Tidal variability of salinity and velocity fields related to intense point‐source submarine groundwater discharges into the coastal ocean

Abstract

Velocity and hydrography measurements were used to determine the tidal variability and detailed structure of an intense (< 43,200 m 3 d 21 ) point-source submarine groundwater discharge from a spring located in the coastal ocean of the Yucatá n 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 21 ambient horizontal flow and by the < 40u 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 21 vertical flows at low tides and , 0.05 m s 21 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.

Tidal variations of turbulence at a spring discharging to a tropical estuary

“…During the highest tidal elevation, bottom temperature decreased and the horizontal mean flow reversed with respect to that observed during low tide, indicating that the hydrostatic pressure inhibited groundwater discharge. Although no negative values of vertical mean velocity component were observed, seawater inflow into the aquifer could be expected when pressure in the karst cavity becomes lower than the pressure exerted by the tide [Valle-Levinson et al, 2011].…”

“…The system being studied is located in karst terrain in the Yucatan peninsula in Mexico. This type of terrain is found widespread throughout the world and is characterized by limestone or dolomite bedrock, composed predominantly by calcium carbonate that can be dissolved to form caves and subterranean conduits [Valle-Levinson et al, 2011]. The conduits allow submarine groundwater to discharge directly into the ocean or estuary.…”

“…The conduits allow submarine groundwater to discharge directly into the ocean or estuary. The intensity of discharge coming from these systems is determined by differences in pressure in the karst cavity and that exerted by tide at the outflow site [e.g., Kim and Hwang, 2002;Taniguchi, 2002;Valle-Levinson et al, 2011]. These studies have mainly focused on tidal influence on seepage discharges, which increase at low tides.…”

“…This indicates that there are other factors influencing TKEP such as the hydraulic head, or piezometric gradient between sea level and water table, the porosity (or conductivity) of the karst cavity, and the actual buoyancy of the discharge [Valle-Levinson et al, 2011]. These factors must be taken into account in future studies that should also incorporate hydrological components.…”

Coastal Karst Groundwater in the Mediterranean: A Resource to Be Preferably Exploited Onshore, Not from Karst Submarine Springs

“…Among them, karst submarine springs (KSMS) are the most common and are known everywhere offshore carbonate rock formations, especially along the coasts of Florida (see e.g., [9,10]) and of Yucatan [11,12]. However according to [8], more than 90% of them occur along the Mediterranean coasts ( Figure 1) where the most spectacular ones are described.…”