Determining the deep current structure in the Gulf of Mexico

This study determines the structure of the deep flow in the Yucatan Strait and the Gulf of Mexico using hydrographic, current meter, drifter, and model data. Beginning in the Yucatan Strait, the flow below 1000 meters was found to flow into the Gulf of Mexico through the center and out of the Gulf along both sides. The models and observations show mean transports of approximately 30 Sv and variability of 5–10 Sv. The mass and heat balances appear to hold independently above and below the 1000 meter level, exhibiting high coherence between the extent of the Loop Current and the deep flow in the Yucatan Strait.; Geostrophic evidence, supported by drifters, current meters, and models, suggests deep cyclonic flow exists in the Gulf of Mexico, which exhibits means of 1–3 cm/s in the central and eastern portions. At 900 meters, the Lagrangian drifters show higher mean velocities in some areas; however, the means may not be well resolved. Although model data is in basic agreement with the observations, the model indicates higher mean velocities on the continental slope. The geostrophic shear between 1000 and 2500 meters is generally less than 5 cm/s, in both the mean and instantaneous values. High variability is evident in all of the data types. Specifically, the variability is twice the mean in the hydrographic and drifter data, and an order of magnitude larger in the current meter data. This variability is consistent with the presence of topographic Rossby waves. Such waves are the result of the low stratification in the Gulf and are forced by interactions between the Loop Current and the West Florida Shelf.