Palaeolimnological evidence for an east–west climate see-saw in the Mediterranean since AD 900

Abstract

During the period of instrumental records, the North Atlantic Oscillation (NAO) has strongly influenced interannual precipitation variations in the western Mediterranean, while some eastern parts of the basin have shown an anti-phase relationship in precipitation and atmospheric pressure. Here we explore how the NAO and other atmospheric circulation modes operated over the longer timescales of the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). High-resolution palaeolimnological evidence from opposite ends of the Mediterranean basin, supplemented by other palaeoclimate data, is used to track shifts in regional hydro-climatic conditions. Multiple geochemical, sedimentological, isotopic and palaeoecological proxies from Estanya and Montcortés lakes in northeast Spain and Nar lake in central Turkey have been crosscorrelated at decadal time intervals since AD 900. These dryland lakes capture sensitively changes in precipitation/evaporation (P/E) balance by adjustments in water level and salinity, and are especially valuable for reconstructing variability over decadal-centennial timescales. Iberian lakes show lower water levels and higher salinities during the 11th to 13th centuries synchronous with the MCA and generally more humid conditions during the 'LIA' (15th-19th centuries). This pattern is also clearly evident in tree-ring records from Morocco and from marine cores in the western Mediterranean Sea. In the eastern Mediterranean, palaeoclimatic records from Turkey, Greece and the Levant show generally drier hydro-climatic conditions during the LIA and a wetter phase during the MCA. This implies that a bipolar climate see-saw has operated in the Mediterranean for the last 1100 years. However, while western Mediterranean aridity appears consistent with persistent positive NAO state during the MCA, the pattern is less clear in the eastern Mediterranean. Here the strongest evidence for higher winter season precipitation during the MCA comes from central Turkey in the northeastern sector of the Mediterranean basin. This in turn implies that the LIA/MCA hydroclimatic pattern in the Mediterranean was determined by a combination of different climate modes along with major physical geographical controls, and not by NAO forcing alone, or that the character of the NAO and its teleconnections have been non-stationary.

Vegetation dynamics in the Northeastern Mediterranean region during the past 23 000 yr: insights from a new pollen record from the Sea of Marmara

“…A role of the Siberian High (SH), which is responsible for severe cold and dry winter conditions and polar/continental air outbreaks over the Aegean Sea (Rohling et al, 2002), is instead invoked to explain the evidence of 8.2 event in Tenaghi Philippon record ) and centennial-scale SST cooling events in the Aegean Sea (Marino et al, 2009). Finally, comparison of palaeolimnological records from Eastern and Western Mediterranean has highlighted that NAO forcing alone cannot explain the hydrology pattern in Eastern Mediterranean since 900 AD (Roberts et al, 2012). In order to precisely establish the correlation between these two climate systems (SH/NAO) during the late-glacial and Holocene, it is necessary to make a comparison of our data with high-resolution pollen sequences from areas not affected by the SH (i.e.…”

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

“…In contrast, isotope records from western Mediterranean lakes do not show such a pattern, suggesting a possible NW-SE bipolar contrast in climate history across the Mediterranean during the Holocene. In more recent syntheses of the mid-Holocene climatic transition in the Mediterranean, Roberts et al (2011Roberts et al ( , 2012 observed that both model output and proxy data suggest an east-west division in the Mediterranean climate history. Regarding the western Mediterranean, they also noted that early Holocene changes in precipitation were smaller in magnitude and less coherent spatially, and that rainfall reached a maximum during the mid-Holocene, around 6000-3000 cal BP, before declining to present-day values.…”

The Islamic cemetery at 33 Bartomeu Vicent Ramon, Ibiza: investigating diet and mobility through light stable isotopes in bone collagen and tooth enamel

“…The sites differ in age, with those on the mainland all being late medieval (thirteenth/fourteenth to sixteenth centuries) while the Balearic sites are earlier (tenth to thirteenth centuries). The decrease in rainfall in the western Mediterranean during the Medieval Climatic Anomaly might be expected to favour millet and sorghum, both drought resistant and with short growing seasons, but this event dates to the eleventh to thirteenth centuries (Roberts et al 2012), and so largely overlaps both the mainland and insular sites.…”