Oceanographic instrument returned to URI by African fisherman after two years at sea
Todd McLeish, 401-874-7892
NARRAGANSETT, R.I. -- March 15, 2005 -- In early January 2003, 92 subsurface floats were loaded on a truck for the start of a long scientific voyage. One of them has unexpectedly returned to the University of Rhode Island, thanks to a fisherman working off the coast of the West African country of Guinea.
The floats – oceanographic instruments that measure water temperature, pressure and oxygen content every six hours – were being used as part of a National Science Foundation-funded research project to determine the processes that mix water in the ocean horizontally.
According to URI Oceanography Professors David Hebert and Thomas Rossby, the plan was to place clusters of floats at five different locations and at two different depths near the Cape Verde Islands off West Africa in an area where the currents are weak. The combination of how the cluster of floats separated from each other, and their measurements of temperature and oxygen, allows the researchers to calculate the rate of mixing in the ocean.
“In order to model the ocean's circulation for climate studies, it is necessary to understand how the ocean mixes both horizontally and vertically,” said Hebert. “At this time, we have a reasonable understanding of how the ocean mixes vertically but a much poorer understanding of how eddies stir and mix the ocean horizontally. As far as I know, our experiment is the first one explicitly designed to address the question of horizontal mixing beneath the ocean's surface.”
One of the subsurface floats, deployed April 6, 2003, surfaced prematurely after 420 days under water and transmitted its data to the URI scientists via satellite. It remained on the surface of the ocean for 185 days and traveled on ocean currents eastward toward Africa, where fisherman Osman Kamara found the float and brought it to Conakry, the capital of Guinea. Contact information on the float allowed the fisherman to call Hebert to arrange for the return of the 6-foot, torpedo-shaped device, with assistance from the U.S. Embassy.
“While the actual recovery of the floats is not critical or even expected, it’s often useful to see how well the floats survive after being underwater for long periods,” said Hebert. “It turned out to be in excellent condition.”
The float was equipped with a novel oxygen sensor made by a Norwegian company, Aanderaa Instruments, and the return of the instrument has allowed the company to assess how well the sensor fared from prolonged exposure in the ocean.
Photo at right: African fisherman Osman Kamara (middle) with friends after recovering oceanography instrument.
Photo above: Oceanography professors David Hebert and Thomas Rossby (l-r) with one of the instruments that hd been launched two years ago.