David Salas-Monreal

Sea-Level Slopes and Volume Fluxes Produced by Atmospheric Forcing in Estuaries: Chesapeake Bay Case Study

Abstract Time series at eight locations in Chesapeake Bay and the adjacent inner shelf were used to determine the relative influence of the wind and barometric pressure effects on subtidal sea-level variability and slopes in the estuary. Special emphasis was placed on the lower Chesapeake Bay, where inverse barometric effects accounted for up to 32% of the subtidal sea-level variations, and wind forcing accounted for more than 67% of the variance. The wind frequency from any given direction varied from one station to another due to the nonsynoptic characteristics of atmospheric pressure in Chesapeake Bay. In the northern bay, northwesterly winds were most frequent in winter, and southerly winds were most frequent in summer. In the southern bay, northeasterly winds were most frequent in fall and winter, and southwesterly winds dominated in the summer. These winds produced sea-level responses as follows: northeasterly winds caused water to pile up in the southwestern corner of the bay, whereas southwesterly winds produced water-level depressions in the same area. This study is one of the few to document the influence of atmospheric pressure gradients on estuarine sea-level slopes. It was found that atmospheric pressure gradients produced sea-level slopes of the same order of magnitude (10−7) as those induced by westerly–easterly winds. In contrast to previous studies, the volume fluxes calculated here, with geostrophy, geostrophy plus wind stress, and the continuity constraint, showed drainage of the bay with northerly and northwesterly winds and filling of the bay with southeasterly winds.

Role of Near-Bottom Currents in the Distribution of Sediments within the Southern Bay of Campeche, Gulf of Mexico

Abstract The sediment distribution in the southern Bay of Campeche is mainly governed by wind-induced currents and mesoscale cyclonic eddies. An increase in sediment grain size toward the sea is attributed to the presence of a convergence zone that sorts the sediments from heavier to lighter. A small anticyclonic eddy near the coast leads to a concentration of sediments westward of the Grijalva-Usumacinta River. We combined current profiles and charts of the distribution of magnetic susceptibility within sediments with a hydrodynamic numerical model to elucidate the distribution of the major sedimentary units in the Southern Bay of Campeche, Gulf of Mexico. Acoustic Doppler current profiles and geostrophic velocity data were used to set the water velocity at the open boundaries of the applied numerical model. The model was forced by the dominant winds. Sediment on the southeastern side of the bay is dominated by carbonates because of a lack of river discharge and other systems that contribute terrigenous sediments. In the southernmost side of the bay, where the major rivers are located, the bottom sediments are mainly of terrigenous origin.

Continuously stratified flow dynamics over a hollow

[1] To study the effects of bathymetric depressions (hollows) on continuously stratified flows, measurements of current velocity and water density profiles were obtained over two hollows in the lower Chesapeake Bay. Measurements showed an acceleration of the middepth flow as it moved toward the deepest part of the hollow, in contrast to the deceleration expected from two-dimensional Bernoulli-type dynamics. The acceleration was attributed to lateral water intrusions that were most apparent during floods, as corroborated by observations in a transverse section that crossed the deepest part of one of the hollows. The flow acceleration toward the deepest part of the hollows during flood, favored by lateral water intrusions, was deflected toward the right (looking landward) owing to Coriolis accelerations. In general, during ebb and flood, the dynamics over the hollows could be explained with three-dimensional Bernoulli-type dynamics (pressure gradient balanced by advection) modified by Coriolis acceleration. Outside the hollows, the dynamics were between pressure gradient and friction (stress divergence). The transition from frictionally dominated dynamics (outside the hollow) to advection-dominated dynamics (inside the hollow) appears at the region where the bathymetric slope equals the bottom drag coefficient.