Microbial responses to ocean alkalinity enhancement in seasonally hypoxic coastal sediments.

Background: Enhanced benthic weathering (EBW) is a promising marine carbon dioxide removal (mCDR) strategy, where alkaline minerals are added to the seafloor. Upon weathering, these artificially deposited minerals release alkalinity to the water column, which ultimately leads to CO Methods: To investigate the effects of EBW, sediment core incubations with added alkalizing minerals were carried out and shifts in bacterial communities identified and linked to sedimentary properties. Surface sediments with supernatant water from a seasonally hypoxic basin in the Baltic Sea off the eastern coast of northern Germany were collected and either calcite (limestone) or silicate (dunite) added and kept under oxic (avg. 263 ± 34 μM O Results: Bacterial surface sediment communities responded to the different oxygen availabilities in the overlying bottom waters independent of the mineral addition as reflected in cluster formation via Principal Coordinates Analysis (PCoA). Although, by contrast, mineral addition induced less pronounced changes, the relative abundances of several rare taxa changed significantly, such as chemolithoautotrophs associated with the sulfur and nitrogen cycles. Conclusion: Our findings provide important insights into the response of microbial communities to EBW, but also highlight the necessity of field-based studies to accurately assess the effects of EBW on coastal ecosystems.