How fast is the Patagonian shelf-break acidifying?

Anthropogenic carbon (C-ant) concentration is determined according to the TrOCA method, from carbonate system data and hydrographic parameters collected during two consecutive spring cruises (2007 and 2008) in the Argentinean Patagonian shelf-break zone between 36 degrees S and 50 degrees S. C-ant has intruded the water column until intermediate depths, with no C-ant below 1000 m, in the deeper waters (i.e., North Atlantic Deep Water and Antarctic Bottom Water) of the Northern sector of the study area (i.e., North of 38 degrees S). The higher C-ant concentration is observed in Subantarctic Shelf Water in the Southern region, whereas in the Northern sector both Tropical Water and South Atlantic Central Water are equally affected by C-ant intrusion. The Antarctic Intermediate Water represents the depth-limit achieved by Cant penetration, reinforcing the role that this water mass plays as an important vehicle to transport C-ant to the oceans interior. The estimated Cant average (method precision) is 46.6 +/- 5.3 mu mol kg(-1) considering the full depth of the water column. The ocean acidification state (Delta pH) shows an average (+/- standard deviation) of -0.11 +/- 0.05, thus, indicating an annual pH reduction of -0.0010 yr(-1) since the Industrial Revolution (c.a. 1750). The degree of aragonite saturation is lowered towards undersaturation levels of calcite. The Patagonian shelf and shelf-break zones-a strong CO2 sink region in the global ocean-are likely a key area for Cant intrusion in the southwestern South Atlantic Ocean.