Extreme snow metamorphism in the Allan Hills, Antarctica, as an analogue for glacial conditions with implications for stable isotope composition
Extreme snow metamorphism in the Allan Hills, Antarctica, as an analogue for glacial conditions with implications for stable isotope composition
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DOI：
10.3189/2015jog15j027
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发表时间：
2015-01-01
影响因子：
3.4
通讯作者：
Matzl, Margret
中科院分区：
文献类型：
--
作者：
Dadic, Ruzica;Schneebeli, Martin;Matzl, Margret
了解接近零积累区的物理过程可以帮助我们更好地理解极地冰芯记录，特别是在积累率低于今天的时期。我们报告了南极洲Allan Hills 5米厚岩心的测量结果，包括使用计算机断层扫描的物理性质，δ D和δ O-18的稳定同位素比率以及Pb-210的活度。岩心为高度变质的刚体，结构均匀稳定，但近表面有离散层。观察到的地层结构是由独特的沉积和沉积后过程共同作用形成的。不规则的δ D和δ O-18信号不遵循地层层序，暗示沉积层中微观压力梯度引起的沉积后改造，这种压力梯度可能是由于风存在时粗糙表面上的强制通风或沉积层与大气之间的交替温度梯度造成的。我们的研究结果还表明，在大风条件下，撞击雪的形成具有较高的初始密度和大气与积雪之间的空气交换。0.3 m以下Pb-210的活度低于检测极限，这意味着大部分岩心的年龄超过100年。我们的结论是，艾伦山的记录提供了一个独特的机会来研究可能影响冰期冰芯记录的重要过程。
Understanding physical processes in near-zero accumulation areas can help us to better understand polar ice-core records, particularly during periods when accumulation rates were lower than today. We report measurements from a 5 m firn core from the Allan Hills, Antarctica, which include physical properties using computer tomography, stable isotope ratios delta D and delta O-18, and Pb-210 activity. The core shows a highly metamorphosed firn with homogeneous and stable structure, but with discrete layers near the surface. The observed firn structure is caused by a combination of unique depositional and post-depositional processes. The irregular delta D and delta O-18 signal does not follow the stratigraphic sequence and implies post-depositional modification caused by microscopic pressure gradients in the firn that can result from either forced ventilation over rough surfaces in the presence of wind or alternating temperature-gradients between the firn and the atmosphere. Our results also indicate impact snow deposition under high winds and with a high initial density and air exchange between the atmosphere and the snowpack. Pb-210 activity below 0.3 m falls below the detection limit, implying that most of the core is more than 100 years old. We conclude that the Allan Hills record provides a unique opportunity to investigate important processes that would have affected ice-core records from glacial periods.