Beryllium isotopes of sediments from the Portuguese margin

A high resolution study of authigenic Be isotopes (10Be and 9Be) combined with continuous relative paleointensity records has been performed along the same marine sedimentary sequences from the Portuguese margin (NE Atlantic) covering the past 300 kyr in order to assess relationships between geomagnetic moment variations and 10Be production rate variations. A careful examination of the various ways of taking into account environmental disturbing effects on the authigenic 10Be concentration leads to the conclusion that the most reliable proxy of cosmonuclide production rates is presently the authigenic 10Be/9Be ratio. Eight intervals of significant authigenic 10Be/9Be enhancement evidence geomagnetic moment drops related to global paleomagnetic excursions, some being already admitted, others being proposed as new geomagnetic features. Since, unlike sedimentary magnetic remanence, the authigenic 10Be/9Be records dipole moment variations without significant acquisition delay, it provides better constraints on their timing. Comparison of 10Be/9Be and benthic delta18O records from the same cores suggests that dipole moment lows preferentially occurred during or at the end of interglacial episodes, with a quasi-period of 100 kyr.

Paleomagnetic and beryllium isotope record of West Equatorial Pacific sediments

The reliability of paleomagnetic records as proxies of the geomagnetic field intensity is still a matter of controversy since volcanic materials hardly provide continuous records, and marine sediments are suspected to carry a remanence biased by post-depositional realignments and/or by overprints. Such long standing debate emphasizes the need for the development of methods independent from paleomagnetism to decipher geomagnetic intensity variations. High resolution measurements of authigenic 10Be/9Be along with a detailed sedimentary record of directional and relative paleointensity variations evidence, over the 0.6-1.3 Ma time interval, frequent and recurrent excursions or short events in the late Matuyama and the early Brunhes epochs, among which two Brunhes-Matuyama reversal precursors and an intra-Jaramillo excursion. The results of this study confirm the idea of a highly unstable geomagnetic field as suggested by paleomagnetic evidences.

(Table 2) Concentration of heavy metals and organic carbon, and 210Pb activity of sediments near Büsum, eastern Wadden Sea

A 3.38 m long sediment core raised from the tidal flat sediments of the 'Blauortsand' in the Wadden Sea northwest of Büsum (Schleswig-Holstein, Germany) was analysed in order to investigate long term changes in sediment pollution with Pb, Cu, Zn and Cd. Comparison with the topographic maps since 1952 and 210Pb activity allowed a general dating of the sediment succession in the core. The heavy metal concentrations including 210Pb of the < 20 µm grain-size fraction in thick sediment slices below 1.30 m indicated background niveaus. Their values increased and reached modern levels in the upper sediment layers of the core above 1 m. The increments for Pb, Cu, Zn was 1 to 3 fold and Cd up to 11 fold since the second half of the 19th century. More investigations are needed to quantify the geographical extent and history of the contaminations shown in this pilot study.

Composition of bottom sediments and interstitial waters from the Gdansk Bay

Contents of mercury and zinc in reduced sediments and interstitial waters of the Gdansk Bay in the Baltic Sea were investigated. It was found that sediments contain 0.7 ppm Hg, of which 0.008 ppm.(0.4% of total) is dissolved in interstitial water, and 91 ppm Zn, of which 0.15 ppm (0.45% of total) is dissolved in interstitial water. Differences in contents in different layers (0-5 and 25-30 cm) can be attributed to anthropogenic influence. Aderage concentration of mercury in the upper sediment layer is 27% higher and one of zinc is 40% higher than those found in the lower sediment layer. In addition, distribution of zinc in grain size fractions of the sediments was investigated, and some data on cadmium content were obtained.