Previous methods assumed the composition of seawater was the same around the globe. But the study team's data from about 1,000 seawater samples showed global variations. Their new definition allows for the first time to accurately calculate ocean heat content and take into account small differences in salinity.
Salinity affects ocean density, and changes in density help drive huge vertical ocean circulation patterns. This in turn affects the atmosphere and our climate.
Seawater science can help climate change forecasts
David Fogarty, Reuters 22 Dec 08;
SINGAPORE (Reuters) - A team of scientists has come up with a new definition of seawater which is set to boost the accuracy of projections for oceans and climate.
Oceans help regulate the planet's weather by shifting heat from the equator to the poles. Changes in salinity and temperature are major forces driving global currents as well as circulation patterns from the surface to the seabed.
Understanding exactly how much heat the ocean can absorb and accounting for tiny differences in salinity are crucial for scientists to figure how oceans affect climate and how that interaction could change because of global warming.
"Getting these circulations right is central to the task of quantifying the ocean's role in climate change," said Trevor McDougall of Australia's state-backed research body the CSIRO, who is part of the international team that updated the methods to define sea water.
He said the new definition allows for the first time to accurately calculate ocean heat content and take into account small differences in salinity. Previous methods assumed the composition of seawater was the same around the globe.
Seawater is a mixture of 96.5 percent pure water with the remainder comprising salts, dissolved gases and other matter. McDougall said data from about 1,000 seawater samples showed global variations.
There were small but significant differences in the composition of seawater between the North Pacific and North Atlantic, for example.
"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.
McDougall said salinity affects ocean density, and changes in density help drive huge vertical ocean circulation patterns.
"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 constant circulation of heat by the oceans and atmosphere keeps the planet livable.
"What we're doing is providing a more accurate way of estimating that circulation," McDougall said.
McDougall chairs the Scientific Committee on Oceans Research, an international guiding body, and said he expected the new methods to be formally backed by the Intergovernmental Oceanographic Commission at a meeting in June next year.
(Editing by Jerry Norton)