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Holocene climate proxy data, with a focus on European terrestrial records
Bas van Geel
Institute for Biodiversity and Ecosystem Dynamics, Universiteit van Amsterdam
Kruislaan 318, 1098 SM Amsterdam, The Netherlands
Lake deposits are an important archive for palaeoclimate studies. For example, a record of
annually laminated lake sediments from Holzmaar showed that the early Holocene was
interrupted by two short periods (ca 200-300 years) of climatic deteriorations, the Preboreal
Oscillation and the Boreal Oscillation. Drastic changes in varve thickness and varve
composition indicate cooler and wetter climatic conditions during winter (Brathauer et al.,
2000). A considerable increase of the thickness of laminae of Maar lakes around 800 cal
BC (Zolitschka and Negendank, 1998) may well be the effect of increased precipitation and
erosion, because there is a considerable amount of evidence for a shift to cooler and wetter
climatic conditions from a variety of other natural archives. However, the recorded
contemporaneous increase of palynological human impact indicators may indicate that an
increased human population density was - partly or only - responsible for increased erosion
and soil dust, and therefore increased deposition of sediments. Cores from shallow lakes or
cores taken near lake borders may show climate induced lake level changes in a better way
than cores from deep lakes. A detailed synchroneity of Holocene lake level changes is
evident from a study in the Jura mountains, the French Pre-Alps and the Swiss Plateau. A
comparison of this lake level record with GISP data, North Atlantic ice-rafting debris
events and the fluctuations of the radiocarbon content of the atmosphere suggests
teleconnections in a complex cryosphere-ocean-atmosphere system (Magny, 1993; in
press), with an important role of the sun as the triggering factor.
Holocene peat deposits are valuable archives for the study of climate change. Comparisons
of the fluctuations of the 14C content in raised bog deposits with the changing species
composition of the peat-forming plants shows - like the above-mentioned lake level record
- that changing solar activity plays an important role. A Preboreal Oscillation - with
evidence for a temporary decline in solar activity as its cause - has been recorded in peat
deposits (van der Plicht et al., submitted), and the evidence for a sun-induced shift to
cooler, wetter climatic conditions around 850 cal BC is clearly reflected in raised bog
deposits (van Geel et al., 1996, 1998). The Little Ice Age climate anomalies are also
reflected as wet shifts in European peat deposits (Mauquoy et al., 2002).
Based on the study of natural archives, there is strong evidence for an important role of the
sun in Holocene climate changes (compare Bond et al., 2001; Neff et al., 2001). However,
changes in solar activity are very small and clear amplification mechanisms have not yet
been identified with certainty. Cosmic ray intensity, modulated by solar wind, might play a
role as an amplification mechanism for solar forcing of climate change. Cosmic rays could
have an effect on the formation of clouds (Svensmark and Friis-Christensen, 1997).
However, there is evidence from the past (spatial patterns of climate change; van Geel and
Renssen, 1998) showing that changing intensities of UV radiation might be more important
as part of an amplification mechanism than fluctuations of the cosmic ray intensity (van
Geel et al., 2001). Measurements of palaeo-UV levels could be important for understanding
the role of the sun in climate change. The fluctuations of UV-absorbing compounds in the
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walls of pollen grains probably can be used for the reconstruction of changing UV-levels in
the past (Rozema et al., 2002).
References
Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S.,
Lotti-Bond, R., Hajdas, I. and Bonani, G., 2001. Persistent solar influence on North
Atlantic climate during the Holocene. Science 294: 2130-2136.
Brathauer, U., Brauer, A., Negendank, J.F.W. and Zolitschka, B., 2000. Rasche
Klimaänderungen am Beginn der heutigen Warmzeit. Zweijahresbericht
GeoForschungsZentrum Potsdam (1998/1999): 29-33.
Magny, M., 1993. Solar influences on Holocene climatic changes illustrated by
correlations between past lake-level fluctuations and the atmospheric 14C record.
Quaternary Research 40: 1-9.
Magny, M., in press. Holocene climate variability as reflected by mid-European lakelevel fluctuations, and its probable impact on prehistoric human settlements.
Quaternary International
Mauquoy, D., van Geel, B., Blaauw, M. and van der Plicht, J., 2002. Evidence from
northwest European bogs shows ‘Little Ice Age’ climatic changes driven by
variations in solar activity. The Holocene 12: 1-6.
Neff, U., Burns, S.J., Mangini, A., Mudelsee, M., Fieltmann, D. and Matter, A., Strong
coherence between solar variability and the monsoon in Oman between 9 and 6 kyr
ago. Nature 411: 290-293.
Rozema, J., van Geel, B., Björn, L.O., Lean, J. and Madronich, S., 2002. Towards solving
the UV puzzle. Science 296: 1621-1622.
Svensmark, H. and Friis-Christensen, E., 1997. Variation of cosmic ray flux and global
cloud coverage: a missing link in solar-climat relationships. Journal of Atmospheric
and Solar-Terrestrial Physiscs 59: 1225-1232.
van der Plicht, J., van Geel, B., Bohncke, S.J.P., Bos, J.A.A., Blaauw, M., Speranza,
A.O.M., Muscheler, R. and Björck, S., submitted. Early Holocene solar forcing of
climate change in Europe.
van Geel, B., Buurman, J. and Waterbolk, H.T., 1996. Archeological and paleoecological
indications for an abrupt climate change in The Netherlands and evidence for
climatological teleconnections around 2650 BP. Journal of Quaternary Science 11:
451-460.
van Geel, B., van der Plicht, J., Kilian, M.R., Klaver, E.R., Kouwenberg, J.H.M.,
Renssen, H., Reynaud-Farrera, I. and Waterbolk, H.T., 1998. The sharp rise of ∆14C
ca. 800 cal BC: possible causes, related climatic teleconnections and the impact on
human environments. Radiocarbon 40: 535-550.
van Geel, B., Renssen, H. and van der Plicht, J., 2001. Evidence from the past: solar
forcing of climate change by way of cosmic rays and/or by solar UV? Proceedings
Workshop on Ion-Aerosol-Cloud Interactions, Geneva, ed. J. Kirkby, CERN 2001007: 24-29.
Zolitschka, B., Negendank, J.F.W., 1998. A high resolution record of Holocene
palaeohydrological changes from Lake Holzmaar, Germany. Paläoklimaforschung,
25; ESF Special Issue 17, 37-52.
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Caption for illustration:
The Subboreal-Subatlantic transition in a raised bog deposit in the Netherlands. The
darker, more decomposed Subboreal peat was deposited under relatively warm and dry
climatic conditions. After a decline of solar activity (reflected by a strong increase of the
radiocarbon content) the peat composition showed a drastic change. The lighter colored
Subatlantic peat was formed under cooler, wetter climatic conditions. The reconstruction
of the species composition of the peat-forming vegetation, which is based on the analysis
of macrofossils, gives support to the idea of climate change.
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