Description: Deep-seabed polymetallic nodule mining can have multiple adverse effects on benthic communities, such as permanent loss of habitat by removal of nodules and habitat modification of sediments. One tool to manage biodiversity risks is the mitigation hierarchy, including avoidance, minimization of impacts, rehabilitation and/or restoration, and offset. We initiated long-term restoration experiments at sites in polymetallic nodule exploration contract areas in the Clarion-Clipperton Zone that were (i) cleared of nodules by a preprototype mining vehicle, (ii) disturbed by dredge or sledge, (iii) undisturbed, and (iv) naturally devoid of nodules. To accommodate for habitat loss, we deployed 〉2000 artificial ceramic nodules to study the possible effect of substrate provision on the recovery of biota and its impact on sediment biogeochemistry. Seventy-five nodules were recovered after eight weeks and had not been colonized by any sessile epifauna. All other nodules will remain on the seafloor for several years before recovery. Furthermore, to account for habitat modification of the top sediment layer, sediment in an epibenthic sledge track was loosened by a metal rake to test the feasibility of sediment decompaction to facilitate soft-sediment recovery. Analyses of granulometry and nutrients one month after sediment decompaction revealed that sand fractions are proportionally lower within the decompacted samples, whereas total organic carbon values are higher. Considering the slow natural recovery rates of deep-sea communities, these experiments represent the beginning of a ~30-year study during which we expect to gain insights into the nature and timing of the development of hard-substrate communities and the influence of nodules on the recovery of disturbed sediment communities. Results will help us understand adverse long-term effects of nodule removal, providing an evidence base for setting criteria for the definition of “serious harm” to the environment. Furthermore, accompanying research is needed to define a robust ecosystem baseline in order to effectively identify restoration success.

Description: The crises of climate change and biodiversity loss are interlinked and must be addressed jointly. A proposed solution for reducing reliance on fossil fuels, and thus mitigating climate change, is the transition from conventional combustion-engine to electric vehicles. This transition currently requires additional mineral resources, such as nickel and cobalt used in car batteries, presently obtained from land-based mines. Most options to meet this demand are associated with some biodiversity loss. One proposal is to mine the deep seabed, a vast, relatively pristine and mostly unexplored region of our planet. Few comparisons of environmental impacts of solely expanding land-based mining versus extending mining to the deep seabed for the additional resources exist and for biodiversity only qualitative. Here, we present a framework that facilitates a holistic comparison of relative ecosystem impacts by mining, using empirical data from relevant environmental metrics. This framework (Environmental Impact Wheel) includes a suite of physicochemical and biological components, rather than a few selected metrics, surrogates, or proxies. It is modified from the “recovery wheel” presented in the International Standards for the Practice of Ecological Restoration to address impacts rather than recovery. The wheel includes six attributes (physical condition, community composition, structural diversity, ecosystem function, external exchanges and absence of threats). Each has 3–5 sub attributes, in turn measured with several indicators. The framework includes five steps: (1) identifying geographic scope; (2) identifying relevant spatiotemporal scales; (3) selecting relevant indicators for each sub-attribute; (4) aggregating changes in indicators to scores; and (5) generating Environmental Impact Wheels for targeted comparisons. To move forward comparisons of land-based with deep seabed mining, thresholds of the indicators that reflect the range in severity of environmental impacts are needed. Indicators should be based on clearly articulated environmental goals, with objectives and targets that are specific, measurable, achievable, relevant, and time bound.

Description: Data for estimating heat flow in the western Black Sea are provided, based on measurements made during Expedition MSM34 (R/V Maria S. Merian). Data are located in the Bulgarian and Romanian Sector of the Black Sea in water depths ranging from 420 to 1500 m. Data were always collected with the GEOMAR-owned 6 m long heat-probe tool, consisting of 22 Thermistors (at 26 cm spacing) along a sensor-string, a reference pressure gauge and calibration thermometer (T100 sensor). Raw data are required to be calibrated relative to the T100 sensor. Calibration data for both expeditions are provided in form of temperature offsets for each thermistor. Data provided include per station all original (raw) data for each deployment (temperature as function of time, pressure/Depth) for each thermistor, as well as initial results after separating each individual measurement sequence into penetration files (pen-files) where the temperature calibration has been applied. Results report an average thermal Gradient, heat-flux and thermal conductivity over the total penetraiton Depth of 6m. Detailed information (temperature and thermal conductivity as function of depth at each location) is given in graphical form as well as ascii data per individual penetration.

Description: During RV SONNE cruise SO242/2 (September 2015) to the DISCOL site in the Peru Basin (SE Pacific), pyrosome carcasses were collected at the seafloor. Aboard, these carcasses were stored frozen and in the lab on land, they were freeze-dried and ground to fine powder. Their carbon and nitrogen content, δ13C and δ15N were measured on an elemental analyzer coupled with a isotope ratio mass spectrometer (EA-c-IRMS).

Description: During RV SONNE cruise SO242/2 (September 2015) to the DISCOL site in the Peru Basin (SE Pacific), pyrosome carcasses were collected at the seafloor. Aboard, these carcasses were stored frozen and in the lab on land, they were freeze-dried and ground to fine powder. Total fatty acid in pyrosome tissue were extracted following the Bligh and Dyer method and their isotopic compositions and concentrations were measured on a gas chromatograph coupled with an isotopic ratio mass spectrometer (EA-c-IRMS).

Description: During RV SONNE cruise SO242/2 (September 2015) to the DISCOL site in the Peru Basin (SE Pacific) push cores of sediment were taken in the abyssal plains with ROV Kiel 6000 (GEOMAR). The sediment cores were sliced in 0-2 and 2-5 cm intervals and stored frozen until further processing ashore. In the lab on land, sediment samples were freeze-dried, ground to fine powder, phospholipid-derived fatty acids (PLFAs) in the sediment were extracted following the Bligh and Dyer method and they were measured on a gas chromatograph coupled with an isotopic ratio mass spectrometer (EA-c-IRMS).

Description: During RV SONNE cruise SO242/2 (September 2015) to the DISCOL site in the Peru Basin (SE Pacific), pyrosome carcasses were at the seafloor. Aboard, these carcasses were stored frozen and in the lab on land, they were freeze-dried and ground to fine powder. Phospholipid-derived fatty acids (PLFAs) in pyrosome tissue were extracted following the Bligh and Dyer method and their isotopic compositions and concentrations were measured on a gas chromatograph coupled with an isotopic ratio mass spectrometer (EA-c-IRMS).