Major volcanic eruptions deposit large amounts of strong acids in polar ice. Two such volcanic eruptions are Laki, A.D. 1783, at high latitude (64 °N), and Tambora, A.D. 1815, close to the Equator (8°S). The acid ice layers from these eruptions are easily reached by shallow drilling, and the acidity of the ice cores obtained has been determined by a solid electrical conductivity method (ECM), and in some cases by liquid pH measurements. The strong acid is identified by chemical anion analysis. Sulfate is the dominant anion in both of these volcanic events.
Atmospheric thermonuclear-bomb tests ejected radioactive debris into the atmosphere. Two major groups of such tests are those carried out by the Americans in 1952-54 at low latitude (11°N) and by the Russians in 1961-62 at high latitude (75°N). Radioactive debris from these events was deposited in polar snow, and can be detected by specific total β activity measurements. The radioactive layers serve as dating horizons in the firn. The total β activities were measured at least 10 years after ejection, thus the measured activities were mainly due to 90Sr and 137Cs.
The amount of 90Sr and 137Cs ejected into the atmosphere is known. We assumed a similar global distribution pattern of bomb-produced total β activity and strong acids from violent volcanic activity, and were able to calculate that both major volcanic events produced some 300 million tons of sulphuric acid. This is in agreement with other estimates of the Tambora eruption, which are based on studies of ice cores from Antarctica.