Measurements of gases in ancient ice have allowed scientists to reconstruct past ocean temperatures with unprecedented precision.

To understand the history of the global ocean, Bernhard Bereiter at the Scripps Institution of Oceanography in La Jolla, California, and his colleagues turned to two noble gases, krypton and xenon. As the sea cools, the amounts of krypton and xenon dissolved in the water rise, and atmospheric levels of the gases are gradually depleted.

The team measured xenon and krypton levels in air trapped in cores of ancient Antarctic ice. The researchers extrapolated from those levels to ocean concentrations, which could then be translated into global ocean temperatures.

The team found that between 20,000 and 10,000 years ago, the global ocean warmed by an average of 2.6 degrees Celsius. The surface temperature of the Antarctic continent shows the same warming pattern over that period, suggesting an important role for the Southern Hemisphere in global climate trends, the authors say.