowed southeastward as a density current along the western Adriatic slope. Its northeastern part reached the steep edge of the Jabuka Pit and sank rapidly to the bottom, where it was observed a month after its generation. However, the core of the NAdDW current continued to follow the western slope as a density current, taking a detour around the pit on its southeastern side, and sinking to the bottom in the eastern segment of the pit. The detour and sinking at the Jabuka Pit slope was estimated with an analytical model to be 1.1m/km. Finally, the upper lighter part of the NAdDW current crossed the Palagruǽa Sill and followed the western slope entering the South Adriatic Pit and contributing to the water mass dynamics there. Another NAdDW branch was found at the very bottom of the middle of the Palagruǽa Sill, although being less pronounced than the one that moved over the western slope. [Copyright &y& Elsevier]

Abstract: Sedimentological parameters of 206 box-core tops and 387 van Veen grab samples were analysed so as to understand the distribution, source and sedimentation rates in the shelf and upper slope of the southern Southeastern Brazilian margin. Most of the parameters (bulk organic matter constituents, δ13C, and ɛNd) can be grouped on northern and southern sectors, separated by a sharp boundary. This suggests that sediment sources and sedimentary processes are different in both regions. The southern sector of the study area is more influenced by cold waters coming from the southern portion of the South American shelf and the organic fraction revealed an important role played by the primary productivity in the sedimentation. Also, ɛNd values indicate that part of the inorganic fraction of the southern sector sediments are allochtonous, probably coming from younger rocks of the Andean chain probably reaching the shelf through the La Plata river runoff. In the northern part of the study area the sedimentation is controlled almost exclusively by the meandering of Brazil Current. Compositional and isotope bulk organic parameters showed a more complex mixing of terrigenous and pelagic fractions. Also, ɛNd values are associated with the precambrian rocks of the Brazilian shield. The whole area exhibits sedimentation rates, varying from 5 to 660mmkyr-1. [Copyright &y& Elsevier]

A numerical model is used to investigate coastal upwelling in the South Brazil Bight. The wind in the area is predominantly from the northeast, especially m summer, which is upwelling favorable. Reversals of the wind direction are frequent and intense during the winter, due to the passage of frontal systems. The offshore circulation is dominated by the Brazil Current, which flows southward meandering around the 200 m isobath. Significant shelf-break upwelling has being associated with Brazil Current cyclonic meanders. To assess the relative importance of the two processes in the pumping of South Atlantic Central Water (SACW) onto the continental shelf, three cases are analyzed: (1) wind-driven upwelling: (2) upwelling induced by Brazil Current meanders and(3) both effects aet.ing together. The results show that in the coastal area upwelling/downwelling is mainly caused by the wind, whereas the cyclonic meanders of the Brazil Current are the dominant mechanism in the generation of vertical velocities over the shell break and slope. This meander-induced upward motion brings the SACW to shallower depths, where it is influenced by the wind. In this situation, when both effects act together. the SACW penetrates all the way to the coast. [ABSTRACT FROM AUTHOR]

The occurrence of an episodic chlorophyll plume detected on the West Florida Shelf between 1979 and 1986 was confirmed in March 1995 with shipboard data and in March 1998 with new ocean color data from the SeaWiFS sensor. New evidence is presented to support the hypothesis that diatom blooms off Apalachicola Bay are the precursor of the seasonal West Florida Shelf plume, and that the nutrient requirements for such blooms, especially silicate, can be supported by river discharge. The observations indicate that the impact of rivers is maximal over the middle shelf and decreases over the outer shelf. Salinity and discharge measurements support the concept that the Apalachicola River had a major impact at distances exceeding 100 km from the coast and that it plays an important role in the formation of offshore blooms. Preliminary analyses suggest that successional processes lead to cryptophytes dominating in the offshore blooms. [Copyright &y& Elsevier]

Long-term current meter data from the continental shelf region of the Great Barrier Reef show that there exists a zone of oceanic inflow onto the shelf. This oceanic inflow splits into two branches on meeting the continental shelf slope, resulting in two net longshore currents on the slope, one to the north and the other to the south of the separation point. In 1981 this separation point was located between 17°S and 18°S. This circulation was successfully predicted using a depth-averaged two-dimensional model in which the regional sea level gradient is explicitly added in the momentum equations. The resulting circulation on the continental shelf is controlled by an oceanic inflow of 0·58 Sv, spread over 500 km of the shelf edge both north and south of the separation point. The inflow appears measurably impeded by the presence of coral reefs, with >50% of the inflow occurring in a 150 km long area where reef density is small. Satellite images confirm this spatial variability. Longshore currents on the shelf generated by the inflow are modulated by the wind and tides, which can deflect the mean current away from areas of high reef density and generate localized outflows to the Coral Sea. Oceanic inflow is believed to be important because it flushes the shelf even in the absence of wind; it controls the dominant direction of across-shelf and along-shelf spread of spawn material from reefs; it makes it possible for upwelled water to spread quickly over the GBR shelf; it may also protect coral reefs by preventing river plumes from spreading onto the outer shelf. [Copyright &y& Elsevier]

A depth-integrated numerical model with grid resolution 500 m has been used to simulate tides around the Lofoten Islands in northern Norway. The model spans more than 3° latitude and covers a sea area of approximately 1.2×105 km2. The fine spatial resolution resolves the important fine scale features of the bottom topography on the shelf and the complex coastline with fjords and islands. Boundary conditions at the oceanic sides of the model domain are obtained by interpolation from a large-scale tidal model covering the Nordic Seas and implemented with the flow relaxation scheme (FRS). The semi-diurnal components M2, S2 and N2 and the diurnal component K1 are simulated. Harmonic constants for sea level are compared with observations from 21 stations. The best fit is found for the M2 component with a standard deviation between the observed and modelled amplitude and phase of 2.3 cm and 2.5°, respectively. The standard deviation for the other smaller components ranges between 1.5–2.8 cm and 5.3–16.7°. Current fields from the model are compared with observations in four locations: the Moskenes sound, the Gimsøy channel, the Tjeldsund channel and the Sortland channel. In the Sortland channel, the model predicts a dominant diurnal K1 current in agreement with observations. [Copyright &y& Elsevier]

Results of a program of observations carried out on the northern Portuguese shelf and slope, between July 1996 and June 1999 are used to characterise the main physical processes of the winter regime. The data set includes time series of waves and currents at mid-shelf (86 m depth) and of winds, atmospheric pressure and sea level at the coast, as well as hydrographic and suspended particle matter (SPM) observations carried during three multidisciplinary surveys. The wave regime was found to be characterised by highly energetic conditions during the winter, with storm events leading to waves of significant heights exceeding 5 m with mean periods of over 10 s. Prevailing southerly winds force a downwelling regime over the shelf with poleward flow at mid-shelf (~10–20 cm/s) and offshore transport in the bottom Ekman layer. Episodic strong upwelling events can occur during this period, leading to important changes in the near bottom stratification at mid-shelf. Tidal currents at mid-shelf are dominated by the contribution of the M2 tide (~3 cm/s) and are polarised in the cross-shelf direction, reflecting the guiding effect of the Porto Canyon. [Copyright &y& Elsevier]