Description: Deep-sea mining for manganese nodules appears to be an attractive option to supply the growing demand for metal resources. The technologies are advancing and the costs for deep-sea mining are dropping. The effect on the deep-sea ecosystems, in particular on microbial processes is hardly understood, making environmental management and monitoring efforts hard to focus. Long-term mining simulations can be used to assess the effects of deep-sea mining and the potential for recovery. We revisited a large-scale disturbance and recolonization (DISCOL) experimental area in the Peru Basin, 26 years after the disturbance and compared the disturbances with fresh tracks and reference areas. State of the art technologies and methods, such as, operations with a remotely operated vehicle (ROV), in situ flux measurements, estimation of biogeochemical parameters and activities, and investigation of microbial community structures via next generation sequencing, allowed the investigation of disturbances, related to deep-sea mining operations. During the disturbance simulations, surface sediment was removed, and suboxic subsurface layers were exposed. These deeper sediment layers had different microbial communities, lower amount of labile organic matter, less microbial biomass, and reduced activities. After 26 years, the organic matter did not rebuild, and cell numbers ,activities, and the assimilation efficiency stayed low. Only the community structure appeared to be recovered.

Description: Kelps (Phaeophyceae, Laminariales) function as ecosystem engineers along many Arctic rocky shores. With ongoing climate change, the frequency and intensity of marine heatwaves are increasing. Further, extensive meltwater plumes darken Arctic fjords. It was the aim of this study to analyse the future development of Arctic kelp forest ecosystems. We conducted a laboratory experiment, in which we determined physiological and biochemical responses of Agarum clathratum and Saccharina latissima to a marine heatwave scenario (4, 7, and 10°C) being acclimated to either low-light (3 µmol photons m²/s) or in-situ-light (120 µmol photons m²/s) conditions. Grown sporophytes were sampled in Nuup Kangerlua, Greenland from a sampling depth between 7-10 m. Meristematic discs were cut (diameter 2 cm) and distributed equally between treatments and replicates. The discs acclimated to the light conditions for two days, before the 12 days heatwave scenario started, followed by a five-day recovery period. Maximum quantum yield of photosystem II (Fv/Fm) measurements were measured every second day, using a pulse amplitude modulated fluorometer (Portable Chlorophyll Fluorometer PAM-2100, Heinz Walz GmbH, Effeltrich, Germany). The following kelp response parameters were measured before (day 6), at the peak (day 18) and after (day 23) the experimental heatwave. Growth was analysed by measuring the discs dry weight (g). Rapid light curves were measured with a pulse amplitude modulated fluorometer (Portable Chlorophyll Fluorometer PAM-2100, Heinz Walz GmbH, Effeltrich, Germany), using irradiance steps between 0-611 µmol photons m²/s to derive photosynthesis vs. irradiance curve parameters (Pmax, alpha, EK). Dark respiration and net photosynthetic rates were measured with a 4-channel optode set-up (FireStingO2 Fibre-Optic Oxygen Meter FSO2-C4, PyroScience Sensor technology, Aachen, Germany) by analysing the oxygen evolution in response to different light intensities within a 25 ml Schott bottle, each containing meristematic discs. Pigment content was analysed with a High-Performance Liquid Chromatograph (HPLC, LaChromElite® system, L-2200 autosampler (chilled), DA-detetctor L-2450; VWR-Hitachi International GmbH, Darmstadt, Germany). Total phlorotannin concentration was analysed with the Folin-Ciocalteau assay, using a phloroglucinol dilution series (C6H6O3, Sigma-Aldrich: 0–1000 µg/ml).

Description: Polymetallic nodules in deep-sea habitats of the Pacific Ocean will be subject to commercial exploitation in the near future but the potential effects of such mining activities on benthic life are difficult to assess. Here we present results from a recent revisit onboard RV SONNE (leg SO242/2) to the site of the “DISturbance and reCOLonization experiment” (DISCOL), a large scale benthic impact study initiated in 1989 in a polymetallic nodule area in the Peru Basin (tropical south-eastern Pacific). The area was artificially disturbed by a plow harrow to simulate manganese nodule extraction. In 2015, Meiofauna samples were collected and analysed at two different spatial scales in the framework of the JPI Oceans' programme ‘Ecological Aspects of Deep-Sea Mining’ to study the response and recovery rate of benthic faunal communities. At a macroscale, meiofauna densities and community composition were compared between two stations within the DISCOL experimental area (DEA) and three undisturbed reference stations. No long-term disturbance effects could be identified, most likely because high sediment heterogeneity in the disturbed and reference sites resulted in large variation in meiofauna communities. However, additional ROV push core sampling at selected microhabitats within the disturbance tracks (white patches, ripple crests and ripple valleys) revealed significant differences at a microscale for two out of three tracks. Meiofauna abundances were significantly reduced at all sites compared to outside track control samples with the exception of ripple valleys. Lowest densities were found at the white spot habitats where disturbances in 1989 exposed deeper sediment layers and where lowest pigment and organic matter contents were found. The study demonstrates that physical disturbances as they will be associated with mining will most likely result in long-term impacts on meiofauna communities in nodule areas. However, the results also show that detailed investigations at small spatial scales may be required to discriminate disturbance effects on meiofauna communities from natural variability.

Description: Arctic coastal ecosystems are rapidly changing due to climate warming. This makes modeling their produc- tivity crucially important to better understand future changes. System primary production in these systems is highest dur- ing the pronounced spring bloom, typically dominated by di- atoms. Eventually the spring blooms terminate due to sili- con or nitrogen limitation. Bacteria can play an important role for extending bloom duration and total CO2 fixation through ammonium regeneration. Current ecosystem mod- els often simplify the effects of nutrient co-limitations on al- gal physiology and cellular ratios and simplify nutrient re- generation. These simplifications may lead to underestimations of primary production. Detailed biochemistry- and cell- based models can represent these dynamics but are difficult to tune in the environment. We performed a cultivation experiment that showed typical spring bloom dynamics, such as extended algal growth via bacterial ammonium remineralization, reduced algal growth and inhibited chlorophyll synthesis under silicate limitation, and gradually reduced nitrogen assimilation and chlorophyll synthesis under nitrogen limitation. We developed a simplified dynamic model to represent these processes. Overall, model complexity in terms of the number of parameters is comparable to the phytoplankton growth and nutrient biogeochemistry formulations in common ecosystem models used in the Arctic while improv- ing the representation of nutrient-co-limitation-related processes. Such model enhancements that now incorporate in- creased nutrient inputs and higher mineralization rates in a warmer climate will improve future predictions in this vulnerable system.

Description: Future supplies of rare minerals for global industries with high-tech products may depend on deep-sea mining. However, environmental standards for seafloor integrity and recovery from environmental impacts are missing. We revisited the only midsize deep-sea disturbance and recolonization experiment carried out in 1989 in the Peru Basin nodule field to compare habitat integrity, remineralization rates, and carbon flow with undisturbed sites. Plough tracks were still visible, indicating sites where sediment was either removed or compacted. Locally, microbial activity was reduced up to fourfold in the affected areas. Microbial cell numbers were reduced by ~50% in fresh “tracks” and by 〈30% in the old tracks. Growth estimates suggest that microbially mediated biogeochemical functions need over 50 years to return to undisturbed levels. This study contributes to developing environmental standards for deep-sea mining while addressing limits to maintaining and recovering ecological integrity during large-scale nodule mining.

Description: Investigations carried out during leg SO242/2 of RV SONNE to the DISCOL experimental area in Sep. 2015 show that the removal of the reactive surface layer by disturbances created in 1989 is still reflected in altered microbial standing stocks and activities. Based on measurements of microbial carbon assimilation rates (inorganic carbon uptake, oxygen uptake, leucine uptake) and the carbon and nitrogen content of the sediment, we estimated the time needed post-disturbance for microbial regrowth and community turnover to reach initial population sizes. According to these calculations, microbial cell numbers are expected to recover in less than a year. Surprisingly, 26 years after the disturbance, population sizes still do not reach the level found at reference sites. Also the community structure still differs at the disturbed sites. Various explanations for the lack of growth are possible: Grazing, viral lysis, removal of manganese nodules, and a lack of labile organic matter are some of the potential mechanisms which may limit microbial population growth, in spite of the relatively high carbon assimilation rates.