Role of ocean eddies in glacial cycles

冰期周期约为10万年，是地球近代地质史上最大的气候变化。然而，虽然冰期旋回被认为是由地球轨道参数的变化驱动的，但我们对气候系统如何设法放大辐射强迫的细微变化，使其进入冰和沉积物岩心中记录的大冰期旋回，仍然知之甚少。在冰期和间冰期之间，大气中的二氧化碳水平增加了约50%，从而作为一种温室气体放大了辐射强迫。这种额外碳的主要来源是海洋，特别是环流和分层的变化，因为碳在较冷的水中更容易溶解，化学反应也更强烈。最近的模拟研究表明，全球海洋分层对南大洋的涡流特别敏感。这个项目的目的是研究漩涡在冰川循环中的作用。我们研究的新颖之处在于，我们提出了一个范围广泛的数值实验，我们将整合长达5000年的时间，这足以使海洋与它的强迫和明显的湍流涡场达到平衡。这代表了一个主要的计算挑战，因为漩涡发生在几十公里的尺度和几个月的时间尺度上。为了达到必要的计算效率，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，在南方有一个重新进入的通道，代表南大洋。我们称这种模型为“涡流解析盒模型”。我们的关键假设是，风的力量、潮汐的力量（导致内部波浪的破裂和混合）、海面温度、海冰覆盖和大陆架过程的变化，都可以改变南大洋的环流和结构，并与涡旋场协同作用，使温度层上下移动。如果温度表面上升，那么由于溶解度和化学反应性的增加，海洋的碳储存能力就会增加，而且由于海洋的碳含量大约是大气的50倍，这可能足以解释在冰期和间冰期之间观测到的大气二氧化碳增加。我们将使用涡解析盒模型进行广泛的数值实验，以研究风强迫、潮汐强迫、海面温度、海冰覆盖和陆架过程对大气CO2的单独和综合贡献。

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.