Øresund, also spelled Öresund, and more commonly known in English as the Sound (Danish: Øresund, pronounced [ˈøːɐsɔnˀ]; Swedish: Öresund, pronounced [œrəˈsɵnːd]) and locally in both countries called just Sundet, is the strait that separates the Danish island Zealand from the southern Swedish province of Scania. Its width is 4 kilometres (2.5 mi) at the narrowest point between Kronborg Castle at Helsingør in Denmark, and the northern harbour of Helsingborg in Scania. The strait has also lent its name to the Øresund Region of 3.8 million inhabitants on both the Danish and Swedish sides. Since this area covers all of Denmark east of Great Belt and all of Scania, its area of more than 20,000 square kilometres (7,700 sq mi) doesn't give a full picture of the very high population density around the sea. A more narrow area, including the four Danish provinces (Danish: Landsdel) Byen København, København omegn, Nordsjælland and Østsjælland together with the 17 (out of 33 possible) Scanian municipalities which either are located by the Øresund, or which border to a such municipality, roughly the population which lives no more than 30 km from the shores of Øresund. Together they have an area of 6,000 square kilometres with 2.9 million inhabitants.
The Øresund Bridge (which includes a 3 km tunnel) between the Danish capital Copenhagen and the largest city of Scania, Malmö, was inaugurated on 1 July 2000 by Queen Margrethe II of Denmark and King Carl XVI Gustaf of Sweden. However the HH Ferry route, between Helsingør, Zealand, Denmark and Helsingborg, Scania, Sweden, in the northern part of Øresund, where it is narrowest, remains one of the world's busiest international ferry routes with more than 70 departures from each harbour per day,
It is first attested on a Danish runestone from about 950, where it is written ura suti, i.e. Ø̄rasundi (in the dative case). The West Norse and Icelandic form is Eyrarsund. The first part of the word is øre (Old Norse eyra) "ear", and the second part is sund, i.e. strait or narrow seaway. The Øresund is so called because øre "ear" is a term for a small piece of land between two waters, and the Øresund stretches between two such "ears", from Siellands Øre to Skan-Øre.
According to linguist Ole Lauridsen in the Danish radio program Sproghjørnet the first part "øre" comes from an antiquated term for a beach consisting of gravel and pebbles. Compare with the Danish city name Korsør, where the coast does not form an "ear". The "ear" interpretation is a later rationale to explain the name.  
The northern boundary between Øresund and Cattegat is a line which goes from Gilleleje at Zealand's northern peak to the westernmost point of Kullaberg at the smaller peninsula north of Helsingborg, known as Kullahalvön. In the south, the boundary towards the Baltic Sea starts at Stevns Klint, at the westernmost peak of the peninsula just south of Køge Bay, Stevns Peninsula to Falsterbo at the Falsterbo peninsula. Its eastern boundary is uncomplicated, the Swedish coast line, but to the west there is a question whether Amager is to be considered to be the largest island in Øresund, or if it's a part of Zealand. Amager has eight connections with Zealand (two street bridges, a road bridge, a motorway bridge, a dual track railway tunnel, an underground metro and a bicykle bridge) as well as a combined motorway and dual track railway to Scania and Sweden. Amager also has a population of 180.000, but it is still usually regarded to be an island.
Streams, animals and salinity
Øresund, like other Danish and Danish-German straits, is at the border between oceanic salt water (which has a salinity of more than 30 PSU) and less salty Baltic Sea. As Cattegat in the north has almost oceanic conditions and the Baltic Sea (6–7 PSU, in its main basin) has brackish water, Øresund's water conditions are rather unusual. The streams are very complex, but the surface stream is often northbound (from the Baltic Sea) which gives a lower surface salinity, though streams can change from one day to another. The average surface salinity is about 10–12 PSU in the southern part but above 20 PSU north of Helsingør.
Near the seafloor, conditions are more stable and salinity is always oceanic (above 30 PSU) below a certain depth that varies between 10 and 15 metres. In the southern part, however, the depth is 5–6 metres (outside the rather narrow waterways Drogden and Flintrännan), and this is the definite border of oceanic salt water, therefore also a border for many maritime species of animals. In the central Baltic Sea only 52 known salt-water species reside, compared to around 1500 in the North Sea. Close to 600 species are known to exist in at least some part of Øresund. Well-known examples, for which the bottom salinity makes a distinct breeding border, include lobster, small crabs (Carcinus maenas), several species of flatfish and the burning jellyfish (Cyanea article); the latter can sometimes drift into the southwest Baltic sea, but it cannot reproduce there.
The daily tides exist, but the lunar attraction cannot force much water to move from west to east or vice versa, in narrow waters where the current is either northbound or southbound. So, not much of the difference in water levels in Øresund is due to daily tides, and other circumstances "hide" the little tide that still remains. The current has a much stronger effect on the water level, compared to the tide, but strong winds may also affect the water level. During exceptional conditions, such as storms and hurricanes, oceanic water may suddenly flow on all depths into the Baltic Sea. Such events give depths in southern Baltic Sea new fresh water, with higher salinity, which makes it possible for especially cod to breed in the Baltic Sea. If no such inflow of oceanic water to the Baltic Sea occurs for around a decade, the breeding of cod becomes endangered.
Political control of Øresund has been an important issue in Danish and Swedish history. Denmark maintained military control with the coastal fortress of Kronborg at Elsinore on the west side and Kärnan at Helsingborg on the east, until the eastern shore was ceded to Sweden in 1658, based on the Treaty of Roskilde. Both fortresses are located where the strait is 4 kilometres wide.
In 1429, King Eric of Pomerania introduced the Sound Dues which remained in effect for more than four centuries, until 1857. Transitory dues on the use of waterways, roads, bridges and crossings were then an accepted way of taxing which could constitute a great part of a state's income. The Strait Dues remained the most important source of income for the Danish Crown for several centuries, thus making Danish kings relatively independent of Denmark's Privy Council and aristocracy.
A fixed connection was opened across the strait in 2000, the Øresund Bridge.
- Amager (western part is artificial enlargement from Øresund, or from Kalvebodene more precicely)
- Peberholm – an artificial island
- Middelgrundsfortet – an artificial island
- Flakfortet – an artificial island
- Ven (Hven in Danish)
- Gråen – an artificial island outside port of Landskrona (enlargements from Øresund in the 17th and 20th centuries)
- "Bælthavet og Sundet" (in Danish). Danish Meteorological Institute. Retrieved 30 March 2013.
- Danish side province areas - http://www.dst.dk/da/Statistik/emner/areal/areal-for-kommuner-og-regioner.aspx - these four provinces have a total area of 2.769 km2; Danish side population - below a population pyramide at - http://www.dst.dk/da/Statistik/emner/befolkning-og-befolkningsfremskrivning/folketal.aspx - 4th quarter 2014 (1 October 2014), was the aggregated population 1.967.934. The area equals Danish region Hovedstaden without the remote Baltic island Bornholm but including the cities south-western suburbs (Østsjælland). For the area and population of the Swedish side, 17 municipalities which are either located by the Øresund or border a municipality which does, please see Scania#Population, there is a thorough table based at Swedish statistic bureau SCB figures of areas and population. At 3,201 km² live 925,982 people. Conclusion: around both sides of Øresund, in an area of 5,970 km², live 2,893,916 people, by far the largest metropolitan area in Scandinavia. Although the area has no political functions (which it shares with the larger Øresund Region), the figure illustrates the high population density around Øresund, and does so in a better way than what Øresund Region does
- Gluver, Henrik; Dan Olsen (1998). "2.7 Øresund Bridge, Denmark-Sweden". Ship Collision Analysis. Rotterdam: A. A. Balkema. ISBN 90-5410-962-9.
Øresund (the Strait) is, like the Great Belt, an important water way for the international ship traffic between the North Sea and the Baltic Sea.
- at http://www.scandlines.se/tider-och-priser/tidtabell.aspx press "Tidtabell 2 jan-31 maj 2015", PDF file.
- Danmarks runeindskrifter no. 117.
- Ordbog over det danske Sprog "et smalt stykke land imellem to store vande, fra et land til andet. [...] Øresund kaldes saaledes fordi det begynder ved Siellands Øre og ved Øster-Søen ved et Øre, som er Skan-Øre. "
-  Radio clip in Danish discussing the origin of the name Øresund.
- Katlev, Jan (2000). Politikens Etymologisk Ordbog. Copenhagen: Politikens Forlag. p. 694. ISBN 87-567-6200-3.
af ør, øre 'gruset strandbred' + sund.
- Menefee, Samuel Pyeatt, "The Strait Dues and Access to the Baltic Sea" in Renate Platzoder and Philomene Verlaan (eds.), The Baltic Sea: New Developments in National Policies and International Co-Operation (1996), pp. 101–32.
|Wikimedia Commons has media related to Oresund.|
- Øresunddirekt – Official public information site for the inhabitants of the Øresund region
- Øresund Trends – An official public information site with up-to-date information on the region, available in English
- Øresundstid – The History of the Øresund Region (English) (Swedish) (Danish)