| 总结: | Despite a growing body of work that uses diatom δ 30Si to reconstruct past changes in silicic acid utilisation, few studies have focused on calibrating core top data with modern oceanographic conditions. In this study, a microfiltration technique is used to divide Southern Ocean core top silica into narrow size ranges, separating components such as radiolaria, sponge spicules and clay minerals from diatoms. Silicon isotope analysis of these components demonstrates that inclusion of small amounts of non-diatom material can significantly offset the measured from the true diatom δ 30Si. Once the correct size fraction is selected (generally 2-20μm), diatom δ 30Si shows a strong negative correlation with surface water silicic acid concentration (R 2=0.92), highly supportive of the qualitative use of diatom δ 30Si as a proxy for silicic acid utilisation. The core top diatom δ 30Si matches well with mixed layer filtered diatom δ 30Si from published in situ studies, suggesting little to no effect of either dissolution on export through the water column, or early diagenesis, on diatom δ 30Si in sediments from the Southern Ocean. However, the core top diatom δ 30Si shows a poor fit to simple Rayleigh or steady state models of the Southern Ocean when a single source term is used. The data can instead be described by these models only when variations in the initial conditions of upwelled silicic acid concentration and δ 30Si are taken into account, a caveat which may introduce some error into quantitative reconstructions of past silicic acid utilisation from diatom δ 30Si. © 2012.
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