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1. Gulf of Alaska ice-marginal lake area change over the Landsat record and potential physical controls

   https://doi.org/10.5194/tc-15-3255-2021  

   Field, Hannah R. ; Armstrong, William H. ; Huss, Matthias ( January 2021 , The Cryosphere)

   null (Ed.)

   Abstract. Lakes in contact with glacier margins can impact glacierevolution as well as the downstream biophysical systems, flood hazard, andwater resources. Recent work suggests positive feedbacks between glacierwastage and ice-marginal lake evolution, although precise physical controlsare not well understood. Here, we quantify ice-marginal lake area change inunderstudied northwestern North America from 1984–2018 and investigateclimatic, topographic, and glaciological influences on lake area change. Wedelineate time series of sampled lake perimeters (n=107 lakes) and findthat regional lake area has increased 58 % in aggregate, with individualproglacial lakes growing by 1.28 km2 (125 %) and ice-dammed lakesshrinking by 0.04 km2 (−15 %) on average. A statisticalinvestigation of climate reanalysis data suggests that changes in summertemperature and winter precipitation exert minimal direct influence on lakearea change. Utilizing existing datasets of observed and modeled glacialcharacteristics, we find that large, wide glaciers with thick lake-adjacentice are associated with the fastest rate of lake area change, particularlywhere they have been undergoing rapid mass loss in recent times. We observe adichotomy in which large, low-elevation coastal proglacial lakes havechanged most in absolute terms, while small, interior lakes at highelevation have changed most in relative terms. Generally, the fastest-changinglakes have not experienced the most dramatic temperature or precipitationchange, nor are they associated with the highest rates of glacier mass loss.Our work suggests that, while climatic and glaciological factors must playsome role in determining lake area change, the influence of a lake'sspecific geometry and topographic setting overrides these external controls. 

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2. Molecular Signatures of Glacial Dissolved Organic Matter From Svalbard and Greenland

   https://doi.org/10.1029/2020GB006709  

   Kellerman, Anne M. ; Vonk, Jorien ; McColaugh, Stephanie ; Podgorski, David C. ; van Winden, Elise ; Hawkings, Jon R. ; Johnston, Sarah Ellen ; Humayun, Munir ; Spencer, Robert G. M. ( March 2021 , Global Biogeochemical Cycles)

   Glaciers and ice sheets cover over 10 % of Earth's land surface area and store a globally significant amount of dissolved organic matter (DOM), which is highly bioavailable when exported to proglacial environments. Recent rapid glacier mass loss is hypothesized to have increased fluxes of DOM from these environments, yet the molecular composition of glacially derived DOM has only been studied for a handful of glaciers. We determine DOM composition using ultrahigh resolution mass spectrometry from a diverse suite of Arctic glacial environments, including time series sampling from an ice sheet catchment in Greenland (Russell Glacier) and outflow from valley glaciers in catchments with varying degrees of glacial cover in Svalbard. Samples from the Greenland outflow time series exhibited a higher degree of similarity than glacier outflow between glaciers in Svalbard; however, supraglacial meltwater samples from Greenland and Svalbard were more similar to each other than corresponding glacial outflow. Outflow from Russell Glacier was enriched in polyphenolic formulae, potentially reflecting upstream inputs from plants and soils, or inputs from paleosols overridden by the ice sheet, whereas Svalbard rivers exhibited a high level of molecular richness and dissimilarity between sites. When comparing DOM compositional analyses from other aquatic systems, aliphatic, and peptide‐like formulae appear particularly abundant in supraglacial meltwater, suggesting the DOM quickly metabolized in previous incubations of glacial water originates from energy‐rich supraglacial sources. Therefore, as glaciers lose mass across the region, higher‐quality fuel for microbial degradation will increase heterotrophy in coastal systems with ramifications for carbon cycling.

    

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3. The Holocene dynamics of Ryder Glacier and ice tongue in north Greenland

   https://doi.org/10.5194/tc-15-4073-2021  

   O'Regan, Matt ; Cronin, Thomas M. ; Reilly, Brendan ; Alstrup, Aage Kristian ; Gemery, Laura ; Golub, Anna ; Mayer, Larry A. ; Morlighem, Mathieu ; Moros, Matthias ; Munk, Ole L. ; et al ( January 2021 , The Cryosphere)

   Abstract. The northern sector of the Greenland Ice Sheet is considered to beparticularly susceptible to ice mass loss arising from increased glacierdischarge in the coming decades. However, the past extent and dynamics ofoutlet glaciers in this region, and hence their vulnerability to climatechange, are poorly documented. In the summer of 2019, the Swedish icebreakerOden entered the previously unchartered waters of Sherard Osborn Fjord, whereRyder Glacier drains approximately 2 % of Greenland's ice sheet into theLincoln Sea. Here we reconstruct the Holocene dynamics of Ryder Glacier andits ice tongue by combining radiocarbon dating with sedimentary faciesanalyses along a 45 km transect of marine sediment cores collected betweenthe modern ice tongue margin and the mouth of the fjord. The resultsillustrate that Ryder Glacier retreated from a grounded position at thefjord mouth during the Early Holocene (> 10.7±0.4 ka cal BP) and receded more than 120 km to the end of Sherard Osborn Fjord by theMiddle Holocene (6.3±0.3 ka cal BP), likely becoming completelyland-based. A re-advance of Ryder Glacier occurred in the Late Holocene,becoming marine-based around 3.9±0.4 ka cal BP. An ice tongue,similar in extent to its current position was established in the LateHolocene (between 3.6±0.4 and 2.9±0.4 ka cal BP) andextended to its maximum historical position near the fjord mouth around 0.9±0.3 ka cal BP. Laminated, clast-poor sediments were deposited duringthe entire retreat and regrowth phases, suggesting the persistence of an icetongue that only collapsed when the glacier retreated behind a prominenttopographic high at the landward end of the fjord. Sherard Osborn Fjordnarrows inland, is constrained by steep-sided cliffs, contains a number ofbathymetric pinning points that also shield the modern ice tongue andgrounding zone from warm Atlantic waters, and has a shallowing inlandsub-ice topography. These features are conducive to glacier stability andcan explain the persistence of Ryder's ice tongue while the glacier remainedmarine-based. However, the physiography of the fjord did not halt thedramatic retreat of Ryder Glacier under the relatively mild changes inclimate forcing during the Holocene. Presently, Ryder Glacier is groundedmore than 40 km seaward of its inferred position during the Middle Holocene,highlighting the potential for substantial retreat in response to ongoingclimate change. 

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4. Nutrient Uptake in the Supraglacial Stream Network of an Antarctic Glacier

   https://doi.org/10.1029/2020JG005679  

   Bergstrom, A. ; Gooseff, M. N. ; Singley, J. G. ; Cohen, M. J. ; Welch, K. A. ( September 2020 , Journal of Geophysical Research: Biogeosciences)

   In polar regions, where many glaciers are cold based (frozen to their beds), biological communities on the glacier surface can modulate and transform nutrients, controlling downstream delivery. However, it remains unclear whether supraglacial streams are nutrient sinks or sources and the rates of nutrient processing. In order to test this, we conducted tracer injections in three supraglacial streams (62 to 123 m long) on Canada Glacier in the Taylor Valley, of the McMurdo Dry Valleys, Antarctica. We conducted a series of additions including nitrate (N), N + phosphate (P), N + P + glucose (C), and N + C. In two reaches, N‐only additions resulted in N uptake. The third reach showed net N release during the N‐only addition, but high N uptake in the N + P addition, indicating P‐limitation or N + P colimitation. Coinjecting C did not increase N‐uptake. Additionally, in these systems at low N concentrations the streams can be a net source of nitrogen. We confirmed these findings using laboratory‐based nutrient incubation experiments on sediment collected from stream channels on Canada Glacier and two other glaciers in the Taylor Valley. Together, these results suggest there is active biological processing of nutrients occurring in these supraglacial streams despite low sediment cover, high flow velocities, and cold temperatures, modifying the input signals to proglacial streams. As glaciers worldwide undergo rapid change, these findings further our understanding of how melt generated on glacier surfaces set the initial nutrient signature for subglacial and downstream environments.

    

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5. The impacts of warming on rapidly retreating high-altitude, low-latitude glaciers and ice core-derived climate records

   Thompson, L. G. ; Davis, M. E. ; Mosley-Thompson, E. ; Porter, S. E. ; Corrales, G. V. ; Shuman, C. A. ; Tucker, C. J. ( January 2021 , Global and planetary change)

   null (Ed.)

   Alpine glaciers in the low- and mid-latitudes respond more quickly than large polar ice sheets to changes in temperature, precipitation, cloudiness, humidity, and radiation. Many high-altitude glaciers are monitored by ground observations, aerial photography, and satellite-borne sensors. Regardless of latitude and elevation, nearly all nonpolar glaciers and ice caps are undergoing mass loss, which compromises the records of past climate preserved within them. Almost without exception, the retreat of these ice fields is persistent, and a very important driver is the recent warming of the tropical troposphere and oceans. Here we present data on the decrease in the surface area of four glaciers from low- to mid-latitude mountainous regions: the Andes of Peru and northern Bolivia, equatorial east Africa, equatorial Papua, Indonesia, and the western Tibetan Plateau. Climate records based on oxygen isotopic ratios (δ18O) measured in ice cores drilled from several glaciers in these regions reveal that the records from elevations below ~6000 m above sea level have been substantially modified by seasonal melting and the movement of meltwater through porous upper firn layers. Fortunately, δ18O records recovered from higher altitude sites still contain well-preserved seasonal variations to the surface; however, the projected increase in the rate of atmospheric warming implies that climate records from higher elevation glaciers will eventually also be degraded. A long-term ice core collection program on the Quelccaya ice cap in Peru, Earth’s largest tropical ice cap, illustrates that the deterioration of its climate record is concomitant with the increase in mid-troposphere temperatures. The melting ice and resulting growth of proglacial lakes presents an imminent hazard to nearby communities. The accelerating melting of glaciers, if sustained, ensures the eventual loss of unique and irreplaceable climate histories, as well as profound economic, agricultural, and cultural impacts on local communities. 

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