Abrupt climate changes of the last deglaciation detected in a western Mediterranean forest record

Abstract

Abstract. Evidence for abrupt changes in western Mediterranean climate between 20 and 6 cal ka BP is examined in marine core MD95-2043 (Alborán Sea), using pollen data for temperate Mediterranean forest development and pollen-based climate reconstructions using the modern analogue technique (MAT) for annual precipitation (Pann) and mean temperatures of the coldest and warmest months (MTCO and MTWA). Major climatic shifts with parallel temperature and precipitation changes occurred at the onsets of Heinrich Event 1 (equivalent to the Oldest Dryas), the Bölling-Allerød (BA), and the Younger Dryas (YD). Multi-centennial-scale oscillations in forest development related to regional precipitation (Pann) variability occurred throughout the BA, YD, and early Holocene, with drier atmospheric conditions 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 (events at 11.4, 10.1, 9.3, 8.2 and 7.4 cal ka BP). The forest record also indicates multi-centennial variability within the YD interval and multiple Preboreal climate oscillations. 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 jet stream 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 Alborán Sea by ~200 years (surface water age ~600 years) during the Lateglacial.

Strengths and Weaknesses of Quantitative Climate Reconstructions Based on Late-Quaternary Biological Proxies

“…The most striking violation of this basic requirement is provided by the recent study of Fletcher et al (2010) where they use a 3350-sample data-set of terrestrial modern pollen assemblages from a variety of continental sedimentary environments in a MAT-based climate reconstruction for a marine core from the Alboran Sea, despite the well-known differences in taphonomy of terrestrial and marine pollen assemblages. The authors deleted Pinus from the modern and fossil samples because of its over-representation in marine assemblages.…”

“…It is particularly important that all the modern and fossil assemblages are from the same sedimentary environment to minimise variation due to taphonomy, basin size, relevant source areas, etc (cf. Fletcher et al 2010 In order to deal with the problems of taxa responding to different environmental variables, Guiot (1990) derives 'palaeo-bioclimatic operators' to weight preferentially the dissimilarity calculated between the modern and fossil pollen assemblages. An ordination (usually a principal components analysis) is made of all the modern samples, and the distribution of taxa are examined to identify the component axis that is most strongly related to the climatic variable of interest.…”

“…lakes) (Bjune et al 2010) and hence have comparable taphonomies (cf. Minckley & Whitlock 2000;Whitmore et al 2005;Gonzales et al 2009a;Tonello et al 2009;Fletcher et al 2010;Goring et al 2010).…”

Rapid climatic variability in the west Mediterranean during the last 25 000 years from high resolution pollen data

“…This is mainly due to the scarcity of high-resolution sequences covering the last 25 000 years in this region. There is also a lack of robust quantitative estimates of climate parameters in Southern Europe and the Mediterranean for the last 25 000 years (Huntley and Prentice, 1988;Huntley et al, 1999;Allen et al, 2002;Cheddadi et al, 1997Cheddadi et al, , 1998Davis et al, 2003;Brewer et al, 2007;Fletcher et al, 2009;Dormoy et al, 2009).…”

Radiogenic isotopes for deciphering terrigenous input provenance in the western Mediterranean

“…In the Iberian Mediterranean region, pollen sequences reflected a significant environmental variability during the Holocene (Carrión, 2002;Combourieu Nebout et al, 2009;Carrión et al, 2010;Fletcher et al, 2010). The major transition from mesophytic optimum (warm and humid conditions) with a relatively high lake levels to xerophytic conditions and high fire activity is traced to the period from 7.5 to 5.0 ka cal.…”