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

海水中氧原子（d18 O）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。海洋中的大多数深层内陆水团都是在南大洋形成或改变的，并下沉填充在世界各大洋中循环的深层。海水中的d18 O特征可以用作这些次表层水团的示踪剂，一旦它们下沉到深度。南大洋和南太平洋是水团形成的关键位置，因此，对于了解全球翻转环流，碳循环和气候动态。然而，关于海水d18 O的数据，特别是在次表层，几乎不存在南太平洋和南大洋。此外，我们根据海洋碳酸盐（如珊瑚和有孔虫）中的d18 O特征对过去温度和海洋过程的理解依赖于这样一种假设，即地下水体的氧同位素组成随时间的变化是名义上的，这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。调查人员将对美国GEOTRACES科学考察南太平洋（GP 17-OCE）和南极大陆边缘阿蒙森海（GP 17-ANT）期间从深度断面收集的样本进行海水d18 O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正在经历快速的环境变化，包括整个南极周围冰架融化最快。该项目将支持在主要是本科和西班牙裔服务机构的教学和推广工作的多样化参与的发展。外联活动将提供充分的机会，让代表性不足群体的学生在正式和非正式场合参与进来。海水的d18 O和d2 H与盐度之间存在正相关关系，但海水与盐度之间的同位素关系的区域变化受到很大的限制。温度重建依赖于d18 O的方解石微化石生物沉淀在海水中的平衡，并保存在海洋沉积物中，只有定量的海水d18 O（d18 Osw），其中碳酸盐沉淀是已知的。尽管这些古估计依赖于现代海水的d18 O，但表面测量很少，而且南太平洋和南大洋的次表面数据更加有限。填补这一数据的根本空白，以量化降水，蒸发和冰川融水对内部海水质量的d18 O和d2 H的影响，这与我们对海洋环流和更广泛的气候动力学的理解具有全球相关性。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，使海水d18 O和d2 H分析与传统的IRMS（同位素比质谱法）相比，运行速度更快，成本更低。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度，精度和偏移。获得d18 Osw直接有助于GP 17-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GP 17-ANT规定的量化TEI分布中的梯度和表征的目标，该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识产权进行评估来支持。优点和更广泛的影响审查标准。

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.