『Abstract
　This study reports daily water discharge and suspended sediment load concentrations and Sm-Nd and Rb-Sr isotopic systematics and major and trace elements concentrations of twelve monthly sampled suspended load sediments of the Solimoes（後のoの頭に〜） and Madeira rivers, the two major Andean tributaries of the Amazon, during the year 2004.
　As observed in other long-term monitoring studies of Amazon Rivers, the maximum of suspended sediment load occurs before or during the rising water period (i.e. during the rainy Season). In 2004, the Solimoes（後のoの頭に〜） river exported 〜289×10⁶ tonnes of suspended sediments and the Madeira River 294×10⁶ tonnes which correspond to erosion rates of 129 and 214 T/km²/yr for the Solimoes and Madeira rivers basins, respectively. Both the Solimoes and Madeira suspended sediments are enriched in LREE over HREE and exhibit similar MREE enrichment; the difference being that the Madeira sediments are more fractionated than the Solimoes ones. When plotted in Al2O3-CaO+Na2O-K2O diagram, the suspended sediments of the Solimoes and Madeira rivers exhibit two different weathering trends which suggests that these sediments evolved along two different trends starting from felsic rocks with different chemical compositions. The Nd isotopic compositions (εNd) of the Solimoes sediments (-8.9 to 9.9) are slightly more radiogenic than the corresponding values of the Madeira sediments (-10.8 to -12.1). The ⁸⁷Sr/⁸⁶Sr isotopic compositions of the Madeira sediments (0.728 to 0.740) are significantly more radiogenic than those of the Solimoes (0.713 to 0.717). Together with other major elements and REE evidences, these isotopic compositions suggest that the Solimoes sediments are more influenced by Andean volcanic arc detritus than the Madeira sediments that might be due to input of young basaltic products owing to strong volcanic activity in Ecuador.
　Mineralogical compositions as well as Nd isotopic compositions do not vary seasonally. Based on our data set and on previous published studies, we have calculated that the Nd suspended sediment flux dominates the Nd total flux (i.e., dissolved + suspended sediment) exported to the Atlantic Ocean by the Amazon River representing 〜98％ of the Nd total flux and having a global εNd isotopic composition of -10.3. Contrary to Nd isotopic compositions, Sr isotopic compositions vary seasonally in both rivers. The explanation for this variation remains unclear. We suspect increasing physical weathering during the rainy season to be the main cause of this seasonal control in favouring landslides and river bank erosion that might induce input of more radiogenic sediments not easily mobilized during low water level. We calculated that the Sr isotopic composition of the dissolved load exported by the Amazon River to the Atlantic Ocean is not seasonally dependent and remain fairly constant (0.715-0.716). By contrast, the Sr isotopic composition of the suspended load is strongly affected by the seasonal variation varying from 0.714 in the dry season to 0.730 in the rainy season. Consequently the total Sr isotopic composition (dissolved + suspended sediment) is also seasonally controlled varying from 0.716 to 0.722. We finally suggest that large seasonally controlled Sr isotopic variations of great river is a phenomenon that has been underestimated in previous paleo-climatic and paleo-oceanic studies and should be taken into account in further studies.

Keywords: suspended sediment; Amazon River; Nd-Sr isotopic composition; erosion; flux』

1. Introduction
2. General description of the study area
　2.1. Geological setting
　2.2. Hydrological mean features
3. Sampling and analytical procedures
　3.1. sampling and samples treatment
　3.2. Geochemistry
　3.3. Mineralogy
4. Results
　4.1. Relationship between water discharge and suspended sediment load
　4.2. Major elements, Rb, Sr, and REE concentrations
　4.3. Nd and Sr isotopic composition of suspended sediments
　4.4. Mineralogical composition
5. Discussion
　5.1. Difference in weathering and provenance between the Solimoes and Madeira rivers
　5.2. Seasonal Sr isotopic variation and global isotopic signature
6. Conclusion
Acknowledgements
Appendix A. Supplementary data
References