UTILIZING MICROFOSSIL COMMUNITY ECOLOGY TO UNDERSTAND SPATIAL AND TEMPORAL CHANGES IN THE SAN DIEGO MARGIN OXYGEN MINIMUM ZONE

Paleoecological records can be utilized to quantify ecological responses to changes in oceanography and climate, including changes to ocean oxygenation. Specifically, quantifying past expansions and contractions of the California margin oxygen minimum zone (OMZ) is critical for understanding and predicting future OMZ shifts in response to anthropogenic climate change. Associations between community ecology and modern hydrographic gradients can ground-truth the analysis of community paleoecology to reconstruct past ocean conditions. Here we analyze microfaunal assemblages across a vertical transect from the San Diego margin using two complementary methods: spatial analysis across a gradient of modern oxygenation and temporal analysis utilizing down-core sampling. Six sediment cores (15-35 cm in length) recovered from a vertical transect (85 m to 1200 m water depth) perpendicular to shore were collected and benthic community assemblages from core tops were analyzed. Two cores were age dated using 14C radiocarbon and age models of sedimentation were developed; complete down-core analysis of benthic communities was completed on these two cores. Benthic foraminifera across the OMZ spatial gradient revealed an inverse relationship between density and diversity. Multivariate statistical analyses of down-core records (past 2 ky) of upper OMZ (524 m water depth) core reveals two distinct cohorts of non-sequential communities, which indicate intradecadal and intracentennial variability in the upper boundary of the San Diego margin OMZ during the interval 180-1368 CE. Analyses of core-top metazoan microfossil assemblages across modern spatial hydrographic gradients allow for the definition of relationships between complete benthic community assemblages and in situ environment. These findings expand our understanding of community level response to changes in oxygenation.