Climate Change and the Oceans

我提出的研究涉及地球气候系统中的两个基本反馈过程/大气CO2浓度和海洋环流强度。反馈过程放大了由地球围绕太阳的轨道变化等因素造成的气候外部强迫。这两个过程在现代气候系统中发挥着重要作用，但它们在过去的作用，特别是它们在未来气候变化中的预测作用是不确定的。这一建议的主要目的是通过重建这两个系统在过去关键时刻的行为来减少这种不确定性。拟议研究的第一部分涉及大气中二氧化碳的浓度。CO2是一种重要的温室气体，因此大气CO2的量的变化被认为对地球气候具有重要的控制作用。事实上，在过去的250万年里，地球的气候在极冷时期（称为冰期）和相当温暖的时期（像今天这样的间冰期）之间振荡。重要的是，气候的这些波动伴随着大气CO2浓度（pCO 2）的变化。冰盖增减的总驱动力是地球绕太阳轨道的微妙变化，这影响到高纬度地区接收到的太阳辐射的数量和季节分布。CO2浓度的变化可能会全球化并增强这种轨道强迫。负责改变pCO 2的确切机制尚不清楚，但可能涉及海洋（地球上最大的碳储存库，可以以足够快的速度做出反应）。为了研究这一作用，我建议产生一个记录过去的海洋酸度（pH值）在海洋的各种敏感地区使用硼同位素组成的浮游和底栖有孔虫（钙质单细胞原生生物，是常见的整个海洋，并保存在深海沉积物）。由于海洋的酸度在很大程度上决定了二氧化碳分压，我将能够从这个记录中确定二氧化碳在冰盖变大和变小的过程中是如何从深海储存和释放的，并可能分离出它在导致从一种气候状态转变到另一种气候状态中的作用。这一建议的第二部分涉及海洋环流。赤道从太阳接收更多的热量，比两极更热，正是这种温度梯度驱动了海洋（和大气）环流。海洋环流的大西洋部分是环流系统中特别重要和敏感的部分。在这里，墨西哥湾流将温暖的咸水从低纬度带到北大西洋。然后这些沃茨冷却，热量散失到大气中，密度变大（含盐的冷水比新鲜的温水密度大），结果下沉。然后，它们在深处向南流动，形成对流单体的返回臂。这种环流模式释放的热量不仅对改善欧洲海洋气候很重要，而且可以通过确定海冰形成的北冰洋的水温来影响地球的整体气候。海冰具有高度的反射性，更多的海冰会导致更多的太阳能量被反射回太空，从而影响全球温度。这种环流模式在未来气候情景中的作用是不确定的;减少这种不确定性的一种方法是检查地质学过去的海洋环流。我建议使用一种新的分析技术，涉及铁锰结壳（金属结壳，沉淀非常缓慢地从海水深处）的激光显微取样重建的强度和模式的循环在过去的气候显着冷（在冰川时期）和温暖比今天（上新世中期）。

The research I propose concerns two fundamental feedback processes within the Earth's climate system / the concentration of atmospheric CO2 and the circulation strength of the oceans. Feedback processes amplify any external forcing of the climate caused by, for example, variations in the Earth's orbit around the sun. Both processes play important roles in the modern climate system, yet their roles in the past, and in particular, their predicted roles in future climate change are uncertain. It is the principal aim of this proposal to reduce this uncertainty by reconstructing the behaviour of these two systems at key times in the past. The first part of the proposed research concerns the concentration of carbon dioxide in the atmosphere. CO2 is an important greenhouse gas such that variations in the amount of atmospheric CO2 are thought to have an important control on the Earth's climate. Indeed, over the last 2.5 million years the climate of the Earth has oscillated between periods of extreme cold (called glacial periods) and comparable warmth (interglacial periods like today). Importantly, these swings in climate have been accompanied by changes in the concentration of atmospheric CO2 (pCO2). The overall driving force for the waxing and waning of ice sheets are subtle variations in the orbit of the Earth around the sun, which influence the amount and seasonal distribution of solar radiation received at high latitudes. Variations in the concentrations of CO2 probably globalise and enhance this orbital forcing. The exact mechanisms responsible for altering pCO2 are not known but probably involve the oceans (the largest store of carbon on the planet that can respond with sufficient rapidity). In order to examine this role, I propose to generate a record of past ocean acidity (pH) in a variety of sensitive areas of the ocean using the boron isotopic composition of planktic and benthic foraminifera (calcareous single celled protists that are common throughout the ocean and are preserved in deep sea sediments). Since the acidity of the ocean largely determines pCO2, I will be able, from this record, to identify how CO2 is stored and released from the deep sea during the waxing and waning of the ice sheets and potentially isolate its role in causing the transitions from one climate state to another. The second part of this proposal concerns the circulation of the oceans. The Equator, which receives more heat from the sun, is hotter than the poles, and it is this temperature gradient that drives ocean (and atmospheric) circulation. The Atlantic portion of ocean circulation is a particularly important and sensitive part of the circulation system. Here, the Gulf Stream carries warm, salty water from the low latitudes to the North Atlantic. These waters then cool, lose heat to the atmosphere and become dense (salty cold water is denser than fresh warm water) and, as a result, sink. They then flow southward at depth, forming the return arm of the convection cell. The release of heat by this mode of circulation is not only important in ameliorating the climate of maritime Europe, but it can influence the overall climate of the planet by determining the water temperature in the Artic seas, where sea-ice forms. Sea-ice is highly reflective and more sea-ice results in more of the Sun's energy being reflected back into space, and hence can influence global temperature. The role of this circulation pattern in future climate scenarios is uncertain; one way to reduce this uncertainty is to examine ocean circulation in the geological past. I propose to use a new analytical technique, involving the laser microsampling of ferromanganese crusts (metallic encrustations that precipitate very slowly from seawater at depth) to reconstruct the strengths and patterns of circulation in the past when the climate was significantly colder (during glacial periods) and warmer than today (the Mid-Pliocene).