『Abstract
The Yarlung Tsangpo-Brahmaputra river drains a large portion
of the Himalaya and southern Tibetan plateau, including the eastern
Himalayan syntaxis, one of the most tectonically active regions
on the globe. We measured the solute chemistry of 161 streams
and major tributaries of the Tsangpo-Brahmaputra to examine the
effect of tectonic, climatic, and geologic factors on chemical
weathering rates. Specifically, we quantify chemical weathering
fluxes and CO2 consumption by silicate weathering
in southern Tibet and the eastern syntaxis of the Himalaya, examine
the major chemical weathering reactions in the tributaries of
the Tsangpo-Brahmaputra, and determine the total weathering flux
from carbonate and silicate weathering processes in this region.
We show that high precipitation, rapid tectonic uplift, steep
channel slopes, and high stream power generate high rates of chemical
weathering in the eastern syntaxis. The total dissolved solids
(TDS) flux from the this area is greater than 520 tons km-2
yr-1 and the silicate cation flux more than 34 tons
km-2 yr-1. In total, chemical weathering
of the total CO2 consumption by silicate
weathering in the Brahmaputra catchment is derived from only 4%
of the total land area of the basin. Hot springs and evaporite
weathering provide significant contributions to dissolved Na+
and Cl- fluxes throughout southern Tibet, comprising
more than 50% of all Na+ in some stream systems. Carbonate
weathering generates 80-90% of all dissolved Ca2+ and
Mg2+ cations in much of the Yarlung Tsangpo catchment.』
1. Introduction
2. Geologic setting
2.1. The Yarlung Tsangpo-Brahmaputra and the Tibetan plateau
2.2. Namche Barwa and the eastern syntaxis of the Himalaya
3. Climate, vegetation, and hydrology of the Yarlung Tsangpo-Brahmaputra
3.1. Hydrology and climate of the Yarlung Tsangpo-Brahmaputra
3.2. Physical erosion rates in the Yarlung Tsangpo-Brahmaputra
basin
4. Sampling and chemical analysis
4.1. Stream solute chemistry
4.2. Composition of stream bedload
4.3. Chemical flux measurements
5. Results and discussion
5.1. The solute chemistry of the Nyang, Po and Yarlung Tsangpo
5.2. Timing of stream sampling and flux estimates
5.3. Correction for atmospheric and hot-spring inputs to stream
water dissolved ions
5.4. Silicate versus carbonate weathering reactions
5.5. Chemical denudation rates in the Yarlung Tsangpo-Brahmaputra
basin
5.6. Relationships between climate, tectonics, and chemical weathering
5.7. The role of the eastern syntaxis of the Himalaya on the
chemical weathering budget of the Brahmaputra
6. Conclusions and implications
Acknowledgments
References