Partitioning of physical and biogeochemical contributions to short-term variability of pCO2 in a coastal upwelling system: a quantitative approach

Abstract

A considerable body of literature has addressed the role that coastal upwelling systems may play in global processes, especially in the ocean carbon cycle. It is often difficult to separate the effects of physical and biogeochemical processes on the partial pressure of carbon dioxide (pCO2) in coastal upwelling systems due to the tight coupling between these processes. In this work we propose a novel approach to quantify physical (advection and diffusion of inorganic carbon species, in situ warming) and biogeochemical (production and consumption of inorganic carbon species) effects on surface pCO2 using an inverse method. It is applied to the Ría de Vigo, a large coastal indentation in the NW Iberian shelf. Physical and biogeochemical processes affecting surface pCO2 variability are quantified during spring, summer, autumn and winter. Our results show the dominance of vertical advection, turbulent diffusion and net ecosystem production of organic carbon (ΔCorg) components over other processes (calcification and surface warming) on a short timescale (2 to 4 d). The study reveals that physical transport of inorganic carbon species explains -50% of the observed pCO2 variability and ΔCorg accounts for most of the remaining 50%.