Coastal Water Transport Research Articles

Satellite-Derived Lagrangian Transport Pathways in the Labrador Sea

The offshore transport of Greenland coastal waters influenced by freshwater input from ice sheet melting during summer plays an important role in ocean circulation and biological processes in the Labrador Sea. Many previous studies over the last decade have investigated shelfbreak transport processes in the region, primarily using ocean model simulations. Here, we use 27 years of surface geostrophic velocity observations from satellite altimetry, modified to include Ekman dynamics based on atmospheric reanalysis, and virtual particle releases to investigate seasonal and interannual variability in transport of coastal water in the Labrador Sea. Two sets of tracking experiments were pursued, one using geostrophic velocities only, and another using total velocities including the wind effect. Our analysis revealed substantial seasonal variability, even when only geostrophic velocities were considered. Water from coastal southwest Greenland is generally transported northward into Baffin Bay, although westward transport off the west Greenland shelf increases in fall and winter due to winds. Westward offshore transport is increased for water from southeast Greenland so that, in some years, water originating near the east Greenland coast during summer can be transported into the central Labrador Sea and the convection region. When wind forcing is considered, long-term trends suggest decreasing transport of Greenland coastal water during the melting season toward Baffin Bay, and increasing transport into the interior of the Labrador Sea for water originating from southeast Greenland during summer, where it could potentially influence water column stability. Future studies using higher-resolution velocity observations are needed to capture the role of submesoscale variability in transport pathways in the Labrador Sea.

Accumulation and Cross-Shelf Transport of Coastal Waters by Submesoscale Cyclones in the Black Sea

High- and medium-resolution satellite optical imagery show that submesoscale cyclonic eddies (SCEs) trap coastal waters and induce their rapid cross-shelf transport. Due to the presence of a rigid boundary, the convergence is observed in the coastal part of SCEs. It causes accumulation of suspended matter, which spins inward in a spiral motion toward the SCE core. Small SCEs with a radius of 1–10 km transport waters with local anomalies in the concentration of chlorophyll, total suspended matter and temperature to a distance of up to 150 km and are observed for more than 10 days. Lagrangian calculations based on realistic NEMO numerical model are used to estimate the fate of the coastal waters in such SCEs. The eddy entrains the largest number of particles during its separation from the coast when its vorticity reaches the maximum. Then, the SCE weakens, which is accompanied by the flattening of initially risen isopycnals and deepening of the trapped coastal waters. The described mechanism shows that coastal SCEs may cause intense short-period cross-shelf transport of the biological and chemical characteristics, and is another process affecting the functioning of the marine ecosystems.

NUMERICAL SIMULATION OF DRIFTWOOD TRANSPORT BY WAVES IN A LABORATORY BASIN

Driftwood plays an important role in coastal ecosystems but, in large accumulations, can have negative impacts and pose hazards to navigation, infrastructure and communities (Murphy et al. 2021). The ability to accurately predict the fate and transport of coastal driftwood is central to informing sustainable management practices. However, there is a paucity of numerical modelling studies focused on driftwood transport in coastal waters (Murphy et al. 2021). Models developed for rivers (e.g. Ruiz-Villanueva et al. 2014) lack consideration of processes affecting driftwood transport and accumulation in coastal environments, such as wind waves. Murphy et al. (2020) conducted experiments in a 50-m by 30-m wave basin, wherein model driftwood was released and tracked within a 1/30 scale physical model of a sandy beach system with various coastal structures. The tests revealed that several factors influence the mobility of coastal driftwood exposed to waves, beaching and washoff processes in particular.

Disparity of Bladder Cancer Incidence Among Male Workers Across Industries: A Population Based Cohort Study From South Korea.

This study aimed to investigate the bladder cancer risk across workers' industries. This study was conducted using Korean National Health Insurance claims data. Workers were included in this study to build a retrospective cohort of the entire working population. Workers' industries were divided into 77 industries according to the Korean Standard Industry Classification division category. The standardized incidence ratio was calculated by comparing 77 industries according to the Korean Standard Industry Classification with the educational public officer. Bladder cancer risk was particularly high in the following industrial sectors: passenger land transport, except transport via railways; sea and coastal water transport; restaurants and mobile food service activities; telecommunications; and computer programming, consultancy, and related activities. Our result provides evidence regarding the disparity of bladder cancer incidence among male workers across industries.

Study on the Impact of Typhoon Maria (2018) on Suspended Sediment in Hangzhou Bay, China

Sediment transport in coastal waters has an important impact on the siltation of port channels and changes in the estuary ecological environment. The southeast coast of China is often hit by typhoons, which can affect the suspended sediment concentration (SSC) in coastal waters. In this study, we used Geostationary Ocean Color Imager (GOCI) data to analyze SSC variations in Hangzhou Bay during Typhoon Maria (2018), and the influencing factors were also analyzed. The results showed that: (1) During the typhoon’s transit, the SSC in Hangzhou Bay (HZB) increased by 200–800 mg/L, which was one-fold higher than the day before the typhoon. The variation of SSC on the south bank was noticeable, and the typhoon effect on SSC lasted for 2–3 days; (2) The wind speed and significant wave height (SWH) increased during the typhoon. In general, in the early stage of the typhoon, the SSC in HZB was affected by the wind, and in the interim and late period, SSC was influenced by the effect of wind and wave height; (3) Typhoon “Maria” accelerated the transport of sediment and land-based pollutants from land to sea; the effect of residual current and wind stress are the driving mechanisms for seaward sediment transport. However, mechanisms and driving factors of sediment transport in coast water are complex and diverse. The results of this study can help to understand the processes of riverbed erosion and deposition in Hangzhou Bay and adjacent waters. They are also significant for the study of nearshore hydrodynamic characteristics of typhoons and channel engineering.

Problems and prospects of the revival of coastal water transport in the Northern Black sea of Ukraine

The article examines the problems and prospects of the revival of coastal water transport in the Northern Black Sea Coast of Ukraine. One of the main features of seaside cities is the use of water transport, which is one of the oldest forms of transport and remained the most important until the advent of transcontinental railways in the second half of the 19th century. Small hydrofoils were widely used on the territory of the Odesa coast, and the restoration of these routes and infrastructure will bring undeniable benefits. At the moment, a limited number of vessels are operating. The main reason for the restoration of this type of transport is the extreme necessity due to the destruction of bridges and railway junctions along the coastal zone of Ukraine due to the bombings of the Russian Armed Forces. It will take a lot of time and money to restore bridges and crossings throughout the country, so an alternative in the form of the SPK can help restore connections between all southern regions of Ukraine and the Black Sea near abroad. Although there are not many factories for the production of this type of ships, there are enough of them around the world, buying them is faster and easier than building bridges with the complete restoration of the entire infrastructure, as well as its demining.
 The article presents the history of the use of small vessels on hydrofoils, gives an example of the restoration of seasonal water traffic on the route Bilhorod-Dnistrovskyi – Ovidiopol settlement – Bilhorod-Dnistrovskyi, as an alternative to the destroyed bridge in Zatoka. Considered the history of the construction of a railway-car bridge between two torn parts of the Budak spit (1955) so that it would not be necessary to travel an extra 40 kilometers along the perimeter of the Dniester estuary from the extreme south of Odesa region – Vylkove, Kiliya, Izmail, in the direction of Odesa. An analysis of the latest research and publications in the field of urban planning, economics, organization of tourist transportation, etc. was made.

Eddy‐Driven Transport of Particulate Organic Carbon‐Rich Coastal Water Off the West Antarctic Peninsula

AbstractThe Southern Ocean is characterized by high eddy activity and high particulate organic carbon (POC) content during summer, especially near Antarctica. Because it encircles the globe, it provides a pathway for inter‐basin exchange. Here, we use satellite observations and a high‐resolution ocean model to quantify offshore transport of coastal water rich in POC off the West Antarctic Peninsula. We show that nonlinear cyclonic eddies generated near the coast often trap coastal water rich in POC during formation before propagating offshore. As a result, cyclones found offshore that were generated near the coast have on average higher POC content in their interior than cyclones generated locally offshore. This results in a POC enrichment of 5.7 ± 3.0 Gg C year−1 in offshore waters off the Peninsula. Actual POC enrichment is likely substantially larger, since about half of the volume transport of coastal water is driven by small eddies that are missed by observations.

Offshore transport of particulate organic carbon in the California Current System by mesoscale eddies

The California Current System is characterized by upwelling and rich mesoscale eddy activity. Cyclonic eddies generally pinch off from meanders in the California Current, potentially trapping upwelled water along the coast and transporting it offshore. Here, we use satellite-derived measurements of particulate organic carbon (POC) as a tracer of coastal water to show that cyclones located offshore that were generated near the coast contain higher carbon concentrations in their interior than cyclones of the same amplitude generated offshore. This indicates that eddies are in fact trapping and transporting coastal water offshore, resulting in an offshore POC enrichment of 20.9 ± 11 Gg year−1. This POC enrichment due to the coastally-generated eddies extends for 1000 km from shore. This analysis provides large-scale observational-based evidence that eddies play a quantitatively important role in the offshore transport of coastal water, substantially widening the area influenced by highly productive upwelled waters in the California Current System.

A 3-D finite volume model for sediment transport in coastal waters

A 3-D model has been developed to simulate sediment transport and bed change induced by currents and waves in coastal waters. The currents are calculated with the 3-D phase-averaged shallow water flow equations, the wave characteristics are determined with a horizontal 2-D wave spectral transformation model, and multiple-sized non-cohesive suspended load and bed load are simulated using a non-equilibrium transport model. The classical mixing length model is modified to determine the horizontal and vertical eddy viscosity considering the effects of current, waves, and wave breaking. A new approach is proposed in the present 3-D model framework to calculate the bed grain shear stress, which is applied to determine the equilibrium bed-load transport rate and near-bed suspended-load concentration. The flow and sediment transport equations are numerically solved using an implicit finite volume method on a hexahedral mesh constructed with horizontal telescoping (quadtree) rectangular cells and vertical sigma coordinate. The difference in the near-bed cells for flow and suspended load calculations is avoided by adding the bed load to the suspended load in the first flow cell above the bed. The developed model has been tested in four laboratory and field cases. It reasonably well reproduces the measured water levels, flow velocities, sediment concentrations, and bed changes.

Hydro-biogeochemical processes and their implications for Ulva prolifera blooms and expansion in the world's largest green tide occurrence region (Yellow Sea, China)

The hydro-biogeochemical processes in the world's largest area of green tide occurrence, off the Jiangsu coast in the Yellow Sea, are investigated in the summer, and their implications for Ulva prolifera blooms are discussed. The results show that the offshore transport of coastal water and the inshore upwelling of offshore bottom water both occur off the Jiangsu coast, and the upwelling position is consistent with the 20- to 30-m isobath off the Subei Shoal. The upwelling results in nutrient supplementation off the shoal, where a rapid decrease in the suspended particulate matter content contributes to good light conditions. As a result, a high-value area of phytoplankton is formed within the 20- to 30-m isobath. Eutrophication in the shoal has provided nutrients for the frequent occurrence of Ulva prolifera in recent years, whereas the upwelling area off the shoal has served as a “service station” or “courier station” for floating Ulva prolifera and promoted the species' propagation. The propagation of Ulva prolifera in the upwelling area and its blooms within the Subei Shoal can have a spatially synergistic effect, leading to its large-scale development. Our findings reveal the mechanisms that trigger the world's largest green tides from the perspective of physical-biogeochemical interactions.

Why and How Do We Study Sediment Transport? Focus on Coastal Zones and Ongoing Methods

Scientific research on sediment dynamics in the coastal zone and along the littoral zone has evolved considerably over the last four decades. It benefits from a technological revolution that provides the community with cheaper or free tools for in situ study (e.g., sensors, gliders), remote sensing (satellite data, video cameras, drones) or modelling (open source models). These changes favour the transfer of developed methods to monitoring and management services. On the other hand, scientific research is increasingly targeted by public authorities towards finalized studies in relation to societal issues. Shoreline vulnerability is an object of concern that grows after each marine submersion or intense erosion event. Thus, during the last four decades, the production of knowledge on coastal sediment dynamics has evolved considerably, and is in tune with the needs of society. This editorial aims at synthesizing the current revolution in the scientific research related to coastal and littoral hydrosedimentary dynamics, putting into perspective connections between coasts and other geomorphological entities concerned by sediment transport, showing the links between many fragmented approaches of the topic, and introducing the papers published in the special issue of Water on “Sediment transport in coastal waters”.

Numerical Study of Hydrodynamic and Solute Transport with Discontinuous Flows in Coastal Water

This paper aimed to develop a depth-averaged explicit model for flow and pollutant transport in coastal waters based on the shallow water equations and the mass advection-diffusion equation. The proposed model was discretized using the finite volume method (FVM) with triangular cells. Then, it applied Roe’s approximate Riemann solution to compute the water momentum flux on the grid interfaces. This model enabled the higher accuracy in capturing the dry-wet moving fronts (discontinuous problems for flow and solute). The high-resolution scheme was evaluated to solve the advection and diffusion terms for mass transport. The model was verified by comparing the predictions of analytical solutions, laboratory tests, and other simulations for Gironde estuary with good computational accuracy. The developed model was also used to calculate the circulation and the motion of chemical oxygen demand (COD) pollutants from the sewage outfalls in the Zhuanghe coastal water with dry and wet moving boundaries. The research results showed that the residual current directions of spring and neap tides were basically the same in the Zhuanghe coastal water. However, the tide residual current of spring tide was slightly greater than that of the neap tide. In addition, there were tide residual currents from the northeast to the southwest in nearshore water and from the southwest to the northeast outside the banks, respectively. The tidal flows in the alongshore direction were strong, resulting in highly spread concentration distributions. In particular, the COD concentration reached some parts of the southern water. It could be seen that the excessive pollutant discharge from the sewage outfalls located at Zhuanghe district would cause serious pollution in aquaculture water near Shicheng island.

Numerical study on pollutant transport in Dalian bay based on hydrodynamic model

Based on the depth-averaged two-dimensional shallow water and pollutant transport equation, the coupling model of water flow and water quality with explicit scheme is developed in this study. The unstructured triangular grid is adopted to locally refine the mesh around sewage outlet or in high-gradient regions of terrain change for the coupling model. The finite volume method is applied to ensure the conservation of mass for each element. This hydrodynamic model applies the Roe solver approximate Riemann solution with second-order accuracy to compute the water momentum flux on the grid interface. Taking Dalian Bay as the research object, the numerical model established is used to simulate the hydrodynamic characteristics and pollutant transport process. The computed results of the tide level, flow current and flow direction agree well with the measured data in Dalian Bay. The spatial and temporal distribution of pollutant in water are analyzed and discussed in this study. Simulated results show that the two-dimensional hydrodynamic and pollutant transport model can accurately simulate the mass transport in coastal waters, and it can provide a scientific basis on coastal water environment protection for the research water.

A depth-averaged 2-D model of flow and sediment transport in coastal waters

A depth-averaged 2-D model has been developed to simulate unsteady flow and nonuniform sediment transport in coastal waters. The current motion is computed by solving the phase-averaged 2-D shallow water flow equations reformulated in terms of total-flux velocity, accounting for the effects of wave radiation stresses and general diffusion or mixing induced by current, waves, and wave breaking. The cross-shore boundary conditions are specified by assuming fully developed longshore current and wave setup that are determined using the reduced 1-D momentum equations. A 2-D wave spectral transformation model is used to calculate the wave height, period, direction, and radiation stresses, and a surface wave roller model is adopted to consider the effects of surface roller on the nearshore currents. The nonequilibrium transport of nonuniform total-load sediment is simulated, considering sediment entrainment by current and waves, the lag of sediment transport relative to the flow, and the hiding and exposure effect of nonuniform bed material. The flow and sediment transport equations are solved using an implicit finite volume method on a variety of meshes including nonuniform rectangular, telescoping (quadtree) rectangular, and hybrid triangular/quadrilateral meshes. The flow and wave models are integrated through a carefully designed steering process. The model has been tested in three field cases, showing generally good performance.

Ocean colour opportunities from Meteosat Second and Third Generation geostationary platforms

Abstract. Ocean colour applications from medium-resolution polar-orbiting satellite sensors have now matured and evolved into operational services. These applications are enabled by the Sentinel-3 OLCI space sensors of the European Earth Observation Copernicus programme and the VIIRS sensors of the US Joint Polar Satellite System programme. Key drivers for the Copernicus ocean colour services are the national obligations of the EU member states to report on the quality of marine, coastal and inland waters for the EU Water Framework Directive and Marine Strategy Framework Directive. Further applications include CO2 sequestration, carbon cycle and climate, fisheries and aquaculture management, near-real-time alerting to harmful algae blooms, environmental monitoring and forecasting, and assessment of sediment transport in coastal waters. Ocean colour data from polar-orbiting satellite platforms, however, suffer from fractional coverage, primarily due to clouds, and inadequate resolution of quickly varying processes. Ocean colour remote sensing from geostationary platforms can provide significant improvements in coverage and sampling frequency and support new applications and services. EUMETSAT's SEVIRI instrument on the geostationary Meteosat Second Generation platforms (MSG) is not designed to meet ocean colour mission requirements, however, it has been demonstrated to provide valuable contribution, particularly in combination with dedicated ocean colour polar observations. This paper describes the ongoing effort to develop operational ocean colour water turbidity and related products and user services from SEVIRI. SEVIRI's multi-temporal capabilities can benefit users requiring improved local-area coverage and frequent diurnal observations. A survey of user requirements and a study of technical capabilities and limitations of the SEVIRI instruments are the basis for this development and are described in this paper. The products will support monitoring of sediment transport, water clarity, and tidal dynamics by providing hourly coverage and long-term time series of the diurnal observations. Further products and services are anticipated from EUMETSAT's FCI instruments on Meteosat Third Generation satellites (MTG), including potential chlorophyll a products.

Seasonal thermal fronts on the northern South China Sea shelf: Satellite measurements and three repeated field surveys

AbstractSeasonal thermal fronts associated with wind‐driven coastal downwelling/upwelling in the northern South China Sea are investigated using satellite measurements and three repeated fine‐resolution mapping surveys in winter, spring, and summer. The results show that vigorous thermal fronts develop over the broad shelf with variable widths and intensities in different seasons, which tend to be approximately aligned with the 20–100 m isobaths. Driven by the prevailing winter/summer monsoon, the band‐shaped fronts were observed with a magnitude exceeding 0.1°C/km in the subsurface, and accompanied by energetic coastal downwelling/upwelling due to shoreward/offshore Ekman transport. The downward/upward tilting of seasonal thermoclines across the shelf exceeds 20 m, significantly contributing to the development of thermal fronts over the shelf. In addition, the diagnostic analysis of Potential Vorticity (PV) suggests that the summer frontal activities induced by the coastal upwelling are more stable to convection and symmetric instabilities in comparison to the winter fronts associated with downwelling‐favorable monsoon forcing. This is primarily due to their essential differences in the upper ocean stratification and horizontal buoyancy gradients arising from wind forcing. At the same time, the coastal currents are substantially regulated by the seasonal winds. An expected lag correlation between the velocity from mooring measurements and alongshore wind stress is detected near the frontal region. These results indicate that seasonal wind forcing plays an important role in the frontal activities and coastal water transport over the shelf.

Numerical model of wave-current interaction based on unstructured quadtree grid for nearshore coastal waters

According to the characteristics of complex topography, hydrology, sediment transport in coastal waters, the aim of this paper is to develop an implicit, depth-averaged 2-D numerical mode of coupling current and wave for coastal area. The hydrodynamic model is the two dimensional depth averaged non-linear shallow water equations with an unstructured non-staggered and multiple-level quadtree rectangular mesh with local refinement for important region. In this non-staggered system, primary variables u -, v -velocity, and water level are stored on the same set of grid points in order to simplify the program code, and fluxes at cell faces are determined using the Rhie and Chow’s momentum interpolation method to avoid spurious checkerboard oscillations. The discretized algebraic equations are solved iteratively using the GMRES method with ILUT preconditioning for speeding the computation. The Wave model is a two-dimensional spectral wave action model of taking into account the effect of wave breaking, shoaling, refraction, diffraction, wave-current interaction, bottom friction. The wave model readily provides the radiation stresses for the hydrodynamic model. The coupling model has been tested against measurement data for steady flow around a spur-dyke in a laboratory flume and tidal flows in Gironde Estuary, France and Grays Harbor, USA. The model reasonably well reproduces the temporal and spatial variations of water level, current speed and wave height observed in the measurements. It shows that the coupling current and wave model can simulate accurately the questions of tide and wave for complex domain, the modeling approach presented herein should be useful in engineering application and environmental protection for coastal area.

AN IMPLICIT 2-D DEPTH-AVERAGED FINITE-VOLUME MODEL OF FLOW AND SEDIMENT TRANSPORT IN COASTAL WATERS

An implicit depth-averaged 2-D finite volume model has been developed to simulate sediment transport and bed morphological changes under actions of currents and waves near coastal inlets. The model computes the depth-averaged 2-D shallow water flow and non-equilibrium transport of total-load sediment, accounting for the effects of wave radiation stresses and turbulent diffusion induced by currents, waves and wave breaking. The model uses a quadtree rectangular mesh to locally refine the mesh around structures of interest or where the topography and/or flow properties change rapidly. The grid nodes are numbered by means of an unstructured index system for more flexibility of mesh generation. The SIMPLEC algorithm is used to handle the coupling of water level and velocity and the Rhie and Chow's (1983) momentum interpolation method is adopted to determine the intercell fluxes on non-staggered grid. Well-developed longshore current and wave setup determined with the reduced 1-D momentum equations are used as the cross-shore boundary conditions. The model has been tested in several laboratory and field cases, showing good performance. In particular, it can use a long time step and is efficient in computation on a PC platform. It has a potential for simulation of long-term coastal morphodynamic processes.

Interannual and Decadal Variations in Cross-Shelf Transport in the Gulf of Alaska

Abstract The marine ecosystem of the Gulf of Alaska (GOA) is one of the richest on the planet. The center of the GOA is characterized by high-nutrient and low-chlorophyll-a concentration. Recent observational studies suggest that advection of iron-rich coastal water is the primary mechanism controlling open ocean productivity. Specifically, there is evidence that mesoscale eddies along the coastal GOA entrain iron-rich coastal waters into the ocean interior. This study investigates the cross-shelf transport statistics in the GOA using a free-surface, hydrostatic, eddy-resolving primitive equation model over the period 1965–2004. The statistics of coastal water transport are computed using a model passive tracer, which is continuously released at the coast. The passive tracer can thus be considered a proxy for coastal biogeochemical quantities such as silicate, nitrate, iron, or oxygen, which are critical for explaining the GOA ecosystem dynamics. On average along the Alaska Current, it has been shown that at the surface while the advection of tracers by the average flow is directed toward the coast consistent with the dominant downwelling regime of the GOA, it is the mean eddy fluxes that contribute to offshore advection into the gyre interior. South of the Alaskan Peninsula, both the advection of tracers by the average flow and the mean eddy fluxes contribute to the mean offshore advection. On interannual and longer time scales, the offshore transport of the passive tracer in the Alaskan Stream does not correlate with large-scale atmospheric forcing, nor with local winds. In contrast in the Alaska Current region, stronger offshore transport of the passive tracer coincides with periods of stronger downwelling (in particular during positive phases of the Pacific decadal oscillation), which trigger the development of stronger eddies.

Nutrient and phytoplankton dynamics off the west coast of Vancouver Island during the 1997/98 ENSO event

Abstract Six research cruises were conducted off the west coast of Vancouver Island between April and October of 1997 and 1998 as part of the Canadian GLOBEC project to compare nutrient and phytoplankton dynamics between ENSO (1997) and non-ENSO (1998) years. Limited sampling also was conducted during three cruises in 1999. During the 1997 ENSO period, there was a shallow thermocline (∼10 m) that resulted in a shallower mixed layer, lower salinity and density, and stronger summer stratification. In general on the shelf, the 1997 growing season was characterized by higher nitrate (7.5 μM) and silicic acid (17 μM) concentrations, lower total chlorophyll (∼76 mg m −2 ), lower phytoplankton carbon biomass (0.2 mg C L −1 ), and lower diatom abundance and biomass than in 1998. Phytoplankton assemblages were dominated by nanoplankton in 1997 and by diatoms in 1998. These results suggest that the 1997 ENSO was responsible for a reduction in the growth and biomass of larger phytoplankton cells. In mid-1998, the hydrographic characteristics off the west coast of Vancouver Island changed suddenly. The 1997 poleward transport of warm water reversed to an equatorward transport of coastal water in July 1998, which was accompanied by normal summer upwelling. During 1998, a large diatom bloom (mainly dominated by Chaetoceros debilis , Leptocylindrus danicus and to a lesser extent by Skeletomema and Pseudo-nitzschia sp.) was observed in July over the continental shelf. This large bloom resulted in chlorophyll concentrations of up to 400 mg m −2 , primary productivity of up to 11 g C m −2 d −1 , and near undetectable dissolved nitrogen concentrations at some of the shelf stations in 1998. In contrast, during 1997, the sub-tropical waters that were advected over the slope, resulted in low chlorophyll a and primary productivity (generally −2 d −1 ). Therefore, there was a sharp contrast between the very high primary productivity on the shelf in July 1998, due to normal nutrient replenishment from summer upwelling and outflow from the Strait of Juan de Fuca, and the lower primary productivity during the 1997 ENSO year. During 1998, non-ENSO conditions resulted in phytoplankton biomass that was twice as high on the shelf as that measured in regions beyond the continental shelf of the west coast of Vancouver Island.