Polar wander caused by the Quaternary glacial cycles and fluid Love number
Polar wander caused by the Quaternary glacial cycles and fluid Love number
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DOI：
10.1016/s0012-821x(02)00598-8
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发表时间：
2002-06
影响因子：
5.3
通讯作者：
M. Nakada
中科院分区：
文献类型：
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作者：
M. Nakada
由第四纪冰川循环引起的地球自转扰动对深部地幔的粘度提供了重要的约束，因为它们代表了地球对表面负荷再分配的长波长响应。然而，预测的现今极移速度（PWS）对下地幔粘度（ηlm）、670 km深度处的密度跃变以及岩石圈厚度和粘度（例如，Sabadini和Peltier，Geophys。J. R. Astron.Soc.66（1981）553-578; Yuen等人，J. Geophys. Res. 87（1982）10745-10762; Peltier和Wu，Geophys.保留信函10（1983）181-184; Wu和Peltier，Geophys，J.R. 76（1984）753-791; Peltier，J. Geophys. Res. 89（1984）11303-11316; Vermeersen等人，J. Geophys. 102（1997）27689-27702; Mitrovica和Milne，J. Geophys. Res. 103（1998）985-1005;约翰斯顿和Lambeck，Geophys. 136（1999）537-558; Nakada，Geophys. 143（2000）230-238）。对于ηlm<5× 1021 Pa·s和弹性岩石圈的地球模型，现今的PWS对与670 km深度处的密度跃变相关的M1模式（浮力模式）非常敏感[Mitrovica and Milne，J. Geophys.第103（1998）985-1005号决议]。然而，对于具有粘弹性岩石圈的地球模型，M1模式的贡献不太显著[Nakada，Geophys. 143（2000）230-238]。这是由于这种贡献取决于M1模的相对强度Δ k2 T（M1）/kfT，其中Δ k2 T（M1）是M1模的潮汐勒夫数（k2 T）的大小，kfT是流体极限（流体勒夫数）中k2 T的值。具有粘弹性岩石圈的地球模型的kfT值大于弹性岩石圈的kfT值，而较厚的弹性岩石圈的kfT值小于较薄的弹性岩石圈的kfT值。因此，对于具有粘弹性岩石圈的地球模型，PWS主要对下地幔粘度敏感，而不管670 km密度不连续的行为。这种关系也解释了为什么预测的PWS随弹性岩石圈厚度的增加而增加。也就是说，由于弹性岩石圈较厚时的Δ k2 T（M1）/kfT值大于弹性岩石圈较薄时的Δ k2 T（M1）/kfT值，因此在弹性岩石圈较厚的情况下，M1模的贡献更大。
Perturbations of the Earth’s rotation caused by the Quaternary glacial cycles provide an important constraint on the viscosity of the deep mantle because they represent a long-wavelength response of the Earth to surface load redistribution. The predicted present-day polar wander speed (PWS) is, however, sensitive to both the lower mantle viscosity (ηlm), the density jump at 670 km depth, and the lithospheric thickness and viscosity (e.g., Sabadini and Peltier, Geophys. J. R. Astron. Soc. 66 (1981) 553–578; Yuen et al., J. Geophys. Res. 87 (1982) 10745–10762; Peltier and Wu, Geophys. Res. Lett. 10 (1983) 181–184; Wu and Peltier, Geophys, J. R. Astron. Soc. 76 (1984) 753–791; Peltier, J. Geophys. Res. 89 (1984) 11303–11316; Vermeersen et al., J. Geophys. Res. 102 (1997) 27689–27702; Mitrovica and Milne, J. Geophys. Res. 103 (1998) 985–1005; Johnston and Lambeck, Geophys. J. Int. 136 (1999) 537–558; Nakada, Geophys. J. Int. 143 (2000) 230–238). For earth models with ηlm<5×1021Pa s and an elastic lithosphere, the present-day PWS is very sensitive to the M1 mode (buoyancy mode) related to the density jump at 670 km depth [Mitrovica and Milne, J. Geophys. Res. 103 (1998) 985–1005]. The contribution of the M1 mode, however, is less significant for earth models with a viscoelastic lithosphere [Nakada, Geophys. J. Int. 143 (2000) 230–238]. This is due to the fact that this contribution depends on the relative strength of the M1 mode, Δk2T(M1)/kfT, where Δk2T(M1) is the magnitude of tidal Love number (k2T) of the M1 mode and kfTis the value of k2Tin the fluid limit (fluid Love number). The magnitude of kfTfor earth models with a viscoelastic lithosphere is larger than that for an elastic lithosphere, and it is smaller for a thicker elastic lithosphere than for a thinner one. Thus, for earth models with a viscoelastic lithosphere, the PWS is mainly sensitive to the lower mantle viscosity regardless of the behavior of the 670 km density discontinuity. This relation also explains why the predicted PWS increases with increasing thickness of an elastic lithosphere. That is, since the value of Δk2T(M1)/kfTwith a thicker elastic lithosphere is larger than that with a thinner elastic lithosphere, the M1 mode will have a higher contribution in the case of a thicker elastic lithosphere.