A
Heinrich event is a natural phenomenon in which large armadas of
icebergs break off from glaciers and traverse the North Atlantic. First described by marine geologist
Hartmut Heinrich (Heinrich, H., 1988), they occurred during five of the last seven glacial periods or "ice ages" over the past 640,000 years (Hodell, et al., 2008). Heinrich events are particularly well documented for the
last glacial period but notably absent from the penultimate glaciation (Obrochta et al., 2014). The icebergs contained rock mass, eroded by the glaciers, and as they melted, this material was dropped to the sea floor as
ice rafted debris (abbreviated to "IRD").
The icebergs' melting caused extensive amounts of fresh water to be added to the North Atlantic. Such inputs of cold and fresh water may well have altered the density-driven,
thermohaline circulation patterns of the ocean, and often coincide with indications of global climate fluctuations.
Various mechanisms have been proposed to explain the cause of Heinrich events, most of which imply instability of the massive
Laurentide Ice Sheet, a continental glacier covering north eastern North America during the last glacial period. Other northern hemisphere ice sheets were potentially involved as well (Fennoscandic, Iceland/Greenland). However, the initial cause of this instability is still debated.
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https://en.wikipedia.org/wiki/Heinrich_event