Seasonal changes in the radiogenic and stable strontium isotopic composition of Xijiang River water: Implications for chemical weathering
Seasonal changes in the radiogenic and stable strontium isotopic composition of Xijiang River water: Implications for chemical weathering
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DOI：
10.1016/j.chemgeo.2013.02.004
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发表时间：
2013-04
期刊：
影响因子：
3.9
通讯作者：
G. Wei;Jinlong Ma;Y. Liu;Luhua Xie;Weijian Lu;W. Deng;Zhong‐Yuan Ren;T. Zeng;Yonghong Yang
中科院分区：
文献类型：
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作者：
G. Wei;Jinlong Ma;Y. Liu;Luhua Xie;Weijian Lu;W. Deng;Zhong‐Yuan Ren;T. Zeng;Yonghong Yang
大型河流Sr同位素系统的季节变化可以有效地跟踪区域化学风化的时间变化，并有助于更好地约束全球海洋Sr同位素收支。然而，这样的记录很少。本文报道了西江中游桂平河水中放射成因和稳定Sr同位素（~（87）Sr/~（86）Sr和δ ~（88）Sr）的一年时间序列。通过记录河水中Sr同位素和主要离子组成的季节变化，研究了流域化学风化的时间变化。河水~（87）Sr/~（86）Sr值在0.708487 ~ 0.710336之间，大部分<0.7092，表明碳酸盐岩风化作用的贡献占主导地位。高87 Sr/86 Sr值（>0.7092）通常伴随着高Rb/Sr比、低pH值和溶解无机碳（DIC）δ 13 C，并且出现在河流通量较大的时期。这表明，在雨季，硅酸盐岩石风化对河水化学的贡献增强。河水δ 88 Sr的季节变化较大，在0.147‰ ~ 0.661‰之间，δ 88 Sr值较高，一般对应于较高的87 Sr/86 Sr值。同样，低δ 88 Sr值（<0.3‰）表明碳酸盐岩风化的主要贡献，而高δ 88 Sr值可能代表硅酸盐岩强烈风化的贡献。利用时间序列数据，估算出西江Sr浓度、87 Sr/86 Sr和δ 88 Sr的通量加权平均值分别为1.00μmol/L、0.70960和0.38‰。Sr浓度和87 Sr/86 Sr结果与以前的估计接近，而δ 88 Sr值是世界上大型河流中最高的记录之一，并接近海水。我们的研究结果表明，通过热带/亚热带地区的大型河流排水可以发挥重要作用，在调节全球海洋的稳定Sr同位素收支。
Seasonal changes in strontium (Sr) isotopic systematics in large rivers can effectively track temporal variations in regional chemical weathering, and help to better constrain the Sr isotopic budget of global oceans. However, such records are scarce. Here we present a year-long time-series of both radiogenic and stable Sr isotope measurements (87Sr/86Sr and δ88Sr) from river water at Guiping, in the middle reaches of the Xijiang River, South China. Temporal changes in chemical weathering in the drainage basin were investigated by recording seasonal changes in the composition of both Sr isotopes and major ions in the river water. River water87Sr/86Sr values range from 0.708487 to 0.710336, with most values being <0.7092, indicating a dominant contribution from the weathering of carbonate rocks. High87Sr/86Sr values (>0.7092) are generally accompanied by high Rb/Sr ratios, and low pH and δ13C of dissolved inorganic carbo (DIC) and occur during periods of large river flux. This indicates that the contribution to the chemistry of river water from the weathering of silicate rocks is enhanced during rainy seasons. Seasonal variation in river water δ88Sr is large, from 0.147‰ to 0.661‰, with higher δ88Sr values generally corresponding to higher87Sr/86Sr values. Again, low δ88Sr values (<0.3‰) suggest a dominant contribution from the weathering of carbonate rocks, whereas the high δ88Sr values may represent a contribution from intensive weathering of silicate rocks. Using the time-series data, we estimated the flux-weighted averages of Sr concentration,87Sr/86Sr, and δ88Sr for the Xijiang River to be 1.00μmol/L, 0.70960, and 0.38‰, respectively. The Sr concentration and87Sr/86Sr results are close to previous estimates, while the δ88Sr value is amongst the highest recorded for the large rivers of the world, and is close to that of seawater. Our results indicate that large rivers draining through tropical/sub-tropical regions could play an important role in regulating the stable Sr isotopic budget of global oceans.