Modelling North Atlantic's Heinrich events and associated impacts on the Earth System

未来的气候变化涉及陆地、海洋、冰冻圈和大气中物理过程之间复杂的相互作用。此外，按照所有自然标准，预测下个世纪的变化可能是“迅速的”。为了对冰-海洋-大气-生物圈系统未来行为模式的预测有信心，根据过去地球系统的快速变化对模式进行测试和评估是有价值的。虽然对未来的变化没有直接的类似物，但过去的快速事件使我们能够研究模型模拟响应过程、反馈和时间尺度的能力。过去的气候行为记录在冰芯、海洋沉积物芯、洞穴和湖泊沉积物以及地貌地貌中。从这些数据可以看出，在长时间尺度上（冰期至间冰期，100 kyr）存在明显的气候循环，在千年时间尺度上（1.5 kyr - 16 kyr周期）存在更快速的变化。一种快速变化是北大西洋周围冰盖上的冰山大量释放，正如水柱变新鲜和海洋沉积物岩心内冰筏碎片（IRD）沉积增加（海因里希事件）所表明的那样。地球系统对这些快速变化的反应几乎是瞬时的，从格陵兰岛的冰芯中可以发现气温几乎同步变化，这强调了气候对北大西洋淡水强迫的敏感性。通过植被的变化观察到进一步的反馈，表明不仅温度变化，而且降水也在变化。在这些时期，全球冰川的移动支持了全球变冷的信号。同时，非洲西海岸的上升流增强，表明南大西洋信风的强度增加。虽然这些数据告诉我们与海因里希事件相关的地球系统变化的时间和空间格局，但需要数值模式来量化与这些短期气候振荡相关的重要过程。数值模拟已经被用来揭示北大西洋变冷对全球气候的重要性，然而，这些海因里希事件的许多方面仍然在很大程度上无法解释。第一，引发冰盖涌动并产生大量冰山的机制。其次，在海洋记录中观测到的沉积物在远距离上由冰山运输的模式。第三，气候系统中存在的反馈和遥相关，产生了与这些事件相关的同步和非同步全球信号的大量证据。本项目旨在通过使用新开发的全耦合GCM来解决这些问题，该GCM包括详细的全动态大气-海洋模型，结合冰盖模型、植被模型和碳循环模型。该模型包括同位素表示，可以离线耦合到粉尘和甲烷排放模型。该模型将用于研究与海因里希事件和相关地球系统变化相关的机制和时间。了解地球系统内的这些过程和反馈，并能够将模拟结果与这些过去气候事件的数据进行比较，将使我们有信心使用这些模型来预测地球系统未来的响应。

Future climate change involves complex interactions between physical processes on land, in the ocean, in the cryosphere, and in the atmosphere. Moreover, by all natural standards the changes predicted over the next century are likely to be 'rapid'. To have confidence in the predictions of models for the future behaviour of the ice-ocean-atmosphere-biosphere system, it is valuable for models to be tested and evaluated against past rapid Earth System changes. Although there are no direct analogues for future change, past rapid events allow us to investigate the ability of models to simulate the processes, feedbacks and time scales of response. Past climate behaviour is recorded within ice cores, marine sediment cores, cave and lake deposits and in geomorphological land forms. From these data there are clear climate cycles both on long time scales (glacial to interglacial, 100 kyr) and more rapid variations on millennial time scales (1.5 kyr - 16 kyr periods). One type of rapid variation is the massive release of icebergs from the ice sheets surrounding the North Atlantic, as indicated by freshening of the water column and increased deposition of Ice Rafted Debris (IRD) within marine sediment cores (Heinrich events). The Earth system response to these rapid changes are nearly instantaneous, with near synchronous changes in air temperature identified from ice cores in Greenland, emphasizing the sensitivity of the climate to freshwater forcing in the North Atlantic. Further feedbacks are observed through changes in vegetation, indicating changes in not only temperature but also in precipitation. Advances of glaciers across the globe at these times support a global cooling signal. While enhanced upwelling along the West coast of Africa points towards an increase in the strength of the South Atlantic trade winds. While these data tell us the timing and spatial pattern of Earth system changes associated with Heinrich events, numerical models are required to quantify the important processes related to these short term climate oscillations. Numerical modelling has already been used to reveal the importance of freshening of the North Atlantic to global climate, however, a number of aspects of these Heinrich events remain largely unexplained. Firstly, the mechanism for the trigger of ice sheet surging that produces the large number of icebergs. Secondly, the mode within which sediment is transported by the icebergs over the large distances observed within the marine records. Thirdly, the feedbacks and teleconnections which exist within the climate system that produces the wealth of evidence of both synchronous and asynchronous global signals associated with these events. This project aims to address these issues by using a newly developed fully coupled GCM which includes a detailed fully dynamic atmosphere-ocean model, combined with an ice sheet model, a vegetation model and a carbon cycle model. The model includes isotopic representation and can be coupled offline to dust and methane emission models. The model will be used to investigate the mechanisms and timings associated with the Heinrich events and associated Earth system changes. Understanding these processes and feedbacks within the Earth system and being able to compare the modelled results to the data of these past climatic events will give us confidence in using these models to predict future responses of the Earth system.