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

GCM climatology 34Ma

(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)

The Global Ocean Conveyor

FRESH WATER

NADW

AABW

AAIW

How the deep oceans are ventilated:Thermohaline circulation