Oxygenation and ventilation of Southern CA marine basins through the Holocene: evidence from benthic microfossil assemblages and foraminiferal oxygen and carbon stable isotope records

Hannah M Palmer, University of California, Davis, Earth and Planetary Sciences and Bodega Marine Laboratory, Bodega Bay, United States, Tessa M Hill, University California Davis, Earth and Planetary Sciences and Bodega Marine Laboratory, Davis, CA, United States, Prof. Lowell D Stott, PhD, University of Southern California, Los Angeles, CA, United States, Peter D Roopnarine, California Academy of Sciences, Department of Invertebrate Zoology & Geology, Institute for Biodiversity Science and Sustainability, San Francisco, CA, United States and Dorothy K Pak, University of California Santa Barbara, Marine Science Institute, Santa Barbara, CA, United States
Abstract:
Silled basins provide a natural laboratory in which we can constrain timing and implications of changes to intermediate water ventilation. Benthic foraminifera and microfossil metazoan assemblages can be utilized both as proxies for past change, using known environmental associations, including oxygen affinity, as well as examined ecologically in conjunction with geochemical environmental reconstructions. Investigation of intermediate water ventilation through the Holocene is critical to providing baselines for modern change and for understanding scales of variability within the recent past. This study provides a needed comparison to the well-studied Santa Barbara Basin to better quantify changes in intermediate water through the Holocene. Here, we quantify benthic foraminiferal and metazoan assemblages in three sediment cores, EW9504-05PC (San Clemente Basin, 1818 m water depth), EW9504-08PC (San Nicolas Basin, 1442 m water depth), and EW9504-09PC (Tanner Basin, 1194 m water depth) and generate a new, higher resolution stable carbon and oxygen isotope record from planktonic foraminifera Globigerina bulloides and benthic foraminifera Cibicides mckannai. Age models for all cores are radiocarbon based and include 2 age dates per core in the Holocene. Preliminary analysis of individual C. mckannai from coretop sediments show consistent oxygen and carbon isotope values between individuals, verifying their utility as records of benthic environment through time. Oxygen isotope analysis of G. bulloides from core EW 9504-09PC (Tanner Basin, 1194 m) shows stable sea surface conditions from 4.5 to 1.5 ky (δ18O = -.015 - 0.41 ‰) and a transition to colder/saltier sea surface from 1.5 - 1 ky (δ18O = 0.95 - 1.3 ‰). Relative abundance of two benthic foraminiferal taxa Bolivina spissa (low-oxygen associated) and Quinqueloculina sp. (high oxygen associated) is stable through time (10ka-0) in the core from San Nicolas Basin while highly variable during the same time period at Tanner Basin. This may indicate that Tanner Basin (1194m) experiences greater temporal variability in oxygenation than San Nicolas Basin (1442 m).
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