Spätquartäre Sedimentationsgeschichte des Meerfelder Maares (Westeifel).—Mikrostratigraphie jahreszeitlich geschichteter Seesedimente

Zwei Sedimentkerne aus dem zentralen Teil des Meerfelder Maares wurden mikrostratigraphisch ausgewertet. Diatomologische Untersuchungen weisen die überwiegend organischen Ablagerungen als jahreszeitlich geschichtet aus. Die daraufhin durchgeführte Warvenzählung erlaubt es, jeden Sedimentabschnitt absolut zu datieren. Klimaschwankungen und anthropogene Einflüsse können nachgewiesen und datiert werden. Sie steuern den wechselnden Sedimentaufbau und erklären die unterschiedlichen Sedimentationsraten.researc

Investigating Maar Formation and the climate history of Southern Argentina–the Potrok Aike Maar Lake Sediment Archive Drilling Project (PASADO)

Evidence is increasing that the Southern Ocean plays a key role in the global climate system. The southern hemisphere contains more than 90% of the world’s ice, and eighty-one percent of its total surface area is covered by oceans. On global terms, the most extreme oceanic character is encountered between 40°S and 60°S latitude, where land (Patagonia and a few islands) comprises only 2% of the surface area. Terrestrial archives of past climate changes are thus extremely scarce at these latitudes. As Patagonia is subject to shifts in polar and mid-latitude winds, pressure fi elds, and precipitation regimes, as well as to variations related to the El Niño Southern Oscillation (ENSO) and the Antarctic Oscillation (AO), it has the unique potential to record variations in the hydrological cycle, changes in aeolian dust deposition, the frequency of volcanic activity, and other natural forces that control climatic conditions. Lake sediments can provide important archives for such terrestrial climatic and environmental reconstructions. In the semi-arid steppe region of Patagonia, however, most of the lakes are periodically dry or ephemeral. One exception is the 100-m-deep crater lake Laguna Potrok Aike (Fig. 1), a 770 ± 220 thousand year old maar situated in the province of Santa Cruz, Argentina. The lake is located in the Pali Aike Volcanic Field (Fig. 2), the southernmost back-arc Neozoic volcanic fi eld of South America. As Laguna Potrok Aike has not been reached by any Pleistocene ice advance during the last 1 Ma, it is potentially the only mid-latitude lake in the Southern Hemisphere with a continuous sedimentary record covering several glacial to interglacial cycles. In addition to global reconstructions, regional climatic variations represent other important aspects of research.Fil: Zolitschka, Bernd. Universitat Bremen; AlemaniaFil: Corbella, Hugo. Universidad Nacional de la Patagonia Austral; ArgentinaFil: Maidana, Nora Irene. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ohlendorf, Christian. Universitat Bremen; Alemani

Responses of testate amoebae assemblages (Amoebozoa: Arcellinida) to recent volcanic eruptions, inferred from the sediment record in Laguna Verde, southern Patagonia, Argentina

There is little knowledge about testate amoebae in lakes and their responses to volcanic eruptions. To address this knowledge gap, we studied the paleoecology of these protists in a sediment record from Laguna Verde, a lake located east of the southern Patagonian Ice Field, in Santa Cruz Province, Argentina. The lake is under the influence of volcanic eruptions from Lautaro Volcano, Chile, ~ 42 km WNW of Laguna Verde. We evaluated the response of 11 testate amoeba morphospecies in the lake to the last four Lautaro eruptions, using a 61-cm sediment core. Calcium (Ca), a major element of volcanic ash, was the most important variable explaining testate amoeba variability in the three zones determined by detretended correspondence analysis. We identified four declines in testate amoeba abundance and diversity associated with tephra deposition. Poisson regression analysis revealed that Difflugia immanata, D. bidens, and D. glans strain “glans” decrease after deposition of tephra layers. In contrast, Centropyxis constricta strain “constricta,” C. aculeata strain “aculeata” and Zivkovicia compressa respond positively to ash deposition. Our findings suggest a high resilience of testate amoebae to stochastic events such as volcanism because the same assemblage (D. immanata, D. bidens, and D. glans strain “glans”) inhabited the lake before and after the ashfalls. Nevertheless, several volcanic eruptions during the last ~ 300 years may have weakened this resilience and had a long-term effect on community diversity. Multivariate analysis showed that potassium (K) plays a significant role in shaping assemblage composition. Because of the low K content of the Lautaro tephra, we infer that higher potassium concentrations in sediments are not related with volcanic events, but rather, are associated with terrestrial input. Future studies, however, will be needed to identify the source of K in the sediment record and its relationship with testate amoebae assemblages. Our study demonstrates the potential for using lacustrine testate amoebae as environmental proxies, and illustrates the direct effects of volcanic ash deposition on their assemblage composition, diversity and distribution in southern Patagonia.Fil: Charqueño Celis, Norma Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Administración de Parques Nacionales. Parque Nacional "Nahuel Huapi"; ArgentinaFil: Sigala, Itzel. Universidad Nacional Autónoma de México. Instituto de Geofísica; MéxicoFil: Zolitschka, Bernd. Universitat Bremen. Institut Fuer Geographie; AlemaniaFil: Pérez, Liseth. Technische Universitat Carolo Wilhelmina Zu Braunschweig. Iinstitut fur Geosysteme und Bioindikation; AlemaniaFil: Mayr, Christoph. Institut Fur Geographie, Friedrich-alexander-universit; Alemania. Universitat Erlangen Nuremberg; Alemania. Ludwig Maximilians Universitat; AlemaniaFil: Massaferro, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Administración de Parques Nacionales. Parque Nacional "Nahuel Huapi"; Argentin

New vegetation history reconstructions suggest a biostratigraphic assignment of the lowermost Rodderberg interglacial (Germany) to MIS 11

Along with the ongoing climate crisis, research efforts increasingly focus on Pleistocene environmental archives. Interglacial periods are of special interest, as they offer crucial information about natural interactions (i.e. not influenced by human activities) between climate and ecosystems within a climatic setting comparable to the Holocene and/or climate change projections. The sedimentary infill of the Rodderberg crater, 10 km south of the city of Bonn (Germany), records several glacial-interglacial cycles in superposition, which makes it a rare and promising environmental archive. One of the most challenging targets is to establish a robust chronological framework for the Rodderberg sediment sequence. In the present study we reconstruct the vegetation history of the basal and most prominent interglacial sequence, the lowermost Rodderberg interglacial (LRI), and apply the principles of pollen biostratigraphy to estimate the depositional age. At the base of the sequence steppe tundra conditions prevailed during the cryocratic phase before the onset of the interglacial. Rising temperatures caused afforestation of the landscape with boreal forests during the protocratic phase, which subsequently were replaced by temperate forests in the mesocratic phase. The sequence continues under unstable vegetation conditions characterized by temperate forests dominated by Carpinus and Abies during the oligocratic phase. During the terminal part of the LRI, the telocratic phase, boreal to nemoboreal forests covered the landscape. Due to climatic deterioration these forests collapsed and a steppe tundra evolved again (cryocratic phase). This climate-driven glacial-interglacial cycle is followed by an interstadial with rather closed nemoboreal forest vegetation. Based on the occurrences of characteristic taxa as well as the vegetation assemblages and succession, we refrain from correlating the LRI with any of the warm stages between c. 240 and 180 ka BP, i.e. roughly corresponding to MIS 7. A correlation with the Holsteinian, which was previously physically dated to c. 340e325 ka BP, cannot unambiguously be excluded, however, the absence of Pterocarya during the LRI argues against it. Instead, the LRI has striking similarities with the Kärlich interglacial, which has been previously physically dated to c. 400 ka BP, making it chronologically equivalent to MIS 11

Late Quaternary Araucaria forest and Campos (grasslands) vegetation dynamics inferred from a high-resolution pollen record from Lagoa Dourada in southern Brazil

Forest-grassland mosaics are ecosystems with sharp contrasts. Factors controlling their heterogeneity have interested researchers worldwide. To date, only few natural remains of these ecosystems exist, such as the Araucaria and Campos region in southern Brazil. Different paleoecological studies elucidate the vegetation and climate history of the region, documenting shifts between forests and grasslands since the Middle Holocene. However, uncertainty remains about whether system shifts were sudden or gradual and on the importance of driving factors and triggers such as climate, change and disturbance. We reconstruct the paleoecological history of the Araucaria forest-grassland mosaics in Paraná state in decadal to sub-decadal resolution during the Holocene. High resolution pollen analysis documents that in this region the expansion of woodlands occurred gradually while sedimentological analyses reveal stepwise shifts of the precipitation regime of the region. During the Early Holocene (10300-8300 cal yr BP), the landscape was characterized by grassland-dominated Campos vegetation, with sporadic occurrences of arboreal taxa. Araucaria angustifolia was present initially in small abundances. In the Mid-Holocene (8300-4000 cal BP), a transition to more humid conditions fostered the development of woodlands. The establishment of Araucaria angustifolia near the lake occurred around 7300 cal yr BP, together with a general expansion of woodlands. In the Late Holocene (4000-150 cal yr BP), Araucaria angustifolia became dominant within forest patches with a second stepwise expansion around 3300 cal yr BP. The onset of Euro-American land use during the last two centuries intensified erosion and altered species composition, reflected in sediment and pollen data. In addition, Lagoa Dourada documents vegetational changes that seem to coincide with the 8.2 ka event and the Little Ice Age

High-resolution paleomagnetic records from Laguna Potrok Aike (Patagonia, Argentina) for the last 16,000 years

Holocene and Late-glacial records documenting variations in direction and intensity of the geomagnetic field during the last 16,000 cal. BP are presented for Southern Patagonia. This continuous high-resolution terrestrial record from Laguna Potrok Aike (51°58´S, 70°23´W) was recovered within the SALSA(South Argentinean Lake Sediment Archives and modeling) project. Mineral magnetic measurements indicate that pseudo single-domain magnetite is the major carrier of the remanence allowing the reliable determination of stable natural remanent magnetization inclinations and declinations from alternatingfield demagnetization and principal component analysis. Paleomagnetic secular variation records reveal most of the familiar features of declination and inclination that have previously been reported in other records from South Argentina but conspicuous centennial-scale differences are also observed. The results illustrate the potential of paleosecular variations records for dating sedimentary sequences in southern South America.Fil: Gogorza, Claudia Susana. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física Arroyo Seco; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; ArgentinaFil: Irurzun, Maria Alicia. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física Arroyo Seco; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; ArgentinaFil: Sinito, Ana Maria. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física Arroyo Seco; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; ArgentinaFil: Lisé Pronovost, Agathe. Université du Québec a Montreal; CanadáFil: St Onge, Guillaume. Université du Québec a Montreal; CanadáFil: Haberzettl, Torsten. Universitat Jena; AlemaniaFil: Ohlendorf, Christian. Universitat de Bremen; AlemaniaFil: Kastner, Stephanie. Universitat de Bremen; AlemaniaFil: Zolitschka, Bernd. Universitat de Bremen; Alemani