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.

Interstitial water chemistry at DSDP Leg 79 Holes

Interstitial water analyses of samples collected at Sites 544-547 of DSDP Leg 79 are presented. In Site 547 chloride concentrations increase to almost 80% of the halite saturation values. Gypsum occurrences in the sediments immediately overlying the halite deposit can be explained in terms of migration of Ca**2+ and SO2**2- from the underlying evaporites. At shallower depths sulfate concentrations decrease rapidly as a result of sulfate reduction processes. The same processes lead to the removal of calcium in the form of calcium carbonate. At Site 547, the chloride concentration depth profile suggests a maximum of dissolved chloride which may be the result of advective flow from nearby (abput 6 km) evaporite salt diapirs.

(Table 1) Physical properties of sediments at DSDP Holes 79-545 and 79-547A

Laboratory measurements of the acoustic and physical properties of deep-sea sediments and rocks are important for the interpretation of seismic reflection and refraction data and estimation of in situ physical property values. Furthermore, the results of such measurements can be used to design geoacoustic models of the upper oceanic crust that can relate the physical properties of deep-sea sediments to lithology, depth of burial, and diagenetic effects (Hamilton, 1980; Milholland et al., 1980). The purpose of this paper is to report the results of laboratory measurements of wet-bulk density, compressionalwave velocity, and velocity anisotropy on sediments cored during DSDP Leg 79. The sample suite consists of 11 calcareous claystones and clay-rich chalks recovered between 370 to 720 m sub-bottom at Holes 545 and 547A.

Biomarker proxies on ODP Holes 151-912A and 151-912B

A novel and promising biomarker proxy for reconstruction of Arctic sea ice conditions was developed and is based on the determination of a highly branched isoprenoid with 25 carbons (IP25). IP25 records have been restricted to the last 150 kyr BP. We present a biomarker record from Ocean Drilling Program (ODP) Site 912, going back to the Pliocene-Pleistocene boundary and indicating that sea ice of variable extent occurred in the Fram Strait/southern Yermak Plateau area at least since about 2.2 Ma. Furthermore, our data support the idea that a combination of IP25 and open water, phytoplankton biomarker data ("PIP25 index") may give a more reliable and quantitative estimate of past sea ice cover (at least for the study area). The study reveals that the novel IP25/PIP25 biomarker approach has potential for semi-quantitative paleo-sea ice studies covering the entire Quaternary and could motivate further detailed high resolution research on ODP/IODP material using this proxy.