Die Entwicklung des Lebens im Präkambrium und seine geologische Bedeutung

Zusammenfassung Das Studium präkambrischer Lebensvorgänge und Organismen, das heute auch auf stabile biogene chemische Verbindungen (Chemofossilien) erweitert wird, erfordert eine genaue Zeitskala, besondere Forschungsmethoden und eine zweckmäßige Klassifikation. Die ersten 2000 Millionen Jahre des Lebens werden als die Zeit der Prokaryonten (Bakterien und Blaualgen) beschrieben. Die Entwicklung aller höherer Organismen (Eukaryonten) begann erst vor 1200–1400 Millionen Jahren. Während des Mittel- und Jungpräkambriums (und bis zum Ordovizium) bildeten Blaualgen und Bakterien vielfach biogen-sedimentäre Strukturen, die Stromatolithen, unter denen die säulenförmig-verzweigten Formen Anzeichen einer Evolution aufweisen. Wir können sie daher, mit entsprechenden Methoden, als wichtige Leitfossilien für die Gliederung und Korrelation präkambrischer Sedimentserien verwenden. Der evolutionäre Ursprung der vielzelligen Tiere (Metazoen), wohl von Algenkolonien, läßt sich wegen der Kleinheit und Hinfälligkeit der sie zusammensetzenden Zellgruppen nicht paläontologisch nachweisen. Erst größere Tiere, die widerstandsfähige Gewebe und eine genügend starke Muskulatur besitzen, können erkennbare Lebensspuren in Sedimentgesteinen hinterlassen. Die ältesten sicher bekannten und charakteristischen fossilen Metazoen sind etwa 600–650 Millionen Jahre alt. Sie besaßen noch keine Kalkschalen, aber morphologisch sind sie hoch entwickelt (Anneliden und primitive Arthropoden sind in der Ediacara-Fauna nachgewiesen), so daß eine längere Entwicklungsperiode der Metazoen anzunehmen ist, bevor sie als Zeitmarken des jüngsten Präkambriums stratigraphisch verwendbar werden.

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The study of Precambrian life processes and organisms which today extends to stable biogenic chemical compounds (chemical fossils), requires a precise time scale, special research methods, and an appropriate classification. The first 2000 million years of life comprise the time of the Prokaryota (bacteria and bluegreen algae). The evolution of all higher, eucaryote, organisms began 1200–1400 million years ago. During Middle and Late Precambrian (and until Ordovician) time, blue-green algae and bacteria built abundant biogenic-sedimentary structures, the stromatolites, of which the columnar-branching forms show indications of evolution. With suitable methods we can utilize them as important index fossils for subdivision and correlation of sequences of Precambrian strata. The evolutionary origin of Metazoa, presumably from algal colonies cannot be documented by fossils because of the small size and destructibility of such small groups of cells. Only larger animals, with resistant tissues and stronger muscles can leave recognizable trace fossils in sediments. The oldest known distinctive assemblage of fossil Metazoa is about 600–650 million years old. They did not form calcareous shells but morphologically they are advanced. Annelids and primitive arthropods occur in the Ediacara fauna. We have to assume a longer period of evolution for the Metazoa preceding their appearance as stratigraphic markers of the youngest Precambrian rocks.

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Résumé L'étude des organismes fossiles anté-cambriens et des molécules biogéniques stables dans les roches doit être basée sur une échelle géochronologique précise, sur des méthodes spécialisées et sur une propre classification systématique. Les 2 premiers milliards d'années de l'histoire de la vie sont le temps des bactéries et des algues bleues (procaryotes). L'évolution de tous les organismes possédant des cellules nuclées et des organelles (eucaryotes) commença il y a 1,2–1,4 milliards d'années. Les algues bleues et les bactéries formaient des édifices stromatolithiques pendant l'antécambrien moyen et supérieur et jusqu'à l'ordoviclen. A cause des processus évolutifs qui se produisaient pendant l'antécambrien, les stromatolithes en colonnes ramifiées peuvent servir comme fossiles indicateurs pour les corrélations des séries sédimentaires. Les animaux multicellulaires ont évolué probablement à partir des algues coloniales. Les premiers groupes de cellules, étant fragiles et de petite taille, ne pouvaient pas laisser de traces fossiles dans les roches. Les premiers animaux métazoaires fossiles étaient des organismes plus grands possédant des tissus résistants et une musculature assez puissante pour former dans les sédiments des traces de processus de leur vie (locomotion etc.). L'âge des plus anciens métazoaires characteristiques est 600–650 millions d'années. Ils ne possédaient pas encore de coquilles minéralisées. Ils étaient assez évolués (annélides et arthropodes primitives existaient dans la faune Édiacarienne) pour en justifier l'hypothèse d'un éspace de temps assez long précédant l'époque finale de l'antécambrien pour laquelle la faune Édiacarienne peut servir comme premier indice zonal biostratigraphique basé sur des animaux fossiles.

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Die Anomalie der Wassertemperatur und der Zirkulation im Nordpazifischen Ozean und an der Küste Perus im Jahre 1955

Zusammenfassung Die Anomalien der Wassertemperatur des Nordpazifik im Jahre 1955 stehen offensichtlich in Verbindung mit einer ausgeprägten Anomalie der atmosphärischen Zirkulation. Als Beleg dafür wird die Karte der mittleren Luftdruckabweichung 1955 gebracht. Anschließend werden die Verhältnisse an der peruanischen Küste besonders behandelt. Das Kaltwasser-Jahr 1955 war hier besonders ausgeprägt, war allerdings nur das Zentraljahr einer dreijährigen kalten Periode. Übernormale Windstärke (im Südostpassat) deutet auch hier auf eine Anomalie der atmosphärischen Zirkulation als Ursache der Erscheinung. Abschließend wird die langjährige Wassertemperatur-Reihe von Puerto Chicama (Peru) mitgeteilt.

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Some notes on the anomalies of sea surface temperatures and of atmospheric circulation observed in the north pacific ocean and on the coast of peru in 1955

Summary The anomalies of sea surface temperature observed in the North Pacific Ocean during the year of 1955 are, evidently associated with a pronounced anomaly of atmospheric circulation. A map showing the mean deviation of atmospheric pressure gives evidence of these correlations. The conditions on the coast of Peru is given special consideration. The cold-water-year 1955 is strongly marked, though being only the coldest year in a three years' period of low sea surface temperatures. Above-normal windforces associated with the south-east trade wind indicate that also here the cause of the phenomenon is to be sought in an anomaly of atmospheric circulation. At the end of the paper, a some thirty years' series of sea surface temperature observations from Puerto Chicama (Peru) is given.

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Notes sur les anomalies de la température des eaux superficielles et de la circulation atmosphérique dans l'océan Pacifique Nord et sur la côte du Pérou en 1955

Résumé Les anomalies de la température des eaux superficielles se sont évidemment trouvées être associées à des anomalies prononcées de la circulation atmosphérique. La carte de l'écart moyen de la pression atmosphérique en 1955, ci-inclus, en fait preuve. Les conditions rencontrées sur la côte du Pérou font l'objet d'une étude spéciale. L'année de 1955 qui montra des températures particulièrement basses n'était, cependant, que l'année la plus froide de trois années successives aux températures basses. La force anormale par excès du vent (associée aux alizés du sud-est) y indique, elle aussi, que l'anomalie de la circulation atmosphérique est la cause de ce phénomène. Une série d'observations de la température des eaux effectuée à Puerto Chicama (Pérou) pendant la période de 1925 à 1957 se trouve dans le tableau 12 à la fin de ce travail.

     

Dynamics of stationary wave anomalies during the 1986/87 El Niño

The dynamics of the wintertime atmospheric response to the 1986/87 El Niño SST anomalies is studied. A GCM used for this purpose simulates a wave train over the Pacific/North American (PNA) region that agrees closely in amplitude with that observed, but phase shifted 30° to the east. Linear baroclinic model experiments are performed in order to determine the origin of the GCM and observed stationary wave anomalies, with particular focus on the cause for GCM failure. Diagnostics with the linear model reveal that the GCM and observed wave train anomalies are maintained by very different processes. In the GCM, the forcing due to tropical diabatic heating and transient vorticity fluxes are equally important over the PNA region. In the observations, the transient vorticity fluxes assume the primary role. The cause for these discrepancies is traced to the different dynamic influences of suppressed rainfall near Indonesia. The associated diabatic cooling is found to excite a large amplitude wave train over the PNA region in the GCM, while no significant extratropical response to cooling is found in the observations. The combined effects of the diabatic cooling and the reorganization of the storm track transients by the remotely forced wave train acts to shift the GCM's wave train well to the cast of that observed. Due to uncertainties in the observed diabatic forcing, however, it is not clear to what extent the GCM's failure is due to errors in the simulated anomalous forcing and/or to the GCM's mean climate error.This paper was presented at the Second International Conference of Modelling on Global Climate Variability, held in Hamburg 7–11 September 1992 under the auspices of the Max Planck Institute for Meteorology. Guest Editor for these papers is L. Dümenil Correspondence to: M Ting     

AMS radiocarbon dating and varve chronology of Lake Soppensee: 6000 to 12000 14C years BP

For the extension of the radiocarbon calibration curve beyond 10000 ¹⁴C y BP, laminated sediment from Lake Soppensee (central Switzerland) was dated. The radiocarbon time scale was obtained using accelerator mass spectrometry (AMS) dating of terrestrial macrofossils selected from the Soppensee sediment. Because of an unlaminated sediment section during the Younger Dryas (10000–11000 ¹⁴C y BP), the absolute time scale, based on counting annual layers (varves), had to be corrected for missing varves. The Soppensee radiocarbon-verve chronology covers the time period from 6000 to 12000 ¹⁴C y BP on the radiocarbon time scale and 7000 to 13000 calendar y BP on the absolute time scale. The good agreement with the tree ring curve in the interval from 7000 to 11450 cal y BP (cal y indicates calendar year) proves the annual character of the laminations. The ash layer of the Vasset/Killian Tephra (Massif Central, France) is dated at 8230±140 ¹⁴C y BP and 9407±44 cal y BP. The boundaries of the Younger Dryas biozone are placed at 10986±69 cal y BP (Younger Dryas/Preboreal) and 1212±86 cal y BP (Alleröd/Younger Dryas) on the absolute time scale. The absolute age of the Laacher See Tephra layer, dated with the radiocarbon method at 10 800 to 11200 ¹⁴C y BP, is estimated at 12350 ± 135 cal y BP. The oldest radiocarbon age of 14190±120 ¹⁴C y BP was obtained on macrofossils of pioneer vegetation which were found in the lowermost part of the sediment profile. For the late Glacial, the offset between the radiocarbon (10000–12000 ^14C y BP) and the absolute time scale (11400–13000 cal y BP) in the Soppensee chronology is not greater than 1000 years, which differs from the trend of the U/Th-radiocarbon curve derived from corals.     

The transition from subduction to continental collision: crustal structure in the North Canterbury region, New Zealand

The North Canterbury region marks the transition from Pacific plate subduction to continental collision in the South Island of New Zealand. Details of the seismicity, structure and tectonics of this region have been revealed by an 11-week microearthquake survey using 24 portable digital seismographs. Arrival time data from a well-recorded subset of microearthquakes have been combined with those from three explosions at the corners of the microearthquake network in a simultaneous inversion for both hypocentres and velocity structure. The velocity structure is consistent with the crust in North Canterbury being an extension of the converging Chatham Rise. The crust is about 27 km thick, and consists of an 11 km thick seismic upper crust and 7 km thick seismic lower crust, with the middle part of the crust being relatively aseismic. Seismic velocities are consistent with the upper and middle crust being composed of greywacke and schist respectively, while several lines of evidence suggest that the lower crust is the lower part of the old oceanic crust on which the overlying rocks were originally deposited.
The distribution of relocated earthquakes deeper than 15 km indicates that the seismic lower crust changes dip markedly near 43S. To the south-west it is subhorizontal, while to the north-east it dips north-west at about 10. Fault-plane solutions for these earthquakes also change near 43S. For events to the south, P -axes trend approximately normal to the plate boundary (reflecting continental collision), while for events to the north, T -axes are aligned down the dip of the subducted plate (reflecting slab pull). While lithospheric subduction is continuous across the transition, it is not clear whether the lower crust near 43S is flexed or torn.     

A computer simulation study of Al/Si ordering in gehlenite and the paradox of the low transition temperature

The ordering of Al and Si in gehlenite is considered using computer simulation. The enthalpy of ordering ΔH per 2Al+2Si atoms is found to be 0.52 eV. It is dominated by the nearest neighbour interaction, but the analysis is carried out to fifth neighbours. The nearest neighbour interaction differs significantly from that for other materials. The structure does not have a connected network of ordering sites, which mainly accounts for the unobservably low transition temperature for Al/Si ordering. Two alternatives are given for the likely ordering pattern.     

The need for international co-operation in the management of coastal environments

The coastal zones are areas of high biological productivity and intense human pressure. Environmental challenges arise from pollution and from urban and industrial development. Administrative, social and legal challenges centre upon the need for sound management of coastal zone resources, as an important component of national strategies for sustainability. A number of specific actions have been set out in Agenda 21, the principal product of the Earth Summit held in Rio de Janeiro in 1992. But these need to be carried forward within cross-sectoral, integrated coastal area management procedures. International action is also needed because marine ecosystems rarely coincide with national boundaries, and are affected by international economic, social and legal decisions.

International scientific co-operation on marine issues is already well established, and many regional action plans and Conventions have been adopted. Technological co-operation is less advanced. Such efforts need to be intensified, and continuously adapted. Sound plans for the future must be based on good science, critical economic evaluation of resources, sensitive evaluation of social and cultural factors and of the needs of local communities, evaluation of the risks of climate change, sea-level rise and other changes, and monitoring as a basis for continuing adaptation.     

Distribution of attached algae in estuaries

Preliminary studies on distributions of attached algae in British estuaries suggest that the estuaries might be classified on the basis of the flora in the upper reaches. This could contribute to biological assessment of water quality in estuaries.