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

• Published in: Climate of the past Vol. 16; no. 1; pp. 387 - 407
• Main Authors: Zou, Jianjun, Shi, Xuefa, Zhu, Aimei, Kandasamy, Selvaraj, Gong, Xun, Lembke-Jene, Lester, Chen, Min-Te, Wu, Yonghua, Ge, Shulan, Liu, Yanguang, Xue, Xinru, Lohmann, Gerrit, Tiedemann, Ralf
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 20-02-2020; Copernicus Publications
• Subjects: Abyssal environment; Carbon cycle; Carbon dioxide; Carbon dioxide atmospheric concentrations; Carbon dioxide concentration; Carbon sequestration; Climate; Cold; Cold spells; Cold weather; Deep water; Deep water formation; Deoxygenation; Exports; Geochemistry; Groundwater; Ice formation; Interglacial periods; Intermediate water; Intermediate water masses; Intervals; Kuroshio Current; Oceanic ventilation; Oceans; Oscillations; Outgassing; Oxidoreductions; Oxygen; Oxygenation; Perturbation; Production management; Proxy; Salinity; Sea ice; Sea ice formation; Sea surface; Surface salinity; Trade winds; Tropical environments; Variation; Ventilation; Philippine Sea; China; Japan; Okinawa
• ISSN: 1814-9332; 1814-9324; 1814-9332
• DOI: 10.5194/cp-16-387-2020

The deep-ocean carbon cycle, especially carbon sequestration and outgassing,
is one of the mechanisms to explain variations in atmospheric CO2
concentrations on millennial and orbital timescales. However, the potential
role of subtropical North Pacific subsurface waters in modulating
atmospheric CO2 levels on millennial timescales is poorly constrained.
An increase in the respired CO2 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 CO2 sequestration at mid-depth waters, along
with the termination of atmospheric CO2 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.