glacial isostatic adjustment and coastline modelling glenn milne dept of geological sciences...
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GLACIAL ISOSTATIC ADJUSTMENT AND COASTLINE MODELLING
Glenn Milne
Dept of Geological SciencesUniversity of Durham, UK
Outline
(1) General GIA
• What is GIA?
• Key observables
• General model components
• Constraining model parameters
(2) Modelling coastline evolution
• General idea
• Predicting GIA-induced sea-level change
• Example predictions
d18O=1000 x18O/16O(sample) - 18O/16O(standard)
18O/16O(standard)
Oxygen Isotope Record
GLACIAL ISOSTATIC ADJUSTMENT
Surface Mass Redistribution
Earth Earth Response
• Relative sea level• Geopotential• Rotation vector• 3D solid surface deformation
ModelSurface load + Rotational potential
Rheological Earth model
Better understanding of GIA process
Constraints on Earth rheology
Constraints on surface mass redistribution
GIA MODEL
Earth Forcing Earth Rheology
Rotational potential
Euler equations
Surface loading
Ice
Interdisciplinary approachOcean
Sea-level equation
Other?
Ice dammed lakes Sediment redistribution
Impulse response formalism Linear Maxwell rheology 1D structure
Ice history and earth rheology are the key inputs
Constraining Model Parameters
• Largest uncertainties associated with ice sheet histories and earth rheology
•Near-field data give best constraints on local ice histories
• Near-field and far-field data can be effectively used to constrain earth viscosity structure
• Far-field sea-level data give best constraints on integrated ice melt signal
• Both forward and inverse modelling techniques are used
Modelling Coastline Evolution
(Associated with GIA)
• Position of coastline is influenced by rising/falling relative sea level AND advancing or retreating marine-based ice
Modelling Coastline Evolution Driven by GIA-Induced Sea-Level Changes
• Accuracy of prediction will depend on accuracy of the present-day topography data set and the accuracy of the relative sea-level prediction
• GIA model does not include tectonic motions or sediment flux (associated with marine or fluvial processes)
j p jT(θ,φ,t )=T(θ,φ,t )-RSL(θ,φ,t )
• Choose optimal model parameters and predict changes in relative sea level for period of interest
• Compute palaeotopography via the relation
Eustatic Sea-Level Change
ice ice
water water
-ρ ΔV (t)ΔS(t)=
ρ A
• Mass conservation
• Earth is rigid and non-rotating
• Ice and water have no mass
Glaciation-Induced Sea-Level Change
S(t) = G(t) – R(t)
• Geoid perturbation, G(t) geopotential perturbed directly by surface mass redistribution and changing rotational potential and indirectly by earth deformation caused by these forcings
• Solid surface perturbation, R(t) vertical earth deformation associated with surface mass redistribution and changing rotational potential
• Surface mass conservation, HG(t)
VOW(t) = G(t) – R(t) + HG(t)AO
HG(t) = VOW(t) AO-1 – AO
-1 G(t) – R(t)
“eustatic” “syphoning”
+ HG(t)
Sea-Level Model
● Original theory published by Farrell and Clark (1976).
● Theory extended to include:
(1) Time-dependent shorelines (Johnston 1993; Peltier
1994; Milne et al. 1999).
(2) Glaciation-induced perturbations to Earth
rotation (Han and Wahr 1989; Bills and James 1996;
Milne and Mitrovica 1996; 1998).
(3) The influence of marine-based ice sheets
(Milne 1998; Peltier 1998).
Some Comments on the Sea-Level Algorithm
• Computing ∆G and ∆R requires knowledge of the sea-level change since this is a key component of surface load. Iterative process required at each time step in computation.
• Sea loading in given by C(θ,Φ,t) S(θ,Φ,t). Continent function can only be determined when RSL is known. Iterative process required over each glacial cycle.
• High spatial resolution computations are computationally intensive (CPU and disk space).
20 kyr BP
10 kyr BP
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