Dissolved organic matter (DOM) and microbial enzymes in the Ross Sea

In the Ross Sea the dissolved organic matter and the role of culturable heterotrophic microbes in its degradation are almost unknown. In the carbon cycle, dissolved organic carbon (DOC) concentration and its optically significant fraction, the chromophoric component (CDOM) are important for DOM budget estimates. Within the CELEBeR project [Circumpolar Deep Water (CDW) Effects on glaciaL mElting and on Bulk of Fe in the Western Ross sea - PNRA], DOC and CDOM, culturable heterotrophic bacteria and the enzymatic activities, expressed by bacterial isolates, were examined in the Ross Sea during the austral summer 2017, in relation to CDW contribution. The covered areas were the Drygalski Ice Tongue and the nearby Terra Nova Bay polynya (A) and the continental Shelf Break area near Cape Adare (B). Within the area A, the lowest DOC (38.33 µM), CDOM (a280 of 0.27 m-1) and SUVA254 (0.54 L mg-1 m-1) were measured at 225 m (CDW); the highest DOC (63.29 µM), CDOM (a280 of 1.39 m-1) and SUVA254 (1.6 L mg-1 m-1) were recorded at the northernmost area B (DCM), also characterized by the lowest spectral slopes (SR= 1.37). Heterotrophic bacteria ranged from 5.0x101 (CDW) to 7.0x103 CFU/ml (DCM); aminopeptidase and alkaline phosphatase were the most expressed enzymes. Based on microbial cells counting, the distribution of heterothrophic bacteria seems to be not affected by DOC concentration and its composition, as highlighted by the lack of correlations between the two variable sets.