When Viruses Attack: Algal Blooms Affect Global Carbon Cycles

Scientists behind a new study have found that algal blooms, at least when attacked by viruses, can affect global carbon cycles.

When we talk about global warming, most people focus on how much carbon gets pumped into the atmosphere. But in order to get a complete picture, scientists must also consider carbon fixation, which is the pumping of carbon out of the atmosphere and fixing it into organic molecules by photosynthesis.

Phytoplankton - single-celled photosynthetic organisms - may account for less than one percent of the total photosynthetic biomass on Earth, but tiny as they are, they are the ocean's most powerful carbon traps, fixing almost half of the world's organic carbon.

It's phytoplankton that multiply and form algal blooms thousands of miles in area that can be seen from space. Algal blooms may have a tendency to grow quickly and disappear suddenly, but they are currently still wreaking havoc on the Great Lakes, polluting their waters to the point that federal officials announced plans to restore the lakes by the year 2020.

Scientists set out to answer the question, "How much carbon does such a bloom fix, and what happens to that carbon when the bloom dies out?"

The findings were published in a press release by the Weizmann Institute of Science.

It turns out that when phytoplankton are starved or infected with viruses they impact the global carbon cycle. The same cannot be said if they're eaten by other marine life because its carbon will simply be passed up the food chain. However, viruses make the situation a bit more complicated.

What happens is some dead organisms, rather than sinking to the ocean floor and taking their absorbed carbon with them, may be scavenged by certain bacteria the in surface waters. These remove the organic carbon and release it back into the atmosphere through respiration.

By combining satellite data with their field measurements, scientists were able to measure the effect of viruses on phytoplankton blooms on large, open ocean areas for the first time.

According to their estimates, an algal patch of around 1,000 square kilometers - which forms within two weeks - can fix around 24,000 tons of organic carbon. That's equivalent to a similar area of rain forest.

And since a single viral infection can wipe out an entire algal bloom, they have more of an effect on global carbon than we previously thought.