Ash from the Tonga volcano fertilized marine ecosystems

Nov. 6 () –

Volcanic ash acted as nutrients in Pacific Ocean ecosystems following the explosive eruption of the Hunga Tonga-Hunga Ha’apai underwater volcano in January 2022.

The GEOTRACES GP21 expedition investigated the impact of this monumental event on the biogeochemistry of the surface waters of the South Pacific Gyre (SPG). The scientists focused in particular on changes in the concentration of trace elements in the ocean and their influence on marine life. The results of this study have now been published in Nature Communications.

For a comprehensive analysis of the effects of the eruption, the researchers used a combination of advanced computer simulations and precise sample analysis. To simulate the spread of volcanic ash after the eruption, they used the HYSPLIT computer model from the National Oceanic and Atmospheric Administration (NOAA) of the United States.

The model simulates the transport of substances in the atmosphere. It was used to calculate the dispersion of volcanic ash at different altitudes for 72 hours and the ash trajectories for up to 315 hours.

During the SONNE SO289 expedition as part of the international GEOTRACES program from February to April 2022, researchers collected water samples along a designated route to analyze the distribution of trace elements and their biogeochemical effects. During the expedition, a large amount of floating tephra, mainly pumice, was observed and collected in the western SPG.

Using radiogenic neodymium isotopes and concentrations of rare earth elements, the researchers were able to identify a marked volcanic inlet in the western SPG. This is the region identified as the primary site of post-eruption deposition based on the volcanic ash dispersion model. Additionally, seawater analyzes of neodymium isotopes and rare earth elements were used to track volcanic input and chlorophyll-a as an indicator of phytoplankton.

In the western South Pacific region, researchers identified significant amounts of trace elements such as iron and neodymium, which normally only enter the ocean in trace amounts through atmospheric dust. The volcanic eruption released an additional 32,000 tons of iron and 160 tons of neodymium. The amount of iron is equivalent to what the region normally receives in a year, while the amount of neodymium is equivalent to one year of global input.

“At the same time, we measured higher concentrations of chlorophyll-a in surface waters, indicating greater growth of phytoplankton and therefore biological activity” says Dr. Zhouling Zhang, research associate at the Paleo-Oceanographic Research Unit and lead author of the study, in a statement.

The team was able to show that trace elements released by volcanic eruptions play an important role for marine life. These elements, particularly the micronutrient iron, They act as nutrients in the ocean that stimulate the growth of phytoplankton.

Phytoplankton play an essential role in the global carbon cycle, absorbing CO2 from the atmosphere through photosynthesis and storing it in the ocean. Therefore, increasing biological productivity can also improve the ocean’s ability to absorb CO2 from the atmosphere, a process that could have a long-term impact on the climate.

The researchers estimate that the release of the micronutrient iron from the HTHH eruption is comparable to the iron fertilization caused by the eruption of Mount Pinatubo in the Philippines in June 1991, when about 40,000 tons of volcanic material were released and measured. a 1.5 ppm slowdown in the increase in atmospheric CO2 about two years after the eruption.

Zhang states: “We think the Hunga Tonga eruption could have a similar effect.”