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The late Holocene lacustrine environmental evolution and paleo-typhoon records are poorly understood around lowland Liyu Lake and mountain Tunlumei Pond in eastern Taiwan. In this study, we use records of diatom populations, magnetic susceptibility, total organic carbon, carbon-to-nitrogen ratio, and δ13C from two lacustrine sediment cores in eastern Taiwan to reconstruct the paleoenvironment and the paleo-typhoon records during the late Holocene. Significant changes in lithology and in multi-proxy data in the record from lowland Liyu Lake (LYL) show that LYL became hydrologically isolated by 2850 cal BP, possibly as a result of landslide-induced alluvial fan formation. Synchronous increases of the diatom-inferred lake level proxy for LYL and regional precipitation proxies reflect a strengthened East Asia summer monsoon since 1600 cal BP. Eutrophication of the water in LYL is also inferred, and this is interpreted to be related to agricultural activities, which provides evidence for changes in land use during the past 200 years. The occurrence of diatom valves in sediment of the mountain Tunlumei Pond (TLM) indicates that the pond area has been stable since 760 cal BP, which reflects an increase in the local precipitation. The decrease of diatom-inferred pH indicates an increase in the input of acid runoff from the watershed during typhoon-triggered heavy rainfall. Both lacustrine records suggest that the typhoon intensity increased during the early Little Ice Age. The sediment records in northeastern Taiwan also suggest an increase in typhoon activity during the late Little Ice Age. The asymmetric pattern of typhoon intensity during the last 1000 years is interpreted to reflect the control exerted by anomalies in both global temperature and the El Nino-Southern Oscillation intensity on typhoon tracks over several centuries.

Influenced by rapid tectonic activities and frequent typhoons, Taiwan is unique in having extremely high rates of uplift, precipitation, denudation, and sedimentation. These dynamic surface processes not only influence landscape evolution and river behavior, but severely affect human societies both at present and in the past. Particularly, mass-movement and flooding events caused by earthquakes and/or typhoons may introduce a huge amount of sediments into river systems, and result in natural hazards due to consequent river-aggradation. The Iron Age Kiwulan Site is a recently discovered archaeological site situated on the margin of the Lanyang Plain in northeastern Taiwan. In its deposits, a cultural hiatus centered on 1150–1350 CE was recognized suggesting that the settlement was abandoned for two hundred years before being recolonized. To find the cause of this cultural break, the river-aggradation history since 800 CE has been reconstructed by a source-to-sink approach using multiple lines of evidence from the Lanyang Source-to-Sink System, northeastern Taiwan. Two particular river-aggradation events that occurred during 875–925 CE and 1400–1500 CE were traced from their source (upland river terrace), through floodplain lakes to their ultimate sink (the Okinawa Trough and Hoping Basin of the Pacific Ocean). However, as these extreme river-aggradation events occurred either significantly earlier or later than the cultural hiatus, dramatic climate and earthquake events are not likely to be the direct causes for the cultural hiatus. Instead, river migration might have been the reason for the abandonment and return of the Kiwulan settlements.

Five sediment cores from the Lomonosov Ridge and the Morris Jesup Rise north of Greenland show the history of sea-ice coverage and primary productivity over the last two glacial cycles. Variations in Manganese content, benthic and planktonic foraminifera, bioturbation, and trace fossil diversity are interpreted to reflect differences in sea-ice cover and sediment depositional conditions between the identified interglacials. Marine Isotope Stage (MIS) 1 and MIS 2 are represented by thin (

Situated at the border between the Southeast Asian continent and the northwestern Pacific, Taiwan's climate is primarily influenced by the East Asian Summer Monsoon (EASM) and episodic tropical cyclones formed in the western Pacific. The lake sediments in Taiwan thus potentially archive the information of typhoon events and past monsoon variability. A high-resolution multi-proxy (total carbon, mass accumulation rate of total carbon, weight percent of wood fragments, δ 13 C of the organic carbon, magnetic susceptibility, chemical weathering index) and well-dated lacustrine record from Dongyuan Lake (22°10′N, 120°50′E; 360 m above sea level) in southern Taiwan was used to reconstruct centennial to millennial timescale EASM oscillations specifically for the transition from the last deglaciation to the Early Holocene (17–9 ka BP). The temporal patterns of proxies on both timescales in our records broadly agree with those in the Greenland ice core, which shows enhanced EASM during the warm period and weakened monsoon during the cold period. Different from northern high-latitude climates, we found two phases in the Mystery Interval, opposite Bolling–Allerod (BA) trend with maximum monsoonal rainfall in the Allerod period and more gradual transition to Younger Dryas event in our record. Likely, other climate forcings beyond the North Atlantic climate jointly modulated the EASM. Changes of sea surface temperature in the western tropical Pacific also might have exerted synergistic control on EASM precipitation in Taiwan on the centennial timescale during the last deglaciation. In addition, several high sedimentation events accompanied by significant amounts of wood fragments were observed and coincide with the paleo-record of mass wasting events identified on various downstream floodplains in Taiwan. Since mass wasting processes were rainfall-driven and threshold-triggered, such coherence possibly indicated an intensification of typhoon activity during the early Holocene. More high-resolution lacustrine records are required to decipher the hydrological variation and climate dynamics that were co-influenced by the Intertropical Convergence Zone (ITCZ) and typhoon activity in Southeast Asia.

The formation, evolution, and potential as a climate archive of Tienchi Pond was evaluated using geomorphology, sedimentology, geochemistry, and AMS radiocarbon measurements of tree ring cores. Tienchi Pond is a small ephemeral lake situated on the subtropical Lanyu Island in the Western Pacific Ocean about 90 km east of southern Taiwan. The lake is situated on a mountain ridge and is today characterized by numerous dead trees and stumps. The position at the boundary between the two main components of the SE Asian monsoon system, the Asian landmass and the Western Pacific, makes this lake particularly interesting as a potential natural climate archive. Since previous studies have shown that the bedrock underlying the lake formed over 2 my ago, a volcanic crater origin was ruled out. Rather, element ratios of K/Ti and Ca/Fe together with 210 Pb dating suggest a recent origin for the lake, probably as the result of a natural damming event in the southern, narrower, part of the lake basin, or as a result of increased precipitation at the end of the Little Ice Age (or a combination of both). Radiocarbon measurements on a dead tree near the lake perimeter show 14 C levels of more than 1.7% modern radiocarbon near the bark, suggesting that the tree died in the early 1970s. In contrast, by correlating a large number of radiocarbon measurements to a northern hemisphere reference curve, it was shown that trees closer to the center of the lake died in the early 20th century. This agrees with a scenario where a small lake formed by initial damming, and gradually grew larger through erosion of the surrounding shore lines caused by rapid lake level oscillations.

Taiwan is particularly sensitive to changes in monsoonal precipitation and to the frequency of typhoon-induced heavy precipitation events. Many parts of this mountainous subtropical island have high erosion rates that produce high sedimentation rates in lakes and offshore ocean basins, and evidence suggests that these rates have varied in the past. A high-resolution 2 ky record of changes in sediment delivery to Dahu, a floodplain lake in northeastern Taiwan, that suggests changes in precipitation has been inferred from organic matter, pollen, and spores in a 12 m sediment core and from the organic matter compositions of soil, catchment plants, and fluvial suspended sediment. From 0 to 1400 AD, the lake experienced repeated flood events, principally resulting from overflows of the “old” Ilan River, one of tributaries of the Lanyang River, that were briefly interrupted ~ 1000 AD by decreased precipitation and/or only localized rainfall. The record of heavy precipitation can be linked to the northward shift of the ITCZ. During the early Little Ice Age, 1400–1600 AD, local erosion fluctuated in association with deforestation and farming, during which the ITCZ shifting varied as well. A decrease in precipitation since 1600 AD is linked with the southward migration of the ITCZ.

The purpose of this study is to improve prehistoric knowledge of paleo-typhoon and winter monsoon activity in the western North Pacific after 8 cal. ka BP. We examine two sediment cores derived from lakes located to the south and north of the Ilan Plain in northeastern Taiwan. Seasonal and typhoon rainfall data over the past several decades are collected for this study region. We also use mineral indicators, K/Rb ratios and grain size to estimate sediment sources, intensity of chemical weathering and rainfall intensity. The results show that the chemical weathering index (K/Rb ratio) of Meihua Lake indicates the continuing effects of autumn rainfall, while coarse grain sizes of Dahu Lake sediments suggest increased intensity in typhoon rainfall. Grain size results reveal that increasing El Nino–Southern Oscillation intensity in the tropical Pacific has intensified the activity of super typhoons in the western North Pacific. Finally, we find that frequent activity of super paleo-typhoons occurred in Taiwan during the La Nina-like state, and the strengthening winter monsoon activity and higher sea surface temperature enhanced plentiful autumn rainfall in El Nino-like state. After comparing our results with the paleo-typhoon data in Japan and south China, we suggest that the tracks of super typhoon are mainly affected by variations in the warm pool and subtropical Northwestern Pacific High in the western Pacific. Copyright © 2012 John Wiley & Sons, Ltd.

A sediment-trap monitoring program measured the fluxes of settling particles and organic carbon in Yuanyang Lake, northern Taiwan, from July 2004 to July 2006 and assessed their relations to the amounts of normal monthly and typhoon-event precipitation. The flux of settling particles varied from 0.7 mg cm−2 month−1 to 14.7 mg cm−2 month−1, and the monthly precipitation ranged from 56 mm to 1218 mm during the survey period. The contributions from typhoon-event precipitation to monthly rainfall amounts were generally larger than 70%. Higher inputs of both particulate and organic carbon into the lake were found during typhoon seasons. Of the annual settling particle loading of 14.9 tons year−1 to the lake floor, 69% occurred during the typhoon months, and 62% of the annual organic carbon loading of 2.3 tons year−1 happened during the typhoon months. These results show the importance of typhoon events on the fluxes of settling particles and organic carbon and their delivery to lakes.

X-ray fluorescence (XRF) scanning of unlithified, untreated sediment cores is becoming an increasingly common method used to obtain paleoproxy data from lake records. XRF-scanning is fast and delivers high-resolution records of relative variations in the elemental composition of the sediment. However, lake sediments display extreme variations in their organic matter content, which can vary from just a few percent to well over 50%. As XRF scanners are largely insensitive to organic material in the sediment, increasing levels of organic material effectively dilute those components that can be measured, such as the lithogenic material (the closed-sum effect). Consequently, in sediments with large variations in organic material, the measured variations in an element will to a large extent mirror the changes in organic material. It is therefore necessary to normalize the elements in the lithogenic component of the sediment against a conservative element to allow changes in the input of the elements to be addressed. In this study we show that Al, which is the lightest element that can be measured using the Itrax XRF-scanner, can be used to effectively normalize the elements of the lithogenic fraction of the sediment against variations in organic content. We also show that care must be taken when choosing resolution and exposure time to ensure optimal output from the measurements.

We present a mineralogical and geochemical study of core MD012404, retrieved from the central Okinawa Trough (OT) of the East China Sea. Our studies reveal that the sediment sources of the core have been changed through time during the past 100 ka. Our mineralogical proxies indicate that the sediments source from the Yangtze River correlates well sea-level changes before 24 ka. Our Ti/Al ratios otherwise indicate an increase of sediment supply from eastern Taiwan after 26 ka. The cooler climate of the Last Glacial Maximum (LGM, 23∼19 ka) led to a reduction in fluvial sediments from the Yangtze River. However, subsequent climate warming (after ∼19 ka) resulted in an abrupt increase in fluvial sediments. After the LGM, the Kuroshio intrusion flow into the OT may have increased. We also infer anomalous changes in eolian sources transported by winter monsoons during the LGM and at 80 ka based on an eolian mineralogical indicator (feldspar). We conclude that the sediment source of core MD012404 is primarily of terrestrial origins, but influenced by sea-level changes and variations in the East Asian monsoon.

Polycyclic aromatic hydrocarbons (PAHs) are usually loaded through atmospheric deposition into a water body and eventually into sediments. We study the PAHs from a 22-cm sediment core collected from the subtropical Feitsui Reservoir in Taiwan, and find the PAHs deposition characteristics in the reservoir, the man-made water body, is different from those in natural water bodies. The surficial sedimentary PAH fluxes are significantly higher than those in the European high altitude mountain lakes and those in the northeastern USA urban/industrial lakes. However, the catchment-corrected PAH fluxes normalized by the ratios of the catchment area to the water surface area are comparable to those of remote lakes in Europe and USA, suggesting the sedimentary PAHs in the reservoir is fluvial dominated, i.e., the reservoir system concentrated the atmospheric PAHs from the catchment area into the sediments. PAHs distribution found in the Feitsui Reservoir indicates both biogenic and anthropogenic origins. We also find the vehicular transport upstream of the reservoir is likely one of the PAHs sources to this reservoir.

Two approximately 400 ky long sedimentary records from the eastern Mediterranean Sea were used to study the factors determining why some sapropels are more or less completely erased while others are preserved. X-ray radiographs, bulk density, organic carbon content, Fe/Al and Mn/Al ratios were used to reconstruct initial thickness and burn-down ratios of sapropels S1 to S11. The results show that, at the low-sedimentation rate, open ocean settings studied, initial carbon content of the sapropel, as well as post-sapropel sedimentation rate and carbon flux have had only limited influence on the preservation of sapropels. In contrast, the regional position relative to the deep-water source controlling bottom water current intensity and bottom water oxygenation played a major role in the preservation of the sapropels. Furthermore, orbitally controlled variations in the intensity of subsequent summer insolation maxima also seem to play an important role in the preservation potential of sapropel layers. Subsequent strong insolation maxima resulting in thick sapropels tend to act as a lid, preventing further burn-down of the older sapropels below. The long and well-dated records also offer an opportunity to study the response of the benthic fauna to the drastic environmental changes related to the formation of sapropels. The sediment in the two cores is generally characterized by mottled burrows, with only scarce occurrences of distinct trace fossils such as Scolicia, Thalassinoides, Chondrites, and Trichichnus. The meager ichnofauna is attributed to the well-oxygenated and warm bottom waters in an oligotrophic environment typical for non-sapropel times. The sparse ichnofauna and the lack of tiered ichnocoenosis render existing models of bioturbational response to changes in bottom water oxygenation unsuitable for this kind of environments. However, observations on individual traces support earlier studies that suggest that the trace fossils Trichichnus and Chondrites are the result of chemosymbiotic activities that benefit from reducing conditions in the pore water, and that the producers of Scolicia have a preference for well-oxygenated conditions and sandy substrates. (c) 2006 Elsevier B.V All rights reserved.

A quantitative scanning electron microscope study of coccolithophores was sampled during the summer and winter from the surface waters over the continental shelf of the East China Sea (ECS) was conducted. In all, only ten coccolithophorid taxa were observed during the investigation periods. Emiliania huxleyi (Lohmann) Hay et Mohler and Gephyrocapsa oceanica Kamptner were predominant among the coccolithophorid flora during both seasons. E. huxleyi increased its relative abundance seaward, while G. oceanica concentrated in inner shelf area. These two species accounted for over half of the coccolithophores in the middle shelf of the ECS. These dominant taxa are eurythermal, occurring in patchy and “bull‘s-eyes” distributions in both the summer and winter, respectively. Special emphasis has been paid to the overall distribution and intra-species frequency of malformed cells of the two dominant species, as well as other minor species. Malformed cells occurred so frequently in both seasons that the frequency amounted to as much as 80% in both dominant species. The malformation was manifested largely by corroded defects. A comparison of the malformed distribution with the hydrological and nutrient parameters suggests that the malformation was caused mainly by a deficiency of nitrate in the ambient waters.

Coccolithophorids in the northeastern and central South China Sea (SCS) were surveyed in March and October 1996. The cell density of coccolithophorids ranged from 25 x 103 cells L-1 to 31 x 103 cells L-1 in sea-surface water (0–25 m in depth), and from 12 x 103 cells L-1 to 62 x 103 cells L-1 in subsurface water (150 m in depth). The lowest cell number was recorded in the subsurface (150 m in depth) in the central gyral area, while the highest one was at the same depth in the northeastern realm. A total of thirty-one species were identified. The species richness in the northeastern SCS is higher than in the central area. Emiliania huxleyi (Lohmann) Hay et Mohler, Gephyrocapsa oceanica Kamptner, Umbellosphaera Paasche spp. And Syracosphaera Lohmann spp. Dominated the surface assemblages, whereas Florisphaera profunda Okada et Honjo, Gladiolithus flabellatus (Halldal et Markali) Jordan et Chamberlain predominated in the subsurface layer. In contrast, Palusphaera vandeli Lecal emend. R. E. Norris presented in both surface and subsurface assemblages.

Last glacial to Holocene paleoceanography of the northern South China Sea was inferred from nannofossil variations and several hydrographic proxies from a piston core, SCS90-36 (17°59.70′N, 111°29.64′E, water depth 2050 m). The upper part of the sedimentary sequence (dated 15.5 to 1.2 ka) provided a high-resolution record whereas part of the sediments older than 15.5 ka was lost due to erosion. A correspondence analysis of the nannofossil succession suggests that the paleoceanography developed in four stages. The first stage (26−13.3 ka) has a fairly well-preserved diverse nannoflora dominated by Gephyrocapsa and Florisphaera profunda. The floral composition together with high concentration of ketones (C37) and organic carbon indicates high surface-water fertility. The second stage, the deglacial period (13.3−10.7 ka), had an increased surface-water turbidity and a stronger influence of Pacific open-ocean waters as evidenced by the decrease of Florisphaera profunda and increase of Emiliania huxleyi, respectively. A preservation peak of calcareous microfossils centered at 12 ka correlates to the global preservation event of Termination I. The third stage, early Holocene (10.7−4.4 ka), is marked by a gradual increase of F. profunda and small placolith taxa at the expense of E. huxleyi. The floral composition indicates that conditions were more oligotrophic compared to the pre-Holocene. The preservation of nannofossils became progressively worse, indicating a rise of the nannofossil lysocline. In sediments deposited at 5.5 and 4 ka, nannofossil preservation improves, probably reflecting a local cooling event. During the last stage, from 4.4 to 1.2 ka, E. huxleyi, Umbilicosphaera and large Reticulofenestra increased their relative abundance to replace small placoliths. Further stratification of the surface water column may have been responsible for this floral succession.

Ti/Al molar ratios of sediments in various sedimentary environments are used to explain sediment transportation from source regions to sink areas. Samples were collected from outcrops, soils, fluvial, lake, and marine sediment environments. Initial Ti/Al molar ratios of sediments are controlled by those of parent soils or rocks. These ratios tend to decline gradually as a result of heavy-mineral gravity fractionation during transportation. Sedimentary Ti/Al molar ratios in sink areas such as lakes and pelagic environments are lower than those in source regions. In this study, for the Changjiang River, Huanghe River, and Kaoping River, Ti/Al molar ratios decline considerably from downstream to estuary environments. Additionally, well sorted aeolian sands have extremely low Ti/Al molar ratios in northern China. The Ti/Al molar ratios of aerosol particles found in Taiwan and the East China Sea show reduced ratios as a result of Asia Dust Storm episodes. Furthermore, lower Ti/Al molar ratios in deep ocean sediments were discovered by tracing the distribution of sedimentary Ti/Al molar ratios in the South China Sea. When sea levels dropped during glacial periods, the river estuary was closer to deep marine areas and carried more terrestrial sediments into deep marine environments. The closer estuary with relatively higher Ti/Al ratio would lead increase of Ti/Al molar ratios in deep sea sediments. In this study, Ti/Al molar ratio is promoted as a new proxy to help with understanding changes in sedimentary environments.