RECENT PALEOCEANOGRAPHIC HISTORY OF THE SAN DIEGO MARGIN, CALIFORNIA: A BENTHIC FORAMINIFERAL PERSPECTIVE

Foraminiferal assemblages respond to changes in marine biogeochemistry and are widely used as biological proxies for oceanographic parameters. In this study, we compare modern marine conditions and recent environmental records within the same data set, in order to detail foraminiferal community response to oceanographic conditions. A set of sediment cores from a depth transect along the San Diego margin (7.5 km across; 86-1175 m below sea level; 32°48'36.00"N, 117°24'59.76"W) is utilized to explore how benthic foraminiferal assemblages respond to environmental variation across a continental margin and through a down-core record of the recent past. Two species of benthic foraminifera, Bolivina spp. and Uvigerina peregrina, reveal a complex response to a suite of hydrographic parameters, including temperature, dissolved oxygen, carbonate chemistry, and organic matter flux. Core-top samples showed proportional abundance of both species increasing as oxygen decreased. This trend continues into the oxygen minimum zone (OMZ), with Bolivina spp. as the dominant species in the upper margin of the OMZ. Both species decrease substantially with depth through the core of the OMZ. In order to understand recent changes along this margin in the context of these results, we then investigate a series of two short cores: MV1217-3-3 (700 m water depth; 20 cm length) and MV1217-2-3 (528 m water depth; 26 cm length). Located within the modern OMZ, site MV1217-3-3 exhibits limited variation in abundances, providing evidence for a stable OMZ over the past 2000 years. At the upper margin of the OMZ, variation in MV1217-2-3 abundances indicates vertical range fluctuations of low oxygen waters over the same time period. Evaluating oceanographic conditions over recent timescales via foraminiferal assemblages and geochemical data, as this study does, can provide a mechanism for predicting and interpreting the future alteration of significant environmental parameters like oxygenation.