Evaluating the biological carbon pump in a water mass transformation framework

The ocean’s biological carbon pump forms a fundamental component of the global carbon cycle, impacting atmospheric carbon dioxide on a range of timescales. Difficulty in observing and simulating the ocean biosphere mean that even the magnitude of the contemporary biological pump, as well as its variability and susceptibility to change, remains highly uncertain. Here, we demonstrate that novel understanding can be derived from considering the global biological carbon pump in a framework based on water mass transformation. Specifically, we quantify the physical and biogeochemical processes that move organic matter across temperature (T) and salinity (S) surfaces in a pre-industrial control simulation of GFDL’s Earth System Model. This aggregate approach reduces the complexity associated with the heterogeneity of the ocean biosphere, while the use of T and S coordinates inherently incorporates critical constraints in both ocean circulation (which conserves T and S) and biogeochemical processes (through their T-dependence). As such, the framework provides an insightful lens through which to consider the biological carbon pump and its impact on global climate.