Our Research

Also in Retreat of Southern Hemisphere Sea Ice, 127 000 years BP

The study of the last interglacial sea ice requires a cross-disciplinary team of scientists in the fields of climate modelling, sea ice dynamics, and ice/marine sediment cores.

 

The “Retreat of Southern Hemisphere Sea Ice, 127 000 years BP” project will focus on modelling the major last interglacial SH sea ice retreat event.  Below a general overview of our (most recent and ongoing) research on the last interglacial sea ice is given.

 

Isotope-enabled climate model simulations

Our group recently identified a substantial retreat in Southern Hemisphere (SH) sea ice during the Last Interglacial. Holloway et al. (2016) use statistical techniques to combine data from ice cores drilled on the East Antarctic Ice Sheet with isotope-enabled climate model simulations to determine the state of the ice sheet and Southern Hemisphere sea ice during the last interglacial Antarctic climate optimum, ~128 000 years ago. The results suggest that a major retreat of Southern Hemisphere sea ice is the best explanation for the early last interglacial ice core data. Holloway et al. (2017) then perform a multi-ice and ocean core data-model evaluation to assess the magnitude and spatial pattern of this sea ice retreat. These model/ice core syntheses conclude that Antarctic winter sea ice area was reduced by >58 % at the onset of the last interglacial.

Figure 3 from Holloway et al. (2017). Antarctic winter sea ice extent at 128,000 years ago and at present. (a) Spatial pattern of δ18O anomalies (Last Interglacial run – Preindustrial run) in response to sea ice retreat that provides the best agreement with the δ18O ice core data at 128 000 years ago (filled circles). (b) Winter (September) sea ice fraction (mauve shading) and 15% concentration threshold (grey contour) from 1978 to 2013 satellite observations. (c) As in Figure 3b but for the simulated winter sea ice fraction from the Last Interglacial experiment that best agrees with the δ18O ice core data at 128 000 years ago, corresponding to Figure 3a. Filled circles in Figures 3 b and 3c show the reconstructed sea ice extent (sie) and summer sea surface temperature (SSST) estimates, categorized using sea ice proxy data from marine sediment cores, during the modern (Figure 3b) and the LIG (Figure 3c) sea ice minimum.

 

Marine sediment cores

Matthew Chadwick is a Phd student working on the project “Reconstructions of Antarctic sea-ice at the peak of the last interglacial (marine isotope stage 5e)”. The aim of the work is to get a picture for the extent of sea ice around Antarctica during the period 120 000-130 000 years before present, with a focus on the timing of the minimum extent and whether that minimum occurs synchronously or asynchronously around Antarctica. To do this Matthew will be using diatom species assemblages from marine sediment core records around Antarctica. The cores are chosen to be far enough south to hopefully pick up the edge of the winter sea ice.

Valve of the Eucampia antarctica diatom species. The abundance of this species is often used as an indicator of iron availability and the symmetry of the valve has been used to infer the SST.