Collaborative Research: US GEOTRACES GP17-OCE: Size-Fractionated Particle Collection and Analysis from Ultra-Oligotrophic to Antarctic Waters

地理示踪是一项正在进行的国际努力，目的是研究和了解低丰度(“痕量”)元素和同位素在世界海洋中的分布情况。微量元素既包括海水中自然存在的化学成分，也包括人类影响的化学成分。它们在地球的功能中有几个重要的作用，使它们成为研究的焦点：1)它们的稀有性已知限制了作为海洋食物网基础的微型植物的生长；2)世界偏远地区的微量元素分布显示了地球的大气、海洋、地壳和生态系统如何在大的行星尺度上协同工作；3)关于这些痕量成分的知识很难获得，但也是在快速变化的世界中改进地球气候的计算机模型的重要组成部分。太平洋覆盖了地球的近三分之一，这个项目的焦点是很少采样的南太平洋，其中包括大约四分之一的世界海洋容量。作为GEOTRACES对这一偏远地区考察的一部分，该项目有三个主要目标：1)提供采样设备和人员，以采集海洋中大量的颗粒物，因为海水中的许多化学成分都是以颗粒物的形式存在的；2)记录海洋颗粒物样本，并将其分发给GEOTRACES多个实验室的合作者；3)在位于佐治亚州萨凡纳和加利福尼亚州圣克鲁斯的实验室分析海洋颗粒物中约20多种微量元素的丰度。一名博士后学者和两名研究生将参与这项研究的现场和实验室方面。GP-17 OCE南太平洋研究考察计划于2022年底至2023年初进行两个月。它由两个横断面组成：沿法属波利尼西亚和南大洋之间约150°W方向的南向横断面，它将从低粉尘、低生物量的少营养亚热带环流中采样大的生物和地球化学梯度，尽管更具生产力的区域是水团形成和锋面混合的复杂区域，并进入南大洋。一条沿67°S向东进入智利的断面将采样受高蛋白石和南极影响的南大洋、深水热液影响以及横跨南美大陆边缘的样品。调查人员将使用大容量的现场泵从水柱中收集粒度分级的颗粒物，并将分配给多个合作者；他们将操作和维护将部署在探险中的颗粒物敏感光学设备。这项研究旨在解决三个主要假设：1)从微小浮游生物主导的环流通过锋面区域进入蛋白石和棕囊藻主导的极地水域的大生物梯度将在颗粒输出、颗粒组成、痕量元素和同位素(TEI)的清除以及碳和TEI的再矿化长度尺度上呈现出大的梯度；2)颗粒铁在除强烈热液影响的区域外的大部分水柱中都以成岩(壳源)相为主，成岩颗粒的来源将反映外部气溶胶粉尘、沉积物、热液来源和大陆输入的输入，这在总消化后确定的TEI比率中是明显的；3)浊度与光束衰减系数的光学比率对氢氧化铁的丰度很敏感，因此是富含铁的自生和致岩颗粒输入的高分辨率指示器。这一奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

GEOTRACES is an ongoing international effort to study and understand how low-abundance (“trace”) elements and isotopes are distributed in the world’s oceans. Trace elements include both naturally occurring and human-influenced chemical components of seawater. They have several important roles in the functioning of the Earth that make them a focus of study: 1) their rarity is known to limit the growth of microscopic plants which are the base of ocean food webs; 2) the distributions of trace elements in remote parts of the world show how Earth’s atmosphere, ocean, crust, and ecosystems work together on large, planetary scales; 3) knowledge of these trace components is difficult to acquire but is also an important component to improving computer models of Earth’s climate in a rapidly changing world. The Pacific Ocean covers nearly a third of the planet, and the rarely sampled South Pacific Ocean at the focus of this project includes approximately a quarter of the world’s ocean volume. As part of a GEOTRACES expedition to this remote region, this project has three main goals: 1) to provide the sampling equipment and personnel to collect large volumes of particles from the ocean, because many chemical components in seawater are in particle forms; 2) to document and distribute ocean particle samples to collaborators of many GEOTRACES laboratories; 3) to analyze ocean particles for abundances of approximately two dozen trace elements at laboratories in Savannah, GA and Santa Cruz, CA. A post-doctoral scholar and two graduate students will participate in both field and laboratory aspects of the research.The GP-17 OCE research expedition to the South Pacific Ocean is planned for two months in late 2022 into early 2023. It comprises two transects: a southward transect along approximately 150ºW between French Polynesia and the Southern Ocean which will sample large biological and geochemical gradients from the low-dust, low-biomass oligotrophic sub-tropical gyre, though more productive regions of complex regions of watermass formation and frontal mixing, and into the Southern Ocean. An eastward transect along 67ºS and into Chile will sample the high-opal and Antarctic-influenced Southern Ocean, deep-water hydrothermal influences, and across the South American continental margin. The investigators will use large-volume in-situ pumps to collect size-fractionated particles from the water column which will be distributed to multiple collaborators; and they will operate and maintain particle-sensitive optical equipment to be deployed on the expedition. The research aims to address three main hypotheses: 1) that the large biological gradients from pico-plankton dominated gyre through frontal regions into opal- and Phaeocystis-dominated polar waters will present large gradients in particle export, particle composition, scavenging of trace elements and isotopes (TEIs), and remineralization length-scales of both carbon and TEIs; 2) that particulate iron is dominated by lithogenic (crustally-derived) phases throughout most of the water column, with the exception of regions of strong hydrothermal influence, and that lithogenic particle origins will reflect inputs of external aerosol dust, sediments, hydrothermal sources, and continental inputs as evident via TEI ratios determined after total digestion; 3) that the optical ratio of turbidity to beam attenuation coefficient is sensitive to iron-oxyhydroxide abundances thus acting as a high-resolution indicator of iron-rich authigenic and lithogenic particle inputs.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.