Carbonate production in mesophotic and deeper settings on the northern flank of the Sicilian Channel (Terrible and Nameless Banks, Central Mediterranean)

Despite extensive research on shallow-water carbonate systems, Mediterranean mesophotic environments remain poorly documented. This exploratory analysis integrates paleontological and sedimentological analyses of seafloor samples dredged during the R/V Meteor M191 expedition to investigate factors controlling carbonate production in deeper settings of the Sicilian Channel. Samples were studied after collection to assess living communities and later prepared as thin sections for petrographic analysis. In the mesophotic zone, carbonate production is dominated by phototrophs. The shallower, irregular summit of the Terrible Bank is characterized by actively growing coralline algae. Conversely, the deeper, smoother summit of the Nameless Bank displays no signs of active growth, and with recent to sub-recent production represented by dead algal crusts. In aphotic settings, production shifts to heterotrophic communities, including cold-water corals and deep-water oysters. This overall distribution of benthic carbonate producers is mainly driven by the interplay of seafloor topography and hydrodynamics. On the Terrible Bank, the relatively shallow, irregular topography of the summit provides a suitable substrate with sufficient light availability and water mixing to promote the active growth of coralline algae. Deeper, where solar energy is absent, mixing of the water column and food availability are promoted by the steep slopes, sustaining heterotrophic communities. The sedimentary substrates colonized by recent to sub-recent carbonate producers allow for the reconstruction of a plausible and coherent geological history of the banks, tracing a transition from a shallow-water tropical carbonate factory of presumed Late Miocene age to a younger temperate factory, which might have preceded the establishment of the current factory by several hundreds of thousands of years (at least based on the existing age information on compositionally similar fossil carbonates recovered in the Sicily Channel). The current slow accumulation rates, coupled with the presence of abandoned fishing gear, underscore the fragility of these modern benthic ecosystems.