Geochemistry and isotopic ratios of samples obtained during R/V Akademik Nikolaj Strakhov cruise ANS24

New petrological and geochemical data were obtained for basalts recovered during cruise 24 of the R/V "Akademik Nikolay Strakhov" in 2006. These results significantly contributed to the understanding of the formation of tholeiitic magmatism at the northern end of the Knipovich Ridge of the Polar Atlantic. Dredging was performed for the first time both in the rift valley and on the flanks of the ridge. It showed that the conditions of magmatism have not changed since at least 10 Ma. The basalts correspond to slightly enriched tholeiites, whose primary melts were derived at the shallowest levels and were enriched in Na and depleted in Fe (Na-TOR type). The most enriched basalts are typical of the earlier stages of the opening and were found on the flanks of the ridge in its northernmost part. Variations in the ratios of Sr, Nd, and Pb isotopes and lithophile elements allowed us to conclude that the primary melts generated beneath the spreading zone of the Knipovich Ridge were modified by the addition of the enriched component that was present both in the Neogene and Quaternary basalts of Spitsbergen Island. Compared with the primitive mantle, the extruding magmas were characterized by positive Nb and Zr anomalies and a negative Th anomaly. The formation of primary melts involved melting of the metasomatized depleted mantle reservoir that appeared during the early stages of opening of the Norwegian-Greenland Basin and transformation of the paleo-Spitsbergen Fault into the Knipovich spreading ridge, which was accompanied by magmatism in western Spitsbergen during its separation from the northern part of Greenland.

Stable isotopic record of planktonic foraminifera of the Pacific Ocean

We determined the d18O and d13C of individual Globigerinoides ruber and Pulleniatina obliquiloculata from sediment traps located from 5°N to 12°S along 140°W in the Pacific Ocean to evaluate the effects of varying [CO3=] on shell d18O and d13C. Variations in the offset between shell d13C and d13CDIC (Dd13Cs-DIC) are attributed to differences in [CO3]2-, temperature, and shell size between sample sites. When Dd13Cs-DIC of G. ruber was corrected for variations in [CO3]2- using the experimental slope of Bijma et al. (1998), the residual Dd13Cs-DIC was correlated with mixed layer temperature (+0.10±0.04 per mil °C**-1). The slope of this temperature effect is consistent with experimental results. In P. obliquiloculata, Dd13Cs-DIC and temperature were strongly anticorrelated (?0.14±0.03 per mil C**-1). We are unable to separate the influences of [CO3]2- and temperature in this species without independent experimental data. Correcting for [CO3]2- variability on d18Os of G. ruber improves the accuracy of estimated sea surface temperatures.

Neodymium isotopic data, radiocarbon dates and calibrated ages of sediment samples off the La Plata Estuary, southeastern South America

The continental margin off the La Plata Estuary (SE South America) is characterized by high fluvial sediment supply and strong ocean currents. High-resolution sediment-acoustic data combined with sedimentary facies analysis, AMS-14C ages, and neodymium isotopic data allowed us to reconstruct late Quaternary sedimentary dynamics in relation to the two major sediment sources, the La Plata Estuary and the Argentine margin. Sediments from these two provinces show completely different dispersal patterns. We show that the northward-trending La Plata paleo-valley was the sole transit path for the huge volumes of fluvial material during lower sea levels. In contrast, material from the Argentine margin sector was transported northwards by the strong current system. Despite the large sediment volumes supplied by both sources, wide parts of the shelf were characterized by either persistent non-deposition or local short-term depocenter formation. The location and formation history of these depocenters were primarily controlled by the interplay of sea level with current strength and local morphology. The high sediment supply was of secondary importance to the stratigraphic construction, though locally resulting in high sedimentation rates. Thus, the shelf system off the La Plata Estuary can be considered as a hydrodynamic-controlled end-member.