The response of two-phase hydrothermal systems to changing magmatic heat input at mid-ocean ridges

We develop numerical simulations of two-phase flow in a NaCl-H2O fluid subject to time varying basal heat flux boundary conditions in order to understand the response of hydrothermal vent temperature and salinity to changing magmatic heat input. The results show that periodic changes in basal heat input on a time scale of several years will not be detected in a continuous time series record of temperature measurements. Fluctuations in vent salinity may be recorded, however. For models with monotonic decay of the magmatic heat flux, a decline in vent temperature may not be observed for several years; however, once single phase conditions are established at the base of the system, a pulse of brine-derived fluid is expected to appear at the surface, followed by a gradual decline of salinity to the seawater value. The pulse of brine salinity is expected to occur before an observed decline in vent temperature. Observed rapid changes in vent temperature and salinity associated with either eruptive or non-eruptive magmatic events are not likely a result of changes in basal heat flux.