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Coupled Atmosphere (coupled + atmosphere)

Distribution by Scientific Domains

Earth and Environmental Science	100%

Selected Abstracts

Mass-independent fractionation of sulfur isotopes in sulfides from the pre-3770 Ma Isua Supracrustal Belt, West Greenland

GEOBIOLOGY, Issue 4 2006
D. PAPINEAU
ABSTRACT Redox chemistry of the coupled atmosphere,hydrosphere system has coevolved with the biosphere, from global anoxia in the Archean to an oxygenated Proterozoic surface environment. However, to trace these changes to the very beginning of the rock record presents special challenges. All known Eoarchean (c. 3850,3600 Ma) volcanosedimentary successions (i.e. supracrustal rocks) are restricted to high-grade gneissic terranes that seldom preserve original sedimentary structures and lack primary organic biomarkers. Although complicated by metamorphic overprinting, sulfur isotopes from Archean supracrustal rocks have the potential to preserve signatures of both atmospheric chemistry and metabolic fractionation from the original sediments. We present a synthesis of multiple sulfur isotope measurements (32S, 33S and 34S) performed on sulfides from amphibolite facies banded iron-formations (BIFs) and ferruginous garnet-biotite (metapelitic) schists from the pre-3770 Ma Isua Supracrustal Belt (ISB) in West Greenland. Because these data come from some of the oldest rocks of interpretable marine sedimentary origin, they provide the opportunity to (i) explore for possible biosignatures of sulfur metabolisms in early life; (ii) assess changes in atmospheric redox chemistry from ,3.8 Ga; and (iii) lay the groundwork to elucidate sulfur biogeochemical cycles on the early Earth. We find that sulfur isotope results from Isua do not unambiguously indicate microbially induced sulfur isotopic fractionation at that time. A significantly expanded data set of ,33S analyses for Isua dictates that the atmosphere was devoid of free oxygen at time of deposition and also shows that the effects of post-depositional metamorphic remobilization and/or dilution can be traced in mass-independently fractionated sulfur isotopes. [source]

Simulated changes in active/break spells during the Indian summer monsoon due to enhanced CO2 concentrations: assessment from selected coupled atmosphere,ocean global climate models

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2007
Sujata K. Mandke
Abstract The simulations by ten coupled GCMs under the Intergovernmental Panel on Climate Change Assessment Report-4 are used to study the implication of possible global climate change on active/break spells of the Indian summer monsoon (ISM). The validation of the mean daily cycle of the summer monsoon precipitation over the Indian core region and the spatial pattern of the ISM precipitation climatology with observation suggest that six models simulate fairly well, whereas four models differ from observation. Thus, the identification of active/break spells is confined to six models. The sensitivity to climate change has been assessed from two experiments, namely, 1% per year CO2 increase to doubling and 1% per year CO2 increase to quadrupling. The changes in the daily mean cycle and the standard deviation of precipitation, frequency, and duration of active/break spells in future climate change are uncertain among the models and at times among two experiments. The break composite precipitation anomalies strengthen and spread moderately (significantly) in the doubled (quadrupled) CO2 experiment. Copyright © 2006 Royal Meteorological Society [source]

Meridional energy transport in the coupled atmosphere,ocean system: scaling and numerical experiments

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 644 2009
Geoffrey K. Vallis
Abstract We explore meridional energy transfer in the coupled atmosphere,ocean system, with a focus on the extratropics. We present various elementary scaling arguments for the partitioning of the energy transfer between atmosphere and ocean, and illustrate those arguments by numerical experimentation. The numerical experiments are designed to explore the effects of changing various properties of the ocean (its size, geometry and diapycnal diffusivity), the atmosphere (its water vapour content) and the forcing of the system (the distribution of incoming solar radiation and the rotation rate of the planet). We find that the energy transport associated with wind-driven ocean gyres is closely coupled to the energy transport of the midlatitude atmosphere so that, for example, the heat transport of both systems scales in approximately the same way with the meridional temperature gradient in midlatitudes. On the other hand, the deep circulation of the ocean is not tightly coupled with the atmosphere and its energy transport varies in a different fashion. Although for present-day conditions the atmosphere transports more energy polewards than does the ocean, we find that a wider or more diffusive ocean is able to transport more energy than the atmosphere. The polewards energy transport of the ocean is smaller in the Southern Hemisphere than in the Northern Hemisphere; this arises because of the effects of a circumpolar channel on the deep overturning circulation. The atmosphere is able to compensate for changes in oceanic heat transport due to changes in diapycnal diffusivity or geometry, but we find that the compensation is not perfect. We also find that the transports of both atmosphere and ocean decrease if the planetary rotation rate increases substantially, indicating that there is no a priori constraint on the total meridional heat transport in the coupled system. Copyright © 2009 Royal Meteorological Society [source]