59. Anthropogenic carbon distribution and ocean acidification state in the Patagonian shelf break region

Iole B. M. Orselli (1)*, Rodrigo Kerr (1), Rosane G. Ito (2), Virgínia M. Tavano (1,3) and Carlos A. E. Garcia (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, Brazil.
2 Instituto Oceanográfico, Universidade de São Paulo (USP), Praça do Oceanográfico 191, São Paulo, 05508-120, SP, Brazil.
3 Laboratório de Fitoplâncton e Micro-organismos Marinhos, Instituto de Oceanografia, Universidade Federal do Rio Grande (FURG), Av. Itália km 8, Rio Grande, 96203-900, RS, Brazil.

Background
Oceans are known to play an important role in absorption of CO2 released in the atmosphere. Motivated by the increasing emissions by human activity, reaching a record value since 1750, many studies have been conducted to understand and quantify the anthropogenic carbon (Cant) absorption, distribution and effects in the oceans.

Methods:
Cant concentration was determined through both TrOCA and CT0 methods in the Patagonian shelf break (36°S-50°S), from hydrographic and carbonate data sampled during two consecutive spring cruises (2007 and 2008).

Findings
Results show Cant absorption in the entire water column, with low values in the deeper region of the northern study area, and no Cant above 1000 m (by TrOCA). Higher Cant values were observed near Río de La Plata mouth (TrOCA), while higher values for CT0 were found south of 40°S. Cant average values were (± methods precision) of 67.59 ± 3.5 mol kg-1 and 89.30 ± 1.3 mol kg-1 for TrOCA and CT0, respectively. Using Cant results, the state of oceanic acidification (pH) was distinctly estimated from both methods, with average values (± standard deviation) of –0.179 ± 0.168 and –0.173 ± 0.052 for TrOCA and CT0, respectively, indicating an annual pH reduction of –0.001 yr-1 since 1750. Calcite and aragonite saturation levels are not yet at a risk position, although may be affected by Cant absorption and ocean acidification (except for aragonite in depth levels: 1060 m at 47.4°S/59.5°W, 1500 m at 38.4°S/53.5°W and 2013 m at 38.4°S/53°W).

Conclusions
The Patagonian shelf break, which is considered one of the strongest CO2 sinking region in the World Ocean, seems to be an important area for Cant absorption, and the results showed here shed some new light on knowledge of the CO2 system behaviour in the area.