Measuring fluid flow and heat output in seafloor hydrothermal environments

Abstract

We review techniques for measuring fluid flow and advective heat output from seafloor hydrothermal systems and describe new anemometer and turbine flowmeter devices we have designed, built, calibrated, and tested. These devices allow measuring fluid velocity at high‐ and low‐temperature focused and diffuse discharge sites at oceanic spreading centers. The devices perform at ocean floor depths and black smoker temperatures and can be used to measure flow rates ranging over 2 orders of magnitude. Flow velocity is determined from the rotation rate of the rotor blades or paddle assembly. These devices have an open bearing design that eliminates clogging by particles or chemical precipitates as the fluid passes by the rotors. The devices are compact and lightweight enough for deployment from either an occupied or remotely operated submersible. The measured flow rates can be used in conjunction with vent temperature or geochemical measurements to obtain heat outputs or geochemical fluxes from both vent chimneys and diffuse flow regions. The devices have been tested on 30 Alvin dives on the Juan de Fuca Ridge and 3 Jason dives on the East Pacific Rise (EPR). We measured an anomalously low entrainment coefficient (0.064) and report 104 new measurements over a wide range of discharge temperatures (5°–363°C), velocities (2–199 cm/s), and depths (1517–2511 m). These include the first advective heat output measurements at the High Rise vent field and the first direct fluid flow measurement at Middle Valley. Our data suggest that black smoker heat output at the Main Endeavour vent field may have declined since 1994 and that after the 2005–2006 eruption, the high‐temperature advective flow at the EPR 9°50′N field may have become more channelized, predominately discharging through the Bio 9 structure. We also report 16 measurements on 10 Alvin dives and 2 Jason dives with flow meters that predate devices described in this work and were used in the process of their development. This includes the first advective measurements in the Lau Basin and at the EPR 9°39.5′N. We discuss potential error sources and how they may affect the accuracy of measurements by our devices and other devices. In particular, we use the turbulent plume theory to evaluate the effect of entrainment of ambient seawater.

Near‐vent chemical processes in a hydrothermal plume: Insights from an integrated study of the Endeavour segment

“…Averaging all along axis, temperature measurements ( Figure 2) in the 1900-2100 m depth range gives an average temperature anomaly of 0.0438C, similar to previous measurements [e.g., Baker and Massoth, 1987;Thomson et al, 1992;Kellogg and McDuff, 2010]. Based on published data, black smoker vent fluid temperatures at Endeavour are between 300 and 3808C [Butterfield et al, 1994;Seyfried et al, 2003;Bao et al, 2008;Lin et al, 2016;Germanovich et al, 2015]. A single vent in the Main Endeavour field has been monitored through the ONC cabled observatory and has maintained a temperature of 333 6 28C (1r) over a 6 year interval (September 2010 to July 2016; data at http://dmas.uvic.ca/DataSearch) consistent with the published vent fluid temperatures.…”

Depth‐Dependent Permeability and Heat Output at Basalt‐Hosted Hydrothermal Systems Across Mid‐Ocean Ridge Spreading Rates

“…Note that the velocity perturbation at the seafloor ( ) is of particular interest since it can be measured by seafloor instruments such as a direct flow meter (e.g., Germanovich et al, ) or camera systems that use image analysis methods (e.g., Crone et al, ; Mittelstaedt et al, ). It is expressed as: …”

A fault‐driven circulation model for the Lost City Hydrothermal Field

“…The heat output obtained from equation (7) is much less than observed at high-temperature hydrothermal systems at mid-ocean ridges, which is typically~100 MW [e.g., Lowell et al, 2013]. The predicted estimates Geophysical Research Letters 10.1002/2016GL072326 of mass flow and heat output at LCHF could be tested by direct measurement using flow meters and temperature probes deployed from a human-occupied vehicle or remotely operated vehicle or other devices [e.g., Germanovich et al, 2015].…”