『Abstract
　The application of the molybdenum (Mo) isotope system as a proxy for determining changes in the redox state of the oceans is predicted on the assumption that the composition of continental input can be characterised from crustal rock types, and remains constant. However, it has recently been shown that the δ^98/95Mo composition of global rivers varies between 0.15‰ and 2.4‰ and is therefore systematically heavier b than the average composition of the continental crust (〜0‰). In order to understand the processes that control Mo-isotope fractionation during weathering this study presents δ^98/95Mo and Mo abundance data for rivers (and estuarine samples) from Iceland that drain predominantly basaltic terrains. Resolvable differences are observed in the isotopic composition of the riverine Mo sources; ice (δ^98/95Moice＞1.8‰), basaltic bedrock (δ^98/95Mobedrock 〜0.0‰) and hydrothermal waters (δ^98/95Mohydrothermal 〜-3.4‰). Systematic changes in the dissolved Mo-isotope composition are also observed within river catchments, with δ^98/95Mo values increasing from 〜0‰ in glacial rivers (close to the source) to 〜1‰ downstream, consistent with Mo-isotopes being fractionated during weathering. Analysis of other riverine phases (bedload, colloids and iron-precipitates) demonstrates that these phases preferentially incorporate light Mo-isotopes, and remain coupled to the dissolved load during riverine transportation. A δ^98/95Mo profile through the Borgarfjordur（後のoの頭に¨、dはゼルタ） estuary exhibits a predominantly conservative mixing behaviour, but suggests that the release of isotopically light Mo from the particulate and/or colloidal phases may occur in the low salinity part of the estuarine mixing zone.

Keywords: molybdenum (Mo) isotopes; basaltic weathering; riverine inputs; estuarine mixing』

1. Introduction
2. Geological setting, climate and sample localities
　2.1. Geological setting and climate
　2.2. Sample localities
3. Sampling methods and analytical techniques
　3.1. Sampling methods
　3.2. δ^98/95Mo and [Mo] analyses
4. Results
　4.1. Southeast Iceland
　4.2. West Iceland
　4.3. Borgarfjordur（後のoの頭に¨、dはゼルタ） estuary
5. Discussion
　5.1. Sources of dissolved riverine Mo
　　5.1.1. Glacial ice
　　5.1.2. Underlying bedrock
　　5.1.3. Hydrothermal Mo
　5.2. Mo-isotope fractionation during weathering and riverine transportation
　5.3. Borgarfjordur（後のoの頭に¨、dはゼルタ） estuary δ^98/95Mo profile
　5.4. Implications for oceanic Mo-isotope budgets
6. Conclusions
Acknowledgements
References