Feasibility of reconstructing the basin–scale sea surface partial pressure of carbon dioxide from sparse in situ observations over the South China Sea

Abstract. Sea surface partial pressure of CO₂ (pCO₂) data with high spatial-temporal resolution are important in studying the global carbon cycle and assessing the oceanic carbon uptake capacity. However, the observed sea surface pCO₂ data are usually limited in spatial and temporal coverage, especially in marginal seas. This study provides an approach to reconstruct the complete sea surface pCO₂ field in the South China Sea (SCS) with a grid resolution of 0.5º × 0.5º over the period of 2000–2017 using both remote-sensing derived pCO₂ and observed pCO₂. Empirical orthogonal functions (EOFs) were computed from the remote sensing derived pCO₂. Then, a multilinear regression was applied to the observed pCO₂ as the response variable with the EOFs as the explanatory variables. EOF1 explains the general spatial pattern of pCO₂ in the SCS. EOF2 shows the pattern influenced by the Pearl River plume on the northern shelf and slope. EOF3 is consistent with the pattern influenced by coastal upwelling along the north coast of the SCS. The reconstructions always agree with observations. When pCO₂ observations cover a sufficiently large area, the reconstructed fields successfully display a pattern of relatively high pCO₂ in the mid-and-southern basin. The rate of sea surface pCO₂ increase in the SCS is 2.383 μatm per year based on the spatial average of the reconstructed pCO₂ over the period of 2000–2017. All the data for this paper are openly and freely available at PANGAEA under the link https://doi.pangaea.de/10.1594/PANGAEA.921210 (Wang et al., 2020).