Last interglacial and penultimate glacial sea surface temperature anomalies for the region south of 40°S, resampled to 2000 year resolution

Southern Ocean marine sediments provide an important archive of Quaternary glacial-interglacial climate changes. Sea surface temperature (SST) reconstructions in the Southern Ocean depend exclusively on the fossils or geochemical signatures of planktic organisms, but the strengths of these SST proxies remain poorly quantified in this region. To improve confidence in Southern Ocean paleoclimate reconstructions, we first evaluated the reliability of SST proxies employed at Quaternary glacial-interglacial time scales, focusing on three key potential problems: advection/dispersion, seasonality, and non-thermal influences. On that basis, we selected foraminifera assemblages, long-chain alkenones (UK'37 index), diatom assemblages, and the Globigerina bulloides Mg/Ca ratio as the most reliable SST proxies in the Southern Ocean. We also revised calibrations where appropriate, using core-top sediment databases. Overall, Southern Ocean SST reconstructions using these recommended proxies and calibrations should be robust when averaging across multiple sites and proxy types, but should be treated with caution when analysing spatial variability, a small number of sites, or a single proxy type. We have applied these recommendations to a synthesis of Southern Ocean SST over the penultimate glacial and last interglacial (LIG). Similar to previous studies, we find that LIG warming at 40°S to 60°S reached 1.6 ± 1.1°C (annual mean) or 1.9 ± 1.3°C (austral summer: JFM) relative to present. Annual / summer cooling in the penultimate glacial maximum reached -3.6 ± 1.0°C / -4.0 ± 1.2°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.