Studies of 26Al and 10Be as Potential Constraints on Paleoproductivity and Extraterrestrial Influx

海洋中~(26)Al(半衰期0.72My)和~(10)Be(~(1.5)My)的来源功能和地球化学途径密切相关。这些放射性同位素主要是由宇宙射线与大气成分相互作用产生的，它们以几乎恒定的比例通过湿散落和干散落进入海洋，并通过颗粒清除作用沉积到海底。10Be的清除时间相当于103年的海洋混合时间，而26Al的清除时间大约短30倍。因此，10Be更容易被输送到粒子通量高或生产率高的地区，如海洋边缘，在那里10Be/26Al的沉积比远远高于它们的生产比。这些特征--相对稳定的源函数，恒定的产生率，以及具有差异去除的高粒子反应性--使这两种核素成为一对适合于追踪地球化学和地球物理过程的核素。在这个项目中，南加州大学的研究人员将评估沉积物中10Be/26Al比率作为古粒子通量或古生产力的替代指标的实用性，以及利用沉积物岩心中的3He/26Al比率来探索影响地球结合星际尘埃粒子(IDP)通量及其随时间变化的因素。10Be和26Al将在海水、沉积物捕集物和沉积物样品以及沉积物岩心中的3He样品中进行测量。还将对沉积物捕集器和沉积物样品进行U-Th同位素、27Al、9Be、蛋白石、碳酸盐和其他化学成分的测量。所获得的数据将用于研究10Be和26Al的分布和通量的时空变化以及引起这些变化的机制。将研究颗粒组成和再矿化对沉积10Be/26Al信号的影响，以更好地约束10Be/26Al替代信号，该替代将应用于赤道太平洋和南极的沉积岩心，以了解以地表水高营养和低叶绿素为特征的地区的生产力变化。沉积岩芯中3He/26Al和3He/230Th的耦合测量将检验IdP的过去变化。

ABSTRACTOCE-0117895The source functions and geochemical pathways of 26Al (half-life 0.72 My) and 10Be (1.5 My) in the sea are closely linked. These radioisotopes, produced mainly by the interaction of cosmic rays with the atmospheric constituents, enter the ocean via wet and dry fallout with a nearly constant ratio and deposit to the seafloor through particle scavenging. The scavenging time of 10Be is comparable to the ocean mixing time of ~103 years,but that of 26Al is about 30 times shorter. As a consequence, 10Be is more readily transported to areas of high particle flux or high productivity such as ocean margins, where the deposition ratio of 10Be/26Al becomes much higher than their production ratio. These features -relatively stable source function, constant production ratio,and high particle reactivity with differential removal -render the two nuclides as a pair suitable for tracing geochemical and geophysical processes.In this project, researchers at the University of Southern California will evaluate the utility of the 10Be/26Al ratio in sediments as a proxy for paleo-particle flux or paleoproductivity, and the use of the 3He/26Al ratio in sediment cores to probe the factors affecting the flux of earth-bound interplanetary dust particles (IDP) and its variation with time. Measurements of 10Be and 26Al will be carried out on samples of seawater, sediment-trap material, and sediment, and of 3He in sediment cores. Measurements of U-Th isotopes, 27Al, 9Be, opal, carbonates and other chemical components will also be made on sediment trap and sediment samples. Data so obtained will be used to study the spatial and temporal variations in the distribution and flux of 10Be and 26Al and the mechanisms causing the variations. The influence of particle composition and remineralization on the sedimentary 10Be/26Al signals will be investigated to constrain better the 10Be/26Al proxy which will be applied to sediment cores from the equatorial Pacific and the Antarctic to provide an understanding of the productivity changes in areas characterized by high-nutrients and low-chlorophyll of the surface water. Past variations in IDP will be examined by the coupled measurements of 3He/26Al and 3He/230Th in sediment cores.