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Late Holocene vegetation, climate and human impacts were investigated using palynologiacal and marco-charcoal data from lacustrine sediments from a lowland lake of eastern Taiwan. On the basis of sixteen 210Pb dates and six radiocarbon dates, a reliable stratigraphic chronology was established. The 2680 year records of vegetation history and fire frequency indicated five distinctive stages, reflecting the exhibits of climate changes and human activities. During 2680–2410 cal yr BP, the lake was shallow and the climate was relatively cool, according to the domination of wetland and upper montane forest pollen. The following period during 2410–1510 cal yr BP, the increase of low montane forest pollen and the overall high value of fire frequency indicated the warm and less humid climate. During 1510-560 cal yr BP, the low montane forest pollen remained high values, and the climate was warm and stable. During 560-130 cal BP, the low pollen concentration companying with high frequency of nearby taxa, Lagerstroemia inferred to increase in soil erosion. The period with intensive soil erosion can link to the occurrences of extremely precipitation. It may correlate to the frequent typhoons during the Little Ice Age, during which the reduction of the West Pacific Warm Pool and expansion of the Northwestern Pacific High enhanced westerly shift of typhoon track toward Taiwan and southern China. During last 130 cal yr BP, the strong impacts of human activities were indicated by the low arboreal pollen, high cultivated Poaceae, and more fire events. It is worth to note that the global temperate anomalies could be identified within this lowland lacustrine sediments, including the Medieval Warm Period and the Little Ice Age, based on the proxies of pollen-inferred temperature. Pollen signals including cultivated Poaceae pollen and pollen diversity index indicate significant human agriculture during the intervals of 2680–2410 cal yr BP, and during 1510 cal yr BP to modern time, which may be linked to the local environment changes, leading to the population variation in eastern lowland Taiwan.

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.

Sun Moon Lake is the first dam reservoir constructed in Taiwan with the capability of generating hydroelectricity satisfying the whole Taiwan need during the Japanese colonial period since 1934 CE. Now, the Sun Moon Lake is one of the biggest hydropower stations in Taiwan and has become an important touring area. During World War II (1944–1945 CE), the hydroelectric power plant at Sun Moon Lake was bombed by the U.S. air force, which caused severe damage to the dam structure. More recently, the dam structure was also damaged during the 1999 CE Chi-Chi earthquake whose epicenter is nearby in the Nantou County. A suite of cores were taken from both Sun Lake and Moon Lake, and two selected cores, Sun 2–1 and SM 16 4–3, from Sun Lake were detailed studied with multiple analyses, including X-ray imaging, magnetic susceptibility, visible spectrophotometry, X-ray fluorescence (XRF) scanning, and mineral analysis. We discovered that the increase of Ca content in the sediments not only clearly indicates when the dam was constructed at Sun Moon Lake but also records evidence of structure repairs after both the World War II bombing and the Chi-Chi earthquake. Additionally, the yellow turbidite, X-ray image, and low-Ca signals in Core Sun 2–1 strongly correlate to the typhoon events that caused severe floods in the watershed of Zhuoshui River. The turbidite layers caused by the 1963 Gloria Typhoon are also characterized by conspicuous high peak of Fe/Mn in both cores. This study shows that XRF scanning results are useful for recognition of human activity and for high precipitation event correlation. Moreover, the appearance of charcoal layers shows evidence of forest burning and slash-and-burn activities by humans during the past 4,000 years back to the Middle Neolithic Age.

Polarity reversals of the geomagnetic field have occurred through billions of years of Earth history and were first revealed in the early 20th century. Almost a century later, details of transitional field behavior during geomagnetic reversals and excursions remain poorly known. Here, we present a multidecadally resolved geomagnetic excursion record from a radioisotopically dated Chinese stalagmite at 107-91 thousand years before present with age precision of several decades. The duration of geomagnetic directional oscillations ranged from several centuries at 106-103 thousand years before present to millennia at 98-92 thousand years before present, with one abrupt reversal transition occurring in one to two centuries when the field was weakest. These features indicate prolonged geodynamo instability. Repeated asymmetrical interhemispheric polarity drifts associated with weak dipole fields likely originated in Earth's deep interior. If such rapid polarity changes occurred in future, they could severely affect satellites and human society.

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.

Recent reduction in high-latitude sea ice extent demonstrates that sea ice is highly sensitive to external and internal radiative forcings. In order to better understand sea ice system responses to external orbital forcing and internal oscillations on orbital timescales, here we reconstruct changes in sea ice extent and summer sea surface temperature (SSST) over the past 130,000 yrs in the central Okhotsk Sea. We applied novel organic geochemical proxies of sea ice (IP25), SSST (TEXL86 ) and open water marine productivity (a tri-unsaturated highly branched isoprenoid and biogenic opal) to marine sediment core MD01-2414 (53°11.77′N, 149°34.80′E, water depth 1123 m). To complement the proxy data, we also carried out transient Earth system model simulations and sensitivity tests to identify contributions of different climatic forcing factors. Our results show that the central Okhotsk Sea was ice-free during Marine Isotope Stage (MIS) 5e and the early-mid Holocene, but experienced variable sea ice cover during MIS 2–4, consistent with intervals of relatively high and low SSST, respectively. Our data also show that the sea ice extent was governed by precession-dominated insolation changes during intervals of atmospheric CO2 concentrations ranging from 190 to 260 ppm. However, the proxy record and the model simulation data show that the central Okhotsk Sea was near ice-free regardless of insolation forcing throughout the penultimate interglacial, and during the Holocene, when atmospheric CO2 was above ∼260 ppm. Past sea ice conditions in the central Okhotsk Sea were therefore strongly modulated by both orbital-driven insolation and CO2-induced radiative forcing during the past glacial/interglacial cycle.

The 2008 Mw 7.9 Wenchuan Earthquake produced two major rupture zones: one in the Yingxiu-Beichuan fault zone (YBF) and another in the Anxian-Guanxian fault zone (AGF). A shallow trench was dug in Bajiaomiao village, Dujiangyan, Sichuan Province, which experienced a ∼4.3 m vertical offset during this large earthquake. The hanging wall of the YBF in this trench includes fault gouge and breccia. Optical microscope observations and X-ray diffraction (XRD) measurements show obvious differences between the fault gouge and breccia. Moreover, rock magnetism measurements were collected and include mass magnetic susceptibility (MS), Isothermal Remnant Magnetization (IRM), Saturation Isothermal Remnant Magnetization (SIRM), high-temperature thermo-magnetism (K–T) and magnetic hysteresis loops. Several cm-thick magnetic mineral anomalies are observed close to the Wenchuan Earthquake surface rupture zone of the YBF. Magnetite and Fe-sulfide are the main magnetic carrier materials for the fault rocks close to the surface rupture zone, including 3 cm-thick fault gouge and 3 cm-thick fault breccia, while the other fault breccia, further from the surface rupture zone, contains the paramagnetic minerals. The possible magnetic change is attributed to newly-formed magnetite from paramagnetic minerals at high temperatures (>500 °C) during the large earthquake, implying that the YBF has ever experienced high-temperature thermal pressurization earthquake slip dynamics. Moreover, the YBF has also experienced high-temperature frictional melting earthquake slip dynamics, constrained by the multiple vein pseudotachylite. These high-temperature earthquake slip processes may be responsible for the high dip angle thrust characteristic of the YBF.

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.

When an earthquake occurs, magnetic minerals are formed in the gouge under the combined action of frictional heating and fluid. Generally, the gouge is altered, and a detailed analysis of neoformed minerals is difficult. The Taiwan Chelungpu fault Drilling Project provided continuous records of the active Chelungpu fault gouges. By analyzing the magnetic parameters along the 16 cm thick gouge which houses the principal slip zone of the 1999 Chi-Chi earthquake (Mw 7.6), we observed a 4 cm shift between the maximum of magnetic susceptibility and the maximum of remanence. The maximum magnetic susceptibility is localized along the principal slip zone. The main identified magnetic minerals are magnetite and goethite, which have very different magnetic parameters. We propose that the maximum of the concentration of magnetite and goethite corresponds to the maximum of magnetic susceptibility and remanence, respectively. By modeling the concentration of these two magnetic minerals, we explain satisfactorily the profiles of magnetic susceptibility and remanence. This quantitative modeling indicates that ~200 ppmv of magnetite formed in the principal slip zone and its main contact area. Similarly, ~1% of goethite is formed in the center of the gouge, where the fluids are more enriched in iron. We propose that the magnetite and goethite are formed and altered during seismic cycles. Key Points Investigate the magnetic mineral assemblage in the Chi-Chi fault gougeClarify the distribution of goethite and magnetite in the gougePropose a model for goethite and magnetite distributions within the gouge

To study the Holocene paleomagnetic field in Taiwan area, we performed a series of magnetic experiments to a marine sediment core OR1-715-21 obtained from the offshore of eastern Taiwan during the OR1-715 cruise. Analyzed magnetic properties show that the remanent magnetization carriers of the core are uniformly dominated by single-domain and pseudo-single-domain magnetite, revealing a suitable material for relative paleointensity (RPI) estimation. The stable and well defined characteristic remanent magnetization (ChRM) provides the reliable determination of the inclination and declination. Dipole moments were further calculated by using the RPI and inclination data. The variation of the dipole moments compares well to the CALS10k.1b model (a continuous model of archaeomagnetic and lake sediment data for the past 10000 years), implying the dominance of the dipole field in Taiwan area. Though the real declination is unavailable because of lacking core orientation during coring, we could correct the values based on some critical conditions. If the paleosecular variation (PSV) is considered, the virtual geomagnetic pole (VGP) is generally suggested to vary between 80°N and 90°N instead of coinciding with the geography North Pole. To fit the condition considering the PSV effect, the ChRM declination had to be rotated 180° to get the corrected declination. As a result, variation patterns of the paleo-inclination, -declination, and paleointensity could be suitably determined in the study. Outcomes of these analyses reveal that the paleomagnetic field in Taiwan region should be dominantly driven from the dipole field under the PSV effect for the last 7500 years.

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.

Primary rock magnetism analysis was performed on samples from the Jiulong outcrop across the Anxian–Guanxian fault of the 2008 Wenchuan Earthquake rupture zone. The protolith of hanging wall of this outcrop is the upper Triassic sediments, which formed the fault breccia and gouge by repeated large earthquakes. The footwall of this outcrop contains Jurassic grayish-green and dark-purple sandstones. The average magnetic susceptibility value of the gouge is slightly less than that of potential protolith. Based on the primary rock magnetism, the main magnetic carriers are Fe-sulfides for the gouge, magnetite for the fault breccia, and magnetite and hematite for the Jurassic grayish-green and dark-purple sandstones. Possibly during or after repeated large earthquakes (just like the 2008 Mw 7.9 Wenchuan Earthquake), it transformed the magnetic mineral from magnetite to Fe-sulfides by low thermal decomposition processes along the Anxian–Guanxian earthquake fault, which induces the slightly less average magnetic susceptibility values of the gouge than that of potential protolith. If this magnetic mineral changed only because of repeated large earthquake process, the heating by low velocity seismic slip friction and seismic fluid could possibly have been less than 300 °C. If this magnetic mineral of the Anxian–Guanxian earthquake fault is only induced after repeated large earthquakes, the earth surface process acts an important role for the magnetic mineral change. More other further studies should be done to verify the primary magnetic mineral phase change and discriminate the time of this magnetic mineral variation.

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.

We studied diatoms in a 55.5-cm-long sediment core from a subalpine lake in northern Taiwan, Tsuifong Lake (TFL), to investigate environmental changes from AD 490 to present. Diatom assemblages of the last century were dominated by acidophilous species, whereas alkaliphilous taxa dominated the record between AD 1480 and 1910. Over the studied time frame, four decadal periods with high precipitation were inferred from evidence of elevated soil input from the watershed, supported by the stable isotope signatures (δ15N, δ13C) of organic matter and magnetic susceptibility of the sediments. We compared the inferred changes in pH of TFL to values obtained from three other Taiwanese subalpine lakes. The present study revealed that elevated precipitation was associated with increased solar irradiance over the last five centuries, with a stable dry period between AD 490 and 1450. Acidification of TFL in the last ~100 years was a consequence of deforestation and acid rain. peerReviewed

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.

This study used a paleomagnetic method to analyze the marine sediment core, called MD01-2414, taken from the Okhotsk Sea during the IMAGES VII cruise in 2001. The results indicate that the Brunhes/Matuyama boundary appeared at the depth of 27.76 m, with the age of 0.78 Ma. The lower and upper bounds of the Jaramillo event are located at 36.96 and 34.74 m depth, respectively. Cobb mountain event is found at a depth between 40.67 m and 41.06 m. Close to the bottom of the core, normal polarity is observed; it is proposed to be the termination of the Olduvai normal event. This event implies that this core signifies an age interval of about 1.8 Ma. Excursions could be identified from the paleomagnetic directional record, such as Kamikatsula, Santa Rosa; the relative paleo-intensity secular variation pattern also helped to delimit magnetic excursions in the Brunhes normal epoch, e.g. Iceland Basin event, Big Lost event, etc. Thus, the age model of this core can be well established. Based on the age model, the variations of magnetic susceptibility and ARM/χ of this core indicated that highly abundant but relatively coarse grain of magnetic minerals appeared in the even stages of oxygen isotope chronology, while low abundance with finer grain appeared in the interglacial periods. This suggests that there are different sources and transportation pathways of the sediments deposited in the area studied during glacial and interglacial periods. During the glacial time, terrigenous sediments containing abundant magnetic minerals eroded by the ice river from the Kamchatka peninsula were brought into the central Okhotsk Sea by the West Kamchatkan current (WKC), while the central and western parts of the Okhotsk Sea were completely covered by sea ice. During the interglacial time, the WKC and the East Sakhalin current (ESC) brought lots of terrigenous sediments from the north and west (the Siberia continent), which contain less abundant magnetic minerals and dilute the signal of magnetic susceptibility.

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.

We describe the environmental variation in the Banda Sea over the past 820 ka by using the magnetic parameters and oxygen isotope data from the core MD012380. Overall, characteristics of the magnetic parameters show simultaneous variation with marine isotope stage (MIS), especially in the last 420 ka. There are fewer, coarser and more oxidative magnetic minerals in glacial periods, and turn to opposite conditions in interglacial periods. Spectral results clearly present the Milankovitch periods over the last 820 ka, especially the eccentricity period (400-ka and 100-ka). However, the magnetic data shows different pattern before and after 420 ka. Thus, we segmented the time-series data into two periods: MIS 20 to MIS 12 and MIS 11 to MIS 1. During MIS 20 to MIS 12, the spectra of magnetic data show clear periods related to the obliquity (41-ka) and precession (23-ka and 19-ka), while they present only the eccentricity period (100-ka) during MIS 11 to MIS 1. This feature, which splits the late Pleistocene at around 420 ka, could be attributed to the mid-Brunhes event (MBE). In the Banda Sea, main factor controlling the variation of the magnetic minerals is considered as the fluctuation of the Indonesian Throughflow (ITF) intensity due to sea-level change. Thus, the magnetic data show clear 400-ka and 100-ka periods (main MIS cycle). Besides, the eccentricity signals are relatively dominant in the last ∼420 ka, implying that the ITF might become more important after the MBE in the Banda Sea.

In this study, we synthesized the fossil pollen data from 10 lake sediments and 2 land cores to integrate the alteration of forest covered areas in northern Taiwan with changes in humidity and temperature over the last 2000 years. The abundance of arboreal pollen, fern spores and Tsuga pollen in the pollen and spore assemblages were used as indicators. Our results suggested that the climate in northern Taiwan was stably cool and dry during 2000–1000 cal. yr BP, but changed to wet and warm during 1000–500 cal. yr BP, which corresponded to the Medieval Warm Period (MWP). In addition, an increased density and dispersal of Tsuga pollen corresponding to 500–200 cal. yr BP was observed, which corresponded to the Little Ice Age (LIA). In recent years, a decline in Tsuga pollen density and increased fern spore density has been observed, which indicates an increase in temperature associated with elevated rainfall. Based on the synthesized data set, we conducted GIS mapping of such changes in the north of Taiwan over time. The results revealed that the temporal and spatial climate changes could be inferred from the palynological GIS mapping method, and that the fluctuations in temperature over time matched well with the global climate events, including MWP, LIA and recent warming.

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.

In order to study how the Holocene Central Asian climate is coupled to the global climate system, a 4.24 m long lake core from western Inner Mongolia in China was studied using a multiproxy approach. Sedimentology and geochemical parameters such as gypsum and dolomite content, presence of lakeshore sand changing to aeolian sand, and changes in paleomagnetic properties bear witness to a trend toward a generally drier climate over the late Holocene. Aridification is linked to the southward retreat of the northern boundary of the Asian summer monsoon, leaving central Asia under the influence of the westerly belt. The weakening of the Asian summer monsoon in turn was caused by an orbitally driven decrease in summer insolation. The weakening summer insolation also likely increased the intensity of the Siberian High pressure system, further promoting aridification of central Asia. On a shorter time scale, the multiproxy record shows the climate to have been relatively dry during the Medieval Warm Period (AD 800–1100) with the ensuing humid environment at the end of this period gradually turning to become extremely dry (AD 1100–1550) at the Little Ice Age Maximum. Switches in the North Atlantic Oscillation caused these changes through a teleconnection in the form of westerlies. These westerlies provided most of central Asia’s moisture after the retreat of the Asian summer monsoon. The central Asian climate therefore corresponds closely with late Holocene European climate changes.

This study described the diatoms appeared in the sediments of Liyu Lake, a lowland natural lake situated at Hualen, eastern Taiwan. A total of 50 species was found in the sediments of this eutrophic lake. In them, 8 species were reported for the first time in Taiwan. They are: Cymbella thienemannii, Navicula absoluta, Navicula bacillum, Frustulia rhomboides var. crassinervia, Gyrosigma procerum, Nitzschia paleacea Epithemia smithii and Eunotia subarcuatioides. The ultrastructures of each species were described on the basis of observations under a scanning electron microscope. The ecological implications of the occurrence of these diatom species in this lake were inferred.

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).

We reconstruct the earth magnetic field in the Brunhes epoch at the Banda Sea by studying the paleomagnetic data from core MD012380, collected during the International Marine Global Change Study (IMAGES) VII Cruise in 2001. Magnetic analysis is carried out for whole core with a sampling spacing of 1 cm by using u-channel. Magnetic susceptibility (χ), nature remanent magnetization (NRM), anhysteretic remanent magnetization (ARM), and isothermal remanent magnetization (IRM) are measured in our paleomagnetic experiment. Results show the low latitude geomagnetic field variation at the Banda Sea during the last ∼820 kyr. Except for the Brunhes/Matuyama boundary (BMB), there is no clear signal of reverse events in paleo- inclination and paleo-declination patterns. However, the synthetic paleointensity curve displays the asymmetrical saw-tooth pattern that can be used for determining reverse events, and shows a maximum intensity drop at the BMB. The characteristics of paleointensity provide a useful tool to identify reverse signals and improve the difficulties from only using inclination and declination patterns, especially at low latitude. With the help of paleointensity, inclination and declination, we have identified five reverse events. Furthermore if we consider the secular variation effect, we think that the strong negative inclination observed in our study may be the zonal time-averaged field with paleo secular variation, rather than non-dipole effect within the Brunhes epoch.

Characterized by extended seasonal sea-ice cover, the Okhotsk Sea is widely considered one possible source of the North Pacific Intermediate Water (NPIW). Therefore, reconstructing the characteristics of the sediments that resulted from the ice-melting pulses of this northeastern Asian sea during glacial–interglacial cycles is crucial to understanding past climatic changes and NPIW formation in the northwest Pacific Ocean. Here, we produced the detailed mineralogy and geochemistry of the upper 20 m of the sediments of IMAGES Core MD012414, which was drilled in the central part of the Okhotsk Sea. This depth covers the last 500 kyrs. The mineralogical data show that in glacial periods, the sediments were predominantly composed of quartz and plagioclase with a volume of about 80%, indicating that they were mainly from the surrounding landmasses. During interglacial periods, however, biogenetic calcite and amorphous opal drastically increased from less than 5% to a remarkable 40–60%, while the element ratios Mg/Al, Ca/Al and Si/Al also had anomalous increases from 0.2 to 0.5, 0.12 to 1.2 and 3.5 to 10, respectively. These characteristics of the sediments in interglacial periods strongly suggest that the melting of permanent ice opened a gateway, thereby letting the northwest Pacific warmer water flow into the Okhotsk Sea, which subsequently increased biogenetic productivity during the deglacial periods. In addition, in early interglacial periods, the bottom water became anoxic, as evidenced by the presence of dolomite and the enrichment of the Mn/Al and P/Al ratios more than 25 to 200 times. The fact that these trends did not occur in stage 7 strongly suggests that stage 8 may have been a warmer glacial period.

Marine sediments preserve useful information for reconstructing oceanographic conditions and environmental changes in the past. In this study, the authors have evaluated an efficient near-infrared reflectance spectroscopy (NIRS) method for simultaneous determination of total C (TC), total inorganic C (TIC), total organic C (TOC), magnetic susceptibility (MS), the ratio of di- and tri-unsaturated C 37 alkenones ( U 37 k ′ ) , and δ 18 O of foraminiferal shells in marine sediments. Near-infrared diffused reflectance spectra (1100–2500 nm) of 172 sediments recovered from the IMAGES Core MD972151, located in the southwestern South China Sea, were analyzed and correlated with the abovementioned parameters using partial least squares regression (PLSR) procedures. The leave-one-out cross-validation results showed that TC and TIC were successfully predicted ( r 2 > 0.93) while MS, U 37 k ′ , and δ 18 O were estimated with moderate accuracy ( r 2 > 0.76). The concentrations of TOC, however, could not be estimated with high precision ( r 2 = 0.34), which is possibly a result of the low and narrow range of organic C in this specific core. The results indicate that NIRS has the potential to be a rapid analytical tool for continuous marine core examination, although uncertainties associated with TOC need further investigation.

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.

We conducted a detailed rock magnetic study on upper 80 m of Jing’erwa core from the Nihewan basin. The results indicate that the sediments from Jing’erwa core are suitable for relative paleointensity study, and anhysteretic remanent magnetization (ARM) can be used as the normalization parameter of the natural remanent magnetization (NRM). Our relative paleointensity data of upper 80 m of Jing’erwa core provide a continuous record of the intensity variation during the last 0.8 Ma, which correlates well with the results from marine sediments cores in the Pacific Ocean. This means that the sediments records are reliable for relative paleointensity of Earth’s magnetic field, and suggests that these sediments have recorded the real changes of geomagnetic field, which would provide a new method for regional stratigraphic correlation.

As a result of oblique collision, the Taiwan orogen propagates southward. The Hengchun peninsula in the southern tip of the Taiwan Central Range, preserving the youngest, the least deformed and the most complete accretionary prism sequences, allows therefore better understanding of the tectonic evolution of Taiwan orogen. On the Hengchun peninsula, four main stages of paleostress can be recognized by the analysis of brittle tectonics. After recording the first two stages of paleostress, rocks of the Hengchun peninsula (the Hengchun block) have undergone both tilting and counterclockwise rotation of about 90j. The structural boundaries of this rotated Hengchun block are: the Kenting Melange zone in the southwest, the Fongkang Fault in the north, and a submarine backthrust in the east. The angle of this rotation is principally calculated by the paleomagnetic analysis data and a physical model experiment. Through a systematic back-tilting and back-rotating restoration, the original orientations of the four paleostress stages of Hengchun peninsula are recognized. They are, from the ancient to the recent, a NW-SE extension, a combination of NW-SE transtension and NE-SW transpression, a NE-SW compression, and finally a combination of NE-SW transtension and NW-SE transpression. This result can be explained by a phenomenon of stress axes permutation, instead of a complex polyphase tectonism. This stress axes permutation is caused by the horizontal compression increase accompanying the propagation of the accretionary prism. Combining the tectonic and paleomagnetic data with paleocurrent and stratigraphic data enables us to reconstruct the tectonic evolution of the Hengchun peninsula. This reconstruction corresponds to the deformation history of a continental margin basin, from its opening to its intense deformation in the accretionary prism. D 2002 Elsevier Science B.V. All rights reserved.

SUMMARY We conducted a mineral magnetic study on sand samples from the Taklimakan desert, Tarim Basin in western China. Modern sands were collected at 19 sites in the central and western parts of the Taklimakan desert. We carried out low-field susceptibility measurements, ARM and IRM acquisitions, high- and low-temperature measurements and hysteresis measurements on these samples. Nearly stoichiometric magnetite is the dominant magnetic mineral of these samples. The presence of titanomagnetite is unlikely, and contributions from a high-coercivity mineral(s) are minor. Magnetic grain size is estimated to be that of larger pseudo-single domain or even greater. We compared the hysteresis data against loess samples from both pristine and weathered loess sections from the Chinese Loess Plateau. We found an apparent decreasing grain size trend from the Taklimakan to the central Loess Plateau through the western Loess Plateau. These lines of evidence favour the idea that the Taklimakan desert is one of the potential dust source areas, even though it is located more than 2000 km west of the central Loess Plateau.

By using bulk samples, rock magnetic measurements were performed to discriminate between pyrrhotite- and greigite-bearing shallow marine sediments that are now uplifted above sea level in southwestern Taiwan. Thermal demagnetization of a composite isothermal remanent magnetization (IRM) was found to be effective in differentiating between the two types of sediments. To check the thermal instability and estimate the true unblocking temperature (TB) spectra of sediments containing these minerals, saturation IRMs (SIRMs) were imparted at each temperature step during demagnetization. While pyrrhotite-bearing samples showed unambiguous TB temperature spectra, greigite-bearing samples underwent considerable alteration which is responsible for most of the decrease in magnetization during thermal demagnetization. Such thermal instability of greigite is a practical and important clue for its identification. Zero-field warming of IRM from 5 to 300 K sensitively indicates the presence of pyrrhotite and trace magnetite in bulk samples without any magnetic separation.

The main purpose of this study is to analyse striated micro-faults and other types of fractures (including tensile and shear joints, and veins), in order to elucidate their relationships with regional folds and thrusts and regional tectonic stress. We take the fold-thrust belt (i.e., the foothills and the Hsuehshan range) in NW Taiwan as a case study, which is a product of the Plio-Pleistocene arc-continent collision. A total of about 760 and 1700 faults and other fractures, respectively, were collected at 41 sites in the field. We have identified four sets of bed-perpendicular joints in the study area. The observation of joints and bedding at each site indicates that most of the penetrative joint sets developed in the earlier tectonic stage of the pre-folding/pre-tilting event, illustrating the fact that the intersection of joint sets lies along the line perpendicular to the bedding plane. We thus interpret these sets as tectonic fractures under deep-seated tectonic stress. We used the regional fold axes as reference to define the four fracture sets. However, we found that complexity in the study area makes this rather tentative. Principal stress axes σ1, σ2, σ3, were calculated by means of inversion of fault slip data at each site. The ratio Φ that defines the shape of stress ellipsoid is generally small, indicating that the value of the maximum principal stress axe σ1 is much larger compared to that of σ2 and σ3, which are approximately equal. The paleostress regime was characterized by a combination of thrust and strike-slip tectonic regimes. Based on their geometric relationships with tilted bedding, we found most of striated micro-faults were strongly related to the regional folding and can be categorized as early-, during, and late-folding stages. We characterized two major directions for the compressive event, oriented N110–120°E and N150–160°E respectively, which provide additional evidence to delineate the debates about paleostress changes in the Taiwan mountain building process.

[1] During an earthquake, physical and chemical transformations lead to alteration and formation of minerals in the gouge layer. Altered and neoformed minerals can be used as tracers of some earthquake processes. In this study, we investigate pyrite and magnetic minerals within the host Chinshui siltstone and the 16-cm-thick gouge. This gouge hosts the principal slip zone of Chi-Chi earthquake (Mw7.6, 1999). In the Chinshui siltstone, pyrite framboids of various sizes and euhedral pyrite are observed. The magnetic mineral assemblage comprises stoichiometric magnetite, greigite, and fine-grained pyrrhotite. The pyrite content is generally reduced in the gouge compared to the wall rock. The magnetic mineral assemblage in the gouge consists of goethite, pyrrhotite, and partially oxidized magnetite. The pyrrhotite, goethite and some magnetite are neoformed. Pyrrhotite likely formed from high temperature decomposition of pyrite (>500°C) generated during co-seismic slip of repeated earthquakes. Goethite is inferred to have formed from hot aqueous co-seismic fluid (>350°C) in association with the 1999 Chi-Chi event. Elevated fluid temperatures can also explain the partial alteration of magnetite and the retrograde alteration of some pyrrhotite to pyrite. We suggest that characterization of neoformed magnetic minerals can provide important information for studying earthquake slip zones in sediment-derived fault gouge.

International audience; During an earthquake, the physical and the chemical transformations along a slip zone lead to an intense deformation within the gouge layer of a mature fault zone. Because the gouge contains ferromagnetic minerals, it has the capacity to behave as a magnetic recorder during an earthquake. This constitutes a conceivable way to identify earthquakes slip zones. In this paper, we investigate the magnetic record of the Chelungpu fault gouge that hosts the principal slip zone of the Chi-Chi earthquake (Mw 7.6, 1999, Taiwan) using Taiwan Chelungpu-fault Drilling Project core samples. Rock magnetic investigation pinpoints the location of the Chi-Chi mm-thick principal slip zone within the 16-cm thick gouge at ~1 km depth. A modern magnetic dipole of Earth magnetic field is recovered throughout this gouge but not in the wall rocks nor in the two other adjacent fault zones. This magnetic record resides essentially in two magnetic minerals; magnetite in the principal slip zone, and neoformed goethite elsewhere in the gouge. We propose a model where magnetic record: 1) is preserved during inter-seismic time, 2) is erased during co-seismic time and 3) is imprinted during post-seismic time when fluids cooled down. We suggest that the identification of a stable magnetic record carried by neoformed goethite may be a signature of friction-heating process in seismic slip zone.

Marine geology in the region between Taiwan and Luzon is characterized by a convergent tectonics in the south and an oblique arc-continent collision in the north. In the collision zone six geologic provinces are recognized. They are the Manila Trench, the accretionary prism of the Hengchun Ridge, the sutural basin of the Southern Longitudinal Trough, the subduction melange of the Huatung Ridge, the forearc basins of the Taitung and the North Luzon Troughs, and the volcanic arc of the North Luzon Ridge. The oceanic crust of the South China Sea is subducting eastward beneath the Philippine Sea plate along the Manila Trench south of 20°N. Further to the north, the Trench has changed progressively its axis toward the west from the subduction melanges off southeastern Taiwan at 3 Ma to the Hengchun peninsula of southern Taiwan at 2-1 Ma, and then to the present-day location off southwestern Taiwan. Because of the continuing collision and the westward shifting of the Manila Trench, sediments deposited in the region are passively incorporated into the accretionary prism and deformed to the Hengchun Ridge. After the collision the Southern Longitudinal Trough, consisting of a 2 km thick of orogenic sediments, represents a sutural basin superposed on the plate boundary between the accretionary prism of the Hengchun Ridge (Asian continent) and the subduction melange of the Huatung Ridge (Philippine Sea plate). The Huatung Ridge is a bathymetric high connected to the southern Coastal Range and is characteristic of low, negative free-air gravity and magnetic anomalies. The Ridge contains deeply weathered sedimentary blocks with abraded deep-water late Pliocene foraminifera and identical clay mineral compositions as those in the onshore Lichi Melange. This implies that at least a portion of the Huatung Ridge is composed of melange materials and represents a former subduction zone extending from the Lichi Melange of the southern Coastal Range. The North Luzon Trough and the Taitung Trough are the constructed foreac basins with 2 km of orogenic sediments unconformably overlying the volcanic islands and the subduction melange. The Taitung Trough is southward connected to the North Luzon Trough through a bathymetric passage, which was formed by narrowing the North Luzon Trough as a consequence of clockwise rotation of the Lutao volcanic island during the late Pleistocene. A detailed study of the four Neogene tectonostratigraphic units in the Coastal Range shows that the overall history of the formation of the Range can be related to the present-day geologic provinces and the on-going collision processes in the region off southeastern Taiwan. The Range had evolved from a southward accretion of the Shuilien-Loho remnant forearc basin and the Chimei volcanic pair at 2 Ma, followed by the Chengkung-Taiyuan remnant forearc basin and the Chengkuangao volcanic island pair at 1 Ma, and the Taitung Trough and the Lutao volcanic island pair presently in process. By analogy, the northern part of the North Luzon Trough and the Lanhsu volcanic island will be accreted to the Coastal Range in the next million years. The paired forearc basin-volcanic island accretion model proposed in this study may thus have implications for mountain ranges that evolved from similar tectonics of oblique arc-continent collision.

Paleomagnetic results obtained from over 2100 cores sampled at 132 early Pliocene to late Pleistocene sites in the Coastal Range of eastern Taiwan indicate that, since the late Pliocene, the margin of the Philippine Sea plate has undergone a clockwise rotation of about 30° as a direct consequence of the Plio-Pleistocene collision of this plate with the Chinese Continental plate. The rotation is diachronic and started between 3 and 4 Ma ago in the northern Coastal Range then propagated southward at an average speed of the order of 70 ± 10 km/Ma. This value is in very good agreement with estimates of the southward propagation of the collision between the Philippine Sea plate and the Eurasian margin in Taiwan. It is suggested that the rotation reflects the deformation of the Philippine Sea plate at depth and does not results from the shallow deformations involved in the building of the Coastal Range orogen.

Variations in sea surface temperature (SST), productivity, and biogenic components such as total organic carbon (TOC), carbonate, and opal contents measured from IMAGES (International Marine Global Changes Study) core MD972142 provide information about long-term paleoceanographic changes during the past similar to 870000 years in the southeastern South China Sea (SCS). MD972142 U-37(k)-SSTs varied from 25 to 29 degrees C, paralleling the glacial to interglacial changes. MD972142 biogenic components show relatively high carbonate and opal, and low TOC contents in interglacial stages, and low carbonate and opal and high TOC contents in glacial stages, and these variations appear to be sensitive to regional terrestrial sediment input and productivity. Our analysis indicates that the MD972142 carbonate record is primarily controlled by terrestrial sediment inputs that are associated with sea level fluctuations during past glacial-interglacial stages. The TOC record reflects past glacial-interglacial changes in both monsoon-induced productivity and terrestrial organic matter input in the SCS. The TOC record exhibits several short-term peaks that are associated with lower U-37(k)-SSTs (especially in MIS 2 - 4, 10, 12), perhaps implying a much strengthened winter monsoon. The opal record shows relatively high content in most interglacial stages, which appears to be linked to increased summer monsoon upwelling or increased siliceous sediment input by more precipitation and river runoff during warm climate conditions. The TOC and opal contents both show long-term increasing trends since the mid-Brunhes, most noticeably from similar to 330 kya. The long-term trends observed in this study are most likely attributable to changes in SCS hydrography, productivity, and/or preservation in response to the increased strength of the East Asian monsoon system on possibly tectonic timescales.

Over 2100 samples were collected from 130 sedimentary sites of early Pliocene to Pleistocene age in the Coastal Range of Eastern Taiwan. Their lithology is mainly unmetamorphosed marls, siltstones and sandstones and the formations are folded and faulted at different scales. Different shapes of the susceptibility ellipsoid were observed from an oblate form, with K min closely perpendicular to the bedding plane, to a “pencil” structure, with K min a K int forming a girdle around K max , reflecting an increasing tectonic contribution to the magnetic fabric. At sites where fault tectonic analysis is available, the magnetic lineation is perpendicular to the main compression. These results have a twofold significance: first, confirming previous preliminary results, they show that in such visually undeformed sediments the magnetic fabric may be, at least in part, of tectonic origin. Second, when considered together with recent paleomagnetic and tectonic data, they suggest that in the Plio-Pleistocene sediments of the Coastal Range of Taiwan the magnetic lineation arises from the compression due to the collision of the Philippine Sea and the Eurasian plates. In our interpretation, the stress pattern has rotated clockwise along with the structures during this collision.

The ground-based magnetic signature of particle precipitation fromthe ring current to low latitude regions during the recovery phase of a geomagnetic storm on 23 December,1995,has been inferred by studying photometric 630.0nm nightglow at a low latitude station,Kolhapur(7.5°N,144.7°E; Geomagnetic,dip latitude 10.6° N) and magnetograms(H,D andZ)of nearby low latitude stations.The maximum optical emission occurredsimultaneously with the maximum positive(north ward)excursions in theH trace of low latitude magnetograms associated with negative H excursions at high latitude observatories.Generally,an increase in Z componentoccurred at all low latitude stations.A large intensity increase of aboutseven times in 630.0nm emission was observed at around 2:15 hrs I.S.T on23 December,1995.The 630.0nm enhancement maximised at the time ofhigh Dst or Kp index during the night.In addition,the ionosonde experiment conducted at Ahmedabad(13.8°N,144.7°E;Geomagnetic)showed theenhancement of peak electron densities in the F-region and sudden lowering of the F layer in the ionosphere.A possible explanation of the effect isgiven in terms of emergence of energetic neutral atoms(Hydrogen or Oxygen) from high energy protons in a typical charge exchange process in thering current depositing energy into the thermosphere-ionosphere system,also possibly due to changes in the composition of the thermosphere-ionosphere during magnetic storms that would enhance the 630.0nm emissions.

The 21 September 1999 Chi-Chi earthquake(M(subscript L)=7.3)was the largestinland quake occurred in Taiwan in the past 100 years.According to directfield observations,a significant thrust rupture was occurred along the activeShuangtung fault and Chelungpu fault.From the integrated displacementderived from free-field strong motions around the source area,horizontaldisplacements over 9m and vertical offsets reaching 3.4m are obtainedat the station TCU068 located nearby the northern section ofChelungpu fault.Based on the field observations of slip distribution overthe entire 77-km surface break and the integrated displacement waveforms,we have arrived at the following findings:An obvious small offset at about3 sec prior to the principal offset is observed at two sites close to the southernpart of Shuangtung fault.This small offset is not shown on the otherstations.We propose that a relatively small event,probably with a magnitudeof about 6.0,occurred about 3 sec before the major rupture,that islocated at the Shuangtung fault about 8km east of the Chelungpu fault.The induced northward propagating rupture along the Chelungpu faulthas reached a maximum permanent offset over 9m at the northern sectionof fault.This northern section of the Chelungpu fault was identified as oneof the heaviest damaged areas.

The Central Weather Bureau has implemented the Taiwan StrongMotion Instrumentation Program(TSMIP)to collect high-quality instrumentalrecordings of strong earthquake shaking.Deployment of theaccelerographs started in August 1992.By June 1997,629 stations hadbeen deployed.Each operating free-field station includes triaxial accelerometers,a digital recording sub-unit,a power supply and a timing system.Since the first installation in August 1992,this network has recorded 2482earthquakes.The local magnitudes of these earthquakes ranged from 1.7to 7.1 and thousands of high-quality digital accelerograms were collected.The quality of 16-bit data is shown to be much better than the conventionalstrong-motion data(either analog or 12-bit digital recordings).These newrecordings provide an excellent database for making various earthquakeengineering and seismological studies.