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Measurements show large decadal variability in the rate of accumulation in the atmosphere that is not driven by emissions. The decade of the 1990s experienced enhanced carbon accumulation in the atmosphere relative to emissions, while in the 2000s, the atmospheric growth rate slowed, even though emissions grew rapidly. These variations are driven by natural sources and sinks of due to the ocean and the terrestrial biosphere. In this study, we compare three independent methods for estimating oceanic uptake and find that the ocean carbon sink could be responsible for up to 40% of the observed decadal variability in atmospheric accumulation. Data-based estimates of the ocean carbon sink from mapping methods and decadal ocean inverse models generally agree on the magnitude and sign of decadal variability in the ocean sink at both global and regional scales. Simulations with ocean …