AUSTRALIA – A recent study shows that smoke from the severe 2019-2020 Australian bushfires caused massive, long-lasting algae blooms to form off the coast of Antarctica.
“The phytoplankton bloom in this region was unprecedented in the 22-year satellite record and lasted for around four months,” says co-author Professor Peter Strutton, “What made it more extraordinary is that the part of the season when the bloom appeared is usually the seasonal low point in phytoplankton, but the smoke from the Australian bushfires completely reversed that.”
The effects of wildfires are not confined to these landlocked systems – winds will often carry the smoke and ash emitted from these fires to the ocean. For example, a 2019 wildfire in Edmonton, Canada burned so intensely that its smoke crossed the Atlantic Ocean and was observed in the United Kingdom. And, wildfires can affect local water bodies while they are burning and long after they have been extinguished. Smoke from a wildfire was linked to a coral die-off in Indonesia in the 1990s; iron-rich smoke caused a phytoplankton bloom that suffocated corals.
In the study concerning the Southern Ocean bloom, scientists tracked the plumes of smoke to see if they could be linked to the bloom using a combination of satellite data and autonomous sensors already in the water surrounding the area where the bloom formed. As in Indonesia, the authors found that iron, a nutrient used by phytoplankton, was three times more abundant. Wildfires also release CO2 into the atmosphere – an essential component for photosynthesizing plankton – that may have further accelerated the algae bloom.
While there is not anything inherently bad about an algae bloom, the ‘fertilizer effect’ of iron and CO2 can lead to eutrophication (similar to what happens in the Gulf of Mexico): when this bulk of nutrients enters the ocean, it causes algae populations to boom. Once the algae die off, the microbes that consume the dead algae deplete oxygen in the process and suffocate species incapable of moving far away.