Rekonstruktion kontinentaler Niederschläge

In present-day climates both temporal and spatial variations in precipitation can be significant, with substantial influence on ecosystems and human societies. Coupled atmosphere–ocean climate models have shown that small-scale global temperature variations can substantially alter the global precipitation budget and especially the regional distribution of rainfall. For instance, all future global warming scenarios predict global precipitation to increase between 1.4% and 2.3% per one degree of warming (IPCC2007), which can be attributed to a higher water-holding capacity of the atmosphere at elevated temperatures. However, regional variations in precipitation change can vary significantly.

Terrestrial palaeo-precipitation values can be estimated by palaeobotanical proxy-methods, as well as zoological methods. One of the latter uses herpetofaunal assemblages (Böhme et al. 2006). Principally, the method is based on the observation that climate and especially precipitation serves as a direct predictor for the herpetofaunal distribution and species richness and yields robust and widely applicable modelling results. According to their ecophysiological strategies and adaptations to maintain thermoregulation, water balance and gas exchange, amphibians and reptiles (excluding non-fossorial snakes) are assorted into six ecophysiologic groups. The relative frequencies of these groups show in recent communities a highly significant correlation to the mean annual precipitation, with mean prediction errors between 250 and 275 mm. The application of this palaeoprecipitation tool to fossil assemblages with rich amphibian and reptile records (low taphonomical bias with respect to herpetofauna) from alluvial sediments, paleosoils, caves, fissure fillings, pond and swamp deposits, and channel-fill sediments, expand significantly the spectrum of palaeoenvironments from which precipitation data can be obtained. This methodology is especially powerful in the ‘dry end’ of the climate system.

Ensemble means and ±1σ conﬁdence intervals (grey shaded area) of the relative mean annual precipitation, MAPt/MAP0 (×100%) for the Paratethys area (Central and Eastern Europe), obtained from averaging over N = 1000 random age models, each consistent with the given age uncertainties in the original data set (black bars in Fig. 3A). Horizontal black bars represent the raw data with age uncertainties.

The application of this method to the Neogene terrestrial archive of Eurasia provides a new and deeper inside into regional climate and ecosystem evolution and their driving global mechanisms.

A large database of hundreds of suitable fossil locality provides a dense and continuous precipitation record over Europe.

Burdigalian to Messinian precipitation from Europe. (A) Absolute mean annual precipitation (MAP) values for SW-Europe (red) and Central + Eastern Europe (black) (B) Ratio of MAP relative to recent; 100% means no change relative to recent (dotted line).

By this we are also able to reconstruct non-analogous climates (climate states which has no analogues today), like the Late Miocene washhouse climates (Böhme et al. 2008). A washhouse climate is a extra-tropical climate, characterized by warm-subtropical temperature and a significantly enhanced hydrologic cycle.

Events associated with the Tortonian temporary closure of the Panama Isthmus. Horizontal bars: Washhouse climate in Europe (magenta); global cool periods (grey) (Kaminski et al., 1989b; Helland and Holmes 1997; Duncan and Helgason 1998; Thiede et al., 1998; Billups and Schrag 2002; John and Krissek 2002; Diekmann et al., 2003; Westerhold et al., 2005). A—Estimated European freshwater run-off in Sv (1 Sv = 106 m3 s− 1) relative to recent (blue) and TMg/Ca (green) as in Fig. 4; black arrows indicate periods of enhanced moisture transport into high northern latitudes. B—lower envelope of obliquity (Laskar et al., 2004); the decrease in tilt angle causes increasingly cool summers at high latitudes (blue arrow). C— Variation of Northern Component Water (NCW = proto-NADW) from Poore et al. (2006); “stronger” and “weaker” refer to the present day (dashed line). D—brown: Closing history of the Central American Seaway (CAS) according to Kameo and Sato (2000); blue: timing of the most severe Paciﬁc carbonate crash episodes (Lyle et al., 1995; Roth et al., 2000); light green: periods of intense upwelling off Benguela as indicated by nanoplankton productivity (Kastanja et al., 2006; Krammer et al., 2006); dark green: timing of the ﬁrst Great American Biotic Interchange Marshall, 1985; magenta: Vallesian crisis in European mammals (Agusti et al., 2003).

Höhenverbreitungsmodell der Riesensalamander bei trockenem Klima und niedrigem Grundwasserspiegel (oben) und feuchtem Klima und höherem Grundwasserspiegel (unten) (siehe Vasilyan & Böhme, 2012).

Publikationen

Böhme, M., Ilg, A., Ossig, A. & Küchenhoff, H. 2006: New method to estimate paleoprecipitation using fossil amphibians and reptiles and the middle and late Miocene precipitation gradients in Europe.- Geology 34(6): 425-428; doi: 10.1130/G22460.1; 2 figures, 1 table, Data Repository item 2006083.

Böhme, M., Ilg, A., Winkelhofer, M. 2008: Late Miocene "washhouse" climate in Europe.- Earth Planet. Sci. Lett. 275(3-4): 393-401, doi:10.1016/j.epsl.2008.09.011.

Böhme, M., Winklhofer, M., Ilg, A. 2011: Miocene precipitation in Europe: Temporal trends and spatial gradients.- Palaeogeography, Palaeoclimatology, Palaeoecology 304: 212-218, doi:10.1016/j.palaeo.2010.09.028.

Böhme M., Vasilyan D., Winklhofer M. 2012. Habitat tracking, range dynamics and palaeoclimatic signiﬁcance of Eurasian giant salamanders (Cryptobranchidae) — indications for elevated Central Asian humidity during Cenozoic global warm periods. Palaeogeography, Palaeoclimatology, Palaeoecology doi:10.1016/j.palaeo.2012.04.032.

Vasilyan, D., Böhme M. 2012: Pronounced Peramorphosis in Lissamphibians— (Urodela, Cryptobranchidae) from the Paleocene–Eocene Thermal Maximum of Mongolia. - PLoS ONE 7(9): e40665