Oxygen variance and meridional oxygen supply in the Tropical North East Atlantic oxygen minimum zone     

J. Hahn  P. Brandt  R. J. Greatbatch  G. Krahmann  A. Körtzinger 《Climate Dynamics》2014,43(11):2999-3024

The distribution of the mean oceanic oxygen concentration results from a balance between ventilation and consumption. In the eastern tropical Pacific and Atlantic, this balance creates extended oxygen minimum zones (OMZ) at intermediate depth. Here, we analyze hydrographic and velocity data from shipboard and moored observations, which were taken along the 23°W meridian cutting through the Tropical North East Atlantic (TNEA) OMZ, to study the distribution and generation of oxygen variability. By applying the extended Osborn–Cox model, the respective role of mesoscale stirring and diapycnal mixing in producing enhanced oxygen variability, found at the southern and upper boundary of the OMZ, is quantified. From the well-ventilated equatorial region toward the OMZ core a northward eddy-driven oxygen flux is observed whose divergence corresponds to an oxygen supply of about 2.4 μmol kg^?1 year^?1 at the OMZ core depth. Above the OMZ core, mesoscale eddies act to redistribute low- and high-oxygen waters associated with westward and eastward currents, respectively. Here, absolute values of the local oxygen supply >10 μmol kg^?1 year^?1 are found, likely balanced by mean zonal advection. Combining our results with recent studies, a refined oxygen budget for the TNEA OMZ is derived. Eddy-driven meridional oxygen supply contributes more than 50 % of the supply required to balance the estimated oxygen consumption. The oxygen tendency in the OMZ, as given by the multidecadal oxygen decline, is maximum slightly above the OMZ core and represents a substantial imbalance of the oxygen budget reaching about 20 % of the magnitude of the eddy-driven oxygen supply.  相似文献   

New high‐resolution age data from the Ediacaran–Cambrian boundary indicate rapid,ecologically driven onset of the Cambrian explosion     

Ulf Linnemann  Maria Ovtcharova  Urs Schaltegger  Andreas Grtner  Michael Hautmann  Gerd Geyer  Patricia Vickers‐Rich  Tom Rich  Birgit Plessen  Mandy Hofmann  Johannes Zieger  Rita Krause  Les Kriesfeld  Jeff Smith 《地学学报》2019,31(1):49-58

The replacement of the late Precambrian Ediacaran biota by morphologically disparate animals at the beginning of the Phanerozoic was a key event in the history of life on Earth, the mechanisms and the time‐scales of which are not entirely understood. A composite section in Namibia providing biostratigraphic and chemostratigraphic data bracketed by radiometric dating constrains the Ediacaran–Cambrian boundary to 538.6–538.8 Ma, more than 2 Ma younger than previously assumed. The U–Pb‐CA‐ID TIMS zircon ages demonstrate an ultrashort time frame for the LAD of the Ediacaran biota to the FAD of a complex, burrowing Phanerozoic biota represented by trace fossils to a 410 ka time window of 538.99 ± 0.21 Ma to 538.58 ± 0.19 Ma. The extremely short duration of the faunal transition from Ediacaran to Cambrian biota within less than 410 ka supports models of ecological cascades that followed the evolutionary breakthrough of increased mobility at the beginning of the Phanerozoic.  相似文献   

A computationally efficient approach for estimating high-rate satellite clock corrections in realtime   总被引：9，自引：5，他引：4  

Maorong Ge  Junping Chen  Jan Dou?a  Gerd Gendt  Jens Wickert 《GPS Solutions》2012,16(1):9-17

Realtime satellite clock corrections are usually estimated using undifferenced phase and range observations from a global network. Because a large number of ambiguity parameters must be estimated, the computation is time-consuming. Consequently, only a sparse global network of limited number of stations is processed by most IGS Realtime Analysis Centers with an update rate of 5 s. In addition, it is very desirable to build the capability to simultaneously estimate clock corrections for multi-GNSS constellations. Although the estimation can be sped up by epoch-differenced observations that eliminate ambiguities, the derived clocks can contain a satellite-specific bias that diminishes the contribution of range observations. We introduce a computationally efficient approach for realtime clock estimation. Both the epoch-differenced phase and undifferenced range observations are used together to estimate the epoch-differenced satellite clocks and the initial clock bias for each satellite and receiver. The biased clock corrections accumulated from the estimated epoch-differenced clocks are then aligned with the estimated clock biases and provided as the final clock corrections to users. The algorithm is incorporated into the EPOS-RT software developed at GFZ (GeoForschungsZentrum) and experimentally validated with the IGS global network. The comparison with the GFZ rapid products shows that the accuracy of the clock estimation with the new approach is comparable with that of the undifferenced approach, whereas the computation time is reduced to one-tenth. As a result, estimation of high-rate satellite clocks from a large reference network and tracking satellites of multi-GNSS constellations becomes achievable.  相似文献   

Significant seasonal variation in the hydrogen isotopic composition of leaf-wax lipids for two deciduous tree ecosystems (Fagus sylvativa and Acerpseudoplatanus)     

Dirk Sachse  Ansgar Kahmen  Gerd Gleixner 《Organic Geochemistry》2009,40(6):732-742

Compound specific hydrogen isotope ratios (δD) of long chain sedimentary n-alkanes, which mostly originate from the leaf waxes of higher terrestrial plants, are increasingly employed as paleoclimate proxies. While soil water is the ultimate hydrogen source for these lipids and the isotopic fractionation during biosynthesis of lipids is thought to remain constant, environmental parameters and plant physiological processes can alter the apparent hydrogen isotopic fractionation between leaf-wax lipids and a plant’s source water. However, the magnitude and timing of these effects and their influence on the isotopic composition of lipids from higher terrestrial plants are still not well understood. Therefore we investigated the seasonal variability of leaf-wax n-alkane δD values for two different temperate deciduous forest ecosystems that are dominated by two different tree species, Beech (Fagus sylvatica) and Maple (Acerpseudoplatanus).We found significant seasonal variations for both tree species in n-alkane δD values of up to 40‰ on timescales as short as one week. Also, the isotopic difference between different n-alkanes from the same plant species did vary significantly and reached up to 50‰ at the same time when overall n-alkane concentrations were lowest.Since δD values of soil water at 5 and 10 cm depth, which we assume represent the δD value of the major water source for the investigated beech trees, were enriched in autumn compared to the spring by 30‰, whereas n-alkane δD values increased only by 10‰, we observed variations in the apparent fractionation between beech leaf derived n-alkanes and soil water of up to 20‰ on a seasonal scale. This observed change in the apparent fractionation was likely caused by differences in leaf water isotopic enrichment. Based on mechanistic leaf water models we conclude that changes in the isotopic difference between water vapor and soil water were the most likely reason for the observed changes in the apparent fractionation between n-alkanes and soil water.The large variability of n-alkane concentrations and δD values over time implies a continuous de novo synthesis of these compounds over the growing season with turnover times possibly as short as weeks. The signal to reach the soil therefore represents an integrated record of the last weeks before leaf senescence. This holds true also for the sedimentary record of small catchment lakes in humid, temperate climates, where wind transport of leaf-wax lipids is negligible compared to transfer through soil and the massive input of leaves directly into the lake in autumn.  相似文献   

The fractal properties of geochemical landscapes as an indicator of weathering and transport processes within the Eastern Alps     

Gerd Rantitsch   《Journal of Geochemical Exploration》2001,73(1)

Variations in surface morphology and lithology provide an opportunity to study lithologic and morphologic influences on the spatial pattern of stream-sediment geochemistry within two contrasting environments of the Eastern Alps (Hohe Tauern Range and Gurktaler Alpen Range). The fractal dimension, a measure of surface roughness over a variety of scales, is used to model the dissipation of erosive products due to climatic controlled denudation and fluvial mass transport. Based on a spatial correlation analysis, specific elemental concentrations are used as indicators for a dominant lithotype. Fractal geometry of these elements has been estimated by sequential Gaussian simulation of the area/perimeter relationship (Dal) and by the estimation of multifractal spectra. It is shown that within a 510–780 km² survey area the spatial variations of Al, Ga, Ni and Ca can be approximated by single fractals but for those of Ag and Sn multifractal models must be used. Fractal properties derived from simulated surfaces are explainable by the process controlling the spatial structure of the data. Climatic and tectonic parameters apparently influences Dal at large scales. At smaller scales rock-type variation exert an additional influence on Dal.  相似文献   

Three-dimensional numerical study of cell broadening during cold-air outbreaks     

Gerd Müller  Andreas Chlond 《Boundary-Layer Meteorology》1996,81(3-4):289-323

The boundary-layer development and convection-pattern transition typically occurring in cold-air outbreaks is studied using three-dimensional simulations. The simulations include the secondary-flow transition starting with the relatively small-scale boundary-layer rolls developing during the initial phase and ending with mesoscale cellular convection patterns. The application of a computational grid, whose horizontal mesh size enables the resolution of the small-scale initial patterns and whose domain size is large enough to capture mesoscale convection patterns, overcharges even state-of-the-art supercomputers. In order to bypass the computer storage problem, the horizontal size of the model domain and the horizontal resolution of the computational grid are adjusted to the scale of the dominant convective structures. This enables the simulation of convection cells whose horizontal scales increase up to values exceeding the size of the initial model domain. The model is applied to conditions of a cold-air outbreak observed during the ARKTIS 1991 experiment. The most important characteristics of the observed situation are revealed by the model. Sensitivity studies are performed in order to investigate the relation between cell broadening and various physical processes. The artificial cutoff of liquid-water formation prevents the enlargement of convective scales. Latent heating due to condensation and especially radiative cloud-top cooling are identified as processes leading to cell broadening. We propose a conceptual model that elucidates the mechanism by which cloud-top cooling may generate larger aspect ratios.  相似文献   

Die Temperatur an der Oberfläche des Europäischen Mittelmeeres     

Gerd Axel Becker 《Ocean Dynamics》1980,33(6):255-282

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Some measurements of the development of the surface inversion in Central Alaska during winter     

Gerd Wendler  K. O. L. F. Jayaweera 《Pure and Applied Geophysics》1972,99(1):209-221

Summary The strong cooling rates of the surface air, which are observed in Fairbanks in winter immediately following clearing of the sky, can, in the first hours, be explained solely by the negative radiation balance. Later on, gravity drainage of cold air from the surrounding hills into the lower valley contributes about 30% to the observed energy loss of the air above the valley. Energy balance calculations show that the negative radiation balance is compensated mainly by sensible (62%) and soil heat flux (32%) while condensation contributes only a small 6%.

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Zusammenfassung Die starken Abkühlungsraten der bodennahen Luftschicht, die im Winter in Fairbanks beobachter werden, wenn die Bewölkung abnimmt, können in den ersten Studen allein durch die negative Strahlungsbilanz erklärt werden. Später hat der katabatische Wind, der kalte Luft von den Fairbanks umgebenden Hügeln in das niedriger liegende Tal bringt, einen Anteil an dem Energieverlust der Luft über dem Tal von etwa einem Drittel. Die Berechnung der Wärmebilanz zeigt, dass die negative Strahlungsbilanz hauptsächlich vom sensiblen Wärmestrom (62%) und dem Wärmestrom aus dem Boden (32%) kompensiert wird, während die Kondensation nur 6% beiträgt.

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Der Anteil der Strahlung an der Ablation von Hintereis- und Kesselwandferner (Ötztaler Alpen,Tirol) im Sommer 1958     

Prof. Dr. Herfried Hoinkes  Dr. Gerd Wendler 《Theoretical and Applied Climatology》1968,16(2-3):195-236

Zusammenfassung Der vorliegende Bericht befaßt sich mit der Berechnung des Anteils der Strahlungsbilanz an der Ablation auf 15,5 km² Gletscherflächen während der Ablationsperiode 1958. Die Gletscherflächen wurden in 175 Flächenelemente bestimmter Neigung und Richtung zerlegt und die direkte Sonnenstrahlung relativ zur horizontalen Fläche wurde für die Gletscher ermittelt. Die effektiv mögliche Sonnenscheindauer wurde für 177 Punkte auf den Gletscherflächen durch Vermessung bestimmt und daraus die Reduktion der Sonnenstrahlung durch die Horizontabschirmung berechnet. Der Gesamtverlust an direkter Sonnenstrahlung durch Neigung, Exposition und Horizontabschirmung betrug für alle Gletscher in der Ablationsperiode Mai bis September etwa acht Prozent. Durch die Wirkung der diffusen Strahlung verringert sich der Verlust auf etwa sechs Prozent für die Globalstrahlung der Ablationsperiode 1958. Ausgehend von der registrierten Sonnenscheindauer in Vent (1900 m), und der registrierten Globalstrahlung beim Hochjochhospiz (2410 m) sowie am Kesselwandferner (3240 m) wurde die Globalstrahlung für alle Gletscher berechnet. Aus der beobachteten Schneebedeckung der Gletscher und aus Messungen wurde die Albedo für die einzelnen Monate ermittelt und damit die kurzwellige Strahlungsbilanz abgeschätzt. Zusammen mit der von der Bewölkung abhängigen langwelligen Strahlungsbilanz wurde die gesamte Strahlungsbilanz für verschiedene Albedowerte in der Ablationsperiode 1958 berechnet. Für jeden Tag wurde die Höhe der Null-Grad-Isotherme ermittelt und damit die Größe der Gletscherfläche, auf der Schmelzung möglich war.Die durch die Strahlungsbilanz verursachte Schmelzung wurde zu 21,4·10⁶ m³ Wasser berechnet oder zu 64% der beobachteten Gesamtablation von 33,5·10⁶ m³ Wasser. Der Anteil der Strahlung an der Eisablation ergab sich zu 61%, der an der Schneeablation zu 66%, was gut mit den Ergebnissen detaillierter Studien des Wärmehaushaltes an einzelnen Punkten auf Gletschern übereinstimmt. Es wird somit auch für die gesamte Gletscherfläche und die gesamte Ablationsperiode bestätigt, daß die Strahlung die wichtigste Energiequelle für die Ablation auf den Gletschern der Alpen ist.

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Summary The present report deals with the calculation of the contribution of net radiation towards ablation on 15.5 km² of glacier surface during the ablation period 1958. The glaciers were subdivided into 175 surface elements of specific slope and exposure, and direct solar radiation calculated in relation to a horizontal surface for all glaciers. The local duration of bright sunshine throughout the year was surveyed for 177 points on the glaciers, and reduction of solar radiation owing to screening of the horizon by mountains calculated. The total loss in direct solar radiation owing to slope, exposure and screening, amounted to about eight per cent on an average for all glaciers in the ablation period May to September. Due to the contribution of diffuse radiation this loss is reduced to about six per cent of total short-wave radiation in the ablation period 1958. Based on the recorded duration of bright sunshine in Vent (1900 m), on the recorded total short-wave radiation at Hochjochhospiz (2410 m), and on the Kesselwandferner (3240 m), total short-wave radiation was calculated for all glaciers. Observations of snow cover on glaciers and measurements of albedo allowed an estimate to be made of the short-wave radiation budget in single months. Together with the long-wave radiation budget the total radiation budget for typical values of albedo during the ablation period 1958 could be calculated. For each day the height of the freezing level was determined, and the size of the glacier surface with possible melting.The ablation caused by net radiation was calculated as 21.4·10⁶ m³ of water, i. e. 64 per cent of the observed total ablation of 33.5·10⁶ m³ of water. The contribution of radiation towards melting of ice was 61 per cent, towards melting of snow 66 per cent. This is in fair agreement with the results of detailed investigations of heat budget on single spots of glaciers. The present results, which are valid for the whole glacier surface and the total ablation period, confirm that solar radiation is the most important source of energy for ablation on glaciers in the Alps.

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Résumé Le présent mémoire se rapporte au calcul de la part du bilan de radiation revenant à l'ablation d'une surface de glaciers de 15.5 km² durant la période d'ablation de 1958. On a divisé les glaciers en 175 éléments de surface selon leur exposition et leur pente. On a alors déterminé pour les glaciers le rayonnement solaire direct relativement à une surface horizontale. On a en outre déterminé par mensuration la durée d'insolation maximum possible pour 177 points des glaciers et on en a tiré la réduction du rayonnement solaire par suite de l'ombre portée par l'horizon. La perte totale en rayonnement solaire direct due à la pente, à l'exposition et à l'ombre portée par l'horizon représente environ 8% pour tous les glaciers durant la période d'ablation de mai à septembre. Par suite du rayonnement diffus, la perte se réduit à environ six pour-cent par rapport à la radiation globale pour la période d'ablation de l'année 1958. La radiation globale a été calculée pour tous les glaciers en partant de l'insolation mesurée à Vent (1900 m d'altitude) et de la radiation globale enregistrée à l'hospice du Hochjoch (2410 m) ainsi qu'au Kesselwandferner (3240 m).On a estimé ensuite l'albédo mensuel par des mesures et des observations de la couverture de neige et on en a tiré le bilan de radiation à ondes courtes. En y ajoutant le bilan de radiation à longues ondes dépendant de la nébulosité, on a calculé le bilan total de radiation pour la période d'ablation 1958 et cela pour diverses valeurs de l'albédo. Pour chaque jour, on a déterminé l'altitude de l'isotherme de zéro degré ainsi que la grandeur de la surface du glacier qui en découle et où la fonte fut possible. L'eau de fonte due au bilan de radiation fut calculée à 21.4·10⁶ m³, c'est à dire 64% des 33.5·10⁶ m³ d'eau d'ablation mesurée. La part d'ablation due au rayonnement est de 61% pour la glace, de 66% pour la neige, ce qui correspond très bien aux résultats d'études détaillées de l'économie thermique faites à certains points de glaciers. Par là, on confirme que pour la période d'ablation totale ainsi que pour la surface totale du glacier, le rayonnement est la source d'énergie la plus importante pour l'ablation sur les glaciers des Alpes.

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Mit 10 Abbildungen  相似文献   

Effects of Anthropogenic Estrogens Nonylphenol and 17α‐Ethinylestradiol in Aquatic Model Ecosystems     

Burkhard A. Hense  Gabriele F. Severin  Gerd Pfister  Gerhard Welzl  Wolfgang Jaser  Karl‐Werner Schramm 《洁净——土壤、空气、水》2005,33(1):27-37

Microcosm tests were conducted to investigate the effects of the estrogenic substances nonylphenol (NP) and 17α‐ethinylestradiol (EE) on aquatic ecosystems. Maximum concentrations of 9 to 120 μg L^—1 NP resp. 49 to 724 ng L^—1 EE were induced by controlled release. The controlled release method allows the establishment of a continuous concentration course. The microcosms proved to run robustly with abiotic conditions close to natural. They developed biocenosis with similar characteristics as in natural ecosystems and, considering their given level of complexity, they can be used to describe possible risks for the environment. Both tested chemicals unveiled the potential to affect the plankton communities in the tested concentration range. NP exposure caused a reduction of Cladocera and Copepoda abundances and disturbed the phytoplankton structure. A NOEC_community of 30 μg L^—1 was calculated. In the first EE study, a flood in the lake where the microcosm water was collected caused additional stress and thereby a high variability, both between the microcosms and in each microcosm over time. Probably therefore the only effect found was a reduction of Copepoda abundance. In a second EE study Cladocera and Copepoda abundances were reduced, from which the phytoplankton benefited. Although a final interpretation is difficult for results of microcosm tests, there are indications that the found effects of EE and perhaps also NP may be caused at least partially by endocrine disruptive activity.  相似文献