Larry O'Hanlon, Discovery News - During a period of natural global warming 55 million years ago, ocean plant life kicked 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." Scientists studying the remains of those plants are starting to understand how they helped cool the Earth.
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.
"I think the main contribution here is that the PETM is our best example of a natural carbon cycle experiment," said PETM expert James Zachos, who also works at U.C. Santa Cruz, but was not involved in Paytan's research.
"This study is suggesting that the peaks in barite observed in the deep sea...are accurately reflecting changes in the accelerated, though temporary, sequestration of carbon by one process -- higher algal production," Zachos told Discovery News.
That doesn't mean Earth is likely to repair the damage done by current global warming in any timely way, however, he cautions.
"Unfortunately, this process is slow and thus lags the buildup of carbon in the atmosphere," said Zachos.
In fact, said Paytan, the barite accumulation went on for about 170,000 years. That suggests it takes a lot longer to cool off a hot Earth than to heat up a cool planet.