marées

Marées, or tides, are the regular rise and fall of sea level along coastlines caused primarily by the gravitational forces exerted by the Moon and the Sun on the Earth's oceans. The Moon’s gravity creates bulges on the near and far sides of the Earth; as the planet rotates, shorelines move into and out of these bulges, producing high and low tides. The Sun’s gravity also contributes to the effect, though it is less strong than the Moon’s. The resulting tides depend on the relative positions of the Moon and Sun, the alignment during lunar phases, and the geometry of the coastline and seafloor.

Most coastlines experience two high tides and two low tides each lunar day, a pattern called semidiurnal. Some areas have only one high and one low tide per day (diurnal), while others show mixed tides with varying heights. The tidal range—the difference between high and low water—varies with location, season, and ocean depth. When the Sun, Moon, and Earth align during full or new moons, tidal ranges are larger, producing spring tides; when the Sun and Moon are at right angles, the tides are smaller, producing neap tides.

Tides influence coastal processes, navigation, and human activities. They drive coastal erosion, shape estuaries and intertidal ecosystems, and affect sediment transport. Tidal energy is explored as a renewable resource in some regions. Scientists monitor tides with tide gauges and predict them using models that decompose the signal into tidal constituents.