Paleoproductivity Modes in Central Mediterranean During MIS 20—MIS 18: Calcareous Plankton and Alkenone Variability.

Paleoproductivity is reconstructed across a Mediterranean benchmark record, the Early/Middle Pleistocene Montalbano Jonico section, cropping out in southern Italy. High‐resolution coccolithophore and alkenone data (C37 and C37:2/C38:2 ratio) were collected in order to extend the data set on Mediterranean paleoproductivity pattern and forcing mechanisms. The multi‐proxy record indicates low productivity during glacial and stadial phases and enhanced productivity during interglacial and interstadials. Increased surface water turbidity, cold‐water temperature and polar‐subpolar low salinity water incursion appear as the dominant controls for low productivity during Marine Isotope Stage (MIS) 20. Enhanced productivity during MIS 19c was sustained by warmer surface waters, coupled with a seasonal precipitation regime, providing higher nutrient availability. Productivity increases during interstadials with respect to stadials, in relation with enhanced land‐derived nutrient input through river discharge during wetter winters. The productivity scenario we propose is similar to those reconstructed from deep‐sea records in the central and western Mediterranean during Dansgaard‐Oeschger oscillations over the last 70 ka. This indicates that similar forcing mechanisms acted on productivity dynamics on a regional scale over different times. We suggest that migration of the westerly wind system over the Mediterranean and the polar water inflow influenced productivity on a regional scale. The acquired data set provides new evidences on the environmental significance of the C37:2/C38:2 ratio and on its relation with surface water productivity. Plain Language Summary: Coccolithophores are calcifying unicellular algae and one of the most important marine phytoplankton group. In the present‐day oceans their distribution strongly depends on environmental factors such as nutrient concentration, surface water temperature, sunlight availability. Therefore, changes in fossil coccolithophore assemblages are successfully used for paleoclimatic and paleoceanographic reconstructions. They are also the source of organic compounds (the alkenones), which provide estimation of paleotemperature and paleoproductivity. We used variations of coccolithophore assemblages and of alkenones to identify paleoproductivity variations in the central Mediterranean, in a nearshore environment, during a key Quaternary paleoclimate interval. Our approach benefited of other paleoenvironmental indicators such as sea surface temperature and stable oxygen and carbon isotopes available at the studied section. We find that past climate changes clearly affected coccolithophore productivity at our site. Paleoproductivity was clearly favored by warm surface waters and by seasonal nutrient availability resulting by enhanced humidity over the central Mediterranean region. Our data also provide new indications on the relation between coccolithophore assemblage and alkenone variations through climate phases which may have future implication on their use for paleoenvironmental reconstruction. Key Points: Coccolithophore and alkenones underline productivity changes in a reference Early/Middle Pleistocene record from the central MediterraneanProductivity proxies reflect millennial‐scale climate changes with low/high values during cold and drier/warm and wetter conditionsSimilarity with the Dansgaard‐Oeschger oscillations scenario suggests a common regional climate forcing over productivity through time [ABSTRACT FROM AUTHOR]