Research
Our research projects cover a broad range of topics, from carbon and environmental processes in Arctic landscapes and biological processes in the Atacama Desert to the reconstruction of past climate events using marine archives. With our expertise in 14C dating, we also contribute to archaeological research questions.
MOMENTplus | Microbial Carbon Turnover with 14CO2 | Evolution at the dry limit | ENSO Modoki | Our Way to Europe | Kopf | The Forgotten Part of Carbon Cycling | CARBOPERM | ULDETIS | Polar and Mountain Regions in a Changing Climate
MOMENT/MOMENTplus
BMFTR FKZ: 03F1002C | 2023-2029
Permafrost regions are an important component of the global climate system, as their soils store large amounts of organic matter that has so far largely remained preserved in permanently frozen ground. Permafrost thaw alters key biological and chemical processes in soils, as well as vegetation. Increased plant productivity may stimulate additional CO2 emissions from thawing soils, while changes in soil moisture can shift the balance between the uptake and release of CO2, CH4 and N2O. However, how these coupled greenhouse gas fluxes will develop over the coming decades remains highly uncertain, making it difficult to predict future climate conditions.
Building on the previous MOMENT project, MOMENTplus investigates how vegetation, microorganisms and soil properties influence fluxes of the greenhouse gases CO2, CH4 and N2O. The project combines field measurements on Disko Island in West Greenland with laboratory studies and modelling approaches. It is organised into three closely connected subprojects.
Subproject 1, in which the our research group is involved, examines how vegetation, microorganisms and soil properties control the biogeochemical processes that lead to the release or uptake of CO2, CH4 and N2O. The subproject focuses on three main questions, which are addressed by the Cologne researchers together with partners from the Universities of Hamburg and Hannover and GFZ Potsdam:
1) How do long-term changes in temperature and soil moisture affect microbial communities, their activity and the quality of soil organic matter?
2) How do vegetation and root exudates influence microbial processes and the greenhouse gas balance?
3) How does the stabilisation of organic carbon on mineral particles change under changing climate conditions?
Microbial carbon turnover and greenhouse gas formation from permafrost soils revealed by 14CO2 analysis
AWI KOP 171; RiS ID 10715 | 2017-2026
The Arctic is warming about four times faster than the global average. As temperatures rise, permafrost soils are thawing, exposing large stores of previously frozen organic carbon to microbial decomposition. This can lead to higher releases of CO2 and CH4, which may further amplify climate change. However, the magnitude of this feedback over the coming decades remains uncertain.
The temperature sensitivity of microbial decomposition is a key factor controlling how much organic carbon may be released from permafrost soils. So far, it has mainly been studied in laboratory incubation experiments. Another important aspect is the presence of different carbon pools, as organic matter often becomes older, more processed and potentially less available with increasing soil depth. However, laboratory studies can only partly capture the high spatial and biogeochemical complexity of Arctic landscapes. Field studies are therefore urgently needed, but still rare.
Against this background, the project investigates the degradability of organic matter in high-Arctic permafrost soils near the research station in Ny-Ålesund, Svalbard, operated by AWI and the French Polar Institute IPEV. Compared with Siberia or Alaska, high-Arctic sites have so far received less attention. At the same time, substantial warming has already been documented on Svalbard, while the effects of rising soil temperatures remain insufficiently understood.
The project aims to determine the degradability of organic matter at different soil depths and to examine how sensitive these processes are to changes in temperature and moisture conditions. To this end, CO2 samples were collected using soil respiration chambers and depth-specific gas samplers. Soil samples were also taken for 14C analyses of microbial membrane lipids, incubation experiments and molecular biological analyses. The results are expected to provide insights into the source and age of the carbon used by microorganisms, as well as into the effects of increased temperature and moisture on carbon turnover in permafrost soils.
Earth – Evolution at the dry limit - Reconstructing changes of water sources and availability by combined lipid biomarker and online stable isotope and radiocarbon analysis
DFG CRC 1211 | 2016-2024
The hyper-arid soils of the Atacama Desert provide a model region for studying life and landscape development under extremely dry conditions. Water availability is the key factor controlling biological activity, plant occurrence and surface processes. These processes are strongly influenced by short moisture events, mainly caused by fog and rare rainfall, which are linked, among other factors, to ENSO and the Pacific Decadal Oscillation (PDO). This creates pronounced gradients along latitude and elevation. Although liquid water is only rarely available in the Atacama Desert, short moisture events can leave long-lasting traces in landscapes and soils. However, it is still poorly understood how such episodes shape biological colonisation, vegetation development and slow surface processes.
During the first project phase, our research group investigated past water availability and its implications for life in these extremely carbon-poor soils. To this end, lipid biomarkers from plants and microorganisms were analysed and combined with stable carbon isotope and radiocarbon analyses. The results showed that plant and microbial life increase strongly in abundance and diversity from the hyper-arid core of the Atacama Desert towards more humid sites. Living and fossil Tillandsia plants proved to be suitable archives for reconstructing past fog moisture, using nitrogen isotopes in plant tissue and hydrogen isotopes in leaf waxes. The results indicate a pronounced dry phase in the late medieval period, associated with prolonged droughts and a major ENSO anomaly.
In the second project phase, we investigated how different water sources and environmental conditions are reflected in the stable isotope signatures (δ2H, δ13C, δ15N, δ34S) of living Tillandsia plants. In addition, traces of plant and microbial life along moisture and depth gradients were identified and dated using lipid biomarker and radiocarbon analyses. In the field of radiocarbon dating, new methods were developed that make it possible to date ultra-small samples containing as little as 1–20 µg C.
Publications
Jaeschke, A. et al. (2024). Evaluating the isotopic composition of leaf organic compounds in fog-dependent Tillandsia landbeckii across the coastal Atacama Desert: Implications for hydroclimate reconstructions at the dry limit. Global and Planetary Change, 235. https://doi.org/10.1016/j.gloplacha.2024.104393
Jaeschke, A. et al. (2024). Microbial hotspots in a relict fog-dependent Tillandsia landbeckii dune from the coastal Atacama Desert. Global and Planetary Change, 234. https://doi.org/10.1016/j.gloplacha.2024.104383
Rosinger, C. et al. (2023). Rewetting the hyper-arid Atacama Desert soil reactivates a carbon-starved microbial decomposer community and also triggers archaeal metabolism. Science of The Total Environment, 892. https://doi.org/10.1016/j.scitotenv.2023.164785
Wennrich, V. et al. (2024). Late Pleistocene to modern precipitation changes at the Paranal clay pan, central Atacama Desert. Global and Planetary Change, 233. https://doi.org/10.1016/j.gloplacha.2023.104349
Contreras, S. et al. (2022). Leaf wax composition and distribution of Tillandsia landbeckii reflects moisture gradient across the hyperarid Atacama Desert. Plant Systematics and Evolution, 308. https://doi.org/10.1007/s00606-021-01800-0
Kusch, S. et al. (2020). Tracing life at the dry limit using phospholipid fatty acids – does sampling matter? Soil Biology and Biochemistry, 141. https://doi.org/10.1016/j.soilbio.2019.107661
Jaeschke, A. et al. (2019). Variation in δ15N of fog-dependent Tillandsia ecosystems reflect water availability across climate gradients in the hyperarid Atacama Desert. Global and Planetary Change, 183. https://doi.org/10.1016/j.gloplacha.2019.103029
Rethemeyer, J. et al. (2019). Current sample preparation and analytical capabilities of the radiocarbon laboratory at CologneAMS. Radiocarbon, 61. https://doi.org/10.1017/RDC.2019.16
Stolz, A. et al. (2019). Improvements in the measurement of small 14CO2 samples at CologneAMS. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 439. https://doi.org/10.1016/j.nimb.2018.12.008
Stolz, A. et al. (2017). Radiocarbon measurements of small gaseous samples at CologneAMS. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 406. https://doi.org/10.1016/j.nimb.2017.03.031
"ENSO-Modoki" on the rise under global warming conditions? A view from the past
DFG SPP 527 (IODP/ODP) | 2021-2024
PIs: Dr. Andrea Jaeschke und Prof. Dr. Oliver Friedrich
Recent observations show that, in addition to the “classic” El Niño–Southern Oscillation (ENSO), another expression of this climate phenomenon occurs: El Niño Modoki. In classic El Niño and La Niña events, the strongest sea-surface temperature anomalies and associated changes in thermocline depth occur mainly in the eastern/western tropical Pacific. In El Niño Modoki, by contrast, warming and thermocline deepening are concentrated in the central tropical Pacific, while the eastern and western parts of the ocean tend to cool. During La Niña Modoki, this pattern is reversed. This altered distribution of ocean temperatures changes atmospheric circulation, shifting precipitation patterns, particularly in tropical South America and the western Pacific region. Its effects may also extend far beyond the tropics, including an increased frequency of hurricanes in the Gulf of Mexico and warming in subpolar regions of both hemispheres, which could further accelerate ice-sheet melting.
In this project, geological climate archives were used to improve our understanding of how ENSO Modoki may develop in the future. ENSO-Modoki-like conditions were reconstructed for time periods with different climatic boundary conditions, particularly with regard to atmospheric pCO2, global ice volume and insolation. These factors are known to influence the expression of classic ENSO events and may therefore also play an important role in ENSO Modoki variability.
Analytically, high-resolution reconstructions of sea-surface temperatures (SST) and thermocline temperatures (subT) were generated along a west–east transect across the tropical Pacific. In addition to the interval from the Middle Pleistocene to the Holocene, covering the last 300,000 years and characterised by comparatively low pCO2 concentrations and high Northern Hemisphere ice volume, the project also investigated the early Pliocene, between 4.85 and 5.15 million years ago, when pCO2 levels were similar to today and Northern Hemisphere ice sheets were largely absent. Water temperatures were reconstructed using Mg/Ca analyses of planktonic foraminifera and alkenone analyses. The SST data are used to infer ENSO Modoki variability, while the subT data provide insights into associated changes in thermocline depth. By comparing these reconstructions with reference datasets and applying linear models, the project aims to identify key controls on ENSO Modoki variability and thereby contribute to more reliable predictions of future developments.
Our Way to Europe
DFG-Sonderforschungsbereich 806 | 2013-2021
The DFG-Sonderforschungsbereich 806 “Our Way to Europe” investigated the dispersal of anatomically modern humans from Africa to Europe. Depending on the region, the time frame studied ranges from the first appearance of anatomically modern humans in East Africa around 190,000 years ago to the settlement of Central and Southeastern Europe during the Late Pleistocene.
A central question was which factors promoted or limited human mobility. In addition to climate and environmental conditions, cultural developments, population densities and human decision-making also played important roles. The interaction of these factors varied across regions and time periods, shaping whether populations moved into new habitats, retreated from them or settled there permanently.
To address these questions, the project combined archaeological and geoscientific methods to reconstruct climate, environmental conditions, cultures and settlement dynamics along major migration routes. Sediment archives from Chew Bahir in southern Ethiopia, for example, show that a humid but highly variable climate at the end of Marine Isotope Stage 5 (MIS 5) was followed by drier and more stable conditions during MIS 4 and the early MIS 3. This development coincides with genetic evidence for a successful dispersal of anatomically modern humans from East Africa and suggests a possible link between climate, environmental stability and migration.
Through comparative case studies at local, regional and continental scales, the project helped to improve our understanding of human migration as a complex interplay of climate, environment, cultural developments and human decision-making.
Publications
Sylvestre, F. et al. (2026). Decadal-scale droughts disrupted the African Humid Period in the Sahara. Nature, 652. https://doi.org/10.1038/s41586-026-10336-7
Jaeschke, A. et al. (2020). Holocene hydroclimate variability and vegetation response in the Ethiopian Highlands (Lake Dendi). Frontiers in Earth Science, 8. doi.org/10.3389/feart.2020.585770
Thienemann, M. et al. (2017). Organic geochemical and palynological evidence for Holocene natural and anthropogenic environmental change at Lake Dojran (Macedonia/Greece). The Holocene, 27. doi.org/10.1177/0959683616683261
Wagner, B. et al. (2016). Late Glacial and Holocene environmental history of the Ethiopian Highlands inferred from a 12 m long sediment record from Dendi crater lakes. Quaternary International, 404. https://doi.org/10.1016/j.quaint.2015.08.103
Foerster, V. et al. (2012). Climatic change recorded in the sediments of the Chew Bahir basin, southern Ethiopia, during the last 45,000 years. Quaternary International, 274. doi.org/10.1016/j.quaint.2012.06.028
Kopf – Kohlenstoff im Permafrost
BMBF 03F0764E | 2017-2021
Permafrost regions are highly sensitive to climate change and store large amounts of organic carbon. As permafrost thaws, this organic matter can be decomposed by microorganisms and released as greenhouse gases. At the same time, rising temperatures and changing site conditions may promote plant growth and increase carbon uptake. Whether permafrost landscapes will act as net sources or sinks of greenhouse gases in the future therefore remains a key uncertainty in climate projections.
The collaborative KoPf project investigated how greenhouse gas fluxes change in thawing permafrost and which carbon sources they originate from. Analyses of 14CO2 and 14CH4 make it possible to determine whether the released gases derive mainly from young organic material, such as recent vegetation, or from older, previously frozen carbon pools.
Publications
Melchert, J. O. et al. (2022). Sources of CO2 produced in freshly thawed Pleistocene-age Yedoma permafrost. Frontiers in Earth Science, 9. https://doi.org/10.3389/feart.2021.737237
Wotte, A. et al. (2017). 14CO2 analysis of soil gas: Evaluation of sample size limits and sampling devices. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 413. https://doi.org/10.1016/j.nimb.2017.10.009
Wotte, A. et al. (2017). 14CO2 processing using an improved and robust molecular sieve cartridge. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 400. https://doi.org/10.1016/j.nimb.2017.04.019
Höfle, S. T. et al. (2015). Characterisation of bacterial populations in Arctic permafrost soils using bacteriohopanepolyols. Organic Geochemistry, 88. https://doi.org/10.1016/j.orggeochem.2015.08.002
Höfle, S. et al. (2013). Organic matter composition and stabilization in a polygonal tundra soil of the Lena Delta. Biogeosciences, 10. doi.org/10.5194/bg-10-3145-2013
The Forgotten Part of Carbon Cycling: Organic Matter Storage and Turnover in Subsoils (SUBSOM)
DFG Research Unit 1806 | 2013-2022
Soils store large amounts of organic carbon, a substantial fraction of which is found in the subsoil between 30 cm and 2 m depth. This carbon is often several hundred to several thousand years old and is therefore considered relatively stable against microbial decomposition. At the same time, fresh organic inputs continuously enter the subsoil, for example through roots, root exudates and dissolved organic compounds. These inputs can stimulate microbial decomposition processes and potentially mobilise older carbon pools.
Why organic matter can persist in the subsoil over long periods is still not fully understood. Possible explanations include stronger binding to minerals, a chemical composition that is more resistant to decomposition, low microbial activity, or unfavourable environmental conditions such as low temperatures and limited oxygen availability. Spatially restricted “hot spots” of biological activity, for example around roots or soil fauna, may also play an important role.
The project investigates the storage and turnover of organic matter in forest soils using coordinated field and laboratory experiments. Several subprojects examine soil physical, soil chemical and biological processes together, with the aim of developing a conceptual model that improves our understanding of organic matter storage and turnover in the subsoil.
Publications
Kalks, F. et al. (2021). Geogenic organic carbon in terrestrial sediments and its contribution to total soil carbon. SOIL, 7. doi.org/10.5194/soil-7-347-2021
Ahrens, B. et al. (2020). Combination of energy limitation and sorption capacity explains 14C depth gradients. Soil Biology and Biochemistry, 148. doi.org/10.1016/j.soilbio.2020.107912
Wordell-Dietrich, P. et al. (2019). Vertical partitioning of CO2 production in a Dystric Cambisol. Biogeosciences Discussions. doi.org/10.5194/bg-2019-143
Angst, G. et al. (2018). Soil organic carbon stocks in topsoil and subsoil controlled by parent material, carbon input in the rhizosphere, and microbial-derived compounds. Soil Biology and Biochemistry, 122. https://doi.org/10.1016/j.soilbio.2018.03.026
Angst, G. et al. (2016). Tracing the sources and spatial distribution of organic carbon in subsoils using a multi-biomarker approach. Scientific Reports, 6. doi.org/10.1038/srep29478
CARBOPERM: Carbon in Permafrost – Formation, Transformation and Release
BMBF: 03G0836E | 2013-2016
In Arctic permafrost soils, large amounts of organic matter have accumulated over geological timescales. So far, much of this carbon has remained preserved in permanently frozen ground. With increasing warming, however, it may become available again for microbial decomposition. As a result, permafrost landscapes could become a larger source of greenhouse gas emissions in the future and trigger an important feedback in the global climate system.
The CarboPerm project investigates the formation, transformation, degradability and release of organic carbon in northern Siberian permafrost. Its aim is to understand how climate- and environment-driven changes affect carbon cycling in Arctic ecosystems, and how thawing permafrost soils may contribute to future carbon and trace gas budgets.
To address this, the project combines studies of present-day carbon cycling with reconstructions of past environmental conditions and soil formation processes. Field measurements and permafrost cores from the Lena Delta, the Kolyma Lowland and the New Siberian Islands provide insights into the production, decomposition and preservation of organic matter over approximately the last 200,000 years. A particular focus is placed on the Eemian interglacial around 125,000 years ago, whose environmental conditions are considered a possible analogue for future developments in the Arctic.
By combining field measurements, soil chemical and organic geochemical analyses, and modelling approaches, CarboPerm helps to improve our understanding of carbon dynamics in permafrost environments. The results are intended to support more reliable assessments of future changes and their significance for the global carbon cycle.
Publications
Höfle, S. T. et al. (2015). Characterisation of bacterial populations in Arctic permafrost soils using bacteriohopanepolyols. Organic Geochemistry, 88. https://doi.org/10.1016/j.orggeochem.2015.08.002
Höfle, S. et al. (2013). Organic matter composition and stabilization in a polygonal tundra soil of the Lena Delta. Biogeosciences, 10. doi.org/10.5194/bg-10-3145-2013
ULDETIS: Ultrasensitive Detection of Isotopes
University of Cologne Excellence Initiative, DFG | 2014-2017
ULDETIS brings together geoscientists and nuclear physicists with the aim of combining the complementary expertise of these usually separate fields to address new scientific questions.
The project focuses on the development of new techniques for ultra-trace isotope analysis and their application in key projects in both fundamental and applied research. Methodologically, this will be achieved by advancing and combining accelerator mass spectrometry, ICP mass spectrometry and high-resolution radiometric spectrometry. These developments will be supported by new analytical and preparative approaches as well as innovative digital data acquisition.
In line with the broad range of methods to be developed, the research objectives are diverse and address fundamental questions in geo- and cosmochemistry, nuclear physics, environmental science and archaeology. These different fields are connected by the unique shared research infrastructure and expertise available at the University of Cologne.
Impacts of Climate Change on Polar and Mountain Regions – From Assessment to Action
IAEA Interregional Project 5153 | 2013-2014
Polar and mountain regions are among the areas most strongly affected by climate change. Despite their geographical diversity, they share key elements of the cryosphere: frozen ground, snow, glaciers and sensitive land–water ecosystems. However, rising temperatures are affecting these systems at a particularly rapid pace. Glaciers are retreating, ice sheets are losing mass, and meltwater contributes to sea-level rise.
These changes affect not only natural ecosystems, but also the livelihoods of many people. In mountain regions, glaciers and snowpacks are important sources of water for drinking water supply, agriculture, energy production and tourism. Their decline can therefore have far-reaching consequences for water availability, food security and local economies.
The project aims to investigate the impacts of climate change on the cryosphere and on the quality of land–water ecosystems in polar and mountain regions. To this end, international study sites on several continents are considered, including regions in Canada, South America, Greenland, Europe, Central Asia, China and East Africa. This broad regional comparison is intended to help assess changes across different regions and provide a basis for concrete adaptation and protection measures.