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doi:10.2204/iodp.proc.336.106.2012

Microbiology

Sediments were cored with the APC and the sediment/​basement interface was cored with the XCB at three sites (U1383, U1382, and U1384). In Hole U1383D, 44.3 m of sediment was cored. Of this cored interval, the lowermost 1 m was XCB-cored basalt and limestone-cemented breccia (0.76 m of basement was recovered). In Hole U1383E, 44.2 m of sediment and 1 m of basaltic basement were cored, of which 0.3 m was recovered. Hole U1382B was drilled midway between Holes 395A and U1382A; here, 90.0 m of sediment was APC cored and 8.8 m was advanced with the XCB, recovering a sedimentary breccia from between 90 and 91 mbsf and basaltic basement from the bottom of the hole. In Hole U1384A, 94.7 m of sediment is underlain by basalt and limestone-cemented breccia, of which 1 m was drilled and 0.6 m was recovered.

As described in “Lithostratigraphy,” the sediment was nannofossil ooze with layers of foraminiferal sand. The lowermost several meters of the sedimentary pile are composed of brown clay. Sediments from Hole U1382B showed moderately rounded rock fragments concentrated in layers or dispersed in the ooze. These fragments ranged from coarse sand to pebble in grain size and consisted of serpentinized mantle peridotite, gabbro, troctolite, and basalt. Both XCB cores from Hole U1382B also contained coarse sediment with predominantly serpentinite clasts, including soapstone and talc-tremolite schist. The occurrence of these rock fragments was consistent with the polymict sedimentary breccia recovered during basement drilling at Sites 395 and U1382. The deformed and metasomatized lithologies encountered in Hole U1382B corroborated the hypothesis that this material was transported to the Site U1382 area in North Pond by mass wasting events and that its source was oceanic core complex, probably in the southern rift mountains.

Each of the four holes cored were intensively sampled for microbiology and interstitial water analyses, as described in detail in “Microbiology” in the “Methods” chapter (Expedition 336 Scientists, 2012a). The sampling program was similar for each of the holes. In total, 167 whole-round samples for interstitial waters and 691 whole-round samples for microbiologic analyses were collected. Sampling resolution was increased in the bottom section. As described in “Microbiology” in the “Methods” chapter (Expedition 336 Scientists, 2012a), whole-round cores were preserved for shore-based molecular analysis to provide a detailed description of the microbial community. Shipboard enrichment cultures were established to enrich for different metabolic functional groups. These cultures will be analyzed on shore for both metabolic activity and community composition. Sediment samples were also analyzed for oxygen using optodes as described in “Inorganic geochemistry” in the “Methods” chapter (Expedition 336 Scientists, 2012a). Hard rock samples were sectioned and allocated following previous strategies established during the hard rock drilling phase of the expedition. Multiple basalt samples were provided for RNA/DNA, geochemistry, and culture analyses. All requests were filled to the best ability of the group given the time and materials available.

To examine the potential for contamination in the sediment whole-round core used for microbiological analysis, the density of fluorescent microspheres in the interior and exterior of sediment cores was examined (see “Microbiology” in the “Methods” chapter [Expedition 336 Scientists, 2012a] for details). These analyses were conducted in a shore-based laboratory after the end of the expedition, using an Axiovert epifluorescence microscope with 40× objective magnification (305 µm × 305 µm field of view) with random selection of 20–40 fields of view. Phosphate-buffered saline (PBS)-suspended sediment sample (20 µL) (see “Microbiology” in the “Methods” chapter [Expedition 336 Scientists, 2012a]) was filtered on 0.2 µm mesh polycarbonate 25 mm diameter filters for these analyses. The results of these analyses are presented in Table T5. Not surprisingly, several of the cored sediment sections from all sediment holes had abundant microsphere contamination in the interior and exterior of the cores, as can be expected due to the sandy and disturbed nature of some of the sediment intervals. Many sections had microsphere-free interiors even when the exterior portion of the core was contaminated.

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