Description: With increasing demand for mineral resources, extraction of polymetallic sulphides at hydrothermal vents, cobalt-rich ferromanganese crusts at seamounts, and polymetallic nodules on abyssal plains may be imminent. Here, we shortly introduce ecosystem characteristics of mining areas, report on recent mining developments, and identify potential stress and disturbances created by mining. We analyze species’ potential resistance to future mining and perform meta-analyses on population density and diversity recovery after disturbances most similar to mining: volcanic eruptions at vents, fisheries on seamounts, and experiments that mimic nodule mining on abyssal plains. We report wide variation in recovery rates among taxa, size, and mobility of fauna. While densities and diversities of some taxa can recover to or even exceed pre-disturbance levels, community composition remains affected after decades. The loss of hard substrata or alteration of substrata composition may cause substantial community shifts that persist over geological timescales at mined sites.

Description: Does not include abstract

Description: Does not include abstract

Description: Rare earth elements and yttrium (REY) are often used as proxies to describe past enviromental conditions or to track element sources. Calcium phosphates are commonly used as archives for REY, but our study of the upper 10 m of deep-sea sediments from the equatorial Pacific, where REY are controlled by Ca phosphates, show that the shale-normalized (SN) REY patterns are heavily impacted by early diagenesis. The Ca phosphates incorporate REY from ambient pore waters without major fractionation, and thus, their REYSN patterns are similar to the pore-water REYSN pattern [1]. Our data from the Clarion Clipperton Zone (CCZ) and from the Peru Basin reveal such incorporation of pore-water REY into the Ca phosphates over long geographical distances and over a rather wide range of oxic to suboxic pore-water conditions. The pore-water REYSN patterns from the Peru Basin show similar features as seawater (e.g., heavy REY enrichment, negative CeSN and positive YSN anomalies), whereas the pore-water REYSN patterns from the CCZ display middle REY enrichment, the development of a negative CeSN-anomaly with depth, and either no or a slightly negative YSN-anomaly [1]. The differing pore-water REYSN patterns are possibly due to different REY sources to the pore water. These results cast doubt on the approach of using marine Ca phosphates as archives for the REY distribution or the Nd isotope composition of seawater, because the REY are derived from pore water and the Ca phosphates therefore do not preserve a primary seawater REY signal.

Description: Large quantities of methane are stored in hydrates and permafrost within shallow marine sediments in the Arctic Ocean. These reservoirs are highly sensitive to climate warming, but the fate of methane released from sediments is uncertain. Here, we review the principal physical and biogeochemical processes that regulate methane fluxes across the seabed, the fate of this methane in the water column, and potential for its release to the atmosphere. We find that, at present, fluxes of dissolved methane are significantly moderated by anaerobic and aerobic oxidation of methane. If methane fluxes increase then a greater proportion of methane will be transported by advection or in the gas phase, which reduces the efficiency of the methanotrophic sink. Higher freshwater discharge to Arctic shelf seas may increase stratification and inhibit transfer of methane gas to surface waters, although there is some evidence that increased stratification may lead to warming of sub-pycnocline waters, increasing the potential for hydrate dissociation. Loss of sea-ice is likely to increase wind speeds and sea-air exchange of methane will consequently increase. Studies of the distribution and cycling of methane beneath and within sea ice are limited, but it seems likely that the sea-air methane flux is higher during melting in seasonally ice-covered regions. Our review reveals that increased observations around especially the anaerobic and aerobic oxidation of methane, bubble transport, and the effects of ice cover, are required to fully understand the linkages and feedback pathways between climate warming and release of methane from marine sediments.

Description: One of the world‘s biggest manganese nodule fields on Earth is found in the Clarion-Clipperton Fracture Zone (CCZ) in the NE Pacific Ocean at 4-5 km water depth. Commercial deep-sea mining activities will affect the deep-sea environment1. We assess the recovery state of controlled anthropogenic disturbances within the CCZ which were created between 1 day and up to 37 years prior to sampling. Here, we present pore-water and solid-phase data of the upper 20 cm of sediment of disturbed sites in comparison with adjacent undisturbed reference sites. We focus on the impact of anthropogenic disturbances on the geochemical conditions of the sediments.

Description: Effects of seafloor disturbance on sediment biogeochemistry have been studied in the DISCOL Experimental Area (DEA) during leg SO242-1 and 242-2 of RV SONNE (Aug./Sep.2015). A variety of approaches have been employed including investigations in retrieved sediment cores (solid phase and pore water geochemistry, shipboard oxygen microprofiles) as well as lander- and ROV-based in situ flux studies with micro sensors and benthic chambers. Several levels of disturbance and spatiotemporal scales were addressed: Types of Disturbances included disruption of sediments as well as removal of sediments and nodules. Comparisons were carried out between distant sites of contrasting disturbance level (plough track vs. reference area off DEA) as well as between microhabitats identified within disturbed areas (e.g., elevations, depressions, excavated subsurface layers). Post-disturbance time scales that were addressed ranged from minutes (experimental nodule removal by ROV) and weeks (Epibenthos sledge deployments during the first leg) to years (plough harrow tows during the original disturbance experiment in 1989). This contribution introduces the habitats studied and the methods employed to investigate disturbance effects. Furthermore, first results on biogeochemical zonations and interfacial fluxes are presented and discussed with regard to predictions based on geochemical models.

Description: Potential effects on deep-sea benthic microbial communities and biogeochemical functions in response to seafloor disturbance by polymetallic (‘manganese’) nodule mining were investigated in the DISCOL Experimental Area (DEA). In 1989 the 〉10 km2 large DEA in the Peru Basin was disturbed by repeated ploughing, representing the largest benthic impact experiment ever carried out to date to investigate ecosystem impacts of deep-sea mining. Historical ‘plough tracks’ and a 5 weeks old track from Epibenthic Sledge sampling (‘EBS-track’) were studied in Sep. 2015 as part of the JPI Oceans project ‘MiningImpact’. Microbial communities and functions were assessed based on sediment analyses, shipboard incubations, and in situ flux studies with autonomous benthic chamber and micro-profiler systems. Investigations were carried out by ROV at specific microhabitats in plough- and EBS-tracks and compared to conditions off track and in reference areas outside the DEA. In the tracks where the disturbance removed parts of the reactive surface layer or even exposed organically poorer and more consolidated subsurface sediments, microbial and biogeochemical characteristics were affected and resembled conditions in deeper sediment layers, even after 26 years. Microbial biomass, organic matter degradation activity, respiration rates, and microbial secondary production were generally reduced. Microbial community structure in the EBS-track differed significantly from undisturbed surface sediments while in the historical plough marks recovery of communities over the past decades cannot be ruled out due to their large spatial heterogeneity. Extending the scope of earlier post-impact studies to microbiology, the results suggest long-term effects of nodule mining right at the basis of the benthic food web. Further studies are required to assess consequences for higher trophic levels and the time needed for ecosystem recovery, and to address the suitability of microbial communities and functions as impact indicators for routine monitoring in the context of nodule mining in the deep sea.