OK team…here is where we left off last time…..with conclusions from ice sheet modelling The most...
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Transcript of OK team…here is where we left off last time…..with conclusions from ice sheet modelling The most...
OK team…here is where we left off last time…..with conclusions from ice sheet modelling
• The most pronounced ice sheet fluctuations occurred in the West Antarctic Ice Sheet
• Most increase in extent can be attributed to sea-level lowering
• Lower ice temperatures lead to increase in ice extent, but the associated accumulation drop acted to cancel this effect
• According to Huybrechts steady-state glacial reconstruction, the Antarctic Ice Sheet may have contributed 16 m to global sea-level lowering at the LGM
The next step is to include global climate modeling as means to drive ice sheets…..
Global Climate Models – Driving Antarctic Ice with Global Climate
• Horizontal resolution: ~200 to 500 km
• Vertical levels: ~20
• Time step: ~20 minutes
Other equations/parameterizations:
• solar radiation• infrared radiation• clouds• convection• surface boundary layer
• soil• vegetation• snow•prescribed ice sheet
• ocean• sea ice
Typical surface components:
• velocity (u,v,w)• mass• temperature• water vapor• p = R T
Atmospheric 3-D grid-scale equations:
conservation of momentum
conservation of mass
conservation of energy
ideal gas law
GCM basic equations
Dv
Dt 2v
1
p g F
DDt
v C D
DE
Dt p
d1
dt
Q
p RT
(Source: Zachos et al, 2001)
The Problem: Traditional “Snapshot” GCM studies do not account for the time-continuous nature of climatic change on orbital and longer time scales.
Proxy climate records show inherently time-continuous sequences of change:•Long-term trends•Transitions•Transient events
Foraminifera and 18O
18O in CaCO3 precipitated from seawaterf(T, 18Oseawater, metabolic effects)
As T , 18O and as S , 18O
In the today’s high latitude and deep ocean, T is small, so foram 18O recordschanges in seawater isotopic composition
In other parts of the ocean or further backin time it is often difficult to completelyseparate T and 18Oseawater effects
Foram 18O varies withseawater 18O because ofthe exchange of O isotopesbetween H2O and HCO3
=
and other C-bearing ionsdissolved in seawater.
H2O in the hydrospherevaries mainly because ofthe distillation of the lighterisotope (16O) from theheavier isotope (18O) duringatmospheric processes(evaporation, transport,condensation)