Measuring Total Heat Flux at 9^o50'N, East Pacific Rise, using Autonomous Underwater Vehicle Sentry

Abstract:

Hydrothermal circulation at mid-ocean ridges (MOR) plays an important role in the exchange of heat and matter between the oceanic crust and the global ocean, and supports unique deep-sea ecosystems. The East Pacific Rise at 9^o50'N hosts hydrothermal circulation atop an active magmatic system that has erupted twice since 1991. Numerous, detailed studies have been conducted in this area over the past 35 years, however, measuring in-situ advective heat flux from hydrothermal vents both globally and at this site has remained challenging. In December of 2018, we used autonomous underwater vehicle Sentry to survey the water column above the active vent sites, in order to estimate total heat and mass flux. In addition to its standard instrumentation, Sentry was equipped with an acoustic Doppler velocimeter and two SBE3 temperature probes, mounted on two auxiliary poles spaced 1.3 m vertically apart. The survey was carried out at an altitude of ~20 m above the vent field, covering an area of ~0.1 km^2. Tracklines spaced in a 5 m x 5 m grid within the axial summit trough, and centered on the Bio9 vent. Temperature anomalies of up to 1 ^oC and ~60 m in diameter above the Bio9, P, and Tica vents. We also observed elevated vertical current velocities around Bio9. Analysis of these data will likely provide important constraints on small-scale hydrothermally-induced circulation patterns above vent sites, and heat and mass flux at a fast-spreading MOR hydrothermal field.