Carbon and oxygen net community production in the eastern tropical Atlantic estimated from a moored buoy

Abstract

A mooring at 6S, 10W has been equipped with an oxygen optode and a Carioca sensor for monitoring hourly oxygen (O 2) and the fugacity of CO 2 (fCO 2) at 1.5 m depth since June 2006. Due to biofouling, the oxygen time series lasted between 72 days in 2008 to 159 days in 2009. Using an alkalinity-salinity relationship determined for the area, dissolved inorganic carbon (DIC) is calculated. Short-term and long-term net community productions (NCP) are calculated using a mass balance approach for DIC and O 2 under the assumption of no mixing conditions. The mooring site is always supersaturated in oxygen except in 2007 when depleted oxygen waters are observed from June to September, during the upwelling season. Averaging all the short time events, NCP calculated from the rates of changes of O 2 and DIC leads to a NCP of 16.6 6.1 mmol C m -2d -1, ranging from 14.7 mmol C m -2d -1 in 2008 to 17.4 mmol C m -2d -1 in 2006. The mean daily oxygen biological production rate determined over the whole time series shows a significant year to year variability with 7.5 mmol C m -2d -1 in 2008 to 15.6 mmol C m -2d -1 in 2009. A photosynthetic quotient ranging between 1.0 to 1.3 has been determined when both carbon and oxygen NCP values are available. © 2012 by the American Geophysical Union.