Holocene palaeoclimates of Hokkaido: developing a temporal moisture balance model from raised peat for comparison with equivalent Atlantic records.

在北大西洋、欧洲和加拿大东部陆地上进行的广泛研究表明，这些地区过去的气候以千年为周期变化。最近对东海沉积物岩心的研究表明，在西太平洋也可以看到类似的洋流和气候变化模式。然而，在过去的一万年中，平行的太平洋-大西洋气候事件的存在需要更严格和更广泛的测试，特别是使用两个地区同等的气候变化记录。该提案旨在建立日本北部北海道岛隆起的泥炭沼泽过去气候变化的记录，以补充欧洲和加拿大许多基于泥炭的过去气候变化记录，从而使两个海洋盆地之间的记录能够进行比较。新的北海道记录将是日本同类记录中的第一个，因此该提案将作为利用日本养殖沼泽研究过去气候变化的概念证明，利用地下水位重建。通过将日本的沼泽气候记录与欧洲和北美的同等记录进行比较，可以实现对北大西洋和西太平洋过去气候的差异和相似之处的公平和相对直接的比较，因为所有的记录都将响应类似的气候参数。该提案旨在验证以下假设：(1)日本北部的气候具有周期性行为，包括由东亚季风和/或黑潮强度的变化直接驱动的千年节奏；(2)千年尺度事件的时间与北大西洋地区记录的时间同步。众所周知，沼泽是欧洲过去气候变化记录的来源。英国和丹麦的开创性研究表明，沼泽地下水位与气温/降水变化之间存在密切联系。这种联系之所以存在，是因为凸起的沼泽呈圆顶状，这样生活在上面的植物就能从大气中吸收所有的水和营养。一旦降雨和蒸发之间的平衡发生变化，这种变化就会反映在沼泽的水位上。泥炭沼泽保存了过去地下水位和气候变化的记录，因为它们随着时间的推移不断积累泥炭。泥炭是由曾经生活在沼泽表面的植物和动物的尸体组成的。随着气候和沼泽地下水位的变化，生活在沼泽上的植物和动物群落的组成将发生变化，以反映沼泽表面普遍的湿度，这反过来又决定了沉积的泥炭的类型。通过研究(1)泥炭中的植物和(2)动物遗骸以及(3)泥炭分解的程度，可以重建过去的地下水位。拟议的项目将采用所有三种测量沼泽表面湿度的方法。这些措施将结合起来，产生一个单一的、高分辨率的重建过去7000年的水平衡变化。该项目需要高标准的时间控制，以便与其他地区的事件进行有意义的比较；因此，该项目将使用AMS放射性碳定年法和火山灰层分析来构建研究地点的年龄深度模型。日本是一个活跃的火山地区，在整个地区的沼泽、湖泊和海洋沉积物中存在着大量的火山灰层。近年来，日本研究人员对这些火山灰层进行了地球化学表征，并确定了高水平的年代。在与欧洲和北美的上升沼泽记录和其他“大西洋”的过去气候变化档案（如格陵兰冰芯）进行比较之前，将把上升沼泽的水分平衡记录与现有的本地和区域古气候记录（如湖泊水位数据、中国的黄土序列和洞穴主题）进行比较。

Extensive studies in the North Atlantic Ocean and on land in Europe and Eastern Canada have shown that past climates have varied on a millennial-scale cycle in those regions. Recent studies of sediment cores from the East China Sea suggest that a similar pattern of ocean current and climate variability is visible in the western Pacific. However, the existence of parallel Pacific-Atlantic climatic events over the last 10,000 years requires more rigorous and wider testing, in particular using equivalent well-dated records of climate change in both regions. This proposal aims to establish a record of past climate change from raised peat bogs on Hokkaido Island, northern Japan, to complement the many European and Canadian peat-based records of past climate change, so enabling a comparison of the records between the two ocean basins. The new Hokkaido records will be the first of their kind in Japan, therefore this proposal will act as a proof-of-concept for the use of Japanese raised bogs in research into past climate change, using watertable reconstruction. By comparing Japanese raised bog climate records with equivalent European and North American records a fair and relatively straightforward comparison of the differences and similarities between the past climates of the North Atlantic and western Pacific can be achieved since all of the records will be responding to similar climatic parameters. This proposal aims to test the hypotheses that (1) the climate of northern Japan has a cyclic behaviour including a millennial pacing immediately driven by changes in the East Asian Monsoon and/or the strength of the Kuroshio Current and that (2) the timings of millennial-scale events are synchronous with those recorded in the North Atlantic region. Raised bogs are already well known sources of records for past climatic change in Europe. Pioneering research in Britain and Denmark has demonstrated that there is a close link between bog watertable levels and changes in air temperature/precipitation. This link exists because raised bogs are gently domed so that the plants living on them receive all of their water and nutrients from the atmosphere. As soon as the balance between rainfall and evaporation changes this shift is reflected in the bog water level. Records of past watertable positions and therefore climate change are preserved in peat bogs because they continuously accumulate peat over time. The peat is composed of the dead remains of plants and animals that once inhabited the bog surface. As climate and the bog watertables change through time the composition of the plant and animal communities living on the bog will shift to reflect the prevailing bog surface wetness and this in turn determines the type of peat that is deposited. Past watertable levels are reconstructed by studying (1) the plant and (2) animal remains in peat as well as (3) the level of breakdown of the peat. The proposed project will employ all three measures of bog surface wetness. The measures will be combined to produce a single, high resolution reconstruction of change in the water balance over the last 7000 years. The project demands a high standard of dating control to enable meaningful comparisons with events from other regions; therefore the project will use both AMS radiocarbon dating and the analysis of volcanic ash layers to construct an age-depth model for the study site. Japan is an active volcanic region and numerous ash layers exist in bogs, lakes and ocean sediments across the region. These ash layers have been geochemically characterised and dated to a high standard by Japanese researchers in recent years. The raised bog moisture balance record will be compared to existing local and regional palaeoclimate records (e.g. lake-level data, loess sequences from China, and speleothems) before comparisons are made with European and North American raised bog records and other 'Atlantic' archives of past climatic change such as the Greenland ice cores.