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1. Hydraulic transmissivity inferred from ice-sheet relaxation following Greenland supraglacial lake drainages

   https://doi.org/10.1038/s41467-021-24186-6  

   Lai, Ching-Yao ; Stevens, Laura A. ; Chase, Danielle L. ; Creyts, Timothy T. ; Behn, Mark D. ; Das, Sarah B. ; Stone, Howard A. ( December 2021 , Nature Communications)

   null (Ed.)

   Abstract Surface meltwater reaching the base of the Greenland Ice Sheet transits through drainage networks, modulating the flow of the ice sheet. Dye and gas-tracing studies conducted in the western margin sector of the ice sheet have directly observed drainage efficiency to evolve seasonally along the drainage pathway. However, the local evolution of drainage systems further inland, where ice thicknesses exceed 1000 m, remains largely unknown. Here, we infer drainage system transmissivity based on surface uplift relaxation following rapid lake drainage events. Combining field observations of five lake drainage events with a mathematical model and laboratory experiments, we show that the surface uplift decreases exponentially with time, as the water in the blister formed beneath the drained lake permeates through the subglacial drainage system. This deflation obeys a universal relaxation law with a timescale that reveals hydraulic transmissivity and indicates a two-order-of-magnitude increase in subglacial transmissivity (from 0.8 ± 0.3  $${\rm{m}}{{\rm{m}}}^{3}$$ m m 3 to 215 ± 90.2  $${\rm{m}}{{\rm{m}}}^{3}$$ m m 3 ) as the melt season progresses, suggesting significant changes in basal hydrology beneath the lakes driven by seasonal meltwater input. 

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2. Shallow Fracture Buffers High Elevation Runoff in Northwest Greenland

   https://doi.org/10.1029/2022GL101151  

   Culberg, Riley ; Chu, Winnie ; Schroeder, Dustin M. ( December 2022 , Geophysical Research Letters)

   The expansion of refrozen ice slabs in Greenland's firn may enhance meltwater runoff and increase surface mass loss. However, the impermeability of ice slabs and the pathways for meltwater export from these regions remain poorly characterized. Here, we present ice‐penetrating radar observations of extensive meltwater infiltration and refreezing beneath ice slabs in Northwest Greenland. We show that these buried ice complexes form where supraglacial streams or lakes drain through surface crevasses into relict firn beneath the ice slabs. This suggests that the firn can continue to buffer mass loss from surface meltwater runoff and limit meltwater delivery to the ice sheet bed even after ice slabs have formed. Therefore, a significant time lag may exist between the initial formation of ice slabs and the onset of complete surface runoff and seasonal meltwater drainage to the subglacial system in interior regions of the ice sheet.

    

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3. Tidewater-glacier response to supraglacial lake drainage

   https://doi.org/10.1038/s41467-022-33763-2  

   Stevens, Laura A. ; Nettles, Meredith ; Davis, James L. ; Creyts, Timothy T. ; Kingslake, Jonathan ; Hewitt, Ian J. ; Stubblefield, Aaron ( October 2022 , Nature Communications)

   The flow speed of the Greenland Ice Sheet changes dramatically in inland regions when surface meltwater drains to the bed. But ice-sheet discharge to the ocean is dominated by fast-flowing outlet glaciers, where the effect of increasing surface melt on annual discharge is unknown. Observations of a supraglacial lake drainage at Helheim Glacier, and a consequent velocity pulse propagating down-glacier, provide a natural experiment for assessing the impact of changes in injected meltwater, and allow us to interrogate the subglacial hydrological system. We find a highly efficient subglacial drainage system, such that summertime lake drainage has little net effect on ice discharge. Our results question the validity of common remote-sensing approaches for inferring subglacial conditions, knowledge of which is needed for improved projections of sea-level rise.

    

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4. Repeat Subglacial Lake Drainage and Filling Beneath Thwaites Glacier

   https://doi.org/10.1029/2020GL089658  

   Malczyk, G. ; Gourmelen, N. ; Goldberg, D. ; Wuite, J. ; Nagler, T. ( December 2020 , Geophysical Research Letters)

   Active subglacial lakes have been identified throughout Antarctica, offering a window into subglacial environments and their impact on ice sheet mass balance. Here we use high‐resolution altimetry measurements from 2010 to 2019 to show that a lake system under the Thwaites Glacier undertook a large episode of activity in 2017, only four years after the system underwent a substantial drainage event. Our observations suggest significant modifications of the drainage system between the two events, with 2017 experiencing greater upstream discharge, faster lake‐to‐lake connectivity, and the transfer of water within a closed system. Measured rates of lake recharge during the inter‐drainage period are 137% larger than modeled estimates, suggesting processes that drive subglacial meltwater production, such as geothermal heat flux or basal friction, are currently underestimated.

    

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5. Neogene‐Quaternary Uplift and Landscape Evolution in Northern Greenland Recorded by Subglacial Valley Morphology

   https://doi.org/10.1029/2021JF006395  

   Paxman, Guy J. G. ; Tinto, Kirsty J. ; Austermann, Jacqueline ( December 2021 , Journal of Geophysical Research: Earth Surface)

   The landscape hidden beneath the Greenland Ice Sheet remains one of the most sparsely mapped regions on Earth, but offers a unique record of environmental conditions prior to and during widespread glaciation, and of the ice sheet's response to changing climates. In particular, subglacial valleys observed across Greenland may preserve geomorphological information pertaining to landscape and ice sheet evolution. Here we analyze the morphology of a subglacial valley network in northern Greenland using bed elevation measurements acquired during multi‐year airborne radio‐echo sounding surveys. Channel profile morphologies are consistent with a primarily fluvial origin of the network, with evidence for localized modification by ice and/or meltwater. Gravity and magnetic anomalies suggest that the spatial organisation of the valley network is influenced by regional‐scale geological structure, implying a long‐lived and well‐established hydrological system. We also document two knickzones in the valley longitudinal profile and terraces above the channel floor in the lower course of the network. These observations, combined with stream power modeling, indicate that northern Greenland experienced two episodes of relative base level fall during the Neogene (∼150 m at ca. 12–3.7 Ma and ∼380 m at ca. 8.2–2.8 Ma) that resulted in channel profile adjustment via incision and knickzone retreat. The timing of the inferred base level fall correlates with other onshore and offshore records of uplift, denudation, and/or relative sea level change, and we suggest that tectonic and/or mantle‐driven uplift played an important role in the genesis of the modern landscape of northern Greenland.

    

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