沉积物-水界面流固相互作用及铁的传输机制

铁(Fe)是海洋浮游植物赖以生长的关键痕量营养元素。地质年代中大洋Fe输入量的波动，调控着冰期-间冰期大气CO2浓度的变化。边缘海沉积物-水界面流体与固体的相互作用(简称流固相互作用)及Fe传输，是大洋Fe输入的关键过程之一，其定量解析是海洋底部边界层理论和大洋“铁假说”面临的最重要挑战。本项目聚焦重点资助方向之(四)“西太平洋流固与海气界面物质能量交换过程”，通过铀、钍系天然放射性同位素(224Ra/228Th、234Th/238U等)不平衡手段，结合底部边界层的流场观测，在厘米级的微观尺度上准确解析沉积物-水界面流体交换和湍动能耗散的内在关联，建立定量表征二者关系的动力方程；精准量化Fe的界面通量及迁移机制，进而探究Fe在海底雾状层的传输。项目的实施，可望实现底部边界层流固相互作用由定性到定量研究的跨越，构建海洋底部边界层的新理论框架。

Iron (Fe) is an essential micronutrient for marine phytoplankton. Changes in Fe supply to the ocean are suggested to be an important driver for the glacial/interglacial cycles in atmospheric carbon dioxide concentration in the geological past. Fluid-solid interactions at the sediment-water interface in the marginal seas and subsequent transport of Fe in the Benthic Nepheloid Layer are an important pathway of Fe input into the open ocean. Accurate quantification of these processes, however, is a major challenge in the field of Earth Science. In this project, we propose to utilize the 224Ra/228Th disequilibrium method to quantify fluid exchange rate and benthic Fe flux across the sediment-water.interface in the marginal seas adjacent to the West Pacific Ocean. In conjunction with measurements of the flow field in the Benthic Boundary Layer (BBL), we will set out to establish a mechanistic relation of turbulent kinetic dissipation rate and fluid exchange flux at the sediment-water interface. In addition, we will use the naturally occurring 234Th/238U isotope pair to investigate particle scavenging rate of dissolved Fe in the Benthic Nepheloid Layer. In the meantime, vertical transport of dissolved Fe in the overlying water column will be quantified using the radium quartet (223Ra, 224Ra, 226Ra, and 228Ra) in conjunction with a one-diemsional diffusion/advection model. The accomplishment of this project will finally lead to the establishment of the framework of a novel theory of the BBL.