4,345 research outputs found
Laterites and paleoclimates. Weathering processes and anthropogenic impact
The European Union of Geosciences held its 9th biannual meeting in Strasbourg, March 23â27, 1997. During this meeting, Symposium No. 63, Weathering Processes: Mineral deposits and soil formation in tropical enĂironments, was merged with Symposium No. 78, Anthropogenic Impact on Weathering processesco-sponsored by IGCP Project 405. The
resulting symposium No. 63, Weathering processes and Anthropogenic Impact, was held under the sponsorship
of EUROLAT1 and attracted 36 oral and poster presentations and about 100 participants, reflecting the interest of the Earth Sciences community in weathering processes and anthropogenic impact
Nuclear bars and blue nuclei within barred spiral galaxies
Multicolour near IR photometry for a sample of 32 large barred spiral
galaxies is presented. By applying ellipse fitting techniques, we identify
significant isophote twists with respect to the primary bar axis in the nuclear
regions of 70 \%\ of the sample. These twists are identified in galaxies
as late as SBbc and are clearly distinguishable from spiral arm morphology. At
most seven of the galaxies with isophote twists are inferred to possess
secondary (nuclear) bars, the axis ratios of which appear to correlate with
morphological type. The remainder may result from triaxial bulges, or from
oblate bulges misaligned with the primary bar. The near IR colour distributions
in these data show evidence for (red) circumnuclear star forming rings in 4
galaxies. The majority of the sample (19) also possess striking blue nuclear
regions, bluer than typical old stellar populations by 0.3 mag. in (J--H)
and 0.23 mag. in (H--K). Such blue colours do not appear to correlate
with the presence of nuclear rings or pseudo--rings, nor with the activity of
the host galaxy (as determined from emission--line spectroscopic
characteristics). Several mechanisms to explain this blue colour are
considered.Comment: 24 pages plain LaTex( including table captions), 5 tables and 18
figures. Accepted for publication in MNRAS. Paper and tables available via
anonymous ftp://143.167.4.101/pub/papers as sqiid-paper.tex and
table1,2,3.tex, table4.ps, table5.ps. Figures available as postcript upon
request to first Autho
A mesocosm experiment investigating the effects of substratum quality and wave exposure on the survival of fish eggs
In a mesocosm experiment, the attachment of bream (Abramis brama) eggs to spawning substrata with and without periphytic biofilm coverage and their subsequent survival with and without low-intensity wave exposure were investigated. Egg attachment was reduced by 73% on spawning substrata with a natural periphytic biofilm, compared to clean substrata. Overall, this initial difference in egg numbers persisted until hatching. The difference in egg numbers was even increased in the wave treatment, while it was reduced in the no-wave control treatment. Exposure to a low-intensity wave regime affected egg development between the two biofilm treatments differently. Waves enhanced egg survival on substrata without a biofilm but reduced the survival of eggs on substrata with biofilm coverage. In the treatment combining biofilm-covered substrata and waves, no attached eggs survived until hatching. In all treatments, more than 75% of the eggs became detached from the spawning substrata during the egg incubation period, an
Strontium as a tracer of weathering processes in a silicate catchment polluted by acid atmospheric inputs, Strengbach, France
This paper determines the weathering and atmospheric contributions of Ca in surface water from a small spruce forested silicate catchment (NâE France) receiving acid atmospheric inputs. The bedrock is a granite with K-feldspar and albite as dominant phases. The calcium content in plagioclase is low and the Ca/Na ratio in surface water is high, reflecting other sources of calcium from those expected from the weathering of major mineral phases. The biotite content is low. Only traces of apatite were detected while no calcite was found in spite of a major hydrothermal event having affected the granite. The strontium isotopic ratio 87Sr/86Sr and Sr content was used as a tracer of weathering and was determined in minerals and bulk bedrock, open field precipitation, throughfall, soil solution, spring and stream water. The Sr isotopic ratio of the reacting weathering end-member was predicted by simulating the alteration of the granite minerals by incorporating strontium into the waterârock interaction kinetic code KINDIS. In the early stages of waterârock interaction, K-feldspar and biotite strongly influence the isotopic composition of the weathering solution whereas, the Na-rich plagioclase appears to be the main long-term reactive weathering end-member. Approximately 50% of dissolved Sr in streamwater are atmospherically derived. The 87Sr/86Sr ratios of exchangeable Sr in the fine fraction at 1-m depth from a soil profile indicate that the amount of exchangeable Sr seems essentially controlled by atmospheric inputs. The exception is the deep saprolite where weathering processes could supply the Sr (and Ca). Na-Plagioclase weathering obviously control the chemistry and the isotopic composition of surface waters. The weathering of trace mineral plays a secondary role, the exception is for apatite when plagioclase is absent. Our hydrochemical, mineralogical and isotopic investigations show that a major part of the strong Ca losses detected in catchment hydrochemical budgets that result from the neutralization of acid precipitation has an atmospheric origin. Consequently, in the long term, in such areas, the availability of such an exchangeable base cation might be strongly limited and surface waters consequently acidified
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