EVIDENCE FOR RE-DISTRIBUTION OF CS-137 ALASKAN TUNDRA, LAKE, AND MARINE-SEDIMENTS

Tundra sampling conducted during 1989-1990 at Imnavait Creek, Alaska ( 68 degrees 37'N, 149 degrees 17'W) indicated that inventories of Cs-13 7 were close to expectations, based upon measured atmospheric depositi on for this latitude band. Typically observed at a depth of 4-10 cm, p eak accumulations of Cs-137 were associated with organic materials, ab ove any mineral soil. Accumulated inventories of Cs-137 in tundra decr eased by up to 50% along a transect to Prudhoe Bay (70 degrees 13'N, 1 48 degrees 30'W). Atmospheric deposition of Cs-137 decreased with lati tude in the Arctic, but declines in deposition would have been relativ ely small over this distance (200 km). This finding suggests a recent loss of Cs-137 from tundra over the northern parts of the transect bet ween Imnavait Creek and Prudhoe Bay. This hypothesis is supported by o bservations of maximum Cs-137 accumulations occurring in surface layer s of the more northern tundra rather than at depth (as at Imnavait Cre ek), as well as by indications of higher Cs-137 accumulations in a lak e inlet. On the other hand, marine sediments collected in the Bering S ea and Chukchi Seas, including the Yukon River delta region, show appa rently lower inventories compared to tundra or lake sediments, althoug h complete inventories are unavailable due to radiocesium buried to de pths (> 20 cm) beyond the sampling capabilities used.