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Abstract Dissolved organic matter (DOM) in glacier runoff is aliphatic‐rich, yet studies have proposed that DOM originates mainly from allochthonous, aromatic, and often aged material. Allochthonous organic matter (OM) is exposed to ultraviolet radiation both in atmospheric transport and post‐deposition on the glacier surface. Thus, we evaluate photochemistry as a mechanism to account for the compositional disconnect between allochthonous OM sources and glacier runoff DOM composition. Six endmember OM sources (including soils and diesel particulate matter) were leached and photo‐irradiated for 28 days in a solar simulator, until >90% of initial chromophoric DOM was removed. Ultrahigh‐resolution mass spectrometry was used to compare the molecular composition of endmember leachates pre‐ and post‐irradiation to DOM in supraglacial and bulk runoff from the Greenland Ice Sheet and Juneau Icefield (Alaska), respectively. Photo‐irradiation drove molecular level convergence between the initially aromatic‐rich leachates and aromatic‐poor glacial samples, selectively removing aromatic compounds (−80 ± 19% relative abundance) and producing aliphatics (+75 ± 35% relative abundance). Molecular level glacier runoff DOM composition was statistically indistinguishable to post‐irradiation leachates. Bray‐Curtis analysis showed substantial similarity in the molecular formulae present between glacier samples and post‐irradiation leachates. Post‐irradiation leachates contained 84 ± 7.4% of the molecular formulae, including 72 ± 17% of the aliphatic formulae, detected in glacier samples. Our findings suggest that photodegradation, either in transit to or on glacier surfaces, could provide a mechanistic pathway to account for the disconnect between proposed aromatic, aged sources of OM and the aliphatic‐rich fingerprint of glacial DOM.
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Eroding Permafrost Coastlines Release Biodegradable Dissolved Organic Carbon to the Arctic Ocean
Coastal erosion mobilizes large quantities of organic matter (OM) to the Arctic Ocean where it may fuel greenhouse gas emissions and marine production. While the biodegradability of permafrost‐derived dissolved organic carbon (DOC) has been extensively studied in inland soils and freshwaters, few studies have examined dissolved OM (DOM) leached from eroding coastal permafrost in seawater. To address this knowledge gap, we sampled three horizons from bluff exposures near Drew Point, Alaska: seasonally thawed active layer soils, permafrost containing Holocene terrestrial and/or lacustrine OM, and permafrost containing late‐Pleistocene marine‐derived OM. Samples were leached in seawater to compare DOC yields, DOM composition (chromophoric DOM, Fourier transform ion cyclotron resonance mass spectrometry), and biodegradable DOC (BDOC). Holocene terrestrial permafrost leached the most DOC compared to active layer soils and Pleistocene marine permafrost. However, DOC from Pleistocene marine permafrost was the most biodegradable (33 ± 6% over 90 days), followed by DOC from active layer soils (23 ± 5%) and Holocene terrestrial permafrost (14 ± 3%). Permafrost leachates contained relatively more aliphatic and peptide‐like formulae, whereas active layer leachates contained relatively more aromatic formulae. BDOC was positively correlated with nitrogen‐containing and aliphatic formulae, and negatively correlated with polyphenolic and condensed aromatic formulae. Using estimates of eroding OM, we scale our results to estimate DOC and BDOC inputs to the Alaska Beaufort Sea. While DOC inputs from coastal erosion are relatively small compared to rivers, our results suggest that erosion may be an important source of BDOC to the Beaufort Sea when river inputs are low.
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- PAR ID:
- 10527168
- Publisher / Repository:
- JGR Biogeosciences
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 129
- Issue:
- 7
- ISSN:
- 2169-8953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1029/2024JG008233
