Publications

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2017
Kumar, A, Borgen M, Aluwihare LI, Fenical W.  2017.  Ozone-activated halogenation of mono- and dimethylbipyrrole in seawater. Environmental Science & Technology. 51:589-595.   10.1021/acs.est.6b03601   AbstractWebsite

Polyhalogenated N-methylbipyrroles of two different structure classes have been detected worldwide in over 100 environmental samples including seawater, bird eggs, fish, dolphin blubber, and in the breast milk of humans that consume seafood. These molecules are concentrated in the fatty tissues in comparable abundance to some of the most important anthropogenic contaminants, such as the halogenated flame-retardants and pesticides. Although the origin of these compounds is still unknown, we present evidence that the production of these materials can involve the direct ozone activated seawater halogenation of N-methylbipyrrole precursors. This observation shows that environmental polyhalogenated bipyrroles can be produced via an abiotic process, and implies that the ozone activated halogenation of a variety of natural and anthropogenic seawater organics may be a significant process occurring in surface ocean waters.

2016
Moran, MA, Kujawinski EB, Stubbins A, Fatland R, Aluwihare LI, Buchan A, Crump BC, Dorrestein PC, Dyhrman ST, Hess NJ, Howe B, Longnecker K, Medeiros PM, Niggemann J, Obernosterer I, Repeta DJ, Waldbauer JR.  2016.  Deciphering ocean carbon in a changing world. Proceedings of the National Academy of Sciences of the United States of America. 113:3143-3151.   10.1073/pnas.1514645113   AbstractWebsite

Dissolved organic matter (DOM) in the oceans is one of the largest pools of reduced carbon on Earth, comparable in size to the atmospheric CO2 reservoir. A vast number of compounds are present in DOM, and they play important roles in all major element cycles, contribute to the storage of atmospheric CO2 in the ocean, support marine ecosystems, and facilitate interactions between organisms. At the heart of the DOM cycle lie molecular-level relationships between the individual compounds in DOM and the members of the ocean microbiome that produce and consume them. In the past, these connections have eluded clear definition because of the sheer numerical complexity of both DOM molecules and microorganisms. Emerging tools in analytical chemistry, microbiology, and informatics are breaking down the barriers to a fuller appreciation of these connections. Here we highlight questions being addressed using recent methodological and technological developments in those fields and consider how these advances are transforming our understanding of some of the most important reactions of the marine carbon cycle.

2015
Arakawa, N, Aluwihare L.  2015.  Direct identification of diverse alicyclic terpenoids in Suwannee River fulvic acid. Environmental Science & Technology. 49:4097-4105.   10.1021/es5055176   AbstractWebsite

The chemical complexity of dissolved organic matter (DOM) obstructs our ability to definitively recover source compounds from within DOM, an objective which has the capacity to alter our understanding, of carbon sequestration on a. global scale. To advance compositional studies of DOM we have applied a previously published reduction method to an environmental standard, Suwannee River Fulvic Acid (SRFA). The reduction products, comprising 12% of the prereduced carbon, were then separated by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GCXGC-TOF-MS). estilts indicate that the majority of obsetved reduced compounds corresponded to alicyclic hydrocarbons in the size range C-10 to C-17. Cyclic terpenoids are the only biomolecule class with contiguous, alicyclic carbon backbones of this size. These terpenoid reduction products contain series offset by CH2 and exhibit great isomeric diversity, features previously inferred from ultrahigh resolution mass spectrometry and NMR studies of unreduced SRFA. Reduction of Taxodium leaf litter as a Source material to SRFA confirmed the prevalence of tetpenoids in SRFA and provided insight into the parent compounds that must be diagenetically modified on relatively short time scales. These data corroborate several recent studies that suggest alicydic hydrocarbons to be important components of longer-lived DOM.

2013
Collins, DB, Ault AP, Moffet RC, Ruppel MJ, Cuadra-Rodriguez LA, Guasco TL, Corrigan CE, Pedler BE, Azam F, Aluwihare LI, Bertram TH, Roberts GC, Grassian VH, Prather KA.  2013.  Impact of marine biogeochemistry on the chemical mixing state and cloud forming ability of nascent sea spray aerosol. Journal of Geophysical Research-Atmospheres. 118:8553-8565.   10.1002/jgrd.50598   AbstractWebsite

The composition and properties of sea spray aerosol, a major component of the atmosphere, are often controlled by marine biological activity; however, the scope of impacts that ocean chemistry has on the ability for sea spray aerosol to act as cloud condensation nuclei (CCN) is not well understood. In this study, we utilize a mesocosm experiment to investigate the impact of marine biogeochemical processes on the composition and mixing state of sea spray aerosol particles with diameters<0.2 mu m produced by controlled breaking waves in a unique ocean-atmosphere facility. An increase in relative abundance of a distinct, insoluble organic particle type was observed after concentrations of heterotrophic bacteria increased in the seawater, leading to an 86 +/- 5% reduction in the hygroscopicity parameter () at 0.2% supersaturation. Aerosol size distributions showed very little change and the submicron organic mass fraction increased by less than 15% throughout the experiment; as such, neither of these typical metrics can explain the observed reduction in hygroscopicity. Predictions of the hygroscopicity parameter that make the common assumption that all particles have the same bulk organic volume fractions lead to overpredictions of CCN concentrations by 25% in these experiments. Importantly, key changes in sea spray aerosol mixing state that ultimately influenced CCN activity were driven by bacteria-mediated alterations to the organic composition of seawater.

Prather, KA, Bertram TH, Grassian VH, Deane GB, Stokes MD, DeMott PJ, Aluwihare LI, Palenik BP, Azam F, Seinfeld JH, Moffet RC, Molina MJ, Cappa CD, Geiger FM, Roberts GC, Russell LM, Ault AP, Baltrusaitis J, Collins DB, Corrigan CE, Cuadra-Rodriguez LA, Ebben CJ, Forestieri SD, Guasco TL, Hersey SP, Kim MJ, Lambert WF, Modini RL, Mui W, Pedler BE, Ruppel MJ, Ryder OS, Schoepp NG, Sullivan RC, Zhao DF.  2013.  Bringing the ocean into the laboratory to probe the chemical complexity of sea spray aerosol. Proceedings of the National Academy of Sciences of the United States of America. 110:7550-7555.   10.1073/pnas.1300262110   AbstractWebsite

The production, size, and chemical composition of sea spray aerosol (SSA) particles strongly depend on seawater chemistry, which is controlled by physical, chemical, and biological processes. Despite decades of studies in marine environments, a direct relationship has yet to be established between ocean biology and the physicochemical properties of SSA. The ability to establish such relationships is hindered by the fact that SSA measurements are typically dominated by overwhelming background aerosol concentrations even in remote marine environments. Herein, we describe a newly developed approach for reproducing the chemical complexity of SSA in a laboratory setting, comprising a unique ocean-atmosphere facility equipped with actual breaking waves. A mesocosm experiment was performed in natural seawater, using controlled phytoplankton and heterotrophic bacteria concentrations, which showed SSA size and chemical mixing state are acutely sensitive to the aerosol production mechanism, as well as to the type of biological species present. The largest reduction in the hygroscopicity of SSA occurred as heterotrophic bacteria concentrations increased, whereas phytoplankton and chlorophyll-a concentrations decreased, directly corresponding to a change in mixing state in the smallest (60-180 nm) size range. Using this newly developed approach to generate realistic SSA, systematic studies can now be performed to advance our fundamental understanding of the impact of ocean biology on SSA chemical mixing state, heterogeneous reactivity, and the resulting climate-relevant properties.

2012
Samo, TJ, Pedler BE, Ball GI, Pasulka AL, Taylor AG, Aluwihare LI, Azam F, Goericke R, Landry MR.  2012.  Microbial distribution and activity across a water mass frontal zone in the California Current Ecosystem. Journal of Plankton Research. 34:802-814.   10.1093/plankt/fbs048   AbstractWebsite

Ocean fronts with accumulated biomass and organic matter may be significant sites of enhanced microbial activity. We sampled a frontal region (the A-Front) separating oligotrophic and mesotrophic water masses within the California Current Ecosystem (CCE) to assess the influence of frontal hydrography on several microbial parameters. Samples for heterotrophic bacterial, viral and flagellate abundance, dissolved and particulate carbon and nitrogen, transparent particles and bacterial carbon production were collected at 6 depths from the surface to 100 m with 59 conductivity/temperature/depth casts along a 26-km northerly transect across the front. Relative to adjacent oligotrophic and mesotrophic waters, the frontal transition displayed peaks in the mean estimates of cell-specific bacterial carbon and bulk bacterial production, particulate organic carbon and particulate organic nitrogen concentrations, and the abundance and size of transparent particles. Bacterial carbon production increased approximate to 5-fold northward from oligotrophic waters to the frontal zone, in agreement with an increase in the frequency of dividing cells, but bacterial abundance was lower than at adjacent stations. This may be partially explained by high chlorophyll, elevated virus:bacteria ratios and low nanoflagellate grazer abundance at the front. Our data suggest that CCE fronts can facilitate intense biological transformation and physical transport of organic matter, in sharp contrast to adjacent low productivity waters, and harbor dynamic microbial populations that influence nutrient cycling.