12:30 PM - 12:45 PM
★ [MIS34-11] Reconstruction of changes in marine primary productions by biomarker analysis of sediments from the Gulf of Cadiz during
Keywords:North Atlantic Ocean, Pliocene, MIS M2, Biomarker, Diatom, Mediterranean Outflow Water
We detect C27 to C29 sterols (eukaryotic algae biomarker), long-chain alkenones (haptophyte biomarker), dinosterol (dinoflagellate biomarker), and long-chain alkyl diols (eustigamatophyte and diatom biomarkers) from all studied samples. The C28 and C30 1,14-diols are known as Proboscia diatoms biomarker, while esutigmatophyte are assumed as the main origin of C28 and C30 1,13-diols and C30 1,15-diol in marine sediment. Recently, upwelling indices based on diol composition such as Diol Index 1 and 2 (DI1 and DI2) were proposed (e.g. Rampen et al., 2014). Concentrations of long-chain alkenones and C28 sterol to total organic carbon (TOC) increased at ca. 4.2 Ma. The C28 sterols were mainly composed of brassicasterol, which is the major sterol alkenone-producing haptophyte. Thus, these results suggest increase of haptophyte production. While, consecutive contourite sediment was found after 4.5–4.2 Ma. Hence, we cannot eliminate possibility that the increases of these biomarker concentrations are attributed to efficient preservation of sedimentary organic matter due to development of contourite depositional system. On the other hand, the 1,14-diol concentrations as well as DI1 and DI2 values increased during 3.4–3.2 Ma, which indicates high contributions of Proboscia diatom to marine production. Benthic foraminiferal δ18O records indicate that global climate was thought to be colder during 3.4–3.2 Ma even in the warm Pliocene epoch (Lisiecki and Raymo, 2005). Particularly, local maximum of foraminiferal δ18O values was observed at cold period of the MIS M2 (ca. 3.35–3.24 Ma). Thus, increases of diatom productions in the GoC might be explained by ocean and wind circulation changes caused by global cooling. Furthermore, sea surface temperature (SST) estimated in the IODP U1313 site (mid-latitudinal Atlantic Ocean) indicated that the North Atlantic Current (NAC) was weakened and glacial-like ocean circulation was established from 3.4 Ma to MIS M2 (Naafs et al., 2010). From these results, it is concluded that diatom productions increased as results of penetration of the AF into the GoC permitted by the glacial-like ocean circulation and enhanced vertical mixing during 3.4–3.2 Ma.