Compared to the ocean carbon sink found in most parts of the global ocean, the tropical Atlantic Ocean represents a significant source of carbon to the atmosphere. Furthermore, the Amazon River plume is a strong sink of atmospheric carbon dioxide (CO_{2 atm}) in the western tropical Atlantic Ocean, which largely influences the biogeochemical dynamics of the land-aquatic continuum in this region. Anthropogenic activities have a significant influence on the Amazon River and its coastal shelf system, thus a better understanding of the impact on carbon emissions and sinks is required. However, large observational gaps in both time and space restrict process understanding and quantification of this region’s carbon fluxes and budgets. To better constrain the carbon cycle components of the Amazonas shelf system, we combine highly-resolved continuous measurements of partial pressure of CO₂ (pCO₂) with an ocean biogeochemistry simulation of the tropical Atlantic using the MITgcm-Darwin model. Model output shows that the carbon absorbed by the Amazon River plume in the form of pCO₂ increased by 10 µatm from 2016 to 2022. As a response of higher CO₂ uptake, surface-ocean total alkalinity and dissolved inorganic carbon also increase over time. The model also depicts a spatial gradient in the river-to-ocean transition. Model evaluation of these results is presented, but it is challenging due to lack of biogeochemical observations in Amazon River plume region. To overcome this, high-resolution pCO₂ measurements are carried out with a ship-of-opportunity line along the coast of Brazil (Brazilian-SOOP line). These data will ultimately provide an updated perspective of air-sea carbon fluxes in this important region and will support further evaluation and optimization of the ocean biogeochemistry model.

Primary Presenter: Karel Castro-Morales, Friedrich Schiller University Jena (karel.castro.morales@uni-jena.de)

Authors:

Nuno Serra,   ()

Dustin Carroll,   ()

Tobias Steinhoff,   ()

Leticia Cotrim da Cunha,   ()

Arne Körtzinger,   ()