<p>Understanding past ecosystems in the Arctic and subarctic oceans is important to project ecosystem development under enhanced warming. Sedimentary ancient DNA (sedaDNA) is a fantastic proxy providing information with sufficient taxonomic width and depth to comprehensively reconstruct past ecosystems. This study uses shotgun metagenomics of 42 sediment samples to decipher phyto- and zooplankton community changes over the last glacial-interglacial cycle back to the Eemian in the subarctic western Bering Sea. We aim to understand the sensitivity of plankton community composition to climate changes and its consequences on food web dynamics and carbon export. Our results indicate that micro- phytoplankton, like sea-ice associated diatoms, and cold-adapted chlorophytes, along with crustaceous zooplankton (copepods) dominated during the last glacial period. Contrarily, pico/nano-sized phytoplankton and the diatom family Chaetocerotaceae accompanied by heterotrophic protists and reduced abundance of copepods characterized the interglacial plankton communities. Further, we identified profound differences between the Holocene and Eemian. Particularly, the Holocene records a pronounced increase of pico-sized cyanobacteria, whereas in the Eemian, cold-water related taxa like Bathycoccaceae and Triparmaceae sub-dominate the community, supporting unique communities in both interglacials, challenging an analogy to future warming scenarios. In summary, our study shows evidence for a shift from micro-sized towards pico-sized phytoplankton with climate warming in the Holocene, accompanied by a more diverse zooplanktonic community dominated by bacterial grazing heterotrophic protists. Under future warming, decreased phytoplankton cell size and shifts in the grazing communities could affect food web linkages and result in reduced potential carbon sequestration and export in the subarctic Bering Sea, weakening its function as an effective carbon sink.</p>
<p>Understanding marine ecological systems is a challenging task that requires probing of different comparable states and comprehensive time series analysis. In this approach, we analyze sedimentary ancient DNA recovered from marine sediments which function as an extensive archive of past biota, as they conserve snapshots of the ecological community from the time of its DNA deposition. We examine metagenomic shotgun data from 22 samples as a time series ranging 124 kyrs from a probed sediment core recovered from the Shirshov Ridge in the Bering Sea basin to explore the possibilities of paleometagenomic network analyses. Looking at the presence and abundance of different taxa inhabiting the ocean at certain periods and climatic conditions including (1) the last interglacial (Eemian), (2) the last glacial period, and (3) the modern interglacial (Holocene), we reconstruct and analyze ecological networks and inspect how they have changed and adapted over time. Moreover, by developing extensive network analysis methods including species interaction enrichment and comparable simulation models we evaluate the viability of identifying complex connections and relationships between organisms, as well as the influence of reconstructed environmental factors. Our analysis establishes an initial pipeline for paleometagenomic network analyses and enables further research, e.g. network comparison of multiple marine sites to better understand past ecological mechanisms.</p>
<p>Animal body size provides information about the trophic position and reproductive strategies of species, and the presence of environmental stressors. The distribution of body sizes in fossils can be easily measured, making it an important tool for paleoecological studies. However, preservational and collection biases might influence the primary measurements and thus the results. Intuitively, smaller specimens of the same species should be more prone to destructive processes such as fracturing and dissolution. It is often assumed that body size distributions in death assemblages reflect those in living populations. We test this assumption.<br>Using the body size distributions in monospecific assemblages of Devonian ammonoids, we show that common depositional environments yield distinct distributions of conch sizes. We then simulate postdepositional conditions in recent analogues of these environments. If conch size is proportional to robustness (or disintegration rate), sedimentation rates and mixing intensities characterizing these recent analogues allow us to reconstruct conch size distributions observed in Devonian counterparts of these environments.<br>The results show that shape parameters of body size distributions (skewness and kurtosis) are modified in predictable ways in sedimentary environments. This implies that fossil body size distributions are not a direct reflection of ecological signals, but can be altered by postdepositional processes. We conclude that parameters of body size distributions, such as mean and dispersion, may not be comparable with parameters in standing populations. If changes in these parameters coincide with changes in the depositional environment, the effect of (post)depositional processes needs to be considered.</p>
Ammonoids of the subfamily Paratornoceratinae are characterised by disc-shaped adult conchs; furthermore they display a wide range of ontogenetic pathways leading to a similar adult conch morphology. The subfamily Paratornoceratinae occurs in the late early Famennian shelf sediments of various regions from the Anti-Atlas of Morocco to the Canning Basin of Western Australia; where endemic species of the genera Paratornoceras and Acrimeroceras appear in stratigraphic succession. We revise the species Paratornoceras lentiforme (Sandberger, 1857) and describe the new species Paratornoceras thuringense Korn, Bartzsch & Weyer n. sp., P. harounense Korn & Ebbighausen n. sp., P. ayense Korn & Buchwald n. sp., P. peterseni Korn & Buchwald n. sp., Acri meroceras hoppeckense Korn & Buchwald n. sp., A. ropicense Korn, Bartzsch & Weyer n. sp. and A. saalense Korn, Bartzsch & Weyer n. sp.
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