Seasonal dynamics and net production of dissolved organic carbon in an oligotrophic coastal environment

• Published in: Marine ecology. Progress series (Halstenbek) Vol. 456; pp. 7 - 19
• Main Authors: Vila-Reixach, Gemma, Gasol, Josep M., Cardelús, Clara, Vidal, Montserrat
• Format: Journal Article
• Language: English
• Published: Inter-Research 07-06-2012
• Subjects: Coasts; Dissolved organic carbon; Marine; Marine ecosystems; Phytoplankton; Primary productivity; Respiration; Sea water; Seas; Seasons; Surface water
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps09677

To understand dissolved organic carbon (DOC) seasonal dynamics in a coastal oligotrophic site in the north-western Mediterranean Sea, we monitored DOC concentrations monthly over 3 yr, together with the meteorological data and the food-web-related biological processes involved in DOC dynamics. Additional DOC samples were taken in several inshore–offshore transects along the Catalan coast. We found DOC concentrations of ~60 μmol C l−1in winter, with increasing values through the summer and autumn and reaching 100 to 120 μmol C l−1in November. There was high inter-annual variability in this summer DOC accumulation, with values of 36, 69 and 13 μmol C l−1for 2006, 2007 and 2008, respectively. The analysis of the microbial food-web processes involved in the DOC balance did not reveal the causes of this accumulation, since the only occasion on which we observed net DOC production (0.3 ± 1 μmol C l−1d−1on average) was in 2007, and the negative DOC balance of 2006 and 2008 did not prevent DOC accumulating. The DOC accumulation episodes coincided with low rates of water renewal (average 0.037 ± 0.021 d−1from May to October) compared with those of winter to early spring (average 0.11 ± 0.048 d−1from November to April). Indeed, the amount of DOC accumulated each year was inversely correlated with the average summer rainfall. We hypothesize that decreased DOC turn-over due to photochemical or biological processes—mostly active during the summer—and low water renewal rate combine to determine seasonal DOC accumulation and influence its inter-annual variability.