Untersuchung über die Verteilung von Spurengasen in der freien Atmosphäre

Zusammenfassung Die vorliegende Arbeit behandelt die Ergebnisse von Messflügen zur Bestimmung der Konzentrationsverteilung von Spurengasen in der freien Atmosphäre. Auf Grund dieser Aufstiege war es erstmals möglich, den Gehalt der Atmosphäre an Schwefeldioxyd und Stickstoffdioxyd bis in Höhen von 6000 m zu erfassen. Die gewonnene mittelere Konzentrations-verteilung bietet die Basis zu Abschätzungen über den Haushalt und die mittlere Verweilzeit von SO₂ und NO₂ in der Troposphäre.

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Summary This paper deals with the results of aircraft ascents for the measurement of the vertical distribution of atmospheric trace gases in the free atmosphere. The aircraft ascents permitted for the first time to measure the SO₂- and NO₂-concentration up to 6000 m. On the basis of the average distribution assumptions on the tropospheric budget of SO₂ and NO₂ as well as on the average tropospheric residence time of these gases were made.

     

High resolution simulation of recent Arctic and Antarctic stratospheric chemical ozone loss compared to observations

Simulations of polar ozone losses were performed using the three-dimensional high-resolution (1^∘ × 1^∘) chemical transport model MIMOSA-CHIM. Three Arctic winters 1999–2000, 2001–2002, 2002–2003 and three Antarctic winters 2001, 2002, and 2003 were considered for the study. The cumulative ozone loss in the Arctic winter 2002–2003 reached around 35% at 475 K inside the vortex, as compared to more than 60% in 1999–2000. During 1999–2000, denitrification induces a maximum of about 23% extra ozone loss at 475 K as compared to 17% in 2002–2003. Unlike these two colder Arctic winters, the 2001–2002 Arctic was warmer and did not experience much ozone loss. Sensitivity tests showed that the chosen resolution of 1^∘ × 1^∘ provides a better evaluation of ozone loss at the edge of the polar vortex in high solar zenith angle conditions. The simulation results for ozone, ClO, HNO₃, N₂O, and NO _y for winters 1999–2000 and 2002–2003 were compared with measurements on board ER-2 and Geophysica aircraft respectively. Sensitivity tests showed that increasing heating rates calculated by the model by 50% and doubling the PSC (Polar Stratospheric Clouds) particle density (from 5 × 10⁻³ to 10⁻² cm⁻³) refines the agreement with in situ ozone, N₂O and NO _y levels. In this configuration, simulated ClO levels are increased and are in better agreement with observations in January but are overestimated by about 20% in March. The use of the Burkholder et al. (1990) Cl₂O₂ absorption cross-sections slightly increases further ClO levels especially in high solar zenith angle conditions. Comparisons of the modelled ozone values with ozonesonde measurement in the Antarctic winter 2003 and with Polar Ozone and Aerosol Measurement III (POAM III) measurements in the Antarctic winters 2001 and 2002, shows that the simulations underestimate the ozone loss rate at the end of the ozone destruction period. A slightly better agreement is obtained with the use of Burkholder et al. (1990) Cl₂O₂ absorption cross-sections.     

Vergleich von marokkanischen Kreide-Küstenaufschlüssen und Tiefseebohrungen (DSDP): Stratigraphie,Paläoenvironment und Subsidenz an einem passiven Kontinentalrand

In comparison to other regions round the North Atlantic, good exposures in the Moroccan coastal basins offer an excellent opportunity to study the Mesozoic development of a passive continental margin including the relationship between oceanic and coastal sediments and datum levels of the pelagic fossils. From south to north, the Cretaceous sediments of the coastal basins of Tarfaya, Agadir, Essaouira and at the margin of the Meseta are described and compared with each other regarding macro- and microfauna, sedimentology, and paleoenvironment. For the mainly marine 2500 m resp. 1700 thick Cretaceous sequences of Agadir and Essaouira, a correlation of ammonite and foraminiferal zones is proposed. Probably both sections were formed in one basin, but certain facies differences were caused by different water depths since Middle Cretaceous times. Most of the early Cretaceous sediments of the Tarfaya region in the south and of the Meseta in the north are of continental origin. Late Cretaecous sediments of these regions reveal, however, principal differences, especially in view of the macrofauna. On the Meseta, the macrofauna is typical of the Mediterranean faunal province, whereas the Tarfaya fauna is characterized by north-boreal elements. This is explained by the influence of upwelling in connection with the initiation of an oceanic deep-sea circulation, which also can be traced into the Agadir section. As a result, already during Turonian times, here bituminous marls with chert layers are deposited. These are missing farther to the north, but later nannomarls, chalk, chert layers and, in addition, locally phosphates are formed there, too. Generally, during the Cretaceous period, a tendency towards decreasing sedimentation rates and a relative increase of the percentage of pelagic components such as planktonic foraminifera in the local sediment can be observed, indicating a sharp decrease of the terrigeneous influx and a landward transgression of the oceanic water mass. If the global eustatic curve for the Cretaceous oceans is compared to the local bathymetric curves of the Moroccan coastal basins, one can distinguish between local phenomena and global events (Turonian and Campanian transgressions). In comparing the Cretaceous sections of DSDP sites 370 and 137 with the Agadir sequence on the continent, an attempt is made to reveal the development of the marginal North Atlantic, related to an increase of the paleodepth and the influence of the CCD. At Cape Bojador, in a transect across the continental margin from inland wells to the upper rise (DSDP site 397), the subsidence history of the uniformly subsiding ?marginal basin“ is derived. In the Jurassic, the rates of subsidence as well as those of sedimentation reach the order of magnitude of about 100 m/million years. The early Cretaceous subsidence increases up to 140 m/million years. As a result, sedimentation soon cannot keep pace, the water depth at the outer margin increases, and the shelf edge and continental slope are formed. In the last 100 million years, the subsidence decreases more or less exponentially. For the well subdivided Cretaceous sequences of the coastal basins described above, the interrelationship between subsidence, paleowaterdepth, and sedimentation rate has been worked out in more detail.     

Selective zooplanktivory of an invasive Ponto-Caspian mysid and possible consequences for the zooplankton community structure of invaded habitats

The impact of invasive alien species on native species is of increasing global concern. Invasive species can cause food-web shifts that have severe consequences for native species and ecosystems. However, the mechanisms by which the invaders influence the native communities are poorly understood. Here we investigated the interactions of the invasive Ponto-Caspian mysid Limnomysis benedeni with native freshwater zooplankton in laboratory and mesocosm experiments. This mysid migrates between benthic and pelagic zones and thereby forms a potential trophic link between these habitats. In laboratory predation experiments, L. benedeni fed both on Daphnia galeata and D. magna, and predation rates depended on the sizes of predator and prey but not on the availability of light. However, no predation was observed at prey sizes greater than 2 mm, which appears to be the upper size limit for a successful prey capture by L. benedeni. In outdoor mesocosm experiments, L. benedeni strongly decreased the densities of cladocerans, rotifers and copepod nauplii within a few days, while the densities of copepods were unaffected. Prey selection indices provide further evidence for strongly selective predation of L. benedeni on different zooplankton taxa. The presence of phytoplankton as an additional resource for the omnivorous mysid led to a lower predation pressure of L. benedeni on Cladocera and rotifers, indicating that the presence of alternative prey modulates the strength of the top-down effect of invasive mysids on the zooplankton community. These results suggest that the invasion of L. benedeni can have profound and complex impacts on the community structure of the native zooplankton fauna and that mysid invasions potentially have whole-ecosystem consequences.     

Impact of livestock management on water quality and streambank structure in a semi-arid,African ecosystem

Natural resource management may change local and regional ecosystems, especially in drought-prone environments. Livestock are commonly kept as a source of capital in agriculturally dominated communities in Southern Africa, but the mis-management of available forage and water resources has led to significant land and water degradation. In Northwest Zimbabwe, to reverse trends in environmental degradation a community-based conservation program was established that uses intensive Holistic Management Planned Grazing (HMPG) to restore lost habitat and re-establish natural vegetation. We examined riparian ecosystem structure and water quality to compare the environmental impact of this management to nearby communal lands during a drought. The results demonstrate that concentrating livestock on ephemeral stream standing pools results in reduced water quality and altered riparian ecosystem structure. These results were not significantly different from what was observed when wildlife utilized similar water resources without livestock influence. When water is scarce, as during extreme droughts, livestock usage of surface water resources must be weighted against community water needs. The long-term regional benefits of HMPG may prevail over short-term reductions in local water quality but more research is needed to assess all the consequences of such management.     

Ra-partitioning between phlogopite and silicate melt and 226Ra/Ba–230Th/Ba isochrons

In this study we experimentally determine phlogopite/melt partition coefficients of Ra and other trace elements in a lamproitic system. This work was achieved using an analytical technique (LA-ICP-MS) with low detection limits (~ 0.01 fg) permitting the measurement of the very low Ra concentrations feasible in experiments (~ 1 ppb). D_Ra^{phlogopite/melt} was determined to 2.28 ± 0.44 and 2.84 ± 0.47 in two experiments, the ratio D_Ra/D_Ba is around 1.6. The compatibility of Ra in phlogopite results from an ionic radius being close to the apex of the lattice strain parabola for earth alkalis in the large XII-coordinated interlayer site of phlogopite. A re-evaluation of D_Ra and D_Ra/D_Ba for magmatic minerals containing appreciable Ra, yields D_Ra^mineral/melt ranging from ~ 2.6 for phlogopite down to 2–3 ? 10^? 5 for pyroxenes, and D_Ra/D_Ba^mineral/melt from ~ 4 for leucite to 2 ? 10^? 2 for orthopyroxene. The influence of melt composition on D_Ra/D_Ba is less than 10%. All investigated minerals have different D_Ra/D_Ba, strongly fractionating Ra from Ba. Thus, for magmatic systems, (²²⁶Ra)/Ba in the various minerals is not constant, these minerals do not form a straight line in the (²²⁶Ra)/Ba–(²³⁰Th)/Ba system at the time of crystallization and thus, there is no (²²⁶Ra)/Ba–(²³⁰Th)/Ba isochron at t₀. ²²⁶Ra–²³⁰Th–Ba mineral dating is thus applicable only to model ages calculated from mineral–glass pairs with known D_Ra.