Deciphering ocean carbon in a changing world

Abstract

Dissolved organic matter (DOM) in the oceans is one of the largest pools of reduced carbon on Earth, comparable in size to the atmospheric CO2 reservoir. A vast number of compounds are present in DOM, and they play important roles in all major element cycles, contribute to the storage of atmospheric CO2 in the ocean, support marine ecosystems, and facilitate interactions between organisms. At the heart of the DOM cycle lie molecular-level relationships between the individual compounds in DOM and the members of the ocean microbiome that produce and consume them. In the past, these connections have eluded clear definition because of the sheer numerical complexity of both DOM molecules and microorganisms. Emerging tools in analytical chemistry, microbiology, and informatics are breaking down the barriers to a fuller appreciation of these connections. Here we highlight questions being addressed using recent methodological and technological developments in those fields and consider how these advances are transforming our understanding of some of the most important reactions of the marine carbon cycle.

Keywords: cyberinfrastructure; dissolved organic matter; marine microbes.

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.

Fig. 2.

Significant advances that have occurred independently in three fields—microbial ecology, geochemistry, and informatics—have positioned oceanographers for a deeper understanding of the ocean's carbon cycle. The integration of these three fields is yielding insights into the reactions at the foundation of the global carbon cycle. BLAST, basic local alignment search tool; FT-ICRMS, Fourier transform ion cyclotron resonance mass spectrometry; GC-IRMS, gas chromatography isotope ratio mass spectrometry; GC-MS, gas chromatography mass spectrometry; LC-MS, liquid chromatography mass spectrometry; NMR, nuclear magnetic resonance spectroscopy.