Quantifications of global chemical weathering fluxes applying new lithological maps and new parameterizations

Abstract

The quantification of chemical weathering fluxes plays an important role for many processes in the Earth system. Chemical weathering regulates, for example, the pCO2 in the atmosphere over long geological time scales, influences the ocean carbon cycle or releases nutrients that are then available for ecosystems. Chemical weathering is dependent on several parameters, like water fluxes, temperature or the type of lithology. Most weathering models distinguish between carbonate and silicate weathering. In order to quantify the proportion and distribution of carbonates and silicate rocks on the global land surface, global lithological maps are the basis for the research. A continuous improvement of these maps is needed to further enhance weathering models. For this purpose a new global map database was developed, that reports on the distribution and types of unconsolidated sediments, which covers in this map approximately half of the global land surface. The Global Unconsolidated Sediments Map database (GUM) comprises 911,551 polygons and provides information about sediment types and subtypes, grain sizes, mineralogy, age and thickness of the sediments. The GUM allowed for analyzing the weathering behavior of loess sediments, which are highly dynamic eolian sediments. It could be shown that loess sediments show a similar weathering pattern than carbonate sedimentary rocks and a new parameterization for loess-derived alkalinity fluxes was developed. By applying this new function, the global alkalinity flux rates increase by about 16% as if compared to neglecting loess sediments. Subsequently, the alkalinity fluxes of loess deposits were quantified for the Last Glacial Maximum and the Mid-Holocene as well. It could be shown that increased alkalinity fluxes from loess deposits during the LGM are compensating for the general decreased alkalinity fluxes derived by silicate weathering and are hence keeping the global alkalinity fluxes stable between glacial-interglacial time scales. In the third part of this thesis, the quantification of alkalinity fluxes from basaltic regions was improved by considering not only temperature, but also the age of the surface basaltic rocks. A study of alkalinity fluxes from 33 basaltic volcanic areas shows that active Holocene basaltic areas provide ~10 times higher alkalinity flux rates than inactive volcanic fields. This observation led to the development of a new scaling law that increases global CO2 consumption rates by the consideration of young volcanic systems by about 60%. This thesis shows that global weathering models still can be improved. Enhanced global lithological maps, providing different kinds of information about sediments and rocks are needed to better understand regional and local processes and to be able to upscale them properly to the global scale. By applying enhanced maps, it could be shown that loess sediments and young basaltic volcanic fields increase global alkalinity fluxes, which could be especially interesting for past times in the Earth’s history, since both, loess sediments and volcanoes, are highly dynamic in their evolution.