The 4.2 ka event in the vegetation record of the central Mediterranean

Abstract

Abstract. In this paper, the variation in forest cover in the central Mediterranean region, reflected by percentage changes in the arboreal pollen record, has been examined in relation to the 4.2 ka event. A total of 36 well-dated and detailed pollen records from latitudes between 45 and 36∘ N were selected and their vegetation dynamics between 5 and 3 ka examined in relation to the physiographic and climatic features of the study area and to the influence of human activity on past vegetation, as suggested by anthropogenic pollen indicators. We have found that the sites located between 43 and 45∘ N do not show any significant vegetation change in correspondence with the 4.2 ka event. Several sites located on the Italian Peninsula between 39 and 43∘ N show a marked opening of the forest, suggesting a vegetation response to the climate instability of the 4.2 ka event. Between 36 and 39∘ N, a forest decline is always visible around 4.2 ka, and in some cases it is dramatic. This indicates that this region was severely affected by a climate change towards arid conditions that lasted a few hundred years and was followed by a recovery of forest vegetation in the Middle Bronze Age. Human activity, especially intense in southern Italy, may have been favored by this natural opening of vegetation. In Sardinia and Corsica, no clear change in vegetation is observed at the same time. We suggest that during the 4.2 ka event southern Italy and Tunisia were under the prevalent influence of a north African climate system characterized by a persistent high-pressure cell.

Influence of the North Atlantic subpolar gyre circulation on the 4.2 ka BP event

“…A short event centered at 4200 cal BP (and possibly around 3900 cal BP) showing a decrease of Fagus in favor of Quercus may be indicative of a brief spell of moderate dryness. This change can be related to a lower temperate forest development seen in the central Italy records of Lago di Vico and Lagaccione (Magri and Sadori, 1999;Magri, 1999) and in the Gulf of Gaeta (Di Rita et al, 2018). In central Italy and in the Gulf of Lion, pollen data do not show a significant change in vegetation but only a modification of the forest composition that corresponds to a slight decrease in precipitation (Di Rita and Magri, 2019; this issue).…”

Western Mediterranean hydro-climatic consequences of Holocene ice-rafted debris (Bond) events

“…Central European palaeoclimatic archives, such as the well-dated Spannagel Cave speleothems in the Central Alps provide evidence of a cold and winter-dry climate around 4.2 ka (Mangini et al, 2007;Fohlmeister et al, 2012). Furthermore, in central and southern Italy, many speleothems and pollen records indicate a cold and dry climate around 4.2 ka (Margaritelli et al, 2016;Zanchetta et al, 2016;Di Rita and Magri, 2019). However, Western Mediterranean palaeo-environmental archives do not show uniform climatic patterns around 4.2 ka (Bini et al, 2018), although multiple studies report an arid interval at that time: in northeastern Spain a prominent speleothem record indicates cold and dry conditions around 4.2 ka.…”

A multidisciplinary study of an exceptional prehistoric waste dump in the mountainous inland of Calabria (Italy): Implications for reconstructions of prehistoric land use and vegetation in Southern Italy

“…(2011) came to quite different conclusions, partly based on the same record (Monticchio), for the nearby but lower Basilicata. They concluded that repeated phases of increased fluvial activity are probably climatically driven (see also Figure 10), implying a far more variable climatic record than described by Di Rita and Magri (2019). Furthermore, they stated that ‘it is in the last 2000 years that human impact forces enhanced geomorphic activity’.…”

“…Detailed mid/late-Holocene palaeorecords for the uplands of mainland Southern Italy are scarce and limited to those for Lago Trifoglietti (De Beaulieu et al, 2017;Joannin et al, 2012) and for Lago Grande di Monticchio (Allen et al, 2002). Di Rita and Magri (2019) reviewed the impact of the 4.2 ka event in the vegetation record of the central Mediterranean and concluded that for both palaeorecords changes in vegetation related to this climatic event are uncertain. Moreover, they stated that for Monticchio 'no vegetation change is unambiguously attributed to human impact' by Allen et al (2002), though Allen et al reported that 'the last 2000 years are made distinctive by evidence for forest clearance and agricultural activity'.…”