Review of Benthic Impact Experiments Related to Seabed Mining

Abstract

Abstract In anticipation of seabed mining, several groups over the past decade have undertaken deep-water experiments that resuspended or disturbed the surficial sediment to examine the impact on the environment. A major outcome of these experiments has been the development of mathematical modeling of the suspended sediment plume. However, fieldsampling programs have been hampered by problems encountered during execution, lack of definition in scientific program and poor location control on setting of sediment traps on deepwater moorings. The rationale of repeating the disturber-type experiments by many countries interested in deep seabed mining should be questioned. With limited resources for deep water environmental studies, the emphasis on disturber experiments is perplexing when basic biology of the potential mining sites is poorly characterized, designed experiments are poorly controlled, and mining systems/equipment have not been designed or selected. Several critical environmental issues remain in regard to deep seabed mining. Addressing these concerns should be the priority in the coming decades. Introduction Disturbance of the benthic environment by commercial deep sea mining is a critical issue identified in studies of the environmental aspects of seabed mining (1–3). Potential impacts related to the mining collector operating on the seafloor have been addressed in several field manipulative experiments by simulating the collecting system's disruption of sediment and by re-suspending sediment. In the Peru Basin, German scientists created an original experiment utilizing a large-scale disturbance and following the recovery over a period of seven year. In 1989, the sediment at the German study site was physically disturbed by plowing with a modified farm harrow a circular area, approximately 102 km, crossing the area 78 times in 4150 m depth (4). The aim was to simulate the collector tracks and focus on recolonization after a large-scale physical disturbance. The findings of these multiyear studies are presented in a forthcoming special issue of Deep-Sea Research. This paper will focus on the so-called Benthic Impact Experiments (BIE); the resuspension experiments designed to "simulate the environmental affects of sediment resuspension by deep seabed mining operations and to assess the environmental impact of sediment redeposition on the deepsea benthos" (5). Chronology In the early 1990's, the benthic impact experiments began with a joint NOAA/Russian effort (6, 7). In 1994, Metal Mining Agency of Japan (MMAJ) initiated the Japan Deep-Sea Impact Experiment, termed JET (8). Their focus was on examining the meiofauna, those organisms operationally defined as between 30 µm and 300 µm. In 1995, Interoceanmetal Joint Organization (IOM) carried out a benthic impact experiment (IOM BIE'95) within the IOM claim area in the Clarion-Clipperton Fracture Zone (9). In 1997, India (10) performed a benthic impact experiment in the central Indian Basin. Benthic Disturber A system to simulate mining collector was designed, built, tested and operated by Sound Ocean System Inc. (Redmond, Washington)(11). As Brockett and Richard (12) report the system was "designed to fluidize, lift and discharge large volumes of sediment from the seafloor and suspend them in the water column at an altitude of 5 to 10 m above sea floor".