Improved Quantification of Ocean Carbon Uptake by Using Machine Learning to Merge Global Models and pCO₂ Data

Abstract The ocean plays a critical role in modulating climate change by sequestering CO 2 from the atmosphere. Quantifying the CO 2 flux across the air‐sea interface requires time‐dependent maps of surface ocean partial pressure of CO 2 (pCO 2 ), 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 CO 2 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) pCO 2 product is a new approach to estimating the temporal evolution of surface ocean pCO 2 and air‐sea CO 2 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 pCO 2 for 1982–2018. The resulting reconstruction by LDEO‐HPD is in better agreement with independent pCO 2 observations than other currently available observation‐based products. Within uncertainties, LDEO‐HPD global ocean uptake of CO 2 agrees with other products and the Global Carbon Budget 2020.