Dieter Meischner

Three hundred eighty thousand year long stable isotope and faunal records from the Red Sea: Influence of global sea level change on hydrography

Stable isotope and faunal records from the central Red Sea show high-amplitude oscillations for the past 380,000 years. Positive δ18O anomalies indicate periods of significant salt buildup during periods of lowered sea level when water mass exchange with the Arabian Sea was reduced due to a reduced geometry of the Bab el Mandeb Strait. Salinities as high as 53‰ and 55‰ are inferred from pteropod and benthic foraminifera δ18O, respectively, for the last glacial maximum. During this period all planktonic foraminifera vanished from this part of the Red Sea. Environmental conditions improved rapidly after 13 ka as salinities decreased due to rising sea level. The foraminiferal fauna started to reappear and was fully reestablished between 9 ka and 8 ka. Spectral analysis of the planktonic δ18O record documents highest variance in the orbital eccentricity, obliquity, and precession bands, indicating a dominant influence of climatically - driven sea level change on environmental conditions in the Red Sea. Variance in the precession band is enhanced compared to the global mean marine climate record (SPECMAP), suggesting an additional influence of the Indian monsoon system on Red Sea climates.

Paleoenvironmental events during the last 13,000 years in the central Red Sea as recorded by pteropoda

A high-resolution record was obtained by investigating a sedimentary sequence from two cores taken in the central Red Sea (R/V Meteor cruise 5, leg 2). The numerical variations between nonmigratory and migratory pteropods and their stable isotopic record were studied together with variations in the carbonate and total organic carbon content in order to estimate changes in the structure of the water column during the last 13 kyr. The results indicate the existence of a highly stratified water column during deglaciation and early Holocene (13–8.5 ka). During this period the depth of the mixed layer varied between less than 50–100 m at most, and productivity was markedly reduced in comparison to the recent situation. The intermediate and deep water were constantly highly depleted in oxygen. A pronounced Younger Dryas event was recognized at 10.4 ka which coincides with an arid phase on the border land. The oxygenation of the intermediate water improved remarkably after 7.5 ka and peaked during the period between 4.6 and 2.0 ka. During this period the mixed layer reached its present depth and the productivity which was maximal during middle Holocene attained present level during the last 4.6 kyr.

Carbonate preservation and climatic changes in the central Red Sea during the last 380 kyr as recorded by pteropods

Numerical abundances of pteropods and planktic foraminifera, and the mode of pteropod preservation, were determined in core KL 11 taken from the central part of the Red Sea. The abundance of pteropods (shells/g dry sediment) was compared to that of planktic foraminifera (% Pt/Pf + Pt) — a technique that permits detection of changes in carbonate preservation for the last 380 kyr. The numerical abundance of pteropods is influenced by the properties of the water column, and preservation is influenced by the bottom water. During the last ∼ 200 kyr (except during isotope stage 5.5) carbonates are in general well preserved. During this period the abundance pattern of the pteropods and planktic foraminifera is very similar and follows the climatic signal of the Red Sea with high numbers during the interglacial stages, changing to very low numbers during glacial maximum conditions. The similar abundance trends of the two groups, and between them and the δ18O curve, indicates abundance is strongly linked to salinity. From isotope stage 6 to the bottom of the core the pteropods occur in low numbers, unlike the planktic foraminifera, which continue to display the high-amplitude glacial-interglacial cyclicity. The deviations, mainly during interglacial stages, between the abundance pattern of the two groups and the low % Pt/Pf + Pt values, indicate a significant change in carbonate preservation. Distinctive carbonate dissolution intervals are recognized in the Red Sea, correlating to large scale deep water dissolution events of the ‘mid-Brunhes dissolution cycle’ in the Indian Ocean. The anti-estuarine circulation pattern of the Red Sea prevents a direct connection between the deep water masses of the two oceans and rules out the likelihood that changes in the deep water circulation caused these carbonate dissolution events. The numerical variations between nonmigratory epipelagic and migratory mesopelagic pteropods were used to evaluate changes in the structure of the water column. Abundance maxima of mesopelagic pteropods, as in the recent Red Sea, indicate an aerated water column with ≥0.5 ml O2/l oxygen concentrations at the minimum zone. Mesopelagic abundance maxima coincide commonly with negative monsoonal index values indicating a more aerated water column connected to increasing aridity in the Red Sea region. Abundance maxima of epipelagic pteropods indicate a strongly stratified water column, at times causing severe depletion in oxygen at intermediate water depths. Epipelagic peak events coincide often with positive monsoon index values implying an overall milder and more humid climate in the Red Sea, probably associated with enhanced precessional-controlled southwest monsoon activity.

Response of Red Sea deep-water agglutinated foraminifera to water-mass changes during the Late Quaternary

Abstract The distribution of deep-water agglutinated foraminifera was determined in core material taken in the central Red Sea by the R/V Meteor , cruise 5, leg 2. The sedimentary record represents the last 380 kyr, which includes four glacial/interglacial cycles. The agglutinate assemblage is of low diversity, and in general is a minor component of the benthic foraminifera. It comprises 14 species belonging to the following genera: Ammobaculites, Lagenammina, Plotnikovina, Pseudogaudryina, Reophax, Sahulia, Siphotextularia, Spiroplectinella, Textularla and a doubtful genus of unknown taxonomic position: ‘ Psammosphaera ’. Three sub-groups were identified in the core according to their occurrence either in interglacial stages or in both glacial and interglacial intervals, reflecting mainly tolerance to salinity variations. Exceptional bottom-water conditions during the last 60 kyr caused a remarkable decrease in the abundance and diversity of this group. The development of dysaerobic bottom water between approx. 60 and 26 kyr, the presence of a deep-water mass of extremely high salinity (ca. 55%.) between 26 and 13 kyr, and the occurrence of anoxic bottom sediments between 12.9 and 9.6 kyr seem to have caused the extreme impoverishment. During the last 9.6 kyr the agglutinated foraminifera gradually recolonized the deep water. A diverse assemblage composed of the above mentioned genera is found in Holocene sediments only in the core top sample. In addition, small (63–149 μm), noncanaliculate organic cemented agglutinated foraminifera belonging to the genera Ammodiscus, Cribrostomoides, ‘Eggerella’, Glomospira, Haplophragmoides, Morulaeplecta, Spiroplectammina, Paratrochammina and Trochammina are preserved preferentially only in the uppermost part of the core (0–28 cm depth), in sediments younger than 3 kyr.

Gibt es rezente rot-sedimente in der Adria?

Abstract Are there recent red sediments in the Adriatic? Fossil marine red sediments are generally regarded as an indication of a warm paleoclimate with alternating wet and dry seasons. At the Istrian coast of the northern Adriatic Sea, terra rossa is transported into adjacent bays under the mediterranean climatic conditions. In spite of this it does not result in red sediments. The Limski Canal near Rovinj (Jugoslavia) offers an opportunity to study the sedimentary processes. Studies of sediment cores just after collecting as well as chemical and mineralogical analyses led to the conclusion that on the way from the original red soil to the final marine sediment the iron material of the terra rossa is dissolved and reprecipitated by at least two different processes: 1. ( 1 ) During fluviatile transportation and coastal erosion the hematite of the terra rossa is destroyed very rapidly. Reprecipitated Fe 3+ -hydroxides may age to goethite. 2. ( 2 ) The Fe 3+ -hydroxides carried to the sea bottom are gradually burrowed, thus reaching the zone of negative Eh and low pH conditions. Fe 3+ is reduced and partly fixed in Fe 2+ -minerals (siderite, pyrite), partly the Fe 2+ migrates following the concentration gradient to the sediment-water interface. Here it is re-oxidized and reprecipitated as Fe 3+ -hydroxides. Therefore no definite conclusion linking the final marine sediment with the state of oxidation and the climatic conditions under which the original material was formed is possible. In the opinion of the authors the marine diagenetic cycle of dissolution and reprecipitation is one of the most important factors in the distribution and enrichment of certain elements in marine sediments, especially with regard to iron, manganese and phosphorus.

Der pliozäne Teich von Willershausen am Harz

Willershausen liegt im westlichen Vorland des Harzes, mitten in Deutschland. Hier wurden bis 1975 von einer Ziegelei eine Tongrube und eine Sandgrube betrieben. Jahrzehntelang haben Privatsammler und Palaontologen aus einer einzelnen Karbonatbank im Ton aussergewohnlich gut erhaltene Fossilien geborgen.

Präparation von Wirbeltierknochen aus tonigen Sedimenten mittels Wasserstoffperoxyd

ZusammenfassungWasserstoffperoxyd läßt sich zur Reinigung von Wirbeltierknochen aus tonigen Sedimenten verwenden. Diese Methode arbeitet einfach, schnell, schonend, sauber, gründlich und billig. Sie kann schon im Gelände angewandt werden und Hinweise für die Grabung geben.

Aus der Praxis

ZusammenfassungGeschichte und Zustand der Göttinger paläontologischen Sammlung werden kurz referiert und die Notwendigkeit einer Originalkartei gezeigt. Aufbau und Organisation dieser Kartei werden an Hand von Abbildungen ausgefüllter Karteikarten geschildert. Die gesamte Form und Einzelheiten der Organisation werden begründet.