Is Atlantic Ocean circulation collapsing?

该项目利用气候模型更好地了解大西洋环流的稳定性和可变性及其对地表气候的控制。科学背景：大西洋环流在调节地球表面气候方面至关重要。通过将相对温暖，咸，浅的赤道水向北输送到高纬度地区，在那里它冷却，下沉并在深处向南返回，这种净环流（称为大西洋经向翻转环流，AMOC）驱动全球规模的洋流在地球周围重新分配热量。我们从过去的地质学中知道，当AMOC较弱时，地球表面会经历几度的强烈冷却，特别是在北方半球，那里会经历特别寒冷和痛苦的冬天。此外，AMOC的快速变化被认为是末次盛冰期（2.1万年前）以来已知发生的突然变暖和变冷事件的原因。所有这些都很重要，因为最近的观测表明AMOC正在变弱，但我们不能确定，因为仪器记录很短（2004年至今）。这些观测结果能用大西洋环流的自然变化来解释吗？或者它们代表着一种更长期的放缓？ 回答这些问题的唯一方法是将联合收割机气候模拟与过去AMOC的记录相结合，从而将观测时间向后延伸，以（i）评估AMOC的可变性和稳定性，以及（ii）找出最近的减弱是否是长期趋势的一部分。然而，对过去没有直接的观察。相反，我们必须从海洋化学的地质记录（称为地球化学示踪剂）中推断出物理海洋环流。在气候模式中包括这些示踪剂，可以直接比较模拟的环流地球化学观测。 项目目标：候选人将把AMOC的地球化学示踪剂纳入快速大气-海洋环流模式（FAMOUS）。使用这个工具，候选人将运行气候模拟，以评估过去的AMOC，并为短期仪器记录提供背景。研究问题的例子：自末次盛冰期（21000年前至今）以来，AMOC的变化是如何变化的？AMOC崩溃需要什么样的作用力，在过去的21000年里它崩溃过吗？AMOC是否存在多个稳定状态？目前大西洋环流有多稳定？[近期]崩溃的风险是什么？这项令人兴奋和新颖的工作提出了我们对气候-海洋相互作用的理解的最严格的测试之一，并将直接挑战地球系统科学中的一些现有范式;例如，大西洋环流可以有多个稳定状态的开创性概念。学生将开发一个非常抢手的，多学科的技能组合，促进发展的跨学科领域的研究是在气候科学的前沿。根据这项工作的性质，并由于其及时性，博士候选人有很大的潜力影响国际研究的方向正在进行这一主题，从而建立一个世界知名的声誉创新科学。

This project uses climate modelling to better understand the stability and variability of Atlantic Ocean circulation and its control on surface climate. SCIENTIFIC BACKGROUND:Atlantic Ocean circulation is vital in regulating Earth's surface climate. By transporting relatively warm, salty, shallow equatorial water north to the high latitudes, where it cools, sinks and returns southwards at depth, this net-circulation (known as Atlantic Meridional Overturning Circulation, AMOC) drives global-scale ocean currents to redistribute heat around the planet. We know from the geological past that when AMOC is weak, Earth's surface undergoes strong cooling of several degrees, particularly in the Northern Hemisphere, which experiences especially cold and bitter winters. Furthermore, rapid changes in AMOC are thought to have been responsible for abrupt warming and cooling events known to have taken place since the Last Glacial Maximum (21 thousand years ago).All of this is important because recent observations suggest that AMOC is getting weaker, but we do not know for sure, because the instrumental record is so short (2004 to present). Could these observations be explained by natural variability in Atlantic circulation? Or do they represent a longer term slowing down? The only way to answer these questions is to combine climate modelling with records of past AMOC, thus extending the observations backwards in time to (i) assess AMOC's variability and stability, and (ii) find out whether the recent weakening is part of a longer term trend. However, no direct observations exist for the past. Instead, we must infer the physical ocean circulation from geological records of ocean chemistry, known as geochemical tracers. Including these tracers in climate models enables the direct comparison of simulated circulation to geochemical observations. PROJECT AIM:The candidate will incorporate geochemical tracers of AMOC to a fast atmosphere-ocean general circulation model (FAMOUS). Using this tool, the candidate will run climate simulations to evaluate past AMOC and provide context for the short instrumental record. EXAMPLES OF RESEARCH QUESTIONS:- How has variability in AMOC changed since the Last Glacial Maximum (21 thousand years ago to present)?- What forcings are required for AMOC to collapse and did it ever collapse in the last 21 thousand years?- Do multiple stable states of AMOC exist?- How stable is current Atlantic Ocean circulation? What is the risk of [near]-future collapse?POTENTIAL FOR HIGH IMPACT RESEARCH:This exciting and novel work presents one of the strictest tests of our understanding of climate-ocean interactions and will directly challenge some of the existing paradigms in Earth System science; for example, the seminal notion that Atlantic Ocean circulation can have multiple stable states. The student will develop a highly sought-after, multidisciplinary skill-set, contributing towards the development of an interdisciplinary field of research that is at the forefront of climate science. By the nature of this work, and due to its timeliness, there is strong potential for the PhD candidate to influence the direction of international research being carried out on this theme, and to thus establish a world-renowned reputation for innovative science.