Search

Chromophoric dissolved organic matter (CDOM) in the Mississippi plume region may have several distinct sources: riverine (terrestrial soils), wetland (terrestrial plants), biological production (phytoplankton, zooplankton, microbial), and sediments. Complex mixing, photodegradation, and biological processes make differentiation of the specific sources of CDOM difficult. Using a combination of high resolution in situ observations on an undulating vehicle, the ECOShuttle, a pumping system mounted on the vehicle, and detailed chemical and biological analyses of discrete samples allowed us to characterize two specific sources of CDOM in the Louisiana Bight: the river water constrained in the upper 12 m of the Mississippi River plume and several subsurface layers of CDOM below the plume. The subsurface CDOM maxima were coincident with steep pycnoclines and sometimes with maxima in chlorophyll a fluorescence. Both sources were actively supplying CDOM to the same location by entirely different processes. The subsurface CDOM was more biologically labile and photochemically refractory than the surface CDOM. Optical properties were also different with a relatively higher protein fluorescence and a lower spectral slope coefficient in the subsurface CDOM. The geographical extent of the two sources was determined by threedimensional mapping of the area, and due to the relatively calm conditions in the summer of 2000, thin layers of CDOM produced in the subsurface were observed throughout the region. While riverine inputs dominated the distribution of CDOM in surface waters

Alterations in colored dissolved organic matter (CDOM) characteristics were examined for an extensive fluorescence data set generated by excitation emission matrix spectroscopy (EEMS). Principal component analysis (PCA) was used to assess changes in fluorescence bandwidth and wavelength shifts of entire peak regions, enhancing previous CDOM characterization that was based on changes observed at a few excitation and emission wavelength pairs. Variability within the data set is expressed as a series of linear terms, which can be used to quantitatively evaluate changes in CDOM fluorescence within the perspective of a single cruise or a large geographic region. In this paper we will present PCA results from a comprehensive fluorescence data set examining seasonal and regional CDOM variability within the Gulf of Mexico.

We examined methods for verifying whether or not ships have performed mid-ocean ballast water exchange (BWE) on four commercial vessels operating in the Pacific and Atlantic Oceans. During BWE, a ship replaces the coastal water in its ballast tanks with water drawn from the open ocean, which is considered to harbor fewer organisms capable of establishing in coastal environments. We measured concentrations of several naturally occurring chemical tracers (salinity, six trace elements, colored dissolved organic matter fluorescence and radium isotopes) along ocean transects and in ballast tanks subjected to varying degrees of BWE (0-99%). Many coastal tracers showed significant concentration changes due to BWE, and our ability to detect differences between exchanged and unexchanged ballast tanks was greatest under multivariate analysis. An expanded dataset, which includes additional geographic regions, is now needed to test the generality of our results.

We performed multispectral in-situ fluorescence measurement of colored dissolved organic matter and chlorophyll in surface water of the West Florida Shelf using West Labs Spectral absorption and Fluorescence Instrument (SAFIre). Continuous measurements underway allowed us to simultaneously map the dispersion of riverine organic material and chlorophyll on the shelf. By using two fluorescence emission ratios we were able to differentiate between riverine and marine CDOM. Our data also showed unusually high concentrations of CDOM offshore. These were attributed to an intrusion of the Mississippi River Plume. We performed limited comparisons between in-situ chlorophyll concentrations measured with SAFIre and chlorophyll values obtained from SeaWiFS satellite data using OC4 and MODIS algorithm. Our results show that, although both algorithms overestimated chlorophyll, MODIS performed better than OC4, particularly in areas with high CDOM concentrations. Analysis of the relationship between chlorophyll and CDOM concentrations within the study area showed regional variability causes by differences in river source.

We investigated the optical properties of surface water in areas of the West Florida Shelf influenced by riverine discharge and by the occurrence of a phytoplankton plume. Results of absorption and fluorescence spectroscopy analyses and determination of dissolved organic carbon (DOC) concentration showed that the injection of riverine colored dissolved organic matter (CDOM) strongly affected the optical properties and DOC concentrations over the shelf. Riverborne nutrients contributed to an increase in primary productivity. However, during the study period, the increase in primary productivity did not result in the production of significant amounts of CDOM. Fluorescence spectroscopy results showed that optical properties of riverine CDOM were lost close to the mouth of the rivers. A simple mathematical model describing mixing between riverine and marine end-members demonstrated that most of the observed changes in optical properties of CDOM along salinity gradients can be explained by mixing. Laboratory mixing experiments between riverine water and seawater indicated that flocculation of organic matter during estuarine mixing did not affect the optical properties of CDOM. Remote-sensing studies of the Gulf of Mexico using historical data from the Coastal Zone Color Scanner show a recurrent, seasonal chlorophyll bloom over the West Florida

We performed absorption spectroscopy and fluorescence analyses on water samples collected in the Arabian Sea during the NE and SW Monsoons of 1994–1995. The strong differences in wind regimes between the Monsoons were reflected in the distribution of colored dissolved organic matter (CDOM). Concentrations of fluorescent dissolved organic matter (FDOM) were highest during the SW Monsoon within 100 km of the coast of Oman. In contrast, highest values during the NE Monsoon were found in offshore regions of the Arabian Sea. During the SW Monsoon, surface CDOM and FDOM correlated inversely with temperature, suggesting that upwelled water was the source of the colored and fluorescent material. Vertical profiles showed an inverse relationship between CDOM absorption and temperature, and a decrease in spectral slope with decrease in temperature, suggesting that deeper waters contain higher molecular weight CDOM than shallow waters. Profiles also showed the presence of a highly colored and fluorescent water mass centered at 250 m corresponding to Persian Gulf Water Mass. This water may be a source of colored organic material to overlying water masses.

The discharge of the Orinoco River significantly affects the optical properties of the water in the Caribbean Sea by increasing primary productivity and introducing large amounts of colored dissolved organic matter (CDOM) to the region. The optical characteristics of the CDOM in the Orinoco River plume were investigated during two cruises to the eastern Caribbean using absorption and fluorescence spectroscopy. We found that high concentrations of dissolved organic carbon (DOC) and abundance of CDOM in the eastern Caribbean were related to the Orinoco River plume. We did not observe changes in optical properties of CDOM in waters with salinities lower than 30. Self-shading from sunlight and the preponderance of riverine material at these low salinities can explain the observed behavior. Changes in the optical properties of the CDOM were observed in stations with salinities higher than 30 and were related to mixing between riverine and marine end-members, and to photodegradation. Light penetration and, consequently, the position of the chlorophyll maxima in areas close to the Gulf of Paria were controlled by the concentration of CDOM. Of the two main fluorophores found in this study, only the humic fluorophore appeared to be related to the absorption of light by CDOM in the visible spectrum. A secondary fluorophore, with excitation and emission in the UV, appeared to be resistant to photodegradation and did not show any relationship with absorbance in the visible range.

Here we report results from an extensive survey of dissolved organic carbon (DOC) in the Arctic Ocean, which was achieved by means of a high-resolution, in situ UV fluorometer deployed on a nuclear submarine. Based on a strong linear correlation observed between fluorescence (320 nm excitation, 420 nm emission) and organic carbon concentrations determined directly by high-temperature combustion, a continuous record of DOC was produced at a keel depth of 58 m along a 2900-km transect north of the Beaufort, Chukchi, East Siberian and Laptev seas. The DOC record, combined with other physical and chemical measurements, identifies areas where river waters cross the shelves and enter the circulation of the Arctic interior. Fluvial sources were found to account for 12-56% of the total DOC in parts of the upper Makarov and Amundsen basins.

High-resolution fluorescence spectroscopy was used to characterize dissolved organic matter (DOM) in concentrated and unconcentrated water samples from a wide variety of freshwater, coastal and marine environments. Several types of fluorescent signals were observed, including humic-like, tyrosine-like, and tryptophan-like. Humic-like fluorescence consisted of two peaks, one stimulated by UV excitation (peak A) and one by visible excitation (peak C). For all samples, the positions of both excitation and emission maxima for peak C were dependent upon wavelength of observation, with a shift towards longer wavelength emission maximum at longer excitation wavelength and longer wavelength excitation maximum at longer emission wavelength. A trend was observed in the position of wavelength-independent maximum fluorescence ( Ex max Em max ) for peak C, with maximum at shorter excitation and emission wavelengths for marine samples than for freshwater samples. Mean positions of these maxima were: rivers Ex max Em max = 340 448 nm; coastal water Ex max Em max = 342 442 nm; marine shallow transitional Ex max Em max = 310 423 nm; marine shallow eutrophic Ex max Em max = 299 389 nm; and marine deep Ex max Em max = 340 438 nm. Differences suggest that the humic material in marine surface waters is chemically different from humic material in the other environments sampled. These results explain previous conflicting reports regarding fluorescence properties of DOM from natural waters and also provide a means of distinguishing between water mass sources in the ocean.

The technique of 3-D fluorescence contouring was applied to samples from the DOC (dissolved organic carbon) Intercalibration Experiment using two different instrument types: a SPEX Fluorolog 2 and a Hitachi F3010. A comparison of results from the two instruments is presented for humic-like and protein-like fluorescence signals. Distinct differences in the composition of fluorescent DOC were observed between surface and deep water which may affect results of DOC measurements obtained by different analytical techniques.

Seawater samples were collected monthly in surface waters (2 and 5 m depths) of the Bay of Marseilles (northwestern Mediterranean Sea; 5°17'30" E, 43°14'30" N) during one year from November 2007 to December 2008 and studied for total organic carbon (TOC) as well as chromophoric dissolved organic matter (CDOM) optical properties (absorbance and fluorescence). The annual mean value of surface CDOM absorption coefficient at 350 nm [aCDOM(350)] was very low (0.10 ± 0.02 m−1) in comparison to values usually found in coastal waters, and no significant seasonal trend in aCDOM(350) could be determined. By contrast, the spectral slope of CDOM absorption (SCDOM) was significantly higher (0.023 ± 0.003 nm−1) in summer than in fall and winter periods (0.017 ± 0.002 nm−1), reflecting either CDOM photobleaching or production in surface waters during stratified sunny periods. The CDOM fluorescence, assessed through excitation emission matrices (EEMs), was dominated by protein-like component (peak T; 1.30–21.94 QSU) and marine humic-like component (peak M; 0.55–5.82 QSU), while terrestrial humic-like fluorescence (peak C; 0.34–2.99 QSU) remained very low. This reflected a dominance of relatively fresh material from biological origin within the CDOM fluorescent pool. At the end of summer, surface CDOM fluorescence was very low and strongly blue shifted, reinforcing the hypothesis of CDOM photobleaching. Our results suggested that unusual Rhône River plume eastward intrusion events might reach Marseilles Bay within 2–3 days and induce local phytoplankton blooms and subsequent fluorescent CDOM production (peaks M and T) without adding terrestrial fluorescence signatures (peaks C and A). Besides Rhône River plumes, mixing events of the entire water column injected relative aged (peaks C and M) CDOM from the bottom into the surface and thus appeared also as an important source of CDOM in surface waters of the Marseilles Bay. Therefore, the assessment of CDOM optical properties, within the hydrological context, pointed out several biotic (in situ biological production, biological production within Rhône River plumes) and abiotic (photobleaching, mixing) factors controlling CDOM transport, production and removal in this highly urbanized coastal area.

[1] Colored Dissolved Organic Matter (CDOM) distribution and signatures provide vital information about the amount and composition of organic material in aquatic environments. This information is critical for deciphering the sources and biogeochemical pathways of organic carbon, and thus vital to the understanding of carbon cycling and budgets. Waters of the West Florida Shelf are heavily influenced by many river systems on Florida's Gulf Coast that, to the first order, control CDOM distributions on the shelf. Three storm events during 2004 and 2005 (Hurricane Charley, Hurricane Wilma, and a Winter Storm) profoundly altered the typical distribution of CDOM fluorescence and absorption properties on the Southern West Florida Shelf. Seasonal surveys revealed that changes in the underwater light field as a result of major hurricanes and resuspension events are linked closely with a number of factors prior to a storm's passing such as the presence of persistent blooms, rainfall and discharge. Additionally, storm track and wind direction were found to play a significant role in CDOM signatures.

Continuous profiles of fluorescence in three channels [chlorophyll, dissolved organic matter (DOM) and flavin] were taken simultaneously in the Black Sea using a pump profiling system. Other parameters measured on each pump cast included temperature, salinity, beam attenuation coefficient (c), nutrients, oxygen and hydrogen sulfide. Chlorophyll fluorescence showed two maxima, a distinct primary maximum at the bottom of the euphotic zone, and a weak secondary maximum at the depth of the sulfide interface. The secondary maximum was associated with a particle maximum and a maximum in microbial activity (electron transport system). Fluorescence in the DOM and flavin channels increased steadily with depth from the surface to 366 m. Flavin fluorescence showed small peaks near the depth where nitrate concentrations approached zero, well above the depth of the secondary chlorophyll maximum. We attribute the secondary chlorophyll maximum solely to the presence of photosynthetic bacteria of the genus Chlorobium.

THE natural fluorescence properties of sea water provide a means of elucidating the complex chemical composition and diverse sources of dissolved organic matter (DOM) in sea water1–6. The positions of excitation and emission maxima for a wide range of natural water samples show remarkable similarity7. High-sensitivity fluorescence spectroscopic studies8 have shown recently that emission maxima for marine and coastal waters differ by 20 nm when the excitation wavelength is 313 nm. Here we present evidence from three-dimensional excitation emission matrix (EEM) spectroscopy that at least three fluorophores are present in waters of the Black Sea. Distinct changes in the relative abundance of these fluorophores are observed as a function of depth. We suggest that three-dimensional fluorescence spectroscopy can be used to distinguish between different types and sources of DOM in natural waters. These findings may have important applications in the field of remote sensing of phytoplankton pigments. For example, a better understanding of the sources of DOM components will help in correcting9,10 remotely sensed data for the presence of gelbstoff (yellow-coloured DOM11, which plays an important part in radiation absorption by surface waters).

The long term goal of this project is to determine sources, sinks and dynamics of Colored Dissolved Organic Matter (CDOM) and Colored Dissolved Organic Carbon (CDOC) optical properties on spatial and temporal scales relevant to physical/biogeochemical/ optical modeling efforts currently in progress for the West Florida Shelf HYCODE site. Predictive capability is needed for modeling in-water light attenuation and visibility in coastal regions. CDOM is one of the most significant and least understood light attenuating components, hence improved understanding of its optical properties, dynamics and spatial and temporal variability will result in improved radiance models in the littoral zone.

The fate of dissolved organic carbon in the ocean interior is poorly constrained. Fluorescence measurements illuminate the relative roles of in situ production and riverine input of at least the coloured carbon fraction.

Accurate characterization of dissolved organic matter (DOM) optical properties is crucial for accurate measurement of chlorophyll from remotely sensed color data and for modelling spectral light penetration in the ocean. In coastal areas, changes in the humic acid: fulvic acid ratio of gelbstoff from riverine to marine environments cause significant changes in the spectral slope parameter but are difficult to predict a priori and impossible to measure without extracting gelbstoff from seawater. Our recent results from a wide variety of natural waters show that DOM optical properties are a function of physical, chemical, and biological processes. Detailed fluorescence spectroscopy shows changes in the optical properties of gelbstoff related to the onset of marine productivity in coastal transition zones which are indicative of changes in chemical composition of DOM. In this paper, we discuss our efforts to use fluorescence to aid interpretation of variability in gelbstoff spectral slopes for development of next generation chlorophyll algorithms and for development of an optical tracer of geochemical processes involving dissolved organic carbon.

Depth profiles of some of the chemical components of dissolved fluorescence in the Black Sea and the Cariaco Trench were measured using ion-pairing high performance liquid chromatography. Both individual compounds and unresolvable complex material were observed in the fraction retained by C18-bonded silica adsorbent. Identifiable individual compounds included riboflavin, lumiflavin, lumichrome, FAD, and FMN. Maxima in riboflavin concentrations occurred in association with maxima in chl a, bchl e, ETS, and bacterial cell numbers. The concentration of the complex material increased with depth, corresponding to an increase in the total dissolved fluorescence. The relative contribution of individual fluorescent compounds to total extractable fluorescence decreased from 13% at the surface to 2% at 270 m.