Energy balance of ice streams
Energy balance of ice streams
复制标题
冰流的能量平衡
DOI：
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发表时间：
2000
影响因子：
3.4
通讯作者：
Charles F. Raymond
中科院分区：
文献类型：
--
作者：
Charles F. Raymond
分析了从润滑良好的冰流的中心部分到边缘的力的横流传递，结果表明，运动诱导的热产生的横向位置有相应的移动。中心的基础产热率可以大大小于由驱动应力给出的局部势能损失率乘以下坡运动的速度。对于速度约为无摩擦床层速度的40%、基础应力约为驱动应力的25%的中等水平的润滑，基础加热是最大值。确定了床上融水产生和排放之间的稳定和不稳定的平衡。速度小于(大于)最大产热速度的稳定稳定状态称为排出限制，因为速度的增加将导致基础熔化的增加(减少)，并且必须(不必)通过增加排出来平衡。结果表明，基础排水系统的逐渐演化和影响基础融化的因素会导致快速和缓慢运动状态之间的不连续跳跃。对南极西部冰流B、D、E和Rutford冰流的6个断面的简化分析表明，它们在两侧的支撑程度和相应的机械加热从中央向侧面移动方面是不同的。“上游B”附近的冰流B的横截面可能会受到生产限制，因为两侧的润滑性和相关支撑特别高。冰流D、冰流E和拉特福德冰流上部的横断面处于排水受限状态。通过侧向阻力产生的基础热量显著减少(在大多数情况下)，以及与低厚度相关的进入基础冰的预期高热流(在某些情况下)倾向于有利于基础冻结。然而，除了一个截面外，所有被检查的截面都将经历基础熔融，在某些情况下，适度的地热热流密度为60m W m−1或更小。冰流B的下部是一个例外，分析表明，地热通量密度必须超过80-100m W−1m才能保持融化。如果不存在这种高地热通量，那么B冰流下部的底部可能正在结冰，这表明B冰流这一部分继续减速。
Abstract Analysis of the cross-flow transmission of force from the central parts of a well-lubricated ice stream to its margins shows that there is a corresponding shift in the lateral location of motion-induced heat generation. The rate of basal heat generation in the center can be substantially smaller than the local rate of potential energy loss given by driving stress times the speed of downslope motion. The basal heating is a maximum for an intermediate level of lubrication for which speed is about 40% of the speed over a friction-less bed and base stress is about 25% of the driving stress. Stable and unstable balances between meltwater production and drainage on the bed are identified. A stable steady state with a speed less (more) than that giving maximum heat generation is termed drainage-(production-) limited, since an increase in speed would lead to increased (decreased) basal melting and must (need not) be balanced by increased drainage. It is shown that gradual evolution of the basal water drainage system and the factors affecting basal melting can cause discontinuous jumps between fast- and slow-moving states. A simplified analysis applied to six cross-sections of West Antarctic Ice Streams B, D, E and Rutford Ice Stream shows them to be diverse in the level of support from the sides and corresponding shift of mechanical heating sideward from their central parts. The cross-sections of Ice Stream B near “Upstream B” may be production-limited, because of especially high lubrication and related support from the sides. Cross-sections in the upper part of Ice Stream D, Ice Stream E and Rutford Ice Stream are in a drainage-limited condition. Substantial reduction of basal heat generation by side drag (in most cases) and expected high heat flow into the basal ice associated with low thickness (in some cases) tends to favor basal freezing. Nevertheless, all of the examined cross-sections except one are expected to experience basal melting with a modest geothermal heat-flux density of 60 m W m−1 or less in some cases. The lower part of Ice Stream B is an exception, where the analysis indicates that geothermal flux density must exceed 80–100 m W−1 m to maintain melting. If this high geothermal flux is not present, then the base of the lower part of Ice Stream B may be freezing, which would suggest continued deceleration of this part of Ice Stream B.