Reconstruction of paleoceanographic changes in the Japan Sea in response to centennial to millennial-scale global climatic changes

本研究旨在通过对日本海深层柱塞岩心的高分辨率分析，阐明日本海古海洋学变化与百年至千年尺度的全球气候变化（Dansgaard-Oeschger [D-O]旋回）的关系。从秋田附近采集的两个活塞岩心KT 94-15-PC-5和PC-9被用于分析整体化学、整体矿物学、沉积结构（如层压和生物扰动）和硅藻组合。在此基础上，对地表水、底水含氧水平的特征和大陆风通量的贡献进行了评价。通过分析这些参数的时空变化，探讨了a)表层水特征和深水氧合水平如何响应d - Cycle， b)这两个参数与D-OCycle之间的相位关系，c)东亚内陆地区由风成物质贡献推断的干旱变化与D-OCycle之间的相位关系。结果表明：(1)日本海暗层沉积物与D-O旋回的间断期有关；(2)暗层沉积物总是保持平行层状，这表明沉积是在缺氧到缺氧的底水条件下进行的；(3)风成物质贡献的突然增加通常与暗层沉积开始的时间一致，但有时会超前或滞后一个样品（约600年）。4)暗层的线沉降速率往往比相邻的浅色层慢，因此暗层的风成通量似乎也比相邻的浅色层小。观测到的一个样品（约600年）在黑暗层沉积开始和风成贡献增加之间的相移可以归因于每个样品代表2.5cm的地层间隔，有时覆盖黑暗陆地和光明层之间的边界。我们先前通过分析ODP 797站点1500年的间隔样品指出，在黑暗层沉积开始后，风成贡献减少的相位滞后可能长达3000年，这似乎是假设的，是由粗糙和不连续的采样造成的。少

This research is aimed to clarify paleoceanographic changes of the Japan Sea in association with centennial to milennial-scale global climatic changes known as Dansgaard-Oeschger [D-O] Cycles through the high resolution analysis of piston cores retrieved from the deeper partrs of the Japan Sea. Two piston cores KT 94-15-PC-5 and PC-9 which were retrieved from the sites off Akita were used for analyzes of bulk chemistry, bulk mineralogy, sedimentary structures such as lamination and bioturbation, and diatom assemblage. Based on the results of these analyzes, character of the surface water, bottom water oxygenationlevel, and contribution of aeolian flux from the continent were evaluated. By examining temporal and spatial changes of these parameters, weinvestigated a) how character of the surface water and oxygenation level of the deep water had been changed in response to D-OCycles, b) what the phase relationship between these two parameters and D-O Cycles was, and c) what the phase rela … More tionship of between aridity changes in inland East Asia deduced from the contribution of aeolian materials and D-O Cycle was.The results suggest 1) the dark layrs in the Japan Sea sediments correlate to interstadials of D-O Cycles, 2) the dark layrs always preserve parallel laminations which suggests deposition under suboxic to euxinic bottom water conditions, 3) sudden increases in contribution of aeolian materials generally coincide with but sometimes lead or lag by one sample (c. a. 600 yrs) from the start of deposition of the dark layrs, and 4) the linear sedimentation rates of the dark layrs tend to be slower than the adjacent light layrs and consequently aeolian flux also seems to have been smaller in the dark layrs than in the adjacent light layrs. The observed phase shift of one sample (c. a. 600 yrs) between the start of the dark layrs deposition and the increase in aeolian contribution could be attributed to the fact each sample represent a 2.5cm stratigraphic interval and sometimes cover the boundary between the dark land light layrs. The possible phase lag of aeolian contribution decrease behind the start of deposition of the dark layrs by as much as 3000 yrs previously pointed out by us based on the analyzes of 1500 yrs interval samples from ODP Site 797 seems to be suppositional and caused by coarse and not continuous sampling. Less