『Abstract
　It is well established that Hf weathers incongruently such that the isotopic compositions in seawater are offset from those of Nd relative to the correlation defined by bulk lithologies of the continental crust. Here we study this process in detail with new records of the seasonal variability of isotope compositions and concentrations of Hf and Nd in four Swiss rivers. The water has been filtered at a pore size of 0.45μm and therefore represents the truly dissolved and the colloidal pool of both elements. The studied rivers drain metamorphic (gneissic) or sedimentary (mixed carbonate/siliciclastic) lithologies. The dissolved isotope data are compared to the isotope compositions and concentrations of the suspended load and different fractions of the actual source rocks in the respective catchments, as well as to concomitant changes in the aqueous chemistry of the major elements.
　Dissolved Nd concentrations span similar ranges for all rivers, whereas Hf concentrations are one order of magnitude lower in the rivers that drain gneissic catchments compared to those draining sedimentary rocks. This primarily results from the retention of most of the Hf in the gneissic zircons, as indicated by the Hf budget of the gneisses, whereas Hf in the sedimentary catchments is readily weathered from fine detrital silicates.
　Large differences are found between the dissolved Hf isotope compositions of the rivers and those of the suspended load and the source rocks, consistent with the release of Hf from a radiogenic rock fraction during weathering. In the metamorphic catchments this primarily reflects that fact that zircons are barely accessible for weathering. The zircon-free portion of the rocks appears to weather congruently as the riverine Hf isotope compositions are similar to the zircon-free portion of the gneisses, rather than being distinctly more radiogenic. Leaching experiments performed to understand the riverine Hf budget in the sedimentary catchments reveal that the carbonate fraction of the sedimentary rocks is extremely radiogenic, yielding Hf isotope compositions up to εHf of +208. However, the Hf concentrations in the carbonate fractions are too low to dominate the riverine Hf budget, which is instead controlled by the weathering of detrital silicate minerals.
　Two of the catchments, a metamorphic and a sedimentary one, show relatively systematic changes towards more radiogenic dissolved Hf isotope compositions as discharge increases. This suggests that continental runoff conditions could be a relevant parameter for the control of the seawater Hf isotope composition, whereby more congruent weathering is achieved during low discharge when Hf is increasingly derived from weathering-resistant unradiogenic minerals.』

1. Introduction
2. Sampling and methods
　2.1. Geological setting
　2.2. Sampling
　　2.2.1. River waters and suspended matter
　　2.2.2. Rock samples
　2.3. Correction for wet depositional and road salt input
　2.4. Chemical processing and blanks
　　2.4.1. River water
　　2.4.2. River suspended matter
　　2.4.3. Metamorphic rocks
　　2.4.4. Sedimentary rocks
　　2.4.5. Chromatographic separation of Hf and Nd
　2.5. Mass spectrometry
　　2.5.1. Hafnium isotopes
　　2.5.2. Neodymium isotopes
　　2.5.3. Isotope dilution measurements of Hf, Sm and Nd
3. Results
　3.1. Major element chemistry of the four rivers
　3.2. Dissolved and suspended Hf, Sm and Nd in the rivers
　3.3. Comparison of Hf, Sm, and Nd in the weathered parent rock to the riverine dissolved and suspended load
　　3.3.1. Igneous rocks from the catchment of the Verzasca
　　3.3.2. Sedimentary rocks from the catchment of the Birs
4. Discussion
　4.1. Controls on the dissolved Hf and REE concentrations in the rivers
　　4.1.1. Lithological controls on dissolved Hf, Sm and Nd concentrations
　　4.1.2. Riverine chemical controls on the dissolved Hf, Sm and Nd concentrations
　4.2. Incongruent weathering of Hf isotopes
　　4.2.1. The metamorphic catchment of the Verzasca
　　4.2.2. The sedimentary catchment of the Birs
　　　4.2.2.1. Hf and Nd budget of the rocks
　　　4.2.2.2. The Hf isotope composition of the leached carbonate
　　　4.2.2.3. Hypothetical mixtures between leached carbonate and detritus
　　　4.2.2.4. Using Ca/Na and Hf/Nd ratios to constrain the contributions from carbonate and silicate weathering to the Hf and Nd budget of the Birs
　　　4.2.2.5. Relationship between discharge, base cation flux, major elemental ratios and Hf isotopes and its implication
5. Conclusions
Acknowledgments
Appendix A. Supplementary data
References