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Heinrich Events

Heinrich events in a coupled ice sheet - climate model

We studied Heinrich events in a coupled ice sheet-climate model. Heinrich events are large scale climate change events of the last ice age. During these events, large parts of the Laurentide Ice Sheet, that was covering present-day Canada, slid into the North Atlantic and weakened the Atlantic deep water formation and thus the meridional overturning circulation. Our model contains components for the atmosphere (ECHAM5 T31L19, ca. 400 km horizontal resolution), the ocean (MPI-OM, about 30 km resolution around Greenland and about 330 km resolution at the equator), the land vegetation (LPJ) and a model of the northern hemisphere ice sheets (mPISM, 20 km resolution). The model was forced with boundary conditions matching the last glacial maximum (21 000 years ago).

This visualization shows the dynamics of the ice sheets during such an event. The flow velocity is color coded. The height of the ice sheets is vertically exaggerated by a factor of 1000. In the ridges (white) the ice is practically not moving. In the blueish areas, it flows as the result of ice-internal deformation, and is stuck to the ground. In the yellow areas, the ice is sliding on deformable sediments or floating on the ocean.

 

The experiment starts at model year 1780 and ends just after year 5000. The numbering of the years is purely model-internal and not related to actual calendar years in any way.

The main event occurs in the Hudson Bay and the adjacent Hudson Strait (red frame the movie display). In the animation, you can watch a small ice stream (yellow colors) propagating upstream in Hudson Strait. Here it expands across most of the Hudson Bay around the year 2200. The ice quickly flows into the Labrador Sea and the ice sheet thins. This thinning weakens the ice stream. It reaches a first minimum at year 2800, but can recover due to ice supplied from the peripheral areas of Hudson Bay. It expands southward again and, following the expansion, retreats back towards the Hudson strait. By year 4000, it has almost completely retreated, but manages a last expansion along the eastern margin of Hudson bay. By year 4800, it finally dies off. Similar, smaller events occur at the Norwegian Coasts.

Details about this simulation can be found in Florian Ziemen (2013): Glacial Climate Variability (PhD Thesis).

The model and the mean state are described in F. A. Ziemen, C. B. Rodehacke, and U. Mikolajewicz (2014): Coupled ice sheet–climate modeling under glacial and pre-industrial boundary conditions (Clim. Past, 10, 1817-1836, 2014).

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