Expedition Objective Research: Early Pliocene Record Of Antarctic Ice Rafting And Paleoenvironmental Conditions, Wilkes Land Margin, Antarctica

知识价值该项目调查了上新世早期南极东部的冰动力学和古环境条件，从冰筏碎片的产生和在IODP 318到南极洲威尔克斯陆地边缘期间收集的沉积物岩心的主要元素地球化学的变化中获得。南极洲的这一部分拥有威尔克斯和奥罗拉冰下盆地，东南极冰盖(EAIS)位于海平面以下，可能不稳定。上新世早期是已知的全球变暖时期，海面温度比目前的南大洋高5.5摄氏度。EAIS在这段时间内的稳定性是一个主要的不确定性，也是一个相当大的争论。最近的气候和冰盖模拟研究表明，与西南极冰盖不同，EAIS在上新世没有崩溃。然而，模型确实表明，它的边缘退回到目前的位置，并且退缩产生了一个重要的海平面分量。威尔克斯地缘是预计撤退幅度最大的地方。在这里，我们收集了IRD产量、古生产力和物源变化的高分辨率记录，以1)检验上新世早期冰川退缩的假说；2)提供足够的分辨率记录，将南极东部的冰川动力学与全球古气候指标在10kyr的时间尺度上进行关联。调查了上新世早期的两个钻孔，陆架上的U1358和大陆隆起上的U1359。冰排碎片(IRD)质量累积率(MAR)将结合U1359站点的大量陆源粒度分析来确定。粒度分析还将有助于解释U1358处货架上的透闪石。这两个地点的沉积物都有5%的陆源成分，因此生物对陆源沉积物中Fe、Ti和Al浓度的颗粒清除可以忽略不计，稳定的元素比值可以用来获得物源信息和当地的古生产力和风化指标。综合的IRD MAR数据，风化作用下的化学变化程度和古生产力，将被用来评估威尔克斯陆地和邻近海洋在上新世早期暖期冰范围和古气候条件的变化。更广泛的影响上新世是最后一个大气二氧化碳与今天相似的时代？S分压和全球地表温度高于现代，增暖程度高于平均水平的高纬度地区。在构造和海洋学上，地球与今天相似，因此，上新世早期是研究当今和不久未来世界冰盖长期稳定性的极好时间间隔。南极冰盖是全球气候系统的重要组成部分，因为它们的高反照率和对海冰形成、海洋环流和海平面的影响。卫星数据表明，目前南极冰盖正在失去质量，质量损失最近加速，导致目前全球海平面上升约0.3毫米/年。然而，由于监测期很短，尚不确定冰盖是否对目前的变暖做出了反应，或者这是否是冰盖系统中短期扰动的表现。对地质记录的短期监测和长期趋势分析对于全面评估气候系统的状况都是至关重要的。这项工作产生的更广泛的重要影响还包括：1)为全球气候研究提供高分辨率的冰冻圈动力学数据；2)其他以短时间间隔为目标的研究人员更容易获得核心材料，采用时间密集的分析方法；3)通过讲座和当地媒体向城市和沿海管理政策的研究人员和普通公众提供信息；4)两个具有不同背景的学生通过参与研究进行教育，这可被认为是这项工作的长期利益的一个重要方面。

Intellectual meritThis project investigates early Pliocene East Antarctic ice dynamics and paleoenvironmental conditions from variations in the production of ice-rafted debris and major element geochemistry of sediment cores collected during IODP Expedition 318 to the Wilkes Land margin of Antarctica. This portion of Antarctica carries the Wilkes and Aurora subglacial basins, where the East Antarctic Ice Sheet (EAIS) is grounded below sea level, and is potentially unstable. The early Pliocene is a known period of global warmth with sea surface temperatures ranging up to 5.5ºC higher than present in the Southern Ocean. The stability of the EAIS in this period of time is a major uncertainty and is considerably debated. Recent climate and ice-sheet modeling studies suggest that, in contrast to the West Antarctic Ice Sheet, the EAIS did not collapse during the Pliocene. However, the models do show that its margin retreated to within the present position and that the retreat generated a significant eustatic sea level component. The Wilkes Land margin is the location where the predicted retreat is the greatest. Here we collect a high-resolution record of IRD production, paleoproductivity, and changes in provenance, to 1) test the hypothesis of glacial retreat during early Pliocene warm periods; and 2) provide a record of sufficient resolution to correlate East Antarctic ice dynamics to global paleoclimatic proxies on 10kyr time scales. Two drillholes with well-dated early Pliocene intervals, Site U1358 on the continental shelf, and Site U1359 on the continental rise, are investigated. Ice-rafted debris (IRD) mass accumulation rates (MAR) will be determined in combination with bulk terrigenous grain-size analyses for Site U1359. Particle size analysis will also aid in the interpretation of the diamictites on the shelf at Site U1358. The sediments at both sites have 5% terrigenous fraction, so that particulate scavenging by organisms on terrigenous sediment concentrations of Fe, Ti and Al is negligible and stable element ratios can be used to derive provenance information and local paleoproductivity and weathering proxies. The integrated datasets of IRD MAR, degree of chemical alteration through weathering, and paleoproductivity, will be used to assess variations in ice extent and paleoclimatic conditions along Wilkes Land and the adjacent ocean, through early Pliocene warm periods.Broader impactsThe Pliocene was the last epoch wherein the atmospheric pCO2 was similar to today?s partial pressure and global surface temperatures were higher than the modern with a larger than average degree of warming occurring at high latitudes. Tectonically and oceanographically the Earth was similar to today and the early Pliocene is, therefore, an excellent time interval to study the long-term stability of ice sheets in a world comparable to the present and the near future. The Antarctic ice sheets are important components of the global climate system, because of their high albedo and influence on sea ice formation, ocean circulation, and sea level. Satellite data suggest that the Antarctic ice sheets at present are losing mass and that mass loss has recently accelerated resulting in a present contribution to global sea level rise of ca. 0.3 mm/yr. Due to the short monitoring period, however, it is uncertain whether ice sheets are responding to the present warming or whether this is an expression of short-term perturbations in the icesheet system. Both short-term monitoring and the analyses of long-term trends in geological records are essential to provide a complete assessment of the state of the climate system. Important broader impacts of this work are further: 1) the availability of high resolution data on cryosphere dynamics for global climate studies, 2) the increased accessibility of the core material for other researchers who target short intervals with time intensive methods of analysis, 3) the PIs activities to inform researchers in urban and coastal management policy and the general public through lectures and local media outlets, and 4) education through research participation of two students of diverse backgrounds, which can be considered an importantlong-term benefit of this work.