December 2001

From University of Rhode Island

URI oceanographers to study spreading and mixing of low oxygen waters off West Africa

Three University of Rhode Island Graduate School of Oceanography (GSO) physical oceanographers have been awarded $1.6 million by the National Science Foundation to determine the processes of stirring and mixing in the ocean on density (horizontal) surfaces in the oceanís interior.

Dave Hebert, H. Thomas Rossby, and Huai-Min Zhang will measure temperature, pressure, and oxygen of subsurface water parcels as they drift and disperse over the course of two years.

The scientists will use acoustically-tracked subsurface floats, called RAFOS floats, deployed in an area of low oxygen that extends thousands of miles to the west of Africa.

This area was chosen because the variations in temperature and oxygen on density surfaces suggest that this is a very good area to investigate the mechanisms of transport, dispersion and mixing that maintain the observed distributions.

They plan to do this by deploying a large number of floats in small groups on two surfaces to study how these clusters of floats move and spread from their initial separation of less than one kilometer to greater than 100 kilometers a year later.

The two depths chosen for the float deployments are thought to have a significantly different character in the currents and mixing processes. By tracking the floats and knowing the temperature and oxygen content of the water they are in, the URI scientists hope to determine how large eddies stir and mix the water.

During the first year of the research project, the GSO team will construct 100 RAFOS floats. In the second year, after construction is complete, the scientists will deploy a cluster of 10 floats each on two density surfaces at five locations.

The deployment of floats, scheduled for spring of 2003, will be made during a one-month cruise to survey the region and deploy four moorings. For more information on RAFOS floats and how they are tracked, see

The information obtained as a result of this project will provide the scientific community with a better understanding of how temperature and oxygen change along a density surface in the ocean.

"In the past few years, we have improved our understanding of how waters mix vertically or across density surfaces," said Hebert. "However, it is not clear how these waters are moved and mixed along density surfaces to produce the smooth changes we observe over hundreds of kilometers."

Ultimately, an improved knowledge of these oceanic processes of transport and mixing will help make models of the ocean more realistic and thereby help scientists to better understand the role of the processes in the regulation of the global climate system.

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, 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 Ocean Technology Center, and the National Sea Grant Library.

This article comes from Science Blog. Copyright © 2004

Archives 2001 E