Variability of the parameters of the CO 2 system in the continental shelf of
Ceará
Andréa Carvalhoa, Nathalie Lefèvrea,b, Rozane Marinsa
a Instituto de Ciências do Mar, UFC, Fortaleza, Ceará, Av. da Abolição 3207, Brasil
b IRD LOCEAN, Université Pierre et Marie Curie Locean, Paris, France
*corresponding author: [email protected]
The necessity for a better understanding of the CO 2 fluxes between the atmosphere
and the ocean has led to a great number of measurements of the variables of the CO 2
system which include total alkalinity (AT), dissolved inorganic carbon (DIC), pH and
partial pressure of carbon dioxide (pCO 2 ) or fugacity of CO 2 . However, despite the
increase of studies and advances in technology, data in the Equatorial Atlantic remain
sparse. In particular, the exchange of carbon between the continental shelf and the
ocean is poorly documented. In order to better understand the processes at the landocean interface, an oceanographic cruise was carried out in October 2012, during the
dry season, in the equatorial Atlantic region, adjacent to the coasts of Ceará and Rio
Grande do Norte, between 03°34’63’’S 038°12’65’’W and 04°51’’27’S 035°48’’01’W.
The partial pressures of CO 2 for the ocean and atmosphere were measured underway
during the cruise by an infrared CO 2 /H 2 O detector Li-Cor model 7000 as well as
physical and biological parameters. The mean temperature and salinity values were
26.7°C and 36.5, respectively, and showed very small variability. Chlorophyll values
were very low suggesting negligible biological activity, which characterizes oligotrophic
regions. The mean surface total alkalinity (AT) value, determined by potentiometric
titration, was 2397.7±5.3 µmol.kg-1 and the mean value of DIC was 2059.2±4.5
µmol.kg-1. Based on these data, this region is, as expected, a source of CO 2 to the
atmosphere. Further measurements are needed to determine the seasonal variability in
this region and the potential impact of river discharge on the surface CO 2 distribution.
Key-words: CO 2 flux, equatorial Atlantic, continental shelf.