The Subtropical Front (STF) separates warm and saltier subtropical waters from the cold, less saline and nutrient-rich subantarctic waters of the Southern Ocean. Determining its past north-south movements is crucial, for instance, to understand the role of such frontal systems on ocean productivity of the subantarctic region, as opposed to increased Fe availability. Three marine cores were recovered south of New Zealand, along a latitudinal transect crossing the modern STF. We have analysed long chain alkenones, as markers of coccolithophore productivity and past sea surface temperatures, n-alkanes and n-alcohols, as proxies for continental input and dust-derived iron and long chain diols as tracers of diatom productivity. Reconstructed SST changes 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 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, between 47 and 50.5°S. An increased productivity and continental input during the glacial and early deglaciation suggest that both Fe fertilization and equatorward migration of fronts likely drove the biological productivity of the region. The SST evolution will also be complemented with a temperature reconstruction based on the relative distribution of isoprenoid GDGTs, the TEXH86 index, which in this region, we believe may record deeper temperatures than coccolithophores

5th Past Global Changes (PAGES) Ocean Sciences Meeting, 9-13 May 2017, Zaragoza

Peer Reviewed