Editorial     

Kamlesh Lulla  M. Duane Nellis  Brad Rundquist 《国际地球制图》2013,28(8)

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Pre-glacial and interglacial pollen records over the last 3 Ma from northwest Canada: Why do Holocene forests differ from those of previous interglaciations?     

Charles Schweger  Duane Froese  James M. White  John A. Westgate 《Quaternary Science Reviews》2011,30(17-18):2124-2133

We synthesize pollen spectra from eleven dated stratigraphic sections from central and northern Yukon. Palaeomagnetic and tephra dating indicates the earliest assemblages, representing closed canopy Pinus and Picea forest, are middle-late Pliocene age. More open forest conditions, indicated by increased Poaceae and with evidence of permafrost, are dated at ca 3 Ma. While Pinus pollen is abundant at 3 Ma, it is reduced in records after 2.6 Ma, and subsequent Pleistocene interglacial forest records are repeatedly dominated by Picea, along with Alnus and small but significant amounts of Abies. Surface sample comparisons indicate that Abies was more widespread and abundant in past interglaciations than at present and that Middle-Pleistocene Picea–Abies forest grew in the northern Yukon Porcupine Basin, 500 km beyond modern Abies limits. In contrast, Pinus, which occurs today in southern and central Yukon, was not a significant component of these Pleistocene interglacial forests. Late-Holocene pollen assemblages with rare Abies and high Pinus are the most distinct in the past 2.6 Ma. Possible factors driving Holocene difference are paleoclimate, paludification, changes in megafaunal herbivory and an unusual fire regime. Anthropogenic burning is a factor unique to the Holocene, and if it is shown to be important in this case, it would challenge our notion of what constitutes boreal wilderness.  相似文献   

Real-time multivariate indices for the boreal summer intraseasonal oscillation over the Asian summer monsoon region   总被引：3，自引：0，他引：3  

June-Yi Lee  Bin Wang  Matthew C. Wheeler  Xiouhua Fu  Duane E. Waliser  In-Sik Kang 《Climate Dynamics》2013,40(1-2):493-509

The boreal summer intraseasonal oscillation (BSISO) of the Asian summer monsoon (ASM) is one of the most prominent sources of short-term climate variability in the global monsoon system. Compared with the related Madden-Julian Oscillation (MJO) it is more complex in nature, with prominent northward propagation and variability extending much further from the equator. In order to facilitate detection, monitoring and prediction of the BSISO we suggest two real-time indices: BSISO1 and BSISO2, based on multivariate empirical orthogonal function (MV-EOF) analysis of daily anomalies of outgoing longwave radiation (OLR) and zonal wind at 850 hPa (U850) in the region 10°S–40°N, 40°–160°E, for the extended boreal summer (May–October) season over the 30-year period 1981–2010. BSISO1 is defined by the first two principal components (PCs) of the MV-EOF analysis, which together represent the canonical northward propagating variability that often occurs in conjunction with the eastward MJO with quasi-oscillating periods of 30–60 days. BSISO2 is defined by the third and fourth PCs, which together mainly capture the northward/northwestward propagating variability with periods of 10–30 days during primarily the pre-monsoon and monsoon-onset season. The BSISO1 circulation cells are more Rossby wave like with a northwest to southeast slope, whereas the circulation associated with BSISO2 is more elongated and front-like with a southwest to northeast slope. BSISO2 is shown to modulate the timing of the onset of Indian and South China Sea monsoons. Together, the two BSISO indices are capable of describing a large fraction of the total intraseasonal variability in the ASM region, and better represent the northward and northwestward propagation than the real-time multivariate MJO (RMM) index of Wheeler and Hendon.  相似文献   

Erratum: Breit–Pauli energy levels, transition probabilities and lifetimes for 3d⁵ levels in Fe iv of astrophysical interest     

Charlotte Froese Fischer  Robert H. Rubin 《Monthly notices of the Royal Astronomical Society》2004,355(4):1400-1400

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Floodplain stratigraphy of the ice jam dominated middle Yukon River: a new approach to long‐term flood frequency     

Joanne M. Livingston  Derald G. Smith  Duane G. Froese  Chris H. Hugenholtz 《水文研究》2009,23(3):357-371

Floodplain stratigraphy is used as a new method for reconstructing ice jam flood histories of northern rivers. The method, based on reconstruction of the sedimentary record of vertically‐accreting floodplains, relies on stratigraphic logging and interpretation of floodplain sediments, which result from successive ice jam floods, and radiocarbon dating of inter‐flood organic material for chronology. In a case study along a reach of the Yukon River that straddles the Yukon–Alaska border, the method is used to develop a record of ice jam flooding for the last 2000 years. Detailed chronostratigraphic logs from three sites along the Yukon River indicates that the long‐term recurrence interval varies depending on location, but ranges from approximately once in 25 years to once in 38 years (or a probability of ca 3–4% in any given year). This is broadly similar to the 4·5% probability of recurrence calculated from archival and gauged data at Dawson City, Yukon Territory, for the period 1898–2006. Two of the three study locations, with sufficient chronology, suggest a decrease in flood frequency in the last several hundred years relative to the preceding period at each site, broadly corresponding to the Little Ice Age, suggesting climate exerts some control over long‐term ice jam flood frequency. This study demonstrates that the floodplain sedimentary record offers the potential to extend records of ice jam flooding in remote, ungauged northern rivers and provides a broader temporal context for assessing the frequency and variability of ice jam flooding. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Celebrating fifty years of NASA and Earth observations from space. Part II: Land-use and land-cover change science     

Kamlesh Lulla  M. Duane Nellis  Brad Rundquist 《国际地球制图》2013,28(2)

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Vietnam’s Earth observation satellites launch a major milestone in remote sensing capability     

Kamlesh Lulla  M. Duane Nellis  Brad Rundquist 《国际地球制图》2013,28(6)

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Paleoecology of Beringian “packrat” middens from central Yukon Territory, Canada     

Grant D. Zazula  Duane G. Froese 《Quaternary Research》2005,63(2):189-198

Rodent middens from ice-rich loess deposits are important new paleoenvironmental archives for Eastern Beringia. Plant macrofossils recovered from three middens associated with Dawson tephra (ca. 24,000 ¹⁴C yr B.P.) at two sites in Yukon Territory include diverse graminoids, forbs, and mosses. These data suggest substantial local scale floristic and habitat diversity in valley settings, including steppe-tundra on well-drained soils, moist streamside meadows, and hydric habitats. Fossil arctic ground squirrel burrows and nesting sites indicate that permafrost active layers were thicker during Pleistocene glacial periods than at present on north-facing slopes.  相似文献   

Detecting post-depositional sediment disturbance in sandy deposits using optical luminescence   总被引：3，自引：0，他引：3  

Mark D. Bateman  Claire H. Boulter  Andrew S. Carr  Charles D. Frederick  Duane Peter  Michael Wilder 《Quaternary Geochronology》2007,2(1-4):57-64

Post-depositional mixing or exhumation is common in surficial sediments, yet may be unobservable from field evidence. However, any disturbance may have significant consquences in terms of establishing a reliable luminescence age determination. Optically stimulated luminescence (OSL) measurements, particularly measurements at the single grain level, can be used to gain an insight into both contemporary and past post-depositional processes.

This paper examines sites from Texas and Florida (USA) with independent chronological control to demonstrate the potential effects of varying degrees of bioturbation on OSL. Results show that contemporary soil forming processes clearly impact on the palaeodose (D_e) replicate distributions which are measured in order to derive an OSL age. Significant levels of scatter and apparently zero dose grains are observed in the upper-most sediments; declining with depth from the surface. D_e replicates from undisturbed and fully bleached sediments are unskewed, show low overdispersion (OD) and comparable single grain and single aliquot OSL ages. Bioturbated sediments, however, may show highly skewed multi-model D_e distributions with higher OD values, zero dose grains at depth, and significant diffences between single grain and single aliquot results. True burial ages may be derived from minimally bioturbated sediments through the application of statistical analysis such as finite mixture modelling to isolate D_e components. However, for significantly bioturbated sediments, the latter approach, even at the single grain level, produces inaccurate ages. In such cases we argue that additional evidence (both dating and contexual) may be required to identify with confidence the burial D_e population.  相似文献   

Lunar heat flow and regolith structure inferred from interferometric observations at a wavelength of 49.3 cm     

F.Peter Schloerb  Duane O. Muhleman  Glenn L. Berge 《Icarus》1976,29(3):329-341

We discuss observations of the Moon at a wavelength of 49.3 cm made with the Owens Valley Radio Observatory Interferometer. These observations have been fit to models in order to estimate the lunar dielectric constant, the equatorial subsurface temperature, the latitude dependence of the subsurface temperature, and the subsurface temperature gradient. The models are most consistent with a dielectric constant of 2.52 ± 0.01 (formal errors), an equatorial subsurface temperature of 249_?5⁺⁸K, and a change in the subsurface temperature with latitude (ψ), which is proportional to cos^0.38ψ. Since the temperature of the Moon has been measured by the Apollo Lunar Heat Flow Experiment, we have been able to use our determination of the equatorial temperature to estimate the error in the flux density calibration scale at 49.3cm (608 MHz). This results in a correction factor of 1.03 ± 0.04, which must be applied to the flux density scale. This factor is much different from 1.21 ± 0.09 estimated by Muhleman et al. (1973) from the brightness temperature of Venus and apparently indicates that the observed decrease in the brightness temperature of Venus at long wavelengths is a real effect.The estimates of the temperature gradient, which are based on the measurement of limb darkening, are small and negative (temperature decreases with depth) and may be insignificantly different from zero since they are only as large as their formal errors. We estimate that a temperature gradient in excess of 0.6K/m at 10m depth would have been observed. Thus, a temperature gradient like that measured in situ at the Apollo 15 and 17 landing sites in the upper 2m of the regolith is not typical of the entire lunar frontside at the 10m depths where the 49.3 cm wavelength emission originates. This result may indicate that the mean lunar heat flow is lower than that measured at the Apollo landing sites, that the thermal conductivity is greater at 10m depth than it is at 2m depth, or that the radio opacity is greater at 10m depth than at 2m depth. The negative estimates of the temperature gradient indicate that the Moon appeared limb bright and might be explained by scattering of the emission from boulders or an interface with solid rock. The presence of solid rock at 10m depths will probably cause heat flows like those measured by Apollo to be unobservable by our interferometric method at long wavelengths, since it will cause both the thermal conductivity and radio opacity of the regolith to increase. Thus, our data may be most consistent with a change in the physical properties of the regolith to those of solid rock or a mixture of rock and soil at depths of 7 to 16m. Our results show that future radio measurements for heat flow determinations must utilize wavelengths considerably shorter than 50 cm (25 cm or less) to avoid the rock regions below the regolith.  相似文献