“…During PEACETIME, the contribution of cells > 2 µm in diameter and cells > 5 µm in diameter to total phytoplankton biomass increased with depth, and this trend was associated with a significant increase in the contribution of diatoms to total phytoplankton biomass, which reached at least 30 % in the DCM of all stations, and was particularly high (nearly 50 %) in the most stratified station, located in the Ionian Sea. Deep maxima in diatom abundance are common in the Mediterranean Sea during stratified conditions (Ignatiades et al, 2009;Siokou-Frangou et al, 2010;Mena et al, 2019) and are often associated with peaks in biogenic silica (Crombet et al, 2011). The increased prevalence of diatoms at the base of the euphotic layer, which illustrates the ecological diversity of this group (Kemp and Villareal, 2018), is likely a result of multiple adaptations and mechanisms, including high growth efficiency under low light conditions (Fisher and Halsey, 2016), buoyancy regulation (Villareal et al, 1996), the ability to exploit transient nutrient pulses through luxury uptake and storage (Kemp and Villareal, 2013;Cermeño et al, 2011) and the enhanced ammonium assimilation mediated by microbial interactions in the phycosphere (Olofsson et al, 2019).…”