Carbonate aggregate mineralogy and stable isotopes at DSDP Site 87-583

Crystalline aggregates composed of calcium carbonate were recovered in the uppermost 50 m of Nankai Trough sediments during DSDP Leg 87A. These aggregates decomposed with time to masses of sandy calcite as determined by X-ray diffraction analysis. Petrographic and scanning electron microscopy revealed textures suggestive of a precursor phrase prior to calcite, and this precursor has been tentatively identified as the mineral ikaite, CaCO3*6H2O. Stable isotope data suggest a large component of terrigenous organic matter as the carbon source, consistent with the appearance of these aggregates in highly reducing pyritic sediments containing abundant plant remains. We propose that these nodules formed in euxinic basins on the upper part of the Trough slope under normal seafloor conditions of pressure and temperature. Calculated temperatures of formation of this phase are not unusually low. The specimens from Site 583 are the first reported occurrences of ikaite in active margin sediments.

Hydrostatic pressure affects aggregate transformation and organic carbon transport: in and beyond the twilight zone: Experiment December 2010

This work aimed to explore evaluated the effects of the increased of hydrostatic pressure on a defined bacterial community on aggregates formed from an axenic culture of marine diatoms by simulating sedimentation to the deep sea by increase of hydrostatic pressure up to 30 bar (equivalent to 3000 m water depth) against control at ambient surface pressure. Our hypothesis was that microbial colonization and community composition and thus microbial OM turnover is greatly affected by changes in hydrostatic pressure during sinking to the deep ocean.

(Table 1, page 171) Thorium and cobalt content of the total aggregate of manganese nodules from various locations

A criterion is suggested for discrimination between ferromanganese oxide minerals, deposited after the introduction of manganese and associated elements in sea water solution at submarine vulcanism, and minerals which are slowly formed from dilute solution, largely of continental origin. The simlultaneous injection of thorium into the ocean by submarine vulcanism is indicated, and its differentiation from continental thorium introduced into the ocean by runoff is discussed.