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Improved quantification of ocean carbon uptake by using machine learning to merge global models and pCO2 data
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  • Lucas Gloege,
  • Monica Yan,
  • Tian Zheng,
  • Galen A McKinley
Lucas Gloege
Columbia University

Corresponding Author:[email protected]

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Monica Yan
Columbia University
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Tian Zheng
Columbia University
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Galen A McKinley
Lamont Doherty Earth Observatory of Columbia University
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Abstract

The ocean plays a critical role in modulating climate change by sequestering CO2 from the atmosphere. Quantifying the CO2 flux across the air-sea interface requires time-dependent maps of surface ocean partial pressure of CO2 (pCO2), which can be estimated using global ocean biogeochemical models (GOBMs) and observational-based data products. GOBMs are internally consistent, mechanistic representations of the ocean circulation and carbon cycle, and have long been the standard for making spatio-temporally resolved estimates of air-sea CO2 fluxes. However, there are concerns about the fidelity of GOBM flux estimates. Observation-based products have the strength of being data-based, but the underlying data are sparse and require significant extrapolation to create global full-coverage flux estimates. The Lamont Doherty Earth Observatory-Hybrid Physics Data (LDEO-HPD) pCO2 product is a new approach to estimating the temporal evolution of surface ocean pCO2 and air-sea CO2 exchange. LDEO-HPD uses machine learning to merge high-quality observations with state-of-the-art GOBMs. We train an eXtreme Gradient Boosting (XGB) algorithm to learn a non-linear relationship between model-data mismatch and observed predictors. GOBM fields are then corrected with the predicted model-data misfit to estimate real-world pCO2 for 1982-2018. A benefit of this approach is that model-data misfit has reduced temporal skewness compared to the observed pCO2 that is the target variable for other machine-learning based reconstructions. This supports a robust reconstruction by LDEO-HPD that is in better agreement with independent observations than other estimates. LDEO-HPD global ocean uptake of CO2 is in agreement with other products and the Global Carbon Budget 2020.