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

本项目通过IODP 318考察队在南极威尔克斯陆缘收集的浮冰碎屑产生的变化和沉积物岩心的主要元素地球化学特征，研究上新世早期南极东部的冰动力学和古环境条件。南极洲的这一部分包含威尔克斯和奥罗拉冰下盆地，东南极冰盖（EAIS）在海平面以下，可能不稳定。上新世早期是一个已知的全球变暖时期，海洋表面温度比现在的南大洋高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，并且存在相当大的争议。最近的气候和冰盖模型研究表明，与南极西部冰盖相反，EAIS在上新世期间没有崩塌。然而，模式确实显示它的边缘退缩到现在的位置之内，并且这种退缩产生了一个显著的海平面上升分量。威尔克斯地边缘是预计撤退最严重的地方。为了验证上新世早期暖期冰川退缩假说，我们收集了高分辨率的IRD生成、古生产力和物源变化记录；2)提供足够分辨率的记录，将南极东部的冰动力与10年时间尺度上的全球古气候代用物联系起来。对位于陆架的U1358位点和位于陆脊的U1359位点两个具有较好年代的早上新世层段的钻孔进行了研究。冰筏碎屑（IRD）质量积累率（MAR）将结合U1359站点的大块陆源粒度分析来确定。粒度分析也将有助于解释U1358站点货架上的晶粒岩。这两个地点的沉积物中均含有5%的陆源组分，因此生物对陆源沉积物中Fe、Ti和Al含量的颗粒清除作用可以忽略不计，稳定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。IRD - MAR综合数据集、风化化学变化程度和古生产力将用于评估上新世早期暖期期间威尔克斯陆及其邻近海洋的冰范围和古气候条件的变化。更广泛的影响上新世是大气二氧化碳分压与今天相似的最后一个时代。S分压和全球地表温度高于现代，高纬度地区的增温程度大于平均水平。从构造学和海洋学的角度来看，地球与今天相似，因此，上新世早期是一个很好的时间间隔，可以研究与现在和不久的将来相当的世界上冰盖的长期稳定性。南极冰盖是全球气候系统的重要组成部分，因为它们具有高反照率，并对海冰形成、海洋环流和海平面产生影响。卫星数据表明，南极冰盖目前正在失去质量，而且质量损失最近加速，导致目前全球海平面每年上升约0.3毫米。然而，由于监测周期较短，尚不确定冰盖是在对目前的变暖作出反应，还是这是冰盖系统短期扰动的一种表现。短期监测和对地质记录中的长期趋势的分析对于提供对气候系统状态的完整评估是必不可少的。这项工作的重要的更广泛的影响进一步：1)为全球气候研究提供高分辨率冰冻圈动力学数据；2)增加了其他研究人员对核心材料的可及性，这些研究人员以时间密集型的分析方法为目标，以短时间间隔为目标；3)通过讲座和当地媒体渠道向城市和沿海管理政策的研究人员和公众提供信息；4)通过两名不同背景的学生的研究参与进行教育。这可以被认为是这项工作的一个重要的长期利益。

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.