ALBERT

Description: Petrological, geochemical, and geophysical gradients along the SE volcanic zone in Iceland imply systematic variations in melting and crystallization conditions and in magma supply and eruption rates. At the southern tip of the zone, in Vestmannaeyjar, alkali basalt magmas are generated by small degrees of melting under a thick lithosphere. Farther north, in the Hekla-Katla region, greater degrees of melting result in the generation of transitional basalt magmas. Magma supply rates exceed eruption rates, and melts begin to accumulate at the base of the crust, as indicated by magnetotelluric evidence. Uniform rare earth element patterns in the Hekla-Katla basalts may be explained by homogenization in the melt accumulation zone or by uniform melting conditions. Infrequent replenishment of magma reservoirs in this region leads to mixing of compositionally diverse magmas and, consequently, to basalts with diverse phenocryst compositions and textures. Even farther north, in central Iceland, the melting anomaly associated with the SE zone has developed to the same degree as it has beneath the SW axial rift zone, leading to similar magmatic conditions. High magma supply rates and low cooling rates inhibit fractionation and lead to the eruption of voluminous olivine tholeiites. In these areas a broad spectrum of melt compositions is generated by variable degrees of melting over a wide depth range. The compositional diversity, e.g., in large ion lithophile element enrichment, is masked somewhat by reequilibration and mixing of melts on ascent and in the melt accummulation zone. Compositional diversity may be preserved, however, in the melt accummulation zone in a lateral direction away from the rift axis since distal parts of the melt zone are fed only by melts segregating at greater depths. The variations in magmatic conditions along the SE zone, which are analogous to those inferred along propagating rifts, may be related to a mantle blob that ascended beneath central Iceland 2–3 m.y. ago, spread out laterally and triggered a southward propagating rift.

Description: For over thirty years man has studied “outer space” and installed satellites which watch the surface of the Earth. The great depths of the world ocean are, however, practically unknown and there is an urgent need to put abyssal benthic laboratories into “inner space” in order to study basic phenomena of interest to marine science and climatology as well as man's impact on the oceans. In view of the numerous problems related to global change, as a first step emphasis should first be on the role of the oceans and their inherent processes, which are the focus of such international programmes as the World Ocean Circulation Experiment (WOCE) and the Joint Global Ocean Flux Study (JGOFS). Multi-disciplinary registration of key events at selected key sites investigating the variability in time and space are of the utmost importance. The same methods and techniques must be used for the study of human impacts on the deep oceans caused by mining of metalliferous resources and by waste disposal as well as in basic studies. However, the investigation of the inner space of our planet has certain requirements. As long-term and large-scale investigations become more and more important, development of automized systems, largely independent from research vessels will be required. This will demand high capacities of energy for all technical functions as well as high storage capacities for data and samples. As a consequence the needs for two different—although overlapping—functional approaches are defined for future deep-sea deployments. (A) A system for long-term registration of the natural variability and long-term monitoring of human impacts: (B) A system for short-term observations and short-time experimentations. This report summarizes their technological demands. The envisioned interdisciplinary technology should deliver information on physical, biological and geochemical processes and their variabilities in the deep oceans. The prospected systems need to have the ability for real time video observation, data transfer and experimental manipulation, as well as sensing and sampling facilities with large storage capacities for long-term deployments. Prospective costs of the described multipurpose abyssal benthic laboratory will presumably exceed the funds for deep-sea research of a single country. A joint European effort could solve this problem and help to manifest a leading role for European marine science in international deep-sea and global change research.

Description: Die Genese der Maare wird hauptsächlich an Beispielen aus der Eifel erläutert. Die Maarkessel sind durch phreato-magmatische Explosionen entstanden . Es werden die hydrologischen Voraussetzungen für diese Prozesse erörtert. Ob ein lavafördernder Vulkan oder ein Maar entsteht, hängt nicht von der Stellung zum Gewässernetz ab, sondern von Vorgängen im Magmenreservoir. Voraussetzung für die Entstehung von Maaren ist die Existenz von Tuffschloten. Wenn in solche Tuffschlote die Rinnsale kleinerer Täler hineinfließen, kommt es zu phreatischen Explosionen in geringer Tiefe (wohl nicht tiefer als 50 m). Dadurch bilden sich Sprengtrichter von wenigen Hundert m Durchmesser mit gleichmäßigen Tuffwällen. Größere Bäche oder Flüsse können tiefer in die Tuffschlote hinabfließen, so daß erst in etwa 300-500 m Tiefe die Explosionen ausgelöst werden. Da in diesem Fall mehr Wasser mit mehr heißem Gestein in Berührung kommt, werden die Explosionen heftiger, können aber keinen Trichter nach oben durchbrechen. Das in der Explosionskammer zertrümmerte Gestein wird durch enge Kanäle in mehreren Strahlen hinausgepreßt, so daß kilometerweite schmale Tuffbahnen entstehen. In den durch die Dampfexplosion erzeugten Hohlraum brechen große Schollen aus dem Dach ein. Es kann durch die Explosionen ein Sog den Schlot hinab entstehen, der sich in große Tiefen fortpfanzt, so daß ultrabasische Gesteine mit nach oben gerissen werden (Meerfelder Maar und Dreiltt Weiher in der Eifel). Das Grundwasser im Schiefergebirge dürfte nicht ausreichen, um phrealilchc Explosionen zu erzeugen. Die Tuffschlote und damit auch die Maare haben innerhalb der Vulkanfelder eine Randposition, die lavafördernden Vulkane herrschen dagegen in den Zentren vor; das läßt sich außer in der Westeifel auch deutlich an der Chaine des Puys in der Auvergne zeigen.

Description: The Deep Basin Experiment (DBE) is an international effort and apart of the World Ocean Circulation Experiment with the principal objective of improving our knowledge of the subthermocline circulation. The DBE fieldwork is focussed on the Brazil Basin and this report is concemed with a moored array situated along its southem boundary which was installed in early 1991 to measure the inflow and outflow to the Basin and to investigate the Brazil Current near 30S. This moored array was a joint undertaking by the Institut für Meereskunde of the University of Kiel and the Woods Hole Oceanographic Institution. Moorings were deployed on Meteor Cruise 15, leg I and retrieved on Meteor cruise 22, legs 3 and 4. A total of 57 conventional current meters and two Acoustic Doppler Current Profilers were set on 13 moarings with some concentration within the Brazil Current and the Vema Channel. CTDs were taken at each mooring site as well as in between. Some of the recovered instruments were reset in the Hunter Channel, a suspected additional connection between the Argentine Basin and the Brazil Basin. A later report will summarize this data after it is recovered in May 1994.

Description: Intact sediment cores from the Vøring-Plateau (Norwegian Sea) were incubated under in situ temperature on board ship with and without the addition of natural detritus to follow the reaction of deep-sea benthic microbial communities to nutrient enrichment. Concentration and enzymatic decomposition of organic material, total microbial number, biomass and production were followed in timecourse experiments. The addition of decomposable organic material caused an immediate stimulation of microbial metabolic processes: following the induction of enzymatic activity, microbial biomass production increased. During the initial period of incubation metabolic processes were also stimulated in the untreated "control" sediments. This "incubation effect" competed with the "feeding effect" caused by the enrichment with organic material.

Description: The simultaneous incorporation of radiolabelled thymidine and leucine was followed in intact muddy sand sediments from the North Sea. As it could be shown, incorporation activities covaried over sediment depth. Parallel analysis of the enzymatic decomposition of organic material (by means of the hydrolysis of fluoresceindiacetate) revealed that stimulations of microbial biomass production coincided with stimulations of enzymatic activities although maxima of both processes occurred at different sediment depths.