The relationship between average annual surface temperature, accumulation and ablation rates, and glacial mass balance

Milankovitch Theory: When 65N summer insolation low, ice accumulates and have glaciation When 65N summer insolation high, ice ablates and have interglaciation Note: orbital configuration of maximum and minimum

Model Assumptions Temperatures get colder and accumulation/ablation ratio increases with increasing altitude and latitude Equilibrium line is at higher elevation towards the south, meets Earth’s surface (sea level) at climate point Climate point moves N or S in direct proportion to summer insolation Moves >10 degrees latitude over several 10’s of thousands of years When it is N of continental edge, continents are ice free When it dips onto continent, ice accumulates Elevation of ice adds to accumulation area

Timing of insolation forcing and ice sheet response Rate responds to forcing Minimum insolation – maximum rate of ice accumulation Maximum ice volume occurs during period of rising insolation as much of ice sheet is still in accumulation area Lag between minimum insolation and maximum ice volume is ~¼ of one cycle

Activity: Write out the ice-elevation feedback Note this feedback is reduced once the ice is so high that little moisture makes it to the interior of the ice sheet

Benthic foraminiferal d18O record for last full glacial-interglacial cycle

Spectral analysis of: Summer insolation (65N) Benthic foram record 2.75-0.9 Ma Benthic foram record 0.9 – 0 Ma

Corals as record of past glacial/interglacial cycles: Reefs created on uplifting coastlines are good records of past sea level Uplift separates reefs formed during different sea level events, even if absolute sea level was similar (escalator effect) Correcting for uplift makes it possible to calculate initial sea level