intro to glacial systems present vs. past glaciation glacier classification glaciers and time ...
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Intro to Glacial SystemsPresent vs. past glaciationGlacier classificationGlaciers and timeGlaciers as systemsOpen vs. closedEnergy fluxes and reservoirsMass fluxes and reservoirs
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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
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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)
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What do we know?S. LaurentideS. and E. FennoscandianAtlantic shelvesRussiaCordilleraN. CanadaXXX
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Glacier Classification Ice SheetsIce Sheets: Subcontinental+ in scaleDictate their own topography (unconstrained)
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Ice CapsIce CapsLocal to regional in scaleDictate their own topography (eventually)
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Ice Caps
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GlaciersVariable in scaleControlled by existing topography (constrained)
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Glacier TypesValley glaciersLength>>widthCirque glaciersLength ~ width
- Glacier TypesNiche glaciersLength
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Ice ShelvesFloating terminiNourished from up-ice and aboveAblate by basal melt and calving
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Subspecies of Glaciers: OutletOutlet glacier (from ice cap or sheet)
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Ice FieldsTransection glacier (ice field)Radial flow, but topographically confined
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PiedmontPiedmont glacier (unconfined at toe)
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Piedmont
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AdjectivesCalvingHanging
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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
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Glaciers as SystemsBest viewed as an open systemMass & energy inRadiation, rock debris, snowMovement & workErosion, transport, depositionMass & energy outLong-wave radiation, till, meltwater AtmosphereLithosphereHydrosphereAtmosphereLithosphereHydrosphereINPUTSOUTPUTS
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Glacier SystemsIce Sheets
Glaciers
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The Global CryosphereIce Sheets and their behaviorTheoryAntarcticaLaurentideFennoscandian/BarentsDominantly from Hughes, T. J. (1998) Ice SheetsSugden & John, 1976
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Theory: first approximationIce sheets are defined as subcontinental or larger ice masses that define their own topography.
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Schematic: second approximation
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Theory: Ice Sheet FlowAs the ice deforms, it moves away from its initial point both downward and outward
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Schematic: Ice Sheet FlowPureshearSimpleshearcombinationscomplexities
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Ice Sheet StabilityIce sheets, unlike glaciers, commonly display instability associated with positive feedback loops
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(negativefeedback)(positivefeedback)As ice sheet shrinks, ablation area decreasesAs ice sheet shrinks, accumulation area decreases
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Antarctic Ice Sheet12.5 x 106 km2Partly terrestrial-basedEast AntarcticPartly marine-basedWest Antarctic Ice Sheet (WAIS)
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W.A.I.SheetLarsen I.S.
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Ice ShelvesFloatingThin (X00 m)Variable budgetMajor loss = calvingUnstable!Pinning points
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Topographic ProfileSurface slopesBed elevationsIce shelves
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Ice FlowlinesIce sheet flow is more complex than one might think!
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NunataksMcMurdo Dry ValleysNunataks (unglaciated terrain surrounded by ice) are surprisingly significantIce reconstructionBiological refugiaEcological curiositiesCourtesy NASA; Earth Observatory
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Ice StreamsFocused flow within an ice sheetVelocity x 100+Drains ice domesCarves bed
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Ice sheet initiationTheoriesHighland/windwardMountains firstInstantaneous glacierizationLowlands firstMarine ice transgressionOceans first
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Past ice sheetsAlternative hypothesesArrows = wind/H2OBlack = nucleationHow can they be tested?
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LaurentideSugden (1977)Simple profile modelSingle central domeEquilibrium ice sheet
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LaurentideClark+ (1996)Inferred from upliftSeveral domesDynamic ice sheetTruth?This plus time variation
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Laurentide decayRadiocarbon datedVariable ratesarea = volume = sea levelLaurentide drives Barents?
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Fennoscandian/BarentsSensitive to sea levelEarly initiation?Late growth?Early decay?
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