A high resolution record of chlorine-36 nuclear-weapons-tests fallout from Central Asia

摘要

The Inilchek Glacier, located in the Tien Shan Mountains, central Asia, is unique among mid-latitude glaciers because of its relatively large average annual accumulation. In July 2000, two ice cores of 162 and 167 meters (m) in length were collected from the Inilchek Glacier for (chlorine-36) ~(36)Cl analysis a part of a collaborative international effort to study the environmental changes archived in mid-latitude glaciers worldwide. The average annual precipitation at the collection site was calculated to be 1.6 m. In contrast, the reported average annual accumulations at the high-latitude Dye-3 glacial site, Greenland, the mid-latitude Guliya Ice Cap, China, and the mid-latitude Upper Fremont Glacier, Wyoming, USA, were 0.52, 0.16 and 0.76 m, respectively. The resolution of the ~(36)Cl record in one of the Inilchek ice cores was from 2 to 10 times higher than the resolution of the records at these other sites and could provide an opportunity for detailed study of environmental changes that have occurred over the past 150 years. Despite the differences in accumulation among these various glacial sites, the ~(36)Cl profile and peak concentrations for the Inilchek ice core were remarkably similar in shape and magnitude to those for ice cores from these other sites. The ~(36)Cl peak concentration from 1958, the year during the mid-1900s nuclear-weapons-tests period when ~(36)Cl fallout was largest, was preserved in the Inilchek core at a depth of 90.56 m below the surface of the glacier (74.14-m-depth water equivalent) at a concentration of 7.7 x 10~5 atoms of ~(36)Cl/gram (g) of ice. Peak ~(36)Cl concentrations from Dye-3, Guliya and the Upper Fremont glacial sites were 7.1 x 10~5, 5.4 x 10~5 and 0.7 x 10~5 atoms of ~(36)Cl/g of ice, respectively. Measurements of ~(36)Cl preserved in ice cores improve estimates of historical worldwide atmospheric deposition of this isotope and allow the sources of ~(36)Cl in ground water to be better identified.