The last forests on Antarctica: Reconstructing flora and temperature from the Neogene Sirius Group, Transantarctic Mountains

Fossil-bearing deposits in the Transantarctic Mountains, Antarctica indicate that, despite the cold nature of the continent’s climate, a tundra ecosystem grew during periods of ice sheet retreat in the mid to late Neogene (17–2.5 Ma), 480 km from the South Pole. To date, palaeotemperature reconstruction has been based only on biological ranges, thereby calling for a geochemical approach to understanding continental climate and environment. There is contradictory evidence in the fossil record as to whether this flora was mixed angiosperm-conifer vegetation, or whether by this point conifers had disappeared from the continent. In order to address these questions, we have analysed, for the first time in sediments of this age, plant and bacterial biomarkers in terrestrial sediments from the Transantarctic Mountains to reconstruct past temperature and vegetation during a period of East Antarctic Ice Sheet retreat. From tetraether lipids (MBT’/CBT palaeothermometer), we conclude that the mean continental summer temperature was ca. 5 °C, in agreement with previous reconstructions. This was warm enough to have allowed woody vegetation to survive and reproduce even during the austral winter. Biomarkers from vascular plants indicate a low diversity and spatially variable flora consisting of higher plants, moss and algal mats growing in microenvironments in a glacial outwash system. Abietane-type compounds were abundant in some samples, indicating that conifers, most likely Podocarpaceae, grew on the Antarctic continent well into the Neogene. This is supported by the palynological record, but not the macrofossil record for the continent, and has implications for the evolution of vegetation on Antarctica

Tandem application of C-C bond-forming reactions with reductive ozonolysis

Several variants of reductive ozonolysis, defined here as the in situ generation of aldehydes or ketones during ozonolytic cleavage of alkenes, are demonstrated to work effectively in tandem with a number of C-C bond-forming reactions. For reactions involving basic nucleophiles (1,2- addition of Grignard reagents, Wittig or Horner-Emmons olefinations, and directed Aldol reactions of lithium enolates) the one-pot process offers a rapid and high-yielding alternative to traditional two-step protocols

The Lc3-synthase gene B3gnt5 is essential to pre-implantation development of the murine embryo

BACKGROUND: Glycosphingolipids (GSL) are integral components of mammalian cell membranes that are involved in cell adhesion and cell signaling processes. GSL are subdivided into structural series, like ganglio-, lacto/neolacto-, globo- and isoglo-series, which are defined by distinct trisaccharide cores. The beta1,3 N-acetylglucosaminyltransferase-V (B3gnt5) enzyme catalyzes the formation of the Lc3 structure, which is the core of lactoseries derived GSL. RESULTS: The biological significance of the glycoconjugates produced by the B3gnt5 enzyme was investigated by inactivating the B3gnt5 gene in the mouse germline. The disruption of the B3gnt5 protein-coding region in mouse embryonic stem cells resulted in reduced Lc3-synthase activity, supporting its specific contribution to lactoseries derived GSL synthesis. Breeding of heterozygous mutant mice failed to produce any viable progeny homozygous for the B3gnt5-null allele. The genotypic examination of embryos from heterozygous crosses showed that the disruption of the B3gnt5 gene leads to pre-implantation lethality. This finding was compatible with the expression pattern of the B3gnt5 gene in the pre-implantation embryo as shown by in situ hybridization. The analysis of GSL profiles in embryonic stem cells heterozygous for the B3gnt5-null allele confirmed the reduced levels of lactoseries derived GSL levels and of other GSL species. CONCLUSION: The disruption of the B3gnt5 gene in mice affected the expression of lactoseries derived GLS and possibly of protein-bound beta3GlcNAc-linked glycans, thereby demonstrating an essential contribution of these glycoconjugates in early embryonic development, and supporting the importance of these glycoconjugates in cell differentiation and adhesion processes

Experimental-Evidence For Carbonate Stability In The Earths Lower Mantle

We present experimental results on the stability of carbonates up to 50 GPa and at high temperatures (1500-2500 K). The experiments were conducted in a laser-heated diamond anvil cell and the run products were characterized by analytical transmission electron microscopy. Dolomite is shown to break down to a CaCO3 + MgCO3 assemblage at pressures between 20 and 50 GPa. No decarbonatation was evident, suggesting that carbonates remain stable under these conditions with respect to rocksalt oxide + CO2 assemblages. Equimolar mixed powders of dolomite + enstatite and dolomite + olivine were transformed into magnesite + calcic perovskite and into magnesite + calcic and magnesian perovskites + magnesiowustite, respectively. The very strong partitioning of Ca in silicates suggests that magnesite is the stable carbonate in the presence of silicates in the Earth's lower mantle down to at least 1500 km. Finally, eutectoid or eutectic intergrowth of magnesiowustite and magnesite is observed, suggesting a possible mutual solubility between these two phases at high pressures and high temperatures. Lower mantle magnesiowustite may provide an alternative host for carbon in the Earth's lower mantle