The Quest for Bioluminescent 'Milky Seas'—What the Smallest Organisms on Earth Have to Tell Us About the Biggest Questions in Earth System Science

‘Milky seas’ are an uncommon and mysterious form of bioluminescence involving massive swaths of steadily glowing ocean. Across the centuries, mariner encounters paint a consistent picture of milky seas appearing as snowfields under dark, starry skies, with their light extending to the horizon and brightening the limb like distant aurorae. Some recount the surreal feeling of their vessels hovering or riding an unseen swell above upon an impossibly flat plain. The phenomenon is thought to be caused by luminous bacteria, emitting light upon achieving critical populations via a communicative process called quorum sensing. However, the environmental circumstances responsible for milky sea formation, structure, composition, and exact reasons for occurring remain unclear--making them a modern-day science mystery. Their inherent remote, transient, and elusive nature make the space platform, and in particular Earth-viewing satellites equipped with low-light sensors, our best hope for learning more about milky seas and their role in nature.

This presentation details how a new-generation of low-light visible satellite sensors—the Day/Night Band (DNB) on NOAA's Visible Infrared Imaging Radiometer Suite (VIIRS)—is able to detect and quantify milky seas for the first time. Nightly DNB imagery sequences reveal contiguous swaths of luminous waters drifting with the currents and persisting for days up to weeks on end in the historically-reported milky sea hot-zones of the Northwest Indian Ocean and the Maritime Continent. Characteristics of the satellite-retrieved sea surface temperature, oceanic biomass, and analyses of surface current dynamics in milky sea environments have inspired a ‘Natural Flask’ hypothesis, wherein natural processes serve to isolate and incubate a uniquely cultured body of water. These satellite observations have also opened the possibility of deploying to an active milky sea for in situ sampling.

We highlight a milky sea event spotted in mid-2019—a massive glowing sea spanning over 100,000 km² (the same size as Iceland) that persisted in a region south of Java for at least 40 days. The case was later confirmed by a yacht crew, yielding the first known surface-based photos of a milky sea. We explore possible connections to the Indian Ocean Dipole and the Indian Monsoonal modes, and consider the air-sea-biosphere interactions at the forefront of Earth System science. Understanding the nuances of milky seas can shed light how primary production may respond to a changing climate, including extreme behaviors of the microbial carbon pump response, and how coupled-system processes communicate and indeed connect across scales from microscopic to global. Arriving at solutions to this scientific mystery will require breaking down the traditional silos of atmospheric science, oceanography, and marine biology / microbial ecology.