The Baltic Sea saltwater inflow, known as the major Baltic inflow (MBI), refers to a significant influx of saline water from the North Sea into the Baltic Sea through the Danish straits. In the Baltic Sea, dense seawater from the North Sea sinks to the bottom and moves along the seabed, displacing the often oxygen-depleted water in the deep basins. Simultaneously, it transports new oxygen-rich water to the deep basins. These inflows are crucial for the Baltic Sea's ecosystem because they alleviate the oxygen depletion that commonly occurs in the deep basins of the poorly mixed sea, and at the same time, they prevent eutrophication caused by internal nutrient loading.
The two-layer circulation of the Baltic Sea presented as a schematic figure. Major Baltic inflows (MBIs) bring saline water from the North Sea to the Baltic Sea through the Danish straits. Dense ocean water sinking to the depths of the Baltic Proper advances northward along the seafloor, displacing the low-oxygen water present in the deep basins.
The water in the Baltic Sea is brackish, meaning it has a low salinity. Each year, approximately 550 cubic kilometers of freshwater from rainfall and rivers within its drainage basin flow into the Baltic Sea. However, only about 100 km³ of water evaporates from the Baltic Sea into the atmosphere annually. This results in an excess of approximately 450 km³ of fresh water each year, which accounts for about two percent of the total volume of the Baltic Sea. To maintain a stable water level over the long term, the excess water flows out of the Baltic Sea through the Danish straits into the North Sea. Periodic counterflow from the North Sea to the Baltic Sea prevents the Baltic from gradually turning into a freshwater basin.[1]
The saltwater inflow, known as the major Baltic inflow (MBI), is said to occur when there is a strong overflow of saline water from the North Sea to the Baltic Sea over the cross-sections of the Darss Sill (Belt Sea) and the Drogden Sill (The Sound). Such an flow almost entirely destroys the salinity stratification in the areas of the sills for several days. Typically, the inflow event must last for at least five days to be classified as an MBI. During extremely powerful events, the Baltic Sea receives over 100 km³ of very saline water from the ocean, whereas during weaker MBIs, the volume is less than 100 km³, averaging around 70 km³.[2]
Major Baltic inflows primarily occur during winter and early spring because weather conditions are most favorable for the inflow of saline water. First, the Baltic Sea must experience easterly and southeasterly winds for about 20 to 30 days, reducing precipitation within the Baltic Sea drainage basin, enhancing outflow from the basin, and causing a drop in the sea level.[3] Before the arrival of the saline inflow, the Baltic Sea's surface level is typically around 26 centimeters lower than usual.[2] Following this, a roughly one-month period of westerly winds begins, during which the sea level in the Kattegat rises, and pressure differences force the saline water from the North Sea through the narrow Danish straits into the Baltic Sea.[3] Throughout the entire inflow process, the Baltic Sea's water level rises on average by about 59 cm, with 38 cm occurring during the preparatory period and 21 cm during the actual saline inflow. The MBI itself typically lasts for 7–8 days.[2]
The two principal time series of MBIs in the Baltic Sea. The newer DS5 time series (green bars above, Mohrholz 2018) is based on observations from the Darss Sill and includes all saltwater inflow events lasting over 5 days. The older FM96 time series (blue bars below, Fischer and Matthäus, 1996) has data gaps after 1976 when the l/v Gedser Rev ended salinity measurements. The newer time series shows cyclical variations in the occurrence of saline inflows at approximately 30-year intervals.
Occurrence of MBIs
The formation of an MBI requires specific, relatively rare weather conditions. Between 1897 and 1976, approximately 90 MBIs were observed, averaging about one per year.[2] Occasionally, there are even multi-year periods without any MBIs occurring. Large inflows that effectively renew the deep basin waters occur on average only once every ten years.[according to whom?]
Very large MBIs have occurred in 1897 (330 km3), 1906 (300 km3), 1922 (510 km3), 1951 (510 km3), 1993/94 (300 km3),[4] and 2014/2015 (300 km3).[5] Large MBIs have on the other hand been observed in 1898 (twice), 1900, 1902 (twice), 1914, 1921, 1925, 1926, 1960, 1965, 1969, 1973, 1976, and 2003.[4] The MBI that started in 2014 was by far the third largest MBI in the Baltic Sea. Only the inflows of 1951 and 1921/1922 were larger than it.[6]
Previously, it was believed that there had been a genuine decline in the number of MBIs after 1980, but recent studies have changed our understanding of the occurrence of saline inflows.[3][7] Especially after the lightship Gedser Rev discontinued regular salinity measurements in the Belt Sea in 1976, the picture of the inflows based on salinity measurements remained incomplete. At the Leibniz Institute for Baltic Sea Research (Warnemünde, Germany), an updated time series has been compiled, filling in the gaps in observations and covering Major Baltic Inflows and various smaller inflow events of saline water from around 1890 to the present day. The updated time series is based on direct discharge data from the Darss Sill and no longer shows a clear change in the frequency or intensity of saline inflows. Instead, there is cyclical variation in the intensity of MBIs at approximately 30-year intervals.[7][8]
Effects on the state of the Baltic Sea and its ecosystem
Major Baltic inflows (MBIs) are the only natural phenomenon capable of oxygenating the deep saline waters of the Baltic Sea, making their occurrence crucial for the ecological state of the sea.[6] The salinity and oxygen from MBIs significantly impact the Baltic Sea's ecosystems, including the reproductive conditions of marine fish species such as cod, the distribution of freshwater and marine species, and the overall biodiversity of the Baltic Sea.[9]
The heavy saline water brought in by MBIs slowly advances along the seabed of the Baltic Proper at a pace of a few kilometers per day, displacing the deep water from one basin to another.[10] Although some oxygen is transported from the North Sea to the Baltic Sea, only a small portion of the oxygen responsible for renewing the deep basins originates from the Baltic Sea entrance area. In the southwestern basins of the Baltic Sea (Arkona sea, Bornholm basin), there is already oxygen present in the water column, and the role of the saltwater pulse is to entrain and direct it towards the deep basins of the sea.[11]
It has been observed that the oxygen supplied by saline inflows is consumed more rapidly in the Baltic Proper than before. In 1993, the oxygen replenishment was depleted in about 17 months, in 2003, it took approximately 13 months, and in 2015, it was exhausted in just six months.[6]
The intense oxygen consumption in the Baltic Sea's seafloor is due to prolonged nutrient loading and the impacts of climate change.[3] Although a single MBI can oxygenate both the deep water hydrogen sulfide and ammonia, multiple consecutive inflows would be required to raise the oxygen level to a satisfactory level. The so-called "oxygen debt" was estimated to be about 20 million tons in 2020. This is the amount of oxygen that should be transported to the Baltic Proper via saline inflows to raise its oxygen concentration to the 3 mL/L level observed after the MBI of 1993. With a single 200 km³ MBI, approximately 2 million tons of oxygen are transported.[12]
^Climate Change in the Baltic Sea. 2021 Fact Sheet. Baltic Sea Environment Proceedings n°180. HELCOM/Baltic Earth 2021.
^"Arandan Itämeren seurantamatka: suolapulssi etenee eteläisellä Itämerellä, Suomenlahden ja Selkämeren fosforipitoisuus viime talvea korkeampi" (in Finnish). Finnish Environment Institute. 2015-02-12. Retrieved 2023-07-24.
^Neumann, Thomas; Radtke, Hagen; Seifert, Torsten (2017-01-25). "On the importance of Major Baltic Inflows for oxygenation of the central Baltic Sea: IMPORTANCE OF MAJOR BALTIC INFLOWS". Journal of Geophysical Research: Oceans. 122 (2): 1090–1101. doi:10.1002/2016JC012525.
^Rolff, Carl; Walve, Jakob; Larsson, Ulf; Elmgren, Ragnar (2022-11-01). "How oxygen deficiency in the Baltic Sea proper has spread and worsened: The role of ammonium and hydrogen sulphide". Ambio. 51 (11): 2308–2324. doi:10.1007/s13280-022-01738-8. ISSN 1654-7209. PMC9481832. PMID 35737272.
August 23, 2023
major, baltic, inflow, baltic, saltwater, inflow, known, major, baltic, inflow, refers, significant, influx, saline, water, from, north, into, baltic, through, danish, straits, baltic, dense, seawater, from, north, sinks, bottom, moves, along, seabed, displaci. The Baltic Sea saltwater inflow known as the major Baltic inflow MBI refers to a significant influx of saline water from the North Sea into the Baltic Sea through the Danish straits In the Baltic Sea dense seawater from the North Sea sinks to the bottom and moves along the seabed displacing the often oxygen depleted water in the deep basins Simultaneously it transports new oxygen rich water to the deep basins These inflows are crucial for the Baltic Sea s ecosystem because they alleviate the oxygen depletion that commonly occurs in the deep basins of the poorly mixed sea and at the same time they prevent eutrophication caused by internal nutrient loading The two layer circulation of the Baltic Sea presented as a schematic figure Major Baltic inflows MBIs bring saline water from the North Sea to the Baltic Sea through the Danish straits Dense ocean water sinking to the depths of the Baltic Proper advances northward along the seafloor displacing the low oxygen water present in the deep basins Contents 1 The process for MBI formation 2 Occurrence of MBIs 3 Effects on the state of the Baltic Sea and its ecosystem 4 ReferencesThe process for MBI formation EditThe water in the Baltic Sea is brackish meaning it has a low salinity Each year approximately 550 cubic kilometers of freshwater from rainfall and rivers within its drainage basin flow into the Baltic Sea However only about 100 km of water evaporates from the Baltic Sea into the atmosphere annually This results in an excess of approximately 450 km of fresh water each year which accounts for about two percent of the total volume of the Baltic Sea To maintain a stable water level over the long term the excess water flows out of the Baltic Sea through the Danish straits into the North Sea Periodic counterflow from the North Sea to the Baltic Sea prevents the Baltic from gradually turning into a freshwater basin 1 The saltwater inflow known as the major Baltic inflow MBI is said to occur when there is a strong overflow of saline water from the North Sea to the Baltic Sea over the cross sections of the Darss Sill Belt Sea and the Drogden Sill The Sound Such an flow almost entirely destroys the salinity stratification in the areas of the sills for several days Typically the inflow event must last for at least five days to be classified as an MBI During extremely powerful events the Baltic Sea receives over 100 km of very saline water from the ocean whereas during weaker MBIs the volume is less than 100 km averaging around 70 km 2 Major Baltic inflows primarily occur during winter and early spring because weather conditions are most favorable for the inflow of saline water First the Baltic Sea must experience easterly and southeasterly winds for about 20 to 30 days reducing precipitation within the Baltic Sea drainage basin enhancing outflow from the basin and causing a drop in the sea level 3 Before the arrival of the saline inflow the Baltic Sea s surface level is typically around 26 centimeters lower than usual 2 Following this a roughly one month period of westerly winds begins during which the sea level in the Kattegat rises and pressure differences force the saline water from the North Sea through the narrow Danish straits into the Baltic Sea 3 Throughout the entire inflow process the Baltic Sea s water level rises on average by about 59 cm with 38 cm occurring during the preparatory period and 21 cm during the actual saline inflow The MBI itself typically lasts for 7 8 days 2 The two principal time series of MBIs in the Baltic Sea The newer DS5 time series green bars above Mohrholz 2018 is based on observations from the Darss Sill and includes all saltwater inflow events lasting over 5 days The older FM96 time series blue bars below Fischer and Matthaus 1996 has data gaps after 1976 when the l v Gedser Rev ended salinity measurements The newer time series shows cyclical variations in the occurrence of saline inflows at approximately 30 year intervals Occurrence of MBIs EditThe formation of an MBI requires specific relatively rare weather conditions Between 1897 and 1976 approximately 90 MBIs were observed averaging about one per year 2 Occasionally there are even multi year periods without any MBIs occurring Large inflows that effectively renew the deep basin waters occur on average only once every ten years according to whom Very large MBIs have occurred in 1897 330 km3 1906 300 km3 1922 510 km3 1951 510 km3 1993 94 300 km3 4 and 2014 2015 300 km3 5 Large MBIs have on the other hand been observed in 1898 twice 1900 1902 twice 1914 1921 1925 1926 1960 1965 1969 1973 1976 and 2003 4 The MBI that started in 2014 was by far the third largest MBI in the Baltic Sea Only the inflows of 1951 and 1921 1922 were larger than it 6 Previously it was believed that there had been a genuine decline in the number of MBIs after 1980 but recent studies have changed our understanding of the occurrence of saline inflows 3 7 Especially after the lightship Gedser Rev discontinued regular salinity measurements in the Belt Sea in 1976 the picture of the inflows based on salinity measurements remained incomplete At the Leibniz Institute for Baltic Sea Research Warnemunde Germany an updated time series has been compiled filling in the gaps in observations and covering Major Baltic Inflows and various smaller inflow events of saline water from around 1890 to the present day The updated time series is based on direct discharge data from the Darss Sill and no longer shows a clear change in the frequency or intensity of saline inflows Instead there is cyclical variation in the intensity of MBIs at approximately 30 year intervals 7 8 Effects on the state of the Baltic Sea and its ecosystem EditMajor Baltic inflows MBIs are the only natural phenomenon capable of oxygenating the deep saline waters of the Baltic Sea making their occurrence crucial for the ecological state of the sea 6 The salinity and oxygen from MBIs significantly impact the Baltic Sea s ecosystems including the reproductive conditions of marine fish species such as cod the distribution of freshwater and marine species and the overall biodiversity of the Baltic Sea 9 The heavy saline water brought in by MBIs slowly advances along the seabed of the Baltic Proper at a pace of a few kilometers per day displacing the deep water from one basin to another 10 Although some oxygen is transported from the North Sea to the Baltic Sea only a small portion of the oxygen responsible for renewing the deep basins originates from the Baltic Sea entrance area In the southwestern basins of the Baltic Sea Arkona sea Bornholm basin there is already oxygen present in the water column and the role of the saltwater pulse is to entrain and direct it towards the deep basins of the sea 11 It has been observed that the oxygen supplied by saline inflows is consumed more rapidly in the Baltic Proper than before In 1993 the oxygen replenishment was depleted in about 17 months in 2003 it took approximately 13 months and in 2015 it was exhausted in just six months 6 The intense oxygen consumption in the Baltic Sea s seafloor is due to prolonged nutrient loading and the impacts of climate change 3 Although a single MBI can oxygenate both the deep water hydrogen sulfide and ammonia multiple consecutive inflows would be required to raise the oxygen level to a satisfactory level The so called oxygen debt was estimated to be about 20 million tons in 2020 This is the amount of oxygen that should be transported to the Baltic Proper via saline inflows to raise its oxygen concentration to the 3 mL L level observed after the MBI of 1993 With a single 200 km MBI approximately 2 million tons of oxygen are transported 12 References Edit Itameren muoto ala ja tilavuus in Finnish Finnish Meteorological Institute Retrieved 2023 07 24 a b c d Matthaus Wolfgang Franck Herbert 1992 12 01 Characteristics of major Baltic inflows a statistical analysis Continental Shelf Research 12 12 1375 1400 Bibcode 1992CSR 12 1375M doi 10 1016 0278 4343 92 90060 W ISSN 0278 4343 a b c d Lehmann Andreas Myrberg Kai Post Piia Chubarenko Irina Dailidiene Inga Hinrichsen Hans Harald Hussy Karin Liblik Taavi Meier H E Markus Lips Urmas Bukanova Tatiana 2022 02 16 Salinity dynamics of the Baltic Sea Earth System Dynamics 13 1 373 392 Bibcode 2022ESD 13 373L doi 10 5194 esd 13 373 2022 ISSN 2190 4979 a b Inflows to the Baltic Swedish Meteorological and Hydrological Institute 2014 01 15 Retrieved 2023 07 24 Itameren suolapulssin liikkeet ihmetyttavat tutkijoita in Finnish Yle News 2016 08 05 Retrieved 2023 07 24 a b c Meier H E Markus Vali Germo Naumann Michael Eilola Kari Frauen Claudia 2018 04 12 Recently Accelerated Oxygen Consumption Rates Amplify Deoxygenation in the Baltic Sea Journal of Geophysical Research Oceans 123 5 3227 3240 Bibcode 2018JGRC 123 3227M doi 10 1029 2017JC013686 ISSN 2169 9275 a b Mohrholz Volker 2018 Major Baltic Inflow Statistics Revised Frontiers in Marine Science 5 doi 10 3389 fmars 2018 00384 ISSN 2296 7745 Major Baltic Inflow statistics IOW www io warnemuende de Retrieved 2023 07 23 Climate Change in the Baltic Sea 2021 Fact Sheet Baltic Sea Environment Proceedings n 180 HELCOM Baltic Earth 2021 Arandan Itameren seurantamatka suolapulssi etenee etelaisella Itamerella Suomenlahden ja Selkameren fosforipitoisuus viime talvea korkeampi in Finnish Finnish Environment Institute 2015 02 12 Retrieved 2023 07 24 Neumann Thomas Radtke Hagen Seifert Torsten 2017 01 25 On the importance of Major Baltic Inflows for oxygenation of the central Baltic Sea IMPORTANCE OF MAJOR BALTIC INFLOWS Journal of Geophysical Research Oceans 122 2 1090 1101 doi 10 1002 2016JC012525 Rolff Carl Walve Jakob Larsson Ulf Elmgren Ragnar 2022 11 01 How oxygen deficiency in the Baltic Sea proper has spread and worsened The role of ammonium and hydrogen sulphide Ambio 51 11 2308 2324 doi 10 1007 s13280 022 01738 8 ISSN 1654 7209 PMC 9481832 PMID 35737272 Retrieved from https en wikipedia org w index php title Major Baltic inflow amp oldid 1168549188, wikipedia, wiki, book, books, library,
