Fire, water and the air we breathe

As wildfires in the Arctic continue to blaze, MATHIEU ARDYNA and DOUGLAS HAMILTON are trying to figure out if they may be having an unforeseen effect. Could they be responsible for an increase in phytoplankton?

Phytoplankton are the primary source of photosynthesis in the ocean: they take in carbon dioxide and nutrients, then use the energy from sunlight to generate the building blocks of life, releasing oxygen in the process. But the availability of the three primary nutrients—nitrogen, phosphorus and iron—needed to fuel this process is not uniform across the world’s seven seas. In many open ocean areas, nitrogen is abundant in surface waters, but iron is not. The opposite is true for the Arctic Ocean, where it is the nitrogen supply that limits primary productivity.

In the summer of 2014, we observed an unusually large phytoplankton bloom in the Laptev Sea—approximately 850 kilometres south of the North Pole—from satellite-derived maps of chlorophyll a (a form of chlorophyll used in photosynthesis). But an analysis of the “usual suspects” to see where the nitrogen was coming from—such as sea ice melt, river discharge and ocean upwelling—didn’t turn up any source that would account for the large supply of nitrogen necessary for the bloom to have occurred.

So we looked up and out of the water, to the atmosphere and land, to consider the potential role of wildfires. We rapidly discovered that a large wildfire had occurred upwind in Siberia that same summer. Could this be the nitrogen source we were looking for?

A smoky nutrient cocktail

It turns out that because of biomass consumption and the entrainment of local soils by warm updrafts, fire smoke is a cocktail of the nutrients, including nitrogen, needed for phytoplankton growth in the Arctic. Climate models are designed, in part, to simulate the atmospheric lifetimes of elements like nitrogen from their source through their chemical evolution in the atmosphere to their return to the land or ocean surface. But in the first simulations we examined, the mass of nitrogen being deposited into the Arctic Ocean was not enough to match the amount needed to support the bloom we had observed.

The first reason we considered for this shortfall is that because fires in Siberia are remote, they are rarely measured directly. This means the extent of fire emissions may be underestimated, as is the case in other parts of the world. But reconciling this gap with the scientific literature did not fully explain the situation, so we dug a little deeper.

There has been a lot of media coverage about the increase in peat fires in Siberia due to thawing permafrost. In particular, the “zombie fire” aspect of peat fires (a phenomenon whereby peat can continue to burn deep underground and resurface somewhere else) has attracted a lot of attention.

We began to wonder what the nitrogen contribution of peat fires might be, and that was when we found the second cause of our “missing” nitrogen: peat was not represented at all in our initial emissions estimates, but as a dense organic material that has accumulated over a long period of time, it is likely to release more nitrogen per unit mass consumed than a traditional tree or shrub fire would.

By putting these elements together, we were able to reconcile the nitrogen budget and formulate a hypothesis: smoke from boreal forest fires could have a fertilizing effect on life in the Arctic Ocean.

Anomaly vs. precursor

The question is: if fires in the Arctic are providing a sufficient source of fertilizer to support ocean life, then what does a future with more fires mean for the delicate balance of ecosystems in the Arctic region?

Our study raised more questions than answers. More observations are needed to understand this emerging climate-driven change in biogeochemical cycles, including its impact on sea ice. It is important to ask whether the anomalous bloom we observed in 2014 was a rare example of multiple processes “lining up” to create the conditions for life to flourish, or a climate change-induced sign of trouble ahead. Making observations in the remote and challenging Arctic environment is logistically challenging, but the use of autonomous profiling systems, coupled with improved satellite observations, could provide access to critical data.

“Can fire and water mix to create life?” is a fascinating question that is beginning to take hold in the research psyche. More evidence and a deeper understanding of how climate change affects nutrient cycling in the Arctic are clearly needed.