Constraints on deep water age and particle flux in the Equatorial and South Atlantic Ocean based on seawater ²³¹Pa and ²³⁰Th data

High-precision measurements of ²³¹ Pa and ²³⁰Th in filtered seawater and suspended particulate matter samples are reported for the Equatorial and South Atlantic. Distributions of ²³¹ Pa and ²³⁰Th clearly indicate the influence of advection, as evidenced by departures from scavenging models that predict a linear increase with depth for these tracers. Application of a scavenging-mixing model implies a deep water transit time of Ο60-100 years from the northern source water regions. The average particulate ²³¹Pa/²³⁰Th activity ratio is 0.0498 ± 0.0160, a factor of Ο2 lower than the ²³¹Pa/²³⁰Th production ratio of 0.093 and in agreement with reported excess ²³¹Pa/²³⁰Th ratios of 0.06 ± 0.004 in Holocene sediments north of 50°S in the Atlantic. These water column data further suggest that lateral eddy diffusive transport combined with enhanced scavenging in high-particle flux marginal regions (boundary scavenging) is weakly expressed in the Atlantic. Particle fractionation of these tracers is also indicated by the elevated fractionation factors of F_Th/Pa = 4.32-24.04 (ave. = 9.97 ± 4.98) compared to values of ˜1-4 in the Southern Ocean.