Rapid changes in global river particulate organic carbon flux

Abstract

Oceanic sequestration of river-exported particulate organic carbon (POC) is an important carbon sink, yet current global carbon budgets often overlook the temporal variability of land–ocean POC export under recent anthropogenic perturbations. Here we estimate trends in near-surface POC flux for 2,409 global rivers from 1984 to 2018 using a satellite-based retrieval framework (Aqua-OC). We find temporal trends in the POC flux in 47% of rivers (1,122 out of 2,409), with 33% (784 rivers) exhibiting increasing trends. Satellite-constrained global river POC flux increases by ~20%, from 144 ± 29 Mt yr−1 in the 1980s to 171 ± 35 Mt yr−1 in the 2010s. These increases are largely driven by tropical deforestation and Arctic permafrost thaw, which outweigh the dampening effects of dams across the Northern Hemisphere. We identify that previously poorly surveyed high-standing islands exhibit an approximately threefold higher increase rate in POC flux than the global mean and contribute disproportionately (~14%) to global river POC export despite covering only ~3% of Earth’s land area. Our analysis reveals rapid decadal changes in global POC transfer within the land-to-ocean aquatic continuum, emphasizing the need to include the temporal variability and spatial heterogeneity of river carbon flux into global carbon budgets. Satellite observations suggest an approximate 20% increase in global riverine particulate organic carbon export to the ocean over the past four decades, driven primarily by tropical deforestation and Arctic permafrost thaw.