『Abstract
We examined the fluvial geochemistry of the Huang He (Yellow
River) in its headwaters to determine natural chemical weathering
rates on the northeastern Qinghai-Tibet Plateau, where anthropogenic
impact is considered small. Qualitative treatment of the major
element composition demonstrates the dominance of carbonate and
evaporite dissolution. Most samples are supersaturated with respect
to calcite, dolomite, and atmospheric CO2
with moderate (0.710-0.715) 87Sr/86Sr ratios,
while six out of 21 total samples have especially high concentrations
of Na, Ca, Mg, Cl, and SO4 from weathering
of evaporites. We used inversion model calculations to apportion
the total dissolved cations to rain-, evaporite-, carbonate-,
and silicate-origin. The samples are either carbonate- or evaporite-dominated,
but the relative contributions of the four sources vary widely
among samples. Net CO2 consumption rates
by silicate weathering (6-120×103 mol/km2/yr)
are low and have a relative uncertainty of 〜40％. we extended the
inversion model calculation to literature data for rivers draining
orogenic zones worldwide. The Ganges-Brahmaputra draining the
Himalayan front has higher CO2 consumption
rates (110-570×103 mol/km2/yr) and more
radiogenic 87Sr/86Sr (0.715-1.24) than the
Upper Huang He, but the rivers at higher latitudes are similar
to or lower than the Upper Huang He in CO2
uptake by silicate weathering. In these orogenic zones, silicate
weathering rates are only weakly coupled with temperature and
become independent of runoff above 〜800 mm/yr.』
1. Introduction
2. Study area
2.1. Geography
2.2. Geology
2.3. Climate, hydrology, and vegetation
3. Sampling and analytical methods
4. Results and discussion
4.1. Major elements and strontium
4.1.1. Evaporite dissolution and sulfide oxidation
4.1.2. Carbonate weathering
4.1.3. Silicate weathering
4.1.4. Strontium system
4.2. Inversion calculation
4.2.1. The model
4.2.2. End-member designation
4.2.3. Model uncertainty and sensitivity
4.2.4. Inversion results
4.3. Flux calculations
4.4. Upper versus lower reaches
4.5. Comparison to rivers in other orogenic zones
5. Conclusions
Acknowledgments
References