{{short description|Stage in evolution of the Baltic Sea}} thumb|350px|Littorina Sea around 7000 years BP. {{Evolution of the Baltic Sea}} '''Littorina Sea''' (also '''Litorina Sea''') is a geological brackish water stage of the Baltic Sea, which existed around 8500–4000 BP and followed the Mastogloia Sea (initial Littorina Sea), a transitional stage from the Ancylus Lake.{{sfn|Rosentau|Klemann|Bennike|Steffen|2021|loc=2. Regional setting}}
This stage and form of the body of water is named after common periwinkle (''Littorina littorea''), then a prevailing mollusc in the waters, which indicates its salinity.{{sfn|Wefer|2002}}
[[File:Littorina sea transgressions in Blekinge by Yu En.svg|thumb|Graph the multiple changes in relative sea level at Blekinge in southeastern Sweden since the initial Littorina Sea stage]] thumb|Example of a Littorina Sea high stand terrace in Finland thumb|Boulder field in Finland created during Littorina Sea existence == Overview == The last fully fresh water stage in the Baltic basin, the Ancylus Lake ended at 9,800 {{abbr|ka cal.|years ago calibrated to 2013 terrestrial and marine standards}} BP when salt water from the world ocean started entering the Mastogloia Sea in the Great Belt region commencing an initial Littorina Sea which as a saline or brackish sea continues to this day. These initial transgressions were incomplete and occurred at different times in different areas of the Baltic basin lasting until 8.5 ka cal. BP.{{sfn|Rosentau|Klemann|Bennike|Steffen|2021|loc=4.4. RSL data and tendencies during the 9.8–8.5 ka BP (ILS stage)}}{{sfn|Björck|1995}}{{sfn|Donner|1995}} The transition timings from fresh to brackish water that mark the onset of the Littorina Sea are not yet clearly defined. They may have been in the northern Great Belt region around 9.0 ka cal. BP and east of the Darβ Sill which is at the western end of the Baltic Sea, at sites so far studied, are after 8.5 ka cal. BP and this is the definite onset of the Littorina Sea.{{sfn|Rosentau|Klemann|Bennike|Steffen|2021|loc=2. Regional setting}}
Between 8 and 6 ka cal. BP the mid-Holocene relative sea level rise has been studied in more detail than later changes in water level in the Littorina Sea.{{sfn|Rosentau|Klemann|Bennike|Steffen|2021|loc=4.1. RSL indicators}} The Holocene climatic optimum is now defined as about 8 to 4.8 cal. ka BP and resulted in northern Europe in a period of warm, and dry climate.{{sfn|Van Wirdum|Andrén|Wienholz|Kotthoff|2019|loc=Hypoxia Between c. 8–4 ka BP}}
The Ångermanland region of northern Sweden had the highest post-glacial rebound in northern Europe, so between 9.1 and 7.8 ka cal. BP relative sea level dropped here from {{cvt|152| to |128|m}} above sea level. Transitional regions in the eastern Baltic show positive relative sea level tendencies until between 7.5 and about 7.1 ka cal BP, when they become negative. The final melting of the Laurentide ice sheet followed by much lower rate of global sea-level rise took place at this general time, between 8 and 7 ka cal. BP.{{sfn|Rosentau|Klemann|Bennike|Steffen|2021|loc=4.5.2. Transitional regions}}{{sfn|Rosentau|Klemann|Bennike|Steffen|2021|loc=4.5.3. Regions with positive RSL tendencies}} The southern and western Baltic basin has a negative trend in relative sea level throughout the Holocene.{{sfn|Rosentau|Klemann|Bennike|Steffen|2021|loc=4.5.3. Regions with positive RSL tendencies}} So it is known that near the Denmark straits this area was {{cvt|20|m}} below sea level around 8.5 to 8.0 ka cal. BP, but the area around the Usedom/Rügen islands had up to {{cvt|5|m}} higher relative sea level at the same time.{{sfn|Rosentau|Klemann|Bennike|Steffen|2021|loc=4.5.3. Regions with positive RSL tendencies}} There is only a good fit in timing of relative sea levels with global ice history studies in this later negative relative sea level group, meaning that the calculated contribution of ice loading in the global ice models is likely wrong for the eastern Baltic region.{{sfn|Rosentau|Klemann|Bennike|Steffen|2021|loc=5. Conclusion}} A transgression of the Baltic widened its ocean link, allowing it to reach a peak of salinity during the warmer Atlantic period of European climatology. At this peak, the sea bore twice the volume of water and covered 26.5% more land than it does today.{{sfn|Wefer|2002}} Diatom studies of the sediments of the Landsort Deep off Sweden suggest that the highest surface water salinities occurred between 7.1 and 5.4 ka BP,{{sfn|Van Wirdum|Andrén|Wienholz|Kotthoff|2019|loc=Historical Hypoxia in the Baltic Sea}} about the time of the Littorina Sea high stand.{{sfn|Rosentau|Klemann|Bennike|Steffen|2021|loc=2. Regional setting}} The halocline developed causing a stratified water column, due to the inflow of North Sea water into the deep waters of the Baltic basin. {{sfn|Van Wirdum|Andrén|Wienholz|Kotthoff|2019|loc=Hypoxia During the Holocene Thermal Maximum}}
The transition about 4 ka cal. BP to today's Baltic Sea, which could also be called the late Littorina Sea is ill defined. After the Holocene climatic optimum, land uplift exceeded world ocean sea level rise, and the resulting shallowing of the sills in the Baltic basin resulted in a gradual decrease in salinity.{{sfn|Van Wirdum|Andrén|Wienholz|Kotthoff|2019|loc=Hypoxia Between c. 8–4 ka BP}} Some have it complete by 3.0 cal ka BP and it is characterised by microfossil changes from those of a typical high salt marine environment.{{sfn|Rosentau|Klemann|Bennike|Steffen|2021|loc=2. Regional setting}} As the period ended, the features of the modern coast appeared, including lagoons, spits, and dunes.{{sfn|Wefer|2002}} Notable exceptions include steep terraces such as the Øresund where the recession of sea level exposes less dry land.{{sfn|Wefer|2002}}
== Ecology == [[File:FMIB 52802 Littorina litorea.jpeg|thumb|Common periwinkle shells are found in deposits from the Littorina Sea]] As revealed in the marine microfossil record in today's deepest part of the Baltic Sea, which includes freshwater surface diatoms ''Aulacoseira islandica'' and ''Stephanodiscus neoastraea'',{{sfn|Van Wirdum|Andrén|Wienholz|Kotthoff|2019|loc=Subunit 2a}} before 7.1 ka cal. BP the water ecosystem had low productivity as inherited from the Ancylus Lake stage but there is evidence of transient greater productivity in response to brackish conditions.{{sfn|Van Wirdum|Andrén|Wienholz|Kotthoff|2019|loc=Table 2}} This includes by 7.2 ka cal. BP the presence of ''Chaetoceros'' resting spores.{{sfn|Van Wirdum|Andrén|Wienholz|Kotthoff|2019|loc=Subunit 2a}} At 7.4 ka cal. BP the brackish surface layers allowed for the first time ''Cyclotella radiosa'' and ''Pantocsekiella comensis''.{{sfn|Van Wirdum|Andrén|Wienholz|Kotthoff|2019|loc=Subunit 2a}}
There was a period of high marine productivity associated with the high saline, hypoxic bottom period.{{sfn|Van Wirdum|Andrén|Wienholz|Kotthoff|2019|loc=Table 2}} in the period 5.4–2.4 ka cal. This period had organisms in the fossil record not found in today's Baltic. These include ''Pseudosolenia calcar-avis'' which is presently found in tropical and subtropical seas, ''Thalassionema nitzschioides'' which no longer occurs in the Baltic north of the Bornholm Basin, ''Chaetoceros mitra'' no longer found in the Baltic but present in today's North Sea.{{sfn|Van Wirdum|Andrén|Wienholz|Kotthoff|2019|loc=Subunit 1d (c. 7.1–5.4 cal ka BP)}} ''Octactis speculum '' which definitely requires high salinity is only present between 6.8 and 5.4 ka cal. BP.{{sfn|Van Wirdum|Andrén|Wienholz|Kotthoff|2019|loc=Subunit 1d (c. 7.1–5.4 cal ka BP)}}
As brackish conditions were re-established intermediate productivity ecosystems similar to the present day Baltic Sea were established.{{sfn|Van Wirdum|Andrén|Wienholz|Kotthoff|2019|loc=Table 2}} Chaetoceros resting spores are mostly abundant and Pseudosolenia calcar-avis is rare after 5.4 ka cal. BP. Chaetoceros mitra resting spores do not appear after about 4.7 ka cal.BP.{{sfn|Van Wirdum|Andrén|Wienholz|Kotthoff|2019|loc=Subunit 1c (c. 5.4–0.9 cal ka BP)}}
During the period, from the Ancylus Lake, temperate deciduous forest had crept north to cover the littoral hinterland and thus coastal regions of the sea.{{sfn|Aichner|Ott|Słowiński|Noryśkiewicz|2018|loc=Figure 3.}} The deep sediment pollen record shows a relative increase in say pine tree pollen grains possibly due to less humid warm conditions in summer during the Holocene climatic optimum.{{sfn|Van Wirdum|Andrén|Wienholz|Kotthoff|2019|loc=Hypoxia During the Holocene Thermal Maximum}}
== References == ;sources {{refbegin}} * {{cite journal |last=Björck |first=Svante|author-link=Svante Björck|title=A Review of the History of the Baltic Sea, 13.0–8.0 ka BP |journal=Quaternary International |volume=27 |pages=19–40 |publisher=Elsevier |year=1995 |doi=10.1016/1040-6182(94)00057-C |bibcode=1995QuInt..27...19B }} * {{cite book|last=Donner|first=J.|year=1995|title=The Quaternary History of Scandinavia|publisher=Cambridge University Press|pages=210 |isbn=9780521417303}} * {{cite book | last=Wefer | first=Gerold | title=Climate Development and History of the North Atlantic Realm | publisher=Springer | year=2002 | isbn=3-540-43201-9 | pages=217–219 }} * {{cite journal|last1=Rosentau|first1=A.|last2=Klemann|first2=V.|last3=Bennike|first3=O.|last4=Steffen|first4=H.|last5=Wehr|first5=J.|last6=Latinović|first6=M.|last7=Bagge|first7=M.|last8=Ojala|first8=A.|last9=Berglund|first9=M.|last10=Becher|first10=G.P.|last11=Schoning|first11=K.|year=2021|title=A Holocene relative sea-level database for the Baltic Sea|journal=Quaternary Science Reviews|volume =266|at=107071|doi=10.1016/j.quascirev.2021.107071|doi-access=free}} *{{cite journal|last1=Aichner|first1=B.|last2=Ott|first2=F.|last3=Słowiński|first3=M.|last4=Noryśkiewicz|first4=A.M.|last5=Brauer|first5=A.|last6=Sachse|first6=D.|year=2018|title=Leaf wax n-alkane distributions record ecological changes during the Younger Dryas at Trzechowskie paleolake (northern Poland) without temporal delay|journal=Climate of the Past|volume=14|issue=11|pages=1607–1624|doi=10.5194/cp-14-1607-2018|doi-access=free|bibcode=2018CliPa..14.1607A|hdl=21.11116/0000-0000-FF16-9|hdl-access=free}} *{{cite journal|last1=Van Wirdum|first1=F.|last2=Andrén|first2=E.|last3=Wienholz|first3=D.|last4=Kotthoff|first4=U.|last5=Moros|first5=M.|last6=Fanget|first6=A.S.|last7=Seidenkrantz|first7=M.S.|last8=Andrén|first8=T.|date=18 February 2019|title=Middle to Late Holocene variations in salinity and primary productivity in the Central Baltic Sea: a multiproxy study from the Landsort Deep|journal=Frontiers in Marine Science|volume=6|at=51|doi=10.3389/fmars.2019.00051|doi-access=free}} {{refend}} {{Pleistocene Lakes and Seas}}
Category:History of the Baltic Sea Category:Holocene Category:7th millennium BC Category:6th millennium BC Category:5th millennium BC Category:8th millennium BC