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Ice Sheet Mass Balance (Factors influencing sealevel (Not always from…
Ice Sheet Mass Balance
Comparing Methods
Shepherd 2012
Methods show agreement regionally
i.e. Within error, mb trends
= similar region-by-region
Gives confidence despite error sources for each method
Some trends overlap more vs others
I - O vs Gravimetry
Fine detail - don't agree very well
Overall - similar mb trends(& interannual)
Not all methods display error bars
∴ difficult discerning agreement
Combining MB Methods
Memin (2012)
Determining nature of thickness Δ
i.e. did surface elevation Δ due to:
ice thickness Δ
air content Δ
(i.e. firn compaction)
No one method can detect this
Together, altimetry & gravimetry can
Altimetry - detect Δ surface height of ice sheet
Gravimetry - discern whether ice or air thickness Δ
(from characteristic gravity signals)
Combining
MB Methods
Mass balance methods measure different quantities
∴ Can generate NEW msmts by combining methods
Possible to constrain GIA by combining methods ?
Sea level rise
Still not able to accurately attribute SLR to parts of cryosphere
Holocene sea level = much higher than today
--> tens to hundreds metres sealevel rise
Rapid sealevel rise periods e.g. Meltwater Pulse 1A
Sealevel rise is almost never uniform
Dynamic sealevel
Even with no RSL Δ
Undulations exist in ocean surface
--> balance ocean velocities
Wind driven & work via ocean height change - eddies etc
Actual sea level Δ
can have counterintuitive response i.e. local rise RSL off W. Antarctica
Factors influencing sealevel
Not always from cryosphere (ice melt/loss)
Thermal expansion
(water volume Δ)
Seafloor spreading
Sedimentation
Continental collision
(∴ less shallow ocean & coastlines)
2-4 relate to basin volume Δ
Timescales
RSL : Controls
1 yr - 10 kyr
Cryosphere
Lakes / gwater
Thermal expansion
1 Myr - 100 Myr
Seafloor spreading
Continental collision
Sedimentation
Evidence Cryosphere not only cause RSL Δ
RSL Δ occurred before Antarctica existed (~formed 34Myr)
