Repeated advance and retreat of the East Antarctic Ice Sheet on the continental shelf during the early Pliocene warm period.
Repeated advance and retreat of the East Antarctic Ice Sheet on the continental shelf during the early Pliocene warm period.
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上新世早期温暖期，东南极冰盖在大陆架上反复进退。
DOI：
10.1016/j.palaeo.2015.01.009
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
H.
中科院分区：
文献类型：
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作者：
Reinardy B.T.I.;Escutia C.;Iwai;M.;Jimenez-Espejo F.J.;Cook C.;van de Flierdt T. and Brinkhuis;H.
对阿德利海岸外大陆架 IODP 站点 U1358 回收的沉积物岩心进行的硅藻分析表明，岩心下部包含一个可追溯到上新世下部的海链藻带 (Thalassiosira innuraZone) 的组合，其范围为 4.2 Ma 至 5.12 Ma。根据对上新世早期岩心部分的宏观和微观岩性描述，从代表该地点上接地线逐渐前进和后退的重岩中解释了四个相。相 1a 和 1b 包含来自碎屑 a 轴方向的明显方向信号，具有多个组构发育阶段以及冰下变形沉积物中常见的脆性和延性变形特征。相 1c 和 1d 是精细层状的，并且是在开阔的海洋条件下沉积的。沉积模型中的四个相首次提供了直接证据，证明冰至少有四次穿过威尔克斯冰下盆地附近的陆架，中间被三个开放海洋条件时期所隔开，表明在上新世早期比现在温暖的时期，该地点内陆的接地冰退缩。开放海洋条件的时间与先前在邻近海隆地点的发现相关，这些发现也表明了冰缘的振荡。这具有重要意义，因为首先它表明东南极冰盖（EAIS）是动态的，即使在相对较短的时间内，它对气候和海洋强迫的敏感度也可能比以前想象的要高得多。其次，它表明用于解释接地线从上升处前进和后退的代理可以与接地线从架子迁移的直接证据联系起来。它还对 EAIS 在当前持续变暖条件下的未来行为和敏感性具有重要影响。结合上升的结果，本文为该地区上新世期间的新冰盖模型提供了关键的冰范围目标。
Diatom analysis of a sediment core recovered at IODP Site U1358 on the continental shelf off the Adélie Coast indicated that the lower section of the core contained an assemblage dating back to theThalassiosira innuraZone of the lower Pliocene that ranges from 4.2 to 5.12 Ma. Based on lithological descriptions at both a macro- and micro-scale of this early Pliocene part of the core, four facies were interpreted from the diamictons representing the progressive advance and retreat of the grounding line over the site. Facies 1a and 1b contain a distinct directional signal from the orientation of the a-axis of clasts with several phases of fabric development along with both brittle and ductile deformation features that are common in sediments that have been subglacially deformed. Facies 1c and 1d are finely laminated and were deposited in open marine conditions. The four facies within the depositional model provide for the first time direct evidence for ice advancing across the shelf adjacent to the Wilkes Subglacial Basin on at least four occasions separated by three periods of open marine conditions indicating retreat of grounded ice inland of the site during a warmer than present early Pliocene. The times of open marine conditions are correlated with previous findings from the neighbouring rise sites that also indicated an oscillating ice margin. This has significant implications because firstly it suggests a dynamic East Antarctic Ice Sheet (EAIS) that is probably far more sensitive to climatic and oceanic forcing even during relatively short time periods than had previously been thought. Secondly it suggests that proxies used to interpret the advance and retreat of the grounding line from the rise can be linked with direct evidence of grounding line migration from the shelf. It also has important implications for the future behaviour and sensitivity of the EAIS under present continuing warming conditions. Together with results from the rise, this paper provides a crucial ice extent target for a new ice sheet model of this region during the Pliocene.