Gamma Spectrometric Pb-210 Dating of Sedimentation Rates in Gulf of Mexico and It’s Enviromental Implications

• Main Authors: Hui-chi Huang, 黃惠祺
• Other Authors: Shang-de Luo
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/23261016497713031579

碩士 === 國立成功大學 === 地球科學系專班 === 97 === The sedimentation rate of sediments around continental margin is an important parameter to study the changes in coastal marine environment. It could explain material transport and flux between land and ocean, buried speed of organic carbons, and changes in other chemical composition. Besides, it could be used to evaluate the impact of human activities on global environment. The major purpose of this research is to study the characteristic of the sediments of the Gulf of Mexico and the distribution of sedimentation rate by comparing and examining the relationship between the flux and sedimentation rates gathered from sedimentary collector. By the means of international cooperation, this research collected sediment cores from the Gulf of Mexico, southeastern United States and utilized Gamma spectrometer to measure the vertical distribution of Pb-210 activity inside the sediment cores. The mass sedimentation rate of sediments could then be estimated based on the excess Pb-210 activity. Among the eight sediment core samples of the Gulf of Mexico, their terrain is basically divided into the continental shelf and the continental slope. On the continental shelf the porosity of three cores has big changes, indicating similar lithological character. In contrast, the porosity of the five cores on the continental slope significantly. Particularly in core GC233#4 (650m) at deepest water depth the changes of porosity is much greater than in other cores, indicating the intense compaction effect in this core. The research result indicates that no matter on the continental shelf or slope, the value of excess Pb-210 is much greater that supported by Ra-226 in sediments and that the excess Pb-210 in sediment decays exponentially with the depth and the distribution of excess Pb-210 is not significantly influenced by biological perturbation. It exhibits that the estimated mass sedimentation rate is approximately 0.056-0.061g/cm2/yr in the continental shelf and 0.018-0.041g/cm2/yr in the stable continental slope. The research result points to that the sedimentation rate of continental shelf is generally higher than the rate of continental slop. It concluded the flux of excess Pb-210 scavenged by setting particles on the continental shelf is generally higher than on the continental slope. The sedimentation rate decreased with increasing the water depth, suggesting that the shallower continental shelf is an important reservoir for the materials from land-based sources, marine organic carbons, and other biogenic substances. Key words: Pb-210, Ra-226, Compaction, Sedimentation rate, Flux