title: Early diagenetic processes generate iron and manganese oxide layers in the sediments of Lake Baikal, Siberia.
abstract: Distinct layers of iron(III) and manganese(IV) (Fe/Mn) oxides are found buried within the reducing part of the sediments in Lake Baikal and cause considerable complexity and steep vertical gradients with respect to the redox sequence. For the on-site investigation of the responsible biogeochemical processes, we applied filter tube samplers for the extraction of sediment porewater combined with a portable capillary electrophoresis instrument for the analyses of inorganic cations and anions. On the basis of the new results, the sequence of diagenetic processes leading to the formation, transformation, and dissolution of the Fe/Mn layers was investigated. With two exemplary cores we demonstrate that the dissolution of particulate Fe and Mn is coupled to the anaerobic oxidation of CH₄ (AOM) either via the reduction of sulphate (SO₄(2-)) and the subsequent generation of Fe(II) by S(-II) oxidation, or directly coupled to Fe reduction. Dissolved Fe(II) diffuses upwards to reduce particulate Mn(IV) thus forming a sharp mineral boundary. An alternative dissolution pathway is indicated by the occurrence of anaerobic nitrification of NH₄(+) observed at locations with Mn(IV). Furthermore, the reasons and consequences of the non-steady-state sediment pattern and the resulting redox discontinuities are discussed and a suggestion for the burial of active Fe/Mn layers is presented.
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-6047 Kastanienbaum, Switzerland. beat.mueller@eawag.ch.
authors.forename: Natascha T
authors.initials: NT
authors.lastname: Torres
authors.forename: Lawrence M
authors.initials: LM
authors.lastname: Och
authors.forename: Peter C
authors.initials: PC
authors.lastname: Hauser
authors.forename: Gerhard
authors.initials: G
authors.lastname: Furrer
authors.forename: Helmut
authors.initials: H
authors.lastname: Brandl
authors.forename: Elena
authors.initials: E
authors.lastname: Vologina
authors.forename: Michael
authors.initials: M
authors.lastname: Sturm
authors.forename: Helmut
authors.initials: H
authors.lastname: Bürgmann
authors.forename: Beat
authors.initials: B
authors.lastname: Müller
mesh_terms: D000693:Anaerobiosis; D004784:Environmental Monitoring; D005290:Ferric Compounds / Q000032:analysis / Q000737:chemistry*; D019015:Geologic Sediments / Q000737:chemistry*; D060106:Lakes / Q000737:chemistry*; D017895:Manganese Compounds / Q000032:analysis / Q000737:chemistry*; D008697:Methane / Q000737:chemistry; D010084:Oxidation-Reduction; D010087:Oxides / Q000032:analysis / Q000737:chemistry*; D012800:Siberia; D013431:Sulfates / Q000737:chemistry; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry
chemical_list: D005290:Ferric Compounds; D017895:Manganese Compounds; D010087:Oxides; D013431:Sulfates; D014874:Water Pollutants, Chemical; C000499:ferric oxide; C027424:manganese oxide; D008697:Methane