9th International Estuarine Biogeochemistry Symposium—Estuaries and enclosed seas under changing environmental conditions     

Gerhard Kattner  Christa Pohl 《Marine Chemistry》2007

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The postglacial history of three Picea species in New England, USA     

Matts Lindbladh  George L Jacobson Jr.Molly Schauffler 《Quaternary Research》2003,59(1):61-69

Given the difficulty of separating the three Picea species—P. glauca, P. mariana, and P. rubens (white, black, and red spruce)—in the pollen record, little is known about their unique histories in eastern North America following deglaciation. Here we report the first use of a classification tree analysis (CART) to distinguish pollen grains of these species. It was successfully applied to fossil pollen from eight sites in Maine and one in Massachusetts. We focused on the late glacial/early Holocene (14,000 to 8000 cal yr B.P.) and the late Holocene (1400 cal yr B.P. to present)—the two key periods since deglaciation when Picea has been abundant in the region. The result shows a shift from a Picea forest of P. glauca and P. mariana in the late glacial to a forest of P. rubens and P. mariana in the late Holocene. The small number of P. rubens grains identified from the late glacial/early Holocene samples (<5%) suggests that that species was either absent or rare at most of the sites. The occurrence and distribution of the three species do not reveal any geographic or temporal trend during late glacial time, but the data suggest that they were distributed in local patches on the landscape. The results of this study indicate that the recent population expansion of Picea (1000 to 500 cal yr B.P.) was likely the first time since deglaciation that P. rubens was abundant in the region.  相似文献   

Channel Bed Mobility Downstream from the Elwha Dams,Washington*     

Molly Pohl 《The Professional geographer》2004,56(3):422-431

Dams are a major source of fragmentation and degradation of rivers. Although substantial research has been conducted on the environmental impacts of large structures in the United States, smaller dams have received less attention. This study evaluated the impact of two dams of moderate size, the Elwha Dams, on the downstream channel system using field data collection at river cross‐sections. The relationship of average boundary shear stress (τ_o) to critical shear stress (τ_cr) served as the basis for determining channel bed material mobility under the two‐year and ten‐year flood events. The channel had the greatest channel bed mobility at the natural cross‐section upstream from the dams, low bed mobility between the structures, and an increase in channel bed mobility in the low gradient river segment near the mouth of the river. Low bed mobility tended to be associated with a lack of channel system complexity, including reduction or loss of bars and low alluvial terraces and their associated young riparian communities. Although these run‐of‐the‐river dams do not modify streamflow greatly, the loss of sediment from the channel system has had a substantial impact on bed mobility and geomorphic and biotic complexity of the Elwha River.  相似文献   

High-resolution rainfall variability simulated by the WRF RCM: application to eastern France     

Romain Marteau  Yves Richard  Benjamin Pohl  Carmela Chateau Smith  Thierry Castel 《Climate Dynamics》2015,44(3-4):1093-1107

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Pre-eruptive and syn-eruptive conditions in the Black Butte, California dacite: Insight into crystallization kinetics in a silicic magma system     

Molly C. McCanta  Malcolm J. Rutherford  Julia E. Hammer 《Journal of Volcanology and Geothermal Research》2007,160(3-4):263-284

A series of experiments and petrographic analyses have been run to determine the pre-eruption phase equilibria and ascent dynamics of dacitic lavas composing Black Butte, a dome complex on the flank of Mount Shasta, California. Major and trace element analyses indicate that the Black Butte magma shared a common parent with contemporaneously erupted magmas at the Shasta summit. The Black Butte lava phenocryst phase assemblage (20 v.%) consists of amphibole, plagioclase (core An_77.5), and Fe–Ti oxides in a fine-grained (< 0.5 mm) groundmass of plagioclase, pyroxene, Fe–Ti oxides, amphibole, and cristobalite. The phenocryst assemblage and crystal compositions are reproduced experimentally between 890 °C and 910 °C, ≥ 300 MPa, X_H2O = 1, and oxygen fugacity = NNO + 1. This study has quantified the extent of three crystallization processes occurring in the Black Butte dacite that can be used to discern ascent processes. Magma ascent rate was quantified using the widths of amphibole breakdown rims in natural samples, using an experimental calibration of rim development in a similar magma at relevant conditions. The majority of rims are 34 ± 10 μm thick, suggesting a time-integrated magma ascent rate of 0.004–0.006 m/s among all four dome lobes. This is comparable to values for effusive samples from the 1980 Mount St. Helens eruption and slightly faster than those estimated at Montserrat. A gap between the compositions of plagioclase phenocryst cores and microlites suggests that while phenocryst growth was continuous throughout ascent, microlite formation did not occur until significantly into ascent. The duration of crystallization is estimated using the magma reservoir depth and ascent rate, as determined from phase equilibria and amphibole rim widths, respectively. Textural analysis of the natural plagioclase crystals yields maximum growth rates of plagioclase phenocryst rims and groundmass microlites of 8.7 × 10^− 8 and 2.5 × 10^− 8 mm/s, respectively. These rates are comparable to values determined from time-sequenced samples of dacite erupted effusively from Mount St. Helens during 1980 and indicate that syneruptive crystallization processes were important during the Black Butte eruptive cycle.  相似文献   

Nicht senkrechte Schwingungsrichtungen bei der U-Tisch-Betrachtung von Calcit-Körnern     

R. Rath  D. Pohl 《Contributions to Mineralogy and Petrology》1970,29(1):74-75

Deviation of the extinction positions from 90° regarding calcite grains at the universal stage.  相似文献   

Zweiachsig erscheinende Calcite und Dolomite     

R. Rath  D. Pohl 《Contributions to Mineralogy and Petrology》1971,32(1):74-78

Zusammenfassung Die Zweiachsigkeit von Calciten und Dolomiten wird durch Zwillingslamellen erklärt. Die Größe des Achsenwinkels hängt vom Volumenanteil der gleich orientierten Lamellen und vom Zwillingswinkel ab. Die Doppelbrechung hat nur geringen Einfluß.

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Biaxial interference figures in calcite and dolomite

The biaxiality of calcites and dolomites is explained by twin lamellae. The amount of the axial angle depends from the part of volume built up by the lamellae of equal orientation, and from the twin angle. The birefringence is of minor influence.

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Optisches Verhalten lamellarer Verwachsungen     

B. Rath  D. Pohl 《Contributions to Mineralogy and Petrology》1971,33(3):239-244

Zusammenfassung Die zur Angabe des optischen Verhaltens von Calcit-Zwillingslamellen abgeleiteten Formeln werden auf den Fall gleichartig verwachsener Lamellen zweier verschiedener Mineralarten erweitert, deren gegenseitige Orientierung durch ein einziges Gesetz fixiert ist. Die Anwendung auf die fünf von Brown, Fyfe und Turner aufgestellten Verwachsungsgesetze teilweise in Calcit umgewandelten Aragonits favorisiert zwei.

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Optical behaviour of twin lamellae

The formulae for calculating the optical behaviour of calcite twin lamellae are extended to the case of lamellae, that belong to two different minerals, whose orientation is given by one law only. The application to aragonite partially inverted to calcite favours two of the five laws given by Brown, Fyfe and Turner.

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The Effect of Vegetation Productivity on Millet Prices in the Informal Markets of Mali, Burkina Faso and Niger     

Molly E. Brown  Jorge E. Pinzon  Stephen D. Prince 《Climatic change》2006,78(1):181-202

Systematic evaluation of food security throughout the Sahel has been attempted for nearly two decades. Food security analyses have used both food prices to determine the ability of the population to access food, and satellite-derived vegetation indices that measure vegetation production to establish how much food is available each year. The relationship between these two food security indicators is explored here using correspondence analysis and through the use of Markov chain models. Two sources of quantitative data were used: 8 km normalized difference vegetation index (NDVI) data from the Advanced Very High Resolution Radiometers (AVHRR) carried on the NOAA series of satellites, and monthly millet prices from 445 markets in Mali, Niger and Burkina Faso. The results show that the growing season vegetation production is related to the price of millet at the annual and the seasonal time scales. If the growing season was characterized by erratic, sparse rainfall, it resulted in higher prices, and well-distributed, abundant rainfall resulted in lower prices. The correspondence between vegetation production and millet prices is used to produce maps of millet prices for West Africa.  相似文献   

The exceptional Oder flood in summer 1997 — distribution patterns of the oder discharge in the Pomeranian Bight     

Herbert Siegel  Wolfgang Matthäus  Regina Bruhn  Monika Gerth  Günther Nausch  Thomas Neumann  Christa Pohl 《Ocean Dynamics》1998,50(2-3):145-167

The exceptional Oder flood in summer 1997 was a unique event in order to investigate the impacts on and the consequences for the ecosystem of the Baltic Sea of about 6.5 km³ additional water loaded with nutrients and contaminants and discharged within only 5 weeks. About 15 institutions participated in this investigation in both the Szczecin Lagoon and the Pomeranian Bight. The Baltic Sea Research Institute Warnemünde studied the water and nutrient inflow, the spreading of the Oder discharge, and the impact of the discharge on the ecosystem. The main topic of the presented investigations is a detailed study of the spatial and temporal spreading of the extreme river discharge in the Pomeranian Bight and the southern Baltic Sea by satellite data, ship observations and continuous buoy measurements as well as numerical modelling. The meteorological conditions were characterized by mainly easterly winds which guided the outflowing riverine water along the German coast into the Arkona Sea. The spatial and temporal development of the distribution patterns of the Oder discharge was monitored by about 80 Sea Surface Temperature (SST) images of NOAA satellites. Shipborne measurements showed that the vertical extent of the Oder plume ranged between 5 and 7 metres. The concentrations of inorganic nutrients, except higher silicate, were comparable to typical winter/early spring values (seasonal maximum) in this region. The high dilution effect of the flood water reduced the concentration of contaminants and thus, prevented a direct negative impact of trace metals and chlorinated organic compounds on the marine environment. Coupled physical-biochemical modelling in combination with SST-images demonstrated the temporal development and satellite data in the visible spectral range delivered the maximum extent of discharged river water into the southern Arkona Sea where a further western transport was limited by the upwelling region off Hiddensee. Thus, all detected effects of the Oder flood were confined to the Pomeranian Bight and the southern Arkona Sea, without long-term consequences for the ecosystem.  相似文献