Tides and currents in a two-inlet coastal lagoon: Laguna de Términos, México

Abstract

Laguna de Términos, the largest coastal lagoon in México with a surface area of 2500 km2, is connected to the Gulf of México via two major ocean inlets. Fifty percent of the lagoon water volume is renewed every 9 days, mostly as a function of tidal exchange. Two month-long field measurement periods indicate that the tide is mostly mixed, mainly diurnal with a mean range of 0.3 m. In the tidal inlets, peak currents measure 1.3 m s-1, and are mostly mixed, mainly semidiurnal. Processes at tidal frequencies explain approximately 70% of the water level variability; and approximately 95 and 65% of the current variability in the inlets and inside the lagoon, respectively. The remaining low-frequency variability is attributed to meteorological forcing. The lagoon receives a mean freshwater discharge of 378 m3 s-1 from three rivers, but the inlets are still well mixed with only a weak gravitational circulation in one of the inlets. Measurements from a single tidal cycle in March 1995 indicate that the net fluxes of salt and suspended sediment during this period were directed towards the Gulf of México in both inlets, mostly as a result of advective dominance opposed by lagoon-directed tidal dispersion and vertical shear fluxes.