Browsing by Author "Zappa, Christopher J."

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    Basal channels drive active surface hydrology and transverse ice shelf fracture
    (Science, 2018-06-13) Dow, Christine F.; Lee, Won Sang; Greenbaum, Jamin S.; Greene, Chad A.; Blankenship, Donald D.; Poinar, Kristin; Forrest, Alexander L.; Young, Duncan A.; Zappa, Christopher J.
    Ice shelves control sea-level rise through frictional resistance, which slows the seaward flow of grounded glacial ice. Evidence from around Antarctica indicates that ice shelves are thinning and weakening, primarily driven by warm ocean water entering into the shelf cavities. We have identified a mechanism for ice shelf destabilization where basal channels underneath the shelves cause ice thinning that drives fracture perpendicular to flow. These channels also result in ice surface deformation, which diverts supraglacial rivers into the transverse fractures. We report direct evidence that a major 2016 calving event at Nansen Ice Shelf in the Ross Sea was the result of fracture driven by such channelized thinning and demonstrate that similar basal channel-driven transverse fractures occur elsewhere in Greenland and Antarctica. In the event of increased basal and surface melt resulting from rising ocean and air temperatures, ice shelves will become increasingly vulnerable to these tandem effects of basal channel destabilitization.
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    Observations of submesoscale eddy-driven heat transport at an ice shelf calving front
    (Springer Nature, 2022-06-22) Friedrichs, Drew M.; McInerney, Jasmin B. T.; Oldroyd, Holly J.; Lee, Won Sang; Yun, Sukyoung; Yoon, Seung-Tae; Stevens, Craig L.; Zappa, Christopher J.; Dow, Christine F.; Mueller, Derek; Steiner, Oscar Sepulveda; Forrest, Alexander L.
    Antarctica’s ice shelves buttress the continent’s terrestrial ice, helping slow the loss of grounded ice into the ocean and limiting sea level rise. Ice-ocean interaction plays a critical role in ice shelf stability by driving basal melt rates. Consequently, improved prediction of the future state of ice shelves lies in understanding the coastal ocean mechanics that deliver heat to their cavities. Here, we present autonomous glider-based observations of a coherent structure at the calving front of a cold-water cavity ice shelf (Nansen Ice Shelf, East Antarctica). This ~10 km-wide eddy dominated the local ocean circulation in the austral summer of 2018/2019, promoting an upwelling of cold ice shelf water and a deepening of warm surface water. Microstructure turbulence measurements show a resulting maximum vertical heat transport of 10 W m−2 at depths equivalent to the ice shelf draft. Similar eddy-driven heat transport further into the ice shelf cavity would support enhanced summertime melt in regions of shallower ice draft.