Concentrations of dissolved 230Th in the ocean water column increase with depth due to scavenging and downward particle flux. Due to the 230Th scavenging process, any change in the calcium carbonate (CaCO3) fraction of the marine particle flux due to changes in biological CaCO3 hard shell production as a consequence of progressing ocean acidification would be reflected in the dissolved 230Th activity. Our prognostic simulations with a biogeochemical ocean general circulation model using different scenarios for the reduction of CaCO3production under ocean acidification and different greenhouse gas emission scenarios (RCPs 8.5 to 2.6) reveal the potential for deep 230Th measurements to detect reduced CaCO3 production at the sea surface. The time of emergence of an acidification induced signal on dissolved 230Th is of the same order of magnitude as for alkalinity measurements. Yet, deep ocean 230Th concentrations are less affected by seasonal and multiyear variability than surface alkalinity. Thus, deep ocean 230Th observations could be advantageous to guide monitoring and detection campaigns. Furthermore, given that the precision of 230Th measurements may potentially improve in the near future, earlier detection of ocean acidification impact signals would be possible. Our results indicate that the deep Pacific Ocean and the deep Southern Ocean are the most suitable regions for selected regular reoccupations of deep reaching 230Th stations.
Heinze C., Ilyina T. & Gehlen M., 2017. The potential of 230Th for detection of ocean acidification impacts on pelagic carbonate production. Biogeosciences Discussions 1-22. Article.