Factors influencing the characteristics and distribution or surface organic matter in the Pacific-Atlantic connection

KROCK, B.; KOCH, B.P.; BARRERA, F.,; GARZÓN CARDONA, J.E; LARA, R.J.; FABRO, E.

JOURNAL OF MARINE SYSTEMS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2017 vol. 175 p. 36 - 45

0924-7963

The present work reports the first data set on particulate organic carbon (POC) and nitrogen (PON), and the high-resolution modelling of their stable isotope variability in the Patagonian Cold Estuarine System (PCES), with focus on particulate organic matter (POM) origin and distribution in dependence on physical, chemical and biological parameters. POC, PON, stable carbon (δ13C) and nitrogen isotopes (δ15N), dissolved organic nitrogen, phaeopigments, diatom, dinoflagellate and heterotrophic bacteria (HB) abundance are reported for 17 stations in different waters masses in the southern end of the Argentine shelf in late summer 2012. Most parameters denote clear differences between Beagle- Magellan Water (BMW), Subantarctic Shelf Water (SSW) and Subantarctic Water (SAW). POC and PON decreased from maxima in BMW to intermediate values in SSW and minima in SAW. They highly significantly correlated with each other and with fluorescence indicators of diagenetic maturity of dissolved humic matter. This, together with the inverse correlations of salinity with POC and PON, and the wide range of C:N ratios indicate that a fraction of POM in the study area is derived from terrestrial runoff, superimposed on autochthonous components from plankton in different life stages. HB abundance correlated highly significantly with POC and dissolved organic matter (DOM), likely reflecting a resource control of HB and a significant contribution of bacterial biomass to POM in the nanoparticle fraction. The direct relationship between HB and dissolved humics suggests bacterial uptake of DOM fractions otherwise considered refractory.POM complexity was reflected in a wide variation of δ13C, despite the narrow temperature range of this region. POC stable isotope variability could be accounted for in this work by a model with a degree of detail hitherto not reported in the literature. A multiple regression including C:N ratio, ammonium and the quotient between log abundance of diatoms, dinoflagellates and HB explained 92% of δ13C variance, mostly produced by ammonium. Despite the strong effect of this nutrient on δ13C, δ15N variability was largely explained by a strong inverse relationship with the fraction of unutilized nitrate, suggesting dominance of nitrate uptake. However, the assessment of the quantitative influence of the uptake of presumably isotopically heavier ammonium derived from continental runoff on marine δ15N-POM is unknown and requires the investigation of the isotopic composition of dissolved inorganic nitrogen in the PCES.The presented new information and its comparison with data from other sectors of the Argentine shelf constitute a contribution to an approach for the understanding of the organic matter dynamics that can be potentially expanded to the entire Southwest Atlantic.