ALBERT

Description: A multi-proxy analysis based on planktic foraminiferal abundances and derived SSTs, abundances of alkenone compounds and alkenone SSTs as well as stable isotopes measurements was performed for Site 975 (ODP Leg 161) from the slope of the South Balearic-Islands basin (Western Mediterranean) across late MIS 6 to early MIS 5d periods with emphasis on the climate progression of the last inter-glacial period. A number of abrupt climate changes related to alternative influence of northern nutrient rich and southern oligotrophic water masses were revealed. Among climate fluctuations, Heinrich Event 11 and cooling events C 27, C 26, C 25, C 24, C23 which had been detected earlier in the North Atlantic, were recognised. However, in comparison to the eastern North Atlantic mid-latitude region, at Site 975 events C27 and C26 seem to be significantly more pronounced. This fact along with evidence of two-phase climate optimum with the SSTs maximum reached during its later phase implies close similarity in climate dynamics between the Western Mediterranean and the Nordic Seas. It is proposed that postglacial effects in the Nordic Seas had an influence on the western Mediterranean climate via atmospheric circulation and competed with the insolation effect.

Description: A pronounced intra-interglacial MIS 11 cold event was revealed in the North Atlantic by sea surface temperature (SST) and salinity (SSS) reconstructions. SSTs were established using TEX86-indices derived from relative abundances of glycerol dialkyl glycerol tetraethers (GDGTs) of Thaumarcheota and alkenone-based Uk’37 indices. To assess variations in palaeo-SSS, the hydrogen isotopic (δD) compositions of long chain alkenones were determined. For further interpretation, the obtained SST and SSS reconstructions were compared to relative planktic foraminiferal abundances, ice rafted debris (IRD) counts and δ18O records from benthic and planktic foraminifera. According to our data, the temperature amplitude of the aforementioned cold event reached 7 °C. We assume that this value might combine the actual cooling with an additional effect of a vertical migration of the Thaumarchaeota to deeper and, therefore, colder water layers, which might occur due to an enhanced intensity of open ocean upwelling which is generally characteristic for this location during cooling episodes. This explanation is also supported by changes in stable oxygen isotopes of deep-living planktic foraminiferal species G. truncatulinoides (s) and (d). A pronounced increase of δ18O values contemporaneous with the cold event might indicate a change of habitat conditions of these species towards colder temperatures. Another evidence of enhanced upwelling intensity during this episode might be derived from increased relative abundance of planktic foraminiferal species G. bulloides, whose geographical distribution is related to upwelling zones. A salinity drop was registered before the SST decrease. Because the intra-interglacial MIS 11 cold event occurred during the phase of slowly decreasing benthic δ18O values, we assume that it might be related to the late phase of the circum-North Atlantic ice sheet decay. Therefore, its nature might resemble the one of the 8.2 ka Holocene event.