Trophic and microbial patterns in the Ross Sea area (Antarctica): spatial variability during the summer season

In open regions of the Ross Sea the role of the microbial community in the turnover of organic matter has still scarcely been investigated; indeed, very little is known on how microbial dis-tribution and functional diversity respond to environmental conditions and hydrographic structures. During the austral summer 2017, two pelagic areas of the Ross Sea [the Drygalski Ice Tongue and the nearby Terra Nova Bay polynya (A area) and the continental Shelf Break area near Cape Adare (C area)] were studied at selected depths [surface, Deep Chlorophyll Maximum (DCM), Circumpolar Deep Water (CDW), deep waters]. Trophic properties [nu-trient concentrations, particulate (POC), dissolved organic carbon (DOC) and its optically significant fraction (CDOM) were measured, together with the main hydrological variables. Microbial community abundance [total prokaryotes, living, dead and actively respiring frac-tion, high- and low nucleic acid cells (HNA and LNA), pico- and nanoeukaryotes, culturable heterotrophic bacteria], composition and metabolism (as whole community and isolated bac-teria) were also assessed. Through a multidisciplinary dataset, this study highlighted the variable response of mi-crobial abundance, diversity and metabolism of the microbial community to the changing local environmental conditions of the Ross Sea. Different forcings, such as the organic matter inputs (mostly of detrital nature) released from the Drygalski glacier in the A area and a coastal-to-offshore gradient in the C area, coexisted within this extreme ecosystem. This re-sulted in a significant spatial segregation of the edaphic parameters and of the microbial community distribution and metabolic activity patterns.