Age determination of sediment cores from the northern Mid-Atlantic Ridge

We construct age models for a suite of cores from the northeast Atlantic Ocean by means of accelerator mass spectrometer dating of a key core, BOFS 5K, and correlation with the rest of the suite. The effects of bioturbation and foraminiferal species abundance gradients upon the age record are modeled using a simple equation. The degree of bioturbation is estimated by comparing modeled profiles with dispersal of the Vedde Ash layer in core 5K, and we find a mixing depth of roughly 8 cm for sand-sized material. Using this value, we estimate that age offsets between unbioturbated sediment and some foraminifera species after mixing may be up to 2500 years, with lesser effect on fine carbonate (< 10 µm) ages. The bioturbation model illustrates problems associated with the dating of 'instantaneous' events such as ash layers and the 'Heinrich' peaks of ice-rafted detritus. Correlations between core 5K and the other cores from the BOFS suite are made on the basis of similarities in the downcore profiles of oxygen and carbon isotopes, magnetic susceptibility, water and carbonate content, and via marker horizons in X radiographs and ash beds.

X-ray fluorescence (XRF) measurements of two sediment cores from the Ceara Rise

Die XRF-Daten wurden an Archivhälften der Schwerelotkerne GeoB4402-2 und GeoB4407-3 erhoben, die am Nordwest-Hang des Ceará-Rückens gezogen wurden. Der Ceará-Rücken liegt im westlichen, äquatorialen Atlantik im Ablagerungsgebiet des Amazonas. Die Messdaten wurden mit dem XRF-Kern-Scanner "CORETEX (Corescanner Texel)" im Marum in Bremen erhoben, der auf dem Prinzip der Röntgenfluoreszenzanalyse beruht (gemessene Auflösung: 1 cm). Der Sedimenteintrag, speziell der Eintrag von terrigenem Material (durch Verwitterung entstandenes Material auf den Kontinenten), in die Ozeane ist ein immer noch schlecht verstandener Prozess, der aber für eine Vielzahl von geologischen Fragestellungen von entscheidender Bedeutung ist. Der terrigene Sedimenteintrag am Ceará-Rücken ist nahezu ausschließlich vom Amazonas geprägt. Die abgelagerten Sedimente auf dem Ceará-Rücken können als Zwei-Komponentensystem beschrieben werden. Eine Quelle ist der terrigene Eintrag aus dem Amazonas. Die zweite Quelle ist biogenes Kalziumkarbonat, dass vom kalkigen Plankton (vor allem Coccolithophoriden und zum Teil Foraminiferen) aus der oberen Wassersäule stammt. Heutzutage ist der westliche, tropische Atlantik die Hauptpassage des Transfers von warmem Oberflächenwasser vom Süd- in den Nordatlantik. Die Abgabe von Wärme und Feuchtigkeit aus den Tropen könnte im Zusammenhang mit kurzfristigen Klimawechseln stehen. Untersuchungen an Hand von Aufzeichnungen aus der nördlichen Hemisphäre weisen darauf hin, dass kurzfristige Klimaschwankungen der Nordhemisphäre zu Veränderungen der atmosphärischen Zirkulation in niedrigen Breiten auf einer Zeitskala von nur wenigen Tausenden Jahren führen können. Eine wichtige Frage dabei ist, wie der spätpleistozäne Eintrag von Terrigen-Material durch den Amazonas gesteuert ist durch Klimaschwankungen in den Tropen in Wechselwirkung mit den Vereisungs- und Abschmelzphasen der Nordhemisphäre. Hierbei sind sowohl die Glazial-Interglazial Zyklen als auch kurzfristige Klimaschwankungen wie die Dansgaard-Oeschger-Zyklen und die mit ihnen verbundenen Heinrich-Ereignisse von Bedeutung.

X-ray fotos of 10 sediment cores from the Baltic Sea

Various types of trace fossils have been studied on radiographs of sediment cores from the Western Baltic since the early nineteen sixties. lnvestigations on the endo- und epifauna including their habitats and population densities carried out independently by biologists helped to identify the processes of their formation and classify the structures. Biogenic traces are ubiquitous in both sandy and muddy sediments of the Great Belt, where the bottom waters are weil oxygenated through inflows from the North Sea (through Kattegat-Skagerrak). Almost all types of bioturbation structures encountered in the Kiel Bay are also observed in a variety of shapes and forms, and can be considered as representative for the Western Baltic area. Polychaetes, bivalves and echinoderms were recorded at the sediment surface of the cores, and also in living positions in the sediment. The different types of burrows having distint outlines ('trace fossis'), and those having indistinct outlines ('biodeformational strctures'), and their varying abundance encountered in the area have been linked, wherever possible, to the sediment type, and to the macro-benthos.

Planktic foraminiferal abundance and stable oxygen isotope ratios of sediment cores from the Southern California Borderlands

A variety of evidence suggests that average sea surface temperatures (SSTs) during the last glacial maximum in the California Borderlands region were significantly colder than during the Holocene. Planktonic foraminiferal delta18O evidence and average SST estimates derived by the modern analog technique indicate that temperatures were 6°-10°C cooler during the last glacial relative to the present. The glacial plankton assemblage is dominated by the planktonic foraminifer Neogloboquadrina pachyderma (sinistral coiling) and the coccolith Coccolithus pelagicus, both of which are currently restricted to subpolar regions of the North Pacific. The glacial-interglacial average SST change determined in this study is considerably larger than the 2°C change estimated by Climate: Long-Range Investigation, Mapping, and Prediction (CLIMAP) [1981]. We propose that a strengthened California Current flow was associated with the advance of subpolar surface waters into the Borderlands region during the last glacial.

Charcoal records of two sediment cores off SW Africa

We analyze sedimentary charcoal records to show that the changes in fire regime over the past 21,000 yrs are predictable from changes in regional climates. Analyses of paleo- fire data show that fire increases monotonically with changes in temperature and peaks at intermediate moisture levels, and that temperature is quantitatively the most important driver of changes in biomass burning over the past 21,000 yrs. Given that a similar relationship between climate drivers and fire emerges from analyses of the interannual variability in biomass burning shown by remote-sensing observations of month-by-month burnt area between 1996 and 2008, our results signal a serious cause for concern in the face of continuing global warming.