Community level physiological profiles and extracellular enzymatic activities in the Circumpolar Deep Water (CDW) of the Ross Sea

In the Ross Sea, warm Circumpolar Deep Water (CDW) intrudes onto the continental shelf preferably on the western sector and flows into the ice shelf cavities, affecting the ice shelf melting rates. In fact, the intrusion of the warm CDW onto the Antarctic shelf area is one of the recognized drivers of ice shelf melting. Moreover, this water mass is the primary source of heat, salt, nutrients and iron (Fe) onto the Antarctic continental shelves playing an important role on the shelf physical and biological processes. An oceanographic cruise was performed in the framework of the CELEBeR (CDW effects on glacial melting and on bulk of Fe in the Western Ross Sea) project (funded by Italian National Research Programme in Antarctica) in January - February 2017 aboard of R/V Italica, addressed to study microbial community level physiological profiles (by Biolog ecoplate) and extracellular enzymatic activities (EEA) of leucine-aminopeptidase, beta-glucosidase and alkaline phosphatase in the intruding CDW of the Western Ross Sea. The investigated areas covered: a) the Antarctic continental shelf break area near Cape Adare (North Victoria Land); b) the coastal area near the edge of the Mariner and Aviator glaciers; c) the Drygalski Ice Tongue and the nearby Terra Nova Bay polynya. The functional diversity (catabolic potential) was assessed using the Average Well Color Development (AWCD). Moreover, Richness (R) and Shannon-Weaver index (H), analysis of variance (ANOVA) and principal component analysis (PCA) were used to depict the differences of the microbial functional diversity in the studied areas. Differences in potential metabolic pathways were detected in the different sampling areas. The measured enzymatic activity rates suggested the potential ability of the microbial community to decompose proteins, carbohydrates and organic phosphates. Different levels of EEA were measured as a function of the CDW proximity - or not - to the glaciers and the trophism of the investigated area.