Collaborative Research: Constraining the Temporal Resolution and Geochronology of Holocene Sediment Records from the Antarctic Continental Shelf

该奖项由极地方案办公室南极地质学和地球物理学方案提供，支持一个项目，调查南极沉积物中的古环境代用记录，并改进确定记录年龄的方法。南极大陆边缘栖息盆地的海洋沉积物岩心为该地区晚第四纪环境条件提供了重要的代用记录。这些沉积岩芯通常缺乏碳酸盐微体化石，主要通过加速器质谱法测量散装有机碳的碳-14（14 C）含量来确定年代。然而，沉积物-水界面处有机物的放射性碳年龄不为零（所谓的碳储层问题），需要对岩芯以下的14 C年龄进行“校正”，这可能高达1000 - 3000年。此外，底栖生物对上层沉积物柱的生物扰动会使沉积物岩心中保存的代用记录模糊不清，从而限制了这种沉积物记录的时间分辨率。在南极大陆架的大部分地区，表层沉积物的放射性碳年龄和底栖生物混合的深度尚不确定，本项目将对大量有机物的碳同位素组成和无载体铅-210的活性进行高分辨率的岩芯下分析，以确定表层沉积物的放射性碳年龄和沉积物混合的深度-在几个南极大陆架盆地层。这项工作将检查在Scholleart Drift（Gerlache海峡中部，南极半岛西部），Vega Drift（威德尔海西北部，南极半岛东部）以及尼尔森盆地和冰山巷（MacRobertson Shelf，南极东部）收集的卡斯滕岩心。之所以选择这些研究区，是因为（1）为这些样品收集的数据将直接有益于正在进行的对从这些地点采集的高质量长沉积物岩心的研究，（2）这些地点提供了一系列对比鲜明的环境，包括表层沃茨的储层年龄、沉积环境的能量、底栖生物群的范围和类型，和接近再悬浮和残余有机物质的潜在来源，这将允许评估这些因素对南极大陆架表层沉积物放射性碳年龄的相对重要性。放射化学测定将利用加速器质谱法测量碳同位素，并利用高灵敏度伽马光谱法分析铀系核素，这两种技术以前曾成功用于南极大陆架沉积物。 南极大陆架是海洋深水形成、季节性海冰形成和海洋初级生产的重要区域，这些过程很可能受到未来气候变化的强烈影响。预测这一区域将如何受到未来气候变化的影响和调节未来气候变化的能力，关键取决于对南极边缘过去气候变化期间状况的了解。该项目将在这方面作出重大贡献，提供准确破译和解释南极大陆架全新世沉积物岩心记录所需的关键数据。此外，通过提高我们对沉积环境和底栖生物群落对放射性碳年代学和南极沉积物记录分辨率的影响的认识，这项工作将有助于选择未来可能提供高质量古环境记录的地点。该项目还将在多个层面做出教育贡献，包括本科生和研究生研究以及基于网络的公共宣传。

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports a project to investigate paleoenvironmental proxy records in Antarctic sediments and improve approaches to determine the age of the records. Marine sediment cores from perched basins on the Antarctic continental margin have provided important proxy records of environmental conditions in this region during the late Quaternary. Typically lacking in carbonate microfossils, these sediment cores have primarily been dated by using the carbon-14 (14C) content of bulk organic carbon, measured by accelerator mass spectrometry. However, the non-zero radiocarbon age of organic matter at the sediment-water interface (the so-called carbon reservoir problem) necessitates a "correction" to down-core 14C ages, which may be as much as 1,000-3,000 years. In addition, bioturbation of the upper sediment column by benthic organisms serves to smear the proxy records preserved in sediment cores, thus limiting the temporal resolution of such sediment records. For most of the Antarctic shelf, the radiocarbon age of surface sediments and the depth of mixing by benthic organisms are not known with any certainty.This project will undertake high-resolution down-core analyses of the carbon isotopic composition of bulk organic matter and the activity of unsupported lead-210 in order to establish the radiocarbon age of surface sediments and the depth of the sediment mixed-layer in several Antarctic shelf basins. The work will examine Kasten cores collected in the Scholleart Drift (central Gerlache Strait, west Antarctic Peninsula), the Vega Drift (northwestern Weddell Sea, east Antarctic Peninsula), and the Nielsen Basin and Iceberg Alley (MacRobertson Shelf, East Antarctica). These study areas have been selected because (1) the data collected for these samples will be of direct benefit to ongoing studies of high-quality long sediment cores recovered from these sites, and (2) these sites provide a range of contrasting environments in terms of reservoir age of surface waters, energy of depositional environment, extent and type of benthic biota, and proximity to potential sources of re-suspended and relict organic material, which will allow evaluation of the relative importance of these factors for the radiocarbon age of surface sediments on the Antarctic shelf. The radiochemical determinations will make use of accelerator mass spectrometry for carbon isotope measurements, and high-sensitivity gamma spectrometry for analysis of uranium-series nuclides, two techniques that have been previously used with success for Antarctic shelf sediments. The Antarctic continental shelves are important regions of oceanic deep-water formation, seasonal sea-ice formation, and marine primary production - processes that are likely to be strongly influenced by future climatic change. The ability to predict how this region will be affected by, and modulate, future climate change is critically dependent on an understanding of conditions on the Antarctic margin during past climatic variations. This project will make a significant contribution in this regard, by providing key data that are required to accurately decipher and interpret Holocene sediment-core records from the Antarctic continental shelf. In addition, by improving our understanding of the effects of depositional environment and benthic community on the radiocarbon chronology and resolution of Antarctic sediment records, this work will assist in the selection of future sites that are likely to provide high-quality paleoenvironmental records. This project will also make educational contributions at several levels, including undergraduate and graduate research as well as web-based public outreach.