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).