LAST INTERGLACIAL (MIS 5E) HYDROGRAPHIC AND PRIMARY PRODUCTIVITY CONDITIONS IN COASTAL SOUTHERN CALIFORNIA BASED ON DINOFLAGELLATE CYSTS

The dinoflagellate cyst record from Ocean Drilling Program Hole 893A in Santa Barbara Basin (SBB), southern California, is examined at sub-millennial scale resolution ∼150-110 kyr. A qualitative and quantitative (modern analogue technique) approach utilizing dinoflagellate cyst abundance and assemblage composition changes is used to reconstruct and observe shifts in marine primary productivity and sea-surface salinity and temperature within the general context of climate and ocean circulation. The addition of dinoflagellate cyst data to the literature in the SBB resolves discrepancies for hydrological parameters previously reconstructed based on other microfossil and geochemical proxies, which provides greater detail into the evolution of interglacial periods and ocean stratification. Throughout the sequence, dinoflagellate cyst assemblages are dominated by the upwelling-related heterotrophic cysts of Brigantedinium spp., while changes in the relative abundances of thermophilic taxon Spinferites mirablis, cold water taxon Selenopemphix undulata, and oceanic taxa such as Impagidinium spp. and Operculodinium centrocarpum indicate the development of at least three intervals in the hydrological regime of MIS 5e.

Taxonomically, the presence of cysts of Protoperidinium americanum extends the first occurrence datum of the species beyond MIS 2. Non-reworked cysts of Hystrichokolpoma spp., a lineage thought to have disappeared in the lower Pleistocene, are also documented. The overall dinoflagellate cyst assemblage of MIS 5e is markedly different from the Holocene and the modern, which may indicate a poorer comparability towards its use as an analogue for future warming in the coastal Pacific, but the abundance of autotrophic and heterotrophic cysts are similar, offering a natural baseline and insight into the variability of interglacial conditions.