Millennial-scale variations in sedimentary oxygenation in the western subtropical North Pacific and its links to North Atlantic climate

Abstract

The deep-ocean carbon cycle, especially carbon sequestration and outgassing, is one of the mechanisms to explain variations in atmospheric CO 2 concentrations on millennial and orbital timescales. However, the potential role of subtropical North Pacific subsurface waters in modulating atmospheric CO 2 levels on millennial timescales is poorly constrained. An increase in the respired CO 2 concentration in the glacial deep-ocean due to biological pump generally corresponds to deoxygenation in the ocean interior. This link thus offers a chance to study oceanic ventilation and coeval export productivity based on redox-controlled sedimentary geochemical parameters. Here, we investigate a suite of geochemical proxies in a sediment core from the Okinawa Trough to understand sedimentary oxygenation variations in the subtropical North Pacific over the last 50 000 years (50 ka). Our results suggest that enhanced mid-depth western subtropical North Pacific (WSTNP) sedimentary oxygenation occurred during cold intervals and after 8.5 ka, while oxygenation decreased during the Bölling-Alleröd (B/A) and Preboreal. The enhanced oxygenation during cold spells is linked to the North Pacific Intermediate Water (NPIW), while interglacial increase after 8.5 ka is linked to an intensification of the Kuroshio Current due to strengthened northeast trade winds over the tropics. The enhanced formation of the NPIW during Heinrich Stadial 1 (HS1) was likely driven by the perturbation of sea ice formation and sea surface salinity oscillations in the high-latitude North Pacific. The diminished sedimentary oxygenation during the B/A due to a decreased NPIW formation and enhanced export production, indicates an expansion of the oxygen minimum zone in the North Pacific and enhanced CO 2 sequestration at mid-depth waters, along with the termination of atmospheric CO 2 concentration increase. We attribute the millennial-scale changes to an intensified NPIW and enhanced abyss flushing during deglacial cold and warm intervals, respectively, closely related to variations in North Atlantic Deep Water formation.

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

“…Ohkushi et al, 2013) and with a well-ventilated interval in the Okhotsk Sea (Max et al, 2014; and Okinawa Trough (Zou et al, 2020). During the YD, intermediate depths on the eastern and western Pacific margins were also better-oxygenated (K. G. Max et al, 2014;McKay et al, 2005;Taylor et al, 2017;Tetard et al, 2017;Zou et al, 2020). This relaxation of severe low-oxygen conditions is consistent with enhanced NPIW ventilation during the YD suggested by records near Hokkaido, Japan (Ivanochko & Pedersen, 2004;Shibahara et al, 2007).…”

“…For example, increased oxygenation during HS1 in our record (17-15 ka, BDO > 0.99 ml/L) coincides with oxygenation >1.5 ml/L SBB (K. G. K. Ohkushi et al, 2013) and with a well-ventilated interval in the Okhotsk Sea (Max et al, 2014; and Okinawa Trough (Zou et al, 2020). During the YD, intermediate depths on the eastern and western Pacific margins were also better-oxygenated (K. G. Max et al, 2014;McKay et al, 2005;Taylor et al, 2017;Tetard et al, 2017;Zou et al, 2020).…”

“…A similarly timed low-oxygen event occurred near Vancouver Island from ∼11-10 ka, potentially driven by decreased ventilation and increased productivity (McKay et al, 2005). In addition, dysoxic foraminifera increased in abundance during the early Holocene along the California margin to Baja California and in the western subtropical North Pacific (K. Tetard et al, 2017;Zou et al, 2020), suggesting this low-oxygen event was also widespread. After this early Holocene deoxygenation, suboxic conditions dominate the remainder of our GoA record as evinced by generally higher DCA Axis 1 scores and lower BDO estimates (0.55-0.80 ml/L).…”

Delayed Collapse of the North Pacific Intermediate Water After the Glacial Termination

“…Water mass of the NPIW mainly intrudes into the Okinawa Trough through the channel east of Taiwan and the Kerama Gap, and then upwells in the northern Okinawa Trough (Nakamura et al., 2013; Nishina et al., 2016) (Figures 1a–1c). Millennial‐scale NPIW variations during the last glacial and deglacial has been investigated through changes of the ocean ventilation and export productivity in the Okinawa Trough based on the redox‐controlled sedimentary geochemical parameters and productivity proxy, respectively (Dou et al., 2015; Li et al., 2017; Zou et al., 2020), suggesting a sensitive response of oceanic processes in this region to the NPIW evolution. Here we provided two authigenic uranium (aU) records calculated based on the Natural gamma radiation (NGR) results measured by NGR Logger on the ocean drilling research vessel DV JOIDES Resolution and shore‐based trace element analysis, respectively, from the Integrated Ocean Drilling Program (IODP) Site U1429 sediments in the northern Okinawa Trough (Figure 1), to reconstruct the local oceanic redox conditions and further NPIW evolution through the last 400 ka.…”

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).…”