New paper finds Antarctica had much less sea ice during the last interglacial

A paper published today in Climate of the Past finds Antarctic sea ice extent was much less than the present during the last interglacial period ~120,000 years ago. According to the authors, "During the last interglacial, the [sea ice proxy at 2 sites in Antarctica] are only half of the Holocene levels, in line with higher temperatures during that period, indicating much reduced sea ice extent in the Atlantic as well as the Indian Ocean sector of the Southern Ocean."

Prior research has also shown that Antarctic sea ice has markedly increased over past 7000 years since the Holocene Climate Optimum, when temperatures were significantly higher than the present. 

During the last interglacial, sea levels were 31 feet higher than the present, sea ice extent much less than the present, and Greenland was 8C warmer than the present, all with "safe" levels of CO2. There is no evidence the current interglacial is any different. 

Top graph shows temperature proxy from 2 drilling sites. Horizontal axis is thousands of years before the present. Temperatures were higher than the present during the interglacial ~120,000 years ago. Bottom 2 graphs show a proxy for Antarctic sea ice was only about half of Holocene levels. 

Clim. Past, 9, 2789-2807, 2013 www.clim-past.net/9/2789/2013/ doi:10.5194/cp-9-2789-2013 High-resolution mineral dust and sea ice proxy records from the Talos Dome ice core

S. Schüpbach^1,2,3, U. Federer^1,2, P. R. Kaufmann^1,2, S. Albani⁴, C. Barbante^3,5, T. F. Stocker^1,2, and H. Fischer^1,2
1Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland
²Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
³Environmental Sciences, Informatics and Statistics Department, University of Venice, Venice, Italy
⁴Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA
⁵Institute for the Dynamics of Environmental Processes – National Research Council, Venice, Italy

Abstract. In this study we report on new non-sea salt calcium (nssCa²⁺, mineral dust proxy) and sea salt sodium (ssNa⁺, sea ice proxy) records along the East Antarctic Talos Dome deep ice core in centennial resolution reaching back 150 thousand years (ka) before present. During glacial conditions nssCa²⁺ fluxes in Talos Dome are strongly related to temperature as has been observed before in other deep Antarctic ice core records, and has been associated with synchronous changes in the main source region (southern South America) during climate variations in the last glacial. However, during warmer climate conditions Talos Dome mineral dust input is clearly elevated compared to other records mainly due to the contribution of additional local dust sources in the Ross Sea area. Based on a simple transport model, we compare nssCa²⁺ fluxes of different East Antarctic ice cores. From this multi-site comparison we conclude that changes in transport efficiency or atmospheric lifetime of dust particles do have a minor effect compared to source strength changes on the large-scale concentration changes observed in Antarctic ice cores during climate variations of the past 150 ka. Our transport model applied on ice core data is further validated by climate model data.

The availability of multiple East Antarctic nssCa²⁺ records also allows for a revision of a former estimate on the atmospheric CO₂sensitivity to reduced dust induced iron fertilisation in the Southern Ocean during the transition from the Last Glacial Maximum to the Holocene (T1). While a former estimate based on the EPICA Dome C (EDC) record only suggested 20 ppm, we find that reduced dust induced iron fertilisation in the Southern Ocean may be responsible for up to 40 ppm of the total atmospheric CO₂ increase during T1. During the last interglacial, ssNa⁺ [sea ice proxy] levels of EDC and EPICA Dronning Maud Land (EDML) are only half of the Holocene levels, in line with higher temperatures during that period, indicating much reduced sea ice extent in the Atlantic as well as the Indian Ocean sector of the Southern Ocean. In contrast, Holocene ssNa⁺ flux in Talos Dome is about the same as during the last interglacial, indicating that there was similar ice cover present in the Ross Sea area during MIS 5.5 as during the Holocene.