Monthly Archives: August 2015

Kokanee Glacier Beer and the 1962 “Bomb Horizon”

Posted by William Colgan on August 28, 2015
Cold War Science, Glaciers and Society / No Comments

Dear Kokanee Beer,

I was delighted to hear that, in celebration of Kokanee’s founding in 1962, you’ve decided to sponsor some glaciology research in exchange for the recovery of five liters of glacier ice from 1962. It just so happens that 1962 is also an auspicious year for glaciologists. We glaciologists know 1962 as the “bomb horizon”, due to a worldwide peak in the atmospheric deposition rates of radionuclides derived from thermal weapons testing. Tsar Bomba, the largest thermal-nuclear weapon ever tested, with a yield of over 50 MT, had just been detonated the previous fall (30 October 1961). The USSR conducted about 40 thermal-nuclear weapons tests in 1962, and the US conducted closer to 100! After each test, the radionuclide fallout drifted around the atmosphere for a few weeks before raining down on the landscape, glaciers included.

Fortunately for us glaciologists, the glaciers proved to be really effective in retaining those radionuclides under subsequent snowfall. These days, we can just drill a deep hole in a glacier, lower down a gamma spectrometer, find the peak in radioactivity, and get a quick estimate of the 1962 depth. As you can see from the attached graph of radioactive 137Cs decay with depth, the present-day radioactivity of the 1962 “bomb horizon” is about equivalent to the background radioactivity found today at the glacier surface. So, 1962 melted glacier water is definitely not worse to drink than 2015 melted glacier water, I was just thinking that instead of calling your beer Deja Brew, maybe you should perhaps consider Thermonuclear Haze or even Cesium Peak to really give a fair nod to your 1962 glacier roots?

Yours truly,

William Colgan, Ph.D.

Thermo_Wiki2

Figure 1 – Annual count of world wide thermo-nuclear weapons tests between 1945 and 2013. By far, 1962 was the peak in number of weapons tested. (from Wikipedia)

Thermo_profile

Figure 2 – Profile of radioactive cesium (137Cs) with depth, as well as control profile from a  cadmium (109Cd) source located on the detector, recovered from the Devon Ice Cap in the Canadian Arctic in 2005. The arrow points to the apparent 1962 “bomb horizon”. We talk about using this independent dating technique for ice cores in Colgan and Sharp (2008).

Colgan, W. and M. Sharp. 2008. Combined oceanic and atmospheric influences on net accumulation on Devon Ice Cap, Nunavut, Canada. Journal of Glaciology. 54: 28-40.

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