Southern Ocean sea surface temperature synthesis: Part 2. Penultimate glacial and last interglacial

The last interglacial (LIG: similar to 130 to 115 thousand years before present) is often used as an analogue for near-future climate warming. Antarctic Ice Sheet response to LIG warming is of particular interest, because of its implications for sea level rise. Comparison between LIG climate simulations and proxy-based reconstructions of Southern Ocean sea surface temperature (SST) remains challenging, due to high uncertainties in both reconstructions and simulations. In this two-part study, the accompanying paper (Part 1) addressed uncertainties in the SST reconstructions by evaluating proxies relevant to Southern Ocean SST, and made recommendations for which proxies and respective calibrations are most reliable on glacial-interglacial time scales in this region. In the second part (this paper), we now apply these recommendations to a synthesis of Southern Ocean SST over the penultimate glacial and LIG. Similar to previous studies, we find that LIG warming at 40 degrees S to 60 degrees S reached 1.6 +/- 1.1 degrees C (annual mean) or 1.9 +/- 1.3 degrees C (austral summer: JFM) relative to present. Annual/summer cooling in the penultimate glacial maximum reached -3.6 +/- 1.0 degrees C/-4.0 +/- 1.2 degrees C, similar to the last glacial maximum. Compared with the previous LIG SST syntheses, our reported uncertainties more strongly reflect geographic variability and dating errors, as we have reduced errors in the individual temperature reconstructions and do not date records by aligning peaks in their SST. However, the reconstruction errors are still important, and we do not recommend detailed interpretation of temperature records from small numbers of sites. Instead, comparisons of our new synthesis with model simulations should focus only on the regional average. (C) 2021 The Author(s). Published by Elsevier Ltd.