Role of ocean eddies in glacial cycles

冰川周期约为10万年，是地球近代地质史上最大的气候变化。然而，尽管冰川循环被认为是由地球轨道参数的变化驱动的，但我们仍然对气候系统如何设法将辐射强迫的微妙变化放大到记录在冰和沉积物芯中的大型冰川循环中的理解非常有限。大气中的二氧化碳水平在冰期和间冰期之间增加了约50%，因此作为温室气体放大了辐射强迫。这些额外碳的主要来源是海洋，特别是循环和分层的变化，因为碳在较冷的水中更易溶解和化学反应。最近的模拟研究表明，全球海洋分层对南大洋的涡旋特别敏感。该项目的目的是研究涡旋在冰川循环中的作用。我们研究的新颖之处在于，我们提出了一系列广泛的数值实验，我们将整合长达5,000年，这足以使海洋与其强迫达到平衡，并具有明确的湍流涡流场。这代表了一个主要的计算挑战，因为涡流发生在数十公里的尺度和数月的时间尺度上。为了实现必要的计算效率，我们将在一个简化的海洋域中工作，跨越经度20度和纬度120度，向南有一个代表南大洋的折返通道。我们称这个模型为“涡流分辨箱模型”。我们的主要假设是，风强迫，潮汐强迫，导致打破内波和混合，海面温度，海冰覆盖，和货架过程的变化都可以修改南大洋的环流和结构，并与涡流场，移动温度层向上或向下。如果温度表面上升，那么由于溶解度和化学反应性的增加，海洋的碳储存能力增加，并且由于海洋也含有大约50倍于大气的碳，这可能足以解释观测到的冰期和间冰期之间大气CO2的增加。我们将进行广泛的数值实验与我们的涡解箱模式，调查风强迫，潮汐强迫，海面温度，海冰覆盖，和货架过程对大气CO2的单独和组合的贡献。

Glacial cycles, with periods of about 100,000 years, represent the largest variations in climate in the recent geological history of the earth. However, while glacial cycles are believed to be driven by variations in the earth's orbital parameters, we still have a very poor understanding of how the climate system contrives to amplify subtle changes in radiative forcing into the large glacial cycles that are recorded in ice and sediment cores. Atmospheric CO2 levels increase by about 50% between glacial and interglacial periods, thus acting as a greenhouse gas to to amplify the radiative forcing. The prime suspect for the source of this additional carbon is the ocean, and in particular changes in circulation and stratification, since carbon is more soluable and chemically reactive in colder water. Recent modelling studies suggest that the global ocean stratification is particularly sensitive to eddies in the Southern Ocean. The aim of this project is to investigate the role of eddies in glacial cycles. The novel aspect of our study is that we propose a wide range of numerical experiments we will integrate for up to 5,000 years, which is sufficient for the ocean to come into equilibrium with its forcing, and with an explicit turbulent eddy field. This represents a major computational challenge since eddies occur on scales of tens of kilometers and time scales of months. In order to achieve the necessary computational efficiencies, we will work in a simplified ocean domain, spanning 20 degress in longitude and 120 degrees in latitude, with a re-entrant channel to the south representing the Southern Ocean. We term this model an 'eddy-resolving box model'. Our key hypothesis is that changes in wind forcing, tidal forcing which leadings to breaking internal waves and mixing, sea surface temperatures, sea ice cover, and shelf processes can all modify the circulation and structure of the Southern Ocean and, in concert with the eddy field, move the temperature layers up or down. If the temperature surfaces rise, then the carbon storage capacity of the oceans increases, due to increased solubility and chemical reactivity, and since the ocean also holds roughly 50 times as much carbon as the atmosphere, this may be sufficient to explain the observed atmospheric CO2 increase between glacial and interglacial periods. We will perform a wide range of numerical experiments with our eddy resolving box model to investigate the individual and combined contributions of the wind forcing, tidal forcing, sea surface temperatures, sea ice cover, and shelf processes on atmospheric CO2.