SGER: Determining Equatorial Upwelling Rates with a Novel Geochemical Tracer Technique

在探索项目中，研究人员提议开发一种基于同位素铍7的新同位素技术，以推断沿赤道的上升流速度。2009年4月，由美国国家科学基金会资助的前往赤道东大西洋的研究邮轮将收集铍7样本。邮轮轨道是拟议研究的理想之地。将占用赤道以外的几个站进行多次混合层测量，并在冷舌区域上升流区内进行铍7的几个剖面，主要集中在东经5°至西经10°之间的区域。铍7剖面将与CTD站利用研究人员开发的成熟技术同时收集。需要检验的关键假设是，观测到的混合层铍7浓度是上升流速度的一个极其敏感的指标。铍7的两个性质使其成为研究上升流的理想示踪剂。首先，它的来源功能和水柱分布(混合层和次混合层深度之间的高对比度)使其成为上升流的敏感指标。其次，它的特征时间尺度足够长，足以积分几周内的上升流，但仍然对季节性时间尺度的变化敏感，不像示踪剂有明显更长的半衰期。上升流是影响全球海洋内气候动力学和生物地球化学循环的一个重要物理过程。由于涉及的速度相对较小，直接测量上升流是困难的，因此必须通过示踪剂观测提供的间接方法来推断。如果成功，这种方法将为海洋学界提供一个重要的示踪工具。这些发现将被纳入合作调查员教授的本科生和研究生课程。

In the exploratory project, the investigators propose to develop a novel isotopic technique, based on the isotope Beryllium 7, to infer rates of upwelling along the equator. Beryllium 7 samples will be collected on an NSF-funded research cruise to the equatorial eastern Atlantic in April, 2009. The cruise track is ideal for the proposed study. Several stations away from the equator will be occupied to make numerous mixed layer measurements and several profiles of Beryllium 7 within the areas of upwelling in the cold tongue region, focusing primarily on the region between 5°E and 10°W. The Beryllium 7 profiles will be collected simultaneously with the CTD stations using well established techniques developed by the investigators. The key hypothesis to be tested is the idea that the observed mixed layer Beryllium 7 concentration is an extremely sensitive indicator of the upwelling rate. Two properties of Beryllium 7 make it an ideal tracer for investigation of upwelling. First, its source function and water column distribution (high contrast between mixed layer and sub-mixed layer depth) allow it to be a sensitive indicator of upwelling. Secondly, its characteristic time scale is long enough to integrate upwelling over periods of weeks but still be sensitive to variations on seasonal timescales, unlike tracers with significantly longer half-lives.Broader Impacts. Upwelling is an important physical process affecting climate dynamics and biogeochemical cycling within the global ocean. Direct measurements of upwelling are difficult because of the relatively small velocities involved, and it must therefore be inferred by indirect methods such as those provided by tracer observations. If successful, this method will provide an important tracer tool to the oceanographic community. The findings will be incorporated into undergraduate and graduate courses that the co-investigator teaches.