What the oceans do for us: One phytoplankton's waste….

Beautiful image isn’t it.  This is a phytoplankton bloom - basically a truck load of phytoplankton all grouped in one area.  Phytoplankton are the tiniest of the tiny plants.

Consisting of just a single cell, they spend their life drifting around the oceans (and indeed freshwater too).  You may have heard some of the names of the most common kinds of phytoplankton – like diatoms, dinoflagellates, and coccolithophores.  Just like plants on the land, phytoplankton need sunlight, nutrients like nitrates and phosphates, and carbon dioxide. Also just like plants on the land, phytoplankton photosynthesise.

Photosynthesis in the terrestrial environment goes a little something like this.  The leaves of plants are green because they contain chlorophyll, which is is really good at absorbing sunlight.  This energy is combined with carbon dioxide (also absorbed through their leaves) and water (which primarily comes from the roots) which results in a chemical reaction that gives the plant glucose (sugar) and oxygen.

For our phytoplankton the process is remarkably similar, but the phytoplankton don’t have leaves – or roots.  Instead they absorb all the bits they need directly through their cell wall.  The glucose produced by photosynthesis is used up by the phytoplankton, but the oxygen…well that’s what is known as a waste product.  That’s good news for you, me, and life on Earth. Oxygen may only make up ~21% of the atmosphere but if it were to disappear tomorrow we would be up the proverbial creek, and a paddle wouldn’t help us even if we did have one.  The jury is still out on just how much oxygen these tiny plants contribute to the atmosphere – NASA estimates 50 – 85%.  Even at the lower end of the scale that’s still a hefty amount.  There have been a number of studies looking at the photosynthesis of phytoplankton.  Here’s just a couple of open access papers:

Late Cambrian oxygen

Back in 2011, Matthew Saltzman from Ohio State University and colleagues published a paper looking at some huge changes in atmospheric oxygen content during the Cambrian period.  Apparently at around the time of the mass extinctions, oxygen declined dramatically, but picked up again.  The most likely source of this oxygen?  Yup phytoplankton.

Variation is everywhere

The amount of oxygen produced by phytoplankton isn’t constant.  It can change depending on where you are, and what time of year it is.  Dr Sarma from Nagoya University and colleagues studied oxygen production in Sagami Bay in Japan between May and October 2002.  They found that the August was peak oxygen time, whilst October saw the least amount.

More carbon dioxide = more oxygen? Not quite

With us lot pumping more and more carbon dioxide into the atmosphere, you might think that for phytoplankton this isn’t so bad.  After all carbon dioxide is vital for photosynthesis – and we like photosynthesis because it gives us oxygen.  Well its not quite that simple.  In 2013 Dr Kim from Chonnam National University  and colleagues took a look at how predicted future climates might impact coastal phytoplankton photosynthesis.

Image:  Taken by the European Space Agency, ESA Envisat in December 2011.  This phytoplankton bloom is about 600 km off the east coast of the Falkland Islands, which lies in the southern part of the Atlantic Ocean.