River Sources of Dissolved Inorganic Carbon in the Gulf of Trieste (N Adriatic): Stable Carbon Isotope Evidence
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River inputs can significantly affect carbon dynamics in the costal ocean. Here, we investigate the influence of four rivers (Isonzo/Soča, Timavo/Reka, Rižana, and Dragonja) on inorganic carbon (C) in the Gulf of Trieste in the northern Adriatic Sea using stable isotope signatures of dissolved inorganic carbon (δ13CDIC). In 2007, rivers exported 1.03 × 1011 g C in the form of dissolved inorganic carbon (DIC) to the Gulf of Trieste with the lowest export observed in the Dragonja and the highest in the Isonzo/Soča. River plumes were associated with higher total alkalinity (TA) and pCO2 values compared with Gulf of Trieste waters, but their inputs showed high spatial variability. The δ13CDIC values and the isotopic mass balance suggested that river input during the spring of 2007 represented about 16 % of DIC at our study site VIDA, located in the southeastern part of the Gulf of Trieste. During autumn of 2007, the riverine contribution of DIC was less pronounced (3 %) although the river export of C was higher relative to the spring season. Convective mixing with the Gulf of Trieste waters and bora wind events appear to reduce the riverine contribution to the DIC system. Our results suggest that river plumes play an important role in C cycling in the Gulf of Trieste by direct inputs of higher riverine DIC and by increased biological uptake of DIC promoted by the supply of riverine nutrients.
KeywordsRivers Carbonate system Stable carbon isotopes Coastal region
This research was financially supported by the Slovenian Research Agency under Research Programmes P1-0143, Canada Excellence Research Chair (CERC) in Ocean Science and Technology and LDEO contribution #7773. Special thanks are given to Corey Lambert for providing laboratory analysis at the University of Michigan. The authors would like to thank Mateja Poje and Mojca Dobnikar Tehovnik from the Slovenian Environmental Agency for providing the river monitoring data. The authors are grateful to the Associate Editor and two anonymous reviewers for their marked interest, constructive comments, and suggestions that improved the manuscript.
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