Testing lichenometric techniques in the production of a new growth-rate (curve) for the Breiðamerkurjökull foreland, Iceland, and the analysis of potential climatic drivers of glacier recession
D. Evans, S. Guðmundsson, Jonathan L. Vautrey, Kate Fearnyough, W. G. Southworth
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引用次数: 7
Abstract
ABSTRACT Independent dating of closely-spaced moraines on the west Breiðamerkurjökull foreland is used to test the accuracy of the size frequency (SF) and largest lichen (5LL) lichenometric dating techniques. The 5LL technique derived the most accurate ages for three undated moraines within the dated sequence but growth rates and lag times produced by the two methods (5LL = 0.71 mm yr−1 and 11 years; SF = 0.64 mm yr−1 and 7 years) were not significantly different. We therefore reject previous conclusions that any one technique is demonstrably inferior to the other, at least for dating glacial landforms created over the last 130 years in SE Iceland. Comparisons of climate trends and recession rates indicate that air temperature anomalies, particularly those of the summer, are the strongest driver of glacier retreat. No clear relationship between NAO trends and glacier retreat were identified, although a positive and/or rising trend in NAO is associated with the slowing of ice retreat overall, and the marked readvances of the mid-1950s, mid-1970s and mid-1990s are all coincident with positive and/or rising NAO 5yr moving averages. Summer and annual temperature trends, not the NAO, clearly show that recent accelerated global warming is driving the marked recession of the period 1995–2015. Over the last 100 years temperature has been the major driver of glacier terminus oscillations at west Breiðamerkurjökull but it is clear that extreme decreases in winter precipitation (i.e. 1960–1973) have the potential to increase retreat rates significantly even during times of below average annual temperatures.
摘要利用Breiðamerkurjökull西部前陆紧密间隔冰碛的独立测年方法,验证了尺寸频率(SF)和最大地衣(5LL)测年技术的准确性。5LL技术在确定日期的序列中得到了三个未确定日期的冰碛最准确的年龄,但两种方法产生的生长速率和滞后时间(5LL = 0.71 mm yr - 1和11年;SF = 0.64 mm yr - 1和7年)无显著差异。因此,我们拒绝先前的结论,即任何一种技术明显不如另一种技术,至少对于冰岛东南部过去130年形成的冰川地貌定年而言。对气候趋势和衰退率的比较表明,气温异常,特别是夏季的气温异常,是冰川退缩的最大驱动力。NAO趋势与冰川退缩之间没有明确的关系,尽管NAO的积极和/或上升趋势与总体冰退缩的减缓有关,并且20世纪50年代中期、70年代中期和90年代中期的显著上升都与NAO的积极和/或上升的5年移动平均相一致。夏季和年度气温趋势,而不是国家气象组织,清楚地表明,最近加速的全球变暖正在推动1995-2015年期间的明显衰退。在过去的100年里,温度一直是西部Breiðamerkurjökull冰川末端振荡的主要驱动因素,但很明显,冬季降水的极端减少(即1960-1973年)即使在低于年平均气温的时期也有可能显著增加退缩率。
期刊介绍:
Geografiska Annaler: Series A, Physical Geography publishes original research in the field of Physical Geography with special emphasis on cold regions/high latitude, high altitude processes, landforms and environmental change, past, present and future.
The journal primarily promotes dissemination of regular research by publishing research-based articles. The journal also publishes thematic issues where collections of articles around a specific themes are gathered. Such themes are determined by the Editors upon request. Finally the journal wishes to promote knowledge and understanding of topics in Physical Geography, their origin, development and current standing through invited review articles.