Subtidal Water Exchange between Caimanero Lagoon and the Adjacent Inner Shelf, West Coast of México: Seasonal Circulation Pattern and Its Implication

Abstract

Current and sea level measurement data from three ∼75-day deployments at the inlet and the inner shelf of the Caimanero Lagoon were used with data of wind, evaporation, and river discharge to describe the seasonal subtidal exchange in the shelf–lagoon system. During the dry season, the estuary mouths were partially closed by the littoral drift; however, at the shelf, the oceanic mean sea level rose because of a steric response to advection of warm water on the continental shelf. In addition, the annual oscillation reached its maximum in August. Both events induced a barotropic flow of sea water lagoonward. Dry season currents were 8–10 cm s−1. During the wet season, estuary mouths were reopened as result of river discharges, which caused a barotropic flow toward the sea. During this period, river transport occurred at times scales of 2∼10 days; the magnitude of the transport was larger than that caused by the sea level. Wet season currents were 10–40 cm s−1. The observation that this barotropic flow occurred during both seasons is the principal discovery of this work and demonstrates that the barotropic motion is an important component of net circulation. The shelf circulation during the dry season showed a two layer system with a cross-shore flow toward the shore with velocities of about ±5–10 cm s−1, while longshore current flow was southward on the surface and northward (up gulf) below 15 m. This current pattern apparently contributes to the transport of shrimp larvae to the shore, acting as the driving mechanism, knowing that shrimp postlarvae in the area appear in June and disappear in middle August. During the wet season, on the other hand, inner shelf circulation shows currents of mainly barotropic flow that respond to hurricanes with maximum velocities of about 40 cm s−1.