Carl G. Johnson

Transport of sludge-derived organic pollutants to deep-sea sediments at deep water dump site 106

Linear alkylbenzenes (LABs), coprostanol and epi-co-prostanol, were detected in sediment trap and bottom sediment samples at the Deep Water Dump Site 106 located 185 km off the coast of New Jersey, in water depths from 2400 to 2900 m. These findings clearly indicate that organic pollutants derived from dumped sludge are transported through the water column and have accumulated on the deep-sea floor. No significant difference in LABs isomeric composition was observed among sludge and samples, indicating little environmental biodegradation of these compounds. LABs and coprostanol have penetrated down to a depth of 6 cm in sediment, indicating the mixing of these compounds by biological and physical processes

Identification of a novel alkenone in Black Sea sediments

Abstract We report the identification of a novel long-chain ketone in Holocene Black Sea sediments. Based on chemical properties, and chromatographic and mass spectrometric characteristics, this compound has been identified as a di-unsaturated C36 ethyl ketone. Further analyses indicated the position and configuration of the double bonds, and the novel alkenone was determined to be hexatriaconta-(16E,21E)-dien-3-one. While this compound is present in only trace quantities in Unit I sediments, it is the most abundant alkenone in portions of Unit II. Its presence thus apparently pre-dates the invasion of Emiliania huxleyi in the Black Sea. The down-core profiles and isotopic compositions suggest that the precursor for the C36:2 alkenone may be distinct from that of the C37-39 alkenones, however the biological origin of this novel compound is presently unknown.

Measuring the Photochemical Production of Carbon Dioxide from Marine Dissolved Organic Matter by Pool Isotope Exchange

CO(2) is the major known product of solar photolysis of marine dissolved organic matter (DOM). Measuring the rate of this globally significant process is hindered by low rates per unit volume, high background CO(2) in seawater, and ubiquitous contamination. Current methods utilize CO(2)-free seawater matrices, possibly introducing artifacts. Alternatively, pool isotope exchange (PIE) replaces most of the samples DI(12)C with DI(13)C at natural pH and temperature, so that (12)CO(2) from DOM photooxidation elevates (12)CO(2)/(13)CO(2) ratios in irradiated samples compared to dark controls. (12)CO(2)/(13)CO(2) ratios are then measured using a modified GC-IRMS. The minimum detectable concentration change (three standard deviations) is 300 nmol DI(12)C/kg. Methods for minimizing contamination while exchanging, transferring, sealing, and irradiating samples, and for recovering and purifying CO(2) are presented. Results from PIE agree within uncertainties with those from CO(2)-free coastal seawater, suggesting that both methods apply to river-dominated coastal waters. However, photooxidation in the open ocean, which likely dominates the global flux despite lower rates per unit volume, involves DOM that differs from coastal DOM, so that coastal agreement cannot validate open-ocean studies. Major advantages of PIE are use of nearly unperturbed seawater matrices, potential to incubate samples in situ to obtain depth-integrated rates directly, and potential to use larger samples to measure open-ocean waters.

Climate oscillations reflected within the microbiome of Arabian Sea sediments

Selection of microorganisms in marine sediment is shaped by energy-yielding electron acceptors for respiration that are depleted in vertical succession. However, some taxa have been reported to reflect past depositional conditions suggesting they have experienced weak selection after burial. In sediments underlying the Arabian Sea oxygen minimum zone (OMZ), we performed the first metagenomic profiling of sedimentary DNA at centennial-scale resolution in the context of a multi-proxy paleoclimate reconstruction. While vertical distributions of sulfate reducing bacteria and methanogens indicate energy-based selection typical of anoxic marine sediments, 5–15% of taxa per sample exhibit depth-independent stratigraphies indicative of paleoenvironmental selection over relatively short geological timescales. Despite being vertically separated, indicator taxa deposited under OMZ conditions were more similar to one another than those deposited in bioturbated intervals under intervening higher oxygen. The genomic potential for denitrification also correlated with palaeo-OMZ proxies, independent of sediment depth and available nitrate and nitrite. However, metagenomes revealed mixed acid and Entner-Dourdoroff fermentation pathways encoded by many of the same denitrifier groups. Fermentation thus may explain the subsistence of these facultatively anaerobic microbes whose stratigraphy follows changing paleoceanographic conditions. At least for certain taxa, our analysis provides evidence of their paleoenvironmental selection over the last glacial-interglacial cycle.

Sea slicks: variability in chemical composition and surface elasticity

Surface-active organic matter collected from the air-sea interface is examined using mass spectrometry. The mass spectra reveal significant spatio-temporal variability in the chemical composition of sea slick materials. This compositional variability leads to differences in observed surface pressure-elasticity relationships.

Innovative methods for determining alkenone unsaturation indices

Abstract Standards, total lipid extracts and crudely fractionated samples as well as extensively purified alkenone references were analyzed by conventional single column gas chromatography (GC), selective two-dimensional GC (GC–GC), comprehensive two-dimensional GC (GC×GC) and high resolution mass spectrometry (HRMS). U 37 K′ indices, defined as [C 37:2 ]/[C 37:2 +C 37:3 ], for independently analyzed standards showed GC–GC average accuracy of 0.014 and precision ±0.008 and HRMS average accuracy of 0.001 and precision ±0.007. The HRMS limit of precision is approximately ±0.008 for “real world samples” applied to the MS probe at greater than a few nanograms of the lesser alkenone component. Both of the two-dimensional GC techniques and HRMS indicate the presence of coeluting compounds in typical alkenone fractions that are not resolved by single dimensional GC. U 37 K′ indices measured by GC–GC, GC×GC and HRMS for total lipid extracts were generally observed to have lower U 37 K′ indices than their purified alkenone fractions.

Mass Spectrometric Identification of the Radical Adducts of a Fluorescamine-Derivatized Nitroxide

The radical adducts of fluorescamine-derivatized 3-aminomethyl-2,2,5,5-tetrarnethyl-1-pyrrolidinyloxy free radical are readily identified by mass spectrometry employing a solid source probe and electron impact ionization.

Allochthonous sources and dynamic cycling of ocean dissolved organic carbon revealed by carbon isotopes

We present concentration and isotopic profiles of total, size, and polarity fractionated dissolved organic carbon (DOC) from Station ALOHA, an oligotrophic site in the North Pacific Ocean. The data show that between the surface and 3500 m, low molecular weight (LMW) hydrophilic DOC, LMW hydrophobic DOC and high molecular weight (HMW) DOC constitute 22-33%, 45-52% and 23-35% of DOC respectively. LMW hydrophilic DOC is more isotopically depleted (δ13C of -23.9‰ to -31.5‰ and Δ14C of -304‰ to -795‰; mean age of 2850 to 15000 14C years) than the LMW hydrophobic DOC (δ13C of -22‰ to -23‰ and Δ14C of -270‰ to -568‰; 2470 to 6680 years) and HMW DOC (δ13C of ~ -21‰ and Δ14C of -24‰ to -294‰; 135-2700 years). Our analyses suggest a large fraction of DOC may be derived from allochthonous sources such as terrestrial and hydrothermal DOC, and cycle on much longer timescales of >10,000 yr, or enter the ocean as pre-aged carbon.

No. 2 fuel oil compound retention and release by Mytilus edulis : 1983 Cape Cod Canal oil spill

Retention and release of No. 2 fuel-oil compounds by Mytilus edulis contaminated by a small oil spill in the Cape Cod Canal in 1983 was studied for the population in situ and for a subsample transplanted to a clean laboratory seawater system. Compounds analyzed include C13 to C24 n-alkanes; pristane; phytane; C2-, C3-naphthalenes; fluorene; phenanthrene; C1-, C2-, C3-phenanthrenes; fluoranthene; pyrene and dibenzothiophene. Biological half-lives were determined for the compounds from Day-3 to Day-29 following the spill and ranged from 1.5 days for C2-naphthalenes to 9.9 days for C2-phenanthrenes. Gas chromatographic-mass spectrometer analyses of C2- and C3-phenanthrenes revealed changes in relative abundance of compounds within isomer groups from samples at Day-29 to the time when no further detection of fuel oil was noted. The study also demonstrated the feasibility of training an analyst unfamiliar with analyses of hydrocarbons in tissues to conduct high-resolution glass capillary GC analyses.

Correlation studies of mass spectral patterns and elasticity of sea-slick materials

Variations in the chemical composition of surfactants from natural sea slicks are compared to variations in surface elasticity using mass spectrometry, Langmuir film balance measurements, and multivariate statistical techniques. It is shown that the information on chemical class and molecular structure contained in the mass spectra is strongly correlated with measured static elasticity and can be used to estimate film elasticity at a given surface pressure.