ALBERT

Beschreibung: Zircon is a common mineral in continental crustal rocks. As it is not easily altered in processes such as erosion or transport, this mineral is often used in the reconstruction of geological processes such as the formation and evolution of the continents. Zircon can also survive under conditions of the Earth’s mantle, and rare cases of zircons crystallizing in the mantle significantly before their entrainment into magma and eruption to the surface have been reported1,2,3. Here we analyse the isotopic and trace element compositions of large zircons of gem quality from the Eger rift, Bohemian massif, and find that they are derived from the mantle. (U–Th)/He analyses suggest that the zircons as well as their host basalts erupted between 29 and 24 million years ago, but fragments from the same xenocrysts reveal U–Pb ages between 51 and 83 million years. We note a lack of older volcanism and of fragments from the lower crust, which suggests that crustal residence time before eruption is negligible and that most rock fragments found in similar basalts from adjacent volcanic fields equilibrated under mantle conditions. We conclude that a specific chemical environment in this part of the Earth’s upper mantle allowed the zircons to remain intact for about 20–60 million years.

Beschreibung: Piceamycin, a new macrolactam polyketide antibiotic, was detected by HPLC-diode array screening in extracts of Streptomyces sp. GB 4-2, which was isolated from the mycorrhizosphere of Norway spruce. The structure of piceamycin was determined by mass spectrometry and NMR experiments. It showed inhibitory activity against Gram-positive bacteria, selected human tumor cell lines and protein tyrosine phosphatase 1B. The Journal of Antibiotics (2009) 62, 513-518; doi:10.1038/ja.2009.64; published online 17 July 2009

Beschreibung: Seafloor vents spewing mineral-rich plumes of hydrothermal fluid — termed black smokers — can persist at mid-ocean ridges for decades or longer. Earthquake data indicate that ongoing magma injection may determine their locations.

Beschreibung: The enhanced Arctic warming over the past three decades is attracting much attention. Combining forward and inverse models with observations suggests that regional changes in aerosol concentrations have contributed significantly.

Beschreibung: The transport of warm and salty Indian Ocean waters into the Atlantic Ocean—the Agulhas leakage—has a crucial role in the global oceanic circulation1 and thus the evolution of future climate. At present these waters provide the main source of heat and salt for the surface branch of the Atlantic meridional overturning circulation (MOC)2. There is evidence from past glacial-to-interglacial variations in foraminiferal assemblages3 and model studies4 that the amount of Agulhas leakage and its corresponding effect on the MOC has been subject to substantial change, potentially linked to latitudinal shifts in the Southern Hemisphere westerlies5. A progressive poleward migration of the westerlies has been observed during the past two to three decades and linked to anthropogenic forcing6, but because of the sparse observational records it has not been possible to determine whether there has been a concomitant response of Agulhas leakage. Here we present the results of a high-resolution ocean general circulation model7, 8 to show that the transport of Indian Ocean waters into the South Atlantic via the Agulhas leakage has increased during the past decades in response to the change in wind forcing. The increased leakage has contributed to the observed salinification9 of South Atlantic thermocline waters. Both model and historic measurements off South America suggest that the additional Indian Ocean waters have begun to invade the North Atlantic, with potential implications for the future evolution of the MOC.

Beschreibung: The tectonically driven closure of tropical seaways during the Pliocene epoch (approx5–2 million years (Myr) ago) altered ocean circulation and affected the evolution of climate. Plate tectonic reconstructions show that the main reorganization of one such seaway, the Indonesian Gateway, occurred between 4 and 3 Myr ago. Model simulations have suggested that this would have triggered a switch in the source of waters feeding the Indonesian throughflow into the Indian Ocean, from the warm salty waters of the South Pacific Ocean to the cool and relatively fresh waters of the North Pacific Ocean. Here we use paired measurements of the delta18O and Mg/Ca ratios of planktonic foraminifera to reconstruct the thermal structure of the eastern tropical Indian Ocean from 5.5 to 2 Myr ago. We find that sea surface conditions remained relatively stable throughout the interval, whereas subsurface waters freshened and cooled by about 4 °C between 3.5 and 2.95 Myr ago. We suggest that the restriction of the Indonesian Gateway led to the cooling and shoaling of the thermocline in the tropical Indian Ocean. We conclude that this tectonic reorganization contributed to the global shoaling of the thermocline recorded during the Pliocene epoch, possibly contributing to the development of the equatorial eastern Pacific cold tongue.

Beschreibung: Oceanic fixed-nitrogen concentrations are controlled by the balance between nitrogen fixation and denitrification. A number of factors, including iron limitation, can restrict nitrogen fixation, introducing the potential for decoupling of nitrogen inputs and losses. Such decoupling could significantly affect the oceanic fixed-nitrogen inventory and consequently the biological component of ocean carbon storage and hence air–sea partitioning of carbon dioxide. However, the extent to which nutrients limit nitrogen fixation in the global ocean is uncertain. Here, we examined rates of nitrogen fixation and nutrient concentrations in the surface waters of the Atlantic Ocean along a north–south 10,000 km transect during October and November 2005. We show that rates of nitrogen fixation were markedly higher in the North Atlantic compared with the South Atlantic Ocean. Across the two basins, nitrogen fixation was positively correlated with dissolved iron and negatively correlated with dissolved phosphorus concentrations. We conclude that inter-basin differences in nitrogen fixation are controlled by iron supply rather than phosphorus availability. Analysis of the nutrient content of deep waters suggests that the fixed nitrogen enters North Atlantic Deep Water. Our study thus supports the suggestion that iron significantly influences nitrogen fixation5, and that subsequent interactions with ocean circulation patterns contribute to the decoupling of nitrogen fixation and loss.

Beschreibung: Caboxamycin, a new benzoxazole antibiotic, was detected by HPLC-diode array screening in extracts of the marine strain Streptomyces sp. NTK 937, which was isolated from deep-sea sediment collected in the Canary Basin. The structure of caboxamycin was determined by mass spectrometry, NMR experiments and X-ray analysis. It showed inhibitory activity against Gram-positive bacteria, selected human tumor cell lines and the enzyme phosphodiesterase.

Beschreibung: Gombapyrones A–D, new members of the α-pyrone family of secondary metabolites, were produced by Streptomyces griseoruber Acta 3662, which was isolated from bamboo tree rhizosphere. The strain was characterized by its morphological and chemotaxonomical features and by 16S rDNA sequencing as S. griseobuber. The gombapyrone structures were determined by mass spectrometry and by NMR experiments, and were found to have an inhibitory activity against protein tyrosine phosphatase 1B and glycogen synthase kinase 3β.