Sedimentmikrobioiogie und ihre geologischen Aspekte

The influence of bacteria on recent sediments was first discussed in 1885, whenFischer andGazert were discussing the cycle of substances in the sea as well as in sediments. The influence of bacteria on the cycling of C, N, S, P in recent sediments and the open sea was soon accepted by marine geologists. Nevertheless, only very few experiments have, so far, shown more than qualitative and quantitative data collection in various restricted areas. This is due to the extensive and complicated chain of reactions on the surface of sediments and in the sediment itself. Biologists are asking for the amount of organic and inorganic matter which is reworked and released to the sea. Geologists usually emphasize the amount of substances which are sedimentated. For biologists the sediment is only part of their dominant ecosystem (the sea). While, for geologists the “sea” is only furnishing and influencing their first range system sediment. How much then, are bacteria involved in the slow process of conversion from a recent sediment to sedimentary rocks? Bacteria influence more or less strongly and to a more or less advanced degree of diagenesis:

1. The organic matter in sediments and the final form in which it is found.
2. The anions CO₃ ^2?, NO₃ ^?, OH-, SO₄ ^2?, PO₄ ^3? as well as their intermediate stages and the resulting minerals.
3. The cations H⁺, NH₄ ⁺, Ca²⁺, Fe²⁺, Fe³⁺, and a series of metals which are dissolved or precipitated by microbial activities as for example Fe, Mn, Cu, Ag, V, Co, Mo, Ni, U, Se, Zn.
4. The equilibrium of silicium. At least diatoms and radiolarians are precipitating silica, while other reactions which have been proved are not yet shown to influence marine sediments.
5. p_H-values and oxidation-reduction potentials of the sediment.
6. The composition of interstitial waters.
7. The surface activity of minerals, since bacteria are growing especially on particle surfaces.
8. The energy content and temperature of sediments.
9. The texture of fine grained sediments.
10. The fossilization of microfauna, macrofauna and trace fossils.

Sedimentology and mineralogy may also influence the bacterial activities and the composition of the microflora within sediments. Methods and problems of sediment microbiology are demonstrated by some investigations in the German Bay (North Sea) in connection with the first German Underwater Station (UWL). Ecological work proves to be difficult in various directions. The main cause of difficulties in microbiological work on sediments are the great variety of different factors influencing the environment (microbial, chemical, physical, mineralogical), the difficulty of taking representative samples, and the small amount of data which has been collected so far.     

Paläogeographie und Tiefseesedimente des Atlantischen Ozeans

Ohne Zusammenfassung     

Scientific detector workshop 2022 on-sky performance verification of near-infrared e−APD technology for wavefront sensing and demonstration of e−APD pixel performance to improve the sensitivity of large science focal planes

Near-infrared adaptive optics as well as fringe tracking for coherent beam combination in optical interferometry require the development of high-speed sensors. Because of the high speed, a large analog bandwidth is required. The short exposure times result in small signal levels which require noiseless detection. Both requirements cannot be met by state-of-the-art conventional CMOS technology of near-infrared arrays as has been attempted previously. A total of five near-infrared SAPHIRA 320 × 256 pixel HgCdTe e⁻APD arrays have been deployed in the wavefront sensors and in the fringe tracker of the VLTI instrument GRAVITY. The current limiting magnitude for coherent exposures with GRAVITY is m_k = 19, which is made possible with ADP technology. New avalanche photo-diode array (APD) developments since GRAVITY include the extension of the spectral sensitivity to the wavelength range from 0.8 to 2.5 μm. After GRAVITY a larger format array with 512 × 512 pixels has been developed for both AO applications at the ELT and for long integration times. Since dark currents of <10⁻³ e⁻/s have been demonstrated with 1Kx1K e⁻APD arrays and 2Kx2K e⁻APD arrays have already been developed, the possibilities and adaptations of e⁻APD technology to provide noiseless large-format science-grade arrays for long integration times are also discussed.