Superoxide reactions in seawater: evaluating the impact of superoxide on trace metal redox cycles and dust dissolution in the open ocean.

Heller, Maija (2009) Superoxide reactions in seawater: evaluating the impact of superoxide on trace metal redox cycles and dust dissolution in the open ocean. (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, Germany, 230 pp.

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Abstract

The major external source of iron (Fe), which is an essential nutrient for all aquatic organisms, to the Ocean is through aeolian deposition of dust. The Superoxide radical (O2-) is a key species affecting metal redox speciation and has been shown to cycle Fe between the thermodynamically favoured, but poorly soluble, Fe(III) species and the more bioavailable reduced Fe(II) form. The primary hypothesis that this thesis examines is whether there is significant dissolution of recently deposited aeolian dust by O2- in the surface waters around Cape Verde in the Atlantic Ocean. A secondary goal was to fully identify and determine the significance of all reactions involving O2- in the open ocean. Due to problems with the methods in the existing published literature I was compelled to develop and evaluate new techniques and methods which could be successfully used for the field expeditions in this work.This includes a new theoretical basis for the interpretation of the data as in many cases the existing theory was too simplistic giving rise to serious artifacts. The first manuscript describes the optimized methodology I developed for the calibration and determination of O2- fluxes in seawater which avoids most of all the discrepancies found in previous works. This was achieved through the application of an O2- thermal source for use as calibration source for both concentration and flux measurements. O2- reactions with dissolved organic matter is the subject of my 2nd manuscript as little is known about these reactions which may be important for the cycling and oxidation of organic matter. This work found in waters close to Cape Verde a relative small but significant contribution from organic material to the O2- decay. The 3rd manuscript examines the question of which processes control dust dissolution in seawater. My results indicate that while ligand promoted and thermal dissolution appeared to be clearly important, the experiments in natural waters were highly variable and most of this variability was apparently related to dynamic factors attributed to changes in surface seawater chemistry occurring over both spatial and temporal scales. Key amongst these factors was most likely the abundance of colloidal metal species and ligands. The last manuscript describes work on superoxide decay kinetics in the Southern Ocean where measurements of O2- decay kinetics throughout the water column were performed. In this work Cu was found to be the major sink of O2- in the Southern Ocean despite being strongly organically complexed. This indicates that the Cu organic complexes react directly with O2-. Contrastingly the reaction with Fe was relatively slow throughout the water column suggesting that organic complexes of iron do not react significantly with O2-.

Document Type: Thesis (PhD/ Doctoral thesis)
Thesis Advisor: Wallace, Douglas W.R. and Körtzinger, Arne
Keywords: Marine chemistry; Superoxid,seawater,trace metals,photochemistry, biogeochemical cycles, chemical speciation and complexation Superoxid,Seewasser,Spurenmetalle,Photochemie,Biogeochemische Kreisprozesse,Chemische Spezifikation und Komplexierung
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
Open Access Journal?: Yes
Projects: SOPRAN
Date Deposited: 13 Jan 2012 13:18
Last Modified: 23 Nov 2012 09:26
URI: http://oceanrep.geomar.de/id/eprint/13503

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