Preboreal fluctuation

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The preboreal fluctuation was a sudden change in climate at the beginning of the Holocene . It took place in the period 9,350 to 9,200 BC. Chr. , And can be in the north and east of the North Atlantic area prove.

definition

The term präboreale fluctuation, even präboreale oscillation , in English preboreal oscillation , abbreviated PBO , going to Lowe and others (1994) and especially on S. Bjorck (1996). However, as early as the 1960s, detailed pollen analysis studies in Central Europe had shown that the original rapid warming at the beginning of the preboreal was followed by a cooling phase. Karl-Ernst Behre called this the Youngest Dryas Period in 1978 in analogy to the previous Younger Dryas . H. Zoller , who works in Switzerland , had already called it the Piottino Oscillation in 1960 ; J. Iversen gave it the name Friesland oscillation or Friesland phase in Denmark in 1973 , but it is now equated with the Rammelbeek phase .

Dating

The preboreal fluctuation was only a very brief event that occurred between the two radiocarbon plateaus of the preboreal. These two plateaus are at 10,000 to 9,900 (9,599 to 9,472 BC) and 9,600 to 9,500 (8,998 to 8,900 BC) radiocarbon years, respectively . Bjorck (1997) consequently placed the fluctuation at 11,300 to 11,150 years BP , i.e. H. in the period 9,350 to 9,200 BC In the Netherlands van der Plicht et al. (2004) put the preboreal fluctuation in the period 9,450 to 9,300 BC. Chr.

description

The preboreal fluctuation, identical to the Bond event 8 , recognizable from the δ 18 O values ​​of the ice cores in Greenland and from varva deposits in Europe , is characterized by a cool and humid climate in north-western and central Europe. The worsening of the climate is documented in changes in the vegetation, in reductions in aquatic biomass, in an increase in soil erosion, in a negative δ 18 O anomaly, in increases in the deuterium and 13 C content in tree rings and in advances or stoppages in the Norwegian and Finnish ice sheet . Brackish water penetrated the Baltic Sea . In Iceland , too , the conditions were cooler than in the previous, early preboreal, recognizable by proxies made of lake sediments and glacial moraines. The cooling was not as strong as in the Younger Dryas . Records in Greenland also confirm ice advances in the early preboreal, which can be attributed to a cool climate with increased precipitation at the same time . Only towards the end of the preboreal fluctuation did the climate recover to such an extent that the mainland ice sheet began to melt. Around 9,300 BC The climate became very humid, with an increase in the atmospheric 14 C content and a decrease in the atmospheric carbon dioxide content .

Effects on vegetation

The response of the vegetation to the cooling was not uniform everywhere. In contrast to the only insignificantly changing pioneer vegetation of Iceland and southern Sweden , the expanding birch - pine forest in Germany and Denmark showed a much greater susceptibility to the deteriorating growth conditions. In northern Germany, for example, the preboreal fluctuation is characterized by a decline in pines and a simultaneous increase in herbal plants such as juniper (Juniperus) and crowberries (Empetrum) . In the Netherlands, the expansion of the birch forest (mainly Betula pubescens, occasionally also Populus ) began with the onset of the preboreal fluctuation around 9,450 BC. An end. The prevailing dry, continental climate favored an open grassland from now on, as evidenced by the significant growth of sweet grasses (Poaceae) . After the end of the Rammelbeek phase, a birch-poplar forest spread again, and pines were also to be found again at that time.

causes

The main cause of the preboreal fluctuations occurring on both sides of the North Sea may have been a greatly increased freshwater inflow and its influence on the thermohaline circulation . This is underpinned by a clear, simultaneous increase in the atmospheric 14 C / 12 C ratio. A slowdown in thermohaline circulation may shift the polar front further south. The freshwater influx can be explained by the drainage of the Baltic ice reservoir and the Agassizsee .

Another cause is possibly the rise in cosmogenic nuclides such as 10 Be and 14 C (around 9,300 BC), which indicate a decrease in solar activity .

Climate-historical development

It now seems to be clear that the preboreal oscillation occurred in two stages. The initial cold phase (Rammelbeek phase) was characterized by a continental climate with warm, dry summers and cold winters. Ice cores in Greenland show that there is very little snow accumulation in this section . From around 9,300 BC. In Northwest Europe, humid conditions set in; in Greenland, normal interglacial conditions returned. The second section was associated with a significant decrease in Sonnan activity.

See also

Individual evidence

  1. ↑ JJ Lowe, among other things: Climatic changes in areas adjacent to the North Atlantic during the glacial – interglacial transition . In: Journal of Quaternary Science . tape 9 , 1994, pp. 185-198 .
  2. ↑ S. Bjorck, among others: Synchronized terrestrial-atmospheric deglacial records around the North Atlantic . In: Science . tape 274 , 1996, pp. 1155-1160 .
  3. ↑ K.-E. Behre: The climatic fluctuations in the European pre-boreal . In: Petermanns Geographische Mitteilungen . tape 2 , 1978, p. 97-102 .
  4. ^ H. Zoller: Pollen analysis studies on the vegetation history of insubric Switzerland . In: Memorandum of the Swiss Society for Natural Sciences . tape 83 , 1960, pp. 45-156 .
  5. ^ J. Iversen: The development of Denmark's Last Glacial . In: Geological Survey of Denmark . Volume V (Series, 7-C), 1973, pp. 126 .
  6. ↑ S. Bjorck, inter alia: The Preboreal oscillation around the Nordic Seas: terrestrial and lacustrine responses . In: Journal of Quaternary Science . tape 12 , no. 6 , 1997, pp. 455-465 .
  7. ↑ a b J. Van der Plicht, among others: The Preboreal climate reversal and a subsequent solar-forced climate shift . In: Journal of Quaternary Science . tape 19 , no. 3 , 2004, p. 263-269 .
  8. ^ SO Rasmussen, among others: A new Greenland ice core chronology for the last glacial termination . In: Journal of Geophysical Research . 111, D06102, 2006.
  9. ↑ T. Litt, H.-U. Schmincke, B. Kromer: Environmental response to climatic and volcanic events in central Europe during the Weichselian Lateglacial . In: Quaternary Science Reviews . tape 20 , 2003, p. 7-132 .
  10. ↑ WR Kapsner, among others: Dominant influence of atmospheric circulation on snow accumulation in Greenland over the last 18,000 years . In: Nature . tape 373 , 1995, pp. 52-54 .
  11. ↑ K.-E. Behre ,: Investigations into the late glacial and early post-glacial vegetation history of East Frisia . In: Ice Age and the Present . tape 17 , 1966, pp. 69-84 .
  12. ↑ JAA Bos, among others: Early Holocene environmental change in the Kreekrak area (Zeeland, SW-Netherlands): a multi-proxy analysis . In: Palaeogeography, Palaeoclimatology, Palaeoecology . tape 227 , 2005, pp. 259-289 .
  13. ↑ TA Wijmstra, A. de Vin: De Dinkel new canal section . In: T. van der Hammen, TA Wijmstra (Ed.): Upper Quaternary of the Dinkel Valley (=  Med. Rijks Geol. Dienst NS . Band 22 ). 1971, p. 101-129 .
  14. ↑ M. Hald, S. Hagen: Early Preboreal cooling in the Nordic seas region triggered by meltwater . In: Geology . tape 26 , 1998, pp. 615-618 .
  15. ^ TG Fisher, inter alia: Preboreal oscillation caused by a glacial Lake Agassiz flood . In: Quaternary Science Reviews . tape 21 , 2002, p. 873-878 .