Variations in the marine ⁸⁷Sr/⁸⁶Sr record are largely driven by riverine export of weathering-derived strontium. Among the large river systems, the Ganga and the Brahmaputra deliver a disproportionately large flux of radiogenic Sr (i.e., high ⁸⁷Sr/⁸⁶Sr) to the ocean. Understanding the sources and processes that make these river systems such important contributors of radiogenic Sr to seawater has been the focus of many studies; extremely radiogenic silicate and carbonate rocks of the Lesser Himalayan formations impart river water with high ⁸⁷Sr/⁸⁶Sr values. Furthermore, dissolved ⁸⁷Sr/⁸⁶Sr compositions show large temporal variability in both headwater and floodplain catchments; the magnitude of these fluctuations is higher than is observed in any other major river globally. Here, we present dissolved and depth-specific suspended particulate Sr time-series data from the rivers Ganga and Brahmaputra with weekly resolution during the monsoon and monthly resolution during the non-monsoon seasons of 2010–2011. We find that dissolved ⁸⁷Sr/⁸⁶Sr compositions of both rivers show substantial short-term variability with week-to-week changes as large as 0.0134 ⁸⁷Sr/⁸⁶Sr units. Dissolved ⁸⁷Sr/⁸⁶Sr compositions correlate strongly with suspended particulate ⁸⁷Sr/⁸⁶Sr compositions at all depths. To understand the short-term variability of dissolved ⁸⁷Sr/⁸⁶Sr, we developed a hydro-geochemical mixing model using literature-derived Sr concentration and ⁸⁷Sr/⁸⁶Sr values of major tributaries combined with 5-day integrated rainfall as a proxy for unavailable discharge data. Results indicate that short-term changes in dissolved ⁸⁷Sr/⁸⁶Sr are largely driven by spatio-temporal rainfall variability across the Ganga and Brahmaputra watersheds. We also observe strong correlations between the dissolved ⁸⁷Sr/⁸⁶Sr and the particulate ⁸⁷Sr/⁸⁶Sr along the depth-profile in both rivers as well as in other large rivers globally. Hence, we corroborate the findings from Tipper et al. (2021) and propose that in-stream interactions with radiogenic sediments during transport further contribute to dissolved ⁸⁷Sr/⁸⁶Sr variability.

海洋中的⁸⁷ Sr / ⁸⁶ Sr记录的变化主要是由河流中的风化锶导出的。在大型河流系统中，恒河和雅鲁藏布江向海洋输送的放射源锶（即⁸⁷ Sr / ⁸⁶ Sr高）的流量过大。了解使这些河流系统成为放射性Sr对海水的重要贡献者的来源和过程一直是许多研究的重点。小喜马拉雅地层的极具放射源性的硅酸盐和碳酸盐岩赋予河水⁸⁷ Sr / ⁸⁶ Sr的高值。此外，溶解了⁸⁷ Sr / ⁸⁶Sr成分在源头和洪泛区流域均表现出较大的时间变化性。这些波动的幅度高于全球任何其他主要河流。在这里，我们展示了来自Ganga和Brahmaputra河流的溶解的和特定深度的悬浮颗粒Sr时间序列数据，季风期间为每周分辨率，2010-2011年非季风季节为每月分辨率。我们发现两条河流的溶解⁸⁷ Sr / ⁸⁶ Sr组成均显示出明显的短期变化，周变化幅度高达0.0134 ⁸⁷ Sr / ⁸⁶ Sr单位。溶解的⁸⁷ Sr / ⁸⁶ Sr成分与悬浮颗粒⁸⁷密切相关在所有深度的Sr / ⁸⁶ Sr成分。为了了解溶解的⁸⁷ Sr / ⁸⁶ Sr的短期变化，我们建立了一个水文地球化学混合模型，使用文献得出的Sr浓度和主要支流的⁸⁷ Sr / ⁸⁶ Sr值并结合5天综合降雨量作为替代指标。无法获得排放数据。结果表明，溶解的⁸⁷ Sr / ⁸⁶ Sr的短期变化在很大程度上是由恒河和雅鲁藏布江流域的时空降雨变化引起的。我们还观察到溶解的⁸⁷ Sr / ⁸⁶ Sr与颗粒⁸⁷ Sr /之间的强相关性⁸⁶沿着两条河的深度分布，以及在全球其他大型河流锶。因此，我们证实了蒂珀（Tipper）等人的发现。（2021年），并提出在运输过程中与放射源沉积物的流内相互作用进一步有助于溶解的⁸⁷ Sr / ⁸⁶ Sr变异性。