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The Middle Pleistocene Transition is the most recent re-organization of the climate system, happened between 1.2 and 0.7 Ma. Marine sediments outcropping in Sicily have been a relevant source of information on the paleoclimatic and paleoenvironmental evolution of the Mediterranean Sea, over this time window. Among others, by describing the very cold phase and the marked sea level fall associated with the top MIS 22, which is lithologically expressed by a calcarenite bed colonized by the Arctica islandica northern guest.
Here we investigate ostracod assemblages from marine sediments in the southwestern Sicily. Sediments, ascribed to the late Calabrian Stage, have in-depth been studied by foraminifera, coccolith and pteropod specialists. Our results support previous micropaleontological paleoenvironmental reconstructions, but also include original elements that better define the paleobathymetric and bottom condition evolution. By grouping infralittoral, circalittoral and bathyal taxa, ostracods describe a significant sea level fall up to the A. islandica calcarenite bed and then a rise to circalittoral and bathyal environments during the interglacial MIS 21. The abundance increases of ostracod taxa able to survive in low-oxygen environments and a significant diversity loss point to the establishment of water column stratification and seafloor dysoxia, in the lower part of MIS 21. Finally, Bythocythere turgida is the only northern guest found in our samples, associated with A. islandica specimens. However, during the interglacial period we note subtle but significant percentage variations in ostracod groups that may have been driven by productivity changes, rather than real sea level variations. These changes may be associated to Atlantic Meridional Overturning Circulation weakening phases and to millennial-scale cold spells that punctuated MIS 21.
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