Do phytoplankton produce more oxygen than a rainforest?  If so, does the oxygen they produce go into the atmosphere or does it just remain dissolved in the ocean?

By Sarah Sambolich, NBC Naturalist 2014. Edited by the NBC Research Committee.

There is a misconception that the rainforests contribute significantly to the oxygen we breathe. In reality, the animals and microscopic life living in the rainforest consume most of the oxygen. As a result, the net production of oxygen by the rainforest or any forest is actually close to zero. The commonly reported figure of the rainforests contributing 20% of the Earth’s oxygen supply is definitely a misrepresentation. The Amazon rainforest has also been affected by human-caused with annual fires that reduce the oxygen it can supply for the ecosystem.

However, phytoplankton in the ocean can also produce oxygen. Phytoplankton are microscopic marine algae that have chlorophyll, rely on the sun to live, and grow in the upper part of the ocean. They are essential to the food chain of the marine animals. Scientist have agreed that 50-80% of the oxygen in the Earth’s atmosphere comes from phytoplankton carrying out photosynthesis. So yes, phytoplankton do produce more oxygen than a rainforest! The reason for this 30% range of difference is the fact that phytoplankton concentration varies depending on the time of the year. With more sunlight in spring and summer, there will be more phytoplankton blooms (shown as an areas of paler blue and green in the satellite image). Conversely in winter, there will be fewer phytoplankton blooms with the reduced sunlight and availability of nutrients.

Rather than just increasing dissolved oxygen in the ocean, the oxygen produced by the phytoplankton has a direct impact on atmospheric oxygen. Dissolved oxygen comes from two sources: the atmosphere and submerged plants or phytoplankton in the water. Saltwater carries significantly less dissolved oxygen compared to freshwater sources. The oxygen produced by the phytoplankton as a byproduct of photosynthesis enters the ocean water but then is released as a gas to the atmosphere. In turn oxygen from the atmosphere dissolves in the surface ocean in a constant cycle to sustain marine life.

So yes, preventing deforestation and forest fires are crucial in ecosystem health and maintenance. However, monitoring the quality of the seawater is just as in important in ensuring that phytoplankton can participate in photosynthesis as effectively as possible. Cleaner water facilitates the transfer of oxygen to the atmosphere.

Here’s to a breath of fresh air at the bay!