Atmospheric CO2 concentrations present a repetitive pattern of gradual decline and rapid increase during the last climate cycles, closely related to temperature and sea level change. During the Last Glacial Maximum (LGM; 23-19 kyr BP), when sea level was ca. 120 m below present, the ocean must have stored additionally about 750 Gt carbon. There is consensus that the Southern Ocean represents a key area governing past and present CO2 change. The latter is not only of high scientific but also of socio-economic and political concern since the Southern Ocean provides the potential for an efficient sink of anthropogenic carbon. However, the sensitivity of this carbon sink to climate-change induced reorganizations in wind patterns, ocean circulation, stratification, sea ice extent and biological production remains under debate. Models were not yet able to reproduce the necessary mechanisms involved, potentially due to a lack of the dynamic representation/resolution of atmospheric and oceanic circulation as well as missing carbon cycling. Data on past Southern Ocean hydrography and productivity are mainly from the Atlantic sector, thus do not adequately document conditions in the Pacific sector. This sector is not only the largest part of the Southern Ocean, but it also represents the main drainage area of the marine-based West Antarctic Ice Sheet (WAIS). In the proposed study we aim to generate paleo-data sets with a newly established proxy method from sediment core transects across the Pacific Southern Ocean. This will enhance the baselines for the understanding and modeling of the Southern Ocean's role in carbon cyling, i.e. ocean/atmosphere CO2 exchange and carbon sequestration. It will also allow insight into the response of the WAIS to past warmer than present conditions. Paired isotope measurements (oxygen, silicon) will be made on purified diatoms and radiolarians to describe glacial/interglacial contrasts in physical and nutrient properties at surface and subsurface water depth. This will be used to test (i) the impact of yet unconsidered dust-borne micronutrient deposition on the glacial South Pacific on shifts of primary productivity, Si-uptake rates and carbon export, (ii) the 'silicic-acid leakage' hypothesis (SALH) and (iii) the formation and extent of surface water stratification. Diatom and radiolarian oxygen isotopes will provide information on the timing of surface ocean salinity anomalies resulting from WAIS melt water. Climate model simulations using a complex coupled atmosphere ocean general circulation model (AOGCM) in combination with a sophisticated ocean biogeochemical model including Si-isotopes will be used for comparison with the paleo records. The analysis will cover spatial as well as temporal variability patterns of Southern Ocean hydrography, nutrient cycling and air-sea CO2-exchange. With the help of the climate model we aim to better separate and statistically analyse the individual impacts of ocean circulation and bio
Soil microorganisms can mobilize and immobilize phosphorus (P), and therefore strongly affect the availability of P to plants. In this project we hypothesize that the ratio of labile P to microbial P increases during the transition from acquiring to recycling ecosystems. Microbial and plant P uptake will be studied with 33P that will be quantified in microbial and plant biomass as well as in lipids. To what extent microorganisms immobilize and mobilize P during decomposition of soil organic matter will be explored with a 14C/33P labeled monoester. Seasonal dynamics of actual and potential P mineralization (33P dilution and phosphatase activity), and microbial P immobilization will be studied with soils of the transition from acquiring to recycling ecosystems. The contribution of litter-derived P will be explored in a litter exclusion experiment in the field. Spatial patterns of microbial and plant P mineralization in the rhizosphere will be explored by analyses of areas of high acid and alkaline (=microbial-derived) phosphatase activity by soil zymography, and their relations with areas of high rhizodeposition (14C imaging). In conclusion, we will analyse mechanisms of actual and potential microbial P mineralization and immobilization, localization, and consequences for P uptake by plants.
Glendonites are pseudomorphs after the mineral ikaite (CaCO3 x 6H2O) and composed of calcite (CaCO3). In the past, they have been used as a paleo-thermometer because the primary mineral ikaite, according to observations and experiments, seems to be formed at temperatures near freezing, high alkalinity and high phosphate concentrations in marine sediments. An enigmatic occurrence of the largest glendonites known world-wide, in the Early Eocene Fur Formation of northwestern Denmark offers the unique possibility to shed more light on the actual mechanism and controlling parameters of ikaite formation. Right in the aftermath of the Paleocene-Eocene thermal maximum, a time known for its global pertubation in the global carbon cycle, the formation of authigenic calcium carbonate concretions start in the Fur Formation. In a specific stratigraphic interval inbetween these concretions, the glendonites can be found. We will investigate if termperature changes or changes in geochemical parameters of the Danish Basin caused the sudden formation of ikaite during a time interval that was based on known paleoclimatic reconstructions (semi tropic) not favorable for ikaite formation.
Chlorinated ethylenes are prevalent groundwater contaminants. Numerous studies have addressed the mechanism of their reductive dehalogenation during biodegradation and reaction with zero-valent iron. However, despite insight with purified enzymes and well-characterized chemical model systems, conclusive evidence has been missing that the same mechanisms do indeed prevail in real-world transformations. While dual kinetic isotope effect measurements can provide such lines of evidence, until now this approach has not been possible for chlorinated ethylenes because an adequate method for continuous flow compound specific chlorine isotope analysis has been missing. This study attempts to close this prevalent research gap by a combination of two complementary approaches. (1) A novel analytical method to measure isotope effects for carbon and chlorine. (2) A carefully chosen set of well-defined model reactants representing distinct dehalogenation mechanisms believed to be important in real-world systems. Isotope trends observed in biotic and abiotic environmental dehalogenation will be compared to these model reactions, and the respective mechanistic hypotheses will be confirmed or discarded. With this hypothesis-driven approach it is our goal to elucidate for the first timdehalogenation reactions.
Vorkommen, Häufigkeit, chemische Zusammensetzung und Mischungszustand jener Aerosolpartikel in der Erdatmosphäre, an denen sich durch heterogene Nukleation in unterkühlten Wolken Eis bilden kann (Ice Nucleating Particles = INP), werden experimentell untersucht. Diese Informationen sind wichtig für das Verständnis der Niederschlagsbildung, und finden in parametrisierter Form Eingang in meteorologische Modelle zur Vorhersage des Niederschlages. Das Projekt verwendet hierbei im Wesentlichen physikalische Methoden zur Identifikation und Isolation der Partikel aus der Atmosphäre, und nachfolgend elektronenmikroskopische Methoden zur mineralogischen Analyse einzelner Partikel. Die Identifikation jener wenigen Aerosolpartikel (ca. 1 von 10.000 bis 1 von 100.000), die Eisbildungsfähigkeit besitzen, erfolgt, indem eine Aerosolprobe einer Unterkühlung unter 0°C und Wasserdampfübersättigung ausgesetzt wird, und die an INP entstehenden Eiskristalle fotografiert und gezählt werden. Es werden sowohl Aerosolpartikel aus luftgetragenem Aerosol untersucht (aus dem Eiskeimzähler FINCH) wie auch Partikel, die aus einer Luftprobe auf einem Silizium-Probenträger niedergeschlagen und danach als INP identifiziert wurden (Eiskeimzähler FRIDGE). Eine dritte und vierte Methode (Ice-CVI und ISI) isolieren eisbildungsfähige Partikel, indem aus einer angesaugten Probe von Wolkenluft die Eiskristalle strömungstechnisch von den übrigen Luftbestandteilen getrennt werden. Alle Eiskeimproben werden im Rasterelektronenmikroskop auf Größe, Morphologie, Mischungszustand und chemische Zusammensetzung untersucht und die Ergebnisse der verschiedenen Ansätze verglichen. In Feldexperimenten werden Atmosphärenproben verschiedener geographischer Provenienz (Mitteleuropa, Forschungsstation Jungfraujoch, Wüstenstaub, Vulkanstaub) erhalten. In Laborexperimenten wird mit vorher gesammelt und charakterisierten Modellsubstanzen gearbeitet. Weiterhin wird durch tägliche Messungen der Anzahl-Konzentration und Zusammensetzung von Eiskeimen am Taunus Observatorium nahe Frankfurt über einen längeren Zeitraum untersucht, ob es Saisonalitäten, bevorzugte Quellgebiete (z.B. Wüsten, Industrie, etc.) und biologische Einflussfaktoren (z.B. Pollen, Pflanzenabrieb, Bakterien) für das Vorkommen von Eisnuklei gibt.
Verlässliche Vorhersagen von Wetter und Klimawandel erfordern ein gutes Verständnis der Eisbildung in troposphärischen Wolken. Von besonderer Bedeutung ist dabei die sogenannte heterogene Eisnukleation durch atmosphärische Aerosolpartikel. Das hier beantragte Projekt beinhaltet eine umfassende Untersuchung der heterogenen Eisnukleation in Zirruswolken und Mischphasenwolken, gemeinsam mit 8 weiteren Projekten der Forschergruppe INUIT. Eisbildung durch Kontaktgefrieren wird für einzelne Tröpfchen in einem elektrodynamischen Levitator (Paulfalle) untersucht. Experimente zum Einfluss von Aerosolen auf Immersionsgefrieren, Kontaktgefrieren und Depositionsnukleation werden in der AIDA-Wolkenkammer und einer neuen dynamischen Wolkenkammer durchgeführt, falls diese wie geplant bis Anfang 2016 zur Verfügung stehen wird. Hauptziele und Arbeitspakete des Projekts sind (a) Untersuchungen zum Immersionsgefrieren, Kontaktgefrieren und zur Depositionsnukleation von INUIT-2 Referenzaerosolen in enger Zusammenarbeit mit allen anderen lNUlT-2-Partnern, (b) AIDA-Wolkensimulationsexperimente mit redispergierten atmosphärischen Aerosolen die auf Filtern gesammelt wurden (in Zusammenarbeit mit RP8), (c) AIDA-Experimente mit porösen Partikeln zur Untersuchung des Einflusses von Kapillarkondensation und Prä-aktivierung auf Eisnukleationsprozesse, (d) EDB-Experimente zur Kontaktnukleation mit atmosphärisch relevanten und komplexen Aerosolen, (e) Untersuchungen zu den grundlegenden Mechanismen des Kontaktgefrierens, (f) die Entwicklung einer umfassenden und einheitlichen Parametrisierung heterogener Eisnukleation in enger Zusammenarbeit mit RP3 und RP5, (g) erste Experimente zur Kontaktnukleation in einer neuen Wolkenkammer unter Nutzung der Expertise aus langjährigen Experimenten zum Kontaktgefrieren und mit der Wolkensimulationskammer, (h) die Durchführung von zwei AIDA-Messkampagnen, eine nur für die INUIT-2- Partner und eine mit internationaler Beteiligung, bei denen Labormethoden und Feld Instrumente für die Messung von Aerosolen und eisbildenden Partikeln getestet und miteinander verglichen werden um hohe internationale Standards in der Eisnukleationsforschung zu entwickeln und zu erhalten. Die Aktivitäten an der AIDA-Wolkenkammer bieten auch eine gute Verknüpfung der Labor-, Feld und Modellieraktivitäten innerhalb der Forschergruppe INUIT und mit externen Partnern. In Ergänzung der laufenden INUIT-Arbeiten möchten wir in weiteren drei Jahren der Forschergruppe folgende neue Schwerpunkte setzen: die Eisnukleationseigenschaften von porösen Partikeln, Immersionsgefrieren und Depositionsnukleation von größenselektierten Partikeln mit Durchmessern bis zu einigen Mikrometern, die Quantifizierung von Kontaktgefrierraten von atmosphärisch relevanten komplexen Aerosolpartikeln, und erste Wolkenkammerexperimente zum Kontaktgefrieren. Außerdem werden wir die Erstellung und Pflege einer neuen Datenbank für Laborergebnisse zur heterogenen Eisnukleation unterstützen.
Pflanzen im Allgemeinen und Bäume im Speziellen reagieren sehr sensibel auf klimatische Veränderungen. Der Kohlenstoff- und Wasserhaushalt wird unter Feldbedingungen gemessen und gibt so Aufschluss über physiologische Regelmechanismen (z.B. zwischen Wasserhaushalt und dem Öffnungsgrad der Stomata) oder das Baumwachstum. Mit Hilfe von systemischen Modellen interpretieren wir die ökophysiologischen Messungen und folgern daraus, wie weit sich einzelne Baumarten an veränderte klimatische Bedingungen anpassen können und ab wann artspezifische physiologische Grenzen erreicht werden. Im Wallis wachsen Waldföhren und Flaumeichen zumindest zeitweise am Rande ihrer physiologischen Möglichkeiten. Erste Resultate zeigen, warum die Flaumeiche (Quercus pubescens) unter den herrschenden klimatischen Bedingungen physiologische Vorteile gegenüber der Waldföhre (Pinus sylvestris) hat.
Organic matter (OM) composition and dynamic in subsoils is thought to be significantly different from those in surface soils. This has been suggested by increasing apparent 14C ages of bulk soil OM with depth suggesting that the amount of fresh, more easily degradable components is declining. Compositional changes have been inferred from declining ä13C values and C/N ratios indicative for stronger OM transformation. Beside these bulk OM data more specific results on OM composition and preservation mechanisms are very limited but modelling studies and results from incubation experiments suggest the presence and mineralization of younger, 'reactive carbon pool in subsoils. Less refractory OM components may be protected against degradation by interaction with soil mineral particles and within aggregates as suggested by the very limited number of more specific OM analysis e.g., identification of organic compound in soil fractions. The objective of this project is to characterize the composition, transformation, stabilization and bioavailability of OM in subsurface horizons on the molecular level: 1) major sources and compositional changes with depth will be identified by analysis of different lipid compound classes in surface and subsoil horizons, 2) the origin and stabilization of 'reactive OM will be revealed by lipid distributions and 14C values of soil fractions and of selected plant-specific lipids, and 3) organic substrates metabolized by microbial communities in subsoils are identified by distributional and 14C analysis of microbial membrane lipids. Besides detailed analyses of three soil profiles at the subsoil observatory site (Grinderwald), information on regional variability will be gained from analyses of soil profiles at sites with different parent material.
Up to recent years, the study of trends and variability of the salinity (and freshwater) distributions was hampered by the lack of temporal and spatial resolution of the available observations (Wang DFG form 54.011 - 1/12 page 3 of 6 et al., 2010). With the onset of the Argo programme, the number of observed salinity profiles have significantly increased. The many Argo profiles distributed evenly over the year provide not only the means to calculate seasonally averaged salinity (and freshwater) distributions, but they can also be used to calculate regional Gravest Empirical Modes (GEMs) parameterized by pressure and dynamic height. Dynamic height is measured by altimetry and high quality altimeter data are available since 1992. GEMs will be used to construct from altimetry high resolution (in time and space) salinity, temperature and density fields. The objectives of the proposal are to - combine Argo/CTD profiles and altimetry to calculate temporal and spatial high resolution salinity fields in the mixed layer and in the upper 1500-2000m for the time period 1992 - 2013 for the subpolar and the subtropical Atlantic. - Construct regional freshwater budgets for the mixed layer and the upper 1500-2000m and estimate the contributions of the main processes to the observed change - Follow salinity anomalies from their origin along their circulation pathways, and study involved mechanisms (for instance role of eddies, mean circulation) for shallow, intermediate and deep water masses - Investigate changes in the formation of North Atlantic mode waters in the subpolar and subtropical gyre
Sediment erosion and transport is critical to the ecological and commercial health of aquatic habitats from watershed to sea. There is now a consensus that microorganisms inhabiting the system mediate the erosive response of natural sediments ('ecosystem engineers') along with physicochemical properties. The biological mechanism is through secretion of a microbial organic glue (EPS: extracellular polymeric substances) that enhances binding forces between sediment grains to impact sediment stability and post-entrainment flocculation. The proposed work will elucidate the functional capability of heterotrophic bacteria, cyanobacteria and eukaryotic microalgae for mediating freshwater sediments to influence sediment erosion and transport. The potential and relevance of natural biofilms to provide this important 'ecosystem service' will be investigated for different niches in a freshwater habitat. Thereby, variations of the EPS 'quality' and 'quantity' to influence cohesion within sediments and flocs will be related to shifts in biofilm composition, sediment characteristics (e.g. organic background) and varying abiotic conditions (e.g. light, hydrodynamic regime) in the water body. Thus, the proposed interdisciplinary work will contribute to a conceptual understanding of microbial sediment engineering that represents an important ecosystem function in freshwater habitats. The research has wide implications for the water framework directive and sediment management strategies.
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