LATE PLEISTOCENE OSTRACOD RESPONSES TO MILLENNIAL CLIMATE EVENTS OF DEOXYGENATION AND SEA LEVEL RISE IN THE CALIFORNIA BORDERLAND

Ostracod community diversity from a shallow continental margin sediment core (MV0811-15JC, 418 meters water depth) from Santa Barbara Basin, California, provides evidence for millennial-scale changes in seafloor environments from 16.1–3.4 ka. Previously, late Pleistocene sequences described from this margin record millennial-scale episodes of deoxygenation, habitat compression, and chemosynthesis associated with climatic warming. Here we identify 20 ostracod taxonomic groups, mainly at the generic level over the last deglacial that exhibit changes in density, diversity, and community similarity. We compare these with changes in foraminiferal and molluscan assemblages earlier documented in core MV0811-15JC. Multivariate statistical approaches help identify relative similarity between ostracod communities, and those species that most strongly determine community similarity and dissimilarity. Pre-Termination IA ostracod assemblages are diverse and abundant and are marked by cryophilic and cosmopolitan deep-water species (Argilloecia sp., Loxoconchidea spp., Cytheropteron spp.), many of which have previously been reported in Bering and Okhotsk Sea glacial sediments. Bølling-Allerød sequences are depauperate and are followed by Younger Dryas ostracod assemblages that are compositionally mixed with both deep and shallow-water, and phytal taxa. A dominance of shallow-water, margin taxa in the Younger Dryas, despite deepening due to deglacial sea level rise, suggest the assemblages resulted from downslope reworking and are not in situ. In contrast, Middle Holocene are dominated by phytal, shallow water taxa (Aurila spp.) in association with chemosynthetic trophic webs and related molluscan bacterivores. This record of millennial-scale successional patterns enrich paleoecological reconstructions of the California Borderlands and challenge existing environmental attributions of ostracod taxa in relation to latitudinal and bathymetric environments.