Oxidation Camouflages Terrestrial Organic Matter to Appear Marine-like
Aleksandar I. Goranov, Susan J. Carter, Ann Pearson, Patrick G. Hatcher
Abstract
High Resolution Image Download MS PowerPoint Slide The export of terrestrial organic matter (TOM) to the ocean has been traditionally viewed to be minimal or only of significance in near-coastal continental margins. The broadly accepted explanation for the widespread loss of terrestrial lignin biomarkers and apparent disappearance of the <−25‰ stable carbon isotopic signature (δ 13 C) of TOM is that TOM is almost fully degraded before reaching the open ocean. Oceanic carbon (δ 13 C value ≥ −22‰) is therefore thought to be derived primarily from algae. However, an alternative explanation for the different molecular and δ 13 C signatures in terrestrial and marine environments may be that oxidative processing transforms TOM to appear marine-like. To test this hypothesis, we subjected eight TOM samples to a strong oxidation gradient. At carbon losses typical of TOM degradation during transport and sedimentation (above 60%), the differentiators of provenance disappeared, leaving a residue that was marine-like both chemically (aliphatic- and nitrogen-rich) and isotopically (δ 13 C enrichment of 4 to 9‰). This challenges the validity of conventional two-endmember mixing models, suggesting that a much larger fraction than previously estimated of the organic matter found in the ocean may originate from terrestrial sources, impacting global models of carbon cycling and sequestration.