Stephen A. Macko
University of Virginia, Environmental Sciences, Faculty Member
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GIFT workshops are a two-and-a-half-day teacher enhancement workshops organized by the EGU Committee on Education and held in conjunction with the EGU annual General Assembly. The program of each workshop focuses on a different general... more
GIFT workshops are a two-and-a-half-day teacher enhancement workshops organized by the EGU Committee on Education and held in conjunction with the EGU annual General Assembly. The program of each workshop focuses on a different general theme each year. Past themes have included, for example, ``The Polar Regions'', ``The Carbon Cycle'' and ``The Earth From Space''. These workshops combine scientific presentations
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ABSTRACT The amplification of L-enantiomers of amino acids from racemates was likely a precondition for the origin of life on Earth. Engel and Nagy1 first reported that seven protein amino acids in the Murchison meteorite exhibited a... more
ABSTRACT The amplification of L-enantiomers of amino acids from racemates was likely a precondition for the origin of life on Earth. Engel and Nagy1 first reported that seven protein amino acids in the Murchison meteorite exhibited a significant L-enantiomer excess, leading to speculation that meteorite bombardment during the earliest stages of Earth history provided these essential building blocks for the development of life. Stable isotope signatures of amino acids extracted from the Murchison meteorite confirmed the extraterrestrial origin and stereochemistry of these compounds2,3. However, until recently, plausible explanations for the observed magnitude of the L-enantiomer excess in Murchison have been lacking. Alternative methods for the asymmetric amplification of L-amino acids have recently been reportede.g.4,5 that are consistent with that observed in the Murchison meteorite. A model is presented for the synthesis and subsequent alteration of amino acids on the parent body of the Murchison meteorite that is consistent with the stereochemistry presently observed.
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Carbonaceous meteorites are relics of ancient parent bodies from the time of formation of our solar system, about 4.5 billion years ago. They contain many of the organic compounds (e.g. amino acids) that are considered the building blocks... more
Carbonaceous meteorites are relics of ancient parent bodies from the time of formation of our solar system, about 4.5 billion years ago. They contain many of the organic compounds (e.g. amino acids) that are considered the building blocks of life. Experiments that attempt to simulate the synthesis of amino acids from inorganic precursors results in racemates. However, we have observed
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... the Ark of Bulrushes used to float the infant Moses down the Nile, and the boat of Gilgamesh in Mesopotamia), waterproofing pottery vessels and reed baskets, the construction of buildings (such as the Tower of Babel), walls and roads,... more
... the Ark of Bulrushes used to float the infant Moses down the Nile, and the boat of Gilgamesh in Mesopotamia), waterproofing pottery vessels and reed baskets, the construction of buildings (such as the Tower of Babel), walls and roads, gluing flint and stone utensils to wooden ...
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Piston coring and trawling on the northern California continental slope (450-600 m) recovered shells and live organisms typical of a" cold" seep community. The presence of gascharged sediments,... more
Piston coring and trawling on the northern California continental slope (450-600 m) recovered shells and live organisms typical of a" cold" seep community. The presence of gascharged sediments, hydrates, and nearby oil seepage suggests that this habitat is like ...
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Compound specific isotope analysis (CSIA) has been used to measure the δ13C of selected individual polycyclic aromatic hydrocarbons (PAHs) from a crude oil that was exposed to enhanced microbial biodegradation. Twenty-one liters of a... more
Compound specific isotope analysis (CSIA) has been used to measure the δ13C of selected individual polycyclic aromatic hydrocarbons (PAHs) from a crude oil that was exposed to enhanced microbial biodegradation. Twenty-one liters of a crude oil were introduced to series of separate 5 m×5 m wetland plots along the San Jacinto River, Texas. Smaller grids were established within each area
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ABSTRACT Substantial information regarding the history, source and transfer of both carbon and nitrogen to and within the deep sea lies in the chemical and isotopic signals of organic materials. Isotopic and chemical characterization of... more
ABSTRACT Substantial information regarding the history, source and transfer of both carbon and nitrogen to and within the deep sea lies in the chemical and isotopic signals of organic materials. Isotopic and chemical characterization of sediment trap samples indicate that the captured particulate materials are an organic rich food source for abyssal organisms which become highly altered at or just below the sediment water interface. An enrichment in nitrogen isotopes with a decline in the amount of nitrogen that can be characterized as amino acids is indicative of the diagenetic pathway, possibly the result of peptide bond hydrolysis, followed by bacterial utilization of the free amino acids or shorter chain peptides. Nearly 100% of the nitrogen can be characterized as amino acids in sediment trap materials, whereas only approximately 2 to 4% of the nitrogen in surficial sediments could be identified as being amino acids. Porewater amino acids are chemically distinct from the bound amino acids within the sediments and are typically present at heightened levels (μm/L) only in the upper 10 cm of sediment. The decline in porewater amino acids correlates closely, on a molar basis, with the increase in the porewater ammonium over that depth range. Elucidation of the transfer of organic carbon and nitrogen in deep-sea food chains is facilitated through the use of stable isotopic compositions of tissues of higher trophic level animals and their potential prey items. Trophic levels in food webs are delineated by an approximately 30%∘; enrichment in 15N with each level. Through new developments in isotope geochemistry, routine characterization of the 13C compositions of individual molecular components is now possible. Such a union of chemical analysis with isotopic compositions now offers a unique, extremely powerful tool in the delineation of production, and utilization of carbon compounds produced by abyssal organisms.
ABSTRACT Carlo E. Laj received the Excellence in Geophysical Education Award at the 2011 AGU Fall Meeting Honors Ceremony, held on 7 December in San Francisco, Calif. The award honors “a sustained commitment to excellence in geophysical... more
ABSTRACT Carlo E. Laj received the Excellence in Geophysical Education Award at the 2011 AGU Fall Meeting Honors Ceremony, held on 7 December in San Francisco, Calif. The award honors “a sustained commitment to excellence in geophysical education by a team, individual, or group.”
Drylands typically have strong seasonal variation in rainfall and primary productivity. This study examines the effects of seasonal change in grass-derived resource availability on the base of the food chain of a mammalian predator.... more
Drylands typically have strong seasonal variation in rainfall and primary productivity. This study examines the effects of seasonal change in grass-derived resource availability on the base of the food chain of a mammalian predator. Seasonal changes in live grass cover were measured in two vegetation types at the Sevilleta National Wildlife Refuge in central New Mexico, USA. Non-invasive genetic sampling of scat was used to identify individuals in the local coyote (Canis latrans) population. Stable carbon and nitrogen isotope analysis of hair removed from scats of 45 different coyotes was used to assess seasonal variation in the diet of mammalian coyote prey that came from C4 grasses. Live grass cover increased from the spring to the summer and fall; contribution of C4 grasses to the diet of mammalian coyote prey increased from the summer to the fall and was higher in grassland areas. There were significant differences in the seasonal patterns in the prey diet between grassland and ...
Research Interests: Mass Spectrometry, Diet, Climate, Mammals, Carbon Isotopes, and 9 moreHair, Animals, New Mexico, Poaceae, Nitrogen Isotopes, Ecosystem, Seasons, Food Chain, and Coyotes(Hair, Animals, New Mexico, Poaceae, Nitrogen Isotopes, Ecosystem, Seasons, Food Chain, and Coyotes)
(Hair, Animals, New Mexico, Poaceae, Nitrogen Isotopes, Ecosystem, Seasons, Food Chain, and Coyotes)
... 128 STEPHEN A. MACKO, PATRICK L. PARKER, ALFONSO V. BOTELLO REFERENCES BLUMER, M. & SASS, J. (1972). Indigenous and petroleum-derived hydrocarbons in a polluted sediment. ... WINTERS, JK, O'DONNELL, R.,... more
... 128 STEPHEN A. MACKO, PATRICK L. PARKER, ALFONSO V. BOTELLO REFERENCES BLUMER, M. & SASS, J. (1972). Indigenous and petroleum-derived hydrocarbons in a polluted sediment. ... WINTERS, JK, O'DONNELL, R., BATTERTON, JC & VAN BAALEN, C. (1976). ...
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An abyssal station on the Hatteras Abyssal Plain (5411 m) and two hadal stations in the Puerto Rico Trench (7460 and 8189 m) were sampled to obtain quantitative information on the abundance and biomass of metazoan meiofauna and, for... more
An abyssal station on the Hatteras Abyssal Plain (5411 m) and two hadal stations in the Puerto Rico Trench (7460 and 8189 m) were sampled to obtain quantitative information on the abundance and biomass of metazoan meiofauna and, for comparative purposes, bacteria and ...
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... 2.2. Analytical methods. 2.2.1. Elemental composition. Total organic carbon (TOC) and total nitrogen (TN) were determined in 25 mg sediment samples, using a Carlo Erba EA 1110 analyzer. Inorganic carbon was removed prior to the... more
... 2.2. Analytical methods. 2.2.1. Elemental composition. Total organic carbon (TOC) and total nitrogen (TN) were determined in 25 mg sediment samples, using a Carlo Erba EA 1110 analyzer. Inorganic carbon was removed prior to the analyses with hydrochloric acid. ...
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The early search for the amino acids in the lunar surface fines indicated such a low amount of the amino acids that it was deemed insignificant, and possibly contamination. Although later studies departed in some ways from the earlier... more
The early search for the amino acids in the lunar surface fines indicated such a low amount of the amino acids that it was deemed insignificant, and possibly contamination. Although later studies departed in some ways from the earlier results, they were not pursued. In this paper we critically evaluate the results from the Apollo missions from the new perspective
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Keil R.G. and Fogel M.L. Submitted. Stable carbon isotopic composition of amino acids in sediments along the Washington coast. submitted to Limnology and Oceanography. Arnarson T., and Keil R.G. In Press. Mechanisms of natural organic matter sorption to montmorillonite surfaces in sea water. Mari...more
ABSTRACT Inorganic and organic geochemistry are applications of analytical chemistry to solve Earth science problems by analyzing the composition of geological and biological systems. Measurements and characterization of unknown... more
ABSTRACT Inorganic and organic geochemistry are applications of analytical chemistry to solve Earth science problems by analyzing the composition of geological and biological systems. Measurements and characterization of unknown substances are used for making policy decisions, exploring mineral resources, pollution prevention, and management of environmental hazards. Geochemical exploration methods use trace element geochemistry to identify the “fingerprints” of certain minerals and rocks and to discover new deposits. Environmental geochemistry has become an essential tool for determining where man-made or natural distributions of elements can become a potential environmental health hazard. Organic geochemistry adds a valuable contribution to determining the nature, origin, and distribution of organic constituents in the environment.
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The δ 13 C, δ 15 N, and δ 34 S stable isotopic values of feathers from pre-fledged Laughing Gulls (Larus atricilla) in coastal Virginia and Jamaica Bay, New York were used to examine dietary variation during the nestling period. The tip... more
The δ 13 C, δ 15 N, and δ 34 S stable isotopic values of feathers from pre-fledged Laughing Gulls (Larus atricilla) in coastal Virginia and Jamaica Bay, New York were used to examine dietary variation during the nestling period. The tip portions of the feathers were used to indicate ...
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The organic-rich, Middle Proterozoic Nonesuch Formation is part of a thick volcaniclastic rift-fill sequence (Mid-Continent Rift System, northern Wisconsin and Upper Peninsula Michigan) with a mild thermal history. Despite... more
The organic-rich, Middle Proterozoic Nonesuch Formation is part of a thick volcaniclastic rift-fill sequence (Mid-Continent Rift System, northern Wisconsin and Upper Peninsula Michigan) with a mild thermal history. Despite stratigraphic/sedimentologic ...
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Washed platelets isolated from rats 24 hr after oral treatment with a Prudhoe Bay crude oil (PBCO) showed a substantial inhibition of aggregation induced by ADP, arachidonic acid, or epinephrine. In vitro addition of a dimethyl sulfoxide... more
Washed platelets isolated from rats 24 hr after oral treatment with a Prudhoe Bay crude oil (PBCO) showed a substantial inhibition of aggregation induced by ADP, arachidonic acid, or epinephrine. In vitro addition of a dimethyl sulfoxide extract of PBCO or its aliphatic, aromatic, or heterocyclic fractions to washed platelets also resulted in an inhibition of aggregation. ADP release was inhibited in platelets to which an extract of PBCO or its fractions were added in vitro or in platelets isolated from rats treated in vivo with PBCO. Thromboxane B2 release was increased in platelets isolated from rats intubated with PBCO or in platelets to which a dimethyl sulfoxide extract of the aromatic or heterocyclic fraction was added. However, thromboxane B2 release was inhibited in platelets to which PBCO or the aliphatic fraction extracts were added. The results indicate that PBCO inhibits platelet aggregation presumably by bringing about alterations in the platelet plasma membrane. Inhibition of ADP release could contribute to the inhibition of aggregation but thromboxane B2 is believed not to play a significant role.
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Mussels, clams, and tube worms collected in the vicinity of hydrocarbon seeps on the Louisiana slope contain mostly "dead" carbon, indicating that dietary carbon is largely derived from seeping oil and gas. Enzyme... more
Mussels, clams, and tube worms collected in the vicinity of hydrocarbon seeps on the Louisiana slope contain mostly "dead" carbon, indicating that dietary carbon is largely derived from seeping oil and gas. Enzyme assays, elemental sulfur analysis, and carbon dioxide fixation studies demonstrate that vestimentiferan tube worms and three clam species contain intracellular, autotrophic sulfur bacterial symbionts. Carbon isotopic ratios of 246 individual animal tissues were used to differentiate heterotrophic (8(13)C = -14 to -20 per mil), sulfur-based (8(13)C = -30 to -42 per mil), and methane-based (8(13)C = <-40 per mil) energy sources. Mussels with symbiotic methanotrophic bacteria reflect the carbon isotopic composition of the methane source. Isotopically light nitrogen and sulfur confirm the chemoautotrophic nature of the seep animals. Sulfur-based chemosynthetic animals contain isotopically light sulfur, whereas methane-based symbiotic mussels more closely reflect the heavier oceanic sulfate pool. The nitrogen requirement of some seep animals may be supported by nitrogen-fixing bacteria. Some grazing neogastropods have isotopic values characteristic of chemosynthetic animals, suggesting the transfer of carbon into the background deep-sea fauna.
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Records of carbon and nitrogen isotopes in biogenic silica and carbon isotopes in planktonic foraminifera from deep-sea sediment cores from the Southern Ocean reveal that the primary production during the last glacial maximum was lower... more
Records of carbon and nitrogen isotopes in biogenic silica and carbon isotopes in planktonic foraminifera from deep-sea sediment cores from the Southern Ocean reveal that the primary production during the last glacial maximum was lower than Holocene productivity. These observations conflict with the hypothesis that the low atmospheric carbon dioxide concentrations were introduced by an increase in the efficiency of the high-latitude biological pump. Instead, different oceanic sectors may have had high glacial productivity, or alternative mechanisms that do not involve the biological pump must be considered as the primary cause of the low glacial atmospheric carbon dioxide concentrations.
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Southern African savannas are mixed plant communities where C3 trees co-exist with C4 grasses. Here foliar δ15N and δ13C were used as indicators of nitrogen uptake and of water use efficiency to investigate the effect of the rainfall... more
Southern African savannas are mixed plant communities where C3 trees co-exist with C4 grasses. Here foliar δ15N and δ13C were used as indicators of nitrogen uptake and of water use efficiency to investigate the effect of the rainfall regime on the use of nitrogen and water by herbaceous and woody plants in both dry and wet seasons. Foliar δ15N increased as aridity rose for both C3 and C4 plants for both seasons, although the magnitude of the increase was different for C3 and C4 plants and for two seasons. Soil δ15N also significantly increased with aridity. Foliar δ13C increased with aridity for C3 plants in the wet season but not in the dry season, whereas in C4 plants the relationship was more complex and non-linear. The consistently higher foliar δ15N for C3 plants suggests that C4 plants may be a superior competitor for nitrogen. The different foliar δ13C relationships with rainfall may indicate that the C3 plants have an advantage when competing for water resources. The differences in water and nitrogen use likely collectively contribute to the tree–grass coexistence in savannas. Such differences facilitate interpretations of palaeo-vegetation composition variations and help predictions of vegetation composition changes under future climatic scenarios.
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Research Interests: Multidisciplinary, Carbon Isotopes, Fossils, Animals, Mollusca, and 2 moreSnails and Amino Acids(Snails and Amino Acids)
(Snails and Amino Acids)
The Cretaceous/Tertiary (K/T) boundary, with an age of 65 million years before present, is associated with the mass extinctions of dinosaurs and other terrestrial and marine organisms. Evidence for the K/T boundary is reported in both... more
The Cretaceous/Tertiary (K/T) boundary, with an age of 65 million years before present, is associated with the mass extinctions of dinosaurs and other terrestrial and marine organisms. Evidence for the K/T boundary is reported in both marine and non-marine stratigraphic units. The ...
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Abstract Nitrogen (N) isotope patterns are useful for understanding carbon and nitrogen dynamics in mycorrhizal systems but questions remain about how different N forms, fungal symbionts, and N availabilities influence δ 15 N signatures.... more
Abstract Nitrogen (N) isotope patterns are useful for understanding carbon and nitrogen dynamics in mycorrhizal systems but questions remain about how different N forms, fungal symbionts, and N availabilities influence δ 15 N signatures. Here, we studied how biomass allocation and δ 15 N patterns in Pinus sylvestris L. cultures were affected by nitrogen supply rate (3% per day or 4% per day relative to the nitrogen already present), nitrogen form (ammonium versus nitrate), and mycorrhizal colonization by fungi with a greater ( ...