大陸邊緣沉積物的沉積速率是研究沿岸海洋環境變化的重要指標參數，藉由沉積速率的變化可以瞭解由陸地到海洋間的物質傳輸、通量、有機碳埋藏速率或其他化學組成的變化，並可以用它評估近代人類活動對環境變化的影響。
本研究以國際合作方式採集美國東南部墨西哥灣的沉積物岩芯，並以Gamma能譜儀測定沉積物柱樣中鉛-210沉積物活度的垂直分佈情形，沉積物中的質量沉積速率將根據測定的過剩鉛-210 活度而估算之。主要目的是比較並探討沉積物收集器所得到的質量沉積速率和通量間關係，以探討墨西哥灣沉積物的特性及質量沉積速率分布情形。
墨西哥灣的沉積物中，所採的八個岩芯依據地形分為大陸棚和大陸斜坡，而大陸棚上三個測站的孔隙率變化不大，表示其岩性接近，大陸坡上的五個測站的孔隙率在最深處GC233#4 (650 m) 明顯比其他測站變化大，顯示在此測站受到強烈的壓縮作用。
無論大陸坡或大陸棚上過剩的鉛-210的值遠高於鐳-226所衰變的鉛-210的值，結果表明沉積物中過剩210Pb隨深度呈現指數衰減，且沉積物不受生物擾動影響，所估算沉積物的質量沉積速率在大陸棚約為0.056-0.061g/cm2/yr，大陸斜坡約為0.018-0.041g/cm2/yr，發現大陸棚的質量沉積速率普遍高於大陸斜坡，表明大陸棚沉積物中顆粒物於沉降過程中清除水體的Pb-210的量比大陸斜坡大。而沉積速率隨水深逐漸遞減，同時也說明淺水的大陸棚是陸源輸入物質及其他生源物質的重要儲藏場。

關鍵字：Pb-210、Ra-226、壓縮作用、沉積速率、通量

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

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