| Summary: | Based on their characteristic properties, the water masses of the Gulf of Mexico and their vertical stratification are discussed. The T-S relationships specific to the region are presented. For the basin waters, below a sill depth of about 2000 m, the potential temperature, salinity and dissolved-oxygen concentrations show no measurable horizontal variation, although weak vertical density gradients evidence slight positive stability. Variations in the characteristics of the water in the following layers are shown, and the likely origins of these water masses are identified: North Atlantic Deep Water, Subantarctic Intermediate Water, oxygen minimum layer and Subtropical Underwater. For the winter, season, the property distributions in the mixed surface layers are described. On the basis of dynamic computations and GEK measurements, the general winter circulation patterns within the Gulf are examined. The mode most often observed in the eastern Gulf is one dominated by the Loop Current; water enters through Yucatan Strait as the Yucatan Current and flows in a clockwise loop which extends well in the Gulf and exits via Florida Strait. The extent of penetration and location of this loop is quite variable. In other seasons, large current rings are known to separate from the Loop Current. In contrast, the winter circulation in the western Gulf seems more predictable; it consists primarily of a clockwise cell centered over the western central Gulf, having broad westward flow for its southern limb, a narrow east northeastward flow for its northern limb and flanked to the north by a west-southwestward current along the outer Texas-Louisiana shelf.
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