Physical Characteristics

The Loop Current

The most distinctive circulation feature in the Gulf of Mexico is the Loop Current. This can be seen clearly using Advanced Very High Resolution Radiometer (AVHRR) imagery in the winter when the temperature gradients are sharp. The origin of the Loop Current is external to the Gulf of Mexico. The North Equatorial Current, which is the southern leg of the north Atlantic subtropical gyre, flows west into the Caribbean Sea. These waters then enter the Gulf of Mexico through the Yucatan Channel forming the Loop Current. This current makes a clockwise loop as it moves through the Gulf and exits out of the Straits of Florida. The Loop Current is inherently unstable, and its northern extent changes with time, producing warm-core eddies that spin off with a periodicity of about 13 months (e.g., Sturges, 1994) providing oligotrophic waters to the western portion of the Gulf.

As the Loop Current extends north and east, its influence on the west Florida shelf increases. For example, by providing a dynamic height high near the Louisiana coast, it effectively drives relatively fresh, nutrient rich, waters from the Mississippi Delta onto the west Florida shelf. While the Loop Current itself does not flow onto the shelf, waters from the Loop Current may be transported onto the shelf via the formation of smaller scale filaments or by Ekman transport. Thus, the Loop Current may be an important factor influencing the shelf circulation without flowing directly on the shelf (e.g., Weisberg et al., 1996).

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