Evaluation of Mixed Layer-Upper Thermocline Interaction and Geochemical Transport using 7Be

海洋中碳和营养物的流动受到物理混合和生物过程之间复杂联系的控制。特别是，需要充分了解混合过程，以平衡系统内的地球化学通量，但质量和能量在海洋内转移的方式仍然是海洋科学中更具挑战性的问题之一。例如，对新生产的地球化学估计需要对混合层和上部温跃层之间的混合进行正确的参数化，但对这一区域的输送过程还没有完全了解，在这一项目中，迈阿密大学的研究人员将继续研究7Be（半衰期= 53.3天）作为上部温跃层输送过程的示踪剂。因此，它是研究季节性时间尺度上发生的混合过程的一个有价值的工具，填补了使用短寿命（天）和长寿命示踪剂（年）所获得的知识空白。 7Be是宇宙射线产生的放射性核素，通过降雨沉积在海洋表面，并混合在表面混合层中。这种核素在放射性衰变之前穿透上部温跃层的程度将部分取决于垂直混合和平流过程的强度。混合层深度的季节性变化的模型表明，然而，大多数的7Be中发现的温跃层是残留的，包含在以前的混合层。这意味着，与知识的深度历史的混合层和大气输入，配置文件的7Be可以用来阐明运输性能。这项研究将在百慕大的时间序列站进行，这将使研究小组能够跟踪混合层的演变，测量输入函数，并跟踪全年的7Be分布。这一信息与混合层季节性发展模型相结合，将用于评估上部温跃层的混合情况。这些结果将反过来被应用到配置文件（同时作为最佳可行技术时间序列的一部分测量）的溶解物种，如营养物质，O2和DOC，以估计其运输跨越混合层温跃层边界。就更广泛的影响而言，该项目将有助于在最佳技术服务站进行的研究，同时对混合层和上层温跃层之间的质能相互作用产生重要的新见解，从而引起更广泛的海洋学界的兴趣。此外，该项目将为新的研究生提供部分支持。 这项研究的结果将很容易纳入研究生课程（“海洋过程示踪剂”），作为一个说明性的案例研究。

The flux of carbon and nutrients within the ocean is controlled by complex linkages between physical mixing and biological processes. In particular, adequate understanding of mixing processes is required to balance geochemical fluxes within the system, but the manner in which mass and energy are transferred within the ocean remain one of the more challenging issues in ocean science. For example, geochemical estimates of new production require correct parameterization of mixing between the mixed layer and upper thermocline, but transport processes in this region are not completely understood.In this project, investigators at the University of Miami will continue studies of 7Be (half-life = 53.3 d) as a tracer of transport processes in the upper thermocline. As such, it is a valuable tool for studying mixing processes that occur over a seasonal timescale and fills a gap in knowledge gained from the use of short-lived (days) and long-lived tracers (years). 7Be is a cosmic ray produced radioactive nuclide and is deposited upon the ocean surface by rainfall and is mixed within the surface mixed layer. The extent to which this nuclide penetrates the upper thermocline before it decays radioactively will depend in part on the strength of vertical mixing and advective processes. Models of the seasonal changes in the mixed layer depth indicate however that most of the 7Be found in the thermocline is remnant of that contained in previous mixed layers. The implication is that with knowledge of the depth history of the mixed layer and atmospheric input, profiles of 7Be can be used to elucidate transport properties. This study will be done at the time-series station in Bermuda, which will allow the research team to follow the evolution of the mixed layer, measure the input function, and track the 7Be distribution over the course of the year. This information, combined with models of the seasonal development of the mixed layer, will be used to assess mixing in the upper thermocline. These results will in turn be applied to profiles (measured concurrently as part of the BATS time-series) of dissolved species such as nutrients, O2 and DOC to estimate their transport across the mixed layer-thermocline boundary. In terms of broader impacts, this project will contribute to on-going studies at the BATS site while yielding important new insights into the mass-energy interaction between the mixed layer and upper thermocline, thereby being of interest to the wider oceanographic community. Additionally, the project will provide partial support for a new graduate student. Results from this study will readily be incorporated into a graduate course ("Tracers of Oceanographic Processes") as an illustrative case-study.