65. Spatial variation of total alkalinity and total dissolved inorganic carbon along the Brazilian continental shelf-break and slope: preliminary results

Mariah Borges (1), Iole Orselli (1)*, Rodrigo Kerr (1)

1 Laboratório de Estudos dos Oceanos e Clima, Instituto de Oceanografia, Universidade Federal do Rio Grande (FURG), Av. Itália km 8, Rio Grande, 96203-900, RS, Brasil.

Background
The lack of long-term measurements of carbonate system parameters along Brazilian continental shelf and slope hinders correct characterization of those parameters in this region. Together with questionable and few previous measurements, the accuracy desired to infer about ocean acidification state in Southwestern Atlantic Ocean is still an open question.

Methods
Seawater samples were collected in early spring of 2014 (October) along south and south-eastern continental shelf-break and slope of Brazil to infer about the carbonate system parameters and to correct characterize values of each regional water masses. Another ocean cruise in the area is expected to occur in November 2015. Total alkalinity (AT) and total dissolved inorganic carbon (CT) were determined in a closed cell by potentiometric titration following Dickson (2007).

Findings
It was possible to identify six water masses in the region (temperature°C – T; salinity – S): Plata Plume Water (PPW) with T>10 and S<33.5; Subtropical Shelf Water (STSW), which has two ranges, T>14 and 33.5<S<35.3, and T>18 and 35.3<S<36; Tropical Water (TW), with T>18.5 and S>36; South Atlantic Central Water (SACW) with T>18.5 and S>34.3; Antarctic Intermediate Water (AAIW), with 2 <T<6 and 33.8<S<34.8; and North Atlantic Deep Water (NADW) with 1.5<T<4 and 34.8<S<35. AT ranged between 2200 and 2400 µmol kg-1 and CT between 1950 and 2400 µmol kg-1. AT is highly related with salinity, which decrease towards the seabed. CT is related with temperature and salinity.

Conclusions
This study is a preliminary characterization of the hydrographic and biogeochemistry parameters distribution in the Brazilian continental shelf and slope. A qualitative comparison with available climatology shows high values of AT and CT for these data, reinforcing the need for more sampling efforts. Following steps for this research is to quantify the anthropogenic carbon by distinct methodologies, focusing on estimate acidification state of the region.