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141.
Mohammed Ikramuddin Michael E. Lipschutz Everett K. Gibson 《Meteoritics & planetary science》1979,14(1):69-80
Seven trace elements (Ag, Co, Cs, Ga, In, Te, Tl) are either completely retained or are lost to the same extent in Abee samples heated at 700 °C for one week at 10?5-10?3 atm Ne or in 10?5 atm H2. Bi and Se are lost significantly more easily and Zn is better retained in samples heated in Ne than in H2. Zn retention varies inversely with ambient Ne pressure. Mobile element transport seems unaffected by physical interactions in the gas phase but may reflect solid-state surface effects. During week-long heating at low pressures (initially ~ 10?5 atm H2) S is mobilized only at 1000 °C while C contents decrease progressively from 600–1000 °C. Apparent activation energies for C are 60 kcal/mole below 700 °C and 16 kcal/mole above this temperature suggesting diffusive loss from different hosts and/or processes over different temperature intervals. In E4–6 chondrites C and S contents largely reflect nebular fractionation and condensation processes. 相似文献
142.
Buzasi D Catanzarite J Laher R Conrow T Shupe D Gautier III Kreidl T Everett D 《The Astrophysical journal》2000,532(2):L133-L136
We have used the star camera on the Wide-Field Infrared Explorer satellite to observe the K0 III star alpha UMa, and we report the apparent detection of 10 oscillation modes. The lowest frequency mode is at 1.82 μHz, and it appears to be the fundamental mode. The mean spacing between the mode frequencies is 2.94 μHz, which implies that all detected modes are radial. The mode frequencies are consistent with the physical parameters of a K0 III star, if we assume that only radial modes are excited. Mode amplitudes are 100-400 μmag, which is consistent with the scaling relation of Kjeldsen & Bedding. 相似文献
143.
144.
Quaternary climate change and Heinrich events in the southern Balkans: Lake Prespa diatom palaeolimnology from the last interglacial to present 总被引:1,自引:0,他引:1
145.
Melanie Beck Jürgen Köster Bert Engelen Jan M. Holstein Antje Gittel Martin Könneke Thomas Riedel Kai Wirtz Heribert Cypionka Jürgen Rullkötter Hans-Jürgen Brumsack 《Ocean Dynamics》2009,59(2):371-383
Microbial activity in permeable tidal flat margin sediments is enhanced by two main processes. First, organic matter is supplied
by rapid sedimentation at prograding tidal flat margins. Second, surface and deep pore water advection lead to a replenishment
of the dissolved organic matter and sulfate pools. Increasing microbial activity towards the low water line is reflected in
sulfate and methane profiles as well as in total cell numbers, sulfate reduction rates, and remineralization products. The
impact of high sedimentation rates on pore water biogeochemistry is confirmed by inverse modeling reproducing the depth profiles
obtained by measurements. In central parts of the tidal flats, low sedimentation rates and pore water flow velocities limit
microbial activity despite the high availability of electron acceptors for microbial respiration such as sulfate. Therefore,
tidal flat margins with high microbial activity are of special importance for budgeting biogeochemical cycling in tidal flat
areas. 相似文献
146.
Nicole Kowalski Olaf Dellwig Melanie Beck Maik Grunwald Sibylle Fischer Maike Piepho Thomas Riedel Holger Freund Hans-Jürgen Brumsack Michael E. Böttcher 《Ocean Dynamics》2009,59(2):333-350
Tidal and seasonal behaviour of the redox-sensitive trace metals Mn, Fe, Mo, U, and V have been investigated in the open-water
column and shallow pore waters of the backbarrier tidal flats of the island of Spiekeroog (Southern North Sea) in 2002 and
2007. The purpose was to study the response of trace metal cycles on algae blooms, which are assumed to cause significant
changes in the redox state of the entire ecosystem. Trace metal data were complemented by measurements of nutrients and enumeration
of algae cells in 2007. Generally, Mn and V show a tidal cyclicity in the water column with maximum values during low tide
which is most pronounced in summer due to elevated microbial activity in the sediments. Mo and U behave almost conservatively
throughout the year with slightly increasing levels towards high tide. Exceptions are observed for both metals after summer
algae blooms. Thus, the seasonal behaviour of the trace metals appear to be significantly influenced by productivity in the
water column as the occurrence of algae blooms is associated with an intense release of organic matter (e.g. transparent exopolymer
particles, TEP) thereby forming larger organic-rich aggregates. Along with elevated temperatures in summer, the deposition
of such aggregates favours microbial activity within the surface sediments and release of DOC, nutrients and trace metals
(Mn, Mo and V) during the degradation of the aggregates. Additionally, pronounced reducing conditions lead to the reduction
of Mn(IV)-oxides and Fe(III)-(oxihydr)oxides, thereby releasing formerly scavenged compounds as V and phosphate. Therefore,
pore-water profiles show significant enrichments in trace metals especially from July to September. Finally, the trace metals
are released to the open water column via draining pore waters (esp. Mo, Mn, and V) and/or fixed in the sediment as sulphides
(Fe, Mo) and bound to organic matter (U). Non-conservative behaviour of Mo in oxygenated seawater, first observed in the investigation
area by Dellwig et al. (Geochim Cosmochim Acta 71:2745–2761, 2007a), was shown to be a recurrent phenomenon which is closely coupled to bacterial activity after the breakdown of algae blooms.
In addition to the postulated fixation of Mo in oxygen-depleted micro-zones of the aggregates or by freshly formed organic
matter, a direct removal of Mo from the water column by reduced sediment surfaces may also play an important role. 相似文献
147.
Andrea Lübben Olaf Dellwig Sandra Koch Melanie Beck Thomas H. Badewien Sibylle Fischer Rainer Reuter 《Ocean Dynamics》2009,59(2):263-275
The spatial and temporal distributions of chromophoric dissolved organic matter (CDOM) and dissolved organic carbon (DOC)
was studied in the East-Frisian Wadden Sea (Southern North Sea) during several cruises between 2002 and 2005. The spatial
distribution of CDOM in the German Bight shows a strong gradient towards the coast. Tidal and seasonal variations of dissolved
organic matter (DOM) identify freshwater discharge via flood-gates at the coastline and pore water efflux from tidal flat
sediments as the most important CDOM sources within the backbarrier area of the Island of Spiekeroog. However, the amount
and pattern of CDOM and DOC is strongly affected by various parameters, e.g. changes in the amount of terrestrial run-off,
precipitation, evaporation, biological activity and photooxidation. A decoupling of CDOM and DOC, especially during periods
of pronounced biological activity (algae blooms and microbial activity), is observed in spring and especially in summer. Mixing
of the endmembers freshwater, pore water, and open sea water results in the formation of a coastal transition zone. Whilst
an almost conservative behaviour during mixing is observed in winter, summer data point towards non-conservative mixing. 相似文献
148.
We examined the phylogeographic structure of two congeneric, direct-developing, intertidal whelks endemic to New Zealand, Cominella virgata and C. maculosa. A total of 855 specimens were collected from 23 rocky shore locations and we used them to determine the level of DNA sequence variation at the mitochondrial DNA (mtDNA) cytochrome c oxidase subunit I gene. Cominella virgata and C. maculosa have relatively high levels of haplotype diversity but low levels of nucleotide diversity. Sample sites formed regional groups that were composed of genetically differentiated populations, a finding consistent with their limited dispersal abilities. Cominella virgata showed higher levels of regional differentiation than C. maculosa, and there were also species-specific differences in genetic patterns within some regions. Both species exhibited genetic homogenisation among proximate sites within groups, suggesting some dispersal does occur between areas that are not connected by contiguous rocky shore habitat. 相似文献
149.
Thomas Soltwedel Nina Jaeckisch Nikolaus Ritter Christiane Hasemann Melanie Bergmann Michael Klages 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1856-1872
Five photographic transects, covering some 830 m2 of seafloor in total, were analyzed to characterize the megabenthic community along a bathymetric gradient covering water depths from 1200 to 5500 m in the eastern Fram Strait. Megafaunal densities ranged between 11 and 38 ind. m−2. The highest densities were found at 1650 m and the lowest densities occurred at 3000 m depth. The number of taxa and morphotypes ranged between 4 at 5500 m and 27 at 1650 m water depth. Ophiocten gracilis, a small white unidentified amphipod, Kolga hyalina, and Bathycrinus carpenteri were the dominant and characteristic species on the slope and continental rise. Elpidia heckeri dominated in the Molloy Hole, the deepest depression known in the Arctic Ocean. Megafaunal zonation patterns appeared to be mainly controlled by food availability, as indicated by phytodetrital matter measured at the seafloor, and by benthic biomass in the sediments, as indicated by sediment-bound particulate proteins and phospholipids. By contrast, physical factors, including water depth and seabed properties such as sediment porosity and hard substrata (e.g., dropstones), appear to play a secondary role in determining megabenthic zonation patterns along the bathymetric HAUSGARTEN gradient. 相似文献
150.
This paper reports on the outcomes of a project that engaged researchers and fishers together in adapting participatory social science approaches to the purposes and the constraints of community-based fisher organizations. The work was carried out in the Scotia-Fundy Region of Atlantic Canada (the Bay of Fundy and Scotian Shelf) between 1999 and 2003. After a period of reflection on what was collectively learned from our experiences in this project, the academics went back to the community partners in a recent workshop for further discussion and refinement of the lessons. We conclude that true participatory fishery research, utilized in support of community-based management, can be a particularly powerful tool. However, it has few effective shortcuts, it must deal early in the research process with power imbalances, and it should involve significant political engagement and empowerment through co-learning. This assessment of participatory research in coastal fisheries also has significant implications for how we think of social capital and on how we may develop community-based resource management for a sustainable future. 相似文献