Impact of seamount subduction on margin fluid dynamics: distribution, seafloor emissions, and upwards migration pathways at the northern Ecuador continental shelf (SUPER-MOUV cruise, 2024)

Fluid circulation along active margins represents a key geological process that influences geochemical cycles, sedimentary dynamics and the occurrence of seismic activity and associated natural hazards. The SUPER-MOUV oceanographic cruise (January–February 2024) aimed to investigate seafloor manifestations of these fluid circulations and their relationship with seismic activity along the active margin of northern Ecuador. Multibeam data (bathymetry), water column data (seismic profiles and bathymetry), high-resolution seismic profiles, and in-situ observations from the Nautile submersible were combined to complement data from the HIPER cruises (bathymetry, deep seismic imaging) and a dense grid of industrial seismic profiles. This dataset allows us to reveal seabed fluid manifestations in areas where topographic irregularities, such as seamounts, subduct and create preferential pathways for fluid migration within the upper plate. At approximately latitude ~0°15’N latitude, the subduction of the Atacames seamounts oceanic topography carried by the Nazca plate correlates spatially with extensive seabed fields of carbonate mounds (up to 300 meters long and 15 meters high) build on the continental shelf, the majority of which is associated with active fluid emissions in the water column. Samples collected by the Nautile submersible reveal that these concretions incorporate centimetric clasts containing Eocene foraminifers. This finding suggests a vigorous, “mud-volcano-type” fluid circulation event, which was capable of transporting clasts from the earliest sedimentary deposits resting on the oceanic basement of the Ecuadorian forearc basins, to the seabed surface. Seismic profiles interpretation, including seismic attribute analysis, enabled the characterization of fluid accumulations at depths and highlight their circulation pathways associated with faults, fractures, diapirs and litho-stratigraphic discontinuities. Notably, some diapiric structures, located directly beneath seabed fluid emissions, root as deep as 3 seconds two-way travel time (TWT) into a highly fractured acoustic basement, consistent with the presence of Eocene clasts on the seafloor and suggests the existence of a potentially deeper fluid source.