13 results on '"Prahl FG"'
Search Results
2. Alkenone abundance and its relationship to the coccolithophore assemblage in Gulf of California surface waters
- Author
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Malinverno, E, Prahl, F, Popp, B, Ziveri, P, MALINVERNO, ELISA, Prahl, FG, Popp, BN, Ziveri P., Malinverno, E, Prahl, F, Popp, B, Ziveri, P, MALINVERNO, ELISA, Prahl, FG, Popp, BN, and Ziveri P.
- Abstract
Profiles of alkenone concentration, the abundance of the calcified alkenone-producing species Emiliania huxleyi and Gephyrocapsa oceanica as well as nutrient and phytoplankton pigment concentrations were measured through the euphotic zone in surface waters of the Gulf of California during cruises in two different summers (2004, 2005) and one winter (2005). As determined using a biomarker and pigment inventory approach, E. huxleyi and G. oceanica, always the most abundant coccolithophore species at all sampling sites and seasons, represented only a minor fraction of total haptophytes which themselves constituted only a minor fraction of the total phytoplankton community. In winter, alkenone concentration was highest at the surface and displayed relatively uniform values with depth throughout the nutrient-replete euphotic zone. In summer, it display a subsurface peak in nitrate-depleted waters situated just above the nitracline and the deep chlorophyll maximum layer (DCML), a feature found to be well-developed at most sites. Maximum biomarker abundance was comparable in the two seasons, although the putative alkenone-producing coccolithophore species were more abundant in winter than in summer. Estimates of cellular alkenone content for the combined abundance of E. huxleyi and G. oceanica at each sampling depth showed that cells residing in the nitratedepleted upper euphotic zone in summer were typically more enriched than those residing in nutrient-replete waters found deeper in the euphotic zone or throughout the euphotic zone in winter. The former estimates were very similar to values documented in laboratory cultures of E. huxleyi harvested in a nutrient-depleted stationary growth phase and the latter to those harvested in an exponential growth phase, under the influence of incipient light limitation. Overall, our findings imply that calcifying forms of E. huxleyi and G. oceanica can account for the measured alkenone concentration at all sites and sampling times.
- Published
- 2008
3. Myrionecta rubra population genetic diversity and its cryptophyte chloroplast specificity in recurrent red tides in the Columbia River estuary
- Author
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Herfort, L, primary, Peterson, TD, additional, McCue, LA, additional, Crump, BC, additional, Prahl, FG, additional, Baptista, AM, additional, Campbell, V, additional, Warnick, R, additional, Selby, M, additional, Roegner, GC, additional, and Zuber, P, additional
- Published
- 2011
- Full Text
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4. Climate regime shifts and reorganization of fish communities: the essential fatty acid limitation hypothesis
- Author
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Litzow, MA, primary, Bailey, KM, additional, Prahl, FG, additional, and Heintz, R, additional
- Published
- 2006
- Full Text
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5. Biogeochemical characterization of suspended particulate matter in the Columbia River estuary
- Author
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Prahl, FG, primary, Small, LF, additional, and Eversmeyer, B, additional
- Published
- 1997
- Full Text
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6. Lipid composition of a marine ammonium oxidizer grown at 5 and 25 °C
- Author
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Jones, RD, primary and Prahl, FG, additional
- Published
- 1985
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7. North Pacific deglacial hypoxic events linked to abrupt ocean warming.
- Author
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Praetorius SK, Mix AC, Walczak MH, Wolhowe MD, Addison JA, and Prahl FG
- Subjects
- Alaska, Aquatic Organisms metabolism, Carbon metabolism, Diatoms metabolism, Feedback, Foraminifera metabolism, Geologic Sediments chemistry, History, Ancient, Oxygen chemistry, Oxygen metabolism, Pacific Ocean, Solubility, Temperature, Global Warming history, Ice Cover, Oxygen analysis, Seawater chemistry
- Abstract
Marine sediments from the North Pacific document two episodes of expansion and strengthening of the subsurface oxygen minimum zone (OMZ) accompanied by seafloor hypoxia during the last deglacial transition. The mechanisms driving this hypoxia remain under debate. We present a new high-resolution alkenone palaeotemperature reconstruction from the Gulf of Alaska that reveals two abrupt warming events of 4-5 degrees Celsius at the onset of the Bølling and Holocene intervals that coincide with sudden shifts to hypoxia at intermediate depths. The presence of diatomaceous laminations and hypoxia-tolerant benthic foraminiferal species, peaks in redox-sensitive trace metals, and enhanced (15)N/(14)N ratio of organic matter, collectively suggest association with high export production. A decrease in (18)O/(16)O values of benthic foraminifera accompanying the most severe deoxygenation event indicates subsurface warming of up to about 2 degrees Celsius. We infer that abrupt warming triggered expansion of the North Pacific OMZ through reduced oxygen solubility and increased marine productivity via physiological effects; following initiation of hypoxia, remobilization of iron from hypoxic sediments could have provided a positive feedback on ocean deoxygenation through increased nutrient utilization and carbon export. Such a biogeochemical amplification process implies high sensitivity of OMZ expansion to warming.
- Published
- 2015
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8. Solvent-extractable polycyclic aromatic hydrocarbons in biochar: influence of pyrolysis temperature and feedstock.
- Author
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Keiluweit M, Kleber M, Sparrow MA, Simoneit BR, and Prahl FG
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- Anthracenes isolation & purification, Hot Temperature, Models, Molecular, Phenanthrenes isolation & purification, Solvents, Charcoal chemistry, Poaceae chemistry, Polycyclic Aromatic Hydrocarbons isolation & purification, Wood chemistry
- Abstract
Despite the increasing agricultural use of biochar as a way of combining the utilization of biomass for energy production with the removal of CO(2) from the atmosphere, it is not known how variations in pyrolysis temperature and feedstock type affect concentration and composition of polycyclic aromatic hydrocarbons (PAHs) that inevitably form and associate with biochar. To close this knowledge gap, we quantified 11 unsubstituted three- to five-ring PAHs as well as alkylated forms of phenanthrene and anthracene in grass and wood chars produced in 100 °C increments across a temperature range (100 to 700 °C). Our results show that solvent-extractable PAH concentrations in biochars produced at heat treatment temperatures (HTTs) of 400 and 500 °C greatly exceed those observed at higher and lower temperature, supporting a low HTT solid-phase formation mechanism operable at temperatures commonly used for industrial biochar production. The maximum extractable yield of 'pyrolytic' unsubstituted PAHs for grass (22 μg g(-1) at HTT = 500 °C) greatly exceeds the value for wood (5.9 μg g(-1)). Moreover, PAH signatures (e.g., total monomethylphenanthrene to phenanthrene ratios, MP/P ~2-3) at intermediate temperatures (400 °C) resemble those of fossil oils rather than that commonly attributed to pyrolytic products. Further research is needed to characterize the PAH evolution in modern pyrolysis reactors and assess the fate of biochar-bound PAHs in soils and sediments. Various commonly applied PAH ratios and indicator compounds show promise as markers for specific feedstock materials and pyrolysis conditions of biochars in environmental systems.
- Published
- 2012
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9. Characterization of unusual alkenones and alkyl alkenoates by electron ionization gas chromatography/mass spectrometry.
- Author
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Rontani JF, Prahl FG, and Volkman JK
- Abstract
Unusual long-chain, diunsaturated alkenones and alkyl alkenoates exhibiting double bonds separated by three methylene units instead of the more usual five were characterized by electron ionization (EI) gas chromatography/mass spectrometry. In a first step, the positions of the double bonds of these compounds (isolated from Holocene Black Sea sediments) were confirmed after OsO4 treatment and silylation. Mass spectra of the resulting tetratrimethylsilyloxy derivatives allowed unambiguous determination of the positions of unsaturations. The EI mass spectra of the non-derivatized compounds were then compared with those of the alkenones and alkyl alkenoates having double bonds separated by five methylene units. Specific fragment ions resulting from gamma-H rearrangements were found to be prominent in EI mass spectra of these unusual 'Black Sea' diunsaturated alkenones and alkyl alkenoates. These fragment ions can be used to characterize these compounds in natural samples without the need for laborious derivatization treatments., (Copyright 2006 John Wiley & Sons, Ltd.)
- Published
- 2006
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10. Distribution of membrane lipids of planktonic Crenarchaeota in the Arabian Sea.
- Author
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Sinninghe Damsté JS, Rijpstra WI, Hopmans EC, Prahl FG, Wakeham SG, and Schouten S
- Subjects
- Crenarchaeota physiology, Ecology, Marine Biology, Crenarchaeota metabolism, Membrane Lipids metabolism, Water Microbiology
- Abstract
Intact core tetraether membrane lipids of marine planktonic Crenarchaeota were quantified in water column-suspended particulate matter obtained from four depth intervals ( approximately 70, 500, 1,000 and 1,500 m) at seven stations in the northwestern Arabian Sea to investigate the distribution of the organisms at various depths. Maximum concentrations generally occurred at 500 m, near the top of the oxygen minimum zone, and the concentrations at this depth were, in most cases, slightly higher than those in surface waters. In contrast, lipids derived from eukaryotes (cholesterol) and from eukaryotes and bacteria (fatty acids) were at their highest concentrations in surface waters. This indicates that these crenarchaeotes are not restricted to the photic zone of the ocean, which is consistent with the results of recent molecular biological studies. Since the Arabian Sea has a strong oxygen minimum zone between 100 and 1,000 m, with minimum oxygen levels of <1 microM, the abundance of crenarchaeotal membrane lipids at 500 m suggests that planktonic Crenarchaeota are probably facultative anaerobes. The cell numbers we calculated from the concentrations of membrane lipids are similar to those reported for the Central Pacific Ocean, supporting the recent estimation of M. B. Karner, E. F. DeLong, and D. M. Karl ( Nature 409:507-510, 2001) that the world's oceans contain ca. 10(28) cells of planktonic Crenarchaeota.
- Published
- 2002
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11. Photosynthetic fractionation of 13C and concentrations of dissolved CO2 in the central equatorial Pacific during the last 255,000 years.
- Author
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Jasper JP, Hayes JM, Mix AC, and Prahl FG
- Subjects
- Animals, Atmosphere, Carbon Dioxide analysis, Carbon Isotopes, Carbonates analysis, Carbonates metabolism, Eukaryota chemistry, Geologic Sediments chemistry, Geologic Sediments microbiology, Ice analysis, Marine Biology, Oxygen Isotopes, Pacific Ocean, Paleontology, Plankton chemistry, Seawater, Water Microbiology, Carbon Dioxide metabolism, Eukaryota metabolism, Geologic Sediments analysis, Photosynthesis, Plankton metabolism
- Abstract
Carbon isotopically based estimates of CO2 levels have been generated from a record of the photosynthetic fractionation of 13C [is equivalent to epsilon(p)] in a central equatorial Pacific sediment core that spans the last approximately 255 ka. Contents of 13C in phytoplanktonic biomass were determined by analysis of C37 alkadienones. These compounds are exclusive products of Prymnesiophyte algae which at present grow most abundantly at depths of 70-90 m in the central equatorial Pacific. A record of the isotopic composition of dissolved CO2 was constructed from isotopic analyses of the planktonic foraminifera Neogloboquadrina dutertrei, which calcifies at 70-90 m in the same region. Values of epsilon(p), derived by comparison of the organic and inorganic delta values, were transformed to yield concentrations of dissolved CO2 [is equivalent to c(e)] based on a new, site-specific calibration of the relationship between epsilon(p) and c(e). The calibration was based on reassessment of existing epsilon(p) versus c(e) data, which support a physiologically based model in which epsilon(p) is inversely related to c(e). Values of PCO2, the partial pressure of CO2 that would be in equilibrium with the estimated concentrations of dissolved CO2, were calculated using Henry's law and the temperature determined from the alkenone-unsaturation index U(K/37). Uncertainties in these values arise mainly from uncertainties about the appropriateness (particularly over time) of the site-specific relationship between epsilon(p) and 1/c(e). These are discussed in detail and it is concluded that the observed record of epsilon(p) most probably reflects significant variations in delta pCO2, the ocean-atmosphere disequilibrium, which appears to have ranged from approximately 110 microatmospheres during glacial intervals (ocean > atmosphere) to approximately 60 microatmospheres during interglacials. Fluxes of CO2 to the atmosphere would thus have been significantly larger during glacial intervals. If this were characteristic of large areas of the equatorial Pacific, then greater glacial sinks for the equatorially evaded CO2 must have existed elsewhere. Statistical analysis of air-sea pCO2 differences and other parameters revealed significant (p<0.01) inverse correlations of delta pCO2 with sea surface temperature and with the mass accumulation rate of opal. The former suggests response to the strength of upwelling, the latter may indicate either drawdown of CO2 by siliceous phytoplankton or variation of [CO2]/[Si(OH)4] ratios in upwelling waters.
- Published
- 1994
- Full Text
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12. Diploptene: an indicator of terrigenous organic carbon in Washington coastal sediments.
- Author
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Prahl FG, Hayes JM, and Xie T-M
- Subjects
- Alkanes analysis, Bacteria, Carbon Isotopes, Chemistry, Organic, Fresh Water analysis, Oceans and Seas, Organic Chemistry Phenomena, Plants, Seawater analysis, Soil Microbiology, Triterpenes chemistry, Triterpenes metabolism, Washington, Carbon analysis, Fresh Water chemistry, Seawater chemistry, Soil analysis, Triterpenes analysis
- Abstract
The pentacyclic triterpene 17 beta(H),21 beta(H)-hop-22(29)-ene (diploptene) occurs in sediments throughout the Columbia River drainage basin and off the southern coast of Washington state in concentrations comparable to long-chain plantwax n-alkanes. The same relationship is evident for diploptene and long-chain n-alkanes in soils from the Willamette Valley. Microorganisms indigenous to soils and soil erosion are indicated as the biological source and physical process, respectively, for diploptene in coastal sediments. Similarity between the stable carbon isotopic composition (delta 13CPDB) of diploptene isolated from soil in the Willamette Valley (-31.2 +/- 0.3%) and from sediments deposited throughout the Washington coastal environment (-31.2 +/- 0.5%) supports this argument. Values of delta for diploptene in river sediments are variable and 8-17% lighter, indicating that an additional biological source such as methane-oxidizing bacteria makes a significant contribution to the diploptene record in river sediments. Selective biodegradation resulting from a difference in the physicochemical association within eroded particles can explain the absence of the more-13C-depleted form of diploptene in Washington coastal sediments, but this mechanism remains unproven.
- Published
- 1992
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13. Copepod fecal pellets as a source of dihydrophytol in marine sediments.
- Author
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Prahl FG, Eglinton G, Corner ED, and O'hara SC
- Abstract
Dihydrophytol(3,7,11,15-tetramethylhexadecanol) was identified in the nonsaponified lipid fraction of fecal pellets from the copepod Calanus helgolandicus fed in the laboratory on a unialgal diet. Direct deposition in the fecal pellets of certain zooplankton species may explain the presence of dihydrophytol in marine sediments. Microbial reduction of phytol in sediment cores does not account for the origin of this compound in all sedimentary environments.
- Published
- 1984
- Full Text
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