Reconstructing sea level changes during the last interglacial,127-116,000 years
ago, yields insights on the stability of large continental ice sheets
during a period of relative warmth similar to the present day.
Evidence of a sudden melting episode suggests tipping points in the climate system.
In an article recently published in Nature, O’Leary et al. found strong evidence supporting the idea that sea level rise was not gradual but instead proceeded in jumps during the last interglacial. To reconstruct sea level changes, O’Leary et al. combined a precisely dated stratigraphy obtained from a coral reef in western Australia with a geophysical model accounting for local subsidence of the ocean floor due to various effects (e.g., tectonic activity, post-glacial rebound, gravitational pull by ice sheets, sinking of the reef, etc). Since the top of the coral reef is usually at a constant depth relative to local sea level, a dated stratigraphy provides a precise measurement of the sea level over the lifetime of the reef. O’Leary et al. inferred from this coral reef that sea level was relatively constant from 127,000 to 119,000 years ago, at about 3-to-4 meters above present day sea level. Sea level then sharply increased around 118,000 years ago, increasing to about 9 meters above present day sea level. The release of so much water over a relatively short period (a few thousand years) supports the idea that ice sheets may have tipping points when responding to gradual global warming (as Earth experienced during the last interglacial). This pulse of fresh water could have come from a sudden collapse of the West or East Antarctica ice sheets, with a smaller contribution from the Greenland ice sheet as well. Because the same ice sheets are essentially intact today, the phenomenon could potentially repeat itself in response to anthropogenic warming.
Citation: O’Leary M.J. et al., 2013: Ice sheet collapse following a prolonged
period of stable sea level during the last interglacial, Nature Geoscience,
6, 796-800. (http://www.nature.com/ngeo/journal/v6/n9/full/ngeo1890.html)