Geochemical and stratigraphic evidence of environmental change at Lynch's Crater, Queensland, Australia     

Joanne Muller  Raphael A.J. Wüst  Dominik Weiss  Yi Hu 《Global and Planetary Change》2006,53(4):269

This is one of the first applications of geochemical proxies to define changes in vegetation, hydrology and atmospheric dust influence on a peat deposit in the southern hemisphere. A 6.6 m deep peat record from Lynch's Crater in NE-Queensland, Australia, provides a sensitive  5000 to 30,000 cal years BP archive of environmental change. The deposit consists of 1.5 m of ombrotrophic peat underlain by a minerotrophic peat. Within the minerotrophic section, sponge spicules and diatom fragments offer evidence of prolonged flooding of the peat environment resulting in several layers containing (up to 50%) high inorganic material. The Ca and Mg data display episodes of enhanced dust influx and nutrient recycling and support previous palynological studies that show a Pleistocene to Holocene switch from sclerophyll woodlands to rainforest vegetation.  相似文献   

Post‐excavation deterioration of the Copney Bronze Age Stone Circle Complex: A geomorphological perspective     

Patricia A. Warke  Joanne M. Curran  Bernard J. Smith  Mark Gardiner  Claire Foley 《Geoarchaeology》2010,25(5):541-571

Post‐excavation deterioration of stones from under blanket peat at the Copney Bronze Age Stone Circle Complex in County Tyrone, Northern Ireland, proceeded through widespread scaling, flaking, and splitting of stones. Investigation showed that prior to burial the porphyritic stones already possessed a complex legacy of geological weaknesses derived from hydrothermal alteration and tectonic deformation. Analysis indicated that significant alteration occurred during approximately 2000 years of burial under acidic peat cover, with development of a secondary porosity, alteration of primary minerals, and the opening of preexisting lines of weakness within the stones. Burial under peat also resulted in “bleaching” the stones so that they appeared white in color following excavation. These alterations during burial left the stones in a significantly weakened state and particularly susceptible to the effects of subaerial weathering processes. Data underline the potential fragility of excavated stonework and highlight the need to plan for its aftercare before complete excavation is undertaken. © 2010 Wiley Periodicals, Inc.  相似文献   

Oxygen stable isotope ratios from British oak tree-rings provide a strong and consistent record of past changes in summer rainfall     

Giles H. F. Young  Neil J. Loader  Danny McCarroll  Roderick J. Bale  Joanne C. Demmler  Daniel Miles  Nigel T. Nayling  Katja T. Rinne  Iain Robertson  Camilla Watts  Matthew Whitney 《Climate Dynamics》2015,45(11-12):3609-3622

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Financial instruments for disaster risk management and climate change adaptation     

Joanne Linnerooth-Bayer  Stefan Hochrainer-Stigler 《Climatic change》2015,133(1):85-100

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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   

Remnant riparian vegetation,sediment and nutrient loads,and river rehabilitation in subtropical Australia          下载免费PDF全文

Jon Olley  Joanne Burton  Virgilio Hermoso  Kate Smolders  Joe McMahon  Belinda Thomson  Andrew Watkinson 《水文研究》2015,29(10):2290-2300

A decline in the ecosystem health of Australia's Moreton Bay, a Ramsar wetland of international significance, has been attributed to sediments and nutrients derived from catchment sources. To address this decline the regional management plan has set the target of reducing the loads by 50%. Reforestation of the channel network has been proposed as the means to achieve this reduction, but the extent of revegetation required is uncertain. Here we test the hypothesis that sediment and nutrient loads from catchments decrease proportionally with the increasing proportion of the stream length draining remnant vegetation. As part of a routine regional water quality monitoring program sediment and nutrient loads were measured in 186 flow events across 22 sub‐catchments with different proportions of remnant woodland. Using multiple linear regression analysis we develop a predictive model for pollutant loads. Of the attributes examined a combination of runoff and the proportion of the stream length draining remnant vegetation was the best predictor. The sediment yield per unit area from a catchment containing no remnant vegetation is predicted to be between 50 and 200 times that of a fully vegetated channel network; total phosphorus between 25 and 60 times; total nitrogen between 1.6 and 4.1 times. There are ~48 000 km of streams in the region of which 32% drain areas of remnant vegetation. Of these 17 095 km are above the region's water storage dams. We estimate that decreasing the sediment and phosphorus loads to Moreton Bay by 50% would involve rehabilitating ~6350 km of the channel network below the dams; halving the total nitrogen load would require almost complete restoration of the channel network. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

A quasar in a compact group of galaxies at  z= 0.7      

M. N. Bremer  Joanne C. Baker †  Matthew D. Lehnert 《Monthly notices of the Royal Astronomical Society》2002,337(2):470-476

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Evaluation of image analysis methods used for quantification of particle angularity     

Solomon Tafesse  Joanne M. Robison Fernlund  Wenjuan Sun  Fredrik Bergholm 《Sedimentology》2013,60(4):1100-1110

Angularity is an important parameter in the characterization of particle morphology that is used to interpret the transport history of particles in sedimentary deposits. In the past, visual classification using silhouette charts was widely used to determine particle angularity, but this approach is subjective and time‐consuming. With advances in modern image analysis techniques and low‐cost software packages, it is possible to rapidly quantify particle angularity more objectively than using visual classification methods. This study re‐examines the performance of three existing image analysis methods and one new image analysis procedure, applied to six rock and sediment samples that were visually different in angularity. To facilitate comparison between the angularity results, measurements were reduced to rankings for each aggregate sample. These results show that the four image analysis methods rank the angularity of the samples differently, and that none rank the mean angularity index in the same order as the angularity ranking using visual classification. Therefore, further research is needed to develop an image analysis method that can quantify the angularity of sedimentary particles more precisely.  相似文献   

The deglacial history of NW Alexander Island,Antarctica, from surface exposure dating     

Joanne S. Johnson  Jeremy D. Everest  Philip T. Leat  Nicholas R. Golledge  Dylan H. Rood  Finlay M. Stuart 《Quaternary Research》2012,77(2):273-280

Recent changes along the margins of the Antarctic Peninsula, such as the collapse of the Wilkins Ice Shelf, have highlighted the effects of climatic warming on the Antarctic Peninsula Ice Sheet (APIS). However, such changes must be viewed in a long-term (millennial-scale) context if we are to understand their significance for future stability of the Antarctic ice sheets. To address this, we present nine new cosmogenic ¹⁰Be exposure ages from sites on NW Alexander Island and Rothschild Island (adjacent to the Wilkins Ice Shelf) that provide constraints on the timing of thinning of the Alexander Island ice cap since the last glacial maximum. All but one of the ¹⁰Be ages are in the range 10.2–21.7 ka, showing a general trend of progressive ice-sheet thinning since at least 22 ka until 10 ka. The data also provide a minimum estimate (490 m) for ice-cap thickness on NW Alexander Island at the last glacial maximum. Cosmogenic ³He ages from a rare occurrence of mantle xenoliths on Rothschild Island yield variable ages up to 46 ka, probably reflecting exhumation by periglacial processes.  相似文献   

A magnetic survey of Explorer Seamount— Recent spreading at the Explorer trench     

Wu Mingxian  Patrick J. C. Ryall  Joanne Bryan 《中国海洋湖沼学报》1986,4(2):183-195

In 1981 a magnetic and bathymetric survey was carried out over Explorer Seamount located approximately between 48°50′ and 49°30′N and 130°40′ and 131°30′W. During the cruise four pillow fragments were dredged from peaks in this area. Based on the observed magnetic data, it was identified that the main peak of Explorer Seamount should be of the Bruhnes age while the magnetic high in the NW of study area would be Gauss. This would yield a spreading rate of about 2 cm per year for the Matuyama epoch. The results of intensities of remanence measured from the pillow fragments indicate that the ages are less than 10⁶ years. Similarly the Curie temperature is consistent with ages of around 10⁶ years. An attempt was made to model the observed magnetic field using a series of uniformly magnetized NE-SW trending blocks of alternating polarity. Agreement between the model and observed results is satisfied. Oxidation ratios calculated from measured samples suggest that the main peak of Explorer Seamount is not far from the present day ridge axis, which agrees with the younger interpretation from the magnetic profiles. The results mentioned above strongly, but not conclusively, favour an interpretation in which the southeastern peak of Explorer Seamount is of the Bruhnes age and the recent spreading is at Explorer trench, then the Sovanco Fracture Zone should be thought of as a complex triangular area between the northern end of Juan de Fuca Ridge and Explorer Seamount rather than as a simple transform fault as defined conventionally.  相似文献