[A-OS13] Marine ecosystems and biogeochemical cycles: theory, observation and modeling

[AOS13-02] The Variations of O₂/Ar-Net Community Production and Air-sea Carbon Dioxide Flux in the southern East China Sea before and after Typhoon Maria.

*Kai-Jung Kao¹, Wei-Jen Huang¹, Wen-Chen Chou^2,3,4, Gwo-Ching Gong^2,3, Hsiao-Chun Tseng², Veran Weerathunga¹ (1.Department of Oceanography, National Sun Yat-sen University, Kaohsiung, Taiwan., 2.Institute of Marine Environment and Ecology, National Taiwan Ocean University, Keelung, Taiwan., 3.Center of Excellence for the Oceans, National Taiwan Ocean University, Keelung, Taiwan., 4.Graduate Institute of Marine Biology, National Dong Hwa University, Pingtung, Taiwan.)

Keywords:N2O refined O2/Ar net community production, Kuroshio intrusion, Temperature effect, Net community activity, Mixing effect

The continental shelves, which account for 33% of the net community production (NCP) and 15–21% of the net annual carbon dioxide (CO₂) sink of the global ocean, exert a profound influence on the global ocean carbon cycle. However, the frequently-occurred physical processes (ex., upwelling, eddy) and the extreme weather event regulate the variations of the partial pressure of carbon dioxide (pCO₂) and the NCP on the continental shelf, which remains poorly understood. High spatial resolution sea surface pCO₂ and O₂/Ar-NCP were measured through an underway pCO₂ system and the Equilibrator Inlet Mass Spectrometry (EIMS) in the southern East China Sea (sECS) before (July 6–9, 2018) and after (July 13–17, 2018) Typhoon “Maria.” Surface pCO₂ were 325.1 ± 18.3 and 322.9 ± 17.4 µatm on the upwelling regions of shelf break and middle shelf, respectively, pre-typhoon. Post-typhoon, the surface pCO₂ dropped to 315.5 ± 15.9 and 305.7 ± 7.2 µatm on the shelf break and middle shelf, respectively. Additionally, the NCP were 15.0 ± 0.9 and 28.0 ± 12.4 mmol C m^-2 d^-1 on the shelf break and middle shelf, respectively, pre-typhoon. Post-typhoon, the NCP elevated to 40.2 ± 20.2 and 56.9 ± 15.8 mmol C m^-2 d^-1 on the shelf break and middle shelf, respectively. Our analysis demonstrates that controlling factors of pCO₂ variations are the temperature effect (38 to 40%), net biological activities (-33 to -36%), and mixing (-24%) before and after the typhoon. During our study period, the upwelling regions in sECS acted as strong sinks of atmospheric CO₂ (−4.2 ± 1.2 to −14.1 ± 1.2 mmol m^-2 d^-1). We suggested that the temperature change, net biological activities, and mixing during the upwelling process characterized the biogeochemical responses over the sECS.