Ice Ages Study Uses Ancient Plankton To Determine Temperature And Sea Level Over 5.3 Million Years

By Ben Wolford on April 16, 2014 1:06 PM EDT

Scientists are using ancient plankton to try to learn more about temperature and sea level changes during the ice ages. (Photo: Shutterstock)

Scientists are using ancient plankton to try to learn more about temperature and sea level changes during the ice ages. (Photo: Shutterstock)

When an ice age happens, it gets colder before it gets icier, according to new measurements by a team of international scientists. Their findings reshuffle the timeline of the onset of the current ice age, which began more than 2 million years ago and continues today.

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Before this study, which appears in the journal Nature on Wednesday, scientists believed the present glacial age began around 2.5 million years ago with the formation of the polar ice caps and a sharp drop in global temperatures. But by tapping oxygen isotope levels in plankton fossils, the researchers discovered the temperature change occurred around 2.7 million years ago. Ice sheets formed about 550,000 years later.

"The observed decoupling of temperature and ice-volume changes provides crucial new information for our understanding of how the ice ages developed," said study co-author Gavin Foster, of the University of Southampton, in a statement. He said this knowledge is useful for the oil and gas industry because historic sea levels offer clues on how coastal sediment are layered.

"Our record is also of interest to climate policy developments," Foster added, "because it opens the door to detailed comparisons between past atmospheric [carbon dioxide] concentrations, global temperatures, and sea levels, which has enormous value to long-term future climate projections." In other words, knowing the conditions that precipitated the beginning and end of the ice could offer clues about when the current one will end.

An ice age is a period of relative global chill marked by the existence of ice sheets, like the ones currently covering Greenland, the Arctic, and Antarctica. They last from tens to hundreds of millions of years. During an ice age, faster and less variable temperature fluctuations cause the ice sheets to advance (a glacial cycle) or retreat (an interglacial cycle). The Earth has experienced an interglacial cycle for the past 11,000 years, since the last time glaciers descended. Scientists know of five ice ages in Earth's history.

During an ice age, sea levels are lower because more water is trapped in solid sheets above sea level. Snow and ice contain higher concentrations of the isotope oxygen-16; oceans contain more of the heavier oxygen-18. Incidentally, plankton use the oxygen in the ocean (along with carbon and calcium) to build their shells. In this way, the concentration of oxygen isotopes in these shells is a record book of sea level and temperature.

For the present study, sientists recovered the record by drilling long cores into the sediments on the floor of the Mediterranean Sea to examine the plankton fossils. "This is the first step for reconstructions from the Mediterranean records," said lead author Eelco Rohling of Australian National University. "Our previous work has developed and refined this technique for Red Sea records, but in that location it is restricted to the last half a million years because there are no longer drill cores. In the Mediterranean, we could take it down all the way to 5.3 million years ago."

Above photo courtesy of Shutterstock

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