Paleo Slide Set: Heinrich Events: Marine Record of Abrupt Climate Changes in the Late Pleistocene
H-6 at ca. 60,000 years ago is currently the oldest commonly accepted Heinrich event.

The graph on the left shows how the lithic fraction would oscillate in a hypothetical core extracted from a 
continental shelf margin in the North Atlantic. How could such different sediments be created in the same location? 
In short, the environmental conditions during sediment deposition on the ocean floor changed rapidly over time 
as the position and dynamics of the large continental ice sheets shifted. The precise glaciological conditions 
during a Heinrich event remain a mystery, but all of the scientific evidence points to Heinrich events requiring 
a significant drop in sea surface temperatures, a reduction in the flux of planktonic foraminifera, and an extension 
of the ice sheet onto the continental shelf, where deposition of ice rafted detritus, (IRD) occurred.

The figure on the right shows the probable differences in ice extent and sediment processes during Heinrich 
events and the corresponding non-Heinrich intervals. The key features of sediment delivery during Heinrich 
events are the presence of icebergs, meltwater plumes and probably massive gravity flows called turbidites. 
All of these processes, occurring within cold stadial events, produce sediments with high lithic content and 
deposit ice rafted detritus. In contrast, non-Heinrich events are distinguished by hemipelagic sediments with 
high foraminifer content. They are formed at the margin between coastal and pelagic environments and are deposited 
during warm interstadial periods. Because Heinrich and non-Heinrich sediments formed in different environmental 
conditions, these events tell us much about fluctuations in climatic conditions in the North Atlantic over the last 
60,000 years. 

Photo Credits:
John T. Andrews, Thomas G. Andrews 
NOAA Paleoclimatology Program and INSTAAR, University of Colorado, Boulder