Global Ocean pCO2 Variation Regimes: Spatial Patterns and the Emergence of a Hybrid Regime

The variability in ocean surface partial pressure of carbon dioxide (pCO(2)), driven by both physical and biological processes, substantially influences air-sea carbon exchange. It is widely recognized that the pCO(2) variation at a specific ocean location is primarily dominated by either thermal or nonthermal effects. However, the distinct pCO(2) variation regimes, their global distribution, and the mechanisms underlying such patterns have yet to be fully determined due to a paucity of global observations. Through the use of observation-based products and an eddy-resolving ocean simulation, this study demonstrates the presence of three distinct regimes in the global ocean: one in which sea surface temperature (SST) is the dominant control on pCO(2) variations; another in which dissolved inorganic carbon (DIC) is the primary control; and a third previously uncharacterized hybrid regime where pCO(2) variations are governed by seasonally-varying factors. This hybrid regime is generally located between SST- and DIC-dominated regimes and occupies approximately 15% of the global ocean. The regimes broadly exist in zonal bands that are closely linked to the relative strengths of SST and DIC variances. Seasonally-varying mixed-layer depth, mesoscale variability (quantified in terms of eddy kinetic energy), and biological processes modulate local pCO(2) variations and play significant roles in shaping the global pattern of regime distributions. Understanding the distribution of pCO(2) regimes, including the hybrid regime revealed in this study, as well as their different oceanic drivers, is essential for future predictions of ocean carbon uptake in response to global warming.