Microscale dynamics promote segregated denitrification in diatom aggregates sinking slowly in bulk oxygenated seawater

Abstract Sinking marine particles drive the biological pump that naturally sequesters carbon from atmosphere. Despite their small size, compartmentalized nature of promotes intense localized metabolic activity by bacterial colonizers. Yet mechanisms promoting onset denitrification, a metabolism arises once oxygen is limiting, remain to be established. Here we show experimentally slow sinking aggregates composed diatoms—important primary producers for global export—support active denitrification even among bulk oxygenated water typically thought exclude anaerobic metabolisms. Denitrification occurs at anoxic microsites distributed throughout particle and within microns particle’s boundary, fluorescence-reporting bacteria nitrite can released into column due segregated dissimilatory reduction nitrate nitrite. Examining intact broken diatoms as organic sources, slowly leaking cells promote more growth, allow have lower oxygen, generally support greater denitrification.