Sediment Pa-231/Th-230 as a recorder of the rate of the Atlantic meridional overturning circulation: insights from a 2-D model

A two dimensional scavenging model is used to investigate the patterns of sediment Pa-231/Th-230 generated by the Atlantic Meridional Overturning Circulation ( AMOC) and further advance the application of this proxy for ocean paleocirculation studies. The scavenging parameters and the geometry of the overturning circulation cell have been chosen so that the model generates meridional sections of dissolved Th-230 and Pa-231 consistent with published water column profiles and an additional 12 previously unpublished profiles measured in the North and Equatorial Atlantic. The processes that generate the meridional sections of dissolved and particulate Th-230, dissolved and particulate Pa-231, dissolved and particulate Pa-231/Th-230, and sediment Pa-231/Th-230 are discussed in detail. The results indicate that the relationship between sediment Pa-231/Th-230 at any given site and the overturning circulation is very complex. They clearly show that constraining past changes in the strength and geometry of the AMOC requires an extensive data set and they suggest strategies to maximize information from a limited number of samples.