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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, they occurred during the past glacial periods or "ice ages" and are particularly well documented for the last glacial period. The icebergs contained rock mass, which has been eroded by the glaciers, and as they melted, this matter was dropped onto the sea floor as ice rafted debris (abbreviated to "IRD"). The icebergs' melting caused prodigious 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 implies instability of the massive Laurentide ice sheet, a continental glacier covering North America during the last glacial period. Other northern hemisphere ice sheets were potentially involved as well (Scandinavia, Iceland, Greenland). However, the initial cause of this instability is still debated. == About the events == The strict definition of Heinrich events is the climatic event causing the IRD layer observed in marine sediment cores from the North Atlantic: a massive collapse of northern hemisphere ice shelves, and the consequent release of a prodigious volume of icebergs. By extension, the name Heinrich events can also refer to the associated climatic anomalies registered at other places around the globe, at approximately the same time periods. The events are rapid: they last probably less than a millennia, a duration varying from one event to the next, and their abrupt onset may occur in mere years (Maslin ''et al.''. 2001). Heinrich events are clearly observed in many North Atlantic marine sediment cores covering the last glacial period; the lower resolution of the sedimentary record before this point makes it more difficult to deduce whether they occurred during other glacial periods in the Earth's history. Some (Broecker 1994, Bond & Lotti 1995) identify the Younger Dryas event as a Heinrich event, which would make it H0. Heinrich events appear related to some, but not all, of the cold periods preceding the rapid warming events known as Dansgaard-Oeschger (D-O) events, which are best recorded in the NGRIP Greenland ice core. However, difficulties in synchronising marine sediment cores and Greenland ice cores to the same time scale cast aspersions on the accuracy of this statement. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Heinrich event」の詳細全文を読む スポンサード リンク
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