The Fate of Terrestrial Organic Carbon in the Marine Environment

Understanding the fate of terrestrial organic carbon (C-org) delivered to oceans by rivers is critical for constraining models of biogeochemical cycling and Earth surface evolution. C-org fate is dependent on both intrinsic characteristics (molecular structure, matrix) and the environmental conditions to which fluvial C-org is subjected. Three distinct patterns are evident on continental margins supplied by rivers: (a) high-energy, mobile muds with enhanced oxygen exposure and efficient metabolite exchange have very low preservation of both terrestrial and marine C-org (e.g., Amazon subaqueous delta); (b) low-energy facies with extreme accumulation have high C-org preservation (e.g., Ganges-Brahmaputra); and (c) small, mountainous river systems that sustain average accumulation rates but deliver a large fraction of low-reactivity, fossil C-org in episodic events have the highest preservation efficiencies. The global patterns of terrestrial C-org preservation reflect broadly different roles for passive and active margin systems in the sedimentary C-org cycle.