Late Quaternary palaeoclimatic and palaeoecological changes in the Mediterranean Sea
This research presents a detailed study of the planktonic foraminiferal records of eleven sediment cores taken from a west-east transect in the Mediterranean Sea. Correlations are based on biostratigraphy, oxygen isotope stratigraphy and assisted by AMS 14C dating. This study assesses the potential to define a foraminiferal biostratigraphy of basin-wide validity. Principal Component Analysis (PCA) is used to determine variabilities in the planktonic foraminiferal records. The first principal component groups species on its positive and negative sides in such a way that this axis may be interpreted as an expression of SST variations. This interpretation is corroborated by its close similarity to oxygen isotope records. Mean PCA scores confirm previous observations that the temperature gradient in the eastern Mediterranean basin follows the same eastward increasing trend at glacial times as it does today. In contrast, the inferred sea surface temperatures (SST) from the western Mediterranean basin suggest a reversed gradient compared to the present. Preliminary results are discussed from the unprecedented high resolution marine records from two eastern Mediterranean cores. Based on PCA and planktonic foraminiferal ratios of warm, oligotrophic mixed layer species relative to cool, more eutrophic species, a series of cool episodes is observed throughout the Holocene. The cyclicity of these events is calculated at approximately 1300 years, a figure comparable with Holocene climate fluctuations recognised previously in the North Atlantic Ocean and the Greenland Ice Sheet. Micropalaeontological investigation of two western Mediterranean cores shows for the first time that abrupt cold spells, associated with Atlantic Heinrich-events, affected the Mediterranean Sea. Unusually high abundances of the subpolar species N. pachyderma (leftcoiling) in the Gulf of Lions reflect a thriving of a normally rare taxon in the western Mediterranean, in response to distinct, short term, episodes of favourable habitat development.