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881.
882.
Summary An empirical investigation has been conducted on the practical methods of obtaining the spectra of micropulsation activity, and the interpretational limits which can be applied to the detailed use of spectra computed by the Power Spectral Density (PSD) method. Results indicate that sufficiently high resolution may be obtained reliably from the PSD method for it to be regarded as a useful improvement over handscaling methods. The limitation is shown to remain in the selection of events rather than in computational or instrumental properties. 相似文献
883.
Graham Ryder 《Geochimica et cosmochimica acta》1982,46(9):1591-1601
Systematic variations of the mineral chemistry of ferroan anorthosite 60025, which is probably a mixture of closely related materials, suggest that lunar anorthosites formed by strong fractional crystallization and near-perfect adcumulate growth, without trapping liquid. The parent liquid for the most primitive samples was saturated with olivine, plagioclase, pigeonite, and chromite, and evolved to one saturated with plagioclase, pigeonite, high-Ca pyroxene, and ilmenite. The parent liquid also had a very low Na2O content, and combined with strong fractional crystallization this explains the steep trend of anorthosites on an Mg1 (atomic 100 × Mg/(Mg + Fe)) v. An diagram. The mineral and chemical data for other anorthosites are consistent with such a model. Near-perfect adcumulation can occur if growth takes place at the crystal-liquid interface without the physical accumulation of crystals grown elsewhere, and is encouraged by the shifts in phase boundaries with pressure.Anorthosites are probably the remnants of a crust floating on, and crystallizing at the surface of, a magma ocean originally of bulk Moon composition. Mineralogical and trace element data suggest that the parental liquid for the most primitive anorthosites had previously crystallized no plagioclase and some but perhaps very little pyroxene. Hence the bulk Moon appears to be similar to that proposed by Ringwood (1976) but to have even lower alkalis, a subchondritic ratio, and REE abundances and patterns close to chondritic. The mare basalt sources are not directly complementary to the feldspathic crust, because experimental and trace element data indicate that they are too magnesian and contain too much high-Ca pyroxene. Other crustal rocks, such as the Mg-suite samples, are not closely related to anorthosites; in addition to their chemical differences they have a different crystallization sequence: ol → plag → px, in contrast with the ol → px → plag inferred for anorthosite parental liquid evolution. 相似文献
884.
Stuart Wier 《Physics of the Earth and Planetary Interiors》1981,24(1):30-32
Immediately after the Oaxaca earthquake of November 29, 1978, the rate of occurrence of earthquakes (magnitude mb ? 4.9) increased all along the Mid-America Trench, and stayed above the average level for the area for five months. The highest rate was recorded in the month just after the Oaxaca earthquake, after which the rate gradually declined for five months. No aftershocks of the Oaxaca earthquake are included in the counts. The past seismicity history of the area suggests that it is unlikely that the simultaneous timing is a simple matter of coincidences. These observations suggest that motion of the Cocos plate is episodic, and that stress changes are rapidly transmitted throughout the plate. 相似文献
885.
Kathleen R. Laird Astrid Michels Chloë T.L. Stuart Susan E. Wilson William M. Last Brian F. Cumming 《Quaternary Science Reviews》2007,26(25-28):3328-3343
Paleoclimatic records from the climatically sensitive Canadian prairies are relatively rare due to the scarcity of study sites with continuous Holocene stratigraphic sequences. Oro Lake, a meromictic lake in the dry grasslands of Saskatchewan (Canada), contains a continuous Holocene diatom record spanning the last 10,000 years. Here we present analyses at three different time scales and resolution: (1) 1–3 yr resolution of the past 80 years, (2) century-scale analysis of the Holocene, and (3) decadal-scale analysis of the past 7000 years. Recent changes in the diatom assemblages and their respective salinity inferences were significantly related to measured effective moisture (precipitation minus evaporation, P−ET). The droughts of the 1930s, and a wet period during the 1950s are clearly evident in the diatom record, suggesting the Oro Lake record contains a sensitive archive of past climatic conditions. Century-scale analysis of the diatom record during the Holocene is consistent with a cool and moist climate in the early Holocene (prior to ca 9700 cal yr BP, 8600 14C yr BP). An abrupt increase in diatom-inferred salinity at 9600 cal yr BP (8500 14C yr BP) indicates the onset of an arid climate, with continuing arid conditions throughout the mid-Holocene. Decadal-scale analysis of the past 7000 years suggests that the mid-Holocene was more complex, with extended periods of increased variability in precipitation, particularly between ca 5800–3600 cal yr BP (5000–3200 14C yr BP) which is characterized by intervals of increased effective moisture. The past 2000 years is characterized by reduced salinities and generally wetter conditions in comparison to the mid-Holocene. The combination of the different scales of analyses in this study provides a detailed account of the dynamic nature of climate from sub-decadal to millennial scale in the Oro Lake region within the Palliser Triangle. Climate model predictions suggest that the Canadian prairie region may see a higher frequency of extreme droughts under projected global warming, potentially similar to the most arid periods seen during the mid-Holocene when many lake basins completely dried out. 相似文献
886.
It has been argued that public doubts about climate change have been exacerbated by cold weather events seen as a form of disconfirming evidence for anticipated ‘warming’. Although a link between perceptions of climate and weather is well-established, such assumptions have not been empirically tested. Here we show, using nationally representative data, that directly following a period of severe cold weather in the UK, three times as many people saw these events as pointing towards the reality of climate change, than as disconfirming it. This we argue was a consequence of these cold winters being incorporated into a conceptualisation of extreme or ‘unnatural’ weather resulting from climate change. We also show that the way in which people interpret cold weather is associated with levels of pre-existing scepticism about climate change, which is in turn related to more general worldviews. Drawing attention to ‘extreme’ weather as a consequence of climate change can be a useful communication device, however this is problematic in the case of seasonal cold. 相似文献
887.
R. W. Grobe J. Alvarez-Marrón U. A. Glasmacher F. M. Stuart 《International Journal of Earth Sciences》2014,103(2):539-561
Apatite fission-track (AFT) and (U+Th)/He (AHe) data, combined with time–temperature inverse modelling, reveal the cooling and exhumation history of the Iberian Massif in eastern Galicia since the Mesozoic. The continuous cooling at various rates correlates with variation of tectonic boundary conditions in the adjacent continental margins. The data provide constraints on the 107 timescale longevity of a relict paleolandscape. AFT ages range from 68 to 174 Ma with mean track lengths of 10.7 ± 2.6 to 12.6 ± 1.8 μm, and AHe ages range from 73 to 147 Ma. Fastest exhumation (≈0.25 km/Ma) occurred during the Late Jurassic to Early Cretaceous main episode of rifting in the adjacent western and northern margins. Exhumation rates have decreased since then and have been approximately one order of magnitude lower. Across inland Galicia, the AFT data are consistent with Early Cretaceous movement on post-Variscan NE trending faults. This is coeval with an extensional episode offshore. The AHe data in this region indicate less than 1.7 km of denudation in the last 100 Ma. This low exhumation suggests the attainment of a mature landscape during Late Cretaceous post-rift tectonic stability, whose remains are still preserved. The low and steady rate of denudation prevailed across inland Galicia despite minor N–S shortening in the northern margin since ≈45 Ma ago. In north Galicia, rock uplift in response to NW strike-slip faulting since Early Oligocene to Early Miocene has caused insufficient exhumation (<3 km) to remove the Mesozoic cooling signal recorded by the AFT data. 相似文献
888.
Sharyn M. Hickey Stuart R. Phinn Nik J. Callow Kimberly P. Van Niel Jeff E. Hansen Carlos M. Duarte 《Estuaries and Coasts》2017,40(5):1215-1226
Ecological (poleward) regime shifts are a predicted response to climate change and have been well documented in terrestrial and more recently ocean species. Coastal zones are amongst the most susceptible ecosystems to the impacts of climate change, yet studies particularly focused on mangroves are lacking. Recent studies have highlighted the critical ecosystem services mangroves provide, yet there is a lack of data on temporal global population response. This study tests the notion that mangroves are migrating poleward at their biogeographical limits across the globe in line with climate change. A coupled systematic approach utilising literature and land surface and air temperature data was used to determine and validate the global poleward extent of the mangrove population. Our findings indicate that whilst temperature (land and air) have both increased across the analysed time periods, the data we located showed that mangroves were not consistently extending their latitudinal range across the globe. Mangroves, unlike other marine and terrestrial taxa, do not appear to be experiencing a poleward range expansion despite warming occurring at the present distributional limits. Understanding failure for mangroves to realise the global expansion facilitated by climate warming may require a focus on local constraints, including local anthropogenic pressures and impacts, oceanographic, hydrological, and topographical conditions. 相似文献
889.
Air-sea fluxes: 25 years of progress 总被引:3,自引:0,他引:3
Stuart D. Smith Christopher W. Fairall Gerald L. Geernaert Lutz Hasse 《Boundary-Layer Meteorology》1996,78(3-4):247-290
During the past quarter century the study of air-sea interaction has evolved from a small branch of marine climatology to play a key role in the modelling of the coupled system of ocean and atmosphere. Knowledge of air- sea fluxes has grown, based on Monin-Obukhov similarity theory for surface boundary layers and on direct and indirect techniques of measuring the fluxes. This has been the basis for providing boundary conditions needed to couple atmospheric and oceanic circulation models that are used to forecast weather and climate. An overview of current understanding is followed by a discussion of parameterisation schemes and a chronicle of some of the experimental work that has tested theories and quantified their conclusions. 相似文献
890.
Sea surface wind stress and drag coefficients: The hexos results 总被引:17,自引:1,他引:17
Stuart D. Smith Robert J. Anderson Wiebe A. Oost C. Kraan Nico Maat Janice De Cosmo Kristina B. Katsaros Kenneth L. Davidson Karl Bumke Lutz Hasse Helen M. Chadwick 《Boundary-Layer Meteorology》1992,60(1-2):109-142
Turbulent fluxes have been measured in the atmospheric surface layer from a boom extending upwind from the Dutch offshore research platform Meetpost Noordwijk (MPN) during HEXMAX (Humidity Exchange over the Sea Main Experiment) in October–November, 1986. We started out to study eddy flux of water vapour, but discrepancies among simultaneous measurements made with three different anemometers led us to develop methods to correct eddy correlation measurements of wind stress for flow distortion by nearby objects. We then found excellent agreement among the corrected wind stress data sets from the three anemometers on the MPN boom and with eddy correlation measurements from a mast on a tripod. Inertial-dissipation techniques gave reliable estimates of wind stress from turbulence spectra, both at MPN and at a nearby ship. The data cover a range of wave ages and the results yield new insights into the variation of sea surface wind stress with sea state; two alternative formulas are given for the nondimensional surface roughness as a function of wave age. 相似文献