9627613 Edmund The aims of this continuing project are; (1) to characterize the chemical compositions of the pristine large rivers of Eastern Siberia and their fluxes to the Arctic Ocean; (2) to investigate the factors controlling weathering rates in low temperature environments as compared to those operating in similar geologic terrains in the Tropics; (3) to constrain the effects that the large expansion of peri-glacial environments characteristic of the glacial maxima had on weathering fluxes; (4) to provide base-line data for the environment likely to be most impacted by future greenhouse warming. This work will provide insights on the biogeochemical effects that will result from the climatic and hydrologic changes to be expected from anthropogenic global warming. In addition the results will allow estimates to be made of the effects of climatic deterioration, i.e. glacial maximum conditions, on global weathering fluxes, presently a topic of much controversy owing, mainly, to lack of data. Strong constraints will also be place on the assumptions used in global climate models of the geologic past that invoke a pCO2-weathering feedback to stabilize the greenhouse effect. Extensive field work has been carried out in the basins of the Lena, Yana and Kolyma. Data from steams draining the igneous and metamorphic basement rocks of the Aldan Shield and Trans-Baikal Highland in the Lena headwaters give areal chemical fluxes comparable to those from the Guayana Shield in the drainage of the Orinoco, this despite the fact that latter has an annual average temperature~50oC warmer and receives at least four times the amount of precipitation. While the chemical yields are comparable the severity of weathering, as indicated by Na/K ratios and the 87 Sr/86Sr values, is much less in the Siberian basins. In the Tropics weathering of basement is essentially complete, to kaolinite and gibbsite, but extremely slow, "transport limited". In cold climates frost action continually generates fresh re action surfaces at all scales leading to essentially an "exposure limited" situation. In addition rivers draining the complete range of sedimentary rock types give fluxes similar to those observed in lower latitudes e.g. the large rivers of China. It is proposed to extend this work to the other important rivers of the region, the Anabar, Olenek, Indigirka and Anadyr, and to make a complete characterization of the major, minor and trace element geochemistry and of the isotopic systematics of the dissolved and particulate organic carbon and nitrogen systems of the fluvial regimes in this unglaciated but cold-dominated environment.
