[1] This paper investigates the interplay between river discharge and winds in forcing coastal buoyant outflows. During light winds a plume influenced by the Earth's rotation will flow down shelf (in the direction of Kelvin wave propagation) as a slender buoyancy-driven coastal current. Downwelling favorable winds augment this down-shelf flow, narrow the plume, and mix the water column. Upwelling favorable winds drive currents that counter the buoyancy-driven flow, spread plume waters offshore, and rapidly mix buoyant waters. Two criteria are developed to assess the wind influence on a buoyant outflow. The wind strength index (W s ) determines whether a plume's along-shelf flow is in a wind-driven or buoyancy-driven state. W s is the ratio of the wind-driven and buoyancy-driven along-shelf velocities. Wind influence on across-shelf plume structure is rated with a timescale (t tilt ) for the isopycnal tilting caused by wind-driven Ekman circulation. These criteria are used to characterize wind influence on the Delaware Coastal Current and can be applied to other coastal buoyant outflows. The Delaware buoyant outflow is simulated for springtime high-river discharge conditions. Simulation results and W s values reveal that the coastal current is buoyancy-driven most of the time (jW s j < 1 on average). Wind events, however, overwhelm the buoyancy-driven flow (jW s j > 1) several times during the high-discharge period. Strong upwelling events reverse the buoyant outflow; they constitute an important mechanism for transporting fresh water up shelf. Across-shelf plume structure is more sensitive to wind influence than the along-shelf flow. Values of t tilt indicate that moderate or strong winds persisting throughout a day can modify plume width significantly. Plume widening during upwelling events is accompanied by mixing that can erase the buoyant outflow.

Coastal buoyant outflows from rivers and estuaries previously have been studied with field research, laboratory experiments, and numerical models. There is a dire need to evaluate model performance in light of coastal current observations. This research simulates the Delaware Bay outflow and compares results with observations of estuarine and shelf conditions. Observations include an estuarine salinity climatology, a record of freshwater delivery to the shelf, coastal current salinity mappings, and surface drifter data. Simulation efforts focus on spring 1993 and spring 1994, the primary field study period. The simulation is forced with river discharge, winds, and tides; only tidal-averaged results are discussed. Estuarine salinity results are consistent with the observed lateral salinity pattern, vertical structure, and response to river discharge. Salinities within the lower bay agree with observations, but the simulation overestimates the along-estuary salinity gradient. Observed and simulated freshwater delivery exhibit the same amplitude of response to river discharge and winds. The simulation produces a buoyant outflow that is generally consistent with the observed buoyancy signature, width, length, and vertical structure over a variety of river discharge and wind conditions. The simulated coastal current, however, tends to be somewhat shorter and fresher than observed. Simulated surface drifter paths exhibit the observed onshore advection during downwelling winds as well as offshore transport and current reversals during upwelling winds. A statistical evaluation based on shelf salinity mappings indicates that the model reproduces the observed variance and has only a small bias (less than 10% of plume buoyancy signature). The rms error of 1.2 psu is linked to the shorter and fresher nature of the simulated coastal current. Observational comparisons discussed in this paper indicate that the model can simulate many coastal current features and its response to river discharge and wind forcing.

Three cross-shelf transects were conducted off northern Oregon in February, 2003, coincident with flooding of Coast Range rivers, to assess the riverine impact on coastal ocean biogeochemistry. During downwelling conditions, low salinity river-influenced water was located in a narrow band near the coast and contained elevated macronutrient, iron, and organic carbon concentrations. Wind relaxation allowed the river-influenced water to spread out at the surface across the shelf. Nutrients supplied by the rivers could result in winter carbon fixation equating to ,20% of the summer upwelling carbon fixation if conditions are suitable for phytoplankton growth, which is likely on the basis of recent studies. This implies that wintertime production may be significant and requires further study. Iron supplied by the rivers is sufficient to support the entire summer upwelling production and because downwelling conditions prevail during the winter and minimize cross-shelf transport, this iron may be retained on the shelf to support the summer phytoplankton blooms. Of the major eastern boundary current systems, the northern California Current (including Oregon) and Portugal Current (i.e., Iberian Peninsula) have the highest riverine discharge rates normalized to coastline length. In contrast, riverine inputs to the central California, Canary (i.e., northwest Africa), Benguela and Peruvian Current systems averaged only 3-35% of that in Oregon. This patchy riverine input (and narrower shelves) might explain why iron limitation is more widespread off California and Peru than Oregon. These results show that small coastal rivers, characteristic of the U.S. Pacific Northwest, can significantly alter coastal biogeochemical cycles and influence ecosystem structure.The coastal ocean plays a key role in global biogeochemical cycles and marine food webs. In recent years, advances have been made in linking atmospheric and physical dynamics to ecosystem structure and function during the productive summer season in eastern boundary current systems. Unfortunately, that progress has not been matched by increased study or enhanced understanding of wintertime conditions. In fact, relatively little is known about wintertime biogeochemical or food web conditions in these types of systems.Results from modeling and field observations show that the wintertime physical dynamics of eastern boundary current systems are quite different than during the summer upwelling season. Off Oregon for example, mean wintertime coastal wind direction is to the north and strong north/northeastward propagating storms frequently occur (Halliwell and Allen 1987;Strub et al. 1987). Northward winds cause onshore Ekman transport of surface waters, leading to development of a downwelling front at the 100-150-m isobath (Allen and Newberger 1996; Austin and Barth 2002). In the region of the front, the water column can be vertically homogenous (Barth et al. unpubl.). Currents inshore of the front are predominately to the north, and cross-shelf circulation is believ...