Collaborative Research: Vertical gradients in Southern Ocean Radiocarbon across the major climate transitions of the last 30,000 years

南大洋在确定大气二氧化碳变异性和深海碳储量方面具有不成比例的影响，因为它是一个既有上升流又有深水形成的区域。因此，人们投入了相当大的努力来了解南大洋的条件和过程，这些条件和过程最终导致了最后一个冰河时期大气中二氧化碳的减少。放射性碳原则上是这一时期海洋/大气碳循环的最具诊断性的示踪剂。然而，现有的南大洋放射性碳数据在时间和空间上仍然有限，同时还存在一些基本的不确定性，使我们无法对上一个冰河期的碳循环得出确凿的结论。这个项目涉及一个协调的计划，对过去3万年来南大洋海洋变化的三个不同档案进行放射性碳测量。这些档案包括海洋沉积物序列和深海珊瑚样本，旨在捕捉表层、中层和深水碳循环对气候强迫的响应。该计划的目标是扩展现有的放射性碳测量，同时直接解决目前限制现有放射性碳观测应用的一些主要不确定性。该项目将作为一个自然的平台，让代表性不足的学生参与STEM学科，并将包括从当地社区学院和州立大学招募的本科生和硕士水平的学生。更具体地说，该项目包括：(1)在莫桑比克外海新获得的沉积物序列（IODP Site U1477）中进行浮游生物-底栖有孔虫放射性碳年龄测量，具有极高的分辨率；该区底栖有孔虫放射性碳变化监测了亚南极表层海洋的放射性碳变化；二)。从塔斯马尼亚岛附近的中等水深处收集的一组深海珊瑚样本中的u系列/放射性碳年龄对；在这一系列样品中表达的放射性碳变率旨在与莫桑比克有孔虫序列进行直接比较；（iii）南大西洋深海沉积序列中现有的（但尚未确定的）浮游生物-底栖有孔虫年龄深度对的扩展；这些地点的底栖有孔虫放射性碳变化应反映经向翻转环流（MOC）的深部分支。其目的是提供新的观测结果，这些观测结果将作为气候强迫和碳循环之间关系模型的直接测试，这些观测结果本身和通过释放现有测量的潜力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Southern Ocean holds disproportionate influence in setting atmospheric CO2 variability and carbon storage in the deep ocean because it is a region featuring both upwelling and deep-water formation. Consequently, considerable effort has been devoted to understanding the Southern Ocean conditions and processes that ultimately led to lower atmospheric CO2 during the last ice age. Radiocarbon is in principle the most diagnostic tracer for ocean/atmosphere carbon cycling over this time period. However, the existing body of radiocarbon data for the Southern Ocean is still limited temporally and spatially, while also suffering from some essential uncertainties that preclude firm conclusions about carbon cycling during the last ice age. This project involves a coordinated program of radiocarbon measurements in three distinct archives of Southern Ocean oceanographic change that span the last 30,000 years. These archives, including both marine sediment sequences and deep-sea coral samples, are located so as to capture the surface, intermediate and deep-water carbon cycle response to climate forcing. The objective of this program is to extend existing radiocarbon measurements while also directly resolving some of the principal uncertainties that currently limit the application of existing radiocarbon observations. The program will serve as a natural platform for engagement of underrepresented students to STEM disciplines and will include undergraduate and masters-level students recruited from local community colleges and state universities.More specifically, the project includes i.) planktonic-benthic foraminiferal radiocarbon age measurements in a newly acquired sediment sequence off Mozambique (IODP Site U1477) that features exceptionally high resolution; the bottom water at this location is recently ventilated water subducted just south of the Subtropical Convergence, and, therefore, the benthic foraminiferal radiocarbon variability monitors that of the sub-Antarctic surface ocean; ii.) U-series/radiocarbon age pairs in a set of deep-sea coral samples collected from intermediate water depths off Tasmania; the radiocarbon variability expressed in this series of samples is intended as a direct comparison to that of the Mozambique foraminiferal sequence; iii.) extension of existing (but not yet definitive) planktonic-benthic foraminiferal age depth pairs in abyssal South Atlantic sedimentary sequences; the benthic foraminiferal radiocarbon variability at these sites should reflect the deep branch of the Meridional Overturning Circulation (MOC). The intention is to provide new observations that, both on their own and by unlocking the potential of existing measurements, will serve as direct tests of models of the relationship between climate forcing and carbon cycling.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.