The goal of this project, funded by the National Science Foundation, is to understand how mixing along constant density surfaces (e.g., horizontally) occurs in the open ocean. This region was chosen because there is a low oxygen tongue present due to the high primary production occurring off the African coast.
To address the issue, the scientific team will deploy 92 isopycnal RAFOS floats in clusters at five locations and two depths per location. These subsurface floats, of which 50 contain oxygen sensors in addition to pressure and temperature sensors, will be deployed for approximately two years. At the end of their mission, they drop a release weight, return to the surface and transmit their data via the ARGOS satellite back to GSO.
The positions of the floats underwater are determined from the arrival time of an acoustic signal transmitted by four sound sources. The time that it takes the sound to travel from the sound sources allows the float's location to be determined by triangulation.
"Nowadays, oceanographers have a reasonably good idea of the processes that mix water vertically in the open ocean, but we still don't understand how eddies stir and mix the waters horizontally," said Hebert. The deployment of these subsurface floats will help address this topic."
Two technicians from the Woods Hole Oceanographic Institution's Rigging Shop, John Kemp and Jim Ryder, will deploy the sound source moorings. The paths that the floats take will also tell scientists about the circulation in this poorly understood region In addition to deployment of the floats and sound source moorings, a high resolution hydrographic survey of the region will be conducted during the 38-day cruise. The scientific team will be sailing on the 168' R/V SEWARD JOHNSON II operated by the Harbor Branch Oceanographic Institution. They leave in mid-March to catch the ship in Las Palmas, Canary Islands, and return at the end of April.
Several GSO graduate students, Elias August, Bronwyn Cahill and Regina Rodrigues, and a student from Dalhousie University, Audrey Barnett, will also be part of the research expedition. They will be joined by Sandy Fontana and Maggie Baez of GSO to complete the scientific party.
The URI Graduate School of Oceanography is one of the country's largest marine science education programs, and one of the world's foremost marine research institutions. Founded in 1961 in Narragansett, RI, GSO serves a community of scientists who are researching the causes of and solutions to such problems as acid rain, harmful algal blooms, global warming, air and water pollution, oil spills, overfishing, and coastal erosion. GSO is home to the Coastal Institute, the Coastal Resources Center, Rhode Island Sea Grant, the Institute for Archaeological Oceanography, and the National Sea Grant Library.