Ramona A. A. Schneider

Bio: Ramona A. A. Schneider is an academic researcher from Stockholm University. The author has contributed to research in topics: Thermoluminescence dating & Geology. The author has an hindex of 1, co-authored 1 publications receiving 3 citations.

Paleoglacial footprint and fluvial terraces of the Shaluli Shan, SE Tibetan Plateau

Abstract: This study provides mapping of glacial and fluvial geomorphology in the Shaluli Shan region on the eastern margin of the south-eastern Tibetan Plateau. Based on TanDEM-X 12 m elevation data and Goo ...

Age, formation and significance of loess deposits in central Sweden

Abstract: Loess deposits are common in the mid‐latitudes and are excellent records of past climate, landscape change and dust. However, loess deposits are seldom reported from Fennoscandia. Here we investigate two former glaciofluvial areas in central Sweden, Brattforsheden and Bonäsheden, where post‐glacial loess and sand dune activity have been documented previously. Based on detailed mapping, grain size, scanning electron microscopy and optically stimulated luminescence dating analyses, we confirm the presence of loess deposits at the sites and extend the known area of loess coverage. Our results suggest that loess deposits are more common than previously thought in Sweden. The results also demonstrate that basal parts of the loess are often mixed with underlying sediment, which may be a common feature of thin loess deposits close to former ice margins. Quartz luminescence is well suited for dating these deposits, but ages from the mixed basal loess layers are older than expected, while ages from undisturbed loess extend to c. 5 ka. The loess ages contrast with the timing of main dune activity in these areas, which is dominantly in the 1–3 kyr post‐deglaciation (c. 10.9–10.5 cal kyr BP). We suggest that either sediment mixing during soil formation is responsible for the mid‐Holocene loess ages, or that the loess deposits record periodic landscape destabilization into the mid‐Holocene. Furthermore, there is a clear topographic control on aeolian sedimentary facies, with loess mantling high ground and dunes restricted to valleys. Loess deposits are also primarily found to the south and southwest of source areas, implying transport from the north and east. This pattern contrasts with evidence for NW winds inferred from associated sand dunes. At present, the reasons for this mismatch are unclear, although one possible explanation is that silts deposited at higher elevations were affected by Ekman flow deflection of NW surface winds.

High-latitude forcing of diatom productivity in the southern Agulhas Plateau during the past 350kyr Paleoceanography

Abstract: The hydrography of the Indian-Atlantic Ocean gateway has been connected to high-latitude climate dynamics by oceanic and atmospheric teleconnections on orbital and suborbital timescales. A wealth of sedimentary records aiming at reconstructing the late Pleistocene paleoceanography around the southern African continent has been devoted to understanding these linkages. Most of the records are, however, clustered close to the southern South African tip, with comparatively less attention devoted to areas under the direct in fl uence of frontal zones of the Southern Ocean/South Atlantic. Here we present data of the composition and concentration of the diatom assemblage together with bulk biogenic content and the alkenone-based sea surface temperature (SST) variations for the past 350kyr in the marine sediment core MD02-2588 (approximately 41°S, 26°E) recovered from the southern Agulhas Plateau. Variations in biosiliceous productivity show a varying degree of coupling with Southern Hemisphere paleoclimate records following a glacial-interglacial cyclicity. Ecologically well-constrained groups of diatoms record the glacial-interglacial changes in water masses dynamics, nutrient availability, and strati fi cation of the upper ocean. The good match between the glacial maxima of total diatoms concentration, Chaetoceros spores abundance, and opal content with the maximum seasonal cover of Antarctic ice and the atmospheric dust records points to a dominant Southern Hemisphere forcing of diatom production. Suborbital variability of SST suggests rapid latitudinal migrations of the Subtropical Front and associated water masses over the southern Agulhas Plateau, following millennial contractions and expansions of the subtropical gyres. Warmings of the upper ocean over site MD02-2588 during terminations IV to I occurred earlier than that in the Antarctic Vostok, which is indicative of a Northern Hemisphere lead. Our multiparameter reconstruction highlights how high-latitude atmospheric and hydrographic processes modulated orbital highs and lows in primary production and SST as triggered by northward transport of Si, eolian dust input, and latitudinal migrations of frontal zones.

Different glacier status with atmospheric circulations in Tibetan Plateau and surroundings

Abstract: Glacial melting in the Tibetan Plateau affects the water resources of millions of people. This study finds that—partly owing to changes in atmospheric circulations and precipitation patterns—the most intensive glacier shrinkage is in the Himalayan region, whereas glacial retreat in the Pamir Plateau region is less apparent.

Changes in Tibetan Plateau latitude as an important factor for understanding East Asian climate since the Eocene: a modeling study

Abstract: Previous climate modeling studies suggest that the surface uplift of the Himalaya–Tibetan plateau (TP) is a crucial parameter for the onset and intensification of the East Asian monsoon during the Cenozoic. Most of these studies have only considered the Himalaya–TP in its present location between ∼26°N and ∼40°N despite numerous recent geophysical studies that reconstruct the Himalaya–TP 10° or more of latitude to the south during the early Paleogene. We have designed a series of climate simulations to explore the sensitivity of East Asian climate to the latitude of the Himalaya–TP. Our simulations suggest that the East Asian climate strongly depends on the latitude of the Himalaya–TP. Surface uplift of a proto-Himalaya–TP in the subtropics intensifies aridity throughout inland Asia north of ∼40°N and enhances precipitation over East Asia. In contrast, the rise of a proto-Himalaya–TP in the tropics only slightly intensifies aridity in inland Asia north of ∼40°N, and slightly increases precipitation in East Asia. Importantly, this climate sensitivity to the latitudinal position of the Himalaya–TP is non-linear, particularly for precipitation across East Asia. The simulated precipitation patterns across East Asia are significantly different between our scenarios in which a proto-plateau is situated between ∼11°N and ∼25°N and between ∼20°N and ∼33°N, but they are similar when the plateau translates northward from between ∼20°N and ∼33°N to its modern position. Our simulations, when interpreted in the context of climate proxy data from Central Asia, support geophysically-based paleogeographic reconstructions in which the southern margin of a modern-elevation proto-Himalaya–TP was located at ∼20°N or further north in the Eocene.

A Review of Climatic Controls on δ 18 o in Precipitation over the Tibetan Plateau: Observations and Simulations

Abstract: HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. A review of climatic controls on δ18O in precipitation over the Tibetan Plateau: Observations and simulations Tandong Yao, Valérie Masson-Delmotte, Jing Gao, Wusheng Yu, Xiaoxin Yang, Camille Risi, Christophe Sturm, Martin Werner, Huabiao Zhao, You He, et al.

Geomorphology of the Aran Valley (Upper Garonne Basin, Central Pyrenees)

Abstract: ABSTRACT Geomorphological mapping in mountain regions is key for a better understanding of past and present environmental dynamics. Here, we present a 1:25000 scale geomorphological map covering 553 km2 of the Aran Valley, Upper Garonne Basin (Central Pyrenees). The map identifies 44 different geomorphological units classified under glacial, periglacial, nival, karst, slope, alluvial, and fluvial categories. The area includes geomorphic evidence of past Quaternary glaciations reconstructed based on the distribution of moraines from the valley floor to the highest cirques. Following deglaciation of the valley, the landscape was mainly reshaped by periglacial, slope, alluvial and fluvial processes. In addition to paleoenvironmental reconstruction, the map can also be used to promote geoheritage and geoconservation, as well as for planning. As such, it is of relevance for areas exposed to natural hazards, since present-day slope failures and debris flows frequently impact the villages and infrastructures across the valley floor.