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首页> 外文期刊>Pure and Applied Geophysics >Separation of the Geodetic Consequences of Past and Present Ice-Mass Change: Influence of Topography with Application to Svalbard (Norway)
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Separation of the Geodetic Consequences of Past and Present Ice-Mass Change: Influence of Topography with Application to Svalbard (Norway)

机译：过去和现在的冰体变化的大地测量结果的分离：地形的影响及其在斯瓦尔巴群岛的应用（挪威）

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Polar regions such as Greenland, Svalbard and Antarctica are deforming today because of both the present-day ice-mass (PDIM) change of glaciers and the glacial isostatic adjustment (GIA) following the Pleistocene deglaciation. Observations handled in these areas contain both the contributions from the PDIM change and GIA. This study aims at separating them by considering two specific gravity variation-to-vertical displacement ratios. We first review the case of the viscoelastic rebound (GIA) subsequent to the Pleistocene deglaciation leading to a ratio C ~ν. The outcome of previous studies is that C ~ν is approximately equal to -0.15 μGal/mm and almost independent of the deglaciation history, ice geometry and viscosity profile of the mantle. Similarly we consider the elastic deformation resulting from PDIM change which leads to a second ratio C ~(e,N). Several studies have shown that C ~(e,N) ≈ -0.26 μGal/mm if one assumes that the changing glaciers are thin layers over the surface of a spherical Earth model. In this case, we show that the separation between the contributions from PDIM change and GIA is unique if both gravity and height changes observations are available at the same station. Next, we focus on C ~(e,N) and show that according to the deglaciation/glaciation context and from colocated gravity variation and ground vertical velocity measurements one can deduce a range of possible values for C ~(e,N). Studying the influence of the topography on C ~(e,N) we first show that it tends to positive values if most of surrounding ice-mass changes above the altitude of the observation site and to values lower than -0.26 μGal/mm if changes are below. We next apply our general formalism to the case of the past and PDIM changes in Svalbard, Norway. We compute the ratio C ~(e,N) at the geodetic observatory at Ny-?lesund and show the influence of the topography of the surrounding glaciers on the measured gravity and uplift rates. We show that if the ice-mass change is spatially uniform, C ~(e, N) does not depend on the speed of ice-mass change, and hence the separation of the contributions from PDIM changes and GIA can still be done univocally. However, if the ice-mass change is not spatially uniform, C ~(e, N) depends on both the speed of ice-mass change and the volume of ice-change rate.
机译：格陵兰，斯瓦尔巴特群岛和南极洲等极地地区今天正在变形，这是因为当今冰川的冰质量（PDIM）变化和更新世冰消之后的冰川等静压调整（GIA）。在这些领域中处理的观察结果既包含PDIM变更和GIA的贡献。这项研究旨在通过考虑两个比重与垂直位移之比来分离它们。我们首先回顾了更新世脱冰导致黏度C〜ν后的粘弹性回弹（GIA）的情况。先前研究的结果是C〜ν大约等于-0.15μGal/ mm，并且几乎与脱冰历史，地幔的冰几何形状和粘度曲线无关。类似地，我们考虑由PDIM变化导致的弹性变形，该变形导致第二比率C〜（e，N）。多项研究表明，如果假设变化的冰川是球形地球模型表面上的薄层，则C〜（e，N）≈-0.26μGal/ mm。在这种情况下，我们表明，如果重力和高度变化的观测值在同一站点可用，则PDIM变化和GIA的贡献之间的区别是唯一的。接下来，我们将重点放在C〜（e，N）上，并表明根据冰消冰河作用和共同定位的重力变化和地面垂直速度测量，可以得出C〜（e，N）的可能值范围。研究地形对C〜（e，N）的影响后，我们首先表明，如果周围大部分冰块的质量变化高于观测点的高度，则其趋向于正值;如果变化，则其趋向于低于-0.26μGal/ mm在下面。接下来，我们将一般形式主义应用于挪威斯瓦尔巴特群岛的过去和PDIM的变化。我们在Ny-lesund的大地观测站计算比率C〜（e，N），并显示出周围冰川的地形对测得的重力和上升速率的影响。我们表明，如果冰块质量变化在空间上是均匀的，则C〜（e，N）并不取决于冰块质量变化的速度，因此仍然可以唯一地完成PDIM变化和GIA的贡献分离。但是，如果冰块变化在空间上不均匀，则C〜（e，N）取决于冰块变化的速度和冰块变化率的大小。

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