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Ernst Sorge and glaciological ingenuity

The most satisfying experiment that I ever did was done with glass beakers and a cheap thermometer. A student, Mark Aikman, and I were trying to learn more about the composition of our local glacial till – the sediment deposited in our region by the Laurentide Ice Sheet. The till is a mixture of the local limestone, which is soluble in strong acid, and material from the Canadian Shield to the north, which is not soluble. Dissolve the till in acid and you get a measure of the ratio of local to distantly derived components. The distant or “erratic” component must have been delivered by the ice sheet.

One day, Mark wandered into my office wearing a worried look. His samples were still fizzing vigorously even after immersion in acid for the stipulated time, 30 minutes. By pestering my colleagues in chemistry I found that the time was a red herring. The author of the methods textbook we were using had blundered, prescribing an inadequate amount of hydrochloric acid. Mark and I were able to clear up this point with a thermometer because the reaction of hydrochloric acid with calcium carbonate, the basic ingredient of limestone, is exothermic – it releases energy in the form of a known amount of heat per amount of reaction products.

This “finding”, new to us if not to chemistry, matched nicely the field work of another student, Dan Stokes. Dan had tried to explain the genesis of the till by counting different-coloured rocks in roadside exposures. The limestone is grey, while the erratics from the Canadian Shield are pink or black, making a striking contrast. The upshot of all this AIS (absurdly inexpensive science) was that most of the till is local, having been carried no more than 2 to 5 km by the ice, but about one eighth is distantly derived, having originated who knows how many hundred kilometres up-glacier. What does this mean? Search me.

When it comes to cheap glaciology, Ernst Sorge has the Trent University geography department beaten soundly. No contest. Sorge overwintered at Eismitte, in the middle of Greenland, during 1930–31, while the leader of the expedition, Alfred Wegener, sledded back towards the coast that he was destined never to reach. Documenting his results in Publication 23 of the International Association of Scientific Hydrology in 1938, Sorge says that he and his companions Fritz Loewe and Johannes Georgi were short not only of many necessities of life, such as a living hut, but also of scientific instruments. They solved the hut problem by digging a hole in the snow, but if they wanted to make measurements they would have to improvise.

Sorge’s most important instrument was his Firnschrumpfschreiber or firn compaction recorder. (Firn is snow that has settled part way to the density of ice, but isn’t there yet.) It was “contrived out of pieces of board, sheet metal, jam jars, wire, string, paper and ice” and measured the rate at which two horizontal arms frozen into the firn, 1–2 metres apart vertically, approached each other. Sorge smuggled a pen into the apparatus somehow. The jam jars served as recording drums, hand-turned, so that the pen would have something to write on. They worked very well, allowing measurements of the compaction rate with a precision of one part in a thousand.

The stimulus for the instrument was the observation that their cave was settling. Sorge wanted to know whether the settling betokened the impending collapse of his home. It cannot have taken him long to make his five Firnschrumpfschreiber, because during the course of the winter he also dug a 50-foot-deep shaft in which to install them and actually made a large number of measurements. Besides, he remarks that, “During an overwintering one has time to commune with one’s self about how Nature is unfolding around one.”

The results from the Firnschrumpfschreiber and from density measurements in the walls of the shaft showed that the compaction rate decreases, and the density increases, with depth. More importantly, they are steady at any given depth, and are now immortalized as the basis for Sorge’s Law: the density remains constant at any given depth in a cold column of settling snow.

I have nothing against billion-dollar satellite missions, and I bet Sorge and his companions got sticky, but all in all, the jam jars were a sound scientific investment.

Posted by Graham Cogley on January 4, 2010 3:00 PM | Permalink