Showing papers in "Terrestrial Atmospheric and Oceanic Sciences in 2005"

A Review on the Western North Pacific Monsoon: Synoptic-to-Interannual Variabilities

Abstract: In this paper we review the observed structure and evolution characteristics of the western North Pacific monsoon on various time scales, including its annual cycle, synoptic wave activity, intraseasonal oscillations, and interannual variabilities. On the synoptic (2-10-day) timescale, summertime synoptic waves and equatorial symmetric and anti-symmetric modes are often observed, and they may be responsible for triggering tropical cyclone genesis. On the intraseasonal scale, there are significant spectrum peaks at bi-weekly (10-20-day) and lower-frequency (20-70-day) bands. On the interannual time scale, the monsoon is greatly modulated by and possibly feeds back to the El Nino-Southern Oscillation (ENSO). The paper reviews our current understanding of physical mechanisms that give rise to the synoptic-scale, intraseasonal and interannual variabilities, and multi- scale interactions among these motions. The comparison between the Indian monsoon and the western North Pacific monsoons in terms of their differences in precipitation and circulation patterns, dominant time scales, and global teleconnection is also illustrated. Finally we discuss some remaining issues related to the western North Pacific monsoon variabilities.

Earthquake Prediction Studies Using Radon as a Precursor in N-W Himalayas, India: A Case Study

Abstract: Many theoretical and empirical algorithms have been proposed in the literature for radon release; however whilst its relation with earthquake occurrence has been developed on occasions, there have been no specific complete studies of this phenomenon. In this study, radon monitoring was carried out using emanometry technique at Palampur and Dalhousie stations in the Kangra valley of Himachal Pradesh (India) from June 1996 to September 1999. Discrete radon concentrations were recorded in soil-gas and groundwater at both the stations. Radon anomalies were correlated with microseismic events recorded along the Main Boundary Thrust (MBT) of N-W Himalaya in the grid (30-34°N, 74-78°E). The influence of meteorological parameters viz, temperature, rainfall, relative humidity and wind velocity on radon concentration was qualitatively evaluated. The radon exhalation showed positive correlation with temperature, rainfall, relative humidity and negative correlation with wind velocity. Both positive and negative radon anomalies were recorded. The study reveals the precursory nature of radon anomalies and their correlation with microseismic events in 62% of the cases but prediction of earthquakes is yet a remote possibility. From the analysis it has been found that radon anomaly is not only influenced by seismic parameters but also by meteorological parameters and the nature of carrier gases/fluids. To learn more about the phenomenon, simultaneous recording of various gases (He, CO2, CH4) and meteorological parameters, together with multiple continuous measurements of radon have been suggested.

Calculating highly fluctuated suspended sediment fluxes from mountainous rivers in Taiwan

Abstract: Small drainage basins, highly fractured rock, high relief, and steep gradients make Taiwan watersheds particularly sensitive to episodic events such as typhoons and earthquakes, and to various types of anthropogenic disturbance. Here we analyze the characteristics of a long-term hydrological dataset from Taiwan and re-evaluate methods used to calculate sediment loads for Taiwan's event-driven rivers. We suggest using the rating curve method stratified clown to seasonal levels to reflect the rapid changes in the relationship between water discharge and suspended sediment load. A program is developed to determine the optimal time-interval for constructing rating curves, and is used to calculate hourly, daily, yearly, and long-term mean suspended sediment loads. Seasonal rating curves applied to hourly discharges are particularly critical to calculate sediment fluxes and concentrations in response to episodic events, particularly typhoons. The calculated cumulative long-term mean sediment fluxes for the Jhou-Shuei and Bei-Nan Rivers are considerably smaller than those calculated using monthly weighted average (MWA) method (Dadson et al. 2003). The MWA method likely over-estimates the mean load clue to more frequent sediment observations during high-flow events.

Soil Gas Radon Spectra and Earthquakes

Abstract: Continuous soil gas radon monitoring in real time with improved solid- state detector is carried out in south-central and southern Taiwan. The time series register spike-like anomalies which could be precursors of earthquakes. Monitoring stations located in a brecciated zone of active fault at Taiwan 3 and faults at Taiwan 1 showed drastic variations of radon when the terrain is stressed before the onset of earthquake. In contrast, the spectrum recorded at a station sited on a craton Akron 1 which is sited on a craton shows no significant radon variations. To actually prove that the variation of the time series is related to stress, a fourth station was anchored in a sand column (209 L) with exactly the same type of radon detector system. The time series recorded in this manner shows higher background level and spikes of high radon counts as it is stressed. Temperature and moisture variations are not affecting radon counts.

Volume Transport through the Taiwan Strait: A Numerical Study

Abstract: A fine grid resolution model with realistic bathymetry was constructed to study the spatial and temporal structures of flow through the Taiwan Strait where observations are limited. The model covers an expanded domain that includes the entire East China Sea and South China Sea, as well as the region occupied by the Kuroshio. The fine-resolution model derives its open boundary conditions from a larger scale Western Pacific Ocean model. Two numerical weather products from the European Center for Medium-Range Weather Forecasts and National Centers for Environmental Prediction, and one satellite observation-based wind set (QSCAT) are used to force the ocean model. Model experiments suggested that the best simulation is achieved when the model is driven by the QSCAT wind forcing. Several important features are reproduced in the model simulation. The volume transport is northward and largest in summer while minimal volume transport is southward and occurs in fall and winter. The general trend of volume transport is related to the seasonal reversal of monsoon winds. The present model also suggests that flow in the entire Taiwan Strait is to the southwest during periods of strong northeasterly wind. The annual average transport based on the present model is 1.09 Sv (1 Sv=10^6 m^3S^(-1)), which is smaller than most published values based on shipboard Acoustic Doppler Current Profiler (sb-ADCP) observations. The result suggests that sb-ADCP observations are biased toward estimates in summer and fair weather since bad weather during the winter northeast monsoon often prevents seagoing observations.

Fumarolic Gas Composition of the Tatun Volcano Group, Northern Taiwan

Abstract: Giggenbach bottle technique is used to systematically analyze fumarolic gas composition of the Tatun Volcano Group, northern Taiwan. The area is quite active hydrothermally and is also considered volcanically active. The gas composition of fumarolic samples is predominantly steam water with CO2 as the dominant component after de-watering. Minor components include sulfur species (mainly H2S and SO2), N2 and CH4. Interestingly, in the study area, H2S concentration is always much higher than SO2 for all measured fumarolic gases. This result resembles the typical composition of low temperature fumaroles, when comparisons are made on a worldwide basis. Hsiao-you-keng and Liou-huang-ku were selected as testing sites to discuss factors pertaining to weather and sampling time as these may affect fumarolic gas composition. Test results show that the length of sampling time in this area mainly depends on the saturation of alkali solution. Furthermore, based on continuous data, gas composition of fumaroles seems not to be affected by weather factors. This implies that the de-gassing system in the Tatun volcanic area is quite steady and generated no significant variation in gas composition during the study period. These results indicate that current sampling and analytical procedures are suitable for volcanic gas study and further surveillance in the Tatun volcanic area.

Geochemical Characterization and Temporal Changes in Parietal Gas Emissions at Mt. Etna (Italy) During the Period July 2000-July 2003

Abstract: Several types of natural gas emissions (soil gas, low temperature fumaroles, gas bubbling in mud pools) were collected monthly on Mt. Etna volcano between July 2000 and July 2003 both from its summit and its flanks. Samples were analysed for the determination of the concentrations of CO2, CH4, He, H2, CO as well as the isotopic ratios of 13C/14C of CO2 (δ^13C) and He (R/Ra). The analysed gases were chemically divided into two groups: air-contaminated (from sites closer to the summit vents of Mt. Etna) and CO2-rich. Among the latter, samples from the lower SW flank of the volcano showed high contents of biogenic thermogenic and/or microbial CH4. Isotopic shift in the δ^13C values is caused by input of organic CO2 and/or by interaction between magmatic CO2 and shallow ground water as a function of water temperature and CO2 flux from depth. Based on a graphic method applied to δ^13C(subscript TDIC) of some ground water, the inferred isotopic composition of the pristine magmatic gas at Mt. Etna is characterised by δ^13C values ranging from -2 to -1‰. During the period July 2000-July 2003 significant variations were observed in many of the investigated parameters almost at all monitored sites. Seasonal influences were generally found to be negligible, with only a limited effect of air temperature changes on soil CO2 and ground temperature in only two of the air-contaminated sites. The largest chemical anomalies were observed in the air-contaminated sites, probably because of the strong buffering power of local ground water on gases released through the most peripheral areas where the CO2-rich sites are located. The anomalous changes observed during the study period can be explained in terms of progressive gas release from separate batches of magma that ascend towards the surface in a step-wise manner. Data relevant to the period following the 2002-03 eruption suggest that magma kept accumulating beneath the volcano, thus increasing the probability of a new large eruption at Mt. Etna.

Validation of Satellite-Derived Sea Surface Temperatures for Waters around Taiwan

Abstract: 1 Department of Environmental Biology and Fisheries Science, National Taiwan Ocean University, Keelung, Taiwan, ROC 2 Center for Atmospheric and Oceanic Studies, Faculty of Science, Tohoku University, Sendai, Japan 3 Ocean Data Bank of National Center for Ocean Research, Taipei 106, Taiwan * Corresponding author address: Prof. Ming-An Lee , Department of Environmental Biology and Fisheries Science, National Taiwan Ocean University, Keelung, Taiwan, ROC; E-mail: malee@mail.ntou.edu.tw In order to validate the Advanced Very High Resolution Radiometer (AVHRR)-derived sea surface temperatures (SST) of the waters around Taiwan, we generated a match-up data set of 961 pairs, which included in situ SSTs and concurrent AVHRR measurements for the period of 1998 to 2002. Availability of cloud-free images, i.e., images with more than 85% of cloud-free area in their coverage, was about 2.23% of all AVHRR images during the study period. The range of in situ SSTs was from 10.5°C to 30.8°C. The satellite derived-SSTs through MCSST and NLSST algorithms were linearly related to the in situ SSTs with correlation coefficients of 0.985 and 0.98, respectively. The MCSSTs and NLSSTs had small biases of 0.009 C° and 0.256 C° with root mean square deviations of 0.64 C° and 0.801 C°, respectively, therefore the AVHRR-based MCSSTs and NLSSTs had high accuracy in the seas around Taiwan. (

Carbon Dioxide and Radon Geohazards over a Gas-bearing Fault in the Siena Graben (Central Italy)

Abstract: The eastern master fault of the Siena Graben (central Italy), known as Rapolano Fault, is a place of migration of a large amount of CO2-rich gas from deep geothermal reservoirs. Under particular topographical and meteo-climatic conditions, large emissions of carbon dioxide can represent serious hazards to human and animal life. Carbon dioxide is a carrier gas for radon (Rn), the concentrations of which are high in the soil despite the low U content of the overburden. CO2 pressure also drives the upwelling of thermal waters producing at the surface, in some places, radioactive (226Ra rich) travertine formations, inducing higher soil-gas Rn levels. Three main types of hazards, mechanical, toxicological and radio-ecological, may occur depending on the upwelling fluid phases (gas alone or gas plus water). Gas distribution and partitioning in different micro-environments (e.g., soil pores, groundwater, ground-atmosphere interface) should be taken into account when planning hazard-assessment surveys.

A Modeling Study of Typhoon Toraji (2001): Physical Parameterization Sensitivity and Topographic Effect

Abstract: This paper investigates the dependence of simulated track, central pressure, maximum wind, and accumulated rainfall of Typhoon Toraji (2001) on physical parameterizations, using the fifth-generation Pennsylvania State University- National Center for Atmospheric Research Mesoscale Model (MM5). The model configuration includes three nested domains with grid size of 60,20, and 6.67 km, respectively. Three sets of five numerical experiments on cumulus, cloud microphysics, and planetary boundary layer (PBL) parameterizations are performed (15 experiments totally). Among subgrid-scale cumulus schemes tested, the simulated typhoon with the Grell scheme has the best track. For grid-scale cloud microphysics scheme examined, all storms have similar tracks, with the best simulated track using the Goddard Graupel cloud microphysics scheme. The PBL parameterization substantially affects the simulated typhoon tracks, and the storm with the Medium-Range Forecast model PBL has track and intensity that most resemble actual observations. An experiment with the best scheme from each of three sets of physical parameterization experiments has the best performance in terms of central pressure, maximum wind and accumulated rainfall; it can simulate the westward turning of Toraji's track right before the landfall. Standard deviation and ensemble (arithmetic) mean are calculated for each set of physical parameterization experiments. The ensemble-mean track and rainfall distribution are much closer to the observations than each individual experiment. A combination of the topographically- and environmentally-induced vertical moisture fluxes, calculated based on the flux model of Lin et al. (2001), corresponded well to the hourly surface rainfall distribution. An analysis of nondimensional parameters for typhoon's track continuity over the Taiwan island shows that Typhoon Toraji's track discontinuity is consistent with the control parameter analysis proposed by Lin et al. (2002). The westward turning of Toraji's track right before the landfall may be caused by horizontal advection process due to flow blocking, on the basis on a momentum budget analysis.

Seasonal Variability of Carbon Chemistry at the SEATS Time-Series Site, Northern South China Sea Between 2002 and 2003

Abstract: Analyses of total carbon dioxide (TCO2) and titration alkalinity (TA) in the mixed-layer was performed approximately bimonthly at the SEATS time series site (18°15'N, 115°35'E) in the northern South China Sea (SCS) from March 2002 to April 2003. These measurements and the calculated-f CO2 were then used to document their seasonal variations and to estimate the seasonal air-sea flux of CO2 during the observed period at the site. Results show that the normalized TCO2 (NTCO2=TCO2 x 35/S) fluctuates seasonally between ～1972 and ～1997 μmol kg^(-1), with the highest value in winter. The decline of NTCO2 in spring-summer mainly results from in situ biological utilization, while the resurgence of NTCO2 in fall-winter is due to entrainment of the TCO2 -rich subsurface waters from below. TA varies from ～2190 to ～2220 μmol kg^(-1) in tandem with salinity, suggesting the prime control of physical processes. fCO2 increases progressively from spring to summer, reaches a maximum in July (～382 μatm), then decreases from fall to winter to a minimum (-347 μatm) in January with an amplitude of ～35 μatm. The seasonal variability of fCO2 is in phase with temperature changes but is inversely correlated with the fluctuation of NTCO2, suggesting that the fCO2 seasonality is primarily controlled by temperature changes, though other factors have compensated partially to yield the observed low amplitude of its variability. The sea-to-air CO2 fluxes for spring, summer, fall and winter are estimated to range from 0.00±0.01 to -0.02±0.05, +0.03±0.01 to +0.23±0.06, +0.18±0.10 to +0.45±0.25, and -0.62±0.20 to -1.42±0.46 molC m^(-2) year^(-1), respectively. Throughout the year, the annual flux is calculated to be -0.11±0.08 -0.23±0.18 molC m^(-2) year^(-1) during the observed period. Furthermore, although there is a drawdown of NTCO2 of ～25 μmol kg1 from winter to summer, which implies a net community production of 6.80±0.77 mmolC m^(-2) year^(-1) in the mixed layer at the SEATS site, there is no corresponding change of nitrate observed, suggesting other sources of nitrogen required to sustain the new production.

Geophysical Well Log Study on the Paleoenvironment of the Hydrocarbon Producing Zones in the Erchungchi Formation, Hsinyin, SW Taiwan

Abstract: Gamma ray log facies of nine wells were used to reflect the vertical profile of grain size and were combined with well sample data to deduce the paleoenvironment of the Erchungchi ”A” Member in the Hsinyin and Pachanchi areas. Four log facies were recognized in the studied intervals: a thick funnel-shaped facies representing a prograding delta; a thin funnel-shaped facies representing a crevasse splay; a boxcar-shaped fades representing a distributary channel; a bell-shaped facies representing a fluvial or deltaic channel. The paleoenvironment of the Erchungchi ”A” Member in the Hsinyin area is mainly an imbricated delta system whose thickest lobe is located in Well S-1. The delta was first deposited in the headstreams of the submarine channels, followed by mudstones as cap rocks which seal hydrocarbons in stratigraphic traps. There are many submarine channels in southwestern Taiwan, so similar stratigraphic hydrocarbon trap conditions may occur elsewhere in southwestern Taiwan.

Age model and oxygen isotope stratigraphy of site ODP1202 in the southern Okinawa Trough, northwestern Pacific

Abstract: The two sedimentary sequences drilled at Holes 1202B and 1202D were correlated based upon direct lithologic observation, shipboard logging of magnetic susceptibility, and bulk density to form a stacked record of 410 m in length. Calcareous nannofossil and planktic foraminiferal occurrences confine the bottom of the record to be younger than 85 ka, whereas the sediments in the interva~225-280 mbsf in Hole 1202D are apparently of turbidite origin. Eleven AMS carbon-14 datings of planktic foraminifera and scaphopod samples from Hole 1202B suggest that the upper 110 m has a continuous record dating back over the past 28 thousand years. An oxygen isotope stratigraphy based upon planktic foraminifera Neogloboquadrina dutertrei was established from the stacked sequence. The upper part of the δ^18 O profile can be well correlated to that from the central Okinawa Trough site DGKS9603 (Li et al. 2001) in both trend and absolute values whereas the lower part is considered to belong to marine oxygen isotope stage 4. The sedimentation rates have been always high at this site, ranging from 1.5 to 16 meters per thousand years.

Preliminary Results from Seismic Monitoring at the Tatun Volcanic Area of Northern Taiwan

Abstract: To enhance our understanding of the seismic characteristics of the Tatun volcanic area, a small aperture seismic array consisting of 5 seismic stations has been deployed in the area since May 2003. Each of the seismic stations was installed with both short-period and broadband sensors to record micro-earthquakes as well as long-period volcanic tremors. The preliminary results of the seismic monitoring of the Tatun volcanic area show a large number of shallow micro-earthquakes clustered beneath the Chihsingshan volcano and Tayoikeng areas. Among these, some swarms were also detected. Intensifying the issue further, some complex seismograms with harmonic codas and seismic tremors have been identified. Considlerable crustal heterogeneity in the Tatun volcanic area is indicated by the presence of strong coda waves. Combining our findings with other geological and geochemical observations, we postulate that volcanic activities might not be totally extinct in the Tatun volcanic area. Thus, further investigations of Tatun volcanic area ought be conducted to examine the possibility of such potential volcanic activity.

Characterization of the Pleistocene Volcanic Chain of the Bicol Arc, Philippines: Implications for Geohazard Assessment

Abstract: Several active volcanic arcs are present in the Philippine Mobile Belt, the region enclosed by the Philippine Trench and the Manila-Negros-Cotabato Trench systems. One of the most prominent among them is the Bicol Arc, a~260km long volcanic arc located in the central-eastern margin of the Philippine Mobile Belt. The Bicol Arc hosts three of the active volcanoes in the country, including the Mayon Volcano, which has erupted repeatedly within the last decade. Aside from the three active volcanoes, there are at least nine other Pleistocene major volcanic centers that make up the volcanic arc. Although the rocks from the arc range in composition from basalt to rhyolite, they are mostly basaltic andesites and andesites. Magma mixing and fractional crystallization accompanied the generation of these rocks. The rocks exhibit typical island arc geochemical signatures. In addition, the Sr and Y ratio plots suggest that the Bicol Arc is mainly composed of mantle-wedge derived magmas with some samples from Bacon-Manito and Culasi showing similarities to adakites. Along-arc geochemical variation may be related to the variation in crustal thickness of the volcanic arc. The petrological and geochemical characterizations of the rocks provide information on how the volcanic centers evolved. This is important in assessing the attendant geohazards related to this volcanic arc.

A Sensitivity Study of Regional Climate Simulation to Convective Parameterization Schemes for 1998 East Asian Summer Monsoon

Abstract: A sensitivity study of regional climate simulations over East Asia to three convective parameterization schemes (CPSs), the Grell, Kain-Fritsch, and Anthes-Kuo schemes, was conducted using a regional climate model, SNURCM with a 60 km horizontal resolution. Nesting experiments with a 20 km horizontal resolution were also performed in order to investigate the sensitivity of CPSs to horizontal resolution. In all runs with 60 km horizontal resolution, seasonal mean precipitation, low-and upper-level wind, and temporal and spatial variation of monsoon fronts over East Asia were simulated with a certain difference between CPSs. With higher horizontal resolution, all the schemes were likely to increase slightly the total precipitation amount and the precipitation intensity due to the increase of convective rain, but differences in the spatial distribution of precipitation between CPSs were relatively small. There were prominent differences in vertical profiles of wind, temperature, water vapor, and atmospheric hydrometeors amongst CPSs, although the vertical structures of those in GR and KF runs were similar to each other. Sensitivities of the vertical structure of most atmospheric variables to horizontal resolution were relatively smaller than they were to CPSs except for cloud water. Surface energy fluxes, in particular incoming solar radiation and latent heat between CPSs were different to each other because of differences in the vertical structure of atmospheric hydrometeors. Diurnal variation of precipitation was also sensitive to not only CPSs but also horizontal resolution. In this study, the AK scheme reproduced the East Asian Summer precipitation properly because of intrinsic triggering assumptions and the spectral nudging technique. The GR scheme was on the whole suitable to simulate the general features of East Asian summer monsoon in 1998 such as heavy precipitation, atmospheric vertical structure, and temporal evolution of the East Asian Summer monsoon. The KF scheme had the worst statistics in precipitation simulation due to large convective precipitation portion. Consequently, the AK and GR schemes simulated more reasonably the 1998 summer flood over East Asia which was affected by anomalous large-scale conditions.

Dynamics of orographic rain associated with the passage of a tropical cyclone over a mesoscale mountain

Abstract: 1 Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina, USA 2 Division of Microscale and Mesoscale Meteorology, National Center for Atmospheric Research, Boulder, Colorado, USA * Corresponding author address: Dr. Yuh-Lang Lin, Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina, USA; E-mail: yl_lin@ncsu.edu In this study, the Penn State/NCAR Mesoscale Model Version 5 (MM5) was used to simulate Supertyphoon Bilis (2000) in order to improve the prediction and the understanding of dynamics of orographic rainfall associated with the passage of typhoons over the Central Mountain Range (CMR) of Taiwan. The rainfall prediction is significantly improved by bogussing a vortex, compared to a previous study (Lin et al. 2002). We identified several common ingredients present in this case which are responsible for producing heavy rainfall. The most important ingredients appear to be the presence of convective available potential energy (CAPE), a potentially unstable layer, a very moist airstream impinging on the CMR, and the presence of a low level wind maximum associated with the outer circulation of the typhoon. A simple moisture flux model was also used to estimate rainfall, which compares well with observations. In addition, we also found that the orographic rainfall is dominated by moisture convergence and the contribution of moisture advection in the vicinity of the mountain is negligible. (

A Tendency of Cloud Ratio Associated with the Development of Tropical Water and Ice Clouds

Abstract: The ratio of column-integrated cloud content between ice and liquid phases (CR) is a good indicator of cloud dynamics (e.g., convective or stratiform) and radiative properties. Clouds are more stratiform when the CR is larger and more convective for smaller CR values. In this study, a tendency equation of the cloud ratio is derived. The tendency of the cloud ratio (∂CR/∂t) is determined by six major cloud micro physical processes: vapor condensation and deposition as cloud sources, rainfall and evaporation of rain as the sinks of water clouds, and melting of graupel and accretion of cloud water by precipitation ice as the major conversion processes between water and ice clouds. Apparently, ∂CR/∂t is related to water cycling processes among vapor and different categories of clouds, and links the amount of water vapor and clouds with temperature through latent heating. An analysis of the tendency of the cloud ratio is carried out using hourly zonal-mean data based on a 2D cloud-resolving simulation with the imposed forcing from the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment. During the genesis and decay stages of clouds (a zonal-mean surface rain rate of smaller than 0.3 mm h^(-1)), the tendency of the cloud ratio is mainly controlled by the processes related to the vapor condensation and deposition. During the mature stage of clouds (a zonal-mean surface rain rate of larger than 0.3 mm h^(-1)), the tendency of the cloud ratio is determined by conversion between water and ice clouds through melting of graupel and accretion of cloud water by precipitation ice.

A 28,000 Year U37 K' Sea-Surface Temperature Record of ODP Site 1202B, the South ern Okinawa Trough

Abstract: 1 Department of Earth Sciences, National Cheng kung University, Tainan, Taiwan, ROC 2 Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire, USA. 3 Department of Geosciences, National Taiwan University, Taipei, Taiwan, ROC * Corresponding author address: Prof. Meixun Zhao, Department of Earth Sciences, National Cheng kung University, Tainan, Taiwan, ROC; E-mail: Meixun.Zhao@Dartmouth.edu An U37 K sea-surface temperature (SST) record of the last 28 kyr has been obtained for ODP Site 1202B (24°48.24’N, 122°30’E; water depth 1274 m), drilled offshore of NE Taiwan in the southern part of the Okinawa Trough. This millennial-scale record reveals a glacial-interglacial SST difference of 5°C, larger than SST changes at similar latitude of the open Pacific Ocean, but is similar in amplitude with SST changes of the western Pacific’s marginal seas, such as the northern South China Sea (SCS). Comparison with a planktonic oxygen isotope record from the same site reveals that the last deglaciation warming was synchronous with ice volume changes, but lagged the warming in Greenland’s ice core record and in the monsoon record from the Hulu Cave of Eastern China. The enhanced glacial cooling for this site was likely caused by several factors, including the variability of the Kuroshio, sea level variations, and coastline shift. (

Modern Seismic Observations in the Tatun Volcano Region of Northern Taiwan: Seismic/Volcanic Hazard Adjacent to the Taipei Metropolitan Area

Abstract: The Tatun volcano group is located adjacent to the Taipei metropolitan area in northern Taiwan and was a result of episodic volcanisms between 2.8 and 0.2 Ma. Earthquake data collected over the last 30 years are analyzed to explore seismicity patterns and their associated mechanisms of faulting in the area. Using a Joint Hypocenter Determination (JHD) method, a few sequences of relocated earthquake hypocenters are tightly clustered; these seemed to be blurry in the original catalog locations. Numerous earthquakes, previously unnoticed and not reported in the CWB catalog, have been identified from careful examination of the continuous recordings of a nearby broadband seismic station. These newly identified earthquakes show similarities in waveforms and arrival time differences between direct P- and S-waves indicating that their hypocenter locations are very close to each other and their source mechanisms are similar. A relatively high b-value of 1.22 is obtained from the analysis of crustal earthquakes (depth < 30 km) in the region, which may suggest that clustered local seismicity in the Tatun volcanic region probably resulted from subsurface hydrothermal or volcano-related activities. Focal mechanism solutions determined in this study are dominated by normal faulting. Thus, these earthquake clusters are most probably associated with hydrothermal/magmatic activities in a back-arc extensional environment.

Foraminiferal Oxygen Isotope Stratigraphy and High-Resolution Organic Carbon, Carbonate Records from the Okinawa Trough (IMAGES MD012404 and ODP Site 1202)

Abstract: Biogenic carbonate and organic carbon content of two deep sea cores (MD012404 and ODP site 1202) are measured to reconstruct surface ocean productivity variations in areas of the Okinawa Trough in the Western Pacific where the modern climate is highly sensitive to the East Asian monsoon and precipitation/river runoff. Based on foraminiferal isotope stratigraphy and AMS (superscript 14)C dating, the age models of the cores indicate that core MD012404 shows relatively low sedimentation rates with 50 cm ky^(-1) on average, and that the sedimentation rates in core ODP 1202 are extremely high with an average of 500 cm ky^(-1). Total organic carbon (TOC) and carbonate contents in core ODP 1202 are 0.56% and 6.80% on average, respectively, and are 0.62% and 15.86%, respectively, in core MDO 12404. The relatively high carbonate contents in core MD012404 imply high carbonate productivity in the central Okinawa Trough. The sedimentary composition of core ODP 1202 is composed principally of terrestrial silt and clay, indicating enormous terrestrial flux from land and a carbonate dilution effect in the southern Okinawa Trough. The variations of TOC in core MD012404 reveal a dominant 23 kyr cycle, suggesting that the surface ocean productivity in the Okinawa Trough area appears to be driven by precession changes in the East Asian monsoon. High-frequency oscillations in the TOC records in core MD012404 also indicate that the surface ocean productivity changes share a similar structure with the climatic variability characteristic of northern high latitudes.

Interdecadal Changes in Heavy Rainfall in China during the Northern Summer

Abstract: 1 School of Earth and Environmental Sciences, Seoul National University, Seoul, Korea 2 Laboratory for Atmosphere, NASA/Goddard Space Flight Center, Greenbelt, MD, USA 3 Science system and Applications, Inc., Lanham, MD, USA 4 Key Laboratory of Environmental Change and Natural Disaster, Institute of Resources Science, Beijing Normal University, China * Corresponding author address: Prof. Chang-Hoi Ho, School of Earth and Environmental Sciences, Seoul National University, Seoul, Korea; E-mail: hoch@cpl.snu.ac.kr Using ground observations of daily rainfall over China during summer (June August) for the period 1961 95, we examined interdecadal changes in the distribution of rainy events as a function of the rain rate and assessed their contributions to the total summer rainfall. We found that central China was wetter, and northern and southern China were drier in the decades following 1979 as compared to the earlier decades. The interdecadal changes in the Chinese summer rainfall are closely linked to those in large-scale circulations: the southward displacement of a westerly wind at the levels of 200 and 850 hPa over East Asia and an enhanced 850 hPa northerly wind over central-eastern China. The corresponding 850 hPa relative vorticity increased (decreased) over central (northern and southern) China where the summer rainfall has increased (decreased) during the later decades. Interestingly, the change in the total number of rainy events was found to be negligible during the entire period of data collection. Across the overall region (mostly eastern China), a large amount of interdecadal changes is accounted for by less than 20% of the total number of rainy events in the heavy-to-extremely-heavy categories (≥~25 mm day 1 − ). The possible causes-associated with large-scale circulations-and the implications of the present results are discussed. (

Hydrochemical changes in spring waters in Taiwan: Implications for evaluating sites for earthquake precursory monitoring

Abstract: To evaluate potential monitoring sites as well as useful ions which are capable of serving as earthquake precursors, ten subsurface water bodies in different tectonic domains in southwestern, northern and northeastern Taiwan were selected. They included the deep circulation of hot springs, shallower artesian springs and groundwater. Most of the hot springs clearly show chemical anomalies which correlate with earthquake events during the monitoring periods. Against this, the groundwater does not correspond to any events. Hot springs from deeper reservoirs are superior to artesian springs and groundwater from shallower reservoirs. The artesian spring from the smaller subsurface water body is superior to the groundwater from larger reservoirs. Aside from this, anions, especially chloride, outperform cations as geochemical precursors for earthquake monitoring. It is unambiguous that the major factors that determine the usefulness of chemical anomalies in the waters for earthquake precursory monitoring are the kinds, the depths and the size of reservoirs and the ion species of the subsurface water bodies.

A Refined Historical Record of Volcanic Eruptions around Taiwan: Tectonic Implications in the Arc-continent Collision Area

Abstract: The historical record of volcanic eruptions is extremely important for natural hazard reduction, especially in densely inhabited areas. In concert with clarification of contradictory points in the historical eruptions' record, we have modified the locality, eruption size, and timing of submarine volcanic eruptions around Taiwan. Three out of five submarine eruption records (catalog numbers 0801-04, 0801-05 and 0802-01) in northern offshore Taiwan can be clearly traced. These events indicate that volcanic activity in this area is still in progress; and hence a program for volcanic hazard reduction should be seriously considered in northern Taiwan. Two events (catalog numbers 0801-03 and 0801-02) shown to have occurred in the southeast offshore region of Taiwan appear to be related to the Eurasian Continental Plate's eastwardly subduction under the Philippine Sea Plate. However, the new seismic wave travel time tomography of the subduction zone will be needed to clarify this. The refined results shall contribute to the Smithsonian Institution's Global Volcanism Program and the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) for editing the next version of the Catalog of Active Volcanoes of the World.

Morphology, Hydrodynamics anti Sediment Characteristics of the Changyun Sand Ridge offshore Western Taiwan

Abstract: The Changyun Ridge, a shelf sand ridge located off the western coast of Taiwan, is a tide-dominated sand body. This ridge is defined by the 50-m isobath and consists of two smaller ridges. The eastern Changyun Ridge is about 65 km long and 15 km wide and approximately parallel to the western shoreline of Taiwan. The western Changyun Ridge has a length of 53 km and a maximum width of 26 km, trending northwest-southeast normal to the Taiwan western coast. The eastern ridge has morphologic characteristics similar to those of typical linear sand ridges. Tidal currents show distinct bidirectional patterns with speeds exceeding 100 cm s^(-1) strong enough to move sandy sediments. Large to very large sand waves occur on the western Changyun Ridge and sand waves seldom appear on the eastern Changyun Ridge, implying that the former is presently active while the latter becomes inactive or moribund. The configuration and distribution of these two ridges further suggest that the ridges developed sequentially from near-shore to offshore, presumably in response to a westward progressive decrease in velocity and change of flow direction of the north-flowing tidal currents. Following the transgression beginning about 15000 years ago, the sea waters from the South China Sea began to flow over the sea floor between the Penghu Islands and Taiwan and the paleo-tidal currents finally excavated the sea bed into a channel now known as the Penghu Channel. Sands and mud are winnowed out but gravel and shell fragments have lagged behind in the Penghu Channel and only medium to fine-grained sands and mud carried by the strong tidal currents to the Changyun Ridge and beyond. Mainly medium to coarse-grained sands have accumulated on the Changyun Ridge to form sand banks. At the northern outlet of the Penghu Channel, the shoaling topography of the Changyun Ridge has caused a decrease in tidal current velocity and the subsequent deposition of sands, forming the present Changyun sand ridge. The formation of the eastern and western Changyun sand ridges is probably affected mostly by the tidal current patterns in the areas north of the Penghu Channel.

Core Description and a Preliminarily Sedimentology Study of Site 1202D, Leg 195, in the Southern Okinawa Trough

Abstract: ODP Site 1202 of Leg 195 was designed primarily for a high-resolution study of the paleoceanography of the Kuroshio Current in the southern Okinawa Trough off NE Taiwan. Four holes were drilled in which Hole 1202D is described in detail in this study for an assessment of core quality for paleoceanography study and understanding of sedimentological features, especially turbidite sedimentation and the sediment provenances during the Late Quaternary in the southern Okinawa Trough. Pelagic mud with insignificant silt or sand layers is observed from the core top down to 133 m (mbsf; Marine Isotope Stages 1-3), but the silt-sand layer ratio (SLR: total thickness of silt and sand layers/1.5 m of core) increases gradually from a value of ＜10% between 133 and 167 m to values ＞50% between 223 and 279 m, followed by decreases to values ＜10% between 310 and 337 m and to ＜3% between 337 and 407 m (Stage 4). These silt-sand layers were most likely derived by fine-grained turbidite gravity flows, which were very active during Stages 3 and 4. Slate fragments, quartz grains, mica flakes and volcanic detritus are the major components in the coarse fraction of wash residues (＞250μm). Slate fragments are commonly found in fine-grained turbidite dominant intervals (160-280 m), while mica flakes can be observed in the muds throughout the core. The major detrital components were derived primarily from the Miocene slate belt of the pre-collision accretionary prism of the Central Range in northern Taiwan. The occurrence of volcanics could represent submarine volcanic activity in the active-opening Okinawa Trough back-arc basin off NE Taiwan. Shallow-marine fossils including benthic foraminifers, echinoids, bryozoans and mollusks are also found in the fine-grained turbidite dominant intervals. These fossil assemblages could have been deposited in the shallow shelf and then transported to the depositional site along with voluminous terrigenous materials derived from Taiwan, via submarine channels or by slope failures due to frequent earthquakes induced by plate convergence/collision and extension in the southwestern Okinawa Trough off NE Taiwan. It is concluded that the top 133 m of the core is better suited for paleoceanographic reconstruction.

Geochemistry of major constituents, boron and boron isotopes in pore waters from ODP site 1202, Okinawa Trough

Abstract: geochemical results show that major constituents and boron content varied largely in pore fluids and possibly were affected by sulfate reduction, recrystallization of biogenic carbonate or silica, ash alteration, and organic matter degradation. Mixing of fluids along high-porosity sandy layers or fracture zones also changes the pore water chemical compositions significantly. The down-core distribution of B and δ 11 B in the pore waters are sensitive tracers for assessing fluid migration and water/sediment interaction at various depths. Pore water B content at Site 1202 falls in a range between 0.25 and 1.16 mM compared to that of 0.42 mM in seawater. The δ 11 B values, however, vary considerably from ~32.7 to 50.9 0 00 relative to the seawater value of 39.5 0 00. The δ 11 B vs. 1/B plot indicates that sedimentary B released from clays is the most important source to pore waters, resulting in elevated B with low δ 11 B. Other processes including precipitation of calcium carbonate, fluid advection through high-porosity permeable sandy horizons, interaction with terrigenous sediments and/or ash alteration may also modify the B and δ 11 B distributions.

Gas Hazard Induced by Methane and Hydrogen Sulfide Seepage in the NW Peloponnesus Petroliferous Basin (Greece)

Abstract: Gas seeps along the Ionian coast of the northwestern Peloponnesus (Greece) constitute a severe hazard for humans and buildings. Methane, migrating from deep carbonatic hydrocarbon reservoirs, is seeping in amounts potentially explosive and hydrogen sulfide is beyond the levels that induce toxicological diseases and lethal effects. The seeps are related to intense methane microseepage in the surrounding areas (orders of 10^1 to10^5 mg m^(-2)d^(-1) over 10^4 m^2 areas, at least) and produce significant CH4-H2S enrichments in the atmosphere. Gas-charged sediments in the seafloor and bubbling plumes present a high risk for offshore constructions and facilities.

Environmental Change in the Southwestern Coastal Plain of Taiwan since Late Pleistocene: Using Multiple Proxies of Sedimentary Organic Matter

Abstract: In an attempt to discriminate between organic matter sources and reconstruct further the paleoenvironment of the southwestern coastal plain of Taiwan, organic carbon and nitrogen content (C/N) ratios and isotope composition (δ13C and δ15N) are measured for sedimentary core samples collected from San-liao-wan, Zai-kang and Yihju in the southwestern coastal plain of Taiwan. Heavy δ13C values (up to -14.3‰) and high C/N ratios (average 9.3) with good correlation indicate that this area underwent a period of relative aridity from early Marine Isotopic Stage (MIS) 2 to the early MIS 1. In MIS 1, the δ13C and C/N ratio both vary initially before later steadying, indicating that the environment became progressively more stable, with C3 plants becoming dominant again. The Zai-kang core appears to have come from a shallow lagoon system that potentially preserved the record of δ15N from autochthonous primary producers. Regional organic source variation is revealed through the high δ15N values and constant C/N ratios in MIS 1 of the Zai-kang core. This may suggest that man- groves and macrophytes were the main aquatic organic matter source in the Zai-kang area during MIS 1.

Calcareous Nannofossils and Variation of the Kuroshio Current in the Okinawa Trough During the Last 14000 Years

Abstract: A quantitative census study on calcareous nannofossils from sediments of Site 1202 recovered by ODP Leg 195 and surface sediments from the East China Sea was carried out to obtain a high-resolution nannofossil record of the change of the Kuroshio Current during the late Quaternary. Two nannofossils ratio indices were designed and employed in this study: (1) ratio of Florisphaera profunda against F. profunda, Emiliania huxleyi and Gephyrocapsa oceanica (F-EG ratio) as a nannofossil proxy of the Kuroshio Current, (2) ratio of G. oceanica against F. profunda and E. huxleyi and G. oceanica (G-FE ratio) as a proxy of near-coast environment. Results from the 14 surface nannofossil samples demonstrate that the F-EG ratio is ＞15% in the assemblage lying directly under the main route of the Kuroshio Current, whereas it is very low (＜10%) in sediments off the current. High ratios G-FE (＞30%) were seen from all samples on the East China Sea continental shelf or from near-coast cores. Down hole nannofossil record from the top 60 mbsf sediment interval at ODP Hole 1202B reflects the change of the Kuroshio Current in the last glacial and postglacial period since 14 ka. Extreme low F-EG ratio together with very high G-FE ratio at Hole 1202B during the time of the latest Pleistocene and the earliest Holocene suggest the absence of the Kuroshio Current in the area studied. The event of intrusion of the Kuroshio Current was clearly recorded by a dramatically increase of F-EG ratio and notably a reduction in the G-FE ratio around 9 ka. Furthermore, based on the variation of the F-EG ratio and δ(superscript 18)O of planktonic foraminifera Neogloboquadrina dutertrei, variation of the Kuroshio Current in the Holocene shows three long-term cycles (with a periodicity of ~3000 yr).