Deglacial and Holocene vegetation and climatic changes in the southern Central Mediterranean from a direct land–sea correlation

Abstract

Abstract. Despite a large number of studies, the long-term and millennial to centennial-scale climatic variability in the Mediterranean region during the last deglaciation and the Holocene is still debated, including in the southern Central Mediterranean. In this paper, we present a new marine pollen sequence (core MD04-2797CQ) from the Siculo-Tunisian Strait documenting the regional vegetation and climatic changes in the southern Central Mediterranean during the last deglaciation and the Holocene. The MD04-2797CQ marine pollen sequence shows that semi-desert plants dominated the vegetal cover in the southern Central Mediterranean between 18.2 and 12.3 ka cal BP, indicating prevailing dry conditions during the deglaciation, even during the Greenland Interstadial (GI)-1. Across the transition Greenland Stadial (GS)-1 – Holocene, Asteraceae-Poaceae steppe became dominant till 10.1 ka cal BP. This record underlines with no chronological ambiguity that even though temperatures increased, deficiency in moisture availability persisted into the early Holocene. Temperate trees and shrubs with heath underbrush or maquis expanded between 10.1 and 6.6 ka, corresponding to Sapropel 1 (S1) interval, while Mediterranean plants only developed from 6.6 ka onwards. These changes in vegetal cover show that the regional climate in southern Central Mediterranean was wetter during S1 and became drier during the mid- to late Holocene. Wetter conditions during S1 were likely due to increased winter precipitation while summers remained dry. We suggest, in agreement with published modeling experiments, that the early Holocene increased melting of the Laurentide Ice Sheet in conjunction with weak winter insolation played a major role in the development of winter precipitation maxima in the Mediterranean region in controlling the strength and position of the North Atlantic storm track. Finally, our data provide evidence for centennial-scale vegetation and climatic changes in the southern Central Mediterranean. During the wet early Holocene, alkenone-derived cooling episodes are synchronous with herbaceous composition changes that indicate muted changes in precipitation. In contrast, enhanced aridity episodes, as detected by strong reduction in trees and shrubs, are recorded during the mid- to late Holocene. We show that the impact of the Holocene cooling events on the Mediterranean hydroclimate depend on baseline climate states, i.e. insolation and ice sheet extent, shaping the response of the mid-latitude atmospheric circulation.

North–south palaeohydrological contrasts in the central Mediterranean during the Holocene: tentative synthesis and working hypotheses

“…This is supported by correlations between changes in lake level and NAO (North Atlantic Oscillation) indice over the last millennium (Magny et al, 2011c). Micro-or macro-charcoal and pollen data offer additional support for identifying drought periods favourable to increased frequency of fires as well as to forest declines or the expansion of dry-tolerant plants (Vannière et al, 2008(Vannière et al, , 2011Desprat et al, 2013;Combourieu Nebout et al, 2009. In addition, in the case of Lake Ledro, sedimentological analyses of deep cores enabled us to establish a flood frequency record .…”

“…The numbers in brackets after the names of the sites on the right-hand side of the figure refer to the points located on the map in the upper panel. The Ledro, Accesa and west-central Europe lake-level records are from Magny et al (2007Magny et al ( , 2012b and from ; the records from cores GeoB 7622 and GeoB 5804-4 are from Lamy et al (2006); the record from Siles is from Carrión (2002); the record from core MD04-2797 is from Desprat et al (2013), that from central Tunisian rivers is from Ziehlhofer and Faust (2008); the record from core MD95-2043 is from Fletcher et al (2013); and the record from core GA-112 is from Schilman et al (2001). Horizontal brackets point out a possible complexity of events (see discussion in the text).…”

“…The winter mid-latitude circulation and associated storms reaching Europe may have been determined by a complex interplay between the mid-latitude temperature gradient, the tropical convection and the surface contrast at the North American East coast, which have varied along the Holocene due to changes in insolation and ice-sheet extent (Brayshaw et al, 2011). In particular, in order to explain an increased winter precipitation during the 10000-7000 cal BP interval, Desprat et al (2013) pointed to a possible southern location of the mid-latitudes jet, strengthening the Mediterranean cyclogenesis, in agreement with model simulations in response to a weaker boreal winter insolation (Brayshaw et al, 2011) and to a rapid LIS melting associated with a suppression of the deep convection in the Labrador Sea and a cooling the eastern North Atlantic (Carlson et al, 2008). …”

Holocene vegetation and climate changes in the central Mediterranean inferred from a high-resolution marine pollen record (Adriatic Sea)

“…Both methods have been used extensively for the Holocene climate reconstruction from terrestrial and marine pollen records located in the Mediterranean region (e.g. Davis et al, 2003;Pross et al, 2009;Joannin et al, 2012;Kotthoff et al, 2008a, b;Combourieu-Nebout et al, 2009;Dormoy et al, 2009;Desprat et al, 2013;Sadori et al, 2013) with results that are generally supported by other independent proxies (e.g. lake levels, alkenones, charcoals, etc.)…”

“…This steppic vegetation is recorded in numerous regional pollen records (e.g. Watts et al, 1996;Magri and Sadori, 1999;Denèfle et al, 2000;Allen et al, 2002;Bordon et al, 2009;Kotthoff et al, 2011;Combourieu-Nebout et al, 2009;Fletcher et al, 2010;Desprat et al, 2013). Steppic pollen taxa indicate that coldarid climate conditions prevailed over the whole Mediterranean Basin and especially in the Adriatic Basin during the Younger Dryas (Figs.…”