Archaea,the tree of life,and cellular evolution in eukaryotes

The early history of life harbours many unresolved evolutionary questions, none more important than the genomic origin and cellular evolution of eukaryotes. An issue central to eukaryote origin concerns the position of eukaryotes in the tree of life and the relationship of the host lineage that acquired the mitochondrion some two billion years ago to lineages of modern-day archaea. Recent analyses indicate that the host lineage branches within the Archaea, prompting the search for novel archaeal lineages that can improve our understanding of the cellular evolution of eukaryotes. Here we give a brief review of the studies on Archaea, the tree of life and the cellular evolution of eukaryotes, which is followed by an overview of recent progress fueled by new genomic technologies and recent status of archaeal research in China. Future directions for the study of early evolution are considered.     

The First Mesozoic Heterodactyl Bird from China

1 Introduction Enantiornithines were the dominant birds nearly worldwide throughout the entire span of the Cretaceous (Chiappe, 1995; Feduccia, 1996). The adaptive radiation of opposite birds is little known besides the disparity of rostral morphology in Boluochia (Zhou, 1995), Longipteryx (Zhang et al., 2001), Longirostravis ( Hou et al., 2004), and the presence of stomach contents that reflect a diversity of diets. Like the structure of rostrum, differentiation of the locomotor apparatu…     

Metamorphic Evolution of Iron-rich Mafic Cumulates from the Otztal-Stubai Crystalline Complex, Eastern Alps, Austria

Olivine-rich rocks containing olivine + orthopyroxene + spinel+ Ca-amphibole ± clinopyroxene ± garnet are presentin the central Ötztal–Stubai crystalline basementassociated with eclogites of tholeiitic affinity. These rockscontain centimetre-sized garnet layers and lenses with garnet+ clinopyroxene ± corundum. Protoliths of the olivine-richrocks are thought to be olivine + orthopyroxene + spinel dominatedcumulates generated from an already differentiated Fe-rich () tholeiitic magma that was emplaced into shallowcontinental crust. Protoliths of the garnet-rich rocks are interpretedas layers enriched in plagioclase and spinel intercalated ina cumulate rock sequence that is devoid of, or poor in, plagioclase.U–Pb sensitive high-resolution ion microprobe dating ofzircons from a garnet layer indicates that emplacement of thecumulates took place no later than 517 ± 7 Myr ago. Aftertheir emplacement, the cumulates were subjected to progressivemetamorphism, reaching eclogite-facies conditions around 800°Cand >2 GPa during a Variscan metamorphic event between 350and 360 Ma. Progressive high-P metamorphism induced breakdownof spinel to form garnet in the olivine-rich rocks and of plagioclase+ spinel to form garnet + clinopyroxene ± corundum inthe garnet layers. Retrogressive metamorphism at T 650–680°Cled to the formation of Ca-amphibole, chlorite and talc in theolivine-rich rocks. In the garnet layers, högbomite formedfrom corundum + spinel along with Al-rich spinel, Ca-amphibole,chlorite, aspidolite–preiswerkite, magnetite, ilmeniteand apatite at the interface between olivine-rich rocks andgarnet layers at P < 0·8 GPa. Progressive desiccationof retrogade fluids through crystallization of hydrous phasesled to a local formation of saline brines in the garnet layers.The presence of these brines resulted in a late-stage formationof Fe- and K-rich Ca-amphibole and Sr-rich apatite, both characterizedby extremely high Cl contents of up to 3·5 and 6·5wt % Cl, respectively. KEY WORDS: cumulates; Variscan metamorphism; SHRIMP dating; högbomite; saline brines     

Maximum extent of the Eurasian ice sheets in the Barents and Kara Sea region during the Weichselian

Based on field investigations in northern Russia and interpretation of offshore seismic data, we have made a preliminary reconstruction of the maximum ice-sheet extent in the Barents and Kara Sea region during the Early/Middle Weichselian and the Late Weichselian. Our investigations indicate that the Barents and Kara ice sheets attained their maximum Weichselian positions in northern Russia prior to 50 000 yr BP, whereas the northeastern flank of the Scandinavian Ice Sheet advanced to a maximum position shortly after 17 000 calendar years ago. During the Late Weichselian (25 000-10 000 yr BP), much of the Russian Arctic remained ice-free. According to our reconstruction, the extent of the ice sheets in the Barents and Kara Sea region during the Late Weichselian glacial maximum was less than half that of the maximum model which, up to now, has been widely used as a boundary condition for testing and refining General Circulation Models (GCMs). Preliminary numerical-modelling experiments predict Late Weichselian ice sheets which are larger than the ice extent implied for the Kara Sea region from dated geological evidence, suggesting very low precipitation.     

VARIATIONS OF SNOW DEPTH AND DURATION IN THE SWISS ALPS OVER THE LAST 50 YEARS: LINKS TO CHANGES IN LARGE-SCALE CLIMATIC FORCINGS

A study of snow statistics over the past 50 years at several climatological stations in the Swiss Alps has highlighted periods in which snow was either abundant or not. Periods with relative low snow amounts and duration are closely linked to the presence of persistent high surface pressure fields over the Alpine region during late Fall and in Winter. These high pressure episodes are accompanied by large positive temperature anomalies and low precipitation, both of which are unfavorable for snow accumulation during the Winter. The fluctuations of seasonal to annual pressure in the Alpine region is strongly correlated with anomalies of the North Atlantic Oscillation index, which is a measure of the strength of the westerly flow over the Atlantic. This implies that large-scale forcing, and not local or regional factors, plays a dominant role in controling the timing and amount of snow in the Alps, as evidenced by the abundance or dearth of snow over several consecutive years. Furthermore, since the mid-1980s, the length of the snow season and snow amount have substantially decreased, as a result of pressure fields over the Alps which have been far higher and more persistent than at any other time this century. A detailed analysis of a number of additional Alpine stations for the last 15 years shows that the sensitivity of the snow-pack to climatic fluctuations diminishes above 1750 m. In the current debate on anthropogenically-induced climatic change, this altitude is consistent with other studies and estimates of snow-pack sensitivity to past and projected future global warming.     

Ribbon sandstones in the Pennsylvanian Waddens Cove Formation, Sydney Basin, Atlantic Canada: the influence of siliceous duricrusts on channel-body geometry

Channelized bodies up to 9 m thick in the Pennsylvanian Waddens Cove Formation show low width: thickness ratios (8:1 to 14:1), up to four vertically stacked storeys, and deep incision into associated floodplain strata. The presence of lateral accretion sets up to 6 m thick indicates that the migration of bank-attached bars was a major channel-filling process. The progressive rise in elevation of the basal part of the accretion surfaces where the sets adjoin the steeply inclined sides of the channel bodies shows that the channel floor aggraded progressively as the bars approached the channel sides. In planform, the river system probably showed a low-sinuosity, incised valley within which the channel followed a more sinuous and partially confined course. The alluvium surrounding the channel bodies includes sandstone sheets attributed to crevasse splay and levee accumulation. The upper strata of many sheet's and some channel bodies contain siliceous duricrusts (ganisters) which formed by pedogenic lithification of sandy material commencing shortly after the landforms became inactive. The channel bodies contain duricrust-bearing slumpblocks and show stepped margins over duricrusts. The stepped nature of the banks suggests that duricrusts were an important factor in confining the reach, and we suggest that channel-body geometry was influenced, although not necessarily controlled, by the presence of the lithified layers. Alternation in the Waddens Cove Formation of grey, coal-bearing zones with red, duricrust-rich zones is attributed to water-table fluctuation in response to base-level changes. The low width: thickness ratios and aggradation mode'of the channel bodies may in part reflect channel incision and subsequent aggradation resulting from these allocyclic events.     

Holocene (Neoglacial) moraine and proglacial lake chronology, Barnes Ice Cap, Canada

Lichen diameters and radiocarbon dates from the western and southern margins of the Barnes Ice Cap yield a growth curve similar to that from southeastern Baffin Island. As a consequence, the moraine chronology of the northern and western Barnes Ice Cap needs revision, as does the chronology of the large proglacial lakes that existed north of the present Barnes Ice Cap. The revised chronology indicates that moraines were formed along the western margin of the Barnes Ice Cap during the following intervals: (1) less than 100 years ago; (2) 400–500 B.P.; (3) ca. 750 B.P.; (4) ca. 1000 B.P.; (5) ca. 1600 B.P.; (6) ca. 2100 B.P.; and (7) 2800 to 3100 B.P. As the western margin of the Barnes Ice Cap retreated, punctuated by stillstands and readvances, the northern margin of the Barnes Ice Cap lay athwart a series of westerly draining valleys, and a complex of proglacial lakes were dammed between the ice margin and the height of land. This sequence is traced by means of well-developed shorelines, lacustrine deltas, and spillways; specific lake levels are dated by lichenometry.
The Barnes Ice Cap moraine sequence is more complex than other Neoglacial records fringing mountain glaciers in Colorado, Alaska and Lappland. However, the chronology for the western Barnes Ice Cap closely resembles independent moraine chronology of mountain glaciers in Cumberland Peninsula, Baffin Island, and thus indicates that the difference between the Baffin Island climatic record and the general Neoglacial/Holocene climatic record (Denton & Karlén, Quaternary Research 7 , 1977) is real. Comparison of specific data from Swedish Lappland and Baffin Island shows substantial agreement. Although Neoglacial records may be globally synchronous, the case for a 2500 year periodicity of glacial fluctuations is not proven: a 300 to 600 year return interval is suggested for the period between 0 and 3000 B.P.     

Altimeter Signal-to-Noise for Deep Ocean Processes in Operational Systems

The ocean signal for this study is the sea surface height due to the slowly varying (greater than 5-day) ocean processes, which are predominantly the deep ocean mesoscale. These processes are the focus of present assimilation systems for monitoring and predicting ocean circulation due to ocean fronts and eddies and the associated environmental changes that impact real time activities in areas with depths greater than about 200 m. By this definition, signal-to-noise may be estimated directly from altimeter data sets through a crossover point analysis. The RMS variability in crossover differences is due to instrument noise, errors in environmental corrections to the satellite observation, and short time period oceanic variations. The signal-to-noise ratio indicates that shallow areas are typically not well observed due to the high frequency fluctuations. Many deep ocean areas also contain significant high frequency variability such as the subpolar latitudes, which have large atmospheric pressure systems moving through, and these in turn generate large errors in the inverse barometer correction. Understanding the spatial variations of signal to noise is a necessary prerequisite for correct assimilation of the data into operational systems.     

TEMPERATURE EFFECTS ON AIRGUN SIGNATURES1

Experiments in an 850 litre water tank were performed in order to study temperature effects on airgun signatures, and to achieve a better understanding of the physical processes that influence an airgun signature. The source was a bolt airgun with a chamber volume of 1.6 cu.in. The pressure used was 100 bar and the gun depth was 0.5 m. The water temperature in the tank was varied between 5°C and 45°C. Near-field signatures were recorded at different water temperatures. Typical signature characteristics such as the primary-to-bubble ratio and the bubble time period increased with increasing water temperature. For comparison and in order to check whether this is valid for larger guns, computer modelling of airguns with chamber volumes of 1.6 and 40 cu.in. was performed. In the modelling the same behaviour of the signatures with increasing water temperature can be observed. The increase in the primary-to-bubble ratio and the bubble time period with increasing water temperature can be explained by an increased mass transfer across the bubble wall.