Single-grain OSL dating of glaciofluvial quartz constrains Reid glaciation in NW Canada to MIS 6     

Martina Demuro  Duane G. Froese  Lee J. Arnold  Richard G. Roberts 《Quaternary Research》2012,77(2):305-316

Improved chronological control on the penultimate advance of the Cordilleran Ice Sheet in northwest Canada (the Reid glaciation) is required for a better understanding of late Quaternary palaeoclimatic and palaeoenvironmental change in eastern Beringia. However, reliable dating of glaciation events beyond the last glacial maximum is commonly hindered by a lack of directly dateable material. In this study we (i) provide the first combined minimum and maximum age constraint on the Reid glaciation at Ash Bend, its reference locale in the Stewart River valley, northwestern Canadian Cordillera, using single-grain optically stimulated luminescence dating of quartz; and (ii) compare the timing of the Reid glaciation with other penultimate ice sheet advances in the region with the aim of establishing improved glacial reconstructions in eastern Beringia. We obtain ages of 158 ± 18 ka and 132 ± 18 ka for glaciofluvial sands overlying and underlying the Reid till, respectively. These ages indicate that the Reid advance, at its reference locale, occurred during MIS 6. This precludes an earlier MIS 8 age, and suggests that the Reid advance may have been synchronous with the Delta glaciation of central Alaska, and is likely correlative with the Mirror Creek glaciation in southern Yukon.  相似文献   

Vertical cloud structures of the boreal summer intraseasonal variability based on CloudSat observations and ERA-interim reanalysis     

Xianan Jiang  Duane E. Waliser  Jui-Lin Li  Christopher Woods 《Climate Dynamics》2011,36(11-12):2219-2232

The boreal summer intraseasonal variability (BSISV), which is characterized by pronounced meridional propagation from the equatorial zone to the Indian Continent, exerts significant modulation of the active/break phases of the south Asian monsoon. This form of variability provides a primary source of subseasonal predictive skill of the Asian summer monsoon. Unfortunately, current general circulation models display large deficiencies in representing this variability. The new cloud observations made available by the CloudSat mission provide an unprecedented opportunity to advance our characterization of the BSISV. In this study, the vertical structures of cloud water content and cloud types associated with the BSISV over the Indian Ocean and subcontinent are analyzed based on CloudSat observations from 2006 to 2008. These cloud structures are also compared to their counterparts as derived from ERA-interim reanalysis. A marked vertical tilting structure in cloud water is illustrated during the northward propagation of the BSISV based on both datasets. Increased cloud liquid water content (LWC) tends to appear to the north of the rainfall maximum, while ice water content (IWC) in the upper troposphere slightly lags the convection. This northward shift of increased LWC, which is in accord with local enhanced moisture as previously documented, may play an important role in the northward propagation of the BSISV. The transition in cloud structures associated with BSISV convection is further demonstrated based on CloudSat, with shallow cumuli at the leading edge, followed by the deep convective clouds, and then upper anvil clouds. Some differences in cloud water structures between CloudSat and ERA-interim are also noted, particularly in the amplitudes of IWC and LWC fields.  相似文献   

Organic micropollutants in marine plastics debris from the open ocean and remote and urban beaches   总被引：2，自引：0，他引：2  

Hirai H  Takada H  Ogata Y  Yamashita R  Mizukawa K  Saha M  Kwan C  Moore C  Gray H  Laursen D  Zettler ER  Farrington JW  Reddy CM  Peacock EE  Ward MW 《Marine pollution bulletin》2011,62(8):1683-1692

To understand the spatial variation in concentrations and compositions of organic micropollutants in marine plastic debris and their sources, we analyzed plastic fragments (∼10 mm) from the open ocean and from remote and urban beaches. Polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), dichloro-diphenyl-trichloroethane and its metabolites (DDTs), polybrominated diphenyl ethers (PBDEs), alkylphenols and bisphenol A were detected in the fragments at concentrations from 1 to 10,000 ng/g. Concentrations showed large piece-to-piece variability. Hydrophobic organic compounds such as PCBs and PAHs were sorbed from seawater to the plastic fragments. PCBs are most probably derived from legacy pollution. PAHs showed a petrogenic signature, suggesting the sorption of PAHs from oil slicks. Nonylphenol, bisphenol A, and PBDEs came mainly from additives and were detected at high concentrations in some fragments both from remote and urban beaches and the open ocean.  相似文献   

PECORA IX: Spatial Information Technology For Remote Sensing: Today And Tomorrow     

M. Duane Nellis 《The Professional geographer》1985,37(2):220-221

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Ten years of NASA's Aqua satellite's successful contributions to Earth Observation science     

Kamlesh Lulla  M. Duane Nellis  Bradley Rundquist 《国际地球制图》2013,28(4)

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The Landsat Global Archive: a valuable global resource     

Kamlesh Lulla  M. Duane Nellis  Brad Rundquist 《国际地球制图》2013,28(4)

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China-Brazil Earth Resources Satellite Collaboration is a success     

Kamlesh Lulla  M. Duane Nellis  Brad Rundquist 《国际地球制图》2013,28(5)

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Celebrating fifty years of NASA and Earth observations from space. Part IV: Global water cycle and water resources research     

Kamlesh Lulla  M. Duane Nellis  Brad Rundquist 《国际地球制图》2013,28(4)

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Burial and preservation of a 30,000 year old perennial snowbank in Red Creek valley,Ogilvie Mountains,central Yukon,Canada     

Denis Lacelle  Melanie St-Jean  Bernard Lauriol  Ian D. Clark  Antoni Lewkowicz  Duane G. Froese  Stephen C. Kuehn  Grant Zazula 《Quaternary Science Reviews》2009,28(27-28):3401-3413

This study describes the origin and age of a body of massive ground ice exposed in the headwall of a thaw slump in the Red Creek valley, central Yukon, Canada. The site is located beyond the limits of Pleistocene glaciation in central Yukon and within the southern limit of the modern continuous permafrost zone. The origin of the massive ground ice, which is preserved under a fine-grained diamicton containing thin layers of tephra, was determined through ice petrography, stable O-H isotope composition of the ice, and gas composition of occluded air entrapped in the ice. The age of the massive ground ice was established by identifying the overlying tephra and radiocarbon dating of a “muck” deposit preserved within the ice. Collectively, the results indicate that the massive ground ice formed by snow densification with limited melting-refreezing and is interpreted as being a buried perennial snowbank. The muck deposit within the ice, which yielded an age of 30,720 ± 340 ¹⁴C a BP, and the Dawson tephra (25,300 ¹⁴C a BP) overlying the perennial snowbank, indicates that the snowbank accumulated at roughly the transition between marine isotope stages 3 and 2. Dry climatic conditions at this time and possibly high winds enabled the snowbank to accumulate in the absence of extensive local valley glaciation as occurred in the mountains to the south. In addition to documenting the persistence of relict permafrost and ground ice to warming climate in regions where they are predicted to disappear by numerical models, this study presents evidence of an isotopic biosignature preserved in a body of massive ground ice.  相似文献   

Some thoughts on the integration of spatial analysis and Geographic Information Systems   总被引：5，自引：0，他引：5  

Duane F. Marble 《Journal of Geographical Systems》2000,2(1):31-35

It is past time for us to examine the relationship that exists between what we commonly call spatial analysis on the one hand, and geographic information systems or GIS on the other. GIS technology is widely used but seems to incorporate only a portion of the tools found in spatial analysis. Spatial analysis can be accused of overly simplistic approaches that severely limit its practical utility. This paper suggests that discarding myopic views and meeting upon a common ground of increased knowledge of modern computing concepts and techniques, including object-orientation, can prove extremely fruitful to both sides.  相似文献