Chih-Chieh Su

SEDIMENTATION DYNAMICS IN THE EAST CHINA SEA ELUCIDATED FROM 210PB, 137CS AND 239.240PU

Sedimentation dynamics in the East China Sea was investigated based on profiles and inventories of 210 Pb , 137 Cs and ex 239,240 Pu in sediment cores collected from various settings in this marginal sea. The derived sedimentation rates vary by two orders of magnitude, from ; 2 to 0.02 cm yr y1 , and generally decrease southward along the inner shelf and eastward offshore. This pattern is consistent with the dispersal of Yangtze River-derived sediments by the current and tidal systems. y2 y1 . The weighted mean sedimentation rate over the shelf ca. 0.3 g cm yr appears to be higher than fluvial inputs from the y2 y1 . Yangtze River and Taiwan 0.14 g cm yr . The discrepancy can be reduced by considering the effect of sediment . mixing which renders sedimentation rates overestimated and the possibility of additional sediment input from the Yellow Rivers dispersal system. Spatial variations of the observed nuclide inventories in sediments suggest extensive sediment redistribution, boundary scavenging of 210 Pb, and large inputs of 137 Cs and 239,240 Pu from Yangtze Rivers drainage basin.

210Pb, 137Cs and 239,240Pu in East China Sea sediments: sources, pathways and budgets of sediments and radionuclides

Profiles of 210 Pb, 137 Cs and 239;240 Pu measured in 83 sediment cores collected from various sedimentary regimes in the East China Sea were analyzed to elucidate the sources, routes and budgets ofsediments as well as these radionuclides. Distributions ofsedimentation rates and nuclide inventories reveal alongshore transport ofsediments, 137 Cs and 239;240 Pu from the mouth of the Yangtze River toward the south, largely confined to the inner-shelf area (water depth 6 70 m). Mass balance calculations suggest that the East China Sea is a sink for the particle-reactive 210 Pb and 239;240 Pu, with about one-sixth oftheir sedimentary budgets supplied via boundary scavenging. In contrast, due to lower affinity of 137 Cs for particles and rapid turnover of the shelf water, the East China Sea serves as a source for 137 Cs. About two-thirds ofthe cumulative input of 137 Cs have been transported out ofthe East China Sea, leaving the remaining one-third stored in the bottom sediments and the overlying water column. As for the sediment budget, mass balance cannot be established due to a shortfall in sediment supply of more than 30% based on a comparison between input terms documented thus far and the sedimentation flux derived from this study. It is very likely that we have overestimated the sediment burial flux or that long-distance transport from the Yellow River’s dispersal system to the East China Sea is underestimated. Alternatively, the imbalance could be explained by the discrepancy between sediment input and output on decadal to centennial timescales. 7 2002 Elsevier Science B.V. All rights reserved.

Linkages between turbidites in the southern Okinawa Trough and submarine earthquakes

[1] Turbidite layers in surficial ( 6.8) submarine earthquakes recorded in the region since the 20th century. The repeating pattern of turbidite layers reported here on decadal to centennial time scales suggests what may be the long-term rhythm of seismic activities at this tectonically active plate boundary. INDEX TERMS: 0932 Exploration Geophysics: Radioactivity methods; 1035 Geochemistry: Geochronology; 3022 Marine Geology and Geophysics: Marine sediments—processes and transport; 3025 Marine Geology and Geophysics: Marine seismics (0935); 7221 Seismology: Paleoseismology. Citation: Huh, C.-A., C.-C. Su, W.-T. Liang, and C.-Y. Ling (2004), Linkages between turbidites in the southern Okinawa Trough and submarine earthquakes, Geophys. Res. Lett., 31, L12304, doi:10.1029/2004GL019731.

Effects of environmental regulations on heavy metal pollution decline in core sediments from Manila Bay

We investigated the high-resolution heavy metal pollution history of Manila Bay using heavy metal concentrations and Pb isotope ratios together with (210)Pb dating to find out the effects of environmental regulations after the 1990 s. Our results suggested that the rate of decline in heavy metal pollution increased dramatically from the end of the 1990 s due to stricter environmental regulations, Administrative Order No. 42, being enforced by the Philippines government. The presented data and methodology should form the basis for future monitoring, leading to pollution control, and to the generation of preventive measures at the pollution source for the maintenance of environmental quality in the coastal metropolitan city of Manila. Although this is the first report of a reduction in pollution in Asian developing country, our results suggest that we can expect to find similar signs of pollution decline in other parts of the world as well.

Records of submarine natural hazards off SW Taiwan

Abstract In the past few years, large earthquakes and torrential rain hit southern Taiwan and induced severe submarine hazards off the SW coast. Marine sediments (turbidites) provide valuable records with which to study and understand the formation of these submarine geo-hazards. The Pingtung Earthquake (two major events (ML=7.0) plus many aftershocks), on 26 December 2006, triggered turbidity currents that severed submarine cables in the Fangliao and Gaoping submarine canyons. This caused significant economic loss. In addition to earthquake activity, typhoons and torrential rains that induced flooding are also important mechanisms responsible for the formation of turbidites. On 8–9 August 2009 Typhoon Morakot brought heavy rains to southern Taiwan, causing serious landslides and flooding on land. The typhoon also caused submarine cable breaks in the Gaoping Canyon. All such events are likely to be recorded in the marine sediments of the canyon system, and by analysing these records we may be able to reconstruct the history of past earthquakes and floods in the region. Chirp sonar profiles, in conjunction with core analysis, including X-ray radiographs, grain size and 210Pb analysis, are used to identify the sources, transport and deposition of the turbidites (or hyperpycnite) and to reconstruct the history of earthquakes and flooding in the study area. Results indicate that these submarine hazards are not only related to earthquake and floods but that the unique geological and hydrological setting also plays an important role in the initiation of these submarine geo-hazards.

Factors controlling temporal and spatial variations of atmospheric deposition of 7Be and 210Pb in northern Taiwan

(1) Fluxes of 7 Be and 210 Pb monitored at two contrasting sites in northern Taiwan were studied along with meteorological data to elucidate factors controlling their temporal and spatial variations. The 9 year time series of both nuclides at Nankang in the Taipei Basin show dependence on wet precipitation and follow an annual cycle regulated by typhoons, monsoons, and mei-yu¨. Superimposed on the annual cycle are interannual variation caused by El Nino-Southern Oscillation and intraseasonal oscillations due to the passage or invasion of fronts, cold surges, dust storms, and the Pacific high-pressure system. The observed 7 Be/ 210 Pb ratios are indicative of the source regions of the fallout nuclides, with higher ratios from high-altitude rain and lower ratios from dry fallout and low-altitude rain. The 2 year time series at Yangminshan shows that 7 Be and 210 Pb fluxes at the mountainous site are in phase with those at Nankang. However, nuclide fluxes at Yangminshan are 4-5 times those at Nankang. After combining results from this and other ancillary studies at Yangminshan, we suggest that (1) in applying fallout nuclides to study the Earths surface processes, the assumption of constant flux should be made judicially according to the timescales involved, and that (2) the application of fallout nuclides to study soil erosion in hilly areas must consider not only control by wet and dry precipitation but also by direct contact and interaction of clouds with soils enhancing nuclide fluxes.

Rifting under steam—How rift magmatism triggers methane venting from sedimentary basins

During opening of a new ocean magma intrudes into the surrounding sedimentary basins. Heat provided by the intrusions matures the host rock creating metamorphic aureoles potentially releasing large amounts of hydrocarbons. These hydrocarbons may migrate to the seafloor in hydrothermal vent complexes in sufficient volumes to trigger global warming, e.g. during the Paleocene Eocene Thermal Maximum (PETM). Mound structures at the top of buried hydrothermal vent complexes observed in seismic data off Norway were previously interpreted as mud volcanoes and the amount of released hydrocarbon was estimated based on this interpretation. Here, we present new geophysical and geochemical data from the Gulf of California suggesting that such mound structures could in fact be edifices constructed by the growth of black-smoker type chimneys rather than mud volcanoes. We have evidence for two buried and one active hydrothermal vent system outside the rift axis. The vent releases several hundred degrees Celsius hot fluids containing abundant methane, mid-ocean-ridge-basalt (MORB)-type helium, and precipitating solids up to 300 m high into the water column. Our observations challenge the idea that methane is emitted slowly from rift-related vents. The association of large amounts of methane with hydrothermal fluids that enter the water column at high pressure and temperature provides an efficient mechanism to transport hydrocarbons into the water column and atmosphere, lending support to the hypothesis that rapid climate change such as during the PETM can be triggered by magmatic intrusions into organic-rich sedimentary basins.

Occurrence of azaarenes in sediments of the Danshuei River, Taiwan: the use of azaarenes as indicator of anthropogenic source to the estuarine system.

Azaarenes belong to the newly identified classes of anthropogenic pollutants. To our knowledge, this study presents the first result of pollution history of azaarenes and their controlling factors in estuary. To understand the transport mechanisms, surface sediment samples were collected from 18 sites of the Danshuei River during the summer and the winter of 2005. The highest concentrations of azaarene, 21.9 ng g−1 for 2‐ring, 9.89 ng g−1 for 3‐ring, and 9.17 ng g−1 for 4‐ring, were observed in midstream surface sediments near the Shi–Zi–Tou waste water pumping station. Therefore, this waste water pumping station not only provides a good sediment accumulation environment but also discharges small particle size sediments, which contain mass amounts of azaarenes into the Danshuei River. This research also finds highly significant covariations among 3‐ring and 4‐ring azaarenes, which suggests similar source strengths and transport mechanisms for these compounds. Additionally, core samples were collected from two sites of the Danshuei River and analyzed to determine the pollution history. Values found in the core sediments correspond to pollution events in recent history. Contaminant inputs via in situ burning of dumping field and wastewater discharge for the periods of 1975–1985 and 2004–2005, respectively, were two major sources of azaarenes to the Danshuei River.

210Pb deposition in the far East Asia: Controlling factors of its spatial and temporal variations

In order to better understand the behavior of (210)Pb deposition in Far East Asia, comprehensive data of monthly (210)Pb deposition, which includes several time-series and spatial distribution data at 14 stations in Japan and 2 stations in Taiwan, were analyzed. Pb-210 deposition at most of the sites exhibited a typical seasonal change with higher values in winter and lower values in summer; especially, the greatest (210)Pb deposition in the world occurred in winter at sites beside the Japan Sea. The deposition behavior of (210)Pb in Far East Asia differed between winter and summer. The meteorological phenomenon peculiar to winter of the Japan Sea side, i.e., formation of the Japan Sea convergence zone, might cause the high (210)Pb concentration in rainwater, as may heavy snowfall. The (210)Pb concentration in rainwater showed long-term variability, although this differed between winter and summer. This long-term variability may be related to climatological factors such as El Niño.

A comprehensive sediment dynamics study of a major mud belt system on the inner shelf along an energetic coast

Globally mud areas on continental shelves are conduits for the dispersal of fluvial-sourced sediment. We address fundamental issues in sediment dynamics focusing on how mud is retained on the seabed on shallow inner shelves and what are the sources of mud. Through a process-based comprehensive study that integrates dynamics, provenance, and sedimentology, here we show that the key mechanism to keep mud on the seabed is the water-column stratification that forms a dynamic barrier in the vertical that restricts the upward mixing of suspended sediment. We studied the 1000 km-long mud belt that extends from the mouth of the Changjiang (Yangtze) River along the coast of Zhejiang and Fujian Provinces of China and ends on the west coast of Taiwan. This mud belt system is dynamically attached to the fluvial sources, of which the Changjiang River is the primary source. Winter is the constructive phase when active deposition takes place of fine-grained sediment carried mainly by the Changjiang plume driven by Zhe-Min Coastal Currents southwestward along the coast.