South Tasman Sea alkenone palaeothermometry over the last four glacial/interglacial cycles

Abstract

Alkenone palaeothermometry has demonstrated a wide spatial and temporal applicability for the reconstruction of sea-surface temperatures (SST). Some oceanic realms, however, remain poorly studied. We document U37K' index data for two sediment cores retrieved from the South Tasman Sea, one west of New Zealand (SO136-GC3) and the other southeast of Tasmania (FR1/94-GC3), extending back 280 kyr BP for the former and 460 kyr BP for the latter. High climatic sensitivity on orbital time scales is observed at both locations, particularly west of New Zealand, where typical glacial/interglacial SST amplitudes always span more than 7 °C. Southeast of Tasmania, SST amplitudes are lower in amplitude (4.3 to 6.9 °C) with the exception of Termination IV, which involved a SST change over 8 °C. The evolution of maximum glacial cooling through time is different at each location. Offshore New Zealand, maximum cooling during glacial stages increases with time, whereas south of Tasmania maximum cooling decreases with time. In addition, our data suggest heterogeneity in the spatial expression of SST during the penultimate and last glacial stages. These glacial periods are recorded differently in both areas, with Marine Isotopic Stage 6 being warmer than Marine Isotopic Stage 2 west of New Zealand, but slightly colder southeast of Tasmania. The area southwest of New Zealand appears susceptible to expansions and contractions of the Western Pacific Warm Pool and/or meridional migrations and changes in intensity of currents associated with the Tasman Front. The region southeast of Tasmania seems more sensitive to thermal changes as seen at high southern latitudes.