Discontinuous Flow, Ice Texture, and Dirt Content in the Basal Layers of the Devon Island Ice Cap
Discontinuous Flow, Ice Texture, and Dirt Content in the Basal Layers of the Devon Island Ice Cap
复制标题
德文岛冰盖基底层的不连续流、冰纹理和污垢含量
作者：
R. Koerner;D. A. Fisher
摘要 1972 年和 1973 年，用 CRREL 热钻从德文岛冰盖顶部获取了地表至基岩岩心。核心最下方 5 m 的氧同位素、微粒浓度和冰结构存在非常明显的变化。冰床上方 2.6 至 4.4 m 处有一段同位素冷、非常细的气泡冰，微粒浓度很高，被认为代表着最后一个冰河时代。其上方和下方都有粗糙的、同位素温暖的、干净的冰。对于冰床上方 1.2 m 处，冰再次变得更细，微粒浓度较高，但气泡浓度非常低，并且同位素在核心中最热。虽然两个核心都存在较大的差异，但细节上却存在显着差异，尽管核心相距仅 27 m。对这些变化进行统计分析后发现，每个岩心至少缺失 25-30% 的原始连续剖面。近基岩冰内的断层可能是造成这种影响的部分原因，但气泡结构也提供了不规则非层流的证据。由于德文岛冰芯中的晶体尺寸和微粒浓度之间存在密切关系，因此表明南极和格陵兰冰盖中脏层的细粒性质是由于污垢包裹体的影响而不是剪切的影响。德文岛核心中陡峭的同位素梯度被证明是可能发生剪切的证据，而剪切不会影响晶体结构的任何变化。冰床附近的透明冰被认为是一种构造特征，但冰盖对其床没有影响，证实了冰盖冻结在其床上的非侵蚀性质。就古气候历史而言，这意味着，由于基岩效应，中等深度（即<400 m）的冰盖只能提供过去大约 5 000 年的连续信息。 5 000 至 10 000 B.P. 之间时间序列变得稍微不连续并且超过 10 000 B.P.如此不连续，以至于只能得出广泛的气候推论。
Abstract Surface-to-bedrock cores obtained with a CRREL thermal drill were taken in 1972 and 1973 from the top of the Devon Island ice cap. There are very pronounced variations in oxygen isotope, micro-particle concentration, and ice texture in the lowermost 5 m of the core. There is a section of isotopically cold, very fine bubbly ice with high micro-particle concentrations between 2.6 and 4.4 m above the bed, considered to represent the Last Ice Age. There is coarse, isotopically warm, clean ice above and below this. For 1.2 m above the bed, the ice is finer again with high micro-particle concentrations but it shows very low bubble concentration and is isotopically the warmest in the core. While the broad variations are common to both cores, in detail there are significant variations despite the fact that the cores were taken only 27 m apart. The variations, when analysed statistically, show that at least 25–30% of the originally continuous profile is missing from each core. Faulting within the near-bedrock ice may be responsible for some of the effect but bubble fabric also gives evidence for irregular non-laminar flow. Because of the strong relationship between crystal size and micro-particle concentrations in the Devon Island cores, it is suggested that the fine-grained nature of dirty layers in the Antarctic and Greenland ice sheets is due to the effect of the dirt inclusions and not of shearing. Steep isotopic gradients in the Devon Island cores are shown to be evidence for possible shearing, which does not effect any change in the crystal texture. Clear ice near the bed is considered a tectonic feature, but the lack of effect on its bed by the ice cap confirms the non-erosional nature of an ice cap frozen to its bed. In terms of paleoclimatic history, it means that, because of bedrock effects, ice caps of intermediate depth (i.e. <400 m) can give continuous information only over the last approximate 5 000 years. Between 5 000 and 10 000 B.P. the time series becomes slightly discontinuous and beyond 10 000 B.P. so discontinuous as to allow only broad climatic inferences to be drawn.