How the Oceans Once Ended Global Warming

Dec. 26, 2007 -- Last time Earth suffered a carbon-induced fever, it was the oceans that helped saved the day, say marine scientists in California.

Massive ocean-bottom accumulations of the mineral barite show that the last severe global warming episode 55 million years ago was accompanied by several thousands of years of ocean plant life kicking into high gear. All that productivity captured excessive carbon from the atmosphere and dropped it to the ocean floor, where it was buried -- or "sequestered."

"Basically what we're trying to say is the increasing barite accumulation rate is really generally recording greater productivity and not just changes in ocean chemistry," said Adina Paytan, an oceanographer at the University of California at Santa Cruz.

She is the author of a report on barite in the deep sea which appears in the December issue of the journal Geology, published by the Geological Society of America.

Barite, also known as barium sulfate, is a good indicator of productivity, Paytan said, because all living things contain a lot of the element barium in their tissues. When organisms in the life-rich upper waters die, they sink to the sea floor, taking that barium with them. At great depths that barium reaches its saturation point in the water and combines with sulfur to create the mineral barite.

In other words, barite is a secondary product of boom times in the sunny surface waters of a warmer world.

The new research contrasts with previous work on the signs of changing ocean productivity 55 million years ago -- what's called the Paleocene-Eocene Thermal Maximum (PETM) -- by looking for direct products of living organisms, Paytan told Discovery News.

If the barite speaks the truth about what turned down the thermostat during the PETM, it also could be a clue to how Earth will eventually respond to current global warming.