Models evaluate the impact of the collapse of the West Antarctic ice sheet and of sea ice reduction on the isotopic composition of precipitation on the East Antarctic Plateau, compared to isotopic records from the last Interglacial period.

Nature Communications by Holloway et al.

The last interglacial period, which spans from 130 000 to 115 000 years ago, was characterised by a climate warmer than today and a global sea level 6 to 9 meters higher than today. Such a sea level rise requires an important amount of ice loss from the Antarctic Ice Sheet. In this study, Holloway et al. evaluate the impact of a West Antarctic Ice Sheet collapse and of a major sea ice retreat on the isotopic composition of precipitation in Antarctica using climate model experiments which include water isotopes. They compare the simulation results with isotopic composition from ice cores from East Antarctica at Dronning Maud Land, Dome F, Vostok and Dome C, where the records extend throughout the last interglacial period and in particular at the Antarctic isotope peak which occurred 128 000 years ago.

The models indicate that a complete loss of the West Antarctic Ice Sheet (and when the resulting meltwater is added to the Southern ocean) results in a decrease of the isotopic composition of precipitation at all ice core locations, notably due to changes in atmospheric circulation, the seasonality of precipitation and the meltwater that enters the Southern Ocean from the melted ice sheet. This is not observed in ice core records 128 000 years ago, as illustrated in Fig. 1. A retreat of winter sea ice area of around 65% compared to the pre-industrial period on the other hand, predicts both the magnitude and the spatial pattern of the 128 000 isotope peak. Note that these results do not dismiss the hypothesis of a collapse of the West Antarctic Ice Sheet, but simply postpone the collapse to later during the interglacial period.

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Fig 1: Spatial pattern obtained for isotopic composition and sea ice extent 128 000 years ago with the simulation: a) precipitation weighted anomalies relative to pre-industrial with the removal of the West Antarctic Ice Sheet and addition of the meltwater to the Southern Ocean, b) precipitation weighted anomalies for a 65% winter sea ice retreat relative to pre-industrial and, c) September sea ice concentration fractionation corresponding the results presented in b); the blue contour presents the 1978-2013 satellite observations.

Sea ice takes an important role in the climate system as sea ice cover increases the surface albedo and insulates the ocean from heat loss, wind stress and gaseous exchanges with the atmosphere. Still, models fail to simulate the recent sea ice extent in Antarctica from satellite observations. Using the sea ice retreat of 128 000 years ago as a test to validate sea ice models could help with future predictions of Southern hemisphere sea ice change in the context of climate change.

Holloway, M. D. et al. Antarctic last interglacial isotope peak in response to sea ice retreat not ice-sheet collapse. Nature communications 7 (2016).

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