Drivers of fluorescent dissolved organic matter in the global epipelagic ocean

Fluorescent dissolved organic matter (FDOM) in open surface waters (< 200 m) of the Atlantic, Pacific, and Indian oceans was analysed by excitation-emission matrix (EEM) spectroscopy and parallel factor analysis (PARAFAC). A four-component PARAFAC model was fit to the EEMs, which included two humic- (C1 and C2) and two amino acid-like (C3 and C4) components previously identified in ocean waters. Generalized-additive models (GAMs) were used to explore the environmental factors that drive the global distribution of these PARAFAC components. The explained variance for the humic-like components was substantially larger (> 70%) than for the amino acid-like components (< 35%). The environmental variables exhibiting the largest effect on the global distribution of C1 and C2 were apparent oxygen utilisation followed by chlorophyll a. Positive non-linear relationships between both predictor variables and the two humic-like PARAFAC components suggest that their distribution are biologically controlled. Compared with the dark ocean (> 200 m), the relationships of C1 and C2 with AOU indicate a higher C1/AOU and C2/AOU ratios of the humic-like substances in the dark ocean than in the surface ocean where a net effect of photobleaching is also detected. C3 (tryptophan-like) and C4 (tyrosine-like) variability was mostly dictated by salinity (S), by means of positive non-linear relationships, suggesting a primary physical control of their distributions at the global surface ocean scale that could be related to the changing evaporation-precipitation regime. Remarkably, bacterial biomass (BB) only contributed to explain a minor part of the variability of C1 and C4.

Citation

Drivers of fluorescent dissolved organic matter in the global epipelagic ocean 2016, 61 (3):1101 Limnology and Oceanography

Acknowledgements

We thank C.M. Duarte for the coordination of the Malaspina expedition; the chief scientists of the seven legs, the staff of the Marine Technology Unit (CSIC-UTM) and the Captain and crew of R/V Hesp erides for their outright support during the circumnavigation. Also, we thank the Physics block for collecting, calibrating and processing the CTD data. Dolors Blasco for facilitating the nutrients data. T.S.C acknowledges funding through a predoctoral fellowship (reference AP2009-2138) from the Ministerio de Educaci on, Cultura y Deporte. A. Fuentes-Lema and E. Ortega- Retuerta for their contribution to sampling collection and measurements. A. Gomes for coordinating the bacterial analyses. J. Otero was supported by “Junta para la Ampliaci on de Estudios” Fellowship (JAEDoc program 2011) from the CSIC and ESF. M. Nieto-Cid was funded by the EU FP/-IOF project FeBOL-220172 and the CSIC Program “Junta para la Ampliaci on de Estudios” co-financed by the ESF. B. Horstkotte was supported by JAE 2010 Postdoctoral fellowship from the CSIC. This study was financed by the Malaspina 2010 circumnavigation expedition (grant number CSD2008–00077).