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
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)