On 16 July 2015, off the coast of Brittany, the maxi trimaran Spindrift 2 was cruising in a light breeze. The moon lit up the surface of the sea and in the wake of the multihull, sparkling glitter. The water seemed to be adorned with thousands of fluorescent colors, similar to northern lights. A delightful scene for the fourteen sailors on board.

This surprising but natural phenomenon is not an underwater firework display. From space, NASA has able to detect and photograph these green, blue and orange events. But what exactly is this spectacle given by Mother Nature?

©Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC

Thanks to phytoplankton, the ocean absorbs CO2 and provides us with the oxygen we breathe. Phytoplankton, or algae, are also the first link in the food chain: A high density of plankton means more fish, mollusks, and more marine mammals which feed on them, increasing biodiversity. During springtime, blooming phytoplankton occurs and results in these magnificent colors patterns in the ocean.

The algae bloom: a seasonal phenomenon

It is actually high-density levels of phytoplankton cells in the ocean that produces these effects. This phenomenon only occurs seasonally, because it requires the conjunction of several conditions: the water must be rich in nutrients and sunlight must be able to penetrate up to a few meters deep for photosynthesis to occur. The water must also have a sufficiently high oxygen level for this chemical process to start and be visible. Thus, algae blooms are only visible when the cold coastal currents that run along the continents bring to the surface nutrient laden waters (upwelling), as in northern Brittany, for example.

©USGS/NASA/Landsat 7 

A little but not too much…

While algae bloom is generally a sign of a healthy ocean, eutrophication (accumulation of nutrients – nitrate, phosphate, silicate, and calcium) in certain coastal areas can lead to an excess of algae blooms, some of which are toxic. This phytoplankton surplus can result from agricultural spills, or urban and industrial sources which are packed in nitrogen and phosphorus, required by phytoplankton. In turn, an excess of phytoplankton can cause the death of other marine organisms.

@Kevin Wolf on Unsplash