Distribution of 137Cs in lichens, mosses and pine needles along the transect from the north to the south of Western Siberia

Abstract

The ¹³⁷Cs content in mosses (Hylocomium splendens), lichens (Cladonia stellaris) and the needles of the Siberian pine (Pinus sibirica) and the common pine (Pinus sylvestris) along the transect from the north to the south of Western Siberia from N. 67.5° to N. 55° has been investigated. The appearance of ¹³⁷Cs here is linked to the nuclear weapon tests at Novaya Zemlya. The measurements have shown that at all sampling points south of N. 59.6° there is a very sharp decrease in the ¹³⁷Cs specific activity in all components of the ecosystem (in mosses and lichens by about 20 times, and in the needles of conifers by 100 times) instead of a smooth decrease. This fact can be explained by the existence of the global atmospheric circulation consisting of three circulation cells in the Northern hemisphere. It is just around N. 60° that the boundary between the Polar cell and the circulation cell of midle latitudes is drawn. At this boundary, the counter surface air flows of these cells (in our case, a contaminated flow from the north and a clean one from the south) collide and generate the upward air flows here that take ¹³⁷Cs away. In addition, there is water vapor condensation in the upward flows resulting in snowfalls, rains and thunderstorms. And with these precipitation events, large amounts of ¹³⁷Cs should have fallen out to the north of the Polar cell boundary during the Novaya Zemlya tests. The areas south around of N. 60° have been supposed to remain clean, which is what is being observed.

Keywords: (137)Cs; Coniferous needles; Global atmospheric circulation; Liches; Moss.