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




Over, Jin-Si R.J.

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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. Changes in cyst abundances, concentrations, diversity, and assemblages reflect climatic and ocean circulation changes, and are successfully used to make quantitative reconstructions of past sea surface temperatures and annual primary productivity with the modern analogue technique based on a dinoflagellate cyst database from the northeast Pacific. The dominance of heterotrophic dinoflagellate cyst taxa Brigantedinium spp. throughout most of the section indicates coastal upwelling is an important influence on the basin. Based on the dinoflagellate cyst assemblages, five cyst zones are identified and approximately correspond to the marine isotope stage boundaries and their associated changes in sea surface temperatures and sea level. Cooler intervals, MIS 6 and MIS 5d, are characterized by cold-water indicator species Selenopemphix undulata whereas thermophyllic taxon Spiniferites mirabilis characterizes MIS 5e. In contrast to other studies in the Pacific, the data shows 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 of heterotrophic and autotrophic taxa in the latest MIS 5e implies enhanced primary productivity as a result of 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 sea surface temperatures were higher than modern conditions. The quantitative reconstructions appear to be less reliable, and show wide sea surface temperature changes across MIS 6 to 5d (~6.2-10.7°C in February; ~12.6-20.3°C in August) similar to modern ranges, while annual primary productivity was confined to a higher narrower range (~456-586 g C m-2 yr-1).



paleoenvironments, climate, dinoflagellate cysts, Last interglacial, Santa Barbara, reconstruction