HR Wallingford, Howbery Park, Wallingford, Oxfordshire, OX10 8BA, UK.
National Oceanography Centre, European Way, Southampton, SO14 3ZH, UK.
Sci Rep. 2020 Mar 19;10(1):5075. doi: 10.1038/s41598-020-61837-y.
Deep sea mining concerns the extraction of poly-metallic nodules, cobalt-rich crusts and sulphide deposits from the ocean floor. The exploitation of these resources will result in adverse ecological effects arising from the direct removal of the substrate and, potentially, from the formation of sediment plumes that could result in deposition of fine sediment on sensitive species or entrainment of sediment, chemicals and nutrients into over-lying waters. Hence, identifying the behaviour of deep-sea sediment plumes is important in designing mining operations that are ecologically acceptable. Here, we present the results of novel in situ deep sea plume experiments undertaken on the Tropic seamount, 300 nautical miles SSW of the Canary Islands. These plume experiments were accompanied by hydrographic and oceanographic field surveys and supported by detailed numerical modelling and high resolution video settling velocity measurements of the in situ sediment undertaken in the laboratory. The plume experiments involved the controlled formation of benthic sediment plumes and measurement of the plume sediment concentration at a specially designed lander placed at set distances from the plume origin. The experiments were used as the basis for validation of a numerical dispersion model, which was then used to predict the dispersion of plumes generated by full-scale mining. The results highlight that the extent of dispersion of benthic sediment plumes, resulting from mining operations, is significantly reduced by the effects of flocculation, background turbidity and internal tides. These considerations must be taken into account when evaluating the impact and extent of benthic sediment plumes.
深海采矿涉及从海底提取多金属结核、富钴结壳和硫化物矿床。这些资源的开采将产生不利的生态影响，原因是直接去除了底质，并且可能形成沉积物羽流，从而导致细沉积物沉积在敏感物种上或使沉积物、化学物质和养分卷入上覆水域。因此，确定深海沉积物羽流的行为对于设计生态可接受的采矿作业非常重要。在这里，我们介绍了在加那利群岛西南 300 海里的特罗皮克海山进行的新型深海羽流原位实验的结果。这些羽流实验伴随着水文和海洋学野外调查，并得到了详细的数值模拟和实验室中对原位沉积物进行的高分辨率视频沉降速度测量的支持。羽流实验涉及控制海底沉积物羽流的形成，并测量在专门设计的着陆器上测量距羽流起源设定距离处的羽流沉积物浓度。这些实验被用作验证数值扩散模型的基础，然后该模型被用于预测由全尺寸采矿产生的羽流的扩散。结果表明，采矿作业产生的海底沉积物羽流的扩散程度由于絮凝作用、背景浑浊度和内部潮流的影响而大大降低。在评估底栖沉积物羽流的影响和范围时，必须考虑到这些因素。
