Journal Article

Dissolved Oxygen Recovery in the Oxygen Minimum Zone of the Arabian Sea in Recent Decade as Observed by BGC‐Argo Floats

Qiu, Yun, Jing, Chunsheng, Lin, Xinyu, Liu, Tongtong, Ni, Xutao, Wang, Lei, Li, Hongliang

2024

Overview

The Arabian Sea (AS) hosts the world's thickest and most intense oxygen minimum zone (OMZ), and previous studies have documented a dramatic decline of dissolved oxygen (DO) in the northeastern AS in recent decades. In this study, using the recently released data from Biogeochemical‐Argo floats, we found a surprising trend of recovery in deoxygenation within the core region of the OMZ in the AS (ASOMZ) since 2013. The average DO concentration increased by approximately threefold, from ∼0.63 μM in 2013 to ∼1.68 μM in 2022, and the thickness of the ASOMZ decreased by 13%. We find that the weakening of Oman upwelling resulting from the weakening of the summer monsoon is the main driver of oxygenation in the ASOMZ. In addition, the reduction of primary production linked to warming‐driven stratification reinforces deoxygenation recovery at depth. Plain Language Summary The deoxygenation of the ocean is one of the most important changes occurring in the marine environment, impacting marine biodiversity, primary production, and carbon and nitrogen biogeochemical cycles. Ocean deoxygenation can cause the expansion of naturally occurring low dissolved oxygen (DO) water bodies known as OMZs. As the world's thickest and most intense oxygen minimum zone (OMZ), the Arabian Sea (AS) has undergone a dramatic decrease in DO, particularly in the northeastern AS in recent decades. Based on an unprecedented collection of DO from biogechemical‐Argo floats over the past decade, we found a surprising trend of recovery in deoxygenation within the core region of the OMZ in the AS (ASOMZ) since 2013. The average DO concentration in the ASOMZ increased by almost thrice, and the thickness decreased by 13%. Weakening of the summer monsoon over the AS and strengthening of stratification induced by global warming are possible causes for the recovery from deoxygenation. OMZs have major impacts on global carbon and nitrogen cycles. Our findings not only overturn the previous view of the deoxygenation trend in the ASOMZ but also provide valuable insights for projection model studies of global OMZs. Key Points Deoxygenation in the oxygen minimum zone in the Arabian Sea has been recovered during the past decade The decrease in Oman upwelling due to the weakening of the summer monsoon is likely the main mechanism for the increase in dissolved oxygen The strengthening of stratification in the AS leading to a decrease in production also contributed to the recovery of deoxygenation

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Biodiversity / Biogeochemical cycle / Biogeochemical cycles / Biogeochemistry / Carbon / Carbon cycle / Climate change / Deoxygenation / Dissolved oxygen / Drifters / Floats / Global warming / Marine environment / Monsoons / Nitrogen / Nitrogen cycle / Ocean circulation / Oceans / Overturn / Oxygen / oxygen minimum zone / Oxygenation / Primary production / Projection model / Recovery / southwestern monsoon / Stratification / Summer / Summer monsoon / the Arabian Sea / Thickness / Upwelling