The Preboreal oscillation around the Nordic Seas: terrestrial and lacustrine responses

Abstract

The occurrence of an early Preboreal climatic cooling/oscillation (PBO) in lacustrine and glacial records from northwest Europe, Iceland and Greenland is reviewed and documented. The often subtle response of the proxy records to this oscillation, in combination with its short duration, make it difficult to detect. Owing to its chronostratigraphic position between the 10000–9900 and 9600–9500 14C plateaux (c. 11300–11150 calendar yr BP) it is also difficult to 14C date with precision. We find that the vegetation response to the PBO varies between sites and regions. In contrast to the pioneer vegetation in Iceland and southern Sweden, the expanding birch–pine forest in Germany–Denmark was more susceptible to deteriorating growing conditions. The combined lacustrine, tree‐ring and glacial records imply that the PBO was characterised by cool and humid conditions throughout northwestern and central Europe. This is documented by vegetation changes, decreased aquatic production, increased soil erosion, increased 2H and 13C content in tree‐rings, readvances or stillstands of the ice sheet in Norway and Finland, and ingression of brackish water into the Baltic. Icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous Preboreal period, but not as extreme as during the Younger Dryas. Greenland records suggest that the early Preboreal was characterised by ice readvances, as an effect of cool climate and increased precipitation (in relation to the Younger Dryas). It was not until the end of the PBO that climate was warm enough to melt the land‐based ice sheet. This Preboreal oscillation, found on both sides of the Nordic Seas, is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the Nordic Seas, which is implied by a simultaneous and distinct rise in the atmospheric 14C/12C ratio. A slow‐down of the thermohaline circulation may temporarily have pushed the Polar Front further south. © 1997 John Wiley & Sons, Ltd.

Environmental and climatic changes in the Jura mountains (eastern France) during the Lateglacial–Holocene transition: a multi-proxy record from Lake Lautrey

“…14 summarise the succession of climatic events recognised from core 6. This sequence of events in general shows a good agreement with that established for the North Atlantic region and west-central Europe (Lotter et al, 1992;Björck et al, 1997 andBjörck et al, 1998;Grafenstein et al, 1999;Ammann et al, 2000;Brauer et al, 2000) and provides some additional indications discussed below.…”

“…between 10,120±40 and 9975±45 14 C yr BP and corresponds to the Preboreal oscillation (PBO) (Lotter et al, 1992;Björck et al, 1997). It was preceded by a short-lived minimum at level 289 cm.…”

“…Finally, the two successive cooling events centred at ca 11,350 and 11,200 cal yr BP have equivalents in the GRIP record, the second corresponding to the PBO (Lotter et al, 1992;Björck et al, 1997) and the first to a precursor episode. Such multiple cold oscillations during the early Holocene have also been observed on the Swiss Plateau Magny et al, 2003) and in Sweden (Björck and Wastergard, 1999).…”

Holocene palaeohydrological changes in the northern Mediterranean borderlands as reflected by the lake-level record of lake ledro, northeastern Italy

“…at the time of the Preboreal oscillation (Björck et al, 1997). This complexity echoes that observed for the same time window at Lake Accesa and, as a working hypothesis, may have resulted from different successive forcing factors (deglaciation and solar activity) as discussed by van der Plicht et al (2004) and Bos et al (2007).…”

Climate versus human-driven fire regimes in Mediterranean landscapes: the Holocene record of Lago dell’Accesa (Tuscany, Italy)

“…2). Magny et al (2006) associated this phase, which is accompanied by a slight decrease in tree pollen, with the Preboreal Oscillation (see Björck et al, 1997;Sangiorgi et al, 2002;Cacho et al, 2006). Both the pollen data from the central lake (this study) and littoral cores (Drescher-Schneider et al, 2007) record an expansion of deciduous thermophilous trees at ca 11,000 cal.…”