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

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的控制。海洋深处的大部分内部水团都是在南大洋形成或改变的，然后下沉，填满在世界海洋中循环的深层。海水中的d18O特征可以作为这些地下水团沉入深处的示踪剂。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、碳循环和气候动力学的关键地点。然而，关于南太平洋和南大洋的海水，特别是地下海水的d18O的数据实际上是不存在的。此外，基于海洋碳酸盐（如珊瑚和有孔虫）的d18O特征，我们对过去温度和海洋过程的理解依赖于以下假设：地下水团块的氧同位素组成随时间的变化是名义的，这可以在本项目中使用新技术在更广泛的基础上直接测试。研究人员将对美国GEOTRACES科学考考队在南太平洋（GP17-OCE）和南极大陆边缘的阿蒙森海（GP17-ANT）从深度样带收集的海水d18O进行分析。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了迅速的环境变化，包括整个南极周围冰架的融化速度最快。这个项目将支持在一个主要是本科生和西班牙裔服务机构的教学和外展工作中多种参与的发展。外联活动将提供充分的机会，让来自正式和非正式环境中代表性不足群体的学生参与进来。从第一性原理可知，海水的d18O和d2H与盐度呈正相关，但对海水与盐度同位素关系的区域变化约束较差。只有当碳酸盐沉淀的海水d18O （d18Osw）已知时，依靠方解石微化石中与海水平衡沉淀并保存在海洋沉积物中的d18O进行温度重建才能定量。尽管这些古估计依赖于现代海水的d18O，但表面测量很少，而且在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，量化降水、蒸发和冰川融水对内部海水团d18O和d2H的影响，对我们了解海洋环流和更广泛的气候动力学具有全球意义。新型激光光谱技术的发展和改进，如离轴集成腔输出光谱（OA-ICOS）和腔衰荡光谱，与传统的IRMS（同位素比质谱）相比，可以快速运行海水d18O和d2H分析，并具有成本效益。该项目的一个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、精密度和偏移量。获取d18Osw直接有助于GP17-OCE描述近场和远场微量元素和同位素（TEI）输入的目标，以及GP17-ANT描述的量化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。该奖项反映了美国国家科学基金会的法定使命，并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。

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.