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Dissolved organic matter (DOM) in the epipelagic ocean is produced by marine organisms and consumed by microbes. Thus, the distributional patterns of DOM quantity and quality in surface waters are possibly related to marine ecological provinces. In this study, surface waters collected throughout the Pacific Ocean were used to investigate the geographical distributions of fluorescent DOM (FDOM) quantity and quality. An excitation-emission matrix and parallel factor analysis revealed two humic-like and two protein-like components. The levels of humic-like components showed clear meridional trends with some zonal variability and were highest and lowest in the northern high-latitude and the subtropical provinces, respectively. The photochemical reactivity, determined by the ratio of two humic-like components, was found to be lowest in the subtropical provinces, implying that the major factor controlling the geographical distribution of humic-like components is the degree of photobleaching. The distributional patterns differed between levels of two protein-like components, i.e., tryptophan-like and tyrosine-like. The ratio of tyrosine-like to tryptophan-like components was established as a possible indicator of microbial degradability, and the highest ratio occurred in subtropical provinces. A negative correlation was found between this ratio and the chlorophyll a concentration. Such geographical distributions of protein-like components imply that relatively recalcitrant protein-like components are distributed uniformly throughout the surface waters, but substantial contributions of reactive fractions occur in regions characterized by high biological production. Cluster analysis with the FDOM composition clarified that the diagenetic states of DOM were similar and variable in the northern high-latitude and the subtropical provinces, respectively. [ABSTRACT FROM AUTHOR]

Surface water samples were collected from 43 streams distributed throughout watersheds of mixed land use in southern Ontario, Canada. Absorbance and fluorescence spectroscopy with parallel factor analysis (PARAFAC) was used to characterize dissolved organic matter (DOM). DOM characteristics were related to environmental variables, microbial activity indicators (bacterial production and extracellular leucine aminopeptidase activity), and riparian land use to understand better how these factors influence DOM in streams. PARAFAC produced a six-component model (C1 to C6). Temperature correlated with each PARAFAC component, suggesting that water source, drainage area, and light penetration broadly affected DOM characteristics. C1 and C2 represented terrestrial, humic-like DOM fluorophore groups and comprised 41-65% of stream DOM fluorescence. C5, a tryptophan-like component, related negatively to a humification index but positively to leucine-aminopeptidase activity and recently produced DOM, suggesting that C5 consisted of autochthonous, microbially produced DOM. C3, C4, and C6 showed signs of quinone-like, humic-like, and microbial transformable fluorophores. The distribution of these potentially redox-active PARAFAC components indicated that DOM was in a more reduced state in streams with higher bacterial production and agricultural land use than in streams with increased wetlands area, which had greater relative abundance of the oxidized quinone-like component. Anthropogenic land use and microbial activity altered the quantity and quality of DOM exported from human-affected streams from that observed in forest- and wetland-dominated streams. DOM in agriculturally affected streams was likely more labile and accessible to the microbial community than DOM in wetland streams, which supported low rates of microbial activity. [ABSTRACT FROM AUTHOR]

Chromophoric dissolved organic matter (CDOM) was surveyed along the 160°W transect from the equatorial to the subarctic Pacific. CDOM characteristics were evaluated through the measurement of fluorescence intensity at 320 nm excitation and 420 nm emission and of absorption coefficient (a) at 320 nm, both indicative of marine humic-like CDOM. In the surface layer (~200 m), different levels but similar optical characteristics of CDOM were found among the oceanic regions studied. In the mesopelagic (200-1000 m) and abyssal layers (1000 m-bottom), levels of fluorescence intensities were linearly correlated to those of absorption coefficients, with a similar slope between these layers. However, the intercept of the linear relationship between the two optical parameters was significantly lower for the mesopelagic layer than for the abyssal layer. Differences between intercepts were consistent with the transport of optically distinct CDOM to the mesopelagic layer through the formation of the North Pacific intermediate water (NPIW). At wavelengths shorter than 300 nm, the absorption coefficients of CDOM in the surface layer systematically deviated from the natural logarithmic relationships between absorption coefficients and wavelengths in the 320-350 nm range. This class of CDOM, estimated using absorption coefficient at 275 nm, was defined as surface-specific CDOM and may be derived from biocomponents. Surface-specific CDOM was higher in the relatively young mode water than in old NPIW, suggesting that this class of CDOM is semi-labile. [ABSTRACT FROM AUTHOR]

The distributions of fluorescent components in dissolved organic matter (DOM) from Ise Bay, Japan, were determined by excitation emission matrix (EEM) fluorescence spectroscopy combined with parallel factor analysis (PARAFAC). Three terrestrial humic-like, one marine humic-like, and three non-humic-like fluorescent components were identified by PARAFAC, and the environmental dynamics of individual fluorescent components in the bay area were evaluated. The observed linear relationships between salinity and abundance of two of the three humic-like components in the bay area indicate a terrestrial origin and conservative mixing behavior of these components. On the other hand, nonconservative mixing for the other terrestrial and the marine humic-like components was observed, indicating that the sources of these were other than solely riverine inputs. Thus, in addition to riverine sources, this terrestrial humic-like component may receive inputs from biogeochemical reworking of terrestrial DOM and/or particulate organic matter, while the most likely sources for the marine humic-like component are estuarine biological activity and/or microbial reworking of plankton-derived DOM. From the spatial distributions in the bay area as well as their relationships with salinity, two of the non-humic-like components were suggested to be of autochthonous estuarine origin and likely represent biologically labile components. Microbial degradation processes were suggested to be important factors driving the dynamics of another non-humic-like component. This study exemplifies the potential applicability of EEM-PARAFAC in studies of fluorescent DOM dynamics in estuaries. [ABSTRACT FROM AUTHOR]