Atmospheric inputs of volcanic iron around Heard and McDonald Islands, Southern ocean

Abstract

Atmospheric deposition of iron to anemic waters in the Southern Ocean (SO) can relieve marine phytoplankton growth limitation. The northern Kerguelen plateau, in the iron-limited Indian sector of the SO, hosts vast annual spring blooms of marine phytoplankton, evidencing seasonal iron supply mechanisms. This study reports the first atmospheric measurements of iron concentration and solubility near and downwind of the volcanically active islands of Heard and McDonald Islands (HIMI) on the Kerguelen plateau. Using a combination of atmospheric tracers (radon and black carbon), air-mass back-trajectories, and trace metal ratios in aerosols, we detected emission from Heard Island in aerosols up to 500 km downwind from HIMI. The latter emissions were characterized by enrichment in molybdenum (Mo, ∼100 to 3000-fold), chromium (Cr) and nickel (Ni) (both ∼5 to 40-fold) in aerosols compared to Heard Island basaltic rocks. This phenomena reflects the greater volatility of Mo, Cr and Ni compared to the lithogenic reference trace metal aluminum (Al) under volcanic eruption atmospheric conditions. Our study highlights that volcanic emissions from Heard Island's main volcano, Big Ben, should be considered an additional source of atmospheric Fe supply to marine ecosystems near and downstream of the Kerguelen plateau, alongside other volcanic clusters in the Southern Hemisphere.