Surface deformation, gravity and the geoid from a three-dimensional convection model at low Rayleigh numbers     

Claire Harvey Craig  Dan McKenzie 《Earth and Planetary Science Letters》1987,83(1-4)

The two-dimensional surface deformation, gravity field and geoid are calculated from the temperature fields of a number of numerical models of constant viscosity three-dimensional convective flows, heated from within and from below, using the appropriate Green's functions. The admittance is positive, with positive gravity anomalies above hot rising regions, except for large aspect ratio circulations with undeformable lower boundaries. The surface deformation and the geoid are insensitive to the short wavelength features of the temperature variation. The gravity field is less smooth, though still does not clearly indicate the narrowness of the upwelling and downwelling regions at large Rayleigh numbers. When the lower boundary of the convecting region is deformable, the gravity field is dominated by lateral temperature variations within the upper thermal boundary layer, even when their contribution to the overall circulation is small. The variation of surface deformation with Rayleigh number agrees well with that expected from simple boundary layer arguments when the circulation is driven by heating from below, but less well when the heating is internal. These results suggest that the convective upwelling beneath regions showing positive geoid and residual depth anomalies is more localized than the horizontal extent of these features would suggest.  相似文献   

Dangers of multiyear averaging in analyses of long-term climate trends     

Claire L Parkinson 《Climate Dynamics》1989,4(1):39-44

Multiyear averaging in studies seeking long-term trends can be risky and misleading. It is shown here that a change of 1 year in the starting point of the averaging done in generating a multiyear-average sequence can make a dramatic difference in the appearance of the sequence, even including whether the apparent trend is upward or downward. An example is given in which the same time series, when grouped to 3-year averages by starting in turn at the first, second, and third points of the series, yields one 3-year-average sequence that is monotonically increasing, a second 3-year-average sequence that is monotonically decreasing, and a third 3-year-average sequence that has constant values. Furthermore, it is proven in general that such series can be created for n-year averages for any integer n > 2, and can be extended to exceed any desired length. Finally, historical sea-ice data from Iceland are used to illustrate with a long-term climate data set the misrepresentation of climate statistics which can occur through selective multiyear averaging.  相似文献   

The respiratory health hazards of volcanic ash: a review for volcanic risk mitigation   总被引：1，自引：3，他引：1  

Claire J. Horwell  Peter J. Baxter 《Bulletin of Volcanology》2006,69(1):1-24

Studies of the respiratory health effects of different types of volcanic ash have been undertaken only in the last 40 years, and mostly since the eruption of Mt. St. Helens in 1980. This review of all published clinical, epidemiological and toxicological studies, and other work known to the authors up to and including 2005, highlights the sparseness of studies on acute health effects after eruptions and the complexity of evaluating the long-term health risk (silicosis, non-specific pneumoconiosis and chronic obstructive pulmonary disease) in populations from prolonged exposure to ash due to persistent eruptive activity. The acute and chronic health effects of volcanic ash depend upon particle size (particularly the proportion of respirable-sized material), mineralogical composition (including the crystalline silica content) and the physico-chemical properties of the surfaces of the ash particles, all of which vary between volcanoes and even eruptions of the same volcano, but adequate information on these key characteristics is not reported for most eruptions. The incidence of acute respiratory symptoms (e.g. asthma, bronchitis) varies greatly after ashfalls, from very few, if any, reported cases to population outbreaks of asthma. The studies are inadequate for excluding increases in acute respiratory mortality after eruptions. Individuals with pre-existing lung disease, including asthma, can be at increased risk of their symptoms being exacerbated after falls of fine ash. A comprehensive risk assessment, including toxicological studies, to determine the long-term risk of silicosis from chronic exposure to volcanic ash, has been undertaken only in the eruptions of Mt. St. Helens (1980), USA, and Soufrière Hills, Montserrat (1995 onwards). In the Soufrière Hills eruption, a long-term silicosis hazard has been identified and sufficient exposure and toxicological information obtained to make a probabilistic risk assessment for the development of silicosis in outdoor workers and the general population. A more systematic approach to multi-disciplinary studies in future eruptions is recommended, including establishing an archive of ash samples and a website containing health advice for the public, together with scientific and medical study guidelines for volcanologists and health-care workers.  相似文献   

Development and Application of Oxygen and Carbon Isotopic Measurements of Biogenic Carbonates by Ion Microprobe   总被引：1，自引：0，他引：1  

Claire Rollion-Bard  Denis Mangin  Michel Champenois 《Geostandards and Geoanalytical Research》2007,31(1):39-50

The analytical capabilities of the ims 1270 ion microprobe (SIMS) in determining O and C isotope compositions in biogenic carbonate samples have been tested. Results indicated that, with a spot size of ≊ 30 μm, the average reproducibility at the 1s level was 0.3‰ for oxygen isotopes and 0.6‰ for carbon isotopes. Nevertheless, this reproducibility can reach 0.2‰ for oxygen isotope determinations during some sessions. These reproducibilities allowed us to perform analyses on biogenic carbonate samples for environmental studies. In this paper, examples of oxygen and carbon isotope measurements are presented for a modern coral and the Holocene scleractinian coral, Porites lutea.  相似文献   

Substrate kinetics of DMSP-lyases in axenic cultures and mesocosm populations of <Emphasis Type="Italic">Emiliania huxleyi</Emphasis>     

Michael Steinke  Claire Evans  Gareth A. Lee  Gill Malin 《Aquatic Sciences - Research Across Boundaries》2007,69(3):352-359

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Comment on “The Chemical Nature of Phosphorus in Subtropical Lake Sediments”     

William F. Kenney  Andrew D. Chapman  Claire L. Schelske 《Aquatic Geochemistry》2015,21(1):1-6

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Response of large benthic foraminifera to climate and local changes: Implications for future carbonate production     

Gita R. Narayan  Claire E. Reymond  Marleen Stuhr  Steve Doo  Christiane Schmidt  Thomas Mann  Hildegard Westphal 《Sedimentology》2022,69(1):121-161

Large benthic foraminifera are major carbonate components in tropical carbonate platforms, important carbonate producers, stratigraphic tools and powerful bioindicators (proxies) of environmental change. The application of large benthic foraminifera in tropical coral reef environments has gained considerable momentum in recent years. These modern ecological assessments are often carried out by micropalaeontologists or ecologists with expertise in the identification of foraminifera. However, large benthic foraminifera have been under-represented in favour of macro reef-builders, for example, corals and calcareous algae. Large benthic foraminifera contribute about 5% to modern reef-scale carbonate sediment production. Their substantial size and abundance are reflected by their symbiotic association with the living algae inside their tests. When the foraminiferal holobiont (the combination between the large benthic foraminifera host and the microalgal photosymbiont) dies, the remaining calcareous test renourishes sediment supply, which maintains and stabilizes shorelines and low-lying islands. Geological records reveal episodes (i.e. late Palaeocene and early Eocene epochs) of prolific carbonate production in warmer oceans than today, and in the absence of corals. This begs for deeper consideration of how large benthic foraminifera will respond under future climatic scenarios of higher atmospheric carbon dioxide (pCO₂) and to warmer oceans. In addition, studies highlighting the complex evolutionary associations between large benthic foraminifera hosts and their algal photosymbionts, as well as to associated habitats, suggest the potential for increased tolerance to a wide range of conditions. However, the full range of environments where large benthic foraminifera currently dwell is not well-understood in terms of present and future carbonate production, and impact of stressors. The evidence for acclimatization, at least by a few species of well-studied large benthic foraminifera, under intensifying climate change and within degrading reef ecosystems, is a prelude to future host–symbiont resilience under different climatic regimes and habitats than today. This review also highlights knowledge gaps in current understanding of large benthic foraminifera as prolific calcium carbonate producers across shallow carbonate shelf and slope environments under changing ocean conditions.  相似文献   

Characterization of Mason Gully (H5): The second recovered fall from the Desert Fireball Network   总被引：1，自引：0，他引：1       下载免费PDF全文

Kathryn A. Dyl  Gretchen K. Benedix  Phil A. Bland  Jon M. Friedrich  Pavel Spurný  Martin C. Towner  Mary Claire O'Keefe  Kieren Howard  Richard Greenwood  Robert J. Macke  Daniel T. Britt  Angela Halfpenny  James O. Thostenson  Rebecca A. Rudolph  Mark L. Rivers  Alex W. R. Bevan 《Meteoritics & planetary science》2016,51(3):596-613

Mason Gully, the second meteorite recovered using the Desert Fireball Network (DFN), is characterized using petrography, mineralogy, oxygen isotopes, bulk chemistry, and physical properties. Geochemical data are consistent with its classification as an H5 ordinary chondrite. Several properties distinguish it from most other H chondrites. Its 10.7% porosity is predominantly macroscopic, present as intergranular void spaces rather than microscopic cracks. Modal mineralogy (determined via PS‐XRD, element mapping via energy dispersive spectroscopy [EDS], and X‐ray tomography [for sulfide, metal, and porosity volume fractions]) consistently gives an unusually low olivine/orthopyroxene ratio (0.67?0.76 for Mason Gully versus ~1.3 for typical H5 ordinary chondrites). Widespread “silicate darkening” is observed. In addition, it contains a bright green crystalline object at the surface of the recovered stone (diameter ≈ 1.5 mm), which has a tridymite core with minor α‐quartz and a rim of both low‐ and high‐Ca pyroxene. The mineralogy allows the calculation of the temperatures and ?(O₂) characterizing thermal metamorphism on the parent body using both the two‐pyroxene and the olivine‐chromite geo‐oxybarometers. These indicate that MG experienced a peak metamorphic temperature of ~900 °C and had a similar ?(O₂) to Kernouvé (H6) that was buffered by the reaction between olivine, metal, and pyroxene. There is no evidence for shock, consistent with the observed porosity structure. Thus, while Mason Gully has some unique properties, its geochemistry indicates a similar thermal evolution to other H chondrites. The presence of tridymite, while rare, is seen in other OCs and likely exogenous; however, the green object itself may result from metamorphism.  相似文献   

The PROWQM physical–biological model with benthic–pelagic coupling applied to the northern North Sea     

Jae-Young Lee  Paul Tett  Ken Jones  Sarah Jones  Patrick Luyten  Claire Smith  Karen Wild-Allen   《Journal of Sea Research》2002,48(4):57

PROWQM, a 1-D depth resolving model which couples physical and microbiological processes in the water column with sedimentation/resuspension and benthic mineralisation processes, has been used to simulate seasonal changes of chlorophyll, nutrients and oxygen at the PROVESS north site (59°20′N 1°00′E) in the North Sea. PROWQM is derived from the 3-D model COHERENS, and improves COHEREN's benthic and pelagic biology.The physical sub-model of PROWQM implicitly solves turbulence closure equations forced by climatological, or realistic high-frequency, meteorological and tidal data. The pelagic biological sub-model 2MPPD includes a ‘diatomy’ microplankton (mp1) and a ‘flagellatey’ (or microbial loop) microplankton (mp2), the cycling of silicon and nitrogen, slow-sinking detritus, and fast-sinking phytodetritus. Phytodetritus is formed by shear-driven aggregation of particulate material, using a simple algorithm for bulk processes that is derived by considering the interactions of single cells. The microplankton compartments include heterotrophic bacteria and protozoa as well as phytoplankton, and most microplankton rates are specified with the aid of a ‘heterotroph fraction’ parameter, which was 0.125 for mp1 and 0.6 for mp2. The microbiological system is closed by mesozooplankton grazing pressures imposed as time varying series determined from observed zooplankton abundance. The benthic boundary sub-model includes a superficial fluff layer and a nutrient element reservoir in the consolidated sediment. Particulate material in the fluff layer can be resuspended (in response to bed stress by near-bed flows), mineralised or carried by bioturbation into the underlying, consolidated, sediment, where it is mineralised and its nutrients returned to the water-column at rates mainly dependent on (implicit) macrobenthic pumping. Benthic denitrification can occur when mineralisation rates exceed oxygen supply.Verification of the PROWQM numerical implementation used test cases and checks for nutrient element conservation. Simulations with realistic forcing, for a range of parameter values, were compared with historic observations in the NOWESP data set and during FLEX76, and with those made during the PROVESS cruises in autumn 1998. PROWQM provided a good simulation of the seasonal succession from a diatom-dominated spring bloom to summer dominance by small flagellates. The simulations included sedimentation of organic matter from the spring bloom, and qualitatively realistic behaviour of the fluff layer, but decay rates were too slow and there was almost no denitrification. The simulated surface mixed layer was too shallow during the summer. Simulated annual net microplankton primary production was in between 59 and 91 g C m⁻² y⁻¹. A large proportion of mineralisation, 28–47% of nitrogen and 40–67% of silicon mineralisation, took place as a result of the decay of sinking and resuspended detritus whilst in the water column.PROWQM is discussed in relation to other models that have been used to simulate this part of the North Sea, in particular the simpler ECOHAM1 and the more complex ERSEM, and in relation to PROWQM's evolution from COHERENS.  相似文献   

Comparison between two processes of determination of particulate organic carbon in sea water     

Claire Copin-Montegut  Gérard Copin-Montegut 《Marine Chemistry》1973,1(2):151-156

A process of determination of organic carbon in particulate matter in sea water by dry oxidation and infra-red analysis is described. It was used concurrently with a chromic-acid wet oxidation process upon 123 samples taken at various depths in the Gulf of Guinea, each sample being divided into two equal parts. The ratio between the values of organic carbon by dry oxidation and wet oxidation is 1.09 ± 0.03.  相似文献