NRL Scientists Detect 'Milky Sea' Phenomena

Since the 17th century, "milky seas" have been associated more commonlywith maritime folklore than scientific knowledge. They are mentioned inthe Jules Verne classic 20,000 Leagues Under the Sea. Until thissatellite detection was achieved by NRL researchers, the phenomena hadonly been reported in ship's logs and their descriptions were subjectto the uncertainties of human perception. Mariners have described thephenomena as giving the impression of sailing upon a field of snow orgliding over the clouds--all under the darkness of a moonless night.The glowing waters appear to extend to the horizon in all directions,and can last from several hours to several days. They are thought to becaused by enormous populations of bacterial bioluminescence, but theirephemeral nature has made it difficult to place appropriately equippedresearch craft in their locations.

Dr. Steven Miller, from NRL's Marine Meteorology Division,explained that the milky sea presented in the paper was detected by theDefense Meteorological Satellite Program (DMSP). These polar-orbitingsatellites feature the Operational Linescan System (OLS) instrument,which was designed primarily to monitor global cloudiness under bothsolar and lunar illumination. To achieve nighttime detection, the OLSuses a sensor capable of registering extremely low levels of visiblelight. This system has been used to detect terrestrial and atmosphericemission sources such as fires, lightning, and human activity (citylights, fishing boats, etc.) around the world. However, there have beenno previous reports or demonstrations of the OLS being used to detectbioluminescence.

Dr. Miller and the research team searched ship reports of milky seasightings since 1992 and compared these with archived OLS satellitedata. A British merchant vessel, the S.S. Lima, was transiting thenorthwestern Indian Ocean on the night of January 25, 1995 when itencountered the milky sea. Enhancement of OLS imagery collected roughly30 minutes after the ship's report of initial sighting revealed amassive region of low-level light emission. The glowing waters spannedan area roughly the size of Connecticut (over 15000 km^2) and lasted atleast three nights. The event took place in the northwest Indian Ocean,approximately 280 km off the Somali coast. The boundaries of thefeature matched closely with a surface ship's reported entry and exitof the brightly glowing waters.

Although such observations cannot be fully explained based on the knownfeatures of any light-emitting organism, these so-called "milky seas"are hypothesized to be manifestations of strong bioluminescenceproduced by colonies of bacteria associated with a microalgal bloom inthe surface waters. Because of the lack of scientific observations, afull explanation of milky seas has remained elusive. With the currentstate of satellite technology, and sampling limitations, remote sensingresearchers have generally thought that the detection ofbioluminescence emission from space was unlikely if not impossible.

Demonstration of their detection by low-light detectors on current andfuture satellite systems provides a possible means to targeting theseevents in the future by properly equipped research vessels. Thiscreates opportunities for new research and insight pertaining to thecause, role, and implications of these poorly understood phenomena,said Dr. Miller. Professor. J. Woodland Hastings of Harvard University,a leader in the field of bioluminescence and communicator of this paperto PNAS, called this research a "beautiful discovery."

In addition to Dr. Miller, theresearch team consisted of Dr. Steven Haddock from Monterey BayAquarium Research Institute, Dr. Christopher Elvidge from the NationalGeophysical Data Center, and Mr. Thomas Lee from NRL's MarineMeteorology Division.