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Access Type
WSU Access
Date of Award
January 2022
Degree Type
Thesis
Degree Name
M.S.
Department
Geology
First Advisor
Mark Baskaran
Abstract
Disequilibria between long-lived parents and short-lived particle-reactive daughters has been extensively used over the past six decades as tracers and chronometers in aquatic system. In particular, the particle-reactive progeny of 226Ra (210Po, half-life, T1/2 = 138.4 days and 210Pb, T1/2 = 22.3 years) has been widely utilized to quantify oceanic processes such as: export fluxes of particulate organic carbon and nitrogen, biogenic silica, residence time and scavenging rate of particulate and dissolved 210Po and 210Pb, settling velocity of particles, and remineralization rates of biogenic particulate matter. Furthermore, 210Pb in the ocean serves as a tracer for stable Pb and both 210Po and 210Pb serve as analogs for key micronutrient and lithogenic elements such as Cu, Zn, Fe, Al, Th, etc. A large number of papers have been published on the vertical profiles of particulate and dissolved 210Po and 210Pb from the deep-ocean water column showing disequilibrium between 210Pb and 210Po with 210Po/210Pb activity ratio (AR) of >1.1 and/or < 0.9 in discrete water depth layers, although, secular equilibrium with AR of 1.0±0.1 is expected. To investigate this further, a critical and in-depth review of 210Po-210Pb-226Ra published data requires a thorough scrutiny of the methodology, rigorous data analyses, and synthesis. For each of the published data set for water depths >1,000 m, the total water column inventories of dissolved 210Po and 210Pb, as well 226Ra, were calculated. The 210Po:210Pb disequilibrium was found in many discrete water depths between 500 m from surface to 200 m above ocean floor in all of the published data. However, many of the activity ratios calculated based on their inventories showed equilibrium. From deep water and whole column inventories of 210Pb and 226Ra, disequilibrium was found ubiquitously, with highly varying residence time of 210Pb. Global variations in the average concentration of 226Ra as well as the vertical variations in the whole water column are also observed. Average surface water concentrations of 210Pb in the global oceans is found to be correlated with the latitude and showed overall decrease in concentration from mid-latitudes to poles, similar to 210Pb fallout. The partitioning coefficients for 210Po (Kd)Po and 210Pb (Kd)Pb and the fractionation factor are synthesized for the global ocean. The settling velocity of particulate matter, based on the gradient in the particulate 210Pb, is summarized and compared to the values obtained based on particulate 230Th. This is the most rigorous data analysis conducted ever on the 210Po-210Pb-226Ra disequilibria for the global oceans. Keywords: 210Pb, 210Po, 226Ra, Disequilibrium in water column, Residence Time of 210Po and 210Pb
Recommended Citation
Planaj, Denada, "Deep-Ocean Water Disequilibrium 210po-210pb-226ra: A Global Review Of Research Over Six Decades" (2022). Wayne State University Theses. 894.
https://digitalcommons.wayne.edu/oa_theses/894