The central role of Dissolved Organic Matter (DOM) in the ocean carbon cycle and the influence of DOM on numerous physical, chemical, and biological processes are widely recognized, but fundamental questions about the sources, reactivity, and cycling of DOM remain to be answered. Many of the answers to these questions lie hidden within the chemical structures of DOM, but characterization of DOM is challenging because concentrations are low and salts are abundant in seawater. Novel approaches to the isolation and chemical characterization of DOM are beginning transformations of this major carbon reservoir. Tangential-flow ultrafiltration has emerged as a powerful approach for the isolation of different size classes of marine organic matter. Recent efforts in the characterization of ultrafiltered material have provided a wealth of new information about marine DOM. Over the next three years research will focus on the characterization of seawater DOM and build upon major findings of the past three years of research on the characterization of ultrafiltered DOM. The major objectives of the proposed research are: 1) to investigate relationships among size, composition, and microbial reactivity of marine organic matter, and 2) to characterize the distribution and cycling of terrigenous DOM in the ocean.
