Air-sea CO2 fluxes for the Brazilian northeast continental shelf in a climatic transition region

Oceanographic cruises were carried out in October 2012 (3 degrees S -5 degrees S and 38,5 degrees W -35,5 degrees W) and in September 2014 (1 degrees S-4 degrees S and 43 degrees W-37 degrees W), measuring atmospheric and sea surface CO2 fugacity (fCO(2)) underway in the northeast coast of Brazil. Sea surface water samples were also collected for chlorophyll a, nutrients and DOC analysis. During the second cruise, the sampling area covered a transition between semi-arid to more humid areas of the coast, with different hydrologic and rainfall regimes. The seawater fCO(2)(SW), in October 2012, was in average 400.9 +/- 7.3 mu atm and 391.1 +/- 63 mu atm in September 2014. For the atmosphere, the fCO(2)(air) in October 2012 was 375.8 +/- 2.0 mu atm and in September 2014, 368.9 +/- 2.2 mu atm. The super-saturation of the seawater in relation to the atmosphere indicates a source of CO2 to the atmosphere. The entire study area presents oligotrophic conditions. Despite the low concentrations, Chl a and nutrients presented significant influence on fCO(2)(SW), particularly in the westernmost and more humid part of the northeast coast, where river fluxes are three orders of magnitude larger than eastern rivers and rainfall events are more intense and constant. fCO(2)(SW) spatial distribution presented homogeneity along the same transect and longitudinal heterogeneity, between east and west, reinforcing the hypothesis of transition between two regions of different behaviour. The fCO(2)(SW) at the eastern portion was controlled by parameters such as temperature and salinity. At the western portion, or was influenced by nutrient and Chl a. Calculated instantaneous CO2 flux ranged from + 1.66 to + 724 mmol m(-2) d(-1) in the first cruise and + 0.89 to + 14.62 mmol m(-2) d(-1) in the second cruise. (C) 2017 Elsevier B.V. All rights reserved.