Surprisingly, Rashid's team was also able to score another first with their analysis of this sediment core a record of the temperature at the sea surface in the North Atlantic.
They drew on knowledge readily known to chemists that the amount of magnesium trapped in calcite crystals can indicate the temperatures at which the crystals formed. The more magnesium present, the warmer the waters were when the tiny organisms were alive.
They applied this analysis to the remains of the benthic organisms in the cores and were able to develop a record of warming and cooling of the sea surface in the North Atlantic for the last half-million years.
Having this information will be useful as scientists try to understand how quickly the major ocean currents shifted as glacial cycles came and went, Rashid said.
The researchers were also able to gauge the extent of the ancient Laurentide Ice Sheet that covered much of North America during the last 130,000 years.
As that ice sheet calved off icebergs into the Atlantic, Rashid said that the "dirty underbelly" of those icebergs carried gravel out into the ocean. As the bergs melted, the debris fell to the bottom and of the ocean floor. The more debris present, the more icebergs had been released to carry it, meaning that the ice sheet itself had to have been larger.
"Based on this, we've determined that the Laurentide Ice Sheet was probably largest during the last glacial cycle than it was during any of the three previous cycles," he said.
During the last glacial cycle, the Laurentide Ice Sheet was more than a kilometer (.6 miles) thick and extended to several miles north of Ohio State.
|Contact: Harunur Rashid|
Ohio State University