Researchers have discovered that the ocean's chemical makeup is less stable and more greatly affected by climate change than previously believed. The researchers report in the December 12, 2008 issue of Science* that during a time of climate change 13 million years ago the chemical makeup of the oceans changed dramatically. The researchers warn that the chemical composition of the ocean today could be similarly affected by climate changes now underway – with potentially far-reaching consequences for marine ecosystems.
"As CO2 increases and weather patterns shift, the chemical composition of our rivers will change, and this will affect the oceans," says co-author Ken Caldeira of the Carnegie Institution's Department of Global Ecology. "This will change the amount of calcium and other elements in ocean salts."
The research team, which included Caldeira, Elizabeth M. Griffith and Adina Paytan of the University of California, Santa Cruz, plus two other colleagues, studied core samples of deep oceanic sediment recovered from the Pacific Ocean Basin. By analyzing the calcium isotopes in grains of the mineral barite in different layers, they determined that between 13 and 8 million years ago the ocean's calcium levels shifted dramatically. The shift corresponds to the growth of the Antarctic ice sheets during the same time interval. Because of the huge volume of water that became locked up in the ice cap, sea level also dropped.
"The climate got colder, ice sheets expanded, sea level dropped, and the intensity, type, and extent of weathering on land changed," explains Griffith.
"This caused changes in ocean circulation and in the amount and composition of what rivers delivered to the ocean," adds Paytan. "This in turn impacted the biology and chemistry of the ocean."
Calcium-bearing rocks such as limestone are the largest storehouse of carbon in the Earth's carbon cycle because they are primarily made up of calcium carbonate. "The ocean's calcium cycle is closely linked to atmospheric carbon dioxide and the processes that control seawater's acidity," says Caldeira.
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