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

海洋中26Al（半衰期0.72 My）和10Be （1.5 My）的源函数和地球化学路径密切相关。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干湿沉降物进入海洋，并通过粒子清除沉积到海底。10Be的清除时间与~103年的海洋混合时间相当，而26Al的清除时间则短约30倍。因此，10Be更容易被输送到高颗粒通量或高生产力的区域，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，恒定的生产比和高颗粒反应性与微分去除-使这两种核素作为一对适合于追踪地球化学和地球物理过程。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比率作为古颗粒通量或古生产力的代理的效用，并利用沉积物岩心中的3He/26Al比率来探索影响地球行星际尘埃颗粒（IDP）通量的因素及其随时间的变化。将对海水、沉积物捕集器材料和沉积物样品以及沉积物岩心中的3He进行10Be和26Al的测量。U-Th同位素、27Al、9Be、蛋白石、碳酸盐和其他化学成分的测量也将在沉积物陷阱和沉积物样品上进行。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及其引起变化的机制。研究颗粒组成和再矿化对沉积10Be/26Al信号的影响，以便更好地约束10Be/26Al代理，并将其应用于赤道太平洋和南极沉积物岩心，以了解地表水高营养低叶绿素特征地区的生产力变化。过去IDP的变化将通过沉积物岩心中3He/26Al和3He/230Th的耦合测量来检验。

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.