I. Rhenium and Iridium in Natural Waters. II. Methyl Bromide: Ocean Sources, Ocean Sinks, and Climate Sensitivity. III. CO₂ Stability and Heterogeneous Chemistry in the Atmosphere of Mars
Part I: Rhenium and iridium were measured in natural waters by isotope dilution and negative thermal ionization mass spectrometry, following clean chemical separation from 200 mL (Re) and 4 L (Ir) samples. In the Pacific Ocean, Re is well-mixed in the water column, confirming predictions of conserva...
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Format: | Thesis |
Language: | English |
Published: |
1996
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Online Access: | https://thesis.library.caltech.edu/14479/ https://thesis.library.caltech.edu/14479/2/Anbar_AD_1996.pdf https://resolver.caltech.edu/CaltechTHESIS:01202022-231109666 |
Summary: | Part I: Rhenium and iridium were measured in natural waters by isotope dilution and negative thermal ionization mass spectrometry, following clean chemical separation from 200 mL (Re) and 4 L (Ir) samples. In the Pacific Ocean, Re is well-mixed in the water column, confirming predictions of conservative behavior. The Re concentration is 7.42 ± 0.04 ng kg⁻¹. The concentration of Ir in the oceans is fairly uniform with depth and location, ranging from 2.9 to 5.7 x 10⁸ atoms kg⁻¹. Pristine river water contains ≈ 20 x 10⁸ atoms kg⁻¹ while polluted rivers have 50 - 100 x 10⁸ atoms kg⁻¹. Concentrations in the Baltic Sea are much lower than expected from conservative estuarine mixing, indicating rapid removal of ≈75% of riverine Ir. Under oxidizing conditions, Ir is scavenged by Fe-Mn oxyhydroxides. Ir is enriched in anoxic waters relative to overlying oxic waters, indicating that anoxic sediments are not a major Ir sink. The residence time of dissolved Ir in the oceans is 10³ - 10⁴ years, based on these and other observations. The amount of Ir in Ktr boundary sediments is ≈10³ times the total quantity in the oceans. Part II: The biogeochemistry of methyl bromide (CH₃Br) in the oceans was studied using a steady-state mass-balance model. CH₃Br concentrations are sensitive to temperature and the rate of CH₃Br production. Model production rates correlate strongly with chlorophyll concentrations, indicating CH₃Br biogenesis. This correlation explains discrepancies between two observational studies, and supports suggestions that the ocean is a net sink for atmospheric CH₃Br. The Southern Ocean may be a CH₃Br source. Part III: High resolution, temperature-dependent CO₂ cross sections were incorporated into a 1-D photochemical model of the Martian atmosphere. The calculated CO₂ photodissociation rate decreased by as much as 33% at some altitudes, and the photodissociation rates of H₂O and O₂ increased by as much as 950% and 80%, respectively. These results minimize or even reverse the sense of the CO₂ chemical stability ... |
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