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Intro to Glacial Systems

Intro to Glacial Systems. Present vs. past glaciation Glacier classification Glaciers and time Glaciers as systems Open vs. closed Energy fluxes and reservoirs Mass fluxes and reservoirs. Present vs. Past Glaciation. Now – One major (Antarctica) and one minor (Greenland) ice sheets

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Intro to Glacial Systems

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  1. Intro to Glacial Systems • Present vs. past glaciation • Glacier classification • Glaciers and time • Glaciers as systems • Open vs. closed • Energy fluxes and reservoirs • Mass fluxes and reservoirs

  2. Present vs. Past Glaciation • Now – One major (Antarctica) and one minor (Greenland) ice sheets • Then – At least three major (Antarctica, Laurentide, Fennoscandian) and several minor (Greenland, Cordilleran, Patagonian…) ice sheets

  3. Antarctica – 12,535,000 km2 Greenland – 1,726,400 Laurentide – 147,250 Fennoscandia – 3,800 Rockies/AK – 76,900 Asia – 115,000 Alps – 3,600 S. America – 26,500 Australasia – 1,000 TOTAL – 14,898,000 13,800,000 2,295,300 13,337,000 6,666,700 2,610,100 3,951,000 37,000 870,000 30,000 44,383,000 Present vs. PastPresent Past (After Flint, 1971)

  4. What do we know? • S. Laurentide • S. and E. Fennoscandian • Atlantic shelves • Russia • Cordillera • N. Canada X X X

  5. “Glacier” Classification – Ice Sheets • Ice Sheets: Subcontinental+ in scale • Dictate their own topography (unconstrained)

  6. Ice Caps • Ice Caps • Local to regional in scale • Dictate their own topography (eventually)

  7. Ice Caps

  8. Glaciers • Variable in scale • Controlled by existing topography (constrained)

  9. Glacier Types • Valley glaciers • Length>>width • Cirque glaciers • Length ~ width

  10. Glacier Types • Niche glaciers • Length << width

  11. Ice Shelves • Floating termini • Nourished from up-ice and above • Ablate by basal melt and calving

  12. Subspecies of Glaciers: Outlet • Outlet glacier (from ice cap or sheet)

  13. Ice Fields • Transection glacier (“ice field”) • Radial flow, but topographically confined

  14. Piedmont • Piedmont glacier (unconfined at toe)

  15. Piedmont

  16. Adjectives • Calving • Hanging

  17. Glacier Response Times • Glaciers are (by definition) permanent. • Each responds to climate across characteristic time-scales: • Ice sheets – ~ 103 years • Ice caps – ~ 102 years • Glaciers – ~ 101 years • Glacierets – ~ years

  18. Glaciers as Systems • Best viewed as an open system • Mass & energy in • Radiation, rock debris, snow • Movement & work • Erosion, transport, deposition • Mass & energy out • Long-wave radiation, till, meltwater INPUTS OUTPUTS Atmosphere Atmosphere GLACIER Lithosphere Lithosphere Hydrosphere Hydrosphere

  19. Glacier Systems • IceSheets • Glaciers

  20. The Global Cryosphere Sugden & John, 1976 • Ice Sheets and their behavior • Theory • Antarctica • Laurentide • Fennoscandian/Barents • Dominantly from Hughes, T. J. (1998) Ice Sheets

  21. Theory: first approximation • Ice sheets are defined as subcontinental or larger ice masses that define their own topography.

  22. Schematic: second approximation

  23. Theory: Ice Sheet Flow • As the ice deforms, it moves away from its initial point – both downward and outward

  24. Schematic: Ice Sheet Flow Pure shear combinations Simple shear complexities

  25. Ice Sheet Stability • Ice sheets, unlike glaciers, commonly display instability associated with positive feedback loops

  26. “Normal” (negative feedback) As ice sheet shrinks, ablation area decreases (positive feedback) As ice sheet shrinks, accumulation area decreases

  27. Antarctic Ice Sheet • 12.5 x 106 km2 • Partly terrestrial-based • East Antarctic • Partly marine-based • West Antarctic Ice Sheet (WAIS)

  28. Larsen I.S. W.A.I.Sheet

  29. Floating Thin (X00 m) Variable budget Major loss = calving Unstable! “Pinning points” Ice Shelves

  30. Topographic Profile • Surface slopes • Bed elevations • Ice shelves

  31. Ice Flowlines • Ice sheet flow is more complex than one might think!

  32. Nunataks • McMurdo Dry Valleys • Nunataks (unglaciated terrain surrounded by ice) are surprisingly significant • Ice reconstruction • Biological refugia • Ecological curiosities Courtesy NASA; Earth Observatory

  33. Ice Streams • Focused flow within an ice sheet • Velocity x 100+ • Drains ice domes • Carves bed

  34. Ice sheet initiation • Theories • Highland/windward • Mountains first • “Instantaneous glacierization” • Lowlands first • Marine ice transgression • Oceans first

  35. Past ice sheets • Alternative hypotheses • Arrows = wind/H2O • Black = nucleation • How can they be tested?

  36. Laurentide • Sugden (1977) • Simple profile model • Single central dome • “Equilibrium ice sheet”

  37. Laurentide • Clark+ (1996) • Inferred from uplift • Several domes • “Dynamic ice sheet” • Truth? • This plus time variation

  38. Laurentide decay • Radiocarbon dated • Variable rates • Δarea = Δvolume = Δsea level • Laurentide drives Barents?

  39. Fennoscandian/Barents • Sensitive to sea level • Early initiation? • Late growth? • Early decay?

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