Will the changing Arctic ecosystem reverse climate change… or make matters worse?

In 2011, Dr. Kevin Arrigo and his team were monitoring the effects of climate change in the Arctic Ocean when they noticed something surprising: phytoplankton was blooming under the ice. This went completely against the accepted science… there was no way, it was thought, that these microscopic creatures could possibly be getting enough sunlight through the snowy ice to keep up their photosynthesis. To compound the strangeness, it was still considered too early in the summer season for the ice to be retreating and for the phytoplankton to start blooming.

Yet, here they were--60 miles inland on the Arctic ice, with a greenish hue peering through the ice. In their subsequent paper, Arrigo and his colleagues postulated that this effect might be tied to the “thinning ice cover and proliferation of melt ponds” over the past few decades, which would allow more light to sneak down through cracks and thin parts of the ice.

This explosion of phytoplankton population could upset the delicate balance of the food web. Phytoplankton are at the bottom of the Arctic food pyramid, but that doesn’t mean they aren’t important. In fact, quite the opposite: they are the base that supports the rest of the critters above them. How goes the phytoplankton, so goes the rest of the Arctic marine life. Miles learned about this a few years back in Alaska, in a Science Nation episode produced for the National Science Foundation by Kate Tobin:

Global warming and climate change were considered to be the likely culprits of this increased blooming, but there was scant evidence to support that claim. So, another Arctic researcher, Dr. Chris Horvat of Harvard, set out to make a model of Arctic sea ice thickness over the years and how that correlates to the recorded phytoplankton blooms each season.

Using satellite data, data gathered on the ice, and older mathematical models, Horvat created a new model that predicts how much of the Arctic sea under the ice would get enough light to sustain a phytoplankton bloom. When he crunched the numbers, the trend was obvious: thinner ice due to global warming increases the amount of light available for phytoplankton.

“The proportion [in green] of the Arctic Ocean in July, from about 1980 to the present, in which sufficient light reaches under the sea ice to permit a bloom.” Credit: Chris Horvat.

“The proportion [in green] of the Arctic Ocean in July, from about 1980 to the present, in which sufficient light reaches under the sea ice to permit a bloom.” Credit: Chris Horvat.

But why does this all matter? Well, both main factors of climate change at play here: the amount of heat our planet absorbs from sunlight and the amount of carbon dioxide in our atmosphere. Sunlight warms up our planet and greenhouse gases such as carbon dioxide trap that warmth, so to avoid a runaway warming of the planet we need to cut down on one or, preferably, both of those.

The issue here is we don’t yet know how this changing Arctic ecosystem will affect the equation.

On the one hand, the amount of sunlight absorbed is going up. As Horvat’s model shows, the Arctic sea ice is allowing more sunlight through. This means that less and less of this warming sunlight is being bounced back out into space by the usually highly reflective ice. More sunlight absorbed means the sea surface temperatures in the area rise--not good. And we’re not talking chump change either: “One recent study estimates that [the melting Arctic sea ice is] equivalent to adding another 25 percent to global greenhouse emissions.”

On the other hand, phytoplankton is blooming like never before. The photosynthesis that the phytoplankton use actually takes carbon dioxide out of the atmosphere. When these organisms die (or their predators eat them and eventually die), they sink to the bottom of the ocean, taking the greenhouse-warming carbon with them. More heat can escape and temperatures can go down--a good thing. And, again, this is not a small impact we’re talking about: across the whole ocean, phytoplankton pump 10 gigatons of carbon out of the atmosphere, which is about as much as humans are putting into the atmosphere right now. Considering the Arctic has some of the most productive phytoplankton in the world, an increase in blooms up North could bring down the amount of carbon in the atmosphere.

Phytoplankton observed blooming under Arctic ice in 2011. Image credit: NASA.

Phytoplankton observed blooming under Arctic ice in 2011. Image credit: NASA.

The scientists understand the stakes here, but they still need to do more research to understand how this changing Arctic piece will fit into the puzzle of climate change. Remember, they didn’t even know that phytoplankton was even blooming under the ice until 6 years ago! Horvat and his colleagues note in their paper that “the presence or lack of nutrients may also limit the genesis of blooms,” so figuring out how much light the phytoplankton are getting is only the beginning.

Horvat, on his blog, says it is hard to tell how this will affect climate change: “If the blooms occur in addition to those as the sea ice retreats, it is conceivable that more carbon is being taken up in the Arctic than previously [thought]. However if now there is still only one annual bloom or period of phytoplankton growth, but it just occurs several months earlier, the impact on carbon fixation may be small. We need more observations to know!!!” The number of exclamation marks is his choice, but I agree with the imperative.

One thing is certain: whichever way the scales in the Arctic tip, they will have tipped due to human-caused climate change.

 

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Banner image credit: NASA.