Collaborative Research: Lead-210 and Polonium-210 as tracers for scavenging and export: GEOTRACES Pacific Meridional Section

国际GEOTRACES计划的目标是了解微量化学元素及其同位素在海洋中的分布。这些化学物质在海洋中发挥着重要作用，如营养物质、当前和过去海洋过程的示踪剂以及人类活动造成的污染物。它们的地球化学循环对碳循环、气候变化和海洋生态系统等不同领域的研究有直接影响。该项目将使用两种天然放射性核素-铅-210和钋-210-的测量，以提供有关影响微量元素和同位素（TEI）的过程速率的重要信息，这些信息将在2018年美国GEOTRACES考察期间在太平洋进行测量。这里提出的研究将解决GEOTRACES科学计划内制定的关键任务。海洋中的许多过程无法直接观测到，但诸如钋-210（半衰期= 138天）和铅-210（半衰期= 22.3年）等示踪剂具有独特的化学性质和相关的衰变时间尺度，可以用来对它们的速率和途径提供重要的限制。本研究的目标是：1）使用Pb-210，沿着另一个测量Be-7的项目，在气溶胶和降水中表征气溶胶和TEI源，2）使用Po-210和Pb-210确定颗粒反应性TEI通过水柱的清除率，（3）以上层水体中Po-210 / Pb-210不平衡作为颗粒有机碳（POC）沉降通量的替代指标，（4）以Pb-210为示踪剂，研究了热液作用对TEIs水柱分布的影响。这项工作将建立在通过GEOSECS，GEOTRACES和独立研究等项目获得的世界海洋（特别是太平洋）Po/Pb分布数据库的基础上。作为该项目的一部分，将培训一名研究生。首席研究员Cochran计划通过他在美国自然历史博物馆（纽约）的兼职任命，将有关GEOTRACES采样策略的信息纳入“海洋”巡回展览的规划中。项目合作伙伴Kadko计划通过日本基金会全球海洋观测伙伴关系卓越中心将GEOTRACES的工作纳入国际研究生课程。

The goal of the international GEOTRACES program is to understand the distributions of trace chemical elements and their isotopes in the oceans. These chemical species play important roles in the ocean as nutrients, tracers of current and past oceanographic processes, and as contaminants from human activity. Their biogeochemical cycling has direct implications for research in such diverse areas as the carbon cycle, climate change, and ocean ecosystems. This project will use measurement of two natural radionuclides -- lead-210 and polonium-210 -- to provide important information about the rates of processes that affect trace elements and isotopes (TEIs) that will be measured during a U.S. GEOTRACES expedition in the Pacific Ocean in 2018. The research proposed here will address key tasks formulated within the GEOTRACES Science Plan. Many processes in the ocean cannot be observed directly but tracers such as polonium-210 (half-life = 138 days) and lead-210 (half-life = 22.3 years) that have unique chemical properties and relevant decay timescales can be used to provide important constraints on their rates and pathways. The goals of this research are to: 1) use Pb-210, along with another project measuring Be-7, in aerosols and precipitation to characterize aerosol and TEI sources, 2) determine scavenging rates of particle-reactive TEIs through the water column using Po-210 and Pb-210, 3) use Po-210 / Pb-210 disequilibrium in the upper water column as a proxy for the sinking flux of particulate organic carbon (POC), and 4) use Pb-210as a tracer of the influence of hydrothermal processes on water column distributions of TEIs. This work will build on a database of Po/Pb distributions in the world ocean (and the Pacific Ocean, in particular) obtained through programs such as GEOSECS, GEOTRACES, and independent studies. A graduate student will be trained as part of this project. The lead investigator, Cochran, plans to incorporate information about GEOTRACES sampling strategies in the planning for a travelling exhibition on "The Oceans" through his adjunct appointment at the American Museum of Natural History (New York). Project partner Kadko plans to incorporate GEOTRACES work in an international graduate course through the Nippon Foundation, Partnership for Observation of the Global Oceans Center of Excellence.