Pinpointing abrupt climate change in Patagonia using tephrochronology and improved age modelling

重建过去的气候变化对于理解地球气候的自然变异性，特别是过去变化的幅度、时间和速率至关重要。为了成功地实现这些目标，重要的是要从一个广泛的全球网络中定量地评估过去的变化，并确保所有记录都准确地确定日期。这将允许在区域之间进行精确的比较，以便测试空间和时间变化的模型。北半球的数据集符合这些标准，尽管定量的古气候数据仍然相对稀缺。这些数据，尤其是定量数据，来自南半球的数据甚至更少，尽管我们正在收集这样一个数据集，涵盖了过去~2万年的气候变化，从巴塔哥尼亚约47度。这些数据包括详细的摇蚊（不咬人的蠓）和稳定的同位素记录，这些记录将根据仪器数据进行校准，以及沉积学，地球化学，花粉和宏观化石数据。这些数据将构成该地区过去气候变化的详细、定量重建。然而，在某种程度上，每一个古气候记录都只能与它的年代控制一样准确，如果这些记录很差，那么其他记录之间的比较误差就会大大增加。为了在该地区产生一个非常高精度的年代学框架，我们的目标是为基于沉积的古气候重建开发一个基于泥层的年代学。Tephra是由火山爆发产生的，从地质学的角度来看，它几乎是瞬间沉积的，在湖泊和其他沉积层中留下了与时间平行的标记层。如果对这些沉积环境（如湖泊）进行岩心取芯，确定年代，并对其序列进行分析，以确定火山层位的存在，就可以确定一段时间内区域性火山事件的数量。一旦从岩心序列中提取出麻风碎片，就可以对它们进行物理和地球化学分析，以确定来自源火山的麻风碎片，更具体地说，是来自个别火山喷发的麻风碎片。我们的方法是发展巴塔哥尼亚南部火山区部分地区（南纬44至47度）的区域温度年代学，因为除了我们正在创造的记录外，该地区还有机会发展许多优秀的湖泊古环境档案。我们将对靠近该地区主要平流层火山的3个湖泊进行取样。每个地点都在火山的下风处，应该能提供自上一个冰河时代结束以来所有（即使是最小的）爆炸性喷发的优秀档案。我们将使用一种新的岩心扫描技术来识别主要的地球化学趋势（ItraX），以及磁剖面来识别每个岩心中的所有温层。然后，我们将使用一系列技术对每个热毯层进行详细的地球化学和物理分析，使我们能够将热毯来源为火山，并为每个热毯提供单独的地球化学和/或物理特征。这种方法将使我们能够建立一个区域温度年代学，以及区域火山历史的频率和性质的详细图片。然后，温度年代学不仅可以应用于我们的古气候序列（其中至少有七个清晰的温度层），还可以应用于将来将从该地区采样的沉积古环境档案。与其他年龄测定相结合，我们将能够以越来越高的精度对序列进行年龄控制建模，并能够通过使用tephras精确地关联序列。

Reconstructing past climate change is fundamental for understanding the natural variability of Earth's climate, in particular the magnitude, timing and rates of past change. In order to successfully achieve these aims it is important to assess past changes quantitatively, from a wide global network, and that all records are accurately dated. This will allow precise comparisons between regions in order to test models of spatial, as well as temporal variability. Datasets from the Northern Hemisphere exist that follow these criteria, although quantitative palaeoclimate data are still relatively scarce. These data and particularly quantitative data are even rarer from the Southern Hemisphere, although we are in the process of collecting such a dataset covering the last ~20,000 years of climate change from Patagonia around 47 deg S. The data include detailed chironomid (non-biting midge) and stable isotope records that will be calibrated against instrumental data, as well as sedimentological, geochemical, pollen and macrofossil data. Together these will comprise a detailed, quantitative reconstruction of past climate change for the region. To some extent, though, every palaeoclimatic record is only as good as its chronological controls, and if these are poor the errors of comparison between other records increase hugely. In order to produce a very high precision chronological framework in this region we aim to develop a tephra-based chronology for sediment-based palaeoclimate reconstructions. Tephra is produced by explosive volcanic eruptions and its virtually instantaneous deposition, in geological terms, leads to the provision of time-parallel marker horizons being left in lakes and other sedimentary deposits. If these sedimentary environments, such as lakes, are cored, dated, and the sequences analysed for the presence of tephra horizons, one can determine the number of regional volcanic events over a period of time. Once the tephra shards have been extracted from the core sequences they can be analysed physically and geochemically in order to characterise tephras from source volcanoes and more specifically from individual eruptions. Our approach is to develop the regional tephrochronology for part of the Southern Volcanic Zone of Patagonia (44 to 47 deg S), as there are opportunities in this region to develop many excellent lacustrine palaeoenvironmental archives in addition to the records we are creating. We will core 3 lakes close to the major stratovolcanoes in the region. Each site is downwind of the volcanoes and should provide an excellent archive of all (even the smallest) explosive eruptions since the end of the last ice age. We will identify all the tephra layers in each core using a novel core scanning techniques which identifies major geochemical trends (ItraX) as well as magnetic profiling, which should also pick out tephra layers. We will then perform detailed geochemical and physical analyses on each tephra layer using a range of techniques, allowing us to source the tephra to a volcano and provide individual geochemical and/or physical characteristics for each tephra. This approach will allow us to build a regional tephrochronology as well as a detailed picture of the frequency and nature of regional volcanic history. The tephrochronology can then be applied to not only our palaeoclimate sequences (in which there are at least seven clear tephra horizons) but also to sedimentary palaeoenvironmental archives that will be sampled in the future from the region. Coupled with other age determinations we will be able to model age controls on the sequences with increasing accuracy as well as being able to correlate between sequences precisely through the use of the tephras.