Submarine source

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Meteogenic underwater sources emerge close to a receiving body of water and / or under water . These include: Subfluvial karst springs in rivers , subliminal karst springs in freshwater lakes and submarine karst springs in the coasts and shallow seawater sections

Submarine karst spring near Brela ( Biokovo )

Karst springs "under water"

Properties in the karst

Underwater springs initially represented ordinary springs, the fresh water of which emerges from karst areas at the end of extended paths (up to the size of caves ) . The waters of the karst springs collected in karstification-capable rock layers (more or less calcareous mountains). In long geological times, groundwater (from the interstices between pores and tectonically caused cracks / fissures / crevices) could expand into real underground waterways and then escape. The karstification processes regularly end, either on damming, loose or solid layers of rock or on a so-called “ groundwater receiving stream ”. The “receiving water” body of water can basically be a river, a lake or a sea.

Subfluvial karst spring

Landsat 8, 2015,
19 (sub-) fluvial karst springs , Upper Evrotas , Peloponnese

Karst springs that emerge near or in a flowing water are rarely documented in an easily accessible manner. A chain of 19 karst springs is documented, which arise on the right edge of the Polje -like "Pellana Basin" (between Taygetos and Parnonas mountains, southern Peloponnese ) in the bank area or even directly in the water of the Upper Evrotas . Four of these sources are great.

Sublime karst spring

Sublime karst springs, Lake Ohrid , Albania / Macedonia ( Grabensee )

Karst springs in still waters (freshwater lakes ) are also rarely documented. Such sources are documented from the Dinarides and its southern foothills in Albania , as well as from karstified southern Turkey ( Dumanli sublime karst spring ). The hydrogeologically ancient Lake Ohrid (up to 289 m deep freshwater lake, Albanian - Macedonian southern border) lies in a Pliocene rift basin . The amount of water in so-called subliminal "spring fields" and several very large so-called "feeder springs" on today's lake shore form a considerable part of the hydrological system of the inflowless lake. The water masses flow through karst water channels from the basin of the Macedonian Lake Prespa, which is only about 13 km away and 150 m higher .

Submarine karst spring

With high levels of karst water, meter-large, circular areas form on the surface of the sea , which are smoother and less rippled than the surrounding area. This clearly shows the emergence of fresh water (generally lower density than sea water, i.e. lighter) from a submarine karst spring.
Interest in this type of spring has increased since the end of the 20th century, primarily for three reasons: Increasing water demand, water shortage due to climatic changes, especially in metropolitan areas, which are not climatically favored anyway, and increased scientific, especially hydrogeological, interest based on knowledge the multiple chloride contamination and the " Messinian salinity crisis " that occurred several times .

Formation of submarine springs

Submarine sources are relatively common

If the water level of a groundwater receiving river rises and is ultimately higher than the outlet point, there is an underwater source . The changes in the height of sea water levels are attempted to be explained by various geological theories. There are two approaches to submarine Mediterranean sources. The sea level in the Mediterranean has risen by approx. 120 m since the last ice ages (late Pleistocene ), so that karst springs on Mediterranean coasts may have become submarine because polar ice layers melted and the sea level rose as a result. However, it can no longer be said for all Mediterranean sources that they probably became submarine in the Pleistocene. Findings in tectonics, the very young "plate tectonics", the discovery of particularly deep karst formation and lagoon-like deposits on the up to 2500 m deep Mediterranean floor make submarine karst springs several million years old conceivable.

Block diagram of the submarine karst springs of Port Miou ( fr: Exsurgence de Port-Miou Cassis , Marseille )
Submarine karst spring, Port Miou, southern France

The submarine source " fr: Exsurgence de Port Miou " near Marseille has been scientifically proven by measurements that it has a further corridor to a deep submarine karst source and that this deeper corridor is still not reached by dives at −223 m (as of 2015) . Multiple leaks, including deep ones, are now assumed for a number of Mediterranean sources. These deep outlets can no longer be explained by changes in sea level height of 120 m since the last ice age. Findings at Port Miou and other coastal and submarine springs in Croatia, France, Crete, Lebanon with deep tunnels, e.g. B. approx. 500 m in Almyros near Heraklion, Crete are therefore attributed to the "Messinian salinity crisis". According to this theory, which has now been considered secure, the Mediterranean water had completely evaporated apart from remains in the period of the late Miocene (5.96 to 5.33 Ma) (closure of the Strait of Gibraltar ).

Climate and karst springs

Scheme of karst spring types

There are permanent and temporary water-bearing submarine karst springs. Whether they pour their fresh water into the sea continuously or only periodically depends on the climatically-related precipitation times and amounts, which are very different in the neighboring Mediterranean countries. Permanent springs are characterized by the fact that the water pressure is always strong enough for a steady flow of fresh water to enter the sea. These springs are connected to a karst system, which has sufficient water resources or whose inflow area is sufficiently extensive so that sufficient water inflows prevail even in long dry periods.

Occurrence of submarine springs

Opened carbonate rock, worldwide
Croatian karst area Vrulja Bay, near Brela , Biokovo

Over about 20% of the ice-free land areas worldwide are exposed carbonate rocks. Many karst areas are directly adjacent to the sea. It is therefore likely that there are submarine karst springs on many sea coasts around the world. However, most of the karst springs, near the coast or submarine, are located in the Mediterranean.

The not very deep Adriatic borders the Dinarides in the east, which are consistently strongly karstified and have a semi-arid climate. There are more than 300 coastal and submarine karst springs here. Permanent springs usually occur near the coast. However, there are some smaller submarine springs near larger islands (such as at Cres ). Temporary water-bearing sources come from z. B. in the vicinity of the Croatian Adriatic islands and near the Pelješac peninsula, but they also occur in low coastal areas. In dry periods, seawater enters the peripheral part of the karst river system (submarine Estavelle ).

On the Adriatic coast, most of the permanent springs exist at the foot of large mountains (such as the Učka , Velebit , Biokovo or the Konavle area ). The karst waterways end z. B. in the Bay of Bakar (southeast of Rijeka ), the Velebit Canal ( Kvarner Bay ), the "Bay of Kaštela" (near Split ), the "Vrulja Bay" north of Brela (Biokovo), in the Bay of Kotor ( Montenegro ), namely the two submarine estavelles "Gurdić" in Kotor and "Sopot" in Risan . The submarine source “Sopot” also has a second outlet near the coast about 10 m above sea level during the maximum discharge.

Water quality - increasing water demand

In Spain (Moraig-Quelle), France (Port Miou), Greece (Kiveri), Lebanon (Chekka), extensive construction measures - also scientifically supported several times - have been undertaken at large submarine springs in order to reduce the enormous amounts released for the growing (agricultural) economy and to make the population usable. That is why these and some other karst springs are well documented. The measures at the sources mentioned, with the exception of the water extraction in Kiveri (Peloponnese), which was successfully completed in 1972, are essentially considered to have failed economically and ecologically because the proportion of undesired chlorides in the fresh water tapped remained abortively high even with high hydraulic water pressure in the rainy season ( Salt water intrusions ). Obviously, with submarine karst springs and those that have connections to the sea - even with great technical use - one must always be prepared for the fact that the intrusion of salt water - also under the mainland, as is typical of the karst - is currently hardly economically controllable.

Kiveri: alternative to saline well irrigation

Submarine karst
springs, Peloponnese
Tracer- tested path to the karst spring at Kiveri

The geological relief of the north-eastern Peloponnese (500–700 m) is not very deep and karstified to a high degree. Numerous karst springs arise from the limestone formations, which mostly pour their water into eight large and other small fertile but drainless plains ( poljes ). From there, the waters pass through "Katavothren" (Greek for ponore) and then through karst water corridors and caves to the north into the Gulf of Corinth and to the east into the Argolic Gulf . The “Dini” karst spring near Kiveri on the waters edge of the Argolic Gulf, which has been documented since ancient times, is so large that its fresh water was protected from mixing with sea water as early as 1972 by a 150 m long concrete wall. Controllable weirs keep the fresh water level always so far above the salt water sea level (several meters) that the physically heavier salt water does not mix with the fresh water. The high annual average discharge of 10 m 3 / s has only 0.3 g / l chloride! No other karst spring project in the Mediterranean reaches less than ten times these chloride values, ie brackish water always penetrates karst water channels.

The fresh water, which seeps into rock pores and karst crevices after use in settlements and (agriculturally) economically used areas of Arcadia or flows off in ponors, can be polluted with high nitrate values ​​and a variety of other pollutants - in the future, with increasing chemicalization of agriculture, perhaps even more - Drinking water quality cannot be achieved. At the collection point in Kiveri, the water is led through an approx. 15 km long concrete channel into the Argos plain, where it is to replace the irrigation , which has already led to the groundwater salinisation of the fertile plain through numerous deep wells.

Contained karst spring "Dini" near Kiveri , Argolic Gulf

See also

credentials

  1. ↑ A. Pentecost (see literature) differentiates between sources that are “meteogenic” (due to precipitation containing CO 2 ) or “thermogenic” (coming from the earth's crust)
  2. ↑ For the seepage-like exchange of fresh water and sea water cf. USGS, e.g. B. "Submarine ground-water discharge ..." under web links
  3. ^ P. Fleury et al: Submarine springs and coastal karst aquifers: a review. 2007, p. 85.
  4. ↑ a b M. Balkalowicz: Karst at depth below sea ... 2014.
  5. ^ A. Morfis, H. Zojer: Karst Hydrogeology of the Central and Eastern Peloponnesus (Greece). Graz 1986, pp. 214-218.
  6. ↑ T. Hauffe et al .: Spatially… gastropod biodiversity… Lake Ohrid. 2011.
  7. ↑ If afterwards the water level sinks to a permanently lower point than before, there are also deeper karstifiable rocks, there are no impermeable intermediate layers in the way, the karstification process continues to the new lowest point. If long periods of geological history elapse, the karst water corridors or additional karst water corridors arise and deeper outlet points are formed. See also M. Balkalowicz: Karst at depth below sea…. 2014, p. 97.
  8. ^ V. Gornitz: The Great Ice Meltdown ... 2012.
  9. ↑ E. Gilli: Deep speleological salt contamination in Mediterranean karst aquifers: perspectives for water supply. In: Environmental Earth Sciences. Volume 74, Issue 1, July 2015, pp. 101-113; See also fr: Exsurgence de Port-Miou
  10. ^ A b P. Fleury et al.: Submarine springs and coastal karst aquifers. 2007.
  11. ↑ P. Fleury et al.: Submarine springs and coastal karst aquifers 2007, p. 81.
  12. ^ A b D. Ford, P. Williams: Karst Hydrogeology and Geomorphology. 2007.
  13. ↑ Rainy winter months, very dry, hot summers. Diverse mountain ranges and fertile basins (Poljen, which have numerous ponors and / or Estavellen ) alternate. See also Ford & Williams, Figure 6.30, p. 183, cf. Reading list
  14. ^ P. Fleury et al: Submarine springs and coastal karst aquifers: a review. 2007, p. 81.
  15. ^ S. Milanović: Hydrogeological characteristics…. 2007, p. 758.
  16. ^ ID Mariolakos, DI Mariolakos: The Argon Field in Arcadia… 2005.
  17. ↑ M. Psychoyou et al .: Groundwater quality and nitrate pollution in the Argolis region. Peloponnese. 2012.

literature

  • A. Morfis, H. Zojer: Karst Hydrogeology of the Central and Eastern Peloponnesus (Greece). In: Steir. Contribution z. Hydrogeology. 37/38, Graz 1986.
  • COST 621, Final Report, Groundwater Management of coastal karst aquifers. Brussels 2005.
  • A. Pentecost: Travertines. Springer-Verlag, Berlin / Heidelberg 2005. (English)
  • ID Mariolakos, DI Mariolakos: The Argon Field in Arcadia, the sinkhole of Nestani village, God Poseidon and the submarine Dini spring in the Argolic Gulf (Peloponnisos, Greece). A geomythological approach of the Poseidon's birth. Presentation for the International Speleology Congress, Athens 2005.
  • S. Milanovič: Hydrogeological characteristics of some deep siphonal springs in Serbia and Montenegro karst. In: Environmental Geology. 51, Heidelberg / Berlin, Jan. 2007, pp. 755-759.
  • P. Fleury, M. Bakalowicz, G. de Marsily: Submarine springs and coastal karst aquifers: A review. In: Journal of Hydrology. Amsterdam 2007, p. 339.
  • D. Ford, P. Williams: Karst Hydrogeology and Geomorphology. Revised edition. Chichester 2007.
  • EJ Rohling, K. Grant, M. Bolshaw, AP Roberts, M. Siddall, Ch. Hemleben, M. Kucera: Antarctic temperature and global sea level closely coupled over the past five glacial cycles. In: Nature Geoscience. 2, 2009. (nature.com)
  • T. Hauffe, C. Albrecht, K. Schreiber, K. Birkhofer, S. Trajanovski, T. Wilke: Spatially explicit analysis of gastropod biodiversity in ancient Lake Ohrid. In: Biogeosciences. 8, 2011, pp. 175-188.
  • M. Psychoyou, A. Sgoubopoulou, S. Rizos, G. Giannoussa, P. Kerkides: Groundwater quality and nitrate pollution in the Argolis region. Peloponnese. Athens, July 2012.
  • V. Gornitz: The Great Ice Meltdown and Rising Seas: Lessons for Tomorrow. NASA, Goddard Institute for Space Studies , Earth Sciences Division, New York 2012. (giss.nasa.gov)
  • M. Balkalowicz: Karst at depth below the sea level around the Mediterranean due to the Messinian crisis of salinity. Hydrogeological consequences and issues. In: Geologica Belgica. 17, 2014.
  • Chr. Kottmeier et al .: New perspectives on interdisciplinary earth science at the Dead Sea: The DESERVE project. In: Science of The Total Environment. 544, 2016, pp. 1035-1058.

Web links

Imagery

Commons : Underwater Sources  - Collection of images, videos and audio files