Impact of episodic vertical fluxes on sea surface pCO₂

Episodic events like hurricanes, storms and frontal-and eddy-driven upwelling can alter the partial pressure of CO₂ (pCO₂) at the sea surface by entraining subsurface waters into the surface mixed layer (ML) of the ocean. Since pCO₂ is a function of total dissolved inorganic carbon (DIC), temperature (T), salinity and alkalinity, it responds to the combined impacts of physical, chemical and biological changes. Here, we present an analytical framework for assessing the relative magnitude and sign in the short-term perturbation of surface pCO₂ arising from vertical mixing events. Using global, monthly, climatological datasets, we assess the individual, as well as integrated, contribution of various properties to surface pCO₂ in response to episodic mixing. The response depends on the relative vertical gradients of properties beneath the ML. Many areas of the ocean exhibit very little sensitivity to mixing owing to the compensatory effects of DIC and T on pCO₂, whereas others, such as the eastern upwelling margins, have the potential to generate large positive/negative anomalies in surface pCO₂. The response varies seasonally and spatially and becomes more intense in subtropical and subpolar regions during summer. Regions showing a greater pCO₂ response to vertical mixing are likely to exhibit higher spatial variability in surface pCO₂ on time scales of days.