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A major fraction of particulate organic carbon (POC) in the deep ocean remains molecularly uncharacterized. In an effort to determine the chemical characteristics and source(s) of sinking POC, we studied a nonhydrolyzable fraction of sinking POC using 13C NMR (nuclear magnetic resonance) spectroscopy and analytical pyrolysis. 13C NMR spectra and products from analytical pyrolysis of the nonhydrolyzable fraction exhibit a strongly aliphatic character that is distinct from that of bulk POC. The aliphatic nature of this fraction is consistent with its low stable carbon isotope values. We hypothesize that the nonhydrolyzable fraction derives to a significant extent from a refractory component of organisms that selectively accumulates, resulting in its manifestation as a major part of POC sinking to the deep ocean and in underlying sediments. © 2006 Elsevier Inc. All rights reserved.

The picoplankton Aureococus anophagefferens can use dissolved organic nitrogen in many forms, including peptides, chitobiose, acetamide, and urea. It can metabolize these nitrogen sources at higher rates than many other bacteria. This allows it to outgrow other phytoplankton that can only use inorganic nitrogen.

Marine research indicates that neutral sugars, acetate and lipid molecules bond to form a common macromolecule used in photosynthesis. As much as seven-tenths of ultrafiltered dissolved organic matter and one-fifth of total DOC in surface sea water contains acyl oligosaccarides which have been synthesized through photosynthesis. Roughly equal measurements of macromolecular dissolved organic carbon are contained within photosynthesis building block molecules at sites in the Atlantic and Pacific oceans.

The elemental composition of organic material in environmental samples - including atmospheric organic aerosol, dissolved organic matter, and other complex mixtures - provides insights into their sources and environmental processing. However, standard analytical techniques for measuring elemental ratios typically require large sample sizes (milligrams of material or more). Here we characterize a method for measuring elemental ratios in environmental samples, requiring only micrograms of material, using a Small Volume Nebulizer (SVN). The technique uses ultrasonic nebulization of samples to generate aerosol particles (100-300 nm diameter), which are then analyzed using an aerosol mass spectrometer (AMS). We demonstrate that the technique generates aerosol from complex organic mixtures with minimal changes to the elemental composition of the organic and that quantification is possible using internal standards (e.g., NH415NO3). Sample volumes of 2-4 uL with total solution concentrations of at least 0.2-g/L form sufficient particle mass for elemental ratio measurement by the AMS, despite only a small fraction (~ 0.1 %) of the sample forming fine particles while the remainder end up as larger droplets. The method was applied to aerosol filter extracts from the field and laboratory, as well as to dissolved organic matter (DOM) from the North Pacific Ocean. In the case of aerosol particles, the mass spectra and elemental ratios from the SVN-AMS agree with those from online AMS sampling; similarly, for DOM, the elemental ratios determined from the SVN-AMS agree with those determined using combustion analysis. The SVN-AMS provides a platform for the rapid quantitative analysis of the elemental composition of complex organic mixtures and non-refractory inorganic salts from microgram samples with applications that include analysis of aerosol extracts, and terrestrial and atmospheric dissolved organic matter. [ABSTRACT FROM AUTHOR]

Nearly all iron dissolved in the ocean is complexed by strong organic ligands of unknown composition. The effect of ligand composition on microbial iron acquisition is poorly understood, but amendment experiments using model ligands show they can facilitate or impede iron uptake depending on their identity. Here we show that siderophores, organic compounds synthesized by microbes to facilitate iron uptake, are a dynamic component of the marine ligand pool in the eastern tropical Pacific Ocean. Siderophore concentrations in iron-deficient waters averaged 9 pM, up to fivefold higher than in iron-rich coastal and nutrient-depleted oligotrophic waters, and were dominated by amphibactins, amphiphilic siderophores with cell membrane affinity. Phylogenetic analysis of amphibactin biosynthetic genes suggests that the ability to produce amphibactins has transferred horizontally across multiple Gammaproteobacteria, potentially driven by pressures to compete for iron. In coastal and oligotrophic regions of the eastern Pacific Ocean, amphibactins were replaced with lower concentrations (1–2 pM) of hydrophilic ferrioxamine siderophores. Our results suggest that organic ligand composition changes across the surface ocean in response to environmental pressures. Hydrophilic siderophores are predominantly found across regions of the ocean where iron is not expected to be the limiting nutrient for the microbial community at large. However, in regions with intense competition for iron, some microbes optimize iron acquisition by producing siderophores that minimize diffusive losses to the environment. These siderophores affect iron bioavailability and thus may be an important component of the marine iron cycle. [ABSTRACT FROM AUTHOR]