Weekly period meanders and eddies are persistent features of Gulf Stream frontal dynamics from Miami, Florida, to Cape Hatteras, North Carolina. Satellite imagery and moored current and temperature records reveal a spatial pattern of preferred regions for growth and decay of frontal disturbances. Growth regions occur off Miami, Cape Canaveral, and Cape Fear due to baroclinic instability, and decay occurs in the confines of the Straits of Florida between Miami and Palm Beach, between 30° and 32°N where the stream approaches the topographic feature known as the Charleston bump and between 33°N and Cape Hatteras. Eddy decay regions are associated with elongation of frontal features, offshore transport of momentum and heat, and onshore transport of nutrients. Onshore transport of new nitrogen from the nutrient‐bearing strata beneath the Gulf Stream indicates that frontal eddies serve as a “nutrient pump” for the shelf. New nitrogen flux to the shelf due to Gulf Stream input could support new production of 7.4×1012 g C yr−1 or about 8 million tons carbon per year if all nitrate were utilized. Calculations indicate that approximately 70% of this potential new production is realized, yielding an annual new production for the outer shelf of 4.3×1012 g C.

We study the development and evolution of buoyant river plumes on the continental shelf. Our calculations are based on three-dimensional numerical simulations, where the river runoff is introduced as a volume of zero salinity water in the continuity equation and mixing is provided by the model's turbulence closure scheme and wind forcing.In the absence of wind forcing the modeled fiver plumes typically consist of an offshore bulge and a coastal current in the direction of Kelvin wave propagation. We propose a plume classification scheme based on a bulk Richardson number, which expresses the relative magnitude of the buoyancy-induced stratification versus the available mixing. When the ratio of the discharge and shear velocities is greater (less) than 1, the plume is categorized as supercritical (subcritical); that is, the width of the bulge is greater (less) than the width of the coastal current. Supercritical plumes are often characterized by a meandering pattern along the coastal current, caused by a baroclinic instability process. For a given discharge, subcritical plumes are produced by large mixing and/Or shallow water depths. In the presence of wind forcing the favorable conditions for offshore removal of coastal low-salinity waters include high river runoff and strong upwelling-favorable wind stress. When the rivers are treated as individual sources of freshwater ("point source" behavior), the wind-driven flow may exhibit substantial spatial variability. Under the above removal conditions, strong offshore transport takes place in "jetlike" flow regions within the river plume, in contrast to the downwind acceleration of adjacent waters. When the rivers are treated as a long "line source" of freshwater, the plume region resembles a coastal low-salinity band and the above removal conditions trigger offshore transport that is most pronounced at the "head" of the source. control the fate of fivefine waters and related materials afterPaper number 95JC03024. 0148-0227/96/95JC-0302455.00 their release in the coastal ocean. Our main objective is to describe the generation and evolution of a fiver plume on the continental shelf and determine the important factors that govern its offshore expansion and, consequently, the removal mechanism of fiver-borne materials.The frontal structure of a fiver plume has been discussed by several investigators. Earlier studies, such as those by Kao et al. [1977], Kao [1981], Ikeda [1984], and Csanady [1984], recognized the importance of nonlinearity, Coriolis, and friction in the development of the buoyant plume. McClimans [1986] identifi•ed the following three major processes that characterize the dynamics of the seaward expansion of the river flow: (1) acceleration, resulting from the balance between inertia and gravity (buoyancy) forces; (2) mixing, governed by turbulence due to bottom and interfacial friction; and (3) geostrophy, where the balance between Coriolis and the developed cross-shore pressure gradient (due to "freshening" of coastal waters) generates an alongshore coas...

We report results from a 1-year (September 1987 to September 1988) moored current meter array spanning the continental margin off French Guiana near 8 ø N in the western tropical Atlantic. Current profiles were recorded at three sites: at the shelf break, over the mid-continental slope, and at the base of the continental rise. Upper level mean currents showed a northwestward flowing North Brazil Current (NBC) and offshore retrofiection of this flow into the North Equatorial Countercurrent from late summer through about January. Generally weak upper level mean flows were observed during the spring (February-June). Persistent northwestward mean flow was observed at 900 m depth over the continental slope, indicating northward transport of Antarctic Intermediate Waters in a subsurface boundary flow at speeds of 10-15 cm s -1 . Deep currents over the continental rise showed a strong southeastward Deep Western Boundary Current (DWBC) extending from 2500 m to the bottom, with mean core speeds of nearly 30 cm s -1 at 4300 m depth. Transport estimates based on these data and a few geostrophic sections suggest a DWBC transport of 20-40 x 106 m z s -1 at this location. Low-frequency current fluctuations were dominated by a well-defined 40-to 60-day oscillation with peak-to-peak meridional velocity amplitudes of • 1 m s -1 during the fall. Analysis of historical coastal zone color scanner imagery suggests that these oscillations are related to quasi-periodic generation and subsequent westward movement of • 400 km diameter eddies from the NBC retroflection. These results contrast sharply with earlier indications of a quasi-permanent "Demerara Eddy" in this region, and suggest that this commonly observed feature is in fact a transient phenomenon associated with the time-dependent behavior of the NBC retrofiection.

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Observations from the WOCE PCM-1 moored current meter array east of Taiwan for the period September 1994 to May 1996 are used to derive estimates of the Kuroshio transport at the entrance to the East China Sea. Three different methods of calculating the Kuroshio transport are employed and compared. These methods include 1) a ''direct'' method that uses conventional interpolation of the measured currents and extrapolation to the surface and bottom to estimate the current structure, 2) a ''dynamic height'' method in which moored temperature measurements from moorings on opposite sides of the channel are used to estimate dynamic height differences across the current and spatially averaged baroclinic transport profiles, and 3) an ''adjusted geostrophic'' method in which all moored temperature measurements within the array are used to estimate a relative geostrophic velocity field that is referenced and adjusted by the available direct current measurements. The first two methods are largely independent and are shown to produce very similar transport results. The latter two methods are particularly useful in situations where direct current measurements may have marginal resolution for accurate transport estimates. These methods should be generally applicable in other settings and illustrate the benefits of including a dynamic height measuring capability as a backup for conventional direct transport calculations. The mean transport of the Kuroshio over the 20-month duration of the experiment ranges from 20.7 to 22.1 Sv (1 Sv ϵ 10 6 m 3 s Ϫ1) for the three methods, or within 1.3 Sv of each other. The overall mean transport for the Kuroshio is estimated to be 21.5 Sv with an uncertainty of 2.5 Sv. All methods show a similar range of variability of Ϯ10 Sv with dominant timescales of several months. Fluctuations in the transport are shown to have a robust vertical structure, with over 90% of the transport variance explained by a single vertical mode. The moored transports are used to determine the relationship between Kuroshio transport and sea-level difference between Taiwan and the southern Ryukyu Islands, allowing for long-term monitoring of the Kuroshio inflow to the East China Sea.

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Low‐frequency current and temperature time series from the outer shelf between Cape Canaveral, Florida, and Cape Romain, South Carolina, are compared with shipboard hydrographic data, satellite VHRR, coastal and buoy winds, and coastal sea level during the period from February to June 1980. Low‐frequency current and temperature variability along the shelf break was primarily produced by cyclonic, cold core Gulf Stream frontal eddies. These disturbances traveled to the north at speeds of 50 to 70 cm s−1 with periods of 5 to 9 days throughout the experiment and produced cold cyclonic perturbations of the northward mean flow and temperature fields over an along‐shelf coherence scale of 100 km. Frontal eddies appear to be an important mechanism in the observed eastward transport of northward momentum and heat along the shelf edge. They also appear to play a key role in the transfer of eddy kinetic and potential energy back to the mean flow, which suggests an upstream formation region and shear‐induced dissipation. Upwelling velocities of about 10−2 cm s−1 in the cold core provide the major source of new nutrients to the outer shelf. Subtidal flow variability at the 40‐m isobath was a mixed response to Gulf Stream and wind forcing. Barotropic along‐shelf current oscillations were coherent with the local winds and coastal sea level at periods of 3–4 and 10–12 days over along‐shelf scales of 400 km with small phase lags, suggesting a nearly simultaneous frictional equilibrium response to coherent wind‐induced sea level slopes.