REIMAGINATION: REconstructing and understanding the IMplications of surface 14C AGe changes In the North Atlantic for overturning circulaTION

大西洋的传送带环流是全球气候系统的基本组成部分，将热量从低纬度输送到高纬度，从而使北欧变暖。这种环流的强度在过去被认为是突然变化的，在上一次冰川时期，导致了十年内超过10摄氏度的快速气候变化。今天这种性质的变化会对社会产生严重的影响，所以我们想更多地了解这种流通的敏感性。为了做到这一点，我们将研究过去快速气候和环流变化的间隔。为了更好地了解这些过去的环流变化，我们将重建北大西洋表层和深水中放射性碳的浓度。这被称为放射性碳储集期，它对海洋环流的速度高度敏感。因此，通过重建水库年龄，我们可以判断海洋在快速气候变化期间的循环速度。如果我们想要用放射性碳作为年代测定工具，告诉地质和考古物体和事件的年龄，我们还需要知道过去的储集层年龄。放射性碳可以被认为是地质样品的秒表。然而，对于海洋样本，当我们按下GO时，时钟上已经有一些时间。启动时钟前的这段额外时间是水库年龄，我们必须知道它是什么，才能准确地说出地质时间。因此，通过重建储集层年龄，我们将提高对快速循环和气候变化的理解，并改进地球和考古科学中最重要的测年工具。为了重建放射性碳库年龄，我们需要测量样品的放射性碳含量，并独立知道其年龄，这样我们就可以计算出当样品形成时时钟上已经有什么。为了做到这一点，我们将对取自北大西洋沉积物岩芯的贝壳进行放射性碳测量，并将它们与一系列令人兴奋的新技术配对，这些技术可以确定它们的年龄。首先，我们将在沉积物岩芯中寻找火山灰的层，我们可以用它们的Ar含量来确定年代，并与冰芯和冰岛上的火山灰层进行精确的年代匹配。其次，我们可以观察海洋表面温度记录的变化，并将这些记录与在冰芯中准确测定日期的相同事件进行匹配。第三，我们将使用沉积物中的钍浓度来判断在这些灰分和温度结合点之间积累了多少沉积物。第四，我们将使用统计模型将所有这些信息结合起来，这也将很好地衡量我们结果中的不确定性。这项工作将绘制北大西洋水库年龄以及过去1万到5万年来它们是如何变化的地图，并特别关注快速气候变化的时代。为了帮助我们将水库年龄与不同的环流制度联系起来，我们将使用一个可以模拟放射性碳的气候模型。我们将使这个模型的海洋环流以不同的方式运行，并看看哪种环流最符合我们的数据。这将使我们更好地了解过去海洋环流如何变化导致快速气候变化，并提高对未来海洋环流可能如何运行的信心。最后，我们将把我们的储集层年龄图打包成一个工具，供地球科学家和考古学家使用，以改进他们的放射性碳测年。

The Atlantic Ocean's conveyor belt circulation is a fundamental component of the global climate system, transporting heat from low to high latitudes, and thus warming Northern Europe. The strength of this circulation is thought to have varied abruptly in the past, giving rise to rapid climate changes of more than 10 degrees C in a decade during the last glacial period. Changes of this nature today would have a severe impact on society, so we want to know more about the sensitivity of this circulation. In order to do this, we will study intervals of rapid climate and circulation change in the past. To better understand these past circulation changes we will reconstruct the concentration of radiocarbon in surface and deep waters in the North Atlantic Ocean. This is known as a radiocarbon reservoir age, and it is highly sensitive to the rate of ocean circulation. Therefore, by reconstructing reservoir ages, we can tell how quickly the ocean was circulating during intervals of rapid climate change. We also need to know what the reservoir age was in the past if we want to use radiocarbon as a dating tool, to tell the age of geological and archeological objects and events. Radiocarbon can be thought of as a stopwatch for a geological sample. For a marine sample, however, there is already some time on the clock when we press go. This extra time before starting the clock is the reservoir age, and we must know what it is in order to accurately tell geological time. By reconstructing reservoir ages, we will therefore improve understanding of rapid circulation and climate change, and also improve the most important dating tool used in earth and archeological sciences. To reconstruct radiocarbon reservoir ages we need to measure the radiocarbon content of a sample, and also to know its age independently, so we can work out what was already on the clock when the sample formed. To do this we will make radiocarbon measurements on shells taken from sediment cores from the North Atlantic, and pair them with a range of exciting new techniques that can tell their age. Firstly we will look for layers of volcanic ash in the sediment cores, which we can date using their argon content, and match to precisely dated ash layers in ice cores and on Iceland. Secondly we can look at changes in sea surface temperature records, and match these to the same events that are precisely dated in ice cores. Thirdly we will use the concentration of thorium in sediments to tell how much sediment accumulated between these ash and temperature tie points. Fourthly, we will combine all this information using statistical modelling, which will also provide a good measure of the uncertainty in our results. This work will create maps of reservoir ages and how they changed in the North Atlantic over the last 10 to 50 thousand years, with a special focus on times of rapid climate change. To help us link the reservoir ages to different circulation regimes, we will use a climate model that can simulate radiocarbon. We will make this model's ocean circulation operate in different ways, and see which circulations best match our data. This will allow us to better understand how ocean circulation changed in the past to cause rapid climate change, and improve confidence in how ocean circulation may operate in the future. Finally, we will package our reservoir age maps into a tool that can be used by earth scientists and archeologists to improve their radiocarbon dating.