Is Atlantic Ocean circulation collapsing?

该项目使用气候模拟来更好地了解大西洋环流的稳定性和可变性及其对表层气候的控制。科学背景：大西洋环流对调节地球表面气候至关重要。这种净环流(称为大西洋子午线翻转环流，AMOC)通过将相对温暖、含盐的浅赤道水向北输送到高纬度，在那里冷却、下沉并向南返回，从而驱动全球范围的洋流在地球周围重新分配热量。我们从过去的地质中了解到，当AMOC较弱时，地球表面会经历几度的强烈降温，特别是在经历了特别寒冷和寒冷的冬天的北半球。此外，AMOC的快速变化被认为是自上一次冰盛期(21000年前)以来已知的突然变暖和冷却事件的原因。所有这一切都很重要，因为最近的观察表明AMOC正在减弱，但我们不确定，因为仪器记录如此之短(2004年至今)。这些观察结果可以用大西洋环流中的自然变化来解释吗？或者，它们代表了一种更长期的放缓？回答这些问题的唯一方法是将气候模拟与过去AMOC的记录结合起来，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较长期趋势的一部分。然而，过去并不存在直接的观测。取而代之的是，我们必须从海洋化学的地质记录中推断出海洋的物理循环，这种化学记录被称为地球化学示踪剂。在气候模型中加入这些示踪剂，可以直接将模拟的环流与地球化学观测进行比较。项目目的：候选者将把AMOC的地球化学示踪剂纳入快速大气-海洋环流模式(FANAME)。使用这个工具，候选人将运行气候模拟来评估过去的AMOC，并为简短的仪器记录提供背景。研究问题的例子：-自上一次冰盛期(21000年前至今)以来，AMOC的变异性发生了怎样的变化？-AMOC需要什么压力才能崩溃，在过去的21000年里它曾经崩溃过吗？-AMOC存在多种稳定状态吗？-当前大西洋环流的稳定性如何？[不久]未来崩塌的风险是什么？高影响研究的潜力：这项令人兴奋和新颖的工作对我们对气候-海洋相互作用的理解提出了最严格的考验之一，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种稳定状态的开创性概念。该学生将发展非常受欢迎的、多学科的技能，为发展处于气候科学前沿的跨学科研究领域做出贡献。根据这项工作的性质和及时性，这位博士候选人有很大的潜力影响正在进行的关于这一主题的国际研究的方向，从而在创新科学方面建立世界知名的声誉。

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.