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Taking the Ocean’s Temperature

Scientists find a better way to gauge the high seas.
June 28, 2002

Even though over seventy percent of the earth’s surface is ocean-more than one billion-billion tons of water-oceanographers still know very little about it. Compared to the sophisticated data collection and information technologies used for atmospheric research, science’s ability to forecast, or even record, ocean conditions remains antiquated.

An international collaborative effort, called the Global Ocean Data Assimilation Experiment, last month announced plans to improve the process. The group intends to tie together a world-wide army of oceanographic floats and satellites in order to get an unprecedented daily view of the high seas. Organizers say these new space and water-based systems will fill the longstanding gap in ocean monitoring abilities that has prevented our ability to better understand the ocean and forecast its constantly changing face.

According to Neville Smith, chair of the project’s international steering team, plans began to form in 1998 as a number of satellites that would provide a wealth of needed ocean data got ready to launch. The satellite Jason-1, launched by NASA last December, uses an altimeter to precisely measure aspects of ocean-surface topography, such as surface conditions, circulation and sea levels. Satellites soon to launch will measure surface winds and other phenomena.

But satellites alone are not enough, says Phil Sharfstein, the data manager for the U.S. component of the assimilation experiment, based at the Navy’s Fleet Numerical Meteorology and Oceanographic Center in Monterey, CA. “The main problem is that there’s just not that much data out there,” he says. For example, satellites can measure current sea levels, but predicting future levels requires information that a satellite can’t collect, such as salinity and deep-sea temperatures.

To acquire this data, the assimilation experiment partnered with Argo, an international effort to create a global network of deep-diving oceanographic sensors. Ships or planes drop Argo’s sensor floats–each about the size and shape of a scuba tank-into the high seas. Typically, a floats sink to about 2,000 meters, measures salinity and water temperature for two weeks, then surfaces and transmits its location and collected data to a satellite (distances traveled between visits to the surface reveal the movement of deep-ocean currents). The float then sinks again, repeating this cycle for up to five years.

Dean Roemmich, a physical oceanographer at the Scripps Institution of Oceanography in La Jolla, CA, says Argo’s aims to have about 3,400 floats in the water within three years. More than 400 are already operating; funding has been allocated by various countries for 1,500 more over the next two years, and money has been promised for the remaining 1,500. The U.S. will pay for about half of the total with other countries such as Japan, France and Canada funding the rest. The assimilation experiment will gather massive amounts of data from Argo floats, satellites and traditional sources. Sharfstein says preparations to process and disseminate it all are well under way at data centers around the globe.

Partners anticipate feeding this new data into computer models that will allow everything from long-term ocean forecasts to a clearer picture of daily conditions-or “nowcasts.” This may lead to a long-term comprehensive record of ocean conditions that improves our understanding of global warming. Other potential benefits include allowing companies to plot the safest routes for their ships and enabling the military to better plan of naval operations.

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