The carbon sink of the Coral Sea, the world's second largest marginal sea, weakened during 2006-2018

Siqi Zhang; Yan Bai; Xianqiang He; Shujie Yu; Zigeng Song; Fang Gong; Qiankun Zhu; Delu Pan

doi:10.1016/j.scitotenv.2023.162219

The carbon sink of the Coral Sea, the world's second largest marginal sea, weakened during 2006-2018

Sci Total Environ. 2023 May 10:872:162219. doi: 10.1016/j.scitotenv.2023.162219. Epub 2023 Feb 13.

Authors

Siqi Zhang¹, Yan Bai², Xianqiang He³, Shujie Yu³, Zigeng Song⁴, Fang Gong⁵, Qiankun Zhu⁵, Delu Pan⁶

Affiliations

¹ State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China; State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China; University of Chinese Academy of Sciences, Beijing, China.
² State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China; School of Oceanography, Shanghai Jiao Tong University, Shanghai, China. Electronic address: baiyan@sio.org.cn.
³ State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China; Ocean College, Zhejiang University, Zhoushan, China.
⁴ State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China; College of Oceanography, Hohai University, Nanjing, China.
⁵ State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China.
⁶ State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China; State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China.

PMID: 36791862
DOI: 10.1016/j.scitotenv.2023.162219

Abstract

The latest reports show that the ocean absorbs approximately 26 % of anthropogenic CO₂ and that the carbon sink of the global ocean (air-sea CO₂ flux) is continually increasing, while variations in different marginal seas are complicated. The Coral Sea, the second largest marginal sea in the world, is characterized by a generally oligotrophic basin and borders the biodiversity hotspot of Great Barrier Reef. In this study, we proposed a semianalytical method and reconstructed the first high-resolution satellite-based pCO₂ and air-sea CO₂ flux dataset from 2006 to 2018 for the Coral Sea. This dataset performed well in the basin (RMSE<10 μatm, R² > 0.72) and coral reef areas (RMSE<12 μatm, R² > 0.8) based on validation by a massive independent dataset. We found that sea surface pCO₂ is increasing (1.8 to 2.7 μatm/year) under the forcing of increasing atmospheric CO₂, and the pCO₂ growth rate in water is faster than that in the atmosphere. The combination of increasing sea surface pCO₂, high pCO₂ seawater from coral reef areas, and the low depletion capacity of the oligotrophic basin led to a gradual weakening of the carbon sink in the Coral Sea, with the 2016 carbon sink being 52 % of that in 2006. This weakening was more pronounced after strong El Niño events (e.g., 2007, 2010, and 2016), with the corresponding high SST and low wind speed further weakening the carbon sink. This understanding of the long-term change in the Coral Sea provides new insight on the carbonate system variation and carbon sink capacity evolution in seawater under increasing atmospheric CO₂.

Keywords: Air–sea CO(2) flux; Carbonate system; Coral Sea; Long time series variation; Remote sensing inversion.