Preprints
https://doi.org/10.5194/gmd-2020-105
https://doi.org/10.5194/gmd-2020-105
Submitted as: model evaluation paper
 | 
29 Jul 2020
Submitted as: model evaluation paper |  | 29 Jul 2020
Status: this preprint was under review for the journal GMD. A final paper is not foreseen.

Evaluation of asymmetric Oxygen Minimum Zones in the tropical Pacific: a basin-scale OGCM-DMEC V1.0

Kai Wang, Xiujun Wang, Raghu Murtugudde, Dongxiao Zhang, and Rong-Hua Zhang

Abstract. The tropical Pacific Ocean holds the world’s two largest Oxygen Minimum Zones (OMZs), showing a prominent hemispheric asymmetry, with a much stronger and broader OMZ north of the equator. However, there is a lack of quantitative assessments of physical and biological regulations on the asymmetry of tropical Pacific OMZs. Here, we apply a fully coupled basin-scale model (OGCM-DMEC V1.0) to investigate the impacts of physical supply and biological consumption on the dynamics of OMZs in the tropical Pacific. We first utilize observational data to evaluate and improve our model simulation, and find that mid-depth DO is more sensitive to the parameterization of background diffusion. Enhanced background diffusion results in higher DO concentrations at mid-depth, leading to significant improvement of our model capability to reproduce the asymmetric OMZs. Our study shows that while physical supply of DO is increased in majority of the tropical Pacific due to enhanced background diffusion, there is little increase in the largest OMZ to the north. Interestingly, enhanced background diffusion results in lower rates of biological consumption over ~ 300–1000 m in the entire basin, which is associated with redistribution of dissolved organic matter (DOM). Our analyses demonstrate that weaker physical supply in the ETNP is the dominant process responsible for the asymmetric DO in the core OMZs (~ 200–600 m) while higher biological consumption to the north plays a larger role in regulating DO concentration beneath the OMZs (~ 600–800 m), with implication for the asymmetric OMZs. This study highlights the roles of physical supply and biological consumption in shaping the asymmetric OMZs in the tropical Pacific, underscoring the need to understand both physical and biological processes for accurate projections of DO variability.

This preprint has been withdrawn.

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Kai Wang, Xiujun Wang, Raghu Murtugudde, Dongxiao Zhang, and Rong-Hua Zhang

Interactive discussion

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Interactive discussion

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
Kai Wang, Xiujun Wang, Raghu Murtugudde, Dongxiao Zhang, and Rong-Hua Zhang

Model code and software

Sensitivity of asymmetric Oxygen Minimum Zones in the tropical Pacific: OGCM-DMEC V1.0 Kai Wang, Xiujun Wang, Raghu Murtugudde, Dongxiao Zhang, and Ronghua Zhang https://doi.org/10.5281/zenodo.3890689

Kai Wang, Xiujun Wang, Raghu Murtugudde, Dongxiao Zhang, and Rong-Hua Zhang

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Short summary
We improve and evaluate a basin-scale model’s ability to simulate spatial distribution of mid-depth oxygen in the tropical Pacific that holds the world’s two largest Oxygen Minimum Zones (OMZs). We find that low oxygen levels in the mid-ocean are largely due to extremely weak physical mixing, but the asymmetric OMZs (i.e., larger OMZ to the north) are attributable to both physical and biological processes, i.e., weaker physical supply over 200-600 m and higher biological consumption below 600 m.