On the effects of divide migration, along-ridge flow, and basal sliding on isochrones near an ice divide
On the effects of divide migration, along-ridge flow, and basal sliding on isochrones near an ice divide
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分水岭迁移、沿山脊流动和基底滑动对冰分水岭附近等时线的影响
DOI：
10.1029/2008jf001025
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发表时间：
2009
影响因子：
--
通讯作者：
F. Navarro
中科院分区：
文献类型：
--
作者：
C. Martín;R. Hindmarsh;F. Navarro
雷蒙效应的作用强烈地影响了分隔区雷达层的几何形状，雷蒙效应由于冰的非线性流变而导致雷达层的上升。众所周知，这些层的详细几何形状储存了冰冻圈变化、局部变薄和分水岭形成年龄的记录，并据推测提供了有关分水岭横向运动的信息。这种横向运动可能是由侧翼冰流的变化引起的，因此分隔区包含了冰流动力学的记录。也有人提出，分岔位置的大扰动会消除雷蒙机构运行的累积效应，导致雷蒙凸起消失。由于雷蒙德效应对冰芯的年龄-深度关系有很强的影响，因此了解其作用是局部的（导致强烈的隆起形成）还是分布的在冰芯解释中至关重要。冰分雷达层几何形状的详细演变仍然知之甚少。采用全热-力耦合瞬态模型，定性地探讨了分界偏移对雷达层几何形状的影响。出现了某些定性特征，可用于推断冰冻圈变化的历史，特别是在远离通常地质定年地点的地区。关于滑动对雷蒙效应作用的影响仍然存在不确定性。在一定条件下，滑动的存在可以抑制或消除雷蒙效应的运行。如果这通常是正确的，那么冰分水岭的年代可能只是分水岭底部冻结的日期。我们证明滑动并不一定能消除凸起的形成。分水岭形成的日期很可能是山脊在某一特定地点的位置的日期。雷蒙隆起的演变被沿脊的气流削弱。我们定量地探讨了这种效应的强度，使用尺度分析表明，这种减弱可以有效地用一个参数来描述，即沿山脊斜率与跨界曲率的比值。
[1] Radar layer geometry in divide areas is strongly influenced by the operation of the Raymond effect, which causes upwarping of the layers as a consequence of the nonlinear rheology of ice. The detailed geometry of these layers is known to store a record of change in the cryosphere, of local thinning, and of the age of formation of the divide and has been surmised to provide information about lateral motion of divides. Such lateral motion can be caused by changes in flanking ice streams, and the divide area thereby contains a record of ice stream dynamics. It has also been suggested that a large perturbation of divide position will obliterate the cumulative effects of the operation of the Raymond mechanism, leading to the disappearance of Raymond bumps. Since the Raymond effect has a strong influence on the age-depth relation in ice cores, knowledge of whether its operation is localized (leading to strong bump formation) or distributed is crucial in the interpretation of ice cores. The detailed evolution of ice divide radar layer geometry remains poorly understood. Employing a full thermomechanically coupled transient model, we qualitatively explore the effect of divide migration on radar layer geometry. Certain qualitative features emerge which can be used to infer history of cryosphere change, in particular, in areas distant from the usual sites of geological dating. There remains uncertainty about the influence of sliding on the operation of the Raymond effect. Under certain conditions, the existence of sliding can damp or eliminate the operation of the Raymond effect. If this is generally true, then dating of ice divides may simply be a date for the freezing of the divide bottom. We show that sliding does not necessarily eliminate the formation of bumps. Dates of divide formation are likely to be dates for the location of the ridge at a particular spot. Raymond bump evolution is weakened by flow along the ridge. We explore quantitatively the strength of this effect, using a scaling analysis to show that the weakening can efficiently be described by one parameter, the ratio of along-ridge slope to a measure of the across-divide curvature.