Publisher: PANGAEA - Data Publisher for Earth & Environmental Science
Project: NWO | The Dawn of a Greenhouse ... (2300180216), NWO | Reconstructing the the ev... (2300166023)
Antarctic ice sheet and Southern Ocean paleoceanographic configurations during the late Oligocene are not well resolved. They are however important to understand the influence of high-latitude Southern Hemisphere feedbacks on global climate under CO2 scenarios (between 400 and 750 ppm) projected by the IPCC for this century, assuming unabated CO2 emissions. Sediments recovered by the Integrated Ocean Drilling Program (IODP) at Site U1356, offshore of the Wilkes Land margin in East Antarctica, provide an opportunity to study ice sheet and paleoceanographic configurations during the late Oligocene (26-25 Ma). Our study, based on a combination of sediment facies analysis, magnetic susceptibility, density, and X-Ray Fluorescence geochemical data, shows that glacial and interglacial sediments are continuously reworked by bottom-currents, with maximum velocities occurring during the interglacial periods. Glacial sediments record poorly ventilated, low-oxygenation bottom water conditions, interpreted to result from a northward shift of westerly winds and surface oceanic fronts. Interglacial sediments record more oxygenated and ventilated bottom water conditions and strong current velocities, which suggests enhanced mixing of the water masses as a result of a southward shift of the Polar Front. Intervals with preserved carbonated nannofossils within some of the interglacial facies are interpreted to form under warmer paleoclimatic conditions when less corrosive warmer northern component water (e.g. North Atlantic sourced deep water) had a greater influence on the Site. Spectral analysis on the late Oligocene sediment interval show that the glacial-interglacial cyclicity and related displacements of the Southern Ocean frontal systems between 26-25 Ma were forced mainly by obliquity. The paucity of iceberg rafted debris (IRD) throughout the studied interval contrasts with earlier Oligocene and post-Miocene Climate Optimum sections from Site U1356 and with late Oligocene strata from the Ross Sea, which contain IRD and evidence for coastal glaciers and sea ice. These observations, supported by elevated sea surface paleotemperatures, the absence of sea-ice, and reconstructions of fossil pollen between 26 and 25 Ma at Site U1356, suggest that open ocean water conditions prevailed. Combined, these evidences suggest that glaciers or ice caps likely occupied the topographic highs and lowlands of the now marine Wilkes Subglacial Basin (WSB). Unlike today, the continental shelf was not over-deepened and thus ice sheets in the WSB were likely land-based and marine-based ice sheet expansion was likely limited to coastal regions.
To quantitatively reconstruct the kinematic evolution of Central and Eastern Anatolia within the framework of Neotethyan subduction accommodating Africa-Eurasia convergence, we paleomagnetically assess timing and amount of vertical axis rotations across the Ulukisla and Sivas regions. We show paleomagnetic results from ~30 localities identifying a coherent rotation of a block - comprising the southern Kirsehir Block, the Ulukisla basin, the Central and Eastern Taurides, and the southern part of the Sivas basin. This block experienced a ~30° counter-clockwise vertical axis rotation since Oligocene time. Sediments in the northern Sivas region show clockwise rotations. We use the rotation patterns together with known fault zones to argue that the counter-clockwise rotating domain of south-central Turkey was bounded by the Savcili Thrust Zone and Deliler-Tecer Fault Zone in the north and by the African-Arabian trench in the south, the western boundary of which is poorly constrained and requires future study. Our new paleomagnetic constraints provide a key ingredient for future kinematic restorations of the Anatolian tectonic collage. We combine our extensive new dataset with existing data (Guerer et al., 2018, and references therein) to identify the dimension of rotating domains in Central and Eastern Anatolia, and identify structures that may have accommodated these rotations. Paleomagnetic interpretations and statistical analyses were carried out using the platform independent portal Paleomagnetism.org (Koymans et al., 2016).
Project: NWO | The Dark Age of the Lowla... (2300172486)
Supplemental material, Appendix_A_and_B for Controls on late-Holocene drift-sand dynamics: The dominant role of human pressure in the Netherlands by Harm Jan Pierik, Rowin J van Lanen, Marjolein TIJ Gouw-Bouman, Bert J Groenewoudt, Jakob Wallinga and Wim Z Hoek in The Holocene
Project: NWO | ODEX4all Open Discovery a... (2300182466), NWO | XCiDE: Crossing the Combu... (2300153186)
Performance for different ratios between the positive and the negative cases in the training set. This file shows the performance on a balanced test set as a function of the ratio of positive and negative cases in the training set. (XLSX 14 kb)