AN EXPLANATION FOR THE ANOMALOUS ACCUMULATION OF WORLD GLACIAL ICE DURING THE ILLINOIAN GLACIATION UNDER AN INSOLATION MAXIMUM 150,000 YR BP

In the SPECMAP deep-sea core record, the glacial ice volume, as indicated by the delta 18O proxy, reaches a maximum at 150ka despite a peak in summer caloric insolation at all latitudes from 65° N southward. About this time the Eurasian ice sheet approached a maximum, with a continuous ice mass from Ireland eastward to the Lena River in Siberia, with most of Northern Hemisphere ice lying south of 65°N. The model to explain this anomaly involves optimum storm paths and favorable precipitation patterns for ice sheet growth due to a relatively warmer subpolar sea surface in the Labrador Sea and eastward. The warmer seas were caused by an oceanic conveyor belt associated with a stronger and more saline outflow from the Mediterranean Sea than today, but probably without strong deepwater formation in the Nordic Sea. The orbital factor that caused the higher Med salinity was a smaller polar axis tilt that increased the Austral winter insolation. This increase simultaneously warmed latitudes south of the equator relative to the Sahara summer, and diminished the latitudinal temperature difference that drives the African summer monsoons. Weaker monsoons caused greater aridity in the Med region than today and a stronger and more saline outflow at Gibraltar. This orbital control of monsoons and Med salinity is consistent with the known increases in world ice volume at 231ka, 190ka, 119ka, 70ka, and 22ka, and the inverse effect is consistent with ice volume decreases at 174ka and 86ka. This model is quite superior to the classical Milankovitch hypothesis of direct thermal control of ice volume by orbital changes.