Subatlantic

The Subatlantic is the current climatic age of the Holocene epoch. It started at about 2,500 years BP and is still ongoing. Its average temperatures were slightly lower than during the preceding Subboreal and Atlantic. During its course the temperature underwent several oscillations which had a strong influence on fauna and flora and thus indirectly on the evolution of human civilizations. With intensifying industrialisation, human society started to stress the natural climatic cycles with increased greenhouse gas emissions. The term subatlantic was first introduced in 1889 by Rutger Sernander to differentiate it from Axel Blytt's atlantic. It follows upon the previous subboreal. According to Franz Firbas (1949) and Litt et al. (2001) it consists of the pollen zones IX and X. This corresponds in the scheme of Fritz Theodor Overbeck to the pollen zones XI and XII. In climate stratigraphy the subatlantic is usually subdivided into an older subatlantic and a younger subatlantic. The older subatlantic corresponds to pollen zone IX (or XI in an alternate nomenclature made of more zones) characterized in central and northern Europe by beech or oak-beech forests, the younger subatlantic to pollen zone X (or XII in the alternate nomenclature made of more zones). In eastern Germany Dietrich Franke subdivides the subatlantic into four stages (from young to old): The beginning of the subatlantic is usually defined as 2,400 calendar years BP or 450 BC. Yet this lower limit is by no means rigid. Some authors prefer to define the start of the subatlantic as 2,500 radiocarbon years which represents roughly 625 BC. Occasionally the onset of the subatlantic has even been pushed back as far as 1200 BC. According to Franz Firbas the changeover from the subboreal (pollen zone VIII) to the older subatlantic (pollen zone IX) is characterized by the recession of hazel and lime and the simultaneous spreading of hornbeam due to anthropogenic influences. This recession was not synchronous. It occurred in the western reaches of the Lower Oder valley between 930 and 830 BC, whereas in southwestern Poland this event had taken place already between 1170 and 1160 BC. The beginning of the younger subatlantic at 1250 AD coincides with the medieval population increase and distinguishes itself by an increase in pine and in indicator plants for human settlements. In Silesia this event can be dated between 1050 and 1270 AD. If one equates the onset of the younger subatlantic with the first maximum of beech occurrence it shifts back to Carolingian times around 700 AD. The summer temperatures of the subatlantic are generally somewhat cooler (by up to 1.0 °C) than during the preceding subboreal, the yearly average temperatures reduced by 0.7 °C. At the same time the winter precipitations augmented by up to 50%. Overall the climate during the subatlantic therefore tends to cooler and wetter conditions. The lower limit of the glaciers in Scandinavia descended during the subatlantic by 100 to 200 meters.