Geochemistry of Yukon and Copper River Tributaries, Alaska

Alaska is already beginning to be affected by changes in global climate which make it a good location to study the feedback effects between climate, the water cycle and the carbon cycle. Using river dissolved elements and Sr isotopes we examine changes and/or differences in chemical weathering between watersheds in predominantly permafrost areas and glacial watersheds. Tributaries of the Tanana, Yukon, Nenana and Copper rivers were sampled during the early snow melt in late May and the late permafrost/glacial melt period in September of 2007. Waters are predominantly Ca—HCO₃^–/SO₄ which is typical of glaciated terrains. ⁸⁷Sr/⁸⁶Sr isotopes indicate three potential end-members, young basalts, radiogenic silicates and marine carbonates. The results are consistent with weathering observed in glaciated regions with trace calcites and salts dominating the dissolved load; however we have evidence for silicate weathering. Results also indicate that permafrost watersheds experience more progressive silicate weathering than glacial watersheds.