The surface hydrology of Antarctica’s floating ice

Imagine an area the size of US state Rhode Island, some 3000 km2, breaking off from land, collapsing, and floating away. Picture Brown University completely submerged houses falling into Atlantic Ocean. Luckily for residents Providence rest state, Island is a relatively stable land mass, so such collapse unrealistic scenario. But if it were built on Antarctic ice shelf, story would be little different.NASA’S EARTH OBSERVATORYPPT|High-resolutionIce flows across Antarctica continues to do as reaches edge mass extends over ocean. The huge tongues often remain attached continent. Anything that remains grounded part sheet; shelf. Floating shelves surround three-quarters Antarctica’s coast make up about 11% its total area. One largest, Ross Ice Shelf, roughly France. George VI Shelf shown in opening image, taken by NASA’s Landsat 8 January 2020.It may seem intuitive all added ocean melting raise global sea level, but that’s not case. By Archimedes’s principle, water have already displaced their own weight, disintegration or won’t change level. do, however, regulate speed glaciers land. As figure 1, act hold back. Take shelf away, are free flow Any liquid take with them will Of Earth’s fresh water, 70% stored ice; equivalent 58 meters sea-level rise melt.Figure 1. Resistive stresses restrain flowing Some sheet left floats surface, where prevents more accelerating contributing increased (Image Sammie Buzzard Donna Padian.)PPT|High-resolutionAlthough located thousands kilometers away anywhere else Earth, loss has consequences. It can circulation, temperature, salinity when cold, collapsed melts. Furthermore, sudden collapses destroy habitats penguins various other creatures.In 2002 Larsen B suddenly disintegrated spectacularly. shattered smaller pieces was dispersed surrounding less than month. Scientists observed several major ice-loss events past few decades, including B’s next-door neighbors. A 1995, 2017 C lost iceberg larger areas combined.11. B. Davies, “The growing rift,” AntarcticGlaciers.org (19 June 2017).In case B, Peninsula, most northern region one warmer Antarctica, surface melting. accumulates form lakes 4 km long. covered those lakes, just before collapsed, started drain after another. suspect chain reaction draining key shelf.22. A. F. Banwell, D. R. MacAyeal, O. V. Sergienko, Geophys. Res. Lett. 40, 5872 (2013). https://doi.org/10.1002/2013GL057694 Figure 2 shows NASA satellite imagery breakup: small blue-colored features middle photo lakes.Figure 2. which totaled February 2002. solid white dark right ocean, fragments ice. speckled melt present at time likely contributed shelf’s instability. (Courtesy MODIS, Earth Observatory.)PPT|High-resolutionBetween 2012 2016, 199 ± 26 gigatons per year.33. M. Meredith et al., Ocean Cryosphere Changing Climate: Special Report Intergovernmental Panel Climate Change, H.-O. Pörtner eds. (2019), chap. 3. Researchers climate-science community hotly debate how much future what rate. Part focuses whether direction bed slope beneath influence rate, known marine ice-sheet considered unstable slopes downward point becomes afloat toward center. Another possibility, ice-cliff instability, arises cliffs collapse.44. Pattyn, Nat. Commun. 9, 2728 (2018). https://doi.org/10.1038/s41467-018-05003-z Both instabilities theoretical possibilities yet observed, choice include models produces wide range predictions contribution rise.55. T. L. Edwards Nature 566, (2019). https://doi.org/10.1038/s41586-019-0901-4Although many currently unscathed, researchers investigating risk related human effects climate.66. G. Vaughan Change 2013: Physical Science Basis—Working Group I Contribution Fifth Assessment Stocker eds., Cambridge U. Press (2013), 4. Lakes caused snow been Antarctica,77. E. Bell Clim. 8, 1044 https://doi.org/10.1038/s41558-018-0326-3 Arctic Greenland Sheet, frozen To understand planet’s regions, need How well computer capturing thermodynamics shelves? they melting, going?Antarctica’s changing surfaceSection:ChooseTop pageABSTRACTAntarctica’s sur... <<Science polesSimulating w...The polar regio...ReferencesThe sheets made In areas, layer snow, sometimes tens thick, lies top Over time, forms sheets. falls older below compacted eventually dense enough Called meteoric ice, derived precipitation, almost always means snow.The complicates estimates ice-shelf because any produced through down snow. Although methods detect observations limited don’t provide accurate values. Many amount based regional climate models, scientists still lot learn itself: deep goes, is, properties space time.One thing glaciologists sure gets quite cold. When drains refreezes, causes two important changes alters density temperature. intuitive: Filling lots fluffy, airy freezes denser originally. cases, refreezes lenses, layers, solid, impermeable They centimeters thick.88. Hubbard 7, 11897 (2016). https://doi.org/10.1038/ncomms11897 3 examples lake formation shelves.Figure Glaciologist Heïdi Sevestre points lenses wall separates pits Antarctica. Project MIDAS, Swansea University, Aberystwyth University.)PPT|High-resolutionThe second change, occurs release latent heat phase heats ambient temperature 0 °C, constant-temperature, isothermal, develops depth meltwater reached.For form, become saturated meltwater. isothermal extend no longer percolate it. maximum reach pore-closure expedite saturation Because mostly meltwater, then stuck can’t permeate farther. begins saturate upward, volume needed fully snow–water mixture.Once accelerate multiple processes. First, darker thus lower albedo, reflectivity. Consequently, absorb shortwave solar energy up, positive feedback loop leads melting.Second, itself additional existing crevasses weight shelf—known overburden lithostatic pressure—acts close crevasses. pressure counteract open crevasse horizontally vertically. With penetrates whole consequence collapse, depending experiencing. addition, bends That process instability B.22. https://doi.org/10.1002/2013GL057694Science polesSection:ChooseTop sur...Science poles <<Simulating regio...ReferencesGiven logistics getting there taking measurements, observing processes especially difficult. Satellites information. visible, example, optical images, soon surfaces refreeze, possible determine contain distinguish Other complicating factors clouds blocking satellite’s view substantial proportion 24 hours darkness South Pole experiences five months year. UK’s Halley Research Station farther north Brunt endure “only” around 100 days year.Automatic weather stations information conditions even people aren’t monitor them. Only number locations, monitored network instruments, maintain retrieve data from. 2020 2021 field seasons disrupted COVID-19 pandemic, operations severely curtailed, travel. date, had only coronavirus cases. majority data-gathering fieldwork canceled postponed 2020–21 season, personnel who traveled continent maintaining instrumentation rather doing new science.Although allowed continue during 2021–22 season stringent quarantine requirements, wait least another year collect valuable measurements radar surveys, reveal inner structure should drill cores. climates looking air bubbles trapped cores (see article Mark Maslin, Physics Today, May 2020, page 48).Simulating waterSection:ChooseTop w... <<The lack direct essential predicting continent’s shelves. Cardiff Georgia Tech collaborating develop MONARCHS, first comprehensive model (The acronym stands Model Surface Hydrology Stability. love tenuous acronym.) collaborators use assess vulnerable events.One particular interest C. neighbor former fourth largest. Shelves, originally four, named Carl Anton Larsen, Norwegian whaling captain sailed along front 1893. 4), D remain.Figure Two shelves, east peninsula 1995 2002, respectively. Sea now fills place. Recently (not shown) experienced potentially conditions, 2017. Observatory.)PPT|High-resolutionLarsen hit headlines broke shelf.99. Hogg, H. Gudmundsson, 540 (2017). https://doi.org/10.1038/nclimate3359 production natural event doesn’t necessarily indicate concerned images revealed shelf.The sits deep, remaining For times provided location large suggests something formation. certain shape involving refreezing effect.To simulate processes, balance transfer also melts path surface.1010. S. Buzzard, Feltham, Flocco, 12, 3565 https://doi.org/10.5194/tc-12-3565-2018 significant computing power dedicated vertical percolation happens scales meters, whereas travel laterally kilometers. simulation horizontal transport takes minutes laptop. percolating vertically mean running simulations supercomputer.Although cause refreeze,1111. J. Adv. Model. Sys. 10, 262 https://doi.org/10.1002/2017MS001155 work moves affects stability. Could headed fate similar B?The regionsSection:ChooseTop regio... <<ReferencesMuch mentioned this applicable beyond Arctic, Sheet formed. ways, behaves similarly Most Greenland’s grounded, sheet, lubricate base. slides faster, quickly, accelerates rise.Meltwater apply seawater oceans, although scale salt. Ponds contribute seasonal retreat breakup disappears each summer increasing temperatures.As temperatures knowing role regions becoming increasingly important. discovering fast-flowing rivers waterfalls, complicate understanding hydrology. Additionally, comprehend effect warming base warm, develop, damage level increasing: Between 1992 2017, estimated 7.6 mm level,1212. IMBIE team, 558, 219 https://doi.org/10.1038/s41586-018-0179-y two-fifths occurring since 2008.The sizes water’s high capacity slow respond change. appears humanity committed centuries until equilibrium state. Understanding better, allow society plan protect communities consequences, ensure humanity’s actions going forward problem worse.ReferencesSection:ChooseTop regio...References <<1. 2017). Google Scholar2. https://doi.org/10.1002/2013GL057694, ScholarCrossref3. Scholar4. https://doi.org/10.1038/s41467-018-05003-z, ScholarCrossref5. https://doi.org/10.1038/s41586-019-0901-4, ScholarCrossref6. 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