The Contribution of Nutrients and Water Properties to the Carbonate System in Three Particular Areas of the Tropical Atlantic (NE-BRAZIL)

Abstract

Tropical waters show different regional aspects due to specificities in their nutrient biogeochemical cycles, which can affect the carbon system and influence their regional role as sinks or sources of CO2. This study was performed on particular tropical areas that present a different seasonal behaviour related to the carbon cycle observed in the late rainy season (July 2013). Understanding the CO2 drawdown and outgassing potential in these areas is needed to call attention to more long-term monitoring efforts and protect understudied tropical coastal systems more efficiently. This study is focused on nutrient values, hydrological data, biogeochemical carbon behaviour linked to the carbonate system and includes estimates of CO2 fluxes in three contrasting areas off the northeastern Brazilian shelf: 1) an urbanised estuary (Recife-REC), 2) a coastal Island (Itamaracá-ITA) and 3) an oceanic archipelago (Fernando de Noronha-FN). In general, REC acted as a source, while ITA and FN as carbon sinks. In ITA, despite the high DIC and Total Alkalinity observed (mean ~2360 μmol·kg-1), the sink is associated with an effective cascading of atmospheric CO2 associated with turbulent shallow waters coupled with biogenic removal of and precipitation of CaCO3 by coralline algae. FN acted as a sink, linked to minor decreases in Total Alkalinity (mean~2295 μmol·kg-1) influenced by ammonium-based primary production, nitrogen fixation and sporadic entrainment of nutrient rich waters in the upper thermocline. More studies in different western tropical Atlantic coastal systems can improve the knowledge of tropical shelf seas and their contribution to the ocean carbon budget under specific regional trophic regimes.