Heinrich events—or more accurately, Heinrich layers—are recurrent conspicuous sediment layers, usually 10 to 15 centimeters thick, with coarse rock components that interrupt the otherwise fine-grained oceanic deposits in the North Atlantic. Discovered and described for the first time in the 1980s by geologist Hartmut Heinrich, U.S. geochemist Wally Broecker later officially named them Heinrich layers, which has become a standard term in paleoceanography.

The presence of Heinrich layers has been established throughout the North Atlantic, from off Iceland, southward to a line running from New York to North Africa. Such coarse rock debris could only have been transported such a great distance from its point of origin in the Hudson Bay by icebergs.

"The actual significance of these Heinrich events, however, lies in the fact that, along with the melting phase and release of icebergs, large quantities of fresh water were introduced into the North Atlantic," says Lars Max, paleoceanographer at MARUM—Center for Marine Environmental Sciences at the University of Bremen and first author of the study. As part of their work, he and his co-authors reconfigure the interrelationships among Heinrich layers, freshwater supply, and changes in the ocean circulation. A thin freshwater lens lying atop millions of cubic kilometers of water during the Heinrich events is presently considered to be the cause of the disruption of the Atlantic Meridional Overturning Circulation (AMOC), or its complete shutdown, with profound regional and global climatic consequences. The AMOC is just one segment of the global conveyor belt of ocean currents that is driven by temperature and salinity and plays a significant role in the climate system.