Tidal variability of salinity and velocity fields related to intense point-source submarine groundwater discharges into the coastal ocean
Limnol. Oceanogr., 56(4), 2011, 1213-1224 | DOI: 10.4319/lo.2011.56.4.1213
ABSTRACT: Velocity and hydrography measurements were used to determine the tidal variability and detailed structure of an intense (~ 43,200 m3 d−1) point-source submarine groundwater discharge from a spring located in the coastal ocean of the Yucatán peninsula, Mexico. Measurements were obtained during a dry season with a combination of towed, profiling, and fixed instrumentation. The goal of these observations was to understand the effects of tides on the velocity and salinity structure of the water column that determine mixing and dispersion processes at spatial scales from meters to kilometers. Tidally averaged flows were characterized by an upward jet flanked by asymmetric downdrafts. The asymmetry was caused by a ~ 0.1 m s−1 ambient horizontal flow and by the ~ 40° angle (relative to the vertical) of discharge. The spatially averaged salinity distributions exhibited lowest values at low tides and highest values at high tides. This was attributed to tidal variations of hydrostatic pressure acting on the spring outflow, which allowed ∼1 m s−1 vertical flows at low tides and < 0.05 m s−1 vertical velocities at high tides. The vertical momentum balance consisted of upward accelerations produced by buoyancy and inertia from the spring and downward accelerations from gravity. On the basis of this balance and of energetic considerations, the vertical extent of the spring discharge likely depends on the density contrast between ambient and discharge waters (buoyancy forces), the upward speed of the spring (inertia forces), and the depth of the water column (hydrostatic pressure force), all of which vary with tides.