Abstract
Observations of water level, current velocity, river discharge, wind and salinity were collected in the Maroni estuary, on the border of French Guiana and Suriname during the wet season of 2018 to explore subtidal circulation patterns. Measurements are complimented by the application of analytical models with an aim to diagnose forcing mechanisms responsible for producing subtidal flows during the day of data collection and to extrapolate these findings to other time periods with variable wind and river forcing. Subtidal along-channel flows were found to be dominated by river discharge, with seaward directed velocities found throughout the channel section reaching 40 cm s − 1 . This pattern was altered with strong southwesterly winds, which produced and inverse gravitational circulation pattern despite the elevated river discharge. Secondary, or cross-channel flows, displayed a three-layer vertical structure in the main channel due to a combination of channel curvature and tidal asymmetry in the lateral baroclinic pressure gradient. The pressure gradient was produced by a salinity intrusion front that only manifested in the channel during flood tide. This is the first comprehensive study of tidal and subtidal flow dynamics in the Maroni estuary.
Highlights
Subtidal circulation, or the flow that remains after tidal currents have been removed, is responsible for the transport and fate of sediments, pollutants, larvae, and all other water-borne materials in estuaries
Estuarine circulation has been attributed to gravitational circulation which results from along-channel density gradients and subsequently produces a two layer flow structure with inflow at depth and outflow near the surface [2]
Results have shown that along-channel subtidal flows during the day of data collection were driven by river discharge since the wind-driven flow opposed density-driven flow
Summary
The flow that remains after tidal currents have been removed, is responsible for the transport and fate of sediments, pollutants, larvae, and all other water-borne materials in estuaries. The Northern coast of South America, including French Guiana, Suriname, Guyana and Venezuela experience persistent southwesterly winds that are blowing directly on-shore and up-estuary [7] This could be an important (yet unexplored) feature of this region in terms of estuarine dynamics since studies have found that onshore winds can reduce or even reverse estuarine exchange flows [8,9]. [8] used observations from the microtidal and partially mixed York River Estuary in Virginia to demonstrate how along-channel wind plays a dominant role in governing the estuarine circulation They found that up-estuary winds reduce or even reverse the tidally averaged vertical shear which reduces vertical stratification while down-estuary winds enhance the tidally averaged vertical shear, which interacts with the along-channel density gradient to increase stratification. These findings are revealing, but it is unknown if they will translate to estuaries with a larger tidal range or systems with different stratification patterns
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