Pollen analyses off Senegal: Evolution of the coastal palaeoenvironment during the last deglaciation

Pollen and dinoflagellate cysts from marine sediments in core A180-48 (15°19′N, 18°06′W; 2450 m water depth; 530 cm length) are used to reconstruct palaeoenvironmental conditions of nearshore tropical west Africa during the last deglaciation. High concentrations and influxes of pollen and dinoflagellate cysts between 11 000 and 10 000 yr BP are interpreted as reflecting an increase in continental trade-wind circulation and related coastal upwelling at 15°N latitude. The sea-surface temperature difference between glacial and interglacial times was not as strong as previously suggested. Together with local (fresh) ground-water input, this smaller temperature difference may explain the persistence of the Rhizophora mangrove and Guinean gallery forests near the shore until their massive extension during the early Holocene humid maximum around 9500 yr BP. Pollen data from the core are compared with data from Rosilda N110-Z, from the continental shelf at the same latitude.     

A new approach to define surface/sub-surface transition in gravel beds

The vertical structure of river beds varies temporally and spatially in response to hydraulic regime, sediment mobility, grain size distribution and faunal interaction. Implicit are changes to the active layer depth and bed porosity, both critical in describing processes such as armour layer development, surface-subsurface exchange processes and siltation/ sealing. Whilst measurements of the bed surface are increasingly informed by quantitative and spatial measurement techniques (e.g., laser displacement scanning), material opacity has precluded the full 3D bed structure analysis required to accurately define the surface-subsurface transition. To overcome this problem, this paper provides magnetic resonance imaging (MRI) data of vertical bed porosity profiles. Uniform and bimodal (?? _g = 2.1) sand-gravel beds are considered following restructuring under sub-threshold flow durations of 60 and 960 minutes. MRI data are compared to traditional 2.5D laser displacement scans and six robust definitions of the surface-subsurface transition are provided; these form the focus of discussion.     

The shape of the dark matter halo in the early-type galaxy NGC 2974

We present H  i observations of the elliptical galaxy NGC 2974, obtained with the Very Large Array. These observations reveal that the previously detected H  i disc in this galaxy is in fact a ring. By studying the harmonic expansion of the velocity field along the ring, we constrain the elongation of the halo and find that the underlying gravitational potential is consistent with an axisymmetric shape.
We construct mass models of NGC 2974 by combining the H  i rotation curve with the central kinematics of the ionized gas, obtained with the integral-field spectrograph SAURON. We introduce a new way of correcting the observed velocities of the ionized gas for asymmetric drift, and hereby disentangle the random motions of the gas caused by gravitational interaction from those caused by turbulence. To reproduce the observed flat rotation curve of the H  i gas, we need to include a dark halo in our mass models. A pseudo-isothermal sphere provides the best model to fit our data, but we also tested an NFW halo and modified Newtonian dynamics, which fit the data marginally worse.
The mass-to-light ratio M / L _I increases in NGC 2974 from 4.3 M_⊙/L_⊙, _I at one effective radius to 8.5 M_⊙/L_{⊙, I} at 5  R _e. This increase of M / L already suggests the presence of dark matter: we find that within 5  R _e at least 55 per cent of the total mass is dark.     

Insights into preservation of fossil plant cuticles using thermally assisted hydrolysis methylation

The chemical composition of Cretaceous leaf remains showing exceptionally well preserved cuticles was investigated using pyrolysis gas chromatography–mass spectrometry (Py-GC–MS) and thermally assisted hydrolysis methylation (THM)-GC–MS. Samples of Coniferales (Frenelopsis) and Ginkgoales (Nehvizdya penalveri) leaf remains were collected from freshwater and coastal marine depositional environments. Material for pyrolysis included (i) untreated leaves and cuticles obtained after extraction from mineral rock matrix and bleaching, (ii) kerogen fraction from both materials, (iii) non-hydrolysable fraction from kerogen. The THM-GC–MS data from untreated leaves and bleached cuticles show that the fossil cuticle geopolymer essentially released aliphatic components upon thermal treatment, with a dominance of fatty acids (FAs) and n-alkanes/n-alkenes. The FAs are essentially resistant to bleaching and remain after solvent extraction. They occur mainly as short chain compounds ranging from C₆ to C₁₆ and with maximum abundance at C₈–C₉. The n-alkanes/n-alkenes from kerogen and the non-hydrolysable residue occur mainly as short chain compounds in the range C₁₀–C₁₆, with the highest abundance at C₉–C₁₂. The THM-GC–MS pyrograms of the fossil cuticles differ from those of cutan from fresh living plants. They support the preservation model via polymerization of monomers derived from cutin or from unsaturated cell FAs.     

Stratification and water mass formation in the Arctic Ocean: some implications for the nutrient distribution

The mixing processes and the water formations (transformations) in the Arctic Ocean are reviewed and their influence on the stratification discussed. The relations between the stratification and the nutrient distribution are examined. The interactions between drifting sea ice and advected warmer and nutrient-rich waters favour an early biological activity. By contrast, in the central Arctic Ocean and over comparably deep shelf areas such as the northern Barents Sea, the possibilities for large productivity are more limited because of late melting, less nutrient supply, and in the central Arctic, less available light. The sedimentation of organic matter on the shelves and the remineralisation into cold, dense waters formed by brine rejection and draining off the shelves lead to a loss of nutrients to the deep waters, which must be compensated for by advection of nutrient rich waters to the Arctic Ocean.
Possible effects of a reduction of the river run-off on the stratification and the nutrient distribution are discussed.     

Une méthode de simulation de l'évolution des profils d'altération

Calculations of transfer of elements between minerals and aqueous solutions can be extended to water open systems. With this method, we can obtain steady state for water composition. Furthermore, evolution in space and time of a weathering profile can be computed.     

Embracing postcolonial geographies: Contributions by Dame Evelyn Stokes to the development of postcolonial geography in New Zealand

Abstract: This paper acknowledges Dame Evelyn Stokes’ introduction of postcolonial critical analysis of Māori/Pākehā relationships before postcolonialism was established as a field of theoretical enquiry. The paper reviews research I have done on some of the issues faced by the Mashantucket Pequots in the wider context of the contribution Dame Evelyn Stokes was making to similar debates in New Zealand. She emphasized that Māori research and knowledge provide a different world view and that this world view needs to be taken into account in any geographical study of New Zealand. Only in this way will it be possible to avoid the continued marginalization of Māoris from nation building in their own country.