9304843 Edmond Unrestricted access and sampling is currently possible in the great rivers of the Russian Far East. Two very successful expeditions have taken place to the Aldan, the major tributary of the Upper Lena (1991), and to the Kolyma (1992). All significant tributaries were sampled for water chemistry and for their suspended and bed material. The data now available for the Aldan system clearly show the effects of frost cracking in accelerating weathering in this periglacial environment. The Archean Aldan Shield appears to weather at rates at least an order of magnitude faster than its Tropical analogue, The Guayana Shield in the Orinoco drainage. Similarily the rates of weathering of the platform carbonates of the Lena Plateau are not inhibited by the low temperatures. Concentration levels during the period of summer flow are comparable to those of the Yangtze, which drains geologically similar terrain. These comparison give insight on the effects of climatic deterioration on the geochemical cycle, a topic of much general interest at the present time. It is planned to extend this work to the main stem of the Upper Lena and to the other large rivers of the region, the Indigrika, Yana, Anadyr and Amur. ***
