Climate of the last 125 kyr at Skytrain Ice Rise, Antarctica

There is intense interest in the future stability of the West Antarctic Ice Sheet (WAIS).  Models range widely in their predictions and in the physics they include.  Because the timescales for ice sheets are long, our best hope of constraining the solutions is to look at the past behaviour of WAIS. The last interglacial (LIG) is a particularly important time because Antarctic temperature was higher than present and some models predict the complete loss of WAIS and of the large ice shelves adjacent to it.

Within the WACSWAIN (WArm Climate Stability of the West Antarctic ice sheet in the last INterglacial) project, in 2019 we retrieved a 651 metre ice core to the bed of Skytrain Ice Rise. This ice rise is adjacent to the Ronne Ice shelf and the WAIS, but is expected to have maintained an independent ice flow because of the protection afforded by the Ellsworth Mountains.  The ice core has been processed and analysed continuously for a range of analytes, including water isotopes, methane and major chemistry.

In this presentation we will first describe the dating of the ice core achieved in the top half of the ice column by annual layer counting supplemented by fixed horizons, and deeper down by ice flow modelling supplemented by tie points from chemistry, ¹⁰Be, as well as atmospheric CH₄ and δ¹⁸O. The core is continuous through the last glacial period, and most of the last interglacial. Discontinuities occur near the base, in the ice at the older end of the LIG, so that although older ice may be  present, we can only interpret the core to 125 ka.

Overall, the ice core record shows the clearly recognisable pattern of all the Antarctic Isotopic Maxima seen in East Antarctic ice cores over the last glacial cycles. In the early part of the Holocene, we see a very interesting pattern representing thinning of the ice rise and retreat of the Ronne Ice shelf.  This allows us to add reliable dates to the history of ice retreat in the early Holocene.

In the LIG, the record of marine ions in the ice suggest that the Ronne Ice Shelf was present at least from 125 ka onwards. This rules out occurrence of some of the more extreme retreats of WAIS that would have led to seaways between the Weddell, Amundsen and Ross Seas.  We see somewhat higher water isotope ratios in the LIG than the Holocene, possibly consistent with some drawdown of WAIS in sectors other than the Weddell region.