Abstract Temporal variations in hydrographic parameters and nutrients were observed in a 300 m de... more Abstract Temporal variations in hydrographic parameters and nutrients were observed in a 300 m deep submarine canyon (Hungtsai Trough) near the southern tip of Taiwan. A vigorous oscillation below the surface layer has been observed which relates closely to an internal tidal wave generated from the nearby Luzon Strait. The vertical movement can be measured by monitoring an 18 °C isothermal depth which shows an up-and-down oscillation between 90 and 240 m with an average displacement of 110 m within a tidal cycle, a scale significantly larger than has been reported elsewhere. The frequency of this oscillation coincides with the surface tide but in an almost opposite phase. All hydrographic and chemical parameters (oxygen, density, fluorescence, transmittance and nutrients including nitrate, phosphate and silicate) synchronize with the tidal movement, as judged by normalized plots against temperature. When the nutrient-rich deep water upwells and becomes an outcrop over the trough rim at 100 m deep, it is swept horizontally by the strong alongshore tidal current. Consequently, the trough acts as a source point to supply extra nutrients to the coastal ecosystem.
During Typhoon Mindulle in early July 2004, the Choshui River (central-western Taiwan) discharged... more During Typhoon Mindulle in early July 2004, the Choshui River (central-western Taiwan) discharged ~72 Mt of sediment to the eastern Taiwan Strait; peak concentrations were ≥200 g/L, ~35%-40% of which was sand. Box-core samples and CHIRP (compressed high-intensity radar pulse) sonar records taken just before and after the typhoon indicate that the hyperpycnal sediment was fi rst deposited adjacent to the mouth of the Choshui, subsequently re suspended and transported northward (via the Taiwan Warm Current), and redeposited as a patchy coastal band of mud-dominated sediment that reached thicknesses of 1-2 m within megaripples. Within a month most of the mud was gone, probably continuing its northward transit, but more mud appeared in late August in response to Typhoon Aere. Following autumn and winter storms, the entire nearshore area was again sand dominated by early spring.
Terrestrial, Atmospheric and Oceanic Sciences, 1992
Upwelling of the Kuroshio subsurface water at the shelf break near the northern tip of Ta iwan is... more Upwelling of the Kuroshio subsurface water at the shelf break near the northern tip of Ta iwan is an important oceanic phenomenon, that results from impingement of the Kuroshio onto the continental shelf and causes profound chemical and biological responses. This upwelling region was frequently ob served in the past as a pool of cold water. However, such temperature contrast does not exist throughout the year due to the cooling of the shelf water in win ter. Consequently, it has never been established until now that the upwelling is a year-round phenomenon. In this study, monthly cruises were conducted from August 1990 to July 1991, and a one year-long monthly record of up welling was evidenced from the distribution of temperature, nitrate and dis solved oxygen. The last, which revealed the structure of the upwelling dome in winter similar to those in other months, was an especially useful indicator of upwelling when tem perature or nitrate concentration fa iled to show the whole picture of upwelling. Undersaturation of oxygen in the surface water at the upwelling center was observed during December-May. The average downward flux of oxygen in the upwelling area was computed to be 0.034 moVm 2 /day in March 1991. According to a box model for thermal and mass balance, an upwelling speed of about 5 m/day was required to maintain the oxygen-deficiency in the surface layer. The upwelling velocity yielded a total volume transport of 0-2 Sv and nitrate transport of 2x10 9 gN/day to the top 60m in the upwelling area of 2900km 2 •
With the discoveries of Bottom Simulating Reflectors (BSRs), large and dense chemosynthetic commu... more With the discoveries of Bottom Simulating Reflectors (BSRs), large and dense chemosynthetic communities and rapid sulfate reductions in pore space sediments, gas hydrates may exist in offshore southwestern Taiwan. Methane concentrations in pore space sediments have been measured to investigate if fluids and gases are derived from dissociation of gas hydrates. Very high methane concentrations and very shallow depths of sulfate methane interface (SMI) imply the high methane flux underneath the seafloor. Linear sulfate gradients, low total organic carbon (TOC) have been combined to describe the process of anaerobic methane oxidation (AMO) and calculate the iffusive methane flux in Chuang et al. (2010). However, the appearance of concave (or non-linear) profiles of sulfate in some cores might indicate advective fluid flows. Hence, the methane flux may be much greater under advective conditions. In this study, numerical transport-reaction models were applied to calculate the methane flux...
Deep Sea Research Part I: Oceanographic Research Papers, 2018
Abstract Sulfate reduction could go through dissimilatory sulfate reduction and anaerobic methane... more Abstract Sulfate reduction could go through dissimilatory sulfate reduction and anaerobic methane oxidation couple with sulfate reduction (AOM-SR) with pyrite the end product. While AOM-SR is an important process in oxidizing methane and limiting methane entering the ocean, there is limited information available regarding pyrite formation and preservation under methane dominated environment. The purpose of this study is to report pyrite formation and preservation at a methane dominated environment, the YuanAn Ridge, where methane seeps have been observed, and to evaluate how would that differ from typical anoxic environment. Pore water methane, sulfate, dissolved sulfide, barium, and sediment pyrite, barium/Al ratio and organic carbon in sediments were analyzed from sediments collected by piston cores on board the R/V Ocean Researcher I (OR-I) from the study environment. The results showed methane flux is controlling pyrite formation in this methane dominated environment. Pyrite concentration is linearly correlated with methane flux with exceptions to shallower sulfate methane transition zone (SMTZ) sites where methane could have vent directly to the overlying water and contribute less to the pyrite formation. The more methane entering the SMTZ, the more pyrite formed and preserved in the sulfate methane transition zone sediments. Authigenic pyrite from dissimilatory sulfate reduction is a small fraction of the pyrite found in the methane dominant and low in organic carbon environment, with majority of pyrite derived from AOM-SR. Large spatial variations on rate of sulfate reduction, pyrite and methane concentrations were observed in the studied area sediments. Depth of sulfate methane transition zone varied between 1 and 14 m and is a log function of methane flux. Pore water sulfate profiles displayed three different types, linear, concave up and down, indicating methane flux have varied in time. Pyrite burial efficiency is high, approximately 50% of sulfate entering the SMTZ were preserved in sediments as pyrite. This efficiency of sulfate reduction through AOM-SR is much higher than pyrite formation from dissimilatory sulfate reduction in normal marine sediments. The AOM-SR and pyrite formation occurred at depth within the SMTZ favor a higher degree of pyrite preservation. Time require for the pyrite formation is about 4400 years in the YAR sediments, based on diffusion model calculation of barium sulfate precipitation.
Terrestrial, Atmospheric and Oceanic Sciences, 2006
Bacteria sulfate reduction is a major pathway for organic carbon oxidation in marine sediments. U... more Bacteria sulfate reduction is a major pathway for organic carbon oxidation in marine sediments. Upward diffusion of methane from gas hydrate deep in the sedimentary strata might be another important source of carbon for sulfate reducing bacteria and subsequently induce higher rates of sulfate reduction in sediments. Since abundant gas may migrate upward to the surface as a result of tectonic activity occurring in the accretionary wedge, this study investigates the effect of methane migration on the sulfate reduction process in continental margin sediments offshore southwestern Taiwan. Piston and gravity core samples were taken in order to evaluate vertical and spatial variations of sulfate and methane. Pore water sulfate, sulfide, methane, sediment pyrite, and organic carbon were extracted and analyzed. Rapid sulfate reduction, high pyrite contents in sediments and higher concentrations of dissolved sulfide and methane were found in the study area with relatively low organic carbon concentrations. Up to 300 µmole g-1 of pyrite, 10 mM dissolved sulfide and 9 mM methane were found in the study region. Sulfate depletion was as shallow as ~1 m beneath the sediment/water interface. At similar water depths, however, low methane and pyrite were found in some areas with almost no sulfate reduction.
Page 1. TAO, Vol.6, No.l, 115-128, March 1995 Variations of Calcium Carbonate, Organic Carbon and... more Page 1. TAO, Vol.6, No.l, 115-128, March 1995 Variations of Calcium Carbonate, Organic Carbon and Their Isotopie Compositions in Surface Sediments of the East China Sea DAVID D. SHEU1, WEN-CHEN JOU1, MlNG-JUE ...
Bulk heavy metal Fe, Mn, Zn, Cu, Pb, Cd , Al, organic carbon and carbonate concentrations, grain ... more Bulk heavy metal Fe, Mn, Zn, Cu, Pb, Cd , Al, organic carbon and carbonate concentrations, grain sizes, and d C of the organic carbon distributions were studied in sediments collected throughout the East China Sea continental shelf and the Yangtze River Delta. The results demonstrated that terrigenous sediments from the Yangtze River is a dominating factor controlling the spatial variations of heavy metals and organic carbon concentrations on the East China Sea continental shelf. In addition, grain size and recent anthropogenic influences are also major factors modifying the spatial and vertical variations of heavy metals. Large spatial variations with a band type distribution of heavy metals, grain size, organic carbon and carbonate were observed. Higher concentrations of heavy metal and light d C 13 of the organic carbon were found primarily in the Deltaic and inner shelf sediments. The band type distribution generally followed the coastline with little variations in the Ž . north-south direction. Away from the Delta and inner shelf west-east direction , most heavy metal concentrations decreased rapidly with the exception of Cd where high concentrations of Cd were also found in the carbonate-rich shelf break sediments. Coarse-grained relict sediments and biogenic carbonate are two primary diluting agents for the fine-grained aluminosilicate sediments from the Yangtze River with high concentrations of heavy metals. Unusually high concentrations of Cu, Pb, and Cd showed both spatially and vertically that more pollution prevention measures are needed in the Yangtze River drainage basin in order to prevent further heavy metal pollution of the East China Sea inner continental shelf.
Results of geophysical and geochemical surveys imply the potential existence of gas hydrates offs... more Results of geophysical and geochemical surveys imply the potential existence of gas hydrates offshore southwestern Taiwan. For gas geochemistry studies, cored sediments have been collected to analyze methane concentration. Though there might be gas leakages during sampling procedures, very high methane concentrations have been detected. The profiles of methane and sulfate reveal very shallow depths of sulfate methane interface (SMI) at some cores. In order to realize that the main process for sulfate consumption is the anaerobic methane oxidation or the organic matter degradation, samples from five cores (MD05-2911, MD05-2912, MD05-2913, GT1 and GT39B) have been selected for ∀C-CH4, ∀C-CO2 and ∀C-DIC analysis. The Cdepletion around the depths of SMI can be observed both from ∀C-CH4 and ∀C-DIC profiles. The depths of C-depletion in methane and DIC are discordant. This may infer the carbon cycling around the depths of SMI. Parts of HCO3 (composed lighter ∀C-DIC) derived from the AOM r...
Temporal variations in gas hydrate related geochemical signatures under different deposition cond... more Temporal variations in gas hydrate related geochemical signatures under different deposition conditions are the primary purposes of this study. Accreted wedge located offshore Southwestern Taiwan receives high terrigenous river materials, 100 MT/yr, at present time. It is not clear how seep environment varied during the past glacial. A 25 meters long piston core was taken offshore Southwestern Taiwan on r/v Marion DuFresne. Short piston cores and box cores were also taken on r/v OR-1. Samples were analyzed for pore water dissolved sulfide, sulfate, methane, chloride, del O18, calcium, magnesium, alkalinity, pH, and sediment AVS, pyrite, inorganic carbon, del O18, C13. Changes in deposition environment play a major role in the study area. Three stages of geochemical processes are identified in the 25 meters long core, interchange between reduce and oxic depositional environments, with reducing condition in the top 10 m, oxic in between 10-20 meter and reducing below the 20 meter. Hig...
Abstract Temporal variations in hydrographic parameters and nutrients were observed in a 300 m de... more Abstract Temporal variations in hydrographic parameters and nutrients were observed in a 300 m deep submarine canyon (Hungtsai Trough) near the southern tip of Taiwan. A vigorous oscillation below the surface layer has been observed which relates closely to an internal tidal wave generated from the nearby Luzon Strait. The vertical movement can be measured by monitoring an 18 °C isothermal depth which shows an up-and-down oscillation between 90 and 240 m with an average displacement of 110 m within a tidal cycle, a scale significantly larger than has been reported elsewhere. The frequency of this oscillation coincides with the surface tide but in an almost opposite phase. All hydrographic and chemical parameters (oxygen, density, fluorescence, transmittance and nutrients including nitrate, phosphate and silicate) synchronize with the tidal movement, as judged by normalized plots against temperature. When the nutrient-rich deep water upwells and becomes an outcrop over the trough rim at 100 m deep, it is swept horizontally by the strong alongshore tidal current. Consequently, the trough acts as a source point to supply extra nutrients to the coastal ecosystem.
During Typhoon Mindulle in early July 2004, the Choshui River (central-western Taiwan) discharged... more During Typhoon Mindulle in early July 2004, the Choshui River (central-western Taiwan) discharged ~72 Mt of sediment to the eastern Taiwan Strait; peak concentrations were ≥200 g/L, ~35%-40% of which was sand. Box-core samples and CHIRP (compressed high-intensity radar pulse) sonar records taken just before and after the typhoon indicate that the hyperpycnal sediment was fi rst deposited adjacent to the mouth of the Choshui, subsequently re suspended and transported northward (via the Taiwan Warm Current), and redeposited as a patchy coastal band of mud-dominated sediment that reached thicknesses of 1-2 m within megaripples. Within a month most of the mud was gone, probably continuing its northward transit, but more mud appeared in late August in response to Typhoon Aere. Following autumn and winter storms, the entire nearshore area was again sand dominated by early spring.
Terrestrial, Atmospheric and Oceanic Sciences, 1992
Upwelling of the Kuroshio subsurface water at the shelf break near the northern tip of Ta iwan is... more Upwelling of the Kuroshio subsurface water at the shelf break near the northern tip of Ta iwan is an important oceanic phenomenon, that results from impingement of the Kuroshio onto the continental shelf and causes profound chemical and biological responses. This upwelling region was frequently ob served in the past as a pool of cold water. However, such temperature contrast does not exist throughout the year due to the cooling of the shelf water in win ter. Consequently, it has never been established until now that the upwelling is a year-round phenomenon. In this study, monthly cruises were conducted from August 1990 to July 1991, and a one year-long monthly record of up welling was evidenced from the distribution of temperature, nitrate and dis solved oxygen. The last, which revealed the structure of the upwelling dome in winter similar to those in other months, was an especially useful indicator of upwelling when tem perature or nitrate concentration fa iled to show the whole picture of upwelling. Undersaturation of oxygen in the surface water at the upwelling center was observed during December-May. The average downward flux of oxygen in the upwelling area was computed to be 0.034 moVm 2 /day in March 1991. According to a box model for thermal and mass balance, an upwelling speed of about 5 m/day was required to maintain the oxygen-deficiency in the surface layer. The upwelling velocity yielded a total volume transport of 0-2 Sv and nitrate transport of 2x10 9 gN/day to the top 60m in the upwelling area of 2900km 2 •
With the discoveries of Bottom Simulating Reflectors (BSRs), large and dense chemosynthetic commu... more With the discoveries of Bottom Simulating Reflectors (BSRs), large and dense chemosynthetic communities and rapid sulfate reductions in pore space sediments, gas hydrates may exist in offshore southwestern Taiwan. Methane concentrations in pore space sediments have been measured to investigate if fluids and gases are derived from dissociation of gas hydrates. Very high methane concentrations and very shallow depths of sulfate methane interface (SMI) imply the high methane flux underneath the seafloor. Linear sulfate gradients, low total organic carbon (TOC) have been combined to describe the process of anaerobic methane oxidation (AMO) and calculate the iffusive methane flux in Chuang et al. (2010). However, the appearance of concave (or non-linear) profiles of sulfate in some cores might indicate advective fluid flows. Hence, the methane flux may be much greater under advective conditions. In this study, numerical transport-reaction models were applied to calculate the methane flux...
Deep Sea Research Part I: Oceanographic Research Papers, 2018
Abstract Sulfate reduction could go through dissimilatory sulfate reduction and anaerobic methane... more Abstract Sulfate reduction could go through dissimilatory sulfate reduction and anaerobic methane oxidation couple with sulfate reduction (AOM-SR) with pyrite the end product. While AOM-SR is an important process in oxidizing methane and limiting methane entering the ocean, there is limited information available regarding pyrite formation and preservation under methane dominated environment. The purpose of this study is to report pyrite formation and preservation at a methane dominated environment, the YuanAn Ridge, where methane seeps have been observed, and to evaluate how would that differ from typical anoxic environment. Pore water methane, sulfate, dissolved sulfide, barium, and sediment pyrite, barium/Al ratio and organic carbon in sediments were analyzed from sediments collected by piston cores on board the R/V Ocean Researcher I (OR-I) from the study environment. The results showed methane flux is controlling pyrite formation in this methane dominated environment. Pyrite concentration is linearly correlated with methane flux with exceptions to shallower sulfate methane transition zone (SMTZ) sites where methane could have vent directly to the overlying water and contribute less to the pyrite formation. The more methane entering the SMTZ, the more pyrite formed and preserved in the sulfate methane transition zone sediments. Authigenic pyrite from dissimilatory sulfate reduction is a small fraction of the pyrite found in the methane dominant and low in organic carbon environment, with majority of pyrite derived from AOM-SR. Large spatial variations on rate of sulfate reduction, pyrite and methane concentrations were observed in the studied area sediments. Depth of sulfate methane transition zone varied between 1 and 14 m and is a log function of methane flux. Pore water sulfate profiles displayed three different types, linear, concave up and down, indicating methane flux have varied in time. Pyrite burial efficiency is high, approximately 50% of sulfate entering the SMTZ were preserved in sediments as pyrite. This efficiency of sulfate reduction through AOM-SR is much higher than pyrite formation from dissimilatory sulfate reduction in normal marine sediments. The AOM-SR and pyrite formation occurred at depth within the SMTZ favor a higher degree of pyrite preservation. Time require for the pyrite formation is about 4400 years in the YAR sediments, based on diffusion model calculation of barium sulfate precipitation.
Terrestrial, Atmospheric and Oceanic Sciences, 2006
Bacteria sulfate reduction is a major pathway for organic carbon oxidation in marine sediments. U... more Bacteria sulfate reduction is a major pathway for organic carbon oxidation in marine sediments. Upward diffusion of methane from gas hydrate deep in the sedimentary strata might be another important source of carbon for sulfate reducing bacteria and subsequently induce higher rates of sulfate reduction in sediments. Since abundant gas may migrate upward to the surface as a result of tectonic activity occurring in the accretionary wedge, this study investigates the effect of methane migration on the sulfate reduction process in continental margin sediments offshore southwestern Taiwan. Piston and gravity core samples were taken in order to evaluate vertical and spatial variations of sulfate and methane. Pore water sulfate, sulfide, methane, sediment pyrite, and organic carbon were extracted and analyzed. Rapid sulfate reduction, high pyrite contents in sediments and higher concentrations of dissolved sulfide and methane were found in the study area with relatively low organic carbon concentrations. Up to 300 µmole g-1 of pyrite, 10 mM dissolved sulfide and 9 mM methane were found in the study region. Sulfate depletion was as shallow as ~1 m beneath the sediment/water interface. At similar water depths, however, low methane and pyrite were found in some areas with almost no sulfate reduction.
Page 1. TAO, Vol.6, No.l, 115-128, March 1995 Variations of Calcium Carbonate, Organic Carbon and... more Page 1. TAO, Vol.6, No.l, 115-128, March 1995 Variations of Calcium Carbonate, Organic Carbon and Their Isotopie Compositions in Surface Sediments of the East China Sea DAVID D. SHEU1, WEN-CHEN JOU1, MlNG-JUE ...
Bulk heavy metal Fe, Mn, Zn, Cu, Pb, Cd , Al, organic carbon and carbonate concentrations, grain ... more Bulk heavy metal Fe, Mn, Zn, Cu, Pb, Cd , Al, organic carbon and carbonate concentrations, grain sizes, and d C of the organic carbon distributions were studied in sediments collected throughout the East China Sea continental shelf and the Yangtze River Delta. The results demonstrated that terrigenous sediments from the Yangtze River is a dominating factor controlling the spatial variations of heavy metals and organic carbon concentrations on the East China Sea continental shelf. In addition, grain size and recent anthropogenic influences are also major factors modifying the spatial and vertical variations of heavy metals. Large spatial variations with a band type distribution of heavy metals, grain size, organic carbon and carbonate were observed. Higher concentrations of heavy metal and light d C 13 of the organic carbon were found primarily in the Deltaic and inner shelf sediments. The band type distribution generally followed the coastline with little variations in the Ž . north-south direction. Away from the Delta and inner shelf west-east direction , most heavy metal concentrations decreased rapidly with the exception of Cd where high concentrations of Cd were also found in the carbonate-rich shelf break sediments. Coarse-grained relict sediments and biogenic carbonate are two primary diluting agents for the fine-grained aluminosilicate sediments from the Yangtze River with high concentrations of heavy metals. Unusually high concentrations of Cu, Pb, and Cd showed both spatially and vertically that more pollution prevention measures are needed in the Yangtze River drainage basin in order to prevent further heavy metal pollution of the East China Sea inner continental shelf.
Results of geophysical and geochemical surveys imply the potential existence of gas hydrates offs... more Results of geophysical and geochemical surveys imply the potential existence of gas hydrates offshore southwestern Taiwan. For gas geochemistry studies, cored sediments have been collected to analyze methane concentration. Though there might be gas leakages during sampling procedures, very high methane concentrations have been detected. The profiles of methane and sulfate reveal very shallow depths of sulfate methane interface (SMI) at some cores. In order to realize that the main process for sulfate consumption is the anaerobic methane oxidation or the organic matter degradation, samples from five cores (MD05-2911, MD05-2912, MD05-2913, GT1 and GT39B) have been selected for ∀C-CH4, ∀C-CO2 and ∀C-DIC analysis. The Cdepletion around the depths of SMI can be observed both from ∀C-CH4 and ∀C-DIC profiles. The depths of C-depletion in methane and DIC are discordant. This may infer the carbon cycling around the depths of SMI. Parts of HCO3 (composed lighter ∀C-DIC) derived from the AOM r...
Temporal variations in gas hydrate related geochemical signatures under different deposition cond... more Temporal variations in gas hydrate related geochemical signatures under different deposition conditions are the primary purposes of this study. Accreted wedge located offshore Southwestern Taiwan receives high terrigenous river materials, 100 MT/yr, at present time. It is not clear how seep environment varied during the past glacial. A 25 meters long piston core was taken offshore Southwestern Taiwan on r/v Marion DuFresne. Short piston cores and box cores were also taken on r/v OR-1. Samples were analyzed for pore water dissolved sulfide, sulfate, methane, chloride, del O18, calcium, magnesium, alkalinity, pH, and sediment AVS, pyrite, inorganic carbon, del O18, C13. Changes in deposition environment play a major role in the study area. Three stages of geochemical processes are identified in the 25 meters long core, interchange between reduce and oxic depositional environments, with reducing condition in the top 10 m, oxic in between 10-20 meter and reducing below the 20 meter. Hig...
Uploads
Papers by Saulwood Lin