Activity, Distribution, and Biodiversity of Hydrothermal Vent Sites in the Red Sea

The Red Sea Rift is a young (~13 Ma) ultra-slow spreading center (<16 mm/yr) with warm (~21°C) and saline (~41‰) deep-water conditions, thick Miocene evaporite sequences, and high heat flow. Active hydrothermal venting remained unconfirmed until 2022/23, when diffuse low-temperature venting was discovered at Hatiba Mons (23°N) and Mabahiss Mons volcanoes (25°N). The Meteor expedition M194 HEXPLORES (October–November 2023) aimed to survey the rift for active venting, test if an ultra-slow ridge with high heat flow hosts more hydrothermal activity than models predict, and study vent fluid chemistry, mineralization, and biology.
During M194, four new hydrothermal areas were found between ~17°N and 25°N, showing that active venting is widespread and more common than expected. All sites have low-temperature diffuse venting (<60°C) on larger axial volcanoes, where fault pathways channel fluids. Even near the Afar hotspot, the southern magma-rich segment shows only low-T venting, indicating this hydrothermal style marks the Red Sea's current tectonic stage.
At Hatiba Mons, the largest axial volcano in the rift, an extensive Fe-rich mound field is the largest active vent field known from any slow- or ultra-slow-spreading ridge. Gravity cores found sphalerite, pyrite, barite, and anhydrite at 2–3 m depths, together with barite fluid inclusion data indicate that these deposits formed from hotter (~300°C), high-salinity fluids, suggesting a dynamic hydrothermal history with earlier high-temperature phases. The discovery of CO₂-rich hypersaline brine pools on Mabahiss and Hatiba Mons volcanoes, with salinities exceeding 60‰ and temperatures of 23–28°C, might be volcanic hydrothermal endmembers of the well-known deep axial brines, such as Atlantis II, and highlight evaporite influence on Red Sea rift geochemistry.
Biologically, all vent sites were dominated by chemosynthetic microbial mats, with sparse macrofauna. Opportunistic polychaetes and amphipods appeared in the mats. The scarcity of vent-endemic fauna may result from low sulfide levels, high salinity and temperature, and biogeographic isolation of the Red Sea.
HEXPLORES shows the Red Sea Rift has more hydrothermal activity than thought, driven by ultra-slow spreading, high heat flow, and evaporite-magma interactions. Hatiba Mons illustrates an evolutionary arc from high-T systems to present low-T venting, driving microbial communities, offering a rare window into hydrothermal processes during the birth of an ocean basin.