Mechanistic Drivers of Reemergence of Anthropogenic Carbon in the Equatorial Pacific

Relatively rapid reemergence of anthropogenic carbon (C_ant) in the Equatorial Pacific is of potential importance for its impact on the carbonate buffering capacity of surface seawater and thereby impeding the ocean's ability to further absorb C_ant from the atmosphere. We explore the mechanisms sustaining C_ant reemergence (upwelling) from the thermocline to surface layers by applying water mass transformation diagnostics to a global ocean/sea ice/biogeochemistry model. We find that the upwelling rate of C_ant (0.4 PgC yr⁻¹) from the thermocline to the surface layer is almost twice as large as air-sea C_ant fluxes (0.203 PgC yr⁻¹). The upwelling of C_ant from the thermocline to the surface layer can be understood as a two-step process: The first being due to diapycnal diffusive transformation fluxes and the second due to surface buoyancy fluxes. We also find that this reemergence of C_ant decreases dramatically during the 1982/1983 and 1997/1998 El Niño events.