16,995 research outputs found
Implications of coral reef buildup for the controls on atmospheric CO2 since the Last Glacial Maximum
We examine the effect on atmospheric CO2 of the occurrence of increased shallow water carbonate deposition and regrowth of the terrestrial biosphere following the last glacial. We find that contrary to recent speculations that changes in terrestrial carbon storage were primarily responsible for the observed similar to20 ppmv late Holocene CO2 rise, a more likely explanation is coral reef buildup and other forms of shallow water carbonate deposition during this time. The importance of a responsive terrestrial carbon reservoir may instead be as a negative feedback restricting the rate of CO2 rise possible in the early stages of the deglacial transition. This separation in time of the primary impacts of regrowth of the terrestrial biosphere and increased shallow water carbonate deposition explains the occurrence of an early Holocene carbonate preservation event observed in deep-sea sediments. We demonstrate that their combined influence is also consistent with available proxy estimates of deep ocean carbonate ion concentration changes over the last 21 kyr. Accounting for the processes that act on the carbonate chemistry of the ocean as a whole then allows us to place strong constraints on the nature of the remaining processes that must be operating at the deglacial transition. By subtracting the net CO2 effect of coral reef buildup and terrestrial biosphere regrowth from recent high-resolution ice core data, we highlight two periods, from 17.0 to 13.8 kyr and 12.3 to 11.2 kyr BP characterized by sustained rapid rates of CO2 increase (> 12 ppmv kyr(-1)). Because these periods are coincident with Southern Hemisphere "deglaciation,'' we argue that changes in the biogeochemical properties of the Southern Ocean surface are the most likely cause
The Nature of the Chemical Process. 1. Symmetry Evolution - Revised Information Theory, Similarity Principle and Ugly Symmetry
Three laws of information theory have been proposed. Labeling by introducing
nonsymmetry and formatting by introducing symmetry are defined. The function L
(L=lnw, w is the number of microstates, or the sum of entropy and information,
L=S+I) of the universe is a constant (the first law of information theory). The
entropy S of the universe tends toward a maximum (the second law law of
information theory). For a perfect symmetric static structure, the information
is zero and the static entropy is the maximum (the third law law of information
theory). Based on the Gibbs inequality and the second law of the revised
information theory we have proved the similarity principle (a continuous higher
similarity-higher entropy relation after the rejection of the Gibbs paradox)
and proved the Curie-Rosen symmetry principle (a higher symmetry-higher
stability relation) as a special case of the similarity principle. Some
examples in chemical physics have been given. Spontaneous processes of all
kinds of molecular interaction, phase separation and phase transition,
including symmetry breaking and the densest molecular packing and
crystallization, are all driven by information minimization or symmetry
maximization. The evolution of the universe in general and evolution of life in
particular can be quantitatively considered as a series of symmetry breaking
processes. The two empirical rules - similarity rule and complementarity rule -
have been given a theoretical foundation. All kinds of periodicity in space and
time are symmetries and contribute to the stability. Symmetry is beautiful
because it renders stability. However, symmetry is in principle ugly because it
is associated with information loss.Comment: 29 pages, 14 figure
Comparison between random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers with high resolution melt analyses in genetic variation analysis among selected sorghum genotypes
Understanding the genetic diversity of germplasm is essential in plant breeding programmes and germplasm management. Molecular markers are efficient and effective tools widely used for assessing genetic diversity among crop genotypes. Recently, high resolution melt analysis (HRM) has been reported for detecting genetic variability. However, there is limited information on the use of HRM in conjunction with other molecular marker techniques for assessing genetic variation in sorghum [Sorghum bicolor (L.) Moench]. This study was conducted to compare random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers with HRM analyses to determine genetic variation among selected sorghum genotypes. Eight diverse sorghum accessions obtained from the plant genetic resources, Department of Agriculture, Forestry and Fisheries/South Africa were subjected to both analyses. DNA was extracted from fresh leaves of the eight accessions and amplified using three RAPD and three SSR primers. The HRM analysis was performed and temperature normalised melting curves and difference plots were created and results compared. Both the molecular markers and HRM revealed variations among the accessions. The HRM melting profiles fairly well correlated with results from the RAPD and SSR analysis. The clustering of sorghum accessions using SSR marker highly corresponded with the HRM analysis. Therefore, the HRM can be a useful tool in genetic diversity and classification of sorghum genotypes without post-PCR analysis or processing.Key words: Genetic diversity, high resolution melt analysis, RAPD, simple sequence repeat, sorghum
The search for Hesperian organic matter on Mars: Pyrolysis studies of sediments rich in sulfur and iron
Jarosite on Mars is of significant geological and astrobiological interest as it forms in acidic aqueous conditions that are potentially habitable for acidophilic organisms. Jarosite can provide environmental context and may host organic matter. The most common analytical technique used to search for organic molecules on the surface of Mars is pyrolysis. However, thermal decomposition of jarosite produces oxygen, which degrades organic signals. At pH values greater than 3 and high water to rock ratios jarosite has a close association with goethite. Hematite can form by dehydration of goethite or directly from jarosite under certain aqueous conditions. Goethite and hematite are significantly more amenable for pyrolysis experiments searching for organic matter than jarosite. Analysis of the mineralogy and organic chemistry of samples from a natural acidic stream revealed a diverse response for organic compounds during pyrolysis of goethite-rich layers but a poor response for jarosite-rich or mixed jarosite-goethite units. Goethite units that are associated with jarosite but do not contain jarosite themselves should be targeted for organic detection pyrolysis experiments on Mars. These findings are extremely timely as future exploration targets for Mars Science Laboratory include Hematite Ridge, which may have formed from goethite precursors
Organic compound-mineral interactions: using flash pyrolysis to monitor the adsorption of fatty acids on calcite
Fatty acids are near ubiquitous organic compounds in living organisms in the Earth’s biosphere. Following death of an organism in the marine environment its fatty acids may survive descent to the sea bed where they can be juxtaposed with minerals. The aim of this study was to investigate the interaction of fatty acids with the common marine mineral calcite. Adsorption of tetradecanoic acid (C14) on calcite results in a sigmoidal or “s” isotherm. Flash pyrolysis experiments were conducted on samples of fatty acid adsorbed onto calcite and were compared with similar experiments on pure fatty acid and on salts of a fatty acid. Flash pyrolysis of pure tetradecanoic acid generated unsaturated and saturated hydrocarbons and a series of unsaturated and saturated low molecular weight fatty acids. Flash pyrolysis of free tetradecanoic acid salt produced saturated and unsaturated hydrocarbons, an aldehyde and a homologous series of saturated and unsaturated ketones, one of which was a symmetrical mid chain ketone (14-heptacosanone). Flash pyrolysis data from adsorbed tetradecanoic acid samples suggested that adsorption is analogous to the formation of the calcium salt of tetradecanoic acid. A key characteristic of the flash pyrolysis products of adsorbed fatty acids and fatty acid salts was the production of ketones with higher molecular weights than the starting fatty acids. Ketonisation was not observed from the flash pyrolysis of pure acid which implied the catalytic significance of the calcite mineral surface. The abundance of hydrocarbons relative to ketones in the pyrolysates negatively correlated with the proportion of fatty acids adsorbed to the surface of calcite. The ability to use flash pyrolysis to diagnose the nature of fatty acid interactions with mineral surfaces provides a valuable tool for monitoring the fate of these important lipids at the Earth’s surface as they pass into the geosphere and are subjected to diagenetic processes
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