Coccolithophore production and calcification in the western Tethys Ocean during the Albian-Cenomanian

Coccolithophore photosynthesis and biocalcification influence the organic and inorganic carbon cycle and atmospheric CO2 absorption into the oceans. We investigated the Upper Albian-Lower Cenomanian interval of the Piobbico Core-Monte Petrano composite section (Umbria-Marche Basin, Italy) to understand if changes in nannofossil assemblages and calcite paleofluxes can be linked to variations in the ocean alkalinity. Total nannofossil calcite paleofluxes were gathered for the Marne a Fucoidi (marlstones and marly limestones) and Scaglia Bianca (limestones) from the absolute abundances of the most common taxa and volume/mass of individual taxon, obtained by counting all nannofossil specimens in 1 mm2 of ultrathin sections and by normalizing to 1 year. Precise sedimentation rate estimates are available based on high-resolution integrated biostratigraphy, chemostratigraphy and cyclostratigraphy. Out of 36, only 10 genera constitute 95% of nannofossil assemblages. The amount of calcite produced by individual nannofossil taxa is highly variable and strictly dependent on the ultrastructure and dimensions. Lithostratigraphically, the beginning of the limy sedimentation of the Scaglia Bianca does not align with changes in nannofossil paleofluxes since the increase occurs in the transitional interval with lowered terrigenous input (in late Albian times). Paleoenvironmental changes in temperature, fertility, chemistry influenced calcareous nannoflora with species-specific responses. Overall, high terrigenous input (Marne a Fucoidi) limited coccolithophore calcification, while fluctuations in nannofossil calcite paleofluxes (Scaglia Bianca) might derive from changes in marine carbonate chemistry (ocean alkalinity) possibly affecting calcification patterns at species-specific level.