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

海洋中的碳和营养物质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，但海洋内质量和能量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，新产量的地球化学估计需要正确的混合层和上层温跃层之间混合的参数，但这一地区的输送过程还没有完全了解。在这个项目中，迈阿密大学的研究人员将继续研究7Be(半衰期=53.3d)，作为上层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宝贵工具，填补了通过使用短寿命(天)和长寿命(年)示踪剂而获得的知识空白。7Be是一种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。这种核素在辐射衰变之前穿透上层温跃层的程度将部分取决于垂直混合和平流过程的强度。然而，混合层深度的季节变化模型表明，在温跃层中发现的7Be大部分是先前混合层中的残留物。这意味着，在知道混合层的深度历史和大气输入的情况下，7Be的剖面可以用来阐明输运性质。这项研究将在百慕大时间序列站进行，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7Be在一年中的分布。这些信息，结合混合层的季节发展模式，将被用来评估上层温跃层的混合。这些结果将反过来应用于溶解物种的剖面(作为BATS时间序列的一部分同时测量)，如营养物、O2和DOC，以估计它们跨越混合层-温跃层边界的输送。在更广泛的影响方面，该项目将有助于BATS站点正在进行的研究，同时对混合层和上层温跃层之间的质量-能量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，该项目将为一名应届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(“海洋过程的追踪者”)，作为说明性的个案研究。

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.