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Geobiology

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https://www.readbyqxmd.com/read/28771908/bacteriohopanepolyols-along-redox-gradients-in-the-humboldt-current-system-off-northern-chile
#1
E D Matys, J Sepúlveda, S Pantoja, C B Lange, M Caniupán, F Lamy, R E Summons
Marine oxygen minimum zones (OMZs) are characterized by the presence of subsurface suboxic or anoxic waters where diverse microbial processes are responsible for the removal of fixed nitrogen. OMZs have expanded over past decades and are expected to continue expanding in response to the changing climate. The implications for marine biogeochemistry, particularly nitrogen cycling, are uncertain. Cell membrane lipids (biomarkers), such as bacterial bacteriohopanepolyols (BHPs) and their degradation products (hopanoids), have distinctive structural attributes that convey information about their biological sources...
August 3, 2017: Geobiology
https://www.readbyqxmd.com/read/28737010/carbonate-ooids-of-the-mesoarchaean-pongola-supergroup-south-africa
#2
M Siahi, A Hofmann, S Master, C W Mueller, A Gerdes
Ooids from the Mesoarchaean Chobeni Formation, Pongola Supergroup, KwaZulu-Natal, South Africa are older than any ooids reported to date. They are made of dolomite and ankerite and show concentric, radial-concentric, micritic, and radial fabrics. Radial ooids are interpreted to have originated from high-Mg-calcite and probably formed by microbial activity in a low-energy regime, while concentric ooids had an aragonite precursor and formed biotically under agitated/high-energy environmental conditions. Micritic ooids formed via the recrystallization of concentric ooids...
July 24, 2017: Geobiology
https://www.readbyqxmd.com/read/28691279/paleoecology-of-neoproterozoic-hypersaline-environments-biomarker-evidence-for-haloarchaea-methanogens-and-cyanobacteria
#3
R Schinteie, J J Brocks
While numerous studies have examined modern hypersaline ecosystems, their equivalents in the geologic past, particularly in the Precambrian, are poorly understood. In this study, biomarkers from ~820 million year (Ma)-old evaporites from the Gillen Formation of the mid-Neoproterozoic Bitter Springs Group, central Australia, are investigated to elucidate the antiquity and paleoecology of halophiles. The sediments were composed of alternating laminae of dolomitized microbial mats and up to 90% anhydrite. Solvent extraction of these samples yielded thermally well-preserved hydrocarbon biomarkers...
July 10, 2017: Geobiology
https://www.readbyqxmd.com/read/28670785/constraining-the-timing-of-the-great-oxidation-event-within-the-rubisco-phylogenetic-tree
#4
B Kacar, V Hanson-Smith, Z R Adam, N Boekelheide
Ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase (RuBisCO, or Rubisco) catalyzes a key reaction by which inorganic carbon is converted into organic carbon in the metabolism of many aerobic and anaerobic organisms. Across the broader Rubisco protein family, homologs exhibit diverse biochemical characteristics and metabolic functions, but the evolutionary origins of this diversity are unclear. Evidence of the timing of Rubisco family emergence and diversification of its different forms has been obscured by a meager paleontological record of early Earth biota, their subcellular physiology and metabolic components...
July 3, 2017: Geobiology
https://www.readbyqxmd.com/read/28603946/benthic-foraminifera-contribution-to-fjord-modern-carbon-pools-a-seasonal-study-in-adventfjorden-spitsbergen
#5
J Pawłowska, M Łącka, M Kucharska, N Szymańska, K Koziorowska, K Kuliński, M Zajączkowski
The aim of this study was to determine the amount of organic and inorganic carbon in foraminifera specimens and to provide quantitative data on the contribution of foraminifera to the sedimentary carbon pool in Adventfjorden. The investigation was based on three calcareous species that occur commonly in Svalbard fjords: Cassidulina reniforme, Elphidium excavatum and Nonionellina labradorica. Our results show that the species investigated did not contribute substantially to the organic carbon pool in Adventfjorden, because they represented only 0...
June 12, 2017: Geobiology
https://www.readbyqxmd.com/read/28603844/seaweed-morphology-and-ecology-during-the-great-animal-diversification-events-of-the-early-paleozoic-a-tale-of-two-floras
#6
S T LoDuca, N Bykova, M Wu, S Xiao, Y Zhao
Non-calcified marine macroalgae ("seaweeds") play a variety of key roles in the modern Earth system, and it is likely that they were also important players in the geological past, particularly during critical transitions such as the Cambrian Explosion (CE) and the Great Ordovician Biodiversification Event (GOBE). To investigate the morphology and ecology of seaweeds spanning the time frame from the CE through the GOBE, a carefully vetted database was constructed that includes taxonomic and morphometric information for non-calcified macroalgae from 69 fossil deposits...
June 12, 2017: Geobiology
https://www.readbyqxmd.com/read/28627099/fossils-proxies-and-models-geobiology-at-critical-transitions-in-the-proterozoic-paleozoic
#7
EDITORIAL
J D Schiffbauer, N Bykova, A D Muscente
No abstract text is available yet for this article.
July 2017: Geobiology
https://www.readbyqxmd.com/read/28387043/controls-on-the-evolution-of-ediacaran-metazoan-ecosystems-a-redox-perspective
#8
F Bowyer, R A Wood, S W Poulton
A growing number of detailed geochemical studies of Ediacaran (635-541 Ma) marine successions have provided snapshots into the redox environments that played host to the earliest known metazoans. Whilst previous compilations have focused on the global evolution of Ediacaran water column redox chemistry, the inherent heterogeneity evident in palaeogeographically distinct environments demands a more dissected approach to better understand the nature, interactions and evolution of extrinsic controls on the development of early macrobenthic ecosystems...
July 2017: Geobiology
https://www.readbyqxmd.com/read/28387009/paleoecology-and-paleoceanography-of-the-athel-silicilyte-ediacaran-cambrian-boundary-sultanate-of-oman
#9
D A Stolper, G D Love, S Bates, T W Lyons, E Young, A L Sessions, J P Grotzinger
The Athel silicilyte is an enigmatic, hundreds of meters thick, finely laminated quartz deposit, in which silica precipitated in deep water (>~100-200 m) at the Ediacaran-Cambrian boundary in the South Oman Salt Basin. In contrast, Meso-Neoproterozoic sinks for marine silica were dominantly restricted to peritidal settings. The silicilyte is known to contain sterane biomarkers for demosponges, which today are benthic, obligately aerobic organisms. However, the basin has previously been described as permanently sulfidic and time-equivalent shallow-water carbonate platform and evaporitic facies lack silica...
May 2017: Geobiology
https://www.readbyqxmd.com/read/28378894/a-theory-of-atmospheric-oxygen
#10
T A Laakso, D P Schrag
Geological records of atmospheric oxygen suggest that pO2 was less than 0.001% of present atmospheric levels (PAL) during the Archean, increasing abruptly to a Proterozoic value between 0.1% and 10% PAL, and rising quickly to modern levels in the Phanerozoic. Using a simple model of the biogeochemical cycles of carbon, oxygen, sulfur, hydrogen, iron, and phosphorous, we demonstrate that there are three stable states for atmospheric oxygen, roughly corresponding to levels observed in the geological record. These stable states arise from a series of specific positive and negative feedbacks, requiring a large geochemical perturbation to the redox state to transition from one to another...
May 2017: Geobiology
https://www.readbyqxmd.com/read/28371135/climate-and-geochemistry-as-drivers-of-eucalypt-diversification-in-australia
#11
E N Bui, A H Thornhill, C E González-Orozco, N Knerr, J T Miller
Eucalypts cover most of Australia. Here, we investigate the relative contribution of climate and geochemistry to the distribution and diversity of eucalypts. Using geostatistics, we estimate major element concentrations, pH, and electrical conductivity at sites where eucalypts have been recorded. We compare the median predicted geochemistry and reported substrate for individual species that appear associated with extreme conditions; this provides a partial evaluation of the predictions. We generate a site-by-species matrix by aggregating observations to the centroids of 100-km-wide grid cells, calculate diversity indices, and use numerical ecology methods (ordination, variation partitioning) to investigate the ecology of eucalypts and their response to climatic and geochemical gradients...
May 2017: Geobiology
https://www.readbyqxmd.com/read/28299862/the-neoarchaean-surficial-sulphur-cycle-an-alternative-hypothesis-based-on-analogies-with-20th-century-atmospheric-lead
#12
M Gallagher, M J Whitehouse, B S Kamber
We revisit the S-isotope systematics of sedimentary pyrite in a shaly limestone from the ca. 2.52 Ga Gamohaan Formation, Upper Campbellrand Subgroup, Transvaal, South Africa. The analysed rock is interpreted to have been deposited in a water depth of ca. 50-100 m, in a restricted sub-basin on a drowning platform. A previous study discovered that the pyrites define a nonzero intercept δ(34) SV-CDT -Δ(33) S data array. The present study carried out further quadruple S-isotope analyses of pyrite, confirming and expanding the linear δ(34) SV-CDT -Δ(33) S array with an δ(34) S zero intercept at ∆(33) S ca...
May 2017: Geobiology
https://www.readbyqxmd.com/read/28256065/volcanic-ash-supports-a-diverse-bacterial-community-in-a-marine-mesocosm
#13
V Witt, P M Ayris, D E Damby, C Cimarelli, U Kueppers, D B Dingwell, G Wörheide
Shallow-water coral reef ecosystems, particularly those already impaired by anthropogenic pressures, may be highly sensitive to disturbances from natural catastrophic events, such as volcanic eruptions. Explosive volcanic eruptions expel large quantities of silicate ash particles into the atmosphere, which can disperse across millions of square kilometres and deposit into coral reef ecosystems. Following heavy ash deposition, mass mortality of reef biota is expected, but little is known about the recovery of post-burial reef ecosystems...
May 2017: Geobiology
https://www.readbyqxmd.com/read/28158920/the-geobiological-nitrogen-cycle-from-microbes-to-the-mantle
#14
REVIEW
A L Zerkle, S Mikhail
Nitrogen forms an integral part of the main building blocks of life, including DNA, RNA, and proteins. N2 is the dominant gas in Earth's atmosphere, and nitrogen is stored in all of Earth's geological reservoirs, including the crust, the mantle, and the core. As such, nitrogen geochemistry is fundamental to the evolution of planet Earth and the life it supports. Despite the importance of nitrogen in the Earth system, large gaps remain in our knowledge of how the surface and deep nitrogen cycles have evolved over geologic time...
May 2017: Geobiology
https://www.readbyqxmd.com/read/28128527/sulphur-cycling-in-a-neoarchaean-microbial-mat
#15
N R Meyer, A L Zerkle, D A Fike
Multiple sulphur (S) isotope ratios are powerful proxies to understand the complexity of S biogeochemical cycling through Deep Time. The disappearance of a sulphur mass-independent fractionation (S-MIF) signal in rocks <~2.4 Ga has been used to date a dramatic rise in atmospheric oxygen levels. However, intricacies of the S-cycle before the Great Oxidation Event remain poorly understood. For example, the isotope composition of coeval atmospherically derived sulphur species is still debated. Furthermore, variation in Archaean pyrite δ(34) S values has been widely attributed to microbial sulphate reduction (MSR)...
May 2017: Geobiology
https://www.readbyqxmd.com/read/28044397/selenium-iv-vi-reduction-and-tolerance-by-fungi-in-an-oxic-environment
#16
C E Rosenfeld, J A Kenyon, B R James, C M Santelli
Microbial processes are known to mediate selenium (Se) oxidation-reduction reactions, strongly influencing Se speciation, bioavailability, and transport throughout the environment. While these processes have commonly been studied in anaerobic bacteria, the role that aerobic fungi play in Se redox reactions could be important for Se-rich soil systems, dominated by microbial activity. We quantified fungal growth, aerobic Se(IV, VI) reduction, and Se immobilization and volatilization in the presence of six, metal-tolerant Ascomycete fungi...
May 2017: Geobiology
https://www.readbyqxmd.com/read/28452176/microbial-acceleration-of-aerobic-pyrite-oxidation-at-circumneutral-ph
#17
E Percak-Dennett, S He, B Converse, H Konishi, H Xu, A Corcoran, D Noguera, C Chan, A Bhayyacharyya, T Borch, E Boyd, E E Roden
Pyrite (FeS2 ) is the most abundant sulfide mineral on Earth and represents a significant reservoir of reduced iron and sulfur both today and in the geologic past. In modern environments, oxidative transformations of pyrite and other metal sulfides play a key role in terrestrial element partitioning with broad impacts to contaminant mobility and the formation of acid mine drainage systems. Although the role of aerobic micro-organisms in pyrite oxidation under acidic-pH conditions is well known, to date there is very little known about the capacity for aerobic micro-organisms to oxidize pyrite at circumneutral pH...
April 27, 2017: Geobiology
https://www.readbyqxmd.com/read/28434198/eukaryotic-diversity-in-late-pleistocene-marine-sediments-around-a-shallow-methane-hydrate-deposit-in-the-japan-sea
#18
M Kouduka, A S Tanabe, S Yamamoto, K Yanagawa, Y Nakamura, F Akiba, H Tomaru, H Toju, Y Suzuki
Marine sediments contain eukaryotic DNA deposited from overlying water columns. However, a large proportion of deposited eukaryotic DNA is aerobically biodegraded in shallow marine sediments. Cold seep sediments are often anaerobic near the sediment-water interface, so eukaryotic DNA in such sediments is expected to be preserved. We investigated deeply buried marine sediments in the Japan Sea, where a methane hydrate deposit is associated with cold seeps. Quantitative PCR analysis revealed the reproducible recovery of eukaryotic DNA in marine sediments at depths up to 31...
April 23, 2017: Geobiology
https://www.readbyqxmd.com/read/28419718/shifting-microbial-communities-sustain-multiyear-iron-reduction-and-methanogenesis-in-ferruginous-sediment-incubations
#19
M S Bray, J Wu, B C Reed, C B Kretz, K M Belli, R L Simister, C Henny, F J Stewart, T J DiChristina, J A Brandes, D A Fowle, S A Crowe, J B Glass
Reactive Fe(III) minerals can influence methane (CH4 ) emissions by inhibiting microbial methanogenesis or by stimulating anaerobic CH4 oxidation. The balance between Fe(III) reduction, methanogenesis, and CH4 oxidation in ferruginous Archean and Paleoproterozoic oceans would have controlled CH4 fluxes to the atmosphere, thereby regulating the capacity for CH4 to warm the early Earth under the Faint Young Sun. We studied CH4 and Fe cycling in anoxic incubations of ferruginous sediment from the ancient ocean analogue Lake Matano, Indonesia, over three successive transfers (500 days in total)...
April 17, 2017: Geobiology
https://www.readbyqxmd.com/read/28397387/a-geochemical-study-of-the-ediacaran-discoidal-fossil-aspidella-preserved-in-limestones-implications-for-its-taphonomy-and-paleoecology
#20
N Bykova, B C Gill, D Grazhdankin, V Rogov, S Xiao
The Ediacara biota features the rise of macroscopic complex life immediately before the Cambrian explosion. One of the most abundant and widely distributed elements of the Ediacara biota is the discoidal fossil Aspidella, which is interpreted as a subsurface holdfast possibly anchoring a frondose epibenthic organism. It is a morphologically simple fossil preserved mainly in siliciclastic rocks, which are unsuitable for comprehensive stable isotope geochemical analyses to decipher its taphonomy and paleoecology...
April 11, 2017: Geobiology
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