The West Antarctic ice sheet (WAIS) has long been considered vulnerable to rapid ice loss and satellite data show that the Amundsen Sea embayment of WAIS is losing ice at particularly alarming rates. Since much of the bed beneath WAIS lies below sea level, loss of sufficient ice would open seaways across the continent underneath the ice sheet, with profound impacts on Southern Ocean circulation, Antarctic climate and global sea level. Biological data from the sea around Antarctica suggests that a seaway once existed between the Ross and Weddell seas but its route and timing was not defined. In fact, very little is known about when such seaways last closed, or whether they will open again.

In this study, ice2sea researchers have shown that the most likely routes across West Antarctica are a pair of indirect seaways connecting the Weddell and Ross seas, via the Amundsen Sea.  A direct connection between the Weddell and Ross seas is extremely unlikely either in the past or future, as a new analysis of coastal species distributions suggests. This suggests that species migrated between Amundsen and Weddell seas (seaway A-W) and, probably, between Amundsen and Ross seas (A-R), Bellingshausen and Weddell seas (B-W) and Amundsen and Bellingshausen seas (A-B).  Continued ice-loss at current rates would be sufficient to open seaways A-W and A-B in around 1200 years which indicates a future vulnerability – but also that seaways may have opened in recent interglacial periods.  A recent ice-sheet reconstruction suggested that seaways were last open during a warm stage roughly 200,000 years ago. We suggest, however, that this could have occurred as recently as 100,000 years ago when temperatures were higher than present for several millennia and Antarctica very likely contributed to sea level several metres above present.

Publication: Vaughan, D. G., D. B. A. Barnes, P. T. Fretwell, and R. G. Bingham (2011), Potential seaways across West Antarctica, Geochem. Geophys. Geosyst., 12(10), 1-11.