Seasonal Turbulence Variability on the Continental Shelf

ABSTRACT This work presents turbulence data collected in the Gulf of Mexico in an attempt to quantify the source or sources of turbulent dissipation along the continental shelf and any possible causes for its seasonal change. In addition, this work is an effort to assist those concerned with mixing and transport problems working in similar environments. Multiple offshore research cruises were held in both the Gulf of Mexico and the Atlantic Ocean for data collection. The basis of the work is a tethered profiler that measures dissipation-scale turbulence as well as temperature and conductivity at high-resolution. This data is compared against that collected by an in situ acoustic Doppler current profiler and wind meter along with salinity and conductivity measurements taken during the casts. The primary location for this study is a flat, featureless location in the northeastern portion of the Gulf known as Apalachee Bay in water of 20 meters depth. Because of the extremely gradual slope of the shelf in this region, this location is approximately 20 nautical miles off shore. Due to the tidal and wind variations in the area, along with the extreme seasonal temperature swings and surface freshwater flux, it has been found that a significant amount of turbulent energy is absorbed in this region. Density calculations indicate an abrupt seasonal overturning of the water column; cooling during the winter months creates a thermally homogeneous water column. What little stratification does exist, however, is subsequently overturned by a combination of the reversal of the along-isobath currents and increasing winds. Late summer profiles showed a well-mixed water column with very little remaining stratification.