Coastal marine megaripple fields are metabolic hotspots with highly dynamic oxygen exchange

Megaripples are current-generated seafloor bedforms of well-sorted sand or gravel and wavelengths over 1 m. In this aquatic eddy covariance study, we measured large rates of benthic primary production and respiration for a shallow-water sandy megaripple field exposed to strong tidally driven currents and intense sunlight. Current and light were the main short-term drivers of a highly dynamic oxygen exchange. Daytime oxygen release as high as 300 mmol m⁻² d⁻¹ and nighttime oxygen uptake up to −100 mmol m⁻² d⁻¹ were likely sustained by current-driven transport of oxygen, nutrients, and organic matter (fuel) into and out of the sand and superimposed by rapid internal cycling. Seasonal differences in temperature (45%) and light (69%) between April and September were the main long-term drivers of substantially greater rates of gross primary production and respiration in September. The megaripples functioned as an intense metabolic hotspot with carbon cycling rates larger than those of most near-shore sediments.