Shelf and Coastal Boundary Layer Currents, Miskito Bank of Nicaragua

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Abstract
A 2-year study of the currents and salinity (density) fields has been conducted on the broad, shallow Miskito Bank of the eastern coast of Nicaragua. Observations across the Bank show a southward-flowing low-salinity, seaward-thinning wedge of highly turbid water trapped against the coast within the first 25-40 km offshore. This so-called coastal boundary layer grades seaward into a northward-flowing shelf current of opensea salinity that is essentially free of suspended sediment. Detailed transects across the coastal boundary layer show the salinity (density) structure to be closely coupled to the high-speed jet of south-flowing water. Velocity and density measurements from the coastal boundary layer allow quantitative evaluation of each of the terms in the momentum balance equation and of the effect that each has on the circulation dynamics. The Coriolis force, the baroclinic and barotropic pressure gradient forces, and the internal friction force make important contributions to the on-offshore force balance. In the longshore balance, only the baroclinic pressure gradient force was found to be insignificant. A marked difference in this balance of forces was observed in the upper and lower layers of the water column in both the alongshore and on-offshore balances.

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