TY - JOUR
T1 - Sulfate reduction below the sulfate-methane transition in Black Sea sediments
AU - Holmkvist, Lars
AU - Kamyshny, Alexey
AU - Vogt, Christoph
AU - Vamvakopoulos, Kyriakos
AU - Ferdelman, Timothy G.
AU - Jørgensen, Bo Barker
N1 - Funding Information: We thank Martina Meyer, Thomas Max, Andrea Schipper and Kirsten Imhoff at the Max Planck Institute for Marine Microbiology for assistance in the laboratory with analyses of sulfur speciation. We thank Natascha Riedinger from The Max Planck Institute for Marine Microbiology and Antje Vossmeyer from Department of Marine Sciences, University of Georgia (Athens, USA), for assistance with methane analysis. We thank Nina Knab (University of Southern California, USA) for sampling the sediment used to study the magnetic nodules and Vera Lukies from the Center for Marine Environmental Sciences (MARUM in Bremen, Germany) for assistance with magnetic susceptibility measurements. XRD analyses were performed by the research group Crystallography, Dept. of Geosciences, University of Bremen. We are grateful to Christian Borowski from the MPI for planning and leading the M72-5 METEOR cruise. Finally, we thank the captain and crew of the RV METEOR for a successful expedition. This study was financially supported by the Max Planck Society and the Danish National Research Foundation.
PY - 2011/5/1
Y1 - 2011/5/1
N2 - A sudden increase in salinity about 7000 years ago caused a shift in the deposited sediments of the Black Sea from limnic to brackish-marine. Due to the development of an anoxic deep water basin and a relatively high sulfate concentration, organic matter is mineralized primarily through sulfate reduction in modern Black Sea sediments. Earlier studies showed that sulfate-reducing bacteria are abundant within the limnic sub-surface sediment in spite of extremely low concentrations of sulfate and organic carbon. A main objective of the present study was therefore to understand the depth distribution of sulfate reduction across the different sediment units, even deep below the sulfate-methane transition. Our study combined experimental measurements of sulfate reduction using 35S radiotracer with analyses of sulfur and iron geochemistry in pore water and sediment. Potential sulfate reduction rates were measured with 35S in sediment samples that were amended with sulfate and organic substrates and incubated in time-series up to 48h. Sulfate reduction could thereby be detected and quantified at depths where concentrations of sulfate were otherwise too low to enable calculation of the rates. The results demonstrate that sulfate-reducing bacteria are active several meters below the sulfate-methane transition in Black Sea sediments. The cryptic sulfate reduction below the sulfate-methane transition may be driven by sulfate produced from re-oxidation of reduced sulfur species with oxidized iron minerals buried in the deep limnic sediment.
AB - A sudden increase in salinity about 7000 years ago caused a shift in the deposited sediments of the Black Sea from limnic to brackish-marine. Due to the development of an anoxic deep water basin and a relatively high sulfate concentration, organic matter is mineralized primarily through sulfate reduction in modern Black Sea sediments. Earlier studies showed that sulfate-reducing bacteria are abundant within the limnic sub-surface sediment in spite of extremely low concentrations of sulfate and organic carbon. A main objective of the present study was therefore to understand the depth distribution of sulfate reduction across the different sediment units, even deep below the sulfate-methane transition. Our study combined experimental measurements of sulfate reduction using 35S radiotracer with analyses of sulfur and iron geochemistry in pore water and sediment. Potential sulfate reduction rates were measured with 35S in sediment samples that were amended with sulfate and organic substrates and incubated in time-series up to 48h. Sulfate reduction could thereby be detected and quantified at depths where concentrations of sulfate were otherwise too low to enable calculation of the rates. The results demonstrate that sulfate-reducing bacteria are active several meters below the sulfate-methane transition in Black Sea sediments. The cryptic sulfate reduction below the sulfate-methane transition may be driven by sulfate produced from re-oxidation of reduced sulfur species with oxidized iron minerals buried in the deep limnic sediment.
KW - Black Sea
KW - Potential sulfate reduction
KW - Re-oxidation
KW - Sulfate reduction
KW - Sulfur species
UR - http://www.scopus.com/inward/record.url?scp=79953095519&partnerID=8YFLogxK
U2 - https://doi.org/10.1016/j.dsr.2011.02.009
DO - https://doi.org/10.1016/j.dsr.2011.02.009
M3 - Article
SN - 0967-0637
VL - 58
SP - 493
EP - 504
JO - Deep-Sea Research Part I: Oceanographic Research Papers
JF - Deep-Sea Research Part I: Oceanographic Research Papers
IS - 5
ER -
