Mass Balance & Modelling

Modelled SMB Budget

Gardner et al 2011

Modelled surface mass balance from meteorological data

Showed highly negative SMB of outlet glacier tongues

Queen Eliz Islands, Canadian High Arctic

Importance MB Monitoring

Assess how climate ∆ affects glaciers

Glacier response effects

= most felt by downstream catchments in Himalayas & Alps

e.g. glacier fed water supplies, irrigation schemes, HEP, global sealevel

Numerical Models Needed

Predicting MB ∆ in response to climate

Dictates public policy on GHG emissions

Models require:

1. Mass balance data

accumulation/ablation

available or prediction

2. Ice flux data

ice velocity & thickness

3. Apply flow law

thickness - needs surface & bed topography

Glens flow law which applies:
surface grad, ice thickness & hardness

Role Numerical Models

Relate climate ∆ to ELA / mass balance ∆ to investigate

  • past climate & glacier response
  • future climate ∆ & glacier response

(Golledge & Hubbard, 2011)

e.g. Reconstructing LGM extent Iceland ice

ELA depressed 500m from today (Bingham 2003)

Value of modelling

  1. Shows which factors / controls = most important
  1. Reveal great variability of individual glacier response to climate
  1. Allow investigation magnitude of different controls

Why models
= useful

  1. Can hold factors constant
    ∴ study controls in isolation
  1. Reveal responses to given forcings vary greatly
  • btwn individual glaciers
  • in time (response times vary)

Model Drawbacks

Simplifications of reality

∴ Based on assumptions that restrict accuracy

Often assume:

1. Geometrically simplified cross-sections

2. Flow regime

assume local stresses drive ice flow

4. Motion mechanism

basal sliding input poorly reproduced

3. Given ice distribution to start with

Glacier may respond to non-climatic stimuli

1. Surge glaciers

Do not flow in response to surface profile ∆

--> Geothermal flux ∆ can induce basal sliding ∆ ∴ affecting flux

2. Tidewater glaciers

= characterised by calving cycles

Largely decoupled from atmos climate ∆

Ensemble of model runs

Gives broad sense of how glaciers respond