The isotopic composition of Si in biogenic silica (BSi), such as opal buried in the oceans' sediments, has changed over time. Paleorecords suggest that the isotopic composition, described in terms of δ³⁰Si, was generally much lower during glacial times than today. There is consensus that this variability is attributable to differing environmental conditions at the respective time of BSi production and sedimentation. The detailed links between environmental conditions and the isotopic composition of BSi in the sediments remain, however, poorly constrained. In this study, we explore the effects of a suite of offset boundary conditions during the Last Glacial Maximum (LGM) on the isotopic composition of BSi archived in sediments in an Earth System Model of intermediate complexity (EMIC). Our model results suggest that a change in the isotopic composition of Si supply to the glacial ocean is sufficient to explain the observed overall low(er) glacial δ³⁰Si in BSi. All other processes explored trigger model responses of either wrong sign or magnitude or are inconsistent with a recent estimate of bottom water oxygenation in the Atlantic Sector of the Southern Ocean. Caveats, mainly associated with generic uncertainties in today's pelagic biogeochemical modules, remain.

中文翻译：

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EMIC海洋中的硅同位素：对径流，铁供应和气候的敏感性

随着时间的推移，生物硅（BSi）中硅的同位素组成（例如埋在海洋沉积物中的蛋白石）已经发生了变化。史料中表明，同位素组成，以术语描述δ ³⁰硅在冰川时期通常比今天低得多。人们普遍认为，这种变化可归因于BSi生产和沉积各自时间的不同环境条件。环境条件与沉积物中BSi同位素组成之间的详细联系仍然存在，但约束较弱。在这项研究中，我们在中等复杂度（EMIC）的地球系统模型中探索了最后一次冰河极大期（LGM）期间一系列偏移边界条件对沉积物中BSi同位素组成的影响。我们的模型研究结果表明，在Si中供应到冰海洋同位素组成的变化是足以解释所观察到的总的（更）低冰δ ³⁰BSi中的Si。探索的所有其他过程均触发了符号或幅度错误的模型响应，或者与最近对南大西洋大西洋海域底部水氧化的估计不一致。目前主要存在与上层生物地球化学模块一般不确定性有关的警告。