GG4058 Advanced Glaciology

Introduction Recent glacier retreat - almost global phenomenon

1928 2002

2009

Blomstrandbreen, Svalbard Greenland and Antarctic Ice Sheets also losing mass Global and regional climate change

Warming in the Arctic is double that for the globe from 19th to 21st century and from late 1960s to present.

IPCC Anthropogenic greenhouse gases

CO2 CH4 and N2O Concentrations - far exceed pre-industrial values - increased markedly since 1750 due to human activities

IPCC Glacier retreat and sea level change We’re all doomed… 150 years ago, mountain people were really worried about advancing glacier. they thought they were doomed… How will glaciers and ice sheets change in future? Essay:

How much will glaciers and ice sheets contribute to sea-level change in the 21st Century?

2,000 - 3,000 words

Deadline: Friday 6th November, 5.00 pm Course text:

Glaciers and Glaciation, Second edition What do we need to know? Climate

Mass balance

Hydrology

Dynamics

Calving Mass & Energy Balance

Miage Glacier, Italy Mass balance:

definition

Net change in mass over specified time period (generally 1 year)

Sum of • winter balance (accumulation) • summer balance (ablation)

Larsbreen, Svalbard Accumulation area (gains greater than losses)

Kvalfangerbreen, Svalbard Ablation area (losses greater than gains)

Calving Kvalfangerbreen, Svalbard Equilibrium line (losses equal to gains)

Kvalfangerbreen, Svalbard Accumulation Annual accumulation layers on Glaciar Zongo, Bolivia Precipitation: primary input of mass on most glaciers

• hard to measure • uncertain relationship with accumulation Wind during and following snowfall

Pre-existing snow is commonly eroded and redistributed:

Long-term accumulation greater or less than precipitation Glacier accumulation areas can be regarded as giant snow drifts

Accumulation higher than precipitation

Accumulation less than precipitation Avalanching In high-relief environments avalanches can contribute almost all of the accumulation

Taweche glacier, Khumbu Himalaya

Inner Hornsund, Svalbard Ablation Melting: linear function of available energy Energy Balance

Qm = SW + LW + H + L + R + T

Qm Energy for melting Ablation of clean ice

• linear function of available energy

Qm = SW + LW + H + L + R + T

Qm Energy for melting SW Solar radiation (Shortwave) Ablation of clean ice

• linear function of available energy

Qm = SW + LW + H + L + R + T

Qm Energy for melting SW Solar radiation (Shortwave) LW Terrestrial and atmospheric radiation (Longwave) Ablation of clean ice

• linear function of available energy

Qm = SW + LW + H + L + R + T

Qm Energy for melting SW Solar radiation (Shortwave) LW Terrestrial and atmospheric radiation (Longwave) H Sensible heat heat exchange Ablation of clean ice

• linear function of available energy

Qm = SW + LW + H + L + R + T

Qm Energy for melting SW Solar radiation (Shortwave) LW Terrestrial and atmospheric radiation (Longwave) H Sensible heat heat exchange L Latent heat exchange Ablation of clean ice

• linear function of available energy

Qm = SW + LW + H + L + R + T

Qm Energy for melting SW Solar radiation (Shortwave) LW Terrestrial and atmospheric radiation (Longwave) H Sensible heat heat exchange L Latent heat exchange R Energy from rain Ablation of clean ice

• linear function of available energy

Qm = SW + LW + H + L + R + T

Qm Energy for melting SW Solar radiation (Shortwave) LW Terrestrial and atmospheric radiation (Longwave) H Sensible heat heat exchange L Latent heat exchange R Energy from rain T Energy used to warm or cool ice Solar radiation Solar spectrum peaks in visible wavelengths:

~ 0.50 µm with lesser amounts of UV and near IR Input of solar radiation depends on

• latitude and time of year • slope aspect

• state of the atmosphere Reflected fraction: albedo Dark surfaces: low ! most SW absorbed ! = SWout / SWin Reflected fraction: albedo Light surfaces: high ! most SW reflected ! = SWout / SWin Absorbed SW = SW (1 " ! ) Longwave radiation:

Emitted by earth and atmosphere LW flux is a function of surface temperature:

Stephan-Bolzmann Law:

E* = # T4

# Stephan-Bolzmann constant 5.67 x 10-8

T temperature in Kelvins

(0 K = absolute zero 0° C = 273 K) LW radiated by glacier at 0° C (273 K)

(5.67 x 10-8) x 2734

= 315 W m-2

LW radiated by Dr Singh at 37° C (310 K)

(5.67 x 10-8) x 3104

= 524 W m-2 Net LW

= LWin - LWout Sensible heat exchange:

Transfer of heat from warm air to cold surface or from warm surface to cold air

Wind chill:

Removal of warm boundary layer by cold winds Sensible heat flux needs turbulence:

• Increases with windspeed

• Increases with temperature difference

• Complex physics

• Bulk transfer functions Latent heat flux Molecular bonds: hydrogen bonds hold water molecules together

Breaking bonds requires energy -> Water to vapour (evaporation),

-> Ice to water (melting): Molecular bonds: water

Formation of bonds releases energy <- Vapour to water (condensation),

Water to ice <- (freezing):

Latent Heat Phase changes involve latent heat exchange

Evaporation: -1 -> 2,500 J g required

Melting: -> 334 J g-1 required Phase changes involve latent heat exchange

Condensation: <- Releases 2,500 J g-1

Freezing: Releases <- 334 J g-1 Rime ice formation: supercooled water -> ice

Source of latent heat: 334 J g-1 Sublimation: Energetically = melting + evaporation Requires 2834 J g-1 Sublimation forms: ice pinnacles (penitentes), Khumbu Glacier Infuence of debris cover Østrem curves:

Thick debris inhibits melt Thin debris accelerates it

Typical thickness vs. melt rate curves Modified surface energy balance: Qm = SW + LW + H + L + R + T + C

conductive heat flux Melt rate with varying albedo

40

a = 0.10 35 Debris covered ice a = 0.15 Dirty ice a = 0.20 30 a = 0.25 Slightly dirty ice a = 0.30 25

20

15 Melt rate (mm/day) 10

5

0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Debris thickness (m)

SW 400W/m2 LW 100W/m2 k 1.28W/m.K

Average albedos from Paterson, 1994 Ice temperature

‘Warm ice’ @ pressure-melting point

‘Cold ice’ below pmp

How does ice become ‘warm’?

What controls ice temperature? Surface heat sources

Refreezing of water raises temperature of snowpack

Latent heat release

334,000 Joules per kilogram Ice lenses (horizontal) and glands (vertical) formed by refreezing of percolating meltwater

artificial lenses and glands made from percolating ink

(photos: Carl Bøggild) superimposed ice: continuous ice layer at base of snowpack: forms where large amounts of snow are melted and re-frozen Snow with ice layers

1 year

Superimposed ice

Previous year’s firn

density snow superimposed ice glacier ice snowline equilibrium line Subsurface heat sources

Frictional heat (deformation of ice and sliding)

Geothermal heat Strain heating (ice creep):

Temperate ice 70m below surface of Hansbreen, Svalbard Geothermal heat flux mW m-1 milliWatts per square metre

Estimate for Svalbard:

c. 70 mW m-1 Heat conduction: e.g. from warm bed to cold surface

Heat advection: transport of warmer (or colder) ice by ice flow Polythermal Glaciers

Blatter and Hutter (1991) classification

• Heating by surface refreezing

• Heating by strain and/or geothermal heat

• Advection and conduction