Further studies on the chordal-hop theory of ionospheric long-range propagation

Summary This paper presents new results of the author's investigations on ionospheric propagation in Australia from 1952 to 1957. Considerations on path attenuation are followed by a discussion on the propagation paths to North America and Western Europe. Conclusions are in agreement with the author's previous publications in this field.

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Zusammenfassung In dieser Arbeit behandelt der Verfasser neue Ergebnisse seiner Untersuchungen über ionosphärische Ausbreitung in Australien von 1952 bis 1957. Auf eine Betrachtung über die Signalschwächung folgt eine Diskussion über die Ausbreitungswege nach Nordamerika und Westeuropa. Die Folgerungen stimmen mit den früheren Veröffentlichungen des Verfassers auf diesem Gebiet überein.

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Résumé L'auteur expose les nouveaux résultats de ses recherches sur la propagation ionosphérique en Australie de 1952 à 1957; il considère l'affaiblissement de la propagation des signaux et les chemins suivis par les ondes vers l'Amérique du Nord et vers l'Europe occidentale. Ces résultats concordent avec ceux qu'il a publiés précédemment.

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Benthic photosynthesis in submerged Wadden Sea intertidal flats

In this study we compare benthic photosynthesis during inundation in coarse sand, fine sand, and mixed sediment (sand/mud) intertidal flats in the German Wadden Sea. In situ determinations of oxygen-, DIC- and nutrient fluxes in stirred benthic chamber incubations were combined with measurements of sedimentary chlorophyll, incident light intensity at the sediment surface and scalar irradiance within the sediment. During submergence, microphytobenthos was light limited at all study sites as indicated by rapid response of gross photosynthesis to increasing incident light at the sea floor. However, depth integrated scalar irradiance was 2 to 3 times higher in the sands than in the mud. Consequently, gross photosynthesis in the net autotrophic fine sand and coarse sand flats during inundation was on average 4 and 11 times higher than in the net heterotrophic mud flat, despite higher total chlorophyll concentration in mud. Benthic photosynthesis may be enhanced in intertidal sands during inundation due to: (1) higher light availability to the microphytobenthos in the sands compared to muds, (2) more efficient transport of photosynthesis-limiting solutes to the microalgae with pore water flows in the permeable sands, and (3) more active metabolic state and different life strategies of microphytobenthos inhabiting sands.     

Exposure of phytoplankton to ekofisk crude oil

Solutions of Ekofisk crude oil in sea water were prepared by slow stirring for 21h in a closed system. Headspace and GC/MS techniques were applied to establish dose composition and levels. The standardized test medium produced in a closed system contained approximately 14 mg oil per litre and was dominated by low molecular weight aromatic hydrocarbons and phenols.The toxicity of the standarized oil-containing medium to three marine diatoms was studied in a cage culture turbidostat and by conventional batch culture technique. The three algal species differed in sensitivity to the oil compounds, but showed identical ranking in both test systems.Standardized test medium diluted to 50% with respect to oil content stopped the growth of the most sensitive alga, Skeletonema costatum. For comparison naphthalene was applied and gave 50 % growth reduction at a concentration of 400 μg litre^?1. The growth of Chaetoceros ceratosporum was only slighty affected by the full strength standard test medium, which had no influence on the growth of Phaeodactylum tricornutum, the least sensitive organism. The presence of an oil layer on the surface of the standard test medium during the growth test greatly increased its toxicity and blocked completely the photosynthesis even of P. tricornutum after 4 days.     

Lysosomal injury and MFO activity in the liver of flounder (Platichthys flesus L.) in relation to histopathology of hepatic degeneration and carcinogenesis

Flounder (Platichthys flesus L.), 18–48 cm total length were sampled in the mouth of the Elbe River during a 3-year interdisciplinary project ‘Fish Diseases in the Wadden Sea’. Lysosomal changes (lysosomal membrane stability) and the activity of biotransforming enzymes (MFOs/EROD) were measured parallel to investigations of ultrastructural changes in liver cells, tissue pathologies and macroscopically visible changes. The aim of the study was to investigate if these cyto- and biochemical parameters were able to reflect contaminant induced biological effects. Interlinking of the results of the MFO activity to the pathological alterations observed at the electron- and light-microscopic levels as well as during macroscopic inspection of identical individuals evidenced that the activity of the biotransformation enzymes (EROD) was not induced in healthy livers, increased considerably with the onset of liver changes and dropped again in those livers with degenerative, preneoplastic and neoplastic lesions. In contrast, concurrent studies of lysosomal membrane stability measured in parallel showed a decrease with the onset and progression of liver lesions from reversible to irreversible, neoplastic change.     

Deep crustal structure and rheology of the Gascoyne volcanic margin,western Australia

Interpretation of deep seismic reflection data across the Gascoyne Margin reveals six distinct seismic facies units related to the tectono-magmatic breakup history. On the outer Exmouth Plateau four large scale units are identified: (1) an extensively block-faulted upper crust; (2) a middle-crustal unit of discontinuous, undulatory reflectors; (3) a reflection-free deep crustal unit; and (4) a lower-crustal band of low-frequency, high-amplitude reflectors. Two additional units are found near the continent-ocean boundary (COB); (5) seaward-dipping reflectors (SDR); and (6) landward-dipping reflectors in the lower crust below the SDR. The lower-crustal high-reflectivity band, located near the top of a high-velocity unit (V_p > 7 kms^–1), is interpreted as magmatic underplating. There is a spatial correlation between the underplated area and the presence of extensive upper-crustal block-faulting and intrusive rocks in the shallow crust. The undulatory middle-crustal reflector unit is also only identified in the outer plateau area, and is interpreted as a zone in which the upper-crustal faults terminate. The inner parts of the margin consist of a deep basin showing little upper-crustal faulting and no evidence of middle crustal deformation or underplating. Theoretical modeling of the effect of rifting and magmatic underplating on crustal strength profiles suggests that the brittle-ductile transition may migrate at least 5 km upwards during several million years after the underplating event. Based on the seismic interpretation and crustal strength modeling we propose that the seismic structure of the outer Exmouth Plateau is severely modified by a transient change in the crustal rheological structure associated with magmatic underplating.     

Longitudinal and depth variation of bacterioplankton productivity and related factors in a temperate estuary

Bacterioplankton productivity (BP) spatial variation was investigated in relation to potential resources, including primary productivity and dissolved organic matter, in the micro-tidal Neuse River–Pamlico Sound estuarine system, North Carolina, USA. Estuarine BP was predicted to correlate with the trophic gradient, decreasing along the salinity gradient in parallel with the decrease in organic matter and primary productivity. This prediction was tested over four years at spatial scales ranging from kilometers to meters along the riverine axis and with depth. The general pattern of BP across the salinity gradient was unimodal and matched the phytoplankton patterns in peak location and variability. Peak locations varied with discharge, especially in 2003 when above average discharge moved peaks downstream. Spatial coherence of BP with other variables was much less at short time scales. The effect of temperature, nutrients, and phytoplankton on BP varied by location, especially fresh versus brackish stations, although only temperature explained more than 20% of the BP variation. Depth variation of BP was as great as longitudinal variation and bottom samples were often higher than surface. BP was strongly correlated with particulate organic carbon at the pycnocline and bottom, highlighting the importance of particulate matter as a resource. Station-averaged BP and phytoplankton data corresponded well with two published meta-analyses, although the offset of the freshwater station suggested longitudinal differences in community composition or resource availability.     

Spatial and seasonal variability of sediment accumulation potential through controlled flooding of the beels located in the polders of the Ganges-Brahmaputra-Meghna delta of Southwest Bangladesh

The Ganges-Brahmaputra-Meghna (GBM) delta plain within Bangladesh is one of the most vulnerable to relative sea level rise (RSLR) in the world especially under current anthropogenically modified (i.e., embanked) conditions. Tidal river management (TRM) as practiced in coastal regions of Bangladesh may provide an opportunity to combat RSLR by raising the land level through controlled sedimentation inside beels (depression within embanked polders) with re-opening of polders. To date, TRM has been applied to tide-dominated coastal regions, but the potential applicability of TRM for the beels within the polders of river-dominated and mixed flow (MF) regimes remains to be assessed. We apply a calibrated 2D numerical hydromorphodynamic model to quantify sediment deposition in a beel flooded through breaching of the polder dike under conditions of river-dominated, tide-dominated and MF regimes for different seasons and applying different regulation schemes for the flow into the beel. Simulation results show considerable seasonality in sediment deposition with largest deposition during the monsoon season. The potential of controlled flooding is highest in the tide-dominated region, where sediment accumulation can be up to 28 times higher than in the river-dominated region. Regulating flow into a beel increases trapping efficiency, but results in slightly lower total deposition than without regulation. We conclude that re-establishing flooding of the beel within the polder without regulating the flow into the beel through breaching of the polder dike is a promising strategy for the mixed and tide-dominated flow regions in the delta as the sediment accumulation can raise the land surface at a higher rate than RSLR and effective SLR (ESLR). In the more upstream river-dominated section of the delta, accumulation rates would be much lower, but the pressure of sea level rise on these areas is lower as well. Owing to the abundant availability of sediment, application of controlled flooding like TRM therefore provides an opportunity to counteract the impact of RSLR and ESLR by means of land raising, particularly along the tidal river reaches in the GBM delta.     

Assessment of three temperature reconstruction methods in the virtual reality of a climate simulation

The performance of statistical climate reconstruction methods in the pre-instrumental period is uncertain, as they are calibrated in a short instrumental period but applied to much longer reconstructions time spans. Here, the virtual reality created by a climate simulation of the past millennium with the model ECHO-G is used as a test bed of three methods to reconstruct the annual Northern Hemisphere temperature. The methods are Composite plus Scaling, the inverse regression method of Mann et al. (Nature 392:779–787, 1998) and a direct principal-components regression method. The testing methodology is based on the construction of pseudo-proxies derived from the climate model output, the application of each of these methods to pseudo-proxy timeseries, and the comparison of their result with the simulated mean temperature. Different structures of the noise have been used to construct pseudo-proxies, ranging from the simulated grid-point precipitation. Also, one sparse and one denser pseudo-proxy network, co-located with two real networks, have been considered. All three methods underestimate the simulated variations of the Northern Hemisphere temperature, but the Composite plus Scaling method clearly displays a better performance and is robust against the different noise models and network size. The most relevant factor determining the skill of the reconstruction appears to be the network size, whereas the different noise models tend to yield similar results.