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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-348
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-348
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 16 Oct 2019

Submitted as: research article | 16 Oct 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Scars in the Abyss: Reconstructing sequence, location and temporal change of the 78 plough tracks of the 1989 DISCOL deep sea disturbance experiment in the Peru Basin

Florian Gausepohl1,2, Anne Hennke1, Timm Schoening1, Kevin Köser1, and Jens Greinert1,2 Florian Gausepohl et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
  • 2Christian-Albrechts-University Kiel, Kiel, Germany

Abstract. High-resolution optical and hydroacoustic seafloor data acquired in 2015 enabled the reconstruction of disturbance tracks of a past Benthic Impact Experiment that was conducted in 1989 in the Peru Basin in the course of former German environmental impact studies associated with manganese nodule mining. Based on this information, the disturbance level of the experiment regarding the plough impact and distribution and re-deposition of sediment from the evolving sediment plume was assessed qualitatively. Through this, the evolution over the 26 years of a number of the total 78 disturbance tracks could be analyzed which highlights the considerable difference between natural sedimentation in the deep-sea and sedimentation of a resettled sediment plume. Such plumes are seen as one of the most concerning impact associated with potential Mn-nodule mining.

Problems in data processing became eminent while dealing with old data from the late 80s, at a time when GPS was just invented and underwater navigation was in an infant stage. However, even today the uncertainties of underwater navigation and the use of a variety of acoustical and optical sensors at different resolutions require detailed post-processing in terms of absolute geographic positioning to improve the overall accuracy of the data. In this study, a ship-based bathymetric map of the survey area was used as absolute geographic reference and a workflow was applied successfully resulting in the most accurate geo-referenced dataset of the DISCOL Experimental Area to date. The new field data were acquired with sensors attached to GEOMARs AUV Abyss and the 0.5 × 1° EM122 multibeam system of RV SONNE during cruise SO242 -1 while the old data first needed to be found and compiled before they could be digitized and properly georeferenced for the presented joined analyses.

Florian Gausepohl et al.
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Florian Gausepohl et al.
Data sets

Geo-referenced acoustic and optical data sets from the DISCOL area in the Peru-basin acquired during RV SONNE cruise SO242/1 F. Gausepohl, A. Hennke, T. Schoening, K. Köser, and J. Greinert https://doi.pangaea.de/10.1594/PANGAEA.905616

Kongsberg EM122-acquired bathymetric grid from working area of SONNE cruise SO242/1 at the DISCOL area, Peru-basin. A. Hennke and J. Greinert https://doi.pangaea.de/10.1594/PANGAEA.905579

Merged and geo-referenced bathymetric raster from AUV dives during SONNE cruise SO242/1 A. Hennke, J. Greinert, and A. Steinführer https://doi.pangaea.de/10.1594/PANGAEA.905580

Merged and geo-referenced Side Scan Sonar map from AUV dives during SONNE cruise SO242/1 F. Gausepohl, A. Hennke, A. Steinführer, and J. Greinert https://doi.pangaea.de/10.1594/PANGAEA.905617

Geo-referenced photo mosaics from AUV dives during SONNE cruise SO242/1 T. Schoening, K. Köser, F. Gausepohl, A. Hennke, and J. Greinert https://doi.pangaea.de/10.1594/PANGAEA.905581

Florian Gausepohl et al.
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Short summary
In the course of former German environmental impact studies associated with manganese nodule mining, the DISCOL experiment was conducted in 1989 in the Peru basin. The disturbance tracks created by a plough harrow that was toughed through the area are still apparent and could be located by high resolution mapping techniques. The analysis presented in this study reveals the age sequence and the temporal change of the tracks which facilitates more detailed sample interpretations within the area.
In the course of former German environmental impact studies associated with manganese nodule...
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