Pleistocene variability of Antarctic Ice Sheet extent in the Ross Embayment
Pleistocene variability of Antarctic Ice Sheet extent in the Ross Embayment
复制标题
DOI：
10.1016/j.quascirev.2011.12.012
复制
发表时间：
2012-02
影响因子：
4
通讯作者：
R. McKay;T. Naish;R. Powell;P. Barrett;R. Scherer;F. Talarico;P. Kyle;Donata Monien;G. Kuhn;C. L. Jackolski;T. Williams
中科院分区：
文献类型：
--
作者：
R. McKay;T. Naish;R. Powell;P. Barrett;R. Scherer;F. Talarico;P. Kyle;Donata Monien;G. Kuhn;C. L. Jackolski;T. Williams
ANDRILL 麦克默多冰架项目 (AND-1B) 获取的岩心为冰川沉积序列的新沉积模型提供了基础，该模型反映了过去 2.0 Ma 罗斯海湾西部海洋冰盖的周期性冰期-间冰期波动。尽管冰盖前进过程中存在周期性侵蚀、沉积学解释固有的不确定性以及有限数量的年代数据，但很明显，更新世晚期AND-1B地点的冰下到接地带沉积占主导地位，间冰期仅由冰架沉积物的薄层间隔代表。每个层序的特征都是冰下块状混积岩，向上进入冰川混积岩和泥岩。这提供了第一个直接证据，表明在过去 780ka 中，位于罗斯海湾的海洋南极冰盖在接地状态和漂浮状态之间振荡至少 7 次，这意味着米兰科维奇轨道的影响。 AND-1B 中的不整合面跨越了中更新世过渡期的大部分（~200 kyr），据推断代表罗斯海湾海洋冰盖在 0.8 Ma 时广泛扩张。 1.0 Ma 之前，间冰期的特点是钻探地点处于开放水域，具有大量火山碎屑沉积物和偶尔的硅藻土沉积物。这些可能对进动（∼20-kyr）或倾角（∼40-kyr）轨道控制做出了响应。在末次盛冰期下的间冰期沉积物中，出现了从埃里伯斯山改造而来的 6.7 m 的声石玻璃，这需要过去 250 ka 内钻探地点周围罗斯海西部的开放海洋或冰架条件，这意味着在海洋同位素阶段 7 或 5 期间，罗斯冰架的范围与今天相似或不那么大。
Cores acquired by the ANDRILL McMurdo Ice Shelf Project (AND-1B) provide the basis for a new sedimentation model for glacimarine depositional sequences that reflect cyclic glacial–interglacial fluctuations of a marine-based ice sheet in the western Ross Embayment over the past 2.0 Ma. Notwithstanding periodic erosion during advances of the ice sheet, uncertainties inherent to the sedimentological interpretation, and a limited number of chronological datums, it is clear that subglacial to grounding-zone sedimentation was dominant at the AND-1B site during the Late Pleistocene with interglacials being represented only by thin intervals of ice-shelf sediment. Each sequence is characterised by subglacial, massive diamictite that pass upwards into glacimarine diamictites and mudstones. This provides the first direct evidence that the marine-based Antarctic Ice Sheet has oscillated between a grounded and floating state at least 7 times in the Ross Embayment over the last 780ka, implying a Milankovitch orbital influence. An unconformity in AND-1B, that spans most (∼200 kyr) of the Mid-Pleistocene Transition is inferred to represent widespread expansion of a marine-based ice sheet in the Ross Embayment at 0.8 Ma. Prior to 1.0 Ma, interglacial periods are characterised by open-water conditions at the drill site with high abundances of volcanoclastic deposits and occasional diatomaceous sediments. These may have responded to precession (∼20-kyr) or obliquity (∼40-kyr) orbital control. The occurrence of 6.7 m of phonolitic glass reworked from Mt Erebus in interglacial deposits beneath Last Glacial Maximum till requires open ocean or ice shelf conditions in the western Ross Sea around the drill site within the past 250 ka and implies a Ross Ice Shelf similar to or less extensive than today during Marine Isotope Stage 7 or 5.