EarthRef.org Reference Database (ERR) -- Huh et al. 1998

Fundamental to the global carbon cycle over geologic time scales in the control of atmosphere CO2 by aluminosilicate weathering. Much of the information on the rates of this process comes from rivers in the tropics and subtropics. To understand the possible climatic influences systematic studies are needed for the arctic/subarctic regions. This is the second in a series of papers addressing this problem by systematic studies of the pristine rivers of the Russian Far East. The region to the east of the Siberian Platform (Hugh et. al., 1998) is a geologically complex terrain formed by the Mesozoic collision and accretion of the Siberian Kolyma plates. Because of the arid continental climate, it has not been glaciated in the recent past. Thus, it is possible to study weathering processes in an artic environment dominated solely by cryogenic interactions without contamination by heterogeneous components derived from scrouring glaciers. All the major rivers and their tributaries in this area have been sampled on expeditions to individual basins (similar to 100 samples) on a reconnaissance basis at falling stage, usually in July and August. The total dissolved cation levels (TZ(+)) are moderate (up to similar to 3,100 mu Eq), and the major ion chemistry is indicative of Ca-aluminosilicate and carbonate weathering with significant contributions from black shales in some tributaries. The Si/TZ(+*), Si/(Na* + K) and Sr-87/Sr-86 ratios indicate that the weathering is superficial, i.e., only to cation-rich secondary minerals. The areal total dissolved solid fluxes range from 0.04 to 0.39 X 10(6) mol/km(2)/yr, up to an order of magnitude lower than for the Amazon-Orinoco draining the Andres in the tropics (0.6-4.1 X 10(6) mol/km(2)/yr). The CO2 consumption by aluminosilicate weathering (18-230 X 10(3) mol/km(2)/yr) is also at the lower end of the range observed in the Amazon-Orinoco headwaters (143-1,000 X 10(3) mol/km(2)/yr). However, as the North American counterparts in similar latitudes and with comparable relief, the Mackenzie, Yukon, and Fraser draining the Rockies, also have high dissolved solids (0.2-2.9 X 10(6) mol/km(2)/yr) and CO2 (19-1,750 X 10(3) mol/km(2)/yr) fluxes, these low values seem to be more a function of lithology than simply climate. Ice action in cold environments appears to overcome the inhibiting effects of the decreased temperatures and lack of precipitation in producing a high chemical yield but results in superficial weathering in the case of aluminosilicates. Copyright (C) 1998 Elsevier Science Ltd.