This session will include three blocks, each focussing on one of the aspects mentioned in the title: Critical Zone (CZ) functioning, CZ reconstruction, and geochemical techniques in CZ research.

1) Critical Zone functioning in the Anthropocene
Understanding the functioning of the CZ is crucial, as it affects e.g. soil fertility, weathering and erosion rates, recharge processes, and transit times. It is crucial to estimate the vulnerability and recovery-time of the critical zone and associated landscape in order to plan the sustainable use of water and soil resources, and to protect ecohydrological systems under climate or land use change. This session block will therefore focus on natural and disturbed landscape evolution, including key processes of the CZ, such as weathering, soil erosion, ecohydrological processes and soil organic matter dynamics.

2) Reconstructing the evolution of CZ, based on soils, sediments and geomorphology
The reconstruction of the CZ’s past evolution is an essential prerequisite for estimating its further evolution. This session block focusses on the mutual relationships between geomorphology, sediments and soils, and on the use of sediments and soils for reconstructing landscape evolution. These archives also provide a multitude of proxies (pollen, plant-derived lipids and alkanes, molluscs, etc.), allowing for palaeovegetation and palaeoclimate reconstruction. Holistic approaches are needed to obtain a synthesis of the information from the various archives.

3) Using the geochemical composition of soils and sediments for tracing provenance, anthropogenic activities and pollution pathways in CZ research
The focus of this session block is on geochemical approaches, including isotopy studies, (i) for characterizing soils and sediments with respect to their provenance, (ii) for detecting anthropogenic activities and tracing pollution pathways in the CZ, (iii) for geochemical mapping and studying the spatial distribution of chemical elements, and (iv) for obtaining a better understanding of water-rock interaction, physico-chemical and biological processes within the CZ.

Research on all three aspects included in this session is needed in order to understand the present CZ functioning and potentially predict its further evolution in times of accelerated global change. Such research also requires significant support from observatory structures through the development of CZ Observatories (CZOs) to continuously deliver long term data on any compartment of the CZ using highly instrumented field sites.