The Mediterranean region and the Levant have returned some of the clearest evidence of a climatically dry period occurring around 4200 years ago. However, some regional evidence is controversial and contradictory, and issues remain regarding timing, progression, and regional articulation of this event. In this paper, we review the evidence from selected proxies (sea-surface temperature, precipitation, and temperature reconstructed from pollen, δ 18 O on speleothems, and δ 18 O on lacustrine carbonate) over the Mediterranean Basin to infer possible regional climate patterns during the interval between 4.3 and 3.8 ka. The values and limitations of these proxies are discussed, and their potential for furnishing information on seasonality is also ex-plored. Despite the chronological uncertainties, which are the main limitations for disentangling details of the climatic conditions, the data suggest that winter over the Mediterranean involved drier conditions, in addition to already dry summers. However, some exceptions to this prevail -where wetter conditions seem to have persisted -suggesting regional heterogeneity in climate patterns. Temperature data, even if sparse, also suggest a cooling anomaly, even if this is not uniform. The most common paradigm to interpret the precipitation regime in the Mediterranean -a North Atlantic Oscillation-like pattern -is not completely satisfactory to interpret the selected data.

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Reconstruction of last millennia Sea Surface Temperature (SST) evolution is challenging due to the difficulty retrieving good resolution marine records and to the several uncertainties in the available proxy tools. In this regard, the Roman Period (1 CE to 500 CE) was particularly relevant in the socio-cultural development of the Mediterranean region while its climatic characteristics remain uncertain. Here we present a new SST reconstruction from the Sicily Channel based in Mg/Ca ratios measured on the planktonic foraminifer Globigerinoides ruber. This new record is framed in the context of other previously published Mediterranean SST records from the Alboran Sea, Minorca Basin and Aegean Sea and also compared to a north Hemisphere temperature reconstruction. The most solid image that emerges of this trans-Mediterranean comparison is the persistent regional occurrence of a distinct warm phase during the Roman Period. This record comparison consistently shows the Roman as the warmest period of the last 2 kyr, about 2 °C warmer than average values for the late centuries for the Sicily and Western Mediterranean regions. After the Roman Period a general cooling trend developed in the region with several minor oscillations. We hypothesis the potential link between this Roman Climatic Optimum and the expansion and subsequent decline of the Roman Empire.

Abstract. A new high-resolution deglacial and Holocene sea surface temperature (SST) reconstruction is presented for the Alboran Sea (western Mediterranean), based on Mg∕Ca ratios measured in the planktonic foraminifera Globigerina bulloides. This new record is evaluated by comparison with other Mg∕Ca SST records and previously published alkenone SST reconstructions from the same region for both the Holocene and glacial periods. In all cases there is a high degree of coherence between the different Mg∕Ca SST records but strong discrepancies when compared to the alkenone SST records. We argue that these discrepancies are due to differences in the proxy response during deglaciation which we hypothesize to reflect a resilience strategy of G. bulloides, changing its main growth season, and consequently Mg∕Ca records a shorter deglacial warming than alkenones. In contrast, short-term Holocene SST variability is larger in the Mg∕Ca SST than in the alkenone SST records. We propose that the larger Mg∕Ca SST variability is a result of spring temperatures variability, while the smoothed alkenone SST variability represents averaged annual temperatures. The Mg∕Ca SST record differentiates the Holocene into three periods: (1) the warmest SST values occurred during the Early Holocene (11.7–9 cal. kyr BP), (2) a continuous cooling trend occurred during the Middle Holocene that culminated in the coldest Holocene SST having a double cold peak structure centred at around 4.2 cal. kyr BP, and (3) the Late Holocene (4.2 cal. kyr BP to present) did not follow any clear cooling/warming trend although millennial-scale oscillations were enhanced. This SST evolution is discussed in the context of the changing properties in the Atlantic inflow water associated with North Atlantic circulation conditions and also with local hydrographical and atmospheric changes. We propose that a tight link between North Atlantic circulation patterns and the inflow of surface waters into the Mediterranean played a major role in controlling Holocene climatic variability of this region.