North Atlantic salinity linked to tropics.

• Position: Ice Age

Sudden shifts in temperature over Greenland and tropical rainfall patterns during the last ice age have been linked for the first time to rapid changes in the salinity of the North Atlantic Ocean. This research provides further solid evidence that climate change can have a direct and rapid impact on ocean circulation and chemistry.

"It's a very complicated system," points out lead researcher Matthew Schmidt, who carried out the work as a graduate student at the University of California, Davis, and now is a visiting National Oceanic & Atmospheric Administration Climate and Global Change postdoctoral fellow at the Georgia Institute of Technology, Atlanta.

Schmidt and his team reconstructed a 45,000- to 60,000-year-old record of ocean temperature and salinity from the chemical traces in fossil shells of tiny planktonic animals recovered from deep sea sediment cores. They compared their results to the record of abrupt climate change recorded in ice cores from Greenland. At that time, much of North America and Europe was a frigid sheet of ice, but the ice records show repeated patterns of sudden warming, called Dansgaard-Oeschger cycles, when temperatures in Greenland rose by 5-10[degrees]C over a few decades. Those cycles were matched by rapid changes in surface-water salinity in the North Atlantic. The Atlantic got saltier during cold periods, and fresher during warm intervals. The freshening likely reflects shifts in rainfall patterns, mostly in the tropics. "Suddenly, we're looking at a record that links moisture balance in the tropics to climate change,"...