Significant methane undersaturation during austral summer in the Ross Sea (Southern Ocean)

• Main Authors: Ye, Wangwang, Bange, Hermann W., Arévalo-Martínez, Damian L., He, Hailun, Li, Yuhong, Wen, Jianwen, Zhang, Jiexia, Liu, Jian, Wu, Man, Zhan, Liyang
• Format: Text
• Language: English
• Published: 2022
• Subjects: Austral; Ross Sea; Southern Ocean; Sea ice
• Online Access: https://doi.org/10.5194/bg-2021-334; https://bg.copernicus.org/preprints/bg-2021-334/

Dissolved methane (CH 4 ) was measured at 9 stations along a transect at 75° S in the Ross Sea during austral summer in January 2020. CH 4 undersaturation (mean: 82 ± 20 %) was found in the water column, with a mean air-sea CH 4 flux density of −0.58 ± 0.48 μmol m −2 day −1 , which suggests that the Ross Sea was a net sink for atmospheric CH 4 during the austral summer. Simple box-model calculations revealed that the CH 4 depletion should occur in the surface mixed layer because of CH 4 oxidation and advection of CH 4 -poor waters. We propose that freshwater injection caused by sea-ice melting in summer dilutes CH 4 concentrations within the surface layer and thus increases its potential for atmospheric CH 4 uptake in the Ross Sea. Thus, we argue that both CH 4 consumption and sea-ice melting are important drivers of CH 4 undersaturation, which implies that the high-latitude area of the Southern Ocean is a sink for atmospheric CH 4 . We estimated that the Southern Ocean (> 65° S) takes up about 0.02 % of the global CH 4 emissions and thus represents a minor sink for atmospheric CH 4 .