The circulation in the Gulf of Maine has an important baroclinic component. It appears to be driven mostly by the density contrast between high‐salinity slope water which enters from the Atlantic and fresher waters which are formed in the Gulf or which enter from the Scotian shelf. Hydrographie surveys in three successive spring seasons suggest that slope water accumulates in Georges Basin, driving a counterclockwise surface circulation which brings Scotian shelf water westward into the Gulf and contributes to the eastward jet along the inner edge of Georges Bank. The slope water also crosses a sill and enters Jordan Basin, where it provides a potential energy source which may enhance a counterclockwise gyre partly driven by nearshore buoyancy sources and perhaps the wind. The coastal limb of the gyre turns offshore east of Penobscot Bay. Part of the separated coastal current recirculates in Jordan Basin, and part of it continues into Wilkinson Basin, generating a clockwise eddy as it passes over Jeffreys Bank. There is little evidence for recirculating surface flow in Wilkinson Basin. Instead, the surface water appears to split into branches feeding the Jordan Basin gyre, the Georges Bank jet, and an export path to Nantucket Shoals. The Jordan and Georges branches seem to be divided by the denser slope water in Georges Basin, and this may be the central process controlling the vernal intensification of the circulation in the Gulf. A more complete dynamical understanding awaits models which include the baroclinic influence of boundary waters.

Simultaneously measured Eulerian currents and spatially extensive subsurface temperatures have provided a time series of eight synoptic, three‐dimensional views of the Gulf Stream frontal zone along the Carolina continental margin. Two large‐amplitude meanders were observed to progress through the study area between Charleston and Cape Hatteras during February 1979. Each meander had a vertically coherent, skewed wave‐like subsurface structure. The Eulerian velocity and temperature signatures produced by the meanders at the 250‐m level over the 390‐m isobath reflect this skewness. At a particular instrument, the in‐phase increases in temperature and downstream velocity associated with an approaching meander crest occurred during a longer time interval than did the more rapid decreases in these quantities following the crest's passage. Typically, the downstream velocity component at this level fluctuated from about −20 cm s−1 to near 100 cm s−1, while the cross‐stream component varied approximately ±25 cm s−1 about a near‐zero mean. For a particular meander, the maximum in the offshore velocity component led the downstream maximum in time in a manner typical of progressive wave motions; however, the lead time was always less than one quarter of a meander period implying that u and υ were not in quadrature, as would have been the case for stable waves. The two meanders were observed downstream of the area off Charleston where a seaward deflection of the stream is often found. Subsurface temperature data from February 10, 1979, show that on that date the degree of deflection was greatest near the surface, and that almost no deflection existed within the deeper reaches of the water column. According to later data, the deflection decreased as the meanders progressed alongshore away from the area, suggesting that the vertical structure of the deflection observed on the tenth may have been associated with the late stages of a meander passage. Filaments of warm Gulf Stream water extended southwestward ‘behind’ the crests of the two meanders. The filaments were relatively shallow features, extending from the surface to a depth of a few tens of meters. They were oriented essentially parallel to the bottom contours over the outer shelf and upper slope, and were separated from the main body of the Gulf Stream by cool water. The presence of the cool water between the stream and the filaments at the surface was due to upwelling of water from deep within or below the main stream. Peaks in the time series of vorticity components indicate that maximum cyclonic relative vorticity occurred behind the meander crests, in the leading portion of the trough near where a warm filament joined a meander crest. The meanders may have been initiated upstream of our study area, and then ‘amplified’ by the deflection process off Charleston. Energy flux calculations for the region off Onslow Bay indicate that meander kinetic energy was being converted to mean energy there. It seems likely that the deflection produces meander growth within the 100...

The eastern Maine coastal current flows southwestward, carrying cold and nutrient-rich waters along the coast from the tidally stirred eastern gulf toward the central and western gulf, where in summer the~aters are warmer and more stratified. The current typically turns offshore before reaching Penobscot Bay, near the central coast, at a location determined largely by the distribution of dense slope water in Jordan Basin. The slope water, which enters the gulf as a deep inflow from the Atlantic Ocean, thus plays a major role in determining the intensity, direction and timing of the delivery of nutrients to the interior gulf. In this paper, we use data from two cruises in August 1987 to examine the variability and nutrient transport of the coastal current, especially to show the important physical linkages between the deep slope water, the structure of the coastal current, and its likely significant effect on biological productivity in the gulf.

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The seasonal baroclinic circulation in the Gulf of Maine is partly determined by the distribution of dense water that enters from the continental slope and spreads over sills into the deep basins of the Gulf. The slope water enters the Gulf as an intermittent deep flow through the Northeast Channel, which provides the principal connection with the Atlantic Ocean. Warm‐core rings from the Gulf Stream occasionally approach the mouth of the Northeast Channel, and at times, ring water contributes to or modifies the inflowing slope water. For example, sequential surveys in June and July of 1986 showed that a ring streamer crowded against Georges Bank and brushed obliquely across the channel mouth. The resulting inflow in July flooded the channel mouth with streamer‐modified slope water, which overwhelmed the more usual Maine Intermediate Water outflow noted 1 month earlier. Compared to previous years, relatively little slope water was found inside the Gulf in June 1986, and it is tempting to speculate that a delayed spin‐up of the interior baroclinic circulation began with the major inflow episode observed in July. Warm‐core rings from the Gulf Stream may influence the timing, intensity, and structure of the circulation and dependent processes that develop each year in the Gulf of Maine. A test of this hypothesis will require long‐term monitoring of the Northeast Channel region, coupled with seasonal hydrographic surveys and current measurements at strategic locations inside the Gulf of Maine.

Abstract. For estuarine-dependent species, especially those that spawn offshore and whose larvae must reach estuarine nursery areas, advective transport through tidal inlets may be a major factor influencing recruitment variability. We examined the role of tidal forcing on particle transport through a narrow, microtidal inlet along the Texas coast by using a threedimensional hydrodynamic and particle transport model. Although tidal forcing is relatively small in the study area, tidal currents through the inlet effectively transport passive particles a distance of about 15 km landward of the inlet. The majority of the particles that enter the inlet are transported to regions that are not suitable for larval settlement. There is limited tidal dispersion of the particles into the bays due to shoreline geometry and bathymetry. Most of the particles that enter the inlet are expelled offshore in the ebb tidal jet resulting in estuarine-shelf exchange of particles. When acting alone, tidal forcing is not effective at retaining particles in a suitable estuarine habitat, suggesting that other physical or biological mechanisms are required to maintain larvae in an estuarine habitat or that there is substantial along-shelf transport of larvae.

Hydrographic measurements indicate that the thermocline and the phytoplankton-rich chlorophyll maximum layer are vertically displaced over a rocky pinnacle in the central Gulf of Maine by internal waves with maximum amplitudes of 27 m. Such predictable downwelling events are linked to rapid, 2-to 3-fold increases in chlorophyll a, an indicator of phytoplankton concentration, in pulses of warm water recorded 4 cm above the bottom (29-m depth). The 1.5-5.6'C temperature fluctuations had an average period of 10.6 min and were generated on both ebb and flood tides. Local lee waves and the arrival of solitons propagated from Georges Bank are hypothesized to explain the timing of the internal waves. Because internal waves and chlorophyll mxima are pervasive features of stratified temperate seas, this mechanism of food coupling should be common in other rocky subtidal habitats.Despite the long-acknowledged dependence of bottomdwelling populations on pelagic processes (1), relatively little is known about how events in the water column influence organisms inhabiting rocky subtidal habitats along the underwater coastline of continents at high latitudes and on offshore ledges, banks, and seamounts. Recent benthicpelagic coupling research has linked the impingement of an oxygen minimum layer (2) and topographically enhanced currents (3) to the vertical zonation of invertebrate communities on Pacific seamounts. The importance of understanding the process of food supply to the sea floor is underscored by the finding that the input of particulate organic carbon can regulate the size and distribution of populations in soft bottom habitats (4, 5). Moreover, the timing ofphytoplankton supply is thought to influence the evolution of benthic invertebrate reproductive strategies (6).Internal waves are generated when the ebb tide forces a shallow thermocline over the edge of a steep bottom feature such as a bank, ledge, or continental shelf (7). A prominent depression ofthe thermocline is produced on the downstream side and held over the abrupt bottom until the ebbing currents slacken. The released depression propagates away from the topographic feature as a packet of internal waves (8, 9). Because of their ability to move phytoplankton-rich chlorophyll maximum layers downward (10-12), internal waves are a likely mechanism of benthic-pelagic food coupling. To date, investigations of internal wave effects on phytoplankton distribution have been restricted to the water column, and it is not evident that downwelled chlorophyll maximum layers could reach the rough surface of rocky bottoms where topographically induced upwelling could redirect downward flow (13-15).We studied benthic-pelagic coupling at Ammen Rock Pinnacle (ARP), a rocky ledge located 105 km offshore in the central Gulf of Maine characterized by steep bottom topography, swift currents (averages, 12.7-25.5 cm/sec) and abundant populations of suspension-feeding sponges, anemones, bryozoans, and ascidians ( Fig. 1 and refs. 16 and 17). Observations of rapid vertical...