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

Abstract

Abstract. High-resolution optical and hydro-acoustic sea floor data acquired in 2015 enabled the reconstruction and exact localization of disturbance tracks of a past deep-sea recolonization experiment (DISCOL) that was conducted in 1989 in the Peru Basin during a German environmental impact study associated with manganese-nodule mining. Based on this information, the disturbance level of the experiment regarding the direct plough impact and distribution and redeposition of sediment from the evolving sediment plume was assessed qualitatively. The compilation of all available optical and acoustic data sets available from the DISCOL Experimental Area (DEA) and the derived accurate positions of the different plough marks facilitate the analysis of the sedimentary evolution over the last 26 years for a sub-set of the 78 disturbance tracks. The results highlight the remarkable difference between natural sedimentation in the deep sea and sedimentation of a resettled sediment plume; most of the blanketing of the plough tracks happened through the resettling of plume sediment from plough tracks created later. Generally sediment plumes are seen as one of the important impacts associated with potential Mn-nodule mining. For enabling a better evaluation and interpretation of particularly geochemical and microbiological data, a relative age sequence of single plough marks and groups of them was derived and is presented here. This is important as the thickness of resettled sediment differs distinctly between plough marks created earlier and later. Problems in data processing became eminent for data from the late 1980s, at a time when GPS was just invented and underwater navigation was in an infant stage. However, even today the uncertainties of underwater navigation need to be considered if a variety of acoustical and optical sensors with different resolution should be merged to correlate accurately with the absolute geographic position. In this study, the ship-based bathymetric map was used as the absolute geographic reference layer and a workflow was applied for geo-referencing all the other data sets of the DISCOL Experimental Area until the end of 2015. New high-resolution field data were mainly acquired with sensors attached to GEOMAR's AUV Abyss and the 0.5∘ × 1∘ EM122 multibeam system of RV Sonne during cruise SO242-1. Legacy data from the 1980s and 1990s first needed to be found and compiled before they could be digitized and properly geo-referenced for our joined analyses.

Importance of Spatial Autocorrelation in Machine Learning Modeling of Polymetallic Nodules, Model Uncertainty and Transferability at Local Scale

“…They have an ellipsoid shape, with their long axes oriented downslope. Their depth varies between 2-5 m with remarkable flat and horizontal seafloors [67]. This downslope direction has been observed in other low reflectivity PMN-free patches in Peru Basin, connected with downslope sediment transport [68].…”

“…In this northern part, lies the "DISturbance and reCOLonization" (DISCOL) experimental area (DEA). Inside the DEA (Figure 1), disturbance experiments were conducted to assess the environmental impact produced by a plough harrow [66,67]. The DEA is spatially heterogeneous regarding the seafloor morphology, geochemical properties, and PMN distribution, with many authors highlighting the need for further research [62][63][64]68,69].…”

“…The DEA itself has low relief, gentle slopes (<3 • ), longitudinal abyssal furrows, and areas with low reflectivity backscatter values and no PMN, hereafter called black patches (Figure 1). The sediments are layered clayey silts and silty clays, with foraminiferous residues and shell fragments [67,70].…”

Copper-binding ligands in deep-sea pore waters of the Pacific Ocean and potential impacts of polymetallic nodule mining on the copper cycle

“…The plow track samples had the labile organic-rich, reactive top-layer removed, mixed, or turned around with the associated plume blanketing the surface sediments 18 , 35 , 40 , 42 , 43 . The plow tracks in the DEA are not homogenous 44 and show various disturbance features previously classified as microhabitats 18 . For the study presented here we sampled sediment cores in a “valley” – a small furrow within the plow tracks – and a “white patch” – a spot where the sediment has likely been turned upside down and the lighter colored, deeper sediment has been exposed at the surface.…”

Scientific Challenges and Present Capabilities in Underwater Robotic Vehicle Design and Navigation for Oceanographic Exploration Under-Ice

“…Last but not least, high-resolution maps are essential for ecosystem research and as basis for assessing the ecological status of seafloor habitats, and for establishing marine protected areas. New technologies are available to combine mapping and video surveys as an efficient way of creating ecological knowledge of baselines and of disturbances [83,84].…”