Ocean science news, explainers, and statistics covering marine environments, currents, climate, coasts, seafloor research, and the changing global ocean.
A barrier island is a long, narrow body of sand that runs roughly parallel to a mainland coast and is separated from it by a bay, lagoon, marsh, or tidal creek. Waves, tides, wind and storms continually rearrange its sediment. The island acts as a mobile buffer that absorbs ocean energy before it reaches sheltered…
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Geologists classify estuaries into four major types according to how their basins formed: drowned river valleys, bar-built estuaries, tectonic estuaries and fjords. The shape inherited from sea-level rise, sediment movement, crustal motion or glaciers influences every later tide and current. The system describes origin rather than present-day water circulation. A fjord can behave like a…
Estuary salinity zones divide the transition from river water to seawater into named concentration ranges. In a common system, tidal fresh water is below 0.5 parts per thousand. Oligohaline water spans 0.5 to 5, mesohaline water 5 to 18, polyhaline water 18 to 30 and euhaline water approaches open-ocean salinity. The boundaries help scientists compare…
Seawater becomes denser as it cools or gains dissolved salt. It becomes less dense as it warms or is diluted by fresh water. Pressure compresses water slightly at depth, so an exact density calculation includes temperature, salinity and pressure together. The differences are modest, but gravity acts on entire water masses. Dense water tends to…
