Riverine input of terrestrial dissolved organic matter (DOM) is an important component of the marine carbon cycle and drives net carbon dioxide production in coastal zones. DOM exports to the Arctic Ocean are likely to increase due to melting of permafrost and the Greenland Ice Sheet, but the quantity and quality of DOM exports from deglaciated watersheds in Greenland, as well as expected changes with future melting, are unknown. We compare DOM quantity and quality in Greenland over the melt seasons of 2017–2018 between two rivers directly draining the Greenland Ice Sheet (meltwater rivers) and four streams draining deglaciated catchments that are disconnected from the ice (nonglacial streams). We couple these data with discharge records to compare dissolved organic carbon (DOC) exports. DOM sources and quality differ significantly between watershed types: fluorescence characteristics and organic molar C:N ratios suggest that DOM from deglaciated watersheds is derived from terrestrial vegetation and soil organic matter, while that in glacial watersheds contains greater proportions of algal and/or freshly produced biomass and may be more reactive. DOC specific yield is similar for nonglacial streams (0.1–1.2 Mg/km²/year) compared to a glacial meltwater river (0.2–1.1 Mg/km²/year), despite orders of magnitude differences in instantaneous discharge. Upscaling based on land cover leads to an estimate of total DOC contributions from Greenland between 0.2 and 0.5 Tg/year, much of which is derived from deglaciated watersheds. These results suggest that future warming and ice retreat may increase DOC fluxes from Greenland with consequences for the Arctic carbon cycle.

中文翻译：

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从格陵兰冰川流域和冰川消融流域出口的有机物在数量和质量上的差异

河流中的陆地溶解有机物（DOM）输入是海洋碳循环的重要组成部分，并驱动沿海地区的二氧化碳净产量。由于多年冻土和格陵兰冰原的融化，向北冰洋的DOM出口量可能会增加，但是从格陵兰冰川流域的DOM出口的数量和质量以及未来融化的预期变化尚不清楚。我们比较了2017-2018年融化季节格陵兰岛的DOM数量和质量，两条河流直接排放格陵兰冰原（融水河），四股河流排放与冰层分离的冰川集水区（非冰川河流）。我们将这些数据与排放记录结合起来，以比较溶解有机碳（DOC）的出口。流域类型之间的DOM来源和质量明显不同：荧光特征和有机摩尔C：N比值​​表明，来自冰河流域的DOM来自陆生植被和土壤有机质，而冰川流域的DOM中含有更多比例的藻类和/或新鲜产生的生物质，可能更具反应性。非冰川流的DOC比产量相似（0.1–1.2 Mg / km² /年）与冰川融水河（0.2–1.1 Mg / km ² /年）相比，尽管瞬时排放量存在数量级差异。根据土地覆盖率进行升级，估计格陵兰岛的DOC总贡献量在每年0.2至0.5 Tg之间，其中大部分来自冰川消融的流域。这些结果表明，未来的变暖和退冰可能会增加格陵兰的DOC通量，从而影响北极的碳循环。