Pub Date : 2018-11-06DOI: 10.14379/iodp.sp.379add.2018
K. Gohl
The West Antarctic Ice Sheet (WAIS) is largely marine based and thus highly sensitive to both climatic and oceanographic changes. Therefore, the WAIS has likely had a very dynamic history over the last several million years. A complete collapse of the WAIS would result in a global sea level rise of 3.3–4.3 m, yet the world’s scientific community is not able to predict its future behavior. Moreover, knowledge about past behavior of the WAIS is poor, in particular during geological times with climatic conditions similar to those expected for the near and distant future. Reconstructions and quantifications of partial or complete WAIS collapses in the past are urgently needed for constraining and testing ice sheet models that aim to predict future WAIS behavior and the potential contribution of the WAIS to global sea level rise. Large uncertainties exist regarding the chronology, extent, rates, and spatial and temporal variability of past advances and retreats of the WAIS across the continental shelves. These uncertainties largely result from the fundamental lack of data from drill cores recovered proximal to the WAIS. The continental shelf and rise of the Amundsen Sea are prime targets for drilling because the records are expected to yield archives of pure WAIS dynamics unaffected by other ice sheets and the WAIS sector draining into the Amundsen Sea Embayment (ASE) currently experiences the largest ice loss in Antarctica (Paolo et al., 2015). We propose a series of drill sites for the ASE shelf where seismic data reveal seaward-dipping sedimentary sequences that span from the preglacial depositional phase to the most recent glacial periods. Our strategy is to drill a transect from the oldest sequences close to the bedrock/basin boundary at the middle–inner shelf transition to the youngest sequences on the outer shelf in the eastern ASE. If the eastern ASE is inaccessible due to sea ice cover, a similar transect of sites can be drilled on the western ASE. The core transect will provide a detailed history of the glacial cycles in the Amundsen Sea region and allow comparison to the glacial history from the Ross Sea sector. In addition, deep-water sites on the continental rise of the Amundsen Sea are selected for recovering continuous records of glacially transported sediments and detailed archives of climatic and oceanographic changes throughout glacial–interglacial cycles. We will apply a broad suite of analytical techniques, including multiproxy analyses, to address our objectives of reconstructing the onset of glaciation in the greenhouse to icehouse transition, processes of dynamic ice sheet behavior during the Neogene and Quaternary, and ocean conditions associated with the glacial cycles. The five principal objectives of Expedition 379 are as follows: 1. To reconstruct the glacial history of West Antarctica from the Paleogene to recent times and the dynamic behavior of the WAIS during the Neogene and Quaternary, especially possible partial or fu
南极西部冰盖(WAIS)主要是海洋冰盖，因此对气候和海洋变化高度敏感。因此，在过去的几百万年里，WAIS可能有一个非常动态的历史。WAIS的完全崩溃将导致全球海平面上升3.3-4.3米，但世界科学界无法预测其未来的行为。此外，人们对西洋带过去的行为知之甚少，特别是在气候条件与近期和遥远未来的气候条件相似的地质时期。为了限制和测试旨在预测未来WAIS行为和WAIS对全球海平面上升的潜在贡献的冰盖模型，迫切需要重建和量化过去部分或完全的WAIS崩塌。在横跨大陆架的西风带过去进退的年代学、范围、速率和时空变异性方面存在很大的不确定性。这些不确定性很大程度上是由于缺乏从WAIS近端恢复的岩心数据。大陆架和阿蒙森海的上升是钻探的主要目标，因为这些记录有望产生不受其他冰盖影响的纯WAIS动态档案，而流入阿蒙森海海湾(ASE)的WAIS部分目前经历了南极洲最大的冰损失(Paolo等人，2015)。我们提出了一系列的ASE陆架钻探点，地震数据揭示了从冰期前沉积阶段到最近冰期的向海倾斜沉积序列。我们的策略是从靠近基岩/盆地边界的最古老的层序到东部陆架外层最年轻的层序进行样带钻探。如果东部的ASE由于海冰覆盖而无法进入，则可以在西部的ASE钻探类似的样带。核心样带将提供阿蒙森海地区冰川循环的详细历史，并可与罗斯海地区的冰川历史进行比较。此外，还选择了阿蒙森海大陆隆起的深水点，以恢复冰川运输沉积物的连续记录和整个冰期-间冰期旋回的气候和海洋变化的详细档案。我们将应用广泛的分析技术，包括多代理分析，来实现我们的目标，重建从温室到冰窖过渡的冰川开始，新第三纪和第四纪的动态冰盖行为过程，以及与冰川旋回相关的海洋条件。379远征队的五个主要目标如下:重建西南极洲从古近纪到近代的冰川史，新第三纪和第四纪WAIS的动力学行为，特别是WAIS可能的部分或全部崩塌，以及WAIS对过去海平面变化的贡献。重点特别放在研究地球大气中二氧化碳分压超过400ppm以及大气和海洋温度高于目前水平时WAIS的响应。2. 将阿蒙森海冰盖动态的wais近端记录与全球冰量变化记录以及空气和海水温度的替代记录相关联。3.研究暖环极深水(CDW)侵入阿蒙森海湾大陆架与暖水条件下海洋冰盖边缘稳定性的关系。4. 重建中新世中期以来可能发生的主要WAIS向中、外大陆架推进的过程，并将其时间和过程与其他南极大陆架进行比较。5. 确定第一次冰盖扩张到ASE大陆架的时间及其与玛丽伯德地隆起的可能关系。远征379国际海洋发现计划(IODP)远征379是基于IODP钻井提案839-Full和839-Add(可在http://iodp.tamu.edu/scienceops/expeditions/amundsen_sea_ice _sheet_history.html获得)。在经过IODP科学评估小组的评估后，这次考察计划由研究船(R/V) JOIDES Resolution进行，该船与JOIDES Resolution科学运营商(JRSO)签订了合同。在本科学招股书发表时，该考察计划于2019年1月18日在智利蓬塔阿雷纳斯开始，并于2019年3月20日在智利蓬塔阿雷纳斯结束。本报告中描述的运输、钻井、取心和井下测量总共有56天的时间(有关当前的详细时间表，请参阅http://iodp.tamu.edu/scienceops)。 有关JOIDES决议上设施的更多详细信息可在http://iodp.tamu.edu/publicinfo/drillship.html上找到。几十年来，Amundsen Sea Embayment (ASE)排水部分一直被认为是西南极冰盖(WAIS)最脆弱的部分，因为在接地线处水深很大，而且缺乏实质性的冰架(Hughes, 1981)。这种形态的冰川被认为容易迅速或失控地退缩(Schoof, 2007)。最近的模型表明，导致该部门WAIS崩溃的阈值可能已经超过(Joughin et al.， 2014)，即使在相对温和的温室气体排放情景下，大部分冰盖也可能消失(DeConto和Pollard, 2016)。模式预估由于在若干领域缺乏约束而受到限制，最明显的是缺乏对冰川历史的详细重建。在ASE的钻探将为控制冰盖稳定性的几个关键问题提供测试。首先，它将提供一个流域冰川历史的直接记录，该流域只接收来自WAIS的冰，允许在WAIS历史和低纬度记录之间进行清晰的比较。流入ASE的冰位于海平面以下，因此可以通过冰史与海平面变化的相关性来测试海洋冰盖的不稳定性。虽然目前在接地线前面只有一个非常小的冰架，但在其历史上的某些时间点上，该海堤曾有过冰架(Kirshner等人，2012)，这将使研究接地线历史与冰架历史的关系成为可能。今天，温暖的环极深水(CDW)正在撞击阿蒙森海大陆架，导致冰层底部融化;重建过去的CDW入侵(Hillenbrand et al.， 2017;Minzoni等人，2017)将评估温水与过去接地线位置的大规模变化之间的关系。这些测试将在目前南极洲任何地方冰负质量平衡最大的流域进行(Paolo et al.， 2015)，因此对未来的预测最感兴趣。最后，这次考察将作为IODP南极考察的一部分
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Pub Date : 2018-08-24DOI: 10.14379/iodp.sp.383.2018
F. Lamy, G. Winckler, C.A. Alvarez Zarikian
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