Annotated record of the detailed examination of Mn deposits from the SO 79 (SEDIPERU - TUSCH) expedition from R/V Sonne

The research cruise SO79 with RV SONNE (April 18 to June 09 1992) aimed to assess the impact of a potential mining activity on the sensitive deep-sea ecosystem of the Peru Basin. Up to now only results of reconnaissance surveys of the extended manganese nodule field discovered in 1978 in the Peru Basin are available. The hydroacoustic, sedimentological, and geochemical studies on data and sample material of SO79 came to the following results: a small-scaled variation in thickness respectively type of surface sediments shown by the sediment echosounder respectively the side-scan-sonar is assumably due to variations in deposition or erosion. The composition of sediments is controlled by climatic cycles of different length which were caused by the variable influence of glaciation of the northern hemisphere. We think that during the quaternary a deep-water circulation reduced in intensity and O2-content may have produced a suboxic diagenetic environment which led to a remobilization and redeposition of Mn forming manganese nodules in the oxic surface sediments. Near the distinct redox boundary at about 10 cm depth the growth conditions for nodules are extremely favourable. Due to the great variability of sediments the impact of deep-sea mining will be highly variable and the disturbance of the seafloor will change the ecosystem considerably.

1992年4月18日至6月9日期间，‘索恩号’（RV SONNE）执行的SO79科考航次，旨在评估潜在深海采矿活动对秘鲁海盆敏感深海生态系统的影响。迄今为止，仅可获取1978年于秘鲁海盆发现的广布锰结核（manganese nodule）矿区的普查勘探结果。本次基于SO79航次数据与样品材料开展的水声学、沉积学及地球化学研究，得出以下结论：沉积回声测深仪（sediment echosounder）与侧扫声呐（side-scan-sonar）分别观测到表层沉积物的厚度与类型存在小规模空间变异，推测该变异由沉积或侵蚀作用的变化所致。沉积物的组成受不同时长的气候旋回调控，这类旋回源于北半球冰川作用产生的可变影响。我们认为，第四纪期间，深水环流的强度与含氧量均出现衰减，由此形成了次氧化成岩环境，使得锰元素发生再活化与再沉积，进而在含氧表层沉积物中形成锰结核。在约10厘米深度处的清晰氧化还原界面附近，锰结核的生长条件极为优越。由于沉积物的空间变异性极强，深海采矿的影响将呈现高度异质性，海底扰动也将对该区域生态系统造成显著改变。