With Speed and Violence Fred Pearce - Global Commons Institute

fell by up to 3-6°F in northern Europe, and the Eskimos reached Scotland in
their kayaks.
Bond's study was an extraordinary piece of detective work. But it raises more
questions than it answers. Two stand out. What, if any, is the relationship
between these cycles and other parts of the climate system, such as
Broecker's ocean conveyor? And, of course, what causes the mysterious
pulse?
Heinrich originally argued that his ice armadas must be the result of some
instability in the North American ice sheet that caused periodic collapses
into the North Atlantic. There might thus be some link to big freshwater
breakouts like that which triggered the Younger Dryas event. Certainly they
involved huge amounts of ice. But the timing is fuzzy. Bond argued that
while instabilities in the ice sheet could explain Heinrich events, only some
of his pulses produced Heinrich events. So instability in ice sheets is unlikely
to explain the pulses themselves, which in any case seem to have been
unaffected by glaciations. By 2001, Bond believed he had confirmed the
answer that many suspected all along.
He went back to the Greenland ice cores to look for evidence of solar
cycles. There is no known direct marker for solar cycles in the cores. But
other researchers had discovered that isotopic traces of cosmic rays
bombarding the atmosphere were left in the ice cores—and that when solar
radiation is at its most intense, cosmic rays are literally blown away from the
solar system. Thus fewer "cosmogenic" isotopes, like carbon-14 and
beryllium-10, are left in the ice cores during periods of strong solar
radiation.