AUTHOR=Chen Shuangling , Sutton Adrienne J. , Hu Chuanmin , Chai Fei TITLE=Quantifying the Atmospheric CO2 Forcing Effect on Surface Ocean pCO2 in the North Pacific Subtropical Gyre in the Past Two Decades JOURNAL=Frontiers in Marine Science VOLUME=8 YEAR=2021 URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2021.636881 DOI=10.3389/fmars.2021.636881 ISSN=2296-7745 ABSTRACT=

Despite the well-recognized importance in understanding the long term impact of anthropogenic release of atmospheric CO₂ (its partial pressure named as pCO₂air) on surface seawater pCO₂ (pCO₂sw), it has been difficult to quantify the trends or changing rates of pCO₂sw driven by increasing atmospheric CO₂ forcing (pCO₂sw^atm_forced) due to its combination with the natural variability of pCO₂sw (pCO₂sw^nat_forced) and the requirement of long time series data records. Here, using a novel satellite-based pCO₂sw model with inputs of ocean color and other ancillary data between 2002 and 2019, we address this challenge for a mooring station at the Hawaii Ocean Time-series Station in the North Pacific subtropical gyre. Specifically, using the developed pCO₂sw model, we differentiated and separately quantified the interannual-decadal trends of pCO₂sw^nat_forced and pCO₂sw^atm_forced. Between 2002 and 2019, both pCO₂sw and pCO₂air show significant increases at rates of 1.7 ± 0.1 μatm yr^–1 and 2.2 ± 0.1 μatm yr^–1, respectively. Correspondingly, the changing rate in pCO₂sw^nat_forced is mainly driven by large scale forcing such as Pacific Decadal Oscillation, with a negative rate (-0.5 ± 0.2 μatm yr^–1) and a positive rate (0.6 ± 0.3 μatm yr^–1) before and after 2013. The pCO₂sw^atm_forced shows a smaller increasing rate of 1.4 ± 0.1 μatm yr^–1 than that of the modeled pCO₂sw, varying in different time intervals in response to the variations in atmospheric pCO₂. The findings of decoupled trends in pCO₂sw^atm_forced and pCO₂sw^nat_forced highlight the necessity to differentiate the two toward a better understanding of the long term oceanic absorption of anthropogenic CO₂ and the anthropogenic impact on the changing surface ocean carbonic chemistry.