Previous   |    Next

doi:10.2204/iodp.proc.336.203.2015

Introduction

The majority of habitable environments on the Earth are dark biosphere separated from sunlight. About one-third of all biomass and about three-fourths of all prokaryotic cells on the Earth are in the sediments buried in the oceanic subsurface (Whitman et al., 1998). Kallmeyer et al. (2012) report that total cell abundance in subseafloor sediments (2.9 × 10²⁹) is about 92% less than the previous estimated values by Whitman et al. (1998) (35.5 × 10²⁹). During this decade, basaltic ocean crust has been focused on as a new deep submarine biosphere (Bach and Edwards, 2003). To date, Juan de Fuca Ridge in the eastern Pacific has been a primary study site for basaltic ocean crust because water-rock reactions in basaltic crusts can be clearly observed there (e.g., Wheat et al., 2000; Fisher et al., 2003). In the Juan de Fuca basaltic oceanic crust, iron cycling, both oxidation and reduction, supports metabolic activity in basalts; however, the microorganisms responsible for Fe oxidation in basalts are not identified (Orcutt et al., 2011). From September to November 2011, Integrated Ocean Drilling Program (IODP) Expedition 336 explored the deep biosphere at North Pond, on the western flank of the Mid-Atlantic Ridge (Expedition 336 summary [Expedition 336 Scientists, 2012]). The North Pond sedimentary environment is oligotrophic and low temperature (10°–15°C) and allows fast seawater circulation (2–3 m/h) (Langseth et al., 1984). Therefore, the site is a good target for comparison to Juan de Fuca Ridge, which has higher temperatures (~60°C) and slower seawater circulation (approximately 1400–1500 kg/day) (Wheat et al., 2003). However, North Pond sediment contains low organic carbon contents (<0.3 wt%) (Ferdelman et al., 2011), which makes life detection at this site challenging. In this study, we analyze organic carbon and carbon isotopes of basalts and sediments collected from North Pond to understand the origin and formation of carbon compounds in relation to possible microbial activity in the basaltic crust.

Top of page   |    Previous   |    Next