Process-based typology of the global coastal ocean based on physical and biogeochemical controls of the sea surface CO2 dynamics

Significant progress has been made regarding the spatial distribution of sources and sinks of atmospheric CO₂ within the global coastal ocean. The physical and biochemical drivers that govern these CO₂ sources and sinks as well as their variability on seasonal timescales are, however, poorly understood. In this study we aim at filling this knowledge gap and assess to what extend the CO₂ dynamics in the coastal ocean is controlled by the adjacent open ocean or conversely is dominated by continental influence. We use the global ocean biophysical model MOM6-COBALT, carefully evaluated against a well-established coastal data-product (Laruelle et al., 2017), to quantify the individual influences of the oceanic transport, thermal changes, freshwater influence, and biological activity on the annual mean spatial distribution of CO₂ sources and sinks as well as their seasonal variability for the coastal ocean worldwide. Our analysis reveals complex spatial and temporal dynamics, depending on the coastal region and/or the time scale investigated (seasonal or annual) resulting from interactions and compensations between the different processes. We identify five typical behaviors of coastal systems (i.e., coastal regions under biological drawdown, vertical transport, imprint of land, dominated by intracoastal alongshore currents, and weak CO₂ sources and sinks coastal regions) and propose a processed-based typology of the coastal ocean based on the processes that control the spatial and seasonal air-sea CO₂ dynamics.