Search

In this study, pollen records from lakes and bog in Taiwan were used to reconstruct regional climatic trends for the last 4000 years. The study sites included Chitsai and Li-yu Lakes (central Taiwan), Dongyuan Bog and Lake (southern Taiwan), and Sonlou Lake (northeastern Taiwan). The results provide an integrated approach to identify subtle changes during this period, despite local differences and some minor chronological differences. Based on radiocarbon dating, the climatic trends can be summarized as: a relatively prominent cold period, 3870–1920 BP (1920 BC–30 AD) and a period of successive warm/cold fluctuations; a warm period, 1920–1590 BP (30AD–360 AD, corresponding to the Roman Warm Period, RWP); followed by a cooling period 1590–1190 BP (360 AD–760 AD, corresponding to the Migration Period Cooling, MPC); a warm period 1190–650 BP (760 AD–1300 AD, corresponding to Medieval Climate Anomaly, MCA); and a cold period: 650–100? BP (1300 AD–1850? AD, corresponding to the Little Ice Age, LIA). Two cold peaks during the period corresponding to the LIA and relatively less humid conditions during the period corresponding to the MCA were also identified.

Laminated sediments in the Taipei Basin which are tentatively assigned to the antepenultimate glacial period were studied to discern the paleoclimatic significance. Analyses of multi proxies including pollen, mineralogy, grain size, and loss on ignition (LOI) were carried out on three 50 cm thick intervals of a 23.7 m thick laminated section of the Hsinchuan Core, western Taipei. The couplets are commonly composed of 2–7 mm light grey layers and 2–3 mm dark grey layers. Major components in the light grey layer are quartz (>70%) associated with clay minerals (illite). Clay minerals increase in the dark grey layer and can dominate. A pollen study indicates that the light grey layers are characterized by more abundant warm elements such as Cyclobalanopsis and Castanopsis , while the dark grey layers have more abundant cool elements including Pinaceae ( Pinus , Picea , Tsuga ), Alnus and significant amounts of Poaceae. Study of the present pollen calendar of the Taipei Basin indicates that Pinus appears during winter–spring and Cyclobalanopsis and Castanopsis appear during early summer. The studied couplets are thus very possibly seasonal deposits of the ancient lake. Spectrum analysis for the thickness variation of the light grey laminae, believed to represent most of the annual precipitation changes in summer–autumn, shows prominent El Nino Southern Oscillation (ENSO) peaks of 3–4 and 6–7 year periods. This may indicate that ENSO events occurred during the middle Pleistocene glaciation.

Pollen record derived from the sediment core of Lake Li-yu Tan, central Taiwan, provides valuable information of vegetation history, climate change, and agricultural activity. Subtropical evergreen forests dominated the uplands surrounding this lake from 2.6 ka BP, indicating the climate was warm. However, the appearance of warm-temperate forest vegetation suggests two relatively cool periods, prior to 2.3 ka BP and between 1.6 and 1.2 ka BP. Based on the presence of cultivated pollen, including Poaceae (>40 μm), Lagerstroemia , and Melia , agricultural activity was expansive between 1.6 and 1.2 ka BP and from 0.6 ka BP. This study also provides the first charcoal record in Taiwan. Natural fires occurred frequently during the interval 2.6 to 1.7 ka BP, as shown by continuous and stable charcoal influxes. Decline in charcoal influxes elucidates that fires decreased during the interval 1.7 to 1.6 ka BP. Fire events resulting from agricultural activity occurred between 1.6 and 1.2 ka BP. The high fluctuation of charcoal influxes during this period also indicates charcoal production by humans, presumably near the lake, based on the appearance of large charcoal particles (>500 μm). Fires decreased gradually from 1.2 ka BP.

A total of 233 samples from the upper 16 m of the Toushe peat core retrieved in central Taiwan were measured for TOC and δ13CTOC values. From these samples, 17 selected samples with large δ13CTOC fluctuations were analyzed for n-alkane and δD of the C27 and C29 n-alkanes. Combining with the detailed high-resolution pollen and geochemical records, this study reveals more detailed climatic variations in terms of temperature and precipitation as well as abrupt climatic events during the past 30 Kyrs. Before the Last Glacial Maximum (LGM), climate was cold and damp with predominantly woodland vegetation in Toushe Basin, and turned to cold and dry after 25 Kyr BP. Climatic conditions there were the worst during LGM over the past 30 Kyrs, especially around 23 and 18 Kyr BP when the woodland was diminished and C4 grass was dominated. Although short durations of relatively wet conditions could be found at 17, 16 and 14 Kyr BP, cold and dry climates were prevailing during 29.5–28, 24–22, 17–15 and 13–11.5 Kyr BP, corresponding to Heinrich (H) Events 3, 2, 1, and Younger Dryas (YD), respectively. During the early Holocene, dry climate occurred at ∼11, ∼10, 9.7–9.2 and ∼8 Kyr BP; whereas wet condition appeared at 10.3, 9.8, 9–7.5 Kyr BP. In the middle Holocene, climate kept warm and moderate wet in the first half period, but many dry events existed in the second half following a cold and dry event at 6 Kyr BP. After a sharply warm peak at 5.2 Kyr BP, the climate in Toushe turned to cold quickly, and tree/shrub vegetation disappeared completely with the replacement of C3 grasses. In the late Holocene, climate was relatively wetter with predominant C3 grasses in the basin. Our climatic interpretations based on the peat records agree well with the Greenland ice core and Chinese speleothem records on millennium time scales during the last glacial period. Dry climates corresponding to weakening of the East Asian Summer Monsoon (EASM) during the Heinrich events and Younger Dryas in central Taiwan and eastern China demonstrate the climatic forcing on such long time scales in concert with regional monsoon climate. However, the discrepancies exist between our peat record and the Dongge/Hulu stalagmite record on: (1) the age of H2; (2) climate intensities of LGM and H1; and (3) wetness condition during Holocene. These observations call for further study on high-resolution climatic changes especially on moisture budget in the East Asian monsoonal region.

The cold intensity of the last glacial stadials corresponding to marine isotope stage (MIS) 5d (or 5b), MIS 4 and MIS 2 in terrestrial East Asia monsoon area is not discussed much due to the paucity of long continuous pollen records. A palynological study of drilling cores from three closely-linked intramontane basins (Toushe, Sun-moon Lake and Yuchi) in central Taiwan provides a history of shifting altitudinal vegetation zones in surrounding mountains during late Quaternary climate changes. By integrating these records, we found that the alpine conifer forest approached its lowest altitude, about 614 m, during the earliest stadial (≒MIS 5d or 5b), and 745 m during the early stadial (≒MIS 4) based on records of Yuchi Basin and Sun-moon Lake. In addition, the pollen records of Toushe Basin and Sun-moon Lake show more temperate conditions for the late stadial (≒MIS 2) than the early stadial (≒MIS 4). This leads to an interpretation of a decreasing intensity of stadials during the last glaciation, which might follow the regional insolation amplitude. Such a decreasing trend in coldness during the last glacial stadials does not exist in the record for the South China Sea which reflects a different sensitivity and response to climatic forcings between terrestrial and marine.

Microfossils and a U–Pb age dating on zircon grains in the tuff beds exposed in the axial part of the Tsukeng anticline along the Pinglin River in the Western Foothills near Nantou, central Taiwan, show an occurrence of the Eocene volcanics unconformably beneath the uppermost part of the Latest Oligocene Wuchihshan Formation. This is the first discovery of the Eocene tuff exposed in the Western Foothills. The proposed Miocene “Tsukeng Formation” and “Takeng Formation” of Ho et al. (1956) named for sequences exposed in the Nantou area, Western Foothills, have to be abandoned and the standard Oligocene–Miocene lithostratigraphy used commonly in the Western Foothills of northern Taiwan is properly applicable in central Taiwan. The thick pink–brown–green colored volcanics unconformably beneath the uppermost Wuchihshan Formation is named for the first time as the Pinglin Tuff which contains Late Middle Eocene calcareous nannofossils (Zone NP16) consistent with a U–Pb age dating (38.8 ± 1 Ma) on zircon grains in the tuff. The Pinglin Tuff is overlying the Middle Eocene Chungliao Formation which contains indigenous larger foraminifera Discocyclina dispansa ex. interc. sella-dispansa and calcareous nannofossils of Zones NP14–15. The Middle Eocene Pinglin Tuff and Chungliao Formation represent the Paleogene syn-rift sequence unconformably overlain by the Latest Oligocene–Miocene post-rift sequence. This is the first document with conclusive paleontological data and age dating showing an occurrence of Paleogene marine rift basin exposed in the Western Foothills. This study also confirms similar Tertiary basin architecture between the Taiwan Strait–Pearl River Mouth Basin in the NE South China Sea and the Western Foothills onland central Taiwan.

The Western Foothills of Taiwan was known to be composed of Late Oligocene to Pleistocene shallow marine strata continuously deposited on the stable passive Chinese continental margin without significant stratigraphic break. Here we present multiple micropaleontological evidences, including occurrence of larger foraminifera Discocyclina dispansa ex. interc. sella-dispansa and calcareous nannoplanktons, to show that there are Middle Eocene marine strata (first named as the Chungliao Formation) exposed in the Tsukeng anticline of the Western Foothills, central Taiwan. Occurrences of intact tests with thin delicate outer rims and well-preserved embryonic chambers suggest that the Discocyclina dispansa ex. interc. sella-dispansa (Lutetian to Bartonian in the Tethys region) are buried indigenously on shallow inner shelf during an episodic transgression in the Early Middle Eocene. The conclusion is consistent with a biostratigraphy study of calcareous nannoplanktons (Zones NP14–15) in the shale/sandstone alternations overlying the Discocyclina-bearing bed of the Chungliao Formation and calcareous nannofossils of Zone NP16 integrated with an age dating of 38.8 ± 1 Ma (Late Middle Eocene) on zircon grains of the overlying Pinglin Tuff. The Middle Eocene syn-rift sequences (Chungliao Formation and Pinglin Tuff) exposed along the Tsukeng anticline are unconformably covered by the latest Oligocene–Miocene post-rift sequence, a scenario similar to what have been drilled in the East China Sea-Taiwan Strait-South China Sea. This rift basin (named as the Nantou Basin) is sitting on the Peikang Basement High margin which further extends southwestward to the Central Uplift of the Pearl River Mouth Basin in the northern slope of the South China Sea. The present work documents a hitherto unknown occurrence of the exposed early Tertiary marine rift basin sequence in the Western Foothills of Taiwan. The study extends our knowledge of the Western Foothills geohistory from the Late Oligocene downward to the Early Middle Eocene. The occurrence of the Paleogene Nantou rift basin in the Western Foothills may also suggest that there could have similar Paleogene rift sequences exposed in other parts of the Taiwan mountain belt like the Hsuehshan Range and the Central Range east of the Western Foothills.

Landslides and debris flows rarely occurred during historical times in the tectonically active Coastal Range of eastern Taiwan. This topographic stability, however, contrasts greatly with the widespread existence of terraced alluvial fans and fan-deltas on the Hua-tung coast which fringes the range. This study focuses on the two largest fan–terrace systems on the Hua-tung coast, both of which consist of alluvial fans (plane-view areas up to 8 km 2 ) larger than their contributing catchments. Stratigraphic data show that both systems were in sandy, wave-dominated settings during de-glacial times. The systems were then disturbed by a catastrophic landslide/debris-flow event (or events), which brought enormous amounts of gravel (Facies Gm) into the systems, deforming previously-deposited marine sands (Facies Sm) and shallowing the seafloor. The combined Gm/Sm complex yields multiple radiocarbon dates ranging from 11.3 to 8.3 ka cal BP, with a cluster around 8.6 ka cal BP. This mass-wasting event has been unique since the emergence of its contributing catchment 0.2–0.3 Ma ago. The low frequency of such an event could reflect the great resistance of rock mass in the source areas to weathering and erosion. The common blockage of valley floors by giant-boulder piles, which limits channel incision and sediment transport, could also increase the apparent stability of the mountain. The trigger of landslides in the Coastal Range has been linked to large earthquakes. Additionally, we propose that the great magnitude and duration of the observed early Holocene event were caused by the contemporaneous prolonged rainfall (and/or high frequency of typhoons) associated with the East Asian summer monsoon maximum.

High-resolution pollen records from Taiwan, Japan and Sakhalin document regional vegetation changes during Dansgaard-Oeschger (D-O) cycles during the last glacial. During the period from the cold phase (GS 18/19) to warm phase (D-O 19), the biome shift from temperate conifer forest to cold/cool conifer forest in Japan and from subtropical forest to temperate deciduous/conifer forest in Taiwan. The vegetation in D-O 17, cool mixed forest in central Japan, temperate deciduous broadleaf forest in western Japan and subtropical forest in Taiwan, indicates warm condition but not wet in all area. These vegetation changes lead to biome shift from MIS (Marine Isotope Stage) 4 to MIS 3. The abundance of Cryptomeria japonica and Fagus crenata in D-O 12 and D-O 8 indicates wet conditions brought by the strong summer monsoon through the Islands and high snowfall brought by the inflow of the Tsushima Warm Current into the Sea of Japan. The registration of other D-O warming events in MIS 3, although reflected by shifts in the abundance of key species, is not sufficient to produce changes in biomes. Development of cold deciduous forest in HS (Heinrich events) 1 in Sakhalin, Hokkaido and central Japan was conspicuous and was much larger than that in YD. Vegetation response in YD was small scale and within the same biome in the East Asian Islands. In D-O 1 at the termination of the last glacial, the same taxa that developed in the early Holocene, cold evergreen needleleaf trees in northern region, temperate deciduous broadleaf trees in central and western Japan, and warm-temperate evergreen trees in Taiwan, increased.

A pollen record sampled from a valley basin in southern Taiwan shows the environmental change—specifically vegetation and climate—that has occurred there since 22,000 cal. yr BP. In contrast to the subtropical evergreen forest found there today, temperate broadleaved and conifer mixed forest occupied the basin between 22,000 and 16,000 cal. yr BP, which suggests that climate conditions were considerably cold during the Last Glacial Maximum (LGM) and early deglacial period. During the interval from 16,000 to 11,400 cal. yr BP, this basin was situated near an ecotone of two altitudinal vegetation zones, i.e. a temperate conifer, broadleaved mixed forest and a warm-temperate evergreen forest, which suggests the gradually warming climate conditions of the late-glacial period. The climate experienced further warming between 11,400 and 8200 cal. yr BP, as evidenced by the dominance of warm-temperate evergreen forest elements. Subsequently, the subtropical evergreen forest prevailed in the basin between 8200 and 4100 cal. yr BP, which reflects a considerably warmer mid-Holocene. In addition, tropical evergreen forest appeared in the area circa 6100 cal. yr BP, marking the Holocene Thermal Optimum (HTO). Following that, a warm-temperate evergreen forest thrived between 4100 and 2100 cal. yr BP. Finally a subtropical evergreen forest began its reemergence in the basin from 2100 cal. yr BP and continues to grow there today. From a comparison of these changes in vegetation, we propose that 1) the annual mean temperature of the LGM was at least 7 °C lower than today and 2) the HTO was at least 2 °C higher than present.

Pollen records from two cores retrieved from a valley basin in southern Taiwan show major changes in vegetation and climate occurring during the Holocene. Between 11 400 and 8200 cal. yr BP, the uplands surrounding this valley were dominated by the highland forest components of Maesa, Ardisia, Castanopsis, Cyclobalanopsis, Deutzia, Hydrangea, Ligustrum and Carpinus, which indicates the period was cooler than present. An increase in lowland forest components, such as Aglaia, Phoenix, Calamus, Glochidion and Schefflera , between 8200 and 4100 cal. yr BP, indicates a warmer period than present. It also marks the Holocene thermal optimum. The basin experienced cool climate conditions during the interval 4100 to 2100 cal. yr BP, evidenced by a decrease in lowland forest components. Finally, the climate became warm again from 2100 cal. yr BP, which is analogous to the climate conditions there today. We also identify four submillennial climate phases from pollen assemblages and swamp facies. Highland forest components increased in relative abundance, while the entire valley hosted a herb-dominant swamp, suggesting that the water-table was lower and the climate was cooler. We assert that the East Asian summer monsoon was weaker during these periods (10 600—10 300 cal. yr BP, 9400—8600 cal. yr BP, 7300—7000 cal. yr BP and 5700—5200 cal. yr BP).

Pollen records from two sediment cores taken from Ilan Plain, northeastern Taiwan provide new insights into the environmental and cultural history of the last 4200 years. The record indicates a relatively warm climate at around 4200 cal b.p. The environmental conditions would have been suitable for people whose settlements and activities were mainly in the littoral zone during this period. However, at ca. 3800 cal b.p., elements tolerant of brackish water dominated the vegetation, indicating that the environment was influenced by marine incursion. The remarkable increase in wetland flora suggests the presence of widespread marshlands thereafter. It is quite conceivable that settlement movement from the fluvial plain to hills between 3800 and 2400 cal b.p. can be correlated with the environmental changes in lowlands. A conspicuous gap in the archaeological sequence between 2400 and 1300 cal b.p. corresponds chronologically with a period of heavy rainfall or frequent typhoons as indicated by the aggradational episode in the Lanyang drainage basin as well as the flourishing of Alnus forests. The persistence of frequent landslides and climate deterioration would have had a dramatic impact on ancient humans and led to abandonment of the settlements. By 1300 cal b.p. a lowland flora is widespread indicating a shift from a marsh to a terrestrial environment in response to a well-developed fluvial plain. Decrease of landslides and the amelioration in climate could have advantages to human activities again. However, both the pollen and archaeological records indicate that intensive colonisation had a profound effect upon the vegetation within the Ilan region about 400 years ago.

The East Asian monsoon Holocene optimal period has been debated both about duration and whether conditions were a maximum in thermal conditions or in precipitation. In this study we show Holocene climate variability inferred by a forest reconstruction of a subalpine pollen sequence from peat bog deposits in central Taiwan, based on modern analogues of various altitudinal biomes in the region. A warmer interval occurred between 8 and 4 ka BP (calibrated 14 C years) when the subtropical forests were more extensive. The Holocene thermal optimum is represented by an altitudinal tropical forest at 6.1–5.9 ka BP and 6.9 ka BP and only the latter was accompanied by wet conditions, indicating decoupling of thermal and precipitation mechanism in the middle Holocene. Abrupt and relative severe cold phases, shown by biome changes, occurred at about 11.2–11.0 ka BP; 7.5 ka BP; 7.2 ka BP; 7.1 ka BP; 5.2 ka BP, 5.0 ka BP and 4.9 ka BP. A spectral analysis of pollen of a relatively cold taxon — Salix, reveals that the time series is dominated by a 1500 yr periodicity and similar to the cold cycle reported in the marine records of Indian and western Pacific Oceans. The cold–warm conditions inferred by the change of forests show close relationship to solar energy in comparison with the production rate of Be-10.

The pollen record from the Toushe Basin (23°49′N; 120°53′E; 650 m above sea level), a peat bog of central Taiwan, displays a continuous vegetation history of the past 96,000 yr BP of monsoon Asia. Instead of today's closed subtropical evergreen broadleaved forest dominated by Machilus – Castanopsis surrounding the basin, temperate deciduous forest predominated during most of the last glacial. In early MIS 4, Alnus reaches the highest value of the whole sequence (60–70%) representing temperate deciduous forest and relatively cold and arid conditions. Following this stadial, Alnus and herbs (mainly Cyperaceae) dominated alternately, with a minor increase of Castanopsis. Peaks of monolete spores between cal. 42.2 and 37.0 kyr BP (kyr BP represent calibrated years) indicate episodic wet conditions. The later glacial, especially between 23.2 and 18.7 kyr BP, shows a high percentage of Gramineae, indicating dry and possibly sometimes cold conditions. The late glacial shows a remarkable increase of warm-temperate to temperate forest elements, such as Ilex , Cyclobalanopsis and Symplocos. At about 15.1 kyr BP a peak of monolete spores indicates wet–warm conditions. A subsequent sharp increase of Salix and then Gramineae between 13.0 and 11.6 kyr BP corresponds to the Younger Dryas. A warming event at 11.5 kyr BP is also evident. The Holocene is characterized by warm–wet conditions of the overwhelmingly abundant monolete spores since 10.7 kyr BP and the prominent increase of Castanopsis .

The coastal morphology of Taiwan exhibits characteristics of collisional tectonism superimposed upon global sea level changes. The island's eastern coast is situated on the accreted Luzon arc alongside the NE–SW trending plate boundary. To the west, the Central Range, Hsueshan Range and Western Foothills are the fold and thrust belts of the island. They are the raised continental shelf and slope sediments or meta-sediments of the Chinese continental margin. The northern and southern coasts of the island are in the two tips of these belts. The western coastal area is mostly in the foreland of the orogen. Situated on the accreted arc proximal to the collision zone, the middle and southern portions of the eastern coast have high uplift rates of up to 9–10 mm/yr. Holocene transgression deposits reach 50 m amsl or more. There are commonly 3–4 flights of Holocene terraces. Thrusts and warping are recognizable along the northern and southern coasts because they trend perpendicular to the main fold and thrust belts of the island. The Holocene uplift rates are typically about 0–5 mm/yr. Higher rates occur in the upthrown limbs of the thrusts or areas proximal to up-warping axes. Sitting on the foreland basin, the development of the western coast is related to the westwardly propagation of fold and thrust belts which in turn are influenced by the lithological rigidity of the underlying basement. Coastal areas underlain by two Mesozoic basement highs are relatively stable or have low subsiding rates (about 2–3 mm/yr). Between these basement highs lie an area occupied by the west front of the fold and thrust belts, which has an uplift rate similar to the northern and southern coasts. To the south of the basement highs, the coastal plains probably conceal newly developed folds or faults where SW trending, paleo-incised valleys and domes of Late Pleistocene and Holocene age exist beneath the coastal plains’ surfaces as indicated by several tens of drilling cores from the plains. This suggests an incipient stage of fold and thrust belt development. The southwestern-most coastal plains are believed to be a piggy-back basin of the fold and thrust belts, showing a higher subsidence rate (6–8 mm/yr) than other parts of the western coast.

We used radiometric dates from 19 sites to determine the Holocene uplift rates of the 140-km-long Hua-tung coast in eastern Taiwan. These rates ensure that the formation of major marine terraces on the coast, several tens of meters in height, is related to the deglacial relative sea-level cycle, with which the uplift rates were further constrained by the elevations of the marine-terrace elements. Uplift rates are less than 4 mm/yr in the northernmost 30 km-long coast, and are 4–7 mm/yr in the adjacent 30-km-long coast. The rest of the coast is generally uplifted 7–9 mm/yr, with local troughs ( 700 m) and high (>40 m) mudstone platforms are observed to slope below the sea level. These changes in uplift rate or style are all accommodated on the surface by warping. Most of them are irrelevant to the known bedrock structures, suggesting a change in uplift style, and perhaps also mechanics, of the coast during the Holocene.

Based on the palynological study of two alpine lakes of the central mountains and a lake at 460 m elevation in northeastern Taiwan, a warm event which lasted several hundred years from about cal 2 ka, followed a cool-dry interval from about cal 3.7–2.0 ka. Evidence indicates a warmer annual temperature of 1–2°C and relatively higher precipitation during the warm interval compared with the cool-dry interval. Sea level at cal 2–1.5 ka is estimated to have been 130–150 cm higher than at present based on data from the Penghu Islands off western Taiwan (Chen and Liu, Quaternary Research 45, 254–262, 1996). In northern Taiwan, the corresponding sea level rise is recognized by a widening of the estuary in the Taipei Basin (Lin, Development of Taipei City, pp. 159–246, 1981), which is consistent with the distribution of archaeological sites around cal 2 ka. The age of lower river terraces in northern (Lanyang) and southern (Erhjen) Taiwan, are consistently in the range cal. 2.5–1.5 ka. This suggests an island-wide morphological process, probably relating to climate change. This study discusses the inferred climate change and possible morphological responses.

Last Glacial Maximum (LGM) carbon storage in eastern Asia is a key issue for understanding the sinks and sources of paleocarbon. Palynological data with good time constraint for the LGM in a peat bog from a site at 650 m above mean sea level in central Taiwan, together with data from low-lying deltaic and basin deposits of Taiwan and South China, increase our understanding about vegetational evolution and possible terrestrial carbon storage in this area and probably eastern Asia. Contrasting to today's Machilus–Castanopsis forest zone around the peat bog, the vegetation before the LGM was dominated by Alnus, a relatively xerophytic element in Taiwan. An increase in herbs and decrease in spores during the LGM is recognized when compared with Holocene and modern assemblages. A less humid interval dominated by herbs (>50%) occurred between 21 and 15.8 ka. Basin deposits in northern Taiwan and deltaic deposits in central Taiwan show that during the LGM Artemisia, Umbelliferae and Gramineae were the main components contrasting with the Pinus or Cyclobalanopsis-dominant assemblages in the rest of the last glacial. Thus, less humid conditions lasted about 5000 to 6000 years in the LGM even on this very humid island. This may also be true in eastern Asia where a large area of the widely exposed continental shelf may have been occupied by grasslands and the uplands of South China were occupied by less dense coniferous or temperate forests during the LGM in contrast to the modern subtropical forest. This scenario improves our understanding of the terrestrial paleocarbon storage.

High resolution paleoceanographic proxy records from a deep-sea core in the northern South China Sea (SCS) and palynological records from a lake core in central Taiwan have been measured for the last 25 kyr. The variations in these proxy records are interpreted in terms of the past variation in the Asian monsoons. The two consistent and complementary records suggest that the East Asian monsoon system has fluctuated significantly from a strengthened winter monsoon during the last glaciation (25,000-12,000 yr BP) through a moderate to weak winter and summer monsoons during the deglaciation (12,000-10,000 yr BP) to an enhanced summer monsoon in the Holocene. Strengthening of the winter monsoon during the glacial is deduced from decreases in winter SST and increases in productivity indicators, such the abundances of alkenones and total organic carbon in the SCS. A stronger summer monsoon during the Holocene is inferred from the increases in floral productivity, the sedimentation rate of peat, the deposition of storm-related clay layers in the lake sediment, and the higher abundance of thermophyte Castanopsis. The 25 kyr paleomonsoon history registered in the SCS core and the Taiwan lake sediments is in agreement with the climatic records of the Chinese Loess plateau.

A sediment core collected from the Sun Moon Lake in middle Taiwan was investigated for 210 Pb and 239,240 Pu. Based on the decrease of excess 210 Pb with depth, the mean sedimentation rate in the lake during the past half century is about 0.9 cm yr −1 , which is unequivocally supported by the appearance of the 1963 plutonium fallout maximum at 26–28 cm. The short-term sedimentation rate is one order of magnitude greater than 14 C-based long-term sedimentation rates in the lake reported previously. This may be attributed to the deterioration of soil conservation associated with the construction of a dam five decades ago. Total downcore inventories of excess 210 Pb and 239,240 Pu are 54.5 dpm cm −2 and 0.21 dpm cm −2 , respectively. This 210 Pb inventory requires a flux of 1.7 dpm cm −2 yr −1 at steady state, which is similar to 210 Pb fluxes observed at other sites in the western Pacific rim. The inventory of 239,240 Pu is in excellent agreement with documented cumulative 239,240 Pu from global fallout (0.96 ± 0.07 mCi km −2 ) at the 20–30°N latitudinal band. Our data suggest that the Sun Moon Lake is an ideal setting for monitoring atmospheric fallout and environmental changes in this region.

This paper discusses the relative Holocene sea level change in a small lowland of Takagami, located on the central part of the Choshi Peninsula, easternmost of Kanto district. Samples obtained by drilling machine and peat-corer were used for radiocarbon dating, sedimentary facies observation and analysis of molluscan, diatom and pollen assemblages. Our data, combined with our first report (OTA et al., 1985), reveal that the Postglacial transgression has started at c. 10, 000y.B.P. at the latest. A rapid sea level rise has continued till c. 7, 000y.B.P., followed by a decrease of water depth. The upper limit of marine deposits is about 4.0m above mean sea level. The culmination of relative sea level rise has occurred at about 5, 500y.B.P., judged by clustering of radiocarbon ages of the lowest terrestrial peat bed in c. 5, 000-5, 500y.B.P. Since then, sea level probably has lowered to the present position without any intermittent uplift.

Over 1000 marine and terrestrial pollen diagrams and Some hundreds of vertebrate faunal sequences have been studied in the Austral-Asian region bisected by the PEPII transect, from the Russian arctic extending south through east Asia, Indochina, southern Asia, insular Southeast Asia (Sunda), Melanesia, Australasia (Sahul) and the western south Pacific. The majority of these records are Holocene but sufficient data exist to allow the reconstruction of the changing biomes over at least the past 200,000 years. The PEPII transect is free of the effects of large northern ice caps yet exhibits vegetational change in glacial cycles of a similar scale to North America. Major processes that can be discerned are the response of tropical forests in both lowlands and uplands to glacial cycles, the expansion of humid vegetation at the Pleistocene-Holocene transition and the change in faunal and vegetational controls as humans occupy the region. There is evidence for major changes in the intensity of monsoon and El Nino-Southern oscillation variability both on glacial-interglacial and longer time scales with much of the region experiencing a long-term trend towards more variable and/or drier climatic conditions. Temperature variation is most marked in high latitudes and high altitudes with precipitation providing the major climate control in lower latitude, lowland areas. At least some boundary shifts may be the response of vegetation to changing CO2 levels in the atmosphere. Numerous questions of detail remain, however, and current resolution is too coarse to examine the degree of synchroneity of millennial scale change along the transect. (C) 2003 Elsevier Ltd and INQUA. All rights reserved.

Pollen analysis of a 15.0 m core covering the past 3500 years from the Ilan Plain, northeastern Taiwan, displays a record of environmental changes and climate trends for the late Holocene. At about 3500 yr B.P., brackish water-tolerant elements, such as Bruguiera and Acrostichum, dominated the vegetation, reflecting that the environment was influenced by marine excursions. Following this period, wetland elements Poaceae and Cyperaceae were abundant between ca. 3350 and ca. 3100 yr B.P. Then pioneer taxon Alnus increased at the expense of those herbs in the later part of the interval ca. 3100 and ca. 2000 yr B.P. This suggests a shift from a primarily coastal (ca. 3500 yr B.P.) to wetland (ca. 3350 yr B.P.) and then finally terrestrial (ca. 2000 yr B.P.) environment at the coring site. Since then, the present fluvial plain has existed. Humidity conditions which were interpreted from the amount and variations of fern spore probably indicate a strengthening of the monsoon at ca. 3200, ca. 2000, and ca. 900 yr B.P., respectively. The Medieval Warm Period is also apparent indicated by the amount of arboreal elements based on pollen concentrations ca. 1300 to ca. 900 yr B.P. Significant human-induced vegetation changes occurred between ca. 1300 and ca. 900 yr B.P. and over the last 400 years.

A 3.5m core taken from Chitsai Lake (altitude 2890m) of central Taiwan shows the vegetational and environmental changes in a Tsuga forest since 5000yr BP. During about 5300-4840yr BP(Zone 4), the Tsuga forest experienced a dear fluctuation toward a Tsuga-Cyclobalanopsis mixed forest. The high percentages of Cyclobalanopsis in the lower half of this zone (Subzone4b) indicate the last episode of the mid Holocene warm interval. Tsuga forest was well established in the later half of this zone. The extremely abundant spores as well as the finest sediments together indicate high lake level and moist climatic conditions. Between about 4840 and 3730 yr BP (Zone3), a warmer episode occurred in which Cyclobalanopsis increased slightly compared with Subzone 4a. Following this, during about 3730-2030yr BP (Zone 2), the relatively high percentages of Abies, Ericaceae and Tsuga as well as lower percentages of Alnus and Pinus indicate cooler but stable environmental conditions, Zone 1 represents vegetational changes during the last 2000 years. The increase in Cyclobalanopsis indicates warmer conditions than before. The remarkable decline of Tsuga and Ericaceae accompanying the increase in the secondary forest elements such as Alnus and Pinus may indicate a change in environment. The larger grain size of silt in Zone 1than in Zone 4, a higher erosion which may be due to stronger precipitation seasonality in a warmer climate. The upper 15cm shows rapid increase in secondary forest elements such as Pinus and Alnus. Whether it is related to the increasing atmosphere CO2 is worthy of further investigation.