Strontium isotopic compositions of dissolved and suspended loads from the main channel of the Yangtze River

The concentrations of Sr and 87Sr/86Sr isotopic ratios have been measured in the dissolved loads from the main channel of the Yangtze River. The result shows that the Yangtze River mainstream water has considerably higher Sr concentration (202–330 μg kg−1) and slightly lower 87Sr/86Sr ratio (0.7098–0.7108) than the global average runoff values of dissolved Sr (78 μg kg−1) and 87Sr/86Sr ratio (0.7119). The 87Sr/86Sr values of 0.7098–0.7108 in river waters result from the intense weathering of carbonate and evaporate rocks that enriched in the Yangtze River drainage basin. The calculated result based on the end-member mixing model shows that about 91% of total dissolved Sr are derived from the weathering of carbonate and evaporate rocks and the other 9% derived from the weathering of silicate rock. The Yangtze River transports about 1.86 × 1011 g yr−1 (2.12 × 109 mol yr−1) of dissolved Sr annually to the East China Sea, with an average 87Sr/86Sr of 0.7108. The calculated “87Srexcess flux” of the Yangtze River is about 2.12 × 107 mol yr−1, indicating the important impact on seawater Sr isotope evolution. The measured 87Sr/86Sr ratios of suspended particulate matters in the Yangtze River water ranging from 0.7178 to 0.7252, are about 0.015 higher than that of corresponding dissolved loads, reflecting more important contribution of silicate particles in suspended particulate matters and preferential dissolution of carbonate rocks during basin weathering.