Gulf of Mexico Loop Current

1. Gulf of Mexico Loop Current Tom Collow Physical Oceanography December 1, 2010

2. The Gulf of Mexico Loop current is an ocean current that transports warm water from the Caribbean Sea into the Gulf of Mexico. • The current brings the warm water through the Florida Straits and to the west of the Bahamas, where it begins to flow north and connect with the Gulf Stream. • The loop current is typically 200-300 km. wide, 800 m. deep, and travels at a speed of 0.8 m/s making it one of the fastest currents in the Atlantic Ocean. • Transport (T) = 250,000 m * 800 m * 0.8 m/s = 160 million m3/s • Periodically, the current bulges northward in the Gulf of Mexico and an eddy breaks off and moves slowly to the west-southwest at a speed of about 3 – 5 km/day. This eddy, known as a loop current eddy or a warm core ring rotates clockwise due to the coriolis force. • The Loop Current usually produces a new eddy every 6 to 11 months.

4. Eddy Separation • Possible causes include (Leben, 2005) • The Beta Effect – It is the natural tendency of eddies to move westward in the Northern Hemisphere due to the change in the coriolis parameter with latitude • Upstream Eddies – Anticyclonic eddies advect into the Gulf of Mexico through the Yucatan Channel which effect the behavior of the loop current • Lower level Eddies – During separation of the surface eddy, another eddy forms below the original eddy which rotates in the opposite direction which promotes the detachment of the surface eddy from the overall current

5. Measuring the loop current • Two main variables • Sea Surface Height • Sea Surface Temperature • In the ocean, temperature is a function of sea surface height (thermal expansion of warmer water will cause warmer water to have a higher sea surface height) • It is easier to measure the sea surface height since it can be done through remote sensing (satellites) which will allow complete areal coverage • A study by Leben, 2005 uses the 17 cm. sea surface height contour to estimate the location of the loop current and eddies.

6. Loop current and hurricanes • The main energy source for hurricanes is the thermal energy from warm water. Hurricanes generally require water temperatures greater than 26°C • The loop current provides a deep layer of very warm water for a hurricane to develop and intensify • Not all disturbances that cross the loop current will intensify. Tropical systems also require little wind shear in the atmosphere which is independent of the loop current • Two prime examples of loop current hurricane intensification occurred during the 2005 Atlantic hurricane season (the most active season on record).

7. Above is the track of Hurricane Katrina along with contours of sea surface height. Notice the rapid strengthening that occurred as the storm passed over the loop current.

8. Above is the track of Hurricane Rita which occurred about one month after hurricane Katrina. A similar rapid deepening phenomenon is seen as the storm travels over the loop current

9. BP Oil Spill Impacts On April 20, 2010, an explosion of the Deepwater Horizon oil rig caused 185 million gallons of oil to be leaked into the Gulf of Mexico over the next several months (Wilson, 2010) There were many fears that oil would enter the loop current and move toward Florida and eventually in into the Gulf Stream. However, the loop current split due to the processes described before, causing most of the oil to slowly drift to the west rather than move toward Florida.

10. References • Leben, R. R. (2005), Altimeter-derived loop current metrics, in Circulation in the Gulf of Mexico: Observations and Models, Geophys. Monogr. Ser., vol. 161, edited by W. Sturges and A. Lugo-Fernandez, pp. 181–201, AGU, Washington, D. C. • Masters, Jeffrey. (2010). The Gulf of Mexico loop current: A primer. Retrieved from http://www.wunderground.com/hurricane/loopcurrent.asp. • Playford, Adam. (2010, June 8). Double-whammy: Oil confirmed deep below surface and may be rounding Florida's tip. The Palm Beach Post. Retrieved from http://www.palmbeachpost.com/news/state/double- whammy-oil-confirmed-deep-below-surface-and-734289.html. • Wilson, Elizabeth K. (2010, Sept. 23). Oil spill’s size swells. Chemical and Engineering News. Retrieved from http://pubs.acs.org/cen/news/88/i39/8839notw7.html