Presenter: Steven Miller (Colorado State University)

Description:
‘Milky seas,’ a termed coined by 19^th century mariners, are a rare form of marine bioluminescence involving large swaths of ocean glowing steadily at night. Witnesses compare them to a ‘snowfield,’ extending to the horizon, with light bright enough to read by. They are thought to be caused by luminous bacteria colonizing an algal bloom, producing light upon exceeding a critical population via quorum sensing. However, accounts paint an inconsistent picture of their structure, and the environmental circumstances conducive to milky sea formation remain almost entirely unknown. This paper shows how a new low-light visible satellite sensor—the Day/Night Band (DNB)— detects milky seas in an unprecedented way. A 10-year survey of DNB imagery has uncovered 12 distinct milky sea cases within the historical hot-spots of the Arabian/Somali Sea and Maritime Continent. These glowing waters drift with the currents and persist over days to weeks. The temperature and biomass properties of milky sea water environments, including their preferred formation within doldrums—inspire a ‘natural flask’ hypothesis for milky sea incubation. We highlight an event that occurred south of Java in 2019—a massive milky sea (100,000 km²; the size of Kentucky) that persisted over several weeks. Its concurrency to another event in the Banda Sea suggests an air-sea coupled connection to the Indian Ocean Dipole, similar to hypothesized connections between milky seas and the western Indian Monsoon modes. Perhaps the most important immediate outcome is that with our newfound ability detect and track milky seas remotely, research vessels can be directed toward a milky sea in-progress to collect the in situ sampling necessary learn more about them. The capability blazes a new pathway for marine ecology and air-sea interaction research surrounding the phenomenon. With the power of new-generation satellites, we are finally poised to transition from maritime lore to scientific knowledge.