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81.
The early Holocene is characterised by rapid climate change events, which in the North Atlantic region are often associated with changes in thermohaline circulation. Superimposed on this in northwest Europe is localised evidence for human impact on the landscape, although separating climatic and anthropogenic mechanisms for environmental change is often difficult. Biotic and sedimentological evidence from a lacustrine sequence from the Inner Hebrides, Scotland, shows a considerable reduction in inferred local woodland centred upon 8250 cal. yr BP. These data correlate precisely with a distinctive rise in the charcoal:pollen ratio and hence suggest a possible Mesolithic human impact upon the vegetation around this time. A quantitative temperature reconstruction from chironomid analyses from the same sequence, supported by sedimentological data, indicates that the fall in arboreal pollen taxa occurred as climate warmed significantly during the early Holocene. This warming was followed by a significant cold event, with mean July temperatures reduced by 2°C, that lasted for at least 320 years ca. 7790–7470 cal. yr BP. Woodland recovered during this phase suggesting that the vegetation during the 8250 cal. yr BP interval was likely to have been responding to human activity, and not climate, and hence it is possible at specific sites to separate the influence of these key drivers of environmental change. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
82.
83.
Heather Norris Nicholson 《Area》2001,33(2):128-140
Home movies provided valuable insights into childhood experiences during much of the twentieth century. Contrasting footage of children in rural and urban setting in Northern England between c.1937 and 1970, viewed through the cinematic gaze of two male amateur film-makers underpins this discussion of childhood geographies in the past. Issues explored in the paper include the social construction of childhood, power relations and visual representation of children, and the role of home movie-making in shaping memories and constituting ideas and ideologies about family and children. 相似文献
84.
A re-evaluation of the olivine-spinel geothermometer 总被引:1,自引:0,他引:1
Peter L. Roeder Ian H. Campbell Heather E. Jamieson 《Contributions to Mineralogy and Petrology》1979,68(3):325-334
The Irvine olivine-spinel geothermometer, as formulated by Jackson (1969), appears to yield magmatic temperatures when applied
to plutonic rocks such as the Stillwater Complex but Evans and Wright (1972) have demonstrated that it gives temperatures
in excess of 2,000 ° C when applied to volcanic assemblages. A re-evaluation of the geothermometer has shown that more realistic
temperatures can be obtained for volcanic rocks by using a different free energy value of FeCr2O4 in the formulation. The revised geothermometer gives temperatures in the range 1,100–1,300 ° C for samples from Kilauea and
500–800 ° C for basic plutonic rocks from layered intrusions, indicating that Mg and Fe2+ have re-equilibrated at subsolidus temperatures in these intrusions as suggested by Irvine (1965). This theory was tested
by heating uncrushed natural samples from layered intrusions to magmatic temperatures for periods ranging from two days to
four weeks. The result was a marked increase in the Mg/Fe2+ ratio in the spinels and a decrease in the Mg/Fe2+ ratio in the olivines, confirming that considerable subsolidus re-equilibration had taken place in the unheated samples. 相似文献
85.
Heather Norris Nicholson 《GeoJournal》2004,59(4):323-333
After the appearance of a portable Kodak cine camera in 1923, home moving making grew steadily in popularity in the years
leading up to and following World War II. Cine enthusiasts, particularly in the pre-war period, tended to be male, white and
middle class, although exceptions exist, and they tended to travel with their cameras much as earlier generations had documented
their experiences in written and artistic form. Despite their amateur status, they were often very professional in their approach
to cinematography and they produced material for a range of domestic and public audiences on varied topics and in different
genres. Specialist publications and the rapid growth of local amateur film societies fostered the rise of an active non-professional
film movement; the result is a highly distinctive although neglected component of film history. With reference to materials
held at the North West Film Archives in Manchester, England, this discussion considers the rise of non-professional filmmaking
at the regional level during the decades before and after the second world war. Making and showing home movies is placed within
various socio-cultural contexts. The imagery discloses much about visual practice, including filmmakers' perceptions and their
relationships with different kinds of subject matter. The making of holiday footage, in Mediterranean settings, and its subsequent
screening in domestic or public places, connects with broader issues of visualization, social practice and leisure-related
consumption.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
86.
Leslie H. Taylor Shawn M. Shellito Heather U. Abello Peter A. Jumars 《Estuaries and Coasts》2005,28(4):500-509
Acoustic backscatter from an active sonar system over a range of six frequencies between 265 kHz and 3 MHz in the tidally
dominated Damariscotta River estuary, Maine, United States, revealed that the major emergence event of the night commenced
on the first tidal deceleration after dark (3.5–4 h after local slack), irrespective of flow direction. Emergence traps identified
the mysid shrimp,Neomysis americana, as the dominant migrator. Water-column-integrated, acoustically estimated biovolume at our 10-m deep study location increased
by a factor of about 6 during these large events, entirely dominating the holoplanktonic contribution and likely being a major
component in benthic-pelagic coupling. Application of the same algorithm used to locate this nighttime emergence revealed
a parallel but considerably smaller daytime emergence event near the same phase of the tide. Daytime trap samples failed to
recover the organisms responsible, but transmissometry rejected the alternative hypothesis that we observed resuspension events.
We suspect, but have yet only weak evidence, that animals emerging in daylight are copepods rather than mysids. 相似文献
87.
Seismogenic zone structure beneath the Nicoya Peninsula, Costa Rica, from three-dimensional local earthquake P- and S-wave tomography 总被引:3,自引:0,他引:3
88.
Heather Clegg Brian Horsfield Heinz Wilkes Jaap Sinninghe Damst Martin P. Koopmans 《Organic Geochemistry》1998,29(8):1953-1960
Hydrous pyrolysis experiments were performed on the Ghareb Formation (Upper Cretaceous, Jordan), a carbonate- and organic-rich (TOC 19.6%) source rock, using a temperature range of 200 to 360°C (72 h). The original sediment contains only low amounts of carbazoles, (maximum 2.2 μg/g bitumen for 1-methylcarbazole). With increasing thermal maturation, intense generation begins at temperatures only in excess of 300°C, reaching a maximum at 360°C. Likewise, during natural maturation, generation occurs at later stages of maturity (e.g. for Tithonian source rocks at >0.81% Rr and for Posidonia Shale at >0.88% Rr). Some isomeric changes during hydrous pyrolysis do not resemble those in nature whereas others do. The relative abundances of selected C1- and C2-alkylcarbazoles on ternary diagrams reveal differences, whereas the benzo[a]carbazole/benzo[a]carbazole+benzo[c]carbazole ratio is closely similar. The latter result supports the contention that maturation plays a key role in controlling carbazole distributions in source rocks. However, the results for alkylcarbazoles, especially the C2-carbazoles, are not easy to interpret. 相似文献
89.
90.
Brian Fry Donald M. Baltz Mark C. Benfield John W. Fleeger Arian Gace Heather L. Haas Zoraida J. Quiñones-Rivera 《Estuaries and Coasts》2003,26(1):82-97
Brown shrimp (Farfantepenaeus aztecus) are an important commercial aquatic species experiencing loss of inshore marsh nursery habitat in coastal Louisiana. To
study inshore brown shrimp movements and identify aspects of essential habitat important for sustaining brown shrimp populations,
we collected juvenile brown shrimp in April and May 2000, the time of annual maximum brown shrimp abundance, in a small 1-km2 marsh area on the central Louisiana coast. Drop sampling showed average shrimp densities of 1.6–2.4 m−2 in shallow marsh ponds and seining indicated lower densities of 0.5–0.9 m−2 in nearby shallow channel and open bay sites. Smaller shrimp (< 50 mm) fed disproportionately on benthic diatoms and small
harpacticoid copepods, while large shrimp fed more frequently on larger-bodied amphipods and tanaids. We developed novel chemical
approaches to estimate patterns of shrimp residency and movement using carbon and nitrogen stable isotopic determinations.
Resident shrimp had isotopic values similar to average foods and showed consistent isotopic spacings between fast and slow
turnover tissues. Residency was highest (47–55%) in ponds and shallow channel habitats and much less in open bays and deep
channels (4–27%). There was sparse evidence for dietary specialization among individull shrimp. The results support the view
that small 10–20 mm postlarval and juvenile brown shrimp arriving in estuaries from offshore waters continue movement through
sub-optimal habitats (deep channels and open bays), but exhibit much less movement once an optimal habitat (marsh ponds or
shallow channel margins) is reached. This study also indicated that combining estimates of shrimp densities, residency, growth
rate, and mortality allows evaluation of the importance of different habitat types for shrimp production. Shallow ponds that
in many ways resemble fertile aquaculture ponds appear to be hot spots for brown shrimp production, and coastal preservation
and restoration efforts should focus on these areas as important for sustaining shrimp fisheries. 相似文献