How fast is the Patagonian shelf-break acidifying?

Abstract 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°S and 50°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°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 C ant penetration, reinforcing the role that this water mass plays as an important vehicle to transport C ant to the oceans interior. The estimated C ant average (± method precision) is 46.6 ± 5.3 μmol kg − 1 , considering the full depth of the water column. The ocean acidification state (ΔpH) 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 CO 2 sink region in the global ocean—are likely a key area for C ant intrusion in the southwestern South Atlantic Ocean.