Earthsky Interviews
Private: Earth’s ‘milky seas’ are visible from space
06-09-2006 - Biodiversity
This one was off the coast of Somalia, in the Indian Ocean. It was about the size of the state of Connecticut.
Steve Miller: _Milky seas are a word that comes from the annals of maritime folklore, where basically layman on non-scientific vessels have witnessed these fantastic displays of glowing ocean waters at night._
That’s Steve Miller, a satellite meteorologist with the Naval Research Laboratory in Monterey, California. He said scientists think it’s possible that bioluminescent bacteria cause the milky sea phenomenon.
Steve Miller: _My co-author, Steve Haddock, and I actually grew a culture of luminous bacteria. And the appearance of the bacteria when it’s fully glowing is somewhat similar to your glow-in-the-dark silly putty. It doesn’t look too, too bright to the eye. But then when you put that against a very, very dark background, like the sky, it does look incredibly bright. And what we believe is going on is that the bacteria has reached a sufficient concentration to begin glowing. And the reason for that glow is still one of those items of debate._
Thanks today to “NASA”:http://www.nasa.gov.
Excellent “website about milky seas”:http://www.lifesci.ucsb.edu/~biolum/organism/milkysea.html run in part by Steve Miller.
Dr. Miller added some comments to this story:
1) Our calculations of the number of bacteria participating in the 1995 milky sea: 40 billion-trillion, based on the total measured light per unit area, the total area (15,400 km^2 – on par with Connecticut as mentioned in the paper!) and the estimated per-cell light emission, is on par with the total number of such prokaryotic cells estimated to inhabit the top 200m of all the oceans of the world. Put in another way, if you could somehow stack the bacteria on top of each other you could build a “tower” that was over 300 times higher than the width of our solar system. It’s consistent with what it would take to achieve the autoinduction for bacteria to glow.
2) The satellite sensor used in this study, the “Operational Linescan System (OLS)”:http://www.inquinamentoluminoso.it/dmsp/dmsp.html, which flies aboard the “Defense Meteorological Satellite Program”:http://www.ngdc.noaa.gov/dmsp/index.html satellite constellation, has a very unique capability to detect extremely low light levels. Up to 100 million times fainter than sunlight and a million times more sensitive than almost every other “visible light” satellite sensor. This enables the OLS to detect things at night like moonlight reflection off clouds and snow cover, city lights, fires, lava flows, lightning flashes, and the aurora. Until recently, we thought bioluminescence was not possible (due to the small spatial scale and duration of most events like we discussed), but this did not consider the widespread and persistence of milky seas!
3) Just wanted to emphasize that this work presents the first image of a milky sea, corroborated precisely by surface observers. Besides confirming irrefutably that these are not local optical illusions, the imagery reveals for the first time the full scale and structure of such an event. Perhaps most importantly, it gives scientists a newfound hope that satellite remote sensing can be used to target these elusive events as they occur and finally settle the longstanding debates concerning how and why they form.
4) The “white water” of a milky sea may very well be composed of blue/green light (the emission spectrum of most strains of luminous bacteria). At low light emission levels, our eyes default to the rod cells of the retina which do not have color discrimination capability like the cone cells do. Since on a moonless night far removed from artificial light emissions there won’t be much natural light other than stars, the milky sea will still appear to have enormous contrast against the surroundings even if the absolute light emission isn’t high enough to trigger our cone cell response (to discern color). Having said this, it’s also possible that there could be a collection of organisms, some emitting blue/green, others emitting yellow, that in concert would produce a white appearance even at cone-cell-sensitive light levels. We need more in situ observations to answer these questions!
5) Sailors have reported a loss of depth perception during milky seas. This makes sense, because all parts of the water surface are emitting light, eliminating shadows between swells as might be observed during moonlight conditions. As such, the swell can be “felt” (i.e., the ship moves up and down) even though the water appears flat and stationary.
6) I didn’t feel that I provided a very good statement on the possible implications of an improved knowledge about milky seas. These are truly extraordinary events. If they are indeed produced by luminous bacteria like we think, then we are talking about an unprecedented display of the marine biosphere. By its surreal nature, the topic seems to have transcended science and truly captured the imagination of a far wider audience than the marine ecology community.
Some literature references made to milky seas (there are others out there): 1) H. Melville’s “Moby Dick” 2) J. Verne’s “20,000 Leagues Under the Seas” 3) Darwin: Voyage of the Beagle (most likely a not a true milky sea, but rather a widespread dinoflagellate flashing waters event, since he cites the light coming off wind-whipped whitecaps as opposed to the steady, uniform glow we associate with milky seas).
“Scientific paper on milky seas”:http://www.lifesci.ucsb.edu/~haddock/abstracts/miller-milkyseas.pdf by Steve Miller and his colleagues for the National Academy of Sciences.
*Our thanks to:*
Steve Miller
Satellite Meteorologist
Naval Research Laboratory
Monterey, California