December 22, 2008

Scientists Look To Seawater To Project Climate Change

A new definition of seawater could boost the accuracy of projections for oceans and climate, scientists said.

Oceans shift heat from the equator to the poles, regulating the planet's weather. Changes in salinity and temperature are major forces driving global currents as well as circulation patterns from the surface to the seabed.

For scientists to figure out how oceans affect climate and how that interaction could change due to global warming, they must first understand exactly how much heat the ocean can absorb and account for tiny differences in salinity.

Trevor McDougall of Australia's state-backed research body the CSIRO said getting these circulations right is central to the task of quantifying the ocean's role in climate change. He is part of the international team that updated the methods to define seawater.

The new definition now allows scientists to accurately calculate ocean heat content and take into account small differences in salinity. Methods in the past assumed the composition of seawater was the same around the world.

McDougall said seawater is a mixture of 96.5 percent pure water with the remainder comprising salts, dissolved gases and other matter. Data from about 1,000 seawater samples showed global variations, he said.

For example, he said there were small but significant differences in the composition of seawater between the North Pacific and North Atlantic.

"We've got along quite well for 30 years without delving deeper into what the sea salt is composed of," said McDougall, of the CSIRO's Wealth from Oceans Flagship in Hobart in the southern Australian state of Tasmania.

But ever more complex computer models and greater demands to project how oceans and climate will behave in a warmer world mean an increasing need for more precise data.

Salinity affects ocean density, and changes in density help drive huge vertical ocean circulation patterns, McDougall said.

He said water sinks to the bottom and rises to the top in a very slow circulation that accounts for about half of the heat that the globe needs to transport from the equator to the poles.

The planet remains habitable through the constant circulation of heat by the oceans and atmosphere.

"What we're doing is providing a more accurate way of estimating that circulation," McDougall said.

McDougall said he expected the new methods to be formally backed by the Intergovernmental Oceanographic Commission at a meeting in June next year.


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