DISCOL – Revisited (SO242/1 & SO242/2)
In the framework of the JPI Oceans Pilot Action “Ecological Aspects of Deep-Sea Mining” two consecutive research cruises were conducted to the DISCOL area to investigate the condition of the ecosystem 26 years after the initial impact created in 1989. With that, the DISCOL area represents the longest study of a man-made disturbance in a deep-sea environment worldwide.
Thereby, cruise SO242 was divided into two legs – SO242/1 (28 July 2015 – 25 August 2015) and SO242/2 (28 August 2015 – 1 October 2015), each of which had different objectives and used different gear to re-investigate the ecosystem within the DISCOL area.
The main objective of the first leg was to re-map – both visually and acoustically – and to re-sample the seafloor (inside and outside the plough marks) and the water column for biological, geochemical and oceanographic studies using latest technology to achieve sampling and mapping in as much detail as possible. The most important objective of the seafloor mapping was to completely map the original DEA area with AUV‐based multibeam, sidescan and photo mosaicking in high resolution to ensure detailed insight into the current state of the environment and to acquire well georeferenced data enabling comparisons to data acquired before. The exact locations of the old plough tracks from the initial disturbance in 1989 were of particular interest. Sidescan and multibeam data allowed the AUV to navigate between 7 and 3.5m altitude for subsequent photo surveys with the objective of determining the changes in macro‐fauna abundance and plough mark recolonization. Knowing the exact location of plough marks and the impact they still have was a precondition to be able to plan biological and geochemical sampling during SO242/1 and SO242/2 in the best possible manner. Biological samples with video‐guided multicorer, box corer, epibenthic sledge and amphipod‐traps were taken to investigate the ecosystem recovery compared to the last study in 1996. In addition to taxonomic studies and abundance measurements, the biological samples will also be investigated using state‐of‐the‐art genetic fingerprinting technologies. The distribution of macro‐fauna was also investigated during visual OFOS‐based stations. Geochemical samples from gravity and multi corer deployments aimed at learning more about the geochemical conditions (in particular oxygen penetration depth) inside and outside the plough marks and ‘plume’‐covered areas and at study changes in comparison to previous analyses from 1996. Oceanographic studies involving landerbased CTD, ADCP and thermistor mooring measurements aimed at better characterizing the physical environment of the deep sea and in particular at deriving data that could be used for a small‐scale disturbance experiment using the epi benthic sled as plume‐generating tool (Greinert, J. ed., 2015).
Leg 242/2 extended the investigations started during leg 242/1 with a focus on biogeochemical and biological sampling and observations, including comparative studies of the composition of benthic communities (all size classes) as well as of ecosystem functions (remineralization rates, transfer of matter and energy in food webs, ecotoxicology). In addition, observations were continued of the physicochemical characteristics of the DEA, including the overlying benthic boundary layer. The nodule fields surrounding the DEA were used as references for undisturbed areas. A large proportion of the work was based on autonomous instruments and sensor modules that were deployed by means of ROV and lander systems. In addition, ROV-manipulated and telemetry guided instruments such as the Ocean Floor Observatory System were used for targeted sampling and surveys. Food-web experiments including some small-scale disturbances were carried out and sampled directly at the seafloor by the ROV (Boetius, A. ed., 2015).
Boetius, A., ed. (2015) RV SONNE Fahrtbericht / Cruise Report SO242-2: JPI OCEANS Ecological Aspects of Deep-Sea Mining, DISCOL Revisited, Guayaquil - Guayaquil (Equador), 28.08.-01.10.2015 . GEOMAR Report, N.Ser. 027 . Helmholtz-Zentrum für Ozeanforschung, Kiel, 552 pp. DOI 10.3289/GEOMAR_REP_NS_27_2015.
Greinert, J., ed. (2015) RV SONNE Fahrtbericht / Cruise Report SO242-1: JPI OCEANS Ecological Aspects of Deep-Sea Mining, DISCOL Revisited, Guayaquil - Guayaquil (Equador), 28.07.-25.08.2015 . GEOMAR Report, N.Ser. 026 . Helmholtz-Zentrum für Ozeanforschung, Kiel, 290 pp. DOI 10.3289/GEOMAR_REP_NS_26_2015.