Source characterization of dissolved organic matter in the eastern Beagle Channel from a spring situation

MALITS, A.; MONFORTE, C.; IACHETTI, C.; GEREA, M.; LATORRE, M.

JOURNAL OF MARINE SYSTEMS

ELSEVIER SCIENCE BV

Año: 2023

0924-7963

Dissolved organic matter (DOM) was analyzed by its optical and fluorescent propertiesin order to study its distribution, source and transformation in relation to microbialabundances, chlorophyll and physicochemical gradients along a transect in the easternBeagle Channel (BC) during austral spring 2019. Moreover, DOM evolution wasfollowed during three tidal cycles in two fixed stations (F1, F2) separated by theMackinlay Strait, a hydrographic frontier between water masses under strongercontinental influence (inner sector) and that of less modified Sub-Antarctic waters(outer sector). The fluorescence signals of protein- and humic-like compounds wereused as a proxy for labile and non-labile material, respectively, while the concentrationof nano-, pico- and virioplankton populations, chlorophyll a (Chl a) and dissolvedorganic carbon (DOC) were used as a proxy for biological activity. Moreover, severalspectroscopic indices, such as the indicator of microbially produced DOM (BIX), theFreshness index (FIX), an indicator of molecular weight, the Slope Ratio (SR) and anindicator of chromophoric DOM (CDOM), were used to trace the quality and origin ofDOM. Chl a concentration was generally low in the sampling area (< 1 μg L-1) butincreased towards the end of the campaign and especially during the visit of F1 alongwith the concentration of picoeukaryotes and the protein-like fluorophores evidencingthe onset of a bloom event. Protein-like fluorophores peaked in the euphotic zone ofthe inner sector of the BC while humic-like material of terrestrial origin washomogeneously distributed throughout the water column and showed a decreasinggradient towards the outer sector and Atlantic waters. Furthermore, the inner sectorwas characterized by higher amounts of CDOM, high molecular weight material andmore recalcitrant DOM. Accumulation of autochthonous humic-like material in bottomwaters of the inner sector along with enhanced values of FIX and BIX preceded bycolored organic material suggest an efficient functioning of the microbial carbon pumpfueled by terrestrial DOM sources in these waters.