GEOTRACES Arctic section: Application of 210Po and 210Pb distribution at contrasting interface regimes of Western Arctic

在这个项目中，参加2015年美国北极GEOTRACES考察队的一组调查人员将研究自然存在的放射性同位素铅-210和钋-210在北冰洋西部和中部的分布。预计这些测量将非常有助于实现美国北极GEOTRACES考察的目标：即确定控制海洋中关键微量元素和同位素分布的过程和量化通量，并确定这些分布对不断变化的环境条件的敏感性。有些微量元素是生命所必需的，有些是已知的生物毒素，还有一些很重要，因为它们可以用作海洋中各种物理、化学和生物过程的示踪剂。海洋中铅-210的主要来源是大气，它是由氡-222衰变产生的。在海洋中，它衰变成钋-210。钋-210的半衰期（138天）和铅-210的半衰期（22.3年）提供了“自然时钟”，用来研究诸如元素在下沉粒子上的吸附以及元素在海洋边缘和深海盆地之间的运输等过程。首席研究员建议在三个“界面”集中采样和调查过程：表面的空气-海冰界面，生物产生的颗粒和水之间的界面，以及非生物颗粒和水之间的界面。研究者提出了以下三个假设：1)在海气界面，钋-210/铅-210的比值可以用来测定海冰（以及冰内沉积物）的“年龄”。2)在生物-水界面，上层水体中遇到的不同生物源颗粒类型会影响钋-210和铅-210的分选和再矿化深度。3)在颗粒-水界面处，水柱中的重悬浮沉积物层将成为从周围水体中强化清除钋和铅的区域。这些过程对于了解其他关键颗粒反应性微量元素（如铁、铅和锰）的分布非常重要。为了验证这些假设，研究人员将沿着GEOTRACES北极西部剖面取样并分析大约400个溶解和颗粒（大大小小的）样本、10个多年冰芯、浮冰沉积物和融化池中的水，以检测钋-210和铅-210。大约一半的样品将集中在四个指定的“超级站”，其中一半位于高度动态的上层水柱中，另一半靠近海底，底部沉积物的再悬浮会影响元素循环。深度将根据区域大气输入、生态系统以及与测量其他微量元素和同位素的小组协调取样来选择。其余的样本将是冰芯、融化池的水、海冰中的浮冰沉积物和大气气溶胶样本。拟议的工作将与其他GEOTRACES密切协调。更广泛的影响与GEOTRACES项目作为一个整体密切相关，以加强(1)研究基础设施，为生物地球化学清除模型提供广泛的钋-210和铅-210数据，(2)指导研究生和本科生进行教育，通过实例教学；从提议的研究，（3)代表性不足的学生参与地球科学的职业生涯，(4)海洋放射化学毕业生的研究培训，以及5）通过出版物，演讲和专门的公共韦恩州立大学网站（www.clas.wayne.edu）和GEOTRACES （www.geotraces.org）广泛传播结果。

In this project, a team of investigators participating in the 2015 U.S. Arctic GEOTRACES expedition will study the distribution of the naturally-occurring radioactive isotopes lead-210 and polonium-210 in the western and central Arctic Ocean. These measurements are expected to be very useful in helping to meet the goals of the U.S. Arctic GEOTRACES expedition: namely, to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes (TEIs) in the ocean, and to establish the sensitivity of these distributions to changing environmental conditions. Some trace elements are essential to life, others are known biological toxins, and still others are important because they can be used as tracers of a variety of physical, chemical, and biological processes in the sea. A primary source of lead-210 to the oceans is from the atmosphere, where it is produced from the decay of radon-222. In the oceans, it decays to polonium-210. The half-lives of polonium-210 (138 days) and lead-210 (22.3 years) provide "natural clocks" with which to investigate processes such as the sorption of elements on to sinking particles, and the transport of elements between the ocean margins and deep basins.The lead investigator proposes to concentrate sampling and investigate processes at three "interfaces:" the air-sea-ice interface at the surface, the interface between biologically produced particles and water, and the interface between non-biological particles and water. The investigator proposes the following three hypotheses: 1) At the air-sea interface, the polonium-210/lead-210 ratios can be used to "age date" the sea ice (and sediments contained within the ice). 2) At the biotic-water interface, different biogenic particle types encountered in the upper waters will affect the fractionation and remineralization depths of polonium-210 and lead-210. 3) At the particle-water interface, layers of resuspended sediments in the water column will be zones of enhanced polonium and lead scavenging from the surrounding waters. These processes are important for understanding the distributions of other key particle-reactive trace elements such as iron, lead, and manganese. To test these hypotheses, the investigator will sample and analyze about four hundred dissolved and particulate (large and small) samples, 10 multi-year ice cores, ice-rafted sediments, and water from melt ponds for polonium-210 and lead-210 along the GEOTRACES Western Arctic section. About half of the samples will be focused at the four designated "super stations", with half of these in the highly dynamic upper water column and the other half near the sea floor where resuspension of bottom sediments can affect element cycling. The depths will be chosen according to regional atmospheric input, ecosystems, and coordinated sampling with groups measuring other trace elements and isotopes. The remainder of the samples will be ice cores, water from melt ponds, ice-rafted sediments in sea ice, and atmospheric aerosol samples. The proposed work will be closely coordinated with other GEOTRACES. The broader impacts are closely linked to the GEOTRACES program as a whole to enhance (1) research infrastructure by providing a broad array of polonium-210 and lead-210 data useful for biogeochemical scavenging models, (2) education by mentoring graduate and undergraduates, teaching by example
from proposed research, (3) participation of under-represented students careers in the geosciences, (4) research training of graduates in marine radiochemistry, and 5) broad dissemination of results through publications, presentations, and on dedicated public Wayne State University websites (www.clas.wayne.edu) and at GEOTRACES (www.geotraces.org).