24.10.2025/Kiel. A study led by MARUM - Centre for Marine Environmental Sciences at the University of Bremen - with the participation of five GEOMAR scientists summarises how iron from hydrothermal vents can be transported across entire ocean basins. They form where seawater enters hot zones beneath the seafloor through cracks in the Earth's crust. The overview study, entitled "Iron's Irony", has now been published in the journal Communications Earth & Environment.
How is iron transported from hydrothermal vents across entire ocean basins? The research results have been summarised and reinterpreted in a study by twelve scientists from German marine research centres led by MARUM - Centre for Marine Environmental Sciences at the University of Bremen - with the participation of GEOMAR Helmholtz Centre for Ocean Research Kiel. The overview study entitled "Iron's Irony" has now been published in the journal Communications Earth & Environment.
Hydrothermal vents transport metal-rich solutions
Hydrothermal vents form when metal-rich fluids, heated to over 300 degrees Celsius, rise through the oceanic crust and mix with the cold seawater near the seabed. Chemical reactions cause the iron-bearing particles from the hydrothermal solution to colour the water black. For this reason, such vents are also known as "black smokers".
"Most of the iron released with the hot fluids reacts immediately with oxygen and sulphur compounds, precipitating as minerals. However, a small fraction remains dissolved for surprisingly long periods - bound to tiny molecules or influenced by microbes - and can thus transport nutrients far beyond the immediate vent sites," explains Dr Solveig Bühring, lead author of the study and geomicrobiologist at MARUM.
Iron plays a key role
By combining geochemical, microbiological and model-based approaches, the research team was able to show how hydrothermal systems are part of global nutrient cycles. "The findings are so exciting because iron plays a key role in marine ecosystems. It supports primary production - the formation of biomass from CO by microorganisms such as phytoplankton - a crucial foundation for life in the ocean. Iron is involved in essential biological processes such as photosynthesis, respiration and nitrogen fixation," says Dr Stefanie Böhnke-Brandt, co-author and geomicrobiologist at GEOMAR.
For a long time, researchers assumed that iron-rich dust from the atmosphere was the most important external source of iron for the oceans. In recent years, however, the distribution of trace elements such as iron has been systematically mapped worldwide, in particular through the international GEOTRACES programme. The results show that hydrothermal activity along the mid-ocean ridges in all ocean basins is a previously underestimated, significant source of iron for the world's oceans. The hydrothermal plumes contribute to the supply of bioavailable iron to remote marine regions and thus to the productivity of the ocean in distant regions.
Iron is scarce in many parts of the ocean. As a result, primary production, i. e. the growth of phytoplankton at the ocean surface, is often lower than it could be. When iron from hydrothermal sources enters such nutrient-poor areas, it can significantly increase the productivity of the oceans. The more plankton grows and sinks to the depths, the more CO is bound from the atmosphere and stored in the ocean - a climate-relevant process and an important part of the global carbon cycle," says Stefanie Böhnke-Brandt.