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. Present vs. Past PresentPast  Antarctica – 12,535,000 km 2  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 (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 – ~ 10 3 years –Ice caps – ~ 10 2 years –Glaciers – ~ 10 1 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 Atmosphere Lithosphere Hydrosphere Atmosphere Lithosphere Hydrosphere INPUTSOUTPUTS

19. Glacier Systems  Ice Sheets  Glaciers

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

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

23. Schematic: second approximation

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

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

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

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

28. Antarctic Ice Sheet  12.5 x 10 6 km 2  Partly terrestrial-based –East Antarctic  Partly marine-based –West Antarctic Ice Sheet (WAIS)

29. W.A.I.Sheet Larsen I.S.

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

31. Topographic Profile  Surface slopes  Bed elevations  Ice shelves

32. Ice Flowlines  Ice sheet flow is more complex than one might think!

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

34. Ice Streams  Focused flow within an ice sheet –Velocity x 100+ –Drains ice domes –Carves bed

35. Ice sheet initiation  Theories –Highland/windward  Mountains first –“Instantaneous glacierization”  Lowlands first –Marine ice transgression  Oceans first

36. Past ice sheets  Alternative hypotheses –Arrows = wind/H 2 O –Black = nucleation  How can they be tested?

37. Laurentide  Sugden (1977) –Simple profile model –Single central dome  “Equilibrium ice sheet”

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

39. Laurentide decay  Radiocarbon dated –Variable rates –Δarea = Δvolume = Δsea level –Laurentide drives Barents?

40. Fennoscandian/Barents  Sensitive to sea level –Early initiation? –Late growth? –Early decay?