MacKenzie A B, Stewart A, Cook G T, Mitchell L, Ellet D J, Griffiths C R
Scottish Universities Environmental Research Centre, Scottish Enterprise Technology Park, East Kilbride, G75 0QF, Scotland, UK.
Sci Total Environ. 2006 Oct 1;369(1-3):256-72. doi: 10.1016/j.scitotenv.2006.04.012. Epub 2006 Jun 6.
Results are presented for a study of manmade and natural radionuclides in north east Atlantic continental shelf and slope sediments to the west of Scotland. The data are interpreted in the context of sediment mixing and accumulation processes and are used to establish the westward extent of contamination of the sediment system. Offshore shelf and slope sediments were found to have post-glacial sedimentation rates of the order of 1 cm ky(-1) but nearshore sediments had much higher accumulation rates of the order of 0.1 cm y(-1). Surface mixed layer depths of up to 6 cm were observed and non-local mixing affected most of the slope sediments, resulting in advective transport of surface sediment to depths of up to 10 cm. Biodiffusion coefficients for offshore shelf and slope sediments were dominantly in the range 10(-8) to 10(-9) cm2 s(-1). The study confirmed that seawater contaminated with Sellafield waste radionuclides is dominantly entrained to the east of 7 degrees W and, consistent with this, higher levels of Sellafield derived radionuclides were confined to nearshore sediments, with lower levels to the west of 7 degrees W. 238Pu/(239,240)Pu data indicated that Sellafield contributed 75-91% of the total plutonium in coastal sediment but only about 4-8% of the total in slope sediments. By analogy, it can be concluded that a similar situation will apply to other contaminants in seawater entering the north east Atlantic via the North Channel.
本文展示了对苏格兰以西东北大西洋大陆架和斜坡沉积物中人造及天然放射性核素的研究结果。这些数据在沉积物混合和积累过程的背景下进行了解释，并用于确定沉积物系统向西的污染范围。近海大陆架和斜坡沉积物的冰后期沉积速率约为1厘米/千年，但近岸沉积物的积累速率要高得多，约为0.1厘米/年。观察到表面混合层深度可达6厘米，非局部混合影响了大部分斜坡沉积物，导致表层沉积物平流输送至深度达10厘米处。近海大陆架和斜坡沉积物的生物扩散系数主要在10^(-8)至10^(-9)平方厘米/秒范围内。该研究证实，受塞拉菲尔德核废料放射性核素污染的海水主要在西经7度以东被夹带，与此一致的是，较高水平的源自塞拉菲尔德的放射性核素局限于近岸沉积物，而在西经7度以西水平较低。钚-238/钚-239、钚-240数据表明，塞拉菲尔德贡献了沿海沉积物中总钚的75 - 91%，但在斜坡沉积物中仅占总量的约4 - 8%。由此类推，可以得出结论，通过北海峡进入东北大西洋的海水中的其他污染物也会出现类似情况。
