Deep Currents in the Gulf of Mexico

Abstract

Direct current measurements using moored arrays have been made below 1000 m in the eastern, central and western Gulf of Mexico basin. The major low frequency velocity fluctuations in the lower 1000 to 2000 m of the water column in the three regions have the characteristics of topographic Rossby waves (TRWs). Spectral peaks are observed at periods of about 25 days and 40 to 100 days. Motions are highly coherent with depth. Variances increase toward the bottom despite the very weak stratification of the deep waters of the Gulf. Wave-lengths are about 150?250 km and phase propagation is offshore with energy propagation westward. A group velocity of about 9 km day?1 could be directly estimated from significantly coherent signals between eastern and western arrays. This value is consistent with estimates derived from the dispersion relation and is higher than the westward translation speed of 3 to 6 km day?1 of the large anticyclonic eddies shed from the Loop Current. It appears that a major source of TRWs are the fluctuations of the Loop Current and there is evidence that the deep water fluctuations become progressively more decoupled from upper layer currents as the TRWs and warm eddies propagate into the western basin.