资源环境科技发展态势分析平台

Rivers regulate the global carbon cycle by transferring particulate organic carbon (POC) from terrestrial landscapes to marine sedimentary basins, but the processes controlling the amount and composition of fluvially-exported POC are poorly understood. We propose that hydrodynamic sorting processes modify POC fluxes during fluvial transit. We test this hypothesis by studying POC transported along a ∼1200 km reach of the Rio Bermejo, Argentina. Nanoscale secondary ion mass spectrometry (nanoSIMS) revealed that POC was either fine, mineral-associated organic matter, or coarse discrete organic particles. Mineral-associated POC is more resistant to oxidation and has a lower particle settling velocity than discrete POC. Consequently, hydraulic sorting and downstream fining amplify the proportion of fine, mineral-associated POC from ∼55% to ∼78% over 1220 km of downstream transit. This suggests that mineral-associated POC has a great probability of export and preservation in marine basins than plant detritus, which may be oxidized to CO₂ during transit.