Hydrothermal iron from the earth’s interior as fertiliser of photosynthesis in the ocean

forthcoming

HARVEST investigates how iron released from submarine volcanoes stimulates the growth of phytoplankton, especially in nutrient-poor ocean regions. Iron is known to be a limiting nutrient for photosynthesizing plankton, but research has mostly focused on iron delivery via atmospheric dust. The contribution of iron from hydrothermal sources – leached out of hot rock along the volcanically active plate boundaries – has been largely overlooked. This process, however, may drive a significant component of primary production in iron-limited ocean areas. HARVEST addresses this critical knowledge gap through a holistic investigation of hydrothermal iron sources on the seafloor, and the mechanisms by which iron is transported to the ocean’s sunlit surface layer. A focus is on shallow seamounts in volcanic arcs and hotspots, which are hypothesised to have the most direct hydrothermal impact on surface waters, but remain the least studied. Measuring, modelling and comparing iron fluxes from shallow versus deep submarine sources, HARVEST advances from local through regional to global scales. Its main fieldwork area around Tonga-Lau features large and recurrent phytoplankton blooms, and the range of tectonically relevant settings. HARVEST will track iron-laden hydrothermal plumes, their dispersal, and their effects on phytoplankton, using ship-based surveys, autonomous vehicles and long-term moorings. Dedicated ocean models with a biogeochemical compartment will simulate the transport of hydrothermal plumes on regional and global scales, away from their hydrothermal sources, and into the sunlit ocean layer. This will clarify the role of hydrothermal iron on primary production and on the carbon cycle in present and future climate scenarios. Thus HARVEST will reveal the overlooked contribution of submarine volcanism to ocean fertilisation, opening up new views into the interconnectedness of solid earth, oceans, and marine life.