Jahrestagung der Arbeitsgemeinschaft
Stabile Isotope e.V.
26.–29. September 2021 | TU Darmstadt
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Block 3: Paläoklima, Sedimentologie, Boden
12:15 - 12:30
Carbon isotope excursions in a Paleocene to early Eocene lignite bearing succession at the southern edge of the proto-North Sea (Schöningen, Germany)
1Senckenberg Forschungsinstitut und Naturmuseum Frankfurt, Deutschland; 2Technische Universität Darmstadt, Institut Für Angewandte Geowissenschaften, Deutschland; 3Senckenberg Biodiversity and Climate Research Centre (SBiK-F), Frankfurt am Main, Deutschland; 4Goethe Universität Frankfurt, Institut für Geowissenschaften, Frankfurt am Main, Deutschland; 5Stanford University, Department of Earth System Science, Department of Geological Sciences, USA
Long-term effects of present global warming on ecosystems on timescales beyond those covered by the human record of the last few centuries are still a matter of speculation. Since long-term greenhouse periods and short-term warming events occurred repeatedly in the history of the earth, they may be the subject for detailed studies on the reaction of ecosystems to global warming on different timescales. The Early Eocene Climatic Optimum (EECO) and its superposed short-term warming events such as the Paleocene-Eocene Thermal Maximum (PETM) represent the last greenhouse period before today which is especially suited for comparisons to the presently developing greenhouse since fauna and flora had reached an evolutionary state already similar to today.
The sedimentary succession of the former Helmstedt Lignite Mining District in northern Germany covers the entire Paleogene greenhouse phase and its gentle demise between the upper Paleocene and the early middle Eocene almost continuously in an estuarine situation at the southern edge of the proto-North Sea. Due to the interaction between changes in sea level, salt withdrawal in the subsurface and climate-related changes in runoff from the hinterland the area was subject to frequent changes between marginal marine and terrestrial conditions, repeatedly leading to peat formation. This offers the rare opportunity to study Paleocene–Eocene near-coastal ecosystems and to trace the effects of long- and short-term climate perturbations on the diversity and composition of the plant communities across 10 million years during the Paleogene greenhouse.
Here, we present high-resolution carbon isotope data of bulk organic matter (δ13CTOC) from a 98 m thick sequence from the lower part of the succession (Schöningen Formation). We observed six negative carbon isotope excursions (CIEs) reflecting massive short-term carbon cycle perturbations, which can be related to the PETM, probably to the Eocene Thermal Maximum 2 and to the EECO. Palynological analysis proved that shifts in δ13CTOC valuesare correlated with changes in the peat forming wetland vegetation. Furthermore, the PETM-related CIE shows a distinct rebound to higher δ13CTOC valuesshortly after the onsetof the CIE, which is here recognized as a common feature of terrestrial and marginal marine PETM-records worldwide and may be related to changes in the vegetation.
12:30 - 12:45
18O analyses of bulk lipids as novel paleoclimate tool in loess research – a pilot study
1Physische Geographie mit SP Paläoumweltforschung, Technische Universität Dresden, Deutschland; 2Institut für Grundwasserwirtschaft, Technische Universität Dresden; 3Bodenbiogeochemie, Martin-Luther-Universität Halle-Wittenberg; 4Universität Novi Sad, Serbien
The analysis of the stable oxygen isotopes 18O and 16O has revolutionized paleoclimate research since the middle of the last century. Particularly, 18O of ice cores from Greenland and Antarctica is used as paleotemperature proxy and 18O of deep-sea sediments is used as proxy for global ice volume. Important terrestrial archives to which 18O as paleoclimate proxy is successfully applied are for instance speleothems, lake sediments or tree rings. By contrast, 18O applications to loess-paleosol sequences (LPSs) are scarce, despite for instance a compound-specific 18O analytical tool for sugar biomarkers was developed and presented already years ago (Zech et al., 2014. Geochimica et Cosmochimica Acta 126, 614-623).
Here we present a first continuous 18O record (n=50) for the LPS Crvenka in Serbia, SE Europe, spanning the last glacial-interglacial cycle. From a methodological point of view, we took advantage of a recently proposed paleoclimate/-hydrological tool/proxy based on bulk 18O analyses of plant-derived lipids. The 18Olipid values range between -10.2 ‰ and +23.0 ‰ and are systematically more positive in the interglacial and interstadial (paleo-)soils compared to the loess layers. In our conference contribution, we compare our 18Olipid record from the LPS Crvenka with the marine oxygen-isotope stages as well as with the Greenland 18Oice core records revealing the famous Dansgaard-Oeschger events (stadials and interstadials). Concerning the interpretation of our LPS 18Olipid record, we will discuss several influencing factors, such as temperature-control on 18O, relative humidity-dependent evaporative leaf water enrichment, post-sedimentary effects and pool-effects.
Zech, M., Mayr, C., Tuthorn, M., Leiber-Sauheitl, K. and Glaser, B., 2014. Oxygen isotope ratios (18O/16O) of hemicellulose-derived sugar biomarkers in plants, soils and sediments as paleoclimate proxy I: Insight from a climate chamber experiment. Geochimica et Cosmochimica Acta 126, 614-623.
12:45 - 13:00
Plant and fungal contributions to soil organic matter fractions assessed by 13C and 15N isotope natural abundances
1Department of Agroecology, Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, Germany; 2Department of Biology, Indiana University Bloomington, IN, USA; 3Department Soil Ecology, Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, Germany; 4Chair of Soil Science, School of Life Sciences, Technical University of Munich, Freising, Germany; 5Soil Science of Temperate Ecosystems, Büsgen-Institute, Georg-August University Göttingen, Germany; 6Department of Geosciences and Natural Resource Management, University of Copenhagen, Denmark
Soil organic matter (SOM) consists of a multitude of organic compounds forming a continuum of decay, from fresh detritus to highly processed organic matter stabilized on mineral surfaces. To date, we still lack crucial knowledge about the contribution of plant and microbial residues to SOM fractions and we know almost nothing about the contribution of distinct fungal functional guilds such as arbuscular (AM), ectomycorrhizal (ECM), and saprotrophic (SAP) fungi to SOM fractions.
Aiming to address this knowledge gap, we investigated sources of particulate and mineral associated organic matter (POM and MAOM) around trees with distinct mycorrhizal types, Liriodendron tulipifera (AM association) and Quercus alba (ECM association), in a temperate deciduous forest in Indiana, USA. In ECM-associated systems, we expect ECM fungi to be the main contributors to SOM, while in AM-associated systems, SAP fungi will mainly contribute to SOM due to the facilitation by AM fungi.
To assess various sources of SOM fractions, we combined stable isotope natural abundance analyses with measurements of microbial residues using amino sugars. Specifically, the 13C and 15N signatures of large-, medium- and small-sized POM and MAOM fractions were analyzed and compared to that of leaves and roots of the two dominant tree species as well as to tissues of mycorrhizal and saprotrophic fungi. The sources of C and N to SOM fractions were calculated by a Bayesian inference isotope mixing model.
Our data revealed a shift from relatively 13C- and 15N-depleted POM, which is close to the isotopic composition of plant material, to 13C- and 15N-enriched MAOM. Mixing model calculations suggests a higher contribution of plant (~ 76 %) than fungal inputs to POM for both tree systems, with a higher contribution of saprotrophic (SAP) fungi than ectomycorrhizal (ECM) fungi (~ 17 % and ~ 5 %, respectively). In contrast, the model for MAOM fractions suggests a dominance of fungal residues relative to plant C, with SAP fungi contributing more than ECM fungi in most SOM fractions, even under the ECM tree. As expected, AM fungal residues contribute only little to SOM fractions. Microbial necromass - measured as amino sugars - confirmed the important role of ECM and SAP fungal residues for SOC storage in both, POM and MAOM fractions.
Overall, our results highlight the importance of distinct fungal functional guilds for soil C storage and call for future studies on the role of mycorrhizal types for soil C storage in a changing world.
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