Paleo Slide Set: Heinrich Events: Marine Record of Abrupt Climate Changes in the Late Pleistocene
Micrograph detailing the sand-size fraction in core HU87033-009.

In the 1980s, Hartmut Heinrich extracted samples at regular increments from northeastern Atlantic sediment cores.
He next analyzed these samples, counting the number of both lithic and planktonic foraminifera shell fragments. 
He then divided the number of foraminifera by the total number of particles (foraminifers plus lithic fragments). 
What these calculations demonstrated to Heinrich, and subsequently to the rest of the scientific community, 
was that the relative number of foraminifera and lithics in particular North Atlantic sediment cores fluctuated 
in a surprising manner, as this slide and the next illustrate. Samples like the one shown here contain nearly all 
foraminifers. 

Photo Credits:
Anne Jennings 
Institute of Arctic and Alpine Research, University of Colorado-Boulder Boulder, Colorado