Award: OCE-2346285

The global carbon cycle is a framework of how organic materials move across the planet, namely, its atmospheric, terrestrial (i.e., land), and aquatic (fluvial, oceanic) interfaces. This framework influences Earth’s weather and climate and the movement of organic building blocks (carbon) necessary to sustain living organisms and ecosystems. Decades of research have characterized many of the processes occurring on our planet allowing us to develop fundamental knowledge on the sources and transport of organic molecules.

Fluvial systems are a critical subject of research as they are key transport channels for moving organic material between land and the atmosphere/oceanic interfaces. As carbon leaches from soils into upstream fluvial environments, it begins to undergo a variety of biogeochemical processes such as sunlight-driven photochemical oxidation, biological degradation (including enzymatic oxidation), and Fenton-like oxidation (occurring in the dissolved phase driven by dissolved metals, or on suspended particle surfaces driven by minerals). Because of the major differences in composition of fluvial versus oceanic organic matter, researchers have concluded that these biogeochemical processes destroy nearly 100% of fluvial organics and convert them to atmospheric gases.  This implies that effectively all land-derived inputs of carbon end up being transported to the atmosphere, leaving the ocean and terrestrial carbon cycles disconnected. Therefore, the oceanic carbon cycle is treated as though it is primarily of algal origin.

This project proposed and tested a new alternative, namely, that a high proportion of terrestrial organic carbon survives to enter the oceans while being camouflaged by oxidation processes to appear marine-like (i.e., of algal origin). As part of this project, we tested photochemical and Fenton oxidations. Through various analytical approaches we observed that terrestrial, land-derived compounds can be converted to compounds that appear marine-like. Most notably, we employed stable carbon isotopes (δ¹³C), the currently preferred approach to source determination, and showed that upon oxidation, carbon of known terrestrial origin (confirmed by δ¹³C values of ≤ -25 ‰) becomes transformed to a pool of carbon having structural and isotopic features resembling marine organic matter (δ¹³C values ≥-22 ‰). This important finding indicates that carbon isotopes may be fractionated by effective “distillation” through fluvial networks, coupling their reactive continuum into marine environments.  This implies it is likely that the terrestrial inputs to the oceans are higher than previously estimated. Our findings indicate that current global cycle models need to be revisited and readjusted for the occurrence of this previously underestimated process.

 

Last Modified: 01/19/2026
Modified by: Aleksandar Ivaylov Goranov