Abstract

Energetic current events occurring in the deep water region of the Gulf of Mexicoare identified, including especially: surface-intensified eddies; deep barotropic motions, sometimes with bottom intensification; atmospheric storm-generated motions, and mid-water current jets. We have searched for such events in the literature, measurements, and numerical model output, seeking situations where the magnitudes of currents over the period of an event are considerably greater than the background currents for the region or for situations where the current characteristics were known to be associated with a particular class of event. Examples of the major classes of energetic current events are shown. Suggestions are made for additional measurements and knowledge needed.

Introduction

With the exception of a few individuals (e.g., Pequegnat1), the common belief of a decade or more ago was that energetic currents in the Gulf of Mexico were confined to the upper waters-surely no deeper than the sill of the Yucatan Channel (approximately 2000 m) and perhaps not much deeper than the sill at the Florida Straits (800 m). Now we recognize a number of classes of currents in the deep waters of the Gulf, and some are known to extend to the greatest depths in that basin.

These currents have been the focus of many recent measurements and studies supported by the oil and gas industry and the Minerals Management Service of the U.S. Department of the Interior. Improved characterization of these currents and their causal mechanisms will lead to improved design criteria for, and to estimation and mitigation of impacts on, technology for ultra-deep water oil and gas exploration and production.

Here we briefly discuss and present examples of currents from the deep water region of the Gulf. Classes of currents considered are:

  1. currents resulting from energetic, episodic atmospheric events (e.g., tropical cyclones such as hurricanes, extratropical cyclones, and cold air outbreaks);

  2. surfaceintensified currents arising from major surface circulation features (i.e., the Loop Current, the anticyclonic eddies derived there from, both cyclonic and anticyclonic eddies spun up in the Gulf; and other low-frequency circulation features driven by local wind stress distributions);

  3. currents extending from about 800 m through the deeper water column, sometimes with bottom intensification; and

  4. high-speed, subsurface-intensified currents.

Observations
Currents caused by energetic atmospheric events.

Perhaps the class of phenomena that longest has been of concern to oil and gas operators comprises those currents resulting from strong, episodic wind events. In the Gulf of Mexico there are three general classes of such events: tropical cyclones (especially hurricanes), extratropical cyclones, and cold air outbreaks. These episodic events can result in extreme waves and can cause currents with speeds of 100-150 cm/s over the continental shelves. Recent examples are given in Nowlin et al.2 who also show that such currents reach significant speeds even at depths of 500 m over the slope.

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