Mysteries of the blue ocean

From Planet Earth, On Line, 29 November 2010

Scientists used to think the open ocean was a watery desert. Now we're starting to understand the diversity of life there and the profound influence it has on our climate. Types of plankton that were once dismissed turn out to play a vital role in the carbon cycle. Until recently cyanobacteria have been thought to dominate carbon fixation in the open ocean. However, the photic zone also has a high biomass of small eukaryotic phytoplankton - that is, photosynthesising plankton with a complex cellular structure - which are capable of CO₂ fixation. The eukaryotic phytoplankton community has long
been a 'black box' - we have known little of its composition or of its contribution to CO₂ fixation. It is only by determining how much CO₂ these different groups fix into biomass that we can get a full understanding of the Earth's carbon cycle.

Ascertaining this contribution has been a thorny problem for biological oceanographers for decades. However, using flow cytometry - a technique borrowed from medical research that can physically separate (and hence 'sort') cells based on their size and fluorescence properties - we have now been able to measure how much CO₂ is being fixed by different phytoplankton groups. For the complete article see: http://planetearth.nerc.ac.uk/features/story.aspx?id=840