Drivers of fluorescent dissolved organic matter in the global epipelagic ocean
T.S. Catala, X.A. Alvarez-Salgado, J. Otero, F. Iuculano, B. Companys, B. Horstkotte, C. Romera-Castillo, M. Nieto-Cid, M. Latasa, X.A.G. Moran, J.M. Gasol, C. Marrase, C.A. Stedmon, I. Reche
and Oceanography, volume 61, issue 3, pp. 1101-1119, (2016)
Fluorescent dissolved organic matter, Global epipelagic ocean, Excitation-emission matrix
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.
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