Corrosive Ocean 55 Million Years Ago May Have Implications for Modern Global Warming

About 55 million years ago, an abrupt global warming even triggered a highly corrosive deep water current through the North Atlantic Ocean. Now, scientists are taking a closer look at the phenomenon in order to see what implications this may have for future climate warming.

In this latest study, the researchers examined the acidification of the ocean that occurred during the Paleocene Eocene Thermal Maximum (PETM). During this period, the Earth warmed 9 degrees Fahrenheit in response to a rapid rise in carbon dioxide in the atmosphere. This resulted in one of the largest mass extinctions in the deep ocean.

"There has been a longstanding mystery about why ocean acidification caused by rising atmospheric carbon dioxide during the PETM was so much worse in the Atlantic compared to the rest of the world's oceans," said Kaitlin Alexander, lead author of the new study, in a news release. "Our research suggests the shape of the ocean basins and changes to ocean currents played a key role in this difference. Understanding how this event occurred may help other researchers to better estimate the sensitivity of our climate to increasing climate dioxide."

The researchers recreated the ocean basins and land masses that existed 55 million years ago in a global climate model. Simulations revealed that the ridge that existed on the ocean floor between the North and South Atlantic became filled with extremely corrosive water from the Arctic Ocean. This mixed with sense salty water from the Tethys Ocean and sank to the seafloor, where it accumulated. In fact, the water was so corrosive that it dissolved all of the calcium carbonate produced by organisms that settled on the ocean floor.

"The corrosive water spread south through the Atlantic, then east into the Southern ocean and eventually made its way to the Pacific," said Tim Bralower, one of the researchers. "The pattern of the event corresponds very closely to what the sediment records tell us. Those records show almost 100 percent dissolution of calcium carbonate in the South Atlantic sediment."

The findings actually suggest that enormous amounts of carbon dioxide are needed to increase temperatures by 9 degrees Fahrenheit. In addition, the research suggests that other factors made the Atlantic bottom water more corrosive than in other ocean basins.

"Today we are emitting carbon dioxide into the atmosphere ten times faster than the rate of natural carbon dioxide emissions during the PETM," said Alexander. "If we continue as we are, we will see the same temperature increase that took a few thousand years during the PETM occur in just a few hundred years. This is an order of magnitude faster and likely to have profound impacts on the climate system."

The findings are published in the journal Nature Geoscience.

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