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

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。这些化学物质在海洋中扮演着重要的角色，它们是营养物、当前和过去海洋过程的示踪剂，以及人类活动产生的污染物。它们的生物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具有直接意义。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（TEIs）的过程速率的重要信息，这些过程将于2018年在太平洋进行的美国GEOTRACES考察期间测量。这里提出的研究将解决GEOTRACES科学计划中制定的关键任务。海洋中的许多过程不能直接观察到，但具有独特化学性质和相关衰变时间尺度的示踪剂，如钋-210（半衰期= 138天）和铅-210（半衰期= 22.3年），可用于对其速率和途径提供重要限制。本研究的目标是：1)利用Pb-210以及另一个测量气溶胶和降水中Be-7的项目来表征气溶胶和TEI源；2)利用Po-210和Pb-210确定颗粒反应性TEI通过水柱的清除速率；3)利用上层水柱中的Po-210 / Pb-210不平衡作为颗粒有机碳（POC）下沉通量的代表；4)利用Pb-210作为热液过程对TEI水柱分布影响的示踪剂。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。首席研究员科克伦计划通过他在美国自然历史博物馆（纽约）的兼职工作，将GEOTRACES取样策略的信息纳入“海洋”巡回展览的计划中。项目合作伙伴Kadko计划通过日本基金会全球海洋卓越观察中心伙伴关系将GEOTRACES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.