Do carbonate liquids become denser than silicate liquids at pressure? Constraints from the fusion curve of K<Subscript>2</Subscript>CO<Subscript>3</Subscript> to 3.2 GPa

Brackets on the melting temperature of K₂CO₃ were experimentally determined at 1.86 ± 0.02 GPa (1,163–1,167°C), 2.79 ± 0.03 GPa (1,187–1,195°C), and 3.16 ± 0.04 GPa (1,183–1,189°C) in a piston-cylinder apparatus. These new data, in combination with published experiments at low pressure (<0.5 GPa), establish the K₂CO₃ fusion curve to 3.2 GPa. On the basis of these experiments and published thermodynamic data for crystalline and liquid K₂CO₃, the high-pressure density and compressibility of K₂CO₃ liquid were derived from the fusion curve. The pressure dependence of the liquid compressibility (K′₀ = dK ₀/dP, where K ₀ = 1/β₀) is between 16.2 and 11.6, with a best estimate of 13.7, in a third-order Birch–Murnaghan equation of state (EOS). This liquid K′₀ leads to a density of 2,175 ± 36 kg/m³ at 4 GPa and 1,500°C, which is ∼30% lower than that reported in the literature on the basis of the falling-sphere method at the same conditions. The uncertainty in the liquid K′₀ leads to an error in melt density of ± 2% at 4 GPa; the error decreases with decreasing pressure. With a K′₀ of 13.7, the compressibility of K₂CO₃ at 1,500°C and 1 bar (K ₀ = 3.8 GPa) drops rapidly with increasing pressure ( ), which prevents a density crossover with silicate melts, such as CaAlSi₂O₈ and CaMgSi₂O₆, at upper mantle depths.     

Biomass estimation using Landsat-TM and -ETM+. Towards a regional model for Southern Africa?

Grazing and fire are major factors influencing the savanna ecosystems of Southern Africa. In both grazing and conservation areas overgrazing is an important reason for degradation of vegetation and soil. Insufficient fire management can cause a change in the species composition and may influence the soil negatively. For adequate planning purposes the knowledge of available biomass is indispensable. High-resolution satellite systems can provide such knowledge on a large scale. Three study areas in Southern Africa contributed to a first survey. Gutu District is situated in Zimbabwe. In its Communal Lands a high population density leads to severe degradation of vegetation and soil. The South African test sites are located in Kruger National Park and Madikwe Game Reserve. Therefore a wide ecological range from highly degraded to slightly disturbed savanna ecosystems is included. Satellite images of both Landsat-5 (TM) and Landsat-7 (ETM+) were applied. After cross-calibration of the two different satellite systems, indices applied to radiance and reflectance showed significant correlations with ground truth data of grass and other foliage biomass. Including new data from Hluhluwe National Park (South Africa) into the regression models improved the results, indicating that a regional model for savanna ecosystems in Southern Africa could be found. This revised version was published online in August 2006 with corrections to the Cover Date.     

A complete sea-breeze circulation cell derived from aircraft observations

Using an instrumented aircraft, a complete sea-breeze circulation cell was sampled from its offshore end to the sea-breeze front over land and up to a height of approximately 1000 m AMSL. Many of its typical features can be resolved in detail mainly by cross-sectional analysis. These are: the diverging onshore flow in the lower layers over the sea the convergence over land at the seabreeze front and the connected cross-frontal circulation, a distinct return flow in the upper layers, the propagation of the seaward end of the cell over water, as well as the propagation of the front over land, the baroclinicity as a driving mechanism of the cell and also budget and frontogenesis terms.     

Precession‐scale cyclicity in the fluvial lower Eocene Willwood Formation of the Bighorn Basin,Wyoming (USA)

Little is known about controls on river avulsion at geological time scales longer than 10⁴ years, primarily because it is difficult to link observed changes in alluvial architecture to well‐defined allogenic mechanisms and to disentangle allogenic from autogenic processes. Recognition of Milankovitch‐sale orbital forcing in alluvial stratigraphy would provide unprecedented age control in terrestrial deposits, and also exploit models of allogenic forcing enabling more rigorous testing of allocyclic and autocyclic controls. The Willwood Formation of the Bighorn Basin is a lower Eocene fluvial unit distinctive for its thick sequence of laterally extensive lithological cycles on a scale of 4 to 10 m. Intervals of red palaeosols that formed on overbank mudstones are related to periods of relative channel stability when gradients between channel belts and floodplains were low. The intervening drab, heterolithic intervals with weak palaeosol development are attributed to episodes of channel avulsion that occurred when channels became super‐elevated above the floodplain. In the Deer Creek Amphitheater section in the McCullough Peaks area, these overbank and avulsion deposits alternate with a dominant cycle thickness of ca 7·1 m. Using integrated stratigraphic age constraints, this cyclicity has an estimated period of ca 21·6 kyr, which is in the range of the period of precession climate cycles in the early Eocene. Previous analyses of three older and younger sections in the Bighorn Basin showed a similar 7 to 8 m spacing of red palaeosol clusters with an estimated duration close to the precession period. Intervals of floodplain stability alternating with episodes of large‐scale reorganization of the fluvial system could be entirely autogenic; however, the remarkable regularity and the match in time scales documented here indicate that these alternations were probably paced by allogenic, astronomically forced climate change.     

Swash zone sediment transport modes

The result of field experiments, designed to investigate the relative proportions of bedload and suspended load, are described. The ratio of bedload to suspended sediment load in the swash zone is examined in both swash and backwash on four beaches by measuring the amounts collected in a sediment trap. Bedload transport is found to dominate the backwash. The relative proportions of bedload and suspended load change over the tidal cycle, with increasing bedload dominance at low tide. The total amount of sediment transported as swash and backwash is noticeably greater at high tide than at low tide. More sediment is transported on the flood tide than on the ebb.     

Symmetrische Stylolithen

Ohne Zusammenfassung     

Short-Term Response of a Downstream Marine System to the Partial Opening of a Tidal-River Causeway

The spillway gates of the Petitcodiac Causeway, a hydraulic structure ~35 km upstream of the mouth of the Petitcodiac River in New Brunswick, Canada, were permanently opened in April 2010. The short-term effect opening the spillway gates had on downstream intertidal mudflats of the upper Bay of Fundy was investigated. Specifically, a multivariate before-after-control-impact design was used to determine if opening the spillway gates affected the invertebrate community (crustaceans, polychaetes, and molluscs), abiotic sediment conditions (sediment water content, mean particle size, penetrability, and depth of the apparent redox potential discontinuity), or resource availability (sediment chlorophyll a concentration and organic matter content) of five intertidal mudflats (two impacted sites, three reference sites) spanning Chignecto Bay, the northern arm of the upper Bay of Fundy, up to 5 months post-opening. No biologically or statistically meaningful differences were detected between impacted and reference sites for any of the measured variables. This suggests that opening the causeway did not have a quantifiable impact on these intertidal mudflats, at least within half a year of the opening. This is likely a result of the macrotidal nature of the Bay of Fundy that overwhelmed any immediate changes to hydrodynamics that occurred after the opening of the causeway gates.     

Investigation of star formation toward the Sharpless 155 H II region

We present a comprehensive study of star formation toward the H II region Sharpless 155(S155).Star-formation activities therein were investigated based on multi-wavelength data from optical to the far-infrared.The surface density distribution of selected 2MASS sources toward S155 indicates the existence of a compact cluster,which is spatially consistent with the position of the exciting source of the H II region,HD 217086.A sample of more than 200 sources with excessive emission in the infrared were selected based on their 2MASS color indices.The spatial distribution of the sample sources reveals the existence of three young subclusters in this region,among which subcluster A is spatially coincident with the bright rim of the H II region.In addition,photometric data from the WISE survey were used to identify and classify young stellar objects(YSOs).To further explore the evolutionary stages of the candidate YSOs,we fit the spectral energy distributions of 44 sources,which led to the identification of 14 Class I,27 Class II and 3 Class HI YSOs.The spatial distribution of the classified YSOs at different evolutionary stages presents a spatiotemporal gradient,which is consistent with a scenario of sequential star formation.On the other hand,Herschel PACS observations toward the interface between S155 and the ambient molecular cloud disclose an arc-shaped dust layer,the origin of which could be attributed to the UV dissipation from early type stars,e.g.HD 217061,in S155.Four dusty cores were revealed by the Herschel data,which hints at new generations of star formation.     

Genetic effects of a large-scaleSpartina alterniflora (smooth cordgrass) dieback and recovery in the northern Gulf of Mexico

A large-scale dieback event struck marshes along the northwestern Gulf of Mexico coast during summer 2000, in apparent response to a prolonged and severe drought. Along the Louisiana coast, large areas of the dominant marsh species,Spartina alterniflora, turned brown, followed by death of at least the aboveground structures of entire plant mortality. Key ecological and genetic measures were studied in a dieback-affected marsh in southwest Louisiana (C83 marsh, Sabine National Wildlife Refuge), for which existed predieback ecologic and genetic datasets. Effects on genetic diversity only were studied in a second set of sites in southeastern Louisiana (near Bay Junop), where the dieback was more widespread. We hypothesized that stem density, live aboveground biomass, and genetic diversity would be significantly reduced compared to predieback conditions and to nearby unaffected marshes. Stem densities and biomass levels approached predieback conditions 14 months after first observance of the dieback in the Sabine marsh and were similar to or exceeded the same measures for a nearby unaffected marsh. DNA extracted from leaf samples in the Sabine and Bay Junop sites was used to construct genotype profiles using AFLPs and analyzed using the complement of Simpson’s Index (1-D), the richness measure G/N, average heterozygosity <H>, and the estimated proportion of polymorphic genes <P>. Genetic diversity was relatively unaffected by the dieback at either the Sabine or Bay Junop sites. Evidence from field observations and the results of the genetic analyses suggest that seedling recruitment is an important factor in the recovery of both the Bay Junop and C83 sites, although re-growth from surviving below-ground rhizomes appeared to dominate recovery at the latter site. Survival of below-ground structures, leading to the rapid recovery observed, indicates a high level of resilience of the Sabine marsh to drought-induced stress. Still, the genetic diversity ofS. alterniflora-dominated marshes may be promoted by occasional disturbance events, which produce open areas in which seedling recruitment can occur.