Collaborative Research: RUI: Southeast Pacific and Southern Ocean Seawater Isotopes Determined from US GEOTRACES GP17-OCE and GP17-ANT Samples

合作研究：RUI：从美国 GEOTRACES GP17-OCE 和 GP17-ANT 样品中测定东南太平洋和南大洋海水同位素

• 批准号: 2049664
• 负责人: Amy Wagner
• 金额: $ 23.91万
• 依托单位: University Enterprises, Incorporated
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-07-01 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2049664&HistoricalAwards=false
• 关键词: Collaborative; Research; RUI; Southeast; Pacific

The stable isotopic composition of the oxygen atom in seawater (d18O) is controlled by evaporation, precipitation, and riverine or glacial meltwater input. Most of the deep interior water masses in the ocean are formed or modified in the Southern Ocean and sink to fill the deep layers that circulate throughout the world’s oceans. The d18O signatures in seawater can be used as tracers for these sub-surface water masses once they sink to depth. The Southern Ocean and South Pacific are critical locations for water mass formation and thus, for understanding global overturning circulation, carbon cycling and climate dynamics. However, data on the d18O of seawater, particularly in the sub-surface, is virtually nonexistent for the South Pacific and Southern Ocean. Moreover, our understanding of past temperature and oceanic processes based on the d18O signature in marine carbonates (e.g. corals and foraminifera) have relied on the assumption that variations in the oxygen isotopic composition of the sub-surface water masses are nominal through time, which can be directly tested on a wider basis using new technologies during this project. Investigators will conduct analyses of seawater d18O from samples collected from depth transects during the US GEOTRACES science expedition to the South Pacific (GP17-OCE) and the Amundsen Sea sector of the Antarctic continental margin (GP17-ANT). This ocean region is of particular significance because it is experiencing rapid environmental changes in the past few decades, including the fastest melting of ice shelves around the entire Antarctic. This project will support the development of diverse involvement in teaching and outreach efforts in a primarily undergraduate and Hispanic serving institution. The outreach activities will provide ample opportunities to engage students from underrepresented groups in both formal and informal settings. It is well-established from first principles that d18O and d2H of seawater have a positive relationship to salinity, but regional variations in the isotopic relationship of seawater to salinity are poorly constrained. Temperature reconstructions relying on d18O in calcite microfossils biologically precipitated in equilibrium with seawater and preserved in marine sediments are only quantitative if the seawater d18O (d18Osw) in which that carbonate was precipitated is known. Despite the reliance of these paleo-estimations on the d18O of modern seawater, surface measurements are few and far between and sub-surface data in the South Pacific and Southern Oceans is even more limited. Filling this fundamental gap in data to quantify the influence of precipitation, evaporation and glacial melt water on the d18O and d2H of interior seawater masses is globally relevant to our understanding of ocean circulation and broader climate dynamics. The development and improvement of new laser-based spectroscopy techniques such as off-axis integrated cavity output spectroscopy (OA-ICOS) and cavity ring-down spectroscopy, allows for seawater d18O and d2H analyses to be run quickly and cost effectively compared to traditional IRMS (Isotope Ratio Mass Spectrometry). A core aim of this project is to compare and contrast IRMS and OA-ICOS analyses to address accuracy, precision and offsets between methods. Obtaining d18Osw directly contributes to the GP17-OCE stated aims of characterizing near- and far-field trace element and isotope (TEI) inputs and to the GP17-ANT stated aims of quantifying gradients in TEI distributions and characterizing, glacial meltwater inputs in the Amundsen Sea and Southern Ocean.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

海水中氧原子的稳定同位素组成 (d18O) 受蒸发、降水和河流或冰川融水输入控制。海洋中的大部分深层内部水团是在南大洋形成或改变的，并下沉以填充在世界海洋中循环的深层。一旦这些地下水团沉入深处，海水中的 d18O 特征就可以用作这些地下水团的示踪剂。南大洋和南太平洋是水团形成的关键地点，因此也是了解全球翻转环流、碳循环和气候动态的关键地点。然而，关于南太平洋和南大洋海水（尤其是地下海水）d18O 的数据实际上不存在。此外，我们基于海洋碳酸盐（例如珊瑚和有孔虫）中的 d18O 特征对过去温度和海洋过程的理解依赖于这样的假设：地下水团的氧同位素组成随时间的变化是名义上的，可以在本项目期间使用新技术在更广泛的基础上直接进行测试。研究人员将对美国 GEOTRACES 南太平洋科学考察 (GP17-OCE) 和南极大陆边缘阿蒙森海区 (GP17-ANT) 期间从深度样带收集的样品中的海水 d18O 进行分析。这个海洋区域具有特别重要的意义，因为它在过去几十年里经历着快速的环境变化，包括整个南极洲周围冰架融化最快的情况。该项目将支持在一个主要是本科生和西班牙裔的服务机构中发展多元化的教学和外展工作。外展活动将为在正式和非正式场合吸引来自代表性不足群体的学生提供充足的机会。从第一原理来看，海水的 d18O 和 d2H 与盐度呈正相关，但海水同位素关系与盐度的区域变化却很少受到限制。仅当已知沉淀碳酸盐的海水 d18O (d18Osw) 时，依赖于与海水平衡生物沉淀并保存在海洋沉积物中的方解石微化石中的 d18O 的温度重建才是定量的。尽管这些古估计依赖于现代海水的 d18O，但地表测量却很少且相差甚远，南太平洋和南大洋的地下数据更加有限。填补这一基本数据空白，以量化降水、蒸发和冰川融水对内部海水团 d18O 和 d2H 的影响，对于我们对海洋环流和更广泛的气候动态的理解具有全球意义。新型激光光谱技术的开发和改进，例如离轴积分腔输出光谱 (OA-ICOS) 和腔衰荡光谱，与传统的 IRMS（同位素比质谱法）相比，可以快速且经济高效地进行海水 d18O 和 d2H 分析。该项目的核心目标是比较和对比 IRMS 和 OA-ICOS 分析，以解决方法之间的准确性、精确度和偏移问题。获得 d18Osw 直接有助于 GP17-OCE 规定的表征近场和远场痕量元素和同位素 (TEI) 输入的目标，以及 GP17-ANT 规定的量化 TEI 分布梯度和表征阿蒙森海和南大洋冰川融水输入的目标。该奖项反映了 NSF 的法定使命，并被认为值得通过以下方式获得支持： 使用基金会的智力价值和更广泛的影响审查标准进行评估。