US GEOTRACES PMT: the geochemistry of size-fractionated suspended particles collected by in-situ filtration

加州大学圣克鲁兹分校的一名研究人员将分析从海洋中收集的海洋颗粒的化学成分。海洋颗粒将沿着美国GEOTRACES太平洋经向样带（PMT）收集两种尺寸，1-51um和51um，该样带将沿着西经152°从阿拉斯加到塔希提岛取样。较小的颗粒通常悬浮在海水中，与海水中的溶解元素相互作用，而较大的颗粒则倾向于下沉，这意味着这些元素可以被运送到海底。我们将测量一系列微量元素（如铁、铝、锌、锰、镉、铜、钴、钛和钡），其中一些是生命所必需的，另一些是海洋过程的示踪剂，以及主要的生物产生的载体相（如颗粒有机碳和生物矿物、碳酸钙和生物二氧化硅），这些颗粒是从美国PMT部分收集的大小分级颗粒中收集的。这些数据将用于评估颗粒浓度、组成和大小分布对微量元素及其同位素（TEIs）循环和去除的相对重要性。研究结果不仅有助于实现GEOTRACES项目的总体目标，而且还将为其他科学界提供关键信息，这些科学界对粒子在通过生物碳泵从大气中吸收碳的过程中所起的作用感兴趣。一名研究生和一名博士后将在这个项目上得到支持和培训，本科生将参与这项工作的几个方面。本研究的结果将被纳入研究者所教授的课堂课程。这位科学家还将与一名科学记者合作，后者将随探险队航行，向公众翻译这项研究的过程和初步结果。颗粒作为多种微量元素和同位素的源和汇，在海洋中微量元素和同位素的循环和分布中起着重要作用。颗粒清除溶解的TEIs是许多颗粒相关TEIs的主要清除术语，但人们对其了解甚少，并且代表了我们对许多TEIs生物地球化学循环的理解的主要不确定性。TEIs的清除受颗粒大小、浓度和组成的影响，而随后通过下沉去除颗粒则受颗粒聚集和分解等颗粒动力学过程的影响。我们将测量在美国GEOTRACES Pacific Meridional样带（PMT）上通过原位过滤收集的大小分级颗粒（1-51um; 51um）的主要（颗粒有机质、碳酸钙、蛋白石、成岩颗粒）和次要（颗粒微量金属）相组成。PMT将是美国GEOTRACES项目的第一个子午线部分，将跨越地表生产力、生物群落组成、地下二氧化硅浓度和方解石饱和层深度的许多梯度。因此，预计美国PMT剖面在颗粒浓度、组成和大小分布方面会发生巨大变化，从而使我们能够研究控制海洋清除效率的因素。

A researcher at the University of California, Santa Cruz will analyze the chemical composition of marine particles collected from the ocean. Marine particles will be collected in two size classes, 1-51um and 51um along the U.S. GEOTRACES Pacific Meridional Transect (PMT), which will sample from Alaska to Tahiti along 152°W. The smaller particles generally remain suspended in seawater, where they can interact with dissolved elements in seawater, whereas the larger particles tend to sink which means these elements can be transported to the bottom of the ocean. We will measure a suite of trace elements (e.g. iron, aluminum, zinc, manganese, cadmium, copper, cobalt, titanium, and barium), some of which are required for life, and others that act as tracers of oceanographic processes, as well as the major biologically-produced carrier phases (e.g. particulate organic carbon and the biominerals, calcium carbonate and biogenic silica) in the size-fractionated particles collected from the US PMT section. The data will be used to assess the relative importance of particle concentration, composition, and size distribution on the cycling and removal of trace elements and their isotopes (TEIs). Results will not only contribute to the overall goal of the GEOTRACES program, but also provide critical information to other science communities interested in the role of particles in sequestering carbon from the atmosphere through a process known as the biological carbon pump. A graduate student and a postdoc will be supported and trained on this project, and undergraduate students will be involved in several aspects of this work. The results from this study will be integrated into class curricula taught by the researcher. The scientist will also work with a science journalist who will sail on the expedition to translate the process and initial results of this research to the public. Particles play essential roles in the cycling and distribution of trace elements and isotopes (TEI) in the ocean by being sources and sinks for many TEIs. The scavenging of dissolved TEIs by particles is a major removal term for many particle-associated TEIs, but is poorly understood and represents a major uncertainty in our understanding of the biogeochemical cycling of many TEIs. The scavenging of TEIs is affected by particle size, concentration, and composition, whereas the subsequent removal of particles by sinking is influenced by particle dynamics processes such as particle aggregation and disaggregation. We will measure the major (particulate organic matter, calcium carbonate, opal, lithogenic particles) and minor (particulate trace metals) phase compositions of size-fractionated particles (1-51um; 51um) collected by in-situ filtration on the the US GEOTRACES Pacific Meridional Transect (PMT). The PMT will be the first meridional section of the US GEOTRACES program and will cross many gradients in surface productivity, biological community composition, subsurface silica concentrations, and depth of the calcite saturation horizon. Therefore, the US PMT section is expected to vary dramatically in particle concentration, composition, and size distribution, allowing us to examine the factors controlling scavenging efficiency in the ocean.