Browsing by Subject "CLIMATIC CHANGES"

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  • Strani, Flavia; Pushkina, Diana; Bocherens, Herve; Bellucci, Luca; Sardella, Raffaele; DeMiguel, Daniel (2019)
    The intermontane Anagni Basin (Frosinone, central Italy) is an important region for Italian biochronology and paleoecology due to the presence of two rich fossil assemblages dated to the Early (Coste San Giacomo) and Middle Pleistocene (Fontana Ranuccio). These sites have yielded a vast collection of large fossil mammals with a well-documented presence of fossil equids in both localities (represented mostly by isolated teeth). Coste San Giacomo is dated to around 2.1 Ma, thereby having recorded the effects of the onset of the Quaternary glacial cycles, which led to a gradual trend toward colder and more arid conditions in the Northern Hemisphere. The fossil equids of this site belong to the first group of grazing stenonid equids of the genus Equus that spread to the Italian Peninsula during the so called "Elephant- Equus" event, which marked the appearance of new large mammals living in herds in open and arid environments. The site of Fontana Ranuccio is dated to around 400 ka, close to the MIS 12-11 succession (the "Mid-Brunhes event"), which marked the end of the Middle Pleistocene Transition. The fossil horses from Fontana Ranuccio represent one of the oldest caballoid (or "true horses") populations of the Italian Peninsula. The Anagni Basin, thus, provides important data to investigate paleoecological adaptations of these groups of equids in response to two critical environmental and climatic shifts of the Pleistocene. We explore their niche occupation by examining long-term dental wear patterns and tooth enamel carbon and oxygen stable isotopic composition. Both taxa appear to have exhibited a narrow dietary niche, displaying a clear abrasive (highly specialized) grass-rich diet. In particular, caballoid equids from Fontana Ranuccio show a more abrasion-dominated mesowear signature. Stenonid equids from Coste San Giacomo exploited broader and more diverse landscapes during the Early Pleistocene, whereas caballoid horses from Fontana Ranuccio appeared to have limited their dietary adaptations to a stricter grazing behavior in more closed environments.
  • Schenk, Frederik; Bennike, Ole; Valiranta, Minna; Avery, Rachael; Björck, Svante; Wohlfarth, Barbara (2020)
    The global climate transition from the Lateglacial to the Early Holocene is dominated by a rapid warming trend driven by an increase in orbital summer insolation over high northern latitudes and related feedbacks. The warming trend was interrupted by several abrupt shifts between colder (stadial) and warmer (interstadial) climate states following instabilities of the Atlantic Meridional Overturning Circulation (AMOC) in response to rapidly melting ice sheets. The sequence of abrupt shifts between extreme climate states had profound impacts on ecosystems which make it challenging to reliably quantify state variables like July temperatures within a non-analogue climate envelope. For Europe, there is increasing albeit inconclusive evidence for higher stadial summer temperatures than initially thought. Here we present a comprehensive floral compilation of plant macrofossils from lake sediment cores of 15 sites from S-Scandinavia covering the period similar to 15 to 11 ka BP. We find evidence for a continued presence of plant species indicating high July temperatures throughout the last deglaciation. The presence of hemiboreal plants in close vicinity to the southern margin of the Fennoscandian Ice Sheet implies a strong thermal summer forcing for the rapid ice sheet melt. Consistent with some recent studies, we do not find evidence for a general stadial summer cooling, which indicates that other reasons than summer temperatures caused drastic setbacks in proxy signals possibly driven by extreme winter cooling and/or shorter warm seasons. (C) 2020 The Authors. Published by Elsevier Ltd.
  • Nevalainen, Liisa; Lami, Andrea; Luoto, Tomi P.; Manca, Marina (2014)
    We investigated 2500 years of community succession in Cladocera from the sediments of a mountain lake (Lake Piramide Inferiore) located in the Khumbu Valley close to Mt. Everest in the Nepalese Himalayas. Our objective was to determine late Holocene changes in cladoceran species composition and abundance in a biogeographical context and with respect to previous proxy-based paleolimnological data (algal pigments and organic content). The results suggested that cladoceran fauna of Lake Piramide Inferiore was species-poor and dominated by Chydorus cf. sphaericus throughout the sequence. The sediment profile recorded the occurrence of Alona guttata type individuals, which were attributed to Alona werestschagini Sinev 1999 based on their morphology and the species' current distributional range, and this was the first record of its presence in the Himalayas. In addition, a periodic long-term succession of melanic Daphnia (Ctenodaphnia) fusca Gurney, 1907 and non-melanic D. (Daphnia) dentifera Forbes 1893 was observed in the sediments. The millennia-long cladoceran community changes, although subtle due to the C. cf. sphaericus dominance, were in general agreement with the previous proxy-data of lake productivity following the regional paleoclimatic development and apparently partly driven by bottom-up mechanisms. The periodic occurrence and success of D. fusca and D. dentifera throughout the late Holocene in Lake Piramide Inferiore, combined with the knowledge of their phenotypic properties (i.e. carapace melanization) and previous investigations on their contemporary and past distribution in Khumbu Valley, suggested that they may have responded to altered underwater UV radiation regimes. Furthermore, they may have even periodically excluded each other subsequent to changes in the underwater UV environment. The results indicated the usefulness of fossil cladoceran analysis as a tool in biogeographical research, since the occurrence of species in space and time can be observed through sediment records and taxonomic identity of the remains may be resolved with the help of regional faunal distribution.
  • Pulido-Santacruz, Paola; Aleixo, Alexandre; Weir, Jason T. (2020)
    The incidence of introgression during the diversification process and the timespan following divergence when introgression is possible are poorly understood in the neotropics where high species richness could provide extensive opportunities for genetic exchange. We used thousands of genome-wide SNPs to infer phylogenetic relationships, calculate ages of splitting, and to estimate the timing of introgression in a widespread avian neotropical genus of woodcreepers. Five distinct introgression events were reconstructed involving taxa classified both as subspecies and species including lineages descending from the basal-most split, dated to 7.3 million years ago. Introgression occurred between just a few hundred thousand to about 2.5 million years following divergence, suggesting substantial portions of the genome are capable of introgressing across taxa boundaries during a protracted time window of a few million years following divergence. Despite this protracted time window, we found that the proportion of the genome introgressing (6-11%) declines with the time of introgression following divergence, suggesting that the genome becomes progressively more immune to introgression as reproductive isolation increases.
  • Etu-Sihvola, Heli; Bocherens, Hervé; Drucker, Dorothée; Junno, Aripekka; Mannermaa, Kristiina; Oinonen, Markku; Uusitalo, Joonas; Arppe, Laura (2019)
    Paleodietary research is a complex field, which requires large sets of background information. Owing to increasing interest and activity in the field, a substantial amount of archaeological isotope baseline data exist for Northern Europe, consisting mainly of animal bone collagen δ13C, δ15N, and δ34S values. However, the data are scattered into dozens of publications written in multiple languages and less-accessible formats, making the data laborious to use. This article presents the first compilation work of this data, the open access dIANA database (Dietary Isotopic baseline for the Ancient North; https://www.oasisnorth.org/diana.html), aimed to support (paleo)dietary research in the Baltic Sea area. The database work is complemented with new analyses of archaeological and (pre-)modern domestic and wild fauna from Finland and Russia broadening the selection of analysed species in the database. We present and discuss data examples, which on one hand show existing spatiotemporal isotope patterns related to diet and differences in the environmental carbon sources and on the other, also visualize the current status of baseline research and the need for further analyses in the circum-Baltic area.