Subatlantic

The Subatlantic is the last and present current period of the Holocene. It lasted for about 2500 years. His average temperatures are slightly lower than in the previous Subboreal and Atlantikum. In its course, several variations in temperature, indirectly influenced their immediate ecological impacts on flora and fauna and the history of human civilization clearly occurred. With the intensification of industrialization, however, the human society has superimposed on natural climate cycles in the last two centuries, with rapid increase in greenhouse gas emissions.

• 5.1 Development in the Baltic region
• 5.2 Development in the North Sea area

Conceptual history and stratigraphic position

The term Subatlantic (ie below the Atlantic period ), often referred to as Nachwärmezeit, was coined by Rutger Sernander to distinguish Axel Blytts Atlantikum. The Subatlantic following the immediately preceding Subboreal. It contains according to the scheme of Franz Firbas (1949 ) and by Litt, among others (2001), the pollen zones IX and X respectively by Fritz Theodor Overbeck pollen zones XI and XII.

( - Late Nachwärmezeit pollen zone X and XII) divided Klimastratigraphisch is the Subatlantic usually in a Mature Subatlantic (pollen zone IX or XI Early Nachwärmezeit or book time or oak-beech -time) and in a junior Subatlantic. The Subatlantic belongs to and forms the Subepoche of Jung- Holocene.

Dietrich Franke has for East Germany even the four following steps ( from young to old):

• The latest Subatlatikum: 1800 AD to the present: modern times
• Junior Subatlantic: 1250 AD to 1800 AD: Middle Ages
• Middle Subatlantic: 500 AD to 1250 AD: mass migration and Slavs time
• Mature Subatlantic: 500 BC to 500 AD: Pre-Roman Iron Age, Roman period and the beginning of the Great Migration

Temporal classification

Note: Only the fields marked with a black dividing line boundaries are more or less exactly; they are based on annual layers in lake sediments in north-central Europe and are, strictly speaking, only for air levels. The other boundaries are determined unsafe and not rigid. In particular, the boundary between Central and Jungholozän is highly variable. In the stages of culture the different regional development is observed.

Age

The beginning of the Subatlantikums is usually to 2400 calendar years BP or 450 BC. This limit is not to be considered as absolutely rigid. Some authors prefer to define the beginning of the Subatlantikums 2500 radiocarbon years, which corresponds to about 625 BC. Occasionally the onset is also up to 1200 moved back BC.

According to Franz Firbas the transition from Subboreal (pollen zone VIII ) for older Subatlantic (pollen zone IX) is characterized by the decline of the hazel and lime at the same time, human- aided spread of hornbeam. The decline took place but not everywhere at the same time. For this event were 930-830 BC determined, for example, in the western lower Oder valley, however, in south-western Poland ( Lower Silesia), this transition was already 1170-1160 BC instead.

The beginning of the Younger Subatlantikums (1250 AD) coincides with the medieval population expansion and is characterized by increasing proportions of the jaw and increasing settlement pointer. For him, values ​​are observed in Lower Silesia 1050-1270 AD. Will the beginning of the Younger Subatlantikums but linked to the occurrence of the Book ( 1 book maximum), so he has brought forward already in the Carolingian period (700 AD) be.

Historical Climate History

Summer temperatures of Subatlantikums total of cooler and up to 1.0 ° C lower than in Subboreal, the annual average temperatures by up to 0.7 ° C. Winter precipitation, however, are simultaneously increased by up to 50 %; the climate tends consequently wet and cold in direction. The average lower limit of the glacier fell in Scandinavia during the Subatlantikums by 100 to 200 meters.

The Subatlantic started from the middle of the 1st millennium BC, nor with the so-called optimum of the Roman period, which lasted until the beginning of the 4th century. In this time falls almost exactly the classical antiquity. This optimum is characterized by a temperature spike, which is centered at 2500 years BP. He expresses himself in Europe in particular by 0.6 ° C compared to the rest of Subatlantic increased winter temperatures, but was still 0.3 ° C below the values ​​in the previous Subboreal. Cores from the inland ice of Greenland as against the younger Subboreal a significant rise in temperature.

The subsequent, comparatively short and weak cold period is called pessimum the migration period. A temperature decline of 0.2 ° C in average temperatures and 0.4 ° ​​C in the winter temperatures centered at 350 AD and 1600 years BP. This change to a drier and colder climate could be the native to Central Asia Huns have led it to train to the west, which in turn the migrations of Germanic peoples were triggered. At the same time the Byzantine Empire saw its first heyday, and Christianity established itself in Europe as influential monotheistic religion.

The end of the medieval warm period is the early 14th century dates ( Minimum Temperature at 1350 AD). In this period were numerous documented famines and the great plague (the " Black Death "). Many settlements were abandoned in this period and waste places. It is believed that had (perhaps by 50%) decreased the population of central Europe grave.

Significantly longer and colder places, was the subsequent pessimum, which had its peak after a brief warming by the year 1500, 1550-1860, and as the Little Ice Age (English Little Ice Age) is known. The snowline was lowered in this period in the northern hemisphere by 100 to 200 meters. This period saw a number of cataclysmic events ( the Thirty Years War, French Revolution ). Parallel the later part of the Renaissance took place and led to the Enlightenment. Industrialization began here.

On the Little Ice Age was followed by the current climate optimum, also called Modern optimum, reinforced by anthropogenic influences (see the industrial age, the greenhouse effect, global warming). It is characterized by a marked rise in temperature in the period 1910-1940, but mainly by the rapid warming of the past 50 years.

Atmosphere

Measurements on ice cores from Antarctica and Greenland show for atmospheric greenhouse gases each other a similar evolution. After a temporary minimum in the preceding Subboreal Attlantikum and it came during the Subatlantikums in the concentrations of carbon dioxide, nitrous oxide and methane to a gradual increase, but the more or less drastically soared parallel to the temperature gradient from the year 1800. Thus, the CO2 concentration of methane has increased from 280 ppm to today's value of about 400 ppm, from 700 to 1800 ppb and N2O from 265 to 320 ppb. One of this magnitude comparable in some event had even taken place during the transition to the Holocene, but this process required at that time over 5000 years. The anthropogenic greenhouse emissions can under their short duration, an unprecedented experiment in Earth dar. often completely unconsidered remains this release juvenile water from fossil fuel sources such as coal, lignite, natural gas and petroleum.

Sea ​​level

In the 2,500 years of Subatlantikums global sea level was indeed constant but increased by only 1 meter. However, this rather low rate of 0.4 mm / year changed drastically from the late 19th century. So 22 centimeters rise were measured for the period 1880-2000, which corresponds to a rate of 1.83 mm / year. Even 50 millimeters were recorded alone for the last 20 years using satellite, this area corresponds to a new rate of 2.5 mm / year and thus a six- fold increased speed.

Development in the BSR

With the third Littorina transgression was reached in elders Subatlantic in the Baltic region of present-day sea level. Sea level rise was up to 1 meter, since he hovered around the zero line. It established itself Limnaea the - Sea ( postlittorine phase). The Limnaea - sea possessed compared to the previous Littorinameer a lower salt content, which was due to an isostatic flattening of the Danish straits Little Belt, Great Belt and Øresund. Thus, the snail Littorina littorea was gradually displaced by the freshwater snail Limnaea ovata. Years ago, about 1300, there was in the Middle Subatlantic again to a weak sea-level rise. However, the salinity remained on the wane and new Süßwassertaxa could immigrate. So finally the Limnaea Sea was from the Mya - sea ( sand gaper Mya arenaria immigration of around 400 years ago) and thus separated from the Baltic Sea in today's younger and youngest Subatlantic.

Development in the North Sea area

In older Subatlantic followed the slight sea level declining or sea level standstill during the Sub-boreal with the Dunkirk transgression another increase from current levels.

Vegetation history trends

The moist - cool older Subatlantic (pollen zone IXa ) is characterized in Central Europe through the mixed oak forest, in the increasingly established Book ( mixed oak forests with linden and elm or oak mixed forests with ash and beech ). In wet locations, alder-ash forests settled. The mixed oak forest still holding out during the humid - temperate Middle Subatlantikums (pollen zone IX b ), but had optima of beech and hornbeam (oak mixed forest with beech or oak mixed forests with elm, hornbeam and beech ). During the humid - temperate, the current climate very similar younger Subatlantic (pollen zone X a) established the mixed beech forest or a pure beech forest. Dominating was now, however, which began in the Bronze Age anthropogenic arable, meadow, pasture and forest use. The current youngest Subatlantic (pollen zone X b ) also has a humid temperate climate with a marked, decreasing from west to east Jahresniederschlagsgradienten. Untreated, original forests are not as good as more and have made a cultural forest floor space.

In northwestern Germany the mixed oak forest (EMW ) remained during the Elder Subatlantikums with around 40 % of the tree pollen while determining element, but showed strong fluctuations among a decline in younger Subatlantic. Elms and lime trees as components of oak mixed forest remained constant. The alders went from initially 30 % to 10% back. Even the pine trees were down, but showed in the Last Subatlantic a huge, forestry -related spread. Hazel (15%), birch ( 5%) and willow ( <1%) preserved in about their holdings. Significantly, however, was the significant spread of beech (from 5 to 45%) and hornbeam ( from 1 to 15%). According to HM Müller been triggered by the increase in Humidität from about 550 BC and then beneficiary by the easing of settlement activity during the migration period.

The proportion of herbs ( including cornflowers, Log growths, sorrel and plantain ) of the total pollen also grew very significantly ( from 15 to 65%). Also Getreidetaxa were detected increased; they show an increase of 5 to 30% of the increased farming in the younger Subatlantic.

In northern Germany ( East Holstein ) the historical development of vegetation was very similar. Also noteworthy here is the rapid increase of non- arboreal pollen from 30 to over 80 % in the younger Subatlantic (including an increase in grain from 2 to about 20%). Among the tree pollen of the mixed oak forest has retained its position with 30 %. The alder posted here also a decrease ( from 40 to 25 %). In about the same ( with minor fluctuations) birch, beech and hornbeam remained (but at the beginning of the Younger Subatlantikums latter had a clear optimum). Also striking here is the rise of the jaw in the Last Subatlantic.

The following marker horizons could be excreted in East Holstein ( from young to old):

• Kiefer rise ( K) - 1800 AD - for forestry -related
• Book Summit 2 (F 2)
• Book summit 1 (F 1) - around 1300 AD Around 800 AD in Lower Saxony AD
• Hazel Maximum 5 (C 5) - climate-related - 200 to 400 AD.

Fauna

The faunal diversity is realized through the promoted since the mid-18th century industrialization and its accompanying environmental degradation strongly in decline. Alarming proportions adopted from 1985 this development. So is the Living Planet Index by the year 2000 in the vertebrates a decline in biodiversity by 40%. Particularly hard hit are animals in freshwater ecosystems, their biodiversity (mainly by habitat loss and water pollution ) declined by 50%.

Summary

The noticeable since the Neolithic Revolution in the Atlantic period already become human impact on their environment was reinforced during the Subatlantikums rapidly. The Last Subatlantic should represent in the earth's history so far initial period, pushing in which anthropogenically forced spikes ( environmental stimuli ) by far natural control loops in the background. Whether and to what extent these anthropogenic inputs may be compete with the geological past catastrophic events remain undecided.