evidence: The ocean plays a crucial role in the global carbon cycle and climate. Every year, it absorbs, on average, 25% of the anthropogenic CO2 emitted to the atmosphere from burning fossil fuels and land-use change1,2. The ocean will be the main storage for most of the CO2 emitted to the atmosphere from human activities, absorbing more than half of the cumulative emissions on a timescale of 1000 years, and between 60% and 85% on timescales of 10,000 years or longer3. The ocean CO2 sink responds mainly to the increase in atmospheric CO2 and is the result of processes taking place on different timescales: the dissolution of anthropogenic CO2 at the surface, its buffering by carbonate chemistry, and its transport to the intermediate and deep ocean by ocean circulation4. This uptake is modulated by the variable growth rate in atmospheric CO25. Furthermore, the ocean carbon reservoir is also sensitive to climate variability and climate change6,7, which modulates the response of the ocean CO2 sink to anthropogenic CO2 emissions, generates variability, and can alter both the decadal rate of change and long-term storage of carbon in the ocean.