Global synthesis and analysis of deep-sea hydrothermal time-series data: Toward a characterization of the outflow dynamics

Abstract:

Time-series records of mid-ocean ridge hydrothermal fluid properties and flow rates have the potential to help constrain the hydrogeology, subsurface circulation patterns, heat, mass, and chemical fluxes, and habitat conditions within young oceanic crust. This potential has motivated a concerted international effort to acquire such records from a variety of geologically distinct vent fields at numerous locations along the mid-ocean ridge system. However up until now, the global database has not been systematically explored. These records have only been analyzed in a piecemeal fashion, which is problematic because hydrothermal time-series records from individual sites typically exhibit enigmatic modes of episodic and periodic variability that are difficult to interpret in isolation. In this study, we conduct a systematic analysis of the extant set of hydrothermal time-series records from several mid-ocean ridge sites where observatory-style experiments have been conducted (including, LSHF, TAG, EPR 9°50’N and MEF).

We show that most temperature records, regardless of location or geological setting, display systematic tide-related variability, with the strongest signal at the principal semidiurnal tidal periods (M2, S2, N2 and K2). Cross-spectral multi-taper methods applied to the temperature and bottom pressure records reveal robust phase relationships, particularly for the high-temperature, black-smoker records, as predicted by poroelastic theory. These results suggest that tidal pressures diffusely propagate through the formation, perturbing fluid velocities and temperatures, resulting in phase lags between the seafloor loading and the exit-fluid temperatures. Here, we use multi-layer analytical and numerical models to constrain the subseafloor permeability, skin depth, and Darcy velocities required to explain the phase lag observations.