Enigmatic persistence of dissolved organic matter in the ocean

Marine dissolved organic matter can persist for millennia, but the reasons for this phenomenon are unknown. This Perspective describes and compares two concepts - intrinsic and emergent recalcitrance - explaining marine organic matter persistence. Marine dissolved organic matter (DOM) contains more carbon than the combined stocks of Earth's biota. Organisms in the ocean continuously release a myriad of molecules that become food for microheterotrophs, but, for unknown reasons, a residual fraction persists as DOM for millennia. In this Perspective, we discuss and compare two concepts that could explain this persistence. The long-standing 'intrinsic recalcitrance' paradigm attributes DOM stability to inherent molecular properties. In the 'emergent recalcitrance' concept, DOM is continuously transformed by marine microheterotrophs, with recalcitrance emerging on an ecosystems level. Both concepts are consistent with observations in the modern ocean, but they imply very different responses of the DOM pool to climate-related changes. To better understand DOM persistence, we propose a new overarching research strategy - the ecology of molecules - that integrates the concepts of intrinsic and emergent recalcitrance with the ecological and environmental context.

Automated summary

This perspective discusses the long-term persistence of marine dissolved organic matter, comparing and contrasting two concepts, and proposing a new research strategy that integrates intrinsic and emergent recalcitrance concepts.