Previous studies have shown that the continental shelf and slope area off northeastern Taiwan is a region where the material exchange processes between the East China Sea and open ocean are most rigorous under the influences of the Kuroshio and the monsoons. In order to understand the topographic effects on the particulate flux and the transport path of the settling particles in this region, this study has conducted a series of field measurements using time-series sediment traps and current meters as tools. The temporal and spatial variations on the current, the particulate flux and the particle-size distribution as well as the activity and flux of 210 Pb and 210 Po are presented in this thesis. The biological productivity and the runoff of main rivers from Taiwan were not correlated with the particulate fluxes in our study area. However, the variations of the particulate flux in the canyon and on the slope areas were clearly affected by the tidal currents, showing good positive correlation with their amplitudes. The particulate, 210 Pb and 210 Po fluxes all showed an increase toward the ocean bottom but a decrease away from the shore, suggesting that the transports of particle and particle reactive elements were strongly influenced by the lateral transport process in the study area. Highest fluxes were observed in the Mien-Hua Canyon(MHC) and the lower slope southwest of the canyon. Intermediate values were observed in the South Okinawa Trough and the North Mien-Hua Canyon(NMHC). The intercanyon slope and the shallow traps in the NMHC had lowest values. The particulates and particle reactive elements were transported out of the shelf or upper slope area essentially through the MHC toward the slope southwest of the canyon. The NMHC and the intercanyon area were not major pathways for these materials. The fluxes of particle, 210 Pb and 210 Po in the study area were generally at least an order of magnitude greater than those observed from other continental margins in the world, except for the lowest values at the intercanyon station and the shallow water in the NMHC. Thus the continental margin off northeastern Taiwan is one of the most important areas for material exchanges with open oceans in the world. The trapped particulates were mainly silt with variable sand fractions. High sand contents were observed in the MHC and the lower slope southwest of the canyon, the intermediate values were in the outlet of the MHC and the NMHC, and the lowest in the South Okinawa Trough. This shows that the sand content decreases awayfrom the shore. On the contrary, silt and clay fractions in percent increase away from the shore. Under the influence of tidal currents, the settling sand particles in the MHC and its adjacent lower slope were laterally transported from resuspended sandy sediments of the continental shelf and upper slope area adjoining the head of the MHC. The fluxes of sand, silt and clay all decreased toward the South Okinawa Trough but increased toward the bottom. This particle-size distribution pattern also reflected the effect of lateral transport process in the study area. Variations of the 210 Pb activity in this study area were generally correlated inversely with the particulate flux and the sand content, indicating the effect of dilution of the mass flux and the sand content, but were positively correlated with the silt and clay contents because they were major 210 Pb scavengers. No apparent correlations of 210 Po with the mass flux and the three particle-size fractions were observed, suggesting that the variation of 210 Po activity was not related to the mass fluxes or the three particle-size fractions. High 210 Pb activities were found to be associated with high contents of POC, Mn and Fe. Correlations of 210 Pb with both Mn and Fe indicate that the oxide and hydroxide precipitates of Mn and Fe supplied from sediments on the continental shelf, upper slope area and submarine hydrothermal activities might serve as important mechanisms for enhanced 210 Pb scavenging. The relationship between the 210 Pb activity and the POC content might reflect either the settling mode of the fine particles incorporated with fecal pellets or aggregates, or sharing the same source with fine particles. The variatio ns of 210 Po activity were not correlated with Mn, Fe, major components or biogenic components, implying that the association of 210 Po with biogenic components might be masked by the enormous terrigenous materials. Except for the upper-trap samples collected at the intercanyon slope and the NMHC, the 210 Po activity was lower than the 210 Pb activity with 210 Po/210 Pb ratios less than unity. Based on comparisons of 210 Pb and 210 Po with relevant parameters and references of past studies, we can propose several possible mechanisms to explain why the ratios were less then unity: 1. 210 Pb was preferentially scavenged by advecting and settling particulates of terrigenous origin. 210 Po, known to be biophilic, might remain associated with the suspended organic particulates which could be dissolved or not settling. Moreover, the oxide and hydroxide precipitates of Mn and Fe in the study area would further enhance the scavenging of 210 Pb. 2. The particulates in suspension were favorable for differentiation between 210 Pb and 210 Ponuclides while those settled in sediments would allow them to grow toward the secular equilibrium. Therefore, the trapped particulates might be in frequent suspension and short in deposited sediments during their lateral transport. 3. The 210 Pb supplied from the East Asia aerosol in large quantity was accumulated in water column abd carried by the Kuroshio to the study area. The intrusion and eddies of Kuroshio off northeastern Taiwan could bring large amount of 210 Pb into the region of continental shelf and slope, allowing particulates to scavenge 210 Pb more effectively from the surrounding water. The upper trap in the NMHC and that in the intercanyon site yield lowest particulate flux but highest POC content. With less terrigenous material and more biogenic components in these samples, 210 Po/210 Pb ratios were greater than unity and variations of 210 Pb activity were hardly correlated with those of POC contents but were inversely correlated with those of Mn contents. However, the 210 Po activities of upper trap at the intercanyon site were well positively correlated with POC and PIC contents, indicating effects of the fresh biogenic particles. Based on the mass balance calculations of particulate and 210 Pb fluxes, current data and other related data gathered in this study, we may infer the sedimentation dynamics and transport path of the settling particles below 300m depth in the study area. Under the influence of tidal oscillation, terrigenous sediments on the shelf and the shelf break as well as the upper slope would be resuspended and carried into the MHC and transported further away. Most of the sand particles would deposit in the canyon while part of the silt and clay would be transported to the South Okinawa Trough directly and the rest to the lower slope southwest of the MHC. The particulate flux at the lower slope southwest of MHC might also have a portion of particulates swept from the upper slope by the Kuroshio eddies. As the NMHC and the intercanyon sites are located in the central area of the Kuroshio eddies, the particulates from the continental shelf and upper slope area would be blocked, resulting in very low particulate fluxes. High particulate fluxes observed in the lower NMHC trap should largely be due to resuspension of the sediments from the banks of the canyon.

In order to understand the source, transport pathway and sink of settling particulates in the sea off northeast Taiwan, three moorings with six sediment traps (about 100 m and 300 m above bottom) were deployed on the northern slope of the Ilan ridge (T17S and T18S) and in the South Okinawa trough (T19S). The mooring deployed at T17S was lost due to a connecting ring which was rusted and broken. The duration of the mooring was 6 months (late November, 1999 to early May, 2000) with sampling intervals at 15 days each. When the moorings were recovered, seawater samples were collected for filtration near each station and a box core at T19S was also taken so that the settling particulates, suspended particulates and bottom sediments can be compared for their characteristics. The results show that higher apparent mass fluxes were observed in January, February and early April, 2000 at T18S. The apparent mass fluxes vary between 11 and 91 g/m2/d at T18S, and between 6 and 22 g/m2/d at T19S. The time-series variations of the Pb-210 activity are between 46 and 76 dpm/g at T18S, and between 79 and 122 dpm/g at T19S, the values of which are much higher than those of T18S. The temporal Po-210 variations range between 18 and 90 dpm/g at T18S, and from 65 to 193 dpm/g at T19S. The Po-210 activity and its variation are greater at T19S than at T18S. The 210Po/210Pb activity ratios are less than unity at about 0.8 at T18S, and greater than unity at about 1.3 at T19S. The total Po-210 activity in all water columns varies between 0.2 and 16 dpm/100kg while the total Pb-210 activity varies between 28 and 43 dpm/100kg. The mean total 210Po/210Pb activity ratio is about 0.3, indicating that Po-210 was easily scavenged and removed from water columns by particulate matter. The box core taken at T19S has Po-210 activity ranging from 54 to 121 dpm/g and Pb-210 activity from 51 to 90 dpm/g. The 210Po/210Pb activity ratio is greater than unity in the upper 6 cm, indicating an excess of Po-210 activity. Below 6 cm Po-210 and Pb-210 are nearly at equilibrium. The 210Po/210Pb activity ratios in the water columns observed after the first deployments were higher than those observed after the second deployments. However, the 210Po/210Pb activity ratios of the settling particulates collected from the first trap deployments were lower than those from the second trap deployments. These changes might be attributed to earthquakes which occurred mainly before the second mooring period. These earthquakes could have caused a large quantity of terrigenous particulates with higher 210Po/210Pb activity ratio to be transported out to the study area in addition to resuspended shelf and slope sediments. These settling particulates, being enriched in organic matter with higher activity ratio, could preferentially scavenge Po-210 from the water column, resulting in much higher 210Po/210Pb activity ratios.

The purposes of this study are to understand the variations of the particulate and dissolved Pb-210 and Po-210 in profiles in the South China Sea and to estimate the residence time of these nuclides through their extent of radioactive disequilibrium. The profiles of Pb-210 and Po-210 in particulate and dissolved phases were measured at four stations in the northern South China Sea (station B, C, D and F) and three in the Bashi Channel (stations W2, W3 and W5) from four Ocean Researcher I cruises (ORI-575, ORI-580, ORI-588 and ORI-606). At Station C two profiles were taken, one before and the other after a typhoon to see its effect, if any, during the ORI-588 cruise. As the associated Ra-226 profiles were not measured their relations to Pb-210 profiles are not available for discussion in this thesis. The mean suspended particulate matter (SPM) concentration for each station is about 0.2 mg/kg with small deviations. Activities of Pb-210 and Po-210 in the northern South China Sea were all higher than those in the sea off NE Taiwan easured during the KEEP program. The dissolved Pb-210 profiles generally display a maximum around 15 to 25 dpm/100kg in the surface layer due to atmospheric input, and a minimum of about 5 to 15 dpm/100kg from 300 to 1000 m. The activities below 1000 m vary only slightly with a deep maximum as high as 20 dpm/100kg around 2000 to 3000 m, as seen at Station C. The particulate Pb-210 is around 3 to 5 dpm/100kg with small variation for the entire water column. The dissolved Po-210 profiles are somewhat similar to the dissolved Pb-210 profiles, but lower by about 5 to 10 dpm/100kg in activity. The mean residence time is about 0.76 year for total Po-210 in the entire water column, and 0.35 to 2.13 years for total Pb-210 in the mixed layer. At each station, Po-210 is deficient relative to Pb-210 in either the particulate or dissolved phase. The mean total Po-210/Pb-210 activity ratio is about 0.58, indicating that Po-210 is more effectively scavenged. It is imperative to understand the fate and pathway of the missing Po-210. Judging from its biophilic nature, Po-210 may have been absorbed or consumed by biomass and enriched in various tropic levels in the food chain, in addition to being scavenged and removed by sinking particles.

Abstract The purposes of this study are to understand the variations of the particulate and dissolved 210Pb and 210Po profiles in the water column of Gaoping Submarine Canyon(GSC) and to compare the distributions of the two nuclides in settling particles and sediments. Different types of samples taken in this area were analyzed for 210Pb and 210Po in order to understand processes involved in the particulate transport. Seawater samples were collected from Ocean Researcher III Cruise (ORIII-1192 in Nov, 2006). Sediment trap was deployed on Jun 21, 2000 and recovered on Jul 20, 2000 (ORIII-634). Sediments cores collected from ORIII-642 on Jul 21, 2000 (Core A-B) and ORIII-696 on Apr 7, 2001 (Core D-F) using multicorer. The profiles of 210Pb and 210Po in water column could be divided into two types one is estuarine and the other is oceanic. The profiles of dissolved nuclides in estuarine stations (CW1 to 3) are lower than in the oceanic stations (CW4-5). Because stations CW1 to 3 are controlled by large amount of terrigenous particles, scavenging in the three stations is quite obvious. The nuclide activities of the settling particles decrease with depth, probably due to dilution by resuspended surface sediment of lower activities, similar to observations in this study area. The downcore distributions of 210Pb and 210Po show clearly disequilibria between the two nuclides and suggested that sediment deposited in GSC has been disturbed down to 40-50 cm deep. All the data indicate the 210Po in the water column and in the settling particles as well as in the surface sediments is strongly deficient relative to its parent, 210Pb. Using a box-model and considering the influence of horizontal transports, we may calculate the residence times of 210Po in the 100m water layer in the GSC, to be 2.1d for the dissolved phase and 7.0 d for the particulate phase with a total 210Pb residence time is 3.8d.

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This study has analyzed Pb-210 activity in cores taken from northern coastal South China Sea (SCS) and the area west of the Luzon Strait (LS) in order to estimate the sedimentation rates and the mass accumulate rates which allow a direct comparison with measured settling particulate fluxes. Also, the particulate and dissolved Po-210 and Pb-210 distributions in a water column located to the west of the LS were measured and compared with earlier data. Core samples were collected at Stations G and H (box cores) during the ORI-688 cruise (July, 2003) and at M1, F and 1 (box cores) during the ORI-722 cruise (June and July, 2004). The water column samples were collected at S7 during the ORI-763 curise (August, 2005). Stations H, G and 1 are located in the continental shelf of the northern SCS; Stations, M1, F and S7 are located in the deep water area west of the LS. The water content of the cores at F and M1 west of the LS is mostly around 40%~55%, while that of the cores at H, G and 1 in the coastal area of the northern SCS ranges about 25%~37%. The total organic matter as estimated from the total loss on ignition at F and M1 is, respectively, about 6% and 12% on the average. The coastal cores contain about 3%~8% total organic matter. The Pb-210 activity generally decreases with the core depth but reaches a constant at a certain depth, below which the excess Pb-210 vanishes in the core. Based on the excess Pb-210 distributions in the cores, the estimated sedimentation rates vary between 16 and 52cm/100yr. At M1 station, the mean Pb-210 flux and the mean mass flux are, respectively, 129 dpm/m2/d and 0.55 g/m2/d as determined from the deepest sediment trap(2848m) (Chung et al., 2004). These values are much smaller than what were estimated from the cores: the Pb-210 flux at 201 dpm/m2/d and the mass flux at 5.3 g/m2/d. The Pb-210 flux obtained from the trap is 65% of that measured from the core, and the mass flux from the trap is only 10% of that from the core. These large differences may arise from an over estimation of the sedimentation rate in the core (due to bioturbation) and near-bottom lateral transport of sediments from elsewhere. Compared to the basin west of the LS, the mass flux at the coastal area is much higher but the Pb-210 flux is much lower, probably due to the fact that shallow water has little amount of Pb-210 to be scavenged and no boundary scavenging effect has been observed. The Pb-210 specific activity at S7 station ranges from 155 to 900 dpm/g; the Po-210 activity at this station ranges from 78 to 507dpm/g. The particulate Po/Pb ratio is about unity at 1800m depth, but the ratio at all other depths is less than unity, indicating that the Po-210 is deficient relative to Pb-210 in particles at this station. The total (dissolved + particulate) Po/Pb ratio in the water column is generally less than unity, showing Po-210 deficiency relative to Pb-210 probably due to absorption and/or adsorption of Po-210 by plankton and other organisms. The Po/Pb ratio for the water column averages about 0.6, corresponding to a mean residence time of 0.83yr for Po-210 removal.

The liquid argon target of the DEAP-3600 dark matter detector is contained by an extremely radiopure acrylic vessel. Alpha decays from the inner surface of the acrylic vessel are a source of background. If a fraction of the alpha energy is observed, or if the recoiling nucleus from the alpha decay is observed, the event will not be separated from a dark matter candidate event. In addition to the low level of inherent contamination from uranium and thorium, the Pb-210 from Rn-222 diffusion during manufacturing must be measured. The limit for the DEAP-3600 acrylic vessel is 1.1 × 10^−20 g/g Pb-210. By vaporizing a large quantity of acrylic and counting the concentrated residue with an ultralow background HPGe well detector and a low background alpha spectrometer, the bulk acrylic was found to have an upper limit of 10^−19 g/g Pb-210. The design, installation, commissioning, operation, and analysis for various aspects of the acrylic assay are described. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2014-01-14 19:27:47.533

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