Miocene high frequence vegetation and climate variability

The recognition of high-frequency patterns and cycles in sedimentary and paleontological records and their calibration to the astronomical target curve, improved our knowledge of paleo-climate. Within the Pannonian basin complex, drill cores and geophysical data document the influence of 100-kyr and 400-kyr eccentricity cycles (Juhsz et al. 1999; Hohenegger et al. 2007; Harzhauser et al., 2004). Benthic life in Lake Pannon was shown to have been influenced by precessional cycles, which have periodically allowed pioneer taxa to settle the deeper parts of the lake (Harzhauser and Mandic, 2004). Recently, several sub-Milankovitch signals, which are independent from global glaciation effects, have been detected in Neogene lake sediments as well. Kloosterboer-van Hoeve et al. (2006) documented ~10, ~2.5 and ~1.5 ka periodicities related to long period variations in solar activity in Early Pliocene pollen records of Greece. Multi-decadal to centennial variability of the Gleissberg (~80, 140-110 yr) and Suess (~250-200 yr) cycles of solar activity modulated the sedimentary record in a Pleistocene maar lake in Southern Africa (Garcin et al., 2006) and in a Pleistocene-Holocene bog in New Mexico (Jiménez-Moreno et al., 2008) . Even Schwabe cycles of solar activity (10-12 yr) are deciphered from Holocene lake deposits (Theissen et al., 2008). These sub-Milankovitch cycles, however, are undocumented in Miocene deposits so far. To address this problem, we will investigate 4 drill-cores, representing time-slices of c. 11.0, 10.4, 9.8 and 8.8 Ma. All cores are situated in the Vienna Basin and thus the geographic component, influencing differences in the pollen-spectra of the cores will be minimised. Pollen and dinoflagellates will be analysed in an ultra-high resolution sampling (one sample per cm). Geochemical (carbonate content, total carbon, organic carbon, sulphur) and geophysical (magnetic susceptibility, gamma-logging) analyses will supplement the data. This method will reveal decadal-, centennial- and millennial-scale changes of vegetation, surface water productivity and drainage. These changes will be analysed in terms of variation in insolation to decipher the climatic variability during the Late Miocene. Moreover, the cores bracket the crucial period of the Vallesian Crises, which triggered the decline of wetlands and the opening of the landscapes in Europe and caused a synchronous shift in mammal communities. An improved understanding of the climate history might thus help to re-evaluate this major break.

The main focus of the project was describing environmental and climatic changes in the Miocene on a decadal to millennial scale. Detecting such high-frequency climatic fluctuations in proxy data and understanding their impact on the paleoenvironments helps to achieve a deeper understanding of Earths climate system in the past and is important for serious predictions of future climate behavior.The herein proposed methodology relies on a best fit scenario in which detected cyclicities in the geological record (if present in several proxies with distinct frequency ratios) are compared with known sub-Milankovitch cycles with similar frequency ratios. Ideally, such patterns should reflect the relation between the lower and upper Gleissberg cycles (~5080 and ~90140 years), the de Vries/Suess cycle (~200-210 years), the ~500-years-cycle, the ~1000-years-cycle and the Hallsatt-cycle (~2400 years) and others. The presence of such a repetitive frequency pattern in the geological archive is a solid argument to suggest solar forcing and to estimate sedimentation-rates. Each of the investigated localities represents slightly different depositional conditions (estuarine, lagoonal lacustrine, offshore lacustrine) as well as different climate scenarios (Mid-Miocene Climatic Optimum, Early Tortonian warm phase and Tortonian transition) Nevertheless, all localities showed the clear presence of sub-millennial-scale environmental shifts in vegetation, surface water productivity, bottom water conditions, salinity and sediment input. These are linked to small-scaled climate changes, such as changing precipitation and/or wind regime in the lake settings and additionally to the influence by precession-driven sea-level change in the marine key study. For none of the examples, temperature was recognized as driving factor, as this seems to be a more stable parameter on these short temporal scales of few millennia.An important outcome is the very prominent presence of the 1500-year-cycle. Considering all known sub-Milankovitch cyclicities, this 1500-year-cycle remains un-resolved so far as it has no direct link to solar activity. Nevertheless, its presence in all proxies as well as its modulating force on small-scale solar cycles documents it as a strong factor for environmental evolution.The observed patterns are comparable to Holocene case studies. Therefore, the potential of high-resolution studies beyond the 14C range is shown as a tool to identify pre-Pleistocene paleoenvironmental and paleoclimatical history on a decadal scale.