Abstract
During the period of instrumental records, the North Atlantic Oscillation (NAO) has strongly influenced inter-annual 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 cross-correlated 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 1100years. 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 hydro-climatic 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.
Highlights
A recent issue of debate in the reconstruction and understanding of climate dynamics during the Medieval Climate Anomaly (MCA, Stine, 1994) is the spatio-temporal character of temperature anomalies and their synchroneity around the globe
Spatial patterns in hydro-climate revealed by proxy data have the potential to distinguish between alternative modes of past atmospheric circulation
This relationship is clearest in parts of Iberia and northern Morocco, where increases in precipitation are associated with anomalous high pressure dominance over Northern Europe
Summary
A recent issue of debate in the reconstruction and understanding of climate dynamics during the Medieval Climate Anomaly (MCA, Stine, 1994) is the spatio-temporal character of temperature anomalies and their synchroneity around the globe The Mediterranean basin is influenced by some of the most important mechanisms acting upon the global climate system (Xoplaki, 2002) It marks a transitional zone between the North African–Arabian arid zone dominated by subtropical high pressure and central–northern Europe affected by westerly circulation. The strongest positive correlation with the NAO index is located over Iberia (Fig. 1) linked to anomalous high pressure dominance over Northern Europe and below normal sea level pressure over the Azores region (negative NAO conditions) With this surface NAO pattern, the 500hPa geopotential level is anomalously high (low) in the area of the Icelandic Low and anomalously low (high) across the regions of the subtropical anticyclone and Europe in general, which forces North Atlantic low pressure systems to follow a more northern route and is associated with drier winters in Spain. We use statistical analysis to examine correlations between lake records located at the western and easternmost extremes of the Mediterranean basin in order to test the spatial coherence of hydrological changes during the last millennium
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