The Biogeochemical Legacy of Arctic Subglacial Sediments Exposed by Glacier Retreat

Abstract

During past periods of advance, Arctic glaciers and ice sheets overrode soil, sediments, and vegetation and buried significant stores of organic matter (OM); these glaciers are now shrinking rapidly due to climate warming. Little is known about the biogeochemical processing of the OM buried beneath glacier ice which makes the processes associated with deglaciation difficult to predict. Subglacial sediments exposed at receding glacier fronts may represent a legacy of past biogeochemical processes. Here, we analyzed sediments from retreating fronts of 19 Arctic glaciers for their mineralogical and elemental composition, contents of major nutrients, OM biomarkers (aliphatic lipids and lignin‐derived phenols), 14C age, and microbial community structure. We show the character of the sediments is mostly determined by local glaciation history and bedrock lithology. Most subglacial sediments offer high amounts of readily bioavailable phosphorus (i.e., loose, labile, and Fe/Al P fractions) but lack readily accessible carbon substrates. The subglacial OM originated mainly from overridden terrestrial vascular plants. The results of OM biomarker analysis and 14C dating suggest the OM substrates degrade in the subglacial environment and are reworked by the resident microbial communities. We argue the biogeochemical legacy of the perishing subglacial environments is an important determinant for the early processes of proglacial ecological succession.

Glacier shrinkage will accelerate downstream decomposition of organic matter and alters microbiome structure and function

“…In fact, some of the clades identified by phylofactorization, such as members of Comamonadaceae, may be constituents of this "gray" food web rather than actually suppressing decomposition. Members of Comamonadaceae are found in abundance within subglacial sediments globally (Vinšová et al, 2022), and interestingly, are also known to oxidize carbon-monoxide in glacier surface sediments (i.e., cryoconite, Franzetti et al, 2016). As glacier influence on GFSs diminishes, their environment becomes more favorable to benthic photoautotrophs, which increasingly sustain a "green" food web and thereby creates niches for bacterial decomposers (i.e., heterotrophs).…”

Fossil organic carbon utilization in marine Arctic fjord sediments

“…However, considering the size 17 of the reservoir and the vulnerability of the glacial ecosystems 19 , further quantitative research into this topic is necessary. Recent studies of the environment based on both modern glacial sediments 51 and paleo CO 2 isotopic compositions 11 indicate that similar utilization of old, previously "locked up" OC may also occur on shore, indicating a larger geographical scope of OC petro utilization. Therefore, in order to fully grasp the impact of glacial retreat on global carbon budgets, studying these processes in both marine and terrestrial settings may be needed, given the IPCC projections based on the low emission RCP2.6 scenario predict global glacial mass loss of 18% in 2100 relative to 2015, suggesting long lasting effects even in the event of zero anthropogenic GHG emissions 19 .…”

Catchment characteristics and seasonality control the composition of microbial assemblages exported from three outlet glaciers of the Greenland Ice Sheet

“…The origin of these soil bacteria in the IS proglacial stream might therefore be a mixture of the two processes described above, namely lateral erosion and dust deposition. On the other hand, we cannot dispute potential subglacial sources of soil bacteria, mainly by glacial erosion of overridden mature soils ( Vinšová et al, 2022 ).…”

“…In contrast, the subglacial environment (at the glacier bed) is characterized by the complete absence of light and restricted gas availability, which can lead to the development of anoxia ( Wadham et al, 2004 ; Lamarche-Gagnon et al, 2019 ). Here, active prokaryotic life is represented by facultatively anaerobic heterotrophs utilizing legacy organic carbon substrates ( Vinšová et al, 2022 ) as well as chemolithoautotrophs ( Boyd et al, 2011 , 2014 ) and methanogens ( Boyd et al, 2010 ; Stibal et al, 2012b ; Dieser et al, 2014 ). As glaciers seasonally melt, these different habitat types become hydrologically connected ( Cameron et al, 2020 ), and entrained microbial cells are exported from the glacial habitat and into proglacial streams.…”