We use a coupled physical-biogeochemical model to investigate the drivers and mechanisms responsible for the spatiotemporal variability of the partial pressure of carbon dioxide in seawater (pCO2) and associated air-sea CO2 fluxes in the Northern Humboldt Current System (NHCS). The highly productive upwelling region, 300 km from the shore and between 5 and 17 °S, is shown to be a strong CO2 source with an averaged flux of 5.60 ± 2.94 mol C m −2 year−1, which represents an integrated carbon flux of 0.028 ± 0.015 Pg C year−1. Through a series of model experiments, we show that the high pCO2 is primarily the result of coastal upwelling, which is incompletely compensated by biology. Specifically, the supply of dissolved inorganic carbon (DIC)-rich waters to the surface pushes pCO2 up to levels around 1100 μatm. Even though biological production is high, it reduces pCO2 only by about 300 μatm. We show that this relatively low degree of biological compensation results from a spatio-temporal decoupling between the counteracting effects of biological production and the
transport and mixing of DIC. The contribution of the outgassing and the processes affecting CO2 solubility, associated with the seasonal cycle of heating and cooling, are minor. We demonstrate that seawater pCO2 is more sensitive to changes in DIC and sea surface temperature, while alkalinity plays a minor role.

Date & Time: Tue Feb 06 2024 11:00:00 GMT+0100 (Central European Standard Time)
Room: 45-55 5th floor room 417

zoom: https://ird-fr.zoom.us/j/98685498044?pwd=bC9HUDJMemkwVUx2bWthWFIxQkNOdz09