Late Holocene aeolian sedimentation in the Tottori coastal dune field, Japan Sea, affected by the East Asian winter monsoon

摘要

Many dune fields that have formed along the southern coast of the Japan Sea are influenced by the north-westerly winter monsoon, which transports beach sand landwards. The Tottori coastal dune field of the Japan Sea has not been disturbed much by human activities until the 20th century and thus is expected to provide a continuous record of the relationships between the winter monsoon and aeolian sedimentation. We examined new ground-penetrating radar profiles and optically stimulated luminescence (OSL) ages of quartz sand from transverse dune ridges in the western part of the dune field in addition to existing data in the eastern part. This allowed us to extend the study period to cover the past 1000 years and to effectively compare the sedimentary record with other coastal dune fields in East Asia and other palaeoenvironmental proxies. OSL ages from older dune sediments suggest considerable aeolian activity from the 10th to 12th century AD, whereas a hiatus of dune sediment record between the 12th and 15th centuries was detected. These results suggest that during the Medieval period aeolian activity was low or that extensive erosion removed most of the deposits. Since the late 15th century, dune sedimentation has apparently been broadly continuous, though with periods of higher and lower activity. In both of the eastern and western parts, most of the dune ridges accreted landwards, but clear seaward accretion occurred during the 18th century, possibly reflecting a decrease in wind strength that restricted sand transport. In contrast, two significant landward accretion events are inferred to have occurred from the late 15th to 17th centuries and around 1840, corresponding to periods of increased dust fall in China, which suggests an enhanced winter monsoon, and to cold periods suggested by the decline of the sunspot number. The timing of periods of inactive and active dune sedimentation, inferred from alternations of organic soil and aeolian sand, in other coastal dune fields of East Asia appears to be concordant with corresponding periods in the Tottori dune field. We thus propose that other Japan Sea dune fields may also provide a valuable record of East Asian winter monsoon fluctuations. (C) 2015 Elsevier Ltd and INQUA. All rights reserved.