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361.
The purpose of this study was to assess the differences in the abundance and activity of the bacterioplankton at sites with varied boating activity, and to determine the response of the communities to additional petroleum pollution. Three sites, including two marinas and a site on Bogue Sound in coastal North Carolina, were selected for monthly experiments. Seasonal patterns of bacterioplanktonic abundance and diesel fuel biodegradation for each site were examined, and possible correlations with intensity of boating activities were explored. Bacterioplanktonic communities at the three sites in this study were more similar in their structure and biodegradation potential than would have been expected from previous studies. We found no differences in the abundance and biodegradation potential of theses communities at the three sites, and only a slightly elevated number of hydrocarbon degraders at one of the marinas. Patterns of biodegradation were more closely related to total bacterial abundance, rather than number of petroleum hydrocarbon degraders. There was a strong seasonal pattern in bacterial abundance and biodegradation at all three sites. The bacterioplanktonic Community at all sites responded similarly to additions of diesel fuel. Bacterial abundance and productivity were both elevated to some extent, and number of petroleum hydrocarbon degraders changed relatively little. These data indicate that marinas may not profoundly after the bacterioplankton and that coastal waters often have resident bacterial communities capable of degrading petroleum hydrocarbon pollution. 相似文献
362.
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364.
Information from 117 questionnaires and focus groups in four villages in the Okavango Delta, Botswana was used to identify households exposed to different levels of risk in order to relate them to various livelihood activities and coping strategies. Current household strategies such as migration and diversification that are used to cope with recurring hazards such as drought, reduced flooding and animal disease are becoming more limited because of fencing policies and changed flooding regimes. In the light of future challenges such as climate change and increased upstream water abstractions, the heavy reliance on government assistance will probably increase especially among female-headed households and high-risk households. Without targeted initiatives based on spatial and social distributions of risk, then the dependency syndrome of Botswana is likely to continue and be exacerbated. 相似文献
365.
Martin Melles Julie Brigham-Grette Olga Yu. Glushkova Pavel S. Minyuk Norbert R. Nowaczyk Hans-W. Hubberten 《Journal of Paleolimnology》2007,37(1):89-104
The ca. 13 m long sediment core PG1351, recovered in 1998 from the central part of Lake El’gygytgyn, NE Siberia, was investigated
for lithostratigraphy, water content, dry bulk density (DBD), total organic carbon (TOC), total nitrogen (TN), total sulphur
(TS) and biogenic silica (opal) contents, and for TOC stable isotope ratios (δ13CTOC). The event stratigraphy recorded in major differences in sediment composition match variations in regional summer insolation,
thus confirming a new age model for this core, which suggests that it spans the last 250 ka BP. Four depositional units of
contrasting lithological and biogeochemical composition have been distinguished, reflecting past environmental conditions
associated with relatively warm, peak warm, cold and dry, and cold but more moist climate modes. A relatively warm climate,
resulting in complete summer melt of the lake ice cover and seasonal mixing of the water column, prevailed during the Holocene
and Marine Isotope Stages (MIS) 3, 5.1, 5.3, 6.1, 6.3, 6.5, 7.1–7.3, 7.5, 8.1 and 8.3. MIS 5.5 (Eemian) was characterized
by significantly enhanced aquatic primary production and organic matter supply from the catchment, indicating peak warm conditions.
During MIS 2, 5.2, 5.4, 6.2 and 6.4 the climate was cold and dry, leading to perennial lake ice cover, little regional snowfall,
and a stagnant water body. A cold but more moist climate during MIS 4, 6.6, 7.4, 8.2 and 8.4 is thought to have produced more
snow cover on␣the perennial ice, strongly reducing light penetration and biogenic primary production in␣the lake. While the
cold–warm pattern during␣the past three glacial–interglacial cycles is probably controlled by changes in regional summer insolation,
differences in the intensity of the warm phases and in the degree of aridity (changing snowfall) during cold phases likely
were due to changes in atmospheric circulation patterns.
This is the seventh in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and
its catchment in NE Russia. JulieBrigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue. 相似文献
366.
Steven L. Forman James Pierson Jeaneth Gómez Julie Brigham-Grette Norbert R. Nowaczyk Martin Melles 《Journal of Paleolimnology》2007,37(1):77-88
This study focused on the luminescence dating of sediments from Lake El’gygytgyn, a meteorite impact crater 100 km north of
the Arctic Circle in northeast Siberia, formed 3.58 Ma ago. The sediment is principally eolian deposited in to a lake with
nearly permanently ice. The fine-grained polymineral and quartz extracts taken from nine distinct levels from the upper 12.3 m
of sediment core PG1351 were dated by infrared stimulated (IRSL) and green stimulated luminescence (GSL) using multiple aliquot
additive dose procedures. The veracity of these ages is evaluated by comparing to an age model for the core derived from magnetic
excursions and from correlation of variations of the magnetic susceptibility record to similar magnitude variations in δ 18O in the Greenland Ice core record. The IRSL ages from the upper 9 m of core correspond well with the independent age control
for the past ca. 200 ka. However, sediments deeper in the core at 12.3 m with an inferred age of ca. 250 ka age yield a saturated
IRSL response and therefore a non-finite OSL age. The youngest sediment dated from 0.70 m depth yielded the IRSL age of ca.
11.5 ka, older than the corresponding age of 9.3–8.8 ka, indicating a discrepancy in dating the youngest sediments in the
upper 1 m of core. This study confirms the utility of IRSL by the multiple aliquot additive dose method to date sediments
<200 ka old from eastern Siberia.
This is the sixth in a series of eleven papers published in this special issue dedicated to initial studies of El’gygytgyn Crater Lake and
its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue. 相似文献
367.
Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy-permitting resolution 总被引:4,自引:6,他引:4
Barnier Bernard Gurvan Madec Thierry Penduff Jean-Marc Molines Anne-Marie Treguier Julien Le Sommer Aike Beckmann Arne Biastoch Claus Böning Joachim Dengg Corine Derval Edmée Durand Sergei Gulev Elizabeth Remy Claude Talandier Sébastien Theetten Mathew Maltrud Julie McClean Beverly De Cuevas 《Ocean Dynamics》2006,56(5-6):543-567
Series of sensitivity tests were performed with a z-coordinate, global eddy-permitting (1/4°) ocean/sea-ice model (the ORCA-R025 model configuration developed for the DRAKKAR project) to carefully evaluate the impact of recent state-of-the-art numerical schemes on model solutions. The combination of an energy–enstrophy conserving (EEN) scheme for momentum advection with a partial step (PS) representation of the bottom topography yields significant improvements in the mean circulation. Well known biases in the representation of western boundary currents, such as in the Atlantic the detachment of the Gulf Stream, the path of the North Atlantic Current, the location of the Confluence, and the strength of the Zapiola Eddy in the south Atlantic, are partly corrected. Similar improvements are found in the Pacific, Indian, and Southern Oceans, and characteristics of the mean flow are generally much closer to observations. Comparisons with other state-of-the-art models show that the ORCA-R025 configuration generally performs better at similar resolution. In addition, the model solution is often comparable to solutions obtained at 1/6 or 1/10° resolution in some aspects concerning mean flow patterns and distribution of eddy kinetic energy. Although the reasons for these improvements are not analyzed in detail in this paper, evidence is shown that the combination of EEN with PS reduces numerical noise near the bottom, which is likely to affect current–topography interactions in a systematic way. We conclude that significant corrections of the mean biases presently seen in general circulation model solutions at eddy-permitting resolution can still be expected from the development of numerical methods, which represent an alternative to increasing resolution. 相似文献
368.
From rifting to spreading in the eastern Gulf of Aden: a geophysical survey of a young oceanic basin from margin to margin 总被引:1,自引:0,他引:1
Sylvie Leroy Pascal Gente Marc Fournier Elia d'Acremont Philippe Patriat Marie-Odile Beslier Nicolas Bellahsen Marcia Maia Angelina Blais Julie Perrot Ali Al-Kathiri Serge Merkouriev Jean-Marc Fleury Pierre-Yves Ruellan Claude Lepvrier Philippe Huchon 《地学学报》2004,16(4):185-192
A geophysical survey in the eastern Gulf of Aden, between the Alula–Fartak (52°E) and the Socotra (55°E) transform faults, was carried out during the Encens–Sheba cruise. The conjugate margins of the Gulf are steep, narrow and asymmetric. Asymmetry of the rifting process is highlighted by the conjugate margins (horst and graben in the north and deep basin in the south). Two transfer fault zones separate the margins into three segments, whereas the present‐day Sheba Ridge is divided into two segments by a transform discontinuity. Therefore segmentation of the Sheba Ridge and that of the conjugate margins did coincide during the early stages of oceanic spreading. Extensive magma production is evidenced in the central part of the western segment. Anomaly 5d was identified in the northern and southern parts of the oceanic basin, thus confirming that seafloor spreading in this part of Gulf of Aden started at least 17.6 Ma ago. 相似文献
369.
370.
Dating of palaeomagnetic records from Finnish lake sediment cores using pollen analysis 总被引:1,自引:0,他引:1
Pertti Huttunen Julie Stober 《Boreas: An International Journal of Quaternary Research》1980,9(3):193-202
Palaeomagnetic and palynological studies have been made of the sediments of two Finnish lakes. Geomagnetic field changes in Finland can be traced since lake sediments record the ambient geomagnetic field at, or close to, the time they are deposited. Pollen analyses provided a useful method of dating these changes since 14 C dates proved to be misleading. 相似文献