He Isotopic Composition of Micrometeorites as a Tool for Evaluating Sedimentation Rates

9402019安德森宇宙尘埃微粒在太阳系内部旅行时，由于其表面积与体积的比例，它们会获得大量的惰性气体。当这些粒子进入地球大气层时，那些足够小的粒子以宇宙速度进入地球大气层而不会受到侵蚀，被称为微陨石，并保留了它们的稀有气体，包括氦。微型陨石不仅具有高氦浓度，而且它们的3He/4He比值也非常高，比陆源物质高出几个数量级。微陨石最终沉入海底，在那里它们与其他沉积物混合。该项目将使用大量沉积物中氦的浓度和同位素组成作为衡量沉积物中微陨石浓度的指标。如果地质历史上微陨石向地球的通量保持不变，那么它们在沉积物中的浓度可以用来定量地评价沉积速率和不同沉积组分的通量以及这些通量随时间的变化。这项研究将检验这样的假设，即微陨石到沉积物的通量随着时间的推移保持不变，并且沉积物中的微陨石在感兴趣的时间尺度上保持其氦。如果成功，这种方法将把我们观察高分辨率沉积速率的能力扩大到数百万年。

9402019 ANDERSON During their travel in the inner solar system, fine cosmic dust particles acquire large amounts of noble gases owing to their surface to volume ratio. When these particles enter the earth's atmosphere, those sufficiently small to enter the earth's atmosphere at cosmic velocities without suffering ablation, are called micrometeorites and retain their noble gases, including He. Not only do the micrometeorites have high He concentrations, but they also have very high 3He/4He ratios, several orders of magnitude above that of terrigenous materials. The micrometeorites eventually settle down to the bottom of the ocean where they are mixed with other sediments. This project will use the bulk sediment He concentration and isotopic composition as a measure of micrometeorite concentration in the sediments. If the flux of micrometeorites to the earth has remained constant in geological past, then their concentration in sediments can be used to quantitatively evaluate sedimentation rates and the fluxes of different sedimentary components and changes in these fluxes through time. This research will test the assumptions that the flux of micrometeorites to the sediments have stayed constant over time and that the micrometeorites in sediments retain their He for time-scales of interest. If successful, this approach will expand our ability to look at high resolution sedimentation rates to millions of years.