Multi-decadal scale variability in autumn-winter rainfall in south-western Australia since 1655 AD as reconstructed from tree rings of Callitris columellaris   总被引：1，自引：0，他引：1  

Louise E. Cullen  Pauline F. Grierson 《Climate Dynamics》2009,33(2-3):433-444

We present the first tree-ring based reconstruction of rainfall for the Lake Tay region of southern Western Australia. We examined the response of Callitris columellaris to rainfall, the southern oscillation index (SOI), the southern annular mode (SAM) and surface sea temperature (SST) anomalies in the southern Indian Ocean. The 350-year chronology was most strongly correlated with rainfall averaged over the autumn-winter period (March–September; r = ?0.70, P < 0.05) and SOI values averaged over June–August (r = 0.25, P < 0.05). The chronology was not correlated with SAM or SSTs. We reconstructed autumn-winter rainfall back to 1655, where current and previous year tree-ring indices explained 54% of variation in rainfall over the 1902–2005 calibration period. Some variability in rainfall was lost during the reconstruction: variability of actual rainfall (expressed as normalized values) over the calibration period was 0.78, while variability of the normalized reconstructed values over the same period was 0.44. Nevertheless, the reconstruction, combined with spectral analysis, revealed that rainfall naturally varies from relatively dry periods lasting to 20–30 years to 15-year long periods of above average rainfall. This variability in rainfall may reflect low-frequency variation in the El Niño-Southern Oscillation rather than the effect of SAM or SSTs.  相似文献   

A survey of the inorganic chemistry of bottled mineral waters from the British Isles     

Pauline L. Smedley 《Applied Geochemistry》2010

The inorganic chemistry of 85 samples of bottled natural mineral waters and spring waters has been investigated from 67 sources across the British Isles (England, Wales, Scotland, Northern Ireland, Republic of Ireland). Sources include boreholes, springs and wells. Waters are from a diverse range of aquifer lithologies and are disproportionately derived from comparatively minor aquifers, the most represented being Lower Palaeozoic (10 sources), Devonian Sandstone (10 sources) and Carboniferous Limestone (9 sources). The waters show correspondingly variable major-ion compositions, ranging from Ca–HCO₃, through mixed-cation–mixed-anion to Na–HCO₃ types. Concentrations of total dissolved solids are mostly low to very low (range 58–800 mg/L). All samples analysed in the study had concentrations of inorganic constituents well within the limits for compliance with European and national standards for bottled waters. Concentrations of NO₃–N reached up to half the limit of 11.3 mg/L, although 62% of samples had concentrations <1 mg/L. Concentrations of Ba were high (up to 1010 μg/L) in two spring water samples. Such concentrations would have been non-compliant had they been classed as natural mineral waters, although no limit exists for Ba in European bottled spring water. In addition, though no European limit exists for U in bottled water, should a limit commensurate with the current WHO provisional guideline value for U in drinking water (15 μg/L) be introduced in the future, a small number of groundwater sources would have concentrations close to this value. Two sources had groundwater U concentrations > 10 μg/L, both being from the Welsh Devonian Sandstone. The highest observed U concentration was 13.6 μg/L.  相似文献   

Influence of mesh size and core penetration on estimates of deep-sea nematode abundance,biomass, and diversity     

D. Leduc  P.K. Probert  S.D. Nodder 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(10):1354-1362

It is essential to maximize the information that can be gathered in deep-sea studies by thoroughly assessing sample processing methods. Nematodes are commonly used for the study and monitoring of deep-sea floor habitats, but the potential effects of different methods on the quantification of community attributes remain to be quantified. Here, we consider key methodological elements by comparing the effect of sediment depth and mesh size (63, 45, and 32 μm) on: (1) estimates of nematode community attributes, and (2) the sampling effort required to detect changes in these attributes at a bathyal site on the Chatham Rise, south-west Pacific Ocean. The 63 μm mesh retained most (95%) of the nematode biomass but a lower proportion (53–71%) of the nematode abundance. Retention efficiency of common species on this mesh ranged from 12 (Hapalomus sp.) to >88% (Comesomatidae spp.). The 63 μm mesh yielded significantly lower diversity estimates than the finer meshes, and failed to detect differences in community structure observed using the 45 and 32 μm mesh sizes. Sediment depth had a substantial effect on all measured community attributes, highlighting the importance of sufficient core penetration into the sediment (≥5 cm) for adequately characterizing nematode distribution. Power analysis showed that using a 32 μm mesh and deepest core penetration led to relatively few (3–8) samples being required to detect significant changes in nematode diversity indices relative to coarser mesh sizes. Characterization of nematode diversity and community structure using appropriate and robust methods of sampling is suggested as a sensitive and efficient tool for the assessment of anthropogenic impacts on deep-sea ecosystems.  相似文献   

Lunar and solar daily variations of the geomagnetic field at Toolangi     

Pauline Green 《Pure and Applied Geophysics》1972,101(1):194-204

Summary Mean hourly values of magnetic declination, horizontal intensity and vertical intensity observed at Toolangi during two ten year periods (1924–1933 and 1949–1958) have been analysed to determine their solar and luni-solar diurnal components. The results, showing the variations of the first four harmonic components with season, degree of magnetic activity and annual sunspot number, are tabulated and discussed. It is shown that there are marked differences in the dependence ofS andL on the various parameters and a tentative explanation of this phenomenon is given.  相似文献   

Observations of the limb effect in potassium λ7699     

J. C. Lopresto  Pauline M. Kraus  A. K. Pierce 《Solar physics》1994,149(2):243-247

Center-to-limb observations of the Ki 7699 line made on 30 days over a five-year period using the McMath-Pierce Solar Telescope at Kitt Peak are presented. Both a relative and absolute limb effect have been derived from the data. Our determination of the limb effect in Ki 7699 shows a linear increase to the limb amounting to about 40 m s^–1.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.  相似文献   

Insights into river bank erosion processes derived from analysis of negative erosion‐pin recordings: observations from three recent UK studies     

Pauline Couper  Tim Stott  Ian Maddock 《地球表面变化过程与地形》2002,27(1):59-79

Recent studies of river bank erosion in three catchments in the UK have been characterized by the persistent occurrence of negative erosion‐pin results. The cause of these negative recordings is considered with reference to field data from the Afon Trannon, Nant Tanllwyth and River Arrow, and to a laboratory study of freeze–thaw and desiccation processes. It seems that there is potential for, and in some cases evidence of, a number of different circumstances that generate negative results, but none of these alone is sufficient to explain all incidents. Factors considered include: deposition of sediment during high flows; soil fall from the upper parts of the bank on to lower erosion pins; loosening of the soil surface and expansion/contraction of the soil mass with fluctuations in temperature and moisture content; movement of the erosion‐pin within the bank and human interference. Each has its own implications for the use of erosion pins. Further issues arise when including negative data in subsequent data analysis, and it is demonstrated that attempts to correlate erosion rates with hydro‐meteorological data in order to ascertain causes of erosion will be influenced by the way in which negative data are handled. It is thus suggested that any study of river bank erosion using erosion pins should state whether or not negative data were obtained, and if so, how they were included in data analysis. Failure to include this information could lead to comparison of mean erosion rates that reflect bank processes very differently. The studies presented here offer a clear example of the value of ‘anomalous’ field data: results which do not appear to fit expected patterns can reveal as much about the processes in operation as those that do. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Empirical test of the spectral invariants theory using imaging spectroscopy data from a coniferous forest     

Petr Lukeš  Miina Rautiainen  Pauline Stenberg  Zbyněk Malenovský 《International Journal of Applied Earth Observation and Geoinformation》2011

The spectral invariants theory presents an alternative approach for modeling canopy scattering in remote sensing applications. The theory is particularly appealing in the case of coniferous forests, which typically display grouped structures and require computationally intensive calculation to account for the geometric arrangement of their canopies. However, the validity of the spectral invariants theory should be tested with empirical data sets from different vegetation types. In this paper, we evaluate a method to retrieve two canopy spectral invariants, the recollision probability and the escape factor, for a coniferous forest using imaging spectroscopy data from multiangular CHRIS PROBA and NADIR-view AISA Eagle sensors. Our results indicated that in coniferous canopies the spectral invariants theory performs well in the near infrared spectral range. In the visible range, on the other hand, the spectral invariants theory may not be useful. Secondly, our study suggested that retrieval of the escape factor could be used as a new method to describe the BRDF of a canopy.  相似文献   

Tropical variability and stratospheric equatorial waves in the IPSLCM5 model     

Pauline Maury  François Lott  Lionel Guez  Jean-Philippe Duvel 《Climate Dynamics》2013,40(9-10):2331-2344

The atmospheric variability in the equatorial regions is analysed in the Earth System Model pre-industrial simulation done at IPSL in the framework of CMIP5. We find that the model has an interannual variability of about the right amplitude and temporal scale, when compared to the El-Niño Southern Oscillation (ENSO), but that is too confined to the western Pacific. At the intra-seasonal periods, the model variability lacks of large-scale organisation, and only produces one characteristic Madden-Julian Oscillation every 10 winters typically. At shorter time-scales and in the troposphere, the model has Rossby and Kelvin Convectively Coupled Equatorial Waves (CCEWs), but underestimates the Kelvin CCEWs signal on OLR. In the model stratosphere, a composite analysis shows that the Temperature and velocities fluctuations due to the Kelvin waves are quite realistic. In the model nevertheless, the stratospheric waves are less related to the convection than in the observations, suggesting that their forcing by the midlatitudes plays a larger role. Still in the model, the Kelvin waves are not predominantly occurring during the life cycle of the tropospheric Kelvin CCEWs, a behaviour that we find to be dominant in the observations. The composite analysis is also used to illustrate how the waves modify the zonal mean-flow, and to show that the model Kelvin waves are too weak in this respect. This illustrates how a model can have a reasonable Kelvin waves signal on the velocities and temperature, but can at the same time underestimate their amplitude to modify the mean flow. We also use this very long simulation to establish that in the model, the stratospheric equatorial waves are significantly affected by ENSO, hence supporting the idea that the ENSO can have an influence on the Quasi-Biennial Oscillation.  相似文献   

Trace elements in speleothems as recorders of environmental change     

Ian J. Fairchild  Pauline C. Treble 《Quaternary Science Reviews》2009,28(5-6):449-468

Speleothems are now established as important palaeoenvironmental archives and contain a number of suitable proxies, although trace elements have been much less widely used than oxygen and carbon isotopes. The complexity of the cave environment helps to explain this since the fluids from which speleothems form vary greatly in composition in space (even within a cave chamber), seasonally, and over longer periods. Understanding the forcing factors for this variability is the key to decoding the significance of the trace element records.A variety of techniques are available for trace element work and it is important to understand the strengths and limitations of each and also to seek an understanding, e.g. by micro-imaging techniques, of whether the elements are associated with inclusions in the CaCO₃, or are isolated within the crystal lattice. For some elements there is a more-or-less predictable relationship between element ratios to Ca in the water and in the calcite. Individual trace elements may be derived from atmospheric deposition, superficial deposits or bedrock and can be recycled in soil processes before being transferred to the cave. Some components show an instantaneous response to water infiltration, whereas others are only leached by slow-flowing seepage waters. Changing in the proportion of water from fracture-fed and seepage-flow aquifer compartments is an important factor in influencing trace element supply. High flows lead to higher fluxes of soil-derived colloidally transported elements. Conversely, under relatively dry conditions, degassing of CO₂ results in “prior calcite precipitation” upflow of the site of speleothem deposition and leads to higher ratios of Sr/Ca and Mg/Ca. Some trace element variations in speleothems over time are induced during crystal growth whereby faster growth leads to a greater departure from equilibrium element partitioning.Despite the demonstrated temperature-dependence of Mg partitioning into calcite, attempts at deriving palaeotemperature records from speleothems have been so far confounded by variations in solution Mg/Ca and/or crystallographic effects. A number of case studies have effectively used trace elements such as speleothem Mg as records of palaeo-aridity, using supporting arguments from modern monitoring or covariations with other parameters such as stable isotopes. Sr and U isotopes can also be indicators of palaeohydrology, although Sr isotope variations can also reflect varying aeolian input. Considerable progress has been made in decoding the meaning of annual trace element variations using criteria for understanding dripwater hydrology and pH. This should lead in the future to more specific interpretations of how seasonality evolves through time.  相似文献   

Integrated surface water–groundwater modelling in the context of increasing water reserves of a regional Sahelian aquifer     

S. Massuel  B. Cappelaere  G. Favreau  C. Leduc  T. Lebel  T. Vischel 《水文科学杂志》2013,58(7):1242-1264

Abstract

Despite the Sahelian drought of the 1970s–1990s, the unconfined aquifer in southwest Niger exhibits a multidecadal increase in groundwater reserves. Recent changes in land surface conditions have enhanced runoff and thus indirect groundwater recharge below endorheic ponds. This paper presents a model-based investigation of surface runoff and groundwater recharge at mesoscale (～5000 km²). A new lumped-conceptual runoff model applicable to the large number of ungauged endorheic catchments is specially developed, derived from an existing fine-scale, physically-based hydrologic model. Runoff simulated for sites identified as groundwater recharge sources are used to derive recharge forcing for a Modflow-based model of the aquifer. The rising water table trend and its spatial distribution over the period 1992–2003 are generally well simulated, albeit smoothed year-to-year dynamics. Comparison with alternative methods of recharge estimation suggests, however, that there may presently exist more recharging sites and/or contributing surfaces than those considered so far.

Citation Massuel, S., Cappelaere, B., Favreau, G., Leduc, C., Lebel, T. & Vischel, T. (2011) Integrated surface water–groundwater modelling in the context of increasing water reserves of a regional Sahelian aquifer. Hydrol. Sci. J. 56(7), 1242–1264.  相似文献