Ice and firn heterogeneity within Larsen C Ice Shelf from borehole optical televiewing
Ice and firn heterogeneity within Larsen C Ice Shelf from borehole optical televiewing
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DOI：
10.1002/2016jf004047
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发表时间：
2017-05
期刊：
影响因子：
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通讯作者：
D. Ashmore;B. Hubbard;A. Luckman;B. Kulessa;S. Bevan;A. Booth;P. K. Munneke;M. O’Leary;Heïdi Seve
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文献类型：
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作者：
D. Ashmore;B. Hubbard;A. Luckman;B. Kulessa;S. Bevan;A. Booth;P. K. Munneke;M. O’Leary;Heïdi Seve
利用钻孔光学电视（OPTV）探测了拉森C冰架（LCIS）的内部结构。我们报告了2014年和2015年春季从LCIS的北方和中部采集的一组5个~90 m长的OPTV测井曲线，记录了发光二极管照明的、几何正确的井壁图像。我们使用基于阈值的技术来估计冰柱的再冻结冰含量，并利用最近校准的密度-光度关系来揭示其结构。所有地点都很密集，受表面融化的强烈影响，经常有重新冻结的冰层，平均密度在1.87到90米之间，从862到894 kg m−3不等。我们定义了四个不同的单位，包括LCIS，并将这些冰的来源，动态历史，和过去的融化事件。这些单位是原位流冰与渗透冰（U1），流冰，经历了增强致密化（U2），厚的再冻结冰（U3），平流大陆冰（U4）。我们表明，OPTV导出的积雪空气含量模式与以前的估计一致，但很大一部分积雪空气包含在U4中，我们解释为沉积在接地线的内陆。LCIS的结构受到风驱动融化的东西梯度的强烈影响，靠近南极半岛的地点主要由再冻结冰组成。冰架中心的融化也很大，超过40%的整个图像冰柱由再冻结的冰组成。
We use borehole optical televiewing (OPTV) to explore the internal structure of Larsen C Ice Shelf (LCIS). We report a suite of five ~90 m long OPTV logs, recording a light‐emitting diode‐illuminated, geometrically correct image of the borehole wall, from the northern and central sectors of LCIS collected during austral spring 2014 and 2015. We use a thresholding‐based technique to estimate the refrozen ice content of the ice column and exploit a recently calibrated density‐luminosity relationship to reveal its structure. All sites are dense and strongly influenced by surface melt, with frequent refrozen ice layers and mean densities, between the depths of 1.87 and 90 m, ranging from 862 to 894 kg m−3. We define four distinct units that comprise LCIS and relate these to ice provenance, dynamic history, and past melt events. These units are in situ meteoric ice with infiltration ice (U1), meteoric ice which has undergone enhanced densification (U2), thick refrozen ice (U3), and advected continental ice (U4). We show that the OPTV‐derived pattern of firn air content is consistent with previous estimates, but that a significant proportion of firn air is contained within U4, which we interpret to have been deposited inland of the grounding line. The structure of LCIS is strongly influenced by the E‐W gradient in föhn‐driven melting, with sites close to the Antarctic Peninsula being predominantly composed of refrozen ice. Melting is also substantial toward the ice shelf center with >40% of the overall imaged ice column being composed of refrozen ice.