The changing ocean biogeochemistry in the Earth system

The ocean plays an essential role in regulating Earth’s climate; it is also essential for regulating the Earth’s biogeochemical cycles of carbon, nitrogen, and oxygen. Long-term (at the end of this century) changes in ocean biogeochemical cycles will be determined by the pace of anthropogenic emissions and resulting climate change. For the ocean carbon cycle, Earth system models (ESMs) within the 6th Climate Model Intercomparison Project project that while the ocean carbon sink continues to grow with rising emissions, the fraction of emissions that is taken up declines as atmospheric CO2 rises, resulting in a positive carbon–climate feedback. By contrast, near-term (until 2040) changes will be masked by internal climate variability. ESMs in concert with observations are key to constrain the response of ocean biogeochemical cycles to ongoing climate change. Yet, predictive understanding of how ocean biogeochemical cycles would respond to rapid and strong changes in emissions is currently missing. Such knowledge is critical in support of monitoring and verification of political actions for strong and rapid decarbonization. I will talk about recent progress and challenges in our understanding of the long-term and near-term fate of the ocean biogeochemical cycles under changing climate.