Contrasting Export of Particulate Organic Carbon From Greenlandic Glacial and Nonglacial Streams

Abstract

On￢ﾀﾐgoing shrinkage of Greenland's icecap, permafrost thaw, and changes in precipitation are exposing its landscapes to erosion and remobilization of ancient organic carbon (OC) held in soils and sedimentary rocks. The fate of this OC and potential feedbacks to climate are still unclear. Here, we show that the glacial Zackenberg river (Northeastern Greenland) exports aged particulate OC (POC, uncalibrated radiocarbon ages of ￢ﾈﾼ4,000ￂﾠyears). Many of the smaller periglacial streams affected by abrupt permafrost thaw transport substantially older POC (up to 32,000ￂﾠyears), especially with enhanced discharge following intense precipitation. Mineralogical analysis, and density and size fractionation of soils and both glacial and nonglacial river sediments reveal that OC is largely associated with phyllosilicate minerals, suggesting stabilization against microbial processing. Enhanced export of ancient, mineral￢ﾀﾐassociated OC as a consequence of summer rainfall may accelerate translocation of OC from terrestrial to marine environments, but could have limited consequences for climate.