Low-Frequency Current Variability Observed at the Shelfbreak in the Northeastern Gulf of Mexico: May-October 2004
NAVAL RESEARCH LAB STENNIS SPACE CENTER MS OCEANOGRAPHY DIV
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High-resolution current measurements were made in the Northeastern Gulf of Mexico by the Naval Research Laboratory NRL as part of its Slope to Shelf Energetics and Exchange Dynamics SEED project. The major goal of SEED is to understand the mechanisms that transfer properties across the shelf slope. Fourteen acoustic Doppler current profilers ADCPs were deployed just west of the DeSoto Canyon on the shelf and down the slope from May to November, 2004 to measure nearly full water column current profiles. Currents were found more variable on the shelf than on the slope but in the mean strongly tended to follow bathymetry, particularly on the slope. During the SEED time period currents were driven by both local and remote winds, by cyclonic eddies associated with the Loop Current extension and Loop Current rings, by smaller eddies associated with the cyclonic eddies, by frontal meanders or streamers associated with the eddies, and by tropical storms. Currents were highly barotropic, accounting for more than 80 of the eddy kinetic energy EKE. Current magnitudes generally increased from west to east, towards the DeSoto Canyon. Tropical storms had a relatively minor short-term effect upon mass transports. Cross-shelf transports were much smaller than the along-shelf transports. Onshore transports were stronger on the western side of the array while offshore transports were stronger on the eastern side of the array near the DeSoto Canyon. Offshore transports generally occurred during eastward flow periods, onshore transports during westward flow periods, and both during eddy periods. Mesoscale eddies also provided contributions to cross-shelf exchange. Large scale circulation features could be determined from the first two empirical-orthogonal function EOF modes which accounted for 83 of the variance and were strongly related to the integrated wind stress.
- Physical and Dynamic Oceanography