Palynostratigraphic and Paleoenvironmental Characterization of Upper Miocene Sediments from Western Ross Sea, Antarctica

该奖项由极地方案办公室南极地质和地球物理方案提供，支持一个调查晚中新世时期南极冰盖和南大洋相互作用的项目。大量的地质证据表明，地球气候系统在中新世晚期发生了巨大的变化。这些变化包括最大的前更新世冰期海平面低的立场，在新生代，300公里的极锋北移，多个脉冲的冰漂流，全球碳同位素（d13 C）的转变，全球海洋盐度降低，以及几个事件的南大洋深海平原侵蚀。主要是根据深海代用资料推断，晚中新世气候变化与南极冰川加剧有关，虽然这些代用资料的解释基本上是根据正确的地质和地球化学原理，但由于南极大陆边缘的具体环境条件尚未确定，关于与南极冰冻圈的联系的结论是模棱两可的。本孢粉学研究的基本目的是解决以下问题：什么是晚中新世间冰期和冰川的环境条件（即盐度，温度和海冰覆盖）在西部罗斯海内外大陆架？第二个目标是：1。加强现有的罗斯海孢粉地层从罗伯茨角项目开发。确定Brancolini及其同事在1995年和Bart及其同事在2000年描述的向北方盆地陆架边缘的主要冰川推进是否确实是晚中新世事件，如果是，在这个冰川时期存在的环境条件是什么。确定南极环境变化对低纬度气候变化的影响，重点是与墨西拿盐度危机的联系以及全球盐度下降的原因。事实上，新的孢粉学数据从大西洋海岸的古直布罗陀门槛表明，一个显着的舌形连接降低海平面发生在晚中新世，限制大西洋流入地中海在危机的开始。在本研究的第一部分，孢粉学的日期，内大陆架芯DVDP 10和11将进行分析。根据底栖有孔虫和硅藻的分布，其他人先前的工作表明，在中新世至上新世期间，罗斯海内大陆架存在着开阔海洋/冰川条件的循环。棘囊藻的分布可以验证这一理论。在本研究的第二部分，将对以前从北方盆地外大陆架获得的材料进行孢粉学分析。最近的地震地层分析表明，沉积物与一个主要的晚中新世（？）在罗斯海西北部的外大陆架上，冰川的前进暴露在广阔的区域内。这些沉积物中所含的孢粉应该可以检验出露岩层是否确实是在中新世晚期沉积的。由于南极和北极海洋孢粉的基本类型相似，古环境重建将以北极现有的生态数据为基础，同时也要以南极沃茨的数据为基础。DVDP站点10和11最近生成的氧同位素（d18 O）记录应提供南极冰量变化的合理代理，并评估环境变化是否与冰量变化有关。除了环境方面，本研究所产生的生物地层学信息应提供改进的年代地层学支持未来拟议的南极地质钻探计划，如SHALDRIL和ANDRILL。

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports a project to investigate the interaction of the Antarctic ice sheet and the Southern Ocean during the late Miocene time period. Numerous lines of geological evidence show that the Earth climate system changed dramatically during the late Miocene. These changes include the largest pre-Pleistocene glacioeustatic sea-level low stands during the Cenozoic, a 300-km northward shift of the Polar Front, multiple pulses of ice rafting, a global carbon isotopic (d13C) shift, a global reduction in ocean salinity, and several episodes of Southern Ocean abyssal-plain erosion. Primarily on the basis of deep-sea proxy data, it has been inferred that late Miocene climatic changes were related to Antarctic glacial intensification.Although these proxy data interpretations are based on fundamentally sound geological and geochemical principles, the conclusions concerning linkages to the Antarctic cryosphere are equivocal because the specific environmental conditions at the Antarctic continental margins have not yet been established. The fundamental purpose of this palynological study is to address the following question: What were the environmental conditions (i.e. salinity, temperature, and sea ice-cover) during late-Miocene interglacials and glacials on the western Ross Sea inner and outer continental shelf?The secondary goals are to:1. Enhance the existing Ross Sea palynostratigraphy developed from the Cape Roberts Project.2. Determine if the major glacial advance to the Northern Basin shelf edge, described by Brancolini and colleagues in 1995 and Bart and colleagues in 2000, was indeed a late Miocene event, and if so, what were the environmental conditions existing during this glacial period.3. Determine the effect of Antarctic environmental changes on low-latitude climate change, focusing on linkage with the Messinian Salinity Crisis and the reason behind the global salinity reduction. Indeed, new palynological data from the Atlantic coast of the paleo-Gibraltar threshold suggests that a significant Antarctic-linked lowering of sea level occurred during the late Miocene, restricting Atlantic inflow into the Mediterranean Sea at the beginning of the crisis.In the first part of this study, the palynology of the well-dated, inner continental shelf cores DVDP 10 and 11 will be analyzed. Prior work by others showed, on the basis of benthic foraminifer and diatom distribution, that cycles of open-marine/glacial conditions existed on the Ross Sea inner continental shelf during the Mio-Pliocene. Dinocyst distribution should test this theory. In the second part of this study, a palynological analysis of previously acquired material from the Northern Basin outer continental shelf will be conducted. Recent seismic-stratigraphic analyses indicated that the sediments associated with a major late Miocene (?) glacial advance are exposed over a broad area, on the northwestern Ross Sea outer continental shelf. Palynomorphs contained in these sediments should test if indeed, the outcrops were deposited during the late Miocene. Because basic types of Antarctic and Arctic marine palynomorphs are similar, paleoenvironmental reconstruction will be based on existing ecological data from the Arctic, as well as that from Antarctic waters. The oxygen isotopic (d18O) record recently generated for DVDP sites 10 and 11 should provide a reasonable proxy for Antarctic ice-volume changes and evaluate if environmental changes were related to ice-volume changes. In addition to the environmental aspect, the biostratigraphic information generated by this study should provide improved chronostratigraphic support for future proposed Antarctic geological drilling programs, such as SHALDRIL and ANDRILL.