『Abstract
　The main scope of this study is to investigate parameters controlling chemical weathering rates for a large river system submitted to subarctic climate. More than 110 river water samples from the Mackenzie River system (northern Canada) have been sampled and analyzed for major and trace elements and Sr isotopic ratios in the dissolved phase. The three main morphological units are reflected in water chemistry. Rivers from the Canadian Shield are very dilute, dominated by silicate weathering (Millot et al., 2002), whereas the rivers of the Rocky and Mackenzie Mountains as well as the rivers of the sedimentary Interior Platform are dominated by carbonate weathering and are SO4 rich. Compared to the rivers of the Mackenzie and Rocky Mountains, the rivers of the interior plains are organic, silica, and Na rich and constitute the dominant input term to the Mackenzie River mainstream. Rivers of the Canadian Shield area do not significantly contribute to the Mackenzie River system. Using elemental ratios and Sr isotopic ratios, a mathematical inversion procedure is presented that distinguishes between solutes derived from silicate weathering and solutes derived from carbonate weathering. Carbonate weathering rates are mostly controlled by runoff, which is higher in the mountainous part of the Mackenzie basin. These rates are comparable to the carbonate weathering rates of warmer areas of the world. It is possible that part of the carbonate weathering is controlled by sulfide oxidative weathering, but its extent remains difficult to assess. Conversely to what was stated by Edmond and Huh (1997), overall silicate weathering rates in the Mackenzie basin are low, ranging from 0.13 to 4.3 tons/km²/yr (Na+K+Ca+Mg), and confirm the negative action of temperature on silicate weathering rates for river basins in cold climates. In contrast to what has been observed in other large river systems such as the Amazon and Ganges Rivers, silicate weathering rates appear 3 to 4 times more elevated in the plains than in the mountanous headwaters. This contradicts the “Raymo hypothesis” (Raymo and Ruddiman, 1992). Isotopic characterization of suspended material clearly shows that the higher weathering rates reported for the plains are not due to the weathering of fine sediments produced in the mountains (e.g., by glaciers) and deposited in the plains. Rather, the relatively high chemical denudation rates in the plains are attributed to lithology (uncompacted shales), high mechanical denudation, and the abundance of soil organic matter derived from incomplete degradation and promoting crystal lattice degradation by element complexation. The three- to fourfold factor of chemical weathering enhancement between the plains and mountains is similar to the fourfold factor of enhancement found by Moulton et al.(2000) between unvegetated and vegetated watershed. This study confirms the negative action of temperature on silicate weathering for cold climate but shows that additional factors, such as organic matter, associated with northern watersheds are able to counteract the effect of temperature. This acceleration by a factor of 4 in the plains is equivalent to a 6℃ increase in temperature.』

『本研究の主な目的は、亜北極気候帯に注ぐ大河川系の化学風化速度をコントロールするパラメータを調べることである。マッケンジー河川系（北部カナダ）からの110以上の河川水試料が採取され、溶存相中の主要元素と微量元素およびSr同位体比が分析された。3つの主な形態的単位が水の化学的性質に反映される。カナダ楯状地からの河川は非常に希薄で、珪酸塩風化が優勢であり（Millot et al., 2002）、一方、堆積性の中央台地の河川と同様にロッキーとマッケンジー山脈の河川は炭酸塩風化が優勢で、SO4に富む。マッケンジーとロッキー山脈の河川に比べ、内部平原の河川は有機物、シリカ、およびNaに富み、マッケンジー川本流への主要なインプット成分となっている。カナダ楯状地地域の河川は、マッケンジー河川系に重要な貢献はしていない。元素比とSr同位体比を用いて、珪酸塩風化由来する溶質と炭酸塩風化に由来する溶質を区別する数学的反転法が示してある。炭酸塩風化速度は主として流出量にコントロールされ、マッケンジー流域の山岳部で高い。これらの速度は、世界のもっと温暖地域の炭酸塩風化速度と比較できる。炭酸塩風化の一部は硫化物酸化風化によりコントロール可能性があるが、その大きさは評価が難しいままである。Edmond and Huh（1997）により述べられたこととは逆に、マッケンジー流域での全体の珪酸塩風化速度は低く、0.13〜4.3トン/km²/年 (Na+K+Ca+Mg)の範囲であり、寒冷気候の河川流域での珪酸塩風化速度に対する温度の負の作用を確認している。アマゾンとガンジス川のような他の大河川系で観察されてきたこととは対照的に、珪酸塩風化速度は山岳源流より平野で3〜4倍高いように見える。これは『Raymo仮説』（Raymo and Ruddiman, 1992）と矛盾する。浮遊物質の同位体特性の同定から、平野で報告された高い風化速度は山岳（例えば、氷河作用による）で生産された細粒堆積物の風化によるものではなく、平野で堆積したことが明らかに示される。むしろ、平野での比較的高い化学削剥速度は、岩相（未固結頁岩）、高い機械的削剥、および不完全な分解に由来する土壌有機物の豊富さと元素錯体化による結晶格子分解の促進に起因している。平野と山地間で化学風化が3〜4倍促進されることは、Moulton et al.（2000）により見いだされた非植生流域と植生流域間での4倍の促進と似ている。本研究は、寒冷気候での珪酸塩風化に対する温度の負の作用を確認しているが、北部流域に伴う有機物のような別の要因が温度の影響に反対に作用する可能性を示している。平野でのこの4倍の促進は、温度として6℃の増加に相当する。』

1. Introduction
2. Geological settings of the Mackenzie basin and sample description
3. Sampling and analytical methods
4. Results
　4.1. Major elements and DOC
　4.2. Strontium isotopes in the dissolved load
　4.3. Strontium isotopes in the river sediments
5. Identification of the weathering sources
　5.1. Rivers from the lowlands and foothills
　5.2. Rivers from the highlands and the source of radiogenic Sr
　5.3. Origin of the high sulfate concentrations
6. The inversion method and the calculation of each reservoir contribution
　6.1. Methodology
　6.2. The different hypothesis
7. Chemical denudation rates
　7.1. Contributions of each reservoir
　7.2. Silicate and carbonate chemical weathering rates in the Mackenzie river basin
　7.3. Worldwide comparison
8. What controls chemical weathering rates of silicates in the Mackenzie river basin?
9. Conclusions
Acknowledgments
References