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

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.