The Benthic Chamber experiment in Storfjorden (Norway) 2005 - effects of CO2 on microbes, nanobenthos and meiofauna

Abstract

Carbon capture and storage (CCS) either sub-seabed or in the ocean is considered among the options for reducing future emissions of CO2 to the atmosphere. Such storage does, however, introduce the possibility of CO2 leakage and interaction with marine fauna. It is therefore important to obtain knowledge on possible effects of CO2 that is introduced to the sea floor. Results from experiments on environmental effects of enhanced concentrations of CO2 at the sediment/water interface are presented. The key part of the project was the Japanese Benthic Chamber system (BC) developed to perform experiments with CO2 in sedimentary environments in situ. The BC is equipped with chambers which enclose sections of the sea floor. Two similar experiments were carried out at 400 m depth in Storfjorden, Norway in September, 2005. The pCO2 exposures in the water above the sediment in the chambers were programmed to maintain levels of approximately 5,000 µatm (pH=7.0) and 20,000 µatm (pH=6.3) respectively in two experimental chambers. The pCO2 in the third control chamber was 500 µatm (pH=7.8). This report gives a description of the experiment and the results from measured physical and chemical parameters (pH, NO3, NH4, SiO2 and oxygen) in the water overlying the sediment in the experimental chambers and biological responses (meiobenthos, nanobenthos, bacteria, Archaea, bacterial DNA and ATP, methane production, sulphate reduction) in the chamber sediments. The results from the different research groups and methods clearly show effects of elevated CO2 concentrations on biological processes such as reduced bacterial density and increased nanobenthos densities. Methane formation and sulphate reduction was favoured by the condition in the 5,000 µatm chamber