Heinrich event

A Heinrich event is a natural phenomenon in which large groups of icebergs break off from the Laurentide ice sheet and traverse the Hudson Strait into the North Atlantic.

[5] The icebergs contained rock mass that had been eroded by the glaciers, and as they melted, this material was dropped to the sea floor as ice rafted debris (abbreviated to "IRD") forming deposits called Heinrich layers.

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.

By extension, the name "Heinrich event" can also refer to the associated climatic anomalies registered at other places around the globe, at approximately the same time periods.

For Heinrich event 4, based on a model study reproducing the isotopic anomaly of oceanic oxygen 18, the fresh water flux has been estimated to 0.29±0.05 Sverdrup with a duration of 250±150 years,[10] equivalent to a fresh water volume of about 2.3 million cubic kilometres (0.55 million cubic miles) or a 2 ± 1 m (6 ft 7 in ± 3 ft 3 in) sea-level rise.

[20] Gerard Bond suggests that changes in the flux of solar energy on a 1,500-year scale may be correlated to the Dansgaard-Oeschger cycles, and in turn the Heinrich events; however the small magnitude of the change in energy makes such an exo-terrestrial factor unlikely to have the required large effects, at least without huge positive feedback processes acting within the Earth system.

The addition of fresh water to northern oceans may reduce the strength of the Gulf stream, and allow a southwards current to develop instead.

[23] Rohling's 2004 Bipolar model suggests that sea level rise lifted buoyant ice shelves, causing their destabilisation and destruction.

[25] The results show that a Heinrich event does not cause a cooling around Greenland but further south, mostly in the subtropical Atlantic, a finding supported by most available paleoclimatic data.

More specifically, D-O cold events, and their associated influx of meltwater, reduce the strength of the North Atlantic Deep Water current (NADW), weakening the northern-hemisphere circulation and therefore resulting in an increased transfer of heat polewards in the southern hemisphere.

Eventually, the accumulation of melting reaches a threshold, whereby it raises sea level enough to undercut the Laurentide Ice Sheet, thereby causing a Heinrich event and resetting the cycle.

Hunt & Malin (1998) proposed that Heinrich events are caused by earthquakes triggered near the ice margin by rapid deglaciation.

A reconstruction of how Heinrich events would have likely proceeded, with the Laurentide ice sheet first growing to an unsustainable position, where the base of its periphery becomes too warm, and then rapidly losing ice until it is reduced to sustainable size [ 1 ]
The H1 Heinrich event occurred in the Pleistocene , around 16,000 years ago. Evolution of temperature in the Post-Glacial period since the Last Glacial Period , according to Greenland ice cores . [ 6 ]
Chronology of climatic events of importance for the Last Glacial Period (~last 120,000 years) as recorded in polar ice cores, and approximate relative position of Heinrich events, initially recorded in marine sediment cores from the North Atlantic Ocean. Light violet line: δ 18 O from the NGRIP ice core (Greenland), permil (NGRIP members, 2004). Orange dots: temperature reconstruction for the NGRIP drilling site (Kindler et al ., 2014). Dark violet line: δ 18 O from the EDML ice core (Antarctica), permil (EPICA community members, 2006). Grey areas: major Heinrich events of mostly Laurentide origine (H1, H2, H4, H5). Grey hatch: major Heinrich events of mostly European origine (H3, H6). Light grey hatch and numbers C-14 to C-25: minor IRD layers registered in North Atlantic marine sediment cores (Chapman et al ., 1999). HS-1 to HS-10: Heinrich Stadial (HS, Heinrich, 1988; Rasmussen et al ., 2003; Rashid et al ., 2003). GS-2 to GS-24: Greenland Stadial (GS, Rasmussen et al ., 2014). AIM-1 to AIM-24: Antarctic Isotope Maximum (AIM, EPICA community members, 2006). Antarctica and Greenland ice core records are shown on their common timescale AICC2012 (Bazin et al ., 2013; Veres et al ., 2013).
As well as indicating oceanic productivity, foraminifera tests also provide valuable isotopic data
The lithic proportion of sediments deposited during H3 and H6 is substantially below that of other Heinrich events
The ratio of calcium versus strontium in a North Atlantic drill core (blue; Hodell et al., 2008) compared to petrologic counts of "detrital carbonate" (Bond et al., 1999; Obrochta et al., 2012; Obrochta et al., 2014), the mineralogically distinctive component of Hudson Strait-derived IRD. Shading indicates glaciations ("ice ages").
Present-day ocean circulation . The Gulf Stream , far left, may be redirected during Heinrich events.