Smokers under stress: new insights into the tectonic, magmatic and oceanic modulation of hydrothermal discharge at mid-ocean ridges

Abstract

Hydrothermal systems along mid-ocean ridges (MORs) are a crucial interface between Earth’s deep interior, the seafloor, and the overlying ocean. Although hydrothermal systems are typically thought of as steady-state flow environments, field-based observations indicate that flow rates and temperatures are highly variable over a wide range of spatial and temporal scales. These observations show that flow systems respond to sub-surface processes such as earthquakes, magmatic activity, dissolution/precipitation of fluid minerals, and tidal loading of the oceanic crust and sediments. This variability in subsurface phenomena associated with seafloor flow systems directly impacts both the transfer of heat and matter and therefore, productivity of associated hydrothermal ecosystems. Moving beyond an empirical assessment, however, remains challenging because a complete theoretical framework relating tectonic and magmatic fluctuations to hydrothermal output is currently lacking. Understanding the relationship between tectonic- and magma-induced stress and strain transients, crustal permeability, and the thermo-chemical state of hydrothermal fluids before, during and after an earthquake and magmatic emplacement event is particularly crucial. To address this issue, we curated time series of vent temperatures at the Loki’s Castle and EPR 9°50'N hydrothermal systems, and analyzed them alongside microseismicity catalogs, intermittent sampling of vent fluid chemistry, and a large body of geological, geophysical and biological observations, including proxies for crustal permeability. Results suggest that both short-term (sec to hours) and long-term (decadal) variability in hydrothermal venting is controlled by fluctuations in the permeability field of the underlying crust, which can itself be related to changes in the crustal stress regime. We capture co-seismic, dike-induced and inter-eruptions changes in the fluid flow records indicating tectonic and magmatic control on hydrothermal vent temperature and flow discharge. Using simple analytical models for hydrothermal discharge temperature, elastic stress changes, and permeability-stress relations, we argue that temperature fluctuations can result from changes in permeability caused by either passing seismic waves, magmatic reservoir inflation (/deflation), or intrusions. Our observations and models further imply that short- and long-term fluctuations in tectonic and magmatic activity can modulate hydrothermal output, with potential consequences for deep sea ecosystems. This methodology has the potential to track tectonic and magmatic induced deformation transients in the sub-seafloor from hydrothermal flow records.