High-resolution fjord sediment record of a receding glacier with growing intermediate proglacial lake (Steffen Fjord, Chilean Patagonia)
High-resolution fjord sediment record of a receding glacier with growing intermediate proglacial lake (Steffen Fjord, Chilean Patagonia)
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冰川消退和中间冰期湖不断增长的高分辨率峡湾沉积物记录（斯特芬峡湾，智利巴塔哥尼亚）
DOI：
10.1002/esp.5015
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发表时间：
2020
影响因子：
3.3
通讯作者：
Piret L
中科院分区：
文献类型：
--
作者：
Piret L
前冰期湖泊是有效的沉积物陷阱，但它们对下游沉积物记录重建冰川变率的可靠性的影响尚不清楚。在这里，我们研究了Steffen冰川（智利巴塔哥尼亚，47°S）最近在下游峡湾沉积物中的沉积特征，重点是确定一个正在增长的中间前冰湖的捕获（下游沉积物产量减少）和过滤（去除粗颗粒）的有效性。在Steffen Fjord沿14 km纵向样带收集了4个沉积物岩心，并将沉积物的物理和化学性质与高时间分辨率的航空影像进行了比较。最远端岩心的铯- 137 （137Cs）年代学和沉积物圈闭数据表明，尽管冰川加速消退和Steffen前冰湖的生长，峡湾的沉积物积累仍然相对稳定。这与许多表明前冰期湖泊扩张期间产沙量减少的研究相反。这意味着加速融水产生所导致的沉积物输出的增加可能被不断扩大的前冰湖的沉积物捕获效应所平衡。峡湾沉积物表现出轻微的向上细化，同时洪水引起的粒度峰值明显减少，这很可能是由于扩大的前冰湖的过滤和阻尼作用增强所致。结果表明，前冰期湖泊的过滤作用在1985年达到一个阈值，湖的面积为2.02 km2。在接下来的32年里，额外的5公里冰川退缩对下游的沉积没有任何显著的影响。本研究证实了前冰期湖泊具有沉积物捕集器的作用，但表明：(1)捕集器的作用可被加速的冰川退缩所取代；(2)当湖泊达到一定的临界尺寸时，过滤作用趋于稳定。©2020 John Wiley & Sons, Ltd
Proglacial lakes are effective sediment traps but their impact on the reliability of downstream sediment records to reconstruct glacier variability remains unclear. Here, we investigate the sedimentary signature of the recent recession of Steffen Glacier (Chilean Patagonia, 47°S) in downstream fjord sediments, with a focus on identifying the trapping (decreased downstream sediment yield) and filtering (removal of coarse particles) effectiveness of a growing intermediate proglacial lake. Four sediment cores were collected along a 14 km longitudinal transect in Steffen Fjord and the sediment physical and chemical properties were compared with aerial imagery at high temporal resolution. The caesium‐137 (137Cs) chronology of the most distal core and sediment trap data suggest that sediment accumulation in the fjord remained relatively stable through time, despite the accelerating glacier recession and the growth of Steffen proglacial lake. This is in contrast with many studies that indicate a decrease in sediment yield during proglacial lake expansion. It implies that the increase in sediment export due to accelerating meltwater production may be balanced by the sediment trapping effect of the growing proglacial lake. The fjord sediments show a slight fining upward accompanied by a marked decrease in flood‐induced grain‐size peaks, most likely due to the increasing filtering and dampening effect of the expanding proglacial lake. Our findings show that the filtering effect of the proglacial lake reached a threshold in 1985, when the lake attained an area of 2.02 km2. The additional 5 km of glacier recession during the following 32 years did not have any significant impact on downstream sedimentation. This study confirms that proglacial lakes act as sediment traps but it indicates that (1) the trapping effect can be outpaced by accelerating glacier recession and (2) the filtering effect becomes stable once the lake attains a certain critical size. © 2020 John Wiley & Sons, Ltd.