Dissolved organic
GDC-0941 (DOM): We focused on two categories of dissolved organic matter, the protein-like and the humic-like, which are defined by their excitation-emission wavelengths when analysed via synchronous fluorescence spectroscopy. Samples were collected in triplicate by filtering the seawater through a 0.4-μm pore-size membrane and processed immediately. Traditionally, marine organic matter has been divided into DOM and POM on the basis of its behaviour during filtration. Organic matter retained by filters with pores varying between 0.2 and 1.0 μm is considered POM, whereas the filterable material is considered DOM (Verdugo et al., 2004). Nevertheless, it must be kept in mind that the 0.4 μm cut-off we chose allowed a fraction of the colloids and small bacteria to pass through the filter and thus be incorporated in the DOM. Synchronous fluorescence spectroscopy is an instrumental technique
sympathetic system involves the simultaneous scanning of excitation and emission monochromators, keeping a constant difference between them. We utilised a difference of 25 nm, as suggested by Ferrari and Mingazzini (1995). An excitation-emission wavelength of 275–300 nm was selected for the protein-like signal, while excitation-emission wavelengths of 395–425 and 420–450 nm were selected for the humic-like fraction (De Sousa Sierra et al., 1994). The 2-D spectra, obtained with a Jasco FP50 spectrofluorometer, were corrected by comparison with the spectrum of ultrapure water (Coble, 1996). Due to the semi-quantitative nature of the analysis, the results were expressed as fluorescence units (fu).
