is a term for (yellow coloured) dissolved organic matter in water. Gelbstoff means literally, 'yellow matter
' in German. In a paper of 1976 Kirk
suggested the alternative name 'gilvin' (Latin, gilvus = pale yellow), for the yellow pigments in natural waters, to replace 'yellow substance
' or 'gelbstoff
'. This might of course be easier to handle than CDOM, an abbreviation that stands for “coloured dissolved organic matter
”. Gelbstoff or gilvin, is an important component of water quality in natural waters. Quantitative study of gilvin production is however difficult since gilvin is not a well defined substance. Gelbstoff occurs naturally in waters primarily as a result of tannins released from decaying detritus (non-living particulate organic material). Gelbstoff most strongly absorbs short wavelength light ranging from blue to ultraviolet, whereas pure water absorbs longer wavelength red light. Therefore, non-turbid water with little or no gelbstoff appears blue. The color of water will range through green, yellow-green, and brown as gelbstoff increases. Well in fact I suppose it it well known that if you mix blue and yellow you get green.
The term tannin (from tanna, an Old High German word for oak or fir tree, as in Tannenbaum) refers to the use of wood tannins from oak in tanning animal hides into leather; hence the words "tan" and "tanning" for the treatment of leather. Some of us also know it from a special taste in wine that has been stored in oak wine barrels. The oak is affecting the color, flavor, tannin
profile and texture of the wine. The presence of tannin in peat bogs has also added to the preservation of ‘bog bodies’ by having anti-bacterial properties.
The image above from NASA Earth Observatory
shows multiple shades of green in the North Sea. Some of the greener colours near the coast may be caused by gelbstoff. Gelbstoff resulting from decaying bits of once-living organisms, dissolved organic matter can color ocean waters over a wide enough area to appear in satellite imagery. Farther out to sea, the blue-green shades may result from a mixture of re-suspended sediment and phytoplankton — microscopic marine plants that thrive along coastlines and continental shelves.