Monitoring the sedimentary carbon in an artificially disturbed deep-sea sedimentary environment

Abstract

An area of 0.6 km(2) in the manganese nodule field of the Central Indian Basin was physically disturbed and sediments discharged in the near bottom waters to simulate seabed mining and study its impact on benthic ecosystem. An estimated 2 to 3 tonnes of sedimentary organic carbon (C(org)) was resuspended into the water column during a 9-day experiment. The majority of the sediment cores from within the disturbed area and areas towards the south showed a ~30% increase in C(org) content as well as an increase in carbon burial rates after disturbance, though with a reduction in carbon/phosphorus ratios. High specific surface area (SSA~25 m(2) g(-1)) and low C(org)/SSA ratios (mostly <0.5) are typical of deep-sea sediments. The increased C(org) values were probably due to the organic matter from dead biota and the migration and redeposition of fine-grained, organic-rich particles. Spatial distribution patterns of C(org) contents of cores taken before and after disturbance were used to infer the direction of plume migration and re-sedimentation. A positive relationship was observed between total and labile C(org) and macrobenthos density and total bacterial numbers prior to disturbance, whereas a negative relationship was seen after disturbance owing to drastic reduction in the density of macrofauna and bacteria. Overall decrease in labile organic matter, benthic biota and redistribution of organic matter suggest that the commercial mining of manganese nodules may have a significant immediate negative effect on the benthic ecosystem inducing changes in benthic community structure.

An Overview of Seabed Mining Including the Current State of Development, Environmental Impacts, and Knowledge Gaps

“…Reasons for degradation of the marine environment include drifting sediment plumes and low frequency noise propagation, which could alter species distributions, ecosystem functioning or even seemingly unconnected processes such as carbon cycling (Nath et al, 2012;Le et al, 2017).…”

Evaluation of Resuspended Sediments to Sinking Particles by Benthic Disturbance in the Clarion-Clipperton Nodule Fields

“…The mining of manganese nodules on the seafloor produces sediment plumes and disperses resuspended sediment particles into the water column, resulting in a number of potential impacts on the marine environment and ecosystem (e.g., Jumars 1981;Sharma et al 2001;Khripounoff et al 2006;Nath et al 2012). One of the direct effects is an increased contribution to the sinking particle flux from resuspended sediment during the disturbance period.…”

“…Mining operations discharge resuspended sediment into the water column that inevitably disturbs the marine environment (Khripounoff et al 2006;Nath et al 2012). The impact on the marine ecosystem is thought to depend mainly on the scale of disturbance and the amount of resuspended sediment (Hyun et al 1998;Sharma et al 2001).…”

Distribution and Diagenesis of Phosphorus in the Deep‐Sea Sediments of the Central Indian Basin

“…The CIB is a large abyssal basin, which is rich in ferromanganese nodules and bounded by ridges on three sides and is open to sediment input from the Bay of Bengal in the north‐east (see Nath et al, ). The past studies on the CIB sediments have reported total P (P total ) content (Banakar et al, ; Pattan & Jauhari, ), related sedimentary P to explain the calcium‐bearing phases (Nath et al, ) or have used organic C to P relation to assess the recovery of benthic ecosystem after a disturbance experiment (Nath et al, ). However, the processes that control P diagenesis and quantitative estimates of diffusive fluxes and P fractionation in chemically separable phases are not known.…”