No abstract

The crest of Hydrate Ridge harbors a variety of gas hydrates in near-surface sediments. Hydrate formation and destruction continuously shape the ridge topography. Interstitial Cl-anomaly patterns in conjunction with video-guided sampling have established that the uppermost sediment column contains several distinct layers of gas hydrate which are exposed at the sea floor. A methaneoxidizing bacterial consortium populates the exposures of hydrate; colonies of vent macro-fauna are abundant as well. Discharge of methane from destabilized hydrate at the seafloor stimulates high rates of benthic oxygen consumption. These rates, however, vary by many orders of magnitude spatially and temporally, highlighting the need for implementing seafloor observatories at gas hydrate sites. Two types of hydrate fabrics were observed: A highly porous fabric with an estimated pore space of approx. 60 vol.-% and a massive type, with no visible pore space. Both types contain varying amounts of chloride, which need to be taken into account when estimating hydrate volumes from Cldepletion of pore waters. The porous hydrate has low bulk density, which may cause periodic release of large chunks of hydrate from the sea floor. They float to the surface and leave behind a chaotic topography of mounds and depressions. These pieces of floating hydrates constitute an important transport mechanism for methane from the seafloor directly to the atmosphere.

Certain ammonia synthesis conditions lead to nitriding of a relatively thin surface layer of low‐alloyed “hydrogen‐resistant” steels. For reasons of thermodynamic stability of carbides and nitrides this causes a modification of the first, releasing carbon which can effuse from the steel and can react with diffusing hydrogen to form methane. Depending on the level and the direction of the total component stresses, small separations of grains, parallel to the surface, or cracks across the wall may slowly develop. Thus, the Nelson diagram has only limited validity in the case of materials selection for NH3‐containing synthesis gases.

No abstract

No abstract