IODP expedition 331

Strong and expansive subseafloor hydrothermal activities in the Okinawa trough

authored by

Ken Takai, Michael J. Mottl, Simon H.H. Nielsen, J. L. Birrien, S. Bowden, L. Brandt, A. Breuker, J. C. Corona, S. Eckert, H. Hartnett, S. P. Hollis, C. H. House, A. Ijiri, J. Ishibashi, Y. Masaki, S. McAllister, J. McManus, C. Moyer, M. Nishizawa, T. Noguchi, T. Nunoura, G. Southam, K. Yanagawa, S. Yang, C. Yeats

Abstract

Integrated Ocean Drilling Program (IODP) Expedition 331 drilled into the Iheya North hydrothermal system in the middle Okinawa Trough in order to investigate active subseafloor microbial ecosystems and their physical and chemical settings. We drilled five sites during Expedition 331 using special guide bases at three holes for reentry, casing, and capping, including installation of a steel mesh platform with valve controls for postcruise sampling of fluids. At Site C0016, drilling at the base of the North Big Chimney (NBC) mound yielded low recovery, but core included the first Kuroko-type black ore ever recovered from the modern subseafloor. The other four sites yielded interbedded hemipelagic and strongly pumiceous volcaniclastic sediment, along with volcanogenic breccias that are variably hydrothermally altered and mineralized. At most sites, analyses of interstitial water and headspace gas yielded complex patterns with depth and lateral distance of only a few meters. Documented processes included formation of brines and vapor-rich fluids by phase separation and segregation, uptake of Mg and Na by alteration minerals in exchange for Ca, leaching of K at high temperature and uptake at low temperature, anhydrite precipitation, potential microbial oxidation of organic matter and anaerobic oxidation of methane utilizing sulfate, and methanogenesis. Shipboard analyses have found evidence for microbial activity in sediments within the upper 10-30 m below seafloor (mbsf) where temperatures were relatively low, but little evidence in the deeper hydrothermally altered zones and hydrothermal fluid regime.

Organisation(s)

Institute of Microbiology

External Organisation(s)

Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
University of Hawaiʻi at Mānoa

Type

Article

Journal

Scientific Drilling

Pages

19-27

No. of pages

9

ISSN

1816-8957

Publication date

04.2012

Publication status

Published

Peer reviewed

Yes

ASJC Scopus subject areas

Energy Engineering and Power Technology, Mechanical Engineering

Electronic version(s)

https://doi.org/10.2204/iodp.sd.13.03.2011 (Access: Open)