Intro to Glacial SystemsPresent vs. past glaciationGlacier classificationGlaciers and timeGlaciers as systemsOpen vs. closedEnergy fluxes and reservoirsMass fluxes and reservoirs

Present vs. Past GlaciationNow One major (Antarctica) and one minor (Greenland) ice sheetsThen At least three major (Antarctica, Laurentide, Fennoscandian) and several minor (Greenland, Cordilleran, Patagonian) ice sheets

Present vs. PastPresentPastAntarctica 12,535,000 km2Greenland 1,726,400Laurentide 147,250Fennoscandia 3,800Rockies/AK 76,900Asia 115,000Alps 3,600S. America 26,500Australasia 1,000TOTAL 14,898,00013,800,000 2,295,30013,337,000 6,666,700 2,610,100 3,951,000 37,000 870,000 30,00044,383,000

(After Flint, 1971)

What do we know?S. LaurentideS. and E. FennoscandianAtlantic shelvesRussiaCordilleraN. CanadaXXX

Glacier Classification Ice SheetsIce Sheets: Subcontinental+ in scaleDictate their own topography (unconstrained)

Ice CapsIce CapsLocal to regional in scaleDictate their own topography (eventually)

Ice Caps

GlaciersVariable in scaleControlled by existing topography (constrained)

Glacier TypesValley glaciersLength>>widthCirque glaciersLength ~ width

Glacier TypesNiche glaciersLength

Ice ShelvesFloating terminiNourished from up-ice and aboveAblate by basal melt and calving

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

Ice FieldsTransection glacier (ice field)Radial flow, but topographically confined

PiedmontPiedmont glacier (unconfined at toe)

Piedmont

AdjectivesCalvingHanging

Glacier Response TimesGlaciers are (by definition) permanent.Each responds to climate across characteristic time-scales:Ice sheets ~ 103 yearsIce caps ~ 102 yearsGlaciers ~ 101 yearsGlacierets ~ years

Glaciers as SystemsBest viewed as an open systemMass & energy inRadiation, rock debris, snowMovement & workErosion, transport, depositionMass & energy outLong-wave radiation, till, meltwater AtmosphereLithosphereHydrosphereAtmosphereLithosphereHydrosphereINPUTSOUTPUTS

Glacier SystemsIce Sheets

Glaciers

The Global CryosphereIce Sheets and their behaviorTheoryAntarcticaLaurentideFennoscandian/BarentsDominantly from Hughes, T. J. (1998) Ice SheetsSugden & John, 1976

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

Schematic: second approximation

Theory: Ice Sheet FlowAs the ice deforms, it moves away from its initial point both downward and outward

Schematic: Ice Sheet FlowPureshearSimpleshearcombinationscomplexities

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

(negativefeedback)(positivefeedback)As ice sheet shrinks, ablation area decreasesAs ice sheet shrinks, accumulation area decreases

Antarctic Ice Sheet12.5 x 106 km2Partly terrestrial-basedEast AntarcticPartly marine-basedWest Antarctic Ice Sheet (WAIS)

W.A.I.SheetLarsen I.S.

Ice ShelvesFloatingThin (X00 m)Variable budgetMajor loss = calvingUnstable!Pinning points

Topographic ProfileSurface slopesBed elevationsIce shelves

Ice FlowlinesIce sheet flow is more complex than one might think!

NunataksMcMurdo Dry ValleysNunataks (unglaciated terrain surrounded by ice) are surprisingly significantIce reconstructionBiological refugiaEcological curiositiesCourtesy NASA; Earth Observatory

Ice StreamsFocused flow within an ice sheetVelocity x 100+Drains ice domesCarves bed

Ice sheet initiationTheoriesHighland/windwardMountains firstInstantaneous glacierizationLowlands firstMarine ice transgressionOceans first

Past ice sheetsAlternative hypothesesArrows = wind/H2OBlack = nucleationHow can they be tested?

LaurentideSugden (1977)Simple profile modelSingle central domeEquilibrium ice sheet

LaurentideClark+ (1996)Inferred from upliftSeveral domesDynamic ice sheetTruth?This plus time variation

Laurentide decayRadiocarbon datedVariable ratesarea = volume = sea levelLaurentide drives Barents?

Fennoscandian/BarentsSensitive to sea levelEarly initiation?Late growth?Early decay?

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