Changes in Deep‐Sea Oxygenation in the Northeast Pacific Ocean During 32–10 ka

• Published in: Geophysical research letters 2020-06, Vol.47 (11), p.n/a
• Main Authors: Saravanan, Ponnusamy, Gupta, Anil K., Zheng, Hongbo, Rai, Santosh K., Panigrahi, Mruganka K.
• Format: Article
• Language: English
• Subjects: Benthos; Bølling‐Ållerød; Cascadia margin; Climate change; Climate variations; Environmental changes; Environmental conditions; Foraminifera; Global climate; Intermediate water; Intermediate water masses; Last Glacial Maximum; Nutrient cycles; Ocean circulation; Ocean currents; Oceans; Organic carbon; Oxygen; oxygen minimum zone; Oxygenation; Paleoclimate; Primary production; Productivity; Quaternary; Sediments; upwelling; Variation; Water circulation; Water currents
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2019GL086613

Climatic variations in the northeastern (NE) Pacific Ocean have been related to the strength of intermediate water‐driven productivity and global ocean circulation. Productivity variations and ocean circulation during the late Quaternary may have caused changes in the intensity of the oxygen minimum zone (OMZ). To understand these changes in productivity and resultant OMZ fluctuations, we analyzed benthic foraminiferal assemblages from the Cascadia margin which reveal major faunal and ecological shifts associated with the millennial‐scale climate changes during ~32–10 ka. The intermediate waters were highly variable during ~20–14 ka with increased productivity and nutrient supply to the subsurface during circa 15.5–14.5 ka. Our results suggest that suboxic environmental conditions occurred during the warm interstadials, and the Bølling‐Ållerød event was favorable for the dysoxic species. Our results further indicate that paleoclimate variations in the northeast Pacific region were mainly driven by the Pacific Intermediate Water Current. Plain Language Summary Deep‐sea environmental changes in the northeastern (NE) Pacific have been linked to the primary productivity and poorly ventilated intermediate water. This study aims at documenting the strength of the oxygen minimum zone (OMZ) on the Cascadia margin and its impact on marine biotic community as well as doing a comparison with results from the California margin. The Last Glacial Maximum (LGM) ranges from circa 23 to 18 ka in the proxy records of Cascadia margin sediments (Galbraith et al., 2007, https://doi.org/10.1038/nature06227). Our proxy record suggests weakening of the OMZ during the LGM and a strengthening during ~17–12 ka in response to global climate change. The Cascadia margin experienced intermediate to high organic carbon and low‐oxygen environment during the LGM as is noticeable in this study. The Pacific Intermediate Water was highly variable and productive during circa 15.5–14.5 ka. Our results suggest that paleoclimate variations in the NE Pacific Ocean region were mainly driven by the Pacific Intermediate Water Current. Key Points The Pacific Intermediate Water Circulation was highly variable between ~20 and 14 ka The OMZ strengthened during ~17–12 ka in the Cascadia margin The Bølling‐Ållerød interval is marked by high productivity on the slope off Vancouver Islands