Toshiyuki Fujiki

Palynology of a 250-m core from Lake Biwa: a 430,000-year record of glacial–interglacial vegetation change in Japan

Abstract Lake Biwa is situated in western Honshu, and is the largest and oldest freshwater lake in Japan. During 1982–1983, a long core was drilled to a bottom depth of 1422 m in order to investigate the palaeolimnological record, which contains 911 m of various sedimentary units overlying Palaeozoic–Mesozoic basements. A 249.5-m core of the uppermost bed (T Bed) was palynologically examined at intervals of ca. 2 m. The investigated part of the core covers approximately the last 430,000 years of the mid-Upper Pleistocene and Holocene, and five glacial–interglacial cycles can be recognized. Ten major vegetational zones could be recognized from the bottom to the surface. The zones bearing even numbers, BW-10, 8, 6, 4 and 2, matched glacial periods in which pollen of subarctic taxa (Pinaceae, Betula ) and cool–temperate taxa ( Fagus , Lepidobalanus ) was dominant. In the glacial periods, high pollen values for temperate conifers such as Cryptomeria , Cupressaceae and Sciadopitys indicate interstadial periods. Zones bearing odd numbers, BW-9, 7, 5, 3 and 1, matched interglacial periods with high pollen values for the warm–temperate taxon Cyclobalanopsis , or showed the characteristic appearance of Lagerstroemia , and temperate coniferous taxa ( Cryptomeria , Cupressaceae). There were two vegetational types in the interglacial periods. One was the type indicated by BW-9 and 1 zones, when warm–temperate evergreen broad-leaved trees such as Cyclobalanopsis and Castanopsis showed high pollen values, and the warm–temperate deciduous broad-leaved tree Lagerstroemia was lacking. The climate of these interglacial periods seems to have been cold and dry in winter, and warm and wet in summer. The other was the vegetational type recorded in BW-7, 5 and 3 zones, where Lagerstroemia showed low pollen values, and the warm–temperate evergreen broad-leaved trees mentioned above were poorly represented. The climate seems to have been mild and wet in winter, and cool and wet in summer. The dominant pollen values for cool–temperate deciduous broad-leaved taxa such as Fagus and Lepidobalanus are very important indicators of the initiation of both glacial and interglacial periods in western Japan.

Regulation of the monsoon climate by two different orbital rhythms and forcing mechanisms

The East Asian monsoon is responsible for transferring huge amounts of heat and moisture between the land and the adjacent ocean. Significant changes in its capacity to do this will have direct impacts on regional climatic gradients and global atmospheric circulation. Determining the mechanisms that force long-term variation in monsoon behavior is therefore important for understanding global climate change. Competing theories vary in the degree of importance attached to glacial forcing, other orbital rhythms, and internal feedback mechanisms as primary drivers of change. There is, however, no convincing explanation as to why different proxy records from closely neighboring regions are tuned to different orbital rhythms. Here we present quantitative climatic reconstructions for the past 450 k.y. based on a long pollen record from Lake Biwa in Japan. The data suggest that continental and oceanic air mass temperatures respond predominantly to the 100 k.y. orbital rhythm, whereas the land-ocean temperature gradient and monsoon vigor oscillate mainly at the 23 k.y. insolation cycle. We suggest that the mechanisms for this behavior lie in the differential response of land and ocean to solar forcing, and conclude that the 100 k.y. signal dominates monsoon intensity only when the amplitude of solar forcing falls below a threshold level.

Dating of seasonal snow/firn accumulation layers using pollen analysis

Reliable chronologies in ice cores and snow pits from many alpine glaciers in latitudes between 60° N and 60° S are often difficult to establish owing to problems with annual-layer counting. Problems arise from melting, wind erosion and the negligible amount of precipitation in some seasons, all of which tend to obscure the seasonal variations in δ 18 O and chemical concentrations that are typically used to date ice cores. However, alpine glaciers contain many species of pollen grains that peak at particular times of the year. We used the peaks in Betulaceae, Pinus, Artemisia and a combination of Abies and Picea pollen species to determine the four seasonal layers of a snow pit on Belukha glacier in Russia’s Altai Mountains. Comparing the pollen-dated profiles with wind and precipitation records allows us to determine where a seasonal layer is missing. Thus, the pollen-dating method described here may be a useful tool to measure the annual snow deposition on alpine glaciers, even when some seasonal layers are eroded by wind or missing due to negligible precipitation.

Establishing the Timing of Chemical Deposition Events on Belukha Glacier, Altai Mountains, Russia, Using Pollen Analysis

Abstract In this study, we used a 4.00-m pit on Belukha glacier in Russias Altai region and attempted to establish the timing of chemical deposition events by analyzing pollen profiles. As the pollen deposition of each examined taxon on the glacier surfaces followed a distinct seasonal phenology, seasonal layers could be identified over a two-year period. The seasonal layer boundaries reconstructed from the pollen analyses were in close agreement with the in situ observations and indicated that the snow deposition on the glacier originates mainly from summer precipitation. The record of oxygen isotope ratios showed a relatively high mean value of −13.3‰, which was attributed to the absence of winter depositions. The formate (HCOO−) concentration records displayed seasonal variation with the highest emissions occurring in the spring, and a dust event in the spring of 2003 was detected from the Mg2+, Ca2+, and dust concentration profiles. Taken together, these results suggest the analysis of pollen profiles in combination with chemical data in snow pits and ice cores may lead to better reconstruction of seasonal variation.

Reconstruction of an 8,000-year Environmental History on Pollen Records from Lake Buyan, Central Bali

Open image in new window New evidence from Lake Buyan, a 65-m-deep caldera lake in central Bali, presents an 8,000-year record of vegetation and climate change through palynological and physio-geochemical analyses. The distinct sediment phases associated with relative vegetation fluctuations and change of physio-geochemical index suggest that Bali might have experienced cycles of wet and dry climate change over 8,000 years. Vegetation composed of marshland/gap-colonizers, being coeval with the intensive process of erosion as indicated by an increased input of minerogenic material from the catchment, characterizes the periods when homogeneous lake mud sediments are formed, indicating relatively higher rainfall at period of 8.0–6.6 ka BP, 5.1–3.6 ka BP and 2.8 ka BP to present. At the time when laminated lake sediments commence, e.g., 6.6–5.1 ka BP and 3.6–2.8 ka BP, vegetation of a rather dry and fire-resistant character dominates, in concomitant with lower input of minerogenic material and suggests drier episodes. Regional comparison indicates that human-induced vegetation destruction is insignificant in Bali, except that cultivation activities might have been manifested in the recent 3,000 years, and the climatic variability observed from this core was probably El Nino Southern Oscillation (ENSO)-related.

AMS Radiocarbon Dating and Pollen Analysis of Core Ks0412-3 from Kashibaru Marsh in Northern Kyushu, Southwest Japan

We performed pollen analysis and accelerator mass spectrometry (AMS) radiocarbon dating on cored sediments (KS0412-3) from Kashibaru Marsh, located in the western part of the Sefuri Mountains in northern Kyushu, southwestern Japan, to investigate environmental change around the marsh. Sediment accumulation began in this marsh around cal AD 1200 and continued with an estimated average sedimentation rate of about 4 mm/yr. Human rice cultivation at this location began around cal AD 1300 and was abandoned due to the deposition of a thick sand layer at around cal AD 1400. Since this event, the area has been maintained as a “natural” marsh.

Climate Deterioration and Angkor’s Demise

Open image in new window Reconstruction of the paleoclimate based on analyses of annually laminated sediments in Japan and moat sediments from Angkor Thom in Cambodia indicates that there had been a period of drastic cooling during AD 1430–1500 accompanied by a weakening of monsoon activity. The annual mean temperatures show that—compared to the peak of medieval warm epoch around AD 1150—the mean temperature dropped by nearly 5°C in AD 1430. The climatic cooling brought about the weakening of the summer monsoon, which in turn would have resulted in the delayed arrival of the wet season. This might have had a catastrophic impact on rice cultivation in Cambodia leading to the decline of the Khmer Civilization.

Vegetation Change in the Area of Angkor Thom Based on Pollen Analysis of Moat Deposits

Open image in new window A pollen analysis of the Angkor Thom moat deposits was conducted to determine the environmental background of the growth and decline of the Khmer dynasty. The horizon of vegetation change was discovered at approximately 155 cm depth, at which there was a decrease in tree pollen grains accompanied by a rapid increase in herb pollen grains. The age of this sediment is from 645 ± 30 BP to 640 ± 30 BP, and this vegetation change corresponds to the peak of the Khmer dynasty. Furthermore, it was revealed that Poaceae plants changed from a wild species to a cultivated species based on morphological studies of Poaceae pollen. It is believed that paddy fields expanded around Angkor archaeological sites and the with harvested rice were then brought into the capital city of the Khmer Empire.