Concentrations of interstitial water, methane, and other sediment components related to microorganisms at DSDP Holes 96-618 and 96-619

Radiolabeled products were formed from labeled substrates during anaerobic incubation of sediments from Sites 618, 619, and 622. One set of experiments formed 14CO2, 14CH4, and 35SH2 from 2-14C-acetate and 35S-sulfate; a second set formed 14CH4 from 14C-methylamine or 14C-trimethylamine. Levels of 14CO2 and 35S2 formed were two to three orders of magnitude greater than 14CH4. Production of 14CH4 by Deep Sea Drilling Project (DSDP) sediments was four to five orders of magnitude less than that formed by anoxic San Francisco Bay sediment. However, incubation of Site 622 sediment slurries under H2 demonstrated production of small quantities of CH4. These results indicate that DSDP sediments recovered from 4 to 167 m sub-bottom (age 85,000-110,000 yr.) harbor potential microbial activity which includes sulfate reducers and methanogens. Analysis of pore waters from these DSDP sites indicates that bacterial substrates (acetate, methylated amines) were present.

Benthic foraminifera and phytodetritus species in sediments from DSDP Leg 85, and ODP Legs 113 and 143

From late middle Eocene through earliest Oligocene, high-latitude regions cooled, and by the end of the period, continental ice sheets existed in Antarctica. Diversity of planktonic microorganisms declined, and modern groups of terrestrial vertebrates originated. Coeval faunal changes in deep-sea benthic foraminifers have been related to cooling of deep waters and increased oxygenation. Cooling, however, occurred globally, whereas species richness declined at high latitudes and not in the tropics. The late Eocene and younger lower-diversity, high-latitude faunas typically contain common Epistominella exigua and Alabaminella weddellensis, opportunistic phytodetritus-exploiting species that indicate a seasonally fluctuating input of organic matter to the sea floor. We speculate that the species-richness gradient and increase in abundance of phytodetritus-exploiting species resulted largely from the onset of a more unpredictable and seasonally fluctuating food supply, especially at high latitudes.