Friesland phase

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The Friesland phase was rapid global warming at the beginning of the Holocene .

definition

The term Friesland phase (or Friesland phase), also Friesland fluctuation or Friesland oscillation , was introduced in 1973 by Johannes Iversen in Denmark . It goes back to its type locality Friesland . At that time Iversen had equated it with the preboreal fluctuation , which, however, expired later. Karl-Ernst Behre defined the term as the Friesland fluctuation as early as 1966 .

Temporal position

The Preboreal and thus the Holocene begin with the Friesland phase . It immediately follows the Younger Dryas and is replaced by the preboreal fluctuation (Rammelbeek phase).

Dating

The beginning of the Holocene and thus the Friesland phase is usually associated with the period 9700 to 9610 BC. Chr. Indicated. In a recalibration, the period 9530 to 9500 BC is also included. Envisaged. The end of the Friesland phase is between 9480 and 9400 BC. Dated or recalibrated 9430 to 9350 BC. Chr.

description

The main feature of the Friesland phase is a very rapid warming, illustrated by the increase in summer average temperatures . For the temperature rise, Bos u. a. (2007) based on plant associations a July average value of up to 3 ° C. The δ 18 O values ​​in the ice cores of Greenland show up to around 9570 BC. A sudden increase of 5 ‰, to then slowly decrease again (with a minimum at 9440 BC). The Δ 14 C values ​​show a comparable development, they also increase initially by around 20 ‰ and then gradually return to their original position. The development of δ 15 N and δ 40 Ar is also comparable .

At the same time, however, there was also an increase in precipitation , but the snow accumulation values in Greenland strangely show a minimum between 9470 and 9420 BC. The rise in temperature in turn caused an increase in biological production and a transition to sediments enriched in organic carbon. The increase was not uniform, but was interrupted again by a brief cold relapse, which led to clearings in the birch forest. Towards the end of Friesland phase (.. Period 9500-9450 BC) have in west central Europe lakes reaches a high water level and the atmospheric CO 2 - concentration was greatly increased (from 260 to 330 ppmv).

Effects on vegetation

In general, there was a sharp increase in tree and shrub pollen during the Friesland phase , while sweet grasses (Poaceae) and herbs from higher locations declined .

In the Netherlands , immediately after the sudden warming, the vegetation responded with an expansion of the boreal birch forest in the period 9580 to 9350 BC. BC, including mainly Betula pubescens , Betula nana , but also poplars ( Populus ). This was immediately preceded by a sharp increase in juniper pollen ( Juniperus ). The pine stocks and non-tree pollen, including crowberries ( Empetrum ), were generally declining and the heather-like (Ericales) disappeared (in East and West Friesland , however, the pines still had a brief advance at the beginning of the Friesland phase). Former pine areas were gradually occupied by birch trees. During the brief relapse of the cold, open vegetation with dwarf shrubs and herbs formed again in places .

A further expansion of the forest was abruptly interrupted at the beginning of the Rammelbeek phase and from now on grasslands dominated .

causes

Since no external forcing mechanism can adequately explain the strong warming from the end of the Younger Dryas, the cause must be sought in the internal dynamics of the ocean . It is assumed that the oceanic circulation in the Atlantic follows two stable modes. During the last glacial , the oceans had mostly stabilized in a cooler circulation mode. Ganopolski and Rahmstorf (2001) were able to show, however, that only a slight step is required to switch from cooler to warmer mode. The warming is increased by a positive feedback mechanism called advective feedback . Here, salty water of the lower latitudes is drawn to the sinking areas by the circulation that has started due to the warming - which in turn only intensifies the sinking process.

See also

Individual evidence

  1. ↑ 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 .
  2. ^ SO Rasmussen, among others: A new Greenland ice core chronology for the last glacial termination . In: Journal of Geophysical Research . 111, D06102, 2006.
  3. ↑ B. van Geel, SJP Bohncke, H. Dee: A palaeoecological study of an upper Lateglacial and Holocene sequence from “De Borchert,” The Netherlands . In: Review of Palaeobotany and Palynology . tape 31 , 1981, pp. 367-448 .
  4. ↑ a b Bos, Johanna AA et al .: Preboreal climate oscillations in Europe: Wiggle-match dating and synthesis of Dutch high-resolution multi-proxy records . In: Quaternary Science Reviews . tape 26 , 2007, p. 1927-1950 .
  5. ^ SJ Johnsen, inter alia: The 18O record along the Greenland Ice Core Project deep ice core and the problem of possible Eemian climate instability . In: Journal of Geophysical Research . tape 102 , 1997, pp. 26397-26410 .
  6. ↑ van der Plicht, J. et al: The Preboreal climate reversal and a subsequent solar-forced climate shift . In: Journal of Quaternary Science . tape 19 , no. 3 , 2004, p. 263-269 .
  7. ↑ RB Alley, u. a .: Visual-stratigraphic dating of the GISP2 ice core: Basis, reproducibility, and application . In: J. Geophys. Res. Oceans . tape 102 , 1997, pp. 26367-26381 .
  8. ↑ WZ Hoek, SJP Bohncke: Climatic and environmental events over the load termination, as recorded in The Netherlands; a review . In: Netherlands Journal of Geosciences . tape 81 , 2002, pp. 123-137 .
  9. ↑ SJP Bohncke, WZ Hoek: Multiple oscillations during the preboreal as recorded in a calcareous Gyttja, Kingbeekdal, The Netherlands . In: Quaternary Science Reviews . tape 26 , 2007.
  10. ^ M. Magny, among others: Early-Holocene climatic oscillations recorded by lake-level fluctuations in west-central Europe and in central Italy . In: Quaternary Science Reviews . tape 26 , 2007.
  11. ^ F. Wagner, inter alia: Century-scale shifts in Early Holocene atmospheric CO2 concentrations . In: Science . tape 284 , 1999, pp. 1971-1973 .
  12. ↑ Bos, JAA et al.: 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. ^ T. van der Hammen, TA Wijmstra: The Upper Quaternary of the Dinkel Valley (Twente, Eastern Overijssel, The Netherlands) . In: Mededelingen Rijks Geological Service, Nieuwe Serie . tape 22 , 1971, p. 55-213 .
  14. ^ S. Rahmstorf: Ocean circulation and climate during the past 120,000 years . In: Nature . tape 419 , 2002, pp. 207-214 .
  15. ^ A. Ganopolski, S. Rahmstorf: Rapid changes of glacial climate simulated in a coupled climate model . In: Nature . tape 409 , 2001, p. 153-158 .