Abstract
Here for the first time, we analyze the concentration of dissolved (DOC) and particulate organic carbon (POC), as well as its optical properties (absorbance and fluorescence) from several proglacial streams across Iceland, the location of Europe’s largest non-polar ice cap. We found high spatial variability of DOC concentrations and dissolved organic matter (DOM) composition during peak melt, sampling 13 proglacial streams draining the 5 main Icelandic glaciers. Although glacial-derived organic matter (OM) was dominated by proteinaceous florescence, organic matter composition was variable among glaciers, often exhibiting relatively higher aromatic content and increased humification (based on absorbance and fluorescence measurements) closer to the glacier terminus, modulated by the presence of glacial lakes. Additional sampling locations the in flow path of the river Hvitá revealed that while POC concentrations decreased downstream, DOC concentrations and the autochthonous fraction of OM increased, suggesting the reworking of the organic carbon by microbial communities, with likely implications for downstream ecosystems as glaciers continue to melt. Based on our measured DOC concentrations ranging from 0.11 mg·L−1 to 0.94 mg·L−1, we estimate a potential annual carbon release of 0.008 ± 0.002 Tg·C·yr−1 from Icelandic glaciers. This non-conservative first estimate serves to highlight the potentially significant contribution of Icelandic pro-glacial streams to the global carbon cycle and the need for the quantification and determination of the spatio-temporal variation of DOC and POC fluxes and their respective drivers, particularly in light of increased rates of melting due to recent trends in climatic warming.
Highlights
Glaciers have only recently been recognized as unique ecosystems, with the potential to affect the global carbon cycle [1]
For the first time we investigate the spatial variability of DOC and particulate organic carbon (POC) in proglacial streams in Iceland, highlighting the importance of including Icelandic glaciers in current global organic carbon budgets and further expanding the current understanding of glacial OC composition and the role of glacier-derived OC for downstream carbon fluxes
0.94 mg·L−1 and are comparable with values in other regions (e.g., Alaska, Greenland, European Alps), while POC concentrations exceeded those of the DOC concentration in every investigated proglacial stream
Summary
Glaciers have only recently been recognized as unique ecosystems, with the potential to affect the global carbon cycle [1]. These systems accumulate organic carbon (OC) from the deposition of carbonaceous material derived from terrestrial and anthropogenic sources, in addition to in-situ primary production [1,2,3,4]. Organic carbon stored in glacial ice is released as dissolved and particulate organic carbon (DOC, POC respectively), primarily through melt water at the glacier’s surface, and subglacial flow discharges into proglacial streams toward the ocean [5]. Recent global estimations in a previous study [1] indicate annual exports of glacial DOC and POC of 1.04 Tg·C·yr−1. Current global projections forecast cumulative POC exports of 78 Tg by 2050, more than double the total predicted export of DOC (32.4 Tg) for the same period [1]
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