AUTHOR=Zhang Siqi , Bai Yan , He Xianqiang , Jiang Zhiting , Li Teng , Gong Fang , Yu Shujie , Pan Delu TITLE=Spatial and temporal variations in sea surface pCO2 and air-sea flux of CO2 in the Bering Sea revealed by satellite-based data during 2003–2019 JOURNAL=Frontiers in Marine Science VOLUME=10 YEAR=2023 URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2023.1099916 DOI=10.3389/fmars.2023.1099916 ISSN=2296-7745 ABSTRACT=

The understanding of long-time-series variations in air-sea CO₂ flux in the Bering Sea is critical, as it is the passage area from the North Pacific Ocean water to the Arctic. Here, a data-driven remote sensing retrieval method is constructed based on a large amount of underway partial pressure of CO₂ (pCO₂) data in the Bering Sea. After several experiments, a Gaussian process regression model with input parameters of sea surface temperature, sea surface height, mixed-layer depth, chlorophyll a concentration, dry air mole fractions of CO₂, and bathymetry was selected. After validation with independent data, the root mean square error of pCO₂ was< 24 μatm (R² = 0.94) with satisfactory performance. Then, we reconstructed the sea surface pCO₂ in the Bering Sea from 2003 to 2019 and estimated the corresponding air-sea CO₂ fluxes. Significant seasonal variations were identified, with higher sea surface pCO₂ in winter/spring than in summer/autumn in both the basin and shelf area. Semiquantitative analysis reveals that the Bering Sea is a non-temperature-dominated area with a mean temperature effect on pCO₂ of 12.7 μatm and a mean non-temperature effect of −51.8 μatm. From 2003 to 2019, atmospheric pCO₂ increased at a rate of 2.1 μatm yr⁻¹, while sea surface pCO₂ in the basin increased rapidly (2.8 μatm yr⁻¹); thus, the CO₂ emissions from the basin increased. However, the carbon sink in the continental shelf still continuously increased. The whole Bering Sea exhibited an increasing carbon sink with the area integral of air-sea CO₂ fluxes increasing from 6 to 19 TgC over 17 years. Meanwhile, the seasonal amplitudes in pCO₂ in the shelf area also increased, approaching 14 μatm per decade. The reaction of the continuously added CO₂ in continental seawater reduced the ocean CO₂ system capacity. This is the first study to present long-time-series satellite data with high resolution in the Bering Sea, which is beneficial for studying the changes in ocean ecosystems and carbon sink capacity.