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The Subboreal is a climatic period, immediately before the present one, of the
Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...
. It lasted from 3710 to 450
BCE Common Era (CE) and Before the Common Era (BCE) are year notations for the Gregorian calendar (and its predecessor, the Julian calendar), the world's most widely used calendar era. Common Era and Before the Common Era are alternatives to the or ...
.


Etymology

The composite scientific term ''Subboreal'', meaning "below the Boreal," is derived from the
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...
''sub'' (below, under) and the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
''Βορέας'', from Boreas, the god of the North Wind. The word was first introduced in 1889 by
Rutger Sernander Johan ''Rutger'' Sernander (2November 186627October 1944) was a Swedish botanist, geologist and archaeologist. He was one of the founders of the study of palynology which would later be developed by Lennart von Post, as well as a pioneer in the ea ...
to distinguish it from
Axel Blytt Axel Gudbrand Blytt (19 May 1843 – 18 July 1898) was a Norwegian professor, botanist and geologist. He was the author of a number of books regarding the flora of Norway. Today he is most associated with his role in developing the Blytt-Sernan ...
's
Boreal Boreal may refer to: Climatology and geography *Boreal (age), the first climatic phase of the Blytt-Sernander sequence of northern Europe, during the Holocene epoch *Boreal climate, a climate characterized by long winters and short, cool to mild ...
, which had been established in 1876.


History

The Subboreal followed the
Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
and was followed by the Subatlantic. The Subboreal is equivalent to W. H. Zagwijn's pollen zones IVa and IVb and T. Litt's pollen zone VIII. In the pollen scheme of Fritz Theodor Overbeck, it occupies pollen zone X. In
paleoclimatology Paleoclimatology (British spelling, palaeoclimatology) is the study of climates for which direct measurements were not taken. As instrumental records only span a tiny part of Earth's history, the reconstruction of ancient climate is important to ...
, it is divided into an Older Subboreal and a Younger Subboreal. Historically, the Subboreal is equivalent to most of the
Neolithic The Neolithic period, or New Stone Age, is an Old World archaeological period and the final division of the Stone Age. It saw the Neolithic Revolution, a wide-ranging set of developments that appear to have arisen independently in several pa ...
and the entire
Bronze Age The Bronze Age is a historic period, lasting approximately from 3300 BC to 1200 BC, characterized by the use of bronze, the presence of writing in some areas, and other early features of urban civilization. The Bronze Age is the second pri ...
, which started 4200 to 3800 years ago.


Dating

The Subboreal is usually defined as 5660 to 3710 years BP. The lower limit is flexible, as some authors prefer to use 4400 BCE, or 6350 BP in northwestern
Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populou ...
, even 4830 BC, or 6780 BP, And others use 5000 calendar years, or 3050 BCE. The upper limit of the Subboreal and, therefore the beginning of the Subatlantic, is also flexible and can be attributed to 1170 to 830 BCE, but it is usually fixed at 450 BCE. In
varve A varve is an annual layer of sediment or sedimentary rock. The word 'varve' derives from the Swedish word ''varv'' whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as ''Hvarfig lera'' (va ...
years, the Subboreal corresponds to 5660 to 2750 years BP. The boundary between the older and the younger Subboreal is considered to be 1350 BCE.


Climatic evolution

The climate was generally drier and slightly cooler (by about 0.1 °C) than in the preceding Atlantic but still warmer than today. The temperatures were 0.7 °C higher than during the following Subatlantic. Consequently, in Scandinavia the lower limit of glaciers was 100 to 200 m higher than during the Subatlantic. On the whole, the oscillating temperatures slightly receded in the course of the Subboreal by about 0.3 °C. In the Aegean, the beginning of the Subboreal was marked by a pronounced
drought A drought is defined as drier than normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D.  Jiang, A.  Khan, W.  Pokam Mba, D.  Rosenfeld, J. Tierney, an ...
, centered around 5600 years BP. Of far greater importance was the coming to an end of the
African Humid Period The African humid period (AHP) (also known by other names) is a climate period in Africa during the late Pleistocene and Holocene geologic epochs, when northern Africa was wetter than today. The covering of much of the Sahara desert by grasses, ...
, reflected in the
lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...
s of subtropical
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
(such as
Lake Chad Lake Chad (french: Lac Tchad) is a historically large, shallow, endorheic lake in Central Africa, which has varied in size over the centuries. According to the ''Global Resource Information Database'' of the United Nations Environment Programme ...
) experiencing a rapid fall in their water levels. During the interval 6200 to 5000 years BP, drier conditions were in southern
Mesopotamia Mesopotamia ''Mesopotamíā''; ar, بِلَاد ٱلرَّافِدَيْن or ; syc, ܐܪܡ ܢܗܪ̈ܝܢ, or , ) is a historical region of Western Asia situated within the Tigris–Euphrates river system, in the northern part of the ...
, causing great demographic changes and probably instigating the end of the ancient city of
Uruk Uruk, also known as Warka or Warkah, was an ancient city of Sumer (and later of Babylonia) situated east of the present bed of the Euphrates River on the dried-up ancient channel of the Euphrates east of modern Samawah, Muthanna Governorate, Al ...
. In
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwee ...
, a drastic climatic cooling can be observed around 5000
varve A varve is an annual layer of sediment or sedimentary rock. The word 'varve' derives from the Swedish word ''varv'' whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as ''Hvarfig lera'' (va ...
years BP in the
maar A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallo ...
s of the
Eifel The Eifel (; lb, Äifel, ) is a low mountain range in western Germany and eastern Belgium. It occupies parts of southwestern North Rhine-Westphalia, northwestern Rhineland-Palatinate and the southern area of the German-speaking Community of ...
. In the preceding interval lasting from 8200 till 5000 varve years (
Holocene Climatic Optimum The Holocene Climate Optimum (HCO) was a warm period that occurred in the interval roughly 9,000 to 5,000 years ago BP, with a thermal maximum around 8000 years BP. It has also been known by many other names, such as Altithermal, Climatic Optimu ...
), the July temperatures were on average still 1 °C higher. At the same time, the January temperatures were rising and the yearly
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
increased. In
Northern Africa North Africa, or Northern Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in t ...
and in the
Near East The ''Near East''; he, המזרח הקרוב; arc, ܕܢܚܐ ܩܪܒ; fa, خاور نزدیک, Xāvar-e nazdik; tr, Yakın Doğu is a geographical term which roughly encompasses a transcontinental region in Western Asia, that was once the hist ...
, the interval from 4700 to 4100 years BP had renewed and lasting dry conditions, as is indicated by lake level minima. Between 4500 and 4100 years BP,
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal oscil ...
al precipitations weakened, a possible cause for the upheavals that led to the end of the
Old Kingdom of Egypt In ancient Egyptian history, the Old Kingdom is the period spanning c. 2700–2200 BC. It is also known as the "Age of the Pyramids" or the "Age of the Pyramid Builders", as it encompasses the reigns of the great pyramid-builders of the Fourt ...
. The Levant shows a similar climatic evolution. The dry conditions prevailing in Mesopotamia around 4200 years BP probably resulted in the downfall of the
Akkadian Empire The Akkadian Empire () was the first ancient empire of Mesopotamia after the long-lived civilization of Sumer. It was centered in the city of Akkad () and its surrounding region. The empire united Akkadian and Sumerian speakers under one r ...
.


Carbon dioxide

Levels of
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
had reached at the beginning of the Subboreal its Holocene minimal value of 260 ppm. During the Subboreal, it started rising and reached 293 ppm at the end of the period. As a comparison, today's value is over 400 ppm.


Vegetation history

In
Scandinavia Scandinavia; Sámi languages: /. ( ) is a subregion in Northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. In English usage, ''Scandinavia'' most commonly refers to Denmark, Norway, and S ...
, the Atlantic/Subboreal boundary shows a distinct vegetational change. That is less pronounced in
Western Europe Western Europe is the western region of Europe. The region's countries and territories vary depending on context. The concept of "the West" appeared in Europe in juxtaposition to "the East" and originally applied to the ancient Mediterranean ...
, but its typical mixed oak forest shows quite a fast decline in elm and linden. The decline in linden is not fully understood and might be due to cooling or human interference. The decline in elm is most likely due to elm disease, caused by the
ascomycete Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The defi ...
'' Ceratocystis ulmi'', but climatic changes and anthropogenic pressure on the forests certainly must be considered as well. The decline in elm, with a recession from 20 to 4%, as observed in Eifel maar pollen, has been dated in Central and Northern Europe as from 4000 years BC, but it more likely was diachronous over the interval 4350 to 3780 BC.Kubitz, B. (2000). Die holozäne Vegetations- und Siedlungsgeschichte in der Westeifel am Beispiel eines hochauflösenden Pollendiagrammes aus dem Meerfelder Maar. Dissertationes Botanicae, 339, p. 106. Another important event was the immigration of
European beech ''Fagus sylvatica'', the European beech or common beech is a deciduous tree belonging to the beech family Fagaceae. Description ''Fagus sylvatica'' is a large tree, capable of reaching heights of up to tall and trunk diameter, though more ...
(''Fagus sylvatica'') and
hornbeam Hornbeams are hardwood trees in the flowering plant genus ''Carpinus'' in the birch family Betulaceae. The 30–40 species occur across much of the temperate regions of the Northern Hemisphere. Origin of names The common English name ''hornbeam ...
(''Carpinus betulus'') from their retreats on the
Balkan The Balkans ( ), also known as the Balkan Peninsula, is a geographical area in southeastern Europe with various geographical and historical definitions. The region takes its name from the Balkan Mountains that stretch throughout the who ...
and south of the
Apennines The Apennines or Apennine Mountains (; grc-gre, links=no, Ἀπέννινα ὄρη or Ἀπέννινον ὄρος; la, Appenninus or  – a singular with plural meaning;''Apenninus'' (Greek or ) has the form of an adjective, which wou ...
. That happened also diachronously: beech pollen are found for the first time in the interval 4340 to 3540 BC, hornbeam pollen somewhat later between 3400 and 2900 BC. With the start of the Younger Subboreal is the massive spreading of beech. The establishment of beech and hornbeam was accompanied by indicator plants for human settlements and agriculture like
cereal A cereal is any grass cultivated for the edible components of its grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, germ, and bran. Cereal grain crops are grown in greater quantities and provide more food ...
s and plantain (''
Plantago lanceolata ''Plantago lanceolata'' is a species of flowering plant in the plantain family Plantaginaceae. It is known by the common names ribwort plantain, narrowleaf plantain, English plantain, ribleaf, lamb's tongue, and buckhorn. It is a common weed on c ...
''), and
hazel The hazel (''Corylus'') is a genus of deciduous trees and large shrubs native to the temperate Northern Hemisphere. The genus is usually placed in the birch family Betulaceae,Germplasmgobills Information Network''Corylus''Rushforth, K. (1999). ...
was receding. The relatively-dry climate during the subboreal furthered the spreading of heath plants (
Ericaceae The Ericaceae are a family of flowering plants, commonly known as the heath or heather family, found most commonly in acidic and infertile growing conditions. The family is large, with c.4250 known species spread across 124 genera, making it th ...
).


Sea level

Like in the Atlantic, the global
sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardis ...
kept on rising during the Subboreal but at a much slower rate. The increase amounted to about 1 m, which corresponds to a rate of 0.3 mm per year. At the end of the Subboreal, the sea level was about 1 m below the current value.


Evolution in the Baltic

In the
Baltic Baltic may refer to: Peoples and languages *Baltic languages, a subfamily of Indo-European languages, including Lithuanian, Latvian and extinct Old Prussian *Balts (or Baltic peoples), ethnic groups speaking the Baltic languages and/or originatin ...
the Litorina Sea had already established itself before the onset of the Subboreal. During the Older Subboreal the second Litorina transgression raised the sea level to 1 m below the actual value. After an intermediate Post-litorine Regression the third Litorina transgression reached 60 cm below present and during the beginning Subatlantic, it reached today's value.


Evolution in the North Sea region

In the
North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian ...
region, the
Flandrian transgression The Flandrian interglacial or stage is the name given by geologists and archaeologists in the British Isles to the first, and so far only, stage of the Holocene epoch (the present geological period), covering the period from around 12,000 years ago ...
of the Atlantic was followed by a slight regression or standstill at the beginning of the Subboreal.


References

{{DEFAULTSORT:Subboreal .04 Geological ages Paleoclimatology