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Abstract Reconstructing the strength and depth boundary of oxygen minimum zones (OMZs) in the glacial ocean advances our understanding of how OMZs respond to climate changes. While many efforts have inferred better oxygenation of the glacial Arabian Sea OMZ from qualitative indices, oxygenation and vertical extent of the glacial OMZ is not well quantified. Here we present glacial‐Holocene oxygen reconstructions in a depth transect of Arabian Sea cores ranging from 600 to 3,650 m water depths. We estimate glacial oxygen concentrations using benthic foraminiferal surface porosity and benthic carbon isotope gradient reconstructions. Compared to the modern Arabian Sea, glacial oxygen concentrations were approximately 10–15 μmol/kg higher in the shallow OMZ (<1,000 m), and 5–80 μmol/kg lower at greater depths (1,500–3,650 m). Our results suggest that the OMZ in the glacial Arabian Sea was slightly better oxygenated but remained in the upper 1,000 m. We propose that the small increase in oxygenation of the Arabian Sea OMZ during the last glacial period was due to weaker upper ocean stratification induced by stronger winter monsoon winds coupled with an increase in oxygen solubility due to lower temperatures, counteracting the effects of more oxygen consumption resulting from higher primary productivity. Large‐scale changes in ocean circulation may have also contributed to better ventilation of the glacial Arabian Sea OMZ.
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Ecological and Environmental Stability in Offshore Southern California Marine Basins Through the Holocene
Abstract 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 and environmental change over time using benthic foraminiferal assemblages from sediment cores from three basins across the Southern California Borderlands: Tanner Basin (EW9504‐09PC, 1,194 m water depth), San Nicolas Basin (EW9504‐08PC, 1,442 m), and San Clemente Basin (EW9504‐05PC,1,818 m). We utilize indicator taxa, community ecology, and an oxygenation transfer function to reconstruct past oxygenation, and we 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. Geochemical and assemblage data indicate limited ecological and environmental change through time in each basin across the intervals studied. Early to mid‐Holocene (11.0–4.7 ka) oxygenation below 1,400 m (San Clemente and San Nicolas) was relatively stable and reduced relative to modern. San Nicolas Basin experienced a multi‐centennial oxygenation episode from 4.7 to 4.3 ka and oxygenation increased in Tanner Basin gradually from 1.7 to 0.8 ka. 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.
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- Award ID(s):
- 1832828
- PAR ID:
- 10376550
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Paleoceanography and Paleoclimatology
- Volume:
- 37
- Issue:
- 8
- ISSN:
- 2572-4517
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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