Current and hydrographic conditions at the East Flower Garden Bank in 2011

Abstract

The East Flower Garden Bank (EFGB), part of the Flower Garden Banks National Marine Sanctuary, is located in the northwestern Gulf of Mexico, about 185km southeast of Galveston, Texas. With a width of about 5km, the steep-sided bank rises from water depths of over 100m to within less than 20m of the surface. Four acoustic Doppler current profiler (ADCP) moorings and four temperature/salinity strings were deployed around the EFGB with an additional ADCP on top of the bank for about 1 year. The main objective was to understand the ocean processes over the EFGB and to examine the importance of the topographically induced processes on shelf edge circulation on longer (e.g. days to seasonal) time scales. Currents were generally eastward over the bank in the upper water column. Eddy events occasionally reversed the eastward flow for a few days. Currents in the lower water column tended to align with the bank's bathymetry and mostly were directed offshore at the southern edge of the bank. Wind and eddy events moved both shelf and off-shelf waters over the bank, including waters from as deep as 200m through upwelling and/or mixing processes. Mixed layers changed by as much as 50m in a couple of days. Inertial currents occurred throughout the year and were often much larger than the tidal currents. Commonly, the inertial currents were strong enough to reverse the predominantly eastward current flow on time scales of less than a day. Westward propagating cyclonic eddies (often associated with anticyclonic eddies) likely connect biological activities of the EFGB with the West Flower Garden Bank. Banks such as the EFGB, with large aspect ratios and heights, strongly alter circulation and enhance exchange processes at the shelf break.