Progress on shelf and slope circulation in the northern South China Sea

Influenced by the seasonally reversed monsoons, water exchange through straits, and topography, the shelf and slope circulation in the northern South China Sea (NSCS) is complex and changeable. The typical current system in the NSCS consists of the slope current, South China Sea warm current (SCSWC), coastal current, and associated upwelling (in summer) and downwelling (in winter). This paper reviews recent advances in the study of NSCS shelf and slope circulation since the 1990s, and summarizes the roles of Kuroshio intrusion, the monsoons, topography, and the buoyancy effect of the Pearl River plume in the shelf and slope current system of the NSCS. We also point out some potential scientific issues that require further study, such as the dynamic connection between the internal basin and shelf areas of the NSCS, the persistence of the SCSWC in winter, the temporo-spatial characteristics of downwelling during winter in the NSCS, and its material and energy transport.     

Investigation of three-dimensional circulation and hydrography over the Pearl River Estuary of China using a nested-grid coastal circulation model

The Pearl River Estuary (PRE) in South China's Guangdong Province is a subtropical estuary with highly irregular topography and dynamically complicated circulations. A nested-grid coastal circulation modelling system is used in this study to examine dynamic responses of the PRE to tides, meteorological forcing and buoyancy forcing. The nested-grid modelling system is based on the Princeton Ocean Model and consists of three downscaling subcomponents: including an outer-most model with a coarse horizontal resolution of ~7 km for simulating tidally forced and wind-driven surface elevations and depth-mean currents over the China Seas from Bohai Sea to the northern South China Sea and an innermost model with a fine resolution of ~1.2 km for simulating the 3D coastal circulation and hydrography over the PRE and adjacent coastal waters. Model results during the winter northeast monsoon surge in January and super typhoon Koryn in June of 1993 are used to demonstrate that the 3D coastal circulation and hydrographic distributions in the PRE are affected by tides, winds and buoyancy forcing associated with river discharge from the Pearl River with significant seasonal and synoptic variabilities.     

Simulating the three-dimensional circulation and hydrography of Halifax Harbour using a multi-nested coastal ocean circulation model

Halifax Harbour is located on the Atlantic coast of Nova Scotia, Canada. It is one of the world’s largest, ice-free natural harbours and of great economic importance to the region. A good understanding of the physical processes controlling tides, flooding, transport and dispersion, and hydrographic variability is required for pollution control and sustainable development of the Harbour. For the first time, a multi-nested, finite difference coastal ocean circulation model is used to reconstruct the three-dimensional circulation and hydrography of the Harbour and its variability on timescales of hours to months for 2006. The model is driven by tides, wind and sea level pressure, air-sea fluxes of heat, and terrestrial buoyancy fluxes associated with river and sewage discharge. The predictive skill of the model is assessed by comparing the model simulations with independent observations of sea level from coastal tide gauges and currents from moored instruments. The simulated hydrography is also compared against a new monthly climatology created from all available temperature and salinity observations made in the Harbour over the last century. It is shown that the model can reproduce accurately the main features of the observed tides and storm surge, seasonal mean circulation and hydrography, and wind driven variations. The model is next used to examine the main physical processes controlling the circulation and hydrography of the Harbour. It is shown that non-linear interaction between tidal currents and complex topography occurs over the Narrows. The overall circulation can be characterized as a two-layer estuarine circulation with seaward flow in the thin upper layer and landward flow in the broad lower layer. An important component of this estuarine circulation is a relatively strong, vertically sheared jet situated over a narrow sill connecting the inner Harbour to the deep and relatively quiescent Bedford Basin. Local wind driven variability is strongest in winter as expected but it is also shown that a significant part of the temperature and salinity variability is driven by physical processes occurring on the adjacent inner continental shelf, especially during storm and coastal upwelling events.     

Eurasian Arctic shelf hydrography: Exchange and residence time of southern Laptev Sea waters

The hydrography of the Laptev Sea is significantly influenced by river water and sea-ice processes, which are highly variable over the annual cycle. Despite of an estuarine structure the inner and outer shelf regions are decoupled at times as documented by the stability of a warm intermediate layer formed during summer below the Lena River plume. We demonstrate that a remnant of this warm layer is preserved below the fast ice until the end of winter, while only slightly farther to the north, offshore of the landfast ice in the polynya region, the pycnocline is eroded and no signature of this layer is found. The warm intermediate layer (WIL) formed during summer can be used as tracer for Laptev Sea shelf waters throughout the winter. Thereby, residence times of southern Laptev Sea waters can be estimated to be at least from summer to the end of winter/spring of the following year.     

Process study of coastal circulation over the inner Scotian Shelf using a nested-grid ocean circulation model, with a special emphasis on the storm-induced circulation during tropical storm Alberto in 2006

This study examines main physical processes affecting the three-dimensional (3D) circulation and hydrographic distributions over the inner Scotian Shelf (ISS) in June and July 2006 using a nested-grid coastal ocean circulation modeling system known as the NCOPS-LB. The nested-grid system has five relocatable downscaling submodels, with the outermost submodel of a coarse horizontal resolution of (1/12)° for simulating storm surges and barotropic shelf waves over the Eastern Canadian shelf and the innermost submodel of a fine resolution of ～180 m for simulating the 3D coastal circulation and hydrography over Lunenburg Bay of Nova Scotia in the default setup. The NCOPS-LB is driven by meteorological and astronomical forcing and used to study the storm-induced circulation over the ISS during tropical storm Alberto. Model results demonstrate that the coastal circulation and hydrographic distributions over the ISS are affected significantly by tides, local wind forcing, and remotely generated coastal waves during the study period.     

Distribution and abundance of thaliaceans in the northwest continental shelf of South China Sea, with response to environmental factors driven by monsoon

The distribution and abundance of thaliaceans were studied in relation to physical and biological variables during summer and winter in the northwest continental shelf of South China Sea. Based on the topography and water mass of the surveyed region, it was divided into three subregions: region I (onshore waters of the east Leizhou Peninsula), region II (onshore waters of the east and southeast Hainan Island) and region III (offshore waters from Leizhou Peninsula to Hainan Island). During summer due to a strong southwest monsoon, a cold eddy and coastal upwelling dominated in regions I and II, respectively, whereas the onshore and offshore waters were vertically mixed during winter due to a strong northeast monsoon. A total of 18 thaliacean species (including 3 subspecies) were collected. The mean species richness was higher in summer compared to winter, with the occurrence of higher values during summer and winter at region II and region III, respectively. The average thaliacean abundance is also higher in summer than in winter, with higher values at region I in summer and no significant difference among three subregions in winter. Doliolum denticulatum and Thalia democratica were the dominant species during summer and winter. The results suggested that the seasonal and spatial distribution of thaliacean richness was considered to be the result of physical factors such as temperature and ocean current in summer and winter. Spatial distribution of thaliacean abundance was affected by chlorophyll a concentration increased by the occurrence of coastal upwelling and cold eddy in summer. Southwest and northeast monsoons are shown to play an important role in shaping the distribution of species richness and abundance of thaliaceans in the northwest continental shelf of South China Sea.     

The effects of river discharge and seasonal winds on the shelf off southeastern South America

The Río de la Plata waters form a low salinity tongue that affects the circulation, stratification and the distributions of nutrients and biological species over a wide extent of the adjacent continental shelf. The plume of coastal waters presents a seasonal meridional displacement reaching lower latitudes (28°S) during austral winter and 32°S during summer. Historical data suggests that the wind causes the alongshore shift, with southwesterly (SW) winds forcing the plume to lower latitudes in winter while summer dominant northeasterly (NE) winds force its southward retreat. To establish the connection between wind and outflow variations on the distribution of the coastal waters, we conducted two quasi-synoptic surveys in the region of Plata influence on the continental shelf and slope of southeastern South America, between Mar del Plata, Argentina and the northern coast of Santa Catarina, Brazil. We observed that: (A) SW winds dominating in winter force the northward spreading of the plume to low latitudes even during low river discharge periods; (B) NE winds displace the plume southward and spread the low salinity waters offshore over the entire width of the continental shelf east of the Plata estuary. The southward retreat of the plume in summer leads to a volume decrease of low salinity waters over the shelf. This volume is compensated by an increase of Tropical waters, which dominate the northern shelf. The subsurface transition between Subantarctic and Subtropical Shelf Waters, the Subtropical Shelf Front, and the subsurface water mass distribution, however, present minor seasonal variations. Along shore winds also influence the dynamics and water mass variations along the continental shelf area. In areas under the influence of river discharge, Subtropical Shelf Waters are kept away from the coastal region. When low salinity waters retreat southward, NE winds induce a coastal upwelling system near Santa Marta Cape. In summer, solar radiation promotes the establishment of a strong thermocline that increases buoyancy and further enhances the offshore displacement of low salinity waters under the action of NE winds.     

Wind-driven diversion of summer river runoff preconditions the Laptev Sea coastal polynya hydrography: Evidence from summer-to-winter hydrographic records of 2007–2009

This paper examines the role of atmospheric forcing in modifying the pathways of riverine water on the Laptev Sea shelf, using summer-to-winter hydrographic surveys from 2007 to 2009. Over the two consecutive winter seasons of 2007–2008 and 2008–2009 in the area of the winter coastal polynya, our data clearly link winter surface salinity fields to the previous summer conditions, with substantially different winter salinity patterns preconditioned by summer atmospheric forcing. In the summer of 2007, dominant along-shore westerly winds in the cyclonic regime force the Lena River runoff to flow eastward. In contrast, in the summer of 2008, dominant along-shore easterly winds over the East Siberian Sea and on-shore northerly winds over the Laptev Sea in the anticyclonic regime lock the riverine water in the vicinity of the Lena Delta. Over the coastal polynya area in the southeastern Laptev Sea these patterns precondition a surface salinity difference of 8–16 psu between the winters of 2008 and 2009. Overall, this indicates a residence time of at least half a year for riverine water on the Laptev Sea shelf. Future climate change associated with an enhanced summer cyclonicity over the eastern Arctic may turn more riverine water eastward along the eastern Siberian coast, resulting in weaker vertical density stratification over the Laptev Sea shelf, with possible impact on the efficiency of vertical mixing and polynya dense water production.     

Oceanic upwelling and downwelling processes in waters off the west coast of India

A three-dimensional model based on the Princeton Ocean Model (POM) has been implemented to study the circulation of the west coast of India. The model uses a curvilinear orthogonal horizontal grid with higher resolution near the coast (3–9 km) and a terrain following sigma coordinate in the vertical. The model is able to simulate Lakshadweep High and Lakshadweep Low (LL) during the winter and summer monsoons, respectively. During winter, the downwelling processes noticed along the coast help in the formation of temperature inversions. The inversions can be seen even up to the depths of ～50 m, which agrees with the available ARGO data in the region. Model simulations show that coastal upwelling off Kerala is at its peak in July. The intensity of upwelling reduces along the coast towards north. During the existence of LL, there is a cyclonic eddy in the sub-surface waters over the South-Eastern Arabian Sea, with vertical extent up to the depths of 100–150 m and it is strengthened due to the presence of northward counter current in the shelf region. The southerly coastal jet formed along the southern coast as a result of upwelling is noticed a westward shift along with LL. The location of the eddy off Kerala is tilted towards the open ocean with depth and our experiments suggest that this flow can be understood as a first baroclinic mode.     

Using the Regional Ocean Modeling System (ROMS) to improve the ocean circulation from a GCM 20<Superscript>th</Superscript> century simulation

Global coupled climate models are generally capable of reproducing the observed trends in the globally averaged atmospheric temperature. However, the global models do not perform as well on regional scales. Here, we present results from a 20-year, high-resolution ocean model experiment for the Atlantic and Arctic Oceans. The atmospheric forcing is taken from the final 20 years of a twentieth-century control run with a coupled atmosphere–ocean general circulation model. The ocean model results from the regional ocean model are validated using observations of hydrography from repeat cruises in the Barents Sea. Validation is performed for average quantities and for probability distributions in space and time. The validation results reveal that, though the regional model is forced by a coupled global model that has a noticeable sea ice bias in the Barents Sea, the hydrography and its variability are reproduced with an encouraging quality. We attribute this improvement to the realistic transport of warm, salty waters into the Barents Sea in the regional model. These lateral fluxes in the ocean are severely underestimated by the global model. The added value with the regional model that we have documented here lends hope to advance the quality of oceanic climate change impact studies.     

Study on subtidal circulation and variability in the Gulf of St. Lawrence,Scotian Shelf,and Gulf of Maine using a nested-grid shelf circulation model

This paper examines the subtidal circulation and associated variability in the Gulf of St. Lawrence, the Scotian Shelf, and the Gulf of Maine (GSL-SS-GOM) in 1988–2004 based on results produced by a nested-grid shelf circulation model. The model has a fine-resolution child model (～ (1/12)°) embedded inside a coarse-resolution parent model (～ (1/4)°) of the northwest Atlantic. The combination of the semi-prognostic method and the spectral nudging method is used to reduce the model seasonal bias and drift. The child model reproduces the general features of the observed circulation and hydrography over the study region during the study period. The child model results demonstrate that the time-mean circulation in the GSL is affected by the time-mean atmospheric forcing and inflow through the Strait of Belle Isle. The temporal variability in atmospheric forcing affects the outflow through western Cabot Strait, which in turn affects the transport of the Nova Scotian Current and the gulf-wide cyclonic circulation in the GOM. The simulated seasonal variability of salinity in the top 30 m of the GSL-SS-GOM is mainly affected by the equatorward advection of low-salinity waters from the lower St. Lawrence Estuary to the GOM through the Scotian Shelf. The simulated intraseasonal variability of circulation in the GSL is affected by the variability in the estuarine circulation in response to the temporal variability in atmospheric forcing. On the Scotian Shelf, the intraseasonal variability is mainly driven by the variability of wind forcing and mesoscale and nonlinear dynamics over the shelf break and slope region. The interannual variability in the simulated temperature and salinity are spatially coherent in the intermediate waters in the GSL, which is caused partially by the local response to atmospheric variability and partially by variabilities over the southern Newfoundland Shelf that enter the GSL through the eastern Cabot Strait. By comparison, on the Scotian Shelf, the interannual variability of simulated circulation is affected by anomalies produced by the nonlinear dynamics which are advected equatorwards by the shelf break jet.     

Sensitivity of coastal polynyas and high-salinity shelf water production in the Ross Sea,Antarctica, to the atmospheric forcing

Coastal polynyas around Antarctica are the place of intense air–sea exchanges which eventually lead to the formation of high-salinity shelf waters (HSSW) over continental shelves. Here, the influence of atmospheric forcing on coastal polynyas in the Ross Sea is studied by contrasting the response of a regional ocean/sea-ice circulation model to two different atmospheric forcing sets. A first forcing (DFS3) is based on ERA40 atmospheric surface variables and satellite products. A second forcing (MAR) is produced on the basis of ERA40 with a dynamical downscaling procedure. As compared to DFS3, MAR forcing is shown to improve substantially the representation of small-scale patterns of coastal winds with stronger katabatic winds along the coast. The response of the ocean/sea-ice model to the two forcing sets shows that the MAR forcing improves substantially the geographical distribution of polynyas in the Ross Sea. With the MAR forcing, the polynya season is also shown to last longer with a greater ice-production rate. As a consequence, a greater flow of dense water out of the polynyas is found with the MAR forcing and the properties of HSSW are notably improved as compared to the DFS3 forcing. The factors contributing to the activity of Terra Nova Bay and Ross Ice Shelf polynyas in the model are studied in detail. The general picture that emerges from our simulations is that the properties of HSSW are mostly set by brine rejection when the polynya season resume. We found that coastal polynyas in the Ross Sea export about 0.4 Sv of HSSW which then flows along three separate channels over the Ross Shelf. A 6-month time lag is observed between the peak of activity of polynyas and the maximum transport across the sills in the channels with a maximum transport of about 1 Sv in February. This lag corresponds to the time it takes to the newly formed HSSW to spread from the polynya to the sills (at a speed of nearly 2 cm s⁻¹).     

Seasonal variation of upper layer circulation in the northern part of the East/Japan Sea

Seasonal variation of upper layer circulation in the northern part of the East/Japan Sea and its mechanism were investigated using empirical orthogonal function (EOF) analysis with satellite sea surface heights over the northern East/Japan Sea and a three-dimensional circulation model. The spatial structure and temporal variation of first EOF mode, which explains about 64% of the total variance, indicate that a large cyclonic circulation in the northern East/Japan Sea shows a semi-annual variation with maximum strength in summer and winter. According to numerical model result, the Liman Cold Current, accepted as a major current in the northern East/Japan Sea, is well mixed vertically by the winter monsoon and the current in the upper layer has a relatively deep structure, with a maximum westward speed of about 20 cm/s in winter. On the other hand, in summer the current has a stronger baroclinic structure of velocity than in winter. Numerical experiments showed that in summer the temporal variation of upper layer circulation is controlled by thermal forcing, such as sea surface heat flux and inflow of heat transport into the East/Japan Sea through the Korea/Tsushima Strait. Moreover, the cyclonic circulation in the upper layer of the northern East/Japan Sea is also generated and strengthened by the positive wind stress curl occupying most of the East/Japan Sea during the winter. The seasonal variation of each forcing that drives the circulation is responsible for the strength or weakness of the upper layer circulation in the northern East/Japan Sea. The contribution of each forcing to the seasonal variation of the upper layer circulation is examined through sensitivity experiments. According to these numerical experiments, the upper layer circulation in the northern East/Japan Sea is strengthened twice a year, in winter and summer, and this semi-annual variation is determined by a combination of wind (winter) and thermal (summer) forcing.     

Lagrangian circulation and forbidden zone on the West Florida Shelf

This paper presents some recent results of drifters released on the West Florida Shelf during 1996–1997 and compares with the numerical model results of the wind-driven circulation. Using satellite tracked surface drifters during the one year period from February 1996 to February 1997, a drifter free region, called the “forbidden zone”, is found over the southern portion of the West Florida Shelf. This finding is consistent with historical drift bottle data and with a recent numerical model study of the West Florida Shelf circulation response to climatological wind forcing. Direct drifter simulations by numerical model during March 1996 show a good agreement with both the in situ ADCP current observation and drifter observation. Three mechanisms are proposed for the observed Lagrangian features. The primarily dynamic mechanism is the along-shore wind forcing, which induces a coastal jet that tends to leave the coast and the bottom onshore and near surface offshore transports. The second one is the convergent coastal geometry and bottom topography for the southward flow in central shelf near Tampa Bay that enforces the coastal jet and the bottom and near surface transport. The last is a kinematic one, simply due to the short along-shore Lagrangian excursion, driven by the typical synoptic weather systems. Thus near surface shelf waters over the north may not reach the southern coast of the West Florida. Implication is that surface hazard such as oil spill that may occur outside of the southern West Florida shelf may not greatly impact the southern coastal region except Florida Keys. However, the biological and chemical patches over the north that may occur in the water column such as red tides still can easily reach the southern coastal region through the subsurface and bottom waters.     

Seasonal circulation and influence factors of the Bohai Sea: a numerical study based on Lagrangian particle tracking method

Seasonal circulation of the Bohai Sea (BS) in 1992 was investigated using Lagrangian particle tracking method. The hydrography of the BS was simulated based on an unstructured grid, finite-volume, three-dimensional primitive equation ocean model. With the use of the unstructured triangular grid, the model can easily fit the irregular coastal boundary of the BS. The simulated tides, tidal current, and thermohaline field agreed well with the observations. The transport of particles has three-dimensional structure in the BS. Compared with central Bohai and Bohai Strait, the differences of particles’ transportation between surface and bottom layer in three bays are small. The circulation in the summer is stronger than that in the winter, with the average residual velocity in the surface layer being about 3.7 cm/s during the summer while only 1.8 cm/s during the winter. Using the same model, several well-designed numerical experiments were performed to investigate the effect of oceanic tide, river discharge, wind stress, and thermal stratification on the circulation. It is shown that winds play an important role in the circulation of the BS during both the winter and the summer. Density circulation is important during the summer; however, it is negligible during the winter. River runoff only affects the area around the river mouth. Compared with wind and thermohaline effect, the contribution of tides is small during the summer, and the circulation under only M₂ tidal constituent could not reflect the actual circulation of the BS.     

Abundance distribution and seasonal variations of Calanus sinicus (Copepoda: Calanoida) in the northwest continental shelf of South China Sea

The effect of monsoon, coastal current and temperature on the distribution and seasonal variations of Calanus sinicus abundance were studied. The samples from the northwest continental shelf of South China Sea were collected with 505 μm planktonic nets from July 2006 to October 2007. The abundance of C. sinicus made up 34.28% and 12.34% of all copepods in spring and summer, respectively. The distribution of C. sinicus varied seasonally and regionally. The distribution of C. sinicus ranged between east inshore and offshore waters from the Leizhou Peninsula to Hainan Island, with a mean of 23.00 (±77.78) ind. m⁻³ in spring. In summer it had a mean of 13.74 (±45.10) ind. m⁻³ occurring only in the east inshore waters from Leizhou Peninsula to Hainan Island. C. sinicus was not abundant during autumn and winter seasons. The surveyed area was divided into three sub-regions based on topographical analysis and water mass, region I (included the east inshore waters of Leizhou Peninsula), region II (included the east inshore waters of Hainan Island) and region III (included the offshore waters from Leizhou Peninsula to Hainan Island). The average abundance of C. sinicus within region I was determined to be 115.63 (±145.93) and 68.12 (±84.00) ind. m⁻³ in spring and summer, respectively, values higher than those of regions II and III. Our findings suggested that C. sinicus was transported from the East China Sea to the northwest continental shelf of South China Sea by the Guangdong Coastal Current, which was driven by the northeast monsoon in spring. The presence of a cold eddy, in addition to coastal upwelling driven by the southwest monsoon, provided suitable survival conditions for C. sinicus in summer. This species disappeared in autumn due to high temperatures (>27 °C) and did not begin to enter into the northwest continental shelf of South China Sea from the East China Sea during the period of investigation in winter. The frequency of C. sinicus was low in region III during the year as a result of the South China Sea Warm Current and pelagic waters with high temperature during the spring and summer months.     

Seasonal Variations of Currents over the Western Slope of the Middle Caspian Bed

Results of field observations of current dynamics in the frontal zone of the western Middle Caspian are given. The cyclonic circulation over the western slope in winter is shown to be a unidirectional intense current with velocities up to 100 cm/s. In summer, the current slows down and separates into branches—it turns southwestward and westward at the slope depth down to 150 m, southward and southeastward at the depth of ~100–350 m, and eastward at larger depths. In summer, shelf currents interact with the flow of Middle Caspian cyclonic circulation, resulting in that anticyclonic vortices reach the shelf.     

Impact of tropical cyclones on the evolution of the monsoon-driven upwelling system in the coastal waters of the northern South China Sea

An upwelling system exists in the coastal waters of the northern South China Sea (NSCS), a region that is frequently affected by tropical cyclones in summer. This study investigates the evolution of the NSCS monsoon-driven upwelling system and the effects of the Talim and Doksuri tropical cyclones on the system using in situ observational data obtained at three mooring stations, one land-based meteorological station, and concurrent satellite remote sensing data for the NSCS coastal waters from May to July 2012. The results show that the occurrence and evolution of the upwelling system were mainly controlled by the Asian southwest monsoon, while the eastward current also made important contributions to the upwelling intensity. A decrease in the bottom water temperature and shifts in the along-shore and cross-shore currents were direct evidence of the establishment, existence, and recovery of this upwelling. Tropical cyclones have significant impacts on hydrodynamics and can thus influence the evolution of the NSCS upwelling system by changing the local wind and current fields. Variations in water level and local current systems impeded the development of upwelling during tropical cyclones Talim and Doksuri in the study area, which have low-frequency fluctuations of approximately 2–10 days. These variations were the results of the coupled interactions between local wind fields, coastal trapped waves, and other factors. The hydrodynamic environment of the marine water (including coastal upwelling system) rapidly recovered to normal sea conditions after each cyclone passed due to the relatively short duration of the impact of a tropical cyclone on the dynamic environment of the waters.     

Circulation and connectivity on the Australian North West Shelf

Australia's North West Shelf supports a diverse range of tropical habitats and marine communities, as well as being Australia's most economically significant marine region. This study is the first attempt to describe the ocean circulation across the North West Shelf on time-scales from hours to years, and space scales from 10 km over the entire shelf to 1 km in a selected focus area around the Dampier Archipelago. A series of nested circulation models have been developed with forcing by realistic winds, tides, and larger scale oceanographic conditions (taken from a global circulation model). Dispersion and connectivity patterns have also been estimated over the shelf using particle-tracking techniques. The simulations covered a period of more than 6 years, allowing the tidal, seasonal, and interannual characteristics to be investigated. Model results confirm that the instantaneous current patterns are strongly dominated by the barotropic tide and its spring–neap cycle. However, longer term transports over the inner- and mid-shelf were mainly controlled by wind-driven flow, which followed the seasonal switch from summer monsoon winds to southeasterly trades in winter. Results were shown to be relatively insensitive to adjustable model parameters and sub-model structures. However, model performance was strongly dependent on the quality of the forcing fields. Connectivity results have been represented in terms of a comprehensive set of statistical probabilities that have been made available online (http://www.per.marine.csiro.au/connie). The potential regional-scale connectivity between coral reefs on the North West Shelf has been used to illustrate the approach.     

Numerical modeling of the Patos Lagoon coastal plume,Brazil

The Southern Brazilian Shelf (SBS) is a freshwater-influenced region, but studies on the dynamics of coastal plumes are sparse and lack in space-time resolution. Studies on the dynamics of the Patos Lagoon plume are even more limited. The aim of this paper is to investigate the influence of the principal physical forcing for the formation and behavior of the Patos Lagoon coastal plume. The study is carried out through 3D numerical modeling experiments and empirical orthogonal function (EOF) analysis. Results showed that the amount of freshwater is the principal physical forcing controlling the plume formation. The Coriolis effect enhances the northward transport over the shelf, while the tidal effects contribute to intensify horizontal and vertical mixing, which are responsible for spreading the freshwater over the shelf. The wind effect, on the other hand, is the main mechanism controlling the behavior of the Patos Lagoon coastal plume over the inner SBS in synoptic time scales. Southeasterly and southwesterly winds contribute to the northeastward displacement of the plume, breaking the vertical stratification of the inner continental shelf. Northeasterly and northwesterly winds favor ebb conditions in the Patos Lagoon, contributing to the southwestward displacement of the plume enhancing the vertical stratification along and across-shore. The EOF analysis reveals two modes controlling the variability of the plume on the surface. The first mode (explaining 70% of the variability) is associated to the southwestward transportation of the plume due to the dominance of north quadrant winds, while the second mode (explaining 19% of the variability) is associated to the intermittent migration of the plume northeastward due to the passage of frontal systems over the area. Large scale plumes can be expected during winter and spring months, and are enhanced during El Niño events.