The Critical Zone

The “Critical Zone” is Earth's permeable near-surface layer that extends from the tops of the trees to the bottom of the groundwater1, and from the soil profile to the watershed.

It is a living, breathing, constantly evolving boundary layer where rock, soil, water, air, and living organisms interact. These complex interactions regulate the natural habitat and determine the availability of life-sustaining resources, including our food production and water quality.

Water and atmospheric gases move through the porous Critical Zone, and living systems thrive in its surface and subsurface environments, shaped over time by biota, geology, and climate.

All this activity transforms rock and biomass into the central component of the Critical Zone - soil; it also creates one of the most heterogenous and complex regions on Earth.

The “Critical Zone” has the word “critical” in it, meaning that under stress it may break down entirely or shift to another state, while the word “zone” implies that it traces something like a border (vertically as well as horizontally)2.

Critical Zone processes operate on second-to-eon timescales

The Critical Zone is imprinted by important events over seconds, hours, years, millenia, and geologic time. The present structure and functioning of the Critical Zone reflects:

  • short-term responses to events like rainfall and human activities like land-use changes
  • long-term responses to climatic and tectonic changes over geologic time

The Critical Zone and human society are closely intertwined, impacting each other in myriad ways. Two particularly important issues are

  • climate change
  • land use

Critical Zone Research - we pursue Critical Zone activities in two ways.

In Field laboratories our focus is on bridging time scales and looking into the past of the Critical Zone. Our focus is further on the deep (groundwater and deep weathering) processes taking place at the base of the zone. We explore the Critical Zone from the soil profile to the watershed scale (link).

EarthShape (Earth Surface Shaping by Biota): is a DFG Priority Program that is jointly coordinated by GFZ and Universität Tübingen. Earthshape explores the way biological systems shape the Earth surface: from deep weathering to sediment dynamics. Research will be conducted in the Chilean Coastal Range that features one of Earth’s most spectacular vegetation gradients and is controlled by climate ranging from hyper-arid to humid temperate. It is a natural laboratory to study how biology and topography interact. This latitudinal gradient allows for a “space for time approach” aiming at understanding how the climate change predicted globally can induce biota changes that in turn drive landscape formation.

With methodological developments we explore and develop new tools that serve to investigate the processes in the Critical Zone, its underground structure, and the fluxes of matter.

  • Isotopes in the Critical Zone. We develop new cosmogenic nuclide methods that allow to trace weathering of rock and its rates. We develop metal stable isotopes as labels of fluid-solid interaction and of nutrient uptake by plants. We development and refine novel molecular and stable isotope based proxies to explore how Earth surface processes interact with climate over geological timescales.

  • Helmholtz Laboratory for the Geochemistry of the Earth Surface – HELGES comprises clean laboratories, analytical instruments for concentration and isotope ratio measurements on liquid and solid samples, and facilities for the preparation of samples for cosmogenic nuclide analyses.

  • IsoNose (Isotopic Tools as Novel Sensors of Earth Surface Resources) is a EU Marie Curie Initial Training network coordinated by GFZ. The young researchers will be trained in the use of novel mass-spectrometric methods to be put to use in environmental and Critical Zone issues.

  • Fluid solid interaction in the deep weathering zone - In this specialty of GFZ we make use of the large geoscientific expertise to explore the processes that take place when fluids deep in the weathering zone alter unweathered rock: the mineralogical transformations from the nano to the soil scale, the fluid flow, the microbiologically induced transformations, the geochemical fluxes and the associated isotope fractionation, fluid-induced seismicity, and explore geophysical tools to map the 3D structure of the Critical Zone.

1 Link
Bruno Latour: Some advantages of the notion of “Critical Zone” for                               Geopolitics.Procedia Earth and Planetary Sciences 10, 3-6 (2914)