Last Interglacial (MIS 5e) sea surface hydrographic conditions in coastal southern California based on dinoflagellate cysts

Abstract

The first high resolution record of dinoflagellate cysts ∼110–155 kyr over Termination II and the Last Interglacial in the Santa Barbara Basin, California from ODP Hole 893A details a complex paleoceanographic history. Variation in cyst relative abundances, concentrations, and diversity reflects climatic and ocean circulation changes, and the assemblages are used to make qualitative reconstructions of sea surface temperature (SST) and annual primary productivity. The dominance of heterotrophic Brigantedinium spp. throughout the section indicates an important influence of coastal upwelling on the basin. Based on the dinoflagellate cyst assemblages, five zones are identified, which approximately correspond to the marine isotope stage boundaries and their associated changes in SST and sea level. Cooler intervals, MIS 6 and MIS 5d, are characterized by cold-water indicator species Selenopemphix undulata whereas thermophilic taxon Spiniferites mirabilis characterizes a warm MIS 5e. In contrast to other studies in the Pacific, the data exhibits a one to two-thousand-year cooling event ∼129 kyr that correlates to the Termination II sea level still-stand of the two-step deglaciation. A significant increase in cyst concentrations in the latest MIS 5e implies enhanced primary production due to increased seasonal upwelling and the warm, nutrient rich waters entering the basin after sea level stabilizes near modern levels. The hydrological evolution and cyst signal of the Last Interglacial is similar to the development of the Holocene in the Santa Barbara Basin, but the sustained presence of Spiniferites mirabilis across MIS 5e indicates SSTs were higher than modern conditions. • First high resolution dinocyst study in temperate northeastern Pacific during MIS5e. • SST, upwelling, and sea-level changes drive dinocyst variation in the SBB. • Spiniferites mirabilis and Selenopemphix undulata are best indicators of SST change. • Dinocyst paleoecology consistent with previous geochemical and palynology signals. • Termination II and MIS5e dinocyst assemblages are comparable to Holocene SBB cysts.