Abstract
Abstract. Observations along the southwestern Atlantic WOCE A17 line made during the Dutch GEOTRACES-NL programme (2010–2011) were compared with historical data from 1994 to quantify the changes in the anthropogenic component of the total pool of dissolved inorganic carbon (ΔCant). Application of the extended multi-linear regression (eMLR) method shows that the ΔCant from 1994 to 2011 has largely remained confined to the upper 1000 dbar. The greatest changes occur in the upper 200 dbar in the Subantarctic Zone (SAZ), where a maximum increase of 37 μmol kg−1 is found. South Atlantic Central Water (SACW) experienced the highest rate of increase in Cant, at 0.99 ± 0.14 μmol kg−1 yr−1, resulting in a maximum rate of decrease in pH of 0.0016 yr−1. The highest rates of acidification relative to ΔCant, however, were found in Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW). The low buffering capacity of SAMW and AAIW combined with their relatively high rates of Cant, increase of 0.53 ± 0.11 and 0.36 ± 0.06 μmol kg−1 yr−1, respectively, has lead to rapid acidification in the SAZ, and will continue to do so whilst simultaneously reducing the chemical buffering capacity of this significant CO2 sink.
Highlights
The Atlantic Ocean contains the largest store of anthropogenic carbon (Cant) of all the world’s oceans, accounting for approximately 38 % of the total Cant inventory (Sabine et al, 2004)
Acidification rates that deviate from the rate that is expected from Cant increases alone have been observed in upper Labrador Sea Water, Subarctic Intermediate Water (SAIW), and eastern North Atlantic Central Water
The continuing uptake of Cant in the southwestern Atlantic has been assessed through application of extended multilinear regression (eMLR) to two data sets collected in 1994 and 2011
Summary
The Atlantic Ocean contains the largest store of anthropogenic carbon (Cant) of all the world’s oceans, accounting for approximately 38 % of the total Cant inventory (Sabine et al, 2004). The southwestern Atlantic has been occupied several times over the past 20 years, and several techniques to determine Cant have been applied to the WOCE ’94 A17 transect by Ríos et al (2010) These methods included C* (Gruber et al, 1996), TrOCA (Tracer combining Oxygen, inorganic Carbon and total Alkalinity; Touratier et al, 2007), φCT◦ (Vázquez-Rodríguez et al, 2009a), and TTD (transit time distributions; Waugh et al, 2006) and showed general conformity in the distribution of Cant. Acidification rates that deviate from the rate that is expected from Cant increases alone have been observed in upper Labrador Sea Water (uLSW), SAIW, and eastern North Atlantic Central Water (eNACW; Vázquez-Rodríguez et al, 2012) These variations have been attributed to a combination of climatic and biological effects. Based on the measurements performed on the CRM throughout both cruises, DIC was measured with a precision of ±1.0 μmol kg−1 and the precision of AT was ±1.1 μmol kg−1
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