Science 327, 860–863 (2010)

Credit: BOGDAN P. ONAC

Conventional wisdom holds that as ice sheets grew over Europe and North America during the last glacial period — about 120,000 to 20,000 years ago — sea level fell in bumpy fits and starts, eventually dropping to about 130 metres below today's levels. Scientists now report that 81,000 years ago, sea levels reached about 1 metre higher than today, owing to ice sheets rapidly melting between periods of growth.

To reconstruct sea level throughout the last glacial period, a team led by Jeffrey Dorale of the University of Iowa and Bogdan Onac of the University of South Florida looked to the caves that dot the southern coast of the Spanish island of Mallorca. The deposition of crusty layers of carbonate minerals in these caves records past sea levels. When the team dated these deposits, they found a period of high seas about 84,000 to 80,000 years ago that punctuated the trend in sea level decline.

If the rapid rise in sea level is confirmed by other records, it will suggest that the 100,000-year climate cycle thought to underlie recent ice ages may not fully explain the waxing and waning of ice sheets.