Heinrich event
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Heinrich events, named for paleoclimatologist Hartmut Heinrich, are abrupt episodes during the last glacial. Their principal "footprint" is in layers of ice-rafted detritus at intervals in sediment cores from the North Atlantic, but other indications are seen near-globally. Six such events, labelled H1-H6, have been identified. There is some evidence that H3 and H6 are different. Heinrich events are regarded as profound and catastrophic events, with likely armadas of icebergs launched from the Hudson Strait. Alley and MacAyeal (1994) estimate the volume of freshwater discharged by a typical Heinrich event as 370 km3.
Various mechanisms are proposed to explain the events, most centering around the activity of the Laurentide ice sheet, with the most popular being internal oscillations of the ice sheet (although there has been speculation that the dynamically unstable West Antarctic Ice Sheet may play a role in triggering these events).
Heinrich events are related to Dansgaard-Oeschger events seen most clearly in Greenland ice cores with Heinrich events occurring during the cold period of some D-O cycles.
Ice rafted detritus (or debris) (IRD)
The original observations by Heinrich (1988) were of six layers in ocean sediment cores with extremely high lithic fragment percentages in the 180 micrometer to 3 mm size range. The larger size fractions cannot be transported by ocean currents, and are thus interpreted as having been carried by icebergs or sea ice. The signature of the events in the cores varies considerably with distance from the source region - there is an "IRD" belt at, very roughly, 50 N. H1,2,4,5 have source regions near the Hudson Strait. H3 ,6 may have different sources in different regions. The detrital layers thin by an order of magnitude from the Labrador Sea to the European end of the present iceberg route.
Within the layers the presence of foraminifera shells drops by an order of ten and diagnostic northern forams appear
Timing
The table below shows approximate timings for the Heinrich events. There are difficulties in establishing exact dates. Some (e.g. [link]) identify the Younger Dryas event as a Heinrich event, which would make it H0.
The first dates are taken from Hemming, 2004; the second from [Bond]; the third from [Vidal fig 6]
Event Age, KyrHemming Bond VidalH1 16.8 14 H2 24 23 22 H3 ~31 29 H4 38 37 35 H5 45 45 H6 ~60
H1,2 are dated above by C14; H3-6 are dated by correlation to Greenland GISP2.
Heinrich events in previous glacials?
Hemming (2004) reports that there is little published evidence for Heinrich events in previous glacial periods.
External links
- [William C. Calvin, "The great climate flip-flop"] adapted from Atlantic Monthly, 281(1):47-64 (January 1998).
- [D.L. Hartmann, "Heinrich Events"]: outline notes and full references (pdf file)
- [(Gerald Bond) "Recent, Abrupt Climate-Cooling Cycle Found"]: Columbia University Press Release, December 11, 1995:
- [IPCC TAR section 2.4.3 How Fast did Climate Change during the Glacial Period?]
References
- Bond, G., Heinrich, H., Broecker, W., Labeyrie, L., McManus, L., Andrews, J., Huon, S., Jantschik, R., Clasen, S., Simet, C., Tedesco, K., Klas, M., Bonani, G. and Ivy, S. (1992) Evidence for massive discharges into the North-Atlantic Ocean during the last glacial period, Nature, 360, 245-249.
- Heinrich, H. (1988) Origin and consequences of cyclic ice rafting in the Northeast Atlantic Ocean during the past 130,000 years, Quaternary Research, 29, 142-152.
- Hemming, S. R. (2004) Heinrich events: Massive late pleistocene detritus layers of the North Atlantic and their global climate imprint, Reviews of Geophysics, 42, RG1005.
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