[ACG56-P04] Macroalgal metabolism and carbon budgets affect atmospheric CO2 uptake in a temperate Sargassum bed
Keywords:macroalgal bed, CO2 sink, metabolism, blue carbon, carbon dynamics
Macroalgal beds are considered to be one of the vegetated coastal ecosystems (i.e., blue carbon ecosystems) that act as atmospheric CO2 sinks. Macroalgal metabolisms and carbon budgets affect CO2 sequestration by macroalgal beds, but its relationships are still poorly understood. In this study, we investigated air–water CO2 exchange and budgets of dissolved inorganic carbon, total alkalinity, and dissolved organic carbon (DOC) in a temperate Sargassum bed during the productive winter. We estimated the metabolism of macroalgae and carbon budgets by using a field-bag method, a degradation experiment, and mass balance modelling over a diurnal cycle. Our results showed that macroalgal metabolism and carbon budgets affected atmospheric CO2 uptake in and around the Sargassum bed. The macroalgal metabolism formed water with low CO2 and high DOC that was then exported offshore. This export process potentially promotes CO2 uptake in and around macroalgal beds.