The potential of 230 Th for detection of ocean acidification impacts on pelagic carbonate production

• Published in: Biogeosciences
• Main Authors: C. Heinze, T. Ilyina, M. Gehlen
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2018
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Ocean acidification
• Online Access: https://doi.org/10.5194/bg-15-3521-2018; https://doaj.org/article/0ae9b714e22c40e4900981558aecb90d

Concentrations of dissolved 230 Th in the ocean water column increase with depth due to scavenging and downward particle flux. Due to the 230 Th scavenging process, any change in the calcium carbonate (CaCO 3 ) fraction of the marine particle flux due to changes in biological CaCO 3 hard-shell production as a consequence of progressing ocean acidification would be reflected in the dissolved 230 Th activity. Our prognostic simulations with a biogeochemical ocean general circulation model using different scenarios for the reduction of CaCO 3 production under ocean acidification and different greenhouse gas emission scenarios – the Representative Concentration Pathways (RCPs) 8.5 to 2.6 – reveal the potential for deep 230 Th measurements to detect reduced CaCO 3 production at the sea surface. The time of emergence of an acidification-induced signal on dissolved 230 Th is of the same order of magnitude as for alkalinity measurements. Interannual and decadal variability in factors other than a reduction in CaCO 3 hard-shell production may mask the ocean-acidification-induced signal in dissolved 230 Th and make detection of the pure CaCO 3 -induced signal more difficult so that only really strong changes in marine CaCO 3 export would be unambiguously identifiable soon. Nevertheless, the impacts of changes in CaCO 3 export production on marine 230 Th are stronger than those for changes in POC (particulate organic carbon) or clay fluxes.