The bi-polar seesaw and CO2: Is there anything special about 'Terminal seesaw events'?

近年来出现了一种解释晚更新世冰期-间冰期气候转变的新范式。根据这一范式，不再明确区分在“轨道”和“千禧年”时间尺度上运行的机制。因此，冰河时代缓慢的轨道(日晒)步调将产生强烈的正反馈，而正反馈本身可能出现在更短的时间尺度上。大气二氧化碳的冰期-间冰期波动是这一概念的象征；它们显然对冰期-间冰期辐射强迫做出了重要贡献，但它们似乎是通过与不对称的半球间气候异常(“两极拉锯”)有关的快速变化而累积的。然而，并不是所有大气二氧化碳的快速变化都与冰期-间冰期的转变有关。这提出了一个重要的问题：过去是什么控制了千禧年的二氧化碳变化，以及去冰期和中期的二氧化碳脉冲有什么特别之处(如果有的话)。目前的数据不允许我们充分解决这些问题。需要的是一套新的南大洋上升流和深水通风的高分辨率重建，它可以与冰芯年代学联系起来，从而与北大西洋气候突变的类似详细记录相比较。这个项目旨在提供这些重建，并因此将我们对过去千年二氧化碳变异性的理解建立在比迄今可能的更强有力的观测基础上。

A new paradigm has emerged in recent years for explaining late Pleistocene glacial-interglacial climate transitions. According to this paradigm, a clear distinction between mechanisms that operate on 'orbital' and on 'millennial' timescales is no longer made. The slow orbital (insolation) pacing of the ice-ages would thus engender strong positive feedbacks, which could themselves emerge on much shorter timescales. Glacial-interglacial fluctuations in atmospheric CO2 are emblematic of this notion; they clearly make an important contribution to glacial-interglacial radiative forcing, but they appear to accrue through rapid changes that are somehow linked with asymmetric inter-hemispheric climate anomalies (the 'bipolar seessaw'). However, not all rapid changes in atmospheric CO2 are associated with glacial-interglacial transitions. This raises the important question of what has controlled millennial CO2 changes in the past, and what (if anything) is special about deglacial versus mid-glacial CO2 pulses. Current data does not allow us to address these questions adequately. What is needed is a new set of high-resolution reconstructions of Southern Ocean up-welling and deep-water ventilation, which can be linked to the ice-core chronology and thus compared with similarly detailed records of abrupt North Atlantic climate variability. This project sets out to provide these reconstructions, and on thus place our understanding of past millennial CO2 variability on a more robust observational footing than has hitherto been possible.