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Marine Scientists Begin Expedition to Arabian Sead and Indian Ocean; Area's Monsoons May Provide Clues to Global Climate

Cheryl Dybas
(703) 306-1070
NSF PR 94-77
November 29, 1994

In an area surrounded by political unrest, human tragedy,and extreme climatic conditions lies one of Earth's most biologically-rich bodies of water, the Arabian Sea, tucked in the northwest corner of the Indian Ocean. This sea- within-anocean may also contain clues to one of today's most pressing scientific questions: what is the role of carbon dioxide in global climate?

One major factor makes the Arabian Sea an ideal location for climate research: its seasonal reversals of wind direction and rainfall patterns, called monsoons. The Arabian Sea is flanked by northeast Africa, the Arabian Peninsula, and India. These land masses, especially the Tibet Plateau north of India, influence weather conditions by helping to create powerful monsoons. Monsoons occur twice each year in this area, once during summer and once during winter. During the summer monsoon, damp air over the Arabian Sea moves north, producing heavy rains over Africa and India. In the winter monsoon, the opposite occurs, creating a dry season.

The most biologically productive period in the Arabian Sea is during the summer monsoon. Prevailing winds cause nutrient rich deeper waters to flow toward the surface at this season. This "upwelled" water, loaded with nutrients and carbon dioxide, spurs rapid and widespread marine plant growth and subsequent marine animal production. In contrast, during the winter monsoon, carbon dioxide and nutrient flow from the depths to the surface falls off, and plant and animal productivity is low. "Nowhere else in the world can scientists witness such extreme fluctuations," says Neil Andersen, director of NSF's chemical oceanography program. "That's what makes this area a perfect site for studying a wide range of carbon dioxide exchange processes among marine plants and animals, and between the sea and the air."

An investigation of the area -- a study known as the Arabian Sea Expedition -- recently began. The expedition is supported by several U.S. agencies, with the National Science Foundation funding the Arabian Sea Process Study under an umbrella program, the Joint Global Ocean Flux Study (JGOFS). Oceanographers taking part in this international, multiinstitutional program are researching the relationship between the region's powerful monsoons and massive seasonal changes in the biological and chemical characteristics of the Arabian Sea. More than 240 scientists and technicians from 30 different institutions are participating in the 16- month study. Some 17 oceanographic research cruises will take place aboard the vessel Thomas G. Thompson, operated by the University of Washington.

"This program will help scientists answer some of the fundamental questions about Earth's carbon dioxide cycle," says Andersen. "One of these questions is whether the Arabian Sea acts as a source or a sink for carbon dioxide."

Participants in the National Science Foundation- supported World Ocean Circulation Experiment (WOCE) are planning a simultaneous expedition to the Indian Ocean. The principal objectives of WOCE in the Indian Ocean are to describe, explain, and quantify this ocean's circulation. "Such a survey has never before been attempted on this scale in the Indian Ocean," says Richard Lambert, director of NSF's physical oceanography program. "These studies will complement the efforts of the Arabian Sea Process Study."

Scientists know little about the details of how and in what quantities water, heat, salt, and nutrients are brought into the Indian Ocean, transported within and between its different basins, and then re-exported after a certain period of time. To find out, researchers will measure the ocean's currents at particular points using moored current meters, surface drifters, and subsurface floats. Says Lambert, "These studies, along with measurements of changes in upper-ocean temperatures, are particularly important in the northern Indian Ocean, where the annual monsoon cycle causes rapid changes in its circulation."

WOCE work will be conducted from the research vessel Knorr, operated by the Woods Hole Oceanographic Institution. Scientists from more than a dozen U.S. institutions, accompanied by participants from many other nations, will take part in the expedition, launched on December 1, 1994, and continuing until late January 1996.

Once all observations from the WOCE and JGOFS cruises are collected and examined, scientists hope to develop a better understanding of the role of carbon dioxide in Earth's climate, and how ocean circulation may be involved in the carbon cycle.

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