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In diesem einleitenden Beitrag des Themenschwerpunktes wird der
Hintergrund der internationalen Klimaverhandlungen erläutert und
die Ergebnisse des Kopenhagen-Akkords vorgestellt. Angesichts des
Scheiterns der Kopenhagener Konferenz muss die zeitnahe Schließung
eines rechtlich bindenden, globalen Klimaabkommens als unwahrscheinlich
gelten. Die Klimapolitik wird zukünftig verstärkt auf nationalstaatlicher
und transnationaler Ebene erfolgen.
Abschied von KyotoPlus?
(2012)
Die Ergebnisse des Klimagipfels von Kopenhagen sind eine bittere
Enttäuschung für die EU. Ihr ist es nicht gelungen, ihren Führungsambitionen
beim globalen Klimaschutz gerecht zu werden und die
Konferenz zur Weichenstellung für ein rechtsverbindliches Klimaabkommen
nach 2012 zu nutzen. Damit steht die Union vor grundlegenden
strategischen Fragen zum Kurs ihrer Klimapolitik.
Gescheiterte Klimapolitik?
(2012)
Der Kopenhagener Klimagipfel 2009 ist mit Spannung erwartet worden.
Erreicht wurde lediglich ein Minimalkonsens. Der Autor liefert eine
akteurszentrierte Deutung des Kopenhagener Abkommens und stellt die
Frage nach dem Präzedenzcharakter der Verhandlungen: Handelte es sich
um ein einmaliges Versagen multilateraler Diplomatie oder um einen
Vorgeschmack auf die weltpolitische Routine des 21. Jahrhunderts?
Die Zivilgesellschaft hat dazu beigetragen, dass die Klimakonferenz in
Kopenhagen zu einem Medienereignis wurde. Fernab großer Demonstrationen
haben Nichtregierungsorganisationen (NRO) seit Jahren
einen guten Zugang zu den internationalen Klimaverhandlungen. Am
Beispiel von Chile wird gezeigt, wie Nichtregierungsorganisationen
durch professionellen Lobbyismus ihre Positionen in politische Prozesse
einspeisen. Sie befinden sich in einem Spannungsfeld von Kooperation
und Instrumentalisierung durch politische Entscheidungsträger.
Wie Klimaschutz finanzieren?
(2012)
Zur Finanzierung von Klimaschutz müssen öffentliche Mittel gezielt
eingesetzt werden. Dies beinhaltet auch die Rahmenbedingungen für
private Finanzströme signifikant zu verbessern. Anhand einer Problemanalyse
bestimmen die Autoren Eckdaten für diese Hebelwirkung.
Öffentliche Anschubfinanzierung kann somit die Grundlage für private
Investitionen sein. Dies wird exemplarisch an der Internationalen
Klimaschutzinitiative des Bundesumweltministeriums diskutiert.
China und Indien
(2012)
Der Artikel analysiert die neue Rolle aufsteigender Schwellenländer
in den internationalen Klimaverhandlungen am Beispiel Chinas und
Indiens. Die Ablehnung verbindlicher Reduktionsziele für Treibhausgase
wurde in Kopenhagen als Blockadepolitik beider Länder gewertet.
China und Indien können sich in ihrer Position behaupten, da ihr
gestiegenes Gewicht in der multipolaren Weltordnung und die Untätigkeit
führender Industrieländer ihre Verhandlungsposition stärkt. Die
Autorin diskutiert Kooperationsmöglichkeiten auf subnationaler Ebene,
die die Blockadeposition nationaler Regierungen umgehen können.
Der Autor diskutiert die Chancen und Risiken bei der Einbindung
des Südens in die internationale Klimapolitik. Lange Zeit hatten die
Entwicklungsländer am wenigsten zum Klimawandel beigetragen,
wären aber am stärksten von ihm betroffen. Mittlerweile jedoch tragen
diese Länder in erheblichem Maße selbst zum Klimawandel bei. Allerdings
setzen deren Regierungen auf Zeit. Sie erwarten Ressourcentransfers.
Dies verstärkt auch alte Probleme des ‚Rent-Seeking‘.
Klimapolitik am Ende?
(2012)
Einleitung
(2012)
Intra-continental mountain belts typically form as a result of tectonic forces associated with distant plate collisions. In general, each mountain belt has a distinctive morphology and orogenic evolution that is highly dependent on the unique distribution and geometries of inherited structures and other crustal weaknesses. In this thesis, I have investigated the complex and irregular Cenozoic orogenic evolution of the Central Kyrgyz Tien Shan in Central Asia, which is presently one of the most active intra-continental mountain belts in the world. This work involved combining a broad array of datasets, including thermochronologic, magnetostratigraphic, sediment provenance and stable isotope data, to identify and date various changes in tectonic deformation, climate and surface processes. Many of these changes are linked and can ultimately be related to regional-scale processes that altered the orogenic evolution of the Central Kyrgyz Tien Shan. The Central Kyrgyz Tien Shan contains a sub-parallel series of structures that were reactivated in the late Cenozoic in response to the tectonic forces associated with the distant India-Eurasia collision. Over time, slip on the various reactivated structures created the succession of mountain ranges and intermontane basins which characterises the modern morphology of the region. In this thesis, new quantitative constraints on the exhumation histories of several mountain ranges have been obtained by using low temperature thermochronological data from 95 samples (zircon (U-Th)/He, apatite fission track and (U-Th)/He). Time-temperature histories derived by modelling the thermochronologic data of individual samples identify at least two stages of Cenozoic cooling in most of the region’s mountain ranges: (1) initially low cooling rates (<1°C/Myr) during the tectonic quiescent period and (2) increased cooling in the late Cenozoic, which occurred diachronously and with variable magnitude in different ranges. This second cooling stage is interpreted to represent increased erosion caused by active deformation, and in many of the sampled mountain ranges, provides the first available constraints on the timing of late Cenozoic deformation. New constraints on the timing of deformation have also been derived from the sedimentary record of intermontane basins. In the intermontane Issyk Kul basin, new magnetostratigraphic data from two sedimentary sections suggests that deposition of the first Cenozoic syn-tectonic sediments commenced at ~26 Ma. Zircon U-Pb provenance data, paleocurrent and conglomerate clast analysis reveals that these sediments were sourced from the Terskey Range to the south of the basin, suggesting that the onset of the late Cenozoic deformation occurred >26 Ma in that particular range. Elsewhere, growth strata relationships are used to identify syn-tecotnic deposition and constrain the timing of nearby deformation. Collectively, these new constraints obtained from thermochronologic and sedimentary data have allowed me to infer the spatiotemporal distribution of deformation in a transect through the Central Kyrgyz Tien Shan, and determine the order in which mountain ranges started deforming. These data suggest that deformation began in a few widely-spaced mountain ranges in the late Oligocene and early Miocene. Typically, these earlier mountain ranges are bounded on at least one side by a reactivated structure, which probably corresponds to the frictionally weakest and most suitably orientated inherited structures for accommodating the roughly north-south directed horizontal crustal shortening of the late Cenozoic. Moreover, tectonically-induced rock uplift in the Terskey Range, following the reactivation of the bounding structure before 26 Ma, likely caused significant surface uplift across the range, which in turn lead to enhanced orographic precipitation. These wetter conditions have been inferred from stable isotope data collected in the two magnetostratigraphically-dated sections in the Issyk Kul basin. Subsequently, in the late Miocene (~12‒5 Ma), more mountain ranges and inherited structures appear to have started actively deforming. Importantly, the onset of deformation at these locations in the late Miocene coincides with an increase in exhumation of ranges that had started deforming earlier in the late Oligocene‒early Miocene. Based on this observation, I have suggested that there must have been an overall increase in the rate of horizontal crustal shortening across the Central Kyrgyz Tien Shan, which likely relates to regional tectonic changes that affected much of Central Asia. Many of the mountain ranges that started deforming in the late Miocene were associated with out-of-sequence tectonic reactivation and initiation, which lead to the partitioning of larger intermontane basins. Moreover, within most of the intermontane basins in the Central Kyrgyz Tien Shan, this inferred late Miocene increase in horizontal crustal shortening occurs roughly at the same time as an increase in sedimentation rates and a significant change sediment composition. Therefore, I have suggested that the overall magnitude of deformational processes increased in the late Miocene, promoting more flexural subsidence in the intermontane basins of the Central Kyrgyz Tien Shan.
Klimapolitik International
(2012)
Der Klimawandel birgt globale Risiken. Dies ist weithin anerkannt. Umstritten ist die Frage, wie diesen Gefahren zu begegnen ist. 14 Jahre nach Kyoto ist klar: Klimapolitik ist Interessenpolitik. Das zeigte zuletzt die UN-Klimakonferenz 2011 in Durban mit ihren unverbindlichen Ergebnissen. In diesem Sammelband analysieren Experten Ursachen für das Scheitern der vergangenen Klima-Konferenzen und Konsequenzen für die künftige Klimapolitik. Insbesondere geht es um die Politik der Akteure China und Indien, um die Rolle der NGOs und die Klimafrage in der Entwicklungspolitik. Zugleich wird die deutsche Klimapolitik diskutiert und die Politik Brandenburgs von der verantwortlichen Ministerin vorgestellt.
The Tibetan Plateau is the largest elevated landmass in the world and profoundly influences atmospheric circulation patterns such as the Asian monsoon system. Therefore this area has been increasingly in focus of palaeoenvironmental studies. This thesis evaluates the applicability of organic biomarkers for palaeolimnological purposes on the Tibetan Plateau with a focus on aquatic macrophyte-derived biomarkers. Submerged aquatic macrophytes have to be considered to significantly influence the sediment organic matter due to their high abundance in many Tibetan lakes. They can show highly 13C-enriched biomass because of their carbon metabolism and it is therefore crucial for the interpretation of δ13C values in sediment cores to understand to which extent aquatic macrophytes contribute to the isotopic signal of the sediments in Tibetan lakes and in which way variations can be explained in a palaeolimnological context. Additionally, the high abundance of macrophytes makes them interesting as potential recorders of lake water δD. Hydrogen isotope analysis of biomarkers is a rapidly evolving field to reconstruct past hydrological conditions and therefore of special relevance on the Tibetan Plateau due to the direct linkage between variations of monsoon intensity and changes in regional precipitation / evaporation balances. A set of surface sediment and aquatic macrophyte samples from the central and eastern Tibetan Plateau was analysed for composition as well as carbon and hydrogen isotopes of n-alkanes. It was shown how variable δ13C values of bulk organic matter and leaf lipids can be in submerged macrophytes even of a single species and how strongly these parameters are affected by them in corresponding sediments. The estimated contribution of the macrophytes by means of a binary isotopic model was calculated to be up to 60% (mean: 40%) to total organic carbon and up to 100% (mean: 66%) to mid-chain n-alkanes. Hydrogen isotopes of n-alkanes turned out to record δD of meteoric water of the summer precipitation. The apparent enrichment factor between water and n-alkanes was in range of previously reported ones (≈-130‰) at the most humid sites, but smaller (average: -86‰) at sites with a negative moisture budget. This indicates an influence of evaporation and evapotranspiration on δD of source water for aquatic and terrestrial plants. The offset between δD of mid- and long-chain n-alkanes was close to zero in most of the samples, suggesting that lake water as well as soil and leaf water are affected to a similar extent by those effects. To apply biomarkers in a palaeolimnological context, the aliphatic biomarker fraction of a sediment core from Lake Koucha (34.0° N; 97.2° E; eastern Tibetan Plateau) was analysed for concentrations, δ13C and δD values of compounds. Before ca. 8 cal ka BP, the lake was dominated by aquatic macrophyte-derived mid-chain n-alkanes, while after 6 cal ka BP high concentrations of a C20 highly branched isoprenoid compound indicate a predominance of phytoplankton. Those two principally different states of the lake were linked by a transition period with high abundances of microbial biomarkers. δ13C values were relatively constant for long-chain n-alkanes, while mid-chain n-alkanes showed variations between -23.5 to -12.6‰. Highest values were observed for the assumed period of maximum macrophyte growth during the late glacial and for the phytoplankton maximum during the middle and late Holocene. Therefore, the enriched values were interpreted to be caused by carbon limitation which in turn was induced by high macrophyte and primary productivity, respectively. Hydrogen isotope signatures of mid-chain n-alkanes have been shown to be able to track a previously deduced episode of reduced moisture availability between ca. 10 and 7 cal ka BP, indicated by a 20‰ shift towards higher δD values. Indications for cooler episodes at 6.0, 3.1 and 1.8 cal ka BP were gained from drops of biomarker concentrations, especially microbial-derived hopanoids, and from coincidental shifts towards lower δ13C values. Those episodes correspond well with cool events reported from other locations on the Tibetan Plateau as well as in the Northern Hemisphere. To conclude, the study of recent sediments and plants improved the understanding of factors affecting the composition and isotopic signatures of aliphatic biomarkers in sediments. Concentrations and isotopic signatures of the biomarkers in Lake Koucha could be interpreted in a palaeolimnological context and contribute to the knowledge about the history of the lake. Aquatic macrophyte-derived mid-chain n-alkanes were especially useful, due to their high abundance in many Tibetan Lakes and their ability to record major changes of lake productivity and palaeo-hydrological conditions. Therefore, they have the potential to contribute to a fuller understanding of past climate variability in this key region for atmospheric circulation systems.
The role of feedback between erosional unloading and tectonics controlling the development of the Himalaya is a matter of current debate. The distribution of precipitation is thought to control surface erosion, which in turn results in tectonic exhumation as an isostatic compensation process. Alternatively, subsurface structures can have significant influence in the evolution of this actively growing orogen. Along the southern Himalayan front new 40Ar/39Ar white mica and apatite fission track (AFT) thermochronologic data provide the opportunity to determine the history of rock-uplift and exhumation paths along an approximately 120-km-wide NE-SW transect spanning the greater Sutlej region of the northwest Himalaya, India. 40Ar/39Ar data indicate, consistent with earlier studies that first the High Himalayan Crystalline, and subsequently the Lesser Himalayan Crystalline nappes were exhumed rapidly during Miocene time, while the deformation front propagated to the south. In contrast, new AFT data delineate synchronous exhumation of an elliptically shaped, NE-SW-oriented ~80 x 40 km region spanning both crystalline nappes during Pliocene-Quaternary time. The AFT ages correlate with elevation, but show within the resolution of the method no spatial relationship to preexisting major tectonic structures, such as the Main Central Thrust or the Southern Tibetan Fault System. Assuming constant exhumation rates and geothermal gradient, the rocks of two age vs. elevation transects were exhumed at ~1.4 ±0.2 and ~1.1 ±0.4 mm/a with an average cooling rate of ~50-60 °C/Ma during Pliocene-Quaternary time. The locus of pronounced exhumation defined by the AFT data coincides with a region of enhanced precipitation, high discharge, and sediment flux rates under present conditions. We therefore hypothesize that the distribution of AFT cooling ages might reflect the efficiency of surface processes and fluvial erosion, and thus demonstrate the influence of erosion in localizing rock-uplift and exhumation along southern Himalayan front, rather than encompassing the entire orogen.Despite a possible feedback between erosion and exhumation along the southern Himalayan front, we observe tectonically driven, crustal exhumation within the arid region behind the orographic barrier of the High Himalaya, which might be related to and driven by internal plateau forces. Several metamorphic-igneous gneiss dome complexes have been exhumed between the High Himalaya to the south and Indus-Tsangpo suture zone to the north since the onset of Indian-Eurasian collision ~50 Ma ago. Although the overall tectonic setting is characterized by convergence the exhumation of these domes is accommodated by extensional fault systems.Along the Indian-Tibetan border the poorly described Leo Pargil metamorphic-igneous gneiss dome (31-34°N/77-78°E) is located within the Tethyan Himalaya. New field mapping, structural, and geochronologic data document that the western flank of the Leo Pargil dome was formed by extension along temporally linked normal fault systems. Motion on a major detachment system, referred to as the Leo Pargil detachment zone (LPDZ) has led to the juxtaposition of low-grade metamorphic, sedimentary rocks in the hanging wall and high-grade metamorphic gneisses in the footwall. However, the distribution of new 40Ar/39Ar white mica data indicate a regional cooling event during middle Miocene time. New apatite fission track (AFT) data demonstrate that subsequently more of the footwall was extruded along the LPDZ in a brittle stage between 10 and 2 Ma with a minimum displacement of ~9 km. Additionally, AFT-data indicate a regional accelerated cooling and exhumation episode starting at ~4 Ma. Thus, tectonic processes can affect the entire orogenic system, while potential feedbacks between erosion and tectonics appear to be limited to the windward sides of an orogenic systems.
The India-Eurasia continental collision zone provides a spectacular example of active mountain building and climatic forcing. In order to quantify the critically important process of mass removal, I analyzed spatial and temporal precipitation patterns of the oscillating monsoon system and their geomorphic imprints. I processed passive microwave satellite data to derive high-resolution rainfall estimates for the last decade and identified an abnormal monsoon year in 2002. During this year, precipitation migrated far into the Sutlej Valley in the northwestern part of the Himalaya and reached regions behind orographic barriers that are normally arid. There, sediment flux, mean basin denudation rates, and channel-forming processes such as erosion by debris-flows increased significantly. Similarly, during the late Pleistocene and early Holocene, solar forcing increased the strength of the Indian summer monsoon for several millennia and presumably lead to analogous precipitation distribution as were observed during 2002. However, the persistent humid conditions in the steep, high-elevation parts of the Sutlej River resulted in deep-seated landsliding. Landslides were exceptionally large, mainly due to two processes that I infer for this time: At the onset of the intensified monsoon at 9.7 ka BP heavy rainfall and high river discharge removed material stored along the river, and lowered the baselevel. Second, enhanced discharge, sediment flux, and increased pore-water pressures along the hillslopes eventually lead to exceptionally large landslides that have not been observed in other periods. The excess sediments that were removed from the upstream parts of the Sutlej Valley were rapidly deposited in the low-gradient sectors of the lower Sutlej River. Timing of downcutting correlates with centennial-long weaker monsoon periods that were characterized by lower rainfall. I explain this relationship by taking sediment flux and rainfall dynamics into account: High sediment flux derived from the upstream parts of the Sutlej River during strong monsoon phases prevents fluvial incision due to oversaturation the fluvial sediment-transport capacity. In contrast, weaker monsoons result in a lower sediment flux that allows incision in the low-elevation parts of the Sutlej River.
Paleomagnetic dating of climatic events in Late Quaternary sediments of Lake Baikal (Siberia)
(2004)
Lake Baikal provides an excellent climatic archive for Central Eurasia as global climatic variations are continuously depicted in its sediments. We performed continuous rock magnetic and paleomagnetic analyses on hemipelagic sequences retrieved from 4 underwater highs reaching back 300 ka. The rock magnetic study combined with TEM, XRD, XRF and geochemical analyses evidenced that a magnetite of detrital origin dominates the magnetic signal in glacial sediments whereas interglacial sediments are affected by early diagenesis. HIRM roughly quantifies the hematite and goethite contributions and remains the best proxy for estimating the detrital input in Lake Baikal. Relative paleointensity records of the earth′s magnetic field show a reproducible pattern, which allows for correlation with well-dated reference curves and thus provides an alternative age model for Lake Baikal sediments. Using the paleomagnetic age model we observed that cooling in the Lake Baikal region and cooling of the sea surface water in the North Atlantic, as recorded in planktonic foraminifera δ18 O, are coeval. On the other hand, benthic δ18 O curves record mainly the global ice volume change, which occurs later than the sea surface temperature change. This proves that a dating bias results from an age model based on the correlation of Lake Baikal sedimentary records with benthic δ18 O curves. The compilation of paleomagnetic curves provides a new relative paleointensity curve, “Baikal 200”. With a laser-assisted grain size analysis of the detrital input, three facies types, reflecting different sedimentary dynamics can be distinguished. (1) Glacial periods are characterised by a high clay content mostly due to wind activity and by occurrence of a coarse fraction (sand) transported over the ice by local winds. This fraction gives evidence for aridity in the hinterland. (2) At glacial/interglacial transitions, the quantity of silt increases as the moisture increases, reflecting increased sedimentary dynamics. Wind transport and snow trapping are the dominant process bringing silt to a hemipelagic site (3) During the climatic optimum of the Eemian, the silt size and quantity are minimal due to blanketing of the detrital sources by the vegetal cover.
Im Landschaftszustand und in der Landschaftsentwicklung kommen funktionale Beziehungen zwischen dem naturbedingten Energie-, Wasser- und Stoffhaushalt einerseits und den Auswirkungen der Landnutzung andererseits zum Ausdruck. Gegenwärtig verändert der globale Anstieg der bodennahen Temperaturen vielerorts den landschaftlichen Energie-, Wasser- und Stoffhaushalt, wobei besonders in Trockengebieten zu erwarten ist, dass dieser Trend in Verbindung mit einer unangepassten Landnutzung das Regenerationsvermögen der Vegetation einschränkt und zur Zerstörung der Bodendecke führt. Für die Mongolei und für benachbarte Gebiete Asiens sind in Szenarien zur globalen Erwärmung hohe Werte des Temperaturanstiegs prognostiziert worden. Eine globale Einschätzung der anthropogen induzierten Bodendegradation hat diese Region als stark oder extrem stark betroffen eingestuft. Vor diesem Hintergrund wurde im Uvs-Nuur-Becken, das im Nordwesten der Mongolei und damit in einer der trockensten Regionen des Landes gelegen ist, untersucht, wie sich der globale Temperaturanstieg auf der lokalen und regionalen Ebene widerspiegelt und wie der Landschaftshaushalt dabei verändert wird. Die Auswirkungen des sommerlichen Witterungsverlaufes auf den Landschaftszustand sind 1997 bis 1999 an einem Transsekt erfasst worden, das sich zwischen dem Kharkhiraa-Gebirge am Westrand des Beckens und dem See Uvs Nuur im Beckeninneren von den Polsterfluren und Matten der alpinen Stufe über die Gebirgswaldsteppe, die Trockensteppe bis zur Halbwüste erstreckt. An neun Messpunkten wurden witterungsklimatische Daten in Verbindung mit Merkmalen der Vegetation, des Bodens und der Bodenfeuchte aufgenommen. Die im Sommer 1998 gewonnenen Messwerte wurden mit Hilfe einer Clusteranalyse gebündelt und verdichtet. Auf dieser Grundlage konnten landschaftliche Zustandsformen inhaltlich gekennzeichnet, zeitlich eingeordnet und durch Zeit-Verhaltens-Modelle (Stacks) abgebildet werden. Aus den Zeit-Verhaltens-Modellen wird ersichtlich, dass man Zustandsformen, in denen die Hitze und die Trockenheit des Sommers 1998 besonders stark zum Ausdruck kommen, an allen Messpunkten beobachten kann, nimmt man die Station auf dem fast 3.000 m hohen Gipfel des Khukh Uul sowie die grundwasserbeeinflusste Station in unmittelbarer Seenähe aus. In ihrer extremen Form sind Trockenperioden jedoch nur im Beckeninneren und am Fuß der Randgebirge, also in der Halbwüste, in der Trockensteppe und in der Wiesensteppe aufgetreten. Im Bergwald sowie im Bereich der alpinen Matten und Polsterfluren fehlen sie. Am stärksten sind die grundwasserfreien Bereiche der Halbwüste von der Hitze und Niederschlagsarmut des Sommers 1998 betroffen. An vier Fünfteln der Tage des Beobachtungszeitraumes herrscht an diesem Messpunkt extreme Trockenheit. Es fällt entweder gar kein Niederschlag oder nur so wenig, dass der seit dem Frühjahr erschöpfte Bodenwasservorrat nicht aufgefüllt wird. Das Verhältnis zwischen Niederschlag und potenzieller Verdunstung liegt hier bei 1:12. In der Halbwüste zeichnet sich eine fortschreitende Desertifikation ab, zumal hier eine nichtangepasste Weidenutzung dominiert, in der Ziegen eine immer größere Rolle spielen. Dies gilt insbesondere für Bereiche in Siedlungsnähe. Örtlich ist auch der Bestand der Trockensteppe gefährdet, die sich an die Halbwüste zum Beckenrand hin anschließt. Hier ist nicht nur die Viehdichte am höchsten, sondern hier werden auch die meisten unbefestigten Fahrwege wild angelegt und die Bodendecke damit zerstört. Dies kann im Endeffekt zu einem Übergreifen von Prozessen der Desertifikation führen. Aus methodischer Sicht zeigt sich, dass die Kennzeichnung landschaftlicher Zustandsformen durch Zeit-Verhaltens-Modelle die Ermittlung der Auswirkungen von Witterung und Klima auf den Landschaftszustand erleichtert, da sie deren Aussage konzentriert. Zur Interpretation der Ergebnisse ist jedoch ein Rückgriff auf die beschreibende Darstellung der Messwerte notwendig. Die im westlichen Uvs-Nuur-Becken und seinen Randgebirgen angewandte Verfahrensweise ermöglicht es, globale Aussagen zur globalen Erwärmung der Kontinente regional oder lokal zu überprüfen und zu untersetzen."
This study investigated the slope carbonates of two Miocene carbonate systems: the Maltese Islands (in the Central Mediterranean) and the Marion Plateau (Northeastern Australia, drilled during ODP Leg 194). The aim of the study was to trace the impact of the Miocene cooling steps (events Mi1-Mi6) in these carbonate systems, especially the Mi3 event, which took place around 13.6 Ma and deeply impacted the marine oxygen isotope record. This event also profoundly impacted oceanographic and climatic patterns, eventually leading to the establishment of the modern ice-house world. In particular, East Antarctica became ice covered at that period. The rational behind the present study was to investigate the impact that this event had on shallow water systems in order to complement the deep-sea record and hence acquire a more global perspective on Miocene climate change. The Maltese Islands were investigated for trends in bulk-rock carbon and oxygen isotopes, as well as bulk-rock mineralogy, clay minerals analysis and organic geochemisty. Results showed that the mid Miocene cooling event deeply impacted sedimentation at that location by changing sedimentation from carbonate to clay-rich sediments. Moreover, it was discovered that each phase of Antarctic glaciation, not just the major mid Miocene event, resulted in higher terrigenous input on Malta. Mass accumulation rates revealed that this was linked to increased runoff during periods when Antarctica was glaciated, and thus that the carbonate sediments were “diluted” by clay-rich sediments. The model subsequently developed to explain this implies feedback from Antarctic glaciations creating cold, dense air masses that push the ITCZ Northward, thus increasing precipitation on the North African subcontinent. Increased precipitation (or stronger African monsoon) accelerated continental weathering and runoff, thus bringing more terrigenous sediment to the paleo-location of the slope sediments of Malta. Spectral analysis of carbonate content and organic matter geochemical analysis furthermore suggest that the clay-rich intervals are similar to sapropelic deposits. On the Marion Plateau, trends in oxygen and carbon isotopes were obtained by measuring Cibicidoides spp foraminifers. Moreover, carbonate content was reconstructed using a chemical method (coulometer). Results show that the mid Miocene cooling step profoundly affected this system: a major drop in accumulation rates of carbonates occurs precisely at 13.8 Ma, around the time of the East Antarctic ice sheet formation. Moreover, sedimentation changes occurred at that time, carbonate fragments coming from neritic environments becoming less abundant, planktonic foraminifer content increasing and quartz and reworked glauconite being deposited. Conversely, a surprising result is that the major N12-N14 sea-level fall occurring around 11.5 Ma did not impact the accumulation of carbonates on the slope. This was unexpected since carbonate platform are very sensitive to sea-level changes. The model developed to explain that mass accumulation rates of carbonates diminished around 13.6 Ma (Mi3 Event) instead of 11.5 Ma (N12-N14 event), suggests that oceanic currents were controlling slope carbonate deposition on the Marion Plateau prior to the mid-Miocene, and that the mid Miocene event considerably increase their strength, hence reducing the amount of carbonate being deposited on slope sites. Moreover, by combining results from deep-sea oxygen isotopes with sea-level estimates based on coastal onlaps made during Leg 194, we constrain the amplitude of the N12-N14 sea-level fall to 90 meters. When integrating isotopic results from this study, this amplitude is lowered to 70 meters. A general conclusion of this work is that the mid Miocene climatic shift did impact carbonate systems, at least at the two locations studied. However, the nature of this response was highly dependant on the regional settings, in particular the presence of land mass (Malta) and the absence of a barrier to shelter from the effects of open ocean (Marion Plateau).