Total and free enzymes in the Ross Sea during the austral summer 2017

The Ross Sea, one of the most productive seas of the South Ocean, includes polynyas, marginal ice zones, coastal areas and open sea that contribute differently to biological processes. To identifying responses of plankton compartment to climate change, an oceanographic PNRA campaign (P-ROSE Project) was here carried out in January-February 2017. Two polynyas occurred, a small near the Terra Nova Bay (TNB) and a larger one between the Ross Ice Shelf and Cape Adare. The variability of extracellular enzymatic activity (a proxy of organic matter degradation) in relation to environmental conditions (temperature, salinity and total phytoplankton biomass) was studied along longitudinal and latitudinal transects. Hydrolysis rates of aminopeptidase (LAP), beta-glucosidase (GLU) and alkaline phosphatase (AP) and -for the first time in this area- the corrispective free enzymes (dissolved in waters) were determined. Results showed decreasing trends in the TNB from coastal to off-shore stations and from surface to depth for LAP, that were related positively to temperature (T) and negatively to salinity (S) and depth (p <0.01%). High values in the N-S transect of offshore stations were observed, probably due to fresh organic matter. LAP were positively correlated with T and negatively with S and depth (p <0.01%). GLU was positively correlated with AP and LAP (p <0.05%). Free enzymes ranging from 17 to 99% on total showed variability among stations and high percentages for free-GLU at DCM.