Centre for Environment, Fishery and Aquaculture Science, Cefas, Lowestoft, NR33 0HT, UK.
Glob Chang Biol. 2015 Jun;21(6):2206-14. doi: 10.1111/gcb.12854. Epub 2015 Mar 6.
Light in the marine environment is a key environmental variable coupling physics to marine biogeochemistry and ecology. Weak light penetration reduces light available for photosynthesis, changing energy fluxes through the marine food web. Based on published and unpublished data, this study shows that the central and southern North Sea has become significantly less clear over the second half of the 20th century. In particular, in the different regions and seasons investigated, the average Secchi depth pre-1950 decreased between 25% and 75% compared to the average Secchi depth post-1950. Consequently, in summer pre-1950, most (74%) of the sea floor in the permanently mixed area off East Anglia was within the photic zone. For the last 25+ years, changes in water clarity were more likely driven by an increase in the concentration of suspended sediments, rather than phytoplankton. We suggest that a combination of causes have contributed to this increase in suspended sediments such as changes in sea-bed communities and in weather patterns, decreased sink of sediments in estuaries, and increased coastal erosion. A predicted future increase in storminess (Beniston et al., 2007; Kovats et al., 2014) could enhance the concentration of suspended sediments in the water column and consequently lead to a further decrease in clarity, with potential impacts on phytoplankton production, CO2 fluxes, and fishery production.
海洋环境中的光是连接物理、海洋生物地球化学和生态学的关键环境变量。弱光穿透力降低了光合作用可用的光量，改变了海洋食物网中的能量通量。基于已发表和未发表的数据，本研究表明，北海中部和南部在 20 世纪下半叶变得明显不那么清澈。特别是在所调查的不同地区和季节，与 1950 年后的平均塞奇深度相比，1950 年前的平均塞奇深度下降了 25%至 75%。因此，在 1950 年前的夏季，东安格利亚永久性混合区的大部分（74%）海底都在光区范围内。在过去的 25 年以上，水清澈度的变化更可能是由于悬浮沉积物浓度的增加，而不是浮游植物。我们认为，导致悬浮沉积物增加的原因有多种，包括海底群落和天气模式的变化、河口沉积物沉降减少以及海岸侵蚀增加。未来风暴活动的增加（Beniston 等人，2007 年；Kovats 等人，2014 年）可能会增加水柱中悬浮沉积物的浓度，从而导致透明度进一步降低，对浮游植物生产力、CO2 通量和渔业生产产生潜在影响。
