Kathleen Stoof-Leichsenring’s research while affiliated with Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung and other places

Mountains with complex terrain and steep environmental gradients are biodiversity hotspots such as the eastern Tibetan Plateau (TP). However, it is generally assumed that mountain terrain plays a secondary role in plant species assembly on a millennial time‐scale compared to climate change. Here, we investigate plant richness and community changes during the last 18,000 years at two sites: Lake Naleng and Lake Ximen on the eastern TP with similar elevation and climatic conditions but contrasting terrain. We applied plant DNA metabarcoding to lake sediments leveraging a new regional reference database for taxa identification. Furthermore, we developed a simplified species dispersal model named SMARC. This was used to simulate species migration along river valleys in response to past climate change at the taxonomic resolution of the sedimentary ancient DNA (sedaDNA) approach. Statistical analyses, including ordination‐based ecological trajectory analysis, yielded a significant match between sedaDNA and simulated results at single taxon and community levels including certain site‐specific differences. Steep terrain downstream of Lake Naleng enhances connectivity to glacial lowland refugia during postglacial warming. In contrast, gentle terrain over long distances implies weak connectivity to the lowland and thus resulted in a strong migration lag at Lake Ximen. Likewise, terrain differences among our sites defined the different connectivity to alpine refugia during late‐Holocene cooling. Our consistent proxy‐ and model‐based results, for the first time, indicate that dispersal related migration lags in complex mountain terrain lead to uneven vegetation trajectories at sites with similar climatic conditions mainly because of differences in connectivity to refugia. Ultimately our results indicate that connectivity to refugia is a first‐order factor for species migration in addition to elevation‐related climatic conditions shaping the postglacial vegetation trajectory in mountainous terrain. This has hitherto largely been ignored when forecasting mountain vegetation responses to climate change and related risk assessment.

Understanding the response of long-term aquatic environmental changes in lakes to ongoing climate change and human activities is key to forecasting future lake conditions. In this study, we infer the Holocene limnological changes in Emu Co, a proglacial lake in Nianbaoyuze on the eastern Tibetan Plateau, from sedimentary ancient DNA (sedaDNA) data, and palynomorph, element, lithological, and grain-size analyses. We developed a transfer function based on Siberia and Tibet/China surface sedimentary DNA and applied it to Emu Co sedaDNA to trace lake conductivity changes. The results show that the conductivity of Emu Co was high during 12.6− 9.7 cal ka BP, often surpassing 1000 μs cm − 1 , driven by elevated summer solar radiation. The freshwater influx from glacial meltwater and precipitation, however, reduced the lake's conductivity as the climate warmed and humidified. This led to a decrease in the abundance of taxa characterised by high conductivity. Freshwater pulses, triggered by climatic fluctuations, likely led to significant variations in conductivity within the overarching downward trend. By 8 cal. ka BP, lake recharge conditions stabilised and conductivity reached a lower level of~70 μs cm − 1. The warm and humid mid-Holocene (8− 5 cal. ka BP) provided suitable habitat conditions for many submerged freshwater taxa. After 5 cal. ka BP, the growth of submerged taxa was restricted, as indicated by a shift from asexual to sexual reproduction in macrophytes, likely in response to suboptimal conditions of a colder and drier climate. Since 1 cal. ka BP, human activities might have increased lake nutrient levels, with an enhanced richness of macrophytes. Our results indicate how millennial-scale hydrological changes in a lake are related to glacial retreat and catchment changes in the alpine region of the Tibetan Plateau, which is today facing climate change much greater than the global average.

Terrigenous organic matter in marine sediments is considered a significant long-term carbon sink, yet our knowledge regarding its source taxa is severely limited. Here, we leverage land-plant ancient DNA from six globally distributed marine sediment cores covering the Last Glacial-Holocene transition as a proxy for the share, accumulation rate, preservation, and composition of terrigenous organic matter. We show that the spatial and temporal plant composition as revealed by sedaDNA records reflects mainly the vegetation dynamics of nearby continents as revealed by comparison with pollen from land archives. However, we also find indications of a global north-to-south translocation of sedaDNA. The plant composition shows that upland vegetation is strongly underrepresented in the record compared to riverine and coastal sources. We also find that plant sedaDNA has a higher accumulation rate in samples from the Late Glacial, which is characterized by high runoff and mineral load. Thus plant DNA in marine sediments allows for new perspectives on the global linkages between the terrestrial and marine carbon cycle which would benefit from a more quantitative understanding of DNA preservation and dispersal. This represents the basis of 1 how climate change and land-use change translate into carbon-sink dynamics and also informs about natural carbon-capture solutions.

Ancient environmental DNA (aeDNA) from lake sediments has yielded remarkable insights for the reconstruction of past ecosystems, including suggestions of late survival of extinct species. However, translocation and lateral inflow of DNA in sediments can potentially distort the stratigraphic signal of the DNA. Using three different approaches on two short lake sediment cores of the Yamal peninsula, West Siberia, with ages spanning only the past hundreds of years, we detect DNA and identified mitochondrial genomes of multiple mammoth and woolly rhinoceros individuals—both species that have been extinct for thousands of years on the mainland. The occurrence of clearly identifiable aeDNA of extinct Pleistocene megafauna (e.g. >400 K reads in one core) throughout these two short subsurface cores, along with specificities of sedimentology and dating, confirm that processes acting on regional scales, such as extensive permafrost thawing, can influence the aeDNA record and should be accounted for in aeDNA paleoecology.

This study is based on multiproxy data gained from a 14C-dated 6.5 m long sediment core and a 210Pb-dated 23 cm short core retrieved from Lake Rauchuagytgyn in Chukotka, Arctic Russia. Our main objectives are to reconstruct the environmental history and ecological development of the lake during the last 29 kyr and to investigate the main drivers behind bioproduction shifts. The methods comprise age-modeling, accumulation rate estimation, and light microscope diatom species analysis of 74 samples, as well as organic carbon, nitrogen, and mercury analysis. Diatoms have appeared in the lake since 21.8 ka cal BP and are dominated by planktonic Lindavia ocellata and L. cyclopuncta. Around the Pleistocene–Holocene boundary, other taxa including planktonic Aulacoseira, benthic fragilarioid (Staurosira), and achnanthoid species increase in their abundance. There is strong correlation between variations of diatom valve accumulation rates (DARs; mean 176.1×109 valves m2 a1), organic carbon accumulation rates (OCARs; mean 4.6 g m-2 a-1), and mercury accumulation rates (HgARs; mean 63.4 µg m-2 a-1). We discuss the environmental forcings behind shifts in diatom species and find moderate responses of key taxa to the cold glacial period, postglacial warming, the Younger Dryas, and the Holocene Thermal Maximum. The short-core data likely suggest recent change of the diatom community at the beginning of the 20th century related to human-induced warming but only little evidence of atmospheric deposition of contaminants. Significant correlation between DAR and OCAR in the Holocene interglacial indicates within-lake bioproduction represents bulk organic carbon deposited in the lake sediment. During both glacial and interglacial episodes HgAR is mainly bound to organic matter in the lake associated with biochemical substrate conditions. There were only ambiguous signs of increased HgAR during the industrialization period. We conclude that if increased short-term emissions are neglected, pristine Arctic lake systems can potentially serve as long-term CO2 and Hg sinks during warm climate episodes driven by insolation-enhanced within-lake primary productivity. Maintaining intact natural lake ecosystems should therefore be of interest to future environmental policy.

Using pollen analysis and metabarcoding of plant sedimentary ancient DNA (sedaDNa), we infer the floristic diversity in the vicinity of Lake Balyktukel, Ulagan Plateau, the Altai Mountains, over the last 7 kyr. The SedaDNA method identified 200% more taxa than found by morphological pollen analysis. In particular, it revealed that the dominant tree for the last 7 kyr was Larix rather than Pinus, which was less frequent in the vicinity of Lake Balyktukel. About 7 ka, larch forest mixed with dwarf birch was widespread on the Ulagan Plateau. The period between 5.3 and 3.4 kyr BP was characterized by the maximal spread of larch forest with an understorey cover of Vaccinium vitis-idaea. Pollen-based annual precipitation reconstruction indicates the most humid phase was between 6.95 and 4.3 ka, and generally coincides with maximal phytodiversity. The most bioproductive period of the lake was from 7 to 6 ka. After that, the trophicity of the lake decreased until 4.5 ka. The appearance of Hippuris vulgaris and increase in Ranunculus subgen. Batrachium at about 5.3–5 ka may indicate the extension of shallow-water ecotopes. Between 3.7 and 3.5 ka, the cyanobacterium Anabaena – an indicator of increased organic matter and algal blooms – was widespread. A planktic thermophilic cladoceran Bosmina longirostris appeared after 1.8 ka and colonized the lake, suggesting an increase in lake trophicity. The last 100 years have been characterized by dramatic changes in the cladoceran community reflecting significant warming of climate.

Using pollen analysis and metabarcoding of plant sedimentary ancient DNA, we establish the floristic diversity in the vicinity of Lake Balyktukel, Ulagan Plateau, the Altai Mountains, over the last 7 kyr. Analysis of plant DNA from lake bottom sediments is used for the first time to characterize the past vegetation of the Altai Mountains. The sedimentary ancient DNA (sedaDNA) method identified 200% more taxa than found by morphological pollen analysis. In particular, it revealed that the dominant tree for the last 7 kyr was Larix rather than Pinus, which was less frequent in the vicinity of Lake Balyktukel. The DNA analysis also revealed 19 macrophyte taxa, while the pollen method revealed only two taxa. Our paleorecord also includes non-pollen palynomorphs and cladoceran analyses. About 7 kyr BP, larch forest mixed with dwarf birch was widespread on the Ulagan Plateau. The period between 5.3 and 3.4 kyr BP is characterized by the maximal spread of larch forest with a cover of Vaccinium vitis-idaea in the vicinity of lake. Pollen-based annual precipitation reconstruction indicates the most humid phase was between 6.95 and 4.3 kyr BP, that generally coincides with maximal phytodiversity. The most bioproductive period of the lake was from 7 to 6 kyr BP. After that the trophicity of the lake decreased until 4.5 kyr BP. The appearance of Hippuris vulgaris and increase in Ranunculus subgen. Batrachium at about 5.3–5 kyr BP may indicate the extension of shallow-water ecotopes. Between 3.7 and 3.5 kyr BP, the cyanobacterium Anabaena and Ranunculus subgen. Batrachium – indicators of increased organic matter and algal blooms – were widespread. A planktic thermophilic cladoceran Bosmina longirostris appears after 1.8 kyr BP and colonized the lake, suggesting an increase in lake trophicity. In the last 500 years, there have been blooms of the cyanobacteria Aphanizomenon and Microcystis. The last 100 years have been characterized by dramatic changes in the cladoceran community reflecting significant warming of climate. Keywords: alpha & beta diversity, Altai, pollen, sedaDNA, Cladocera, lake Suggested Citation: Rudaya, Natalia and Karachurina, Svetlana and Frolova, Larisa and Kuzmina, Olga and Cao, Xianyong and Chepinoga, Victor and Stoof-Leichsenring, Kathleen and Biskaborn, Boris and Herzschuh, Ulrike and Nigmatullin, Niyaz and Vnukovskaya, Julia and Grekov, Ivan and Pestryakova, Liudmila, Terrestrial Vegetation and Lake Aquatic Community Diversity Under Climate Change During the Mid–Late Holocene in the Altai Mountains. Available at SSRN: https://ssrn.com/abstract=4379661 or http://dx.doi.org/10.2139/ssrn.4379661

This study is based on multiproxy data gained from a 14C-dated 6.5 m long sediment core and a 210Pb-dated 23 cm short core retrieved from Lake Rauchuagytgyn in Chukotka, Arctic Russia. The main objectives are to reconstruct the environmental history and ecological development of the lake during the last 29k years and to investigate the main drivers behind bioproduction shifts. The methods comprise age-modeling and accumulation rate estimation, light-microscope diatom species analysis (74 samples), organic carbon, nitrogen, and mercury analysis. Diatoms have appeared in the lake since 21.8 cal ka BP and are dominated by planktonic Lindavia ocellata and L. cyclopuncta. Around the Pleistocene-Holocene boundary, other taxa including planktonic Aulacoseira and benthic fragilarioid (Staurosira) and achnanthoid species increase in their abundance. There is strong correlation between variations of diatom valve accumulation rates (DAR, mean 176.1 109 valves m2 a1), organic carbon accumulation rates (OCAR, mean 4.6 g m-2 a-1), and mercury accumulation rates (HgAR, mean 63.4 µg m-2 a-1). We discuss the environmental forcings behind shifts in diatom species and found responses of key-taxa to the cold glacial period, postglacial warming, Younger Dryas, and the Holocene Thermal Maximum. The short core data likely suggest recent change of the diatom community at 1907 CE related to human-induced environmental change. Significant correlation between DAR and OCAR in the Holocene interglacial indicates within-lake bioproduction as the main source of carbon deposited in the lake sediment. During both glacial and interglacial episodes HgAR is mainly bound to organic matter in the lake associated to biochemical substrate conditions. There were only ambiguous signs of increased HgAR during the industrialization period. We conclude that pristine Arctic lake systems can serve as CO2 and Hg sinks during warming climate driven by insolation-enhanced within-lake primary productivity. Maintaining intact natural lake ecosystems should therefore be of interest to future environmental policy.

The Holocene environmental history of NE Germany is strongly influenced by postglacial climate development, paraglacial processes, and in more recent times by human activities. The objective of this study is to infer millennial-scale natural and man-made palaeoenvironmental variability in the Groß-Glienicker lake system. The study was initiated by the Alfred Wegener Institute with close cooperation to the Naturkundemuseum Potsdam and the University of Potsdam. Here, we show first analytical results.