Reconstructions of Antarctic sea-ice at the peak of the last interglacial (marine isotope stage 5e)

Sea-ice plays a fundamental role in regulating global marine ecosystems, ocean circulation and anthropogenic climate change. Sea-ice is predicted to retreat in both the Southern and Northern Hemispheres over the coming decades. This uncertainty arises because there has not been a recent sea-ice retreat event in the Southern Hemisphere to constrain models. To help tackle this problem, we have recently published a new assessment of last interglacial sea-ice extent, based on ice core data. This reconstruction indicates a likely 65% (+/-)7% reduction in Antarctic winter sea-ice cover (Holloway et al. 2016) (Figure 1). Intriguingly, this suggests that the last interglacial is potentially an excellent and unique analogue for the predicted shrinking of Southern Hemisphere sea-ice (up to 58%) by the end of the 21st century (Stocker et al., 2013).

However, the Holloway et al. (2016) calculation of a 65% reduction in sea ice is based solely on ice core data. This proposed retreat therefore urgently requires checking against marine core data, since these allow a more direct measurement of the past position of the sea-ice edge. Some existing microfossil based Southern Ocean reconstructions contain evidence of warmer sea surface temperatures and greatly reduced sea-ice extent during the peak of the last interglacial (Allen & Peck, submitted and refs. therein). But these previous studies are on marine sediment cores located too far north to accurately constrain the position of the sea-ice edge, and they have insufficient chronological control, or sample resolution, to accurately resolve the timing and magnitude of the last interglacial sea-ice minimum.