SHIFTING WATERS SHARING : SCIENCE LAB

STUDY suggests the Industrial Revolution wasn't the initial trigger for Arctic warming.

Long ago, the Arctic and Atlantic Oceans existed in harmony, with warm and salty Atlantic waters gently flowing into the Arctic.

The Arctics layered nature - sea ice on top, cool fresh water in the middle and warm, salty water at the bottom - helped maintain a boundary between the polar ocean and the warmer Atlantic.

But more recently, the Atlantic's water began flowing in faster, transforming the Arctic Ocean into something closer to the Atlantic.

The process, called Atlantification, is one of the reasons that the Arctic is warming faster than any other ocean.

Satellites offer some of the clearest measurements of changes in the Arctic Ocean and sea ice. But their records go back only around 40 years, so team including Tommaso Tesi, a researcher at the Institute of Polar Sciences-CNR, Italy studied sediment cores from the seafloor that record 800 years of changes in the Arctic.

Their analysis of shells and other properties in the sediment found Atlantification started around the dawn of the 20th century.

Yueng-Djern Lenn, a physical oceanographer in Wales who was not involved with the research, sees a difference between this early Atlantification and the current, rapid process, largely driven by melting Arctic sea ice.

''It's too soon after the start of the Industrial Revolution'' for melting to have been the trigger for the early mixing, he said.

One possibility, Dr. Tesi said, is that earlier natural warming may have made the Arctic Ocean flows of recent decades.

''Could it be that we destabilized a system that was already shifting?'' he asked. [ Sabrina Imbler ]