Spurred by fears that the Earth may be entering an age of rapid warming, scientists have begun the most ambitious research program ever undertaken to understand how the world's oceans work and how the seas and their tiniest inhabitants regulate the planet's air and weather.

Once content to study a single estuary or reef, marine scientists now approach the oceans as a single, giant, integrated whole, a sort of grand circulatory system capable of shuttling vast amounts of heat and nutrients around the planet.

Their goal, they say, is nothing less than answering the most basic questions about the oceans, the mysterious medium that covers 70 percent of the Earth.

"This is the first time the problem has been tackled like this," said Peter Brewer of the Woods Hole Oceanographic Institute. "Previously, people would get up at a meeting and talk about their little piece of the puzzle. Now, we can begin to talk about the whole puzzle."

"What's new is our ability to realistically talk about doing this kind of research on global scales," said Hugh Ducklow of the University of Maryland's Horn Point Environmental Laboratory. "Only in the last few years have we finally had the tools and the expertise to adopt a world view of the oceans."

Over the next decade, an international navy of scientists will deploy buoys and balloons to study the role of tropical oceans as engines of weather. They will release remote sensing devices and chemical tracers to track ocean currents, at the surface and at depths reaching several miles, to see how heat and cold are shuttled about the planet on conveyor belts of water. And they will peer into underwater volcanoes and deep-sea vents to see how new minerals are added to the ocean.

Perhaps most ambitiously, the scientists will attempt to chart the complete cycle of nutrients such as nitrogen, phosphorous and the supreme element of life, carbon.

The journey that carbon makes is an elaborate one. Pushed by winds, carbon dioxide in the atmosphere mixes with surface waters, where it is absorbed by marine plants, which are eaten by grazing ocean herbivores, only to slowly sink to the bottom of the sea as waste. There, carbon may be stored for hundreds or even thousands of years, until deep ocean currents rescue it and bring it back to the surface to be used by living things all over again.

The reason the studies are so important, scientists say, is that carbon is the central ingredient in scenarios that predict the Earth will warm dramatically in the next century. In the atmosphere, carbon in the form of carbon dioxide traps heat and warms the Earth. On land, carbon is stored in trees, plants and soil, but in the ocean, carbon is packaged in tiny marine plants known as phytoplankton and in dissolved organic chemicals.

"Before we did these experiments, we had only the fuzziest of ideas of how to describe something as basic as the carbon cycle in the oceans," Brewer said. "Now, we've managed to put all these pieces together and we're getting a realistic picture of how the ocean operates biogeochemically."

Based on their studies, scientists are coming up with solid numbers that describe the movement and pace of carbon cycling through the oceans, data that is crucial for understanding the climate changes forecast for the next century due to the accumulation of pollutants such as carbon dioxide in the atmosphere. Some of the these numbers will be discussed publicly for the first time at a major symposium scheduled here next week at the National Academy of Sciences.

Researchers warn that a relatively small change in the biological productivity of marine plants could have a large impact on climate. There is 50 times as much dissolved organic carbon in sea water as in the atmosphere, so a 2 percent change in marine carbon could lead to a doubling of atmospheric carbon levels.

Indeed, researchers suspect that biological processes, such as annual blooms of plankton, might be the most important piece of the climate puzzle. There is already some evidence that there have been extremely rapid flip-flops of planktonic growth in the past and if the ocean's tiny plants are pushed too far by changes in their environment, they may respond either with a tremendous growth spurt or a massive die back.

Marine scientists say that only recently have they had the tools and know-how to tackle such questions on a global scale.

Only in last few years have supercomputers become widely available to run elaborate simulations of how the oceans work, based on numbers provided by scientists in the field. These computer models, still in their infancy, will be used to predict how the carbon cycle and the patterns of plankton growth and death will change in the future.

In addition, researchers recently for the first time had a satellite that could be used to study plankton growth in the oceans. Although that satellite stopped functioning, the National Aeronautics and Space Administration is moving ahead with plans for a second one capable of scanning the color, and therefore the chlorophyll and productivity, of the oceans.

And only recently have scientists begun to suspect what a large role the oceans play in the planet's climate. Over the last decade, for example, researchers studying ice cores dug in frozen glaciers of Greenland and Antarctica realized there was a direct link between carbon dioxide, climate and the oceans.

Moreover, they found that changes in Pacific currents, which result in the so-called El Nino warming of the waters off the western coast of South America, are capable not only of altering whole ecosystems in Peru, but also of bringing wet weather to the southeastern United States and drought to Australia.

"We realized that we needed to understand the currents in the Pacific to understand the weather in North America," said Phil Taylor, an oceanographer at the National Science Foundation, the U.S. agency that funds much of the new research. "That got everybody's attention."