Sliding-no Sliding Zone Effect and Age Determination of Ice Cores
Sliding-no Sliding Zone Effect and Age Determination of Ice Cores
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冰芯的滑动-无滑动区效应及年龄测定
DOI：
10.1016/0033-5894(76)90050-8
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发表时间：
1976
影响因子：
2.3
通讯作者：
J. Weertman
中科院分区：
文献类型：
--
作者：
J. Weertman
目前，在季节同位素波动不再可测量的深度采集的冰芯的冰的年龄是根据对冰盖纵向变薄的Dansgaard-Johnsen-Nye分析来估计的。如果冰芯是从钻穿冰层的一个洞中取出的，而这个洞是从冰盖上有冰层从床上滑过的区域流到冰层不能从床上滑过的区域的，那么这种年龄估计就会出现严重的错误。世纪营钻孔位于冰中，可能有这样的流动历史。在停止滑动的区域，水平冰速度在冰盖下部减小，而在冰盖上部增大。平均冰速保持不变。结果，当冰穿过滑动-无滑动过渡带时，冰盖的上部被拉伸，下部被压缩。上半部分被拉伸到1/2的应变，下半部分被压缩到1/2的应变。dansgaard - johnson - nye分析得出的冰的年龄被低估了；年龄误差约为h/a数量级，其中h为冰厚，a为积累速率。（如果使用Johnsen等人的理论来确定冰的年龄，则会出现更大的误差。）如果冰从一个不发生滑动的地区流入发生滑动的地区，则存在类似大小的年龄误差。伯德站的钻孔在冰中，可能有这样的流动历史。在这种情况下，冰的年龄被高估了。如果可以探测到年同位素波动，那么“滑动-无滑动带”效应将使冰盖上表面的冰经过该区域时，积累速率似乎发生了突然变化。
At present the age of ice from ice cores taken at depths where the seasonal isotope fluctuations no longer are measurable is estimated from the Dansgaard-Johnsen-Nye analysis of the longitudinal thinning of ice sheets. A significant error occurs in such an age estimate if ice cores are taken from a hole drilled through ice that has flowed from a region of the ice sheet where ice slides over its bed to a region where it cannot slide over its bed. The Camp Century drill hole is in ice which may have had such a flow history. In the zone where sliding ceases to take place, the horizontal ice velocity decreases in magnitude in the lower part of the ice sheet while it increases in the upper part. The average ice velocity remains unchanged in value. As a consequence the upper part of the ice sheet is stretched and the lower part is compressed as ice moves through the sliding-no sliding transition zone. The upper part is stretched to a strain of the order of 1/2 and the lower part is compressed to a strain that is of the order of 1/2. The age of ice from the Dansgaard-Johnsen-Nye analysis is underestimated; the error in the age is of the order of h/a, where h is the ice thickness and a is the accumulation rate. (Larger errors occur if the theory of Johnsen et al. is used to determine the age of the ice.) An error in age of a similar magnitude exists if ice flows from a region in which sliding does not take place into a region in which it does. The Byrd Station drill hole is in ice which probably has such a flow history. In this situation the age of the ice is overestimated. If the annual isotope fluctuations are detectable the sliding-no sliding zone effect will make it appear that a sudden change in the accumulation rate occurred at the time the ice at the upper surface of the ice sheet passed over this zone.