COVIS Detects Interconnections Between Atmospheric, Oceanic and Geologic systems at a Deep Sea Hydrothermal Vent

Abstract:

COVIS (Cabled Observatory Vent Imaging Sonar) is an innovative sonar system designed to quantitatively monitor focused and diffuse flows from deep-sea hydrothermal vent clusters. From 9/2010 to 9/2015, COVIS was connected to the NEPTUNE observatory at Grotto vent in the Main Endeavour Field, JdFR. COVIS monitored plumes and diffuse discharge by transmitting high-frequency (200-400 kHz), pulsed acoustic waves and recording the backscattered signals to yield time series of plume heat and volume transports, plume bending, and diffuse flow area.

Temporal variations indicate the rate of hydrothermal plume mixing with the ambient seawater increases with the magnitude of ocean currents. Such current-driven entrainment links the dynamics of a deep-sea hydrothermal plume with oceanic and atmospheric processes. We estimate the direction and relative amplitude of the local bottom currents from the bending angles of the plumes. A comparison with currents from an ADCP (~80 m south of Grotto) reveals significant complexity in the mean bottom flow structure within a hydrothermal vent field. Diffuse flow area, temperature, and faunal densities vary periodically reflecting some combination of tidal pressure and current interactions.

The heat transport time series suggests the heat source driving the plume remained relatively steady for 41 months. Local seismic data reveals that increased heat transport in 2000 followed seismic events in 1999 and 2000 and the steady heat flux from 10/2011 to 2/2015 coincided with quiescent seismicity. Such a correlation points to the close linkage of a seafloor hydrothermal system with geological processes.

These findings demonstrate the intimate interconnections of seafloor hydrothermal systems with processes spanning the Earth's interior to the sea surface. Further, they (and the time-series acquired by COVIS) testify to the effectiveness and robustness of employing an acoustic-imaging sonar for long-term monitoring of a seafloor hydrothermal system.