Recycling of Organic Matter in the Sediments of Santa Monica Basin, California Borderland

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• 作者：Tomoko Komada ; David J. Burdige ; Cédric Magen ; Huan-Lei Li…
• 关键词：Methane ; Radiocarbon ; Stable carbon isotope ; Anaerobic ; Remineralization ; Pore water
• 刊名：Aquatic Geochemistry
• 出版年：2016
• 出版时间：December 2016
• 年：2016
• 卷：22
• 期：5-6
• 页码：593-618
• 全文大小：1148KB
• 刊物类别：Earth and Environmental Science
• 刊物主题：Geochemistry; Hydrology/Water Resources; Hydrogeology; Water Quality/Water Pollution;
• 出版者：Springer Netherlands
• ISSN：1573-1421
• 卷排序：22

文摘

Geochemical and isotopic data for the uppermost 1.2 m of the sediments of the central Santa Monica Basin plain were examined to better understand organic matter deposition and recycling at this site. Isotopic signatures (Δ14C and δ13C) of methane (CH₄) and dissolved inorganic carbon (DIC) indicate the occurrence of anaerobic oxidation of CH₄ that is fueled by CH₄ supplied from a relict reservoir that is decoupled from local organic carbon (C_org) degradation and methanogenesis. This finding was corroborated by a flux budget of pore-water solutes across the basal horizon of the profile. Together these results provide a plausible explanation for the anomalously low ratio between alkalinity production and sulfate consumption reported for these sediments over two decades ago. Shifts in Δ14C and δ13C signatures of C_org have previously been reported across the 20-cm depth horizon for this site and attributed to a transition from oxic to anoxic bottom water that occurred ~350 years BP. However, we show that this horizon also coincides with a boundary between the base of a hemipelagic mud section and the top of a turbidite interval, complicating the interpretation of organic geochemical data across this boundary. Radiocarbon signatures of DIC diffusing upward into surface sediments indicate that remineralization at depth is supported by relatively 14C-enriched C_org within the sedimentary matrix. While the exact nature of this C_org is unclear, possible sources are hemipelagic mud sections that were buried rapidly under thick turbidites, and 14C-rich moieties dispersed within C_org-poor turbidite sections.