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

Abstract

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.

Methylation index of Overly Branched tetraether lipids (MOB): a proxy for deep ocean (de)oxygenation?

“…Given persistent low O2 conditions in the Cascadian Ridge region since 32,000 years ago (cf. Saravanan et al, 2020),…”

Reconstructing Paleo‐oxygenation for the Last 54,000 Years in the Gulf of Alaska Using Cross‐validated Benthic Foraminiferal and Geochemical Records

“…At ODP Site 1017, on the slope near Point Conception on the California margin, local productivity may have driven pore-water deoxygenation during the Bølling whereas incursion of low-oxygen intermediate waters may have contributed to dysoxia during the Allerød (Taylor et al, 2017). OMZ intensification on the Cascadia Margin also occurred during the B/A following a dramatic increase in primary productivity related to intense upwelling driven by changes in the California Undercurrent (McKay et al, 2005;Saravanan et al, 2020). High productivity has also been reported during the B/A in the Bering Sea and during the Allerød in the Okhotsk Sea (Max et al, 2014 NPIW extends to the eastern parts of the North Pacific and low-oxygen conditions in Okhotsk Sea Intermediate Water (OSIW) influence the GoA and the eastern North Pacific margin (Max et al, 2014;.…”

Enhanced Carbonate Dissolution Associated With Deglacial Dysoxic Events in the Subpolar North Pacific

“…North Pacific paleoceanographic records document increases in OMZ extent and intensification, particularly during the Bolling‐Allerod (B/A) and early Holocene, which correspond to intervals of abrupt warming (Belanger et al., 2020; Cannariato & Kennett, 1999; Davies et al., 2011; Jaccard & Galbraith, 2012; Moffitt et al., 2015; Ohkushi et al., 2013; Praetorius et al., 2015; Saravanan et al., 2020; Sharon et al., 2021; Shibahara et al., 2007; Zou et al., 2020). Proposed drivers of these low‐oxygen events include enhanced productivity and respiration of organic carbon at intermediate depths (Davies et al., 2011; Gray et al., 2018; Preatorius et al., 2015, 2020), which would not only reduce dissolved oxygen content, but could also promote dissolution via the production of carbonic acid during respiration (de Villiers, 2005; Boudreau & Canfield, 1993).…”