Collaborative Research: US GEOTRACES Pacific Meridional Transect: Sources and Sinks of Neodymium Isotopes and Rare Earth Elements

国际GEOTRACES项目的目标是了解海洋中微量化学元素及其同位素的分布。钕（Nd）同位素和稀土元素（REE）被广泛认为是水运的示踪剂和海洋微量元素来源的指示物。钕同位素已被指定为GEOTRACES探险测量的“关键参数”。该项目将在2018年的太平洋GEOTRACES探险中测量Nd同位素。北太平洋是测量Nd同位素的一个特别有趣的地方，因为北太平洋和北大西洋深水代表了深海组成的两个末端成员，迄今为止在北太平洋获得的少量数据与基于已知水类型混合的预期不同。从塔希提岛到阿拉斯加的美国GEOTRACES太平洋经向样带（PMT）将在解开北太平洋钕同位素比率的“谜团”方面发挥重要作用。PMT的设计目的是对海洋中最古老的水域进行广泛采样，包括阿拉斯加海岸边缘、火山沉积物、源自火山弧、亚洲和北美大陆的经向尘埃梯度，以及生物生产力的大梯度。本项目的主要目的是对沿样带的海水Nd同位素比值进行表征。为了解决太平洋Nd和REE循环的基本问题，研究人员还将量化边界交换效应、大气输入、颗粒来源、生物生产力的影响以及进出海水的通量，以评估Nd和REE源和汇，并校准Nd同位素作为太平洋古环流代用物。具体的研究重点包括：(1)浅水和深水的Nd同位素特征；(2)与阿拉斯加火山弧陆架相关的边缘过程，研究颗粒、沉积物和海水之间的Nd同位素和REE的化学交换；(3)经向尘埃源的变化及其影响；(4)底部沉积物类型、成分、网状层之间的关系及其对水柱的影响；(5)孔隙水流对水柱的影响；(6)深水与沉积档案（如鱼牙化石、铁锰氧化物镀层）之间的信号传递。该项目将促进博士后研究科学家的职业生涯，并支持众多本科生。

The goal of the international GEOTRACES program is to understand the distributions of trace chemical elements and their isotopes in the oceans. Neodymium (Nd) isotopes and rare earth elements (REE) are widely recognized for their utility as tracers of water transport and as indicators of the sources of trace elements to the oceans. Neodymium isotopes have been designated as "key parameters" to be measured on GEOTRACES expeditions. This project would measure Nd isotopes on a 2018 GEOTRACES expedition in the Pacific Ocean. The North Pacific is a particularly interesting place to measure Nd isotopes because North Pacific and North Atlantic deep waters represent the two end-members of deep ocean composition, and the few data available so far in the North Pacific differ from expectations based on mixing of known water types.The US GEOTRACES Pacific Meridional Transect (PMT) from Tahiti to Alaska will play an important role in solving the "mystery" of North Pacific neodymium isotope ratios. The PMT is designed to extensively sample the oldest waters in the ocean, along with Alaskan coastal margins, volcanogenic sediments, the meridional dust gradient originating from volcanic arcs and the Asian and North American continents, and large gradients in biological productivity. The primary purpose of this project is to characterize the Nd isotope ratio of seawater along the transect. In order to address fundamental questions on the Nd and REE cycle in the Pacific, the investigators will also quantify boundary exchange effects, atmospheric inputs, provenance of particles, impacts of biological productivity, and fluxes into and out of seawater, in order to assess Nd and REE sources and sinks, and to calibrate Nd isotopes as a paleocirculation proxy in the Pacific. Specific focus areas include: (1) Nd isotopic characterization of the shallow and deep waters, (2) margin processes associated with the Alaska volcanic arc shelf, to study chemical exchanges between particulates, sediments, and seawater Nd isotopes and REE, (3) changing meridional dust sources and its impacts, (4) relationships between bottom sediment types, compositions, nepheloid layers, and their influence on the water column, (5) the effects of pore water flow on the water column; (6) the signal transfer between the deep water and sedimentary archives (e.g., fossil fish teeth, Fe-Mn oxide coatings). The project will advance the career of a postdoctoral research scientist, and support numerous undergraduate students.