Exploration of the sedimentary biosphere in Bengal Fan (IODP Exp. 354)

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Author(s): Adhikari, Rishi Ram; Heuer, Verena Bernadette; Elvert, Marcus; Hoshino, Tatsuhiko; Inagaki, Fumio; Kallmeyer, Jens; Morono, Yuki; Wörmer, Lars; Hinrichs, Kai-Uwe
Author Affiliation(s): Primary:
University of Bremen, MARUM-Center for Marine Environmental Sciences, Bremen, Germany
Japan Agency for Marine-Earth Science and Technology, Japan
German Research Centre for Geosciences, Germany
Volume Title: AGU 2018 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2018; American Geophysical Union 2018 fall meeting, Washington, DC, Dec. 10-14, 2018. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The subseafloor biosphere plays a major role in global elemental cycles, however, opportunities for exploring the deep subseafloor by scientific drilling are limited. Especially the subseafloor biosphere in the Indian Ocean has rarely been investigated in detail so far. During International Ocean Discovery Program Expedition 354 (February - March 2015, Singapore - Colombo, Sri Lanka) we sampled sediments from seven sites along an 8°N transect. Here we present our explorative results about the Bengal Fan biosphere. We quantified (i) prokaryotic cells using epifluorescence microscopy after detaching cells from the sediment, (ii) bacterial endospores by analyzing the diagnostic biomarker dipicolinic acid (DPA) through detection of fluorescence from the terbium-DPA complex, and (iii) microbial activity by analyzing hydrogen utilization potential based on the activity of hydrogenase enzymes, which are ubiquitous in subsurface microorganisms. We measured highest cell concentrations of ca. 107 cells cm-3 in shallow sediments close to the seafloor; these concentrations are lower than in most marine continental margin settings. The cell concentrations decreased exponentially with depth. Endospore concentrations scattered between ca. 105 and 107 cells g-1 sediment and outnumber prokaryotik cells at greater depths. We could not observe a clear relationship of endospore concentrations and sediment depth; instead, endospores appear to be linked to lithology and total organic carbon content. Potential hydrogenase enzyme activity scattered in the µ molar to µ molar range of H2 g-1d-1. Similar to previous observations, per-cell hydrogen utilization depends on vertical biogeochemical zones, which could be due to the differences in hydrogen utilization requirements/efficiency of the respective metabolic processes such as sulfate reduction, methanogenesis, fermentation etc. We observed some interesting shifts in biogeochemical profiles at some depths which may be caused by some episodic sedimentation. Based on our observations, we suggest that the origin and quality of the primarily terrigenous sedimentary material influences microbial activity in the deep biosphere of Bengal Fan sediments.
Year of Publication: 2018
Research Program: IODP2 International Ocean Discovery Program
Key Words: 07 Marine Geology and Oceanography; Bay of Bengal; Bengal Fan; Biosphere; Ecology; Expedition 354; Indian Ocean; International Ocean Discovery Program; Marine sediments; Sediments
Coordinates: N080023 N080026 E0884432 E0855058
Record ID: 2019032007
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