A preliminary 1‐D model investigation of tidal variations of temperature and chlorinity at the Grotto mound, Endeavour Segment, Juan de Fuca Ridge

Abstract

Tidal oscillations of venting temperature and chlorinity have been observed in the long-term time series data recorded by the Benthic and Resistivity Sensors (BARS) at the Grotto mound on the Juan de Fuca Ridge. In this study, we use a one-dimensional two-layer poroelastic model to conduct a preliminary investigation of three hypothetical scenarios in which seafloor tidal loading can modulate the venting temperature and chlorinity at Grotto through the mechanisms of subsurface tidal mixing and/or subsurface tidal pumping. For the first scenario, our results demonstrate that it is unlikely for subsurface tidal mixing to cause coupled tidal oscillations in venting temperature and chlorinity of the observed amplitudes. For the second scenario, the model results suggest that it is plausible that the tidal oscillations in venting temperature and chlorinity are decoupled with the former caused by subsurface tidal pumping and the latter caused by subsurface tidal mixing, although the mixing depth is not well constrained. For the third scenario, our results suggest that it is plausible for subsurface tidal pumping to cause coupled tidal oscillations in venting temperature and chlorinity. In this case, the observed tidal phase lag between venting temperature and chlorinity is close to the poroelastic model prediction if brine storage occurs throughout the upflow zone under the premise that layers 2A and 2B have similar crustal permeabilities. However, the predicted phase lag is poorly constrained if brine storage is limited to layer 2B as would be expected when its crustal permeability is much smaller than that of layer 2A.

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

“…The buoyant plumes issuing from seafloor hydrothermal vents are strong sound reflectors primarily due to the presence of intense temperature fluctuations produced by the turbulent mixing between high-temperature vent fluids and cold seawater (Xu et al, 2017a). The strong sound reflection from the plume presents an opportunity for estimating its thermal properties such as temperature anomalies and heat flux from measured acoustic backscatter through inversion.…”

“…The strong sound reflection from the plume presents an opportunity for estimating its thermal properties such as temperature anomalies and heat flux from measured acoustic backscatter through inversion. Under this goal, we have developed a forward model based on the acoustic formulas presented by Xu et al (2017a) using the plume properties derived from an integral plume model as inputs .…”

“…For the 400 kHz transmission in COVIS Imaging mode, this length scale is ∼2 mm. Assuming the turbulence on this scale is homogeneous and isotropic, the volume backscattering cross-section ( b ), can be estimated theoretically as a function of the variance of the temperature field using the formulas given in Xu et al (2017a) as follows: 1.42 10 C is the thermal expansion coefficient; Φ t (K) is the isotropic, 3D spectrum for temperature and  Κ 2k is the Bragg wavenumber for backscatter. The expressions of Φ t for turbulent temperature structures in the inertial-convective subrange and the viscous-convective subrange are given in Equations 3 and 4, respectively (Ross, 2003),…”

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

“…We begin by presenting a 1-D model aimed at predicting the perturbations of the pressure, temperature, and velocity of fluids moving through a layered oceanic upper crust subjected to periodic fluctuations in seafloor pressure, imposed by tidal cycles (Figure 1). Our model is a generalization of the homogeneous permeability model of Jupp and Schulz (2004), and it extends the preliminary approach of Xu et al (2017), who derived twolayer solutions for the phase lag of vent temperatures relative to tides but did not completely analyze the system behavior and solution space.…”

Anhydrite‐Assisted Hydrothermal Metal Transport to the Ocean Floor—Insights From Thermo‐Hydro‐Chemical Modeling

“…One key parameter controlling hydrothermal flow pattern and, thereby, hydrothermal mass and energy fluxes is permeability. Permeability versus depth profiles can be inferred from laboratory and in situ measurements in bore holes and on drill cores (Becker & Fisher, 2000;Fisher, 1998), seismic data (Carlson, 2014;Ingebritsen & Manning, 2010), hydrothermal heat fluxes (Lowell & Germanovich, 1994;Wilcock & McNabb, 1996), and the poro-elastic response to tidal phase shifts (Barreyre et al, 2014(Barreyre et al, , 2018Barreyre & Sohn, 2016;Crone et al, 2011;Xu et al, 2017). All of these data sets point to high permeabilities between 10 −14 and 10 −12 m 2 (and sometimes up to 10 −10 m 2 ) in the oceanic layer 2A decreasing exponentially with depth to values of 10 −16 to 10 −14 m 2 in layer 2B and below-with some estimates based on hydrothermal heat fluxes and tidal phase shifts giving higher values of up to approx.…”