Evidence for re-distribution of137Cs in Alaskan tundra, lake, and marine sediments

Tundra sampling conducted during 1989–1990 at Imnavait Creek, Alaska (68°37′N, 149°17′W) indicated that inventories of137Cs were close to expectations, based upon measured atmospheric deposition for this latitude band. Typically observed at a depth of 4–10 cm, peak accumulations of137Cs were associated with organic materials, above any mineral soil. Accumulated inventories of137Cs in tundra decreased by up to 50% along a transect to Prudhoe Bay (70°13′N, 148°30′W). Atmospheric deposition of137Cs decreased with latitude in the Arctic, but declines in deposition would have been relatively small over this distance (200 km). This finding suggests a recent loss of137Cs from tundra over the northern parts of the transect between Imnavait Creek and Prudhoe Bay. This hypothesis is supported by observations of maximum137Cs accumulations occurring in surface layers of the more northern tundra rather than at depth (as at Imnavait Creek), as well as by indications of higher137Cs accumulations in a lake inlet. On the other hand, marine sediments collected in the Bering Sea and Chukchi Seas, including the Yukon River delta region, show apparently lower inventories compared to tundra or lake sediments, although complete inventories are unavailable due to radiocesium buried to depths (> 20 cm) beyond the sampling capabilities used.