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Auxiliary data include one file with alkenone-derived UK'37 data and sea surface temperatures (SST). On these data Figs. 7 and 8 of the manuscript are based. The SST are derived from UK'37 by using the transfer function: SST = 29.876 UK'37 - 1.334 of Conte et al. (2006). The data are against the ages (in A.D.) of samples derived from cores GT91-1 (39[deg]59'23"N, 17[deg]45'25"E), GT89-3 and GT90-3 (both 39[deg]45'43"N, 17[deg]53'55"E ). Also included are composite records for UK'37 and SST. For creating the composite records, GT-89-3 was taken as reference core. In the overlapping period the GT89-3 data seem in general lower than the GT91-1 data. To accommodate for this in the composite record, the average difference (0.0343 UK'37 units; equivalent to 1.023 [deg]C) was subtracted from the GT91-1 record. Hereafter, for each depth in the overlapping interval the respective values (UK'37 or SST) of GT89-3 and GT91-1 were averaged. We have also averaged with 16 additional alkenone measurements, from 1793 to 1851, performed in the GT90-3 core.

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Selected multi-proxy and accurately dated marine and terrestrial records covering the past 2000 years in the Iberian Peninsula (IP) facilitated a comprehensive regional paleoclimate reconstruction for the Medieval Climate Anomaly (MCA: 900-1300 AD). The sequences enabled an integrated approach to land-sea comparisons and, despite local differences and some minor chronological inconsistencies, presented clear evidence that the MCA was a dry period in the Mediterranean IP. It was a period characterized by decreased lake levels, more xerophytic and heliophytic vegetation, a low frequency of floods, major Saharan eolian fluxes, and less fluvial input to marine basins. In contrast, reconstruction based on sequences from the Atlantic Ocean side of the peninsula indicated increased humidity. The data highlight the unique characteristics of the MCA relative to earlier (the Dark Ages, DA: ca. 500-900 years AD) and subsequent (the Little Ice Age, LIA: 1300-1850 years AD) colder periods. The reconstruction supports the hypothesis of Trouet et al. (2009, doi:10.1126/science.1166349), that a persistent positive mode of the North Atlantic Oscillation (NAO) dominated the MCA.

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