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Life beneath the seafloor of the
South Pacific Gyre
IODP Expedition 329 co-chief scientists: Steven
D'Hondt (University of Rhode Island) and Fumio Inagaki
(Japan Agency for Marine-Earth Science and Technology)
Integrated
Ocean Drilling Program (IODP) Expedition 329 cored and
logged deep-sea sediment and basement at a series of sites
in the South Pacific Gyre. The seven proposed sites are characterized
by different levels of marine productivity and different basement
ages (6 Ma to 84-124.6 Ma), which will potentially demonstrate
varying subseafloor conditions and different microbial communities.
Proposed drilling will sample as deep as 171 meters below
the seafloor, including up to 100 meters below the sediment
into the basaltic basement at three sites.
South Pacific seafloor bathymetry map (Smith and Sandwell
1997) illustrating tectonic setting and location of proposed
sites (circled numbers; white = primary sites, gray = secondary
sites). White circles = nearest DSDP drill sites; blue circles
= nearest ODP drill sites.
The primary purposes of the expedition were to:
- document the nature of microbial communities and test
the energetic limit to life in the most food-poor deep-sea
sediment (what is the SLOWEST metabolic rate at which a
microbe can survive?) and
- test the influence of crust age and sediment thickness
on microbial communities, availability of electron donors
and acceptors, and the hydrologic evolution of crustal basalt.
This project addresses fundamental questions about the subseafloor
biosphere including the following. Are the communities in
mid-gyre subseafloor sediments uniquely structured, i.e. as
this is the first mid-gyre microbiology expedition, how will
these sites compare to those previously studied nearer to
the continents? Do they contain previously unknown kinds of
organisms? Is their primary electron donor organic matter
from the surface world or hydrogen from in situ radioactive
splitting of water? Do their activities and composition vary
with properties of the surface world, such as sea surface
chlorophyll concentrations or organic flux to the seafloor?
Is microbial activity sustainable in subseafloor basalt by
mineral oxidation (e.g., oxidation of iron in the basaltic
minerals) or other processes for tens of Myrs after basalt
formation? [Prior work indicates oxidation pathways should
be absent by 20 Mya, and we will sample both younger and older
rocks during this expedition to test this.] Are microbial
communities recognizably present in subseafloor basalts older
than 13 Ma? [There is evidence for microbial activity in older
rocks, but no definitive indications of in situ microbes
in these older rocks.]
Learn more about the science and outreach associated with
our South Pacific Gyre expedtions from the links below.
> See the South Pacific Gyre IODP Drilling Proposal [PDF]
> About our major programs
> Our expedition
schedule
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