Figure 13.2 Periodic surges of icebergs during the last ice age appear to have modulated temperatures of the northern hemisphere by lowering the salinity of the far north Atlantic and reducing the meridional overturning circulation. Data from cores through the Greenland ice sheet (1), deep-sea sediments (2,3), and alpine-lake sediments (4) indicate that: Left: During recent times the circulation has been stable, and the polar front which separates warm and cold water masses has allowed warm water to penetrate beyond Norway. Center: During the last ice age, periodic surges of icebergs reduced salinity and reduced the meridional overturning circulation, causing the polar front to move southward and keeping warm water south of Spain. Right: Similar fluctuations during the last interglacial appear to have caused rapid, large changes in climate. The Bottom plot is a rough indication of temperature in the region, but the scales are not the same. From Zahn (1994).