Late Quaternary changes in the Westerly Winds over the Southern Ocean

气候变化已被归因于大气中温室气体（如二氧化碳）浓度的增加。这些测量到的大气中二氧化碳的增加在一定程度上受到世界海洋在表面吸收二氧化碳（例如通过扩散和生物泵）与从深海储存库向大气释放旧碳（例如通过上升流和向外气体）的能力变化的控制。在世界各大洋中，（通过模式）已确定南大洋在调节全球大气二氧化碳方面发挥着主要作用，特别是在冰期-间冰期时间尺度上。这是因为表面的营养物质含量很高，表明生物泵对它们的利用不完全，而且由于风驱动的海洋环流变化可以将储存在深海水库中的旧碳带到地面。南半球西风（SHW）强度的变化影响着南大洋环流，并控制着这种富含碳的深水到达海洋表面的量。因此，热带副热带的强度或位置的任何变化，如最近观测到的风的增强，都可能影响南大洋是大气二氧化碳的净源还是净汇。目前，我们对上海西洋线过去变化的认识主要基于南美洲的地质代用记录、南非的一次代用记录和新西兰的两次代用记录。除坎贝尔岛外，对西南偏西风带核心所在的南大洋的西南偏西风变化没有研究。Stager等人（2012）认为，这种空间分辨率的缺乏是我们对过去气候理解的主要限制。因此，尽管目前的大气环流模式使用了多种过程（生物、海洋化学和海洋物理），但它们要么无法产生过去大气CO2变化的幅度，要么与地质现场数据不一致。在此，我们建议通过在南大洋的三个主要板块中分别生成代理记录来大幅提高地质数据的空间分辨率，重点是位于sh - w核心带的亚南极岛屿。我们应用一种新的硅藻代替物来代替由一系列标准沉积学和生物地球化学代替物独立控制的过去风力。新的替代方法是基于海风直接将海水喷雾吹过岛屿，以及它对西海岸湖泊和池塘盐度的影响。这种方法适用于亚南极群岛，那里的水体具有明显的西向东电导率梯度。这种电导率梯度决定了哪些硅藻群落存在于湖泊中。一旦定量建立硅藻与电导率的关系，沉积在放射性碳定年沉积物岩心中的亚化石硅藻群落就可以用来重建电导率随时间的变化，从而重建过去的相对风力。我们已经在麦格理岛证明了这种方法的有效性，我们也在马里恩岛和坎贝尔岛测试了它的可行性。该提案旨在为坎贝尔和马里恩群岛以及合恩角群岛的进一步工作提供资金支持。为了解释我们的数据，我们将利用新的古气候模式比较项目3 (PMIP3) AOGCM（气候模式）模拟，进行一系列的环流模式运行，以探索小海温强度的长期变化及其驱动过程。这些实验将允许对新的代理风强度重建进行全面的模式观测评估。最终，这项工作将有助于为模拟过去风强度变化对深海碳库上涌影响的模式提供改进的边界条件，并提高我们对过去全球大气CO2变化与温度之间关系的理解。

Public summaryClimate changes have been attributed to the increasing concentrations of greenhouse gases (e.g. CO2) in our atmosphere. These measured increases in atmospheric CO2 are partly controlled by changes in the ability of the world's oceans to absorb CO2 at the surface (e.g. via diffusion and the biological pump) versus release of old carbon to the atmosphere from deep ocean reservoirs (e.g. via upwelling and out gassing).Of the world's oceans, the Southern Ocean has been identified (by models) as playing a major role in modulating global atmospheric CO2, particularly on glacial-interglacial timescales. This is because surface nutrients are high indicating their incomplete utilisation by the biological pump, and because wind driven changes in ocean circulation can bring old carbon stored in deep ocean reservoirs to the surface. Changes in the strength of the Southern Hemisphere Westerly Winds (SHW) influence Southern Ocean circulation and control how much of this carbon rich deep water reaches the ocean surface. Thus any change in the strength or position of the SHW such as the recently observed intensification of the winds, could influence whether the Southern Ocean acts as a net source or sink of atmospheric CO2.At present our understanding of past changes in the SHW is based mainly on geological proxy records from South America, one record from South Africa, and two from New Zealand. With the exception of Campbell Island there are no studies of changes in the SHW in the Southern Ocean where the core of the SHW wind belt is located. This lack of spatial resolution has been identified by Stager et al. (2012) as a major limitation in our understanding of past climate. As a result, although present General Circulation Models use a variety of processes (biology, ocean chemistry, and ocean physics), they either fail to produce the magnitude of past atmospheric CO2 variations or do not agree with geologic field data. Here we propose to substantially improve the spatial resolution of the geological data by generating proxy records in each of the three major sectors of the Southern Ocean, focusing on sub-Antarctic islands situated in the core belt of the SHW. We apply a novel diatom proxy for past wind strength independently controlled by a range of standard sedimentological and biogeochemical proxies. The new proxy is based on the direct transfer of sea spray across the islands by wind, and its effect on the salinity of west coast lakes and ponds. This works on sub-Antarctic islands where there is a marked west-east conductivity gradient in water bodies across the island. This conductivity gradient determines which diatom communities are present in the lakes. Once this diatom- conductivity relationship is established quantitatively, the subfossil diatom communities deposited in radiocarbon dated sediment cores can be used to reconstruct changes in conductivity through time, and hence past relative wind strength.We have demonstrated that this approach works at Macquarie Island and we have also tested its feasibility at Marion and Campbell Islands. This proposal is for funding to support further work on Campbell and Marion Islands, and in the Cape Horn archipelago. To interpret our data we will carry out a series of General Circulation Model runs to explore the long term changes in SHW strength and the processes driving them, by taking advantage of the new Paleoclimate Modelling Intercomparison Project 3 (PMIP3) AOGCM (climate model) simulations. These experiments will allow comprehensive model-observation evaluation of the new proxy wind strength reconstructions.Ultimately this work will help provide improved boundary conditions for models which simulate the impact of past changes in wind strength on the upwelling of deep ocean carbon reservoirs, and improve our understanding of the relationship between past changes in global atmospheric CO2 and temperature.