The effect of lateral variations in Earth structure on Last Interglacial sea level
The effect of lateral variations in Earth structure on Last Interglacial sea level
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DOI：
10.1093/gji/ggab289
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发表时间：
2021-09-11
影响因子：
2.8
通讯作者：
Mitrovica, Jerry X.
中科院分区：
文献类型：
--
作者：
Austermann, Jacqueline;Hoggard, Mark J.;Mitrovica, Jerry X.
人们普遍认为，末次间冰期（LIG;类似于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、规模和空间模式存在很大争议。从当地观测数据中提取过去全球平均海平面的一个困难是，它们的海拔需要进行冰川均衡调整（GIA）的校正，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，但来自地震学、地球动力学和矿物物理学的证据表明，地幔内部存在巨大的横向粘度变化。在这项研究中，我们构建了一个新的地球内部结构的模型，通过转换剪切波速度到粘度使用参数化矿物物理实验和地球动力学约束地球的热结构。我们使用这个3-D地球结构，其中包括岩石圈厚度的变化和粘度的横向变化，计算第一个3-D GIA预测LIG海平面。我们发现，有和没有横向地球结构的预测之间的差异可以米到10米的前冰盖的近场，并在其远场高达几米。我们演示了如何前隆动态和大陆勒韦林的横向变化的地球结构的影响，特别关注那些网站与突出的LIG海平面记录。从四个3-D GIA计算结果表明，占横向结构可以采取行动，以增加当地的海平面高达类似1.5垫塞舌尔和最低限度地减少它在西澳大利亚州。我们承认，这一结果只是基于一些模拟，但如果稳健的话，这一转变使这两个地点对全球平均海平面的估计更加一致。我们进一步证明，模拟与一个合适的径向粘度分布可用于局部近似的3-D GIA结果，但这些径向配置文件不能简单地通过平均粘度低于海平面指标网站。
It is generally agreed that the Last Interglacial (LIG; similar to 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 lOs 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 similar to 1.5 mat 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.