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For centuries, sailors have encountered an intriguing phenomenon that ignites curiosity: expansive stretches of ocean that emit an ethereal glow during the night. Known as “milky seas,” these glowing patches can illuminate the surroundings enough for one to read by their light and can cover regions as vast as 100,000 square kilometers, with some displays being detectable from space.
This captivating bioluminescent occurrence, while documented by mariners throughout history, remains poorly understood by scientists due to its rarity, primarily occurring in isolated areas of the Indian Ocean, away from significant human observation. A prevailing hypothesis suggests that the luminescent effect is attributed to a microscopic bacterium named Vibrio harveyi.
To enhance predictions regarding the occurrence of milky seas, a team from Colorado State University (CSU) has established a comprehensive database that chronicles sightings spanning the last 400 years. In a recent publication in the journal Earth and Space Science, this database encompasses firsthand accounts from sailors, reports submitted to the Marine Observer Journal over an 80-year time frame, and modern satellite data. Significantly, this marks the first aggregated collection of milky sea data in three decades, revealing that such events predominantly transpire in the Arabian Sea and Southeast Asian regions. Moreover, statistical analysis indicates a correlation with climate phenomena like the Indian Ocean Dipole and the El Niño Southern Oscillation.
These climate dynamics are recognized for their influence on global weather systems, prompting scientists to explore potential links between milky seas and climate variability.
Justin Hudson, a Ph.D. student at CSU and the primary author of the study, highlighted that this database is pivotal for predicting milky sea occurrences. He emphasized the aim of deploying research vessels to these sites promptly to gather vital data on the biological and chemical factors at play, which could provide insights into how these phenomena integrate with other Earth system processes.
Hudson further noted that the areas where milky seas manifest boast substantial biological diversity and play critical roles in marine fisheries.
“Studying a phenomenon without adequate data is incredibly challenging,” Hudson remarked. “Up until now, we have only one known photograph captured at sea level, which emerged serendipitously in 2019. There’s still so much to uncover regarding the mechanisms, implications, and the ecological significance of these events.”
Understanding Milky Seas: Formation and Significance
Bioluminescence is a widespread phenomenon seen across various species, such as the iconic glow of fireflies. However, the precise mechanics behind milky seas remain elusive to researchers.
An encounter in 1985, when a research vessel came across a milky sea, provided some clues. Scientists were able to collect water samples and discovered a specific strain of luminous bacteria thriving on surface algae. This finding suggested that the bacteria could be responsible for the uniform glow. Yet, it remains a singular data point, and more extensive observations are necessary for a complete understanding. Researchers are now endeavoring to leverage sporadic satellite imagery to fill in these gaps.
Hudson posited that the consistent occurrence of milky seas in specific regions suggests a biological process linked to the activity of bacteria.
“The locations tied to this phenomenon predominantly lie around the northwest Indian Ocean, particularly near Somalia and Socotra, Yemen, where nearly 60% of recorded events have been documented,” he explained. “We also recognize that phases of the Indian monsoon influence biological activity in these regions through variations in wind and current dynamics. This indicates that milky seas could represent an underappreciated aspect of carbon and nutrient movement within the Earth system, especially as we deepen our understanding of bacteria’s critical roles in the global carbon cycle, both on land and in aquatic environments.”
Professor Steven Miller, a co-author of the paper who has been investigating milky seas at CSU, highlighted the potential the new database holds for advancing first-hand research on these phenomena.
“Milky seas embody remarkable manifestations of our biosphere, whose roles in ecological systems we have yet to fully grasp,” Miller stated. “Their existence hints at untapped connections between the ocean surface and the atmosphere, alongside the complex interplay between microscopic organisms and global environmental processes. The integration of historical seafaring accounts with contemporary satellite observations enables us to transition from folklore to measurable scientific insights.”
The study contributes to Hudson’s ongoing research within CSU’s Department of Atmospheric Science, as he prepares to finalize his thesis this summer. He expressed hope that the database could illuminate further discourse on milky seas and their ecological implications.
“The significance of milky seas to their surrounding ecosystems remains largely unknown. They may signify either a thriving marine ecosystem or signal distress; the bacteria implicated can sometimes negatively impact marine life, including fish and crustaceans,” Hudson advised. “Having this data available puts us in a better position to explore and answer critical questions about milky seas, rather than relying on chance encounters for exploration.”
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