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

• Main Authors: Moran, S. Bradley, Shen, Chuan-Chou, Weinstein, Sarah E., Hettinger, L. H., Hoff, J. H., Edmonds, Henrietta N., Edwards, R.Lawrence
• Other Authors: Department of Earth Sciences
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union (AGU) 2001
• Subjects: Southern Ocean; South Atlantic Ocean
• Online Access: http://ir.lib.ncku.edu.tw/handle/987654321/59746

High-precision measurements of Pa-231 and Th-230 in filtered seawater and suspended particulate matter samples are reported for the Equatorial and South Atlantic, Distributions of Pa-231 and Th-230 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 similar to 60-100 years from the northern source water regions. The average particulate Pa-231 /Th-230 activity ratio is 0.0498 +/- 0.0160, a factor of similar to2 lower than the Pa-231 /Th-230 production ratio of 0.093 and in agreement with reported excess Pa-231/Th-230 ratios of 0.06 +/- 0.004 in Holocene sediments north of 50 degreesS 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 F-Th/Pa = 4.32-24.04 (ave. = 9.97 +/- 4.98) compared to values of similar to1-4 in the Southern Ocean.