『Abstract
　The first data on the distribution of the stable isotopes of silicon in marine and freshwater systems are reported. Both marine and riverine δ³⁰Si are more positive than δ³⁰Si of igneous rocks, suggesting isotopic fractionation during weathering and clay formation and/or biomineralization. The δ³⁰Si value for dissolved silicic acid from several ocean basins is ＋1.1±0.3‰ (n = 69). More positive values are found in surface waters, due to discrimination against ³⁰Si during biogenic opal formation by diatoms. The deep Pacific Ocean is depleted in ³⁰Si relative to the deep Atlantic by roughly 0.4‰. δ³⁰Si of riverine dissolved silicon averages ＋0.8±0.3 (n = 8). The biologic fractionation of silicon isotopes coupled with effects associated with thermohaline circulation appears to play a significant role in controlling the distribution of silicon isotopes in the sea. The average δ³⁰Si value of inputs of silicon to the ocean most likely falls between ＋0.3 and ＋0.9‰, and that of the outputs falls between ＋0.9 and ＋1.9‰, probably in the neighborhood of ＋1.0‰.』

1. Introduction
2. Materials and methods
　2.1. Sample collection and analysis
3. Results
　3.1. Silicon isotope composition of rivers
　3.2. Silicon isotope composition of seawater
　3.3. Silicon isotope composition of mid-ocean ridge hydrothermal fluids
4. Discussion
　4.1. Field versus laboratory estimate of fractionation
　4.2. Control of the silicon isotopic composition of rivers
　4.3. Control of the silicon isotopic composition of seawater
　4.4. The marine silicon isotope budget
　4.5. Implications for future studies
Acknowledgments
References