Geochemical transect of Alaska--the chemical weathering of soil as it relates to climate and biota

In August, 2007, the U.S. Geological Survey (USGS), in cooperation with Natural Resources Conservation Service, U.S Forest Service, Bureau of Land Management, Geological Survey of Canada (GSC), and several Alaska Native Corporations completed a soil geochemical survey along a 630-mile transect from Prudhoe Bay to Prince William Sound. Soils were collected both by depth and horizon from 177 sites at 5-mile intervals along the existing Trans-Alaska Pipeline System and along portions of the proposed Alaska Natural Gas Pipeline route. The transect traverses nine ecoregions, various bedrock lithologies, and numerous land-cover and land-use categories. Many of the sites were in areas of either continuous or discontinuous permafrost. By sampling from north to south across distinct ecoregions and soil parent materials, we can assess the influences of biota and climate on chemical and physical weathering rates, soil formation processes, and geochemical cycles within various regions. Preliminary results indicate that calcium concentrations in soils from the Beaufort Coastal Plain and the Copper River Basin are elevated relative to the other ecoregions. This is consistent with the calcareous nature of the coastal plain soils that give rise to the plant communities of the non-acidic tundra and the evaporative-capillary concentration of calcium described by others in Copper River Basin soils. Soils from interior Alaska (Ray Mountains, Yukon-Tanana upland, and Tanana-Kuskokwim lowland ecoregions) have higher thorium and lead concentrations than the ecoregions to the north or south. This may derive from the underlying bedrock composition, but more detailed evaluation is necessary. This study supports the timely establishment of geochemical baselines in a region undergoing rapid changes in climate and potential development, and will aid in the refinement of sampling protocols in remote areas of continuous and discontinuous permafrost for the joint USGS/GSC/Mexican Geological Survey Tri-National North American Soil Geochemical Landscapes Project.