Terrestrial paleoclimate analysis in using tufas developed in temperate-subtropical regions

为了重建温带-亚热带地区高分辨率的陆地古气候学，我们重点研究了淡水碳酸盐凝灰岩，分析了化学和同位素，并观察了几个地区的凝灰岩矿床。结果表明：1)层状结构是方解石沉降率随温度变化的季节性变化(Kano et al.，2003)，2)凝灰岩结构记录了人为的变化，如农业排水和地下水坝的建设。在上述结果的基础上，利用从新井、高桥县(冈山县)、Kikai(鹿儿岛县)和宫古县(冲绳县)采集的标本进行了气候学分析。3)氧同位素比值通常与水温相关，并记录了全球变暖的近期趋势。我们发现在凝灰岩中记录了个别的降雨事件(Kano等人，2004年)。从Niimi采集的凝灰岩表现出0.1 mm级的棕色带，与X射线微分析仪分析结果中的Si和Al X射线强度峰相对应。这些条带可视为粘土含量较高的层位。5)尼密一次降雨后5天的水质监测结果证实了棕带与降雨的关系。雨后，水中粘土含量急剧增加，达到正常水平的7倍。6)对山西的一个古凝灰岩中国进行了进一步的分析，提出了Moi-Stage 3(C.A.50ka)比现在更潮湿。我们的研究发现了许多关于年度分层和分析程序的沉积条件和起源的新发现，并成功地提出了一个新的研究主题--凝灰岩-气候学。

In order to reconstruct high-resolution terrestrial paleoclimatology in temperate-subtropical regions, we have focused to freshwater carbonate tufa, analyzed chemistry and isotopes, and observed tufa deposits collected from several localities. Results indicated that 1)laminated texture is formed by temperature-dependent seasonal change in calcite precipitation rate (Kano et al.,2003), and that 2)tufa textures record artificial alterations, such as agricultural water drainage and construction of subsurface dams.Based on the above-mentioned results, climatological analyses have been performed using specimens collected from Niimi, Takahashi (Okayama Prefecture), Kikai (Kagoshima Prefecture), and Miyako (Okinawa Prefecture). We demonstrated that 3)oxygen isotopic ratio is usually correlated with water temperature and records recent trend of the Global Warming. We found that 4)individual rain events were recorded in tufa (Kano et al.,2004). Tufas, such as one collected from Niimi, exhibit 0.1mm-order brown bands, which correspond to peaks of Si- and Al-X-ray strength from analytical results of X-ray micro-analyzer. The bands can be regarded as horizons of high clay contents. 5)The relation between brown bands and rain events was proven by the fact observed during 5-day monitoring of water properties after a rain event at Niimi. Clay contents in water drastically increased up to seven times of the normal level after the rain event. 6)We further performed analysis on a paleo-tufa in Shanxi Province, China, and suggested that the climate in MOI-stage 3 (c.a. 50ka) was more humid than now.Our research revealed many new findings on depositional conditions and origin of annual lamination and analytical procedure, and could successfully proposed a new research theme called as "Tufa-climatology".