Momarsat 2026 – From Seconds to Decades: Tracking Changes at hydrothermal vents

The French research vessel Pourquoi pas ? headed to Faial Island in the Azores for the Momarsat 2026 cruise, bringing together two powerful deep-sea exploration platforms: the Nautile manned submersible and the Ulyx Autonomous Underwater Vehicle (AUV). For the first time in 16 years, both will operate side by side during the cruise.

At 1700 m depth, the battery-powered EMSO-Azores Observatory monitors the Lucky Strike hydrothermal vent field, a dynamic environment shaped by active geological processes along the slow-spreading Mid-Atlantic Ridge. The observatory is designed to capture environmental variability across a remarkable range of spatial scales—from the kilometre-scale fluid circulation that drives hot, focused black-smoker vents to the centimetre- and decimetre-scale gradients that structure biological communities, from microorganisms to large megafauna.

Since 2010, the annual Momarsat cruises have maintained and progressively developed this long-term observatory. Instruments and moorings are recovered using submersibles, thoroughly checked and repaired on board, and then redeployed. These repeated operations generate unique long-term, multidisciplinary time series, allowing scientists to track environmental and biological changes over timescales ranging from seconds to decades.

Running from 25 August to 13 September 2026, Momarsat 2026 marks a new chapter for the observatory. The Nautile will conduct daily instrument recovery and sampling, while Ulyx, operating at night, will map the seafloor and collect high-resolution sonar and environmental data. Its sensors will characterize water masses through measurements including conductivity, temperature, depth, oxygen, turbidity and fluorescence. Both systems are capable of reaching depths of up to 6000 m, opening new possibilities for coordinated exploration and observation.

With 75 people on board, including crew, submersible pilots, scientists from multiple disciplines, a doctor—and musician Molécule—the cruise combines cutting-edge technology, long-term observation and multidisciplinary science to better understand how hydrothermal vent ecosystems change over time. 

Follow our adventures here: https://www.facebook.com/CampagneMomarsat/

Photo: The research vessel Pourquoi pas ? arriving on the Faïal island, in the Azores. It has the Nautile manned submersible and the Ulyx AUV on board. Photo credits: Audrey Mat (top picture) and Stephane Lesbat (bottom pictures). (c) Momarsat 2026, EMSO-Azores.

Authors: Jozée Sarrazin, Marjolaine Matabos (Ifremer Deep-sea lab, UMR BEEP)