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Simulation of the Holocene climate evolution in Northern Africa: The termination of the African Humid Period 总被引:2,自引:0,他引:2
The Holocene climate evolution in Northern Africa is studied in a 9000-yr-long transient simulation with a coupled atmosphere–ocean–vegetation model forced by changes in insolation and atmospheric greenhouse gas concentrations. The model simulates in the monsoonal domains a significant decrease in precipitation under influence of the orbitally forced reduction in summer insolation. In the Western Sahara region, the simulated mid-Holocene transition from humid to arid conditions (the termination of the African Humid Period) is highly non-linear with the occurrence of centennial-scale climate fluctuations due to the biogeophysical feedback between precipitation and vegetation cover. This result is in agreement with proxy data from the Western Sahara region. The other monsoonal regions experience a more gradual climate evolution that linearly follows the insolation forcing, which appears in disagreement with available lake level records. 相似文献
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Andrew N. Ostrovsky Reishi Takashima Matthew H. Dick Andrei V. Grischenko Hiroshi Nishi Shunsuke F. Mawatari 《Cretaceous Research》2006,27(6):859-862
A small collection of recrystallised, encrusting colonies of a single species from the Mikasa Formation (lower Middle Cenomanian), represents the first record of cheilostome (malacostegan or anascan) bryozoans from Hokkaido, Japan. 相似文献
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J. C. Kurtz N. D. Detenbeck V. D. Engle K. Ho L. M. Smith S. J. Jordan D. Campbell 《Estuaries and Coasts》2006,29(1):107-123
Coastal ecosystems are ecologically and commercially valuable, productive habitats that are experiencing escalating compromises
of their structural and functional integrity. The Clean Water Act (USC 1972) requires identification of impaired water bodies
and determination of the causes of impairment. Classification simplifies these determinations, because estuaries within a
class are more likely to respond similarly to particular stressors. We reviewed existing classification systems for their
applicability to grouping coastal marine and Great Lakes water bodies based on their responses to aquatic stressors, including
nutrients, toxic substances, suspended sediments, habitat alteration, and combinations of stressors. Classification research
historically addressed terrestrial and freshwater habitats rather than coastal habitats. Few efforts focused on stressor response,
although many well-researched classification frameworks provide information pertinent to stressor response. Early coastal
classifications relied on physical and hydrological properties, including geomorphology, general circulation patterns, and
salinity. More recent classifications sort ecosystems into a few broad types and may integrate physical and biological factors.
Among current efforts are those designed for conservation of sensitive habitats based on ecological processes that support
patterns of biological diversity. Physical factors, including freshwater inflow, residence time, and flushing rates, affect
sensitivity to stressors. Biological factors, such as primary production, grazing rates, and mineral cycling, also need to
be considered in classification. We evaluate each existing classification system with respect to objectives, defining factors,
extent of spatial and temporal applicability, existing sources of data, and relevance to aquatic stressors. We also consider
classification methods in a generic sense and discuss their strengths and weaknesses for our purposes. Although few existing
classifications are based on responses to stressors, may well-researched paradigms provide important information for improving
our capabilities for classification, as an investigative and predictive management tool. 相似文献
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