Measuring alkalinity fluxes at the water-sediment interface in aquatic ecosystems of the Tunisian littoral: impact on pH and inorganic carbon storage

Abstract

In the context of climate change and rising atmospheric CO2, coastal marine sediments, rich in algae and seagrass beds, are potential blue carbon sinks and thus contribute to climate mitigation. However, ocean acidification due to CO2 fluxes has been the subject of scientific debate for over 20 years. Indeed, sediments, through the anaerobic reactions of early diagenesis, promote the production of alkalinity in pore water, which can mitigate the effects of open-water acidification. The aim of this research is to model pore water alkalinity concentrations in four different Tunisian coastal ecosystems, in order to quantify the release of benthic alkalinity and the precipitation of authigenic carbonates. The results show that these sediments are an important source of alkalinity, with fluxes ranging from 1.1 to 7.27 mmol m-2 d-1. Additionally, the elevated alkalinity can promote the precipitation of carbonates, enabling the sediments to act as a sink for inorganic carbon.