Chapter 2 - Chemical Characterization and Cycling of Dissolved Organic Matter

Abstract

This chapter summarizes advances in our knowledge of dissolved organic matter (DOM) composition, with a particular emphasis on studies completed over the last decade that utilize high-field nuclear magnetic resonance, high-resolution mass spectrometry, proteomics, and related immunochemical assays. Up to 75% of marine DOM can now be recovered for analysis using solid-phase extraction, ultrafiltration, or electrodialysis/reverse osmosis. Spectral and chemical analyses show carbohydrates, proteins, and structurally complex carboxyl-rich aliphatic matter (CRAM) contribute the majority of characterized material. The chemical composition of DOM has a large impact on its accumulation and residence time in the ocean. Carbohydrates and proteins are cycled much more quickly, have much shorter residence times and lower global inventories than CRAM. Processes that lead to the accumulation of carbohydrates and proteins are highly selective, and only a specific fraction of these biopolymers escape degradation to accumulate as DOM. The origin and fate of CRAM are largely unknown, although recent studies suggest a portion of this material has been subjected to elevated temperatures, either in hydrothermal systems or during biomass burning of terrestrial organic matter before transport to the ocean. Radiocarbon measurements and global surveys of deep-sea DOM concentration are providing new insights into the location and timescale of refractory DOM removal processes, significantly enhancing our understanding of CRAM cycling.