Seafloor, ice core: wobbling in tandem.

Water-temperature changes imprinted in Atlantic Ocean sediments correspond to air-temperature fluctuations frozen in Greenland's ice cap', scientists report in the Sept. 9 NATURE.

The two temperature records match nicely helping to draw a broader picture of the turbulent climate changes that occurred during the most recent ice age, 100,000 to 10,000 years ago, the researchers say.

"That the warm-cold oscillations in the ice [SN: 12/12/92, p.404] also would show up in the ocean record had been proposed but never documented before," says Gerard Bond, a geologist with Columbia University's Lamont-doherty Earth Observatory in Palisades, N.Y. He and his co-workers tracked sea-surface temperature changes through the past 90,000 years by checking ocean sediment cores for the abundance of Neogloboquadrina pachyderma, the main zooplankton in surface water, whose numbers increase as the water cools. They found that the jittery temperature switches lumped together into cycles of 6,000 to 10,000 years. During these phases, both air and water temperatures wobbled toward cooling.

The ocean record also shows that each cooling cycle culminated in a brief but hefty burst of ice-sheet calving, sending armadas of icebergs drifting out across the northern Atlantic. Most of the icebergs broke off the Laurentide ice sheet, a huge glacier in Canada that advanced through the Hudson Strait. Then, temperatures jumped several degrees within decades, followed by a new cycle of gradual cooling, Bond says.