AUTHOR=Lefèvre Nathalie , Flores Montes Manuel , Gaspar Felipe L. , Rocha Carlos , Jiang Shan , De Araújo Moacyr C. , Ibánhez J. Severino Pino TITLE=Net Heterotrophy in the Amazon Continental Shelf Changes Rapidly to a Sink of CO2 in the Outer Amazon Plume JOURNAL=Frontiers in Marine Science VOLUME=4 YEAR=2017 URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2017.00278 DOI=10.3389/fmars.2017.00278 ISSN=2296-7745 ABSTRACT=
The Amazon continental shelf and adjacent oceanic area were sampled for inorganic and organic carbon parameters in order to improve data coverage and understanding of carbon cycling dynamics within this important region. Seasonal coverage of the Amazon plume on the French Guiana continental shelf further north, was provided by CO2 monitoring using a merchant ship sailing from France to French Guiana (2006–2016). Salinity ranged from 1 to 36 (transects in April 2013, and May 2014). At salinity below 10, strong outgassing was observed with fugacity of CO2 (fCO2) over 2,000 μatm. This region displayed net heterotrophy, fueled by organic matter with terrestrial origin, as shown by δ13C and δ15N values of suspended particles. A δ13C cross shelf average of −31% was measured during May 2014, contrasting with oceanic values in excess of −20%. The reactivity of this terrestrial material resulted in the local production of dissolved inorganic and organic carbon as well as fluorescent humic compounds. Further offshore, the dilution of freshwater by ocean waters created a sink for CO2, enhanced by biological activity. The strongest CO2 drawdowns, associated with high chlorophyll