Site U1365 | Site U1366 | Site U1368 | Site U1369 | Site U1370 | Site U1371
IODP Expedition 329:
Subseafloor Life in the South Pacific Gyre
Site U1367 Summary
PDF file is available for download.
Site U1367 was selected as a drilling target because (1)
its microbial activities and cell counts were expected to be characteristic of
a setting midway between the western gyre edge and the gyre center, and (2) its
basement age renders it a reasonable location for testing the extent of basalt
alteration and openness to flow in a thinly sedimented region of ~33.5 Ma
The principal objectives at Site U1367 are (1) to document
the habitats, metabolic activities, genetic composition and biomass of
microbial communities in subseafloor sediment with very low total activity, (2)
to test how oceanographic factors control variation in sedimentary habitats,
activities and communities from gyre center to gyre margin, (3) to quantify the
extent to which these sedimentary communities may be supplied with electron
donors by water radiolysis, (4) to determine how habitats, potential activities
and, if measurable, communities in subseafloor basalt vary with crust age and hydrologic regime (from ridge crest to abyssal plain).
Site U1367, at 4285 m water depth, is located in ocean crust formed during magnetic polarity Chron 13n [33.3 – 33.7 Ma]. The
complete sedimentary succession, from seafloor to underlying basalt, was
recovered by APC in Holes U1367B through U1367E. The sediment/basalt contact
varies by a few meters from hole to hole. The lowermost sediment and fragments
of the underlying basalt were recovered by RCB in Hole U1367F. Core recovery of
the basalt was unusually low (11%). Continuous infall of basaltic debris forced
us to terminate the hole early, preventing us from reaching sufficient depth
below seafloor to deploy downhole logging tools.
sediment at Site U1367 is composed of ~6 meters of pelagic clay (Unit I)
overlying ~16 meters of Oligocene carbonate ooze (Unit II). The principal
components of the clay are smectite and mica-group members, phillipsite (a
zeolite), and red-brown to yellow-brown semi-opaque oxide (RSO). The ooze is
composed mainly of coccolithophores and RSO, accompanied by foraminifera. The
clay and the ooze differ significantly in several physical properties,
including porosity, bulk density, electrical conductivity, magnetic
susceptibility and natural gamma radiation. Although unit thickness and
composition vary from hole to hole, the general composition is very similar in
Manual cell counts are much lower than at the same
sediment depths cored by all previous scientific ocean drilling expeditions.
They decline rapidly with initial depth below the seafloor. Dissolved oxygen,
nitrate and phosphate are present deep in the column.
The recovered sequence of basement rock is composed of
pillow basalt fragments with prominent chill margins. Secondary mineralization
and wall-rock interaction is limited in the recovered basalt. However, it is
likely that the most altered portions of the basalt were not recovered.
A wide range of microbiology experiments was initiated on
board the JOIDES Resolution. Experiments
on major microbial processes and experiments for enumeration of viable microbes
were initiated at selected depths ranging from near the sediment/water
interface to ~30 m into the basaltic basement. Subsamples were routinely taken
from all of the distinct lithologic units for postcruise molecular assays and