Preprints
https://doi.org/10.5194/bg-2021-145
https://doi.org/10.5194/bg-2021-145

  18 Jun 2021

18 Jun 2021

Review status: this preprint is currently under review for the journal BG.

Episodic subduction patches in the western North Pacific identified from BGC-Argo float Data

Shuangling Chen1, Mark L. Wells2,1, Rui Xin Huang3, Huijie Xue2, Jingyuan Xi1, and Fei Chai1,2 Shuangling Chen et al.
  • 1State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China
  • 2School of Marine Sciences, University of Maine, Orono, ME, USA
  • 3Woods Hole Oceanographic Institution, Woods Hole, MA, USA

Abstract. Subduction associated with mesoscale eddies is an important but difficult to observe process that can efficiently export carbon and oxygen to the mesopelagic zone (100–1000 db). Using a novel BGC-Argo dataset covering the western North Pacific (20–50° N, 120–180° E), we identified imprints of episodic subduction using anomalies in dissolved oxygen and spicity, a water mass marker. These subduction patches were present in 4.0 % (288) of the total profiles (7,120) between 2008 and 2019, situated mainly in the Kuroshio Extension region between March and August (70.6 %). Unlike eddy subduction processes observed at higher latitudes, roughly half (52 %) of these episodic events injected carbon- and oxygen-enriched waters below the annual permanent thermocline depth (450 db), with > 20 % occurring deeper than 600 db. Export rates within these subductions are estimated to be on the order of 85–159 mg C m−2 day−1 and 175 to 417 mg O2 m−2 day−1. These mesoscale events would markedly increase carbon removal above that due to biological gravitational settling as well as oxygen ventilation in the region, both helping to support the nutritional and metabolic demands of mesopelagic organisms. Climate-driven patterns of increasing eddy kinetic energies in this region imply that the magnitude of these processes will grow in the future, meaning that these unexpectedly effective small-scale subduction processes need to be better constrained in global climate and biogeochemical models.

Shuangling Chen et al.

Status: open (until 07 Aug 2021)

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Shuangling Chen et al.

Shuangling Chen et al.

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Short summary
Subduction transports surface waters to the oceanic interior, which can supply significant amounts of carbon and oxygen to the twilight zone. Using a novel BGC-Argo dataset covering the western North Pacific, we successfully identified the imprints of episodic shallow subduction patches. These subduction patches were observed mainly in spring and summer (70.6 %), and roughly half of them extended below ~450 m, injecting carbon- and oxygen-enriched waters into the ocean interior.
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