Sea surface temperature variability in the central-western Mediterranean Sea during the last 2700 years : a multi-proxy and multi-record approach

Abstract

Unidad de excelencia María de Maeztu MdM-2015-0552

This study presents the reconstructed evolution of sea surface conditions in the central-western Mediterranean Sea during the late Holocene (2700 years) from a set of multi-proxy records as measured on five short sediment cores from two sites north of Minorca (cores MINMC06 and HERMC-MR3). Sea surface temperatures (SSTs) from alkenones and Globigerina bulloides Mg= Ca ratios are combined with δ18O measurements in order to reconstruct changes in the regional evaporation-precipitation (E-P) balance. We also revisit the G. bulloides Mg= Ca-SST calibration and readjusted it based on a set of core-top measurements from the western Mediterranean Sea. Modern regional oceanographic data indicate that Globigerina bulloides Mg= Ca is mainly controlled by seasonal spring SST conditions, related to the April-May primary productivity bloom in the region. In contrast, the alkenone-SST signal represents an integration of the annual signal. The construction of a robust chronological framework in the region allows for the synchronization of the different core sites and the construction of "stacked" proxy records in order to identify the most significant climatic variability patterns. The warmest sustained period occurred during the Roman Period (RP), which was immediately followed by a general cooling trend interrupted by several centennial-scale oscillations. We propose that this general cooling trend could be controlled by changes in the annual mean insolation. Even though some particularly warm SST intervals took place during the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA) was markedly unstable, with some very cold SST events mostly during its second half. Finally, proxy records for the last centuries suggest that relatively low E-P ratios and cold SSTs dominated during negative North Atlantic Oscillation (NAO) phases, although SSTs seem to present a positive connection with the Atlantic Multidecadal Oscillation (AMO) index.