Heinrich event

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An indication of the timing of Heinrich events during the last glacial
An indication of the timing of Heinrich events during the last glacial

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. The freshwater originated from the Laurentide and possibly European (Grusset et al. 2000) ice sheets.

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, which are seen most clearly in Greenland ice cores; Heinrich events occur during the cold period of some D-O cycles.

Coupled ocean and atmosphere climate modelling shows (Ganopolski and Rahmstorf 2001) that both Heinrich and Dansgaard-Oeschger events may be triggered by relatively minor changes of freshwater loading into the Nordic Seas (respectably 0.15 Sv increase by and 0.03 Sv decrease). The results confirm that a Heinrich event does not cause a cooling around Greenland but further south, mostly in subtropical Atlantic, a finding supported by most available paleoclimatic data.

Contents

[edit] 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

[edit] Timing

The table below shows approximate timings for the Heinrich events. There are difficulties in establishing exact dates. Some (e.g. [1]) 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, Kyr 
               Hemming           Bond          Vidal
H1             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.

[edit] Heinrich events in previous glacials?

Hemming (2004) reports that there is little published evidence for Heinrich events in previous glacial periods.

[edit] External links

[edit] 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.
  • Grousset, F. E., Pujol, C., Labeyrie, L., Auffret, G., Boelaert, A. (2000) Were the North Atlantic Heinrich events triggered by the behavior of the European ice sheets? Geology, 28, 123-126
  • Ganopolski, A., Rahmstorf, S. (2001) Rapid changes of glacial climate simulated in a coupled climate model, Nature 409, 153-158.
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