Fluvial-aeolian sedimentary facies, Sossusvlei, Namib Desert

Sedimentary facies exert a primary control on sandstone diagenesis and reservoir quality. The Namib Sand Sea with its Sossusvlei playa-lake is often considered as a modern analogue for sandstone reservoirs. Remote sensing in combination with ground observations allowed us to map the facies distribution pattern of associated fluvial and aeolian sediments. Laboratory spectral signature measurements were used to further improve the separability of six major facies: modern aeolian sand, bypass surface, mud pool/mud drapes, heavy mineral lag, aeolian reworked and fossil dune remnant. Using a supervised classification algorithm trained by field observations, a combination of Principal Component Analysis, band ratios, texture and geomorphologic indices has shown the best result. This made it possible to create a map outlining the facies distribution pattern of the Sossusvlei area at a scale of 1:10 000. We propose this as a possible workflow to efficiently map and monitor desert environments and to investigate the interplay of aeolian and fluvial sediments, including their linked implications on diagenesis. This could improve paleoclimate modelling and even allow facies mapping on other planets

Comparative Analysis of Expressed Sequence Tag (EST) Libraries in the Seagrass Zostera marina Subjected to Temperature Stress

Global warming is associated with increasing stress and mortality on temperate seagrass beds, in particular during periods of high sea surface temperatures during summer months, adding to existing anthropogenic impacts, such as eutrophication and habitat destruction. We compare several expressed sequence tag (EST) in the ecologically important seagrass Zostera marina (eelgrass) to elucidate the molecular genetic basis of adaptation to environmental extremes. We compared the tentative unigene (TUG) frequencies of libraries derived from leaf and meristematic tissue from a control situation with two experimentally imposed temperature stress conditions and found that TUG composition is markedly different among these conditions (all P < 0.0001). Under heat stress, we find that 63 TUGs are differentially expressed (d.e.) at 25°C compared with lower, no-stress condition temperatures (4°C and 17°C). Approximately one-third of d.e. eelgrass genes were characteristic for the stress response of the terrestrial plant model Arabidopsis thaliana. The changes in gene expression suggest complex photosynthetic adjustments among light-harvesting complexes, reaction center subunits of photosystem I and II, and components of the dark reaction. Heat shock encoding proteins and reactive oxygen scavengers also were identified, but their overall frequency was too low to perform statistical tests. In all conditions, the most abundant transcript (3–15%) was a putative metallothionein gene with unknown function. We also find evidence that heat stress may translate to enhanced infection by protists. A total of 210 TUGs contain one or more microsatellites as potential candidates for gene-linked genetic markers. Data are publicly available in a user-friendly database at http://www.uni-muenster.de/Evolution/ebb/Services/zostera