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Die Meteor Expedition M70 erforscht spezielle Tiefenwasserökosysteme am Meeresboden von submarinen Bergen und den Kontinentalrändern des zentralen und östlichen Mittelmeers. Im Rahmen des EU Projekts HERMES werden bathyale Korallenökosysteme im westlichen Tyrrhenischen Meer, dem Ionischen Meer sowie der südlichen Adria untersucht (Fahrtabschnitt M 70/1 unter Leitung Prof. Dr. A. Freiwald). Anschließend werden erst kürzlich entdeckte Ökosysteme an Methanquellen des tiefen Nilfächers in einer gemeinsamen Aktivität des ESF EUROCORES-Projekts MEDIFLUX und des deutschen Geotechnologien-Projekts MUMM II erforscht (Fahrtabschnitt M 70/2 unter Leitung Prof Dr. A. Boetius). Schließlich stehen Prozesse von submarinen Fluidzirkulation an Gas- und Fluidaustritten vor Israel und an den "Anaximander Seebergen" südlich der Türkeiküste im Fordergrund der Forschung (Fahrtabschnitt M70/3 unter Leitung von Prof. Dr. G. Bohrmann). Die Reise wird am 24.09.2006 in La Valetta (Malta) beginnen und am 09.12.2006 in Limassol (Zypern) enden.
Die Dissertation wurde im Rahmen des von der Deutschen Forschungsgemeinschaft geförderten interdisziplinären Sonderforschungsbereiches 268 "Kultur- und Sprachentwicklung im Natrurraum Westafrikanische Savanne" angefertigt. Dabei war die Kartierung und Analyse von Landbedeckungs- und Landnutzungsveränderungen in einem Ausschnitt des nigerianischen Tschadbeckens Zielsetzung vorliegender Arbeit. Trotz eines recht großen allgemeinen Interesses am Tschadsee, dem größten See Westafrikas, fällt es schwer, topographische und thematische Information über diese Region zu erlangen. Viele Zusammenhänge bezüglich seiner Vergangenheit und seiner zukünftigen Entwicklung sind bis heute nicht geklärt. Soweit Daten zur Landbedeckung und Landnutzung bereits verfügbar waren, wurden sie aufbereitet und im Rahmen des regionalen geographischen Informationssystems FirGIS strukturiert gegliedert aufgenommen. Als hauptsächliche Datenquelle wurde jedoch auf Fernerkundungsdaten der Region zurückgegriffen. Sie liefern meist die einzige großflächig vorhandene, aktuelle und vor allem multitemporale Information über das Untersuchungsgebiet. Die Auswertung der Fernerkundungsdaten erfolgte mit Methoden der digitalen Bildverarbeitung. Aktuelle und historische Luftbilder wurden visuell interpretiert und anschließend vektoriell digitalisiert. Satellitenszenen wurden vorwiegend digital direkt im Rasterdatenmodell bearbeitet. Nach der Datenaufbereitung mit verschiedenen Techniken der Bildverarbeitung erfolgte die Auswertung mittels digitaler Klassifizierung. Weitere wichtige Bearbeitungsschritte bei der Ergebnisfindung waren unterschiedliche multitemporale Darstellungsweisen, die Berechnung von Vegetationsindizes sowie Verschneidungstechniken zur Aufdeckung von Veränderungen. Die Auswertung aller Daten erfolgte nach einem einheitlichen mehrstufigen Klassifizierungssystem, das für die Verhältnisse im Tschadbecken entwickelt wurde. Die aus den Fernerkundungsdaten abgeleiteten Ergebnisse gliedern sich nach vier verschiedenen Dimensionen der Zeit. Die Ausgangsbasis bildet eine digitale aktuelle Kartierung der Landbedeckung und Landnutzung eines mehr als 3500 km² großen Ausschnittes des nigerianischen Tschadbeckens im Maßstab 1 : 25 000. Aufbauend auf der aktuellen Landnutzungskartierung wurde für einen etwa 1100 km² großen zentralen Teilausschnitt aus dem Gesamtuntersuchungsgebiet das dynamische Verhalten der Landbedeckungs- und Landnutzungseinheiten im Jahresverlauf untersucht. Dazu konnten fünf SPOT-XS-Satellitenszenen der Vegetationsperiode 1995/96 herangezogen werden. Als Zusammenfassung aus den phänologischen Analysen aller im Untersuchungsgebiet auftretenden Objekte und ihrem entsprechenden unterschiedlichen Spektralverhalten zu verschiedenen Zeitpunkten wurde eine detaillierte Landbedeckungs- und Landnutzungskartierung der Saison 1995/96 angefertigt. Sie ging aus einer komplexen hierarchischen Satellitenbildklassifizierung mit differenzierten Zuweisungsregeln hervor. Mit den Erfahrungen aus der Untersuchung zur saisonalen Dynamik wurden in einem weiteren Schritt alle für das Teiluntersuchungsgebiet zur Verfügung stehenden Satellitenszenen ausgewertet, um Erkenntnisse über interannuelle Unterschiede der zu verschiedenen Zeitpunkten aufgenommenen Satellitenszenen zu gewinnen und deren Ursachen aufzudecken. Als ideale Grundlage wurden multitemporale Vegetationsindizes verglichen, Veränderungskarten abgeleitet und Niederschlagsdaten zur Interpretation hinzugezogen. Eine 24jährige Zeitreihe der klassifizierten Vegetationsindizes ermöglicht eine zusammenfassende Interpretation. Die Auswertung historischer Luftbilder von 1957 und der Vergleich mit den Luftbildern von 1990 ermöglichte schließlich die Beurteilung langfristiger Entwicklungen im engeren Untersuchungsgebiet. Die Ergebnisse sind in Form einer historischen Karte, als Veränderungskarten und quantitativ festgehalten. Ein wichtiges Ergebnis der vorliegenden Arbeit besteht in der Strukturierung aller verwendeten Grundlagendaten zum Thema Landbedeckung und Landnutzung im Tschadbecken einschließlich seiner Nachbargebiete innerhalb des regionalen geographischen Informationssystemes FirGIS. In ihm sind neben den Ausgangsdaten alle Ergebnisse und die zum Thema gehörigen Zusatzinformationen enthalten. Es ermöglicht damit eine zukünftige Fortschreibung durch thematische, räumliche oder zeitliche Ausdehnung. Das Geoinformationssystem FirGIS bietet außerdem die Möglichkeit, bereits vorhandene wie auch zukünftige Information anderen Interessenten vor allem auch vor Ort zur Verfügung zu stellen.
Bayesian Networks are computer-based environmental models that are frequently used to support decision-making under uncertainty. Under data scarce conditions, Bayesian Networks can be developed, parameterized, and run based on expert knowledge only. However, the efficiency of expert-based Bayesian Network modeling is limited by the difficulty in deriving model inputs in the time available during expert workshops. This thesis therefore aimed at developing a simple and robust method for deriving conditional probability tables from expert estimates in a time-efficient way. The design and application of this new elicitation and conversion method is demonstrated using a case study in Xinjiang, Northwest China. The key characteristics of this method are its time-efficiency and the approach to use different conversion tables based on varying levels of confidence. Although the method has its limitations, e.g. it can only be applied for variables with one conditioning variable; it provides the opportunity to support the parameterization of Bayesian Networks which would otherwise remain half-finished due to time constraints. In addition, a case study in the Murray-Darling Basin, Australia, is used to compare Bayesian Network types and software to improve the presentation clarity of large Bayesian Networks. Both case studies aimed at gaining insights on how to improve the applicability of Bayesian Networks to support environmental management.
Eisnukleierende Partikel (INP) sind ein wichtiger Bestandteil des atmosphärischen Aerosols. Trotz ihrer geringen Konzentrationen in der Atmosphäre haben sie Einfluss auf die Bildung von Eiskristallen und auf den Niederschlag. Durch Änderungen in Anzahlkonzentration oder anderer Eigenschaften der INP können sich Wolkenparameter wie Lebensdauer und Tröpfchendichte ändern, was weiter eine Ursache für Änderungen im globalen Strahlungshaushalt sein kann.
Der Anteil zum globalen Strahlungshaushalt durch „Wolken-Anpassungen aufgrund von Aerosolen“, stellt weiterhin die größte Unsicherheit des Strahlungsantriebes dar. Aus diesem Grund sind Messungen und Studien über atmosphärische Aerosole und INP notwendig. Im Rahmen dieser Arbeit wurde der Eiskeimzähler FINCH („fast ice nucleus chamber“) grundlegend überholt und für Messungen von INP optimiert. FINCH ist ein in-situ Eiskeimzähler der durch Mischung unterschiedlicher Luftströme eine Übersättigung der Probeluft mit Wasserdampf erzeugt, um auf diese Weise die zu untersuchenden Aerosolpartikel zu Eiskristallen wachsen zu lassen. Am Ende einer Wachstumskammer werden die Partikel durch eine Optik, dem FINCH-OPS, anhand von Streueigenschaften klassifiziert und ausgewertet. Um FINCH im erwarteten Umfang benutzen zu können, wurden am F-OPS der Laser und die zur Detektion des Streulichts benutzen Photomultiplier ersetzt. Weiter wurde die Software zur Detektion der Partikel neu entwickelt. Durch diese Änderungen ist es möglich Partikelanzahl, Partikelgröße sowie eine Information über die Form der Partikel abzuleiten. Über einen weiteren Photomultiplier im F-OPS ist es zudem möglich eine Information über Fluoreszenz des Partikels zu gewinnen, um so auf einen biologischen Ursprung des Partikels zu schließen. Vorangegangene Probleme durch elektromagnetische Einstrahlung und dadurch entstandene Inkonsistenzen während Messungen konnten im Rahmen dieser Arbeit identifiziert und ausgeschlossen werden. Ebenfalls konnten die zur Flusskühlung benutzen Wärmetaucher als Ursache für Verunreinigungen und Kontamination ausgemacht werden. Auch dieser, für Messungen ungeeignete Zustand, wurde im Rahmen dieser Arbeit behoben.
Ausführliche Charakterisierungsmessungen konnte die Funktionsfähigkeit des F-OPS, als einzelnes Messgerät ohne FINCH-Kammer, belegen. Durch Messungen mit einer steuerbaren Lichtquelle in der Optik konnte zudem die elektrische Verarbeitung sowie die Zählqualität der Optik verifiziert werden. Weiter kann durch diese Experimente gezeigt werden, dass mit dem F-OPS größenaufgelöst gemessen werden kann.
Auch in den ersten Streulichtexperimenten mit Testaerosol kann die Funktionsfähigkeit der Optik gezeigt werden. Für Partikelgröße von Dp > 400 nm wird eine Zähleffizienz von 25% eines TSI 3025 CPCs erreicht. Die über den F-OPS abgeleitete Partikelgröße kann durch Messungen mit monodispersen Aerosolpartikeln und einer parallelen Messung mit einem TSI 3330 OPS parametrisiert werden. Weiter kann die Fluoreszenz von ausgewählten Referenzstoffen gezeigt werden.
Im Betrieb von F-OPS hinter der FINCH-Kammer, also FINCH als Komplettsystem, wurden weitere Charakterisierungsmessungen durchgeführt. Es wurde festgestellt, dass die Anzahlkonzentration der Partikel nach Schließen eines Ventils exponentiell abfällt. Die Partikel folgen demnach nicht nur einem laminaren Fluss durch die Kammer. 50% der Partikel haben nach ca. 13 s die Kammer verlassen. Auch wurde ermittelt, dass ca. 40% der Partikel in der Kammer verloren gehen.
Erste Aktivierungsexperimente zeigen, dass Eispartikel in der Kammer auf eine Größe von Dp > 6 µm anwachsen. Durch Nullfiltermessungen in Aktivierungsphasen, sowie Ändern des zur Aktivierung notwendigen feuchten Flusses, wird zudem gezeigt, dass die Aktivierung der INP durch Mischung erfolgt und außerdem keine Fremdpartikel aktiviert werden. Die neue Steuerung der Kammer lässt es zu Temperaturen in etwa einer Stunde gezielt anzusteuern. Es wird gezeigt, dass Schwankungen in der Sättigung hauptsächlich durch Temperaturphänomene beeinflusst werden.
Abschließend wurden beispielhaft Laborexperimente mit Snomax© durchgeführt, welche sehr gut mit Werten aus der Literatur verglichen werden konnten. Auch eine erste Außenluftmessung am Jungfraujoch (Schweiz) wird in dieser Arbeit präsentiert. Die gemessenen INP-Konzentrationen im gezeigten Zeitraum liegen zwischen 1,4 ± 4,1 L-1 und 53 ± 30 L-1 und entsprechen somit wiederum bekannten Literaturwerten.
Die fortschreitende Versauerungsdynamik der Waldböden führt zu einer zunehmenden Gefährdung von Waldökosystemen durch Nährstoffmangel. Um eine Risikoabschätzung vornehmen zu können, werden flächendeckende Informationen zu den für die Bodenversauerung relevanten Waldbodeneigenschaften benötigt. Vor diesem Hintergrund ist auf der Grundlage von acht Prädiktoren/-gruppen ein wissensbasiertes Prognosemodell zur Mächtigkeit des kalkfreien Bodenbereiches in den Waldböden des Kantons Basel-Landschaft (Nordwestschweiz) entwickelt worden. Die Ergebniskarte liefert für 87 % der Waldfläche nachvollziehbare, kleinräumig differenzierte Informationen zur Ausprägung dieser Bodeneigenschaft. Mithilfe der vorliegenden Modellergebnisse lassen sich zukünftig die Basensättigung der Waldböden flächendifferenziert abschätzen und Waldstandorte mit unzureichender Nährstoffversorgung identifizieren. Langfristig stellt das Modell zudem eine wichtige Grundlage zur Beurteilung des Versauerungsrisikos dar.
In this thesis, laboratory investigations have been conducted to investigate several processes occurring during the melt segregation (crystal settling and compaction processes), as well as during emplacement of plutons. With the help of three different sets of centrifuge experiments rates of these three magmatic processes have been evaluated. In the first series of the centrifuge experiments, the diapiric ascent of buoyant material from two source layers at different depths was studied. Through five models, the hypothesis of ascending diapirs was tested and it was demonstrated whether a rising diapir ascends straight upward or if its ascent might be deviated by another buoyant, softer – and consequently easier to travel through – layer which is located within the overburden strata. We were interested under which conditions they can be formed. For this purpose we placed perturbations on top of both the buoyant layers; either with a set-off of both the protrusions (for three of these experiments), or with both protrusion sitting directly on top of each other (for one of the experiments). In the first experiment, we omitted the perturbations, to test which pathways diapirs take which grow from natural Rayleigh-Taylor instabilities. Three others experiments differed in the viscosity contrast between the overburden and the buoyant material. Through the experimental runs, the effects of different overburden viscosities and perturbation positions on the number of the diapirs were observed. The modeling results show that two diapirs rising from the offset perturbations do not take the same pathway through the overburden layer. Rather, each diapir takes a different pathway, with the deeper diapir piercing through its overburden while rising, regardless if it was a buoyant layer or denser overburden layers. However, when the two perturbations were situated directly above each other in the different PDMS layers, this resulted in the formation of one big diapir rather than several smaller ones, and the overburden layer was less deformed than with offset perturbations. Diapiric structures as those derived from the models without perturbation and where the perturbation are offset occur within Great Kavir Basin (Iran), where numerous salt diapirs grew from several salt horizons, which show a similar spatial distribution. The resulting structure observed in the model where the two perturbations situated directly above each other, is close to what is observed in composite batholiths such as the Flasergranitoid Zone within the Bergsträßer Odenwald Crystalline Complex (Germany). The second series of models were aimed to study crystal settling within a magma. For this purpose experiments with an artificial magma of 30 vol% olivine in 70 vol% basaltic melt were conducted to elucidate the formation mechanisms and time scales of gravitational cumulates. Through the experiments, two physical processes have been observed: (i) purely mechanical compaction, and (ii) chemical compaction induced by dissolution and re-precipitation of settled crystals. The results reveals that the mechanical settling of the dense olivine suspension occurs at about 1/6 the speed of simple Stokes settling, and a sedimentation exponent n of 4.1 is found. Evidences of chemical compaction induced by dissolution and re-precipitation of settled crystals have been highlighted by a detailed analysis of the fine structure of olivine grain boundaries. This last has revealed (1) the presence of Ca, which is characteristic only for MORB-melt, at the interface of two adjacent Ol-grains even when no melt is present; (2) a not fully crystallized boundary layer between two adjacent olivine grains. The crystal size distribution curves and the grain size growth exponent n ~3.6 indicate that diffusion controlled Ostwald ripening is the dominant crystal growth mechanism in concentrated magmatic suspensions. Finally, the formation times in natural olivine adcumulates have been calculated. The last series of centrifuge experiments deals with the crystal-melt settling-floating mechanism in a system composed of natural two pyroxene gabbro. The results have revealed a vertical evolution of the major and trace elements in the melt phase. Then, a numerical modelling of the sedimentation process of the crystals has been made in order to describe the compaction evolution with time. In comparing the numerical simulation with the centrifuge modelling, the stratification of the compacted layer in the runs is reproduced in numerical models. Moreover, on the base of the numerical and centrifuge modelling, a sedimentation exponent describing a deviation of settling in concentrated suspensions from Stokes sedimentation has been evaluated. Finally, the numerical simulation is applied to the Muskox intrusion to estimate the formation time and the melt fraction evolution in using the hindered sedimentation model calculations.
The Izu–Bonin–Mariana volcanic arc is situated at a convergent plate margin where subduction initiation triggered the formation of MORB-like forearc basalts as a result of decompression melting and near-trench spreading. International Ocean Discovery Program (IODP) Expedition 352 recovered samples within the forearc basalt stratigraphy that contained unusual macroscopic globular textures hosted in andesitic glass (Unit 6, Hole 1440B). It is unclear how these andesites, which are unique in a stratigraphic sequence dominated by forearc basalts, and the globular textures therein may have formed. Here, we present detailed textural evidence, major and trace element analysis, as well as B and Sr isotope compositions, to investigate the genesis of these globular andesites. Samples consist of K2O-rich basaltic globules set in a glassy groundmass of andesitic composition. Between these two textural domains a likely hydrated interface of devitrified glass occurs, which, based on textural evidence, seems to be genetically linked to the formation of the globules. The andesitic groundmass is Cl rich (ca. 3000 µg/g ), whereas globules and the interface are Cl poor (ca. 300 µg/g ). Concentrations of fluid-mobile trace elements also appear to be fractionated in that globules and show enrichments in B, K, Rb, Cs, and Tl, but not in Ba and W relative to the andesitic groundmass, whereas the interface shows depletions in the latter, but is enriched in the former. Interestingly, globules and andesitic groundmass have identical Sr isotopic composition within analytical uncertainty ( 87Sr∕86Sr of 0.70580 ± 10 ), indicating that they likely formed from the same source. However, globules show high δ11 B (ca. + 7 ‰ ), whereas their host andesites are isotopically lighter (ca. – 1 ‰ ), potentially indicating that whatever process led to their formation either introduced heavier B isotopes to the globules, or induced stable isotope fractionation of B between globules and their groundmass. Based on the bulk of the textural information and geochemical data obtained from these samples, we conclude that these andesites likely formed as a result of the assimilation of shallowly altered oceanic crust (AOC) during forearc basaltic magmatism. Assimilation likely introduced radiogenic Sr, as well as heavier B isotopes to comparatively unradiogenic and low δ11B forearc basalt parental magmas (average 87Sr∕86Sr of 0.703284). Moreover, the globular textures are consistent with their formation being the result of fluid-melt immiscibility that was potentially induced by the rapid release of water from assimilated AOC whose escape likely formed the interface. If the globular textures present in these samples are indeed the result of fluid-melt immiscibility, then this process led to significant trace element and stable isotope fractionation. The textures and chemical compositions of the globules highlight the need for future experimental studies aimed at investigating the exsolution process with respect to potential trace element and isotopic fractionation in arc magmas that have perhaps not been previously considered.
Holocene climate was characterised by variability on multi-centennial to multi-decadal time scales. In central Europe, these fluctuations were most pronounced during winter. Here we present a record of past winter climate variability for the last 10.8 ka based on four speleothems from Bunker Cave, western Germany. Due to its central European location, the cave site is particularly well suited to record changes in precipitation and temperature in response to changes in the North Atlantic realm. We present high-resolution records of δ18O, δ13C values and Mg/Ca ratios. Changes in the Mg/Ca ratio are attributed to past meteoric precipitation variability. The stable C isotope composition of the speleothems most likely reflects changes in vegetation and precipitation, and variations in the δ18O signal are interpreted as variations in meteoric precipitation and temperature. We found cold and dry periods between 8 and 7 ka, 6.5 and 5.5 ka, 4 and 3 ka as well as between 0.7 and 0.2 ka. The proxy signals in the Bunker Cave stalagmites compare well with other isotope records and, thus, seem representative for central European Holocene climate variability. The prominent 8.2 ka event and the Little Ice Age cold events are both recorded in the Bunker Cave record. However, these events show a contrasting relationship between climate and δ18O, which is explained by different causes underlying the two climate anomalies. Whereas the Little Ice Age is attributed to a pronounced negative phase of the North Atlantic Oscillation, the 8.2 ka event was triggered by cooler conditions in the North Atlantic due to a slowdown of the thermohaline circulation.
Holocene climate was characterised by variability on multi-centennial to multi-decadal time scales. In central Europe, these fluctuations were most pronounced during winter. Here we present a new record of past winter climate variability for the last 10.8 ka based on four speleothems from Bunker Cave, Western Germany. Due to its central European location, the cave site is particularly well suited to record changes in precipitation and temperature in response to changes in the North Atlantic realm. We present high resolution records of δ18O, δ13C values and Mg/Ca ratios. We attribute changes in the Mg/Ca ratio to variations in the meteoric precipitation. The stable C isotope composition of the speleothems most likely reflects changes in vegetation and precipitation and variations in the δ18O signal are interpreted as variations in meteoric precipitation and temperature. We found cold and dry periods between 9 and 7 ka, 6.5 and 5.5 ka, 4 and 3 ka as well as between 0.7 to 0.2 ka. The proxy signals in our stalagmites compare well with other isotope records and, thus, seem representative for central European Holocene climate variability. The prominent 8.2 ka event and the Little Ice Age cold events are both recorded in the Bunker cave record. However, these events show a contrasting relationship between climate and δ18O, which is explained by different causes underlying the two climate anomalies. Whereas the Little Ice Age is attributed to a pronounced negative phase of the North Atlantic Oscillation, the 8.2 ka event was triggered by cooler conditions in the North Atlantic due to a slowdown of the Thermohaline Circulation.
Abrupt climate changes of the last deglaciation detected in a Western Mediterranean forest record
(2010)
Abrupt changes in Western Mediterranean climate during the last deglaciation (20 to 6 cal ka BP) are detected in marine core MD95-2043 (Alboran Sea) through the investigation of high-resolution pollen data and pollen-based climate reconstructions by the modern analogue technique (MAT) for annual precipitation (Pann) and mean temperatures of the coldest and warmest months (MTCO and MTWA). Changes in temperate Mediterranean forest development and composition and MAT reconstructions indicate major climatic shifts with parallel temperature and precipitation changes at the onsets of Heinrich stadial 1 (equivalent to the Oldest Dryas), the Bölling-Allerød (BA), and the Younger Dryas (YD). Multi-centennial-scale oscillations in forest development occurred throughout the BA, YD, and early Holocene. Shifts in vegetation composition and (Pann reconstructions indicate that forest declines occurred during dry, and generally cool, episodes centred at 14.0, 13.3, 12.9, 11.8, 10.7, 10.1, 9.2, 8.3 and 7.4 cal ka BP. The forest record also suggests multiple, low-amplitude Preboreal (PB) climate oscillations, and a marked increase in moisture availability for forest development at the end of the PB at 10.6 cal ka BP. Dry atmospheric conditions in the Western Mediterranean occurred in phase with Lateglacial events of high-latitude cooling including GI-1d (Older Dryas), GI-1b (Intra-Allerød Cold Period) and GS-1 (YD), and during Holocene events associated with high-latitude cooling, meltwater pulses and N. Atlantic ice-rafting. A possible climatic mechanism for the recurrence of dry intervals and an opposed regional precipitation pattern with respect to Western-central Europe relates to the dynamics of the westerlies and the prevalence of atmospheric blocking highs. Comparison of radiocarbon and ice-core ages for well-defined climatic transitions in the forest record suggests possible enhancement of marine reservoir ages in the Alboran Sea by 200 years (surface water age 600 years) during the Lateglacial.
Abrupt climate changes of the last deglaciation detected in a western Mediterranean forest record
(2009)
Abrupt changes in Western Mediterranean climate during the last deglaciation (20 to 6 cal ka BP) are detected in marine core MD95-2043 (Alboran Sea) through the investigation of high-resolution pollen data and pollen-based climate reconstructions by the modern analogue technique (MAT) for annual precipitation (Pann) and mean temperatures of the coldest and warmest months (MTCO and MTWA). Changes in temperate Mediterranean forest development and composition and MAT reconstructions indicate major climatic shifts with parallel temperature and precipitation changes at the onsets of Heinrich stadial 1 (equivalent to the Oldest Dryas), the Bölling-Allerød (BA), and the Younger Dryas (YD). Multi-centennial-scale oscillations in forest development occurred throughout the BA, YD, and early Holocene. Shifts in vegetation composition and (Pann reconstructions indicate that forest declines occurred during dry, and generally cool, episodes centred at 14.0, 13.3, 12.9, 11.8, 10.7, 10.1, 9.2, 8.3 and 7.4 cal ka BP. The forest record also suggests multiple, low-amplitude Preboreal (PB) climate oscillations, and a marked increase in moisture availability for forest development at the end of the PB at 10.6 cal ka BP. Dry atmospheric conditions in the Western Mediterranean occurred in phase with Lateglacial events of high-latitude cooling including GI-1d (Older Dryas), GI-1b (Intra-Allerød Cold Period) and GS-1 (YD), and during Holocene events associated with high-latitude cooling, meltwater pulses and N. Atlantic ice-rafting. A possible climatic mechanism for the recurrence of dry intervals and an opposed regional precipitation pattern with respect to Western-central Europe relates to the dynamics of the westerlies and the prevalence of atmospheric blocking highs. Comparison of radiocarbon and ice-core ages for well-defined climatic transitions in the forest record suggests possible enhancement of marine reservoir ages in the Alboran Sea by 200 years (surface water age 600 years) during the Lateglacial.
This study aims to assess the skill of regional climate models (RCMs) at reproducing the climatology of Mediterranean cyclones. Seven RCMs are considered, five of which were also coupled with an oceanic model. All simulations were forced at the lateral boundaries by the ERA-Interim reanalysis for a common 20-year period (1989–2008). Six different cyclone tracking methods have been applied to all twelve RCM simulations and to the ERA-Interim reanalysis in order to assess the RCMs from the perspective of different cyclone definitions. All RCMs reproduce the main areas of high cyclone occurrence in the region south of the Alps, in the Adriatic, Ionian and Aegean Seas, as well as in the areas close to Cyprus and to Atlas mountains. The RCMs tend to underestimate intense cyclone occurrences over the Mediterranean Sea and reproduce 24–40 % of these systems, as identified in the reanalysis. The use of grid nudging in one of the RCMs is shown to be beneficial, reproducing about 60 % of the intense cyclones and keeping a better track of the seasonal cycle of intense cyclogenesis. Finally, the most intense cyclones tend to be similarly reproduced in coupled and uncoupled model simulations, suggesting that modeling atmosphere–ocean coupled processes has only a weak impact on the climatology and intensity of Mediterranean cyclones.
This paper is a contribution to the special issue on Med-CORDEX, an international coordinated initiative dedicated to the multi-component regional climate modelling (atmosphere, ocean, land surface, river) of the Mediterranean under the umbrella of HyMeX, CORDEX, and Med-CLIVAR and coordinated by Samuel Somot, Paolo Ruti, Erika Coppola, Gianmaria Sannino, Bodo Ahrens, and Gabriel Jordà.
Der Erdfall „Seeloch" bei Bad Hersfeld ist ein etwa kreisrunder Einbruch im Buntsandstein mit einem Durchmesser von ca. 80 m, der auf Subrosionsvorgänge lm Zechsteinsalinar zurückgeführt wird. Einbrüche dieser Art sind typisch für Salzhänge, wie an anderen Beispielen gezeigt wird. Kaminartige Durchbrüche durch mehrere hundert Meter mächtiges Deckgebirge können nur entstehen, wenn eine vorgegebene Klüftung vorhanden ist. Ähnliche Erscheinungen sind über Lösungshohlräumen beobachtet worden, die beim Absaufen von Kaliwerken entstanden. Erfahrungen aus dem Salinenbetrieb zeigen, daß auch im Steinsalz größere Hohlräume längere Zeit existieren können, ohne daß es zu Bodensenkungen oder Erdfällen kommt. Die Sedimente des „Seeloch" sind palynologisoh und stratigraphisch bearbeitet worden. Das besondere Ergebnis dieser Untersuchungen ist daß Interglazial-Alter (Riß-Würrn) des Profilabschnittes. Die bisher untersuchten Salzauslaugungssenken enthalten Ablagerungen des Tertiärs, Altpleistozäns oder des Holozäns. Aus den Korrosionssenken des nordöstlichen Hessens waren bisher nur kohlig-torfige Ablagerungen bekannt geworden, die ein oberpliozänes bis altpleistozänes oder postglaziales Alter haben. Mit den Schichten aus dem "Seeloch" von Kathus werden erstmals Ablagerungen beschrieben, für die ein eemzeitliches Alter (Riß-Würm-Interglazial) wahrscheinlich ist.
We present the analysis of the impact of convection on the composition of the tropical tropopause layer region (TTL) in West-Africa during the AMMA-SCOUT campaign. Geophysica M55 aircraft observations of water vapor, ozone, aerosol and CO2 during August 2006 show perturbed values at altitudes ranging from 14 km to 17 km (above the main convective outflow) and satellite data indicates that air detrainment is likely to have originated from convective cloud east of the flights. Simulations of the BOLAM mesoscale model, nudged with infrared radiance temperatures, are used to estimate the convective impact in the upper troposphere and to assess the fraction of air processed by convection. The analysis shows that BOLAM correctly reproduces the location and the vertical structure of convective outflow. Model-aided analysis indicates that convection can influence the composition of the upper troposphere above the level of main outflow for an event of deep convection close to the observation site. Model analysis also shows that deep convection occurring in the entire Sahelian transect (up to 2000 km E of the measurement area) has a non negligible role in determining TTL composition.
We present the analysis of the impact of convection on the composition of the tropical tropopause layer region (TTL) in West-Africa during the AMMA-SCOUT campaign. Geophysica M55 aircraft observations of water vapor, ozone, aerosol and CO2 show perturbed values at altitudes ranging from 14 km to 17 km (above the main convective outflow) and satellite data indicates that air detrainment is likely originated from convective cloud east of the flight. Simulations of the BOLAM mesoscale model, nudged with infrared radiance temperatures, are used to estimate the convective impact in the upper troposphere and to assess the fraction of air processed by convection. The analysis shows that BOLAM correctly reproduces the location and the vertical structure of convective outflow. Model-aided analysis indicates that in the outflow of a large convective system, deep convection can largely modify chemical composition and aerosol distribution up to the tropical tropopause. Model analysis also shows that, on average, deep convection occurring in the entire Sahelian transect (up to 2000 km E of the measurement area) has a non negligible role in determining TTL composition.
Global modelling of continental water storage changes : sensitivity to different climate data sets
(2007)
Since 2002, the GRACE satellite mission provides estimates of the Earth's dynamic gravity field with unprecedented accuracy. Differences between monthly gravity fields contain a clear hydrological signal due to continental water storage changes. In order to evaluate GRACE results, the state-of-the-art WaterGAP Global Hydrological Model (WGHM) is applied to calculate terrestrial water storage changes on a global scale. WGHM is driven by different climate data sets to analyse especially the influence of different precipitation data on calculated water storage. The data sets used are the CRU TS 2.1 climate data set, the GPCC Full Data Product for precipitation and data from the ECMWF integrated forecast system. A simple approach for precipitation correction is introduced. WGHM results are then compared with GRACE data. The use of different precipitation data sets leads to considerable differences in computed water storage change for a large number of river basins. Comparing model results with GRACE observations shows a good spatial correlation and also a good agreement in phase. However, seasonal variations of water storage as derived from GRACE tend to be significantly larger than those computed by WGHM, regardless of which climate data set is used.
Abiotic formation of n-alkane hydrocarbons has been postulated to occur within Earth's crust. Apparent evidence was primarily based on uncommon carbon and hydrogen isotope distribution patterns that set methane and its higher chain homologues apart from biotic isotopic compositions associated with microbial production and closed system thermal degradation of organic matter. Here, we present the first global investigation of the carbon and hydrogen isotopic compositions of n-alkanes in volcanic-hydrothermal fluids hosted by basaltic, andesitic, trachytic and rhyolitic rocks. We show that the bulk isotopic compositions of these gases follow trends that are characteristic of high temperature, open system degradation of organic matter. In sediment-free systems, organic matter is supplied by surface waters (seawater, meteoric water) circulating through the reservoir rocks. Our data set strongly implies that thermal degradation of organic matter is able to satisfy isotopic criteria previously classified as being indicative of abiogenesis. Further considering the ubiquitous presence of surface waters in Earth’s crust, abiotic hydrocarbon occurrences might have been significantly overestimated.
Wildfire is the most common disturbance type in boreal forests and can trigger significant changes in forest composition. Waterlogging in peatlands determines the degree of tree cover and the depth of the burnt horizon associated with wildfires. However, interactions between peatland moisture, vegetation composition and flammability, and fire regime in forest and forested peatland in Eurasia remain largely unexplored, despite their huge extent in boreal regions. To address this knowledge gap, we reconstructed the Holocene fire regime, vegetation composition, and peatland hydrology at two sites located in predominantly light taiga (Pinus sylvestris Betula) with interspersed dark taiga communities (Pinus sibirica, Picea obovata, Abies sibirica) in western Siberia in the Tomsk Oblast, Russia. We found marked shifts in past water levels over the Holocene. The probability of fire occurrence and the intensification of fire frequency and severity increased at times of low water table (drier conditions), enhanced fuel dryness, and an intermediate dark-to-light taiga ratio. High water level, and thus wet peat surface conditions, prevented fires from spreading on peatland and surrounding forests. Deciduous trees (i.e. Betula) and Sphagnum were more abundant under wetter peatland conditions, and conifers and denser forests were more prevalent under drier peatland conditions. On a Holocene scale, severe fires were recorded between 7.5 and 4.5 ka with an increased proportion of dark taiga and fire avoiders (Pinus sibirica at Rybnaya and Abies sibirica at Ulukh–Chayakh) in a predominantly light taiga and fire-resister community characterised by Pinus sylvestris and lower local water level. Severe fires also occurred over the last 1.5 kyr and were associated with a declining abundance of dark taiga and fire avoiders, an expansion of fire invaders (Betula), and fluctuating water tables. These findings suggest that frequent, high-severity fires can lead to compositional and structural changes in forests when trees fail to reach reproductive maturity between fire events or where extensive forest gaps limit seed dispersal. This study also shows prolonged periods of synchronous fire activity across the sites, particularly during the early to mid-Holocene, suggesting a regional imprint of centennial- to millennial-scale Holocene climate variability on wildfire activity. Humans may have affected vegetation and fire from the Neolithic; however, increasing human presence in the region, particularly at the Ulukh–Chayakh Mire over the last 4 centuries, drastically enhanced ignitions compared to natural background levels. Frequent warm and dry spells predicted by climate change scenarios for Siberia in the future will enhance peatland drying and may convey a competitive advantage to conifer taxa. However, dry conditions will probably exacerbate the frequency and severity of wildfire, disrupt conifers' successional pathway, and accelerate shifts towards deciduous broadleaf tree cover. Furthermore, climate–disturbance–fire feedbacks will accelerate changes in the carbon balance of boreal peatlands and affect their overall future resilience to climate change.
Wildfire is the most common disturbance type in boreal forests and can trigger significant changes in forest composition. Waterlogging in peatlands determines the degree of tree cover and the depth of the burning horizon associated with wildfires. However, interactions between peatland moisture, vegetation composition and flammability, and fire regime in forested peatland in Eurasia remain largely unexplored, despite their huge extent in boreal regions. To address this knowledge gap, we reconstructed the Holocene fire regime, vegetation composition and peatland hydrology at two sites in Western Siberia near Tomsk Oblast, Russia. The palaeoecological records originate from forested peatland areas in predominantly light taiga (Pinus-Betula) with increase in dark taiga communities (Pinus sibirica, Picea obovata, Abies sibirica) towards the east. We found that the past water level fluctuated between 8 and 30 cm below the peat surface. Wet peatland conditions promoted broadleaf trees (Betula), whereas dry peatland conditions favoured conifers and a greater forest density (dark-to-light-taiga ratio). The frequency and severity of fire increased with a declining water table that enhanced fuel dryness and flammability and at an intermediate forest density. We found that the probability of intensification in fire severity increased when the water
level declined below 20 cm suggesting a tipping point in peatland hydrology at which wildfire regime intensifies. On a Holocene scale, we found two scenarios of moisture-vegetation-fire interactions. In the first, severe fires were recorded 45 between 7.5 and 4.5 ka BP with lower water level and an increased proportion of dark taiga and fire avoiders (Pinus sibirica at Rybanya and Abies sibirica at Ulukh Chayakh) mixed into the dominantly light taiga and fire-resister community of Pinus
sylvestris. The second occurred over the last 1.5 ka and was associated with fluctuating water tables, a declining abundance of fire avoiders, and an expansion of fire invaders (Betula). These findings suggest that frequent high-severity fires can lead to compositional and structural changes in forests when trees fail to reach reproductive maturity between fire events or where extensive forest gaps limit seed dispersal. This study also shows prolonged periods of synchronous fire activity across the sites, particularly during the early to mid-Holocene, suggesting a regional imprint of centennial to millennial-scale Holocene climate
variability on wildfire activity. Increasing human presence in the region of the Ulukh-Chayakh Mire near Teguldet over the last four centuries drastically enhanced ignitions compared to natural background levels. Frequent warm and dry spells predicted for the future in Siberia by climate change scenarios will enhance peatland drying and may convey a competitive advantage to conifer taxa. However, dry conditions, particularly a water table decline below the threshold of 20 cm, will probably exacerbate the frequency and severity of wildfire, disrupt conifers’ successional pathway and accelerate shifts towards more fire-adapted broadleaf tree cover. Furthermore, climate-disturbance-fire feedbacks will accelerate changes in the carbon balance of forested boreal peatlands and affect their overall future resilience to climate change.
The analysis of charcoal fragments in peat and lake sediments is the most widely used approach to reconstruct past biomass burning. With a few exceptions, this method typically relies on the quantification of the total charcoal content of the sediment. To enhance charcoal analyses for the reconstruction of past fire regimes, and to make the method more relevant to studies of both plant evolution and fire management, more information must be extracted from charcoal particles. Here, I burned in the laboratory seven fuel types comprising 17 species from boreal Siberia, and build on published schemes to develop morphometric and finer diagnostic classifications of the experimentally charred particles. As most of the species used in this study are common to Northern Hemisphere forests and peatlands, these results can be directly applicable over a broad geographical scale. Results show that the effect of temperature on charcoal production is fuel dependent. Graminoids and Sphagnum, and wood (trunk) lose the most mass at low burn temperatures, whereas heathland shrub leaves, brown moss, and ferns retain the most mass at high burn temperatures. In contrast to the wood of trunk, the wood of twigs retained their mass at intermediate temperature. This suggests that species with low mass retention at hotter burning temperatures might be underrepresented in the fossil charcoal record. Charred particle aspect ratio (L/W) appeared to be the strongest indicator of the fuel type burnt. Graminoid charcoals are more elongate than those of all other fuel types, leaf charcoals are the shortest and bulkiest, and twig and wood charcoals are intermediate. Finer diagnostic features were the most useful in distinguishing between wood, graminoid, and leaf particles, but further distinctions within these fuel types are difficult. High-aspect-ratio particles dominated by graminoid and Sphagnum morphologies are robust indicators of cooler surface fires. Contrastingly, abundant wood and leaf morphologies and low-aspect-ratio particles likely indicate higher-temperature fires. However, the overlapping morphologies of leaves and wood from trees and shrubs make it hard to distinguish between high-intensity surface fires combusting living shrubs and dead wood and leaves or high-intensity crown fires combusting living trees. Despite these limitations, the combined use of charred-particle aspect ratios and fuel morphotypes can aid in more robustly interpreting changes in fuel source and fire type, thereby substantially refining histories of past wildfires. Further fields of investigation to improve the interpretation of the fossil charcoal records will require: i) More in-depth knowledge of plant anatomy for a better determination of fuel sources; ii) Relate the proportion of particular charcoal morphotypes to the quantity of biomass; iii) Link the chemical composition of fuels, combustion temperature, and charcoal production. The advanced use of image-recognition software to collect data on other charcoal features could also aid in extracting fire temperatures as well as a change in particles morphology and morphometry during particles transportation.
The analysis of charcoal fragments in peat and lake sediments is the most widely used approach to reconstruct past biomass burning. With a few exceptions, this method typically relies on the quantification of the total charcoal content of the sediment. To enhance charcoal analyses for the reconstruction of past fire regimes and make the method more relevant to studies of both plant evolution and fire management, the extraction of more information from charcoal particles is critical. Here, I used a muffle oven to burn seven fuel types comprising 17 species from boreal Siberia (near Teguldet village), which are also commonly found in the Northern Hemisphere, and built on published schemes to develop morphometric and finer diagnostic classifications of the experimentally charred particles. I then combined these results with those from fossil charcoal from a peat core taken from the same location (Ulukh-Chayakh mire) in order to demonstrate the relevance of these experiments to the fossil charcoal records. Results show that graminoids, Sphagnum, and wood (trunk) lose the most mass at low burn temperatures (<300 ∘C), whereas heathland shrub leaves, brown moss, and ferns lose the most mass at high burn temperatures. This suggests that species with low mass retention in high-temperature fires are likely to be under-represented in the fossil charcoal record. The charcoal particle aspect ratio appeared to be the strongest indicator of the fuel type burnt. Graminoid charcoal particles are the most elongate (6.7–11.5), with a threshold above 6 that may be indicative of wetland graminoids; leaves are the shortest and bulkiest (2.1–3.5); and twigs and wood are intermediate (2.0–5.2). Further, the use of fine diagnostic features was more successful in separating wood, graminoids, and leaves, but it was difficult to further differentiate these fuel types due to overlapping features. High-aspect-ratio particles, dominated by graminoid and Sphagnum morphologies, may be robust indicators of low-temperature surface fires, whereas abundant wood and leaf morphologies as well as low-aspect-ratio particles are indicative of higher-temperature fires. However, the overlapping morphologies of leaves and wood from trees and shrubs make it hard to distinguish between high-intensity surface fires, combusting living shrubs and dead wood and leaves, and high-intensity crown fires that have burnt living trees. Distinct particle shape may also influence charcoal transportation, with elongated particles (graminoids) potentially having a more heterogeneous distribution and being deposited farther away from the origin of fire than the rounder, polygonal leaf particles. Despite these limitations, the combined use of charred-particle aspect ratios and fuel morphotypes can aid in the more robust interpretation of fuel source and fire-type changes. Lastly, I highlight the further investigations needed to refine the histories of past wildfires.
We have used the SLIMCAT 3-D off-line chemical transport model (CTM) to quantify the Arctic chemical ozone loss in the year 2002/2003 and compare it with similar calculations for the winters 1999/2000 and 2003/2004. Recent changes to the CTM have improved the model's ability to reproduce polar chemical and dynamical processes. The updated CTM uses σ-θ as a vertical coordinate which allows it to extend down to the surface. The CTM has a detailed stratospheric chemistry scheme and now includes a simple NAT-based denitrification scheme in the stratosphere.
In the model runs presented here the model was forced by ECMWF ERA40 and operational analyses. The model used 24 levels extending from the surface to ~55 km and a horizontal resolution of either 7.5°×7.5° or 2.8°×2.8°. Two different radiation schemes, MIDRAD and the CCM scheme, were used to diagnose the vertical motion in the stratosphere. Based on tracer observations from balloons and aircraft, the more sophisticated CCM scheme gives a better representation of the vertical transport in this model which includes the troposphere. The higher resolution model generally produces larger chemical O3 depletion, which agrees better with observations.
The CTM results show that very early chemical ozone loss occurred in December 2002 due to extremely low temperatures and early chlorine activation in the lower stratosphere. Thus, chemical loss in this winter started earlier than in the other two winters studied here. In 2002/2003 the local polar ozone loss in the lower stratosphere was ~40% before the stratospheric final warming. Larger ozone loss occurred in the cold year 1999/2000 which had a persistently cold and stable vortex during most of the winter. For this winter the current model, at a resolution of 2.8°×2.8°, can reproduce the observed loss of over 70% locally. In the warm and more disturbed winter 2003/2004 the chemical O3 loss was generally much smaller, except above 620 K where large losses occurred due to a period of very low minimum temperatures at these altitudes.
We have used the SLIMCAT 3-D off-line chemical transport model (CTM) to quantify the Arctic chemical ozone loss in the year 2002/2003 and compare it with similar calculations for the winters 1999/2000 and 2003/2004. Recent changes to the CTM have improved the model's ability to reproduce polar chemical and dynamical processes. The updated CTM uses σ-θ as a vertical coordinate which allows it to extend down to the surface. The CTM has a detailed stratospheric chemistry scheme and now includes a simple NAT-based denitrification scheme in the stratosphere.
In the model runs presented here the model was forced by ECMWF ERA40 and operational analyses. The model used 24 levels extending from the surface to ~55km and a horizontal resolution of either 7.5° x 7.5° or 2.8° x 2.8°. Two different radiation schemes, MIDRAD and the CCM scheme, were used to diagnose the vertical motion in the stratosphere. Based on tracer observations from balloons and aircraft, the more sophisticated CCM scheme gives a better representation of the vertical transport in this model which includes the troposphere. The higher resolution model generally produces larger chemical O3 depletion, which agrees better with observations.
The CTM results show that very early chemical ozone loss occurred in December 2002 due to extremely low temperatures and early chlorine activation in the lower stratosphere. Thus, chemical loss in this winter started earlier than in the other two winters studied here. In 2002/2003 the local polar ozone loss in the lower stratosphere was ~40% before the stratospheric final warming. Larger ozone loss occurred in the cold year 1999/2000 which had a persistently cold and stable vortex during most of the winter. For this winter the current model, at a resolution of 2.8° x 2.8°, can reproduce the observed loss of over 70% locally. In the warm and more disturbed winter 2003/2004 the chemical O3 loss was generally much smaller, except above 620K where large losses occurred due to a period of very low minimum temperatures at these altitudes.
Artificial drainage of agricultural land, for example with ditches or drainage tubes, is used to avoid water logging and to manage high groundwater tables. Among other impacts it influences the nutrient balances by increasing leaching losses and by decreasing denitrification. To simulate terrestrial transport of nitrogen on the global scale, a digital global map of artificially drained agricultural areas was developed. The map depicts the percentage of each 5’ by 5’ grid cell that is equipped for artificial drainage. Information on artificial drainage in countries or sub-national units was mainly derived from international inventories. Distribution to grid cells was based, for most countries, on the "Global Croplands Dataset" of Ramankutty et al. (1998) and the "Digital Global Map of Irrigation Areas" of Siebert et al. (2005). For some European countries the CORINE land cover dataset was used instead of the both datasets mentioned above. Maps with outlines of artificially drained areas were available for 6 countries. The global drainage area on the map is 167 Mio hectares. For only 11 out of the 116 countries with information on artificial drainage areas, sub-national information could be taken into account. Due to this coarse spatial resolution of the data sources, we recommended to use the map of artificially drained areas only for continental to global scale assessments. This documentation describes the dataset, the data sources and the map generation, and it discusses the data uncertainty.
The crystal structure of the high temperature phase of anilinium bromide, C6H5NH3⊕Br⊖ , was studied by X-ray and neutron diffraction at T = 343 K. The refinement supports disordered positions of the -NH3⊕ group. A split-atom model is proposed which includes disorder of the benzene ring. The thermal parameters, hydrogen bond distances, and other experimental data (NMR, NQR, inelastic neutron scattering) are in accordance with this model.
The turnover time of terrestrial ecosystem carbon is an emergent ecosystem property that quantifies the strength of land surface on the global carbon cycle–climate feedback. However, observation- and modeling-based estimates of carbon turnover and its response to climate are still characterized by large uncertainties. In this study, by assessing the apparent whole ecosystem carbon turnover times (τ) as the ratio between carbon stocks and fluxes, we provide an update of this ecosystem level diagnostic and its associated uncertainties in high spatial resolution (0.083∘) using multiple, state-of-the-art, observation-based datasets of soil organic carbon stock (Csoil), vegetation biomass (Cveg) and gross primary productivity (GPP). Using this new ensemble of data, we estimated the global median τ to be 43+7−7 yr (median+difference to percentile 75−difference to percentile 25) when the full soil is considered, in contrast to limiting it to 1 m depth. Only considering the top 1 m of soil carbon in circumpolar regions (assuming maximum active layer depth is up to 1 m) yields a global median τ of 37+3−6 yr, which is longer than the previous estimates of 23+7−4 yr (Carvalhais et al., 2014). We show that the difference is mostly attributed to changes in global Csoil estimates. Csoil accounts for approximately 84 % of the total uncertainty in global τ estimates; GPP also contributes significantly (15 %), whereas Cveg contributes only marginally (less than 1 %) to the total uncertainty. The high uncertainty in Csoil is reflected in the large range across state-of-the-art data products, in which full-depth Csoil spans between 3362 and 4792 PgC. The uncertainty is especially high in circumpolar regions with an uncertainty of 50 % and a low spatial correlation between the different datasets (0.2<r<0.5) when compared to other regions (0.6<r<0.8). These uncertainties cast a shadow on current global estimates of τ in circumpolar regions, for which further geographical representativeness and clarification on variations in Csoil with soil depth are needed. Different GPP estimates contribute significantly to the uncertainties of τ mainly in semiarid and arid regions, whereas Cveg causes the uncertainties of τ in the subtropics and tropics. In spite of the large uncertainties, our findings reveal that the latitudinal gradients of τ are consistent across different datasets and soil depths. The current results show a strong ensemble agreement on the negative correlation between τ and temperature along latitude that is stronger in temperate zones (30–60∘ N) than in the subtropical and tropical zones (30∘ S–30∘ N). Additionally, while the strength of the τ–precipitation correlation was dependent on the Csoil data source, the latitudinal gradients also agree among different ensemble members. Overall, and despite the large variation in τ, we identified robust features in the spatial patterns of τ that emerge beyond the differences stemming from the data-driven estimates of Csoil, Cveg and GPP. These robust patterns, and associated uncertainties, can be used to infer τ–climate relationships and for constraining contemporaneous behavior of Earth system models (ESMs), which could contribute to uncertainty reductions in future projections of the carbon cycle–climate feedback. The dataset of τ is openly available at https://doi.org/10.17871/bgitau.201911 (Fan et al., 2019).
The turnover time of terrestrial carbon (τ) controls the global carbon cycle – climate feedback and, yet, is poorly simulated by the current Earth System Models (ESMs). In this study, by assessing apparent carbon turnover time as the ratio between carbon stocks and fluxes, we provide a new, updated ensemble of diagnostic terrestrial carbon turnover times and associated uncertainties on a global scale using multiple, state-of-the-art, observation-based datasets of soil organic carbon stock (Csoil), vegetation biomass (Cveg) and gross primary productivity (GPP). Using this new ensemble, we estimated the global average τ to be 42$% &' years when the full soil depth is considered, longer than the previous estimates of 23$) &* years. Only considering the top 1 m (assuming maximum active layer depth is up to 1 meter) of soil carbon in circumpolar regions yields a global τ of 35$) &' years. Csoil in circumpolar regions account for two thirds of the total uncertainty in global τ estimates, whereas Csoil in non-circumpolar contributes merely 9.38%. GPP (2.25%) and Cveg (0.05%) contribute even less to the total uncertainty. Therefore, the high uncertainty in Csoil is the main factor behind the uncertainty in global τ, as reflected in the larger range of full-depth Csoil (3152-4372 PgC). The uncertainty is especially high in circumpolar regions with a behaviour of ESMs which could contribute to uncertainty reductions in future projections of the carbon cycle - climate feedback. The dataset of the terrestrial turnover time ensemble (DOI: 10.17871/bgitau.201911) is openly available from the data portal: https://doi.org/10.17871/bgitau.201911 (Fan et al., 2019) uncertainty of 50% and the spatial correlations among different datasets are also low compared to other regions. Overall, we argue that current global datasets do not support robust estimates of τ globally, for which we need clarification on variations of Csoil with soil depth and stronger estimates of Csoil in circumpolar regions. Despite the large variation in both magnitude and spatial patterns of τ, we identified robust features in the spatial patterns of τ that emerge regardless of soil depth and differences in data sources of Csoil, Cveg and GPP. Our findings show that the latitudinal gradients of τ are consistent across different datasets and soil depth. Furthermore, there is a strong consensus on the negative correlation between τ and temperature along latitude that is stronger in temperate zones (30ºN-60ºN) than in subtropical and tropical zones (30ºS30ºN). The identified robust patterns can be used to infer the response of τ to climate and for constraining contemporaneous behaviour of ESMs which could contribute to uncertainty reductions in future projections of the carbon cycle - climate feedback. The dataset of the terrestrial turnover time ensemble (DOI:10.17871/bgitau.201911) is openly available from the data portal: https://doi.org/10.17871/bgitau.201911 (Fan et al., 2019).
Abstract:
The mid Miocene represents an important target for paleoclimatic study because the atmospheric CO2 concentration ranged from near modern values to ∼800 ppm, while a large, dynamic Antarctic ice sheet was likely to have been present throughout much of this interval. In this special issue, Modestou et al. (2020) (doi.org/10.1029/2020PA003927) reconstruct deep ocean warmth based on the clumped isotopic composition of benthic foraminifera, a technique that allows the ice volume and thermal components of the benthic oxygen isotope stack to be separated. These data reveal a very warm deep ocean while simultaneously suggesting that continental ice volume may, at times, have been greater than today. Here, I review these results in the context of recent developments in geochemical proxies and ice sheet modeling, and explore how the presence of a large Miocene ice sheet could be reconciled with CO2 at least as high as present. More broadly, I argue that many of the 'paradoxes' that pepper the paleoclimate literature result as much from our imperfect understanding of the proxies, as from our understanding of the climate system. Robust proxies with a well-understood mechanistic basis, as employed by Modestou et al. (2020), as well as advances in model-data comparability usher in a new era of palaeoclimate research; an exciting future of untangling Earth's myriad past climate states awaits.
Plain Language Summary:
Reconstructing climate variation in Earth's geologic past informs us of the broad features of warm climates, which is relevant to preparing for climate change over the coming centuries. Moreover, these data can be compared to state-of-the-art climate models, which provides a test of the degree to which our models can reproduce warm climate states. A paper recently published in this journal applies a new method in order to reconstruct the temperature of the deep ocean in the middle Miocene (between 17 and 12 million years ago), when the atmospheric CO2 concentration was naturally similar to or higher than it is today. Coupled with decades of previous study, these exciting results depict an unfamiliar world characterized by a warm deep ocean, and yet a large ice sheet was present on Antarctica. Both models and data agree that the Antarctic ice sheet in the Miocene was highly responsive to changes in the atmospheric CO2 concentration, a clear cause of concern in the context of ongoing anthropogenic climate change.
Dargestellt werden die Veränderungen eines Podsol-Braunerde-Standortes unter Wald hinsichtlich der Bodeneigenschaften und Vegetation nach ca. 20jähriger Verregnungvon Abwässern einer Stärkefabrik. Bei den chemischen Bodenparametern zeigten sich als Folge der Abwasserverregnung in sich schlüssige und z. T. extreme Auswirkungen auf die Acidität, die Kationengehalte, di~ Kohlenstoff-, Stickstoff- und Phosphorvorräte sowie die Mineralisationsdynamik. Die Überdüngung und Eutrophierung des Standortes wurde außerdem durch Vegetationsaufnahmen, die Auswertung ihrer mittleren ökologischen Zeigerwerte sowie Vegetationsanalysen belegt. Die hier beobachteten Folgewirkungen der Abwasserverregnung im Wald als auch die Auswertung entsprechender Berichte aus der Literatur lassen die Verwendung von Waldflächen zur Abwasserbeseitigung grundsätzlich bedenklich erscheinen.
On the observation of mesospheric air inside the arctic stratospheric polar vortex in early 2003
(2005)
During several balloon flights inside the Arctic polar vortex in early 2003, unusual trace gas distributions were observed, which indicate a strong influence of mesospheric air in the stratosphere. The tuneable diode laser (TDL) instrument SPIRALE (Spectroscopie InFrarouge par Absorption de Lasers Embarqués) measured unusually high CO values (up to 600 ppb) on 27 January at about 30 km altitude. The cryosampler BONBON sampled air masses with very high molecular Hydrogen, extremely low SF6 and enhanced CO values on 6 March at about 25 km altitude. Finally, the MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) Fourier Transform Infra-Red (FTIR) spectrometer showed NOy values which are significantly higher than NOy* (the NOy derived from a correlation between N2O and NOy under undisturbed conditions), on 21 and 22 March in a layer centred at 22 km altitude. Thus, the mesospheric air seems to have been present in a layer descending from about 30 km in late January to 25 km altitude in early March and about 22 km altitude on 20 March. We present corroborating evidence from a model study using the KASIMA (KArlsruhe Simulation model of the Middle Atmosphere) model that also shows a layer of mesospheric air, which descended into the stratosphere in November and early December 2002, before the minor warming which occurred in late December 2002 lead to a descent of upper stratospheric air, cutting of a layer in which mesospheric air is present. This layer then descended inside the vortex over the course of the winter. The same feature is found in trajectory calculations, based on a large number of trajectories started in the vicinity of the observations on 6 March. Based on the difference between the mean age derived from SF6 (which has an irreversible mesospheric loss) and from CO2 (whose mesospheric loss is much smaller and reversible) we estimate that the fraction of mesospheric air in the layer observed on 6 March, must have been somewhere between 35% and 100%.
During several balloon flights inside the Arctic polar vortex in early 2003, unusual trace gas distributions were observed, which indicate a strong influence of mesospheric air in the stratosphere. The tuneable diode laser (TDL) instrument SPIRALE (Spectroscopie InFrarouge par Absorption de Lasers Embarqués) measured unusually high CO values (up to 600 ppb) on 27 January at about 30 km altitude. The cryosampler BONBON sampled air masses with very high molecular Hydrogen, extremely low SF6 and enhanced CO values on 6 March at about 25 km altitude. Finally, the MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) Fourier Transform Infra-Red (FTIR) spectrometer showed NOy values which are significantly higher than NOy* (the NOy derived from a correlation between N2O and NOy under undisturbed conditions), on 21 and 22 March in a layer centred at 22 km altitude. Thus, the mesospheric air seems to have been present in a layer descending from about 30 km in late January to 25 km altitude in early March and about 22 km altitude on 20 March. We present corroborating evidence from a model study using the KASIMA (KArlsruhe Simulation model of the Middle Atmosphere) model that also shows a layer of mesospheric air, which descended into the stratosphere in November and early December 2002, before the minor warming which occurred in late December 2002 lead to a descent of upper stratospheric air, cutting of a layer in which mesospheric air is present. This layer then descended inside the vortex over the course of the winter. The same feature is found in trajectory calculations, based on a large number of trajectories started in the vicinity of the observations on 6 March. Based on the difference between the mean age derived from SF6 (which has an irreversible mesospheric loss) and from CO2 (whose mesospheric loss is much smaller and reversible) we estimate that the fraction of mesospheric air in the layer observed on 6 March, must have been somewhere between 35% and 100%.
Mean age of stratospheric air can be derived from observations of sufficiently long lived trace gases with approximately linear trends in the troposphere. Mean age can serve as a tracer to investigate stratospheric transport and long term changes in the strength of the overturning Brewer-Dobson circulation of the stratosphere. For this purpose, a low-cost method is required in order to allow for regular observations up to altitudes of about 30 km. Despite the desired low costs, high precision and accuracy are required in order to allow determination of mean age. We present balloon borne AirCore observations from two mid latitude sites: Timmins in Ontario/Canada and Lindenberg in Germany. During the Timmins campaign five AirCores sampled air in parallel from a large stratospheric balloon and were analysed for CO2, CH4 and partly CO. We show that there is good agreement between the different AirCores (better than 0.1 %) especially when vertical gradients are small. The measurements from Lindenberg were performed using small low-cost balloons and yielded very comparable results. We have used the observations to extend our long term data set of mean age observations at Northern Hemi-sphere mid latitudes. The time series now covers more than 40 years and shows a small, statis-tically not significant positive trend of 0.15 ± 0.18 years/decade. This trend is slightly smaller than the previous estimate of 0.24 ± 0.22 years/decade which was based on observations up to the year 2006. These observations are still in contrast to strong negative trends of mean age as derived from some model calculations.
Mean age of stratospheric air can be derived from observations of sufficiently long-lived trace gases with approximately linear trends in the troposphere. Mean age can serve as a tracer to investigate stratospheric transport and long-term changes in the strength of the overturning Brewer–Dobson circulation of the stratosphere. For this purpose, a low-cost method is required in order to allow for regular observations up to altitudes of about 30 km. Despite the desired low costs, high precision and accuracy are required in order to determine mean age. We present balloon-borne AirCore observations from two midlatitude sites: Timmins in Ontario/Canada and Lindenberg in Germany. During the Timmins campaign, five AirCores sampled air in parallel with a large stratospheric balloon and were analysed for CO2, CH4 and partly CO. We show that there is good agreement between the different AirCores (better than 0.1 %), especially when vertical gradients are small. The measurements from Lindenberg were performed using small low-cost balloons and yielded very comparable results. We have used the observations to extend our long-term data set of mean age observations at Northern Hemisphere midlatitudes. The time series now covers more than 40 years and shows a small, statistically non-significant positive trend of 0.15 ± 0.18 years decade−1. This trend is slightly smaller than the previous estimate of 0.24 ± 0.22 years decade−1 which was based on observations up to the year 2006. These observations are still in contrast to strong negative trends of mean age as derived from some model calculations.
MIPAS-Envisat is a satellite-borne sensor which measured vertical profiles of a wide range of trace gases from 2002 to 2012 using IR emission spectroscopy. We present geophysical validation of the MIPAS-Envisat operational retrieval (version 6.0) of N2O, CH4, CFC-12, and CFC-11 by the European Space Agency (ESA). The geophysical validation data are derived from measurements of samples collected by a cryogenic whole air sampler flown to altitudes of up to 34 km by means of large scientific balloons. In order to increase the number of coincidences between the satellite and the balloon observations, we applied a trajectory matching technique. The results are presented for different time periods due to a change in the spectroscopic resolution of MIPAS in early 2005. Retrieval results for N2O, CH4, and CFC-12 show partly good agreement for some altitude regions, which differs for the periods with different spectroscopic resolution. The more recent low spectroscopic resolution data above 20 km altitude show agreement with the combined uncertainties, while there is a tendency of the earlier high spectral resolution data set to underestimate these species above 25 km. The earlier high spectral resolution data show a significant overestimation of the mixing ratios for N2O, CH4, and CFC-12 below 20 km. These differences need to be considered when using these data. The CFC-11 results from the operation retrieval version 6.0 cannot be recommended for scientific studies due to a systematic overestimation of the CFC-11 mixing ratios at all altitudes.
MIPAS-Envisat is a satellite-borne sensor which measured vertical profiles of a wide range of trace gases from 2002 to 2012 using IR emission spectroscopy. We present geophysical validation of the MIPAS-Envisat operational retrieval (version 6.0) of N2O, CH4, CFC-12, and CFC-11 by the European Space Agency (ESA). The geophysical validation data are derived from measurements of samples collected by a cryogenic whole air sampler flown to altitudes of up to 34 km by means of large scientific balloons. In order to increase the number of coincidences between the satellite and the balloon observations, we applied a trajectory matching technique. The results are presented for different time periods due to a change in the spectroscopic resolution of MIPAS in early 2005. Retrieval results for N2O, CH4, and CFC-12 show partly good agreement for some altitude regions, which differs for the periods with different spectroscopic resolution. The more recent low spectroscopic resolution data above 20 km altitude show agreement with the combined uncertainties, while there is a tendency of the earlier high spectral resolution data set to underestimate these species above 25 km. The earlier high spectral resolution data show a significant overestimation of the mixing ratios for N2O, CH4, and CFC-12 below 20 km. These differences need to be considered when using these data. The CFC-11 results from the operation retrieval version 6.0 cannot be recommended for scientific studies due to a systematic overestimation of the CFC-11 mixing ratios at all altitudes.
Chlorine and bromine atoms lead to catalytic depletion of ozone in the stratosphere. Therefore the use and production of ozone-depleting substances (ODSs) containing chlorine and bromine is regulated by the Montreal Protocol to protect the ozone layer. Equivalent effective stratospheric chlorine (EESC) has been adopted as an appropriate metric to describe the combined effects of chlorine and bromine released from halocarbons on stratospheric ozone. Here we revisit the concept of calculating EESC. We derive a refined formulation of EESC based on an advanced concept of ODS propagation into the stratosphere and reactive halogen release. A new transit time distribution is introduced in which the age spectrum for an inert tracer is weighted with the release function for inorganic halogen from the source gases. This distribution is termed the release time distribution. We show that a much better agreement with inorganic halogen loading from the chemistry transport model TOMCAT is achieved compared with using the current formulation. The refined formulation shows EESC levels in the year 1980 for the mid-latitude lower stratosphere, which are significantly lower than previously calculated. The year 1980 is commonly used as a benchmark to which EESC must return in order to reach significant progress towards halogen and ozone recovery. Assuming that – under otherwise unchanged conditions – the EESC value must return to the same level in order for ozone to fully recover, we show that it will take more than 10 years longer than estimated in this region of the stratosphere with the current method for calculation of EESC. We also present a range of sensitivity studies to investigate the effect of changes and uncertainties in the fractional release factors and in the assumptions on the shape of the release time distributions. We further discuss the value of EESC as a proxy for future evolution of inorganic halogen loading under changing atmospheric dynamics using simulations from the EMAC model. We show that while the expected changes in stratospheric transport lead to significant differences between EESC and modelled inorganic halogen loading at constant mean age, EESC is a reasonable proxy for modelled inorganic halogen on a constant pressure level.
Chlorine and bromine atoms can lead to catalytic destruction of ozone in the stratosphere. Therefore the use and production of ozone depleting substances (ODS) containing chlorine and bromine is regulated by the Montreal Protocol to protect the ozone layer. Equivalent Effective Stratospheric Chlorine (EESC) has been adapted as an appropriate metric to describe the combined effects of chlorine and bromine released from halocarbons on stratospheric ozone. Here we revisit the concept of calculating EESC. We derive a new formulation of EESC based on an advanced concept of ODS propagation into the stratosphere and reactive halogen release. A new transit time distribution is introduced in which the age spectrum for an inert tracer is weighted with the release function for inorganic halogen from the source gases. This distribution is termed the “release time distribution”. The improved formulation shows that EESC levels in the year 1980 for the mid latitude lower stratosphere were significantly lower than previously calculated. 1980 marks the year commonly defined as the onset of anthropogenic ozone depletion in the stratosphere. Assuming that the EESC value must return to the same level in order for ozone to fully recover, we show that it will take more than 10 years longer than currently assumed in this region of the stratosphere. Based on the improved formulation, EESC level at mid-latitudes will reach this landmark only in 2060. We also present a range of sensitivity studies to investigate the effect of changes and uncertainties in the fractional release factors and in the assumptions on the shape of the release time distributions. We conclude that, under the assumptions that all other atmospheric parameters like stratospheric dynamics and chemistry are unchanged, the recovery of mid latitude stratospheric ozone would be expected to be delayed by about a 10 years, in a similar way as EESC.
During SPURT (Spurenstofftransport in der Tropopausenregion, trace gas transport in the tropopause region) we performed measurements of a wide range of trace gases with different lifetimes and sink/source characteristics in the northern hemispheric upper troposphere (UT) and lowermost stratosphere (LMS). A large number of in-situ instruments were deployed on board a Learjet 35A, flying at altitudes up to 13.7 km, at times reaching to nearly 380 K potential temperature. Eight measurement campaigns (consisting of a total of 36 flights), distributed over all seasons and typically covering latitudes between 35° N and 75° N in the European longitude sector (10° W–20° E), were performed. Here we present an overview of the project, describing the instrumentation, the encountered meteorological situations during the campaigns and the data set available from SPURT. Measurements were obtained for N2O, CH4, CO, CO2, CFC12, H2, SF6, NO, NOy, O3 and H2O. We illustrate the strength of this new data set by showing mean distributions of the mixing ratios of selected trace gases, using a potential temperature – equivalent latitude coordinate system. The observations reveal that the LMS is most stratospheric in character during spring, with the highest mixing ratios of O3 and NOy and the lowest mixing ratios of N2O and SF6. The lowest mixing ratios of NOy and O3 are observed during autumn, together with the highest mixing ratios of N2O and SF6 indicating a strong tropospheric influence. For H2O, however, the maximum concentrations in the LMS are found during summer, suggesting unique (temperature- and convection-controlled) conditions for this molecule during transport across the tropopause. The SPURT data set is presently the most accurate and complete data set for many trace species in the LMS, and its main value is the simultaneous measurement of a suite of trace gases having different lifetimes and physical-chemical histories. It is thus very well suited for studies of atmospheric transport, for model validation, and for investigations of seasonal changes in the UT/LMS, as demonstrated in accompanying and elsewhere published studies.
During SPURT (Spurenstofftransport in der Tropopausenregion, trace gas transport in the tropopause region) we performed measurements of a wide range of trace gases with different lifetimes and sink/source characteristics in the northern hemispheric upper troposphere (UT) and lowermost stratosphere (LMS). A large number of in-situ instruments were deployed on board a Learjet 35A, flying at altitudes up to 13.7 km, at times reaching to nearly 380 K potential temperature. Eight measurement campaigns (consisting of a total of 36 flights), distributed over all seasons and typically covering latitudes between 35° N and 75° N in the European longitude sector (10° W–20° E), were performed. Here we present an overview of the project, describing the instrumentation, the encountered meteorological situations during the campaigns and the data set available from SPURT. Measurements were obtained for N2O, CH4, CO, CO2, CFC12, H2, SF6, NO, NOy, O3 and H2O. We illustrate the strength of this new data set by showing mean distributions of the mixing ratios of selected trace gases, using a potential temperature – equivalent latitude coordinate system. The observations reveal that the LMS is most stratospheric in character during spring, with the highest mixing ratios of O3 and NOy and the lowest mixing ratios of N2O and SF6. The lowest mixing ratios of NOy and O3 are observed during autumn, together with the highest mixing ratios of N2O and SF6 indicating a strong tropospheric influence. For H2O, however, the maximum concentrations in the LMS are found during summer, suggesting unique (temperature- and convection-controlled) conditions for this molecule during transport across the tropopause. The SPURT data set is presently the most accurate and complete data set for many trace species in the LMS, and its main value is the simultaneous measurement of a suite of trace gases having different lifetimes and physical-chemical histories. It is thus very well suited for studies of atmospheric transport, for model validation, and for investigations of seasonal changes in the UT/LMS, as demonstrated in accompanying and elsewhere published studies.
Die Freisetzung von Fluorchlorkohlenwasserstoffen (FCKW) in die Atmosphäre ist seit Inkrafttreten des Montreal-Protokolls zum Schutz der Ozonschicht im Jahr 1987 reglementiert. Aber die ozonzerstörenden Gase sind äußerst langlebig. Sie können erst in der Stratosphäre, also in Höhen oberhalb von etwa zehn Kilometern, durch kurzwelliges, energiereiches Sonnenlicht gespalten werden. Messungen der FCKW und ihrer Ersatzstoffe am Institut für Atmosphäre und Umwelt erlauben es, die Lebenszeiten dieser Substanzen zu bestimmen und damit auch ihr Potenzial, die Ozonschicht zu schädigen und zur Klimaerwärmung beizutragen. Sie stellen einen wichtigen Beitrag zur Klimaforschung dar.
One possible approach to study systematically the influence of the deformation regime on the geometry of geological structures like folds and boudins is analogue modelling. For a complete understanding of the resulting structures, consideration of the third dimension is required. This PhD study deals with scaled analogue modelling under constriction and plane-strain conditions to improve our knowledge of folding and boudinage of lower crustal rocks in space and time. Plasticine is an appropriate analogue material for rocks in the lower crust. Therefore, this material was used for the experiments. The macroscopic behaviour of most types of plasticine is quite similar to rocks undergoing strain-rate softening and strain hardening regardless of the different microscopic aspects of deformation. Therefore, if one is aware that the stress exponent and viscosity increase with increasing strain, the original plasticine types used with stress exponents ranging from 5.8 to 8.0 are adequate for modelling geologic structures. The same holds for plasticine/oil mixtures. Thus, plasticine and plasticine/oil mixtures can be used to model the viscous flow of different rock types in the lower crust. If climb-accommodated dislocation creep and associated steady-state flow is assumed for the natural rocks, the plasticine/oil mixtures should be used, which flow under steady-state conditions. Three different experimental studies of plane-strain coaxial deformation of stiff layers, with viscosity η2 and stress exponent n2, embedded in a weak matrix, with viscosity η1 and stress exponent n1, have been carried out. The undeformed samples (matrix plus layer) were cubes with an edge length of 12 cm. All experimental runs have been carried out at T = 25 ± 1°C and varying strain rates ė, ranging from 7.9 x 10 high -6 s high -1 to 1.7 x 10 high -2 s high -1, until a finite longitudinal strain of 30% – 40% was achieved. The first experimental study improved the understanding about the evolution of folds and boudins when the layer is oriented perpendicular to the Y-axis of the finite strain ellipsoid. The rock analogues used were Beck’s green plasticine (matrix) and Beck’s black plasticine (competent layer), both of which are strain-rate softening modelling materials with stress exponent n = ca. 8. The effective viscosity η of the matrix plasticine was changed by adding different amounts of oil to the original plasticine. At a strain rate ė of 10 high -3 s high -1 and a finite strain e of 10%, the effective viscosity of the matrix ranges from 1.2 x 10 high 6 to 7.2 x 10 high 6 Pa s. The effective viscosity of the competent layer has been determined as 4.2 x 10 high 7 Pa s. If the viscosity ratio is large (> ca. 20) and the initial thickness of the competent layer is small, both folds and boudins develop simultaneously. Although the growth rate of the folds seems to be higher than the growth rate of the boudins, the wavelength of both structures is approximately the same as is suggested by analytical solutions. A further unexpected, but characteristic, aspect of the deformed competent layer is a significant increase in thickness, which can be used to distinguish plane-strain folds and boudins from constrictional folds and boudins. In the second experimental study, the impact of varying strain rates on growing folds and boudins under plane strain have been investigated. The strain rates used range from 7.9 x 10 high -6 s high -1 to 1.7 x 10 high -2 s high -1. The stiff layer and matrix consist of non-linear viscous Kolb grey and Beck’s green plasticine, respectively, both of which are strain-rate softening modelling materials with power law exponents (n) and apparent viscosities (η) ranging from 6.5 to 7.9 and 8.5 x 10 high 6 to 7.2 x 10 high 6 Pa s, respectively. The effective viscosity (η) of the matrix plasticine was partly modified by adding oil to the original plasticine. At the strain rates used in the experiments the viscosity ratio between layer and matrix ranges between 3 and 10. Different runs have been carried out where the layer was oriented perpendicular to the principal strain axes (X>Y>Z). The results suggest a considerable influence of the strain rate on the geometry of the deformed stiff layer including its thickness. This holds for every type of layer orientation (S ┴ X, S ┴ Y, S ┴ Z). If the stiff layer is oriented perpendicular to the short axis Z of the finite strain ellipsoid, the number of the resulting boudins and the thickness of the stiff layer increase, whereas the length of boudins decreases with increasing strain rate. If the stiff layer is oriented perpendicular to the long axis, X, of the finite strain ellipsoid, enlargement of the strain rate results in increasing wavelength of folds, whereas the number of folds and the degree of thickening of the stiff layer decreased. If the stiff layer is oriented perpendicular to the intermediate Y-axis of the finite strain ellipsoid enlargement of the strain rate results in a decreasing number of boudins and folds associated with increasing wavelengths of both structures. The wavelength of folds is approximately half of the boudins wavelength. This is true for the case where folds and boudins develop simultaneously (S ┴ Y) and for cases where both structures develop independently (folds at S ┴ X and boudins at S ┴ Z). In the third experimental study, scaled analogue experiments have been carried out to demonstrate the growth of plane-strain folds and boudins through space and time. Previous 3D-studies are based only on finite deformation structures. Their results can therefore not be used to prove if both structures grew simultaneously or in sequence. Plane strain acted on a single stiff layer that was embedded in a weak matrix, with the layer oriented perpendicular to the intermediate Y-axis of the finite strain ellipsoid. Two different experimental runs have been carried out using computer tomography (CT) to analyse the results. The first run was carried out without interruption. During the second run, the deformation was stopped in each case at longitudinal strain increments of 10%. Every experiment was carried out at a temperature T of 25°C and a strain rate, ė, of ca. 4 x 10 high -3 s high -1 until a finite longitudinal strain of 40% was achieved with a viscosity contrast m of 18.6 between the non-linear viscous layer (Kolb brown plasticine) and the matrix (Beck’s green plasticine with 150 ml oil kg high -1). The apparent viscosity, η, and the stress exponent, n, for the layer at a strain rate ė = ca. 10 high -3 s high -1 and a finite strain e = 10% are 2.23 x 10 high 7 Pa s and n = 5.8 and for the matrix 1.2 x 10 high 6 Pa s and 10.5. These new data that result from incremental analogue modelling corroborate previous suggestions that folds and boudins are coeval structures in cases of plane-strain coaxial deformation with the stiff layer oriented perpendicular to the intermediate Y-axis of the finite strain ellipsoid. They will be of interest for all workers who are dealing with plane-strain boudins and folds, where the fold axes are parallel to the major axis (X) of the finite strain ellipsoid. As has been demonstrated by the first experimental study, coeval folding and boudinage under plane strain, with S ┴ Y, are associated with a significant increase in the thickness of the competent layer. The latter phenomenon does not occur in other cases of simultaneous folding and boudinage, such as bulk pure constriction. To study the impact of layer thickness on the geometry of folds and boudins under pure constriction, we carried out additional experiments using different types of plasticine for a stiff layer and a weaker matrix to model folding and boudinaging under pure constriction, with the initially planar layer oriented parallel to the Xaxis of the finite strain ellipsoid. The stiff layer and matrix consist of non-linear viscous Kolb brown and Beck’s green plasticine, respectively, both of which are strain-rate softening modelling materials. Six runs have been carried out using thicknesses of the stiff layer of 1, 2, 4, 6, 8 and 10 ± 0.2 mm. All experimental runs were carried out at a temperature T of 30 ± 2°C and a strain rate, ė, of ca. 1.1 x 10 high -4 s high -1 until a finite longitudinal strain of 40% was achieved with a viscosity contrast m of 3.1 between the stiff layer (Kolb brown plasticine) and the matrix (Beck’s green plasticine). The apparent viscosity, η, and the stress exponent, n, for the layer at a strain rate ė = ca. 10 high -3 s high -1 and a finite strain e = 10% are 2.23 x 10 high 7 Pa s and n = 5.8 and for the matrix 7.2 x 10 high 6 Pa s and 7.9. Our results suggest a considerable influence of the initial thickness of the stiff layer on the geometry of the deformed stiff layer. There is no evidence for folding in XY=XZ-sections if the initial thickness of the competent layer is larger than ca. 8 mm. If the initial thickness of the competent layer is set at ca. 10 ± 0.2 mm, both folds and boudins develop simultaneously. However, the growth rate of the boudins seems to be higher than the growth rate of the folds. A further expected, but characteristic, aspect of the deformed competent layer is no change in thickness of the competent layer, which can be used to distinguish plane-strain folds and boudins from constrictional folds and boudins. The model results are important for the analysis and interpretation of deformation structures in rheologically stratified rocks undergoing dislocation creep under bulk constriction. Tectonic settings where constrictional folds and boudins may develop simultaneously are stems of salt diapirs, subduction zones or thermal plumes. To make (paleo) viscosimetric statements possible, the rheological data of the different plasticine types were related to the geometrical data. When comparing the normalized dominant wavelength Wd obtained from the deformed layer of the models with the theoretical dominant wavelength (Ld) calculated using the Smith equation (1977, 1979), the latter probably also holds when folding and boudinage develop simultaneously (S ┴ Y) and when boudins develop independently (S ┴ Z), but can obviously not be applied at very low viscosity ratios as is indicated by the low-strain-rate experiments.
Die METEOR-Fahrt 71 umfasst 3 biologisch und biogeochemisch orientierte Fahrtabschnitte mit insgesamt 50 Schiffstagen im östlichen Mittelmeer und hat folgende Ziele: Der Abschnitt METEOR 71-1 dient der physikalischen, biogeochemischen und biologischen Probengewinnung im Bereich der Anaximander Mountains. Es gibt nur einige wenige Seeberge im östlichen Mittelmeeres, die weitgehend isoliert vom übrigen Ozean sind und in einer Region liegen, die sich durch ein im Vergleich zum Weltozean sehr warmes Tiefenwasser von rund 14 °C auszeichnet. Hauptziel der Untersuchungen an einem Gipfel der Anaximander Mountains ist die Beantwortung der Frage, ob sich ein Seeberg-Ökosystem in einer oligotrophen Region mit warmen Tiefenwasser in Bezug auf seinen Einfluß auf das umgebende Strömungs- und Nährstoffregime, die Produktivität und Verteilung der Nahrungsketten, sowie in Bezug auf die Größe der „Sphere of interference“, das heißt dem Einflußbereich des Seamounts auf den umgebenden Wasserkörper, ähnlich verhält wie entsprechende Erhebungen im Nordostatlantik. Die Expedition METEOR 71-2 beschäftigt sich mit der Biodiversität in der Tiefsee des östlichen Mittelmeeres und ihren Steuerungsfaktoren (Tiefe, Küstenabstand, Nahrungsverfügbarkeit). Zum einen geht es um eine möglichst vollständige Erfassung der Artenzusammensetzung in zwei Referenzregionen durch Vielfachbeprobung an der selben Stelle, zum anderen um die Unterschiede des Arteninventars und des Artenreichtums in Abhängigkeit von der Tiefe und vom Küstenabstand. Die Arbeitsgebiete von jeweils 17 sm x 5 sm sind das Ierapetra-Becken südlich Kreta. (> 4000m Tiefe) und ein Gebiet der gleichen Größe weiter südlich (2800 m Tiefe doppelter Abstand zur Küste).Die Untersuchungen berücksichtigen alle Grössenklassen des Benthos (Mega-, Macro-, Meiound Nanofauna), um Gemeinsamkeiten und Unterschiede in der Abhängigkeit der Biodiversität von Ökofaktoren zu erkennen. Damit sollen die Struktur und die Funktion der Lebensgemeinschaften am äußerst oligotrophen Tiefseeboden des levantinischen Beckens besser und detaillierter verstanden werden. Arbeiten der Expedition METEOR 71-3 zielen auf die Klärung der Frage, ob im heutigen Mittelmeer Phosphatverlust und unvollständige Nitratnutzung, oder Stickstoff-Fixierung im ultraoligotrophen östlichen Mittelmeer für isotopisch abgereicherte d15N Signaturen von Sedimenten und Schwebstoffen verantwortlich sind. Ein Nebenziel ist die Gewinnung zusätzlicher Oberflächensedimente, um die Datenbasis für Eichungen des UK´37-Index und Abschätzung der Nährstoffakkumulationsraten in Sedimenten im Mittelmeers zu verbessern. Dazu werden auf Schnitten durch das östliche Mittelmeer Nährstoffprofile beprobt, Proben für Messungen der 15N/14N-Verhältnisse in Nitrat, gelöstem organischem Stickstoff, in Sinkstoffen und Oberflächensedimenten gewonnen, Untersuchungen des Phytoplanktons sowie Messungen von N2-Fixierungsraten durchgeführt. Weiter werden molekulare Techniken eingesetzt, um das Vorhandensein und die Transkription der nifH-Gene für das Nitrogenase-Enzym diazotropher Organismen zu überprüfen. Die Methoden zielen auf das nifHGen und seine Transkripte und geben Aufschluss über das Potential für Stickstofffixierung. Die Ergebnisse werden zeigen, ob das Gen aktiv in der Plankton-Gemeinschaft transkribiert wird. Ferne wird mit der DNA Sequenzanalyse neben der Anwesenheit auch die Diversität der diazotrophen Organismen etabliert. Schließlich wird im Verlauf der Fahrt an einer Station im Rhodos-Becken eine Sedimentfalle ausgebracht.