Exploring the occurrence of and explanations for nighttime spikes in dissolved oxygen across coral reef environments

Primary production due to photosynthesis results in daytime oxygen production across marine and freshwater ecosystems. However, a prevalent, globally-occurring nighttime spike in dissolved oxygen (DO) challenges our traditional assumption that oxygen production is limited to daylight hours, particularly in tropical coral reefs. When considered in the context of ecosystem oxygen budget estimates, these nocturnal spikes in DO could account for up to 24 percent of the daytime oxygen production. Here we show, 1) the widespread nature of this phenomenon, 2) the reproducibility across tropical marine ecosystems, 3) the lack of a consistent abiotic mechanism across all datasets we examined, and 4) the observation of nighttime DO spikes in vitro from incubations of coral reef benthic samples. Our study suggests that in addition to physical forcing, biological processes may be responsible for the production of oxygen at night, a finding that demands additional research.