gelbstoff
The optically measurable component of dissolved organic matter in water, which primarily occurs naturally from tannin released from decaying detritus. As the amount of organic matter increases, it causes the water to appear green, yellow-green, and then brown.
uncountable
The problem of the Gelbstoff in the sea
Where it comes from
Borrowed from German Gelbstoff (literally “yellow substance”) (coined by K. Kalle in a 1966 article: see the quotation), from German gelb (“amber, yellow”) (ultimately from Proto-Indo-European *ǵʰelh₃wós (“yellow”), from *ǵʰelh₃- (“green, yellow”) + *-wós (“suffix forming adjectives from verb stems”)) + German Stoff (“matter, stuff, substance”) (from Proto-West Germanic *stoppōn (“to close; to fill, stop up”), possibly ultimately from Proto-Indo-European *(s)tew- (“to hit; to push”)).
Adapted from the Wiktionary entry gelbstoff (CC BY-SA 4.0).