High-resolution paleoecological analysis of recent disturbance in a southern Chilean Nothofagus forest

A 1600 year paleoecological record of environmental change is developed from a small lake in the Nothofagus forest of southern Chile (45.5°S, 72°W). High resolution fossil pollen, charcoal, sedimentological, and chrysophycean stomatocyst analyses are used to investigate the impacts of natural and anthropogenic disturbances on terrestrial and lacustrine environments. Chronological control is based on a combination of ²¹⁰Pb and ¹⁴C dating. Temporal resolution during the past 150–200 yr is ca. 8 yr/sample. The macroscopic charcoal record correlates very closely with historical and dendroecological records of 20th century anthropogenic burning in this region. The chrysophyte stratigraphy indicates that this burning had immediate impacts on the lake itself, while the pollen record provides evidence for a succession of vegetation changes lagging slightly behind the disturbance. These palynological changes are very similar to the pollen signal of European disturbance in northeastern North America. Pre-European shifts in chrysophyte assemblages may be due to the influence of earthquake activity on the lake, though there is no corroborative evidence in the pollen or charcoal records. This study demonstrates that high resolution paleoecological methods can be used to help bridge the temporal gap between traditional ecological and paleoecological studies of environmental change in the temperate forests of southern South America.     

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Solar and meteoritic abundance of silicon

Recent lifetime measurements on excited electronic states of neutral silicon (Beckeret al., Phys. Lett. In press, 1980) lead to a reassessment of widely used experimental transition probabilities Garz, Astron. Astrophys., 26, 471–477, 1973 of Si I lines. This translates into a 25% downward revision of the Si abundance determined from the solar spectrum.A solar atomic ratio, Si/Ca = 15.5 is inferred. This value coincides with that found in carbonaceous chondrites, but contrasts with ordinary and enstatite chondrites.     

Isotopic age and metamorphic history of the banded gneiss at Danmarkshavn,East Greenland

Along the northern part of the East Greenland coast the Caledonian structures are superimposed on an older fold system called the Carolinidian. Traces of this Carolinidian belt are preserved in a few isolated fragments within the Caledonian fold belt. According to Haller (1970) one of these fragments exhibiting the typical Carolinidian NNW to NW-trending infrastructural folds is the peninsula of Germania Land which is accessible near the Danish weather station Danmarkshavn. The rock sampled there is a banded gneiss of granodioritic composition with steeply inclined, NNW-trending layers. Isotopic age determinations yielded essentially two groups of ages: 1) 3,000±150 m.y. (zircon suite and Rb/Sr whole rock analyses of layers) and 2) 320–380 m.y. (Rb/Sr mineral isochrons, U-Th-Pb on sphene, K/Ar on hornblende and biotite). The egg-shaped zircons support a sedimentary origin of the banded gneiss and in conjunction with the Rb/Sr whole rock ages determine the age of formation of the banded gneiss (or its last high grade metamorphism) some 3,000 m.y. ago. No other Precambrian metamorphism or orogeny is recorded in the rock. The ages between 320–380 m.y. date a thermal event of lower amphibolite facies grade related to a late Caledonian spasm.The new isotopic data reveal the existence of very old rocks in the hinterland — away from the direction of thrusting—of the East Greenland Caledonian belt. With respect to the age of the Carolinidian fold system three geological interpretations are compatible with the results of this study:

Über die Vertikalverteilung und jahreszeitliche Entwicklung der Larvendichte vonDreissena polymorpha Pallas im Pelagial des unteren Zürichseebeckens im Jahre 1974

The freshwater musselDreissena polymorpha Pallas was sighted for the first time in Lake Zürich about 1969. This meant a real problem for the water treatment of lake water. By means of a pump and vertical net hauls it was tried to add more information to the scarce results on Lake Zürich. Additional dates about temperature, depth of Secchi disk visibility and beam transmittance were collected. There was a first appearance of the larvae ofD. polymorpha at the beginning of June. Following the mean temperature of the epilimnion the number of individuals/m² reached max. 210,000. The greatest concentration measured in 1974 of larvae/m³ was 54,375 at a depth of 4 m. The last appearance ofD. polymorpha was observed at the end of October.

     

Amethod of estimating leaf temperatures in a plant community

Summary A method was devised for using profiles of directional long-wave radiation to estimate plant radiating temperatures at any height in a crop. Limited testing of the method was carried out using tubular net radiometers which had one hemisphere covered by a radiation shield equipped with a temperature sensor.The results indicated that, in the absence of solar radiation, profiles of effective radiating temperature in a crop could be obtained to an accuracy of between 0.2 and 0.3°C at any level while day time values were of the order of 0.3 to 0.4°C.

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Eine Methode zur Abschätzung der Blattemperatur in einer Pflanzengemeinschaft

Zusammenfassung Es wurde eine Methode entwickelt, die es erlaubt, die Strahlungstemperatur von Pflanzen in beliebiger Höhe innerhalb eines Bestandes aus Profilen der langwelligen Strahlungsbilanz abzuschätzen. Eine beschränkte Zahl von Versuchen wurde ausgeführt, bei denen zylinderförmige Strahlungsbilanzmesser verwendet wurden, deren eine Hemisphäre durch einen Strahlungsschirm verdeckt war, an dem ein Temperaturmeßgerät angebracht war. Die Resultate zeigen, daß bei fehlender Sonnenstrahlung Profile der effektiven Strahlungs-temperatur in beliebiger Höhe innerhalb eines Bestandes bis zu einer Genauigkeit von 0.2 bis 0.3°C gemessen werden können. Untertags wurden Genauigkeiten von 0.3 bis 0.4° erzielt.

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With 2 Figures     

The mass and moment of inertia of the Earth

Recent revisions of geodetic and astronomical constants by the International Association of Geodesy and the International Astronomical Union lead to improved values for the earth's mass and moment of inertia. Corrections to be applied to these values before they are used as constraints in the inversion of seismic data are discussed.     

A Late‐glacial chironomid record from Hawes Water,northwest England

This paper presents the results of a high‐resolution Late‐glacial chironomid stratigraphy from Hawes Water, a small carbonate lake in northern Lancashire. The samples were from a core taken from the terrestrialised margin of the present lake, which represents an intermediate depth between the true littoral and the profundal. The chironomid assemblage showed a high degree of sensitivity to both broad‐scale and short‐term temperature changes. Comparison with an existing proxy temperature record (δ¹⁸O) for the site confirmed the presence of four temperature inversions within the Late‐glacial Interstadial. A mean July air temperature inference model, derived from acid, soft‐water lakes in Norway and Svalbard, was applied to the data. Despite the absence of carbonate lakes within the Norwegian training set, there was a close similarity between trends in estimated July air temperature and the δ¹⁸O trace, with a particularly strong correspondence in the periods of clay deposition. This suggests that this model is highly robust. The inferred maximum Interstadial temperature was 13.4°C, dropping initially to 7.5°C in the Loch Lomond Stadial. Temperatures reach a maximum of nearly 10°C in this period, cool for a short period before rising rapidly to 13.2°C at the start of the Holocene. These temperatures are similar to but slightly higher than those estimated for Whitrig Bog, southeast Scotland, and lower than those inferred from coleopteran‐based models for sites in South Wales. Copyright © 2004 John Wiley & Sons, Ltd.     

Saturn eddy momentum fluxes and convection: First estimates from Cassini images

We apply an automated cloud feature tracking algorithm to estimate eddy momentum fluxes in Saturn's southern hemisphere from Cassini Imaging Science Subsystem near-infrared continuum image sequences. Voyager Saturn manually tracked images had suggested no conversion of eddy to mean flow kinetic energy, but this was based on a small sample of <1000 wind vectors. The automated procedure we use for the Cassini data produces an order of magnitude more usable wind vectors with relatively unbiased sampling. Automated tracking is successful in and around the westward jet latitudes on Saturn but not in the vicinity of most eastward jets, where the linearity and non-discrete nature of cloud features produces ambiguous results. For the regions we are able to track, we find peak eddy fluxes and a clear positive correlation between eddy momentum fluxes and meridional shear of the mean zonal wind, implying that eddies supply momentum to eastward jets and remove momentum from westward jets at a rate . The behavior we observe is similar to that seen on Jupiter, though with smaller eddy-mean kinetic energy conversion rates per unit mass of atmosphere (). We also use the appearance and rapid evolution of small bright features at continuum wavelengths, in combination with evidence from weak methane band images where possible, to diagnose the occurrence of moist convective storms on Saturn. Areal expansion rates imply updraft speeds of over the convective anvil cloud area. As on Jupiter, convection preferentially occurs in cyclonic shear regions on Saturn, but unlike Jupiter, convection is also observed in eastward jet regions. With one possible exception, the large eddy fluxes seen in the cyclonic shear latitudes do not seem to be associated with convective events.