Data Keeps Drifting In

Author: Laura Bracken, CARTHE Outreach Manager

After a month at sea conducting a variety of experiments, the Ronald H. Brown has returned home but data continues to pour in. As the ship circled the Gulf of Mexico (GoM), conducting cross-shelf transects, scientists onboard released 25 custom-made, GPS-equipped, biodegradable CARTHE drifters, described in the post “New biodegradable surface drifters to survey the ocean currents of the Gulf.” The drifters can transmit their location every 5 minutes for 1-3 months, providing scientists at the Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE) with accurate tracks of the ocean currents.

This experiment is unprecedented and will provide a much needed picture of how currents behave near the shelf.  CARTHE has conducted 3 large scale experiments in the northern GoM but by adding the full range of this vast body of water they will gain a better understanding of Gulf-wide dynamics.

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Figure 1. Cumulative map of ship track, drifter tracks, and hurricane tracks

The above map shows the ship track in green. The individual drifter tracks in black, with red dots indicating their last known position. The purple line that crosses Mexico represents Hurricane Franklin, while the purple line that stretches from the Bay of Campeche to Texas represents Hurricane Harvey. Luckily the ship was already home before Harvey developed, but was required to alter its course to avoid Franklin. Hopefully analysis of the drifter tracks near these storms will provide some information about how storms impact ocean currents.

As expected, there are several areas where drifters were retained over the shelves, mainly moving slowly across the shelf, rather than moving into the body of the Gulf. Of particular interest is the Yucatan Shelf.

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Figure 2. Yucatan shelf

The historical drifter database of the GoM shows a gap on the Yucatan Shelf/Campeche Bank (cf. Miron et al 2017).  These deployments will contribute to filling that particular gap. On the Bay of Campeche (west of the Campeche Bank) there are observations of a quasi-permanent cyclonic gyre (called the Campeche Gyre) that models have trouble to represent in the mean.  The drifters deployed in the region are expected to sample this cyclonic circulation, though this has not been seen yet.

CARTHE scientists will continue to track the progress of the drifters, to compare to previous drifter data, and to work towards better understanding how material in the Gulf of Mexico is transported by the ever changing surface currents.

Thank you to the crew of the Ronald H. Brown and the scientists and students who facilitated the release of the CARTHE drifters.

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