THE FLUVIAL GEOCHEMISTRY OF THE RIVERS OF EASTERN SIBERIA - II - TRIBUTARIES OF THE LENA, OMOLOY, YANA, INDIGIRKA, KOLYMA, AND ANADYR DRAINING THE COLLISIONAL ACCRETIONARY ZONE OF THE VERKHOYANSK AND CHERSKIY RANGES/

Fundamental to the global carbon cycle over geologic time scales in th e control of atmosphere CO2 by aluminosilicate weathering. Much of the information on the rates of this process comes from rivers in the tro pics and subtropics. To understand the possible climatic influences sy stematic 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 geologica lly complex terrain formed by the Mesozoic collision and accretion of the Siberian Kolyma plates. Because of the arid continental climate, i t has not been glaciated in the recent past. Thus, it is possible to s tudy weathering processes in an artic environment dominated solely by cryogenic interactions without contamination by heterogeneous componen ts derived from scrouring glaciers. All the major rivers and their tri butaries in this area have been sampled on expeditions to individual b asins (similar to 100 samples) on a reconnaissance basis at falling st age, 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 ch emistry is indicative of Ca-aluminosilicate and carbonate weathering w ith significant contributions from black shales in some tributaries. T he Si/TZ(+), Si/(Na* + K) and Sr-87/Sr-86 ratios indicate that the we athering 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 A mazon-Orinoco headwaters (143-1,000 X 10(3) mol/km(2)/yr). However, as the North American counterparts in similar latitudes and with compara ble relief, the Mackenzie, Yukon, and Fraser draining the Rockies, als o have high dissolved solids (0.2-2.9 X 10(6) mol/km(2)/yr) and CO2 (1 9-1,750 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 envir onments appears to overcome the inhibiting effects of the decreased te mperatures and lack of precipitation in producing a high chemical yiel d but results in superficial weathering in the case of aluminosilicate s. Copyright (C) 1998 Elsevier Science Ltd.