Controls on the distribution of fluorescent dissolved organic matter during an under-ice algal bloom in the western Arctic Ocean.

In this study we used fluorescence excitation and emission matrix spectroscopy, hydrographic data, and a self-organizing map (SOM) analysis to assess the spatial distribution of labile and refractory fluorescent dissolved organic matter (FDOM) for the Chukchi and Beaufort Seas at the time of a massive under-ice phytoplankton bloom during early summer 2011. Biogeochemical properties were assessed through decomposition of water property classes and sample classification that employed a SOM neural network-based analysis which classified 10 clusters from 269 samples and 17 variables. The terrestrial, humic-like component FDOM (ArC1, 4.98 ± 1.54 Quinine Sulfate Units (QSU)) and protein-like component FDOM (ArC3, 1.63 ± 0.88 QSU) were found to have elevated fluorescence in the Lower Polar Mixed Layer (LPML) (salinity ~29.56 ± 0.76). In the LPML water mass, the observed contribution of meteoric water fraction was 17%, relative to a 12% contribution from the sea ice melt fraction. The labile ArC3-protein-like component (2.01 ± 1.92 QSU) was also observed to be elevated in the Pacific Winter Waters mass, where the under-ice algal bloom was observed (~40-50 m). We interpreted these relationships to indicate that the accumulation and variable distribution of the protein-like component on the shelf could be influenced directly by sea ice melt, transport, and mixing processes and indirectly by the in situ algal bloom and microbial activity. ArC5, corresponding to what is commonly considered marine humic FDOM, indicated a bimodal distribution with high values in both the freshest and saltiest waters. The association of ArC5 with deep, dense salty water is consistent with this component as refractory humic-like FDOM, whereas our evidence of a terrestrial origin challenges this classic paradigm for this component.

Resolving DOM fluorescence fractions during a Karenia brevis bloom patch on the Southwest Florida Shelf.

Organic matter can be supplied naturally from land through rivers or produced in-situ in the marine environment. Current methods of examining natural bulk dissolved organic matter (DOM) are not able to discriminate multiple sources of DOM. A diagnostic tool to identify DOM sources is critical to determine possible sources of organic nutrients that influence K. brevis harmful algal bloom (HAB) development. This study applied multi-wavelength fluorescence coupled with a supervised pattern recognition technique (e.g., parallel factorial analysis (PARAFAC) using samples collected from river, estuary and shelf waters where the toxic dinoflagellate Karenia brevis off of Sanibel Island, Florida was observed. The PARAFAC model distinguished four different fractions of DOM components containing humic-like and protein-like components. The derived terrestrial humic-like material was indicative of land-based sources while the tryptophan-like component was likely produced from in-situ biological production. The study developed and tested the hypothesis that the direct relationship of the protein-like DOM fluorescence with K. brevis cell density indicated that the bloom patch was most likely supported by organic nutrients produced in-situ. The results demonstrated that multi-wavelength fluorescence analysis coupled with PARAFAC modeling technique simultaneously resolved DOM fluorescence fractions and their possible sources-information that are critical in explaining harmful algal bloom formation.

Nitrogen isotope fractionation in a continuous culture system containing phytoplankton and blue mussels.

An experiment was conducted to examine the fractionation of nitrogen stable isotopes in a continuous culture system containing field collected estuarine phytoplankton and blue mussels, Mytilus edulis. Nitrate and phosphate were added to culture vessels at concentrations above ambient levels and nitrogen isotope ratios (δ15N) were measured in particulate matter (PM) and blue mussels over the course of the 15-day experiment. The added nutrients resulted in large productivity and chlorophyll increases in the system. Study results indicate that rapid and significant nitrogen isotope fractionation can occur during incorporation by phytoplankton grown under conditions of excess dissolved inorganic nitrogen, as shown by δ15N values depleted by as much as 9‰ in PM from the higher nutrient treatments. These lower δ15N values were also reflected in mussels exposed to culture vessels effluents. Therefore, nitrogen concentration needs to be considered when using δ15N values in biota as indicators of anthropogenic nitrogen inputs.

Application of fluorescence and PARAFAC to assess vertical distribution of subsurface hydrocarbons and dispersant during the Deepwater Horizon oil spill.

We evaluated the use of excitation and emission matrix (EEM) fluorescence and parallel factorial analysis (PARAFAC) modeling techniques for monitoring crude oil components in the water column. Four of the seven derived PARAFAC loadings were associated with the Macondo crude oil components. The other three components were associated with the dispersant, an unresolved component and colored dissolved organic matter (CDOM). The fluorescence of the associated benzene and naphthalene-like components of crude oil exhibited a maximum at ∼1200 m. The maximum fluorescence of the component associated with the dispersant (i.e., Corexit EC9500A) was observed at the same depth. The plume observed at this depth was attributed to the dispersed crude oil from the Deepwater Horizon oil spill. Results demonstrate the application of EEM and PARAFAC to simultaneously monitor selected PAH, dispersant-containing and humic-like fluorescence components in the oil spill region in the Gulf of Mexico.

Determination of brevetoxin in recent marine sediments.

Harmful algal blooms (HAB) of Karenia brevis (K. brevis) produce a suite of lipid soluble polyether brevetoxins, known to cause environmental, health and economic ill effects. There is evidence that K. brevis has increased in abundance over the past 50 years, but the dataset is incomplete. The objective of this paper was to analyze sediment from an area where K. brevis blooms have occurred and investigate if these compounds are incorporated into the underlying sediment, thus potentially allowing the use of brevetoxins as an indicator of past K. Brevis blooms. The results from LC-ESI-MS-MS analyses of brevetoxin analogs detected in surficial sediments from three sites (Fort Meyers Beach [FMB], Big Hickory Pass [BHP] and Big Carlos Pass [BCP]) along the Southwest Florida coastline with prior HAB history are promising. The analogs detected from BHP sediments were PbTx-2 and PbTx-3 with values of 0.81 and 3.1 ng g(-1) dry sediment, respectively. The detected PbTx-2 from BCP was 3.6 ng g(-1) dry sediment, while the detected PbTx-3 from BCP was 9.7 ng g(-1) dry sediment. PbTx-3 was only detected at the FMB site (2.7 ng g(-1) dry sediment). The detection of brevetoxins in recent sediments where K. brevis have occurred indicates brevetoxin incorporation into marine sediments.