EAST ANTARCTIC ICE SHEET BEHAVIOR DURING THE PLIOCENE

Climatic conditions in the Pliocene, especially the amount of polar ice, are an important and debated topic. Important because atmospheric CO₂levels are estimated to have been 400 ppm, similar to todays. Both proxy data and global climate models suggest warmer temperatures, at least 2 degrees C above pre-industrial levels. One consequence of the warmer conditions was higher sea level. Just how much higher is debated, probably somewhere between 12 and 30 meters higher than today. Addressing this question is the focus of the PLIOMAX project. The melting of Greenland and West Antarctic ice sheets can provide about fifteen meters of sea level rise above present levels. However sea level rise of more than fifteen meters would require some melting of the East Antarctic Ice Sheet (EAIS). For decades the EAIS has been considered stable, not likely to melt unless global climate warmed considerably more than today. Sedimentary evidence from scientific ocean drilling and Andrill suggest mid-Pliocene melting, at least in the lower elevations of the EAIS.

To further address the question of EAIS Pliocene melting we have examined early Pliocene through Pleistocene sediments at ODP Site 693 in the Weddell Sea, adjacent to Dronning Maud Land margin, a high elevation coastal region. The sediments are dominated by terrigeneous material, primarily fine silt, with less than 10% coarse fraction, considered ice-rafted. ⁴⁰Ar/³⁹Ar fingerprinting of hornblendes gives a consistent age of about 500 my, suggesting a similar or constant sediment source. Independent wavelet analysis of both down-core XRF data and spectral analysis on individual sediment samples from fully recovered cores indicate a high sedimentation rate (10 cm/1000years) and an obliquity pacing. Discontinuous recovery between middle and upper Pliocene, and Pleistocene sediments does not allow us to identify mid-Pliocene and Pleistocene boundaries. However, given the lower Pliocene sedimentation rate, either sedimentation slowed considerably in the middle Pliocene to Pleistocene or there was considerable erosion. We speculate that erosion, possibly associated with the mid-Pliocene warm period, which likely consisted of extensive melting, removed part of the record.