Site U1365 | Site U1367 | Site U1368 | Site U1369 | Site U1370 | Site U1371
IODP Expedition 329:
Subseafloor Life in the South Pacific Gyre
Site U1366 Summary
PDF file is available for download.
The scientific objectives at Site U1366 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
assess from porewater chemistry how basement habitats and potential activities
vary in the underlying basalt with crust age and sediment thickness (from ridge
crest to abyssal plain).
Site U1366, at 5127 m water depth, is located in
ocean crust formed during the Cretaceous Normal Superchron (CNS). The complete
sedimentary succession, from seafloor to underlying basalt, was recovered by
APC in Hole U1366F. Partial successions, from seafloor to various depths, were
also recovered from Holes U1366B through U1366E.
sediment at Site U1366 is primarily clay. It is assigned to two lithologic
units: zeolitic metalliferous pelagic clay (Unit I) and metalliferous clay
(Unit II). The principal components of the sediment are smectite, mica-group
members, phillipsite and red-brown to yellow-brown semi-opaque oxide (RSO).
Manganese nodules are relatively common at the seafloor and at depth in Unit I.
The nodules generally produce peaks in natural gamma radiation and magnetic
susceptibility. Both clay and zeolite exhibit overall trends of decreasing
abundance with increasing depth.
Cell counts are much lower than at the same sediment
depths in all sites previously cored by scientific ocean drilling. They do not
exhibit any consistent trend with depth. Dissolved oxygen, nitrate and phosphate
are present deep in the column.
A wide range of microbiology experiments was initiated
shipboard. 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 nearly 50 m into the basaltic basement.
Subsamples for post-cruise molecular assays and microbiological experiments
were routinely taken from all of the distinct lithologic units.