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1. Methane emissions from proglacial lakes: A synthesis study directed toward Lake Agassiz

   https://doi.org/10.1016/j.quascirev.2024.108975  

   Brosius, Laura S; Walter_Anthony, Katey M; Lowell, Thomas V; Anthony, Peter; Chanton, Jeffery P; Jones, Miriam C; Grosse, Guido; Breckenridge, Andy J (November 2024, Quaternary Science Reviews)

   QSR (Ed.)

   Large proglacial lakes could have been a significant methane source during the last deglaciation. Today, proglacial lakes are small and mostly limited in the northern hemisphere to the margins of ice sheets in Greenland, Alaska, and Canada, but much larger proglacial lakes collectively flooded millions of square kilometers in the northern hemisphere over the last deglacial period. We synthesize new and existing methane flux measurements from modern proglacial lakes in Alaska and Greenland and use these data together with reconstructed lake area and bathymetry, new paleorecords of sediment organic geochemistry, carbon accumulation, and other proxies to broadly constrain the possible deglacial methane dynamics of a single large North American proglacial lake, Lake Agassiz. While large influxes of glaciogenic material contributed to rapid organic carbon burial during initial lakes phases, limited bioavailability of this carbon is suggested by its likely subglacial origin and prior microbial processing. Water depths of >20 m across 37–90% of the lake area facilitating significant oxidation of methane within the water column further limited emissions. Later phases of lake lowering and subsequent re-expansion into shallow aquatic and subaerial environments provided the most significant opportunity for methane production according to our estimates. We found that Lake Agassiz was likely a small source [0.4–2.7 Tg yr−1 mean (0.1–9.9 Tg yr−1 95% CI)] of methane during the last deglaciation on par with emissions from modern wildfires. Although poor constraints of past global proglacial lake areas and morphologies currently prevent extrapolation of our results, we suggest that these systems were likely an additional source of methane during the last deglacial transition that require further study. 

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2. Monitoring tropical debris-covered glacier dynamics from high-resolution unmanned aerial vehicle photogrammetry, Cordillera Blanca, Peru

   https://doi.org/10.5194/tc-11-2463-2017  

   Wigmore, Oliver; Mark, Bryan (January 2017, The Cryosphere)

   The glaciers of the Cordillera Blanca, Peru, are rapidly retreating and thinning as a result of climate change, altering the timing, quantity and quality of water available to downstream users. Furthermore, increases in the number and size of proglacial lakes associated with these melting glaciers is increasing potential exposure to glacier lake outburst floods (GLOFs). Understanding how these glaciers are changing and their connection to proglacial lake systems is thus of critical importance. Most satellite data are too coarse for studying small mountain glaciers and are often affected by cloud cover, while traditional airborne photogrammetry and lidar are costly. Recent developments have made unmanned aerial vehicles (UAVs) a viable and potentially transformative method for studying glacier change at high spatial resolution, on demand and at relatively low cost.Using a custom designed hexacopter built for high-altitude (4000–6000 m a. s. l. ) operation, we completed repeat aerial surveys (2014 and 2015) of the debris-covered Llaca Glacier tongue and proglacial lake system. High-resolution orthomosaics (5 cm) and digital elevation models (DEMs) (10 cm) were produced and their accuracy assessed. Analysis of these datasets reveals highly heterogeneous patterns of glacier change. The most rapid areas of ice loss were associated with exposed ice cliffs and meltwater ponds on the glacier surface. Considerable subsidence and low surface velocities were also measured on the sediments within the pro-glacial lake, indicating the presence of extensive regions of buried ice and continued connection to the glacier tongue. Only limited horizontal retreat of the glacier tongue was observed, indicating that measurements of changes in aerial extent alone are inadequate for monitoring changes in glacier ice quantity. 

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3. Using a Paired Chironomid δ ¹⁸ O and Aquatic Leaf Wax δ ² H Approach to Reconstruct Seasonality on Western Greenland During the Holocene

   https://doi.org/10.1029/2020PA004169  

   Corcoran, Megan_C; Thomas, Elizabeth_K; Morrill, Carrie (April 2021, Paleoceanography and Paleoclimatology)

   Abstract The Arctic hydrological cycle is predicted to intensify as the Arctic warms, due to increased poleward moisture transport during summer and increased evaporation from seas once ice‐covered during winter. Records of past Arctic precipitation seasonality are important because they provide a context for these ongoing changes. In some Arctic lakes, stable isotopes of oxygen and hydrogen (δ¹⁸O and δ²H, respectively) vary seasonally, due to seasonal changes in precipitation δ¹⁸O and δ²H. We reconstruct precipitation seasonality from Lake N3, a well‐dated lake sediment archive in Disko Bugt, western Greenland, by generating Holocene records of two proxies that are produced at different times of the year, and therefore record different lake water seasonal isotopic compositions. Aquatic plants synthesize waxes throughout the summer, and their δ²H reflects winter‐biased precipitation δ²H at Lake N3, whereas chironomids synthesize their head capsules between late summer and winter, and their δ¹⁸O reflects summer‐biased precipitation δ¹⁸O at Lake N3. During the middle Holocene at Lake N3, aquatic plant leaf wax was strongly²H‐depleted, while chironomid chitin was¹⁸O‐enriched. We guide interpretations of these records using sensitivity tests of a lake water and energy balance model, where we change precipitation amount and isotope seasonality inputs. The sensitivity tests suggest that the contrasting trends between proxies were likely caused by an increase in precipitation amount during all seasons and an increase in precipitation isotope seasonality, in addition to proxy‐specific mechanisms, highlighting the importance of understanding lake‐ and proxy‐specific systematics when interpreting records from sediment archives. 

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4. Glacial Isostatic Adjustment Shapes Proglacial Lakes Over Glacial Cycles

   https://doi.org/10.1029/2022GL101191  

   Austermann, J.; Wickert, A. D.; Pico, T.; Kingslake, J.; Callaghan, K. L.; Creel, R. C. (December 2022, Geophysical Research Letters)

   Abstract As ice sheets load Earth's surface, they produce ice‐marginal depressions which, when filled with meltwater, become proglacial lakes. We include self‐consistently evolving proglacial lakes in a glacial isostatic adjustment (GIA) model and apply it to the Laurentide ice sheet over the last glacial cycle. We find that the locations of modeled lakes and the timing of their disappearance is consistent with the geological record. Lake loads can deflect topography by >10 m, and volumes collectively approach 30–45 cm global mean sea‐level equivalent. GIA increases deglaciation‐phase lake volume up to five‐fold and average along‐ice‐margin depth ≤90 m compared to glaciation‐phase ice volume analogs—differences driven by changes in the position and size of the peripheral bulge. Since ice‐marginal lake depth affects grounding‐line outflow, GIA‐modulated proglacial lake depths could affect ice‐sheet mass loss. Indeed, we find that Laurentide ice‐margin retreat rate sometimes correlates with proglacial lake presence, indicating that proglacial lakes aid glacial collapse. 

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5. In a PICL: The sedimentary deposits and facies of perennially ice‐covered lakes

   https://doi.org/10.1111/sed.12522  

   Rivera‐Hernandez, Frances; Sumner, Dawn Y.; Mackey, Tyler J.; Hawes, Ian; Andersen, Dale T.; Girardclos, ed., Stéphanie (October 2018, Sedimentology)

   Abstract Perennially ice‐covered lakes can have significantly different facies than open‐water lakes because sediment is transported onto the ice, where it accumulates, and sand grains preferentially melt through to be deposited on the lake floor. To characterize the facies in these lakes, sedimentary deposits from five Antarctic perennially ice‐covered lakes were described using lake‐bottom observations, underwater video and images, and sediment cores. One lake was dominated by laminated microbial mats and mud (derived from an abutting glacier), with disseminated sand and rare gravel. The other four lakes were dominated by laminated microbial mats and moderately well to moderately sorted medium to very coarse sand with sparse granules and pebbles; they contained minor interstitial or laminated mud (derived from streams and abutting glaciers). The sand was disseminated or localized in mounds and 1 m to more than 10 m long elongate ridges. Mounds were centimetres to metres in diameter; conical, elongate or round in shape; and isolated or deposited near or on top of one another. Sand layers in the mounds had normal, inverse, or no grading. Nine mixed mud and sand facies were defined for perennially ice‐covered lakes based on the relative proportion of mud to sand and the style of sand deposition. While perennially ice‐covered lake facies overlap with other ice‐influenced lakes and glaciomarine facies, they are characterized by a paucity of grains coarser than granules, a narrow range in sand grain sizes, and inverse grading in the sand mounds. These facies can be used to infer changes in ice cover through time and to identify perennially ice‐covered lakes in the rock record. Ancient perennially ice‐covered lakes are expected on Earth and Mars, and their characterization will provide new insights into past climatic conditions and habitability. 

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