Vegetation and climate history during the last glacial-interglacial cycle at Lake Van, eastern Anatolia

This study investigated the first continuous high-resolution pollen record from Lake Van, eastern Anatolia that encompasses the last glacial-interglacial cycle (~130 ka BP). The reconstructed paleovegetation documents a series of climatic and environmental events and yields information about vegetation succession in the Near East. Palynological analyses were extracted from the lacustrine sedimentary record obtained during the drilling campaign at the ’Ahlat Ridge’ in 2010. Being located in a semi-arid region, the regional environment at Lake Van is characterized by a continental climate. Therefore, the reconstruction of vegetation from the detailed palynological investigations reflects an alternation of an oak-steppe forest and a dwarf-shrub steppe/desert steppe vegetation. In general, cold and arid environmental conditions can be characterized by the dominance of Ephedra, Artemisia, chenopods and grasses, whereas increased temperature and moisture availability suggest more favorable environmental conditions for the expansion of a warm-temperate steppe-forest (e.g. Quercus). These climate cycles were strongly associated with changes in the oceanic and atmospheric circulation of the North Atlantic Ocean. In eastern Anatolia the climate evolution within the last interglacial (~130- 111 ka BP) can be described as a relatively stable warm period with one pronounced short-term climate setback (C 25 cooling event; ~115 ka) towards the end of the last interglacial period. Timing and length of the interglacial conditions are comparable with southern European pollen records. Furthermore, the palynological sequence at Lake Van documents a vegetation succession with several climatic phases: (i) the Pistacia phase and the Quercus-Ulmus phase during the initial warming (130.9- 127.2 ka BP) indicating summer dryness and mild winter conditions; (ii) the Carpinus phase (127.2-124.1 ka BP) suggesting slightly colder temperatures with higher moisture availability; and (iii) the increasing Pinus phase at ~124 ka, which marks the onset of colder/drier climate conditions, that extended into the interval of global ice growth. In general, the diversity of woody taxa within the forest composition is significantly lower in the Near East compared to the eastern Mediterranean interglacial sequences. The major difference between the last interglacial at Lake Van in comparison to the Holocene is the relatively high amount of Pinus during the Eemian, indicating a considerably higher continentality index during the climate optimum as compared to the recent interglacial. Throughout the last glacial (~74.7-14.7 ka BP), the detailed nature of the Lake Van pollen record allows the identification of several millennial-scale vegetational and environmental changes, which can be correlated with the stadial-interstadial patterns of the Dansgaard-Oeschger (D-O) events observed in the North Greenland ice core record (NGRIP). Relatively warm and humid climate conditions during the D-O interstadials enabled the emergence of an open steppe forest at Lake Van. This study is a first attempt to establish a continuous charcoal record over the last glacial-interglacial cycles in the Near East, and to document an initial immediate response to millennial-scale climate and environmental variability. Fire regimes, confirmed to more warm/dry conditions, were considerably less frequent during glacial or cooling periods. Within the last glacial, the Marine Isotope Stage (MIS) 3 is characterized by a slightly higher fire activity than MIS 2 and 4. New insights of paleovegetation and climate variability at Lake Van demonstrate the great potential of paleoenvironmental reconstruction. It allows the comparison with other long continental pollen records from the Near East and the eastern Mediterranean region, to contribute to the discussion of climate change and to improve the understanding of vegetational changes in the eastern Anatolia region

Assessing changes in global fire regimes

PAGES, Past Global Changes, is funded by the Swiss Academy of Sciences and the Chinese Academy of Sciences and supported in kind by the University of Bern, Switzerland. Financial support was provided by the U.S. National Science Foundation award numbers 1916565, EAR-2011439, and EAR-2012123. Additional support was provided by the Utah Department of Natural Resources Watershed Restoration Initiative. SSS was supported by Brigham Young University Graduate Studies. MS was supported by National Science Centre, Poland (grant no. 2018/31/B/ST10/02498 and 2021/41/B/ST10/00060). JCA was supported by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 101026211. PF contributed within the framework of the FCT-funded project no. UIDB/04033/2020. SGAF acknowledges support from Trond Mohn Stiftelse (TMS) and University of Bergen for the startup grant ‘TMS2022STG03’. JMP participation in this research was supported by the Forest Research Centre, a research unit funded by Fundação para a Ciência e a Tecnologia I.P. (FCT), Portugal (UIDB/00239/2020). A.-LD acknowledge PAGES, PICS CNRS 06484 project, CNRS-INSU, Région Nouvelle-Aquitaine, University of Bordeaux DRI and INQUA for workshop support.Background The global human footprint has fundamentally altered wildfire regimes, creating serious consequences for human health, biodiversity, and climate. However, it remains difficult to project how long-term interactions among land use, management, and climate change will affect fire behavior, representing a key knowledge gap for sustainable management. We used expert assessment to combine opinions about past and future fire regimes from 99 wildfire researchers. We asked for quantitative and qualitative assessments of the frequency, type, and implications of fire regime change from the beginning of the Holocene through the year 2300. Results Respondents indicated some direct human influence on wildfire since at least ~ 12,000 years BP, though natural climate variability remained the dominant driver of fire regime change until around 5,000 years BP, for most study regions. Responses suggested a ten-fold increase in the frequency of fire regime change during the last 250 years compared with the rest of the Holocene, corresponding first with the intensification and extensification of land use and later with anthropogenic climate change. Looking to the future, fire regimes were predicted to intensify, with increases in frequency, severity, and size in all biomes except grassland ecosystems. Fire regimes showed different climate sensitivities across biomes, but the likelihood of fire regime change increased with higher warming scenarios for all biomes. Biodiversity, carbon storage, and other ecosystem services were predicted to decrease for most biomes under higher emission scenarios. We present recommendations for adaptation and mitigation under emerging fire regimes, while recognizing that management options are constrained under higher emission scenarios. Conclusion The influence of humans on wildfire regimes has increased over the last two centuries. The perspective gained from past fires should be considered in land and fire management strategies, but novel fire behavior is likely given the unprecedented human disruption of plant communities, climate, and other factors. Future fire regimes are likely to degrade key ecosystem services, unless climate change is aggressively mitigated. Expert assessment complements empirical data and modeling, providing a broader perspective of fire science to inform decision making and future research priorities.Peer reviewe

A new high-resolution pollen sequence at Lake Van, Turkey, during MIS 6-7

A new detailed pollen and oxygen isotope record of the penultimate interglacial-glacial cycle, corresponding to the Marine Isotope Stage (MIS) 7–6 (c. 242.5–131.2 ka before present), has been generated from the "Ahlat Ridge" (AR) sediment core at Lake Van, Turkey. The presented record displays the highest temporal resolution for this interval with a mean sampling interval of ~540 years. Integration of all available proxies shows three intervals of effective moisture, evidenced by the predominance of forested landscapes (oak-pine steppe forest), which can be correlated with MIS 7e, 7c, and 7a. The warmest stage in terms of highest temperate tree percentages is MIS 7c, while the amplitude of MIS 7e appears to be truncated by a shift to colder/drier climatic conditions. The detailed comparison between the penultimate interglacial complex (MIS 7) to the last interglacial (Eemian, MIS 5e) and the current interglacial (Holocene, MIS 1) provides a vivid illustration of possible differences of successive climatic cycles. Intervening periods of open steppe landscape correlate with MIS 7d and 7a, favouring local erosion and detrital sedimentation. The predominance of steppe elements during MIS 7d indicates very cold/dry climatic conditions. In contrast, the occurrence of more temperate tree percentages throughout MIS 7b points to relatively mild conditions, in agreement with atmospheric CO2 concentration and oxygen isotope records. Despite the general dominance of dry/cold desert-steppe vegetation during the penultimate glacial (MIS 6), this period can be divided into two parts: an early stage (c. 193–157 ka BP) with pronounced oscillations in tree percentages, and a later stage (c. 157–131 ka BP) with lower tree percentages and subdued oscillations. The occurring vegetation pattern is analogous to the MIS 3 to MIS 2 division during the last glacial in the same sedi–159 ka BP) as described in marine pollen records, which indicates cooler but relatively wetter climate conditions during the penultimate glacial. In comparison with long European pollen records, speleothem isotope records from the Near East, and global climate parameters (e.g., insolation, atmospheric CO2 content), the new high-resolution Lake Van record presents an improved insight into regional vegetation dynamics and climate variability in the eastern Mediterranean region

Pollen and non-pollen palynomorph counts from Lake Van, Turkey

We illustrate the response of local and regional vegetation, aquatic ecosystem, and fire activity to volcanic eruptions in close connection to prevailing climate conditions. To understand these complex responses, we selected five volcaniclastic depositions in the Lake Van (Turkey) sediments from different interglacial/glacial periods. We analyzed high-resolution pollen data, non-pollen palynomorphs (NPPs), and microscopic charcoal particles (>20 µm) from annually laminated lacustrine sediments with precise age control, allowing us to quantify recovery time in varve years. This study highlights that the extent and duration of the volcanic event, the thickness of subsequent volcanic deposits, the respective climatic conditions strongly influence the impact on terrestrial and aquatic ecosystems

Volcanic impact on terrestrial and aquatic ecosystems in the Eastern Mediterranean

Abstract Natural disturbances such as volcanic eruptions provide a unique opportunity to study past ecological dynamics. Here we illustrate the response of terrestrial and aquatic ecosystems to volcanic eruptions in connection to prevailing climate conditions. We selected five volcaniclastic depositions in the Lake Van (Turkey) sediments from different interglacial/glacial periods (Marine Isotope Stages 3 to 9e). Using high-resolution pollen data, non-pollen palynomorphs, and microscopic charcoal particles we attempted to disentangle climatic and volcanic forcing of natural environmental disturbances. Our results highlights that the thickness of subsequent volcanic deposits and the respective climatic conditions strongly influence the impact on terrestrial and aquatic ecosystems. The most common response to ash deposition is a shift towards herbaceous taxa and abrupt fire activity. The affected herbaceous vegetation recovers to pre-eruption levels in 20 to 40 varve-years. The lake water experiences intensified productivity due to subsequent nutrient input and significant increase in aquatic microfossils. Our findings pave the way for disentangling climatic and volcanic forcing of natural environmental disturbances