Cryosphere Lecture 3

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less than 1% change in Solar Irradiance since ‘
‘The Little Ice Age’
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Milankovitch (1941) Precession:
The season in which the earth is nearest/furthest from the sun (~20 ka)
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Tilt:
What angle is the earth tilted at? ( ‘obliquity’) (~40 ka)
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Eccentricity:
How round is the orbit? (~100 ka)
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Ablation Surface melt
Function of energy balance (energy deficit or surplus at glacier surface) net solar (shortwave) radiation
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LGM
Last Glacial Maximum
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Ice leaves behind its ‘footprint’:
Erosional forms Depositional forms
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Help us to reconstruct
past ice masses & indirectly, climate
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Erosional forms Different scales
Micro Striations Crescentic gouges
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Meso (scale)
Roche moutonnees Crag & tails
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Macro (scale)
Cirques U-shaped valleys Hanging valleys Fjords
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Depositional forms include:
Moraines Kames Eskers Kettle lakes
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Moraines are made on of several types:
Terminal moraines Lateral moraines Medial moraines Push moraines
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Example of a moraiane:
Cordillera Huyhuash, Peru (swisseduc.ch) and Kaskawulsh Glacier
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Drumlins (subglacial)
Streamlined landforms that may occur in ‘swarms’
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Kames
Mound-like hills of layered sand and gravel Material deposited in an ice-supported cavity Ice melts leaving heap of sediment
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Eskers
Long sinuous ridges of stratified sand and gravel May be formed by meltwater stream flowing underneath stagnant glacier ice From tens of m up to a hundred km long
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An example of a former Ice sheet include
Laurentide Ice Sheet and the eurasian Ice Sheet and the british Ice sheet
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Examples of expanded Ice sheets include
patagonia, NZ, Iceland, Antartic Ice Sheet, Greenland
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Change in incoming radiation as a result of Milankovitch cycles is actually quite small... So how does this cause ice ages?
Positive feedback mechanisms: Ice/albedo feedback Changes in carbon dioxide Ice/elevation feedback Changes in sea level Ocean circulation and polar amplification
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Amplification of temperature trend due to feedbacks involving
sea ice & snow cover
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Increase albedo
=> more incoming radiation reflected back => greater potential for temperature lowering => Glaciation
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Decrease albedo
less incoming radiation reflected back => greater potential for temperature rise => Deglaciation
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Albedo: Reflectivity of the surface (% incoming radiation reflected albedo figures include
Fresh Snow: 75-90 % Sea Ice: 30-40 % Land: < 30 % Road: 5-10% Water: 2-4%
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Ice sheets have ice thicknesses of 1000s of metres
=> adds elevation to ice sheet locality => alters local & global climate Temperature cools with elevation => less melt Snowfall increases with elevation (cold air holds less moisture) => more accumulation => Mass balance becomes more positive => Ice
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CO2 in the atmosphere is lower during glacial periods
Cause or effect? Complex system...
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Effect of ice: Increased sea ice cover
Inhibits CO2 exchange between atmosphere & ocean at poles => leads to lower CO2 in the atmosphere (Stephens and Keeling, 2000)
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Allows formerly marine regions to be glaciated
=> more sea level fall => more land for glaciation => ice sheet grows more & albedo feedback
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Increases elevation of high topography
elevation feedback
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Ice is a major influence on ocean circulation which in turn is a
major influence on climate
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GCMs
(Global Climate Models)
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Laurentide =
topographic barrier to atmospheric circulation=> affected jet stream & weather patterns
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Impact of former ice sheets modelled using
GCMs (Global Climate Models)
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Polar amplification, Term first coined by Manabe & Stouffer, 1980
Expected to be stronger in Northern Hemisphere than Southern Hemisphere Less potential for ice/ albedo feedback in S. Hem. due to sea ice distribution
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Milankovitch (1930):Key to ice ages is summer insolation in
high northern latitudes
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Other cards in this set

Card 2

Front

Milankovitch (1941) Precession:

Back

The season in which the earth is nearest/furthest from the sun (~20 ka)

Card 3

Front

Tilt:

Back

Preview of the front of card 3

Card 4

Front

Eccentricity:

Back

Preview of the front of card 4

Card 5

Front

Ablation Surface melt

Back

Preview of the front of card 5
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