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What Causes Heinrich Events?
Hunt, A.G. and Malin, P.E.  1998.  Possible Triggering of Heinrich Events by Ice-Load-Induced Earthquakes.  Nature 393: 155-158.

What was done
Past research has identified six Heinrich events in the North Atlantic Ocean over the last 75,000 years.  These massive ice discharges correlate well with long-term global cooling trends and have been postulated to result from changes in earth's orbital parameters that alter the receipt of solar radiation at the planet's surface.  However, Hunt and Malin pursue a new line of thinking by examining the consequences of the stresses and strains on the earth's crust and mantle that were produced by the expanding and contracting of the great Laurentide ice sheet during the last glacial epoch.

What was learned
The authors discovered that the six known Heinrich events were closely associated in time with ice-load-induced earthquakes around the former edges of the Laurentide ice sheet.  They then develop the hypothesis that Heinrich events may have been caused by this seismic activity and discuss the empirical evidence that supports their conjecture.

What it means
If Hunt and Malin's hypothesis is correct, climate variations associated with Heinrich events are the product of crustal, rather than orbital, mechanics and may be causes of climatic perturbations rather than the result of them.  This possibility raises the further specter of a previously unrecognized feedback phenomenon that may be capable of causing millennial-scale oscillations in climate.  Since this phenomenon is not included in the current generation of general circulation models of the atmosphere, it could significantly limit their reliability as predictors of future climate.

Reviewed 15 October 1998