Studies Related to Establishing a Valid Radiocarbon Ventilation Rate for the Glacial Ocean

确定海洋通气率在最后一次冰期和非冰期期间的变化，对于重建与地球气候重大变化有关的全球海洋环流变化至关重要。在这个项目中，哥伦比亚大学拉蒙特-多尔蒂地球天文台的研究人员将试图解决研究这些现象的科学家所面临的一些主要问题。该项目的主要目标是利用同时代的浮游(表层栖息)和海底(海底栖息)有孔虫的放射性碳年龄来确定比现在早21,000-14,000年的深水时代。为此，有必要对来自不同深度和地点的样品进行多个放射性碳测年。最近的工作表明，由于沉积柱内存在次生碳酸盐相，某些岩心位置可能不适合进行精确的放射性碳测年。该项目的第二个主题是调查这些阶段的存在，如果可能的话，确定哪些地点最终对确定海洋通气率是或多或少有效的。这一目标将通过对已知产生异常~(14)C年龄的样品进行溶解实验来实现，目的是单独分离不同的相并确定其年代。将通过使用Lohmann(1995)开发的有孔虫壳重指标重建深海碳酸盐离子浓度的变化来研究碳储存和海洋环流的变化。该项目的另一个目标将是利用陆基证据调查在最后一次冰期结束和冰川消融期间发生的事件的相对时间。这项工作将基于冰川特征的精确测年和冰川末期消退留下的冰雹的暴露测年。广泛的影响：这项研究应该回答有关全球气候变化的一些基本问题--冰川时期的海洋环流有多大不同，以及海洋环流的变化对过去的气候有何影响。这些研究的结果将为古和未来的气候模型提供重要的制约因素。

ABSTRACTOCE-0435703Determining how ocean ventilation rates changed during the last glacial and deglacial periods is fundamental to reconstructing global changes in ocean circulation related to major shifts in the Earth's climate. In this project, researchers at the Lamont-Dougherty Earth Observatory of Columbia University will attempt to resolve some of the major problems that have confronted scientists studying these phenomena.The main objective of the project is to use radiocarbon ages from contemporaneous planktonic (surface dwelling) and benthic (bottom dwelling) foraminifera to define the age of deep waters over the period 21,000 - 14,000 14C years before the present time. To this end it will be necessary to make multiple radiocarbon dates on samples from various depths and locations. Recent work has suggested that some core locations may be unsuitable for precise radiocarbon dating due to the presence of secondary carbonate phases forming within the sediment column. A second theme of this project is to investigate the presence of these phases and if possible, determine which sites are ultimately more or less valid for determining ocean ventilation rates. This goal will be addressed by carrying out dissolution experiments on samples that are known to yield anomalous 14C ages, the aim being to isolate and date individually the different phases. Changes in carbon storage and ocean circulation will be investigated by reconstructing changes in deep sea carbonate ion concentrations using the foraminiferal shell weight proxy developed by Lohmann (1995). A further aim of the project will be to use land-based evidence to investigate the relative timing of events occurring at the close of the last glacial period and during deglaciation. This work will be based on precise dating of glacial features and exposure dating of moraines left by retreating glaciers at the end of glacial times.Broader impacts: This study should provide answers to some fundamental questions concerning changes in global climate -- how different was ocean circulation during glacial time and how, if at all, have changes in ocean circulation affected climate in the past. The results from these studies will provide important constraints for paleo- and future climate models.