Chapter 7 - Reasons Behind the Long-Term Stability of Dissolved Organic Matter

Abstract

Marine dissolved organic matter (DOM) is an enigmatic pool of carbon. It originates largely from marine biota, but it contains more than a thousand times more carbon than all living organisms in the oceans combined. Accumulation occurs because a small fraction of fixed carbon resists microbial mineralization in the ocean for millennia. The reason behind the long-term stability of DOM remains unknown. In this chapter, current hypotheses are discussed. Most likely, an interplay of different mechanisms cause some organic molecules to persist in the ocean for several thousand years. Shortage of essential nutrients, food web mechanisms, and gradients in microbial community structure may cause an accumulation of DOM over months to decades. During this intermediate accumulation, DOM can be subject to secondary, stabilizing abiotic modifications. An alternative idea proposes extreme substrate dilution as a stabilization mechanism, suggesting DOM stability may be independent of molecular structure.