The role of hydrodynamic and biogeochemistry on CO 2 flux and p CO 2 at the Amazon River mouth

Abstract. Recent estimates indicate that the lower Amazon River outgasses significant amounts of carbon dioxide (CO 2 ) that was not previously accounted for the global inland water carbon budget. Detailed evaluation of seasonal variability and controlling mechanisms behind the CO 2 fluxes in this large and complex area remains incomplete. Previous observations throughout the Amazon basin showed that higher CO 2 fluxes (FCO 2 ) and partial pressure of CO 2 ( p CO 2 ) occur during high water and higher wind intensity seasons. The influence of wind and water speed, depth of water column, as well as respiration of allochthonous and autochthonous organic matter, are frequently assigned as the main control variables. Here, we assess the influence of a set of biogeochemical and hydrodynamic parameters on the seasonal variation of FCO 2 and pCO 2 near the Amazon River mouth. FCO 2 , p CO 2 and biogeochemical and hydrologic analyses were carried out from 2010 to 2016 during four different hydrological periods per year ( N = 25) in the North Channel of the Amazon River mouth. FCO 2 and p CO 2 were used as independent variables and analyzed against 33 biogeochemical, hydrodynamic and meteorological parameters along the hydrological seasons. The highest FCO 2 and p CO 2 was obtained at high discharge season (11.28 ± 7.82 μmol m −2  s −1 and (4575 ± 429 μatm, respectively) when most of these parameters tend to be higher. Among the 33 parameters analyzed, the significant correlations with FCO 2 and p CO 2 ( p p CO 2 and FCO 2 in the Amazon River mouth area. For a better estimation and understanding of carbon budgets in tropical rivers it is still required to verify and to quantify more deeply the relationship among CO 2 evasion and others hydrodynamic, meteorological and biogeochemical variables.