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

加州大学圣克鲁斯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。沿美国地理跟踪太平洋子午线(PMT)从阿拉斯加到塔希提岛(沿152°W)将收集两种大小的海洋颗粒，1-51um和51um。较小的颗粒通常保持悬浮在海水中，在那里它们可以与海水中溶解的元素相互作用，而较大的颗粒倾向于下沉，这意味着这些元素可以被输送到海洋底部。我们将测量一套微量元素(例如铁、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，以及从美国PMT部分收集的粒度分级颗粒中主要的生物产生的载体相(例如颗粒有机碳和生物矿物、碳酸钙和生物成因二氧化硅)。这些数据将被用来评估颗粒浓度、组成和粒度分布对痕量元素及其同位素(TEI)的循环和去除的相对重要性。这些结果不仅将有助于实现GEOTRACES计划的总体目标，还将为其他对颗粒物通过生物碳泵从大气中隔离碳的作用感兴趣的科学界提供关键信息。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。这项研究的结果将被整合到研究人员教授的课堂课程中。这位科学家还将与一名科学记者合作，后者将在探险中航行，向公众翻译这项研究的过程和初步结果。颗粒是许多痕量元素和同位素(TEI)的源和汇，在海洋中痕量元素和同位素的循环和分布中起着至关重要的作用。颗粒对溶解的TEI的清除是许多与颗粒相关的TEI的主要去除术语，但人们对此知之甚少，并且在我们对许多TEI的生物地球化学循环的理解中存在着重大的不确定性。TEI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的过程则受颗粒聚集和解聚等颗粒动力学过程的影响。我们将测量美国地质勘探局太平洋子午线(PMT)上通过现场过滤收集的粒度分级颗粒(1-51um；51um)的主要(颗粒有机物、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计划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，美国PMT部分预计将在颗粒浓度、组成和尺寸分布方面发生巨大变化，使我们能够检查控制海洋清扫效率的因素。

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.