Changes in ocean circulation and the global carbon cycle during the last interglacial-glacial transition: Marine Isotope Stage 5a to 4

最后一个冰期被北半球气候中反复出现的千年尺度的高振幅变化所打断，这种变化被称为Dansgaard-Oeschger （D-O）振荡。这些事件的特点是冷暖交替极为迅速，格陵兰岛和欧洲西北部的温度上升有时在几十年内超过10摄氏度。D-O振荡的发现为气候研究提供了重大刺激，并引发了对未来气候变化可能性质的争论，但对这些事件的起源知之甚少。海洋环流是地球气候系统的一个基本组成部分。众所周知，环流的变化与全球气候的重大变化有关，包括冰期-间冰期转变以及更快速的事件，如D-O振荡。大约75,000年前，从最后一个间冰期（类似于今天）过渡到完全的冰期，大陆冰盖大量堆积，大气中二氧化碳含量减少。这一时期也首次出现了D-O气候变率，表明在末次间冰期的相对稳定和冰期的不稳定之间的一个临界阈值已经跨越。然而，关于海洋环流在不断演变的气候系统中的作用及其此时的明显阈值行为，目前存在着根本的不确定性。该项目将调查MIS 5a/4过渡期间大西洋环流的变化及其在全球气候变化中的作用。该项目将提高我们对海洋环流和气候变化之间联系的理解，因此将为相关领域的科学家和潜在的决策者提供信息。将对取自北大西洋的五个沉积物岩心分别进行古气候重建，覆盖东部和西部盆地的中深水。利用养分分布和碳化学指标重建MIS 5a/4期间的深海化学结构演变，利用动力古环流指标评估海底洋流速度和质量体积输运的物理变化。将重建结果与冰芯记录和绝对定年的洞穴沉积物进行直接的时间关联，将有助于建立极其可靠的年龄模型，这对于研究重建变化与其他气候相关参数（如冰量和大气二氧化碳）之间的潜在线索和滞后至关重要。来自南大洋大西洋/印度区的一个地核将产生进一步的环流代理记录。这将为海洋环流变化和全球碳循环之间的相对时间提供明确的证据。作为该项目的一部分所产生的数据将为区分地球气候系统在向完全冰川条件过渡和冰川气候不稳定开始期间的关键物理和化学变化提供关键约束。

The last glacial period was punctuated by repeated, high-amplitude millennial-scale shifts in northern hemisphere climate known as Dansgaard-Oeschger (D-O) oscillations. These events were characterised by the extremely rapid alternation between cold and warmer conditions with temperature increases over Greenland and NW Europe sometimes exceeding 10 degrees Celsius within a few decades. The discovery of D-O oscillations has provided a major stimulus for climate research and fuelled debate over the possible nature of climate change in the future, yet very little is known about the origin of these events. Ocean circulation is a fundamental component of Earth's climate system. Changes in circulation are known to be associated with major shifts in global climate, including glacial-interglacial transitions as well as more rapid events such as D-O oscillations. The transition from the last interglacial period (similar to today) to full glacial conditions, around 75,000 years ago, saw a large build-up of continental ice sheets and a decrease in atmospheric CO2. This period also saw the first appearance of D-O climate variability, suggesting that a critical threshold, between the relative stability of the last interglacial and the instability of glacial times, had been crossed. However, fundamental uncertainties currently exist concerning the role of ocean circulation within the evolving climate system and its apparent threshold behaviour at this time. This project will investigate changes in Atlantic Ocean circulation and their role in global climate change during the MIS 5a/4 transition. The project will improve our understanding of the links between ocean circulation and climate change and will therefore inform scientists working in related fields and potentially policy makers. Palaeoclimate reconstructions will be made on each of five sediment cores taken from the North Atlantic, covering both east and west basins in intermediate and deep waters. Proxies for nutrient distribution and carbon chemistry will be used to reconstruct the evolving deep ocean chemical structure during MIS 5a/4 while dynamical palaeocirculation proxies will enable assessment of physical changes in bottom current speed and mass volume transport. Direct temporal correlation of the reconstructions with records from ice cores and absolutely dated cave deposits will enable the development of extremely robust age models, vital for investigation of potential leads and lags between the reconstructed changes and other climate relevant parameters such as ice volume and atmospheric CO2. A further circulation proxy record will be produced from a core from the Atlantic/Indian sector of the Southern Ocean. This will provide unambiguous evidence for the relative timing between changes in ocean circulation and the global carbon cycle. The data produced as part of this project will provide critical constraints for differentiating between key physical and chemical changes in Earth's climate system during the transition to full glacial conditions and the onset of glacial climate instability.