Timing and trigger mechanisms of abrupt cold events during the Holsteinian interglacial based on analyses of annually laminated sediments
Zusammenfassung der Projektergebnisse
Based on similarities with regard to orbital climate forcing, Marine Isotope Stage (MIS) 11 represents one of the closest astronomical analogues for present and future climate. Hence, insights into the climate variability of MIS 11 can contribute to a better understanding of the climatic evolution of the present (Holocene) interglacial as it would occur without human interference. Since the Holsteinian interglacial is widely accepted to be the terrestrial equivalent of MIS 11c in central Europe, the two cold events that are documented within Holsteinian records from sites across NW-Europe gain crucial relevance. The goal of project was to examine the timing and trigger mechanisms of these two cold events during the Holsteinian based on analyses of annually laminated sediments from the site Dethlingen, northern Germany. The study applies a multi-proxy approach including palynological, micropaleontological, sedimentological, geochemical and time series analyses within a well constrained varve chronology. The vegetation succession at Dethlingen as inferred from pollen data shows the prevalence of mild climatic conditions during the Holsteinian and suggest a general warming trend and decreasing seasonality over the course of the interglacial. The data show that the Holsteinian interglacial was punctuated by abrupt and gradual changes in the abundances of temperate plant taxa. These changes indicate considerable intra-interglacial climate variability. In particular, two marked declines of temperate taxa leading to the transient development of boreal and sub-boreal forests were triggered by centennial-scale climate oscillations, here termed Older and Younger Holsteinian Oscillations (OHO and YHO). These oscillations occurred ~6000 and ~9000 years after the onset of the interglacial pioneer forestation in central Europe, respectively. To assess the impact of the OHO and YHO on terrestrial ecosystems and to investigate the underlying driving mechanisms, the critical intervals at Dethlingen were subjected to decadal-scale palynological and sedimentological analyses. The data show that the OHO comprises a 90-year-long decline and subsequent 130-yearlong recovery of temperate taxa. Owing to its highly characteristic imprint on vegetation dynamics, the OHO can be identified in pollen records from the British Isles to Poland. A close inspection of individual pollen records from that region reveals the prevalence of colder winters during the OHO, with a gradient of decreasing temperature and moisture availability towards eastern Europe. This pattern points to a weakened influence of the westerlies and/or stronger influence of the Siberian High connected to the OHO. The vegetation dynamics during the YHO shows a decline of temperate taxa and the expansion of pioneer trees. In contrast to the OHO, frost-sensitive taxa continued to thrive. This suggests that mean winter temperatures remained relatively high (>0 ºC) during the YHO pointing to a decrease of summer warmth. The YHO had a duration of 300 years and is centred within a long-term (~1500-year) decline and subsequent, millennial-scale recovery of temperate taxa. Because the impact of the OHO and the YHO on the vegetation was markedly different, both climate oscillations may have been caused by different trigger mechanisms. For the OHO, the inferred regional-scale winter cooling over central Europe lasting for several decades points to a decrease in ocean heat transport, eventually related to a transient slowdown in North Atlantic Deep Water formation. This view is supported by the resemblance of the OHO to the 8.2 ka event of the Holocene with regard to the duration, imprint on terrestrial ecosystems, spatial pattern of the climatic impact, timing within the respective interglacial, and prevailing interglacial boundary conditions. In contrast, the presence of frost-sensitive taxa during the YHO appears to exclude a reduction in oceanic heat transport as proposed for the OHO. Instead, the long-term and gradual changes in the abundances of temperate taxa suggest a connection of the YHO to orbital forcing. We conclude the goal of the project to examine the timing and trigger mechanisms of the two cold events during the Holsteinian based on analyses of annually laminated sediments from the site Dethlingen, northern Germany, have been attained.
Projektbezogene Publikationen (Auswahl)
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(2009). Vegetation setbacks within the Holsteinian interglacial (MIS 11) as recorded in an annually-laminated core from Dethlingen paleolake, Northern Germany. Geophysical Research Abstracts, Vol. 11
Koutsodendris, A., Müller, U.C., Brauer, A., Pross, J.
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(2010). A climatically driven abrupt vegetation setback during the Holsteinian interglacial (MIS 11). Cioppino workshop “Transient changes in past warm climates”, Urbino, Italy
Koutsodendris, A., Müller, U.C., Pross, J., Brauer, A., Fletcher, W.F., Lotter, A.F.
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(2010). Intra-Holsteinian (MIS 11) climate variability reconstructed from microfacies and micropaleontological analyses of the Dethlingen core (northern Germany). 18th International Sedimentological Congress (ISC), Mendoza, Argentina
Koutsodendris, A., Müller, U.C., Pross, J., Brauer, A., Lotter, A.F.
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(2010). Vegetation dynamics and climate variability during the Holsteinian interglacial based on a pollen record from Dethlingen (northern Germany). Quaternary Science Reviews, 29: 3298-3307
Koutsodendris, A., Müller, U.C., Pross, J., Brauer, A., Kotthoff, U., Lotter, A.F.
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2010. Trophic state shifts within the Holsteinian interglacial (Middle Pleistocene) as recorded in an annually-laminated diatomite from Dethlingen (Northern Germany). 10th Nederlands Aarwetenschappelijk Congres (NAC), Veldhoven, The Netherlands
Verhagen, F.T.M., Koutsodendris, A., Lotter, A.F.
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(2011). A short-term climate oscillation during the Holsteinian interglacial (MIS 11c): Characteristics, spatial extent and potential triggering mechanisms. 18th INQUA-Congress, Bern, Switzerland
Koutsodendris, A., Pross, J., Müller, U.C., Brauer, A., Fletcher, W.J., Lotter, A.F.
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(2011). Sub-decadal- to decadal-scale climate cyclicity during the Holsteinian interglacial (MIS 11) evidenced in annually laminated sediments. Climate of the Past, 7: 987-999
Koutsodendris, A., Brauer, A., Pälike, H., Müller, U.C., Dulski, P., Lotter, A.F., Pross, J.
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(2011). Subdecadal- to decadal-scale climate variability during the Holsteinian interglacial (MIS 11) evidenced in varves from northern Germany. Geophysical Research Abstracts, Vol. 13
Koutsodendris, A., Brauer, A., Pälike, H., Pross, J., Müller, U.C., Lotter, A.F.
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AA short-term climate oscillation during the Holsteinian interglacial (MIS 11c): An analogy to the 8.2 ka climatic event? Global and Planetary Change
Koutsodendris, A., Pross, J., Müller, U.C., Brauer, A., Fletcher, W.J., Kühl, N., Kirilova, E., Verhagen, F.T.M., Lücke, A., Lotter, A.F.
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Evolution of a Holsteinian (MIS 11c) palaeolake based on a 12-ka-long diatom record from Dethlingen (northern Germany)
Koutsodendris, A., Lotter, A.F., Kirilova, E., Verhagen, F.T.M., Brauer, A., Pross, J.
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Comparison of the paleoclimatic significance of higher land plant biomarker concentrations and pollen data: A case study of lake sediments from the Holsteinian interglacial. Organic Geochemistry
Regnery, J., Püttmann, W., Koutsodendris, A., Mulch, A., Pross, J.
