GPS radio holography as a tool for remote sensing of the atmosphere, mesosphere, and terrestrial surface from space

GPS radio occultation (RO) signals are highly coherent and precise, and thus sufficient for holographic investigation of the atmosphere, ionosphere, and the Earth's surface from space. In principle, three-dimensional radio-holographic remote sensing is possible by using new radio holographic equations to retrieve the radio field within the atmosphere from a radio field known at some interface outside the atmosphere. A simplified two-dimensional form of the radio-holographic equations which are developed under an assumption of local spherical symmetry can be used to obtain two-dimensional radio images of the atmosphere and terrestrial surface. To achieve this, radio holograms recorded by a GPS receiver onboard a low earth orbit (LEO) satellite at two GPS frequencies can be used and focused synthetic aperture principle applied. Analysis of GPS/MET RO data is presented to show the effectiveness of a radio-holographic approach. It is shown that the amplitude of GPS radio signals (in addition to phase data) can be used to obtain detailed altitude profiles of the vertical gradient of refractivity in the atmosphere and electron density in the mesosphere. The results demonstrate the applicability of GPS radio holography for a detailed global study of the natural processes in the atmosphere and mesosphere. Electronic Publication     

Direct measurements of volume transports through Fram Strait

Heat and freshwater transports through Fram Strait are understood to have a significant influence on the hydrographic conditions in the Arctic Ocean and on water mass modifications in the Nordic seas. To determine these transports and their variability reliable estimates of the volume transport through the strait are required. Current meter moorings were deployed in Fram Strait from September 1997 to September 1999 in the framework of the EU MAST III Variability of Exchanges in the Northern Seas programme. The monthly mean velocity fields reveal marked velocity variations over seasonal and annual time scales, and the spatial structure of the northward flowing West Spitsbergen Current and the southward East Greenland Current with a maximum in spring and a minimum in summer. The volume transport obtained by averaging the monthly means over two years amounts to 9.5 ± 1.4 Sv to the north and 11.1 ± 1.7 Sv to the south (1 Sv = 10⁶ m³s⁻¹). The West Spitsbergen Current has a strong barotropic and a weaker baroclinic component; in the East Greenland Current barotropic and baroclinic components are of similar magnitude. The net transport through the strait is 4.2 ± 2.3 Sv to the south. The obtained northward and southward transports are significantly larger than earlier estimates in the literature; however, within its range of uncertainty the balance obtained from a two year average is consistent with earlier estimates.     

雅鲁藏布中新生代深水沉积盆地形成和演化(Ⅰ)——喜马拉雅造山带沉积特征及演化

通过对喜马拉雅三叠纪到第三纪区域沉积特征分析,阐明了雅鲁藏布喜马拉雅特提斯造山带从裂谷—被动大陆边缘—前陆盆地的沉积盆地演化史。随着以雅鲁藏布带为代表的喜马拉雅特提斯打开,三叠纪到早侏罗世为特提斯早期裂开的大陆边缘裂谷盆地。早期裂谷中心部位不是现在大陆缝合线的雅鲁藏布一带,而在低分水岭带。晚侏罗世到早白垩世,雅鲁藏布江南测为典型被动大陆边缘,其沉积盆地沉降、海平面变化与沉积作用相吻合。晚白垩世到第三纪为前陆盆地演化阶段,从沉积作用可以识别出晚白垩世晚期为造山第一暮,第三纪初为第二幕。     

High temperature alteration minerals and thermal brines,Reykjanes, Iceland

The geothermal area on Reykjanes, Iceland has been investigated mineralogically. The temperature within the studied area is very variable from 30–300° C. Mineral zones corresponding to the temperature conditions in the area are found. Accidental changes in the geothermal system are also reflected in the mineralogy by formation of anhydrite. Changes in temperature conditions in the field are indicated by epidote occurrence at 40° C and retrograd formation of montmorillonite.     

Petrogenesis of contrasting granitoid plutons in western Bohemia (Czech Republic)

Summary Late-Variscan granitoid plutons in western Bohemia (Bor, Waidhaus-Rozvadov) have distinct petrographic, geochemical and isotopic features that suggest different magmatic evolutions. The Bor pluton comprises a suite of metaluminous tonalites and quartz diorites (Bor I), weakly peraluminous (monzo-)granites and granodiorites (Bor II) and medium-aluminous, late vein-forming leucomonzogranites (Bor III). The Waidhaus-Rozvadov pluton is strongly peraluminous, comprising a cordierite-biotite granitoid (CBG), the Rozvadov granite (ROG), the Bärnau granite (BÄG) and the subordinate, highly evolved Kreuzstein (Kíový kámen) granite (KG). Geochemical parameters and initial⁸⁷Sr/⁸⁶Sr ratios straddle the boundary between I- and S-type granites in the Bor pluton and are characteristic of purely S-type granites in the Waidhaus-Rozvadov pluton.The Bor II granitoids have been dated by the Rb-Sr whole-rock method at 341±17 Ma (I_Sr = 0.70724±0.00060). K-Ar biotite and muscovite ages of all units of the Bor pluton are mainly in the range 321-315 Ma. The K-Ar mineral ages are in good agreement with recently published U-Pb zircon data of these rocks. The different units of the Waidhaus-Rozvadov pluton have yielded less well-constrained Rb-Sr whole-rock ages, ranging from 313 to 300 Ma. However, the intrusion sequence is constrained by K-Ar muscovite ages (312-302 Ma), which define a systematic decrease towards the chemically more evolved granite types. Taken as a whole, it seems likely that the new radiometric ages characterize two temporally distinct periods of late-Variscan granitoid intrusion. The regional significance of these periods is emphasized by contemporaneous ages previously found in the adjacent northeastern Bavarian granitoids.The initial Sr and Nd isotope systematics indicate that the Bor and the WaidhausRozvadov plutons were derived from different source rocks. The Bor granitoids reflect the influence of less evolved crustal material which may have been similar to paragneisses of the Teplá-Barrandian region, including the Zone of ErbendorfVohenstrauß (ZEV). The Waidhaus-Rozvadov granitoids probably resulted from anatexis of rocks resembling surrounding Moldanubian paragneisses or metapelites. In addition, the two plutons exhibit poorly defined, opposite trends of Nd_(T) variation which are ascribed to assimilation processes.

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Petrogenese kontrastierender Granitplutone in Westböhmen (Tschechien)

Zusammenfassung Spätvariscische Granitplutone in Westböhmen (Bor, Waidhaus-Rozvadov) weisen petrographische, geochemische und isotopische Kontraste auf, die unterschiedliche magmatische Entwicklungen nahelegen. Der Bor Pluton umfaßt metalumine Tonalite und Quarzdiorite (Bor I), schwach peralumine (Monzo-)granite und Granodiorite (Bor II) und mäßig alumine, gangbildende Leukomonzogranite (Bor III). Der WaidhausRozvadov Pluton besitzt stark peralumine Zusammensetzung und läßt sich in einen Cordierit-Biotit Granitoid (CBG), den Rozvadov Granit (ROG), den Bärnau Granit (BÄG) und den stofflich hochentwickelten Kreuzstein (Kíový kámen) Granit (KG) untergliedern. Geochemische Parameter und initiale⁸⁷Sr/⁸⁶Sr-Verhältnisse liegen im Falle des Bor Plutons im Übergangsbereich zwischen I- und S-Typ Graniten und im Falle des Waidhaus-Rozvadov Plutons im Bereich reiner S-Typ Granite.Die Bor II Granitoide wurden nach der Rb-Sr Gesamtgesteinsmethode auf 341±17 Ma (I_Sr = 0.70724±0.00060) datiert. K-Ar Biotit- und Muskovitalter der Bor Granitoide liegen zwischen 321 and 315 Ma. Die K-Ar Mineralalter stehen im Einklang mit den kürzlich publizierten U-Pb Zirkondaten dieser Gesteine. Die verschiedenen Teilintrusionen des Waidhaus-Rozvadov Plutons liefern weniger gut definierte Rb-Sr Gesamtgesteinsalter zwischen 313 and 300 Ma. Die Intrusionsabfolge läßt sich dennoch durch K-Ar Muskovitalter festlegen (312-302 Ma), die eine systematische Abnahme von den weniger zu den starker entwickelten Granittypen aufweisen. Als Ganzes betrachtet dokumentieren die neuen radiometrischen Daten zwei zeitlich voneinander getrennte spdtvariscische Intrusionsereignisse. Die regionale Signifikanz dieser Ereignisse wird durch eine analoge Altersverteilung in den benachbarten nordostbayerischen Granitoiden untermauert.Anhand der initialen Sr und Nd Isotopensystematik können für die Bor und Waidhaus-Rozvadov Plutone unterschiedliche Quellen abgeleitet werden. Die Bor Granitoide spiegeln den Einfluß von gering entwickelten krustalen Material wider, das ähnliche stoffliche Eigenschaften besaß, wie Paragneise des Teplá-Barrandiums und der Zone von Erbendorf-Vohenstrauss (ZEV). Die Waidhaus-Rozvadov Granitoide lassen sich als Derivate moldanubischer Paragneise and Metapelite oder vergleichbarer Gesteine auffassen. Die zwei Plutone weisen schwach ausgeprägte gegensätzliche Nd_(T)-Variationen auf, was auf unterschiedliche Assimilationsprozesse zurückgeführt wird.

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With 10 Figures     

A Sr isotope study on fluorite and siderite from post-orogenic mineral veins in the eastern Harz Mountains,Germany

Rb–Sr isotope data for siderite and fluorite from sediment-hosted epithermal mineral veins in the eastern Harz Mountains (Germany) are presented. Several fluorite and siderite-bearing paragenetic stages have been proposed for these veins, with the most important mineralization being related to a quartz–sulfide and a subsequent calcite–fluorite–quartz stage, which occurred at 226±1 and 209±2 Ma, respectively. Our Rb–Sr data do not permit the identification of distinct generations of siderite and fluorite, but rather reveal straight internal mixing relations, reflecting mixing of fluids or differential fluid–rock interaction processes. This indicates merely two significant phases of mineral deposition related to the quartz–sulfide and calcite–fluorite–quartz stages. It is shown that the Paleozoic sedimentary host rocks of the veins are the most likely source for the siderite Sr, whereas fluorite displays a two-component mixture between sedimentary Sr and radiogenic Sr derived from locally occurring Permian metavolcanic rocks. Editorial handling: B. Lehmann     

Restoration of submerged vegetation in shallow eutrophic lakes – A guideline and state of the art in Germany

One of the most serious problems caused by eutrophication of shallow lakes is the disappearance of submerged macrophytes and the switch to a turbid, phytoplankton-dominated state. The reduction of external nutrient loads often does not result in a change back to the macrophyte-dominated state because stabilising mechanisms that cause resilience may delay a response. Additional internal lake restoration measures may therefore be needed to decrease the concentration of total phosphorus and increase water clarity. The re-establishment of submerged macrophytes required for a long-term stability of clear water conditions, however, may still fail, or mass developments of tall-growing species may cause nuisance for recreational use. Both cases are often not taken into account when restoration measures are planned in Germany, and existing schemes to reduce eutrophication consider the topic inadequately. Here we develop a step-by-step guideline to assess the chances of submerged macrophyte re-establishment in shallow lakes. We reviewed and rated the existing literature and case studies with special regard on (1) the impact of different internal lake restoration methods on the development of submerged macrophytes, (2) methods for the assessment of natural re-establishment, (3) requirements and methods for artificial support of submerged macrophyte development and (4) management options of macrophyte species diversity and abundance in Germany. This guideline is intended to help lake managers aiming to restore shallow lakes in Germany to critically asses and predict the potential development of submerged vegetation, taking into account the complex factors and interrelations that determine their occurrence, abundance and diversity.     

Carbon isotopic fractionation during a mesocosm bloom experiment dominated by Emiliania huxleyi: Effects of CO2 concentration and primary production

We investigated the effect of CO₂ and primary production on the carbon isotopic fractionation of alkenones and particulate organic matter (POC) during a natural phytoplankton bloom dominated by the coccolithophore Emiliania huxleyi. In nine semi-closed mesocosms (∼11 m³ each), three different CO₂ partial pressures (pCO₂) in triplicate represented glacial (∼180 ppmv CO₂), present (∼380 ppmv CO₂), and year 2100 (∼710 ppmv CO₂) CO₂ conditions. The largest shift in alkenone isotopic composition (4-5‰) occurred during the exponential growth phase, regardless of the CO₂ concentration in the respective treatment. Despite the difference of ∼500 ppmv, the influence of pCO₂ on isotopic fractionation was marginal (1-2‰). During the stationary phase, E. huxleyi continued to produce alkenones, accumulating cellular concentrations almost four times higher than those of exponentially dividing cells. Our isotope data indicate that, while alkenone production was maintained, the interaction of carbon source and cellular uptake dynamics by E. huxleyi reached a steady state. During stationary phase, we further observed a remarkable increase in the difference between δ¹³C of bulk organic matter and of alkenones spanning 7-12‰. We suggest that this phenomenon is caused mainly by a combination of extracellular release of ¹³C-enriched polysaccharides and subsequent particle aggregation induced by the production of transparent exopolymer particles (TEP).     

Geochronology of high-pressure rocks on Sifnos (Cyclades,Greece)

Polymetamorphic rocks of Sifnos (Greece) have been investigated by Rb-Sr, K-Ar, and fission track methods. Critical mineral assemblages from the northern and southernmost parts of Sifnos include jadeite+quartz+3T phengite, and omphacite+garnet +3T phengite, whereas the central part is characterized by the assemblage albite+chlorite+epidote+2M ₁ phengite.K-Ar and Rb-Sr dates on phengites (predominantly 3T) of the best preserved high P/itTmetamorphic rocks from northern Sifnos gave concordant ages around 42 m.y., indicating a Late Lutetian age for the high P/T metamorphism. Phengites (2M ₁+3T) of less preserved high P/T assemblages yielded K-Ar dates between 48 and 41 m.y. but generally lower Rb-Sr dates. The higher K-Ar dates are interpreted as being elevated by excess argon.K-Ar and Rb-Sr ages on 2M ₁ phengites from central Sifnos vary between 24 and 21 m.y. These ages date a second, greenschist-facies metamorphism which overprinted the earlier high-pressure metamorphic rocks.