Lake Ohrid’s tephrochronological dataset reveals 1.36 Ma of Mediterranean explosive volcanic activity

Tephrochronology relies on the availability of the stratigraphical, geochemical and geochronological datasets of volcanic deposits, three preconditions which are both often only fragmentary accessible. This study presents the tephrochronological dataset from the Lake Ohrid (Balkans) sediment succession continuously reaching back to 1.36 Ma. 57 tephra layers were investigated for their morphological appearance, geochemical fingerprint, and (chrono-)stratigraphic position. Glass fragments of tephra layers were analyzed for their major element composition using Energy-Dispersive-Spectroscopy and Wavelength-Dispersive Spectroscopy and for their trace element composition by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry. Radiometric dated equivalents of 16 tephra layers and orbital tuning of geochemical proxy data provided the basis for the age-depth model of the Lake Ohrid sediment succession. The age-depth model, in turn, provides ages for unknown or undated tephra layers. This dataset forms the basis for a regional stratigraphic framework and provides insights into the central Mediterranean explosive volcanic activity during the last 1.36 Ma.

1.36 million years of Mediterranean forest refugium dynamics in response to glacial–interglacial cycle strength

The sediment record from Lake Ohrid (Southwestern Balkans) represents the longest continuous lake archive in Europe, extending back to 1.36 Ma. We reconstruct the vegetation history based on pollen analysis of the DEEP core to reveal changes in vegetation cover and forest diversity during glacial–interglacial (G–IG) cycles and early basin development. The earliest lake phase saw a significantly different composition rich in relict tree taxa and few herbs. Subsequent establishment of a permanent steppic herb association around 1.2 Ma implies a threshold response to changes in moisture availability and temperature and gradual adjustment of the basin morphology. A change in the character of G–IG cycles during the Early–Middle Pleistocene Transition is reflected in the record by reorganization of the vegetation from obliquity- to eccentricity-paced cycles. Based on a quantitative analysis of tree taxa richness, the first large-scale decline in tree diversity occurred around 0.94 Ma. Subsequent variations in tree richness were largely driven by the amplitude and duration of G–IG cycles. Significant tree richness declines occurred in periods with abundant dry herb associations, pointing to aridity affecting tree population survival. Assessment of long-term legacy effects between global climate and regional vegetation change reveals a significant influence of cool interglacial conditions on subsequent glacial vegetation composition and diversity. This effect is contrary to observations at high latitudes, where glacial intensity is known to control subsequent interglacial vegetation, and the evidence demonstrates that the Lake Ohrid catchment functioned as a refugium for both thermophilous and temperate tree species.

What about Dinner? Chemical and Microresidue Analysis Reveals the Function of Late Neolithic Ceramic Pans

The Late Neolithic palafitte site, Ustie na Drim, in the northern part of Lake Ohrid (North Macedonia), excavated in 1962, offered ceramic fragments of large, flat, elongated pans. These artifacts could be dated by relative chronology to roughly around 5200–5000 BC. According to their shape and technological traits, the ceramic pans were probably used for baking. The attached materials on the surface of studied pan fragments were sampled for consequent chemical and microscopical analyses (i.e., analyses of starch, phytoliths, and microscopic animal remains). An immunological method revealed the presence of pork proteins in samples. The presence of organic residues of animal origin was, moreover, confirmed by the detection of cholesterol using gas chromatography coupled to mass spectrometry. Analysis of detected microscopic botanical objects revealed starch grains of several plants (i.e., oak, cattail, and grasses). An interesting find was the hair of a beetle larva, which could be interpreted contextually as the khapra beetle, a pest of grain and flour. Based on our data, we suppose that the ceramic pans from Ustie na Drim were used for the preparation of meals containing meat from common livestock in combination with cereals and wild plants.

Unlocking the power of lake multiproxy analyses by understanding subsurface biosphere processes

<p>Lake sediments bear valuable information allowing multidisciplinary research to address paleoclimatic and paleoenvironmental reconstructions at regional to global scales. Sedimentological, geochemical, paleontological and biological tools are commonly used to tackle these questions, which are generally driven by a set of intricated parameters. Among them, the importance of biogeochemical cycling is largely acknowledged in the lake (paleo-) water columns and has been at the heart of most paleolimnological studies. The way these signals are transferred to lake sediments has largely been studied. However, microbial communities - the principal actors in the biogeochemical cycling framework - keep being active in the sediment, and continue to influence the preservation and retention of organic and inorganic matter while buried. Gathered within the “early diagenesis” black box, these processes, once qualified, can help better interpret the proxies they may influence, and even constitute new ones. Within this work, we provide examples showing that the integration of studies of the subsurface biosphere within geo- and paleo-limnology investigations can help unlock or secure the potential of multiproxy analysis for reconstructing the paleoenvironments, paleoclimates and paleo-ecology of lake basins. The use of now well-developed OMICS methods, through the analysis of environmental and/or ancient DNA and lipids in particular has been coupled to mineralogical, isotopic and magnetic information in the Dead Sea (Levant) to demonstrate the differential preservation of mineralogic and sedimentologic signals along the last two glacial-interglacial cycles (Thomas et al., 2015, 2016; Ebert et al., 2018). Similar signals have been unlocked in Lake Towuti (Indonesia) and in Laguna Potrok Aike (Argentina) (Vuillemin et al., 2015, 2017). In Lake Ohrid (North Macedonia/Albania), environmental DNA has provided limited inputs on that perspective (Thomas et al., 2020), but has shown that ancient/fossil DNA could provide valuable information regarding the lake primary productivity and the status of its watershed land-cover. Integrating OMICS methods to tackle the identity and activity of the ancient and modern subsurface biosphere of lakes therefore holds an immense potential not only for microbiology investigations, but also for paleoclimatic and paleoenvironmental reconstructions.</p><p>Ebert et al. (2018) Overwriting of sedimentary magnetism by bacterially mediated mineral alteration. Geology <strong>46</strong>, 2–5.</p><p>Thomas et al. (2016) Microbial sedimentary imprint on the deep Dead Sea sediment. The Depositional Record 1–21.</p><p>Thomas et al. (2020) Weak influence of paleoenvironmental conditions on the subsurface biosphere of lake ohrid over the last 515 ka. Microorganisms <strong>8</strong>, 1–20.</p><p>Thomas et al. (2015) Impact of paleoclimate on the distribution of microbial communities in the subsurface sediment of the Dead Sea. Geobiology <strong>13</strong>, 546–561.</p><p>Vuillemin et al. (2015) Recording of climate and diagenesis through fossil pigments and sedimentary DNA at Laguna Potrok Aike, Argentina. Biogeosciences Discussions <strong>12</strong>, 18345–18388.</p><p>Vuillemin et al. (2017) Preservation and Significance of Extracellular DNA in Ferruginous Sediments from Lake Towuti , Indonesia. Frontiers in Microbiology <strong>8</strong>, 1–15.</p>

DNA barcoding in recognition of Gammarusflock diversity and distribution in the ancient Lake Ohrid

Lake Ohrid, located on the Balkan Peninsula at the Albanian-Macedonian border, is the oldest European lake (1.3-1.9 My old) and one of the world’s smallest ancient lakes. Taking into account the size of the lake and its biodiversity, it harbors the highest level of endemism, especially within amphipod crustaceans (ca. 90%) with the endemic Gammarus species flock. Our previous studies upon this flock have shown a substantial decoupling between molecular and morphological diversity, existence of cryptic species and puzzling speciation history. In order to explore sources of observed diversity, in the current study we are investigating ecological preferences of the species within the flock, based on their distribution in depth gradient, in relation to molecular diversity based on DNA barcoding. In the study over 200 barcodes were generated and combined with 173 previously published. The specimens were collected from all depth ranges of Lake Ohrid as well as from springs located on or near the banks of the lake. Within the species flock, 13 BIN’s were identified, 12 previously known and one newly recognized, representing separate lineage and putatively a new species. Two of the flock species were found only in the springs: G. sketi and G. cryptosalemaai. G. sketi, previously found only in springs on the southern banks of Lake Ohrid, has now also been discovered in springs in its north-eastern part. Both species show low haplotypic diversity. All remaining species were recorded from the depth between 20 and 60 meters, that is characterized by the highest ecological diversity with different types of substrates: stones, macrophytes, abundant Dreissena shells as well as sand and silt. Among them G. sywulai, G. macedonicus, G. cryptoparechiniformis, G. lychnidensis, G. ochridensis, G. parechinifromis were found exclusively within this depth range. The three latter species represent single BIN and share haplotypes, at the same time this BIN has the highest number of haplotypes in comparison to others. The remaining species found on this depth represent separate BINs with different levels of haplotype diversity. Only G. lychnidensis, G. stankokaramani and G. solidus were found below the depth of 60 meters, in a quite homogenous environment dominated by silt. In the deepest parts of the lake, between 260 and 290 meters, only G. solidus was found. This species is represented only by three haplotypes while G. stankokaramani is characterized by multiple haplotypes partially shared with G. lychnidensis. The shared haplotype represents the only G. lychnidensis occurrences on the depths below 60 meters. Summarizing, the highest abundance of BINs, species and haplotypes was recovered from the most ecologically diversified depth range of the lake (20 to 60 meters). This suggests that ecological heterogeneity could be the main driver of Gammarus species flock diversification in the ancient Lake Ohrid. Due to the complex pattern of morphological diversity, DNA barcoding proved to be the best if not the only method in identification of the species flock diversity.

Half-precession signals in Lake Ohrid and their spatial and temporal connection to proxy records in the European realm

<p>Lake Ohrid is located on the Balkan Peninsula between Albania and North Macedonia. It is considered Europe’s oldest lake and thus is a valuable archive for studies that focus on the change of local (hydro-)climate during the last 1.36 million years (e.g., Francke et al. 2016; Wagner et al. 2019). During an International Continental Scientific Drilling Program (ICDP) campaign in 2013, geophysical downhole logging by the Leibniz Institute for Applied Geophysics acquired continuous datasets of physical properties. Additionally, 2100 m of sediment core was obtained from different sites, the deepest with a length of 570 m (Wagner et al. 2014).</p><p>Investigations of half-precession (HP) cycles (~9,000 – 12,000 years) have been given only a small role or have been completely neglected in previous cyclostratographic studies. In this study we focus on HP signals in Lake Ohrid and investigate the temporal variability of this signal over the last one million of years. Next to a connection of HP cycles to interglacials, we see a more pronounced correlation of the HP signal to natural gamma radiation logs in the younger part of the record.</p><p>We relate the results from Lake Ohrid to a variety of proxy records from the European mainland and marine sediment cores from the Atlantic and the Mediterranean. Certain patterns, such as the increased visibility of the HP signal in interglacials, occur in most records, but differences, like variations in the amplitude modulation of the filtered HP signal, need to be investiagted in more detail. Nevertheless, the HP cycles are contained in all of the investigated sites, although the records are influenced by different climatic systems. This illustrates that HP signals cannot be connected to a certain climatic system, but can occur simultaneously in records with different proxy signal origins.</p><p>HP cycles are a relevant part of natural climate variability - also in Europe - and allow a more detailed investiagtion of sedimentary systems.</p><p> </p><p>References:</p><p>Francke, A., Wagner, B., Just, J., Leicher, N., Gromig, R., Baumgarten, H., … & Giacco, B. (2016). Sedimentological processes and environmental variability at Lake Ohrid (Macedonia, Albania) between 637 ka and the present, Biogeosciences , 13, 1179–1196.</p><p>Wagner, B., Wilke, T., Krastel, S., Zanchetta, G., Sulpizio, R., Reicherter, K., …. & Vogel, H. (2014). The SCOPSCO drilling project recovers more than 1.2 million years of history from Lake Ohrid, Sci. Drill. , 17, 19-29.</p><p>Wagner, B., Vogel, H., Francke, A., Friedrich, T., Donders, T., Lacey, J. H., … & Zhang, X. . (2019). Mediterranean winter rainfall in phase with African monsoons during the past 1.36 million years, Nature , 573(7773), 256-260.</p>

Weak Influence of Paleoenvironmental Conditions on the Subsurface Biosphere of Lake Ohrid over the Last 515 ka

Lacustrine sediments are widely used to investigate the impact of climatic change on biogeochemical cycling. In these sediments, subsurface microbial communities are major actors of this cycling but can also affect the sedimentary record and overprint the original paleoenvironmental signal. We therefore investigated the subsurface microbial communities of the oldest lake in Europe, Lake Ohrid (North Macedonia, Albania), to assess the potential connection between microbial diversity and past environmental change using 16S rRNA gene sequences. Along the upper ca. 200 m of the DEEP site sediment record spanning ca. 515 thousand years (ka), our results show that Atribacteria, Bathyarchaeia and Gammaproteobacteria structured the community independently from each other. Except for the latter, these taxa are common in deep lacustrine and marine sediments due to their metabolic versatility adapted to low energy environments. Gammaproteobacteria were often co-occurring with cyanobacterial sequences or soil-related OTUs suggesting preservation of ancient DNA from the water column or catchment back to at least 340 ka, particularly in dry glacial intervals. We found significant environmental parameters influencing the overall microbial community distribution, but no strong relationship with given phylotypes and paleoclimatic signals or sediment age. Our results support a weak recording of early diagenetic processes and their actors by bulk prokaryotic sedimentary DNA in Lake Ohrid, replaced by specialized low-energy clades of the deep biosphere and a marked imprint of erosional processes on the subsurface DNA pool of Lake Ohrid.