1. 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…..

2. 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:

3. conservation of momentum conservation of mass conservation of energy ideal gas law GCM basic equations

4. GCM climatology 34Ma

6. (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

7. Foraminifera and  18 O  18 O in CaCO 3 precipitated from seawater f(T,  18 O seawater, metabolic effects) As T,  18 O and as S,  18 O In the today’s high latitude and deep ocean,  T is small, so foram  18 O records changes in seawater isotopic composition In other parts of the ocean or further back in time it is often difficult to completely separate T and  18 O seawater effects

9. Foram  18 O varies with seawater  18 O because of the exchange of O isotopes between H 2 O and HCO 3 = and other C-bearing ions dissolved in seawater. H 2 O in the hydrosphere varies mainly because of the distillation of the lighter isotope ( 16 O) from the heavier isotope ( 18 O) during atmospheric processes (evaporation, transport, condensation)

12. The Global Ocean Conveyor FRESH WATER

13. NADW AABW AAIW How the deep oceans are ventilated: Thermohaline circulation