The impact of potential leakage from the sub-seabed CO2 storage site on the phosphorus transformation in marine sediments – An experimental study

Abstract

Carbon Capture and Storage (CCS) in the sub-seabed geological formations is a method of mitigation of carbon dioxide (CO2) emissions to avoid anthropogenic climate change. While CCS can be one of the most promising technologies to reduce atmospheric CO2 in the short and medium term, it raises serious concerns about the potential leakage of gas from storage sites. In the present study, the impact of acidification induced by CO2 leakage from a sub-seabed storage site on geochemical pools, and thus the mobility, of phosphorus (P) in sediment was investigated during laboratory experiments. The experiments were conducted in a hyperbaric chamber at a hydrostatic pressure of 900 kPa, which simulates pressure conditions at a potential sub-seabed CO2 storage site in the southern Baltic Sea. We performed three separate experiments in which the partial pressure of CO2 was: 352 μatm (corresponding pH = 7.7); 1815 μatm (corresponding pH = 7.0), and 9150 μatm (corresponding pH = 6.3). Under pH 7.0 and 6.3, apatite P is transformed into organic and non-apatite inorganic forms, which are less stable than CaP bonds and can be more easily released into the water column. At pH 7.7, P released during mineralization of organic matter and microbial reduction of FeP phases is bound with Ca, and the concentration of this form increases. The obtained results indicate that acidification of bottom water can reduce the efficiency of P burial in marine sediments, which contributes to an increase in P concentration in the water column and promote eutrophication especially in shallow areas.