Substantial trace metal input from the 2022 Hunga Tonga-Hunga Ha’apai eruption into the South Pacific Ocean

29 October 2024

The Hunga Tonga-Hunga Ha’apai (HTHH) volcano violently erupted on 15^th January 2022, producing a volcanic plume that reached the lower mesosphere and generating tsunami waves across the globe. As the largest submarine eruption for nearly one and a half centuries, it provides an invaluable opportunity to investigate the impacts of major volcanic eruptions on oceanic biogeochemistry.

Zhang and co-workers (2024, see reference below) investigate the impact of the 2022 HTHH eruption on the biogeochemistry of the South Pacific Gyre (SPG) surface waters using field observations made on an across-Pacific expedition (GEOTRACES GP21) starting one month after the eruption. Using radiogenic neodymium isotopes and rare earth element concentrations, they are able to fingerprint a marked volcanic impact on the western SPG, the region identified as the primary site of post-eruption deposition based on a volcanic ash dispersal model. This impact may extend to regions further east via atmospheric ash dispersal and surface current transport. They also demonstrate a coincident enhancement of trace metal and chlorophyll-a concentrations in surface waters providing evidence for a stimulation of biological activity in response to eruption-derived micronutrient inputs. They estimate that the iron release from the HTHH eruption (32±8 kt) was comparable to the amount of iron fertilization from the giant eruption of Mount Pinatubo in June 1991 (40 kt), which was associated with atmospheric carbon/oxygen anomalies.

This finding offers new insights into the impacts of major volcanic eruptions on oceanic biogeochemistry, with implications for nutrient cycling and ecosystem dynamics in the SPG and beyond.

**Figure 1**: **Changes in Nd isotopic composition (ε_Nd) and concentration, and selected Rare Earth Element (REE) ratios in the surface water (uppermost 3-5 m) along GP21.** (a) ε_Nd, (b) Nd concentration measured by isotope dilution, (c) Post-Archean Australian Shale (PAAS) normalized Ce anomaly (Ce/Ce*_PAAS), (d) PAAS normalized heavy REE enrichment. The location of the pumice is indicated by a red arrow pointing downwards. The region of ash deposition within 3 days of the eruption, based on the NOAA HYSPLIT volcanic ash dispersion model, is shown by the transparent grey box.

**Figure 2: Changes in surface water (uppermost 3-5 m) trace metal concentrations and total chlorophyll a (TChl-a) inventory in the euphotic layer of the South Pacific Gyre (170°E-90°W).** (a) Surface dissolved manganese (dMn) and aluminium (dAl) concentrations; (b) surface dissolved iron (dFe) concentration and TChl-a inventory in the euphotic layer; (c-f) cross plots of surface dAl, dMn, dFe, and TChl-a inventory versus Nd isotopic composition (ε_Nd).

Reference:

Zhang, Z., Xu, A., Hathorne, E., Gutjahr, M., Browning, T.J., Gosnell, K.J., Liu, T., Steiner, Z., Kiko, R., Yuan, Z., Liu, H., Achterberg, E.P., Frank, M., 2024. Substantial trace metal input from the 2022 Hunga Tonga-Hunga Ha’apai eruption into the South Pacific. Nat Commun 15, 8986. Access the paper: https://doi.org/10.1038/s41467-024-52904-3

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