scholarly journals Atmospheric composition and climate on the early Earth

2006 ◽  
Vol 361 (1474) ◽  
pp. 1733-1742 ◽  
Author(s):  
James F Kasting ◽  
M. Tazewell Howard
Keyword(s):  
Isotopic Composition ◽  
Isotope Fractionation ◽  
Atmospheric Composition ◽  
Early Earth ◽  
Geothermal Heat ◽  
Sulphur Isotope ◽  
Ocean Ridges ◽  
Early Atmosphere ◽  
Isotopic Records

Oxygen isotope data from ancient sedimentary rocks appear to suggest that the early Earth was significantly warmer than today, with estimates of surface temperatures between 45 and 85°C. We argue, following others, that this interpretation is incorrect—the same data can be explained via a change in isotopic composition of seawater with time. These changes in the isotopic composition could result from an increase in mean depth of the mid-ocean ridges caused by a decrease in geothermal heat flow with time. All this implies that the early Earth was warm, not hot. A more temperate early Earth is also easier to reconcile with the long-term glacial record. However, what triggered these early glaciations is still under debate. The Paleoproterozoic glaciations at approximately 2.4 Ga were probably caused by the rise of atmospheric O 2 and a concomitant decrease in greenhouse warming by CH 4 . Glaciation might have occurred in the Mid-Archaean as well, at approximately 2.9 Ga, perhaps as a consequence of anti-greenhouse cooling by hydrocarbon haze. Both glaciations are linked to decreases in the magnitude of mass-independent sulphur isotope fractionation in ancient rocks. Studying both the oxygen and sulphur isotopic records has thus proved useful in probing the composition of the early atmosphere.

scholarly journals Hydrogen-Nitrogen Greenhouse Warming in Earth's Early Atmosphere

Science ◽  
2013 ◽  
Vol 339 (6115) ◽  
pp. 64-67 ◽  
Author(s):  
Robin Wordsworth ◽  
Raymond Pierrehumbert
Keyword(s):  
Atmospheric Composition ◽  
Early Earth ◽  
Greenhouse Warming ◽  
Mixing Ratio ◽  
The Past ◽  
Early Atmosphere ◽  
Global Cooling ◽  
Surface Liquid ◽  
Atmospheric Mass ◽  
Global Mean

Understanding how Earth has sustained surface liquid water throughout its history remains a key challenge, given that the Sun’s luminosity was much lower in the past. Here we show that with an atmospheric composition consistent with the most recent constraints, the early Earth would have been significantly warmed by H2-N2collision–induced absorption. With two to three times the present-day atmospheric mass of N2and a H2mixing ratio of 0.1, H2-N2warming would be sufficient to raise global mean surface temperatures above 0°C under 75% of present-day solar flux, with CO2levels only 2 to 25 times the present-day values. Depending on their time of emergence and diversification, early methanogens may have caused global cooling via the conversion of H2and CO2to CH4, with potentially observable consequences in the geological record.

Sulphur-isotope geochemistry of silver–selpnarsenide vein mineralization, Cobalt, Ontario

1986 ◽  
Vol 23 (10) ◽  
pp. 1551-1567 ◽  
Author(s):  
M. D. Goodz ◽  
D. H. Watkinson ◽  
V. Smejkal ◽  
Z. Pertold
Keyword(s):  
Isotopic Composition ◽  
Isotope Fractionation ◽  
Isotope Geochemistry ◽  
Wall Rock ◽  
Sulphur Isotope ◽  
Vein Formation ◽  
Metavolcanic Rocks ◽  
Isotope Study ◽  
Vein Deposits ◽  
Sulphur Isotopic Composition

The silver–sulpharsenide vein deposits of Cobalt, Ontario, crosscut basement Archean metavolcanic rocks, Proterozoic strata, and younger Proterozoic diabase sills. A petrographic and sulphur-isotope study of the metallic minerals was initiated to assess possible genetic models of vein formation. Discrete differences exist between the sulphur-isotope compositions of basement sulphides (δ34S = + 4.0‰), brecciated wall-rock sulphides (+ 3.5‰), and vein sulphides (+ 2.3‰). The δ34S values consistently increase with distance from the vein centres. Sulphur-isotope fractionation trends are similar for all the vein deposits studied. Sulphur-isotope data suggest that sulphides were deposited between 130 and 254 °C. Based on the assumption of equilibrium between chalcopyrite and galena, the initial δ34S of the fluid was between + 5.0 and + 11.0‰. The release of sulphur during the reaction of Archean pyrite with Proterozoic formational brines to form pyrrhotite is proposed to explain the heavy sulphur isotopic composition of the fluid. This process could also have provided the Ni, Co, and As, known to be concentrated in some pyrite, that was deposited in the silver veins. Interpretation of mineral paragenesis and geothermometry indicate that temperature decreased and aS2 increased as deposition proceeded.

scholarly journals Sulphur isotopes of alkaline magmas unlock long-term records of crustal recycling on Earth

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
William Hutchison ◽  
Rainer J. Babiel ◽  
Adrian A. Finch ◽  
Michael A. W. Marks ◽  
Gregor Markl ◽  
...  
Keyword(s):  
Lithospheric Mantle ◽  
Isotope Fractionation ◽  
Temporal Variations ◽  
Geological Time ◽  
Sulphur Isotope ◽  
Crustal Recycling ◽  
Magma Sources ◽  
Alkaline Magmas ◽  
Age Range

Abstract Earth’s surface and mantle sulphur reservoirs are connected via subduction, crustal recycling and volcanism. Although oceanic hotspot lavas currently provide the best constraints on the deep sulphur cycle, their restricted age range (<200 Ma) means they cannot reveal temporal variations in crustal recycling over Earth history. Sulphur-rich alkaline magmas offer the solution because they are associated with recycled sources (i.e. metasomatized lithospheric mantle and plumes) and, crucially, are found throughout the geological record. Here, we present a detailed study of sulphur isotope fractionation in a Mesoproterozoic alkaline province in Greenland and demonstrate that an enriched subduction-influenced source (δ34S of +1 to +5‰) can be reconstructed. A global δ34S compilation reveals secular variation in alkaline magma sources which support changes in the composition of the lithospheric mantle and/or Ga timescales for deep crustal recycling. Thus, alkaline magmas represent a powerful yet underutilized repository for interrogating crustal recycling through geological time.

Long-term Aptian marine osmium isotopic record of Ontong Java Nui activity

Geology ◽  
2021 ◽  
Author(s):  
Hironao Matsumoto ◽  
Rodolfo Coccioni ◽  
Fabrizio Frontalini ◽  
Kotaro Shirai ◽  
Luigi Jovane ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Volcanic Eruptions ◽  
Hydrothermal Activity ◽  
Published Data ◽  
Isotopic Data ◽  
Oceanic Plateaus ◽  
Carbon Burial ◽  
Organic Carbon Burial ◽  
Isotopic Records

The early to mid-Aptian was punctuated by episodic phases of organic-carbon burial in various oceanographic settings, which are possibly related to massive volcanism associated with the emplacement of the Ontong Java, Manihiki, and Hikurangi oceanic plateaus in the southwestern Pacific Ocean, inferred to have formed a single plateau called Ontong Java Nui. Sedimentary osmium (Os) isotopic compositions are one of the best proxies for determining the timing of voluminous submarine volcanic episodes. However, available Os isotopic records during the age are limited to a narrow interval in the earliest Aptian, which is insufficient for the reconstruction of long-term hydrothermal activity. We document the early to mid-Aptian Os isotopic record using pelagic Tethyan sediments deposited in the Poggio le Guaine (Umbria-Marche Basin, Italy) to precisely constrain the timing of massive volcanic episodes and to assess their impact on the marine environment. Our new Os isotopic data reveal three shifts to unradiogenic values, two of which correspond to black shale horizons in the lower to mid-Aptian, namely the Wezel (herein named) and Fallot Levels. These Os isotopic excursions are ascribed to massive inputs of unradiogenic Os to the ocean through hydrothermal activity. Combining the new Os isotopic record with published data from the lowermost Aptian organic-rich interval in the Gorgo a Cerbara section of the Umbria-Marche Basin, it can be inferred that Ontong Java Nui volcanic eruptions persisted for ~5 m.y. during the early to mid-Aptian.

scholarly journals Changes to the chemical state of the northern hemisphere atmosphere during the second half of the twentieth century

2016 ◽  
Author(s):  
Mike J. Newland ◽  
Patricia Martinerie ◽  
Emmanuel Witrant ◽  
Detlev Helmig ◽  
David R. Worton ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Large Scale ◽  
Atmospheric Composition ◽  
The Arctic ◽  
Major Influence ◽  
Secondary Products ◽  
Alkyl Nitrates ◽  
Mixing Ratios ◽  
Wide Range

Abstract. The NOX (NO and NO2) and HOX (OH and HO2) budgets of the atmosphere exert a major influence on atmospheric composition, controlling removal of primary pollutants and formation of a wide range of secondary products, including ozone, that can influence human health and climate. However, there remain large uncertainties in the changes to these budgets over recent decades. Due to their short atmospheric lifetimes, NOX and HOX are highly variable in space and time, and so the measurements of these species are of very limited value for examining long term, large scale changes to their budgets. Here, we take an alternative approach by examining long-term atmospheric trends of alkyl nitrates, the formation of which is dependent on the atmospheric NO / HO2 ratio. We derive long term trends in the alkyl nitrates from measurements in firn air from the NEEM site, Greenland. Their mixing ratios increased by a factor of 4–5 between the 1970s and 1990s. This was followed by a steep decline to the sampling date of 2008. Moreover, we examine how the trends in the alkyl nitrates compare to similarly derived trends in their parent alkanes (i.e. the alkanes which, when oxidised in the presence of NOX, lead to the formation of the alkyl nitrates). The ratios of the alkyl nitrates to their parent alkanes increase from around 1970 to the late 1990's consistent with large changes to the [NO] / [HO2] ratio in the northern hemisphere atmosphere during this period. These could represent historic changes to NOX sources and sinks. Alternatively, they could represent changes to concentrations of the hydroxyl radical, OH, or to the transport time of the air masses from source regions to the Arctic.

scholarly journals On the isotopic composition of precipitation in tropical stations (*).

1985 ◽  
Vol 15 (1-2) ◽  
pp. 121-140 ◽  
Author(s):  
Roberto Gonfiantini
Keyword(s):  
Isotopic Composition ◽  
Water Vapour ◽  
Seasonal Variations ◽  
Pacific Islands ◽  
Continental Effect ◽  
The Mean

Some of the trends and characteristics of the isotopic composition oh precipitation in tropical stations are discussed. Stations in small Pacific islands show a variation with latitude, with lower 8-values between 15°N and 1S°S and higher values at higher. Inland stations are depleted in heavy isotopes with respect to coastal stations but sometimes this continental effect is rather complex, as f,or instance in África. Mean monthly 8-values show a remarkable correlation with the amount of precipitation, but the slope variations do not show a clear dependence on the mean long term 8-value,as should be expected theoretically. In Southern American stations the seasonal variations of the meanmonthly 5-values are correlated and they are greater in inland stations due to con-tinentaly. The possible effects of recycling of water vapour by evapotranspiration are also discussed.

scholarly journals Chlorine isotope composition in chlorofluorocarbons CFC-11, CFC-12 and CFC-113 in firn, stratospheric and tropospheric air

2015 ◽  
Vol 15 (12) ◽  
pp. 6867-6877 ◽  
Author(s):  
S. J. Allin ◽  
J. C. Laube ◽  
E. Witrant ◽  
J. Kaiser ◽  
E. McKenna ◽  
...  
Keyword(s):  
Isotope Fractionation ◽  
Isotope Composition ◽  
Stratospheric Ozone ◽  
Standard Uncertainty ◽  
Gas Chromatography Mass Spectrometry ◽  
Sources And Sinks ◽  
Chlorine Isotope ◽  
Tropospheric Measurements ◽  
Single Detector

Abstract. The stratospheric degradation of chlorofluorocarbons (CFCs) releases chlorine, which is a major contributor to the destruction of stratospheric ozone (O3). A recent study reported strong chlorine isotope fractionation during the breakdown of the most abundant CFC (CFC-12, CCl2F2, Laube et al., 2010a), similar to effects seen in nitrous oxide (N2O). Using air archives to obtain a long-term record of chlorine isotope ratios in CFCs could help to identify and quantify their sources and sinks. We analyse the three most abundant CFCs and show that CFC-11 (CCl3F) and CFC-113 (CClF2CCl2F) exhibit significant stratospheric chlorine isotope fractionation, in common with CFC-12. The apparent isotope fractionation (&amp;varepsilon;app) for mid- and high-latitude stratospheric samples are respectively −2.4 (0.5) and −2.3 (0.4) ‰ for CFC-11, −12.2 (1.6) and −6.8 (0.8) ‰ for CFC-12 and −3.5 (1.5) and −3.3 (1.2) ‰ for CFC-113, where the number in parentheses is the numerical value of the standard uncertainty expressed in per mil. Assuming a constant isotope composition of emissions, we calculate the expected trends in the tropospheric isotope signature of these gases based on their stratospheric 37Cl enrichment and stratosphere–troposphere exchange. We compare these projections to the long-term δ (37Cl) trends of all three CFCs, measured on background tropospheric samples from the Cape Grim air archive (Tasmania, 1978–2010) and tropospheric firn air samples from Greenland (North Greenland Eemian Ice Drilling (NEEM) site) and Antarctica (Fletcher Promontory site). From 1970 to the present day, projected trends agree with tropospheric measurements, suggesting that within analytical uncertainties, a constant average emission isotope delta (δ) is a compatible scenario. The measurement uncertainty is too high to determine whether the average emission isotope δ has been affected by changes in CFC manufacturing processes or not. Our study increases the suite of trace gases amenable to direct isotope ratio measurements in small air volumes (approximately 200 mL), using a single-detector gas chromatography–mass spectrometry (GC–MS) system.

scholarly journals What controls the stable isotope composition of precipitation in the Asian monsoon region?

2017 ◽  
Author(s):  
Le Duy Nguyen ◽  
Ingo Heidbüchel ◽  
Hanno Meyer ◽  
Bruno Merz ◽  
Heiko Apel
Keyword(s):  
Isotopic Composition ◽  
Asian Monsoon ◽  
Precipitation Amount ◽  
Climatic Conditions ◽  
Monsoon Region ◽  
Asian Monsoon Region ◽  
Air Mass ◽  
Local Factors ◽  
Regional Factors ◽  
Isotopic Records

Abstract. This study analyzes the influence of local and regional climatic factors on the stable isotopic composition of rainfall in the Vietnamese Mekong Delta as part of the Asian monsoon region. It is based on 1.5 years of weekly rainfall samples. Their isotopic content is analyzed by Local Meteoric Water Lines (LMWL) and single-factor regressions. Additionally, the contribution of several regional and local factors is quantified by multiple linear regressions (MLR) of all possible factor combinations and by relative importance analysis, a novel approach for the interpretation of isotopic records. The local factors are extracted from local climate records, while the regional factors are derived from atmospheric backward trajectories of water particles. The regional factors, i.e. precipitation, temperature, relative humidity and moving distance of the backward trajectories, are combined with equivalent local climatic parameters to predict the response variables δ18O, δ2H, and d-excess of precipitation at the station of measurement. The results indicate that (i) MLR can much better explain the isotopic variation of precipitation (R2 = 0.8) compared to single-factor linear regression (R2 = 0.3); (ii) the isotopic variation in precipitation is controlled dominantly by regional moisture regimes (~ 70 %) compared to local climatic conditions (~ 30 %); (iii) the most important climatic parameter during the early rainy season is the precipitation amount along the trajectories of air mass movements; (iv) the influence of local precipitation amount and temperature is not significant during the early rainy season, unlike the regional precipitation amount effect; (v) secondary fractionation processes (e.g. sub-cloud evaporation) take place mainly in the dry season, either locally for δ18O and δ2H, or along the air mass trajectories for d-excess. The analysis shows that regional and local factors vary in importance over the seasons, and that the source regions and transport pathways, and in particular the climatic conditions along the pathways, have a large influence on the isotopic composition of rainfall. The proposed methods thus proved to be valuable for the interpretation of the isotopic records in rainfall and the factors controlling it. The results illustrate that the interpretation of the isotopic composition in precipitation as a recorder of local climatic conditions, as for example performed for paleo records of water isotopes, may not be adequate in the Southern part of the Indochinese Peninsula, and likely also not in other regions affected by monsoon processes. However, the presented approach could open a pathway towards better and seasonally differentiated reconstruction of paleoclimates based on isotopic records.

Sign in / Sign up

Export Citation Format

Share Document