Lava plus nitrate equals growth
Scientists explain an unexpected algae super bloom.
As Hawaii's Kilauea volcano erupted in July 2018, scientists from the University of Hawaii and the University of Southern California Dornsife noticed something odd.
A huge bloom of algae started forming and spreading in the surrounding North Pacific Ocean, despite the fact that millions of tonnes of hot lava were pouring into the water.
NASA satellite photos of the eruption clearly showed that ocean around the volcano was turning green. The satellite had detected huge amounts of chlorophyll, the green pigment in algae and other plants that converts light into energy.
USC geochemist Seth John and colleagues from the two universities wanted to know what had happened, and now they have presented what they think is the answer in a paper published in the journal Science.
Their study shows that the green plume in the ocean around the volcano contained the perfect cocktail for plant growth – a fertile mix of higher nitrate levels, silicic acid, iron and phosphate.
Nitrogen is a natural fertiliser for plants. With such rich conditions, the algae bloom exploded, expanding hundreds of kilometres into the Pacific Ocean. But that was surprising.
"There was no reason for us to expect that an algae bloom like this would happen," says John. "Lava doesn't contain any nitrate."
The researchers believe the nitrogen was stirred up from the deep ocean. As the hot lava poured in, it forced an upwelling of colder, deep ocean water. When the water rose, it carried nitrogen and other particles to the surface that helped the algae grow.
"All along the coast of California, there is regular upwelling," says John. "All the kelp beds and marine creatures that inhabit those ecosystems are basically driven by those currents that draw fertilising nutrients up from deep water to the surface.