Constructing a tephrochronology framework for the last interglacial - glacial transition

自然档案，如来自海洋和湖泊的冰芯和沉积物记录，为过去气候和环境变化的模式提供了相当多的证据。对这些记录的详细调查对于提高我们对自然气候事件的理解至关重要，特别是因为人类活动被认为正在改变全球气候系统。最后一个暖期，特别是间冰期（10万多年前）是理解当前暖期结束时可能导致地球冰川化的机制、时间和环境反应的最接近的模拟。然而，重建过去气候事件的顺序和时间受到较大的定年误差和缺乏合适的定年技术的阻碍。因此，匹配和比较来自海洋、大陆和冰盖的气候记录以了解环境对气候事件的反应是有问题的。火山灰是实现同步和直接比较不同自然档案的关键工具。火山爆发后，火山灰的瞬时沉积和扩散通常发生在大面积的地理区域，这些被合并为不同自然档案中的不同标志层。近年来，人们已经清楚地认识到，这些火山灰沉积物实际上可以追溯到数千公里外的火山源头，因此，这为自然档案的精确关联提供了一种关键技术。一份详细的记录或框架，给出过去火山喷发的年龄和化学成分，对于成功地应用这一技术至关重要。唯一具有必要的时间分辨率和独立的年代控制来提供这一信息的档案是格陵兰冰盖。这个档案可能包含来自附近的火山灰沉积物，如冰岛，甚至更远的来源，如阿拉斯加或低纬度火山。从格陵兰冰盖内的这些来源追踪火山事件，将使他们能够精确地确定冰在年层中积累的年代。然而，由于冰芯材料中存在的低浓度灰烬，这些层往往无法用肉眼识别。然而，这些视界可以通过分析冰本身的化学特征来探测。将采用一种特殊的技术，利用这些化学数据，精确定位并提取12.3万至7万年前冰芯物质中的火山灰颗粒。每一层的地球化学分析将提供每次喷发的指纹，以确定其火山来源，并建立与其他地质记录中确定的同一矿床的联系。除了传统的地球化学技术（电子探针）提供9种化学元素外，将采用一种新的方法来提供额外的30种化学元素。这项技术还没有被用来分析冰芯中包含的一些小的火山颗粒，但是有可能促进火山来源的具体识别和火山灰沉积物的区分。构建这样一个框架将提供最后一次间冰期结束和最后一次寒冷期开始期间火山活动的时间和频率的详细记录。该方案将对自然档案的精确关联，以比较气候事件的时间和环境响应在地球历史上的关键时刻在广泛分离的地方具有长期意义。更好地了解自然气候事件的模式确实有助于我们预测在当前暖期结束时可能出现的事件的可能触发因素和顺序。

Natural archives, such as ice-cores and sediment records from the oceans and lakes provide considerable evidence for the pattern of past climatic and environmental changes. Detailed investigations of such records are fundamental for improving our understanding of natural climatic events particularly as human activities are thought to be altering the global climate system. The last warm episode or interglacial period in particular, (over 100,000 years ago) serves as the closest analogue for understanding the mechanisms, timing and environmental responses that may lead to a glaciated Earth at the end of the current warm episode. Reconstructing the sequence and timing of past climatic events, however, is hampered by large dating errors and the lack of suitable dating techniques. Matching and comparing climatic records from the oceans, continents and ice-sheets in order to understand the environmental responses to climatic events are therefore problematic. A key tool for enabling the synchronisation and direct comparison of different natural archives is volcanic ash. Instantaneous deposition and dispersal of volcanic ash following an explosive eruption often occurs over large geographical areas and these are incorporated as distinct marker layers within different natural archives. In recent years, it has become clear that these ash deposits can actually be traced over thousands of kilometres from volcanic sources, therefore, providing a key technique for the precise correlation of natural archives. A detailed record or framework giving the age and chemical composition of past volcanic eruptions is essential for the successful employment of this technique. The only available archive with the necessary temporal resolution and independent dating control to provide this information is the Greenland ice-sheet. This archive is likely to contain ash deposits from nearby sources such as Iceland and even more distal sources such as Alaska or low-latitude volcanoes. Tracing volcanic events from such sources within the Greenland ice-sheet will enable their precise dating as the ice accumulates in annual layers. More often than not, however, these layers cannot be identified with the naked eye due to the low concentration of ash present in the ice-core material. These horizons however, can be detected through analysis of the chemical signature of the ice itself. A specially-adopted technique will be applied to use these chemical data to pinpoint and extract volcanic ash particles within the ice-core material between 123,000 and 70,000 years ago. Geochemical analysis of each layer will provide a fingerprint of each eruption to identify its volcanic source and to establish links to the same deposit identified in other geological records. In addition to the traditional geochemical technique (electron microprobe) that provides 9 chemical elements, a new method will be employed to provide an additional 30 chemical elements. This technique has as yet, not been used to analyse some of the small volcanic particles contained within the ice-core - but has the potential to advance the specific identification of volcanic sources and differentiation of volcanic ash deposits. Constructing a framework of this kind will provide a detailed record of the timing and frequency of volcanic activity during the end of the last interglacial and the beginning of the last cold episode. This scheme will be of long-term significance for the precise correlation of natural archives to compare the timing of climatic events and the environmental responses in widely separated localities at a critical time in the Earth's history. A better understanding of the pattern of natural climatic events will indeed assist us to predict the likely triggers and sequence of events that may be looming at the end of the current warm episode.