Photosynthetic zone

Carbon isotopes, 813C reflect temperature of photosynthetic zone -20 to -27 %o... 

The observations have shown that consideration must be given to several different processes of carbonate deposition and/or silica or iron oxide deposition in contact which such bacterial mats. Obviously some important lithification processes take place within the decay zone below the active photosynthetic zone. In most of the cases where lithification was observed there, it was carbonate lithification of a type not related to the photosynthetic depletion of C02. Different filamentous and coccoid cyanobacteria can become more or less lithified depending on slime production, mobilization, outer morphology and microenvironments. 

Until recently it has been assumed that sulfate-reducing bacteria always required a strictly anaerobic environment. These environments are found in deep coastal-plain areas, oil-field brines, and in black (organic-rich), waterlogged soils and muds associated with rivers, lakes, and swamps. Sulfate reduction has also been observed in local microenvironments such as those created by the decay of a fish buried in otherwise oxidizing sediments (Berner 1971). Contrary to traditional belief, active sulfate reduction has also been observed in the presence of dissolved oxygen in the photosynthetic zone of microbial mats (Canfield and Des Marais 1991). 

Another layering that occurs within the 1000 metre surface ocean is the distinction between seawater receiving solar irradiation (the photic zone) and the dark water below. The sun provides heat, UVR, and photosynthetically active... 

Hydrothermal vents and cold seeps, in deep zones of the oceans, are rich in microorganisms, mollusks, and worms, but without other forms of life that characterize the coasts (in particular photosynthetic organisms and their symbionts) and seamounts. 

Cells are isothermal systems—they function at essentially constant temperature (they also function at constant pressure). Heat flow is not a source of energy for cells, because heat can do work only as it passes to a zone or object at a lower temperature. The energy that cells can and must use is free energy, described by the Gibbs free-energy function G, which allows prediction of the direction of chemical reactions, their exact equilibrium position, and the amount of work they can in theory perform at constant temperature and pressure. Heterotrophic cells acquire free energy from nutrient molecules, and photosynthetic cells acquire it from absorbed solar radiation. Both kinds of cells transform this... 

Thin polymer films have many possible technical applications. Transistors and light-emitting diodes are the obvious ones. In ultra-thin films, one may even approach an electronics of molecular dimension. Molecular electronics will be a future challenge for basic and applied science. Nature applies it on a large scale in the reaction centers of the photosynthetic process, where photoinduced mobile charges are separated in some analogy to the separation of the photo-(p-n)-pair in the junction zone of a semiconductor (see Section 13.3.1). 

Chrost, R. J., U. Munster, H. Rai, D. Albrecht, P. K. Witzel, and J. Overbeck. 1989. Photosynthetic production and exoenzymatic degradation of organic matter in the euphoric zone of a eutrophic lake. Journal of Plankton Research 11 223-242. 

The primary engine that drives these ocean interior variations is the photosynthetic fixation of carbon into organic matter by marine phytoplankton in the fight-illuminated upper ocean (euphoric zone) (see Fig. 1.1). Along with carbon, nutrient elements such as nitrogen, phosphorus, iron and many others are taken up and assimilated. Most of the resulting organic matter is either respired or reminerafized... 

Natural populations of Trichodesmium which are often found in the upper layers of the euphotic zone (see Chapter 16 by Karl et al, this volume), appear to be adapted to high light with a relatively shallow compensation depth (typically 100-200 imol quanta s ) for photosynthesis (Carpenter, 1983a,b LaRoche and Breitbarth, 2005). Several early studies considered the light-photosynthesis relationships o Trichodesmium (e.g., Lewis et al, 1988 Li et al, 1980). Half saturation (4) constants for photosynthesis are reported to be about 300 pmol quanta m s (based on results from four studies, LaRoche and Breitbarth, 2005). See LaRoche and Breitbarth (2005) for a recent comprehensive summary of observed physiological and photosynthetic parameters for Trichodesmium. 

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