Abstract
Abstract. Abrupt changes in Western Mediterranean climate during the last deglaciation (20 to 6 cal ka BP) are detected in marine core MD95-2043 (Alboran Sea) through the investigation of high-resolution pollen data and pollen-based climate reconstructions by the modern analogue technique (MAT) for annual precipitation (Pann) and mean temperatures of the coldest and warmest months (MTCO and MTWA). Changes in temperate Mediterranean forest development and composition and MAT reconstructions indicate major climatic shifts with parallel temperature and precipitation changes at the onsets of Heinrich stadial 1 (equivalent to the Oldest Dryas), the Bölling-Allerød (BA), and the Younger Dryas (YD). Multi-centennial-scale oscillations in forest development occurred throughout the BA, YD, and early Holocene. Shifts in vegetation composition and (Pann reconstructions indicate that forest declines occurred during dry, and generally cool, episodes centred at 14.0, 13.3, 12.9, 11.8, 10.7, 10.1, 9.2, 8.3 and 7.4 cal ka BP. The forest record also suggests multiple, low-amplitude Preboreal (PB) climate oscillations, and a marked increase in moisture availability for forest development at the end of the PB at 10.6 cal ka BP. Dry atmospheric conditions in the Western Mediterranean occurred in phase with Lateglacial events of high-latitude cooling including GI-1d (Older Dryas), GI-1b (Intra-Allerød Cold Period) and GS-1 (YD), and during Holocene events associated with high-latitude cooling, meltwater pulses and N. Atlantic ice-rafting. A possible climatic mechanism for the recurrence of dry intervals and an opposed regional precipitation pattern with respect to Western-central Europe relates to the dynamics of the westerlies and the prevalence of atmospheric blocking highs. Comparison of radiocarbon and ice-core ages for well-defined climatic transitions in the forest record suggests possible enhancement of marine reservoir ages in the Alboran Sea by 200 years (surface water age 600 years) during the Lateglacial.
Highlights
Numerous palaeoclimate records from Greenland ice cores, North Atlantic marine sequences and Northern European terrestrial sequences indicate that the last glacial-interglacial transition was punctuated in the North Atlantic region by abrupt climate changes (e.g. NGRIP members, 2004; Bjorck et al, 1996; Dansgaard et al, 1993; Lehman and Keigwin, 1992; Bard et al, 1987)
While questions remain about the ultimate role of internal climate variability, solar activity, volcanism and other forcings in the origin of these climatic oscillations, several lines of evidence including geological and modelling studies point to disruption of the oceanic thermohaline circulation (THC) by punctuated meltwater discharge as a likely mechanism for abrupt cooling of the North Atlantic region (e.g. Fleitmann et al, 2008; Flesche Kleiven et al, 2008; Renssen et al, 2007; Donnelly et al, 2005; Nesje et al, 2004; Teller et al, 2002; Clark et al, 2001)
We focus on the pollen percentage record of temperate Mediterranean forest (TMF), a summary category which groups all pollen types typical of the thermomediterranean to supramediterranean altitudinal forests, namely Acer, Alnus, Betula, Corylus, Fraxinus excelsior type, Populus, Taxus, Ulmus, Quercus deciduous type, Quercus evergreen type, Quercus suber type, Cistus, Coriaria myrtifolia, Olea, Phillyrea, and Pistacia
Summary
Numerous palaeoclimate records from Greenland ice cores, North Atlantic marine sequences and Northern European terrestrial sequences indicate that the last glacial-interglacial transition was punctuated in the North Atlantic region by abrupt (millennial- and centennial-scale) climate changes (e.g. NGRIP members, 2004; Bjorck et al, 1996; Dansgaard et al, 1993; Lehman and Keigwin, 1992; Bard et al, 1987). In order to improve our understanding of the wider impacts of perturbation of the North Atlantic climate and the mechanisms underlying the transmission of climatic changes, highresolution palaeoclimate records are required from beyond the North Atlantic region. In this respect, the Mediterranean is a key region, being characterised by close atmospheric and oceanic linkages to the North Atlantic region and by a distinct climatic regime and teleconnections to distant climate patterns including the African and Asian monsoons. As such, outstanding questions remain regarding the timing, nature and mechanisms of abrupt climate changes in the Western Mediterranean region
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