mass balance of ice sheets (part i) - university of...
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Mass balance of ice sheets (part I)
AOSS 604 (004)
Outline for todayAOSS 604 (004)
(1) Some preliminary definitions - What do we mean by mass balance, accumulation and ablation?
(2) Where do we find ice?
(3) Some more definitions - What is the difference between an ice sheet and a glacier? - What is the equilibrium line, accumulation area and ablation area?
(4) Surface energy balance of a glacier - What controls the equilibrium line of an ice sheets/glacier?
(5) Melting vs. snowfall (which wins)
Outline for todayAOSS 604 (004)
(1) Some preliminary definitions - What do we mean by mass balance, accumulation and ablation?
(2) Where do we find ice?
(3) Some more definitions - What is the difference between an ice sheet and a glacier? - What is the equilibrium line, accumulation area and ablation area?
(4) Surface energy balance of a glacier - What controls the equilibrium line of an ice sheets/glacier?
(5) Melting vs. snowfall (which wins)
Ice sheet
Definitions
A glacier must have:(1) An area where snow accumulates in excess of melting
(2) Another area where the wastage of snow or ice usually exceeds the accumulation
(3) A transer of mass from the first region to the second-Adapted from M. Meir, 1963
Ice sheet
Definitions
-Adapted from M. Meir, 1963
A glacier must have:(1) An area where snow accumulates in excess of melting
(2) Another area where the wastage of snow or ice usually exceeds the accumulation
(3) A transer of mass from the first region to the secondDynamics
Ice sheet
Definitions
A glacier must have:(1) An area where snow accumulates in excess of melting
(2) Another area where the wastage of snow or ice usually exceeds the accumulation
(3) A transer of mass from the first region to the second-Adapted from M. Meir, 1963
Mass balance
Ice sheet
Ice shelf
Snow fall Definitions
Accumulation: All processes by which mass is added to a glacier or ice sheet
Ice sheet
Ice shelf
Snow fall Definitions
Accumulation: All processes by which mass is added to a glacier or ice sheetPrimarily snow, but also freezing along bed, avalanches, blowing snow, freezing of water in the snowpack
Ice sheet
Ice shelf
Definitions
surface melting
warm ocean waterbasal melting
iceberg calving
Ablation: All processes by which mass is removed from a glacier or ice sheet
Ice sheet
Ice shelf
Definitions
surface melting
warm ocean waterbasal melting
iceberg calving
Ablation: All processes by which mass is removed from a glacier or ice sheetPrimarily melting from surface, but also iceberg calving and melting from base
50% of mass lost from Greenland and Antarctica
DefinitionsAccumulation: All processes by which mass is added to a glacier or ice sheet
Mass gained
DefinitionsAccumulation: All processes by which mass is added to a glacier or ice sheet
Ablation: All processes by which mass is removed from a glacier or ice sheet
Mass gained
Mass lost
DefinitionsAccumulation: All processes by which mass is added to a glacier or ice sheet
Ablation: All processes by which mass is removed from a glacier or ice sheet
Mass gained
Mass lost
Mass Balance = Accumulation - Ablation
DefinitionsMass Balance = Accumulation - Ablation
sometimes called “winter balance” sometimes called “summer balance”
DefinitionsMass Balance = Accumulation - Ablation
sometimes called “winter balance” sometimes called “summer balance”
Usually consider mass balance over 1 (or more) years- winter accumulation is partly balanced by summer ablation- thickness and length of glaciers are constantly fluctuating
Some final definitions . . .Mass Balance = Accumulation - Ablation
Specific mass balance = mass balance at a point in space
Some final definitions . . .Mass Balance = Accumulation - Ablation
Specific mass balance = mass balance at a point in space
AccumulationAblation
Some final definitions . . .Mass Balance = Accumulation - Ablation
Specific mass balance = mass balance at a point in space
AccumulationAblation
Net mass balance = mass balance integrated over glacier area
Where do we find ice sheets and glaciers?
AOSS 604 (004)
Where do we find ice sheets and glaciers?
AOSS 604 (004)
Greenland Ice Sheet
Quelcuaya I ce C ap Mt. K enya
Antarctic I ce S heet
New Guinea
Himalaya
Swiss G laciersAlaskan G laciers
Patagonia
Where do we find ice sheets and glaciers?
AOSS 604 (004)
Greenland Ice Sheet
Quelcuaya I ce C ap Mt. K enya
Antarctic I ce S heet
New Guinea
Himalaya
Swiss G laciersAlaskan G laciers
Patagonia
Polar regions
Mountains
Where do we find ice sheets and glaciers?
AOSS 604 (004)
(1) Polar regions Very cold (Less solar radiation)
(2) Mountains Temperature decreases with elevation (lapse rate)
Schematic of a (grounded) glacierAccumulation zone
Ablation zoneSnow accumulation
Snow melting
Schematic of a (grounded) glacierAccumulation zone
Ablation zoneSnow accumulation
Snow melting
Equilibrium Line
Schematic of a (grounded) glacierAccumulation zone
Ablation zoneSnow accumulation
Snow melting
Equilibrium Line
Dynamic flux of ice
Significance of the Equilibrium LineAccumulation zone
Ablation zoneSnow accumulation
Snow melting
Equilibrium Line
Increase
Significance of the Equilibrium LineAccumulation zone
Ablation zoneSnow accumulation
Snow melting
Equilibrium LineAdvances
Increase
Significance of the Equilibrium LineAccumulation zone
Ablation zoneSnow accumulation
Snow melting
Equilibrium LineRetreats
Decrease
Significance of the Equilibrium LineAccumulation zone
Snow accumulation
Snow melting
Equilibrium Line
What happens when:(1) You increase the amount of melt?(2) You decrease the amount of melt?(3) You increase snowfall and melt?(4) Decrease snowfall and melt?
Significance of the Equilibrium LineAccumulation zone
Snow accumulation
Snow melting
Equilibrium Line
What happens when:(1) You increase the amount of melt?(2) You decrease the amount of melt?(3) You increase snowfall and melt?(4) Decrease snowfall and melt?
Bottom line: Equilibrium line is diagnostic of the health of a glacier
Where do we find ice (revisited)
Equilibrium line
Where do we find ice (revisited)
Equilibrium line
Equilibrium line depends on(1) Temperature (i.e., melt)(2) Snowfall
How does the equilibrium line change?
AOSS 604 (004)
How does the equilibrium line change?
AOSS 604 (004)
Approach:(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
(2) At the equilibrium line accumulation = ablation
(3) Find how the equilibrium line altitude changes with perturbations in air temperature, snow fall, net radiation
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
Energy Available to melt ice/snow = ?
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
Energy Available to melt ice/snow = ?
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
Energy Available to melt ice/snow = ?
Energy available to melt ice/snow
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
Energy Available to melt ice/snow = ?
Energy available to melt ice/snow
Net radiation
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
Energy Available to melt ice/snow = ?
Energy available to melt ice/snow
Net radiationsensible heat input
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
Energy Available to melt ice/snow = ?
Energy available to melt ice/snow
Net radiation
sensible heat input
latent heat input due to condensation and evaporation
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
Energy Available to melt ice/snow = ?
Energy available to melt ice/snow
Net radiation
sensible heat input
latent heat input due to condensation and evaporation
heat supplied by freezing rain
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
Energy Available to melt ice/snow = ?
Energy available to melt ice/snow
Net radiation
sensible heat input
latent heat input due to condensation and evaporation
heat supplied by freezing rain
heat conducted away from the surface
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
Energy Available to melt ice/snow = ?
Neglect freezing rain and heat conduction away from the surface
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
Energy Available to melt ice/snow = ?
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
Energy Available to melt ice/snow = ?
Proportional to (air temperature - surface temperature)
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
Energy Available to melt ice/snow = ?
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
Energy Available to melt ice/snow = ?
At the melting point of ice the surface temperature is zero
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
(2) At the equilibrium line accumulation = ablation
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
Melt over the summer season is then:
How does the equilibrium line change?
AOSS 604 (004)
(1) Calculate amount of melt during the summer by applying an energy balance to the surface of the ice
(2) At the equilibrium line accumulation = ablation