The East Asian winter monsoon is characterized by cold and dry air blown out from the Siberian high to the surrounding lows. Cold and dry northwesterly is the most common feature of the winter monsoon around the Japanese islands. This cold wind refrigerates the surface water along the Far East coast of Russia in the Japan Sea. Modern oceanographic observations indicate that sea-ice formation along the coast during the extremely cold winter is an important process for the deep-water formation. Thus, combination of sea-ice and deep-water formation in the Japan Sea is the signal of stronger winter monsoon. Occurrence of the ice-rafted debris (IRD), which is a proxy of sea-ice extend, and of an radiolarian species, Cycladophora davisiana, which is a proxy of cold and oxygenated deep water, might be the two standards of the strength of winter monsoon. We examined the records of two proxies during the last 160 ky in the cores from the Japan Sea. Both records showed the fluctuation with millennial time-scale during oxygen isotope stage 3-5 and they suggested the East Asian winter monsoon fluctuation in the same time-scale. The intervals of frequent occurrence of the IRD and Cycladophora davisiana might suggest the strong periods of the East Asian winter monsoon. The fluctuation of the East Asian summer monsoon during stage 3-5 was recorded as sediment lithology (dark layer), the Japan Sea sediments are very unique marine sediments to obtain both summer and winter monsoon records in a core.
The dose estimation method of optically stimulated luminescence (OSL) dating has improved greatly over the last few years, and has been increasingly used in dating various Quaternary sediments. However, the age range of OSL dating using quartz, determined both by the saturation dose and the dose rate, makes its applicability limited only up to about 100 ka. This paper reviews the various ongoing researches, which aims to extend the age range of luminescence dating, using quartz isothermal thermoluminescence (ITL), quartz red TL, feldspar blue OSL with fading correction, and feldspar red OSL. In addition, the luminescence properties of quartz have been found to depend on its host rock type and environment after denudation. Fast and medium OSL components of quartz, which are most suitable for dating, are not always available from sediments, which have been recently denudated and transported short distance. OSL of volcanic quartz gives age underestimation, because of the anomalous fading. Possible solutions for dealing with these problematic samples are suggested.
To study the role of mountain uplift on Asian monsoon, a series of coupled ocean-atmosphere general circulation model experiments are performed. Mountains are uplifted from 0% (no mountain) to 140% where 100% corresponds to the control experiment. The land-sea distribution is the same for all experiments and mountain heights are varied uniformly over the entire globe. Systematic changes in circulation as well as precipitation fields are found with progressive mountain uplift. A north-south jump of the 500 hPa zonal wind axis around the longitude of the Tibetan plateau is found with mountain height higher than 60% between the winter and summer season. On the other hand the jet axis stayed in the northward position all the year round in the experiments with lower mountains. Summertime precipitation is confined in the deep tropics around 10 ºN in the no-mountain (M0) case, but it moves inland on the Asian continent with mountain uplift. Associated with this, an intensification of the Pacific subtropical anticyclone and trade winds is found. The Baiu-like precipitation belt in East Asia clearly appeared at mountains higher than 60%. Surface wind distribution over the Indian Ocean and the Maritime Continent region drastically changed by mountain uplift. Summertime southwesterly monsoon flow does not cover the northernmost Arabian Sea region so that upwelling is inactive all the year round when mountain is lower than 40%. Changes in climatic area based on Koppen-type climate classification are also investigated. It is found that desert area is the largest in the no-mountain case and decreases in its area extent with mountain uplift.
The idea that uplift of Himalaya and Tibet caused onset and enhancement of Asian Monsoon is not new, but it has never been tested because the knowledge on the timing and mode of onset and evolution of the Asian Monsoon as well as those of Himalaya and Tibet uplift has not been sufficient. Situation changed recently due to the drastic progress in reconstruction of Asian Monsoon evolution through intensive studies of loess in China as well as of hemipelagic sediments of the Japan Sea. The knowledge on the timing and process of Himalaya-Tibet uplift has also been accumulated. In addition, climate model, which is necessary to examine the linkage between Himalaya-Tibet uplift and monsoon onset and evolution, has improved drastically. In this synthesis, I summarized recent advances in our knowledge on the onset, evolution, and variability of Asian Monsoon, and reconstructed probable process of its evolution based on compilation of the paleoclimate data. Then, I compared individual reconstructed steps of the Asian Monsoon evolution with individual stages of Asian Monsoon simulated for every step of Himalaya-Tibet uplift by climate models, so as to specify the degree of Himalaya-Tibet uplift that best explains the Asian Monsoon evolution. The history of Himalaya-Tibet uplift reconstructed in this way is compared with current knowledge on the tectonic history of Himalaya-Tibet uplift. Paleoclimatic reconstruction suggests that desertification in inland Asia and onset of Asian Monsoon started approximately at 22 Ma, and evolved stepwise approximately at 8 Ma and 4 Ma. Such stepwise evolution of Asian Monsoon seem to correspond to uplift stage of 40, 60, and 80% of present height of Himalaya and Tibet according to climatic model simulation by Abe et al. (2003). These estimates are basically conformable with the current knowledge on uplift history of Himalaya and Tibet.
In this paper, we reviewed and discussed the recent progress and perspectives mentioned in the research of paleo Asian monsoon activities from the records of loess-paleosol sequences and lacustrine sediments in East Asia. Loess-paleosol sequences and lacustrine sediments in East Asia have been recorded terrestrial environmental changes associated with East Asian monsoon activities since the beginning of Quaternary. The researches to reconstruct the activities of paleo East Asian monsoon started in 1982 by Heller and Liu (1982), and has been stored much information on the formation and variability of the monsoon in the last two decades. Onset of loess deposition might begin in 2.6 Ma, and after that the fluctuations of the monsoon activities have been reflected the glacial-interglacial cycles controlled by the Milankovitch forcing. Also, the millennial time-scale variation of the monsoon activities can be recognized in the last glacial time. The recent research on Red Clay underlying the loess-paleosol sequence may point out that the formation of the monsoon activities dates back to 7 or 8 Ma.
The in-situ terrestrial cosmogenic nuclides (TCN) are produced from the interactions with cosmic ray bombardments with terrestrial rocks. The TCN exposure history measurement method is undergoing major developments in the Earth Science field. This method can be applied to various geological problems including tectonics, coastal environments changes and climate changes. The method is employed in the geological studies of which time scale ranges from 102 to 107 years using currently established method (3He, 10Be, 21Ne, 26Al, and 36Cl). Combining measurements of nuclides which have different half-lives is particularly useful to determine the history of the surface process and hence quartz grains have been widely used for this types of research since they contain both in-situ 10Be and 26Al. In this paper we present some examples using TCN to reveal past histories of earth surface processes. Tibetan plateau is the widest plateau in the world and the detailed mechanisms of its tectonics have been under debate. TCN have revealed new insights into the Himalaya-Tibet regional tectonics in these days and its impact on the global climatic evolutions. In this short paper, we introduce the theory and some applications of study using TCN.
Our recent study revealed that the metamorphic nappe in the Himalaya appeared at~14 Ma and stopped its southward advancement at 11 to 10 Ma, and the frontal range of the Himalaya started its rapid uplift at 1 Ma. In addition, our data suggest that the Himalaya has reached present elevation at least before 11 Ma. Several lines of evidence on the paleo-altitude of the Tibetan plateau commonly indicate that the Tibetan plateau has also reached present elevation by ~14 Ma: timing of onset of N-S trending normal faults caused by E-W extension, estimate of paleo-altitude by means of middle Miocene fossil plants and δ 18O of carbonate in the graben-fill. Strong upwelling during 10 to 8 Ma, which has hitherto been considered to be evidence of beginning of Indian summer monsoon, is reported not only from Indian Ocean but also from Pacific Ocean and Atlantic Ocean. It might be linked to global cooling caused by expansion of Antarctica ice-sheet at 10 to 8 Ma. We must re-examine the linkage between evolution and uplift of Himalaya-Tibetan plateau and development of monsoon climate, taking new discovery that the middle crust of Tibet is partially melted into consideration.
Large rivers in Asia have been controlled by the uplifts of the Himalayas and Tibetan Plateau in their origin, distribution and history during the late Cenozoic. Deltas formed by these large rivers have been forming wide delta plains and prograding onto shelves during the Holocene. Sea-level changes have impacted the evolution of deltas, particularly their stacking pattern of deltaic sediments and facies. A delta has evolved from an aggradational delta during the rise of sea level to a progradational delta during the subsequent sea-level stand and fall. Moreover delta progradation has lead more wave-dominated coastal environments. Deltas of various stages in this delta evolutional model can be seen in Asia and in the world at present.