Acoustic and In‐Situ Observations of Deep Seafloor Hydrothermal Discharge: An OOI Cabled Array ASHES Vent Field Case Study

Abstract

Along mid-ocean ridges and atop seamounts, geothermally heated and chemically altered seawater exits near the seafloor as discharge of hydrothermal fluids that transfer considerable amounts of heat and chemicals from the earth's interior to the overlying ocean (German et al., 2016; German & Von Damm, 2006). Within a vent field, hydrothermal venting often occurs in a variety of settings, ranging from focused flows (i.e., plumes) issuing from individual vents (e.g., black smokers) to diffuse flows from the sides of sulfide mounds, isolated cracks, lava tubes, and areas of permeable seafloor (

Sonar Observation of Heat Flux of Diffuse Hydrothermal Flows

“…This article extends the work reported in Xu et al. (2021) with the goal of quantifying the heat output from a portion of the ASHES Vent Field on Axial Seamount. The earlier article gives references to the literature as well as a detailed description of the data provided by the Cabled Observatory Vent Imaging Sonar (COVIS).…”

“…(2021). The sources of warm water at the two sites are diverse, with small, nearly point sources evident in video observation, wider sources due to dispersal by tube worm bushes, and even possible sheet‐like sources emanating from cracks (Xu et al., 2021). Close video inspection at some sites showed a few focused flows emitting slightly turbid water.…”

“…A 3D single‐point velocity meter deployed at the International District hydrothermal vent field on the southeastern side of Axial's caldera, approximately 30 m distant from ASHES, has provided times series of transverse current components at a height of approximately 1 m. The measured current components oscillate with typical amplitudes of about 1 cm/s with excursions approaching and sometimes exceeding 2 cm/s. The effect of current on diffuse‐flow activity at ASHES is discussed in (Xu et al., 2021). It is of particular importance that the standard deviation of temperature is very nearly equal to the mean anomaly.…”

“…It was not possible to obtain contemporaneous thermistor and sonar data, and the temporal variability of diffuse‐flow activity at this site introduces uncertainty in the comparison. We have not attempted to quantify this uncertainty, but the sonar observations reported in (Xu et al., 2021) indicate that most of the variation is due to current variation, with little long‐term variation. This prompts temporal averaging of the ping‐to‐ping correlation as discussed below.…”

“…COVIS was installed in July 2018 on the Ocean Observatories Initiative (OOI) Regional Cabled Array at the ASHES vent field on Axial Seamount. The resulting data have been used to obtain time series of diffuse-flow activity, primarily through estimation of the area of diffuse flow regions (Xu et al, 2021). The present effort seeks to extend this work and that of Jackson et al (2017), to provide a method for sonar observation of the heat output of diffuse flows.…”