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  • 1
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    Cyclostratigraphy and paleoenvironmental inference from downhole logging of sediments in tropical Lake Towuti, Indonesia (2021)
    Springer Netherlands
    Details
    Publication Date: 2023-06-14
    Description: Lake Towuti is located on central Sulawesi/Indonesia, within the Indo Pacific Warm Pool, a globally important region for atmospheric heat and moisture budgets. In 2015 the Towuti Drilling Project recovered more than 1000 m of drill core from the lake, along with downhole geophysical logging data from two drilling sites. The cores constitute the longest continuous lacustrine sediment succession from the Indo Pacific Warm Pool. We combined lithological descriptions with borehole logging data and used multivariate statistics to better understand the cyclic sequence, paleoenvironments, and geochronology of these sediments. Accurate chronologies are crucial to analyze and interpret paleoclimate records. Astronomical tuning can help build age-depth models and fill gaps between age control points. Cyclostratigraphic investigations were conducted on a downhole magnetic susceptibility log from the lacustrine facies (10–98 m below lake floor) from a continuous record of sediments in Lake Towuti. This study provides insights into the sedimentary history of the basin between radiometric ages derived from dating a tephra layer (~ 797 ka) and C14-ages (~ 45 ka) in the cores. We derived an age model that spans from late marine isotope stage (MIS) 23 to late MIS 6 (903 ± 11 to 131 ± 67 ka). Although uncertainties caused by the relatively short record and the small differences in the physical properties of sediments limited the efficacy of our approach, we suggest that eccentricity cycles and/or global glacial-interglacial climate variability were the main drivers of local variations in hydroclimate in central Indonesia. We generated the first nearly complete age-depth model for the lacustrine facies of Lake Towuti and examined the potential of geophysical downhole logging for time estimation and lithological description. Future lake drilling projects will benefit from this approach, since logging data are available just after the drilling campaign, whereas core descriptions, though more resolved, only become available months to years later.
    Description: Deutsche Forschungsgemeinschaft (DE)
    Description: Projekt DEAL
    Keywords: ddc:551 ; Paleoclimate ; Geophysical downhole logging ; Cyclostratigraphy ; Lake Towuti ; Indo Pacific Warm Pool
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 2
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    When Do Subpollen Particles Become Relevant for Ice Nucleation Processes in Clouds? (2022)
    Details
    Publication Date: 2024-02-09
    Description: When exposed to sufficiently humid environments, pollen grains burst and release large quantities of small subpollen particles (SPPs) which carry ice nucleating macromolecules. In this study, for the first time we develop a physically based parameterization describing the bursting process of pollen by applying a turgor pressure parameterization and quantify the impact SPPs have on overall ice nucleation in clouds. SPPs are generated from simulated birch pollen emissions over Europe for a 10‐day case study in spring. We found SPP concentrations to surpass pollen grain concentrations by 4–6 orders of magnitude leading to an abundance of biological ice nuclei from SPPs in the range of 103−104 m−3. However, it is found that these concentrations lead to only small changes in hydrometeor number densities and precipitation. Addressing the question when SPPs become relevant for ice nucleation in clouds, we conducted a sensitivity investigation. We find that amplifying ice nucleation efficiency of biological particles by factors greater 100 increases the ice particle numbers by up to 25% (T ≈ 268 K). Strong reductions show in cloud droplet number concentration and water vapor at these temperatures while water vapor is increasing at 600 m. Overall, we found a net reduction of water in the atmosphere as liquid and particularly water vapor density is reduced, while frozen water mass density increases above 257 K. Findings indicate an alteration of mixed‐phase cloud composition and increased precipitation (up to 6.2%) when SPPs are considered as highly efficient biological ice nuclei.
    Description: Key Points Subpollen particles (SPPs) reach freezing altitudes in large number concentrations. Nucleation efficiency of SPPs affects both amplitude and sign of impact on nucleation processes. Relevant impact requires greatly increased nucleation efficiency of the SPPs.
    Description: H2020 European Research Council http://dx.doi.org/10.13039/100010663
    Description: University of Toronto Scarborough Department of Physical and Environmental Sciences Travel Award
    Description: Ministry of Science, Research and the Arts Baden‐Württemberg
    Description: Deutsche Forschungsgemeinschaft
    Description: https://doi.org/10.35097/830
    Keywords: ddc:551.5 ; subpollen particle ; SPP ; biological ice nucleation ; burst parameterization
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 3
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    Mediterranean winter rainfall in phase with African monsoons during the past 1.36 million years (2019)
    In:  Nature
    Details
    Publication Date: 2020-02-12
    Description: Mediterranean climates are characterized by strong seasonal contrasts between dry summers and wet winters. Changes in winter rainfall are critical for regional socioeconomic development, but are difficult to simulate accurately and reconstruct on Quaternary timescales. This is partly because regional hydroclimate records that cover multiple glacial–interglacial cycles with different orbital geometries, global ice volume and atmospheric greenhouse gas concentrations are scarce. Moreover, the underlying mechanisms of change and their persistence remain unexplored. Here we show that, over the past 1.36 million years, wet winters in the northcentral Mediterranean tend to occur with high contrasts in local, seasonal insolation and a vigorous African summer monsoon. Our proxy time series from Lake Ohrid on the Balkan Peninsula, together with a 784,000-year transient climate model hindcast, suggest that increased sea surface temperatures amplify local cyclone development and refuel North Atlantic low-pressure systems that enter the Mediterranean during phases of low continental ice volume and high concentrations of atmospheric greenhouse gases. A comparison with modern reanalysis data shows that current drivers of the amount of rainfall in the Mediterranean share some similarities to those that drive the reconstructed increases in precipitation. Our data cover multiple insolation maxima and are therefore an important benchmark for testing climate model performance.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 4
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    TERENO-SOILCan: a lysimeter-network in Germany observing soil processes and plant diversity influenced by climate change (2016)
    In:  Environmental Earth Sciences
    Details
    Publication Date: 2020-02-12
    Description: The aim of TERENO (TERrestrial ENvironmental Observatories) is to collect long-term observation data on the hydrosphere, biosphere, pedosphere, lower atmosphere and anthroposphere along multiple spatial and temporal gradients in climate sensitive regions across Germany. The lysimeter-network SOILCan was installed as a part of TERENO between March and December 2010 within the four observatories. It represents a long-term large-scale experiment to study the effects of climate and management changes in terrestrial ecosystems, with particular focus on the impact of these changes on water, energy and matter fluxes into groundwater and atmosphere. SOILCan primarily focuses on soil hydrology, the carbon and nutrient cycle and plant species diversity. Time series measurements of states and fluxes at high spatial and temporal resolution in the soil and biosphere are combined with remote sensing information for the development and calibration of process-based models simulating impacts of climate change in soil processes at field to regional scale. Within the framework of SOILCan, 132 fully automated lysimeter systems were installed at 14 highly equipped experimental field sites across the four TERENO observatories. Relevant state variables of grassland and arable ecosystems are monitored characterizing climate, hydrology and matter fluxes into the atmosphere and within the hydrosphere as well as plant species diversity. Lysimeters are either being operated at or near their original sampling location or were transferred within or between the four TERENO observatories thereby using temperature and rainfall gradients to mimic future climatic conditions (space for time), which allow measuring impacts of climate change on terrestrial ecosystems. The lysimeters are cultivated as grassland (intensive, extensive and non-used) or arable land, the latter with a standardized crop rotation of winter wheat—winter barley—winter rye—oat. This publication describes the general design of the SOILCan experiment including a comprehensive description of the pedological characteristics of the different sites and presents a few exemplary results from the first years of operation.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 5
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    Vivianite formation in ferruginous sediments from Lake Towuti, Indonesia (2020)
    In:  Biogeosciences
    Details
    Publication Date: 2021-02-18
    Description: Ferruginous lacustrine systems, such as Lake Towuti, Indonesia, are characterized by a specific type of phosphorus cycling in which hydrous ferric iron (oxyhydr)oxides trap and precipitate phosphorus to the sediment, which reduces its bioavailability in the water column and thereby restricts primary production. The oceans were also ferruginous during the Archean, thus understanding the dynamics of phosphorus in modern-day ferruginous analogues may shed light on the marine biogeochemical cycling that dominated much of Earth's history. Here we report the presence of large crystals (〉5 mm) and nodules (〉5 cm) of vivianite – a ferrous iron phosphate – in sediment cores from Lake Towuti and address the processes of vivianite formation, phosphorus retention by iron and the related mineral transformations during early diagenesis in ferruginous sediments. Core scan imaging, together with analyses of bulk sediment and pore water geochemistry, document a 30 m long interval consisting of sideritic and non-sideritic clayey beds and diatomaceous oozes containing vivianites. High-resolution imaging of vivianite revealed continuous growth of crystals from tabular to rosette habits that eventually form large (up to 7 cm) vivianite nodules in the sediment. Mineral inclusions like millerite and siderite reflect diagenetic mineral formation antecedent to the one of vivianite that is related to microbial reduction of iron and sulfate. Together with the pore water profiles, these data suggest that the precipitation of millerite, siderite and vivianite in soft ferruginous sediments stems from the progressive consumption of dissolved terminal electron acceptors and the typical evolution of pore water geochemistry during diagenesis. Based on solute concentrations and modeled mineral saturation indices, we inferred vivianite formation to initiate around 20 m depth in the sediment. Negative δ56Fe values of vivianite indicated incorporation of kinetically fractionated light Fe2+ into the crystals, likely derived from active reduction and dissolution of ferric oxides and transient ferrous phases during early diagenesis. The size and growth history of the nodules indicate that, after formation, continued growth of vivianite crystals constitutes a sink for P during burial, resulting in long-term P sequestration in ferruginous sediment.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 6
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    Sedimentological, geochemical, petrophysical, and geochronological data on drill cores and samples from the 2019 Lake Constance (Germany) drilling campaign with Hipercorig (2021)
    GFZ Data Services
    Details
    Publication Date: 2022-05-28
    Description: The basin sediments of Lake Constance encompass superior records of glacial to late glacial and Holocene environmental conditions but were hitherto not recovered from greater depths due to the lack of high-quality but inexpensive coring instruments. In a test and commissioning campaign in 2019, a new scientific coring device, called Hipercorig, was deployed and recovered from two parallel boreholes a 20 and a 24 m long drillcore and one two-m-long surface core (Harms et al. 2020, Schaller et al. 2022). The drill site is in 200 m deep waters close to the northwestern lake shoreline near the town of Hagnau and was selected based on new seismic surveys. They revealed an up to 150 m thick sediment fill of the overdeepened Lake Constance basin created by several advance and retreat cycles of the Rhine Glacier during the mid to late Quaternary. The deposits comprise proglacial sediments overlain by glaciolacustrine and finally lake strata. The latter make up the top 12 m of the core recovered while below sandy intercalations indicate downward increasing influence of dynamic sedimentation pulses that were deposited through subaquatic channel systems fed by declining glaciers and meltwater pulses from the north. The cores retrieved were sampled for microbiology and pore fluids at University of Constance (Germany). They were opened at Bern University (Switzerland) in fall 2019, sedimentologically described, instrumentally logged, and sampled for further studies including age dating. These data served to identify 14 lithotypes that were differentiated into three chronostratigraphic units based on a 14C- and OSL-based age model. The cores section base with the proglacial unit is about 13.7 ka BP old while the lacustrine strata cover Bølling-Alerød and Holocene ages. A prominent turbiditic event layer could be dated at 9.5 ka BP, coeval with the largest Holocene Alpine rock slide, the Flimser Bergsturz, that caused damming of the river Rhine and finally an outburst reaching as turbidite even northern Lake Constance. These initially gained data sets and the instruments utilized are described in the data description.
    Language: English
    Type: info:eu-repo/semantics/workingPaper
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  • 7
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    Aerosol-cloud-radiation interaction during Saharan dust episodes: The dusty cirrus puzzle (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-06-06
    Description: Dusty cirrus clouds are extended optically thick cirrocumulus decks that occur during strong mineral dust events. So far, they have been mostly documented over Europe associated with dust-infused baroclinic storms. Since today's global operational numerical weather prediction models neither predict mineral dust distributions nor consider the interaction of dust with cloud microphysics, they cannot simulate this phenomenon. We have performed ICON-ART limited-area simulations with 2 km grid spacing to understand and predict the formation of dusty cirrus clouds. Based on these simulations, we postulate that the dusty cirrus forms through a mixing instability of moist clean air with drier dusty air. A corresponding sub-grid parameterization is suggested and tested in the ICON-ART model. Only with help of this special sub-grid parameterization ICON-ART is able to simulate the formation of the dusty cirrus, which leads to substantial improvements in cloud cover and radiative fluxes compared to simulations without this parameterization. A statistical evaluation over six Saharan dust events with and without observed dusty cirrus shows robust improvements in cloud and radiation scores. The ability to simulate dusty cirrus formation removes the linear dependency on mineral dust aerosol optical depth from the bias of the radiative fluxes. This suggests that the formation of dusty cirrus clouds is the dominant aerosol-cloud-radiation effect of mineral dust over Europe. At the IUGG we will present first simulations with the dusty cirrus parameterization in the global ICON-ART model and discuss the occurrence of dusty cirrus in Asia.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 8
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    Aerosol and radiation observations and forecasts including aerosol-radiation-cloud interaction (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-06-06
    Description: For efficient planning and integration of photovoltaic power plants into the power grids, better knowledge of the aerosol-cloud-radiation interaction and more accurate radiation forecasts are needed. However, most operational numerical weather prediction models rely on an aerosol climatology and ignore the spatio-temporal variability of the atmospheric aerosol. In special weather conditions like Saharan dust outbreaks or extended wildfires, this leads to significant deficiencies in the operational forecasts. At Deutscher Wetter­dienst (DWD) and Karlsruhe Institute of Technology (KIT) the project "PermaStrom" aims to improve radiation forecasts. Using the ICON-ART modeling system the emission, transport, and deposition of mineral dust, black carbon from vegetation fires, and sea salt are explicitly simulated. To achieve the project goals and to examine in detail, the effect of Saharan dust on solar radiation, accurate and extensive measurements of the Saharan dust in the atmosphere and of the ground reaching solar radiation is needed. In our presentation, we will show results for several strong dust episodes in Germany. Dust clouds transported from the Saharan region to Germany are detected and tracked using ceilometer, spectroscopic and broadband radiation measurements from several sites within the measurement network of the DWD. We will focus on the direct and indirect aerosol effects and how these affect the solar irradiance at the ground. Furthermore, we will show how the implementation of prognostic mineral dust in the ICON-ART NWP model can improve the radiation forecasts during such events.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 9
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    Authigenic minerals reflect microbial control on pore waters in a ferruginous analogue (2023)
    In:  Geochemical Perspectives Letters
    Details
    Publication Date: 2023-12-19
    Description: Ferruginous conditions prevailed in the oceans through much of Earth’s history. However, minerals recording these conditions remain difficult to interpret in terms of biogeochemical processes prior to lithification. In Lake Towuti, Indonesia, ferruginous sediments are deposited under anoxic sulfate-poor conditions similar to the Proterozoic oceans, allowing the study of mineralogical (trans)formations during microbial diagenesis. Comprehensive pore water geochemistry, high resolution geochemical core profiles, and electron microscopy of authigenic minerals revealed in situ formation of magnetite, millerite, and abundant siderite and vivianite along a 100 m long sequence. Framboidal magnetites represent primary pelagic precipitates, whereas millerite, a sulfide mineral often overlooked under sulfate-poor conditions, shows acicular aggregates entangled with siderite and vivianite resulting from saturated pore waters and continuous growth during burial. These phases act as biosignatures of microbial iron and sulfate reduction, fermentation and methanogenesis, processes clearly traceable in pore water profiles. Variability in metal and organic substrates attests to environment driven processes, differentially sustaining microbial processes along the stratigraphy. Geochemical profiles resulting from microbial activity over 200 kyr after deposition provide constraints on the depth and age of mineral formation within ferruginous records.
    Language: English
    Type: info:eu-repo/semantics/article
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