A comparison of the chemical characteristics of oceanic DOM and extracellular DOM produced by marine algae

The chemical characteristics of extracellular high molecular weight (HMW) d issolved organic matter (DOM) from 3 species of marine phytoplankton were c ompared to HMW DOM in seawater. Thalassiosira weissflogii, Emiliania huxley i and Phaeocystis sp., were grown in nutrient enriched seawater that had be en previously ultrafiltered to remove HMW DOM. The extracellular HMW DOM pr oduced in these cultures was isolated by ultrafiltration and characterized using nuclear magnetic resonance (NMR) spectroscopy, and molecular level an alyses. All species exude DOM rich in polysaccharides, and the exudates of T. weissflogii and E. huxleyi closely resemble acyl heteropolysaccharides ( APS) previously identified as major constituents of naturally occurring mar ine HMW DOM. Degradation of the T. weissflogii exudate alters the chemical composition of the DOM, which we attribute to differences in the reactivity of specific polysaccharides. The component within the exudate that most re sembles seawater DOM has a slower degradation rate relative to the total po lysaccharide fraction. Our study indicates that APS isolated from the surfa ce ocean can have a direct algal source and that APS may accumulate in seaw ater as a result of its metabolic resistance.