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Ice Sheet Melt & Sea level (Elastic Rebound (Ice mass weighs down…
Ice Sheet Melt & Sea level
Ice loss affects sea level
On 2 timescales:
Long term
(1-20 kyr)
Global isostatic adjustment of asthenosphere
Short term (years/decades)
Crustal rebound
Gravitational effects
Rotational effects
1. Global Isostatic Adjustment
1. Mass of ice sheets
weigh down lithosphere
∴ displace viscous mantle beneath
causes bulging at peripheral margin
2. Ice sheet loss -
--> mantle flows back to initial state
as lithosphere rebounds
Surrounding subsidence occurs where peripheral bulging was
How GIA
affects
sealevel
Doesnt affect actual sea level rise much
Affects how we measure it
e.g. Isostatic rebound gives appearance RSL = falling
--> even if SL = stable, since land uplifted
e.g.
GIA
Effects
Important when assessing ice sheet mass
i.e. Greenland thinning
How much is due to GIA?
Greenland experiences both uplift & subsidence in different places
Ferroscandinavian IS Removal
Scandinavian uplift @ present from IS removal
--> Complicates sea level change signal
Appears as if sealevel is falling more than is
Lag
Lithospheric response (uplift / subsidence) exhibits lag
Present response = result of ice volume
change ~20-40 kyr ago
Modelling GIA
= Dificult since both are poorly constrained
Requires:
Ice history (long term change of ice masses)
Mantle properties
Short-term Response Sealevel to Ice Loss
Gravity
Crustal rebound
Result: sea level rise = spatially heterogeneous
Rotational effects
Gravity
Ice changes gravitational pull from a location ( local mass )
∴ Ocean pulled by gravity change from ice
--> Sealevel higher beside ice mass than without ice present
∴ Ice shrinks --> RSL ocean drops there --> Displaced elsewhere
Elastic Rebound
Ice mass weighs down crust
∴ Ice loss causes crustal rebound
Rebound over longer wavelenght than GIA
--> as crust is stiffer vs mantle
∴ Oceanfloor also rebounds
Displaced water goes elsewhere
Rotational Effects
Earth bulges @ Equator (elliptical shape)
∴ Sealevel @ Equator = further from centre Earth
Equatorial bulge will follow axis
i.e. large scale rise/fall in sealevel
Axis of rotation moves towards area of mass los
Implication: Non-uniform global sealevel change
True north
= axis of rotation position on Earth surface
True Polar Wander
= mvmt of axis (pole) to area of loss
Observed in response to Greenland ice loss
2005-2011 - True N moved toward Greenland
∴ Non-uniform sealevel change globally