Ice streams in the Laurentide Ice Sheet: Identification, characteristics and comparison to modern ice sheets
Ice streams in the Laurentide Ice Sheet: Identification, characteristics and comparison to modern ice sheets
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DOI：
10.1016/j.earscirev.2015.01.011
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发表时间：
2015-04
影响因子：
12.1
通讯作者：
M. Margold;C. Stokes;C. Clark
中科院分区：
文献类型：
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作者：
M. Margold;C. Stokes;C. Clark
本文提出了一个全面的审查和合成的冰流在劳伦提斯冰盖（LIS）的基础上，包括以前假设的冰流，并包括一个协调一致的努力，以寻找其他从整个冰盖床的新的映射清单。该清单包括117条冰流，这些冰流是根据各种证据确定的，包括它们的底形印记、大尺度地貌/地形、冰碛物特性和海洋沉积物记录中的冰筏碎片。尽管在硬基岩地区识别冰流存在不确定性，但不太可能错过任何主要的冰流。在末次冰盛期，劳伦蒂德冰流形成了一种排水模式，与现代冰盖的速度模式非常相似。大型冰流有广泛的发病区，并由多个支流，冰通过高海拔地区排水，冰流的间距显示出一定程度的空间自组织，迄今尚未得到承认。地形对冰流的位置起着主要的控制作用，但在冰盖的西部和南部边缘沿着有很大的区域，那里的河床由较弱的沉积基岩组成，冰流的网络可能在很短的时间内反复改变方向。由于冰盖退缩到其低浮雕内部，几个冰流显示没有对应的地形或底层地质，也许是由局部积累的加压冰下融水促进。它们与大多数其他冰流轨迹的不同之处在于它们的长宽比要低得多，并且没有现代的类似物。很少有人试图确定冰流的开始和停止的日期，但很明显，冰流在冰川消退期间打开和关闭，而不是保持相同的轨迹，因为冰缘退缩。我们提供了一个一阶估计冰流活动的变化，在冰川消退，并表明，约30%的利润率是由冰流在末次盛冰期（类似于今天的南极冰盖），但这减少到15%和12%，分别在12 cal ka BP和10 cal ka BP。冰流排水网络中的这些变化在多大程度上代表了对气候驱动的不断变化的质量平衡或与气候无关的内部冰动力反馈（或两者）的简单和可预测的重新调整，这在很大程度上是未知的，代表了未来工作的一个关键领域。
This paper presents a comprehensive review and synthesis of ice streams in the Laurentide Ice Sheet (LIS) based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed. The inventory includes 117 ice streams, which have been identified based on a variety of evidence including their bedform imprint, large-scale geomorphology/topography, till properties, and ice rafted debris in ocean sediment records. Despite uncertainty in identifying ice streams in hard bedrock areas, it is unlikely that any major ice streams have been missed. During the Last Glacial Maximum, Laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets. Large ice streams had extensive onset zones and were fed by multiple tributaries and, where ice drained through regions of high relief, the spacing of ice streams shows a degree of spatial self-organisation which has hitherto not been recognised. Topography exerted a primary control on the location of ice streams, but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock, and where networks of ice streams switched direction repeatedly and probably over short time scales. As the ice sheet retreated onto its low relief interior, several ice streams show no correspondence with topography or underlying geology, perhaps facilitated by localised build-up of pressurised subglacial meltwater. They differed from most other ice stream tracks in having much lower length-to-width ratios and have no modern analogues. There have been very few attempts to date the initiation and cessation of ice streams, but it is clear that ice streams switched on and off during deglaciation, rather than maintaining the same trajectory as the ice margin retreated. We provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30% of the margin was drained by ice streams at the LGM (similar to that for present day Antarctic ice sheets), but this decreases to 15% and 12% at 12 cal ka BP and 10 cal ka BP, respectively. The extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate, or internal ice dynamical feedbacks unrelated to climate (or both) is largely unknown and represents a key area for future work to address.