AUTHOR=Zhang Miaoyin , Zhu Xueming , Ji Xuanliang , Zhang Anmin , Zheng Jingjing 

TITLE=Controlling factor analysis of oceanic surface pCO2 in the South China Sea using a three-dimensional high-resolution biogeochemical model

JOURNAL=Frontiers in Marine Science

VOLUME=10

YEAR=2023

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2023.1155979

DOI=10.3389/fmars.2023.1155979

ISSN=2296-7745

ABSTRACT=<p>The oceanic surface pressure of CO<sub>2</sub> (<italic>p</italic>CO<sub>2</sub>) is an essential parameter for understanding the global and regional carbon cycle and the oceanic carbon uptake capacity. We constructed a three-dimensional physical-biogeochemical model with a high resolution of 1/30° for the South China Sea (SCS) to compensate for the limited temporal coverage and limited spatial resolution of the observations and numerical models. The model simulated oceanic surface <italic>p</italic>CO<sub>2</sub> from 1992 to 2021, and the empirical orthogonal function analysis (EOF) of the model results is conducted for a better understanding of the seasonal and interannual variations of oceanic surface <italic>p</italic>CO<sub>2</sub> in this region. The model results showed that the SCS serves as an atmospheric CO<sub>2</sub> source from March to October and a sink from November to February, with a domain-averaged climatological oceanic surface <italic>p</italic>CO<sub>2</sub> value that varies between 357 and 408 μatm, and the temporal variation was positively correlated with the variation of sea surface temperature (SST). The majority of the SCS showed a long-term increasing trend for oceanic surface <italic>p</italic>CO<sub>2</sub> with a value of (1.19±0.60) μatm/a, which is in response to the continuously rising atmospheric CO<sub>2</sub> concentration. The first EOF mode is positively correlated with the Niño 3 index with a correlation coefficient of 0.51 when the Niño 3 leads 5 months, and the second EOF mode is correlated with the PDO index when the PDO leads 7 months, which suggests an influence of climate variability on the carbonate system. Moreover, it was found that the long-term trend rate of oceanic surface <italic>p</italic>CO<sub>2</sub> was mainly controlled by total CO<sub>2</sub> (TCO<sub>2</sub>) through the decomposition of influence factors, and SST variation took a dominant role in seasonal variations of <italic>p</italic>CO<sub>2</sub>. With rapid global warming and continuous release of CO<sub>2</sub>, the carbonate system in the SCS may change leading to calcite and aragonite saturation.</p>