Chapter12, Ruddiman, 2nd edition, THE LAST GLACIAL MAXIMUM


This diagram shows the Boundary Conditions of CO2 and Ice sheets at the Last Glacial Maximum, about 20,000 years ago. Note where the solar radiation input for summer and winter were at this time as well.




Top map: reconstructed ocean temps for August, Last Glacial Maximum, relative to present.

Bottom map: Sea Surface Temperature Anomalies, Last Glacial Maximum, relative to present.



Two different reconstructions of ice thickness. Most recent models suggest a thinner ice sheet at 21 ka.
What is the evidence for each model?



What was the World like at the Last Glacial Maximum? Windy, Cold, lots of Glacial Flour flying around.





Evidence not only on land, fossil sand dunes, but also deposits in nearshore ocean sediments.



How do scientists figure out interpretations of empirical data? What do the data indicate about climatic conditions? Comparisons of GCM models input with boundary condition simulations, with modern distributions of pollen, geologic evidence. Must avoid circular reasoning, so must use inputs separate from proxies, e.g. atmospheric composition, ice volume and extent.









Prairie pollen indicates drier conditions, oak pollen indicates warmer conditions, spruce pollen indicates colder conditions.




Pollen diagrams for abundance of spruce, oak, and grasses over past 13,000 years (C14 ages). From lake sediments in Minnesota.





Vegetation distribution, comparing modern, glacial reconstruction from pollen data, and GCM simulation. Note they don't exactly match up.





GCM simulations of modern versus LGM climate and jet stream path, based on boundary conditions interpreted from geological evidence.



What were the sources of water for closed basin lakes? What was the timing of their rise and fall? Evidence?