Probing Individual Particles Generated at the Freshwater-Seawater Interface through Combined Raman, Photothermal Infrared, and X-ray Spectroscopic Characterization.

Sea spray aerosol (SSA) is one of the largest global sources of atmospheric aerosol, but little is known about SSA generated in coastal regions with salinity gradients near estuaries and river outflows. SSA particles are chemically complex with substantial particle-to-particle variability due to changes in water temperature, salinity, and biological activity. In previous studies, the ability to resolve the aerosol composition to the level of individual particles has proven necessary for the accurate parameterization of the direct and indirect aerosol effects; therefore, measurements of individual SSA particles are needed for the characterization of this large source of atmospheric aerosol. An integrated analytical measurement approach is required to probe the chemical composition of individual SSA particles. By combining complementary vibrational microspectroscopic (Raman and optical photothermal infrared, O-PTIR) measurements with elemental information from computer-controlled scanning electron microscopy with energy-dispersive X-ray analysis (CCSEM-EDX), we gained unique insights into the individual particle chemical composition and morphology. Herein, we analyzed particles from four experiments on laboratory-based SSA production using coastal seawater collected in January 2018 from the Gulf of Maine. Individual salt particles were enriched in organics compared to that in natural seawater, both with and without added microalgal filtrate, with greater enrichment observed for smaller particle sizes, as evidenced by higher carbon/sodium ratios. Functional group analysis was carried out using the Raman and infrared spectra collected from individual SSA particles. Additionally, the Raman spectra were compared with a library of Raman spectra consisting of marine-derived organic compounds. Saccharides, followed by fatty acids, were the dominant components of the organic coatings surrounding the salt cores of these particles. This combined Raman, infrared, and X-ray spectroscopic approach will enable further understanding of the factors determining the individual particle composition, which is important for understanding the impacts of SSA produced within estuaries and river outflows, as well as areas of snow and ice melt.

Dihydrodinophysistoxin-1 Produced by Dinophysis norvegica in the Gulf of Maine, USA and Its Accumulation in Shellfish.

Dihydrodinophysistoxin-1 (dihydro-DTX1, (M-H)-m/z 819.5), described previously from a marine sponge but never identified as to its biological source or described in shellfish, was detected in multiple species of commercial shellfish collected from the central coast of the Gulf of Maine, USA in 2016 and in 2018 during blooms of the dinoflagellate Dinophysis norvegica. Toxin screening by protein phosphatase inhibition (PPIA) first detected the presence of diarrhetic shellfish poisoning-like bioactivity; however, confirmatory analysis using liquid chromatography-tandem mass spectrometry (LC-MS/MS) failed to detect okadaic acid (OA, (M-H)-m/z 803.5), dinophysistoxin-1 (DTX1, (M-H)-m/z 817.5), or dinophysistoxin-2 (DTX2, (M-H)-m/z 803.5) in samples collected during the bloom. Bioactivity-guided fractionation followed by liquid chromatography-high resolution mass spectrometry (LC-HRMS) tentatively identified dihydro-DTX1 in the PPIA active fraction. LC-MS/MS measurements showed an absence of OA, DTX1, and DTX2, but confirmed the presence of dihydro-DTX1 in shellfish during blooms of D. norvegica in both years, with results correlating well with PPIA testing. Two laboratory cultures of D. norvegica isolated from the 2018 bloom were found to produce dihydro-DTX1 as the sole DSP toxin, confirming the source of this compound in shellfish. Estimated concentrations of dihydro-DTX1 were >0.16 ppm in multiple shellfish species (max. 1.1 ppm) during the blooms in 2016 and 2018. Assuming an equivalent potency and molar response to DTX1, the authority initiated precautionary shellfish harvesting closures in both years. To date, no illnesses have been associated with the presence of dihydro-DTX1 in shellfish in the Gulf of Maine region and studies are underway to determine the potency of this new toxin relative to the currently regulated DSP toxins in order to develop appropriate management guidance.

The role of a PSP-producing Alexandrium bloom in an unprecedented diamondback terrapin (Malaclemys terrapin) mortality event in Flanders Bay, New York, USA.

Diamondback terrapins (Malaclemys terrapin) are a threatened or endangered species in much of their range along the U.S. Atlantic and Gulf coasts. Over an approximately three-week period from late April to mid-May 2015, hundreds of adult diamondback terrapins were found dead on the shores of Flanders Bay, Long Island, New York, USA. Concurrent with the mortality event, elevated densities of the paralytic shellfish toxin (PST)-producing dinoflagellate, Alexandrium fundyense (>104 cells L-1) and high levels of PST in bivalves (maximal levels = 540 µg STX eq. 100 g-1 shellfish tissue) were observed in the Flanders Bay region, resulting in shellfish bed closures in regional tributaries. Gross and histologic postmortem examinations of terrapins revealed no physical trauma to individuals or a common, underlying disease process to explain the deaths. PST compounds (0.2-12.5 µg STX eq. 100 g-1) were present in various M. terrapin tissues collected over the duration of the mortality event. High-throughput sequencing revealed that the ribbed mussel (Geukensia demissa, a PST vector) was present in the gastrointestinal tracks of all terrapin samples tested. While the potential of PST to cause mortality in chelonians has not been well-characterized, in the absence of other significant findings from necropsies and pathological analyses, we provide evidence that PST in shellfish was likely high enough to cause or contribute to the mortality in these small (<2.0 kg) animals.

Marine microgels as a source of cloud condensation nuclei in the high Arctic.

Marine microgels play an important role in regulating ocean basin-scale biogeochemical dynamics. In this paper, we demonstrate that, in the high Arctic, marine gels with unique physicochemical characteristics originate in the organic material produced by ice algae and/or phytoplankton in the surface water. The polymers in this dissolved organic pool assembled faster and with higher microgel yields than at other latitudes. The reversible phase transitions shown by these Arctic marine gels, as a function of pH, dimethylsulfide, and dimethylsulfoniopropionate concentrations, stimulate the gels to attain sizes below 1 µm in diameter. These marine gels were identified with an antibody probe specific toward material from the surface waters, sized, and quantified in airborne aerosol, fog, and cloud water, strongly suggesting that they dominate the available cloud condensation nuclei number population in the high Arctic (north of 80°N) during the summer season. Knowledge about emergent properties of marine gels provides important new insights into the processes controlling cloud formation and radiative forcing, and links the biology at the ocean surface with cloud properties and climate over the central Arctic Ocean and, probably, all oceans.

DIMETHYLSULFONIOPROPIONATE STORAGE IN PHAEOCYSTIS (PRYMNESIOPHYCEAE) SECRETORY VESICLES(1).

Despite the global importance of dimethylsulfoniopropionate (DMSP)/dimethyl sulfide (DMS) and their role in climate regulation, little is known about the mechanisms of their production and storage in Phaeocystis sp., a major contributor of DMS in polar areas. Phaeocystis secretes polymer microgels, by regulated exocytosis, remaining in condensed phase while stored in secretory vesicles (Chin et al. 2004). In secretory cells, vesicles also store small molecules, which are released during exocytosis. Here, we demonstrated that DMSP and DMS were stored in the secretory vesicles of Phaeocystis antarctica G. Karst. They were trapped within a polyanionic gel matrix, which prevented an accurate measurement of their concentration in the absence of a chelating agent such as EDTA. Understanding the production and the export mechanisms of DMSP and DMS into seawater is important because of the impact the cellular and extracellular pools of these highly relevant biogeochemical metabolites have on the environment. The pool of total DMSP in the presence of Phaeocystis may be underestimated by as much as half. Obtaining accurate budget measurements is the first step toward gaining a better understanding of key issues related to the DMS ocean-air interaction and the effect of phytoplankton DMS production on climate change.