Paleo Slide Set: The Ice Ages
Climate forcing on glacial-interglacial timescales

As the scientific quest to unlock the mysteries of the ice ages enters its fourth century, 
this slide summarizes our current understanding of the climate forcing (changes in insolation), 
and the climate response that we observe in the geologic record on glacial - interglacial timescales. 
The top panel is June insolation at 65N, in watts/m2, calculated by Berger (1978). The three lower 
panels are all geologic records of glacial-interglacial change. d18O is a measure of the ratio 
of the two stable isotopes of oxygen (18O and 16O). d18O in foraminifer skeletons is affected by 
both temperature and the amount of 16O preferentially locked away in ice sheets, and up on this 
graph corresponds to negative d18O values, and indicates interglacial conditions.

Down on this graph, more positive d18O, corresponds to glacial conditions that are colder, 
and have more ice present. This SPECMAP record is a composite (average) of many d18O records, 
intended to represent globally-averaged changes, while the record from ODP Site 677 (bottom graph), 
represents a single region in the North Atlantic. The final geologic record comes from a loess deposit.

Photo Credits:
Thomas G. Andrews
NOAA Paleoclimatology Program