Uptake of dissolved oxygen during marine diagenesis of fresh volcanic material

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• 作者：D.J. Hembury^a ; ^{d.hembury@noc.soton.ac.uk} ; M.R. Palmer^a ; G.R. Fones^b ; R.A. Mills^a ; R. Marsh^a ; M.T. Jones^c
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：2012
• 期刊代码：27_00167037
• 类别：ear
• 出版时间：1 May, 2012
• 卷：84
• 期：Complete
• 页码：353-368
• 文件大小：977 K

摘要

Convergent plate volcanism typically occurs close to the oceans, hence a high proportion of fresh, highly reactive, volcanogenic material is rapidly deposited onto the seafloor. Previous studies () have shown that dissolved oxygen (O₂) is extensively depleted in the pore waters of ash deposited in the South China Sea from the 1991 Pinatubo eruption. Here, we report the results of an extensive field, laboratory and modelling study of dissolved O₂ concentrations and ancillary geochemical data (pore water NO₂ + NO₃ and solid phase Fe^II/Fe^III and organic carbon) in the sediments surrounding the volcanic island of Montserrat, Lesser Antilles. Dissolved O₂ is depleted to zero within 0.3 cm of the sediment-water interface in sites containing the thickest layers of volcanogenic material (35 cm), compared to a penetration depth of 鈭? cm in sites with minimal ash loading of <0.5 cm. Experimental studies using volcanogenic sediment in a flow-through cell obtained similar O₂ consumption rates to those observed in studies of individual minerals and basalt (). These results, and comparison with other geochemical data, lead us to conclude that the dominant mechanism for dissolved O₂ uptake in volcanogenic sediments is oxidation of silicate-bound Fe^II by a coupled electron transfer reaction. The observation that rapid dissolved O₂ uptake by volcanogenic sediments is a ubiquitous feature of deposition of fresh volcanic material in the oceans may have global implications. While the global amount of dissolved O₂ consumed by this process is trivial compared to that resulting from oxidation of organic carbon, the widespread deposition of volcanic ash from massive explosive eruptions may lead to enhanced preservation of organic carbon in marine sediments and thus lowering of atmospheric CO₂ concentrations during critical periods in Earth history.