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: 1737151
• 负责人: Chandranath Basak
• 金额: $ 14.26万
• 依托单位: Columbia University
• 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: 2017-09-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1737151&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.

在现代公海中，海水中的钕 (Nd) 同位素值通常可以通过水团的混合来解释。因此，Nd 被认为是一种“准保守”示踪剂。这种“准保守”行为隐含着这样的假设：沿着水团流路径不存在重要的 Nd 源。这是使用海洋沉积物中储存的 Nd 同位素作为过去海洋环流示踪剂的基本原理。近年来，一些关于 Nd 源、汇和生物地球化学循环的研究挑战了这种传统观点，并提出了其他 Nd 来源，例如：（i）与改变海水 Nd 同位素比率的颗粒交换，或（ii）添加孔隙水 Nd 受与沉积物反应的影响。为了成功地使用 Nd 同位素作为水质量示踪剂代理，必须了解这些限制。因此，本项目将研究这些替代的 Nd 源（和汇），以评估它们对海水 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环流示踪剂的局限性。资金支持博士后研究员的职业发展，为研究生提供现场经验，并为本科生提供研究经验。项目研究人员将收集构成现代 Nd 循环不同组成部分的样本（例如，过滤的海水、水柱颗粒、东南印度-南大洋 (SEISO) 巡航期间的孔隙水和同时发生的井下沉积物样本）。 SEISO 巡航路线将：(i) 覆盖南大洋起源的主要水体（南极模式水、南极中层水、上环极地深水和下环极地深水），(ii) 广泛穿越东南印度洋海岭，以及 (iii) 采样亚南极锋以北的地区，今天正在形成亚南极模式水。将分析海水和孔隙水 Nd 同位素和稀土元素，从而能够表征南大洋水团、潜在反应性山脊岩石对海水 Nd 同位素的影响，以及孔隙水 Nd 通量对底层水 Nd 同位素的影响。除了提高对 Nd 循环的理解外，该项目的数据将为解释研究巡航的其他数据集提供重要信息，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学家的兴趣。科学家。