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Title: Tracing the cycling of Pb and Cd from natural and anthropogenic sources through the troposphere and ocean
Author: Bridgestock, Luke James
ISNI:       0000 0004 6495 5260
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2015
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Anthropogenic emissions have been a major source of numerous trace elements to the environment during the past century, causing significant perturbations of their global biogeochemical cycles. This thesis focuses on the use of isotopic variations to study the cycling of Pb and Cd, derived from natural and anthropogenic sources, in the Tropical Atlantic Ocean. To this end, a novel method to determine the Pb isotope composition and concentration of seawater is presented. This method is applied to (1) surface seawater and aerosol samples collected in the Tropical Atlantic, to reassess the relative importance of anthropogenic and natural Pb sources to the surface seawater of this region following the global phase out of leaded petrol, and (2) seawater depth profiles collected in the eastern Tropical Atlantic, to study the transient penetration of historic anthropogenic Pb emissions into the ocean interior. The results reveal significant Pb contributions from mineral dust to surface seawaters of about 30 – 50 %. This is the first time a significant proportion of naturally derived Pb has been detected in Atlantic surface seawaters and can be viewed as the success of environmental policy. Furthermore, it is shown that the removal of atmospheric particles by dry deposition plays an important role in the observed mineral dust Pb contributions to surface seawater. The Pb isotope compositions and concentrations within the interior of the eastern Tropical Atlantic are consistent with values expected from the transport of transient anthropogenic Pb inputs by ocean circulation, thus enabling insights into ventilation timescales and pathways. Finally, we present among the first data on the Cd isotope composition of atmospheric aerosols, which were collected in the eastern Tropical Atlantic. These results are used to assess the utility of isotope variations to trace the long-range atmospheric transport of anthropogenic and natural Cd sources to the ocean.
Supervisor: van der Flierdt, Tina ; Rehkamper, Mark Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral