Fig. 1.

Oceanic DOM is a complex mixture of molecules that are produced and consumed by billions of heterotrophic and autotrophic microbes in each liter of seawater. These heterogeneous molecules have varied reactivities toward microbial metabolism, including high reactivity (labile DOM, wide arrows) and minimal reactivity (refractory DOM, narrow arrows). Microbe−DOM interactions affect the concentration and fate of atmospheric CO₂, the accumulation of refractory carbon in the deep ocean, and flux of carbon through the ocean's food webs.