Chemical Characterization of Dissolved Organic Matter (DOM) in Seawater: Structure, Cycling and the Role of Biology

Tracy Quan, Ph.D., 2005
Daniel Repeta, Advisor

The goal of this thesis is to investigate three different areas relating to the characterization of dissolved organic matter (DOM). The first section used periodate over-oxidation to analyze the previously unidentified fraction of HMWDOM. The majority of the carbon in two HMWDOM samples was over-oxidizable, including 70% of the aliphatic NMR signal, with a high degree of branching. Based on the 1H NMR spectra data, it was concluded that 6-deoxysugars were the primary compounds in the unidentified fraction of HMWDOM.

In the second section, a new method was presented for the purification of individual underivatized amino acids hydrolyzed from HMWDOM, using cation exchange chromatography and high-pressure liquid chromatography (HPLC) with C18 and strong cation exchange (SCX) columns. Six amino acids were isolated from HMWDOM with sufficient purity and quantity for radiocarbon analysis. These amino acids had a range of ?14C values, from 121‰ to –454‰.

The final section investigates biological controls on dissolved organic nitrogen (DON). Total hydrolyzable amino acids (THAA), and nucleic acids were measured for four incubations: a control, a grazer added, a zero virus, and a 10 times virus. Comparison to the control showed THAA and nucleic acid release were influenced by viruses but not grazers.