How Kilauea’s lava fed a massive phytoplankton bloom

Kilauea’s 2018 eruption gave a surprising boost to ocean algae.

Metals in the lava could have helped fuel a 150-kilometer-long phytoplankton bloom off the coast of Hawaii — but unexpectedly, heat was an even more important ingredient. Superhot lava interacting with deep ocean water may have churned up buoyant plumes of deep-sea nutrients that kept the tiny algae well-fed, researchers report in the Sept. 6 Science.

Each day from June 3 to August 6, 2018, Kilauea spewed 50 to 100 cubic meters of metal- and nutrient-rich lava per second into the Pacific Ocean (SN: 1/29/19). Three days after lava first entered the ocean, satellite images showed a patch of water enriched in chlorophyll-a — the pigment that can make plants and algae green — off the island of Hawaii. Once the lava stopped flowing into the ocean, the patch dissipated within a week.

Amid peak bloom, scientists analyzed the patch’s seawater to determine why the phytoplankton suddenly flourished. The water contained a rich, phytoplankton-fertilizing serum of nitrate, silicic acid and phosphate, as well as iron, manganese and cobalt, microbial oceanographer Samuel Wilson of the University of Hawaii at Manoa and colleagues found.

Concentrations of silicic acid and trace metals, some of which can help algae grow, were similar to those of Kilauea’s basalt lava. But nitrate was the primary driver for the bloom, the team found, and its source was a mystery. The lava itself contains hardly any nitrogen for ocean microbes to convert into nitrate.

Instead, the nutrient probably came from the deep, Wilson’s team says. Near the island, the seafloor slopes steeply, allowing already fast-moving lava to rapidly reach deeper waters. Those waters contain abundant nitrate, in contrast to the surface waters.

This previously undetected mechanism, in which hot lava helps launch buoyant plumes of nutrients upward from deep waters, could be commonplace in the ocean, the scientists say. Although harder to spot than surface eruptions like Kilauea, submarine volcanoes may be similarly capable of fueling brief but intense phytoplankton blooms.