『Abstract
Water and sediment samples were collected from the headwaters
(the Tuotuo River and Chumaer River) of the Yangtze River, Tongtian
River and Jinsha River (HTJR) originating from the Qinghai-Tibet
Plateau (QTP). Sr and 87Sr/86Sr have been
measured to analyze temporal and spatial variation characteristics
and determine relative contributions from atmospheric inputs,
anthropogenic activities and rock weathering. These results show
that Sr in the HTJR waters ranges from 1.37 to 11.07 μmol L-1,
and 87Sr/86Sr from 0.70948 to 0.71409. The
headwaters Tuotuo River and Chumaer River receive 〜95% of their
Sr from evaporite dissolution. The influence of evaporite decreases
gradually downwards from source area as increase in discharge.
Silicate weathering contributes 4.9%-28.2% of dissolved Sr to
the Jinsha River mainstream and 11.5%-42.4% to the tributaries,
87Sr/86Sr ranges from 0.71034 to 0.71177
in the Jinsha River mainstream, which is higher than those in
other reaches of the Yangtze River. In the Jinsha River suture
belt, granitoids and metamorphic rocks with relatively high 87Sr/86Sr
are exposed. Moreover, carbonate weathering is another important
source of Sr in the Jinsha River waters. It is estimated that
15.9%-46.8% of Sr in the mainstream and 37%-64.5% of Sr in the
tributaries are derived from carbonate weathering. Contribution
from atmospheric precipitation to the Sr in the HTJR is from 0.75%
to 6.1% and influence of anthropogenic activities is slight.
The 87Srex flux forcing changes
in seawater Sr isotopic composition is 1.13×106 mol
a-1 for the HTJR at Yibin, being far lower than those
in the Ganges and Brahmaputra and merely accounting for 1.36%
of the total carried by the global rivers. Therefore, impact of
the HTJR on steady increase of seawater 87Sr/86Sr
ratio since 40 Ma may be very small.
Keywords: Qinghai-Tibet Plateau; Chemical weathering; Riverine
Sr isotopic compositions』
1. Introduction
2. Study area
3. Sampling and analysis
4. Results and discussions
4.1. Dissolved Sr and Sr isotopic characteristics in river
waters
4.2. The different sources of Sr in river waters
4.2.1. Atmospheric input
4.2.2. Anthropogenic contribution
4.2.3. Silicate Sr
4.2.4. Carbonate Sr
4.2.5. Evaporite Sr
4.3 The Sr and 87Sr fluxes in the HTJR
4.4. Spatial variation of Sr isotopic compositions in the Yangtze
River waters and sediments
5. Conclusion
Acknowledgements
References