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

International audienceWith rising temperatures, glaciers are retreating globally. The Greenland icecap has experienced record melt in the past decade (The IMBIE Team, 2020), amplifying freshwater discharge and transport of sediment and dissolved constituents (Hawkings et al., 2015; Meire et al., 2016). Cascading effects on downstream ecosystems remain uncertain, as additional nutrient input could enhance primary productivity in marine environments (e.g., Arrigo et al., 2017; Meire et al., 2017). Conversely, increased turbidity caused by the generally high suspended sediment loads of glacial outflow limits light penetration and thereby suppresses phytoplankton growth (Holding et al., 2019; Hopwood et al., 2020). In addition, retreating icecaps and glaciers expose previously covered landscapes to erosion, generally causing elevated sediment release until stabilization by colonizing vegetation (e.g., Ballantyne, 2002). Erosion rates are projected to increase throughout the Arctic due to rapid thaw and destabilization of permafrost (e.g., Hugelius et al., 2020; Olefeldt et al., 2016; Turetsky et al., 2020), as well as intensifying rain events caused by a shift from snow-to rain-dominated precipitation (e.g., Bintanja & Andry, 2017). Erosion of soils or recent vegetation litter can act as a carbon sink on geological timescales if the released organic carbon (OC) is rapidly buried in marine sediments (e.g., Hilton et al., 2015; Hovius et al., 2011). On the other hand, erosion constitutes a carbon source to the atmosphere if ancient permafrost soil or rock-derived (petrogenic) carbon is mineralized during transport or in marine environments (e.g.