Investigating the effect of hydrothermal conditions on the subvent biosphere of the Okinawa backarc basin

Author(s): Brandt, L. D.; House, C. H.; Nunoura, T.; Yanagawa, K.
Author Affiliation(s): Primary:
Pennsylvania State University, Department of Geosciences, University Park, PA, United States
Japan Agency for Marine-Earth Science and Technology, Japan
Volume Title: AGU 2013 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2013; American Geophysical Union 2013 fall meeting, San Francisco, CA, Dec. 9-13, 2013. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: IODP Expedition 331 to the Okinawa backarc basin provided an opportunity to study an interesting subset of the ocean floor -- the subsurface environment surrounding an active hydrothermal vent. The subsurface sediments of the Iheya North Field within the mid-Okinawa trough are affected by high temperature fluids. In addition, the Okinawa backarc basin is situated on a continental margin. This particular environment has a unique set of conditions for investigating the vertical variability in microbial communities with depth as conditions become increasingly restrictive. IODP Expedition 331 Site C0014, located 450 m east of the active vent, has a surface temperature of 5°C and has no evidence of hydrothermal alteration. Temperature increases with depth at an estimated rate of 3°C/m. Below a depth of ∼10 mbsf, the sedimentary sequence is hydrothermally altered to a pale, gray clay with alteration products illite and montmorillonite. Thus, Site C0014 represents an ideal location to characterize whether 1) the microbial community structure shifts from non-hydrothermal margin microorganisms toward a more temperature-adapted group of microorganisms, or 2) repeating clades represented throughout the sediment column are seemingly adapting to the increasingly extreme conditions. DNA from sediments (0-44 mbsf) was extracted using a modified protocol from the MoBio PowerSoil(Registered) DNA Isolation kit. Primers were designed to amplify the V6-V9 region of the 16S rRNA gene. Select samples were sequenced with the Roche 454 FLX sequencer at The Pennsylvania State University. The amplicon data suggest that the subvent biosphere resides in the top 12-14 meters below seafloor (mbsf). The archaeal sequences abruptly disappear beyond the 14 mbsf horizon. The phylum Euryarchaeota, dominated by Deep Sea Hydrothermal Vent Group 6 (DHVEG-6) and ANME-1, are present throughout the top 14 meters. However, there is an increasingly stronger signal of non-Euryarchaeota clades Marine Crenarchaeotic Group (MCG) and Terrestrial Hot Spring Group (THSCG) below 8 mbsf. Additionally, the bacterial phylum Chloroflexi is present until the 8-10 mbsf horizon. Together, the data indicate a niche for potentially higher-temperature adapted organisms below 8 mbsf, where temperature may become a limiting factor for survival.
Year of Publication: 2013
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 22 Environmental Geology; Expedition 331; IODP Site C0014; Integrated Ocean Drilling Program; North Pacific; Northwest Pacific; Okinawa Trough; Pacific Ocean; West Pacific
Coordinates: N274725 N274725 E1265403 E1265403
Record ID: 2015025285
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