A Heinrich event is one of the six events identified in 1988 by the German geologist Hartmut Heinrich. These events were identified in the North Atlantic using sedimentary layers specific to the ocean floor. On the ocean floor there are large quantities of detritus scraped off by glaciers. These six events, graded from H1 (most recent) to H6 (oldest), occurred during the last ice age. H1 is believed to have occurred about 15,000 years ago and H6 about 60,000 years ago. The time between two events is not regular and oscillates between 5,000 and 10,000 years. These periods are associated with global climate changes.
These deposits come from major break-ups that affected the large North American ice sheet and took place over quite short periods of time (a few centuries). Fossil analysis shows a depletion of flora and fauna, as well as a decrease in water salinity and a significant cooling of surface water by 2 to 6°.
During these periods, millions of cubic kilometres of fresh water must have poured into the Northern Atlantic, significantly modifying ocean currents both on the surface and in the depths.
The exact causes and mechanisms involved are still not clearly understood.