ULTRA-HIGH-RESOLUTION PROXY RECORD OF LAST MILLENNIUM NORTH ATLANTIC TEMPERATURE ANOMALIES ('ULTRA')

许多海洋双壳类软体动物的壳，特别是北极岛屿的壳，都有年生长带。通过稳定的氧同位素剖面（显示海水温度的季节性循环）以及标记活的个体和反复捕获后的增量增长，可以证明北极地区的波段是每年一次的。计算增量表明，这个物种具有非凡的寿命：班戈小组于2006年从冰岛水域收集的一个活标本，将在这里提出的研究中形成一个中心板块，每年至少有500个增量。这被认为是科学界已知的最长寿的非殖民地动物。此外，我们已经能够将这些活着的个体的生长序列与从海底打捞的死壳进行交叉匹配，以构建长期的绝对年表。交叉匹配表明，同一区域内的个体对相同的环境（可能是气候）刺激做出反应。在冰岛北部，我们已经确定，生长增量的宽度与海水温度之间存在显著的统计关系，在较温暖的年份，增加的增量更大。我们现在已经构建了一个交叉匹配的记录，涵盖了该地区过去1000年的历史，我们建议在这个项目中使用这个已经组装好的档案。我们将分析年增长增量中包含的稳定氧同位素。通过仔细比较同位素测量结果与过去50年收集的海水温度和其他变量的本地仪器记录，我们将能够可靠地将同位素数据转换为温度重建。这将有助于测试仅基于增量宽度的重建的鲁棒性。我们有初步的数据表明，在过去的1000年里，冰岛北部发生了重大的水文变化，特别是北大西洋极地锋（NAPF）的迁移，将温暖的伊明格流与寒冷的东冰岛流分开。这些变化与北大西洋更广泛的环流直接相关。正是这个环流系统——北大西洋经向翻转环流（AMOC）——目前提供了控制欧洲西北部气候的热量。通过从北极记录的氧同位素中非常详细地重建冰岛北部NAPF在过去1000年里位置的变化，我们将增强我们对系统中翻转的频率和这些转变的速度的理解。对AMOC的直接测量仅在几年前才得以实现。较长的记录——对于确定AMOC对扰动（特别是流入海洋的淡水通量的增加）的敏感性至关重要——依赖于代理记录。政府间气候变化专门委员会第四次评估报告（IPCC, 2007）强调了生成此类记录的重要性。IPCC指出，对过去1300年各种仪器和代理气候记录的汇编提供了大尺度地表平均温度变化的关键证据，并明确强调了最近变暖的显著性，特别是在过去的二三十年。然而，IPCC也认识到，迫切需要通过更新现有记录（其中许多记录是20年前收集的）和生成地理覆盖范围更广的额外古气候序列，特别是早期古气候序列，来减少这些汇编中的不确定性。本提案旨在通过对北极岛屿年增量的氧同位素分析生成独特的1000年古温度记录来实现这一目标，以确定与冰岛北部大陆架NAPF经向迁移有关的温度异常的自然变率。

The shells of many marine bivalve molluscs, in particular Arctica islandica, contain annual growth bands. The fact that the bands in Arctica are annual has been demonstrated by stable oxygen isotope profiles across the growth increments, which show seasonal cycles of seawater temperature, and by marking live individuals and examining the incremental growth after repeated recaptures. Counting the increments demonstrates that this species has extraordinary longevity: one live specimen from Icelandic waters collected by the Bangor group in 2006, and which will form a central plank in the research proposed here, has at least 500 annual increments. This is considered the longest-lived non-colonial animal known to science. Furthermore, we have been able to cross-match the growth series from such live individuals with dead shells dredged from the seabed to construct long absolute chronologies. Cross-matching demonstrates that individuals within a region respond to the same environmental, possibly climatic, stimuli. North of Iceland we have established that there is a significant statistical relationship between the width of the growth increments and seawater temperature, with wider increments being laid down in warmer years. We have now constructed a cross-matched record covering the last 1000 years from this region and it is this already assembled archive that we propose to use in this project. We will analyse the stable oxygen isotopes contained within the annual growth increments. By carefully comparing the isotope measurements with local instrumental records of seawater temperature and other variables collected over the last 50 years, we will be able to convert reliably the isotope data into temperature reconstructions. This will help test how robust the reconstructions based on increment width alone are. We have preliminary data which suggest that there were major hydrographic changes north of Iceland during the last 1000 years, notably the migration of the North Atlantic Polar Front (NAPF) separating the warm Irminger Current from the cold East Icelandic Current. These changes are directly linked to the wider circulation of the North Atlantic. It is this circulation system - the North Atlantic meridional overturning circulation (AMOC) - that currently provides the heat that controls the climate of NW Europe. By reconstructing, in great detail, the variability in the position of the NAPF north of Iceland over the last 1000 years from the oxygen isotopes in the Arctica record, we will enhance our understanding of how frequent the flips in the system are and how quickly these transitions take. Direct measurement of the AMOC have only been available for a few years. Longer records - which are crucial for identifying the sensitivity of the AMOC to perturbations, notably increases in freshwater flux to the ocean - rely on proxy records. The importance of generating records such as this was highlighted in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC, 2007). IPCC stated that the compilation of various instrumental and proxy climate records over the last 1300 years provides critical evidence of the variations in average large-scale surface temperatures, and clearly emphasize the prominence of the recent warming, especially in the last two to three decades. However, IPCC also recognise that there is an urgent need to reduce the uncertainty in such compilations, via the update of existing records, many of which were assembled up to 20 years ago, and the generation of additional, especially early, palaeoclimate series with much wider geographic coverage. This proposal seeks to contribute to this goal through the generation of a unique 1000-year palaeotemperature record based on oxygen isotopic analysis of annual increments of Arctica islandica in order to identify the natural variability of temperature anomalies linked to the meridional migration of the NAPF on the north Icelandic shelf.