SUMMARY It is generally agreed that the Last Interglacial (LIG; ∼130–115 ka) was a time when global average temperatures and global mean sea level were higher than they are today. However, the exact timing, magnitude and spatial pattern of ice melt is much debated. One difficulty in extracting past global mean sea level from local observations is that their elevations need to be corrected for glacial isostatic adjustment (GIA), which requires knowledge of Earth’s internal viscoelastic structure. While this structure is generally assumed to be radially symmetric, evidence from seismology, geodynamics and mineral physics indicates that large lateral variations in viscosity exist within the mantle. In this study, we construct a new model of Earth’s internal structure by converting shear wave speed into viscosity using parametrizations from mineral physics experiments and geodynamic constraints on Earth’s thermal structure. We use this 3-D Earth structure, which includes both variations in lithospheric thickness and lateral variations in viscosity, to calculate the first 3-D GIA prediction for LIG sea level. We find that the difference between predictions with and without lateral Earth structure can be metres to 10s of metres in the near field of former ice sheets, and up to a few metres in their far field. We demonstrate how forebulge dynamics and continental levering are affected by laterally varying Earth structure, with a particular focus on those sites with prominent LIG sea level records. Results from four 3-D GIA calculations show that accounting for lateral structure can act to increase local sea level by up to ∼1.5 m at the Seychelles and minimally decrease it in Western Australia. We acknowledge that this result is only based on a few simulations, but if robust, this shift brings estimates of global mean sea level from these two sites into closer agreement with each other. We further demonstrate that simulations with a suitable radial viscosity profile can be used to locally approximate the 3-D GIA result, but that these radial profiles cannot be found by simply averaging viscosity below the sea level indicator site.

中文翻译：

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地球结构横向变化对末次间冰期海平面的影响

总结 人们普遍认为，末次间冰期（LIG；~130​​-115 ka）是全球平均气温和全球平均海平面高于今天的时期。然而，冰融化的确切时间、幅度和空间模式存在很大争议。从当地观测中提取过去全球平均海平面的一个困难是它们的海拔需要为冰川均衡调整 (GIA) 进行校正，这需要了解地球内部的粘弹性结构。虽然这种结构通常被认为是径向对称的，但地震学、地球动力学和矿物物理学的证据表明，地幔内存在巨大的横向粘度变化。在这项研究中，我们通过使用矿物物理实验的参数化和地球热结构的地球动力学约束将剪切波速度转换为粘度，构建了地球内部结构的新模型。我们使用这个 3-D 地球结构（包括岩石圈厚度的变化和粘度的横向变化）来计算 LIG 海平面的第一个 3-D GIA 预测。我们发现，在前冰盖的近场，有和没有地球横向结构的预测之间的差异可能是几米到几十米，而在它们的远场，则可以达到几米。我们展示了横向变化的地球结构如何影响前凸动态和大陆杠杆作用，特别关注那些具有显着 LIG 海平面记录的地点。四个 3-D GIA 计算的结果表明，考虑横向结构可以使塞舌尔的当地海平面升高 1.5 m，而在西澳大利亚则最低限度地降低海平面。我们承认这一结果仅基于少数模拟，但如果稳健，这种转变会使这两个地点的全球平均海平面估计值彼此更加一致。我们进一步证明，具有合适径向粘度分布的模拟可用于局部近似 3-D GIA 结果，但无法通过简单地平均海平面指示点以下的粘度来找到这些径向分布。但如果是稳健的，这种转变会使这两个地点的全球平均海平面估计值更加一致。我们进一步证明，具有合适径向粘度分布的模拟可用于局部近似 3-D GIA 结果，但无法通过简单地平均海平面指示点以下的粘度来找到这些径向分布。但如果是稳健的，这种转变会使这两个地点的全球平均海平面估计值更加一致。我们进一步证明，具有合适径向粘度分布的模拟可用于局部近似 3-D GIA 结果，但无法通过简单地平均海平面指示点以下的粘度来找到这些径向分布。