Diatom and Oxygen Isotope Evidence of Pliocene Antarctic Ice Sheet Dynamics and Ross Sea Paleoceanography

摘要在480万至340万年前的上新世早期，全球气温高于现在，导致罗斯冰架和西南极冰盖的消退。了解过去地质时期冰量减少和温度上升时海洋动力学的变化，将改进对这些条件的预测模型。拟议研究的主要目标是开发南极大陆附近上新世海洋条件的新氧同位素记录。海底有孔虫碳酸盐测试的氧同位素值已成为古海洋学研究的全球标准，但有孔虫在高纬度沉积岩心中稀少。相反，这项研究将利用保存在罗斯海海洋沉积物岩心中的硅藻二氧化硅的氧同位素测量。该项目是使用这种方法的第一次尝试，将促进对全球海洋动力学和上新世期间冰盖-海洋相互作用的理解。该项目将促进两名职业生涯早期科学家的专业发展，并作为研究生和本科生研究人员的培训。PIS将利用这个项目向高中生介绍极地/海洋研究以及稳定同位素地球化学。通过NSTA和极地教育者国际与教师的合作，将确保为年轻学生实施优秀的STEM学习活动和课程。该项目将从与全球底栖有孔虫氧同位素记录相互对比的硅藻丰富的沉积物中产生高分辨率的氧同位素记录。在上新世早期沉积并由ANDRILL项目(和-1B)回收的硅藻硅锥为这一目标提供了理想的材料。AND-1B岩芯中的硅藻土单元几乎是纯的，几乎没有蛋白石形成的证据。该岩心的硅藻氧同位素记录有可能在大气二氧化碳浓度较高的时期限制有关罗斯海和南大洋古海洋学和南极冰盖历史的挥之不去的不确定性。具体地说，氧同位素变化将被用来限制上新世罗斯海水温和/或淡水通量的变化。来自AND-1B核心的硅藻物种数据被用来推断季节性海冰覆盖的范围和持续时间、海表面温度和中水平流到大陆架的变化。然而，硅藻氧同位素记录将第一次直接测量上新世南极大陆边缘的水/氧同位素值。

AbstractDuring the Early Pliocene, 4.8 to 3.4 million years ago, warmer-than-present global temperatures resulted in a retreat of the Ross Ice Shelf and West Antarctic Ice Sheet. Understanding changes in ocean dynamics during times of reduced ice volume and increased temperatures in the geologic past will improve the predictive models for these conditions. The primary goal of the proposed research is to develop a new oxygen isotope record of Pliocene oceanographic conditions near the Antarctic continent. Oxygen isotope values from the carbonate tests of benthic foraminifera have become the global standard for paleo-oceanographic studies, but foraminifera are sparse in high-latitude sediment cores. This research will instead make use of oxygen isotope measurements from diatom silica preserved in a marine sediment core from the Ross Sea. The project is the first attempt at using this method and will advance understanding of global ocean dynamics and ice sheet-ocean interactions during the Pliocene. The project will foster the professional development of two early-career scientists and serve as training for graduate and undergraduate student researchers. The PIs will use this project to introduce High School students to polar/oceanographic research, as well as stable isotope geochemistry. Collaboration with teachers via NSTA and Polar Educators International will ensure the implementation of excellent STEM learning activities and curricula for younger students. Technical DescriptionThis project will produce a high-resolution oxygen isotope record from well-dated diatom rich sediments that have been cross-correlated with global benthic foraminifera oxygen isotope records. Diatom silica frustules deposited during the Early Pliocene and recovered by the ANDRILL Project (AND-1B) provide ideal material for this objective. Diatomite unites in the AND-1B core are nearly pure, with little evidence of opal formation. A diatom oxygen isotope record from this core offers the potential to constrain lingering uncertainties about Ross Sea and Southern Ocean paleoceanography and Antarctic Ice Sheet history during a time of high atmospheric carbon dioxide concentrations. Specifically, oxygen isotope variations will be used to constrain changes in the water temperature and/or freshwater flux in the Pliocene Ross Sea. Diatom species data from the AND-1B core have been used to infer variations in the extent and duration of seasonal sea ice coverage, sea surface temperatures, and mid-water advection onto the continental shelf. However, the diatom oxygen isotope record will provide the first direct measure of water/oxygen isotope values at the Antarctic continental margin during the Pliocene.