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

合作研究：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: 2049577
• 负责人: Elisabeth Sikes
• 金额: $ 30.68万
• 依托单位: Rutgers University New Brunswick
• 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=2049577&HistoricalAwards=false
• 关键词: Collaborative; Research; Southeast; Pacific; Southern

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（d18O）的稳定同位素组成受蒸发、降水和河流或冰川融水输入的控制。海洋中的大部分深层内部水团在南大洋中形成或改变并下沉以填充海洋。一旦这些地下水团沉入深处，海水中的 d18O 特征就可以用作示踪剂。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。基于海洋碳酸盐（例如珊瑚和有孔虫）中 d18O 特征的过去温度和海洋过程依赖于这样的假设：地下水团的氧同位素组成的变化是名义上的时间，可以在该项目期间使用新技术在更广泛的基础上直接进行测试，研究人员将从美国 GEOTRACES 南太平洋 (GP17-OCE) 和阿蒙森海科学考察期间收集的深度样线样品中进行海水 d18O 分析。南极大陆边缘部分（GP17-ANT）这一海洋区域具有特别重要的意义，因为它在过去几十年中经历着快速的环境变化，包括整个冰架融化速度最快的区域。南极。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开展多元化的教学和外展工作。外展活动将为来自代表性不足的群体的学生提供充分的机会，让他们参与正式和非正式的活动。从第一原理来看，海水的 d18O 和 d2H 与盐度呈正相关，但海水与盐度同位素关系的区域变化很少受到依赖 d18O 的温度重建的约束。尽管这些古估计依赖于现代海水的 d18O，但只有在已知沉淀碳酸盐的海水 d18O (d18Osw) 时，方解石微化石中的 d18O 才能定量。南太平洋和南大洋的地下数据很少且相距甚远，填补这一基本数据空白以量化其影响的能力更加有限。内部海水团 d18O 和 d2H 上的降水、蒸发和冰川融水与我们对海洋环流和更广泛的气候动力学的理解在全球范围内相关。新型激光光谱技术（例如离轴积分腔输出光谱）的开发和改进。 (OA-ICOS) 和腔衰荡光谱法，与传统的 IRMS（同位素比率质量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、精度和偏移问题，直接有助于 GP17-OCE 表征近场和远场迹线的目标。元素和同位素 (TEI) 输入以及 GP17-ANT 规定的目标是量化 TEI 分布的梯度并表征阿蒙森冰川融水输入海洋和南大洋。这反映了 NSF 的法定使命，并且通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。