Secular variations in zonal harmonics of Earth’s geopotential and their implications for mantle viscosity and Antarctic melting history due to the last deglaciation
Secular variations in zonal harmonics of Earth’s geopotential and their implications for mantle viscosity and Antarctic melting history due to the last deglaciation
复制标题
地球位势的纬向谐波的长期变化及其对地幔粘度和末次冰川消融导致的南极融化历史的影响
DOI：
10.1093/gji/ggx116
复制
发表时间：
2017
影响因子：
2.8
通讯作者：
J.
中科院分区：
文献类型：
--
作者：
Nakada;M.;Okuno;J.
基于卫星激光测距观测的地球位势的纬向谐波的长期变化，${\skew4\dot{J}_n}$，包含有关由于冰川均衡调整 (GIA) 以及最近冰川和格陵兰岛和南极冰盖融化而导致的地球变形的重要信息。在这里，我们检查 GIA 引起的 ${\skew4\dot{J}_n}$、$\skew4\dot{J}_n^{{\rm{GIA}}}$ (2 ≤n≤ 6)，这些值源自 IPCC 2013 年报告 (AR5) 中的可用位势纬向速率和最近的融化，以探讨从深度相关的下地幔粘度和 GIA 冰模型推断出的附加信息的可能性。分析$\skew4\dot{J}_2^{{\rm{GIA}}}$和相对海平面变化。 $\skew4\dot{J}_n^{{\rm{GIA}}}$ 对下地幔粘度和全球平均海平面 (ESL) ～130 m 的 GIA 冰模型的敏感性表明，无论本研究采用何种 GIA 冰模型，n=3 和 4 的长期速率主要是由下地幔对南极冰盖融化的粘性响应引起的。此外，基于可用位势纬向长期速率对 $\skew4\dot{J}_n^{{\rm{GIA}}}$ 的分析表明，对于南极 ESL 分量为 ∼20 或 ∼30 m 的 GIA 冰模型，获得了满足均匀纬向长期速率 n=2、4 和 6 的允许的下地幔粘度结构，但没有满足的粘度解$\skew4\dot{J}_3^{{\rm{GIA}}}$ 和 $\skew4\dot{J}_5^{{\rm{GIA}}}$ 值。此外，从每个奇数纬向长期速率得出的下地幔粘度和GIA冰模型的推断模型与满足GIA诱导的偶数纬向长期速率的推论模型明显不同。偶数和奇数纬向长期速率的推论模型之间的差异可能部分归因于> 2的位势纬向长期速率的不确定性，特别是由于轨道几何结构的弱点而导致奇数纬向长期速率的不确定性。如果至少在 n< 5 的长期速率下克服这个问题，那么 $\skew4\dot{J}_n^{{\rm{GIA}}}$ 的分析将有可能对下地幔粘度结构和 GIA 冰模型提出更有说服力的约束，特别是对于 GIA 界有争议的南极融化历史。
Secular variations in zonal harmonics of Earth's geopotential based on the satellite laser ranging observations, ${\skew4\dot{J}_n}$, contain important information about the Earth's deformation due to the glacial isostatic adjustment (GIA) and recent melting of glaciers and the Greenland and Antarctic ice sheets. Here, we examine the GIA-induced ${\skew4\dot{J}_n}$, $\skew4\dot{J}_n^{{\rm{GIA}}}$ (2 ≤n≤ 6), derived from the available geopotential zonal secular rate and recent melting taken from the IPCC 2013 Report (AR5) to explore the possibility of additional information on the depth-dependent lower-mantle viscosity and GIA ice model inferred from the analyses of the $\skew4\dot{J}_2^{{\rm{GIA}}}$ and relative sea level changes. The sensitivities of the $\skew4\dot{J}_n^{{\rm{GIA}}}$ to lower-mantle viscosity and GIA ice model with a global averaged eustatic sea level (ESL) of ∼130 m indicate that the secular rates forn= 3 and 4 are mainly caused by the viscous response of the lower mantle to the melting of the Antarctic ice sheet regardless of GIA ice models adopted in this study. Also, the analyses of the $\skew4\dot{J}_n^{{\rm{GIA}}}$ based on the available geopotential zonal secular rates indicate that permissible lower-mantle viscosity structure satisfying even zonal secular rates ofn= 2, 4 and 6 is obtained for the GIA ice model with an Antarctic ESL component of ∼20 or ∼30 m, but there is no viscosity solution satisfying $\skew4\dot{J}_3^{{\rm{GIA}}}$ and $\skew4\dot{J}_5^{{\rm{GIA}}}$ values. Moreover, the inference model for the lower-mantle viscosity and GIA ice model from each odd zonal secular rate is distinctly different from that satisfying GIA-induced even zonal secular rate. The discrepancy between the inference models for the even and odd zonal secular rates may partly be attributed to uncertainties of the geopotential zonal secular rates forn> 2 and particularly those for odd zonal secular rates due to weakness in the orbital geometry. If this problem is overcome at least for the secular rates ofn< 5, then the analyses of the $\skew4\dot{J}_n^{{\rm{GIA}}}$ would make it possible to put more convincing constraints on the lower-mantle viscosity structure and GIA ice model, particularly for the controversial Antarctic melting history in GIA community.