Monday, February 9, 2015

Detection of a Bioluminescent Milky Sea From Space

A milky sea is a phenomenon where the surface of the sea produces an intense uniform glow that extends to the horizon in all directions. These phenomena have been reported by mariners since the 17th century. However, due to the nature of both this phenomena and the scarcity of scientific observations, an explanation remains elusive. There was only one chance encounter between this phenomenon and a research vessel, which, in its report, expostulated that the glow could be caused by luminous bacteria (Vibrio harveyi) living with colonies of the microalga Phaeocystis. The little that is known about milky seas is based off of archived ship logs and is subject to human interpretation. Based on 235 documented cases since 1915, the "typical" milky sea (only seen at night) glows over an extensive area, is independent of wind speed, can last from several hours to several days, and may be associated with oceanographic fronts. More than 70% of reported milky seas were in the northwest Indian Ocean, most commonly during the summer southwest monsoon, with another smaller cluster (17%) in the waters near Java, Indonesia. The difficulty of collecting observations over the world's oceans makes the task of learning about the milky seas phenomenon well suited to remote sensing by satellites. The first detection of a milky sea event by satellite sensors was in the northwest Indian Ocean on January 25, 1995. Unprocessed nighttime visible imagery indicated the presence of a large, bright feature near the SS Lima, which was observed to persist over the next two nights. Digital enhancement and filtering of the imagery separates the coherent feature from the background noise. The satellite reveals the structure of this massive event, spanning an area of at least 15,400 km^2 on Jan. 25, and expanding to >17,700 km^2 the next day. The persistence of the feature over several days allowed for the examination of its spatial evolution in relation to local sea surface currents. The Navy Layered Ocean Model revealed there was a cold-core eddy centered on the northern part of the feature, partially explaining its observed counterclockwise rotation. A rare opportunity to match satellite low-light sensor observations to surface reports has resulted in the first satellite measurements of bioluminescence from a milky sea. Satellite remote sensing represents the only viable means of targeting this elusive class of marine bioluminescence.
Miller, S., Haddock, S., Elvidge, C., & Lee, T. (2005). Detection of a Bioluminescent Milky Sea From Space. Proceedings of the National Academy of Sciences, 102(40), 14181-14184. Retrieved from


  1. Now that they are able to track Milky Sea events hopefully this will allow for further study of the causes of the event.

  2. The success of the mapping of this event using satellite sensing and imagery is exciting because it means that mapping techniques such as this can be used in the future to track other oceanic events that otherwise couldn't have been tracked or researched.

  3. An otherwise extremely rare occurrence that would be incredibly hard to locate and study. But with the help of GIS we are able to see and study these satellite images to see the scale and range.