Sea surface temperature and subtropical front movement in the South Tasman Sea during the last 800 ka

Abstract

Hemisphere mid-latitude westerlies contribute to the ventilation of the deep Southern Ocean (SO), and drive changes in atmospheric carbon dioxide (CO2) and the global climate. As the westerlies control directly oceanic fronts, the movement of the subtropical front (STF) reflects the westerlies migration. Thus it is important to understand the relationships between STF movement and the weaterlies, ventilation of the deep SO, ice volume and atmospheric CO2. To this end, we use two new high-resolution records from early Marine Isotope Stage (MIS) 20 (∼800 ka) of sea surface temperature (SST) based on U37k’ paleo-thermometer and benthic oxygen isotope (δ18OB) at Ocean Drilling Program (ODP) Site 1170B in the southern Tasman Sea (STS), to construct linkages between the marine records and atmospheric proxies from Antarctic ice-cores. During the last 800 ka, the average SST (10.2°C) at Site 1170B is 1.8°C lower than today (annual average 12°C). The highest average SST of 11.6°C occurred during MIS 1, and the lowest average SST of 7.8°C occurred during MIS 2. The warmest and coldest records of 14.7°C and 6.2°C occurred in the MIS 5 and MIS 2, respectively. In the glacial-interglacial cycles of the last 800 ka, variability of reconstructed SST shows that the STF moved northward or southward more than 3° of latitude compared with its present location. In the warmest stage MIS 5, the STF shifted to its southernmost location of ∼49°S. In contrast, in the coldest stage MIS 2, the STF moved to its northernmost location of ∼43°S. In response to orbital cycles, the westerlies movement led ice volume and atmospheric CO2 changes, but it was in phase with change in Antarctic atmospheric temperature. Ice volume only preceded atmospheric CO2 only a little at the 23-ka precession band, lagged the atmospheric CO2 at the 100-ka eccentricity band, and was in phase with atmospheric CO2 at the 40-ka obliquity band.