The fluvial geochemistry of the rivers of Eastern Siberia: III. Tributaries of the Lena and Anabar draining the basement terrain of the Siberian Craton and the Trans-Baikal Highlands

The conventional view of the climatic influence on weathering is that weath ering rates are strongly temperature-dependent due to the near-exponential relationship (Clausius-Clapeyron) between temperature acid the saturation v apor pressure of water, and hence precipitation and runoff. This is a centr al theme in the Earth "thermostat" model, i.e., weathering of aluminosilica te rocks on continents acts through the greenhouse effect as a negative fee dback on atmospheric CO2. However, there is very little direct field eviden ce to support this hypothesis. To remedy the lack of systematic geochemical data for cold high latitude rivers as compared to the tropics, large, pris tine drainages of Eastern Siberia have been studied. Here, data from baseme nt terrains of the Siberian Craton are reported. The low Si to total cation ratios suggest a superficially weathered system. The total dissolved solid s flux of 0.39 X 10(6) mol/km(2)/yr and the CO2 uptake flux of 149 x 10(3) mol/km(2)/yr are similar to those of the tropical cratonic systems and the collisional/accretionary zone of northeastern Siberia, but about a factor o f 3 lower than for the orogenic zones of the western Americas at both low a nd high latitudes. The lack of systematic climatic effects on the solute an d CO2 fluxes is ascribed to the unique non-glacial frost shattering process es which continuously expose fresh rock surfaces and, thus, overcome the ef fect of temperature inhibition on high-latitude shields and to the lateriti c cover that seals in the weathering front away from the weathering agents on the tropical shields. No primary climatic effects on weathering rates on the present Earth were detected. Copyright (C) 1999 Elsevier Science Ltd.