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Oxygenation of offshore Southern California marine basins through the Holocene
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  • Hannah M Palmer,
  • Tessa M Hill,
  • Esther Kennedy,
  • Peter D Roopnarine,
  • Sonali Langlois,
  • Katherine Reyes,
  • Lowell Stott
Hannah M Palmer
University of California, Davis, University of California, Davis

Corresponding Author:hmpalmer@ucdavis.edu

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Tessa M Hill
University of California, Davis, University of California, Davis
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Esther Kennedy
University of California Davis, University of California Davis
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Peter D Roopnarine
California Academy of Sciences, California Academy of Sciences
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Sonali Langlois
Santa Rosa Junior College, Santa Rosa Junior College
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Katherine Reyes
Dominican University of California, Dominican University of California
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Lowell Stott
University of Southern California, University of Southern California
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In the face of ongoing marine deoxygenation, understanding timescales and drivers of past oxygenation change is of critical importance. Marine sediment cores from tiered silled basins provide a natural laboratory to constrain timing and implications of oxygenation changes across multiple depths. Here, we reconstruct oxygenation change over time using benthic foraminiferal assemblages from three sediment cores, EW9504-09PC (Tanner Basin, 1194 m water depth), EW9504-08PC (San Nicolas Basin, 1442 m), and EW9504-05PC (San Clemente Basin, 1818 m) across the Southern California Borderlands. We utilize indicator taxa, community ecology, and an oxygenation transfer function to reconstruct past oxygenation, and directly compare reconstructed dissolved oxygen to modern measured dissolved oxygen. We generate new, higher resolution carbon and oxygen isotope records from planktic (Globigerina bulloides) and benthic foraminifera (Cibicides mckannai) from Tanner Basin. Early to mid-Holocene (11.2-4.7 ka) oxygenation below 1400 m (San Clemente and San Nicolas Basins) was relatively stable and reduced relative to modern. San Nicolas Basin experienced a multi-centennial oxygenation episode from 4.7-4.2 ka and oxygenation increased in Tanner Basin gradually from 5.5-1.9 ka. Oxygenation of these offshore basins is synchronous with an increase in oxygenation in Santa Barbara Basin at ~6 ka and may be due to increased oxygenation of North Pacific Intermediate Water. Yet across all three depths and time intervals studied, dissolved oxygen is consistently within a range of intermediate hypoxia (0.5-1.5 ml L-1 O2). Variance in reconstructed dissolved oxygen was similar to decadal variance in modern dissolved oxygen and reduced relative to Holocene-scale changes in shallower basins.