Testing the fidelity of neodymium isotopes as a paleocirculation tracer in the Southeast Indian-Southern Ocean

测试钕同位素作为东南印度-南大洋古循环示踪剂的保真度

• 批准号: 1811798
• 负责人: Chandranath Basak
• 金额: $ 14.26万
• 依托单位: CSUB Auxiliary for Sponsored Programs Administration
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-10-01 至 2020-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1811798&HistoricalAwards=false
• 关键词: Testing; fidelity; neodymium; isotopes; paleocirculation

In the modern open ocean neodymium (Nd) isotope values of seawater are often explained by the mixing of water masses. As such, Nd is recognized as a "quasi-conservative" tracer. Implicit in this "quasi-conservative" behavior is the assumption that no significant source of Nd exists along the water mass flowpath. This is the basic principle behind using Nd isotopes archived in marine sediments as a tracer of past ocean circulation. In recent years, several studies of Nd sources, sinks, and biogeochemical cycling has challenged this conventional wisdom and proposed additional sources of Nd, such as: (i) exchange with particulates that modifies seawater Nd isotope ratios, or (ii) addition of pore water Nd influenced by reactions with sediment. To successfully use Nd isotopes as a water mass tracer proxy, it is essential to understand these limitations. Therefore, this project will examine these alternative sources (and sinks) of Nd to evaluate their impact on the quasi-conservative behavior of seawater Nd. This research will help to constrain the limitations of Nd isotopes as a tracer of past ocean circulation. Funding supports career development for a postdoctoral researcher, provides field experience for a graduate student, and provides research experience for an undergraduate student.Project investigators will collect samples that constitute the different components of modern Nd cycle (e.g., filtered seawater, water column particulates, pore waters and concurrent down hole sediment samples) during a cruise in the Southeast Indian-Southern Ocean (SEISO). The SEISO cruise track will: (i) cover major water masses of Southern Ocean origin (Antarctic Mode Water, Antarctic Intermediate Water, Upper and Lower Circumpolar Deep Water), (ii) extensively transit over the southeast Indian Ridge, and (iii) sample the region just north of the Subantarctic Front, where Subantarctic Mode Water is forming today. Seawater and pore water Nd isotopes and Rare Earth Elements will be analyzed, thereby allowing characterization of the Southern Ocean water masses, the effects on seawater Nd isotopes from potentially reactive ridge rocks, and the influence of pore water Nd flux on bottom water Nd isotopes. Besides improving the understanding of Nd cycling, data from this project will provide important information for interpreting other datasets from the research cruise, and will be of interest to a wide range of climate scientists as well as biogeochemical modelers, chemical and biological oceanographers, and polar scientists.

在现代开放的海洋新近山（ND）中，海水的同位素值通常用水块的混合来解释。因此，ND被认为是“准保守”示踪剂。在这种“准保守”行为中隐含的是假设，即沿水量流道不存在任何明显的ND来源。这是使用ND同位素在海洋沉积物中存档的基本原理，作为过去海洋循环的示踪剂。近年来，对ND来源，水槽和生物地球化学循环的几项研究挑战了这种传统的智慧，并提出了其他ND的其他来源，例如：（i）与颗粒交换，以改变海水ND同位素比率，或（ii）添加孔隙水对沉积物的反应影响。要成功使用ND同位素作为水质示踪剂代理，必须了解这些局限性。因此，该项目将检查ND的这些替代来源（和下沉），以评估其对海水ND准保守行为的影响。这项研究将有助于限制ND同位素作为过去海洋循环的示踪剂的局限性。资金支持博士后研究人员的职业发展，为研究生提供现场经验，并为本科生提供研究经验。项目调查人员将收集构成现代ND周期不同组成部分的样品（例如，过滤的海水，水柱，孔隙水，孔隙水，孔隙水和下降孔储层样品，在南方海洋中），在South South Soune Oce in South Seach Oce in Southeaser中）。 SEISO巡航轨道将：（i）覆盖南大洋起源的主要水质量（南极模式水，南极中间水，上和下圆形的深水），（ii）在印度山脊东南山脊上广泛过境，（iii）采样了该区域的北部北极前沿北部北部模式水的北部，该区域如今在其中形成了下北骨的水。将分析海水和孔隙水ND同位素以及稀土元素，从而允许对南方海水质量的表征，对潜在反应性山脊岩石的海水ND同位素的影响以及孔隙水ND磁通量对底部水ND同位素的影响。除了提高对ND循环的理解外，该项目的数据还将提供重要的信息，以解释研究巡游中的其他数据集，并将引起广泛的气候科学家以及生物地球化学建模者，化学和生物海洋学家以及极地科学家的关注。