Paleoclimatic reconstruction of past interglacial periods and their transitions in the iberianpenínsula and its surrounding seas

Zusammenfassung

This study combines cave speleothems and marine sediments to gain an insight into the climate variability of the Iberian Peninsula (IP) and its surrounding seas associated with previous warm interglacial periods. In particular, it centres in the time period from 530 to 65 kyr BP, thus covering the interglacials comprised within the Marine Isotopic Stages (MIS) 13, 11, 9, 7, and 5, and their associated transitions such as glacial terminations and also the onset of the last glaciation. The speleothems are used as archives for changes in atmospheric moisture availability by means of stable isotopes and Mg/Ca analysis. The studied speleothems correspond mostly from the Balearic Islands (Minorca and Mallorca) but also from the Pyrenees. Marine conditions for the penultimate termination (T-II) and the MIS 5 have been reconstructed in the base to three sediment cores from three different marine locations around the IP: the Cantabrian Sea, the Alboran Sea, and the Balearic Sea. Surface conditions were explored by means of pair analyses of δ18O and Mg/Ca ratios measured in carbonate shells of the planktonic foraminifera Globigerina bulloides. These measurements let to the reconstruction of Sea Surface Temperatures (SST) and sea water δ18Osw values as a proxy of major changes in the regional precipitation/evaporation balance or, during some brief intervals, as an indicator of the arrival of melting waters. In addition, changes in the intensity of western Mediterranean deep convection are explored through additional measurements of grain size distribution and XRF-geochemical ratios performed in the Balearic core (MD99-2343). The studied speleothem collection provides a nearly continuous 450 kyr record, unique for the Mediterranean region, that allows, for the very first time, to reconstruct the hydroclimate of several interglacial periods (MIS 13, 11, 9, 7, and 5). Interglacial periods are characterized by light δ13C and low Mg/Ca ratios pointing to enhanced precipitation and climate amelioration that allowed the expansion of the vegetation cover. On the contrary, heavier/higher δ13C and Mg/Ca ratios during glacial stages highlight their dry conditions with reduced vegetation activity. Glacial terminations (T-III, IV, and V) appear as periods of low rates in speleothem growth while T-II is only represented by growth interruptions. The marine δ18Osw for the T-II supports the occurrence of a major freshening event with comparable light values in the Cantabrian and Mediterranean Sea in correspondence to the Heinrich Event (HE) 11. This major and rapid melt event should have caused major distortions in the hydrological conditions of the Balearic Islands, stopping speleothem growths. Previous terminations are represented by an early light δ18Ospeleo anomaly, likely reflecting that this early deglacial major melting over the Atlantic Ocean was a rule for deglacial initiations. The MIS 5 is studied in detail through the integrated study of marine and speleothem records. During the Last Interglacial (LIG), the sea surface temperature evolution was heterogeneous around the IP with gradients among the three studied seas larger than those from today. The LIG ended earlier in the Cantabrian Sea than in the western Mediterranean Sea, which was coincident with an accelerated aridification phase that marked the glacial inception in a Minorca speleothem at 116.5 kyr BP and preceding the Greenland Stadial 25 (GS). This was the first of a series of stadials that punctuated the early glaciation and where the sea thermal gradient almost disappeared around the IP. These intense coolings during stadials led the development of drier but intense westerlies over southern European latitudes that favoured deep convection in the western Mediterranean Sea. In contrast to this regional homogeneity among the studied records during stadial periods, the interstadials periods were rather heterogeneous pointing to much complex ocean-atmosphere interconnections during these warm intervals.