The Presence and Widespread Distribution of Dark Sediment in Greenland Ice Sheet Supraglacial Streams Implies Substantial Impact of Microbial Communities on Sediment Deposition and Albedo

Leidman, S. Z.; Rennermalm, Å. K.; Muthyala, Rohi; Guo, Qizhong; Overeem, I.

doi:10.1029/2020gl088444

Cited by 9 publications

(9 citation statements)

References 72 publications

(148 reference statements)

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“…Supraglacial streams and sediment were pervasive throughout the study area. Sediment seemed to consolidate into supraglacial floodplains and melt ponds similar to results found by Leidman et al (2020). Smaller streams tended to have relatively more sediment versus larger and more highly incised channels.…”

Section: Resultssupporting

confidence: 70%

“…Supraglacial streams, for example, are responsible for 12% of the ice albedo variability despite only covering 2% of the ice surface (Ryan et al, 2018). In some regions of the ice sheet, supraglacial streams can also contain expanses of dark sediment deposits covering up to 25% of the channel bed furthering this albedo reduction (Leidman et al, 2020). Understanding the spatial distribution of these features can facilitate a more process-based understanding of satellite-derived albedo measurements (Moustafa et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

“…Additionally, knowing the extent of hydrologic features on the surface of Antarctica can help improve predictions of ice shelf instability (McGrath et al, 2012). Climate models show that the areal coverage of supraglacial surface water will increase with climate warming especially in northeast Greenland, exacerbating the effect of ice sheet melting (Igneczi et al, 2016). Understanding the effect of changing land cover is therefore important for assessing the impact of ice sheets on large scale ocean circulation and sea level rise (Rennermalm et al, 2007;Bakker et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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Terrain-Based Shadow Correction Method for Assessing Supraglacial Features on the Greenland Ice Sheet

Leidman

Rennermalm

Lathrop

et al. 2021

Front. Remote Sens.

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The presence of shadows in remotely sensed images can reduce the accuracy of land surface classifications. Commonly used methods for removing shadows often use multi-spectral image analysis techniques that perform poorly for dark objects, complex geometric models, or shaded relief methods that do not account for shadows cast on adjacent terrain. Here we present a new method of removing topographic shadows using readily available GIS software. The method corrects for cast shadows, reduces the amount of over-correction, and can be performed on imagery of any spectral resolution. We demonstrate this method using imagery collected with an uncrewed aerial vehicle (UAV) over a supraglacial stream catchment in southwest Greenland. The structure-from-motion digital elevation model showed highly variable topography resulting in substantial shadowing and variable reflectance values for similar surface types. The distribution of bare ice, sediment, and water within the catchment was determined using a supervised classification scheme applied to the corrected and original UAV images. The correction resulted in an insignificant change in overall classification accuracy, however, visual inspection showed that the corrected classification more closely followed the expected distribution of classes indicating that shadow correction can aid in identification of glaciological features hidden within shadowed regions. Shadow correction also caused a substantial decrease in the areal coverage of dark sediment. Sediment cover was highly dependent on the degree of shadow correction (k coefficient), yet, for a correction coefficient optimized to maximize shadow brightness without over-exposing illuminated surfaces, terrain correction resulted in a 49% decrease in the area covered by sediment and a 29% increase in the area covered by water. Shadow correction therefore reduces the overestimation of the dark surface coverage due to shadowing and is a useful tool for investigating supraglacial processes and land cover change over a wide variety of complex terrain.

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Section: Resultssupporting

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Terrain-Based Shadow Correction Method for Assessing Supraglacial Features on the Greenland Ice Sheet

Leidman

Rennermalm

Lathrop

et al. 2021

Front. Remote Sens.

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“…Despite their relatively low spatial coverage, supraglacial streams explain 12% of Greenland's albedo variability in the ablation zone (Ryan et al, 2018). One reason for this is that supraglacial streams consolidate low albedo (0.09) sediment along their beds (Ryan et al, 2018;Leidman et al, 2021b). Sediment is transported onto the surface of the Greenland Ice Sheet by windborne transport from local proglacial moraines and valleys (Bøggild et al, 2010;Nelson et al, 2014;Humbert et al, 2020) as well as, but to a lesser extent, accumulation of fine dust particles from long-range sources such as Asia (Bory et al, 2002;Bory et al, 2003), surface melting of ice containing outcroppings of Pleistocene era long-range dust (Bøggild et al, 2010;Cooper et al, 2018), landslides (Svennevig, 2019), and thrust faulting (Moore et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Intra-seasonal variability in supraglacial stream sediment on the Greenland Ice Sheet

Leidman

Rennermalm²,

Muthyala³

et al. 2023

Front. Earth Sci.

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On the surface of the Greenland Ice Sheet, the presence of low-albedo features greatly contributes to ablation zone meltwater production. Some of the lowest albedo features on the Ice Sheet are water-filled supraglacial stream channels, especially those with abundant deposits of consolidated cryoconite sediment. Because these sediments enhance melting by disproportionately lowering albedo, studying their spatial extent can provide a better understanding of Greenland’s contribution to global sea level rise. However, little is known about the spatial distribution of supraglacial stream sediment, or how it changes in response to seasonal flow regimes. Here, we surveyed a supraglacial stream network in Southwest Greenland, collecting imagery from seven uncrewed aerial vehicle (UAV) flights over the course of 24 days in 2019. Using Structure-from-Motion-generated orthomosaic imagery and digital elevation models (DEMs), we manually digitized the banks of the supraglacial stream channels, classified the areal coverage of sediment deposits, and modeled how the terrain influences the amount of incoming solar radiation at the Ice Sheet surface. We used imagery classified by surface types and in-situ spectrometer measurements to determine how changes in sediment cover altered albedo. We found that, within our study area, only 15% of cryoconite sediment was consolidated in cryoconite holes; the remaining 85% was located within supraglacial streams mostly concentrated on daily inundated riverbanks (hereafter termed floodplains). Sediment cover and stream width are highly correlated, suggesting that sediment influx into supraglacial drainage systems widens stream channels or darkens previously widened channels. This reduces albedo in floodplains that already receive greater solar radiation due to their flatness. Additionally, the areal extent of stream sediments increased in August following seasonal peak flow, suggesting that as stream power decreases, more sediment accumulates in supraglacial channels. This negative feedback loop for melting may delay Greenland’s runoff to the latter end of the melt season. This study shows in unprecedented detail where and when sediment is deposited and how these deposits potentially impact the Ice Sheet surface energy balance. These findings may allow for better prediction of how supraglacial floodplains, and the microbiomes they contain, might change in response to increased melting.

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“…This produces dark-coloured material which can further reduce the albedo of the glacial surface, a process known as the 'bio-albedo effect' (Takeuchi et al 2001;Cook et al 2017). However, studies investigating these biological-melt feedbacks have largely been conducted on Arctic and Antarctic glaciers (Säwström et al 2002;Hodson et al 2005;Stibal et al 2008;Uetake et al 2010;MacDonell and Fitzsimons 2012;Zarsky et al 2013;Bagshaw, et al 2013;Lutz et al 2017;Holland et al 2019;Leidman et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Factors controlling the net ecosystem production of cryoconite on Western Himalayan glaciers

et al. 2022

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In situ experiments were conducted to determine the Net Ecosystem Production (NEP) in cryoconite holes from the surface of two glaciers (Patsio glacier and Chhota Shigri glacier) in the Western Himalaya during the melt season from August to September 2019. The study aimed to gain an insight into the factors controlling microbial activity on glacier surfaces in this region. A wide range of parameters, including sediment thickness, TOC %, TN %, chlorophyll-a concentration, altitudinal position, and grain size of the cryoconite mineral particles were considered as potential controlling factors. From redundancy analysis, the rate of Respiration observed in cryoconite at Chhota Shigri glacier was predominantly explained by sediment thickness in cryoconite holes (37.1 % of the total variance, p < 0.05) with Photosynthesis largely explained by the chlorophyll-a content of the sediment (39.6 %, p < 0.05). NEP was explained primarily by the TOC content and sediment thickness in cryoconite holes (35.8 % and 22.1 % respectively, p < 0.05). The altitudinal position of the cryoconite is strongly correlated with biological activity, suggesting that the stability of cryoconite holes was an important factor driving primary productivity and respiration rate on the surface of Chhota Shigri glacier. We calculated that the number of melt seasons required to accumulate organic carbon in thin sediment layers (<0.3 cm), based on our measured NEP rates, ranged from 11 to 70 years, indicating that the organic carbon in cryoconite holes largely derives from allochthonous inputs, such as elsewhere on the glacier surface. Phototrophic biomass in the same thin sediment layer of cryoconite was estimated to take atleast 4 months to be produced in situ (with mean estimated time upto 1.7 ± 1.5 years). Organic matter accumulated inside the cryoconite holes both through allochthonous deposition 2 and via biological activity on the glacier surface in these areas may have the potential to export dissolved organic matter and associated nutrients to downstream ecosystems. Given the importance of Himalayan glaciers as a vital water source for millions of people downstream, this study highlights the need for further investigation in aspects of the quantification of in situ produced organic matter and its impact on supraglacial melting in the Himalaya.

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The Presence and Widespread Distribution of Dark Sediment in Greenland Ice Sheet Supraglacial Streams Implies Substantial Impact of Microbial Communities on Sediment Deposition and Albedo

Cited by 9 publications

References 72 publications

Terrain-Based Shadow Correction Method for Assessing Supraglacial Features on the Greenland Ice Sheet

Terrain-Based Shadow Correction Method for Assessing Supraglacial Features on the Greenland Ice Sheet

Intra-seasonal variability in supraglacial stream sediment on the Greenland Ice Sheet

Factors controlling the net ecosystem production of cryoconite on Western Himalayan glaciers

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