Access Type

Open Access Thesis

Date of Award

January 2017

Degree Type

Thesis

Degree Name

M.S.

Department

Geology

First Advisor

Mark Baskaran

Abstract

The contrasting geochemical behavior of two long-lived progeny of 222Rn, namely 210Po and 210Pb, provide valuable insights on the extent of recycling of biogenic particulate matter and their preferential removal from the water column. A total of 135 water samples were collected and analyzed from six vertical profiles for 210Po and 210Pb along the US GEOTRACES East Pacific Zonal Transect. This study shows decreasing atmospheric 210Pb flux from the measured 210Pb activity in aerosols indicating an overall decrease from east to west along the cruise transect. Differences in scavenging intensities, inventories, and residence times of 210Po and 210Pb at key interfaces that include biotic (upper 60 and 300 m), sediment-water (bottom 300 m) and hydrothermal (bottom 300 m at the East Pacific Rise, EPR) stations were calculated and compared. This thesis presents a new approach to address the differences in the scavenging intensities and residence times by integrating the activities (decays per minute per 100L, dpm 100L-1) of 210Po and 210Pb at key interfaces as well as in the whole column, showing direct evidence for the linkage between the biological activity remineralization of 210Po in the mixed layer in the continental shelf waters off of Peru. 210Po / 210Pb and 210Pb / 226Ra activity ratios vary at different depth intervals establishing disequilibria between 210Po and 210Pb in the water column and disequilibrium is observed between 210Pb and 226Ra throughout the water column, as shown in other major ocean basins. Lastly, intense scavenging of 210Po and 210Pb in the upper 300 m of the EPR site was observed due to high amounts of dissolved and colloidal Fe and Mn, whereas, lower scavenging was noted in the upper and bottom 300 m at the most oligotrophic station. Overall, radionuclides of 210Po, 210Pb and 226Ra serve as geochemical mechanisms to investigate and understand the biogeochemical processes in the marine environment.

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