A global mean sea-surface temperature dataset for the Last Interglacial (129–116 kyr) and contribution of thermal expansion to sea-level change

Abstract. A valuable analogue for assessing Earth’s sensitivity to warming is the Last Interglacial (LIG; 129–116 kyr), when global temperatures (0−+2 °C) and mean sea level (+6–11 m) were higher than today. The direct contribution of warmer conditions to global sea level (thermosteric) are uncertain. We report here a global network of LIG sea surface temperatures (SST) obtained from various published temperature proxies (e.g. faunal/floral assemblages, Mg/Ca ratios of calcareous plankton, alkenone UK’37). Each reconstruction is averaged across the LIG (anomalies relative to 1981–2010), corrected for ocean drift and with varying seasonality (189 annual, 99 December-February, and 92 June–August records). We summarise the current limitations of SST reconstructions for the LIG and the spatial temperature features of a naturally warmer world. Because of local δ18O seawater changes, uncertainty in the age models of marine cores, and differences in sampling resolution and/or sedimentation rates, the reconstructions are restricted to mean conditions. To avoid bias towards individual LIG SSTs based on only a single (and potentially erroneous) measurement or a single interpolated data point, here we average across the entire LIG. To investigate the sensitivity of the reconstruction to high temperatures, we also report maximum values during the first 5 ka of the LIG (129–124 kyr). The global dataset provides a remarkably coherent pattern of higher SST increases at polar latitudes than in the tropics, with comparable estimates between different SST proxies. We report mean global annual SST anomalies of 0.2 ± 0.1 °C and a maximum of 0.9 ± 0.2 °C respectively. Using the reconstructed SSTs suggests a mean thermosteric sea level rise of 0.01 ± 0.1 m and a maximum of 0.13 ± 0.1 m respectively. The data provide an important natural baseline for a warmer world, constraining the contributions of Greenland and Antarctic ice sheets to global sea level during a geographically widespread expression of high sea level, and can be used to test the next inter-comparison of models for projecting future climate change. The dataset described in this paper, including summary temperature and thermosteric sea-level reconstructions, are available at https://doi.org/10.1594/PANGAEA.904381 (Turney et al., 2019).