Near-field hydro-isostasy: the implementation of a revised sea-level equation
Near-field hydro-isostasy: the implementation of a revised sea-level equation
复制标题
近场水力均衡：修正海平面方程的实施
DOI：
--
复制
发表时间：
1999
期刊：
影响因子：
--
通讯作者：
James L. Davis
中科院分区：
文献类型：
--
作者：
G. Milne;J. Mitrovica;James L. Davis
摘要
我们描述了现有的海平面方程如何错误地预测了冰盖的次大地水准面地理区域在冰川消融期间海平面(从而海洋负荷)的变化。我们接着提出了一个克服这个问题的新的海平面方程，并描述了如何利用众所周知的谱技术以引力自洽的方式求解这个方程。将新理论应用于预测加拿大东北部的相对海平面历史和现今三维固体表面形变速率(基于单一地球模型，其特征是岩石圈厚度为100亿千米，上、下地幔粘度分别为5×1020和5×1021兆帕·S)，表明当使用原始理论预测表面负荷的海洋分量时，引入了显著的误差。对RSL曲线的预测表明，在已获得数据并用于约束地球粘性结构和冰盖历史的模型的地点，误差约为40%。这一误差将严重偏离基于原始理论的地幔粘性结构和冰层厚度的估计。此外，在一些地区，对三维形变率的预测差异高达25%，因此，未来使用这些数据来约束冰川均衡调整过程模型的应用程序应该采用改进的海平面理论。相反，根据预测的RSL曲线对逆衰减时间的估计(在观测误差范围内)对新理论引入的表面载荷的改善不敏感。因此，基于该参数化和原始海平面方程的粘性结构推论不受海洋载荷误差的影响。最后，新理论预测，在冰川后时期，海平面将上升(即全球均匀)，比原来的理论确定的海平面低约11米。因此，根据远场RSL数据和原始海平面理论估计最后一次冰期最大时的全球冰预算将太小，约为10%。
Summary
We describe how the existing sea-level equation incorrectly predicts the change in sea level (and thus the ocean load) in ice-covered, subgeoidal geographic regions during periods of deglaciation. We go on to present a new sea-level equation that overcomes this problem and we describe how this equation can be solved in a gravitationally self-consistent manner by employing a well-known spectral technique. Application of the new theory to predict relative sea-level (rsl) histories and present-day, 3-D, solid surface deformation rates in northeastern Canada (based on a single earth model characterized by a lithospheric thickness of 100 km and upper and lower mantle viscosities of 5 × 1020 and 5 × 1021 Pa s, respectively) demonstrates that a significant error is introduced when the original theory is employed to predict the oceanic component of the surface load. Predictions of rsl curves show a discrepancy of ~ 40 per cent at sites where data have been obtained and employed to constrain models of earth viscosity structure and ice-sheet histories. This error will significantly bias estimates of mantle viscosity structure and ice thicknesses that are based on the original theory. In addition, predictions of 3-D deformation rates differ by up to 25 per cent in some regions and so future applications that employ these data to constrain models of the glacial isostatic adjustment process should adopt the improved sea-level theory. In contrast, estimates of inverse decay times from the predicted rsl curves are insensitive (to within the observational error) to the improvement in the surface load introduced by the new theory. Thus, viscosity structure inferences based on this parametrization and the original sea-level equation are unaffected by the error in the ocean load. Finally, the new theory predicts a eustatic (i.e. globally uniform) rise in sea level over the postglacial period that is ~ 11 m lower than that determined via the original theory. Therefore, estimates of the global ice budget at the last glacial maximum based on far-field rsl data and the original sea-level theory will be too small by ~ 10 per cent.