Assessing the impacts of recent volcanic eruptions on the marine environment of the Canary Islands

The Canary Islands constitute an active volcanic intraplate archipelago. Two eruptions have occurred in the 21^st century so far at the youngest and most active islands: a submarine eruption at El Hierro island in 2011, and a subaerial eruption at La Palma in 2021. The effects of these volcanoes on the marine environment were assessed during the eruption and monitored over the following years.

The submarine eruption of Tagoro volcano at El Hierro caused severe physical-chemical perturbations on the surrounding oceanic environment, such as large increases in temperature and water acidification. Moreover, the volcano released large amounts of reduced chemical species into the surrounding waters, which were rapidly oxidized upon contact with seawater. This process caused severe oxygen depletion, leading to suboxic and even anoxic conditions over wide areas, with oxygen concentrations decreasing up to -96%. Deoxygenated water plumes extended over areas larger than 460 km² and were transported by local circulation and mesoscale structures such as eddies, allowing detectable oxygen anomalies to persist tens of kilometers from the eruption site.

However, the affected marine ecosystem showed a strong capacity for recovery in the following years. As the eruptive phase transitioned into a long-lasting hydrothermal stage (which remains active), the Tagoro volcano became an important source of dissolved inorganic nutrients to the regional ocean. Emitted fluids are strongly enriched in silicate, phosphate, and nitrogen species, particularly ammonium. This highlights the importance of submarine volcanism for marine biogeochemical cycles and its fertilizing potential.

The 2021 subaerial eruption of the Tajogaite volcano at La Palma further illustrated the impacts of volcanic activity on the ocean through the formation of lava deltas. Lava entering the sea generated pronounced anomalies throughout the water column, including extreme turbidity, reduced pH, and elevated temperatures. A localized lava-induced upwelling was detected as heated waters rose and were replaced by deeper, colder waters. However, this process did not stimulate phytoplankton growth; instead, a sharp decline in chlorophyll-a (up to -69%) indicated a negative impact on primary producers over several kilometers from the coast.

Overall, this integrated study advances understanding of how volcanic activity shapes oceanographic conditions, biogeochemical cycles, and ecosystem resilience, while providing valuable guidance for ocean monitoring and crisis management during future volcanic emergencies in the Canary Islands.