Ice sheet models solve the equations for ice flow and the resistive forces in th

Question

Ice sheet models solve the equations for ice flow and the resistive forces in three-dimensions and through time, based on a given temperature forcing and a given bed topography. The following questions are based on an ice sheet model for the last British-Irish Ice Sheet, published by Hubbard and others in 2009. This model can be accessed here (http://www.tellus.geo.su.se/tellus1/tellus2/en/assignments/icesheetmodel.wmv).

The model run begins 38 k yr before present (BP) and progresses in 100 year increments up to 10 k yr BP. The present landmasses are illustrated in color, whereas historical coastlines are represented by grey lines. The blue line in the top left represents air temperature (an upwards movement of the line represents an increase in air temperature and visa versa). The green line represents ice sheet buildup (down) and decay (up). Note the time arrow moving along these lines during the model run. The color legend indicates the rate of ice flow from 0 m yr-1 (dark blue) to very rapid (pink =1000 m yr-1). Explore the model by running it a few times.

After viewing a complete model run how would you describe the general behavior (flow rate, ice sheet dimensions) of the British ice sheet during the last glacial cycle (dynamic/stable)? Does the ice sheet reach its maximum extent in all locations at any one time? What implications does your answer above have for how we should understand reconstructions based on glacial geological evidence, such as Figure 4 in the paper Dy-ke and others published in Quaternary Science Reviews in 2002 (access this paper)(http://www.tellus.geo.su.se/tellus1/tellus2/en/assignments/paper12.pdf) which shows ice sheet margins and ice surface contours at the Last Glacial Maximum?

Explanation / Answer

After viewing the model run, one would clearly see that the British-Irish Ice Sheet behaviour was very dynamic in terms of the rate of ice flow as well as the ice sheet dimensions. Many instances the rate of ice flow crosses over 700 m/yr and in some instances reaches up to 1000m/yr. Even the extent of ice cover varies significantly throughout the model period.

Yes, it reaches its maximum extent in all locations during 20.55 to 19.85 thousand years BP.

The Fig. 4 of the paper Dy-ke and others published in Quaternary Science Reviews in 2002, also map the ice sheet extent and contours during the Last Glacial Maximum (LGM) which is around the same time as mentioned in the previous answer, 20,000 BP. Both the studies employ different methodology of modelling and evidence bases techniques and arrive at roughly the same extent but with different boundaries. The implication may be that the modelling technique produces a fairly accurate result as the evidence bases glacial geological reconstructions.

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