Toshiro Naruse

Snowline elevation and eolian dust flux in the Japanese islands during isotope stages 2 and 4.

Abstract Changes in snowline elevation and dust flux clearly contrast the paleoenvironments of the Japanese Islands during Isotope Stages 2 and 4. A lower snowline elevation and a smaller dust flux during Isotope Stage 4 suggests a climate with a cold and dry summer dominated by winter monsoonal precipitation between 70 and 55 ka. A higher snowline elevation and a larger dust flux during Isotope Stage 2 indicates a climate with a cold and very dry summer with a minimized winter monsoon precipitation especially around 18 ka. A drier climate during Stage 2 can be explained by (1) a lowering of sea surface temperature in the Japan Sea by blocking the warm Tsushima Current during a sea-level lowering; (2) the extension of sea ice over the northern part of the Japan Sea and the Sea of Okhotsk; and (3) weakening of the summer monsoon and the southern migration of the polar front. The increase in dust flux in both Stages 2 and 4 suggests an intensification of westerlies and winter monsoon during these stages. A bigger dust flux in Stage 2 than Stage 4 reflects (1) stronger westerlies and winter monsoon, and (2) the emergence of continental shelf which became an important dust source.

Origin and derived courses of eolian dust quartz deposited during marine isotope stage 2 in East Asia, suggested by ESR signal intensity

The ESR signal intensity of fine quartz (finer than 20 μm) during marine isotope stage (MIS) 2 in the Japanese Islands is spatially. Under the assumption that the values of ESR signal intensity of eolian fine quartz reflect those of the quartz at the in-source areas, the source area and trajectory of eolian dust are tentatively reconstructed. In northern Japan, where the ESR signal intensity is high (10–12), the eolian dust seems to have originated from Siberia and Mongolia where the Precambrian rocks with a high ESR signal intensity are widely exposed. In central and southern Japan, where the ESR signal intensity is medium (5.8–8.7), the eolian dust seems to be supplied from central Asia where Paleozoic–Mesozoic rocks with a medium ESR signal intensity are widely exposed. For the southernmost islands of Japan, where the ESR intensity signal increases again (9.7–13.4), seem to have an eolian dust supply from areas south of Himalayan Range where the Precambrian rocks are widely exposed. On the basis of ESR intensity signals, three major courses of eolian dust transport in MIS 2 are proposed: the winter monsoon in eastern and northern Japan, the summer subtropical jet in western and southern Japan, and the winter subtropical jet in the southernmost islands of Japan.

Holocene evolution of the outer lake of Hwajinpo Lagoon on the eastern coast of Korea; environmental changes with Holocene sea-level fluctuation of the East Sea (Sea of Japan).

The evolution of the outer lake of Hwajinpo Lagoon in Korea has been reconstructed using environmental proxies (lithologic, geochemical, and fossil data) with a chronology established using 7 accelerator mass spectrometry (AMS) radiocarbon dates. Grain size, water content, and X-ray analyses from the core of outer coastal lakes (HJ99) were used to reconstruct sedimentary environments by using total organic carbon, C/N, S, and C/S chemical proxies. Assemblages of mollusc remains also provided paleoenvironmental information. The environmental changes of the outer lake of Hwajinpo Lagoon can be divided into 6 depositional phases. The basin of the Hwajinpo was exposed and underwent a weathering process before the Holocene period. The muddy sand layer on the weathered bedrock indicated an estuarine system about 6000 BP. The laminated layer implies that the lagoonal system was anoxic between about 5500-2800 BP. The marl layer implies a relatively oxic lagoonal condition with mollusc presence about 2500 BP. The layer of very low sulfur content indicates a freshwater lake system isolated by a sand barrier about 1700 BP. Beginning about 1000 BP, the river system deposits progress progradation on the marl layer. Two erosional landforms could be related with a high standing sea level span during Holocene. These high-stands are dated at 5700 BP and 2200 BP and are supposed to have formed erosional landforms of about 1.6 amsl and 0.8 amsl, respectively. Environmental changes of the outer lake of Hwajinpo Lagoon are considered due mainly to the lake-and sea-level fluctuation during Holocene.

Mineral Composition of Clay Fractions and Oxygen Vacancies in Silt‐Sized Quartz in Soils on the Ka‐Etsu Plateau, Fukui, Central Japan—Possibility of Eolian Dust Brought from Northern Asia as Parent Material of Soils

Fine- to medium-textured soils are distributed on the Early Pliocene rocks and Pleistocene sandy sediments in the Ka-Etsu plateau. The Jingaoka (JIN) soil was classified into Aluandic Andosols by WRB, and Low-humic Non-allophanic Kuroboku soils by the Fourth Committee for Soil Classification and Nomenclature of the Japanese Society of Pedology, although it was similar morphologically to Yellow-Brown Forest soils. On the other hand, the Tomitsu (TMI) and Yamamuro (YAM) soils were classified into Hyperdystri-Chromic Cambisols by WRB, and Typic Yellow-Brown Forest soils by the Fourth Committee for Soil Classification and Nomenclature based on the morphological, physical and chemical properties. These soils were influenced considerably by the Akahoya tephra, especially the JIN soil. Based on the results of clay-mineralogical analysis and the measurement of the ESR-signal intensity associated with the oxygen vacancies in fine quartz, a large part of parent materials in the soils distributed on the Ka-Etsu plateau was derived from the eolian dust which was brought with the NW winter monsoon from the Precambrian sediments in the northern part of the Asian continent during MIS 2 (24–11 thousand years ago) at the Last Glacial Maximum. The parent materials of the fine-textured JIN soil located on the highest terrace near the rocky coastline were mostly composed of eolian dust, although the influenced of the Akahoya tephra was recognized. The parent materials of the TMI soil were admixed with a small amount of autochthonous materials from the sandy coast located windward. In the YAM soil which was located on the side of a hilly area distant from the coastline, the ESR-signal intensity in fine quartz was considerably low, and the admixture of autochthonous materials was also considered since the texture of this soil was coarser than that of the JIN and TMI soils.