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  Then – At least three major (Antarctica, Laurentide, Fennoscandian) and several minor (Greenland, Cordilleran, Patagonian…) ice sheets

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)

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

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

Ice Caps  Ice Caps –Local to regional in scale –Dictate their own topography (eventually)

Ice Caps

Glaciers  Variable in scale  Controlled by existing topography (constrained)

Glacier Types  Valley glaciers –Length>>width  Cirque glaciers –Length ~ width

Glacier Types  Niche glaciers –Length << width

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

Subspecies of Glaciers: Outlet  Outlet glacier (from ice cap or sheet)

Ice Fields  Transection glacier (“ice field”) –Radial flow, but topographically confined

Piedmont  Piedmont glacier (unconfined at toe)

Piedmont

Adjectives  Calving  Hanging

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

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

Glacier Systems  Ice Sheets  Glaciers

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

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

Schematic: second approximation

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

Schematic: Ice Sheet Flow Pure shear Simple shear combinations complexities

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

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

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

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

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

Topographic Profile  Surface slopes  Bed elevations  Ice shelves

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

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

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

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

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

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

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

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

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