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Springs have long been important for humans as a source of fresh water, especially in arid regions which have relatively little annual rainfall. Springs are driven out onto the surface by various natural forces, such as gravity and hydrostatic pressure. A spring produced by the emergence of geothermally heated groundwater is known as a hot spring.
Geysers also differ from non-eruptive hot springs in their subterranean structure: geysers have constrictions in their plumbing that creates pressure build-up. [ 10 ] As the geyser fills, the water at the top of the column cools off, but because of the narrowness of the channel, convective cooling of the water in the reservoir is impossible.
Hydrothermal circulation in the oceans is the passage of the water through mid-oceanic ridge systems.. The term includes both the circulation of the well-known, high-temperature vent waters near the ridge crests, and the much-lower-temperature, diffuse flow of water through sediments and buried basalts further from the ridge crests. [3]
For example, a vent fluid with a 2.24 wt. % NaCl salinity has the critical point at 400 °C (752 °F) and 280.5 bars. Thus, water emerging from the hottest parts of some hydrothermal vents can be a supercritical fluid, possessing physical properties between those of a gas and those of a liquid. [7] [8]
Hot spring water often contains large amounts of dissolved minerals. The chemistry of hot springs ranges from acid sulfate springs with a pH as low as 0.8, to alkaline chloride springs saturated with silica, to bicarbonate springs saturated with carbon dioxide and carbonate minerals. Some springs also contain abundant dissolved iron.
Wind-induced upwelling is generated by temperature differences between the warm, light air above the land and the cooler denser air over the sea. In temperate latitudes , the temperature contrast is greatly seasonably variable, creating periods of strong upwelling in the spring and summer, to weak or no upwelling in the winter.
Evidence has shown that eddy pumping-induced upwelling and downwelling may play a significant role in shaping the way that carbon is stored in the ocean. Despite the fact that research in this field is only developing recently, first results show that eddies contribute less than 5% of the total annual export of phytoplankton to the ocean interior.
In the period between 1967 and 2000 the decrease in oxygen concentration in the shallow waters, between 0 and 300 meters, was 10 times faster in the coastal ocean compared to the open ocean. [12] This has led to an increase of hypoxic zones , which can lead to a change in behaviour of the aquatic flora and fauna.