Distribution and cycling of terrigenous dissolved organic matter in the ocean

Terrigenous dissolved organic matter (DOM) is continuously discharged by rivers into the ocean, yet its distribution and reactivity within ocean basins remain poorly defined aspects of the global carbon cycle1. Direct evidence for the presence of terrigenous DOM in the open ocean has been found only in dissolved humic substances isolated from surface waters of the eastern equatorial Pacific Ocean2. Here we report the detection of low concentrations of lignin—a biopolymer found only in terrestrial vegetation—in DOM collected from the Pacific and Atlantic oceans, indicating that terrigenous DOM is distributed throughout the ocean water column. Higher lignin concentrations in Atlantic waters, relative to Pacific waters, reflect terrigenous DOM concentrations that are 2.6 times higher in the Atlantic. This finding is consistent with the 3.6-times greater riverine water-discharge to the Atlantic Ocean3,4, and with known patterns of ocean circulation5. It appears that terrigenous DOM comprises only a small fraction (0.7–2.4%) of the total DOM in the ocean, and that its oceanic residence time (21–132yr) is much shorter than that of marine DOM6,7. The regeneration of nutrients during rapid cycling of terrigenous DOM could contribute to high rates of primary production in the coastal ocean.