Kooperativer Bibliotheksverbund

UID:

Format: xix, 223 Seiten , Illustrationen, Diagramme

Content: The concept of hydrologic connectivity summarizes all flow processes that link separate regions of a landscape. As such, it is a central theme in the field of catchment hydrology, with influence on neighboring disciplines such as ecology and geomorphology. It is widely acknowledged to be an important key in understanding the response behavior of a catchment and has at the same time inspired research on internal processes over a broad range of scales. From this process-hydrological point of view, hydrological connectivity is the conceptual framework to link local observations across space and scales. This is the context in which the four studies this thesis comprises of were conducted. The focus was on structures and their spatial organization as important control on preferential subsurface flow. Each experiment covered a part of the conceptualized flow path from hillslopes to the stream: soil profile, hillslope, riparian zone, and stream. For each study site, the most characteristic structures of the investigated domain and scale, such as slope deposits and peat layers were identified based on preliminary or previous investigations or literature reviews. Additionally, further structural data was collected and topographical analyses were carried out. [...]

Note: Kumulative Dissertation , Dissertation Universität Potsdam 2018

Additional Edition: Erscheint auch als

Language: English

Keywords: Hochschulschrift

DOI: 10.25932/publishup-42454

URN: urn:nbn:de:kobv:517-opus4-424542

URL: http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-424542

Author information: Blume, Theresa

Author information: Merz, Bruno

UID:

Format: x, 121 Seiten , Illustrationen

Content: The deciduous needle tree larch (Larix Mill.) covers more than 80% of the Asian boreal forests. Only a few Larix species constitute the vast forests and these species differ markedly in their ecological traits, most importantly in their ability to grow on and stabilize underlying permafrost. The pronounced dominance of the summergreen larches makes the Asian boreal forests unique, as the rest of the northern hemisphere boreal forests is almost exclusively dominated by evergreen needle-leaf forests. Global warming is impacting the whole world but is especially pronounced in the arctic and boreal regions. Although adapted to extreme climatic conditions, larch forests are sensitive to varying climatic conditions. By their sheer size, changes in Asian larch forests as range shifts or changes in species composition and the resulting vegetation-climate feedbacks are of global relevance. It is however still uncertain if larch forests will persist under the ongoing warming climate or if they will be replaced by evergreen forests. It is therefore of great importance to understand how these ecosystems will react to future climate warmings and if they will maintain their dominance. One step in the better understanding of larch dynamics is to study how the vast dominant forests developed and why they only established in northern Asia. A second step is to study how the species reacted to past changes in the climate. The first objective of this thesis was to review and identify factors promoting Asian larch dominance. I achieved this by synthesizing and comparing reported larch occurrences and influencing components on the northern hemisphere continents in the present and in the past. The second objective was to find a possibility to directly study past Larix populations in Siberia and specifically their genetic variation, enabling the study of geographic movements. For this, I established chloroplast enrichment by hybridization capture from sedimentary ancient DNA (sedaDNA) isolated from lake sediment records. The third objective was to use the established method to track past larch populations, their glacial refugia during the Last Glacial Maximum (LGM) around 21,000 years before present (ka BP), and their post-glacial migration patterns. To study larch promoting factors, I compared the present state of larch species ranges, areas of dominance, their bioclimatic niches, and the distribution on different extents and thaw depths of permafrost. The species comparison showed that the bioclimatic niches greatly overlap between the American and Asian species and that it is only in the extremely continental climates in which only the Asian larch species can persist. I revealed that the area of dominance is strongly connected to permafrost extent but less linked to permafrost seasonal thaw depths. Comparisons of the paleorecord of larch between the continents suggest differences in the recolonization history. Outside of northern Asia and Alaska, glacial refugial populations of larch were confined to the southern regions and thus recolonization could only occur as migration from south to north. Alaskan larch populations could not establish wide-range dominant forest which could be related to their own genetically depletion as separated refugial population. In Asia, it is still unclear whether or not the northern refugial populations contributed and enhanced the postglacial colonization or whether they were replaced by populations invading from the south in the course of climate warming. Asian larch dominance is thus promoted partly by adaptions to extremely continental climates and by adaptations to grow on continuous permafrost but could be also connected to differences in glacial survival and recolonization history of Larix species. Except for extremely rare macrofossil findings of fossilized cones, traditional methods to study past vegetation are not able to distinguish between larch species or populations. Within the scope of this thesis, I therefore established a method to retrieve genetic information of past larch populations to distinguish between species. Using the Larix chloroplast genome as target, I successfully applied the method of DNA target enrichment by hybridization capture on sedaDNA samples from lake records and showed that it is able to distinguish between larch species. I then used the method on samples from lake records from across Siberia dating back up to 50 ka BP. The results allowed me to address the question of glacial survival and post-glacial recolonization mode in Siberian larch species. The analyzed pattern showed that LGM refugia were almost exclusively constituted by L. gmelinii, even in sites of current L. sibirica distribution. For included study sites, L. sibirica migrated into its extant northern distribution area only in the Holocene. Consequently, the post-glacial recolonization of L. sibirica was not enhanced by northern glacial refugia. In case of sites in extant distribution area of L. gmelinii, the absence of a genetic turn-over point to a continuous population rather than an invasion of southern refugia. The results suggest that climate has a strong influence on the distribution of Larix species and that species may also respond differently to future climate warming. Because species differ in their ecological characteristics, species distribution is also relevant with respect to further feedbacks between vegetation and climate. With this thesis, I give an overview of present and past larch occurrences and evaluate which factors promote their dominance. Furthermore, I provide the tools to study past Larix species and give first important insights into the glacial history of Larix populations.

Note: Dissertation, Universität Potsdam, 2022 , Table of Contents Summary Deutsche Zusammenfassung Table of Contents 1 Introduction 1.1 Larix forests in a changing climate 1.2 The genus Larix 1.3 Larix distribution in the world and their dominance in northern Asia 1.4 Methods to study past species dynamics 1.4.1 Modern genetic marker studies 1.4.2 Lake sediments as archives of the past 1.4.3 Pollen and macrofossils 1.4.4 Metabarcoding of sedimentary ancient DNA 1.4.5 Metagenomic shotgun sequencing 1.4.6 Target enrichment by hybridization capture 1.5 Thesis Objectives 1.6 Thesis outline & author contributions 2 Manuscript I 2.1 Abstract 2.2 Introduction 2.3 Material and methods 2.3.1 Bioclimatic limits 2.3.2 Pollen, macrofossil, and DNA datasets 2.3.3 Ice sheets 2.4 Results 2.4.1 Bioclimatic limits of Larix and its distribution on permafrost 2.4.2 Glacial occurrence patterns of Larix 2.5 Discussion 2.5.1 Are differences in species bioclimatic limits responsible for disparity in Larix distribution across continents? 2.5.2 Do high latitude glacial refugia guarantee larch dominance? 2.5.3 What role does postglacial migration play in larch dominance? 2.5.4 Fire as an additional factor 2.5.5 Outlook 2.6 Conclusion 2.7 Acknowledgements 2.8 Author contributions 2.9 References 3 Manuscript II 3.1 Abstract 3.2 Introduction 3.3 Methods 3.3.1 Sample material 3.3.2 Laboratory work 3.3.3 Data analysis 3.4 Results 3.4.1 Overview of the shotgun and hybridization capture data sets 3.4.2 Ancient DNA authenticity 3.4.3 Retrieval of the Larix chloroplast genome 3.5 Discussion 3.5.1 Taxonomic classification—conservative approach results in low numbers of assignment 3.5.2 Target enrichment success—Larix reads increased by orders of magnitude along with other taxonomic groups 3.5.3 Complete retrieval of ancient Larix chloroplast genomes 3.5.4 Larix sibirica variants present over time 3.5.5 Larch forest decline over the last 7000 years 3.6 Conclusion 3.7 Acknowledgments 3.8 Author contributions 3.9 References 4 Manuscript III 4.1 Abstract 4.2 Introduction 4.3 Results & Discussion 4.3.1 Chloroplast and repetitive DNA enrichment in the sedaDNA samples 4.3.2 A wider pre-glacial distribution of L. sibirica 4.3.3 Larix gmelinii formed northern LGM refugia across Siberia 4.3.4 Postglacial colonization history - differences among larch species 4.3.5 Environment likely plays a more important role than biogeography 4.4 Conclusion 4.5 Material & methods 4.5.1 Sample material 4.5.2 Sequence data analysis 4.6 Data availability 4.7 Acknowledgments 4.8 Author contributions 4.9 References 5 Discussion and synthesis 5.1 Hybridization capture is a well-suited method to study ancient species dynamics 5.1.1 Advantages and limitations of shotgun sequencing 5.1.2 Successful hybridization capture enrichment using chloroplast DNA 5.1.3 Challenges in single-copy target enrichment 5.1.4 Limitations and potentials to improve sedaDNA capture studies 5.2 Factors promoting Asian larch dominance 5.3 Drivers of Larix species distribution 5.3.1 Implications for larch forests under climate warming 5.4 Conclusion 5.5 Outlook 6 References 7 Appendix 7.1 Appendix to manuscript I 7.2 Appendix to manuscript II 7.3 Appendix to manuscript III 7.3.1 Material and Methods 7.3.2 Additional Results & Discussions 7.3.3 References Acknowledgements Eidesstattliche Erklärung

Language: English

Keywords: Hochschulschrift

DOI: 10.25932/publishup-55878

URN: urn:nbn:de:kobv:517-opus4-558782

URL: https://doi.org/10.25932/publishup-55878

UID:

Format: VI, 108 Blätter , Illustrationen

Content: Assumed comparable environmental conditions of early Mars and early Earth in 3.7 Ga ago – at a time when first fossil records of life on Earth could be found – suggest the possibility of life emerging on both planets in parallel. As conditions changed, the hypothetical life on Mars either became extinct or was able to adapt and might still exist in biological niches. The controversial discussed detection of methane on Mars led to the assumption, that it must have a recent origin – either abiotic through active volcanism or chemical processes, or through biogenic production. Spatial and seasonal variations in the detected methane concentrations and correlations between the presence of water vapor and geological features such as subsurface hydrogen, which are occurring together with locally increased detected concentrations of methane, gave fuel to the hypothesis of a possible biological source of the methane on Mars. Therefore the phylogenetically old methanogenic archaea, which have evolved under early Earth conditions, are often used as model-organisms in astrobiological studies to investigate the potential of life to exist in possible extraterrestrial habitats on our neighboring planet. In this thesis methanogenic archaea originating from two extreme environments on Earth were investigated to test their ability to be active under simulated Mars analog conditions. These extreme environments – the Siberian permafrost-affected soil and the chemoautotrophically based terrestrial ecosystem of Movile cave, Romania – are regarded as analogs for possible Martian (subsurface) habitats. Two novel species of methanogenic archaea isolated from these environments were described within the frame of this thesis. It could be shown that concentrations up to 1 wt% of Mars regolith analogs added to the growth media had a positive influence on the methane production rates of the tested methanogenic archaea, whereas higher concentrations resulted in decreasing rates. Nevertheless it was possible for the organisms to metabolize when incubated on water-saturated soil matrixes made of Mars regolith analogs without any additional nutrients. Long-term desiccation resistance of more than 400 days was proven with reincubation and indirect counting of viable cells through a combined treatment with propidium monoazide (to inactivate DNA of destroyed cells) and quantitative PCR. Phyllosilicate rich regolith analogs seem to be the best soil mixtures for the tested methanogenic archaea to be active under Mars analog conditions. Furthermore, in a simulation chamber experiment the activity of the permafrost methanogen strain Methanosarcina soligelidi SMA-21 under Mars subsurface analog conditions could be proven. Through real-time wavelength modulation spectroscopy measurements the increase in the methane concentration at temperatures down to -5 °C could be detected. The results presented in this thesis contribute to the understanding of the activity potential of methanogenic archaea under Mars analog conditions and therefore provide insights to the possible habitability of present-day Mars (near) subsurface environments. Thus, it contributes also to the data interpretation of future life detection missions on that planet. For example the ExoMars mission of the European Space Agency (ESA) and Roscosmos which is planned to be launched in 2018 and is aiming to drill in the Martian subsurface

Note: kumulative Dissertation , Dissertation, Universität Potsdam, 2015 , Table of contents Preface Table of contents Summary Zusammenfassung 1. Introduction 1.1. Environmental conditions on past and present Mars 1.2. Detection of methane on Mars 1.3. Methanogenic archaea 1.4. Description of study sites 1.5. Aims and approaches 1.6. Overview of the publications 2. Publication I: Methanosarcina soligelidi sp. nov., a desiccationandfreeze-thaw-resistant methanogenic archaeon from a Siberianpermafrost-affected soil 3. Publication II: Methanobacterium movilense sp. nov.,ahydrogenotrophic, secondary-alcohol-utilizing methanogen fromthe anoxic sediment of a subsurface lake 4. Publication III: Influence of Martian Regolith Analogs on the activityand growth of methanogenic archaea,with special regard to long-term desiccation 5. Publication IV: Laser spectroscopic real time measurements ofmethanogenic activity under simulated Martian subsurface conditions 6. Synthesis and Conclusion 6.1. Synthesis 6.2. Conclusion and future perspectives 7. References 8. Acknowledgments

Language: English

Keywords: Hochschulschrift

URN: urn:nbn:de:kobv:517-opus4-73010

URL: http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-73010

UID:

Format: xx, 167 Seiten : Illustrationen, Diagramme

Content: Throughout the last ~3 million years, the Earth's climate system was characterised by cycles of glacial and interglacial periods. The current warm period, the Holocene, is comparably stable and stands out from this long-term cyclicality. However, since the industrial revolution, the climate has been increasingly affected by a human-induced increase in greenhouse gas concentrations. While instrumental observations are used to describe changes over the past ~200 years, indirect observations via proxy data are the main source of information beyond this instrumental era. These data are indicators of past climatic conditions, stored in palaeoclimate archives around the Earth. The proxy signal is affected by processes independent of the prevailing climatic conditions. In particular, for sedimentary archives such as marine sediments and polar ice sheets, material may be redistributed during or after the initial deposition and subsequent formation of the archive. This leads to noise in the records challenging reliable reconstructions on local or short time scales. This dissertation characterises the initial deposition of the climatic signal and quantifies the resulting archive-internal heterogeneity and its influence on the observed proxy signal to improve the representativity and interpretation of climate reconstructions from marine sediments and ice cores. To this end, the horizontal and vertical variation in radiocarbon content of a box-core from the South China Sea is investigated. The three-dimensional resolution is used to quantify the true uncertainty in radiocarbon age estimates from planktonic foraminifera with an extensive sampling scheme, including different sample volumes and replicated measurements of batches of small and large numbers of specimen. An assessment on the variability stemming from sediment mixing by benthic organisms reveals strong internal heterogeneity. Hence, sediment mixing leads to substantial time uncertainty of proxy-based reconstructions with error terms two to five times larger than previously assumed. A second three-dimensional analysis of the upper snowpack provides insights into the heterogeneous signal deposition and imprint in snow and firn. A new study design which combines a structure-from-motion photogrammetry approach with two-dimensional isotopic data is performed at a study site in the accumulation zone of the Greenland Ice Sheet. The photogrammetry method reveals an intermittent character of snowfall, a layer-wise snow deposition with substantial contributions by wind-driven erosion and redistribution to the final spatially variable accumulation and illustrated the evolution of stratigraphic noise at the surface. The isotopic data show the preservation of stratigraphic noise within the upper firn column, leading to a spatially variable climate signal imprint and heterogeneous layer thicknesses. Additional post-depositional modifications due to snow-air exchange are also investigated, but without a conclusive quantification of the contribution to the final isotopic signature. Finally, this characterisation and quantification of the complex signal formation in marine sediments and polar ice contributes to a better understanding of the signal content in proxy data which is needed to assess the natural climate variability during the Holocene.

Note: Dissertation, Universität Potsdam, 2023 (publikationsbasierte Dissertation) , CONTENTS 1 Introduction 1.1 Introduction to climate reconstructions 1.1.1 Radiocarbon as a tracer of time 1.1.2 Environmental information stored in snow 1.2 Challenges of climate reconstructions 1.2.1 The particle flux 1.2.2 Modifications after the initial deposition 1.2.3 Sampling and measurement uncertainty 1.3 Objectives and overview of the thesis 1.4 Author contributions to the Manuscripts 2 Age-heterogeneity in marine sediments revealed by three-dimensional high-resolution radio-carbon measurements 2.1 Introduction 2.2 Methods 2.2.1 Study approach 2.2.2 Core setup and sampling 2.2.3 Estimation of the sediment accumulation rate 2.2.4 Estimation of the sediment mixing strength 2.2.5 Estimation of the net sediment displacement 2.2.6 Visual assessment of mixing 2.3 Results 2.3.1 Radiocarbon measurements 2.3.2 Sediment accumulation rate 2.3.3 Sediment mixing estimates 2.3.4 Spatial structure of sediment mixing 2.3.5 Components of age uncertainty 2.4 Discussion 2.4.1 Spatial scale of sediment heterogeneity 2.4.2 Potential implications for palaeo-reconstructions 2.4.3 Suggested 14C measurement strategy 2.5 Conclusions 2.6 Supplementary Material 2.6.1 Supplementary figures and tables 2.6.2 Supplementary table 3 Local-scale deposition of surface snow on the Greenland ice sheet 3.1 Introduction 3.2 Data and methods 3.2.1 Study site 3.2.2 SfM photogrammetry 3.2.3 Additional snow height and snowfall data 3.2.4 Estimation of surface roughness 3.3 Results 3.3.1 Relative snow heights from DEMs 3.3.2 Temporal snow height evolution 3.3.3 Day-to-day variations of snowfall 3.3.4 Changes in surface roughness 3.3.5 Implied internal structure of the snowpack 3.4 Discussion 3.4.1 Changes of surface structures 3.4.2 Implications for proxy data 3.4.3 Implications for snow accumulation 3.4.4 SfM as an efficient monitoring tool 3.5 Conclusions 3.6 Appendix 3.6.1 Additional information 3.6.2 Accuracy estimates and validation 3.6.3 Validation 3.6.4 Overall snow height evolution 3.6.5 Surface roughness 4 A snapshot on the buildup of the stable water isotopic signal in the upper snowpack at east-grip, Geenland ice sheet 4.1 Introduction 4.2 Methods and data 4.2.1 Study site 4.2.2 DEM generation 4.2.3 Isotope measurements 4.2.4 Simulation of the snowpack layering 4.2.5 Expected uncertainty 4.3 Results 4.3.1 Snow height evolution 4.3.2 Mean isotopic records 4.3.3 Combining isotopic data with snow height information 4.3.4 Observed vs. simulated composition 4.3.5 Changes in the isotope signal over time 4.4 Discussion 4.4.1 Evolution of the snow surface 4.4.2 Two-dimensional view of isotopes in snow 4.4.3 Buildup of the snowpack isotopic signal 4.5 Conclusion 5 General discussion and conclusions 5.1 Heterogeneity in sedimentary archives 5.1.1 Quantifying archive-internal heterogeneity 5.1.2 Relation between signal and heterogeneity 5.2 Methods to improve climate reconstructions 5.3 Implications for climate reconstructions 5.4 Concluding remarks Bibliography A the role of sublimation as a driver of climate signals in the water isotope content of surface snow: laboratory and field experimental results A.1 Introduction A.2 Methods A.2.1 Laboratory experimental methods A.2.2 Field experimental methods A.3 Results A.3.1 Laboratory experiments A.3.2 Field experiments A.4 Discussion A.5 Conclusions B Atmosphere-snow exchange explains surface snow isotope variability Acknowledgments Eidesstattliche Erklärung

Language: English

Keywords: Hochschulschrift

URL: https://doi.org/10.25932/publishup-58286

UID:

Format: x, 136 Seiten , Illustrationen, Diagramme, Karten

Content: Over the last decades, the rate of near-surface warming in the Arctic is at least double than elsewhere on our planet (Arctic amplification). However, the relative contribution of different feedback processes to Arctic amplification is a topic of ongoing research, including the role of aerosol and clouds. Lidar systems are well-suited for the investigation of aerosol and optically-thin clouds as they provide vertically-resolved information on fine temporal scales. Global aerosol models fail to converge on the sign of the Arctic aerosol radiative effect (ARE). In the first part of this work, the optical and microphysical properties of Arctic aerosol were characterized at case study level in order to assess the short-wave (SW) ARE. A long-range transport episode was first investigated. Geometrically similar aerosol layers were captured over three locations. Although the aerosol size distribution was different between Fram Strait(bi-modal) and Ny-Ålesund (fine mono-modal), the atmospheric column ARE was similar. The latter was related to the domination of accumulation mode aerosol. Over both locations top of the atmosphere (TOA) warming was accompanied by surface cooling. Subsequently, the sensitivity of ARE was investigated with respect to different aerosol and spring-time ambient conditions. A 10% change in the single-scattering albedo (SSA) induced higher ARE perturbations compared to a 30% change in the aerosol extinction coefficient. With respect to ambient conditions, the ARETOA was more sensitive to solar elevation changes compared to AREsur f ace. Over dark surfaces the ARE profile was exclusively negative, while over bright surfaces a negative to positive shift occurred above the aerosol layers. Consequently, the sign of ARE can be highly sensitive in spring since this season is characterized by transitional surface albedo conditions. As the inversion of the aerosol microphysics is an ill-posed problem, the inferred aerosol size distribution of a low-tropospheric event was compared to the in-situ measured distribution. Both techniques revealed a bi-modal distribution, with good agreement in the total volume concentration. However, in terms of SSA a disagreement was found, with the lidar inversion indicating highly scattering particles and the in-situ measurements pointing to absorbing particles. The discrepancies could stem from assumptions in the inversion (e.g. wavelength-independent refractive index) and errors in the conversion of the in-situ measured light attenuation into absorption. Another source of discrepancy might be related to an incomplete capture of fine particles in the in-situ sensors. The disagreement in the most critical parameter for the Arctic ARE necessitates further exploration in the frame of aerosol closure experiments. Care must be taken in ARE modelling studies, which may use either the in-situ or lidar-derived SSA as input. Reliable characterization of cirrus geometrical and optical properties is necessary for improving their radiative estimates. In this respect, the detection of sub-visible cirrus is of special importance. The total cloud radiative effect (CRE) can be negatively biased, should only the optically-thin and opaque cirrus contributions are considered. To this end, a cirrus retrieval scheme was developed aiming at increased sensitivity to thin clouds. The cirrus detection was based on the wavelet covariance transform (WCT) method, extended by dynamic thresholds. The dynamic WCT exhibited high sensitivity to faint and thin cirrus layers (less than 200 m) that were partly or completely undetected by the existing static method. The optical characterization scheme extended the Klett–Fernald retrieval by an iterative lidar ratio (LR) determination (constrained Klett). The iterative process was constrained by a reference value, which indicated the aerosol concentration beneath the cirrus cloud. Contrary to existing approaches, the aerosol-free assumption was not adopted, but the aerosol conditions were approximated by an initial guess. The inherent uncertainties of the constrained Klett were higher for optically-thinner cirrus, but an overall good agreement was found with two established retrievals. Additionally, existing approaches, which rely on aerosol-free assumptions, presented increased accuracy when the proposed reference value was adopted. The constrained Klett retrieved reliably the optical properties in all cirrus regimes, including upper sub-visible cirrus with COD down to 0.02. Cirrus is the only cloud type capable of inducing TOA cooling or heating at daytime. Over the Arctic, however, the properties and CRE of cirrus are under-explored. In the final part of this work, long-term cirrus geometrical and optical properties were investigated for the first time over an Arctic site (Ny-Ålesund). To this end, the newly developed retrieval scheme was employed. Cirrus layers over Ny-Ålesund seemed to be more absorbing in the visible spectral region compared to lower latitudes and comprise relatively more spherical ice particles. Such meridional differences could be related to discrepancies in absolute humidity and ice nucleation mechanisms. The COD tended to decline for less spherical and smaller ice particles probably due to reduced water vapor deposition on the particle surface. The cirrus optical properties presented weak dependence on ambient temperature and wind conditions. Over the 10 years of the analysis, no clear temporal trend was found and the seasonal cycle was not pronounced. However, winter cirrus appeared under colder conditions and stronger winds. Moreover, they were optically-thicker, less absorbing and consisted of relatively more spherical ice particles. A positive CREnet was primarily revealed for a broad range of representative cloud properties and ambient conditions. Only for high COD (above 10) and over tundra a negative CREnet was estimated, which did not hold true over snow/ice surfaces. Consequently, the COD in combination with the surface albedo seem to play the most critical role in determining the CRE sign over the high European Arctic.

Note: Dissertation, Universität Potsdam, 2021 , CONTENTS 1 INTRODUCTION 1.1 Motivation: Aerosol and cloud relevance to Arctic amplification 1.2 Theoretical background 1.2.1 Atmospheric aerosol 1.2.2 Aerosol in the Arctic 1.2.3 Cirrus clouds 1.3 Research questions 2 METHODS 2.1 lidar remote sensing techniqu 2.1.1 Elastic and Raman lidar equations 2.1.2 lidar signal corrections 2.1.3 Derivation of particle optical properties and related uncertainties 2.2 Lidar systems 2.2.1 Ground-based system KARL 2.2.2 Air-borne system AMALi 2.2.3 Space-borne system CALIOP 2.3 Ancillary instrumentation 2.3.1 Radiosondes 2.3.2 Sun-photometers 2.3.3 Radiation sensors 2.4 Modeling tools 2.4.1 Air mass backward trajectories 2.4.2 Aerosol microphysics retrieval algorithm 2.4.3 Radiative transfer model SCIATRAN 2.4.4 Multiple-scattering correction model 2.4.5 Simplified cloud radiative effect model 3 ARCTIC AEROSOL PROPERTIES AND RADIATIVE EFFECT (CASE STUDIES) 3.1 Aerosol in the upper troposphere (Spring) 3.1.1 Overview of aerosol observations and air mass origin 3.1.2 Modification of aerosol optical and microphysical properties 3.1.3 Aerosol radiative effect (ARE) 3.2 Sensitivities of the spring-time Arctic ARE 3.2.1 Sensitivity on aerosol related parameters 3.2.2 Sensitivity on ambient conditions 3.3 Aerosol in the lower troposphere (Winter) 3.3.1 Overview of remote sensing and in-situ measurements 3.3.2 Aerosol properties from the remote sensing perspective: KARL and CALIOP 3.3.3 Aerosol microphysical properties from in-situ and remote sensing perspectives 3.4 Discussion and Conclusions 4 DEVELOPMENT OF A CIRRUS CLOUD RETRIEVAL SCHEME 4.1 Fine-scale cirrus cloud detection 4.1.1 Selection of cirrus clouds 4.1.2 Wavelet Covariance Transform method 4.1.3 Revised detection method: Dynamic Wavelet Covariance Transform 4.2 Comparison of dynamic and static cirrus detection 4.3 Cirrus cloud optical retrievals 4.3.1 Existing cirrus optical retrievals: double-ended Klett and Raman 4.3.2 Temporal averaging within stationary periods 4.3.3 Revised optical retrieval: constrained Klett method 4.4 Comparison to established optical retrievals 4.5 How uncertainties in cirrus detection affect the optical retrievals? 4.6 Discussion 4.6.1 Limitations of cirrus retrieval schemes 4.6.2 Strengths of the revised retrieval scheme 4.7 Conclusions 5 LONG-TERM ANALYSIS OF ARCTIC CIRRUS CLOUD PROPERTIES 5.1 Overview of cirrus occurrence and meteorological conditions over Ny-Ålesund 5.2 Quality assurance of optical properties 5.2.1 Specular reflection effect 5.2.2 Investigation of extreme cirrus lidar ratio values 5.2.3 Multiple-scattering correction 5.3 Overview of cirrus optical properties over Ny-Ålesund 5.4 Inter-relations of cirrus properties 5.5 Dependence on meteorological conditions 5.5.1 Cirrus clouds in the tropopause 5.6 CRE estimation at TOA: sensitivity analysis 5.7 Conclusions 6 CONCLUSIONS AND OUTLOOK A CIRRUS DETECTION SENSITIVITIES a.1 Wavelet Covariance Transform - dilation sensitivity a.2 Wavelet Covariance Transform - wavelength dependency B CIRRUS OPTICAL CHARACTERIZATION SENSITIVITIES b.1 Reference value accuracy and limitations b.2 Inherent uncertainties of constrained Klett C MULTIPLE-SCATTERING CORRECTION FOR CIRRUS CLOUDS D SEASONAL CIRRUS PROPERTIES: DESCRIPTIVE STATISTICS BIBLIOGRAPHY

Language: English

Keywords: Hochschulschrift

DOI: 10.25932/publishup-53036

URN: urn:nbn:de:kobv:517-opus4-530366

URL: https://doi.org/10.25932/publishup-53036

URL: https://nbn-resolving.org/urn:nbn:de:kobv:517-opus4-530366

URL: https://d-nb.info/1248561724/34

Author information: Rex, Markus 1966-

UID:

Format: X, 104, A-57 Seiten , Illustrationen, Diagramme

Content: With Arctic ground as a huge and temperature-sensitive carbon reservoir, maintaining low ground temperatures and frozen conditions to prevent further carbon emissions that contrib-ute to global climate warming is a key element in humankind’s fight to maintain habitable con-ditions on earth. Former studies showed that during the late Pleistocene, Arctic ground condi-tions were generally colder and more stable as the result of an ecosystem dominated by large herbivorous mammals and vast extents of graminoid vegetation – the mammoth steppe. Characterised by high plant productivity (grassland) and low ground insulation due to animal-caused compression and removal of snow, this ecosystem enabled deep permafrost aggrad-ation. Now, with tundra and shrub vegetation common in the terrestrial Arctic, these effects are not in place anymore. However, it appears to be possible to recreate this ecosystem local-ly by artificially increasing animal numbers, and hence keep Arctic ground cold to reduce or-ganic matter decomposition and carbon release into the atmosphere. By measuring thaw depth, total organic carbon and total nitrogen content, stable carbon iso-tope ratio, radiocarbon age, n-alkane and alcohol characteristics and assessing dominant vegetation types along grazing intensity transects in two contrasting Arctic areas, it was found that recreating conditions locally, similar to the mammoth steppe, seems to be possible. For permafrost-affected soil, it was shown that intensive grazing in direct comparison to non-grazed areas reduces active layer depth and leads to higher TOC contents in the active layer soil. For soil only frozen on top in winter, an increase of TOC with grazing intensity could not be found, most likely because of confounding factors such as vertical water and carbon movement, which is not possible with an impermeable layer in permafrost. In both areas, high animal activity led to a vegetation transformation towards species-poor graminoid-dominated landscapes with less shrubs. Lipid biomarker analysis revealed that, even though the available organic material is different between the study areas, in both permafrost-affected and sea-sonally frozen soils the organic material in sites affected by high animal activity was less de-composed than under less intensive grazing pressure. In conclusion, high animal activity af-fects decomposition processes in Arctic soils and the ground thermal regime, visible from reduced active layer depth in permafrost areas. Therefore, grazing management might be utilised to locally stabilise permafrost and reduce Arctic carbon emissions in the future, but is likely not scalable to the entire permafrost region.

Note: Dissertation, Universität Potsdam, 2024 , Table of contents ABSTRACT ZUSAMMENFASSUNG ABBREVIATIONS AND NOMENCLATURE CHAPTER 1: INTRODUCTION 1.1 SCIENTIFIC BACKGROUND 1.1.1 ARCTIC GROUND 1.1.2 THE PHENOMENON OF PERMAFROST 1.1.3 ARCTIC NON - PERMAFROST AREAS 1.1.4 HYPOTHESIS 1.2 AIMS AND OBJECTIVES 1.3 METHODS 1.3.1 FIELD METHODS AND SAMPLING APPROACH 1.3.2 STUDY AREA SELECTION 1.3.3 LABORATORY METHODS 1.4 THESIS ORGANISATION CHAPTER 2: LARGE HERBIVORES ON PERMAFROST – A PILOT STUDY OF GRAZING IMPACTS ON PERMAFROST SOIL CARBON STORAGE IN NORTHEASTERN SIBERIA 2.1 ABSTRACT 2.2 I NTRODUCTION 2.3 STUDY AREA 2.4 METHODS 2.4.1 FIELD SAMPLING APPROACH 2.4.2 LABORATORY WORK 2.4.3 DATA ANALYSIS AND EXTERNAL DATA 2.5 RESULTS 2.5.1 VEGETATION ASSESSMENT 2.5.2 SEASONAL THAW DEPTH 2.5.3 CARBON PARAMETERS (TOC, TOC/TN RATIOS , AND Δ13 C RATIOS ) 2.5.4 GRAIN SIZE DISTRIBUTION AND WATER CONTENT 2.5.5 STATISTICS AND CORRELATION ANALYSIS 2.6 DISCUSSION 2.6.1 EFFECTS OF GRAZING ON VEGETATION STRUCTURE AND PERMAFROST THAW 2.6.2 CARBON ACCUMULATION UNDER GRAZING IMPACT 2.6.3 METHODOLOGICAL LIMITATIONS OF THE PILOT STUDY 2.7 CONCLUSION 2.8 DATA AVAILABILITY STATEMENT 2.9 AUTHOR CONTRIBUTIONS 2.10 FUNDING 2.11 ACKNOWLEDGEMENTS 2.12 CONFLICT OF INTERESTS CHAPTER 3: IMPACTS OF REINDEER ON SOIL CARBON STORAGE IN THE SEASONALLY FROZEN GROUND OF NORTHERN FINLAND: A PILOT STUDY 3.1 ABSTRACT 3.2 I NTRODUCTION 3.3 STUDY AREA 3.4 METHODS 3.4.1 FIELD WORK 3.4.2 LABORATORY ANALYSIS 3.4.3 DATA ANALYSIS AND CALCULATIONS 3.5 RESULTS 3.5.1 CORE DESCRIPTIONS 3.5.2 VEGETATION 3.5.3 CARBON PARAMETERS 3.5.6 COMPARATIVE DATA ANALYSIS 3.6 DISCUSSION 3.6.1 REINDEER IMPACT ON SOIL CARBON STORAGE 3.6.2 REINDEER IMPACT ON VEGETATION 3.6.3 REINDEER IMPACT ON GROUND CHARACTERISTICS 3.6.4 SOC DENSITY AND STOCKS ACROSS THE KUTUHARJU STATION AREA 3.6.5 METHODOLOGICAL LIMITATIONS OF THE PILOT STUDY DESIGN 3.6.6 IMPLICATIONS OF THE PILOT STUDY FOR FUTURE RESEARCH 3.7 CONCLUSION 3.8 DATA AVAILABILITY 3.9 AUTHOR CONTRIBUTION 3.10 COMPETING INTERESTS 3.11 ACKNOWLEDGEMENTS 3.12 FUNDING TABLE 3-1 TABLE 3-2 TABLE 3-3 CHAPTER 4: LIPID BIOMARKER SCREENING TO TRACE RECENT LARGE HERBIVORE INFLUENCE ON SOIL CARBON IN PERMAFROST AND SEASONALLY FROZEN ARCTIC GROUND 4.1 ABSTRACT 4.2 I NTRODUCTION 4.3 STUDY AREA 4.4 METHODS 4.4.1 SAMPLING APPROACH 4.4.2 LABORATORY ANALYSIS 4.4.3 LIPID BIOMARKER INDICES 4.4.4 STATISTICS 4.5 RESULTS 4.5.1 TOC 4.5.2 C/N RATIO 4.5.3 STABLE CARBON ISOTOPE RATIO 4.5.4 ABSOLUTE N- ALKANE CONCENTRATION 4.5.5 AVERAGE CHAIN LENGTH 4.5.6 CARBON PREFERENCE INDEX 4.5.7 HIGHER - PLANT ALCOHOL INDEX 4.5.8 STATISTICAL RESULTS 4.6 DISCUSSION 4.6.1 EFFECTS OF GRAZING INTENSITY ON BIOMARKER SIGNALS 4.6.2 EFFECTS OF GROUND THERMAL REGIME ON SOIL OM DEGRADATION 4.6.3 I MPACT OF HERBIVORY ON PERMAFROST OM STORAGE 4.7 CONCLUSION 4.8 ACKNOWLEDGEMENTS 4.9 COMPETING INTERESTS 4.10 AUTHOR CONTRIBUTION 4.11 FUNDING 4.12 DATA AVAILABILITY CHAPTER 5: SYNTHESIS 5.1 ECOSYSTEM CHANGES UNDER THE IMPACT OF LARGE HERBIVORES 5.2 GRAZING EFFECTS ON SOIL ORGANIC MATTER DECOMPOSITION 5.3 F EASIBILITY OF UTILISING HERBIVORY IN THE ARCTIC 5.4 RESEARCH IMPLICATIONS FOR SUCCESSFUL PLANNING AND USE OF ARCTIC HERBIVORY REFERENCES 93 FINANCIAL AND TECHNICAL SUPPORT APPENDIX 1 APPENDIX I ORGANIC CARBON CHARACTERISTICS IN ICE - RICH PERMAFROST IN ALAS AND YEDOMA DEPOSITS , CENTRAL YAKUTIA, SIBERIA APPENDIX II WHAT ARE THE EFFECTS OF HERBIVORE DIVERSITY ON TUNDRA ECOSYSTEMS ? A SYSTEMATIC REVIEW (ABSTRACT) APPENDIX III SUPPLEMENTARY MATERIAL TO CHAPTER 2: LARGE HERBIVORES ON PERMAFROST – A PILOT STUDY OF GRAZING IMPACTS ON PERMAFROST SOIL CARBON STORAGE IN NORTHEASTERN SIBERIA APPENDIX IV SUPPLEMENTARY MATERIAL TO CHAPTER 3: IMPACTS OF REINDEER ON SOIL CARBON STORAGE IN THE SEASONALLY FROZEN GROUND OF NORTHERN FINLAND : A PILOT STUDY APPENDIX V SUPPLEMENTARY MATERIAL TO CHAPTER 4: A PILOT STUDY OF LIPID BIOMARKERS TO TRACE RECENT LARGE HERBIVORE INFLUENCE ON SOIL CARBON IN PERMAFROST AND SEASONALLY ROZEN ARCTIC GROUND APPENDIX VI SUPPLEMENTARY MATERIAL TO APPENDIX IV: ORGANIC CARBON CHARACTERISTICS IN ICE - RICH PERMAFROST IN ALAS AND YEDOMA DEPOSITS , CENTRAL YAKUTIA, SIBERIA ACKNOWLEDGEMENTS - DANKSAGUNG

Language: English

Keywords: Hochschulschrift

DOI: 10.25932/publishup-62424

URL: https://doi.org/10.25932/publishup-62424

Author information: Große, Guido 1976-

UID:

Format: 149 Seiten , Illustrationen, Diagramme

Content: Vegetation change at high latitudes is one of the central issues nowadays with respect to ongoing climate changes and triggered potential feedback. At high latitude ecosystems, the expected changes include boreal treeline advance, compositional, phenological, physiological (plants), biomass (phytomass) and productivity changes. However, the rate and the extent of the changes under climate change are yet poorly understood and projections are necessary for effective adaptive strategies and forehanded minimisation of the possible negative feedbacks. The vegetation itself and environmental conditions, which are playing a great role in its development and distribution are diverse throughout the Subarctic to the Arctic. Among the least investigated areas is central Chukotka in North-Eastern Siberia, Russia. Chukotka has mountainous terrain and a wide variety of vegetation types on the gradient from treeless tundra to northern taiga forests. The treeline there in contrast to subarctic North America and north-western and central Siberia is represented by a deciduous conifer, Larix cajanderi Mayr. The vegetation varies from prostrate lichen Dryas octopetala L. tundra to open graminoid (hummock and non-hummock) tundra to tall Pinus pumila (Pall.) Regel shrublands to sparse and dense larch forests. Hence, this thesis presents investigations on recent compositional and above-ground biomass (AGB) changes, as well as potential future changes in AGB in central Chukotka. The aim is to assess how tundra-taiga vegetation develops under changing climate conditions particularly in Fareast Russia, central Chukotka. Therefore, three main research questions were considered: 1) What changes in vegetation composition have recently occurred in central Chukotka? 2) How have the above-ground biomass AGB rates and distribution changed in central Chukotka? 3) What are the spatial dynamics and rates of tree AGB change in the upcoming millennia in the northern tundra-taiga of central Chukotka? Remote sensing provides information on the spatial and temporal variability of vegetation. I used Landsat satellite data together with field data (foliage projective cover and AGB) from two expeditions in 2016 and 2018 to Chukotka to upscale vegetation types and AGB for the study area. More specifically, I used Landsat spectral indices (Normalised Difference Vegetation Index (NDVI), Normalised Difference Water Index (NDWI) and Normalised Difference Snow Index (NDSI)) and constrained ordination (Redundancy analysis, RDA) for further k-means-based land-cover classification and general additive model (GAM)-based AGB maps for 2000/2001/2002 and 2016/2017. I also used Tandem-X DEM data for a topographical correction of the Landsat satellite data and to derive slope, aspect, and Topographical Wetness Index (TWI) data for forecasting AGB. Firstly, in 2016, taxa-specific projective cover data were collected during a Russian-German expedition. I processed the field data and coupled them with Landsat spectral Indices in the RDA model that was used for k-means classification. I could establish four meaningful land-cover classes: (1) larch closed-canopy forest, (2) forest tundra and shrub tundra, (3) graminoid tundra and (4) prostrate herb tundra and barren areas, and accordingly, I produced the land cover maps for 2000/2001/2002 and 2016/20017. Changes in land-cover classes between the beginning of the century (2000/2001/2002) and the present time (2016/2017) were estimated and interpreted as recent compositional changes in central Chukotka. The transition from graminoid tundra to forest tundra and shrub tundra was interpreted as shrubification and amounts to a 20% area increase in the tundra-taiga zone and 40% area increase in the northern taiga. Major contributors of shrubification are alder, dwarf birch and some species of the heather family. Land-cover change from the forest tundra and shrub tundra class to the larch closed-canopy forest class is interpreted as tree infilling and is notable in the northern taiga. We find almost no land-cover changes in the present treeless tundra. Secondly, total AGB state and change were investigated for the same areas. In addition to the total vegetation AGB, I provided estimations for the different taxa present at the field sites. As an outcome, AGB in the study region of central Chukotka ranged from 0 kg m-2 at barren areas to 16 kg m-2 in closed-canopy forests with the larch trees contributing the highest. A comparison of changes in AGB within the investigated period from 2000 to 2016 shows that the greatest changes (up to 1.25 kg m 2 yr 1) occurred in the northern taiga and in areas where land cover changed to larch closed-canopy forest. Our estimations indicate a general increase in total AGB throughout the investigated tundra-taiga and northern taiga, whereas the tundra showed no evidence of change in AGB within the 15 years from 2002 to 2017. In the third manuscript, potential future AGB changes were estimated based on the results of simulations of the individual-based spatially explicit vegetation model LAVESI using different climate scenarios, depending on Representative Concentration Pathways (RCPs) RCP 2.6, RCP 4.5 and RCP 8.5 with or without cooling after 2300 CE. LAVESI-based AGB was simulated for the current state until 3000 CE for the northern tundra-taiga study area for larch species because we expect the most notable changes to occur will be associated with forest expansion in the treeline ecotone. The spatial distribution and current state of tree AGB was validated against AGB field data, AGB extracted from Landsat satellite data and a high spatial resolution image with distinctive trees visible. The simulation results are indicating differences in tree AGB dynamics plot wise, depending on the distance to the current treeline. The simulated tree AGB dynamics are in concordance with fundamental ecological (emigrational and successional) processes: tree stand formation in simulated results starts with seed dispersion, tree stand establishment, tree stand densification and episodic thinning. Our results suggest mostly densification of existing tree stands in the study region within the current century in the study region and a lagged forest expansion (up to 39% of total area in the RCP 8.5) under all considered climate scenarios without cooling in different local areas depending on the closeness to the current treeline. In scenarios with cooling air temperature after 2300 CE, forests stopped expanding at 2300 CE (up to 10%, RCP 8.5) and then gradually retreated to their pre-21st century position. The average tree AGB rates of increase are the strongest in the first 300 years of the 21st century. The rates depend on the RCP scenario, where the highest are as expected under RCP 8.5. Overall, this interdisciplinary thesis shows a successful integration of field data, satellite data and modelling for tracking recent and predicting future vegetation changes in mountainous subarctic regions. The obtained results are unique for the focus area in central Chukotka and overall, for mountainous high latitude ecosystems.

Note: Dissertation, Potsdam, Universität Potsdam, 2022 , Contents Abstract Zusammenfassung Contents Abbreviations Motivation 1 Introduction 1.1 Scientific background 1.2 Study region 1.3 Aims and objectives 2 Materials and methods 3.1 Section 4 - Strong shrub expansion in tundra-taiga, tree infilling in taiga and stable tundra in central Chukotka (north-eastern Siberia) between 2000 and 2017 3.2 Section 5 - Recent above-ground biomass changes in central Chukotka (NE Siberia) combining field-sampling and remote sensing 3.3 Section 6 - Future spatially explicit tree above-ground biomass trajectories revealed for a mountainous treeline ecotone using the individual-based model LAVESI 4 Strong shrub expansion in tundra-taiga, tree infilling in taiga and stable tundra in central Chukotka (north-eastern Siberia) between 2000 and 2017 Abstract 1 Introduction 2 Materials and methods 2.1 Field data collection and processing 2.2 Landsat data, pre-processing and spectral indices processing 2.3 Redundancy analysis (RDA) and classification approaches 3 Results 3.1 General characteristics of the vegetation field data 3.2 Relating field data to Landsat spectral indices in the RDA model 3.3 Land-cover classification 3.4 Land-cover change between 2000 and 2017 4 Discussion 4.1 Dataset limitations and optimisation 4.2 Vegetation changes from 2000/2001/2002 to 2016/2017 Conclusions Acknowledgements Data availability statement References Appendix A. Detailed description of Landsat acquisitions Appendix B. MODIS NDVI time series from 2000 to 2018 Appendix C. Landsat Indices values for each analysed vegetation site Appendix D. Fuzzy c-means classification for interpretation of uncertainties for land-cover mapping Appendix E. Validation of land-cover maps Appendix F. K-means classification results Appendix G. Heterogeneity of natural landscapes and mixed pixels of satellite data Appendix H. Distribution of land-cover classes and their changes by study area 5 Recent above-ground biomass changes in central Chukotka (NE Siberia) combining field-sampling and remote sensing Abstract 1 Introduction 2 Materials and methods 2.1 Study region and field surveys 2.2 Above-ground biomass upscaling and change derivation 3 Results 3.1 Vegetation composition and above-ground biomass 3.2 Upscaling above-ground biomass using GAM 3.3 Change of above-ground biomass between 2000 and 2017 in the four focus areas 4 Discussion 4.1 Recent state of above-ground biomass at the field sites 4.2 Recent state of above-ground biomass upscaled for central Chukotka 4.3 Change in above-ground biomass within the investigated 15–16 years in central Chukotka 5 Conclusions Data availability statement Author contributions Competing interests Acknowledgements References Appendix A. Sampling and above-ground biomass (AGB) calculation protocol for field data 6 Future spatially explicit tree above-ground biomass trajectories revealed for a mountainous treeline ecotone using the individual-based model LAVESI Abstract 1 Introduction 2 Materials and methods 2.1 Study region 2.2 LAVESI model setup, parameterisation, and validation 2.2.4 LAVESI simulation setup for this study 2.2.5 Validation of the model’s performance 3 Results 3.1 Dynamics and spatial distribution changes of tree above-ground-biomass 3.2 Spatial and temporal validation of the contemporary larch AGB 4 Discussion 4.1 Future dynamics of tree AGB at a plot level 4.2 What are the future dynamics of tree AGB at the landscape level? 5 Conclusions Data availability Acknowledgements References Appendix B. Permutation tests for tree presence versus topographical parameters Appendix C. Landsat-based, field, and simulated estimations of larch above-ground biomass (AGB). 7 Synthesis 7.1 What changes in vegetation composition have happened from 2000 to 2017 in central Chukotka? 7.2 How have the above-ground biomass (AGB) distribution and rates changed from 2000 to 2017 in central Chukotka? 7.3 What are the spatial dynamics and rates of tree AGB change in the upcoming centuries in the northern tundra-taiga from 2020 to 3000 CE on the plot level and landscape level? References Acknowledgements

Language: English

Keywords: Hochschulschrift

URL: https://doi.org/10.25932/publishup-54845