From sailors to satellites: investigating the maritime mystery of bioluminescent milky seas

Abstract

Bioluminescence, the ability of living organisms to produce and emit light, has been a topic of human imagination and scientific study for millennia. Bioluminescence is observed in a myriad of forms in the ocean, among these bioluminescent displays milky seas stand out as perhaps one of the rarest, most poorly understood, and most awe-inspiring forms of bioluminescence. Milky seas are delineated from other more common forms of bioluminescence by their steady, non-flashing, eponymous white/green/gray glow which can cover 100,000 km2 of the nocturnal ocean surface for possibly months at a time. Poetic descriptions of milky seas by eyewitnesses have compared this phenomenon to an episode of the 'Twilight Zone', the biblical apocalypse, and an ocean haunted by spirts. Recent advances in spaceborne low-light imager technology, allowing milky seas to be identified remotely via satellite imagery, have greatly expanded our ability to study this phenomenon. Despite these technological advances and a modest compendium of published scientific literature on milky seas dating back to the 1700s, scientific understanding on milky seas has been historically limited by their remote, rare, and ephemeral nature. In addition, scientific research on milky seas has suffered the repeated loss of historical datasets. This dissertation presents a collection of research that seeks to understand the global/macroscale properties (e.g. distribution and timing) of milky seas as well as more local and intrinsic properties that inform on their predictability. Combining centuries of eyewitness accounts with recent satellite imagery, we reconstruct and build upon lost databases of milky sea observations. Leveraging this new and expanded database, we begin to address questions about milky sea occurrence, structure, and connection to the greater earth system. The scientific analysis enabled by this database and the plethora of modern atmospheric and oceanic datasets allows new connections between milky seas, the South Asian and Indo-Australian monsoons, the Indian Ocean Dipole, and the El Niño Southern Oscillation to be drawn. These connections, which serve as sources of predictability, guided this research toward the first known prediction of a milky sea event, and offer the potential for proactive in-situ sampling of a milky sea event which is necessary to fully answer questions pertaining to their composition and formation mechanisms. Furthermore, case study analysis of milky sea events near Java, Indonesia reveals insights into the physical processes that form, sustain, and eventually annihilate milky sea events. By way of this case study analysis, we test the natural flask hypothesis for milky seas, which postulates a physical mechanism for milky sea environments. Analysis of scatterometry data reveals the potential for coincident biological signals to be correlated with previously identified milky sea events, expanding the tools available to study and track the phenomenon from space across the lunar cycle and potentially overcome the limitations of current low-light visible observations.