The last 100,000 years in the western Mediterranean: Sea surface water and frontal dynamics as revealed by coccolithophores

A quantitative analysis was carried out on coccolith assemblages from two Pleistocene cores (K1 and K10) from the western Mediterranean. The distribution of selected coccolithophore species provides new paleoclimatic and paleoceanographic data. A continuous sequence from the top of Isotope Stage 5 to the Holocene was recorded. The reversal in dominance between Gephyrocapsa muellerae and Emiliania huxleyi was dated in both cores at ca. 73 ka. At about 47 ka, E. huxleyi shows a regular increase, whereas G. muellerae progressively decreases in abundance. During interglacial periods, high concentrations of coccoliths are observed, whereas in glacial times, coccoliths are more diluted and the percentage of reworked forms increases as a consequence of the higher terrigenous input. After taking careful account of the dilution factor, we conclude that the production of coccolithophores was higher during warm periods. Maxima in coccolith concentrations coincide with highstand episodes, probably as a result of the intensification of the Atlantic flux into the Mediterranean across the Gibraltar Strait. This intensification could have produced an increase in nutrient content in the surface Mediterranean waters. During cold periods, the western Mediterranean front underwent a reduction in activity, probably due to an increase in the saline and/or thermal gradients between the superficial waters, and intermediate waters in the Liguro Provencal basin.