Geological, geophysical, and geobiological investigation of the inactive Nawaay`as hydrothermal vent field at West Valley, Juan de Fuca Ridge

Abstract

In 2022, an area of now-inactive hydrothermal venting, named the Nawaay`as field, was discovered on a sediment-covered volcanic mound within the axial valley of the West Valley segment of the Juan de Fuca Ridge, northeast Pacific Ocean. Analysis of multibeam backscatter imagery of the ridge segment indicates that volcanic activity along the ridge has resulted in, at minimum, two distinct eruptive events along the valley floor. Younger lava flows emanated from a volcano located near the southern end of the valley, then flowed north, paving over areas of bathymetric lows, but flowing around and thus preserving areas of relative bathymetric highs, including the volcanic mound that hosts the Nawaay`as field. Geochemical and petrographic analysis of Nawaay`as hydrothermal rock samples indicate that the deposit formed over venting temperatures ranging from ∼100 to 300 °C. Although the valley floor is generally sediment-free, trace metal concentrations within the sulfide-rich rock samples suggest that hydrothermal fluids interacted with buried sediments. Distinct differences in deep-sea sponge communities were observed between basaltic and inactive sulfidic substrates at West Valley, indicating that inactive hydrothermal deposits are unique seafloor habitats. Observations of shimmering water, vent-associated fauna, and recent seismic activity suggest the presence of active hydrothermal venting to both the north and south of Nawaay`as. With recent increased interest in the mineral resource potential of the seafloor, studies of inactive vent sites such as Nawaay`as are critical to ensure informed, risk-mitigating marine policy decisions are made in the future.