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

大西洋的输送带环流是全球气候系统的一个基本组成部分，它将热量从低纬度输送到高纬度，从而使北欧变暖。这种环流的强度被认为在过去发生了突然变化，在最后一个冰期的十年内导致了10摄氏度以上的快速气候变化。今天这种性质的变化将对社会产生严重影响，所以我们想更多地了解这种循环的敏感性。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。为了更好地理解这些过去的环流变化，我们将重建北大西洋表层和深海中放射性碳的浓度。这被称为放射性碳储集年龄，它对海洋环流的速度非常敏感。因此，通过重建水库年龄，我们可以知道在快速气候变化期间海洋的循环速度有多快。如果我们想用放射性碳作为测年工具，告诉地质和考古物品和事件的年龄，我们还需要知道过去水库的年龄。放射性碳可以被认为是地质样本的秒表。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了。在开始计时之前的这个额外时间就是储层年龄，我们必须知道它是什么，以便准确地判断地质时间。因此，通过重建水库年龄，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。为了重建放射性碳储层的年龄，我们需要测量样品的放射性碳含量，也需要独立地知道它的年龄，这样我们就可以计算出样品形成时钟上已经有什么了。为此，我们将对从北大西洋沉积物岩心中提取的贝壳进行放射性碳测量，并将其与一系列令人兴奋的新技术相结合，以确定它们的年龄。首先，我们将在沉积物岩心中寻找火山灰层，我们可以使用它们的氩含量来确定年代，并将其与冰芯和冰岛的精确年代的火山灰层相匹配。其次，我们可以观察海洋表面温度记录的变化，并将这些变化与冰芯中精确确定年代的相同事件相匹配。第三，我们将利用沉积物中钍的浓度来判断在这些灰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，这也将为我们的结果中的不确定性提供一个很好的衡量标准。这项工作将绘制出北大西洋水库年龄的地图，以及它们在过去的1万到5万年里是如何变化的，特别关注气候快速变化的时期。为了帮助我们将水库的年龄与不同的循环制度联系起来，我们将使用一个可以模拟放射性碳的气候模型。我们将让这个模型的海洋环流以不同的方式运行，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的变化是如何引起快速气候变化的，并提高对未来海洋环流如何运作的信心。最后，我们将把我们的储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定年法。

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.