Diatoms can also drive large-scale phytoplankton bloom in southwest Indian Ocean

August 15th, 2009 - 3:43 pm ICT by ANI  

Washington, August 15 (ANI): In a new research, scientists have found that the large-scale autumn bloom of microscopic marine algae known as phytoplankton in the southwest Indian Ocean was driven by diatoms in 2005, not by nitrogen-fixing blue-green algae.

The observations were made by researchers based at the National Oceanography Centre, Southampton (NOCS), during a 2005 hydrographic survey south and east of Madagascar while aboard the royal research ship RRS Discovery.

Previously, it had been thought that the large-scale autumn bloom that develops in this region is driven by nitrogen-fixing blue-green algae, or cyanobacteria, called Trichodesmium, colonies of which the researchers found to be abundant.

However, the 2005 bloom was dominated by a diatom - a type of phytoplankton - the cells of which play host to another nitrogen-fixing cyanobacterium called Richella intracellularis, with Trichodesmium apparently playing second fiddle.

Diatoms have relatively large cells, and when they die, they sink down the water column, carrying with them carbon that is ultimately derived from carbon dioxide drawn from the atmosphere though the process of photosynthesis.

“Carbon dioxide is a greenhouse gas, and enhanced export of carbon to the deep ocean in the bodies of diatoms is an important natural mechanism by which the ocean regulates atmospheric carbon dioxide and our climate,” said team member Dr Alex Poulton of the NOCS.

According to the researchers, their findings will have an impact on modelling and satellite studies of the Madagascar bloom.

“Future research will also need to account for the magnitude of carbon export associated with diatoms and their nitrogen-fixing guests in the southwest Indian Ocean, and indeed other subtropical oceanic settings,” said Dr Poulton. (ANI)

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