Linkages among the bioreactivity, chemical composition, and diagenetic state of marine dissolved organic matter

Bacterial growth and the chemical composition of dissolved organic matter (DOM) were followed during a 10-d decomposition experiment with fresh, algal-derived DOM from an Arctic ice flee. During the experiment similar to 30% of the dissolved organic carbon (DOC) was used by bacteria, indicating the highly reactive nature of this fresh DOM. Over half of the DOC consumption was accounted for as losses of combined neutral sugars and amino acids. The initial composition of the DOM was characterized by high neutral sugar (14% DOG) and amino acid (7.4% DOG) yields and the dominance of glucose (similar to 75 mol%) and glutamic acid (similar to 25 mol%). During microbial degradation the neutral sugar and amino acid yields decreased, and the molecular composition of the DOM became more uniform. The relatively constant abundance of D amino acids and the dramatic changes in the neutral sugar and amino acid compositions indicated that bacteria were important in shaping the chemical composition of marine DOM by selectively removing bioreactive components and by leaving behind biorefractory components. Based on principal component analysis and other parameters, neutral sugars and amino acids were found to be excellent indicators of the diagenetic state and bioavailability of marine DOM.