Late Quaternary vegetation changes around Lake Rutundu,Mount Kenya,East Africa: evidence from grass cuticles,pollen and stable carbon isotopes

Woody, subalpine shrubs and grasses currently surround Lake Rutundu, Mount Kenya. Multiple proxies, including carbon isotopes, pollen and grass cuticles, from a 755‐cm‐long core were used to reconstruct the vegetation over the past 38 300 calendar years. Stable carbon‐isotope ratios of total organic carbon and terrestrial biomarkers from the lake sediments imply that the proportion of terrestrial plants using the C₄ photosynthetic pathway was greater during the Late Pleistocene than in the Holocene. Pollen data show that grasses were a major constituent of the vegetation throughout the Late Pleistocene and Holocene. The proportion of grass pollen relative to the pollen from other plants was greatest at the last glacial maximum (LGM). Grass cuticles confirm evidence that C₄ grass taxa were present at the LGM and that the majority followed the cold‐tolerant NADP‐MEC₄ subpathway. Copyright © 2003 John Wiley & Sons, Ltd.     

Application of the global modal approach to the spiral galaxies

We have tested the applicability of the global modal approach in the density wave theory of spiral structure for a sample of spiral galaxies with measured axisymmetric background properties. We report here the results of the simulations for four galaxies: NGC 488, NGC 628, NGC 1566, and NGC 3938. Using the observed radial distributions for the stellar velocity dispersions and the rotation velocities we have constructed the equilibrium models for the galactic disks in each galaxy and implemented two kinds of stability analyses - the linear global analysis and 2D-nonlinear simulations. In general, the global modal approach is able to reproduce the observed properties of the spiral arms in the galactic disks. The growth of spirals in the galactic disks can be physically understood in terms of amplification by over-reflection at the corotation resonance. Our results support the global modal approach as a theoretical explanation of spiral structure in galaxies. This revised version was published online in August 2006 with corrections to the Cover Date.