Week 1: Importance of glaciers Flashcards by Elle Kinsman

Glacier =

Snow and ice mass which, if accumulates to sufficient thickness, deforms under own weight and flows (Sugden 1994)

Cover 10% Earth’s surface
75% freshwater

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IMPORTANCE OF GLACIERS

Glacio-EUSTASY (global)

Glacio-ISOSTASY (local)

Local/global climate systems

Ice cores/palaeoclimate records

Hazards

Glacial ‘respiration’ and nutrient fluxes

Source of water

Tourism

Sediment resources (sands/gravels)

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Glacio-isostasy

England/Scotland rises 102mm/yr

Will take 10-20,000 years to re-equilibriate

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Local/global climate systems

Greenland meltwater –> Labrador Sea

1) reduce surface convection in N Atlantic due to freshwater flux
2) slows gyre
3) affects NW Europe’s summer climate

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Hazards

Outburst floods (GLOF)

Surges

Ice avalanches

–> position important e.g. earthquakes, geothermal heat flux

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Glacial respiration and nutrient fluxes

Hodsen et al 2007: CO2 flux of cryconite across an entire arctic suprglacial ecosystem

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Size facts

AIS 30.1 million km3

GIS 2.28 million km3

EQUIVALENT TO 70M OF SEA LEVEL

Other smaller make up 180,000 km3

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Controls on glacier distribution (and explained)

LATITUDE
- low solar energy = less energy to melt ice

ALTITUDE

thinner air holds less heat energy
-> glaciers near equator!

CONTINENTALITY

no moisture source = drier air
rain shadow effect
ALSO sea ice reduces moisture from oceans e.g. Europe

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Types of classification

SIZE/RELATIONSHIP TO TOPOGRAPHY

BASAL THERMAL REGIME

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Classification; size/relationship to topography

Largest = ice sheets = unconstrained by topography

Transition from constrained –> unconstrained as grows

Example of constrained: valley/cirque/niche glacier

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Classification; basal thermal regime

Cold-based, warm, polythermal

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Marine glaciers: ice rise =

Ice moves towards sea, bumps into island and rises over

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Marine glaciers: sea-ice ice shelf =

Long term, thickens until shelf forms e.g. N Pole

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Direction of ice flow

Acc zone –> ELA –> ablation zone

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ELA = (and usual value)

Altitude when acc = abl

Usually 0.6 i.e. contour below 60% of total glacier area

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Acc > abb

+ve mass balance
Low temps +/ greater snowfall
Decrease ELA

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Acc < abl

-ve mass balance
High temps +/ less snowfall
Increase ELA

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Identifying mass balance

Annual misbalance

Aerial photos/satellite images

Accumulation Area Ratio (AAR)

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Methods of acc (major to minor)

Snow
Wind blown drift
Avalanches
Condensation (rime = rapid frost formation)
Freezing rain/external water

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Methods of abl (major to minor)

Calving (wet/dry, DOMINANT)
Melting (top down thinning)
Wind blown drift (scoured from top)
Avalanches
Evaporation
Sublimation (e.g. Antarctica)
DEFLATION

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How does ice form?

Reduce voids and increase density
e.g. New snow = 50-70kg/m2
Glacier ice = 830-917kg/m2

Firn =

Snow which has survived a melt season

Forms ice when air can’t transit in/out of system

Types of snow zone

Warm/wet

Cold/dry

Warm/wet snow zone, how ice forms

Melting
Refreezing
Rounding
Joining 
... of grains

Cold/dry snow zone, how ice forms

Sintering = bonds form under heat and pressure

Why is englacial ice not a simple layer cake stratigraphy?

Disruptions to layers relating to annual acc of snow | e.g. partial avalanches 'jumble' = new structures due to compression/extension

Controls on ice formation

Temperature Accumulation

Temperature: control on ice formation

Warmer = faster | Important control on transformation

Accumulation: control on ice formation

More snow = faster formation

Examples of differing ice formation

ALASKA Warm/wet with lots of snow into system High densities at shallow depths = faster formation Ice at 13m GREEENLAND Colder/drier Takes longer for ice to form Ice at 66m

Controls on calving (and explained)

1) Water depth Hf = (pw/pi)Dw "Critical floatation depth" - will float if less than = calving feedbacks 2) Water T Bottom up thinning 3) Tidal variation Flexing 4) Glacier crevassing 5) Water discharge from glacier

Freshwater density

1000 kg/m3

Seawater density

1030 kg/m3

Ice density

900 kg/m3

Grounding line =

Point at which glacier begins to float

Calving front =

Where calving occurs If calving front = grounding line --> "tidewater glacier" N.B. Doesn't occur in cold polar environment e.g. Antarctica; 100s km from grounding line

Energy balance at glacier surface:

Qm = Qs + Ql + Qh + Qe Qm = energy available to melt ice Qs = solar shortwave radiation Ql = longwave (emitted) radiation Qh = sensible heat transfer Qe = latent heat transfer

What affects energy balance at glacier surface?

ALBEDO i.e. Supraglacial debris cover (- albedo affected by surface texture/material made up of/debris cover)

Typical albedos of clean ice vs debris covered ice

34-51% 10-15%

THIN debris =

Increased absorption/re-radiation = more ablation e.g. Cryconite holes = thin patches, accelerate abl not thick enough for blanket effect

THICK debris =

Less conduction = increased protection = less ablation N.B. ?False impression of +ve mass balance Can bury glaciers for decades!

Measuring glacial mass balance

DIRECT METHODS GEODETIC (REMOTE SENSING) HYDROLOGICAL CLIMATIC CALCULATIONS GRAVITY CHANGES KINEMATIC MASS BUDGET

Measuring glacial mass balance; direct methods

Accumulation - snow pits = depth/density Ablation - stakes = ice surface changes

Measuring glacial mass balance; geodetic

Aerial photos = area/altitude changes different years = vol changes - DIFFICULT Repeat satellite radar altimetry (radio waves) and LIDAR (Light Detection and Ranging - laser pulses) = thickness changes within mm - v useful for remote areas/large continental sheets

Measuring glacial mass balance; hydrological

Net balance = option - runoff - evaporation :) water resources/prediction/management - favours small glaciers b/c data collection required - can't distinguish changes in snow/ice vol vs water storage

Measuring glacial mass balance; climatic calculations

Meteorological data --> calculate surface energy balance and ablation Statistical methods based on T POSITIVE DEGREE DAYS (Braithwaite 1995) = sum of mean daily T for which T>0'C - assumes uniform conditions across large area - ignores calving

Measuring glacial mass balance; gravity changes

Gravity Recovery And Climate Experiment satellites Ice has a gravity influence e.g. Alaska has summer/winter fluctuations but long term trajectory = -ve mass balance

Measuring glacial mass balance; kinematic mass budget

FOR MARINE TERMINATING GLACIERS 1) Surface mass balance (climate model) 2) Mass lost from marginal flow (remote sensing)

Steep mb gradient =

High rates acc/abl | Moist mid latitudes e.g. Norway

Shallow mb gradient =

Low rates acc/abl | Arid/polar latitudes e.g. Arctic, Canada

Why isn't mb gradient linear

Should be due to lapse rate (0.4-0.9'C/100m) - acc increases with altitude UNTIL too cold for pption - debris cover - shading by topography - avalanching