microtidal

Microtidal is a term used in coastal and marine science to describe tidal regimes with a small vertical range. In common classifications, microtidal coasts have a tidal range of less than 2 meters, while mesotidal and macrotidal regimes have higher amplitudes.

These conditions occur in enclosed or semi-enclosed seas and along broad, shallow shelves where bathymetry and basin geometry damp tidal energy. Friction, reduced open-ocean forcing, and the absence of strong resonance limit the tidal response.

Its characteristics include weak tidal currents and relatively small elevations of high and low water. Tidal constituents may be diurnal or semidiurnal, but amplitudes are modest. Tidal flats and estuarine channels exist but are less dynamic, and sediment transport is often governed more by river inflows, wind waves, and longshore processes than by tides. Exchange between basins occurs more slowly, leading to longer residence times in lagoons and bays.

Implications for ecosystems and human activity include more pronounced salinity and temperature gradients in some estuaries, reduced tidal mixing, and lower potential for tidal energy extraction. Coastal morphodynamics in microtidal regions tend toward gentle shorelines with gradual depth increases.

Examples of microtidal environments include the Baltic Sea, the Black Sea, parts of the Mediterranean, and other enclosed or semi-enclosed seas where tidal ranges are typically well under 1 meter to a couple of meters.