Snapshot of cooling and drying before onset of Antarctic Glaciation
Snapshot of cooling and drying before onset of Antarctic Glaciation
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南极冰川爆发前的冷却和干燥快照
DOI：
10.1016/j.epsl.2014.07.032
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发表时间：
2014
影响因子：
5.3
通讯作者：
R. DeConto
中科院分区：
文献类型：
--
作者：
S. Feakins;S. Warny;R. DeConto
摘要南极洲晚始新世-渐新世过渡(EOT)经历了一次重大的冰川推进。由于缺乏可接近的露头和困难的钻探后勤，人们对南极半岛在始新世晚期主要冰移之前的水文条件知之甚少。在这里，我们用邻近南极半岛顶端的海洋沉积岩芯NBP0602A-3C的替代证据来研究水文条件，其沉积物的年代为35.9±1.1 Ma，提供了EOT之前的条件快照。我们根据植物叶蜡氢同位素证据(δD WAX)和之前发表的花粉组合证据重建了最新始新世的条件，并与模拟过渡之前、期间和之后条件的气候模型实验进行了比较。NBP0602A-3C晚始新世沉积的孢粉表明，地貌以山毛榉(Nothofagid)为主。在同一沉积物中，C28正构烷酸的δD蜡值平均为−2 0 2±7‰(1σ，n=2 2)。水和蜡之间适当的净分馏(ϵ蜡/w)的不确定性在古沉淀δD重建中提供了最大程度的不确定性，因此我们使用两个合理的分馏−100和−60‰来将平均降水δD值的可能范围限制在−113和−151‰之间。模型实验证实，与大陆内部大得多的变化相比，南极半岛顶端的同位素组成对温度变化的敏感性较低。在整个采样间隔内，花粉丰度从105GDW下降到103GDW−1代表着向更接近冻土带的条件冷却和干燥。随着植被从森林转移到水分胁迫较大的冻土带，30‰的δD蜡值趋于更正值的趋势可以用较小的分馏来解释。模型结果与数据基本一致，并量化了南极半岛顶端约7至2°C和700至600 mm a−1整个延时温度的冷却和干燥过程，δD的同位素位移仅约为−15‰。花粉和树叶蜡的替代物在过渡之前重建植被和水文条件，通过EOT的模型实验提供了陆地转化的替代物-地面定量。
Abstract The late Eocene to Oligocene transition (EOT) witnessed a major ice advance on Antarctica. Because of the paucity of accessible outcrops and difficult drilling logistics, little is known about hydrological conditions in the Antarctic Peninsula during the late Eocene prior to the major ice advance. Here we study hydrological conditions with proxy evidence from marine sediment core NBP0602A-3C, adjacent to the tip of the Antarctic Peninsula, with sediments dated to 35.9±1.1 Ma providing a snapshot of conditions prior to the EOT. We reconstruct conditions during the latest Eocene based on plant leaf wax hydrogen isotopic evidence (δ D wax) paired with previously-published evidence from pollen assemblages, and compared to climate model experiments simulating conditions before, during and after the transition. The pollen from late Eocene sediments of NBP0602A-3C indicate a Nothofagidites (southern beech) dominated landscape. In the same sediments, δ D wax values average− 202±7‰(1σ, n= 22) for the C 28 n-alkanoic acid. Uncertainty around the appropriate net fractionation between water and wax (ϵ wax/w) provides the largest degree of uncertainty in paleoprecipitation δ D reconstructions and we therefore use two reasonable fractionations− 100 and− 60‰ to constrain the likely range of average precipitation δ D values to between− 113 and− 151‰. Model experiments confirm that isotopic compositions show low sensitivity to temperature changes at the tip of the Antarctic Peninsula, in comparison to much larger changes in the continental interior. Across the interval sampled, a decline in pollen abundance from 10 5 to 10 3 gdw− 1 represents cooling and drying towards more tundra-like conditions. The 30‰ trend in δ D wax values towards more positive values can best be explained by smaller fractionations as the vegetation shifted from forest to tundra, with greater water stress. Model results are broadly consistent with the data and quantify the cooling and drying across the full EOT from ca. 7 to 2° C and 700 to 600 mm a− 1 with an isotopic shift in δ D of only about− 15‰ at the tip of the Antarctic Peninsula. Pollen and leaf wax proxies reconstruct vegetation and hydrological conditions prior to the transition, and model experiments through the EOT provide proxy-groundtruthed quantification of terrestrial transformations.
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影响因子：
4
作者：
M. Kirby;S. Feakins;Nicole Bonuso;Joanna M. Fantozzi;C. Hiner
通讯作者：
M. Kirby;S. Feakins;Nicole Bonuso;Joanna M. Fantozzi;C. Hiner
影响因子：
5
作者：
D. Sachse;J. Radke;G. Gleixner
通讯作者：
D. Sachse;J. Radke;G. Gleixner
影响因子：
5.2
作者：
L. Ivany;T. Brey;M. Huber;Devin P. Buick;B. Schöne
通讯作者：
L. Ivany;T. Brey;M. Huber;Devin P. Buick;B. Schöne
影响因子：
64.8
作者：
Schefuss, E;Schouten, S;Schneider, RR
通讯作者：
Schneider, RR