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

MALITS, ANDREA; MONFORTE, CHIARA; IACHETTI, CLARA; GEREA, MARINA; LATORRE, MAITÉ

JOURNAL OF MARINE SYSTEMS

ELSEVIER SCIENCE BV

Año: 2023 vol. 240

0924-7963

Dissolved organic matter (DOM) was analyzed by its optical and fluorescent properties in order to study itsdistribution, source and transformation in relation to microbial abundances, chlorophyll and physicochemicalgradients along a transect in the eastern Beagle Channel (BC) during austral spring 2019. Moreover, DOMevolution was followed during three tidal cycles in two fixed stations (F1, F2) separated by the Mackinlay Strait,a hydrographic frontier between water masses under stronger continental influence (inner sector) and that of lessmodified Sub-Antarctic waters (outer sector). The fluorescence signals of protein- and humic-like compoundswere used as a proxy for labile and non-labile material, respectively, while the concentration of nano-, pico- andvirioplankton populations, chlorophyll-a (Chl-a) and dissolved organic carbon (DOC) were used as a proxy forbiological activity. Moreover, several spectroscopic indices, such as the indicator of microbially produced DOM(BIX), the Freshness index (FIX), an indicator of molecular weight, the Slope Ratio (SR) and an indicator ofchromophoric DOM (CDOM), were used to trace the quality and origin of DOM. Chl-a concentration wasgenerally low in the sampling area (< 1 μg L􀀀 1) but increased towards the end of the campaign and especiallyduring the visit of F1 along with the concentration of picoeukaryotes and the protein-like fluorophoresevidencing the onset of a bloom event. Protein-like fluorophores peaked in the euphotic zone of the inner sectorof the BC while humic-like material of terrestrial origin was homogeneously distributed throughout the watercolumn and showed a decreasing gradient towards the outer sector and Atlantic waters. Furthermore, the innersector was characterized by higher amounts of CDOM, high molecular weight material and more recalcitrantDOM. Accumulation of autochthonous humic-like material in bottom waters of the inner sector along withenhanced values of FIX and BIX preceded by colored organic material suggest an efficient functioning of themicrobial carbon pump fueled by terrestrial DOM sources in these waters.