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CO2变化和深海碳储存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，人们付出了相当大的努力，以了解南大洋的条件和过程，最终导致较低的大气CO2在最后一个冰河时期。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，南大洋现有的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，无法对上一个冰河时期的碳循环得出确切的结论。该项目涉及一个协调的放射性碳测量计划，在过去3万年的南大洋海洋变化的三个不同档案中进行测量。这些档案包括海洋沉积物序列和深海珊瑚样本，其定位是为了记录表层、中层和深水碳循环对气候强迫的反应。该计划的目标是扩展现有的放射性碳测量，同时也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。该计划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生。在莫桑比克（IODP站点U1477）新获得的沉积物序列中进行的南极-底栖有孔虫放射性碳年龄测量具有非常高的分辨率;该位置的底层水是最近在亚热带辐合带以南俯冲的通风水，因此，底栖有孔虫放射性碳变化监测亚南极表层海洋; ii.）U系列/放射性碳年龄对在一组深海珊瑚样本收集从中间水深处关闭塔斯马尼亚;放射性碳的变化表示在这一系列的样品是作为一个直接的比较，莫桑比克有孔虫序列; iii.）在南大西洋深海沉积序列中，现有的（但尚未确定的）深海-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）的深层分支。其目的是提供新的观测结果，无论是通过自身还是通过释放现有测量的潜力，都将作为气候强迫和碳循环之间关系模型的直接测试。该奖项反映了NSF的法定使命，并被认为值得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来支持。

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.