Reconstruction of past shifts in the position of the subtropical front South of New Zealand since the last glacial period

Abstract

The Subtropical Front (STF) separates warm and saltier subtropical waters from the cold, less saline and nutrient-rich subantarctic waters of the Southern Ocean. Changes in the latitudinal position of the STF are thought to be crucial for the global climate system but past migrations of the STF are not always well constrained due to the insufficient spatial resolution covered by paleorecords. Three marine cores were recovered south of New Zealand, along a latitudinal transect crossing the modern STF position. We are analysing long chain alkenones, as markers of coccolithophore productivity and past sea surface temperatures, and also n-alkanes and n-alcohols, as proxies for continental input. Preliminary results show a 3-4°C temperature gradient during the Holocene between the core locations, while during the last glacial period no temperature gradient existed, with a consistent 8-9°C recorded at all three sites. This suggests a northward displacement of the STF during the cold glacial climate and the prevalence of subantarctic waters at the core sites. The SST evolution will also be compared with changes in past productivity and the input of continental material